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外文翻译--板材的的等径角挤压 英文版.pdf

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外文翻译--板材的的等径角挤压 英文版.pdf

MaterialsScienceandEngineeringA4762008178–185EqualchannelangularextrusionofflatproductsV.M.SegalEngineeredPerformanceMaterials,11228LemenReceived19February2007receivedinrevisedformAbstractAofItadv©2007ElsevierB.V.Allrightsreserved.K1.tionAnmentinSuchfebetweenattractiSPDmationoptimizationofprocessingcharacteristics.Irrespectiveofprocessinggoal,materialandtemperature–strainrateconditions,themechanicsofSPDshouldprovideintensiveanduniformstrains,simplesheardeformationmodeandlowstresses.AmongaECAEtrialimperfectimajoritywimposefolloproductsization.firstplates,calpracticalwellarepublicationsdetails2.LetsconsiderECAEofarectangularbilletFig.1withthicknessT,widthWandlengthLthroughsharpcornerchannelswithtoolangle90◦.Original1andfinal2billetpositionsareshowninFig.1bylongchainandsolidlines,correspondingly.Asthe09215093/doifewknownmethodsofSPD,equalchannelangularextrusionispresentlyconsideredasthemostpromisingforindusapplications.However,realizationofECAEstillremainsve.Despiteofextensiveactivityinthefield,absoluteofthepublishedworksdealtwithelongatedbilletsasasoriginallydescribedin1.Thesebarsorrodslikebilletsrestrictionsonmaterials,characteristicsofECAEandwingprocessing.Theyaredifficulttouseassemifinished∗Tel.15175483417.Emailaddressvladimirsegalcomcast.net.billetwidthWremainsthesameandthebilletismovedinsidethechannelsasarigidbody,theflowisnearplaneandtheplasticzoneislocalizedaroundacrossingplaneofchannels.Itisknown6thatthestress–strainstateandextensionoftheplasticzonestronglydependonboundaryconditionsimposedbyaninletchannel1andanoutletchannel2.Thus,correspondingconditionsshouldbeanalyzedfirst.2.1.InletchannelAtthebeginningofECAE,thewelllubricatedbilletisplacedintotheinletchannel.Anactualfrictionforcedependsonreal–seefrontmatter©2007ElsevierB.V.Allrightsreserved.10.1016/j.msea.2007.04.092ThepaperconsidersequalchannelangularextrusionECAEofsufficientlystressanalysisisperformedinsideplasticzoneandinletandoutletchannelstheprocessingmechanicsandstrategytodesigntoolsareformulated.antagesforprocessingofmassiveslablikebilletsandtechnologycommercializationeywordsECAEOptimizationofprocessingFlatproductsLargescalecommercializationIntroductionThecontrolofmaterialstructuresbysevereplasticdeformaSPDpresentssignificantscientificandpracticalinterest.importantadvantageofthisapproachisstructurerefinetothesubmicronscalethatcanbeattainedinbulkbillets,acosteffectivemannerandfordifferentmetalsandalloys.ultrafinegrainedstructures,usuallyintherangefromawmicronsto0.2micron,provideareasonablecompromisehighstrengthandsatisfactoryductilitythatisespeciallyveforstructuralapplications.Forcommercializationofsubstantialprogressshouldbemadeintherelateddefortechniques.Thekeyfactorsaredeformationmethodand∗RdSuiteA,WhitmoreLake,MI48198,USA20April2007accepted24April2007longrectangularbilletswithdifferentwidthtothicknessratiosW/T.dependingoncontactfrictionandthebilletgeometry.OptimizationisshownthatflatbilletswithW/Tgreatermuch1provideimportanttechnicalonthelargemetallurgicalscale.andstilltherearenoreportsonprocesscommercialIncontrast,ECAEofflatbilletsfollowedbyrolling,introducedin2,correspondstouniversalproductssuchassheets,stripsandfoils.Togetherwithothertechnologiadvantages,thisprocessingconceptofECAEpresentsgreatperspectives.WhileECAEofelongatedbilletsisnowinvestigated,specialfeaturesoftheECAEofflatbilletsnotunderstoodandwerenotdisclosedinjustafewrelated3–5.ThepresentpaperaddressessomeimportantoftheECAEtechnologyinthecaseofflatbillets.ProcessingmechanicsV.M.Segal/MaterialsScienceandEngineeringA4762008178–185179Fig.1.ECAEofrectangularbillets.plasticnelsimilaronσwherepplasticlocalpressurecontactlubricantmentpressurepwheresholinearsupposeandDelta1pHerefisafullcontactareabetweenbilletandwalls.Whenτ1isknownforspecificconditions,themaximumincrementoftheextrusionpressureinthestationaryrectangularchannelwithfourfrictionwallsFig.2aisDelta1pY2n−11mτ1/Ym2HereparametersnL/TandmW/Tdefinerelativebilletlengthandwidth.Inparticular,m1correspondstotheordinarycaseoflongbarorrodlikebillets,mgreatermuch1correspondstoflatplatelikebilletsandmlessmuch1correspondstostriplikebillets.Formulae1and2showthat,dependingonnandm,theextrusionpressurepemaybesignificantlybiggerthanthematerialflowstressYevenforlowfrictionτ1.Theeffectivewaytoreducecontactfriction,increasetoollifeandpunchstabilityisviamovablechannelwalls7.InonepossiblecaseFig.2b,fordetailsee7,theinletchannelisformedbyonestationarydiewallandrectangularslotoftheslider2,whichmovestogetherwiththebillet1.ThatwayfrictionincrementarewpressurealltothicknessbeTheforpressureratiosureforfunctionlongbilletscontactandnormalpressurebetweenmaterialandchanwalls.Assumingthatastressstateinsidethechannelistolinearplasticcompression,thenormalpressureσnchannelwallsisFig.2an∼p−YpistheaxialpressureandYisthematerialflowstress.If∼Y,thepressureσn∼0,andforlongbilletswithL/Tgreatermuch1thecontactisformedbytransversebuckling.Suchirregular,contactprovideslowfrictionforce.Ifp2Y,thenormalσnY,andtheplasticcontactapproximatestothefullareabetweenbilletandchannel.Inthiscase,thesamewillresultinlargefrictionforceandsignificantincreofpressureDelta1palongachannellength.Then,theextrusionpeisep1Delta1p1p1istheaxialpressureatthechannelentry.ExperimentswthatinallcasestheincrementofpressureDelta1pchangesintheproportionwiththechannellengthL.Thatallowsonetothateffectiveplasticfrictionτ1isuniformlydistributedtheDelta1pmaybecalculatedbytheformulaτ1fFig.2.Distributionoffrictionininletchannelswithastationaryiseliminatedalongthreechannelwalls.ThemaximumofextrusionpressureisDelta1pYn−1parenleftBigτ1YparenrightBig3InanothercaseFig.2c,twosidewallsoftheinletchannelformedbymovablesliders2,3whereasbackandfrontdieallsarestationary.Correspondingly,theincrementofthepunchisDelta1pY2n−1parenleftBigτ1YparenrightBig4Itisinformativetocompareresultsofformulae2–4.Incases,theextrusionpressureincreaseswiththebilletlengthration.Foreffectiveprocessing,thisratioshouldsufficientlylarge.Practically,nisselectedbetween4and8.incrementDelta1p/YisalmosttwiceaslargeforFig.2cthanFig.2b.ForthestationarychannelFig.2a,theextrusionalsostronglydependsonthebilletwidthtothicknessm.However,thisratiodoesnotaffecttheextrusionpresinbothcasesofmovablechannelwalls.Calculatedresultstypicalconditionsn6,τ1/Y0.15areshownonFig.3inofm.ThreecharacteristicsituationsareoutlinedIbilletsm1IIplatelikebilletsmgreatermuch1IIIstriplikemlessmuch1.ItisevidentthatECAEoflongand,especially,wallsbthreemovablewallsctwomovablesidewalls.180V.M.Segal/MaterialsScienceandEngineeringA4762008178–185Fig.3.EffectofbilletratiomontheincreaseofpressurealonginletchannelL/T6,τ1/Y0.15with1stationarywalls2threemovablewalls3twomovablewalls.striplikebilletsinstationarychannelsresultsinthemultifoldincreasestresshardchannelmoechannelsflat2.2.nelchangebottommaterialsticking7andusing7Fig.5.Sliplinesolutionwithdifferentfrictioninchannels.stitutedbyelasticfrictionµbetweenslider1andguidePlate2.Duringextrusion,theslider1usuallyremainsfreeandsomeslipandshearstressesτ2shouldbedevelopedalongthebilletcontactguideτthesliderstablemaybilletCorrespondingnottioncoef2.3.τoftheextrusionpressureincomparisonwiththeflowY.Inthesecases,ECAEofsufficientlylargebilletsandmaterialscanbeperformedonlyindieswithmovablewallsatpowerfulpresses.However,forflatbillets,twovablechannelwallsprovideinsignificantreductionofthextrusionpressure.Therefore,simpledieswithstationaryinletandordinarypressescanbeusedinmanycasesoflargebillets.OutletchannelIncontrasttotheinletchannel,lubricationoftheoutletchanisachallengingproblemFig.4a.Becauseofthesharpintheextrusiondirection,highnormalpressureatthewall,intensiveslipanduncoveringoftheatomiccleanalongabottomcontactsurfaceO1B,heavyscratches,andgallingcanbeobservedevenwiththebestlubricants.Thatleadstohighextrusionpressure,poorbilletsurfaceintensivediewear.AlltheseproblemscanbeeliminatedbyamovableslideralongthebottomchannelwallFig.4b.ThatwayplasticfrictionbetweenmaterialanddieissubFig.4.StationaryoutletchannelaandoutletsurfaceO1Btoovercomefrictionbetweensliderandaplate2fO1Bµp1WT5HerefO1BisanareaofthecontactsurfaceO1BandµiscoefficientofCoulombsfriction.Atnormalconditions,thespeedisclosetotheextrusionspeed.Asfrictionisnotaphenomenon,certaindeviationsintheslidermovementbeobserved.Ifstressesτ2exceedplasticfrictionbetweenandslider,theflowbecomessimilartothestationarydie.boundaryconditionsintheoutletchanneldoprovidealocalizedplasticzoneandsimplesheardeformamodenecessaryforeffectiveprocessing6.Therefore,theficientµshouldbesufficientlylow.PlasticdeformationzoneInletandoutletchannelsdefinefrictionboundaryconditions1,τ2fortheplasticzone.AsliplinesolutionisshownonFig.5channelwithmovablebottomwallb.V.M.Segal/MaterialsScienceandEngineeringA4762008178–185181forthecaseτ1τ21.Itissupposedthatthematerialbehaviorissimilartotheidealplasticbody28.ThesliplinefieldincludescentralfanFEDO,mixedboundaryareaCDEanddeadmetalareaO1CA.Thecentralangleofthedeadareaisψ1η1η2−π6Anglesη1,η2arecalculatedbyformulae8η1bracketleftbiggπ−Arccosτ1/k2bracketrightbigg,η2bracketleftbiggπ−Arccosτ2/k2bracketrightbigg,whereparticulartooutletlimitthefullhighLthatmaterialsnotplicityapplications.ties.bewhenlineandorderτandparametersinletpressurenel,orwithforsidefurthere3.3.1.tions,rotationspass.introducedmostdierotationserties.ofbeneficiallater3.2.ψoftheplasticzoneFig.5issmall.Inthiscase,materialstrainingduringcrossingtheplasticzoneincludesmainlytwosimpleshearsalongboundariesDOandAFO6.Approximately,suchaccumulatedshearisequivalenttosingleshearγ2alongsliplineO1Oofthecorrespondingzerosolutionwhenψ0.Fig.6showstransformationoftheunitmaterialelementabcdintoparallelograma1b1c1d1causedbyshearγ3Inthepaper,wewillusethesamedesignationofrouteslikein7tounderlinethateachbasicrouteisindependentfromothers.Similarroutesbutwithdifferentdesignationwerealsousedin3.kY/√3isthematerialshearflowstress.Solutionsforcasesofτ1,τ2wereconsideredin6.NowwecangatherresultsandoutlinetheoptimalstrategydesignECAEprocessing.Firstofall,notethatthestationarychannelalwaysinducesthelubricationproblem.Inthesituationτ2→k,τ1→0,asliplineanalysis6,7givesforentrypressureattheinletchannelp1/Y∼2.3.Thatresultsincontactbetweenbilletandchannelwallsandleadstotheextrusionpressurepeinallpracticalcasesoflongchannels/Tgreatermuch1andfinitefrictionτ10.Infact,publisheddatashowtheextrusionpressuremaybeashighasp/Y∼79.Formostatlowprocessingtemperatures,solargepressuresareadmissibleformoderntoolalloys.Therefore,despitesim,stationaryoutletchannelsareunpracticalforindustrialWithapropermovablebottomwalloftheoutletchannelFig.4b,frictionτ1,τ2andcoefficientµaresmallquantiUndertheseconditions,thesliplinefieldofFig.5canconsideredasasmallmodificationofthezerosolutionτ1τ2µψ0andtheplasticzoneisthesingleslipO1O.Then,usingtheperturbationmethodforsliplines10omittingintermediateresults,withaccuracytothesecondofmagnitude,formulae5and6give2∼µY,ψ∼τ1µYktheentrypressureinsidetheinletchannelisp1Y∼2√3τ1Yµparenleftbigg112√2parenrightbigg7InaccordancewithEq.7,thereisasufficientroomforτ1andµtoformthelocalcontactbetweenbilletandchannelwithlowfriction,iftheincrementoftheextrusionDelta1palsoremainsmoderate.WithmovableoutletchantheinletchannelmaybeperformedasstationaryFig.2awithtwomovablewallsFig.2c.AswaspreviouslyshownFig.3,thesimplestationarychanneliseffectiveforflatbilletsthelengthtothicknessratioL/TmorethanfourwhereaslongbilletsL/TlandstriplikebilletsL/Tlessmuchlmovablewallsarenecessary.Therefore,onlythefirstcasewillbeconsidered.1Analternativesolutionforτ1τ2followsfromFig.4byreversinganxtrusiondirection.2Thisapproximationisvalidyetafterthefirstpass.Fig.6.MaterialdistortionduringonepassECAE.MultipassprocessingBasicroutesToaccumulatelargeshearstrainsandcontroltheirorientaECAEshouldberepeatedanumberoftimeswithbilletabouttheaxisofsymmetryX,Y,ZFig.1aaftereachForflatbillets,thebasicsystemofrotationsorrouteswasin23RouteAnorotation.RouteBbilletrotatesalternatively±90◦aboutaxisZ.RouteCbilletrotates180◦aboutaxisZRouteDbilletrotates90◦intothesamedirectionaboutaxisZ.Duringrotations,asquareflatbilletswithLWisthepreferablebecausetheycanbeprocessedintothesamewithanyrotation.Numerouscombinationsofpossibleresultindifferentmicrostructures,texturesandpropAlthoughthebasicroutesprovidethesimplestsystemsrotationsonlyaroundaxisZ,otherroutesmaybemoreinspecialcases.Someofthemwillbeconsidered.DistortionofmaterialelementsForlowcontactfrictioninbothchannels,thecentralangle

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