Deformation-behaviorofanextrudedMg–Dy–Zn-alloywith

DeformationbehaviorofanextrudedMg–Dy–ZnalloywithlongperiodstackingorderedphaseGuangliBia,n,YuandongLia,XiaofengHuanga,TijunChena,JiansheLianb,ZhonghaoJiangb,YingMaa,YuanHaoaaStateKeyLaboratoryofAdvancedProcessingandRecyclingofNon-ferrousMetals,LanzhouUniversityofTechnology,Lanzhou730050,ChinabKeyLaboratoryofAutomobileMaterials,CollegeofMaterialsScienceandEngineering,JilinUniversity,NanlingCampus,Changchun130025,ChinaarticleinfoArticlehistory:Received28June2014Receivedinrevisedform30October2014Accepted3November2014Availableonline11November2014Keywords:Mg–Dy–ZnalloyMicrostructureMechanicalpropertiesSurfaceobservationDeformationbehaviorabstractDeformationbehaviorofanextrudedMg–2Dy–0.5Zn(at%)alloywasinvestigatedunderuniaxialtensiletestatarangeofstrainratesof3
105–3
101s1andtemperaturerangingfromroomtemperature(RT)to3001C.Themicrostructureofthealloywasmainlycomposedofα-Mg,(Mg,Zn)xDyparticlephaseandalargenumberoflongperiodstackingordered(LPSO)phases.Thetensiletestingresultsindicatedthatstrainratesensitivityexponent(m)generallyincreasedwithincreasingtemperatureanddecreasingstrainrate.Interestingly,mexhibitedtwodifferentvaluesinlogσlog_εcurvesat3001C,indicatingthattheplasticdeformationmechanismofthealloyoccurredtochange.Thesurfaceandmicrostructureobservationsofthetensilespecimensaftertensionrevealedthatthedeformationbehaviorofthealloywassimilartothatofthemetalmatrixcomposites,wheretheloadtransferredfromtheMgmatrixtotheLPSOphaseatlowtemperatures(RT2001C)underdifferentstrainratesandat3001Cunderhighstrainrates,whilethegrainboundaryslidingaccommodatedbydislocationslipdominatedthewholedeformationbehaviorat3001Cunderlowstrainrates.Thealloyexhibitedaquasi-superplasticdeformationwithanelongation-to-failureof105%at3001Cand3
105s1.Thequasi-superplasticdeformationwasattributedtothestablegrainsretainedbytheprecipitationoftheLPSOphasewithgoodthermalstabilityingraininterioratanelevatedtemperature.&2014ElsevierB.V.Allrightsreserved.1.IntroductionOwingtotheirlightweight,highspecialstrengthandstiffness,magnesiumalloyshaveattractedmoreattentionasoneofthelightestmetallicstructurematerials.Atpresent,mostmagnesiumalloyproductsareonlycastingcomponents,suchasgaugepanel,steeringwheelsandengineblocksappliedinautomobileindustry.However,fewwroughtmagnesiumalloyshavebeenappliedbecauseoftheirpoorformability.Itiswellknownthatmagnesiumandmagnesiumalloyshaveahexagonalclose-packed(hcp)crystalstructurewithlowsymmetryandfewslipsystems,thustheyalwaysexhibitpoorductilityespeciallyatroomtemperature,whichalsolimitstheirpracticalapplication[1].Therefore,itisnecessarytounderstandthedeformationbehaviorofmagnesiumalloystofurtherimprovetheirformabilityduringthehot-workingprocess.Recently,anovellongperiodstackingordered(LPSO)phasehasbeenobservedintheas-castandheattreatedMg–RE–Zn(RErepresentsrareearthelements)alloys.TheLPSOphaseisnotonlyalong-periodchemical-orderedstructurebutalsoastacking-orderedstructure[2].Thephasecontainsvarioustypesandtheunitcellofeachtypeconsistsofdifferentstackingsequences,suchas10H(ABACBCBCAB),14H(ACBCBABABABCBC),18R(ABABABCA-CACABCBCBC)and24R(ABABABABCACACACABCBCBCBC)types[3].Amongthem,the18R-and14H-typeLPSOstructuresarecommonlyobservedinthepreviousstudies.The18R-typeLPSOstructurecouldtransformintoa14H-typeLPSOstructureduringheattreatmentorhotdeformation[4–6].Furthermore,theLPSOphaseiscoherentwiththemagnesiummatrixandhasagoodthermalstabilityandhighhardness[7–9].Thus,thephaseisconsideredtobeadesirableheatresistantphasetoimprovehigh-temperaturepropertiesofmagnesiumalloys.ThepreviousinvestigationsindicatethatwroughtMg–RE–ZnalloyscontainingtheLPSOphaseexhibitexcellenttensilestrengthsatbothroomandelevatedtemperatures[2,10–13].Themicrostructure,mechanicalpropertiesanddeformationbehaviorofthesealloyshavebeenwidelyinvestigated[14–22].ThehighmechanicalContentslistsavailableatScienceDirectjournalhomepage:://dx.doi.org/10.1016/j.msea.2014.11.0020921-5093/&2014ElsevierB.V.Allrightsreserved.nCorrespondingauthor.Tel./fax:þ869312973564.E-mailaddress:[e-mail](G.Bi).MaterialsScience&EngineeringA622(2015)52–60propertiesofthesealloysareascribedtothegrainrefinementandtheLPSOphasestrengthening.Thedeformationbehaviorsofthe18R-and14H-typeLPSOstructuresinMg12ZnYphaseareall〈112̄0〉(0001)slipatlowtemperatures[16,23].Additionally,thepreviousliteratureshavedemonstratedthatthemorphology,scale,amountanddistributionoftheLPSOphasesignificantlyaffectthedefor-mationbehaviorofMg–RE–Znalloys[6,24,25].Usually,strainhardening,dynamicrecoveryanddynamicrecrystallizationoccurduringdeformationforthealloysatdiffer-entstrainratesandtemperatures.TheformationoftheLPSOphasecouldcontributetothecompleteDRXandinhibitthegraingrowthofthealloysatelevatedtemperatures[11,17].Thedis-persivedistributionoftheLPSOphaseandthecompleteDRXcouldalsoresultinanobtainmentoftheoptimumprocessingparametersandthesafetydeformationconditionsintheproces-singmap[26,27].Moreover,Garc´esetal.[22]studiedthedeformationbehaviorofrapidlysolidified