Effect-of-gradient-thermal-distribution-on-butt-jo

EffectofgradientthermaldistributiononbuttjoiningofmagnesiumalloytosteelwithCu–Znalloyinterlayerbyhybridlaser–tungsteninertgasweldingGangSong⇑,GuangyeAn,LimingLiuKeyLaboratoryofLiaoningAdvancedWeldingandJoiningTechnology,SchoolofMaterialsScienceandEngineering,DalianUniversityofTechnology,Dalian116024,People’sRepublicofChinaarticleinfoArticlehistory:Received11July2011Accepted3September2011Availableonline8September2011Keywords:A.FerrousmetalsandalloysD.WeldingF.MicrostructureabstractExperimentalinvestigationsonbuttweldingofmagnesiumalloytosteelbyhybridlaser–tungsteninertgas(TIG)weldingwithCu–Znalloyinterlayerarecarriedout.Theresultsshowthatthegradientthermaldistributionofhybridlaser–TIGwelding,controlledbyoffsetadjustment,hasanoticeableeffectonmechanicalpropertiesandmicrostructureofthejoints.Particularly,attheoffsetof0.2mm,defect-freejointsareobtained,andthetensilestrengthcouldattainamaximumvalueof203MPa.Moreover,thefractureofthejointwiththe0.2mmoffsethappensintheweldseamofMgalloyinsteadoftheMg/Feinterface.OwningtotheadditionoftheCu–Znalloyinterlayer,ametallurgicalbondingbetweenMgalloyandsteelisachievedbasedontheformationofintermetalliccompoundsofCuMgZnandsolidsolutionsofCuandAlinFe.Meanwhile,thesameelementdistributiontendencyofFeandAlindicatestheintimateinteractionbetweenFeandAlincurrentexperimentalconditions.2011ElsevierLtd.Allrightsreserved.1.IntroductionMagnesiumalloys,duetotheuniqueproperties,havebeencon-sideredaspromisingstructurematerialstolowerweightandenergyconsumptioninautomobileindustry[1–4].However,steelsarethemostcommonmaterialsforstructuralcomponentsinthecurrentautobody[5].Thereliabledissimilarcombinationofmag-nesiumalloysandsteelwillexpandutilizationofmagnesiumalloysinvehiclefabrication.Therefore,itisdrawingincreasingattentiontojointogethermagnesiumalloysandsteeltoachieveacceptableproperties.Therearedifficultiesencounteredwhenitinvolvesdissimilarweldingofmagnesiumalloysandsteelinvirtueofthegreatdiffer-encesintheirmetallurgicalandphysicalproperties.Themainproblemsarethequitedifferentmeltingpointsandalmostnointersolubilitybetweenmagnesiumalloysandsteel[6].Frictionstirwelding(FSW)hasbeenutilizedintheweldingofmagnesiumalloysandsteel[5,7–10].Abeetal.[5]realizedbuttweldingofmildsteelandmagnesiumalloybyFSWandinvestigatedtheeffectsofthepinrotatingspeedandpinoffsetonthestrengthandmicrostructureofthejoints.ChenandNakata[7]reportedthatthepresenceofzinccoatpromotedtheformationofliquidlowmeltingMg–ZneutecticproductsattheinterfaceofMg–FejointsbyFSW.Bymethodoflaserpenetrationbrazingwelding,Miaoetal.[11,12]investigatedtheeffectoflaseroffsetsonjointperformanceofmagnesiumalloyandsteel,indicatingthatthejoiningofMgalloyandsteelwasformedbydiffusing.However,thefracturepathsofthejointsobtainedbytheabovemethodswerealmostalongMg/Feinterfaces,suggestingthattheMg/Feinterfacewastheweakpositioninthedissimilarweldingofmag-nesiumalloysandsteel.DuetonointersolubilitybetweenMgandFe,elementsofNiandCuwereemployedtoimprovetheinteractionbetweenthedissim-ilarmetals,andmetallurgicalbondingwasrealizedbydiffusionbrazingandeutecticbonding[13,14].LiuandQi[3,6,15–17]usedpuremetalsastheinterlayerinthelapjoiningofMgalloytosteelbyhybridlaser–TIGwelding.ItwasreportedthattheadditionofCucouldrealize‘‘semimetallurgical’’bondingbetweenMgalloyandsteel[16].However,nocompletemetallurgicalbondinghasbeenrealizedintheworks.ToimplementthemetallurgicalbondingbetweenMgalloyandsteel,theCu–ZnalloyistriedtobeutilizedastheinterlayerbasedonthattheadditionofCucouldrealizetheMg/Fe‘‘semimetallurgical’’bonding[16]andthepresenceofZncouldimprovetheMg/Feweldability[7–9]aspreviouslymentioned.Hybridlaser–TIGweldingcombinestheadvantagesofbothlaserweldingandTIGwelding.Thepulsedlaserweldingprovideshighenergydensityandhighcoolingrate[18],andincomparison,TIGweldingprovideslowenergydensityandmuchmoresolidifi-cationtime.WhenthehybridweldingsetupisfixedwithlaseraheadofTIG,thedistinctheatsourcesencompassedinhybridweldingcouldprovidesignificantdifferentdistributionofthermal0261-3069/$-seefrontmatter2011ElsevierLtd.Allrightsreserved.doi:10.1016/j.matdes.2011.09.006⇑Correspondingauthor.Tel./fax:[phone].E-mailaddress:[e-mail](G.Song).MaterialsandDesign35(2012)323–329ContentslistsavailableatSciVerseScienceDirectMaterialsandDesignjournalhomepage:–TIGwelding.Mean-while,thegradientthermaldistributioncouldbecontrolledbyadjustingtheoffsetofhybridwelding.Thisthermalcharacteristiccouldbeutilizedtowelddissimilarmaterials,especiallywithahighdifferenceinmeltingpoints.Therefore,itisapromisingweld-ingtechnologytobuttjoinmagnesiumalloysandsteelbypreciselycontrollingthegradientthermaldistribution.Thispaperinvestigatestheeffectofgradientthermaldistribu-tiononthebuttjoiningofmagnesiumalloyandsteelbyhybridlaser–TIGwelding.Themainobjectiveofthisinvestigationistore-vealtherelationshipbetweenthemechanicalpropertiesandmicrostructureofthejointsandtoimplementthesound