| There are huge demands of coatings of corrosion resistance, hydrogen embrittlement resistance and deep-coating property in mining, energy, transportation, marine fields. Based on flake lacquer and Zn-rich coating, combined with passivation coatings of Zn or Al, a sacrificial anode protection coating with laminated barrier and self-passivative healing the zinc-aluminum-chrome coating, was developed by the solidification method similar to electronic pastes. Aiming to replace Cr6+ in sintered zinc-rich coating and develop a more "green" technology, we have carried a thorough study in this thesis.Main components and sintering conditions were optimized to find high anticorrosion zinc-aluminum coatings. Corrosion performance of sintered zinc-aluminum coating was evaluated comprehensively. An anticorrosion mechanism was proposed based on the studies of coating's structure and corrosion behavior. Studies were also done on the self-healing of zinc-aluminum-chromium coatings.Wetter agents and coupler agents were found critical in coating preparation. Wetter not only acted to wet and disperse metal lamella, but also acted to stabilize Zn and Al. Coupler contributed to both excellent adhesion and anticorrosion of coatings. Thickener played an important role in the stability. Binding and anticorrosion of coatings could be improved by replacing chromate with molybdate and silane, with scarifying the self-healing of coatings. Process parameters of coating sintering were formed by orthogonal test method: after dipping in paints, samples were preheated at 110℃for 10 min, then heated to 270℃at the rate of 10℃/min and kept at a constant temperature for 15 min.Effects of irradiation, stirring, pH value and impurity on paints and coatings were studied. Results showed that dark and cool storage conditions and continuous stirring were required for paints. pH value should be kept around 8.7. Sulfate and nitrate had less effect. But chlorides seriously affected coatings'anticorrosion. Silicate and phosphate reduced the paints'stability significantly. Colorful coatings were obtained by adding particles, such as titanium dioxide, molybdenum disulfide, iron oxide red and chromium green. Further studies showed that addition of TiO2 and Cr2O3 improved coatings'anticorrosion, while MoS2 and PTFE deteriorated corrosion behavior, and Fe2O3 had no effect.The composition of sintered zinc-aluminum coating were studied by X-ray photoelectron spectroscopy (XPS), X-ray energy dispersive spectroscopy (EDS), SEM and glow discharge spectrum (GDS). The results showed that the main elements distributed evenly through the whole coating. Zn and Al existed largely in metallic state in sintered ceramic coating. In chromium-free zinc-aluminum coating, the ratio of Al3+ to Al0 was about 1/2. Most of molybdate were reduced to quadrivalent after sintering, Mo4+/Mo6+≈5.XRF, XRD and corrosion dynamic studies showed that thorough dezincification occurred when zinc-aluminum coatings were immersed in 20 mass% NH4NO3 70℃. The accelerated test method of NH4NO3 could not be used to evaluate the anticorrosion of chrome-free zinc-aluminum coatings.Corrosion behaviors of sintered zinc-aluminum coating in seawater were studied by means of SEM, EDS, polarization curves, Ecorr measurement and electrochemical impedance spectroscopy (EIS). It was found that the existence of micro cracks in coatings caused the failure of coatings. The accumulation of corrosion products in coatings had three field effects. First, products increased the coatings'physical resistance; second, hindered the coatings'scarification from providing cathode protection for steel base; third, strengthened the internal stress and reduced the micro cracks. Electrochemical noise of zinc-aluminum coatings in seawater was analyzed showing that Rn decreased.A corrosion model of zinc-aluminum coatings in seawater was developed. Corrosion of coatings developed from the initiation of metastable pitting; formation and extinction of individual pits to development and agglomeration of extensive pits, and to the final breakdown of the coatings.The corrosion behaviors of zinc-aluminum-chromium and zinc-aluminum coatings in seawater were compared by Ecorr and EIS techniques. The direct electrochemical evidences for the self-healing of Cr (Ⅵ) were observed. Some significantly negative Ecorr values were observed for zinc-aluminum-chromium coatings, comparing favorably with impedance behaviors and impedance values. The findings were important for further improving the properties of zinc-aluminum coatings.
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