Effect of Mg on Microstructure and Properties of Cu-Cr-Zr alloy

Cu-0.26Cr-0.14Zr-3.31Mg and Cu-0.26Cr-0.14Zr-8.47Mg alloys were prepared by using vacuum-induction furnace melting, then they were treated by solution (980 ℃×2 h, water quenching）and aging (450 ℃×20 h air cooling). The influence mechanism of Mg content on the microstructure and properties of Cu-Cr-Zr alloys was investigated. The results indicate that as the Mg content increases from 3.31% to 8.47%, the excess Mg in the as-cast structure segregates in a blocky form within the matrix and forms a continuous network Mg-Cu eutectic phase at grain boundaries. After aging treatment, Mg significantly refines the nano-scale precipitates through heterogeneous nucleation effect, resulting in Cr particle sizes in the 8.47 Mg alloy (1-20 nm) being much smaller than those in the 3.31 Mg alloy (20-50 nm). The yield strength and tensile strength of the 8.47Mg alloy reach 410 MPa and 450 MPa, respectively, representing increases of 28% and 12% compared to those of the 3.31 Mg alloy, and the hardness after aging rises to 96 HRB, however, the elongation after fracture decreases from 18% to 12%. The electrical conductivity decreases from 75% IACS to 60% IACS with the Mg content increasing from 3.31% to 8.47%, which primarily caused by electron scattering induced by increased nanoparticle density and the electron trapping effect of Mg-Cu eutectic phases at grain boundaries. This research reveals the dual regulatory mechanism of heterogeneous nucleation to refine grains and inhibition of precipitate coarsening of high-content Mg in Cu-Cr-Zr alloys.