Method of producing an aluminum-zinc-magnesium-copper alloy having improved exfoliation resistance and fracture toughness

A method of producing an aluminum alloy product having superior exfoliation resistance and fracture toughness comprising the steps of:

• a) providing an aluminum-based alloy consisting essentially of 6.6 to 6.8% by weight of zinc, about 2.05 to 2.25% by weight of magnesium, about 2.1 to 2.3% by weight of copper, a maximum of 0.15% by weight of iron, a maximum of 0.12% by weight of silicon, about 0.08 to 0.15% by weight of zirconium, one or more additional grain refining elements selected from chromium, manganese, titanium, boron, vanadium, and hafnium, the total of said additional grain refining elements being between 0.0% and about 0.5% by weight, with the balance aluminum and incidental impurities, wherein the amounts of zinc, copper and magnesium are stoichiometrically balanced in said alloy such that during an aging treatment of said alloy product, substantially all of said copper, magnesium and zinc form MgZn.sub.2 and Al.sub.2 CuMg precipitates upon reaching equilibrium to produce an alloy product having not more than 0.11 wt. percent excess zinc, copper and magnesium;
• b) working said alloy into a predetermined shape;
• c) heat treating said predetermined shape;
• d) quenching said heat treated shape;
• e) aging said heat treated shape for about 4 to 72 hours at about 220.degree. F. to 310.degree. F.;
• and
• f) recovering said aged shape.

A method of producing an aluminum alloy product having superior exfoliation resistance and fracture toughness comprising the steps of

• a) providing an aluminum-based alloy consisting essentially of 6.6 to 6.8% by weight of zinc, about 2.05 to 2.25% by weight of magnesium, about 2.1 to 2.3% by weight of copper, a maximum of 0.15% by weight of iron, a maximum of 0.12% by weight of silicon, about 0.08 to 0.15% by weight of zirconium, one or more additional grain refining elements selected from chromium, manganese, titanium, boron, vanadium, and hafnium, the total of said additional grain refining elements being between 0.0% and about 0.5% by weight, with the balance aluminum, wherein the amounts of zinc, copper and magnesium are stoichiometrically balanced in said alloy such that during an aging treatment of said alloy product, substantially all of said copper, magnesium and zinc form MgZn.sub.2 and Al.sub.2 CuMg precipitates upon reaching equilibrium thereby producing an alloy product having not more than 0.11 wt. percent excess zinc, copper and magnesium;
• b) working said alloy into a predetermined shape;
• c) heat treating said predetermined shape;
• d) quenching said heat treated shape;
• e) aging said heat treated shape in a first step at about 220.degree. F.-270.degree. F. for about 5 to 32 hours followed by aging said heat treated shape in a second step at about 300.degree. F.-325.degree. F. for 6 to 24 hours;
• and
• f) recovering said aged shape.