Al-Zn-Cu-Mg aluminum base alloys and methods of manufacture and use
View Patent ↗A rolled or forged Al—Zn—Cu—Mg aluminum-based alloy wrought product having a thickness from 2 to 10 inches. The product has been treated by solution heat-treatment, quenching and aging, and the product comprises (in weight-%): Zn 6.2-7.2, Mg 1.5-2.4, Cu 1.7-2.1. Fe 0-0.13, Si 0-0.10, Ti 0-0.06, Zr 0.06-0.13, Cr 0-0.04, Mn 0-0.04, Mn 0-0.04, impurities and other incidental elements ≦0.05 each. Alloys per se and aircraft and aerospace uses, as well as methods of making products are also disclosed.
1. A rolled or forged Al—Zn—Cu—Mg aluminum-based alloy wrought product having a thickness from 3 to 9 inches, wherein said product has been treated by solution heat-treatment, quenching and aging, and wherein said product has a volume fraction of recrystallized grains lower than 35% and said product consisting essentially of (in weight-%):
Al
Zn 6.7-7.0
Mg 1.68-1.8
Cu 1.7-1.97
Fe 0-0.13
Si 0-0.10
Ti 0-0.06
Zr 0.08-0.13
Cr 0-0.04
Mn 0-0.04
impurities and other incidental elements ≦0.05 each,
wherein said product comprises the following properties:
a) a minimum life without failure after stress corrosion cracking (SCC) of at least 50 days at a short transverse (ST) stress level of 40 ksi,
b) a conventional tensile yield strength measured in the L direction at quarter thickness of at least 70-0.32t ksi (t being the thickness of the product in inch), and
c) toughness in the L-T direction measured at quarter thickness of at least 42-1.7t ksi √in (t being the thickness of the product in inch).
2. A product according to claim 1 , wherein Fe≦0.07 and Si≦0.07.
3. A product according to claim 1 , wherein
Zn 6.72-6.98
Cu 1.75-1.97.
4. A product according to claim 1 , wherein said product is in an overaged temper.
5. An aircraft or aerospace product comprising a product of claim 4 .
6. A product according to claim 1 , wherein said product is in the T74 temper.
7. A product according to claim 1 wherein the thickness thereof is from 4 to 9 inches.
8. A structural member suitable for the construction of aircraft, comprising a product according to claim 1 .
9. A structural member suitable for the construction of aircraft, incorporating a product according to claim 1 .
10. A process for the manufacture of a rolled or forged aluminum-based alloy wrought product, according to claim 1 , having a volume fraction of recrystallized grains lower than 35% comprising the steps of:
a) casting an ingot comprising
Al
Zn 6.7-7.0
Mg 1.68-1.8
Cu 1.7-1.97
Fe 0-0.13
Si 0-0.10
Ti 0-0.06
Zr 0.08-0.13
Cr 0-0.04
Mn 0-0.04
impurities and other incidental elements ≦0.05 each;
b) homogenizing said ingot at 860-930° F.;
c) hot working with an entry temperature of 640-825° F. said ingot by rolling or forging into a plate with a final thickness from 2 to 10 inches;
d) solution heat treating and quenching said plate;
e) stretching said plate with a permanent set from 1 to 4%;
f) aging said plate by heating at 230-250° F. for 5 to 12 hours and 300-360° F. for 5 to 30 hours, for an equivalent time t(eq) between 31 and 56 hours;
The equivalent time t(eq) being defined by the formula:
t
(
eq
)
=
∫
exp
(
-
16000
/
T
)
ⅆ
t
exp
(
-
16000
/
T
ref
)
where T is the instantaneous temperature in ° K during annealing and T ref is a reference temperature selected at 302° F. (423° K), and t(eq) is expressed in hours.
11. A process according to claim 10 wherein the equivalent time t(eq) is from 33 to 44 hours.
12. A process according to claim 10 wherein time between quenching and stretching is not more than 2 hours.
13. An aircraft or aerospace product comprising a product of claim 1 .
14. A product of claim 1 that is substantially unrecrystallized.
15. A product of claim 1 wherein the alloy consists of
Al
Zn 6.7-7.0
Mg 1.68-1.8
Cu 1.7-1.97
Fe 0-0.13
Si 0-0.10
Ti 0-0.06
Zr 0.08-0.13
Cr 0-0.04
Mn 0-0.04
impurities and other incidental elements ≦0.05 each,
wherein said product comprises the following properties:
a) a minimum life without failure after stress corrosion cracking (SCC) of at least 50 days at a short transverse (ST) stress level of 40 ksi,
b) a conventional tensile yield strength measured in the L direction at quarter thickness of at least 70-0.32t ksi (t being the thickness of the product in inch), and
c) toughness in the L-T direction measured at quarter thickness of at least 42-1.7t ksi √in (t being the thickness of the product in inch).