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GMW GMW3179 Document Information:
Title
Protective Finishes – Zinc Phosphate Type
GM Worldwide
Publication Date:
Jul 1, 2007
Scope:
This standard covers the basic requirements for corrosion
resistant finishes for iron and steel substrates whose basic
characteristic is zinc phosphate treatment and subsequent
protective compound. Parts coated with this coating are typically
used internally for engines and transmissions or in areas where
minimum corrosion protection is required. (e.g. low visible areas
in the passenger compartment) Finishes with oil coatings are not
recommended for usage against plastic surfaces. It is recommended
that preapplied adhesives, sealers and nylon-type patching elements
be applied before supplementary treatments. (code A, B, G, H, W,
& Y.)
Material Description. The material approved to
this specification covers zinc phosphate treatments plus subsequent
protective compounds. This coating system must be free of
hexavalent chromium with no hexavalent chromium in final product
per the requirements of GMW3059. GMW3034 shall be used as a referee
test. This coating process does not generate hydrogen, however,
pretreatment processes i.e. acid pickling could cause hydrogen
absorption. This coating has high permeability, which allows
effusion of hydrogen during curing which might have been absorbed
during acid pickling. This finish could be zinc phosphate only or
different supplemental treatments with zinc phosphate as shown in
Table 2 as different codes of this specification.
Typical Applications. This coating is suitable
for internally threaded parts, parts with internal drive recess,
externally threaded and non-threaded ferrous parts where minimum
corrosion protection and freedom from hydrogen embrittlement are
required.
Remarks. Use of this coating on threaded
surfaces and/or bearing surfaces of joints could affect the
torque-tension relationship. It is recommended that a
torque-tension study of the fastener joint be performed before
releasing this finish on any new application.
Coefficient of friction/torque tension values in this
specification are determined at ambient temperatures. New
applications for this finish should be tested to confirm
performance under application specific, operating conditions.
Finishes with integrated lubricant (Code G & H) conforming
to the requirements of this specification can be used in the
application range of -50 to +120°C. For applications outside of
this temperature range consult your local Material/Fastener
Engineering group.
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