The degree of coloration of aluminum products depends largely on the formation quality of oxide film.Therefore, in the sulfuric acid anodic oxidation solution, the influence of impurities on the oxidation film cannot be ignored. The impurities are mainly metal ions such as copper, iron, aluminum and organic impurities and pollutants, which should be removed in time to maintain the normal use of the solution.

(1) copper ions will displace and deposit on the surface of aluminum parts, resulting in porosity of oxidation film, and reducing transparency, corrosion resistance and electrical insulation performance. Therefore, the content of copper ions is not allowed to exceed 0.02g/L.

(2) the chloride ion content should be lower than 0.2g/L in the cooling water after the tap water or the cooling pipe is broken, otherwise the oxide film generated will be rough and loose, and the surface of aluminum parts will be corroded (breakdown) in serious cases.

(3) aluminum ion in aluminum ion electrolyte increases gradually. When the content is more than 25 g/L, the conductivity of the electrolyte decreases, and the anodized surface of aluminum alloy profiles presents white spots or massive white spots, and the adsorption capacity of the film layer decreases, making dyeing difficult.

(4) iron ions in the iron electrolyte are not allowed to exceed 0.2g/L, or dark streaks will appear.

(5) organic impurities will hinder the formation of oxidation film, film adsorption oil, resulting in uneven coloring, spots.

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