Mechanical Response, Twinning Behaviours and Strain Incompatibility of FSWed-AZ31B Joints Along Different Loading Paths

Friction stir welding (FSW) has been widely acknowledged as a remarkably efficient method to obtain the sound joints. The microstructures of Mg alloys after FSW processing have been investigated in relation to their mechanical properties. However, there is a lack of research on the microstructures, mechanical behavior, and their correlation with the applied loading paths in FSWed joints. In this study, the loading paths tilted angles of 0°, 45°, and 90° (defined as TD, 45° and WD) in respect to the transverse direction (TD) were considered. Results revealed that the value of fracture elongation is gradually increase with the loading direction from TD to welding direction (WD), and the elongation in the WD direction reaches 20%, the ultimate tensile strength exhibited by TD is higher than that of WD and 45°. The microstructure indicates that the main cause of premature fracture in welding joints during TD loading is strain incompatibility resulting from different micro-texture induced deformation mechanisms. Additionally, the proportion of low angle grain boundaries along WD direction is significantly higher than that along 45° direction, which is attributed that basal texture orients 45°, bigger grain size, and the presence of twin crystals can promote grain reorientation, thereby facilitating additional dislocation slip.