Enhanced Corrosion Performance of Epoxy Coatings Painted on ZnAlMg-LDH Conversion Film Vertically Grown on ZAM Steels from Sodium Carbonate Solution

Zinc-aluminum-magnesium (ZAM) steel, with its superior corrosion resistance and mechanical properties, is progressively supplanting traditional galvanized steel and zinc-aluminum steel. In this study, a solution containing sodium carbonate-only was employed as the treatment medium to form a vertically grown layered double hydroxide (LDH) pretreatment layer on the surface of ZAM steel via a simple immersion process at 50 °C. The temperature and salt solution not only provide the conditions for the dissolution of metal ions but also facilitate the formation of LDH products. The resulting LDH pretreatment layer exhibits excellent adhesion to the metal surface and enhances the adhesion of the top epoxy coatings. Furthermore, the "LDH/corrosion inhibitor/epoxy" coating system ensures ZAM steel remains rust-free in a 3.5 wt.% NaCl solution for a minimum of 120 days. This innovative approach offers a promising avenue for extending the durability and service life of ZAM steel in corrosive environments.