GMW 4205

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1 Scope

This specification covers requirements fora corrosion resistant black organic finish over an electrolytically depositedzinc-iron alloy, nickel alloy and/or zinc-nickel alloy substrate.

1.1 MaterialDescription.This coating system shall be free ofchromium. The final product shall conform to GMW3059 requirements. The platingshall be called out on the part drawing per example shown in paragraph 7.

1.1.1MaterialIdentification. Not applicable.

1.2 Cross-Reference of Replaced Specifications.

1.2.1Specifications Qualified to this Material Specification. Notapplicable.

1.3Symbol.Not applicable.

1.4TypicalApplication. This coating is intended primarily forbulk processed small steel parts such as bolts, screw and nuts used on exteriorvisible parts. This coating is especially suitable for internal drive (crossrecess, 6 lobed socket etc.) threaded fasteners and self drilling and tappingscrews.

1.5Remarks. se of this coating system on threaded surface and/or bearingsurface of joints could effect the torque-tension relationship. It isrecommended that a torque-tension study of the fastener joint be performedbefore releasing this finish on any new application.

2 References

Note:Only the latest approved standards areapplicable unless otherwise specified.

2.1Normative

DIN 946

ISO 9227

SAE J1960

SAE/SCAR-5

SAE/SCAR-11

ISO 1463

 ASTM D523

SAE/SCAR-1

SAE/SCAR-7

2.2GM.

GM4260P

GM9071P

GM9540P

GMW3059

GM4265P

GM9501P

GMW3001

2.3 Additional. None.

3Requirements

3.1Requirementson Delivery

3.1.1ChemicalRequirements. Not applicable.

3.1.2MechanicalRequirements. Not applicable.

3.1.3PhysicalRequirements.

3.1.3.1Appearance. This finish shall provide uniform black color on coated parts. Thefinished part shall have a gloss of 4 or higher (20 degree gloss meter per ASTMD523).

Note:Gloss level of the finished parts (whensmall) shall be measured on standard panel (steel, 75×200mm) processed with the production parts.

3.1.3.2 This finish shall not fill driver recess or threads nor interferewith normal fastener installation procedures. The finish shall withstand normalhandling and storage conditions without damage (chipping, flaking or other) andmust not stain or transfer to adjacent parts or operators hands.

3.1.3.3 The total coating system as received shall not adversely affect thedrive system: Internal recess dimensions, hex size, etc. or function of thefastener.

3.1.3.4Thickness. Typical zinc-iron, nickel or zinc-nickel alloy layer shall be (5…20)μm and topcoat layer shall be 25 μmmax, with a total thickness ≤45μm。

3.1.3.4.1 Thickness shall be determined by microscope examination of crosssections taken perpendicular to significant surfaces. See GM4260P, RecommendedPractices for Measuring Thickness of Plated Deposits and Anodic Coatings (SeeGM4260P).

3.1.3.4.2 In Case of bolts and screws, plating thickness shall be determinedat top of head at midpoint of largest continuous surface. In case of nuts,determine at midpoint of flats (wrenching facets).

3.1.3.4.3The maximum thickness of coating which may be applied to threads onthreaded products is limited by the basic thread size (tolerance h or H). Aftercoating, parts must gage with appropriate basic size GD thread gage. Threadsmay be produced undersize/oversize (before coating) to accommodate the coatingthickness, providing the finished product (after coating) meets all specifiedmechanical properties. Where mechanical properties are not specified,undersizing/oversizing is subject to approval by pertinent engineer, and allundersize/oversize shall be within permissible limits as agreed upon.

3.1.3.dhesion.Parts coated to this specification shall show noevidence of blistering or other appearance changes after exposure to humiditytesting per GM4465P for ≥96h. When tape tested per GM9071P, 10min after removal from humiditythere shall be ≤3.0min total peel back (peel back adding both sides of scribed line)from the lines scribed in an “X” and no other peeling in the area under thetape. This is not applicable to threaded fasteners.

Note: This test is applicable for initialapproval, applicator approval and PPAP submission parts.

3.1.3.5WeatheringCharacteristics. Parts coated to this specificationshall show no blistering, peeling, cracking, loss of adhesion, discoloration,or red rust after 1316.7 KJ/m2 in xenon arc per SAE J1960. After weatheringtest finished parts shall have a gloss level of 3 or higher (20 degree glossmeter, per ASTM D528)

Note:The weathering test shall be required to runfor initial approval only.

3.1.3.7CorrosionResistance. Significant surfaces of parts exposedto neutral salt spray per ISO 9227 shall show no white corrosion after 48hexposure, ≤10% white corrosion products after 144h, and no base metal corrosionafter 480h exposure. For this test externally threaded fasteners shall be powerdriven into a tapped hale or nut or steel panel, simulating production usage,removed, then installed finger tight or with a hand driver with proper drivebit into acrylic plastic or other inert panel, and exposed in salt spray at (15…30)°from thevertical to allow wetting per SAE/SCAR-1. Fasteners shall not drip on otherfasteners during the test.

3.1.3.7.1Normal production, processes that are in statistical process controlshall yield parts that are capable of meeting the salt spray requirements.

3.1.3.7.2 A periodic NSS test of the parts being processed on each linerunning this coating shall be conducted with sample size of 3 pieces minimumper line per shift.

3.1.3.7.3Actual processing control checks to be made and recorded shall bebased on chemical manufacturer’s instruction.

3.1.3.7.4 Parts must be NSS tested to meet the corrosion resistancerequirements on significant surfaces for initial approval of the finish,applicators and PPAP submissions. NSS test need not be completed prior toshipment of parts.

3.1.3.7.5 Significant surfaces for test evaluation include but are notlimited to fastener head, socket recess, semswasher and external nut surface.Sharp edges are excluded.

3.1.3.7.6Significant surface on parts other than threaded fasteners shall beall surfaces excluding sharp edges.

3.1.3.8AcceleratedCorrosion Test. Accelerated corrosion test shall beconducted with this finish coated parts,11516629 or similar cross recessed headscrews using production methods(sample size,N≈10 minimum). The testscrews shall be power driven and seated with production type tooling into 60/60galvanized steel test panels that have been painted with standard GMpretreatment, primer, and white base coat/clear coat.

The test screw shall be installed in ahorizontal row seated 25 mm min, apart. The screw shall be tested for 40 cyclesper GM8540P. Accelerated Corrosion Test.

After 24 test cycles, the screw heads shallexhibit no red rust and 30% max. white corrosion coverage. After 40 testcycles, the screw heads shall exhibit 10% max. red rust coverage and 50% max.white corrosion coverage. Note that all visible surfaces of the seated screwheads including screw heads edges shall be included in the percent of corrosioncoverage.

Note: This test is required for the initialapproval of the finish only.

3.1.3.9TemperatureResistance. After heating the parts for 1h at 150℃（parttemperature） the corrosion resistance requirements as specified in paragraph3.1.3.7 shall still be met. This test requirement is only for initial approvalof the finish material.

3.1.3.10GasolineResistance. For initial approval of new material,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 visualexamination. There shall be no color change, wrinkling, or any other change inthe coating appearance.

3.1.3.11Reliefof Hydrogen Embrittlement. ALL parts heat treatedor highly cold worked to a specified core hardness HRC 32 or greater or surfacehardness HRC 35 or greater, that are processed by the finish applicator perSAE/SCAR-5 and tested for de-embrittlement per SAE/SCAR-7. The sample sizefor the SAE/SCAR-7 test shall be per ASTM F1470.

3.1.3.11.1 When supplementary treatment is specified for a part that requiresbaking after plating, the supplementary treatment shall be applied after thebaking operation.

3.1.3.11.2 Hardened parts which have been tempered at <+175℃ shall beheated to +150℃ and held 8 h, or longer, if necessary.

3.1.3.12Torque-Tension Test. Metric threaded fasteners M6and larger shall be subject to torque-tension monitoring through the use ofsurrogate M 10×1.5 test bolts. Ten surrogate bolts shall be processed with theproduction parts. A minimum of 10 bolts per finish line per shift shall bemonitored per SAE/SCAR-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 result shall be maintained on file to be submitted whenrequired.

Table1:Torque Range Values

Note:Engineering drawings for surrogate fastenersfor Torque-tension test are available from Global Engineering Documents/HIS.

3.1.3.13 Coefficient of Friction. The coefficient of friction of threadedfasteners shall be 0.13±0.03(six sigma values) when tested per DIN 946 with thefollowing exceptions:

·  Tightening speed shall be (30±3)min^-1(RPM)

·  Test samples (excluding drivenfasteners) shall be thoroughly cleaned with an appropriate fluid/chemical toremove any grease/oil/wax/other contaminants.

·  Test clamping force shall becalculated as 75% of proof load.

Note:Both, Torque-Tension and Coefficient ofFriction tests are required only for the initial approval of the finish material.Suppliers/Applicators can run either Torque-Tension Test or Coefficient ofFriction Test for quality control.

3.1.4AdditionalRequirements. Not applicable.

3.2ProcessingRequirements. Subparagraphs were not applicable.

3.3PerformanceRequirements. Subparagraphs were not applicable.

3.4Requirementson other Stages during Life Cycle.

3.4.1ChemicalRequirements.

3.4.1.1Recyclability. Parts with this coating shall nothave any negative effect on recyclability of the parts.

3.4.1.2PhysiologicalSafety. The coating material must not cause anyhealth hazard either to line operators or customers.

3.4.2Mechanical Requirements. Not applicable.

3.4.3PhysicalRequirements. Not applicable.

3.4.4AdditionalRequirements. Not applicable.

4 Manufacturing Process

Not applicable.

5 Rules and Regulations

5.1All materials supplied to this specification must comply with therequirements of GMW3001. Rules and Regulations for Material Specifications.

5.2 All materials supplied to this specification must comply with therequirements of GMW3059. Restricted and Reportable Substances for Parts.

6Approved Sources

Suppliers to this specification must beapproved by the Specialist Team/ TDGs. GMNA approved suppliers names are availableon the on-line MATSPC System.

For other GM locations the responsibleengineering group should be contacted to obtain the approved sources in theindividual countries.

7 Coding System

This material specification shall bereferenced in other documents, drawings, VTS, CTS, etc. as follows:

“GMW4205”

Where

GMW =  GM worldwide

4205 =  Specification number

8 Release and Revisions

8.1Release. This material specification was first approved in AG 2001 andpublished in OCT 2001.

8.2Revisions. Not applicable.