When the temperature of the solution exceeds the process specification (24 ° C), the dissolution rate of the film increases, resulting in a decrease in film formation rate, film hardness and film thickness, deterioration in wear resistance and corrosion resistance, and loosening of the oxide film. A powdery film layer appears, and secondly, a decrease in film transparency occurs. And affect the dyeing performance, resulting in the color is not clear enough, even foggy. This is especially important for the workpiece to be dyed. Try to do everything possible to lower the temperature of the solution.
When the temperature of the solution is too low, such as lower than 12 ° C, the thickness of the oxide film can be increased, and the wear resistance is also good, but the brittleness of the film layer is increased, the porosity is small, and it is difficult to dye the dyed part. For this reason, when anodizing aluminum and aluminum alloys, the temperature of the solution must be strictly controlled to prevent the temperature of the solution from being too low.
Anodizing is an exothermic reaction, the heat of formation of the film is very high, and there is Joule heat generation, and the temperature of the solution rises rapidly. For this reason, anodizing should be carried out according to the existing conditions, and corresponding measures are taken to control the solution temperature in a normal process. Within the specification to ensure the quality of the film and the continuous production. When the temperature of the solution is too low, it is not conducive to the requirement of dyeing after anodizing. At this time, the general part can be processed first, and then the dyeing part is needed after the temperature of the solution rises slightly, which is to be mastered by experience.
What is the relationship between the anodization time and the oxide film quality?
Under the same conditions of solution concentration and other process conditions, with the extension of the anodizing time, the oxide film formed on the surface of the part (within a certain range) will gradually thicken and the pores will increase, which is beneficial to dyeing.
Under the same process conditions as above, the anodization time is shortened, the oxide film is thinned, the pores are also reduced, and the dark color is not easily stained. For this reason, in addition to some special cases, such as electrochemical polishing parts, in order to maintain a certain brightness after maintaining anodization, and to shorten the anodizing time, the general anodizing time should not be less than 30min, the need to dye dark parts still need to be extended, especially when the solution temperature is low, sometimes it needs to be extended to 45-60min.
Is the stirring of the solution necessary during anodization?
It is necessary to use a compressed air to agitate the solution during anodization because the heat generated during the anodization, such as a solution accumulated on the surface of the oxide film, causes the oxide film to accelerate to dissolve, thereby degrading the overall performance of the article. The solution is stirred by compressed air to rapidly dissipate the heat generated by the workpiece, and the cooled solution is used to cool the surface of the workpiece to continuously circulate the solution on the surface of the workpiece. Thereby, the normal progress of the oxidation process is ensured, and at the same time, the uniformity of the thickness of the oxide film is also advantageously improved.