Texture and morphology development in zinc-cobalt electrodeposition

The morphology and texture formation in zinc-cobalt coatings electrodeposited onto low carbon steel substrate in an acidic sulphate bath was studied. A non-fibre {11.0} prism was the predominant texture component of the coating at low current density, while, at higher current density, a (00.2) fibre component dominated. A strong adsorption of cobalt and/or some cobalt containing species onto the growing surface of the deposit at low current density was the reason for promoting a 'Field-oriented texture' type of growth, which resulted in a coating morphology consisting of numerous fibres grown almost normal to the substrate surface. At higher overpotentials, the adsorption of the mentioned species was hindered. This led to the progress of lateral growth and development of a (00.2) fibre texture, which resulted in the platelets morphology. Further increasing the current density resulted in numerous needle shape crystallites, which were dispersed on top of the thin platelets which resulted a low angle pyramidal {11.5} texture component, in addition to that (00.2) fibre texture component.