Electrodeposition and Characterization of Fe-P Coating Applied onto Mild Steel Substrate

An optimized acidic bath containing glycine as the complexing agent was used to successfully electrodeposit defect-free and eco-friendly Fe-P coatings with a P content of 13 wt.% onto a St 12 steel substrate. The microstructure, morphology, and corrosion behavior of the coating in a 3.5 wt.% NaCl solution were investigated using scanning electron microscopy (SEM), grazing incident X-ray diffraction (GIXRD), X-ray diffraction (XRD), microhardness, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization tests. The surface of the coating exhibited nodular features without any cracks or defects, and the interface between the coating and the substrate was perfect. The coating showed a nanocrystalline microstructure with the crystallite size of 1.6 nm. The coating was found to enhance the corrosion resistance of the substrate by reducing the corrosion current density (icorr) from 1.8 x 10-5 to 8 x 10-6. This improvement was attributed to the presence of an amorphous iron phosphate hydrate (Fe3(PO4)2 center dot 8H2O) superficial layer on the surface of the coating. Additionally, the coating exhibited higher microhardness (576 +/- 25 HV) compared to the substrate (140 +/- 1 HV).