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

The Mg-6 wt% 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-6 wt% 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 1 wt%, 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.