Ultrasonic vibration with different powers from 0 k W to 1.6 k W 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 k W,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)2protective layer and(ii) reducing the mismatch and disorder between Mg(OH)2 protective layer and Mg alloy surface. Ultrasonic vibration with different powers from 0 k W to 1.6 k W was applied during the tungsten inert gas welding-brazing of Mg / Ti. 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. Powered with ultrasonic power of 1.2 k W, 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 both 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.