Precipitation behavior, microstructure and properties of Cu-0.48Cr-0.4Zn-0.15In-0.1Zr alloy by multi-stage thermomechanical treatment

Abstract

A Cu-0.48Cr-0.4Zn-0.15In-0.1Zr (wt.%) alloy with excellent comprehensive properties was designed and prepared. By optimizing the multistage thermo-mechanical treatment process, the copper alloy had tensile strength of 618 MPa, yield strength of 601 MPa, electrical conductivity of 80.2 % IACS, elongation to failure of 6.3 % and resistance to softening temperature of 562 °C. The main strengthening phases of the alloy were nanoscale Cr phases, and the orientation relationship between the Cr phases with coherent FCC structure and the Cu matrix in the early ageing state was the Cube-on-cube relationship. When the ageing time and temperature increased, the Cr phases gradually turned into semi-coherent or noncoherent BCC structure with N-W or K-S orientation relationship to the matrix. Synergistic addition of Zn and In elements effectively impeded atomic diffusion and grain boundary migration, inhibited the recrystallization behavior of the alloy, which improved the alloy's softening resistance. It was also beneficial to inhibit the long-range diffusion of the Cr atom, thus suppressing the coarsening of Cr phases and delaying the allotropic transition of the Cr phases from the FCC structure to the BCC structure, which in turn resulted in the excellent comprehensive performance of the alloy. Compared with Cu-Cr-Zr alloy, Cu-Cr-Zn-In-Zr alloy under the same process treatment showed a 15.7 % increase in tensile strength, 65.8 % increase in elongation to failure and 19 °C increase in resistance to softening temperature, which could work as an ideal material for the lead frame in very large scale integration circuit.