Effect of ultrasonic melt treatment on thermal kinetics of hypereutectic Al-Si alloy

The effect of ultrasonic melt treatment (UST) on the thermal kinetics of hypereutectic Al-25%Si alloy during eutectic solidification was studied using differential scanning calorimeter. The onset temperature remains roughly constant, and the peak and end temperatures both increase with increasing of heating rate and decrease with increasing of cooling rate for the Al-25%Si alloys untreated and treated with UST. The activation energy of Al-25%Si alloys decreases from 718.5 to 671.4 kJ mol(-1) after UST treatment which is calculated by the Kissinger equation. As well, the nucleation energy decreases from 2.598 x 10(-22) to 1.201 x 10(-22) kJ mol(-1). The eutectic nucleation rate of Al-25%Si alloy treated with UST is much larger than that of the untreated alloy due to the lower activation energy and nucleation energy, so the eutectic structure is refined after UST treatment. Finally, the effect of UST on the precipitation of primary silicon and the eutectic solidification, and the effect of precipitation of primary silicon on followed eutectic solidification are discussed.