Atmospheric Corrosion Behavior of Arc Thermal-Sprayed Zn–30mass%Al and Zn Coatings Under Different Airborne Salt Environments

Abstract Atmospheric exposure tests were conducted to evaluate the long-term corrosion behavior of Zn–30mass%Al thermal-sprayed coatings, Zn thermal-sprayed coatings, and hot-dip galvanized Zn coatings under different airborne salt environmental conditions, and an accelerated outdoor exposure test using artificial seawater was additionally carried out. The corrosion characteristics of each coating were assessed through surface appearance observation, coating thickness measurements, XRD patterns, and cross-sectional analysis using scanning electron microscopy and energy-dispersive X-ray spectroscopy. As a result, corrosion products were observed in all coatings, with distinct differences in their morphology and progression depending on coating composition and thickness. The Zn–30mass%Al thermal-sprayed coating exhibited negligible thickness reduction (< 5%) and no significant microstructural degradation, even under severe airborne salt conditions, demonstrating superior long-term corrosion resistance. In the case of Zn thermal-sprayed coatings, an oxide layer formed in environments subject to severe corrosion. Furthermore, the thinner the coating, the thicker the oxide layer formed, and more defects and voids were observed within the coating. A continuous decrease in the thickness of the hot-dip galvanized coating was observed at both test sites. It is believed that, because the coating surface is smooth, the oxide layer is easily removed by factors such as rainfall. The findings highlight the importance of coating composition and thickness in enhancing the durability of zinc-based protective coatings in airborne salt environments.