Several main factors affecting the quality of anodic oxide film
The current density in a certain extent, the current density increased, film growth rate increased, the oxidation time is shortened, the pores of the membrane formation, easy coloring, and the hardness and wear resistance increased; the current density is too high, it will be because of the impact of Joule heat, the surfaces of the parts of local overheating and the increase of solution temperature, the dissolution rate of film increased, and burned parts; the current density is too low, then the film growth is slow, but the film is dense, the hardness and wear resistance decrease.
Aluminum oxide, used for protection, decoration and pure decoration, uses the upper limit of allowable concentration, that is, sulfuric acid of 20% concentration is used as electrolyte.
Oxidation time: the choice of oxidation time depends on the electrolyte concentration, temperature, anode current density and the required film thickness. Under the same conditions, when the current density is constant, the film growth rate and oxidation is proportional to the time; but when the film grows to a certain thickness, the membrane resistance increased, effect of conductive ability, but also because of the temperature rise, the dissolution rate of membrane increased, so the growth rate of the film will gradually decrease and finally no longer increases.
Sulfuric acid concentration: usually use 15% - 20%. The increase of the concentration of the dissolution rate of membrane increased, the growth rate of the membrane decreased, the membrane porosity is high, strong adsorption capacity, flexibility, good dyeing (easy dyed dark), but the hardness and wear resistance is slightly worse; and reduce the concentration of sulfuric acid, then the oxide growth speed, membrane pore, high hardness, wear resistance good.
Electrolyte temperature: electrolyte temperature has great influence on the quality of oxide film. With the increase of temperature, the dissolution rate of film increases and the film thickness decreases. When the temperature is 22 to 30 degrees Celsius, the film is soft, good adsorption capacity, but the wear resistance is poor; when the temperature is greater than 30 DEG C, the membrane became loose and uneven, sometimes even discontinuous, and the hardness is low, thus losing the use value; when the temperature is between 10 to 20 degrees Celsius when the porous oxide film, strong adsorption capacity, good elasticity, suitable for dyeing, but film of low hardness, poor wear resistance; when the temperature is below 10 DEG C, the increase in the thickness of the oxide film, high hardness, good abrasion resistance, but lower porosity. Therefore, the temperature of the electrolyte must be strictly controlled during production. In order to prepare a thick and hard oxide film, the operation temperature must be reduced. During the process of oxidation, the compressed air is used to mix and lower the temperature, and the hard oxidation is usually carried out at about zero degrees.
Mixing and moving: it can make the electrolyte convection, strengthen the cooling effect, and ensure the uniformity of the solution temperature. It will not cause the quality of the oxide film to decrease because of the partial heating of the metal.
The impurities in the electrolyte in anodic aluminum oxide with potential impurities in the electrolyte with Cl -, F -, NO3 -, Cu2+, Al3+, Fe2+ etc.. The Cl -, F -, NO3 - membrane porosity increased, surface roughness and porosity. If the content exceeds the limit value, and even make the parts corrosion perforation (Cl - F - should be less than 0.05g/L, less than 0.01g/L); when the content of Al3+ in the electrolyte exceeds a certain value, often make the white spots or white appear porphyritic surface, and the adsorption performance of the membrane decreased, dyeing difficulties (Al3+ less than 20g/L); when the Cu2+ content reaches 0.02g/L, dark stripes or black spots may appear on the film; Si2+ often exists in the electrolyte in a suspended state, the electrolyte with brown powder trace turbid, adsorbed on the membrane.
The Aluminum Alloy composition: in general, the other elements in the aluminum metal decreased the quality of the film, and the film has not been aluminum thick, low hardness, Aluminum Alloy different components, in the anodic oxidation treatment can not pay attention to the same slot.