The Film Layer Of Black Anodic Alumina Parts Is Not Colored.

(1) The dye used is not suitable or the dye has decomposed.

(2) The pH of the coloring solution is too high (when the pH increases to 7, the coloring is difficult to make).

(3) Insufficient oxide film thickness.

(4) The oxidized parts are placed for a long time, resulting in the closure of the oxide film pores.

Exclusion method:

(1) Select appropriate dyes to reformulate the coloring solution and replace the original coloring solution.

(2) Lower the pH to the process specification. The pH of the coloring solution has a great influence on the coloring affinity. Therefore, the appropriate pH must be chosen according to the dye. Generally, the pH ranges from 3.5 to 6. Acetic acid and ammonia can be used to adjust the pH. If using soluble anthracene dyes, the pH should be controlled between 4 and 5.5. In this temperature range to increase the acidity, color faster. But high acidity can make the dye fail faster.

(3) Appropriately extend the anodic oxidation time to increase the thickness of the oxide film.

(4) Aluminum parts should be colored immediately after oxidation, and fresh oxide film is easy to color.

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