What are the reasons for the blackening of the surface of die castings after plating for a period of time?

Customers often ask me why the connector shell products provided by other suppliers will have black spots on the surface after a year and a half. Today, let me tell you about it by Dalian LEGO Xiaobian. In fact, there are the following reasons for this bad phenomenon:

1. Let's start from the product itself. The surface of die-casting parts is not dense enough and loose in the process of die-casting, while the product needs to be passivated by concentrated sulfuric acid in the process of electroplating, which simply means that sulfuric acid has corroded to the root of the product, and then the copper bottom and nickel bottom are applied to cover the surface of the product. In addition, the electroplated coating is too thin, which can't be seen in a short time at first, but after a period of time, Black spots will appear.

2. Storage status. For example, some of our electroplating products are packaged, blistered, adhesive tape, etc. they are placed in the warehouse. The warehouse has no constant temperature, no greenhouse controlled ventilation, or it is too wet, which is also part of the reason that affects the moldiness of products.