Ultrasonic spot welded AZ31 magnesium alloy: Microstructure, texture, and lap shear strength

The structural application of ultra-lightweight magnesium alloys inevitably involves welding and joining. A solid-state welding – ultrasonic spot welding (USW) – was conducted on AZ31B-H24 Mg alloy sheet by varying a key parameter of welding energy in this study, aiming to identify the changes in the microstructure, crystallographic texture, and lap shear tensile strength. The grain size was observed to increase with increasing welding energy. Crystallographic texture determined via X-ray diffraction showed a significant change that corresponded well to the change in the deformation and recrystallization mechanisms of the Mg alloy. The lap shear strength first increased with increasing energy input, reached the maximum value at a welding energy of 2000 J, then decreased. The welds generally fractured along the joint interface when the welding energy was lower than 2000 J, while fracture occurred at the periphery of the joint (button pull-out) for the samples made with an energy input of higher than 2000 J.