Al—Zn—Mg alloy product with reduced quench sensitivity
View Patent ↗This relates to an aluminum alloy product, in particular an age-hardenable Al—Zn—Mg type alloy product for structural members, the alloy product combining a high strength with high toughness and reduced quench sensitivity, and having a chemical composition including, in wt. %: Zn about 3 to 11%, Mg about 1 to 3%, Cu about 0.9 to 3%, Ge about 0.03 to 0.4%, Si max. 0.5%, Fe max. 0.5%, balance aluminum and normal and/or inevitable elements and impurities. Furthermore, this relates to a method of producing such aluminum alloy products.
1. A method of manufacturing a wrought aluminium alloy product of an AA7000-series alloy, the method comprising the steps of:
a. casting stock of an ingot of an AA7000-series aluminium alloy comprising an aluminium alloy having a chemical composition comprising, in wt. %:
Zn
3% to 11%,
Mg
1% to 3%,
Cu
0.9% to 3%,
Ge
0.08% to 0.4%,
Si
maximum 0.5%,
Fe
maximum 0.5%,
Ti
maximum 0.5%,
optionally one or more elements selected from the group consisting of:
Mn
at most 0.4%,
Ti
at most 0.3%,
Cr
at most 0.4%,
Zr
at most 0.5%,
Sc
at most 0.5%,
Hf
at most 0.3%,
V
at most 0.4%,
Ag
at most 0.5%,
Li
at most 2.5%,
and optionally at most:
about 0.05% Ca,
about 0.05% Sr,
about 0.004% Be,
balance aluminium and normal and/or inevitable elements and impurities, said normal and/or inevitable elements and impurities being present each <0.05%, total <0.15%;
b. homogenising the cast stock by heating the stock to a temperature in a range of 430 to 490° C., followed by heating to a temperature in a range of >500° C. to 550° C.;
c. hot working the stock by one or more methods selected from the group consisting of rolling, extrusion, and forging;
d. optionally cold working the hot worked stock;
e. solution heat treating (SHT) of the hot worked stock and optionally cold worked stock;
f. cooling the SHT stock at a cooling rate of about 1-3° C. per minute to 150° C. or lower;
g. optionally stretching or compressing the cooled SHT stock or otherwise cold working the cooled SHT stock to relieve stresses;
h. ageing of the cooled and optionally stretched or compressed or otherwise cold worked SHT stock to achieve a desired temper.
2. The method according to claim 1 , wherein the alloy further comprises one or more elements selected from the group consisting of:
Mn
at most 0.4%,
Cr
at most 0.4%, and
Zr
at most 0.5%.
3. The method according to claim 1 , wherein the alloy product has a Zr content in a range of 0.03% to 0.5%.
4. The method according to claim 1 , wherein the alloy product has a Cr content in a range of 0.04% to 0.3%.
5. The method according to claim 1 , wherein the alloy product has a Ge content in a range of 0.08% to 0.35%.
6. The method according to claim 1 , wherein the alloy product has a Ge content in a range of 0.3% to 0.35%.
7. The method according to claim 1 , wherein the alloy product has a Cu content in a range of at least 1.1%.
8. The method according to claim 1 , wherein the alloy product has a Mg content in a range of maximum 2.5%.
9. The method according to claim 6 , wherein the alloy product has a Zn content in a range of 6.1% to 8.5%.
10. The method according to claim 1 , wherein the alloy product has a Zn content in a range of 6.1% to 8.5%, wherein the alloy product has a Ge content in a range of 0.3% to 0.35%.
11. The method according to claim 1 , wherein the alloy product has a Si content in a range of maximum 0.35%.
12. The method according to claim 6 , wherein the alloy product has a thickness in a range of 2 inches (50 mm) to 12 inches (305 mm) at its thickest cross sectional point.
13. The method according to claim 1 , the alloy product being a structural part of an aircraft.
14. The method according to claim 1 , wherein the alloy product is a mould for manufacturing formed plastic products.
15. The method according to claim 1 , wherein the alloy product has a final gauge of at least 2 inches (50 mm).
16. The method according to claim 1 , wherein the alloy product has been hot rolled.
17. The method according to claim 1 , wherein the alloy product has been extruded in an extrusion operation and is press-quenched.
18. The method according to claim 1 , and wherein the cooled SHT stock is stretched or compressed or otherwise cold worked to relieve stresses by a member of the group consisting of levelling, drawing, and cold rolling of the cooled SHT stock.
19. The method according to claim 1 , wherein
Mn
at most 0.3%,
Ti
at most 0.1%,
Zr
0.03% to 0.25%,
Cr
0.04% to 0.2%,
Ge
0.08% to 0.35%,
Cu
1.1% to 2.2%,
Mg
at most 2.5%,
Zn
6.4% to 8.1%, and
Si
at most 0.1%.
20. The method according to claim 1 , wherein
Mn
0.05% to 0.3%,
Ti
at most 0.1%,
Zr
0.03% to 0.15%,
Cr
at most 0.2%,
Ge
about 0.3 to 0.35%,
Cu
1.1% to 2%,
Mg
at most 1.9,
Zn
6.4% to 8.1%,
Si
at most 0.25,
Fe
maximum 0.35%,
Zr
0.03% to 0.2%,
wherein the cooling of the SHT stock is in a furnace at the cooling rate of about 1-3° C. per minute to 150° C. or lower,
wherein the heating temperature of step b. is heating is in a range of 510° C. to 535° C.
wherein the alloy product has a thickness in a range of 2 inches (50 mm) to 12 inches (305 mm) at its thickest cross sectional point.
21. The method according to claim 1 , wherein the heating temperature of step b. is heating is in a range of 505° C. to 540° C.
22. The method according to claim 1 , wherein the heating temperature of step b. is heating is in a range of 510° C. to 535° C.
23. The method according to claim 1 , wherein the Li is included in the wrought aluminum alloy product.