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University POLITEHNICA of Bucharest Faculty of Materials Science and Engineering

Department:Processing of Metallic Materials and Ecometallurgy

No. Senate Decision in . .2017

Summary

Thesis

Research on the possibility of obtaining Al-graphite

(particles) composites in certain zones of parts

By

Eng. Eng. HAZIM F. HASSAN AL-DULIAMI

Supervised by

Professor Dr. Eng. Florin ŞTEFĂNESCU

DOCTORAL COMMITTEE

Chairman Prof. Dr. Eng. Mihai BUZATU From University Politehnica of Bucharest

Scientific Supervisor Prof. Dr. Eng. . Florin ŞTEFĂNESCU From University Politehnica of Bucharest

Reviewer Prof. Dr. Eng. Aurel CRISAN. From University Transilvania of Brasov

Reviewer Prof. Dr. . Eng. Bela VARGA From University Transilvania of Brasov

Reviewer Prof. Dr. Eng Gigel NEAGU From University Politehnica of Bucharest

Bucharest 2017

Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts

2

CONTENT

Chapter I

1.1. INTRODCTION 6

1. 2. Composite materials 7

1.2.1. Classification of composites 7

1.2.2. Composites aluminium - graphite 10

1.3. Wettability in the aluminium - graphite system 21

1.3.1. Behaviour of graphite particles in the molten aluminium 21

1.4. Casting methods to produce aluminium-graphite composite 36

1.4.1. Gravitational casting 36

1.4.2. Centrifugal casting 38

1.4.3. Melt infiltration 39

1.4.4. Liquid Metal Forging 39

1. 5. Melting and deposition of components 40

1.6. Solidification process 42

1.7. Applications of aluminium-graphite composite 44

1.7.1. Thermal properties for Al - graphite composites applications 45

1.7.2. Friction and wear properties for Al-graphite applications 46

Chapter II

2. Objective of present investigation 49

Chapter III

3. Methods of practical research 51

3.1. Materials 51

3.1.1. Metal matrices 51

3.1.2. Complementary materials 51

3.2. Devices 52

3.3. Gravity casting the aluminium - graphite particles composite 54

3.3.1. Pure aluminium sieve - graphite powder method 55

3.3.2. Layers of graphite powder fixed with pure aluminium foils prepared

for gravity casting of Al alloy

55

3.4. Al alloy-graphite powder composite produced by electric arc 59

3.4.1. Melting and deposition in electric arc of graphite powder inside

channels in the surface of aluminium

60

3.4.2. The use of graphite powder inside surface made holes in aluminium

alloy

61

3.4.3 Coating electrode by graphite powder layers 61

3.5. Grinding and polishing processes 62

3.6. Shape characterization 63

3.7. Brinell hardness test 66

3.8. Scanning electron microscope test 66


3

Chapter IV

4. Experimental data 68

4.1. Floating velocity of graphite particles 68

4.2. Analysis of graphite particles 74

4.2.1. Particles size analysis 74

4.2.2 Microscopy 74

4.2.3. X - ray diffraction test 75

4.3. Aluminium - pure aluminium sieve - graphite particles composite

produced by gravity casting

75

4.4. Al alloy - layers of graphite powder - pure aluminium foil composite 81

4.4.1. Optical micrograph of samples 82

4.4.2. Thermal analysis of cast Al-graphite composites 86

4.5. Melting and deposition in electric arc 99

4. 5.1. Melting and deposition in electric arc of graphite inside holes made

in aluminium

99

4.5. 2. Electric arc deposition by using an electrode coated with graphite

powder

105

4.5.3. Electric arc deposition of aluminium alloy over graphite powder

found inside a channel

111

4.6. Hardness of aluminium - graphite particles composite 111

4.7. Surface layer thickness of graphite particle 114

4.8. Scanning electron microscope test 115

Chapter V

5. Conclusions and personal contributions 120

5.1. General conclusions 120

5.2. Conclusions of experimental results 121

5.3. Original contributions 125

Dissemination of research results 126

References 127


4

General Introduction

Composite materials are combinations of two or more materials aggregated at

macroscopic level with the purpose of obtaining enhanced characteristics of the newly

formed material.

In the composition of metal matrix composites are included minimum two

materials: the metal matrix and the reinforcement. The matrix is always a metal -

generally an alloy is employed, and very rarely a pure metal.

Ceramic is used as reinforcement and metal as matrix in typical MMCs, which

results in suitable wear and structural resistance. However, due to thermal differences

and volume increase under temperature factors, it is quite challenging to machine or

weld these MMCs as increasing the temperature affects the properties of the material,

which suffers from distortion and stress in these conditions. To prevent these effects,

aluminium graphite (Al-Gr) MMCs used for new MMCs, generates composites that are

light with high thermal conductivity, machinability and mechanical strength. Also, the

thermal behaviour of these composites can be easily managed to obtain tailored

characteristics based on requirements (thermal expansion) [15].

An inhomogeneous distribution of the graphite particles in aluminium, unsuitable

bonding between the aluminium and floating graphite particles in melt due to density

difference between aluminium and graphite.

In order to achieve a better penetration of the graphite particle into the

aluminium melt, different measures can be taken to reduce the wetting angle.

Moreover, wetting conditions improvement permits to include a bigger proportion of

solid component into the matrix. Many techniques are used for this purpose.

Melting and deposition process can be described as the melting of one

component and deposition of the other component on it. This process can be achieved

by melting one part and deposition of the second part together under pressure, perhaps

with the application of heat, to form a composite material.

Gravitational casting is the simplest method to achieve fabric from composite

materials and consists of the introduction of metal and particles into a mould: sand

mould or permanent mould.


5

Chapter 1

Metal Matrix Composites (MMC):

In the composite of metal matrix composites are included minimum two materials:

the metal matrix and the reinforcement. The matrix is always a metal - generally an alloy

is employed, and very rarely a pure metal. The composite is produced by incorporating

the reinforcement into the matrix. In terms of the matrix composition, metal matrix

composites are preferred to organic matrix composites due to their improved

characteristics: they maintain their strength when the temperature increases, their

transverse strength is superior, they have higher electrical and thermal conductivity and

they resist erosion, etc. Metal matrix composites have higher densities when compared

to polymer matrix composites, which represents a considerable drawback because their

mechanical properties are also reduced. Another drawback is that for producing these

matrix composites, high amounts of energy are needed [21].

Metal matrix composite consists of a matrix metal (aluminium, iron, magnesium,

and cobalt, copper) while the reinforcing material may be silicon carbide, boron carbide,

graphite or alumina. Compared to the engineering metals, these composites offer high

stiffness, high strength, and good electrical and thermal conductivity.

1.2.2. Composites aluminium- graphite.

Aluminium alloys reinforced by graphite particles have received considerable

attention due to potential engineering materials for a variety of anti-friction

applications [28]. In these composites, graphite is significant to improve tribological

properties because graphite-rich film is formed between sliding surfaces [29].

Aluminium is the most popular matrix for the MMCs. Pure aluminium is relatively

weak material. Therefore, for some applications a higher mechanical strength is

required.

1.7. Applications of aluminium-graphite composite

The addition of graphite particles to the aluminium alloy matrices makes them

attractive candidate materials in many tribological applications due to the fact that they

act as solid lubricants and make a self-lubricating alloy. Initially, cast Al/Grp composites

were developed through liquid metallurgy route for automotive antifriction applications.

The essential advantages of this material were low cost, easy machinability and

improved damping capacity which are essential for automotive applications, pistons,

liners and bushings. The pistons of Al/Grp composites tested in diesel engines led to

reduced wear, loss frictional in pistons and rings, freedom from seizure under lubrication

conditions. Using Al-graphite composite caused decreasing in fuel consumption. Similar

results have been obtained by using these pistons in gas-line engines [58,109].


6

Chapter II

2. Objectives of present investigation

This study aims to overcome the floatation velocity of graphite particles (GrP) and

to obtain improvements of the wettability between the graphite particles and aluminium

melt.

New methods of gravity casting and electrical arc process were used in this study

to prepare the Al alloy-graphite particles composite without using the conventional

methods to improve the wettability.

Two methods of gravity casting were used for preparing Al-graphite particles

composite in the first part of the experimental study:

Table 1.14. Application of Al-graphite composite in power electronics

Applications Properties Parts made from Al-graphite

Base plates and coolers

High thermal conductivity

and low density

Heat sinks and heat

spreaders

Low CTE (coefficient of

thermal expansion) and a

low density

Discs and rings

Low friction

Electronic packaging

applications

Low density and high

thermal conductivity


7

The first method:

Pure aluminium sieve was used in a new method for distribution of the graphite

particles - casting the melt aluminium over the sieve, which coats the inner

surface of mould.

Microstructure and optical micrograph analysis were performed to measure the

particles density and shapes factor of specimens.

The second method:

Samples of different Al alloy – layers of graphite particles and foil aluminium

were produced by clay thermal mould casting. The effect of the alloy

composition was studied.

Microstructure and optical micrograph analysis were performed to measure the

particles density and shapes factor of these samples

The cooling curve – the graphite powder percentage is influenced by the time

and temperature during the solidification process.

The second part of the experimental study included producing Al alloy-

graphite particle composite by superficial layering using electric arc to melt the

aluminium. Three methods were used in this part:

a)

Deposition Al alloy - graphite particles in square channel; different particle sizes

of graphite were used.

Analysis of the optical micrograph and investigation of the particle density and

shapes factor for the sample.

b)

Study the effect of electrodes type on Al alloy-graphite particle introduction in

the hole with fixed amount of graphite particles.

Different intensities (ampere) are used in this method in addition to different

electrodes: pure Al (2.5 mm diameter), Al-5Si (2.5 mm diameter), Al-12Si (2.5

mm diameter) and Al-12Si (4.2 mm diameter).

Distribution and incorporation of the graphite particles are studied by

microstructure graphs; the analysis of these graphs aims to determine the

particles density and shapes factors.

c)

Preparation of the Al alloy-graphite particle composite by mixing with an electric

arc. The graphite powder covered the electrode in different amounts.

Using two types of electrodes: pure Al and Al-12Si (diameter 2.5 mm).

Study all parameters (particles density, mean sphericity, mean convexity, mean

aspect ratio, mean perimeter).


8

All specimens of Al alloy- graphite composite were analysed by optical microscope to

determine, microstructure, particle density, mean sphericity, mean aspect ratio, mean

convexity, and mean perimeter.

Chapter III

3.3. Gravity casting the aluminium-graphite particles composite

One of the most important methods for producing Al-graphite particles in this

work is gravity casting by using many ways in order to get the best results, especially

the mixture between the aluminium and the particles of graphite. The flow chart in

Figure 3.5 is showing these ways.

3.3.1. Pure aluminium sieve - graphite powder method

Prepare the clay thermal mould.

Coat the inner surface of the clay thermal mould by pure aluminium sieve

which has the thickness of 2 mm

Distribute the graphite powder (2, 3, 4 vol. %) at the sieve by using adhesive

material to prepare different samples as shown in Figure 3.6.

Fig. 3.5. Flowchart of gravity

casting.


9

Melt the aluminium in crucible at 900 °C by gas furnace and cool it down to

850°C.

Pour the melt in sand mould and leave it to solidify.

Cut and polish all the samples in order to prepare them for examination by

microscope and to analyse them.

3.3.2. Layers of (graphite powder – pure aluminium foils) –Al alloy composite

prepared for gravity casting

Prepare the package containing layers of Al foil - Grp – Al foil- Grp- Al foil

respectively by cutting aluminium foil into pieces of 0.28 g weight and the area

of each piece equal to the base area of the sand cup. One face of the foil has the

adhesive material.

Fix the thermocouple on the sand cup wall and centre, Figure 3.7.

Arrange the layers respectively by using 0.25 wt. %, 0.5 wt. %, 0.75 wt. % of

graphite and fix the layers on the base of cup by mechanical technique.

Make some holes in the package of one sample with 0.75 g graphite powder,

using the same procedure for other sample which is prepared in the previous

steps. Three types of matrices were used: Al (aluminium), Al- 12Si, and Al-

12Si – 1.5 Mg and different weights of graphite powder, available in Tables

3.3, 3.4, 3.5.

Fig. 3.6. Clay thermal mould and its section coated by

sieve and graphite powder.

Fig. 3.7. Clay thermal cup.


10

Melt the aluminium alloys in the furnace gas at 937°C for aluminium and 900-

°C for Al-Si12 and Al-Si12-Mg alloys. Pour it over the layers which have been

prepared inside the cups.

Prepare three thermal analysis samples for each alloy and the temperature read

by the thermocouple.

Log the data on a computer.

Analyse the data by drawing the cooling rate curve and the first derivative curve.

Cut all the samples in centre for structural.

Grind and polish the samples.

Perform metallographic studies on all samples.

Table 3.5. Weight and content of Al–12 Si–1.5 Mg – graphite materials in the clay thermal cup

Table 3.3. Weight and content of aluminium – graphite materials in the clay thermal cup

Weight of aluminium Temperature Cup no.1 Cup no.2 Cup no.3 Cup no.4

4 kg 937⁰C

0.25 wt. %

Gr +

Al alloy

0. 5 wt. %

Gr +

Al alloy

0.75 wt. %

Gr +

Al alloy

aluminium

Table 3.4. Weight and content of Al -12Si – graphite material in the clay thermal cup

Weight of AlSi12

alloy Temperature Cup no.1 Cup no.2 Cup no.3 Cup no.4

3.8 kg 900⁰C

0.25 wt. %

Gr + Al -

12Si alloy

0.5 wt. %

Gr + Al -

12 Si alloy

0.7 wt. %

G r+ Al -

12Si alloy

Al -

12Si alloy

Weight of

Al12Si -

0.25 Mg

Alloy

Temperature Cup no.1 Cup no.2 Cup no.3 Cup no.4 Cup no.5

3.8 kg 900⁰C

0.25 wt. %

r+Al-12Si

1.5 Mg alloy

0.5 wt. %

Gr+Al-12Si

1.5 Mg alloy

0.7 wt. %

Gr+Al-12Si

1.5 Mg alloy

0.7 wt. %

Gr+Al-12Si

1.5 Mg alloy

package

with hole

Al-12Si

1.5 Mg alloy


11

In Tables 3.3, 3.4, and 3.5 are presented the clay thermal cups which contain the

samples of Al alloy-graphite powder-Al foil package. Each cup has a different material

different than the other cup in terms of the graphite powder percentage and aluminium

alloy type.

In the third stage Al-12Si-1.5Mg alloy matrices are used, one of the prepared

samples having some holes on the package. This sample has 0.75 wt. % graphite

powder in two layers and three layers of the Al foils.

3.4. Al alloy-graphite powder composite produced by electric arc

Three methods are used for mixing aluminium alloy and graphite powder by

electric arc process in this thesis. Flowchart 3.9 is showing these methods.

3.4.1. Melting and deposition in electric arc of graphite powder inside

channels in the surface of aluminium

Cut the aluminium into pieces of 100 x 50 x 20 mm.

Make two canals in each piece, having dimensions 100 x 9 x 5 mm, as in Figure

3.10.

Fig. 3.9. Flowchart of melting and mixing Al alloy and graphite powder by

electric arc.


12

Weigh 2 g of graphite powder for three particle size 150, 212, 500 µm.

Insert the powder into the canals.

Use different conditions for electric arc process - two channels 20 V, 141 A and

21.5 V and 202 A.

Clean the samples to remove the layer of oxides and contaminants.

Section the samples to prepare the test specimens by cutting the sample from

centre along the piece.

Cut 10 mm thick samples.

Grind and polish the test specimens.

3.4.2. The use of graphite powder inside surface made holes in aluminium

alloy

Sectioning the aluminium alloy bar which is mention in Table 3.2 in pieces of

60 x 30 x 10 mm.

Make a number of Ø=1mm diameter holes, 5 mm deep, arranging the holes as

shown in Figure 3.13.

Insert 0.1 g graphite inside these holes.

Cover the samples by aluminium foil.

Electric arc deposition of the graphite powder and melt aluminium alloy by

using different electrodes: pure Al, Al-5Si and Al-12Si of 2.5 mm diameter,

and Al-12Si electrode of 4.2 mm diameter.

Fig. 3.10. Sketch of preparing sample to electric arc

process. process.

Fig. 3.13. Sketch of holes given in aluminium samples.


13

Perform the electric arc deposition process in two steps: high intensity of 70A,

for Ø=2.5 mm, 100 A for Ø=4.2 mm, lower 55 A Ø=2.5 mm, and 90 A for

Ø=4.2 mm.

Clean all the samples and cut them into pieces of 30 x 10 x 10 mm.

Grind and polish.

3.4.3 Coating electrode by graphite powder layers

Cut the aluminium alloy into 60 x 30 x 20 mm pieces.

Use two types of electrodes: pure aluminium and Al-12Si, having 2.5 mm in

diameter.

Cover the electrodes used in the deposition process by graphite powder in

different percentage weights 1.5, 3, and 4.5 in two layers.

Coating process by adhesive aluminium foil weighing 0.4 g.

Cover the electrode in copper wire, Figure 3.14.

Use 60 amperes electric current for the deposition process.

Clean the samples after completing the electric arc process.

Cut the specimens to prepare 30 x 20 x 10 mm test samples.

Grind and polish all the test samples.

Chapter IV

4. Experimental data

4.3. Aluminium -pure aluminum sieve – graphite particles composite produced by

gravity casting

The graphite particles have the tendency to segregate because the graphite has a

lower density and it is not wetted by the metallic melt. During the solidification of Al-

Fig. 3.14. Electric arc process for Al alloy by electrode covered by graphite powder

a- covered electrode; b- cross section of covered electrode.

a

b


14

graphite composites, the graphite particles are pushed by the primary dendrites to the

eutectic liquid, which solidifies the last. Graphite particles are not entrapped between

the dendritic branches, because the distance between these branches is small (of about

20 μm). Usually, graphite particles delay the solidification process due to the low

thermal diffusivity. This fact determines the segregation and floating of particles [125].

To reduce the floating of graphite particles, quick cooling is necessary.

The microstructure of aluminum melt: Grp distributed on pure Al sieve samples

in Figures 4.10-4.12 are presented.

Fig. 4.10. Optical micrograph of composite aluminium- 2vol. % graphite particles on

pure Al sieve [100X].

Few particles of graphite appear in Figure 4.10.The low density of Grp compared

to Al melt and the low of volume percentage led to this result.

Fig. 4.11. Optical micrograph of composite aluminium- 3vol. % graphite particles on

pure Al sieve [100X].

The increasing in volume percentage of Grp to 3% leads to the formation of some

Grp agglomerations. The distribution of these agglomerations depends on the site, as

towards the top the agglomerations begin to increase.


15

0

2

4

6

8

2 3

4

Par

ticl

e d

en

dit

y ·

10

(n

0.

par

ticl

es/

mm

2)

Vol. % graphite

0.78

0.8

0.82

0.84

0.86

0.88

0.9

2 3 4

Me

an c

on

vexi

ty

vol. % graphite

Fig. 4.12 Optical micrograph of composite aluminium- 4vol. % graphite particles

on pure Al sieve [100X].

Fig. 4.13. Particle density in aluminuim, by using pure Al sieve with graphite.

Particle density increased with increasing of the volume percentage of graphite

over sieve. Many clusters and agglomerations occurred due to poor adhesion between

the graphite and the pure aluminium sieve. The particle density increased with

approximately 27 % between 2 and 4 vol. %. The increasing of the volume percentage

of graphite led to increasing the graphite particles density into the matrix. Therefore,

the particle density of graphite particles in the aluminium matrix becomes significantly

higher.

Fig. 4.14. Mean convexity of graphite particles in Al composite.


16

0.31

0.315

0.32

0.325

2 3 4

Me

an s

ph

eri

city

Vol. % graphite

0

0.5

1

1.5

2

2.5

3

2 3 4

Me

an a

spe

ct r

atio

Vol. % graphite

Mean sphericity of Grp describes the roundness by using the central moment,

while mean convexity measures the object area and the area of its convex hull (see

Table 3.7). The maximum values of sphericity and the convexity are one.

Fig. 4.15. Mean sphericity of graphite particles in Al composite.

Fig. 4.16. Mean aspect ratio (ratio between maximum feret and minimum feret) of

graphite particles in Al composite.

The mean aspect ratio decreases when increasing the volume percentage of

graphite particles. The percentage of decreasing in mean aspect ratio of graphite

particles is 18 % between 2 vol. % and 4 vol. % Grp. When the shape of particles

becomes sphere, the mean aspect ratio decreases, because the maximum ferret becomes

nearly equal to minimum ferret.

4.4. Al alloy-layers of graphite powder – pure aluminium foil composite

The results of the computer simulation indicated that the procedures and

techniques included in this program can be useful to study the course of the

solidification process for different matrix and amount of graphite particles used as

complementary material. The analysis of the results shows that the way of the

composite solidification is closely related to the assumed thermal boundary conditions

and physical parameters of the materials. Slow cooling of the cast promotes the

segregation of the reinforcement particles during this process. The movement of the

graphite particles is the result of balancing of forces, in which the density of graphite


17

particles and matrix are taken into account. This proves a significant influence of

graphite particles on the solidification process course and thereby, the disparate nature

of the heterophase composite crystallization.

From Figures 4.19, 4.20, and 4.21 some observations can be recorded about Al-

Grp- pure Al foils:

Optical micrographs revealed that a small amount of fine particles has a quite

uniform distribution in Al-0.25 wt. % Grp-pure Al foils and Al-0.5 wt. % Grp-

pure Al foils composites because the wettability between the graphite and

aluminium melt is not good.

Some large Gr particles and, in addition, very fine particle are appeared when the

weight percentage of graphite was increased to 0.75. The fix package on the base of

mould gives more time for this quantity to be incorporated in melt with some cluster

of graphite particles.

The aluminium foils layers are pressed on the graphite particles layers to

grants allow more time for incorporation and to block the particles from moving

upwards.

The overheating of melt to 937 ⁰C improves the wetting between the graphite

particles and aluminium melt.

Fig.4.20. Optical micrograph of

aluminum- 0.5 wt. % graphite – pure Al

foils [50X].

Fig. 4.19. Optical micrograph of

aluminium- 0.25 wt. % graphite – pure Al

foils [50X].

Fig.4.21. Optical micrograph of

aluminium - 0.75 wt. % graphite-pure Al

foils [50X].


18

The amount of Mg addition to aluminium melt enabled the uniform distribution

of the graphite particles in the composites in limit amount 0.4-0.6 wt. %. If the Mg

exceeded 1 wt. % caused agglomeration was [129]. Figures 4.25-4.27 represent

microstructures of graphite particles in Al-Si12-Mg alloy composite.

Fig. 4.22. Optical micrograph of Al - Si12 -

0.25 wt. % graphite – pure Al foils [50X].

Fig. 4.23. Optical micrograph of Al - Si12 -


Fig. 4.24. Optical micrograph of Al - Si12 - 0.75 wt. %

graphite - pure Al foils [50X].

Fig. 4.25. Optical micrograph of Al-Si12-

Mg- 0.25 wt. % graphite – pure Al foils [50X].

Fig. 4.26. Optical micrograph of Al-Si12-Mg -


Fig. 4.27. Optical micrograph of Al - Si12-Mg -



19

Analyzing the images presented in Figures 4.25, 4.26, and 4.27 some information

could be obtained.

- The images reveal the incorporation of graphite particles into the aluminium

matrix, indicating that Mg is very effective in wettability improvement of

graphite particles by molten aluminium.

- Agglomerations took place in some zones. Also, porosity could be found in

some places.

- Residual porosity diminishes with decreasing particle size and with magnesium

content; therefore, the increasing of graphite percentage determines more range

of particle size incorporate in melt.

- A weak bonding between graphite particles and aluminium, means the increase

of graphite particles percentage incorporated into the melt.

- By not using mechanical mixing, other ways to ensure interference between Grp

and the molten matrix are needed.

- The alloying elements such as Mg and Si are very important to increase the

interface bond between Grp and aluminium melt.

4.4.2. Thermal analysis and cooling rate

Automatic analyses of the cooling rate for the samples were performed. Figures

4.28-4.30 present the cooling rate of three samples, each Figure representing the

following samples included in the experimental program; Al-0.25 wt. % Grp, Al-Si12-

0.5 wt. % Grp, Al-Si12-Mg-0.75wt. % Grp.

Fig. 4.28. Cooling curve for Al-0.25 Grp-Al foil composite.


20

Fig. 4.29. Cooling curve for Al-Si12-0.5 Grp-Al foil composite.

Fig. 4.30. Cooling curve for Al-Si12-Mg-0.75 Grp-Al foil composite.


21

540

570

600

630

660

690

720

0 0.25 0.5 0.75

T nu

c. A

l

Wt. % graphite powder

AL

Al-Si12

Al-Si12-1.5Mg

520

540

560

580

600

620

640

660

0 0.25 0.5 0.75

T n

ucl

. EU

T.,

ᵒC


Al

Al-Si12

Al-Si12-1.5Mg

Fig. 4.32. Dependence between the wt. % of Grp and

T nuc. Al (the nucleation aluminium temperature).

It can be noticed that nucleation which develops the eqaxed grain formation is

well promoted as graphite particles are introduced into the melt.

The graphite particles are more likely to be rejected by the solidification front due

to the low relative velocity between the solid-liquid interface and the particles. This

velocity is less than critical compared to velocity for pushing. Rejection occurred rather

than immersion of particles due to the interaction of solid-liquid interface in the low

velocity. The alteration in nucleation and growth mechanism of the micro constituent

associated with the presence of graphite particles is very hard, therefore the quick

solidification of melt reduces the particles rejection [130].

Fig. 4.35. Dependence between the wt. % of Grp and Tnucl EUT

(the nucleation at eutectic point temperature) of composite.

The nucleation and growth is beginning opposite to the thermal gradient. The

addition of alloying elements and graphite into aluminium changes the solidification

process, this is shown in Figure 4.35.


22

0

100

200

300

400

500

600

700

0 0.25 0.5 0.75

T ES,

C


Al

Al-Si12

Al-Si12-1.5Mg

0123456789

0.25 0.5 0.75

Par

ticl

es

de

nsi

ty (

no

. p

arti

cle

s/m

m2 )

Wt. % Grp

AluminiumAl-Si12Al-Si12-Mg

Fig. 4.38. Dependence between the wt. % of Grp

and TES (the end solidification temperature) of composite.

A change in the melt composition has effects on the fluidity and the reactivity of

the melts. The eutectic and primary silicon is agglomerated on the boundary of the

graphite particles. The large quantity of eutectic silicon caused the rejection

phenomenon of graphite at the interface of the eutectic-primary dendrites of

aluminium, where the graphite delays the solidification process, due to its low thermal

diffusivity compared to the aluminium. However, the end solidification temperature is

not significantly affected (Figure 4.38).

Particles density and shape factors

The particles densities of samples are shown in Figure 4.49 and were calculated

by optical graphs

Fig. 4.42. Particles density of Grp in different Al alloys.

One of the important factors which have effect on the particle behavior in Al

alloy is the alloying elements which could improve the incorporation of Grp in the

metallic bath. The value of particle density of Grp was increased with approximately

12.7 % in Al-Si12-Mg, 4.5 % in Al-Si12 and 7.2 % in Al and Grp was increased from

0.25 wt. % to 0.75 wt. %. The particle density in Al-Si12-1.5Mg alloy is higher than in


23

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.25 0.5 0.75

Me

an s

ph

eri

city

Wt. % Grp

AluminiumAl-Si12Al-Si12-Mg

other alloys due to the effect Mg on the improvement of wetting conditions between

the Grp and the melt. (Addition of 3% of Mg to Al melt reduces its surface tension 0.62

Nm-1

at 993 Ko, a reduction of about 30% from its original value).

Fig. 4.43. Mean sphericity of graphite particles in composite.

The particle shape has a significant influence on the flotation effectiveness. Mean

sphericity (see Table 3.8) was has increased by increasing graphite percentage

especially for Grp in Al-Si12-Mg. The characteristic brittle of graphite boundary made

it more exposed to the erosion property. The chemical reaction between the Grp and the

melt could form some compounds on the boundary of the particles. These compounds

can alter the behavior of the particles such as mean sphericity.

4.5. Melting and deposition in electric arc

4. 5. 1. Melting and deposition in electric arc of graphite inside holes made in

aluminium

Al alloy- graphite particles composite samples were prepared using different

electrodes in composition and diameter by melting and deposition processes. Figure

4.54 presents these final samples.

Fig. 4.54. Al alloy-Grp composites obtained by using different electrodes.

The composition of the electrodes was very important for incorporation the

graphite particles. In addition, the size of electrode (cross-section) in contact with the

material to be deposed defines the current density flowing through the electrode. In

order to focus the arc energy at the interface, electrode sections have to be selected

with a proper ratio. When it was applied the electric arc on the Al alloy having holes

filled with Grp, both the rod and the melted Al alloy form a pool.


24

Figure 4.48 shows that the distribution of graphite particles deposit on Al-alloy

(by using Al-Si12 electrode with a diameter of 4.2 mm) is more regular and has low

agglomeration tendency. When increasing Si in the electrode it resulted a high fluidity

and more chance to retain the particles. The increasing in diameter led to increasing in

heat and the matrix was melted in short time. In this case the distribution was

improved.

Fig. 4.48. Optical micrographs of Al alloy- graphite composite by low intensity of electric arc

[50X]: A- Pure Al electrode in diameter of 2.5 mm; B- Al-Si5 electrode in diameter of 2.5 m;

C-Al-Si12 electrode in diameter of 2.5 mm; D- Al-Si12 electrode in diameter of 4.2 mm.

Fig. 4.49. Optical micrographs of A l alloy- graphite composite by high intensity of electric arc

[50X]: A-Pure Al electrode in diameter of 2.5 mm; B- Al-Si5 electrode in diameter of 2.5 mm;

C-Al-Si12 electrode in diameter of 2.5 mm; D- Al-Si12 electrode in diameter of 4.2 mm.

In the case of high intensity, because that causes the diminution of melt viscosity,

a negative effect on the distribution of graphite particles could appear. When the

melting and depositing are made using Al-Si12 electrode of 4.2 mm diameter enough

heat results and the incorporation of Grp in the molten aluminuim is improved.

A

C

B

D

A B

D C


25

0

2

4

6

8

10

12

14

16

a b c d

Par

tica

les

de

nsi

ty ·

no

. par

tica

les/

mm

2

Electrodes type

Lowintensity

0

0.1

0.2

0.3

0.4

0.5

a b c d

Me

an s

ph

eri

city

Electrodes type

Low intensity

High intensty

Fig. 4. 50. Particle density of particles of Al alloy with Grp in the holes. a-Pure Al

electrode with diameter =2.5 mm; b- Al-Si5 electrode with diameter =2.5 mm; c-Al-Si12

electrode with diameter =2.5 mm; d-Al-Si12 electrode with diameter =4.2 mm.

In Fig. 4.50, it results that the particle densities of samples prepared by using

high intensity is higher than for the samples prepared by using low intensity process.

This refers to the interaction between the graphite particles and the molten aluminium.

The electrode type Al-Si12 in diameter of 4.2 mm assures the incorporation of graphite

particles in the melt of Al alloy more than other types of electrodes because of the

large amount of heat. The particle densities for samples prepared by using this

electrode are 2.283 and 1.856 no. particles /mm2 in the case of high intensity and low

intensity respectively. The particle densities for samples prepared by using pure Al

electrode are approximately. 1.81 and 1.737 no. particles / mm2. In this method the

heat generation from electric arc is an important parameter which depends on cross

section of electrode, voltage, and current. Below 1000°C, oxide layer have formed and

the reactivity between Al and C was weak. Therefore the carbon was hardly

incorporated into aluminium. The graphite particles will float to the melt surface in

accordance with the formula: 0, ∑ 0.

Fig. 4.51. Mean sphericity of Grp in Al alloy deposition by different electrodes a-pure Al

electrode of diameter = 2.5 mm; b- Al-Si5 electrode of diameter = 2.5 mm; c-Al-Si12 electrode

of diameter = 2.5 mm; d-Al-Si12 electrode of diameter=4.2 mm.


26

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

a b c d

Me

an c

on

vexi

ty

Electrodes type

Low intensity

High intensty

Mean sphericity of graphite particles incorporated in Al by using pure Al

electrode and Al-Si5 in the case of low intensity are higher than particles incorporation

at high intensity of electric arc. The partial melting of Al occurred by this type of

electrode. But when the other type of electrode of Al-Si12 in diameter of 2.5 mm is

used, high melt for Al occurred, due to the increase in Si percentage at high intensity.

This improved the incorporation and increased the sphericity of incorporated particles.

The negative effect on mean sphericity appeared in high intensity of deposition by Al-

Si12 with diameter 4.2 mm. The amount of heat generated by Al-Si12 of 4.2 mm

diameter can form more flux on the boundary of particles and reduce the sphericity of

these particles.

Fig. 4.52. Mean convexity of Grp in Al alloy deposition by using different electrodes. a- pure

Al electrode in diameter = 2.5 mm; b- Al-Si5 electrode of diameter = 2.5 mm; c-Al-Si12

electrode of diameter = 2.5 mm; d-Al-Si12 electrode of diameter = 4.2 mm.

In Figure 4.52, the type of electrode has no effect on the mean convexity

especially at low intensity of electric arc process. At high intensity of deposition, the

mean convexity was different by using different electrodes, especially in electrode Al-

Si12 in diameter of 4.2 mm. That means that Si content and the diameter of electrode

could be important technological parameter in an electric arc deposition.


27

1.83

1.835

1.84

1.845

1.85

1.855

1.86

1.865

1.87

a b c d

Me

an a

spe

ct r

atio

Electrode type

Low intensity

High intensty

0

20

40

60

80

100

120

140

a b c d

Me

an p

eri

me

ter

Electrode type

Low intensity

High intensty

Fig.4.53. Mean aspect ratio of Grp in Al alloy deposition by using different electrodes. a- pure

Al electrode of diameter = 2.5 mm; b- Al-Si5 electrode of diameter = 2.5 mm; c-Al-Si12

electrode of diameter = 2.5 mm; d-Al-Si12 electrode in diameter = 4.2 mm.

The mean aspect ratio of graphite particles (see Table 3.8) were was a little

affected by the electric arc intensity in all types of electrodes. Only for Al-Si12

electrode with diameter of 4.2 mm the effect was higher, because the large amount of

generated heat was high for an electrode of big diameter. Also, in this case a lot brittle

chemical compounds could be formed.

Fig. 4.54. Mean perimeter of Grp in Al alloy deposition by different electrodes: a-pure Al

electrode of diameter = 2.5 mm; b- Al-Si5 electrode of diameter =2.5 mm; c-Al-Si12 electrode

of diameter = 2.5 mm; d-Al-Si12 electrode of diameter = 4.2 mm.

Each pixel distance of particle graphite was classified according to both the size

of the particle surrounded as well as the distance between adjacent particles. From

Figure 4.54 it is obvious the decreasing in mean perimeter with increasing the

percentage of Si in the electrode and the diameter.

At high intensity of process the mean perimeter is less than in low intensity,

because the number of small individual particles in high intensities is higher than in

low intensity. The sum of pixel distances in the case of small individual particles was

lower than in case of big particles.


28

4.5. 2. Electric arc deposition by using an electrode coated with graphite

powder

Optical micrographs of the cross-section of composites processed by different

techniques are shown in Fig. 4. 56 - 4.61.

From Fig. 4.56 it can be seen that the graphite particles are relatively large at 1.5

wt. % addition. Higher amounts of graphite particles were incorporated and distributed

in the melt of aluminium alloy when the percent of graphite particles covering the

electrode is increased. The amount of graphite layers and copper wire with respect to

the electrode type can also contribute to the distribution of particles. The amount of Grp

which is incorporated in the aluminium melt is increasing with the increase of Grp

percent on the electrode to 3 wt. %. Fine particles of Grp in uniform distribution can be

seen in Figure 4.57.

Fig. 4. 58. Optical micrograph of 4.5 wt. % graphite –Al alloy composite deposition by

using an Al-Si12 electrode [50X].

Fig. 4. 56. Optical micrograph of 1.5 wt. % graphite –

Al alloy composite deposition by using an Al-Si12

electrode [50X].

Fig. 4. 57. Optical micrograph of 3 wt. % graphite –

Al alloy composite deposition by using an Al-Si12

electrode [50X].


29

Figure 4.58 shows higher amounts of graphite particles incorporated and

distributed in the matrix. Alloying elements such as Si, Cu, and Mg affected the

incorporation of Grp into the melt. The copper wire which was added over the electrode

is an important factor for the improvement of wetting conditions. So, copper coating of

Grp can enhance greatly the wettability and forms a good interface bonding between

Grp and aluminium. It was revealed that when Cu appears in the matrix, it forms a

liquid which flows into porous areas and helps in reducing the porosity.

Small amount of Grp is deposited in aluminium by electric arc when using 1.5 wt.

% Grp and covering pure Al electrode due to the absence of alloying elements.

These alloying elements can reduce the melt temperature of the matrix and melt the

matrix in short time.

The distribution of graphite particles is improved in Al-Si12 electrode covered

with graphite particles. The increasing of Grp percent which is covering the electrode

appears to be increasing the particles density. This is illustrated in Figure 4.62.

Fig. 4. 59. Optical micrograph of 1.5 wt. %

graphite –Al alloy composite deposition by

using a pure Al electrode [50X].

Fig. 4. 60. Optical micrograph of 3 wt. %

graphite –Al alloy composite deposition

by using a pure Al electrode [50X].

Fig. 4. 61. Optical micrograph of 4.5 wt. % graphite –Al alloy

composite deposition by using a pure Al electrode [50X].


30

0

2

4

6

8

10

12

14

16

1.5 3 4.5

Par

ticl

e d

en

sity

(n

o.

par

ticl

e/m

m2)

Wt. % Grp

Al-Si12 electrode

Pure Al electrode

0.74

0.76

0.78

0.8

0.82

0.84

1.5 3 4.5

Me

an c

on

vexi

ty

Wt. % Grp

Al-Si12 electrode

Pure Al electrode

Usually, silicon forms a metastable phase with graphite or it is adsorbed on the

surface of the graphite particles. In samples obtained by using an Al-Si12 electrode the

particles density appears higher than in samples obtained by using a pure Al electrode

of approximately 17%, 13.6%, and 10.6% at 1.5, 3, and 4.5 wt. % Grp respectively.

Figures 4.63-4.66 show the effect of graphite percent on mean convexity, mean

sphericity, mean aspect ratio, and mean perimeter of graphite particles respectively.

Fig.4.63. Relationship between the Grp percent and mean convexity of Grp.

The type of electrode does not affect very much the mean convexity. This

geometrical parameter is increasing with approximately 8 % when the graphite content

varies from 1.5 wt. % to 4.5 wt. %.

Fig. 4.62. Particle density of Grp deposition with Al alloy.


31

0

0.1

0.2

0.3

0.4

0.5

1.5 3 4.5

Me

an s

ph

eri

city

Wt. % Grp

Al-Si12 electrode

Pure Al electrode

1.72

1.74

1.76

1.78

1.8

1.82

1.841.86

1.88

1.9

1.5 3 4.5

Me

an a

spe

ct r

atio

n

Wt. % Grp

Al-Si12 electrode

Pure Al electrode

Fig.4.64. Dependence between the Grp percent and mean sphericity of Grp.

The mean sphericity increased with approximately 23 % when graphite varied

from 1.5 wt. % to 4.5 wt. for the sample prepared by using a pure Al electrode and

with approximately 19 % when it was used the Al-Si12 electrode. The brittle

characteristic of graphite particles contributed to turn their shape to sphere because of

the friction between particles.

Fig.4.65. Relationship between the Grp percent and the mean aspect ratio of Grp.

During the development of the electric arc process, fluidity of molten aluminium

is increasing. This causes low porosity and the decrease of the aspect ratio parameter.

For samples obtained by using Al electrode the mean aspect ratio decreased with

approximately 3.8 %, while in the case of an Al-Si12 electrode the aspect ratio

decreased with approximately 4.2%, respectively. The silicon plays an important role

by some chemical compounds which could be found at the boundary of particles.


32

0

20

40

60

80

100

1.5 3 4.5

Me

an p

eri

me

ter

Wt. % Grp

Al-Si12 electrode

Pure Al electrode

Fig.4.66. Dependence between the Grp percent and the mean perimeter of Grp.

Figure 4.66 present the effect of the type of electrode on the mean perimeter. The

increase of the graphite particle percent from 1.5 wt. % to 4.5 wt. % leads to the

decrease of mean perimeter with about 17% for samples obtained with an Al-Si12

electrode and with about 23% for sample prepared by using a pure Al electrode.

4.8. Scanning electron microscope test

Some graphite particles which were identified in the Al-graphite

composite structure were choosing for SEM analysis (Figure 4.74 A and Figure 4.76

A). Both EDAX (spectrum and chemical composition) and mapping techniques were

applied in order to characterize the graphite particles features. The results are presented

in Figure 4.74B, Table 4.9 and Figure 4.75, for the particles in Figure 4.74A. Figure

4.76B, Table 4.10 and Figure 4.77 appear the results for the particles in Figure 4.76A

respectively.

From the SE images presented in Figures 4.74A and 4.74A it can be observe that

amount of graphite is distributed in many places the distribution of Grp particles being

different from an area to another. The high C level in the selected area is a proof of

graphite presence despite of many other companion elements such as Al, O, Cu, Si,

Mg. The presence of various elements such as Cu and Mg around graphite particles can

considered as a benefit factor for their restrain in Al matrix because of favorable effect

on the wettability between the graphite particles and melt aluminum. The high Al level

in graphite particle composition can be considered as a result of Al matrix influence

while the oxygen comes from surroundings (Al oxidation).

The high level of graphite particles are clear in EDAX analysis, this a good

signal for the sufficient conditions to make incorporations between the graphite

particles and aluminum melt.


33

Fig. 4. 74. Graphite particle embedded in Al matrix: A - Secondary electron image; B -

X-ray spectrum in selected area 1.

Table 4. 9. Chemical composition of graphite particle selected area 1(Fig. 4.74 A)

Element

Weight %

Atomic %

C 44.41 61.97

O 9.49 9.95

Cu 1.61 0.43

Mg 0.72 0.5

Al 42.92 26.66

Si 0.85 0.51


34

Fig.4.75. Overlaying of X – ray maps of elements distribution in graphite particle area (see Fig.

4.81A).

Chapter V

5. Conclusions and personal contributions

5.2. Conclusions of experimental results

Aluminium-pure aluminum sieve - Grp composite produced by gravitational casting

- The particle density increased with approximately 27 % when the volume

percentage of graphite deposed over a sieve increased from 2 to 4 vol. %.

- More agglomerations besides some individual particles appeared by increasing the

graphite particles percent from 2 to 4 vol. %.

- Increasing in graphite percentage from 2 to 4 vol. % led to the increase of mean

sphericity from 0.315 to 0.323.

Cu


35

- Mean convexity of graphite particles increases from 0.813 to 0.876 when the

graphite particles content increases from 2 to 4 vol. %.

Al alloy-layers of graphite powder - pure aluminium foil composite

- Little fine particles had an approximately uniform distribution in Al by using 0.25

wt. % Grp-pure Al foils and - 0.5 wt. % Grp-pure Al foils composites, but some

large Grp particles appeared when the weight percentage of graphite increased to

0.75.

- The graphite particles incorporated in Al-Si12 melt are increasing with the increase

of percentage of Grp added in package, in comparison with Al matrix.

- Residual porosity diminishes with the decrease of particle size and with the

magnesium content.

Thermal analysis

- The increase of graphite percentage and addition of alloying elements, Mg and Si,

are reducing the temperatures TM, T nucl Al, TU Al cry, T max Al cry, T nucl EUT, TU EUT, T

max EUT, and TES due to the retention of heat around the graphite particles. This fact

was confirmed by the thermal analysis.

- It was also observed that the introduction of graphite particles in the Al melt

decreases the temperature of solidification.

- Usually, the cooling rate begins with low rate, during the interval of transition from

nucleation to crystallization, and the starts to increase due to the transmission of

heat.

- The value of particles density of Grp increased with approximately 12.7 % in Al-

Si12-Mg and only with 4.5 % in Al-Si12 and 7.2 % in Al, when Grp content

increased from 0.25 wt. % to 0.75 wt. %.

- Mean sphericity and convexity increased by increasing the graphite percentage,

especially for Grp in Al-Si12-Mg.

Melting and deposition in electric arc of composite inside holes made an

aluminium alloy

- Using low intensity of electric arc, the distribution of graphite particles inside holes

made an Al alloy by using an electrode of Al-Si12, having the diameter of 4. 2 mm,

was better than for other type of electrodes.

- The particle density of samples prepared by using high intensity is higher than of

the samples prepared by using low intensity current. Thus, the particle densities for

samples prepared by using an Al-Si12 of 4.2 mm diameter electrode have big

values in the case of high intensity while the particle densities for sample prepared

by using pure Al electrode and low intensities are significantly lower.

- Mean sphericity of graphite deposition in Al alloy at low intensity of electric arc

obtained with pure Al, Al-Si12, and Al-Si12 electrodes, with the diameter of 2.5


36

mm, was more than the same property for samples melted and deposed in high

intensity of current.

- The electrodes type does not affect essentially the mean convexity of graphite

particles deposition in Al alloy at low intensity. However, this property increases in

the melt and deposition processes unfolded by using electrodes of Al-Si5 and Al-

Si12 with the diameter of 2.5 mm, as well as for the Al-Si12 electrode with 4.2 mm

diameter, at high intensity of current.

- The mean aspect ratio of graphite particles was not affected very much when the

electric arc intensity was changed (for all types of electrodes, except the Al-Si12

electrode with the diameter of 4.2 mm).

Electric arc deposition by using an electrode coated with graphite

- The rate of increase in particle densities of samples with 1.5, 3.0, and 4.5 wt. %

Grp are coated an Al-Si12 electrodes in comparison with samples obtained by

using a pure Al electrodes are 16.9 %, 13.6 %, and 10.6 %, respectively.

- The type of electrode has not an important effect on the mean convexity,

especially for a graphite content of 3 wt. % and 4.5 wt. %. At smaller content of

1.5 wt. %, the mean convexity for sample obtained by using Al-Si12 electrode

coated with graphite was greater than samples obtained by using a pure Al

electrode.

- Mean convexity increased with about 5-7 % when the graphite content increased

from 1.5 wt. % to 4.5 wt. %.

- When particles tend to a spherical shape, the value of aspect ratio is diminishing

and there was a decrease of this parameter with the increase of the Grp percent.

- The increase in the graphite particle percent from 1.5 wt. % to 4.5 wt. % leads to

the decrease in mean perimeter with about 18 % for samples by using an Al-Si12

electrode and with 23 % samples obtained by using a pure Al electrode.

Scanning electron microscope test

- SEM analyses pointed out the presence of graphite particles embedded in Al matrix;

- Many other elements such as Al, O, Cu, Mg and Cu were identified as C companion;

- The presence of different elements such as Cu, Mg in the surface layer of Al-

Grp composite is considered as a benefit because of wettability between

graphite and Al melt improvement;

- The high Al level in graphite particle composition can be considered as a result

of Al matrix influence while the oxygen comes from surroundings (Al

oxidation);

- The graphite particles are non- uniform distributed in the Al melt due to its

floating tendency.


37

5.3. Original contributions

The main original contributions of this research are the following:

Calculation of shape factors for different shape of particles: cylinder, conical,

conical truncated, and ellipsoid.

Obtaining a surface layer of gravity cast Al-Grp composite by using a pure

aluminium sieve covered with graphite particles, the sieve being inserted on the

internal surface of a mould.

Production of surface layer of Al-Grp composite making packages with layers

of graphite powder and pure aluminium foil fixed mechanically on the base of

the mould, before the pouring of molten aluminium by gravity casting.

Deposition of aluminium alloy and graphite particles on aluminium to produce

surface layer by using an electric arc. Introduction of Grp in some holes made

on the surface of aluminium alloy and the use of different types of electrodes

for melting and deposition.

Preparation of thin layers of Al alloy–graphite particle composites by the

electric deposition method. The use of a covered electrode with graphite, pure

Al foil, and copper wire.

Insertion of the graphite particles inside a channel made on the surface of an

aluminium alloy, before the melt and deposition under an electric arc to prepare

thin layers of Al-graphite composites on the Al alloy surface.

Dissemination of research results

Scientific papers published

1. Hazim FALEH, Muna NOORI, and Florin STEFANESCU, Properties and

Applications of Aluminium - Graphite Composites, Advanced Materials

Research, ISSN: 1662-8985, VOL. 1128, pp.134-143.

2. Muna NOORI, Hazim FALEH, Mihai CHISAMERA, Florin STEFANESCU ,

and Gigel NEAGU, Wettability of Silicon Carbide Particles by the Aluminium

Melts in Producing Al-SiC Composites, Advanced Materials Research,

ISSN:1662-8985, VOL. 1128, pp. 149-155

Scientific papers accepted to be published

1. Hazim FALEH, Muna NOORI, Florin STEFANESCU, Gigel NEAGU, and

Eduard Marius STEFAN, Wettability in aluminium-graphite particles

composite (review) (poster), "Dunarea de Jos" University of Galati,

International Conference on Material Science, 7th

Edition, 19th

-21st May 2016.

Paper published in advanced Material Research-ISI journal /proceeding.

2. Muna Noori, Hazim Faleh, Mihai Chisamera, Gigel Neagu, Florin Stefanescu

and Eduard Marius Stefan, Properties of Al-SiCp composites (review)

(poster), "Dunarea de Jos" University of Galati, International Conference on


38

Material Science, 7th

Edition, 19th

-21st May 2016. Paper published in

advanced Material Research-ISI journal /proceeding.

3. Hazim Faleh, Muna Noori, Florin Stefanescu, Mihai Chisamera, Gigel Neagu,

EXPERIMENTAL RESEARCH CONCERNING A NEW METHOD TO

PRODUCE ALUMINIUM ALLOY-GRAPHITE PARTICLE COMPOSITE

IN SURFACE LAYERS, U.P.B. Scientific Bulletin, Series B, Chemistry and

Materials Science,Vol….., pp……, ISSN 1454-2331.

4. Muna Noori, Hazim Faleh, Mihai Chisamera, Gigel Neagu, Florin Stefanescu,

Stefan Eduard Marius, SOME ASPECTS CONCERNING A NEW

POSSIBILITY OF Al-SiCP COMPOSITE PRODUCTION, U.P.B. Scientific

Bulletin, Series B, Chemistry and Materials Science,Vol….., pp……, ISSN

1454-2331.

References

[15] J.A. Cornie et al., “Discontinuous Graphite Reinforced Aluminum, and Copper Alloys for

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[109] R. Mahadevan and R Gopal,” Selectively reinforced squeeze cast pistons”, 68th WFC -

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[118] Hazim FALEH, Muna NOORI, and Florin STEFANESCU, "Properties and Applications

of Aluminium - Graphite Composites", Advanced Materials Research, ISSN: 1662-8985,

VOL. 1128, pp.134-143.

[125] D.G. Thomas, “Transport characteristics of suspension: VIII. a note on the viscosity of

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[129] Zhengang Liu , Guoyin Zu, Hongjie Luo, Yihan Liu and Guangchun Yao, "Influence of

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