CHAPTER 1

INTRODUCTION

1.1. OVERVIEW

In many industrial applications, the most important parameter in material

selection is specific strength .For example it is the critical design criterion in

rotating machinery components. Aluminum is a natural candidate for this type of

application because of its low density. However, compared to titanium alloys, the

strength of conventional commercial aluminum alloys is too low for aluminum to be

a better solution. Owing to the many difficulties encountered in the production and

use of titanium alloys, the drive to develop stronger aluminum alloys is very high.

Compared with unreinforced metals, metal-matrix. The FSW of Aluminum and its

alloys has been commercialized and recent interest is focused on joining composite

materials. However, in order to commercialize the process, research studies are required to

characterize and establish process windows. In particular, FSW has inspired researchers to

attempt joining composite materials such as aluminum with fly ash which differ in

properties and sound welds with none or limited intermetallic compounds has been

produced.

Friction stir welding of composite materials remains not fully researched. Friction

stir welding of composite materials such as aluminum fly ash in particular need to be fully

understood due to their different melting temperatures. The high chemical affinity of both

base materials promotes the formation of brittle intermetallic Al/Cu phases, which still

require extensive research. Brittle intermetallic phases develop in the joint zone since fly

ash and aluminum are not very soluble in one another in the solid state. These

intermetallic phases lower the toughness of the weld and lead to cracks during and after the

welding.

Aluminum alloys are widely used to produce aerospace components with high

specific strength. However, researchers published that when traditional welding processes

are applied to these aluminum alloys, they often entail disadvantages that have sometimes

discourage the use of welded components.

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This work investigates about the microstructure and mechanical properties of

composite materials aluminum alloy 6063 and fly ash.

Friction stir welding(FSW) was invented at the welding institute (TWI) of UK in

1991 as a solid state joining technique. And it was initially applied to aluminium alloys.

The basic concept of FSW is remarkably simple. A non-consumable rotating tool with a

specially designed pin and shoulder is inserted into the abutting edges of sheets or plates to

be joined and traversed along the line of joint as shown in Fig.1.1. The tool serves two

primary functions: (a) heating of work piece, and (b) movement of material to procedure

the joint. The heating is accomplished by friction between the tool and the work piece and

plastic deformation of workpiece. The localized heating softens the material around the pin

and combination of tool rotation and translation leads to movement of material from the

front of the pin to the back of the pin. As a result of this process a joint is produced in

‘solid state’. Because of various geometrical features of the tool, the material movement

around the pin can be quite complex. During FSW process, the material undergoes intense

plastic deformation at elevated temperature, resulting in generation of fine and equiaxed

recrystallized grains. The fine microstructure in friction stir welds procedure good

mechanical properties.

FSW is considered to be the most significant development in metal joining in a

decade and is a “green” technology due to its energy efficiency, environment friendliness,

and versatility. As compared to the conventional welding methods, FSW consumes

considerably less energy. No cover gas or flux is used, thereby making the process

environmentally friendly. The joining does not involve any use of filler metal and therefore

any aluminium alloy can be joined without concern for the compatibility of composition,

which is an issue in fusion welding.

When desirable, composite aluminium alloys and composites can be joined with

equal easy. In contrast to the traditional friction welding, which is usually performed on

small axisymmetric parts that can be rotated and pushed against each other to form a joint,

FSW can be applied to various types of joints like butt joints, lap joints, T joints, and fillet

joints.

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Fig.1.1.Schematic drawing of friction stir welding

Ref: R.S.Mishra and Z.Y. Ma (2005)

1.2. PROCESS PARAMETERS

FSW involves complex material movement and plastic deformation. Welding

parameters, tool geometry, and joint design exert significant effect on the material flow

pattern and temperature distribution, thereby influencing the microstructural evolution of

material. In this section, a few major factors affecting FSW process, such as tool geometry,

welding parameters, joint design are addressed.

1.2.1.TOOL GEOMETRY

Tool geometry is the most influential aspect of process development. The tool

geometry plays a critical role in material flow and in turn governs the traverse rate at which

FSW can be conducted. An FSW tool consists of a shoulder and a pin as shown

schematically in Fig.1.2. As mentioned earlier, thetool has two primary functions: (a)

localized heating, and (b) material flow. In the initial stage of tool plunge, the heating

results primarily from the friction between pin and workpiece. The tool is plunged till the

shoulder touches the workpiece. The friction between the shoulder and workpiece results

in the biggest component ofheating. From the heating aspect, the relative size of pin and

shoulder is important, and the other design features are not critical. The shoulder also

provides confinement for the heated volume of material. The second function of the tool is

to ‘stir’ and ‘move’ the material. The uniformity of microstructureand properties as well as

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process loads is governed by the tool design. Generally a concave shoulder and threaded

cylindrical pins are used.

Fig.1.2. Types of FSW Tools

1.2.2.WELDING PARAMETERS

For FSW, two parameters are very important: tool rotation rate (v, rpm) in

clockwise or counter clockwise direction and tool traverse speed (n, mm/min) along the

line of joint. The rotation of tool results in stirring and mixing of material around the

rotating pin and the translation of tool moves the stirred material from the front to the back

of the pin and finishes welding process. Higher tool rotation rates generate higher

temperature because of higher friction heating and result in more intense stirring and

mixing of material as will be discussed later. However, it should be noted that frictional

coupling of tool surface with workpiece is going to govern the heating. So, a monotonic

increase in heating with increasing tool rotation rate is not expected as the coefficient of

friction at interface will change with increasing tool rotation rate.

In addition to the tool rotation rate and traverse speed, another important process

parameter is the angle of spindle or tool tilt with respect to the workpiece surface. A

suitable tilt of the spindle towards trailing direction ensures that the shoulder of the tool

holds the stirred material by threaded pin and move material efficiently from the front to

the back of the pin. Further, the insertion depth of pin into the workpieces (also called

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target depth) is important for producing sound welds with smooth tool shoulders. The

insertion depth of pin is associated with the pin height.

Table 1.1: Main process parameters in friction stir welding

Parameter Effects

Rotation speed Friction heat, stirring, oxide layer breaking and mixing

Welding speed Appearance, heat control

Down force Friction heat

When the insertion depth is too shallow, the shoulder of tool does not contact the

original workpiece surface. Thus, rotating shoulder cannot move the stirred material

efficiently from the front to the back of the pin, resulting in generation of welds with inner

channel or surface groove. When the insertion depth is too deep, the shoulder of tool

plunges into the workpiece creating excessive flash. In this case, a significantly concave

weld is produced, leading to local thinning of the welded plates. It should be noted that the

recent development of ‘scrolled’ tool shoulder allows FSW with 0º tool tilt. Such tools are

particularly preferred for curved joints.

1.3 COMPOSITES

A common example of a composite would be disc brake pads, which consist

of hard ceramic particles embedded in soft metal matrix. Another example is found

in shower stalls and bathtubs which are made of fiber. Imitation granite and cultured

marble sinks and countertops are also widely used. The most advanced examples

perform routinely on spacecraft in demanding environments.

1.3.1 CLASSIFICATION OF COMPOSITES

Composite materials are classified,

a) On the basis of matrix material.

b) On the basis of filler material.

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a) On the basis of Matrix:

1.3.2. Metal Matrix Composites (MMC)

Metal Matrix Composites are composed of a metallic matrix (aluminum,

magnesium, iron, cobalt, copper) and a dispersed ceramic (oxides, carbides) or

metallic (lead, tungsten, molybdenum) phase.

1.3.3. Ceramic Matrix Composites (CMC)

Ceramic Matrix Composites are composed of a ceramic matrix and

imbedded fibers of other ceramic material (dispersed phase).

1.3.4. Polymer Matrix Composites (PMC)

Polymer Matrix Composites are composed of a matrix from thermo set

(Unsaturated Polyester (UP), Epoxy) or thermoplastic (PVC, Nylon, Polystyrene)

and embedded glass, carbon, steel or Kevlar fibers (dispersed phase).

(b) On the basis of Material Structure

1.3.5. Particulate Composites

Particulate Composites consist of a matrix reinforced by a dispersed phase in

form of particles.

o Composites with random orientation of particles.

o Composites with preferred orientation of particles. Dispersed phase of these

materials consists of two-dimensional flat platelets (flakes), laid parallel to

each other.

1.3.6. Fibrous Composites

a. Short-fiber reinforced composites. Short-fiber reinforced composites consist of a

matrix reinforced by a dispersed phase in form of discontinuous fibers.

o Composites with random orientation of fibers.

o Composites with preferred orientation of fibers.

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b. Long-fiber reinforced composites. Long-fiber reinforced composites consist of a

matrix reinforced by a dispersed phase in form of continuous fibers.

o Unidirectional orientation of fibers.

o Bidirectional orientation of fibers (woven).

1.3.7. Laminate Composites

When a fiber reinforced composite consists of several layers with

different fiber orientations, it is called multilayer (angle-ply) composite.

1.4. METAL MATRIX COMPOSITES (MMC)

Metal composite materials have found application in many areas of daily life

for quite some time. Often it is not realized that the application makes use of

composite materials. Here, the Dalmatian sword with its meander structure, which

results from welding two types of steel by repeated forging, can be mentioned.

Materials like cast iron with graphite or steel with high carbide content, as well as

tungsten carbides, consisting of carbides and metallic binders, also belong to this

group of composite materials. For many researchers the term metal matrix

composites is often equated with the term light metal matrix composites (MMCs).

Substantial progress in the development of light metal matrix composites has been

achieved in recent decades, so that they could be introduced into the most important

applications. In traffic engineering, especially in the automotive industry, MMCs

have been used commercially in fiber reinforced pistons and aluminum crank cases

with strengthened cylinder surfaces as well as particle-strengthened brake disks.

These innovative materials open up unlimited possibilities for modern

material science and development; the characteristics of MMCs can be designed

into the material, custom-made, dependent on the application. From this potential,

metal matrix composites fulfill all the desired conceptions of the designer. This

material group becomes interesting for use as constructional and functional

materials, if the property profile of conventional materials either does not reach the

increased standards of specific demands, or is the solution of the problem. However,

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the technology of MMCs is in competition with other modern material technologies,

for example powder metallurgy. The advantages of the composite materials are only

realized when there is a reasonable cost – performance relationship in the

component production. The use of a composite material is obligatory if a special

property profile can only be achieved by application of these materials.

Compared to monolithic metals, MMCs have:

o Higher strength-to-density ratios

o Higher stiffness-to-density ratios

o Better fatigue resistance

o Better elevated temperature properties

o Higher strength

o Lower creep rate

o Lower coefficients of thermal expansion

o Better wear resistance

The advantages of MMCs over polymer matrix composites are:

o Higher temperature capability

o Fire resistance

o Higher transverse stiffness and strength

o No moisture absorption

o Higher electrical and thermal conductivities

o Better radiation resistance

o No out gassing

o Fabric ability of whisker and particulate-reinforced MMCs with conventional

metalworking equipment.

Some of the disadvantages of MMCs compared to monolithic metals and polymer

matrix composites are:

o Higher cost of some material systems

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o Relatively immature technology

o Complex fabrication methods for fiber-reinforced systems (except for

casting)

o Limited service experience

Numerous combinations of matrices and reinforcements have been tried

since work on MMC began in the late 1950s. However, MMC technology is still in

the early stages of development, and other important systems undoubtedly will

emerge. Numerous metals have been used as matrices. The most important have

been aluminum, titanium, magnesium, reinforced with fly ash alloys and super

alloys.

1.5. IMPORTANT MMC SYSTEMS

• Aluminum matrix

Continuous fibers: boron, silicon carbide, alumina, graphite

Discontinuous fibers: alumina, alumina-silica

Whiskers: silicon carbide

Particulates: silicon carbide, boron carbide

• Magnesium matrix

Continuous fibers: graphite, alumina

Whiskers: silicon carbide

Particulates: silicon carbide, boron carbide

• Titanium matrix

Continuous fibers: silicon carbide, coated boron

Particulates: titanium carbide

• Copper matrix

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Continuous fibers: graphite, silicon carbide

Wires: niobium-titanium, niobium-tin

Particulates: silicon carbide, boron carbide, titanium carbide.

• Super alloy matrices

Wires: tungsten

The possibility of combining various material systems (metal – ceramic –

nonmetal) gives the opportunity for unlimited variation. The properties of these new

materials are basically determined by the properties of their single components.

The reinforcement of metals can have many different objectives. The

reinforcement of light metals opens up the possibility of application of these

materials in areas where weight reduction has first priority. The precondition here is

the improvement of the component properties. The development objectives for light

metal composite materials are

• Increase in yield strength and tensile strength at room temperature and above

while maintaining the minimum ductility or rather toughness,

• Increase in creep resistance at higher temperatures compared to that of

conventional alloys,

• Increase in fatigue strength, especially at higher temperatures,

• Improvement of thermal shock resistance,

• Improvement of corrosion resistance,

• Increase in Young’s modulus,

• Reduction of thermal elongation.

To summarize, an improvement in the weight specific properties can result,

offering the possibilities of extending the application area, substitution of common

materials and optimization of component properties. With functional materials there

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is another objective, the precondition of maintaining the appropriate function of the

material. Objectives are for example:

• Increase in strength of conducting materials while maintaining the high

conductivity,

• Improvement in low temperature creep resistance (reaction less materials),

• Improvement of burnout behavior (switching contact),

• Improvement of wear behavior (sliding contact),

• Increase in operating time of spot welding electrodes by reduction of burn outs,

• Production of layer composite materials for electronic components,

• Production of ductile composite superconductors,

• Production of magnetic materials with special properties.

For other applications different development objectives are given,

which differ from those mentioned before. For example, in medical technology,

mechanical properties, like extreme corrosion resistance and low degradation as

well as biocompatibility are expected.

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Fig.1.3 Development curve of the market for modern material

Although increasing development activities have led to system solutions

using metal composite materials, the use of especially innovative systems,

particularly in the area of light metals, has not been realized. The reason for this is

insufficient process stability and reliability, combined with production and

processing problems and inadequate economic efficiency.

Application areas, like traffic engineering, are very cost orientated and

conservative and the industry is not willing to pay additional costs for the use of

such materials. For all these reasons metal matrix composites are only at the

beginning of the evolution curve of modern materials.

Fig. 1.4 Classification of the composite materials within the group of materials

1.6. METAL MATRIX COMPOSITES CLASSIFICATION

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Metal matrix composites can be classified in various ways as shown in fig

1.5. One classification is the consideration of type and contribution of reinforcement

components in particle-, layer-, fiber- and penetration composite materials. Fiber

composite materials can be further classified into continuous fiber composite

materials (multi- and monofilament) and short fibers or, rather, whisker composite

materials.

Fig. 1.5 Classification of the composite materials within the group of materials.

1.7. REINFORCEMENTS

Reinforcements for metal matrix composites have a manifold demand

profile, which is determined by production and processing and by the matrix system

of the composite material. The following demands are generally applicable low

density,

• Mechanical compatibility (a thermal expansion coefficient which is low but

adapted to the matrix),

• Chemical compatibility,

• Thermal stability,

• High Young’s modulus,

• High compression and tensile strength,

• Good processability,

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• Economic efficiency.

These demands can be achieved only by using non-metal inorganic

reinforcement components. For metal reinforcement ceramic particles or, rather,

fibers or carbon fibers are often used. Due to the high density and the affinity to

reaction with the matrix alloy the use of metallic fiber usual fails. Which

components are finally used, depends on the selected matrix and on the demand

profile of the intended application. Every reinforcement has a typical profile, which

is significant for the effect within the composite material and the resulting profile.

The group of discontinuous reinforced metals offers the best conditions for reaching

development targets; the applied production technologies and reinforcement

components, like short fibers, particle and whiskers, are cost effective and the

production of units in large item numbers is possible. The relatively high isotropy of

the properties in comparison to the long-fiber continuous reinforced light metals and

the possibility of processing of composites by forming and cutting production

engineering are further advantages.

1.8. STRENGTHENING MECHANISM OF COMPOSITES

The strengthening mechanisms of the composites are different with different

kind of reinforcing agent morphology such as fibers, particulate or dispersed type of

reinforcing elements.

1.8.1. STRENGTHENING MECHANISM OF FIBER REINFORCED

COMPOSITE

In such type of composite the reinforcing phase carries the bulk of the load

and the matrix transfers the load to the reinforcing phase by the mechanism of seam.

The high strength of the reinforcing phase restrict the free elongation of the matrix

especially in its vicinity, whereas later is free to elongate at some distance away

from the former.

This type of non uniform deformation of the matrix leads to a shear stress at

the matrix reinforcement interface which results tensile stress at the reinforcing

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phase. Thus the stress is transferred to the reinforcing phase. The fibers either may

be continuous or discontinuous in the matrix. In the former case the load is directly

applied to the reinforcing phase and stress is constant over its entire length. In case

of discontinuous fibers, the stress in the fiber increased from zero value at the end to

a maximum value in the centre and thus average tensile strength developed is

always less than those of continuous fibers. For the same when the fracture of the

reinforcing phase, therefore the strength of the discontinuous fiber reinforced

composite increases with increasing the length of the fiber and artifacts that of the

continuous fiber reinforced one. Also the strength of the fiber reinforced composite

will be maximum when the fibers are aligned in the direction of the applied stress

i.e. in the isostrain condition. So the strength of this kind of composite depends on

the volume fraction of the reinforcing element present in the composite, which can

be determined by the simple rule of mixtures.

1.8.2. DISPERSION STRENGTHENING MECHANISM OF

STRENGTHENED COMPOSITE

In the dispersion strengthened composite the second phase reinforcing agents

are finely dispersed in the soft ductile matrix. The strong particles restrict the

motion of dislocations and strengthen the matrix. Here the main reinforcing

philosophy is by the strengthening of the matrix by the dislocation loop formation

around the dispersed particles. Thus the further movement of dislocations around

the particles is difficult.

Degree of strengthening depend upon the several factors like volume % of

dispersed phase, degree of dispersion, size and shape of the dispersed phase, inter

particle spacing etc. In this kind of composite the load is mainly carried out by the

matrix materials.

1.8.3. STRENGTHENING MECHANISM OF PARTICULATE COMPOSITE

In the particulate reinforced composite the size of the particulate is more than

1 μm, so it strengthens the composite in two ways. First one is the particulate carry

the load along with the matrix materials and another way is by formation of

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incoherent interface between the particles and the matrix. So a larger number of

dislocations are generated at the interface, thus material gets strengthened. The

degree of strengthening depends on the amount of particulate (volume fraction),

distribution, size and shape of the particulate etc.

1.9. FLY ASH

Fly ash is one of the residues generated in the combustion of coal. It is an

industrial by-product recovered from the flue gas of coal burning electric power

plants. Depending upon the source and makeup of the coal being burned, the

components of the fly ash produced vary considerably, but all fly ash includes

substantial amounts of silica (silicon dioxide, SiO2) (both amorphous and

crystalline) and lime (calcium oxide, CaO). In general, fly ash consists of SiO2,

Al2O3, and Fe2O3 as major constituents and oxides of Mg, Ca, Na, K etc., as minor

constituent. Fly ash particles are mostly spherical in shape and range from less than

1 μm to 100 μm with a specific surface area, typically between 250 and 600 m2/kg.

The specific gravity of fly ash vary in the range of 0.6-2.8 gm/cc. Physical

properties of fly ash mainly depend on the type of coal burned and the burning

conditions. Class F fly ash is generally produced from burning high rank

(containing high carbon content) coals such as anthracite and bituminous coals,

whereas, Class C fly ash is produced from low rank coals.

Fly ash particles are classified into two types, precipitator and cenosphere.

Generally, the solid spherical particles of fly ash are called precipitator fly ash and

the hollow particles of fly ash with density less than 1.0 g cm-3 are called

cenosphere fly ash. One common type of fly ash is generally composed of the

crystalline compounds such as quartz, mullite and hematite, glassy compound such

as silica glass, and other oxides. The precipitator fly ash, which has a density in the

range 2.0–2.5 g cm-3 can improve various properties of selected matrix materials,

including stiffness, strength, and wear resistance and reduce the density. Coal fly

ash has many uses including as a cement additive, in masonry blocks, as a concrete

admixture, as a material in lightweight alloys, as a concrete aggregate, in flow able

fill materials, in roadway/runway construction, in structural fill materials, as roofing

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granules, and in grouting. The largest application of fly ash is in the cement and

concrete industry, though, creative new uses for fly ash are being actively sought

like use of fly ash for the fabrication of MMCs.

Fly ash material solidifies while suspended in the exhaust gases and is

collected by electrostatic precipitators or filter bags. Since the particles solidify

while suspended in the exhaust gases, fly ash particles are generally spherical in

shape and range in size from 1 μm to 100 μm. They consist mostly of silicon

dioxide (SiO2), which is present in two forms: amorphous, which is rounded and

smooth, and crystalline, which is sharp, pointed and hazardous; aluminum oxide

(Al2O3) and iron oxide (Fe2O3). Fly ashes are generally highly heterogeneous,

consisting of a mixture of glassy particles with various identifiable crystalline

phases such as quartz, mullite, and various iron oxides.

ON THE BASIS OF CHEMICAL COMPOSITION

Two classes of fly ash are defined by ASTM C618: Class F fly ash and Class

C fly ash. The chief difference between these classes is the amount of calcium,

silica, alumina, and iron content in the ash. The chemical properties of the fly ash

are largely influenced by the chemical content of the coal burned

(anthracite, bituminous, and lignite)

Class F fly ash

The burning of harder, older anthracite and bituminous coal typically

produces Class F fly ash. This fly ash is pozzolanic in nature, and contains less than

20% lime (CaO). Possessing pozzolanic properties, the glassy silica and alumina of

Class F fly ash requires a cementing agent, such as Portland cement, quicklime, or

hydrated lime, with the presence of water in order to react and produce

cementations compounds. Alternatively, the addition of a chemical activator such

as sodium silicate (water glass) to a Class F ash can lead to the formation of

a geopolymers.

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Class C fly ash

Fly ash produced from the burning of younger lignite or sub bituminous coal,

in addition to having pozzolanic properties, also has some self-cementing

properties. In the presence of water, Class C fly ash will harden and gain strength

over time. Class C fly ash generally contains more than 20% lime (CaO). Unlike

Class F, self-cementing Class C fly ash does not require an activator. Alkali

and sulfate (SO4) contents are generally higher in Class C fly ashes.

ON THE BASIS OF SIZE, SHAPE AND STRUCTURE:

Precipitator fly ash

It is spherical in nature, the spheres are solid and the density is in the range of 2.0–

2.5 g cm-3.

Cenosphere fly ash

It is also spherical in shape but these spheres are hollow, so the density of this kind

of fly ash is very less as compared to the precipitator fly ash. Here density is less

than 1 gm cm3 (0.3-0.6 gm/cc)

1.10. FLY ASH REUSE

The ways of fly ash utilization include (approximately in order of decreasing

importance)

o Concrete production, as a substitute material for Portland cement and sand

o Embankments and other structural fills (usually for road construction)

o Grout and Flowable fill production

o Waste stabilization and solidification

o Cement clinkers production - (as a substitute material for clay)

o Mine reclamation

o Stabilization of soft soils

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o Road sub base construction

o As Aggregate substitute material (e.g. for brick production)

o Mineral filler in asphaltic concrete

o Agricultural uses: soil amendment, fertilizer, cattle feeders, soil stabilization

in stock feed yards, and agricultural stakes

o Loose application on rivers to melt ice

o Loose application on roads and parking lots for ice control

Other applications include cosmetics, toothpaste, kitchen counter tops, floor and

ceiling tiles, bowling balls, flotation devices, stucco, utensils, tool handles, picture

frames, auto bodies and boat hulls, cellular concrete, geopolymers, roofing tiles,

roofing granules, decking, fireplace mantles, cinder block, PVC pipe, Structural

Insulated Panels, house siding and trim, running tracks, blasting grit, recycled

plastic lumber, utility poles and cross arms, railway sleepers, highway sound

barriers, marine pilings, doors, window frames, scaffolding, sign posts, crypts,

columns, railroad ties, vinyl flooring, paving stones, shower stalls, garage doors,

park benches, landscape timbers, planters, pallet blocks, molding, mail boxes,

artificial reef, binding agent, paints and under coatings, metal castings, and filler in

wood and plastic products.

1.11.STIR CASTING PROCESSStir casting is one of the simplest ways of producing aluminum matrix composites.

However, it suffers from poor incorporation and distribution of the reinforcement. particles

in the matrix. These problems become especially significant as the reinforcement size

decreases due to greater agglomeration tendency and reduced wettability of the particles

with the melt.

The particulate reinforcement aluminium metal matrix composite (PRAMMC) selected

for the present investigation was based on AL-Mg matrix alloy, designated by the

aluminium association as Al-6063. This matrix alloy was chosen since it provides excellent

combination of strength and damage tolerance at elevated and cryogenic temperatures.

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Fig1.6 Stir casting process

A stir casting setup, Consisted of a resistance Muffle Furnace and a stainless Steel

stirrer assembly, was used to synthesize the composite. The stirrer assembly consisted of a

stirrer, which was connected to a variable speed vertical drilling machine with range of 80

to 890 rpm by means of a steel shaft. The stirrer was made by cutting and shaping a

Stainless Steel block to desired shape and size manually. The stirrer consisted of three

blades at an angle of 120° apart. Clay graphite crucible of 1.5 Kg capacity was placed

inside the furnace. The graphical representation of stir casting was shown in Fig.

1.12. MICROSTRUCTURAL EVOLUTION

The contribution of intense plastic deformation and high-temperature exposure

within the stirredzone during FSW results in recrystallization and development of texture

within the stirred zone and precipitate dissolution and coarsening within and around the

stirredzone. Based on microstructural characterization of grains and precipitates,

threedistinct zones, stirred (nugget) zone, thermo-mechanically affected zone (TMAZ), and

heat-affectedzone (HAZ), have been identified as shown in Fig.1.7. The microstructural

changes in various zones have significant effect on postweld mechanical properties.

Therefore, the microstructural evolution during FSW has been studied by a number of

investigators.

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Fig.1.7. A typical macrograph showing various microstructural zones

Ref: R.S. Mishra and Z.Y. Ma (2005)

1.12.1. NUGGET ZONE

Intense plastic deformation and frictional heating during FSW/FSP result in

generation of are crystallized fine-grained microstructure within stirred zone. This region is

usually referred to as nugget zone (or weld nugget) or dynamically recrystallized zone

(DXZ). Under some FSW/FSP conditions, onion ring structure was observed in the nugget

zone as shown in Fig.1.5. In the interior of the recrystallized grains, usually there is low

dislocation density. However, some investigators reported that the small recrystallized

grains of the nugget zone contain high density of sub-boundaries, subgrains, and

dislocations. The interface between the recrystallized nugget zone and the parent metal is

relatively diffuse on the retreating side of the tool, but quite sharp on the advancing side of

the tool.

1.12.2. THERMO-MECHANICALLY AFFECTED ZONE

Unique to the FSW/FSP process is the creation of a transition zone—thermo-

mechanicallyaffected zone (TMAZ) between the parent material and the nugget zone, as

shown in Fig.1.5.The TMAZ experiences both temperature and deformation during

FSW/FSP. The TMAZ is characterized by a highly deformed structure. The parentmetal

elongated grains were deformed in an upward flowing pattern around the nugget zone.

Althoughthe TMAZ underwent plastic deformation, recrystallization did not occur in this

zone due toinsufficient deformation strain. The extent ofdissolution, of course, depends on

the thermal cycle experienced by TMAZ. Furthermore, it wasrevealed that the grains in the

TMAZ usually contain a high density of sub-boundaries.

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1.12.3. HEAT-AFFECTED ZONE

Beyond the TMAZ there is a heat-affected zone (HAZ). This zone experiences a

thermal cycle,but does not undergo any plastic deformation. Some researchers defined the

HAZ as a zoneexperiencing a temperature rise above 250 8C for a heat-treatable aluminum

alloy. The HAZ retains the same grain structure as the parent material. However, the

thermal exposure above 250 8C exerts asignificant effect on the precipitate

structure.Recently, in one research they have investigated the effect of friction stir welding

on microstructure of7050Al-T7451 aluminum alloy. They reported that while FSW process

has relatively little effect onthe size of the subgrains in the HAZ, it results in coarsening of

the strengthening precipitates and thePrecipitate-free zone (PFZ) increases by a factor of 5.

1.13. KEY BENEFITS OF FRICTION STIR WELDING

1.13.1. METALLURGICAL BENEFITS

i. Solid phase process

ii. Low distortion of work piece

iii. Good dimensional stability and repeatability

iv. No loss of alloying elements

v. Excellent metallurgical properties in the joint area

vi. Fine microstructure

vii. Absence of cracking

viii. Replace multiple parts joined by fasteners

1.13.2. ENVIRONMENTAL BENEFITS

i. No shielding gas required

ii. No surface cleaning required

iii. Eliminate grinding wastes

iv. Eliminate solventsrequired for degreasing

v. Consumable materials saving,such as rugs, wire orany other gases

22

1.13.3. ENERGY BENEFITS

i. Improved materials use (e.g., joining different thickness) allows reduction in

weight

ii. Only 2.5% of the energy needed for a laser weld

iii. Decreased fuel consumption in light weight aircraft, automotive and ship

applications

1.14. APPLICATIONS

1.14.1.AEROSPACE

i. Space industry

ii. Civil aviation

iii. Aerospace R&D

1.14.2. SHIPBUILDING

i. Application advances

ii. Parts and components

1.14.3. AUTOMOTIVE INDUSTRY

i. Automotive applications

ii. Tailor welded blanks (TWB´s)

iii. Superplastic forming

1.14.4. OTHERAPPLICATIONS

Aluminum to copper welding is increasinglyused in some practical applications:

i. Heat transfer equipment

ii. Wiring

iii. Electrical and electronics industries

iv. Aesthetical applications

23

1.15. MATERIAL COMPOSITION AND PROPERTIES

In this project the composite materials such as aluminium 6063 reinforced with fly

ash are going to be welded through the friction stir welding. The metal composition of

AA6063 and fly ash is given in the following Table 1.2 and 1.3

Table 1.2: Material composition of 6063 aluminium alloy

Materials Chemical composition (in wt%)

Magnesium 0.47%

Manganese 0.012%

Zinc 0.005%

Ferrous 0.16%

Copper 0.018%

Silicon 0.47%

Chromium 0.006%

Aluminium Balance %

Table 1.3: Chemical composition of fly ash

Component Bituminous Sub bituminous Lignite

SiO2 (%) 20-60 40-60 15-45

Al2O3 (%) 5-35 20-30 20-25

Fe2O3 (%) 10-40 4-10 4-15

CaO (%) 1-12 5-30 15-40

LOI (%) 0-15 0-3 0-5

24

1.16.EXPERIMENTAL PROCEDURE

Aluminium 6063 and fly ash is reinforced by using stir casting process. The

friction stir welding is done after this process. The Fly Ash (F.A) particles which were

used to fabricate the composite have average particle size of less than 40μm and average

density of 2.5 mg/m3 the F.A particle reinforcement varied from 5 to 15 wt pct. The

nominal chemical composition (in wt pct) of the matrix alloy is in table

Metal matrix composite (MMC) is a material composed of two or more distinct phases

(matrix phase and reinforcing phase) and having bulk properties significantly different

from those of any of the constituents. In the present work MMC of aluminium 6063

reinforced with fly ash particles is fabricated by using stir casting process. Tensile strength

and Rockwell hardness of fabricated samples is observed by Rockwell hardness tester and

Universal testing machine. Effect of varying temperature, composition of fly ash and

stirring speed on these properties is studied. In the first phase number of experiments were

reduced to be 3. Present study includes maximization of hardness as objective function and

fatigue strength as a constraint for fly ash based composites. The value of hardness found

to be maximum for the 9% fly ash composition at 720ºC at 650 rpm. It is to be mentioned

that even though hardness value found to be maximum for 9% but due to substantial

reduction in fatigue strength fly ash composition of near about 9% at 720ºC with 650rpm

stirring speed is not recommended for fabrication.

The material used in this investigation was AA6063 reinforced with ash fly. The

chemical compositions of both metals are presented in Table 1.2 and Table 1.3.The rolled

plates of 6 mm thickness were machined to the required size (100 mm X 50 mm) welding

was carried out in butt joint configuration using friction stir welding machine.

The welding parameters such as tool rotational speed, welding speed and axial

force taken into account showed in Fig.1.8.

The welding direction was aligned normal to the rolling direction; the welded joints

were machined to the required dimensions to test the Microstructure and Micro hardness.

Rockwell micro hardness tester was used to measure the micro hardness of welded

samples. The hardness were measured along the transverse direction of the weld in centre.

25

Fig.1.8. Process Parameters taken into account such as translational speed, traverse speed,

downward force

Ref: G. Elatharasan and V.S. Senthil Kumar (2013)

Fig.1.9. Geometry of the tool used in the present study

NOMENCLATURE

a -- TOOL PIN (DIAMETER 5mm, LENGTH 5.8mm)

b -- SHOULDER (DIAMETER 18mm, LENGTH 10mm)

c -- SHANK (DIAMETER 25mm, LENGTH 25mm)

d -- SHANK (DIAMETER 20mm, LENGTH 25mm)

26

Fig.1.9. Friction Stir Welding equipment

Fig.1.8. Friction Stir Welding Machine

1.10Friction stir welding Machine

Table 1.4:Friction stir welding machine specifications

Spindle ISO 40

Spindle motor 11 kW/440 V (AC drive)

Spindle Speed 800 to 3000 RPM

Z axis stroke(Auto) length 300 mm

Z axis stroke(manual-hand wheel) length 25 mm

Z axis rapid traverse 2000 mm/min

Z axis cylinder dimensions 100 x 300 mm (Hydraulic operated)

X axis stroke length 600 mm

X axis feed 0 to 500 mm/min

X axis rapid traverse 5000 mm/ min

X axis cylinder 80 x 600 mm (Hydraulic operated)

Y axis stroke (manual – hand wheel) 200 mm

27

‘T’ slot 18 x 3 mm

Hydraulic power pack motor 2. 2 kW / 440 V

Lubrication Centralized lubrication

Tool holder ISO 40 Arbor

FSW PROCESS PARAMETERS:

Materials : Aluminium 6063 Reinforced with Fly ash

Work piece size : 100 x 50 x 6 mm

Tool : High chromium High Carbon Hardened tool

Tool Size : Shoulder Diameter (D) = 18 mm

: Pin Diameter (d) = 6 mm

: Pin Length (l) = 5.7 mm

Table 1.5: Welding parameters – Rotational speed, Traverse speed, and Axial loads

Axial Load (KN)

Traverse speed (mm/min)

Rotational speed (rpm)

10 KN 60 1300

From the table, Load and traverse speed and Rotational speed are constant.

In this study, we are going to keep all these welding parameters constant. The

variation will be in the weight percentage of fly ash to the aluminium samples. The initial

stage AA6063 and fly ash will be combined using stir casting process. The percentage of

fly ash will be varied with a number of samples and they are being tested fot tensile ,

Hardness and micro structure tests after friction stir welding.

28

CHAPTER 2

LITERATURE SURVEY

G. Elatharasan, and V.S. Senthil Kumar (2013) [1]central composite design technique

and mathematical model was developed by response surface methodology with three

parameters, three levels and 20 runs, was used to develop the relationship between the

FSW parameters (rotational speed, traverse speed, axial force,) and the responses (tensile

strength, Yield strength (YS) and %Elongation (%E) were established. They have

concluded that UTS and YS of the FS welded joints increased with the increase of tool

rotational speed, welding speedand tool axial force up to a maximum value, and then

decreased. And also TE of joints increased with increase of rotational speed and axial

force, but decreased by increasing of welding speed, continuously.

M. Koilraj, et, al., (2012) [2] were optimized friction stir welding process parameters with

respect to tensile strength of the joint and the optimum level of settings were found out.

The optimum levels of the rotational speed, transverse speed, and D/d ratio are 700 rpm, 15

mm/min and 3 respectively. The cylindrical threaded pin tool profile was found to be the

best among the other tool profiles considered. The D/d ratio plays a vital role and

contributes 60% to the overall contribution. Friction stir welding can produce satisfactory

butt welds between AA2219-T87and AA5083-H321 sheets with a joint efficiency of

around 90% (based on alloy AA5083). For this specific material combination, failures

occur in the heat-affected zone of alloy 5083.

S. Rajakumar and V. Balasubramanian (2012) [3]investigated FSW joints on six

different grades of aluminum alloys (AA1100, AA2219, AA2024, AA6061, AA7039,

andAA7075) using different levels of process parameters. Macro structural analysis was

carried out to identify the feasible working range of process parameters. The optimal

welding conditions to attain maximum strength for each alloy were identified using

Response Surface Methodology (RSM). Empirical relationships were established between

the base metal mechanical properties of aluminum alloys and optimized FSW process

parameters. These relationships can be effectively used to predict the optimized FSW

29

process parameters from the known base metal properties such as yield strength,

elongation and hardness.

R.S. Mishra and Z.Y. Ma (2005) [4] have revived that Friction stir welding (FSW) is a

relatively new solid-state joining process. This joining technique is energy efficient,

environment friendly, and versatile. In particular, it can be used to join high-strength

aerospace aluminium alloys and other metallic alloys that are hard to weld by conventional

fusion welding. FSWis considered to be the mostsignificant development in metal joining

in a decade. Recently, friction stir processing (FSP) was developed for microstructural

modification of metallic materials. In this review article, the current state of understanding

and development of the FSW and FSP are addressed. Particular emphasis has been given

to: (a) mechanisms responsible for the formation of welds and microstructural refinement,

and (b) effects of FSW/FSP parameters on resultant microstructure and final mechanical

properties. While the bulk of the information is related to aluminium alloys, important

results are now available for other metals and alloys. At this stage, the technology diffusion

has significantly outpaced the fundamental understanding of microstructural evolution and

microstructure–property relationships.

M.H.Shojaeefard, et, al.,(2013) [5]conducted research on Al–Mg and CuZn34 alloys were

lap joined using friction stir welding during which the aluminum alloy sheet was placed on

the CuZn34 and the process parameters were optimized using Taguchi L9 orthogonal

design of experiments. The rotational speed, tool tilt angle and traverse speed were

theparameters taken into consideration. The optimum process parameters were determined

with reference to tensile shear strength of the joint. The predicted optimal value of tensile

strength was confirmed by conducting the confirmation run using optimum parameters.

Analysis of variance showed that rotational speed is the most dominant factor in deciding

the joint soundness. Optical microscopy and scanning electron microscopy (SEM) analysis

were used to probe the microstructures and chemical compositions.

30

J. Gandra, et, al., (2013) [6]addressed the deposition of AA 6082-T6 coatings on AA

2024-T3 substrates, while focusing on the effect of process parameters, such as, axial

force, rotation and travel speed. Sound aluminium coatings were produced with limited

intermetallic formation at bonding interface. It was observed that low travel and rotation

speeds contribute to an increase of coating thickness and width. Bonding at coating edges

deteriorates for faster travel speeds. The axial force is determinant in achieving a fully

bonded interface.

M. Ghosh, et, al., (2010) [7] were friction stir welded A356 and 6061 aluminum alloys

under tool rotational speed of 1000–1400 rpm and traversing speed of 80–240 mm/min,

keeping other parameters same. Structural characterization of the bonded assemblies

exhibits recovery recrystallization in the stirring zone and breaking of coarse eutectic

network of Al–Si. Dispersion of fine Si rich particles, refinement of 6061 grain size, low

residual stress level and high defect density within weld nugget contribute towards the

improvement in bond strength. Lower will be the tool rotational and traversing speed, more

dominant will be the above phenomena. Therefore, the joint fabricated usinglowest tool

traversing and rotational speed, exhibits substantial improvement in bond strength (_98%

of that of 6061 alloy), which is also maximum with respect to others.

R. Palanivel, et, al., (2012) [8] developed an empirical relationship between FSW process

parameters to predict wear resistance of friction stir welded composite aluminium alloys.

Four factors, five levels central composite rotatable design has been used to minimise the

number of experiments. The working range of optimized welded parameters for good

quality FS welded joints of composite aluminium alloys AA5083H111-AA6351T6 was

found.

L. Dubourg, et, al., (2010) [9]were investigated the effects of process parameterson weld

quality of 1.5-mm 7075-T6 stringers lap-joined on 2.3-mm 2024-T3 skins. Weld quality

was assessed by optical microscopy and bending tests. It was found that: (i) the increase of

the welding speed or the decrease of the rotational speed resulted in a reduction of the

hooking size and top plate thinning but did not eliminated them, (ii) double pass welds by

overlapping the advancing sides improved significantly the weld quality by overriding the

hooking defect, and (iii) change of the rotational direction for a counter clockwise with a

left-threaded probe eliminated the top sheet thinning defect. S–N curves, bending

31

behaviour, failure locations and defect characterisation are also discussed. It was found

that: (i) the tensile strength of FSW joints approached that of the base material but with a

significant reduction in the fatigue life, (ii) the probe plunge and removal locations served

as the key crack nucleation sites in specimens with discontinuous welds, and (iii) double

pass welds with overlapping advancing sides showed outstanding fatigue life and very

good tensile properties.

Y. Javadi, et, al., (2014) [10]optimized residual stresses produced by friction stir welding

(FSW) of 5086 aluminum plates and concluded that The peak of longitudinal residual

stress is occurred in the advancing side (AS) of FSW. 1) The position of peak couldbe

accurately determined by employing the LCR ultrasonic method. 2). The most significant

effect on the longitudinal residual stress peak is related to the feed rate (in comparison with

the other process parameters of FSW). 3) After the feed rate, the rotational speed has

considerable effect on the residual stress peak. 4) The pin and shoulder diameter of FSW

tool has no dominant effect on the longitudinal residual stress peak.

P. Cavaliere, et, al., (2006) [11]was studied the microstructural and mechanical behaviour

of 6056 aluminumalloy Friction Stir Welded by using three different welding speeds (40,

56 and 80 mm/min) and three different tool rotation speeds (1000, 800 and 500 rpm). All

the forces on the tool and the welded material were recorded. The tensile tests performed at

room temperature showed that the material ductility reaches the highest values for 40 and

56 mm/min welding speed and the lowest rotating speed (500 rpm), decreasing strongly as

increasing the rotating speed and the welding speed. The highest tensile strength is reached

in correspondence of the higher rotating speeds (800 and 1000 rpm) for the highest

welding speed used in the present analysis (80 mm/min). The fatigue endurance curves

showed very different response of the material as a function of the different processing

parameters. The plots of the micro hardness (Hv1) versus distance from the weld centre

appear very uniform for the material joined using the lowest rotating speed (500 rpm) and

the lowest welding speeds, in particular for 40 and 56 mm/min.

M.P. Mubiayi and E.T. Akinlabi(2013) [12] reviewed that the friction stir welding of

compositematerials focusing on aluminium reinforced with fly ash has been successfully

conducted. This will provide a comprehensive insight for the current and also provide the

current state of research on FSW between aluminium reinforced with fly ash in order to fill

32

the gaps with new researchapproaches and ideas. Furthermore, new studies on FSW

between aluminium reinforced with fly ash with respect to the process optimization and

selection of cost effective FSW tools to producesound welds still needs to be developed.

Thus, the use of the FSW technique to join aluminium reinforced with fly ash alloys and

material shapes is of importance in the development of their industrial applications.

H. Barekatain,et, al., (2013) [13]conducted friction stir welding between composite

metals AA 1050 aluminum alloy and commercially pure copper. The annealed and

severely plastic deformed sheets were subjected to friction stir welding (FSW) at different

rotation and traverse speeds. Cu was placed in advancing side. Constant offset of

approximately 1 mm was used toward Al side for all welds. A range of welding parameters

which can lead to acceptable welds with appropriate mechanical properties was found. For

the FSWedCGPed samples, it was observed that the welding heat input caused grain

growth and decrease in hardness value at Al side of the stir zone. It was found that,

generally the weakest parts of weld joints of annealed and CGPed samples were Al base

metal and stir zone, respectively. Further investigations showed that several forms of

intermetallic compounds were produced.

R. Beygi, et, al., (2012) [14]studied butt joining of Al−Cu bilayer sheet produced by cold

roll bonding through friction stir welding (FSW). Adefect free joint was obtained. Flow

patterns and mixing of two layers during FSW were investigated. Microstructural

investigations and hardness profile measurements were carried out. It is shown that

material flow in stir zone leads to the formation of banding structure in Cu layer at

advancing side. Traces of Al particles along with Al−Cu intermetallic compounds exist in

the fined grain region of this banding structure which leads to higher hardness values.

H. Bisadi, et, al., (2013) [15]used FSW to join sheets of AA5083 aluminum alloy and

commercially pure copper and the effects of process parametersincluding rotational and

welding speeds on the microstructures and mechanical properties of the joints were

investigated and different joint defects were analyzed. The experiments were performed

with rotational speeds of 600, 825, 1115 and 1550 rpm each of them with welding speeds

of 15 and 32 mm/ min. It was observed that very low or high welding temperatures lead to

many joint defects. Also intermetallic compounds and their effects on the mechanical

33

properties of the joints were investigated. The best joint tensile shear properties were

achieved at the rotational speed of 825 rpm and welding speed\ of 32 mm/min.

P. Xue, et, al., (2011) [16]produced butt joints of 1060 aluminum alloy and commercially

pure copper by friction stir welding (FSW) and the effect of welding parameters on surface

morphology, interface microstructure and mechanical properties was investigated. The

experimental results revealed that sound defect-free joints could be obtained under larger

pin offsets when the hard Cu plate was fixed at the advancing side. Good tensile properties

were achieved at higher rotation rates and proper pin offsets of 2 and 2.5mm; further, the

joint produced at 600rpm with a pin offset of 2mm could be bended to 180◦ without

fracture.The mechanical properties of the FSW Al–Cu joints were related closely to the

interface microstructure between the Al matrix and Cu bulk. A thin, uniform and

continuous intermetallic compound (IMC) layer at the Al–Cu butted interface was

necessary for achieving sound FSW Al–Cu joints. Stacking layered structure developed at

the Al–Cu interface under higher rotation rates, and crack initiated easily in this case,

resulting in the poor mechanical properties.

J. Ouyang, et, al., (2006) [17]concentrated on the temperature distribution and

microstructural evolution of the friction stir welding of 6061 aluminum alloy(T6-temper

condition) to copper. The mechanically mixed region in the joining of the composite

metals 6061 aluminum alloy reinforced with fly ash weld consists mainly of several

intermetallic compounds such as CuAl2, CuAl, and Cu9Al4 together with small amounts

of alpha-Al and the saturated solid solution of Al in Cu. Distributed at the bottom of the

weld nugget are numerous deformed copper lamellae with a high solid-solubility of

aluminum. The measured peak temperature in the weld zone of the 6061 aluminum side

reaches 580 ◦C, which is distinctly higher than the melting points of the Al–Cu eutectic or

some of the hypo- and hyper-eutectic alloys. Higher peak temperatures are expected at the

near interface regions between the weld metal and the stirred tool pin. Distinctly different

micro-hardness levels from 136 to 760HV0.2 are produced corresponding to various

microstructural features in the weld nugget.

L.X. Wei, et, al., (2012) [18]investigated composite friction stir welding of pure

copper/1350 aluminum alloy sheet with a thickness of 3 mm.Most of the rotating pin was

inserted into the aluminum alloy side through a pin-off technique, and sound welds were

34

obtained at a rotation speed of 1000 r/min and a welding speed of 80 mm/min.

Complicated microstructure was formed in the nugget, in which vortex-like pattern and

lamella structure could be found. No intermetallic compounds were found in the nugget.

The hardness distribution indicates that the hardness at the copper side of the nugget is

higher than that at the aluminum alloy side, and the hardness at the bottom of the nugget is

generally higher than that in other regions. The ultimate tensile strength and elongation of

the composite welds are 152 MPa and 6.3%, respectively. The fracture surface observation

shows that the composite joints fail with a ductile-brittle mixed fracture mode during

tensile test.

Y. Yong, et, al., (2010) [19]investigated composite friction stir welding between 5052 Al

alloy and AZ31 Mg alloy with the plate thickness of 6 mm. Sound weld was obtained at

rotation speed of 600 r/min and welding speed of 40 mm/min. Compared with the base

materials, the microstructure of the stir zone is greatly refined. Complex flow pattern

characterized by intercalation lamellae is formed in the stir zone. Microhardness

measurement of the composite welds presents an uneven distribution due to the

complicated microstructure of the weld, and the maximum value of microhardness in the

stir zone is twice higher than that of the base materials. The tensile fracture position locates

at the advancing side (aluminum side), where the hardness distribution of weld shows a

sharp decrease from the stir zone to 5052 base material.

W.B. Lee and S.B. Jung (2004) [20]conducted friction stir welding on copper. Defect free

weld wereproduced on 4 mm thick copper plate at travel speed of 61 mm/min and tool

rotation speed of 1250 rpm using a general tool steel as the welding tool. The stir zone

showed the very fine and equaxied grain structure compared to the base metal which had a

elongated grain and its size is approximately 100 Am. The heat-affected zone (HAZ)

which lies beside the stir zone had a near-equaxied and larger grain structure than that of

the base metal due to annealing effect. Slight softening region was formed in the weld zone

due to lower density of dislocation relative to the base metal. Transverse tensile strength of

FSW copper joint reached about 87% of that of the base metal and showed slight higher

value than that of the EBW copper joint.

Y.F. Sun and H. Fujii(2010) [21] conducted friction stir welding on commercially pure

copper, which includeda welding speed ranged from 200 to 800 mm/min, a rotation speed

35

ranged from 400 to 1200rpm and an applied load ranged from 1000 to 1500 kg. In the stir

zone, a remarkably refined microstructure with average grain size of 3.8_m can be

obtained by increasing the applied load to 1500 kg. In addition, higher applied load can

promote the formation of dislocation cells, while annealing twins and dislocation

entanglements are easy to form under lower applied load. The mechanical properties of the

joints can be improved further by increasing the applied load, rather than only decreasing

the rotation speed at lower applied load. The mechanism of the mechanical property

changes in the copper joints were put forward and clarified from the viewpoint of

microstructural evolution.

Y.F. Sun, et, al.,(2013) [22] were successfully welded the 6061-T6 Al alloy and mild steel

plate with a thickness of 1 mm by the flatspot friction stir welding technique. The rotating

tools with different probe lengths of 1.0, 1.3 and 1.5 mmwere used in the first step, during

which a conventional spot FSW was conducted above a round dent previously made on the

back plate. However, sound Al/Fe welds with similar microstructure and mechanical

properties can still be obtained after the second step, during which a probe-less rotating

tool was used to flatten the weld surface. The sound welds have smooth surface without

keyholes and other internal welding defects. No intermetallic compound layer but some

areas with amorphous atomic configuration was formed along the Al/Fe joint interface due

to the lower heat input. The shear tensile failure load can reach a maximum value of 3607

N and fracture through plug mode. The probe length has little effect on the weld properties,

which indicates that the tool life can be significantly extended by this new spot welding

technique.

A. Heidarzadeh and T. Saeid(2013) [23] carried out experiment to predict the mechanical

properties of friction stir welded pure copperjoints. Response surface methodology based

on a central composite rotatable design with three parameters, five levels, and 20 runs, was

used to conduct the experiments and to develop the mathematical regression model by

using of Design-Expert software. The three welding parameters considered were rotational

speed, welding speed, and axial force. Analysis of variance was applied to validate the

predicted models. The increase in welding parameters resulted in increasing of tensile

strength of the joints up to a maximum value. Elongation percent of the joints increased

with increase of rotational speed and axial force, but decreased by increasing of welding

speed, continuously.

36

Y. Li, et, al.,(1999) [24]friction-stir welding (FSW) of 0.6 cm plates of 2024 Al (140 HV)

to 6061 Al (100 HV) were characterized by residual, equiaxedgrains within the weld zone

having average sizes ranging from 1 to 15 mm, exhibiting grain growth from dynamically

recrystallized grains which provide a mechanism for superplastic flow; producing

intercalated, lamellar-like flow patterns. These flow patterns are visualized by differential

etching of the 2024 Al producing contrast relative to 6061 Al. The flow patterns are

observed to be complex spirals and vortex-like, among others, and to change somewhat

systematically with tool rotation (stirring) speed between 400 and 1200 rpm; depending on

tool orientation.

H.S. Park, et, al., (2004) [25]wereinvestigated the characteristics of the microstructures

and mechanical properties of friction stir welds of 60% Cu–40% Zn alloy (60/40 brass).

The defect-free welds were obtained in a relatively wide range of welding conditions; the

tool rotation speed ranged from 1000 to 1500 rpm with a welding speed from 500 to 2000

mm/min, and 500 rpm—500 mm/min. The microstructures of the welds yielded extremely

fine grains with some deformed grains in the stirred zone (SZ) and elongated grains in the

thermo-mechanically affected zone. The hardness values within the SZ in all welding

conditions were much higher than those of the base metal, increased with a decrease in

heat input. The generation of refined grains in the SZ was a main factor which caused the

hardness increase associated with decreasing heat input. The strengths of the all-SZ

showed relative correspondence to the variation of the hardness values in the SZ.

37

CHAPTER 3

PROBLEM DEFINITION

Friction stir welding is one of the emerging fields in the process of welding and

also to be a reliable method for welding composite materials . The avoidance of filler

materials increases its scope for many applications; Even though it has been used with less

acknowledgment of influencing welding parameters. Because if the parameters are

efficiently used, then the process will utilize less resource and produce high output.

Moreover the parameters are rotational speed, traverse speed and axial load will be

the important one in friction stir welding. Most of the industries are inaccurate and less

precise in their values of friction stir welding over any composite metals. Sound welding of

Friction stir welded of composite materials such as aluminium reinforced with fly ash is

difficult by controlling the process parameters such as rotational speed, traverse speed and

axial load. In composite metals welding

Hence it is in need to find the optimized parameters in the emerging field for better

usage of extincting resources and material managements. Therefore finding of major

influencing factors such as traverse speed, rotational speed and axial load in friction stir

welding will be great work for various applications of composite metals.

The main objective of the work is:

1) To weld the composite metals AA 6063 reinforced with fly ash using

Friction stir welding.

2) To study the microstructure and mechanical properties of the Friction stir

welded AA 6063 reinforced with fly ash.

38

CHAPTER 4

PROJECT METHODOLOGYThe methodology of the microstructure and mechanical properties of the friction

stir welding of aluminium 6063 with fly ash has been presented as flow chart below.

Fig.4.1.Project methodology

CHAPTER 5

RESULTS AND DISCUSSION

39

LITERATURE SURVEY

PROBLEM DEFINITION

SELECTION OF MATERIALS

SELECTION OF PROCESS PARAMETERS

PREPARATION OF TOOL AND WORK PIECE

EXPERIMENTAL SETUP

CONDUCTING EXPERIMENT

TENSILE TEST AND ROCKWELL HARDNESS TEST

STUDY OF MICROSTRUCTURE AND TENSILE AND HARDNESS

BEHAVIOUR

INTERPRETATION OF RESULTS

5.1.WELDED PIECES

The following picture show the actual condition of the Friction Stir Welded work

pieces for the given input such as axial force, rotational speed, traverse speed.

Fig.5.1.Surface morphologies of the FSW AA6063 and fly ash reinforced with 5% of

weight ratio.

Fig.5.2.Surface morphologies of the FSW AA6063 and fly ash reinforced with 10% of

weight ratio.

40

Fig.5.3.Surface morphologies of the FSW AA6063 and fly ash reinforced with 15% of

weight ratio.

5.2.TENSILE STRENGTH TEST

Fig 5.4Dimension for tensile test Samples

41

Fig 5.1 Samples after tensile test

SAMPLE NUMBER Tensile Strength in the base

parent metal ( N/mm2)

Tensile Strength in

the Welded Area

1 (5 % F.A) 110.7 113

2(10 % F.A) 114.3 117

3(15 % F.A) 116 128

Table5.1 Tensile Strength Test Results for three samples

Tensile test was carried out at room temperature using a computerized universal

testing machine. In this study it can be noted that the addition Fly Ash particles improved

the tensile strength of the composites. It is apparent that an increase in the volume fraction

of fly ash particle results in an increase in the tensile strength. The result shows the effect

of the volume fraction on the tensile strength. The tensile strength of SAMPLE 1 (5% Fly

Ash) is 113N/mm2 and this value increases to a maximum of 128 N/mm2 for SAMPLE 3

( fly ash 15%) which is a good improvement in the Tensile strength.

5.3 ROCKWELL HARDNESS TEST

Fig 5.5 Rockwell Hardness Samples

42

Rockwell hardness tester was used to measure the hardness of welded samples.

The hardness were measured along the transverse direction of the weld in centre.

A hardness testing machine is used to measure the hardness of the fly ash

composite samples. The specimens of 25 x 25 x 6 mm was cut from welded samples .

During the test the diamond pyramid indenter with certain shape is penetrated into the

surface of the specimens under certain test force which shall be removed after retained for

certain period of time. After measuring the length of the diagonal lines of the indentation,

the hardness value is gained by looking up to the result.

Table 5.2 Hardness Test Results For three Specimen

SAMPLE NUMBER Hardness (HR)

1 (5 % F.A) 47.8

2(10 % F.A) 48

3(15 % F.A) 49.2

5.5.MICROSTRUCTURE

Microstructures of three samples have been evaluated. The microstructure

evaluation ofthree samples is as follows.

The SEM photomicrographs of the composite are presented in

(Fig.5.8,5.9,5.10). The interface between the alloy and the surface composite is

clean without the presence of defects. The bonding of the surface composite with

the alloy is excellent. The FSP zone reveals uniformly distributed and well bonded

Fly ash particles. The grain size of aluminum alloy is apparently refined by FSW.

The essential requirement to obtain higher mechanical and tribological properties of

surface composite is uniform distribution of ceramic particles in the matrix alloy.

This condition is achieved in the present work. It is difficult to obtain uniform

distribution of ceramic particles using other fabrication methods. FSW induce

severe plastic deformation of the matrix alloy through the rotating pin and shoulder.

The size of the particles is smaller compared to the size of as received particles. The

Fly ash particles undergo fragmentation due to the stirring action of the tool. The

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ceramic particles increase the grain nucleation sites which results in finer grain size

of matrix alloy.

FLY ASH SEM ANALYSIS:

44

Fig.5.7. microstructure of fly ash X150, X500, X1000, X5000

MMC OF FLY ASH 5%, 10% AND 15% PERCENTAGE.

45

Fig.5.8. Microstructure of MMC 5% percentage of fly ash X1000, X1500, X7000

46

Fig.5.9. Microstructure of MMC OF 10% fly ash, X1000, X1500, X6000

Fig.5.10. Microstructure of MMC of 15% fly ash, X1000, X1500, X6000

CHAPTER 5

CONCLUSION

Based on the above investigation it is clear that AA6063/Fly ash composite was

successfully fabricated using FSW. Fly ash particles were uniformly distributed and well

bonded within the matrix alloy. The size of fly ash was reduced due to fragmentation

caused by the stirring action of the tool. The MMCs have been fabricated successfully and

their microstructure evaluations have been studied successfully. Evaluation of the

microstructure shows that the homogeneity of the mixture of the matrix and reinforcement

increases with the increase in the percentage of fly ash particle reinforced in AA6063.The

method of using stir casting process to mix AA6063 and fly with respect to weight ratio is

very important to achieve sound. Microstructure and micro hardness was good when we

use. I concluded that, while joining composite materials such as aluminium reinforced

with fly ash by using friction stir welding process, then it is good to consider the amount of

fly ash particle to be reinforced to the metal for better results of strength and hardness.

47

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