Effects of iron ion contents on composition, morphology, structure and properties of chromium coatings electrodeposited from novel trivalent chromium sulphate electrolyte

Chromium coatings were electrodeposited from a novel trivalent chromium sulphate electrolyte using oxalate as the complexing agent. Energy dispersive spectroscopy, Scanning electron microscopy, X-ray diffraction, Tafel curve, and X-ray photoelectron spectroscopy techniques were used to characterise the compositions, surface morphologies, structures, corrosion resistances, and element chemical states of the coatings. The effects of Fe2+ ions were investigated in detail. Results show that the small amount of iron ions generated coatings containing iron. The coating obtained is actually a Cr–Fe alloy of solid solution structure and microcrack surface morphology. X-ray photoelectron spectroscopy study revealed that a thin Cr(III) oxide film was formed on the surface of the coatings, and Cr(s) and Fe(s) states were observed within the coatings. As Fe2+ ion contents were increased in the electrolyte, the iron content of the coatings significantly increased. The electrodeposited coatings exhibited a crack-free surface morphology when Fe weight content exceeded 30·1%. The coating with 26·3 wt-%Fe had an amorphous structure and the lowest electrochemical activity.