P. PUGALENTHI et al.: STUDY OF THE MICROSTRUCTURES AND MECHANICAL PROPERTIES ...
49–55
STUDY OF THE MICROSTRUCTURES AND MECHANICAL
PROPERTIES OF ALUMINIUM HYBRID COMPOSITES WITH
SiC AND Al
2
O
3
[TUDIJA MIKROSTRUKTUR IN MEHANSKIH LASTNOSTI
ALUMINIJEVIH HIBRIDNIH KOMPOZITOV S SiC IN Al
2
O
3
Palanisamy Pugalenthi
1
, Murugesan Jayaraman
2
, Venkatajalapathy Subburam
1
1
Paavai Engineering College, Department of Mechanical Engineering, NH-44, Pachal, Namakkal District, Pincode: 637018, Tamilnadu, India
2
Velalar College of Engineering and Technology, Department of Mechanical Engineering, Thindal, Erode District, Pincode: 638012,
Tamilnadu, India
Prejem rokopisa – received: 2018-06-08; sprejem za objavo – accepted for publication: 2018-09-13
doi:10.17222/mit.2018.118
Aluminium metal-matrix composites are widely produced with different ceramic compounds as reinforcements to enhance their
properties and to suit various structural applications. The present work involves the fabrication of Al7075 composites with
silicon carbide (SiC) and aluminum oxide (Al2O3) as reinforcements through stir casting. Four specimens were produced with
different compositions comprising SiC (3, 5, 7 and 9 w/%) and Al2O3 2 w/% in all the combinations. Mechanical properties like
ultimate tensile strength (UTS), yield strength (YS), percentage of elongation (% of elongation) and hardness (VHN) were
examined, along with fractography studies. The microstructural characterization of the composites was also studied through
micrographs obtained from the scanning electron microscope (SEM). The test results revealed that the increase in the w/%
fractions of the reinforcement materials caused an increase in the tensile strength, yield strength and hardness of the aluminium
composite, except for the % of elongation, which is reduced with the addition of ceramic particles.
Keywords: stir-casting method, hybrid composites, mechanical properties and microstructure
Kompoziti s kovinsko osnovo iz aluminija se pogosto izdelujejo z razli~nimi kerami~nimi spojinami kot oja~itveno fazo, in s
tem postanejo uporabni za izdelavo razli~nih strukturnih aplikacij. V pri~ujo~i raziskavi so avtorji izdelali kompozite na osnovi
Al zlitine 7075 z dodatkom delcev silicijevega karbida (SiC) in aluminijevega oksida (Al2O3) kot oja~itveno fazo med
preme{avanjem taline. Izdelali so {tiri vzorce z razli~no vsebnostjo SiC (3, 5, 7 in 9 w/%) in v vseh primerih {e z dodatkom
2 w/% Al2O3. Dolo~ili so mehanske lastnosti izdelanih kompozitov - natezno trdnost pri pretrgu (UTS), mejo plasti~nosti (YS),
raztezek (%) in trdoto (VHN). Nato so izvedli {e analize prelomov (fraktografijo) nateznih preizku{ancev s pomo~jo vrsti~nega
elektronskega mikroskopa (SEM). Rezultati preiskav so pokazali, da pove~anje dodatka oja~itvene faze v obliki kerami~nih
delcev povzro~i zvi{anje natezne trdnosti, meje plasti~nosti in trdote, zmanj{a pa se raztezek.
Klju~ne besede: metoda litja s preme{avanjem, hibridni kompoziti, mehanske lastnosti in mikrostruktura
1 INTRODUCTION
Composite materials combine the desirable properties
of the constituent materials and provide enhanced
physical and mechanical properties. Composite materials
find applications in almost all industries today. The auto-
mobile and aerospace industries are constantly in search
of composites that possess higher strength and are lighter
in weight for structural applications. Aluminium is
preferred as a structural material in these areas because
of its light weight. Ceramic particulates are added to the
aluminium base matrix as a reinforcement to fabricate
aluminium metal-matrix composites (AMMCs), which
provide improved strength. Among the aluminium alloy
series, the aluminium 7075 alloy has many favorable
properties, like higher strength, good wear resistance,
higher toughness and stiffness. The ceramic reinforce-
ments added to the aluminium matrix also give further
improvement to the endurance at higher operating tem-
peratures. Most industries prefer metal-matrix compo-
sites with aluminium to take advantage of its ease of
fabrication. Though many casting methods are available,
stir casting is considered for manufacturing AMMCs as
the technique is simple, economical and because of its
capability for large volume production.
The tensile strength and fatigue strengths of a
SiC-whisker-reinforced AA7075 specimen produced by
the powder metallurgy method was tested by Komai et
al.
1
in normal atmospheric and water environments. It
was observed in the report that all the mechanical pro-
perties showed enhanced values, except the elongation to
failure. The pattern of propagation of a crack for fatigue
failure was also studied. The water environment was
found to give a shorter fatigue life due to the effect of
corrosion. Azim et al.
2
produced a MMC with Al2024
base material and Al
2
O
3
as the ceramic reinforcement to
study the change in the mechanical peoperties. The
observtions revealed that the increments in the volume
percentage of Al
2
O
3
caused an increase in the ultimate
tensile strength and a decrease in the ductility.
Materiali in tehnologije / Materials and technology 53 (2019) 1, 49–55 49
UDK 620.1:67.017:669.71:620.168 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 53(1)49(2019)
*Corresponding author e-mail:
mecpugal@yahoo.com

Lee et al.
3
produced SiC
p
-reinforced AA7075 and a
control AA7075 (without SiC
p
) using a pressureless-
infiltration technique in a nitrogen atmosphere. From the
test results it was observed that even the control-AA7075
specimen (without SiC
p
) showed enhanced strength due
to the formation of AlN particles and the SiC-reinforced
specimens revealed still higher values of strength for all
the age-hardening conditions. The powder-metallurgy
route with a centrifugal atomization technique was used
by Hong et al.
4
to fabricate a MMC comprising AA
2024+SiC. The analysis involved a study of the influnce
of clustering on the mechanical properties. The test
results showed that the inclusion of SiC improved the
yield strength and the ultimate strength, while it
decreased the fracture strength.
Kalkanli et al.
5
produced AMMCs by incorporating
SiC particles of around 29 microns into the AA7075
matrix using the vertical pressure-casting technique.
Four test specimens containing SiC particles of (10, 15,
20 and 30) w/% fractions were fabricated and subjected
to tensile and bend tests in the as-cast condition and also
after heat treatment. The specimen with 10 % SiC
p
was
found to give the maximum flexural strength in both the
as-cast condition (450 MPa) and the heat-treated con-
dition (588 MPa), gaining a 10 % and 44 % increment,
respectively, from the base-alloy value. The hardness
values were also observed to increase considerably for
both the as-cast and heat-treated specimens with the
weight percentage of SiC particles. Sajjadi et al.
6
fabri-
cated an Al (A356)/Al
2
O
3P
composite through stir cast-
ing to study the mechanical properties. The observations
suggest that an increase in the ultimate strength and yield
strength could be achieved by increasing the w/% of
Al
2
O
3
and also by reducing the size of the Al
2
O
3
parti-
cles.
Aluminium was reinforced with SiC and Al
2
O
3
(alu-
mina) using differentw/% to experimentally analyse the
behaviour change in the resulting composite by Daljeet-
singh et al.
7
It was found that an increase in the w/% of
the reinforcements caused an increment in the mecha-
nical properties, like hardness, yield strength and
ultimate strength. The influnce of ceramic materials
changes the ductile behaviour of the material to brittle,
as a result of which the elongation decreases. A mathe-
matical model was devolped by Indumathi et al.
8
to
predict the tensile strength and the percentage elongation
of the as-cast composites (Al7075+Al
2
O
3
) through a
design of experiments by taking the size and percentage
fraction of alumina as the parameters. The observations
showed that the UTS of the composite increased by 20 %
and the percentage elongation reduced by approximately
30 % compared to the matrix material.
Uvaraja et al.
9
investigated hybrid MMCs using the
Taguchi technique to obtain optimum input levels for
dry-sliding wear conditions. From the experimental re-
sults it was observed that the samples containing 10w/%
of silicon carbide and 3 w/% of boron carbide have a
high hardness and a good toughness. Furthermore, it was
recommended that this composite with optimum w/%
could be utilised for applications in the heavy-vehicle
sector. Valve-seat inserts were produced from AA7075
and AA7075+SiC
p
composites containing (10, 15, 20
and 25) % reinforcements for a comparative study by
Bhusan et al.
10
It was observed in the course of the study
that when the reinforcements exceed 25 % SiC
p
deficien-
cies like non-uniformity in the distribution of particles, a
poor surface finish and high tool wear arise. These pro-
perties became enhanced in the range 10–15w/% inclu-
sion of SiC
p.
Metal-matrix composites of AA7075-TiC with 4 %
and8%ofTiCwere fabricated using the in-situ casting
method by Baskaran et al.
11
to conduct dry-sliding wear
tests. Taguchi’s L27 orthogonal array design was used to
study the influence of reinforcement quantity, applied
load, sliding velocity and sliding distance on the wear
rate. The experimental results revealed that the applied
load and the sliding velocity were the dominant input
parameters. The optimal combination for achieving the
minimum wear rate was observed as 4w/% of TiC (rein-
forcement), 9.81 N (applied load), 3 m/s (sliding velo-
city) and 1500 m (sliding distance). Wu et al.
12
used a
sintering technique to reinforce B
4
C (7.5 w/%) into the
Al7075 alloy and studied the densification behaviour of
the composite. It was reported that full densification,
good inter-particle bonding and significant improvement
in the mechanical properties were achieved at 530 °C
and 3 min of holding time in a plasma-activated sintering
method.
Vignesh et al.
13
focussed on the behaviour of an
Al7075-Al
2
O
3
metal-matrix composite in an industrial
environment and sea water to study the occurance of
corrosion and a change in the surface morphology. From
the SEM images it was observed that intergranular corro-
sion occurred in the industrial environment and sea water
produced pitting corrosion. Rajeswari et al.
14
attempted
to identify the effect of the input parameters on the
quality of the casting produced (to obtain a defect-free
casting) and mechanical properties like tensile strength
and hardness. The ANOVA results showed that the w/%
of SiC and Al
2
O
3
were the most influential factors,
followed by the stirring speed. It was further reported
that homogenous mixing was ensured at high tempera-
tures due to the improved wettability of the reinforce-
ments.
Tanwir alam et al.
15
produced nanocomposites using
a stir-casting process by reinforcing silicon carbide nano-
particles (mechanically milled) into an aluminium alloy
metal matrix. The nanosize of the particles ensured
improved wettability and also better embedding of the
reinforcement particles into the alloy matrix. The re-
search results showed improvements of 125 % in hard-
ness, 41 % in yield strength, 45 % in ultimate tensile
strength and also an improvement of the compressive
strength from 311 MPa to 603 MPa (at 5 % inclusion of
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50 Materiali in tehnologije / Materials and technology 53 (2019) 1, 49–55

SiC). The fracture study revealed that the debonding and
cracking of the particles were the main causes of
fracture. Ashok et al.
16
utilised stir casting to fabricate
Al8011+SiC composites with a uniform distribution of
SiC
p
in the aluminium alloy matrix. The size effect on
the hardness revealed that the increase in hardness is
caused by a decrease in the particle size of the silicon
carbide. The yield strength and the tensile strength were
reduced for composites containing coarse particles of
silicon carbide. The composite containing 6 w/% SiC
and a particle size of 63 microns gave the highest yield
strength (87 MPa) and tensile strength (111 MPa).
Sambathkumar et al.
17
fabricated an Al7075+SiC+
TiC composite to investigate the mechanical and corro-
sion characteristics. An increase in the reinforcements up
to 15 % by volume increased the microhardness. The
composition containing 10 % by volume of both SiC
p
and TiC
p
gave a tensile strength of 240 MPa, which is an
improvement of 33 % from the base alloy’s tensile
strength. Mavhungu et al.
18
reviewed the advancements
in the manufacturing and processing methods of
AMMCs. The favourable properties of these composites,
like high specific stiffness and strength-to-weight ratio,
were discussed for applications in the automotive in-
dustry.
Kannan et al.
19
compared the mechanical properties
and microstructural characteristics of aluminium nano-
composites with single and hybrid-type reinforcements.
The stir-casting method was used to fabricate three
samples of single-reinforced nanocomposites in which
the reinforcements were included after preheating them
to 400 °C, 500 °C, and 600 °C, respectively. Two hybrid
nanocomposites were also produced in this way, pre-
heating the reinforcements to 500 °C before inclusion.
The results showed that when the w/% of nano-reinforce-
ment did not exceed the2%le v el,thepreheat tem-
perature of 500 °C prevented agglomeration and helped
the uniform distribution of ceramic particles in the alu-
minium matrix.
The present work includes the fabrication of AMMCs
with Al7075 as the matrix and SiC + Al
2
O
3
particles at
different w/% fractions as the reinforcements using a
stir-casting method. The mechanical and metallurgical
characteristics of the samples are studied using
mechanical tests and SEM micrographs.
2 MATERIALS AND METHODS
2.1 Experimental part
2.1.1 Fabrication of composite
The composite specimens were produced using
Al7075 rods that were melted to serve as the matrix for
the ceramic particles of SiC and Al
2
O
3
(30/40 micron
size) that mix with the bulk of the aluminium alloy as
reinforcements in the stir-casting method. The chemical
composition of the Al7075, comprising various elements
by weight percentage, is shown in Table 1.
Table 1: Chemical compositions of Al7075
Mater
ial
Zn Mg Cu Si Mn Fe Cr Ti Al
Weig
ht
5.1 2.185 1.690 0.179 0.146 0.476 0.193 0.045
Balan
ce
A schematic diagram of the stir-casting setup with
different parts is shown in Figure 1.
At the beginning of the fabrication process, the
aluminium rods were cut into small pieces and a graphite
crucible of 6” in size was used for melting the pieces.
Another crucible of 2” in size was used to preheat the
reinforcement materials, i.e., SiC and Al
2
O
3.
The Al7075
alloy was also preheated at 400 °C for good blending.
After preheating, the Al7075 rods were put into the 6”
crucible for melting and the temperature was increased
gradually. At 650 °C the melting started and the process
continued until the Al7075 became liquid at a tempera-
ture of 780 °C.
The preheated reinforcements were now put into the
casting furnace, run electrically, and mixed well with the
base aluminium alloy using the stirrer available in the
setup. To improve the wettability at the interface,2gof
magnesium powder were added to the mixture. The
stirrer can be operated by a motor at 480 min
–1
to 500
min
–1
for a period of 32 s in each spell. The molten
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Materiali in tehnologije / Materials and technology 53 (2019) 1, 49–55 51
Figure 2: Experimental setup for stir casting
Figure 1: Schematic diagram of the stir-casting setup

materials were then poured into a square die of 100 mm
× 100 mm × 10 mm in size. The casting was removed
from the mould after the solidification. Similarly, the
castings of composites containing different weight
percentages of reinforcement materials (3, 5, 7 and 9)
w/% of SiC with 2 w/% of Al
2
O
3
in each composition
were produced. The work was carried out at Karunya
University, Coimbatore and the photograph of the
stir-casting setup used is shown in Figure 2.
2.1.2 Specimen preparation for tests
The specimens used for the tensile tests were first
machined in a milling machine and then cut into the
required dimensions as per the ASTM E8M04 standard
using a wire-cut EDM machine. The tensile tests were
conducted using a Universal Testing Machine with a
constant crosshead displacement rate for all the tests at
25 °C. The mechanical characteristics of the samples,
such as ultimate tensile strength (UTS), ductility
(% elongation) and 0.2 % proof strength, were tested and
the corresponding values obtained. The microhardness
tests were conducted as per the ASTM B557M standard
utilising an applied load of 0.49 N for a period of 15 s.
To study the microstructure of the castings, test
sections were cut from the castings, which were then belt
grinded and polished with different grades of emery
papers. Then the test pieces were again polished with
cloths, washed and dried, after which they were etched
with Keller’s solution. The specimen thus prepared was
then examined under a scanning electron microscope
(SEM) and the micrographs were recorded for studying
the microstructure. The broken specimens of the tensile
tests were used to record the fractographs of the com-
posite specimens with the SEM. The SEM micrographs
clearly show the presence of clusters of SiC particulates
in the fractured portions. During the application of the
load, the cracks begin at these regions of hard clusters
and then run into the ductile base alloy and to the cera-
mic regions that surround it.
3 RESULTS AND DISCUSSION
3.1 SEM Microstructure studies
The SEM micrograph images of the Al7075-SiC-
Al
2
O
3
composites of four different samples are shown in
Figures 3a to 3d. It can be observed from the micro-
graphs that the dispersion of reinforcement particles in
the matrix material is almost uniform. It can thus be
inferred that the stir-casting process has produced a
composite with a homogenous mixture. The micrographs
also clearly depict the presence of filler content in the
composites. The whitish portions are silicon carbide,
whereas the blackish portions are aluminium oxide parti-
cles. The micrograph of Figure 3a presents the compo-
sition of sample 1 containing Al7075 + 3 w/% of SiC +
2 w/% of Al
2
O
3
. The figure shows the uniform distribu-
tion of SiC and Al
2
O
3
ceramic particles in the aluminium
alloy matrix with close-packed grains. The longish
patterns could be due to solidification periods, the
orientation of reinforcements into the matrix caused by
the stirring process, the density and other factors that
influence the settlement of the reinforcement particles
into the matrix material. The micrograph of Figure 3b
presents the composition of sample 2 containing Al7075
+5w/% of SiC+ 2 w/% of Al
2
O
3
. The dispersions of the
SiC and Al
2
O
3
particles are reasonably homogenous,
while the formations of the grain patterns are compara-
tively larger. The formation of clusters of reinforcement
particles can also be seen at some places in the micro-
graph. The characteristics of the composite at these
places would give different results if the test area
happens to coincide exactly with these places of the test
specimen.
The micrograph of Figure 3c presents the compo-
sition of sample 3 containing Al7075 +7 w/% of SiC+ 2
w/% of Al
2
O
3
. The distribution of the SiC and Al
2
O
3
particles in the aluminium alloy matrix is uniform, to
some extent. The random grain orientation with cluster-
ing spots of ceramic particles could be due to an increase
in the weight percentage of silicon carbide particles,
which would influence the solidification pattern. The
micrograph of Figure 3d presents the composition of
sample 4 containing Al7075+9 w/% of SiC+ 2 w/% of
Al
2
O
3
. Though the dispersion of reinforcement particles
is nearly uniform, the presence of silicon carbide is more
pronounced in the micrograph.
3.2 Mechanical Properties
Metal-matrix composite materials with the inclusion
of ceramic reinforcements are fabricated to obtain
favourable mechanical properties from the aggregate
material. Different tests are carried out to quantify the
increment or decrement caused by the reinforcements in
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52 Materiali in tehnologije / Materials and technology 53 (2019) 1, 49–55
Figure 3: SEM micrographs of the composites with different com-
positions: a) Al7075+3 w/%ofSiC+2w/% of Al
2
O
3
, b) Al7075 +
5 w/%ofSiC+2w/% of Al
2
O
3
, c) Al7075 + 7 w/%ofSiC+2w/% of
Al
2
O
3
, d) Al7075 + 9 w/%ofSiC+2w/% of Al
2
O
3

various properties of the base material. The tensile test
specimens were prepared as per the ASTM standard
ASTM E8M04 and specimens fractured under tensile
test are shown in Figure 4.
To evaluate the mechanical properties of the newly
formed composites, tensile test and Vickers microhard-
ness tests were carried out. Table 2 gives the values
obtained from the tests of the ultimate tensile strength,
yield strength, percentage of elongation and microhard-
ness for the four samples.
The analysis of the results clearly shows that the
increment in the silicon carbide content has improved the
ultimate tensile strength of the composite considerably.
The composition containing Al7075+3 w/% of SiC+ 2
w/% of Al
2
O
3
has given a UTS value of 248 MPa,
whereas the gradual increments of SiC in the compo-
sition have shown continuous improvements, with a UTS
value of 325 MPa for sample 4. The hard nature of the
ceramic particles is the cause of the increment in
strength. The improvement in the case of the yield
strength also follows the same trend of continuous
increment.
The results of the hardness tests of the four samples
show a gradual improvement in the hardness values of
the specimens, keeping in trend with the2%w e i g h t
increment of the SiC content in the samples. It is quite
logical that the hard ceramic particles add to the hard-
ness levels of the composite in proportion to the amount
of their inclusion. Abdulhaqq et al.
20
have analysed the
significance of ceramic particles in increasing the hard-
ness of the bulk of aluminium metal-matrix composites.
The presence of the hard ceramic phase leads to a greater
hardness of the composites than that of the base alloy.
Vencl et al.
21
have stated that the hardness of the com-
posite improved significantly with the inclusion of an
increased volume fraction of the ceramic particles.
The one mechanical property that shows a reduction
for an increment of the weight percentage of ceramic
particles in the composite is the strain to failure. It can be
observed from the table that the percentage of elongation
has decreased significantly from 3.44 % (for sample 1)
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Materiali in tehnologije / Materials and technology 53 (2019) 1, 49–55 53
Figure 4: Photograph of tensile-tested fractured specimens
Figure 5: Mechanical properties of Al-MMC samples: a) UTS, b) YS, c) percentage of elongation, d) hardness
Table 2: Test results of mechanical properties for Al-MMC samples
Sample identification UTS (MPa) YS (MPa)
Percentage of
elongation
Hardness (VHN)
Sample no. 1
(Al7075+3% SiC+ 2% Al2O3)
248 81 3.44 96
Sample no. 2
(Al7075+5% SiC+ 2% Al2O3)
272 90 2.48 105
Sample no. 3
(Al7075+7% SiC+ 2% Al2
O
3
)
294 99 2.40 112
Sample no. 4
(Al7075+9% SiC+ 2% Al2O3)
325 107 2.08 119

to 2.08 % (for sample 4). The ceramic particles impart a
brittle nature to the composite proportionate to the
amount of inclusion and decrease the ductile nature,
which could be attributed to the reduction in the elon-
gation property. The values of ultimate tensile strength,
yield strength, percentage of elongation and microhard-
ness of the four samples tabled above are presented as
graphs in Figure 5.
The effect of the inclusion of ceramic particles such
as SiC and Al
2
O
3
in the aluminium alloy composite on
various mechanical properties is clearly depicted in the
above figure. It is obvious from the figure that properties
like the ultimate tensile strength, yield strength and hard-
ness show improved values for all the samples, with the
only exception being the percentage elongation, for
which the values gradually decrease from sample 1 to
sample 4. The cause of this effect has been discussed in
the above section.
3.3 Fracture analysis
Figures 6a to 6d show SEM fractographs of the
Al7075-SiC-Al
2
O
3
hybrid composites produced for
experimental purposes. The broken tensile-test speci-
mens were used for the fracture analysis. The fracture is
mainly of the transgranular type, which absorbs the
maximum energy until the point of fracture, as the bulk
of the material is ductile by nature. The initiation point
of the cracks could be around the reinforcement parti-
cles, which grow progressively and coalesce into a
bigger crack, weakening the spot with a void formation.
Thus, the fractured portion shows both ductile and brittle
modes of operation.
The mode of failure includes the decohesion of the
SiC particles from the matrix at the interface. Dimples
are formed around the silicon carbide particles due to the
applied stress and the edges of these dimples are
elongated, and the surface near the ceramic particle
cracks around the interface. The crack even runs through
these brittle particles. The clustering of ceramic particles
provides an easy spot for a fracture to occur. Thus, from
the images of the fractured samples, the presence of
ceramic particles could be seen, which naturally become
the most stressful part, prone to breakage, giving a brittle
touch to the fracture, which otherwise would be mostly
ductile.
4 CONCLUSIONS
The important conclusions inferred from the studies
carried out on SiC & Al
2
O
3
filled Al7075 alloy compo-
sites are as follows:
• Stir casting is an effective technique to produce
hybrid metal-matrix composites with good misci-
bility.
• SiC and Al
2
O
3
particles of 30/40 microns are added
to the molten Al7075 along with magnesium powder,
which acts as a wetting agent for the uniform distri-
bution of the reinforcements in the aluminium alloy
matrix.
• The tensile strength and yield strength of the SiC &
Al
2
O
3
filled Al7075 alloy composites were found to
increase with an increase in the reinforcements.
• With the w/% increment in ceramic particles, the
percentage elongation of the composite decreased.
• The hardnesses of the SiC & Al
2
O
3
filled Al7075
alloy composites were also found to increase with an
increase in the amount of ceramic particulates added.
• The hard nature of the included ceramic particles
improves the UTS, YS and hardness of the hybrid
composite. The addition of ceramic particles imparts
hardness and reduces the energy-absorbing capacity
of the composite, causing a reduction in the percent-
age of elongation.
• The fractography studies show that the increase in the
weight percentage of the SiC & Al
2
O
3
changed the
mode of failure from ductile to brittle, to some ex-
tent, which could be clearly observed from the
dimples and deformed portions present near the
regions of the fracture.
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54 Materiali in tehnologije / Materials and technology 53 (2019) 1, 49–55
Figure 6: Fracture images of the composites with different compo-
sitions

• The microstructures clearly show the homogeneous
distribution of the hard reinforcing particles in the
matrix and the solidification pattern of the casting,
which would influence the properties of the material.
• The SEM images clearly indicate the uniform distri-
bution of the SiC & Al
2
O
3
particles. The micrographs
of the fractured portions indicate the presence of SiC
particulates in clusters at some points, which initiate
the fracture in the specimen and its hard nature
provides a brittle mode to the otherwise ductile
fracture.
Acknowledgement
The research work was supported by my mother Mrs.
P. Dhanalakshmi and my spouse Mrs. A. M. Uma
Maheswari. Special thanks to Professor Dr. K. K. Rama-
samy and Dr. M. Premkumar from Paavai Engineering
College, Namakkal, India, for their valuable help.
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