Effects of Cr and Zr additions on microstructure and properties of Cu-Ni-Si alloys

Cu-Ni-Si alloys are widely used for electrical applications owing to high strength and high electrical conductivity. In this work, the effects of Cr and Zr additions on microstructure and properties of Cu-Ni-Si alloys were investigated. The addition of Cr and Zr results in formation of Cr3Si and Ni2SiZr intermetallic compounds, respectively, thus increases the electrical conductivity of Cu-Ni-Si alloy and refines the microstructure. Microstructure analysis confirms the presence of δ-Ni2Si precipitates, which strengthens the alloy through Orowan mechanism. Alloying with Zr element deteriorates the mechanical property of Cu-Ni-Si alloy, whereas in the presence of Cr, to the contrary, the ultimate tensile strength is increased, whether Zr is incorporated or not. Moreover, the addition of Zr can decrease the stacking fault energy (SFE) and promote formation of deformation twins. The best integrated performance is obtained through co-addition of Cr and Zr elements. The ultimate strength, elongation and electrical conductivity are 706 MPa, 9.5% and 48.2% IACS, respectively. The precipitation kinetics was discussed in terms of Avrami equation and the activation energy of Ni2Si precipitation was obtained. The calculated activation energies of precipitation are 105, 89, 115 and 111 kJ/mol for Cu-Ni-Si, Cu-Ni-Si-Zr, Cu-Ni-Si-Cr and Cu-Ni-Si-Cr-Zr alloy, respectively.