Trans.NonferrousMet.Soc.China29(2019)1365?1374InfluenceofchemicalmodificationbyY2O3oneutecticSicharacteristicsandtensilepropertiesofA356alloyM.E.MOUSSA1,S.EL-HADAD1,W.KHALIFA2
1.DepartmentofCastingTechnologyCentralMetallurgicalResearchandDevelopmentInstitute(CMRDI),P.O.87,Helwan,Egypt;2.DepartmentofMining,PetroleumandMetallurgicalEngineering,FacultyofEngineering,CairoUniversity,P.O.12613,Giza,EgyptReceived7September2018;accepted27February2019Abstract:ThemodificationofA356aluminum?siliconalloyusingyttriumoxide(Y2O3)wasstudied.Additionlevelsofupto2.5wt.%Y2O3wereinvestigated.ApremixedpowderofAl?30wt.%Y2O3wasaddedtothemeltatabout750°Cusingvortexmethod.Sampleswerethenpouredinsandmold.TheresultsshowedthatevidentmodificationwasobtainedusingtheY2O3addition.Theoptimumlevelwas1.5wt.%,andwascorrespondingtoaeutectictemperaturedepressionfrom568to557°C.TheeutecticSiparticleswererefinedinlengthfrom44.8to8.3μm,andmodifiedinaspectratiofrom6.8to0.98.HigheradditionsofY2O3causedde-modificationoftheeutecticSiparticles.Theductilityofthemodifiedspecimenswasenhancedbymorethan20%comparedtotheunmodifiedones.Thiswasassociatedwithagradualtransferfromcleavagetoamoreductilemodeoffracture.Keywords:hypoeutecticAl?Sialloys;modi?cation;yttriumoxide(Y2O3);ductility;fracturemode1Introduction
TheseriesofaluminumcastalloysbasedontheAl?SisystemarethemostfrequentlyusedAl-alloysgroupduetotheircombinationofpropertiessuchascastability,specificstrengthandresistancetocorrosiveattack.HypoeutecticAl?Sialloysspecificallyconsistofalargevolumefractionofeutecticsilicon.ThemorphologyofeutecticSiisthereforeofprimimportance.Thisisduetoitsreportedeffects[1]onthefinalmechanicalpropertiesofthealloy.IncommercialAl?SialloyssuchasA356orA360,theeutecticSiwasdescribedascoarseneedle-likephase[1,2].ThesecoarseSiparticleswiththeirsharpendspromotestressconcentrationsandhence,theyaredetrimentaltothemechanicalpropertiesasreportedearlier[2,3].Inordertoovercomethisproblem,severalmethodswereproposedandappliedtodecreasingthesizeofthesecoarseparticlesandtoroundingtheirsharpends.Examplesofthesemethodsare:chemicalmodificationviaaddingcertainelements,quenchmodificationbyapplyingrapidcoolingrate,processinginthesemi-solidCorrespondingauthor:S.EL-HADAD;E-mail:shimahassan@cmrdi.sci.egDOI:10.1016/S1003-6326(19)65043-0state,stirringusinganelectromagneticfieldorultrasonicvibrations[4?15].Amongtheaforementionedmodificationmethods[16?24],additionofelementstoactaschemicalmodifiersisthemosteffectivewaytomodifytheeutecticSi.Inthismethod,themorphologyofSiphaseischangedbyminoradditionofelementssuchasNa,SrandSborbyaddingrareearthelementstothemeltwhicheffectivelyalterthesharp-endedSiphasetofibrousmorphologyandaccordinglyenhancethemechanicalpropertiesoftheAl?Sialloys.Differentmechanismsweresuggestedtoexplaintheeutecticmodi?cationbychemicalmodifiers.Themostacceptedmechanismswerethoserelatedtothetwinningof{111}[25,26].AccordingtothetheoreticalcalculationsfoundinRefs.[25,26],thegrowthtwinisformedattheinterface(eutecticSi/modifier)whentheratioofatomicradiusoftheelementrelativetothatofSi(rmodifier/rSi)isabout1.646[27].SincethechemicalmodifierslikeNa,Sr,Sb,Ba,Ca,Y,YbandmischmetalsachievethisatomicradiusratiorelativetoSi,theycanworkperfectlyaschemicalmodifiers[25?27].Concerningtherareearthelements,EuandYbhavethemostoptimumratiosof1.70and1.66respectivelywhile
Y2O3化学改性对A356合金共晶硅特性和拉伸性能的影响 - 论文
