Optimizing Conductivity-Strength Trade-Off in Mg-xZn-yCu-Zr Alloys: Design and Characterization

Abstract

To design magnesium alloys with both high conductivity and high Strength, the effects of copper and zinc content and, as well as hot extrusion on electrical/thermal conductivity and mechanical properties of Mg-xZn-yCu-0.5Zr (x = 0.8, 1.6, 2.4, 5, 6 wt.%; y = 0, 0.5, 1.5, 2, 3 wt.%) alloys at room temperature were studied. The results showed that as the copper content increased, the MgZnCu phase in the alloys gradually increased, leading to a decrease in mechanical properties but an improvement in electrical/thermal conductivity. As zinc content increased, mechanical properties improved while electrical/thermal conductivity decreased. At a ratio of copper to zinc is 1, alloy had the higher electrical/thermal conductivity but lower mechanical properties. This indicates that when zinc atoms exist in the form of MgZnCu phases, they enhance the electrical/thermal conductivity, while zinc existing as solid solution atoms improves mechanical properties. The as-cast Mg-3Zn-1.5Cu-0.5Zr alloy achieved the best comprehensive performance, with electrical conductivity of 20.35 MS/m and thermal conductivity of 138.98 W·m-1·K-1 while its mechanical properties including yield strength of 44MPa, ultimate tensile strength of 151MPa and elongation of 11.9%. After hot extrusion of the optimized composition as-cast Mg-3Zn-1.5Cu-0.5Zr alloy, the alloy’s grains were significantly refined, and the MgZnCu phase was broken down from a continuous network structure into smaller irregular particles. This process notably improved the mechanical properties of the alloy, with only a slight decrease in electrical/thermal conductivity. Additionally, anisotropy in electrical/thermal conductivity was observed in the extruded alloy. The Mg-3Zn-1.5Cu-0.5Zr alloys extruded at 250°C exhibited the best performance, with an electrical conductivity of 19.54 MS/m, thermal conductivity of 133.44 W·m-1·K-1, and mechanical properties including yield strength of 247 MPa, ultimate tensile strength of 289 MPa, and elongation of 20.1%.

Keywords: Magnesium Alloys, MgZnCu phase, conductivity, Mechanical properties