Study On The Development And Mechanism Of The Organic And Inorganic Composite Passivation Technology On The Surface Of Hot-dip Galvanized Steel Sheet

As a widely used technology in the field of metallic surface corrosion protection,the coating is also very suitable for corrosion protection on the surface of galvanized steel.In general,coating or preparing a passivation film or conversion film on the surface of galvanized steel sheet can not only improve its anti-corrosion ability,but also beautify its appearance and adapt to the aesthetic requirements of people in modern society.At first,people used chromate passivated technology to solve the corrosion problem of galvanized steel sheets,its anti-corrosion effect is very good.Moreover,chromate has the ability of self-repairing,so it is an irreplaceable protective coating simply from the point of view of anticorrosion.But Cr⁶⁺is highly toxic to the human body and the environment,countries around the world have severely restricted or even banned their use.Therefore,we need to abandon the process of traditional passivation,which is detrimental to our health,and to explore an environmentally friendly and pollution-free passivated technology to replace it.Single organic or inorganic passivation can meet the requirements of environmental protection and pollution-free,but its effect of passivation and protection is far from chromate,so the research and development of organic-inorganic composite passivation film is very promising.The composition of cerium salt-silane composite passivation film on the surface of galvanized steel sheet was preliminarily studied.The formula and passivated process of each component of cerium salt-silane composite passivation film were determined by orthogonal experiment and single factor variable method.The formula is as follows:vinyl trimethoxysilane 8 mL/L,cerium nitrate hexahydrate 25 g/L,hydrogen peroxide 18 mL/L,methanol 120 mL/L;The optimum passivation conditions are as follows:passivated time 60s,passivated temperature 30?,pH=4..The effect of passivation is not ideal,and the total blackening time of lead acetate drops is only 48.1s.So we determined to modify with water-based epoxy resin,through the neutral salt spray test and acetic acid drop test to determine the optimum content of 250mL/L,the corrosion rate is 0.0680g/?m²·h?,lead acetate lead time It is 425.6s,indicating that the resistance of the yttrium salt-silane-resin composite passivation film prepared after modificated is greatly improved.Compared with the commercial chromate passivation film,the esistance of the modified film is better than that of the commercial chromate passivation film.The corrosion current density is smaller than that of chromate passivation film,the polarization resistance is larger than chromate passivation film,and the corrosion resistance is higher than chromate passivation film.It is possible to replace chromate as a new passivated technology.The SEM and EDS analysis of the cerium salt-silane-resin composite passive film showed that the thickness of the composite passivation film was 80?m,the surface was smooth and dense,the appearance was bright,without pits and cracks.Insitu DRIFTS analysis showed that there were Si-O-Si,Si-O-Zn,Si-O-C,epoxy group and benzene ring in the composite passivation film.The results show that the organosilane in the passivation solution is dehydrated and condensed with epoxy resin and zinc matrix,and then crosslinked to a macromolecule solid network framework,there is an intermolecular dehydration condensation with epoxy resin and zinc matrix in the passivation solution.The inorganic cerium salt is coated in the inner space of the skeleton to form a compact and orderly passivation film,which is closely bound to the surface of the galvanized sheet.The X-ray diffraction analysis shows that there are compounds of Ce and Zn in the passivation film.After the composite passivation film was corroded for 96 h,the morphology of SEM was only partially corroded,the morphology of the matrix was intact,and it was not destroyed by corrosion.After corrosioned,the related groups in the epoxy group such as the epoxy group and the benzene ring disappeared,and the framework of macromolecular network was not destroyed.The corrosioned products were mainly composed of zinc oxide/hydroxide.