O. ÇAVUªOÐLU et al.: STRAIN-RATE-DEPENDENT TENSILE CHARACTERISTICS OF AA2139-T351 ALUMINUM ALLOY
333–348
STRAIN-RATE-DEPENDENT TENSILE CHARACTERISTICS OF
AA2139-T351 ALUMINUM ALLOY
NATEZNA TRDNOST ALUMINIJEVE ZLITINE AA2139-T351 V
ODVISNOSTI OD HITROSTI OBREMENJEVANJA
Onur Çavuºoðlu1, Alan Gordon Leacock2, Hakan Gürün1, Ahmet Güral3
1Gazi University, Faculty of Technology, Department of Manufacturing Engineering, 06500 Teknikokullar-Ankara, Turkey
2University of Ulster, Nanotechnology and Advanced Materials Research Institute, Advanced Metal Forming Research Group, School of
Engineering, Co. Antrim, Northern Ireland BT37 0QB, United Kingdom
3Gazi University, Faculty of Technology, Department of Metallurgical and Materials Engineering, 06500 Teknikokullar-Ankara, Turkey
onurcavusoglu@gazi.edu.tr
Prejem rokopisa – received: 2016-01-05; sprejem za objavo – accepted for publication: 2016-02-22
doi:10.17222/mit.2016.009
Mechanical properties of sheet materials are affected by the strain conditions. In this study, the influence of the strain rate on the
mechanical properties of AA2139-T351 aluminium-alloy sheet materials was studied, by applying uniaxial tensile tests on these
materials at four different strain rates (0.03, 0.003, 0.0003, 0.00003) s–1. Upon analysing the obtained results, it was seen that
the elongation, anisotropy value and the load-carrying ability during the necking were reduced, while the AA2139-T351 yield
strength, tensile strength, work-hardening coefficient and work-hardening rate were not significantly affected by the increasing
strain rate.
Keywords: strain rate, tensile strength, aluminium alloys, AA2139-T351
Na mehanske lastnosti plo~evin vplivajo pogoji obremenjevanja. V {tudiji je prou~evan vpliv hitrosti obremenjevanja na
mehanske lastnosti plo~evine iz aluminijeve zlitine AA2139-T351, z uporabo enoosnega nateznega preizkusa tega materiala pri
{tirih razli~nih hitrostih obremenjevanja (0,03, 0,003, 0,0003, 0,00003) s–1. Iz analize dobljenih rezultatov sledi; raztezek,
vrednost anizotropije in nosilna sposobnost na kontrakcijo so se zmanj{ali, medtem ko se meja te~enja AA2139-T351, natezna
trdnost, koeficient utrjevanja in hitrost utrjevanja niso spreminjale pri pove~ani hitrosti obremenjevanja.
Klju~ne besede: hitrost obremenjevanja, nateznost, aluminijeve zlitine, AA2139-T351
1 INTRODUCTION
The main purpose of the current studies conducted on
the materials used in vehicles, is to observe the fuel con-
sumption when using light materials such as aluminium
and magnesium alloys and, as a result, the reduction of
the CO2 fingerprint.1 Aluminium alloys are widely pre-
ferred in the automotive and aerospace industries
because these materials have superior characteristics
such as low density, high strength and formability capa-
bilities, resource availability, high corrosion resistance,
good thermal and electrical conductivity.1–2
Tensile testing is a widely used method in order to
determine a number of mechanical properties of mate-
rials and their deformation behaviours. Many parameters
obtained from a tensile test may differ depending on the
deformation conditions of the material.3 The strain rate is
known to affect the mechanical properties of many me-
tallic materials by affecting the stress/strain relationship.2
When the studies on the effect of the strain rate on the
mechanical properties of aluminium alloys were exa-
mined, T. Ohwue et al.4 determined, by examining the
mechanical properties depending on the temperature and
strain rate of aluminium/magnesium alloys, that the
tensile strength is not affected by an increase in the strain
rate at room temperature and that the amount of elonga-
tion shows very little tendency to decrease.4 In the study
of Y. Chen et al.5 it was seen that the strain rate had no
significant effect on the tensile behaviour of the AA6xxx
and AA7xxx aluminium alloy series, that a strain-rate
increase had no significant effect on the yield strength
and that this increase only slightly improved the tensile
strength.5 In the study of O. – G. Lodema et al.6 they
determined, by examining the strain rate sensitivity of
the AA1200 and 3103 aluminium alloys, that a slight in-
crease in the tensile strength and elongation amount
occurred depending on the increase of the strain rate
although the yield strength was not affected. M. J. Ha-
dianfard et al.7 determined, at different strain rates of the
AA5182 and AA5754 alloys, that the tensile strength and
the elongation amount decreased with an increase in the
strain rate while the yield strength was not affected due
to the increase in the strain rate. F. Ozturk et al.8 deter-
mined in their study that there is a decrease in the
increase in the strain rate, the elongation amount and the
work-hardening coefficient of the 5052 aluminium alloy
at room temperature. A. L. Noradila et al.9 studied the
tensile properties and work-hardening behaviour of alu-
minium/magnesium alloys. F. Ozturk et al.10 also studied
the work-hardening and strain-sensitivity behaviour of
the high-strength steel sheet in their other study.
Materiali in tehnologije / Materials and technology 51 (2017) 2, 333–348 333
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
UDK 620.17:539.4:669.715 ISSN 1580-2949
Professional article/Strokovni ~lanek MTAEC9, 51(2)333(2017)
Upon considering the studies in the literature, it is
seen that researches were conducted to specify the me-
chanical properties of various aluminium alloys.
A determination of the mechanical properties of
AA2139-T351 has a great importance for the aerospace
industry. In this study, the mechanical properties of the
AA2139-T351 aluminium-alloy sheet material were
studied in detail at different strain rates and the obtained
data was intended to be included into the literature.
2 MATERIAL AND EXPERIMENTAL PART
2.1 Material
In this study, the mechanical properties of the
AA2139-T351 aluminium-alloy sheet material were
examined depending on the strain rate. The chemical
composition of this material is presented in Table 1.
Moreover, microstructure photographs taken in the
rolling direction, plane direction and traverse direction
are also shown in Figure 1.
Tensile-test specimens in line with the ASTM E517
standard were used in the uniaxial tensile tests performed
in order to determine of the mechanical properties. The
cutting process was carried out on a water-jet machine to
minimize the thermal effects that could have occurred in
the sheet material during the preparation of the test spe-
cimens. Also, the notch effect that could have occurred
during the strain was eliminated by polishing the side
surfaces of the test specimens.
2.2 Experimental study
The mechanical properties of the AA2139-T351
aluminium-alloy sheet material depending on the strain
rate at room temperature were determined by using a
mechanical strain meter and an Instron 5500 tensile
meter. According to the standard ASTM E517, the ten-
sion tests at four different strain rates (0.03, 0.003,
0.0003, 0.00003) s–1 were performed on the specimens
with a sheet thickness of 1.6 mm in two different rolling
directions (rolling direction, traverse direction). The
average values were determined by repeating the tests
three times for each parameter in order to reduce the
margin of error. The yield strength, the tensile strength,
the work-hardening coefficient, the total elongation and
the anisotropy values were determined as a result of
these tests, by obtaining true stress/true strain curves
depending on the strain rate. In addition, the strain-rate
sensitivity, work-hardening rate and load capacity on
necking were examined.
3 RESULTS AND DISCUSSION
3.1 Tensile-test results
The change in the mechanical properties of the sheet
material was determined by performing the tensile tests
at the (0.03, 0.003, 0.0003, 0.00003) s–1 strain rates. The
data obtained from the tensile test are given in Table 2.
O. ÇAVUªOÐLU et al.: STRAIN-RATE-DEPENDENT TENSILE CHARACTERISTICS OF AA2139-T351 ALUMINUM ALLOY
334 Materiali in tehnologije / Materials and technology 51 (2017) 2, 333–348
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 2: Yield strength – strain rate relation
Slika 2: Odvisnost meja plasti~nosti – hitrost obremenjevanja
Figure 1: Microstructure of the AA2139-T351 alloy
Slika 1: Mikrostruktura zlitine AA2139-T351
Table 1: Chemical composition of AA2139-T351 sheet-metal material, in mass fractions (w/%)
Tabela 1: Kemijska sestava materiala plo~evine AA2139-T351, v masnih odstotkih (w/%)
Material Cu Mg Ag Mn Si Fe Ti Zr Sn Ni Cr Al
2139-T351 4.80 0.43 0.31 0.27 0.06 0.06 0.06 0.03 <0.01 <0.01 < 0.01 Bal
The strain rate/yield strength relationship of the
AA2139-T351 aluminium alloy is shown in Figure 2.
When Figure 2 is examined, the yield strength between
the minimum (0.00003 s–1) and the maximum (0.03 s–1)
strain ratios is determined to be approximately between
332 MPa and 334 MPa in the rolling direction and bet-
ween 265 and 268 MPa in the traverse direction. The
strain rate and the yield strength are shown to vary to a
very small extent. Therefore, the yield strength of the
AA2139-T351 aluminium alloy is not affected by the
increase in the strain rate. This outcome is found to be in
compliance with the results from the studies conducted
by Y. Chen et al.,5 O. – G. Lodema et al.6 and M. J. Ha-
dianfard et al.5–7
Table 2: AA2139-T351 tensile-test results
Tabela 2: Rezultati nateznih preizkusov AA2139-T351
Dire-
ction
Strain
rate
Yield
strength
Tensile
strength
R
value
Elon-
gation
Harden-
ing coef-
ficient
Rolling 0.03 333.9 502.4 0.730 16.3 0.156
Rolling 0.003 334.9 499.5 1.078 16.2 0.170
Rolling 0.0003 332.7 497.1 1.097 17.2 0.168
Rolling 0.00003 334.0 498.2 1.116 17.3 0.169
Traverse 0.03 266.5 473.4 0.990 15.5 0.179
Traverse 0.003 266.3 475.0 1.052 15.8 0.189
Traverse 0.0003 268.0 476.2 1.198 16.7 0.189
Traverse 0.00003 267.3 480.1 1.219 16.5 0.188
The amount of the tensile strength of a material is an
extremely important parameter for the selection of the
materials in engineering applications. The strain rate/ten-
sile strength relationship is given in Figure 3. The tensile
strength was determined to be 497–502 MPa in the
rolling direction and 473–480 MPa in the traverse direc-
tion in the quasi-static strain-rate tests. The tensile
strength was seen to be effected by the strain rate in a
very small range. While the tensile strength was not
affected by an increase in the strain rate in the study of T.
Ohwue et al.,4 a small increase in the tensile strength was
found to occur in the studies of Y. Chen et al.5 and O. –
G. Lodemo et al.6 Upon increasing the strain rate, the
tensile strength of the material was found to reduce
slightly depending on the occurring failure mechanisms
in the study of M. J. Hadianfard et al.7 The shift me-
chanisms may be delayed, especially in the soft matrix
phase (), due to an increase in the strain rate. In this
case, the tensile strength of the material is thought not to
significantly increase with the increasing strain rate
because it may cause a premature rupture of the pre-
cipitates when the occurring tensile stress directly affects
the precipitates.
The amount of elongation of the sheet-metal ma-
terials is extremely important in terms of sheet-metal
forming processes. The elongation behaviour of a mate-
rial under a desired amount leads to tear formation on the
sheet metal before the sheet metal is formed as desired.
The amount of elongation is known to decrease with an
increase in the strain rate.7–8 Figure 4 shows the elon-
gation behaviour of the AA2139-T351 aluminium alloy
depending on the strain rate. The maximum elongation
occurred at the two lowest strain rates (0.00003 s–1 and
0.0003 s–1) in the rolling direction. The elongation
capability of the material was reduced with the increase
in strain rate.
The material gains strength through the hardening
occurring depending on the dislocation pile-up in the
internal structure of the material during the strain of the
sheet-metal materials. The strain rate may affect the dis-
location pile-up and, consequently, the material strength.
Upon examining the relationship between the work-hard-
ening coefficient and the strain rate in Figure 5, a slight
reduction in the work-hardening coefficient is observed
in the results obtained from the maximum strain-rate
parameter (0.03 s–1), while no change in the low strain
rates is observed. When the overall results are examined,
O. ÇAVUªOÐLU et al.: STRAIN-RATE-DEPENDENT TENSILE CHARACTERISTICS OF AA2139-T351 ALUMINUM ALLOY
Materiali in tehnologije / Materials and technology 51 (2017) 2, 333–348 335
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 3: Tensile strength – strain rate relation
Slika 3: Odvisnost natezna trdnost – hitrost obremenjevanja
Figure 4: Elongation – strain rate relation
Slika 4: Odvisnost raztezek – hitrost obremenjevanja
the work-hardening coefficients obtained in the traverse
direction are seen to be higher than the results obtained
in the rolling direction. In the study of F. Ozturk et al.,8 a
very slight reduction in the coefficient of work hardening
was seen to occur with an increase in the strain rate and
the work-hardening coefficient was determined to
change in a very small range depending on the strain
rate.8–9
When the planar anisotropy value in Figure 6 was
examined, the anisotropy value was found to decrease
with an increase in the strain rate. The decrease in the
amount of elongation due to an increase in the strain rate
supports this conclusion.
In the scope of the study, the sensitivity rate between
the strain-rate values used in the tests for the
AA2139-T351 aluminium-alloy sheet material was
determined. For this purpose, the lowest strain rate of
0.00003 s–1 was selected as the reference value and it
was calculated according to the formulas shown in
Equation (1). When Figure 7 was examined, it was seen
that the strain-rate sensitivity was reduced as long as the
rate range was decreased. When the maximum strain rate
is applied, the decrease in the strain-rate sensitivity is
thought to adversely affect the plastic deformation since
the decrease in the strain-rate sensitivity adversely
affects the plastic deformation in Equation (1):
m ()
( ))
( ))




=
d(ln
d(ln
(1)
In this study, the work-hardening rate was used to
show the ability of the AA2139-T351 aluminium alloys
for work hardens after the occurrence of plastic defor-
mation. Work hardening occurs due to the dislocation
movements and dislocation generation against the crystal
O. ÇAVUªOÐLU et al.: STRAIN-RATE-DEPENDENT TENSILE CHARACTERISTICS OF AA2139-T351 ALUMINUM ALLOY
336 Materiali in tehnologije / Materials and technology 51 (2017) 2, 333–348
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 5: Hardening coefficient – strain rate relation
Slika 5: Odvisnost med koeficientom utrjevanja in hitrostjo obreme-
njevanja
Figure 8: Work hardening rate – true stress relation in the transverse
direction
Slika 8: Odvisnost: hitrost deformacijskega utrjevanja – prava nape-
tost v pre~ni smeri
Figure 6: Anisotropy – strain rate relation
Slika 6: Odvisnost: anizotropija – hitrost obremenjevanja
Figure 7: Strain rate sensitivity – strain rate relation
Slika 7: Odvisnost: ob~utljivost na hitrost obremenjevanja – hitrost
obremenjevanja
structures of alloys.9 The change in the work-hardening
rate due to the strain rate is shown Figures 8 and 9. The
work-hardening rate was determined to decrease with the
increasing stress in the rolling direction. It is possible to
interpret this case as a decrease in the work-hardening
rate with the increase in the amount of strain. When the
work-hardening-rate values obtained in the traverse
direction and the rolling direction are compared, a higher
amount of the work-hardening rate is found in the tra-
verse direction than in the rolling direction. The reason
for this is thought to be the fact that the work-hard-
ening-coefficient result obtained for the traverse direc-
tion is higher than that obtained for the rolling direction
although very close tensile-strength values are obtained.
The behaviour of the material strain due to reaching
the maximum tensile strength up to fracture is referred to
as the necking.10
The load-carrying capacity of a material during its
necking behaviour depending on the strain rate was
studied in the current study. Upon analysing the rela-
tionship between the load-carrying capacity and the
strain rate in Figures 10 and 11, the fracture behaviour
of the material was found to occur early with the
increasing strain rate in the direction of rolling, and the
load capacity of the material during the necking was
determined to decrease with the increasing strain rate.
The materials with a high tensile strength were seen to
show their fracture behaviour earlier in the study of F.
Ozturk et al.8 When the traverse-direction and rolling-
direction losses of the load-carrying ability during the
necking were compared, the earlier fracture was deter-
mined to occur in the rolling direction having a higher
tensile strength.
4 CONCLUSIONS
It was found that the semi-static strain rates, the yield
strength, the tensile strength and the work-hardening
coefficient of the AA2139-T351 aluminium alloy are not
significantly affected by the strain rate. The amounts of
the elongation and anisotropy (r) tend to decrease with
an increase in the strain rate. The material shows a
negative strain-rate sensitivity. The work-hardening rate
was found not to be significantly influenced by the strain
rate. The load-carrying ability during the necking
decreased slightly with the increase in the strain rate.
Acknowledgement
The authors would like to thank the Turkish Council
of Higher Education for the research grant and the
University of Ulster, Advanced Metal Forming Research
Group (AMFOR) for the necessary equipment and
material support.
O. ÇAVUªOÐLU et al.: STRAIN-RATE-DEPENDENT TENSILE CHARACTERISTICS OF AA2139-T351 ALUMINUM ALLOY
Materiali in tehnologije / Materials and technology 51 (2017) 2, 333–348 337
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Figure 9: Work hardening rate – true stress relation in the rolling
direction
Slika 9: Odvisnost: hitrost utrjevanja – prava napetost v smeri valjanja
Figure 11: Rolling-direction loss of the load-carrying ability during
the necking
Slika 11: Zmanj{anje nosilnosti v smeri valjanja od napetosti v vratu
Figure 10: Transverse-direction loss of the load-carrying ability of the
neck strain
Slika 10: Zmanj{anje nosilnosti v pre~ni smeri od napetosti v vratu
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O. ÇAVUªOÐLU et al.: STRAIN-RATE-DEPENDENT TENSILE CHARACTERISTICS OF AA2139-T351 ALUMINUM ALLOY
338 Materiali in tehnologije / Materials and technology 51 (2017) 2, 333–348
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS