Corrosion resistance and formation mechanism of silane-phytic acid passivation film on zincizing layer
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/cm2 to 5.715 × 10-5 A/cm2,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 SiO2.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.
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