Grain refinement mechanism and improved mechanical properties in Mg–Sn alloy with trace Y addition

Abstract Mg-0.5Sn-(0, 0.3 wt%) Y alloys were obtained by casting with a metal mould, then extruded to acquire the as-extruded sheets. The microstructures, and mechanical properties of the alloys were studied. The results indicated that Sn3Y5 particles generated after the addition of Y into the Mg–Sn alloys. This contributed to the presence of fine grains in the extruded Mg-0.5Sn-0.3Y sheets, the size of which decreased from ∼16 μm to ∼4 μm, accompanied by a significant improvement in the mechanical properties. Specifically, with Y addition, the ultimate tensile strength and elongation along the extrusion direction increased by 21% and 191%, respectively. The crystallographic matching relationships between Sn3Y5 and Mg were established via an edge-to-edge matching model. The calculated results illustrated that Sn3Y5 had small crystallographic misorientation with α-Mg, and served as the sites of heterogeneous nucleation for the Mg matrix, which led to grain refinement of Mg-0.5Sn-0.3Y sheets. Meanwhile, the diffraction patterns obtained by transmission electron microscopy along [0001]Mg // [11 2 ‾ 3 ‾ ]Sn3Y5 well agreed with the simulation results and validated the prediction. Furthermore, the macro-texture and work hardening behaviour of the extruded sheets implied that in the tensile test, the as-extruded Mg-0.5Sn-0.3Y sheets underwent both basal and prismatic slips, while only the basal slip was observed in Mg-0.5Sn. As more slip systems were activated and more mobile dislocations could be formed, this in combination with the fine-grain strengthening effect, resulted in the large tensile elongation and high tensile strength of the Mg-0.5Sn-0.3Y sheets.