Influence of ultrasonic vibrations on the microstructure and mechanical properties of Al/Ti friction stir lap welds

Al/Ti dissimilar welds were fabricated by ultrasonic vibrations assisted friction stir welding, which eliminated the tool wear and enhanced the material flow. The peak temperature was lowered, and a pre-heating period was introduced into welding by ultrasonic vibrations. Wider interface and smaller grain structures were observed in the welds due to the reinforced material flows. Ti fragments were spun into the Al alloy, resulting in a mixing zone beside the interface. Atomic diffusion was also enhanced with ultrasonic vibrations, according to the element maps. The strength of the Al/Ti welds was doubled with the influence of ultrasonic vibrations. The fracture was nucleated at the interface and propagated into the base materials. Shear dimple was the dominant characteristic of the fracture morphology, whereas cleavage planes were also found.