Preparation And Formation Mechanism Of Hard Anodized Coloring Film On 6061 Aluminum Alloy

Aluminum and aluminum alloys are widely used in production and life for their low price and excellent properties.The surface treatment process of anodizing with simple operation and high-quality has good application prospect in aerospace,automobile manufacturing,construction and other aspects.Among them,the hard anodize oxidation film of aluminum alloy has great mechanical properties,but its coloring property is limited by the slenderness of the film pore.In this paper,preparation and formation mechanism of colored oxidation film produced by hard anodizing and electrolytic coloring on 6061 aluminum alloy were studied.In this study,hard anodizing was used to prepare the film to be colored,the oxidation time and the oxidation current density were set as the parameters to be optimized in the anodizing process,then a hard anodized film of aluminium which possess the hardness and transparency was prepared.On this basis,a two-step oxidation method is used to obtain a hard anodized film having ordered pores and great conductivity,wherein the time of primary anodization is optimized,and the optimized oxidation time and the oxidation current density are subjected to secondary oxidation.In the electrolytic coloring stage,CuSO₄ and NiSO₄were selected as the main coloring salts of copper and nickel coloring systems respectively,the coloring time and coloring current density were used as the parameters to be optimized in the electrolytic coloring process,the hard anodized coloring film with high color saturation was prepared and the surface of the film do not include obvious defective.The color value,microscopic morphology,element and phase composition of the colored oxide film were investigated by Lab color model,scanning electron microscope（SEM）,energy-dispersive spectroscopy（EDS）and X-ray diffraction（XRD）.In addition,the corrosion resistance and photoaging resistance of samples were studied.The results showed that the film colored by copper was bronzed and the film colored by nickel was bronze;the depositional areas of the two coloring salts in the pores of the film were different,and the copper elemental phase was detected on the surface of the oxide film colored by copper;The corrosion resistance of the colored films is slightly lower than that of the uncolored oxide film,and has great protection effect on the substrate;The results of light aging test displayed that the hard anodized coloring film has advanced light resistance,and the film colored by copper has the phenomenon that the color saturation is increased as the illumination time increasing;Comparing the second anodized coloring samples with first anodized coloring samples,it was observed the deposition metal content after second anodization is higher,the destructive extent on the corrosion resistance of the film decreased,while the sensitivity of the colored film to the light was enhanced,after the illumination,the blackness of the secondary oxidation film colored by copper increased greatly,and the secondary oxidation film colored by nickel is slightly fade.