Solidification Microstructure, Thermal Properties and Hardness of Magnesium Alloy 20 mass% Gd Added AZ91D

Abstract

The solidification microstructure, the thermal property, and the hardness were investigated on AZ91D magnesium alloy and on AZ91D magnesium alloy with 20 mass% gadolinium addition. AZ91D and AZ91D + 20 mass% Gd were solidified by the furnace cooling technique starting from 700°C in an Ar flow atmosphere. The microstructure of AZ91D was composed of main αMg grains and web-like grain boundary phases of eutectic αMg + Mg₁₇Al₁₂, while that of AZ91D + 20 mass% Gd changes into an αMg matrix with dispersed Al₂Gd particles. SEM-EDS analyses showed that the Al content in an αMg matrix of this alloy was very low compared to AZ91D, because Al is consumed in the Al₂Gd particles. Differential thermal analysis and quenching experiments were performed in order to clarify this microstructure formation. The thermal conductivity of this alloy, as measured by the laser-flash method, was 129.2 W/mK at room temperature. This alloy exhibited a substantial variance from that of AZ91D at 45.1 W/mK. A higher Vickers hardness H_V=96.6 was yielded compared to AZ91D at H_V=63.7. These properties were well correlated with the results of microstructure and quantitative analysis.