Microstructure characteristics and tensile property of ultrasonic treated-thixocast A356 alloy

Billets of A356 aluminum alloy were treated using ultrasonic vibrations during solidification. The billets were reheated to the semisolid state at different routes to optimize the procedure. Billets were, then, thixocast using a die casting machine. The results showed that the ultrasonic-treated billets exhibited finely distributed α(Al) globules after reheating and thixocasting. The thixocast ultrasonic-treated billets showed higher ultimate tensile strength and elongation compared with the untreated billets. Moreover, the thixocast parts showed a tendency to ductile fracture under tension when made from ultrasonic-treated billets, while those made of untreated billets showed brittle fracture with obvious straight facets. These results revealed the feasibility and competence of ultrasonic melt treatment as a potential route for preparing billets for thixocasting.