Microstructural engineering of ZnCr coating by incorporation of graphene oxide and its effect on the corrosion behaviour of the coating

In this report, the effect of different amounts of graphene oxide on the corrosion properties and microstructural engineering of ZnCr composite coatings were investigated and correlated. Electrodeposition of ZnCr-graphene oxide (ZnCr-GO) composite coatings was conducted over mild steel substrate using electrolyte baths with different concentrations of dispersed graphene oxide. Incorporation of GO produced relatively more compact, finer and fibrous morphology in the case of ZnCr-GO coatings whereas the ZnCr coating exhibited rougher nodular morphology. Microstructure of the ZnCr coating contained randomly distributed highly Zn and Cr-rich phases whereas, the incorporation of graphene oxide led to evolution of a layered microstructure containing Zn and Cr rich phase layers stacked over each other perpendicular to the coating growth direction. Corrosion properties measured using the potentio-dynamic polarization and impedance spectroscopy methods revealed that both for 1 h and 48 h exposure times, composite coatings were more corrosion resistance than the ZnCr coatings and the corrosion resistance substantially increased with GO content increase in the coatings. Corrosion resistance increase was attributed to the formation of compact morphology, evolution of layered Zn-Cr microstructure which can provide two stage protection involving sacrificial dissolution of Zn and formation of protective Cr-oxide layer in addition to the impermeability of the GO to the passage of the corrosive media.