Recrystallized Al-Zn-Cu-Mg plate with low zirconium
View Patent ↗The present invention is directed to optimization of recrystallization rates on the fatigue crack growth resistance, in the particular case of a Al—Zn—Cu—Mg plate products, and especially on the evolution of da/dN.
1. An Al—Zn—Cu—Mg AA7040 plate product with a thickness of at least about 15 mm comprising:
from about 0.05 to about 0.09 wt % Zr, wherein said product possesses a recrystallization rate greater than 60% at the quarter thickness location.
2. A product according to claim 1 , wherein Zr is present in an amount from about 0.05to about 0.07 wt %.
3. A product according to claim 1 , having a fatigue crack growth rate less than about 10 −4 mm/cycle at ΔK=10 MPa√m for a test performed at R=0.1 in the L-T direction at the T/4 location.
4. An Al—Zn—Cu—Mg alloy according to claim 1 , that when compared with AA7040 having a 20% recrystallization rate, possesses statistically significantly lower crack propagation rates on a ΔK=8 to 20 MPa√m for a test performed at R=0.1 in the L-T direction at the T/4 location.
5. An alloy of claim 4 wherein said ΔK=10 MPa√m.
6. An alloy of claim 4 wherein Zr is present in an amount from about 0.04 to about 0.06 wt %.
7. A product according to claim 1 wherein K IC(L-T) >30 MPa√m.
8. A product according to claim 2 wherein K IC(L-T) >30 MPa√m.
9. A product according to claim 3 wherein K IC(L-T) >30 MPa√m.
10. A product according to claim 7 , wherein K IC(T-L) >25 MPa√m.
11. A product according to claim 7 , wherein K IC(S-T) >25 MPa√m.
12. A product of claim 1 having a recrystallization rate up to about 90%.
13. A method for making a product of claim 1 : comprising rolling a precursor to said product at a temperature that is less than 420 degrees C.
14. A method according to claim 13 , wherein said product is subjected to T7651 temper.
15. A method for making a product of- claim 2 : comprising rolling a precursor to said product at a temperature that is less than 420 degrees C.
16. A method according to claim 13 , wherein said plate is subjected to T7651 temper.
17. A method of claim 13 wherein said temperature is at most 315 degrees C.
18. A method of claim 15 , wherein said temperature is at most 315 degrees C.