Common problems and analysis in anodizing process

Oct. 28, 2021   |   148 views

The anodizing process on the aluminum surface can cover the aluminum substrate with a dense oxide film, which can increase the corrosion resistance, wear resistance and UV resistance of aluminum, and greatly protect the aluminum material.However, many problems often occur in the process of anodizing.

1.   Aluminum salt precipitation

There are white precipitates on the anodizing film, which precipitate due to high chloride ion in the sulfuric acid anodizing tank solution or saturation of aluminum salt.
It is necessary to control the aluminum ion content, preferably less than 20g/L.

2.   Anodizing film stripping

The anodizing process was suddenly stopped, resulting in the stripping of anodizing film.
Check the anodizing procedure and eliminate the fault.

3.   Green film

After nickel salt sealing (including cold sealing with HT200 normal temperature sealing agent), the anodizing film is light green, sometimes exposed to the atmosphere.
Too much nickel is absorbed in micro-pore or the nickel ion or pH value of sealing tank solution is too high.
Adjust the nickel ion and pH value of the sealing tank solution.At present, many manufacturers use HT230 nickel free normal temperature sealing agent for cold sealing, and the sealing effect is also very good.

4.   Anodizing film yellowing

The anodized film is yellow, resulting in a change in the hue of the coloring.
Impurities such as iron and silicon in electrolyte or alloy are mixed into oxide film; Low anodizing temperature or high current density.

5.   Insufficient film thickness

The expected film thickness is not obtained, and the calculation of hanging area is wrong.
Poor electrical contact; Constant voltage anodizing.
Change to constant current anodizing; Check the hanging area; Check electrical contact.

6.   Decrease in film hardness (soft film)

The hardness or wear resistance of anodized film decreases, which is more common in hard anodizing.
High bath temperature or sulfuric acid concentration; Insufficient circulation or stirring of tank liquid.
Reduce tank temperature and strengthen mixing

The quality of anodized film directly affect the product quality. Whether it is dyeing, direct hole sealing or other purposes, the poor quality of anodized film will cause a series of chain reactions.Therefore, anodizing treatment is a link that can not be ignored.