Deterioration mechanism of overlaid heavy-duty paint and thermal spray coatings on carbon steel plates in marine atmospheric environments

Thermal spray coatings, such as Zn, Zn-15Al, Al, and Al-5Mg, combined with heavy-duty paint, are increasingly used to enhance the corrosion resistance of steel structures. However, the overlaid areas of these coatings, particularly in damaged regions, can become weak points for corrosion initiation. To investigate the deterioration mechanisms at the overlaid zones of heavy-duty paint and thermal spray coatings on carbon steel plates, this study designed atmospheric exposure experiments and employed 3D scanning, electrochemical testing, and scanning electron microscope (SEM) - energy-dispersive X-ray spectrometer (EDX) analysis to systematically assess the degradation of the overlaid coatings in marine atmospheric environments. The results indicate that electrochemical reactions at coating defects drive the blistering and delamination of the overlaid coatings. Zn-based coatings, which provide sacrificial protection, exhibit slower failure progression compared to Al-based coatings, which show blistering due to passivation film formation. These findings provide valuable insights for optimizing thermal spray selection and overlaid coating strategies in marine atmospheric environments.