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SciencePressAvailableonlineat(2006)818-823TransactionsofNonferrousMetalsSocietyofChina(I%?%%),WUChuan-song(i$j$j%),ZOUZeng-da(%P@%)KeyLaboratoryofLiquidStructureandHeredityofMaterials,MinistryofEducation,ShandongUniversity,Ji’nan250061,ChinaReceived18October2005;accepted23November2005Abstract:The2mm-thickSiC&D2compositeplateswereelectronbeamweldedatdifferentheatinputs.ThemicrostructuresofweldswereinvestigatedbyOM,TEM,SEM,andXRD,andthepropertiesofweldsweremeasuredwithMTS-810testingsystem.TheresultsshowthatthequantityandsizeofacicularA14C3precipitates(interfacialreactionproduct)decreasewiththeheatinputdecreasing.Whentheheatinputlowersto30J/mm,theformationofneedle-likeA14C3canbeprevented.ThedistributionsofSicinthefusionzonesaremoreuniformthanthatinas-receivedcomposite.TEManalysisrevealsthatthereareA14C3crystalsonthesurfaceofeverysurvivedparticle,theneedle-likeA14C3observedundertheopticalmicroscopeconsistsofmanytabularA&C3crystalswhichhavedifferentorientations.Withtheincreaseofheatinput,thefracturemechanismchangesfromductileonetobrittleone,thequantityoffracturedparticlesonthefracturefacedecreasesandthestrengthandductilityofthewelddecrease.Keywords:SiCdLD2composite;electronbeamwelding;interfacialreaction1IntroductionSicparticlereinforcedaluminumcomposites(SiCdAl)possessexcellentproperties,e.g.highstrength-to-massratio,highstiffness-to-massratio,goodwearresistanceandhigherservicetemperature,thereforetheyareconsideredakindofpromisingstructuralmaterial.Withthegradualreductioninproductioncost,anincreaseinusesandapplicationmaybeexpectedinthenextyears.Forthisreason,weldingtechnologiesofthislundofmaterialhaveattractedalotofattentionrecently.PreviousstudiesrevealthatalmostallfusionweldingprocessesproducedeleteriousmicrostructuralalterationswhentheyareappliedtoSiCdAlcomposites[l-91.InTIGandMIGweldingpool,thestrongrejectionofSicparticlesbysolidificationfrontresultsinmicrosegregationandinhomogeneousparticledistribu-tion,thusreducingthereinforcementefficiency[1-31.ThehighhydrogencontentintheA1matrixcomposites(especiallytheoneproducedbypowdermetallurgicalroutes)andlowflowabilityofmoltenpooltendtoresultinseriousporosityinbothweldandHAZ[2-51.ThevacuumdegassingpriortoweldingcaneliminatetheporositiesintheTIGandMIGwelds[2,3,5].Duringwelding,seriousinterfacereactionbetweenSicparticlesandA1matrixoccursandplate-likeA14C3precipitatesform,whichareverybrittleanddeleterioustothepro-pertiesoftheweld[2,3,7,8].However,throughapplyingAl-Sifillermetaland/orloweringheatinput,theinterfacialreactioncanbereducedorsuppressed[2,3].Byusingsolid-statejoining,theabove-mentionedproblemscanbeeliminated.Thereforemuchmoreresearchworkhasbeendoneinsolid-statejoining(suchasdiffisionbondingandfrictionwelding)ofSicparticlereinforcedaluminumcompositesandresultsareencouraging[10-121.However,thelowproductionefficiencyandsuitabilitylimittheapplicationfieldsofthoseprocedures.Thus,itisstillnecessarytoreconsiderthepossibilityofapplicationofthemoreproductiveweldingprocesses,fusionwelding.Inthispaper,theinfluenceofheatinputonmicrostructureandpropertiesoftheEB(electronbeam)weldsinSiCdLD2werestudied.Theemphasiswasplacedontheanalysisofeffectofweldingcycleontheparticledistribution,A1-Sicinterfacemorphologiesandtheinterfacialreactionproductsinthewelds.TheinfluenceofinterfacialreactiononthepropertiesandfracturemechanismoftheEBweldswerealsodiscussed.Themechanismofinterfacialreactionwasalsoreviewed.Foundationitem:Project(2004BS05010)supportedbyShandongYouthDoctoralFoundation,ChinaCorrespondingauthor:CHENMao-ai;Tel:+86-531-88392711;E-mail:chenmaoai@sdu,edu.cnCHENMao-ai.etaL'Trans.NonferrousMet.SOC.China16(2006)8192Experimental2.1MaterialThematerialusedinthisinvestigationwas2mmthickplateofSicparticlereinforcedLD2aluminum(SiCdLD2).ThevolumefractionofSicparticlewas10%.2.2WeldingmachineandprocedureThe2nunthickas-receivedplatewascutintoto-be-weldedpieceswith500mminlengthand50mminwidth.Beforewelding,thepieceswerecleanedwithacetonethoroughlytoeliminatedirtandgrease.WeldingexperimentswereperformedwithEBW2100115-15OCNC.TheweldingparametersarelistedinTable1.HeatinputsinTable1werecalculatedastheproductofacceleratingvoltageandbeamcurrentdividedbytravelingspeed.2.3MicrostructureanalysisandmechanicaltestingMetallurgicalspecimensweresectionedfromtheweldmentintransversetotheweldingdirection.Thespecimenswerefirstpolishedwithdiamondpasteandwater,andfinallypolishedwithdiamondpasteandalcoholtopreventA14C3thatmaybepresentintheweldfromdecomposing.Afterpolishing,thespecimenswerecleanedwithacetone.PreparedspecimenswereobservedwithNeophto-20opticalmicroscope.QuantitativemetallographywasusedtomeasurethemeansizeofA&inindividualweld.X-raydiffractionwasperformedbyDlmax-rcdiffractometryonthespecimenssectionedfromthetopoftheweldalongtheweldingdirection.TheA1-SicinterfacemorphologyinweldmetalwasexaminedwithH-800transmissionelectronmicroscope.AndthefracturesurfacewasexaminedwithPhilips-515sc