Effect of Fe and Co co-deposited separately with Zn-Ni by electrodeposition on ASTM A624 steel

A comparison between the Zn-Ni, Zn-Ni-Fe and Zn-Ni-Co coatings was performed in this study. The co-deposition process was obtained by electrodeposition on ASTM A624 steel using sulphate baths in acid media and low current density. The characterization of the coatings by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP OES), Energy Dispersive Spectroscopy (EDS), X-ray diffraction (XRD) and Anodic Linear Sweep Voltammetry (ALSV) allowed a detailed analysis of the phases formed and its amounts in the coatings, which enabled to verify the influence of the Fe and Co co-deposited separately with Zn/Ni. The co-deposits showed different characteristics in relation to the deposition efficiency and film thickness, in addition of the topography and surface roughness, which were measured by a confocal optical microscope and of the hardness determined by an ultra-microhardness tester. Finally, the corrosion tests analyzed by open circuit potential, potentiodynamic polarization and Electrochemical Impedance Spectroscopy (EIS) determined the corrosion characteristics of each co-deposit in saline solution. Results showed that Zn-Ni-Co was superior to the others co-deposits in relation to the deposit efficiency and corrosion protection, in contrast, the Zn-Ni-Fe coating showed uniformity and the greater compaction of the surface grains, resulting in lower roughness and higher hardness between the co-deposits studied.