ankit report.doc
TRANSCRIPT
PROJECT REPORT
ON
CHARACTERISTICS AND PROPERTY EVALUATION OF METAL MATRIX
COMPOSITES [MMCs] USING STIR CASTING
Submitted in partial fulfillment of requirements for the award of degree of
BACHELOR OF TECHNOLOGY
In
By
ANKIT PATHAK 1112840020
ANKUSH VERMA 1112840030
AVINASH UPADHYAY 1112840043
ANKUR GOEL 1112840028
Under the guidance of
MR. SAURABH GUPTA
MECHANICAL ENGINEERING DEPARTMENT
BHARAT INSTITUTE OF TECHNOLOGY, MEERUT.
MEERUT-250103
1
CANDIDATE’S DECLARATION
I hereby declare that the work carried out in this project report entitled,
“CHARACTERISTICS AND PROPERTY EVALUATION OF METAL MATRIX
COMPOSITES [MMCs] USING STIR SQUEEZE CASTING”, is presented in partial
fulfillment of the requirements for the award of degree of “Bachelor of Technology” in
Mechanical Engineering with specialization in production & industrial system engineering,
submitted to the Department of Mechanical Engineering, Bharat Institute of Technology,
Meerut, under the guidance of Mr.Saurabh Gupta, Assistant Professor,Department of
Mechanical and Industrial Engineering.
Date: ANKIT PATHAK 1112840020
ANKUSH VERMA 1112840030
AVINASH UPADHYAY 1112840043
ANKUR GOEL 1112840028
Place: Meerut
This is to certify that the above statement made by the candidate is correct to the best of my
knowledge and belief.
(Mr. Saurabh gupta)
Assistant Professor
2
ACKNOWLEDGEMENT
The euphoria and joy, accompanying the successful completion of my task would be
incomplete without the special mention of those people whose guidance and encouragement
made my effort successful.
I am deeply indebted to my guides Mr. Saurabh Gupta, Asst. Professor in the department of
MECHANICAL ENGINEERING, Bharat Institute of Technology, Meerut, whose help,
stimulating suggestions and encouragement helped me in all the time to make my effort
successful.
Especially, I would like to give my special thanks to my parents and my friends, whose
support and motivation inspire me to complete the study.
ANKIT PATHAK 1112840020
ANKUSH VERMA 1112840030
AVINASH UPADHYAY 1112840043
ANKUR GOEL 1112840028
M.TECH-4ND YEAR
3
CONTENTSPAGE NUMBER
ABSTRACT 6
INTRODUCTION 8
COMPOSITES 10
Classification of composites 11
METAL MATRIX COMPOSITES 14
Constituents of MMCs 16
Types of MMCs 17
INTRODUCTION TO ALUMINIUM
MATRIX COMPOSITES 18
PRODUCTION METHODS OF ALUMINIUM
MATRIX COMPOSITES 21
EXPERIMENTAL SET UP AND PROCEDURE
Stir Squeeze Casting Set up 25
Stir Squeeze Casting Procedure 26
DEFINITION & FORMULAE 27
RESULTS AND DISCUSSIONS 28
CONCLUSION 29
FUTURE ASPECTS 30
REFERENCES 31
4
LIST OF FIGURES
Fig no. Name of figure Page no.1 Classification of composite 8
2(a)Typical microstructure of silicon carbide particle/ aluminum
alloy composite18
2(b)Typical microstructure of silicon carbide particle/ aluminum
alloy composite18
3 Some application of AMCs 20
4 Stir Casting 25
5 Diagram of Set up 27
LISTOF TABLES
Table
no.Name of table Page no.
1 Typical reinforcements used in metal matrix composites 16
2A comparative evaluation of the different techniques used for
MMC fabrication22
3 Chemical Composition of A6063 alloy 25
4 Result & discussion 27
5
ABSTRACT
Manufacturing of aluminum alloy based casting composite by stir casting is one of the
most economical method of processing MMC. The aluminum based composites are
increasingly being used in the transport, aerospace, marine, automobile and mineral
processing industries, owing to their improved strength, stiffness and wear resistance
properties. The widely used reinforcing materials for these composites are silicon carbide,
aluminum oxide and graphite in the form of particles or whiskers. The ceramic particles
reinforced aluminum composites are termed as new generation material and these can be
tailored and engineered with specific required properties for specific application
requirements. Particle reinforced composites have a better plastic forming capability than that
of the whisker or fiber reinforced ones, and thus they have emerged as most sought after
material with cost advantage and they are also known for excellent heat and wear resistance
applications .Given the factors of reinforcement type, form, and quantity, which can be
varied, in addition to matrix characteristics, the composites have a huge potential for being
tailored for particular applications. One factor that, to date, has restricted the widespread use
of MMCs has been their relatively high cost. This is mostly related to the expensive
processing techniques used currently to produce high quality composites. The most widely
applied methods for the production of composite materials and composite parts are based on
casting techniques such as the stir casting of porous ceramic pre - forms with liquid metal
alloys and powder metallurgy methods. The cost and the properties of the produced MMC are
highly dependent on the method of their processing.
6
INTRODUCTION
Aluminum alloys are preferred engineering material for automobile, aerospace and
mineral processing industries for various high performing components that are being used for
varieties of applications owing to their lower weight, excellent thermal conductivity
properties. The composites formed out of aluminum alloys are of wide interest owing to their
high strength,fracture toughness, wear resistance and stiffness. Further these composites are
of superior in nature for elevated temperature application when reinforced with ceramic
particle [1].
Alluminium and its alloys are being widely used as matrix for the synthesis of metal matrix
composites (MMCs) by researchers, owing to their abundant availability, easy processing,
low melting point and easy machining. In the world of polymer matrix composites, and
plastics, Al and its alloys maintain their critical importance due to characteristic properties of
metals i.e. ductility, strength and, thermal and electrical conductivity [1]. Higher strength to
weight ratio, ease in alloying and recycling are added advantages of Al and its alloys. [2]
The addition of high strength, high modulus refractory particles to a ductile metal matrix
produce a material whose mechanical properties are intermediate between the matrix alloy
and the ceramic reinforcement. Metals have a useful combination of properties such as high
strength, ductility and high temperature resistance, but sometimes have low stiffness, whereas
ceramics are stiff and strong, though brittle. Aluminium and silicon carbide, for example,
have very different mechanical properties: Young's moduli of 70 and 400 GPa, coefficients of
thermal expansion of 24 X 10-6 and 4 X 10-6/oC, and yield strengths of 35 and 600 MPa,
respectively. By combining these materials, e.g. A6061/SiC/17p (T6 condition), an MMC
with a Young's modulus of 96.6 GPa and yield strength of 510 MPa can be produced [3]. By
carefully controlling the relative amount and distribution of the ingredients of a composite as
well as the processing conditions, these properties can be further improved.
7
COMPOSITE
Composite material are materials made from two or more constituent materials with
significantly different physical and chemical properties, that when combined, produce a
material with characteristics different from the individual component.[4] Many of common
materials (metals, alloys, doped ceramics and polymers mixed with additives) also have a
small amount of dispersed phases in their structures, however they are not considered as
composite materials since their properties are similar to those of their base constituents
(physical property of steel are similar to those of pure iron) . Favorable properties of
composites materials are high stiffness and high strength, low density, high temperature
stability, high electrical and thermal conductivity, adjustable coefficient of thermal
expansion, corrosion resistance, improved wear resistance etc. composite materials are
generally used for buildings, bridges and structures such as boat hulls, swimming pool panels,
race car bodies, shower stalls, bathtubs, storage tanks, imitation granite and cultured marble
sinks and counter tops. the most advanced examples perform routinely on spacecraft and
aircraft in demanding environments.
Composites as engineering materials normally refer to the material with
the following characteristics: 1. These are artificially made (thus, excluding natural material such as wood).
2. These consist of at least two different species with a well defined interface.
3. Their properties are influenced by the volume percentage of ingredients.
4. These have at least one property not possessed by the individual constituents.
Performance of Composite depends on:
1. Properties of matrix and reinforcement,
2. Size and distribution of constituents,
3. Shape of constituents,
4. Nature of interface between constituents.
8
CLASSIFICATION OF COMPOSITES
Composite materials are classified
a. On the basis of matrix material,
b. On the basis of filler material.
Fig1: Classification of composites
9
(a) On the basis of Matrix:1. Metal Matrix Composites (MMC)
Metal Matrix Composites are composed of a metallic matrix (aluminium, magnesium,
iron, cobalt, copper) and a dispersed ceramic (oxides, carbides) or metallic (lead, tungsten,
molybdenum) phase.
2. Ceramic Matrix Composites (CMC)
Ceramic Matrix Composites are composed of a ceramic matrix and imbedded fibers
of other ceramic material (dispersed phase).
3. Polymer Matrix Composites (PMC)
Polymer Matrix Composites are composed of a matrix from thermoset (Unsaturated
polyester (UP), Epoxy) or thermoplastic (PVC, Nylon, Polysterene) and embedded glass,
carbon, steel or Kevlar fibers (dispersed phase).
(b) On the basis of Material Structure:1. Particulate Composites
Particulate Composites consist of a matrix reinforced by a dispersed phase in form of
particles.
1. Composites with random orientation of particles.
2. Composites with preferred orientation of particles. Dispersed phase of these materials
consists of two-dimensional flat platelets (flakes), laid parallel to each other.
2. 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 (length < 100*diameter).
Composites with random orientation of fibers.
Composites with preferred orientation of fibers.
(b) Long-fiber reinforced composites. Long-fiber reinforced composites consist of a matrix
reinforced by a dispersed phase in form of continuous fibers.
Unidirectional orientation of fibers.
Bidirectional orientation of fibers (woven). 10
Laminate Composites
When a fiber reinforced composite consists of several layers with different fiber orientations,
it is called multilayer (angle-ply) composite.
3.Laminar Composites
Laminar composites are found in as many combinations as the number of materials. They can
be described as materials comprising of layers of materials bonded together. These may be of
several layers of two or more metal materials occurring alternately or in a determined order
more than once, and in as many numbers as required for a specific purpose.
11
METAL MATRIX COMPOSITES
(MMCs)
Metal matrix composites, at present though generating a wide interest in research
fraternity, are not as widely in use as their plastic counterparts. High strength, fracture
toughness and stiffness are offered by metal matrices than those offered by their polymer
counterparts. They can withstand elevated temperature in corrosive environment than
polymer composites. Metal Matrix Composites are composed of a metallic matrix (Al, Mg,
Fe, Cu etc) and a dispersed ceramic (oxide, carbides) or metallic phase ( Pb, Mo, W etc).
Ceramic reinforcement may be silicon carbide, boron, alumina, silicon nitride, boron carbide,
boron nitride etc. whereas Metallic Reinforcement may be tungsten, beryllium etc [4]. MMCs
are used for Space Shuttle, commercial airliners, electronic substrates, bicycles, automobiles,
golf clubs and a variety of other applications. From a material point of view, when compared
to polymer matrix composites, the advantages of MMCs lie in their retention of strength and
stiffness at elevated temperature, good abrasion and creep resistance properties [4]. Most
MMCs are still in the development stage or the early stages of production and are not so
widely established as polymer matrix composites. The biggest disadvantages of MMCs are
their high costs of fabrication, which has placed limitations on their actual applications [2].
There are also advantages in some of the physical attributes of MMCs such as no significant
moisture absorption properties, non-inflammability, low electrical and thermal conductivities
and resistance to most radiations [5]. MMCs have existed for the past 30 years and a wide
range of MMCs have been studied. Compared to monolithic metals, MMCs have:
Higher strength-to-density ratios
Higher stiffness-to-density ratios
Better fatigue resistance
Better elevated temperature properties
Higher strength
Lower creep rate
Lower coefficients of thermal expansion
Better wear resistance
12
The advantages of MMCs over polymer matrix composites are: Higher temperature capability
Fire resistance
Higher transverse stiffness and strength
No moisture absorption
Higher electrical and thermal conductivities
Better radiation resistance
No out gassing
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: Higher cost of some material systems
Relatively immature technology
Complex fabrication methods for fiber-reinforced systems (except for casting)
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, and copper alloys and superalloys.
CONSTITUENTS OF MMC
The major constituents of a metal matrix composite material are matrix and reinforcements.
Interface between matrix and reinforcement is also considered as one of the constituents as it
plays a crucial role in determining the properties of the composite.
MATRIX: Metals are essential constituent for fabrication of MMC and choice of matrix
material depends upon strength, temperature of application, density, cost requirement, easy
availability and ease of processing .The major function of matrix is to transfer and distribute
13
the load over the reinforcement. The transfer of load depends on the bonding interface
between the matrix and the reinforcement, however bonding depends on the type of matrix
and the reinforcement along with fabrication technique. Currently the main focus on matrix
material for MMC is given to Aluminium alloys because of unique combination of high
corrosion resistance, low density and excellent mechanical properties [6].
REINFORCEMENT: Second phase materials added to the matrix alloys which normally
enhance strength, stiffness, wear and creep resistances of the composites. The choice of
reinforcement always depends on the final property requirements of the composite system or
the component to be fabricated [6]. SiC has been reported to be the most advantageous
reinforcement for matrix of Aluminium alloys . The key properties of Sic are as under:
High strength
Low thermal expansion
High thermal conductivity
High hardness
High elastic modulus
Excellent thermal shock resistance
Superior chemical inertness [7].
INTERFACE: It is the region that lies between its constituents i.e. matrix and reinforcement.
It plays a crucial role in determining the composite properties. It may contain a simple row of
atomic bonds (e.g. the interface between alumina and pure Al), or reaction products between
matrix and the reinforcement (e.g. Aluminium carbide between Al and C fibers), or
reinforcement coatings (e.g. reinforcement coatings between SiC and titanium matrices). In
comparison (i) stiffening and strengthening rely on load transfer across the interface, (ii)
toughness is influenced by crack detection/fiber pullout, and (iii) ductility is affected by
relaxation of peak stresses near the interface [6].
TYPES OF METAL MATRIX COMPOSITES
14
There are three kinds of metal matrix composites (MMCs):
Particle reinforced MMCs
Short fiber or whisker reinforced MMCs
Continuous fiber or sheet reinforced MMCs
Table provides examples of some important reinforcements used in metal matrix composites
and their aspect (length/diameter) ratios and diameters.
Type Aspect Ratio Diameter, µm Examples
Particle ~ 1 – 4 1 – 25 SiC, Al2O3, BN, B4C
Short fiber or
whisker~ 10 – 1000 0.1 – 25
SiC, Al2O3, Al2O3 +
SiO2, C
Continuous fiber > 1000 3 – 150 SiC, Al2O3, C, B, W
Table 1: Typical reinforcements used in metal matrix composites [8]
Particle or discontinuously reinforced MMCs have become very important because they are
inexpensive with respect to continuous fiber reinforced composites and they have relatively
isotropic properties compared to fiber reinforced composites.
Fig 1 (a) Typical microstructure of continuous alumina fiber/magnesium alloy
composite (b) Typical microstructure of silicon carbide particle/ aluminum alloy
composite [8]
15
INTRODUCTION TO ALUMINIUM
MATRIX COMPOSITES
Aluminium is the most popular matrix for the metal matrix composites (MMCs). The
Al alloys are quite attractive due to their low density, their capability to be strengthened by
precipitation, their good corrosion resistance, high thermal and electrical conductivity, and
their high damping capacity. Aluminum matrix composites (AMCs) have been widely studied
since the 1920s and are now used in sporting goods, electronic packaging, armours and
automotive industries. AMC material systems offer superior combination of properties
(profile of properties) in such a manner that today no existing monolithic material can rival.
Over the years, AMCs have been tried and used in numerous structural, non-structural and
functional applications in different engineering sectors. Driving force for the utilisation of
AMCs in these sectors include performance, economic and environmental benefits. The key
benefits of AMCs in transportation sector are lower fuel consumption, less noise and lower
airborne emissions. With increasing stringent environmental regulations and emphasis on
improved fuel economy, use of AMCs in transport sector will be inevitable and desirable in
the coming years.[25] They are usually reinforced by Al2O3, SiC, C but SiO2, B, BN, B4C,
AlN may also be considered. The aluminum matrices are in general Al-Si, Al-Cu, 2xxx or
6xxx alloys as proposed by the American Aluminum Association the AMCs should be
designated by their constituents: accepted designation of the matrix/abbreviation of the
reinforcement’s designation / arrangement and volume fraction in % with symbol of type
(shape) of reinforcement. For example, an aluminum alloy AA6061 reinforced by particulates
of alumina, 22 % volume fraction, is designated as "AA6061/Al2O3/22p". In the 1980s,
transportation industries began to develop discontinuously reinforced AMCs. They are very
attractive for their isotropic mechanical properties (higher than their unreinforced alloys) and
their low costs (cheap processing routes and low prices of some of the discontinuous
reinforcement such as SiC particles or Al2O3 short fibers) [9]. Some of the examples are
shown in Fig. 2:
1. Cast SiCp/Al attachment fittings multi-inlet fitting for a truss node.
16
2. Brake rotors for German high speed train ICE-1 and ICE-2 developed by Knorr
Bremse AG and made from a particulate reinforced aluminum alloy (AlSi7Mg + SiC
particulates) supplied by Duralcan. Compared to conventional parts made out of cast
iron with 120 kg/piece, the 76 kg of the AMC rotor offers an attractive weight saving
potential.
3. The braking systems (discs, drums, calipers or back-plate) of the New Lupo from
Volkswagen made from particulate reinforced aluminum alloy supplied by Duralcan.
4. AMC continuous fiber reinforced pushrods produced by 3M for racing engines. These
pushrods weigh 40% as much as steel, are stronger and stiffer, and have high
vibration damping.
5. AMC wires also developed by 3M for the core of electrical conductors. The unique
properties of this type of conductor offer substantial performance benefits when
compared to the currently used steel wire reinforced conductors.
17(4)
(5)
(2) (3)(1)
Fig. 3 Some Applications of AMCs [9]
PRODUCTION METHODS OF
ALUMINIUM MATRIX COMPOSITES
Many processes for fabricating aluminium matrix composites are available. For the most part,
these processes involve processing in the liquid and solid state. Some processes may involve
a variety of disposition technique or an in situ process of incorporating a reinforcement
phase.
1. Liquid state processes
a. Stir casting
b. Squeeze infiltration
c. Spray disposition
d. Reactive processing
2. Solid state processes
a. Powder blending and consolidation
b. Diffusion Bonding of foils
3. Physical vapor deposition
Stir casting: This involves incorporation of ceramic particulate into liquid aluminum
melt and allowing the mixture to solidify. Here, the crucial thing is to create good wetting
between the particulate reinforcement and the liquid aluminum alloy melt. The simplest and
most commercially used technique is known as vortex technique or stir-casting technique.
The vortex technique involves the introduction of pre-treated ceramic particles into the vortex
of molten alloy created by the rotating plate.
Infiltration process: Liquid aluminum alloy is injected/infiltrated into the interstices
of the porous pre-forms of continuous fiber/short fiber or whisker or particle to produce
AMCs. The process is widely used to produce aluminum matrix composites
having particle/whisker/short fiber/continuous fiber as reinforcement.
18
Spray deposition: Spray deposition techniques fall into two distinct classes, depending
whether the droplet stream is produced from a molten bath (Osprey process) or by continuous
feeding of cold metal into a zone of rapid heat injection (thermal spray process).
The spray process has been extensively explored for the production of AMCs by injecting
ceramic particle/whisker/short fibre into the spray. AMCs produced in this way often exhibit
inhomogeneous distribution of ceramic particles.
In-situ processing (reactive processing): There are several different processes that
would fall under this category including liquid-gas, liquid-solid, liquid-liquid and mixed salt
reactions. In these processes refractory reinforcement are created in the aluminium alloy
matrix.
Powder blending and consolidation (PM processing): Blending of aluminium alloy
powder with ceramic short fibre/whisker particle is versatile technique for the production of
AMCs. Blending can be carried out dry or in liquid suspension. Blending is usually followed
by cold compaction, canning, degassing and high temperature consolidation stage such as
hot isostatic pressing (HIP) or extrusion.
Diffusion bonding: Diffusion Bonding of foils (foil – fiber – foil) is quite oriented towards
Titanium and Titanium based matrices. Titanium reinforced with long fibers is commercially
produced by the placement of arrays of fibers between thin metallic foils, often involving a
filament winding operation, followed by hot pressing. One of the main problems lies in
avoiding excessive chemical reaction at the fiber/metal interface. In general, the foil – fiber –
foil route is cumbersome and obtaining high fiber volume fraction and homogeneous fiber
distribution is difficult unless special techniques are used. Also the process becomes difficult
when the objective is to produce parts of complex shape.
Physical vapour deposition: Physical vapor deposition is a vapor state processing
method for MMC. The evaporation process is used for fabrication of Titanium reinforced by
monofilaments. It involves passing the fiber through a region having high vapor pressure of
the metal to be deposited, where condensation takes place to produce a thick surface coating.
The vapor is produced by directing a high power electron beam onto the end of a solid bar
feed stock. There is little or no mechanical disturbance of the interfacial region and very
19
uniform distribution of fibers is produced. The fabrication of composite is usually completed
by assembling the coated fibers into a bundle and consolidating by HIP. The fiber volume
fraction can be accurately controlled via the thickness of the deposited coatings and the fiber
distribution is always very homogenous.
Casting, or liquid infiltration, involves infiltration of a fiber bundle by liquid metal. It is not
easy to make MMCs by simple liquid – phase infiltration, mainly because of difficulties with
wetting of ceramic reinforcement by molten metal. Squeeze infiltration involves injection of
liquid metal into the interstices of an assembly of short fibers, usually called a preform.
Composites fabricated with this method have minimal reaction between the reinforcement
and the molten metal because of short dwell time at high temperature and are free from
common casting defects such as porosity and shrinkage cavities.
MethodRange of shape and
size
Metal
yield
Range of
volume
fraction
Damage to
reinforcementCost
Stir casting
Wide range of
shapes, larger size;
upto 500 kg
Very high,
>90%Up to 0.3 No damage
Least
expensive
Squeeze
casting
limited to perform
shape; upto 2 cm
height
Low Up to 0.45 Severe damageModerately
expensive
Powder
Metallurgy
Wide range;
restricted sizeHigh -
Reinforcement
fractureExpensive
Spray
Deposition
Limited shape; large
sizeMedium 0.3 – 0.7 - Expensive
Table 2: A comparative evaluation of the different techniques used for DRMMC
fabrication [11]
20
According to Skibo et al. [10], the cost of preparing composites material using a casting
method is about one-third to half that of competitive methods, and for high volume
production, it is projected that the cost will fall to one-tenth.
Among the variety of manufacturing processes available for discontinuous metal matrix
composites, stir casting is generally accepted as a particularly promising route, currently
practiced commercially. Its advantages lie in its simplicity, flexibility and applicability to
large quantity production. It is also attractive because, in principle, it allows a conventional
metal processing route to be used, and hence minimizes the final cost of the product. This
liquid metallurgy technique is the most economical of all the available routes for metal matrix
composite production, and allows very large sized components to be fabricated. However,
there are some common problems associated with production of MMCs by this method such
as poor reproducibility, porosity, non – uniform distribution of particles in the matrix and
rejection of dispersoids by the melt [12]. Moreover, to overcome some of these problems,
scientists and people all over the world used SQUEEZE casting. It is proved that proper and
controlled stirring followed by squeezing of the material will certainly results in reduction in
defects like porosity. [13][18][19]
21
EXPERIMENTAL SET UP AND
PROCEDURE
STIR – SQUEEZE CASTING SET UP:In this study, Al-SiCp MMC ingots were fabricated through rapid quenching in a stir casting
unit. The schematic drawing of the caster is shown in Fig. 3. Al-6063 aluminium alloy in
form of rods was used as the matrix metal. The furnaces is open hearth furnace. Graphite
crucibles were used and the stirrer rods and the impeller were made of stainless steel. The
stirrer is used for better mixing of al 6063 and SiCp. The temperature varies over range of 0 –
1200oC . The quick quenching unit consisted of a large mild steel vessel for holding water as
quenching medium.
(a)
22
(b)
(c)
Fig.3 PHOTOGRAPH OF STIR CASTING UNIT
23
The chemical composition of A6063 alloy is given as:
COMPONENT Wt. %
Si 0.2 – 0.6
Fe 0.35
Cu 0.1
Mn 0.1
Mg 0.45 – 0.9
Cr 0.1
Zn 0.1
Ti 0.1
Al Balance
Table 3: Chemical Composition of A6063 alloy
STIR CASTING PROCEDURE:
As mentioned above, two open hearth furnaces were incorporated for the process. Furnace A was fed
with 20µm silicon carbide particles (15% and 20%) in a graphite crucible and was brought to a
temperature of around 1000 – 1100oC. This was done so that the SiC particles will be at the same
temperature when added to the melt and it was also targeted on the removal of any trapped gases
inside the SiC particles so as to reduce oxidation. The carbide particles were heated side by side until
Al ingots melt. Meanwhile, furnace B was charged with the Al alloy rods (approx. 85% and 80% by
weight). The temperature of the furnace was increased gradually above 700oC so that the alloy would
come in liquid form.
When the alloy is completed melted Mg was added into the melt before the stirring action so as to
increase the wettability of the Al particles as Mg is a well known wetting agent [12]. Mg ribbon (3%
by weight) were wrapped in Al foil and were introduced inside the melt. After introducing the Mg 24
ribbon wait for a minute. Then put down the graphite crucible from the open hearth furnace.
Immediately stirrer rod with impeller is put in and start rotating it. Also drop the heated SiC powder
into it continuously with constant speed.
The suction created by the nature of the vortex formed will fed the SiC particles inside the melt. The
continuous rotation of the impeller will apply a centrifugal force on the carbide particles and they will
be pushed towards the wall of the crucible. As the density of the carbide particles is larger than the
density of Al particles, they will have a tendency of settling down or agglomerate. But the size of the
carbide particles is very small, therefore they will come on the upper surface of the melt due to the
surface tension. But again, the stirring action and movement of the material due to vortex formation
will fed them inside. This stirring was done for around 1 – 2 minutes so that the SiC particles were
properly distributed into the melt.
The composite material then poured into mould cavity. Pattern are made in the form of rod.
Now we get the composite material in the form of rod and is ready for turning operation.
25
DEFINITION:-
IZOD AND CHARPY IMPACT TESTING
Izod and Charpy impact testing is a method of determining the impact resistance of
materials. An arm held at a specific height (constant potential energy) is released. The arm
hits the sample. The specimen either breaks or the weight rests on the specimen. From the
energy absorbed by the sample, its impact energy is determined. A notched sample is
generally used to determine impact energy and notch sensitivity.
TENSILE TEST
Tensile testing, also known as tension testing is a fundamental materials science test in
which a sample is subjected to a controlled tension until failure. The results from the test are
26
commonly used to select a material for an application, for quality control and to predict how
a material will react under other types of forces. Properties that are directly measured via a
tensile test are ultimate tensile strength, maximum elongation and reduction in area. From
these measurements the following properties can also be determined: Young's modulus
Poisson's ratio, yield strength, and strain-hardening characteristics
FARMULA
Strain Energy
Stress Energy
MEACINING OF SPECIMEN
27
HARDNESS TEST:-
Rockwell Hardness Testing
Hardness is a characteristic of a material, not a fundamental physical property. It is defined as
the resistance to indentation, and it is determined by measuring the permanent depth of the
indentation. More simply put, when using a fixed force (load) and a given indenter, the
smaller the indentation, the harder the material. Indentation hardness value is obtained by
measuring the depth or the area of the indentation
CONCLUSION:
Form the study and the experiment, it has been concluded that:
Al 6063 alloy MMC reinforced with 15% & 20% SiC has been successfully produced
with the help of a conventional Stir Casting set up. The produced MMC was
investigated for turning operation on lathe machine.
The stirring speed has considerable effect on distribution of the SiC particles. As
some amount of particle clustering and absence of SiC was observed. The increase in
stirring speed that provided better homogeneous distribution of SiC particles also
increased susceptibility of porosity.
The hardness of the matrix aluminium alloy is also improved considerably by addition
of SiC particles into it.
The measured weight fraction of SiC particles is very close to its actual value so it can
be stated that the intended amount of reinforcement is essentially mixed in the matrix
alloy and hence the process can be used to produce MMC with good distribution with
optimized parameters specially the stirring speed and the weight fraction of the
reinforcement particles.
28
FUTURE ASPECTS
As per the literature survey and the work done, it has been declared that stir casting is the
most accepted and promising method which is incorporated commercially. But there are
certain limitations of the process as like particle agglomeration, sedimentation of second
phase particles (reinforcement components), and porosity.
Incorporation of Squeezing phenomenon and preheating of the SiC particles helped in the
reduction of these defects to such extent particularly porosity but still the agglomeration is
there.
These defects or limitations can be somewhat eliminated by providing some ultrasonic
vibrations to the melt or electromagnetic stirring the melt or combination of both.
Electromagnetic stirring will help the metal melt to flow throughout the entire volume thereof
and thereby, can effectively prevents sedimentation of second phase particles.
As in case of stir casting, stirring by some impeller or mechanical stirrer is done which allows
the striking of abrasive carbide particles with the blades or fins of the stirrer. This causes
particle cracking resulting in reduction in size of the particle thus increasing the chances of
agglomeration of the particles on the upper surface.
This effect can be minimized or almost omitted by the electromagnetic stirring of the system
carrying the particles and molten melt. Electromagnetic effect produced by a 3Ø AC motor
creates the rotating effect which can be used for this stirring purpose. This type of stirring
will strike out the particle – blade striking from the view and will also help in evenly
distributed stirring effect in the molten melt thus helping to retain the properties of the
abrasive carbides and enhancing the properties of the final composite material. In fact this
system can not only retain but enhance the strength, damping and wear resistance properties
of the reinforced material.
Also the implication of little bit ultrasonic vibrations to the molten melt adds to the proper
distribution of the reinforcement particles in the matrix by improving the wettability
characteristics.
29
REFERENCES
[1] ASM handbook of Composites, Volume 21.
[2] T. W. Clyne, “Metal Matrix Composites: Matrices and Processing,” A Mortensen (ed.)
Elsvier, pp. 1 – 14, 2001.
[3] S. Skolianos, Mechanical behavior of cast SiCp-reinforced Al-4.5%Cu-1.5%Mg alloy,
Mater. Sci. Eng. [1996]
[4] Wikipedia-composite mateials
[4] S. Bandyopadhay, T. Das , and P. R. Munroe , Metal Matrix Composites -The Light Yet
Stronger Metals For Tomorrow, A Treatise On Cast materials,
P 17 - 38
[5] F. L. Matthews and R. D. Rawlings,” Composite Materials: Engineering and Design”,
Chapman & Hall publication, pp. 78 - 80
[6] I. A. Ibrahim, F. A. Mohamed, E. J. Lavernia, “Particle Reinforced Metal Matrix
Composites – A Review”, Journal of Materials Science, 26, pp. 1137 – 1156, 1991
[7] T. P. D. Rajan, R. M. Pillai, B. C. Pal, “Reinforcements coatings and interfaces in
Aluminium Metal Matrix Composites”, Journal of Materials Science 33, pp. 3491 – 3503,
1998
[8] Krishan Kumar Chawla, “Composite materials: science and engineering”, P. 164 – 166
[9] Doel T. J. A., Lorretto M. H. and Bowen P., “Mechanical Properties of Aluminium based
Particulate Metal Matrix Composites”, Journal of Composites, Vol. 24, pp. 270 – 275, 1993
[10] D.M. Skibo, D.M. Schuster, L. Jolla, “Process for preparation of composite materials
containing nonmetallic particles in a metallic matrix, and composite materials”, 1988
30
[11] J. Hashim, L. Looney, M. S. J. Hashmi, “Metal matrix composites: production by the stir
casting method”, Journal of Materials Processing Technology, pp. 1 – 7, 1999
[12] V. Tirth, “Development and Micrography of AA2218 Based Heat Treated 5 Wt%
Al2O3(TiO2) Hybrid MMCs”, MIT International Journal of Mechanical Engineering, Vol. 1,
No. 1, pp. 41 – 48, Jan 2011
[13] Akshay Dvivedi, Pradeep Kumar, Inderdeep Singh, “Development of new Stir Caster
Design for the production of Metal Matrix Composite”, Indian Foundry Journal, 54 (2), pp.
21 – 27, 2008
[14] Fang C. K., Fang R. L., Weng W. P., and Chuang T. H., “Applicability of Ultrasonic
Testing for the Determination of Volume Fraction of Particulates in Alumina – Reinforced
Aluminium Matrix Composites”, Materials Letters, Vol. 23, PP. 217 – 266, 1999
[15] A. Mortensen, Mechanical and Physical Behavior of Metals and Ceramic Compounds,
Riso National Laboratory, Roskilde, Denmark, 1988,
[16] J. W. Kaczmar, K. Pietrzak, W. Wlosinski, The production and application of metal
matrix composite materials, Journal of Materials Processing Technology 106, pp. 58 – 67,
2000
[17] Adem Onat, Hatem Akbulut, Fevzi Yilmaz, Production and characterisation of silicon
carbide particulate reinforced aluminium–copper alloy matrix composites by direct squeeze
casting method, Journal of Alloys and Compounds 436, pp. 375 – 382, 2007
[18] C. S. Lim, A. J. Clegg, The production and evaluation of metal matrix composite
castings produced by a pressure – assisted investment casting process, journal of materials
processing technology 67, pp. 13 – 18, 1997
[19] S. Naher, D. Brabazon, L. Looney, “Simulation of stir casting processes”, Jr. of
Materials Processing Technology, Vol. 143 – 144, pp. 567 – 571, 2003
31
[20] G. S. Haumanth, G. A. Irons, “Particle incorporation by melt stirring for the production
of metal – matrix composites”, Journal of Materials Science 28, pp. 2459 – 2465, 1993
[21] G. Ganesan, K. Raghukandan, R. Karthikeyan, B. C. Pai, “Development of processing
maps for 6061 Al/15% SiC Composite Material”, Materials Science and engineering, A369,
pp. 230 – 235, 2004.
[22] J. U. Ejiofor, R. G. Reddy, “Developments in the Processing and Properties of
Particulate Al – Si Composites”, JOM, PP. 31 – 37, Nov. 1997
[23] D. Brabazon, D. J. Browne, A. J. Carr, “Mechanical Stir Casting of Aluminium Alloys
from the Mushy State: Process, Microstructure and Mechanical Properties”, Materials
Science and Engineering, A326, pp. 370 – 381, 2002
[24] Manoj Singla, D. Deepak Dwivedi, Lakhvir Singh, Vikas Chawla, “Development of
Aluminium Based Silicon Carbide Particulate Metal Matrix Composite”, Journal of Minerals
& Materials Characterisation & Engineering, Vol. 8, No. 6, pp. 455 – 467, 2009
[25] M K SURAPPA, “Aluminium matrix composites: Challenges and
Opportunities” Sadhana Vol. 28, Parts 1 & 2, February/April 2003, pp. 319–334.
32