High strength aluminum alloy
A precipitation hardenable aluminum alloy is disclosed along with a precipitation hardened form of the aluminum alloy and a method of manufacturing an aluminum alloy article from the precipitation hardenable aluminum alloy. The disclosed precipitation hardenable aluminum alloy has a composition that includes, on a weight percent (wt %) basis, 8%-13% zinc, 1.5%-5% magnesium, 0%-5% copper, 0%-2% of zirconium, chromium, or zirconium and chromium in total, and the balance aluminum with no more than 0.5% impurities. The alloy composition is adaptable to a wide range of manufacturing processes including additive manufacturing. The composition of the aluminum alloy also enables the dispersion of strengthening precipitate phases selected from an η-phase precipitate, a θ-phase precipitate, and a T-phase precipitate, while being free of a S-phase precipitate, when precipitation hardened.
1. A precipitation hardenable aluminum alloy having a composition comprising:
12.1 wt % to 12.5 wt % zinc;
3 wt % to 4 wt % magnesium;
0.4 wt % to 1.0 wt % copper;
0.01 wt % to 0.5 wt % zirconium, chromium, or zirconium and chromium in total; and
balance aluminum with no more than 0.2 wt % impurities.
2. The precipitation hardenable aluminum alloy set forth in claim 1 , wherein the aluminum alloy has a modified cracking susceptibility coefficient (mCSC) of 70 or less, and wherein the modified cracking susceptibility coefficient is defined by equation (1)
m CSC=(CSC)( dT ) (1)
wherein CSC is a standard cracking coefficient of the aluminum alloy and dT is a freezing range of the aluminum alloy, the CSC being further defined by equation (2)
CSC
=
(
t
Lf
0.01
′
-
t
Lf
0.1
′
)
(
t
Lf
0.1
′
-
t
Lf
0.6
′
)
(
2
)
wherein, in relation to the aluminum alloy solidifying from 100% liquid to 100% solid as depicted on a liquid fraction versus time fraction curve, t′ Lf0.01 is a time fraction associated with a liquid fraction of 0.01, t′ Lf0.1 is a time fraction associated with a liquid fraction of 0.1, and t′ Lf0.6 is a time fraction associated with a liquid fraction of 0.6, and dT being further defined as a difference between a temperature at which aluminum atoms begin to assemble into their primary face centered cubic (FCC) crystal unit cell structures and a temperature at which there is no more liquid remaining in the aluminum alloy, the dT being reported in degrees Celsius.
3. The precipitation hardenable aluminum alloy set forth in claim 2 , wherein the mCSC of the aluminum alloy is less than 60.
4. The precipitation hardenable aluminum alloy set forth in claim 2 , wherein the mCSC of the aluminum alloy is less than 40.
5. The precipitation hardenable aluminum alloy set forth in claim 2 , wherein the mCSC of the aluminum alloy is less than 30.
6. The precipitation hardenable aluminum alloy set forth in claim 1 , wherein the composition of the precipitation hardenable aluminum alloy comprises:
0.01 wt % to 0.3 wt % zirconium, chromium, or zirconium and chromium in total; and
no more than 0.1 wt % impurities.
7. A precipitation hardened aluminum alloy having a composition comprising:
12.1 wt % to 12.5 wt % zinc;
3 wt % to 4 wt % magnesium;
0.4 wt % to 1.0 wt % copper;
0.01 wt % to 0.5 wt % zirconium, chromium, or zirconium and chromium in total; and
balance aluminum with no more than 0.2 wt % impurities,
wherein the alloy includes an aluminum matrix and a fine dispersion of precipitates within the aluminum matrix, the fine dispersion of precipitates including one or more strengthening precipitate phases selected from an η-phase precipitate, a θ-phase precipitate, and a T-phase precipitate, while being free of a S-phase precipitate.
8. The precipitation hardened aluminum alloy set forth in claim 7 , wherein a phase fraction of the one or more strengthening precipitate phases in the alloy is greater than 10 mol %.
9. The precipitation hardened aluminum alloy set forth in claim 8 , wherein the fine dispersion of precipitates includes the η-phase precipitate and a phase fraction of the η-phase precipitate in the alloy is greater than 10 mol %, or wherein the fine dispersion of precipitates includes the η-phase precipitate and the θ-phase precipitate and a phase fraction of the η-phase precipitate and the θ-phase precipitate in combination in the alloy is greater than 10 mol %, or wherein the fine dispersion of precipitates includes the η-phase precipitate and the T-phase precipitate and a phase fraction of the η-phase precipitate and the T-phase precipitate in combination in the alloy is greater than 10 mol %.
10. The precipitation hardened aluminum alloy set forth in claim 7 , wherein the aluminum alloy has a modified cracking susceptibility coefficient (mCSC) of 70 or less, and wherein the modified cracking susceptibility coefficient is defined by equation (1)
m CSC=(CSC)( dT ) (1)
wherein CSC is a standard cracking coefficient of the aluminum alloy and dT is a freezing range of the aluminum alloy, the CSC being further defined by equation (2)
CSC
=
(
t
Lf
0.01
′
-
t
Lf
0.1
′
)
(
t
Lf
0.1
′
-
t
Lf
0.6
′
)
(
2
)
wherein, in relation to the aluminum alloy solidifying from 100% liquid to 100% solid as depicted on a liquid fraction versus time fraction curve, t′ Lf0.01 is a time fraction associated with a liquid fraction of 0.01, t′ Lf0.1 is a time fraction associated with a liquid fraction of 0.1, and t′ Lf0.6 is a time fraction associated with a liquid fraction of 0.6, and dT being further defined as a difference between a temperature at which aluminum atoms begin to assemble into their primary face centered cubic (FCC) crystal unit cell structures and a temperature at which there is no more liquid remaining in the aluminum alloy, the dT being reported in degrees Celsius.
11. The precipitation hardened aluminum alloy set forth in claim 10 , wherein the mCSC of the alloy is less than 70.
12. The precipitation hardened aluminum alloy set forth in claim 11 , wherein the mCSC of the alloy is less than 30.
13. An aluminum alloy comprising:
12.1 wt % to 12.5 wt % zinc;
3 wt % to 4 wt % magnesium;
0.4 wt % to 1.0 wt % copper;
0.01 wt % to 0.5 wt % zirconium and/or chromium; and
balance aluminum with no more than 0.2 wt % impurities,
wherein the aluminum alloy is configured to be precipitation hardened in a heat treatment process to include an aluminum matrix and a dispersion of precipitates throughout the aluminum matrix, the dispersion of precipitates including an η-phase precipitate, a θ-phase precipitate, and a T-phase precipitate.
14. The aluminum alloy set forth in claim 13 , wherein the η-phase precipitate is MgZn 2 , the θ-phase precipitate is Al 2 Cu, and the T-phase precipitate is Mg 3 Zn 3 Al 2 .
15. The aluminum alloy set forth in claim 14 , wherein the η-phase precipitate and the T-phase precipitate have a total phase fraction of 10 mol % or greater, and wherein the dispersion of precipitates has no S-phase precipitate or an S-phase precipitate with a phase fraction in mol % of no greater than 0.2%.
16. The aluminum alloy set forth in claim 14 , wherein the η-phase precipitate and the θ-phase precipitate have a total phase fraction of 10 mol % or greater, and wherein the dispersion of precipitates has no S-phase precipitate or an S-phase precipitate with a phase fraction in mol % of no greater than 0.2%.
17. The precipitation hardenable aluminum alloy set forth in claim 1 , wherein the composition comprises 0.5 wt % to 1.0 wt % copper.
18. The precipitation hardenable aluminum alloy set forth in claim 1 , wherein the composition comprises 0.7 wt % copper.
19. The precipitation hardenable aluminum alloy set forth in claim 1 , wherein the composition comprises 0.1 to 0.5 wt % zirconium, chromium, or zirconium and chromium.