HOT DEFORMATION AND
MICROSTRUCTURAL
CHARACTERISTICS OF Al AND Si
CONTAINING Mg-3Sn-2Ca (TX32)
ALLOYS: CORRELATION WITH
PROCESSING MAPS
CHALASANI DHARMENDRA
DOCTOR OF PHILOSOPHY
CITY UNIVERSITY OF HONG KONG
AUGUST 2013
CITY UNIVERSITY OF HONG KONG
香港城市大學香港城市大學香港城市大學香港城市大學
Hot Deformation and Microstructural
Characteristics of Al and Si Containing
Mg-3Sn-2Ca (TX32) Alloys:
Correlation with Processing Maps
含 Mg-3Sn-2Ca (TX32) 合金的
鋁與硅之熱加工微型結構特性:
加工效果圖相互關係硏究
Submitted to
Department of Mechanical and Biomedical Engineering 機械與生物醫藥工程系
in Partial Fulfillment of the Requirements
for the Degree of Doctor of Philosophy 哲學博士學位
by
Chalasani Dharmendra
August 2013 二零一三年八月
i
ABSTRACT
The worldwide need to reduce energy consumption has pushed the emergence of light-
weighting technologies and, among them, research towards developing new alloys of
Mg - the lightest of all structural metals - is of great interest for structural applications.
Mg and Mg alloys suffer from poor plasticity due to the hexagonal close packed (HCP)
crystal structure, which results in limited number of individual slip systems for active
deformation. Due to this reason, most Mg alloys develop strong textures during thermo-
mechanical processes such as rolling and extrusion, resulting in pronounced anisotropy.
Formability can be improved by randomizing or weakening the texture either by
modifying the existing alloys with minor additions of other elements or developing new
alloy systems. The response of the intrinsic nature of material to the imposed processing
parameters, namely temperature, strain rate and strain, is of significant importance to
the workability. The knowledge of interrelation between process parameters,
microstructure and mechanical properties will help in achieving reliable wrought
products for longer service. From this view point, the development of a
‘processing map’ is of great significance, which defines ‘safe’ window(s) to process a
material within certain temperature and strain rate range(s).
Among several Mg-Sn-Ca alloys, TX32 alloy (Mg-3Sn-2Ca) is found to be the best
compromise between corrosion resistance and creep strength due to Sn and Ca,
respectively, through the formation of CaMgSn and Mg2Ca intermetallic phases. For
further improvement of strength and/or weakening of texture, additions of aluminum
(0.4 and 1 wt.%) and silicon (0.2 - 0.8 wt.%) are made to develop a set of six cast
alloys. Very limited information is available in the literature on hot workability studies
of these alloys to achieve an irreversible change in the microstructure which is essential
for processing. Metallurgical phenomena are complex and metallic alloys are rate-
sensitive during high temperature deformation, which necessitates metal forming
processes to be carried out within correct ranges of parameters. The technique of
processing map, which is based on dynamic materials model (DMM) involving
irreversible thermodynamics, has proved to be highly successful in accurately
identifying ‘safe’ processing windows. This approach has been adopted by several
researchers in obtaining critical information towards optimizing hot workability and
achieving microstructural control for bulk forming of several metallic materials.
ii
The main aim of the present investigation is to study the hot deformation behavior of
the selected set of TX32 series cast alloys through the development of their processing
maps utilizing the interrelationships between flow stress and a wide range of process
parameters (temperature and strain rate). The emphasis of this study is to establish the
effect of Al and Si additions on the features of processing map of TX32 base alloy with
respect to domains of dynamic recrystallization (DRX), optimum deformation
conditions, flow instability and cracking regimes. Another aim of the study is to identify
the dominant mechanisms of hot deformation through kinetic approach and to establish
an interrelation between the process parameters, microstructure and evolving texture
during compression. The effect of process parameters on the activation of important slip
systems along the compression direction needs to be analyzed in terms of their relative
orientations.
Cylindrical specimens of 10 mm diameter and 15 mm height were machined from the
as-cast billets and uni-axial compression tests were performed in the temperature range
300 ○C to 500
○C at constant true strain rates in the range 0.0003 s
-1 to 10 s
-1 using
computer controlled servo-hydraulic test system. The microstructure and microtexture
characterizations after deformation were carried out using optical microscopy (OM) and
scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS)
and an electron back scattered diffraction (EBSD) facility. Pole figures and Schmid
factors are used to analyse the activity of individual slip systems at various deformation
conditions. Transmission electron microscopy (TEM) was used for select specimens to
supplement the microstructural features. Tensile tests were carried out in the case of
TX32-1Al alloy to correlate the characteristics of different domains by observing the
fracture surfaces of the tested samples in SEM.
The major conclusions drawn from the present study are listed below.
(i) The processing map of cast TX32 alloy exhibits two domains of DRX in the
temperature and strain rate ranges in hot deformation: (a) 300 ○C to 350
○C and
0.0003 s-1
to 0.001 s-1
(Domain 1) and (b) 390 ○C to 500
○C and 0.005 s
-1 to 0.6 s
-1
(Domain 2). Texture evolution as characterized by EBSD analysis indicates that
specimens deformed under conditions in Domain 1 exhibit a basal texture with a
maximum intensity of basal poles located at about 35○ to 45
○ with the
compression direction. At temperatures higher than 400 ○C (Domain 2), texture
was randomized due to increase in the activity of second-order pyramidal slip.
iii
While CaMgSn particles in the matrix contribute to significant back stress to
dislocation moment, the grain boundary phase Mg2Ca reduces the grain boundary
sliding.
(ii) The homogenization treatment of cast TX32 alloy has negligible influence on its
hot deformation behavior and texture evolution, implying that homogenization
step may be eliminated in hot deformation schedules. Compared with the most
widely used AZ31 magnesium alloy, TX32 alloy can be hot worked over a broad
temperature and strain rate range.
(iii) With the addition of 0.4 wt.% Al, the ultimate compressive strength (UCS) of
TX32 alloy has improved in the testing temperature range of 25 ○C to 250
○C,
which may be attributed to the effect of solid solution strengthening. However, the
addition of Al did not significantly change its hot working behavior (300 ○C to
500 ○C) as the basic features of the processing map remain unchanged. At low
temperatures, the alloy exhibited flow instability in the form of flow localization
at intermediate strain rates and adiabatic shear bands at high strain rates.
(iv) The addition of 1 wt.% Al promoted prismatic slip at intermediate temperatures
(between 350 ○C to 400
○C), causing changes to the features of processing map
compared to TX32 alloy. The processing map revealed three workable DRX
domains and a fourth domain related to grain boundary sliding at high temperature
and low strain rate range (430 ○C to 500
○C and 0.0003 s
-1 to 0.002 s
-1) which is
unsuitable for processing. The specimens deformed in lower temperature and
strain rate (Domain 1) exhibited basal textures whereas second-order pyramidal
slip randomized the texture in specimens deformed in high temperature and
intermediate strain rate range (Domain 3).
(v) The alloy with 0.4 wt.% Al and 0.2 wt.% Si has exhibited UCS closer to that of
the TX32 alloy between 25 ○C to 250
○C. However, increased additions of Si
(from 0.4 to 0.8 wt.%) significantly decreased UCS at higher temperatures
(100 ○C to 250
○C), likely due to the differences in intermetallic phases formed
(CaMgSi and Ca2Sn in Si containing alloys vs. CaMgSn and Mg2Ca in TX32) and
the increase of their volume fraction. Moreover, both CaMgSi and Ca2Sn are
distributed in the matrix compared to the presence of Mg2Ca at the grain
boundaries. All the Si-containing alloys have exhibited pronounced ductility at
250 ○C indicating the beginning of hot workability temperature range.
iv
(vi) The processing map of TX32-0.4Al-0.4Si alloy showed a shift of DRX domains
to high temperatures and reduced flow instability regime particularly at high
temperatures as compared to TX32. The addition of 0.4% Si is favorable for
enhancing the hot workability since it widens the processing windows (domains).
The basal poles are spread out from the compression axis and the (0001) <11 2 0>
slip dominated as DRX grains have high Schmid factors for basal slip at low
temperatures (300 and 350 ○C) and low strain rates (0.0003 and 0.001 s
-1). The
texture got randomized at ≥450 ○C at intermediate strain rates in Domain 2.
(vii) The apparent activation energy values obtained through kinetic analyses for these
alloys indicate that the deformation in the low strain rate DRX domain is
controlled by climb and recovery process, whereas the deformation in the high
strain rate DRX domain is attributed to cross-slip since the stacking fault energy
on the pyramidal slip systems is high.
(viii) For 0.6% Si addition to TX32-0.4Al alloy, an additional DRX domain (Domain 3)
occurs at high temperatures and high strain rates. Domain 1 is characterized as
cracking domain, whereas in Domains 2 and 3, DRX is occurring predominantly
by basal slip with climb as a recovery process.
(ix) With further increase in Si (TX32 with 0.4 wt.% Al and 0.8 wt.% Si), the first
DRX domain at low strain rates has shifted further towards high temperature and
the second DRX domain at high temperature shifted to high strain rates.
Deformation is basal slip dominated and the recovery is by climb in both the
domains.
(x) When the volume fraction of intermetallic particles increased steeply (in 0.6 and
0.8% Si-containing alloys), the back stress increases significantly and thus, the
activation of basal slip required considerably high temperatures for its extensive
participation in plastic flow.
Key words: Mg-Sn-Ca (TX) alloy, Hot compression, Flow curves, Processing map,
Kinetic analysis, Microstructure, Dynamic recrystallization, Microtexture,
EBSD, TEM.
vii
TABLE OF CONTENTS
Page
ABSTRACT i
ACKNOWLEDGEMENTS v
LIST OF TABLES xii
LIST OF FIGURES xiii
CHAPTER 1 INTRODUCTION
1.1 Motivation 1-1
1.2 Research problem 1-1
1.3 Scope of the thesis 1-3
CHAPTER 2 LITERATURE REVIEW
2.1 Magnesium and its alloys
2.1.1 Magnesium characteristics 2-1
2.1.2 Alloying elements 2-2
2.1.3 Mg alloys development 2-5
2.1.4 ASTM standard magnesium alloy designations 2-5
2.2 Deformation of magnesium
2.2.1 Schmid factor 2-6
2.2.2 Slip systems in magnesium 2-7
2.2.3 Deformation of polycrystals 2-10
2.2.4 Effect of temperature on the deformation mechanisms 2-12
2.2.5 Effect of alloying addition on deformation 2-13
2.2.6 Creep resistance 2-14
2.3 Hot working
2.3.1 Flow curves and mechanical testing 2-15
2.3.2 Materials modelling in hot deformation
2.3.2.1 Kinetic model 2-17
2.3.2.2 Atomistic model (Ashby and Raj maps) 2-18
2.3.2.3 Dynamic materials model (Processing map) 2-19
2.4 Hot deformation mechanisms
2.4.1 Dynamic recovery 2-21
2.4.2 Dynamic recrystallization (DRX) 2-21
2.4.3 Superplastic deformation 2-23
2.4.4 Void formation 2-23
2.4.5 Flow instability processes 2-24
viii
2.5 Texture (Preferred orientation) 2-24
2.5.1 Texture measurement by X-ray technique 2-24
2.5.2 Neutron diffraction 2-24
2.5.3 Electron backscatter diffraction 2-25
2.5.3.1 Pole figure and inverse pole figure 2-25
2.6 Mg-Sn-Ca (TX) system 2-26
CHAPTER 3 EXPERIMENTAL DETAILS
3.1 Flow chart of the study 3-1
3.2 Preparation of alloys 3-2
3.3 Initial material characterization
3.3.1 X-ray diffraction 3-2
3.3.2 Differential scanning calorimetry (DSC) 3-2
3.3.3 Electron probe micro-analyzer 3-3
3.3.4 Volume fraction of intermetallic particles 3-3
3.4 Compression test 3-3
3.4.1 Data analysis 3-5
3.4.2 Computational procedure 3-5
3.5 Tensile testing 3-6
3.6 Microstructure investigation
3.6.1 Optical microscopy 3-6
3.6.2 Scanning electron microscopy 3-7
3.6.3 Transmission electron microscopy 3-7
3.7 Micro-texture analysis 3-8
CHAPTER 4 HOT WORKABILITY ANALYSIS AND TEXTURE
CHARACTERISTICS OF A TX32 MAGNESIUM ALLOY
IN AS-CAST AND HOMOGENIZED CONDITIONS
4.1 TX32 alloy in an as-cast condition
4.1.1 Initial microstructure and texture of the as-cast material 4-1
4.1.2 Mechanical strength at low temperatures 4-1
4.1.3 Compressive stress-strain behavior under hot working
conditions 4-3
4.1.4 Processing map and microstructures 4-5
4.1.5 Kinetic analysis 4-6
4.1.6 Mechanisms of hot deformation 4-9
4.1.7 Texture evolution – Domain 1 4-10
4.1.8 Texture randomization – Domain 2 4-15
4.1.9 Summary 4-18
ix
4.2 Effect of homogenization on hot deformation behavior of a cast
TX32 magnesium alloy
4.2.1 Cast and homogenized (CH) alloy microstructure 4-19
4.2.2 Flow behavior 4-21
4.2.3 Processing map for CH TX32 alloy 4-22
4.2.4 Comparison of processing maps for TX32 alloy in
AC and CH conditions 4-25
4.2.5 Pole figures and Schmid factor distribution for specimens
in Domain 1 4-27
4.2.6 Texture evolution in Domain 2 4-30
4.2.7 Summary 4-32
CHAPTER 5 HOT WOKABILITY ANALYSIS AND TEXTURE
CHARACTERISTICS OF TX32 MAGNESIUM ALLOY
WITH ALUMINUM ADDITIONS
5.1 Hot deformation behavior of cast TX32-0.4Al alloy
5.1.1 Initial as-cast material microstructure and texture 5-1
5.1.2 Compressive stress-strain behaviour under hot working
conditions 5-3
5.1.3 Processing map 5-4
5.1.4 Kinetic analysis 5-7
5.1.5 Deformation mechanisms 5-8
5.1.6 Texture analysis in Domain 1 5-9
5.1.7 Texture randomization in Domain 2 5-12
5.1.8 Flow instabilities 5-15
5.1.9 Summary 5-17
5.2 Hot deformation and microstructural features of 1% Al containing
TX32 magnesium alloy
5.2.1 Initial as-cast material microstructure 5-18
5.2.2 Mechanical strength at low temperatures 5-20
5.2.3 Flow curves 5-21
5.2.4 Hot deformation behavior and processing map 5-22
5.2.5 Tensile tests and fractography 5-28
5.2.6 Flow instabilities 5-29
5.2.7 Kinetic analysis 5-32
5.2.8 Summary 5-33
5.3 Effect of Al on hot deformation mechanisms and dynamic
recrystallization in TX32 magnesium alloy
5.3.1 Comparison of processing maps 5-34
5.3.2 Deformation mechanism in Domain 1 5-36
5.3.3 Deformation mechanism in Domain 2 of TX32 alloy and
Domain 3 of TX32-1Al alloy 5-39
x
5.3.4 Mechanism in Domain 2 of TX32-1Al alloy 5-41
5.3.5 Mechanism in Domain 4 of TX32-1Al alloy 5-43
5.3.6 Summary 5-45
CHAPTER 6 HOT WOKABILITY ANALYSIS AND TEXTURE
CHARACTERISTICS OF TX32-0.4Al ALLOY
WITH SILICON ADDITIONS
6.1 Initial material characterization of silicon containing TX32-0.4Al alloys
6.1.1 Microstructures 6-1
6.1.2 XRD analysis 6-3
6.1.3 SEM-EPMA analysis 6-4
6.1.4 Differential scanning calorimetry (DSC) analysis 6-5
6.1.5 Volume fraction of intermetallic particles 6-7
6.2 Hot deformation behavior of TX32-0.4Al magnesium alloy with
0.2% Si additions
6.2.1 Flow curves 6-8
6.2.2 Hot working behavior 6-9
6.2.3 Kinetic analysis 6-10
6.2.4 Summary 6-13
6.3 Hot deformation behavior of TX32-0.4Al magnesium alloy with
0.4% Si additions
6.3.1 Mechanical strength at low temperatures 6-14
6.3.2 Flow curves 6-15
6.3.3 Processing map 6-16
6.3.4 Specimens after compression testing 6-17
6.3.5 Microstructures of deformed specimens 6-19
6.3.6 Kinetic analysis 6-20
6.3.7 Flow instability 6-22
6.3.8 Comparison with TX32 and TX32-0.4Al alloys 6-23
6.3.9 Texture evolution 6-23
6.3.10 Summary 6-26
6.4 Hot deformation behavior of TX32-0.4Al magnesium alloy with
0.6% Si additions
6.4.1 Flow curves 6-27
6.4.2 Hot working behavior 6-27
6.4.3 Microstructures and textures 6-30
6.4.4 Kinetic analysis 6-32
6.4.5 Summary 6-34
6.5 Hot deformation behavior of TX32-0.4Al magnesium alloy with
0.8% Si additions
xi
6.5.1 Mechanical strength at low temperatures 6-35
6.5.2 Flow curves 6-36
6.5.3 Processing map of TX32-0.4Al-0.8Si alloy 6-37
6.5.4 Microstructure and texture evolution 6-39
6.5.5 Kinetic analysis 6-44
6.5.6 Summary 6-46
6.6 Effect of silicon on hot deformation mechanisms and dynamic
recrystallization in TX32-0.4Al alloy 6-48
CHAPTER 7 CONCLUSIONS 7-1
CHAPTER 8 SUGGESTIONS FOR FUTURE WORK 8-1
REFERENCES R-1
APPENDICES
Appendix A.1 Compressive flow stress data at various temperatures,
strain rates (έ) and strains (ε) (data corrected for adiabatic
temperature rise) for the TX32 cast alloy A-1
Appendix A.2 Compressive flow stress data at various temperatures,
strain rates (έ) and strains (ε) (data corrected for adiabatic
temperature rise) for the TX32 cast-homogenized alloy A-2
Appendix A.3 Compressive flow stress data at various temperatures,
strain rates (έ) and strains (ε) (data corrected for adiabatic
temperature rise) for the TX32-0.4Al alloy A-3
Appendix A.4 Compressive flow stress data at various temperatures,
strain rates (έ) and strains (ε) (data corrected for adiabatic
temperature rise) for the TX32-1Al alloy A-4
Appendix A.5 Compressive flow stress data at various temperatures,
strain rates (έ) and strains (ε) (data corrected for adiabatic
temperature rise) for the TX32-0.4Al-0.2Si alloy A-5
Appendix A.6 Compressive flow stress data at various temperatures,
strain rates (έ) and strains (ε) (data corrected for adiabatic
temperature rise) for the TX32-0.4Al-0.4Si alloy A-6
Appendix A.7 Compressive flow stress data at various temperatures,
strain rates (έ) and strains (ε) (data corrected for adiabatic
temperature rise) for the TX32-0.4Al-0.6Si alloy A-7
Appendix A.8 Compressive flow stress data at various temperatures,
strain rates (έ) and strains (ε) (data corrected for adiabatic
temperature rise) for the TX32-0.4Al-0.8Si alloy A-8
LIST OF PUBLICATIONS BASED ON THIS THESIS P-1
xii
LIST OF TABLES
Page
Table 2.1: Properties of pure Mg 2-1
Table 2.2: ASTM element code designation for the Mg alloys 2-6
Table 2.3: Characteristics of slip modes in Mg single crystals 2-9
Table 2.4: Activation energies and suggested rate controlling mechanisms
in the hot working of AZ31 alloy (under compression) 2-18
Table 4.1: Peak efficiency conditions and kinetic parameters in the Domains
1 and 2 of the processing maps for the AC and CH TX32 alloys 4-27
Table 6.1: Activation parameters for hot working of TX32, TX32-0.4Al,
and TX32-0.4Al-0.4Si alloys 6-25
xiii
LIST OF FIGURES
Page
Fig. 2.1: (a) The primitive hexagonal unit cell illustrating the axes
a1 = a2 ≠ c and corresponding angles α = β = 90○, γ = 120
○ and
(b) the hexagonal close-packed structure. The primitive hexagonal
unit cell is delineated by thick-solid lines. 2-2
Fig. 2.2: Mg - Al phase diagram (ASM Handbook). 2-3
Fig. 2.3: Directions of the Mg alloy development. 2-5
Fig. 2.4: Diagram of the Schmid factor. 2-6
Fig. 2.5: Schematic of the important planes and directions in the Mg lattice. 2-8
Fig. 2.6: Schematic of the interplanar spacings of (0001), (1012), (1011)
and (1010) planes in Mg. 2-8
Fig. 2.7: Stress vs strain curve in the single crystals of Mg and Mg alloys
compressed along (a) <1010> direction, with expansion
limited to <1 2 10>, and (b) <1 2 10> direction, with expansion
limited to <1010>. 2-10
Fig. 2.8: Influence of the deformation temperature on the CRSS of Mg single
crystals. 2-12
Fig. 2.9: CRSS for the prismatic slip vs. zinc concentration. 2-13
Fig. 2.10: CRSS for the prismatic slip vs. temperature at various
Al concentration. 2-13
Fig. 2.11: Raj map for aluminum showing limiting conditions for damage
nucleation. 2-19
Fig. 2.12: Processing map for the as-cast AZ31 alloy. 2-21
Fig. 2.13: Movement of dislocations to produce polygonization. 2-22
Fig. 2.14: TEM micrographs of a (a) square twist boundary and a
(b) hexagonal twist boundary in copper. 2-23
Fig. 2.15: Orientation of the basal plane (0001) in a hexagonal crystal.
The position of the (0001) pole on the unit sphere with regard to
an external reference frame is described by the two angles α and β. 2-26
Fig. 2.16: Binary phase diagrams of (a) Mg-Sn and (b) Mg-Ca. 2-27
Fig. 2.17: Influence of Sn/Ca ratio on the (a) corrosion rate and
(b) creep resistance of Mg-xSn-xCa alloys. 2-28
Fig. 2.18: Compression creep curves of TX32 alloy compared with AZ91
and AE42 at 80 MPa and (a) 135 and (b) 175 ○C. 2-29
xiv
Page
Fig. 3.1: Schematic flow chart of the experimental procedure. 3-1
Fig. 3.2: (a) A melting furnace, and (b) the cast billets of TX32 alloys. 3-2
Fig. 3.3: (a) Geometry of the specimen for compression testing and
(b) servo-hydraulic compression testing machine. 3-4
Fig. 3.4: Schematic of steps for compression test, microstructure and
texture studies. 3-7
Fig. 3.5: (a) Schematic of EBSD system, (b) a typical EBSD diffraction
pattern, and (c) components of EBSD system. 3-8
Fig. 4.1: (a) Optical micrograph, (b) SEM image with phases marked,
(c) XRD pattern, and (d) Pole figures of the TX32 magnesium
alloy in the as-cast (AC) condition. 4-2
Fig. 4.2: Variation in the ultimate compressive strength (UCS) of the
AC TX32 alloy with temperature (inset shows the
corresponding compressive stress-strain curves). 4-3
Fig. 4.3: True stress – true strain curves obtained for the TX32 alloy
under compression at different strain rates and at the test
temperatures of (a) 300 ○C and (b) 500
○C. 4-4
Fig. 4.4: Processing map for the Mg-3Sn-2Ca (TX32) alloy. The numbers
associated with the contours represent the power dissipation
efficiency in percent. 4-5
Fig. 4.5: Microstructures of the TX32 alloy deformed at 300 ○C/0.01 s
-1
(instability regime) showing flow localization (marked by arrows).
The compression axis is vertical. 4-6
Fig. 4.6: Microstructures of the TX32 alloy deformed at (a) 300 ○C/0.0003 s
-1
(Domain 1), and (b) 500 ○C/0.1 s
-1 (Domain 2).
The compression axis is vertical. 4-7
Fig. 4.7: (a) Variation of the normalized flow stress values (at a strain of 0.5)
with strain rate at different test temperatures. (b) Arrhenius plot
showing the variation of the flow stress for the TX32 alloy
normalized with the shear modulus using the inverse of the
temperature (Kelvin) at different strain rates. 4-8
Fig. 4.8: Crystallographic textures obtained using EBSD for the conditions
from Domain 1. Contour lines referring to 1, 2, and 3 times random
and maximum intensities (“max”) are shown. The x-axis in the
pole figures is the compression axis. 4-10
xv
Page
Fig. 4.9: Schmid factor distribution of the grains for (a) basal (0001) <11 2 0>,
(b) prismatic (1100) <11 2 0> and (c) pyramidal (11 2 2) <11 2 3 >
slip systems for the samples deformed at 300 and 350 ○C/0.0003 s
-1
(Domain 1). 4-11
Fig. 4.10: Microstructure of the TX32 alloy deformed at 350 ○C/0.0003 s
-1
(Domain 1). 4-13
Fig. 4.11: Inverse pole figures relative to the compression direction (CD) for
Domains 1 and 2. 4-13
Fig. 4.12: Transmission electron micrographs of the specimen deformed at
300 ○C/0.0003 s
-1 (Domain 1) of the TX32 alloy showing
(a) dislocation array and (b) tilt boundaries 4-14
Fig. 4.13: Crystallographic textures obtained using EBSD for the conditions
from Domain 2. The X-axis in the pole figures is compression axis. 4-15
Fig. 4.14: Schmid factor distribution of the grains for basal (0001) <11 2 0>,
prismatic (1100) <11 2 0>, and pyramidal (11 2 2) <11 2 3 >
slip systems for the sample deformed at 500 ○C/0.1 s
-1
(condition near to peak efficiency in Domain 2). 4-16
Fig. 4.15: TEM images of the specimen deformed at 500 ○C/0.1 s
-1
(Domain 2) of the TX32 base alloy (a) showing dislocation tangles
and (b) revealing cross-slip. 4-17
Fig. 4.16: (a) Optical micrograph, (b) SEM image (phases marked),
(c) XRD pattern, and (d) pole figures of the TX32 magnesium
alloy in the cast-homogenized (CH) condition. 4-20
Fig. 4.17: Compressive true stress-true strain curves obtained for the TX32
(AC and CH) alloy at different strain rates and at test
temperatures of (a) 350 ○C
and (b) 500
○C. 4-21
Fig. 4.18: Processing map for the TX32 alloy in the CH condition 4-22
Fig. 4.19: Optical microstructures of the CH and AC TX32 alloys deformed
at very low strain rate. The compression axis is vertical. 4-23
Fig. 4.20: Optical microstructures of the CH and AC TX32 alloys deformed
under Domain 2 conditions. The compression axis is vertical. 4-24
Fig. 4.21: Optical microstructures of the CH TX32 alloy deformed at
(a) 300 ○C
/10 s
-1 and (b) 300
○C/1 s
-1 exhibiting an adiabatic shear
band and flow localization (marked by arrows) in the cracking and
instability regimes, respectively, in the processing map.
The compression axis is vertical. 4-25
xvi
Page
Fig. 4.22: Pole figures corresponding to Domain 1 of the CH - TX32 alloy
(The x-axis is the compression axis). 4-28
Fig. 4.23: Schmid factor distribution of the grains for the (a) basal,
(b) prismatic, and (c) pyramidal slip systems of the specimens
deformed under Domain 1. 4-29
Fig. 4.24: Pole figures corresponding to Domain 2 of the CH - TX32 alloy
(The x-axis is the compression axis). 4-31
Fig. 4.25: Schmid factor distribution of the grains for the prismatic
(1100) <11 2 0> slip system for the specimens deformed at
Domain 2 conditions. 4-31
Fig. 5.1: (a) Optical micrograph in the as-cast condition, (b) SEM image
showing intermetallic particles, (c) DSC curve, and (d) pole figures
in the as-cast condition of the TX32-0.4Al magnesium alloy. 5-2
Fig. 5.2: True stress - true strain curves obtained for the TX32-0.4Al alloy
in compression at different strain rates and at the test temperature
of (a) 300 ○C and (b) 450
○C. 5-3
Fig. 5.3: Processing map for the TX32-0.4Al alloy. The numbers associated with
the contours represent efficiency of power dissipation in percent. 5-4
Fig. 5.4: Microstructures of the TX32–0.4Al alloy deformed at
(a) 300 ○C/0.0003 s
−1 and (b) 350
○C/ 0.001 s
−1 (Domain 1).
The compression axis is vertical. 5-5
Fig. 5.5: Optical microstructures of the TX32–0.4Al alloy deformed at
(a) 400 ○C/0.1 s
−1, (b) 450
○C/0.1 s
−1, and (c) 500
○C/0.1 s
−1
(Domain 2). The compression axis is vertical. 5-6
Fig. 5.6: (a) Variation of flow stress with strain rate, and (b) Arrhenius plot
showing the variation of normalized flow stress with (1/T). 5-7
Fig. 5.7: Pole figures corresponding to conditions from Domain 1
(The x-axis in the pole figures is the compression axis). 5-9
Fig. 5.8: Schmid factor distributions for samples deformed at 300 ○C/
0.0003 s-1
and 350 ○C/0.001 s
-1 (Domain 1) conditions (a) basal
(0001) <11 2 0>, (b) prismatic (1100) <11 2 0>, and
(c) pyramidal (11 2 2) >< 3211 slip systems. 5-10
Fig. 5.9: Pole figures corresponding to conditions from Domain 2
(The x-axis in the pole figures is the compression axis). 5-12
xvii
Page
Fig. 5.10: EBSD Schmid factor distribution maps for the sample deformed to
450 ○C/ 0.1 s
-1 (a) for (0001) <11 2 0> slip system (b) for (11 2 2)
>< 3211 slip system. The red and green colors represent high to
moderate Schmid factors. 5-13
Fig. 5.11: Misorientation angle distribution (MOD) for the specimens
compressed at (a) 300 ○C/0.0003 s
-1 (Domain 1) and
(b) 500 ○C/0.1 s
-1 (Domain 2). 5-15
Fig. 5.12: Optical microstructures of TX32-0.4Al alloy deformed at
(a) 300 ○C/10 s
-1 exhibiting adiabatic shear band, and (b) 350
○C/1 s
-1
showing flow localization (marked by arrows) in the cracking and
instability regimes respectively in the map.
The compression axis is vertical. 5-16
Fig. 5.13: (a) Optical micrograph, (b) SEM image showing intermetallic
phases in the as-cast condition of the TX32-1Al magnesium alloy. 5-18
Fig. 5.14: XRD pattern in as-cast condition for TX32-1Al alloy
(inset shows the pattern for TX32 base alloy). 5-19
Fig. 5.15: DSC curves in the as-cast condition for TX32, TX32-0.4Al,
and TX32-1Al alloys. 5-19
Fig. 5.16: Variation of ultimate compressive strength (UCS) for as-cast
TX32, TX32-0.4Al and TX32-1Al alloys with temperature. 5-20
Fig. 5.17: True stress - true plastic strain curves obtained for the
TX32-1Al alloy at (a) 450 ○C and (b) 0.01 s
-1. 5-21
Fig. 5.18: Processing map for the TX32-1Al alloy at a strain of 0.5.
The numbers associated with the contours represent the
efficiency of power dissipation in percent. 5-23
Fig. 5.19: Top view of the specimens deformed at different compression
temperatures and strain rates. The compressive direction
is perpendicular to the viewing plane. 5-24
Fig. 5.20: (a) Optical microstructure of the TX32-1Al alloy compressed at
300 ○C/0.0003 s
-1 (Domain 1). The compression axis is vertical.
(b) Variation of grain size and peak efficiency values with
temperature at 0.0003 s-1
. 5-25
Fig. 5.21: Optical microstructures of the TX32-1Al alloy deformed at
(a) 350 ○C/ 0.001 s
-1, (b) 350
○C/0.01 s
-1, (c) 400
○C/0.001 s
-1,
and (d) 400 ○C/0.01 s
-1 (Domain 2).
The compression axis is vertical. 5-26
Fig. 5.22: Variation of grain size and peak efficiency values with temperature
at 0.1 s-1
. 5-26
xviii
Page
Fig. 5.23: Optical microstructures of the TX32-1Al alloy deformed at
(a) 450 ○C/0.1 s
-1 (Domain 3), (b) 500
○C/0.1 s
-1 (Domain 3),
(c) 450 ○C/0.0003 s
-1 (Domain 4), and (d) 500
○C/0.001 s
-1
(Domain 4). The compression axis is vertical. 5-27
Fig. 5.24: Grain boundary orientation distribution with respect to the
compression axis for the specimen deformed at 450 ○C/0.0003 s
-1
(Domain 4). 5-28
Fig. 5.25: Fracture surface of the TX32-1Al alloy specimen tested in uniaxial
tension at 475 ○C/ 0.0003 s
-1 (Domain 4). 5-29
Fig. 5.26: Fracture surfaces of the TX32-1Al alloy specimens tested in
uniaxial tension at the conditions of (a) 375 ○C/0.01 s
-1 (Domain 2)
and (b) 475 ○C/0.1 s
-1 (Domain 3). 5-30
Fig. 5.27: Microstructures of the TX32-1Al alloy samples deformed at 10 s-1
and the test temperatures (a) 300 ○C and (b) 500
○C which
correspond to the instability regions.
The compression axis is vertical. 5-31
Fig. 5.28: (a) Variation of flow stress with strain rate, and (b) Arrhenius plot
showing the variation of normalized flow stress with (1/T). 5-32
Fig. 5.29: Processing maps for (a) TX32, (b) TX32-0.4Al, and (c) TX32-1Al
alloys. 5-35
Fig. 5.30: TEM microstructures of the specimen deformed at 300 ○C/0.0003 s
-1
(Domain 1) of the TX32-1Al alloy exhibiting (a) planar slip and
(b) polygonized tilt boundary. 5-37
Fig. 5.31: Micro-textures obtained using EBSD for peak efficiency
condition (300 ○C/0.0003 s
-1) in the Domains 1 of the
processing map of (a) TX32 base alloy, (b) TX32-0.4Al, and
(c) TX32-1Al alloys. The x-axis in the pole figures is the
compression axis. 5-38
Fig. 5.32: Schmid factor distribution of the grains for basal (0001) <11 2 0>
slip systems for the specimens deformed at 300 ○C/0.0003 s
-1
(Domain 1) for all the three alloys. 5-39
Fig. 5.33: TEM microstructures of the specimen deformed at 500 ○C/0.1 s
-1
(Domain 3) of the TX32-1Al alloy showing (a) dislocation angles
and (b) twist boundaries.. 5-40
Fig. 5.34: Micro-textures for the (a) TX32 and (b) TX32-1Al alloys,
obtained using EBSD for specimens deformed at 500 ○C/0.1 s
-1
conditions. The x-axis in the pole figures is the compression axis. 5-41
xix
Page
Fig. 5.35: TEM images of the specimen deformed at 400 ○C/0.01 s
-1
(Domain 2) of the TX32-1Al alloy (a) exhibits planar slip and
(b) shows tilt boundaries. 5-42
Fig. 5.36: Micro-textures obtained using EBSD for conditions
(a) 350 ○C/0.01 s
-1 and (b) 400
○C/0.01 s
-1 from the Domain 2 in
the processing map of TX32-1Al alloy. The x-axis in the pole
figures is the compression axis. 5-43
Fig. 5.37: Optical microstructure of the TX32-1Al alloy deformed at
450 ○C/0.001 s
-1 (Domain 4). The compression axis is vertical. 5-44
Fig. 5.38: TEM microstructures of the specimen deformed at
500 ○C/0.0003 s
-1 (Domain 4)
of the TX32-1Al alloy. 5-44
Fig. 5.39: Micro-textures for the specimen deformed at 500 ○C/0.0003 s
-1
(Domain 4) of the TX32-1Al alloy. The x-axis in the pole figures
is the compression axis. 5-44
Fig. 6.1: Optical microstructures in the as-cast condition of the
(a) TX32-0.4Al base alloy, (b) TX32-0.4Al-0.2Si,
(c) TX32-0.4Al-0.4Si, (d) TX32-0.4Al-0.6Si and
(e) TX32-0.4Al-0.8Si magnesium alloys. 6-2
Fig. 6.2: SEM micrographs of the (a) TX32-0.4Al base alloy,
(b) TX32-0.4Al-0.2Si, (c) TX32-0.4Al-0.4Si, (d) TX32-0.4Al-0.6Si
and (e) TX32-0.4Al-0.8Si magnesium alloys in as-cast conditions. 6-3
Fig. 6.3: XRD pattern of TX32-0.4Al-0.8Si alloy in as-cast condition
(inset shows the XRD plot for the TX32-0.4Al-0.4Si alloy). 6-4
Fig. 6.4: (a) Back-scattered electron image of TX32-0.4Al-0.4Si alloy in
as-cast condition with marked intermetallic particles,
(b) Sn, (c) Ca, and, (d) Si distribution maps. 6-5
Fig. 6.5: (a) Back-scattered electron image of TX32-0.4Al-0.8Si alloy in
as-cast condition, (b) Sn, (c) Ca, and, (d) Si distribution maps. 6-6
Fig. 6.6: DSC curves of the Si-containing TX32-0.4Al alloys in
as-cast conditions. 6-6
Fig. 6.7: Volume fraction of intermetallic particles present in the
Si-containing TX32-0.4Al alloys in as-cast conditions. 6-7
Fig. 6.8: True stress - true strain curves obtained for the TX32-0.4Al-0.2Si
alloy in compression at different strain rates and at test
temperatures of (a) 300 ○C and (b) 450
○C. 6-8
Fig. 6.9: Processing map for the TX32-0.4Al-0.2Si alloy. The numbers
associated with the contours represent the efficiency of power
dissipation in percent. 6-10
xx
Page
Fig. 6.10: Microstructures of the TX32–0.4Al-0.2Si alloy deformed at
(a) 300 ○C
/ 0.0003 s
−1 (Domain 1), and (b) 450
○C / 0.1 s
−1
(Domain 2). The compression axis is vertical. 6-11
Fig. 6.11: (a) Variation of flow stress (at a strain of 0.5) with strain rate
at different test temperatures, and (b) Arrhenius plot showing the
variation in normalized flow stress with inverse temperature (kelvin)
at different strain rates of the TX32-0.4Al-0.2Si alloy. 6-12
Fig. 6.12: Variation in the ultimate compressive strength (UCS) of as-cast
TX32, TX32-0.4Al, and TX32-0.4Al-0.4Si alloys with temperature. 6-14
Fig. 6.13: True stress - true strain curves obtained for the TX32-0.4Al-0.4Si
alloy in compression at test temperatures of (a) 300 ○C and
(b) 450 ○C. 6-16
Fig. 6.14: Processing map for the TX32-0.4Al-0.4Si alloy. The numbers
associated with the contours represent power dissipation
efficiency in percent. 6-17
Fig. 6.15: Top and side views of the deformed TX32-0.4Al-0.4Si alloy
specimens in different deformation conditions. The compressive
direction is perpendicular to the viewing plane. 6-18
Fig. 6.16: Microstructure of the TX32-0.4Al-0.4Si alloy deformed at
(a) 350 ○C/ 0.0003 s
−1 (Domain 1), (b) 450
○C/0.1 s
−1,
(c) 500 ○C/0.1 s
−1 (Domain 2) exhibiting the DRX of the as-cast
microstructure. 6-19
Fig. 6.17: Variation of grain size with temperature at 0.0003 s-1
and 0.1 s-1
. 6-20
Fig. 6.18: (a) Variation in flow stress (at a strain of 0.5) with strain rate
at different test temperatures and (b) Arrhenius plot showing the
variation in normalized flow stress with inverse temperature at
different strain rates of the TX32-0.4Al-0.4Si alloy. 6-21
Fig. 6.19: Microstructures of the TX32-0.4Al-0.4Si alloy deformed at
(a) 300 ○C/10 s
-1, and (b) 300
○C/0.1 s
-1 exhibiting (a) adiabatic
shear band and (b) flow localization (marked by arrows), in the
cracking and instability regimes respectively in the map.
The compression axis is vertical. 6-22
Fig. 6.20: Crystallographic textures obtained using EBSD for conditions of:
(a) 350 ○C/0.0003 s
-1 and (b) 500
○C/0.1 s
-1 of TX32-0.4Al-0.4Si
alloy. The compression axis is horizontal. 6-24
Fig. 6.21: Crystallographic textures obtained using EBSD for conditions
of: (a) 300 ○C/ 0.0003 s
-1 and (b) 500
○C/0.1 s
-1 of
TX32-0.4Al alloy. The compression axis is horizontal. 6-25
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Page
Fig. 6.22: True stress - true strain curves obtained for the TX32-0.4Al-0.6Si
alloy in compression at different strain rates and at the test
temperatures of (a) 300 ○C and (b) 500
○C. 6-28
Fig. 6.23: Processing map for the TX32-0.4Al-0.6Si alloy. The numbers
associated with the contours represent power dissipation
efficiency in percent. 6-29
Fig. 6.24: Processing map for the TX32-0.4Al-0.4Si alloy. The numbers
associated with the contours represent power dissipation efficiency
in percent. 6-29
Fig. 6.25: SEM micrograph of the TX32-0.4Al-0.6Si alloy deformed at
300 ○C/ 0.0003 s
-1 (Domain 1) exhibiting void formation at
the hard particles. 6-30
Fig. 6.26: Microstructure of the TX32-0.4Al-0.6Si alloy deformed at
450 ○C/0.0003 s
-1 conditions
(Domain 2).
The compression axis is vertical. 6-31
Fig. 6.27: The micro-textures obtained using EBSD for the condition
450 ○C/0.0003 s
-1 (Domain 2) of the TX32-0.4Al-0.6Si alloy.
The compression axis is horizontal. 6-31
Fig. 6.28: (a) Microstructure (the compression axis is vertical) and
(b) micro-texture (the compression axis is horizontal) of the
TX32-0.4Al-0.6Si alloy deformed at 500 ○C/10 s
-1 (Domain 3). 6-32
Fig. 6.29: (a) Variation in flow stress (at a strain of 0.5) with strain rate at
different test temperatures, and (b) the Arrhenius plot showing the
variation in normalized flow stress with inverse temperature at
different strain rates of the TX32-0.4Al-0.6Si alloy. 6-33
Fig. 6.30: Variation in ultimate compressive strength with temperature for
as-cast TX32, TX32-0.4Al, and TX32-0.4Al alloys with Si
additions. 6-35
Fig. 6.31: True stress - true strain curves obtained for the TX32-0.4Al-0.8Si
alloy in compression at different strain rates and at test temperatures
of (a) 400 ○C and (b) 500
○C. 6-36
Fig. 6.32: Processing map for the TX32-0.4Al-0.8Si alloy. The numbers
associated with the contours represent power dissipation
efficiency in percent. 6-37
Fig. 6.33: Top and side views of the deformed TX32-0.4Al-0.8Si alloy
specimens under different deformation conditions.
The compressive direction is perpendicular to the viewing plane. 6-38
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Page
Fig. 6.34: Microstructure of the TX32-0.4Al-0.8Si alloy deformed at
450 ○C/0.0003 s
-1 (Domain 1). The compression axis is vertical. 6-39
Fig. 6.35: Transmission electron micrographs of the specimen deformed at
450 ○C/0.001 s
-1 (Domain 1) of the TX32-0.4Al-0.8Si alloy
(a) reveals planar slip and (b) shows tilt boundaries. 6-40
Fig. 6.36: (a) Micro-textures and (b) Schmid factor distribution of the grains
for the specimen deformed at 450 ○C/0.001 s
-1 (Domain 1) of the
TX32-0.4Al-0.8Si alloy. The x-axis in the pole figures
is the compression axis. 6-41
Fig. 6.37: Microstructure of the TX32-0.4Al-0.8Si alloy deformed at
500 ○C/10 s
-1 conditions
(Domain 2).
The compression axis is vertical. 6-41
Fig. 6.38: Transmission electron micrographs of the specimen deformed at
500 ○C/10 s
-1 (Domain 2) of the TX32-0.4Al-0.8Si alloy
(a) reveals planar slip and (b) shows tilt boundaries. 6-42
Fig. 6.39: (a) Micro-textures and (b) Schmid factor distributions of the grains
for the specimen deformed at 500 ○C/10 s
-1 (Domain 2) of the
TX32-0.4Al-0.8Si alloy.
The x-axis in the pole figures is the compression axis. 6-43
Fig. 6.40: SEM microstructures of the TX32-0.4Al-0.8Si alloy deformed
at (a) 300 ○C/0.0003 s
-1 showing voids at hard particles, and
(b) 300 ○C/0.1 s
-1 showing crack formation due to joining of
voids at adjacent hard particles. 6-44
Fig. 6.41: (a) Variation in normalized flow stress values (at a strain of 0.5)
with strain rate at different test temperatures, (b) the Arrhenius
plot showing the variation in normalized flow stress values
with inverse of temperature at different strain rates for the
TX32-0.4Al-0.8Si alloy. 6-45
Fig. 6.42: Processing maps for the (a) TX32-0.4Al base alloy,
(b) TX32-0.4Al-0.2Si, (c) TX32-0.4Al-0.4Si, (d) TX32-0.4Al-0.6Si
and (e) TX32-0.4Al-0.8Si alloys. 6-48