Abstract <p>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 (<i>E</i>) on the nucleation mechanism were evaluated using the Scharifker and Hills (S–H) nucleation model. The results indicate that [Mn²⁺] and <i>E</i> 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 Ni_96.9Mn_1.5 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.</p>