Influence of the cooling rate on the structure and mechanical properties of a cast alloy of Al-Mg-Si system
An investigation of influence of the cooling rate on the structure and hardness of a new cast eutectic (α-Al + Mg2Si) alloy of the Al—Mg—Si ternary system showed that the critical cooling rate at which a colonial eutectic structure disappears is ~10^5 K/s. The change-over from laboratory castings wi...
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2009
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| Cite this: | Influence of the cooling rate on the structure and mechanical properties of a cast alloy of Al-Mg-Si system / N.M. Mordovets, Yu.V. Milman, N.P. Korzhova, T.N. Legka, V.V. Kuprin, Yu.N. Podrezov, K.E. Grinkevych, I.V. Voskoboinik, V.H. Melnik // Электронная микроскопия и прочность материалов: Сб. научн . тр. — К.: ІПМ НАН України, 2009. — Вип. 16. — С. 54-59. — Бібліогр.: 9 назв. — англ. |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1860129865261383680 |
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| author | Mordovets, N.M. Milman, Yu.V. Korzhova, N.P. Legka, T.N. Kuprin, V.V. Podrezov, Yu.N. Grinkevych, K.E. Voskoboinik, I.V. Melnik, V.H. |
| author_facet | Mordovets, N.M. Milman, Yu.V. Korzhova, N.P. Legka, T.N. Kuprin, V.V. Podrezov, Yu.N. Grinkevych, K.E. Voskoboinik, I.V. Melnik, V.H. |
| citation_txt | Influence of the cooling rate on the structure and mechanical properties of a cast alloy of Al-Mg-Si system / N.M. Mordovets, Yu.V. Milman, N.P. Korzhova, T.N. Legka, V.V. Kuprin, Yu.N. Podrezov, K.E. Grinkevych, I.V. Voskoboinik, V.H. Melnik // Электронная микроскопия и прочность материалов: Сб. научн . тр. — К.: ІПМ НАН України, 2009. — Вип. 16. — С. 54-59. — Бібліогр.: 9 назв. — англ. |
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| description | An investigation of influence of the cooling rate on the structure and hardness of a new cast eutectic (α-Al + Mg2Si) alloy of the Al—Mg—Si ternary system showed that the critical cooling rate at which a colonial eutectic structure disappears is ~10^5 K/s. The change-over from laboratory castings with a weight of 200g to commercial castings with a weight of 20 kg practically does not influence on the level of mechanical properties under comparable cooling conditions.
|
| first_indexed | 2025-12-07T17:44:17Z |
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54
UDK ∆669.018.28:620.18:620.178.1
Influence of the cooling rate on the structure
and mechanical properties of a cast alloy of Al—Mg—Si
system
N. M. Mordovets, Yu.V. Milman, N. P. Korzhova, T. N. Legka*,
V. V. Kuprin, Yu. N. Podrezov, K. E. Grinkevych,
I. V. Voskoboinik, V. H. Melnik
*Kurdjumov Institute for Metal Physics of NAS of Ukraine, Kiyv
An investigation of influence of the cooling rate on the structure and hardness of a new
cast eutectic (α-Al + Mg2Si) alloy of the Al—Mg—Si ternary system showed that the
critical cooling rate at which a colonial eutectic structure disappears is ~105 K/s.
The change-over from laboratory castings with a weight of 200g to commercial castings
with a weight of 20 kg practically does not influence on the level of mechanical
properties under comparable cooling conditions.
Introduction
At present, aluminum alloys are extensively used in the machine-building,
aerospace, automotive, construction, and ship-building industries. At the same
time, the trend to the replacement of steel components by components made of
lighter alloys, in particular, aluminum alloys, increases. The authors propose a
new approach to the development of competitive alloys based on using of ternary
phase diagrams with the participation of aluminum, that have quasi-binary
eutectic-type sections between an aluminum solid solution and intermetallic
phases. Eutectic alloys the compositions of which are located on quasi-binary
sections are solidified at a constant temperature which is higher than the melting
points of alloys of limit binary systems. To provide a high level of the physical-
mechanical properties due to the purposeful alloying of these alloys, in the matrix
of these alloys, different systems of particles, which do not interact with the
eutectic framework and are stable in some temperature ranges, are formed.
On the basis of the formulated principles, the authors developed a new class
of cast aluminum alloys on the base of the quasi-binary section (α-Al + Mg2Si) of
the Al—Mg—Si ternary diagram (hereafter referred to as ASM alloys) which
surpass traditional commercial Al—Si alloys by physical-mechanical and
corrosion properties. The specific strength of the new ASM alloys is 1,5 times
larger than that of steel 4135 (USA) [1—3]. It has been shown, that the advantages
of the new ASM alloys rise with increasing temperature and testing time.
Properties of the new alloys in the form of castings with a mass of 200 g have
been studied rather thoroughly. At the same time an investigation of the structure
and properties of these cast alloys in variable sections where the cooling rate differs
substantially is of scientific and practical interest. Moreover, from a scientific
standpoint, an investigation of the new alloys obtained in the form of thin ribbons at
a super-high cooling rate of the order of 105 to 107 K/s is of interest.
© N. M. Mordovets, Yu.V. Milman, N. P. Korzhova, T. N. Legka,
V. V. Kuprin, Yu. N. Podrezov, K. E. Grinkevych, I. V. Voskoboinik,
V. H. Melnik, 2009
55
The aim of the present investigation is to study the influence of the cooling
rate on the structure and mechanical properties of complexly alloyed cast
eutectic (α-Al + Mg2Si) alloys of the Al—Mg—Si ternary system.
Materials and Technique
Laboratory castings with a weight of 200 g were made in a resistance
furnace in Al2O3 crucibles. The melt was poured in a copper mould of 25 mm in
diameter. Castings with a weight of 20 kg were smelted in a graphite crucible of
a diameter of 160 mm in an induction melting furnace of a power of 160 W
with a TPChT-160 current source of high (24 kHz) frequency. The melt was
poured into a water-cooled copper mould of 150 mm in diameter. Castings were
made of pure charge materials and master alloys preliminarily heated to a tem-
perature of 250 to 300 ºC to remove adsorbed moisture and prevent saturation
of the melt with hydrogen. Smelting was performed in air using protective
fluxes (75% LiCl + 25% LiF). At the end of each smelting, the melt was blown
through with argon in the furnace. Furthermore, castings were made by pouring
in a massive copper mould with a wall thickness of 31 mm (the diameter
of castings was about 2,8 mm), and thin ribbons with a thickness 70 and 25 µm
were obtained by the method of rapid solidification on a massive copper
drum (the melt-spinning method). The rotation speed of the drum was about
24,5 m/sec.
Investigations were performed by metallographic, thermal, differential
thermal, durometric, and X-ray diffraction (XRD) analyses, mechanical tensile
and tribological tests.
Metallographic specimens were prepared using a standard technique. Their
final polishing was performed using an aqueous suspension of chromium oxide
as an abrasive. The etching of the metallographic specimens was carried out in a
reagent with the following composition: 95% (vol.) of acetic acid and 4% (vol.)
of perchloric acid. A metallographic examination was performed with the help of
NEOPHOT-30 microscope and a Jeol Superprobe-733 electron probe
microanalyzer.
The phase composition was studied with a DRON-UM1 diffractometer in
CuKα-radiation using a graphite single crystal as a monochromator.
The melting points of the alloys and critical points of phase transformation
were determined with units for thermal and differential thermal analysis.
Hardness measurements were carried out by the Vickers method. The load
on an indenter was 50 N. The microhardness of thin rapidly solidified ribbons
was tested with a PMT-3 microhardness tester under a load of 0,2 N.
Short-term tensile test of cylindrical specimens were performed with
recording of loading diagrams in the temperature range of 20—400 ºC using a
generally accepted procedure which includes heating of specimens without
loading for 0,5 h at a testing temperature with subsequent loading to fracture.
The tensile rate was 10-3 s-1.
The tribological test was carried out using an ATDK [4] original unit
according to the sphere–plane contact scheme under conditions of reverse-
forward slip of a spherical indenter over a flat specimen at a temperature of 20
and 200 ºC. The test was performed under a constant load (a quasi-stationary
regime) and with the application of a variable load (dynamic regime). A silicon
nitride Si3N4 ceramic spherical indenter of 8 mm in diameter was used. The sliding
speed was 0,013 m/s, and a load applied to the indenter ranged from 22 to 78 N.
56
The results of experiments are designated by the subscripts “s” and “d” for
static and dynamic regimes, respectively. Wear characteristics (Is and Id), which
correspond to the depth of friction paths in regions of the quasi-stationary and
dynamic loading, were used as criteria of assessment of the fracture mechanism
of a surface.
Results and Discussion
It is known [5] that, depending on the cooling rate, the eutectic transformation
proceeds by different mechanisms. In the present work, the influence of
the cooling rate (Vcool.) of castings in the range 102—107 K/s was investigated
(table 1). Micrographs of microstructures (manufacturing methods Nos. 1—4)
are shown in fig. 1.
As it is seen from fig. 1, a, the structure of the casting of 25 mm in diameter
is an assemblage of primary modified round dendrites of the α solid solution
and the (α-Al + Mg2Si) eutectic of lamellar morphology. The structure of the
rapidly solidified casting of 2,8 mm in diameter is characterized by the presence
of primary non-modified dendrites with axes of higher order (the loss of the
stability of the form of growth of the dendrite takes place) and disperse eutectic
(fig. 1, b). Under the cooling conditions of these two alloys, crystal growth is
controlled by separation diffusion of atoms in the melt ahead of the
crystallization front; in the process of crystallization, the colonial structures,
which are characteristic of cooperative growth of eutectic, form.
At cooling rate of 105 to 107 K/s, which is characteristic of the rapidly
cooled ribbon, cooperative growth of the eutectic cannot occur (fig. 1, c, d).
Similar structures were obtained by super-rapid solidification of alloys of the
Al—Cu and Fe—C systems under analogous conditions [6]. An abrupt
T a b l e 1. Microstructural features of ASM alloy specimens obtained
under different cooling conditions
No. Manufacturing
method
Specimen
size
Vcool.,
K/s Microstructure
1a Smelting in an
induction furnace
(water-cooled
copper mould)
Casting of
150 mm in
diameter
102 Primary crystals of the α-Al phase
(~18 µm) and a lamellar eutectic
(the thickness of plates of the
Mg2Si phase is ∼0,4 µm)
1 Smelting in a
resistance furnace
(copper mould)
Casting of
25 mm in
diameter
7·102 Rounded primary crystals of the
α-Al phase (~14 µm) and a
lamellar eutectic (the thickness of
plates of the Mg2Si phase is
∼0,2 µm)
2 Rapidly cooled bar
(copper mould)
Bar 2,8 mm
in diameter
104 Primary crystals of the α-Al phase
of dendritic shape (~4,2 µm; the
dendritic parameter is ~3,5 µm)
and an eutectic (the size of the
Mg2Si phase is ~0,2 µm)
3 Thickness
of 70 µm
105—106
4
Rapidly cooled
ribbon (by casting
on a copper drum
of 390 mm in
diameter)
Thickness
of 25 µm
107
The Mg2Si phase in the form of
individual particles
57
5 µm
a
5 µm
b
25 µm
с
Mg
Si
10 µm
d
Fig. 1. Microstructure of a hypoeutectic ASM alloy obtained at different cooling
rates: а — 7. 102 К/s; b — 104 К/s; c, d — 105—106 К/s; d — results of X-ray
microanalisys.
T a b l e 2. Hardness of castings and ratio of phases (α-Al : Mg2Si) accor-
ding to XRD data
Method of production State of specimen Hardness,
MPа
Ratio of phases
α-Al : Mg2Si
Cast 929* 92,7 : 7,3 1
Annealing 300 °С/5 hours 1118* 90,9 : 9,1
Cast 1102* 92,9 : 7,1 2
Annealing 300 °С/5 hours 1200* —
3 Cast 1528** 92,9 : 7,1
4 Cast 1499** 96,9 : 3,1
*Load 5 kg; ** Load 20 g.
retardation of diffusion processes hinders growth of phases, as a result of which
the sizes of critical nuclei decrease substantially, and their number substantially
increases. Under these conditions, the colonial eutectic solidification becomes
impossible and fine-grained mixtures of phases form. Such a disperse structure
can be called a “structure of fine conglomerate of phases” [7—9].
Thus, the increase in the cooling rate favours to decreasing in the sizes of
the structural components of the hypoeutectic alloy; the critical cooling rate at
which the colonial eutectic structure disappears is ~105 K/s.
The phase composition of the alloy is characterized by the presence of α-Al
and the Mg2Si phase (table 2, fig. 1, a). In the structure of the thinnest rapidly
solidified ribbon, besides the aforementioned phases, an amorphous phase is
also presents (fig. 2, b).
It is interesting to note that as a result of the change-over from the traditional
casting method to rapid quenching, the ratio of (α-Al : Mg2Si) (specimens
Nos. 1—3) remains practically unchanged (table 2), which indicates the high
stability of the phase composition.
58
20 25 30 35 40 45 50 55 60 65 70 75 80
3183
1591
0
P o w d e rC e ll 2 . 2
Al 93,0%
20
0
22
0
31
1
22
2
M G2SI 7,0%
11
1
20
0
22
0
31
1
22
2
40
0
33
1
42
0
42
2
51
1
ASM 9_21.X_Y
20 25 30 35 40 45 50 55 60 65 70 75 80
2276
1138
0
P o w d e rC e ll 2 . 2
ASM_LNT.X_Y
Fig. 2. X-ray diffraction patterns of rapidly solidified ribbons: а — ribbon with
thickness of 70 µm with crystalline structure (* — Al, ** — Mg2Si); b — ribbon
with thickness of 25 µm with amorphous-crystalline structure.
a b c d e
0
200
400
600
800
1000
1200
1400
1600 3
2
21
H
ar
dn
es
s,
M
Pa
1
Fig. 3. The hardness of specimens of the
ASM alloy which obtained under
different cooling conditions: a, c, e —
cast state; b, d — annealing 300 оС/5
hours. Number of specimen corresponds
to table 2. The hardness of specimens
Nos. 1 and 2 was measured under a load
of 5 kg; the hardness of specimen No. 3
(rapidly quenched ribbon) was measured
under a load of 20 g.
The hardness and microhardness of the investigated specimens are
presented in table 2. The grain refinement of the rapidly quenched casting with
a diameter of 2,8 mm (No. 2) leads to an increase in the hardness (fig. 3).
The values of the hardness of the rapidly quenched ribbons of 70 and 25 µm in
thick are close. From fig. 3 it is seen that the higher the cooling rate of
the specimen, the higher the hardness.
In fig. 4, the microstructure of the laboratory casting with a weight of
200 g (fig. 4, a) and a witness sample obtained by smelting of the commercial
casting with a weight of 20 kg (fig. 4, b) is given. Note, that in order to provide
identical cooling conditions, the ingot with a weight of 20 kg was poured into
the water-cooled mould.
a b
Fig. 4. Microstructure of ASM-alloy in cast state: a — laboratory casting; b —
witness sample obtained from a casting with a weight of 20 kg.
59
Fig. 5. Mechanical properties
of ingots of weight 200 g and
20 kg.
The mechanical properties
determined by tensile test
and tribological properties
of these alloys after the
heat treatment are shown
in fig. 5.
0
50
100
150
200
250
300
350
0
50
100
150
200
250
300
350
indastrial ingot (20 kg)
I S, I
D
, µ
m
σUTS
σ Y
S, σ
U
T
S, M
Pa
laboratory ingot (200 g)
RT
200oC
ID
σUTS IS
σYS IDIS
σYS
ASM20
The data obtained indicate, that when certain solidification conditions are
met, the level of properties of the ASM-alloy of the laboratory casting differ
insignificantly from that of the casting with a weight of 20 kg.
Conclusions
The mechanism of pair eutectic growth in the α-Al—Mg2Si system is
realized in a wide range of cooling rates (to 104 K/s), which makes it possible to
retain the eutectic structure of the alloys and their properties. At the same time,
the ratio of the phases α-Al : Mg2Si remains practically unchanged, which
testifies to the stability of the phase composition. An increase in the cooling rate
leads to the grain refinement of structural elements and an increase in
the hardness.
The change-over from laboratory castings with a weight of 200 g (25 mm
in diameter) to castings with a weight of 20 kg (150 mm in diameter) under
comparable cooling conditions enables us to retain the level of mechanical and
tribological properties of the new Al—Mg—Si cast alloy, which is particularly
important for transition to commercial production.
1. Barabash O. M., Sulgenko O. V., Legkaya T. N., Korzhova N. P. Experimental analysis and
thermodynamic calculation of the structural regularities in the fusion diagram of the system
of alloys Al—Mg—Si // J. of Phase Equilibria. — 2001. — 22, Nо. 1. — P. 5—11.
2. Barabash O. M., Milman Yu. V., Korzhova N. P. et al. Design of new cast aluminium
materials using properties of monovariant eutectic transformation L↔α-Al + Mg2Si //
Materials Science Forum. — 2002. — 396—402. — P. 729—734.
3. Пат. № 83776 України. Ливарний сплав алюмінію / Мільман Ю. В., Легка Т. М.,
Барабаш О. М., Коржова Н. П. та ін. // Бюл. „Промислова власність”. — 2008. —
№ 15.
4. Гринкевич К. Э., Зенкин Н. А. Комплекс диагностической аппаратуры и методология
контроля параметров трибосистемы в динамических условиях испытаний // Контроль.
Диагностика. — 2002. — № 6. — С. 49—51.
5. Бочвар А. А. Исследование механизма и кинетики кристаллизации сплавов
эвтектического типа. — М.—Л.: Глав. ред. лит-ры по цвет. металлургии, 1935. — 115 с.
6. Таран Ю. Н., Мирошниченко И. С., Галушко И. М. О влиянии скорости охлаждения
на формирование структуры сплавов эвтектического типа // Металлофизика. — К.:
Наук. думка, 1974. — 56. — С. 77—83.
7. Таран Ю. Н., Мазур В. И. Структура эвтектических сплавов. — М.: Металлургия,
1978. — 312 с.
8. Мазур В. И., Сердюк А. Г., Таран Ю. Н. Эвтектическая кристаллизация при больших
скоростях охлаждения // Рост и дефекты металлических кристаллов. — К.: Наук.
думка, 1972. — С. 347—352.
9. Таран Ю. Н., Мирошниченко И. С. О трех типах эвтектических структур //
Там же. — С. 339—347.
|
| id | nasplib_isofts_kiev_ua-123456789-17680 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | XXXX-0048 |
| language | Russian |
| last_indexed | 2025-12-07T17:44:17Z |
| publishDate | 2009 |
| publisher | Інститут проблем матеріалознавства ім. І.М. Францевича НАН України |
| record_format | dspace |
| spelling | Mordovets, N.M. Milman, Yu.V. Korzhova, N.P. Legka, T.N. Kuprin, V.V. Podrezov, Yu.N. Grinkevych, K.E. Voskoboinik, I.V. Melnik, V.H. 2011-03-05T22:56:08Z 2011-03-05T22:56:08Z 2009 Influence of the cooling rate on the structure and mechanical properties of a cast alloy of Al-Mg-Si system / N.M. Mordovets, Yu.V. Milman, N.P. Korzhova, T.N. Legka, V.V. Kuprin, Yu.N. Podrezov, K.E. Grinkevych, I.V. Voskoboinik, V.H. Melnik // Электронная микроскопия и прочность материалов: Сб. научн . тр. — К.: ІПМ НАН України, 2009. — Вип. 16. — С. 54-59. — Бібліогр.: 9 назв. — англ. XXXX-0048 https://nasplib.isofts.kiev.ua/handle/123456789/17680 669.018.28:620.18:620.178.1 An investigation of influence of the cooling rate on the structure and hardness of a new cast eutectic (α-Al + Mg2Si) alloy of the Al—Mg—Si ternary system showed that the critical cooling rate at which a colonial eutectic structure disappears is ~10^5 K/s. The change-over from laboratory castings with a weight of 200g to commercial castings with a weight of 20 kg practically does not influence on the level of mechanical properties under comparable cooling conditions. ru Інститут проблем матеріалознавства ім. І.М. Францевича НАН України Influence of the cooling rate on the structure and mechanical properties of a cast alloy of Al-Mg-Si system Article published earlier |
| spellingShingle | Influence of the cooling rate on the structure and mechanical properties of a cast alloy of Al-Mg-Si system Mordovets, N.M. Milman, Yu.V. Korzhova, N.P. Legka, T.N. Kuprin, V.V. Podrezov, Yu.N. Grinkevych, K.E. Voskoboinik, I.V. Melnik, V.H. |
| title | Influence of the cooling rate on the structure and mechanical properties of a cast alloy of Al-Mg-Si system |
| title_full | Influence of the cooling rate on the structure and mechanical properties of a cast alloy of Al-Mg-Si system |
| title_fullStr | Influence of the cooling rate on the structure and mechanical properties of a cast alloy of Al-Mg-Si system |
| title_full_unstemmed | Influence of the cooling rate on the structure and mechanical properties of a cast alloy of Al-Mg-Si system |
| title_short | Influence of the cooling rate on the structure and mechanical properties of a cast alloy of Al-Mg-Si system |
| title_sort | influence of the cooling rate on the structure and mechanical properties of a cast alloy of al-mg-si system |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/17680 |
| work_keys_str_mv | AT mordovetsnm influenceofthecoolingrateonthestructureandmechanicalpropertiesofacastalloyofalmgsisystem AT milmanyuv influenceofthecoolingrateonthestructureandmechanicalpropertiesofacastalloyofalmgsisystem AT korzhovanp influenceofthecoolingrateonthestructureandmechanicalpropertiesofacastalloyofalmgsisystem AT legkatn influenceofthecoolingrateonthestructureandmechanicalpropertiesofacastalloyofalmgsisystem AT kuprinvv influenceofthecoolingrateonthestructureandmechanicalpropertiesofacastalloyofalmgsisystem AT podrezovyun influenceofthecoolingrateonthestructureandmechanicalpropertiesofacastalloyofalmgsisystem AT grinkevychke influenceofthecoolingrateonthestructureandmechanicalpropertiesofacastalloyofalmgsisystem AT voskoboinikiv influenceofthecoolingrateonthestructureandmechanicalpropertiesofacastalloyofalmgsisystem AT melnikvh influenceofthecoolingrateonthestructureandmechanicalpropertiesofacastalloyofalmgsisystem |