Ultrasonic assisted friction stir welding (UaFSW) is a novel variation of conventional friction stir welding (FSW)

which utilizing the external ultrasonic vibration energy to improve the inherent disadvantages of conventional friction stir welding. This article reviews the progress status on ultrasonic assisted friction stir welding of aluminum alloy

including the methods to superimposing ultrasonic vibration energy in FSW

the effects of superimposing ultrasonic vibration energy on the microstructural evolution and mechanical properties of the joints

and the mechanism of superimposing ultrasonic energy in FSW. It shows that UaFSW can reduce the welding loads

improve the joint formation

suppress the weld defects

increase the welding speed

and enhance the joint properties. Multi-physical numerical simulation of UaFSW process shows that all the thermal effect

acoustoplastic effect and friction reduction effect lead to a several difference in thermal processes and plastic material flow comparing with conventional FSW

which resulting in an improved joint formation and mechanical properties as state above. Finally

the challenges and future research topics are emphasized systematically.