渗锌层硅烷-植酸钝化膜的耐腐蚀性及其成膜机理

Corrosion resistance and formation mechanism of silane⁃phytic acid passivation film on zincizing layer

为了提高渗锌层耐腐蚀性能,本文对渗锌层进行硅烷-植酸复合钝化并制备了复合钝化膜,通过正交试验优化了复合钝化液各组分的最佳浓度,采用极化曲线(Tafel)、电化学阻抗(EIS)及中性盐雾试验(NSS)研究了复合钝化膜的耐蚀性,利用扫描电镜(SEM)、能谱分析(EDS)、X射线光电子能谱(XPS)、傅里叶变换红外光谱(FTIR)等测试方法分析表征了钝化膜表面形貌及成分,并分析了复合钝化膜的成膜机理。研究表明:硅烷-植酸复合钝化液的最佳组分为:60 mL/L KH550,8 mL/L植酸,3.5 g/L酒石酸,40 mL/L纳米硅酸钾乳液;与渗锌层相比,复合钝化膜的自腐蚀电位从-1.356 V正移到-1.145 V,腐蚀电流密度从6.843×10^(-4)A/cm^(2)降低至5.715×10^(-5)A/cm^(2),线性极化电阻增大了7倍;24 h盐雾后,复合钝化试样无白锈产生;复合钝化膜覆盖均匀,表面无裂纹,主要由Zn、Fe、Si、P和N元素组成,膜层中元素主要以Si-O-Si/Me、P-O-Si/Me、MeO和SiO_(2)形式存在;在硅烷和植酸的共同作用下,可在渗锌层表面形成一层连续均匀、较致密的钝化膜,提高了基体的耐蚀性。

In order to improve the corrosion resistance of the zincizing layer,silane⁃phytic acid composite passivation was applied to the zincizing layer and a composite passivation film was prepared.The optimal concentrations of each component of the compound passivation solution were determined by orthogonal experiments.The corrosion resistance of the composite passivation film was studied by polarization curves(Tafel),electrochemical impedance spectroscopy(EIS)and neutral salt spray test(NSS).The surface morphology and composition of the passivation film were analyzed by scanning electron microscopy(SEM),energy spectrum analysis(EDS),X⁃ray photoelectron spectroscopy(XPS)and Fourier transform infrared spectroscopy(FTIR).Additionally,the film formation mechanism of the composite passivation film was analyzed.The results showed that,the optimal composition of the silane⁃phytic acid complex passivation solution was as follows:60 mL/L KH550,8 mL/L phytic acid,3.5 g/L tartaric acid and 40 mL/L potassium silicate nanosilicate emulsion.Compared with the zincizing layer,the self⁃corrosion potential of the composite passivation film shifted from-1.356 V to-1.145 V.The corrosion current density decreased from 6.843×10^(-4) A/cm^(2) to 5.715×10^(-5) A/cm^(2),and the linear polarization resistance increased by 7 times.After 24 hours salt spray,the composite passivation specimens did not produce white rust.The composite passivation film coverd uniformly and had no cracks on the surface,and it was mainly composed of Zn,Fe,Si,P and N elements.The elements in the film layers were mainly present in the form of Si-O-Si/Me,P-O-Si/Me,MeO and SiO_(2).The combined action of silane and phytic acid forms a continuous,uniform and dense passivation film on the surface of the zincizing layer,which improves the corrosion resistance of the substrate.