Synthesis and Characterization of Aluminum-Graphene Composite

IDL - International Digital Library
of Technology & Research
Volume 1, Issue 3, Mar 2017 Available at: www.dbpublications.org
International e-Journal For Technology And Research-2017
IDL - International Digital Library 1 | P a g e Copyright@IDL-2017
Synthesis and Mechanical Characterization of
Aluminum-Graphene Metal Matrix by Powder
Metallurgy Technique
A John Knoxa
, Aarish Nawaza
, AltafJilania
,Anand Prakasha
,Sudheer Reddyb
a
Department of Mechanical Engineering, NitteMeenakshi Institute of Technology, Bangalore, 560064,India
b
Professor,Department of Mechanical Engineering, NitteMeenakshi Institute of Technology, Bangalore, 560064,India
Abstract
Composite materials are the go-to materials for a huge range of applications ranging from bio-medical to
aerospace, owing to their superior properties than the monolithic metals. This paper presents the synthesis of
Aluminum-Graphene composite material, with Aluminum being the matrix phase and the ‘Wonder Material’
Graphene being the reinforcing phase, through powder metallurgy technique.The composite material was prepared
by varying the percentage composition (by weight) of Graphene – 0.1%, 0.2%, 0.3% with the hardness and wear
properties being studied. Also included is the microstructure study and the discussion on the effect of closed-die
forging on these samples with conclusions being drawn on forged and unforged composites.
Keywords- Graphene, Aluminum, Powder metallurgy, Microstructure, Forging, Wear, Hardness.
I. Introduction
A Metal Matrix Composite (MMC) is a composite
material in which the matrix comprises of the metal
and the reinforcements are embedded in the metal
matrix. Reinforcements are usually done to improve
the properties such as hardness which vary before and
after the addition of reinforcement and also with the
percentage of reinforcement[1-2]. Thus, MMC serves
as a potential substitute for the conventional metals,
alloys, and the polymers in almost all the applications
due to their superior properties over the unreinforced
alloys.
Aluminum alloy is conventionally used for the design
of medium and high strength composites for
automobiles and aerospace applications. The choice of
Aluminum is usually made by its easy availability and
lower cost of manufacturing. Many techniques have
been developed for producing particulate reinforced
MMCs, such as powder metallurgy and squeeze
casting. Powder metallurgy is preferred as it has
flexibility to produce compositions not possible by
other methods.The sintering step in the powder
metallurgy densifies and strengthens the material[3].
Among all the processes powder metallurgy is the only
process which produces minimal or negligible scrap.
The limitation with this process is that it is not useful
for low melting powder such as Zinc, Tin and
Cadmium. These metals show thermal difficulties
during sintering operations. Mechanical properties of all
the composites are affected by the size, shape and
volume fraction of the reinforcement matrix material
and reaction at the interface.
Jingyue Wang et al carried out work on Aluminum as
matrix material reinforced with Graphene in the form of
nano sheets (GNS) through powder metallurgy process
as a flake form. Through powder metallurgy technique
the ultimate tensile strength of 249 MPa were observed
in the Al composite reinforced with adding only 0.3
wt.% GNSs, which is 62% enhancement when
compared with the unreinforced Al matrix[4].
Why Graphene?
Graphene is a perfect two-dimensional (2-D) lattice of
sp2-bonded carbon atoms[5]. It is one of the strongest
material ever measured with a Young’s modulus of
1TPa[6]. Not just the strength, Graphene has excellent
wear and friction properties making it an ideal lubricant

Volume 1, Issue 3, Mar 2017 Available at:
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largely due to its high mechanical strength resulting in
less wear [7]. It is lighter than air with superior
mechanical, optical and electrical properties as well.
All these properties combined make Graphene
attractive reinforcements for fabricating light weight,
high strength and high performance metal matrix
composites.
II. Experimental Plan
Experimental plan is divided into two stages viz.
powder metallurgy and testing.
Stage1: Involves the process of fine mixing of
powders, compaction at a suitable pressure and
sintering at a temperature of 0.7- 0.8 times of the
melting point of the metal used.
Stage 2: Finishing operations such as grinding and
lapping is done on the sintered composite samples to
see the microstructure. Also, in this stage the effect of
forging is carried out and hardness and wear tests are
performed. Fig. 1 Flowchart of experimental plan
III. Fabrication of Composite
Graphene reinforced MMC is prepared by using dry
compaction powder metallurgy technique. The quantity
of pure Al taken is 20 grams in each sample and
Graphene particles required to fabricate the end
composite are 0.1%, 0.2% and 0.3% by weight. The
process for fabrication of the MMC is same for all the
different composition of Graphene. First, pure Al and
the Graphene powders are weighed and then both the
powders were mixed using sieve mesh of 70 and 100
grade.The ball milling method for mixing the powders
was not adopted since it increases the brittle nature of
the Graphene in the composite.
Then the powder mixture is filled in the die, made
according to ASTM standard, with the help of a funnel.
The compaction process is done in the Universal
Testing Machine at a pressure of 140MPa. Post
compaction, the specimen is kept in an air oven at
100o
C for degreasing and moisture removal. Sintering is
carried out by keeping the composite at 500℃ in a
furnace for one hour which induces strength and
hardness in the specimen and then slowly cooled in air
at room temperature.
Stage 2: Testing
Stage 1: Powder Metallurgy

Since the density of the Al-Gr composite was
around 83.6% to the theoretical density, closed die
forging was performed on all compositions of Gr to
increase the density of the specimens. In close die
forging the specimen is kept in the furnace at 550℃for
30 minutes and then gently hammered because of the
brittle nature of the composite.
The microstructure study, hardness and the wear
tests are performed on the composite samples.
IV. Test Results
4.1 Microstructure Result
In the microstructure several dark spots were
observed as can be seen in the figures below, which
can be Graphene or pores. Graphene flakes can be seen
around the pores. The presence can be confirmed by
comparing the microstructure of Graphene powder as
shown in Fig. 5 and Al-Gr composites as shown in Fig
2(a) - Fig 4(f). It can also be seen in Fig 2(b), Fig 3(d)
and Fig 4(f) that the porosity of the unforged
composites has been decreased after forging and the
particles are much closer to each other and hence the
density of the forged composites has been increased
which can be seen in the figures below. But, the
density could not be increased to 99.5% of theoretical
density, when the ductility sets in, due to the limitation
faced in closed-die forging setup.
Fig. 2 (a) 0.1% Gr composite unforged(b) 0.1% Gr composite
forged
Fig. 3 (c) 0.2% Gr composite unforged(d) 0.2% Gr composite forged
Fig. 4 (e) 0.3% Gr composite unforged(f) 0.3% Gr composite
forged
Fig. 5Graphene powder (100x)
4.2 Hardness Test Result
Rockwell hardness test is conducted on all the
composites at 60 kg load. Round tip Diamond indenter
is used on the specimens. Result of Table 1 shows that
the 0.1% Gr composite has highest hardness value than
other composites because it has least amount of
Graphene in it which causes less Gr-Gr bonding and
doesn’t interfere with Al-Al bonding thus resulting in
high hardness value.
Table 1- Rockwell Hardness Value
Graphene
% in
composite
specimen
type
Trial
1
Trial
2
Trial
3
Mean
hardne
ss

value
0.1% Unforged 42 43 44 43
Forged 63 67 68 66
0.2% Unforged 43 45 44 44
Forged 61 59 63 61
0.3% Unforged 42 46 45 44.33
Forged 55 62 59 58.67
0 % Pure Al 58 62 57 59
4.3 Wear Test Result
Wear test is conducted on wear testing machine –
pin on disc setup - at 2kg load at 400 rpm speed for all
the composites.The wear test couldn’t be carried out
0.3%Gr forged composite as the material broke upon
forging. 0.1%Gr composite has least wear rate because
it has highest hardness value and thus less wear.
The wear rate of forged and unforged composites
for all the compositions of Graphene have been
compared by the computer-generated graphs shown
below.
Graph 1- Comparison of wear rate of 0.1% Gr forged and
unforged composites
Graph 2- Comparison of wear rate of 0.2% Gr forged and
unforged composites
Graph 3- Wear rate of 0.3% Gr composite
V.Conclusion
From the tests conducted to determine the hardness,
wear rate and microstructure the following conclusions
can be drawn:
 Microstructure of forged composites shows less
pores and uniform dispersion of Graphene than in
unforged composites, especially in 0.1%Gr forged
composite. This is due to the increase in density by
Closed-die forging that reduces the pores.
 Hardness value of 0.1% Gr forged composite is
higher than other samples and even pure
Aluminum sample. This is a consequence of
increasing the density which results in increased
bonding between the particles providing strength
and hardness to the material.
 Wear rate of 0.1% Gr forged composite is lesser
because of the high density and less pores in it.
Pores act as stress risers and increase the wear rate
which can be seen in 0.2% Gr and 0.3%Gr
samples.
 0.1% Gr forged composite is the optimum
percentage of Gr in the composite samples
prepared due to its superior hardness and wear

properties and because the other samples (0.2%
and 0.3%Gr) developed cracks upon closed-die
forging while 0.1% Gr sample did not.
 Increase in Graphene percentage more than 0.1%
causes the material to become less and less
ductile due to more Graphene particles
interfering with Al-Al bonds.
 Forged composites have superior properties over
unforged composites due to increased density by
closed-die forging thus having higher hardness
and lesser wear than unforged composites.
References
[1] Ebinezar, Bheemraokamble, Analysis of
Hardness Test for Aluminum Carbon
nanotube metal matrix and Graphene,
Indian Journal of Engineering,
volume10, Number 21, April 2, (2014)
33-39.
[2] Synthesis and Characterization of
Aluminum2024 and Graphene metal matrix
composites by Powder Metallurgy
means,SSRG International Journal of
Mechanical Engineering (SSRG-IJME) –
volume 2 Issue 7–July 2015, 14-18.
[3] Pulkit Garg, Pallav Gupta, Devendra
Kumar, Om Parkash, Structural and
Mechanical Properties of
GrapheneReinforced Aluminum Matrix
Composites, Mater J. Environ. Sci, 7 (5),
2016, 1461-1473.
[4] Jingyue Wang, Zhiqiang Li, Genlian Fan,
Huanhuan Pan, ZhixinChenb and Di Zhanga
“Reinforcement with Graphene nanosheets in
Aluminum Matrix Composites”, Vol. 66,
(2012) 594-597.
[5] A.K. Geim, K.S.Novoselov, Nat. Mater. 6
(2007) 183–191.
[6] G.H.Lee,etal.Science30(2013)1073–
1076.
[7] DianaBerman,AliErdemir
andAnirudhaV.Sumant “Graphene: A new
emerging lubricant” MaterialsToday
Volume17,(2014), 3

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