號鋼機體堆焊金屬層的摩擦性能研究

摘要堆焊是作為材料表面改性的一種經(jīng)濟并且快速的工藝方法，廣泛地應(yīng)用于各個工業(yè)部門零件的制造修復(fù)中。為了能夠有效地發(fā)揮堆焊層的作用，希望采用的堆焊方法得到有較小的母材稀釋、較高的熔敷速度和優(yōu)良的堆焊層性能，即能夠得到優(yōu)質(zhì)、高效、低稀釋率的堆焊技術(shù)。45號鋼基體上堆焊主要是針對摩擦副機械零件表面的磨損，分析了添加劑在磨損表面形成的保護膜的組成、形貌和厚度。目前研究45號鋼基體上堆焊耐磨性能最常用的方法是磨損試驗檢測法和數(shù)值仿真方法,其中磨損試驗法樣品加工過程困難、成本較高并且試驗周期長,而數(shù)值仿真方法快速、經(jīng)濟，但是模型建立難度較大且且計算的結(jié)果精度不高。本次研究采用焊條電弧焊工藝,選擇厚度為5mm的45#鋼板作為基體,在焊接工藝下使用D172焊條進行堆焊,通過光學(xué)顯微鏡(OM)、掃描電鏡(SEM)以及金相試驗研究堆焊熔敷金屬的顯微組織及構(gòu)成,并且測試其樣品的顯微硬度。制備金屬滑動磨損試樣,選用環(huán)塊型摩擦試驗機磨損試驗機進行磨損實驗,對比不同的載荷、滑動距離條件下堆焊金屬層的耐磨性能。經(jīng)掃描電子顯微鏡(SEM)對磨痕形狀外貌進行分析,研究堆焊金屬層在干摩擦條件下的磨損機制。關(guān)鍵詞：45號鋼；堆焊；摩擦；磨損AbstractWeldingisakindofeconomyasthematerialsurfacemodificationandtheprocessmethodofquicklyandwidelyusedinthemanufactureofeachindustrialsectorpartsrepair.Inordertobeabletoeffectivelyplaytheroleofsurfacingweldinglayer,hopesurfacingmethodswitharelativelysmallbasedilution,higherdepositionrateandexcellentperformanceofsurfacingweldinglayer,whichcangethighquality,highefficiency,lowdilutionrateofsurfacingweldingtechnology.Surfacingon45steelsubstratebasicallyistomechanicalpartswearandtearonthesurfaceofthefrictionpair,additiveonthewearsurfaceisanalyzedformthecomposition,morphologyandthicknessoftheprotectivefilm.Currentresearchon45steelsubstratesurfacingweldingwear-resistingperformanceisthemostcommonlyusedmethodistoweartestmethodandnumericalsimulationmethod,theweartestsampleprocessingdifficulty,highcostandlongtestperiod,andthenumericalsimulationmethodisrapid,economic,butthecalculationresultofmodelingisdifficult,andtheaccuracyisnothigh.ThisstudyUSEStheelectrodearcweldingprocess,choosethethicknessof45#steelasmatrix,surfacingelectrodeunderdifferentweldingprocess,throughopticalmicroscope(OM),scanningelectronmicroscope(SEM)andgraphictestandresearch,themicrostructureofthedepositedmetalsurfacingandcomposition,microhardnessandtestthesamples.Preparationofmetalslidingweartest,choosetheM-2000typeweartestertowearexperiment,thecomparisonofdifferentload,slidingdistanceundertheconditionofwearresistanceofsurfacingweldinglayermetal.Byscanningelectronmicroscope(SEM)analysisofgrindingcrackshapeappearance,theoverlayingweldingmetallayerundertheconditionofdryfrictionwearmechanism.Keywords:45#steel;Surfacing;Friction;Wearandtear目錄TOC\o"1-3"\h\uHYPERLINK第一章 緒論 參考文獻[1]王運炎、朱莉，機械工程材料，機械工業(yè)出版社2012年9月第三版[2]XuBinShi,LiuShican,WangHaidou.Developingremanufacturing,constructingcycleeconomyandbuildingsaving-orientedsociety[J].JournalofCentralSouthUniversityofTechnology.2005,12(S2):1-6.[3]徐濱士著.表面工程[M].北京:機械工業(yè)出版社,2000,80.[4]胡邦喜,莽克倫,王靜潔等.堆焊技術(shù)在國內(nèi)石化、冶金行業(yè)機械設(shè)備維修中的應(yīng)用[J].中國表面工程,2006,19(3):4-8.[5]Budiuski,GKenneth.Overviewofsurfaceengineeringandwear[J].ASTMSpecialTechnicalPublication,1996,(1278):4-2l.[6]單際國,董祖玨,徐濱士.我國堆焊技術(shù)的發(fā)展及其在基礎(chǔ)工業(yè)中的應(yīng)用現(xiàn)狀[J].中國表面工程,2002,(4):19-22.[7]徐濱士,劉世參,張偉等.綠色再制造工程及其在我國主要機電裝備領(lǐng)域產(chǎn)業(yè)化應(yīng)用的前景[J].中國表面工程,2006,10:18-20.[8]徐濱士等.再制造工程基礎(chǔ)及其應(yīng)用[M].哈爾濱工業(yè)大學(xué)出版社,2005,10.[9]徐濱士等.廢舊機電產(chǎn)品資源化[R].中國工程院咨詢報告,2003.[10]XuBinshi,ZhuSheng.Advancedrenanufacturingtechnologiesbasedonnano-surfaceengineering[C].Proc.3rdInt.Conf.onAdvancesinProductionEng,1999,Guangzhou:35-43.[11]XuBinShi,LiuShican,ZhuSheng,etal.Roleofresourcerecoveryofwastemachineryandelectronicproductsinsustainabledevelopment[C].ProceedingsoftheWorldEngineersConvention,Shanghai,2004,Vol.G:323-328.[12]周衛(wèi)家.應(yīng)用激光堆焊技術(shù)對磨損軸件的修復(fù)工藝[J].機電工程,2004(11):45-47.[13]邊美華,符婭波.磨損軸件修復(fù)技術(shù)的研究[J].電焊機,2008,10:40-43.[14]何曉麗.艦船的軸系[J].現(xiàn)代艦船,2010（12）:56.[15]薛成,薛殿海.某船尾軸承過度磨損原因分析與修理[J].世界海運,2003,26（2）:49-51.[16]顧卓明.輪機維護和修理[M].北京:人民交通出版社,2001.[17]王月華,石興玉.焊條電弧堆焊技術(shù)分析及應(yīng)用[J].科技資訊,2009(15):98-99.[18]WilliamLucas.Arcsurfacingandcladdingprocess[J].Welding&MetalFabrication,1994,62(2):55-62.[19]何實,李家宇,趙昆.我國堆焊技術(shù)發(fā)展歷程回顧與展望[J].金屬加工（熱加工）,2009,（22）:25-27.[20]曾江.堆焊技術(shù)的發(fā)展及實踐經(jīng)驗的推廣[J].金屬加工（熱加工）,2010（4）:8-9.[21]錢強,包笑冰,崔嶸等.國內(nèi)外大面積耐磨合金復(fù)層板堆焊技術(shù)及其應(yīng)用[J].焊接,1990,（03）:1-4.

附錄（含外文資料和中文譯文）RoleofzinccoatinfrictionstirlapweldingAlandzinccoatedsteelY.C.Chen,T.Komazaki,T.TsumuraandK.Nakata1AC4CcastAlalloyandZncoatedsteelweresuccessfullylapweldedusingfrictionstirweldingtechnology.FullstrengthjointscouldbeobtainedandthejointsfracturedatZncoatedsteelbasemetalside,whileAlalloyandsteelcouldnotbeweldedinthesameweldingconditionsThejoiningmechanismandtheroleofZncoatonfrictionstirlapweldingofAlalloyandZncoatedsteelwereputforward.TheinterventionofZncoatpromotedtheformationofAl–Znlowmeltingpointeutecticstructureattheinterface,whichsignificantlyimprovedtheweldabilityofAlandsteel.Keywords:Frictionstirwelding,Alalloys,steelsIntroductionAsasolidstateweldingtechnology,frictionstirwelding(FSW)processcanweldmanymaterialssuchasAlalloys,2–7Mgalloys,8,9Tialloys,10,11steels12,13andcompositematerials14andcangethighqualityjointsthanfusionweldingtechnology.Suchgoodmeritsarealsoexpectedforjoiningdissimilarmaterials.TheneedoflightweightandexcellentcorrosionresistanceinautomotivebodyconstructionleadtotheincreasinguseofthecombinationofAlalloyandZncoatedsteelinfabricationofvehicles.15,16Therefore,developmentofreliablejointsbetweenAlalloyandZncoatedsteelwasrequired.However,frompresentresearchingstatusofFSWAlandsteel,themajoritystudieswerefocusedonFSWofAlalloyandsteel17–31andtheminorityresearcheshadinvolvedFSWofAlalloyandZncoatedsteel.32,33Fromtheindustrialapplicationpointofview,developingFSWofAlandZncoatedsteelisnecessary.Uptodate,researchesonFSWofAlandincedsteelmainlyincludedthreeaspects,i.e.buttjointresearches,spotjointresearchesandlapjointresearches;studiesonFSWofAlandZncoatedsteelonlyinvolvedlapjointresearches.Studiesonfrictionstirbuttwelding(FSBW)Alandincedsteelwerethemaintrendincurrentresearches.17–26UnlikeinFSBWAlalloys,theoffsetofpinrelativetothebuttlineexertedasign?canteffectonweldqualityforFSBWofAlandsteel.beandco-workers17–19investigatedthefrictionstirweldabilityof5083AlandSS400steel.Themaximumtensilestrengthofajointcouldreach86%ofthatofAlbasemetalathepinthrustdistanceof0?2mmtowardsteel.Similarly,andco-workers22,23investigatedtheweldabilityof6063-T6AlandS45CsteelviaFSBWandshowedthatthetensilestrengthofajointcouldreach75%ofthatofAlbasemetalatanoffsetof0?05mmtowardsteel.Kim24studiedtheFSBWfeasibilityofjoining6061Altomildsteel.Theyreportedthatpinpositionrelativetobuttlineexertedasign?canteffectonthemicrostructureandtensilepropertiesofthejoints.When90%ofthepindiameterwasoffsetintotheAlside,theweldexhibitedmaximumtensilestrengthof240MPa,whichwas86%oftheAlbasemetaltensilestrength.WhenthepinwasmovedintotheAlsidecompletely,thetensilestrengthoftheweldsdecreased.ChenandKovacevic25investigatedtheeffectoftheoffsetofpinpositionontheweldqualityandshowedthatanoffsetof68%ofthepindiameterintotheAlsideledtoabetterquality.Inaddition,inFSBWAlandsteeljoints,someresearchessteelfragmentsandAl–Fecompounds,17,25,26whileothersshoweddifferentresults.22.Forexample,compoundsofAl13Fe4andAl5Fe2weredetectedinFSBW6061-T6andAISI1018steeljoints.25layerofAl4Fewiththicknessof250nmwasfoundinFSBW6056-T4Aland304Asteeljoints.26However,andco-workers’analysisresultsabouthighspeedSBW6063-T6AlandS45Csteelshowedthatwereinthejoint.Intheir,themaximumweldingspeedwas1000mmmin.Studiesonfrictionstirspotwelding(FSSW)ofAlandsteelwererelativelack.27,28Tanaka.Kandco-workersstudiedtheFSSWfeasibilityofAlsheetandmildsteelsheet.27TheyreportedthathighstrengthjointwasobtainedbystirringAlalloyneartheinterfacewithoutinsertingaweldingtooltosteelsurfacefromtheAlalloyside.ThestrengthofFSSWjointwashigherthanthatofresistancespotwelds.Nobrittlecompoundwasobservedattheweldinterfacebesidesathinamorphouslayer.Asforfrictionstirlapwelding(FSLW)ofAlandsteel,theinterfacemicrostructureevolution,mechanicalpropertiesofjointsandtheeffectofparametersonweldqualitywereinvestigated.29–31.studiedthefeasibilityofFSLWacommerciallypureAlplatetoalowcarbonsteelplateandgatedtheeffectsoftheweldingparametersonthejointstrength.29Itwasreportedthatthejointstrengthdependedstronglyonthedepthofthepintiprelativetothesteelsurface;whenthepindepthdidnotreachthesteelsurface,thejointailedunderlowappliedloads.Meanwhile,slightpenetrationofthepintiptothesteelsurfaceincreasedthejointstrength.WatanabereportedtheresultsaboutFSLWof5083AlandSS400steel.30,31TheyshowedthatthejointshearstrengthdecreasedwithincreasingatooltiltangleandapindiameterduetotheformationofathickAl5Feintermetalliccompoundlayeratthejointinterface.Butthepresenceofa,whichwasopenedatthepininsertingpositionofanAlplatebeforewelding,washelpfultoobtainthehighershearstrengthofthejoints.Theoptimalindicatedtheshearstrengthofy77%thatoftheAlbasemetal.Theinterfacemicrostructureexaminationshowedthatnocompoundwasformedatthejointinterface.AlthoughpreviousinvestigationsshowedthattheweldqualityofFSWofAlandsteelwastocontrolbecauseoftheformationofsomecompoundsattheweldinterface,somerecentattemptshaddemonstratedasuccessinjoiningAlandZncoatedsteelusingFSLW.32,33TheadoptionofZnsteelevidentlyimprovedthefrictionstirofAlandsteelthefullstrengthjointscouldbeobtained.32.investigatedtheof1100H24andZncoatedsteelusingFSW.33TheyfoundthattheAl/Zncoatedsteeljointexhibitedconsiderablefractureloadatprobedepthof2.0mm,whileAl/steeljointsweresoweakthattheyfracturedduringofthespecimenforgraphicanalysisatthesameprobedepth.TheyconsideredthatZnplayedaroleoflubricantinthefrictionbetweenAlalloyandsteelsubstrate.CurrentreportingweremainlyfocusedontheprocessinginvestigationsonFSLWofAlalloyandZncoatedsteel.ThestudyofthejoiningmechanismonFSLWofAlalloyandZncoatedsteelwaslimit,especiallythestudyabouttheroleofZncoatinFSLWofAlalloyandZncoatedsteel.StudiesonthistopicareforusnotonlytorevealthefrictionabilitiesofAlalloyandZncoatedsteelbutalsotocomprehendtheeffectofcoatedmetalonthefrictionofdissimilarmaterial.Inthepresentstudy,AC4CcastAlalloyandlowZncoatedsteelareselectedastheexperimentforFSLW.TheAlalloysheetisputontheZnsteelsheet.TheinsertdepthofthetoolisstrictlyonrolledlessthanthethicknessoftheAlalloy.Thatis,heprobetipofthetooldoesnotreachthesurfaceofthencoatedsteelsheetduringwelding.TheistostudymicrostructureevolutionandjoiningmechanismandtheroleofZncoatonofAlandZncoatedsteel.ExperimentalThebasematerialsusedinthepresentstudywerea3AC4CcastAlalloysheetanda0?8mmthicklowZncoatedsteelsheet.Forcomparison,thesamelowcarbonsteelsheetswithoutZncoatwereelectedasexperimentalmaterials.ThechemicalcompomechanicalpropertiesofthebasematerialsshowninTable1.Rectangularweldingsamples,300mmlongby100mmwide,werelongitudinallylapweldedusingan.Afteraseriesoffeasibility,followingexperimentalparameterswereselectedinhepresentstudy.Theweldingparametersarerotationpeedof1500revmin21andweldingspeedof60–120mmmin21.Theupsettingforceoftheweldingtool(madeofSKD61steel)is1ton.Theshoulderdiameterandprobediameterofthetoolare15and5mmrespectively.Thelengthoftheprobeis2?9mmandtheweldingtiltangleis3u.Afterwelding,thejointwascross-sectionedptotheweldingdirectionfortheanalysesandtensiletestsusinganelectricaldischargecuttingmachine.Thecross-sectionsofthespecimenswerepolishedwithdiamondpolishingagent,etchedwithKeller’sreagent(1mLhydrochloricacid,1.5mLnitricacid,2?5mLhydroacidand95mLwater)andobservedbyopticalmicroscopy.BecauseAlalloyandsteelcouldnotbeweldedincurrentexperimentalconditions,graphicanalysisspecimenscouldnotbepre-pared.ThedetailsoftensiletestspecimensandtensiletestresultsofFSWjointsofAC4CandZncoatedsteelreferredtoRef.32.InordertodeterminethemicrostructureevolutionalongthelapinterfaceofAlalloyandZncoatedsteel,athree-dimensionalrectangularcoordinatesystemwasestablishedinthecross-sectionplaneofatypicaljoint.TheXaxisisacrosstheweldfromtheadvancingside(AS)totheretreatingside(RS),theYaxisisthroughthethicknessofthejointfromthesteelsidetotheAlside,andtheZaxisisinthedirectionofwelding.XaxisisthelapinterfaceandYaxispassesthecentreoftheweld.Onheotherhand,forthesakeofobservingthejoiningstatefromanotherangle,allthejointswereseparatedbymanualmanipulation.Inthisway,thejoiningstatusofthelapinterfacecouldbedirectlyobservedfromthefrontface.ThewidthsofjoiningregionsatdifferentweldingparametersareshowninTable2.FracturesurfacesofjointswereusingX-raydiffraction.TheweldingthermalcyclehistoriesalongtheinterfaceduringFSWweremeasuredwithanarrayofKtypethermocouples(0?2mmdiameter)atvariouslocationsdistantfromtheweldcentre.MicrostructurecharacterandelementdistributionalongtheinterfacewerebyscanningelectronmicroscopyequippedwithanenergydispersiveX-rayspectroscopyanalysissystem.ResultsanddiscussionFigure1showsthemicrostructureofthebasematerials.AC4CbasematerialisahypoeutecticAl–Sialloyshowingatypicalhypoeutecticstructure.Thesteelbasematerialshowsstructureduetolowcarboncontent.Figure1cshowsthemicrostructureneartheZncoatsurface.ItcanbeseenfromthisthatthethicknessofZncoatisy10mm.Moreover,becausethiskindofZncoatisproducedusinghotdipgalvanizingprocess,actuallytheZncoatiscomposedofFe–Znintermetalliccompounds.34Elementsanalysiswasper-formedatdifferentpositionofZnrichcoat.ThechemicalcompositionofpointsAandBare75?06Zn–20?73Fe–4?21Aland62?91Zn–34?95Fe–2?15Al(at.-%)respectively.ThedominantelementinZncoatisZnandiron.Moreover,thecontentofZnincreaseswithapproachingthesurfaceoflayer.Thatistosay,thecompositionoflayermoreandmoreapproachespureZnfromtheinterfacetothesurface.Tensiletestresults32showthattheweldingspeedhaseffectonpropertiesofandZnoatedsteelfrictionstirlapjointsatrotationspeedof1500revmin21.Whenspeedis60mmmin21,thejointsfractureattheinterface;whentheweldingspeedis.80mmmin21,allthejointsfractureatsteelside.ItmeansthatfullstrengthAlandZncoatedsteelfrictionstirlapjointscanbeobtainedwhentheweldingareselectedinreason.However,whenusethesameweldingconditionstoweldAlalloysteel,theycannotbewelded.TheseresultthatthepresenceofZnrichcoatgreatlyimproveshefrictionstirlapweldofAlandsteel.Figure2showsatypicaltransversecross-sectionofajointattheweldingspeedof100mmandarectangularcoordinatesystem.ItcanbefandsteelarejoinedtightlyandharacteristicinsideissimilartothatofFSWAlalloyitself.Thatis,thetypicalstirzone(SZ),theaffectedzone(TMAZ)andunstirone(USZ)areobserved.Inthiscase,theauthorsareinterestedintheinterfacestructurefeatureandbservehalfoftheinterfacemicrostructurefromthecentrallinebecausethemicrostructureinASandRSispproximatelysymmetricdistribution.Microstructurebservationsstartfromthecentreoftheweld(pointa)andendthebasematerialzone(pointf).ThedetailsofthemstructuralvariationsaredemonstratedinFig.4.Figure3showsthejoiningstateofajointatsteelsideinYdirectionafterthejointisseparatedbymanualmanipulation.Fromthis?gurewecanseethatfoursigni?cantzonesareproducedafterwelding.Forconvenience,theauthorsde?nethefourzonesaszone1tozone4fromthecentreoftheweldtothebasematerialaccordingtothecharacteristicofdifferentregions.Inaddition,thecorrespondinglocationofmicrostructureanalysisfrompointatopointfisshowninX–Zrectangularcoordinatesystem.Fromthecharacteristicofthefractureandfollowingmicrostructureanalysistheauthorscancon?rmthatzone1isatypicalreactionregion.Thewidthofthisregionobviouslyexceedsthatoftheprobediameter.Theauthorscallitcombinationreactionregion(CRR).Zone2isanarrowtransitionregion(TR).Zone3showsresolidifyingcharacteristic.Moreover,liquid?owtracecanbeseenfromfrontside.Somevoidsremaininthisregionbecauseofinsuf?cient?owbehaviour(see.3b).Fromfollowingstructureanalysiswecanknowthatzone3isaneutecticstructurezone.Theauthorscalliteutecticreactionregion(ERR).Zone4is3Macrostructureoffracturesurfaceatsteelsidethebasematerial(BM).RelationshipsbetweenwidthsofdifferentzonesandweldingspeedsarelistedinTable2.FromTable2wecan?ndthatthewidthofCRRchangesbetween12and13?5mm.Suchvaluesobviouslyexceedthatoftheprobediameter.ThewidthofTRchangesfrom1to2?5mm.ThewidthofERRisy2mm.Thetotalwidthofjoiningregionhangesbetween18and21mm,whichiswiderthanthatoftheshoulderdiameter.Moreover,thelowertheweldingspeeds,thewiderthetotalwidth.Figure4showsthedetailsofthemicrostructuralvariationsmentionedinFigs.2and3.ItcanbeseenfromFig.4athatthejointconsistsofafourlayeredstructure,i.e.MicrostructureinSZofAlalloy,anewintermetalliccompound(IMC)layer,residualZnrichlayerandBMofsteel.Alalloyandsteelarejoinedthroughintermediatereactionzone.Betweentheresi-dualZnrichlayerandSZofAlalloy,thereisanewIMClayer.Thatistosay,theoriginalZnrichcoatispartiallyreplacedbyanewIMClayerattheinterfaceafterwelding.Figure4bshowsthemicrostructureinTMAZ.TheinterfacestructureissimilartothatinFig.4a.ButthethicknessofIMCisthinnerthanthatinSZ.Figure4cshowsthemicrostructureinUSZ.ThisregionisfarfromtheSZbutstillundertheshoulder.Theinterfacemicrostructureinthisregionissigni?-cantlydifferentfromthatinSZ.Thefourlayersstructurementionedabovearestillpresent.Thethick-nessofIMClayer,however,explicitlydecreasescomparedwiththoseinSZandTMAZ.MostofZnrichcoatisremained.ThethicknessofresidualZnrichlayerissimilartothatoforiginalZncoat.Figure4dshowstheadjacentpositionbetweenzone1andzone2.Nosigni?cantintermetalliccompoundisfoundinzone2besidesagap.Zone2isthestartpositionthatAlalloyandZncoatedsteelareinunboundstate.ThepositionisnearYaxispositionoftheedgeofshoulderdiameter.Figure4eshowstheadjacentpositionbetweenzone2zone3.Atypicaleutecticstructure(ES)isfoundinzone3.TheES?llsintotheclearancebetweenAlalloyandZncoatedsteel.Figure4fshowstheadjacentpositionbetweenzone3andzone4.ThepositionofFig.4fhasgreatlyexceededthedomainofshoulderdiameterofthetool.ThethicknessofESsigni?cantlyincreasesbecauseofthelargerclearancebetweentwosheets.Figure5showstherepresentativeconcentrationro?lesofAl,Si,ZnandFecrosstheinterfaceatdifferentzonesbetweenAlalloyandZncoatedsteelbyamapscanningelementanalysis.AlayerinvolvingAl,Fe,ZnandSiisformedattheinterfaceofthejointinzone1.X-raydiffractionanalysisresultsfromfracturesurfaceshowthatFe2Al5andFe4Al13arethemaincompoundsattheinterface.MoreexactanalysistotheIMCwillperformusingTEMinthefuture.Resultsfromzone3showthattheconcentrationpro?lesofAlandZnisdetectedintheESlayer,whichindicatesthatzone3isanAl–Zneutecticstructureregion.Resultsfromzone4showthedistributionofZnandFeinriginalZnrichcoatonthesurfaceofsteel.Asmentionedabove,actuallythiskindofZnrichcoatiscomposedofZnandFe.Inordertofurtherclarifythejoiningmechanism,weldingheatcyclehistoriesaremeasuredwithanarrayofKtypethermduringweldingasshowninFig.6.Itisnotablefromaboveinterfacestructureanalysisresultsthatthepositionof8mmisthelocationofzone3.TheweldingheatcyclehistoryresultsareshowninFig.7.Thepeaktemperaturesatpositionsof0,8and20mmare449,388and239uCrespectively.Figure8showsanAl–Znbinaryphasediagram.35ThemeltingpointofAlandZnis660and420uCrespectively.ThebinaryeutectictemperatureofAl–Zns381uCatZnrichcorner.Inotherwords,thepeaktemperatureinthelapinterfacecentreishigherthanthoseofZnmeltingpointandAl–Zneutecticpoint.Thepeaktemperatureinzone3,i.e.nearYaxispositionoftheedgeofshoulder,isalmostthesametotheeutectictemperatureofAl–Zn.Moreover,fromtheweldingheatcyclehistorywecanknowthatthehightemperaturedwelltimeaboveZnmeltingpointandAl–Zneutecticpointisabout4and9sinthelapinterfacecentre.ThehightemperaturedwelltimeaboveAl–Zneutecticpointisy3?5sinzone3.ItmeansthatliquidAl–Zneutecticstructurecanbeformedbecauseofhighpeaktempera-tureandhasenoughtimeto?llintotheclearancebetweentwosheets.Moreover,theappearanceofeutecticstructureinzone3alsoindicatesthatAl–ZnreactionlayerispresentfromthecentreofweldtotheYaxispositionoftheedgeofshoulder.TheinterventionofZncoatdirectlypromotestheformationofAl–Znlowmeltingpointeutecticstructurealongtheinterface.Accordingtoaboveresults,theauthorsputforwardthefollowingthree-stepjoiningmechanismonFSLWofAlalloyandZncoatedsteel.Figures9and10showtheschematicdiagramofjoiningmechanism.Figure9isthemacroscopicschematicdiagramofthecross-sectionandFig.10isthecorrespondingmicroscopicschematicdiagramoftheinterfacemicrostructureattheweldcentre.TherelativepositionofAl,ZnrichcoatandsteelisshowninFigs.9aand10a,inwhichAlalloysheetisputontheZncoatedsteelsheetwithanaturalclearancebetweenthem.First,thematerialsinweldzonehaveundergonetheco-actionofthehightemperatureactionandseverelyplasticdeformationduringFSW.Inthisway,theoriginalcoarseprimaryAlgrainsandlargeplatelikeeutecticsiliconinthebasematerialhavebeentrans-formedto?negrainsandsmallsiliconparticlesintheSZ.Themetalinthelapinterfacesimultaneouslyundergoesthesyntheticeffectofthethermalcycleandthemechanicalcyclebecauseoftheactionoffriction,stirandextrusionofthetool.Thus,hightemperatureandhighpressurearegeneratedattheinterface.Hightemperature?rstlyleadstothemeltingofpureZnonthesurfaceofZnrichcoatandhighpressuresimultaneouslyresultsintheruptureofsurfaceoxide?lmsatbothsheetssurface,whichpromotestheformationAl–Zneutecticreactionproductswithlowermeltingpoint(seeFig.10b).HighpressureextrudesexcessiveliquidphaseofAl–Zneutecticreactionproductwithbrokenoxide?lmsandsurfacecontaminationfarfromtheweldcentre,spreadsalongtheinterfacetillpilesintothenaturalclearancebetweentwosheets(seeFig.9b).The?nalpositionoftheliquidAl–ZneutecticphasecanreachnearYaxispositionoftheedgeofshoulder,wherethepeaktemperatureisalmostthesametotheAl–Zneutectictemperature.Second,thefreshinterfacesofAlandresidualZnrichlayerareexposedandtheyaretightlyextrudedtogetherafterliquideutecticphaseispushedout.ElementsmutualdiffusionofAlandironoccurs,whichleadstotheformationofanewintermetalliccompoundlayeradjacenttothelapinterfaceoftheweld(seeFigs.9cand10c).ThethicknessofIMClayerincreaseswithincreasingweldtime(seeFigs.9dand10d).Thirdly,duringthecoolingafterwelding,liquidAl–Zneutecticphasetransformstosolideutecticstructure.Inbrief,thepresenceofZndirectlyresultsintheformationofAl–Znlowmeltingpointeutecticstructurealongtheinterface,whichsigni?cantlyimprovedtheweldabilityofAlandsteel.ConclusionsAC4CcastAlalloyandZncoatedsteelweresuccess-fullylapweldedusingFSWtechnology.Themicro-structureevolutionandthetemperaturedistributionsalongtheinterfacewereinvestigated.ThejoiningmechanismonFSLWofAlalloyandZncoatedsteelwasputforward.Themainviewpointswereshownasmfollowing.Thejointcontainedfourdifferentstructurezonesalongthelapinterface,binationreactionregion,transitionregion,eutecticreactionregionandthebasematerial;thejointconsistedoffourlayersstructureverticaltothelapinterface,i.e.MicrostructureinstirzoneofAlalloy,anewintermetalliccompoundlayer,residualZnrichlayerandbasematerialofsteel.ThepeaktemperatureinthelapinterfacecentrewashigherthanthoseofZnmeltingpointandAl–Zneutecticpoint.HightemperatureledtothemeltingofZnrichcoatandpromotedtheformationoflowermeltingpointAl–Zneutecticreactionproduct.LiquidstateAl–Zneutecticreactionproductwasextrudedfarfromtheweldcentre,spreadalongtheinterfacetillpiledintothenaturalclearancebetweentwosheets.Anewinterme-talliccompoundlayerwassimultaneouslyformedattheinterface.Duringthecoolingafterwelding,liquidstateAl–Zneutecticreactionproducttransformedtosolideutecticstructure.鍍鋅層在攪拌摩擦焊接和鍍鋅鋼板Y.C.Chen,T.Komazaki,T.TsumuraandK