The deformation, recrystallisation and texture of three magn(2)

Thelargegraininthecentreofthemicrographisnot

equiaxed;itstretchesfromthetoptothebottomofthe

image.Thesmallrecrystallisedgrainscircledinthe

centreofthemicrographareadjacenttoahighdensity

ofLABsintheunrecrystallisedregion.

ThemicrostructureofZC71followingextrusionat

270uCisshownintheEBSDorientationmicrograph

3EBSDimageshowingmicrostructureofZC71following

extrusionat270uC:smallrecrystallisedgrainsringed

intoprightofimageareassociatedwithHABs;sub-

grainswithinunrecrystallisedgrainareringedinbot-

tomleftof

image4EBSDimageshowingmicrostructureofWE43follow-ingextrusionat360uC:deformationheterogeneitiesareindicatedbyarrows;smallrecrystallisedgrainsringedareassociatedwith

heterogeneitiespresentedinFig.3.ThelargeunrecrystallisedgrainscontainLABsandsubgrains,whicharecircledinthebottomleftoftheimage.ExamplesofLABsthatdissecttheunrecrystallisedgrainsareindicatedbyarrows.Inthetoprightofthemicrographsmallrecrystallisedgrainsareringed;theseareassociatedanHAB.ThemicrostructureofWE43followingextrusionat360uCisshownintheEBSDorientationmicrographspresentedinFigs.4and5.InFig.4,HABsthatcrosstheunrecrystallisedregionareindicatedwitharrows;thesmallgrainsringedareassociatedwiththeHABs.InFig.5,smallgrainsareassociatedwiththesecondphaseparticlesinthecentreofthemicrograph.AnnealedmicrostructuresDuringannealingfor24hat435uCthemicrostructuresofAZ31andZC71fullyrecrystallised;theMLIgrainsizesintheannealedalloyswere25and55mmrespectively.Duringannealingfor24hat525uC

the5EBSDimageshowingmicrostructureofWE43follow-ingextrusionat360uC:mostofsmallrecrystallisedgrainsareassociatedwithsecondphaseparticles

MaterialsScienceandTechnology2007VOL23NO101175

Mackenzieetal.Thedeformation,recrystallisationandtextureofthreemagnesiumalloyextrusions

6Inversepole guresforextrusionaxisdirectionshowingorientationsofunrecrystallisedandrecrystallisedregionsof

extrudedalloys:aAZ31unrecrystallised,bZC71unrecrystallised,cWE43unrecrystallised,dAZ31recrystallised,eZC71recrystallised,fWE43recrystallised

microstructureofWE43alsofullyrecrystallised.

TheMLIgrainsizeoftheannealedWE43was

y100mm,althoughsomegrainswere250to350mmindiameter.

Texture

OrientationdataofEBSDallowstheorientationsof

speci cregionsofthemicrostructuretobecharac-

terised.Theorientationsoftheunrecrystallisedand

recrystallisedregionsintheEBSDorientationmicro-

graphsofAZ31(inFig.2),ZC71(inFig.3)andWE43

(inFig.5)arerepresentedbytheinversepole gures

showninFig.6.Alloftheunrecrystallisedregions¯0.orientation:thebasal(Fig.6a–c)possessan,101¯0.directionsarealignedalongtheplanesand,101

extrusionaxis.IntherecrystallisedgrainsofAZ31¯0.texture(Fig.6d)andZC71(Fig.6e)astrong,101¯ponentisaccompaniedbyaweaker,2

component.InWE43(Fig.6f)therecrystallisedgrains

haveaspreadoforientations,althoughthereisa

tendencyforthebasalplanestoorientateaty45utothe

extrusionaxis.

ThebulktexturesofAZ31,ZC71andWE43intheas

extrudedandannealedstatesaregivenbytheinverse

pole guresshowninFig.7.InAZ31andZC71thebasalplanesareorientatedparalleltotheextrusionaxis.¯ponentisIntheextrudedconditionthe,101¯ponent(Fig.7aaccompaniedbyaweaker,2andb);followingannealingfor24hat435uCthe¯ponentisdominant(Fig.7dande).,2IntheasextrudedWE43therearetwotexturecomponents:oneisorientatedwiththebasalplanesandv1010-wdirectionparalleltotheextrusionaxis,theotherisorientatedwithbasalplanesaty45utotheextrusionaxis(Fig.7c).Afterannealingfor24hat525uCallbasalplanesareorientatedaty45utotheextrusionaxis(Fig.7f).MechanicaltestingThetensile/compressiveratios(asde nedbythe0?2%proofstresses)ofasextrudedandannealedAZ31,WE43andZC71aregiveninTable2.TheAZ31andZC71exhibitsomemechanicalasymmetryintheasextrudedstate;theasymmetryincreasedfollowingannealing.Microstructuralinvestigationofannealedspecimensrevealedextensivetwinningfollowingcompression,butnottensile,testing.TheWE43exhibitedverylittlemechanicalasymmetryineithertheasextrudedorannealedcondition.InWE43verylittletwinningwasobservedfollowingcompressiveortensile

testing.1176MaterialsScienceandTechnology2007VOL23NO10

Mackenzieetal.Thedeformation,recrystallisationandtextureofthreemagnesiumalloyextrusions

7Inversepole guresforextrusionaxisdirectionshowingbulktexturesofasextrudedandannealedAZ31,WE43and

ZC71:aAZ31asextruded,bZC71asextruded,cWE43asextruded,dAZ31annealed,eZC71annealed,fWE43annealed

DiscussionsweepacrossamicrostructuretoproducenewstrainfreeAsextrudedmicrostructuresgrains.Similarpartiallyrecrystallisedmicrostructures

havebeenreportedinAZ31hydrostaticallyextrudedat

IntheextrudedmicrostructuresshowninFigs.2–5the300uC.3

grainsaresmallerthanthoseobservedintheannealedInextrudedZC71(Fig.3),theLABsdissectingthedirectchillcastbillets(Fig.1a–c)becauserecrystallisa-unrecrystallisedregionsmaybedeformationinducedtionhasoccurredduringextrusion.Thebimodalgrainboundaries.InextrudedWE43(Fig.4),HABsextendsizedistributionsarisebecausetheextrusionsareacrosstheunrecrystallisedregion.TheseHABsarepartiallyrecrystallised;thelargegrainsinthecentreofparalleltooneanother,althoughEBSDdataindicatesFigs.2–5areunrecrystallised,whilethesmallergrainsthattheydonothavetwinorientation.Theymaybearerecrystallised.Theunrecrystallisedgrainscontainedkinkbands25thathavearisenasaresultofhighcom-asubstructureconsistingofahighdensityofLABsthatpatibilitystressesgeneratedingrainboundaryregions.developedduringdeformation.MostofthesurroundingLABsform,andasdeformationcontinues,themisor-smallrecrystallisedgrainscontainlittleornodeforma-ientationacrosstheseboundariesincreasesuntiltheytionsubstructurebecauseduringrecrystallisationHABsbecomeHABs.Deformationinducedboundaries,

suchTable2Tensileandcompressive0?2%yieldstrengthsandtensile/compressive0?2%yieldstrengthratios,forAZ31,

WE43andZC71inasextrudedandannealedconditions

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