Evolution of Microstructure, Mechanical Properties and Corrosion Resistance of Ultrasonic Assisted Welded-Brazed Mg/Ti Joint

Ultrasonic vibration with different powers from 0 kW to 1.6 kW was applied during the tungsten inert gas welding-brazing of Mg/Ti. The microstructures, mechanical properties and corrosion resistance of the ultrasonic assisted tungsten inert gas (U-TIG) welded-brazed Mg/Ti joint were characterized. The results showed that, without being subjected to ultrasonic vibration, coarse columnar α-Mg grains occurred in the fusion zone of Mg/Ti joint. However, with ultrasonic power of 1.2 kW, the average grain size of columnar α-Mg grains was refined from 200 µm to about 50 µm and the tensile strength of joints increased ~18% up to 228 MPa. Besides, high fraction of grain boundaries was introduced by grain refinement, contributing to improve the corrosion resistance in two ways: (i) accelerating the formation of Mg(OH)2 protective layer and (ii) reducing the mismatch and disorder between Mg(OH)2 protective layer and Mg alloy surface.