ENHANCED MECHANICAL PERFORMANCE AND REFINED INTERMETALLIC LAYER IN UNDERWATER FRICTION-STIR-WELDED AA5083–Cu DISSIMILAR JOINTS

This research investigates the underwater friction stir welding (UWFSW) of dissimilar AA5083 aluminum and pure-copper plates, aiming to enhance the mechanical performance through precise control of the process parameters and the suppression of excessive intermetallic compound (IMC) formation. The UWFSW was performed using a CNC vertical milling machine under full immersion to regulate the heat input and improve the joint’s integrity. The optimized parameters yielded a maximum tensile strength of 7.5 MPa, impact strength of 7.5 J, and peak microhardness of 111 VH, outperforming conventional dry FSW joints. Optical microscopy and SEM analyses revealed a defect-free joint with a fine equiaxed grain structure in the stir zone, minimal deformation in the parent zones, and a uniform IMC layer of 2–5-µm thickness along the Al–Cu interface. The underwater cooling effect restricted grain coarsening and prevented void formation, resulting in enhanced metallurgical bonding. The study confirms that UWFSW offers a superior route to producing high-strength, corrosion-resistant Al–Cu dissimilar joints, making it highly suitable for marine, cryogenic, and high-performance electrical applications.