Direct–Chill Casting of Light Alloys: Science and Technology

Presents the latest science and technology to solve current problems and advance the field of direct-chill casting Light alloys play an indispensable role in today's industrial society, with aluminium and magnesium two of the most important structural materials used around the world. Direct- chill casting is the principle technology for producing billets and ingots of light alloys. This book thoroughly reviews the science and technology of direct-chill casting of light alloys and important ancillary processes. Emphasizing the needs of industrial research and practice, the book explains how the physico-chemical, thermo-physical, and thermo-mechanical aspects of light alloys all play major roles in the formation of the structure, defects, and properties of the casting. Direct-Chill Casting of Light Alloys begins with an historical overview and then examines liquid metal supply, alloy preparation, and melt transport. Next, the book covers: Melt refining and impurity control Grain refinement Solidification phenomena and casting defects Direct-chill casting technology and operation Post-casting processing Modeling and simulation The book ends with a discussion of key economic considerations in direct-chill casting. The authors of the book are international leaders in the field of solidification and casting research and technology. The material presented is based on a thorough review of the literature and current practice as well as the authors' firsthand experience in research and industry. Direct-Chill Casting of Light Alloys enables technicians, engineers, and researchers to apply all the latest science and technology to solving the current challenges, advancing the field, and creating safe and sustainable commercial operations.

PREFACE AND ACKNOWLEDGEMENTS xi 1 DIRECT–CHILL CASTING: HISTORICAL AND INDUSTRIAL PERSPECTIVE 1 1.1 Industrial Perspective / 1 1.2 Historical Development / 2 References / 27 2 LIQUID METAL SUPPLY, ALLOY PREPARATION, AND MELT TRANSPORT 30 2.1 Plant Layout, Metal Scheduling, and Liquid Supply / 31 2.2 Alloying Elements and Master Alloys / 33 2.3 Furnace Technology / 37 2.3.1 Mixing Technology / 40 2.3.2 Temperature Control / 41 2.4 Melt Transport to and from the Furnace / 43 2.4.1 Furnace Filling / 43 2.4.2 Scrap Charging and Melting / 44 2.4.3 Furnace Cleaning / 46 2.4.4 Molten Metal Transportation from Furnace to Caster / 46 2.5 Chemical Analysis / 49 2.6 Magnesium Melt Protection and Handling / 50 2.7 Safety / 52 References / 53 3 MELT REFINING AND IMPURITY CONTROL 56 3.1 Impurity Sources / 58 3.1.1 Aluminium / 58 3.1.2 Magnesium / 61 3.2 Effect of Impurities / 62 3.2.1 Dissolved Hydrogen / 62 3.2.2 Dissolved Metallic Impurity Elements Including Alkali Metals / 63 3.2.3 Inclusions / 65 3.3 Impurity Removal / 65 3.3.1 Dissolved Metal Impurities / 67 3.3.2 Hydrogen Removal: Degassing / 67 3.3.3 Inclusion Load Minimisation / 73 3.3.4 Inclusion Removal / 74 3.3.5 Alkali Metal Removal / 81 3.3.6 Magnesium Flux Refining / 83 3.3.7 Flux–Free Refi ning of Magnesium / 85 3.4 Measurement of Impurities / 85 3.4.1 Inclusion Measurement / 85 3.4.2 Hydrogen Measurement / 89 3.4.3 Alkali Content Measurement / 91 3.5 Temperature Measurement / 91 3.6 System Layouts, Safety, and Cost Considerations / 92 References / 94 4 GRAIN REFINEMENT 103 4.1 Historical Overview / 103 4.2 Fundamentals of Grain Refinement / 104 4.3 Mechanisms of Grain Refinement in Aluminium and Magnesium Alloys / 112 4.3.1 Grain Refinement through Phases Formed by Alloying Elements during Solidification / 113 4.3.2 Grain Refinement by Added Insoluble Particles / 115 4.3.3 Grain Refinement by Indigenous Insoluble Particles / 121 4.3.4 Grain Refinement by Multiplication of Solidification Sites / 125 4.4 Technology of Grain Refinement in DC Casting / 128 4.4.1 Grain Refining of Aluminium Alloys by Al–Ti–B and Al–Ti–C Master Alloy Rods / 128 4.4.2 Grain Refinement Using Master Alloys Added in the Furnace / 136 4.4.3 Addition of Grain Refiners as Salts, Fluxes, Compounds, and Gases / 137 References / 139 5 SOLIDIFICATION PHENOMENA AND CASTING DEFECTS 144 5.1 Effect of Cooling Rate and Melt Temperature on Solidifi cation of Aluminium Alloys / 144 5.2 Microsegregation / 148 5.3 Effects of Process Parameters on the Dendrite Structure / 149 5.4 Effect of Process Parameters and Alloy Composition on the Occurrence of Specific Structure Defects / 155 5.5 Macrosegregation / 158 5.5.1 Mechanisms of Macrosegregation / 158 5.5.2 Effects of Process Parameters on Macrosegregation during DC Casting / 165 5.5.3 Effect of Composition on Macrosegregation: Macrosegregation in Commercial Alloys / 169 5.6 Hot Tearing / 173 5.6.1 Thermal Contraction during Solidification / 174 5.6.2 Mechanical Properties in the Semi–Solid State / 177 5.6.3 Mechanisms and Criteria of Hot Tearing / 181 5.6.4 Application of Hot–Tearing Criteria to DC Casting of Light Alloys / 191 5.6.5 Effects of Process Parameters on Hot Tearing and Shape Distortions during DC Casting / 196 5.7 Cold Cracking / 204 5.7.1 Mechanical Properties of As–Cast Alloys and Mechanisms of Cold Cracking / 206 5.7.2 Cold–Cracking Criteria / 210 5.7.3 Methods to Prevent Cold Cracking / 218 5.8 Defects Related to the Technology of DC Casting / 219 References / 226 6 DC CASTING TECHNOLOGY AND OPERATION 235 6.1 Introduction / 235 6.2 Mould Technology / 236 6.2.1 Mould Heat Transfer / 237 6.2.2 Water Cooling Heat Transfer / 244 6.2.3 Mould Design: General Development / 249 6.2.4 Electromagnetic DC Casting / 253 6.2.5 Extrusion Billet Mould Technology Variants and Evolution / 255 6.2.6 Gas–Pressurised Hot–Top Mould Operation / 258 6.2.7 Mould Dimensions / 259 6.2.8 Casting Parameters / 266 6.2.9 Rolling Slab Moulds and Cast Start Technology / 271 6.2.10 HDC Casting / 273 6.2.11 Lubrication and Mould Friction / 279 6.3 Other Equipment / 281 6.3.1 Mould Table / 281 6.3.2 Starting Head Base and Starting Heads / 284 6.3.3 Molten Metal Delivery to the Moulds / 289 6.3.4 Molten Metal Level Control / 293 6.3.5 Casting Machine / 298 6.3.6 Ancillary Equipment and Pit Engineering / 300 6.4 Water System / 303 6.4.1 General Description / 303 6.4.2 Water Requirements / 305 6.5 Control Systems / 306 6.5.1 General Requirements / 306 6.5.2 Automated Systems / 307 6.6 Equipment Failure–Related Defects / 310 6.7 Safety Considerations / 311 References / 314 7 POST–CASTING PROCESSING 321 7.1 Introduction / 321 7.2 General / 321 7.3 Inspection and Sawing / 322 7.4 Homogenisation and Stress Relieving / 323 7.5 Sawing and Packaging / 328 7.6 Safety Issues / 329 References / 329 8 MODELLING AND SIMULATION 331 8.1 Introduction and History / 331 8.2 Physical Modelling / 333 8.2.1 Flow Modelling / 333 8.2.2 Water Spray Heat Transfer / 333 8.3 Non–Dimensional Number Analysis / 334 8.4 Mathematical Modelling Methods / 337 8.5 Modelling Requirements / 339 8.5.1 Model Formulation / 339 8.5.2 Boundary Condition and Property Data / 339 8.5.3 Validation and Experimental Verification / 341 8.5.4 Post Processing / 343 8.5.5 Resources: People, Hardware, and Software / 343 8.6 Flow Modelling of Metal Delivery Systems / 344 8.7 Macrosegregation Modelling during DC Casting of Aluminium Alloys / 346 8.7.1 Background / 346 8.7.2 Example of Macrosegregation Simulation / 349 8.8 Stress and Cracking Modelling / 351 8.8.1 Hot Tearing during DC Casting / 352 8.8.2 Cold Cracking during DC Casting / 360 8.9 Modelling of Mould Processes / 363 8.9.1 Mould Distortion, Ingot Shape Modelling, and Control / 363 8.9.2 Air–Gap Formation and Surface Segregation / 368 8.9.3 Gas–Pressurised Mould Meniscus Modelling / 368 8.10 Modelling of Magnesium DC Casting / 369 8.11 Final Remarks on Application of Models / 370 Acknowledgement / 371 Appendix 8.A Analytical Solutions to DC Casting / 371 References / 375 9 ECONOMIC CONSIDERATIONS 383 9.1 DC Product Markets and Margins / 384 9.2 Financial Measures / 386 9.2.1 Examples of the Application of Financial Measures / 387 9.3 Throughput, Audit, Key Performance Indicator (KPI), and Benchmarking Analysis / 395 References / 399 INDEX 400

JOHN F. GRANDFIELD, PhD, is Director of Grandfield Technology Pty Ltd. Dr. Grandfield is a well-known specialist in casting and solidification of light metals. He is an active presenter and organizer of workshops and lectures. DMITRY G. ESKIN, PhD, is Professor at Brunel University. His main scientific contributions are in physical metallurgy of aluminium alloys and solidification processing. Ian F. Bainbridge, PhD, managed production operations and conducted R&D in the aluminium industry for fifty years.