Sometimes, after alkali etching and light treatment, due to insufficient understanding between the previous and next processes, it cannot be immediately transferred to the next process and has to be placed in a cleaning tank for treatment. Little did they know that this treatment is not very safe, as pitting corrosion may occur when there are the following conditions in the cleaning tank.

1. The cleaning tank contains Cl ˉ。 Generally, cleaning tanks contain a certain concentration of Cl ˉ， Especially in the southern region, the water source of water plants comes from rivers and rivers, with poor water quality. Not achieving good disinfection effect and adding excessive bleaching powder, resulting in a relatively high concentration of Cl - in the incoming water ˉ It is corrosive and therefore easily penetrates the oxide film, causing pitting corrosion.

2. The cleaning tank contains metal ions with a positive potential compared to aluminum. These metal ions mainly include Fe2+, Cu2+, Ni2+, etc. They will accelerate the occurrence of pitting corrosion on the surface of aluminum materials, and the larger the potential difference, the more severe the pitting corrosion of aluminum.

Is aluminum stable in neutral salt solutions? Not entirely. It can be passivated and protected, or corroded by the action of certain cations or anions.

If the semi-finished product is prepared for anodizing, it is recommended to discard the free water and air dry it in a place with good environmental conditions to maintain the ability to undergo anodizing treatment on the next working day. However, it should not be dried as it is used for chemical conversion film treatment, otherwise it is not possible to obtain a conversion film quality that meets the quality requirements.

To avoid the occurrence of the above phenomenon, in addition to the tacit cooperation between the previous and subsequent processes, products that cannot be transferred to chemical conversion film treatment in a short period of time can be temporarily immersed in a solution containing oxidizing anions, forming a passivation film on the surface to prevent pitting and other forms of corrosion.