U.S. patent application number 10/487940 was filed with the patent office on 2005-01-06 for aluminum alloy, cast article of aluminum alloy, and method for producing cast article of aluminum alloy.
Invention is credited to Horie, Toshio, Iwahori, Hiroaki, Kawahara, Hiroshi, Shimizu, Yoshihiro, Sugimoto, Yoshihiko, Sugiyama, Yoshio, Yamashita, Minoru.
Application Number | 20050000604 10/487940 |
Document ID | / |
Family ID | 19093992 |
Filed Date | 2005-01-06 |
United States Patent
Application |
20050000604 |
Kind Code |
A1 |
Kawahara, Hiroshi ; et
al. |
January 6, 2005 |
Aluminum alloy, cast article of aluminum alloy, and method for
producing cast article of aluminum alloy
Abstract
An aluminum alloy according to the present invention includes
from 4.0 to 6.0% Mg, from 0.3 to 0.6% Mn, from 0.5 to 0.9% Fe, and
the balance of Al and inevitable impurities when the entirety is
taken as 100% by mass. By appropriately selecting the composition
range of Mg, Mn and Fe, it has been possible to micro-finely
crystallize Al (Mn, Fe) compounds while inhibiting the growth of
primary-crystal Al. As a result, the resulting aluminum alloy is
good in terms of the castability, and shows high strength as well
as high ductility.
Inventors: |
Kawahara, Hiroshi;
(Aichi-ken, JP) ; Shimizu, Yoshihiro; (Aichi,
JP) ; Sugiyama, Yoshio; (Aichi, JP) ; Horie,
Toshio; (Aichi, JP) ; Iwahori, Hiroaki;
(Aichi, JP) ; Sugimoto, Yoshihiko; (Aichi, JP)
; Yamashita, Minoru; (Aichi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Family ID: |
19093992 |
Appl. No.: |
10/487940 |
Filed: |
August 20, 2004 |
PCT Filed: |
August 30, 2002 |
PCT NO: |
PCT/JP02/08854 |
Current U.S.
Class: |
148/440 ;
420/547 |
Current CPC
Class: |
C22C 21/06 20130101;
B22D 21/007 20130101 |
Class at
Publication: |
148/440 ;
420/547 |
International
Class: |
C22C 021/06 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 4, 2001 |
JP |
2001-267932 |
Claims
1. An aluminum alloy for cast products, comprising: from 4.0 to
6.0% magnesium (Mg); from 0.3 to 0.5% manganese (Mn); from 0.5 to
0.9% iron (Fe); from 0.1 to 0.2% titanium (Ti); and the balance of
aluminum (Al) and inevitable impurities when the entirety is taken
as 100% by mass (mass percentage).
2. The aluminum alloy for cast products set forth in claim 1
further comprising from 0.1 to 0.7% chromium (Cr) when the entirety
is taken as 100% by mass.
3. (Cancelled).
4. The aluminum alloy for cast products set forth in claim 1
further comprising from 0.01 to 0.05% boron (B) when the entirety
is taken as 100% by mass.
5. The aluminum alloy for cast products set forth in claim 1
further comprising from 0.001 to 0.01% beryllium (Be) when the
entirety is taken as 100% by mass.
6. The aluminum alloy for cast products set forth in claim 1
further comprising from 0.05 to 0.3% molybdenum (Mo) when the
entirety is taken as 100% by mass.
7. The aluminum alloy for cast products set forth in claim 1,
wherein said inevitable impurities comprise 0.50 or less silicon
(Si) and 0.3% or less copper (Cu) when the entirety is taken as
100% by mass.
8. The aluminum alloy for cast products set forth in claim 1
wherein said Fe is from 0.5 to 0.8% by mass.
9. The aluminum alloy for cast products set forth in claim 1,
further comprising primary-crystal aluminum and compounds which are
dispersed uniformly, the primary-crystal aluminum having a
dendritic cell size of 10 .mu.m or less, the compounds having a
grain diameter of 5 .mu.m or less.
10. The aluminum alloy for cast products set forth in claim 1,
which exhibits a tensile strength of 250 MPa or more as cast being
free from being subjected to a heat treatment after casting.
11. The aluminum alloy for cast products set forth in claim 1,
which exhibits a 0.2% proof stress of 130 MPa or more as cast being
free from being subjected to a heat treatment after casting.
12. The aluminum alloy for cast products set forth in claim 1,
which exhibits a fracture elongation of 13% or more as cast being
free from being subjected to a heat treatment after casting.
13. A cast product made of an aluminum alloy, the cast product
comprising: from 4.0 to 6.0% magnesium (Mg); from 0.3 to 0.5%
manganese (Mn); from 0.5 to 0.9% iron (Fe); from 0.1 to 0.2%
titanium (Ti); and the balance of Al and inevitable impurities when
the entirety is taken as 100% by mass.
14. A process for producing a cast product made of an aluminum
alloy, the process comprising the steps of: pouring an aluminum
alloy molten metal into a die, the aluminum alloy molten metal
comprising: from 4.0 to 6.0% magnesium (Mg); from 0.3 to 0.5%
manganese (Mn); from 0.5 to 0.9% iron (Fe); from 0.1 to 0.2%
titanium (Ti); and the balance of Al and inevitable impurities when
the entirety is taken as 100% by mass; and solidifying the aluminum
alloy molten metal by cooling it after the pouring step.
15. The process for producing a cast product made of an aluminum
alloy set forth in claim 14, wherein said solidifying step is a
step being solidified by cooling at a cooling rate of 20.degree.
C./sec. or more.
Description
TECHNICAL FIELD
[0001] The present invention relates to an aluminum alloy, and a
process for producing a cast product made of an aluminum alloy.
More particularly, it relates to an aluminum alloy which shows
castability suitable for even producing thin-thickness cast
products and the like, and high strength as well as good ductility
even as cast, and a process for producing cast products comprising
the aluminum alloy.
BACKGROUND ART
[0002] Recently, it has been required to lightweight various
products, conventional cast-iron products are about to give way to
light aluminum alloy products rapidly. For example, in the case of
automobiles, it is possible to expect mileage improvement by
lightweighting, and the lightweighting is effective in
environmental improvement as well.
[0003] By the way, high strength and high ductility have come to be
required even for thin-thickness cast products (die-cast products
especially), to which the requirements for strength and ductility
have been moderate relatively. As a method for producing
high-strength and high-ductility thin-thickness cast products, it
has been proposed such a method that the resulting cast products
are heat treated after casting while vacuuming the inside of dies,
or after casting while filling the inside of dies with oxygen
contrarily, for example. However, in such a method, heat treatments
are needed to result in the increment of production costs.
Moreover, the thinner and larger cast products are, the more the
heat treatments cause strains of the cast products (swelling,
deformations, and the like), and accordingly it takes more costs
for the correction.
[0004] Hence, in order to solve such problems, the development of
aluminum alloys which reveal high strength and high ductility even
as cast has been carried out extensively. For example, in {circle
over (1)} Japanese Unexamined Patent Publication (KOKAI) No.
9-3582, {circle over (2)} Japanese Unexamined Patent Publication
(KOKAI) No. 11-293375, {circle over (3)} Japanese Unexamined Patent
Publication (KOKAI) No. 11-193434, and {circle over (4)} Japanese
Unexamined Patent Publication (KOKAI) No. 9-268340, Japanese
Unexamined Patent Publication (KOKAI) No. 9-316581 and Japanese
Unexamined Patent Publication (KOKAI) No. 11-80872, and the like,
there are disclosures on such aluminum alloys. Hereinafter, the
aluminum alloys set forth in the respective publications will be
described in detail.
[0005] In {circle over (1)} Japanese Unexamined Patent Publication
(KOKAI) No. 9-3582, an aluminum alloy cast product is disclosed
which contains Mg: 3.0-5.5% (% by mass: being the same
hereinafter), Zn: 1.0-2.0% (Mg/Zn: 1.5-5.5), Mn: 0.05-1.0%, Cu:
0.05-0.8%, and Fe: 0.1-0.8%. This Al--Mg-Mn--Zn--Cu system alloy
contains Zn and Cu falling in a predetermined range as essential
elements.
[0006] When the present inventors tested and studied cast products
made of this alloy, intermediate phases, such as MgZn.sub.2 and
Mg.sub.32 (Al, Zn).sub.49, are precipitated in the cast products,
strength characteristic change by natural aging, and stress
corrosion cracks appeared. Moreover, it was also understood that
this alloy was such that hot tearing is likely to occur so that it
was not suitable for casing thin-thickness members.
[0007] In {circle over (2)} Japanese Unexamined Patent Publication
(KOKAI) No. 11-293375, a highly ductile aluminum alloy die cast is
disclosed which is characterized in that it comprises Mg: 2.5-7.0%,
Mn: 0.2-1.0%, and Ti: 0.05-0.2%, and Fe in an amount of 0.3% and Si
in an amount of 0.5% or less, a porosity is 0.5% or less at a
heavy-thickness part ranging from 1 to 5 mm, the average
circle-equivalent diameter of crystallized substances is 1.1 .mu.m
or less, and the areal ratio of crystallized substances is 5% or
less. This Al--Mg--Mn--Ti system alloy is such that Fe is treated
as an inevitable impurity and the content is limited to less than
0.3%.
[0008] When the present inventors tested and studied thin-thickness
die-cast products using this alloy, they were such that hot tearing
was likely to occur. Moreover, when the Mg content increased,
shrinkage cavities were likely to occur at the heavy-thickness
center. The occurrence of hot tearing and shrinkage cavities is not
preferable, because it enlarges the fluctuation of strength
characteristic and elongation.
[0009] In {circle over (3)} Japanese Unexamined Patent Publication
(KOKAI) No. 11-193434, an aluminum alloy for high-toughness
die-cast products is disclosed, aluminum alloy which comprises Mg:
3.0-5.5%, Mn: 1.5-2.0%, and Ni: 0.5-0.9%.
[0010] In this Al--Mg-Mn--Ni system alloy, Ni is an essential
constituent element, and the toughness of die-cast products are
improved by adjusting the content appropriately. Moreover, since
the Mn content is much, the crystallized amount of its compounds is
so much that the elongation is 10% approximately as indicated by
the examples.
[0011] In {circle over (4)} (Japanese Unexamined Patent Publication
(KOKAI) No. 9-268340, a highly ductile aluminum alloy is disclosed
which comprises Mg: 0.01 to 1.2%, Mn: 0.5 to 2.5%; and Fe:
0.1-1.5%.
[0012] In this Al--Mg--Mn--Fe system alloy, defects such as hot
tearing and shrinkage cavities, are inhibited from occurring by
decreasing the Mg content so as to merely improve the castability
and elongation. Accordingly, it is seen from the examples as well
that the alloys are not satisfactory in view of the strength
because the tensile strength is even less than 190 MPa. Note that
the aluminum alloys, disclosed in Japanese Unexamined Patent
Publication (KOKAI) No. 9-316581 and Japanese Unexamined Patent
Publication (KOKAI) No. 11-80872, are as poor as this alloy.
DISCLOSURE OF INVENTION
[0013] The present invention has been done in view of such
circumstances. Namely, it is an object to provide an aluminum alloy
in which the occurrence and the like of hot tearing and micro
porosity is less and accordingly which is good in terms of the
castability. In particular, it is an object to provide an aluminum
alloy from which cast products of high strength and good ductility
can be obtained even as cast. Moreover, it is an object to provide
an aluminum alloy whose cast products suffer the time change of
mechanical characteristics and so forth less.
[0014] In addition, it is an object to provide a process for
producing cast products, process in which this aluminum alloy is
used.
[0015] Hence, the present inventors have been studying earnestly in
order to solve this assignment, and have been repeated various
systematic experiments, as a result, have discovered an aluminum
alloy, which is good in terms of the castability, and moreover from
which cast products of high strength and high ductility can be
obtained even as cast, by appropriately controlling the composition
proportion of Mg, Mn and Fe, and have arrived at completing the
present invention.
Aluminum Alloy
[0016] Namely, an aluminum alloy according to the present invention
comprises: from 4.0 to 6.0% magnesium (Mg); from 0.3 to 0.6%
manganese (Mn); from 0.5 to 0.9% iron (Fe); and the balance of
aluminum (Al) and inevitable impurities when the entirety is taken
as 100% by mass.
[0017] Since the present aluminum alloy (Al--Mg--Mn--Fe alloy)
contains Mg, Mn and Fe with an appropriate composition proportion,
the castability is improved, and high strength as well as high
ductility are revealed. Hereinafter, the reasons conceivable at
present and how to arrive at the above-described composition will
be described.
[0018] It has been known that the strength of aluminum alloys is
improved by solving Mg or Mn in Al matrices, however, when
producing thin-thickness die-cast products with Al--Mg--Mn alloys,
hot tearing, porosity and the like, accompanied by solidification
shrinkage, occur so that the castability is poor. Moreover,
correlating therewith, the fluctuation of elongation enlarges.
[0019] Hence, in order to obtain an aluminum alloy which is good in
terms of the castability and which is of high strength and high
ductility, the present inventors focused on the relationship
between the crystallization form of crystallized substances in the
solidification process and the castability or mechanical
properties. And, they ascertained that the hot tearing of cast
products made of aluminum alloys occurs often in brittle liquid
phase portions which reside between primary-crystal Al dendrites
growing in the solidification process. This is believed to be as
follows: upon the solidification shrinkage, shrinkage stresses act
on cast products when the cast products are constricted by dies in
a temperature range (semi-solidus temperature range) in which the
cast products are shaped and begin to have strength in the process
in which the cast products are being formed by the development and
combination of primary-crystal dendrites; and the stresses
concentrate on the brittle liquid phase portions which reside
between the dendrites so as to cause the hot tearing
frequently.
[0020] Hence, the present inventors thought of adding Fe to
Al--Mg-Mn alloys, and changed the crystallization behavior in the
solid-liquid coexisting zone by adjusting the Mn and Fe contents
according to the Mg content so that they succeeded in obtaining
good hot tearing resistance. Specifically, the crystallization
temperature zone of primary-crystal Al was narrowed so that
Al--Mn--Fe eutectics were crystallized between the network
isthmuses of primary-crystal Al, which had finished crystallizing,
without growing the dendrites of primary-crystal Al greatly. And,
since the connection between respective solid phases developed
rapidly under the circumstance, it is believed that the hot tearing
was less likely to occur.
[0021] Moreover, in accordance with the present aluminum alloy,
since Al(Mn, Fe) compounds crystallize micro-finely after
micro-fine Al crystallizes out of the liquid phases as primary
crystals, there are less coarse crystallized substances which
result in lowering the ductility, and accordingly it is believed
that it comes to reveal good ductility while even sustaining high
strength.
[0022] Especially, when the present aluminum alloy can comprise
primary-crystal aluminum and compounds which are dispersed
uniformly, the primary-crystal aluminum having a dendritic cell
size of 10 .mu.m or less, the compounds having a grain diameter of
5 .mu.m or less, it is more suitable in view of the strength and
ductility. Moreover, it is more preferable when the dendritic cell
size of said primary-crystal aluminum can be 5 .mu.m or less and
the grain diameter of said compounds can be 3 .mu.m or less.
[0023] Here, the size of the dendritic cells (dendrite) is a length
when measured in the longitudinal direction, and is an average
value of the measured values for 100 pieces of the cells. Moreover,
the grain diameter of the compounds is assessed in the longitudinal
direction (the maximum length), and is an average value of measured
values on 10 view fields of a structural photograph (view field
area, 70.times.100 .mu.m) which is taken with a magnification of
100 times by using an image processor.
[0024] Thus, in accordance with the present aluminum alloy, even
when thin-thickness die-cast products are produced, for example, it
is possible to obtain cast products provided with sufficient
strength and good ductility without hardly causing porosity such as
hot tearing and shrinkage cavities. For instance, it is possible to
obtain an aluminum alloy which exhibits a 0.2% proof stress of 130
MPa or more and a fracture elongation of 13% or more as cast being
free from being subjected to a heat treatment after casting.
[0025] Moreover, the aluminum alloy solution-strengthened by Mg and
Mn falling in the aforementioned composition range is provided with
an advantage that the change of mechanical properties with time is
less without scarcely causing the hardness change by natural aging.
(Production Process for Cast Product Made of Aluminum Alloy)
[0026] A cast product comprising the above-described present
aluminum alloy can be obtained by the following production process,
for example.
[0027] Namely, a process according to the present invention for
producing a cast product made of an aluminum alloy comprises the
steps of: pouring an aluminum alloy molten metal into a die, the
aluminum alloy molten metal comprising: from 4.0 to 6.0% Mg; from
0.3 to 0.6% Mn; from 0.5 to 0.9% Fe; and the balance of Al and
inevitable impurities when the entirety is taken as 100% by mass;
and solidifying the aluminum alloy molten metal by cooling it after
the pouring step.
[0028] And, it is suitable that said solidifying step can be a step
being solidified by cooling at a cooling rate of 20.degree. C./sec.
or more.
[0029] It is because, with this arrangement, cast products made of
an aluminum alloy can be obtained securely, cast products in which
the above-described micro-fine primary-crystal aluminum and
compounds are dispersed uniformly. It is further preferable that
the cooling rate can be 50.degree. C./sec. or more.
[0030] By the way, the "aluminum alloy" set forth in the present
invention not only involves aluminum alloys as a raw material for
casting but also cast products (manufactured goods) made of
aluminum alloys after casting.
[0031] Namely, the present invention can be grasped as a cast
product made of an aluminum alloy, the cast product comprising:
from 4.0 to 6.0% Mg; from 0.3 to 0.6% Mn; from 0.5 to 0.9% Fe; and
the balance of Al and inevitable impurities when the entirety is
taken as 100% by mass.
[0032] Moreover, the "castability" set forth in the present
specification is a concept which involves not only the molten metal
fluidity, the releasability and the like but also the occurrence
rate and so forth of hot tearing and shrinkage cavities
(porosity)
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 is a cross-sectional view for illustrating avertical
die-casting machine equipped with a die for assessing hot tearing,
die which is capable of varying the constriction length.
[0034] FIG. 2 is a cross-sectional view taken along the line "A-A"
in FIG. 1.
[0035] FIG. 3 is a bar graph for illustrating the relationship
between the constriction length and castability on each test
sample.
[0036] FIG. 4 is a graph for illustrating the relationship between
the hot tearing characteristics and the Fe content.
BEST MODE FOR CARRYING OUT THE INVENTION
A. Mode for Carrying Out
[0037] Next, the present invention will be described in more detail
while naming embodiment modes.
(1) Alloy Composition
{circle over (1)} Mg
[0038] Mg is an element which solves in the matrix of aluminum to
improve the mechanical strength (for example, the tensile strength)
of aluminum alloys. Moreover, Mg is an element which exerts
influences on the ductility and castability of aluminum alloys as
well.
[0039] When Mg is comprised less than 4.0% (percentage by mass,
being the same hereinafter), the improvement of mechanical strength
is not sufficient, especially, it is difficult to secure a proof
stress (a 0.2% proof stress, being the same hereinafter) of 130 MPa
or more. Moreover, when Mg is comprised in excess of 6.0%, the
oxidation of molten metals is significant. In addition, since the
composition of Mn and Fe whose coarse crystallized substances start
crystallizing as primary crystals according to the Mg content
increment moves to a lower concentration side, the ductility is
deteriorated by the crystallization of the coarse crystallized
substances when the Mg content exceeds 6% in the case where Mn and
Fe fall in the aforementioned composition range.
[0040] Therefore, it is preferable that Mg can be comprised from
4.0 to 6.0%, and it is further preferable that it can be comprised
from 4.0 to 5.0%, when the entirety is taken as 100% by mass.
{circle over (2)} Mn
[0041] Mn is an element which improves the mechanical strength of
aluminum alloys by solving in the matrix of aluminum similarly to
Mg, or by generating compounds with aluminum to precipitate them
micro-finely in the matrix. Moreover, it also produces an effect of
improving the anti-seisurability to dies.
[0042] When Mn is comprised less than 0.3%, the improvement of
mechanical strength is not sufficient, and when it is comprised in
excess of 0.6%, it is not preferable because coarse crystallized
substances crystallize to result in lowering the ductility.
[0043] Therefore, it is preferable that Mn can be comprised from
0.3 to 0.6%, and it is further preferable that it can be comprised
from 0.3 to 0.5%, when the entirety is taken as 100% by mass.
{circle over (3)} Fe
[0044] Fe is an element which changes the crystallization process
in solidification to inhibit hot tearing resulting from
solidification shrinkage. Moreover, Fe also produces an effect of
improving the anti-seisurability to dies when die-casting is
carried out.
[0045] When Fe is comprised less than 0.5%, it is insufficient to
change the crystallization process greatly, and the effect of
inhibiting hot tearing is less. On the other hand, when Fe is
comprised in excess of 0.9%, it is not preferable because coarse
crystallized substances crystallize to lower the ductility.
Therefore, it is preferable that Fe can be comprised from 0.5 to
0.9% when the entirety is taken as 100% by mass.
[0046] According to a further study by the present inventors, it
became apparent that it is further preferable that Fe can be
comprised from 0.5 to 0.8% or from 0.5 to 0.7%.
{circle over (4)} Cr
[0047] Cr is an element which improves the mechanical strength of
aluminum alloys by solving in the matrix of aluminum similarly to
Mg and Mn.
[0048] When Cr is comprised less than 0.1%, the improvement of
mechanical strength is not sufficient, and when it is comprised in
excess of 0.7%, it is not preferable because coarse crystallized
substances crystallize to result in lowering the ductility.
[0049] Therefore, it is preferable that Cr can be comprised from
0.1 to 0.7%, and it is further preferable that it can be comprised
from 0.2 to 0.5%, when the entirety is taken as 100% by mass.
{circle over (5)} Ti and B
[0050] Ti and B become the nucleation site of primary-crystal Al.
Accordingly, when those elements are added to increase, the
respective crystalline grain diameters of primary-crystal Al
diminish. As a result, a solid-liquid fluidic state is maintained
to a higher solid-phase ratio side, and consequently the timing of
stress occurrence by solidification shrinkage is put off on a lower
temperature side so that it is believed that the resistance against
hot tearing is improved. Specifically, it is believed as
follows.
[0051] Ti becomes the nucleation site of .alpha.-Al, constitutes
micro-fine structures, and reveals the effects of inhibiting hot
tearing as well as improving the ductility, moreover, can improve
the proof stress of aluminum alloys as well.
[0052] Hence, it is suitable that 0.01-0.3% Ti can be includedwhen
the entirety is taken as 100% by mass. It results from the fact
that, when Ti is comprised less than 0.01%, no micro-fine structure
can be obtained; and when Ti is comprised in excess of 0.3%, coarse
crystallized substances (Al.sub.3Ti and the like) crystallize to
result in lowering the ductility. It is more preferable that Ti can
be comprised from 0.1 to 0.2%.
[0053] B reveals a great effect of micro-fining crystalline grains,
especially when it coexists with Ti.
[0054] When B is comprised less than 0.01%, no micro-fine structure
can be obtained, and when it is comprised in excess of 0.05%, it is
not economical because the variation of crystalline grain diameters
is less. Therefore, in the coexistence with Ti, it is suitable that
0.01-0.05% boron (B) can be included when the entirety is taken as
100% by mass. It is more suitable that it can be comprised from
0.03 to 0.05%. Note that it is economical that B can be added as
titanium boride such as TiB.sub.2 in addition to the case where it
is added as a simple substance.
{circle over (6)} Be
[0055] Be reveals an effect on the oxidation resistance even
independently, and inhibits decrease of Mg resulting from oxidation
when it dissolves.
[0056] Therefore, even being independent (without coexistingwith Ti
and the like), it is suitable that 0.001-0.01% beryllium (Be) can
be included when the entirety is taken as 100% by mass. It is more
suitable that it can be comprised from 0.005 to 0.01%. Of course,
it is needless to say that Be can coexist with Ti and so forth.
{circle over (7)} Mo
[0057] Mo produces an effect of inhibiting the slag generation
accompanied by the oxidation of Al--Mg alloy molten metals.
[0058] When Mo is comprised less than 0.05%, the oxidation
inhibition effect is not sufficient, and when it is comprised in
excess of 0.3%, it is not preferable because coarse crystallized
substances crystallize to result in lowering the ductility.
[0059] Therefore, it is preferable that Mo can be comprised from
0.05 to 0.3%, and it is further preferable that it can be comprised
from 0.1 to 0.2%, when the entirety is taken as 100% by mass.
{circle over (8)} Inevitable Impurities
[0060] As far as inevitable impurities do not exert an adverse
effect on the characteristics of aluminum alloys, the types and
contents are not limited, however, the present inventors found out
that the castability of aluminum alloys, and the strength or
ductility can be improved by controlling the content of Si and Cu,
inevitable impurities.
[0061] Namely, it is suitable that Si, an inevitable impurity, can
be comprised 0.5% or less, and that Cu can be comprised 0.3% or
less.
[0062] Si is an inevitable impurity which is included in aluminum
bare metal, and, when it is contained in excess of 0.5%, it is not
preferable because Mg.sub.2Si precipitates in the matrix by natural
aging to change the mechanical characteristics of aluminum alloys
with time.
[0063] Cu not only promotes hot tearing but also lowers corrosion
resistance. Therefore, when an aluminum alloy according to the
present invention is used as structural members, especially, it is
preferable that it can be comprised 0.3% or less.
(2) Applications
[0064] The present aluminum alloy or process for producing a cast
product can be utilized in a variety of cast products made of
aluminum alloys.
[0065] For example, in the field of automobiles and two-wheeled
vehicles, when the present aluminum alloy or process for producing
the same is used in members for body structures, chassis members,
wheels, space frames, steering wheels (armatures), seat frames,
suspension members, engine blocks, transmission cases, pulleys, oil
pans, shit levers, instrument panels, door impact panes, surge
tanks for intake, pedal brackets, front shroud panels, and the
like, it is possible to produce each of these members at a lower
cost without subjecting them to heat treatments.
[0066] Note that, although the present aluminum alloy is of high
strength and high ductility even as cast, it is naturally advisable
to carry out cold working or heat treatments after casting.
B. EXAMPLES
[0067] Subsequently, while giving examples, the present invention
will be described in more detail.
(Production and Testing of Test Samples)
[0068] (1) Example No. 1
[0069] Aluminum alloys were used which had an alloy composition of
Sample Nos. 1 through 5 and Sample Nos. C1 through C7 set forth in
Table 1, test samples were produced for each of the samples, test
samples whose constriction length was changed variously, and each
of the hot tearing characteristics was assessed. Note that Table 1
indicates themwhile Al, the major component, is abbreviated (being
the same hereinafter).
[0070] To be more precise, as illustrated in FIG. 1, various test
samples were produced by a vertical die-casting machine equipped
with a die whose cavity had a cross-section of 7 mm in thickness
and 10 mm in width and constriction length was changeable
variously, and the hot tearing characteristics assessment was
carried out.
[0071] The casting conditions were such that the melting
temperature was 750.degree. C.; the die temperature was from 50 to
100.degree. C.; the casting pressure was 63.7 MPa; and the plunger
speed was 0.6 m/s. After the respective molten metals were poured
by pressurizing with the plunger (a pouring step), they were
solidified at a cooling rate of 100.degree. C./sec. approximately
(a solidifying step).
[0072] The assessment of the hot tearing resistance was examined by
a constriction length at which a crack occurred. It indicates that
the longer the constriction length is, the less likely an alloy is
to cause hot tearing. The thus obtained test results of the
respective test samples are illustrated in FIG. 3.
[0073] Note that this test was carried out while a 0.5 mmin
thickness.times.10 mm in height insulating sheet was bonded
three-way around the aforementioned cavity in the middle in the
direction of the constriction length in order to localize positions
at which a hot tearing occurred. How this insulating sheet was
bonded three-way is illustrated in FIG. 2, a cross-sectional view
taken along the line "A-A" in FIG. 1.
(2) Example No. 2
[0074] Aluminum alloys were used which had an alloy composition of
Sample Nos. 6 through 14 and Sample Nos. C8 through C10 set forth
in Table 1, and plate-shaped cast products whose thickness was 2
mm, width was 50 mm and length was 70 mm were produced by the
vertical die-casting machine.
[0075] The casting conditions were such that the melting
temperature was 750.degree. C.; the die temperature was from 50 to
100.degree. C.; the casting pressure was 63.7 MPa; and the plunger
speed was 1.4 m/s. Moreover, after the molten metals were poured by
pressurizing with the plunger (a pouring step), they were
solidified at a cooling rate of 100.degree. C./sec. approximately
(a solidifying step)
[0076] From these as-cast plate-shaped cast products, plate-shaped
tensile test samples were produced whose flat-surface portions were
as-cast surfaces. The respective test samples were used to examine
the tensile strength, 0.2% proof stress and fracture elongation.
The results are set forth in Table 2. Note that the tensile test on
the respective test samples was carried out with an autograph
tensile testing machine made by SHIMAZU, and the aforementioned
characteristics were found from the stress-strain diagram obtained
for the respective test samples.
(3) Example No. 3
[0077] Aluminum alloys were used which had an alloy composition of
Sample Nos. 15 through 19 and Sample Nos. C11 and C12 set forth in
Table 1, and as-cast plate-shaped cast products were produced in
the same manner as Example No. 2.
[0078] Here, in order to examine the influence of the mechanical
characteristic change of the respective plate-shaped cast products
with time (artificial aging), the as-cast plate-shaped cast
products, and plate-shaped cast products, the same having been
heated at 175.degree. C. for 10 hours, were prepared, and the
hardness (the Vickers hardness) of the respective plate-shaped cast
products was examined. The results are set forth in Table 3.
[0079] Note that the Vickers hardness was such that ahardness meter
made by AKASHI was used; a load of 5 kg was loaded for 30 seconds;
and the hardness was determined by converting the size of the
indentation made in this instance.
(4) Example No. 4
[0080] Moreover, the relationship between the hot tearing
resistance and Fe content of Al alloy cast products was examined in
detail. Namely, test samples were produced in the same manner as
Example No. 1, test samples which comprised the alloy composition
of Sample Nos. 20 through 26 set forth in Table 4 and had various
constriction lengths. The respective samples were such that the Fe
content was varied mainly while the Mg, Mn and Ti contents were
made equal approximately. Assessing the hot tearing resistance by
the constriction length at which a crack occurred was the same as
the case of Example No. 1 as well. The thus obtained test results
of the respective test samples are illustrated in FIG. 4.
(5) Example No. 5
[0081] The influence of the alloy composition exerting on the
oxidation resistance of Al alloy molten metals was examined. First,
Al alloy molten metals were prepared which comprised the alloy
composition of Sample No. 27 and Sample No. 28. The respective
molten metals weremeasured for the weight in advance. Thesemolten
metals were put in a crucible made of alumina, and were held at
750.degree. C. for 5 hours in an aerial atmosphere.
[0082] After cooling the moltenmetals, the weight of the solidified
Al alloys was measured. And, the weight gain of the Al alloys was
found from the weight difference before and after holding them in
said heating. The results are set forth in Table 5 altogether. Note
that, in Table 5, there are recited the oxidation increment
proportions (oxidation increment rates) with respect to the weight
of the molten metals before holding them in said heating.
(Assessment)
(1) Castability
[0083] It is seen from FIG. 3 that all of the aluminum alloys of
Sample Nos. 1 through 5 falling within the present composition
range had a sufficiently longer constriction length, at which a
crack occurred, than those of Sample Nos. C1 through C7.
Specifically, no crack occurred up to a constriction length of 50
mm for Sample No. 1, a constriction length of 70 mm for Sample Nos.
2 and 3, and a constriction length of 80 mm for Sample Nos. 4 and
5.
[0084] From these, when a proper amount of the Fe content was added
while the Mn content was controlled, it was understood that the hot
tearing resistance is improved remarkably. Moreover, when Ti making
the nucleation sites was added while Mg, Mn and Fe had fallen in
the present composition ranges, it was also appreciated that the
hot tearing resistance was further improved.
[0085] In particular, as can be apparent from Table 4 and FIG. 4,
the Al alloy cast products of Sample Nos. 22 through 24, in which
the Fe content was contained from 0.5 to 0.8% while having Mg, Mn
and Fe fallen within the present suitable composition ranges, were
such that the hot tearing resistance was furthermore improved.
(2) Strength and Ductility
[0086] (1 All of Sample Nos. 6 through 14 were aluminum alloys
falling within the present composition range. And, as can be
understood from Table 2, all of those aluminum alloys exhibited a
tensile strength of 250 MPa or more, a 0.2% proof stress of 130 MPa
or more, and in addition an elongation of 15% or more. Therefore,
even as cast, it was appreciated that the aluminum alloy according
to the present invention reveals good ductility while maintaining
sufficient strength. Especially, there also exist those which
exhibited a tensile strength of 300 MPa or more, a 0.2% proof
stress of 150 MPa or more, and an elongation in excess of 20%.
[0087] Moreover, Sample No. 7, an aluminum alloy of Sample No. 6
with Ti contained, was such that the crystal grains were more
micro-fined so that the ductility was further improved.
[0088] {circle over (2)} On the other hand, the aluminum alloys of
Sample Nos. C8 through C10 falling outside the composition range
according to the present invention could not make the strength and
ductility compatible. For example, since Sample No. C8 was such
that the Mn content exceeded 0.6% by mass, the elongation was less
than 10% so that it was of low ductility, though the tensile
strength and 0.2% proof stress were high. On the contrarily, Sample
No. C9 which comprised less than 0.3% by mass Mn, and Sample No.
C10 which comprised less than 4.0% by mass Mg were such that the
strength was insufficient, though they were of high ductility.
(3) Influence of Aging
[0089] All of Sample Nos. 15 through 19 were aluminum alloys
falling within the present composition range. As can be understood
from Table 3, these aluminum alloys were such that the hardness
variation was insignificant between as cast and after being heated
at 175.degree. C. for 10 hours.
[0090] On the other hand, since the aluminum alloys of Sample Nos.
C11 and C12 included Si abundantly beyond the level of inevitable
impurities, the hardness variation was significant between as cast
and after being heated at 175.degree. C. for 10 hours. That is, age
hardening occurred, and accordingly there arise a fear that the
characteristics are changed by natural aging in aluminum alloys
with such a composition.
(4) Oxidation Resistance
[0091] As indicated by Sample Nos. 27 and 28 of Table 5, when Mo
was further comprised from 0.1 to 0.2% while having Mg, Mn, Ti and
Fe fallen within the present suitable composition ranges, it become
apparent that the Al alloy molten metals show much better oxidation
resistance.
1TABLE 1 Sample Aluminum Alloy Composition (% by Mass) No. Mg Mn Fe
Si Cu Ti Cr 1 4.98 0.31 0.75 Less Less -- -- than 0.1 than 0.01 2
5.68 0.60 0.80 .Arrow-up bold. .Arrow-up bold. 0.15 -- 3 4.98 0.32
0.50 .Arrow-up bold. .Arrow-up bold. .Arrow-up bold. -- 4 4.98 0.32
0.76 .Arrow-up bold. .Arrow-up bold. .Arrow-up bold. -- 5 4.31 0.30
0.76 .Arrow-up bold. .Arrow-up bold. .Arrow-up bold. -- 6 4.30 0.30
0.75 .Arrow-up bold. .Arrow-up bold. -- -- 7 4.31 0.30 0.76
.Arrow-up bold. .Arrow-up bold. 0.15 -- 8 5.68 0.60 0.80 .Arrow-up
bold. .Arrow-up bold. .Arrow-up bold. -- 9 5.62 0.32 0.76 .Arrow-up
bold. .Arrow-up bold. .Arrow-up bold. -- 10 4.79 0.52 0.85
.Arrow-up bold. .Arrow-up bold. 0.16 -- 11 4.98 0.32 0.76 .Arrow-up
bold. .Arrow-up bold. 0.15 -- 12 4.01 0.53 0.76 .Arrow-up bold.
.Arrow-up bold. .Arrow-up bold. -- 13 4.02 0.31 0.75 .Arrow-up
bold. .Arrow-up bold. 0.16 -- 14 4.30 0.30 0.75 .Arrow-up bold.
.Arrow-up bold. -- 0.21 15 5.68 0.60 0.80 .Arrow-up bold. .Arrow-up
bold. 0.15 -- 16 4.79 0.52 0.85 .Arrow-up bold. .Arrow-up bold.
0.16 -- 17 4.01 0.53 0.76 .Arrow-up bold. .Arrow-up bold. 0.15 --
18 4.31 0.30 0.76 .Arrow-up bold. .Arrow-up bold. .Arrow-up bold.
-- 19 4.00 0.50 0.75 0.25 .Arrow-up bold. .Arrow-up bold. -- C1
5.01 0.80 0.75 Less .Arrow-up bold. -- -- than 0.1 C2 4.99 1.20
0.15 .Arrow-up bold. .Arrow-up bold. -- -- C3 5.00 1.20 0.15
.Arrow-up bold. .Arrow-up bold. 0.15 -- C4 3.50 0.80 0.15 .Arrow-up
bold. .Arrow-up bold. -- -- C5 3.50 0.80 0.15 .Arrow-up bold.
.Arrow-up bold. 0.15 -- C6 2.88 0.97 0.96 0.09 .Arrow-up bold. --
-- C7 3.38 0.81 0.74 0.06 0.25 -- -- C8 4.79 1.05 0.91 .Arrow-up
bold. .Arrow-up bold. -- -- C9 4.00 0.10 0.75 .Arrow-up bold.
.Arrow-up bold. -- -- C10 3.00 0.50 0.75 .Arrow-up bold. .Arrow-up
bold. -- -- C11 4.26 -- 0.15 1.98 .Arrow-up bold. -- -- C12 4.00
0.50 0.75 0.75 .Arrow-up bold. 0.16 --
[0092]
2 TABLE 2 0.2% Tensile Proof Fracture Sample Strength Stress
Elongation No. (MPa) (MPa) (%) 6 290 139 20.0 7 324 165 15.0 8 321
160.3 17.7 9 310 154 18.3 10 304 146 21.5 11 284 140 19.6 12 270
135 19.8 13 290 140 23.0 14 298 149 19.0 C8 309 167 9.0 C9 265 120
22.0 C10 260 112 22.6
[0093]
3 TABLE 3 Hardness (HV) After Heat Treatment Sample No. As Cast
(175.degree. C. .times. 10 hr.) 15 79.1 82 16 73.7 76 17 67.3 68 18
70.1 72 19 68 69.2 C11 83.5 107.5 C12 68 78.2
[0094]
4TABLE 4 Sample Aluminum Alloy Composition (% by Mass) No. Mg Mn Ti
Fe Si Cu 20 4.46 0.39 0.14 0.12 Less than 0.1 Less than 0.01 21
4.46 0.36 0.15 0.36 .Arrow-up bold. .Arrow-up bold. 22 4.32 0.37
0.14 0.50 .Arrow-up bold. .Arrow-up bold. 23 4.31 0.30 0.15 0.76
.Arrow-up bold. .Arrow-up bold. 24 4.62 0.32 0.14 0.80 .Arrow-up
bold. .Arrow-up bold. 25 4.55 0.39 0.14 0.88 .Arrow-up bold.
.Arrow-up bold. 26 4.36 0.34 0.12 0.98 .Arrow-up bold. .Arrow-up
bold.
[0095]
5TABLE 5 Oxidation Sample Aluminum Alloy Composition (% by Mass)
Increment No. Mg Mn Ti Fe Mo Si Cu Rate (%) 27 4.46 0.39 0.14 0.12
0.18 Less Less 0.0063 than than 0.1 0.01 28 4.46 0.36 0.15 0.36 --
.Arrow-up bold. .Arrow-up bold. 0.0081
* * * * *