Investigation on Microstructure and Mechanical Properties in the Dissimilar Joining of WE43 to AA7075 Alloy using FSW

This research investigates the alterations in microstructure, microhardness, and joint strength resulting from the dissimilar friction stir welding (FSW) of WE43 magnesium alloy to AA7075 aluminium alloy. The study specifically analyses the role of FSW process parameters in the formation of intermetallic compounds (IMCs), the evolution of grain structure, the resultant microhardness distribution across the weld zone, and the joint tensile strength. A comprehensive microstructural characterization was performed utilizing optical microscopy (OM), field emission scanning electron microscopy with energy-dispersive X-ray spectroscopy (FESEM-EDS), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD). These analyses confirmed significant refinement of grain in the stir zone and the identification of various IMCs at the weld interface. Microhardness mapping indicated a gradient profile, with the weld nugget exhibiting superior hardness attributed to its dynamically recrystallized, fine-grained microstructure. Crucially, the low-heat input FSW (LFSW) variant yielded a substantial increase in the average microhardness, reaching 126 HV within the stir zone (SZ), due to grain refinement caused by severe plastic deformation. This configuration achieved a joint efficiency of approximately 68.7% relative to the WE43 base material. The enhancement in mechanical performance is directly linked to a modified joint preparation strategy that successfully suppressed the formation of brittle AlMg IMCs, instead fostering the creation of harder MgZn, Al2CuMg, and AlMgZn compounds. These findings underscore the efficacy of the LFSW technique in fabricating dissimilar WE43-AA7075 joints with favourable mechanical properties and a consistent microhardness profile. The process parameters are strategically selected to obtain better joint properties with the formation of defect-free joints