Texture evolution and fracture behavior of friction-stir-welded non-flammable Mg–Al–Ca alloy extrusions

Friction stir welding (FSW) was used to successfully join nonflammable Mg85Al10Ca5 (at%) alloy extrusion plates having a high volume fraction of the C36 intermetallic compound. Electron backscatter diffraction (EBSD) combined with digital image correlation allowed us to investigate the texture evolution and tensile behavior of the friction-stir-welded region of the alloy. EBSD results revealed that the friction-stir-welded region could be subdivided into the following three textured zones: a typical nugget-shaped stir zone (SZ), a stir-affected zone (SAZ) in the peripheral region of the SZ, and a torsion-affected zone (TAZ) above the SZ. An analysis of the intragranular misorientation axis (IGMA) suggested that the texture evolution of the SZ and SAZ was due to the simultaneous activation of basal and prismatic slips. Furthermore, the strong basal texture in the TAZ appeared to originate from the activation of pyramidal slip by torsion originating from the rotation of the shoulder of the FSW tool. The friction-stir-welded joint exhibited a lower strength than the base material and finally fractured along the paths through which the rim of the probe of the FSW tool had passed. These results clearly indicate that the fracture behavior of the friction-stir-welded Mg alloy was dominated by geometric softening in the SAZ.