Modification of Mg₂Si morphology in Mg-9%Al-0.7%Si alloy by the SIMA process

The effect of predeformation on the semisolid microstructure of Mg-9%Al-0.7%Si alloy produced by the strain induced melt activation (SIMA) process was studied. Experimental results indicated that a non-dendritic microstructure could be obtained by the SIMA process in the alloy. With the reduction ratio varying from 0% to 30%, the volume fraction of liquid gradually enlarged from 37.26 vol.% to 48.28 vol.%, and the morphology of α-Mg grains transformed from dendritic shape to spherical shape, with a size of 52.16 μm. Also, the liquid islands in the grains become less with the increase of the reduction ratio. In addition, the eutectic Mg₂Si phase transformed from Chinese script shape to globular shape during the isothermal heat treatment. A possible reason of the modification of Mg₂Si morphology is the shifting of the eutectic composition of the liquid towards lower silicon contents with increasing Al content.