2024年4月21日发(作者：东依柔)
EquilibriumpseudobinaryAl±Mg
2
Siphase
diagram
,,,
Preliminaryexperimentsandphasediagramcalculationswereconductedtodeterminetheequilibriumphase
diagramoftheAl±Mg
2
oundthatthereisanarrowternaryphase®eldof
AlzMg
2
seudoeutecticcompositionofAl±13
.
9wt-%Mg
2
Si,apseudoeutectic
reactiontakesplacebetweenthetemperaturesof583
.
5and594³ubilityofMg
2
SiinAlat583
.
5³Cis
calculatedas1
.
91wt-%.MST/4537
eintheDepartmentofMaterialsEngineering,Brunel
University,UxbridgeUB83PH,gisnowintheDepartmentofMaterialsScienceandEngineering,Universityof
Erlangen,Germany(jianzhang7232@).eintheInstituteofMetal
Research,ChineseAcademyofSciences,Shenyang110015,riptreceived20December1999;accepted14
November2000.
#2001IoMCommunicationsLtd.
Introduction
InsitucompositesbasedonAl±Mg
2
SiorMg±Mg
2
Si
hypereutecticalloyshaveshownconsiderablepotential
becauseoftheirlowspeci®rostructureof
suchcompositesisgenerallyaeutecticmatrixwithprimary
Mg
2
dtherather
brittlecharacterofthematerials,advancedprocessing
techniquessuchasrapidsolidi®cation,
1,2
hotextrusion,
3,4
andmechanicalalloying
5,6
ingto
previouswork,itispossibletoembedhardMg
2
Siparticles
inaplasticallydeformablematrixinanAl±Mg
2
Si
compositewithattractivepropertiesbyusingacommon
gravitycastingprocess.
7
Therefore,itispossibletoprepare
thecompositesbyusingamethodthatismorepractical.
However,thesuccessfuldevelopmentofsuchcomposites
dependsonagoodunderstandingoftheequilibrium
diagramoftheAl±Mg
2
Sipseudobinarysystem.
Althoughthereareafewpublicationsonthepseudoeu-
tecticsectionofAlandMg
2
SiinanAl±Mg±Siternary
system,mostattentionhasbeenpaidtotheAlrichcorner.
8
Moreover,detailedinformationonthepseudobinary
system,suchasthecompositionoftheeutecticpointand
thesolubilityofMg
2
SiinAl,werenotconclusiveinthe
literature,whichissummarisedinTable1.
8±12
Almostall
ofthepreviouspublicationsalsoreportedanisothermal
eutecticlineofAlzMg
2
Siinthesystemwithaeutectic
temperatureof593±595³ile,aternaryphase
®eldinthediagramwasreportedinthetemperaturerange
590±594³Cattheeutecticpoint.
12
Therefore,itisessential
toinvestigatethepseudobinarysystemandtoclearthe
confusionintheequilibriumdiagram.
ples
wereetchedandexaminedbyopticalmicroscopyandSEM
(JeolJXA840)withanenergydispersiveX-rayanalysis
(EDS)softheexperimentalprocedureare
reportedelsewhere.
7,14
Phasediagramcalculationwasdone
usingtheThermo-CalcprogramandAlDATA,whichwas
developedbyThermoTechLtd(Guildford,UK).A
pseudobinaryphasediagramofAl±Mg
2
Siwasobtained
asaverticalsectionoftheAl±Mg±Siternarysystemata
®xedMg/Siatomicratio(2:1).
Resultsanddiscussion
Figure1comparesthemicrostructuresoftwoAl±Mg
2
Si
alloyswithdifferentMg
2
ingtoEDS
analysis,thebrightphasewasidenti®edasa-Alandthe
darkparticleswereidenti®edasMg
2
ellaMg
2
Si
wasobviouslyformedbycoupledgrowthwitha-Alasa
rcompounds
weredetectedinthepresentwork.
ThemicrostructureofAl±10wt-%Mg
2
Sialloywas
mainlycomposedofa-Aldendritesandpseudoeutecticsof
AlzMg
2
rthnotingthatsomesmallMg
2
Si
particlescanalsobeobservedinthemicrostructure,as
driticmorphologyof
a-Alindicatedthata-Alwastheprimaryphaseduring
solidi®ards,a-AlandMg
2
Sicosolidi®edasthe
2
Siparticles
hadasmallersizethantheprimaryMg
2
Siparticlesshownin
Fig.1b,andadifferentmorphologytothelamellastructures
producedbycogrowthofAlandMg
2
lievedthat
theseparticleswereformedafterthesolidi®cationofprimary
a-Aldendrites,whichmeansMg
2
SiparticlesaswellasMg
2
Si
pseudoeutecticswereproducedsimultaneouslyduringthe
pseudoeutecticreaction.
IntheAl±15wt-%Mg
2
Sialloy,bothprimaryparticlesof
Mg
2
Sianda-Alcanbeobservedbesidesthepseudoeutectic
mentalresultsshowninFig.1bindicatethat
duringsolidi®cationMg
2
Siparticlesformedasaprimary
phaseanda-Algrainsformedatasimilartimetowhenthe
pseudoeutecticreactionoccurredduringthesubsequent
solidi®-AlgrainsandMg
2
Siparticlesobserved
inFig.1bindicatethattheremaybeaphase®eldinthe
phasediagramwherea-Alandthepseudoeutecticcosolidify
fromtheliquid.
ISSN0267±0836
Experimental
IndustriallypureAl,Mg,andSi(w99
.
8wt-%)wasusedto
meltAl±Mg
2
Sicompositesof10and15wt-%Mg
2
extra
Mgadditionsweredeterminedbyseveralexperimentsand
subsequentcompositionalanalysisinordertoensurethe
resultingcompositionchangeswerewithin1wt-%ofthe
presetvalues.
13
Asaltmixturewasusedformicrostructural
re®nement.
14
C
2
Cl
6
(99
.
9%)waspressedintothemeltfor
twascastinasteelmouldandrodlike
494MaterialsScienceandTechnologyMay2001Vol.17
briumpsuedobinaryAl±Mg
2
Siphasediagram495
a
a10wt-%Mg
2
Si;b15wt-%Mg
2
Si
b
ashowing®brelikepseudoeutecticwithverysmallinter®bre
spacing;bdeepetchedsampleshowinglamellaeutecticswith
relativelylargeinterlamellcerspacing
1MicrostructureofAl±Mg
2
Sicompositeswithdifferent
Mg
2
Sicontents
Itisinterestingtonotethatinbothalloysshownin
Fig.1,thepseudoeutecticmatrixhastwodistinctmorphol-
thecellshaveaverysmallinter®brespacing
(v1mm,asshownintheSEMimageinFig.2a).Onthe
otherhand,someofthepseudoeutecticcellshaveamuch
largerinterlamellaspacing,asshowninthedeepetched
ndoffeatureisrarelyobservedin
normaleutecticsystems,oritcannotbeachievedinsucha
smallarea.(Thein¯uenceofpartialmodi®cationshouldbe
omittedasthemodi®cationtimewaslongenoughinthe
presentexperiments.)Normally,whentheeutecticreaction
occursataconstanttemperature,arelativelyuniform
®brousorlamellastructureisexpected.
15
Itiswellknown
thattheeutectic®breorlamellastructurecanbedescribed
asl
2
n~constant,
16
wherelistheinter®breorinterlamella
iationinthe
inter®breorinterlamellaspacinglshowninFig.1indicates
avaryinggrowthvelocitynintheAl±Mg
2
mayhappenbecauseacurvedinterfaceoccurredduring
solidi®cationand/orthepseudoeutecticformedovera
vedinterfacemaybecausedby
theprimarydendritesorthesegregationofimpuritiesin
r,theprimarydendriteswere
notwelldevelopedinthepresentcase,asshowninFig.1b.
2MicrographsofAl±15wt-%Mg
2
Sialloy(SEM)
Thein¯uenceofimpuritiesmayalsobededucedasaminor
factorsincenoothercompoundsweredetectedbyEDS.
Therefore,thecoexistenceofthetwodifferentmorpholo-
giesinthepseudoeutecticismainlybecauseofthedifferent
formationtemperaturesofthe®breandthelamellaeutectic.
ThismorphologicalchangecanalsobeobservedinAl±Si
eutecticsatdifferentcoolingconditions.
17
BycomparingthemicrostructuresshowninFig.1,itcan
beconcludedthatthepseudoeutecticcompositionofthe
Al±Mg
2
Sisystemisbetween10and15wt-%Mg
2
Si.
Inordertocon®rmthesepreliminaryexperimental
®ndings,phasediagramcalculationoftheternaryAl±
Mg±SisystemwasconductedusingtheThermo-
culatedpseudoeutectic
binaryAl±Mg
2
Siphasediagramasaverticalsectionofthe
xistsanarrow
ternaryphase®eld,AlzMg
2
Sizliquid,inthesystemand
thetemperaturerangeofthisternary®eldincreasedwith
increasingMg
2
Sicontentatthelefthandsideofthe
seudoeutecticcomposition
(Al±13
.
9wt-%Mg
2
Si),Al,Mg
2
Si,andliquidcoexist
Table1SummaryofinformationonAl±Mg
2
Sipseudobinarysystemavailableinliterature
Authors
Mondolfo
Mondolfo
Schmisetal.
Lietal.
Eutecticpoint
T
E
,³C
595
595
593
590±594
Eutecticcomposition,
wt-%Mg
2
Si
13
15
.
9
v10
y14
.
7
SolubilityatT
E
,
wt-%Mg
2
Si
1
.
85
1
.
85
y1
.
9
y7
.
3
Refs.
8,11
9
10
12
MaterialsScienceandTechnologyMay2001Vol.17
briumpsuedobinaryAl±Mg
2
Siphasediagram
Summary
Aternaryphase®eldofAlzMg
2
SizliquidintheAl±
Mg
2
Sipseudobinarydiagramwasdiscoveredafterthe
preliminaryexperimentsandphasediagramcalculation.
Thetemperaturerangeofthisternary®eldisbetween583
.
5
and594³Catthepseudoeutecticpoint,whichiscalculated
asAl±13
.
9wt-%Mg
2
ubilityofMg
2
SiinAlat
583
.
5³Ciscalculatedtobe1
.
91wt-%.Themicrostructureof
theeutecticmatrix,whichcontainsbothsoftandhard
particles,indicatesahopefulprospectfortheenhancement
ofthepropertiesofthecomposites.
Acknowledgements
rsforhishelpwith
thephasediagramcalculation.
Wt-%Mg
2
Si
3CalculatedequilibriumAl±Mg
2
Siphasediagram:pseu-
doeutecticpointatAl±13
.
9wt-%Mg
2
Si;temperature
rangeofternaryregionatthiscompositionbetween
583
.
5and594³C;solubilityofMg
2
SiinAlat583
.
5³Cis
1
.
91wt-%
References
i,,i:.,
1995,33,331.
i:.,1996,44,4611.
i,,i:.,1994,19,
247.
i,,i:.,1996,
31,1529.
yer,,enburg:kd.,
1994,85,372.
,,:.,1998,10,551.
,,,:.,1999,
1,68.
fo:`Metallographyofaluminiumalloys',105;
1943,London,ChapmanandHall.
fo:`Aluminiumalloy:structureandproperties',
566;1976,London,Butterworth.
,enburg,yer:Z.
Metallkd.,1990,11,809.
:in`Metalhandbook',8thedn,(),
396;1973,MaterialsPark,OH,AmericanSocietyforMetals.
,,,,sh,andr.i.
barabash:,1997,38,553.
:PhDDissertation,InstituteofMetalResearch,
ChineseAcademyofSciences,Shenyang,China,1999.
,,,:.,
1999,18,783.
,,:.,1998,33,
5205.
ter:ActaMetall.,1980,28,1489.
ell:JOM,1995,47,(2),38.
between583
.
5and594³ubilityofMg
2
SiinAlis
calculatedas1
.
91wt-%at583
.
5³C.
Theexactsolidi®cationpathofAl±Mg
2
Sialloyscanbe
obtainedfromtheexperimentalresultsandthecalculated
alloyscanbeidenti®edas
hypoeutiectic(Al±10wt-%Mg
2
Si)andhypereutectic(Al±
15wt-%Mg
2
Si),ore,eithera-AlinAl±
10wt-%Mg
2
SialloyorMg
2
SiinAl±15wt-%Mg
2
Sialloy
willformastheprimaryphaseduringsolidi®
pseudoeutecticreactionbeginswhenthetemperatureofthe
surplusliquidreachestheupperlineoftheternaryphase
®ofa-Alformintheternary
®eldaswellasAlzMg
2
±
10wt-%Mg
2
Sialloy,thea-Algrainsformedinthisphase
®eldaredif®culttodistinguishfromtheprimarydendrites,
whichresultedintheconsiderablylargevolumefractionof
hecompositionofAl±
15wt-%Mg
2
Siisnearertothepseudoeutecticpoint,
theactualmicrostructurecontainedahighervolume
fractionofpseudoeutecticAlzMg
2
SicomparedwithAl±
10wt-%Mg
2
Si.
MaterialsScienceandTechnologyMay2001Vol.17
2024年4月21日发(作者：东依柔)
EquilibriumpseudobinaryAl±Mg
2
Siphase
diagram
,,,
Preliminaryexperimentsandphasediagramcalculationswereconductedtodeterminetheequilibriumphase
diagramoftheAl±Mg
2
oundthatthereisanarrowternaryphase®eldof
AlzMg
2
seudoeutecticcompositionofAl±13
.
9wt-%Mg
2
Si,apseudoeutectic
reactiontakesplacebetweenthetemperaturesof583
.
5and594³ubilityofMg
2
SiinAlat583
.
5³Cis
calculatedas1
.
91wt-%.MST/4537
eintheDepartmentofMaterialsEngineering,Brunel
University,UxbridgeUB83PH,gisnowintheDepartmentofMaterialsScienceandEngineering,Universityof
Erlangen,Germany(jianzhang7232@).eintheInstituteofMetal
Research,ChineseAcademyofSciences,Shenyang110015,riptreceived20December1999;accepted14
November2000.
#2001IoMCommunicationsLtd.
Introduction
InsitucompositesbasedonAl±Mg
2
SiorMg±Mg
2
Si
hypereutecticalloyshaveshownconsiderablepotential
becauseoftheirlowspeci®rostructureof
suchcompositesisgenerallyaeutecticmatrixwithprimary
Mg
2
dtherather
brittlecharacterofthematerials,advancedprocessing
techniquessuchasrapidsolidi®cation,
1,2
hotextrusion,
3,4
andmechanicalalloying
5,6
ingto
previouswork,itispossibletoembedhardMg
2
Siparticles
inaplasticallydeformablematrixinanAl±Mg
2
Si
compositewithattractivepropertiesbyusingacommon
gravitycastingprocess.
7
Therefore,itispossibletoprepare
thecompositesbyusingamethodthatismorepractical.
However,thesuccessfuldevelopmentofsuchcomposites
dependsonagoodunderstandingoftheequilibrium
diagramoftheAl±Mg
2
Sipseudobinarysystem.
Althoughthereareafewpublicationsonthepseudoeu-
tecticsectionofAlandMg
2
SiinanAl±Mg±Siternary
system,mostattentionhasbeenpaidtotheAlrichcorner.
8
Moreover,detailedinformationonthepseudobinary
system,suchasthecompositionoftheeutecticpointand
thesolubilityofMg
2
SiinAl,werenotconclusiveinthe
literature,whichissummarisedinTable1.
8±12
Almostall
ofthepreviouspublicationsalsoreportedanisothermal
eutecticlineofAlzMg
2
Siinthesystemwithaeutectic
temperatureof593±595³ile,aternaryphase
®eldinthediagramwasreportedinthetemperaturerange
590±594³Cattheeutecticpoint.
12
Therefore,itisessential
toinvestigatethepseudobinarysystemandtoclearthe
confusionintheequilibriumdiagram.
ples
wereetchedandexaminedbyopticalmicroscopyandSEM
(JeolJXA840)withanenergydispersiveX-rayanalysis
(EDS)softheexperimentalprocedureare
reportedelsewhere.
7,14
Phasediagramcalculationwasdone
usingtheThermo-CalcprogramandAlDATA,whichwas
developedbyThermoTechLtd(Guildford,UK).A
pseudobinaryphasediagramofAl±Mg
2
Siwasobtained
asaverticalsectionoftheAl±Mg±Siternarysystemata
®xedMg/Siatomicratio(2:1).
Resultsanddiscussion
Figure1comparesthemicrostructuresoftwoAl±Mg
2
Si
alloyswithdifferentMg
2
ingtoEDS
analysis,thebrightphasewasidenti®edasa-Alandthe
darkparticleswereidenti®edasMg
2
ellaMg
2
Si
wasobviouslyformedbycoupledgrowthwitha-Alasa
rcompounds
weredetectedinthepresentwork.
ThemicrostructureofAl±10wt-%Mg
2
Sialloywas
mainlycomposedofa-Aldendritesandpseudoeutecticsof
AlzMg
2
rthnotingthatsomesmallMg
2
Si
particlescanalsobeobservedinthemicrostructure,as
driticmorphologyof
a-Alindicatedthata-Alwastheprimaryphaseduring
solidi®ards,a-AlandMg
2
Sicosolidi®edasthe
2
Siparticles
hadasmallersizethantheprimaryMg
2
Siparticlesshownin
Fig.1b,andadifferentmorphologytothelamellastructures
producedbycogrowthofAlandMg
2
lievedthat
theseparticleswereformedafterthesolidi®cationofprimary
a-Aldendrites,whichmeansMg
2
SiparticlesaswellasMg
2
Si
pseudoeutecticswereproducedsimultaneouslyduringthe
pseudoeutecticreaction.
IntheAl±15wt-%Mg
2
Sialloy,bothprimaryparticlesof
Mg
2
Sianda-Alcanbeobservedbesidesthepseudoeutectic
mentalresultsshowninFig.1bindicatethat
duringsolidi®cationMg
2
Siparticlesformedasaprimary
phaseanda-Algrainsformedatasimilartimetowhenthe
pseudoeutecticreactionoccurredduringthesubsequent
solidi®-AlgrainsandMg
2
Siparticlesobserved
inFig.1bindicatethattheremaybeaphase®eldinthe
phasediagramwherea-Alandthepseudoeutecticcosolidify
fromtheliquid.
ISSN0267±0836
Experimental
IndustriallypureAl,Mg,andSi(w99
.
8wt-%)wasusedto
meltAl±Mg
2
Sicompositesof10and15wt-%Mg
2
extra
Mgadditionsweredeterminedbyseveralexperimentsand
subsequentcompositionalanalysisinordertoensurethe
resultingcompositionchangeswerewithin1wt-%ofthe
presetvalues.
13
Asaltmixturewasusedformicrostructural
re®nement.
14
C
2
Cl
6
(99
.
9%)waspressedintothemeltfor
twascastinasteelmouldandrodlike
494MaterialsScienceandTechnologyMay2001Vol.17
briumpsuedobinaryAl±Mg
2
Siphasediagram495
a
a10wt-%Mg
2
Si;b15wt-%Mg
2
Si
b
ashowing®brelikepseudoeutecticwithverysmallinter®bre
spacing;bdeepetchedsampleshowinglamellaeutecticswith
relativelylargeinterlamellcerspacing
1MicrostructureofAl±Mg
2
Sicompositeswithdifferent
Mg
2
Sicontents
Itisinterestingtonotethatinbothalloysshownin
Fig.1,thepseudoeutecticmatrixhastwodistinctmorphol-
thecellshaveaverysmallinter®brespacing
(v1mm,asshownintheSEMimageinFig.2a).Onthe
otherhand,someofthepseudoeutecticcellshaveamuch
largerinterlamellaspacing,asshowninthedeepetched
ndoffeatureisrarelyobservedin
normaleutecticsystems,oritcannotbeachievedinsucha
smallarea.(Thein¯uenceofpartialmodi®cationshouldbe
omittedasthemodi®cationtimewaslongenoughinthe
presentexperiments.)Normally,whentheeutecticreaction
occursataconstanttemperature,arelativelyuniform
®brousorlamellastructureisexpected.
15
Itiswellknown
thattheeutectic®breorlamellastructurecanbedescribed
asl
2
n~constant,
16
wherelistheinter®breorinterlamella
iationinthe
inter®breorinterlamellaspacinglshowninFig.1indicates
avaryinggrowthvelocitynintheAl±Mg
2
mayhappenbecauseacurvedinterfaceoccurredduring
solidi®cationand/orthepseudoeutecticformedovera
vedinterfacemaybecausedby
theprimarydendritesorthesegregationofimpuritiesin
r,theprimarydendriteswere
notwelldevelopedinthepresentcase,asshowninFig.1b.
2MicrographsofAl±15wt-%Mg
2
Sialloy(SEM)
Thein¯uenceofimpuritiesmayalsobededucedasaminor
factorsincenoothercompoundsweredetectedbyEDS.
Therefore,thecoexistenceofthetwodifferentmorpholo-
giesinthepseudoeutecticismainlybecauseofthedifferent
formationtemperaturesofthe®breandthelamellaeutectic.
ThismorphologicalchangecanalsobeobservedinAl±Si
eutecticsatdifferentcoolingconditions.
17
BycomparingthemicrostructuresshowninFig.1,itcan
beconcludedthatthepseudoeutecticcompositionofthe
Al±Mg
2
Sisystemisbetween10and15wt-%Mg
2
Si.
Inordertocon®rmthesepreliminaryexperimental
®ndings,phasediagramcalculationoftheternaryAl±
Mg±SisystemwasconductedusingtheThermo-
culatedpseudoeutectic
binaryAl±Mg
2
Siphasediagramasaverticalsectionofthe
xistsanarrow
ternaryphase®eld,AlzMg
2
Sizliquid,inthesystemand
thetemperaturerangeofthisternary®eldincreasedwith
increasingMg
2
Sicontentatthelefthandsideofthe
seudoeutecticcomposition
(Al±13
.
9wt-%Mg
2
Si),Al,Mg
2
Si,andliquidcoexist
Table1SummaryofinformationonAl±Mg
2
Sipseudobinarysystemavailableinliterature
Authors
Mondolfo
Mondolfo
Schmisetal.
Lietal.
Eutecticpoint
T
E
,³C
595
595
593
590±594
Eutecticcomposition,
wt-%Mg
2
Si
13
15
.
9
v10
y14
.
7
SolubilityatT
E
,
wt-%Mg
2
Si
1
.
85
1
.
85
y1
.
9
y7
.
3
Refs.
8,11
9
10
12
MaterialsScienceandTechnologyMay2001Vol.17
briumpsuedobinaryAl±Mg
2
Siphasediagram
Summary
Aternaryphase®eldofAlzMg
2
SizliquidintheAl±
Mg
2
Sipseudobinarydiagramwasdiscoveredafterthe
preliminaryexperimentsandphasediagramcalculation.
Thetemperaturerangeofthisternary®eldisbetween583
.
5
and594³Catthepseudoeutecticpoint,whichiscalculated
asAl±13
.
9wt-%Mg
2
ubilityofMg
2
SiinAlat
583
.
5³Ciscalculatedtobe1
.
91wt-%.Themicrostructureof
theeutecticmatrix,whichcontainsbothsoftandhard
particles,indicatesahopefulprospectfortheenhancement
ofthepropertiesofthecomposites.
Acknowledgements
rsforhishelpwith
thephasediagramcalculation.
Wt-%Mg
2
Si
3CalculatedequilibriumAl±Mg
2
Siphasediagram:pseu-
doeutecticpointatAl±13
.
9wt-%Mg
2
Si;temperature
rangeofternaryregionatthiscompositionbetween
583
.
5and594³C;solubilityofMg
2
SiinAlat583
.
5³Cis
1
.
91wt-%
References
i,,i:.,
1995,33,331.
i:.,1996,44,4611.
i,,i:.,1994,19,
247.
i,,i:.,1996,
31,1529.
yer,,enburg:kd.,
1994,85,372.
,,:.,1998,10,551.
,,,:.,1999,
1,68.
fo:`Metallographyofaluminiumalloys',105;
1943,London,ChapmanandHall.
fo:`Aluminiumalloy:structureandproperties',
566;1976,London,Butterworth.
,enburg,yer:Z.
Metallkd.,1990,11,809.
:in`Metalhandbook',8thedn,(),
396;1973,MaterialsPark,OH,AmericanSocietyforMetals.
,,,,sh,andr.i.
barabash:,1997,38,553.
:PhDDissertation,InstituteofMetalResearch,
ChineseAcademyofSciences,Shenyang,China,1999.
,,,:.,
1999,18,783.
,,:.,1998,33,
5205.
ter:ActaMetall.,1980,28,1489.
ell:JOM,1995,47,(2),38.
between583
.
5and594³ubilityofMg
2
SiinAlis
calculatedas1
.
91wt-%at583
.
5³C.
Theexactsolidi®cationpathofAl±Mg
2
Sialloyscanbe
obtainedfromtheexperimentalresultsandthecalculated
alloyscanbeidenti®edas
hypoeutiectic(Al±10wt-%Mg
2
Si)andhypereutectic(Al±
15wt-%Mg
2
Si),ore,eithera-AlinAl±
10wt-%Mg
2
SialloyorMg
2
SiinAl±15wt-%Mg
2
Sialloy
willformastheprimaryphaseduringsolidi®
pseudoeutecticreactionbeginswhenthetemperatureofthe
surplusliquidreachestheupperlineoftheternaryphase
®ofa-Alformintheternary
®eldaswellasAlzMg
2
±
10wt-%Mg
2
Sialloy,thea-Algrainsformedinthisphase
®eldaredif®culttodistinguishfromtheprimarydendrites,
whichresultedintheconsiderablylargevolumefractionof
hecompositionofAl±
15wt-%Mg
2
Siisnearertothepseudoeutecticpoint,
theactualmicrostructurecontainedahighervolume
fractionofpseudoeutecticAlzMg
2
SicomparedwithAl±
10wt-%Mg
2
Si.
MaterialsScienceandTechnologyMay2001Vol.17