Research Of Inorganic/Organic Chromium-free Passivation On Surface Of Galvanized Steel Sheet

In this paper, the method of graft polymerization was used to synthetize the hydrophilicacrylic modified epoxy resin by grafting acrylic monomer into the epoxy resin molecular chainand the resin was applied to the composite passivation solution. In this experiment, thephosphomolybdate solution, aqueous acrylic modified epoxy resin, vinyl triethoxy silane andsurface active agent (SDS+OP-10) for the A component and the water soluble modified aminecuring agent LJ810for B component, the two components were used in the preparation of theinorganic/organic chromium-free passivation solution.Optimal conditions for the synthesis of hydrophilic acrylic modified epoxy resin werestudied as: the reaction temperature is120℃, reaction time is5h and the neutralization saltreaction is at60℃for3h. Infrared examination revealed that the acrylic acid monomer withopened double bond was grafted to the epoxy resin. The prepared emulsion of acrylic acidmodified epoxy resin is stability and good at water dispersion, which possess both the propertiesof epoxy resin and acrylic resin with good corrosion resistance and good adhesion.The A composition was determined through the orthogonal experiment and single factor test:phosphomolybdate solution100mL/L, organic silane coupling agent60mL/L, aqueous acrylicmodified epoxy resin emulsion250mL/L and (5+15)g/L surface active agent (SDS+OP-10).The curing ratio of A components and B components of the curing agent is the volume ratio of1﹕0.7. The optimal conditions of the prepared composite chromium-free passivation solution forpassivation of galvanized are as follows: passivation temperature25℃, passivation time60s,drying temperature80℃and drying time40min.The morphology and elements of the passivation film was analyzed by scanning electronmicroscopy (SEM) and the corrosion resistance of the composite film was tested by neutral saltspray test, lead acetate spot test, tafel polarization curves and AC impedance spectroscopy (EIS).The results showed that the composite film is compact, smooth and the main elements of the filmare C, Zn, O, Si, N, P, Mo, etc; the composite passivation film blocked the anode and cathodereaction in the corrosion process of galvanized layer, which effectively reduced the corrosionrate of galvanized sheet; the film have a good adhesion and an excellent corrosion resistance, thecorrosion area is only3%after72h NSS.