Surface Of Q235 Silane Treatment And Research Of Silane Zinc Aluminum Coating

The development of green chrome-free zinc-aluminum coating as a replacement of dacromet(zinc-aluminum coating including chromium) has long been a focus for concern. The new environmentally-friendly zinc aluminum coating is expected to have been widely used in aerospace, transportation, automotive parts,and so on.It has a broad application prospects.Investigated the optimal conditions for deposition silane film on steel Q235through electrochemical impedance spectroscopy(EIS) and scanning electron microscopy(SEM); and analyed the structure of the silane films of on the steel and the model between each other by use of EIS fitting model,FT-IR and EDS. On this basis, attempted to add a certain percentage of Zn, Al powder and the amount of additives in vinyl triethoxysilane to the preparation of green chromium-free silane coating.Seeked the proportion of Zn and Al,wetting and dispersing agent,silane hydrolysis and the baking process of the coating by electrochemical means and a scanning electron microscope. The green chrome-free composite (including Zn, Al powder) coating were successfully prepared. Main conclusion as follows:1、The optimum process conditions of silane film:the concentration of the silane solution is5%, the pH value is4, the hydrolysis time was48hours, and then curing at100℃in30min.2、The corrosion resistance of silane films prepared under different conditions in3.5%NaCl solution was significant difference; the corrosion resistance trend of the silane films under different process conditions is found as follows:pH values:3.0<5.0<4.0, concentrations of silane films:1%<3%<5%<7%, hydrolysis time of silane film:24h<96h<72h<48h, the silane film under different curing temperature:50℃<150℃<100℃, the silane films obtained under different curing time:45min<15min<30min.3、Compared with the immersion, the cathodic(under-0.8V) deposition silane film on steel surface showed the best corrode inhibition performance. When the potential changes in the range of-0.4～1.0V, take the deposition potential of-0.8V, the formation of silane films on Q235Steel showed the best corrosion performance in the above-mentioned corrosive medium.4、The VTES film on the steel surface have the binding mode of the CH2,CH2CH3, SiOCHCH2,SiOCHCH2,SiOSi,SiOH,Si-Cand so on. The silane film combined with metal by chemical combination of keys via Si-O-Fe.5、Through the optimization of the coating liquid, a better ratio is found as follows:zinc and aluminum powder (5:1)28.8g, anhydrous ethanol11g, vinyl triethoxysilane13.2g, deionized water14mL, corrosion inhibitors0.56g, Tween-201g; Suitable curing system:drying (100℃,15min),curing (up to270℃from100℃,holding15min).6、The open circuit potential of silane-based zinc-aluminum composite coatings in3.5%NaCl solution is about-0.8V or so; The open circuit potential of the coating gradually shifted positively by immersion time in3.5%NaCl solution increased, when soaked in192hours, the open circuit potential of composite coating is-0.6V or so.7、With the increase of immersion time in3.5%NaCl solution, the capacitance arc radius of composite coatings showed regular changes consistent with the impedance variation-soak time curve:the corrosion resistance of composite coating in48to96hours ability to decline, and subsequent corrosion resistance increased.8、The silane-based physical play the role of the barrier corrosive medium in3.5%NaCl solution. With the increase of immersion time, the corrosive medium immersed the weaknesses of silane film,and reduce the corrosion resistance of silane films coating. However, the zinc, aluminum powders in the composite coating can play a sacrificial anode to the effect of cathodic protection of Q235steel matrix.