Effects of ultrasonic vibration on the iron-containing intermetallic compounds of high silicon aluminum alloy with 2% Fe

Article abstract of DOI:10.1016/j.jallcom.2009.11.145

The effects of ultrasonic vibration (USV), the combined effects of USV and the addition of Mn on the morphology of iron-containing intermetallic compounds of Al-20Si-2.0Fe-2.0Cu-0.4Mg-1.0Ni alloy have been studied respectively. The mechanism of shape-transformation of Fe-containing phases is also investigated. A large amount of long needle-like β-Al₅FeSi phases accompanied with a few δ-Al₄FeSi₂ phases existed in the matrix of high silicon aluminum alloy with 2% Fe in traditional casting process. The effects of acoustic cavitation and acoustic streaming generated by USV which was applied near the liquidus temperature of this alloy, homogenized the solute distribution field and temperature field of the melt, lowered the concentration level of Fe atoms in solidification front, and decreased the start-freezing temperature of β phase. That the formation of acicular β phase was suppressed, contribute to enlarge the forming temperature range of δ phase of the alloy with certain time of USV imposed near the liquidus temperature. The finest δ particles and only a small amount of β phase were obtained in the matrix of the Fe-containing alloy with USV for 120 s. With the complex effects of USV and addition of 0.5% Mn, the forming of acicular β phase was almost repressed and the Fe-containing phases were in forms of fine Al₄(Fe,Mn)Si₂ and Al₅(Fe,Mn)Si particles in the size of 20-30 μm. Crown Copyright

Full text of DOI:10.1016/j.jallcom.2009.11.145

Journal of Alloys and Compounds 492 (2010) 482–487
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jallcom
Effects of ultrasonic vibration on the iron-containing intermetallic compounds of
high silicon aluminum alloy with 2% Fe
∗
Gu Zhong, Shusen Wu , Huawen Jiang, Ping An
State Key Lab of Materials Processing and Die & Mould Technology, Huazhong University of Science and Technology, Luoyu Road 1037#, Wuhan 430074, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 31 August 2009
Received in revised form
The effects of ultrasonic vibration (USV), the combined effects of USV and the addition of Mn on the mor-
phology of iron-containing intermetallic compounds of Al–20Si–2.0Fe–2.0Cu–0.4Mg–1.0Ni alloy have
been studied respectively. The mechanism of shape-transformation of Fe-containing phases is also inves-
tigated. A large amount of long needle-like ␤-Al5FeSi phases accompanied with a few ␦-Al4FeSi2 phases
existed in the matrix of high silicon aluminum alloy with 2% Fe in traditional casting process. The effects
of acoustic cavitation and acoustic streaming generated by USV which was applied near the liquidus
temperature of this alloy, homogenized the solute distribution field and temperature field of the melt,
lowered the concentration level of Fe atoms in solidification front, and decreased the start-freezing tem-
perature of ␤ phase. That the formation of acicular ␤ phase was suppressed, contribute to enlarge the
forming temperature range of ␦ phase of the alloy with certain time of USV imposed near the liquidus
temperature. The finest ␦ particles and only a small amount of ␤ phase were obtained in the matrix of
the Fe-containing alloy with USV for 120 s. With the complex effects of USV and addition of 0.5% Mn, the
forming of acicular ␤ phase was almost repressed and the Fe-containing phases were in forms of fine
Al4(Fe,Mn)Si2 and Al5(Fe,Mn)Si particles in the size of 20–30 ␮m.
1
9 November 2009
Accepted 19 November 2009
Available online 24 November 2009
Keywords:
Ultrasonic vibration
High silicon aluminum alloy
Iron-containing phase
Microstructure
Crown Copyright © 2009 Published by Elsevier B.V. All rights reserved.
1
. Introduction
High silicon (Si: 18–26%) Al–Si alloy has been considered to
tion elements addition [1,6,7] and melt superheating were widely
studied. With the addition of Mn according to certain ratio of Mn/Fe,
the coarse plate ␤ phase transforms to less detrimental Chinese
be an ideal candidate for making such heat- and wear-resistant
parts as pistons of high speed engines, due to the superior per-
formances of high specific strength, excellent wear resistance and
corrosion resistance, as well as low coefficient of thermal expansion
script Al15(Fe,Mn) Si2 phase [7]. However, increase of Mn content
can not only eliminate the harmful effect of ␤ phase completely, but
also cause high cost and inferior cutting performance for the high
3
hardness polygonal ␣-Al15(Fe,Mn) Si2 phase formed [7–9]. Cur-
3
[
1–3]. Generally, alloy elements, such as Cu, Mg, were added delib-
rently, rapid solidification techniques like spray forming process
which produce fine microstructure, attract considerable interests.
erately to improve the room temperature strength substantially
by solution and precipitation hardening. However, strengthening
Fine ␦-Al FeSi2 phase in the size of 1.4–7.7 ␮m of Al–20Si–5Fe–2X
4
◦
phases like Al Cu and Al CuMg are relatively stable below 150 C,
(X = Cu, Ni, Cr) alloy was obtained through gas atomization, con-
tributing to the hardness increase about 7–17% [6]. The alloys
prepared by spray deposition [1,7] which presented fine ␦ and ␤
phases about 3–8 ␮m, showed excellent strength at room tempera-
ture and elevated temperature. However, the expensive equipment
and complicated process restricted the applications of this process
in industry greatly.
USV was employed in the field of metal’s semi-solid processing
in continuously casting since 1990s. And the process of semi-solid
slurry preparation by ultrasonic vibration now has attracted con-
siderable concerns for the unique merits such as low cost and
high efficiency, simple process, and little pollution to melt and
environment [10–12]. Currently, the refine mechanism of the ␣-
Al dendrites [10,11] and primary Si particles [3,12], as well as the
effects of process parameters [11] on refinement are the main
2
2
◦
and Mg Si will aggregate and coarsen over 180 C that give rise to
2
sharp decrease of high temperature strength [1]. It has been proved
that addition of alloy element Fe was effective to enhance elevated
mechanical properties through forming Fe-containing intermetal-
◦
lic compounds which are still stable at temperature of 300–400 C
[
1,4–7]. Unfortunately, conventional casting technologies produce
coarse plate Fe-bearingintermetallic compounds like␤-Al5FeSiand
-Al FeSi , resulting in inferior mechanical properties.
␦
4
2
In recent years, processes of modifying the harmful Fe-bearing
intermetallic compounds by rapid solidification [1,5–7], neutraliza-
∗ Corresponding author. Tel.: +86 27 87556262; fax: +86 27 87556262.
E-mail addresses: zghust@qq.com (G. Zhong), ssw636@hotmaiol.com (S. Wu).
0
925-8388/$ – see front matter. Crown Copyright © 2009 Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2009.11.145

G. Zhong et al. / Journal of Alloys and Compounds 492 (2010) 482–487
483
Table 1
Chemical compositions of high silicon aluminum alloy (mass%).
Alloy
Si
Cu
Mg
Ni
Fe
Mn
Al
F0
F1
20
20
2.0
2.0
0.4
0.4
1.0
1.0
2
2
0
0.5
Balance
Balance
focuses in the research of manufacturing Al–Si alloy slurry with
USV. Osawa et al. [13] studied the effect of USV on the morphol-
ogy of primary intermetallic compounds of the alloys Al–xSi–4Fe
(
x = 6, 12, 18). However, the shape-changing of Fe-bearing phases
caused by USV and the mechanism of the USV on the morphology
transformation of plate Fe-bearing phases are rarely reported till
now.
In this paper, the effects of USV on the morphology of Fe-
containing intermetallic compounds of high silicon aluminum alloy
Al–20Si–2.0Fe–2.0Cu–0.4Mg–1.0Ni have been studied. The varia-
tions of Fe-containing intermetallic compounds with different USV
time are analyzed. The transformation mechanism of Fe-containing
phases with the complex role of USV and Mn addition is also dis-
cussed.
2.
Experimental procedures
Fig. 1. SEM image of as-cast F0 alloy in traditional casting.
The installation of USV for high silicon Al–Si alloy in references [12] was
employed in this experiment. The applied ultrasonic power in this study was 1.2 kW,
and the frequency of USV was 20 kHz. Ultrasonic vibrator was composed of firmly
connected transducer and amplitude made with titanium alloy.
The compositions of the alloys studied here were listed in Table 1, and
Al–20Si–2.0Cu–0.4Mg–1.0Ni was the base alloy. The raw materials were Al–25.8% Si
(
mass%, the same in the following) and Al–10% Mn master alloy, commercial purity
Al (99.7%), pure Cu (99.99%), pure Mg (99.9%), pure Ni (99.99%), and pure Fe (99.9%).
The liquidus and the solidus temperature of this alloy which were determined by
◦
◦
DSC, are about 702 C and 533 C respectively.
◦
The alloy was melted in a resistance furnace at 820–850 C with complex mod-
ification of 0.08% P in the form of Cu–14% P and 0.6% RE in the form of Al–15% RE,
in which the RE was composed of 63% Ce and 36% La. Then the melt was held at
◦
◦
7
40–780 C, and a metal cup was preheated to about 690 C by the heating furnace
simultaneously. Subsequently, about 600 g liquid metal was poured into the pre-
heated metal cup. The USV was applied on the melt with the ultrasonic vibrator
immersed into the melt 15–20 mm in depth, when the temperature of the liquid
◦
metal cooled down to about 715 C. After the melt was treated with USV for certain
◦
◦
time between 715 C and 690 C, the slurry with certain solid fraction obtained and
then it was poured into the permanent mold of 8 mm in diameter. The application of
◦
USV ended at the temperature of about 690 C. For comparison, conventional casting
◦
samples which formed at the temperature of 820 C, were also made without USV.
The microstructure of the polished specimens was revealed by etching with
0
.5% hydrofluoric acid solution, and examined with an Axiovert 200MAT optical
microscope. In order to analyze the constituent phases and compositions, specimens
were investigated using Quanta 200 environmental scanning electron microscope
(
SEM) fitted with an Energy Dispersive X-ray Spectroscopy (EDS) analysis system.
3
. Results and discussion
3.1. Microstructure of high silicon aluminum alloy containing 2%
Fe
Fig. 1 shows the typical as-cast microstructure of F0 alloy sam-
◦
ple formed at the temperature of 820 C in permanent mold, which
is composed of primary Si (A), eutectic Si (B), dendritic compound
(
white C), acicular compound (bright white D), needle-like com-
pound (light gray E), and a small amount of plate compound (light
gray F). According to earlier studies of the authors [14], compound
C, which can be refined to spherical particles in size of 1–2 ␮m by T6
heat treatment, is AlCuNi phase. And compound D is RE-containing
five-element compound Al–Si–Cu–Ni–RE. An EDS analysis shows
that the needle-like compound E and the plate compound F con-
tain the same elements Al, Si and Fe atoms, as showed in Fig. 2. And
the corresponding compositions contents of E and F are listed in
Table 2. It was pointed out by related studies [4,6,7], that ␦-Al FeSi2
phase commonly presented in high silicon aluminum alloy. As
Fig. 2. EDS spectra of intermetallic compounds of F0 alloy in Fig. 1: (a) the result of
light gray needle-like compound E; (b) the result of light gray plate compound F.
4

4
84
G. Zhong et al. / Journal of Alloys and Compounds 492 (2010) 482–487
Table 2
EDS results (atom percent) of compounds of F0 alloy in liquid forming.
Table 3
EDS results (atom percent) of Fe-containing phases of F0 alloy with USV.
Al
Si
Fe
Marks
Al
Si
Fe
Compound E
Compound F
65.25
53.10
18.06
31.00
16.70
15.90
a
b
c
53.10
51.76
52.25
31.00
30.90
31.06
15.90
17.33
16.70
can be seen from Table 2, the intermetallic compounds E and F
should be monoclinic ␤-Al5FeSi and tetragonal ␦-Al FeSi2 phases
4
3.2. Effects of ultrasonic vibration on the Fe-containing
intermetallic compounds
respectively. Based on the studies of Srivastava et al. and Huang et
al. [5,7], the Fe-containing intermetallic compounds mainly con-
sisted of metastable ␦ phase and a small amount of equilibrium
The variations of Fe-containing phases of high silicon aluminum
alloy with 2% Fe under different USV times are presented in Fig. 3.
As can be seen from Fig. 3a pointed out by arrow, a large number of
long needle-like ␤-Al5FeSi phase in size of 100–200 ␮m distributed
staggered in the matrix of F0 alloy without USV. However, when
␤
phase in the non-equilibrium solidification microstructure of
the spray-deposited alloys Al–(18–25)Si–5Fe–X which experienced
3
5 ◦
−1
a big cooling rate about 10 –10 C s . However, the opposite
results can be seen in our study, that the Fe-containing phases
mainly existed in form of needle-like ␤ phase accompanied with
a few plate ␦ phase of traditional casting F0 alloy. The different
phenomena would be caused by the different solidification condi-
tions of these two kinds of alloys. According to the Al–Si–Fe ternary
phase diagram [6,15], the equilibrium solidification of Al–20Si–5Fe
USV was applied for 60 s near the liquidus temperature of the alloy
◦
(
715 C), the ␤ phase decreased significantly with some refined aci-
cular ␤ phase about 40–80 ␮m remained, and a large amount of
block or polygonal intermetallic compound emerged (light gray in
Fig. 3b designated by arrows, the gray particles were primary Si).
The acicular ␤ phase was further decreased and the block com-
pound more refined and rounded with the effect of USV for 120 s as
shown in Fig. 3c. Continuing to prolong the USV time to 180 s, only
a few short acicular ␤ phase existed in the matrix (Fig. 3d), but the
block intermetallic compounds and the primary Si particles were
coarser compared with those in Fig. 3c.
The long needle-like ␤ phase was substituted by high volume
fraction of block compound with the USV imposed on the F0 alloy.
Therefore, the substitutes must also be Fe-containing compounds
for the solution of Fe in solid Al is less than 0.05% [4]. The EDS
analysis results which were measured for three random points of
different block compounds of the alloys with USV, show that they
all contain Al, Si and Fe atoms, as listed in Table 3. And the com-
positions contents indicate that they were basically the same as
◦
alloy starts with the formation of the ␦ phase at about 820 C, fol-
◦
lowed by the formation of the primary Si phase below 700 C. At the
◦
temperature below 610 C, the previously ␦ phase transforms into
the ␤ phase with peritectic reaction L + ␦-Al FeSi → ␤-Al5FeSi + Si,
4
2
until the ternary eutectic reaction of ␣-Al, Si and ␤ phases occurs
◦
at about 576 C L → ␣(Al) + Si + ␤-Al5FeSi. It is in favor of forming ␦
phase under the big cooling rate of rapid solidification. However,
the average cooling rate of the cast iron mold used in this experi-
◦
−1
ment was less than 10 C s , even at the sample surface was only
◦
−1
about 20 C s . Therefore, the solidification in this mold would fol-
low the sequence of equilibrium solidification events basically. As
a result, most of the formed ␦ phase transformed into ␤ phase via
the peritectic reaction, and coarser ␤ phase appeared for the longer
solidification time compared with spray deposition.
Fig. 3. The variations of Fe-bearing intermetallic compounds of F0 alloy with different USV time (images of samples as-cast): (a) 0 s; (b) 60 s; (c) 120 s; (d) 180 s.

G. Zhong et al. / Journal of Alloys and Compounds 492 (2010) 482–487
485
ꢀ
ꢀ
from C0 to C0 , boundary layer thickness decreased from Xb to Xb
.
The degree of constitutional undercooling also decreased as shown
in Fig. 4 that the constitutional undercooling zone reduced from
the area surrounded by curve T –TL and straight line GL to that
i
ꢀ
ꢀ
ꢀ
surrounded by curve T –TL and straight line GL . All of these are
i
because of the lower level of solute concentration in solidifica-
tion front, which caused by the acoustic streaming and micro-flow
stirring in the melt.
Strong convection caused in the melt for the introduction of USV
◦
at about 715 C, homogenized the solute distribution field and the
temperature field of the melt. When the USV finished, the melt
◦
temperature was about 690 C, and the semi-solid slurry with some
pre-formed phases was obtained. The start-freezing temperature of
␤
phase decreased in subsequent solidification process, for lower
concentration degree of Fe atoms in the melt with USV. Moreover,
◦
−1
a cooling rate about 10 C s higher than that of traditional casting
could be obtained because the forming temperature of semi-solid
◦
processing was about 130 C lower than that of traditional cast-
ing. As a result, the start-freezing temperature of ␤ phase further
declined due to the higher cooling rate. Therefore, Fe-containing
intermetallic compounds of the alloy with USV continue to form in
the form of ␦ phase rather than acicular ␤ phase.
The longer time USV imposing on the melt, the more uniform
solute distribution, and the more difficult to form acicular ␤ phase
in the solidification process. As can be seen from Fig. 3, the needle-
like ␤ phases decreased remarkably (Fig. 3b) and a large number of
block ␦ phases emerged in the matrix with the application of USV.
The ␤ phases kept on decreasing with the increasing time of USV,
and there were only a small amount of ␤ phases with USV treat-
ment for 180 s (Fig. 3d). It can also be seen from Fig. 3, with USV
time prolonged, the block ␦ phase, which was larger than 100 ␮m
without USV as shown in Fig. 1, was refined to about 40–60 ␮m
with the effect of USV for 60 s (Fig. 3b), and further refined to about
30 ␮m for 120 s (Fig. 3c). But coarse ␦ phase of larger than 50 ␮m
acquired with the effect of USV for 180 s (Fig. 3d). The evenly dis-
tributed fields of temperature and solute of the melt generated by
the effect of acoustic cavitation and acoustic streaming, not only
promoted the formation of ␦ phase, but also inhibited the rapid
growth of ␦ phase in a single direction bringing the refinement
of particles. A part of refined needle-like ␤ phase coexisted with
coarse ␦ phase in the F0 alloy with USV 60 s, due to the influence
of USV was not strong enough. And for 120 s, the effect of USV was
sufficient for restricting the forming of ␤ phase, the finest ␦ phase
and only a small amount of ␤ phase were obtained. Whereas, the
␦ phase grew and coarsened gradually for too long holding time
under the USV for 180 s, though the acicular ␤ phase continued to
decrease for the further homogenous solute distribution.
Fig. 4. Effect of USV on the solute and temperature distributions in front of a crystal.
the plate ␦ phase of F0 alloy without USV. So, the conclusion could
be drawn that the forming of long needle-like ␤ phase was sup-
pressed, which was benefit to the formation of ␦ phase with the
effect of USV on the alloy F0.
In the solidification process of this alloy, Fe atoms aggregate in
the solidification front due to the large difference of solubility of Fe
between liquid and solid Al, even a small amount of Fe in the alloy
will cause harmful acicular ␤ phase to form. It was verified [16]
that the start-freezing temperature of ␤ phase was variable, which
decreased with decreasing iron content, increasing cooling rate,
and increasing melt superheat temperature until it merges with the
temperature of Al–Si eutectic reaction eventually. Among which,
the Fe content has the greatest impact on the start-freezing tem-
perature of ␤ phase, which ascends sharply with the increasing iron
content. And longer growth time is obtained because of enlarged
forming temperature range, causing much coarser ␤ phase. The
same result could be observed through simulation of the ␤ phase’s
start-freezing temperature of the alloys Al–20Si–xFe (x = 1, 2, 5)
◦
using JMatPro software, and the simulated results are 587.7 C,
◦
◦
6
21 C, 670 C respectively.
3.3. Combined effects of ultrasonic vibration and Mn addition on
the Fe-containing intermetallic compounds of high silicon
aluminum alloy with 2% Fe
Acoustic cavitation and streaming whose velocity is about
3
1
0–10 times of that of the fluid thermal convection, will be
produced by USV imposing on the metal melt [3,10–12,17,18].
A maximum speed of acoustic streaming about 1.37 m/s can be
reached by this device for USV, based on theoretical calculations.
And it plays an important role in homogenizing the solute distri-
bution field and the temperature field of the melt, accelerating the
heat and mass transfer, as well as dispersing the primary nuclei. The
convection which speeds up uniform distribution of melt tempera-
ture, is strengthened by the combination of micro-flows generated
by the broken of cavitation bubbles and macro-flows of molten melt
induced by acoustic streaming. It is favorable to form homogenous
solute distribution field and temperature field in the melt, with
the application of USV on the melt before solidification, namely
near the liquidus temperature. The effects of USV on the solute and
temperature distribution of crystallization front are shown in Fig. 4.
As can be seen, the solute concentration of crystal front decreased
Fig. 5 shows the typical optical microstructures of F1 alloy con-
taining 0.5% Mn with and without USV in as-cast state. As can be
seen from Fig. 5a, that the intermetallic compounds of F1 alloy
without USV were mainly composed of needle-like ␤ phase and
plate compound A (light gray). With the effect of USV for 120 s, the
␤ phase basically eliminated and a large number of fine particles
(such as the light gray compound B directed by the arrow) emerged
with uniform distribution in the matrix, as shown in Fig. 5b. An
EDS analysis shows that the plate compound A and the particles B
contain the same elements Al, Si, Fe and Mn atoms, and the compo-
sitions contents of A and B are listed in Table 4. Based on the ratio
of compositions, compound A is close to the formula Al (Fe,Mn)Si ,
4
2
and two kinds of compounds with the similar morphologies as B are
close to the formula Al (Fe,Mn)Si2 and Al5(Fe,Mn)Si respectively.
4

4
86
G. Zhong et al. / Journal of Alloys and Compounds 492 (2010) 482–487
of ␦ phase which are occupied by Fe atoms originally, are suitable
to both Fe and Mn atoms. Therefore, Mn atoms were also involved
in the formation of ␦ phase in the solidification process not with
reactions but just a replacement of atoms due to the low Mn con-
tent, leading to coexistence of Fe and Mn atoms in the lattice of ␦
phase. As a result, only a small amount of Fe atoms were substituted
by Mn atoms (illustrated by Table 4) forming the Al (Fe,Mn)Si2
4
compounds. With the addition of Mn, on one hand, it enlarged
the temperature range of forming ␦ phase which promoted the
formation of Al (Fe,Mn)Si2 compound and suppressed the rapid
4
growth of it additionally. On the other hand, it was equivalent to
increase the content of Fe in the alloy, so as to increase the amount
of Fe-containing phases.
Fig. 5b shows that the forming of acicular ␤ phase was almost
repressed in F1 alloy with the combined effects of USV for 120 s
and addition of 0.5% Mn, and the Fe-containing phases consisted of
fine particles Al (Fe,Mn)Si2 and Al5(Fe,Mn)Si in size of 20–30 ␮m.
4
The effect of USV caused uniform distribution of temperature field
and solute field, lowered the start-freezing temperature of ␤ phase
and promoted the formation of ␦ phase. Moreover, the tempera-
ture range of ␦ phase’s formation was further extended with the
addition of Mn which also involved in the formation of ␦ phase
and ␤ phase. Consequently, the small amount of acicular ␤ phase
shown in Fig. 3c transformed into fine Al5(Fe,Mn)Si phase, and was
in coexistence with Al (Fe,Mn)Si phase (Fig. 5b). It was found that
4
2
␤
-Al5FeSi and ␦-Al FeSi2 phases of spray-deposited alloys were
4
difficult to distinguish due to their identical morphologies [7,19].
Therefore, it is not difficult to understand why Al (Fe,Mn)Si2 and
4
Al5(Fe,Mn)Si phases of F1 alloy with USV are in the similar mor-
phologies.
4. Conclusions
(1) A large amount of long needle-like ␤-Al5FeSi phase accompa-
nied with a few plate ␦-Al FeSi2 phase coexisted in the matrix
4
of high silicon Al–Si alloy with 2% Fe in conventional casting
process. However, Fe-containing intermetallic compounds of
the alloy with USV continue to form in the form of ␦ phase
rather than acicular ␤ phases. The finest ␦ particles and only
a small amount of ␤ phase were obtained in the matrix of the
Fe-containing alloy with USV for 120 s.
Fig. 5. Typical optical images of F1 alloy: (a) without USV; (b) with USV for 120.
(
2) The effects of acoustic cavitation and acoustic streaming gen-
erated by USV which is imposed near the liquidus temperature
of the alloy, homogenizes the solute distribution field and the
temperature field of the melt. The mixing effect of USV on
the solidification front lowers the concentration of Fe atoms,
decreases the start-freezing temperature of ␤ phase and pro-
motes the formation of Fe-containing intermetallic compounds
in the form of ␦ phase. The uniform distribution of solute in the
melt restrains the rapid growth of ␦ phase in a single direction,
causing the refinement of block ␦ phase.
Mn is commonly used to reduce the harmful effect of Fe, and the
best neutralizing efficacy would be acquired with the addition as
Mn/Fe = 1/2 [1,7]. It can be observed that the Fe-bearing intermetal-
lic compounds were acicular ␤ phase and plate Al (Fe,Mn)Si phase
4
2
in F1 alloy without USV (Fig. 5a), and more plate compound existed
compared with the microstructure of F0 alloy without Mn (Fig. 1).
The simulated result of the ␤ phase’s start-freezing temperature of
the alloy Al–20Si–2Fe–0.5Mn determined by JMatPro software was
◦ ◦
6
11.5 C, about 10 C lower than that of the alloy with the absence
(
3) The forming of acicular ␤ phase of high silicon aluminum
alloy was almost suppressed by adding 0.5% Mn and the effect
of USV for 120 s, and the Fe-containing phases consisted of
of Mn. As a result, the formation temperature range of ␦ phase was
enlarged by about 10 C for the lower start-freezing temperature
of ␤ phase with the addition of Mn. In this study, the relative con-
tent of Mn in F1 alloy was low (Mn/Fe = 1/4), which developed the
◦
fine Al (Fe,Mn)Si2 and Al5(Fe,Mn)Si particles in the size of
4
2
0–30 ␮m.
positive role in joining the formation of Al (Fe,Mn)Si2 phase. Both
4
Mn and Fe are transition elements, and the positions in the lattices
Acknowledgments
Table 4
EDS results (atom percent) of Fe-containing phases of F1 alloy.
This work was funded by Project 50775086 supported by
National Natural Science Foundation of China, and Project
Marks
Al
Si
Mn
Fe
2
007AA03Z557 supported by the Hi-tech Research and Develop-
A
B
50.10
50.80
32.82
32.15
16.02
02.52
02.44
02.90
13.62
13.87
14.68
ment Program of China. The authors would also like to express their
appreciation to the Analytical and Testing Center, HUST.
66.40

G. Zhong et al. / Journal of Alloys and Compounds 492 (2010) 482–487
487
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