Corrosion resistant aluminum alloys having high amounts of magnesium and methods of making the same
View Patent ↗Systems and methods for continuously casting Al—Mg alloy sheet or plate product having a high amount of magnesium are disclosed. The Al—Mg products have 4 or 6 to 8 or 10 wt. % Mg and are resistant to both stress corrosion cracking and intergranular corrosion.
1. A method comprising:
(a) continuously casting an Al—Mg alloy comprising from about 6 wt. % to about 10 wt. % Mg;
(b) hot rolling the Al—Mg alloy to a thickness of less than 6.35 mm;
(c) annealing the Al—Mg alloy via a furnace, wherein the annealing step comprises:
(i) heating the Al—Mg alloy to a temperature T 1 , wherein T 1 is from about 365° C. to about 500° C., for a period of at least about 2 hours to achieve an O temper; and
(ii) first cooling the Al—Mg alloy from the temperature T 1 to a temperature T 2 , wherein the temperature T 2 is at least about 25° C. less than the temperature T 1 , and wherein the rate of cooling from temperature T 1 to temperature T 2 is not greater than about 100° C. per hour; and
second cooling the Al—Mg alloy from the temperature T 2 to a temperature T 3 , wherein T 3 is at least about 100° C. less than temperature T 2 ,
wherein, after the first and second cooling steps, the Al—Mg alloy comprises a plurality of grains, and wherein the Al—Mg alloy is substantially free of a continuous film of β-phase at the grain boundaries after the Al—Mg alloy has been age sensitized.
2. The method of claim 1 , wherein after the cooling step (c)(ii), the Al—Mg alloy is free of a continuous film of β-phase.
3. The method of claim 1 , wherein the cooling rate of the first cooling step is in the range of from about 30° C./hour to about 60° C./hour.
4. The method of claim 1 , wherein the continuously casting comprises strip casting.
5. The method of claim 1 , wherein the cooling rate of the second cooling step is at least about 100° C./hour.