Oxide inducing the heterogeneous nucleation is an available method to achieve grain refinement. In this study, Mg-Al binary alloys are successfully refined by the inoculation of in-situ oxidation process. The average grain size of Mg-3Al alloy significantly decreases from 1135 to 237 m, with a high grain refining ratio of 79.1%. In the inoculated pure Mg and Mg-1Al alloy, MgO particles are the only oxide products. While with Al content increasing to 3 wt.%, MgAl2O4 is another oxide inclusion product. Both MgO and MgAl2O4 possess the nucleating potency for -Mg grain, where MgAl2O4 exhibits a higher nucleating potency due to the lower misfit with -Mg. Grain refinement of pure Mg and Mg-1Al is attributed to the heterogeneous nucleation of -Mg grain on MgO particles. While grain refinement of Mg-3Al and Mg-6Al alloys should be attributed to the both heterogeneous nucleation events on MgO and MgAl2O4 particles.
