The anodic oxidation of aluminum uses aluminum as an anode and is placed in an electrolyte such as sulfuric acid. An anode voltage is applied to conduct electrolysis. A dense Al2O3 film is formed on the surface of aluminum. The film is composed of a dense barrier layer and a columnar porous structure. The layer consists of a double layer structure. Anodized films can be divided into two major categories: porous type - films formed in acid electrolytic baths such as sulfuric acid, oxalic acid and the like and forming very fine pores perpendicular to the surface; barrier type - in neutral salt electrolytic baths such as ammonium borate The resulting non-porous, extremely thin film, which is commonly used for electrolytic capacitors and the like.
At present, the application of a single anodized aluminum alloy building profile has been significantly reduced in practice, and the electrolytic coloring oxide film, the organic coloring oxide film and the ceramic oxide film, the hard oxide film, the imitating stainless steel oxide film and the like based thereon are reduced. Has been widely used, in general, the factors that affect the oxidation of aluminum alloy coloring are as follows:
1. Influence of impurities in electrolytic solution
The degree of coloring of aluminum alloy products depends on the quality of the oxide film. Therefore, in the anodizing solution of sulfuric acid, the impact of impurities on the oxide film can not be ignored, the impurities are mainly copper, iron, aluminum and other metal ions and organic impurities, should be promptly removed to maintain the normal use of the solution.
(1) Copper ions will be deposited on the surface of aluminum parts, resulting in loose pores in the oxide film, and reduce the transparency, corrosion resistance, and electrical insulation properties. Therefore, the copper ion content must not exceed 0.02 g/L.
(2) Chloride ions come from tap water or cooling water after cooling pipe rupture, chloride ion content should be less than 0.2g/L, otherwise the resulting oxide film is rough and loose, and the surface of the aluminum part is eroded (breakdown).
(3) The aluminum ions in the aluminum ion electrolyte gradually increase. When the content is more than 25 g/L, the conductivity of the electrolyte decreases, the surface of the product shows white spots or blocky white spots, and the adsorption capacity of the film decreases. difficult.
(4) Iron ions in ferric electrolytes are not allowed to exceed 0.2 g/L, otherwise dark streaks will appear.
(5) Organic impurities will hinder the formation of oxide film. After the film absorbs oil stains, the coloration will be uneven and flower spots will appear.
2. Factors affecting the coloring quality of oxide film
(1) If the pre-treatment degreasing process is incomplete, it will cause obvious white spotting on the film layer, which will cause difficulty in coloring.
(2) When the Sn salt concentration in the electrolytic solution is too low, the coloring speed is slow, and when the concentration is higher than 25 g/L, the coloring speed is fast, but it is not easy to grasp, and there is often a large color difference. .
(3) The coloring temperature has a great influence on the coloring. When the temperature is lower than 15°C, the coloring speed is slow. If the coloring temperature is too high, the coloring film will be fogged, and the Sn salt will be easily hydrolyzed and cause the turbidity of the bath.
(4) Time: The coloring time will also affect the coloring quality and color fastness. For example, the coloring time is short, the color is light and easy to fade, the time is long, the color is too dark, and the surface is prone to flowering.
(5) When the coloring voltage is low, the coloring speed is slow, the color change is slow, and the color tone unevenness is easy to occur. When the voltage is high, the coloring speed is fast and the coloring film is easily peeled off.
(6) Additives and stabilizers mainly composed of surfactants are added in the filming of anodic oxidation or electrolytic coloring. The purpose is to stabilize the film formation rate and film thickness, inhibit the dissolution of the oxide film and improve the coloring. Uniformity.
In addition, the pH value, water quality, and coloring tank material all have a certain influence on the coloring quality. Only by ensuring that each parameter is within the control range can the quality of electrolytic coloring oxide film be guaranteed.
At present, the application of a single anodized aluminum alloy building profile has been significantly reduced in practice, and the electrolytic coloring oxide film, the organic coloring oxide film and the ceramic oxide film, the hard oxide film, the imitating stainless steel oxide film and the like based thereon are reduced. Has been widely used, in general, the factors that affect the oxidation of aluminum alloy coloring are as follows:
1. Influence of impurities in electrolytic solution
The degree of coloring of aluminum alloy products depends on the quality of the oxide film. Therefore, in the anodizing solution of sulfuric acid, the impact of impurities on the oxide film can not be ignored, the impurities are mainly copper, iron, aluminum and other metal ions and organic impurities, should be promptly removed to maintain the normal use of the solution.
(1) Copper ions will be deposited on the surface of aluminum parts, resulting in loose pores in the oxide film, and reduce the transparency, corrosion resistance, and electrical insulation properties. Therefore, the copper ion content must not exceed 0.02 g/L.
(2) Chloride ions come from tap water or cooling water after cooling pipe rupture, chloride ion content should be less than 0.2g/L, otherwise the resulting oxide film is rough and loose, and the surface of the aluminum part is eroded (breakdown).
(3) The aluminum ions in the aluminum ion electrolyte gradually increase. When the content is more than 25 g/L, the conductivity of the electrolyte decreases, the surface of the product shows white spots or blocky white spots, and the adsorption capacity of the film decreases. difficult.
(4) Iron ions in ferric electrolytes are not allowed to exceed 0.2 g/L, otherwise dark streaks will appear.
(5) Organic impurities will hinder the formation of oxide film. After the film absorbs oil stains, the coloration will be uneven and flower spots will appear.
2. Factors affecting the coloring quality of oxide film
(1) If the pre-treatment degreasing process is incomplete, it will cause obvious white spotting on the film layer, which will cause difficulty in coloring.
(2) When the Sn salt concentration in the electrolytic solution is too low, the coloring speed is slow, and when the concentration is higher than 25 g/L, the coloring speed is fast, but it is not easy to grasp, and there is often a large color difference. .
(3) The coloring temperature has a great influence on the coloring. When the temperature is lower than 15°C, the coloring speed is slow. If the coloring temperature is too high, the coloring film will be fogged, and the Sn salt will be easily hydrolyzed and cause the turbidity of the bath.
(4) Time: The coloring time will also affect the coloring quality and color fastness. For example, the coloring time is short, the color is light and easy to fade, the time is long, the color is too dark, and the surface is prone to flowering.
(5) When the coloring voltage is low, the coloring speed is slow, the color change is slow, and the color tone unevenness is easy to occur. When the voltage is high, the coloring speed is fast and the coloring film is easily peeled off.
(6) Additives and stabilizers mainly composed of surfactants are added in the filming of anodic oxidation or electrolytic coloring. The purpose is to stabilize the film formation rate and film thickness, inhibit the dissolution of the oxide film and improve the coloring. Uniformity.
In addition, the pH value, water quality, and coloring tank material all have a certain influence on the coloring quality. Only by ensuring that each parameter is within the control range can the quality of electrolytic coloring oxide film be guaranteed.