Crystallization Behavior of Iron-Containing Intermetallic Compounds in Al-Si Alloy Under Ultrasonic Treatment

The acicular beta-AlSiFe phase is most common but detrimental iron-containing intermetallic compounds (IMCs) in Al-Si casting alloys. In this study, ultrasonic field (USF) was applied to modify the acicular iron phases in Al-12Si-2Fe alloy. The results showed that USF treatment leads to different influence at different application temperature region. The application of USF at 720 degrees C facilitates the formation of blocky-shaped alpha-Al12Si2Fe3 phase and suppresses its conversion into the acicular beta-Al9Si2Fe2 phase by the quasi-peritectic reaction. The amount of alpha-Al12Si2Fe3 increases with increasing applied time of USF. The ultrasonic cavitation-induced nucleation is responsible for the morphological modification and phase transformation. USF applied at 610 degrees C causes a fragmentation of beta-Al9Si2Fe2 without composition change, and the cavitation-induced fragmentation is considered as the major reason.