Corrosion Protection of Steel by Using ZnCoFe Alloy Coating (Replacement for Cadium Coating)

Zinc and Zinc alloys have been extensively used as a replacement for Cadmium (Cd) coatings. ZnCo and ZnFe alloys with higher amount of Cobalt and Iron are very difficult to achieve due to anomalism associated with these coatings. Anomalous ZnCoFe alloy is a relatively recent addition in the family of Zn alloys. In this paper the corrosion resistance of ZnCoFe alloys with higher amount of Co (>10%) and Fe (>1%) are examined and compared with the pure Zinc, Cadmium and ZnCoFe alloy with low alloying elements (i.e. 0.5%Co+1%Fe). It is found that an increase in amount of Co > 10 % accounts for a shift in the OCP to a level higher than Zn and in case of >20% shifts somewhere near to Cd yet remains electronegative to steel. The coating shows superior corrosion resistance, in terms of its sacrificial and barrier properties, as compared to Zn, Cd and ZnCoFe (0.5%Co+1%Fe).