中文摘要：

Many investigations have revealed that transition of melt structure can effectively infl uence the fi nal solidifi cation microstructures.In this study,ultrasonic treatment was applied to Al-20%Si melt and Sr-modif ied 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 ref ine the primary Si phase andα-Al of Al-20%Si alloy;strontium can make the morphology of Si phase spheroidized and refi ned as Sr addition changes the faceted growth characteristic of Si phase;however,the ref inement effect of ultrasonic treatment on the primary Si phase andα-Al is weakened by Sr addition.

英文摘要：

Many investigations have revealed that transition of melt structure can effectively influence the final solidification microstructures. In this study, ultrasonic treatment was applied to AI-20%Si melt and Sr-modified AI-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 a-AI of AI-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-AI is weakened by Sr addition.