This specification covers requirements for a corro-sion resistant black finish over an
electrolytically deposited zinc-iron alloy, nickel alloy and/or zinc-nickel alloy substrate.
1.1 Material Description. This coating system shall be free of hexavalent chromate in final
prod-uct per GMW3059 requirements. The plating shall be called out on the part drawing per
example shown in paragraph 7.
1.2 Typical Application. This coating is intended primarily for bulk processed small steel parts
such as bolts, screws and nuts used on exterior and in-terior visible parts (cosmetic
applications). This coating is especially suitable for internal drive (cross recess, 6 lobed
socket etc.) threaded faste-ners and self drilling and tapping screws.
1.3 Remarks. Use of this coating system on threa-ded surface and/or bearing surface of joints
could affect the torque-tension relationship. It is recom-mended that a torque-tension study
of the fastener joint be performed before releasing this finish on any new application.
Note: Only the latest approved standards are ap-plicable unless otherwise specified.
2.1 External Standards/Specifications.
ASTM D523 SAE.USCAR-1
ASTM F1470 SAE.USCAR-5
DIN 946 SAE.USCAR-7
ISO 9227 SAE.USCAR-11
SAE J1960 VDA 621-415
2.2 GM Standards/Specifications.
3.1 Appearance. This finish shall provide uniform black color on coated parts. The finished
part shall have a gloss of 4 or higher (20 degree gloss meter per ASTM D523).
Note: Gloss level of the finished parts (when small) shall be measured on standard panel (steel,
75 x 200 mm) processed with the production parts.
3.2 Thickness. This finish shall not fill driver re-cess or threads nor interfere with normal
fastener installation procedures. The finish shall withstand normal handling and storage
conditions without damage (chipping, flaking or other) and must not stain or transfer to adjacent
parts or operators hands.
3.2.1 The total coating system as received shall not adversely affect the drive system: Internal
re-cess dimensions, hex size, etc. or function of the fastener.
3.2.2 Typical zinc-iron (containing 0.4 – 1.0% Iron), nickel or zinc-nickel (containing 8- 15%
nickel) al-loy layer shall be (5-20) µm and topcoat layer shall be 25 µm max. with a total
thickness ≤ 45 µm. Thickness shall be determined by microscope ex-amination of cross sections
taken perpendicular to significant surfaces. See GM4260P, Recommen-ded Practices for Measuring
Thickness of Plated Deposits and Anodic Coatings.
3.2.3 In case of bolts and screws, plating thickness shall be determined at top of head at
midpoint of largest continuous surface. In case of nuts, deter-mine at midpoint of flats
184.108.40.206 The maximum thickness of coating which may be applied to threads on threaded products
is limited by the basic thread size (tolerance h or H). After coating, parts must gage with
appropriate basic size G0 thread gage. Threads may be pro-duced undersize/oversize (before
coating) to ac-commodate the coating thickness, providing the finished product (after coating)
meets all specified mechanical properties. Where mechanical proper-ties are not specified,
undersizing/oversizing is subject to approval by pertinent engineer, and all undersize/oversize
shall be within permissible li-mits as agreed upon.
220.127.116.11 Recess Fill Test. Apply the coating to sur-rogate P/N 11516629 (4.2x 1.4x1.6 round large
crown washer head screw with 1A cross recess) or equivalent in production environment (sample
size, N= 10 min.). Perform recess tests before and after plating to confirm that the recess
dimensions are correct on the unplated fastener. Check the recess penetration depth, gage
penetration depth and wobble degrees per the drawing requirements (P/N 11516629) to the
following recess data on the coated parts:
Recess Penetration Depth -2.31- 2.77 mm
Gage Penetration Depth - -1.90- 2.36 mm
Wobble Limit--- 10 degrees max.
Refer to GM Standard Parts specification C200 for penetration gaging and C201 for Wobble gaging
Note: The Recess Fill test is required for initial chemicals/ process approval and every PPAP
submission of fasteners with recess drive.
3.3 Adhesion. Parts coated to this specification shall show no evidence of blistering or other
ap-pearance changes after exposure to humidity testing per GM4465P for ≥ 96 h. There shall
be minimum 99.0% of coating (topcoat) retention after the tape adhesion test per GM9071P Method
B. In case of threaded fasteners, steel test panels shall be processed with fasteners for the
Note: This test is applicable for initial approval of chemicals/process, applicator approval
and parts PPAP submission.
3.4 Weathering Characteristics. Parts coated to this specification shall show no blistering,
peeling, cracking, loss of adhesion, discoloration, or red rust after 1316.7 kJ/m2 in xenon
arc per SAE J1960. After weathering test finished parts shall have a gloss level of 3 or higher
(20 degree gloss meter, per ASTM D523).
Note: The weathering test shall be required to run for initial chemicals/ process approval only.
3.5 Corrosion Resistance. Significant surfaces of parts exposed to neutral salt spray per ISO
9227 shall show no white corrosion after 48 h exposure, ≤ 10% white corrosion products after
144 h, and no base metal corrosion after 480 h exposure. For this test externally threaded
fasteners shall be power driven into a tapped hole or nut or steel panel, si-mulating production
usage, removed, then installed finger tight or with a hand driver with proper drive bit into
acrylic plastic or other inert panel, and ex-posed in salt spray at an angle of 15-30 degree
from the vertical to allow wetting per SAE/USCAR-1. Fasteners shall not drip on other fasteners
du-ring the test.
3.5.1 Normal production processes that are in sta-tistical process control shall yield parts
that are capable of meeting the salt spray requirements.
3.5.2 A periodic NSS test of the parts being pro-cessed on each line running this coating shall
be conducted with sample size of three pieces mini-mum per line per shift.
3.5.3 Actual processing control checks to be made and recorded shall be based on chemical
3.5.4 Parts must be NSS tested to meet the corro-sion resistance requirements on significant
surfa-ces for initial approval of the finish, applicators and PPAP submissions. NSS test need
not be comple-ted prior to shipment of parts.
3.5.5 Significant surfaces for test evaluation of fas-teners shall be all exposed surfaces of
the fastener when installed, including but are not limited to fas-tener heads, socket recess,
sems washers and external surface of nuts. Fastener threads and point are excluded unless
otherwise specified on the drawing.
3.5.6 Significant surfaces on parts other than threaded fasteners shall be all surfaces. Deep
re-cesses, such as blind holes and the interior of tubes, are excluded unless otherwise specified
on the drawing.
3.6 Temperature Resistance. After heating the parts for 1 h at + 150°C (part temperature) the
cor-rosion resistance requirements as specified in pa-ragraph 3.5 shall still be met. This test
requirement is only for initial approval of the chemicals/ pro-cess.
3.7 Accelerated Corrosion Test. Part Number 11516629 or similar cross recessed head screws,
coated with this finish in production environment shall be used as sample (sample size N= ten
mi-nimum) for Accelerated corrosion test. The test screws shall be power driven and seated with
pro-duction type tooling into 60/60 galvanized steel test panels that have been painted with
standard GM pretreatment, primer, and white base coat/clear coat. The test screws shall be
installed in a hori-zontal row seated minimum 25 mm apart. The screw shall be tested for 40
test cycles (five pha-ses) per GM9540P, Accelerated Corrosion Test. After 24 test cycles (three
phases), the screw heads shall exhibit no red rust and 30% max. white corrosion coverage. After
40 test cycles, the screw heads shall exhibit 10% max. red rust coverage and 50% max. white
corrosion coverage. Note that all visible surfaces of the seated screw heads inc-luding screw
heads edges shall be included in the percent of corrosion coverage.
Note: This test shall be run with initial approval of chemicals/process and applicator
approvals. Appli-cators are required to perform this test (GM9540P) on processed parts minimum
of two times per year. Parts performance records shall be retained for minimum 3 years for
potential review. At a PPAP submission of a part the latest test results (not older than 6
months) of GM9540P test of the appli-cator can be submitted for approval. The 9540P test shall
be run at the frequency deemed appro-priate by the applicator, such that a confidence in passing
GM9540P requirements is developed. The twice per year minimum frequency requirement must be
3.7.1 VDA 621-415 (Cyclic Corrosion Test). The coating to this specification shall be exposed
per VDA 621-415 Cyclic Corrosion test method. After 3 test cycles of VDA 621-415, the significat
areas shall exhibit no red rust and 10% max. white corro-sion coverage. After 6 test cycles,
the significant areas shall exhibit no red rust.
Note. VDA 621-415 Cyclic Corrosion test could be used by GME as an alternate test method to
3.8 Aluminum Galvanic Corrosion Test. The test fasteners (sample size N=10 minimum) coated with
this finish in production environment shall be power driven and seated with production type
tooling into an aluminum test panel (AA 6061 grade, 4 mm min. thick). The test fasteners shall
be installed in a horizontal row seated minimum 25 mm.apart. The fasteners shall be tested for
40 test cycles (5 pha-ses) per GM9540P, Accelerated Corrosion test. The test fasteners shall
be removed after 40 test cycles and the pit depth in aluminum test panel shall be measured for
each test fastener. The lar-gest pit depth shall not be more than 5% of test panel thickness
for each fastener.
Note: This test is required to be run for the initial approval of chemicals/process of the finish.
3.9 Gasoline Resistance. For initial approval of new materials, coated parts shall be soaked
for 200 ± 2 s in gasoline as described in GM9501P. After removal of the parts, they shall be
allowed to air dry before visual examination. There shall be no color change, wrinkling, or
any other change in the coating appearance.
3.10 Relief of Hydrogen Embrittlement. All parts heat treated or highly cold worked to a
specified core hardness HRC 32 or greater or surface hard-ness HRC 35 or greater, that are
processed through a hydrogen generating process, shall be processed by the finish applicator
per SAE/USCAR-5 and tested for de-embrittlement per SAE/USCAR-7. The sample size for the
SAE/USCAR-7 test shall be per ASTM F1470.
3.10.1 When supplementary treatment is specified for a part that requires baking after plating,
the supplementary treatment shall be applied after the baking operation.
3.10.2 Hardened parts which have been tempered at < +175°C shall be heated to +150°C and held
8 h, or longer, if necessary.
3.11 Torque-Tension Test. Metric threaded faste-ners M6 and larger shall be subject to
torque-tension monitoring through the use of surrogate M10x1.5 test bolts. Ten surrogate bolts
shall be processed with the production parts. A minimum of 10 bolts per finish line per shift
shall be monitored per SAE/USCAR-11, except tightening speed shall be 30 ± 3 min-1 (RPM). The
six (6) sigma torque range values shall be within the listed range (see Table 1). The test results
shall be maintained on file to be submitted when required.
Note: Engineering drawings for surrogate faste-ners for Torque-tension test are available from
Global Engineering Documents/IHS.
3.12 Coefficient of Friction. The coefficient of friction of threaded fasteners shall be 0.13
± 0.03 (six sigma values) when tested per DIN 946 with the following exceptions:
• Test samples (excluding driven fasteners) shall be thoroughly cleaned with an appropriate
flu-id/chemical to remove any grease/oil/wax/other contaminants.
• Test clamping force shall be calculated as 75% of proof load.
Note: Both Torque-Tension and Coefficient of Fric-tion tests are required only for the initial
approval of the chemicals/process. Suppliers/Applicators can run either Torque-Tension Test
or Coefficient of Friction Test for quality control.
Table 1: Torque Range Values
Thread Size Surrogate Bolt Test Nut Test Washer Torque in Nm Tension
Part Number Part Number Part Number SAE/USCAR 11 in kN
M10 x 1.5 11516105 11516090 11502644 48 ± 8 28.3
4 Manufacturing Process
5 Rules and Regulations
5.1 All materials supplied to this specification must comply with the requirements of GMW3001,
Rules and Regulations for Material Specifications.
5.2 All materials supplied to this specification must comply with the requirements of GMW3059,
Re-stricted and Reportable Substances for Parts.
6 Approved Sources
Engineering qualifications of an approved source is required for this specification. Only
sources listed in the GM Materials File (i.e., MATSPC) under this specification number have
been qualified by engi-neering as meeting the requirements of this speci-fication.
For other GM locations, the responsible engineer-ing group should be contacted to obtain the
ap-proved source in that individual country.
7 Coding System
This material specification shall be referenced in other documents, drawings, VTS, CTS, etc.
Material per GMW4205
8 Release and Revisions
8.1 Release. This material specification was first approved in August 2001 and published in
Rev Approval Description (Organization)
A SEP 2004 Complete Revision (GMW Finish