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

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 Mg3Sb2 intermetallic particles. According to the microstructural features, the presence of Mg3Sb2 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 Mg3Sb2 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 Mg3Sb2 intermetallic particles in the Mg matrix. At the higher Sb level of 0.7%, however, strength and hardness decrease due to the coarsening of Mg3Sb2 particles.