Effect of Sb additions on the microstructural stability and mechanical properties of cast Mg–4Zn alloy

Abstract

The effect of 0.15, 0.4, and 0.7 wt.% Sb additions on the microstructure, thermal stability, and mechanical properties of a cast Mg–4% Zn was investigated. Microhardness and shear punch tests (SPT) were used to evaluate the mechanical properties of the alloys in both as-cast condition and after long-term annealing. Addition of Sb resulted in the refinement of the as-cast structure and also the formation of Mg 3Sb 2 intermetallic particles. According to the microstructural features, the presence of Mg 3Sb 2 particles caused excellent stability during long-term high-temperature exposure, resulting in superior thermal stability of the Sb-containing alloys in comparison with the base alloy. The retention of mechanical properties after long annealing treatment is believed to be caused by the strengthening effects of Mg 3Sb 2 intermetallic particles and also by the role of these particles in impeding the growth of α-Mg grains during high-temperature exposure. The highest mechanical properties, obtained for 0.4% Sb addition, can be attributed to the favorable combination of small size and high volume fraction of the Mg 3Sb 2 intermetallic particles in the Mg matrix. At the higher Sb level of 0.7%, however, strength and hardness decrease due to the coarsening of Mg 3Sb 2 particles.