The effects of ultrasonic melt-treatment parameters

such as power density

stirring time

vibration temperature and preheating temperature of mold

on solidification structure of ignition-proof magnesium alloy AZ91D-3Ca were investigated.The results show that solidification structures of ignition-proof magnesium alloy AZ91D-3Ca can be refined by controlling ultrasonic melt-treatment parameters and solidification conditions.Primary grain in the alloy is refined gradually with increasing in the power density in range of 0～5.56W/cm2.However

with power density more than 5.56W/cm2

changes of primary grain in the alloy can be ignored.With the stirring time of 15s

refinement effect of primary grain exhibits desirable.With stirring time increasing in the range of 30～60s

the effect of microstructure refinement can be ignored.In the range of 600～690℃

with the increase of the ultrasonic vibration temperature

primary grain of the alloy is refined firstly and then coarsened

and the critical point is 630℃.From room temperature to 690℃

with preheat temperature of the mold increase

primary grain in the alloy is coarsened increasingly.