The effects of ultrasonic vibration on microstructural changes and mechanical properties of Mg alloy joint

Abstract The weld of AZ31 Mg alloy was performed via ultrasonic vibration assistance process. The metallographic structure observation, scanning electron microscope observation, hardness detection, tensile test and fracture morphology observation were performed to analyze the influences of ultrasonic vibration on the microstructure and mechanical properties of welded joints. In this paper, the ultrasonic vibration with power in the 0–1.5 kW was successfully introduced into the weld pool by filler wire, which had a series of effects on the weld. The results indicated that ultrasonic induced agitation in the molten pool can reduce or even eliminate the porosity in the weld zone. Besides, for joints treated by 1.0 kW ultrasonic process, the average grain size of weld zone decreased to 28 μm, owing to the acoustic flow and cavitation effects caused by ultrasonic process. Under optimized ultrasonic power of 1.0 kW, the sound Mg alloy joint with the maximum tensile strength of 256 MPa was obtained and the fracture surface presented plastic fracture characteristics.