Experimental and theoretical investigation of alkylphosphonic acids as corrosion inhibitors for 3003 aluminum alloy in ethylene glycol aqueous solution

Background The corrosion resistance of 3003 aluminum alloy in glycol-based electrolytes is critical for long-term applications. Alkylphosphonic acids (APAs) are potential inhibitors due to strong self-assembled ability. But how the alkyl chain length influences adsorption behavior, film integrity, and inhibition performance in ethylene glycol aqueous solution (EGAS) on 3003 alloy remains unclear. Method Quantum chemical calculations, potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), contact angle test and weight loss (WL) were used. Significant findings PDP, EIS and WL results show that DDPA is a mixed-type inhibitor with predominant anodic inhibition, and the highest corrosion inhibition efficiency is 84.86% at 1.2 g/L. XPS confirms DDPA bonds to the alloy surface via O atoms in the –PO(OH)₂ group, mainly through bidentate and tridentate coordination. Quantum calculations and contact-angle measurements indicate DDPA benefits from hydrophobicity and spatial packing capability of long alkyl chain, resulting the strongest binding affinity on Al(111) and Al₂O₃(111) surfaces with binding energy at 2.998 and 2.979 eV in EGAS. These findings guide corrosion-resistant coolant system design, enhancing the service reliability of 3003 aluminum alloy.