Md Saquib Bin Reyaz, Murshid Imam, Md Anwar Ali Anshari, Md Parwez Alam, Mani Thakur
Dissimilar aluminum joining, particularly for AA7075-T6 and AA6061-T6, is demanding in various lightweight applications, especially high-speed trains and storage tanks. Tungsten inert gas (TIG) welding is preferred due to its cost-effectiveness, portability, and fast applicability, but joining these alloys through TIG is always challenging due to melting and solidification-related issues. To overcome these issues, in this study, the TIG joint was post-processed via post-weld heat treatment (PWHT) and friction stir processing (FSP), and the results were compared to friction stir welding (FSW). A detailed investigation on microstructure, crystallographic texture, and mechanical properties was carried out for all the welded joints. Results showed that the coarse dendritic structures of the TIG weld (MGS: 46.01 ± 0.94 μm) were completely transformed into equiaxed fine grains after FSP (MGS: 3.34 ± 0.12 μm), while the PHWT moderately refined the grain structures. Electron backscatter diffraction (EBSD) revealed that the grain boundary transformations were maximum of 80.4% for the TIG + FSP joint as compared to other joints. Pole figures revealed strong B/B̅ and C shear textures for the TIG + FSP joint with a maximum pole density value of 8.002, while the TIG joint revealed weak and random textures with the minimum pole density value of 2.039. Phase analysis revealed four types of intermetallic phases: α-Al, η (MgZn 2 ), β (Mg 2 Si), and S (Al 2 CuMg) in the weld region for all types of joints, while the phase fragmentation was highest in the case of the TIG + FSP joint. The TIG + FSP joint exhibited the highest ultimate tensile strength (UTS) of 274 ± 6.2 MPa, elongation of 17.6 ± 0.52%, strain-hardening capacity of 0.47, and hardness of 124 ± 2.1 HV as compared to the rest of the joints. Fractography revealed that the TIG + FSP and FSW joints were featured by dimples and tear ridges with a ductile fracture mode, while TIG and TIG + PWHT joints were featured by cleavage facets, river marks, and macro-voids, yielding a brittle fracture mode. Overall, the TIG + FSP route achieved the finest grain structure, highest HAGB fraction, strongest shear texture, and superior mechanical performance among all processing routes investigated.