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Deformation mechanism at impact test of Al-11

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Deformation mechanism at impact test of Al-11

    Deformation mechanism at impact test of

    Al-11

    Science

    Press

    Availableonlineat,^^^n^,.sciencedirect.com

    ?CIENCED?REC1-0

    Tram.NonferrousMet.Soc.China17(2007)104109

    TransacfiOilsof

    NoilferrousMetals

    SocietyofChina

    www.CSU.edu.cn/ysxb/

    DeformationmechanismatimpacttestorAl11%Sialloyprocessedby

    equalchannelangularpressingwithrotarydie

    MAAi-bin(马爱斌),YNISHIDA2,JIANGJing-hua(江静

    ),N.SAITO,I.SHIGEMATSU2,A.WATAZU

    1.DepartmentofMaterialsScienceandEngineering,HohaiUniversity,Nanjing210098,China;

    2.NationalInstituteofAdvancedIndustrialScienceandTechnology,Shimoshidami,Moriyamaku,

    Nagoya4638560,Japan

    Received29May2006;accepted15September2006

    Abstract:All1%Si(massfraction)alloywastransformedintoaductilematerialbyequal

    channelangularpressing(ECAP)witha

    rotarydie.Twomechanismsatimpacttest,slipdeformationbydislocationmotionandgrainboundarysliding,werediscussed.The

    ultrafinegrainswithmodifiedgrainboundariesandthehighcontentoffineparticles(<1rtm)werenecessaryforattaininghigh

absorbedenergy.Theresultscontradicttheconditionofslipdeformationbydislocationmotio

    nandcoincidewiththatofgrain

    boundarysliding.Manyfinezigzaglineslikeamosaicwereobservedonthesidesurfaceofthet

    estedspecimens.Theseobserved

    linesmayshowgrainboundariesappearedbytheslidingofgrains. Keywords:aluminumalloys;impacttest;equal

    channelangularpressing(ECAP);microstructures;deformationmechanism;grain

    boundarysliding

    1lntroduetion

    AlSieutecticalloysareimportantforindustry,

    especiallyforautomobileindustries.Howeve~thelow fracturetoughnessofthesealloysIimitsbroader industrialapplication.Themicrostructuresofthesealloys consistofeutecticsiliconcrystalsandaluminumcrystals. Thesiliconcrystalshavethree.dimensionallycomplex shapesandareverybrittle.Thelowfracturetoughness originatesinthemicrostructuresofthesealloys.To improvethemicrostructure,sometechnique,forexample, additionofanelementlikesodium.stibium.strontium. areusedinindustry.Theimprovementoftoughness, howeve~islimitedanditisbelievedthatthebrittle propertyofthosealloysisinherent.Toimprovethe microstructuresofalloys,thereareseveralroutessuchas rapidsolidification,heattreatment,plasticdeformation. Amongthem,plasticdeformationisanenergyefficient process.Oneofplasticdeformationprocessesisthe equalchannelangularpressing(ECAP)thathasbeen

    proposedrecentlyandhasbecomeverypopular,because wecangiveunlimitedstraintobulkmaterialswithout

anydimensionalchanges[15].Toimprovethe

    efficiencyoftheECAP,wehavedevelopedanewECAP processthatusesarotarydie,namelyrotary-die equalchannelangularpressing(RDECAP)[67],by

    whichthebilletdoesnotneedtoberemovedfromthe dieandreinsertedintothedieforthenextpass.We reportedthatwecouldattainthehightoughnessofan All1%SialloybythisRDECAP[81.Themechanismof

    thehightoughness,however,hasnotyetbeenmadevery clear.Thepurposeofthepresentworkistodiscussthe deformationmechanismatCharpyimpacttestofthe All1%SialloyprocessedbvRDECAP

    2Experimental

    TheAll1%Si(massfraction)alloycontains

    11.3%Si1.13%Mg1.00%Cu1.10%Niand0.277%Feas

    impurities(designatedasAllI%Sialloy).ThedetaiIsof

    theRDECAPhavebeendescribedelsewhere[6].The RDECAPdieandtheholderwereheldinanelectric furnaceandtheprocesseswerecarriedoutinsidethe furnace.ThebilletsizeofsamplesforRDECAPwas

    l9.5nlnlindiameterand40rnlTlinlength.Thebillets werepressedbyRDECAPf0rl6and32passesat

    623Kand673K.Impacttoughnesstestspecimenswere Correspondingauthor:MAAi-bin;Tel/Fax:+86-25-83787239;E-mail:aibin-ma@hhu.ed

    u.cn;aibin_ma@yahoo.~om

madefrOlilRDECAP

    alongtheIoFtgifudinal

    MAA1hillaL.'TransNonli~rrousMelSacLllina1(2)1

    processedhilletsbymachining

dheetionfhesizeofthetesl

    speeimellst{-z3illnlX4113mincrossSeCtionand34Fttm

    i11lengthwithaUnotchof15[11111inwidthand5nllil

    i11depthSixtestspecimensveelemadeI'romonebiLLet Acomputer-aidedinstrumcFttedChaq~yimpactlest systemwasusedfbrnleastlringIheimpacltoughnessof thesamplesatroomIcmperature.Unpressedsampiesol

    thealloy1erealsotesledI'oIcomparisonOptical mjcroscopywasusedtoobsetvethcIllicroslrucluresA JEOL2010traasmlssioneIecfroii111ici-escape(TEM1and aJEOLJSM5200scallI1ingelectl0?ill1croscope(SEM)

    wereemployedhlrobservationof1aiFtboundaliesand thepoishedsidestirfaceofimpacllestspecin1enlleartO thei?actu)edSillce

    3Rcsnllsall(Jdiscussion

    ThcillIcrest131ctttres0}1aftpressedandRDECAP

    processedsamplesobservedbyopticalmicroscopyare shOWlliI1?口1.ThemicroslructureoftimILIIpressed

    sample.[isshow11mFig11a.mai13h'consists0r dendrit1caltlIlllIlltFtlpriillalvcrystals(whitecrvsta)arid

    e13teelicstlllcture(platelelscoI1andalunl1IItllli)

    SamnplesofFigs1(b)and(c)wcrcpieparcdby16passes and32passesal623KrespectivelyBypressing.silicon cD,sta1sarebrokellIllt()fineparticcsaFtddisperselntile

    a|tlllliliu131matlixhomogeneously.1l,.iwever.manyl51ge liconpartI121esofl5nmremainFl2S]iovestheTEM microslructtlreofa1umI1LIillparlntheAll1%SIaIlay

    processedbyRDE(APfbr32passc^al623KThe

    graIi1ortrralnffamelttsize1sesllmatedI)beabout30(

    nmhvthemicrostmctare

    TheabsorbedenergiesbyCharpyimpactlestingof theAI-I_%Sia_lovvcbeenreportedIFtualpicvious paper[81Theabsorbedenergiesincreasew1ll1the Illcrgaseinnumberofpassesandn1aIIvreach0Jit]

    after32passesat623K.whIchIs0tlFtleSI1lahcrthit11

    thevalue.0qJ."Cnl.Ofthea13pressedalov

    AppearallCeSoflestspeciiIlellsareshown1nFE3Thcsc

    testspe,ai131cnsof"Figs3(a)aFtd(b)aretinpressedand

    pressed-31passesal623K.respecli,..ely.Thelest specIncns1ftheunpressedsaFtlpleIacttlre111abrittle mantier.TheLeStspeclI11ellSWit113.~utllotch.1lOv,,ever, dcfb15111plasticaI1vanddoliOtrraCltlreashownll

    Fig3fblTimaftpressedsamplesofthisallayarecry brittleHo'o,'evei.theabsorbedeFtcrgiesofthespecwtei1s

    pTocessedbvRDECAPaKevclnvhigbMOSlOfenergies areabsorbedplasticdelbrmatioFtelspecimensduring IreDacttestingasshown?Fig.3ThereFore.itis0f

    lmportancetorevca1thelllechatllSill0ftheplastic detqllatjOllThemicrostructureelthisallovCOIlSlStSof Priftlar,1aIu171inumcn-sialsctliectJsifeoFtand

    FiR.IMiet1)stI_UCFtllcsOIAIII%Sialloyobservedbyoptical microscopy:(a)Unpressed:ibl10timesplesbedal623Kc

    32limespressedat623K

    Fig.2TEMmicrogmphol'ttluminamYmatrixinAIII%'S

    alloy'processedbyRDECAffoi32l_J】】al623K

,1AAIbii1ctal.rrdlibNonfen1LMelSoc(I1iilaI7200

    Fig.3Appearanceoftestspecimens:{aiUnpieased

    lb)Pressedtbr32Limesat623K(1Ilesetestspccillleflsilhotl anotchdeformplastitallyariddoTIC[flaCttlrecomplete?)

alunlinumcryslas.othci111termctaIhccompounds

    CuM1.MgeSi,etc.andneedlelikeirOllconlpotmds (FeAI3)as1Illpurity.HOwe',.e1.alailliilumcrystalsalid siliconeutceticcrystalsshouldplatinlpolrantrolesm theDlastirdefoinlatiilllBvRDE(Atheshapeof

    sil1COIlcrystalssimplvcIlaiigesfiei11tl1ci1eh~,orksor plaieleteutecticslieel1crvstas1ntosinlpIeparticIcsTh0

    tealspeehnensofChal'pyimpacttestingarcplaslically deI!OrmedgreatIvthoaghtilev01unlefiactlOilofSljCOI1

    cwslalsremainsunchangodevenalierRD,FCAP processingalldlsequa1to"le?,1UlllerractIO[I[r"le

    tm-pIessedsampleofthisallovI1l11bSC1'redbvehe opticalmicroscopythatwhenLIUpressedsaillplcs

    fracture,fracturecracksadvancealonge/ttecticsilicon c~'stalnetworks[g]SincesiJJcc)nClyslalsarebrittle. nlanysiliconcrvsta]sarebrokendurineRDECAP proeessingandtlsua1]vsevera1vodaat.t2Finedlnsideor

    arcLindliCOIlcp,'sta1s9]JtIexpectedthailf

    severavo1dsaleprcsenluoraottndllCOIlparlldes.

    these?oldswpiovidepathsIbraclurocracksandthe

    speclillellswf'mc[urecasilvTilecxperinlenta]restllta. how.ever.alcopposite.TheabsmbedenergyofCharpy. impacttestingincreaseswlthInereasIi1namber0f RD.ECAPBasses

    ,vccanreeardth1sRD.ECAPprocessedaloYasan

    lsll1COilparticledispersedaluIT1illLlnlcompositefan

    aluIllilllllI1atloycoiltainsaboutI{fYumcfTaction)

    ceramicparticles.tileabsorbedenergy'by(,harpy'impac

    tealIngorthea_l0vcneraIlvdecreases1()about5that

oflrtatrlxdl1ovIllThc1OV~actulctotleJllleSSand

    ductv0rthoseCOII/pOSileaaD2attributedt0the1imited disoeatOilnlotiollCIlarseS1cIWSLal1J5un111

    diameter)aredispersedII1RDE'APprecessedsamples.

    asshown1nFigsIfbland(ctFtOllllhese

    nlleloslrtlcttlres.1tiapparcilllhatdisIocatioil111',Ivcment

    lcxllelllelvrealrtriedanddisocaiOI11luDWbe

    crcatedaroundpartlcCSTherej"ore.1algestraincoaJdIIOI beobla1nedbylillragranulaidjsIcoatl()nII1(ItOil

    InOH1'previouspapf?ediscussedtile

    lnqprovcIlicntoftheilllpacttolighileSSortheAJll'SI

    all0vandobtaine(1cpertnlcnta11vtile_l0winsthree itllpOirantresulls

    1)TheiillprovedimpacttOLlghllcSSisrchltcdto:fa} thebreakaee0fthelargealtlmiiltlllldeildliresand InlerdcndritIcnetworksofeuteeticIllCOIli11theirst

    severalpasses,(blthemodifiedgraiI1t.11grainfiagnlent boundaries.(cultrafincgrainsoiglainffagnlcntsfdI theeontelll)f1iliescoi/paleIesfs'nlerthan1LIill1

    aadc)hoillogenizcdnliclostructtucrestlltingfi-on1 nlullipassRDECAP

    !)Tilea*.,eragcsizcol'lhegiaillSoYgrainnagnlents labeal3?all1afterRDF,AJWlthauinclcased

    numberOfRD-ECAPpasses.beyondaboutLl1._lhe grainorglain[~aglllen|sizedoesUOIclearlydecrease 31MtxliliedglaiilboundariesI'hercsuhsfbrEI3SD (e]ectrollbackscattmdIll'laction~1lOWthaltheI?acLions orhigkanglegrainboundallcsv<ithf>l5art250and

    73rthesanlpIcplcrossedbyItf)API623K

    j"or8andl6llassesreapertIvelv.

Checontribullonof?ichrollkageorIargcajuI11lntllll

    dcndlIcs11ndiillcrdelKhtci1clwork'1fcatcctlc5_11con

    totheIlllproVCllICntofInlpacltoughiIcashasalmost conlpletedjf1lhefirstsexeralpassesIaboatfotlpassesI+ Tllmctbrc.IheIIlcreaseel"thelmpaclloughnessI"Jcvond I"ourpasseslsbasedoeolhcrUlccinnlisnlsTileabsorbed CllelgytrthesampleplcrossedI'ol32passesisIhree timeshigherthantbc,lUe0rthesanlpleprocessedIbr fburpassesTheresultsot'2lillenlitreedahoy,2slIo~',s thattllc~lveragesize0rthegrainsorgiainfragnlcntsis riottheimportantreasonthrtheincleaseorthelmpact toughngasbevondfi)LIrpasses

    TheaxelageStl'ainlaleat(haq)yimpacttestingis kno'A,nasabotlt0.s.AccordingtoIhcCOil~,elltional

    class1llcationofdcformatiollIllCChanisnl1]!I.the del;ainlationat(hayinlpacItcsfingshouldbelhcslip

    delbrnlalioilbydislocationmotioilTonlaketieartile illcchanisnls.wperlbJnledotheiexpelimelltSandhave reportcdIlloilrpleviouspaperJAsaillplcwas

    processedwithl^passesal623KbyRD.ECAPand

    thenheatrrcatcdat,q3Kr.r2hfol10wbvwa{er

MAAlbiii.etIFransNt)nrroLLtS?etS01JnaI2tIIt7I107

    quencllinglsillutiontreahllen1)By'ibisexperinletll, alumillumgraingrov.thOCCL)Isandthea;.eragegrainsize inereasesf_r(11113I)O11lutOabollt8I-Lrl1II"1additionfine siliconparticlesfainallerthanlan1)disapllearatndonly rougllsIliconparticIcsiabou15aMlndlameterl1.elrlaI11 TheabsorbedenergYL1rihisaalnpleIllsfrolll72J-cill

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    boundariesand1iI1esI1jCOIlparticesshou1dbebarl1ers10

    dislcoati0l_111o1iOI1S1neefileilllpaellestii1ofthis SOILItiolltreatedsample"e~"LLScarriedoulatroom teolperaRlrclnlmediateIvatier-llehealtreatnqent.tIle preciPitationotfineparticlesbctbreimpacttuatitlgcan beneglieible

    AsnlcnlIoiledIiifilejlreS'iOtlSrestlIt8],filehiell

    anglegtainboundariesaflelRD-ECAPprocessing shouldeontribnletOtileplasticiLvotCharD.impactlest specimens.thoughtilehighanglegrainboundat1.'Isa barriertodislocalionmotl[in(_IiClLI1ve1V.L"tratTne

    grains~dlllhighanglegrainboundariesandlhelarge COlltenlof1i1esCOI1pall1ces{sillallelfitallIRill1arc

    necessarylbrattaIningltlrtzePIasticdeformationof lmpaclLos[speciIllCtl.Fl1lsCOliClnsioilc0ntradIcLathe eonditioitofthesIipdefcmnatIondislocatio11tlqotlon rhesecxperiillell[arestllIsre111Ind[IS0Ianother

    mechanism.namely.,thegrainbetndar}.sliding(GBS) andcoJnc1dcwlthtileCOIKIiIion【订GBSGBSis

    dornilla11tinriteplasticdelhiinationof13tesentimpact testspecinlcllatheduct[Iib.canbeexplaillcdrcasontb}. GBS.11owel'cr.IlasbeeitobservedOll/V1I1superplasiic defbnnation[2Jandcreepatwslra(11ra[cSandathigh

    tenlpera[tllcs[abe.eO.4r,,whereTviathetnclli11g

    potntAstbrresearchesOII(jBSofLIIt1.afine21itined

    17tatcl'1alscom!ltueisIilnlIalienof(BSaltileatomlc

levelisplOlllineniusinglltOlccttlardynamics[13l4or

    tileManteCarlofJ51due1oIhed1mcultx.of

    expelIillenla]tecMiqne

    Wemadeanatticnlptt11obser~cGBS?lroom

    temperatureillLheInlpacllestspeciMensOfthe A1InS1a_lovploccssedbyRDECAPWcused

    impactlestspecinleltshavingpolishedaidestir[acesTl1e aideSiltFacclMageaofIletestedspcciIllCllobsen'cdby

    scanningelcctrollnilClascap).aleshow11IaFig4.which %.vasRDE('APplocesaed32passesat673KThcaide

    l!aceIiliages(|I_1ui1-pressedspecInlellareaso

    showninFig5lbraconlparisonFiE4(a1sh0shc

    appearallceLl'theLestspecimen.Figs4fblalidare

    Ii11ages(1fanearandad1stalllIocationsli-onlfile1iaclare SLII'eeaS1118rkeclIi1FI4ca1

    Assllov~ninFig5thereareman},bigcracksinthe specli11e11Ilear_l1cI}aeluresurl"aceoftileliltpressed

    sampleTheinlaacsshnw11illtileSalllplelvcrvbrittle. Oi1tilecontrary.MaI1vI11clIileaareobsersedii1botln

    Figs4(b}andcc)Thcle;.Irefewspaces.11keClackslfl Fl5.betweentilese"?ellliesAlLIIllinuIllcrvslaIhas

    fouislipplanesand12slipsystems.1ftheselinesareslip esbydIscoati1nlove1110ntklSliallvse',eralparalleI linessllooldappearaLldlhcyvdlIbe1lloicst1aiglltlines lnadditioneach1ineIsCOlllposedofse%ela1finerlines. namely,htmcllacslipbandMosteltheobservedlines, lowever.arevcPVnilesl11lczIzugli11esandnot stra1ght1lncsTheselIilestirecILIsodones1ikeamosaic rrIleFtJ1_e,these?liesiliavbeaI11beu1idai1esIn

    addi"on.tJlescn11Cllnesarenotcracks.becatlSC1l1c

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