Underwater friction stir welding of AA2017 aluminum: investigation of microstructure and corrosion performance analysis

Aluminum alloy, AA2017 plates were butt welded using underwater friction stir welding (UFSW) with optimized combinations of welding velocities, tool rotational speeds and forging loads. The effect of the process parameters on the microstructure and corrosion properties of UFSW of AA2017 are studied through potentiodynamic polarization, open circuit potential (OCP) monitoring. A digital microscope and scanning electron microscopy (SEM) were utilized for characterizing the morphology of the different zones of welded joint such as stir zone (SZ) and heat affected zone (HAZ) before and after corrosion. The results reveal that welding parameters critically influence the microstructure and corrosion behavior of underwater friction stir welding (UFSW) joints in AA2017 aluminum alloy. Optimal conditions (1000 rpm rotational speed, 20 mm/min welding speed, 5776 N axial force, 0 mm tool offset) produced a defect-free stir zone with fine grains, achieving a corrosion rate of 0.085 mpy and superior resistance in electrochemical tests. Deviations in tool alignment or extreme parameters caused defects like porosity and grain coarsening, increasing corrosion and surface roughness. Precise parameter control is essential for enhancing the durability and corrosion performance of UFSW joints, highlighting their potential for marine applications in harsh environments.