Investigation of Magnetic Pulse Welding on Lap Joint of Similar and Dissimilar Materials Dissertation Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Yuan Zhang, B.S., M.S. Graduate Program in Materials Science and Engineering The Ohio State University 2010 Dissertation Committee: Dr. Glenn S. Daehn, Advisor Dr. Sudarsanam Suresh Babu, co-Advisor Dr. Michael J. Mills Dr. David Rigney Dr. Shelly D.Jepsen Copyright by Yuan Zhang 2010 Abstract The main objective of this research is to investigate the magnetic pulse welding (MPW) process, the resulting joint strength and the interface welding metallurgy. It is known that traditional fusion welding is not able to weld dissimilar materials with different thermal properties, but MPW has been applied to both similar and dissimilar materials. MPW is a solid state impact welding technology that may provide metallurgical bonding without melting and solidification, and there is no significant heat affected zone (HAZ). It shares the same physical principle with explosive welding (EXW) and is good for workpiece with length scale in the order of millimeter to centimeter. This research first compares three impact welding technologies, EXW, MPW and laser impact welding (LIW), for different length scale with different driving system. The joining is likely the result of an instability associated with jetting, which scours the surface clean during impact. It was found that the metallurgical bonding by oblique impact was only realized at the combination of certain impact velocity and impact angle. Taking 0.254mm thick copper alloy 110 plate to plate joint as an example, the suitable impact velocity was larger than 250m/s and the suitable impact angle was within 2º~7º. As a result, the joint interface undergoes high strain rate deformation and the strain rate was established in the order of 106~107s-1. In this research, aluminum alloy, copper alloy, and low carbon steel were ii welded by MPW using electromagnetic force to accelerate the metal. The strengths for both similar and dissimilar material joints were examined by lap shearing test, peeling test and microhardness test, and the similar materials joint was also tested by nanoindentation. The joint strength was greater than that of the base metals and the welded region was hardened by high velocity impact. The tensile failure and peeling failure were outside of the welded region. The welded interface microstructure was characterized by optical microscopy, scanning electron microscopy, electron backscatter diffraction, transmission electron microscopy, and field ion atom probe microscopy. The welded interface indicated wave interface morphology. Due to adiabatic heating and high strain rate deformation, the welded interface microstructure exhibited various features, including grain refinement with large grain boundary misorientation angle, formation of band structure, deformation twins, lamellar grains, and high dislocation density (~estimated to be 1011m-2). Similar materials welding suggested pure solid state bonding, while dissimilar materials joints sometimes contained small amount of intermetallic phase distributed discontinuously in the vertex region of certain waviness along the welded interface. In order to identify the coupled thermal, electromagnetic, and mechanical properties during the impact welding process, a finite element analysis was attempted via LS-DNYA®. Some of the simulation results were compared to the instrumented experiments and the validated model can be used to investigate the successful welding criterion with regard to the impact angle and impact velocity for other materials. iii Dedication In memory of my beloved grandmother, Ms. Fenying Zhang. 谨以此论文献给我挚爱的外祖母，张粉英女士。 iv Acknowledgements My study in the past four years cannot be completed without the help from many individuals and the financial support from American Welding Society. All these efforts help me go through the research work with great pleasure. First, I want to show great appreciation to my advisors Professor Glenn Daehn and Professor Sudarsanam Suresh Babu. They are always the constant source of guidance and support. They motivate me to think with critical perspective and to apply the text book knowledge on solving real problems. They offer me the chance to work on such interesting research topic and create many unique opportunities for me to explore aboard on materials science, all of which enriched my research work at OSU to be a worthwhile experience. After four years working together, I am deeply impressed by their global perspective, noble personalities, hard working, and their passion for discovery. I feel very lucky to have them not only as the mentors and role models, but also as the friends. Thank you, Glenn and Suresh, for your effort and faith on me. I thank Professor Michael Mills and Professor David Rigney for being my dissertation committee. I appreciate their kind help and useful discussions on my research work. I v also want to point out that it was a great pleasure to work as the teaching assistant twice for their Materials Characterization classes. It was not only a great teaching experience but also a nice training for my communication skills. I want to thank the assessment from American Welding Society (AWS) on the impact welding technology and my performance. It is a great honor to be one of the four winners among North American universities for AWS Fellowship Award since 2007. The generous financial support for continuous three years offers me the best opportunity to investigate magnetic pulse welding. I also highly appreciate the SHaRE program from Oak Ridge National Lab (ORNL) sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy, which allows me to use the state-of-the-art facilities freely. These unique opportunities helped me to understand the microstructure evaluation down to atomic level resolution. The scientists at ORNL are all very kind and they offered me nice help on my on-site working, and they are Dr. Michael Miller, Kaye Russell, Kathy Thomas, Dr. Ai Serizawa, Tom Geer, Dr. Ed Kenik, Dr. Hongbing Bei, and Dr. Sang Hoon Shim. It is a great experience to work with such nice and patient scientists. Thanks to Curtis Prothe, Micheal Blakely at Dynamic Materials Corporation and John Kwasegroch, Mike LaHa at Continuum Inc. for their help on the study of different length scales impact welding. Thanks to Pierre L’Eplattenier and Mike Burger at Livermore vi Software Technology Corporation for the great help on LS-DYNA simulation and TrueGrid Mesh. Both Pierre and Mike answered lots of my questions through phone calls and emails regardless the three hours time difference. The experiment work was also carried out with nice help from Ross Baldwin. He is always ready to help. He taught me how to use the facilities and suggested lots of smart approaches. I also want to thank Dan Huber, Hendrik Colijn, and Cameron Begg for their training on FIB, TEM and SEM, and Steve Bright for his help on sample polishing. From day one, I have obtained continuous help from Kathy Babusci. She takes care of the finical issues on my project and also helps me for proof readings on all of my writings. Thanks to the former and current electromagnetic forming group members, Peihui Zhang, Jianhui Shang, Manish Kamal, Mala Seth Dehra, Geoffrey Taber, Kinga Unocic, Scott Golowin, Kristin Banik, Jon Evarts, Jason Johnson, Anupam Vivek, Aaron Washburn, Huimin Wang, Shekhar Srinivasan, Bradley Kabert, Steven Woodward, and Christian Weddeling. Especially thanks to Peihui, she helped on the tubular welding and introduced me to EWI; thanks to Scott and Jianhui, they worked closely with me to help me adapt to new research environment at the very beginning; thanks to Kinga for her help on sample preparation; thanks to Geoff for his constant help and brilliant suggestions during my experiments; thanks to Jason for his outstanding brazing on my broken welding actuators. I also want to thank the group members from computation materials joining group, especially Tapasvi Lolla and Xinghua Yu for their help on microhardness test. vii I also thank my friends at our department. They encouraged completing my study overseas and gave me the chances to express the scientific ideals loudly and confidently in my second language. Especially, thanks to Professor Suliman Dregia, Professor James C. Williams, Dr. Ed Herderick, Clarrisa Yablinsky for help on many mock exams, and they taught me to gratefully cheer for myself rather than keeping happiness deep down inside. Thanks to Dr. Adam Pilchak for his great help on my EBSD sample preparation. Thanks to Dr. Alpesh Shukla, Dr. Libor Kovarik, Dr. Amit Samanta, Dr. Ning Zhou, Dr. Weiqi Luo, Li Sun, Dr. Liang Qi, and Dr. Dong Liang for their general discussions. Last but not least, I also deeply appreciate the love and support from my family. Thanks to my parents’ endless love. They walked me through the frustration and taught me the secret to realize my dreams: work hard with patience. Thanks to my elder sister who always stand with me shoulder by shoulder to face both the happy time and the hard time. Thank you, Mom, Dad, and Sis! Sincere thanks to my wonderful boyfriend, Kuiyu Li for his great understanding and accompany in these years, and I am looking forward to explore more adventure with you in the future. viii Vita Born November 6, 1981……………………...Yinchuan, Ningxia, China 2004…………………………………………..B.S. Materials Science and Engineering Zhejiang University, China 2005…………………………………………. M.S. Innovation of Manufacturing System and Technology, Singapore-MIT Alliance, Singapore 2007…………………………………………. M.S. Materials Science and Engineering The Ohio State University 2005-Present…………………………………Graduate Research Associate The Ohio State University 2007-Present………………………………… American Welding Society Graduate Student Fellowship Publications 1. Application of High Velocity Impact Welding at Varied Different Length Scales, Y. Zhang, S. S. Babu, C.