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