Effect of Li on microstructure, mechanical properties and fracture mechanism of as-cast Mg-5Sn alloy

This work explores trace addition of Li on the magnesium alloy Mg-5Sn, with an emphasis laid on the microstructure, mechanical properties and fracture mechanism. The results reveal that with trace addition of Li, a new Li2MgSn phase forms distributed along the grain boundaries. When the concentration of Li increases, the secondary dendrite arm spacing of the primary α-Mg phase can be refined and the formation of Li2MgSn becomes more favored, and even totally substitute Mg2Sn phase finally. Trace addition of Li can significantly increase the yield stress and elongation to failure of Mg-5Sn alloy during both tensile and compressive tests, and manifests the highest ultimate strengthening effect during compression. The optimal comprehensive mechanical property is achieved in Mg-5Sn-0.3Li, with an ultimate compressive strength of 334 MPa. With the increment of Li, the fracture mechanism shifts from mixture of cleavage fracture and dimple fracture in Mg-5Sn alloy to the mechanism of cleavage fracture in Mg-5Sn-0.3Li and Mg-5Sn-1Li alloy.