7XXX-series aluminium alloy product
The invention relates to a wrought 7xxx-series aluminium alloy product having a composition comprising, in wt. %, Zn 6.40 to 7.50, Mg 2.15 to 2.75, Cu 1.20 to 2.00, and wherein Cu+Mg<4.50, and wherein Mg<2.5+5/3(Cu−1.2), Fe up to 0.25, Si up to 0.25, and optionally one or more elements selected from the group consisting of: (Zr up to 0.3, Cr up to 0.3, Mn up to 0.45, Ti up to 0.25, Sc up to 0.5, Ag up to 0.5), the balance being aluminium and impurities, and having been aged to achieve a conventional tensile yield strength (in MPa) measured in the L-direction measured at quarter thickness of more than 485−0.12*(t−100) MPa (t being the thickness of the product in mm); a minimum life without failure due to stress corrosion cracking (SCC) measured in accordance with ASTM G47-98 of at least 30 days at a short transverse (ST) stress level of 170 MPa; and a minimum K max-dev value without crack deviation due to crack propagation testing in standard atmosphere at room temperature in accordance with ASTM E647-13e01 in L-S direction on CT samples of at least 40 MPa√m on average.
1. A wrought 7xxx-series aluminium alloy product having a composition comprising, in wt. %,
Zn 6.50 to 7.20,
Mg 2.30 to 2.60,
Cu 1.30 to 1.80,
and wherein Cu+Mg<4.50, and wherein Mg<2.5+5/3(Cu−1.2),
Fe up to 0.25,
Si up to 0.25,
and optionally one or more elements selected from the group consisting of:
Zr up to 0.3,
Cr up to 0.3,
Mn up to 0.45,
Ti up to 0.25,
Sc up to 0.5,
Ag up to 0.5,
the balance being aluminium and impurities,
and wherein said product is aged to achieve:
a conventional tensile yield strength (in MPa) measured in the L-direction measured at quarter thickness of more than 485−0.12*(t−100) MPa (t being the thickness of the product in mm);
a minimum life without failure due to stress corrosion cracking (SCC) measured in accordance with ASTM G47-98 of at least 30 days at a short transverse (ST) stress level of 170 MPa; and
a minimum K max-dev value without crack deviation due to crack propagation testing in standard atmosphere at room temperature in accordance with ASTM E647-13e01 in L-S direction on CT samples of at least 40 MPa√m on average, testing in a load controlled fatigue test and crack deviation defined as a crack deviating more than 20° from the intended fracture plane.
2. The wrought 7xxx-series aluminium alloy product according to claim 1 , wherein the Zn-content is at least 6.60%.
3. The wrought 7xxx-series aluminium alloy product according to claim 1 , wherein the Zn-content is maximum 7.10%.
4. The wrought 7xxx-series aluminium alloy product according to claim 1 , wherein
Zn 6.75 to 7.10,
Mg 2.35 to 2.55,
Cu 1.35 to 1.75.
5. The wrought 7xxx-series aluminium alloy product according to claim 1 , wherein
Zn 6.75 to 7.10,
Mg 2.45 to 2.55,
Cu 1.35 to 1.75.
6. The wrought 7xxx-series aluminium alloy product according to claim 1 , wherein said product has a Zr-content in a range of 0.03% to 0.25%.
7. The wrought 7xxx-series aluminium alloy product according to claim 1 , wherein said product has a Cr-content in a range of 0.04% to 0.3%.
8. The wrought 7xxx-series aluminium alloy product according to claim 1 , wherein said product has a Cr-content of up to 0.05%.
9. The wrought 7xxx-series aluminium alloy product according to claim 1 , wherein said product has a Mn-content in a range of 0.05% to 0.4%.
10. The wrought 7xxx-series aluminium alloy product according to claim 1 , wherein said product has a Mn content of up to 0.05%.
11. The wrought 7xxx-series aluminium alloy product according to claim 1 , wherein said product has a sum of Mn+Cr up to 0.05%.
12. The wrought 7xxx-series aluminium alloy product according to claim 1 , wherein said product has a thickness of at least 12.7 mm.
13. The wrought 7xxx-series aluminium alloy product according to claim 1 , wherein said product is an aerospace product.
14. The wrought 7xxx-series aluminium alloy product according to claim 1 , wherein said product is in a T7 condition.
15. The wrought 7xxx-series aluminium alloy product according to claim 14 , wherein the product is in a T7 condition selected from the group consisting of T73, T74, T76, T77, and T79.
16. The wrought 7xxx-series aluminium alloy product according to claim 1 , wherein the product has a thickness of at least 25.4 mm.
17. The wrought 7xxx-series aluminium alloy product according to claim 1 , wherein said product is in the form of a rolled, extruded or forged product.
18. The wrought 7xxx-series aluminium alloy product according to claim 1 , wherein the product is in the form of a rolled product.
19. The wrought 7xxx-series aluminium alloy product according to claim 1 , wherein said product is aged to achieve one or more of:
a conventional tensile yield strength (in MPa) measured in the L-direction measured at quarter thickness of more than 500−0.12*(t−100) MPa (t being the thickness of the product in mm);
a minimum K max-dev value without crack deviation due to crack propagation testing in standard atmosphere at room temperature in accordance with ASTM E647-13e01 in L-S direction on CT samples of at least 50 MPa√m on average, testing in a load controlled fatigue test and crack deviation defined as a crack deviating more than 20° from the intended fracture plane;
a minimum life without failure due to stress corrosion cracking (SCC) measured in accordance with ASTM G47-98 of at least 30 days, at a short transverse (ST) stress level of 205 MPa.
20. The wrought 7xxx-series aluminium alloy product according to claim 1 , wherein the wrought product is an aircraft structural part.
21. The wrought 7xxx-series aluminium alloy product according to claim 1 , wherein the wrought product is an aircraft structural part selected from the group of a wing spar, wing rib, wing skin, floor beam, and fuselage frame.