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