Electro-galvanization of zinc and zinc-nickel onto mild steel for improved corrosion resistance

Pure zinc was electroplated on mild steel sample at specific potential and current density from sulphate bath and its characterization was done by various techniques. Corrosion rate of coating was found using potentio-dynamic polarization technique. Corrosion rate of coating was improved using alloyed coating (zinc-nickel). The main objective was to replace hot-dip galvanization technique with electro-galvanization so as to reduce thickness of coating and also to do away with problem of heat affected zone arising in hot dip galvanization, further enhancing the corrosion resistance of electro-galvanized coating by using alloying elements. Pure zinc was deposited on mild steel via electrodeposition technique at potential and current density values of −1.45 V, −1.55 V, −76 mA/cm2, −97 mA/cm2 respectively. Thickness of coating was measured using surface profilometer. SEM images and XRD data were taken and analysed and finally corrosion rate was calculated using Tafel extrapolation. Further zinc-nickel was electrodeposited on mild steel sample at −1.45 V and −1.55 V and corrosion rate of coating was compared with pure zinc coating. It was observed that for pure zinc coating as the deposition potential increases from −1.45 V to −1.55 V, the corrosion resistance is enhanced. With addition of alloying elements such as nickel the corrosion resistance of coating was slightly increased and also coarse grain structure was obtained when SEM images were compared.