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外文翻译--半固态铝合金(A356)浆料流变成形的充填性能 英文版.pdf

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外文翻译--半固态铝合金(A356)浆料流变成形的充填性能 英文版.pdf

JournalofUniversityofScienceandTechnologyBeqingVolume15,Number7,February2008,Page48ELSEVIERFillingabilityofsemisolidA356aluminumalloyslurryinrheodiecastingYuelongBail.,WeiminMao,SonGao,GuoxingTang,andJunXu1SchoolofMaterialsScienceandEngineering.UniversityofScienceandTechnologyBeijing,Beijing100083.China2NationalEngineeringResearchCenterforNanferrousMetalsComposite.GeneralResearchInstituteforNonferrousMetals,Beijing100088,ChinaReceived20070228AbstractsTheeffectsofslurrytemperature,injectionpressure,andpistonvelocityontherheofillingabilityofsemisolidA356alloyswerestudiedbytherehodiecastingmethods.TheresultsshowthattheslunytemperatureofthesemisolidA356aluminumalloyhasanimportanteffectonthefillingabilitythehighertheslurrytemperature,thebetteristhefillingability,andtheappropriateslurrytemperatureforrheofillingisintherangeof585595°C.Theinjectionpressurealsohasagreateffectonthefillingability,anditisappropriatetotherheofiningwhentheinjectionpressureisintherangeof1525MPa.ThePiStORvelocityalsohasagreateffectonthefillingability,anditisappropriatetotherheofillingwhenthepistonvelocityisintherangeof0.0720.12ds.Thefillingabilityoftheslurrypreparedbylowsuperheatpouringwithweakelectromagneticstirringisverygoodandthemicrostructuraldistributionintherheoformeddiecastingsishomogeneous,whichisadvantageoustothehighqualitydiecasting.02008UniversityofScienceandTechnologyBeijing.Allrightsreserved.KeywordsA356aluminurnalloyrheodiecastingfillingabilitysemisolidTheworkwasfinanciallysupportedbytheNationalNatureScienceFoundationofChinuNo.50774007,theNationalHighTechnologyResearchandDevelopmen1ProgramofchinaN0.2006AA03Z115.andtheNationalKeyBasicResearchProgramofChinaN0.2006CB605203.I1.IntroductionEversincesemisolidmetalformingwasdevelopedbyFlemingsatMITinthe1970s.ithasattractedconsiderableattentioninoverseasanddomestic.Severalexpertshaveparticipatedinthebasicandappliedresearchofthesetechniques.Afterdevelopingforoverthirtyyears,thesehavesuccessfullybeenappliedtomanufacturingvariouskindsofcarandaircraftparts131.However,atpresent,onlythethixoformingtechniqueshavebeenusedforcommercialproductionandthecommercialproductionscaleissmallyet.Thisismainlybecausethepreparingcostofsemisolidslunyandtheenergyconsumptionofbilletreheatingarehigher,andtherecyclingofbleedingdrops,biscuits,gatingsystem,andrejectedcastingsaredifficult.Whencomparedwiththixoformingtechnologies,rehoformingtechniquesofsemisolidmetalshaveseveraladvantages,suchasconsiderablyshorterprocess,easyrecyclingofthegatingsystemandwasteCorrespondingauthorYuelongBai.Emailbalyuelong163.com02IH8UniversityofScienceandlechnolopyBeijing.Allrightsreserved.castings,lowproductioncost,etc.Thus,rehoformingtechniquesarenowbecomingoneofthemostimportantstudysubjects491.LowsuperheatpouringwithweakelectromagneticstirringforashorttimeLSPWESisanewmethodforthepreparationofsemisolidalloysslurries10111,whichrequireslowenergyconsumptionascomparedwiththepreparationofsemisolidalloysbilletsusingonlyelectromagneticstirringatahighpower12131andtheprocesscontrolisconsiderablyconvenient141andtheslurrymicrostructureisbetterthanthatpreparedbytheliquiduscastingtechnology.Therefore,LSPWEScanbeappliedasthekeytechnologyofanewsemisolidrehoformingprocess15.Inthisstudy,thefillingabilityofsemisolidA356alloyslurrypreparedbytheLSPWESmethodwasinvestigatedandtheexperimentalresultscanbeusefulforthedevelopmentofanadvancedrehoformingtechnology.2.ExperimentalTherawmaterialsusedintheexperimentswereAlsoavailableonlineatwww.sciencedirect.comY.L.Baiefal.,FillingabilityofsemisolidA356aluminumalloyslurryinrheodiecasting49commercialA356aluminumalloy.ItscompositionwasSi,7.49wtMg,0.46wtFe,0.16wtandbalanceAl.Theliquidstemperatureandthesolidstemperatureareabout615and555OC,respectively.Intheexperiments,theslurryofA356alloywasfirstpreparedbylowsuperheatpouringwithweakelectromagneticstimng,andthentheslurrywassoakedinaninductionheater.Afterthesoakingprocess,theslurrywasfinallydeliveredquicklyintotheinjectionchamberofthediecastingmachineandformed.Toinvestigatetherheodiecastingfillingabilityoftheabovepreparedslurry,thediewitha1300mmx10mmx3mmspiralcavitywasused.TheschematicdiagramandcrosssectionofthedieisshowninFig.l.Therheoformedspiralsamplelengthmaybeusedasthestandardtoevaluatetheeffectsofslurrytemperature,injectionpressure,andpistonvelocityonthefillingability.Theslurrytemperaturesusedintheseexperimentswereintherangeof585595C,theinjectionpressureswereintherangeof525MPa,andthepistonvelocitieswerebetween0.024and0.072ds.Thepreheateddieandtheinjectionchambertemperaturewere120and300OC,respectively.Fig.1.Schematicdiagramofthedieaanditscrosssectionbunitmm.Themetallographicspecimenswerecutfromthedifferentsitesofthespiralsamplesandroughlyground,finelypolished,andetchedbyanaqueoussolutionof0.501HEThemicrostructurewasobservedandanalyzedwithanopticalmicroscopeforanalyzingthemicrostructuraldistribution.3.Resultanddiscussion3.1.EffectofslurrytemperatureonthefillingabilityTheslurrytemperaturehereisthetemperatureatwhichtheslurrywasdeliveredintotheinjectionchamber.TheexperimentsindicatethattheslurrytemperaturehasagreateffectonthefillingabilityofthesemisolidA356aluminumalloyslurry.ThefillinglengthsofrheoformedspiralsamplesatdifferenttemperaturesareshowninFig.2,inwhichthepistonvelocityis0.072m/s.280E240E,220J2002180.2160m10MPa015MPa100584586588590592594596Formingtemperature/CFig.2.EffectofslurrytemperatureonthefillinglengthofthesemisolidA356alloyslurry.ItcanbeseenfromFig.2thatthevariationtrendoffillinglengthwithincreasingslurrytemperatureissimilarwhethertheinjectionpressureis10,15,or20MPa,anditisobviousthatthefillinglengthincreaseswithincreasingslurrytemperature.Namely,thefillingabilityofthesemisolidA356aluminumalloyslurrybecomesgraduallybetterwiththeincreasingslurrytemperature.Thisisbecausethesolidfractionandapparentviscositydecreasewiththeincreasingslurrytemperature,andtherefore,thefillingresistanceislowerwhentheslurryflowsinthecavityandthefillinglengthincreases.Ontheotherhand,thefreezingtimeoftheslurryresultingfromthehighertemperaturewillbelonger,andthefillingtimemaybelonger.Thus,thehighertheslurrytemperature,thelongeristhefreezingtime,andthebetteristhefillingability.However,iftheslurrytemperatureisconsiderablyhigher,theturbulentflowandthegasentrainmentmaybecaused.Therefore,theappropriateslurrytemperaturesthatensureacompletelycompactedfillingmustbeadopted.ItcanalsobeseenfromFig.2thatthefillingabilityoftheslurrypreparedbylowsuperheatpouringwithweakelectromagneticstirringisverygood.Evenwhentheslurrytemperatureandthereheateddietemperatureare585and120C,respectively,thefillinglengthstillreachesupto100mm,whichindicatesagoodfillingabilityforthecastingswith3mmthicknessand10mmwidth.Iftheslurrytemperaturecontinuouslyincreasesto595C,thefillinglength50J.Univ.Sci.TechnoLBeijing,VoLlS,No.1,Feb2008reachesuptomorethan180nunandisinarangeof180270mm,namely,thefillinglengthwillincreaseto270nunwhentheformingtemperatureandtheinjectionpressureare595°Cand20MPa,respectively.Thus,thecompletefillingforanycomplexdiecavitycanbeensuredbyappropriatelyadjustingtheslunytemperatureandtheinjectionpressure.3.2.EffectofinjectionpressureonthefillingabilityTheinjectionpressureisthestaticpressureexertedonthesemisolidA356aluminumalloyslurryintheinjectionchamber.Itisalsoanimportantparameterintherheodiecastingprocess,andtheeffectofinjectionpressureonthefillinglengthofthespiraldiecastingsundervariousinjectionpressureconditionsisshowninFig.3,inwhichtheslurrytemperatureis585°C.5I0152025ln,jrctionpressureMPaFig.3.Effectofinjectionpressureonthefillinglength.FromFig.3,itcanbeseenthatthefillinglengthisshorterwhentheinjectionpressureislowhowever,thefillinglengthwillincreasewhentheinjectionpressureincreases.Forexample,whentheinjectionpressureis5MPaandthepistonvelocityis0.048ds.thefillinglengthisonly71mm,whichindicatesapoorfillingability.However,whentheinjectionpressureincreasesto15MPa,thefillinglengthwillreachupto110mm,wluchindicatesagoodfillingability.Moreover,iftheinjectionpressureincreasestoabove15MPa,thefillinglengthwillincreaseconsiderablyandwillreachupto120190mm.Thevaryingtrendofthefillinglengthwiththeincreasinginjectionpressuremaybeexplainedasfollowswhentheinjectionpressureislow,thefillingpowerisnotenoughtoovercometheflowresistanceoftheslurry,therefore,thefillinglengthisshortiftheinjectionpressureincreases.theslurrywillgetlargerpowertoovercometheflowresistanceoftheslurry.However,iftheinjectionpressureisveryhighandreachesacriticalvalue,theairinthecavitycannotescapeimmediately,andthefillinglengthwilldecreasebecauseofthehigheradversepressure,andthegasentrapmentmayalsobecaused1,31thus,ahigherpressuremustbeadoptedifgasentrapmentmustbeprevented.ItcanalsobeseenfromFig.3thatwhiletheinjectionpressureincreases,thefillinglengthwillincreaseconsiderablyifthepistonvelocityincreasesatthesametime.Forexample,whenthepistonvelocityis0.096ds,iftheinjectionpressureincreasesto25MPa,thefillinglengthwillreachupto240mm,thatistosay,thefillingabilityisconsiderablybetter.Themainreasonmaybethatthehigherfillingvelocitydecreasestheheatemissionoftheslurryandisfavorablefortheslurrytoflowforalongertimebeforeitfreezes,andtherefore,thefillingabilitywillbecomeconsiderablybetter.TheresultsinFig.3indicatethatiftheexhaustionofthedieisgoodandgasentrainmentcannotappear,ahigherinjectionpressureisfavorabletothefillingability,andthefillingabilityoftheslurrypreparedbylowsuperheatpouringwithweakelectromagneticstirringisalsoverygood.3.3.EffectofpistonvelocityonthefillingabilityThepistonvelocityisthevelocityatwhichthepistonmovesforwardwhentheslurryisfilled.Itisalsoanimportantparameterintherheodiecastingprocess.Fig.4showstheeffectofpistonvelocityonthefillinglength,inwhichtheslurrytemperatureis585°C.mIOMPa0I5MPaA20MPaPistonvelociv/msFig.4.Effectofpistonvelocityonthefillinglength.FromFig.4,itcanbeseenthatthefillinglengthincreaseswithincreasingpistonvelocity.Whentheinjectionpressureis10MPaandthepistonvelocityis0.024ds,thefillinglengthisonly70mm,whichindicatesapoorfillingabilityunderthiscondition.Ifthepistonvelocityincreasesto0.072dsandtheinjectionpressureisalso10MPa,thefillinglengthincreasesandreachesupto100mm.However,ifthepistonvelocityincreasesto0.12ds,thefillinglengthwillincreaseandwillreachupto140mm,whichindiY.LBuietuZ.,FillingabilityofsemisolidA356aluminumalloyslurryinrheodiecasting51catesabetterfillingabilityatthistime.Withincreasingpistonvelocity,theslurryfillingspeedwillincreaseandthefillingtimeinthesamediecavitywillbeshortenedtheheatemissionalsodecreasessothattheslurrywillflowatahighertemperature.Asaresult,theapparentviscosityoftheslurrywillbelowerandtheflowabilitywillalsobegoodthus,thefillinglengthgraduallybecomeslongerintheend.ItcanalsobeseenfromFig.4thatiftheinjectionpressureincreases,thefillinglengthwillconsiderablyincreasewhilethepistonvelocitywillincreasesimultaneously.Forexample,whentheinjectionpressureis20MPaandthepistonvelocityis0.024m/s,thefillinglengthisonly105mm,butifthepistonvelocityincreasesto0.12m/s,thefillinglengthwillincreaseto180mm,whichindicatesthatthisconditionhasagoodfillingability.Thus,itisfavorableforgoodfillingabilitywhentheinjectionpressureisabove15MPaandthepistonvelocityisabove0.096m/s.Thevaryingtrendofthefillinglengthwithincreasingpistonvelocityalsoshowsthatthefillingabilityoftheslurrypreparedbylowsuperheatpouringandweakelectromagneticstirringisverygood.3.4.MicrostructuraldistributionTogettheisotropicandgoodmechanicalproperties,itisrequiredinthesemisolidmetalformingprocessthatthemicrostructuraldistributionisveryhomogeneous,namely,thesphericalprimaryaA1grainsshouldbedistributedhomogeneouslyinthediecasting.Fig.5showsthesitesatwhichthemetallographicspecimenswerecut.BottomCFig.5.Schematicdiagramofthesitesatwhichthemetallographicspecimenswerecut.Fig.6showsthecentermicrostructuresandtheperipherymicrostructuresattheA,B,andCsites.ItcanbeseenfromFig.6thatthesphericalprimaryaA1grainsatthecenterareveryhomogeneouswhetheratA,B,orCsites.However,thesphericalprimaryaA1grainsattheperipheryaresmallerthanthatinthecentertoaverylimitedextentandtheobviousmicrostructuralsegregationcannotbefound,whichindicatesthatthesemisolidslurryfillingisstable.Italsoindicatesthattheslurrypreparedbylowsuperheatpouringwithweakelectromagneticstimngisappropriatetotherheoformingprocess,whichwilllayasolidbasefordiecastingwithhighqualityandgoodmechanicalproperties.Fig.6.MicrostructuresofthemetallographicspecimenscutfromthesemisolidfilledpiecesaatthecenterofsiteAbintheperipheryofsiteAcatthecenterofsiteBdintheperipheryofsiteBeatthecenterofsiteCfinheperipheryofsiteC.4.Conclusionsaluminumalloyhasanimportanteffectonthefillingabilitythehighertheslurrytemperature,thebetteris1TheslurrytemperatureofthesemisolidA356

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