Effect of two-step cryorolling and aging on mechanical and electrical properties of a Cu–Cr–Ni–Si alloy for lead frames applications

Abstract

Abstract High strength and high electrical conductivity Cu–Cr-based alloys are important candidate materials for preparing lead frames, railway contact wires and connects. However, high strength and high electrical conductivity are mutually exclusive in nature. To optimize the mechanical and electrical properties of a Cu–Cr–Ni–Si alloy, the two-step cryorolling and aging (CRA) was carried out in this study. Here, by the analysis of microstructure evolution, precipitation behavior, and corresponding strengthening mechanisms of the alloy at different rolling and aging conditions, we find that the yield strength and electrical conductivity for the two-step CRA sample are improved by 91.3 MPa and 4.9 %IACS (International Annealed Copper Standard) than those of the sample subjected to single-step room temperature rolling and aging (RTRA). The higher yield strength for the two-step CRA sample is mainly determined by the precipitation strengthening contributed from Ni2Si and Cr precipitates, rather than the twin boundary strengthening and dislocation strengthening. In fact, the dislocation density of the two-step CRA sample is lower than that of the single-step RTRA sample because of the faster drop rate of recovery, which weakens the effect of dislocation strengthening. The combination of the first-step aging and second-step CR process for the two-step CRA sample contributes to the formation of more precipitates from the matrix, thereby significantly increasing the precipitation strengthening and decreasing the impurity scattering in the final aging. The results provide a new preparation process and a reliable theoretical approach for optimizing the mechanical and electrical properties of the Cu–Cr alloys.