1、JournalofUniversityofScienceandTechnologyBeqingVolume15/Number7/February2008/Page48ELSEVIERFillingabilityofsemi-solidA356aluminumalloyslurryinrheo-diecastingYuelongBail//WeiminMao/Son&Gao”/GuoxingTang”/andJunXu1)SchoolofMaterialsScienceandEngineering/UniversityofScienceandTechnologyBeijing/Beijing10
2、0083/China2)NationalEngineeringResearchCenterforNan-ferrousMetalsComposite/GeneralResearchInstituteforNon-ferrousMetals/Beijing100088/China(Received2007-02-28)Abstracts/Theeffectsofslurrytemperature/injectionpressure/andpistonvelocityontherheo-fillingabilityofsemisolidA356al-loyswerestudiedbythereho
3、-diecastingmethods/Theresultsshowthattheslunytemperatureofthesemi-solidA356aluminumal-loyhasanimportanteffectonthefillingability；thehighertheslurrytemperature/thebetteristhefillingability/andtheappropriateslurrytemperatureforrheo-fillingisintherangeof585-595C/Theinjectionpressurealsohasagreateffecto
4、nthefillingability/anditisappropriatetotherheo-finingwhentheinjectionpressureisintherangeof15-25MPa/ThePiStORvelocityalsohasagreateffectonthefillingability/anditisappropriatetotherheo-fillingwhenthepistonvelocityisintherangeof0/072-0/12ds/Thefillingabilityoftheslurrypreparedbylowsuperheatpouringwith
5、weakelectromagneticstirringisverygoodandthemicrostructuraldistributionintherheo-formeddiecastingsishomogeneous/whichisadvantageoustothehighqualitydiecasting/02008UniversityofScienceandTechnologyBeijing/Allrightsreserved/Keywords/A356aluminurnalloy；rheo-diecasting；fillingability；semi-solidTheworkwasf
6、inanciallysupportedbytheNationalNatureScienceFoundationofChinu(No/50774007)/theNationalHighTech-nologyResearchandDevelopmen1Programofchina(N0/2006AA03Z115)/andtheNationalKeyBasicResearchProgramofChina(N0/2006CB605203)/I1/IntroductionEversincesemi-solidmetalformingwasdevelopedbyFlemingsatMITinthe1970
7、s/ithasattractedcon-siderableattentioninoverseasanddomestic/Severalexpertshaveparticipatedinthebasicandappliedre-searchofthesetechniques/Afterdevelopingforoverthirtyyears/thesehavesuccessfullybeenappliedtomanufacturingvariouskindsofcarandaircraftparts1-31/However/atpresent/onlythethixo-formingtechni
8、queshavebeenusedforcommercialproductionandthecommercialproductionscaleissmallyet/Thisismainlybecausethepreparingcostofsemi-solidslunyandtheenergyconsumptionofbilletreheatingarehigher/andtherecyclingofbleedingdrops/bis-cuits/gatingsystem/andrejectedcastingsaredifficult/Whencomparedwiththixo-formingte
9、chnologies/reho-formingtechniquesofsemi-solidmetalshaveseveraladvantages/suchasconsiderablyshorterproc-ess/easyrecyclingofthegatingsystemandwasteCorrespondingauthor/YuelongBai/E-mail/bal-02IH)8UniversityofScienceandlechnolopyBeijing/Allrightsreserved/castings/lowproductioncost/etc/Thus/reho-formingt
10、echniquesarenowbecomingoneofthemostimpor-tantstudysubjects4-91/Lowsuperheatpouringwithweakelectromagneticstirringforashorttime(LSPWES)isanewmethodforthepreparationofsemi-solidalloysslurries10-111/whichrequireslowenergyconsumptionascomparedwiththepreparationofsemi-solidalloysbilletsusingonlyelectroma
11、gneticstirringatahighpower12-131；andtheprocesscon-trolisconsiderablyconvenient141andtheslurrymi-crostructureisbetterthanthatpreparedbytheliquiduscastingtechnology/Therefore/LSPWEScanbeap-pliedasthekeytechnologyofanewsemi-solidreho-formingprocess15/Inthisstudy/thefillingabilityofsemi-solidA356alloysl
12、urrypreparedbytheLSPWESmethodwasinvestigatedandtheexperi-mentalresultscanbeusefulforthedevelopmentofanadvancedreho-formingtechnology/2/ExperimentalTherawmaterialsusedintheexperimentswereAY/L/Baiefal//Fillingabilityofsemi-solidA356aluminumalloyslurryinrheo-diecasting49commercialA356aluminumalloy/Itsc
13、ompositionwasSi/7/49wt%；Mg/0/46wt%；Fe/0/16wt%；andbalanceAl/Theliquidstemperatureandthesolidstemperatureareabout615and555OC/respectively/Intheexperiments/theslurryofA356alloywasfirstpreparedbylowsuperheatpouringwithweakelectromagneticstimng/andthentheslurrywassoakedinaninductionheater/Afterthesoaking
14、proc-ess/theslurrywasfinallydeliveredquicklyintotheinjectionchamberofthediecastingmachineandformed/Toinvestigatetherheo-diecastingfillingabilityoftheabove-preparedslurry/thediewitha1300mmx10mmx3mmspiralcavitywasused/Theschematicdia-gramandcrosssectionofthedieisshowninFig/l/Therheo-formedspiralsample
15、lengthmaybeusedasthestandardtoevaluatetheeffectsofslurrytempera-ture/injectionpressure/andpistonvelocityonthefillingability/Theslurrytemperaturesusedintheseexperimentswereintherangeof585-595C/thein-jectionpressureswereintherangeof5-25MPa/andthepistonvelocitieswerebetween0/024and0/072ds/Thepreheatedd
16、ieandtheinjectionchambertemperaturewere120and300OC/respectively/Fig/1/Schematicdiagramofthedie(a)anditscrosssection(b)(unit/mm)/Themetallographicspecimenswerecutfromthedifferentsitesofthespiralsamplesandroughlyground/finelypolished/andetchedbyanaqueoussolutionof0/501%HEThemicrostructurewasob-serveda
17、ndanalyzedwithanopticalmicroscopeforanalyzingthemicrostructuraldistribution/3/Resultanddiscussion3/1/Effectofslurrytemperatureonthefillingabil-ityTheslurrytemperaturehereisthetemperatureatwhichtheslurrywasdeliveredintotheinjectionchamber/Theexperimentsindicatethattheslurrytemperaturehasagreateffecto
18、nthefillingabilityofthesemi-solidA356aluminumalloyslurry/Thefillinglengthsofrheo-formedspiralsamplesatdifferenttemperaturesareshowninFig/2/inwhichthepistonvelocityis0/072m/s/280E240E/220J=200-2180-/-2160-m-10MPa-0-15MPa-100584586588590592594596Formingtemperature/CFig/2/Effectofslurrytemperatureonthe
19、fillinglengthofthesemi-solidA356alloyslurry/ItcanbeseenfromFig/2thatthevariationtrendoffillinglengthwithincreasingslurrytemperatureissimilarwhethertheinjectionpressureis10/15/or20MPa/anditisobviousthatthefillinglengthincreaseswithincreasingslurrytemperature/Namely/thefillingabilityofthesemi-solidA35
20、6aluminumalloyslurrybecomesgraduallybetterwiththeincreasingslurrytemperature/Thisisbecausethesolidfractionandap-parentviscositydecreasewiththeincreasingslurrytemperature/andtherefore/thefillingresistanceislowerwhentheslurryflowsinthecavityandthefill-inglengthincreases/Ontheotherhand/thefreezingtimeo
21、ftheslurryresultingfromthehighertempera-turewillbelonger/andthefillingtimemaybelonger/Thus/thehighertheslurrytemperature/thelongeristhefreezingtime/andthebetteristhefillingability/However/iftheslurrytemperatureisconsiderablyhigher/theturbulentflowandthegasentrainmentmaybecaused/Therefore/theappropri
22、ateslurrytempera-turesthatensureacompletelycompactedfillingmustbeadopted/ItcanalsobeseenfromFig/2thatthefillingabilityoftheslurrypreparedbylowsuperheatpouringwithweakelectromagneticstirringisverygood/Evenwhentheslurrytemperatureandthereheateddietem-peratureare585and120C/respectively/thefillinglength
23、stillreachesupto100mm/whichindicatesagoodfillingabilityforthecastingswith3mmthick-nessand10mmwidth/Iftheslurrytemperaturecon-tinuouslyincreasesto595C/thefillinglength50J/Univ/Sci/TechnoLBeijing/VoLlS/No/1/Feb2008reachesuptomorethan180nunandisinarangeof180-270mm/namely/thefillinglengthwillincreaseto2
24、70nunwhentheformingtemperatureandthein-jectionpressureare595Cand20MPa/respectively/Thus/thecompletefillingforanycomplexdiecavitycanbeensuredbyappropriatelyadjustingtheslunytemperatureandtheinjectionpressure/3/2/EffectofinjectionpressureonthefillingabilityTheinjectionpressureisthestaticpressureexerte
25、donthesemi-solidA356aluminumalloyslurryintheinjectionchamber/Itisalsoanimportantparameterintherheo-diecastingprocess/andtheeffectofinjectionpressureonthefillinglengthofthespiraldiecastingsundervariousinjectionpressureconditionsisshowninFig/3/inwhichtheslurrytemperatureis585C/5I0152025ln/jrctionpress
26、ure!MPaFig/3/Effectofinjectionpressureonthefillinglength/FromFig/3/itcanbeseenthatthefillinglengthisshorterwhentheinjectionpressureislow；however/thefillinglengthwillincreasewhentheinjectionpres-sureincreases/Forexample/whentheinjectionpres-sureis5MPaandthepistonvelocityis0/048ds/thefillinglengthison
27、ly71mm/whichindicatesapoorfillingability/However/whentheinjectionpressureincreasesto15MPa/thefillinglengthwillreachupto110mm/wluchindicatesagoodfillingability/Moreover/iftheinjectionpressureincreasestoabove15MPa/thefillinglengthwillincreaseconsiderablyandwillreachupto120-190mm/Thevaryingtrendofthefi
28、llinglengthwiththeincreasinginjectionpres-suremaybeexplainedasfollows/whentheinjectionpressureislow/thefillingpowerisnotenoughtoovercometheflowresistanceoftheslurry/therefore/thefillinglengthisshort；iftheinjectionpressurein-creases/theslurrywillgetlargerpowertoovercometheflowresistanceoftheslurry/Ho
29、wever/ifthein-jectionpressureisveryhighandreachesacriticalvalue/theairinthecavitycannotescapeimmediately/andthefillinglengthwilldecreasebecauseofthehigheradversepressure/andthegasentrapmentmayalsobecaused1/31；thus/ahigherpressuremustbeadoptedifgasentrapmentmustbeprevented/ItcanalsobeseenfromFig/3tha
30、twhiletheinjec-tionpressureincreases/thefillinglengthwillincreaseconsiderablyifthepistonvelocityincreasesatthesametime/Forexample/whenthepistonvelocityis0/096ds/iftheinjectionpressureincreasesto25MPa/thefillinglengthwillreachupto240mm/thatistosay/thefillingabilityisconsiderablybetter/Themainreasonma
31、ybethatthehigherfillingvelocityde-creasestheheatemissionoftheslurryandisfavorablefortheslurrytoflowforalongertimebeforeitfreezes/andtherefore/thefillingabilitywillbecomeconsiderablybetter/TheresultsinFig/3indicatethatiftheexhaustionofthedieisgoodandgasentrainmentcannotappear/ahigherinjectionpressure
32、isfavorabletothefillingability/andthefillingabilityoftheslurrypreparedbylowsuperheatpouringwithweakelectromagneticstir-ringisalsoverygood/3/3/EffectofpistonvelocityonthefillingabilityThepistonvelocityisthevelocityatwhichthepistonmovesforwardwhentheslurryisfilled/Itisalsoanimportantparameterintherheo
33、-diecastingprocess/Fig/4showstheeffectofpistonvelocityonthefillinglength/inwhichtheslurrytemperatureis585C/-mIOMPa-0-I5MPa-A-20MPaPistonvelociv/(ms)Fig/4/Effectofpistonvelocityonthefillinglength/FromFig/4/itcanbeseenthatthefillinglengthin-creaseswithincreasingpistonvelocity/Whenthein-jectionpressure
34、is10MPaandthepistonvelocityis0/024ds/thefillinglengthisonly70mm/whichin-dicatesapoorfillingabilityunderthiscondition/Ifthepistonvelocityincreasesto0/072dsandtheinjec-tionpressureisalso10MPa/thefillinglengthin-creasesandreachesupto100mm/However/ifthepistonvelocityincreasesto0/12ds/thefillinglengthwil
35、lincreaseandwillreachupto140mm/whichindi-Y/LBuietuZ//Fillingabilityofsemi-solidA356aluminumalloyslurryinrheo-diecasting51catesabetterfillingabilityatthistime/Withincreas-ingpistonvelocity/theslurryfillingspeedwillin-creaseandthefillingtimeinthesamediecavitywillbeshortened；theheatemissionalsodecrease
36、ssothattheslurrywillflowatahighertemperature/Asaresult/theapparentviscosityoftheslurrywillbelowerandtheflowabilitywillalsobegood；thus/thefillinglengthgraduallybecomeslongerintheend/ItcanalsobeseenfromFig/4thatiftheinjectionpressurein-creases/thefillinglengthwillconsiderablyincreasewhilethepistonvelo
37、citywillincreasesimultaneously/Forexample/whentheinjectionpressureis20MPaandthepistonvelocityis0/024m/s/thefillinglengthisonly105mm/butifthepistonvelocityincreasesto0/12m/s/thefillinglengthwillincreaseto180mm/whichindicatesthatthisconditionhasagoodfillingability/Thus/itisfavorableforgoodfillingabili
38、tywhentheinjectionpressureisabove15MPaandthepistonvelocityisabove0/096m/s/Thevaryingtrendofthefillinglengthwithin-creasingpistonvelocityalsoshowsthatthefillingabilityoftheslurrypreparedbylowsuperheatpouringandweakelectromagneticstirringisverygood/3/4/MicrostructuraldistributionTogettheisotropicandgo
39、odmechanicalproperties/itisrequiredinthesemi-solidmetalformingprocessthatthemicrostructuraldistributionisveryhomoge-neous/namely/thesphericalprimarya-A1grainsshouldbedistributedhomogeneouslyinthediecast-ing/Fig/5showsthesitesatwhichthemetallographicspecimenswerecut/BottomCFig/5/Schematicdiagramofthe
40、sitesatwhichthemetal-lographicspecimenswerecut/Fig/6showsthecentermicrostructuresandtheperipherymicrostructuresattheA/B/andCsites/ItcanbeseenfromFig/6thatthesphericalprimarya-A1grainsatthecenterareveryhomogeneouswhetheratA/B/orCsites/However/thesphericalprimarya-A1grainsattheperipheryaresmallerthant
41、hatinthecentertoaverylimitedextentandtheobviousmicro-structuralsegregationcannotbefound/whichindi-catesthatthesemi-solidslurryfillingisstable/Italsoindicatesthattheslurrypreparedbylowsuperheatpouringwithweakelectromagneticstimngisappro-priatetotherheo-formingprocess/whichwilllayasolidbasefordiecasti
42、ngwithhighqualityandgoodmechanicalproperties/Fig/6/Microstructuresofthemetallographicspecimenscutfromthesemi-solidfilledpieces/(a)atthecenterofsiteA；(b)intheperipheryofsiteA；(c)atthecenterofsiteB；(d)intheperipheryofsiteB；(e)atthecenterofsiteC；(f)inheperipheryofsiteC/4/Conclusionsaluminumalloyhasanimportanteffectonthefillingability；thehighertheslurrytemperature/thebetteris(1)Theslurrytemperatureofthesemi-solidA356
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