GM7111M-2004 Corrosion Protective Coatings Phoshate-Zinc-Organic Type.pdf

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ENGINEERING Material Specification
Corrosion Protective Coatings Phoshate/Zinc/Organic Type
1 Scope
2.2 GM Standards/Specifications
This specification covers the basic requirements
for a corrosion protective coating process con-
sisting of zinc phosphate treatment, a zinc ricl
epoxy resin coating, and an aluminum tint or-
ganic top coating. The coating may be applied by
lipping or spraying. Part configuration dictates
3 Requirements
the application process. Internally threaded parts 3.1 Appearance and Cure. Coating shall give a
(nut) shall be coated in a canting centrifuge
uniform metallic gray appearance and shall be
Parts without internal threads can be coated b
)y free from tears, sags and excess coating, which
other processes
affect appearance and performance. It shall not
Note: Any additional approved source of this be oily or tacky to the touch
finish shall have canting centrifuge application 3.2 Thickness. Coating in threads of threaded
products shall not have an adverse effect on
1.1 Material Description. The coating system is
normal installation and removal practices
free of hexavalent chromate. with no hexavalen
3.3 The minimum total coating thickness shal
chromate in final product per GMW3059 require
be 15
ments. GMW3034 will be used as a referee test
This coating process does not generate hydro
3.3.1 The maximum thickness of coating, which
gen, however, pretreatment processes i.e. acid may be applied to threads on threaded products
pickling could cause hydrogen absorption. Non
is limited by the basic thread size(tolerance h or
electrolytically applied zinc rich coating has higl
H).After coating, parts must gage with appropri
permeability, which allows effusion of hydroger
ate basic size GO thread gage. Threads may be
during curing that might have been absorbed
produced undersize/oversize(before coating)to
during acid pickling
accommodate the coating thickness, providing
the finished product (after coating)meets al
2 Typical Application. The coating is suitable
pecified mechanical properties. Where me
for bolts, clips, and other ferrous parts where
chanical properties are not specified, undersiz-
above normal levels of corrosion protection and
ing/oversizing is subject to approval by GM engi-
freedom from hydrogen embrittlement are re
neering, and all undersize/oversize shall be
? uired
within permissible limits as agreed upon
1.3 This finish is not recommended for 360 de
3.3.2 Nuts must gage an appropriate GO thread
gree Nylon Patch Nuts
gage specified on drawings
1.4 Use of this finish on threaded surface and/on
3.4 Corrosion Resistance. Parts coated/plated
bearing surface of joints could affect the torque
to this specification shall be capable of withstand
tension relationship. It is recommended that a
ing neutral Salt spray(NSS)testing per GM4298P
torque-tension study of the fastener joint should
for the minimum of 240 h with no red rust. The
preformed before releasing this finish on a
corrosion testing of the threaded fasteners must

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