Electrodeposited Ni-Cu alloy coatings on mild steel for enhanced corrosion properties

Ni rich single-phase Ni-Cu alloy coatings were obtained on mild steel substrates by electrodeposition from stable alkaline citrate baths. Three different baths were prepared with varying Cu2+ concentration. Electrodeposition experiments were performed in the galvanostatic mode at three different current densities of 10, 20 and 30 mA cm(-2). The coating compositions calculated from EDAX analysis showed that copper content in the coating increased with an increase in copper content of the bath, but decreased with an increase in current density. It was observed that the morphology of the deposits changed from globular to cauliflower with an increase in current density. Deposits from baths containing lower copper content showed more separated and localised cauliflower structures. The roughness of the deposits was also observed to increase with an increase in current density and to some extent with increase in deposition time. The corrosion potential for all coatings was less negative compared to mild steel, indicating barrier protection properties. Corrosion rate was largely affected by the morphology and roughness of the coatings. At higher current densities and higher deposition time, rougher surfaces and gaps and separations between the cauliflower structures were responsible for higher corrosion rate.