Controlling the microstructure and improving the tensile properties of extruded Mg-Sn-Zn alloy through Al addition

This study demonstrates that the addition of 4 wt% Al to Mg-7Sn-1Zn alloy effectively promotes the dynamic recrystallization and dynamic precipitation behaviors during extrusion and significantly improves the tensile properties of the extruded alloy. The Al addition dramatically increases the area fraction of the dynamically recrystallized (DRXed) grains of the extruded alloy. This is mainly attributed to the particle-stimulated nucleation effect induced by undissolved Mg2Sn particles, the increased amount of grain boundaries owing to grain refinement of the billet, and the increase in stress applied during extrusion. The amount of fine Mg2Sn precipitates of the extruded alloy also increases with the Al addition, owing to an increased number of nucleation sites for precipitation; this, in turn, leads to a reduction in the grain size of the extruded alloy through the enhanced grain-boundary pinning effect caused by the precipitates. As a result, the tensile and compressive strengths of the extruded alloy considerably improved with Al addition, which is due to the combined effects of Al solute atoms, undissolved Mg2Sn particles, more Mg2Sn precipitates, and reduced grain size. Furthermore, the grain size reduction caused by the Al addition suppresses the formation of twins-which can act as cracking sites-during tensile deformation; this results in a considerable increase in the tensile elongation of the extruded alloy.