Refill friction stir spot welding of AZ31 magnesium alloy sheets: metallurgical features, microstructure, texture and mechanical properties

Abstract

In the present study, 1 mm-thick AZ31 magnesium alloy sheets were joined by refill friction stir spot welding. The metallurgical features, microstructure, texture and mechanical response of the spot-welded joints were investigated. The effect of welding parameters on the joint performance was comparatively evaluated in terms of the metallurgical features. The results revealed that the highest lap shear strength was achieved by using a rotational speed of 1500 rpm and a plunge depth of 1.4 mm. A fine-grain structure was further observed in the stir zone and the grain size decreased with the lowering of rotational speed and plunge depth. The c-axes of individual grains were parallel with the normal direction in the spot-weld center and gradually inclined toward the transverse direction with the measured location changing from spot-weld center to shoulder outer edge. Furthermore, a remarkable strain localization was observed in the spot weld during tensile deformation. The underline mechanism was discussed based on the initiation and subsequent transfer behaviors of predominate deformation mechanisms in the specific side area of the spot weld.