CREATION OF NEW MAGNESIUM-BASED MATERIAL
USING DIFFERENT TYPES OF REINFORCEMENTS

SYED FIDA HASSAN

NATIONAL UNIVERSITY OF SINGAPORE
2006


CREATION OF NEW MAGNESIUM-BASED MATERIAL
USING DIFFERENT TYPES OF REINFORCEMENTS

SYED FIDA HASSAN
(BSc Eng., BUET, Bangladesh, M. Eng., NUS, Singapore)

A THESIS SUBMITTED
FOR THE DEGREE OF DOCTOR OF PHILOSOPHY
DEPARTMENT OF MECHANICAL ENGINEERING
NATIONAL UNIVERSITY OF SINGAPORE
2006


Preamble

Preamble
This thesis is submitted for the degree of Doctor of Philosophy in the
Department of Mechanical Engineering, National University of Singapore, under the
supervision of Associate Professor Manoj Gupta. No part of this thesis has been
submitted for any degree or diploma at any other Universities or Institution. As far as
this candidate is aware, all work in this thesis is original unless reference is made to
other work. Part of this thesis has been published and accepted for publication in the

following Journals:

Publications: Journals
™

S.F. Hassan and M. Gupta, “Development of Nano-Y2O3 Containing
Magnesium Nanocomposites Using Solidification Processing”, Journal of
Alloys and Compounds, 2006 (in Press).

™

S.F. Hassan and M. Gupta, “Effect of Different Types of Nano-size Oxide
Particulates on Microstructural and Mechanical Properties of Elemental Mg”,
.Journal of Materials Science, 41 (2006) 2229-2236.

™

S.F. Hassan and M. Gupta, “Effect of Particulate Size of Al2O3
Reinforcement on Microstructure and Mechanical Behavior of Solidification
Processed Elemental Mg”, Journal of Alloys and Compounds, 419 (2006)
84-90.

™

S.F. Hassan and M. Gupta, “Effect of length scale of Al2O3 particulates on
microstructural and tensile properties of elemental Mg”, Materials Science
and Engineering A, 425 (1-2) (2006) 22-27.

™


S.F. Hassan and M. Gupta, “Effect of Type of Primary Processing on the
Microstructure, CTE and Mechanical Properties of Magnesium/Alumina
Nanocomposites”, Composite Structures, 72 (1) (2006) 19-26.

Creation of New Mg-Based Material Using Different Types of Reinforcements by S. Fida Hassan

i


Preamble

™

S.F. Hassan and M. Gupta, “Development of high performance magnesium
nano-composites using nano-Al2O3 as reinforcement”, Materials Science and
Engineering A, 392 (2005) 163-168.

™

S.F. Hassan and M. Gupta, “Enhancing Physical and Mechanical Properties
of

Mg

Using

Nano-Sized

Al2O3


Particulates

as

Reinforcement”,

Metallurgical and Materials Transactions A, 36A (2005) 2253-2258.
™

N. Srikanth, Syed Fida Hassan and Manoj Gupta, “Energy Dissipation
Studies of Mg Based Nanocomposites “Using an Innovative Circle-fit
Approach”, Journal of Composite Materials. 38 (22) (2005) 2037-2048.

™

S.F. Hassan and M. Gupta, “Creation of High Performance Mg Based
Composite Containing Nano-size Al2O3 Particulates as Reinforcement”,
.Journal of Metastable and Nanocrystalline Materials, Vol. 23 (2005) pp.
151-154.

™

S.F. Hassan and M. Gupta, “Development of high-performance magnesium
nano-composites using solidification processing route”, Materials Science
and Technology, 20 (2004) 1383-1388.

Creation of New Mg-Based Material Using Different Types of Reinforcements by S. Fida Hassan

ii



Acknowledgement

Acknowledgements
I would like to thank my supervisor Associate Professor Manoj Gupta for
giving me an opportunity to work under him as well as for his priceless guidance,
advice, motivation and patience. In particular, Associate Professor Manoj Gupta’s
recommendations and suggestions have been invaluable for this research work.
I would like to thank my colleagues for their friendship and valuable
suggestions. I am grateful to Mr. Thomas Tan Bah Chee, Mr. Abdul Khalim Bin
Abdul, Mr. Juraimi Bin Madon, Mr. Maung Aye Thein and Mr. Ng Hong Wei of the
Materials Science Laboratory of NUS for their support and assistance. Special thanks
to Mrs. Zhong Xiang Li for her cordial help in metallography for the new types of
nanocomposites.
I would like to acknowledge financial support for this project provided by the
National University of Singapore in the form of Research Scholarship.
Finally, words alone cannot express the thanks I owe to my parents, siblings
and wife for their love, affection and encouragement without which this work would
not have been possible.
I dedicate this work to almighty ALLAH and to his true representatives
for their blessings and causeless descending mercy.

Creation of New Mg-Based Material Using Different Types of Reinforcements by S. Fida Hassan iii


Table of Contents

Table of Contents
Page
i


Preamble
Acknowledgements

iii

Table of Contents

iv

Summary

ix

List of Tables

xi

List of Figures

xiii

Chapter 1

Introduction

Chapter 2

Literature Survey


1

2.1

Introduction

4

2.2

Reinforcement Particulates selection

5

2.3

Particulates Used In Magnesium-Based Composites

8

2.3.1

Silicon Carbide (SiC)

8

2.3.2

Yttria (Y2O3)


9

2.3.3

Titanium Boraide (TiB2)

9

2.3.4

Zirconium Boride (ZrB2)

9

2.3.5

Titanium Carbide (TiC)

10

2.3.6

Boron Carbide (B4C)

10

2.3.7

Zirconia (ZrO2)


10

2.3.8

Alumina (Al2O3)

10

2.3.9

Diamond (C)

11

2.3.10

Copper (Cu)

11

2.3.11

Nickel (Ni)

11

2.3.12

Titanium (Ti)


11

2.4

Fabrication Methods of Magnesium Based MMCs

12

2.4.1

12

Liquid-Phase Processes

2.4.1.1

Conventional Casting

13

2.4.1.2

Infiltration Process

14

2.4.1.3

Squeeze Casting


15

2.4.1.4

In-Situ Process

16

2.4.2

Solid-Phase Process

16

2.4.3

Two-Phase Processes

16

2.4.3.1

Spray Forming

17

2.4.3.2

Disintegrated Melt Deposition


17

Creation of New Mg-Based Material Using Different Types of Reinforcements by S. Fida Hassan

iv


Table of Contents

2.4.3.3
2.6

Compocasting

Summary

Chapter 3

17
18

Materials and Methods

3.1

Overview

20

3.2


Materials

20

3.3

Primary Processing

21

3.3.1

Disintegrated Melt Deposition Technique

21

3.3.2

Blend-Press-Sinter Powder Metallurgy Technique

22

3.4

Extrusion

23

3.5


Density Measurement

23

3.6

Microstructural Characterization

23

3.7

Mechanical Characterization

24

3.7.1

Macrohardness

24

3.7.2

Microhardness

24

3.7.3


Tensile Test

25

3.7.4

Fractography

25

Chapter 4
4.1

4.2

4.3

4.4

Results

DMD Processed nano-Al2O3 Reinforced Nanocomposites

26

4.1.1

Macrostructure


26

4.1.2

Density Measurement

26

4.1.3

Microstructural Characterization

26

4.1.4

Mechanical Properties

27

PM Processed nano-Al2O3 Reinforced Nanocomposites

30

4.2.1

Macrostructure

30


4.2.2

Density Measurement

30

4.2.3

Microstructural Characterization

30

4.2.4

Mechanical Properties

31

DMD Processed nano-Y2O3 Reinforced Nanocomposites

33

4.3.1

Macrostructure

33

4.3.2


Density Measurement

33

4.3.3

Microstructural Characterization

33

4.3.4

Mechanical Properties

34

PM Processed nano-Y2O3 Reinforced Nanocomposites

36

4.4.1

Macrostructure

36

4.4.2

Density Measurement


36

Creation of New Mg-Based Material Using Different Types of Reinforcements by S. Fida Hassan

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Table of Contents

4.5

4.6

4.4.3

Microstructural Characterization

36

4.4.4

Mechanical Properties

37

DMD Processed nano-ZrO2 Reinforced Composites

39

4.5.1


Macrostructure

39

4.5.2

Density Measurement

39

4.5.3

Microstructural Characterization

39

4.5.4

Mechanical Properties

40

PM Processed nano-ZrO2 Reinforced Composites

42

4.6.1

Macrostructure


42

4.6.2

Density Measurement

42

4.6.3

Microstructural Characterization

42

4.6.4

Mechanical Properties

43

4.7 DMD Processed 0.3µm-Al2O3 Reinforced Composites

4.8

4.9

4.7.1

Macrostructure


45

4.7.2

Density Measurement

45

4.7.3

Microstructural Characterization

45

4.7.4

Mechanical Properties

46

PM Processed 0.3µm-Al2O3 Reinforced Composites

48

4.8.1

Macrostructure

48


4.8.2

Density Measurement

48

4.8.3

Microstructural Characterization

48

4.8.4

Mechanical Properties

49

DMD Processed 1µm-Al2O3 Reinforced Composites

51

4.9.1

Macrostructure

51

4.9.2


Density Measurement

51

4.9.3

Microstructural Characterization

51

4.9.4

Mechanical Properties

52

4.10 PM Processed 1µm-Al2O3 Reinforced Composites

54

4.10.1

Macrostructure

54

4.10.2

Density Measurement


54

4.10.3

Microstructural Characterization

54

4.10.4

Mechanical Properties

55

Chapter 5
5.1

45

Discussion

DMD Processed nano-Al2O3 Reinforced Nanocomposites

58

5.1.1

58


Synthesis of Mg and Mg/Al2O3 Materials

Creation of New Mg-Based Material Using Different Types of Reinforcements by S. Fida Hassan

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Table of Contents

5.2

5.3

5.4

5.5

5.6

5.7

5.8

5.9

5.1.2

Microstructural Behavior

58


5.1.3

Mechanical Properties

60

PM Processed nano-Al2O3 Reinforced Nanocomposites

64

5.2.1

Microstructural Behavior

64

5.2.2

Mechanical Properties

65

DMD Processed nano-Y2O3 Reinforced Nanocomposites

69

5.3.1

Synthesis of Mg and Mg/Y2O3 Materials


69

5.3.2

Microstructural Behavior

69

5.3.3

Mechanical Properties

71

PM Processed nano-Y2O3 Reinforced Nanocomposites

76

5.4.1

Microstructural Behavior

76

5.4.2

Mechanical Properties

77


DMD Processed nano-ZrO2 Reinforced Nanocomposites

81

5.5.1

Synthesis of Mg and Mg/ZrO2 Materials

81

5.5.2

Microstructural Behavior

81

5.5.3

Mechanical Properties

83

PM Processed nano-ZrO2 Reinforced Nanocomposites

86

5.6.1

Microstructural Behavior


86

5.6.2

Mechanical Properties

87

DMD Processed 0.3µm-Al2O3 Reinforced Nanocomposites

91

5.7.1

Synthesis of Mg and Mg/Al2O3 Materials

91

5.7.2

Microstructural Behavior

91

5.7.3

Mechanical Properties

93


PM Processed 0.3µm-Al2O3 Reinforced Nanocomposites

98

5.8.1

Microstructural Behavior

98

5.8.2

Mechanical Properties

99

DMD Processed 1µm-Al2O3 Reinforced Nanocomposites

104

5.9.1

Synthesis of Mg and Mg/Al2O3 Materials

104

5.9.2

Microstructural Behavior


104

5.9.3

Mechanical Properties

106

5.10 PM Processed 1µm-Al2O3 Reinforced Nanocomposites
5.10.1

Microstructural Behavior

111

5.10.2

Mechanical Properties

112

Chapter 6
6.1

111

Conclusions and Recommendations

Conclusions: Types of Materials


117

Creation of New Mg-Based Material Using Different Types of Reinforcements by S. Fida Hassan vii


Table of Contents

6.1.1

DMD Processed nano-Al2O3 Reinforced Nanocomposites

117

6.1.2

PM Processed nano-Al2O3 Reinforced Nanocomposites

117

6.1.3

DMD Processed nano-Y2O3 Reinforced Nanocomposites

118

6.1.4

PM Processed nano-Y2O3 Reinforced Nanocomposites


119

6.1.5

DMD Processed nano-ZrO2 Reinforced Nanocomposites

120

6.1.6

PM Processed nano-ZrO2 Reinforced Nanocomposites

120

6.1.7

DMD Processed 0.3µm-Al2O3 Reinforced Composites

121

6.1.8

PM Processed 0.3µm-Al2O3 Reinforced Composites

122

6.1.9

DMD Processed 1µm-Al2O3 Reinforced Composites


123

6.1.10

PM Processed 1µm-Al2O3 Reinforced Composites

123

6.2

Conclusions: Comparative on Reinforcements and Processing

125

6.3

Recommendations for Future Work

127

References

128

Appendix
Appendix A DMD Log Book

138

Appendix B Coefficient of Thermal Expansion


154

Appendix C Density

156

Creation of New Mg-Based Material Using Different Types of Reinforcements by S. Fida Hassan viii


Summary

Summary
This project addresses three points: (1) the feasibility of synthesizing different
types of nano-size oxide ceramic reinforced metal matrix composites using an
innovative solidification processing route commonly known as disintegrated melt
deposition (DMD) and blend-press-sinter powder metallurgy (PM) technique and to
study the effectiveness of the type of processing, (2) the effects of various types of
nano-size oxide ceramic particulates in varying amounts on the microstructural and
mechanical properties of pure magnesium and to identify the most potential type of
reinforcement, and (3) to study the effect of length scale (nanometer to micrometer
size) of the most potential oxide ceramic reinforcement. All the above objectives were
validated by a thorough and in-depth microstructural, physical and mechanical
properties characterization of the extruded samples.
The composite materials were successfully synthesized using both the DMD
and PM techniques followed by hot extrusion. Nano-size particulates of Al2O3, Y2O3
and ZrO2 were separately incorporated as reinforcement in magnesium matrix in the
first stage to select the most potential reinforcement.

The macrostructural


characterization conducted on the composite materials did not show the presence of
defects as macropores or shrinkage cavities in the cases of DMD processed
nanocomposites and surface crack or deformation in the cases of PM processed
nanocomposites, which indicates the feasibility of both the DMD and PM processing
for

synthesizing

nano-size

oxide

ceramic

reinforced

magnesium

based

nanocomposites.
Microstructural characterization revealed fairly uniform distribution of
reinforcement with good interfacial integrity and significant grain refinement in
magnesium matrix for most of the nanocomposites. However, DMD processed

Creation of New Mg-Based Material Using Different Types of Reinforcements by S. Fida Hassan

ix



Summary

samples showed relatively better reinforcement distribution and grain refinement when
compared to the PM processed nanocomposite samples.
Mechanical properties of the materials were analyzed by conducting hardness
(micro as well as macro) and tensile tests. The results of the hardness test revealed that
the matrix hardness of the composite materials was increased by the incorporation of
nano-size Al2O3, Y2O3 and ZrO2. The tensile properties results showed that the
strength, ductility and work of fracture of most of the nanocomposites were
significantly increased as a result of the presence of reinforcement. However, superior
combination of mechanical properties of nano-size Al2O3 reinforced materials made
them most potential candidate for strength based designs (higher yield strength when
compared to magnesium) and damage tolerant designs (higher work of fracture when
compared to magnesium) with good formability among all the developed
nanocomposites.
It is interesting to note that the fracture surface study on the nanocomposites
revealed the change of fracture mode of magnesium matrix from complete cleavage to
mixed mode of ductile and intergranular, dominated by formation, growth and
coalescence of the microscopic voids with the activation of non-basal slip system
triggered by the presence of nano-size oxide particulates.
Effectiveness of Al2O3 particulates to improve room temperature mechanical
properties is found to be: (a) increased with decreasing particulate size (50-nm, 0.3μm
and 1μm used in this study), and (b) within the range of 0.66 to 1.11volume percentage
of reinforcement (0.22 to 2.49 volume percentages used in this study).
Different types of materials are reported separately in this report for easy
readability.

Creation of New Mg-Based Material Using Different Types of Reinforcements by S. Fida Hassan


x


List of Tables

List of Tables
Page
Table 4.1.1

Results of density, porosity and grain morphology of DMD
processed Mg/Al2O3 nanocomposites.

26

Table 4.1.2

Results of room temperature mechanical properties of DMD
processed Mg/Al2O3 nanocomposites.

27

Table 4.1.3

Specific strength and work of fracture of DMD processed
Mg/Al2O3 nanocomposites.

28

Table 4.2.1


Results of density, porosity and grain morphology of PM
processed Mg/Al2O3 nanocomposites.

30

Table 4.2.2

Results of room temperature mechanical properties of PM
processed Mg/Al2O3 nanocomposites.

31

Table 4.2.3

Specific strength and work of fracture of PM processed
Mg/Al2O3 nanocomposites.

32

Table 4.3.1

Results of density, porosity and grain morphology of DMD
processed Mg/Y2O3 nanocomposites.

33

Table 4.3.2

Results of room temperature mechanical properties of DMD
processed Mg/Y2O3 nanocomposites.


34

Table 4.3.3

Specific strength and work of fracture of DMD processed
Mg/Y2O3 nanocomposites.

35

Table 4.4.1

Results of density, porosity and grain morphology of PM
processed Mg/Y2O3 nanocomposites.

36

Table 4.4.2

Results of room temperature mechanical properties of PM
processed Mg/Y2O3 nanocomposites.

37

Table 4.4.3

Specific strength and work of fracture of PM processed
Mg/Y2O3 nanocomposites.

38


Table 4.5.1

Results of density, porosity and grain morphology of DMD
processed Mg/ZrO2 nanocomposites.

39

Table 4.5.2

Results of room temperature mechanical properties of DMD
processed Mg/ZrO2 nanocomposites.

40

Table 4.5.3

Specific strength and work of fracture of DMD processed
Mg/ZrO2 nanocomposites.

41

Table 4.6.1

Results of density, porosity and grain morphology of PM
processed Mg/ZrO2 nanocomposites.

42

Creation of New Mg-Based Material Using Different Types of Reinforcements by S. Fida Hassan


xi


List of Tables

Page
Table 4.6.2

Results of room temperature mechanical properties of PM
processed Mg/ZrO2 nanocomposites.

43

Table 4.6.3

Specific strength and work of fracture of PM processed
Mg/ZrO2 nanocomposites.

44

Table 4.7.1

Results of density, porosity and grain morphology of DMD
processed 0.3µm-Al2O3 particulates reinforced composites.

45

Table 4.7.2


Results of room temperature mechanical properties of DMD
processed 0.3µm-Al2O3 particulates reinforced composites.

46

Table 4.7.3

Specific strength and work of fracture of DMD processed
0.3µm-Al2O3 particulates reinforced composites.

47

Table 4.8.1

Results of density, porosity and grain morphology of PM
processed 0.3µm-Al2O3 particulates reinforced composites.

48

Table 4.8.2

Results of room temperature mechanical properties of PM
processed 0.3µm-Al2O3 particulates reinforced composites.

49

Table 4.8.3

Specific strength and work of fracture of PM processed 0.3µmAl2O3 particulates reinforced composites.


50

Table 4.9.1

Results of density, porosity and grain morphology of DMD
processed 1µm-Al2O3 particulates reinforced composites.

51

Table 4.9.2

Results of room temperature mechanical properties of DMD
processed 1µm-Al2O3 particulates reinforced composites.

52

Table 4.9.3

Specific strength and work of fracture of DMD processed 1µmAl2O3 particulates reinforced composites.

53

Table 4.10.1

Results of density, porosity and grain morphology of PM
processed 1µm-Al2O3 particulates reinforced composites.

54

Table 4.10.2


Results of room temperature mechanical properties of PM
processed 1µm-Al2O3 particulates reinforced composites.

55

Table 4.10.3

Specific strength and work of fracture of PM processed 1µmAl2O3 particulates reinforced composites.

57

Creation of New Mg-Based Material Using Different Types of Reinforcements by S. Fida Hassan xii


List of Figures

List of Figures
Page
7

Figure 2.2.1

Schematic diagram showing contact angle formed between
reinforcement, molten matrix and air phases.

Figure 3.3.1

Schematic diagram of Disintegrated Melt Deposition technique.


22

Figure 4.1.1

Representative
micrographs
showing:
nano-Al2O3
reinforcement distribution in the case of Mg/1.11Al2O3
nanocomposite (using FESEM) in (a) and grain morphology for
Mg and Mg/1.11Al2O3 in (b) & (c), respectively.

27

Figure 4.1.2

Representative SEM fractographs showing brittle-ductile like
features in the cases of: (a) & (b) unreinforced Mg and (c) & (d)
1.11-volume percentage of nano-Al2O3 reinforced Mg,
respectively.

28

Figure 4.1.3

Representative SEM fractographs showing: (a) straight lines
due to slip in the basal plane in Mg, (b) uneven lines
supposedly due to combined effect of basal and non-basal slip
[20] in Mg/1.11Al2O3, respectively.


29

Figure 4.2.1

Representative
micrographs
showing:
nano-Al2O3
reinforcement distribution in Mg/1.11Al2O3 sample (using
Quanta 3D) in (a) and grain morphology for Mg and
Mg/1.11Al2O3 in (b) & (c), respectively.

31

Figure 4.2.2

Representative SEM fractographs showing brittle-ductile like
features in the cases of: (a) & (b) unreinforced Mg, and (c) &
(d) 0.66-volume percentage of nano-Al2O3 reinforced Mg,
respectively.

32

Figure 4.3.1

Representative micrographs showing: nano-Y2O3 reinforcement
distribution in the case of Mg/1.11Y2O3 nanocomposite (using
FESEM) in (a) and grain morphology for Mg and Mg/0.66Y2O3
in (b) & (c), respectively.


34

Figure 4.3.2

Representative SEM fractographs showing: brittle-ductile like
features in unreinforced Mg (a) and (b) & (c) in Mg/0.22Y2O3,
and intergranular microcracks in Mg/1.11Y2O3 (d),
respectively.

35

Figure 4.4.1

Representative micrographs showing: nano-Y2O3 reinforcement
distribution in the case of Mg/1.11Y2O3 nanocomposite (using
FESEM) in (a) and grain morphology for Mg and Mg/0.22Y2O3
in (b) & (c), respectively.

37

Creation of New Mg-Based Material Using Different Types of Reinforcements by S. Fida Hassan xiii


List of Figures

Figure 4.4.2

Page
Representative SEM fractographs showing brittle-ductile like
38

features in the cases of: (a) & (b) unreinforced Mg, and (c) &
(d) Mg/0.22Y2O3, respectively.

Figure 4.5.1

Representative micrographs showing: nano-ZrO2 reinforcement
distribution in the case of Mg/1.11ZrO2 composite (using
FESEM) in (a) & (b) and grain morphology for Mg and
Mg/1.11ZrO2 in (c) & (d), respectively.

40

Figure 4.5.2

Representative SEM fractographs showing: (a) brittle-ductile
like features in Mg, and (b) intergranular crack propagation in
Mg/0.22ZrO2, respectively.
Representative micrographs showing: nano-ZrO2 reinforcement
distribution in Mg/1.11ZrO2 (using FESEM) in (a) and grain
morphology for Mg and Mg/1.11ZrO2 in (b) & (c), respectively.

41

Figure 4.6.2

Representative SEM fractographs showing combined brittle and
ductile like features in the cases of: (a) & (b) unreinforced Mg,
and (c) & (d) Mg/0.22ZrO2, respectively.

44


Figure 4.7.1

Representative micrographs showing: Al2O3 reinforcement
distribution and its interfacial integrity in the case of
Mg/1.11Al2O3 composite (using SEM) in (a) & (b) and grain
morphology for Mg and Mg/0.66Al2O3 in (c) & (d),
respectively.

46

Figure 4.7.2

Representative SEM fractographs showing: brittle-ductile like
features in unreinforced Mg (a) and Mg/1.11Al2O3 (b) & (c),
and crack arrest at reinforcement in Mg/2.49Al2O3,
respectively.

47

Figure 4.8.1

Representative
micrographs
showing:
reinforcement distribution and its interfacial
Mg/1.11Al2O3 (using SEM & FESEM) in (a) &
morphology for Mg and Mg/0.66Al2O3 in
respectively.


0.3µm-Al2O3
integrity in
(b) and grain
(c) & (d),

49

Figure 4.8.2

Representative SEM fractographs showing brittle-ductile like
features in the cases of: (a) & (b) unreinforced Mg, (c) & (d)
Mg/1.11Al2O3, respectively.

50

Figure 4.9.1

Representative micrographs showing: Al2O3 reinforcement
distribution with good interfacial integrity in the case of
Mg/1.11Al2O3 composite (using SEM) in (a) and grain
morphology for Mg and Mg/2.49Al2O3 in (b) & (c),
respectively.

52

Figure 4.6.1

43

Creation of New Mg-Based Material Using Different Types of Reinforcements by S. Fida Hassan xiv



List of Figures

Representative SEM fractographs showing: brittle-ductile like
features in unreinforced Mg (a) and Mg/1.11Al2O3 (b) & (c),
and interfacial debonding in Mg/1.11Al2O3 (d) respectively.
Figure 4.10.1 Representative micrographs showing: Al2O3 reinforcement
distribution and its interfacial integrity in the case of
Mg/1.11Al2O3 composite (using SEM & FESEM) in (a) & (b)
and grain morphology for Mg and Mg/0.66Al2O3 in (c) & (d),
respectively.

53

Figure 4.10.2 Representative SEM fractographs showing: brittle-ductile like
features in unreinforced Mg (a) & (b) and in Mg/1.11Al2O3 (c)
& (d), (e) particle shear in Mg/1.11Al2O3 and (f) microcracks in
Mg/2.49Al2O3, respectively.

56

Creation of New Mg-Based Material Using Different Types of Reinforcements by S. Fida Hassan

xv

Figure 4.9.2

55



Chapter 1: Introduction


Introduction

Chapter 1: Introduction
Magnesium based materials has extensive demand for applications that stretch
from automobile and aerospace industries in replacement of aluminum and steel to
electronic and computer industries in replacement of plastics [1-6]. The early 1990s are
considered to be the renaissance for magnesium as a structural material due to
environmental concerns, increasing safety and comfort levels, a significant
improvement in the corrosion resistance of high purity magnesium alloys, rising fuel
prices and lowering of prices of primary magnesium metal induced huge demand from
automobile industry. A recent industrial review revealed that there are sixty different
types of components, from instrument panels to engine components, in which
magnesium is used or is being developed for use. The use of magnesium in automobile
parts is predicted to increase globally at an average rate of 15 percent per year. This
growing requirements of high specific mechanical properties with weight savings has
fueled significant research activities in recent times targeted primarily for further
development of magnesium based composite materials [7-50].
The word Composite Materials in advanced materials science and technology
has been coined to give dignity and renewed impetus to a very old yet simple idea:
putting dissimilar materials to work in coherence so as to achieve a new material
whose properties are different in scale and kind from those of any of the constituents.
Mixing of clay and straw as building material is an example of composite materials
dates back to centuries BC. The emergence of novel processing techniques coupled
with the need for lighter materials with high specific mechanical properties in recent
years, especially in automobile, aerospace, space, electronics and sports industries [14, 47-49], has catalyzed considerable scientific and technological interest in the
development of numerous high-performance composite or hybrid materials as serious


Creation of New Mg-Based Material Using Different Types of Reinforcements by S. Fida Hassan

1


Introduction

competitors to the traditional engineering alloys. The majority of such materials are
metallic matrices such as aluminum and magnesium reinforced with high-strength,
high-modulus and often brittle second phases, in the form of fibers, whiskers and
particulates. The reinforced matrices offer potential for significant improvements in
efficiency, reliability and mechanical performance over the traditional and newer
generation monolithic alloys. The aligned continuous fiber reinforced composites offer
very high directional properties such as high specific strength along the reinforcement
direction [40-49]. Conversely, in applications where such extreme properties are not a
requirement, the discontinuous metal-matrix composites consisting particulates,
whiskers or nodules are preferred, because they offer substantially improved
mechanical properties compared to the monolithic alloy and provide the additional
advantage of being machinable and workable. In particular, the particulate-reinforced
metal-matrix composites are attractive because they exhibit near isotropic properties
when compared to the continuously reinforced counterparts, and are easier to process
using standard metallurgical processing such as powder metallurgy, direct casting,
rolling and extrusion [1, 7-8, 50-51]. The end properties of composite materials are
governed by a number of factors such as types of processing, matrix constitution, type,
size, volume fraction and morphology of the reinforcement. Among these factors,
selection of stiffer and stronger reinforcement compatible with metallic matrix and
type of processing to tailor a microstructure with near uniform distribution of
reinforcement phase in the matrix with improved integrity at the matrix-reinforcement
interfaces coupled with the minimal porosity is remained as most critical factors in

realizing the best properties from the resultant composite.
In recent years, significant improvement in many properties of magnesium
has been achieved with the use of discontinuous reinforcement beyond the limits

Creation of New Mg-Based Material Using Different Types of Reinforcements by S. Fida Hassan

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Introduction

dictated by traditional alloying. Although the use of these reinforcements leads to an
improvement in strength characteristics of magnesium, the intrinsic limited ductility
[52] worsens and restricts further the most needed formability of structural parts [1, 734, 40-45]. However, some reports on simultaneous improvement in strength and
ductility of magnesium using metastable nano-size precipitation [37-39, 53] provides
the impetus to the selection of thermally stable and chemically compatible [54-55]
nano-size oxide ceramic particulates i.e., Al2O3, Y2O3, and ZrO2. Reacting metallic
oxide ceramic, i.e., Al2O3, Y2O3, and ZrO2, promise ductile formulation and are easily
available. They also exhibit high stiffness and high temperature mechanical properties
[59, 60] which are even higher in nano-scale structure and excellent oxidation
resistance. Search of open literature revealed only one attempt was made using nanosize Al2O3, Y2O3, and ZrO2 as reinforcements [25]. However, no attempt is made so
far to synthesize the Mg based nanocomposite reinforced with these particulates using
solidification process like Disintegrated Melt Deposition (DMD) technique [56] or
simple blend-press-sinter powder metallurgy (PM) technique and to study its effect on
the microstructural and mechanical properties of pure magnesium.
Accordingly, the primary aim of the present study was to synthesize
magnesium based nanocomposites containing nano-size Al2O3, Y2O3, and ZrO2
particulate reinforcements using DMD and blend-press-sinter PM techniques. Primary
processed nanocomposites were subsequently hot extruded and characterized for their
microstructural and mechanical behaviors. Particular emphasis was placed to study the

effect of primary processing and the presence of nano-sized oxide particulates as
reinforcement on the microstructure and mechanical response of commercially pure
magnesium matrix. Effect of length scale of reinforcement, from nanometer to
micrometer, for the most potential oxide reinforcement was also investigated.

Creation of New Mg-Based Material Using Different Types of Reinforcements by S. Fida Hassan

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Chapter 2: Literature Survey


Literature Survey

Chapter 2: Literature Survey
2.1

Introduction
In recent years, applications of magnesium stretch from aerospace and

automobile industries in replacement of aluminum and steel to electronic and computer
industries in replacement of plastics [2]. It is the eighth most abundant element and
estimated that about 1.93 mass percentage of earth’s crust consists of magnesium, and
the oceans contain about 0.13 mass percentage of magnesium [3]. Magnesium has a
density value of 1.74 gm/cm3, which is about two third of density of aluminum and
one quarter of that of iron. Magnesium also exhibits high specific strength, good
castability (also suitable for high pressure die casting), good machinability, good
weldability under controlled atmosphere and is readily available in international
market. Commercially used magnesium materials are mostly alloys with major

alloying elements of manganese, aluminum, zinc, zirconium and rare earths [59].
Although magnesium as an element was discovered in 1808 by British Sir Humphrey
Davy and isolated from its ore magnesium oxide in 1828 by French scientist Antoine
Alexander Bussy, it took almost 100 years for magnesium to be applied in structural
application and the World War II (1939-1944) [59] pushed the usage to its peak an
estimated 320,000 tonnes in 1944 mainly in fighter aircraft. After the war was over the
demand of magnesium fell sharply. The early 1990s are considered to be the
renaissance for magnesium as a structural material due to environmental concerns,
increasing safety and comfort levels, a significant improvement in the corrosion
resistance of high purity magnesium alloys, rising fuel prices and lowering of prices of
primary magnesium metal induced huge demand from automobile industry [1-2, 6,
59]. A recent industrial review revealed that there are sixty different types of
components, from instrument panels to engine components, in which magnesium is

Creation of New Mg-Based Material Using Different Types of Reinforcements by S. Fida Hassan

4


Literature Survey

used or is being developed for use and the use of magnesium in automobile parts is
predicted to increase globally at an average rate of 15 percent per year [6]. Regulations
on electromagnetic radiation limit also turned consumer electronics (like mobile
phone, notebook and camera) producers to use magnesium due its good resistance to
electromagnetic radiation [2].
Materials scientists and engineers around the globe are working round the
clock to develop new materials and new processing routes to improve and replace the
existing one and meet this surge in demand of advanced engineering and technological
developments. Major challenge in the development of magnesium based structural

materials is to achieve improvement in strength without compromising the intrinsic
limited ductility [52]. However, most widely reported second phase reinforcements, in
general, deteriorate the intrinsic limited ductility of magnesium required for the most
needed solid state formability of structural parts and remain one of the major concern
in its fabrication and application in recent days, although strength improves
significantly and at times even beyond the limit of traditional alloying [6-34, 40].
Interestingly it has been observed that extremely fine dispersed second phase
reinforcements can cause simultaneous increase in strength and ductility in brittle
metal matrix like magnesium [60] as has been reported in relation to the presence of
metastable finer precipitation [37-39, 53] and eventually became the impetus for the
selection of thermally stable, stiff and strong [57-58] Al2O3 Y2O3, and ZrO2
particulates in this study.

2.2

Reinforcement Particulates Selection
Particulates are the most common and cheapest reinforcement materials that

lead to isotopic properties in the end composite, a must for common structural
applications. Selection of stiffer and stronger reinforcement compatible with metallic
Creation of New Mg-Based Material Using Different Types of Reinforcements by S. Fida Hassan

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Literature Survey

matrix and type of processing to tailor a microstructure with near uniform distribution
of reinforcement phase in the matrix with improved integrity at the matrixreinforcement interfaces coupled with the minimal porosity [7-8, 61] remain as most
critical factors in realizing the best properties from the resultant composite. A wide

range of materials mostly ceramics such as carbides, borides or oxides particulates has
been used as reinforcement. But the most widely investigated reinforcing ceramics
with pure magnesium and commercial grade magnesium alloys, for example SiC
particulates [1, 7-16, 40], has limited success due to the high brittleness in non-reacting
ceramic-Mg formulations.
The selection of reinforcement for a metal matrix composite is a careful
process that must consider the physical and chemical properties of the base materials
involved.

The physical problems of compatibility can often be associated with

respective thermal and stress performance of the constituent materials. The main
consideration is that the metallic matrix material should possess sufficient
characteristics (strength and ductility) so that it can ensure transfer of load to the
reinforcement material with minimal discontinuities.

The thermal expansion

properties are of significance because various stresses will be induced in one of the
constituent materials depending upon operating temperature. Chemical compatibility
can be a far more complex consideration than physical compatibility.

The most

important compatibility relates to the wetting and reaction of the reinforcement
particulates and the matrix. It is now widely accepted that in order to maximize
interfacial bonding strength in metal matrix composites, it is necessary to promote
wetting, control chemical reactions, and minimize oxide formation. A measure of
wettability can be obtained by measuring the contact angle (θ) (see Figure 2-1) formed
between a solid reinforcement particulates and the molten matrix material.


Creation of New Mg-Based Material Using Different Types of Reinforcements by S. Fida Hassan

The

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