不同铁含量的碱性Zn-Fe合金镀层在3种溶液中的耐蚀性能

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

含铁量低于1%(质量分数,下同)的Zn-Fe合金具有优异的耐腐蚀性能,有必要对其耐蚀性及机理做深入研究。采用动电位极化技术和交流阻抗方法(EIS)研究了未钝化的纯Zn镀层和碱性Zn-Fe合金镀层(含铁0.15%～0.89%)在0.2 mol/L Na2B4O7-H3BO3,含0.05 mol/L Cl-的0.2 mol/L Na2B4O7-H3BO3和1%NaCl溶液中的耐蚀性能,采用XRD法研究了不同镀层的晶体结构。结果表明:少量铁在锌中的存在明显影响锌的耐蚀性能,含铁0.15%～0.60%的Zn-Fe合金镀层腐蚀电阻和反应电阻都较纯Zn层的大,腐蚀电流密度较小,在一定电位范围内形成的电化学钝化膜耐Cl-点蚀的能力强;含铁量为0.29%的合金表现出了最好的耐蚀性;Zn-Fe合金镀层与碱性纯Zn镀层的晶体结构相同,都是六方密排结构,铁在Zn-Fe合金中不是以独立相而是以固溶相的形式存在。

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.