I believe that those who have bought galvanized self-drilling screws have encountered such a situation, and the surface of the self-drilling screws has changed from the original color to black in a short period of time. Some customers think that there is a problem with the quality of the product and buy inferior drill nails. In fact, it is not. The blackening of galvanized drill tail nails is a very normal phenomenon, and it is not considered to be of poor quality.
The reason why the galvanized drill tail nails gradually darken from bright color is due to the oxidation reaction. The zinc layer is normally oxidized to ZnO, which is white, and in the absence of oxygen, it is oxidized to ZnO2, which is black. Galvanized drill tail nails are particularly prone to appear in the humid south (acid rain). Before the zinc layer is completely corroded and oxidized, the drill nail will not rust. Once you find that the galvanized drill tail nails are black, you should understand that the environment has been oxidized and corroded. It is necessary to add other anti-rust measures as soon as possible, and double or even multiple protections can make the galvanized drill tail nails last longer.