Corrosion Behavior of Electrogalvanizied Coating and Zinc-Aluminum Coating in Cyclic Salt Spray Environment

Electro-galvanized coating and zinc-aluminum coating were prepared on the cold-rolled plate substrate, and a 42 d cyclic salt spray test was carried out. Scanning electron microscopy (SEM), XRD analysis and electrochemical tests were used to investigate the corrosion morphology, corrosion product composition and electrochemical behaviors of these coating samples after different periods of time of cyclic salt spray test. The results showed that the corrosion resistance of the zinc-aluminum coating was stronger than that of the electro-galvanized coating, and the electro-galvanized coating completely failed after 28 d cyclic salt spray test, and the zinc-aluminum coating did not fail after 42 d test. In the cyclic salt spray test environment, the common corrosion products of the two samples were ZnO, Zn₅(CO₃)₂(OH)₆, Zn₅(OH)₈Cl₂·H₂O and Fe₃O₄. The corrosion products of galvanized coating also contained Zn₄CO₃(OH)₆ and FeOOH, while the corrosion products of zinc-aluminum coating contained protective Al₂O₃.