Cause analysis and control measures of hard anodized dissolution of aluminum alloy parts

The thickness and hardness of the hard anodic oxide film are closely related to the electrolyte concentration, electrolyte temperature, current density, oxidation time and alloy composition. The occurrence of the dissolution phenomenon of parts also mainly depends on the above factors.

Influence of electrolyte concentration

In the sulfuric acid hard anodizing process, generally speaking, the lower the sulfuric acid content in the solution, the higher the hardness of the oxide film. However, for aluminum alloys with copper content (such as LY12), it is not advisable to use low-concentration electrolyte, otherwise it will easily cause the parts to dissolve. Therefore, the electrolyte should also be selected according to the material in the mixed acid hard anodizing process. Organic acid, the purpose is to increase the oxidation temperature and reduce the difficulty of production.

Influence of electrolyte temperature

In general, as the temperature decreases within the specified range of the process, the hardness and wear resistance of the film will gradually increase. In order to obtain a high-quality oxide film solution, the temperature fluctuation should be as small as possible and best controlled. In the range of ±2°C, when the local heat cannot be dissipated in time due to excessive current, the oxide film will be completely or partially dissolved. In order to control the electrolyte temperature within an excellent range, aluminum alloy anodizing should be laid on the inner wall of the electrolytic cell. Cooling equipment such as cooling pipes.

The effect of current density

Increasing the current density can increase the growth rate of the oxide film and shorten the time to obtain the required film thickness, thereby improving production efficiency. However, when the current density rises to a certain limit value, the opposite result will be obtained because too high current density will Increase the thermal effect in the pores of the oxide film to accelerate the dissolution of the oxide film. Of course, too low current density will not work, it will greatly reduce the growth rate of the oxide film. Practice shows that the current density is better in the range of (0.8-2.5) Mdm2. During the oxidation process, the smaller the current density fluctuation, the better. In the initial stage of oxidation, the production operation should be implemented by gradually increasing the current density to the specified value within a certain period of time (0.5~2min).