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.
An aluminum-based in-situ composites reinforced with Mg2Si and Si particles were produced by centrifugal casting A1-20Si-5Mg alloy. The microstructure of the composites was examined, and the effects of temperature on fracture behavior of the composite were investigated. The results show that the average fraction of primary Si and Mg2Si particles in the composites is as high as 38%, and ultimate tensile strengths （UTS） of the composites first increase then decrease with the increase of test temperature. Microstructures of broken specimens show that both the particle fracture and the interface debonding affect the fracture behavior of the composites, and the interface debonding becomes the dominant fracture mechanism with increasing test temperature. Comparative results indicate that rich particles in the composites and excellent interface strength play great roles in enhancing tensile property by preventing the movement of dislocations.
