Effect of aging treatment on microstructure and mechanical properties of Cu–Ag alloys

Cu–6 wt.%Ag, Cu–12 wt.%Ag and Cu–24 wt.%Ag alloys were prepared by vacuum melting, solution treating at 740 °C for 4 h and aging at 450 °C for different times. The effect of aging treatment was investigated by observing the microstructure and determining the hardness. During aging treatment, discontinuous precipitation reaction can occur along high-angle grain boundaries and continuous precipitation reaction within Cu dendritic arms. Abundant high-angle grain boundaries result in a precipitation reaction that is predominantly discontinuous in Cu–6 wt.%Ag while net-like eutectic colonies surrounding Cu dendritic arms result in a precipitation reaction that is predominantly continuous in Cu–24 wt.%Ag. In Cu–12 wt.%Ag, continuous precipitates within Cu dendrites coexist with discontinuous precipitates next to high-angle grain boundaries. Aging only for 1 h can significantly increase the hardness although the precipitation reaction is insufficient. The increasing rate of the hardness becomes slow as aging time longer than 1 h. The hardness keeps approximately constant for Cu–12 wt.%Ag and Cu–24 wt.%Ag and slightly decreases for Cu–6 wt.%Ag with increasing aging time from 16 to 37 h. The precipitation reaction during aging treatment has more significant hardening benefit to the alloys with lower Ag contents.