International Scientific Journal
published monthly as the organ of
the Committee of Materials Science
of the Polish Academy of Sciences
of Materials Science
© Copyright by International OCSCO World Press. All rights reserved. 2007
Using severe plastic deformation
to prepare of ultra fine - grained materials
by ECAP method
S. Rusz a,* , K. Malanik b
a Faculty of Mechanical Engineering, VSB–Technical university of Ostrava,
17 listopadu 15, 708 33 Ostrava–Poruba, Czech Republic
b VUHZ Dobra a. s., 738 01 Dobra, Czech Republic
* Corresponding author: E-mail address: firstname.lastname@example.org
Received 22.10.2007; published in revised form 01.11.2007
Purpose: The purpose of the paper is to design a tool and propose a procedure for verification of development
of structure at equal channel angular pressing. The goal is to obtain after extrusion the semi-products of AlCuMg
alloys a fine-grain structure which one hand increases strength properties and plasticity, and on the other hand is
possible to use it at selected cases for subsequent deformations under conditions of „super-plastic state“.
Design/methodology/approach: The experiments were aimed the verification of functionality of the
proposed equipment, determination of deformation resistance, deformability and change of structure at extrusion of
the alloy AlCu4Mg2. Deformation forces were measured at extrusion. The average grain size in cross direction was
determined by quantitative metallographic methods. TEM analysis of the structure of AlCu4Mg2 were also made.
Findings: The structural analysis of AlCu4Mg2 alloy made by TEM has demonstrated a perfect suitability of the
ECAP die design. The process results in a very fine grain structure (100-200 nm) throughout the sample overall
volume, at which the starting average grain size was 150 μm.
Practical implications: Aluminium alloys of super fine granularity structure are basic intermediate products
realised by ECAP technologies. The state of super fine granularity facilitates forming of material in the so-called
‘superplastic state’. The achievement of the desired structure depends primarily on the tool geometry, number of
passages through the die, magnitude and speed of deformation, process temperature, and lubrication mode.
Originality/value: It has been demonstrated that the extrusion technology is suitable for attaining of grain
nano-structure in the material investigated in order to determine the number of extrusion cycles needed and the
appropriate canal angle with corresponding internal and external bend radii. The obtained results make for success
of further investigative efforts in the area.
Keywords: Severe plastic deformation; Die geometry; Microstructures analyse; ECAP technology
MATERIALS MANUFACTURING AND PROCESSING
The technology, ECAP – Equal Channel Angular Pressing,
belongs to technologies of accelerated development and
represents top items of R&D agenda in the world. Severe plastic
straining is achieved in ECAP by pressing the sample through a
die as illustrated schematically in Fig. 1. The sample is machined
to fit within a channel which passes through the die in an L
shaped configuration [1,4]. For the situation where the angle
between the two parts of the channel is equal to 90°, the test
sample will undergo straining by shear as it passes from one part
of the channel to the other: this shearing is illustrated in Fig. 2. It
is apparent from Fig. 1 that the sample emerges from the die
without any change in the cross-sectional dimensions. Thus, this
process is distinct from the more conventional metal working
S. Rusz, K. Malanik
Archives of Materials Science and Engineering
processes such as rolling and extrusion where there is a
concomitant reduction in the cross-sectional dimensions of the
work piece. In practice, it is convenient to define three separate
planes within the sample associated with ECAP: these planes are
indicated in Fig. 1 and they are plane X perpendicular to the
longitudinal axis and planes Y and Z parallel to the side face and
the top face of the sample at the point of exit from the die,
respectively. To understand the effect of these different
processing routes, it is instructive to examine the internal
shearing patterns as illustrated in Fig. 3 where the planes
labelled 1 through 4 denote the shearing which occurs on the
first four pressings through the die: the planes designated X, Y
and Z in Fig. 3 correspondent to the planes illustrated in Fig.
1on the as pressed sample.
Fig. 1. Shearing associated by a single passage through the die
Inspection of Fig. 3 shows the shearing patterns are dependent
upon the processing route. For example, in route C there are
repetitive sheerings on the same plane whereas in route A there
are two shearing planes intersecting at an angle of 90° and in
routes Ba and Bc there are four distinct shearing planes
intersecting at angles of 120° [2,6].
2. Principles of shearing on passage
through The ECAP die.
through The ECAP die
Since the cross-sectional area of the sample is unchanged on a
single passage through the die, it is apparent that repetitive pressings
may be undertaken in order to achieve very high total strains.
The strain imposed on the sample in a single passage through
the die is dependent primarily upon the angle ? between the two
separate parts of the channel within the die. There is also a minor
dependence upon the angle ? at the outer arc of curvature where
the two channels intersect. In practice, however it can be shown
that the imposed strain is close to ~ 1when ? = 90°for all values
of ? [3,7,9].
In Fig.2, where ? represents an intermediate situation, the
shear strain is ? = a´u/d´u , where d´u = ad and a´u may be
obtained form the relationships a´u = (a´t + tu) = (rc´ + as), as =
adcot (?/2+?/2), ab´= dc´= ( as + os?) = rc´+ od? and (os –
od ) = adcosec (?/2+?/2), so that a´u = 2adcot (?/2+?/2) +
Fig. 2. Principle of equal – channel angular pressing where ? is
the angle of intersection of the two channels and ? is the angle
subtended by the arc of curvature at the point of intersection
Therefore, the shear strain for this intermediate condition is given
Since the same strain is accumulated in each passage
through the die, the strain after N cycles is therefore given by
ec cosg cot2
Thus, the strain may be estimated from equation (2) for any
pressing conditions provided the angles ? and ? are known. A
relationship is derived which may be used to calculate the
imposed strain after any number of selected pressing cycles .
Plastic deformation realised with use of the ECAP technology
represents a complex process, which depends on great number of
factors, such as homologous temperature of deformation Th, (Th
= Ttav/Tt), grain size dz, strain rate ?o??? , magnitude of octahedral
stress at deformation ?8, particularly in relation to the magnitude
of the modulus of elasticity E (?8/E represents homologous
stress), but also on density of structural surfaces (particularly
dislocations; vacancies), on purity, etc. ECAP cold deformation is
significantly dependent on the latter factors.
Influence of magnitude of plastic deformation on
characteristics of the alloy AlCu4Mg2 is at the use of technology
ECAP connected with increase of internal energy. Internal energy
increases till the limit value, which depends on method of
deformation, purity, grain size, temperature, etc. Increment of
internal energy is directly related to the quantity and character of
lattice defects in extruded alloy, i.e. that volume of energy
absorbed by structure at
contamination of the matrix, with reduction of grain size, with
drop of deformation temperature [8,10].
As a result of non-homogeneity of deformation at the ECAP
(selected planes and direction of slippage) the internal energy
increment at different places of the formed alloy is also different.
deformation increases with
2. Principles of shearing on passage
Using severe plastic deformation to prepare of ultra fine - grained materials by ECAP method
Volume 28 Issue 11 November 2007
For example value of internal energy is different at slip planes, at
the boundaries and inside the cells. It is possible to observe higher
internal energy also in proximity of precipitates, segregations and
hard structural phases. For usual technologies, pure metals,
medium magnitude of deformation and temperature the value of
the stored energy is said to be of approx. 10 Jmol-1. Density of
dislocations, concentration of vacancies and total surface of walls
of cell structure increases at cold extrusion in proportion to
magnitude of plastic deformation [1, 13, 15]. If no softening
processes occur at forming, then dislocation density depends
linearly on magnitude of plastic deformation in accordance with
the well-known equation:
is a initial dislocation density,
is a constant,
is magnitude of deformation.
Flow stress, which is necessary for continuing
deformation, is a function number of lattice defects, particularly
of dislocations, and it can be expressed by the equation :
is a value of initial flow stress,
is a constant,
are modules of elasticity in shear, Burgers’
vector. Size of sub-grains and magnitude of
deformation are in direct relation, when size
of sub-grains decreases with increased
We have designed a tool and proposed a procedure for
verification of development of structure at equal channel angular
pressing. Normal AlCuMg alloys were used for manufacturing of
the input semi-product. Our target was to obtain after extrusion
the semi-products with a fine-grain structure [11, 12]. Such a
structure on one hand increases strength properties and plasticity,
and on the other hand it is possible to use it at selected cases for
subsequent deformations under conditions of „super-plastic state“.
Obtaining of the necessary structure in extruded samples depends
primarily on the tool’s geometry, number of passes through the
die, obtained magnitude of deformation, temperature, etc.
3. Experimental verification
3. Experimental verification
The experiments were aimed at verification of functionality of
the proposed equipment, determination of deformation resistance,
deformability and change of structure at extrusion of the alloy
AlCu4Mg2. The experiments were made on the equipment, which
is demonstrated in Figs 3-6. Original input examples were made
from hot-formed semi-products. Square section of the input
samples was 8 x 8 x 28 mm. The samples were extruded at the
temperature of approx. 20 oC. In order to increase deformation in
the volume of the sample, the samples were turned after each
internal extrusion around the longitudinal axis by 90o and extruded
again. Initial shape of the sample as well as shapes of samples after
individual stages of extrusion are shown in the Fig 3.
Fig. 3. Initial state and states after extrusion
Deformation forces were measured at extrusion. There was
also the average value of true deformation resistance and strain
rate calculated. Structure analysis was made with use of the
transmission electron microscope. The initial structure contained
usual inter-metallic phases, corresponding to the given
composition of the alloy, which precipitated predominantly at the
grain boundaries [6, 14]. The average grain size in cross direction
was determined by quantitative metallographic methods. It varied
around 150 µm. The basic mechanical properties were determined
by tensile tests: strength Rm = 220 MPa, ductility A5 = 15 % and
hardness HB (2,5/62/30) ~ 70. Examples of structures analysed
by TEM after first and fourth passage through the ECAP die in
different places of sample.
Fig. 4. Pattern structure of ALCu4Mg2 alloy a) after the first
passage dies, b) after the second passage (middle of specimen)
Fig. 5. Pattern structure of ALCu4Mg2 alloy a) after the third
passage, b) after the 4th passage (middle of specimen)
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Fig. 6. Pattern structure of ALCu4Mg2 alloy after the 4th passage
(edge of specimen)
Structural analysis of AlCu4Mg2 alloy made by TEM has
demonstrated a perfect suitability of the ECAP die design. It has
been also demonstrated that the extrusion technology is suitable
for attaining of grain nano-structure in the material investigated
concerning the number of extrusion cycles needed and the
appropriate canal angle with corresponding internal and external
bend radii. High deformation degrees and providing for a great
number of shearing planes, grain boundary dislocations were
eliminated. The process results in a very fine grain structure
(100-200 nm) throughout the sample overall volume, at which the
starting average grain size was 150 ?m. The results attained make
for success of further investigative efforts in the area.
The authors would like to acknowledge gratefully that the
Ministry of Trade and Commerce project MPO No. 2A–1TP/124,
sponsored this work.
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and properties of