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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/Silicon

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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_microscope

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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.

http://www.ceramicbulletin.org/http://www.ceramicbulletin.org/http://www.ceramicbulletin.org/

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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