Abstract:A modification of Mg₂Si in the hypereutectic Mg-4%Si alloy (mass fraction) with Sr was investigated. Two types of Mg₂Si in the alloys were found: polygonal primary Mg₂Si and Chinese script type eutectic Mg₂Si. Adding Al-10% Sr master alloy to the Mg-4%Si alloy clearly reduced the average size of primary Mg₂Si and changed the morphology of eutectic Mg₂Si from Chinese script type to polyhedral or fine fibre shape. The refinement of primary Mg₂Si is mainly attributed to the heterogeneous nucleation mechanism induced by the Sr-rich particles. The modification of eutectic Mg₂Si results from the dissolved Sr, which alters the preferred growth manner of the eutectic.

Key words: Mg-Si alloy; Al-Sr alloy; Mg₂Si; modification; refinement