Proceedings of the National Conference on
Trends and Advances in Mechanical Engineering,
YMCA Institute of Engineering, Faridabad, Haryana.., Dec 9-10, 2006
MECHANICAL AND WEAR PROPERTIES OF PARTICLE
REINFORCED ALUMINIUM COMPOSITE
Karunakara.S1, Lokesh G.N2, Dr. H.B.Niranjan3, R.Seetharamaiah4 , ShanthaKumar G.C5
1
Department of Mechanical Engineering, Lecturer, Dayananda Sagar College of Engineering, Bangalore-78
Department of Mechanical Engineering, Lecturer,Acharya Institute of Technology, Bangalore-90
3
Dept.of Mechanical Engineering, Professor ,M. S. Ramaiah Institute of Technology, Bangalore-54
4
Dept.of Mechanical Engineering, Senior lecturer, Dayananda Sagar College of Engineering, Bangalore-78
5
Dept.of Mechanical Engineering, Senior lecturer, Acharya Institute of Technology, Bangalore-90
1,2,3,4,5
Email:[email protected],[email protected],[email protected],
[email protected]
2
Abstract
In recent years, Metal Matrix Composites (MMC) are gaining more popularity when compared with the
conventional alloys especially in aerospace sectors, because MMCs posses higher hardness, better wear
resistance, high strength and lower weight. Aluminium and its alloys are widely used as matrix material, in
which several reinforced like Silicon carbide, glass, etc. Beryl (Be3Al2 (SiO3)6) has been selected as
reinforcement in Aluminium alloy matrix because of its high hardness, low density (which is same as
aluminium) and naturally available as a gem stone in powdered form. Al-356 has been chosen as matrix
material because of its high strength, relatively good formability and it is used in aerospace, automobile
industries, truck frames and structures. The present investigation is an attempt made to disperse beryl particles
in Al-356 base alloy by liquid metallurgy technique and to study its effect on Al alloy wear and mechanical
properties. Percentage of beryl particulate reinforcement has been varied from 2% to 10% by weight of base
alloy. Beryl of particle size of around 20micron was successfully dispersed in Al-356 alloy and properties are
tested, the composite with 6% beryl showed peak increase in tensile strength over its base matrix and composite
with 10% beryl showed maximum increase in wear resistance and hardness over its base matrix.
1.0 Introduction
A composite material can be defined as a macroscopic combination of two or more distinct materials, having
recognizable interface between them. However, because composite are generally used for their structural
properties the definition can be restricted to include only those materials that contain a reinforcement supported
by a binder (matrix) material. Thus, composite typically have a discontinuous fiber or particle phase that is
stiffer and stronger than the continuous matrix phase. Composites can be dived into different class. One simple
classification scheme is to separate them according to reinforcement forms.
Reinforcement is considered to be a “particle” if all of its dimensions are roughly equal. Thus, particulatereinforced composites include those reinforced by spheres, rods, flakes and other irregular shapes of roughly
equal axes.
Fiber-reinforced composites contain reinforcements having length much greater than their cross-sectional
dimensions. Such a composite is considered to be a discontinuous fiber or short fiber composite if its properties
vary with fiber length. On the other hand, when the length of the fiber is such that any further increase in length
does not increase the elastic modulus of the composite, the composite is considered to be continuous fiber
reinforced [1].
2.0 Metals-Matrix Composites
Metal-matrix composites (MMCs) are engineered combinations of two are more materials where tailored
properties is achieved by systematic combinations of different constituents. Conventional monolithic materials
have limitations in respect of achievable combinations of strength, stiffness and density. Engineered MMCs
consisting of continuous or discontinuous fibers, whiskers or particles in a metal achieve combinations of very
high specific strength and specific modulus. Furthermore, systematic design and synthesis procedures allow
unique combinations of engineering properties in composites like elevated temperature, strength, damping
property, electrical and thermal conductivities and friction coefficient.
By carefully controlling the relative amounts and distribution of ingredients constituting a composite, as well as
the processing conditions, MMCs can be imparted with a tailored set of useful engineering properties, which can
be realized with conventional monolithic materials [2].
1
3.0 Matrix Materials
The metals commonly used as matrix materials are Aluminium, Copper, Magnesium, Zinc, Lead and Titanium.
Aluminium is being the most extensively utilized matrix metal because of its, lightweight, availability and ease
of fabrication and fairly high mechanical properties [3]. The Aluminium alloys used as matrix are AluminiumSilicon, Aluminium-Copper, Aluminium-Silicon-Magnesium, Aluminium-Zinc, and Aluminium-Copper- Zincmagnesium.
4.0 Properties of the Base Matrix
4.1 Physical properties
Density, g/cc: 2.68
Brinell hardness: 40-60; 500kg load, 10mm ball estimated from Brinell hardness
4.2 Mechanical properties
Tensile strength: 152MPa
Elongation (%): 3 in 50mm
4.3 Thermal properties
Melting point: 557 degree centigrade
Solidius: 557 degree centigrade
Liquidius: 613 degree centigrade
4.4 Chemical composition of Aluminium-356
Aluminum (Al): 91.85%
Copper (Cu): 0.2%
Iron (Fe): 0.4%
Magnesium (Mg): 0.35%
Manganese (Mn): 0.25%
Silicon (Si): 6.5%
Titanium (Ti): 0.2%
Zinc (Zn): 0.25%
4.5 Chemical composition of Beryl
Silicon dioxide (SiO2 ): 61.95%
Alumina (Al2 O3) : 18.42%
Beryl oxide (BeO): 10.10%
Iron oxide (Fe2 O3): 6.38%
Calcium oxide (CaO): 2.02%
Magnesium oxide (MgO): 0.32%
Sodium oxide (Na2 O): 0.65%
Potassium oxide (K2 O): 0.13%
Manganese oxide (MnO): 0.04%
5.0 Experimental Details
5.1 Preparation of composite material
The composites can be prepared either by powder metallurgy technique or foundry technique. In the present
study, the Aluminium metal matrix composites with varying weight percentage of particulates were prepared
through foundry route. The composites were tested by varying sliding duration under different normal loads.
1.
Melting of alloy
• Required amount of aluminium alloy is taken in a graphite crucible and placed in an electrical
resistance furnace of 4KW rating with a temperature control unit, having variation tolerance of
±2degree centigrade. A schematic diagram of stir casting technique using melting furnace is shown in
Fig 1.
• The furnace is switched on; the temperature controller is set to furnace temperature of 760 degree
centigrade. The temperature was regularly monitored by a chromel / alumel handled thermocouple with
temperature indicator.
2
Proceedings of the National Conference on
Trends and Advances in Mechanical Engineering,
YMCA Institute of Engineering, Faridabad, Haryana.., Dec 9-10, 2006
•
•
•
•
•
The liquid melt was degassed to remove gas absorbed. Inert gas flushing was adopted for this purpose.
Pure and dry nitrogen gas was flushed through the melt. The nitrogen gas from the cylinder is made to
pass through three flasks. The flask was an empty bottle where the pressure of the incoming gas was
stabilized. The second flask contains concentrated sulphuric acid, which absorbs impurities if any in
the gas. Further the gas was passed through the third flask containing calcium carbonate wherein the
moisture if present is absorbed. Thus the pure and dry nitrogen is flushed through the liquid metal at a
rate of four liters per minute for ten minutes.
To counter the effects of degassing, the melt was modified by addition of Al-Ti master alloy, which
also helps to accomplish the grain refining.
The reinforcement material is preheated to temperature of 900 degree centigrade to improve
wettability. The melt was stirred to obtain a well-defined vortex. Particulates heated to 900 degree
centigrade were dispersed in to melt through this vortex at a rate of 10grams per minute. The stirring
was continues for some more time and its speed of rotation is controlled using a dimmer-stat.
The melt particle slurry was poured in to the preheated (300 degree centigrade) metallic moulds.
The mould is allowed to solidify.
Fig. 1 schematic view of melting furnace
2. Evaluation of mechanical properties
Tensile strength
Tensile test was conducted on SHIMATZU Dynamic testing machine. The test was carried as per A.S.T.M
standard. All the samples were tested for strength. The reported values are an average of two tests.
Hardness test
Hardness was determined on hardness specimen. The test was carried out three different locations on specimen
to negate the possible effect of indenter resting on the order particle.
Wear properties
Wear test was carried out on all samples by Pin on disc method. The computer-backed pin on disc machine
consists of EN steel disc (case hardened to 80 RHN to a depth of 3mm) and a pin holder above it. The specimen
is fixed to pin holder so as that flat surface of the specimen makes full contact with the disc. The speed of the
disc, the diameter of the rotation and the load can be varied. A pre-set timer switches off the disc motor to the
set time. The weight loss is measured after each trial using an electronic balance with an accuracy of 0.0001gms.
The test was carried out at four sliding distances under varying normal loads of 5N, 10N, 15N & 20N.
3. Specimen preparation for microphotography
A 20mm diameter and 20mm thick piece is cut from the casting for microphotography. One face of the
specimen was well finished by scrubbing it against emery papers of size 200,400,600 and 800 rotating it through
3
90 degrees at equal intervals. Then it was polished using polishing machine. Then the specimens were observed
through the optical microscope and microphotographs were taken and it is shown in Fig (6, 7, 8 & 9).
6.0 Results and Discussion
Strength
The addition of beryl particles do not deteriorate the tensile strength of the matrix material but enhance its
tensile strength as can be seen in Fig 2. The peak tensile strength can be observed for addition of six percent by
weight of beryl particles. The presence of hard particles may be responsible for improvement in strength.
Hardness
The results of the hardness test are shown in Fig 3. It is clear that the hardness increases with different
percentages of ceramic particles as against the base matrix. The increase in hardness may be attributed to the
presence of hard ceramic particles in the matrix.
The hardness of beryl is 7.5-8 on Mho’s scale. The particulates are harder than the base matrix, hence the
overall
hardness of the composite increases.
Wear
The wear resistance in terms of weight loss is shown in Fig (4 & 5). The weight loss is taken as the measure of
wear resistance as the higher weight loss implies lesser wear resistance. It is observed that the base matrix has
higher weight loss as compared to composites. Composite with 10% beryl shows minimal weight loss
The decrement in the weight loss is due to the increment in the hardness of the composite. The experiment was
carried for different loads to see the effect of the normal load. As the load increases, the weight loss also
increases which is due to the increase in normal load acting on the contact area, which is true irrespective of
quantity of beryl particle addition as can be seen in Fig 5.
Typical microphotograph of matrix material and the composite is shown in Fig (6 & 7). It can be seen for the
latter that the particle being embedded in the matrix.
The weight loss of the composite also increases as the sliding duration increases and this may be due to the fact
that the wear debris may get adhered to the sliding surfaces, leading to three body abrasion between the
contacting surfaces as can be seen from microphotograph in Fig (8 & 9).
66
180
64
160
62
Hardness BHN
200
UTS MPa
140
120
100
80
60
60
58
56
54
40
52
20
50
48
0
0
2
4
6
8
0
10
2
4
6
8
10
Beryl Weight %
Beryl Weight %
Fig. 2 Tensile strength of aluminium beryl
composite for different weight percent of
beryl particles
Fig. 3 Hardness of aluminium beryl composite
for different weight percent of beryl particles
4
0.012
0.014
0.01
0.012
W e ight los s in gra m s
W e ig h t lo s s in g ra m s
Proceedings of the National Conference on
Trends and Advances in Mechanical Engineering,
YMCA Institute of Engineering, Faridabad, Haryana.., Dec 9-10, 2006
0.008
0.006
0.004
0.002
0
5 New tons
10 New tons
15 New tons
20 New tons
0.01
0.008
0.006
0.004
0.002
0
0
2
4
6
8
10
0
2
4
6
8
10
Beryl Weight%
Beryl weight %
Fig. 4 Effect of addition of Beryl on wear
for normal load of 10Newtons
Fig. 5 Effect of addition of various percentages
(in terms of weight loss) of Beryl on wear rate
Fig
2 Microphotograph
ofof
base
matrix
Fig
Fig.
26Microphotograph
Microphotograph
of
base
base
matrix
matrix
Fig. 7 Microphotograph of Aluminium beryl
composite
Fig. 8 Microphotograph of base matrix after
wear
Fig. 9 Microphotograph of Aluminium beryl
composite after wear
7.0 Conclusions
•
•
•
•
Beryl particles can be used as reinforced material.
The additions of Beryl as particulate do not deteriorate the properties.
Tensile strength of the material is high for addition of 6 percent by weight of Beryl particles.
The increase in addition of Beryl particles in terms of weight percentage increases the hardness of the
matrix material.
5
•
•
Wear resistance of the composites increases with increase in hardness.
The weight loss of the 10% composite at 20N and for 5 minutes duration is 34% less when compared to the
base matrix.
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