Processing of Magnesium Metal Composites Through Stir Casting


Scientific Study, 2017
58 Pages, Grade: 9.1

Excerpt

LIST OF FIGURES

3.1 Stir casting schematic diagram

5.1 Horizontal metal cutting band saw
5.2 Digital weighing machine
5.3 Stir casting equipment
5.4 Squeeze casting setup
5.5 Temp. Controller with data acquisitioning system
5.6 Lathe machine with three jaw chuck

6.1 Types of squeeze casting

7.1 Methodology used for this work

8.1 Mg ingot
8.2 Measured weights of Mg ingot
8.3 Al ingot
8.4 Zn ingot
8.5 Boron carbide sample
8.6 B4C used in the casting
8.6 Titanium carbide sample
8.7 Nano level TiC powder used in the casting
8.8 Carbon nanotube powder sample
8.9 CNT powder sample used in the casting
8.10 Structure of CNT
8.11 Multi walled CNT or MWCNT

9.1 Cutting of Mg ingot into smaller pieces
9.2 Weight measurement using digital weighing M/c
9.3 Heating of ingot mixture inside the induction furnace
9.4 Uniform mixing of reinforcement powder before preheating
9.5 Adding of reinforcement powder mixture to the molten ingot mixture through a funnel
9.6 Manual Variation of RPM of Stirring blade
9.7 Transfer of molten composite into the casting die
9.8 Squeeze casting through pressure ram
9.9 Removal of casting die from the fixture
9.10 Facing process of the cast
9.11 Turning process of the cast
9.12 Specimen just after casting process
9.13 Specimen just after finishing process

10.1 Schematic diagram for machining of tensile test specimens
10.2 Tensile test specimens
10.3 Specimen machined for SEM and XRD tests
10.4 Emery papers
10.5 Unpolished and non etched specimens
10.6 Specimens after emery polishing and etching

11.1 Stress vs strain graph for SRM AL7Z1
11.2 SRM AL7Z1 after fracture
11.3 Stress vs strain graph for SRM AL12Z1
11.4 SRM AL12Z1 after fracture
11.5 Stress vs strain graph for SRM AL14Z1
11.6 SRM AL14Z1after fracture
11.7 Micro Vickers hardness test equipment
11.8 Magnification of 50X -SRM AL7Z1
11.9 Magnification of 100X- SRM AL7Z1
11.10 Magnification of 200X -SRM AL7Z1
11.11 Magnification of 500X -SRM AL7Z1
11.12 Magnification of 50X SRM-AL12Z1
11.13 Magnification of 100X -SRM AL12Z1
11.14 Magnification of 200X -SRM AL12Z1
11.15 Magnification of 500X -SRM AL12Z1
11.16 Magnification of 50X- SRM AL14Z1
11.17 Magnification of 100X -SRM AL14Z1
11.18 Magnification of 200X -SRM AL14Z1
11.19 Magnification of 500X -SRM AL14Z1
11.20 XRD image for SRM AL7Z1
11.21 XRD image for SRM AL12Z1
11.22 XRD image for SRM AL14Z1
11.23 SEM image at Magnification of 250-SRM AL7Z1
11.24 SEM image at Magnification of 500-SRM AL7Z1
11.25 SEM image at Magnification of 1000 -SRM AL7Z1
11.26 SEM image at Magnification of 2000 -SRM AL7Z1
11.27 SEM image at Magnification of 700-SRM AL12Z1
11.28 SEM image at Magnification of 1300-SRM AL12Z1
11.29 SEM image at Magnification of 2500 -SRM AL12Z1
11.30 SEM image at Magnification of 5000-SRM AL12Z1
11.31 SEM image at Magnification of 600-SRM AL14Z1
11.32 SEM image at Magnification of 1300-SRM AL14Z1
11.33 SEM image at Magnification of 2500-SRM AL14Z1
11.34 SEM image at Magnification of 5000-SRM AL14Z1

Image sources: Author's own work

LIST OF TABLES

3.1 Mechanical properties and chemical composition of Mg alloys
3.2 Mechanical properties and chemical composition of Mg alloys

8.1 Thermal and mechanical properties of pure Mg
8.2 Thermal and mechanical properties of pure Al
8.3 Thermal and mechanical properties of pure Zn
8.4 Thermal and mechanical properties of pure B4C
8.5 Thermal and mechanical properties of pure TiC
8.6 Thermal and mechanical properties of pure MWCNT

11.1 Tensile test results tabulated for SRM AL7Z1
11.2 Tensile test results tabulated for SRM AL12Z1
11.3 Tensile test results tabulated for SRM AL14Z1
11.4 Tensile test results comparison test
11.5 Tabulated results for Micro Vickers hardness test

LIST OF ABBREVIATIONS

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ABSTRACT

Magnesium matrix composites are potential materials for various applications of aerospace and defense organizations due to their low density, good mechanical and physical properties. The improvement of specific strength, stiffness, damping behavior, wear behavior, creep and fatigue properties are significantly influenced by the addition of reinforcing elements into the metallic matrix compared to the conventional engineering materials. This report presents an overview on the effects of different reinforcements in the magnesium and its alloy, so as to improve their mechanical and metallurgical properties. The morphology of microstructure and its effect on the physical properties of the magnesium is also discussed here. The micrograph showed that there was distribution of Boron carbide(B4C), Titanium carbide(TiC) and Carbon nanotubes(CNT) throughout the matrix. These nano particles were strengthening the magnesium nano novel composite through dispersion strengthening. Moreover, from the results, we understood that there was a considerable improvement in the tensile strength and hardness compared to the parent material.

ACKNOWLEDGEMENT

We would like to extend our gratitude to all the people who helped in bringing this project to fuition. First, we would like to thank the management for their academic and technical support. We are also thankful to director (E&T). Dr. C.Muthamizhchelvan.

We are highly indebted to Dr. S.Prabhu, PhD, Professor and Head, Dept. of Mechanical engineering for his guidance and for providing us the necessary information regarding the project and also for his cordial support.

We would like to express our sincere gratitude to our guide, Dr. A.Razal Rose, for his valuable guidance, consistent encouragement, personal caring, timely help and providing us with an excellent atmosphere for doing this research. All through the work, in spite of his busy schedule, he has extended affable support to us for completing this research work.

This project would not have completed without the help of Lab assistants in the Manufacturing lab and Metallurgical lab who were always there to guide us through the minute details of operating each equipment used for the tests. We take this opportunity to express our appreciation for the excellent support provided by all other staff members for their active involvement and their valuable inputs in making the project successful.

CHAPTER 1 INTRODUCTION

All the mechanical industries have a very specific aim, to minimize the effort and increase the efficiency of a system. This case applies to all the diverse fields of research under mechanical engineering. For the manufacturing sector, the main motive of the engineer is to improve the mechanical and metallurgical properties of a given material. In today’s fast paced developing world, we need materials which are light in weight without compromising the strength of the material. The high strength materials can be obtained by carrying out various conventional casting techniques. Stir casting allows fabricating materials which satisfy the required conditions of the product having light weight and high specific strength.

1.1 The Need to Fabricate Magnesium Metal Composites

Metal Matrix Composites (MMCs) are finding increasing applications in many of today’s industries. Magnesium and its alloys have gained widespread attention and popularity in scientific research as well as commercial application as energy conservation and performance demands are increasing because of their low density, approximately two-third of that of aluminium, and high specific strength compared to other structural metals. These properties are important in automotive and aerospace applications to reduce fuel consumption. However the application of Magnesium alloys is limited due to poor creep resistance at high temperatures and low modulus. Therefore, REINFORCEMENTS are needed to improve the properties of the base metal. MMCs fabricated from magnesium will provide attractive alternatives to aluminum MMCs.

1.2 Scope of Investigation

The improvement of specific strength, hardness, tensile strength, density, and other mechanical properties are significantly influenced by the addition of reinforcing elements into the metal matrix .This report presents the overview on the casting work and testing carried out on three different Magnesium composites having varying amounts of reinforcement materials, highlighting their merits and demerits.

CHAPTER 2 LITERATURE SURVEY

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CHAPTER 3 BACKGROUND OF THE WORK

The materials are broadly classified into two different categories, namely, Metals and Non metals. These materials have further been classified into;

- Ferrous metals - These are metals which contain iron (Fe) as their components.
- Non ferrous metals- These are metals which do not contain Fe as their components.

Non ferrous metals include Aluminium, Magnesium, Copper, Nickel, etc

Commercially, pure metals are used for various purposes ; aluminium for foil, copper for coils of electrical conductors, nickel and chromium for plating and gold for electrical contacts. Although pure metals have somewhat limited properties, these properties can be enhanced and modified by alloying.

An alloy is composed of two or more chemical elements, at least one of which is a metal. The majority of metals used in the engineering field applications are some form of alloys. Two terms are essential to describe alloys :

1) Solute - It is the minor element that is added to the solvent
2) Solvent - It is the major element of the alloy

Magnesium (Mg) is the lightest engineering metal available, and it has good vibration damping characteristics. Its alloys are used in structural and non structural applications whenever weight is of primary importance. Uses of magnesium alloys range from aircraft and missile components, material handling equipment, portable power tools, ladders, luggage, bicycles, sporting goods and general lightweight components.

3.1 Magnesium Alloys

Because it is not sufficiently strong in its pure form, magnesium is alloyed with various elements in order to gain certain specific properties, particularly high strength to weight ratio. A variety of Mg alloys have good casting, forming and machining characteristics. Because they oxidize rapidly (pyrophoric) , a fire hazard exists, and precautions must be taken when machining Mg. However, products made from Mg alloys are not a fire hazard in normal use.

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[Note - Percentage of component/solute is taken by weight of the total solvent present]

3.2 Why should we select Magnesium ?

Apart from Mg alloys showing great specific strength to weight ratio, Magnesium is also the third most abundant metallic element (2%) in the Earth’s crust, coming after iron and aluminium. Most magnesium comes from sea water, which contains 0.13% Mg in the form of Magnesium chloride. So its is farely simple to extract Mg electrolytically or by thermal reduction.

Table 3.1 Mechanical properties and chemical

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Among the major developments in materials in recent years are composite materials. In fact composite materials are now one of the most important classes of engineered materials, because they offer several outstanding properties compared to conventional materials.

A composite material is a combination of two or more chemically distinct and insoluble phases; its properties and structural performance are superior to those of the constituents acting independently.

It consists of a base material which is known as MATRIX and the elements added to this matrix for strengthening purposes is known as REINFORECMENTS.

3.3 Metal Matrix Composites (MMCs)

The advantages of a metal matrix over a polymer matrix are its higher elastic modulus, its resistance to elevated temperatures, and its higher toughness and ductility.

Matrix materials in these composites are usually aluminium, aluminium-lithium, magnesium, copper, titanium, and superalloys. Fiber materials or reinforcements can be graphite, aluminium oxide, silicon carbide, boron, molybdenum, and tungsten. The elastic modulus of non metallic fibers ranges between 200 Gpa and 400Gpa, with tensile strength being in the range from 2000Mpa to 3000Mpa.

Table3.2 : MMCs with applications

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3.4 Magnesium Composites

MMCs fabricated from Mg provides attractive alternatives to Al MMCs. It is widely popular due to its low density, almost two-third of that of aluminum. As the lightest metal structural material, Mg composites ehibit many advantages over monolithic magnesium or magnesium alloys, such as high elastic modulus, high strength , superior creep and wear resistances at elevated temperatures.

However there is a reduction in ductility. This taken care by judicious selection of reinforcements. The most commonly used reinforcements are Silicon Carbide (SiC), Aluminium Oxide(Al2O3), and Titanium Carbide(TiC). SiC and other carbide reinforcements increase the ultimate tensile strength , yield strength , hardness , ductility, and wear resistance of Mg and its alloys.

Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process.

3.5 Stir Casting

Stir casting is used widely to fabricate Al and Mg based composites. This technique causes the molten mixture inside the induction furnace to rotate at high speeds, causing the reinforcement particles to mix thoroughly throughout the mixture. It promotes dispersion strengthening.

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Figure 3.1: Stir casting schematic diagram

3.6 Dispersion Strengthened Composites

Metals and metal alloys may be strengthened and hardened by the uniform dispersion of several volume percent of fine particles of a very hard and inert material. The dispersed phase may be metallic or nonmetallic oxide materials are often used .Again, the strengthening mechanism involves interactions between the particles and dislocations within the matrix, as with precipitation hardening. The dispersion strengthening effect is not as pronounced as with precipitation hardening; however, the strengthening is retained at elevated temperatures and for extended time periods because the dispersed particles are chosen to be non reactive with the matrix phase. For precipitation-hardened alloys, the increase in strength may disappear upon heat treatment as a consequence of precipitate growth or dissolution of the precipitate phase.

CHAPTER 4 OBJECTIVE OF THE PROJECT

- Upon extensive research in the respected and renowned journals, we found that a lot of work has been going on fabrications of light weight materials. So considerable number if journals were studied and we came to know about the structural and mechanical properties of magnesium, especially its extremely light weight. We further found that substantial work has been carried out with different aluminium percentages in the magnesium composites, but very limited work had been carried using squeeze casting technique with the aluminum percentages of 7%, 12% and 14%. Thus the main aim of our project is to fabricate a new series of magnesium composites with the respective new proportions of aluminium.

- This research work deals with the stir casting technique accompanied by squeeze casting as this method produces castings which promote recyclability of materials, are easy to dispose because they are environment friendly and clean. The fabricated materials can also be put in as a referential use for scientists and engineers to use these composites for further research as well as structural purposes.

- We also plan on improving the mechanical and metallurgical properties of the magnesium alloys and the morphology of microstructure is dealt in this research work.

CHAPTER 5 EXPERIMENTAL WORK

The following were the equipments that were required for the fabrication of the composite specimens ;

5.1 Horizontal Metal Cutting Bandsaw

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Figure 5.1: Horizontal metal cutting bandsaw

- This machine was used to cut the magnesium ingot (weight =4kg) into smaller and lighter pieces so as to accommodate the pieces inside the induction furnace for heating purpose.

- The saw band (cutting tool) is made up of High Speed Steel (HSS), which slides perpendicular to the axis of the ingot fixed on the vice of the machine.

- As the saw band slides over the metal to be cut, the weight of the bandsaw arm pushes the cutting tool downwards.

- The metal is cut according to the set thickness, and after the process, the metal is cut and collected on the guideway.

5.2 Digital Weighing Machine

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Figure 5.2: Digital weighing machine

- The weight of the cut magnesium pieces are measured by the digital weighing machine, so that we can measure the magnesium ingot quantity up to 1kg.

- The total weight of the magnesium allowed is not more than 1kg since the casting die cannot accommodate more than that and we also need to add the reinforcements. We need to avoid the over spilling of the material.

- Estimated amount of magnesium should be around 950g to 990g.

- The total amount of mixture, that is, including the reinforcements and the aluminium and zinc ingots

should not exceed a total weight of 1kg.

- The magnesium ingot pieces, after being weighed, are undergone through burring, a process to clean the metal off all dust and impurities to prevent excess amount of slag.

5.3 Stir Casting Equipment used in this Research work

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Figure 5.3: Stir casting equipment

- The stir casting apparatus consists of an induction furnace which has a cavity to store the material for heating it to molten form

- A stirring screw is fit right above the induction furnace, whose stirring blades enter the furnace.

- The stirring screw is controlled by an automated arm, which can lift the screw as well as drop the screw inside the furnace.

- Depending on the requirement, the speed of the stirrer screw can be controlled through an automated system

having a feedback mechanism.

- The furnace has an outlet called the runner, to which a gate is connected. This gate runs all the way down to the squeeze casting setup.

- This stir casting setup is controlled by a temperature controller and data acquisition system.

5.3.1 Squeeze casting setup

- This setup consists of a pressure ram which is fir on top of a casting die.
- The die is kept on a fixture to hold on to the die, so that it can withstand the load from the pressure ram.
- The pressure ram is controlled by a hydraulic press, which can be operated by a controller as per the requirement.
- The pressure ram is directly on top of the casting die, so when the molten metal enters the die through the runner, the pressure ram is activated and the ram compresses the molten metal inside the die.
- The die is then kept for 10min to let the molten metal cool by air.
- The die is then taken off from the fixture and the screws are taken off.
- The casting is then taken out from the die and taken for further processing.

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Figure 5.4: Squeeze casting setup

5.3.2 Temperature controller with Data Acquisition System

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Figure 5.5: Temp. controller with data acquisitioning system

- The temperature controller is a system which is linked to the Stir casting setup.
- It is used to regulate the heat inside the induction furnace of the stir casting system.
- This system consists of a temperature controller, which shows the temperature that is required by the operator.
- The display showing Preheat temperature controller shows the temperature to which the induction furnace is preheated to, before addition of the raw materials.
- The Temperature Indicator display shows the actual temperature inside the furnace.
- Therefore it is a system of feedback mechanism, continuously trying to reach the required temperature.
- The Pressure display shows the amount of Pressure force that is applied on the molten metal inside the die.

[...]

Excerpt out of 58 pages

Details

Title
Processing of Magnesium Metal Composites Through Stir Casting
College
SRM University
Grade
9.1
Authors
Year
2017
Pages
58
Catalog Number
V376163
ISBN (eBook)
9783668547360
ISBN (Book)
9783668547377
File size
3607 KB
Language
English
Tags
processing, magnesium, metal, composites, through, stir, casting
Quote paper
Akshansh Mishra (Author)Anish Das Gupta (Author), 2017, Processing of Magnesium Metal Composites Through Stir Casting, Munich, GRIN Verlag, https://www.grin.com/document/376163

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