(英文文献)Tensile properties of extruded ZK60-RE alloys

镁合金资料

MaterialsScienceandEngineeringA349(2003)207Á

212

http://www.77cn.com.cn/locate/msea

TensilepropertiesofextrudedZK60ÁREalloys

ChunjiangMa*,ManpingLiu,GuohuaWu,WenjiangDing,YanpingZhu

StateKeyLaboratoryofMetalMatrixComposites,ShanghaiJiaotongUniversity,Shanghai200030,People’sRepublicofChina

Received19February2002;receivedinrevisedform23September2002

Abstract

ZK60ÁREalloysweremadebymeltingZK60alloyandcerium-richrareearth(RE)metalinanelectricfurnace.ThecontentofREis0,0.5,1,1.5,2,3wt.%RE,respectively.TheinfluenceofREonmicrostructureandtensilemechanicalpropertiesofZK60magnesiumalloyswasstudied.Theresultsshowedthatcerium-richmischmetal(MM)hadanobviouseffectofreducingthegrainsizeoftheas-extrudedZK60alloys.TheultimateandyieldstrengthsofextrudedZK60ÁREalloyswereimprovedbytheadditionofRE.TheultimateandyieldstrengthincreasedwithincreasingREcontentintherangeinvestigated.Itisalsofoundthattheultimatestrengthandyieldstrengthdecreasewithincreasingextrusiontemperature.TheimprovementoftensilepropertiesofZK60ÁREalloyswasduetotheextrusiontextureandthefinemicrostructureinducedbyREadditions.#2002ElsevierScienceB.V.Allrightsreserved.

Keywords:ZK60alloy;Rareearths(RE);Extrusion;Microstructure;Tensileproperties

1.Introduction

Magnesiumalloyisthelighteststructuralmaterialapplicableinaerospaceandautomobileindustry,andithashighspecificstrengthandhighstiffnessandgooddampingcapacity.Furthermore,magnesiumresourcesareabundantandmagnesiumproductscanbeeasilyrecycled.Therefore,theuseofmagnesiumalloysisincreasing.However,duetoitshcpstructure,magne-siumalloyspresentpoorductility.Magnesiumalloysaremainlyusedforautomobilecomponents,whichareproducedbyadie-castingprocess[1].Inordertoachievemoresubstantialstructuralapplicationsofmagnesiumalloys,itisnecessarytodevelopwroughtmagnesiumproductssuchasrolledsheetorextrudedbarsandtubings.However,magnesiumalloyshavelowtensilestrengthandpoorductilitycomparedwithaluminumalloys.Recently,ithasbeenreportedthatrareearth(RE)additionscanimprovecastingcharac-teristics,corrosionresistance,hightemperaturetensilestrengthandambienttensileyieldstrengthofas-castmagnesiumalloys[2Á6].However,theeffectofREonthetensilepropertiesofextrudedmagnesiumalloyshas

*Correspondingauthor.Fax:'86-21-6293-2548.E-mailaddress:cjma@http://www.77cn.com.cn(C.Ma).

notbeenreported.Inordertoimprovethemechanicalproperties,especiallythetensileyieldstrength,ZK60magnesiumalloyscontainingREwerehotextrudedandthemicrostructureandmechanicalpropertiesarepre-sentedinthispaper.

2.Experimental

Inthepresentexperiments,ZK60waschosenasthemasteralloy.REadditionsweremadeintheformofcerium-richmischmetal(MM).Thechemicalcomposi-tionofMMisshowninTable1.TheZK60ÁREalloysweremadebymeltingZK60alloyinanelectricresistancefurnacebeingflushedcontinuouslywithSF6andCO2gasatabout7208C,thentheREof0.5,1,1.5,2,3wt.%wereadded,respectively.Themeltwasheldatthattemperatureforabout20mintoensurethattheREwascompletelydissolved.Afterthatthemeltwaspouredinametalmoldoff45mmandtheZK60ÁREalloybarsweremade.ThecompositionsofZK60ÁREalloysarelistedinTable2.TheingotZK60alloyswerethenhotextrudedintobarsoff12mmattemperatures300,340,380,and4208C,respectively,withanextrusionratioof10:1.Someoftheas-extrudedbarsweremachinedintotensilespecimenswithagauge

0921-5093/02/$-seefrontmatter#2002ElsevierScienceB.V.Allrightsreserved.PII:S0921-5093(02)00740-2

镁合金资料

Table1

ChemicalcompositionofMMElement

Compositionwt.%

Ce50.2

La26.67

Nd15.28

Pr5.37

Fe0.65

Si0.01

Mg0.38

Mn0.11

Ca0.01

P0.003

Fig.1.TransversemicrostructureofZK60ÁREalloysextrudedat3808C.(a)ZK60;(b)ZK60Á1%RE;(c)ZK60Á2%RE;and(d)ZK60Á

3%RE.

lengthof25and5mmindiameter.MicrostructurewasobservedbyopticalmicroscopyandcompositionofphaseswasexaminedbyEDX.Thetensilefracture

surfaceswereobservedbyscanningelectronmicroscopy(PHILIPSSEM515).

3.Resultsanddiscussion3.1.Microstructure

Fig.1(aÁd)showsthetransversemicrostructureofZK60ÁREalloysafterextrusionat3808C.AsshowninFig.1(a),themicrostructureofas-extrudedZK60alloyconsistsofsmallparticlesidentifiedasMg2Zn3phaseembeddedinthematrix.Thegrainsizeisabout20mm.When1%REwasadded,somewhitedeformedRE-containingintermetallicsemergedinthematrix.TheRE-containingintermetallicswereidentifiedbyEDXasMgÁZnÁREcompounds(Fig.2).ThequantityofRE-containingintermetallicsincreasedwiththeREcontentasshowninFig.1(bÁd).ThegrainsizeofZK60ÁREalloysdecreasedcontinuouslyfrom20mmtoonly2Á3mmwhen2Á3%REwasadded.Obviously,REhasan

镁合金资料

C.Maetal./MaterialsScienceandEngineeringA349(2003)207Á212209

Fig.3.MicrostructureofZK60ÁREalloysalongextrusiondirectionextrudedat3808C.(a)ZK60Á1.5RE;and(b)ZK60Á3RE.Extrusiondirectionis

horizontal.

Fig.4.OpticalmicrostructureofZK60Á2%REalloysextrudedatdifferenttemperatures.(a)3008C;(b)3408C;(c)3808C;and(d)4208C.

Table2

ChemicalcompositionofstudiedZK60ÁREalloyNominalalloy

Composition,wt.%Mg

ZK60

ZK60Á0.5REZK60Á1REZK60Á1.5REZK60Á2REZK60Á3RE

BulkBulkBulkBulkBulkBulk

Zn5.635.915.695.625.695.65

Zr0.430.490.460.450.410.49

Ce0.320.640.971.291.88

La0.140.270.420.560.81

Nd0.030.0610.0850.110.16

http://www.77cn.com.cnparingwiththeas-castZK60ÁREalloys[7],themicrostructuresofas-extrudedZK60ÁREalloysweregreatlyrefinedandthecoarsenet-likeRE-containingintermetallicswerebrokenanddispersedinthematrixuniformly.Itisobviouslyconfirmedthatdynamicrecrystallizationoccurredduringhotextrusionandthemicrostructurewasrefined.Themicrostructurerefine-mentcausedbyREadditionsmaybeintroducedbyfollowfactors.First,additionofREchangedthesolidusand,therefore,resultedinadecreaseinthesolidificatio …… 此处隐藏：11950字，全部文档内容请下载后查看。喜欢就下载吧 ……