beta Phase Growth and Precipitation in the 5xxx Series Aluminum Alloy System

xx Chapter 1: Introduction and Motivation . 1 1.1 Motivation . 1 1.2 Organization of Thesis . 3 Chapter 2: Background literature review . 7 2.1 The 5xxx series aluminum alloy system . 7 2.2 The Al – Mg phase diagram. 9 2.3 The Sensitization process . 10 2.3.1 The metastable β’ phase . 11 2.3.2 Equilibrium β phase . 12 2.4 β phase corrosion . 13 2.4.1 Galvanic corrosion . 13 2.4.2 Stress corrosion cracking . 13 2.4.3 Corrosion Testing. 16 2.5 Key factors that impact β phase precipitation . 17 2.5.1 The impact of grain boundary character on β phase precipitation . 17 2.5.2 General microstructure evolution and Impact of Grain size . 22 viii 2.5.3 Effect of prior strain on precipitation . 27 2.5.4 Effect of thermal treatment . 27 2.6 Mg segregation mechanisms . 29 2.7 Sensitization remediation . 32 2.5 In situ heating in TEM . 36 2.6 Summary of current understanding . 38 Chapter 3: Experimental Methods . 39 3.1 Material Selection . 39 3.2 Material preparation . 42 3.2.1 TEM sample preparation . 42 3.2.2 Bulk SEM preparation for EBSD . 44 3.2.3 Cold rolling and Thermomechanical processing procedure . 47 3.2.5 Bulk ASTM G67 corrosion testing . 52 3.2.6 Ex situ heating experiments . 53 3.3 In situ TEM heating procedure . 53 3.3.1 Post heat treatment analysis . 54 3.3.3 Precipitate measurements. 57 3.3.4 In situ video analysis . 59 3.3.5 Activation energy calculations . 59 3.4 Atom probe tomography . 60 ix 3.5 In situ heating EELs experiments . 61 Chapter 4: Grain Boundary Misorientation Dependence of β Phase Precipitation in an AlMg Alloy . 64 4.1 Abstract . 64 4.2 Background/Motivation . 64 4.3 Conclusions . 73 Chapter 5: Direct Measurement of the effect of cold rolling on β phase precipitation kinetics in 5xxx series aluminum alloys . 75 5.1 Abstract . 75 5.2 Introduction . 75 5.3 Experimental . 79 5.3.1 Sample Preparation . 79 5.3.2 Precipitate Characterization and GBs Analysis . 80 5.3.3 Precipitate Growth Kinetics Analysis . 81 5.4 Results . 82 5.4.1 Effect of rolling reduction on β phase precipitate density and size . 82 5.4.2 Precipitate nucleation and growth . 83 5.4.3 Precipitate distribution with respect to GBs misorientation . 88 5.5 Discussion . 91 5.6 Conclusions . 97 x 5.6.1 Impact of pre strain on precipitate size and density . 97 5.6.2 Growth rate differences caused by pre strain . 97 Chapter 6: The Effect of Thermo-Mechanical Processing on the Microstructure and Corrosion Resistance of Aluminum Alloy 5083-H116 . 99 6.1 Abstract . 99 6.2 Introduction and Background . 100 6.3 Experimental Methods . 104 6.3.1 Thermomechanical Processing . 104 6.3.2 Sensitization, Corrosion Testing, and Microstructural Analysis . 106 6.4 Results and Discussion . 107 6.4.1 Mass Loss as a Function of Thermomechanical Processing . 107 6.4.2 Microstructural Analysis . 109 6.5 Conclusions . 116 Chapter 7: Metastable Precipitates in 5xxx Aluminum Alloys as Predominant Failure Mechanism in Aluminum 5xxx Alloys . 117 7.1 Abstract . 117 7.2 Background . 118 7.3 Methods. 122 7.4 Results and Discussion . 124 7.5 Conclusions . 132 xi Chapter 8: Atom Probe Tomography analysis of pipe diffusion in 5456 aluminum alloy . 133 8.1 Abstract . 133 8.2 Introduction . 133 8.3 Experimental Procedure . 136 8.4 Results and Discussion . 137 8.5 Conclusions . 148 Chapter 9: Observation of β phase remediation during in situ TEM heating experiments and its bulk scale impact on corrosion resistance. 150 9.1 Abstract .