Materials and Manufacturing Processes, 29: 691–696, 2014
Copyright # Taylor & Francis Group, LLC
ISSN: 1042-6914 print=1532-2475 online
DOI: 10.1080/10426914.2014.892978
Workability Study on 99.04% Pure Aluminum Processed by ECAP
S. Surendarnath1, K. Sankaranarayanasamy1, and B. Ravisankar2
1
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2
Department of Mechanical Engineering, National Institute of Technology, Tiruchirappalli, India
Department of Metallurgical and Materials Engineering, National Institute of Technology, Tiruchirappalli, India
This paper presents the workability of pure aluminum processed by equal channel angular pressing (ECAP) with different routes and the
increasing number of passes. The experiments have been carried out to ECAP die using channel angle (2/) of 90 and corner angle (w) of
20 . The ECAP samples were carried out up to three successive passes using Route A and C. The annealed and ECAPed samples were used
to find out the mechanical property. Workability of the material is an important process parameter for the material to withstand up to initial
cracking. The workability studies were looked into the normal compression tests on cylindrical sample machined from ECAP samples with a
constant diameter of 20 mm with different aspect ratios 0.75, 1.0, and 1.5. Mechanical property and fractography studies were carried out
before and after ECAP process. The observed results have been validated through Cockcroft ductile fracture criterion. An increased mechanical property with a little step down in formability of the consequent ECAP at the second and third passes of both the Routes was
observed.
Keywords CP aluminum; ECAP; Fractography; Mechanical properties; Workability study.
and inhomogeneity of aluminum, magnesium, and lead
alloy using the higher channel angle (90 ) and increased
the flow property of the material. A complete study of
microstructural characterization using commercially
pure aluminum processed by ECAP was done by
El-Danaf; Hoseinia et al.; and Kawasakia et al. [7–10].
Iwahasi et al. [11] proposed the modified equivalent
plastic strain equation,
INTRODUCTION
Equal channel angular pressing (ECAP) is playing
a significant role in severe plastic deformation
techniques for producing nanostructure materials.
Vladimir Segal (1995) initially developed ECAP. The
grain size acts the main role to develop high strength
and ductility of the materials. Valiev and Langdon,
and Shanmugasundaram et al. [1, 2] improved the mechanical properties with high specific strength and ductility
through Hall–Petch relation,
K
ry ¼ r0 þ pffiffiffi
d
1
/ w
/ w
ep ¼ pffiffiffi 2 cot
þ
þ w cosec
þ
2 2
2 2
3
ð1Þ
ð2Þ
where / is the channel angle and w is the corner angle.
Sivaraman and Uday Chakkingal [12] investigated the
workability of CP aluminum resulted in improved mechanical properties with a slight decrement in workability
compared with the annealed samples. Soliman et al.
[13] investigated the properties of CP aluminum processed by ECAP using two processing routes up to four
successive passes. The average grain size, misorientation
angle, and high angle grain boundaries (HAGB) were
investigated from both X and Y planes. In Route Bc,
the average grain size was decreased rapidly than the
Route A condition of both the plane conditions. At
the same time, misorientation angle and HAGB percentage were increased reasonable amount than the Route A
of both the planes. The compressive strength is higher
than the tensile strength for all the passes and routes.
Makhlouf et al. [14] investigated the microstructure
and mechanical property improvement of CP aluminum
processed by equal channel angular extrusion (ECAE)
up to four passes using route C and Bc. After the ECAE
process, the X-ray diffraction (XRD) peak shows the
grain refinement and lattice orientations clearly, as well
as the yield strength and hardness value enhanced the
where K is a material constant, d is the average grain
size, ry is the allowable stress, and r0 is the frictional
stress. Many severe plastic deformation techniques such
as ECAP, HPT (Zhilyaev et al. [3]), multidirectional
forging, twist extrusion, cyclic-extrusion compression,
and ARB have been formulated by Saito et al. [4]. The
main advantages of ECAP are obtaining a large strained
material without change in the workpiece dimension and
repeating the same workpiece many times. Kiyotaka
Nakashima et al. [5] carried out the experiments on
the pure aluminum die consisting of two intersecting
channel angle (u) with an angle from 90 to 157.5 .
The maximum strain was imposed in the 90 channel
die. Cetlin et al. [6] investigated the reduction of crack
Received November 13, 2013; Accepted January 17, 2014
Address correspondence to S. Surendarnath, Department of Mechanical Engineering, National Institute of Technology, Tiruchirappalli –
620015, India; E-mail: surendarmech@gmail.com
Color versions of one or more of the figures in the article can be
found online at www.tandfonline.com/lmmp.
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S. SURENDARNATH ET AL.
consecutive passes. Dieter [15] reported the workability
of various materials under various conditions. Workability is an important process limit for materials to
withstand up to initial cracking of the material on the
outer surface. It mainly depends on the ductile fracture
and its mode of failures in various materials.
Cockcroft and Latham have proposed the equation
for a ductile fracture criterion of metals. The workability
plays main role in materials and the mode of operation.
Therefore, workability ¼ fl (material) f2 (operation)
[16]. Abdel Rahman [16] investigated the workability
of the material using normal compression and tension
test. From the experimentally validated result, the values
were plotted and fitted in the straight line which related
the fracture strain of the material and the strain
increment ratio (b). Equation of the workability line
method determined the magnitude of the stress needed,
which was used in material and the operation. Gouveia
et al. [17] investigated the experimental and theoretical
research work of both Cockcroft and Latham and
Oyane regarding the ductile fracture criterion for the
various geometrical profiles under different loading conditions. Cockcroft and Latham [18] proposed the most
generally applicable ductile fracture criterion. The Cockcroft and Latham ductile fracture criterion equation is
based on the combination of the effective stress and
effective strain of the material.
Zef
rh d e ¼ C
ð3Þ
0
where rh is the ultimate tensile stress, e and ef are
the effective strain and effective strain at failure, C is
the material constant. Agena et al. [19] investigated the
workability of 6082 Al alloy of Freudenthal fracture
criterion using both cylindrical and flanged specimens.
After deformation, the circular cross section of the
workpiece became elliptical in shape due to material
anisotropy, which was reflected in the flow stress.
Narayanamurthy et al. [20] investigated the six general
fracture criteria to calculate the failure in metal forming
operation using the spheroidized steel experimental
result. All the six ductile fracture criteria of material
constant were determined in terms of integral stress
function through the axial strain and the hoop strain
of the test data of spheroidized steel. The newly
proposed criterion can be determined using effective
stress, mean stress, and maximum stress of the deformed
sample.
In this study, we have investigated the workability of
commercially pure aluminum before and after ECAP
process under various processing conditions up to three
passes.
EXPERIMENTAL DETAILS
The commercially pure aluminum (99.04%) was
machined to 25 mm diameter and 80 mm length. The
specimens were annealed at 350 C for 1 h and cooled
in the furnace itself before ECAP processing. The
schematic diagram of the die with a channel diameter
of 25 mm, channel angle (2u) of 90 , and corner angle
(w) of 20 is shown in Fig. 1(a), and die setup is
shown in Fig. 1(b). The workpiece was extruded with
a constant speed of 1 mm=s using a 100 ton hydraulic
press. Molybdenum disulfide (MoS2) was applied as a
lubricant substance in the specimen to reduce the
friction.
For the mechanical property study, the tensile test
specimen was machined from the ECAP sample with
5:1 proportion as per ASTM E8 M11 standard. The testing sample dimensions are shown in Fig. 2. Tensile test
was accomplished using a 30 KN Instron machine at
the constant speed of 0.5 mm=min. For each condition,
three trials were made in finding out the errors. The
material flow properties such as strength coefficient (K)
and strain-hardening exponent (n) were estimated using
power law Eq. (4) from the normal compression test
data of the annealed and ECAP samples with the
10 mm in diameter and 15 mm in height as given in
Table 1.
r ¼ Ken
FIGURE 1.—(a) Schematic diagram of conventional die; (b) Conventional die setup.
ð4Þ
WORKABILITY STUDY ON 99.04% PURE ALUMINUM PROCESSED BY ECAP
FIGURE 2.—Dimensions of tensile test specimen.
TABLE 1.—Material flow property obtained from the normal compression
test ECAP specimens.
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Conditions
Annealed
First pass
Second pass Route A
Second pass Route C
Third pass Route A
Third pass Route C
K (MPa)
N
226
238
250
274
289
319
0.22
0.26
0.31
0.45
0.451
0.423
RESULTS AND DISCUSSION
After completing the ECAP, the specimens were cut
into the longitudinal direction to measure the hardness
values. The hardness values were measured on the top
surface of the ECAPed specimen with a gap of 2.5 mm
distance from the center position. The hardness values
were uniform in all the regions. The hardness measurement mainly depended on the strain imposed on the
material. The hardness measurement was carried out in
all the routes up to the third pass as shown in Fig. 3. After
FIGURE 3.—Vickers microhardness along the surface of the annealed and
various processing routes of ECAP specimen.
693
annealing, the sample showed an average value of 37 HV.
After the first pass, the hardness value reached 53 HV and
in the corresponding second pass, the maximum hardness
value obtained were 61.6 and 63 HV in RA and RC,
respectively. In the third pass, the hardness was 66.5
and 68 HV in RA and RC, respectively.
The tensile test results were plotted in Fig. 4(a).
A gradual increment in the tensile strength of the ECAP
specimen can be seen in the consecutive passes. After
annealing condition, the tensile strength was 144 MPa.
After a first pass, the tensile strength reaches 191 MPa.
After the successive second and third passes of Route
A, the tensile strength was 199 and 201 MPa, respectively.
Similarly, in Route C, the UTS were 207 and 218 MPa.
Figure 4(b). shows the percentage of elongation to the
failure with subsequent passes. The percentage of failure
elongation of the before ECAP sample was 26% and it
reduced to 17% in RA and 15.7% in RC at the end of
third pass. The fractography study was carried out from
the tensile test samples using a scanning electron microscope. It was seen that the ECAP samples from the first
pass to the third pass showed a ductile fracture in all the
specimens. The specimens initially formed the necking
and then they developed failures. This is clearly visible
in the SEM images shown in Fig. 5.
For the workability study of the ECAP samples,
a simple compression test was followed using cylindrical
specimens with the aspect ratio (h=d) of 0.75, 1.0, and
1.5. The diameter was constant for all the aspect ratio
20 mm. For reducing the errors, two specimens were
machined for each condition. The compression test data
were used to find out the strain increment ratio (a) and
the fracture strain of the material. The strain increment
ratio of different processing routes is given in Table 2.
The specimens were compressed under incremental
load conditions, and when a specimen was in uniform
deformation the middle portion of the specimen bulged.
The upsetting was carried out still the occurrence of
visible cracks on the outer barrel of the specimen. After
upsetting, the axial and circumferential strain were
estimated from the specimen initial and final dimension.
From the initial and final gage height of the compressed
sample, the compressive strain (eZ) was estimated. The
circumferential strain or hoop strain (eh) was estimated
from the specimen initial and the final diameter. The
axial versus circumferential strain was plotted to find
the slope of the line. All the compression-tested materials were nearer to the linear fit of the line. It indicated
that the ECAP specimens in all the processing routes
showed the homogeneous condition of the material.
The Cockcroft and Latham constant C1 was calculated from the tensile test result and the effective fracture
strain of the material. The various processing routes of
ECAP results are given in Table 3. The workability
diagram of various ECAP samples is shown in Fig. 6.
Figure 6 shows the compressive and circumferential
strain of the samples.
The axial vs. hoop strain of the annealed sample was
experimentally validated through the empirical formula,
and also the different passes of ECAP samples were
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S. SURENDARNATH ET AL.
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FIGURE 4.—(a) Tensile strength vs. no. of passes; (b) Percentage of elongation vs. no. of passes.
FIGURE 5.—Fracture surface of the ECAPed tensile test samples (a) First pass; (b) Second pass RA; (c) Second pass RC; (d) Third pass RA; (d) Third
pass RC.
TABLE 2.—Strain increment ratio (a) of various ECAP samples.
(Aspect ratio)
0.75
1.0
1.5
Annealed
First pass
Second pass RA
Second pass RC
Third pass RA
Third pass RC
0.538
0.531
0.522
0.536
0.527
0.520
0.527
0.510
0.507
0.512
0.513
0.510
0.516
0.507
0.504
0.503
0.50
0.498
WORKABILITY STUDY ON 99.04% PURE ALUMINUM PROCESSED BY ECAP
TABLE 3.—Cockcroft and Latham ductile fracture criteria (C1) for various
processing routes.
C1 (MPa)
Annealed
First pass
Second pass Route A
Second pass Route C
Third pass Route A
Third pass Route C
27.52
30.6
33.05
40.26
35.92
39.17
695
succeeding passes. From the observed result, it clearly
shows the ECAP results in reduction of workability
compared to the annealed sample. The second pass,
Route C, has slightly higher workability than Route
A. Finally, the third pass, both the routes of ECAP samples have a lesser workability than the second pass.
Route C is better than Route A for better formability
and better strength than Route A of ECAP.
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REFERENCES
FIGURE 6.—Workability diagram for annealed and various ECAPed
samples.
validated and compared with the annealed samples. The
annealed samples have superior formability than the
ECAP samples. At the end of the first pass, the workability is little bit reduced than the annealed samples.
At the end of the second pass, the workability of RA
has slightly decreased than that of Route C. However,
the workability limits are very close and more or less
the same. At the end of third pass, the workability
decreased a little bit compared to the second pass in
both the routes. As the successive passes, the workability
of the material decreases because of increase in strength
and the hardness of material, this is clearly observed in
this work. The workability plays a significant role in
the metal forming processes such as to withstand the
material without losing their property.
CONCLUSIONS
Workability on CP aluminum processed by ECAP has
been investigated successfully. The ECAP of commercial
aluminum results in improving the mechanical properties like strength and hardness. The Cockcroft
and Latham constant C clearly shows the ductility of
the material for various processing routes and the
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