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CHAPTER 1
1. INTRODUCTION
The ever-increasing demand for light weight, economy and environmental purpose haslead to the development of advanced materials. MMCs are widely used in industries, as they
have excellent mechanical properties and wear resistance. So in this project introduced
particulate-reinforced hybrid composites because of it is cost less than fiber-reinforced
composites owing to the lower cost of fibers and manufacturing cost. In addition to improved
physical and mechanical properties, particulate-reinforced hybrid composites are generally
isotropic and they can be processed through conventional methods used for metals. Thus, the
silicon carbide, alumina, graphite reinforced with aluminum composites are increasingly used as
substitute materials for high temperature applications.
There have been continuous efforts to develop new manufacturing processes using
Aluminum based alloy materials for such as automotive engine components, wear resistance
components, and also heavy applications. As the automotive engine components play an
important role by transferring the explosive impact from the explosion chamber to the
connecting rod, high thermal resistance and great structural strength is required to endure
extremely high temperature and pressure. Gravity die-casting, squeeze casting, hot forging,
powder forging, stir casting processes have been generally used for the manufacturing of
aluminum materials.Among them, application of the stir casting process is dominant enough to
occupy over 90% of composites manufacturing in the modern industry. However, as feed
materials of the stir casting process are handled at the completely molten state,
Its final product undergoes inhomogeneous solidification, which damages the integrity.
Moreover, they have dendrite microstructures, which lower the strength of material. Recently,
the challenged hot forging process is suitable for high strength products, because the work piece
experiences a significant amount of work hardening. However, its requirement for large forming
load and the poor generosity on the product geometry could not be overlooked. This project deals
with the selection of better material for the process of more hardness and temperature resistance,
in that Aluminum hybrid composite are produced by A6061 as matrix material and silicon
carbide/alumina/graphite as reinforcement in different composition. Different sample are
produced by using stir casting methods. Various tests have been conducted to evaluate the
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different properties of Aluminum composites and they are compared with commercial
Aluminum alloy.
1.1INTRODUCTION TO COMPOSITES:Composite materials are engineering materials made from two or more constituent
materials that remain separate and distinct on a macroscopic level while forming a single
component. There are two categories of constituent materials: matrix and reinforcement. At least
one portion of each type is required. The matrix material surrounds and supports the
reinforcement materials by maintaining their relative positions. The reinforcements impart their
special mechanical and physical properties to enhance the matrix properties. A synergism
produces material properties unavailable from the individual constituent materials. Due to the
wide variety of matrix and reinforcement materials available, the design potentials are incredible.
The physical properties of composite materials are generally not isotropic in nature. For
instance, the stiffness of a composite panel will often depend upon the directional orientation of
the applied forces or moments. In contrast, an isotropic material has the same stiffness regardless
of the directional orientation of the applied forces or moments. The relationship between
forces/moments and strains/curvatures for an isotropic material can be described with the
following material properties like Young's Modulus, the Shear Modulus and Poisson's Ratio.
1.2CONSTITUENTS OF COMPOSITEComposites are composed of two phase. They are:
Matrix phase Dispersed phase
The primary phase having a continuous character is called matrix. Matrix is usually
ductile and less hard phase. It holds the dispersed phase and shares a load with it.
The second phase is embedded in the matrix in a discontinuous form. R, and protect the
this secondary phase is called Dispersed phase. Dispersed phase is usually stronger than the
matrix, therefore it is sometimes called reinforcing phase.
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1.3RESINSThe primary functions of the resin are to transfer stress between the reinforcing fibers, act
as a glue to hold the fibers together from the fibers from mechanical and environmental damage.
The most common resins used in the production of FRP grating are polyesters.
1.4REINFORCEMENTThe primary function of fibers or reinforcement is to carry load along the length of the
fiber to provide strength and stiffness in one direction.
1.5 FILLERS
Fillers are used to improve performance and reduce the cost of a composite by lowering
compound cost of the significantly more expensive resin and importing benefits as shrinkage
control, surface smoothness, and crack resistance.
1.6ADDITIVESAdditives and modifier ingredients expand the usefulness of polymers, enhance their
process ability or extend product durability.
1.7 PROPERTIES ENHANCEMENT BY COMPOSITES
Strength Stiffness Fatigue life Thermal conductivity Density
Wear resistance1.8NEED FOR COMPOSITES
Due to fuel crisis of the world, yet lighter weight material are needed in various field
such as aerospace, transportation, automobile and construction sector.
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CHAPTER 2
2. TYPES OF COMPOSITES
Fibrous composites Laminated composites Particulate composites2.1 FIBROUS COMPOSITES
A fiber is characterized by the length being much greater compared to its cross sectional
dimension. The dimensions of the reinforcement determine its capacity of contributing its
properties to the composites.
2.2 LAMINATED COMPOSITES
Laminate composite consists of layers with different anisotropic orientation or of a matrix
reinforced with a dispersed phase in form of sheets, when a fiber reinforced composites consists
of several layers with different fiber orientation, it is multilayer(angle ply) composite. Laminate
composites provide increased mechanical strength in two directions and only in one direction,
perpendicular to the preferred orientation of fibers or sheet, mechanical properties of the
materials are low.
2.3 PARTICULATE COMPOSITES
As the name itself indicates, the reinforcement is of a particle in nature(platelets or also
include class). It may be spherical cubic, tetragonal, a platelet or of other regular or irregular
shape, but it is approximately equated.
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CHAPTER 3
3. MATRIX
Matrix provides a medium for binding and holding the reinforcement or fillers together
into a solid. It protects the reinforcement from environmental degradation, serves to transfer load
from one insert (fiber, flake or particles) to the other. And also it provides finish, colour, texture,
durability and other functional properties.
3.1 FUNCTIONS OF A MATRIX
In a composite material, the matrix material serves the following functions:
Holds the fibers together Protects the fibers from the environment Distributes the loads evenly between fibers so that all fibers are subjected to the same
amount of strain
Enhances transverse properties of laminate Improves impact and fracture resistance of a component Carry inter laminar shear
3.2 PROPERTIES OF A MATRIX
The needs or desired properties of the matrix which are important for composite structure are
as follows:
Reduced moisture absorption Low shrinkage Low efficient of thermal expansion Must be elastic to transfer load to fibers Dimensional stability Strength at elevated temperature Should be easily process able into the final composite shape
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3.3 TYPES OF MATRIX (MATERIALS)
Polymer matrix composites (PMC) Ceramic matrix composites (CMC) Metal matrix composites (MMC)
3.3.1. POLYMER MATRIX COMPOSITES (PMC)
Polymer matrix composite (PMC) is the material consisting of a polymer (resin) matrix
combined with a fibrous reinforcing dispersed phase. Polymer matrix composites are very
popular due to their low cost and simple fabrication methods.
Use of non-reinforced polymers as structure materials is limited by low level of theirmechanical properties; tensile strength of one of the polymers-epoxy resin is 20000psi
(140Mpa). In addition to relatively low strength, polymer materials possess low impact
resistance.
3.3.2. CERAMIC MATRIX COMPOSITES (CMC)
Ceramic matrix composites (CMC) are a material consisting of a ceramic matrix
combined with a ceramic (oxides, carbides) dispersed phase. Matrix composites are designed to
improve toughness of conventional ceramic, the main disadvantage of which is brittleness.
Ceramic matrix composites are reinforced by either continuous (long) fibers or
discontinuous (short) fibers.
3.3.3. METAL MATRIX COMPOSITES:
Metal matrix composites (MMCs) are engineered materials formed by the combination of
two or more materials, at least one of which is a metal, to obtain enhanced properties. MMCs tend to
have higher strength/density and stiffness density ratios, compared to monolithic metals. They also
tend to perform better at higher temperatures, compared to polymer matrix composites.
Though MMCs have been in existence since the 1960s, their commercial applications
have been limited due to their higher cost and lack of proper understanding. More recently
developed MMCs, especially cast aluminum-fly ash composites, have the potential of being cost
effective, ultra light composites, with significant applications. Such composites, if properly
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developed, can be applied for us in automotive components, machine parts and related industries.
Aluminum and magnesium are lightweight materials, when compared to iron and steel.
However, they do not have the strength requirements necessary for several applications. Metal
matrix composites manufactured by dispersing coal fly ash in common aluminum alloys improve
mechanical properties such as hardness and abrasion resistance.
Metal-matrix composites are either in use or prototyping for the Space Shuttle,
commercial airliners, electronic substrates, bicycles, automobiles, golf clubs, and a variety of
other applications. While the vast majorities are aluminum matrix composites, a growing number
of applications require the matrix properties of super alloys, titanium, copper, magnesium, or
iron.
Like all composites, aluminum-matrix composites are not a single material but a family
of materials whose stiffness, strength, density, and thermal and electrical properties can be
tailored. The matrix alloy, the reinforcement material, the volume and shape of the
reinforcement, the location of the reinforcement, and the fabrication method can all be varied to
achieve required properties. Regardless of the variations, however, aluminum composites offer
the advantage of low cost over most other MMCs. In addition, they offer excellent thermal
conductivity, high shear strength, excellent abrasion resistance, high-temperature operation,
nonflammability, minimal attack by fuels and solvents, and the ability to be formed and treated
on conventional equipment.
Aluminum MMCs are produced by casting, powder metallurgy, in situ development of
reinforcements, and foil-and-fiber pressing techniques. Consistently high-quality products are
now available in large quantities, with major producers scaling up production and reducing
prices. They are applied in brake rotors, pistons, and other automotive components, as well as
golf clubs, bicycles, machinery components, electronic substrates, extruded angles and channels,
and a wide variety of other structural and electronic applications. Superalloy composites
reinforced with tungsten alloy fibers are being developed for components in jet turbine engines
that operate temperatures above 1,830 F.
Graphite/copper composites have tailorable properties, are useful to high temperatures in
air, and provide excellent mechanical characteristics, as well as high electrical and thermal
conductivity. They offer easier processing as compared with titanium, and lower density
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compared with steel. Ductile superconductors have been fabricated with a matrix of copper and
superconducting filaments of niobium-titanium. Copper reinforced with tungsten particles or
aluminum oxide particles is used in heat sinks and electronic packaging.
Titanium reinforced with silicon carbide fibers is under development as skin material for
the National Aerospace Plane. Stainless steels, tool steels, and Incomer are among the matrix
materials reinforced with titanium carbide particles and fabricated into draw-rings and other
high-temperature, corrosion-resistant components.
Metal matrix composite (MMC) is engineered combination of the metal (Matrix) and hard
particle/ceramic (Reinforcement) to get tailored properties. MMCs are either in use or
prototyping for the space shuttle, commercial airliners, electronic substrates, bicycles,
automobiles, golf clubs, and a variety of other applications.
Like all composites, aluminum-matrix composites are not a single material but a family of
materials whose stiffness, strength, density, thermal and electrical properties can be tailored. The
matrix alloy, reinforcement material, volume and shape of the reinforcement, location of the
reinforcement and fabrication method can all be varied to achieve required properties. The aim
involved in designing metal matrix composite materials is to combine the desirable attributes of
metals and ceramics. The addition of high strength, high modulus refractory particles to a ductile
metal matrix produce a material whose mechanical properties are intermediate between the
matrix alloy and the ceramic reinforcement. Metals have a useful combination of properties such
as high strength, ductility and high temperature resistance, but sometimes have low stiffness,
whereas ceramics are stiff and strong, though brittle. Aluminium and silicon carbide, for
example, have very different mechanical properties: Young's moduli of 70 and 400 GPa,
coefficients of thermal expansion of 24 106 and 4 106/C, and yield strengths of 35 and
600 MPa, respectively. By combining these materials, e.g. A6061/SiC/17p (T6 condition), an
MMC with a Young's modulus of 96.6 GPa and a yield strength of 510 MPa can be produced.
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By carefully controlling the relative amount and distribution of the ingredients of a composite as
well as the processing conditions, these properties can be further improved. The correlation
between tensile strength and indentation behavior in particle reinforced MMCs manufactured by
powder metallurgy technique. The microstructure of SiC reinforced aluminium alloys produced
by molten metal method. It was shown that stability of SiC in the variety of manufacturing
processes available for melt was found to be dependent on the matrix alloy involved.
Among discontinuous metal matrix composites, stir casting is generally accepted as a
particularly promising route, currently practiced commercially. Its advantages lie in its
simplicity, flexibility and applicability to large quantity production. It is also attractive because,
in principle, it allows a conventional metal processing route to be used, and hence minimizes the
final cost of the product. This liquid metallurgy technique is the most economical of all the
available routes for metal matrix composite production and allows very large sized components
to be fabricated. The cost of preparing composites material using a casting method is about one-
third to half that of competitive methods, and for high volume production, it is projected that the
cost will fall to one-tenth. In general, the solidification synthesis of metal matrix composites
involves producing a melt of the selected matrix material followed by the introduction of a
reinforcement material into the melt, obtaining a suitable dispersion. The next step is the
solidification of the melt containing suspended dispersions under selected conditions to obtain
the desired distribution of the dispersed phase in the cast matrix. In preparing metal matrix
composites by the stir casting method, there are several factors that need considerable attention,
including the difficulty of achieving a uniform distribution of the reinforcement material,
wetability between the two main substances, porosity in the cast metal matrix composites, and
chemical reactions between the reinforcement material and the matrix alloy. In order to achieve
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the optimum properties of the metal matrix composite, the distribution of the reinforcement
material in the matrix alloy must be uniform, and the wet ability or bonding between these
substances should be optimized. The literature review reveals that the major problem was to get
homogenous dispersion of the ceramic particles by using low cost conventional equipment for
commercial applications. In the present work, a modest attempt have been made to compare the
dispersion of SiC particles in Al matrix fabricated with the help of different processes viz. (a)
without applying stirring process (b) with manual stirring process (c) a two-step mixing method
of stir casting. An effort has been made to establish a relationship between hardness, impact
strength and weight fraction of SiC in particle reinforced MMCs developed with the help of two
- step mixing method of stir casting technique.
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CHAPTER 4
4. HYBRID COMPOSITES
Hybrid composites is a composite that consists of at least three (as opposed to two)
constituents (distinct phases or combination of phases) which are bonded together at the atomic
level in the composites, each of which originates from a separates ingredient material which pre-
exists the composites (i.e., there are, at least three ingredient materials).
There are different types of hybrid composites classified according to the way in which
the component materials are incorporated. Hybrids are designated as i) sandwich type ii) interply
iii) intraply and iv) intimately mixed. In sandwich hybrids, one material is sandwiched between
layers of another, whereas in interply, alternate layers of two or more materials are stacked in
regular manner. Rows of two or more constituents are arranged in a regular or random manner inintraply hybrids while in intimately mixed type, these constituents are mixed as much as possible
so that no concentration of either type is present in the composite material.
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CHAPTER 5
5. TYPES OF REINFORCEMENTS USEDThe two different types of reinforcements used in the project are
Alumina(Al2o3) Silicon Carbide Graphite
Further the base metal used in the project is an alloy ofAluminum namely A6061.
Chemical composition of 6061 is:
Silicon minimum 0.4%, maximum 0.8% by weight Iron no minimum, maximum 0.7% Copperminimum 0.15%, maximum 0.40% Manganese no minimum, maximum 0.15% Magnesium minimum 0.8%, maximum 1.2% Chromium minimum 0.04%, maximum 0.35% Zinc no minimum, maximum 0.25% Titanium no minimum, maximum 0.15% Other elements no more than 0.05% each, 0.15% total RemainderAluminium (95.85%98.56%)
http://en.wikipedia.org/wiki/Siliconhttp://en.wikipedia.org/wiki/Ironhttp://en.wikipedia.org/wiki/Copperhttp://en.wikipedia.org/wiki/Manganesehttp://en.wikipedia.org/wiki/Magnesiumhttp://en.wikipedia.org/wiki/Chromiumhttp://en.wikipedia.org/wiki/Zinchttp://en.wikipedia.org/wiki/Titaniumhttp://en.wikipedia.org/wiki/Aluminiumhttp://en.wikipedia.org/wiki/Aluminiumhttp://en.wikipedia.org/wiki/Titaniumhttp://en.wikipedia.org/wiki/Zinchttp://en.wikipedia.org/wiki/Chromiumhttp://en.wikipedia.org/wiki/Magnesiumhttp://en.wikipedia.org/wiki/Manganesehttp://en.wikipedia.org/wiki/Copperhttp://en.wikipedia.org/wiki/Ironhttp://en.wikipedia.org/wiki/Silicon7/27/2019 Ph1 - Azhagu
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CHAPTER 6
6. EXISTING SYSTEM
Concrete and Material Company in Jackson, Mississippi, formed by the company now
known as Dunn Investment Company located in Birmingham. In 1932,1961 name changed to
Mississippi Materials Company under President Ellis Hoff Pauir. The field of Ai/SiC whisker
composites began in the mid - 1960s with the realization that whiskers or discontinuous fiber
reinforcements can be competitive with continuous fiber reinforced material from the stand point
of mechanical properties. In 1981. Thereafter, began study on the machinability of A1/SiC/Grp
composites for their potential industrial application. Since then a good number of researches are
being made to machine Aluminium metal metric composite using various machining process in
the practical material machining field.
6.1 CURRENT PROCEDURE
The conventional experimental setup of stir casting essentially consists of an electric
furnace and a mechanical stirrer. The electric furnace carries a crucible of capacity 2.5 kg. The
maximum operating temperature of the furnace is 1000oC. The current rating of furnace is single
phase 230V AC, 50 Hz. The aluminimum alloy (A6061) is made in the form of fine scraps using
shaping machine. It amounts to about 2.25 kg. The metal scraps are poured into the furnace and
heated to a temperature just above its liquidus temperature to make it in the form of semi liquid
state (around 600oC). The mixing of aluminimum alloy is done manually for uniformity. Then
the reinforcement powder that is preheated to a temperature of 500oC is added to semi liquid
aluminimum alloy in the furnace. Again reheating of the aluminimum matrix composite is done
until it reaches complete liquid state. Mean while argon gas is introduced into the furnace
through a provision in it for few minutes. During this reheating process stirring is done by
means of a mechanical stirrer which rotates at a speed of 150 rpm. The Aluminimum composite
material reaches completely liquid state at the temperature of about 800oC as the melting point of
aluminimum is 700oC. Thus the completely melted aluminium metal matrix composite is poured
into the permanent moulds and subjected to compaction to produce the required specimen.
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CHAPTER 7
7. LITERATURE SURVEYConcrete and Material Company" in Jackson, Mississippi, formed by the company now
known as "Dunn Investment Company" located in Birmingham. In1932 .1961 name changed to"Mississippi Materials Company" under President Ellis Hoff pauir. The field of Ai/SiC whisker
composites began in the mid-1960s with the realization that whiskers or discontinuous fiber
reinforcements can be competitive with continuous fibre reinforced material from the stand point
of mechanical properties.
In1981. Thereafter, began study on the machinability ofAl/SiC/Grp composites for their
potential industrial application. Since then a good number of researches are being made to
machine Aluminum metal matrix composite using various machining process in the practical
material machining field.
In 2012 V. N. Gaitonde1, S. R. Karnik, M. S. Jayaprakash was conducted on the Some
Studies on Wear and Corrosion Properties of Al/Al2O3/Graphite Hybrid Composites an at-
tempt has been made in the proposed work to study the effects of Graphite (Gr) and Aluminium
oxide (Al2O3) on alu-minum hybrid composites involving both hard and soft reinforcements on
wear and corrosion properties. The experimental results on Al5083-Al2O3-Gr hybrid composites
revealed that the addition of reinforcement improves the hardness and reduces corrosion and
wear rates.
In 2012 Gheorghe IACOB, Gabriela POPESCU, Florin MICULESCU, Mihai, BUZATU
production of Al/Al2O3/Gr powder composites using mechanical alloying the resulting products
have low mechanical properties due to the structural un homogeneity of the obtained material.
Aluminum, alumina and graphite elemental powders have been mechanically alloy. Powder
mixtureswere mill for two hours Experiments indicate that this method is appropriate for
obtaining composites with better homogeneity.
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CHAPTER 8
8. EXPERIMENTAL WORK
8.1 EXPERIMENTAL PROCEDURE FOR STIR CASTING
The conventional experimental setup of stir casting essentially consists of an electric
furnace and a mechanical stirrer. The electric furnace carries a crucible of capacity 2.5kg. The
maximum operating temperature of the furnace is 1000C. The current rating of furnace is single
phase 230V AC, 50Hz. The aluminium alloy (A6061) is made in the form of fine scraps using
shaping machine. It amounts to about 2.25 kg. The metal scraps are poured into the furnace and
heated to a temperature just above its liquidus temperature to make it in the form of semi liquid
state (around 600C). The mixing of aluminium alloy is done manually for uniformity. Then the
reinforcement powder that is preheated to a temperature of 500C is added to semi liquid
aluminium alloy in the furnace. Again reheating of the aluminum matrix composite is done until
it reaches complete liquid state. Mean while argon gas is introduced into the furnace through a
provision in it for few minutes. During this reheating process stirring is done by means of a
mechanical stirrer which rotates at a speed of 150 rpm. The aluminium composite material
reaches completely liquid state at the temperature of about 800C as the melting point of
aluminium is 700C. Thus the completely melted aluminium metal matrix composite is poured
into the permanent moulds and subjected to compaction to produce the required specimen.
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Fig 1-STIR CASTING SETUP
TABLE FOR THE SAMPLE COMPOSITIONS
Table 1-Sample Details
Table 2- Sample Details
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8.2. SCANNING ELECTRON MICROSCOPE
A scanning electron microscope (SEM) is a type of electron microscope that produces
images of a sample by scanning it with a focused beam of electrons. The electrons interact
with electrons in the sample, producing various signals that can be detected and that contain
information about the sample's surface topography and composition. The electron beam is
generally scanned in a raster scan pattern, and the beam's position is combined with the
detected signal to produce an image. SEM can achieve resolution better than 1 nanometer.
Specimens can be observed in high vacuum, low vacuum and in environmental SEM
specimens can be observed in wet condition.
Fig 2-SEM TEST SET UP
http://en.wikipedia.org/wiki/Electron_microscopehttp://en.wikipedia.org/wiki/Electronhttp://en.wikipedia.org/wiki/Topographyhttp://en.wikipedia.org/wiki/Raster_scanhttp://en.wikipedia.org/wiki/Raster_scanhttp://en.wikipedia.org/wiki/Topographyhttp://en.wikipedia.org/wiki/Electronhttp://en.wikipedia.org/wiki/Electron_microscope7/27/2019 Ph1 - Azhagu
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8.2.1. SEM TEST RESULTS
SAMPLE B ZOOM-x250
Fig 3-Scanned Image of Sample B
SAMPLE C ZOOM-x250
Fig 4-Scanned Image of Sample C
SAMPLE D ZOOM-x250
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Fig 5-Scanned Image of Sample D
SAMPLE E ZOOM-x250
Fig 6-Scanned Image of Sample E
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CHAPTER 9
9. ANALYSIS AND TESTING
9.1. TESTING
The following test are analyzed in the composite materials
HARDNESS TEST TENSILE TEST
9.1.1. HARDNESS TEST
The Vickers (HV) test was developed in England is 1925 and was formally known as the
Diamond Pyramid Hardness (DPH) test. The Vickers test has two distinct force ranges, micro
(10g to 1000g).
Fig 7-Hardness Testing Machine
The indenter is the same for both range therefore Vickers hardness values are continuous over
the total range of hardness for metals (typically HV100 to HV1000). . With the exception of test
forces below 200g, Vickers values are generally considered test force independent. In other
words, if the material tested is uniform, the Vickers values will be the same if tested using a 500g
force or a 50kg force. Below 200g, caution must be used when trying to compare results
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Type of Test Sample ID Observed Value
Vickers Hardness Test Sample B (46.6 to 48.1)HV
Sample C (63.9 to 66.0) HV
Sample D (55.2 to 58.8) HV
Sample E (78.4 to 80.7) HV
Table 3-Result of Hardness Test
9.1.2 Other testing procedures
Impact Test
The Charpy impact test, also known as the Charpy V-notch test, is a standardized high which
determines the amount of energy a material during fracture. This absorbed energy is a measure of
a given material's toughness.
With the increase in Al2O3 constituent Impact strength is increases w.r.t. base metal. This is dueto proper dispersion of Al2O3 into the matrix or strong interfacial bonding in between the Al
alloy 6063& Alumina interfaces.
Tensile test
Tensile tests were used to assess the mechanical behavior of the composites and matrix alloy.
The composite and matrix alloy rods were machined to tensile specimens with a diameter of
6mm and gauge length of 30 mm. As the reinforcement wt. % increases, UTS is also increases.
This happens may be due to dispersion of Alumina which creates hindrance to dislocation
motion. This may results increase in tensile strength of reinforced Al 6063 alloy. All these
mechanical tests are done properly as per the standards given in various material testing books.
For these tests we observed improved in mechanical properties of newly manufactured AMMC
material using stir casting as compared to aluminum alloy 6063 and aluminum oxide.
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9.2 SAMPLE IMAGES OF HARNESS SPECIMEN
Fig 8-HARDNESS SAMPLE B
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CHAPTER10
10. DISCUSSION
Aluminium matrix composites are designed to have the toughness of the alloy matrix and
the hardness, stiffness and strength of hard ceramic reinforcements. As a result composite
materials exhibits a good combination of strength and toughness. In addition, composite exhibits
good thermal conductivity and less thermal expansion coefficient. This makes the composite
materials more thermally stable. The addition of ceramic reinforcements leads to strengthening
of the alloy due to following facts: higher dislocation density due to the existence of thermal
residual stress (because of significant difference in thermal expansion coefficient between the
matrix and reinforcement), (ii) elastic and plastic incompatibility between the matrix and
reinforcement which leads to interaction stress, (iii) resistance to flow of the matrix material.
These phenomena lead to higher high temperature strength. As a result composite could be used
at much higher temperature as compared to that of the alloy. At higher thousands hours without
any problem. The P-type and N-type test of the brake drums have been conducted at VRDE,
Ahmednagar. The test result show that the braking efficiency of AMC-brake drum is around
20% higher than that of the cast iron brake drum; while the weight reduction is around 60%.
Additionally, the temperature rise in AMC -brake drum (97o) is considerably less as compared to
that of the cast iron (147oC) brake drum. The report temperature, the hard ceramic phase protect
grain boundary sliding and thus prevent easy flow of material. In view of these facts, attempts
have been made to use composites in several engineering applications. In particulate
composites, ceramic particles either pushed by the solidification front to the last freezing eutectic
phase or get trapped in the tendritic region or at the primary dendrites depending on the size of
particles, size of dendrites and cooling rates. In fact, it is strongly dictated by the alloy
composition and processing parameters. In the present composite systems, particles are more or
less uniformly distributed in the matrix and eutectic silicon phases are surrounding the particles.The interface between the particle and the metallic matrix is found reasonably good. The wear
of materials primarily depends on interfacial strength and the distribution of particles. In
addition, the SiC particles remain protruded over the specimen surface. Thus when the
composite surface comes in contact with the other surface, the effective contact is controlled by
these surfaces. In fact, in composites, these SiC particles being very hard and remain protruded
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over the specimen surface protect the matrix alloy from different types of wear such as sliding,
abrasion, erosion-corrosion etc.
As a result, composites exhibit considerably higher wear resistance as compared to the alloy.
The SiC particles not only improve the strength on the alloy but also resist plastic flow of the
matrix material at high temperature. In fact these particles help in retaining strength of the alloy
at higher temperature. The addition of SiC particles also decreases sticking and adhesion
tendency with the counter surface. Additionally, because of less contact and considerably good
thermal conductivity, temperature rise in composite at affixed applied load and sliding speed is
less as compared to the alloy. All these factors lead to improvement in seizure pressure of the
alloy due to particle additions. In case of erosion- corrosion wear two types of wear mechanisms
are simultaneously occurring on the specimen surface: the corrosion and erosion. The galvanic
corrosion, preferably at the particle-matrix interface is expected to give higher corrosive wear as
compared to the alloy. But the area covered, preferably by nobler ceramic phase, is considerably
high in composite, which leads to reduction in corrosion. These two counter facts may lead to
almost comparable corrosion rate in alloy and composite. But during erosion a considerable
amount of material gets removed either by abrasive types of wear or by impact type of wear.
SiC particles improve wear resistance of the alloy against both these types of wear. It is further
observed that erosive-corrosive wear is primary controlled by the erosive wear. Thus, the
composites perform superior to the alloy under erosive -corrosive environment. The above
discussions, in general, show that the composites have superior wear resistance as compared to
the alloy in most of the tribo environments. These lead to the development of wear resistance
components for automobile and mining applications. Regional Research laboratory, Bhopal has
developed fre A1 Composite components and their performance was evaluated in actual field
conditions. The field trial results were quite encouraging and suggested to carry out further
development for commercial exploitation.
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CHAPTER 11.
11. CONCLUSION
The aluminium alloy hard particle composite can successfully be synthesized by
solidification process (stir casting or vortex technique). Aluminium composite so developed
exhibit uniform distribution of the particle in the matrix and good interface bonding between the
ceramic phase and the metallic matrix. Aluminium composite provides higher wear resistance
than those of the base alloys in all tribo-conditions. In case of high stress abrasive wear, the
improvement is noted to be more at low load and finer abrasive size. Beyond a critical load and
abrasive size, the composite exhibits more or less same wear rate to that of base alloy. Wear rate
increases almost linearly with the applied load. Composites exhibit improved wear resistance
and seizure pressure as compared to the alloy under both dry and lubricated sliding wear.
Further, frictional heating and coefficient of friction are noted to be considerably less in
composite as compared to that in the alloy. The corrosion resistance of the composite is
comparable to the base alloy irrespective of the corrosive media. As the erosive wear is
dominated by erosive wear, the erosive - corrosive wear rate of the composite is noted to be less
than that of alloy.
The mechanical, tribological and electrochemical properties of composite makes it a
potential material for automobile and related engineering applications. Several automobilecomponents like brake drums and cylinder blocks and engineering components like apex inset
for D-15 hydro cyclones are made out of A1-SiC composite. This demonstrates the possibility of
casting of A1-composite in intricate shape of thinner section also (Cylinder Blocks) the
performance evaluation of these components in actual operating conditions demonstrated that the
composite components have the potential to replace the existing components. Cost analysis of
these components showed that these components could be exploited commercially.
The present study deals with the behavior of aluminium alloy based composites,
reinforced with silicon carbide and solid lubricants such as graphite / (PPS.). The first one of the
composites consists of A1. with Silicon Carbide particles (SiCp) and graphite. The other
composite has A1 with Alumina and solid lubricant: Graphite at solid state. Both composites are
fabricated through Stri Casting Method Mechanical properties of the samples are measured by
usual methods such as Hardness, Tensile. The tested samples are examined using Scanning
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Electron microscope (SEM) for the characterization of microstructure on the surface of
composites. The Main Aim is to be results of the proposed Hybrid composites are compared
with A1 based metal matrix composites at corresponding values of test parameters.
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CHAPTER 12
12. REFERENCES
[1] Metal matric composites: production by the stir casting method by J.Hashim, L. Looney*,
M.S.J. Hasmi School of Mechancial and Manufacturing Engineering, Dublin City
University, Dublin 9, Ireland
[2] Simulation of the stir casting process by S. Naher, D. Brabazon, L.Looney, Centre for
Engineering design and Manufacture, Dublin City University, Centre for Engineering
Design and Manufacture, Dublin City University, Dubline, Ireland, Journal of Materials
Processing Technology 143 - 144 (2003) 567 - 571.
[3] mechanical stir casting of aluminimum alloys from the mushy state: process, microstructure
and mechanical properties D. Brabazon, D.J. Browne, A.J. Carr Department of Mechanical
Engineering, University College Deblin, Belfied, Dublin 4, Ireland Materials Science and
Engneering A326 (2002) 370 - 381.
[4] Meta matrix composites: production by the stir casting method J. Hashim, L. Looney, M.S.J.
Hashmi School of Machancial and Manufacturing Engineering, Dublin City Unviersity,
Dublin 9, Ireland Journal of Materials Processing Technology (1999)
[5] Functionally graded aluminium matrix composites Varuan Kevorkijan Maribor, Slovenia,
www.ceramicbulletin.org, February 2003.
[6] Aluminium matrix composites: Challenges and Opprotunities M K SURAPPA
Department of Metallurgy, Indian Institute of Science, Bangalore 560 012, India.
[7] An attempt to understand stir casting process Sudheer Reddy, P.G. Mukunda and H, Suresh
Hebbar Nitte, Meenakshi Institute of technology, Bangalore, India, International conference
on advanced materials and composites (icamc-2007), oct 24-26, 2007.
[8] Study on microstructure and tensile properties of in situ fiber reinforced aluminum matrix
composites Wenxing Zhang, Donglang Chai, Guang Ran, Jingen Zhou State Key
Laboratory for Mechanical Behavior of Materials, School of Materials Science and
Engineering,
[9] Effects of silicon carbide reinforcement on microstructure and properties of case A1-Fe/SiC
particulate composutes: V.S. Aigbodion, S.B. Hassan National Metallurgical Development
Centre, P.M.B. 2116 Jos.Nigeria.
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[10] MECHANCIAL PROPERTIES OF ALUMINIUM METAL MATRIX COMPOSITES
UNDER IMPACT LOADING A.M.S. Hamouda and M.S.J. Hashrni Advanced Materials
Processing Centre School of Mechancial & Manufacture