Microstructure Evolution of A356 Alloy Under Ultrasonic Vibration

Abstract

Grain refinement and modification of eutectic silicon in Al-Si alloy are considered as important task resulting from solidification process. Two different approaches to grain refinement by solidification process have been pursued chemically stimulated and physically induced. The chemical route depends primarily on addition of grain refiner, while the physical relies mainly on the use of external field, such as ultrasonic vibration, which is the subject of this research work. Ultrasonic vibration was used to modify the microstructure of A356 alloy. The effect of ultrasonic vibration on the solidification of the A356 alloy was investigated and the obtained samples were characterized by optical microscopy, scanning electron microscopy (SEM) and mechanical properties as well. The results showed that both the primary aluminium and eutectic silicon were significantly refined; the dendritic primary aluminium became small polygonal and globular in some cases, in addition the plate-like or big spherical eutectic silicon turned into rod-like and small spheres during the solidification process under ultrasonic vibration. The mechanism of the microstructure evolution under ultrasonic vibration was also preliminarily discussed.