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

The current study was aimed to investigate anti-corrosion performance of multi-layer polymeric coatings applied on 6005A and 6082 aluminum alloys under influences of monsoon tropical climate in Thailand. The coated samples representing the material used for a vehicle body of high-speed train were exposed to actual atmosphere of urban (Bangkok City) and marine (Songkhla City) environments. The maximum duration of the continuous exposure test was 18 months. After completion of exposure test, the physical deterioration characteristics of coatings was examined with the aid of scanning electron microscopy (SEM). Electrochemical impedance spectroscopy (EIS) was conducted in 3.5 wt.% NaCl solution at 25C to evaluate the anti-corrosion coating performance after different exposure periods in atmospheric environments. Based on EIS results, the low-frequency impedance of the exposed coatings was higher than 109 cm2, meaning that the anti-corrosion coating could sufficiently protect the alloys against atmospheric corrosion attacks. However, the gradual degradation of anti-corrosion coating was also noted, particularly, when exposed at marine-coastal environment. The quantitative estimation results indicated that the anti-corrosion coating used in the current research could last for approximately 8 and 11 years when exposed in marine-coastal and urban environments, respectively.