Study Of Mechanical Properties On Al 6061 Hybrid Composite by Stir Casting Method

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056
Volume: 04 Issue: 01 | Jan -2017 www.irjet.net p-ISSN: 2395-0072
© 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 1036
STUDY OF MECHANICAL PROPERTIES ON AL 6061 HYBRID COMPOSITE BY
STIR CASTING METHOD
Niranjan K N1, Shivaraj B N2, Sunil kumar M3, Deepak A R4
1Asst. Professor, Dept. of Mechanical Engineering, PNSIT College, Bengaluru, Karnataka, India
---------------------------------------------------------------------***---------------------------------------------------------------------
Abstract - Composite materials are known as advanced
materials for their high strength, high wear resistance, good
damping characteristic and their enhanced high temperature
performance. The hybrid metal matrix composite (HMMCs)
materials are prepared by using stir casting technique.
Development of Al6061alloy based metal matrix Hybrid
composite reinforced with 6wt% of SiC and varying steps of
graphite by 3wt%, 6wt%, and 9wt%. Experimental study was
carried out to investigate the mechanical properties such as
hardness, tensile strength, compression strength. As a result
hardness decreases with the increase in the percentage of Gr,
tensile strength and compression strength increases with the
increase in Gr particulates with the influence of SiC
particulates.
Key Words: Hybrid metal matrix composite (HMMC), stir
casting, Al6061, SIC, Graphite, Reinforcement, Hardness,
Tensile strength, Compression strength.
1. INTRODUCTION
There is a growing interest worldwide in manufacturing
hybrid metal matrix composites [HMMCs] which possesses
combined properties of its reinforcements and exhibit
improved physical, mechanical and tribological properties.
Aluminium-based Metal Matrix Composites (MMCs) have
received increasing attention in recent decades as
engineering materials. Use of single reinforcement in Al
matrix may sometimes lead to deterioration in its physical
properties. However, to overcome the drawback of single
reinforced composites, the concept of use of two different
types of reinforcements is being explored inAl matrix.Ofthe
two reinforcements normally one of the reinforcement will
be a hard phase and the other being a soft lubricating phase.
Hard reinforcements such as SiC, TiO2, Al2O3, TiB2 etc. will
enhance the hardness and abrasive wear resistance of Al
while it has a negative effect on the machinability and
conductivity of Al. To offset these effects,reinforcementslike
graphite which is a solid lubricant and possessing good
conductivity can be dispersed in Al along with hard
reinforcements. The introductionofa ceramic material intoa
metal matrix produces a composite material that results in
an attractive combination of physical and mechanical
properties which cannot be obtained with monolithicalloys.
Interest in reinforcing Al alloy matrices with ceramic
particles is mainly due to the low density, low coefficient of
thermal expansion and high strength of the reinforcements
and also due to their wide availability. Among the various
useful aluminum alloys, Aluminum alloy 6061 is typically
characterized by properties such as fluidity, castability,
corrosion resistance and high strength-weight ratio.
Aluminium alloy-based particulate-reinforced composites
have a large potential for a number of engineering
applications such as transport and construction sectors
where superior mechanical properties like tensile strength,
hardness etc., are essentially required.
2. MATERIALS
2.1 Aluminium 6061
The material used in the present study is Al 6061 whose
chemical composition is listed in Table 1. It therefore has a
low melting point 660°C. The molten metal has high fluidity
and solidifies at constant temperature. It possess excellent
mechanical properties, such as good corrosion resistance,
good deformation behavior, high specific modulus, tensile
strength, hardness, good wear resistanceandlowcoefficient
of thermal expansion.
Table-1: Chemical composition of Al 6061 by wt%.
Cu Mg Si Fe Mn Cr Zn Ti Al
0.22 0.82 0.60 0.25 0.03 0.24 0.10 0.1 Bal
2.2 Silicon Carbide
The reinforcement material used in the investigation was
Silicon carbide in which it is kept constant (6wt %) and it is
composed of tetrahedral of carbon and silicon atoms with
strong bonds in the crystal lattice. It has high thermal
conductivity coupled with low thermal expansion and high
strength giving exceptional thermal shock resistant
properties. It is used in abrasives, refractories,ceramics, and
numerous high-performance applications.

2.3 Graphite
Another reinforcement material used in the present
investigation was Graphite which is diversified into 3wt%,
6wt%, 9wt% at a suitable interval of 3wt% in steps of 3. It is
a solid lubricant which enhances the wearandanti-frictional
properties. The acoustic and thermal properties of graphite
are highly anisotropic. Graphite’s high thermal stability and
electrical and thermal conductivity facilitate its widespread
use as electrodes and refractories in high temperature
material processing applications. Graphite and graphite
powder are valued in industrial application for their self-
lubricating and dry lubricating properties.
3. METHODOLOGY
Melting Of Base Metal Al 6061
Degassing
Impregnation Of Silicon Carbide
+ Graphite Particulates. (3%,
6%, 9%)
Stir Casting Technique
Pouring Of Molten Metal Into
Mould Cavity
Solidification
Machining As Per ASTM
Standards
Study The Mechanical
Properties
Fig-1: Methodology for production of hybrid
composite
4. HYBRID COMPOSITE PRODUCTION
In the present study, stir casting method is used for the
preparation of hybrid composite. In this process Al 6061
bars are cut into small ingots. These ingots are placed in
crucible in which it is kept in electrical resistance furnace.
The ingots are melted at a temperature of 8000 C, after
effective degassing predetermined mass of preheated 6wt%
of SiC is added into the melt and stirred continuously in
order to achieve uniform distribution of particles in the
matrix. Gr of 3wt%, 6wt%, 9wt% at suitable intervals of
3wt% in steps of 3 is then added to the mixture of Al 6061
and SiC. After the mixing of the reinforcements (SiC and Gr)
with the base matrix, the crucible is taken out from the
furnace and the molten metal is pouredintothemetal mould
and allowed to solidify. After the solidification, the casted
specimen is removed from the mould and machined as per
ASTM standards for testing.
Table-2: Composition of the product
Sl.no. Hybrid Composition
1 Al 6061
2 Al 6061+6%SiC
3 Al 6061+6%SiC+3%Gr
4 Al 6061+6%SiC+6%Gr
5 Al 6061+6%SiC+9%Gr
Result Analysis
Solidification

Fig-2: Stir casting technique
Fig-3: Pouring of molten metal into mould cavity
Fig-4: Casted hybrid composite
5. PREPARATION OF SPECIMEN FOR TESTING
5.1 Tensile Test
The tensile tests were conducted on UTM at room
temperature. ThesampleswerepreparedaccordingtoASTM
E8M. The tensile propertiesofthealloysweredeterminedby
performing the tension test on standard cylindrical tensile
specimens. The machining involves facing and turning.
Before to testing, the surface of the specimens was finished
by using 400 grid emery sheets. A typical tensilespecimenas
per ASTM standard is shown in Fig 5.
Lo = Gauge length
Lc = Parallel length
r = Transition radius
So = Original cross section area
d =gauge length diameter
Fig-5: Tensile test specimen
5.2 Compression Test
Compression tests were conducted on a UTM E8M in
accordance with ASTM Standard at room temperature. Load
values were recorded from load indicator, while
displacement measurements were taken using a dial gauge
fixed against the moving platen of the machine. In this test
the compression loads were gradually increased and the
corresponding strain was measured until the specimen
failed. The specimen height before and after the test are
measured using 0.05 accuracy by using vernier. A typical
compression test specimen as per ASTM standard is shown
in Fig 6.
Fig-6: Compression test specimen

5.3 Hardness Test
Hardness, is the measure of a material'sresistancetosurface
indentation, also it is a function of the stress required to
produce some specific types of surface deformation. The
Brinell’s test is frequently used to determine thehardness of
forgings and castings that have a grain structure too course
for Rockwell or Vickers testing. The hardness test was
carried out for the hybrid composite by using 10mm ball
indentation by applying 500kg load for 30 seconds in a
Brinell’s hardness tester. A typical hardnesstestspecimenas
per ASTM standard is shown in Fig 7.
Fig-7: Hardness test specimen
6. RESULT AND DISCUSSION
6.1 Hardness Test
Table-3: Hardness test results
Sl.no. Composition (wt%) BHN
1 Al 6061 85
2 Al 6061+6%SiC 111
3 Al 6061+6%SiC+3%Gr 106
4 Al 6061+6%SiC+6%Gr 98
5 Al 6061+6%SiC+9%Gr 90
Chart-1: Effect of graphite on hardness
Table 3 shows the Brinell’s hardness test result. It is
observed from the graph, the hardness of Al 6061-hybrid
composite decreases significantly with increasingcontent of
the graphite particulate. However, decrease in hardness of
Al6061-hybrid composite possibly due to poor wetting
characteristics of Graphite by Al 6061. A significant increase
in hardness of the alloy matrix can be seen with addition of
SiC particles. The measurements show that an increase in
graphite content for the same amount of SiC reduces
hardness of the composite.
6.2 Tensile Test
Table-4: Tensile test results
Sl.no. Composition (wt%)
Tensile Strength
(MPa)
1 Al 6061 128
2 Al 6061+6%SiC 150
3 Al 6061+6%SiC+3%Gr 141
4 Al 6061+6%SiC+6%Gr 148
5 Al 6061+6%SiC+9%Gr 156
Chart-2: Tensile strength comparison plot
Table 4 shows the tensile test result. From the test it is
inference that the improvement in ultimate tensile strength
in base matrix with 6% SiC, this is due to the fact that SiC is a
hardest ceramic which on reinforcement forms a stronger
composite. From the graph, tensile strength of composites
containing 6 wt% of Sic particulates is higher when
compared to as base Al 6061. It is clear from the graph is
that the tensile strength increases with the increase in the
percentage of Gr particulates.

6.3 Compression Test
Table-5: Compression test results
Sl.no. Composition (wt%)
Compression Strength
(MPa)
1 Al 6061 580
2 Al 6061+6%Sic 650
3 Al 6061+6%Sic+3%Gr 743
4 Al 6061+6%Sic+6%Gr 847
5 Al 6061+6%Sic+9%Gr 987
Chart-3: Compression strength comparison plot
Table 5 shows the compression test result. It can be seen
from the graph is that as the graphite content increases, the
compressive strength of the hybrid composite material
increases monotonically by significant amounts. In fact, as
the graphite content is increased from 3% to 9% the
compressive strength increases due to thegraphiteparticles
acting as barriers to dislocations in the microstructure.
7. CONCLUSIONS
Al 6061 hybrid composite material containing SiC and Gr
particulates were fabricated successfully by varying wt% of
Gr from 3% to 9% using stir casting method. Keeping Sic6%
as constant, by increasing the Gr particulates of 3%,6%,9%,
we can conclude that Hardness of the prepared hybrid
composites is higher than the baseAL 6061alloy.Additionof
6wt% SiC increases hardness considerably. Whereas the
addition of Gr particulates decreases the hardness, but is
higher than the Al6061 alloy. However,decreaseinhardness
of Al6061-hybrid composite possibly due to poor wetting
characteristics of Gr by Al 6061.Tensilestrengthofprepared
Al6061 hybrid composites is higher when compared to base
Al 6061 composite. Addition of 6% SiC and Gr varies from
3% to 9% increases the tensile strength considerably with
respect to base matrix Al6061. It can be seen that as the Sic
and graphite content increases, the compressive strength of
the hybrid composite material is also increases.
ACKNOWLEDGEMENT
To begin with, we would like to thank Dr. Shiva Kumar M,
Principal, P.N.S InstituteofTechnology,forgivingussupport,
encouragement and great interest to shown in each steps of
our research work. we would also like to thank Mr. Umesh T
and Mr. Vinay kumar. J, Department of Mechanical
Engineering, P.N.S.I.T for the valuable suggestions and
guidance.
REFERENCES
[1] Prashant S N et al. “Preparation And Evaluation Of
Mechanical And Wear Properties Of Al6061Reinforced With
Graphite And Sic Particulate Metal Matrix Composites”,
International Journal Of Mechanical Engineering And
Robotics Research ISSN 2278 – 0149 Vol. 1, No. 3, October
2012.
[2] C. Velmurugan et al. “Experimental study on the effect of
sic and graphite particles on weight loss of al 6061 hybrid
composite”. issn: 1949-4866 materials volume 2, number
1/2 pp. 49-68 jotse (2011).
[3] Dr. Rajanna S. “Evaluation Of Mechanical Response Of
Graphite Reinforced Metal Matrix Composite”. Journal Of
Harmonized Research In Engineering Issn2347 – 73931(1),
2013, 39-44.
[4] N. Nanda Kumar et al, “Study of Mechanical Properties of
Aluminium Based Hybrid Metal Matrix Composites”.
International Of Modern Engineering Research (IJMER).
[5] Revanasidappa M D et al, “Mechanical and Wear
Behaviour of Al6061-SiC-Gr Hybrid Composites”. National
Conference on Advances in Mechanical Engineering Science
(NCAMES-2016) ISSN: 2231-5381
[6] Madeva nagaral et al. “mechanical behaviour of
aluminium 6061 alloy reinforced with Al203 & graphite
particulate hybrid metal matrix composites”. International
journal of research in engineering & technology (ijret)vol.1,
issue 2, july 2013, 193-198

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