What is the black spot on the surface of the aluminum plate?

During the production or application of aluminum sheets, black spots sometimes appear on them. What's going on in this situation? Let's study it. The first is the material of the aluminum plate. The upper cover of the aluminum plate produced by the aluminum plate manufacturer is processed from 0.5mm thick LF21 aluminum plate. This type of aluminum plate has a variety of parts of the same material, similar shape, and the same process, while the similarly shaped parts processed at the same time did not have such failures. And this is not a failure caused by a defect in the raw material. So in terms of processing technology, the general process route of silver plating on the upper cover is: machine-added parts-pre-treatment-dipping galvanized-electro-galvanized-electro-copper-electro-silver-spray paint-dipping 823-warehousing.

In the process of aluminum plate electroplating, first of all, it is possible that a certain production link of electroplating has changed, which leads to the occurrence of failures. However, the investigation found that the similar parts processed in the same period did not have such failures under the condition that there was no change in the production conditions. Therefore, factors that cause changes in electroplating production conditions are eliminated. According to previous production experience, the most common cause of discoloration of silver-plated parts is the effect of sulfur on the silver-plated layer.

In the past, it has happened that the parts after silver plating were not packaged and sealed in time, and they were placed in the electroplating workshop for a long time, which caused the silver plating layer to turn yellow. However, after the faulty parts were plated with silver, they were packaged in time and stored in a desiccator. It can be seen that this was not affected by the air atmosphere of the workshop. In terms of painting process, it was found that the painting process of the upper cover has been repaired in batches. The most important reason is that the gap is not plugged, allowing paint mist to enter and adhere to the surface of the silver plating layer and cannot be removed. In order to prevent such failures, it is recommended to seal the gap with 3M tape during the processing to prevent paint mist from entering.

Through this elimination method, the root of the problem was found, and we immediately took measures to prevent the recurrence of hidden dangers, so that the surface of the aluminum plate was as bright as new, and the delivery rate was greatly improved.