Experimental investigation of the impact of aqueous salinity on the performance of underwater friction stir welding

This work presents an experimental study on the influence of water salinity on the mechanical and microstructural performance of underwater friction stir welded (UWFSW) joints produced on 6082-T6 aluminum alloy. Three salinity levels were evaluated: 8 g/L (MB), 20 g/L (MM), and 58 g/L (MR) of NaCl in water. Mechanical tests (tensile, hardness, and impact toughness) and microstructural analyses were carried out to assess the effect of salinity on weld quality. The results show that increasing salinity leads to a progressive deterioration of the mechanical properties, notably a reduction in tensile strength, ductility, and fracture energy. At the microstructural level, higher NaCl concentrations promote the formation of coarse grains, secondary phases, and internal defects associated with localized corrosion. The heat-affected zone (HAZ) is particularly sensitive to these variations, exhibiting more unstable hardness profiles at high salinity.