Abstract:Effects of ultrasonic treatment on microstructures were investigated by introducing the ultrasonic oscillation into AZ91 alloy melts. The results show that the ultrasonic treatment does not change the phase composition but has great influence on solidification microstructures. The area percentage of lamellar eutectic phase increases to the maximum when the applied ultrasonic power is increased to 600 W and then decreases gradually with the further increase of power; meanwhile, the average area of Al₈Mn₅ phase owns a completely opposing variation trend. The area percentage of Mg₁₇Al₁₂ decreases gradually with increasing the applied ultrasonic power. Mechanisms accounted for the refinement and fraction of different intermetallic phases were also discussed.

Key words: AZ91alloy; ultrasonic treatment; microstructure