Age hardening is a process in which heating is done:
Correct Answer: Up to 200 - 450°C for 15 - 30 min and quenching in water
Description: Age hardening—Process of hardening certain alloys by controlled heating and cooling, which usually is associated with a phase change.
Heat Treatment of Gold-Copper Alloys
To soften the alloy, the casting is placed in a furnace for 10 minutes at 700°C and then quenched in water. All intermediate phases in the alloy are changed to a disordered solid solution at 700°C, and the rapid quenching prevents ordering from occurring during cooling. The tensile strength, proportional limit, and hardness are reduced by such a treatment, and the ductility is increased. To harden the alloy, the temperature of the furnace is set between 200°C and 450°C and the casting is heated for 15 to 30 minutes before it is quenched in water. Ideally, before the alloy is age-hardened, it should be subjected to a softening heat treatment to relieve all residual strain hardening before the alloy is hardened again by heat treatment to produce a disordered solid solution. Otherwise the amount of solid-state transformation will not be properly controlled. In metallurgical terminology, the softening heat treatment is referred to as a solution heat treatment and the hardening heat treatment is termed age hardening.
Age hardening reduces the ductility of gold alloys.
Phillips 12 ed page 367, 374
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