Microstructures of an AlSi7Mg alloy by near-liquidus casting

Semi-solid ingots of an AlSi7Mg alloy were obtained using the method of near liquidus casting. Their micro-structures exhibit the characteristics of fine, equiaxed, and non-dendrite, which are required for semi-solid forming. The influences of casting temperature, heat preservation time, and cooling rate on the microstructure were also investigated. The results show that in the temperature region near liquidus the grain size becomes small with a decrease in casting temperature. Prolonging the heat preservation time makes grain crassitude at the same temperature. And increasing the cooling rate makes grain fine. The microstructure of the alloy cast with iron mould is finer than that with graphite mould.