Preparation and corrosion resistance mechanism of chromium-free Zn–Al+CeO2 composite coatings

Abstract

This study aims to fabricate chromium-free Zn–Al + CeO2 composite coatings by integrating CeO2 nanoparticles into the chromium-free Zn–Al coating solution as a strengthening agent and subsequently applying a wet coating method. The corrosion resistance of the coatings was evaluated through NaCl immersion corrosion tests. The microscopic morphology, composition and electrochemical properties of the composite coatings before and after corrosion were analyzed using SEM and an electrochemical workstation. The corrosion resistance mechanism of the coatings was investigated as well. The results revealed that the CeO2 nanoparticles were uniformly distributed on the surface of the composite coating and in the gaps between Zn and Al powders, forming micron-sized particles due to the surface energy effect. The composite coating exhibited a minimum corrosion current density of 0.63 μA cm−2 and a maximum corrosion electrochemical reaction resistance of 35321 Ω cm2. Additionally, a complex precipitate formed by the reaction of certain Ce elements in the composite coating enhanced the cathodic protection of the coating. Moreover, Ce3+ reacted with the OH− generated by microelectrochemical corrosion, resulting in the formation of a precipitate that filled in the gaps between Zn and Al powders. Consequently, this process contributed to the formation of a microporous and flocculent coating structure. In conclusion, the incorporation of CeO2 nanoparticles had a favorable impact on the production of environmentally friendly and corrosion-resistant chromium-free Zn–Al coatings.