| Dacromet coating is widely used because of its good high temperature resistance,corrosion resistance and hydrogen embrittlement.However,in recent years,due to the restriction of hexavalent chromium,it is urgent to develop chromium-free Dacromet coating without chromium.In this paper,the chromium-free corrosion-resistant coating was prepared on the basis of dacromet technology,and its properties were characterized by means of scanning electron microscope(SEM),electrochemical workstation,X-ray diffraction(XRD),ammonium nitrate resistance test,cross-cutting method,etc.The best preparation process of the chromium-free corrosion-resistant coating was determined,and the corrosion mechanism of the chromium-free corrosion-resistant coating was preliminarily discussed.The basic formula was determined by reading relevant literature,and the best was determined by single factor and orthogonal test: zinc powder 14 g,aluminum powder2.72 g,KH-560 13.44 g,modified acrylic resin 2.44 g,sodium hypophosphite 1.4g,polyethylene glycol-400 4.8g,NP-10 5.2g,hydroxyethyl cellulose appropriate amount.At the same time,the related technology was optimized:the drying conditions were80?,10 min,and the curing time was 240?,30 min.The performance test of the prepared coating shows that the p H value of the coating is 7.88 and the viscosity is 41.22 s;The coating can be stored at room temperature for 15 days without deterioration and still has good stability.The performance of the coating was characterized.The surface of the prepared chromium-free corrosion-resistant coating was smooth and flat,the color was silvery gray,and the surface zinc and aluminum powder were closely combined,which could effectively prevent the infiltration of corrosive media.The stability and corrosion resistance of the coating were good.The thickness of the coating is 15 ? 25 ? m,and the adhesion of the chromium-free corrosion-resistant coating is grade 1 by cross-cutting method and tape method,and the adhesion is good The hardness of the coating is 6H,and the hardness is average.Chromium-free corrosion-resistant coating has good corrosion resistance,which can be immersed in salt water for about 400 h and ammonium nitrate solution for about 420 min.The surface of chromium-free corrosion-resistant coating is composed of many elements,which are uniformly distributed.The surface of intact chromium-free corrosion-resistant coating is mainly composed of zinc-rich phase,aluminum-rich phase and zinc-aluminum oxide.In electrochemical test,compared with Q235 steel substrate,the coating has lower current density and negative potential shift,which can provide good protection for the substrate.Immersion corrosion test was carried out on the chromium-free corrosion-resistant coating in 5%Na Cl solution,and the original samples,samples immersed for 10 days and samples immersed for 15 days were characterized respectively.In EDS spectrum,the content of C and O first decreased and then increased,and in XRD diffraction spectrum,the composition phase changed from zinc-rich phase and aluminum-rich phase to a large amount of zinc-aluminum oxide,and the change trend of open-circuit potential with immersion time was first decreased and then increased.According to the change of SEM,EDS elemental analysis and XRD diffraction pattern,with the extension of immersion time,the corrosion process of chromium-free corrosion-resistant coating is firstly the destruction of the resin film on the coating surface,and then the metal powder is activated and starts to react with the corrosive medium,which produces a large number of corrosion products piled up on the coating surface to generate shielding effect again.By analyzing the changes of electrochemical impedance spectroscopy in different periods,it is speculated that the corrosion resistance mechanism of chromium-free corrosion-resistant coating is:physical shielding,sacrificial anode to protect cathode,corrosion inhibition passivation and self-repairing ability. |
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