MaterialsScienceandEngineeringA396(2005)263–270Sicoarseningofspray-formedhighloadinghypereutecticAl–Sialloysinthesemisolidstate∗C.-H.Chiang,ChiY.A.TsaoDepartmentofMaterialsScienceandEngineering,NationalChengKungUniversity,No.1Ta-HsuehRoad,Tainan70101,Taiwan,ROCReceived13September2004;receivedinrevisedform13January2005;accepted19January2005AbstractCoarseningofspray-formedhypereutecticAl–Sialloysinthesemisolidstatewasstudied.ThreeAl–Sialloys,Al–25Si,Al–35SiandAl–45Si,wereemployed.TheeffectsofconvectionoftheSiparticlesintheliquidmatrixatlowsolidfractionsduringthecoarseninginthesemi-solidstatewereinvestigated.Thecoarseningexponent,n,andtherateconstant,,weredetermined.ThecoarseningexponentswereKfoundnottobesensitivetothesolidfractionandSicontentintheAl–35SiandAl–45Sialloys,which,however,weredifferentfromthatofAl–25Sialloy.Therateconstantswerefoundtoincreasewitheitherincreasingsolidfractionordecreasingsolidfaction,dependingontheconditionsbeingconstanttemperatureorconstantSicontent,respectively.©2005ElsevierB.V.Allrightsreserved.Sprayforming;Coarsening;Semisolid;HypereutecticAl–SialloysKeywords:1.Introductioncations,hence,plasticdeformationinthesolidstatebecomesdifcult[7].SprayformingbyOspreyroute[1–3]isanadvancedpro-Semisolidforming[8,9]isawaytoimprovetheforma-cessformanufacturingmaterials.Liquidmetalsareatomizedbilityofspray-formedhypereutecticAl–SialloyswithhighintosmalldropletsbyinertgasanddepositedonasubstratetoSicontents,inwhichthealloysareformedinthetwo-phaseformabillet,whichwasshownasFig.1.Duringtheprocess,region,solidplusliquid.However,thesolidphaseintheliq-liquidmetalsaresolidiedwithhighcoolingratesattherangeuidmatrixcoarsensquiterapidly,whichmayaffectthenal◦23of10–10C/sandneandequiaxed-grainedmicrostruc-microstructuresandmechanicalpropertiessignicantly.Theturesareobtained.HypereutecticAl–Sialloysareversatilecoarseningbehaviorofspray-formedhypereutecticAl