Preparation And Optical Interference Coloring Mechanism Of Colorful Anodic Oxide Films Grown On Aluminum Alloy

As the most widely used non-ferrous metal material,aluminum alloy's surface coloring treatment dramatically improves the beauty,added value,and profit of the products.The traditional electrolytic coloring is monotonous and limited to champagne-bronze-black,so it is challenging to meet the requirements of weather resistance and multicolor of aluminum alloy anodic oxidation film at the same time.This study aims to develop a simple color electrolytic coloring method that can output stably in a single color bath.The correlation between the coloring process,the oxide film's microstructure,and its color characteristics were explored by changing the power parameters,and the color development law and coloring mechanism were clarified.Bragg theory was used for quantitative and finite element simulations to explore the optical interference process behind oxide film's color coloring phenomenon.The results show that three layers of an oxide film with sulfuric acid oxide layer at the top,reflection layer at the middle,and color adjustment layer at the bottom can be formed successively on the aluminum alloy surface after the alternating electrolysis process.The thickness and aperture of the top sulfuric acid oxide layer are controlled by the anodic oxidation time and oxidation voltage in the sulfuric acid step,and the color of the oxide film is not affected.The barrier layer's repair step dissolves and regenerates the top sulfuric acid oxide layer's barrier layer.The voltage of this step will affect the intermediate reflector's structure and affect the coloring color.The lowpressure ac oxidation in the formation step of the intermediate reflection layer forms a soft,irregular pore path and isotropic intermediate reflection layer,which can effectively reflect the incident light and is the coloring's critical structure process.The color control step forms the bottom color adjustment layer,and the thickness of the layer and the structure parameters of the film hole significantly affect the color of the oxide film.When the oxidation time of this step was extended from 55 s to 145 s,the thickness of the bottom color adjustment layer increased from 136 nm to 271 nm,and the color of the oxidation film changed from yellow to green,indicating that the thickness of this layer could be controlled by controlling the oxidation time of this step,and then the color of the coloring could be precisely adjusted.The electrodeposition step in the membrane pore will deposit the sediments composed of Sn O2 and Sn Ox/Sn in the membrane pore at the oxide film's bottom.The sediments' phase and content do not affect the oxide film's color but promote the bright color of the oxide film.The effect of oxide film structure on color is the same as that of Bragg film interference.The middle reflective layer and the aluminum alloy surface are two reflective surfaces in the Bragg thin-film interference structure.The incident light forms the first beam of reflected light in the middle reflecting layer,and the light transmitted over the middle reflecting layer forms the second beam of reflected light on the aluminum alloy surface.The interference between the two beams of reflected light enhances the specific band's light intensity and makes the oxide film show the corresponding color.The reflected light's optical path difference is determined by the middle reflecting layer and the bottom color adjustment layer.The composite refractive index of the top sulfuric acid oxide layer,the middle reflecting layer,and the bottom color adjustment layer are 1.8205,2.004,and 1.819,respectively.According to the Bragg interference formula,the interference wavelength was extended from 636 nm to711nm when the bottom color adjusted layer's thickness was increased from 136 nm to168nm.When the thickness increases from 223 nm to 271 nm,the interference wavelength increases from 421 nm to 524 nm.The results obtained by finite element simulation software show that as the bottom color adjustment layer's thickness increases,the wavelength of the reflection peak shifts red,and the reflectivity curve is consistent with the measured results.The theoretical calculation and simulation results verify the scientific nature of the Bragg interference mechanism.In this experiment,the effect of the multilayer microstructural oxide film's preparation parameters on its structure and color was investigated,and the optical interference coloring mechanism based on multilayer microstructural oxide film was proposed.The correctness of the principle is verified by theoretical calculation and simulation.It has laid a foundation for the study of complex oxide film structure and multilayer microstructure oxide film color development for multi-process,which is of great significance to the theoretical research and practical application of aluminum alloy coloring..