| A new technology, environmentally friendly process, was developed for aluminum alloy coloring. A serial of colored films were prepared by applying constant-current electrolytic coloring in 0.2mol/L NaOH solution. The color serial contained yellow-green, orange, tan, gray and bottle green.During the coloring, the coloring voltage and time dependence of corrosion resistance for colored films were analyzed to confirm optimum parameters with potential amplitude of 5V and 4 min. The colored film obtained was uniform, good wear-resistant, binding force and heat resistance.Corrosion resistances of colored films were evaluated by multi-electrochemical techniques including potentialdynamic, and electrochemical impendance spectroscopy. And microstructure and composition was investigated by surface analysis technology and correlation of film structure and corrosion resistance of films is studied. Rp of anodic and cathodic colored film were 12 kΩ·cm2 and 5 kΩ·cm2respectively in strong acidic media, and both about 70 kΩ·cm2 in strong alkaline media. Colored films can hold good corrosion resistance for 1000h in weak alkaline media and more than 1000h in neutral media. Colored films show good pitting corrosion resistance in both neutral and acidic Cl- contained media. Corrosion resistance of Al alloy had improved after being colored in corresponding media. Surface morphology, elements, microstructure and properties were studied by means of met allograph, Scanning electron microscopy and X-ray Diffraction. The chemical composition of colored film was mainly Al, O, and essential component was oxide and hydrate of aluminum, plus some alloy elements, like Cu, Mg, Fe and Mn. The thickness of colored film was about 5μm, which was thicker than that formed in natural oxidation film.Oxide of alloy elements had a low dissolvability in alkaline solution, so corrosion resistance of colored films was excellent in it. Dispersion distribution of alloy oxide enhanced binding force and hardness in a certain extent.
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