Effects of ultrasonic treatment on the formation of iron-containing intermetallic compounds in Al-12%Si-2%Fe alloys

In general, the iron impurity is detrimental to the mechanical properties of Al–Si alloys. The α-phase and β-phase are the most important and common iron-containing intermetallic compounds (IMCs) in Al–Si alloys. During conventional casting, the acicular β-phase is stable, and considered to be harmful. In this paper, the Al-12%Si-2%Fe alloy was treated by power ultrasound and solidified under different cooling conditions. The effects of ultrasonic treatment (UST) and cooling rate on morphology and composition of IMCs were investigated. The results showed that UST can change the morphology and composition of iron-containing IMCs and promote the formation of metastable α-phase. When the ultrasound was applied at 720 °C, the amount of starlike α-phase increases and the acicular β-phase decreases with increasing applied time of UST. In addition, the polygonal α-phase is formed and substitutes for the β-phase when quenching after UST for 60 s and 120 s, suggesting that the formation of β-phase can be suppressed under this condition. For the case of UST at 610 °C which the β-phase has been nucleated, the β-phase transforms from an acicular shape to the rod-like morphology, indicating that the cavitation-induced fracture of β-phase.