Striking the balance: strength, ductility, and durability in double-sided friction stir welded AA7075-T6 plates

This study investigates the double-sided friction stir welding (DS-FSW) of 16 mm thick AA7075-T6 aluminum alloy plates, focusing on the effect of tool rotational speed (600, 700, and 800 rpm) on thermal behavior, microstructural evolution, mechanical properties, and corrosion resistance. Numerical temperature analysis confirmed that peak temperatures below the alloy’s melting point, validating the solid-state nature of the process. Electron backscatter diffraction (EBSD) revealed pronounced grain refinement and dynamic recrystallization at 700 rpm, producing fine equiaxed grains with a high fraction of high-angle grain boundaries. At 800 rpm, excessive heat input led to grain coarsening and surface cracking, although it yielded the highest flexural strength (∼950 MPa) and ductility (∼5%). Electrochemical analysis demonstrated superior corrosion resistance at 700 rpm, attributed to enhanced passivation. Hardness profiles showed mid-thickness softening associated with the unwelded interface. Scanning electron microscopy (SEM) further corroborated structural and corrosion trends. Overall, DS-FSW at 700–800 rpm offers a promising combination of strength, corrosion resistance, and structural integrity for aerospace applications.