Non-uniform deformation in a friction stir welded Mg–Al–Zn joint during stress fatigue

A friction stir welded (FSW) Mg–3Al–1Zn (AZ31) joint, prepared at a welding speed of 100 mm/min and a rotation rate of 800 rpm, was subjected to stress fatigue test. During fatigue deformation, while the specimen thickness shrank around the nugget zone (NZ)/thermomechanically-affected zone (TMAZ) boundary, it varied little in the NZ middle. Besides, the surface appearance differed between the two sides of a fatigued specimen. This non-uniform deformation was attributed to different grain orientation distributions and sheared material layers in various regions, which influenced the fatigue life and fracture behavior of the joint.