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Journal of Minerals & Materials Characterization & Engineering, Vol. 9, No.1, pp.43-55, 2010
jmmce.org Printed in the USA. All rights reserved
Studies on Al6061-SiC and Al7075-Al2O3 Metal Matrix Composites
G. B. Veeresh Kumar1*, C. S. P. Rao2, N. Selvaraj2, M. S. Bhagyashekar3
1Research Scholar, National Institute of Technology, Warangal, (A.P), India & Department
of Mechanical Engineering, S B M Jain College of Engineering, Jain University,
Jakkasandra (P), Kanakapura (T), Ramanagara (D)-562 112, Karnataka, India.
2Department of Mechanical Engineering, National Institute of Technology, Warangal, (A.P),
3Department of Mechanical Engineering, Don Bosco Institute of Technology, Bangalore,
*Corresponding author: email@example.com
The aluminum based composites are increasingly being used in the transport, aerospace,
marine, automobile and mineral processing industries, owing to their improved strength,
stiffness and wear resistance properties. The widely used reinforcing materials for these
composites are silicon carbide, aluminum oxide and graphite in the form of particles or
whiskers. The ceramic particles reinforced aluminum composites are termed as new generation
material and these can be tailored and engineered with specific required properties for specific
application requirements. Particle reinforced composites have a better plastic forming capability
than that of the whisker or fiber reinforced ones, and thus they have emerged as most sought
after material with cost advantage and they are also known for excellent heat and wear
resistance applications. In this paper it is aimed to present the experimental results of the studies
conducted regarding hardness, tensile strength and wear resistance properties of Al6061-SiC
and Al7075-Al2O3 composites. The composites are prepared using the liquid metallurgy
technique, in which 2-6 wt. %’age of particulates were dispersed in the base mat rix in st eps of 2.
The obtained cast composites of Al6061-SiC and Al7075-Al2O3 and the castings of the base
alloys were carefully machined to prepare the test specimens for density, hardness, mechanical,
tribological tests and as well as for microstructural studies as per ASTM standards. The SiC and
Al2O3 resulted in improving the hardness and density of their respective composites. Further, the
increased %’age of these reinforcements contributed in increased hardness and density of the
composites. The microphotographs of the composites studied revealed the uniform distribution of
44 G. B. Veeresh Kumar, C. S. P. Rao, N. Selvaraj, M. S. Bhagyashekar Vol.9, No.1
the particles in the matrix system. The experimental density values were agreed with that of the
theoretical density values of the composites obtained using the rule of mixture for composites.
The dispersed SiC in Al6061 alloy and Al2O3 in Al7075 alloy contributed in enhancing the
tensile strength of the composites. The wear factor K obtained using computerized pin on disc
wear tester with counter surface as EN31 steel disc (HRC60) and the composite pin as
specimens, demonstrated the superior wear resistance property of the composites.
Key words: Al6061-SiC, Al7075-Al2O3, Metal Matrix Composites, Density, M icrostructure,
Hardness, Mechanical properties, Wear Factor.
Aluminum alloys are preferred engineering material for automobile, aerospace and mineral
processing industries for various high performing components that are being used for varieties of
applications owing to their lower weight, excellent thermal conductivity properties. Among
several series of aluminum alloys, heat treatable Al6061 and Al7075 are much explored, among
them Al6061 alloy are highly corrosion resistant and are of excellent extricable in nature and
exhibits moderate strength and finds much applications in the fields of construction (building and
high way), automotive and marine applications. Aluminum alloy 7075 possesses very high
strength, higher toughness and are preferred in aerospace and automobile sector . The
composites formed out of aluminum alloys are of wide interest owing to their high strength,
fracture toughness, wear resistance and stiffness. Further these composites are of superior in
nature for elevated temperature application when reinforced with ceramic particle .
The literature survey regarding the above alloy systems and their composites are as follows.
G. Straffelini et.al.  reported that the matrix hardness has a strong influence on the dry sliding
wear behavior of Al6061-Al2O3 composites. A. Martin et. al.  in the studies of tribological
behavior on Al6061-Al2O3 composites concluded that a characteristic physical mechanism
involves during the wear process. S.Y. Yu et. al.  demonstrated the effects of applied load and
temperature on the dry sliding wear behavior of Al6061-SiC composites and concluded that the
wear rate decreases with increased applied load. H.C. How and T.N. Baker , in their
investigation of wear behavior of Al6061-saffil fiber, concluded that saffil are significant in
improving wear resistance of the composite. Liang Y. N. et. al.  reported that the MMCs
containing SiC particles exhibit improved wear resistance. Basavarajappa S., et. al.  stated that
the microstructural characteristics, applied load, sliding speed and sliding distance affect the dry
sliding wear and friction of MMCs. However, they conclude that, at higher normal loads (60N),
severe wear and silicon carbide particles cracking and seizure of the composites occurs during
dry sliding. Chandramohan G., et. al.  reported that the sliding distance has the highest effect
on the dry sliding wear behaviour of MMCs than that of the load and sliding speed. Y. Reda et.
Vol.9, No.1 Studies on Al6061-SiC and Al7075 - Al2O3 Metal Matrix Composites 45
al.  and R. Clark et. al. , in their studies on Al7075 reported that, pre-aging at various
retrogression temperatures improves the hardness, tensile properties and electrical resistivity. S.
W. Kim et. al.  concluded that the hardness of aged Al7075 alloy increases. Rupa Dasgupta
et.al. reported the improvement in the hardness, mechanical and sliding wear resistance
properties attained as a result of heat treatment and forming composites by adding 15 wt.% of
SiC. T.J.A. Doel et.al.  reported the improved tensile strength and lower ductility of the
Al7075 reinforced with 5 and 13 μm SiC particles than that of unreinforced material. K. Komai
et.al.  reported the superior mechanical properties Al7075-SiCw composites.
From the above discussion it can be concluded that the not enough data is available on the
mechanical and wear resistance of particulate reinforced Al6061, Al7075 composites. Hence, the
present studies are aimed to fabrication of Al6061-SiC and Al7075-Al2O3 composites containing
various weight %’age of particles and to study their density, microstructure, micro-hardness,
mechanical and wear resistance properties.
2. EXPERIMENTAL DETAILS
The base matrix and the reinforcing phase for the present studies selected were Al6061, Al7075
and particles of Al2O3 and SiC of size 20 μm. Table 1 and table 2 are presented with the
chemical composition of matrix and properties of matrix and reinforcing materials respectively.
The liquid metallurgy technique with optimum care was taken and standard procedure was
followed to obtain the cast composites. The particles were preheated before being introduced into
the vortex and stirring of the molten composite were accomplished for 10 minutes at 400 rpm
starrier speed. Pouring temperatures adopted were 7200C. The cylinders of 22mm X 210mm cast
composites of Al6061-SiC and Al7075-Al2O3 were obtained.
Table 1. Chemical Composition of Al6061 and Al7075 by Weight percentage.
Composition Si Fe Cu Mn Mg Cr Zn Ti Al
Al6061 0.62 0.23 0.22 0.03 0.84 0.22 0.10 0.1 Bal
Al7075 0.4 0.5 1.6 0.3 2.5 0.15 5.5 0.2 Bal
46 G. B. Veeresh Kumar, C. S. P. Rao, N. Selvaraj, M. S. Bhagyashekar Vol.9, No.1
Table 2. Properties of Al6061 and Al7075.
Properties Al6061 Al 7075 SiC Al2O3
Elastic Modulus (Gpa) 70-80 70-80 410 300
Density (g/cc) 2.7 2.81 3.1 3.69
Poisson’s Ratio 0.33 0.33 0.14 0.21
Hardness (HB500) 30 60 2800 1175
Tensile Strength (T) /
Compressive Strength (C)
115(T) 220(T) 3900(C) 2100(C)
The test for density, hardness, tensile strength and wear resistance of the prepared cast matrix
and their composite were carried out as per ASTM standards. The density of material, that is
ratio of weight to volume  was obtained by accurately measuring the weight and the volume
of the composites. Shimadzu Japan make Vickers micro hardness tester served the purpose of
measurement of hardness. Carefully polished and mirror finished specimens were examined
under Lobo make metallurgical microscope to obtain microphotographs. The mechanical
properties were evaluated using Akash make computerized universal testing machine of 40-ton
capacity. Magnam make computerized pin on disc wear testing machine with test material as pin
and high carbon EN31 steel (HRC60) as counter-surface, equipped with LVDT and digital
display system served to record the wear height loss in microns.
3. RESULTS AND DISCUSSIONS
Table 3 is presented with the comparison of theoretical density obtained by rule of mixture and
measured density values by experiment for both the composites studied, further the Figure 1
shows the experimental density values of the both the composites containing various filler
percentages. From the table it can be concluded that the experimental and the theoretical density
values are in line with each other and confirms the suitability of the liquid metallurgy techniques
for the successful composite preparation.
From Figure 1 it can be observed that the densities of composites are higher than that of their
base matrix, further the density increases with increased percentage of filler content in the
composites [17, 18]. From the figure it can be concluded that Al7075-Al2O3 composites exhibits
Vol.9, No.1 Studies on Al6061-SiC and Al7075 - Al2O3 Metal Matrix Composites 47
higher density than that of the Al6061-SiC and can reasoned for the higher density values of
Table 3. Comparison of theoretical and experimental densities of the Al6061-SiC and
Material Density (g/cc) Weight % Reinforcement
0 2 4 6
Theoretical Density 2.70 2.71 2.72 2.73
Experimental Density 2.68 2.69 2.70 2.73
Theoretical Density 2.77 2.79 2.83 2.84
Experimental Density 2.77 2.78 2.81 2.83
D en sity (g m/cc)
Figure 1. Experimental density of Al6061-SiC and Al7075-Al2O3 composites
3.2. Microstructure Studies
Figures 2a-d and 3a-d are presented with the microphotographs of cast Al6061-SiC and Al7075-
Al2O3 composites respectively. From figures it can be observed that, the distributions of
reinforcements in the respective matrix are fairly uniform. Further these figures reveal the
homogeneity of the cast composites. The microphotograph also clearly revels the increased filler
contents in the composites.
48 G. B. Veeresh Kumar, C. S. P. Rao, N. Selvaraj, M. S. Bhagyashekar Vol.9, No.1
Figure 2. Microphotograph of Al6061 alloy and its SiC composites at 200X, a) Cast Al6061
alloy, b) Al6061-2%SiC, c) Al6061-4% SiC, d) Al6061-6% SiC composites.
Figure 3. Microphotograph of Al7075 alloy and its Al2O3 composites at 200X, a) Cast Al7075
alloy, b) Al7075-2% Al2O3, c) Al7075-4% Al2O3, d) Al7075-6% Al2O3 composites.
3.3. Micro – Hardness
The Vickers micro-hardness of cast Al6061 and Al7075 base matrix and their composites
containing 2-6 wt. %’age SiC/Al2O3 are evaluated using diamond indenter at an applied load of
100N are presented in figure 4. From the figure, it can be observed that the hardness of the
composite is greater than that of its cast matrix alloy. The composites containing higher filler
Vol.9, No.1 Studies on Al6061-SiC and Al7075 - Al2O3 Metal Matrix Composites 49
content exhibits higher hardness. Further, it can be observed that the hardness of the Al7075-
Al2O3 composite are higher than that of the composite of Al6061-SiC and is to the fact that the
matrix Al7075 and Al2O3 possess higher hardness .
V H N
Figure 4. Microhardness of Al6061-SiC and Al7075-Al2O3 composites.
3.4. Tensile Strengt h
Figure 5 shows the tensile strength property of Al6061 & Al7075 and their composite containing
SiC & Al2O3 respectively as a function of percentage weight.
Tensile Strength (Mpa)
Figure 5. Variation in Tensile Strength with increasing %’age particulate content.
From figure it can be observed that the tensile strength of the composites are higher than that of
their base matrix also it can be observed that the increase in the filler content contributes in
increasing the tensile strength of the composite. Also from the figure it can be observed that the
tensile strength of the Al7075-Al2O3 composites is higher than that of the composites of Al6061-
SiC. But the %’age increase in tensile strength of Al6061-SiC is 68 where as for Al7075-Al2O3
is 24 which clearly indicates the superiorness of Al6061-SiC composites and hence the greater
50 G. B. Veeresh Kumar, C. S. P. Rao, N. Selvaraj, M. S. Bhagyashekar Vol.9, No.1
contributions of SiC with regards to the increased tensile strength of its composites.
3.5. Tribological Properties
The wear factor, defined as the ratio of wear volume (in mm3) to the product of applied load (in
N) and sliding distance (in meter), is an important parameter, which quantifies the wear
resistance (wear factor). Thus the wear factors of the material studied are presented. Figure 6a-c
and figure 7a-c shows the wear factor for Al6061 and its composites containing SiC under an
applied load of 10N and various sliding speeds and under the sliding speed of 100rpm and
various applied loads respectively. Similarly figures 8a-c and 9a-c show the wear factor for
Al7075 and its composites containing Al2O3.
Figure 6. Variation of Wear Factor at different RPM for Al6061 - SiC composites, under applied
load of 10N and at a speed of (a) 100 rpm, (b) 300 rpm & (c) 500 rpm.
Vol.9, No.1 Studies on Al6061-SiC and Al7075 - Al2O3 Metal Matrix Composites 51
Figure 7. Variation of Wear Factor at different Loads for Al6061 - SiC composites sliding at a
speed of 100rpm under applied load of (a) 20N, (b) 30N & (c) 50N.
52 G. B. Veeresh Kumar, C. S. P. Rao, N. Selvaraj, M. S. Bhagyashekar Vol.9, No.1
Figure 8. Variation of Wear Factor at different RPM for Al7075 - Al2O3 composites sliding,
under applied load of 10N at a speed of (a) 100 rpm, (b) 300 rpm & (c) 500 rpm.
Figure 9. Variation of Wear Factor at different Loads for Al7075-Al2O3 composites sliding at a
speed of 100rpm under applied load of (a) 20N, (b) 30N & (c) 50N.
Vol.9, No.1 Studies on Al6061-SiC and Al7075 - Al2O3 Metal Matrix Composites 53
The significant conclusions of the studies on Al6061-SiC and Al7075-Al2O3 metal matrix
composites are as follows.
1. Liquid metallurgy techniques were successfully adopted in the preparation of Al6061-SiC
and Al7075-Al2O3 composites containing the filler contents upto 6 wt %’age.
2. The densities of the composites are found improved than their base matrix.
3. The microstructural studies revealed the uniform distribution of the particles in the matrix
4. Microhardness of the composites found increased with increased filler content and the
increase in hardness of Al6061-SiC & Al7075-Al2O3 composites are found to be 60-
97VHN & 80-109VHN respectively.
5. The tensile strength properties of the composites are found higher than that of base matrix
and Al6061-SiC composites superior tensile strength properties then that of Al7075-
6. The wear resistance of the composites are higher, further the SiC contributed
significantly in improving the wear resistance of Al6061-SiC composites.
7. From the studies in overall it can be concluded that Al6061-SiC exhibits superior
mechanical and tribological properties.
The authors express their thanks to the Dr. R. Chenraj Jain, Chancellor, Jain University,
Dr. N. Sunderarajan, Vice Chancellor, Jain University, Prof. T.S. Sridhar, Pro-vice Chancellor,
Jain University, Management, Jain Group of Institutions, Bangalore, Dr. Y. Vijay Kumar,
Principal, S B M Jain College of Engineering, Jain University, Jakkasandra (P), Kanakapura (T),
Ramanagara (D)-562 112, Karnataka, and Dr. Anand Bukkmbudhi, Professor and Head,
Mechanical Engineering, S B M Jain College of Engineering and also to the staff of Mechanical
Engineering Department, S B M Jain College of Engineering, for their support and
encouragement during the research studies.
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