Joining of magnesium and aluminum alloys via ultrasonic assisted friction stir welding at low temperature

Intermetallic compounds (IMCs) formed in the stir zone (SZ) of dissimilar friction stir welded aluminum/magnesium (Al/Mg) joint always deteriorate tensile properties. Joining of 6061-T6 Al and AZ31B Mg alloys via ultrasonic assisted friction stir welding (UaFSW) at low temperature was performed to reduce the disadvantages caused by IMCs. A sound Al/Mg joint with smooth surface was obtained based on the stationary shoulder at a high welding speed of 80 mm/min, rotational velocity of 1000 rpm, and ultrasonic power of 1400 W due to the improvement of material flow caused by ultrasonic, indicating the success of low-temperature welding. Meanwhile, joining interface, characterized by the IMCs, was attributed to inter diffusion caused by severe plastic deformation from ultrasonic and friction stirring. The tensile strength and elongation of the Al/Mg joint reached 134 MPa and 1.5%, respectively. The IMCs containing Al2Mg3 formed in the SZ was the main reason of tensile fracture, and then resulted in cleavage fracture. The present study suggests that UaFSW has feasible and potential to join Al/Mg alloys at low temperature, which provides a significant reference for welding joint of dissimilar materials with the IMCs.