Enhanced stress relaxation resistance of Cu–Ni–Si alloy strips through Sn addition and pre-aging treatment

In this study, Cu-3.44Ni-0.86Si- x Sn ( x = 0, 1, 2 wt%) alloy strips were fabricated via two different processing routes, namely the traditional preparation (TP) process and the improved preparation (IP) process. The microstructural evolution, precipitation behavior, and stress relaxation resistance of the alloys were systematically investigated. The results show that the precipitation of Ni 2 Si during pre-aging facilitates grain refinement and increases dislocation density during subsequent cold rolling. Compared with the TP process, the IP-processed alloys exhibit finer and more uniform microstructures, higher hardness, and superior stress relaxation resistance. Notably, the Sn2 alloy subjected to the IP process demonstrates the best performance, with a stress relaxation rate of only 9.5 % after 15 h at room temperature. This enhancement is attributed to the combined pinning effect of the densely distributed Ni 2 Si phases and the additionally precipitated Ni 3 Si phases promoted by Sn, which effectively hinder dislocation motion. These findings reveals a previously unreported dual-phase precipitation mechanism, in which Sn addition promotes the simultaneous formation of Ni 2 Si and Ni 3 Si phases through modulation of solute distribution. Furthermore, this work proposes a novel alloy design strategy that integrates composition-induced phase control with deformation sequence optimization to enhance the stress relaxation resistance of Cu–Ni–Si based alloys.