Materials Transactions, Vol. 44, No. 5 (2003) pp. 845 to 852
Special Issue on Solidification Science and Processing for Advanced Materials
#2003 The Japan Institute of Metals
Influence of Copper and Iron on Solidification Characteristics
of 356 and 380-Type Aluminum Alloys
Piyada Suwanpinij1 , Usanee Kitkamthorn2 , Ittipon Diewwanit1 and Takateru Umeda1
1
Department of Metallurgical Engineering, Faculty of Engineering, Chulalongkorn University,
Phayathai Road, Pathumwan, Bangkok, 10330 Thailand
2
School of Metallurgical Engineering, Institute of Engineering, Suranaree University of Technology, Nakorn Rachsima, Thailand 30000
The influence of copper and iron on the solidification characteristics of two major aluminum foundry alloys was investigated. The thermal
history during solidification of each sample was recorded and compared with the solidification path calculated from the multicomponent
equilibrium and Gulliver-Scheil solidification models. SEM/EDX analysis and optical microscope were used to examine the microstructure of
solidified samples. The amount of phases was also calculated from the latter model and compared with the observed microstructure. Binary
interaction parameters were used in calculation for their practicality. Results show that the high content of copper and iron suppresses the
liquiduses and final solidification temperatures. Moreover, the crystallization of Al2 Cu and Al5 FeSi is very sensitive to copper and iron content
respectively; Al2 Cu increases significantly when copper is added while Al5 FeSi does greatly when iron content is higher.
(Received November 21, 2002; Accepted March 7, 2003)
Keywords: aluminum foundry alloy, solidification, solidification microstructure, intermetallic compound, solidification path prediction
1.
Introduction
Commercial aluminum alloys contain several alloying
elements and impurities. Some of these elements are able to
form complex intermetallic compounds during solidification
while others may just dissolve in the aluminum or precipitate
from the solid solution as separate phases. The amount and
morphology of these intermetallic compounds are highly
crucial to the mechanical properties of castings. Some of
them may be prevented from crystallization by controlling
the amount of the alloying elements which are the main
components of the compound. However, this may not be the
solution for all cases because most of these compounds are
complex having more than two sublattices with possibility of
replacing some elements in the lattices with others.
Studies in the past attempted to identify the compositions
and crystallographic structures of these intermetallics in
order to understand their crystallization sequences during
solidification.1,2) It is important for making a proper alloy
design to study on the solidification paths. If the crystallization sequences are known, the crystallization of undesirable intermetallics can be prevented.
The microstructure of 356-type aluminum foundry alloy
consists of the common dendritic network of aluminum solid
solution with interdendritic silicon and intermetallic compounds. Major intermetallics in this type are Al5 FeSi, Mg2 Si
and Al8 FeMg3 Si6 . Table 1 lists the solid phases in A356.1
aluminum alloy which solidifies at cooling rate between 0.2
and 5 Ks1 .3–14) Because of the limited diffusion during
solidification and the kinetics of nucleation and growth, the
amount and presence of some phases depend on the cooling
rate. Despite all these, the microstructure of 356-type alloy is
relatively not so complicated as that of other alloys with
higher content of alloying elements.
The properties of another aluminum alloy, 380-type alloy,
are highly dependent on the size and shape of intermetallics.
This is because the Aluminum Association (AA) Standard
allows higher content of iron and manganese in such alloy.
Table 1 Phases observed in A356.1 alloys solidified at cooling rate
between 0.2 and 5 Ks1 .
Cooling rate (K/s)
Phase
Temperature (K)
Aluminum FCC
885–883
0.2
Al15 (Fe,Mn)3 Si2
867–844
Al5 FeSi
842–841
Mg2 Si
826–812
Aluminum FCC
886–881
0.6
5.0
Al15 (Fe,Mn)3 Si2
865–843
Al5 FeSi
836–834
Mg2 Si
825–815
Aluminum FCC
887–884
Al15 (Fe, Mn)3 Si2
863–847
Al5 FeSi
838–835
Mg2 Si
821–814
Al8 FeMg3 Si6
814–778
These two elements can form several intermetallic phases
having plate-like or needle-shaped morphology. The sharp
edges of these phases give detrimental effect to castings by
debasing their strength. Among important intermetallics are
Al15 (Fe,Mn)3 Si2 and Al5 FeSi with the possibility of chromium, copper, and manganese replacing iron atoms in the
iron sublattice. Others are Al2 Cu and Al5 Cu2 Mg8 Si6 . The
amount of these intermetallics and the temperatures at which
they crystallize depend on cooling rate and alloy composition.15,16)
In this study, a thermodynamic phase equilibrium calculation software Thermo-Calc and a thermodynamic database
intended for the calculation of aluminum systems were used
to analyze the solidification paths of 356-type and 380-type
alloys. Binary interaction parameters instead of higher order
interaction parameters were used in the calculation in spite of
multicomponent alloys. To predict the solidification paths of
these alloys accurately, ternary and higher order interaction
parameters are essential. However, very little data are
available in the present and, even in the future, higher order
846
P. Suwanpinij, U. Kitkamthorn, I. Diewwanit and T. Umeda
interaction parameters may not be expected to be well
compiled. Therefore, binary interaction parameters are
expected to be far-reaching and adequately applied in
multicomponent alloy system calculation. The tools mentioned above were firstly applied to the effects of copper and
iron on the microstructure of these two alloys. Such
thermodynamic prediction was then compared to the observed microstructure. Secondly, the amount of two intermetallics, Al5 FeSi and Al8 FeMg3 Si6 , in A356 was discussed
by varying the content of iron, silicon and magnesium within
the composition range of the specification of A356.
2.
Experiment and Thermodynamic Modeling
Six 45-gram-weight samples were cut from commercial
alloy ingots and placed in graphite crucibles with dimension
shown in Fig. 1. A K-type thermocouple was placed in the
wall of each crucible 1.5 mm away from the molten alloy.
Melting operation was done in a resistance furnace filled with
inert argon gas. The melting/alloying temperatures for
reference samples 1 and 4, copper-added samples 2 and 5,
and iron-added samples 3 and 6 were 1023, 1123 and 1223 K
respectively. The chemical compositions of samples were
determined by spark emission spectrometer and were listed in
1.5
Table 2.17) All samples were allowed to cool and solidify in
the furnace while their temperatures were monitored by the
thermocouples connected to a data acquisition unit. At the
beginning, the thermocouple was calibrated to allow error
within 1 K. The average cooling rate for all samples was
0.07 Ks1 . Solidified samples were sectioned and prepared
for optical and scanning electron microscope (SEM) observation. Phases were determined by EDX.
The thermodynamic analysis of solidification was done by
Thermo-Calc version M and aluminum database version 2.
Gibbs free energy calculation by this software was based on
the Redlich-Kister equation18)
X
X
Gm ¼
xi Gi þ RT
xi ln xi
i
þ
i
xi xj
j>i
vij ðxi xj Þv ;
v
is a binary interaction parameter. The modeling of
where
silicon phase is based on pure substance with no solubility of
any element in the silicon phase. Details on the calculation
method were referred in19,20) while interaction parameters,
and other thermodynamic properties in the database were
referred in the Thermo-Calc’s User Guide.
In addition to the equilibrium solidification model, the
Gulliver-Scheil solidification model, on the assumption of no
diffusion in solid and complete mixing in liquid, was mostly
used in calculation. The calculation was based on the
following equation;
Cs ¼ kC0 ð1 fs Þðk1Þ
8
Graphite Cover
5
24
Sample
30
Graphite Crucible
8
3.
45
3.1 Solidification of 380-type Alloys
The variation of calculated fraction solid with temperature
in sample 2 is shown in Fig. 2. The calculated values from
Schematic drawing of the graphite crucible.
Sample
where k is equilibrium partition ratio. The content of nine
alloying elements: silicon, copper, iron, manganese, magnesium, chromium, zinc, nickel, and titanium was input as
variables. Afterwards, the calculation was performed to
determine the phases crystallized and their amount as well as
crystallization temperatures at each temperature interval of
0.5 K. The effects of copper and iron were also investigated
by stepping corresponding content of such elements. Moreover, as a guide to control the amount of detrimental phases
in A356 alloy, the variations of Al5 FeSi and Al8 FeMg3 Si6
with some alloying elements were calculated by the GulliverScheil model.
30
Table 2
Alloy
i
X
vij
TC
Fig. 1
XX
Condition
Results and Discussion
Chemical composition (mass percent) of the samples in this study.
Si
Cu
Mg
Fe
Mn
Zn
Ni
Ti
Cr
number
380
356
1
Reference
8.21
2.37
0.03
1.01
0.13
0.08
0.05
0.05
0.03
2
Cu-added
7.87
4.62
0.29
1.01
0.13
0.86
0.05
0.04
0.03
3
Fe-added
7.96
2.41
0.29
1.32
0.11
0.88
0.05
0.05
0.03
4
Reference
7.23
0.02
0.48
0.16
0.002
<0:001
0.003
0.14
0.003
5
Cu-added
6.29
0.17
0.40
0.07
0.004
<0:001
0.001
0.13
0.002
6
Fe-added
6.43
0.01
0.47
0.99
0.006
0.017
<0:001
0.13
0.002
Influence of Copper and Iron on Solidification Characteristics of 356 and 380-Type Aluminum Alloys
847
1000
Gulliver-Scheil fraction solid
880
aluminum FCC
equilibrium fraction solid
950
Temperature, T/K
Temperature, T/K
860
840
silicon
820
800
Solidification
completes (equilibrium)
780
Al15(Fe,Mn)3Si2 starts
Aluminum FCC starts
Al FeSi starts
5
Silicon starts
900
850
800
750
Solidification completes (Scheil)
760
0.2
0.0
0.4
0.6
0.8
700
10000
1.0
Fraction Solid
Temperature, T/K
900
Al (Fe,Mn) Si
15
3 2
aluminum FCC
Al FeSi
5
silicon
800
Al Cu
2
Al5Cu2Mg8Si6
Solidification
completes
750
700
2000
2500
3000
3500
4000
20000
25000
30000
Enthalpy of the Whole System, J/mol
Fig. 2 Calculated weight fraction versus temperature of sample number 2
(Cu-added 380-type alloy).
850
15000
4500
5000
Elapsed Time, t/s
Fig. 3 The observed cooling curve of sample 2 (Cu-added 380-type alloy)
with arrows indicating the calculated crystallization temperatures from the
Gulliver-Scheil model.
both the equilibrium and Gulliver-Scheil solidification
models are almost identical except the temperatures at which
solidification completes. Table 3 and Fig. 3 show the
calculated crystallization temperatures of major phases in
Fig. 4
The enthalpy change of the whole alloy system in sample 2.
the same sample by the Gulliver-Scheil model and compare
them with the experimental results. Due to the limit of
sensitivity in the measurement, only three temperatures, at
which relatively large enthalpy changes occur, could be
detected; they are the temperatures at which aluminum FCC
and silicon start to crystallize and the solidification completes. When Al15 (Fe,Mn)3 Si2 crystallized, abrupt change
could not be detected in the cooling curve, corresponding to
the small enthalpy change as shown in Fig. 4.
Discrepancies between the observed and calculated temperatures for the crystallization of aluminum FCC appear in
Fig. 3. The aluminum FCC crystallized starts to crystallize at
849 K which is 14 K lower than the calculated value. Such
inaccuracy other than the undercooling occurs from that the
thermocouples were not placed in molten alloys but in the
walls of crucibles. The other source of inaccuracy might be
attributed to the Gibbs free energy of the liquid and
aluminum FCC phases. The inaccuracy of the Gibbs free
energy is due to the scarcity of reliable experimental data on
higher order interaction parameters. The present thermodynamic was based on binary interaction parameters only.
Because of the high concentration of solutes in 380 alloy,
contribution from these higher order interactions leads to the
error in the calculated Gibbs free energy of the liquid and
Table 3 Solidification sequence of sample 2 (Cu-added 380-type alloy) and weight percentage of each phase at complete solidification
temperature.
Phase
Calculated
Observed
Crystallization
temperature (K)
Amount
(mass%)
Al15 (Fe,Mn)3 Si2
881.6
1.12
Aluminum FCC
863.1
82.83
Al5 FeSi
857.7
2.90
Silicon
835.0
6.06
Al7 Cu2 Fe
792.6
negligible
N
Al7 Cu4 Ni
786.9
negligible
N
Al2 Cu
784.7
4.94
Y
Al5 Cu2 Mg8 Si6
778.2
0.54
Y
Solidification completed
764.7
Y: Observed in solidification microstructure
N: Not observed in solidification microstructure
Crystallization
temperature (K)
Microstructure
Y
849.0
Y
Y
833.7
Y
P. Suwanpinij, U. Kitkamthorn, I. Diewwanit and T. Umeda
Calculated Temperature from Scheil Model, T/K
848
900
890
880
y=x
fcc aluminum
870
860
850
840
silicon
830
820
820
830
840
850
860
870
880
890
900
Observed Temperature, T/K
Fig. 5 Comparison between the calculated temperatures from the GulliverScheil model and the observed temperatures of aluminum FCC and silicon
in 380-type from various literatures.
aluminum FCC phases. However, binary interaction parameters are practical while the higher order ones derive from
laborious work and consumed time.
The observed crystallization temperatures of aluminum
FCC and silicon from other literatures3–16,20–22) were
collected and compared with the calculated thermodynamic
results of which chemical compositions were input. Compared in Fig. 5, almost all the calculated temperatures for
aluminum FCC are higher than the observed ones not more
than 15 degree. However, the calculated temperatures for
silicon deviate from the observed temperatures 5 degree,
corresponding to this study.
The microstructure of solidified 380-type alloys (sample 1,
2, and 3) contains aluminum FCC, silicon, Al15 (Fe,Mn)3 Si2 ,
Al5 FeSi, Al2 Cu, and Al5 Cu2 Mg8 Si6 . The quantity of phases
in sample 2 was also calculated and is compared with the
detection by SEM with EDX analysis in Table 3. Al7 Cu2 Fe
and Al7 Cu4 Ni, which were predicted to have negligible
amount, could not be detected in the solidified microstructure. The electron micrographs of sample 2 are shown in
Fig. 6. The Al15 (Fe,Mn)3 Si2 phase (usually called the alpha
phase) crystallizes in two different morphologies: dense
idiomorphic and Chinese script as in Figs. 6(a) and (b)
respectively. The former is the primary phase that crystallizes
and normally termed ‘‘sludge’’. Certain sedimentation of the
sludge Al15 (Fe,Mn)3 Si2 phase was found in all samples in
380 series due to the slow cooling rate used in this study. The
Al5 FeSi phase (usually called the beta phase) appears as
platelets or needles which are very distinct (Fig. 6(c)). The
eutectic phase Al2 Cu seems agglomerated pink bubbles (Fig.
6(c)).
For sample 3, the variations of the predicted amount of
intermetallics and calculated crystallization temperature of
major phases with copper are revealed in Figs. 7(a) and (b)
respectively. The quantity of Al2 Cu increases greatly with
Fig. 6 Electron micrographs of sample number 2 (Cu-added 380-type
alloy); 6(a): Al15 (Fe,Mn)3 Si2 which appears in dense idiomorphic, 6(b):
Al15 (Fe,Mn)3 Si2 in Chinese script morphology, 6(c): Al15 FeSi in needle
shape and bubble-like Al2 Cu.
copper content while others varies slightly. The crystallization temperatures of aluminum FCC (liquidus temperature) and silicon decline moderately with copper content
while those of Al15 (Fe,Mn)3 Si2 and Al5 FeSi remain almost
constant. The crystallization temperature of Al5 Cu2 Mg8 Si6
goes down significantly at copper content 1.0–3.0 mass% and
decreases slightly at 3.0–6.5 mass%. In the range of 0.0 to
1.0 mass% of copper, the final solidification temperature
decreases significantly and then rises up to some degree and
decreases slightly.
In the same sample, the relationships between the
predicted amount of intermetallics and calculated crystallization temperatures of major phases with iron are shown in
Figs. 8(a) and (b). With increasing iron content, the amount
of Al5 FeSi rises up remarkably but saturates at about
2 mass% Fe and then decreases moderately. Al8 Fe2 Si does
not crystallize until the iron content is added up to 2.1 mass%
and then increases abruptly. The crystallization temperatures
of aluminum FCC, silicon, Al5 Cu2 Mg8 Si6 , Al2 Cu and the
complete solidification temperature remain unchanged while
those of Al15 (Fe,Mn)3 Si2 and Al5 FeSi increase substantially
and saturated at 2.2 mass% Fe.
Influence of Copper and Iron on Solidification Characteristics of 356 and 380-Type Aluminum Alloys
Al (Fe,Mn) Si
15
3
2
Al Cu
Al Fe Si
Al Cu Mg Si
Al (Fe,Mn) Si
8
2
Al FeSi
5
5
2
8
Al Cu
2
15
6
849
2
3
Al Cu Mg Si
2
5
2
8
6
Al FeSi
8.0
5
(a)
7
5.0
4.0
3.0
2.0
1.0
0.0
0.0
2.0
3.0
Al (Fe,Mn) Si
15
4.0
5.0
6.0
4
3
2
7.0
0
0
3
0.5
1
Al Cu
2
1.5
2
2.5
3
3.5
4
Fe Content, (mass%)
2
Al5 FeSi
Al5 Cu2Mg8 Si6
aluminum FCC
silicon
Solidification completed
(b)
Al8 Fe2 Si
Al5 FeSi
aluminum FCC
Al Cu Mg Si
silicon
Al2 Cu
Al15 (Fe,Mn) 3 Si2
Solidification completes
5
2
8
6
880
950 (b)
860
840
820
800
780
760
0
1
2
3
4
5
6
7
Cu Content, (mass%)
Fig. 7 Effects of copper content on the solidification characteristics of 380type alloy predicted from the Gulliver-Scheil model. (Fe 1.32%, Si 7.96%,
Mg 0.29%, Mn 0.11%, Zn 0.88%, Ni 0.05%, Ti 0.05%, Cr 0.03%); (a) The
relationship between the amount of intermetallics and copper content., (b)
The relationship between the crystallization temperatures of major phases
and copper content.
3.2 Solidification of 356 alloys
Similarly to 380 type, the calculated fraction solid of
sample 5 from the equilibrium and Gulliver-Scheil models in
Fig. 9 is very similar except near the end of solidification.
Table 4 and Fig. 10 compare the calculated crystallization
temperatures of major phases with the experimental result. In
the experiment, only the crystallization of aluminum FCC
and silicon could be observed.
The information about the discrepancy of crystallization
temperature, which was collected from literatures,3–14,21–26)
is revealed in Fig. 11.
Figure 12 shows the solidification microstructure of 356
reference-sample 4. There are aluminum FCC, silicon,
Al5 FeSi, and Al8 Mg3 FeSi6 . The quantity of phases in sample
5 was calculated and is compared in Table 4 with the
detection by SEM with EDX analysis. In contrast, Mg2 Si can
be detected in sample 5 by SEM. The amount of interme-
Crystallization Temperature, T/K
Crystallization Temperature, T/K
5
1
1.0
Cu Content, (mass%)
900
(a)
6
6.0
Mass Percent of Phases
Mass Percent of Phases
7.0
900
850
800
750
0
0.5
1
1.5
2
2.5
3
3.5
4
Fe Content, (mass%)
Fig. 8 Effects of iron content on the solidification characteristics of 380type alloy calculated from the Gulliver-Scheil model. (Cu 2.41%,
Si 7.96%, Mg 0.29%, Mn 0.11%, Zn 0.88%, Ni 0.05%, Ti 0.05%, Cr
0.03%); (a) The relationship between the amount of intermetallics and iron
content., (b) The relationship between the crystallization temperatures of
major phases and iron content.
tallics and the crystallization temperatures of major phases
varying with copper for sample 5 are shown in Figs. 13(a)
and (b). Al5 FeSi increases slightly with copper. Al2 Cu does
not appear until 0.6 mass% Cu and then increases substantially. The crystallization temperatures of aluminum FCC,
silicon and Al5 FeSi go lower slightly with increasing copper
content. In contrast, the final solidification temperature
declined substantially.
Figures 14(a) and (b) show the variation of the calculated
amount of intermetallics and crystallization temperatures of
major phases with iron content for sample 5. According to
Fig. 14(a), Al15 (Fe,Mn)3 Si2 crystallizes in so negligible
amount even at very high content of iron that can not be
shown, corresponding to the observed microstructure. The
amount of Al5 FeSi is very sensitive to iron content. Its
850
P. Suwanpinij, U. Kitkamthorn, I. Diewwanit and T. Umeda
900
950
Gulliver-Scheil fraction solid
equilibrium fraction solid
aluminum FCC
Temperature, T/K
Temperature, T/K
880
860
silicon
840
Solidification
completes (equilibrium)
900
aluminum FCC
silicon
850
5
800
820
Solidification
completes (Scheil)
800
0.0
0.2
0.4
0.6
0.8
750
2000
1.0
Fraction Solid
Al8FeMg3Si6
Al FeSi
2500
Mg Si
2
Solidification
completes (Scheil)
3000
3500
4000
4500
Elapsed Time, t/s
Fig. 9 Calculated weight fraction versus temperature of sample number 5
(Cu-added 356-type alloy).
Fig. 10 Observed cooling curve of sample 5 (Cu-added 356-type alloy)
with arrows indicating the calculated crystallization temperatures from the
Gulliver-Scheil model.
Table 4 Solidification sequence of sample 5 (Cu-added 356-type alloy) and mass percentage of each phase at complete solidification
temperature.
Phase
Calculated
Observed
Crystallization
Amount
Crystallization
temperature (K)
(mass%)
temperature (K)
894.4
93.67
885.2
836.4
Aluminum FCC
Microstructure
Y
Silicon
845.9
4.83
Al5 FeSi
836.3
0.12
Y
Y
Al8 FeMg3 Si6
831.4
0.35
Y
Mg2 Si
826.2
0.20
Y
Al15 (Fe,Mn)3 Si2
816.8
0.0003
N
Solidification completed
815.2
Y: Observed in solidification microstructure
N: Not observed in solidification microstructure
Temperature from Scheil Model, T/K
900
fcc aluminum
890
880
y=x
870
860
silicon
850
840
830
820
820
830
840
850
860
870
880
890
900
Temperature from Literature, T/K
Fig. 11 Comparison between calculated temperatures from the GulliverScheil model and observed temperature of aluminum FCC and silicon in
356-type in various literatures.
Fig. 12 The observed microstructure of sample 4 (reference 356-type
alloy).
Influence of Copper and Iron on Solidification Characteristics of 356 and 380-Type Aluminum Alloys
Al5 FeSi
Al5 Cu2 Mg8 Si6
Mg Si
Al Cu
2
2
Al FeMg Si
8
3
5
6
1
Mg2Si
Al5FeSi
Al8FeMg3Si6
Al8Fe2Si
851
(a)
Mass Percent of Phases
Mass Percent of Phases
(a)
0.8
0.6
0.4
4
3
2
1
0.2
0
0
0
0
0.2
0.4
0.6
0.8
1
0.2
0.4
Mg Si
Al FeMg Si
Al Cu
Solidification completes
Al Cu Mg Si
3
5
6
2
8
6
Crystallization Temperature, T/K
900
880
(b)
860
840
820
800
780
0
0.4
0.6
0.8
1.2
1.4
1.6
Mg2Si
Solidification completed
Al8Fe2Si
(b)
880
860
840
820
800
0
0.2
1
900
2
Crystallization Temperature, T/K
8
Aluminum FCC
Silicon
Al5FeSi
Al8FeMg3Si6
2
5
0.8
Fe Content, (mass%)
Cu Content, (mass%)
aluminum FCC
silicon
Al FeSi
0.6
1.2
1
1.2
0.5
1
1.5
2
Fe Content, (mass%)
Cu Content, (mass%)
Fig. 13 Effects of copper content on the solidification characteristics of
356-type alloy predicted from the Gulliver-Scheil model. (Fe 0.07%, Si
6.286%, Mg 0.403%, Mn 0.004%, Zn < 0:001%, Ti 0.130%, Cr 0.002%);
(a) The relationship between the amount of intermetallics and copper
content., (b) The relationship between the crystallization temperatures of
major phases and copper content.
amount rises up 3.5 mass% per 1.0 mass% Fe increment in
the first range. Beyond 1.2 mass% Fe, its amount saturates
and decreases slightly. In Fig. 14(b), the Al5 FeSi temperature
increases significantly at first but gradually decelerates and
finally saturates from 1.3 mass% Fe. On the other hand, the
liquidus (aluminum FCC temperature) and the complete
solidification temperature as well as the crystallization
temperature of silicon negligibly changed.
As a guide to control the amount of detrimental phases in
A356 alloy, which are needle-shaped Al5 FeSi and Chinese
script Al8 FeMg3 Si6 , their variations in amount with increasing content of silicon, magnesium and iron were calculated
by the Gulliver-Scheil model and are shown in Figs. 15(a)
and (b). The content of these alloying elements input in the
thermodynamic calculation was within a composition range
according to the specification of A356 alloy and other
Fig. 14 Effects of iron content on the solidification characteristics of 356type alloy predicted from the Gulliver-Scheil model. (Cu 0.17%, Si
6.286%, Mg 0.403%, Mn 0.004%, Zn < 0:001%, Ti 0.130%, Cr 0.002%);
(a) The relationship between the amount of intermetallics and iron
content., (b) The relationship between the crystallization temperatures of
major phases and iron content.
elements were set to be zero. At 0.25 mass% Mg, Fig. 15(a),
the needle-like Al5 FeSi starts to crystallize at 0.025 mass%
Fe and then increases substantially and linearly with iron
content. Its amount at 6.5 mass% Si is a slightly higher than
those at 7.0 and 7.5 mass% Si, which are almost exactly equal
along the calculation. The other phase, Al8 FeMg3 Si6 ,
increases linearly until 0.03 mass% Fe and then this phase
stays at about 0.2 mass%. For 0.45 mass% Mg, Fig. 15(b),
Al5 FeSi starts to crystallize at 0.04 mass% Fe and then
increases substantially and linearly, similarly to the case of
0.25 mass% Mg. The amount of Al5 FeSi at 6.5 mass% Si is
slightly higher than those at 7.0 and 7.5 mass% Si.
Al8 FeMg3 Si6 increases linearly from zero until 0.06 mass%
Fe. After that, it stays at about 0.4 mass%, larger amount than
those in 0.25% Mg alloy. The amount of Al8 FeMg3 Si6 is
higher in the order of 7.0 mass% Si, 7.5 mass% Si and
6.5 mass% Si.
852
P. Suwanpinij, U. Kitkamthorn, I. Diewwanit and T. Umeda
Al FeSi at Si 6.5%
Al8 FeMg3 Si6 at Si 6.5%
Al FeSi at Si 7.0%
Al FeMg Si at Si 7.0%
Al FeSi at Si 7.5%
Al FeMg Si at Si 7.5%
5
5
8
5
3
8
aluminum FCC due to the position of thermocouple and
the scarcity of experimental and thermodynamic data
on higher order interaction parameters of the thermodynamic modeling. However, in the present, higher
order interaction parameters can not be well compiled.
Binary interaction parameters are expected to be
adequate in multicomponent alloy system calculation.
6
3
6
(a) 0.6
Mass Percent of Phases
0.5
0.4
Acknowledgements
0.3
0.2
0.1
0
0
0.05
0.1
0.15
0.2
Fe Content, (mass%)
Al FeSi at Si 6.5%
Al8 FeMg3 Si6 at Si 6.5%
Al FeSi at Si 7.0%
Al FeMg Si at Si 7.0%
Al5 FeSi at Si 7.5%
Al8 FeMg3 Si6 at Si 7.5%
5
5
0.6
8
3
REFERENCES
6
(b)
Mass Percent of Phases
0.5
0.4
0.3
0.2
0.1
0
0
0.05
0.1
0.15
0.2
Fe Content, (mass%)
Fig. 15 The variation in amount of Al5 FeSi and Al8 FeMg3 Si6 phases with
iron and silicon content within A356 specification; (a) at magnesium
0.25 mass%, (b) at magnesium 0.45%.
4.
The authors would like to acknowledge the indispensable
support of MTEC (National Metal and Materials Technology
Center) and TJTTP (Thai-Japan Technology Transfer Project). We are also grateful to Asahi Somboon Aluminium
Co., Ltd. and Messrs Tetsuo Moriya and Tatsuo Kawara for
the chemical analyses of the alloys in this paper. We also
thank Mr. Suvanchai Pongsukitwat for his useful advice. In
addition, we owe a debt of gratitude for the experiment
preparation to Mr. Senee Maneepetch.
Conclusions
(1) In this study, crystallization sequence of 380-type
alloys was Al15 (Fe, Mn)3 Si2 ! aluminum FCC !
Al5 FeSi ! silicon ! Al2 Cu ! Al5 Cu2 Mg8 Si6 ;
crystallization sequence of 356-type alloys was aluminum FCC ! silicon ! Al5 FeSi ! Al8 FeMg3 Si6 !
Mg2 Si.
(2) When copper and iron content increases, liquidus and
eutectic temperature of 356 and 380 were suppressed.
(3) The quantity of Al2 Cu increased greatly with the
increasing copper and that of Al5 FeSi increased greatly
with iron content.
(4) Thermodynamic prediction provided an effective way
in studying the effects of alloying elements.
(5) There were small discrepancies between the observed
and calculated temperatures for the crystallization of
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