Characterization and Corrosion Protection Properties of Electrodeposited Zn-Ni-Mn Coatings

Metal structures degrade significantly due to corrosion during their different uses, where significant amounts of aggressive ions are present. Therefore, anodic metals such as Ni, Mn, and Zn are used as protective agents. In this work, uniform, adherent and corrosion-resistant Zn-Ni-Mn coatings have been prepared by electrodeposition on a Cu substrate from a sulfate bath at room temperature. The effect of Mn2+ ions concentration, [Mn2+], in the bath on the as-prepared samples has been investigated. The nucleation process influenced by the [Mn2+] and applied deposition potentials, E, has been investigated according to the typical nucleation model of Scharifker and Hills (S-H). The analysis results show that both [Mn2+] and E have a significant impact on the nucleation mode of Zn-Ni-Mn coatings. The EDX analysis shows that the codeposition behavior can be described as anomalous with Zn as the major element. The SEM analyses indicate that the electrodeposited coatings exhibit a compact and dense morphology with good uniformity, no cracks, and pyramidal-shaped particles with the particle's size is Mn content dependent. The XRD investigation shows the coexistence of eta-Zn and NiZn3 phases known to contribute in improving the corrosion resistance of Zn-Ni-Mn coatings. Linear polarization plots and electrochemical impedance spectroscopy (EIS) techniques indicate that the optimal sample (Zn-55.7-Ni-37.7-Mn-1.6) presents a high corrosion resistance. This is due, according to the XRD and SEM results to the formation of a protective layer during the corrosion process composed of Zn-5(OH)(8)Cl-2 and ZnMn2O4 phases which prevents the progression of corrosion.