Role of Metal Cations on Corrosion of Coated Steel Substrate in Model Aqueous Layer

To elucidate the role of Zn2+ on corrosion of coated steel, the effects of metal cations on the corrosion of carbon steel in the concentrated Cl- aqueous solutions were studied by immersion tests, surface analysis and electrochemical tests. Among the examined metal cations, Zn2+ showed the significant effect on corrosion inhibition of carbon steel in the Cl- aqueous solution at high concentration. XPS analysis results elucidated that Zn2+ can remain on the steel surface after immersed in the solutions with Zn2+. In addition, AFM results showed lower roughness of specimen immersed in the solution with Zn2+ than other solutions with metal cations. EIS measurements showed higher impedance in the solution with Zn2+ than other solutions, and the results suggested that Zn2+ reduced the defect points in the thin oxide film by forming a metal cation layer. Based on the experimental results, Zn2+ may form a layer on the oxide film that protects the Cl- attack in the solution. The findings demonstrated that the formation of Zn layer on the oxide film is one of the main reason for showing high and longtime corrosion resistance of Zn coated steel substrate.