Effect of Al-TiC Master Alloy on As-cast Microstructure of AZ91 Magnesium AlloyHAN Hui,LIU Sheng-fa,KANG Liu-gen,LIU Lin-yan(School of Materials Science and Engineering,Wuhan University of Technology,Wuhan 430070,China)The refining effect of Al-10%TiC master alloy(processed via Casting Contact Reaction Method) on as-cast microstructure of AZ91 alloy was investigated by means of EPMA,SEM and XRD and so on.The results showed that the size of grains decreased with the increasing of adding amount of master alloy,which was reduced from 107 μm(matrix alloy) to 57 μm and the reduced extent was about 55% while adding 0.5%TiC.In addition,the continuous net-like β-phases transformed into discontinuous net-like or granular.The refining mechanism of α-Mg maybe was the in-situ TiCp particles act as the heterogeneous nucleation of primary α-Mg.Moreover,the TiCp particles suspended in the melt were pushed onto the front of solid-liquid interface during crystallization,consequently,which reduceed the rate of growth of primary α-Mg phases and finally resulted in the further refined of α phases.AZ91 magnesium alloy;Al-TiC master alloy;microstructure