ACKNOWLEDGMENTS ................................................. I
Dedication ..................................................... IV
List of publications ........................................... VI
List of Figures ................................................ XI
List of Tables .............................................. XVIII
List of abbrevations and symbols .............................. XIX
Abstract .................................................... XXIII
1 General introduction ......................................... 2
1.1 Background .............................................. 2
1.2 Rationale ............................................... 5
1.3 Objectives .............................................. 6
1.4 Thesis overview ......................................... 8
1.5 State of art and study approach ........................ 10
1.6 Contribution of this work .............................. 12
2 Literature review ........................................... 15
2.1 Introduction ........................................... 15
2.2 Classification and fundamental properties of
magnesium and its alloys ............................... 15
2.3 Magnesium corrosion .................................... 20
2.3.1 General corrosion ............................... 20
2.3.2 Galvanic corrosion .............................. 22
2.4 Oxidation of base and cladding metals .................. 24
2.4.1 Oxidation kinetic growth of magnesium ........... 24
2.4.2 Low temperature oxidation of magnesium .......... 27
2.4.3 High temperature oxidation of magnesium ......... 28
2.4.4 Mechanism of aluminium oxidation ................ 31
2.5 General aspects of oxide behaviour in the rolling
process (oxide fracture and substrate metal
extrusion) ............................................. 35
2.6 Theoretical Models of Oxide fracture and extrude of
underline metals during rolling ........................ 38
2.7 Roll bonding process ................................... 43
2.7.1 General introduction ............................ 43
2.7.2 Mechanism of roll bonding ....................... 43
2.7.3 Theoretical models for bonding strength ......... 46
2.8 Parameters affecting bonding ........................... 46
2.8.1 The initial state of the base metal ............. 47
2.8.2 Rolling temperature ............................. 48
2.8.3 Rolling reduction ............................... 51
2.8.4 Surface preparation ............................. 53
2.8.5 Oxide layer ..................................... 55
2.9 Post heat treatments ................................... 57
2.9.1 Intermetallic phases of Mg/Al joint ............. 59
2.9.2 Intermetallic phases growth mechanism ........... 61
3 Experimental procedure ...................................... 65
3.1 Introduction ........................................... 65
3.2 Initial material ....................................... 65
3.3 Oxidation study ........................................ 67
3.3.1 Introduction .................................... 67
3.3.2 Thermogravimetric analysis ...................... 67
3.3.3 XPS ............................................. 68
3.3.4 GLEEBLE thermo-mechanical simulator ............. 71
3.4 Roll bonding ........................................... 72
3.4.1 Introduction .................................... 72
3.4.2 Surface preparation ............................. 73
3.4.3 Surface roughness measurements .................. 75
3.4.4 Roll bonding process ............................ 77
3.4.5 Post annealing process .......................... 81
3.5 Evaluation of roll bonded material ..................... 82
3.5.1 Evaluation of the bonding quality ............... 82
3.5.2 Microstructure, interface characterization and
layer thicknesses ............................... 83
3.5.3 Mechanical and forming behaviour tests .......... 87
4 Characterization of initial base and cladding sheets ........ 93
4.1 Introduction ........................................... 93
4.2 Characterization of the base (TRC AZ31) sheet .......... 93
4.3 Flow behaviour of base and clad materials .............. 97
4.4 Evaluation of wire-brushed strips ...................... 97
4.5 Oxidation of TRC AZ31 magnesium alloy ................. 103
4.5.1 Introduction ................................... 103
4.5.2 Surface appearance ............................. 103
4.5.3 Thermogravimetric analysis ..................... 103
4.5.4 Intermediate temperature oxidation of TRC AZ31
magnesium alloy ................................ 104
4.5.5 High temperature oxidation of TRC AZ31
magnesium sheet ................................ 109
4.5.6 Oxide composition .............................. 117
4.5.7 Discussion of TRC AZ31 magnesium sheet
oxidation ...................................... 117
4.6 Oxidation of pure aluminium 1050 (clad metal) ......... 126
4.6.1 Introduction ................................... 126
4.6.2 TGA analysis ................................... 127
4.6.3 Evaluation of the XPS spectra .................. 127
4.6.4 Oxide thickness determination .................. 129
4.6.5 Discussion of pure aluminium oxidation ......... 129
4.7 Conclusions ........................................... 132
5 Hot roll bonding of Al/TRC Mg/Al laminate composite ........ 136
5.1 Introduction .......................................... 136
5.2 Microstructures of the roll-bonded Al/TRC Mg/Al
laminated composites .................................. 136
5.2.1 Effect of rolling reduction on the contact
surface evolution .............................. 136
5.2.2 The interface .................................. 137
5.3 Fracture observations of the bonding area ............. 139
5.4 Bonding strength ...................................... 145
5.5 Deformation distribution on the base and cladding
sheet ................................................. 148
5.6 Mechanical properties of the laminate composite ....... 152
5.7 Discussion ............................................ 155
5.7.1 Interface characterization ..................... 155
5.7.2 Bonding strength ............................... 158
5.7.3 Bonding mechanism .............................. 161
5.7.4 Deformation distribution during roll bonding ... 164
5.7.5 Mechanical properties of as-received roll
bonded composite ............................... 166
5.8 Conclusions ........................................... 168
6 Effect of annealing and subsequent hot forming on the
interface evolution, bonding strength, mechanical
properties and deformation behaviour of Al/Mg/Al laminate
composite .................................................. 172
6.1 Introduction .......................................... 172
6.2 Interface identification .............................. 172
6.3 Growth of intermetallic phases ........................ 174
6.4 Bonding strength evolution ............................ 178
6.5 Hardness of intermetallic phases ...................... 179
6.6 Tensile properties and failure mode ................... 180
6.7 Formability of Al/Mg/Al laminate composite ............ 184
6.7.1 Plane strain compression (PSC) testing ......... 184
6.7.2 Subsequent hot rolling of Al/Mg/Al composite ... 187
6.7.3 Deep drawing testing ........................... 188
6.8 Discussion ............................................ 189
6.8.1 Growth kinetics of intermetallic phases ........ 189
6.8.2 Bonding strength ............................... 192
6.8.3 Mechanical properties .......................... 193
6.8.4 Forming behaviour during PSC testing ........... 194
6.8.5 Interface evolution after subsequent hot
rolling ........................................ 199
6.8.6 Deep drawing testing ........................... 200
6.9 Conclusions ........................................... 201
7 Final conclusions and future works ........................ 206
7.1 Summary and final conclusions ......................... 206
7.1.1 Oxidation of the base sheet TRC AZ31 and
cladding sheet aluminium ....................... 206
7.1.2 Bonding strength, mechanical properties and
forming behaviour during roll bonding of
as-rolled Al/Mg/Al composite ................... 208
7.1.3 Intermetallic phases formation, its growth
rate and influence on the bonding strength
and mechanical properties of annealed Al/Mg/Al
roll bonded composite .......................... 210
7.1.4 Formability of as-rolled Al/Mg/Al roll bonded
composite ...................................... 212
7.2 Future work and recommendations ....................... 213
References ................................................. 216
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