j ournal of materi als processi ngtechnology 2 0 9 ( 2 0 0 9 )
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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
