Electrodeposition of amorphous cobalt-manganese alloys on to steel from gluconate baths

Electrodeposition of codeposited Co-Mn alloys on to steel substrates was obtained from an acidic gluconate bath. The effects of several plating variables such as current density, bath composition, pH and temperature, on the potentiodynamic cathodic polarisation curves, cathodic current efficiency of the deposited alloy as well as on the alloy composition were investigated. The codeposition of Mn and Co from these electrolytes follows the normal type of deposition. The cathode current efficiency, f_Co-Mn%, of the alloy is relatively high (≫ 95%). The Mn percentage in the deposits increases with either decreasing current density or increasing [Mn²⁺]/[Co²⁺] concentration ratio in the bath. Anodic linear stripping voltammetry (ALSV) indicated that the ahoy might consist of a solid solution in which manganese is dissolved in cobalt. The Vickers microhardness of Co-Mn alloy electrodeposited from the present bath is higher than those of the parent metals. It is found that the Vickers microhardness values of the alloys are raised by decreasing pH or increasing current density. Increasing the electrolyte temperature greatly decreases the microhardness. These alloys were determined to be amorphous by X-ray diffraction analysis (XRD). Scanning electron microscopy (SEM) photomicrographs were obtained from the surfaces of selected deposits.