Ultrasonic was imposed on 7085 aluminum alloy melt during solidification to measure the temperature change in the melt caused by ultrasonic

and the temperature fluctuation in the melt occurs.Effects of the temperature fluctuation on undercooling nucleation in the aluminum alloy melt were investigated.The results show that cavitation bubbles caused by ultrasonic absorb heat during growth process to decrease the temperature around cavitation bubbles

while heat is released to increase the temperature around when cavitation bubbles collapse.In the experiment

the amplitude of temperature fluctuation is in range of 2～6℃

leading to the initial nucleation temperature increased from 638.4 ℃ to 644.5 ℃.Within the undercooling nucleation region

the temperature fluctuation can enhance the local undercooling degree and increases the maximum nucleation density from 47.1/mm3 to 92.6mm3.In the process of dendrite growth

the temperature fluctuation makes the necking-down dendrite side arm easier to detach

which increases new nucleus in the melt.