Title: Investigation on corrosion properties of bright Zn-Ni alloy coated mild steel

Abstract

Electrodeposition is a renowned surface-modification method to get better surface characteristics, both functional and decorative properties of a broad diversity of materials. Recently, zinc and its alloy coatings are finding several applications, as a sacrificial metallic coating for the protection of mild steel. Zn-Ni alloy coating is the most commonly exploited in commercial applications and it exhibits significantly higher corrosion resistance ability and superior surface morphology than pure zinc. It is used as a replacement for toxic and expensive cadmium coatings. Literature survey revealed that zinc-nickel alloy coating without brightener is dull, unattractive and uneven and has comparatively less corrosion resistance ability. Hence, brighteners are gaining significance. They are found to adsorb on cathode surface (Mild Steel) and thereby modify the surface characteristics of the coating. Adsorption of brightener affects the nature of coating resulting in refined coating, which in turn alters the surface properties especially corrosion resistance of steel. A new brightener CG was synthesized by condensation of Cysteine Hydrochloride and Glutaraldehyde. Electrodeposition of Zn-Ni alloy from Sulphate bath was done in presence of CG. Corrosion studies were carried out using Electrochemical Impedance spectroscopy and Potentiostatic techniques. Surface morphology was studied using SEM, Reflectance spectroscopy and X-Ray Diffraction. Brightener CG was successful in giving bright zinc-nickel alloy deposits. Corrosion techniques confirmed increase in corrosion resistance and protection ability of bright zinc-nickel coatings. Surface studies revealed enhancement of fine grained nature of zinc-nickel alloy crystallites. XRD studies depicted the presence of η and γ- phases of pure zinc and zinc-nickel alloy respectively in the deposits. CG is accountable for increasing the corrosion resistance ability of bright zinc-nickel depositsince refined grain structure is closely associated with corrosion resistance property. It changes the orientation of Zn-Ni alloy crystallites which is accountable for brightness. CG can act as an efficient brightener and can be commercially used.