Characteristics of Dissimilar Ti/Al Butt-Lap Joint Fabricated via Ultrasonic-Assisted Friction Stir Welding

Dissimilar Ti/Al butt-lap joints were fabricated via ultrasonic-assisted friction stir welding, and the material flow was enhanced due to the acoustoplastic effect, inhibiting the formation of welding defects. Ultrasonic vibration refined the microstructures and accelerated the dynamic recrystallization in the nugget zone. Consequently, 10–15% decrease in the average grain diameter and 20% increase in the fraction of high angle grain boundaries were obtained. The intermetallic compounds layer of TiAl₃ generated along the butt-line, while the atomic diffusion layer formed along the lap-line. With the help of ultrasonic activation, the atomic diffusion layer got thickened (from 1.6 to 2.3 μm), improving the peak load/elongation of joint from 1.2 KN/3% to 2.1 KN/6%. Furthermore, the novel double-ultrasonic-sources were utilized, and the joint made by this method exhibited a more satisfactory welding performance; the average grain size of nugget zone decreased to 5 μm, and the peak load/elongation of joint increased to 2.6 KN/8%.