|
Aqueous chromium-free zinc-sintered aluminum coating is composed by the metal slurry, the passivation solution and additives in the coating liquid, by dipping, brushing or spraying in the steel part or member surface, the high-temperature sintering to form aluminum flake zinc The anti-corrosion coating of powder as a main component, having a high corrosion resistance, non-polluting, and heat resistance characteristics, and provide effective protection for the metal substrate. Our group has been the basis of waterborne zinc aluminum coating process starting from the hydrolysis of the silane coupling agent, by the physical properties of the resultant coating appearance of paint adhesion, surface condition, resistance to nitric acid ammonium rapid tests, performance testing, to determine the top of the aqueous silane zinc aluminum coating formulation process: silane (KH-560), methanol, deionized water in a volume ratio of 1:2.5:5, the pH value from 8.0 to 9.0 leveling agent to add between hydrolysis was stirred for 48h; slurry of the resultant hydrolyzate with a metal (zinc powder, aluminum powder, polyethylene glycols of the mass ratio of 4:1:2) were mixed continuously stirred for 3 to 5 hours, during stirring , thickeners, defoamers and other additives to prepare a coating solution. The resulting coating with different content of rare earth lanthanum or cerium salts, NSS, SEM, EDS, EIS and polarization curves and other methods were used to characterize the structure and performance of the coating relatively rare earth salt coated layer. The results show that: the rare earth salt is added, not only to improve the structure of the coating, but also significantly improves the corrosion resistance of the coating; Lanthanum salt added in an amount of 7 g / L, or the rare earths cerium salt is 10 g / L, the resultant coating The layer of resistance to neutral salt spray test of time, respectively, 1200h and 1000h, up to optimal performance. Stereo metallurgical microscope and scanning electron microscopy analysis of the coating surface and cross section morphology, the results showed that the coating uniformity level, continuous metal matrix closely. Through the spectrum analyzer and an X-ray diffraction on the coating element and the phase composition analysis, the results showed that: coating containing Zn, Al, Si, La, or Ce, a C, O, and other elements; main phase is Zn and Al, other elements may be based on such as oxides and hydroxides of the phase distribution in the coating. Using electrochemical impedance spectroscopy and polarization curves of rare earth lanthanum passivation coating, results showed: the coating corrosion process showed significant passivation behavior, so that the corrosion current decreases, the polarization resistance increases, the corrosion resistance of the coating is significantly improved. On the the coating corrosion course of analysis, combined with the structural characteristics of the zinc-aluminum coating, to build a water-based chrome-free zinc-aluminum coating structure model, and a preliminary study based on the mechanism of the anti-corrosion coating.
|