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New extrusion process of Mg alloy automobile wheels

By Juanita Carter,2014-02-18 03:12
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New extrusion process of Mg alloy automobile wheels

    New extrusion process of Mg alloy

    automobile wheels

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    PressTrans.NonferrousMet.Soe.China20(2010)s599s603

    Transactionsof

    NonferrousMetais

    SocietyofChina

    NewextrusionprocessofMgalloyautomobilewheels

    WANGQiang(~),ZHANGZhi.min(张治民),ZHANGXing(~),LIGuo-juIl(李国俊)

    1.CollegeofMaterialsScienceandEngineering,NorthUniversityofChina,Taiyuan030051,China

    2.EngineeringResearchCenterofMagnesium

    baseMaterialProcessingTechnology,MinistryofEducation,

    NorthUniversityofChina,Taiyuan030051,China

    Received23September2009;accepted30January2010

    Abstract:Therecentresearchanddevelopmentofforgedmagnesiumroadwheelwerereviewed.Methodsofflowforming,spin

    forgingofmanufacturingaforgedmagnesiumalloywheelwereintroduced.Anewextrusionmethodwasinvestigatedespecially.

    Extrusionfromhollowbilletwasproposedinordertoenhancethestrengthofspokeportionandreducethem~lmumformingload.

    Bymeansofthedevelopedtechnique.theone.pieceMgwheelswereproducedsuccessfullybyextrusionfromAZ8O+alloy.Atme

    sametime.theexistingproblemsontheresearchanddevelopmentofforgedmagnesiumroadwheelwereanalyzed.111eimpact

testing.radialfatiguetestingandbendingfatiguetestingresultsshowthatAz80+wheelcanm

    eetapplicationrequirementin

    automobileindustry.

    Keywords:magnesiumalloy;roadwheel;extrusion;flow?forming;spinforging

    1Introduction

    Magnesiumalloyispromisingstructurallightmetal becauseofitslowdensities.goodrecyclicalpotentialand abundantresources.whichisexpectedtobecomea next.generationmaterial1-41.Thismaterialisreceived

    specialattentionduetotherenewedinterestinenergy conservation.Itsuseisincreasinginautomobile industriesasareplacementforaluminumandstee1. Magnesiumalloyroadwheelshavetobeconsideredin particularduetotheirbeneficialeffectsuchassafety, comfortandenergysaving.Asasafetyrelated

    component.theessentialfactorsinwheelapplications arethefatiguesgengthandtheimpactstrength.Atthe sametime,weshouldalsotakeaccountofother requirementssuchascorrosionresistanceandcost. Inordertohaveawidespreaduseofmagnesium

    alloywheels,castingandforgingprocesseshavebeen adoptedforwheelmanufacturing.Inthecaseofthe magnesiumalloys.themanufactureoftheentirewheel onlybythecasting(1owpressurediecasting,squeeze casting,gravitycasting)[58resultsininsufficient

    strengthof,forexample,arimportionwhichcarriesa tire,aswellascastingquality(porosity,inclusions)often doesnotmeettherequirements.

    Forgingisanalternativeproductiontechnologyfor Mgalloypartswithhighstrengthrequirements[9].The

    productsmanufacturedbvmisprocessarecharacterized byfine.grainedmicrostructurewithoutporesand improvedmechanicalpropertiescomparedwithcasting Mgparts[1O12].Formagnesiumroadwheelforging, methodsofflow-formingandspinforginghadbeen investigated[1314].Butheavydutypressequipmentis

    usedandthefatiguestrengthcannotmeetapplication requirement[13,15].Toenhancethefatiguestrengthand reducetheformingload.anewextrusionprocessfor magnesiumalloywheelswasintroducedandinvestigated especiallyinthiswork.TheonepieceAZ80+alloy

    wheelwasextrudedsuccessfullybymeansofthe developedtechnique.

    2Forgingtechniqueusedforwheel

    manufacturing

    2.1Forgingandflow-formingprocess

    ThetechniqueofforgedMgalloywheelsrequires thefollowingtwoprocesssteps:forgingthewheeldisc blankandflowformingtherim131.Thebilletsaremade

    bycontinuouscastingprocess,andarehomogenized beforetheformingprocess.Priortotheforgingand flow.formingprocess,thebilletsareheateduptosuitable Foundationitem:Project(50735005)supposedbytheN~ionalNaturalScienceFoundationo

    fChina

    Correspondingauthor:WANGQiang;Tel:+86-3513921398.+86

    13834166948;Fax:+863513921778;Email:ncustwangq@nuc.edu.cn s600WANGQiang,etal/Trans.NonferrousMet.Soc.China20(2010)s599s603

    temperaturetoprovidetherequiredformabilitY. Theforgingconsistsofthreestepsusinghydraulic presswithdifferentpressingpowers.Thefirstforging

    operationwithahighdegreeofreductionprovidesa wheelblank.Thefinalshapeofthewheeldiscismainly achievedbythesecondforging.Theformingprocessis completedbysubsequentdeburringoperationasthelast step.Theflowformingoperationitselfrunsinthree steps:splittinguptheforgedflange,flowformingthe

    rimandcalibratingtherimcontour,asshowninFig.1. Theflowformingdeviceconsistsofmandreland

    tailstockplatetobeusedfor1ockingthewheeldisc. Threeformingrollersarepositionedapproximatelyin 120.orientations:roller1splitsuptheflange.roller2 and3flowformtherimincludingcalibrationofthefinal rimcontour.

    TheZK30alloyprototypewheelhasbeen

    manufacturedbyusingflowformingtechnique.Itsmass

    is6.8kgrepresenting35%masssavingthanforged aluminamwhee1.Highstrengthcanbeachievedinthe rimespeciallyinflowdirectionduetothehigh deformationinducedbyflowformingprocess.However, thepropertiesandinfluenceofflowdirectiononthe materialpropertiesarereducedduetolowerdegreeof (a1

    (c)

    Fig.1Schematicdiagramofflowformingprocess:(a)Process startingposition;(b)Splittingupflange;(c)Flow-formingrim reductionofthewheeldiscsection.Rotar,,fatiguetest showsdurabilitylifetime(84000cyclesunder3000 N?mtest1oad)is8.5%thatoftheseriesaluminumwhee1. Hence.itisnecessarytothickenthewheelsectionsfor achievingtherequired1ifetime.Thustheactua1mass

savingpotentialisreducedto10%15%inregardto

    aluminumwheelbasedonFEAanalysis.

    2.2Forgingandspinforgingprocess

    ThetechniqueofforgedMgalloywheelsconsists ofthethreeprocesssteps[14]:forgingwheelblank,spin forgingrimandrollprocessingrimedgeportion,as showninFig.2.AZ80magnesiumalloycastingwas preparedbycastingandwassubsequentlyforgedto provideawheelblankofashapesubstantiallyidentical withthatoftheeventuallymanufacturedwhee1. Anautomotivewheelisobtainedbyforgingfrom thewheelblankusingforgingmachinewithanupperdie andalowerdie.Theaveragecrystallineparticlesizeof thematerialisreduced.Thenthewheelissubjectedtoa solutiontreatmentandanartificialtreatment.Upon completionofT6treatment.spinforgingiscarriedout. Whi1ethewheelisrotatedtogetherwiththeman&eland thepressmember.arol1ispressedagainstarimofthe fa1

    (b)

    (c)

    Fig.2Schematicdiagramofspinforgingprocess:(a)Blank forging;(b)Spinforging;(c)Rollprocessing WANGQiang,etal/Trans.NonferrousMet.Soc.China20(2010)s599s603

    wheel,SOthattherimmaybefinishedbyaspinning treatment.Finally,thewheelissubjeetedtoarol1 processing.Arollispressedagainstanedgeportionof therimwhiletherotaryplatformtogetherwimthewheel isrotated,micronizingcrystallineparticletoimprovethe resistancetocorrosionoftheedgeportion.

    Thephysicalpropertiesofthewheelusingspin forgingtechniqueareconsiderablyimprovedbythe synergisticeffectofthecrystallineparticlesandtheT6 treatment,especiallythestrengthofarimportionis enhanced.Thetechnicalparameterssuchastemperatures swagingrateandaveragecrystallineparticlesizeare optimized.But,therelatedreportsonfatiguestrength, massandapplicationinstancehavenotbeenseenyet. 3Extrusiontechniqueusedforwheel

    manufacturing

    3.1Extrusionfromhollowbillet

    Themaximumloadwaschosenastheextrusion

    loadduringextrusionprocess.Anewconceptofhollow billetwasproposedandamethodofextrusionfrom hollowbilletwasdeveloped16].Theschematicdiagram

    ofextrusionfromhollowbilletisshowninFig.3. Work

    Fig.3Schematicdiagramofextrusionfromhollowbillet Toinvestigatethepressforceduringextrusionfrom hollowbillet,thefiniteelementsimulationwas conductedusinganimplicitFEcodeMSC/Autoforge. ThedataonAZ80alloyflowstressasfunctionofstrain. strainrateandtemperatureestablishedbasedon compressionexperimenthavetobeintroducedintothe FEpackage.Fig.4showsthecalculationalforce———

    displacementcurvesduringextrusionfromhollowbillet atdifferentEl=d3/dl,whered1iSoutsidediameterof hollowbillet;d2iSilinerdiameterofhollowbillet;andd3 iSdiameterofmandre1.Theresultsshowthatforming forceiSdecreasedenormouslyduringextrusionfrom

    hollowbillet,becauseofthedecreaseofcontactareaand s601

    Reductioninheight/%

    Fig.4Calculationalforce--displacementchives averagepositivestressoninterface.AtthesalTletime,the holeisformeddirectlyandcuttingprocessisreducedfor thepartswithcenterholesuchaswheelbyextrusion fromhollowbillet.

    3.2Extrusionprocessofwheels

    Theextrusiontechniqueofwheels[17]hasbeen developedformagnesiumalloywheelmanufacturing,as showninFig.5.Acanisbackwardextrudedfromhollow (a)

    (b)

    (c)

    Fig.5Schematicdiagramofextrusionprocess:(a)Extruding can;(b)Forgingfrontlip;(C)Expandingrimandbacklip Z\00.IoJuIlj

    s602WANGQiang,etal/Trans.NonferrousMet.Soc.China20(2010)s599s603

    billetmadebyupsettingandpunchingfromascastalloy.

    Uponcompletionofextrusion,thefrontlipisforged fromcanextruded.Therimcontourandbacklipare finallyachievedbyexpanding.Themetalmayflow inwardsandoutwardssimultaneouslyduringforgingthe frontlip.whichmaymakethebilletdeformationat relativelylowforgingforceandthediecavityfilled sufficiently.Atthesametime,thedegreeofreductionof thewheeldiscsectionisenhanced.Highstrengthcanbe achievedinthewheeIdiscsectionduetothehigh deformation.

3.3Exoerimentalresults

    TheAZ80+alloywasproducedbycontinuous

    castingmethodforthewhee1.Thebilletsweremachined inordertoremovetheeffectOfthesurfacelayerofthe ingotandhomogenized(385?,12h)before

    deformation.Extrusionwasconductedunderisothermal conditionsinwhichthedietemperatureswerevaried dependingonthebillettemperature.Thebilletwas heatedtoatemperaturewimin320to380?during

    formingprocess.Theoil-hydraulicpressofcapacity12.5 ?wasemployedandtheaverageformingspeedofa ramwas10mrn/s.Agraphitecoatingwasusedto lubricatebilletandpunchsurface.

    Theone.piecemagnesiumalloywheelsare

    producedaccordingtothepresenttechnique,asshownin Fig.6.Theformingforcewasdecreasedbyextrusion fromhollowbillet.The(13×l0)Jand(14x6)Jwheels

    wereextrudedunderl2.5MNoil.hydraulicpress.The technologyanddiesdesignedhavemanyother advantagessuchasbetterfillingforflange,high productionprecision,lowsurfaceroughnessand convenientmouldunloadingfornear-netshapeforming. Themanufacturecostsarereducedduetousinglimited capacityofpressequipmentandlessformingprocess. Themechanicalpropertiesareremarkablyimproved forAZ80+alloywheelextrudedinthebothrimanddisc section.Theultimatetensilestrengthis300-320MPa andtheelongationisabove10%.Forexample.themass of(14×6)Jwheelis5.2kgrepresenting28%mass savingofaluminumwhee1.Theimpacttesting.radial

    fatiguetestingandbendingfatiguetestingresultsin 1'ablelshowthatthemagnesiumwheelscanmeet applicationrequirementinautomobileindustry. Table1Testingresultsofwheels

    Fig.6AZ80+Mgalloywheelsextruded:(a)(14x6)J;(b) (13x10)J;(c)(13x8)J

    4Conclusions

    1)Methodsofflowformingandspinforgingof

    manufacturingaforgedmagnesiumalloywheelare introducedandtheexistingproblemsareanalyzed.The WANGQiang,etal/Trans.NonferrousMet.Soc.China20(2010)s599s603s603

    fatiguestrength,impactstrength,corrosionresistance andcostaremainfactorsinthemagnesiumroadwheel application.

    2)ExtrusionfromhollowbilletdevelopedforMg alloywheelmanufacturingcannotonlyenhancestrength inthewheeldiscsectionduetothehighdeformation,but alsoreducethemaximumformingloadbecauseof decreasingofcontactareaandaveragestresson interface.

    3)TheonepieceAZ80+alloywheelisextruded

    successfullyfornear-netshapeformingbymeansofthe developedextrusiontechnique.Thetestingresultsshow thatitcanmeetapplicationrequirememinautomobile industry.

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