Simultaneous enhancement of mechanical and electrical properties of Cu–Ni–Si alloys via thermo-mechanical process

Abstract

Developing high-performance copper alloys while simultaneously improving ultimate tensile strength (UTS) and electrical conductivity (EC) has been a key challenge and direction. Two thermo-mechanical processes were employed in this study to achieve simultaneous enhancement of UTS and EC of the Cu-3.08Ni-0.61Si-0.17Zn-0.17Cr-0.04P alloy. After the two-stage cold-rolling and aging process (85% cold-rolling + 450 °C@60 min aging + 95% cold-rolling + 450 °C@30 min aging, referred to as Process A), the alloy's UTS and EC of the alloy are 856 ± 26 MPa and 52.4 ± 0.8% international annealed copper standard (IACS). The mechanical and electrical properties of the alloy with process A are much better than those of the alloy with single stage cold-rolling and aging treatment process (85% cold-rolling + 450@60 min aging, 786 ± 12 MPa, 47.5 ± 0.9% IACS). The UTS of the alloy reaches 905 ± 11 MPa with pre-aging + two-stage cold-rolling-aging (450 °C@90 min pre-aging + process A, referred to as process B), and the EC reaches 52.5 ± 0.2% IACS, indicating that process B enhanced the strength over process A. A large number of nano-scale δ-Ni2Si precipitates are observed in the samples after primary aging of process A and pre-aging of process B, leading to a more diffuse dislocation distribution during subsequent cold-rolling and then promoting further precipitation of the solute atoms during subsequent aging processes. In the samples treated by both process A and B, there are two sizes of δ-Ni2Si phase precipitates, simultaneously enhancing UTS and EC of the Cu–Ni–Si alloy.