Microstructure and mechanical properties of Cu–Ni–Si alloys

The microstructure and mechanical properties of 0.1 wt.% Mg-added and Mg-free Cu–2.0 wt.% Ni–0.5 wt.% Si alloys aged at 400 °C have been examined. The addition of Mg promotes the formation of disk-shaped Ni2Si precipitates. The Cu–Ni–Si–Mg alloy exhibits higher strength and resistance to stress relaxation than the Cu–Ni–Si alloy. The higher strength or stress relaxation resistance is attributable to the reduction in inter-precipitate spacing by the Mg addition or the drag effect of Mg atoms on dislocation motion. The Cu–Ni–Si alloy with a large grain size of 150 μm shows higher stress relaxation resistance than the alloy with a small grain size of 10 μm because of a lower density of mobile dislocations in the former alloy.