Magnesium and its alloys are attractive structural materials due to their low density, high specific strength, and good castability and machinability, enabling their widespread use in transportation, aerospace, and biomedical applications. However, magnesium is highly reactive and therefore prone to rapid corrosion, which limits the durability and service life of magnesium-based components. Corrosion can occur through several mechanisms, including general, crevice, and microbiologically influenced corrosion. Environmentally acceptable inhibitors such as carbonates and cerium-based compounds are promising for slowing magnesium degradation, but further development is still needed.

In this work, a sustainable multilayer coating system was developed to improve magnesium corrosion resistance. A hydrothermally synthesised cerium carbonate hydroxide (CeCO₃OH) base layer was first applied, acting as a protective and pH-buffering passivation layer. To enhance adhesion and connectivity between layers, sodium dodecylbenzene sulfonate (SDBS) was introduced as an interfacial modifier. Finally, a biopolymer epoxy topcoat was applied to provide an additional physical barrier against electrolyte penetration. The optimal SDBS concentration was 0.05 M, facilitating the strongest interaction between the layered hydroxide and epoxy topcoat.

Scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), and X-ray diffraction (XRD) confirmed a highly crystalline CeCO₃OH layer with high cerium content. Corrosion performance was evaluated using potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) in 3.5 wt % NaCl over a wide pH range (2–10). The best coating system (Mg/LH/S_0.05/T) showed excellent protection, with a very low corrosion current of 5.2 nA and a corrosion potential of −1.58 V. Strong corrosion resistance was maintained across pH 2.0 (5.5 nA) to pH 10.0 (2.0 nA). EIS results showed significantly increased impedance, low capacitance (4.5 × 10⁻¹¹ F), and polarisation resistance of 3.6 × 10⁵ Ω. The coating remained stable for up to 40 days, with gradual loss of protection observed after 40–50 days of immersion.