稀土耐熱鎂合金顯微組織和性能的研究.pdf

1、東南大學碩士學位論文稀土耐熱鎂合金顯微組織和性能的研究姓名：強婧申請學位級別：碩士專業(yè)：材料學指導教師：孫揚善20080101AbsUactInvestigationonMicrostructuresandMechanicalPropertiesofMagnesiumHeatResistantAlloyswithRareEarthAdditionsABSTRACTAsthelighteststructuralalloys，magnesi

2、umalloys，offeringgooddampingcapacityhighspecificstrengthandstiffnessareimpressivelyattendedbytheautomotiveindustryInordertoextenditsapplicationOilautomotiveproductS，improvedcreepresistancepropertyisacriticalissueformagne

3、siumbasedalloys，RareearthadditionstoMgareknowntoincreusetheresistancetocreepdeformation，whichledtothedevelopmentofAEseriesalloysHoweverthecreepresistanceofthealloysdecreasesabruptlywhenthetemperatureisabove150℃whichmadet

4、lleminadequateformajorengineandpowertraincomponentsThereforethedevelopmentofnewMgIUalloyswithhighcreepresistanceandrelativelylowcosthasbecomethemostpromisingfieldformagnesiumapplicationsIIlthepresentworkthreeseriesofallo

5、ysbasedonMg4A1withadditionsofRE(mischmetal)，LaandCe，respectivelyhavebeenseparatelyfabricatedandtlleyarenamed[IsAE(MgAIRE)，ALa(MgAI一㈨andACe(MgAICe)alloys，respectivelyAllthesampleswerepreparedbytwodifferentcastmgtechniques

6、，oneispermanentmoldcasting(PC)，theotherishighpressurediecasting(HPDC)Themicrostructures，mechanicalpropertiesaswellashightemperaturecreepresistantpropertiesofthesealloyspreparedhavebeeninvestigatedbyopticalmicroscopy(OM)，

7、X—Raydiffractometer(XRD)，scanningelectronmicroscopy(SEM)，inductivelycoupledplasma(ICP)andequipmentformechanicalpropertytestingTheaimoftheworkistoprovidetheoreticalandpracticalresultsforthefurtherdevelopmentofMgAl—REalloy

8、sTheascastmicrostructuresofthreeseriesofalloysstudiedaresimilarshowingtypicaldendriticmorphologyTbeascaqmicrostructureofAEalloysconsistsoftheaMgmanixlamellarofA14REdistributingatdendriteboundariesTheincreaseofREadditionc

9、ausestheslightrefinementofthemicrostructuresforallthreeseriesalloysThemicrostructureofthealloyspreparedbyhighpressurediecastingconsistingofthesamephasesincomparisonwiththealloyscastinpermanentmoldsHoweverremarkablerefine

10、mentofmicrostructurehavebeenachievedbyusinghighpressurecastingPorositieshavebeenobservedinthealloyswithlowREconcentrationandtheydisappearwhentheREcontentisraisedto4percentsTheresultsoftensiletestsshowthattheyieldstrength

11、，tensilestrengthandductilityincreaseswiththeincreaseofRE(La’Ce)additionsItseems血acthe1antllanunladditionismoreeffectiveonimprovementofmechanicalpropertiesofthealloysstudiedthanthemischmetalandcerium111estrengthespecially

12、theyieldstrength，ofHPDCalloysishigherthanPCalloysThetensilecreeptestsrevealthesignificantimprovementonc陀印resistanceat175℃／70^，田acausedbytheincreaseofrareearthelementsincludingmischmetal，IanthanumandceilumTheresuItsofcre印

13、testsperformedofallthreeseriesalloysstudiedshowthattheeffectofthreekindofREadditions(mischmetal，LaandCe)aresimilaroncreepbehaviorofMgAIbasedalloysTheinvestigationsofthemicrostrucmresofspecimensaRercn∞testsrevealthatthein

14、terphaseA1dREwouldpartlydecomposeintoA12REandAIThealuminumproducedbyabovedecompositiontendstoformMgl7AIl2withMgwhichhavedeleteriouseffectonthecreepresistanceofthealloysAstheRE(includingmischmetal，LaandCe)additionsincreas