Abstract:Hypereutectic Al-Si alloy with variant Mg contents were fabricated by casting, and the effects of Mg content on the microstructure of primary Mg₂Si particles in hypereutectic Al-Si alloys were investigated. The results show that the volume fraction of primary Mg₂Si particles increases linearly with raising the Mg content, but the average size of Mg₂Si particles does not exhibit a corresponding change. When the Mg content is 3%, á1 0 0？ directions have the fastest growth velocity, so that Mg₂Si particles are likely to form octahedron shape. When gradually increasing the Mg content, the distributions of Mg and Si atoms on the solid-liquid interface become inhomogeneous, which results in the formation of irregular octahedron structures.Finally, when the Mg content is about 10%, the morphology of primary Mg₂Si particles changes from the octahedron shape into various complex structures with a large size.

Key words: hypereutectic Al-Si alloys; primary Mg₂Si particles; growth pattern; growth velocity