Effect of Ultrasonic Treatment on Grain Structure, Eutectic Phase and Mechanical Properties of an Al–6.2 wt% Cu Alloy

The microstructural modification of eutectic phase is a crucial factor for the mechanical properties strengthening of the Al–Cu binary alloy. In this paper, Al–6.2% Cu melts were subjected to ultrasonic treatment from 710 or 660 °C with different durations. The microstructural evolutions of primary α-Al grains and α-Al + θ-Al₂Cu eutectic phase under ultrasonication were investigated based on the nucleation and growth behavior. Results indicated that with the increase of ultrasonic processing time, the growth of dendritic or petaloid grains were completely suppressed and noticeable refinement to globular morphology were observed for α-Al grains. Meanwhile, broad lamella-like eutectic structure transformed to debris or even particles with continuous ultrasonication. Accordingly, the area fraction, average length and width of coarsening eutectic lamellas were dramatically reduced. In addition, the decrease of coarsening eutectic phase rather than the refinement of α-Al grains was found to be the main contributor to the enhancement of mechanical properties for Al–6.2% Cu alloy. The mechanisms underlying the transformation of eutectic phase under ultrasonic treatment was also interpreted based on the experimental results.