Effect of current density on corrosion and mechanical properties of electrodeposited Co-W alloy coatings on mild steel

Co-W alloy coatings deposited on mild steel substrates serve as an environmentally friendly alternative to conventional hard chromium plating, offering superior corrosion resistance, hardness, and scratch resistance. In the present work, a novel Co-W electrolytic bath was optimized using the Hull cell method, and uniform alloy coatings were successfully electrodeposited at varying current densities. The electrochemical results indicate that the corrosion rate of the Co-W coating deposited at 1 A dm−2 was approximately 220 times lower than that of bare mild steel. Among the developed coatings, the sample deposited at a current density of 3 A dm−2 demonstrated the highest hardness, which can be attributed to the increased incorporation of tungsten in the alloy with increasing current density. Furthermore, the corrosion current density (icorr) for the Co-W coating deposited at 1 A dm−2 was found to be 8.28 µA cm−2, significantly lower than that of mild steel about 5.25 µA cm−2, confirming its enhanced corrosion protection capability. In addition, the scratch resistance of the coating deposited at 3 A dm−2 was superior to other current density coatings and the mild steel substrate, as evidenced by its lower residual depth of approximately 19.9 µm. This reduced residual depth indicates improved resistance to plastic deformation and enhanced mechanical durability.