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Abstract

A preformed A356 alloys with thixotropic structure (designated SSM-A356) was systematically studied on mechanical properties in order to establish the database for further investigations in forming and heat treatment. Because of the specific microstructure and characteristics, the heat treatment conditions of SSM-A356 were explored through the observations of microstructure and the measurement of micro-hardness. In the investigation of heat treatment, it was observed that the eutectic silicon was refined and spheroidized which is unlikely for conventional processing. The mechanical testing results showed that the yield and ultimate tensile strength of SSM-A356 were respectively around 115% and 34% greater than those of conventional A356, and the elongation was also 2-3 times larger. According to the analysis of fracture mode via fatigue test, the crack propagation was in the way of trans-granular which is a typical type of ductile fracture. Thus, an excellent ductility for SSM-A356 was expected. From the experimental analysis results, it could be concluded that the superior mechanical behaviors of SSM-A356 are basically attributed to the refinement of microstructure and the spheroidization of eutectic silicon. This structure can be maintained during forming by further processing of die or squeeze casting.

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