Effects of gadolinium addition on the microstructure and mechanical properties of Mg–9Al alloy

This research aims to study the significance of Gd addition (0wt%–2wt%) on the microstructure and mechanical properties of Mg–9Al alloy. The effect of Gd addition on the microstructure was investigated via X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The Mg–9Al alloy contained two phases, α-Mg and β-Mg17Al12. Alloying with Gd led to the emergence of a new rectangular-shaped phase, Al2Gd. The grain size also decreased marginally upon Gd addition. The ultimate tensile strength and microhardness of Mg–9Al alloy increased by 23% and 19%, respectively, upon 1.5wt% Gd addition. We observed that, although Mg–9Al–2.0Gd alloy exhibited the smallest grain size (181 μm) and the highest dislocation density (5.1 × 1010 m−2) among the investigated compositions, the Mg–9Al–1.5Gd alloy displayed the best mechanical properties. This anomalous behavior was observed because the Al2Gd phase was uniformly distributed and present in abundance in Mg–9Al–1.5Gd alloy, whereas it was coarsened and asymmetrically conglomerated in Mg–9Al–2.0Gd.