Corrosion Resistance of Electroplated Zinc-Iron Alloy Coatings Containing Different Content of Iron

Pure Zn coating and Zn-Fe alloy coatings with 0.15%～0.89%Fe(mass fraction) were deposited from alkaline cyanide-free electroplating baths.The phase structure of as-plated coatings was analyzed by X-ray diffraction,and their corrosion resistance in borate buffer solution(0.2 mol/L Na2B4O7-H3BO3,pH 8.5),0.2 mol/L Na2B4O7-H3BO3 solution containing 0.05 mol/L Cl-and 1%NaCl solution was evaluated by potentiodynamic polarization method and electrochemical impedance spectroscopy.Results indicate that doping a small amount of Fe leads to significantly improved corrosion resistance of electroplated Zn coating.Namely,Zn-Fe coatings with 0.15%～0.60%Fe possess higher corrosion resistance and reaction resistance as well as lower corrosion current density than Zn coating,and the alloy coating with 0.29%Fe has the best corrosion resistance.Moreover,the chemical passivation layer formed on the surface of Zn-Fe alloy coating in a proper range of potential shows good resistance to pitting induced by Cl-.In the meantime,electroplated Zn and Zn-Fe alloy coatings all have densely packed hexagonal crystal structure,and Fe exists as a solid solution phase in Zn-Fe alloy coatings.