Improving the corrosion resistance of DKP steels with alloy coatings

Steel is durable and cost-effective, but also susceptible to corrosion, which can lead to structural damage. One method of protecting steel sheets against corrosion is electroplating with nickel alloys. Of the metals in the fourth period of the periodic table, Fe, Co and Ni exhibit different than expected co-deposition behaviour. This is called anomalous co-deposition behaviour. However, the resulting film differs from the expected composition based on the deposition rates of each material. This can occur due to differences in surface diffusion rates, adhesion or the formation of intermediate compounds. The present study investigates the effect of solution concentrations of NiSO4∙6H2O, NiCl2∙6H2O, FeSO4∙7H2O, CoSO4∙7H2O, H3BO3 and H3PO4 on the composition of coatings and corrosion resistance of NiFeCo alloy coating. The objective of this study is to obtain a coating with superior corrosion resistance. SEM-EDX was utilised in order to ascertain the composition and morphology of the coatings. Tafel curves were then employed to calculate the corrosion resistance. Accordingly, the optimum concentrations of NiSO4 (0.45 M), NiCl2 (0.30 M), CoSO4 (0.04 M), FeSO4 (0.075 M), H3BO3 (0.03 M) and H3PO4 (0.5 M) were determined for maximum corrosion resistance and minimum current density (1.18 μA/cm2). The corrosion rate of the coating produced in the optimal electrochemical plating bath composition was calculated to be 0.0128 mm/year.