Effects of Cl− and Acetic Acid Contents on the Corrosion Behavior of Al in SWAAT Environment

This study quantitatively investigates the corrosion behavior of aluminum (Al1070) under salt water acetic acid test (SWAAT) conditions, focusing on the effects of chloride ions (Cl−) and acetic acid (CH3COOH) concentration on the pitting corrosion. Potentiodynamic polarization tests showed that increasing Cl− concentration caused a negative shift in corrosion potential (Ecorr) and an increase in corrosion current density (icorr), indicating accelerated passive film breakdown and enhanced pitting susceptibility. Immersion tests and SEM analysis revealed intensified surface discoloration, oxide formation, and crack propagation at higher Cl− levels, confirming localized dissolution. The effect of acetic acid was evaluated for concentrations ranging from 0 to 2000 µL L−1. Higher acetic acid levels lowered solution pH and slightly increased Ecorr and elevated icorr while reducing ΔE(Epit − Ecorr), indicating increased localized corrosion susceptibility. SEM and 3D XCT analyses showed increased pit density, corrosion loss, and pitting showed temporary pit coalescence at intermediate concentrations. Mechanistically, the acidic SWAAT environment (pH 2.8–3.0) positions aluminum in the active corrosion region. Cl− destabilizes the passive oxide layer, initiating pitting, while acetic acid promotes metal dissolution via hydrogen evolution reactions. Their combined action exerts a specific effect, accelerating localized corrosion through chemical oxide layer degradation. These results provide quantitative insights into aluminum corrosion under SWAAT conditions. They could inform the design of corrosion resistant materials and reliability assessments in industrial applications.