Effect of Manganese Content on the Electrodeposition and Corrosion Protection Properties of Ni–Mn Coatings

This study explores the electrodeposition of Ni–Mn coatings on a copper substrate using a sulfate bath with varying Mn2+ ions concentration ([Mn2+] = 0.05, 0.1, 0.2, and 0.4 M). The effects of [Mn2+] and applied potential (E) on the nucleation mechanism were evaluated using the Scharifker and Hills (S–H) nucleation model. The results indicate that [Mn2+] and E significantly influence the electrochemical behavior of Ni–Mn coatings. The energy dispersive X-ray (EDX) examination confirmed the presence of Ni, Mn and S species in the coatings. Scanning electron microscopy (SEM) micrographs revealed the cauliflower-like morphology, globular shape particles and porous cracked surface. XRD analysis reveals the successful incorporation of Mn atoms into the Ni lattice, resulting in the formation of a face-centered cubic (FCC) substitutional Ni(Mn) solid solution. The linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) analyses demonstrate that the incorporation of a small amount of Mn into Ni significantly improved the corrosion resistance. The obtained Ni96.9Mn1.5 coating shows the highest corrosion resistance. SEM and XRD analyses of the oxide layer confirmed the formation of a porous, non-uniform microstructure composed of MnO2 and Ni(OH)Cl which contributes to the protective properties of the coating.