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

## TL;DR

This study shows how adjusting Zn2⁺ concentration in a coating process can significantly improve the corrosion resistance of magnesium-lithium alloys.

## Contribution

The novel contribution is demonstrating that a 12 g/L Zn2⁺ concentration optimizes ceramic coatings for Mg-Li alloys, enhancing corrosion protection.

## Key findings

- A Zn2⁺ concentration of 12 g/L produced a ZnF2-rich coating with isolated pores and high densification.
- The optimal coating achieved a corrosion current density of 4.42 × 10⁻⁸ A/cm² and polarization resistance of 8.5 × 10⁵ Ω·cm².
- Long-term immersion tests confirmed the durability of Zn12 coatings with minimal mass loss.

## Abstract

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.