Effects of alloying on microstructure and mechanical property of AZ91D magnesium alloy

As-cast microstructures and phase compositions of AZ91D alloys after adding alloying elements such as Ce, Si and Ca were observed by optical microscope (OM) and X-ray diffraction (XRD), meanwhile their tensile property and hardness at ambient temperature were tested. The results show that rod-like Al4Ce and Chinese script type Mg2Si phases are formed in the alloys after adding Cc and Si respectively, whereas no new phase is formed after adding Ca and Ca atoms added are mainly dissolved into beta phase. During the solidification process, Al4Ce and Mg2Si phases are pushed into the growth interface and Ca atoms are easy to enrich in the front edge of the growth interface, then the free growth of the dendrite is hindered and as-cast microstructures are refined. The additions of Ce and Ca can improve the whole mechanical property of AZ91D alloy at ambient temperature and the improvement degree of the former is higher than that of the latter. However, the addition of Si can reduce the whole mechanical property of AZ91D alloy at ambient temperature.