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j ournal of materi als processi ngtechnology 2 0 9 ( 2 0 0 9 ) 37903797j our nal homepage: www. el sevi er . com/ l ocat e/ j mat pr ot ecEffects of squeeze casting parameters on the microstructureof LM13 alloyA. Maleki, A. Shafyei, B. NiroumandDepartment of Materials Engineering, Isfahan University of Technology, Isfahan 84156-83111, Iranarti cle i nfoArticle history:Received 24 August 2007Received in revised form27 July 2008Accepted 30 August 2008Keywords:Squeeze castingSolidicationPressureMicrostructureModicationabstractEffects of applied pressure and melt and die temperatures on the microstructure of squeezecastLM13alloywereexamined. Theresultsshowedthatapplicationofpressureduringsolidication decreased the grain size and SDAS of the primary phase and modied theeutecticsiliconparticles. Withapplicationofanexternalpressureofabout100MPa, theaverage SDAS and the average aspect ratio of eutectic silicon particles were reduced from47mand5toabout34mand1.5, respectively. SDASoftheprimaryphaseandtheaverage aspect ratio of eutectic silicon particles decreased slightly with a drop in the meltor die temperatures, reaching to 32m and 1.25, respectively, for the best conditions. 2008 Elsevier B.V. All rights reserved.1. IntroductionUse of aluminum components has increased during the lastdecade partly due to the light weight requirements of trans-portation systems. This would in turn lead to reduced energyconsumption and better environmental protection. Alloys ofAlSiMgNiCufamilyareparticularlyfoundtogivegoodresults for such purposes due to their excellent casting char-acteristicsandmechanicalproperties(AbouEl-Khair, 2005).Solidicationrate (Tiryakiogluet al., 2000), microas wellasmacrostructure, morphologyof eutecticsiliconparticles(Pedersen and Arnberg, 2001), structural integrity and poros-itycontent(VijianandArunachalam, 2006)aresomeoftheparameterswhichhavebeenfoundtoaffectthemechani-cal properties and performance of the castings made of thesealloys.Squeezecastingisamoderncastingprocesswhichhasbeenshowntoimproveall theaforementionedparametersCorresponding author.E-mail address: [email protected] (B. Niroumand).if utilized conscientiously. Inthis process, whichcanberegardedasacombinationofcastingandforgingprocesses(GhomashchiandVikhrov, 2000), ahighpressureisappliedand held on the melt during solidication (Franklin and Das,1984). The inuences of solidication under pressure on theproperties of the castings have beensubject of researchduringlastfourdecades(Chattopadhyay,2007).Differentinvestiga-tionslikethoseofVijianandArunachalam(2005,2006)andYu et al. (2007) on a number of alloy systems have shown thatapplication of pressure during solidication of molten metalschanges the melting point of the alloys, increases the solidi-cation rate, renes the micro as well as the macrostructureand reduces the gas and shrinkage porosities of the castings.High integrity of the squeeze cast components after their heattreatment further improves their mechanical properties (Yueand Chadwick, 1989).These attributes have made squeeze casting a pro-cess capable of producing high-quality components for0924-0136/$ see front matter 2008 Elsevier B.V. All rights reserved.doi:10.1016/j.jmatprotec.2008.08.035j ournal of materi als processi ngtechnology 2 0 9 ( 2 0 0 9 ) 37903797 3791weight-critical applications such as those in automobile man-ufacturing industries.The applied pressure intensity, the melt temperature andthe die preheating temperature have been shown to be amongthe most important squeeze casting parameters affecting themacro as well as the microstructure and mechanical proper-ties of the squeeze cast components (Vijianand Arunachalam,2007). Effects of these parameters on density, macrostructureandhardnessof LM13alloyhavebeenreportedelsewhere(Maleki et al., 2006). However, this paper focuses onthemicrostructure of squeeze cast LM13 alloy andinvestigates theeffects of these casting parameters on the cast structure of thealloy in a limited scale.2. Experimental procedureLM13 alloy is an aluminiumalloy widely used in production ofautomotive pistons and other automobile parts. The standardrange of chemical composition of LM13 alloy (The associationof light alloys reners, 1983) and the actual chemical compo-sition of the alloy employed in this study is shown in Table 1.Themeltwaspreparedinanelectricmufefurnaceandpouredintoapreheatedcylindricaldieofinnerdiameterof50mm and height of 100mm. Pressure was applied by meansof a 100tonnes hydraulic press and held until the end of solid-ication. Table 2 shows the experimental conditions used forsqueeze casting of the samples.Microstructuralinvestigationswerecarriedoutfollowingstandard metallography procedures and using image analysistechniques ona transverse sectioncut 3cmfromthe bottomofthe samples. Microstructural measurements included averagesecondarydendritearmspacing(SDAS) andaverageaspectratioof eutecticsiliconparticles. TheSDASwasmeasuredaccording to ASTM Standard E112 (2004).3. Results and discussion3.1. Effect of pressureFig. 1 shows the microstructures of samples solidied under 0,20, 53, 106, 171 and 211MPa external applied pressures with amelt and die temperature of 730 and 200C, respectively. Themain two constituents in the microstructure of each sampleinclude a primary (Al rich) phase seenas light dendritic areasand an eutectic matrix of phase and silicon particles seen asdarker areas in the micrographs. Closer looks at the eutecticregions of the samples are shown in Fig. 2 where the changesin the morphology of eutectic silicon particles by increasingthe applied pressure can be easily recognized.Table 2 Experimental conditions used for squeezecasting of the samplesFixedparametersVariableparameterPressure, P (MPa) Tm =730 P=0, 20, 53,106, 171, 211Td =200Melt temperature, Tm (C) P=171 Tm =630,680, 730, 780Td =200Die temperature, Td (C) P=171 Td =150, 200,250, 300Tm =730Applicationof pressure during solidicationhas resultedinthe following changes in the microstructure of the samples:3.1.1. Change in the grain size and the secondary dendritearm spacing (SDAS)It is evident fromthemicrostructures presentedinFig. 1that applied pressure causes a decrease in the grain size andthe secondary dendrite arm spacing (SDAS) of the primaryphase.A few points need to be considered in this regard. The rstpointisthesuddenincreaseinthecoolingratecausedbythe improved contact between the metal and the die surface(Ghomashchi and Vikhrov, 2000). The second point is that themelting point (liquidus temperature) of most metals andalloysincreases under pressure according toClausiusClapeyronequation(FranklinandDas, 1984). Accordingtothisequa-tion the increase in the melting point of LM13 alloy is about5.1102 C/MPa. Therefore, undertheexperimentalcondi-tions used in this study, the melting point of the alloy may beincreased by more than 10C upon application of the externalpressure. This characteristic can be utilized to create a sud-den large under cooling in the melt if the melt temperatureand timing of pressure application are accurately controlled.Infactthelargestmeltundercoolingwouldbeachievedifthe pressure were applied when the melt temperature in thediewaslowerthanitsliquidustemperatureandjustabovethe temperature required for swift exponential increase in thenucleation rate (for example about 0.98 of the melting pointof the alloy). Higher cooling rate, especially if coupled with apromptlargeundercoolingasmentionedabove, cancausesignicant renement inthestructureof thesqueezecastsamples.It is noteworthy that the grainsize and SDAS of the squeezecast samplesarecomparablewiththoseof conventionallyinoculatedandcastmicrostructures. Infact, thermal grainrenement induced by squeeze casting balances the chemi-cal grain renement due to inoculation treatment. Besides itseconomical benet such as no need to add inoculants in theTable 1 Chemical composition of LM13 alloyElement Cu Mg Si Fe Mn Ni Zn Pb Sn Ti AlBS 1490LM13 standard (wt%) 0.71.5 0.81.5 1013