Modeling the Effect of Finite-Rate Hydrogen Diffusion on Porosity Formation in Aluminum Alloys

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1、ModelingtheEffectofFinite-RateHydrogenDiffusiononPorosityFormationinAluminumAlloysKENTD.CARLSON,ZHIPINGLIN,andCHRISTOPHBECKERMANNAvolume-averagedmodelforfinite-ratediffusionofhydrogeninthemeltisdevelopedtopredictporeformationduringthesolidificationofaluminumalloys.Thec

2、alculationofthemicro-/macro-scalegasspeciestransportinthemeltiscoupledwithamodelforthefeedingflowandpressurefield.Therateofporegrowthisshowntobeproportionaltothelocallevelofgassupersaturationinthemelt,aswellasvariousmicrostructuralparameters.Parametricstudiesofone-dim

3、ensionalsolidificationunderanimposedtemperaturegradientandcoolingrateillus-tratethatthemodelcapturesimportantphenomenaobservedinporosityformationinalumi-numalloys.Thetransitionfromgastoshrinkagedominatedporosityandtheeffectsofdifferentsolubilitiesofhydrogenintheeutecti

4、csolid,capillarypressuresatporenucleation,andporenumberdensitiesareinvestigatedindetail.Comparisonsbetweenpredictedporositypercentagesandpreviousexperimentalmeasurementsshowgoodcorrespondence,althoughsomeuncer-taintiesremainregardingtheextentofimpingementofsolidonth

5、epores.DOI:10.1007/s11663-006-9013-2ÓTheMinerals,Metals&MaterialsSocietyandASMInternational2007[6,7]I.INTRODUCTIONLeeandHuntexperimentallyobservedporosityformationinaluminumalloysusinganX-raytemper-POROSITY-RELATEDdefectsareamajorcauseofaturegradientstage.Theyfoundt

6、hepressuredropcastingrejectionandreworkinthecastingindustry.causedbyshrinkagetobenegligiblysmall.TheyTheyaretypicallycausedbyalackoffeedingofthedevelopedamicroscalemodelofhydrogendiffusion-shrinkagethatoccursduringsolidificationorbyexces-controlledgrowthbyconsideringa

7、singleporeinsidethesivelevelsofgasspeciesdissolvedinthemelt.Modelingmushyzone.Themodeldoesnotcomputethepressureofporosityformationhasbeenattemptedbymanyfieldinthemushyzone;rather,thepressureisaninputresearchers,datingbacktotheearlyone-dimensional[8,9][1]variable.Atwo

8、odetal.appliedthismodeltoan(1-D)workofPiwonkaandFlemingsandtheseminalAl7Sialloy,andHamiltonetal.[10]incorporateditintoa[2]two-dimensional(