Effect of La addition on the microstructure and mechanical properties of Mg–6 wt% Zn alloys

Abstract

The Mg–6wt% Zn alloys microalloyed with different amounts of La were cast and extruded. The second phase in the as-cast Mg–Zn alloy is Mg4Zn7, which was replaced by Mg–Zn–La intermetallics with orthorhombic structure after La addition. Microalloying with La refined the grain size of dynamic recrystallization slightly, which was due to La solute atom in α-Mg alloy. Addition of La weakened the texture and gave rise to the formation of non-basal texture component, attributing to the existence of La in the form of solute atoms in matrix. The ductility was enhanced significantly by adding La to Mg–6wt% Zn alloy, while the strength was reduced. Such phenomenon was related to the weakening texture of the La containing alloys. The Mg–6Zn–0.2La (wt%) alloy exhibited a superior ductility with the elongation-to-fracture up to 35%. However, with further increasing of La content to 1wt%, the strength of the as-extruded Mg–Zn–La alloys was not improved but the ductility was reduced, suggesting that small addition of La is preferred for the improvement of mechanical properties.