The effect of residual S²⁻ and Cl⁻ on the corrosion and mechanical property of resistance spot welded joints in rocket storage tank

After conducting a compression test on rocket storage tanks, the presence of residual S²⁻ and Cl⁻ ions was detected in the remaining solution. These ions, when concentrated in areas prone to high residual concentrations such as weld seams, can cause corrosion. Therefore, this study focuses on the mechanical properties and corrosion behavior of resistance spot welded (RSW) joints in 2219 aluminum alloy storage tanks in a service environment with a mixed solution of 1 mg/L NaCl and 0.1 mg/L Na₂S. The results indicate that the joint exhibits a tight mechanical bonding wires, with the fusion zone being isolated from the external environment, making it difficult for the corrosive solution to penetrate. However, some pitting corrosion is observed in the base metal and the heat affected zone. The corrosion products mainly consist of Al₂O₃ and AlCl₃. The S²⁻ ions are released in the form of H₂S after hydrolysis. Comparing the mechanical properties of the joints before and after 60 days of immersion, no significant loss in mechanical performance is observed. The joint fractures exhibit a combination of brittle and ductile fracture modes. The presence of S²⁻ and Cl⁻ ions does not affect the safe operation of the rocket propellant tanks.