Improving joint performance of friction stir welded AZ31/ AM60 dissimilar Mg alloys by double-sided welding

Abstract

Two types of welding processes，with double-side friction stir welding (DS-FSW) and single-side friction stir welding (SS-FSW)，were used for dissimilar welding between AM60 and AZ31 Mg alloys in this study. The evolution of texture and microstructure, deformation behavior and mechanical properties of both joints were investigated. The microstructure observation indicated that the microstructure of the joint nugget zone (NZ) under both processes was refined after welding and their grain size was relatively close. The two joints exhibited approximately symmetrical local strong texture distribution characteristics from the advancing side to the retreating side. However, the DS-FSW joint had a larger processing volume and a symmetrical macroscopic weld structure. Due to the symmetry distribution characteristics of texture in NZ, the Schmidt factors for basal slip of the joints from the vicinity of the NZ side to the NZ center showed a decreasing trend, resulting in severe strain localization in both DS-FSW and SS-FSW joints during the tensile process. The tensile tests revealed that the DS-FSW joint exhibited excellent mechanical.properties compared with the SS-FSW joint. This was attributed to its large processing volume, lower volume proportion of the stirring zone and symmetrically distributed weld zone structure improved the deformation coordination of the joint, thereby delaying its premature fracture and exhibiting better mechanical properties.