Effect of P Content on the Corrosion Behavior of Electrodeposited Fe-P Coatings

Abstract

Eco-friendly Fe-P coatings containing different P contents up to 20 wt% were electrodeposited on pure copper substrate. Scanning electron microscopy (SEM), grazing incident X-ray diffraction (GIXRD), microhardness, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization tests were used to investigate the effect of P content on the microstructure and corrosion behavior of the coatings in 3.5 wt% NaCl solution. Results showed that the surface becomes smoother with increasing the P content and superficial microcracks form at 20 wt% P. Coatings containing 5 and 10 wt% P showed a nanocrystalline microstructure, while a fully amorphous microstructure obtained at higher P contents. The best corrosion resistance was seen for the coatings containing 10 and 15 wt% P, which was related to their microstructure and smooth surfaces. Defect-free Fe-P coatings can increase the corrosion resistance of the copper and have the ability to protect the substrate through galvanic effect in which the coating acts as the anode. The coating hardness revealed an inverse Hall-Petch relationship so that the hardness of the coating decreased with decreasing the crystallite size of the deposit.