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JournalofMaterialsProcessingTechnology168(2005)262–269ProcessoptimisationforasqueezecastmagnesiumalloymetalmatrixcompositeM.S.Yonga,∗,A.J.CleggbaSingaporeInstituteofManufacturingTechnology,71NanyangDrive,Singapore638075,SingaporebWolfsonSchoolofMechanicalandManufacturingEngineering,LoughboroughUniversity,Loughborough,LeicestershireLE113TU,UKReceived5January2004;receivedinrevisedform5January2004;accepted27January2005AbstractThepaperreportstheinfluenceofprocessvariablesonazirconium-free(RZ5DF)magnesiumalloymetalmatrixcomposite(MMC)containing14vol.%Saffilfibres.Thesqueezecastingprocesswasusedtoproducethecompositesandtheprocessvariablesevaluatedwereappliedpressure,from0.1MPato120MPa,andpreformtemperaturefrom250◦Cto750◦C.Theprincipalfindingsfromthisresearchwerethataminimumappliedpressureof60MPaisnecessarytoeliminateporosityandthatappliedpressuresgreaterthan100MPacausefibreclusteringandbreakage.Theoptimumappliedpressurewasestablishedtobe80MPa.Itwasalsoestablishedthattoensuresuccessfulpreforminfiltrationapreformtemperatureof600◦Corabovewasnecessary.Fortheoptimumcombinationofapreformpreheattemperatureof600◦Candanappliedpressureof80MPa,anUTSof259MPawasobtainedforthecomposite.Thisrepresentedanincreaseof30%comparedtotheUTSforthesqueezecastbasealloy.©2005ElsevierB.V.Allrightsreserved.Keywords:Magnesiumalloys;Squeezecasting;Metalmatrixcomposites;Mechanicalproperties1.IntroductionMetalmatrixcomposite(MMC)componentscanbeman-ufacturedbyseveralmethods.Themetalcastingrouteisespe-ciallyattractiveintermsofitsabilitytoproducecomplexnearnetshapes.However,castingsproducedbyconventionalcast-ingprocessesmaycontaingasand/orshrinkageporosity.Thetendencyforporosityformationwillbeexacerbatedwhenfi-bresareintroducedbecausetheytendtorestricttheflowofmoltenmetalandcauseevengreatergasentrapmentwithinthecasting.Itispointlesstousefibrestoreinforceacastingifdefectsarepresent,sincetheadditionoffibreswillnotcom-pensateforpoormetallurgicalintegrity.Inordertofulfilthepotentialoffibrereinforcementandproduceporefreecast-ingsthesqueezecastingprocesscanbeselected.Theuniquefeatureofthisprocessisthatmetalispressurisedthroughoutsolidification.Thispreventstheformationofgasandshrink-ageporosityandproducesametallurgicallysoundcasting.∗Correspondingauthor.E-mailaddress:msyong@simtech.a-star.edu.sg(M.S.Yong).Selectionofthisprocessisalsobasedonitssuitabilityformassproduction,easeoffabricationanditsconsistencyinproducinghighqualitycompositeparts.WiththedevelopmentofMMCs,magnesiumalloyscanbettermeetthevariousdemandsofdiverseapplications.Theadditionofreinforcementtomagnesiumalloyproducessu-periormechanicalproperties[1–3]andgoodthermalstability[4,5].Ofthevariouscompositetypes,thediscontinuousandrandomlyorientedfibre-reinforcedcompositesprovidethebest“valuetostrengthratio”.DespitethepotentialadvantageofusingmagnesiumMMCforlightweightandhighstrengthapplications,littleisknownabouttheinfluenceofsqueezeinfiltrationparame-ters.Keyparameters,suchasappliedpressureandpreformtemperaturemustbeoptimised,especiallyforthesqueezeinfiltrationofamagnesium–zincMMC.Theseprocesspa-rameterswereresearchedandtheresultsarepresentedinthispaper.However,itwasfirstnecessarytoselectappropriatefibresandbinderssincetheirselectionisfundamentaltothesuccessoftheMMC.Themaincriteriondeterminingthese-lectionoffibretypeiscompatibilitywiththematrix.Two0924-0136/$–seefrontmatter©2005ElsevierB.V.Allrightsreserved.doi:10.1016/j.jmatprotec.2005.01.012M.S.Yong,A.J.Clegg/JournalofMaterialsProcessingTechnology168(2005)262–269263fibretypesthatareknowntobecompatiblewithmagnesiumareSaffilandcarbon[6].Silicaandalumina-basedbindersarewidelyusedinpreformproduction,mainlyduetotheirhightemperatureproperties[7].However,thereareconcernsaboutchemicalreactionsbetweenmagnesiumalloysandsil-ica[8].Toensurefullinfiltrationofliquidmetalintothefibrepre-form,researchers[9–11]haveemphasisedtheimportanceofpreheatingthepreforms.However,therehasbeenlit-tleresearchtodetermineoptimumpreformtemperatureformagnesiumalloysandthatreportedhasfocusedonAZ91(magnesium–aluminium)alloy.Thewettingcapabilityofthesealloysisdifferent,forinstancethewettingandthein-terfacialreactionbetweenAl2O3reinforcementandcerium,lanthanum(bothrareearthelements)ormagnesiumisfarbetterincomparisontoaluminium.Mostworkonappliedpressurehasfocusedonaluminiumalloysandtheircomposites.However,Ha[12]andChadwick[13]investigatedtheinfluenceofappliedpressureontheshortfreezingrangeMg–Alfamilyofalloys.Theeffectonsolid-ificationwillinevitablybedifferentforlongfreezingrangealloys,suchastheMg–Znfamilyalloysthatarethefocusofthisresearch.Thedifferenceinsolidificationmorphologywillbesignificantwheninfiltratingthemeltintoaporousfi-brepreform.Longfreezingrangealloysretainaliquidphaseoveralongerperiodduringinfiltrationandthismaypromotebetterinfiltration,reducevoidsandconsequentlyimprovethesoundnessofthecomposite.2.ExperimentalmethodologyAzirconium-freemagnesium–4.2%zinc–1%-rareearthsalloy,designatedRZ5DF,wasusedforthisresearch.Severalfibrepreformmaterials,proportionsandbindersystems,wereevaluatedtodeterminetheircompati