11

CHAPTER 2

LITERATURE REVIEW

The materials having low friction properties and more wear

resistance are well suitable for engine bearing applications, because this

assured their life time. The main reason for the increasing wear of bearing

surfaces is due to the starting and stopping of engine and also sudden rise in

load or velocity. The selection of bearing is not only to reduce the amount of

wear but also not to reduce the load carrying capacity. These properties are

achieved by bi-metal/tri-metal structure, wherein the thinner layers of bearing

material are covered with steel backing and this improves higher load

capacity than the thicker ones (Anna & Piotr (2004)). This section is

concerned with the development of bearing materials, requirements of engine

bearing materials, aluminium-based engine bearing alloys, analytical

calculation, identified gaps in the literatures and objectives of the present

study.

2.1 DEVELOPMENT OF BEARING MATERIALS

Aluminium alloys and other lightweight materials have growing

applications in the automotive industry, with respect to reducing the fuel

utilization and shielding the environment, where they can successfully

reinstate steel and cast iron parts. These alloys are extensively used in

buildings and constructions, containers and packaging, marine, aviation,

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aerospace and electrical industries because of their lightweight, corrosion

resistance in most environments or a combination of these properties (Allen

1983).

Aluminum alloys have higher electrical and thermal conductivities

than most other metals and they are usually cheaper than the alloys which are

superior conductors like copper, silver, gold, and so on (Kenneth and Michael

2006). Aluminium-based alloy provides good combination of strength,

corrosion resistance, together with fluidity and freedom from hot shortness

(ASM Hand book 1979)

The use of aluminium-based alloys in engine bearing applications

has increased greatly in the recent years. The aluminium in pure state is

unsuitable for bearing applications and world-wide as many of the vehicles on

the road now run with aluminium-alloy lined crankshaft bearings. Alloys

other than aluminium are also used sometimes for engine bearings, but it is

advisable to harden steel shafts running in aluminium alloy bearings where

high speeds or heavy loading are employed. The various types of bearing

materials used in internal combustion engines are shown in Figure 2.1.

Figure 2.1 Classifications of engine bearing materials

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Hence it becomes more essential to study the material properties of

aluminium and its alloys. The alloying elements like tin/silicon added to

aluminium alloy are likely to give high strength to weight ratio and low

thermal expansion coefficient. These alloys also showed improved strength

and wear resistant properties as the silicon content is increased beyond

eutectic composition. Such properties warrant the use of these materials as

structural components in automotive industries (Srivastava et al 2004).

2.2 REQUIREMENTS OF ENGINE BEARING MATERIALS

Engine bearing materials compromise between high mechanical

strength and anti-friction properties, which are characteristics of the soft

materials. In order to meet such contradictory demands the bearing materials

are designed to have composite structure like particulate, laminate and

combine structure (Refer previous section 1.2.1). The most important

properties required for engine bearing materials are given below:

Toughness

Wear resistance

Seizure resistance (compatibility)

Embeddability

Corrosion resistance

Fatigue strength (load capacity)

Conformability

Shock resistance

Cavitation resistance

High thermal conductivity

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Toughness: The ability of the bearing material to resist the

accumulation of micro-cracks. Latter this may result in catastrophic damage

under cyclic loading.

Wear resistance: Even though the presence of abrasive foreign

particles in the engine oil and under the conditions of intermittent direct

contact, the bearing material is able to maintain its dimensional stability.

Seizure resistance (compatibility): The ability of the bearing

material to resists physical joining when the direct metal-to-metal contact

occurs. High seizure resistance is important when the bearing works in the

mixed regime of lubrication.

Embeddability: The ability of the bearing material to deceive and

sink beneath the surface small foreign particles (dirt, debris, dust etc)

circulating in the lubricating oil. Poor embeddability of a bearing material

leads to accelerate the wear and scratches the shaft and engine surfaces,

results to seizure.

Corrosion resistance: The ability of the bearing materials to resist

chemical attack of oxidized and contaminated lubricant.

Fatigue strength (load capacity): The bearing materials can

withstand an infinite number of cycles for the maximum value of cycling

stress developed inside the internal combustion engines. The cycling stresses

are induced in the bearings due to the combustion and inertia forces

developed inside the internal combustion engines. The bearing materials will

fail, if the bearing load excesses its fatigue strength. Finally the cracks form in

the bearing material, which well spread to the back bearing layer and may

result in flaking out of the material.

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Conformability: It is the ability of the bearing material to

accommodate geometric misalignments of the bearing, its housing or shaft.

Shape irregularities of a bearing with poor conformability may cause

localized decrease of oil clearance to zero, where in the bearing material

experiences excessive wear and high specific loading.

Shock resistance: The ability of the bearing material to absorb

shock loads, because the bearing surface may also subject to shock loads

while in operation. So, the bearing material must be capable of absorbing

them in order to minimize damage to the lining.

Cavitation resistance: The ability of the bearing material to

withstand impact stresses caused by collapsing cavitation bubbles, which

results pressure drops in the flowing lubricant.

High thermal conductivity: The bearing material could able to

facilitate the dissipation of frictional heat if produced during operation.

To optimize or achieve all of the aforementioned properties is a

challenging matter. For example the fatigue strength could be enhanced but at

the cost of a high rate of wear. Similarly low strength and hardness promote

deep embedding and so reduce wear but also support the release of entrapped

particles. Therefore, during operating conditions, the engine bearing material

should achieve the best compromise between the properties’ requirements.

2.3 ALUMINIUM BEARING ALLOYS

Now-a-days, aluminium-based alloy with desirable properties are

used for bearing lining or interlayer. Aluminium alloys, such as Al-Sn, Al-Si,

Al-Sn-Si with or without small additions of Cu, Ni and Mn are most

commonly used bearing materials in the internal combustion engines. So, in

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order to achieve the desired properties and understanding of each element,

multi component phase diagram is required for these alloys. This will be

helpful to understand the nature of secondary phases present in these

developed bearing materials.

2.3.1 Al-Si System

The Al-Si phase diagram is helpful to manage the melting

characteristic of the newly developed bearing material. The amount of Si

required to produce the lowest melting point is 12.6% at the corresponding

temperature 577 °C. The alloy starts to melt at the above temperature which is

called liquidus and below levels it is solidus. Between solidus and liquidus,

the alloy is in partially molten state, i.e., existing both as liquid and solid. The

Figure 2.2 shows the formation of phase, i.e., solubility of Si in Al.

Figure 2.2 Al-Si phase diagram

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It is evident from the diagram that Si also exists as a distinct phase

in the alloy. The large amount of phase has appeared up to 5% of Si content

present in aluminium and this behavior will be used in bearing linings. So, the

addition of silicon to aluminium helps to increase their strength and wear

resistance. Al-Si alloys are extensively used in industrial applications due to

better tribological properties

The additions of silicon in aluminium reduces the thermal

expansion coefficient, increases hardness, corrosion and wear resistance,

ductility, and improves casting and machining characteristics of the alloy.

Porosity is the common casting defect while manufacturing Al-Si alloy. This

will degrade the mechanical properties of the material. Nonmetallic inclusion

is another common defect in cast Al-Si alloys. The above defects reduce the

fatigue and wear resistance of the alloy. The Si phase is important to fatigue

and wear properties of Al-Si alloy. Coarse Si decreases the fatigue strength of

the alloy due to microcrack initiation and higher Si content improves the wear

resistant of Al-Si alloy. The various new processing techniques like semi-

solid processing, squeeze casting, and cosworth process are being developed

to remove the casting defects. These improves the microstructure of the alloy

and also increases the fatigue strength and wear properties (Haizhi 2003)

Yasin & Temel (2008) have found that the hardness of the

Al-40Zn-3Cu alloy has increased while increasing the content of Si. The

appearance of this alloy containing 2% Si is fine particles, but it becomes

coarse when the Si content is more than 2%. Again, the addition of Si content

from 0-5%, gives an opposite effect on the tensile strength. The changes of

the tensile strength showed in three different stages namely an initial sharp

decrease, a gradual increase and a final slow decrease. Abdel-Jaber et al

(2010) have found that by increasing silicon content up to 12% in the casting

alloys, solidification time was increased. But the liquidus temperature was

18

decreased and then increased with increasing percentage of silicon content.

The increase of silicon percentage in Al-Si alloy increases the ultimate tensile

strength and a significant increase of hardness. High coefficient of friction

and less weight loss was also noticed.

Lozano et al (2009) have proved that the wear resistance of the

newly developed hypereutectic Al-Si-Cu alloy was improved due to the small

additions of Si particles and suggested that this alloy is used to eliminate the

existing material for the grey iron liners in engine blocks. The test was

conducted at different loading, sliding speeds and various sliding distances

under lubricated and unlubricated conditions. The abrasion resistance of Al-Si

alloys greatly depends on the morphology and size of the silicon particles as

well as the size of the abrasive particles. Prasad et al (1996) have conducted

the testing of Al-Si alloy against finer and coarser abrasive particles. The

predominating embrittling effect and microcrack trend of the primary silicon

particles showed the way to superior wear properties, while test was

conducted against the finer abrasive particles. But the alloy slides against the

coarser abrasive particles. The generation of higher frictional heating was

suppressed and microcrack trend of the alloys were produced and this

facilitated to carry load and the improved wear resistance properties. So, the

coarser primary silicon particles impose greater wear resistance of the alloy.

The mechanical and physical properties of Al-Si alloy is affected

by the morphology and volume fraction of the primary Si phase. So, the

distribution of Si during solidification is controlled to achieve the desired

properties. i.e., the size and shape of primary Si is dominantly affected by the

cooling rate during solidification. The component produced through the

conventional casting process is good quality, but they have lacked in

providing fine grain structure, limiting their applications. So, the secondary

operations are needed to impart a fine grain structure to cast products.

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Raju et al (2011) have proved that the silicon content was increased, the wear

resistance and corrosion resistance were increased in both spray cast and chill

cast alloys. But wear and corrosion rates were invariably lower in spray cast

alloys because of their microstructural refinement and fine and uniform

distribution of Si in Al matrix.

Torabian et al (1994) have found that the wear characteristic of

Al-Si alloys containing 2-20% Si is strongly reliant on load, sliding velocity,

and composition of the alloy. The load bearing capacity of the alloy was also

improved, while the addition of silicon content from 8-20% under dry

condition using a pin-on-disc type wear testing machine. Torabian et al (1994)

have also found that the wear characteristics of the above said alloy was also

improved due to the addition of 2 to 10 wt% of Pb at various applied loads,

sliding velocity and alloy composition. The wear rate was increased linearly

with the increase of applied load. The results showed that the wear rate was

decreased and load bearing capacity of Al-Si-Pb alloys increased with the

increase in Pb content of the alloy. Prasada et al (2004) have proved that in

the identical applied load, the load bearing capacity of Al-Si alloy was

improved due to the addition of 7% of Si and also significant improvement of

the tensile properties. This was achieved while the alloy subjected to

combined grain refinement and/or modification of cast Al-7Si alloy. It was

also observed that along with the improved wear resistance of alloy, there is a

significant improvement in the tensile properties.

2.3.2 Al-Sn System

Al-Sn alloy provides a combination of good fatigue strength and

surface properties i.e., conformability (softness), compatibility, and dirt

embeddability on the other. These alloys possessing good antifriction

characteristics and corrosion resistance are superior to Al-Pb bearing alloy

materials. But still these alloys have limited fatigue strength and this could be

20

rectified by adding elements which improve the properties of compatibility

and wear resistance. For example, the strength of Al-Sn alloys can be greatly

improved by the addition of copper content up to 1% which brings about solid

solution hardening of the Al phase. Al-Sn alloy is as good as to the tin-based

white metal because of its superior fatigue strength. The hardness and

stiffness of such alloys are equivalent to white metal at room temperatures but

remarkably improved at higher temperatures.

Figure 2.3 Al-Sn phase diagram

From the Al-Sn phase diagram shown in Figure 2.3, it is clearly

understood that there is no solubility that exists and remains as a separate

phase in all proportions depending upon the rate of cooling. The structure of

these alloys having more than 10% Sn has primary Al grains surrounded by

envelopes of Sn. These alloys are used in majority of bearing applications

including big end and main bearings and these properties may be suitable to

replace the conventional bearings like copper-based alloy, and lead-based

alloy, etc.

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The white metal is not suitable for bearing applications due to their

low fatigue strength to withstand the increasing surface stresses. The

aluminium alloy containing 40% Sn offered 20-80% improvements in fatigue

strength at engine operating temperatures of 60-120 0C. So these kinds of

properties were suggested to replace white metal to Al-Sn alloy in cross-head

bearing applications. The addition of copper in this alloy has increased their

hardness and anti-seizure properties (Desvaux 1972). Tripathy et al (2007)

have tried to replace the lead contain copper alloy to Al-Sn alloy, because of

the environmental problems related with lead and also higher cost of copper.

The steel backed and warm rolled Al-Sn alloy containing 10-20% tin revealed

the lowest friction coefficient value of 0.7 and increased the specific wear rate

of alloy from 14.0 x 10-5 to 41.2 x 10-5 mm3/N-m and it was suggested for

bearing applications.

Wu & Zhang (2011) have attempted to find the effect of addition of

Sn in A390 alloy in both as-cast and heat treated conditions and their effects

in microstructure and sliding wear behavior. The microstructure of the alloy

endorsed the disintegrating and spheroidizing of both eutectic and primary

silicon during heat treatment process, whereas only slight changes occurred in

as-cast alloys. The lower friction factors and superior wear resistance were

obtained in the heat treated alloys (with/without addition of Sn) and the same

properties were not achieved in as-cast alloys. Jeong-Keun et al (2002) have

found that the Al-20Sn and Al-40Sn alloys obtained three different kinds of

structure namely elongated, small network and large network during the

addition of Sn. Better wear resistance and lesser friction coefficient were

obtained in large network structure compared to other types of structures and

this exhibited better anti-friction characteristics.

Wislei et al (2006) have studied the effects of corrosion resistance

of the directionally solidified samples of Al-Sn and Al-Zn alloys at various

22

structures. The coarser dendritic structure was beneficial in improving the

corrosion performance of Al-Zn alloys, whereas a ner dendritic structure

resulted in lower corrosion rates in Al-Sn alloys. Eman & Mohammed (2013)

have inferred that the highest wear resistance was obtained in A1-12% Sn

alloy and wear behavior of alloys changed from mild wear (oxidative wear) to

metallic wear when load changed from low to high.

Liu et al (2008) have characterized the mechanical and wear

behavior of Al-Sn bearing alloys at various Sn distributed conditions. The

alloys were prepared by Mechanical Alloying (MA) and sintering. The

microhardness of the sintered Al-Sn alloy was reduced about three to four

times of that of cast Al-Sn alloy. But in MA Al-Sn alloy obtained high

hardness value and it depended on fine grain size and distribution of Sn in Al

matrix. The friction coefficient and wear volume of MA Al-Sn alloy were

increased with increase in applied load, at the same time the wear rate

decreased with increasing applied load. Liu et al (2012) have also studied the

sliding wear performance of the MA Al-20 wt% Sn alloy. During this test, a

tin oxide layer formed uniformly over the worn surface which reduced

considerable wear, and friction coefficient value while resulted in high-load

carrying capability.

2.3.3 Al-Sn-Si System

Davis & Eyre (1994) and Abis et al (1994) attempted to find the

excellent mechanical properties and tribological characteristics of both Al-Si

and Al-Sn alloys which have been extensively used in many engineering

applications, especially in plain bearings, internal combustion engine pistons,

cylinder liners, etc. The presence of Si in aluminium-based alloy improves the

wear resistance, but this was poor seizure resistance properties under

lubricated conditions particularly during starting/warming up of engines.

Al-Sn alloys have good anti-friction characteristics. At the same time, they

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are unable to support heavy loads and have poor fatigue strength while the

engine operates under high loads. To overcome the above mentioned

problems, either Si is to be added into Al-Sn alloy or Sn to Al-Si alloy. These

combinations enhance their ability to support load and fatigue resistance and

are best suitable for engine bearing applications. Pathak & Mohan (2003)

have found that the leaded aluminium alloys were more effective than Al-Sn

alloy. The addition of alloying element also improved the necessary

antiscoring and anti-friction properties and it is also cheaper than tin. The Al-

Pb alloy proved a better soft addition than tin in aluminium alloys, but the

process of adding lead in aluminium alloys is difficult and also lead is

poisonous. Hence, the addition of silicon to Al-Sn alloys or tin to Al-Si alloys

are preferable in plain bearing applications.

Figure 2.4 Al-Sn-Si phase diagram

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Yuan et al (2000) have developed the first series of Al-Sn-Si alloy

and investigated their crystallization behaviour. The microstructure behaviour

was also investigated by using X-ray diffraction as well as optical and SEM.

The Al-Sn-Si alloy belonged to ternary eutectic system and the unfolded

Al-Sn-Si ternary phase diagram is shown in Figure 2.4. The microstructure of

this kind of alloy was ‘peritectic-type’ island shape structure of the Si

surrounded with Sn.

Perrin et al (2004) have demonstrated the better wear resistance of

the AlSnCuSi alloy produced through novel techniques of high-velocity

oxyfuel (HVOF) thermal spraying over the conventional roll bonding

techniques. This technique improved the microstructure and the fatigue test

was also conducted in air at room temperature, at a load ratio of 0.1 and a

frequency of 10 HZ. The results showed that HVOF coated specimen showed

better fatigue resistance. Marrocco et al (2006) have studied the effects of the

wear resistance of the AlSnCuSi alloy prepared through HVOF thermal

spraying and reported that the wear resistance was considerably improved and

that was probably due to the existence of hard Si particles within the structure.

Anil et al (2010) have examined the corrosion behavior of various

alloys like Al-Sn, Al-Si and Al-Sn-Si alloys processed through spray forming

techniques, compared over chill cast alloys. The results revealed that better

corrosion resistance was obtained in both spray formed Al-Si alloys and also

in Al-Sn-Si alloys. Parikshit et al (2009) have attempted to evaluate the

tribological behavior of steel backed Al-10Sn-4Si-1Cu strips sliding against

bearing steel. The strip was prepared by spray depositing the molten alloy on

a steel substrate, followed by different warm rolling conditions. The

coefficient of friction and fretting wear rates of the alloy was compared with

the commercially available Al-Sn based alloy. The results showed that there

was no obvious difference in coefficient of friction at various load conditions,

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but the fretting wear rate of the steel backed strips revealed a decrease in wear

rate with an increase in the amount of warm rolling.

Abd El-Salam et al (2010) have studied the effect of the mechanical

properties of Al-Si alloy at various percentages of the addition of Sn. The

results showed that the mechanical property of the Al-Si alloy was improved

due to the increased hardening. The addition of different alloying elements

modified the microstructure, thus resulting in improved mechanical

properties. Anil et al (2010) have studied the wear parameters of various

spray formed alloys such as Al-6.5Si, Al-12.5Si and Al-12.5Si-25Sn as a

function of applied load, sliding distance and sliding velocity. The additions

of Sn showed the highest wear resistance compared to that of Al-Si alloys and

the wear rate increased with applied pressure. Similarly Al-12.5Si-25Sn

exhibited maximum seizure pressure than compared to other alloys. So this

kind of alloy can be used for higher range of pressure and velocity

applications.

2.3.4 Methods to Improve the Property of the Aluminium-Based

Alloy

The various major methods to improve the quality of aluminium

alloys are composite structures, addition of alloying elements and heat

treatment process.

2.3.4.1 Alloying elements and their effects

Pure aluminium and its alloys still have some problems such as

relatively low strength, and unstable mechanical properties. Rana et al (2012)

have attempted to study the effect of the addition of various alloying elements

with aluminium alloys. For example, the addition of major alloying elements

like Si, Cu, Mg, minor alloying elements like Ni, Sn, microstructure alloying

26

elements like Ti, B, Sr, Be, Mn, Cr and impurity alloying elements like Fe, Zn

were used to modify the microstructure and also it helped to improve the

mechanical properties. The selection of the above said alloying elements were

based on their effects and suitability. For example, silicon increases the

fluidity property and moderate increases strength. Magnesium can impart

good corrosion resistance and weldability or extremely high strength. Copper

has the greatest impact on the strength and hardness of aluminum casting

alloys and it improves the machinability of alloys. Nickel improves the

elevated temperature strength and hardness and tin improves antifriction

characteristic and fluidity of aluminum casting alloys.

Edwards et al (2002) have studied the effect of small additions of

Ti, Zr and V in Al-Si eutectic alloys as a function of chemical composition

and cooling rate. It was observed that the addition of alloying influence the

improvement of microstructure and also mechanical properties. Susanne &

Helmut (2011) have investigated the material characteristics, mechanical

properties and machinability of AlCuMgSn wrought alloy for the additions of

various alloying elements like Cu, Mn and Mg. The strength of the alloy and

machinability were improved due to the addition of Cu. The addition of Mn

assisted free cutting and Mg exhibited less warranty to improve the

machinability.

Garcia et al (2003) have found that the small additions of 0.5-1.5%

of Cu and 0.1-1% of Ni in a hypoeutectic Al-7Si under two conditions, with

or without addition of grain refiner Sr alloy. The presence of eutectic micro

constituent NiAl3 was not affected by Sr presence. Hence their mechanical

properties were also not improved. Therefore, the addition of copper alloying

element along with Sr, gives better microstructure and also improved their

mechanical properties in as-cast condition that avoided the application of

extended heat treatment.

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Kori & Prabhudev (2011) have investigated the wear behavior of

Al-7Si-0.3Mg alloy as a function of alloy composition, normal pressure,

sliding speed and sliding distance. The tests were conducted at constant

temperature of 300 0C and the effects of minor additions of Cu were also

studied. The wear rate of the alloy increased with the increase in normal

pressure, sliding distances and sliding speeds. Under the similar conditions

the small addition of 0.5% Cu reduced the wear rate compared to as-cast

conditions. The results showed that the addition of Cu improved the

mechanical properties and wear behavior due to the change in microstructure

and formation of non-oxide layer between the mating surfaces.

Lim et al (2005) have investigated the effects of mechanical

properties of the LM6 Al-Si alloy due to inclusion of grain refiner Al5Ti1B.

The hardness value was improved by 10% and tensile strength by 39%. The

highest value of hardness and ultimate tensile strength in the castings was

achieved by the optimal level grain-refiner by 0.5%. The optimal level of

grain-refiner was added to irrespective of the section modulus and the

uniform mechanical properties were achieved in entire casting.

2.3.4.2 Composite materials used in engine bearings

Composite structure is also another way to improve the properties

of aluminium-based alloy. The mechanical and tribological properties of pure

Al were improved due to reinforcement of the hard particles such as Al2O3

and SiC. These composite structures increased the value of hardness and also

the coefficient friction and wear loss of the reinforced composite alloy

decreased which was better than pure aluminium bearing (Bekir & Enver

2009).

The tribological property of the A356 Al-Si alloy was also

improved by the addition of 3 wt% of Al2O3. The wear resistance of the

28

composite alloy was significantly improved for the specific load upto 1 MPa,

but the obtained friction values were slightly higher when compared to the

matrix material (Vencl et al 2006). Similarly the friction and wear behavior of

A356/25SiCp Al Metal Matrix Composites (MMC) were investigated. The

results showed that the wear of the MMC material was lower than cast iron

and suggested that this composite material was more suitable to replace the

applicant material for brake rotor applications (Natarajan et al 2006).

Ramachandra & Radhakrishna (2006) have investigated the

properties of Al-Si alloy reinforced with 15 wt% of graphite through various

tests like hardness, dry sliding and erosive wear. The results showed that the

bulk hardness of composite and fluidity of the molten mixture were decreased

with the reinforcement of graphite particles. At the same time, both the slurry

erosive wear resistance and sliding wear resistance of the composite were

decreased with the addition of graphite particles. Okafor and Aigbodion

(2010) have also investigated the effect of addition of various weight

percentage of Zircon Silicate (ZrSiO4) particles in Al-4.5% Cu alloy through

various mechanical tests like hardness, impact and tensile. The results showed

that both the strength and hardness were increased and also there was an

overall reduction in toughness and density. The nature of the properties of

these composites was suggested to various applications like automobile

industries, recreational products and in construction company.

Adamiak (2006) has attempted to find the mechanical properties of

two different intermetallics with various weight percentages of TiAl and

Ti3Al reinforced with AA6061 alloy. For the evaluation purposes these kinds

of composites materials were applied to some practical application like

mechanical milling. Based on the examinations, the results showed that the

hardness of composite materials increased in comparison with the base alloy

and this composite did not influence their tensile properties. Fogagnolo et al

29

(2003) have inferred that the silicon nitride (Si3N4) was reinforced with

mechanical alloying of AA6061. The results showed that the presence of

Si3N4 led to higher values of Ultimate Tensile Strength (UTS).

Angeliki et al (2009) have found that the use of lignite fly ash improved better

strength values when it was reinforced with Al-12% Si alloy.

2.3.4.3 Heat treatment process

In order to achieve the optimal mechanical and tribological

properties of the aluminium-based alloys, it is subjected to heat treatment

process. Abdulwahab (2008) have studied the various mechanical properties

like hardness, tensile strength and impact energy of the Al-Si-Fe-Mn alloy as

as-cast and age hardened conditions. The alloys were prepared by various

percentage of manganese content from 0.1 to 0.5% with constant Si and Fe

composition and Al as the main element. The results showed that the addition

of manganese improved the mechanical properties at both the conditions and

the age hardened samples had showed better mechanical properties than

as-cast alloys. Fangjie et al (2012) have proved that the tribological properties

of the Zn-4Al-3Mg alloy at high temperatures were affected by the additions

of Sn. The uniaxial tensile strength of the alloys maintained at 200 0C, was

equivalent to Pb-5Sn alloy at room temperatures. But, the further addition of

Sn led to extremely weaken the strength of alloy at 200 0C. The typical

fracture of this alloy at room temperature was brittle but at 100 0C and this

property changed to ductile fracture. The further addition of Sn weakened the

ductility. So the amount of addition should be controlled carefully.

Rac et al (2005) have investigated the tribological properties of

hypereutectic A356 Al-Si alloy and thixo cast specimen as as-cast and T6 heat

treatment conditions. Both heat treated and thixo cast materials showed less

friction and wear compared to the base materials. The lower friction

coefficient was obtained at smaller loads but it increased at higher loads and

30

this could be accepted. It was observed that, the predominant wear

mechanism of the alloy was abrasive and adhesive wear. Rao et al (2008)

have analyzed the mechanical properties and sliding wear behaviour of LM6

Al-Si alloy was characterized at various conditions like as-cast, heat treated

and reinforced with SiC particle. The test was conducted by using pin-on-disc

apparatus and sliding against EN32 steel disc at different normal loads and

constant sliding speed. The wear resistance of the alloy significantly

improved due to particle addition and heat treated conditions and friction

coefficient in all conditions was almost constant with different sliding

distances.

Emma & Salem (2010) have proved that the mechanical properties

of Al-Si alloy containing Mg and Cu were improved by heat treatment

process and this was achieved due to structural change of the alloy. The

results showed that the property of the alloys was affected by the influence of

quench rate and also aging process. The yield strength of the alloy was

increased at a smaller rate when quenching was done at 4 0C/s or above. The

yield strength of the alloy after artificial ageing was increased at 170 0C to

210 0C in Mg contained alloy, but decreased in Cu contained alloy.

Temel & Osman (2010) have investigated the friction and wear

properties of ternary Al-Zn-Cu and Al-Zn-Cu-Si alloys as as-cast and heat

treated conditions. The test was conducted under dry sliding conditions and

the obtained results were compared with SAE 660 bronze. In the as-cast

condition, the mechanical properties like hardness value, tensile and

compressive strengths increased upto the addition of 3% of Si, after which the

properties got reversed. But in T7 heat treatment condition, it was observed

that the hardness, tensile and compressive strength of the alloys were lowered

and at the same time the elongation of the alloy was greatly increased. The

31

wear properties of the tested alloys in both as-cast and heat treated conditions

were superior to SAE 660 bronze alloy.

Moradi et al (2009) have proved that the mechanical properties of

A356 aluminium alloy produced through one pass Equal Channel Angular

Processing (ECAP) was improved by means of special heat treatment (T6)

process. The yield strength, ultimate strength and hardness of the alloy were

improved after pre/post artificial aging, but at the same time the ductility was

increased from 5 to 15%. Menargues et al (2009) have investigated the effects

of hardness and wear properties of A356 alloy produced by Sub-Liquidus

Casting (SLC) under as-cast, T5 and T6 heat treatment conditions. The tests

were conducted at different sliding speeds of 0.05 and 0.1 m/s and a constant

load of 5 N. The maximum hardness value was obtained in A356-T6 samples,

so that the specific wear rate and friction coefficient values were also

increased. Zheng & Huang (1998) have studied the effects of the tensile

property of 2195 alloy at various aging treatments. In the lower aging

temperature, the combined properties of strength and ductility of alloy had

enhanced. For, prior deformation before aging promised combined properties

of tensile strength and ductility under T8 heat treatment process. The

age-hardening behavior of the alloy was slightly affected due to pre-aging

after pre-deformation.

2.4 IDENTIFIED GAPS IN THE LITERATURE

After a comprehensive study of the existing literature, a number of

gaps have been observed and are listed below:

Most of the researchers have concentrated on testing of

hardness and tensile properties of the materials. The

mechanical properties like impact and flexural strengths are

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not fully explored even though these properties play an

important role in bearing applications.

Literature review reveals that the researchers have tried out to

characterize the tribological behaviour of aluminium-based

alloys, particularly used in plain bearing applications, mostly

under dry conditions.

Seizure test is another thrust area which has been given less

attention in past studies.

To the best of author’s knowledge, no paper has been

addressed the housing rigidity of engine bearings while

assembling into the housing

The load carrying capacity and the effects of combined

mechanical cum thermal loads acting on the standard engine

bearing have not been fully explored at various oil operating

temperatures and crank angle positions.

2.5 OBJECTIVES OF THE PRESENT STUDY

The properties required for the advent of new bearing material are

lesser weight, ability to withstand the high pressures developed, good wear

resistance at high temperature, good seizure resistance and great mechanical

strength. The main objective of the work is to develop a new bimetal bearing

material and evaluate the appropriateness of this I.C. Engine applications

based on the results of experimental, theoretical and Finite Element Method

Analyses, which includes

a. Selection and preparation of an aluminum-based Al-Sn-Si alloy

particularly used in engine bearings.

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b. Examination of various mechanical properties like hardness,

tensile, flexural, impact and fatigue strength as per ASTM

standards.

c. Estimation of seizure load of the alloy for high temperature

applications.

d. Determination of corrosive rate of the alloy using corrosive test

method.

e. Investigating the effect of tribological properties of the alloy at

various operating conditions like normal load and sliding

distance with constant sliding distance under lubricated

conditions.

f. Building up a model using Artificial Neural Network (ANN)

techniques for the prediction of mass loss.

g. Ensuring the rigidity of bearing.

h. Computation of load carrying capacity of the alloy operating

under different operating temperature using thermo-mechanical

coupled-field analysis.