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% 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 (6%), eutectic (12.5%) and hyper-eutectic (18%) Al-Si alloys, including commercial piston alloys. The results show that ultrasonic treatment of Al-Si alloys can refine grain structures in all types of Al-Si alloys. Significant refinement of primary Si phase in hyper-eutectic Al-Si alloy can be observed as well. In neareutectic or eutectic Al-Si alloys, UST, along with its effect on grain refinement, shows some potential in refining primary Si particles in a wide range of melt temperatures.