Effect of Ni/Si mass ratio on microstructure and properties of Cu-Ni-Si alloy

Cu-Ni-Si alloys with 94 wt% Cu content and different Ni/Si mass ratios were prepared by hot pressing sintering, and then solution treatment and ageing treatment were also performed. Microstructure and phase composition along with electrical conductivity and hardness of the alloys under different treating condition was studied, and then the influence of Ni/Si mass ratio was discussed. Results showed that the as-sintered Cu-Ni-Si alloys mainly consisted of alpha-Cu matrix and some Ni(31)Si(12)particles at the grain boundary as well as delta-Ni2Si phases inside the matrix. After solution treatment, most of the Ni-Si compounds decomposed, but delta-Ni2Si precipitates from the matrix after ageing treatment. With increasing Ni/Si mass ratio, the electrical conductivity and hardness of the alloys increases firstly and then decreases, while a highest combination of them achieved when the mass ratio of Ni/Si was 4:1. The effect of Ni/Si ratio on the electrical conductivity of Cu-Ni-Si alloys can be mainly ascribed to the residual content of Ni/Si in the Cu matrix after ageing treatment. When the mass ratio of Ni/Si is equal to the atomic ratio of delta-Ni2Si phase, most of the Ni and Si atoms would precipitates as delta-Ni2Si, and then the electrical conductivity reaches the highest value.