1、WORLDWIDEENGINEERINGSTANDARDSMaterial Specification GMW16730Cosmetic Coating, Black Zinc-Nickel Based Copyright 2012 General Motors Company All Rights ReservedOctober 2012 Originating Department: North American Engineering Standards Page 1 of 81 ScopeThis specification covers requirements for acorro
2、sion-resistant black finish for small parts.1.1 Material Description. This finish is a bulk-applied finish for small ferrous parts. It consists ofan electroplated zinc-nickel layer with passivationand topcoat.1.2 Symbols. Not applicable.1.3 Typical Applications. This coating is intendedprimarily for
3、 bulk-processed small steel parts, suchas bolts, screws and nuts used on exterior andinterior visible parts (cosmetic applications). Thefinish is especially suitable for internal drive (crossrecess, hexalobular (six-lobed) socket, etc.)threaded fasteners and other parts with smallrecessed features.1
4、.4 Remarks.1.4.1. Electroplating may not be suitable for allmaterials and applications. Each application mustbe reviewed with the responsible MaterialsEngineer before usage.1.4.2. Use of this coating system on threadedsurfaces and/or bearing surfaces of joints couldaffect the torque-tension relation
5、ship. It isrecommended that a torque-tension study of thefastener joint be performed before releasing thisfinish on any new application.1.4.3. This finish is suitable for temperatures up to120 C. Applications with exposures above thistemperature shall be reviewed with the responsibleMaterials Engine
6、er before usage.1.4.4. High-strength or high-hardness steel partsare susceptible to hydrogen embrittlement. Whilecertain precautions and post-plate de-embrittlement baking are generally effective inprotecting the parts from hydrogen embrittlement,they are time sensitive and require extra careduring
7、processing.Electroplating of steel parts with hardness above46 HRc is not recommended.2 ReferencesNote: Only the latest approved standards areapplicable unless otherwise specified.2.1 External Standards/Specifications.AIAG CQI-11 ISO 2813 ISO 17025AIAG CQI-12 ISO 4892-1 SAE J2527ASTM D523 ISO 4892-2
8、 SAE/USCAR-5ASTM F1470 ISO 9227 SAE/USCAR-7ISO 1463 ISO 160472.2 GM Standards/Specifications.GMW3059 GMW14700 GMW14829GMW14333 GMW14729 GMW148722.3 Additional References.TMC003 Material Safety Data Sheet guidancedocuments (available at ).GM Approved Finishers List(available at ).GM Drawing Numbers 1
9、1570102, 11611882,11612005, 11611954, and 11611987.GM Global Fasteners Catalog(available at ).GM Global Primary Gloss Master PGH(available at store.thierry- RequirementsThe parts coated to this specification shall meetthe following technical requirements anddemonstrated by the test methods described
10、. Theappropriate tests for different situations: Newchemical approval, new applicator approval,Production Part Approval Process (PPAP), andregular process control testing, are described inAppendix A. Procedures and requirements for newchemical and applicator approval are described inAppendix B.3.1 A
11、ppearance. This finish shall have a uniformblack appearance. The finish shall have a glosslevel of ten (10) or higher when measured with a60 gloss meter per ASTM D523 or ISO 2813.3.1.1 For chemical approval and referee purposes,the finished parts shall be visually compared to theGM Global Primary Gl
12、oss Master - PGH. TheCopyright General Motors Company Provided by IHS under license with General Motors CompanyNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-GM WORLDWIDE ENGINEERING STANDARDS GMW16730 Copyright 2012 General Motors Company All Rights ReservedOctob
13、er 2012 Page 2 of 8finished parts shall appear more chromatic in colorand higher in gloss.3.1.2 For new chemical approval testing,electroplate and coat both fasteners and glosspanels. The fasteners must be plated and coatedin an automated barrel process in a productionenvironment. The panel may be h
14、and-processed.Before electroplating, the gloss level of the steelpanels shall have a maximum gloss level of 150using a 60 gloss meter per ASTM D523 orISO 2813. Coated fasteners and gloss panels shallbe submitted to the responsible Materials Engineerfor evaluation.3.2 Plating and Coating Thickness.3.
15、2.1 The plating layer thickness is defined as themetallic zinc-nickel layer measured after allspecified supplemental treatments are completed.However, the measurement of plating thicknessdoes not include the topcoat. The zinc-nickelplating layer shall contain (12 to 17)% nickel. Theplating layer thi
16、ckness on significant surfaces shallbe a minimum of 10 m.3.2.2 The plating thickness on bolts and screwsshall be measured on the head. For refereepurposes, in cases when it is not possible toaccurately measure the plating thickness on thehead (e.g., the plating is mechanically damaged orit was alrea
17、dy exposed to a corrosion test), the tipof an unexposed thread may be measured andcompared to a reference part plated in the sameprocess. On nuts, the plating thickness shall bemeasured on the spanner flats.3.2.3 For parts other than threaded fasteners, theplating thickness requirement applies to si
18、gnificantsurfaces as specified on engineering drawings. Ifthe significant surfaces are not defined, then allsurfaces are considered significant.3.2.4 For threaded fasteners, the maximum totalthickness of the plating and topcoat is limited bythe basic thread size (tolerance h or H). Afterplating and
19、topcoat, parts must gauge withappropriate basic size GO thread gage. Threadsmay be produced undersize/oversize toaccommodate the coating, provided that thefinished product meets all specified mechanicalproperties. Where mechanical properties are notspecified, undersizing/oversizing is subject toappr
20、oval by the responsible fastening engineer,and all undersize/oversize shall be withinpermissible limits as agreed upon.3.2.5 Recess Fill Test. The total coating systemshall not adversely affect the drive system (internalrecess dimensions, hex size, etc.) or function ofthe fastener.Using a batch (min
21、imum batch size of (ten) 10) ofuncoated hexalobular internal drive pan headscrews (Part Number 11611882 or equivalent),measure the recess penetration depth againstdrawing requirements to ensure conformance.Coat the parts in a production process and lot size.(Coating the test parts with other similar
22、ly sizedparts to reach production lot size is acceptable.)Measure the recess penetration depth aftercoating. All measurements must meet the drawingrequirement after coating. For Part Number11611882, the maximum penetration depth for thedrive recess is 0.5 mm.3.2.6 For parts other than threaded faste
23、ners,there is no limit on maximum total coatingthickness, as long as the finish meets all otherrequirements and does not negatively affect thefunction of the part.3.2.7 Measurement Method. For refereepurposes, the plating thickness shall bedetermined by microscopic examination of crosssections taken
24、 perpendicular to significant surfacesper ISO 1463. For regular production, x-rayfluorescence (XRF) can be used for platingthickness measurement. The measurement shallbe taken after the entire finishing process iscomplete. The measurement method shall havegood accuracy and be robust to the finish ma
25、terial,substrate material, part size and geometry. In caseof dispute, the supplier must be able todemonstrate a maximum deviation of 10%between its test method and the cross-sectioningmeasurement per ISO 1463 when measuring thesame area of the same part.Note: Plating layer thickness measurement shal
26、lbe reported for each production lot.3.3 Adhesion. Parts coated to this specificationshall show no evidence of blistering or otherappearance changes after exposure to humiditytesting per GMW14729 for a minimum of240 hours. There shall be a minimum of 99.0%coating (topcoat) retention after the tape a
27、dhesiontest per GMW14829 Method B. In the case ofthreaded fasteners, steel test panels shall beprocessed with fasteners for this test.3.4 Corrosion Resistance. After exposure toneutral salt spray (NSS) for 240 hours, coatedparts shall exhibit no appearance change and after1000 hours shall exhibit no
28、 base metal corrosion(red rust) on significant surfaces. The test methodand definition of significant surfaces are as follows:3.4.1 Corrosion Test. Test finished parts perISO 9227 (NSS) with the following additionalrequirements:Copyright General Motors Company Provided by IHS under license with Gene
29、ral Motors CompanyNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-GM WORLDWIDE ENGINEERING STANDARDS GMW16730 Copyright 2012 General Motors Company All Rights ReservedOctober 2012 Page 3 of 8x The sample holder inside the testcabinet/chamber shall be constructed of
30、material resistant to the test environment, i.e.,acrylic and polyvinyl chloride (PVC). Also, thesample holder material shall not affect thecorrosion test results, i.e., metal and wood.x The orientation of the parts during test isslightly slanted to minimize accumulation oftest solution on the finish
31、ed surface.x The placement and orientation of test partsshall be such that parts are not touching andthat they are not shielding each other from thetest environment.x Test parts shall not drip on each other duringthe test.x Parts to be tested shall be as close to “asshipped“ condition as possible. N
32、o specialcleaning or treatments allowed.x Parts shall be aged at the ambient laboratoryconditions (23 3) C and relative humidity of(45 10)% for at least 24 hours before thetest.3.4.2 Significant surfaces for test evaluation offasteners shall be all exposed surfaces of thefastener when installed, inc
33、luding, but not limitedto, fastener heads, socket recess, SEMS washersand external surfaces of nuts. Fastener threadsand points are excluded unless otherwise specifiedon the drawing.3.4.3 Significant surfaces on parts other thanthreaded fasteners shall be all surfaces. Deeprecesses, such as blind ho
34、les and the interior oftubes, are excluded unless otherwise specified onthe drawing.Note: NSS testing shall be performed in-house aspart of the applicators process control plan toensure that parts meet the corrosion resistancerequirements consistently.Note: For chemical and applicator approval,exter
35、nally threaded fasteners shall be power-driveninto a tapped hole or nut against a steel panel(simulating production usage), removed, theninstalled finger-tight or with a hand driver withproper drive bit into acrylic plastic or other inertpanel, and exposed in salt spray at an angle of(15 to 30) degr
36、ees from the vertical.3.4.4. Temperature Resistance. After heating theparts for 24 hours at 150 C (part temperature) thecorrosion-resistance requirements as specified in3.4 shall be met.3.5 Stone Chip and Accelerated Corrosion Test.Parts coated to this specification shall exhibitresistance to stone
37、chipping and abrasion.3.5.1. Part Number 11611882 or similarhexalobular internal drive pan head screws coatedwith production process shall be used for testing.The test screws shall be power driven and seatedwith production-type tooling into plastic test panelsthat are unreactive to the following cor
38、rosion testenvironments. The test screws shall be installed ina horizontal row seated a minimum of 25 mm apartand then tested per 3.5.2 and 3.5.3.3.5.2. Pre-condition the test screws (mounted onthe test panel) to GMW14700 Method C, usingone (1) L and two (2 pt) of gravel.3.5.3. After pre-conditionin
39、g, test parts toGMW14872 EXT, Exposures C and D. AfterExposure C, the screw heads shall exhibit no redrust and 30% maximum white corrosion coverage.After Exposure D, the screw heads shall exhibit10% maximum red rust coverage and 50%maximum white corrosion coverage. Note that allexposed surfaces of t
40、he seated screw heads,including screw head edges and recesses, shall beincluded in the evaluation.3.6 Aluminum Galvanic Corrosion Test. The testfasteners coated with this finish in productionenvironment shall be power driven and seated withproduction-type tooling into an aluminum test panel(AA 6061
41、or AW 6082 grade, (4 to 10) mm thick).The test fasteners shall be installed in a horizontalrow seated a minimum of 25 mm apart. Thefasteners shall be tested per GMW14872 EXT,Exposure D. After exposure, measure the pit depthin the aluminum test panel under each testfastener. The maximum pit depth sha
42、ll not begreater than 0.2 mm.3.7 Gasoline Resistance. Coated parts shall besoaked for (200 2) seconds in gasoline accordingto GMW14333 Mixture A. After removal of theparts, they shall be allowed to air dry before visualexamination. There shall be no color change,wrinkling, or any other change in the
43、 coatingappearance.3.8 Weathering Test. Parts coated to thisspecification shall show no blistering, peeling,cracking, loss of adhesion, discoloration, or redrust after 1316.7 kJ/m2 in xenon arc exposureaccording to SAE J2527 or, optionally, 1500 kJ/mof exposure according to ISO 4892-1 orISO 4892-2.A
44、fter completion of the weathering test, the partsshall have a gloss level drop of four (4) maximum(60 gloss meter, per ASTM D523 or ISO 2813).Copyright General Motors Company Provided by IHS under license with General Motors CompanyNot for ResaleNo reproduction or networking permitted without licens
45、e from IHS-,-,-GM WORLDWIDE ENGINEERING STANDARDS GMW16730 Copyright 2012 General Motors Company All Rights ReservedOctober 2012 Page 4 of 83.9 Relief of Hydrogen Embrittlement. Allelectroplated parts with surface or core hardnessgreater than 353 HV (35 HRc) shall be processedper SAE/USCAR-5 and tes
46、ted for de-embrittlementper SAE/USCAR-7. The sample size for theSAE/USCAR-7 test shall be per ASTM F1470.The maximum material hardness in the drawing orrelevant specification shall be used to determine ifde-embrittlement baking is required. For example,a 10.9 grade fastener has a hardness range of(3
47、2 to 39) HRc. Since the maximum hardness isabove 35 HRc, all parts must be de-embrittlementbaked.If a part is heavily cold-worked or heat-treated tohigh-strength/hardness but is without a maximumhardness limit stated in the drawing orspecification, the applicator shall obtain thehardness data from t
48、he customer in order todetermine if de-embrittlement baking is required.Note: Baking is determined by the maximummeasured hardness of the lot, not the average.3.9.1 When a part requires heat-treatment forhydrogen de-embrittlement after electroplating, thepassivation and topcoat shall be applied afte
49、r theheat-treatment operation. To deviate from thisprocess flow, the desired process (example:passivation before bake) must be validated at thetime of applicator/material approval by repeatingNSS testing per 3.4.1 after baking for 8 hours perSAE/USCAR 5. For these parts, the time to the firstappearance of white and red corrosion must notexceed non-baked parts by more than 48 hours.3.10 Friction Control.
