Modification of Mg2Si in Mg-Si alloys with neodymium

The modification effect of neodymium (Nd) on Mg2Si in the hypereutectic Mg-3%Si (mass fraction) alloy was investigated by optical microcopy, scanning electron microscopy and X-ray diffraction. The results indicate that the morphology of the primary Mg2Si transforms from coarse dendrite into fine polygon with increasing Nd content. The average size of the primary Mg2Si significantly decreases to about 10 mu m with increasing Nd content up to 1.0%, and then becomes coarser again. The modification and refinement of the primary Mg2Si are mainly attributed to the poisoning effect. The NdMg2 phase in the primary Mg2Si transforms into NdSi and NdSi2 compounds as the Nd content exceeds 3.0%. Therefore, it is reasonable to conclude that the proper Nd (1.0%) addition can effectively modify and refine the primary Mg2Si.