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

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.

AllmechanicaltestingwascompletedusinganInstron

5500testingmachineatroomtemperature.Tensile

specimenswithgaugesection6?4mmdiameterand

23mmlength,andcompressivespecimens13mm

diameterand16mmlength,weremachinedfromthe

asextrudedandannealedmaterialparalleltothe

extrusionaxis.Beforecompressionthespecimenswere

cleanedinacetoneandPTFEtapewasplacedbetween

thecompressionspecimensandtheInstronplatensin

ordertoreducefriction.Thecompressionspecimens

weredeformedatarateof0?08mmmin21,andtensile

specimensatarateof0?07mmmin21.Afteryielding

hadoccurredthetestswerestoppedandthespecimens

wereremovedfromthetestrig.1BackscatteredelectronSEMimageofaAZ31andbZC71billetfollowingannealingfor24hat435uCandofcWE43billetfollowingannealingfor24hat525uCtheMLIgrainsizeswerey300mm;inWE43theMLI

grainsizewasy100mm.

Results

Annealedbillet

Themicrostructuresoftheannealeddirectchillcast

AZ31,ZC71andWE43billetsareillustratedbythe

backscatteredelectronSEMimagespresentedin

Fig.1a–crespectively.Precipitatesaredistributed

throughoutthemicrostructure;inWE43andZC71

therealsoappearstobeprecipitatepreferentially

distributedalonggrainboundaries.InAZ31andZC71

Table1ExtrusionparametersforAZ31,WE43andZC71

Alloy

AZ31

ZC71

WE43Extrusiontemperature,uC282270360AsextrudedmicrostructuresExamplesoftheasextrudedmicrostructuresofAZ31,ZC71andWE43areshownintheEBSDorientationmicrographsinFigs.2–5.Eachalloyexhibitsabimodalgrainsizedistribution,wherelargegrainsinthecentreofeachmicrographaresurroundedbysmallerequiaxedgrains.Thelargegrainscontainadeformationsub-structurethatconsistsofLABs.Theselargegrainsareunrecrystallisedregions.Extrusionspeed,mmin212052.051.05

Extrusionratio17717.74

1174MaterialsScienceandTechnology2007VOL23NO10

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