Grain refinement of Mg-Al alloys inoculated by MgAl2O4 powder

As a potent nucleating substrate for α-Mg grain, MgAl2O4 powder was used to inoculate the Mg-Al melt in this study. The effects of MgAl2O4 amount, holding time and Al content on the grain size and grain refining ratio of the inoculated Mg-Al alloys are systematically investigated. The results show that the minimum grain size of Mg-3Al alloy is achieved by adding 2 wt.% MgAl2O4 powder and this alloy exhibits higher grain refining ratio than Mg-5Al and Mg-8Al alloys. The crystallographic misfit calculation indicates the well-matching and possible orientation relationships (ORs) between α-Mg and MgAl2O4. Among these predicted ORs, [10–10]α−Mg//[110]MgAl2O4 in (0002)α−Mg//(1–13)MgAl2O4 possesses the smallest misfit, i.e., 2.34% (fr). Both results of the experiment and crystallographic calculation demonstrate that the grain refinement of Mg-Al alloys is attributed to the MgAl2O4 particles acting as the heterogeneous nucleation substrates for α-Mg grains.