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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
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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.
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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].
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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).
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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.
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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.
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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.
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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.
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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.
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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.
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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].
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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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 -
0.5 wt. % graphite – pure Al foils [50X].
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 -
0.5 wt. % graphite – pure Al foils [50X].
Fig. 4.27. Optical micrograph of Al - Si12-Mg -
0.75 wt. % graphite – pure Al foils [50X].
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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.
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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.
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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
Wt. % graphite powder
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.
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
22
0
100
200
300
400
500
600
700
0 0.25 0.5 0.75
T ES,
C
Wt. % graphite powder
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
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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.
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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.
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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.
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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.
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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].
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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].
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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.
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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.
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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.
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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.
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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
Research on the possibility of obtaining Al-graphite (particles) composites in certain zones of parts
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.
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