Zinc plating Is an inexpensive, decorative and protective coating against corrosion used on iron and steel parts. It is primarily used on hardware, wire goods, stampings, sheet metal and machined components for many different types of industries including automotive, electrical, housing and machinery. After zinc plating, parts are usually treated in a chromate conversion coating in a range of colors to protect against white corrosion. At times, a post sealant, wax, or phosphate coating may also be applied to further enhance corrosion protection. The thickness of a zinc coating may range from 5 microns for mild service conditions to 25 microns for severe service conditions. Salt spray resistance of zinc electroplated parts may vary from 12 hours to over 240 hours dependant on the thickness and post-treatment method selected.
There are primarily three types of zinc plating solutions not including alloys; alkaline cyanide, alkaline non-cyanide, and acid chloride. For many years cyanide zinc plating was the most popular method used in the United States because it is easy and inexpensive to maintain. The covering and throwing power is superior to the acid chloride bath and it is more ductile, uniform and receptive to chromates. Increased regulations and concern for worker safety have made non-cyanide plating options more attractive to plating companies in recent years. The alkaline non-cyanide zinc plating process has many of the same characteristics as the cyanide process in that the deposits are more ductile, uniform and receptive to chromate than acid chloride.
The acid chloride bath can be operated over a wide range of conditions. It has superior leveling and brilliance characteristics as compared to the alkaline processes and it is more efficient. It can also be plated on cast iron and hardened steels. However, the process is very corrosive and the throwing power is only fair.
Typical specifications for zinc plating include QQ-Z-325 and ASTM B633