Feasibility and interface migration characteristics of friction stir lap welding of LA141 Mg-Li alloy

2 mm-thick LA141 plates were successfully friction stir lap welded (FSLW). The similar FSLWLA141 Mg-Li alloy joint appeared a downward hook on the advanced side and an upward cold lap on the retreating side. The load of lap-shear tensile testing reached 2.8 kN, and the joints failed in the interface defects. The interface migration of LA141/LA141 lap joint during FSLW process was driven by forces at interface, such as a frictional force paralleled to the thread, a downward pressure perpendicular to the surface of the thread, the resistance from unsoftened metal and its own gravity. Moreover, the FSLWof AZ31/LA141 and LA141/AZ31 furtherly verified that forces at the interface were critical factors in determining the interface migration during FSLW process.