The New Research Hot Galvanized Plate Trivalent Chromium Passivation Solution And Technology

Galvanization is a kind of common ways of improving corrosion resistance of the steel, but in the humid air zinc layer is etched to form white rust easily,thus losing protection, in order to further extremely high corrosion resistance of zinc coating, galvanizing layer typically passivation treatment, not only improve the quality of the surface and also extend the service life of the steel galvanized layer. Passivated galvanized plate is widely used in household appliances and automotive industry, etc, with the progress of science and the improvement of environmental protection, high pollution, carcinogenicity, traditional chromate passivation already was washed out gradually, the development of new type, low pollution, non-toxic passivation technology is a hotspot of scientific research workers. This paper studies the hot galvanized sheet new trivalent chromium passivation solution and passivation film process, and discusses its forming process and the corrosion mechanism.Through the single factor experiment, orthogonal optimization method to determine the best formulations and processes of the trivalent chromium passivation film is: the chromium chloride 0.8mol·L-1, chromium nitrate 0.3mol·L-1, 4% silicon sol, curing temperature 120℃, curing time of 100 s, passivation solution of p H1.0. By lead acetate drop experiment, NSS, soak salted water, electrochemical test methods of trivalent chromium passivation membrane performance were studied, the results show that the hot galvanized steel sheet of trivalent chromium passivation film make longer soaking time and brine, NSS can achieve 120 h, corrosion potential is moved, corrosion current decreased one order of magnitude, ac impedance increased significantly, and determine the equivalent circuit of passivation film for R(Q(R(QR))); Trivalent chromium passivation film of heat resistance, high adhesion strength and fingerprint resistance performance is good, but poor water resistance effect;By SEM and XRD analysis result, trivalent chromium passivation membrane surface level off, the basic no crack, the compact structure of passivation film, good cover of the galvanized layer,membrane layer is mainly composed of Zn, Cr, O, Fe, P and other elements, its main ingredients for Zn Cr2O4;Adopt the method of intravenous drip and titration, trivalent chromium passivation film and passivation solution almost does not contain Cr6+.Through accelerated corrosion test for corrosion resistance and self-healing trivalent chromium passivation film, hexavalent chromium passivation film and silica passivation film performance comparison study, the results showed that the corrosion of silica passivation film and self-healing capabilities worst, self-healing capabilities trivalent chromium passivation film has improved, can be comparable with the hexavalent chromium passivation film.