Study of the Tribological behavior of as cast Al-4.2%Cu-Al2O3 composite

IOSR Journal of Mechanical and Civil Engineering (IOSR-JMCE)
e-ISSN: 2278-1684,p-ISSN: 2320-334X, Volume 10, Issue 4 (Nov. - Dec. 2013), PP 50-59
www.iosrjournals.org
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Study of the Tribological behavior of as cast Al-4.2%Cu-Al2O3
composite
1
S. Srivastava, 2
P. K. Singh, 2
S. K. Singh, 1
Somya Yadav, 1
Yogesh Srivastav
1
Materials Science & Metallurgical Engineering
1
Maulana Azad National Institute of Technology, Bhopal, M.P. (India)
2
University of Technology, Barkatullah University, Bhopal, M.P. (India)
Abstract: The research work is carried out on the study of tribological property of aluminium based metal
matrix composite material, which is fabricated by using sol-gel technique. The composite material is prepared
through liquid metallurgy method by using varying percentage of Alumina and aluminium and fixed percentage
of copper 4.2%. Test sample billet is fabricated through casting method and has been examined the different
mechanical behaviour such as Vickers Hardness Number, Ultimate Tensile Strength, 0.2% Proof Stress, etc.
From the study, it has been observed that with increase in the alumina content in matrix the ductility of
composite show a contrary effect. The Pin-On-Disc test is used to evaluate the tribological property wear for
composite material and it is observered that tendency of wear rate has improved. The weight losses of the
specimen are measured and wear and friction characteristics are calculated with respect to time. Depth of wear
track, sliding speed, bearing load friction coefficient and wear volume have been shown large sensitivity to the
applied normal load and the testing time (or sliding distance). The XRD and SEM analysis are used to analyse
the wear debris and track; and silent conclusion has been drawn.
Key words: Tribological, composite, wear, pin-on-disc, friction, XRD, SEM.
I. Introduction
Aluminum matrix composites (AMCs) refer to the class of light weight high performance aluminum
centric material systems. The properties of AMCs can be tailored to the demands of different industrial
applications by suitable combinations of matrix, reinforcement and processing route. Presently several grades of
AMCs are manufactured by different routes. Three decades of intensive research have provided a wealth of new
scientific knowledge on the intrinsic and extrinsic effects of ceramic reinforcement vis-a-vis physical,
mechanical, thermo-mechanical and tribological properties of AMCs. In the last few years, AMCs have been
utilized in high-tech structural and functional applications including aerospace, defence, automotive, and
thermal management areas, as well as in sports and recreation. It is interesting to note that research on particle-
reinforced cast AMCs took root in India during the 70’s, attained industrial maturity in the developed world and
is currently in the process of joining the mainstream of materials. This work represents an overview of AMC
material systems on aspects relating to processing, microstructure, properties and applications.
II. Experimental investigation
Selection of materials
The material used in this work was commercially available 99⋅5% pure aluminum with a composition
given in table 1. Commercially pure aluminium is the product of the electrolytic cell process. In this experiment,
the composite of Al-Cu was prepared from commercial pure aluminum with the appropriate addition of 99.99%
small chips of pure tin-metal. Table 2 shows the physical and mechanical properties of pure aluminum.
TABLE 1: Chemical composition of the 99⋅5% pure aluminum.
Element wt.% Si Fe Ti V Cu Mn Al Others
0.063 0⋅36 0⋅003 0⋅006 0⋅002 0⋅037 99⋅557 0⋅002

Study of the Tribological behavior of as cast-Al-Sn/Graphite composite
TABLE 2: Physical and mechanical properties of commercially pure aluminum
III. Procedure for preparation
The experimental set-up used for mixing and casting of composites is shown in Fig 16. It comprises of
a cylindrical sillimanite crucible of 150 mm diameter and 250mm depth with attachment of four baffles to its
sidewalls for proper dispersion of second phase in melt during stirring. The crucible was placed in an electric
heated muffle furnace. It was also equipped with a bottom pouring attachment, which could be closed or opened
by alumina stopper with a lever system. A steel mould was placed beneath the furnace to cast the molten metal.
In the top cover suitable opening was provided to charge materials and insert thermocouples. The temperature of
the furnace could be controlled with an accuracy of about ±50
C. Metallic bath temperature was measured
continuously by chromel /alumel thermocouple. The agitator system could be raised or lowered with the help of
the hanger and steel frame structure. After adjusting the mixer in a central position and required height from the
bottom of the crucible, the motor was bolted and locked while mixing of melt. Three-blade impeller was used
for effective mixing. This design provides very high rates of shear and only axial and radial flow currents are
utilized for mixing without any significant vortex formation due to the presence of baffles. The Al-Cu-Alumina
composites were prepared by liquid metallurgy methods. The required amounts of commercial (approximately
880-900g) pure aluminum with 65 g of copper were charged into the crucible and aluminum was heated to a
temperature 2000
C above its melting point i.e. 6620
C. A mechanical stirrer was inserted into the melt, and
agitation was started at a speed of 35 s-1
. Mixing was done for a period of 60 seconds. The emulsion was poured
into the chilled cylindrical mould placed beneath the crucible. The same procedure was adopted for different
compositions. Cylindrical casting of length 20cm and dia.2cm were obtained.
IV. Evaluation of as-cast Properties of the Composite
The wet chemical analysis was used to determine the percentage of iron in the bulk .The
metallographic specimens were prepared using standard technique and studied under SEM for different feature
present. The density of the composite was determined using Archimedes’ principle by weighing in water and
air. The hardness of the entire composite was measured using a Vickers hardness testing machine. The hardness
of the entire composite was measured using a Vickers hardness testing machine. The hardness was measured using
Vickers hardness instrument Leitz Welzlar at a load of 5Kg. At least 3 indentations have been taken for each point.
Tensile testing of all the Al-alloy-Alumina composite was performed stress along with percentage elongation and
reductions in area were computed from the results.
V. Wear test
Pin-on-disc machine was used for evaluating the wear properties under dry sliding condition. The
cylindrical test pin of 8mm diameter and 40mm length were used against a hardened steel disc of 120 mm
diameter. Wear tests were conducted with variable applied pressure 3.9x10-1
MPa and a sliding speed of 0.5 m/s
with a constant sliding distance of 10000 meters. Wear test were also conducted with selected varying speeds
and sliding distance ranging up to 1000 meters. The initial weight of the specimen was determined in a digital
balance with a precision of ± 0.1 mg. The pin was kept pressed against a rotating steel disc of hardness 58 HRC
under loaded condition. The frictional traction en-counted by the pin in sliding is measured by a PC based data
logging system. On completion of the running through the required sliding distance the specimen pins were
cleaned with acetone, dried and their weight were again determined for ascertaining the weight loss. Wear
debris were analyzed by XRD.
VI. Result and Discussion
1. Physical investigation
The liquid metallurgy methods were used to synthesize the composite materials with different amount
of the alumina content in the matrix. The theoretical density of the composite materials varies from 2.88 g/cc to
2.84 g/cc with alumina content. But the experimental density of the composite materials was found to vary from
2.72 g/cc to 2.70 g/cc along with porosity varies from 5.2 % to 4.9 %. The XRD methods were used to
Typical mechanical properties
Density 2.7g/m3
0.2% yield strength 20MPa
UTS 70MPa
Elongation 50%
Hardness 170Hv

investigate the different phase/element present in the prepared composite materials. Fig 18 shows the XRD
pattern of prepared nano Al2O3 with (012), (104), (110), (133), (024), (116), (018), (214), (119) at an angle of
25.594°, 35.197°, 37.804°, 43.381°, 52.588°, 57.538°, 61.333°, 66.547°, 68.230°. Fig 12(b) shows the XRD
pattern of Al2O3. The XRD scanning from 10°- 80° shows the lines for alumina, 38.86°, for aluminum
respectively.
2. SEM investigation
In casting a homogeneous single phase liquid is cooled below the liquidus line, it transforms into two
liquids, namely aluminum rich and copper rich. The minor ‘Cu’ rich phase segregates out. If the homogeneous
single Al-Cu liquid phase is rapidly cooled, then the minor phase is dispersed uniformly in aluminum rich
matrix. The microstructure of the alloys was investigated by using SEM. Fig. 17 shows the microstructure of
commercially pure aluminum along with composite in Fig. 18. Here copper and Al2O3 nanoparticles is
distributed in aluminum matrix as a separate phase in form of reticular (network) structure along the edges of
aluminum grains with the proper uniform distribution.
3. STUDY OF THE MECHANICAL PROPERTIES
TABLE 3: Mechanical properties of the Al-4.2%Cu-3.4%Alumina composite
The resistance to indentation or scratch is termed as hardness. Among various instruments for measurement of
hardness, Brinell’s, Rockwell’s and Vickers’s hardness testers are significant. Theoretically, the rule of mixture
of the type Hc=vr Hr+vm Hm (suffixes ‘c’, ‘r’, and ‘m’ stand for composite, reinforcement and matrix respectively
and v and H stand for volume fraction and hardness respectively) is valid for composite materials which helps in
approximating the hardness values. Among the variants of reinforcements, the low aspect ratio particle
reinforcements are of much significant in imparting the hardness of the material in which they are dispersed.
Table 6 shows a comparison of the mechanical properties of Al-Cu/Al2O3 composite samples produced by the
liquid metallurgy methods. Fig. 16 shows the variation of mechanical properties with the Alumina content in the
Al-Cu alloys. It is observed that the hardness of the composite materials increases with increasing the alumina
content in the matrix. Alumina is a very ductile materials and it is responsible a factor for increasing the
hardness of the materials.
1 2 3 4 5 6 7 8 9
80
100
120
140
160
180
Mechanicalproperties
Alumina Content (wt%)
VHN
UTS
PS
Fig.1: Variation of hardness with varying alumina content
The uniform distribution and the nature of the interfacial bonding between alumina particles and matrix have an
important relationship on the mechanical properties of a composite material. It has been suggested that alumina
particles, being very hard compared to the aluminium matrix, may be treated as load-bearing constituents. With
a view to extending their applications to structural components, these materials should have a good combination
of strength and ductility. The Al-Cu/Alumina composites with different Al2O3 content show an decrease in the
tensile elongation together with an increase in the ultimate tensile strength of the material, resulting from the
better dispersion of the particles. The magnitudes of these decreases are observed to average approximately
S.No. Composite VHN UTS(MPa) 0.2%PS(MPa) % elongation
1 Al-4.2%Cu-1.6%Al2O3 96.2 147.3 72.9 19.3
2 Al-4.2%Cu -2.7%Al2O3 99.6 152.3 79.1 18.1
3 Al-4.2%Cu -3.4%Al2O3 104 158.4 83.2 17.3
4 Al-4.2%Cu -5.6% Al2O3 109 165.3 87.4 16.9
5 AL-4.2%CU -8.4% AL2O3 116 173.2 93.2 16.3

18%. A strong bond between the reinforcement and matrix helps in the load transfer from the latter to the
former. As a result, fracture takes place in the composite via the reinforcement and not along the interface [1, 2].
Although the alumina is a load bearing constituent, a strong particle/matrix interface helps alumina particles
embed themselves into the matrix properly, improving the wear resistance.
VII. Wear study
1. Effect of sliding distance and load
The variation of bulk wear with sliding distance was studied at different combinations of loads and
sliding velocities. Almost a linear relationship in bulk wear and sliding distance i.e. steady state wear is
observed after an initial running-in period of 500–1000 m in almost all the cases irrespective of load or sliding
velocity used. Fig 2 shows the results for a test conducted at 2 kg load and 0.5m/s sliding velocity. In running
period, the Al-Cu/Alumina composite shows large wear rates. The relation found here is in accordance with the
pattern for most metallic materials derived theoretically as well as observed experimentally [3, 4]. But
irrespective of variables used, bulk wear is large with large alumina content in Al-Cu/Alumina composite. The
free alumina particles are released from the composite material during dry sliding of mating surfaces form a
lubricant film at the interface. Shows the variation of rise in temperature of the test specimen during experiment
with sliding distance. The maximum rise in temperature is found in Al-4.2%Cu-8.4%Al2O3 and minimum in
Al-4.2%Cu-1.6%Al2O3. This type of the behaviour can be explained on the basis of thermal conductivity. Al-
4.2%Cu-1.6%Al2O3 shows high conductivity as Al-4.2%Cu-8.4% Al2O3. Fig.5 shows the SEM micrographs of
wear tracks of Al-Cu/Al2O3 composites (Al-4.2%Cu-3.4%Al2O3) for 2 kg applied load and 0.5 m/s sliding
velocity at 10,000 m sliding distances. This micrograph was taken at the higher magnification (X6000). This
figure is clearly revealed the presence of the oxide layer which might be adhered on the rubbing surface.
2. Effect of applied load
The studies conducted to see the effect of applied load on wear rate revealed that wear rate increases
continuously with load in a linear manner irrespective of the sliding velocity used as it is evident from Fig.6 for
a particular velocity. But in all the cases wear rate first increases with increase in alumina content for all
combinations of loads and sliding velocities used in the present investigation and then increases with decrease
the alumina content. Corresponding temperature curve shown in, clearly reveal that temperature continuously
increases with increase in load but with increase in copper percentage in composite an increase in temperature
rise is observed which is indicative of larger heat dissipation capability of copper. the variation of temperature
and micro hardness of the test specimen with the variation of load. With increase the load on the test specimen,
the composite material bears maximum rise in temperature. The materials at the contacting surface on the pin-
on-disc become soften, which is responsible factor for decreasing the micro hardness of the contacting surface.
0 2000 4000 6000 8000 10000
2
4
6
8
10
12
14
Commulativewear,m
3
x10
-9
Sliding Distance (km)
1.6 % Al2
O3
2.7 % Al2
O3
3.4 % Al2
O3
5.6 % Al2
O3
8.4 % Al2
O3
Fig.2: Variation of bulk wear with sliding distance at 2 kg load and 0.5 m/s sliding velocity for
as-cast Al-Cu/Al2O3 composites.
Fig.3: SEM micrographs of wear tracks of Al-Cu/Alumina composites (Al-4.2%Cu -
3.4%Alumina) for 2 kg applied load and 0.5 m/s sliding velocity at 10,000m sliding distances.

Fig.5 shows the SEM micrographs of wear tracks of Al-Cu/Al2O3 composites (Al-4.2%Cu-3.4%Al2O3) at the
higher magnification for 2 kg applied load and 0.5 m/s sliding velocity at 3000 m sliding distances. The oxides
layer with small amount of the alumina particles are adhered on the material surface. Fig 6 (a) and Fig 6 (b)
shows the SEM micrographs of wear tracks of Al-Cu/alumina composites (Al-4.2%Cu-3.4% Al2O3) for 15 kg
applied load and 0.5 m/s sliding velocity at 3000 m sliding distances (a) worn surface (b) crack surface. The
degree of surface damage (i.e. depth and width of the grooves) depended on the applied load and microstructure
of the material. At the higher load, generally metallic failure is observed as shown in Fig 28 (a). For observing
the mechanistic phenomena at the higher load, the SEM micrograph was taken at the higher magnification, as
shown in Fig 6 (b). While studying the wear tracks at different loads for a particular velocity (from 2 to 15 Kg)
the operating modes changes from oxidative-to oxidative and metallic to metallic as load applied is increased
and wear track observes broken oxide film, deep grooves and delaminating of surface as evident from Fig 6 (b).
In this SEM micrograph some small crack was found at the oxide surface. With increase the load, the produce
cracks within the material by sliding action easily propagate and the form oxidative film at lower load are
ruptured as shown in Fig 6 (b) at 15 Kg load and 0.7m/sec sliding velocity
4 6 8 10 12 14 16
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
WearRate(m
3
/m
3
x10
-12
)
Load (kg)
1.6 % Al2
O3
2.7 % Al2
O3
3.4 % Al2
O3
5.6 % Al2
O3
)
8.4 % Al2
O3
Fig.4: Variation of wear rate with load at 0.5 m/s sliding velocity and running distance 3000 m
for as-cast Al-Cu/ Al2O3 composites
Fig.5: SEM micrographs of wear tracks of Al-Cu/Alumina composites (Al-4.2%Cu-3.4% Al2O3)
for 2 kg applied load and 0.5 m/s sliding velocity at 3000 m sliding distances.
Fig.6: SEM micrographs of wear tracks of Al-Cu/ Al2O3composites (Al-4.2%Cu-3.4% Al2O3) for 15 kg
applied load and 0.5 m/s sliding velocity at 3000 m sliding distances (a) worn surface (b) crack surface (c)
Al2O3
3. Study of the sliding velocity
The role of alumina in sliding contact is provided by layered-lattice structure. The bonds between the
parallel layers are relatively strong. The adsorbed water vapor and other gases from environment onto the
crystalline edges weaken the interlayer bonding forces. It results in easy shear and transfer of the crystalline
platelets on the mating surfaces. Fig 7 shows the variation of wear rate with sliding velocity at 2 kg load, 3000m

running distance. Like all other aluminium alloys/ composites, Al-Cu/ Al2O3 composites also show an initial
decrease in wear rate followed by a sharp increase in wear rate after attaining minima with increase of sliding
velocity for all composites at different loads. But in all the cases wear rate decreases with increase in alumina
content for (say up to 3.4 % Al2O3 in the matrix) all combinations of loads and sliding velocities used. While
that wear rate again decrease with increase the alumina content in the matrix.
Further, variation of wear rate and hardness of worn wear track surface is shown in Fig 8. It clearly
shows highest hardness at minima in wear rate, which is clearly indicative of the presence of hard oxide
particles. With increase in sliding velocity, an oxides particle is removed from the mating surface, due to
decrease the hardness of the composite materials and hence increases the wear rate. For temperature increase
with sliding velocity follows the same trend as observed in the case of variation of temperature with applied
load. Higher velocity gives higher amount of wear loss due to fast rubbing of the contacting surface. Therefore
maximum rise in temperature in the test specimen at the contacting surface occurs. The SEM observations of the
wear tracks at 2.0 Kg load for different sliding velocities are shown in Fig.9 (a–b) and 10(a–c). In Fig.9 (a-b)
shows the SEM observation at the lower and the higher velocity and Fig 10(a-c) show SEM result at the
optimized velocity. SEM micrograph of the wear track in Fig 9(a) was mainly comprised of oxide particles and
the wear track surface is seen to have more pronounced layer of oxide particles adhered at the surface of the
materials. But at the higher velocity, metallic particles come out during wear processes and wear track is seen
clear and smooth as shown in Fig.9 (b).
The minima in the wear rate was found at 1.22 m/sec. Fig. 16 show SEM micrographs of wear tracks of
Al-Cu/ Al2O3 composites (Al-4.2%Cu-3.4% Al2O3) for 2 kg applied load and 1.22 m/s sliding velocity at 3000
m sliding distances (a) worn surface (b) crack observation (c) observation of the oxide layer. Wear rate
continuously increases with increase the sliding velocity due to the formation of thin film of oxide layers along
with metallic layer at the mating surface as shown in Fig 10 (a). This is confirmed from the SEM observation of
the wear track taken at the higher magnification as shown in Fig.10(b).
The oxide layer of the respective metals adhered on the mating surface is clearly visible in this
micrograph. The failure of the materials from the wear process is due to formation and propagation of the crack
within the materials as shown in Fig 10(c). The cracks are formed at the adjacent surface of the materials. An
examination of the three micrographs shows the formation of severe patches and grooves resulting from plastic
deformation of the aluminium alumina composite and relatively small groves and mild patches on 3.4 wt %
alumina composite. This reduction in severity of the worn surface of the composite material is due to the
formation of a Al2O3 lubricating film which prevents the direct contact of the specimen with the rotating steel
disc surface. This formation of the lubricating layer at the sliding surface becomes thicker with more alumina as
the addition of Al2O3 content to the base alloy increases and it is responsible for playing an effective role for
keeping the wear behaviour of the composite low.
4. Study of the surface particles and its mechanistic approach
Figure 11 (a-b) shows the SEM micrograph of wear debris for 2 kg applied load and 1.22 m/s sliding
velocity at 3000 m sliding distances (a) collecting particles (b) examination of the alumina particles. This
observation has been also confirmed by XRD observation as shown in Fig.12. Debris in all figures was mainly
comprised of oxide particles of aluminum and tin. But it also contained some small amount of alumina as shown
in Figure 11(b). In the XRD observation, the aluminum oxide, tin and its oxides (from EDAX observation) and
alumina are found as the main peak. Tin and lead are weak and ductile and hence they decrease the strength
property of aluminium alloys under study. Further, Cu/ Al2O3, being a ductile material, deforms in preference to
the stronger matrix. This reduces the stress concentration in the matrix and makes it more deformable. It is also
found that the alloys containing tin have slightly more strength and hardness but low ductility values compared
to the alloys containing lead.
Al wear particles on the worn surfaces are laminated by the pin on the contact area, forming plough.
Because wear particles contain some aluminum oxide, Zhou et al believed that the oxidation wear was the main
wear mechanism of composites [5]. However, according to the SEM observation of worn surfaces of the
composite and the study of delamination theory of wear, it can be concluded that the delamination wear could be
the main wear mechanism. Dislocations at the mating surface, subsurface crack and void are induced due to the
repeated plastic deformation between the test pin and disc. The cracks extend later and cause break and split of
the hardened surface layer by shear deformation mechanism [6-10].

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
WearRate(m
3
/m
3
x10
-12
)
Velocity (m/sec)
1.6 % Al2
O3
2.4 % Al2
O3
3.4 % Al2
O3
5.6 % Al2
O3
8.4 % Al2
O3
Fig.7: Variation of wear rate with sliding velocity at 2 kg load for Al-Cu/ Al2O3 composites.
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Velocity(m/sec)
Wearrate(m
3
/m
3
)x10
-12
90
100
110
120
130
140
150
160
Microhardness
Fig.8: Variation of micro-hardness and wear rate of worn surface with sliding velocity at 2 kg
load.
Fig.9: SEM micrographs of wear tracks of Al-Cu/ Al2O3 composites (Al-4.2%Cu-3.4% Al2O3)
for 2 kg applied load and 0.5 m/s sliding velocity at 3000 m sliding distances (a) worn surface at
0.25m/sec (b) worn surface at 3.53m/sec
Fig.10: SEM micrographs of wear tracks of Al-Cu/ Al2O3 composites (Al-4.2%Cu-3.4% Al2O3)
for 2 kg applied load and 1.22 m/s sliding velocity at 3000 m sliding distances (a) and (b) worn
surface (c) observation of the oxide layer

Fig.11: SEM micrographs of wear debris of Al-Cu/ Al2O3 composites (Al-4.2%Cu-3.4% Al2O3)
for 2 kg applied load and 1.22 m/s sliding velocity at 3000 m sliding distances (a) collecting
particles (b) examination of the alumina particles.
10 20 30 40 50 60 70 80
0
200
400
600
800
1000
1200
Intensity
2 x Theta
Fig.12: (a) XRD of the wear debris. b) XRD of Al2O3.
5. Friction studies
The characterization of friction behaviour of Al-Cu/Alumina base composite with sliding at the specific
load (i.e. 10N) is illustrated in Fig 13. The Figure show is graphically representation of the results obtained from
the friction experiment at a fixed load and sliding velocity. It is evident from the Fig.13 the friction coefficient
drastically increases during the running in period. During the steady state period the friction coefficient is being
stabilized. In dry sliding, the reason for increasing the wear rate and the coefficient of friction of Al-Cu/ Al2O3
composite as compared with the base alloy is the presence of alumina layer at the sliding surface which acts as
the best solid lubricant. The friction behaviour also varies with applied load. The average value of the friction
coefficient at normal load is shown in Fig.14. In accordance with the figure the decrease of the friction
coefficient corresponds to increase the normal load. The increase rate is especially evident for load change from
10 to 50 kg. On increasing the applied load, lubricating condition of the alumina improves; the alloy
composition starts to play its role in determining the running ability of the test under friction. Fig.15 shows the
variation of coefficient of friction with wt % of alumina content in the matrix. The friction coefficient of the test
materials increases with increase the alumina content in the matrix. With increasing the alumina content, the
thickness of the lubricating film and the amount the alumina in the lubricating film decreases. The alumina
comes more and more contact with sliding surface and results in lowering the frictional coefficients of the
composite materials. The worn surfaces of the samples from the SEM examination are shown in Fig 16. The
worn surfaces of the (Al-4.2%Cu-3.4% Al2O3) samples were noticed to be smoother than those of the (Al-
4.2%Cu-3.4% Al2O3). Generally, the parallel ploughing grooves and scratches can be seen over all the surfaces
in the direction of sliding. These grooves and scratches resulted from the ploughing action of asperities on the
counter disc of significantly higher hardness. The worn surfaces of the samples from the SEM examination are
shown in Fig.16 (a & b). The worn surfaces of the test sample were noticed to be smoother at the higher load
than at the lower load as shown in Fig 14. Generally, the parallel ploughing grooves and scratches can be seen
over all the surfaces in the direction of sliding. These grooves and scratches resulted from the ploughing action
of asperities on the counter disc of significantly higher hardness [11-13].

0 1000 2000 3000 4000 5000
0.28
0.29
0.30
0.31
0.32
0.33
0.34
0.35
0.36
0.37
0.38
0.39
0.40
0.41
0.42
FrictionCoefficient
Sliding Time (Sec)
1.6 % Al2
O3
2.7 % Al2
O3
3.4 % Al2
O3
5.6 % Al2
O3
8.4 % Al2
O3
Fig.13: Friction coefficient variation of Al-Cu/ Alumina composite during sliding time at fixed
specific loads (i.e. 10N) and sliding speeds (1.22 m/sec)
20 25 30 35 40 45 50
0.40
0.41
0.42
0.43
0.44
0.45
0.46
0.47
0.48
0.49
0.50
0.51
0.52
0.53
0.54
FrictionCoefficient
Load (kg)
1.6 % Al2
O3
2.7 % Al2
O3
3.4 % Al2
O3
5.6 % Al2
O3
8.4 % Al2
O3
Fig.14: Coefficient of friction vs. applied load for Al-Cu/ Al2O3 composite at 0.932m/sec
2 4 6 8 10
0.38
0.40
0.42
0.44
0.46
0.48
FrictionCoefficient
Alumina content (wt %)
Fig.15: Variations in the coefficient of friction with the wt % of Al2O3 in the matrix.
Fig.16: SEM micrographs of wear debris of (Al-4.2%Cu-3.4% Al2O3) for 2 kg applied load and
1.22 m/s sliding velocity at 3000 m sliding distances (a) at lower loads (b) at higher loads

VIII. Conclusion
1. The Al-Cu/Alumina composite is being prepared from liquid metallurgical methods. It can be observed from the
present investigation that alumina could be successfully and uniformly distributed in aluminium-Copper base
matrix using impeller mixing chill casting technique.
2. UTS (Ultimate Tensile Strength), 0.2% PS (Proof Stress) and VHN (Vickers Hardness Number) increased with
increases the volume fraction of the alumina in the matrix.
3. The Al-4.2% Cu-8.4% Al2O3 composite showed lower percentage of elongation while compared to Al-4.2%Cu
-1.6% Al2O3 From the present investigation we have also observed that the ductility of composite decreases with
increase the percentage of alumina.
4. The hardness is another affecting parameter which affects the rate of wear, increases with decreases the
percentage of alumina in the matrix.
5. Wear rate with sliding distance shows almost a linear relationship for all combinations of loads and sliding
velocities and composites.
6. Wear rate increases continuously with applied load for all the sliding velocities and composites studied.
7. Low loads and sliding velocities are dominated by oxidative debris whereas higher loads and sliding velocities
are dominated by metallic debris.
8. At low loads and sliding velocities wear track surface is largely covered with oxide layer and smooth in nature
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The coefficient of friction decreases with increase the alumina content in the matrix.
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