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1、RAREMETALSVol.23,No.4,Dec2004,p.340MicrostructuralevolutioncharacterizationoffrictionstirringweldedAZ31magnesiumalloyZHANGHua,LINSanbao,WULin,andFENGJicaiStateKeyLabofAdvancedWeldingProductionTechnology,HarbinInstituteofTechnology,Harbin150001,China(Received2003-12-22)Abstract:Afriction
2、stirringweldingtojoint5mmrolledAZ31magnesiumhadbeendeveloped.Themicrostructuresinvariousregionsincludingtheweldnugget,thermo-mechanicallyaffectedzone(TMAZ)andheataffectedzone(HAZ)wereinvestigatedandcomparedwithunaffectedparentmetalusingopticalmicroscopy.Theresultsshowedthattheheatandmec
3、hanicalprocesshadgreateffectonthemicrostructureevolution.Inweldnugget,theheatwasenoughtoproducesufficientsuperplasticmaterialflowandthemechanicaleffectwasgreatest,andthedynamicrecrystallizationwascompletedthoroughly.InTMAZ,themechanicaleffectwasindirectlyaffectedbytheweldingtoolandonlys
4、omegrainshadundergonedynamicrecrystallization.Thevariousregionswerestudiedindetailtobetterunderstandthemicrostructuralevolutionduringfrictionstirringwelding(FSW).Thecrosssectionnearthe“keyhole”showedclearonionringsbecausethematerialwasstirredonlybytherotationoftheprobeandmaterialsrotate
5、dwiththeprobeanddidnotmovealongweldingdirectionandinverticaldirection,therewasnomaterialflowandtheflowmovementcanberegardedastwodimensionallayerflow.Keywords:frictionstirringwelding;AZ31magnesiumalloy;microstructures;TMAZ;weldnugget;dynamicrecrystallization[Thisprojectwasfinanciallysupp
6、ortedbytheNational863ProjectFoundation(No.2002AA331160).]1IntroductionInordertoreducetheweightofroadvehiclestoimprovemoreenergyefficient,magnesiumalloyparticularlydie-castmagnesiumalloyarebecomingmoreandmoreusefulinautomobileindustry.Usingthetraditionalweldingmethods(withandwithoutfille
7、rmetal)tojointmagnesiumalloyareeasytobringproblems,suchasgasestrappedinpores,lossofalloyingelements,hotcracking,andlowmeltingpointeutecticphaseintheHAZ.Andthetemperatureishigherinthemeltingmethodsresultinginhigherdistortionandhigherresidualstressanddecreasethejointquality[1,2].
