Effect of Ni/Sn ratio on microstructure and properties of Cu-Ni-Sn-P alloy

Cu-1.33Ni-1.35Sn-0.08P(Ni/Sn = 1/1), Cu-0.87Ni-1.82Sn-0.08P (Ni/Sn = 1/2) and Cu-1.78Ni-0.86Sn-0.08P (Ni/Sn = 2/1) alloys were prepared to explore the effect of different Ni/Sn ratios on the microstructure and properties of the alloys. The results showed that the alloy had the best properties when Ni/Sn = 1/2. At peak aging, its tensile strength and conductivity reached 447.3 MPa and 35.5% IACS respectively. Its tensile strength was 65.1 MPa and 88.8 MPa higher than that of the alloys with Ni/Sn = 1/1 and Ni/Sn = 2/1 respectively, and its conductivity was 1.1% IACS and 3.9% IACS higher. All three alloys had obvious dendrite segregation, but the alloy with Ni/Sn = 1/2 had finer dendrites and a more uniform distribution. In addition, the precipitates in the Cu-Ni-Sn-P alloys with Ni/Sn = 1/2 and Ni/Sn = 1/1 were all granular Ni₁₂P₅ phases, and the particles of the former are finer. The precipitates in the Cu-Ni-Sn-P alloy with Ni/Sn = 2/1 were rod-shaped. The strengthening mechanisms of the three alloys were Orowan strengthening, grain boundary strengthening, solid solution strengthening and dislocation strengthening, and Orowan strengthening was dominant. The Cu-Ni-Sn-P alloy with Ni/Sn = 1/2 had finer grains and precipitates, resulting in better tensile strength and electrical conductivity.