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The University of Hull Solidification of Metal THE UNIVERSITY OF HULL SOLIDIFICATION OF METAL ALLOYS IN PULSE ELECTROMAGNETIC FIELDS being a Thesis submitted for the Degree of Doctor of Philosophy, School of Engineering in the University of Hull by Theerapatt Manuwong, M.Eng, (Chulalongkorn University, Thailand) April 2015 Abstract __________________________________________________________ This research studies the evolution of solidification microstructures in applied external physical fields including in a pulse electric current plus a static magnetic field, and a pulse electromagnetic field. A novel electromagnetic pulse device and a solidification apparatus were designed, built and commissioned in this research. It can generate programmable electromagnetic pulses with tuneable amplitudes, durations and frequencies to suit different alloys and sample dimensions for research at university laboratory and at synchrotron X-ray beamlines. Systematic studies were made using the novel pulse electromagnetic field device, together with finite element modelling of the multiphysics of the pulse electromagnetic field and microstructural characterisation of the samples made using scanning electron microscopy, X-ray imaging and tomography. The research demonstrated that the Lorentz force and magnetic flux are the dominant parameters for achieving the grain refinement and enhancing the solute diffusion. At a discharging voltage from 120 V, a complete equaxied dendritic structure can be achieved for Al-15Cu alloy samples, the strong Lorentz force not only disrupts the growing direction of primary dendrites, it is also enough to disrupts the growing directions of primary intermetallic Al2Cu phases in Al-35Cu alloy, resulting a refined solidification microstructures. The applied electromagnetic field also has significant effect on refining the eutectic structures and promoting the solute diffusion in the eutectic laminar structure. The research has demonstrated that the pulse electromagnetic field is a promising green technology for metal manufacture industry. i Dedication ____________________________________________________________ This thesis is dedicated to my Father, Mother, sister and wife, for their love and support throughout my PhD research. ii Acknowledgements __________________________________________________________ I would like to very gratefully acknowledge the Royal Thai Government for awarding me the PhD scholarship to conduct the research. I also would like to express my sincere gratitude to my supervisor, Dr Jiawei Mi for his persistent support and encouragement, academic advice and guidance throughout the PhD project, especially when the direction of my research changed in my second year study, and when uncertain issues arose in designing and building the novel electromagnetic field experimental apparatus. Special thanks go to the academic staff in the School of Engineering University of Hull, including Dr Kevin S Fansey, Dr. Jim Gilbert and Prof Ron Patton and Prof Michael Fagan for their support and encouragement; and the technical staff, particularly Mr Peter L. Kazinczi for helping on designing and building the control system for the electromagnetic field experimental apparatus; Mr Tony Sinclair and Mr Garry Robinson for assistance on microstructural characterisation using scanning electron microscopy, and Mrs Sue Taft for X-ray tomography. Thanks also go to Prof Patrick Grant of Department of Materials, University of Oxford for allowing me to work with his team together at Beamline B16 of Diamond Light Source to conduct the in situ solidification experiments; and beamline scientist Dr Andrew Bodey of I13 on the excellent support of the tomography experiment at beamline I13. Last but not least, I would like to thank my classmates, colleagues, and friends for the many stimulating technical discussions with them, and the personal hep and friendship received from them, including Mr Wei Zhang, Mr J. C. Khong, Mr Dongyue Tang, Mr T. L. Lee, etc just name a few. iii Publications and awarded synchrotron X-ray beamtime __________________________________________________________ The publications generated from my research and the beamtime awarded for future relevant research are: 1. Manuwong, T., et al. "Solidification of Al Alloys Under Electromagnetic Pulses and Characterization of the 3-D Microstructures Using Synchrotron X- ray Tomography", Metallurgical and Materials Transactions A 46, 7, 2908- 2915, (2015). 2. Manuwong, T., et al. “Control of Solidification Microstructure Using Programmable Electro-Magnetic Pulses”, proceeding of 4th International Conference on Advances in Solidification Processes Beaumont Estates, Old Windsor, UK, on 8-11 July 2015. 3. Manuwong, T., et al. “Shocking the Growing Grains during Solidification by Electro-magnetic Pulses", proceeding of TMS 2015 144th Annual meeting & Exhibition, Orlando, FL, USA, on 5-19 March 2015. 4. A manuscript titled “3-D microstructure characterization and modelling of Al alloys under Electromagnetic filed” is under preparation for Acta Materialia. 5. A proposal titled “In situ tomography study of the evolution of solidification microstructures under magnetic pulses” (proposal ID 20141167) has been awarded 9 shift (3 days) of beamtime by TOMCAT of Swiss Light Source, Paul Scherrer Institute (PSI), Switzerland and the experiment conducted on 10-13 June 2015. iv Abbreviation __________________________________________________________ APS Advanced photon source BSRF Beijing synchrotron radiation facility CET Columnar-to-equiaxed transition DLS Diamond light source DS Directional solidification DSO Digital storage oscilloscope DECP Direct-contact electric current pulse EMP Electromagnetic pulse EMS Electromagnetic stirring EMV Electromagnetic vibration EPM Electromagnetic processing of materials ESRF European synchrotron radiation facility ICD Induced current density LINAC Linear accelerator MFD Magnetic flux density PEC Pulse electric current PLW PicoLog for windows PMO Pulse magneto oscillation PSF point spread function RF Radio frequency v SEM Scanning electron microscopy STR Electron storage ring SXRR Synchrotron X-ray radiography TMF Travelling magnetic field vi List of Symbols __________________________________________________________ 휎푦 Yield strength [MPa] 휎표 Material constant for the starting strength [MPa] km Material constant d Diameter of grain [μm] 휇 Material permeability [T m/A] 휇표 Permeability of free space (1.26×10−6 [T m/A]) 휇푟 Relative permeability of copper ρ density of particle [kg/m3] -1 휇푎 Linear attenuation coefficient [cm ] -1 휇푛 Linear attenuation of each element of the alloy [cm ] 휎 Material conductivity [cm-1] w Weight percentage of each element of the alloy e Euler number 푭 Lorentz force generated by EMP [N/m3] FL Lorentz force generated by PEC [mN] B magnetic flux density [T] 2 Je Input electric current density for EMP coil [A/m ] J Induced current density inside the melt [A/m2] I Input electric current for the electric circuit [A] L Length of EMP coil [mm] vii La Active length of the sample for PEC [cm] G Temperature gradient [°C] g Gravity [N/m2] N Number of EMP coil turns [turns] V Voltage from the input circuit [V] 푉푐 Voltage charged into the capacitor [V] 푉푑 Voltage discharged from the capacitor bank [V] 푡푐 Charging time [ms] 푡푑. Discharge time [ms] 푡푓푢푙푙 Time to fully charge the capacitor [ms] 푡푝푢푙푠푒 Time of EMP applied to alloy [ms] 푓푑 Discharge frequency [Hz] 퐼푑 Discharge current [A] R1 Resistance of resister in the charging unit [Ω] Z Total impedance of the coil [Ω] C Capacitance [μF] E Energy stored in the capacitor bank [J] 3 휌푙 Density of the liquid metal [kg/m ] 푝 Pressure [N/m2] 풖 Velocity [mm/s] 2 2 kT Turbulent kinetic energy [mm /s ] 휀 Turbulent energy dissipation [mm2/s3] viii 휇푇 Turbulence viscosity [kg/m·s] 퐼푡 Identity tensor ∇ Laplace operator D Solute diffusion coefficient [m2/s] α Transition distance of atoms [μm] Γ Mean transition frequency [Hz] Pr Probability of transition in the direction Note: Symbols in bold are Vector ix Contents ____________________________________________________________ Abstract ........................................................................................ i Dedication ....................................................................................... ii Acknowledgements ......................................................................... iii Publications and awarded beamline ................................................ iv Abbreviation ..................................................................................... v List of Symbols ............................................................................... vii Contents ....................................................................................... x Chapter 1 : Introduction ................................................................... 1 1.1 Background ............................................................................ 1 1.2 The structure of the thesis ....................................................... 2 Chapter 2 : Literature reviews .......................................................... 4 2.1 Metallic alloys and the solidification processes ............................ 4 2.1.1 Metallic alloys and the mechanical strength ................... 4 2.1.2 The solidification processes and microstructures ............. 5 2.1.3 Directional solidification ........................................... 10 2.1.4 Microstructure refinement during solidification............... 10 2.1.5 Solidification under external physical fields ..................
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