Development of Mg–Zn–Y–Zr casting magnesium alloy with high thermal conductivity

Abstract

Magnesium alloys are used in aircraft because of their light weight. However, for these alloys to be applied in electronic devices, high thermal conductivities are required. Several high-potential compositions of Mg–Zn–Y–Zr alloys were selected by phase composition and their freezing ranges calculated using Thermo-Calc software. The alloys were prepared, and their fluidity, hot tearing susceptibility, mechanical properties, and thermal conductivity were obtained and compared. The alloy composed of Mg–4 wt% Zn–3 wt% Y–0.3 wt% Zr was selected for further investigation, because of its high thermal conductivity and satisfactory mechanical properties. The Mg–4 wt% Zn–3 wt% Y–0.3 wt% Zr alloy's fluidity and hot tearing susceptibility were similar to those of the widespread AZ91 commercial casting magnesium alloy. The influence of a heat treatment regime on the microstructure, thermal conductivity, and mechanical properties of the developed alloy was also investigated. It was established that the room temperature thermal conductivity of the Mg–4 wt% Zn–3 wt% Y–0.3 wt% Zr alloy after aging at 300 °C for 5 h was 105 W/mK. Additionally, the following tensile test results were obtained in aged condition: 120 MPa yield strength, 200 MPa ultimate tensile strength, and 4% elongation. The utilization of solid solution heat treatment at 520 °C for 8 h prior to aging can promote up to 9% increase in elongation. The Mg–4 wt% Zn–3 wt% Y–0.3 wt% Zr casting alloy can be used as a high thermal conductivity material with industrial applications.