GMW-4707-2002

MaterialSpecificationFinish(Coating)GMW4707CorrosionProtectiveCoatingZincPlating/Organic1ScopeThisspecificationcoversrequirementsforanon-oilycorrosionprotectivecoatingconsistingofzincplateandsubsequentaluminumrichtopcoat.1.1MaterialDescription.Thiscoatingsystemmustbefreeofhexavalentchromium,withnohexavalentchromiuminfinalproductperGMW3059require-ments.Theplatingshallbecalledoutonthepartdrawingperexampleshowninsection7.1.2Cross-ReferenceofReplacedSpecifications.GMWGMW4707DeltaMotorsGMdoBrasilGMHoldensGMNAGM7113MISUZUITDCSAAB1.3Symbol.Notapplicable.1.4TypicalApplication.Thecoatingissuitableforinternallyandexternallythreadedandnonthreadedferrouspartswhereahighlevelofcorrosionprotec-tionisrequired.Whenappliedoversteelthatistobecoupledwithaluminum,thecoatingprovidesexcep-tionalgalvanicprotection.1.5Remarks.Useofthiscoatingsystemonthreadedsurfaceand/orbearingsurfaceofjointscouldeffectthetorque-tensionrelationship.Itisrecommendedthatatorque-tensionstudyofthefastenerjointbeperformedbeforereleasingthisfinishonanynewapplication.2ReferencesNote:Onlythelatestapprovedstandardsareappli-cableunlessotherwisespecified.2.1Normative.ASTMF1470DIN946ISO9227SAE/USCAR-1SAE/USCAR-5SAE/USCAR-7SAE/USCAR-112.2GM.GM4260PGM4265PGM9071PGM9501PGM9508PGMW3001GMW30593Requirements3.1RequirementsonDelivery.3.1.1ChemicalRequirements.Notapplicable.3.1.2MechanicalRequirements.Notapplicable.3.1.3PhysicalRequirements.3.1.3.1Appearance.Thiscoatingshallhaveauniformgray/greenappearanceandshallbefreeoftears,sags,andexcesscoatingwhichaffectsappearanceandperformance.Thecoatingshallnotbeoilyortackytothetouch.3.1.3.2Thisfinishshallnotfilldriverrecessorthreadsnorinterferewithnormalfastenerinstallationproce-dures.Thefinishshallwithstandnormalhandlingandstorageconditionswithoutdamage(chipping,flakingorother)andmustnotstainortransfertoadjacentpartsoroperatorshands.3.1.3.3Thetotalcoatingsystemasreceivedshallnotadverselyaffectthedrivesystem:internalrecessdi-mensions,hexsize,etc.orfunctionofthefastener.3.1.3.4Thickness.Thezincplateandpassivationtreatmentthicknessshallbeminimum6μmunlessotherwisespecified.Thetotalcoatingthicknessshallbe(12...20)μm.3.1.3.4.1Thicknessshallbedeterminedbymi-croscopicexaminationofcrosssectionstakenperpendiculartosignificantsurfaces.SeeGM4260P,RecommendedPracticesforMeasuringThicknessofPlatedDepositsandAnodicCoatings.3.1.3.4.2Incaseofboltsandscrews,platingthick-nessshallbedeterminedattopofheadatmidpointoflargestcontinuoussurface.Incaseofnuts,deter-mineatmidpointofflats(wrenchingfacets).©Copyright2002GeneralMotorsCorporationAllRightsReservedOriginatingDepartment:NorthAmericanEngineeringStandards,RecordsandDocumentationApril2002Page1of3CopyrightGMWorldwideReproducedbyIHSunderlicensewithGMWNotforResaleNoreproductionornetworkingpermittedwithoutlicensefromIHS--``````-`-`,,`,,`,`,,`---GMW4707GMWORLDWIDEENGINEERINGSTANDARDS3.1.3.4.3Themaximumthicknessofcoatingwhichmaybeappliedtothreadsonthreadedproductsislimitedbythebasicthreadsize(tolerancehorH).Aftercoating,partsmustgagewithappropriateba-sicsizeGOthreadgage.Threadsmaybeproducedundersize/oversize(beforecoating)toaccommodatethecoatingthickness,providingthefinishedproduct(aftercoating)meetsallspecifiedmechanicalprop-erties.Wheremechanicalpropertiesarenotspeci-fied,undersizing/oversizingissubjecttoapprovalbypertinentengineer,andallundersize/oversizeshallbewithinpermissiblelimitsasagreedupon.3.1.3.5Adhesion.Partscoatedtothisspecificationshallshownoevidenceofblisteringorotherappear-ancechangesafterexposuretohumiditytestingperGM4465Pfor96hminimum.WhentapetestedperGM9071P,10minutesafterremovalfromhumiditytherewillbenomorethan3.0mmtotalpeelback(peelbackaddingbothsidesofscribedline)fromthelinesscribedinan’X’andnootherpeelingintheareaunderthetape.Thisisnotapplicabletothreadedfasteners.Note:Thistestisapplicableforinitialapproval,ap-plicatorapprovalandPPAPsubmissionparts.3.1.3.6CorrosionResistance.SignificantsurfacesofpartsexposedtoneutralsaltsprayperISO9227shallshownobasemetalcorrosionafter480hex-posure.Forthistestexternallythreadedfastenersshallbepowerdrivenintoatappedholeornutorsteelpanel,simulatingproductionusage,removed,thenin-stalledfingertightorwithahanddriverwithproperdrivebitintoacrylicplasticorotherinertpanel,andexposedtosaltsprayat(15...30)fromtheverticaltoallowwetting.Fastenersshallnotdripontootherfas-tenersduringthetest(SAE/USCAR-1).3.1.3.6.1Fornormalproduction,processesthatareinstatisticalprocesscontrolshallyieldpartsthatarecapableofmeetingthesaltsprayrequirments.3.1.3.6.2AperiodicNSStestofthepartsbeingpro-cessedoneachlinerunningthiscoatingshallbecon-ductedwithsamplesizeof3piecesminimumperlinepershift.3.1.3.6.3Actualprocessingcontrolcheckstobemadeandrecordedshallbebasedonchemicalmanufacturer’sinstruction.3.1.3.6.4Significantsurfacesfortestevaluationin-cludebutarenotlimitedtofastenerhead,socketre-cess,semswasherandexternalnutsurface.Sharpedgesareexcluded.3.1.3.6.5Significantsurfacesonpartsotherthanthreadedfastenersshallbeallsurfacesexcludingsharpedges.3.1.3.7GasolineResistance.Forinitialap