The deformation, recrystallisation and texture of three magn

Thedeformation,recrystallisationandtextureofthreemagnesiumalloyextrusionsL.W.F.Mackenzie*1,B.Davis2,F.J.Humphreys1andG.W.Lorimer1

Thedeformation,recrystallisationandtextureofthreemagnesiumalloyextrusions,AZ31,WE43andZC71,havebeeninvestigated.Theextrudedmicrostructureswerepartiallyrecrystallised;thenucleationofnewgrainswasassociatedwithboundaries,deformationfeaturesandsecondphaseparticles.Theunrecrystallisedgrainswereorientatedwith,101¯0.directionsparalleltotheextrusionaxis.InAZ31andZC71therecrystallisedgrainsalsoexhibiteda,2¯ponent,whichevolvedintothemajorcomponentduringannealing.InWE43recrystallisedgrainswereorientatedwiththeirbasalplanesaty45utotheextrusionaxis;thistexturecomponentdominatedthetexturefollowingannealing.Therecrystallisationgraingrowthtexturesappeartobegovernedbygrowthselectionwherealloyingelementschangethegrainboundarybehaviourandorientationrelationshipsforhighmobility.Thetensileandcompressivestrengthsoftheextrusionswereaffectedbythetexture.

Keywords:Magnesiumalloys,Extrusion,Deformation,Recrystallisation,Texture,ElectronbackscattereddiffractionIntroductionparticulatemetalmatrixcomposite(MMC).16ParticleIntheextrudedformsomemagnesiumalloys,includingstimulated17–20nucleationofrecrystallisationmayweaken

AZ31,AZ61andZC71,havebeenreportedtoexhibittexture,andmayhavebeenresponsibleforaanasymmetryoftensileandcompressiveproperties,randomtextureofextrudedWE54.2Evolutionofawhereasothernon-basaltextureincompressedWE53alloy,however,

1–3alloys,suchasWE54,exhibitisotropicbehaviour.Thesedifferenceshavebeenrelatedtohasbeenassociatedwithgraingrowth.21Ithasbeentexture.Theorientationofthebasalplanesinhexagonalspeculatedthatrareearthelementsin uencetextureclosepacked(HCP)materialsin uencestheabilitytothroughsolutedragthatchangesrelativeboundarytwin,andinmagnesiumtwinningcanoccurduringmobilities.22Alternatively,non-basaltexturesmaybecompressionassociatedwithrecrystallisationofnucleationatdefor-4,5paralleltothebasalplanes,butnotinmationfeaturessuchasshearbands.Graingrowthistension.Thistwinningbehaviourresultsinhigherin uentialintheevolutionoftextureofHCPmaterials,tensilethancompressivestrengthsinextrusionswithandrotationsinorientationofy30uaboutthe[0001]basalplanesparalleltotheextrusionaxis.directionareoftenassociatedwithnormalgrainDuringrolling,planestraincompressionandextru-growth.23InsomeMg–Al(–Zn)alloysabnormalgrainsionofsheetmagnesiumthebasalplanesalignwiththegrowthaffectsthetexture.9,10,24sheetsurface;6–10duringaxisymmetricextrusiontheThepresentworkisastudyofdeformation–basalplanesnormallyalignwiththeextrusionaxis.1–3,11recrystallisation–texturerelationshipsinmagnesiumThenon-basaltexturesthatevolveduringequalchannelalloyextrusions.WE43andZC71alloyshavebeenangularextrusionaredependentonprocessinghis-chosenbecauseWEandZCseriesalloyswerethetory.12–14Severalelements,includinglithiumandsubjectofanearlierstudybyBallandPrangnell.2AZ31yttrium,alterthebalanceofdeformationmechanismshasbeenchosenbecauseitisanindustrialalloyonthatcontributetodeformation,whichthereisarelativelylargevolumeofdataavailable.

8andasaconsequencealterthedeformationtexture.

Magnesiumrecrystallisesduringdeformationattem-Experimental

peraturesgreaterthan,150uC.Newgrainsevolveat

grainboundariesanddeformationfeaturessuchEighty-millimetrediameterdirectchillcastbilletsof3,15astwins.Particlestimulatednucleationofrecrystallisa-magnesiumAZ31,WE43andZC71alloyswerereceivedtion(PSN)hasbeenreportedtooccurinZC71–12SiCfromMagnesiumElektronLtd.Thecompositionsof

AZ31andZC71directchillcastbilletswere95?74Mg–

2?96Al–0?293Mn–0?98Znand91?31Mg–0?01Al–1?34Cu–

1MaterialsScienceCentre,SchoolofMaterials,UniversityofManchester,0?78Mn–6?52Zn(wt-%)respectivelyandthatofWE43was

Grosvenor92?73Mg–3?88Y–2?26Nd–0?80Zr–0?10La–0?08Pr(wt-%).2Street,Manchester,M17HS,UKMagnesiumElektronLtd,POBox23,Swinton,Manchester,M278DD,TheAZ31andZC71billetswereannealedfor24hatUK435uC,andtheWE43wasannealedfor24hat525uC*Correspondingauthor,emailluke.mackenzie@andthen16hat450uC.

ß2007InstituteofMaterials,MineralsandMining

PublishedbyManeyonbehalfoftheInstitute

Received15March2007;accepted16June2007

DOI10.1179/174328407X226509MaterialsScienceandTechnology2007VOL23NO101173

Mackenzieetal.Thedeformation,recrystallisationandtextureofthreemagnesiumalloyextrusions

TheextrusionparametersareoutlinedinTable1.

Billetswerepreheatedfor2hbeforeextrusion,and

extrudedatlowtemperaturesinordertominimise

recrystallisation.Followingextrusion,sectionsofthe

AZ31andZC71wereannealedfor24hat435uC;

sectionsoftheWE43wereannealedfor24hat525uC.

Specimenswerecutforexaminationusingspark

erosioninordertoavoidsurfacestrain.Specimenswere

thengroundwith4000gritSiCpaper,polishedwith

0?25mmdiamondpasteandelectropolishedat12Vfor

,25sinasolutionof30mLnitricacidin70mL

ethanolat230uC.

Electronbackscattereddiffraction(EBSD)described

inthepresentpaperwascarriedoutonaPhilipsXL30

eldemissiongunscanningelectronmicroscope

(FEGSEM).DataofEBSDwasacquiredandanalysed

usingHKLChannel5EBSDsoftware(HKL

Technology,Denmark).TheFEGSEMwasoperated

at20kVandthespecimentiltedat70u.Fororientation

mappingthescanstepsizewassetat0?4or0?5mm.In

theEBSDEulercolourcontrastorientationmicro-

graphspresentedinthepresentstudyallextrusion

specimensareviewedalongtheextrusionaxis.High

angleboundaries(HABs).15uandlowanglebound-

aries(LABs).1?5uarerepresentedbythickandthin

blacklines,respectively.Particlesarehighlightedin

white.

BulktextureanalysiswasconductedusingEBSD.The

EBSDscanstepsizewassetatapproximatelytwopoints

pergrain,anddatawascollectedfromatleast2000

grains.Textureisrepresentedusinginversepole gures

fortheextrusionaxisdirection.Ininversepole gures

theintensitylineshavevalues1,2,3,4and5xrandom.

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