Process characteristics of hard oxidation processing

The hard anodized electrolyte is electrolyzed at a temperature of about -10 ° C to + 5 ° C. The oxide film layer generated by the hard anodization has a high resistance, which directly affects the oxidation of the current intensity. In order to obtain a thick oxide film, it is necessary to increase the external voltage. Its purpose is to eliminate the effect of large resistance and keep the current density constant. However, when the current is large, intense heat generation will occur. A large amount of heat is released, and the temperature of the electrolyte around the parts rises sharply. The temperature rise will accelerate the dissolution of the oxide film, so that the oxide film cannot be thickened. In addition, the phenomenon of heat generation is most serious at the contact between the film layer and the metal. If not resolved in time, the local surface of the processed parts will be burned due to the temperature rise. Solution: It is a combination of cooling equipment and stirring. The cooling equipment forcibly lowers the temperature of the electrolyte. The stirring is to make the temperature of the electrolyte in the whole tank uniform, so as to obtain a hard oxide film of higher quality.

What factors affect the hardness and growth rate of the oxide film?

Whether a high-quality hard oxide layer can be formed on the surface of aluminum and aluminum alloy depends on the concentration of the electrolyte, temperature, current density, and the composition of its raw materials.

Electrolyte concentration

When using sulfuric acid electrolyte for hard anodizing, it is generally in the concentration range of 10% to 30%. When the concentration is low, the hardness of the oxide film is high, especially for pure aluminum, but for aluminum alloys with high copper content (CY12) exception. Because aluminum alloys with higher copper content easily generate CuAl2 compounds, this compound dissolves faster during oxidation, and it is very easy to burn aluminum parts. Therefore, it is generally unsuitable to use low-concentration sulfuric acid electrolyte, and it must be oxidized in a high concentration (H2SO4 in 300-400g / L) or adopt the AC-DC superposition method.

Effect of temperature on the film

The temperature of the electrolyte has a great influence on the wear resistance of the oxide film. Generally speaking, if the temperature decreases, the wear resistance of the anodized film of aluminum and aluminum alloy will increase, which is caused by the decrease of the dissolution rate of the electrolyte to the film In order to obtain a higher hardness oxide film. We have to grasp that the hard anodizing treatment is better within the temperature range of ± 2 ℃.