Effect of combined addition of Zr and Mg on the microstructure and properties of a Cu–Cr–Sn–Zn alloy for etching lead frame

Abstract

The effects on microstructure and properties of Cu–Cr–Sn–Zn with combined addition of Zr and Mg elements and their evolutions in the process of solid solution and thermomechanical treatment for etching high pin lead frames were studied. The microstructure was analyzed by OM, SEM, TEM, and EBSD. The results show that Cu–Cr–Sn–Zn and Cu–Cr–Sn–Zn–Zr–Mg alloys have the best performance after primary aging at 440 °C for 4 h and secondary aging at 400 °C for 4 h. The hardness and conductivity of the two alloys are 154 HV&78.3%IACS and 171 HV&77.8%IACS, respectively. Cu–Cr–Sn–Zn–Zr–Mg alloy final products shown better comprehensive performance, with conductivity, tensile strength, and hardness of 81.4%IACS, 580 MPa, and 175 HV respectively. The addition of Zr and Mg elements slows down the precipitation process of Cu–Cr–Sn–Zn alloy, refines the Cr phases, and inhibits the coarsening of Cr phases. Nano Cr clusters and coherent fcc Cr phases were observed during the aging process at 440 °C for 4 h and 400 °C for 4 h, which is difficult to observe in Cu–Cr–Sn–Zn alloy due to the precipitation and coarsening of Cr phases in a rapidly way. The surface roughness of Cu–Cr–Sn–Zn–Zr–Mg alloy without coarsened Cr phases is lower with Sa = 0.2681 μm.