热浸锌层植酸/硅烷复合钝化膜及其耐蚀性能

Preparation of Phytic Acid/Silane Composite Passivation Coating on Hot-Dip Zinc Sheet and Its Corrosion Resistance

为了研制热浸锌层表面高耐蚀、绿色环保的无铬钝化工艺,对热浸锌板进行植酸钝化、硅烷钝化和植酸/硅烷两步复合钝化。采用正交试验和单因素试验对复合钝化工艺进行了优化;采用Tafel曲线、盐雾试验及硫酸铜点滴试验分析复合钝化膜的耐蚀性能,利用场发射扫描电镜(FESEM)观察了钝化膜的表面形貌,通过EDS分析钝化膜的成分,并提出复合钝化膜的结构模型。结果表明:植酸膜与硅烷膜通过"交联-协同作用"在热浸锌表面形成一层致密的保护膜层,较单一钝化膜更致密,耐蚀性能与三价铬钝化膜相当;经植酸/硅烷复合钝化处理后,锌表面生成的钝化膜层阻碍O_2和电子在锌表面和溶液之间的转移和传递,改变了界面反应历程,从而提高了阴极极化,改善了复合钝化膜的耐腐蚀性能。

To develop a green chromium-free passivation process on the surface of hot-dip zinc sheet, hot-dip zinc sheets were treated by the passivation of phytic acid, silane passivation and two step compound passivation process, separately. Orthogonal test and single factor test were used to optimize the composite passivation process. The corrosion resistance of the passive film was studied by Tafel curve. Moreover, the sur- face morphology of the passive film was observed by field emission scanning electron microscope （ FESEM）, and the composition of the passive film was studied by EDS. The structure model of the composite film was put forward. Results showed that phytic acid film and silane film formed a dense layer of protective film on the surface of hot galvanizing by ＂crosslink synergism＂ reaction. The composite passive film was more com- pact than a single passive film, and the corrosion resistance was the same as that of trivalent chromium passivation. After phytic acid / silane treatment, the passive film formed on the surface of zinc inhibited the transfer and devolve of oxygen and electrons between the zinc surface and the solution, and the interface reaction mechanism was changed. Therefore, the cathodic polarization was improved, and the corrosion resist- ance of the composite passivation film was enhanced.