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Mechanical Behaviour and Deformation Mechanisms of Zn-Al-Cu-Mg Alloys

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Mechanical Behaviour and Deformation Mechanisms of Zn-Al-Cu-Mg Alloys Mechanical behaviour and deformation mechanisms of Zn-Al-Cu-Mg alloys Von der Fakultät für Georessourcen und Materialtechnik der Rheinisch-Westfälischen Technischen Hochschule Aachen zur Erlangung des akademischen Grades eines Doktors der Ingenieurwissenschaften genehmigte Dissertation vorgelegt von M.Sc. Zhicheng Wu aus Quyuan, Provinz Hunan, China Berichter: Univ.-Prof. Dr. Sandra Korte-Kerzel Univ.-Prof. Dr.-Ing. Sebastian Münstermann Tag der mündlichen Prüfung: 05.September 2018 Diese Dissertation ist auf den Internetseiten der Universitätsbibliothek online verfügbar To my family Acknowledgements Acknowledgements In the beginning, I would like to express my appreciation to all people who have helped me with my doctoral thesis. Foremost, I would like to express my deepest thanks and sincere appreciation to my advisor Prof. Dr. Sandra Korte-Kerzel, Institute of Physical Metallurgy and Metal Physics (IMM), RWTH Aachen University, for her expert, creative and comprehensive guidance, and encouragement throughout my PhD. My greatest gratitude also goes to Prof. Dr. Günter Gottstein, Institute of Physical Metallurgy and Metal Physics (IMM), RWTH Aachen University, for giving me the opportunity to work at IMM, for suggesting the topic of this dissertation, and for his kind supervision in the first two years of my PhD. My special thanks to my second examiner Prof. Dr. Sebastian Münstermann, Steel Institute (IEHK), RWTH Aachen University, and the chair of my examination committee Prof. Dr. Dieter Georg Senk, Steel Institute (IEHK), RWTH Aachen University, for their insightful comments and discussions. I would like to thank Dr. Stefanie Sandlöbes and Dr. Weiping Hu for the inspiring discussions, insightful corrections, valuable comments and continuous encouragement. Very special thanks to Dr. Stefanie Sandlöbes, for her unswerving support not only in my research, but also in my personal life. I would like to thank my colleagues at IMM for the stimulating discussions, for the introductions and support to experimental equipment, and for all the great time we have had during my PhD period. It was fantastic to work together with them at IMM. In particular, I am grateful to David Beckers for the support in metallography, Thomas Burlet for setting up the creep testing and in-situ testing devices, Jann-Erik Brandenburg for the introduction to SEM, Dr. James Gibson for the technical support and inspiring discussions in nanoindentation, Sebastian Schröders for the introduction to FIB and AFM, Fengxin Mao for the help with MATLAB scripts, and Arndt Ziemons for the alloys casting. I am also grateful to Prof. Dr. Rainer Schmid-Fezter and Dr. Song-mao Liang at TU Clausthal for the cooperation and suggestions for alloy design in our joint projects, Prof. Dr. Christophe Tromas at CNRS-Université de Poitiers for the support with AFM experiments, Xiaoxiao Li at IEHK, RWTH Aachen University for the help with MATLAB scripts, Dr. Konda Gokuldoss Pradeep, Dr. Marcus Hans and Marshal Amalraj at Material Chemistry (MCh), RWTH Aachen University for the support with APT experiments. I would like to extend my thanks to my student assistants Liang Wu, Jing Rao, Yufengnan Wang, An Zhang, Kuan Ding, Shuo Wang and Shanyu Chen for their great work in their theses and hiwi jobs. i Acknowledgements A very special gratitude goes to the German Research Foundation (DFG) for the financial support for my work within projects GO 335/47-1 and KO 4603/5-1. I am also grateful to Federation of German foundry industry e. V. (BDG) for the invitation to industry meet ups on Zn castings, and Dr. Didier Rollez at Grillo-Werke AG for his insightful comments from industry point of view. Finally, I would like to explain my profound gratitude to my family and my friends, especially my parents, who have supported me along the way. Thanks for all your encouragement and support! ii Contents Contents Acknowledgements ................................................................................................................. i Contents ................................................................................................................................ iii List of tables .......................................................................................................................... vi List of figures ........................................................................................................................ vii List of symbols....................................................................................................................... xi List of abbreviations ............................................................................................................. xii 1. Introduction .................................................................................................................... 1 2. Theoretical background .................................................................................................. 4 2.1. Zinc and Zinc alloy .................................................................................................. 4 2.1.1. Alloying elements in Zn .................................................................................... 4 2.1.2. Application of Zn and Zn based alloys .............................................................. 6 2.2. Deformation mechanisms ........................................................................................ 7 2.2.1. Dislocation slip ................................................................................................. 7 2.2.2. Kink bands ......................................................................................................10 2.2.3. Deformation twinning .......................................................................................11 2.2.4. Grain and phase boundary sliding ...................................................................13 2.2.5. Creep ..............................................................................................................14 2.2.6. Activation of deformation mechanisms ............................................................21 2.2.6.1. Thermal activation of dislocations.............................................................21 2.2.6.2. Activation volume .....................................................................................23 2.2.6.3. Activation energy ......................................................................................24 2.2.7. Deformation mechanism maps ........................................................................25 2.3. Nanoindentation .....................................................................................................30 3. Experimental methods and materials .............................................................................34 3.1. Materials ................................................................................................................34 3.2. Sample preparation ................................................................................................34 3.3. Macroscopic mechanical testing .............................................................................35 3.3.1. Constant strain rate tensile testing ..................................................................35 3.3.2. Strain rate jump test ........................................................................................36 3.3.3. Creep test .......................................................................................................36 3.3.4. In-situ straining experiments ............................................................................37 3.4. Nano-indentation experiments ................................................................................38 3.4.1. Constant strain rate and strain rate jump tests ................................................38 3.4.2. Nanoindentation creep tests ............................................................................39 3.5. Microstructure characterisation ..............................................................................40 iii Contents 3.6. Digital image correlation (DIC) measurements .......................................................40 4. Macroscopic mechanical response and mechanisms ....................................................42 4.1. Results and discussion ...........................................................................................42 4.1.1. As-cast microstructure .....................................................................................42 4.1.2. Mechanical properties ...................................................................................46 4.1.3. Fracture surfaces ............................................................................................48 4.1.4. Deformation microstructure ..........................................................................51 4.1.4.1. Room temperature and/or highest strain rate tested (5∙10−4 s-1) ...............51 4.1.4.2. Elevated temperature and/or low strain rate .............................................55 4.2. Conclusions............................................................................................................59 5. Creep of ZnAl4Cu1 alloys ..............................................................................................60 5.1. Results ...................................................................................................................60 5.1.1. Uniaxial tensile creep experiments
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