Process Optimization Of Colored Ti-Zr Conversion Coating On Aluminum Alloy And Research Of Adhesion Force Of The Electrostatic Spraying Coating

As one of the chrome free chemical conversion technologies on the suface of aluminum alloy before electrostatic spraying, Ti-Zr conversion treatment is considered to be the chrome free method most likely to replace the traditional chromate surface treatment, with the advantages of environmental protection and excellent corrosion resistance. Nowadays, the research of Ti-Zr conversion treatment is relatively sufficient, especially the coloured Ti-Zr treatment with nice comprehensive performance in our research group. However, the adhesion force of spraying oganic coating with Ti-Zr conversion coating is less reported, which limited the industrial application of Ti-Zr chemical conversion treatment. Besides, none of the coating-adhesion mechanism of electrostatic spraying coating with Ti-Zr conversion coating has been studied.The research in this thesis was focus on the adhesion force of black electrostatic spraying coating with Ti-Zr conversion coating on the suface of aluminum alloy. By using a coloured Ti-Zr conversion treatment which was obtained by our research group with room temperature reaction, quick coating forming speed and good solution stability, excellent corrosion resistance of Ti-Zr coating has been obtained and the adhesion force of the followed spraying oganic coating has been studied. Also adhesion mechanism of the spraying coating has been explored in this paper, which provides certain theoretical value for the industrial application of combining Ti-Zr treatment and electrostatic spraying coating into use.Firstly, for preparing a Ti-Zr/spraying coating with nice corrosion resistance and excellent adhesion force with the outside organic coating, the optimal conversion time of Ti-Zr coating preparation was 50 s at room temperature. So the yellow conversion coating could be achieved. After the Ti-Zr conversion coating has been formed, the optimal stoving temperature is 100~110℃, and the optimal stoving time is 8~10min.The optimal Ti-Zr coating showed excellent anti-corrosion property and its corrosion current density was reduced to 0.453μA/cm2 from 1.926μA/cm2 of Al alloy substrate.And its polarization resistance Rp was increased to 4685Ω/cm2 from 38667 Ω/cm2. The thickness of the black and bright Ti-Zr/spraying organic coating is 50~60μm. The organic coating has a great adhesion force with the conversion coating, as the result of dry and boiling water Cross cut test has reached a level 0, and the result of the impact test has met the national standard GB2537.4-2008.The compositions of the Ti-Zr/spraying coating was characterized by EDS, XRD and XPS. The result showed that the Ti-Zr coating is in the form of amorphous state including Al2O3, Zr O2, V2O5 or the metal hydroxides, Al F3, Zr F4 and the Al,Ti complex. The main elements of the spraying organic coating were C、O、Al、S、Ca、Ti、Ba.The coating-adhesion mechanism was explored by EDS, XRD and XPS results of the Ti-Zr/organic coating surfaces. The organic coating was connected with Ti-Zr conversion coating or aluminum alloy by a chemical combination. The Ti-Zr coating mainly contain a series of new organic complex, which were combined with the organic colorants and the reactive metal cationics such as Al3+, Ti4+. These new organic complex would have a chemical bond connection with hydroxyl, ether group and epoxy group in the organic powder coating. After all, these chemical reaction enhanced the adhesion force between organic spaying coating and Ti-Zr coating on the suface of aluminum alloy.Finally, the research for wettability of melting powder coating on Ti-Zr conversion coating had showed that, the curing process of powder coating would experience three steps include melting together, spreading and flowing uniformly, then curing. The final wetting Angles of the organic powder coating on Ti-Zr coating was less than 90°, indicating good wetting properties, which also determined he strong adhesion force from the organic coating to substrates.