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 degrees C for 4 h and aging at 450 degrees 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. (c) 2006 Elsevier B.V. All rights reserved.