ALUMINUM-MAGNESIUM-SCANDIUM ALLOYS WITH ZINC AND COPPER

Abstract: Al-Mg-Sc based alloys include additional elements selected from the group comprising Hf, Mn, Zr, Cu and Zn to improve their tensile properties. The alloys are preferably comprised of aluminum and, in wt.%, 1.0-8.0 % Mg, 0.05-0,6 % Sc, 0.05-0.20 % Hf and/or 0.05-0.20 % Zr, and 0.5-2.0 % Cu and/or 0.5-2.0 % Zn. In addition, 0.1-0.8 wt.% Mn may be added to the alloy to improve its strength characteristics further.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to Al-Mg-Sc alloy compositions for use in aerospace applications, and the like, in which zinc, copper and other elements are added to the alloys to improve their tensile properties. 2. Description of the Background Art Aluminum alloys containing magnesium as the principal alloying element have two potential advantages for aircraft structures: they are lighter than the standard 2000 and 7000 series alloys; and unlike the latter materials, they are weldable by conventional fusion techniques, which could lower rnanufacturing costs by reducing the 2-3 million rivets typically used to assemble a commercial airliner. A number of aluminum alloys have been developed in which magnesium is added to aluminum to improve strength. However, these alloys are not particularly suited for aerospace appUcations because their strength levels are not high enough. To address this problem, improved Al-Mg based alloys have been developed in which a dispersoid generating element, such as scandium, is added to the alloy. The addition of scandium to the alloys results in the formation of Al 3 Sc dispersoids, which are intended to prevent recrystallization during thermomechanical processing, thereby imparting significantly greater strength to products made from the alloys. However, the tensile properties of Al-Mg-Sc based alloys deteriorate rapidly with thermomechanical processing and high temperature operations, such as hot rolling, that are necessary to manufacture aircraft fuselage sheet and other components. The degradation in tensile properties occurs because the scandium dispersoids must be small in size and large in number to impart increased strength to the alloy; presumably high temperature manufacturing operations cause them to grow too large to be effective recrystallization inhibitors. One known solution to this problem is to add zirconium to the Al-Mg-Sc alloys. Zirconium acts to stabilize the dispersoids so that they can maintain their strength enhancing characteristics, even after the alloys have been subjected to high temperature operations. Although Al-Mg-Sc-Zr based alloys are thus somewhat suitable for aerospace appUcations, a need stiU remains for aluminum aUoys that are even stronger than presently avaUable aUoys. SUMMARY OF THE INVENTION The present invention fulfills the foregoing need through provision of Al-Mg-Sc based aUoys in which, in addition to a dispersoid stabilizing element, specifically zirconium or hafnium, one or more additional elements are added to the alloys to enhance their tensile properties further. In particular, the addition of various combinations of manganese, copper and zinc to the aUoys have been found to enhance their tensile properties substantiaUy as compared to aUoys containing only a single dispersoid stabilizing element. In addition, it has been discovered that a different dispersoid generating element, hafnium, can be employed to stabilize the dispersoids generated by the scandium. More specificaUy, the present invention comprises aUoys, and products made therefrom, whose wt. % composition comprises 1.0- 8.0% Mg, 0.05-0.6% Sc, 0.6-1.5% Cu and/or 0.6-1.5% Zn, and 0.05-0.20% Hf and/or 0.05- 0.20% Zr, with the balance aluminum and incidental impurities. In addition, 0.1-0.8 wt.% Mn may also be added to the alloy. In experiments on sample aUoys formed in accordance with these criteria, and subjected to rolling and heat treatment operations, substantial improvements in tensile properties, including ultimate tensUe strength, yield strength and elongation, were observed as compared to an Al-Mg-Sc aUoy containing only zirconium as a dispersoid stabilizing element. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS AU of the embodiments of the present invention comprise Al-Mg-Sc based aUoys, and products made therefrom, in which additional elements are added to the alloys to increase strength. It has been discovered previously that addition of zirconium and to an Al-Mg-Sc based aUoy acts to stabilize the Al 3 Sc dispersoids during thermomechanical operations, such as hot rolling. As a result, the tensile properties of the aUoy after processing are substantially improved. Addition of manganese to the Al-Mg-Sc-Zr aUoy has been found to increase its strength even further. The inventors of the present invention have now discovered that Al-Mg-Sc-Zr based aUoys can be strengthened even further through addition of zinc and/or copper to the alloys. In addition, it has been discovered that hafnium can be substituted for or added to the zirconium in these aUoys. In the preferred embodiments of the invention, the aUoys include in wt. % composition, 1.0-8.0% Mg, 0.05-0.6% Sc, 0.6-1.5% Cu and/or 0.6-1.5% Zn, and 0.05- 0.20% Hf and/or 0.05-0.20% Zr, with the balance aluminum and incidental impurities. The most preferred ranges of the recited elements are 4.0-6.0% Mg, 0.2-0.4% Sc, 0.08-0.15% Hf or Zr, 0.6-1.5% Cu and/or Zn, and the balance aluminum and incidental impurities. Within these ranges, alloy compositions of 5.0% Mg, 0.25% Sc, 0.12% Hf and/or 0.12% Zr, 1.0% Cu and/or 1.0% Zn, and the balance aluminum and incidental impurities, are beUeved to provide the best results. In addition, the aUoys can also be formed with 0.1-0.8 wt.% Mn, with the most preferred range being 0.3-0.7% Mn, and 0.6% Mn beUeved to be optimum. The significance of each element in the subject alloys is as foUows. Mg added to the aUoys in the recited amount increases strength and lowers density substantiaUy. However, if Mg is added in amounts above approximately 8%, the resulting aUoys become difficult to process. Sc and Zr are added in combination to generate stable Al 3 Sc(Zr) dispersoids, which as stated previously, substantiaUy increase the strength of the aUoys. Hf, Uke Sc, is another dispersoid generating element that can be used in place of Sc to achieve improvements in strength. However, it has also been discovered that when Hf is used in combination with Sc, the Hf acts Uke Zr to stabilize the Al 3 Sc dispersoids during hot rolling and thermal processing. Thus, Hf can be used either in place of or with Zr. Manganese is also beUeved to enhance the dispersoid stabilizing effect of Zr and Sc. The amounts of Zr, Hf and Mn added to the aUoys must not, however, be above the recited ranges to avoid primary formations in the aUoys that would once again, diminish their tensile and other properties. As wiU be demonstrated by the foUowing examples, copper and/or zinc, when added in the specified amounts, have been found to increase the strength properties of the aUoys substantiaUy as compared to Al-Mg-Sc aUoys containing either zirconium or zirconium and manganese. EXAMPLES 1-3 To test the tensUe properties of aUoys formed in accordance with the present invention, a number of roUed sheet samples were prepared, and subjected to testing. First, a 3" x 9" ingot was cast of each aUoy. The ingots were then subjected, without homogenization, to conventional hot and cold rolling techniques until they were formed into sheets of 0.063" or 0.125" thickness. The sheets were then annealed at 550° F for 8 hours. Conventional testing was then conducted on each sheet to determine the ultimate tensile strength (UTS), yield strength (YS), and elongation (EL). The samples included two of known aUoys, Al-Mg-Sc-Zr and Al-Mg-Sc-Zr-Mn, and three different aUoys meeting the criteria of the subject invention. The results of the tests, and the compositions of each of the tested aUoys are set forth in Table 1. The test results for the 5X-1 and 5X-2 sample aUoys indicate that substantial improvements in UTS and YS are obtained when 1.0% zinc or copper is added to the base Al- Mg-Sc-Zr aUoy. In particular, for the zinc containing 5X-1 sample, the UTS and YS increased approximately 4% and 7%, respectfuUy. The increases in UTS and YS for the copper containing aUoy, 5X-2, were even better at approximately 6% and 15%, respectively. The third sample aUoy, 5X-3, in which 1.0% zinc was added to an Al-Mg-Sc aUoy containing both zirconium and manganese, had stiU better tensUe properties, especiaUy as compared to the basic zirconium containing Al-Mg-Sc aUoy . When compared to the Al-Mg- Sc-Zr-Mn aUoy, the improvements in UTS and YS were approximately 5 and 10%, respectfuUy. Even more significant were the improvements in UTS and YS when compared to the base Al-Mg-Sc-Zr aUoy which were 11% and 22%, respectively. From the test results, it is beUeved that even greater improvements in tensUe properties may be realized if both zinc and copper are added to the aUoys in the preferred ranges of approximately 0.5-2.0% each. In addition to the tensUe property measurements described above, the 0.125" sheets were subjected to TIG (tungsten inert gas) welding tests using Al-4.8% Mg 5183 aUoy filler wire. TensUe specimens were then machined from the sheets with the weld region centered transversely in the reduced section. The tensUe data from these tests are Usted in Table 2. The data show significantly higher strengths in the Zn/Cu modified aUoys, with or without a manganese addition. EXAMPLES 4-6 As discussed previously, it has also discovered that hafnium may be employed instead of or with zirconium to stabilize the Al 3 Sc dispersoids. Thus, in each of the samples set forth in Table 1, hafnium can be substituted for zirconium or added in approximately the same amount, and it is beUeved that similar relative results wUl be obtained. Thus, the addition of zinc and/or copper to Al-Mg-Sc-Hf-Mn aUoys should substantiaUy improve the tensUe properties of these aUoys as weU. The values achieved for the tensUe properties of the aUoys of Examples 1-6 indicate that the aUoys can readily be employed in roUed sheet form for various aerospace appUcations, such as for aircraft fuselage skins, etc. As stated previously, these appUcations for the subject aUoys are particularly attractive because of the superior corrosion resistance and weldabiUty of Al-Mg-Sc aUoys. Although the present invention has been disclosed in terms of a number of preferred embodiments, it wUl be understood that modifications and variations could be made thereto without departing from the scope of the invention as defined in the foUowing claims.

Claims: CLAIMS 1. An aluminum aUoy comprising, in wt. %, 4.0-8.0% Mg, 0.05-0.6% Sc, 0.1-0.8% Mn, 0.5-2.0% Cu or Zn, 0.05-0.20% Hf or Zr, and the balance aluminum and incidental impurities. 2. The aluminum aUoy of claim 1, wherein said aUoy includes both 0.5-2.0% Cu and 0.5-2.0% Zn. 3. The aluminum aUoy of claim 2, wherein said aUoy includes both 0.05-0.20% Hf and 0.05-0.20% Zr. 4. The aluminum aUoy of claim 1, wherein said aUoy includes both 0.05-0.20% Hf and 0.05-0.20% Zr. 5. The aluminum aUoy of claim 1, wherein said aUoy comprises 4.0-6.0% Mg, 0.2- 0.4% Sc, 0.3-0.7% Mn, 0.08-0.15% Hf or Zr, 0.6-1.5% Cu or Zn, and the balance aluminum and incidental impurities. 6. The aUoy of claim 5, wherein said aUoy includes both 0.6-1.5% Cu and 0.6-1.5% Zn. 7. The aluminum aUoy of claim 6, wherein said aUoy includes both 0.08-0.15% Hf and 0.08-0.15% Zr. 8. The aluminum aUoy of claim 5, wherein said aUoy includes both 0.08-0.15% Hf and 0.08-0.15% Zr. 9. The aluminum aUoy of claim 5, wherein said aUoy comprises 5.0% Mg, 0.25% Sc, 0.6% Mn, 0.12% Hf or Zr, 1.0% Cu or Zn, and the balance aluminum and incidental impurities. 10. The aluminum aUoy of claim 9, wherein said aUoy includes both 1.0% Cu and 1.0% Zn. 11. The aluminum aUoy of claim 10, wherein said aUoy includes both 0.12% Hf and 0.12% Zr. 12. The aluminum aUoy of claim 9, wherein said aUoy includes both 0.12% Hf and 0.12% Zr. 13. An aluminum aUoy comprising, in wt. %, 4.0-8.0% Mg, 0.05-0.6% Sc, 0.5-2.0% Cu or Zn, 0.05-0.20% Hf or Zr, and the balance uminum and incidental impurities. 14. The aluminum aUoy of claim 13, wherein said aUoy includes both 0.5-2.0% Cu and 0.5-2.0% Zn. 15. The aluminum aUoy of claim 14, wherein said aUoy includes both 0.05-0.20% Hf and 0.05-0.20% Zr. 16. The aluminum aUoy of claim 13, wherein said aUoy includes both 0.05-0.20% Hf and 0.05-0.20% Zr. 17. The aluminum aUoy of claim 13, wherein said aUoy comprises 4.0-6.0% Mg, 0.2- 0.4% Sc, 0.08-0.15% Hf or Zr, 0.6-1.5% Cu or Zn, and the balance aluminum and incidental impurities. 18. The aluminum aUoy of claun 17, wherein said aUoy includes both 0.6-1.5% Cu and 0.6-1.5% Zn. 19. The aluminum aUoy of claim 18, wherein said aUoy includes both 0.08-0.15% Hf and 0.08-0.15% Zr. 20. The aluminum aUoy of claim 17, wherein said aUoy includes both 0.08-0.15% Hf and 0.08-0.15% Zr. 21. The aluminum aUoy of claim 17, wherein said aUoy comprises 5.0% Mg, 0.25% Sc, 0.12% Hf or Zr, 1.0% Cu or Zn, and the balance aluminum and incidental impurities. 22. The aluminum aUoy of claim 21, wherein said aUoy includes both 1.0% Cu and 1.0% Zn. 23. The aluminum aUoy of claim 22, wherein said aUoy includes both 0.12% Hf and 0.12% Zr. 24. The aluminum aUoy of claim 21, wherein said aUoy includes both 0.12% Hf and 0.12% Zr. 25. A roUed aUoy sheet product comprised of an aluminum aUoy, said aUoy comprising, in wt. %, 4.0-8.0% Mg, 0.05-0.6% Sc, 0.1-0.8% Mn, 0.5-2.0% Cu or Zn, 0.05- 0.20% Hf or Zr, and the balance aluminum and incidental impurities. 26. The roUed aUoy sheet product of claim 25, wherein said aUoy includes both 0.5- 2.0% Cu and 0.5-2.0% Zn. 27. The roUed aUoy sheet product of claim 26, wherein said aUoy includes both 0.05- 0.20% Hf and 0.05-0.20% Zr. 28. The roUed aUoy sheet product of claim 25, wherein said aUoy includes both 0.05- 0.20% Hf and 0.05-0.20% Zr. 29. The roUed aUoy sheet product of claim 25, wherein said aUoy comprises 4.0-6.0% Mg, 0.2-0.4% Sc, 0.3-0.7% Mn, 0.08-0.15% Hf or Zr, 0.6-1.5% Cu or Zn, and the balance aluminum and incidental impurities. 30. The roUed aUoy sheet product of claim 29, wherein said aUoy includes both 0.6- 1.5% Cu and 0.6-1.5% Zn. 31. The roUed aUoy sheet product of claun 30, wherein said aUoy includes both 0.08- 0.15% Hf and 0.08-0.15% Zr. 32. The roUed aUoy sheet product of claim 19, wherein said aUoy includes both 0.08- 0.15% Hf and 0.08-0.15% Zr. 33. The roUed aUoy sheet product of claim 29, wherein said aUoy comprises 5.0% Mg, 0.25% Sc, 0.6% Mn, 0.12% Hf or Zr, 1.0% Cu or Zn, and the balance aluminum and incidental impurities. 34. The roUed aUoy sheet product of claim 33, wherein said aUoy includes both 1.0% Cu and 1.0% Zn. 35. The roUed aUoy sheet product of claim 34, wherein said aUoy includes both 0.12% Hf and 0.12% Zr. 36. The roUed aUoy sheet product of claim 33, wherein said aUoy includes both 0.12% Hf and 0.12% Zr. 37. A roUed aUoy sheet product comprised of an aluminum aUoy, said aUoy comprising, in wt. %, 4.0-8.0% Mg, 0.05-0.6% Sc, 0.5-2.0% Cu or Zn, 0.05-0.20% Hf or Zr, and the balance aluminum and incidental impurities. 38. The roUed aUoy sheet product of claim 37, wherein said aUoy includes both 0.5- 2.0% Cu and 0.5-2.0% Zn. 39. The roUed aUoy sheet product of claim 38, wherein said aUoy includes both 0.05- 0.20% Hf and 0.05-0.20% Zr. 40. The roUed aUoy sheet product of claim 37, wherein said aUoy includes both 0.05- 0.20% Hf and 0.05-0.20% Zr. 41. The roUed aUoy sheet product of claim 37, wherein said aUoy comprises 4.0-6.0% Mg, 0.2-0.4% Sc, 0.08-0.15% Hf or Zr, 0.6-1.5% Cu or Zn, and the balance aluminum and incidental impurities. 42. The roUed aUoy sheet product of claim 41, wherein said aUoy includes both 0.6- 1.5% Cu and 0.6-1.5% Zn. 43. The roUed aUoy sheet product of claim 42, wherein said aUoy includes both 0.08- 0.15% Hf and 0.08-0.15% Zr. 44. The roUed aUoy sheet product of claim 41, wherein said aUoy includes both 0.08- 0.15% Hf and 0.08-0.15% Zr. 45. The roUed aUoy sheet product of claim 41, wherein said aUoy comprises 5.0% Mg, 0.25% Sc, 0.12% Hf or Zn, 1.0% Cu or Zn, and the balance aluminum and incidental impurities. 46. The roUed aUoy sheet product of claim 45, wherein said aUoy includes both 1.0% Cu and l.0% Zn. 47. The roUed aUoy sheet product of claim 46, wherein said aUoy includes both 0.12% Hf and 0.12% Zr. 48. The roUed aUoy sheet product of claim 45, wherein said aUoy includes both 0.12% Hf and 0.12% Zr.

Inventors: DORWARD RALPH C, FERNANDES MICKY T, DORWARD, RALPH, C., FERNANDES, MICKY, T.
Applicants: KAISER ALUMINIUM CHEM CORP, KAISER ALUMINIUM & CHEMICAL CORPORATION
Application year: 2000
Main classification: C22C21
IPC codes: C22C21