Corrosion Resistance Mechanisms in Zinc-Coated Steels

Zinc-coated steels find widespread use in automotive, construction and infrastructure due to their cost-effective and durable corrosion protection. The primary mechanism relies on the redox hierarchy between zinc and iron: zinc preferentially corrodes, serving as a sacrificial anode that protects the steel substrate even when the coating is damaged. This galvanic protection combines with barrier effects provided by the intact zinc layer and its corrosion products. Initial exposure to chloride or atmospheric moisture leads to the formation of zinc hydroxides and carbonates, which transform into more stable, adherent layers such as zinc oxide or zinc hydroxychloride. These layers inhibit further ion transport, slowing corrosion. Alloying elements in the coating bath—such as aluminium, magnesium or antimony—modify the microstructure and phase composition, tailoring the distribution and kinetics of intermetallic phases (e.g. MgZn₂, FeZn₁₃) that influence local electrochemical activity. The formation of an inhibition layer at the steel–zinc interface, often composed of Fe₂Al₅–ₓZnₓ, further regulates diffusion of iron and zinc ions. Advanced galvannealing processes refine coating crystallinity and grain size, improving ductility and reducing microcracking. Modern thermal spray techniques produce aluminium–zinc pseudo-alloys that generate compact, protective phases under prolonged saline exposure. Overall, the synergy between sacrificial corrosion, passivating corrosion products and controlled microstructure underpins the longevity of zinc coatings in aggressive environments.

Research from Nature Portfolio

Recent studies have probed the corrosion kinetics of arc-sprayed aluminium–zinc pseudo-alloys on steel in saline environments, revealing that protective Simonkolleite (Zn₅(OH)₈Cl₂·H₂O) forms after extended immersion, resulting in a compact, adherent film that reduces roughness and impedes ion transport. Electrochemical impedance spectroscopy and open-circuit potential measurements illustrate that the evolving film significantly increases charge-transfer resistance over time. Complementary morphological analyses via field-emission scanning electron microscopy and atomic force microscopy confirm the densification of corrosion products, explaining enhanced corrosion resistance during prolonged exposure to 3.5 wt % NaCl.

Corrosion Resistance Mechanisms in Zinc-Coated Steels publication trend

The graph below shows the total number of articles in corrosion resistance mechanisms in zinc-coated steels across all publications each year (not limited to Nature Index journals).

Technical terms

Galvanic protection: Corrosion prevention by using a more anodic metal (zinc) to protect a less anodic substrate (steel).

Inhibition layer: A reaction zone at the steel–coating interface, typically composed of intermetallic compounds, that regulates ion diffusion.

Eutectic: A mixture of phases solidifying simultaneously at a specific composition and temperature, influencing coating microstructure.

Intermetallic compound: A distinct, ordered phase formed between two or more metals with specific stoichiometry and crystal structure.

Simonkolleite: A zinc hydroxychloride corrosion product (Zn₅(OH)₈Cl₂·H₂O) that forms adherent films enhancing corrosion resistance.

References

1. Corrosion mechanism and kinetics of Al-Zn coating deposited by arc thermal spraying process in saline solution at prolong exposure periods. Scientific Reports (2019).
2. Effect of antimony additions on the microstructure and performance of Zn–Mg–Al alloy coatings. npj Materials Degradation (2024).
3. Towards a dependable TEM characterization of hot-dip galvanized steels with low and high Si content. Materials & Design (2023).
4. The effect of grain refinement on the deformation and cracking resistance in Zn–Al–Mg coatings. Materials Science and Engineering A (2022).