U.S. patent application number 13/023158 was filed with the patent office on 2011-08-11 for aluminum alloy welding wire.
This patent application is currently assigned to Illinois Tool Works Inc.. Invention is credited to Bruce Edward Anderson.
Application Number | 20110194973 13/023158 |
Document ID | / |
Family ID | 43881032 |
Filed Date | 2011-08-11 |
United States Patent
Application |
20110194973 |
Kind Code |
A1 |
Anderson; Bruce Edward |
August 11, 2011 |
ALUMINUM ALLOY WELDING WIRE
Abstract
A composition for welding or brazing aluminum comprises silicon
(Si) and magnesium (Mg) along with aluminum in an alloy suitable
for use in welding and brazing. The Si content may vary between
approximately 4.7 and 10.9 wt %, and the Mg content may vary
between approximately 0.15 wt % and 0.50 wt %. The alloy is well
suited for operations in which little or no dilution from the base
metal affects the Si and/or Mg content of the filler metal. The Si
content promotes fluidity and avoids stress concentrations and
cracking. The Mg content provides enhanced strength. Resulting
joints may have a strength at least equal to that of the base metal
with little or no dilution (e.g., draw of Mg). The joints may be
both heat treated and artificially aged or naturally aged.
Inventors: |
Anderson; Bruce Edward;
(Traverse City, MI) |
Assignee: |
Illinois Tool Works Inc.
Glenview
IL
|
Family ID: |
43881032 |
Appl. No.: |
13/023158 |
Filed: |
February 8, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61303149 |
Feb 10, 2010 |
|
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Current U.S.
Class: |
420/534 ;
148/527; 148/528; 219/121.14; 219/121.46; 219/121.64; 219/137R;
219/75; 228/101; 228/256; 420/541; 420/544; 420/546 |
Current CPC
Class: |
B23K 35/288 20130101;
C22C 21/02 20130101; B23K 35/0227 20130101; B23K 35/0261 20130101;
B23K 35/40 20130101; B23K 35/286 20130101 |
Class at
Publication: |
420/534 ;
420/546; 420/541; 420/544; 228/101; 228/256; 148/528; 148/527;
219/137.R; 219/75; 219/121.46; 219/121.14; 219/121.64 |
International
Class: |
B32B 15/01 20060101
B32B015/01; C22C 21/08 20060101 C22C021/08; C22C 21/16 20060101
C22C021/16; C22C 21/10 20060101 C22C021/10; B23K 35/24 20060101
B23K035/24; B23K 1/20 20060101 B23K001/20; B23K 31/02 20060101
B23K031/02; C22F 1/05 20060101 C22F001/05; C22C 21/14 20060101
C22C021/14; B23K 9/16 20060101 B23K009/16; B23K 10/02 20060101
B23K010/02; B23K 15/00 20060101 B23K015/00; B23K 26/00 20060101
B23K026/00 |
Claims
1. A composition for forming weld or braze joints, comprising:
silicon in a weight percent of between approximately 4.7% inclusive
and 10.9% inclusive; magnesium in a weight percent of between
approximately 0.15% inclusive and 0.50% inclusive; and a remainder
of aluminum and trace components.
2. The composition of claim 1, comprising silicon in a weight
percent of between approximately 4.7% inclusive and 8.0%
inclusive.
3. The composition of claim 2, comprising silicon in a weight
percent of between approximately 5.0% inclusive and 6.0%
inclusive.
4. The composition of claim 1, comprising magnesium in a weight
percent of between approximately 0.15% inclusive and 0.30%
inclusive.
5. The composition of claim 4, comprising magnesium in a weight
percent of between approximately 0.31% inclusive and 0.50%
inclusive.
6. The composition of claim 1, comprising one or more trace
components including iron, copper, manganese, zinc, titanium and
beryllium.
7. The composition of claim 6, wherein the total weight percent of
the trace components does not exceed approximately 0.15 wt % of the
composition.
8. The composition of claim 1, wherein the composition comprises a
spooled or linear wire or rod.
9. The composition of claim 1, wherein the composition comprises a
brazing component.
10. The composition of claim 10, wherein the brazing component
comprises such as brazing rings or paste.
11. The composition of claim 1, wherein the composition comprises a
cladding alloy for cladding aluminum base alloys for brazing to
aluminum or aluminum alloy base metal components.
12. The composition of claim 11, wherein the wire or rod has a
nominal diameter of 0.023 inches, 0.030 inches, 0.035 inches, 0.040
inches, 0.047 inches, 0.062 inches, 0.094 inches, 0.125 inches,
0.156 inches, 0.187 inches, or 0.250 inches.
13. A filler metal product for welding or brazing, comprising: a
spooled or linear wire or rod comprising an alloy of silicon in a
weight percent of between approximately 4.7% inclusive and 10.9%
inclusive, magnesium in a weight percent of between approximately
0.15% inclusive and 0.50% inclusive, and a remainder of aluminum
and trace components.
14. The product of claim 13, comprising silicon in a weight percent
of between approximately 4.7% inclusive and 8.0% inclusive.
15. The product of claim 14, comprising silicon in a weight percent
of between approximately 5.0% inclusive and 6.0% inclusive.
16. The product of claim 13, comprising magnesium in a weight
percent of between approximately 0.15% inclusive and 0.30%
inclusive.
17. The product of claim 16, comprising magnesium in a weight
percent of between approximately 0.31% inclusive and 0.50%
inclusive.
18. A method for making a composition for forming weld or braze
joints, comprising: obtaining an alloy comprising silicon in a
weight percent of between approximately 4.7% inclusive and 10.9%
inclusive, magnesium in a weight percent of between approximately
0.15% inclusive and 0.50% inclusive, and a remainder of aluminum
and trace components; and forming the alloy into a cast, extruded,
drawn, rolled or linear wire or rod suitable for welding or brazing
and cladding on braze-clad sheet.
19. The method of claim 18, wherein the wire or rod has a nominal
diameter of 0.023 inches, 0.030 inches, 0.035 inches, 0.040 inches,
0.047 inches, 0.062 inches, 0.094 inches, 0.125 inches, 0.156
inches, 0.187 inches, or 0.250 inches.
20. A method for forming a weld or braze joint, comprising: melting
or metallurgically bonding at least a portion of a work piece base
metal; adding or bonding to the base metal a filler metal
comprising an alloy of silicon in a weight percent of between
approximately 4.7% inclusive and 10.9% inclusive, magnesium in a
weight percent of between approximately 0.15% inclusive and 0.50%
inclusive, and a remainder of aluminum and trace components; and
allowing the resulting weld or braze joint to solidify.
21. The method of claim 20, wherein melting the base metal and
adding the filler metal is performed by a welding operation that
includes striking an arc between the base metal and a wire or rod
comprising the filler metal.
22. The method of claim 21, wherein the welding operation comprises
a metal inert gas welding operation.
23. The method of claim 22, wherein the welding operation comprises
a pulsed waveform welding process.
24. The method of claim 21, wherein the welding operation comprises
a stick welding operation.
25. The method of claim 20, wherein melting the base metal or
metallurgical bonding to the base metal and adding the filler metal
is performed by an operation that includes heating the base via a
heat source and adding the filler metal by hand, preformed shape
such as a brazing ring or as cladding on brazing sheet.
26. The method of claim 25, wherein the operation comprises a
tungsten inert gas welding process, plasma gas welding process,
electron beam welding process, laser beam welding process, furnace
brazing process, or torch brazing process.
27. The method of claim 20, comprising heat treating a structure
comprising the weld or braze joint.
28. The method of claim 20, comprising aging a structure comprising
the weld or braze joint.
29. The method of claim 20, comprising performing a plurality of
successive passes in which the base metal and/or preceding passes
of the filler metal are melted and additional filler metal is
deposited.
30. The method of claim 29, wherein during at least one successive
pass substantially all magnesium in the respective pass is provided
by the filler metal.
31. The method of claim 20, wherein in a structure comprising the
weld or braze joint, the weld or braze joint has a strength at
least equal to the base metal.
32. A welded or brazed structure made by the method of claim 17.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Non-Provisional of U.S. Provisional
Patent Application No. 61/303,149, entitled "Aluminum Alloy Welding
Wire", filed Feb. 10, 2010, which is herein incorporated by
reference.
BACKGROUND
[0002] The invention relates generally to the field of welding
filler metals, and more particularly to compositions suitable for
welding aluminum alloys.
[0003] Many different processes are known and currently in use for
joining metal articles, including brazing and welding. Both such
operations may be used for joining of aluminum and aluminum alloy
articles. Unlike steels and other metals, aluminum alloys present
unique problems owing, for example, to their metallurgy, their
melting points, the changes in strength as a function of particular
alloying agents, and so forth. Moreover, increasing interest in
both thinner aluminum alloy workpieces on one hand, and thicker
workpieces on the other presents additional difficulties in the
selection of brazing and welding materials that perform well and
provide the desired physical and mechanical properties.
[0004] Brazing operations use a filler metal with a melting
temperature that is lower than the base metal being joined. In
brazing, the base metal is not melted and the alloying elements in
the filler metal are selected for their ability to lower the
melting temperature of the filler metal and to wet the aluminum
oxide always present on the base metal so that a metallurgical bond
can be achieved without melting the base metal. In some
applications, brazing may be conducted in a furnace under vacuum or
protective atmosphere where the temperature is raised until only
the filler metal melts and fills the joint between the solid base
metal members through fluid flow and capillary action. Brazed
joints are commonly used for low strength aluminum alloys, and for
very thin section structures, such as radiators for automobiles,
and for heat exchangers such as those used in heating, ventilation
and air conditioning systems. The temperatures used in brazing may
anneal both non-heat treatable and heat treatable aluminum alloys,
which may alter the mechanical properties achieved either by cold
working or heat treatment and aging operations. Therefore, brazing,
while quite useful in many applications, may not be suitable to
join high strength structural alloys.
[0005] Welding operations join metal parts by melting a portion of
the base metal of each work piece to be joined, as well as by
melting of the filler metal to create a molten weld pool at the
joint. Welding requires concentrated heat at the joint to create
the molten weld pool which upon solidification has a resultant
chemical composition that is a combination of the chemistries of
the filler metal and the base metal. Welding temperatures may often
be controlled to be sufficiently high to melt both the filler metal
and the base metal, but also to keep the heat affected zone of the
base metal to a minimum in order to retain its mechanical
properties.
[0006] The adder materials, both for brazing and welding, are
typically delivered in the form of wire, which, depending upon the
application, may be in the form of continuous lengths that are fed
though a welding torch, or in shorter lengths that may be hand-fed,
or even as rods, such as flux-coated rods for stick welding.
Currently available aluminum alloy brazing and welding wires do
not, however, satisfy the needs of many modern applications. For
example, current products do not offer the desired fluidity during
the joining operation, or the desired strength when combined with
base material in welding applications, particularly when used with
a range of modern welding processes. Moreover, where welding arcs
vary in penetration, heat, weld pool formation, and so forth,
current aluminum alloy wires and compositions do not provide a
desired degree of consistency in terms of the composition and
strength of the ultimate joint.
[0007] There is currently a need for improved aluminum alloy
compositions that are suitable for welding (and brazing)
applications that successfully address such needs.
BRIEF DESCRIPTION
[0008] In accordance with one aspect, the invention provides a
composition for forming weld or braze joints, comprising silicon in
a weight percent of between approximately 4.7% inclusive and 10.9%
inclusive, magnesium in a weight percent of between approximately
0.15% inclusive and 0.50% inclusive and a remainder of aluminum and
trace components. Particular subranges of these are particularly
attractive for their enhanced performance and superior strength.
Moreover, the invention provides a filler metal product for welding
or brazing that comprises a spooled or linear wire or rod
comprising an alloy of silicon in a weight percent of between
approximately 4.7% inclusive and 10.9% inclusive, magnesium in a
weight percent of between approximately 0.15% inclusive and 0.50%
inclusive, and a remainder of aluminum and trace components.
[0009] In accordance with another aspect, the invention offers a
method for forming a weld or braze joint, comprising melting at
least a portion of a work piece base metal, adding to the melted
base metal a filler metal comprising an alloy of silicon in a
weight percent of between approximately 4.7% inclusive and 10.9%
inclusive, magnesium in a weight percent of between approximately
0.15% inclusive and 0.50% inclusive, and a remainder of aluminum
and trace components, and allowing the resulting weld or braze
joint to solidify. Here again, certain processes and subranges are
particularly attractive for their performance and strength
properties. This invention is also intended to cover joints and
structures made by the new methods and materials provided.
DRAWINGS
[0010] These and other features, aspects, and advantages of the
present invention will become better understood when the following
detailed description is read with reference to the accompanying
drawings in which like characters represent like parts throughout
the drawings, wherein:
[0011] FIG. 1 is a diagrammatical view of one exemplary welding
system suitable for use of the new compositions disclosed herein;
and
[0012] FIG. 2 is a diagrammatical view of another exemplary welding
system suitable for use of the new compositions.
DETAILED DESCRIPTION
[0013] The present disclosure provides first a description of the
new compositions offered by the present invention, followed by a
discussion of typical welding operations that may be used
advantageously with the new compositions, and then a discussion of
certain exemplary applications that may benefit from the use of the
compositions. Throughout the discussions, it should be borne in
mind that the new compositions are not necessarily limited to use
in welding, or even as filler metals, but may be useful in other
applications and operations, such as brazing. Similarly, while
references are made to "welding wire", this term should be
understood, when used, as referring to any suitable form of adder
metal, including without limitation, continuous wire intended for
wire feeder applications (e.g., for metal inert gas (MIG) welding),
rod and sticks (e.g., for tungsten inert gas (TIG) and stick
welding), as well as other forms for welding, fusing, brazing,
braze cladding of sheet and similar operations.
[0014] In a first aspect, new compositions are provided for welding
work pieces made from aluminum (Al) and aluminum alloys. In a broad
sense, the compositions comprise 4.7 to 10.9 wt % silicon (Si),
0.15 to 0.50 wt % magnesium (Mg), and the remainder Al with trace
elements ordinarily found in aluminum filler metals. Presently
contemplated embodiments include Si in a range of 4.7 to 8.0 wt %,
and in one embodiment, from 5.0 to 6.0 wt %. Moreover, certain
embodiments comprise Mg in a range of from 0.31 to 0.50 wt % for
enhanced strength in many welds.
[0015] Aluminum, as it is available from the major aluminum
producers of the world, may contain trace element impurities
including but not limited to iron, copper, manganese, zinc,
titanium, and beryllium. In one embodiment, the aluminum alloy
welding wire may further comprise any or all of the following
elements in an amount up to and including: 0.80 wt % Fe, 0.30 wt %
Cu, 0.15 wt %, Mn, 0.20 wt % Zn, 0.20 wt % Ti, and 0.0003 wt % Be
(with all other trace elements limited to each 0.05 wt % and a
total 0.15 wt %).
[0016] In embodiments where the compositions are formed into
welding wire, such wire (e.g. filler metal) may be provided for use
in welding applications in a linear form. The linear wire,
continuous or cut to length, typically has a diameter of at least
0.010 inches and typically less than 0.30 inches. In preferred
embodiments the linear wire has one or more diameters, such as
0.023 inches, 0.030 inches, 0.035 inches, 0.040 inches, 0.047
inches, 0.062 inches, 0.094 inches, 0.125 inches, 0.156 inches,
0.187 inches, and 0.250 inches.
[0017] The amounts of the individual components (e.g. Si and Mg) of
the filler material with the remainder of Al with trace impurities
can be selected to produce a specific filler alloy for a desired
purpose. For example, as noted above the alloy composition
comprises: 4.7 to 10.9 wt % Si, and more particularly, amounts
towards the middle of this range, such as below 8.0 wt %. In
particular embodiments, the Si content may be, for example 5.0 to
6.0 wt % (e.g. 5.2 to 5.8 wt % Si), or between 5.4 to 6.0 wt %
(e.g., 5.5 to 5.8 wt %).
[0018] Within any of these Si ranges the amount of Mg may be varied
between 0.15 wt % and 0.50 wt %, inclusive. In other words, within
any of the above Si ranges, the Mg level may be selected to be 0.17
to 0.40 wt %, 0.20 to 0.30 wt %, 0.22 to 0.30, 0.25 to 0.30 wt %,
0.15 to 0.25 wt %, 0.15 to 0.23 wt %, 0.15 to 0.20 wt %, 0.18 to
0.28 wt %, and/or 0.20 to 0.25 wt %. In a presently contemplated
embodiment, the amount of Mg is towards a higher end of the range,
from 0.31 wt % to 0.50 wt % to allow for enhanced weld strength
independent of dilution from the base metal, as discussed below.
One presently contemplated embodiment intended to be registered
with the Aluminum Association and submitted to the American Welding
Society for certification as an approved aluminum welding alloy is
X4043P which has a Si content of 5.0 to 6.0 wt % and a Mg content
of 0.31 to 5.0 wt %.
[0019] The compositions of the invention are particularly well
suited to welding applications, although they may also be used for
brazing and other operations (e.g., plating). FIGS. 1 and 2
illustrate exemplary welding systems that may advantageously be
used to produce joints in aluminum and aluminum alloy workpieces
using the compositions disclosed herein. As mentioned above, a
range of welding systems and processes may be employed, including
MIG processes, TIG processes, stick welding processes and so forth
(as well as brazing processes). FIG. 1 illustrates an exemplary MIG
system 10 that includes a power supply 12 designed to receive power
from a source 14, and shielding gas from a gas source 16. In many
implementations, the power source will include the power grid,
although other sources will also be common, such as
engine-generator sets, batteries, and other power generation and
storage devices. The shielding gas will typically be provided by
pressurized bottles.
[0020] The power supply 12 includes power conversion circuitry 18
that converts incoming or stored power to a form suitable for
welding. As will be appreciated by those skilled in the art, such
circuitry may include rectifying circuits, converters, inverters,
choppers, boost circuits and so forth. Moreover, the circuitry may
produce alternating current or direct current output, depending
upon the welding process selected. The power conversion circuitry
is coupled to control circuitry 20 for controlling the operation of
the conversion circuitry. In general, the control circuitry will
include one or more processors 22 and memory 24 that stores welding
parameters, setpoints, welding process routines and so forth
executed by the processor for regulating operation of the
conversion circuitry. By way of example, the processor may cause
the conversion circuitry to implement constant current processes,
constant voltage processes, pulse welding processes, short circuit
transfer processes, or any other suitable process adapted for
welding aluminum parts with the compositions disclosed. An operator
interface 28 allows a welding operator to select the welding
process as well as to set welding parameters, such as currents,
voltages, wire feed speeds, and so forth.
[0021] The power supply 12 is coupled via cabling 30 to a wire
feeder 32. The cabling may include power cabling for transmitting
weld power, data cabling for transmitting control and feedback
signals, and gas hose or cabling for providing shielding gas. The
wire feeder 32 includes a spool 34 of welding wire according to the
compositions disclosed. A wire drive 36 draws wire from the spool
and advances the wire to a welding cable 38 coupled to a welding
torch 40. The wire drive will typically operate based upon settings
made on the power supply, although the wire feeder may include its
own processor and memory (not shown) that control or coordinate for
control of the wire feed speed, application of power from the power
supply to the advancing wire, and so forth. It should also be noted
that the wire feeder may include its own interface (not
represented) allowing the welding operator to make changes to the
welding process, the weld settings, the wire feed speed, and so
forth.
[0022] The welding cable 38 conveys power and gas to the welding
torch 40, and may convey data signals (e.g., senses current and/or
voltage) to the wire feeder (and therefrom to the power supply). In
aluminum welding applications, the torch 40 may be adapted with an
internal motor to pull welding wire while the wire feeder 32 pushes
the wire in coordination. A workpiece cable 42 is coupled to the
workpiece 44 to be welded, and allows for a completed circuit to be
established through the torch, welding wire and workpiece to create
a welding arc between the wire and workpiece. This arc is sustained
during welding (under the particular welding process and control
regime selected) and melts the welding wire and, typically, at
least partially melts the workpiece or workpieces to be joined.
[0023] As illustrated by reference number 46 in FIG. 1, the welding
system may be adapted to accept a stick welding torch. Such torches
do not use a continuously spooled and fed welding wire, but stick
electrodes 48, which may be made in accordance with the
compositions disclosed. As will be appreciated by those skilled in
the art, the stick welding torch may be coupled directly to a
welding power supply 12 that performs other welding processes
(e.g., MIG and TIG processes), or for this applications, the power
supply may have more limited capabilities in terms of the available
processes.
[0024] FIG. 2 illustrates an exemplary TIG system that may be used
with the new compositions disclosed. The TIG system 50 also
includes a power supply 52 that, similarly to the system described
above, receives power from a source 54, and shielding gas from a
source 56. As will be appreciated by those skilled in the art, the
shielding gases used will typically be different depending upon the
process selected. The power supply 52 again comprises power
conversion circuitry 58 and associated control circuitry 60. The
control circuitry 60 includes one or more processors 62 and memory
64 for storing weld settings, welding processes, and so forth. Here
again, an operator interface 68 allows the welding operator to set
such welding parameters for the TIG welding process.
[0025] In the TIG welding process, however, wire is not fed to the
workpiece, but only power and gas are conveyed via appropriate
cabling 70. The welding torch 72 receives the power and gas, and
allows for initiation of a welding arc via an internal tungsten
electrode. A workpiece cable 74 is coupled to the workpiece 76 to
allow for completion of the electrical circuit. After an arc is
initiated with the workpiece, welding wire 78 is fed to the weld
location, and is melted, typically with at least some melting of
the workpiece base metal. A foot pedal 78 (or another operator
input device) allows for fine control of the process by the
operator during the time the arc is ongoing and welding is
proceeding.
[0026] It should also be noted that the processes used with the
present compositions may be partially or fully automated. That is,
in some settings, the joints may be programmed for execution by
automated welding systems, robots, and the like. In most such
settings, the welding wire will be fed continuously from a spool,
as discussed above. Moreover, the compositions may be used with a
number of other processes and applications, such as laser welding,
spot welding, laser brazing, and so forth. While the processes may
be designed for joining aluminum and aluminum alloys, the
compositions are in no way limited to such applications, and may be
used for joining non-aluminum base metals, such as steels.
[0027] The methods described above allow for the creation of a weld
pool that contains the melted aluminum filler metal alloy and a
portion of the melted workpiece(s). In certain embodiments the weld
pool will contain more than 20 wt %, more than 30 wt %, more than
40 wt %, more than 50 wt %, more than 60 wt %, more than 70 wt %,
more than 80 wt %, more than 90 wt %, more than 92 wt %, more than
94 wt %, more than 96 wt %, more than 98 wt %, or more than 99 wt %
of the aluminum filler metal alloy with the remaining portion being
made up of molten base workpiece(s).
[0028] Specifications for use of the present compositions may also
advantageously call for heat treating and aging the resulting
aluminum structure. Certain of these operations may be performed at
a temperature greater than room temperature and below the melting
points of the base metal workpiece(s), aluminum filler metal alloy,
and the weld pool. The heat treating step may advantageously occur
for a period of time between 30 minutes and 30 hours (e.g., between
1 hour and 10 hours, for example between 2 hours and 8 hours).
Moreover, processing may include allowing the welded aluminum
structure to age at temperatures above ambient temperatures for a
period of time between 30 minutes and 30 days (e.g. between 1 hour
and 1 week, for example between 2 hours and 12 hours). Still
further, the compositions may benefit from aging at ambient
temperature for periods on the order of from 1 week to 2 years
(e.g., 2 weeks to 1 year, for example 1 month to 6 months).
[0029] It is believed that through the use of the present
compositions and wires, superior welded aluminum structures can be
produced that exhibit superior weld properties, including high
shear and tensile strength compared to aluminum structures welded
with other aluminum filler materials. For example, it is believed
that the compositions offer stronger welded joints through solid
solution strengthening in the as-welded condition and through the
formation and precipitation of intermetallic compounds of Mg and Si
when the welded structure is post-weld heat treated and/or
aged.
[0030] A variety of workpieces and workpiece configurations may
benefit from the present compositions, such as single alloy sheets,
braze clad sheets, plates, tubes, rods, bars, extrusions, castings,
forgings, powdered metal parts, and cermets in all configurations
(e.g. circular, square, triangular), or some combination thereof.
The thicknesses can be any size required to create the desired
welded structure. These compositions work equally well with all
thicknesses of base metal work pieces and with all amounts of
dilution of the weld puddle with melted base material.
[0031] Particularly enhanced properties are provided when used with
aluminum alloy base materials in the 1xxx, 2xxx, 3xxx, 5xxx up thru
3% Mg, 6xxx, and 7xxx series aluminum alloys. More particularly,
base metal workpieces from 6xxx series aluminum alloys may benefit
from the present compositions. Such 6xxx series alloys are
particularly popular for many aluminum structures insomuch as they
are heat treatable. Such structures include, for example,
extrusions, sheets, and plates, and are used to fabricate
automobiles, truck trailers, boats, military vehicles, and
countless other structures.
[0032] For many years the 6xxx series alloys have been welded with
the aluminum-silicon binary alloy 4043. Alloy 4043 is non-heat
treatable. Its as-welded strength is as low as 50% of the strength
of the most widely used 6xxx series alloys joined by this alloy. If
Mg is added to 4043, it becomes a heat treatable ternary alloy
similar to the 6xxx series alloys and if enough Mg is added, will
achieve significantly higher as-welded strength and similar
mechanical properties as the 6xxx base metals when post-weld heat
treated and aged. During the welding operation the weld puddle is
diluted by some amount of melted base metal which is simply
referred to as dilution. When welding 6xxx series base metals with
4043 for example, and dilution occurs, the filler metal is alloyed
with base metal and the puddle acquires some Mg. The amount of
strength increase in the weld puddle depends on the amount of
dilution. Welding codes such as AWS D1.2 have been established for
base metals such as 6061. The code assumes a minimum dilution of
20% base metal and specifies the resultant shear and tensile
strengths that must be met in the final welded assembly. These
codes are used for design purposes and welding procedures are
established to meet them in production.
[0033] However, prior to the present invention, the industry has
not been able to consistently meet these codes for the 6xxx series
alloys. When the chemistry ranges of the base metals and the filler
metals are combined with all of the variables present in the
welding process, the resultant Mg content of the weld puddle after
welding is not consistent and cannot be controlled to the level
required to meet code consistently. Of two common weldment designs
commonly used, the fillet joint and the butt joint, 80% of commonly
employed welds are fillet joints. By virtue of its physical shape,
there is very little dilution when welding a fillet joint. Likewise
when welding butt joints in structures with section thicknesses
over 3/8 inch or thinner than 3/32 inch, there is little or no
dilution. Consequently these weld joints do not draw sufficient Mg
from the base metal to reach the desired strength either as-welded
or post-weld heat treated and aged. This has created a very serious
problem in industry. Aluminum is the metal of choice to reduce
weight and energy consumption, but its use has been hampered by the
filler metals available.
[0034] The present invention solves this problem. It provides an
Al--Si--Mg ternary alloy with a chemistry range that yields the
shear and tensile strengths required by AWS D1.2 for the 6xxx
series alloys with little or no dilution. This filler metal
composition is designed to take into account the chemical range of
Si and Mg that can be experienced in the 6xxx series base alloys
and the variables that can be encountered in the welding
manufacturing process and assure that adequate levels of Si and Mg
are present in the final weld to meet desired strength
requirements. As discussed above, the new metal compositions may
comprise varying amounts of Si and Mg, such as between 4.7 wt % and
10.9 wt % Si, and more particularly between 4.7 wt % and 8.0 wt %,
and still more particularly, between 5.0 wt % and 6.0 wt %. The Mg
component may vary between 0.15 wt % and 0.50 wt %, and between
0.15 wt % and 0.30 wt %, but for enhanced strength, may be between
0.31 wt % and 0.50 wt %.
[0035] Welded joints made via these compositions benefit both from
the performance of the compositions during the joining operation,
and from enhanced properties of the as-welded (or more generally,
the as-joined) structures. For example, the Si component reduces
the melting point and surface tension, providing improved fluidity.
The relatively high Mg content reduces the need to draw Mg from the
base metal for higher strength (e.g., matching the strength of the
base metal). This is particularly useful when joining thinner
sections (from which little melting of the base metal occurs, or in
which little material is available for contribution to the
as-welded joint) as well as thicker sections (which may require
multiple passes with subsequent passes increasingly unable to draw
any Mg from the base metal or from earlier passes).
[0036] For example, 6061 base metal alloy is commonly used in sheet
and plate forms, and is welded with 4043 filler metal. Alloy 6061
is a magnesium-silicon based alloy containing 1 percent magnesium
and 0.6 percent silicon along with a small amount of copper and
chromium. Alloy 6061 achieves its maximum mechanical properties
through heat treatment where the aluminum metal matrix is
strengthened by the precipitation of alloying elements as
intermetallic compounds, in this case magnesium-silicide, the size
and distribution of which throughout the matrix is controlled
through carefully controlled thermal operations. This heat treated
microstructure is quickly destroyed by welding with a typical loss
of mechanical properties in the heat affected zone of the weld,
between 30 and 50 percent. The un-welded tensile strength of 6061
in the -T6 heat treated condition is typically 45 KSI while the
minimum specification as-welded tensile strength is 24 KSI. The
fully annealed tensile strength of 6061 is typically 19 KSI.
Depending on the welding conditions used, there can be portions of
the 6061 base material in the heat affected zone that are fully
annealed. The fully annealed tensile strength of 4043 is also
typically 19 KSI and can be as low as 15 KSI. Moreover, 4043 is a
non-heat treatable alloy.
[0037] Published data used for design purposes indicates mechanical
properties for 6061 welded with 4043 in the as-welded and post-weld
heat treated and aged conditions. This data was developed from
actual welds made in various configurations. The data presumes that
a certain percentage of base metal is melted during the welding
process and is alloyed into the weld puddle resulting in a new
chemistry that is a blend of 4043 and 6061. When this happens, some
magnesium is introduced into the 4043 chemistry and if the base
metal melting is sufficient, the weld puddle becomes an alloy that
is solid-solution strengthened by the magnesium in the as-welded
condition and will respond to heat treatment operations conducted
after welding.
[0038] Table 1 below provides examples of data for 6061 base metal
welded with 4043 both in the as-welded and post-heat treated and
aged conditions:
TABLE-US-00001 TABLE 1 Tensile Strength Base Filler (KSI) Alloy
alloy Temper Spec. condition Minimum Typical 6061-T6 4043 AW AWS
D1.2 24.0 27.0 6061-T6 4043 AW No dilution 15.0 19.0 6061-T6 4043
PWHT Min 20% dil. 6061 42.0 45.0 6061-T6 4043 PWHT No dilution 15.0
19.0 6061-T6 4643 AW Indep. of dilution 24.0 27.0 6061-T6 X4043P AW
Indep. of dilution >24.0 >27.0 6061-T6 4643 PWHT Indep. of
dilution 42.0 45.0 6061-T6 X4043P PWHT Indep. of dilution >42.0
>45.0 Note 2: The as-welded and post-heat treated tensile
strength of the alloy combinations without any dilution of the
melted base metal in the weld puddle fail the AWS D1.2 design
requirements. Note 2: The tensile strength requirements of AWS D1.2
are met without any dilution of melted base metal in the weld
puddle for 4643, and X4043P.
[0039] As noted above, two common weld joint types, fillet joints
and butt joints, make up a majority of all welds. The fillet joint
most generally has a weld-joint angle of 90 degrees that must be
filled with filler metal. For very thin base metal sections the
welding operation necessitates that the amount of base metal
melting be held to an absolute minimum and therefore the amount of
weld puddle dilution by melted base metal is very small. For the
example being used here, using 4043 filler metal, the resulting
weld does not have sufficient magnesium to reach adequate strength
in the as-welded condition and it will not respond to post-weld
heat treatment and aging. This same condition occurs when the
fillet weld is used with thick section sizes being joined. It this
case the bottom of the weld joint may see adequate weld puddle
dilution by melted base metal but as the weld joint is filled with
multiple passes, the filler metal in the later passes is no longer
next to the base material and will have no base metal dilution.
Therefore, once again the weld will not have sufficient magnesium
content to reach acceptable strength in the as-welded condition and
it will not respond to post-weld heat treatment and aging. The
published data and the AWS D1.2 welding code for fillet welds
welded with 4043 recognizes this situation and the mechanical
strength data correctly shows the strength of the weld to be that
of 4043 without dilution. Butt joints on the other hand yield much
higher percentages of base metal melting. For butt welds in 6061
welded with 4043, the published data and AWS D1.2 do assume
adequate weld puddle dilution to achieve the specified strengths in
the as-welded and post-weld heat treated and aged conditions.
However, the amount of weld puddle dilution in butt welds is
difficult to control and reproduce reliably in production welding
operations.
[0040] Table 2 below provides typical maximum design strengths of
fillet welds containing 100% filler metal only for certain
currently available alloy welding wires:
TABLE-US-00002 TABLE 2 Longitudinal Shear Strength Transverse Shear
Strength Filler Alloy (KSI) (KSI) 1100 7.5 7.5 4043 11.5 15.0 4643
13.5 20.0 X4043P >13.5 >20.0 5654 12.0 18.0 5554 17.0 23.0
5356 17.0 26.0
[0041] Butt welds in section sizes greater than 3/8 inches do not
produce enough base-metal melting in the center of the weld to
reach the minimum desired amount of base metal dilution into the
weld puddle. Therefore, because 4043 must obtain magnesium from
dilution by melted base metal into the weld puddle, the control of
resultant mechanical properties in both the as-welded and post-weld
heat treated and aged condition is difficult if not impossible to
obtain reliably on a production basis.
[0042] As noted above, the present compositions may be used with a
variety of welding processes. The development of certain of these
welding processes has complemented the move to produce structures
with thinner section sizes. Processes such as pulsed welding allow
the welding of increasingly thin section sizes due to its
prevention of significant base metal melting. In thin section
structures in particular, the currently available silicon based
welding alloys make it impossible to achieve desired design
strengths and this has limited design options for parts that could
otherwise reduce weight and maintain strength. Developments to
address such problems have included, for example, an alloy
registered as 4643, which was thought to offer a solution for butt
welding thick section 6061 base metals. It can of course be used to
weld thin sections as well where the same problems of lack of
puddle dilution are present. Alloy 4643 is a replication of the
alloy that is obtained from the blending of 20% 6061 and 80% 4043
which results from weld puddle dilution during welding operations.
The lower silicon content of 4643 decreases its fluidity, increases
its melting temperature, and increases its solidification and solid
state shrinkage as compared to 4043. Moreover, 4643 is again
subjected to dilution by the low silicon containing 6xxx series
alloys during welding. The resulting alloys exhibit less than
optimum welding characteristics and increased crack sensitivity
problems when the weld puddle silicon levels fall to 2 percent or
lower during welding. As a result, 4643 has not been adopted as a
viable alternative to 4043 and has been used only in a few
instances to solve specific problems. The alloy has only been
produced in very small quantities and costs as much as seven times
the cost of 4043, making it economically unviable.
[0043] The present compositions address such shortcomings of the
6061/4043 alloy combination. The compositions contain the required
level of magnesium without relying on weld puddle dilution to reach
desired as-welded and post-weld heat treated mechanical properties.
Moreover, the compositions experience sufficient solution and
quench rates during welding such that they will naturally age over
time and increase in strength over the first year at room
temperature. They also provide the fabricator the option to
purchase 6xxx series base alloys in the -T4 temper which is
solution heat treated and quenched but not aged. Then, after
welding with the present compositions, the finished weldment can
simply be aged to achieve strength levels close to that of the -T6
temper.
[0044] Moreover, the present compositions will provide every weld,
regardless of the type or dilution factors, with an automatic
as-welded increase in longitudinal shear strength on the order of
at least 17%, transverse shear strength on the order of at least
33%, and tensile strength on the order of at least 42% when
compared with 4043, and an increase in post-weld heat treated shear
strength on the order of at least 130%.
[0045] Another important consideration is the amount of filler
metal required to produce an adequate weld. Fillet weld shear
strengths are calculated using the fillet's cross sectional throat
dimension along with the published shear strength of the relevant
filler alloy. See Table 1 above for some typical shear strengths of
various pure filler metal alloys. As the fillet size grows as a
result of the welding procedure or the number of passes made, the
increase in throat dimension is not linear with the volume of the
fillet metal used. If the throat dimension is doubled, the volume
required to fill the fillet increases by a factor 4. But the volume
of filler metal required may be even more than this since the
number of weld passes required to fill the fillet rises quickly as
the throat dimension is increased, and welders have to deal with
full weld passes when covering underlying passes. In situations
where there is no penetration of the base metal and the required
weld puddle dilution by melted base metal is not present, designers
are forced to increase the fillet weld throat dimensions in order
to obtain adequate weld strengths. This results in the consumption
of significantly larger quantities of expensive filler metals
raising the cost of the welded structure. The increased strength
obtained by using the present compositions will significantly
reduce cost by reducing the required size of the fillet weld, as
significant weld penetration is not required in order to draw
sufficient Mg into the weld puddle to achieve the desired strength.
Moreover, using the present compositions, welds will naturally age
in the as-welded condition and will age more rapidly as service
temperatures rise. Their mechanical properties will continually
increase over time for at least the first year after welding.
[0046] Regarding the absolute and relative quantities of Si and Mg
in the present compositions, the inventor has recognized that Si
based aluminum welding filler metal alloys fabricated as wire may
be from a hypoeutectic composition. As the Si content increases,
the freezing range decreases and both the liquidus and solidus
decrease. This decrease results in reduced crack sensitivity of the
alloy. The Al--Si alloys are sensitive to solidification cracking
when the silicon level falls between 0.5 and 2.0 wt %. A resulting
Si--Al alloy with Si levels below 4.7 wt % limits the total amount
of base metal dilution possible before reaching the crack sensitive
range. This feature is especially important when TIG welding where
dilution of the weld puddle by melted base metal is relatively high
depending on the welding procedure. Alloys such as the 6xxx series
that derive their mechanical properties though the precipitation of
magnesium silicide during heat treatment are crack sensitive when
welding chemistries fall in the range of 0.6 to 0.8 wt % Si and 0.5
to 1.0 wt % Mg in combination or in other words a total of about 2
wt % magnesium silicide. The 6xxx series alloys most susceptible to
this are the alloys 6005 through and including 6061. This is the
reason that the highest practical limit for Mg in an Al--Si filler
metal alloy is 0.5 wt %. If 4043 filler alloy has obtained a
minimum Mg level of 0.20 wt % through weld puddle dilution by
melted 6xxx base metal, it will develop mechanical properties that
are similar to those obtainable by post-weld heat treatment and
aging of the 6xxx base metals to the -T6 temper. Therefore, I have
specified that the present compositions of X4043P shall have a Si
content of 5.0 to 6.0 wt % and a Mg content of 0.31 to 0.50 wt
%.
[0047] In certain embodiments, the composition has a specified Si
range of 5.0 to 6.0 wt %. The typical target free silicon content
for this embodiment is 5.2 wt %. This chemistry produces a liquid
viscosity with an internal friction of 1.1 centipoises in the alloy
when molten at 1292 degrees F. This is the fluidity that the
industry had come to expect in ER4043 and what has been documented
over the last half century of welding practice as performing
satisfactorily. The Si range of 5.0 to 6.0 wt % is also
advantageous in that it has a direct bearing on the electrical
current required to melt the filler metal during welding. Changes
here would necessitate the changing of the welding procedure
specifications and the preprogrammed welding parameters in many
welding machines used in manufacturing operations around the
world.
[0048] Si content also affects thermal expansion of the alloy. A
reduction of Si content will increase the coefficient of thermal
expansion of the weld bead. For example, a 5.2 wt % Si content in
the composition will yield a coefficient of thermal expansion of
0.94 with pure Al being 1.0. A 3.5 wt % Si content in the
composition will yield a coefficient of thermal expansion of 0.97.
Differences in thermal expansion between Al and known filler metal
compositions cause increased distortion during welding and increase
crack sensitivity as compared to the present compositions. Higher
Si content reduces the solidification and solid state shrinkage
rate. When compared to existing compositions, the higher Si content
of the present compositions produces a higher volume fraction of
eutectic phase which in turn reduces the shrinkage rate of the
molten puddle. Therefore, the present compositions have crack
sensitivity levels as good as or better than currently available
alloys. Thus, the compositions can be used as a direct substitute
for existing compositions, such as 4043, with no changes required
in welding practices or procedures yet, it will provide the
strength benefits greater than 4643, while 4643 has not been
accepted as a direct substitute for 4043.
[0049] Due to the Mg content of the new compositions, they will not
only be used as a direct substitute for 4043 but will provide the
significant advantages of higher shear and tensile strengths in all
types of welds. The instances of failing weld metal mechanical
properties due to the lack of proper base metal dilution in the
weld puddle will be eliminated. The Mg level may be controlled in
this new alloy to remain below the crack sensitive level. The level
is low enough to allow for some additional Mg obtained from
dilution of the weld puddle by melted base metal when welding the
6xxx series alloys. Therefore, the new compositions have a maximum
Mg content of 0.50 wt %. This level provides a safety factor for
the possible additional Mg that might be alloyed into the weld
puddle from dilution of melted base metal. When welding a lower
strength 1xxx or 3xxx series alloy and some weld puddle dilution is
inadvertently obtained, the inventor's alloy X4043P has a built in
safety factor of 0.31 minimum Mg content which will keep Mg at
acceptable levels and this is not found in either ER4043 or
ER4643.
[0050] While only certain features of the invention have been
illustrated and described herein, many modifications and changes
will occur to those skilled in the art. It is, therefore, to be
understood that the appended claims are intended to cover all such
modifications and changes as fall within the true spirit of the
invention.
* * * * *