钢铁表面硅烷锆盐植酸复合转化膜耐腐蚀机理研究

Corrosion Resistance Mechanism of Silane Zirconium Salt Phytic Acid Composite Conversion Coating on Steel Surface

为提高40Cr钢体表面耐腐蚀性能,采用双-[γ-(三乙氧基硅)丙基]-四硫化物(BTESPT)、硝酸锆和植酸在40Cr钢表面制备了具有优异耐蚀性能的硅烷锆盐复合转化膜,采用正交实验法优选了硅烷锆盐复合转化液成膜的工艺条件。采用硫酸铜滴定实验、扫描电镜(SEM)、傅里叶变换红外光谱(FTIR)及电化学测试对复合膜的耐蚀性、形貌、成分、膜层的电位特性进行分析。结果表明:硅烷锆盐复合膜最优工艺为硅烷浓度5%(体积分数),硝酸锆浓度为0.75%(质量分数),溶液pH值为4,反应温度25℃,反应时间50 s;通过硫酸铜点滴试验和电化学测试可以看出掺杂植酸的复合转化膜的耐蚀性比单一硅烷膜和硅烷锆盐膜得到了明显的提升;通过微观形貌观察可以看出,植酸的添加弥补了膜层缺陷,阻碍了腐蚀介质的扩散,增强了膜层的耐腐蚀性。

In order to improve the corrosion resistance of 40Cr steel surface,bis-[7-(triethoxy silicon)propyl]-tetrasulfide(BTESPT),zirconium nitrate and phytic acid were used to prepare silane zirconium salt composite conversion coating with excellent corrosion resistance on the surface of 40Cr steel.The film forming process conditions of silane zirconium salt composite conversion solution were determined by orthogonal tests.The corrosion resistance,morphology,composition and potential characteristics of the composite coating were analyzed by copper sulfate titration,scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FTIR)and electrochemical tests.Results showed that the optimum process of silane zirconium salt composite coating was as follows:silane concentration was 5(volume fraction),zirconium nitrate concentration was 0.75%(mass fraction),pH value of solution was 4,hydrolysis temperature was 25 C,and reaction time was 50 s.Through the results of copper sulfate drop test and electrochemical test,it was found that the corrosion resistance of the composite convesion coating doped with phytic acid was significantly improved compared with that of the silane coating and the silane zirconium salt coating.Through the observation of micro morphology,it was indicated that the addition of phytic acid made up for the defects of the coating,hindered the diffusion of corrosive medium,therefore,enhancing the corrosion resistance of the coating.