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Description / Abstract:
Material Description. This specification covers the basic
requirements for barrel or rack electrodeposited zinc alloy over a
ferrous substrate. Various alloy platings with supplemental
treatments are covered by this specification. This specification
covers functional requirements only. Cosmetic requirements, such as
brightness, shades, tint, etc., are not defined. Material approved
to this specification may not meet special cosmetic/appearance
requirements and must be agreed upon by the purchaser and
applicator. Table 1 lists the zinc alloy finishes covered by this
specification.
For parts calling out this specification without a specific
alloy (or to ZnNi without a Type A or Type B) but contracted and
completing the Production Part Approval Process (PPAP) after
January 1, 2014, the finish shall default to Type B. Parts
completing PPAP or contracted with GM before 2014 may have ZnNi
Type A or Type B.
Due to extremely low availability of applicators, do not specify
ZnCo or ZnFeCo on new designs. For existing designs, consult with
the responsible Design and Materials Engineers to locate sources or
to re-specify the finish.
ZnFe finish applicators are also not widely available. Consult
the responsible Materials Engineer before specifying ZnFe.
Symbols. Not applicable.
Typical Applications. Zinc alloy plating is especially suitable
for small to medium ferrous parts, such as castings, stampings,
clips, fasteners, and other ferrous parts, where levels of
corrosion protection exceeding pure zinc are required.
Remarks.
Electroplating may not be suitable for all materials and
applications. Each application must be reviewed with the
responsible Materials Engineer before usage.
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 (CoF) values in this specification are
determined at ambient temperatures. New applications for this
finish should be tested to confirm performance under
applicationspecific operating conditions.
These finishes are suitable for temperatures from -50 °C to 120
°C and to 150 °C for ZnNi. For applications outside this
temperature range, consult Materials Engineering.
Zinc and zinc corrosion products may cause localized
embrittlement when in contact with stressed Polyamide 6 or 66.
Caution must be taken when specifying these finishes on parts in
contact with Polyamide 6 or 66.
High-strength or high-hardness steel parts are susceptible to
hydrogen embrittlement. While certain precautions and post-plate
de-embrittlement baking are generally effective in protecting the
parts from hydrogen embrittlement, they are time sensitive and
require extra care during processing. Electroplating of steel parts
with hardness above 46 HRc is not recommended. See 3.9 for
precautions against hydrogen embrittlement.