Zinc electroplating is one of the more versatile finishes and can be chromated different colors after plating to achieve different results for a product.
Zinc has a bluish-white deposit that is an excellent, inexpensive, decorative, and sacrificial protective coating against corrosion of steel and iron parts. It is mostly used on nuts, bolts, fasteners, and sheet metal parts, and further protected by an application of chromates and sealers, which help prevent corrosion of both the zinc and the base metal.
Clear or “bluebright” is often used as an inexpensive imitation for chrome plating.
Yellow can be used as is, or as a paint base. Black chromate gives a very smooth, shiny, black finish for decorative purposes or as an excellent corrosion-resistant finish.
Olive Drab is usually used for military applications to match camouflage. The plating can also be dyed after plating for lot identification.
To prepare a part for plating, the part is initially cleaned thoroughly to remove dirt, grease, particulates, and any oxides that have accumulated on the surface. Parts are given a “bath” in an alkaline solution for cleaning, followed by another bath in a weak acid solution to remove the oxides. If any particles or oxides are left on the surface of the part, it could create voids in the plating layer, which can lead to unprotected areas.
Zinc forms a bond with the metal part, leaving a transition layer between the metals. This layer cannot be peeled off like paint because it is atomically infused with the base metal. After a couple of days of being exposed to the atmosphere, the outer surface of the layer becomes zinc oxide. After longer periods of time of environmental exposure, another protective layer is formed, which is zinc carbonate.