Electrodeposition of Cu-Ni Coatings for Marine Protection of Mild Steel

摘要

Copper-Nickel (Cu-Ni) alloys are known to find extensive marine applications due to their excellent resistance to seawater corrosion and bio-fouling. Electrodeposited Cu-Ni coatings having even 20-30% Cu can be a good corrosion resistant in sea water, which is similar to the corrosion rate of Monel 400. In this regard, an electrolytic bath has been formulated for electrodeposition of Cu-Ni alloy on mild steel (MS). A new bath has been optimized by conventional Hull cell method, without the use of any additives. The bath under plating conditions was found to exhibit regular codeposition with preferential deposition of more noble (Cu) than less noble (Ni). The Ni content in the deposit was found to increase with deposition current density (c.d.). Influence of bath constituents and operating parameters on the appearance and composition of deposits were studied, as a measure of their performance against corrosion in 5% NaCl solution, as representative saline water. A variety of deposits were obtained and their corrosion resistances were measured by electrochemical AC and DC methods. Experimental results demonstrated that the corrosion resistance of coatings increased with Ni content in the deposit till at very high c.d. At very high c.d., the deposit was found to be very bright and but brittle due to increased Ni content, evidenced by EDS and SEM analyses. Variation in the phase composition with c.d. was confirmed by XRD study. Corrosion study revealed that Cu-Ni alloy deposited at 3.0 A dm~(-2) was found to be the more corrosion resistant, compared to the coatings at other c.d., deposited from the same bath. Variations in the corrosion behaviour with c.d. have been studied in the light of structure-property relation, and results are discussed.