Morphology and corrosion resistance of Zn-Co and Zn-Co-Fe alloy coatings

Cadmium (Cd) has been extensively used as an excellent corrosion protective coating for steel applications in aerospace, automotive, electrical and fasteners industries. However, Cd is banned due to its toxic nature and strict environmental regulations. In this study, the coating morphology and corrosion resistance of alternative, electrodeposited Zinc-cobalt (Zn-Co) and Zinc-cobalt-iron (Zn-Co-Fe) alloys have been investigated. Coatings with relatively high amounts of Co are very difficult to achieve due to anomalism associated with their deposition and are therefore not much reported so far. In this research Zn-Co and Zn-Co-Fe alloys with varying amount of Co (2 to 4 wt-%) and Fe (up to 1 wt-%) are electrodeposited. The deposition characteristics and microstructure of the Zn-Co alloys changed significantly with the variation in deposition parameter settings and corresponding Co content in the deposits. The sacrificial corrosion protection provided by Zn-Co and Zn-Co-Fe coatings was also studied. It was found that the sacrificial properties and decreases with increasing Co content in the alloy. For high Co content in the alloy, the coating becomes more noble to steel and loses its sacrificial protection.