Zinc Electroplating Process

Electroplating is a process used to reduce the positively charged ions of a desired material, with the help of an electric current. The process also coats a conductive object with a thin layer of the material, such as a metal. Zinc electroplating is one of the most common forms of electroplating and popular because of its relatively low cost, protective nature and attractive appearance. The coating done through this process gives corrosion protection to ferrous components and it can give colors like gold, black or olive drab finish, by post treatment.

The zinc electroplating process can be used to coat nuts, bolts, washers and automotive parts, such as interior components and gas filters. It also provides an effective undercoat for paints, when high corrosion performance is required. The most widely used zinc plating solutions are acid chloride, alkaline noncyanide, and cyanide, and the most widely used zinc alloys for electroplating are zinc-nickel, zinc-cobalt, and zinc-iron.

With the study of zinc electroplating by Electrochemical Noise (EN), it was found that the EN generated during the electroplating of large conglomerate zinc deposit has large potential oscillation amplitude and positive potential drift. However, small noise amplitude and little potential drift was seen in the case of compact zinc deposit. Any metal can be plated through the zinc electroplating process, but the most common are steel and iron, on which the process offers sacrificial protection.

Steps of Commercial Zinc Electroplating
On the commercial scale, zinc electroplating is done by the following steps.

1. Surface of the metal is cleaned in alkaline detergent type solutions, and it is treated with acid, in order to remove any rust or surface scales. Cleanliness is essential for successful zinc electroplating, as the molecular layers of oil or rust can prevent adhesion of the coating.
2. Next, the zinc is deposited on the metal by immersing it in a chemical bath containing dissolved zinc. A DC is applied, which results in zinc being deposited on the cathode. Alkaline zinc baths are used by the finished products, to produce a more consistent zinc thickness, especially in recesses.
3. Hence an increased protection from corrosion is provided, as the corrosion of the deposited zinc is reduced. The zinc coating can increase the time required for the formation of white rust, by ten times. Finished Products also apply sealers, which are now commonly being specified by the automotive industry, further increasing corrosion protection.

It is very difficult to obtain a uniform thickness of coating, with electroplating technique. The thickness of the coating is very much dependent on the geometry of the object being plated, and it is preferentially on the external corners and protrusions of the metal body, hence not much of it is deposited on internal corners and recesses. Zinc electroplating is used to make a clean, smooth and corrosion resistant surface. It also makes an excellent undercoat for powder coating or paint and can leave recesses on complex shaped components without sufficient zinc coating, in order to provide corrosion protection.