Influence of Zn2⁺ Concentration on Ceramic Coatings for Corrosion Protection of Magnesium-Lithium Alloys.

This study investigates the enhancement of corrosion resistance in magnesium-lithium alloys through plasma electrolytic oxidation (PEO) coatings incorporating ZnF2 via in situ synthesis. By adjusting Zn2⁺ concentrations (4-16 g/L) in a zirconium salt-based electrolyte, ceramic coatings with tailored ZnF2 content, thickness, and porosity were fabricated. The optimal Zn2⁺ concentration of 12 g/L yielded a ZnF2-rich coating with isolated pores and enhanced densification (inner layer resistance Ri = 3.01 × 104 Ω⋅cm2), achieving a corrosion current density (icorr) of 4.42 × 10-8 A/cm2 and polarization resistance (Rp) of 8.5 × 105 Ω⋅cm2, representing a 354-fold improvement over untreated LA103Z. Higher Zn2⁺ concentrations (16 g/L) induced interconnected pores and ZnO formation, degrading corrosion resistance. Long-term immersion (168 h in 3.5 wt% NaCl) confirmed the durability of Zn12 coatings (mass loss: 0.6 mg), while Zn4 and Zn16 coatings exhibited severe localized corrosion. The study demonstrates that balancing Zn2⁺ concentration optimizes ZnF2 passivation and pore isolation, offering a scalable strategy for Mg-Li alloy protection in corrosive environments.