Influence of prior deformation on the age hardening of a phosphorus-containing Cu–0.61wt.%Cr alloy

A copper alloy containing 0.61 wt.% Cr and 0.07 wt.% P was solution annealed and cold deformed to true strains ranging from 0.1 to 0.9. After being aged at 510 °C for different times, the deformed alloy was characterized using the measurement of Vickers hardness, optical microscopy and transmission electron microscopy. During the isothermal aging, the hardness of the deformed alloy showed three distinct stages as a function of aging time; this hardness behavior was associated with the interactions between precipitation, recovery and recrystallization. The amount of prior deformation and aging time influenced the interactions of the three processes. On aging, the lightly deformed alloy exhibited a retarded recrystallization process and therefore an efficient hardening response. The heavily deformed alloy (>0.7 strain) showed an accelerated process of recrystallization so that a long time aging (e.g. 60 min) resulted in an inefficient precipitation hardening due to the increased softening with the progress of recrystallization. The results of this study suggest that the precipitation process should occur before the onset of recrystallization during the aging of a deformed supersaturated alloy in order to result in an efficient hardening. This condition can be achieved by controlling the amount of prior deformation, aging temperature and time.