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CHAPTER -2

LITERATURE REVIEW

2.1 INTRODUCTION

During the literature review, an intensified research work is assessed

on aluminum and its alloy – based metal matrix composites because

of low density, good corrosion resistance and excellent mechanical

properties for various engineering applications.

Early MMCs find their tradition confined to military and aerospace

applications. Their extensive usage is hindered due to high production

costs, limited production methods, and restricted product forms. The

factors influencing the type and form of reinforcement are the desired

material properties, ease of processing, and part fabrication. In the

early stages of development, only a limited range of reinforcements

have been used. The stability between the components and the

differences in their thermal properties such as coefficient of thermal

expansion and coefficient of thermal conductivity are the limiting

factors in the compatibility of the two materials used to make the

composite.

The particulate reinforced metal matrix composites possessing

isotropic properties are found to be thermally stable and wear

resistant as compared to monolithic materials.

Based on the literature review, an attempt has been made to

exploit the possibility of usage of fly-ash as a reinforcement material

for Al-Pb metal matrix composite.

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2.2 ROLE OF REINFORCEMENTS IN ALUMINUM MMCs

The literature review reveals that most of the works have concentrated

on Al-SiC metal matrix composites produced using different

techniques. Most of the researchers have used silicone carbide (SiC)

because of its availability in the wide range of grades. Mazen and

Emara [7] and Tan et.al [8] have observed that the presence of SiC in

aluminum can increase its yield strength, young’s modulus and wears

resistance. It has been reported that, alumina (Al2O3) can be the

alternate reinforcement material for SiC because of its stable, inert,

high temperature behavior, and high corrosion resistance [9-11].

Dobrzanski et.al [12] have stated that the presence of Al2O3 particles

can increase the hardness and impede the deformation of the

composite. Titanium Carbide (TiC), borate whiskers, silicon dioxide

(SiO2), diamond, graphite, granulated slag, fly-ash, alumino silicate,

quartz, zirconium dioxide (ZrO2), mica and titanium dioxide (TiO2) are

also being employed as reinforcements in the aluminum based metal

matrix composites. Despite their potential properties, limited

manufacturing processes have hindered their wide commercial usage.

The material used in the present work is fly-ash (waste by-product

from thermal power plants) reinforced Al-Pb matrix alloy.

In the metal matrix composite, the reinforcing particles with

different physical characteristics may result in mismatch at the

interface between matrix and reinforcement. This situation is a

favorable condition to increase the strength since it can increase the

dislocation density and effective in nucleating new grains. The

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reinforcement particles may also stabilize grain size by pinning of the

grain boundaries. It has been presented that, the pinning effect can

increase the strain rate sensitivity and result in super plasticity at

high strain rate [13-15]. The formation of microscopic cavities, which

primarily may occur in the grain boundaries during the high

temperature deformation, is referred to as cavitation. The cavitation

may limit the elongation in the metal matrix composites. Ganguly and

Warren [16] have concluded that, the extent of cavitation has been

increased by the grain boundary sliding due to the presence of

reinforcing particles. They have also suggested that, the use of very

fine reinforcing particles or application of hydrostatic pressure may

minimize the cavitation problem. They have also remarked that the

particle clusters may be the prone areas of crack initiation and the

cracks can be minimized by the uniform distribution of reinforcing

particles.

It has been noticed that, the volume fraction of reinforcement as a

critical factor may control the elastic modulus of the composite. Tan

et. al [8] have observed that the elastic module of composites is

higher when compared to non reinforced matrix at elevated

temperatures. They have also found that both interfacial bond

strength and volume fraction of reinforcement are crucial for effective

transfer of load from matrix to the reinforcement and consequently in

strengthening the composite. By using variety of reinforcements with

different volume fractions it may be possible to optimize the wear and

tear properties of the composites. Mazen and Ahmed [9] and Arpon

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et.al [17] while experimenting separately have examined that the

ceramic reinforcements may contribute low coefficient of thermal

expansion which in turn may increase hardness, stiffness and specific

strength of the composites. In some cases, these characteristics might

have increased the density of the composite slightly depending upon

the volume and density of the reinforcement material.

2.3 MANUFACTURING PROCESSES OF ALUMINUM MMCs

The general processing techniques used to manufacture the

aluminum metal matrix composites are either solid state processing

techniques or liquid state processing techniques. The choice of a

particular process may depend on the matrix, reinforcement, and

service requirement of the composite. In a composite material, the

distribution of reinforcement is the major factor as it can dictate the

morphology, microstructure and finally the mechanical properties.

Proper mixing method must be employed to minimize agglomeration of

reinforcements. Quick pouring and chill casting technique have been

employed to reduce settling of particles [18, 19]. Sometimes, the

secondary processes like extrusion, forging, and rolling operations

may promote better distribution of reinforcements in the composites.

In another study, it has been observed that the reactivity between

reinforcement and the matrix can significantly affect chemistry of the

matrix and the microstructure [20]. In addition, the interfacial

strength may play a vital role during the deformation and fracture of

composite materials. These problems can be minimized by the powder

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metallurgy technique because of its low processing temperatures.

Hence in the present experimental work, the powder metallurgy

technique has been chosen as the processing method for preparing Al-

Pb/fly-ash composites.

2.3.1 Powder Metallurgy Technique of Processing Al MMC

In the literature review, it has been noticed that the aluminum metal

matrix composites consisting of dispersions, particulate whiskers,

fibers have been produced by a variety of powder metallurgical

techniques such as:

(1) Conventional powder metallurgical process involving pressing and

sintering of elemental powders to produce near net shapes.

(2) Hot extrusion, vacuum hot pressing, hot isostatic pressing,

vacuum sintering to produce billets.

(3) Powder forging and powder rolling to produce the components

directly.

(4) Pressure-less sintering and spray forming processes.

The above methods can offer different combinations of cost, shape,

capability and potential properties.

2.4 ALUMINUM POWDER METALLURGY

The powder metallurgy techniques have been observed possessing the

advantage of controlled porosity, attainment of close tolerances,

refined micro structure, near-net shape formability and elimination of

machining scrap losses. It has been noticed that the powder

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metallurgy techniques have shown the capability of developing new or

extended alloy families which is not possible by the casting

techniques. The powder metallurgy process can be extended to the

aluminum materials to increase their utility. The aluminum powder

metallurgy components are having potential applications in the

automotive market because of the need to reduce weight, to lower

emission and to boost fuel economy. In the literature review, some

important powder metallurgy components are employed for engine

cam caps, shock absorber parts, air conditioning compressor parts,

connecting rods, and mirror brackets.

2.4.1 Processing Aluminum by Powder Metallurgy Technique

During literature review the following points are noticed to be the

advantages of processing Al by the powder metallurgy techniques:

(1) Better green strength is obtainable for aluminum alloy powders as

compared to ferrous powders even at a lower compaction pressures.

(2) Low energy is sufficient to process aluminum alloys in contrast to

other materials due to their low sintering temperatures in the range of

500 to 6000C and sintering times in the range of 10 to 60 minutes.

(3) Post sintering treatments like coining, cold forming, sizing, heat

treating, hot forging, anodizing, etc. are applicable with greater ease

on the aluminum alloys. This is owing to higher ductility and unique

characteristics of aluminum.

(4) It is possible to have improved fracture toughness, resistance to

stress corrosion cracking, strength due to fine grain size, improved

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microstructural control, compositional and homogeneity of aluminum

components.

(5) New aluminum alloys may be possible to produce by incorporating

insoluble elements like lead and cobalt in the aluminum.

(6) Aluminum matrix composites with particle, fiber and whisker

reinforcements with wide range of reinforcement levels and improved

uniformity of reinforcement distribution can be easily produced.

Besides these advantages, certain disadvantages are also noticed

during the processing of Al by the powder metallurgy. These may

occur during the compacting or sintering processes.

2.4.1.1 Compacting Problems

Compacting of aluminum in the normal steel dies may generate

serious problems because of its tremendous seizing and galling

characteristics [21, 22]. It has been examined that the presence of

non-reducible oxide film may not permit the development of sufficient

strength in the green briquettes. High compacting pressures are

required to produce briquettes with sufficient strength and density

because of low apparent densities of aluminum powder (0.8 to

1.1gram/cm3) and inferior flow characteristics [21]. The high

compacting pressure in turn may cause more seizure, scoring and

galling of the die wall.

The success of compacting and sintering process may depend to a

great extent on the selection of aluminum powder particle size, shape

and composition [21]. Too fine or flake form of powder may lead to

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poor flow resulting a tendency for cold welding and seizing in the die.

Coarse or spherical powder may exhibit better flow but develop

inferior strength in both green and sintered conditions. In the powder

metallurgy, it has been observed the necessity of admixed or die wall

lubricants to reduce friction between metal powders and die walls and

to minimize die wear. The admixed lubricants can simplify the

compaction and can minimize the interaction between the tooling and

compact during the ejection [23]. However, the admixed lubricants

may have some deleterious effects on some properties of the

briquettes. They usually decrease the green and sintered strengths of

the aluminum powder metallurgical briquettes. Low green strength

results in the formation of cracks, edge blunting, part laminations and

breakage of briquettes prior to sintering. The admixed lubricants may

also cause some difficulties during sintering. It has been noticed that

the faded, weak, and dimensionally non-uniform compacts have been

produced during sintering the green briquettes admixed with

lubricants. Therefore, prior sintering (at temperatures lower than

4200C) must be carried out for aluminum powder metallurgical

components with admixed lubricant. This can avoid the reaction of

decomposition products with aluminum during sintering. During

sintering, if the internal lubricant leaves the residual products in the

composite, it impedes the formation of strong metallurgical bond and

the desired mechanical properties. The lubricant must burn out in a

non-oxidizing atmosphere to prevent the oxidation of aluminum in the

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presence of oxygen. Embrittlement, distortion and discoloring have

also been observed during sintering of the pre-alloyed powders.

Kehl et. al [24] have presented a comparative study on the effect of

lubricant admixtures and die wall lubricants on the dimensional

stability, green and sintered strength of Al – Cu briquettes. They have

used metal-free stearamide wax upto 3wt% as lubricant. When it is

used as die wall lubricant, it is applied with an atomizer to the walls of

pressing tool in the form of 2wt% suspension in ethyl alcohol. The

admixed lubricant in comparison with die wall lubricant lowers the

green strength, decreases true density, and reduces the strength

during sintering. This may be on account of poor wetting and

expansion of the compact during de-waxing. The residues of the wax

reduce the wetting of aluminum particles with the eutectic melt and

thereby reduce the subsequent shrinkage. The result is a net

dimensional change.

Some investigators [5, 25, 26, 27] have used silicone spray with or

without fine graphite powder as die wall lubricant. This produces the

briquettes without scoring on the surface of the compact. Therefore,

the silicone spray is used as the die wall lubricant in the present

experimental investigation.

2.4.1.2 Sintering Problems

In the aluminum powder metallurgy, the presence of aluminum oxide

may cause a major problem during sintering because it is not reduced

by the common furnace atmospheres at the temperatures of sintering

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[21]. The aluminum oxide, which is dense and stable, may acts as a

skin on the aluminum powder particle. This may hinder the diffusion

of particles during sintering. Because of stable oxide layer which can

not be removed by the reducing atmospheres during sintering, weak

sinter necks may develop especially at the places where the oxide layer

is damaged during the compaction. Because of this, the properties of

briquettes sintered from pure aluminum may remain unsatisfactory

even when compacted at high compacting pressures [28].

Some of the problems of aluminum during sintering can be

overcome using the liquid phase sintering [22]. In liquid phase

sintering, the liquid metal penetrates and diffuses into the oxide layer

through the cracks caused by the compaction [29]. The stable oxide

film present on the aluminum particles gets disrupted and in due

course the oxide layer is lifted out. This may result in the inter–

particle bridges to fully establish and give good particle bonding. The

liquid phase may also assist the material transport and the

remainders of the oxide layers may settle as fine particles at the grain

boundaries.

In any powder metallurgical process, the sintering atmosphere is

governed by the material characteristics [30]. The sintering

atmosphere, temperature and humidity conditions may affect the

decrease in density and growth of the sintered briquettes. Nitrogen,

dissociated ammonia, vacuum and argon are observed to be the

common sintering atmospheres used for aluminum products. Dudas

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and Thompson [31] have reported that the surface nitriding has

occurred in the nitrogen atmosphere when the sintering time extends

beyond 40 minutes. When dissociated ammonia is used, the

mechanical properties of the sintered parts are slightly lower than

those sintered in nitrogen. The lower properties of sintered parts in

the dissociated ammonia may be due to the presence of hydrogen

and/or un-dissociated ammonia [31]. Low hardness values have been

reported for nitrogen sintered briquettes [32]. The better properties are

attributed to argon sintered briquettes compared to vacuum sintered

ones due to the absence of any volatization loss of alloying additions.

The maximum ultimate tensile strength is imparted to the aluminium

briquettes with argon sintering. The maximum linear expansion is

observed for aluminum alloy graphite composites sintered in the

nitrogen atmosphere instead of argon and vacuum atmosphere [33].

Therefore, in the present experimental work, the aluminum

composites are sintered in an argon gas atmosphere.

2.5 DEVELOPMENT OF ALUMINUM BASED BEARING MATERIALS

During literature review it has been found that the generally used

bearing materials are white metals. Though these materials have good

seizure resistance, embedability and conformability; the lack of

strength constrain them to be used as bearing materials for the

applications requiring heavy loads, high speeds and high operating

temperatures. This may be the reason for the development of

aluminum alloys and its composites as the bearing materials. The

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various alloying elements are added to improve bearing characteristics

of aluminum based bearing materials [34]. The anti-welding and anti-

scoring characteristics of aluminum alloys can be improved by the

addition of alloying elements which may form discrete soft phase

constituents. The important factor, which governs the seizure

resistance of the bearing metal against the journal, is the mutual

miscibility of bearing metal and journal and the nature of bond

between the atoms of bearing metal and the journal material. For steel

journals, the bearing metal must have an atomic diameter greater by

at least 15% than that of iron and it must have covalent bond [35].

The commercially available materials, which can meet the above

criteria, are Cd, silver (Ag), In, Sn, Pb, gold (Au) and Bi; out of these

both Pb and Sn can offer most attractive combinations of engineering

properties, cost and availability.

Pb is found to be soft and cheaper and has low modulus of

elasticity when compared to Sn. Therefore, Pb is chosen as an alloying

element in the aluminum in the present work.

2.5.1 Powder Metallurgy Technique of Processing Al-Pb Alloy

The leaded aluminum alloys in the form of pre-alloyed powder are

produced by the powder rolling process [36]. The rolling process

causes the mechanical rupturing of the oxide film. This causes clean,

fresh and active aluminum surfaces which can contact with each

other producing metal to metal bond between the neighboring

particles. The rolled green strips have sufficient strength and

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ductility. The coils produced from this material are sintered. It is

found that during the sintering process the diffusion between the

particles improves strength and ductility.

Gopinath [37] has developed sintered Al-17.5% Pb alloy using the

conventional powder metallurgy technique. In this technique, the

powder mix is blended in the double cone blender for 30 minutes and

compacted at 392MPa and 568MPa in a double acting die. The green

briquettes are sintered in the nitrogen atmosphere at 600oC for 1, 3

and 6 hours. For the prepared briquettes, the effect of compaction

pressure and sintering time has been studied. Sastry et. al [38] have

studied the densification behavior of leaded aluminum alloys

processed through attrition milling routes and conventional ball

milling. It has been reported that the attrition milling can be an

effective method for densification of experimental alloys.

Nath et. al [5, 39] have used the conventional powder metallurgy to

produce Al-Pb alloys containing 10, 15, 20 and 25mass% Pb. In this

work, the powder mixtures are compacted in the pressure range of

400 to 600MPa. It has been reported that Al-15mass% Pb alloy have

minimum spring back and maximum green strength and green

hardness. Al-4.5%Cu-Pb admixed alloys are produced by compacting

the powders in the pressure range of 98 to 490MPa using the

conventional powder metallurgy technique. It has also been reported

that the compaction pressure can increase the green and sintering

properties [40, 41].

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2.6 FLY-ASH

In the literature, the fly-ash is described to be a particulate waste by-

product formed as a result of coal combustion in thermal power

plants. It has been reported that the disposal of fly-ash is a major

challenge for the power plants with minimum pollution to the

environment.

The composition of fly-ash may depend upon the coal being burned

in the thermal power plants. In general, the constituents of fly-ash are

silica (SiO2), alumina (Al2O3), and iron oxide (Fe2O3) in major quantity

and oxides of magnesium (Mg), calcium (Ca), sodium (Na), potassium

(K) etc in minor amount. The trace amounts of vanadium oxide and

manganese oxide are also observed in the fly-ash [42]. The morphology

of fly-ash is revealed to comprise of smooth and tiny spherical

particles, either solid or hollow. The solid sphere fly-ash is termed as

precipitator fly-ash and the hollow sphere fly-ash is termed as

cenosphere fly-ash. The density of the precipitator fly-ash is in the

range of 2 to 2.6g/cm3 and its particle size range from 1 to 150µm,

whereas the density of cenosphere fly-ash is in the range of 0.4 to 0.6

grams/cm3 and its particle size range from 10 to 250 µm.

2.6.1 Disposal and Utilization of Fly-ash

It has been reported that the thermal power plants throughout the

world produce hundreds of million tons of fly-ash. Out of this, only a

small portion of the fly-ash is being reused for productive purposes.

The remaining amount of fly-ash is either disposed off in controlled

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landfills or stockpiled for future use. As a result, significant amount of

cost is associated with disposing these vast quantities of fly-ash, and

there is a need to develop new and innovative, yet environmentally

safe applications for the utilization of coal fly-ash. During the last few

decades, extensive research has been carried out to utilize fly-ash as

an engineering material which turns waste into useful product [43].

2.7 ALUMINUM FLY-ASH COMPOSITES

The Al-fly-ash composites are produced by the casting and powder

metallurgy techniques.

2.7.1 Casting Technique

The fly-ash is successfully used as a filler material in the light metals

and alloys by various researchers. Dean Golden [44] has reported that

it is possible to produce the ash alloy cast products by the standard

foundry techniques. Most of the ash alloys find promising applications

in the automotive industry. Rohatgi [45] has demonstrated the

production of ash alloy castings of different shapes and dimensions.

It has been reported that the matrix hardness increases from 65 to 82

HB with the addition of 8volume% of fly-ash. The addition of fly-ash

significantly increases the abrasive wear resistance of aluminum and

consequently leads to wide spread applications in automotive, small

engine and electro mechanical machinery sectors. It has been

observed that the fluidity of the ash alloys is adequate to make variety

of castings and also the cenosphere fly-ash decreases casting densities

and improves its economics further.

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Rohatgi et. al [46] have produced Al-Si alloy (A356) containing 3 –

10 volume% fly-ash using the stir casting technique. They have

observed uniform distribution of fly-ash particles in the small

castings. These composites appear to be attractive products for the

engineering applications. The composite comprising of A356 Al and

fly-ash exhibits high damping capacity as compared to un-reinforced

alloy [47]. For Al-7Si-0.35Mg/fly-ash composites, the interfacial

reactions in liquid metal stir cast components are more when

compared to components produced by the compo-casting technique

[48]. The dimensional stability of A535 alloy is improved by the

addition of fly-ash [49]. Rohatgi et. al [50, 51] have studied the

infiltration of nickel coated and uncoated cenosphere fly-ash particles

with pure aluminum and A356 aluminum alloy manufactured by the

pressure infiltration technique. By the use of pressure infiltration

technique, segregation of fly-ash particles in the casting has been

reduced. The infiltrated length is longer at high pressure or high

temperature. It is also reported that the nickel coating can reduce the

presence of un-infiltrated agglomerates of fly-ash in the composites

and can reduce the infiltration of aluminum into the cavities within

the cenospheres. The abrasive wear of stir cast A356/5volume% fly-

ash composite is similar to the aluminum alloy containing alumina

fibers but superior to the base alloy [52, 53]. The stability of

Al/40volume% fly-ash composite system is studied by Guo et. al [54]

using differential thermal analysis (DTA). The aging characteristics of

aluminum alloy containing hollow spherical particles are studied by

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Rohatgi et. al [55]. Even though the hardness of the as-cast composite

is higher than that of the base alloy, no significant changes in the

aging kinetics are observed.

It has been noticed that AK12/fly-ash composite has high pitting

corrosion in comparison to AK12 aluminum alloy [56]. The presence of

fly-ash particles in the aluminum may decrease its coefficient of

thermal expansion [2]. It has been reported that up-to 20% fly-ash can

be successfully added to the pure aluminum by the stir casting

technique [57]. The hardness, wear resistance and ultimate tensile

strength increase with increase in fly-ash content but the ductility

decreases. In another research, Al–4.5%Cu/fly-ash metal matrix

composite is cast by the stir casting technique [3]. It has been

reported that Al–4.5%Cu/fly-ash metal matrix composite can be used

as a bearing material. Addition of cenosphere fly-ash particles to Al-Si

alloy can increase its hardness and ultimate tensile strength whereas

it can decrease the density and wear loss [58]. The wear resistance of

Al-12wt% Si/fly-ash composites increase with increase in wt% of fly-

ash but decrease with the increase in normal load and track velocity

[59]. Al-4Si–Mg reinforced with fly-ash particles are fabricated by the

stir casting process [60]. It has been observed that increasing of fly-

ash content can increase the porosity in the composite. The 15wt%

fly-ash composite shows highest porosity and lowest hardness. The

tensile, compressive, and impact strengths and hardness are

improved with the increase in fly-ash content in Al-4.5%Cu alloy [4].

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The resistance to dry wear and slurry erosive wear also increase with

increasing fly-ash content.

2.7.2 Powder Metallurgy Technique

Green briquettes of pure aluminum powder upto 20wt% fly-ash are

produced by Guo et. al [61] using the conventional powder metallurgy

technique. Green strength and green density increase with increasing

compaction pressure and decrease with increasing fly-ash content.

The hardness does not change significantly for the briquettes

containing up to 10wt% fly-ash, but it decreases for above 10wt% fly-

ash levels. The sintering has been carried out at 600, 625 and 6450C

for 0.5 to 6 hours in the nitrogen atmosphere for the briquettes

prepared at 414MPa. Upon sintering, density of the green briquettes

decreases. With the increase in fly-ash content, the sintered strength

decreases. Ramana et. al [26] have prepared mixtures of aluminum

powder containing 0, 10 & 20% fly-ash and compacted at 96, 128 and

160MPa. They have also prepared the briquettes for Al–10wt% fly-ash

with various metallic and non-metallic additions [62]. It has been

observed that spring back, ejection pressure, green density, green

strength and hardness increase with increase in compacting pressure

while the true porosity decreases. Angeliki et. al [63] have prepared

Al/fly-ash composites by the powder metallurgy technique and have

reported a decrease in density and an increase in hardness with the

increase in wt% fly-ash. Fly-ash aluminum alloy composites have

been produced by compacting the powder particles in the pressure

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range of 63 to 316MPa [64]. It has been observed that as the

compaction pressure increases the green density increases and the

density decreases with the increase in wt% of fly-ash. The fly-ash

reinforced AA6061 metal matrix composites have been produced using

the cold pressing followed by the hot extrusion [65]. It has been

reported that the hardness and tensile strength of 2wt% fly-ash

composite are better when compared to monolithic alloy after age

hardening. The composites also exhibit better wear resistance

compared to the matrix alloy [66].

From the above, it can be concluded that the aluminum fly-ash

composite components may be produced by the casting and powder

metallurgy techniques. When compared to casting, the powder

metallurgy technique is capable of producing uniform distribution of

particles in the composite with near-net shaped products.

2.8 FLY-ASH AS AN ADDITIVE IN Al-Pb ALLOY

It has been reported that the fly-ash as a waste by-product from

thermal power plants in India may reach 150-170 million tons by the

end of 2012 [67]. Despite the extensive research, the utilization of fly-

ash is found to be low. The shape of fly-ash particle is spherical. The

metal matrix ash composites encompass lower density and lower

stress concentration than the composites with alumina, silicon

carbide particles. This is mainly because of the spherical shape and

low density of fly-ash when compared to the angular shape and high

density of alumina and silicon carbide particle. It has been observed

27

that, the discontinuous reinforced composites incorporating

inexpensive particles in view of their low cost find widest application

in the automotive industry. Among the metal matrix composites, the

greatest attention is focused on aluminum matrix composites. The

addition of fly-ash particles may serve as filler and reinforcement

material and reduces the cost of aluminum composites. It may also

improve selected properties while maintaining others at adequate

levels. Thus, an attempt is made to use the fly-ash particles as an

additive to the metals (Al-Pb) to promote the use of this low cost waste

by – product.

From the literature review, it has been clearly observed that almost

all the research has concentrated on the development of aluminum –

fly-ash composites using the casting technique. An important

requirement is that the fly-ash must be uniformly distributed in the

aluminum matrix, but this distribution is influenced by the tendency

of the particles to float due to density differences and interaction with

the solidifying metal. Guo et. al [61] have stated that these castings

have exhibited segregation and non-uniform distribution of particles

because of difference in density between fly-ash particles and the

melts. The poor wettability of fly-ash particles with the molten metal

has also been reported with the casting techniques. These problems

can be minimized if the components are produced by the powder

metallurgy technique.

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Upto now no significant information has been noticed on the

compacting and sintering behavior of Aluminum-Lead-Fly-ash

particles. The information on compacting and sintering of composite

powder mixture as well as spring back behavior is vital in making high

performance near-net shaped parts by the powder metallurgy

technique. Hence, in the present work Al-Pb/fly-ash composites are

prepared by the powder metallurgy technique and their compacting

and sintering characteristics are evaluated.