Fine grained Mg-3Al-1Zn alloy with randomized texture in the double-sided friction stir welded joints

The improvement in mechanical properties of the AZ31B Mg joint was achieved through texture control by the double-sided friction stir welding technique. The co-direction and counter-direction rotations of the upper and lower tools were adopted for comparison. The results of the microstructure observations showed that, although the grain refinement occurred in both the conventional friction stir welded joint and double-sided friction stir welded joints, the more complex material flows caused mainly by the double tools provided by a randomization of the crystallographic texture in the entire stir zone of the double-sided friction stir welded joints. Additionally, the formation of the {10-12} twin in the double-sided friction stir welded joints was observed and it has a significant effect on the grain reorientation. The results of the tensile test indicated that the random crystallographic texture in the double-sided friction stir welded joints hindered the fracture of the stir zone with low elongation of 18% in the friction stir welded joint. Therefore, relatively higher elongations of 28% and 24% with similar tensile strengths as the friction stir welded joint were achieved in the double-sided friction stir welded joints.