Enhanced corrosion resistance by SnCu-graphene oxide composite coatings

SnCu-graphene oxide composite coatings with different amount of graphene oxide (GO) content were electro-deposited over a mild steel substrate. Morphological, microstructural evolution and electrochemical properties of coatings were investigated as a function of GO content. All the coatings exhibited compact and crack free morphology. Structural characterization revealed the presence of Sn and Cu6Sn5 phase in all the coatings. Addition of GO considerably reduced the grain size of Sn phase while the Cu6Sn5 phase remained unaltered. GO altered the coating texture facilitating growth along the low index planes. Corrosion behaviour of the coatings was examined through potentiodynamic polarization and electrochemical impedance spectroscopy methods. An aspect of "optimum" GO amount for best corrosion resistance for the SnCu-GO composite coatings was witnessed. With the addition of GO, the corrosion rate initially decreased to a minimum value and then, upon further addition of GO, it increased to values much higher than the pristine coating. In the case of lower GO amounts, the textured growth coupled with inertness of GO increased the corrosion resistance whereas, at higher GO concentrations, the galvanic coupling between cathodic GO and anodic SnCu dominated, leading to lowering of the corrosion resistance.