外文翻译--复合材料mg2si-al的冷却斜槽法铸造和其局部重熔演化过程中的半固态微观结构 英文版.pdf

MaterialsScienceandEngineeringA444(2007)99103SemisolidmicrostructureofMg2Si/AlcompositebycoolingslopecastanditsevolutionduringQ.D.Qin,Y.G.Zhao,P.J.Street,acceptedAbstractfabricatedmicrostructure,sizethatareshapeK1.lotminimizingandsemisolidoftureneededisconstitutedofsolidphaseglobulessuspendedintheliquidphase.Thethixotropiceffectofthesemisolidalloysallowsthemtobehandledasamassivesolidandtoattainfluid-likepropertieswhenshearedduringshaping2.ManydifferentroutessuchstraintialRecentlysemisolidKleinerallogrofloofprocessallosphericalSuzukithixoforminginofpotentialasautomobilebrakediscmaterialbecausetheinter-metalliccompoundofMg2Siexhibitshashighmeltingtem-perature,lowdensity,highhardness,lowthermalexpansioncoefficientandreasonablyhighelasticmodulus8.However,0921-5093/$doi:havebeenusedtoproducenon-dendriticmicrostructure,asmagnetohydrodynamic(MHD)stirring,sprayforming,inducedmeltactivated(SIMA)/recrystallisationandpar-melting(RAP),liquidus/near-liquiduscastingetc.38.,Czerwinski911investigatedthefabricationofMgalloyscomponentsbyinjectionmoldingprocess.etal.12studiedtheformationofsemisolidMgAlZnybyextrudedmethod.Wuetal.13constructedamodelonwthmorphologyofsemisolidmetals,usingsolidificationandwspeedoftheliquidasvariationsaffectingthemorphologycrystals.AmongallthetechniquesofSSP,thecoolingslopeCorrespondingauthor.Tel.:+864315094481；fax:+864315095592.E-mailaddress:(Y.G.Zhao).thecoarsereinforcementoftheprimaryMg2Siparticlesinthenormalcompositeleadstopoorproperties.Therefore,thecom-positewithcoarseprimaryMg2Siparticlesneedtobemodifiedtoobtainadequatemechanicalstrengthandductility.IthasbeenreportedthatrareearthelementssuchasCe16,Sr17anditssalts18,19havethepowertomodifythemorphologyofprimaryMg2Si.Asemisolidmicrostructureinthecompositeisexpectedtoimprovethemechanicalproperties.ThesemisolidofMg2Si/AlcompositehasbeenproducedviaSIMAinpre-viousstudy8.However,thistechnologyisrelativecomplexbecauseofrequiringcoldextrusionanddeformation.LessworkhasbeencarriedoutonsemisolidMg2Si/Alcompositebythecoolingslopecastandpartialremeltingprocess.Inthepresentstudy,asemisolidofinsituMg2Si/AlSiCucompositewaspreparedbythecoolingslopecastandpartialremeltingprocess,seefrontmatter2006ElsevierB.V.Allrightsreserved.10.1016/j.msea.2006.08.074KeyLaboratoryofAutomobileMaterialsofMinistryofEducationJilinUniversity,No.142RenminReceived17April2006；AninsituMg2Si/AlSiCucompositewithsemisolidstructurewasandeffectofisothermalholdingtimeonthemorphologythemorphologyofprimaryMg2SiandH9251-AlgrainsinthecompositefactorofH9251-Algrainsincreasewiththeisothermalholdingtime.2006ElsevierB.V.Allrightsreserved.eywords:Semisolid；Aluminum；Composites；Microstructure；MagnesiumsilicideIntroductionIthasbeenwellknownthatsemisolidprocessing(SSP)hasaofsignificantadvantagesoverconventionalcasting,suchasthemacrosegregationandsolidificationshrinkagereducingtheformingtemperature.Thekeythatpermitsthealloystoshapeistheabsenceofdendriticmorphologythesolidphase1.Thetypicalnon-dendriticmicrostruc-partialremeltingprocessCong,W.Zhou,B.XuandDepartmentofMaterialsScience&Engineering,Changchun130025,PRChina15August2006bycoolingslopecastandpartialremeltingprocess.Theas-castandshapefactorofthegrainswereinvestigated.Theresultsshowglobularand/orellipticafterpartialremeltingprocess.Thesizeandisasimpleroute.Theprimaryphaseinthesemisolidybythecoolingslopecasthasbeenreportedtobecomeafterremeltedinthesemisolidstate14.Hagaand14,15investigatedtheproducingprocessofingotsforofAl6Sialloysbycoolingslopecasting.HypereutecticAlSialloyswithhighMgcontentisinfactansitualuminummatrixcompositescontainingalargeamounthardparticlesofMg2Si,andtheMg2Si/Alcompositehasa100Q.D.Qinetal./MaterialsScienceandEngineeringA444(2007)99103Table1ChemicalcompositionsoftheMg2Si/Alcomposite(wt.%)MaterialsAlMgSiCuCrZnNiFeAlSiMgCuBal.13.27611.2813.5230.0050.02399.7%purity)andmagnesium(ingot,98.0%purity)usedtopreparetheexperimentalalloy.About520gofmasteralloymeltwasmolteninagraphitecrucibleinanresistancefurnace.About100gofmagnesiumand26gCu,preheatedat300C,wereaddedintotheAlSimeltatC.Afterholding15min,themeltwerepouredintoamoldviaaaluminumcoolingslope(preheatedat300C)totheinsituMg2Si/Alcompositeingots,andthechem-compositionsarelistedinTable1.TheschematicoftheprocessisshowninFig.1(adoptedfrom15).Sub-,theingotwascutintoaseriesofcubicsamplesofmm12mm12mm.Thepartialremeltingprocesswasinaverticaltubefurnace,andthesampleswereheatedto560Candheldatthetemperaturefor30,60,180andmin,respectively,andthenwerequenchedincoldwater.Metallographicspecimenswerepolishedthroughstandardandthemicrostructureinthemexaminedusinganmicroscopy.A0.5%hydrofluoricacid(HF)aqueouswasusedastheetchantofpolishingsamples.ThegrainFig.2.As-castmicrostructuresofMg2Si/Alcompositesby(a)thenormal200H9262m,andtheH9251-Alwasdendriticaswell.However,afterthesolidwiththecoolingslope,themorphologyofH9251-Alinthecompositebythecoolingslopcastchangesfromtospheralwithadiameterof10H9262m,andtheprimary2Sicrystalsbecomefineobviously,asseeninFig.2b.Oneforitisduetotheincreaseinthenucleationsubstratesthemeltaftercastingwiththecoolingslope；anotherreasonrelatedtotheflowofthemeltontheslope.Theflowingmeltcausepartialfragmentsofthedendritesofthedendritesbyvection.Fig.3adshowstheevolutionofthesemisolidmicrostruc-ofthecompositebythecoolingslopecastwiththetimeofisothermalheattreatmentof30,60,180andmin,respectively.Fig.3ashowsthattheas-castcoarse2Sidendritesarefragmented,changingtoanirregularwithslightlyroundedtips,andthemorphologyofH9251-Alvebecomesglobularwithameansizeof51H9262m.Asthetimeincreasesto60min,themorphologyoftheMg2SiinthecompositebecomesmainlyellipticshapeandtheofH9251-Albecomesmoreglobularwithameansize85H9262mseeninFig.3b.Furthermore,italsoshowsthatsomeH9251-AlgrainsisnotdissolvedcompletelysurvivingintheasindicatedbywhitearrowsinFig.3b.Fig.3cshowsthecast(adoptedfrom8)and(b)thecoolingslopecast.Q.D.Qinetal./MaterialsScienceandEngineeringA444(2007)99103101Fig.castandmicrostructure180notincreasesgrains”H9251surviofasinparticles.liquidduringfurthergrains”shapetreatmenttheasobof“smallerThesolidificationquenchingmay3.SemisolidmicrostructuresoftheMg2Si/Alcompositebythecoolingslope(d)600min.ofthecompositewithaisothermaltreatmentformin.ThemorphologiesoftheMg2SiandH9251-Alparticlesdochangeobviously,however,themeansizeofH9251-Alparticlesto111H9262m.Itisofinteresttonotethatsome“smalleremergeonthesurfaceofthelargeglobulargrainsof-Al,asindicatedbyblackarrowsinFig.3c.Theamountofthevedsmallsolidparticlesincreases,incomparisonwiththat60minholdingtime.Itseemsthattheliquidfractionincreaseswell.Unfortunately,theliquidfractioncouldnotbemeasuredthepresentstudy,becauseofthesurvivedofthesmallsolidPoirieretal.20reportedthatthevolumefractionofofAlCualloyslightlydecreasedatthecoarseningperiodsemisolidisothermaltreatment.Thephenomenonneedsstudy.Fig.4ashowsthatthemorphologyofthe“smalleriscolumnarandsomesurvivedsolidphasesareirregularasdenotedbythewhitearrowinFig.4a.AstheisothermalFromtheticlesofformationFig.4.Metallographsofthecompositeswiththeisothermaltimeof(a)withdifferentisothermalholdingtimeof(a)30min,(b)60min,(c)180mintimeincreasesupto600min,themorphologiesofprimaryMg2SiparticlesandH9251-Algrainsarestillglobular,showninFig.3d.ThesizeoftheH9251-Algrainsincreaseviouslywithameansizeof149H9262m.Inaddition,theamountthesurvivedsolidparticlesevidentlydecreases,andthegrains”onthesurfaceoflargeH9251-Algrainsdisappear.“smallergrains”emergencemaybetheconsequenceofoftheliquidduringhandlingofthesamplesbeforeinwater,andthatemergenceanddisappearancebeduetothedifferenceofthehandletimeforquenching.Fig.4b,itisclearlyindicatedthatthemorphologiesofsurvivedsolidparticlesdonotchangeobviously.Togetbetterunderstandingoftheevolutionofthesolidpar-isofimportant,becauseitdeterminesthefinalgrainsizethecomposite,andthusthemechanicalproperties21.Theofasemisolidstructurebyisothermalholdingfroma180minand(b)600min,showingtheH9251-Al“smallergrains”.102Q.D.Qinetal./MaterialsScienceandEngineeringA444(2007)99103Fig.con8iscastisothermalarmsellipsoidalandclesisjoiningcoarseningtheincanacterizedFwhererespectiisothermalshapetimetimethatthataslosolidvtheofInmicrostructuresofhardFig.ingdissolvcessthe4.successfullyremeltingofobincreasemeanmorphologyH9251timeAcknoneeringFRefer5.TherelationshipofthemeansizeofH9251-Algrainsandtheholdingtime.ventionallycastdendriticstructurehasbeenstudiedearlier.Thetransitionofthesolidphasefromdendriticintospheralthoughttobeduetotheliquidpenetration,namely,theas-grainboundaryispenetratedbyliquidduringthesemisolidholding,causingthefragmentationofthedendriteandthen,thefragmentedarmschangeintospheroidalorgrains.TherelationshipbetweenthegrainsizeoftheH9251-AlparticlesholdingtimeisshowninFig.5.ThesizeoftheH9251-Alparti-increaseswiththeholdingtime.Onecoarseningmechanismthecoalescenceofthegrains,namely,twograinsencountertogetherandformingnewbiggergrain22.AnothermechanismistheOstwaldripening22,23,inwhichlargergrainsgrowandthesmallergrainsremelt.Usingtheimageanalysissystem,thenumberoftheobjectsaselectedarea,andtheperimeterandareaofselectedobjectsbemeasured2.Normally,theshapeofanobjectischar-bytheshapefactorF0definedas2:0=4A0P20(1)A0andP0representtheareaandperimeteroftheobject,vely2.ThechangeoftheshapefactorduringthetreatmentisshowninFig.6.Itisindicatedthatthefactorincreasesrapidlyfrom0.51to0.69withtheholdingfrom30to180minandhowever,amuchlargerholdingcannotresultinaconsiderablechangeofF0,suggestingtheF0seemstoreachtoamaximumvalue.Itisreportedthesolidphaseparticlestendtobecomespherical,but,forlongerholdingtime,thechangeoftheshapeoftheparticleswsdownandevenreversesinthecaseofthehighvaluesofvolumefraction21.Keepinginmindthatthehighsolidolumefractionmeansalsoahighcontiguity,thisreversionfromsphericalshapecanbeattributedtothehardimpingementthesolidparticles,leadingtothelocalshapedistortions21.thepresentstudy,however,thesolidvolumefractionintheislowerrelatively(0.6)accordingtotheresultthequantitativeanalysis,andconsequently,thechanceoftheimpingementisloweraswell.Withincreaseinthehold-106.RelationshipoftheshaperfactoroftheH9251-Algrainsanttheholdingtime.time,thehighercurvaturepartofthesolidparticlewillbeed,andleadingtotheincreaseoftheF0.Finally,thepro-reachestoadynamicequilibriumandtheshapefactorofgrainswillnotchange.ConclusionThesemisolidstructureofinsituMg2Si/Alcompositeisproducedbythecoolingslopecastandpartialprocess.Theresultsshowthat:(a)themorphologyprimaryMg2Siphaseisglobularand/orellipticn