Al—Zn—Mg—Cu alloy with improved damage tolerance-strength combination properties
An Al—Zn—Mg—Cu alloy with improved damage tolerance-strength combination properties. The present invention relates to an aluminum alloy product comprising or consisting essentially of, in weight %, about 6.5 to 9.5 zinc (Zn), about 1.2 to 2.2% magnesium (Mg), about 1.0 to 1.9% copper (Cu), preferable (0.9 Mg−0.6)≤Cu≤(0.9 Mg+0.05), about 0 to 0.5% zirconium (Zr), about 0 to 0.7% scandium (Sc), about 0 to 0.4% chromium (Cr), about 0 to 0.3% hafnium (Hf), about 0 to 0.4% titanium (Ti), about 0 to 0.8% manganese (Mn), the balance being aluminum (Al) and other incidental elements. The invention relates also to a method of manufacturing such as alloy.
1. Method of producing a high-strength, high-toughness AA7xxx-series alloy product having a good corrosion resistance, comprising the processing steps of:
a) casting an ingot having a composition comprising, in wt. %:
Zn 6.9 to 7.9
Mg 1.4 to 2.1
Cu 1.43 to 1.90
Zr up to 0.15
Ti<0.05
Fe<0.05
Si<0.07
Mn 0.15 to 0.30,
Cr 0.15 to 0.20
and other impurities or incidental elements each <0.05, total <0.15, and the balance being aluminium;
b) homogenizing the ingot after casting in a range of 460° C. to 490° C., then cooling the homogenized ingot, and then homogenizing the cooled ingot to a temperature in a range of 460° C. to 490° C.;
c) hot working the homogenized ingot by hot rolling to a desired workpiece form, wherein said hot working the homogenized ingot is by said hot rolling with an absence of forging and an absence of extrusion;
d) solution heat treating said formed workpiece at a temperature and time sufficient to place into solid solution essentially all soluble constituents in the alloy;
e) quenching the solution heat treated workpiece by one of spray quenching or immersion quenching in water or other quenching media;
f) stretching of the quenched workpiece at most 8%;
i) artificially ageing the quenched and stretched workpiece in a two step ageing procedure to achieve a temper selected from the group consisting of T74, T76, T751, T7451, T7651, T77 and T79, wherein the artificial ageing comprises a first ageing step at a temperature in a range of 105° C. to 135° C. for 2 to 20 hours and a second ageing step at a temperature in a range of 135° C. to 210° C. for 4 to 20 hours,
wherein the product has a thickness of 2.5 to 11 inches.
2. The method according to claim 1 , wherein the alloy has 7.2 to 7.9% Zn, 1.4 to 1.90% Mg, 1.43 to 1.80% Cu, and 0.15-0.20% Cr.
3. The method according to claim 2 , wherein the Zr-content in the ingot is 0.06 to 0.15%.
4. The method according to claim 2 , wherein the alloy Ti-content is in a range of 0.03-0.05%.
5. The method according to claim 2 , wherein the alloy product is artificially aged to a T74 or T76 temper.
6. The method according to claim 5 , wherein the alloy has 0.04 to 0.11% Zr.
7. The method according to claim 2 , wherein the alloy product is artificially aged to a T7451 or T7651 temper.
8. The method according to claim 2 , wherein the Zn-content in the ingot is in a range of 7.2 to 7.7%.
9. The method according to claim 8 , wherein the Zn-content in the ingot is in a range of 7.43% to 7.7%.
10. The method of according to claim 2 , wherein the Zr-content in the ingot is 0.06 to 0.15%.
11. The method according to claim 2 , wherein the alloy has 0.04 to 0.11% Zr.
12. The method according to claim 1 , wherein the Zr-content in the ingot is at least 0.06 to 0.13%.
13. The method according to claim 1 , wherein the Zr-content in the ingot is in a range of 0.04 to 0.15%.
14. The method according to claim 1 , wherein the Zr-content in the ingot is in a range of 0.04 to 0.11%.
15. The method according to claim 1 , wherein the product has an EXCO corrosion resistance of “EB” or better.
16. The method according to claim 1 , wherein the product has an EXCO corrosion resistance of “EA” or better.
17. The method according to claim 1 , wherein the method comprises:
a) the casting of the ingot;
b) the homogenizing of the cast ingot;
c) the hot working of the homogenized ingot by hot rolling to a desired workpiece form;
d) the solution heat treating of said workpiece at temperature in a range of 460° C. to 490° C. for time sufficient to place into solid solution essentially all soluble constituents in the alloy;
e) the quenching of the solution heat treated workpiece by one of spray quenching or immersion quenching in water to a temperature lower than 95° C.;
f) the stretching of the quenched workpiece about 1 to 3%;
g) the artificially ageing of the quenched and stretched workpiece to achieve the temper.
18. The method according to claim 17 , wherein the product has the following properties:
exfoliation corrosion resistance (“EXCO”) when measured according to ASTM G34-97 is at least “EA” or better;
tensile yield strength of at least 510 MPa,
an ultimate strength of at least 560 MPa, a notch toughness of at least 1.5 and a UPE of at least 200 kJ/m 2 ;
wherein Mg/Zn is 0.27 or lower.
19. The method according to claim 1 , wherein the ingot composition comprises, in wt. %:
Zn 7.2 to 7.7
Mg 1.4 to 1.79
Cu 1.43 to 1.80
Zr 0.06 to 0.15
Ti<0.05
Fe<0.05
Si<0.07
Mn 0.15 to 0.30,
Cr 0.15 to 0.20
and other impurities or incidental elements each <0.05, total <0.15, and the balance being aluminium.
20. The method according to claim 19 , wherein the method comprises:
a) the casting of the ingot;
b) the homogenizing of the cast ingot;
c) the hot working of the homogenized ingot by a first hot rolling into a pre-worked product;
d) optionally the reheating of the pre-worked product,
e) then hot working the pre-worked product by a second hot rolling to the desired workpiece form;
f) the solution heat treating of said formed workpiece at temperature in a range of 460° C. to 490° C. for time sufficient to place into solid solution essentially all soluble constituents in the alloy;
g) then quenching the solution heat treated workpiece with water;
h) then cold stretching of the quenched workpiece about 1 to 3%;
i) the artificially ageing of the quenched and stretched workpiece in the two step ageing procedure to achieve a desired temper, wherein the artificial ageing comprises a first ageing step at a temperature in a range of 105° C. to 135° C. for 2 to 20 hours and a second ageing step at a temperature in a range of 135° C. to 210° C. for 4 to 20 hours.
21. The method according to claim 20 , wherein the product has the following properties:
exfoliation corrosion resistance (“EXCO”) when measured according to ASTM G34-97 is at least “EA” or better;
tensile yield strength of at least 472 MPa,
an ultimate tensile strength of at least 512 MPa,
inter-granular corrosion resistance of at most 70 μm, and
wherein Mg/Zn is 0.27 or lower.
22. The method according to claim 19 , wherein first hot rolling hot rolls the pre-worked product in a first direction 90° to a second direction in which the second hot rolling hot works the pre-heated ingot.
23. The method of according to claim 19 , wherein the Zr-content in the ingot is 0.06 to 0.13%.
24. The method of according to claim 23 , wherein the Cu-content in the ingot is 1.52 to 1.80%.
25. The method according to claim 24 , wherein
the Zn-content in the ingot is 7.43 to 7.7%,
the Mg-content in the ingot is 1.4 to 1.79%,
the Mn-content in the ingot is 0.19 to 0.3%.
26. The method of according to claim 1 , wherein the Cr-content in the ingot is 0.15%.
27. The method of according to claim 1 , wherein the Cr-content in the ingot is 0.20%.
28. The method according to claim 1 , wherein the ingot composition consists of, in wt. %:
Zn 7.43 to 7.7
Mg 1.4 to 1.79
Cu 1.52 to 1.80
Zr 0.06 to 0.13
Ti 0.03-0.05
Fe<0.05
Si<0.07
Mn 0.19 to 0.30,
Cr 0.15 to 0.20
and other impurities or incidental elements each <0.05, total <0.15, and the balance being aluminium,
wherein the method consists of:
a) the casting of the ingot;
b) the homogenizing of the cast ingot in the range of 460° C. to 490° C., then cooling the homogenized ingot, and then homogenizing the cooled ingot to a temperature in a range of 460° C. to 490° C.;
c) the hot working of the homogenized ingot by a first hot rolling into a pre-worked product;
d) optionally the reheating of the pre-worked product,
e) then hot working the pre-worked product by a second hot rolling to the desired workpiece form;
f) the solution heat treating of said formed workpiece at temperature in a range of 460° C. to 490° C. for time sufficient to place into solid solution essentially all soluble constituents in the alloy;
g) then quenching the solution heat treated workpiece with water;
h) then cold stretching of the quenched workpiece about 1 to 3%;
i) the artificially ageing of the quenched and stretched workpiece in the two step ageing procedure to achieve a desired temper, wherein the artificial ageing consists of a first ageing step at a temperature in a range of 105° C. to 135° C. for 2 to 20 hours and a second ageing step at a temperature in a range of 135° C. to 210° C. for 4 to 20 hours.
29. The method according to claim 28 , wherein first hot rolling hot rolls the pre-worked product in a first direction 90° to a second direction in which the second hot rolling hot works the pre-heated ingot.
30. The method according to claim 29 , wherein the product has the following properties:
exfoliation corrosion resistance (“EXCO”) when measured according to ASTM G34-97 is at least “EA” or better;
tensile yield strength of at least 472 MPa,
an ultimate tensile strength of at least 512 MPa,
inter-granular corrosion resistance of at most 70 μm, and
wherein Mg/Zn is 0.27 or lower.
31. The method of according to claim 28 , wherein the Cr-content in the ingot is 0.15%.
32. The method of according to claim 28 , wherein the Cr-content in the ingot is 0.20%.