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(1.AutomationResearchInstitute,BohaiUniversity,Jinzhou121013,China；2.SchoolofMaterialsScienceandEngineering,DalianUniversityofTechnology,Dalian116024,China;3.SchoolofCirilEnginering,HebeiInstituteofArchitectureCirilEnginering,Zhangjiakou075000,China)

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EffectofultrasonicandelectromagneticfieldsonsolidificationstructureofhypoeutecticAl-Sialloy

FUYing1,LIUChang1,ZHANGYu-bo2,JIEJin-chuan2,LITing-jui2,XIEJun*,3

(1.AutomationResearchInstitute,BohaiUniversity,Jinzhou121013,China；2.SchoolofMaterialsScienceandEngineering,DalianUniversityofTechnology,Dalian116024,China;3.SchoolofCirilEnginering,HebeiInstituteofArchitectureCirilEnginering,Zhangjiakou075000,China)

Abstract：Themorphologyofprimaryα-Alandeutecticsiliconin4004aluminumalloyunderdiversephysicalfieldswasinvestigated.Thediversephysicalfieldsareultrasonic(UST)orelectromagnetic(EMS),andtheircompound(UE).TheresultsshowedthatthesolidificationstructuresofingotscouldberefinedbyusingUSTorEMSsolely.Inparticular,thehigh-intensityultrasonicvibrationhadasignificanteffectonrefiningeutecticsiliconphase.Whenthecompoundfieldwasimposed,boththeprimaryaluminumphaseandtheeutecticsiliconphasewererefined,therefinementeffectisnearlyuniformwiththesamplestreatedbypowerultrasonicsolely,however,therefinementzoneincompoundfieldwouldbelargerthansoleUSTorEMS.

Keywords：powerultrasonic;electromagneticstirring;hypoeutecticAl-Sialloy

IIntroduction

Al-Sialloyshavewidespreadusageinthefieldsofautomotive,aerospaceandmilitaryduetotheirexcellentcastability,highspecificstrengthandgoodwearproperties〔1〕.Inordertoimprovebothcastabilityandmechanicalpropertyofthem,thestandardpracticeisthemodificationofsolidificationmicrostructure.Inrecentyears,manymethodstomodifythesolidifiedstructureofAl-Sialloyhavebeendeveloped.Theseinvolve,seeding〔2〕,mechanicalorelectromagneticstirring〔3〕,ultrasonictreatment〔4〕,electromagneticvibration〔5〕,andsoon.Ithasbeenreportedthatultrasonichasasignificanteffectonrefiningboththeprimaryaluminumphaseandtheeutecticsiliconphase〔6〕.ThecombinationofultrasonicandrotatingelectromagneticfieldwasusedtomodifythemorphologyofprimaryAlandeutecticSiinA356alloy〔7〕.Inthepresentstudy,theeffectofdiversephysicalfields(ultrasonic,electromagneticstirring,andthecombinationoftwofields)onthemorphologyofprimaryα-AlphaseandeutecticsiliconinhypoeutecticAl-Sialloywasinvestigated.

ⅡExperimental method

Inthisstudy, 4004aluminumalloywasused.Theexperimentalsetupsconsistofultrasonicgenerator200Wand22.5KHzfrequency,temperaturemeasurementsystem,andelectromagneticstirringequipment.TheschematicdiagramispresentedinFig.1.The4004alloywasmeltedinanelectricresistancefurnace,andheatedto1023K.Afterholdingforonehour,themoltenmeltwastakenoutfromthefurnaceanddegassedbyusinghexachloroethane(1wt.%ofmoltenmelt),whenthetemperaturedecreasedto967K,itwaspouredintothepre-heatedgraphitemold.Whenthetemperatureofthemeltwas957K,itwastreatedbydiversephysicalfieldi.e.onlyUSTorEMS,thecompoundfieldandwithoutanyphysicalfieldtreatment.Finally,theingot(40mmindiameter, 60mminheight)wascutverticallyfromthecenterandusedformetallographicexaminationandSEManalysis.ThedetailedexperimentalparametersandconditionsareshowninTable1.

ⅢResults and discussion

Themicrostructuresof4004alloyingotsunderdiversephysicalfieldareshowninFig.2.Fig.2ashowsthetypicaldendritestructureofthenormalhypoeutecticAl-Sialloywithoutanytreatment,andthecoarseaciculareutecticsilicondispersesamongthesedendrites.InFig.2b,undertheeffectofelectromagneticstirring,theprimaryα-Alchangesfromdendritetoirregularfinegrain,butthethickandthefibrouseutecticsiliconalsodistributeamongirregularprimaryaluminumphases.Whenthe4004alloymeltistreatedbypowerultrasonic,thesolidificationstructurechangesfromdendriticcrystaltoglobulargrain,andtheaveragegrainsizereducesto137.1μmfrommilimeterrangewithoutanytreatment,asshowninFig.2c.Fig.2ddisplaysthesolidificationstructureofthe4004alloyunderthecompoundphysicalfieldofUSTandEMS.Itcanbeseenthatthereareglobulargrainsandirregularprimaryaluminumgrains,meanwhilethefineeutecticsiliconintersperseamongtheseprimaryα-Alphases.ThissolidificationstructureofcompoundfieldissimilartothatofUST.Owingtotheheateffectofpowerultrasonicandelectromagneticfield,forthesmallingot,thesolidificationrateincompoundfield(UE)isslowerthantheothersolephysicalfields,therefore,therefinementeffectisnotthesuperpositionofUSTandEMS.

Fig.3Averagegrainsizeofprimaryα-Alin4004alloyunderdiversephysicalfield

Fig.4EutecticSimorphologyingots

(a)without, (b)EMS, (c)UST, (d)UE

Thequantitativemetallographicanalysisofα-AlgrainsareshowninFig.3.Withoutanytreatment,theaveragegrainsizeofα-Alisabout480μm,whilewithEMS,thesizedecreasesto240μm.WhentheUSTisapplied,theaveragegrainsizedecreasesto137μm.However,withthecompoundfieldofEMSandUST,theaveragegrainsizeisonly140μm,therefinementeffectisnearlyidenticalwiththeUSTsolely.

Thegrainrefinementmechanismthatoccursunderconditionsofelectromagneticstirringcanbeexplainedasthefragmentationofthedendritescreatedbyturbulenceoftheliquid,there-meltofdendriterootsbytemperaturefluctuationsandflowofliquidarounddendritearms.Relatively,theforcedconvectioncausedbyultrasonicacousticstreamingalsocanleadtothefragmentationofthedendrites〔3〕.Theultrasonicgrainrefinementmechanismshavebeenproposedbasedoncavitation,i.e.cavitation-inducednucleation.Whenthepowerultrasonicisinjectedintothemelt,thenonlineareffectssuchascavitation,acousticstreamingwillgenerate.Ontheeffectofcavitation,therearelotsofcavitationbubblesinthebulkmelt.Lotsofnucleicanbeproducedbycavitation-inducednucleation,resultinginthegrainrefinement.Naturally,thecombinationofultrasonicandelectromagneticfieldwillincreasetheforcedflowofthemelt,therefinementeffectshouldbebetterthanthesolelyultrasonicorelectromagneticstirring.Zhang〔6〕appliedthecompoundfieldofultrasonicandrotatingelectromagneticfieldtotheA356alloyaboveliquidus(about887K)at923Kandwhenthetemperaturedecreasedto883K,thecompoundfieldwasstopped,atthesametimethetreatedmeltwaspouredintoanothergraphitecrucible.Theyshowedthatboththeprimaryaluminumandeutecticsiliconweresignificantlyrefined.However,inthisexperiment,thetreatedmeltwascoolinginthesameonegraphitemold.Whenthecompoundfieldwasappliedintothemelt,theturbulenceofthemeltincreased,inaddition,theheateffectalsoincreased,therefore,forthesmallingot(40mmindiameter, 60mminheight),therefinementeffectofcompoundfieldwasweakened.Therefore,theaveragegrainsizeoftheingottreatedbycompoundfieldisonly140μm,ratherthanthesuperpositionrefinementeffectofUSTandEMS.TheSimorphologyofthe4004alloywasobservedbySEM,asshowninFig.4.

Ingotswithoutanytreatmentexhibitcoarseeutecticsilicondispersedamongtheprimaryα-Al,aspresentedinFig.4a.Fig.4bshowsthattheingottreatedbyEMS,theinter-phasespacingofSiphaseincreasescomparingwiththeingotwithoutanytreatment.Further,theingotswithUSTdisplayfineeutecticsilicon,thesizeismuchsmallerandthemorphologychangesintoshortstickfromacoarseacicularplate-like,asshowninFig.4c.Fig.4dpresentstheeutecticsiliconmorphologyofingotstreatedbycombinationofpowerultrasonicandelectromagneticfield,thesizeandmorphologyarenearlysimilartotheingotwithUSTsolely.

Fig.5EutecticSimorphologicalanalysesof4004alloyunderdiversephysicalfields

Fig.6Three-dimensionaleutecticSimorphology

(a)without, (b)EMS, (c)UST, (d)UE

FromtheFig.5,itcanbeseenthattheaveragelengthofeutecticsiliconwithoutanytreatmentisabout40μmandtheaveragewidth8.5μm.Whilewiththeelectromagneticstirringtreatment,theeutecticsiliconisabout42μminlength,and8μminwidth.However,withtheultrasonictreatment,themorphologyofSigrainisgreatlymodified,theaveragelengthofeutecticsilicondecreasesto17.5μmandtheaveragewidth2.5μm,whilewiththecompoundfield,theaveragesizeofeutecticsiliconisabout15μminlength,and2μminwidth.

Fig.6presentsthethree-dimensionalmorphologyofeutecticsiliconusingSEMonthedeep-etchedsamples.Theeutecticstructureofthealloyundertheascastconditionisrelativelycoarsesiliconflakes,asshowninFig.6a.Fig.6bshowsthattheinter-particlespacingofSigrainsincreaseundertheeffectofEMS.Fig.6cdisplaysthesiliconmorphologyoftheingotwithUST.Thesiliconphasechangestotheshortplatefromthecoarseplate-likeform.Thesimilarresultsalsopresentinthesampletreatedbycompoundfield,asshowninFig. 6d.Themovementofliquidaroundgrowingsiliconflakes,resultingfromtheforcedflowinducedbendingstresscausesfractureinthesilicon,whichhasaverylittlestrength〔7〕.Thebrokensiliconflakes“swim”tootherpartsoftheliquid,duringthistravel,becomegraduallythickenedandbroadened,Fig. 4bandFig.6b.Andtheinter-phasespacingofSiphaseincreases.ThereasonisthattheforcedconvectioncausedbyEMSenablesthediffusiondistanceofsoluteatomstoincrease,thusthecrosswisetransferabilityincreasesresultingintherealizationoftwophasecooperationgrowthbylong-distancediffusion〔8,9〕.

ⅣConclusions

Diversephysicalfieldswereintroducedintothe4004aluminiumalloy.Theresultsshowedthat:

(1)When4004alloymeltwastreatedbyelectromagneticstirringorpowerultrasonicsolely,thesolidificationstructurechangedfromdendriticgrainstonon-dendriticgrains,fortheultrasonictreatedingot,theaveragegrainsizereducedto137.1μm.Whilefortheingotwithcompoundfield,theaveragegrainsizewasabout140μm,therefinementwasnearlyuniformthanwithpowerultrasonicsolely.Itwasconsideredthat,forthesmallingot(40mmindiameter, 60mminheight),duetotheheateffectofultrasonicandelectromagneticfield,thefurtherrefinementeffectwasweakened.However,therefinementzoneincompoundfieldwouldbelargerthansoleUSTorEMS.

(2)Themorphologyofeutecticsiliconof4004alloywasmodifiedfromacoarseacicularplate-likeformwithoutanyphysicalfieldtoafineshortstickformwithultrasonictreatment.Withthetreatmentofcompoundfield,thefinersiliconphasealsoobtained,itwasthemaincontributionofpowerultrasonic,ratherthantheelectromagneticstirring.

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超聲及電磁場(chǎng)場(chǎng)對(duì)亞共晶鋁硅合金凝固組織的影響

付瑩1，劉暢1，張宇博2，接金川2，李廷舉2，謝軍3

(1. 渤海大學(xué) 自動(dòng)化研究院，遼寧 錦州 121013； 2. 大連理工大學(xué) 材料學(xué)院，遼寧 大連 116024；3. 河北建筑工程學(xué)院 土木工程學(xué)院，河北 張家口 075000)

摘要：本文研究了4004鋁合金在不同物理場(chǎng)作用下初生α-Al和共晶硅的形貌特征．不同物理場(chǎng)主要包括超聲場(chǎng)、電磁場(chǎng)、超聲和電磁復(fù)合場(chǎng)．實(shí)驗(yàn)結(jié)果表明，單獨(dú)應(yīng)用超聲或電磁場(chǎng)情況下，鑄錠的凝固組織都達(dá)到了細(xì)化效果．特別是功率超聲場(chǎng)，可以細(xì)化鋁合金中的共晶硅相．當(dāng)施加超聲和電磁復(fù)合場(chǎng)時(shí)，初生α-Al相和共晶硅相都得到細(xì)化，細(xì)化程度與同等條件下施加功率超聲場(chǎng)的細(xì)化效果幾乎等同，但是，復(fù)合場(chǎng)處理的鑄錠細(xì)化區(qū)域明顯得到擴(kuò)大．

關(guān)鍵詞：功率超聲；電磁攪拌；亞共晶鋁硅合金

收稿日期：2015-02-05.

基金項(xiàng)目：國家自然科學(xué)基金項(xiàng)目(No:51074031); 渤海大學(xué)博士啟動(dòng)基金項(xiàng)目(No:bsqd201442).

作者簡(jiǎn)介：付瑩(1983-)，男，博士，講師，主要從事真空冶金技術(shù)方面的研究.

通訊作者：5117832@163.com.

中圖分類號(hào)：O242；P423

文獻(xiàn)標(biāo)志碼：A

文章編號(hào)：1673-0569(2016)01-0070-05