Ceria-embedded MAO process as pretreatment for corrosion protection of epoxy films applied on AZ31-magnesium alloy

We investigated the effect of cerium oxide (Ceria) nanoparticles existing in the external porous structure of microarc oxidation (MAO) coating on the protective behavior and adhesion strength of MAO/epoxy duplex coating implemented on AZ31 Mg alloy. MAO coating was considered as the pretreatment for applying the epoxy layer. The presence of ceria particles affected the morphology of the surface and cross-section of the MAO coating and its corrosion resistance. Embedding ceria nanoparticles in the external porous structure of the MAO layer showed that the MAO structure, in addition to its pretreatment role, acts as the container of ceria particles. The results of the electrochemical impedance spectroscopy (EIS) test on duplex coatings with and without defects and the pull-off test in dry and wet conditions revealed that the presence of ceria at an optimal concentration (3 g/l) improves the protective behavior of the epoxy layer and its adhesion strength. Moreover, ceria nanoparticles with the barrier effect and active protection improved the protective behavior of the dual-layered coating.