Its function is that the metal part of the earphone plug will be oxidized and denatured if exposed for a long time, which will make the use effect worse. The earphone plug is plated with gold to prevent the metal part from being oxidized due to exposure to air, so that the plug can conduct electricity better.
Nickel plating (Ni) can prevent metal from rusting and can be highly polished. Nickel plating on earphone plug is generally used to decorate the metal surface of the plug in order to improve the corrosion resistance of the earphone plug or make its surface more beautiful.