Electroplating means that in the solution containing the metal ions to be plated, the material or article to be plated is used as the cathode, and the plating layer can be obtained on the surface of the substrate through electrolysis. During the electrolysis process, a chemical reaction occurs at the interface between the electrode and the electrolyte, the anode releases electrons for oxidation reaction, and the cathode absorbs electrons for reduction reaction.
Electroplating can cover a layer of uniform and good bonding force on materials or items to change their surface characteristics and appearance, and achieve the purpose of material protection or decoration. Direct current (low voltage, high current) must be used during electroplating, and the current density and energization time can be properly controlled to obtain the required coating thickness.
Corrosion-resistant coatings are commonly used metals such as zinc, cadmium, copper, nickel, or alloys such as zinc-nickel, nickel-tin, nickel-copper, copper-zinc, etc. According to the different electrode potentials when the coating and the base metal form a galvanic couple, they can be divided into anodic coatings and cathodes. There are two types of coating. In corrosive media, the potential of the anodic coating is more negative than that of the base metal, such as galvanized or cadmium on steel. When the coating is damaged, the coating will dissolve as an anode, which has an electrochemical protection effect on the steel, that is, "sacrificial" protection. The thicker the coating, the greater the protection. The potential of the cathodic coating is more positive than that of the base metal. For example, aluminum, copper, and nickel are plated on steel. When the coating is damaged, the coating will accelerate the corrosion of the exposed part of the base metal. It can only protect it when it is completely impermeable. Therefore, the coating should pay attention to its tightness and no damage, and the protective ability determines its porosity. The porosity is low and the protective effect is large. The anti-corrosion effect is to use the coating to isolate the external environment, so that the corrosive medium cannot penetrate into the base metal.
