Differential Effects of Sn and Si Solutes on the Microstructure and Properties of Cu–Ni–Al Alloys with Coherent L12-Γ′ Phases

In order to solve the discontinuous precipitation of nano-spherical γ′ coherent precipitates strengthened Cu–Ni–Al alloys and explore the influence mechanism of trace elements on the microstructure and properties. Herein, the Si and Sn, with same main group but showing different elemental interaction, was selected as the fourth element, and series of alloy composition were designed and prepared in a wide Cu content, and the effect of Si or Sn addition on microstructure, properties at room temperature and thermal stability are investigated. The results demonstrate that Si is completely dissolved into γ and γ′ phase, but a little of Sn solid solution into γ′ phase. The two adding elements can accelerate the precipitation of γ′ phases, suppress the grain boundaries discontinuous precipitation and provide dual-nanostructure strengthening effect, which enhance the hardness and conductivity, and Si exhibits more preferable effect. The thermodynamic calculation and the work function results indicate that the addition of Sn would induce the descending thermal stability of γ and γ′ phase, but Si is beneficial to the improvement of thermal stability of γ and γ′ phase. Compared to Sn, Si is more suitable to be a candidate for the multi-component design of Cu–Ni–Al alloys.