Grain refinement of Mg-Al alloys inoculated by MgAlO powder

As a potent nucleating substrate for α-Mg grain,MgAl2 O4 powder was used to inoculate the Mg-Al melt in this study.The effects of MgAl2 O4 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-3 Al alloy is achieved by adding 2 wt.% MgAl2 O4 powder and this alloy exhibits higher grain refining ratio than Mg-5 Al and Mg-8 Al alloys.The crystallographic misfit calculation indicates the wellmatching and possible orientation relationships(ORs) between α-Mg and MgAl2 O4.Among these predicted ORs,[10-10]α-Mg//[110]MgAl2 O4in(0002)α-Mg//(1-13)MgAl2 O4 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 MgAl2 O4 particles acting as the heterogeneous nucleation substrates for α-Mg grains.