| Because of highly decorative, environmentally friendly and low toxicity, stainless steel chrome-free electrolytic coloring as a new stainless steel coloring technique is attracted by people. But chrome-free electrolytic coloring film is difficult to meet the actual requirements as its low corrosion resistance and wear resistance. To improve the properties of chrome-free electrolytic coloring film, in this paper, firm film processes such as electrolytic polishing, electrolytic activation, harden film and so are studied.Firm film process of pre-processing and post-processing matched with molybdate chrome-free electrolytic coloring system is acquired. The main research contents and results are as follows.1. Because chromic anhydride pollutes the environment and harms to human body,the traditional electrolytic polishing systems’ s range of application is limited. This article studies the effect of phosphoric acid- sulfuric acid system electrolytic polishing and amine additive(UP) by exploring multiple factors experiments, using means of electrochemical test and SEM morphological analysis. The results show gloss,corrosion resistance and wear resistance of colored film can be improved by electrolytic polishing, stainless steel over-corrosion in the process of electrolytic polishing can be effectively prevented by UP.2. The activation mechanism of stainless steel in activation liquid is analyzed by using electrochemical means. And anodic polarization curve of stainless steel in electrolytic activation solution is measured, the current range of electrolytic activation is obtained. The results show activation film generated during electrolytic activation,activation film growth includes three stages that nucleation, growth, forming. Stainless steel can obtain the best effect of electrolytic activation in a small current density(0.067 A / dm2).3. Four factors, three levels orthogonal experiment and single factor experiment are tested for electrolytic polishing, electrolytic activation system on the basis of the above experiments by measuring the parameters of gloss and corrosion time about surface of chrome-free electrolytic coloring film. The effect of electrolytic polishing and electrolytic activation is researched to colored film, and each optimum process recipe is obtained.4. Experiment studies the effect of stainless steel substrate surface state toperformance of electrolytic colored film. Corrosion resistance of colored film is tested by electrochemical means. The results show both matte surface and mechanically polished surface of stainless steel are took by electrolytic polishing and electrolytic activation, the gloss and corrosion resistance of electrolytic colored film are similar.pre-processing research obtained has a strong adaptability to the substrate surface.5. The effect of five kinds of harden methods that boiling water harden film,sodium silicate harden film, potassium dichromate harden film, nickel enclosed preparation harden film, silica sol harden film to electrolytic colored film are tested by electrochemical method and friction and wear testing machine. A layer of transparent organic film covering the colored film after the silica sol harden film,the effect of harden film is good and original color of colored film is remained. Moreover silica sol process is relatively mature, simple preparation, environmentally friendly and low toxicity. The effect of silica sol harden film is better than the other four methods.6. The morphology and phase of chromium-free electrolytic colored film and chromium electrolytic colored film are analyzed by SEM and XPS. Both surfaces are cracks. The cracks of chromium electrolytic colored film which mainly containing O,Cr, Fe and a little of Ni is deeper and its thickness is 15~20μm. Cr which has a self-healing properties and improve the corrosion resistance of the film is existed in the form of hexavalent and trivalent and Fe is divalent and trivalent. The cracks of chromium-free electrolytic colored film which mainly containing O, Mo and a little of Fe is shallower, lesser and denser. Its thickness is 2~3μm. And Mo is existed in the form of hexavalent. Therefore, pre-processing and post-processing can decrease the difference of corrosion resistance and wear resistance between chromium-free electrolytic colored film and chromium electrolytic colored film. |
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