Preparation of Aqueous Epoxy Dispersion and Study of Chrome-free Conversion Treatment on Aluminum Alloy
|Keywords||Dispersions Epoxy Titanium/zirconium Gallic acid ester Aluminum Chrome-free Conversion coating|
This paper mainly was about the study of environmental metal surface treatment.It could be devided into two parts.The first part: In this paper, an aqueous epoxy dispersion was prepared. Firstly,the polyester prepolymer was prepared with NPG and SSIPA. Secondly,-NCOprepolymer were prepared with the polyester prepolymer and IPDI. Thirdly, theaqueous epoxy resin was prepared with-NCO prepolymer and epoxy E-20. Finally,the new aqueous epoxy dispersion was obtained by dispersing the aqueous epoxy resin.The best conditions for aqueous epoxy dispersions were obtained: SSIPA/NPG=1:3and NCO/OH=1.4. The factors influencing on stability of aqueous epoxy dispersionwere investigated and the influence of polyester prepolymer on particle size wasinvestigated. The mechanical properties and corrosion resistance performance of thecoating were good with the aqueous epoxy dispersion and curing agent.The second part: The inorganic/organic composite chrome-free conversioncoating was prepared. The gallic acid ester as organic additive was prepared on thebasis of titanium/zirconium system. And the best conditions for the synthesis of gallicacid ester as follows: time was5h, the temperature was140℃～150℃. Then the bestformula was obtained with orthogonal test. A new conversion coating obtained onaluminium alloy was investigated by FTIR spectra, Open circuit potential curve(OCP),polarization curve, Electrochemical impedance spectra(EIS), Scanning electronmicroscope(SEM), X-ray photoelectron spectroscopy(XPS), Energy dispersionX-ray(EDX), dopping test, mechanical property tests and salt-water immersionexperiments, respectively. The results demonstrated that compared with Ti/Zrconversion coating, gallic acid ester/Ti-Zr conversion coating displayed layerstructure, not granular, and yellow, not colourless. The conversion coating wasconsisted of C, O, Mg, Al, Ti, Si and Zr. At the same time, the composite mechanismof aluminum alloy-TiO-ZrO-gallic acid ester composite conversion coating throughthe bridging action of Ti and Zr was proposed. The composite conversion coating hadbetter corrosion resistance performance, boiling water adhesion, cup test resistanceand film weight than Ti/Zr conversion coating. What’s more, the stability of theconversion solution was not affected. And the composite conversion coating displayedyellow, not colourless.