Grain refinement of binary Al-Si, Al-Cu and Al-Ni alloys by ultrasonication

A systematic experimental study has been made of the combined influence of solute content (1%, 2%, 3%, 5%) and ultrasonic intensity (0, 88, 350, 790, 1400 W/cm2) on grain refinement of Al-Si, Al-Cu and Al-Ni binary alloys. The grain refining efficiency was analyzed using the growth-restriction-factor (GRF) model. Ultrasonication resulted in more activated nucleants in Al-Cu alloys than in Al-Si and Al-Ni alloys by the model. The combination of high solute content and high ultrasonic intensity produced significant grain refinement, including significant refinement of eutectic structures that formed in the Al-5%Si, Al-5%Cu and Al-5%Ni alloys. In particular, high solute content ensured achievement of homogeneous and consistent grain morphology in ultrasonic grain refinement. In addition, excellent grain refinement was achieved in both the Al-5%Cu alloy, which has an equilibrium freezing range of 100 °C, and the Al-5%Ni alloy, which has an equilibrium freezing range of just 5 °C, under the same applied ultrasonic intensity (1400 W/cm2) conditions. The mechanisms for ultrasonic grain refinement of Al alloys are discussed based on experimental findings.