Introduction to Galvanization

Galvanization is a metal coating process in which a ferrous part is coated with a

thin layer of zinc. The zinc
... coating seals the surface of
the part from the
environment, preventing
oxidation and weathering from occurring.

The primary method of
galvanization is “hot dip
galvanization”, which has
been in use for over 150 years.

>Cleaning the part before
galvanization is extremely
important. Surface
contaminants such as grease,
dust, or dirt can compromise
the galvanization process. Generally, parts are cleaned in
a two step process. In the
first step, the part is cleaned in
a hot alkaline solution to
remove any surface
contaminants. In the second step, the part is immersed in a
weak acid solution to remove
rust and scale, resulting in a
clean and smooth surface.

In both dry and wet
galvanization, the part is
immersed in a molten zinc
bath with a temperature of
about 860ºF(460ºC). The zinc
metallurgically bonds to the steel part, resulting in a
transition layer of steel/zinc
alloy between the steel part
and the zinc coating. The
galvanization process results
in a dull gray crystalline surface finish, often referred
to as “spangle”. Within 24-48 hours after
galvanizing, the outer surface
of the zinc coating becomes
zinc oxide. Any post-
galvanization coating
operations, such as powder coating, need to be performed
before this oxidation occurs.
After short term atmospheric
exposure, some of the outer
layer of zinc oxide becomes
zinc hydroxide. After extended atmospheric
exposure, the zinc oxide is
converted to zinc carbonate.
This “patina” provides an
additional layer of protection
to the steel part, helping it to withstand weathering.

Galvanization helps to extend
the life of steel parts by
providing a barrier between
the steel and the atmosphere,
preventing iron oxide from
forming on the surface of the steel. Galvanization also
provides superior corrosion
resistance to parts exposed to
the environment.