Zinc Plating
ZINC is anodic to iron and steel and therefore offers more protection when applied in thin films of 7 to 15 μm (0.3 to 0.5
mil) than similar thicknesses of nickel and other cathodic coatings, except in marine environments where it is surpassed
by cadmium (which is somewhat less anodic than zinc to iron and steel). When compared to other metals it is relatively
inexpensive and readily applied in barrel, tank, or continuous plating facilities. Zinc is often preferred for coating iron and
steel parts when protection from either atmospheric or indoor corrosion is the primary objective. Electroplated zinc
without subsequent treatment becomes dull gray in appearance after exposure to air. Bright zinc that has been
subsequently given a chromate conversion coating or a coating of clear lacquer (or both) is sometimes used as a
decorative finish. Such a finish, although less durable than heavy nickel chromium, in many instances offers better
corrosion protection than thin coatings of nickel chromium, and at much lower cost.
Much recent attention has been focused on the development of techniques for electroplating alloys such as zinc-iron, zincnickel,
and zinc-cobalt. The operating parameters and applications of these coatings is very similar to those for unalloyed
zinc. More detailed information about these techniques is provided in the article "Zinc Alloy Plating" in this Volume.
Plating Baths
Commercial zinc plating is accomplished by a number of distinctively different systems: cyanide baths, alkaline
noncyanide baths, and acid chloride baths. In the 1970s, most commercial zinc plating was done in conventional cyanide
baths, but the passage of environmental control laws throughout the world has led to the continuing development and
widespread use of other processes. Today, bright acid zinc plating (acid chloride bath) is possibly the fastest growing
system in the field. Approximately half of the existing baths in developed nations use this technology and most new
installations specify it.
The preplate cleaning and postplate chromate treatments are similar for all zinc processes; however, the baths themselves
are radically different. Each separate system is reviewed in detail in this article, giving its composition and the advantages
and disadvantages.
Cyanide Zinc Baths
Bright cyanide zinc baths may be divided into four broad classifications based on their cyanide content: regular cyanide
zinc baths, midcyanide or half-strength cyanide baths, low-cyanide baths, and microcyanide zinc baths. Table 1 gives the
general composition and operating conditions for these systems.

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