Effect of Ultrasound on the Interface Morphology and Strength of Ti/Al Alloy Joints Produced by Friction Stir Welding

The interface formation process was investigated in bimetallic joints of commercially pure titanium alloy and 5056 aluminum alloy produced by friction stir welding, including with ultrasonic assistance. Lap welding was performed with the titanium sheet on top of the aluminum one. Macrostructural geometric characteristics were analyzed such as weld width, plunge depth, the total cross-sectional area of defects, and the complexity of the interface between dissimilar layers. It was shown that the application of ultrasound during welding promotes better stirring of titanium and aluminum in the joint and makes their interface more complex, due to which the weld strength usually increases. This effect at low axial load can outweigh the antifriction effect. Experiments showed that ultrasonic-assisted friction stir welding provides the joint strength up to 87% of the aluminum alloy strength.