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Process for Improving Creep Resistance of Zinc-copper Alloys.
U S Pat 3 649 377 1972 Mar; :
Zn sheet approximately 0.025 In thick, strengthened by 0.5-2.0 pct cu, has a much slower rate of creep under constant load at room temperature or above if the alloys are hot-rolled to final size at at least 90 pct thickness reduction and air cooled than if cold- rolled. The rolling temperature should be higher for a cu content up to approximately 2 pct, but not >720 deg. F. Higher concentrations of cu or higher rolling temperatures give poorer mechanical properties. For a minimum creep rate, the temperature should keep the high-cu eta phase dissolved in the zn until air- cooled, upon which the excess precipitates, chiefly at grain boundaries, retarding slip at such locations when stressed. Annealing after hot working decreased the creep resistance. When zn alloys containing various cu contents up to 2 pct were rolled to 0.3 In sheets at 400 deg. F and air cooled, and loaded at 12,000 psi and 90 deg. F in tension, all the cold-rolled alloys showed >100 pct creep/day. With 1.25 pct cu, rolling at 320 deg. F gave approximately 10 pct, and at 640 deg. F, approximately 0.1 pct creep/day. With 1.75-2 pct cu, rolling at 680 deg.-720 Deg. F gave approximately 0.05 pct creep/day. The microstructure of these rolled alloys are discussed but not illustrated.
U.S. Pat. 3,649,377; Mar. 14, 1972; Chem. Abstr. 76:157,504J