Effects of γ-irradiation and strain rate on the tensile and theelectrical properties of Al-4043 alloy

S. El-Gamal n, Gh. MohammedPhysics Department, Faculty of Education, Ain Shams University, Cairo, Egypt

H I G H L I G H T S

� Fracture stress increases while fracture strain decreases as dose and/or εd increases.� The strain rate sensitivity index (m) decreases as the dose of γ-rays increases.� The electrical resistivity (ρ) increases as the dose of γ-rays and/or εd increases.� XRD and SEM indicate the presence of Si-phase distributed within the Al-matrix.� The lattice parameter, calculated from XRD, increases as the dose of γ-rays increases.

a r t i c l e i n f o

Article history:Received 16 May 2013Accepted 12 February 2014Available online 28 February 2014

Keywords:γ-IrradiationStrain rateTensile propertiesElectrical propertiesAl-4043 alloy

a b s t r a c t

Effects of γ-irradiation and strain rate on the tensile and the electrical properties of Al-4043 alloy were

studied. Samples of Al-4043 alloy were exposed to γ-rays using 60Co radiation source with dose rate74 Gy/min at room temperature (RT), in air. The different doses are 0.5, 1, 1.5 and 2 MGy, the samples

were strained with strain rates (εd¼5.4�10–5, 7.6�10�4 and 1.2�10�3 s�1) at RT. It was found that;

(i) the fracture stress (sF) increases as the dose and/or εd increases while the fracture strain (ɛF)decreases (ii) the strain rate sensitivity index (m) decreases as the dose increases and (iii) the electrical

resistivity (ρ) increases as the dose and/or εd increases. Microstructure can be observed using X-raydiffraction technique (XRD) and Scanning Electron Microscope (SEM). It indicates the presence ofSi-phase distributed within the Al-matrix. The interpretation of the results was offered on the ground

that γ-rays interact with the alloy and create point and line defects that hinder the dislocation movementand finely distribute Si-phase leading to an increase in the alloy hardness.

& 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Al-alloys are suitable materials for use in components workingin radiation environments like construction of some reactorinternals and various types of fuel cladding because of their lowcross-section for capture of thermal neutrons, excellent corrosionresistance and thermal conductivity (Kolobneva, 2004; Allenouet al., 2010; Mirandou et al., 2009). Indeed, Al-4043 alloy is usedalso in the automotive and aerospace industry, especially for cylinderblocks, cylinder heads, pistons and valve lifters (Matsuura et al.,2003; Abd El-Khalek, 2009; Haizhi, 2003; Ghoneim et al., 2012).

γ-Irradiation of crystalline metallic materials changes theinternal structure and consequently their microscopic and macro-scopic properties. Such irradiation involves multiple gammaquanta and secondary electron interactions with the host materialvalence and core electrons. Also, there are some interactions withatomic nuclei leading to modifications of crystal structure by theformation of point defects. So, many investigators (Liu et al., 2012;Zaykin and Aliyev, 2002; Alexander, 1997; Reyes-Gasga et al., 1995)were interested in this branch to search for new materials that canwithstand radiation damage.

The thorough surveying of literature has revealed that there isonly one paper (Abd El-Khalek and Abd El-Salam, 2008) handlingthe topic of effect of γ-irradiation on the mechanical properties ofAl–Si alloys. The investigators studied the effect of γ-irradiationand pre-ageing temperature on the mechanical properties of Al–Sialloy. They found that the mechanical parameters show high

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Radiation Physics and Chemistry

http://dx.doi.org/10.1016/j.radphyschem.2014.02.0170969-806X & 2014 Elsevier Ltd. All rights reserved.

n Corresponding author. Tel.: þ966 507473935.E-mail address: samyelgamal@gmail.com (S. El-Gamal).

Radiation Physics and Chemistry 99 (2014) 68–73

structure dependence in both irradiated and pre-aged Al–Si alloyshaving the solid solution structure. As was noticed, little attentionhas been given to this topic, so the aim of present work is to studythe effects of γ-irradiation and strain rate on the tensile andelectrical properties of Al-4043 alloy.

2. Experimental work

Al-4043 alloy was supplied from Alumisr factory-Helwan-Cairo-Egypt in the form of rod of 3 mm in diameter. The chemicalanalysis of the alloy under investigation is given in Table 1. Theserods were cold drawn in steps to wires of 0.6 mm in diameter forstress–strain measurements. A part of the alloy was rolled intosheets of 0.4 mm in thickness for microstructure investigations.The wires and sheets were annealed at 823 K for 1 h; according tothe phase diagram there is small amount of beta phase (Si-phase).

The samples were γ-irradiated using a Russian facility Gammacell 60Co radiation source of half-life time of 5.26 years and doserate of 74 Gy/min. The energy of γ-quanta was between 1.17 and1.33 MeV, with a mean value of 1.25 MeV. The different doses wereobtained via increasing the time of exposing the samples to γ-rays;these doses are 0.5, 1, 1.5 and 2 MGy and were obtained viaaccumulation. γ-irradiation was performed in the Egyptian AtomicEnergy Authority (EAEA). After the irradiation process the sampleswere stretched with strain rates 5.4�10�5, 7.6�10�4 and1.2�10�3 s�1 at RT up to fracture by using a computerized locallymade tensile testing machine. More details about this machinewere mentioned before (Saad et al., 2010).

The electrical properties of Al-4043 samples were investigatedvia measuring dc resistance, at RT, before and after γ-irradiation ofdifferent doses and at different strain rates (5.4�10–5, 7.6�10�4

and 1.2�10�3 s�1) by using an electrometer (Keithley 615) thenthe electrical resistivity (ρ) was calculated.

The microstructure of Al-4043 samples was investigated by XRD (aPhilips X-ray diffractometer, X`Pert, with Cu-Kα radiation, λ¼1.5418 ˚,at RT) and SEM (JEOL GSM-5400 Scanning Microscope Japan). Prior tomicroscopic investigations, the samples were carefully cleaned,mechanically polished and then electrochemically polished.

3. Results

Typical engineering stress–strain curves of Al-4043 samples atdifferent doses of γ-rays (0.5, 1, 1.5 and 2 MGy) and at differentstrain rates (5.4�10�5, 7.6�10�4 and 1.2�10�3 s�1) are shownin Fig. 1. It is obvious that the levels of the stress–strain curveswere strongly affected by doses and strain rates. As the doseincreases, the stress–strain curves were shifted to lower values ofstrain. Also, the same shift was observed with increasing εd.

The dependence of fracture stress (sF) and fracture strain (εF)on the dose of γ-rays at different strain rates (5.4�10–5, 7.6�10�4

and 1.2�10�3 s�1) are shown in Figs. 2 and 3, respectively. Fromthese figures it is clear that; (i) at constant εd, sF increases as thedose increases while εF decreases and (ii) at constant dose,sF increases with increasing εd while εF decreases.

It is known that sF is related to εd by the relationship (Dieter, 1986)

sF ¼ CðεdÞ m ð1Þ

where C is a constant and m is the strain rate sensitivity index.Plotting ln (sF) versus ln (εd), see Fig. 4, gives straight lines andthe slopes represent the m values. Fig. 5 shows the relationbetween m and dose of γ-rays. From the figure it is clear that mdecreases as the dose increases.

Table 1Typical chemical analysis of the Al-4043 alloy.

Elements Al Si Fe Cu Mn Mg Zn Ti OtherCompositions (wt%) 93.22 4.5–6 0.8 0.3 0.05 0.05 0.1 0.2 0.15

0

20

40

60

80

100

Strain, ε

Stre

ss,σ

(MPa

)

0

20

40

60

80

100

Strain, ε

Stre

ss,σ

(MPa

)

0.00 0.05 0.10 0.15 0.20 0.25

0.00 0.05 0.10 0.15 0.20 0.25

0.00 0.05 0.10 0.15 0.20 0.250

20

40

60

80

100

Strain, ε

Stre

ss, σ

(MPa

)

Fig. 1. Stress–strain curves of Al-4043 alloy at different doses and strain rates(5.4�10–5, 7.6�10�4 and 1.2�10�3 s�1) [★ Un-irradiated, ■ 0.5 MGy, □ 1MGy,● 1.5 MGy and ○ 2 MGy].

S. El-Gamal, Gh. Mohammed / Radiation Physics and Chemistry 99 (2014) 68–73 69

Fig. 6 shows the dependence of ρ on the dose at different εdvalues. From the figure, at particular εd, ρ increases with increas-ing the dose and at a certain dose, ρ increases as εd increases.

Some representative XRD patterns of un-irradiated sample andirradiated ones with doses 1 and 2 MGy at constant εd(5.4�10�5 s�1) are shown in Fig. 7-a–c to investigate the effectof dose on the microstructure of Al-4043 samples. Moreover, toinvestigate the effect of εd on the microstructure we chose aparticular dose (2 MGy) and two different strain rates (5.4�10�5

and 1.2�10�3 s�1), see Fig. 7-c and d. It was found that (i) atcertain εd, as the dose increases the intensity of the Si-phaseincreases (Table 2) while the intensity of the Al-matrix decrease(Fig. 7-a, b and c). Also there is a shift to small angles in the 2θ forSi-phase and Al-matrix, (Table 3) (ii) at particular dose, as εdincreases, the broadening of diffraction peaks of Si-phase increasestoo (Fig. 7-d). The lattice parameter could be calculated from thediffraction batterns (Suryanarayana and Grant Norton, 1998) andits change with the dose is shown in Fig. 8 for Si (111), (220) and(311). It was found that, the lattice parameter increases as the doseincreases. SEM micrographs for Al-4043 samples before and afterirradiation at dose 2 MGy are shown in Fig. 9-a and b respectively.

4. Discussions

The levels of stress–strain curves were strongly affected by thedose and εd. As the dose and/or εd increases the stress–straincurves were shifted to lower values of strain (Fig. 1) which means

0.0 0.5 1.0 1.5 2.0 2.5

70

75

80

85

90

95

100

Frac

ture

Str

ess,

σ f (MPa

)

Dose (MGy)

Fig. 2. The dependence of fracture stress (sF) on the dose of γ-rays at differentstrain rates (5.4�10–5, 7.6�10�4 and 1.2�10�3 s�1) [Δ 5.4�10�5, ▲ 7.6�10�4

and ⋇ 1.2�10�3 s�1].

0.0 0.5 1.0 1.5 2.0 2.5

0.14

0.15

0.16

0.17

0.18

0.19

0.20

Frac

ture

Str

ain,

εf

Dose (MGy)

Fig. 3. The dependence of fracture strain (ɛF) on the dose of γ-rays at differentstrain rates (5.4�10–5, 7.6�10�4 and 1.2�10�3 s�1) [Δ 5.4�10�5, ▲ 7.6�10�4,⋇ 1.2�10�3 s�1].

-10 -9 -8 -7 -64.2

4.3

4.4

4.5

4.6

4.7

Ln (ε.)

Ln

( σ)

Fig. 4. The plot between ln (sF) and ln (εd) at different doses of γ-rays.[★ Un-irradiated, ■ 0.5 MGy, □ 1 MGy, ● 1.5 MGy and ○ 2 MGy].

0.0 0.5 1.0 1.5 2.0 2.5

0.032

0.034

0.036

0.038

0.040

0.042

Stra

in r

ate

sens

itivi

ty in

dex,

m

Dose (MGy)

Fig. 5. The relation between strain rate sensitivity index m and the dose.

0.0 0.5 1.0 1.5 2.0

4x10-8

6x10-8

8x10-8

10-7

1.2x10-7

ΩEl

ectr

ical

Res

istiv

ity, ρ

(.m

)

Dose (MGy)

Fig. 6. The dependence of electrical resistivity on the dose [Δ 5.4�10�5,▲ 7.6�10�4, ⋇ 1.2�10�3 s�1].

S. El-Gamal, Gh. Mohammed / Radiation Physics and Chemistry 99 (2014) 68–7370

that the hardness of the material increses. This is because γ-rayscreates more point and line defects (Thompson, 1969) it alsofacilitates the precipitation of more Si-phase (Abd El-Khalek andAbd El-Salam, 2008). These defects hinder the motion of disloca-tion and increase the hardness at the end. Indeed, increasing εdplays a similar role in increasing the material's hardness. Morediscussions will be given later.

When γ-rays interact with a metallic material it can indirectlycause atomic displacements by generating high-energy electronsthrough Compton scattering and pair production. Such interactioncreates point and line defects. With increasing the dose, thedensity of these defects increases and as a result the dislocationpinning centers increase in number which can hinder the disloca-tion movement and increases the material's hardness. Thesedefects also cause precipitation of additional Si-phase and finely

distribute Si-phase because it prevents its coalescence leading to adifficulty in the dislocation movement which increases the hard-ness, i.e., sF increases and ɛF decreases. To investigate the effect ofεd on sF and ɛF, there is a popular relation that correlates betweensF and εd, Norton power law, Eq. (1), from this equation it is clearthat, sF increases as εd does. Indeed, there is a reverse relationbetween sF and ɛF, i.e., increasing sF decreases ɛF. The aforemen-tioned arguments could help in accounting for the data presentedin Figs. 2 and 3.

As far as the literature is concerned and to the best of ourknowledge, the relation between the strain rate sensitivity index(m) and the dose of γ-rays has not been studied before. So, apreliminary discussion was introduced for this point. From theliterature m describes the ability of the metallic material toelongate without fracture or the resistance to prevent neckingduring deformation of the material (Welsch et al., 1994). Asmentioned earlier increasing the dose of γ-rays increases the

0

50

100

150

200

250

300

350C

ount

s/s

2θ

2θ 2θ

2θ

0

50

100

150

200

250

300

350

Cou

nts/

s

0

50

100

150

200

250

300

350

Cou

nts/

s

20 30 40 50 60 70 80 90

20 30 40 50 60 70 80 90

20 30 40 50 60 70 80 90

20 30 40 50 60 70 80 900

50

100

150

200

250

300

350

Cou

nts/

sFig. 7. X-ray diffraction pattern of Al-4043 alloy at (a) εd¼5.4�10�5 s�1, dose 0 Gy, (b) εd¼5.4�10�5 s�1, dose 1 MGy, (c) εd¼5.4�10�5 s�1, dose 2 MGy and (d)εd¼1.2�10�3 s�1, dose 2 MGy.

Table 2The change in intensity of peaks of Si-phase at the crystallographic planes (111),(220) and (311) with the dose of γ-rays.

Dose of γ-rays (MGy) Intensity of peaks of Si-phase at the planes

Si (111) Si (220) Si (311)

0 27.88 17.08 10.311 30.32 20.42 13.892 35.40 24.16 16.52

Table 3The change of 2θ of peaks of Si-phase at the crystallographic planes (111), (220) and(311) with the dose of γ-rays.

Dose of γ-rays (MGy) 2θ of peaks of Si-phase at the planes

Si (111) Si (220) Si (311)

0 28.41 47.29 56.171 28.32 47.12 55.972 28.18 46.96 55.83

0.0 0.5 1.0 1.5 2.0

5.43

5.44

5.45

5.46

5.47

5.48

5.49

Latti

ce p

aram

eter

, a (A

o)

Dose (MGy)

Fig. 8. The change of lattice parameter with the dose at εd¼5.4�10�5 s�1 [■ Si(111), □ Si (220), ● Si (311)].

S. El-Gamal, Gh. Mohammed / Radiation Physics and Chemistry 99 (2014) 68–73 71

hardness of Al-4043 alloy which decreases the ability to elongatewithout fracture, i.e., m decreases (Fig. 5).

Fig. 6 could be interpreted on the basis that many physicalproperties of crystalline metallic materials are governed by latticedefects, their type and density. So, the increase in ρ of irradiatedAl-4043 samples could be due to (i) the increase in the existingdefects density caused by irradiation, (ii) γ-irradiation acceleratesthe precipitation of Si-phase, as will be seen in SEM micrographs,so the amount of Si-phase increases in the irradiated sample.Indeed, the presence of more Si-phase gives higher probability ofSi-vacancy recombination process (Alexander et al., 1996). Suchprocess could redistribute Si-phase which leads to multiplicationof density of dislocations and (iii) distribution and interaction ofdefects with each other. The different types of defects, mentionedearlier, represent obstacles in the motion of electrons through theirradiated samples leading to an increase in ρ. On the other hand,εd increases the work-hardening of Al-4043 alloy due to theincrease of the dislocation density generated during the deforma-tion process (El-Daly, 2004) so, the dislocations become tangledduring their motion leading to an increase in ρ.

XRD patterns, Fig.7a–d, indicate that fcc Al-matrix was detectedat (200) and (220) crystallographic planes while fcc Si wasdetected at the crystallographic planes (111), (220) and (311).The increase in the intensity of Si-phase (Table 2) and conse-quently the decrease in intensity of the Al-matrix mean that thedefects created in Al-4043 alloy due to γ-irradiation enables moreSi-phase to precipitate. Indeed, there is a shift to small angles inthe 2θ for Si-phase and Al-matrix (Table 3) due to the internalstresses that come from dislocations, point defects and Si-phase inAl-4043 alloy (Jenkins and Snyder 1996). With increasing εd, thediffraction peaks of Si-phase broadened (Fig. 7-d) due to theinternal stresses caused by the interaction between more thanone type of defects created during the tensile test at higher strainrate. The precipitations of Si-phase besides the creation of pointand line defects also their interaction with each other induce someinternal stresses which increase the lattice parameter as the doseincreases (Fig. 8).

Because seeing believes, our interpretation was checkedexperimentally by analyisng SEM micrographs for un-irradiatedand irradiated samples (Fig. 9-a and b). Such micrographs revealedtwo phases; a dark and a white phase. As expected, since the alloyis preliminary two phase alloy, the white phase was detected to bea Si-rich phase embedded in dark phase which is the Al-matrix.The Si-phase size distribution is fine and dispersive in the twosamples but for the irradiated sample the of Si-phase is higher.These micrographs confirm that γ-rays enable the precipitation ofadditional Si-phase and can finely distribute it.

5. Conclusions

Effects of γ-irradiation and strain rate on the tensile and theelectrical properties of Al-4043 alloy have been studied and it wasfound that

1. The fracture stress (sF) increases as the dose and/or εdincreases while the fracture strain (εF) decreases.

2. The strain rate sensitivity index (m) decreases as the doseincreases.

3. The electrical resistivity (ρ) increases as the dose and/or εdincreases.The interpretation was offered on the ground that γ-rays createpoint and line defects that hinder the dislocation movementand distribute Si-phase finely leading to an increase in thealloy's hardness.

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