MaterialsScienceandEngineeringA304–306(2001)555–558MicrostructureandmechanicalpropertiesofAl–SialloysproducedbysprayformingprocessV.C.Srivastava∗,R.K.Mandal,S.N.OjhaDepartmentofMetallurgicalEngineering,CentreofAdvancedStudy,InstituteofTechnology,BanarasHinduUniversity,Varanasi221005,IndiaAbstractThemicrostructuralcharacteristicsandmechanicalpropertiesofAl–6.5SiandAl–18Sialloyshavebeeninvestigated.Thealloyswerespray-depositedandhotextrudedat480◦Cwithanareareductionratioof6:1.Themicrostructureofthespray-depositofAl–6.5Sialloyshowedsphericalmorphologyoftheprimary␣-phasewithaglobularshapeoftheeutecticSiphaseintheinter-particleboundaries.Ontheotherhand,afineparticulatemorphologyofprimarySiphaseuniformlydispersedinthematrixofthe␣-phasewasobservedinspray-depositofAl–18Sialloy.Microstructuralrefinementwasfurtherincreasedinthehotextrudedalloys.Theroomtemperaturetensiletestsofsprayformedandextrudedalloysshowedconsiderableincreaseintheirstrengthandductilityoverthatoftheascastalloys.Theimprovementinmechanicalpropertiesofsprayformedalloysisdiscussedinlightofthemicrostructuralmodificationsinducedduringspraydepositionprocess.©2001ElsevierScienceB.V.Allrightsreserved.Keywords:Microstructure;Mechanicalproperties;Sprayformingprocess1.IntroductioninherentinspraydepositionprovideasubstantialchemicalandmicrostructuralhomogeneitytogetherwithrefinementAl–Sialloyspossesslowthermalexpansioncoefficient,ingrainsizeandsecondphaseparticlesize[4–6].highwearresistanceandhighstrengthtoweightratio.AsInthepresentinvestigation,spraydepositionprocesshasaresult,thesealloysfindextensiveapplicationsasstruc-beenemployedtoproduceadiscshapepreformofAl–6.5Situralcomponentsinautomotiveandaerospaceindustries[1].andAl–18Sialloys.Themicrostructuralfeaturesoftheal-Thesearecurrentlyproducedbycastingandpowdermet-loysandtheirrelatedmechanicalpropertiesarereported.allurgymethods.Arelativelyslowcoolingrateassociatedwithacastingprocessrenderscoarseandsegregatedmi-2.Experimentaldetailscrostructur