Corrosion Behavior Of Zn-ni Coatings Deposited By Electrolytic Plasma Processing




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Materials Science & Engineering


Cadmium has been used for years as a sacrificial coating in high-strength steels specially in aerospace industry. Currently, efforts are being made to find a suitable alternative to Cd coatings because of its toxicity and environmental hazard. Zinc-nickel alloy coatings are being extensively studied as a replacement for cadmium coatings since they are environmentally friendly with good corrosion resistance, superior formability and improved welding characteristics. However, Zn-Ni alloys in general, have a more negative potential than Cd due to the high content of Zn in the alloy which dissolves rapidly in corrosive environments. Although Ni is more noble than Zn, for many traditional coating methods the co-deposition of Zn-Ni is anomalous and a higher percent of Zn is present in the final deposit. On the other hand, Ni is more noble than Fe and coating with a high Ni content may posses a higher potential and thus, accelerate corrosion. Thus there is a need for new deposition methods where the Ni content can be controlled.