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CHAPTER – 1

BASIC INTRODUCTION

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1 INTRODUCTION

1.1Company profile

KRUNAL ENGG.

63, Mahadev Estate, CTM

Ahmedabad-380015,

Gujarat (India)

KRUNAL ENGG. ESTATE established in 1995. it having 15 years of experience in

manufacturing and they started aluminum casting for past few year .they become leading

manufacturer of aluminum casting equipment in Gujarat .our ranger of product manufactured

included five. it has following (1) bracket

(2) Arlram bracket (petrol pump pipe fitting)

(3) Elbow (petrol pump)

(4) Motor body cover

(5) Flange(gear box)

With continuous research and development to update the product and technology .KRUNAL

ENGG. Is confident to produce quality product with optimum performance .

Our plant is spread over 3500 sq. feet area .it having latest foundry and equipment with lathe,

CNC turning center, drilling m/c, vibrate m/c, VMC m/c. To meet customer need and

satisfaction .

1.2 Alloy

An alloy is a material that has metallic properties and is formed by combination of two or

more chemical elements of which at least one is a metal. The metallic atoms must dominate

in its chemical composition and the metallic bond in its crystal structure. Commonly, alloys

have different properties from those of the component elements. An alloy of a metal is made

by combining it with one or more other metals or non-metals that often enhances its

properties. For example, steel is stronger than iron which its primary element. The physical

properties, such as density and conductivity, of an alloy may not differ greatly from those of

its component elements, but engineering properties such as tensile strength and shear strength

may be considerably different from those of the constituent materials.

1.2.1 Aluminium

• Pure Al content of maximum 1wt. % of Fe and Si.

• Pure Al is very soft and ductile.

• Low density 2700 kg/m3 comparing to steel which has 7900 kg/m3,

• High thermal and electrical conductivity.

• Low melting point and good resistance to corrosion

1.2.2 Aluminium alloys

In recent years aluminium alloys are widely used in automotive industries. This is particularly

due to the real need to weight saving for more reduction of fuel consumption. The typical

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alloying elements are copper, magnesium, manganese, silicon, and zinc. Surfaces of

aluminium alloys have a brilliant lustre in dry environment due to the formation of a

shielding layer of aluminium oxide. Aluminium alloys of the 4xxx, 5xxx and 6xxx series,

containing major elemental additives of Mg and Si, are now being used to replace steel panels

if various automobile industries. Due to such reasons, these alloys were subject of several

scientific studies in the past few years[1].

1.3 Designation of Aluminium alloys

On the basis of the major alloying element, the aluminium alloys are designated according to

the Aluminium Association Wrought Alloy Designation System which consists of four

numerical digits.

Table 1.1 Al alloy and use [1]

Designation of

aluminium alloys and

their applications Alloy

Main alloying element Applications

1xxx Mostly pure aluminium; no

major alloying additions

Electrical and chemical

industries

2xxx Copper Aircraft components

3xxx Manganese Architectural applications

4xxx Silicon Welding rods, automobile parts

5xxx Magnesium Boat hulls, marine industries

6xxx Magnesium and silicon Architectural extrusions

7xxx Zinc Aircraft components

8xxx Other elements (e.g., Fe, Ni or Ti)

9xxx Unassigned

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1.3.1 Properties of Aluminium alloys

A wide range of physical and mechanical properties can be obtained from very pure

aluminium. The different properties are:

1) Aluminium has a density of about 2.7g/cc which is one third (approximately) the value of

steel.

2) Unlike steel, aluminium prevents progressive oxidation by formation of a protective oxide

layer on its surface on exposure to air.

3) Aluminium alloys exhibit excellent electrical and thermal conductivities. The thermal

conductivity of aluminium is twice that of copper (for the same weight of both materials

used)

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There are two major uses of the 4xxx series – for forging and weld filler alloy. These both

applications are due to the excellent flow characteristics provided by relatively high silicon

content.

Effects of silicon in the Al-Si alloys are as follows:

Thermal expansion is reduced substantially by silicon

Magnetic susceptibility is only slightly decreased by silicon

The lattice parameter is decreased slightly by silicon

Machinability is poor because of the hardness of the silicon

Although many investigations exist in literature and based on the above discussion, it is

evident that there is enough scope for further research of Al-Si(LM-6) alloys especially their

mechanical properties. Therefore the objectives of this study are;

Preparation of Al-Si (LM-6) alloys of eutectic compositions.

To study of their microstructure.

To study of their mechanical properties.

To evaluate their wear behaviour.

1.3.2 Aluminium-Silicon alloy Aluminium-Silicon alloys are of greater importance to engineering industries as they exhibit

high strength to weight ratio, high wear resistance, low density, low coefficient of thermal

expansion etc. Silicon imparts high fluidity and low shrinkage, which result in good cast

ability and weld ability. Al-Si alloys are designated 4xxx alloys according to the Aluminium

Association Wrought Alloy Designation System. The major features of the 4xxx series are:

Heat treatable

Good flow characteristics, medium strength

Easily joined, especially by brazing and soldering

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1.4 Phase Diagram Aluminium-Silicon system is a simple binary eutectic with limited solubility of aluminium in

silicon and limited solubility of silicon in aluminium. There is only one invariant reaction in

this diagram, namely

L → α + β (eutectic)

In above equation, L is the liquid phase, α is predominantly aluminium, and β is

predominantly silicon. It is now widely accepted that the eutectic reaction takes place at

577°C and at a silicon level of 12.6%.

Aluminium-Silicon (Al-Si) casting alloys are the most useful of all common foundry cast

alloys in the fabrication of pistons for automotive engines. Depending on the Si concentration

in weight percentage [3], the Al-Si alloy systems are divided into three major categories:

i. Hypoeutectic (<11 wt % Si)

ii. Eutectic (11-13 wt % Si)

iii. Hypereutectic (14-25 wt % Si)

FIG 1.1 PHASE DIAGRAM FOR AL - SI ALLOY [2]

1.4.1 Al-Si EUTECTIC COMPOSITION

• The microstructure of the Al-Si eutectic. In general, when there are

approximately equal volume fractions of the two phases, Eutectics of binary alloys

exhibit a lamellar structure.

• On the other hand, if one phase is present in a small volume fraction, this

phase tends to be fibrous. As a rule of thumb,

• The eutectic microstructure obtained will tend to be fibrous when the volume

fraction of the minor phase is less than 0.25, otherwise it will tend to be lamellar.

• If both phases in the eutectic are no faceted, the eutectic will exhibit a regular

morphology. In this case, the microstructure is made up of either lamellae or fibers

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having a high degree of regularity and periodicity. On the other hand, if one phase is

faceted, the eutectic morphology is often irregular

• Even though the volume fraction of silicon in the Al-Si binary is less than

0.25, the typical Al-Si eutectic is closer to a lamellar structure than to a fibrous one.

This is usually attributed to the strong anisotropy of growth of silicon and to the

relatively low interfacial energy between Si and Al.

A. B.

FIG 1.2 Eutectic structure

(A) Al –12.9% Si, gravity die cast, “Si Blue” etch

(B) Al –12.9% Si –0.04% Sr, gravity die cast, “Si Blue” etch[6]

1.4.2 Secondary dendrite arm spacing

Depending of the rate of cooling a different result of the dendrite structure is achieved. SDAS

is the distance between these dendrites. With a high solidifications rate the result will be a

short SDAS which provides o fine eutectic structure

Fig1.3 SDAS [4]

1.4.3 Why copper in aluminium-silicon alloys

Copper as an alloying element increase the strength, hardness, fatigue, creep resistance and

machinability in an aluminium-silicon alloy. Strength and ductility are depending on how

copper is distributed in the alloy. Cu is found dissolved in the dendrite matrix or as Al-Cu

rich phases. Alloys with dissolved copper in the matrix shows the most increase of strength

and retains ductility. Continues network of copper at the grain boundaries increases the

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strength to appreciable levels but the ductility decreases. To increase the content of copper in

the alloy a higher hardness is achieved and porosity formation increases. Al-Si alloys that

contains 1.5 % copper has the optimal mechanical properties comparing to alloys having

lower or higher content of copper.

1.4.4 Why magnesium in aluminium-silicon alloys

The coefficient of thermal expansion and its electrical resistively increases a little. Al-Mg

alloys have high strength, good ductility and excellent corrosion resistance. Al-Mg alloys

respond well on heat treatment and a higher ultimate tensile strength and yield strength is

achieved. The purpose of magnesium in aluminium-silicon alloys are to precipitate Mg2Si

particles but a disadvantage is that big intermetallic compounds can appear; those phases

reduce the ductility. In alloys that have an amount of magnesium between 0.05 % to 0.3 %

seems to decrease the amount of porosity.

1.4.5 Why Strontium in Aluminium-silicon Alloys

Strontium is added to refine the structure of the silicon eutectic and in an attempt to increase

ductility it disturbs the planar growth of the silicon eutectic. The silicon eutectic becomes

smaller and more compact. It is complicated to add strontium to aluminium alloys because of

the powerful effects of the oxide film. It is also an expensive way to improve ductility. It is

hard to add strontium without increase the porosity. One theory about strontium is that the

enhanced rate of the strontium means that any moisture in the environment is fast converted

to the surface oxide and hydrogen is released in the melt. If strontium is added to an open

furnace an increase of hydrogen porosity is usually achieved. Addition of pure strontium is

recommended because it has a faster dissolution rate with the melt; it has a lower content of

iron than Al-Si master alloy. Mechanical properties are positively affected by this

modification, the elongation is increased up to 85 % without changes in the tensile or yield

strength

1.4.6Mechanical Properties of Al-Si Alloy

Mechanical properties of Al–Si casting alloys depend not only on their chemical

composition but are also significantly dependent on micro-structural features such as the

morphologies of the Al-rich α-phase and of the eutectic Si particles.

The effects of silicon on the mechanical properties of Al-Si alloys are well studied. The

mechanical properties of the Al-Si alloy are dependent on the size, shape and distribution of

eutectic and primary silicon particles. Small, spherical, uniformly distributed silicon

particles enhance the strength properties of Al-Si alloys. The effect of composition on

mechanical properties of Al-Si alloys is shown in following table 2.1.

It may be observed that as the amount of silicon in the alloy increases, the strength properties

of Al-Si alloys also increase up to the eutectic composition, after which they show a decline

with further increase in the silicon content. However, the hardness increases and the

elongation (%) decrease continuously with increasing silicon content. This may be largely

attributed to the size, shape and distribution of silicon particles in the cast structures up to the

eutectic composition. Silicon is present as fine particles and is uniformly distributed in the

structure, and hence the strength properties increase. However, when the primary silicon

appears as coarse polyhedral particles, the strength properties decrease with increasing silicon

content, but the hardness goes on increasing because of the increase in the number of silicon

particles.

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Table 1.2 Mechanical Properties of Al-Si alloy [14]

Composition

(wt %)

Ultimate

tensile

strength

(MN/ m2)

0.2% tensile

proof stress

(MN /m2)

Elongation

(%)

Hardness

(VHN)

Density

(kg/m3x103)

Al-2%Si 127.3 52.6 12.4 39.5 2.68

Al-4%Si 142.2 58.3 10.2 47.3 2.67

Al-6%Si 155.7 64.8 9.6 55.6 2.65

Al-8%Si 169.6 71.5 7.2 61.6 2.62

Al-11.6%Si 185.4 80.0 5.8 67.0 2.59

Al-12.5%Si 189.0 82.5 5.4 70.0 2.57

Al-15%Si 183.25 77.7 4.7 72.5 2.55

Al-17%Si 175.8 73.7 3.0 76.6 2.53

Al-20%Si 172.4 72.0 2.5 81.0 2.50

1.5 Al BASE GRADE ALLOY

1.5.1 LM-6 (EN 1706 AC-43100) - Aluminium Casting Alloy

(Al-Si12CulMgl)

Colour Code -YELLOW/BLACK

This alloy conforms to BS 1490:1988 LM-6. Castings are standardized in the precipitation

treated (TE) condition, solution treated, artificially aged and stabilized (TF7) condition and

the fully heat treated (TF) condition

1.5.2 Chemical Composition of Material

Chemical composition of the hyper eutectic Al-Si alloy which is used in the experiment is

show in below Table 4.1

Table 1.3 – Chemical composition of material

Material %

Al As Balance

Si 10-13

Fe 1.0 % max

Cu 0.7-1.5 max

Mn 0.5 % max

Mg 0.8-1.5 max

Zn 0.5 max

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Ni 1.5 max

Sn 0.1 max

Pb 0.1 max

Ti 0.2 max

Cr 0.1 max

(a) (b) (c)

FIG 1.4 Microphotographs of LM-6 under a) as-cast, b) melt-treated, and c) heat treated. [21]

1.5.3 Characteristics

• Machinability

In machining this alloy, there is less tendency to drag than with high Silicon alloys containing

no other alloying elements, for example LM6. Ordinary steel tools tend to wear rather quickly

and should not be used. Carbide tipped tools with large rake angles and relatively low cutting

speeds give good results. A cutting lubricant and coolant should be employed. Diamond tools

are commonly used for finish machining.

• Corrosion Resistance

This alloy shows high resistance to corrosion under atmospheric conditions.

• Anodizing

LM-6 may be anodized satisfactorily by the sulphuric acid process. The anodic coating is

dark grey. Anodizing, which produces an oil absorbing surface, is sometimes used to give

improved bearing qualities to pistons made of LM-6. Fluidity

Good, this alloy can be cast into thin sections. PRESSURE TIGHTNESS - Fair, suitable for

leak tight castings. HOT-TEARING - Excellent, resistance to hot tearing is high. TYPICAL

POURING TEMPERATURE -700°C

The actual temperatures may range between 670-780°C and will depend on the mould

configuration. This alloy may form internal shrinkage pipes in heavy sections.

Pattern makers Shrinkage - 1.3% or 1/75.

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1.5.4 Applications

LM-6 alloy is used arlam bracket, arlam bracket (petrol pump) pipe fitting, elbow petrol

pump, motor body cover, adjustable flange (gear box). It has the advantage of good resistance

to wear, good bearing properties and a low coefficient of thermal expansion.

1.6 Degassing

1.6.1 What is Degassing ?

Hydrogen is removed from the molten Al by bubbling an inert gas through the metal. Argon,

hexa-chloro-ethane tablet and nitrogen are typically used, but argon is preferred for the best

metal quality because of the tendency of nitrogen to form Al nitride inclusions and more

dross. By adding a small amount of chlorine to the inert process gas in degassers, non-wetted

inclusions and alkali metal impurities can also be removed more efficiently from the metal.

1.6.2 Degassing principal

Hydrogen degassing of aluminum is based on the principle that the hydrogen gas will move

from an area of high pressure (in the melt) to an area of low pressure (the inert gas).

Hydrogen gas disperses in the molten metal as it would if it were released in any confined

space. It will maintain a constant pressure throughout the melt. When you introduce the inert

gas, the hydrogen throughout the melt will flow into the inert gas. As Hydrogen gas is

removed, it will equalize its pressure throughout the melt. The ability of hydrogen gas to

move through and equalize its pressure in liquid metal is almost as fast as it is in air. It is

there for unnecessary to bring all of the metal in contact with the inert gas. How well and

how fast a heat of aluminum can be degassed is determined by two factors, the transfer rate

across the metal/gas interface and the surface area of gas exposed to the metal.

Gas bubbling hydrogen degassing systems work on the principle of using speciality gasses

(chlorine, Freon or SF6) to speed up the hydrogen transfer across the metal/gas interface to

large bubbles of gas in the metal. There was a practical limit to the hydrogen removal on

humid days because the large bubbles broke the surface and exposed metal to the humid

atmosphere where more hydrogen was picked up. Chlorine was the original gas of choice but

due to its hazardous nature most foundries switched to other gasses. What most foundries

have not considered are the hazardous materials released by the breakdown of any speciality

gas used. Rotary degassing works on the principle of increasing the surface area of an inert

gas exposed to the metal. The greater the surface area the faster the degassing. For a given

volume of gas the smaller the bubble size the greater the surface area and the faster the

degassing. For example a 1" square bubble of gas has a surface area of 6 square inches. If you

divide this bubble into 1/16" square bubbles, the total surface area increases to 96 square

inches. In other words for the same volume of gas the surface area and transfer rate has been

increased 16 times. In addition the small bubbles do not disturb the surface of the molten

metal so there is very little hydrogen pickup from the atmosphere.

1.6.3 Why Degassing need?

Because of hydrogen solubility in molten metal it produce porosity in casting. It reduce the

life of casting product. so use of N2 gas to use degassing process remove hydrogen porosity.

And improve the life of casting parts.

1.7 Sources of hydrogen in molten metal

atmosphere humidity;

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wet metallic charge;

wet furnace lining (crucible, transfer ladles);

wet foundry instruments;

wet fluxes and other consumables;

furnace fuel combustion products containing hydrogen.

1.8 Solubility of hydrogen

FIG 1.5 Solubility of hydrogen in solid/liquid aluminum

Amongst all gases only Hydrogen can be solved in Aluminium. Compared with the solubility

of gases in iron alloys, however, the quantity is rather low.

The solubility of Hydrogen in Aluminium depends on the content of alloys and on the

temperature. The solved quantity furthermore depends on the availability of Hydrogen, which

is usually given as the partial pressure and indicated in Millilitres of the solved gas per 100

Grams of metal. (1013 mbar and 0° Celsius; 1 ppm = 1,1124 ml/100g)

As the solubility of Hydrogen in Aluminium suddenly decreases at a temperature of approx.

600° Celsius during cooling it often comes to porosity caused by frozen gas bubbles. With

pure Aluminium the tendency to porosity is most serious, whereas it is lower with alloys.

This is due to a smaller leap in the solubility of Hydrogen.

These circumstances lead to the fact that the presence of porosity with MIG-welding of

Aluminium is nearly unavoidable.

Pores have negative implications on the static and dynamic strength of welded joints and can

be disturbing anyway. Machining the surfaces opens pores which don´t look nice and may

reduce the adhesion of paint.

Inspectors have trouble to determine the level of acceptable porosity and both fabricators and

customers consider it as just poor work.

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The basic solution to this problem is to keep the level of available Hydrogen as low as

possible. Generally a Hydrogen content of approx. 0,2 to 0,3 ml/100g is considered to be the

maximum permitted level in order to get low porosity. This value is exceeded under practical

conditions quite frequently. Sources of Hydrogen are base material, fi ller material, shielding

gas and atmosphere. Clean storage- and fabrication conditions, preparation of the surfaces

and prevention of all other sources of Hydrogen is the most important rule

1.9 Hydrogen in aluminium

Liquid aluminum actively dissolves hydrogen, which forms as a result of chemical reaction

with water vapor:

2Al + 3H2O = Al2O3 + 6H

Solubility of gaseous hydrogen in liquid aluminium at its melting point (1220.7°F/660.4°C) is

(2.2 cm3 per 100 g).

Solubility of gaseous hydrogen falls sharply when aluminium solidifies: solid aluminium at

melting point contains only (0.05 cm3 per 100 g).

aluminum alloys release excessive amount of hydrogen during Solidification. This results in

porosity defects distributed throughout the solid metal. Size of the hydrogen pores and their

quantity is determined by the initial content of hydrogen, the alloy composition and the

solidification conditions.

1.10 Type of casting defect

1)Air blow hole

2)Hydrogen porosity

FIG 1.6 casting defect

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CHAPTER – 2

EXPERIMENT PROCESS

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2. Company flow chart

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2.1 Basic Procedure of Casting processes

• Select a material for casting process and all experiment.

• Use induction furnace, pit furnace and electrotherm furnace for material melt, where

material heated high melting temperature and change solid to liquid form.

• Permanent mold is preheating to 250 °c for all casting to reduce a thermal shock it is

require preheating in present experimental work when pouring a high temperature

molten metal in mold cavity this time direct contact between metal and mould surface.

• Zircon water based coating is used for mould coating as proved effective and is

known to give excellent surface finish and protect with easily remove cast in mould

cavity

• After melt are degassing with 1 % hexa-chloro-ethane tablet for remove soluble

hydrogen form in molten metal.

• After fluxing, proper degassing and cleaning by cover flux

• Added a grain refinement Al-5Ti-1B , Al-3Ti-1B, in molten metal to refine a structure

and Improved feeding characteristics Increased tear resistance, Improved mechanical

properties, Increased pressure tightness, Improved response to thermal treatment

• Use a grain modifier 100 ppm of Al-Sr, Na, Ca, Ba, and Eu added in molten metal to

reduce Si particle size and become a small round shape.

• Gravity die ( permanent mould) casting and pressure die casting process use for

making a cast by using LM-6 eutectic Al alloy material

• Prepare a sample the metallographic Sample size (1.5 ×1.5×1.5)cm are prepare by

cutting, mounting, grinding, and polishing on no. of silicon carbide grain per square

grade paper and final polishing with diamond paste in disc polishing machine and

check in optical microscope

• Taking a T6 heat-treatment process for relief of internal stresses which is developing

during different machining process where LM6-TF (fully heat treated) heat for 8

hours at 515-525°C, quench in hot water, and heat for 4-16 hours at 160-180°C.

• Prepare a different shape and size sample for no. of test to check a mechanical

property, find hardness, Impact test

2.2 Casting processes

Casting processes are divided into two major categories, expendable mould and Permanent

moulds. Expendable moulds are sand casting, last wax method, vacuum molding and shell

molding. Permanent moulds are high pressure die casting, gravity die casting, and centrifugal

casting and squeeze casting.

2.2.1 Gravity die casting

A gravity die , (permanent mold) casting makes use of a mold which is permanent ,this mold

can be re-use many times before it is discarded or re-built Molten metal is poured into the

mold under gravity only , No external pressure is applied to force the liquid metal into the

mold cavity

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FIG 2.1 GRAVITY(PERMANENT MOULD) DIE CASTING

Usually alloys with a low melting point are used like aluminium and magnesium. This kind

of casting method is used especially in large series manufacturing with an even thickness of

the material. The dies are preheated or pre cooled to about 200 – 300 degrees Celsius. The

metal is poured into the die and force to fill the hold mould is the gravity. Compared to sand

casting gravity die castings provide higher strength and finer structure because of the faster

cooling rate. The faster cooling rate depends on the good heat transfer in the metal die

2.2.2 Pressure die casting.

Pressure die casting is a quick, reliable and cost-effective manufacturing process for

production of high volume, metal components that are net-shaped have tight tolerances.

Basically, the pressure die casting process consists of injecting under high pressure a molten

metal alloy into a steel mold (or tool). This gets solidified rapidly (from milliseconds to a few

seconds) to form a net shaped component. It is then automatically extracted.

FIG 2.2 Pressure die casting

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Depending upon the pressure used, there are two types of pressure die casting namely High

Pressure Die Casting and Low Pressure Die Casting. While high pressure die casting has

wider application encompassing nearly 50% of all light alloy casting production. Currently

low pressure die casting accounts for about 20% of the total production but its use is

increasing. High pressure castings are must for castings requiring tight tolerance and detailed

geometry. As the extra pressure is able to push the metal into more detailed features in the

mold. Low pressure die casting is commonly used for larger and non-critical parts.

However, the machine and its dies are very costly, and for this reason pressure die casting is

viable only for high-volume production

2.3 Grain Refinement and Modification

2.3.1Grain Structure

A fine, equiaxed grain structure is normally desired in aluminum castings. The type and size

of grains formed are determined by alloy composition, solidification rate, and the addition of

master alloys (grain refiners) containing inter metallic phase particles, which provide sites for

heterogeneous grain nucleation.

2.3.2 Grain Refinement Effects

A finer grain size promotes improved casting soundness by minimizing shrinkage, hot

cracking, and hydrogen porosity. The advantages of effective grain refinement are:

Improved feeding characteristics

Increased tear resistance

Improved mechanical properties

Increased pressure tightness

Improved response to thermal treatment

Improved appearance following chemical, electrochemical, and mechanical finishing.

Under normal solidification conditions spanning the full range of commercial casting

processes, aluminum alloys without grain refiners exhibit coarse columnar and/or coarse

equiaxed structures. The coarse columnar grain structure is less resistant to cracking during

solidification and post solidification cooling than the well refined grain structure of the same

alloy shown in Figure

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Fig2.3 As cast Al-7Si ingots showing the effects of grain refinement[10]

2.3.3 Grain Refinement

All aluminum alloys can be made to solidify with a fully equiaxed, fine grain structure

through the use of suitable grain refining additions. The most widely used grain refiners are

master alloys of titanium, or of titanium and boron, in aluminum. Aluminum-titanium

refiners generally contain from 3 to 10 % Ti. The same range of titanium concentrations is

used in Al-Ti-B refiners with boron contents from 0.2 to 1 % and titanium-to-boron ratios

ranging from about 5 to 50. Although grain refiners of these types can be considered

conventional hardeners or master alloys, they differ from master alloys added to the melt for

alloying purposes alone. To be effective, grain refiners must introduce controlled,

predictable, and operative quantities of aluminides (and borides) in the correct form, size, and

distribution for grain nucleation. Wrought refiner in rod form, developed for the continuous

treatment of aluminum in primary operations, is available in sheared lengths for foundry use.

The same grain refining compositions are furnished in waffle form. In addition to grain

refining master alloys, salts (usually in compacted form) that react with molten aluminum to

form combinations of TiAl3 and TiB2 are also available.

2.3.4 Grain Refinement Mechanisms

Despite much progress in understanding the fundamentals of grain refinement, no universally

accepted theory or mechanism exists to satisfy laboratory and industrial experience. It is

known that TiAl3 is an active phase in the nucleation of aluminum crystals, ostensibly

because of similarities in crystallographic lattice spacing. Nucleation may occur on TiAl3

substrates that are un-dissolved or precipitate at sufficiently high titanium concentrations by

peritectic reaction. Grain refinement can be achieved at much lower titanium concentrations

than those predicted by the binary Al-Ti peritectic point of 0.15 %. For this reason, other

theories, such as co nucleation of the aluminide by TiB2 or carbides and constitutional effects

on the peritectic reaction, are presumed to be influential. Recent findings also suggest the

active role of more complex borides of the Ti-Al-B type in grain nucleation.

Additions of titanium in the form of master alloys to aluminum casting compositions

normally result in significantly finer and equiaxed grain structure. The period of effectiveness

following grain refiner addition and the potency of grain refining action are enhanced by the

presence of TiB2. In the testing of some compositions, notably those of the aluminum silicon

family, aluminum borides and titanium boride in the absence of excess titanium have been

found to provide effective grain refinement. However, the requirement of an excess of

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titanium compared to stoichiometric balance with boron in TiB2 is commonly accepted for

optimum grain-refining results, and titanium or higher ratio titanium-boron master alloys are

used almost exclusively for grain size control. The role of boride in enhancing grain

refinement effectiveness and extending its useful duration is observed in both casting and

wrought alloys, forming the basis for its use. However, when the boride is present in the form

of large, agglomerated particles, it assumes the character of a highly objectionable inclusion

with especially damaging effects in machining. Particle agglomeration is found in master

alloys of poor quality, or it may occur as a result of long, quiescent holding periods. For the

latter reason, it is essential that holding furnaces be routinely and thoroughly cleaned when

boron containing master alloys are used.

The objective in every case in which master alloys or other grain refiners are added to the

melt is the release of constituent particles capable of nucleating grain formation to ensure

uniform, fine, equiaxed grain structure. The selection of an appropriate grain refiner,

practices for grain refiner addition, and practices covering holding and pouring of castings

following grain refiner addition are usually developed by the foundry after considering

casting and product requirements and after referral to the performance characteristics of

commercial grain refiners furnished by the supplier. However, grain refiners of the 5Ti-1B

and 5Ti-0.6B types, which are characterized by cleanliness and fine, uniform distribution of

aluminide and boride phases when added to the melt at 0.01 to 0.03 % Ti, should be expected

to provide acceptable grain refinement under most conditions.

2.3.5 Grain modifier

When the alloys are made by direct electrolytic reduction, or when the normal alloys are

treated after simple melting with an alkali fluoride or with sodium or potassium, so-called

‘modified’ alloys result’’, and that ‘‘In the case of the normal alloys, the silicon occurs as

relatively large plates and needles, while in the modified ones the silicon is in a state of high

dispersion’’. The preparation of both normal and modified alloys has been the subject of a

number of patents by Pacz and by the Aluminium Company of America (ALCOA). In the

patents by Pacz, the modified alloys are prepared by melting together aluminium and silicon,

and adding to the melt an alkali fluoride, typically sodium fluoride. In the ALCOA patents,

the liquid alloys are treated with small amounts of sodium or potassium,

One way to improve mechanical properties is to add chemical modifiers which influence

microstructure formation during solidification. Additions in the range of a few 100 ppm of Sr,

Na, Ca, Ba or Eu modify the eutectic Si morphology from coarse plate-like into fine fibrous

and have a beneficial effect on both strength and ductility

Whereas in the previous studies it has been suggested that Sr alone is responsible for the

modified growth of the eutectic Si phase, the present investigations demonstrate that the

growth of modified eutectic Si phase requires Sr–Al–Si co-segregation.

21

Fig 2.4 Optical micrographs of Al–10 wt. % Si–0.1 wt. % Fe alloy showing a eutectic microstructure: (a

and b) unmodified alloy, (c and d) alloy modified by 200 ppm Sr[12].

• Addition grain refinement, modification combined action of both (Al–3Ti–1B + Al–

10Sr) to eutectic alloy significantly refines coarse columnar α-aluminium dendrites to

fine equiaxed α-aluminium dendrites.

• Grain refinement reduces inter-dendrite arm spacing of α-aluminium dendrites.

• After modification, Eutectic silicon particles are spheroidized in the matrix of

aluminium

2.4 Coating

After the mold surface have been heated to the required temperature , a refractory coating in

the form of slurry is sprayed or brushed on to the mold cavity, riser, gate, and runner

surfaces.

French chalk, calcium carbonate suspended in sodium silicate binder and zircon water base

coating is commonly used as a coating for aluminium and magnesium permanent mold

castings.

Coating is dried and then smoothed with steel wool.

Refractory coating:

22

• Protects mold surfaces from erosion and checking.

• Exercises insulating effect and thus helps obtaining progressive and directional

solidification.

• Is kept thin when chilling is needed and vice versa.

• May be repaired and normally replaced after every eight hours work.

Lubricating coatings if sprayed help removal of casting and cores form the mold. A coating

of graphite water paint permits easy removal of a 60-40 brass casting.

Permanent molds, besides refractory coating are given a carbon-aceous soot coating once

every casting cycle.

2.5 Degassing

Degassing is to remove dissolved hydrogen from the melt prior to and as close as practicable

to the casting station. Hydrogen is the only gas that can dissolve significantly in molten Al.

The major source of hydrogen is the combustion of natural gas or oil in holding furnaces.

High ambient humidity is another source of hydrogen, especially during the hot summer

months experienced in many localities. The problem is that hydrogen solubility decreases

rapidly as the metal freezes during casting, and the hydrogen comes out of solution, causing

such casting problems as twisting and flaking in thin section extrusions and blisters on cast

product. Target dissolved hydrogen content depends on the final product application, and can

range from 0.20 ml / 100g Al for general 6xxx extrusion billet down to 0.10 ml / 100g Al for

rolling slab for aerospace applications

Hydrogen is removed from the molten Al by bubbling an inert gas through the metal. Argon,

hexa-chloro-ethane tablet and nitrogen are typically used, but argon is preferred for the best

metal quality because of the tendency of nitrogen to form Al nitride inclusions and more

dross. By adding a small amount of chlorine to the inert process gas in degassers, non-wetted

inclusions and alkali metal impurities can also be removed more efficiently from the metal

FIG. 2.5 Cleaning, Degassing, and Covering process

Cleaning, degassing and covering

• Cleaning fluxes remove oxides and other non-metallic inclusions from the melt

• Drossing fluxes provide a dry dross with a low metal content

• Covering fluxes protect the melt against oxidation and hydrogen pick-up

• A low hydrogen content in the melt reduces gas porosity in the casting

• Removal of impurities improves mechanical properties and avoids distortions during

heat-treatment and machining

23

Chapter – 3

Experimental Work

24

3.1 Introduction.

3.1.1 Problem indentification

In first indenifaction of casing process for particular lm6 aluminium material .we first visited

krunal engg.limited at ctm, Amdavad .first we see the actual process of company which

material use in casting process how to makes different casting parts. But in this casting

process some defect are occurring in casting parts. So we study and analysis whole casting

process of company. After the analysis we find the reason of how to comes this types of

defect. then after study whole process find that presence of hydrogen in atmosphere and not

totally soluble in molten metal.this types of defect occurs. Different between actually

company chart and our improvement chart as under

3.2 Material Selection Present work in which use a material in whole process LM-6 alloy, which is used for p

arlam bracket, elbow petrol pump, motor body cover, adjustable flange (gear box). It has the

advantage of good resistance to wear, good bearing properties and a low coefficient of

thermal expansion.

. Aluminium - Silicon alloys have inherent advantages of being lightweight, having

high specific strength, low coefficient of thermal expansion, good mechanical properties,

good corrosion resistance and good heat transfer ability, which make them suitable

alternatives to replace components made of ferrous alloys

3.2.1 Chemical Composition of Material

Chemical composition of the eutectic (LM-6) Al-Si alloy which is used in the experiment is

show in below Table 4.1

25

Table 3.1 – Chemical composition of material

Material % Al 84.95-87.95

Si 11.900

Fe 0.610

Cu 0.1

Mn 0.489

Mg 0.10

Zn 0.10

Ni 0.10

Pb 0.10

Ti 0.2

Sn 0.05

3.3 Casting Procedure

• Select a material for casting process and all experiment.

• Use induction furnace for material melt, where material heated high melting

temperature and change solid to liquid form.

• Permanent mold is preheating to 250 °c for all casting to reduce a thermal shock it is

require preheating in present experimental work when pouring a high temperature

molten metal in mold cavity this time direct contact between metal and mould surface.

• Zircon water based coating is used for mould coating as proved effective and is

known to give excellent surface finish and protect with easily remove cast in mould

cavity

• After melt are degassing with 1 % Ar and N2 for remove soluble hydrogen form in

molten metal.

• After fluxing, proper degassing and cleaning by cover flux

• Added a grain refinement Al-5Ti-1B , Al-3Ti-1B, in molten metal to refine a structure

and Improved feeding characteristics Increased tear resistance, Improved mechanical

properties, Increased pressure tightness, Improved response to thermal treatment

• Use a grain modifier 100 ppm of Al-Sr, Na, Ca, Ba, and Eu added in molten metal to

reduce Si particle size and become a small round shape.

• Gravity die ( permanent mold) casting and pressure die casting process use for

making a cast by using LM-6 eutectic Al alloy material

3.3.1 Add grain refiner and modifier

The most widely used grain refiners are master alloys of titanium, or of titanium and boron,

in aluminium. Aluminium-titanium refiners generally contain from 3 to 10 % Ti. The same

range of titanium concentrations is used in Al-5Ti-1B, Al-3Ti-1B refiners with boron

contents from 0.2 to 1 % and titanium-to-boron ratios ranging from about 5 to 50.

3.3.2 Preheating a mold

26

To reduce a thermal shock it is require preheating in present experimental work when pouring

a high temperature molten metal in mold cavity this time direct contact between metal and

mold surface.

3.3.3 Prepare a permanent die

A gravity die , (permanent mold) casting makes use of a mold which is permanent ,this mold

can be re-use many times before it is discarded or re-built Molten metal is poured into the

mold under gravity only , No external pressure is applied to force the liquid metal into the

mold cavity

FIG 3.1 PERMANENT MOLD DIE

3.3.4 Coating a mold

A permanent mould casting must be metallurgic ally sound, have good finish and be easily

and rapidly produced. To achieve this, the die must be coated. The die coating is design to

protect the accurately machined die face, control solidification, lubricate all moving parts of

the die, impart to the casting the best possible surface finish and aid release of the casting

from the die. It should also be free from excessive fumes and prevent build-up of residues on

die faces. In experimental work zircon water based solution was used and sprayed with pilot

gun on mould surface as shown in Figure.

Table 3.2 Summary of casting Experimental Details

Casting

Method

Pouring

Temp (C°)

Weight

(kg)

Time

(hr)

Furnace Symbol

Gravity Die

Casting

750 200 5-6 Induction

furnace

H1

Pressure die

Casting

750 200 5-6 Induction

furnace

H2

27

3.4 Flow process chart improvement

28

3.5 Product after degassing by N2 gas

FIG 3.2 component without defect

3.6 Comparison between Degassing by hexacloroethane and Degassing by N2 gas

Product name

Degassing by

hexacloroethane

Degassing by

N2 Gas

Reduction

In

rejection

(%)

Accepted

(%)

Rejected

(%)

Accepted

(%)

Rejected

(%)

(1) arlam bracket

40

60

80

20

40

(2) arlam bracket

(petrol pump)

pipe fitting

30

70

80

20

50

29

(4)motor body

cover

70

30

90

10

20

(5) adjustable

flange (gear

box).

60

40

90

10

30

30

Chapter – 4

REFERENCES

31

REFERENCES

1. ASM International, Metal Handbook, Ninth Edition, Vol. 15 Casting.

2. Sufei Wei, The Centrifugal Casting Machine Company, and Steve Lampman, ASM

International ASM Handbook, Volume 15: Casting p 667-673.

3. Principle of Foundry Technology. By P.L Jain.

4. ASM International, Aluminium-Silicon Casting Alloy: Atlas of Microfractografs,

Page No. 1-9.

5. Influence of ageing process on the microstructure and mechanical properties of

aluminium-silicon cast alloys - Al-9%Si-3%Cu and Al-9%Si-0.4%Mg M.Gwózdz

K.Kwapisz Bachelor Thesis June 2008 Department of Mechanical Engineering

Component Technology Castings Jönköping University Sweden

6. Engineering Tribology Prashanta Sahoo, Prentice –Hall of India Private limited, 2005

ISBN-81-203-2724-1page No.1, 72, 81, 90.

7. Evolution of nickel-rich phases in Al–Si–Cu–Ni–Mg piston alloys with different Cu

additions Yang Yang a, Kuilong Yu a, Yunguo Li a, Degang Zhao b, Xiangfa Liu a

Key Laboratory for Liquid–Solid Structural Evolution and Processing of Materials,

Ministry of Education, Shandong University, Jinan 250061, China 2012

8. John Lenny Jr, M.E Thesis on “Replacing the Cast Iron Liners for Aluminum Engine

Cylinder Blocks: A Comparative Assessment of Potential Candidates”, April-2011.

9. Mark, Udochukwu, Thesis on “The effect of solidification rate on the microstructure

and mechanical properties of as-cast Al – Si eutectic alloy” Department of materials

and metallurgical engineering, Federal University of Technology, Owerri (2006).