Treatment Base of Aluminum Anodizing

　　In acidic electrolytes,oxidation film comes from the surface of aluminum which as the anode.There are various types of electrolytes in aluminium anodizing,main composition with sulfuric acid,chromic acid,oxalic acid or boric acid.One of the most commonly used is acidophobe.Power supply can adopt DC,AC or alternating DC.The voltage is between 5 to 25 volts and the temperature is below 25 ℃.

　　In electrolyze process,the oxidation film is produced by acting on oxygen anions and aluminum.At first,the film was not enough fine,with a certain resistance,gradually became oxidation film by the reaction of negative oxygen ions and aluminium surface.With the increase of the film thickness,the resistance becomes larger and the electrolytic current decreases,there is occured a chemical dissolution in the outer oxidation film contacting with electrolytes,when the speed of oxidation film grown by aluminium surface balances with the rate of chemical dissolution,so that the oxidation film can obtain the maximum thickness under such a electrolytic parameter.The structure of aluminium anodized film is different from other invertible films,there is a 0.01-0.1μm of dense layer near the metal parts of matrix,its top is a honeycomb-like layer formed by many hollow hexagonal pillars,and the total thickness is about to 2 to 100μm.Anodized films produced from various electrolytes are in different hues,some are overall colouring which more apply to the construction industry,some can dye or use the method of hydrolysis and metathesis to make the pigment deposited in the hollow section of the hexagonal pillar and increase aesthetic feeling.

　　The final step are sealing and drying.The corrosion resistance of aluminum products with anodized aluminum film is sometimes better than those by the chromate treatment.In addition to being generally used on architecture industry and household hardware products,the aluminum products is also needed extensively on airplane,automobile and civil ship.The hard anodizing film formed through low-temperature,weakly dissolved electrolyte and 100 to 150 volt of higher voltage,can be used for engineering,mechanical parts and hydraulic components in contact with fibers,paper and rubber.The PTFE is filled in a hexagonal cylinder of general anodized aluminum layer and the parts with extremely low friction coefficient are obtained.

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