A study of grain refinement of AZ91E and Mg-9 wt.% AI alloys using zinc oxide

Grain refinement is a proven method to improve mechanical properties of Mg alloys. In this research, the influence of ZnO on the microstructure of selected magnesium alloys was investigated. For graphite mold casting with an addition of 0.75 wt. % ZnO, the grain size of the AZ91E alloy decreased from 217 μm to 108 μm. For the binary alloy (Mg-9 wt.% Al), the grain size reduced from 288 μm to 93 μm with an addition of 3 wt.% ZnO. No significant fading of ZnO grain refiner was observed for both the alloys. In permanent mold casting process, with an addition of 0.5 wt.% ZnO, the grain size of the AZ91E alloy decreased from 133μm to 79 μm with significant improvements in mechanical properties. Cleavage type fracture was dominant in the base alloy while alloys refined with 0.5 wt.% ZnO showed more quasi-cleavage type fracture.