Investigation Of The Anticorrosion Properities Of Environmental Friendly Composite Silane Passivation Film For Galvanized Steel

Electro galvanized steel sheet is widely used in automobile,household appliance and construction fields cause of its excellent performance and attractive price.However,the Galvanized steel sheet will easily get corroded when it exposure to corrosive environment at long times,which severely limits the application of Galvanized steel sheet.This problem can be well solved by preparation of passive film on the surface of Galvanized steel sheet.The traditional passive film like chromate passivation film and phosphate passivation film work well,but the productive process is not environmentally friendly,cause of lot of wastewater contain heavy metal ions and hydrophosphate will be produced.。Organosilane passivation film is an environment-friendly passive film.In this research,the hydrolysis process of 3-aminopropyl triethoxysilane（KH-550）andγ-glycidyl ether oxypropyl trimethoxysilane（KH-560）were explored respectively,and the optimum hydrolysis parameters were obtained.The hydrolysis parameters of KH-550 silane was as follows:the content of KH550 is 7.5 wt%,the hydrolysis time is 4 h,the hydrolysis temperature is 40℃,the content of ethanol is 20 wt%,and the pH is 9.The hydrolysis parameters of KH560 is as follows:the content of KH560 is 15wt%,the hydrolysis time is 2 h,the hydrolysis temperature is 35℃,the content of methanol is 10 wt%,and the content of pH value is 3.KH-550 and KH-560 silane films were prepared under the optimum hydrolysis conditions,the corrosion current density decreased by five times and two times in 3.5 wt%NaCl solution.It illustrate that both KH-550 silane film and KH-560 silane film can improve the corrosion resistance of galvanized sheet.The silane hydrolysate was compounded according to a certain proportion to obtain the compound silane solution.The composite silane film was prepared under the conditions of passivation time of 150s,curing temperature of 90℃,curing time of 1h and KH-550hydrolysate/KH-560 hydrolysate（m/m）of 1/2.The corrosion resistance,wetting resistance,film adhesion and structural composition of the composite silane film were tested.It is found that the passivation film prepared under this condition has uniform surface without defects and good paint film adhesion.Compared with the untreated galvanized sheet,the corrosion current density in 3.5 wt%NaCl solution is reduced by two orders of magnitude,indicating that the corrosion resistance of two single silanes is improved after compounding.Ti/Zr passivation film was prepared on galvanized sheet by orthogonal test.Passivation formula:K₂TiF₆ content of 0.05 wt%,H₂ZrF₆ content of 0.3 wt%,oxidant content of 0.1 wt%,pH is 4.Ti/Zr passivation film was prepared under the conditions of passivation temperature of 50℃,passivation time of 10 min,curing temperature of 70℃and curing time of 20 min.Ti/Zr-composite silane film was prepared on galvanized sheet by two-step method.The corrosion resistance,structure and composition of the passive film were characterized.It is found that the Ti/Zr passivation film is mainly formed at the section of galvanized sheet,which inhibits the Fe/Zn galvanic cell.The electrochemical test results show that the corrosion resistance efficiency of the passivation film reaches 99.32%.In the 72 h salt spray test,the average corrosion rate of Ti/Zr composite silane passivation film is0.03701 g·m^-2h^-1.It shows that the corrosion resistance of Ti/Zr passivation film is improved after the introduction of Ti/Zr passivation film.