镀锌层硅酸盐钝化工艺及其机理

Optimization of Silicate Passivation Process of Electrodeposited Zinc Coating as well as Formation Mechanism and Corrosion Resistance of the Passivation Film

目前,镀锌层硅酸盐钝化工艺尚不成熟,对其机理的研究也不够深入。为此,通过SEM、EDAX等对镀锌层硅酸盐钝化膜进行了形貌观察和成分分析,并通过NSS试验测试了其耐中性盐雾腐蚀性能,确定了最佳的钝化时间和钝化液pH值、温度,获得了色泽均匀、耐蚀性能优良的硅酸盐钝化膜;通过XPS分析确定了硅酸盐钝化膜的主要成分为SiO2、Zn4Si2O7(OH)2·2H2O、TiCl4、TiO2、Na2SiF6、ZnCl2等化合物。通过工艺条件变化和对钝化膜的成分分析,推测出其成膜机理:在酸性条件下,镀锌层和钝化液在界面处发生锌层溶解、Zn2+与硅酸的反应、Ti3+的氧化等一系列化学反应,从而在镀锌层表面形成主要成分为SiO2、Zn4Si2O7(OH)2·2H2O、TiCl4、TiO2、Na2SiF6、ZnCl2等化合物的钝化膜。

Electrodeposited Zn coating was passivated in silicate solution,and the passivation process was optimized.A scanning electron microscope and an energy dispersive spectrometer were performed to analyze the morphology and elemental composition of the silicate passivation film.The corrosion resistance of the passivation film was evaluated by neutral salt-spray test,and the formation mechanism of the passivation film was discussed.Results indicated that as-prepared silicate passivation film on electrodeposited Zn coating mainly consisted of Si,Zn,O,Ti,Cl,Na,and F.The passivation film obtained under the optimized passivation time as well as optimized pH value and temperature of silicate solution had uniform luster and good corrosion resistance.The formation mechanism of the silicate passivation film was supposed as follows:under acidic condition,electrodeposited Zn coating underwent dissolution at the coating / silicate solution interface,which was accompanied by the reaction of Zn2 +and silicic acid and the oxidation of Ti3 + thereby generating passivation film mainly composed of SiO2,Zn4Si2O7(OH)2·2H2O,TiCl4,TiO2,Na2SiF6,and ZnCl2.