Download Fig. 7 Micrograph of AA6082-5.vol% SiC

Development of a New Aluminum Matrix Composite Reinforced
With Silicon Carbide (SiC)
V. Jeevan, C.S.P Rao & N. Selvaraj
Department of Mechanical Engineering, National Institute of Technology Warangal, India
E-mail : [email protected]
Abstract – The increase in development of new metal
matrix composites is ever increasing and thereby spurt
increase and thrust in development of aluminum based
composites research. Al and its MMCs have wider
applications in automobile and aircraft industries due to
their high strength to weight ratio. Sintered aluminum
matrix composites are quite attractive material for the
automobile industry due to their superior mechanical,
tribological properties and the fabrication advantages
associated with a powder metallurgy process. The objective
of this work was to conduct a detailed assessment of the
microstructure and mechanical properties of AA6082-SiC
composites. The sintering temperatures are varied with
respect to soaking time in nitrogen atmosphere. An
increasing trend was observed in hardness with increase in
volume percentage of silicon carbide.
applied [2]. The reinforcements are being used in the
form of particles, short fiber or whisker, continuous
fiber [3]. The technical difficulties such as fibre damage,
improper fibre orientation, fibre to fibre contact and
high cost are involved in manufacturing of the
continuously reinforced aluminum matrix composites.
Also, the problems associated with fabrication of
whisker reinforced aluminum matrix composites are
faulted internal structure of whiskers and irregular
surface which may contain particulate contamination
with metallic matrix and relatively high cost over
irregular particles. The simple processing and low
material cost has made the particulate reinforced
aluminum matrix composites
(PR AMCs)
preferable to the other form of composite material for
many commercial applications and gaining their
importance due to their low density in combination with
high stiffness, improved wear resistance, low coefficient
of thermal expansion. However, the processing costs
and machining difficulties associated with PR AMCs
component parts has restricted their range of application
to that of specialised components [4,5].
Keywords—Aluminum
Matrix
Composites,
Powder
Metallurgy, Mechanical Properties, Microstructure Sprut
.
I.
INTRODUCTION
Aluminum and its alloys have many outstanding
attributes that lead to a wide range of applications which
require weight reduction and energy savings due to their
low density [1]. Their applications have often been
limited because of their low mechanical and tribological
properties at elevated temperatures. However,
Aluminum and its alloys exhibit poor tribological
properties. Therefore, Aluminum and its alloys can meet
various demands of several applications by the addition
of reinforcement materials which have enhanced
mechanical properties and better thermal stability. These
Aluminum matrix composites (AMCs) combine the
characteristics of metallic matrix along with the
characteristics of reinforcement which improve in
superior mechanical, tribological and thermal expansion
characteristics, but this is usually achieved at the
expense of other properties such as ductility which
depends on the matrix alloy, morphology, size,
volume/weight fraction of the reinforcements, the
material fabrication method and the heat treatment
There are several manufacturing methods to
produce these composite materials, which could be
grouped into three major processing routes depending
on the state of matrix during the fabrication process,
either liquid or semisolid or solid state processing route
[6]. Among them powder metallurgy (P/M) is a proven
technology for producing light weight parts in an
economical manner. Composites fabricated by P/M
route has merits such as less residual voids and
dissolved gases in products, it has better control on the
microstructure and uniform distribution of the
reinforcement especially at higher volume fractions, a
good interface between matrix material and inclusions
because of lower manufacturing temperatures that lead
to less destructive interfacial reactions, near-net-shape
forming of compacts [7]. Among all the powders
aluminum or aluminum alloy based composite powders
are light weight and extremely compressible by
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International Journal on Mechanical Engineering and Robotics (IJMER)
employing low compacting pressures. Sintering of
aluminum matrix composite parts are highly energy
efficient when compared to ferrous or copper based
powders due to the relatively low sintering temperatures
[8]. It has proved its position in automobile, aerospace,
and many other engineering applications due its wear
resistance properties and substantial hardness [9]. A
major drawback in producing PR AMCs is high cost.
The reasons are twofold. Initially the material itself is
costly due to presence of specially synthesized prealloyed powders. These powders are cold pressed, then
hot pressed or sintered and extruded. The second reason
that these alloys are expensive is due to secondary
processing. They are not produced to near net shape and
therefore require extensive forging or machining, which
can be particularly problematical because of the ceramic
component. Conventional P/M processing can overcome
these problems. Only two processing steps are required
(press and sinter) and the part is formed into its final
shape. Thus there is significant potential for press-andsinter processed aluminum P/M composites in order to
provide high stiffness at low cost.
mixtures exhibit uniform die filling and provides good
reproduction of part configuration.
Table 1. Chemical composition of AA6082 by weight
percentage
Chemical composition
Si
Mg
Mn
Fe
Cr
Zn
Cu
Ti
Al
AA 6082
1.0
0.9
0.7
0.5
0.25
0.20
0.10
0.10
Bal.
Table 2. Particle size and Purity details
In this study AA6082-SiC composites have been
fabricated using a “press-and-sinter” P/M process
comprised of blending, compaction, and sintering.
Mixture of five different compositions viz. 0, 5, 10, 15,
and 20vol.% of SiC particulates in aluminum alloy
matrix were prepared using terbula blender. Then, the
sinterability of these composites was investigated at
different levels of temperatures and soaking times. The
effects of the sintering temperature of each composite
on the density and hardness of the sintered parts are also
examined.
Raw Material
Particle Size (Mesh)
Purity
Aluminum
-200/+325
99.50%
Silicon
-325
99.57%
Magnesium
-140
99.67%
Manganese
-325
99.78%
Copper
-325
99.81%
Iron
-100
99.39%
Zinc
-400
99.65%
Titanium
-140
99.10%
Silicon Carbide
-1200
99.00%
II. EXPERIMENTAL PROCEDURE
Initially, series of raw powders were weighed
to the desired alloy chemical composition, placed into a
Nalgene bottle and blended in a turbula blender for 30
minutes, after which a chemical composition similar to
that of wrought AA 6082 alloy was obtained as shown
in Table 1 and Particle size and Purity details were
shown in Table 2. Finally by addition of 5, 10, 15 and
20% of SiC particulates by volume to the base AA 6082
powder and mixed for 20minutes. The obtained powder
mixtures with ceramics were homogeny at macroscopic
level.
Fig. 1 Green compacts of different compositions
Green parts were then sintered in a horizontal tube
furnace (metrex scientific instruments) in a nitrogen
atmosphere. Typically, the sintering temperatures are
570oC and 600oC and all the samples is furnace cooled
to room temperature. The heating profiles at two
intervals are shown in Fig. 2 and Fig. 3. The sintered
density
was
obtained
through
dimensional
measurements as well as by Archimedes displacement
method [10]. The microstructural analyses were carried
out using a scanning electron microscope (SEM) and
hardness tests were carried out using rockwell hardness
B scale as shown in Fig. 4.
The blends were compacted at into cylindrical
pellets (10 mm in diameter and 10 mm in height) using a
uniaxial semi-automatic hydraulic press (svs, India).
Some of the green compacts shown in Fig. 1. The
theoretical density assuming zero porosity was
calculated by Rule of Mixture. The green density of the
compacts was determined from weight and volume
measurements. The AA6082 and AA6082-SiC powder
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International Journal on Mechanical Engineering and Robotics (IJMER)
The hardness measurements were conducted on the
sintered compacts at 100 kgf test load and dwell time 15
seconds. The indentations at macroscopic level are
shown in Fig. 5. The final readings are taken on average
of five indentations.
Fig. 5 Rockwell hardness indentations on the sintered
cylindrical pallets
Fig. 2 Heating profiles for AA6082-SiC upto 570oC
III. RESULTS AND DISCUSSION
Samples for metallography were polished using
standard techniques and etched with kellers reagent. The
sintered composites were analysed for its microstructure
by Scanning Electron Microscopy. The SEM images of
the AA6082 alloy powder with different volume
percentages of SiC are shown in Fig. 6-10.
Fig. 3 Heating profiles for AA6082-SiC upto 600oC
Fig. 6 Micrograph of AA6082
Fig. 7 Micrograph of AA6082-5.vol% SiC
Fig. 4 Rockwell hardness tester
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International Journal on Mechanical Engineering and Robotics (IJMER)
The micrographs clearly indicate the evidence of
minimal porosity in the entire 6082 aluminum alloy and
its SiC composites. The distribution of particles in the
matrix is fairly uniform. However the tendency of
clustering could not be avoided for composites
containing fine SiC. In Fig. 11, the matrix and the
reinforcement can be seen clearly that SiC is uniformly
distributed in the aluminum matrix
Fig. 8 Micrograph of AA6082-10.vol% SiC
Fig. 11 Micrograph of AA6082-15.vol% SiC at high
magnification
Hardness measurements were performed on the
sintered specimens according to ASTM E18-08 with
indenting load of 100kgf and dwell time 15 seconds.
The average hardness data shown in Fig. 12 resulted
from five measurements. The position of indentation on
the sample was chosen randomly. The hardness test
gives a good indication on the strength of the material.
As the SiCp increases from 0 to 20 volume percentage
hardness also increased.
Fig. 9 Micrograph of AA6082-15.vol% SiC
FiG. 12 The variation of hardness with SiC
Fig. 10 Micrograph of AA6082-20.vol% SiC
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International Journal on Mechanical Engineering and Robotics (IJMER)
IV. CONCLUSION
[5]
Adnan Ahmed, Andrew J. Neely, And Krishna
Shankar, “Experimental comparison of the effects
of nanometric and micrometric particulates on the
tensile properties and fracture behavior of al
composites at room and elevated temperatures,”
The Minerals, Metals & Materials Society and
ASM International, metallurgical and materials
transactions A, vol. 42A, pp. 795-815, 2011.
[6]
J.W. Kaczmar, K. Pietrzakc and W. Woosin Aski,
“The production and application of metal matrix
composite materials,” Journal of Materials
Processing Technology, Vol. 106, pp. 58-67,
2000.
[7]
[7]
C. Padmavathi, A. Upadhyayaa and D. Agrawal,
“Effect of microwave and conventional heating
on sintering behavior and properties of Al–Mg–
Si–Cu alloy,” Materials Chemistry and Physics,
vol. 130, pp. 449-457, 2011.
[8]
J.U. Ejiofor and R.G. Reddy, “Developments in
the Processing and Properties of Particulate Al-Si
Composites,” JOM, pp. 31-37, 1997.
K.S. Dunnett, R.M. Mueller and D.P. Bishop,
“Development of Al–Ni–Mg–(Cu) aluminum
P/M alloys,” journal of materials processing
technology, Vol. 198, pp. 31-40, 2008.
[9]
C.D. Boland, R.L. Hexemer Jr, I.W. Donaldson
and D.P. Bishop, “ Industrial processing of a
novel Al–Cu–Mg powder metallurgy alloy,”
Materials Science & Engineering A, vol. 559, pp.
902-908, 2013.
[10]
Jeevan.V,
C.S.P
Rao
and
N.Selvaraj,
“Compaction,
sintering
and
mechanical
properties of Al-SiCp composites,” International
Journal of Mechanical Engineering and
Technology, Vol. 3, pp.565-573, 2012.
During compaction of aluminum alloy based
composite powders, the shape and quality of final
component depends upon the quality of initial manual
compact. Therefore, the manual compact should be
fabricated carefully and proper allowances should be
given terms of dimensions to achieve the desired final
component. In the present study, AA6082 composite
powders accompanied with 0–20 vol.% of SiC particles
were prepared using the conventional press and sinter
method. The microstructure revealed the uniform
dispersion of fine SiC in the aluminum matrix. High
hardness values are obtained at 600oC sintering
temperature under nitrogen atmosphere.
V. REFERENCES
[1]
[2]
[3]
Karl U. Kainer, “Metal Matrix Composites,
Custom-made Materials for Automotive and
Aerospace Engineering,” WILEY-VCH, 2006.
[4]
X.Zhang and M.l.Tan Selection of particulate
reinforcement in P/M metal matrix composites,”
Journal of Materials Processing Technology, vol.
63, pp. 913-917, 1997.
A. Ibrahim, F. A. Mohamed and E.
J. Lavernia, “Particulate reinforced metal matrix
composites - a review,” Journal of Materials
Science, Vol. 26, pp. 1137-1156, 1991.
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