Quantitative Characterization And Performance Study Of The Appearance Color Of Electrogalvanized Zinc

Passivation after galvanizing can greatly improve the corrosion resistance of steel.After treatment with trivalent chromium and hexavalent chromium,a passivation film with good decorative and corrosion resistance can be obtained.However,hexavalent chromium is prone to cancer,and trivalent chromium is converted into hexavalent chromium during long-term use.The state has severely restricted the use of hexavalent chromium.Currently,the color passivation processes used in the market mainly include organic passivation and inorganic passivation.Common chromium-free organic passivation corrosion resistance is good,but poor adhesion and heat resistance,a single inorganic passivation corrosion resistance slightly worse than organic passivation,can not replace the chromate passivation.In this paper,tannic acid and titanium salt were selected for organic inorganic composite color passivation.The corrosion resistance of galvanized steel was improved by achieving synergistic inhibition between organic and inorganic compounds and complementation of properties.Through single factor and orthogonal experiments,the optimum ratio is determined,the composite passivation composition and process are summarized as follows:7.4 g/L C₇₆H₅₂O₄₆,5.4 mL/L TiCl₃,21 m L/L H₂O₂,4.8 g/L NaSiO₃·9H₂O,10 g/L KF,5 mL/L HNO₃,10 mL/L H₃PO₄,3 mL/L H₂SO₄,pH is 1.5,the passivation time 30 s,passivation temperature at room temperature,drying methods for drying.The color passivation film obtained by using this technology has bright color and good corrosion resistance,and the neutral salt spray experiment can reach 66 h.Closed postprocessing by use of 1 g/L passivation after Potassium Permanganate,can further improve the decoration and corrosion resistance of passivation film,neutral salt fog time is 72 h.The results of SEM test show that the color passivation film obtained by this process is compact,free of pore and micro crack.The uniformity of the thickness of the film can be further improved by the closed treatment after passivation.By EDS energy spectrum analysis,the passive film mainly contains Zn,C,O,Fe,P,Ti,K and other elements,of which C and O are more,indicating that tannic acid and zinc form chelating rings on the surface of zinc plating.Through theoretical analysis,the passive film coloration is mainly due to the integrated results of ion polarization,d-d transition and thin film interference.The color of the passivation film was quantified by the XYZ tristimulus value,and Lab color space was introduced to characterize the color of the passivation film in the color space.It was observed that the colors represented by the passivation film color and the representative values are consistent,indicating that the selected color system and the characterization method are reasonable.