Electrochemical evaluation of corrosion behavior and product characterization of Zn–Mg–Al alloy-coated steels in a laboratory-simulated full immersion marine environment

Extensive research has been dedicated to enhancing the corrosion resistance of conventional hot-dip galvanized steel sheets for marine applications. However, the dynamic conditions in marine environments can significantly compromise the protective performance of zinc-based coatings. This study systematically investigates the corrosion behaviors of Zn- and Zn–Mg–Al (ZMA) alloy-coated steels in a continuously flowing marine environment. To this end, immersion tests were conducted on both Zn and ZMA alloy coatings under various immersion times, while focusing on the formation process and microstructure of the corrosion products. Both Zn and ZMA coatings produced similar corrosion products, but their corrosion rates differed significantly. This difference was governed by the kinetics of product formation and the relative amounts of ZnO generated formed as the corrosion product, which was affected by the addition of Mg into the alloy coating. The Mg^{2 +} ions generated from the preferential dissolution of MgZn₂ stabilized the simonkolleite (Zn₅(OH)₈Cl₂·H₂O) phase, increasing the density of the corrosion product layer. In addition, the presence of Mg²⁺ ions suppressed carbonate formation, inhibiting the transformation of dense corrosion products, such as simonkolleite, into more porous structures such as ZnO and hydrozincite (Zn₅(CO₃)₂(OH)₆). These findings demonstrate that Mg addition markedly enhances the long-term corrosion resistance of ZMA alloy coatings, confirming their potential for marine applications.