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Arab Journal of Nuclear Science and Applications, 46(2), (107-114) 2013
Work Hardening Characteristics of Irradiated Al-5356 Alloy
G. Saad*, S.A. Fayek**, A. Fawzy*, H.N. Soliman*, E. Nassr*
* Physics Dpt., Faculty of Education, Ain Shams Univ., Cairo, Egypt.
** Physics Dpt., National Center for Radiation Research and Technology, Nasr City, Cairo, Egypt.
Received: 25/4/2010 Accepted: 28/6/2010
ABSTRACT
The effect of γ-irradiation on the hardening behaviour of Al-5356 alloy has
been investigated by means of stress-strain measurements. Wires irradiated with
different doses D (ranged from 500 to 2000 kGy) were strained at different
deformation temperatures Tw (ranged from 303 to 523K) at constant strain rate
(S.R) of 1.5x10 -3 s -1 . The effect of γ-irradiation on the work hardening parameters
(WHP) yield stress σy, fracture stress σf, total strain εT and work hardening
coefficient χp (=dσ 2 /dε) of Al-5356 alloy were evaluated at the applied deformation
temperature range. The obtained results showed that, increasing the deformation
temperature resulted in a decrease in the WHP, while γ-irradiation exhibited a
reverse effect. The mean activation energy of the deformation process was calculated
using an Arrhenius type relation, and was found to be ~ 80 kJ/mole, close to that of
grain boundary diffusion in aluminum alloys.
Key Words: Stress-Strain/ Strengthening Parameters/ Irradiation-Induced Defects.
INTRODUCTION
In the last decade, because of their enhanced formability and high specific strength, aluminum
alloys have been increasingly utilized as structural components in automobiles and high-speed ships.
During service, these components can be subjected to dynamic loading, such as during impact or
collision with foreign objects. Therefore, the material properties and failure behavior of these alloys at
low and high rates of deformation need to be well understood. Alloy composition, strain rate, service
temperature and microstructure may have an effect on the mechanical properties and failure
mechanisms of aluminum alloys (1–6) .
Alloying elements are usually added to aluminum to increase its strength. Magnesium forms a
solid solution in Al and it can be dissolved up to 10 wt. % at high temperatures (7) . Also, it is attractive
as an alloying element since it is known to enhance the recovery process within Al, which may
enhance superplastic response of this alloy. So, Al–Mg alloys exhibit medium durability and very
good corrosion resistance. These factors cause that this group of materials is widely used as the
construction materials especially for the marine structures subjected to moderate load. Plastic
deformation of discussed alloys during tensile tests occurs according to a dislocation type of
mechanism. Point defects (Mg atoms in the solid solution α or vacancies) cause an anchoring of
dislocations. A detachment of the dislocations requires instantaneous increase in stress σ in order to
liberate the dislocations from the defects. Consequently, a decrease in stress is observed up to
the moment of distortion of the dislocations movement occurring at subsequent defects. A single effect
described above is repeated periodically up to the moment of necking of the stressed sample (8) . This
process, known as serrations or the Portevin–Le Chatelier (PLC) phenomenon, is observed only under
certain conditions at a specific regime of temperature, strain and strain rate (9-12) .
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Arab Journal of Nuclear Science and Applications, 46(2), (107-114) 2013
In many industrial applications, the mechanical properties of Al–Mg alloys are required to be
further improved. One of the methods used to improve the mechanical properties of Al–Mg alloys is
exposuring the alloy to radiation. The primary cause of radiation damage in metals is the displacement
of atoms and electrons (13) . The radiation damage is actually composed of several distinct processes (14) .
These processes and their order of occurrence are as follows:
1. The interaction of an energetic incident particle with the lattice atom.
2. The transfer of kinetic energy to the lattice atom giving birth to a primary knock-on atom (PKA).
3. The displacement of the atom from its lattice site.
4. The passage of the displaced atom through the lattice and the accompanying creation of additional
knock-on atoms.
5. The production of a displacement cascade (collection of point defects created by the PKA).
The radiation damage is concluded when the PKA comes to rest in the lattice as an interstitial.
The result of a radiation damage event is the creation of a collection of point defects (vacancies and
interstitials) and clusters of these defects in the crystal lattice. Several investigations were carried out
to interpret the effect of γ-irradiation on the mechanical and electrical properties of metals and alloys
(15-17) . The results mostly showed that γ-irradiation effect causes increase of the strengthening
parameters and electrical resistivity of the irradiated materials. This was attributed to the irradiationinduced
point defects created in the irradiated materials.
One of the most essential phenomena in deformed irradiated metals or alloys is the workhardening.
The effect of deformation temperature on the work-hardening characteristics of the
irradiated Al based alloys was found to return backs the initial values of the strengthening parameters
(15) . This was attributed to the annihilation of the irradiated defects at their sinks at temperatures where
the defects become appreciably mobile (18) .
The present work is devoted to get an insight and provide some additional information about the
effect of γ-irradiation and the reverse effect of the deformation temperature on the work-hardening
parameters of Al-5356 alloy.
(i) Sample Preparation
EXPERIMENTAL PROCEDURES
This study has been carried out on commercial Al-5356 alloy supplied from Alumisr factory-
Helwan-Cairo-Egypt in the form of rod of 3mm in diameter. The chemical compositions of the alloy
under investigation are given in Table (1). The rods were cold drawn in steps into wires 0.6 mm in
diameter for stress-strain measurements. A part of the alloy was rolled into sheet of 0.3mm in
thickness and 5mm width for microstructure investigation.
Table (1): The chemical compositions of the Al-5356 solder alloy
Al Mg Fe Cu Si Mn Cr Zn Ti Be
93.5-94.5 4.5-5.5 0.4 0.1 0.25 0.05-0.2 0.05-0.2 0.1 0.06-0.2 0.0008
(ii) Heat Treatment and Irradiation Techniques
Samples in the form of sheet (5 x 5 x 0.3 mm) and wires (50 mm in length) were annealed for
5h at 773K in the solid solution region using a thermo regulated furnace. The temperature inside the
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Arab Journal of Nuclear Science and Applications, 46(2), (107-114) 2013
furnace was constant to within ± 2K. After annealing, the specimens were air quenched and then
divided into four sets. One of them is left without radiation (unirradiated), while each of the other
three sets was irradiated for a different dose 500, 1000 and 2000 kGy.
The samples were irradiated using a Russian facility gamma cell Co 60 source (activity 10 4 curi
September 2005) at room temperature in air. The radiation doses were applied with a dose rate of 10
kGy / 135min (in January 2010) for 112.5, 225 and 450 hours to obtain the desired doses.
X-ray diffraction (XRD) patterns for the unirradiated and irradiated samples are shown in Fig.1.
This figure showed that the obtained spectral lines correspond to: i) fcc Al matrix at (1 1 1) and (2 0
0), ii) Mg at (1 0 4), and iii) β-phase (Al3Mg2) at (19 5 1) and (16 16 4) crystallographic planes at
definite positions irrespective of the irradiation dose. Only the relative intensities of these spectral
lines were found to be increased with increasing of the irradiation dose.
Counts
Counts
10000
8000
6000
4000
2000
10000
8000
6000
4000
2000
Al (1 1 1)
Al (200)
Al 3 Mg 2 (19 5 1)
( a )
Al 3 Mg 2 (16 16 4)
Mg (1 0 4)
0
30 40 50 60 70 80
Position [ o 2 Theta]
Al (1 1 1)
Al (200)
Al 3 Mg 2 (19 5 1)
( c )
Al 3 Mg 2 (16 16 4)
Mg (1 0 4)
0
30 40 50 60 70 80
Position [ o 2 Theta]
Counts
701
10000
Counts
8000
6000
4000
2000
Al (1 1 1)
Al (200)
Al 3 Mg 2 (19 5 1)
Al 3 Mg 2 (16 16 4)
Mg (1 0 4)
0
30 40 50 60 70 80
10000
8000
6000
4000
2000
Al (1 1 1)
Position [ o 2 Theta]
Al (200)
Al 3 Mg 2 (19 5 1)
( b )
Al 3 Mg 2 (16 16 4)
Mg (1 0 4)
0
30 40 50 60 70 80
Position [ o 2 Theta]
Fig. (1): X-ray diffraction patterns of the Al-5356 alloy for: (a) unirradiated;
(b) 500 kGy; (c) 1000 kGy; (d) 2000 kGy.
EXPERIMENTAL RESULTS AND OBSERVATIONS
Experimental sets of stress–strain measurements were performed with an average strain rate of
1.5x10 -3 s -1 at different deformation temperatures ranging from 303 to 523K using a tensile testing
machine described elsewhere (19) .
( d )

Arab Journal of Nuclear Science and Applications, 46(2), (107-114) 2013
(a) Effect of γ-Irradiation and Deformation Temperature on the WHP
Fig.2 (a & b) shows a representative two sets of stress–strain curves. The first set (Fig.2a)
represents the stress–strain curves for the unirradiated and irradiated samples carried out at room
temperature (303 K). Similar curves were carried out at deformation temperatures (373, 398, 423, 448,
473 and 523K). While the other set (Fig.2b) represents the effect deformation temperature on the
unirradiated samples. From this figure the following observations can be drawn:
(i) Stress–strain curves of the irradiated samples are shifted towards higher levels with respect
to the unirradiated one. This implies that work-hardening parameters namely, σy, σf, attain higher
values while the fracture strain εT becomes less.
(ii) Increasing the deformation temperature resulted in the reverse effect of that obtained by
irradiation.
(iii) The serration behavior that was observed for the unirradiated samples tested at room
temperature (303 K) was found to disappear at 373 K and higher as well as at irradiation dose of 500
kGy or higher.
Stress ( ) MPa
200
160
120
80
40
T w = 303 K
S.R = 1.5x10 -3 S -1
2000 kGy
1000 kGy
500 kGy
unirradiated
( a )
0
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
Strain ( )
Stress ( ) MPa
770
200
160
120
80
40
Unirradiated
S.R = 1.5x10 -3 S -1
303K 373K
398K
423K 448K
473K
523K
0
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
Strain ( )
Fig. (2): Representative stress–strain curves of Al-5356 alloy for: (a) the unirradiated and
irradiated samples tested at 303K; (b) unirradiated samples at different deformation
temperatures.
The irradiation dose dependence of the yield stress σy and fracture stress σf is shown in Fig. 3a
& b from which it is clear that, the yield stress σy and fracture stress σf increase with increasing the
irradiation dose D, while it decrease with increasing the deformation temperature Tw.

Yield Stress y (MPa)
85
80
75
70
65
60
55
50
45
Arab Journal of Nuclear Science and Applications, 46(2), (107-114) 2013
S.R = 1.5x10 -3 S -1
303K
373K
398K
423K
448K
473K
523K
( a )
0 500 1000 1500 2000 2500
Dose D (kGy)
Fracture Stress f (MPa)
777
180
170
160
150
140
130
120
110
100
S.R = 1.5x10 -3 S -1
( b )
303K
373K
398K
423K
448K
473K
523K
0 500 1000 1500 2000 2500
Dose D (kGy)
Fig. (3): Dependence of the work hardening parameters on D for: (a) the yield stress σy; (b) the
fracture stress σf for Al-5356 alloy specimens tested at different deformation
temperatures.
It has been illustrated before in fig.2a and similar curves straining wires of the unirradiated and
irradiated samples, in the temperatures range (303 to 523K), showed a decrease in the total strain εT
after γ-irradiation and increasing the irradiation dose D as shown in Fig.4. while an increase in εT was
observed by increasing the deformation temperature Tw.
It has been also observed from fig.2 that the stress–strain curves show a parabolic behavior
immediately after yielding. According to Mott, the work-hardening coefficient χp (=dσ 2 /dε) can be
calculated. Fig. 5 shows a representative linear relation between σ 2 and ε for the unirradiated and
irradiated samples tested at 423 K. From these straight lines it can be observed that, irradiation dose
affect greatly the slopes of these lines. The work-hardening coefficient χp was calculated from the
slopes of these straight lines. The χp dependence on irradiation dose is illustrated in fig. 6 from which
it is clear that the work-hardening coefficient χp increases with increasing of the irradiation dose D,
while it decreases with increasing of the deformation temperature Tw.
Total Strain T
0.40
0.38
0.36
0.34
0.32
0.30
0.28
0.26
0.24
0.22
0.20
S.R = 1.5x10 -3 S -1
0 500 1000 1500 2000 2500
Dose D (kGy)
523K
473K
448K
423K
398K
373K
303K
2 ( MPa ) 2
18000
16000
14000
12000
10000
8000
6000
4000
S.R = 1.5x10 -3 S -1
T w = 423 K
0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20
Strain
2000 kGy
1000 kGy
500 kGy
unirradiated
Fig. (4): Dependence of the total strain εT Fig. (5): Representative relation between σ 2 vs. ε
on alloy the irradiation dose D for for Al-5356 alloy tested at 423K forthe
Al-5356 samples tested at different unirradiated and irradiated samples.
deformation temperatures.

Arab Journal of Nuclear Science and Applications, 46(2), (107-114) 2013
The rate of change of χp with irradiation dose (δ χp / δ D) is calculated from the slopes of fig.6
and its dependence on the deformation temperature Tw is shown in fig 7. From this figure it is clear
that (δ χp / δ D) decreases with increasing the deformation temperature.
Work-Hardening Coefficient p (MPa) 2
x 10
1.8
5
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
S.R = 1.5x10 -3 S -1
303K
373K
398K
423K
448K
473K
523K
0 500 1000 1500 2000 2500
Dose D (kGy)
( p / D ) (MPa 2 /kGy)
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40
38
36
34
32
30
28
26
24
S.R = 1.5x10 -3 S -1
22
350 400 450 500 550
Deformation Temperature T (K) w
Fig. (6): Irradiation dose dependence of Fig. (7): Dependence of the rate of change
the work-hardening coefficient χp of χp with irradiation dose on the
for Al-5356 alloy specimens tested deformation temperature Tw.
at different deformation temperatures.
(b) The Activation Energy (Q)
The energy activating the deformation process may be evaluated from the variation of the yield
stress σy as related to the deformation temperature Tw through the kinetic rate equation (19) :
σy = k [ε˙ exp (Q/RT)] m ( 1 )
where k is a material constant, ε˙ is the strain rate, R is the universal gas constant and m is the
strain rate sensitivity index. To estimate the value of the activation energy Q for the deformation
process, the standard Arrhenious plot of ln σy versus 1000/T is to be constructed as shown in fig. 8.
From the slopes of the obtained straight lines, the mean value of the activation energy Q was found 80
kJ/mole independent on the irradiation dose which is in accordance with that obtained in similar work
by Peng Yong-yi (20) .
ln y
4.5
4.4
4.3
4.2
4.1
4.0
3.9
S.R = 1.5x10 -3 S -1
2000 kGy
1000 kGy
500 kGy
unirradiated
3.8
1.8 2.0 2.2 2.4 2.6 2.8 3.0
1000/T K -1
Fig. (8): Arrhenius plot of lnσy vs. 1000/T for Al-5356 alloy.

Arab Journal of Nuclear Science and Applications, 46(2), (107-114) 2013
(1) Effect of γ-Irradiation
DISCUSSION
As has been mentioned before, the primary cause of radiation damage is the displacement of
atoms and electrons due to the creation of the induced defects (13) . Defects produced during irradiation
have an influence upon the structural order- disorder and other properties (21) . In ordered lattice,
migration of vacancies is difficult, so impurity- vacancy recombination process during γ-irradiation
more likely to take place. Hence, these defects (vacancy centers) would redistribute the fine structure
of β-phase configuration and the dislocations become more able to multiply (15) . This may lead to more
strengthening of the irradiated samples. Furthermore, the increase of the irradiation dose leads to an
increase in the creation of the induced defects. Thus the increase in the work hardening parameters σy,
σf and χp consequently the decrease in the total strain εT can be explained. On the other hand, although,
the presence of some retained Mg, Cu, Si atoms in the solid solution treated samples besides β
(Al3Mg2) phase as has been detected from X-ray diffraction analysis which cause an anchoring of the
dislocations created during the plastic deformation, the creation of the induced defects (vacancies) as a
result of γ-irradiation makes it easier for the dislocations to interact with these vacancies rather than
anchored by the other entities. So, the disappearance of the serration behavior by irradiation may be
accounted for.
(2) Effect of Deformation Temperature
It is well known that increasing deformation temperature of strained material results in:
(i) An increase of the thermal agitation for the dislocation glide motion and easier overcoming
the obstacles leading to the increase of dislocation slip distance (22) .
(ii) The annihilation of the present dislocations as well as dislocation induced by plastic strain
once they are formed (23) .
(iii) Increasing the rate of reorientation of the remaining dislocations in a more relaxed
configuration aligned in the direction of the applied stress (24) .
From these viewpoints, the decrease in the work hardening parameters σy, σf, χp and increase in
εT with increasing the deformation temperature Tw (Figs.3, 4 and 6) can be explained. Also, the
disappearance of the PLC phenomenon at higher deformation temperatures may be retained due to the
thermal agitation which assists the dislocations to breakaway from the binning centers.
(3) The Activation Energy (Q)
The value of the energy activating the deformation process Q calculated from fig.6 was found
to be ~ 80 kJ/mole which is in accordance with that needed for the activation energy of grain boundary
diffusion in aluminum alloy and this in agreement with the results obtained in other works (20, 25- 27) .
CONCLUSIONS
The main conclusions to be drawn from this study may be summarized as follows:
(i) The WHP σy, σf, χp and εT were found to be affected by γ-irradiation. Where σy, σf and χp increased
with increasing of the irradiation dose D, while εT decreased. This is due to creation of the
induced defects leading to redistribute the fine structure of β-phase configuration and the
dislocations become more able to multiply.
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Arab Journal of Nuclear Science and Applications, 46(2), (107-114) 2013
(ii) Deformation temperature exhibits a reverse effect of γ-irradiation. This may be attributed to the
annihilation of the irradiated defects.
(iii) The mean value of 80 kJ/mole of the energy for activating the deformation process is found to
correspond to the activation energy of grain boundary diffusion in aluminum alloy.
(iv) γ -irradiation can be find its useful application in improvement the strengthening parameters of
Al-5356 alloy.
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