Effect of cobalt ion concentration of electroplating solution on morphology, phase structure and corrosion resistance of Zinc-Cobalt alloy coatings

The effect of cobalt ion concentration of electroplating solution on morphology, phase structure and corrosion resistance of zinc-cobalt alloy electrodeposits that were obtained from Sulfate- acid solutions by direct current on St37 steel has been studied. SEM, EDS and XRD were used to study the surface morphology, chemical composition and phase structure of coatings. Respectively corrosion behavior of Zn-Co alloy coatings were studied by Tafel polarization experiment in 3.5 wt% NaCl solution. In addition the microhardness of the Zn-Co alloy coatings was examined. The results showed that increasing of cobalt ion content of electroplating solution, increases cobalt content as well as microhardnees of the coating. The cobalt ion in the plating bath strongly affects the chemical content and phase structure, as well as corrosion stability, of Zn-Co alloys. It was also noticed that corrosion resistance of the deposits were highly influenced by the composition and morphology of the coatings. Zn-Co alloy coatings containing 1.2 wt% Co showed the highest corrosion resistance due to its single phase.