Grain refinement and superplastic forming of an aluminum base alloy

Claim 1

A method of producing a high forming rate, high strength superplastic aluminum base alloy comprising the steps of: providing a powdered aluminum base alloy consisting essentially of 6.0 to 8.0 % Zn, 1.5 to 3.5% Mg, 1.0 to 3.0 % Cu, 0.2 to 0.4 % Zr, and 0.2 to 0.5 % Cr, the powder being produced by rapid solidification of the aluminum base alloy in an inert atmosphere; consolidating said powder alloy by thorough outgassing, hot pressing and extrusion at a 4:1 minimum reduction at about 380° C. to 400° C., with approximately 8-10 hours of exposure to this temperature; heating the aluminum base alloy to a uniform rolling temperature which is low enough to avoid recrystallization but high enough to prevent cracking, and rolling at that temperature utilizing cross rolling passes to reduce its thickness about 85% and to provide a sheet of the aluminum base alloy having a subgrain size less than 1.2 μm; heating the sheet of aluminum base alloy to a superplastic forming temperature in a range from 450° C. to 490° C.; and superplastically forming the sheet of aluminum base alloy without substantial delay after reaching the forming temperature at a strain rate in a range of 5×10 -3 to 5×10 -2 per second to obtain maximum elongation.

Claim 2

A method of producing a high forming rate, high strength superplastic aluminum base alloy comprising the steps of: providing a powdered aluminum base alloy consisting essentially of 6.0 to 8.0 % Zn, 1.5 to 3.5% Mg, 1.0 to 3.0 % Cu, 0.2 to 0.4 % Zr, and 0.2 to 0.5 % Cr, the powder being produced by rapid solidification of the aluminum base alloy in an inert atmosphere; consolidating said powder alloy by thorough outgassing, hot pressing and extrusion at a 4:1 minimum reduction at about 380° C. to 400° C., with approximately 8-10 hours of exposure to this temperature; heating the aluminum base alloy to a uniform rolling temperature which is low enough to avoid recrystallization but high enough to prevent cracking, and rolling at that temperature utilizing cross rolling passes to reduce its thickness about 85% and to provide a sheet of the aluminum base alloy having a subgrain size less than 1.2 μm; heating the sheet of aluminum base alloy to a superplastic forming temperature in a range from 450° C. to 490° C.; and superplastically forming the sheet of aluminum base alloy without substantial delay after reaching the forming temperature at a strain rate in a range of 5×10 -3 to 5×10 -2 per second to obtain maximum elongation.