Metal treatment – Stock – Aluminum base
Reexamination Certificate
2000-03-15
2003-06-17
King, Roy (Department: 1742)
Metal treatment
Stock
Aluminum base
C148S438000
Reexamination Certificate
active
06579386
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates generally to the field of welding, and more particularly to an improved filler wire for aluminum alloys and method of welding.
BACKGROUND OF THE INVENTION
Aluminum alloys are used in numerous applications, including car bodies, storage vessels, and the like. One particular type of aluminum alloy is aluminum-lithium alloys. Aluminum-lithium alloys are often used in space vehicles, such as the external tank of the Space Shuttle. Welding aluminum alloys, and in particular aluminum-lithium alloys, is often difficult due to the propensity for weld cracking. Cracks in the weld reduce the strength of the weld and can also create leakage paths in the weld. In particular, a poor weld can result in stress concentrators, reduced resistance to low cycle and high cycle fatigue, and a reduction in corrosion resistance.
Filler wire is used in the welding process. The chemistry, fabrication, and welding process of the filler wire can greatly affect the propensity of the weld to crack. “Chemistry” refers to the elemental components of the filler wire. Herein, any reference to the chemistry or chemical composition of the filler wire by percentage composition shall mean percentage composition by weight (wt. %). “Fabrication” refers to the specialized process that the filler wire is fabricated. “Welding Process” refers to the particular type of welding process used to produce the weld, such as variable plasma arc (VPPA), gas tungsten arc (GTA), gas metal arc (GMA), and soft plasma arc (SPA) welding, as well as the specific parameters surrounding the welding process, such as preheating and the electrode temperature.
Conventional aluminum alloy filler wires do not sufficiently reduce the number of cracks in the weld. As a result, the welded part must often be scrapped or the weld repaired. Weld repair is often accomplished by grinding-out the old weld and then rewelding the parts. Both scrapping the parts and weld repair are expensive and time consuming. Accordingly, the cost and fabrication time of the final product is increased.
SUMMARY OF THE INVENTION
Accordingly, a need has arisen for an improved filler wire. The present invention provides an improved filler wire for aluminum alloys and method of welding that substantially reduces or eliminates problems associated with prior systems and methods.
In accordance with one embodiment of the present invention, titanium and zirconium are added to the filler wire in amounts greater than conventional filler wires, and a nominal amount of silver is also added to the filler wire. The addition of silver is believed to promote the formation of grain boundary phases that improves weldability. The titanium/zirconium/silver filler wire chemistry has been demonstrated to reduce the susceptibility of aluminum alloy welds to cracks.
The present invention may be characterized by the following:
1. An improved weld filler wire for aluminum alloys comprising zirconium in an amount greater than 0.25%, titanium, and silver.
2. The improved weld filler wire of Paragraph 1, wherein the weld filler wire comprises greater than 0.25% titanium.
3. An improved weld filler wire for aluminum alloys comprising titaninum in an amount greater than 0.25%, zirconium, and silver.
4. The improved weld filler wire of Paragraph 1, wherein the weld filler wire further comprises about 0.4% silver.
5. The improved weld filler wire of Paragraph 1, wherein the weld filler wire further comprises copper in an amount ranging from about 4% to about 6%.
6. The improved weld filler wire of Paragraph 1, wherein the weld filler wire further comprises about 6% copper.
7. The improved weld filler wire of Paragraph 2, wherein the weld filler wire further comprises about 0.4% silver.
8. The improved weld filler wire of Paragraph 2, wherein the weld filler wire further comprises copper in an amount ranging from about 0.4% to about 6%.
9. The improved weld filler wire of Paragraph 2, wherein the weld filler wire further comprises about 6% copper.
10. The improved weld filler wire of Paragraph 3, wherein the weld filler wire further comprises about 0.4% silver.
11. The improved weld filler wire of Paragraph 3, wherein the weld filler wire further comprises copper in an amount ranging from about 4% to about 6%.
12. The improved weld filler wire of Paragraph 3, wherein the weld filler wire further comprises about 6% copper.
13. An improved weld filler wire for aluminum alloys comprising 4% to 9% copper, 0.1% to 1.0% silver, 0.15% to 0.5% zirconium, 0.15% to 0.5% titanium, up to 1.0% magnesium, up to 1.0% zinc, 0.5% maximum iron and 0.5% maximum silicon.
14. The improved weld filler wire of Paragraph 13 further comprising 0.1% to 1% manganese.
15. The improved weld filler wire of Paragraph 13 further comprising 0.1% to 1.0% hafnium.
16. The improved weld filler wire of Paragraph 13 further comprising 0.1% to 0.6% scandium.
17. The improved weld filler wire of Paragraph 13 further comprising 0.1% to 1.0% vanadium.
Other technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions, and claims.
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U.S. patent application Ser. No. 09/525,407, Bjorkman et al. no date available.
Bjorkman, Jr. Gerald W. O.
Cho Alex
Russell Carolyn K.
King Roy
Lockheed Martin Corporation
Wilkins, III Harry D.
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