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Study of Sensitization in AA5083 Aluminium Alloy

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Study of Sensitization in AA5083 Aluminium Alloy Study of Sensitization in AA5083 Aluminium Alloy A thesis submitted to The University of Manchester for the degree of Doctor of Philosophy in the Faculty of Science and Engineering 2017 WU WEI SCHOOL OF MATERIALS Corrosion and Protection Centre Contents Contents Contents .................................................................................................................... 2 List of Figures ........................................................................................................... 7 List of Tables ............................................................................................................15 List of Abbreviations ................................................................................................16 Abstract ....................................................................................................................17 Declaration ...............................................................................................................18 Copyright .................................................................................................................19 Publications ..............................................................................................................20 Acknowledgements ..................................................................................................21 Chapter 1 Introduction ..............................................................................................22 1.1 Background.................................................................................................22 1.2 Overall Research Objectives .......................................................................23 1.3 Structure of Thesis ......................................................................................24 Chapter 2 Literature Review .....................................................................................25 2.1 Aluminium and Its Alloys ...........................................................................25 2.1.1 Introduction ......................................................................................25 2.1.2 Elements in Aluminium Alloys .........................................................27 Page 2 2.1.3 Classification of Aluminium Alloys ..................................................28 2.1.4 Aluminium Alloy Families ...............................................................29 2.1.5 Properties of Aluminium Alloys .......................................................30 2.2 Aluminium-Magnesium Alloys ...................................................................33 2.2.1 Introduction ......................................................................................33 2.2.2 Segregation in Al-Mg Alloys ............................................................35 2.2.3 Precipitation in Al-Mg Alloys ...........................................................35 2.3 The Corrosion of Aluminium Alloys ...........................................................39 2.3.1 Introduction ......................................................................................39 2.3.2 Effect of Alloying on Corrosion Behaviour .......................................41 2.3.3 Pitting Corrosion ..............................................................................41 2.3.4 Intergranular Corrosion ....................................................................43 2.3.5 Stress Corrosion Cracking ................................................................45 2.4 Sensitization in Aluminium-Magnesium Alloys...........................................47 2.4.1 Introduction ......................................................................................47 2.4.2 Sensitization in AA5083 Alloy .........................................................48 2.5 Effect of Sensitization on Corrosion Behaviour of AA5083 Alloy ...............51 2.5.1 Effect of Sensitization on Structure of AA5083 Alloy .......................51 2.5.2 Effect of Sensitization on the Susceptibility to Intergranular Corrosion .................................................................................................................54 Page 3 2.6 Effect of Sensitization on Mechanical Properties of AA5083 Alloy .............57 2.6.1 Effect of Sensitization on Hardness Properties ..................................57 2.6.2 Effect of Sensitization on Strength Properties ...................................59 2.7 Effects of Sensitization on the Stress Corrosion Cracking of AA5083 Alloy 62 2.7.1 Testing Methods of Stress Corrosion Cracking .................................62 2.7.2 Roles of Precipitation in Stress Corrosion Cracking ..........................64 Chapter 3 Experimental Method ...............................................................................69 3.1 Materials .....................................................................................................69 3.2 Experimental Procedure ..............................................................................71 3.2.1 Alkaline Etching ...............................................................................71 3.2.2 Sensitization Process ........................................................................71 3.2.3 Nitric Acid Mass Loss Test (NAMLT) ..............................................72 3.2.4 Constant Displacement Stress Corrosion Cracking (SCC) Test .........73 3.3 Analytical Techniques .................................................................................74 3.3.1 Optical Microscopy (OM) ................................................................74 3.3.2 X-ray Diffraction (XRD) ..................................................................75 3.3.3 Scanning Electron Microscopy (SEM) ..............................................75 3.3.4 Energy Dispersive X-Ray Analysis (EDX) .......................................76 3.3.5 Electron Probe Microanalysis (EPMA) .............................................77 3.3.6 Transmission Electron Microscopy (TEM) .......................................77 Page 4 3.3.7 3D Volumetric Reconstruction ..........................................................78 Chapter 4 In-service Sensitization of AA5083 Aluminium Alloy ..............................80 4.1 Introduction ................................................................................................80 4.2 General observation of the in-service sensitized AA5083 alloy....................80 4.3 The Distribution of Constituent Intermetallic Particles ................................83 4.4 Compositional Variation through the Plate Thickness ..................................90 4.5 Failure Analysis of the in Service Cracked Component ...............................96 4.6 Susceptibility to Intergranular Corrosion .....................................................99 4.7 Structure of the Grain Boundaries in the In-service Sensitized AA5083 Alloy ....................................................................................................................... 102 4.8 Conclusions .............................................................................................. 114 Chapter 5 Sensitization of AA5083 Aluminium Alloy at Low Temperature ............. 116 5.1 Introduction .............................................................................................. 116 5.2 Experimental Set-up .................................................................................. 118 5.3. General Observation of the O Temper AA5083 Alloy............................... 119 5.4 Structure of the Grain Boundaries in the Low Temperature Sensitized AA5083 Alloy .............................................................................................................. 125 5.5 Electrochemical Behaviour of the Low Temperature Sensitized AA5083 Alloy ....................................................................................................................... 132 5.6 Susceptibility to Intergranular Corrosion ................................................... 134 5.7 Propagation of Intergranular Corrosion in the Sensitized AA5083 Alloy ... 137 Page 5 5.8 Evolution of Precipitates along Grain Boundaries ..................................... 144 5.9 Conclusions .............................................................................................. 154 Chapter 6 Sensitization and Its Effect on Stress Corrosion Cracking ....................... 156 6.1 Introduction .............................................................................................. 156 6.2 Experimental Set-up .................................................................................. 156 6.2.1 Specimens Fabrication .................................................................... 157 6.2.2 Stress Corrosion Cracking Constant Displacement Loading Test .... 160 6.3 Susceptibility to Intergranular Corrosion of the Sensitized AA5083-H116 Alloy .............................................................................................................. 162 6.4 General Observations of Stress Corrosion Cracking .................................. 164 6.5 The Effect of Sensitization on Crack Propagation ...................................... 170 6.6 Conclusions .............................................................................................. 176 Chapter 7 Conclusions and Suggestions for Future Works ...................................... 178 7.1 Summary .................................................................................................
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