Electrodeposition, Morphology, Composition, and Corrosion Performance of Zn-Mn Coatings from a Deep Eutectic Solvent

Abstract

Different Zn-Mn coatings were successfully electrodeposited on copper substrates from deep eutectic solvent-based electrolytes containing boric acid as an additive. The main objective of this work was to optimize the Zn/Mn ratios and morphologies of the as-electrodeposited Zn-Mn films in order to obtain better corrosion protection performance coatings. The electrodeposition behaviors of Zn-Mn alloys as studied by cyclic voltammetry showed that with increase in electrolyte Mn(II) concentration, Zn(II) ion reduction occurs at higher overpotentials while Mn reduction occurs at lower overpotentials, and this in turn enhances Mn incorporation into the deposit. Characterization results showed that the electrodeposition potential and electrolyte Mn(II) concentration significantly affects the Mn content, crystal structure, surface morphology, and corrosion performance of the deposits. With increase in electrodeposition potential and electrolyte Mn(II) concentration, the alloy Mn increased and the grain morphology was refined. The crystal structure of Zn-Mn deposits consists of Zn and hexagonal close packed e-phase Zn-Mn at low electrodeposition potentials and low electrolyte Mn(II) content. However, at high electrodeposition potentials and electrolyte Mn(II) contents, the crystal structure was only composed of hexagonal close packed e-phase Zn-Mn. Corrosion measurements show that all the Zn-Mn samples have a passivating behavior and exhibits higher corrosion resistances when compared to those from aqueous solutions. Thus, optimum electrodeposition potential and electrolyte Mn(II) concentration were determined producing compact Zn-Mn films with the best corrosion resistance.