Direct-Chill Casting of Light Alloys : Science and Technology

by Grandfield, J. F.; Eskin, D. G.; Bainbridge, Ian

• ISBN13: 9781118022658
• ISBN10: 1118022653
• Format: Hardcover
• Copyright: 2013-09-30
• Publisher: Wiley-TMS

Summary

Direct-chill casting is the major production route for wrought aluminium and magnesium alloys that are later deformed (rolled, extruded, forged) to the final products. To aid in this process, this book provides comprehensive coverage on topics such as the history of process development in this field, industrial applications, including vertical and horizontal casting, melt preparation, fundamentals of solidification in DC casting, and more. The first book targeted for the industrial researcher and practitioner, it pulls together the practice and process of physics with the goal of improving process performance.

Author Biography

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.

Table of Contents

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