experimental study for characterization of mechanical ...methods such as forging, rolling, drawing,...

International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:15 No:04 74

156304-7171-IJMME-IJENS © August 2015 IJENS I J E N S

Abstract— The mechanical behavior of metal matrix composites

is dependent on matrix alloy and reinforcement. The presence of

reinforcement elements significantly affects the nature of matrix

microstructure. Extrusion process is preferred to produce

aluminum alloy at a maximum production rate and a minimum

scrap. The extrusion pressure requirement and the maximum

temperature of the extrudate depend on the alloy and its

metallurgical conditions. In this paper, characteristics of Al

2124/SiCp composites during hot working (extrusion) have been

investigated. Extrusion tests have been conducted on composites

with different volume fraction of SiCp (0%, 10%, and 20%). Also

tensile tests were carried out to investigate the yield strength and

ultimate strength of the extruded samples. The results showed

that extrusion pressure decreased with increasing extrusion

temperature because of the decrease in plastic flow stress. The

extrusion pressures of the composites were much higher than

those of 2124 Al Alloy because the silicon carbide particles act as

hard inclusions. For extrusion pressure, empirical models have

been developed. Also the extrusion pressure of 2124 Al

composites have been predicted by using the constitutive

equations obtained from the experimental results.

Index Term-- Al/SiCp, Constitutive Equations, Hot Extrusion,

Metal matrix composites.

I. INTRODUCTION

PARTICLE reinforced metal matrix composites are the

engineering materials that possess exceptional physical,

mechanical, and thermal properties. Major applications of

metal matrix composites are in aerospace and non-aerospace

industries such as automobiles, and electronics components

[1-3]. Reinforced metal matrix composites are currently being

used in commercial applications because of their desirable

properties and the ability to use standard metal forming

methods such as forging, rolling, drawing, and extrusion. Due

to the presence of hard ceramic reinforcements, the hot

working parameters for composites cannot be adopted easily

[4 and 5]. With the availability of cheaper reinforcement, and

low-cost, high-volume production methods, aluminum matrix

composites have the advantage of being amenable to

conventional metal working operations [6-8]. Aluminum

composites are traded by various enterprises with silicon

carbide (SiC) or alumina as reinforcement, which are

produced by casting techniques. When the final product has a

uniform shape, there are several thermo-mechanical processes

for a later consolidation such as hot extrusion and rolling [9,

10]. As a result of the presence of silicon carbide (SiC)

particles, the elastic properties of SiCp/Al composites at room

temperature have been enhanced; however, the plasticity

properties are reduced. Further investigations of SiCp/Al

composites at high temperature proved that their plastic

properties are exceptional; therefore, the material can be used

in high temperature applications. It has been reported that the

mechanism of deformation at high temperature of aluminum

based composites is different from those of the unreinforced

alloy [11 and 12]. Bulk metal forming processes such as

rolling, forging, and extrusion are influenced by various

parameters from which the constitutive relation, geometry of

the workpiece, and deformation rate. One of the most

important parameters affecting the accuracy of the forming

process is the constitutive relation which represents the

mathematical model for the relationship between the flow

stress of materials, strain rate and the deformation temperature

[13-16].

Producing alloys and composites by powder metallurgy (PM)

techniques are preferred since it reduces cost by minimizing

machining operations and material. Furthermore, PM can be

used for the production of desired parts or products when

other processes are impossible or difficult. Also if the process

is possible but not economically viable, PM would be also

used. Many efforts have been made previously by researchers

to improve the traditional alloys and designated new alloys

[17]. The effect of particle size, volume fraction and matrix

strength on fatigue behavior and particle fracture in 2124

aluminum-SiCp composites were investigated by J. N. Hall et

al. [18]. Ganesan et al. [19] developed the processing maps for

hot working processes of 6061 Al/15% SiCp composite.

Rajamuthamilselvan et al. [20 and 21] examined the hot

deformation behavior and microstructure of 7075 Al/20% SiCp

composite. The effect of silicon carbide particulate volume

fraction on the hot working characteristics of 2124 Al alloy

matrix composites was studied by Bhat et al.[22]. Despite the

appreciated efforts for clarifying the behaviors of different

types of SiCp/Al composites, more experiments and

investigations are still needed for the better understanding of

the correlations among the process parameters such as

Experimental Study for Characterization of

Mechanical Behavior of Al/SiCp Composites

during Hot Working

Osama Mohamed Irfan

Faculty of Engineering, Qassim University, KSA,

on leave from Bani Swef University, Egypt

[email protected]



temperature, strain and strain rate during the hot deformation.

In this paper, the characteristics of Al 2124/SiCp composites

during hot working by extrusion have been studied. The

process has been conducted at various conditions by using

composites with different volume fractions of silicon carbide

particles. Empirical models have been developed for

extrusion pressure. Furthermore, constitutive equations have

been obtained based on the multiple linear regressions from

the experimental results.

II. MATH

II. EXPERIMENTAL WORK

Composites of 2124 Aluminum alloy with different volume

fraction of silicon carbide (0%, 10%, and 20%) have been

manufactured by PM technique. The chemical compositions

are listed in the Table I.

Aluminum powder with additions of silicon carbide powder of

average size 30µm was blended to get the 2124Al/SiCp

composites. The mixture was degassed at 450ºC for 1 hr under

a vacuum pressure. The powder mixture was pressed at a

pressure of ≈78 MPa and 450 ºC to form billets with size of

25mm diameter and 30mm length. The compacts were

sintered for 2hrs in vacuum atmosphere at 500ºC. The

composite billets were loaded into the container and the die

assembly was heated to 500oC using a resistance furnace. A

thermocouple was used to control and measure the

temperature of billet. The billets were soaked for 20min and

then the extrusion process was conducted at the desired

temperature. The extrusion process was carried out by using a

160 Tones hydraulic press. Fig.1 shows the setup for hot

extrusion and the samples prior and after extrusion.

Graphite powder was used as a lubricant for die surfaces to

reduce the friction between billet and walls of the container.

The hot working characteristics of Al 2124/SiCp composites

have been investigated at different volume fraction of silicon

carbide in different conditions. Tables 2 (columns 2, 3, and 4)

shows the extrusion conditions for Al 2124 alloy and its

Al/SiCp composites.

Nomenclature

Pext. extrusion pressure (MPa)

Pdie die pressure (MPa)

Pf friction force (MPa)

R reduction ratio

L billet length (mm)

Db billet entrance diameter (mm)

De billet exit diameter (mm)

v ram velocity (mm/s)

T temperature (oC)

m strain rate sensitivity

ɸ friction shear factor

⍺ semi cone die angle (o)

σo flow stress (MPa)

strain rate ((s-1)

Ain inlet cross sectional area (mm2)

Aout outlet cross sectional area (mm2)

, , K empirical constants

TABLE I CHEMICAL COMPOSITION OF 2124 ALUMINUM ALLOY

Component Al Cu Mg Mn Fe Zn Sr Ti Cr

Wt.% 93 4 1.5 0.5 0.3 0.25 0.2 0.15 0.1

(a) Compacted sintered samples before extrusion

(b) Extrusion test

(c) Samples after extrusion

Fig. 1. Setup of extrusion process

TABLE II

EXAMPLES OF EXTRUSION CONDITIONS FOR 2124 AL

ALLOY AND 2124Al/SiCp COMPOSITES

Sample

No.

Strain

rate s-1

Extrusion

ratio

Temperature oC

Extrusion Pressure (MPa)

0% SiCp

10% SiCp

20% SiCp

1

2

3

0.01

0.01

0.01

2.0

2.0

2.0

300

400

500

24

18.8

15.6

29

22.3

18.3

31.6

24.3

19.8

4

5 6

0.01

0.01 0.01

4.0

4.0 4.0

300

400 500

24

18.8 15.6

28.9

22.4 18.3

31.7

24.3 19.8

7

8 9

0.01

0.01 0.01

6.0

6.0 6.0

300

400 500

24

18.8 15.6

29

22.4 18.3

31.7

24.3 19.8

10

11

12

0.10

0.10

0.10

2.0

2.0

2.0

300

400

500

39.1

30.6

25.3

48.4

37.4

30.6

53.78

41.28

33.6

13

14 15

0.10

0.10 0.10

4.0

4.0 4.0

300

400 500

39.1

30.6 25.4

48.5

37.5 30.7

53.8

41.2 33.6

16

17

18

0.10

0.10

0.10

6.0

6.0

6.0

300

400

500

39.1

30.7

25.4

48.5

37.5

30.7

53.8

41.3

33.6

19 20

21

1.00 1.00

1.00

2.0 2.0

2.0

300 400

500

63.6 49.8

41.3

81.1 62.7

51.3

91.2 70

57

22

23 24

1.00

1.00 1.00

4.0

4.0 4.0

300

400 500

63.6

49.9 41.3

81.2

62.7 51.4

91.3

70.1 57.1

25

26 27

1.00

1.00 1.0

6.0

6.0 6.0

300

400 500

63.7

49.9 41.2

81.2

62.8 51.3

91.3

70.2 57



The experiments were carried out at strain rate varied from

0.01s-1

to 1.0s-1

; temperatures of 300, 400, and 500 oC; and

extrusion ratios of 2, 4, and 6. After extrusion process, the

cross sections were examined for microstructure by using an

optical microscope. Also the mechanism of deformation was

studied. Tensile tests were performed on MTS universal

testing machine with a load capacity of 25 Tones to determine

the ultimate strength and yield strength of the extruded

materials. These tests have been conducted according to

ASTM E8M-01 standard. During the tests, the tensile load as

well as the elongation of a previously marked gauge length in

the specimen was measured with the help of load cell of the

machine and extensometer respectively.

III. RESULTS AND DISCUSSION

A. Extrusion Pressure

Referring to table 2 (columns 5, 6, and 7) the increase in

extrusion temperature resulted in decreasing the pressure. This

occurred because of the effect of high temperature that

decreases the plastic flow stress. Regarding Aluminum 2124

Alloy and the composites, the extrusion pressure increased

with increase in extrusion ratio. Also the extrusion pressure of

the composites is higher than those of 2124 Aluminum Alloy.

The reason of this difference is the presence of silicon carbide

particles that acts as hard insertions. As strain rate increased

from 0.01 to 1.0s-1

at constant temperature and extrusion ratio,

the extrusion pressure is increased by ≈172%, 188%, 192% for

Al 2124 alloy, 2124Al/10% and 2124 Al/20%SiCp

respectively. Furthermore, the extrusion pressure decreased

by ≈33%, 34%, 37% for 2124Al Alloy, 2124Al/10%SiCp,

2124Al/20% SiCp with increasing the temperature of the billet

from 300 to 500oC respectively.

B. Mechanical Properties

The ultimate tensile strength and yield strength of the extruded

2124 Al Alloy and 2124 Al SiCp composites with different

SiCp volume fractions were measured. Fig. 2 shows that the

yield strength as well as ultimate strength of 2124 Al Alloy

and its composites increase with increasing the volume

percentage of silicon carbide particles.

C. Constitutive Equation

The composites used in this study consist of Al 2124 with

various volume fractions (0%, 10%, and 20%) of SiCp

reinforcement. Direct extrusion experiments were conducted

and empirical models were developed for extrusion pressure.

The behavior of the material during extrusion can be

expressed by an equation relating the total extrusion pressure

to both the operating conditions and geometrical parameters.

The extrusion pressure Pext. is the sum of the die pressure Pdie

and friction contribution Pf,

Pext = Pdie + Pf (1)

Compared to the deformation force, the friction force

between the ram of the wall and the container can be neglected

Pdie = lnRBAσo (2)

R = out

in

A

A (3)

Where, Pdie: die pressure, Pf: friction pressure, R: Reduction

ratio, oσ : flow stress at corresponding temperature and strain

rate, A and B are constants to be obtained from

experimental results.

Pf =b

i

D

4Lτ 3

σ

D

4Lυ o

b

(4)

Where, φ: Frictional shear factor, L: Length of billet,

Db: Diameter of billet.

The flow stress influences the die pressure and the friction

term. The shear factor φ can take values ranging from 0 to 1.

The assumption for the present case is φ=1 (i.e. sticky friction

condition between the billet and cylinder wall. The average

strain rate for a die angle and ram velocity v, is given by:

3

eD3

bD

α tan Rln 2

bD v6

ε

(5)

Where, v: ram velocity, De: diameter at exit, ⍺- Semi cone

angle,

m

o εKσ (6)

Where, m: strain rate sensitivity, k: constant, and ε : strain

rate.

The extrusion pressure Pext. as a function of the

characteristics of the material and the geometric parameters

can be obtain by combining equations (1) through (6) with

considering the temperature dependence of σo,

Pext. = K

b

nm D3

4LlnRBATε (7)

Where, A , B , and K are empirical constants.

The extrusion pressure and the ram displacement were

determined experimentally. The extrusion force decreased

after the peak during the steady state region. This decrease is

related to a reduction in the contact surface between the billet

and the cylinder resulting in a reduction of friction force

component. As a result, the value of Pext was used for the

calculation corresponds to the average between the maximum

and the minimum values of extrusion force. Then regression

Fig. 2. Mechanical properties of the extruded 2124 Al Alloy and

2124 Al SiCp Composites



analysis was applied to evaluate the constant k, the strain rate

sensitivity exponent m, and the temperature exponent n. Data

acquisition system has been used during the experiments to

record the temperature, the ram displacement, the time and the

extrusion force. The extrusion output for 2124 Al alloy is

shown in Fig.3. At the beginning of the extrusion process; as

the ram advanced from 0 to 5mm, the extrusion load was low

and constant due to the weak resistance of the solid cylindrical

billet during the deformation. At the end of the first stage, a

rapid rise in pressure was noticed due to compression of the

material in the container prior to extrusion. During this stage

the extrusion load increased significantly to reach its

maximum value. Then the load decreased linearly with

increasing ram displacement till the steady state condition was

reached.

Fig.4 shows the extrusion load versus ram displacement for

2124 Al Alloy and 2124 Al/SiCp composites with different

silicon carbide fractions. For all types of materials, it can be

seen that the extrusion load increases rapidly with the

lowering of punch and reaches the maximum value,

subsequently the extrusion load decreases. According to the

theories of metal forming, this load decrease is attributed to a

shortening billet and a decrease in frictional force at the billet

container interface [5].

The extrusion pressure requirement and the maximum

temperature of the extrudate depend on the alloy and its

metallurgical conditions including billet length, billet

temperature, reduction ratio, cross sectional diameter of the

extrudate, die design and its conditions. Furthermore, it is

important to consider the process parameters such as ram

speed and lubrication. From above figures, it can be observed

that the extrusion load increases with the lowering of punch

and reaches the peak value; subsequently decrease of the

extrusion load. According to metal forming theories, the load

decrease is attributed to a shortening billet and thus a decrease

frictional force at the billet container interface. At the

beginning of the process, the extrusion force was low due to

the weak resistance of the solid cylindrical billet. The rise in

pressure at the end of the stage was due to compression of the

material in the container prior to extrusion. As a result the

value of Pext used for the calculation corresponds to the

average between the maximum and the minimum values of

extrusion force. Extrusion pressure as a function of the

characteristics of the material and the geometric parameters

can be calculated by using equation 7.

The evaluated constants for the model are given in Table 3.

By evaluating the constants, the following empirical relations

were obtained for different materials.

For 2124 Al Alloy,

For 2124 Al/10%SiCp,

For 2124 Al/20%SiCp,

Due to hard particle addition to Al 2124 Alloy, the extrusion

stress increases with increase in the SiCp volume fraction. The

results revealed that extrusion pressure gradually decreased

with increase in extrusion temperature because of the decrease

in plastic flow stress with increase in extrusion temperature.

The extrusion pressure of the Al 2124 Alloy and the

composites gradually increased with increase in extrusion

ratio, because of the increase in plastic flow stress resulting

from the friction between the materials and the extrusion die

and container. The extrusion pressure of the composites were

much higher than those of 2124 Al Alloy because the SiCp act

as hard inclusions which is shown in Tables 2. Increasing of

strain rate from 0.01 to 1.0 s-1

the maximum extrusion

pressure is increased by about 170, 190, 195 % for Al 2124

alloy, 2124Al/10% and 2124 Al/20%SiCp respectively at

constant temperature and extrusion ratio. Increasing the

temperature of the billet from 300oC to 500

oC the extrusion

pressure decreases by about 33, 37, 39% for 2124Al Alloy,

𝑃𝑒𝑥𝑡 . = 5.4952(𝜀)0.2111 (𝑇)−0.8438 1.0252 + 1.5000 𝑙𝑛𝑅 + 4𝐿

√3𝐷𝑏

𝑃𝑒𝑥𝑡 . = 5.4952(𝜀)0.2111 (𝑇)−0.8438 1.0252 + 1.5000 𝑙𝑛𝑅 +

4𝐿

√3𝐷𝑏

𝑃𝑒𝑥𝑡 . = 9.3081(𝜀)0.2242 (𝑇)−0.8961 0.9992 + 1.5872 𝑙𝑛𝑅 +

4𝐿

√3𝐷𝑏

𝑃𝑒𝑥𝑡 . = 11.9974(𝜀)0.2303 (𝑇)−0.9201 1.0364 + 1.6302 𝑙𝑛𝑅 +

4𝐿

√3𝐷𝑏

Fig. 3. Extrusion load versus ram displacement for 2124 Al Alloy

Fig. 4. Extrusion load versus ram displacement

TABLE III

EVALUATED CONSTANTS



2124Al/10%SiCp, 2124Al/20% SiCp respectively at constant

strain rate of 0.01/s and extrusion ratio. Furthermore, the

values of constants K, m and n increase due to work hardening

when the percentage volume of SiCp increases.

D. , Microstructure Examination

The microstructures of the samples extruded in the

temperature range of 300oC and 1.0 s-1 strain rate exhibit flow

bands, these bands being manifestations of flow instabilities

[23] which is shown in Fig.9. The microstructure of the

samples extruded at temperature above 350 oC exhibit wavy

grain boundaries, which are shown in Figs. (5-8). The surface

finish, straightness, and microstructural observations indicate

that the products possess a high surface quality after the

extrusion testing.

IV. CONCLUSION

Hot working by extrusion process has been performed for Al

2124 Alloy and 2124Al SiCp composites to investigate the

behavior of the materials under varying conditions. The

following conclusions have been drawn:

1. Extrusion process at elevated temperature can be

conducted successfully for 2124 Al/SiCp composites.

2. The constitutive equations of extrusion process of 2124 Al

Alloy and 2124 Al SiCp composites have been obtained.

These equations might be useful in the prediction of the

extrusion pressure.

3. The extrusion pressure of both 2124 Al Alloy and 2124 Al

SiCp composites increases with increasing the strain rate.

4. The extrusion pressure of both 2124 Al Alloy and 2124 Al

SiCp composites decreased with increasing extrusion

temperature because of the decrease in plastic flow stress.

5. The extrusion pressure of the 2124 Al Alloy and its

composites gradually increased with increase in extrusion

ratio, because of the increase in plastic flow stress resulting

from the friction between the materials and the extrusion

die and container.

6. The extrusion pressures of the composites are much higher

than those of 2124 Al Alloy because of silicon carbide

particles which act as hard inclusions.

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experimental study for characterization of mechanical ...methods such as forging, rolling, drawing,...

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