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 Hv = 96.6 was yielded compared to AZ91D at Hv = 63.7. These properties were well correlated with the results of microstructure and quantitative analysis. © 2009 Japan Foundary Engineering Society.