Microstructure and mechanical properties of AZ91 alloy produced with ultrasonic vibration

Ultrasonic vibration was introduced into the solidification of the AZ91 magnesium alloy. The coarse dendrite microstructure solidified in the AZ91 alloy without any ultrasonic vibration. However, the microstructure with fine uniform non-dendrite grains was achieved with ultrasonic vibration. According to the analysis of refinement mechanism, it indicated that due to the acoustic cavitation and flows induced by ultrasonic vibration, the most of insoluble impurity particles become active as nucleation centers and the temperature gradient near the solidification front increases, which led to the fine uniform microstructure. Besides, the AZ91 alloy produced with ultrasonic vibration exhibited the improved mechanical properties at room temperature, such as compressive yield strength (94 MPa), ultimate compressive strength (376 MPa) and fracture strain (22.0%).