Morphology modification of Mg2Si by Sr addition in Mg-4%Si alloy

A modification of Mg(2)Si in the hypereutectic Mg-4%Si alloy (mass fraction) with Sr was investigated. Two types of Mg(2)Si in the alloys were found: polygonal primary Mg(2)Si and Chinese script type eutectic Mg(2)Si. Adding Al-10% Sr master alloy to the Mg-4% Si alloy clearly reduced the average size of primary Mg(2)Si and changed the morphology of eutectic Mg(2)Si from Chinese script type to polyhedral or fine fibre shape. The refinement of primary Mg(2)Si is mainly attributed to the heterogeneous nucleation mechanism induced by the Sr-rich particles. The modification of eutectic Mg(2)Si results from the dissolved Sr, which alters the preferred growth manner of the eutectic.