Research On Electrolytic Coloring Black Process And Film Performance Of 2024 Aluminum Alloy

Electrolytic coloration is one of the most important methods which are extensively used in aluminum alloy surface protection and decorative treatment. In this paper, the surface modification of 2024 aluminum alloy was studied by electrolytic coloration. The black oxidation film was well decorative and protective through electrolytic coloration. The film met the standard industrial applications through the selection and control of electrolyte and electrical parameters in the process of anodic oxidation and electrolytic coloring.Sulfuric acid was used as the main electrolyte in anodic oxidation. Experimental parameters, such as the condition of sulfuric acid, oxidation voltage, oxidation time were optimized in orthogonal test. Anodic oxidation film was moderate thickness, uniform and bright by orthogonal test method. Electrolytic coloration of 2024 aluminum alloy studied on the base of it. Electrolytic coloration salt was determined through the single-factor experiments. The condition of main-salts was optimized by orthogonal test. The process parameters, such as coloration time, coloration voltage and sealing time, were optimized in the single-factor experiments. After the electrolytic coloration processing, evaluation standard were the color of film, the uniformity, the brightness. The conclusion was that coloration film presented black, uniform and metallic luster, while corrosion resistance was well, in the condition of Ni SO4 10 g/L, Na WO4 5 g/L, C4H6O6 4 g/L, coloring voltage 4.5V, coloring time 10 min and sealing time 30 min.The properties of film and material distribution of colored layer were on the research. The experiment has studied light-proof aging, heat-resistance, corrosion resistance and wear-resistance. The results showed that the oxidation coloration film in the outdoor 60 days hadn’t appeared to fade. The film was well heat-resistance in 350℃. The wear-resistance was obviously improved compared with the blank sample. The oxidation coloration sample was not changed before and after test. The film with good binding force produced a little wear debris. The corrosion behavior of black anodizing film was tested by soaking test, the polarization curves and electrochemical impedance spectroscopy(EIS).The test result were consistent. The order of corrosion-resistance(from big to small) was the oxidation coloration film> the anodic oxidation film> the blank film. It illustrated that the corrosion-resistance was improved in the oxidation coloration. The experiment has analyzed the membrane appearance, the electrolysis coloration film ingredient and the structure using SEM, XRD, XPS and EDS.The experiment of coloration process was simple and good reproducibility with the coloring voltage of 4.5 V, the coloring solution is stable and environmental. Compared with the other coloring process, the advantages of this coloring process are conserving energy, pure color and low working voltage.