Effect of ultrasonic treatment and Sr addition on microstructure of Al-20%Si alloy

Many investigations have revealed that transition of melt structure can effectively influence the final solidification microstructures. In this study, ultrasonic treatment was applied to Al-20%Si melt and Sr-modified Al-20%Si melt at 720 ℃ (i.e. above liquidus of about 690℃) for 60 s, and then the melt was quickly quenched to room temperature. Experimental results show that ultrasonic treatment can refine the primary Si phase and α-Al of Al-20%Si alloy; strontium can make the morphology of Si phase spheroidized and refined as Sr addition changes the faceted growth characteristic of Si phase; however, the refinement effect of ultrasonic treatment on the primary Si phase and α-Al is weakened by Sr addition