Effect of Si additions on mechanical properties and softening resistance of Cu–Ni-Sn-P alloy

The effects of trace Si element on the microstructure, mechanical properties and high temperature softening resistance of Cu-0.9Ni-1.9Sn-0.1 P (mass fraction, %) alloy were studied using hardness tests, conductivity measurements, SEM, TEM and XRD observations. According to the results, after 70% cold rolling and aging at 450 ℃, the micro-hardness, conductivity and softening temperatures of Cu-0.9Ni-1.9Sn-0.1 P-0.1Si alloy were up to 224.2 HV, 36.4%IACS and 520 ℃. In comparison with Cu-0.9Ni-1.9Sn-0.1 P alloy, the micro-hardness of Cu-0.9Ni-1.9Sn-0.1 P-0.1Si alloy was increased from 192.3 HV to 224.2 HV, and the conductivity increased from 33.6%IACS to 36.4%IACS. TEM analysis shows that adding Si can from precipitated Ni2Si phase with Ni and increase the strength of Cu-0.9Ni-1.9Sn-0.1 P-0.1Si alloy. Moreover, the addition of 0.1% Si can increase the softening temperature of the Cu-0.9Ni-1.9Sn-0.1 P alloy. As a result of annealing at different temperatures, the softening mechanism of the alloy varies. When the annealing at low temperature ( 400 ℃−480 ℃), the annealing softening is related to recovery and recrystallization. When the annealing temperature is high ( 480 ℃−580 ℃), the annealing softening is primarily caused by recrystallized grain growth and the coarsening of second-phase particles．