Anti-Corrosion Performance Evaluation of Polymeric Coatings Applied on Aluminum Alloys Exposed to Tropical Climate Influences of Thailand

This study investigated the anti-corrosion performance of multilayer polymeric coatings applied on 6005A and 6082 aluminum alloys under the influence of the monsoon tropical climate of Thailand. The coated samples, which represented the material used for the vehicle body of high-speed trains, were exposed to real atmospheric conditions of urban (Bangkok City) and marine (Songkhla City) environments. The maximum duration of the continuous exposure test was 18 months. After the exposure test, the physical deterioration characteristics of the coatings were examined with the aid of scanning electron microscopy (SEM) and a pull-off adhesion test. Electrochemical impedance spectroscopy (EIS) was performed in 3.5 wt% NaCl solution at 25 °C to evaluate the coatings’ anti-corrosion performance after various atmospheric exposure periods. Based on the EIS results, the low-frequency impedance of the exposed coatings remained above 109 Ω·cm2, indicating that the anti-corrosion coatings provided sufficient protection against atmospheric corrosion for the alloy. However, gradual degradation of the anti-corrosion coatings was observed, particularly in the marine-coastal environment. Quantitative estimation results suggested that the anti-corrosion coatings used in this study could provide service lives of approximately 8 and 11 years in marine-coastal and urban environments, respectively.