Effect of Sm on the microstructure, mechanical properties and creep behavior of Mg-0.5Zn-0.4Zr based alloys

The present study aims at investigating the effect of additions (0.4, 0.5, 1.5, 3, and 5 wt.%) of samarium on the microstructure, mechanical properties of Mg-0.5Zn-0.4Zr alloy. Experimental results show that a small amount of samarium addition can bring about precipitation of eutectic Mg41Sm5 phases at the grain boundaries and refine the as-cast grains. When samarium content increasing to 3%, a great number of fine plate-shaped precipitates form in the regions close to grain boundaries, and could effectively hinder dislocation slip and play important roles in improving tensile and creep properties. Furthermore, the transition of fracture mode as a function of samarium content can be generally described as follows: trans-granular fracture in Mg-(0.4-0.7)Sm-0.5Zn-0.4Zr alloys, both trans-granular and inter-granular fracture in Mg-1.5Sm-0.5Zn-0.4Zr alloys, and inter-granular fracture in Mg-(3-5)Sm-0.5Zn-0.4Zr alloys. Stress and temperature dependence of the steady-state creep rate were studied over a temperature range of and stress ranges of 200-225 °C and stress range of 60-100 MPa, and creep mechanisms corresponding to different conditions were proposed for the Mg-3Sm-0.5Zn-0.4Zr alloy.