Electroplating and Corrosion study of Zn-Co, Zn-Fe and Zn-Co-Fe Alloys

Zn-Co, Zn-Fe and Zn-Co-Fe coatings were electrodeposited on mild steel from an acid sulphate bath, using thiamine hydrochloride (THC) and citric acid (CA) as additives. Bath constituents and operating parameters were optimized by standard Hull cell method, for peak performance of the coatings against corrosion. The effect of current density (c.d.), pH on the deposit characters, such as corrosion resistance, hardness, thickness, partial current density and CCE were studied and discussed. Corrosion resistances were evaluated by Potentiodynamic polarization and electrochemical impedance spectroscopic (EIS) method. Corrosion resistance of the Zn-Co-Fe coating under optimal c.d. (3.0 A dm-2) was found due to its inherent high dielectric barrier, evidenced impedance signals. High partial current density for zinc in Zn-Co-Fe alloy coating supports the possibility of a synergistic catalytic effect of Co on Fe and vice versa. X-ray diffraction study clearly indicates that a drastic change in corrosion resistance of ternary alloy is due to the change in the phase structure of the coatings, compared to binary alloys. Surface morphology and composition of the coatings were examined by using Scanning Electron Microscopy (SEM), interfaced with Energy Dispersive X-ray Analysis (EDXA) facility, respectively.