Effect of ultrasonic power on microstructure and mechanical properties of AZ91 alloy

Ultrasonic vibration with different powers from 0 W to 700 W was applied during the solidification process of AZ91 alloy. The microstructures and mechanical properties of the treated AZ91 alloy were characterized. Without subject to ultrasonic vibration (0 W of ultrasonic power), the dendrites were coarse and large. Globular grains were obtained in AZ91 alloy subject to high intensity ultrasonic vibration. The grain size was decreased gradually from 202 μm to 146 μm with increasing ultrasonic power. The mechanical properties of the treated alloy were also improved. The ultimate tensile strength was increased from 145 MPa to 195 MPa and elongation to fracture from 2.3% to 5.2% correspondingly with increasing ultrasonic power. The mechanism by which ultrasonic power affects the microstructure and mechanical properties of AZ91 alloy is discussed.