Improving tensile strength, impact toughness and wear resistance of TIG welded dissimilar AA7075-T6/AA6061-T6 joints through friction stir processing

Excellent strength and corrosion resistance make dissimilar AA6061-T6/AA7075-T6 aluminium welding a popular choice in the aviation and automobile industries. Fusion welding may lead to defects like voids, thermal cracks, residual stresses, and coarse grains, which can affect the integrity of the joints. To address these problems, friction stir processing (FSP) was commonly employed to increase the microstructural and mechanical features. This study examined the influence of tool spindle speeds on tungsten inert gas (TIG) welded joints, as well as the microstructural features and their relationship to tensile strength, impact toughness, and wear resistance. As the spindle speed of the tool increased, the dendritic coarse grain structure of TIG-welded joints in the fusion area transformed into equiaxed ultrafine structures in the stir region. For the TIG + FSP welded sample at 1300 rpm, the average grain size decreased by 83.10% and the tensile strength and impact toughness increased by 74.84 and 88.89%, respectively, while the wear rate decreased by 46.87%. The TIG + FSP joint had a high tensile strength of 278 MPa, a good impact toughness of 17 J, and a low wear rate of 86 µm at a tool spindle speed of 1300 rpm, while the TIG welded joint had a lower tensile strength of 159 MPa, an impact toughness of 9 J, and a higher wear rate of 132 µm. The tensile fractured surface of TIG joints showed rough cleavage facets, coarse dimples with some voids, while the TIG + FSP joints showed a fine equiaxed dimples with no voids.