FORMATION OF MICROSTRUCTURE IN AL-SI ALLOYS UNDER ULTRASONIC MELT TREATMENT

It is well known that ultrasonic melt treatment (UST) provides many benefits to casting processing, especially for the refinement or modification of as-cast structure. There is a lack for systematic studies on Al-Si alloys, although a number of reports are available on hypo-eutectic A356-type and hyper-eutectic (18-24 wt% Si) alloys, showing primary Al or Si refinement. In this paper, the effect of UST on the formation of microstructure was systematically analyzed in hypo-eutectic, near-eutectic and hypereutectic Al-Si alloys, including commercial piston alloys. The results show that UST usually results in the refinement of grains and primary Si particles when it is applied in a proper temperature range, while ultrasonic treatment during the whole solidification processing leads to coarsening effect on eutectic Si phase or primary Si particles.