Time-dependent evolution and protective mechanism of hot-dip Zn-based coatings on VW84 rare-earth magnesium alloys

Poor corrosion and wear resistance of magnesium alloys remains a major barrier to their widespread industrial application, and developing low-cost and efficient protective coatings is of great practical significance. In this study, a conventional steel hot-dip galvanizing process was innovatively adapted to VW84 rare-earth magnesium alloys, achieving an Zn-based coating with tunable thickness and strong metallurgical bonding. The results demonstrated that the coating exhibited a multilayer structure comprising an outer Zn-rich alloy layer, a transition zone, and an inner diffusion layer with Mg–Zn intermetallics. By adjusting the immersion time, the coating evolution and protection efficiency were precisely tuned. The 10 min coating achieved the compact and uniform morphology, which displayed excellent wear resistance, with material loss (0.55 mm 3 ) nearly 6.9 times smaller than the substrate (3.76 mm 3 ). Moreover, the 10 min coating exhibited the lowest corrosion current density and highest low-frequency impedance, with a corrosion rate 22.5 times lower than the substrate alloy in 3.5 wt% NaCl solution. And it maintained long-term stability without delamination in 5 wt% salt spray testing. The superior corrosion resistance of the coating is attributed to its compact multilayer structure and the dense accumulation of corrosion products that effectively hinder further electrolyte penetration.