U.S. patent application number 15/582078 was filed with the patent office on 2017-09-28 for flux-cored wire for different-material bonding and method of bonding different materials.
This patent application is currently assigned to KABUSHIKI KAISHA KOBE SEIKO SHO (Kobe Steel, Ltd.). The applicant listed for this patent is KABUSHIKI KAISHA KOBE SEIKO SHO (Kobe Steel, Ltd.). Invention is credited to Hidekazu IDO, Jun KATOH, Katsushi MATSUMOTO, Tsuyoshi MATSUMOTO, Seiji SASABE, Mikako TAKEDA.
Application Number | 20170274479 15/582078 |
Document ID | / |
Family ID | 38371389 |
Filed Date | 2017-09-28 |
United States Patent
Application |
20170274479 |
Kind Code |
A1 |
KATOH; Jun ; et al. |
September 28, 2017 |
FLUX-CORED WIRE FOR DIFFERENT-MATERIAL BONDING AND METHOD OF
BONDING DIFFERENT MATERIALS
Abstract
There are provided a flux cored wire for joining dissimilar
materials with each other, capable of enhancing a bonding strength
upon joining an aluminum-base material with a steel-base material,
and excellent in bonding efficiency, a method for joining the
dissimilar materials with each other, and a bonded joint obtained
by the method. In particular, there is provided a method for
joining dissimilar materials with each other, in the case of melt
weld-bonding of high-strength dissimilar materials with each other,
that is, the high-strength steel member with the high-strength 6000
series aluminum alloy member and in the case of the steel member
being a galvanized steel member. In one mode, use is made of a flux
cored wire wherein the interior of an aluminum alloy envelope is
filled up with a flux, the flux has fluoride composition containing
a given amount of AlF.sub.3 without containing chloride, and the
aluminum alloy of the envelope contains Si in a range of 1 to 13
mass %. If such a flux cored wire is use, it is possible to obtain
a high bonding strength in the case of melt weld-bonding of
high-strength dissimilar materials with each other, that is, the
high-strength steel member with the high-strength 6000 series
aluminum alloy member.
Inventors: |
KATOH; Jun; (Kobe-shi,
JP) ; TAKEDA; Mikako; (Kobe-shi, JP) ; SASABE;
Seiji; (Fujisawa-shi, JP) ; MATSUMOTO; Katsushi;
(Kobe-shi, JP) ; IDO; Hidekazu; (Kobe-shi, JP)
; MATSUMOTO; Tsuyoshi; (Fujisawa-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KABUSHIKI KAISHA KOBE SEIKO SHO (Kobe Steel, Ltd.) |
Kobe-shi |
|
JP |
|
|
Assignee: |
KABUSHIKI KAISHA KOBE SEIKO SHO
(Kobe Steel, Ltd.)
Kobe-shi
JP
|
Family ID: |
38371389 |
Appl. No.: |
15/582078 |
Filed: |
April 28, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12279470 |
Aug 14, 2008 |
9682446 |
|
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PCT/JP07/52041 |
Feb 6, 2007 |
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15582078 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B23K 35/406 20130101;
B23K 35/362 20130101; B23K 2101/18 20180801; B23K 9/232 20130101;
B23K 9/173 20130101; B23K 35/0266 20130101; B23K 2103/20 20180801;
Y10T 428/12757 20150115 |
International
Class: |
B23K 35/02 20060101
B23K035/02; B23K 9/173 20060101 B23K009/173 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 17, 2006 |
JP |
2006-041135 |
Apr 10, 2006 |
JP |
2006-107491 |
Sep 14, 2006 |
JP |
2006-249679 |
Nov 16, 2006 |
JP |
2006-310535 |
Claims
1-7. (canceled)
8: A method for joining dissimilar materials together comprising: a
step of an AC-MIG welding for directly joining an aluminum member
or an aluminum alloy member with a steel member by use of a flux
cored wire wherein a flux containing potassium fluoride, aluminum
fluoride, and at least one fluoride selected from the group
consisting of fluorides of elements of the Group IIA of the
Periodic Table is coated with aluminum or an aluminum alloy.
9: A method for joining dissimilar materials together comprising: a
step of an AC-MIG welding for directly joining an aluminum member
or an aluminum alloy member with a steel member by use of a flux
cored wire formed by coating a flux containing potassium fluoride,
aluminum fluoride, and at least one fluoride selected from the
group consisting of magnesium fluoride, calcium fluoride, strontium
fluoride, and barium fluoride with aluminum or an aluminum alloy,
as a filler metal.
10: A bonded joint wherein an aluminum member or an aluminum alloy
member is joined with a steel member by the method for joining
dissimilar materials together, according to claim 8.
11: A method for joining dissimilar materials together comprising:
a step of joining an aluminum member or an aluminum alloy member
with a steel member by either an AC-MIG welding or a MIG welding by
DC reversed polarity with the use of a flux cored wire, wherein the
flux cored wire is formed by filling up the interior of an envelope
made up of an aluminum member or an aluminum alloy member with a
flux, the flux for filling up is mixed with aluminum fluoride, and
potassium fluoride to be turned into a mixed flux, and a loading
weight of the mixed flux is in a range of 0.1 to 24 mass %, against
the total mass of the flux cored wire.
12: The method for joining dissimilar materials together, according
to claim 11, wherein the mixed flux has a melting point in a range
of 560 to 700.degree. C., and the flux cored wire is not more than
1.6 mm .PHI. in diameter.
13: The method for joining dissimilar materials together, according
to claim 8, wherein the steel member is a galvanized steel member.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a divisional of U.S. patent
application Ser. No. 12/279,470, filed on Aug. 14, 2008, the text
of which is incorporated by reference, which is a National Stage
entry under 35 U.S.C. 371 of PCT/JP07/52041, filed on Feb. 6, 2007
and claims priority to Japanese Patent Application No. 2006-041135,
filed on Feb. 17, 2006, Japanese Patent Application No.
2006-107491, filed on Apr. 10, 2006, Japanese Patent Application
No. 2006-249679, filed on Sep. 14, 2006, and Japanese Patent
Application No. 2006-310535, filed on Nov. 16, 2006.
TECHNICAL FIELD
[0002] The invention relates to a flux cored wire (FCW: Flux Cored
Wire) for joining dissimilar materials with each other, that is, a
steel-base material and an aluminum-base material with each other,
and a method for joining the dissimilar materials with each other.
A technology according to the invention is suitably applicable to
automobiles, railway vehicles, and so forth, in the transportation
field, machine components, construction members such as building
structures, and so forth. The technology is required in the
assembling process for automobile structures.
BACKGROUND ART
[0003] In the case of welding, metal members similar in kind are
generally joined with each other. However, if welding can be
applied to joining of dissimilar metal members such as a steel-base
material (hereinafter referred to merely as a steel member) and an
aluminum-base material (generic term used for pure aluminum and
aluminum alloy, and hereinafter referred to merely as an aluminum
member) with each other (an aggregate of the dissimilar materials
joined), this will enable the aggregate of the dissimilar materials
joined to be used as a structural member of the automobile, and so
forth, thereby significantly contributing to reduction in weight of
the automobile, and so forth.
[0004] However, in the case of joining the steel member with the
aluminum alloy member by welding, a brittle Fe--Al intermetallic
compound is prone to be formed at a joint, so that it has been very
difficult to obtain a reliable joint high in strength (bonding
strength). Accordingly, to effect joining at those aggregates of
the dissimilar materials joined (dissimilar metal members joined),
joining by use of bolts, rivets, and so forth has been adopted in
the past, however, a bonded joint has a problem with its
reliability, air-tightness, cost, and so forth.
[0005] Meanwhile, it has been intended to enhance strength of the
aluminum member as well as the steel member in order to achieve
reduction in weight of automobile components such as an automobile
body, and so forth, so that there has been a tendency to use a
high-strength steel (high tensile steel) member for the steel
member, and to use a high-strength A6000 series aluminum alloy
member with less alloying elements, and excellent in recyclability
among aluminum alloy members.
[0006] In consequence, in the case of joining dissimilar materials
with each other by welding, there has since occurred a change in
joining objects, that is, a change from the conventional joining of
dissimilar materials low in strength with each other, such as
joining of mild steel with pure aluminum or a A5000 series aluminum
alloy, by welding, to joining of dissimilar materials high in
strength with each other, such as joining of the high-strength
steel with the A6000 series aluminum alloy member by welding. With
the joining of those dissimilar materials high in strength with
each other, conditions under which the brittle Fe--Al intermetallic
compound is generated at a joint will vary on a case-by-case basis.
Hence, in order to obtain reliable, and high bonding strength, it
becomes necessary to devise new joining conditions in contrast with
conditions for the conventional joining of the dissimilar materials
low in strength with each other, by welding.
[0007] In the case of joining dissimilar materials such as the
steel member and the aluminum member with each other, the steel
member is high in melting point, and electrical resistance, but low
in thermal conductivity, as compared with the aluminum member, so
that heat evolution on the steel side of a joint will be greater,
thereby causing aluminum lower in melting point to be first fused.
Next, the surface of the steel member undergoes fusion, resulting
in formation of a brittle intermetallic compound of Fe--Al series
on an interface therebetween. As a result, it is not possible to
obtain a high bonding strength.
[0008] Accordingly, there have since been made many reviews and
proposals on a joining method for obtaining the joint of the
dissimilar materials such as the steel member and the aluminum
member. For example, a method for joining the dissimilar materials
together by rolling the same in a vacuum has been proposed (refer
to Patent Document 1). There has also been proposed a method for
making seam welds by interposing a two-layer cladding material made
up of a steel-base material layer and an aluminum alloy layer,
prepared beforehand (refer to Patent Document 2). Further, there
has been proposed a method for pressure joining at a high
temperature (refer to Patent Document 3). Still further, there has
been proposed a method for joining by HIP treatment by interposing
a Ti alloy placed on respective joint surfaces (refer to Patent
Documents 4 and 5). Yet further, there has been proposed a method
for friction welding (refer to Patent Document 6). Then, there has
been proposed a method whereby resistance welding is carried out by
plating the surface of a steel material layer, in contact with
aluminum, with an aluminum alloy beforehand, or by interposing the
two-layer cladding material made up of the steel-base material
layer and the aluminum alloy layer, prepared beforehand (refer to
Patent Documents 7, and 8).
[0009] Those conventional techniques, however, each have the
following problem. For example, the methods for obtaining the joint
of the dissimilar materials such as the steel member and the
aluminum member, according to Patent Documents 1 to 8,
respectively, are in common with each other in that those methods
are applicable to joining of members relatively simple in shape,
such as flat sheets, or the like, with each other, but are not
applicable to joining of members complex in shape with each other
because of constraints imposed on the shape thereof. For this
reason, those methods each have a narrow range of application, and
are inferior in general versatility. Further, those methods each
have a problem in that a joint is confined to a relatively small
portion of the area of the joint, thereby preventing a continuous
joint from being obtained. Still further, because any of those
methods will be complicated in process step, it is not possible to
ensure stability in quality, thereby causing a problem of an
increase in joining cost, and lack of practicality. Yet further,
with the existing welding line, it is not possible to carry out any
of those methods, and in order to carry out any of those methods,
there is the need for adding new facilities to the present
facilities, causing another problem of an increase in capital
cost.
[0010] As one of the background behind the proposals on the various
method for joining the steel-base material with the aluminum-base
material, described as above, there can be cited a phenomenon that
if the steel-base material is joined directly with the
aluminum-base material by fusion, a brittle intermetallic compound
is generated at the joint, thereby causing the joint prone to
cracking. Accordingly, when joining the steel-base material
directly with the aluminum-base material, including the case of
joining using a welding wire, it becomes extremely important how to
prevent as much as possible steel of the steel-base material, and
aluminum of the aluminum-base material from being fused to be mixed
with each other to thereby secure ductility of fused metal parts,
and how to prevent the brittle intermetallic compound from being
formed in the vicinity of an interface between the steel-base
material, and the aluminum-base material
[0011] In contrast to the above, there has been proposed a method
for line-joining or face-joining the steel material with the
aluminum material by arc welding (refer to Non-patent Documents 1,
2, and 3). Further, there has also been proposed a method for
joining the steel material directly with the aluminum material by
MIG brazing in order to secure a sound bonded joint (refer to
Patent Document 9).
[0012] With the method for joining the steel material with the
aluminum material by arc welding, as described in Non-patent
Documents 1, 2, 3, and so forth, holes are provided on the steel
material side of a joint beforehand, and a growth direction of an
intermetallic compound acting as a factor for blocking securing of
strength is controlled by filling up the holes with the aluminum
material, thereby attempting to obtain a high bonding strength.
However, with those methods as described in Non-patent Documents 1,
2, 3, respectively, cracking is prone to occur to beads in the case
of continuous arc welding, so that a welded joint still has a room
for improvement in strength. The same applied to Patent Document
9.
[0013] Further, there has been proposed a method for brazing at a
low temperature so as to prevent a brittle Fe--Al intermetallic
compound from being generated at a joint (refer to Patent Documents
10, 11).
[0014] Still further, in the case of melt welding for those joints
of the dissimilar materials, whereby joining is carried out at a
higher temperature, there has been proposed a method for joining an
aluminum alloy member with a steel member having a surface with
zinc plating applied thereto by pulse MIG welding with the use of a
solid wire made of an aluminum alloy with addition of silicon at
least in a range of 3 to 15 wt % as a welding wire (refer to Patent
Document 12). With this method, upon fusion of the welding wire,
silicon is caused to move toward a base metal to permeate the
interface of a fusion pond, thereby rising in temperature,
whereupon wettability of fused metals is improved to thereby
enhance adhesion properties thereof.
[0015] Further, it has been proposed to enhance the strength of a
welded joint by improving composition of a flux for use in
melt-welding of the joint of the dissimilar materials. For example,
there has been proposed a method for arc welding of a mild steel
with a pure aluminum member, or an A5000 series aluminum alloy
member by use of a wire with a flux incorporated therein, formed by
coating the flux containing a fluoride (cesium fluoride, aluminum
fluoride, potassium fluoride, and aluminum oxide), serving as a
core material, with aluminum, or an aluminum alloy (refer to Patent
Document 13).
[0016] Still further, there has been proposed a method for joining
dissimilar materials together, that is, joining a steel member with
an aluminum member by any of various welding processes such as
magnetic welding, ultrasonic welding, high-frequency welding, spot
welding, and so forth, using a fluoride-based mixed flux containing
potassium fluoride, aluminum fluoride, and so forth, together with
at least one fluoride selected from the group consisting of cesium
fluoride, aluminum fluoride, potassium fluoride, and zinc
fluoride), in as-coated state (refer to Patent Document 14). With
those methods as described, cleaning on the surface of the steel is
urged by the agency of the chemical reaction of the flux as above,
and the wettability as well as adhesion properties of a molten
metal composed of aluminum will be improved, thereby blocking
formation of a brittle and thick intermetallic compound.
[0017] Yet further, there has also been proposed a method for spot
welding of a mild steel with an A6000 series aluminum alloy member
by coating the surface of the aluminum alloy member with a
fluoride-based flux having the effect of causing reduction of a
sturdy oxide film formed on the surface of the aluminum alloy
member to be thereby melt and removed from the surface of the
aluminum alloy member (refer to Patent Document 15). Furthermore,
those fluoride-based fluxes are also used for joining aluminum
alloy members with each other by melt welding and so forth (refer
to Patent Documents 16, and 17). [0018] Patent Document 1: JP-A No.
2000-94162 [0019] Patent Document 2: JP-A No. 11 (1999)-197846
[0020] Patent Document 3: JP-A No. 10 (1998)-185040 [0021] Patent
Document 4: JP-A No. 6 (1994)-198458 [0022] Patent Document 5: JP-A
No. 5 (1993)-8056 [0023] Patent Document 6: JP-A No. 8
(1996)-142755 [0024] Patent Document 7: JP-A No. 6 (1994)-39558
[0025] Patent Document 8: JP-A No. 6 (1994)-63762 [0026] Patent
Document 9: JP-A No. 2003-33865 [0027] Patent Document 10: JP-A No.
7 (1995)-148571 [0028] Patent Document 11: JP-A No. 10
(1998)-314933 [0029] Patent Document 12: JP-A No. 2004-223548
[0030] Patent Document 13: JP-A No. 2003-211270 [0031] Patent
Document 14: JP-A No. 2003-48077 [0032] Patent Document 15: JP-A
No. 2004-351507 [0033] Patent Document 16: JP-A No. 2004-210013
[0034] Patent Document 17: JP-A No. 2004-210023 [0035] Non-patent
Document 1: WELDING JOURNAL, (1963), p. 302 [0036] Non-patent
Document 2: LIGHT METAL WELDING, Vol. 16 (1987) No. 12, p. 8 [0037]
Non-patent Document 3: National Conference of Japan Association of
Welding, Proceedings No. 75 (2004), pp. 260 to 261
DISCLOSURE OF THE INVENTION
Problem to be Solved by the Invention
[0038] Taking into consideration the case where the joint of the
dissimilar materials (welded joint of the dissimilar materials)
formed by weld-bonding the steel member with the aluminum member is
put to use as structural members of the automobile, and so forth,
the joint needs strength capable of withstanding a load (stress)
imposed thereon at the time of automobile collision, and so forth.
Those structural members of the automobile include, for example,
the bonded joints of the dissimilar materials such as side members
made up of the steel members, bumper stay (a bonded member on the
rear side of a bumper reinforcement), and so forth. The bonded
joints of the dissimilar materials according to those conventional
techniques described in the foregoing, respectively, however, are
found lacking in bonding strength if such application as described
is assumed, and still have a room for improvement.
[0039] Further, as a more important problem, there exists a problem
that zinc plating (layer) for general use on the steel member side
of the aggregate of the dissimilar materials joined interferes with
weldability, thereby lowering bonding strength. In particular, with
the aggregate of the dissimilar materials joined, where the steel
member is joined with the aluminum member, the steel member being
coated with hot dip zinc plating or hot dip alloyed zinc plating,
relatively large in plating thickness, will be inferior in
weldability to a bare steel member, thereby exhibiting pronounced
deterioration in the bonding strength thereof.
[0040] This is because in the case of joining together dissimilar
materials, that is, a galvanized steel sheet (zinc plated steel
member), and an aluminum member, there is inevitably generated a
brittle Zn--Fe based intermetallic compound layer attributable to
zing plating besides the brittle intermetallic compound generated
at the joint of the dissimilar materials. Since the Zn--Fe based
intermetallic compound layer is brittle, the same becomes a
starting point of rupture, thereby markedly deteriorating bonding
strength.
[0041] Further, with the spot welding, a joint is confined to a
relatively small portion of the area of the joint, so that it is
not possible to obtain a continuous joint. The spot welding is
therefore efficient, and suitable for use in joining panels with
each other, but is unsuitable for line welding, such as fillet
welding, butt welding, and so forth, required of bimetallic joining
for the structural members of the automobile.
[0042] In the case of the brazing at low temperatures, as described
in Patent Documents 10, and 11, respectively, brazing by use of a
solder of aluminum base, or by use of flux and the solder of
aluminum base has been carried out. However, in the case of the
brazing at low temperatures, a joining temperature range for
members to be joined together needs be strictly controlled so as to
be not lower than the melting temperature of the solder, and not
higher than the melting temperature of the members to be joined
together. Accordingly, in order to apply the brazing at low
temperatures to joining of large sized members such as an
automobile body, and so forth, there is the need for a large
furnace where temperature control can be executed with precision.
Further, the brazing at low temperatures cannot be applied to the
joining of the large sized members such as the automobile body to
require design freedom of the shape of a joint, and so forth
because it takes long time to implement joining by so doing.
[0043] With the method for carrying out the MIG welding using the
solid wire made of the aluminum alloy with addition of silicon, as
a welding wire, as described in Patent Document 12, there exist a
problem in that not only an expensive power supply is required to
effect high precision control of heat input conditions and so
forth, but also the shape of a joint is strictly limited. For this
reason, this method is not applicable to, for example, the large
sized members such as the automobile body, and so forth either.
[0044] In the case of the techniques whereby arc welding, and so
forth, using the fluoride-based mixed flux in as-coated state, are
executed to cope with the problems described in the foregoing,
effects of improvement in arc-weldability, by the agency of the
flux, can be expected. However, the techniques described in Patent
Documents 13, 14, respectively, were found to have a problem in
that upon actual execution of the arc welding, the fluoride-based
mixed flux itself coated to a weld zone was spattered in a large
amount even within a range of normal work conditions, thereby
rendering it difficult to carry out a welding work itself. There
was also a problem that filler metal was found spread due to
excessive improvement in wettability thereof, thereby causing
incomplete formation of a bead.
[0045] The fluoride-based mixed flux composed of a mixture
containing aluminum fluoride, and potassium fluoride, originally
having a melting point lower than that of aluminum, and cesium
fluoride low in melting point, added to the mixture, will have a
melting point thereof further lowered. Accordingly, there arises a
problem in that a large amount of the flux undergoes evaporation at
the time of welding, so that not only deterioration of workability
results due to evolution of fume, and spattering, and so forth, but
also a high bonding strength cannot be obtained because weld metal
composed of aluminum is excessively spread, thereby preventing
formation of a sound bead.
[0046] It is possible to join together the dissimilar materials,
that is, the mild steel with the pure aluminum member, or the 5000
series aluminum alloy member by use of the aluminum wire
incorporating the flux of a fluoride composition as disclosed in
Patent Documents 13, 14, respectively. However, in the case of
weld-bonding of high-strength dissimilar materials with each other,
that is, the high-strength steel member with the high-strength 6000
series aluminum alloy member, by use of the aluminum wire
incorporating the flux of the fluoride composition as disclosed in
Patent Documents 13, 14, respectively, it is not possible to obtain
a high bonding strength. The same applies to the flux of a fluoride
composition in the case of the spot welding as disclosed in Patent
Document 15.
[0047] This is because the brittle Fe--Al intermetallic compound at
the joint of the low-strength dissimilar materials joined with each
other differs in generation conditions from that at the joint of
the high-strength dissimilar materials joined with each other as
previously described, and in order to obtain a reliable and high
bonding strength, it is necessary to devise and create new joining
conditions for joining the high-strength dissimilar materials with
each other. To put it another way, in reality, there have never
been proposed conditions required for the flux composition, and so
forth, in melt weld-bonding of the high-strength dissimilar
materials with each other, that is, the high-strength steel member
with the high-strength 6000 series aluminum alloy member.
[0048] The invention has been developed to solve those problems
described. It is an object of the invention to provide a flux cored
wire for joining dissimilar materials with each other, capable of
enhancing a bonding strength in melt weld-bonding of the
high-strength dissimilar materials with each other, that is, the
high-strength steel member with the high-strength 6000 series
aluminum alloy member, in particular, and excellent in welding
efficiency, and to provide a method for joining the dissimilar
materials with each other.
[0049] Further, another object of the invention is to provide a
joining method capable of obtaining a high bonding strength by
preventing formation of a brittle intermetallic compound at a joint
when joining an aluminum-base material with a steel-base material
while forming a sound bead and to provide a bonded joint obtained
by the method. The invention is intended to enable continuous
joining to be implemented by use of the method according to the
invention, the continuous joining being under fewer constraints in
geometrics and excellent in workability besides being under fewer
constraints in application conditions, and so forth, and excellent
in general versatility.
[0050] Still further, it is still another object of the invention
to provide a method for joining the dissimilar materials such as a
steel member, and an aluminum member together, by arc welding
capable of executing welding with a high bonding strength even if
the steel member is a galvanized steel member.
[0051] To that end, in accordance with one aspect of the invention,
there is provided a flux cored wire for joining dissimilar
materials together, comprising a flux used for joining of
dissimilar materials including an aluminum member or an aluminum
alloy member and a steel member, with each other and an aluminum
alloy envelope, the interior thereof being filled up with the flux,
wherein the flux has fluoride composition containing AlF.sub.3 in a
range of 0.1 to 15 mass % against the total mass of the flux cored
wire without containing chloride. Further, the flux in a range of
0.3 to 20 mss % against the total mass of the flux cored is
preferably filled in the interior of the aluminum alloy
envelope.
[0052] Herein, in order to enhance a bonding strength, the
following mode is preferably adopted. More specifically, an
aluminum alloy of the envelope preferably contains Si in a range of
1 to 13 mass %, the balance being composed of Al and unavoidable
impurities. Further, the aluminum alloy of the envelope preferably
further contains Mn in a range of 0.1 to 0.3 mass %. Still further,
the steel member is preferably a galvanized steel member.
[0053] If the flux cored wire according to the invention is applied
to joining of a high tensile steel member with a 6000 series
aluminum alloy member, this is particularly preferable.
[0054] In another aspect of the invention, there is provided a
method for joining dissimilar materials together comprising the
step of melt-welding the dissimilar materials including a high
tensile steel member and a 6000 series aluminum alloy member, with
each other, by use of the flux cored wire of preferred modes
described above, or described above and to be described later.
[0055] To that end, there may be provided a method for joining
dissimilar materials together comprising the step of an AC-MIG
welding for directly joining an aluminum member or an aluminum
alloy member with a steel member by use of a flux cored wire formed
by coating a flux containing potassium fluoride, aluminum fluoride,
and at least one fluoride selected from the group consisting of
magnesium fluoride, calcium fluoride, strontium fluoride, and
barium fluoride with aluminum or an aluminum alloy, as a filler
metal.
[0056] The steel member described as above is preferably a
galvanized steel member.
[0057] In still another aspect of the invention, there is provided
a bonded joint wherein a steel based member is joined with an
aluminum based member by any of the methods for joining dissimilar
materials together, described in the foregoing.
[0058] A method for joining dissimilar materials together may
comprises the step of joining an aluminum member or an aluminum
alloy member with a steel member by either an AC-MIG welding or a
MIG welding by DC reversed polarity with the use of a flux cored
wire, wherein the flux cored wire is formed by filling up the
interior of an envelope made up of an aluminum member or an
aluminum alloy member with a flux, the flux for filling up is mixed
with aluminum fluoride, and potassium fluoride to be turned into a
mixed flux, and a loading weight of the mixed flux is in a range of
0.1 to 24 mass %, against the total mass of the flux cored
wire.
[0059] The method for joining dissimilar materials together,
described as above, is preferably applied to a galvanized steel
member such as a hot-dip galvanized steel sheet, relatively large
in plating thickness, poorer in weldability than a bare steel, and
exhibiting pronounced deterioration in bonding strength, and so
forth,
[0060] The mixed flux described as above preferably has a melting
point in a range of 560 to 700.degree. C., and the flux cored wire
is preferably not more than 1.6 mm .PHI. in diameter.
Effect of the Invention
[0061] In order to enhance a bonding strength in melt weld-bonding
of high-strength dissimilar materials with each other, such as the
high-strength steel member and the high-strength 6000 series
aluminum alloy member with each other to a reliability level, and
practicality level, there is the need for checking generation of a
brittle intermetallic compound at a joint more than in the case of
joining low-strength dissimilar materials with each other.
[0062] Accordingly, the flux used in the melt weld-bonding of
dissimilar materials with each other is required to have not only
effects of removing an oxide film formed on the surface of a member
to be welded, such as an aluminum alloy member, by reduction, but
also effects of checking growth of an Fe--Al intermetallic compound
layer generated in a weld zone of the steel member. In order for
the flux to exhibit the effects of checking the growth of the
Fe--Al intermetallic compound layer, the flux used in the melt
weld-bonding of the dissimilar materials with each other is
required to act on the surface of the steel member, thereby
fulfilling a function for blocking interdiffusion between Fe and
Al.
[0063] The inventor, et al. have found out that effects of an
action for blocking the interdiffusion between Fe and Al are
profoundly exhibited in a flux of fluoride composition, or
fluoride-base, particularly, in a flux containing AlF.sub.3
(aluminum fluoride). In other words, a flux of fluoride composition
not containing AlF.sub.3 is small in the effects of the action for
blocking the interdiffusion between Fe and Al as compared with the
flux of the fluoride composition containing AlF.sub.3. Accordingly,
the flux of fluoride composition not containing AlF.sub.3 is
capable of enhancing a bonding strength in melt weld-bonding of
low-strength dissimilar materials with each other, but cannot
enhance the bonding strength up to the reliability level, and the
practicality level in the melt weld-bonding of the high-strength
dissimilar materials with each other, such as the high-strength
steel member and the high-strength 6000 series aluminum alloy
member with each other.
[0064] A mechanism for the flux of the fluoride composition
containing AlF.sub.3 exhibiting the effects of the action for
blocking the interdiffusion between Fe and Al, and the effects of
checking the growth of the Fe--Al intermetallic compound layer
still remains unclear. It is presumed, however, that there is a
good possibility of a specific compound being formed to a small
thickness on the surface (a joint surface) of the steel member
beforehand, and such a product blocking or checking the
interdiffusion between Fe and Al.
[0065] That is, it is resumed that the specific compound formed on
the surface of the steel member acts so as to delay a time when the
Fe--Al intermetallic compound layer (an interfacial reaction layer)
is formed between the steel member and the aluminum alloy member,
so that direct joining of Fe and Al, along with progress in the
melt welding, will not be blocked.
[0066] Thus, the invention provides the flux cored wire using the
flux of fluoride composition containing AlF.sub.3, the flux being
filled in the interior of the envelope. Accordingly, the invention
has excellent effects of providing an aggregate of dissimilar
materials joined, and the method for joining dissimilar materials
together, capable of enhancing a bonding strength in melt
weld-bonding of high-strength dissimilar materials with each other,
in particular, the high-strength steel member with the
high-strength 6000 series aluminum alloy member, and excellent in
welding efficiency.
[0067] Further, with the invention, the flux containing aluminum
fluoride and potassium fluoride, with addition of high melting
point fluorides, is used as a filler material, thereby checking
evaporation of the flux at the time of welding, and improving
workability. By use of the flux, excessive spread of a weld metal
composed of aluminum is checked, thereby forming a sound bead, and
generation of the brittle intermetallic compound at a joint is
prevented, so that it is possible to obtain a high bonding
strength.
[0068] Still further, if the AC-MIG welding is adopted as welding
means, this method has fewer constraints in application conditions,
and so forth, excellent general versatility, fewer constraints in
geometrics, and capability of continuous joining, so that joining
of an aluminum base member with a steel base member can be
efficiently implemented.
[0069] Further, with invention, when a fluoride-based mixed flux is
used in welding, dissimilar materials are joined together by use of
either the AC-MIG welding, or the MIG welding by DC reversed
polarity, relatively low in working current, in the case of the arc
welding. By so doing, scattering of the fluoride-based mixed flux
itself is prevented, thereby improving welding workability.
[0070] Still further, with invention, use is made of the flux cored
wire formed by filling up the interior of the envelope of the
aluminum material with the flux instead of coating the weld zone
directly with the fluoride-based mixed flux as with the case of the
conventional technology previously described. By so doing, the
scattering of the fluoride-based mixed flux itself is prevented,
thereby improving the welding workability.
[0071] Yet further, with invention, for the flux filled up in the
wire, use is made of a mixed flux of a specified composition, mixed
with aluminum fluoride, and potassium fluoride, among
fluoride-based mixed fluxes. And the loading weight of the mixed
flux is set relatively small to fall in a range of 0.1 to 24 mass
%, against the total mass of the flux cored wire. By so doing, it
becomes possible to enhance a bonding strength even in the case of
bimetallic joining of a galvanized steel member such as a steel
member coated with hot-dipped zinc plating, and so forth. In
addition, by so doing, scattering of the fluoride-based mixed flux
itself is prevented, ensuring improvement in welding
workability.
[0072] As a result, according to the invention, when an aluminum
member is joined with a steel member, there are fewer constraints
in application conditions, and so forth, excellent general
versatility, and fewer constraints in geometrics. Furthermore, it
is possible to provide a joining technology whereby continuous
joining, necessary in the case of line welding, is enabled,
generation of the brittle Fe--Al intermetallic compound at a joint,
and occurrence of blowholes in the weld zone are reduced,
deterioration in corrosion resistance is less, and welding
workability is improved. Accordingly, the invention can provide a
bonded joint of dissimilar materials (welded joint of dissimilar
materials) applicable to structural members of the automobile, and
so forth.
BRIEF DESCRIPTION OF THE DRAWINGS
[0073] FIG. 1 is sectional view showing one embodiment of a method
for joining dissimilar materials with each other, according to the
invention;
[0074] FIGS. 2A and 2B are plain views schematically showing a mode
of evaluation on the external appearance of weld beads upon joining
of the dissimilar materials for use in explanation about a criteria
for determining acceptability of a bead shape at a bonded
joint;
[0075] FIG. 3 is a cross-sectional view of a flux cored wire
according to one embodiment of the invention; and
[0076] FIG. 4 is sectional view schematically showing one mode of
evaluation on wettability of the weld beads upon joining of the
dissimilar materials.
DESCRIPTION OF REFERENCE NUMERALS
[0077] 1: flux cored wire (wire with a flux incorporated therein)
[0078] 2: aluminum member [0079] 3: steel member [0080] 4: weld
metal [0081] 5: weld line [0082] 6: flux [0083] 7: aluminum member
[0084] 10: welding torch
BEST MODE FOR CARRYING OUT THE INVENTION
[0085] There are specifically described hereinafter embodiments of
the invention and reasons for limitations of various
requirements.
[0086] Further, the invention is more specifically described
hereinafter with reference to working examples. It is to be
understood, however, that the invention be not limited to those
working examples, and it is obvious that modifications and
variations as appropriate may be made in the invention in light of
the teachings described hereinbefore and hereinafter without
departing from the spirit and scope of the invention
[0087] [1]
(Flux Cored Wire)
[0088] A flux cored wire for use in joining dissimilar materials
together, according to one embodiment of the invention, is a flux
cored wire covered with a tubular envelope (also called a hoop)
filled up with a flux in order to enhance efficiency in
melt-welding. The flux cored wire has an advantage in its
applicability for melt-welding in the case of either highly
efficient fully automatic welding, or semiautomatic welding.
[0089] As for a wire diameter of the flux cored wire, it need only
be sufficient to select an optimum diameter according to welding
workability including the characteristics of a wire feeder, for use
in execution of welding in the case of either the highly efficient
fully automatic welding, or the semiautomatic welding, and so
forth. For example, in the case of common CO.sub.2 gas shield arc
welding, MIG welding, and so forth, use may be made of a small
diameter on the order of 0.8 to 1.6 mm .phi. for general purpose
use.
[0090] As for a method for manufacturing the flux cored wire, a
formed wire tubular in shape is first fabricated by a process
comprising the steps of forming an aluminum alloy hoop for the
envelope into a shape resembling the letter U, filling up a formed
hoop in the shape resembling the letter U with a flux, forming a
U-shaped hoop into a tubular wire, and so forth. Thereafter, the
flux cored wire can be manufactured by a common manufacturing
method comprising the step of drawing the formed wire tubular in
shape so as to have a product FCW diameter.
[0091] The flux cored wire (hereinafter referred to merely as a
wire, or an FCW) generally includes a type having a line of
juncture (crevice, opening: hereinafter referred to also as a seam)
on the hoop, and a seamless type having no crevice (without the
line of juncture), fabricated by sealing a line of juncture by
welding and so forth. With the invention, any of those types may be
used. Further, there are several types of cases as to a shape into
which an end of an aluminum sheet is folded at the time of the
tubular wire being formed, lack or presence of seam welding, and so
forth, however, with the invention, use may be made of any of those
types.
(An Aluminum Alloy for Envelope)
[0092] For a tubular envelope (called also as a hoop) of the flux
cored wire, use is made of an aluminum alloy band instead of a
steel band normally in use in order to check formation of an Fe--Al
intermetallic compound layer between steel and an aluminum alloy
member.
[0093] In this case, an aluminum alloy making up the envelope
preferably contains Si in a range of 1 to 13 mass %, the balance
being composed of Al and unavoidable impurities. The main reason
for this is because of necessity of securing fluidity of aluminum
alloy in a molten state, the strength of a joint after
solidification, the strength of the envelope, and so forth. If Si
content is too low, this will cause deterioration in the fluidity,
and strength. On the contrary, if Si content excessively increases,
this will cause weld metal to be more prone to be brittle besides a
tendency of enhancement in the fluidity reaching saturation. Hence,
if Si is to be contained, the Si content is to fall in the range of
1 to 13 mass %.
[0094] In this connection, the less the Si content, the stronger
will be a tendency of enhancement in ductility, so that in the case
of application of the envelope to automobile members of which
impact resistance properties, and so forth are required, use is
suitably made of an aluminum alloy having Si content on a lower
side, particularly in a range of 1 to 3 mass %. In contrast, in the
case of high precision being required of an FCW-feed capacity in
the MIG welding, and so forth, the envelope needs strength, in
which the envelope preferably has Si content in a range of 9 to 13
mass %.
[0095] The aluminum alloy making up the envelope preferably further
contains Mn in a range of 0.1 to 0.3 mass %, in addition to Si, the
balance being composed of Al and unavoidable impurities. The main
reason for this is because of necessity of further securing the
fluidity of the aluminum alloy in the molten state, the strength of
the joint after solidification, the strength of the envelope, and
so forth. If Mn content is too low, those effects described are not
obtained. On the contrary, if Mn content excessively increases,
this will cause the weld metal to be more prone to be brittle
besides the tendency of enhancement in the fluidity reaching
saturation. Hence, if Mn is to be contained, the Mn content is to
fall in the range of 0.1 to 0.3 mass %.
[0096] For an envelope of such an aluminum alloy composition as
above-described, use is preferably made of an aluminum alloy filler
metal standardized for general use. For the aluminum alloy filler
metal of the aluminum alloy composition described, use is
preferably made of an A4047 type containing Si in a range of 11.0
to 13.0 mass %, and not more than 0.15 mass % of Mn. Further, use
can be also made of an A4043 type containing Si in a range of 4.5
to 6.0 mass %, and not more than 0.05 mass % of Mn.
(Flux Composition)
[0097] The flux filled in the interior of the envelope, according
to the invention, is assumed to have fluoride composition without
containing chloride. If a chloride remains in a weld zone, the
chloride acts as a factor for promotion of corrosion of the weld
zone, or the aggregate of the dissimilar materials joined, and
therefore, chloride content is to be controlled. The flux
preferably contains no chloride therein at all, however, taking
cost and practicality into consideration, with the invention,
chloride content is permissible provided that the same is within a
range where corrosion is not promoted. As a guide for this
condition, chloride content is to be kept to not more than 1 mol %
against the flux in total.
[0098] The flux according to the invention similarly permits the
case where oxide is contained as a constituent of the flux. More
specifically, aluminum oxide, sodium oxide, lithium oxide,
diphosphorus pentaoxide, and so forth may be added as appropriate
within a range where effects of fluoride are not impaired. The
upper limit of oxide content is on the order of about 30 mol %
against the flux in total.
[0099] There are cases where it is possible to obtain advantageous
effects of controlling excessive wetting of molten metal, and so
forth, besides decrease in spattering at the time of welding, if
aluminum alloy powders are mixed with the flux according to the
invention to be subsequently added thereto.
[0100] The flux serving as a core material is structured so as to
be enclosed by the envelope of the aluminum alloy, however, if a
loading weight of the flux in the envelope is insufficient, the
flux is not stabilized in weight, so that there arises a problem of
variation occurring to the loading weight (filling factor, content)
of the flux by the region of FCW. To cope with this problem, in the
case of the loading weight of the flux being insufficient, in
particular, it is preferable to mix the flux and the aluminum alloy
powders with the envelope to be filled therein because that will
eliminate or alleviate the problem, and can concurrently gain the
advantage of facilitating fabrication itself of FCW.
[0101] Further, if an addition weight of the aluminum alloy powders
added to the flux is excessively large, there can be the case where
a problem occurs to the FCW-feed capacity besides a possibility
that an arc becomes unstable in the case of arc welding. For this
reason, excessively large addition of the aluminum alloy powders to
the flux should be avoided. If aluminum alloy powders added to the
flux is basically identical in material kind to the composition of
the envelope of the aluminum alloy, this will suffice. Otherwise,
use may be made of aluminum alloy powders differing from the
envelope of the aluminum alloy. The aluminum alloy powders
described as above include the aluminum alloy powders of, for
example, A1000 series, 3000 series, 4000 series, 5000 series, 6000
series, and so forth.
(Fluoride Composition)
[0102] For the basic composition of the flux according to the
invention, a fluoride composition is adopted in order to exhibit
effects of removing an oxide film formed on the surface of a member
to be welded, such as an aluminum alloy member, by reduction, or by
dissolution. The aluminum alloy member before being joined has a
very sturdy oxide film formed on the surface thereof, which
interferes with energization at the time of welding. Accordingly,
if the effects of removing the oxide film on the surface by
reduction are insufficient, a bonding strength cannot be enhanced
up to the reliability level, or the practicality level in the case
of joining high-strength dissimilar materials with each other, such
as a high-strength steel member, and a 6000 series aluminum alloy
member, with each other, by melt weld-bonding.
[0103] For a fluoride having those effects described as above, use
is preferably made of a material containing at least one fluoride
selected from the group consisting of K.sub.3AlF.sub.46,
K.sub.2AlF.sub.6, KF, AlF, CaF, LiF, KAlF.sub.4, K.sub.2TiF.sub.6,
K.sub.2ZrF.sub.6, ZnF.sub.2, ZnSiF.sub.6, and so forth. Further, it
is necessary to avoid use of a fluoride likely to act the factor
for promotion of the corrosion as is the case with the chloride as
previously described if the fluoride remains in the weld zone. The
fluorides described as above by way of example are low in
solubility into an aqueous solution, so that those fluorides have
few deleterious influences described as above. In contrast,
fluorides such as cesium fluoride (CsATF.sub.4), and so forth,
having solubility into an aqueous solution, far in excess of 100
g/ml, are prone to act as the factor for promotion of the
corrosion, and use thereof therefore should be avoided.
(AlF.sub.3)
[0104] The invention has the largest feature in that AlF.sub.3
(aluminum fluoride) in a range of 0.1 to 15 mass %, preferably in a
range of 0.4 to 15 mass % against the total mass of the flux cored
wire is in the flux of the fluoride composition described as above
in order to exhibit effects of an action for blocking
interdiffusion between Fe and Al, and effects of checking growth of
an Fe--Al intermetallic compound layer.
[0105] As described in the foregoing, with the flux of the fluoride
composition, particularly, with the flux containing AlF.sub.3,
there are profoundly exhibited the effects of the action for
blocking the interdiffusion between Fe and Al, and the effects of
checking the growth of the Fe--Al intermetallic compound layer.
With the flux of the fluoride composition containing AlF.sub.3, a
specific compound is formed to a small thickness on the surface (a
joint surface) of the steel member beforehand, and timing for
forming the Fe--Al intermetallic compound layer between the steel
member, and the aluminum alloy member during melt welding is
delayed, thereby blocking, or checking the interdiffusion between
Fe and Al.
[0106] If AlF.sub.3 content is too low, the effects of the action
for blocking the interdiffusion between Fe and Al will be
insufficient as with the case of a flux of a fluoride composition
not containing AlF.sub.3. For this reason, in the case of joining
the high-strength dissimilar materials, such as the high-strength
steel member, and the 6000 series aluminum alloy member, with each
other, by melt welding, the bonding strength cannot be enhanced up
to the reliable level, or the practical level.
[0107] On the other hand, as the AlF.sub.3 content increases, so
does the thickness of the Fe--Al intermetallic compound layer,
however, if the AlF.sub.3 content is excessively high, this will
cause another problem of an increase in spattering and evolution of
fume besides the advantageous effects thereof coming to be
saturated. Hence, the AlF.sub.j content in the flux of the fluoride
composition is to fall in a range of 0.1 to 15 mass %, preferably
in a range of 0.4 to 15 mass %, against the total mass of the flux
cored wire.
[0108] AlF.sub.3 may be contained not necessarily in the form of
AlF.sub.3 but in the form of K.sub.3AlF.sub.6 (25 AlF.sub.3+75 KF),
and K.sub.2AlF.sub.6 (33 AlF.sub.3+67 KF), respectively.
(Flux Loading Weigh)
[0109] The loading weight of the fluoride-based flux in the
envelope of the aluminum alloy (weight of the fluoride-based flux
in the flux cored wire) corresponds to a range of 0.3 to 20 mass %
against the total mass of the flux cored wire. If the loading
weight of the fluoride-based flux in the envelope of the aluminum
alloy exceeds 20 mass % against the total mass of the flux cored
wire, this will cause the effects of the oxide film formed on the
surface of the member to be welded being removed as a result of
reduction to become excessively large. Accordingly, a molten region
excessively expands, causing rather growth of the Fe--Al
intermetallic compound layer, so that there arises a problem with
welding strength. Besides, there occurs an increase in spattering,
and evolution of fume, thereby causing a problem of impairing
workability and the external appearance of the weld zone. On the
contrary, if the loading weight of the fluoride-based flux in the
envelope of the aluminum alloy is less than 0.3 mass % against the
total mass of the flux cored wire, the addition effects of the
fluoride-based flux will be insufficient. In order to ensure the
effects of the flux with reliability, the loading weight of the
flux corresponds more preferably to a range of 5 to 15 mass %
against the total mass of the flux cored wire.
(Melt Welding Method)
[0110] Since there is no particular limitation to a melt welding
method adopted in the joining of the dissimilar metal members,
according to the invention, use can be made of a general-purpose
melt welding method employing a heat source such as an arc, a
laser, and so forth. For example, the MIG method, TIG method, and
laser method, or a hybrid welding method thereof can be used. Upon
actual application of melt welding, various factors, such as the
envelope of the flux cored wire, the flux composition, and so
forth, are taken into consideration according to the shape as well
as the kind of each of the members to be welded together, and the
structure as well as the shape of the aggregate of the dissimilar
materials joined, or joint characteristics as required, thereby
selecting a welding method, and optimizing welding conditions.
[0111] A common welding mechanism (process) in the case of the flux
cored wire according to the invention being applied to the method
for melt welding the dissimilar materials, such as the steel
member--the aluminum alloy member, is as described hereunder
regardless of any method selected out of those melt welding
methods.
[0112] First, an aluminum alloy among respective portions of the
aluminum alloy member and the steel member, to be welded, undergoes
partial melting due to heat being inputted from a suitable source.
Almost simultaneously, there occurs melting of the flux cored wire
according to the invention, fed in the vicinity of the weld zone of
the steel member--the aluminum alloy member. At this point in time,
melting will not occur on the steel member side of the weld zone if
an appropriate heat input condition is set. Further, the oxide film
on the surface of the aluminum alloy member is removed by reduction
by the agency of the flux in as-molten state, whereupon an aluminum
alloy constituent of the envelope of the flux cored wire causes
wetting of the surface of the aluminum alloy member to be then
spread. Thereafter, as an input heat quantity decreases, a molten
zone undergoes solidification, thereby forming a joint.
[0113] With the welding mechanism, the flux cored wire according to
the invention executes not only removal by reduction of the oxide
film on the surface of the member to be welded but also checks the
growth of the brittle Fe--Al intermetallic compound to be generated
in the weld zone of the steel member during the flux being in
as-molten state. That is, the flux according to the invention,
containing AlF.sub.3, in as-molten state, acts on the surface of
steel, and fulfils a function for blocking the interdiffusion
between Fe and Al, thereby enhancing the bonding strength of the
aggregate of the dissimilar materials joined.
(Sheet Thickness of the Steel Member)
[0114] A sheet thickness of the steel member of the joint of the
dissimilar materials is preferably in a range of 0.3 to 3.0 mm. If
the sheet thickness of the steel member is less than 0.3 mm, it is
not possible to ensure strength and rigidity required of the
structural member, and structural material, which is improper. If
the sheet thickness of the steel member exceeds 3.0 mm, it is not
possible to attain reduction in weight of the steel member serving
as the structural member, or the structural material.
(The Steel Member)
[0115] There is no particular limitation to a shape of the steel
member for use in the invention, and use can be made of the steel
member in any shape as appropriate, such as a steel sheet, section
steel, steel pipe, and so forth, for general use as the structural
member, or diverted from application for the structural member,
provided, however, that the steel member is a high tensile steel
(Hi-Ten) having tensile strength not lower than 400 MPa, preferably
not lower than 500 MPa in order to obtain a light-weight
high-strength structural member (the aggregate of the dissimilar
materials joined) such as an automobile member.
[0116] In general, low-strength steel having tensile strength lower
than 400 MPa, and mild steel are each mostly low alloy steel, and
an oxide film thereof is composed of iron oxide, so that the
interdiffusion between Fe and Al is facilitated, and the brittle
Fe--Al intermetallic compound is prone to be formed. Furthermore,
there will be an increase in the sheet thickness necessary for
obtaining strength as required, so that reduction in weight will
have to be sacrificed.
(Zinc Plating)
[0117] If zinc plating is provided on the surface of the steel
member to be joined (at least a joint surface thereof, against the
aluminum alloy member) beforehand, this will enhance wettability of
the flux. Furthermore, since the zinc plating is on the joint
surface interposed between the steel member, and the aluminum alloy
member, there can be gained the advantage of the aggregate of the
dissimilar materials joined having excellent corrosion resistance.
Still further, there can be gained effects of enhancing the bonding
strength by the agency of the following action. Also, at the time
of welding, the zinc plating has effects of delaying timing of
forming an interfacial reaction layer that is the Fe--Al
intermetallic compound. Yet further, presence (interposition) of
the zinc plating causes an increase in resistance heating value at
the tine of the melt welding, a diffusion rate at an interface
between aluminum and steel considerably increases, and aluminum
undergoes diffusion toward steel, thereby gaining effects of
quickly ensuring an excellent jointing state.
[0118] The known zinc plating on the steel member, such as pure
zinc plating, alloy zinc plating, alloying zinc plating, and so
forth, is applicable to the zinc plating described as above.
Further, plating means may include electroplating, hot-dip plating,
alloying treatment applied after the hot-dip plating, and so forth,
and there is no particular limitation to the plating means. A
thickness of the zinc plating, in a normal film thickness (average
film thickness) range of 1 to 20 .mu.m, is sufficient. If the
thickness is too small, a zinc plating film is melted to be
discharged from the joint at the outset of joining at the time of
welding, thereby failing to exhibit the effects of checking
formation of the interfacial reaction layer. In contrast, if the
thickness is too large, a large input heat value is required for
melting and discharging zinc form the joint. If the input heat
value increases, this will cause an increase in quantity of the
aluminum alloy member in the molten state, resulting in an increase
in reduction value of section thickness on the side of the aluminum
alloy member, due to occurrence of chill, so that there is a
possibility that the aggregate of the dissimilar materials joined
cannot be used as the structural member.
(Aluminum Alloy Member)
[0119] There is no particular limitation to a shape of an aluminum
alloy member for use in the invention, and selection, as
appropriate, is made of a sheet member, shaped member, forged
member, or cast member, and so forth, for general use according to
properties required of respective structural members, provided,
however, that the higher the strength of the aluminum alloy member,
the more preferable it is as the structural member as with the case
of the steel member. In this respect, use is made of A6000 series
aluminum alloy of Al--Mg--Si base, high in strength, less in
amounts of alloying elements, and excellent in recyclability, for
general use as this type of the structural member, among the
aluminum alloy members.
[0120] A sheet thickness of the aluminum alloy member for use in
the invention is preferably in a range of 0.5 to 4.0 mm. If the
sheet thickness of the aluminum alloy member is less than 0.5 mm,
the aluminum alloy member is found lacking in strength as the
structural material for the automobile, and so forth, and
absorbency of energy at the time of vehicle body collision, which
is improper. On the other hand, if the sheet thickness of the
aluminum alloy member exceeds 4.0 mm, it becomes impossible to
attain reduction in weight of the aluminum alloy member serving as
the structural member, or the structural material, as with the case
of the steel member.
WORKING EXAMPLES
[0121] There are described hereinafter working examples according
to one embodiment of the invention. BY applying melt-welding to a
commercially available A6063 aluminum alloy sheet overlaid on a
commercially available alloying zinc hot-dip steel sheet (GA) steel
sheet (Hi-Ten) of 590 MPa class, aggregates of the dissimilar
materials joined together were fabricated, and bonding strengths
were evaluated.
TABLE-US-00001 TABLE 1 Flux Flux AlF.sub.3 content content Welded
joint Composition (against a (against a properties (numerical total
mass total mass External Breaking values indicate of FCW) of FCW)
Welding appearance strength Classification No. mixed mol ratios)
mass % mass % method of a bead N/mm Working 1 40AlF.sub.3--60KF 0.3
0.12 MIG 3 .largecircle. example 2 40AlF.sub.3--60KF 1 0.40 MIG 4
.largecircle. 3 40AlF.sub.3--60KF 5 2.00 MIG 4 .circleincircle. 4
40AlF.sub.3--60KF 10 4.00 MIG 4 .circleincircle. 5
40AlF.sub.3--60KF 15 6.00 MIG 4 .circleincircle. 6
40AlF.sub.3--60KF 20 8.00 MIG 3 .circleincircle. 7
75AlF.sub.3--25KF 0.3 0.23 Laser 3 .largecircle. 8
75AlF.sub.3--25KF 1 0.75 Laser 3 .largecircle. 9 75AlF.sub.3--25KF
5 3.75 Laser 4 .circleincircle. 10 75AlF.sub.3--25KF 10 7.50 Laser
4 .circleincircle. 11 75AlF.sub.3--25KF 15 11.25 Laser 4
.circleincircle. 12 75AlF.sub.3--25KF 20 15.00 Laser 3
.circleincircle. 13 K.sub.3AlF.sub.6 0.3 0.10 Laser 3 .largecircle.
14 K.sub.3AlF.sub.5 1 0.25 Laser 4 .largecircle. 15
K.sub.3AlF.sub.6 5 1.25 Laser 4 .circleincircle. 16
K.sub.3AlF.sub.6 10 2.50 Laser 4 .circleincircle. 17
K.sub.3AlF.sub.6 15 3.75 Laser 4 .circleincircle. 18
K.sub.3AlF.sub.6 20 5.00 Laser 3 .circleincircle. 19
K.sub.2AlF.sub.5 0.3 0.10 MIG 3 .largecircle. 20 K.sub.2AlF.sub.5 1
0.33 MIG 4 .largecircle. 21 K.sub.2AlF.sub.5 5 1.65 MIG 4
.circleincircle. 22 K.sub.2AlF.sub.5 10 3.30 MIG 4 .circleincircle.
23 K.sub.2AlF.sub.5 15 4.95 MIG 4 .circleincircle. 24
K.sub.2AlF.sub.5 20 6.60 MIG 3 .circleincircle.
TABLE-US-00002 TABLE 2 Flux Flux AlF.sub.3 content content Welded
joint (against a (against a properties Composition total mass total
mass External Breaking (numerical values indicate of FCW) of FCW)
Welding appearance strength Classification No. mixed mol ratios)
mass % mass % method of a bead N/mm Working 25
10AlF.sub.3--45LiF--30Na.sub.2O--15P2O.sub.5 0.3 0.03 MIG 3
.largecircle. example 26
10AlF.sub.3--45LiF--30Na.sub.2O--15P.sub.2O.sub.5 1 0.10 MIG 4
.largecircle. 27 10AlF.sub.3--45LiF--30Na.sub.2O--15P.sub.2O.sub.5
5 0.50 MIG 4 .circleincircle. 28
10AlF.sub.3--45LiF--30Na.sub.2O--15P.sub.2O.sub.5 10 1.00 MIG 4
.circleincircle. 29
10AlF.sub.3--45LiF--30Na.sub.2O--15P.sub.2O.sub.5 15 1.50 MIG 4
.circleincircle. 30
10AlF.sub.3--45LiF--30Na.sub.2O--15P.sub.2O.sub.5 20 2.00 MIG 3
.circleincircle. Comparative 31 40AlF.sub.3--60KF 0.1 0.04 MIG 1
.DELTA. example 32 40AlF.sub.3--60KF 30 12.00 MIG 2 .DELTA. 33
75AlF.sub.3--25KF 0.1 0.08 Laser 2 .DELTA. 34 75AlF.sub.3--25KF 30
22.50 Laser 2 .DELTA. 35 K.sub.3--AlF.sub.6 0.1 0.03 Laser 1
.DELTA. 36 K.sub.3--AlF.sub.6 30 7.50 Laser 2 .largecircle. 37
K.sub.2--AlF.sub.5 0.1 0.03 MIG 2 .DELTA. 38 K.sub.2--AlF.sub.5 30
9.90 MIG 2 .largecircle. 39
10AlF.sub.3--45LiF--30Na.sub.2O--15P.sub.2O.sub.5 0.1 0.01 MIG 1
.DELTA. 40 10AlF.sub.3--45LiF--30Na.sub.2O--15P.sub.2O.sub.5 30
3.00 MIG 2 .largecircle. 41 20CaF--80KF 0.1 0.00 MIG 1 X 42
20CaF--80KF 30 0.00 MIG 2 .DELTA.
TABLE-US-00003 TABLE 3 K.sub.3AlF.sub.6 flux Flux content AlF.sub.3
content Aluminum alloy (against a (against a of an envelope Welded
joint properties total mass total mass Si Mn External Breaking of
FCW) of FCW) content content Welding appearance strength Elongation
Classification No. mass % mass % mass % mass % method of a bead
N/mm % Working 43 15 3.75 1.0 0.03 Laser 3 .largecircle.
.largecircle. example 44 15 3.75 1.5 0.03 Laser 3 .largecircle.
.largecircle. 45 15 3.75 2.0 0.03 Laser 3 .circleincircle.
.circleincircle. 46 15 3.75 2.5 0.03 Laser 4 .circleincircle.
.circleincircle. 47 15 3.75 2.9 0.03 Laser 4 .circleincircle.
.circleincircle. 48 15 3.75 3.2 0.03 Laser 4 .circleincircle.
.largecircle. 49 15 3.75 5.0 0.03 Laser 4 .circleincircle.
.largecircle. 50 15 3.75 12.0 0.03 Laser 4 .circleincircle.
.largecircle. 51 15 3.75 2.5 0.08 Laser 4 .circleincircle.
.circleincircle. 52 15 3.75 2.5 0.15 Laser 4 .circleincircle.
.largecircle..largecircle..largecircle. 53 15 3.75 2.5 0.28 Laser 4
.circleincircle. .largecircle..largecircle..largecircle. 54 15 3.75
1.0 0.03 MIG 3 .largecircle. .largecircle. 55 15 3.75 1.5 0.03 MIG
3 .largecircle. .largecircle. 56 15 3.75 2.0 0.03 MIG 3
.circleincircle. .circleincircle. 57 15 3.75 2.5 0.03 MIG 4
.circleincircle. .circleincircle. 58 15 3.75 2.9 0.03 MIG 4
.circleincircle. .circleincircle. 59 15 3.75 3.2 0.03 MIG 4
.circleincircle. .largecircle. 60 15 3.75 5.0 0.03 MIG 4
.circleincircle. .largecircle. 61 15 3.75 12.0 0.03 MIG 4
.circleincircle. .largecircle. 62 15 3.75 2.5 0.08 MIG 4
.circleincircle. .circleincircle. 63 15 3.75 2.5 0.15 MIG 4
.circleincircle. .largecircle..largecircle..largecircle. 64 15 3.75
2.5 0.28 MIG 4 .circleincircle.
.largecircle..largecircle..largecircle. Comparative 65 15 3.75 0.7
0.03 Laser 1 .largecircle. .DELTA. example 66 15 3.75 14.0 0.03
Laser 4 .largecircle. X 67 15 3.75 2.5 0.35 Laser 4 .largecircle.
.DELTA. 68 15 3.75 0.7 0.03 MIG 1 .largecircle. .DELTA. 69 15 3.75
14.0 0.03 MIG 4 .largecircle. X 70 15 3.75 2.5 0.35 MIG 4
.largecircle. .DELTA.
[0122] In Tables 1, and 2, there are shown the working examples
obtained by variously changing flux composition, flux content (mass
%: content against a total mass of FCW, and a welding method
[0123] In Table 3, there are shown the working examples obtained by
variously changing the welding method, and Mn content as well as Si
content of an aluminum alloy of an envelope while K.sub.3AlF.sub.6
(25 AlF.sub.3+75 KF), as the composition of a flux, is kept
constant, and the flux content and AlF.sub.3 content of the flux
are also kept constant.
(Member to be Welded)
[0124] In common with Tables 1 to 3, an A6063 aluminum alloy sheet
2. 5 mm in sheet thickness, and a GA steel sheet 1.2 mm in sheet
thickness were prepared, and disposed such that the aluminum alloy
sheet was overlapped over the GA steel sheet with a mutual lapping
width kept in a range of 5 to 20 mm.
(Melt Welding Method)
[0125] In common with Tables 1 to 3, welding by the laser method,
or MIG method was applied to the central part (an overlapped joint
in a single layer) of portions of both the sheets, overlapped as
above, in whole regions in the widthwise direction of both the
sheets. With the laser method, a continuous wave YAG laser as
defocused was adopted under conditions of an output at 2 to 4 kW,
and weld velocity in a range of 0.8 to 2.0 m/min, using Ar as a
shield gas. With the MIG method, conditions of an AC welding
current in a range of 30 to 80 A, a welding voltage in a range of 7
to 18V, and a weld velocity in a range of 15 to 60 cm/min were
adopted.
(Flux Cored Wire) In common with Tables 1, and 2, use was made of
an aluminum alloy filler metal (Si: 12.0 mass %, Mn: 0.1 mass %)
corresponding to A4047, as an envelope and only the composition of
the flux was variously changed. Further, if a weight of the flux in
the flux cored wire corresponds to not more than 1 mass % against
the total weight of a flux cored wire, metal powers were added
thereto. The metal powers were aluminum alloy powders (grain size:
150 .mu.m) of composition corresponding to A4047 as with the case
of the envelope, and addition was made of the metal powers
corresponding to 20 mass % against the total weight of the flux
cored wire.
[0126] In common with Tables 1 to 3, respective fluxes of types
(compositions) shown as below were prepared by melting and
pulverizing to be subsequently processed into the shape of a flux
cored wire 1.2 mm # in wire diameter by the method previously
described. Further, in common with Tables 1 to 3, numerical values
of flux composition indicate mixed mol ratios (100 for total) of
respective flux constituents (the flux constituents not indicating
numerical values each represent a mol ratio at 100). Further, in
common with Tables 1 to 3, the respective fluxes except for the
case of (2) including Na.sub.2O, P.sub.2O.sub.5, shown as below,
did not chloride contain oxide, and did not effectively contain
chloride either, chloride content thereof being less than 0.1 mol %
against a total flux weight.
(Flux Types)
(1) 20CaF-80 KF
[0127] (2) 10 AlF.sub.3-45 LiF-30Na.sub.2O-15P.sub.2O.sub.5 (3)
K.sub.3AlF.sub.6 (25 AlF.sub.3+75KF) (4) K.sub.2AlF.sub.6 (33
AlF.sub.3+67KF)
(5) 75AlF.sub.3-25KF
(6) 40AlF.sub.3-60KF
(Method for Evaluation on the External Appearance of a Bead)
[0128] In common with Tables 1 to 3, visual observation was made on
the external appearance of a bead, including a quantity of spatters
generated during welding, thereby making evaluations in 4 stages.
The evaluations in the 4 stages were carried out, by designating
the most superior external appearance of the bead (in a sensory
test for evaluation) as 4 while designating the most inferior
external appearance as 1.
(Joint Strength)
[0129] In common with Tables 1 to 3, as for joint strength as the
bonding strength of an aggregate of the dissimilar materials
joined, a joint test piece 30 mm in width, including the joint, was
cut off from a bonded joint, thereby having taken measurements on
breaking strength per unit weld line. If the breaking strength is
not less than 250 N/mm, it is represented by symbol
.circleincircle., if the breaking strength is in a range of 200 to
250 N/mm, it is represented by symbol .largecircle., if the
breaking strength is in a range of 100 to 200 N/mm, it is
represented by symbol .DELTA., and if the breaking strength is less
than 100 N/mm, it is represented by symbol X. Herein, unless the
breaking strength is not less than 200 N/mm (.largecircle.), the
aggregate of the dissimilar materials joined cannot be used as the
structural member for the automobile, and so forth.
(Elongation of the Joint)
[0130] In Table 3, elongation (%) of the joint as the bonding
strength of the aggregate of the dissimilar materials joined was
measured. The elongation per unit weld line was measured also by
cutting off a joint test piece 30 mm in width, including the joint,
from the bonded joint. If the elongation is not less than 10%, it
is represented by symbol .largecircle..largecircle..largecircle.
(triple circles, if the elongation is in a range of 7.5 to 10%, it
is represented by symbol .circleincircle. (double circle), if the
elongation is in a range of 5.0 to 7.5%, it is represented by
symbol .largecircle., if the elongation is in a range of 2.5 to
5.0%, it is represented by symbol .DELTA., and if the elongation is
less than 2.5%, it is represented by symbol X. Herein, unless the
elongation is not less than 5.0% (.largecircle.), the aggregate of
the dissimilar materials joined cannot be used as the structural
member for the automobile, and so forth.
(Respective Results of Tables 1, and 2)
[0131] As is evident from Tables 1, and 2, respectively, an
aggregate of the dissimilar materials joined, according to each of
the working examples 1 to 30, has the AlF.sub.3 content as well as
the loading weight of the fluoride-based flux in the envelope of
the aluminum alloy, falling in the range of the conditions
according to the invention, so that the aggregate of the dissimilar
materials joined has excellent external appearance of the bead, and
joint strength.
[0132] In contrast, since an aggregate of the dissimilar materials
joined, according to each of the comparative examples 31 to 42, has
the AlF.sub.3 content as well as the loading weight of the
fluoride-based flux in the envelope of the aluminum alloy, either
insufficient or excessive, so as to fall outside the range of the
conditions according to the invention, the aggregate of the
dissimilar materials joined was found inferior to each of the
working examples described as above in respect of the external
appearance of the bead, and the joint strength.
(Results of Table 3)
[0133] As is evident from Table 3, an aggregate of the dissimilar
materials joined, according to each of the working examples 43 to
64, has not only the Mn content as well as the Si content of the
envelope of the aluminum alloy but also the AlF.sub.3 content as
well as the loading weight of the fluoride-based flux in the
envelope of the aluminum alloy, falling in the range according to
the invention, so that the aggregate of the dissimilar materials
joined was found to have excellent external appearance of the bead,
joint strength, and elongation.
[0134] In contrast, an aggregate of the dissimilar materials
joined, according to each of the comparative examples 65 to 70, has
the Mn content as well as the Si content of the envelope of the
aluminum alloy, either insufficient or excessive, so as to fall
outside the range of the conditions according to the invention, so
that the aggregate of the dissimilar materials joined was found
inferior to each of the working examples described as above in
respect of the external appearance of the bead, joint strength, and
elongation although the same has the AlF.sub.3 content as well as
the loading weight of the fluoride-based flux in the envelope of
the aluminum alloy, regardless of falling within the range
according to the invention.
[0135] On the basis of results of the tests on the working
examples, described as above, there is demonstrated critical
significance of respective requirements of the flux cored wire for
joining dissimilar materials with each other, according to the
invention, excellent in welding efficiency and for enhancing the
bonding strength, in particular, in the case of joining
high-strength dissimilar materials with each other, such as a
high-strength steel member with a 6000 series aluminum alloy
member, by melt weld-bonding.
[0136] [2]
[0137] With another embodiment of the invention, an AC-MIG welding
is adopted as welding means. For the AC-MIG welding, use can be
made of an AC-MIG welder for general use. Because the AC-MIG welder
is capable of controlling heat input to members to be joined
together with precision, it is possible to control an input heat
value in order to execute melt-mixing of aluminum of an aluminum
based material, and steel of an iron based material, and to check
reactions thereof. By so doing, generation of a brittle
intermetallic compound can be prevented at a joint, thereby
preventing deficiency in strength (occurrence of cracking, in
particular) at the joint. Besides the AC-MIG welding, laser welding
is also applicable as the welding means capable of accurately
controlling the input heat value.
[0138] For a welding wire (filler metal), use is made of a wire
with a flux incorporated therein (a flux cored wire) formed by
coating the flux with aluminum, or an aluminum alloy. As for a
diameter of the wire in use, the wire not more than 1.6 mm in
diameter is preferably used because of the necessity of generating
a stable arc under a low current condition in order to reduce the
input heat value as much as possible. If the diameter of the wire
exceeds 1.6 mm, current for obtaining the stable arc becomes
excessively large, so that melting of a base metal tends to become
excessive, thereby posing the risk of generating a brittle
intermetallic compound (Fe--Al base compound).
[0139] For the flux of the welding wire, use is made of a flux
containing aluminum fluoride, and potassium fluoride, together with
at least one fluoride selected from the group consisting of
magnesium fluoride, calcium fluoride, strontium fluoride, and
barium fluoride.
[0140] In the past, use has been made of the fluoride-based mixed
flux containing aluminum fluoride and potassium fluoride, having a
function of melting and removing a sturdy oxide film on the surface
of an aluminum base material. However, since the melting point of
the mixed flux containing aluminum fluoride and potassium fluoride
is very low, that is, lower than the melting point (660.degree. C.)
of aluminum, a large quantity of the flux undergoes evaporation,
thereby causing deterioration in workability such as evolution of
fume, generation of spatters, and so forth. Further, weld metal
composed of aluminum is excessively spread, thereby preventing
formation of a sound bead, so that it is not possible to obtain a
high bonding strength. Accordingly, for the flux of the welding
wire according to the invention, use is made of a flux containing a
flux obtained by adding at least one fluoride, or not less than two
fluorides, selected from the group consisting of magnesium fluoride
(melting point: 1248.degree. C.), calcium fluoride (melting point:
1403.degree. C.), strontium fluoride (melting point: about
1400.degree. C.), and barium fluoride (melting point: 1353.degree.
C.), as high melting point compounds among fluorides of elements of
the Group IIA of the Periodic Table, to the mixed flux containing
aluminum fluoride and potassium fluoride. By addition of those high
melting point fluorides, it is possible to raise the melting point
of the flux to a temperature range of about 700 to 1000.degree. C.,
so that excessive spread of the weld metal composed of aluminum,
otherwise occurring at the outset of welding can be checked, a
sound bead can be formed, and scattering as well as evaporation of
the flux at the time of the welding can be checked, thereby
enabling the evolution of fume, and the generation of spatters to
be reduced. If total content of the high melting point fluorides is
excessively high, the flux will have difficulty with melting,
thereby failing to sufficiently exhibit effects of enhancement in
wettability, and on the other hand, if the total content of the
high melting point fluorides is excessively low, effects of rise in
the melting point of the flux will be insufficient, and therefore,
the total content of the high melting point fluorides preferably
corresponds to 10 to 50% of a total mass of the flux.
[0141] There is no particular limitation to a steel-base material
to which a method for joining dissimilar materials together,
according to the invention, is applied provided that the steel-base
material is material containing iron as the main constituent
thereof such as a steel member, an iron based alloy, and so forth.
However, in the case of using the steel member, a galvanized steel
sheet is preferably used from the viewpoint of securing corrosion
resistance thereof. Further, there is no particular limitation to
the strength of the steel sheet. In the case of conventional
welding of a galvanized steel sheet, an arc becomes unstable by the
agency of zinc vapor as evolved, thereby causing problems of
generation of spatters, and occurrence of porous defects such as
pits, blowholes, and so forth, however, with the method for joining
the dissimilar materials together, according to the invention, an
action of cleaning the surface of the steel sheet by virtue of
advantageous effects of the flux is effectively exhibited, and
molten metal covers the surface of the steel sheet with excellent
wettability, so that the zinc vapor as evolved will be less, and
arc stability will be excellent. In consequence, even in the case
of the welding of the galvanized steel sheet, there occurs few
defects such as blowholes, and so forth, and excellence in dynamic
properties such as fatigue strength, and so forth can be
expected.
[0142] As for welding conditions of the AC-MIG welding in carrying
out the invention, a welding current is preferably at not less than
20 A, more preferably at not less than 30 A, and is preferably at
not more than 100 A, more preferably at not more than 80 A. A
welding voltage is preferably at not less than 5V, more preferably
at not less than 7V, and is preferably at not more than 20V, more
preferably at not more than 18V.
[0143] A welding speed may be decided as appropriate within a range
where excessive melting of Al as well as Fe in the base metal can
be prevented, according to the welding current, and the welding
voltage, described as above, however, taking into consideration
welding efficiency, and so forth, the welding speed is preferably
not less than 15 cm/min, more preferably not less than 20 cm/min,
and is preferably not more than 60 cm/min, more preferably more
than 50 cm/min.
[0144] With the invention, a steel-base material can be joined
directly with an aluminum-base material by the AC-MIG welding.
Accordingly, with the AC-MIG welding, it is possible to expand an
applicable range thereof, and to enhance flexibility thereof while
enabling continuous joining to be implemented, without particular
constraints imposed thereon, provided that proper welding current,
voltage condition, joint shape, and so forth are adopted.
Furthermore, both the steel-base material and the aluminum-base
material each can be in a sound boned state with respective melt
weights thereof, kept at a necessary minimum, and a brittle
intermetallic compound is not prone to be formed at an interface
between the steel-base material, and the aluminum-base material,
thereby obtaining a high bonding strength.
WORKING EXAMPLES
[0145] There are described hereinafter working examples according
to an embodiment of the invention. The method for joining
dissimilar materials together, according to an embodiment of the
invention, was adopted, and there were conducted tests on a lap
fillet welding of an aluminum alloy sheet with an alloying zinc
hot-dip galvanized (GA) steel sheet.
[0146] As shown in FIG. 1, an aluminum alloy sheet 1. 6 mm thick is
overlaid on a GA steel sheet 1. 2 mm thick to thereby form an
overlapped fillet joint, and the AC-MIG welding of the aluminum
alloy sheet with the GA steel sheet was carried out by use of
various flux cored wires. For a shield gas, use was made of argon.
Respective test pieces of both the aluminum alloy sheet, and the GA
steel sheet were each 100 mm.times.300 mm in planar size, and a
flux cored wire 1.2 mm in diameter was used.
[0147] For a flux of the flux cored wire, use was made of NOKOLOCK
(registered trademark) flux that is the mixed flux containing
aluminum fluoride, and potassium fluoride, as a comparative
example, while for working examples, use was made of a flux
obtained by adding either one fluoride or two fluorides, selected
from the group consisting of magnesium fluoride (MgF.sub.2),
calcium fluoride (CaF.sub.2,) strontium fluoride (SrF.sub.2), and
barium fluoride (BaF.sub.2), in total amount corresponding to 10 to
15% of the total mass of the flux, to the NOKOLOCK (registered
trademark) flux.
[0148] Welding conditions were the same as the welding conditions
of the AC-MIG welding, as previously recommended, that is, the
welding current: in a range of 30 to 80 A, the welding voltage: in
a range of 7 to 18V, and the welding speed: in a range of 15 to 60
cm/min.
[0149] Bonded joints as obtained were examined, and evaluations
were made on stability of a bead, and joint strength. The stability
of the bead was evaluated by observation of a shape of the bead of
each of the bonded joints as obtained, rating the case of the bead
being discontinuous as defective (X), and the case of the bead
being continuous with a substantially constant width as good
(.largecircle.) (refer to FIGS. 2A and 2B). Further, the evaluation
on the joint strength was made by sampling a
joint-strength-evaluation test piece 30 mm in sheet width from the
respective bonded joints to conduct a tensile test at velocity of
25 mm/min, thereby using shear tensile strength worked out by the
following expression (1).
joint strength=(load at a maximum load point)/(sectional area of a
joint) (1)
where "sectional area of a joint" is a sectional area an aluminum
alloy sheet, in the thickness-wise direction thereof.
TABLE-US-00004 TABLE 4 Fluorides Evaluation of elements Shear
tensile strength Bead No. of the group IIA* (N/mm.sup.2) stability
1 CaF.sub.2 254 .largecircle. 2 CaF.sub.2, MgF.sub.2 205
.largecircle. 3 none 81 X 4 none 53 X 5 SrF.sub.2 192 .largecircle.
6 BaF.sub.2 155 .largecircle. 7 CaF.sub.2, BaF.sub.2 228
.largecircle. 8 MgF.sub.2 242 .largecircle. 9 SrF.sub.2, CaF.sub.2
173 .largecircle. *The fluoride constituents other than the
fluorides of the elements of the Group IIA of the Periodic Table
are KF, and AlF.sub.3 *The fluoride constituents other than the
fluorides of the elements of the Group IIA of the Periodic Table
are KF, and AlF.sub.3
[0150] The results of evaluation tests are shown in Table 4. In the
cases of employing the flux cored wires according to the invention
(working examples), wherein use was made of the flux containing the
high melting point compounds among the fluorides of the elements of
the Group IIA of the Periodic Table in addition to potassium
fluoride and aluminum fluoride, it was found out that welding
workability was excellent with reduction in evolution of fume, and
generation of spatters, bead stability was excellent, and sound
beads with few blowholes were obtained, as compared with the cases
of employing conventional flux cored wires not containing the high
melting point compounds (comparative examples), so that it was
possible to obtain a high bonding strength in the respective
cases.
[0151] (MIG Welding)
[0152] According to still another embodiment of the invention, the
AC-MIG welding, or the MIG welding by DC reversed polarity,
relatively low in working current, as a welding method employed in
joining dissimilar materials together, among the arc welding, is
selected, and the dissimilar materials are joined together by use
of each of those welding, singly, or by use of combination thereof.
By so doing, scattering of the fluoride-based mixed flux itself is
prevented, thereby improving welding workability.
[0153] With the AC-MIG welding, it is possible to control the heat
input to the members to be joined together with precision by
appropriate combination of reversed polarity and positive polarity,
so that the input heat value can be controlled so as to execute
melt-mixing of aluminum of the aluminum based material, and steel
of the iron based material, and to check the reactions thereof. As
a result, generation of the brittle intermetallic compound at the
joint can be prevented, thereby preventing deficiency in strength
(occurrence of cracking, in particular) at the joint. For the
AC-MIG welding, use can be made of the most common spray MIG
welding method. Needless to say, besides this method, use may be
made of the short-circuiting MIG welding method whereby molten
metal at the tip of an electrode wire moves only at the time of
short circuit, and the pulse MIG welding method whereby a stable
pulse arc is obtainable by instantaneously imparting a pulse peak
current higher than the critical current even if an average welding
current is lower than the critical current.
[0154] The MIG welding by the DC reversed polarity, capable of
stabilizing an arc with ease, is effective in the case of the need
for ensuring bead stability, particularly in the case of, for
example, bimetallic joining of a hot-dip galvanized steel sheet. In
the case of the bimetallic joining of the hot-dip galvanized steel
sheet, occurrence of blowholes in a molten metal zone, due to
destabilization of an arc, will pose a problem in particular. If
the MIG welding by the DC reversed polarity is adopted to cope with
this problem, the arc will be stabilized, rendering it easier to
obtain a stable bead. However, in the case of the AC-MIG welding,
since the heat input to the members to be joined together can be
controlled with precision by appropriately combining the reversed
polarity with the positive polarity, as described in the foregoing,
the input heat value can be controlled, so that the AC-MIG welding
has the advantage of checking generation of brittle intermetallic
compounds. In contrast, in the case of the MIG welding by DC
reversed polarity, there is a possibility that an input heat value
is prone to increase even under the same current condition as that
for the AC-MIG welding, resulting in an increase in generation of
brittle intermetallic compounds. For this reason, in the case of
the MIG welding by DC reversed polarity, it is necessary to execute
welding by increasing a welding speed as much as possible, thereby
reducing the input heat value.
[0155] With other melt welding methods other than the respective
MIG welding described as above, such as the TIG welding method,
various melt welding methods using plasma, electron beam,
high-frequency wave, and so forth, a working welding current is
excessively high, and an input heat value is excessively high as
compared with the respective MIG welding described as above.
Accordingly, the fluoride-based mixed flux itself becomes prone to
scatter during welding, thereby impairing welding workability.
Further, it will be more difficult to check generation of the
brittle intermetallic compound at the joint as compared with the
respective MIG welding described. Furthermore, the spot welding,
and so forth are unsuitable for line welding, such as fillet
welding, butt welding, and so forth, required of bimetallic joining
for the structural members of the automobile, as the object of the
invention.
(Wire with a Flux Incorporated Therein)
[0156] With the invention, for a welding wire (filler metal), use
is made of a wire with a flux incorporated therein, formed by
coating a mixed flux containing potassium fluoride, and aluminum
fluoride, described in the present description later on, with an
aluminum alloy. FIG. 3 shows a cross-section of the wire 1 with the
flux incorporated therein, for use in the invention. For the wire 1
with the flux incorporated therein, for use in the invention, use
can be made of a common wire formed by filling up the interior of a
tubular envelope 7 (also called a hoop) of an aluminum material
with a flux 6. The wire with the flux incorporated therein is also
referred to as a flux cored wire (FCW).
[0157] The flux cored wire includes a seamed type having a seam
(line of juncture: crevice, opening), and a seamless type without a
seam, fabricated by sealing the seam by welding, and so forth. With
the invention, any of those types may be used. However, because the
seamless type is higher in fabrication cost, the flux cored wire
having a seam, for general use, is preferable. There is no
particular limitation to the aluminum alloy to be used in the
envelope of the flux cored wire, use can be made of 4000 series
aluminum alloy including A4043, A4047, and so forth, and 5000
series aluminum alloy including A5356, A5183, and so forth.
Besides, use may be made of aluminum alloy including 3000 series,
6000 series, and so forth.
[0158] The flux cored wire (FCW) having the seam can be
manufactured by a common manufacturing method. More specifically,
the manufacturing method comprises the steps of forming an aluminum
alloy sheet or band into a shape resembling the letter U, filling
up a formed sheet or band in the shape resembling the letter U with
a flux, forming a U-shaped sheet or band into a tubular wire, and
so forth. After a formed wire tubular in shape, with the flux
filled therein, is manufactured, as above, and the common
manufacturing method further comprises the step of drawing the
formed wire tubular in shape to a product FCW (flux cored wire) of
a fine diameter in a range of 0.8 to 2.4 mm .PHI..
(Wire Diameter)
[0159] With the invention, however, it is preferable to render the
diameter of the flux cored wire finer than that in the case of the
common manufacturing method, or to use the flux cored wire finer in
diameter. By so doing, the input heat value is lowered, and a lower
current condition is created upon carrying out the AC-MIG welding,
and the MIG welding by the DC reversed polarity. As a result, the
scattering of the fluoride-based mixed flux itself can be
prevented, and the welding workability can be improved.
Furthermore, formation of the brittle intermetallic compounds can
be checked. For this reason, use is preferably made of the flux
cored wire not more than 1.6 mm .PHI. in diameter. If the diameter
of the wire exceeds 1.6 mm .PHI., current for obtaining a stable
arc will become excessively large, causing the scattering of the
fluoride-based mixed flux itself to increase. Further, melting of
the base metal tends to be on an excessive side, thereby leading to
the formation of the brittle intermetallic compounds (Fe--Al base
compounds). The diameter of the flux cored wire is more preferably
not more than 1.4 mm.
[0160] Thus, with the invention, use is made of the flux cored wire
formed by filling up the interior of the envelope of the aluminum
material with the flux instead of coating the weld zone directly
with the fluoride-based mixed flux as with the case of the
conventional technology previously described. By so doing, the
scattering of the fluoride-based mixed flux itself is prevented,
thereby improving the welding workability. Furthermore, the
formation of the brittle intermetallic compounds is checked.
(Flux Composition)
[0161] With the invention, the composition of the flux used (filled
up) in the flux cored wire is that of the mixed flux {referred to
also as the NOKOLOCK (registered trademark) flux} of a specified
composition, mixed with two-fluoride based fluxes, comprising
aluminum fluoride, and potassium fluoride, in particular, among
fluoride-based fluxes.
[0162] With the use of the mixed flux of the specified composition,
it becomes possible to implement bimetallic joining of a steel
member coated with hot-dipped zinc (including alloying zinc)
plating, and an aluminum member. That is, respective surfaces of
the galvanized steel member, and the aluminum member can be cleaned
up, and the wettability of weld metal is improved. As a result,
bead formation becomes excellent. Furthermore, an Fe--Al
intermetallic compound layer formed at a joint of dissimilar
materials, and formation of a brittle Zn--Fe based intermetallic
compound layer attributable to zing plating can be checked. In
consequence, a bonding strength is enhanced. Needless to say, such
advantageous effects are exhibited even in the case of bimetallic
joining of a bare steel member without zinc plating, and an
aluminum member.
[0163] If the AC-MIG welding, and the MIG welding by the DC
reversed polarity, according to the invention, are carried out
under suitable conditions described hereunder by use of the flux
cored wire of the composition according to the invention, this will
make it possible to obtain a suitable thickness of the interfacial
reaction layer (IMC: intermetallic compound), thereby improving the
joint strength. In contrast, if a common arc welding is applied to
bimetallic joining, an intermetallic compound in excess of 20 .mu.m
in thickness will occur to a weld-interface, bringing about
deterioration in the joint strength. On the other hand, if the
respective MIG welding methods described as above are carried out
under suitable conditions described hereunder by use of the flux
cored wire of the composition according to the invention, the
interfacial reaction layer will be formed to a suitable thickness
not more than 10 .mu.m, so that the joint strength will be
significantly improved. Further, even if the respective MIG welding
methods described as above are carried out under suitable
conditions described hereunder by use of a solid wire made of an
aluminum alloy instead of the flux cored wire of the composition
according to the invention, an intermetallic compound in excess of
20 .mu.m in thickness occurs to the weld-interface, bringing about
deterioration in the joint strength. Thus, the flux of the
composition according to the invention, or the flux cored wire of
the composition according to the invention has a large effect of
checking generation of the intermetallic compound although detained
mechanism thereof is still unknown.
[0164] Other fluoride-based mixed fluxes include, for example,
cesium fluoride, zinc fluoride, and so forth, for use in the case
of the conventional technology previously described as well. Even
those other fluoride-based mixed fluxes each have a function of
cleaning up a material surface to an extent. However, in the case
of those other fluoride-based mixed fluxes, cesium fluoride, zinc
fluoride, and so forth are extremely high in hygroscopicity.
Accordingly, there is concern about possibility of deterioration in
corrosion resistance of a weld metal zone besides a tendency of
moisture absorbed causing blowholes to be prone to occur to the
weld metal. Furthermore, in the bimetallic joining of the steel
member coated with hot-dipped zinc plating, and the aluminum
member, advantageous effects of cleaning up the material surface,
and enhancing the wettability of the weld metal will become
less.
[0165] The melting point of the mixed flux {NOKOLOCK (registered
trademark) flux} is preferably adjusted to a melting point falling
in a range of 560 to 700.degree. C. in order that the respective
effects described in the foregoing can be exhibited although
dependent on the welding conditions by the AC-MIG welding, and the
MIG welding by DC reversed polarity, for the bimetallic joining
including the hot-dip galvanized steel member.
[0166] The melting point of the mixed flux can be appropriately
adjusted by respective mixed amounts (a mixing ratio) of aluminum
fluoride (AlF.sub.3) powders, and potassium fluoride (KF) powders,
and is adjusted according to the welding conditions by the AC-MIG
welding, and the MIG welding by DC reversed polarity, for the
bimetallic joining including the hot-dip galvanized steel member.
In this respect, a ratio of aluminum fluoride on the order of 60
mol % is decided as the upper limit on the basis of eutectic
composition of potassium fluoride and potassium fluoride (KF: 55
mol %, AlF.sub.3: 45 mol %). Then, a remaining ratio (the
remainder) is assigned to potassium fluoride, and both the
fluorides are mixed with each other, whereupon the melting point of
the mixed flux is adjusted so as to fall in a melting point range
of 560 to 700.degree. C.
[0167] If the flux melts in this melting point range (temperature
region), wettability is improved at the outset of welding, so that
molten aluminum neatly enters overlapped portions of the steel
member and the aluminum member, thereby exhibiting a glue-like
effect, and improving a bonding strength. Such an effect as
described will be found pronounced particularly with the hot-dip
galvanized steel member. If the melting point of the mixed flux is
below 560.degree. C., this effect will be less. On the other hand,
if the melting point of the mixed flux exceeds 700.degree. C., weld
metal at the outset of the welding will spread less, so that influx
to the overlapped portions of a joint will become insufficient.
(Flux Filling Factor)
[0168] Herein, however, a filling factor of the NOKOLOCK
(registered trademark) flux into the flux cored wire becomes
important. With the invention, the loading weight of the NOKOLOCK
(registered trademark) flux (the mixed flux) is set relatively
small to fall in a range of 0.1 to 24 mass %, against the total
mass of the flux cored wire.
[0169] With a commercially available conventional flux cored wire
for general use, a flux filling factor is large in excess of 24
mass %. Accordingly, even under common welding conditions by the
AC-MIG welding, and the MIG welding by DC reversed polarity, not
only molten flux in large quantity scatters but also the effects of
enhancement in the wettability are excessive, so that a sound bead
cannot be formed. Furthermore, because welding workability is poor,
and the sound bead cannot be formed, reliability of the weld zone
is impaired.
[0170] Accordingly, with the invention, the upper limit of the
filling factor of the NOKOLOCK (registered trademark) flux into the
flux cored wire is set to a level lower than that for the case of
the commercially available conventional flux cored wire for general
use, that is, less than 24 mass %. If the filling factor of the
flux is 24 mass %, or higher, the filling factor of the flux is
excessively high, so that scattering of the molten flux becomes
excessive, and the bead is excessively spread, thereby preventing
the sound bead from being formed, as described in the
foregoing.
[0171] On the other hand, the lower limit of the filling factor of
the NOKOLOCK (registered trademark) flux is set to 0.1%. If the
filling factor of the NOKOLOCK (registered trademark) flux is too
low, the filling factor becomes the same as that of an aluminum
welding wire (JIS specification: A4043-WY, A4047-WY, A5356-WY,
A5183-WY, and so forth) for forming a bead for general use in the
arc welding. For this reason, if the filling factor of the NOKOLOCK
(registered trademark) flux is less than 0.1%, advantageous effects
of the NOKOLOCK (registered trademark) flux, such as the effects of
enhancement in the wettability, and so forth, cannot be exhibited,
so that it is not possible to obtain a sound and highly reliable
welded joint.
[0172] Thus, the method for joining the dissimilar materials
together, according to the invention, has fewer constraints in
application conditions, and so forth, and is excellent in general
versatility while being under fewer constraints in geometrics upon
joining an aluminum member with a steel member including the
hot-dip galvanized steel member. Further, the invention can
provides a joining technology whereby continuous joining necessary
at the time of the line welding is enabled, generation of the
brittle intermetallic compound at the joint, occurrence of
blowholes in the weld zone, and deterioration in corrosion
resistance are reduced, and welding workability is rendered
excellent. Accordingly, it becomes possible to provide a bonded
joint of dissimilar materials (welded joint of dissimilar
materials) applicable to structural members of the automobile, and
so forth.
(MIG Welding Application)
[0173] Next, there is described hereinafter an application mode of
the AC-MIG welding, and the MIG welding by DC reversed polarity,
according to the method of the invention, for joining the
dissimilar materials together, however, the application mode of the
MIG welding is identical to a common method. FIG. 1 shows one mode
of the application. In FIG. 1, an end 2a of an aluminum member 2 is
overlaid on an end 3a of a hot-dip galvanized steel member (or a
bare steel member) 3 to thereby form an overlapped joint for
joining the respective ends 3a, 2a with each other.
[0174] Thereafter, a welding torch 10, and the flux cored wire 1
according the invention are used, and the welding torch 10 is moved
along a weld line 5 extending along the respective ends 3a, 2a of
the steel member 3, and the aluminum member 2 (in the
back-and-forth direction in the figure), thereby applying the
respective MIG welding methods described as above to the full
length of the weld line 5. In this case, a tilt angle .theta. of
the welding torch 10 is selected as appropriate. In FIG. 1,
reference numeral 4 denotes a weld metal (bead) formed on the weld
line 5.
[0175] In the case of the method for joining the dissimilar
materials together, according to the invention, since the steel
member can be directly joined with the aluminum member, the method
will not be subjected to particular constraints provided that
proper welding current, voltage condition, joint shape, and so
forth are adopted, having advantageous effects of continuous
joining being enabled, together with expansion in an applicable
range, and enhancement in general versatility. Further, it is
possible to obtain a sound boned state with a necessary minimum
melt (diluted) weight of the steel member, in the weld metal such
as the bead and so forth, as previously described, and even in the
case of the hot-dip galvanized steel member, the brittle
intermetallic compound is hard to be formed, so that a high bonding
strength can be obtained.
(Welding Conditions)
[0176] There are described hereinafter preferred welding conditions
in order to enhance the bonding strength of a weld zone (joint)
upon welding application in the cases of the respective MIG welding
methods described as above. As for welding conditions, welding is
preferably applied such that a sound boned state can be obtained
with a necessary minimum melt (diluted) weight of a base metal
without causing excessive melt of the steel member, as the base
metal, in order to check generation of the brittle intermetallic
compound otherwise generated at an interface between the aluminum
member, and the steel member.
(Welding Current)
[0177] Upon application of the AC-MIG welding, and the MIG welding
by DC reversed polarity, the larger amperage of a welding current,
the more prone to scatter is the flux, so that the brittle
intermetallic compound generated on a bond-interface will increase.
For this reason, it is recommendable to execute joining on a low
current condition from the viewpoint of checking such scattering of
the flux, and generation of the brittle intermetallic compound. The
welding current as recommended is not less than 20 A, more
preferably not less than 30 A, and not more than 100 A, more
preferably, not more than 80 A.
(Welding Voltage)
[0178] As for a welding voltage, it is recommendable to execute
joining on a low voltage condition in the cases of both the AC-MIG
welding, and the MIG welding by DC reversed polarity, as with the
case of the welding current. The welding voltage recommendable is
not lower than 5V, more preferably not lower than 7V, and not
higher than 20V, more preferably not higher than 18V.
(Welding Speed)
[0179] In the cases of both the AC-MIG welding, and the MIG welding
by DC reversed polarity, a welding speed may be decided as
appropriate within a range where Fe and Al in the base metal are
not caused to undergo excessive melting, according to the welding
current, and the welding voltage. Taking into consideration welding
efficiency, and so forth, the welding speed in the case of the
AC-MIG welding is preferably not less than 15 cm/min, more
preferably not less than 20 cm/min, and is preferably not more than
60 cm/min, more preferably not more than 50 cm/min.
[0180] In contrast, in the case of the MIG welding by DC reversed
polarity, there is the need for applying welding by increasing the
welding speed as much as possible to thereby reduce the input heat
value in order to check the generation of the brittle intermetallic
compound as previously described. For this reason, the welding
speed is preferably not less than 30 cm/min, more preferably not
less than 50 cm/min, and is preferably not more than 200 cm/min,
more preferably not more than 150 cm/min.
Shield Gas:
[0181] For the shield gas in the cases of both the AC-MIG welding,
and the MIG welding by DC reversed polarity, a gas for general use,
such as Ar, and so forth, can be used as appropriate, and a flow
rate of the shield gas can be selected in a flow rate rage, for
general use, for example, from 10 to 50 L/min, and there is no
particular limitation thereto.
Welding Torch Angle:
[0182] There is no particular limitation to a welding torch (an arc
torch) angle, and in the cases of both the AC-MIG welding, and the
MIG welding by DC reversed polarity, and the angle .theta. is
selected as appropriate according to the relevant welding, welding
conditions of a joint, and so forth.
(Member as Application Object)
[0183] As members as application objects of the method for joining
the dissimilar materials together, according to the invention,
there are cited, for example, construction members to be joined
with each other, such as automobile members, and large sized
panels, made up of the hot-dip galvanized steel member, to be
joined with reinforcing members made up of the aluminum alloy
member, as previously described. In this connection, there can be
cited, for example, bonding such as respective joints of a side
member made up of a rectangular hollow section formed from the
hot-dip galvanized steel sheet, and a bumper reinforcing member, or
a bumper stay, made up of an aluminum alloy extruded hollow
section, obtained by directly overlapping respective ends thereof,
with each other, as shown in FIG. 1, or obtained by overlapping
respective flange faces provided at the respective ends
thereof.
(Steel Member)
[0184] From the viewpoint of ensuring corrosion resistance of the
steel member, and the object of the invention as well, it is
particularly desirable that a zinc (including alloying zinc)
hot-dip galvanized steel member that has been difficult by nature
for use in bimetallic joining can be used in the invention. In the
case of welding of a galvanized steel member, including hot dip
galvanizing, an arc becomes unstable by the agency of zinc vapor as
evolved, thereby causing problems of generation of spatters, and
occurrence of porous defects such as pits, blowholes, and so forth.
However, with the method for joining the dissimilar materials
together, according to the invention, an effect of cleaning up the
surface of the steel sheet by virtue of an effect of the flux is
exhibited, and molten metal covers the surface of the steel sheet
with excellent wettability, so that the zinc vapor as evolved will
be less. In particular, because cesium fluoride, high in
hygroscopicity, is not contained in the flux cored wire according
to the invention, the flux cored wire can be further check
blowholes, and is excellent in arc stability.
[0185] The steel member (iron based material) itself used in the
invention is a steel member such as mild steel, high tensile steel
(Hi-Ten), and so forth. There is no particular limitation to type
and shape of the steel member used in the invention, and use can be
made of a steel member appropriate in shape and material type, such
as a steel sheet, steel section, steel pipe, and so forth, for
general use as a structural member, or diverted from application
for the structural member. However, in order to obtain a high
strength as the structural member, use of the high tensile steel
(Hi-Ten) is preferable.
(Aluminum Member)
[0186] An aluminum member for use in the invention has no
particular limitation to type and shape of an alloy thereof, and
selection, as appropriate, is made of a rolled sheet member, shaped
member such as an extrusion, forged member, cast member, and so
forth, for general use according to properties required of
respective structural members. However, in order to obtain a high
strength as the structural member, use is preferably made of
aluminum alloy of an Al--Mg base, Al--Mg--Si base, or Al--Mg--Zn
base for general use as aluminum alloy capable of meeting
requirements for various properties such as formability, and so
forth, or aluminum alloy of 5000 series, 6000 series, 7000 series,
according to JIS or AAA specification, and so forth. Selection as
appropriate is made out of those aluminum alloys after tempering
treatment is applied thereto according to strength required by the
structural member, and formability.
WORKING EXAMPLES
TABLE-US-00005 [0187] TABLE 5 Evaluation on a welded joint Filling
Sectional factor of shape of a flux of a Shear bead, flux cored
tensile a ratio of External Weight of Remarks wire strength a
(width)/ appearance the fume (Steel sheet No. Classification Mass %
N/mm b (height) of a bead evolved in use) 1 Comparative example 0
Not bonded -- -- -- GA steel sheet 2 Working example 0.1 178
.largecircle. .largecircle. .circleincircle. GA steel sheet 3
Working example 10 256 .largecircle. .largecircle. .largecircle. GA
steel sheet 4 Working example 24 225 .largecircle. .largecircle.
.largecircle. GA steel sheet 5 Comparative example 50 51 X X X GA
steel sheet 6 Working example 10 165 .largecircle. .largecircle.
.largecircle. Bare steel sheet 7 Working example 24 199
.largecircle. .largecircle. .largecircle. Bare steel sheet 8
Comparative example 10 43 X X .largecircle. GA steel sheet 9
Comparative example 10 37 X X .largecircle. GA steel sheet
TABLE-US-00006 TABLE 6 Evaluation on a welded joint Filling
Sectional factor of shape of a flux of a Shear bead, flux cored
tensile a ratio of External Weight of Remarks wire strength a
(width)/ appearance the fume (Steel sheet No. Classification Mass %
N/mm b (height) of a bead evolved in use) 10 Comparative example 0
Not bonded -- -- -- GA steel sheet 11 Working example 0.5 184
.largecircle. .largecircle. .circleincircle. GA steel sheet 12
Working example 13.5 262 .largecircle. .largecircle. .largecircle.
GA steel sheet 13 Comparative example 63 43 X X X GA steel sheet 14
Working example 14.5 249 .largecircle. .largecircle. .largecircle.
GI steel sheet 15 Working example 5 251 .largecircle. .largecircle.
.largecircle. GI steel sheet 16 Working example 24 196
.largecircle. .largecircle. .largecircle. GI steel sheet 17 Working
example 12 220 .largecircle. .largecircle. .largecircle. Bare steel
sheet
[0188] Working examples according to another embodiment of the
invention are described hereinafter. There were conducted tests on
a lap Fillet.COPYRGT. welding of an aluminum alloy sheet with a
steel sheet by use of the method for joining the dissimilar
materials together, according to the invention. In this case, for
the steel sheet, use was made of an alloying zinc hot-dip
galvanized steel sheet (GA steel sheet), a hot-dip galvanized steel
sheet (GI sheet), and a bare (without surface treatment) steel
sheet. Results of the tests in the case of the AC-MIG welding are
shown in Tale 5.
[0189] Further, results of the tests in the case of the MIG welding
by DC reversed polarity are shown in Tale 6.
[0190] In the cases of both the AC-MIG welding, and the MIG welding
by DC reversed polarity, the lap fillet welding of test pieces of
the aluminum alloy sheet and the steel sheet, with each other, was
executed in the mode previously shown in FIG. 1. More specifically,
an end of an aluminum alloy sheet (JIS 5182 alloy) 1.6 mm in
thickness was overlaid on an end of any of the alloying zinc
hot-dip galvanized steel sheet (GA steel sheet), the hot-dip
galvanized iron sheet (GI sheet), and the bare steel sheet (tensile
strength of any of those sheets: 270 MPa), having thereby formed a
lap fillet welded joint. The respective test pieces of the aluminum
alloy sheet and the steel sheet was each 100 mm (width).times.300
mm (length) in planar size, and mutual allowance for overlapping
was 35 mm (a weld line length: 100 mm corresponding to the sheet
width).
[0191] As shown in Tables 5, 6, respectively, the MIG welding of
the aluminum alloy sheet with the galvanized steel sheet was
conducted by use of a flux cored wire with a mixed flux composed of
AlF.sub.3 and KF, the filling factor of the flux being variously
changed. In this case, a mixing ratio of KF to AlF.sub.3, in the
flux, was kept constant for both the working examples and the
comparative examples such that the melting point of the flux
remained constant at 650.degree. C., using the flux composed of a
mixture of KF: 45 mol %, and AlF.sub.3: 55 mol %. In common with
Tables 5, 6, use was made of the flux cored wire 1.2 mm .phi. in
diameter. For an aluminum envelope of the flux cored wire, use was
made of the A4043 type, and in the step of the drawing described
previously, the flux cored wire was formed to the final diameter at
1.2 mm .phi. as above.
[0192] Further, for the sake of comparison, the AC-MIG welding was
applied under the same condition as in the case of the working
examples to respective examples where use was made of a flux cored
wire obtained by substituting cesium fluoride, and zinc fluoride,
used in the past, for part of KF, a flux containing 10 mol % each
of cesium fluoride, and zinc fluoride, together with a mixture of
KF: 45 mol %, and AlF.sub.3: 55 mol %. Those are shown as
comparative examples 8, 9 in Table 5. The filling factor of the
flux of each of the comparative examples 8, 9 was 10 mass %, the
same as that for the working examples. Further, the comparative
examples 8, 9 each had a melting point around 500.degree. C.
[0193] In the cases of both the AC-MIG welding, and the MIG welding
by DC reversed polarity, welding conditions were applied within the
range of the MIG welding conditions, as previously recommended. The
welding speed in the case of the AC-MIG welding: 35 cm/min, and in
the case of the MIG welding by DC reversed polarity, the welding
speed was increased to 80 cm/min in order to check the generation
of the brittle intermetallic compound as previously described.
Further, in the cases of both the AC-MIG welding, and the MIG
welding by DC reversed polarity, the welding current: 75 A, the
welding voltage: 18V, and welding torch angle: 90.degree. were
adopted, and for the shield gas, use was made of argon.
[0194] The welding under the conditions described as above were
applied to the respective examples three times, a test piece was
sampled from respective bonded joints, and various tests were
conducted on the respective test pieces, whereupon respective test
results were averaged out to be used for evaluations. First, as to
shear tensile strength, a joint-strength-evaluation test piece 30
mm in sheet width was sampled from the respective joints bonded
three times, and a tensile test at velocity of 25 mm/min was
conducted on the respective test pieces, thereby having found an
average value of the shear tensile strength for the respective
examples.
[0195] Further, in order to examine a spread effect of the flux,
wettability of the respective bonded joints were examined. For
evaluation on the wettability, a spread width (a) of the weld metal
4, and a height (b) of the weld metal 4 were measured at
appropriate intervals along the weld line, respectively, as shown
in FIG. 4 corresponding to FIG. 1, in schematic form. Thereafter, a
ratio of "a" to "b", a/b, was averaged out along the weld line, and
with the respective samples, the average a/b for each of 3 test
pieces (as obtained from 3 welding tests) was further averaged out.
On the basis of an evaluation criteria for the wettability, it was
determined that a/b on the average in a range less than 0.6
represents the case of the spread width of the weld metal being
adequate, being marked symbol .largecircle., while a/b on the
average at not less than 0.6 is marked symbol X (indicating failure
to form a sound bead due excessive spread of the weld metal).
[0196] As for the welding workability, evaluation was made on
weight of fume evolved during welding, and bead stability. The
weight of the fume evolved was measured according to JIS-Z3930.
More specifically, total fume evolved at the time of the welding
using the respective flux cored wires was collected to thereby find
the weight of the fume evolved per unit time. With the respective
example, the weights of the fume evolved, obtained from the three
welding tests, respectively, were averaged out. If the weight of
the fume evolved, on average, was less than 300 mg/min, it was
rated .circleincircle., if the same is in a range of 300 to 700
mg/min, it was rated .largecircle., and if the same is not less
than 700 mg/min, it was rated X.
[0197] Further, the bead stability was evaluated according to the
criteria based on a bead shape formed, as shown in FIGS. 2A and 2B.
The case where a bead was linearly, and neatly formed as shown in
FIG. 2B with all the three welding tests was rated .largecircle.
while the case where a bead was formed only discontinuously even
during only one of the welding tests was rated X. Those results are
shown in Tables 5 and 6, respectively.
[0198] First, as is evident from Table 5, with each of the working
examples 2 to 4, wherein the flux of the flux cored wire, and the
flux factor were within the respective ranges according to the
invention, and the AC-MIG welding conditions are in the preferable
range, it was found that the wettability of the weld metal was
adequate in spite of bimetallic joining of the alloying zinc
hot-dip galvanized steel sheet (GA steel sheet), an excellent bead
was formed, and the bonding strength was improved. Furthermore, the
weight of the fume evolved due to scattering of molten flux was
found less and welding stability was found excellent. The same
applies to the working examples 6, 7 using the bare steel
sheet.
[0199] In contrast, with the comparative example 1 without flux
filled therein, it was not possible to implement joining itself in
the case of the bimetallic joining of the alloying zinc hot-dip
galvanized steel sheet (GA steel sheet). Further, with the
comparative example 5, wherein a flux cored wire had the same flux
composition as that for the working examples, but its flux filling
factor exceeded the upper limit of the range according to the
invention, the flux filling factor was found excessively high.
Accordingly, with the comparative example 5, it was found that the
wettability of the weld metal was inadequate in the case of the
bimetallic joining of the alloying zinc hot-dip galvanized steel
sheet (GA steel sheet), bead formation was discontinuous, and the
bonding strength was low although joining was implemented.
Furthermore, the weight of fume evolved due to scattering of molten
flux was large, and welding stability was inferior.
[0200] Meanwhile, with the comparative examples 8, 9, using cesium
fluoride, and zinc fluoride, as in the past, a flux filling factor
was the same as that for the working examples, so that the weight
of fume evolved due to scattering of molten flux was found less,
and welding stability was found excellent. However, the wettability
of weld metal was found inadequate, and bead formation was found
discontinuous. For this reason, even though joining was implemented
in the bimetallic joining of the alloying zinc hot-dip galvanized
steel sheet (GA steel sheet), bonding strength was found
considerably poor as compared with the working examples. The reason
for this is presumably because the flux using cesium fluoride, and
zinc fluoride has an excessively low melting point, so that
excessive wettability results, thereby causing excessive spread of
the bead. In addition, since the flux using cesium fluoride, and
zinc fluoride is high in hygroscopicity, the bead becomes unstable
owing to the influence of moisture to be thereby rendered
discontinuous, so that it is deemed that an excellent joint could
not be formed.
[0201] Next, as is evident from Table 6, with each of the working
examples 11, 12, 14 to 16, the flux of the flux cored wire, and the
flux factor were within the respective ranges according to the
invention, and the conditions of the MIG welding by DC reversed
polarity are in the preferable range. As a result, with those
working examples, it was found that the wettability of the weld
metal was adequate in spite of the bimetallic joining of the
alloying zinc hot-dip galvanized steel sheet (GA steel sheet), an
excellent bead was formed, and the bonding strength was improved.
Furthermore, the weight of the fume evolved due to scattering of
molten flux was found less, and welding stability was found
excellent. The same applies to the working example 17 using the
bare steel sheet.
[0202] In contrast, with the comparative example 10 without flux
filled therein, it was not possible to implement joining itself in
the case of the bimetallic joining of the alloying zinc hot-dip
galvanized steel sheet (GA steel sheet). Further, with the
comparative example 13, wherein a flux cored wire had the same flux
composition as that for the working examples, but its flux filling
factor exceeded the upper limit of the range according to the
invention. For this reason, it was found that the wettability of
the weld metal was inadequate in the case of the bimetallic joining
of the alloying zinc hot-dip galvanized steel sheet (GA steel
sheet), bead formation was discontinuous, and the bonding strength
was low although joining was implemented. Furthermore, the weight
of fume evolved due to scattering of molten flux was large, and
welding stability was inferior.
[0203] On the basis of those working examples, there is
demonstrated critical significance of respective requirements of
the invention, such as the flux composition of the flux cored wire,
the flux filing factor, particularly, the bonding strength of the
bimetallic joining of the galvanized steel member with the aluminum
member, and workability.
INDUSTRIAL APPLICABILITY
[0204] The invention can provide a flux cored wire for joining
dissimilar materials with each other, capable of enhancing a
bonding strength in melt weld-bonding of high-strength dissimilar
materials with each other, that is, the high-strength steel member
with the high-strength 6000 series aluminum alloy member, and
excellent in welding efficiency, and a method for joining the
dissimilar materials with each other. Further, it is possible to
obtain a bonded joint of dissimilar materials, such as a galvanized
steel member and an aluminum member, without any constraint on
shapes of base metals to be joined together, without causing
generation of a brittle intermetallic compound at the bonded joint,
excellent in external appearance, and without causing occurrence of
defects such as blowholes, and so forth if joining is executed by
the AC-MIG welding using the flux cored wire according to the
invention, wherein a flux filling factor, and a melting point are
properly controlled. Since the aggregate of the dissimilar
materials joined, obtained as above, is superior in bonding
strength, and welding efficiency, the aggregate can be quite
usefully applied to various structural members of automobiles,
railway vehicles, and so forth, in the transportation field,
machine components, construction members such as building
structures, and so forth. Hence the invention will greatly
contribute to expansion of application for the aggregate of the
dissimilar materials, for example, a steel member and an aluminum
member, joined together, high in strength.
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