Electrodeposition of Zn–Mn alloys on steel from acidic Zn–Mn chloride solutions

Abstract The potentiostatic electrodeposition of zinc–manganese alloys on steel from MnCl 2 and ZnCl 2 solutions, was studied in an aqueous KCl+H 3 BO 3 matrix. Cyclic voltammetry was used to determine the potential ranges where the redox processes of interest were taking place. The obtained Zn and Mn containing films were investigated by means of scanning electron microscopy, energy dispersive X-ray spectrometry and X-ray diffraction. The effects of potential deposition and stirring were studied. At E =−1.65 V/SCE without stirring, it proved possible to obtain Zn–Mn deposits constituted of a single e phase, with approximately 13 at.% Mn. Decreasing the potential or agitating the electrolyte reduced the Mn proportion in the films. At 10.3 at.% Mn, the film obtained is composed of HCP Zn–Mn e and monoclinic ζ (MnZn 13 ) phases. At 3.4% Mn, the film consists of three phases, Zn along with the two previous Zn–Mn phases. All films have a cauliflower morphology and appear to be compact and homogeneous except for the films with the largest Mn contents (at.% Mn>11) where columnar deposits are obtained. Polyethylene glycol was tested as a potential additive. Its main effects were a decrease in the Mn content and inhibition of the ζ phase formation.