Corrosion Resistance of Aluminum and Magnesium Alloys : Understanding, Performance, and Testing

"Valuable information on corrosion fundamentals and applications of aluminum and magnesium Aluminum and magnesium alloys are receiving increased attention due to their light weight, abundance, and resistance to corrosion. In particular, when used in automobile manufacturing, these alloys promise reduced car weights, lower fuel consumption, and resulting environmental benefits. Meeting the need for a single source on this subject, Corrosion Resistance of Aluminum and Magnesium Alloys gives scientists, engineers, and students a one-stop reference for understanding both the corrosion fundamentals and applications relevant to these important light metals. Written by a world leader in the field, the text considers corrosion phenomena for the two metals in a systematic and parallel fashion. The coverage includes: The essentials of corrosion for aqueous, high temperature corrosion, and active-passive behavior of aluminum and magnesium alloys ; The performance and corrosion forms of aluminum alloys ; The performance and corrosion forms of magnesium alloys ; Corrosion prevention methods such as coatings for aluminum and magnesium ; Electrochemical methods of corrosion investigation and their application to aluminum and magnesium alloys. Offering case studies and detailed references, Corrosion Resistance of Aluminum and Magnesium Alloys provides an essential, up-to-date resource for graduate-level study, as well as a working reference for professionals using aluminum, magnesium, and their alloys."--Publisher's website Corrosion Resistance of Aluminum and Magnesium Alloys......Page 6 Contents......Page 10 Preface......Page 22 Acknowledgments......Page 24 Part One Electrochemical Fundamentals and Active–Passive Corrosion Behaviors......Page 26 A. Thermodynamic Considerations of Corrosion......Page 28 1.1. Electrolytic Conductance......Page 29 1.1.1. Faraday Laws......Page 30 1.2. Tendency to Corrosion......Page 31 1.3. The Electrochemical Interface......Page 32 1.3.1. Electric Double Layer......Page 33 1.4. Nernst Equation......Page 34 1.5.1. Standard States in Solution......Page 37 1.5.3. Positive and Negative Signs of Potentials......Page 38 1.6.1. Constant and Degree of Dissociation......Page 39 1.6.2. Activity and Concentration......Page 41 1.6.3. Theory of More Concentrated Solutions......Page 42 1.7. Mobility of Ions......Page 44 1.7.1. Law of Additivity of Kohlrausch......Page 45 1.7.2. Ion Transport Number or Index......Page 46 1.8. Conductance......Page 48 1.10. Gas Electrodes......Page 49 1.11.1. Alloyed Electrodes......Page 50 1.12.1. Metal–Insoluble Salt Electrodes......Page 51 1.12.2. Metal–Insoluble Oxide Electrodes......Page 52 1.13. Electrodes of Oxidation–Reduction......Page 53 1.14.1. Glass Electrodes......Page 54 1.14.2. Copper Ion-Selective Electrodes......Page 55 1.15.1. Chemical Cell with Transport......Page 56 1.15.2. Chemical Cell Without Transport......Page 58 1.16. Concentration Cells......Page 59 1.16.1. Concentration Cell with Difference of Activity at the Electrode and Electrolyte......Page 60 1.16.2. Junction Potential......Page 62 1.17.2. Displacement Cell......Page 66 1.17.3. Complexing Agent Cells......Page 67 1.19. Overlapping of Different Corrosion Cells......Page 68 1.20. Definition and Description of Corrosion......Page 69 1.21. Electrochemical and Chemical Reactions......Page 70 1.21.1. Electrochemical Corrosion......Page 71 1.21.2. Film-Free Chemical Interactions......Page 72 References......Page 73 2.1.1. Description......Page 74 2.1.2. Types of Corrosion......Page 75 2.1.3. Atmospheric Contaminants......Page 76 2.2. Aqueous Environments......Page 78 2.3. Organic Solvent Properties......Page 80 2.4. Underground Media......Page 81 2.5. Water Media Properties......Page 82 2.5.1. Water Composition......Page 83 2.5.2. The Oxidizing Power of Solution......Page 86 2.5.3. Scale Formation and Water Indexes......Page 87 2.6.1. Description......Page 90 2.6.2. The Pilling–Bedworth Ratio (PBR)......Page 91 2.6.3. Kinetics of Formation......Page 95 2.6.4. Corrosion Behaviors of Some Alloys at Elevated Temperatures......Page 97 References......Page 101 Overview......Page 103 3.1.1. Construction of Pourbaix Diagrams......Page 104 3.1.2. Predictions of E–pH Diagrams......Page 106 3.1.3. Utility and Limits of Pourbaix Diagrams......Page 108 3.2.2. Overpotentials......Page 109 3.3.1. The Phenomenon of Passivation......Page 119 3.3.2. Passive Layers and Their Formation......Page 122 3.3.3. Breakdown of Passivity......Page 125 3.3.4. Electrochemical and Physical Techniques for Passive Film Studies......Page 126 3.4.1. The E–pH Diagram of Aluminum......Page 127 3.4.2. Active and Passive Behaviors......Page 130 3.4.3. Pitting Corrosion of Aluminum Alloy 5086......Page 133 3.5.1. E–pH Diagram of Magnesium......Page 135 3.5.2. Passive Mg Layers (Films)......Page 138 3.5.3. Passive Properties and Stability......Page 139 3.5.4. Temperature Influence in Aqueous Media......Page 141 3.5.5. Atmospheric and High-Temperature Oxidation......Page 142 References......Page 143 Part Two Performance and Corrosion Forms of Aluminum and Its Alloys......Page 146 Overview......Page 148 4.1. Physical and General Properties of Aluminum......Page 149 4.2. Cast Aluminum Alloys......Page 150 4.2.1. Designation of Cast Aluminum Alloys and Ingots......Page 151 4.2.2. Alloying Elements......Page 153 4.2.3. Cast Alloys Series......Page 154 4.3.1. Designation of Wrought Aluminum Alloys......Page 155 4.3.2. Alloying Elements......Page 156 4.3.3. Wrought Aluminum Alloys Series......Page 158 4.3.4. Description of the Wrought Alloys Series......Page 161 4.4.1. Aluminum Powders......Page 165 4.4.3. Aluminum Matrix Composites and P/M- MMCs......Page 167 4.4.4. Al MMC Particles and Formation......Page 172 B. Use of Aluminum and Aluminum Alloys......Page 176 4.5.1. Standard General Purpose Aluminum Alloys......Page 177 4.5.2. Some Specific Uses......Page 178 4.6.2. Automotive Sheet and Structural Alloys......Page 179 4.6.6. Electrical Conductor Alloys......Page 181 4.7. Resistance of Aluminum Alloys to Atmospheric Corrosion......Page 182 4.8. Factors Affecting Atmospheric Corrosion of Aluminum Alloys......Page 183 4.9. Water Corrosion......Page 185 4.10. Seawater......Page 186 4.12. Some Aggressive Media: Acid and Alkaline Solutions......Page 187 4.12.1. Acids......Page 189 4.12.2. Alkalis......Page 191 4.13. Dry and Aqueous Organic Compounds......Page 192 4.15. Mercury......Page 193 4.16.1. Performance of the Cast Series......Page 194 4.16.2. Performance of the Wrought Series......Page 196 4.17. Aluminum High-Temperature Corrosion......Page 197 References......Page 198 Overview......Page 201 5.2. Description......Page 202 5.4.2. Surface Pretreatment......Page 204 5.4.4. Aluminum Alloys and Resistance to General Corrosion......Page 205 5.6. Galvanic Series of Aluminum Alloys......Page 206 5.7.1. Cu–Al Galvanic Cell......Page 210 5.7.3. Galvanic Effect of a Coating......Page 211 5.8. Deposition Corrosion......Page 212 5.10. Prevention......Page 213 5.11. Basic Study of Al–Cu Galvanic Corrosion Cell......Page 214 C. Localized Corrosion......Page 215 5.12.2. Kinetics......Page 216 5.12.3. The Pitting Potential......Page 218 5.12.4. Mechanisms......Page 219 5.12.5. Possible Stages of Pitting......Page 220 5.12.6. Prevention of Pitting Corrosion......Page 226 5.12.7. Corrosion Resistance of Aluminum Cathodes......Page 227 5.13.1. General Considerations and Description......Page 228 5.13.2. Poultice Corrosion......Page 230 5.13.4. Water Stains on AA3xxx......Page 231 5.14.1. General Considerations......Page 233 5.14.2. Aluminum Alloys and Filiform Corrosion......Page 234 5.14.3. Kinetics, Mechanism, and Prevention......Page 235 5.14.4. Filiform Occurrence......Page 236 References......Page 237 Overview......Page 240 6.1. Fundamentals of METIC......Page 241 6.1.1. Influence of Metallurgical and Mechanical Treatments......Page 242 6.2.2. Intergranular Corrosion......Page 243 6.2.3. Exfoliation......Page 249 6.3.1. Corrosion Resistance of Brazed, Soldered, and Bonded Joints......Page 256 6.3.2. Welding Fundamentals......Page 258 6.3.3. Welding Influence on Behavior of Aluminum Alloys......Page 261 6.3.4. Frequent Corrosion Types of Welded Aluminum Alloys......Page 264 6.3.5. Corrosion Resistance of Wrought and Cast Al Alloys......Page 266 6.4. Metal Matrix Composites for Nuclear Dry Waste Storage......Page 272 6.5.3. Algae (Eukaryotes)......Page 274 6.6.3. Soils......Page 275 6.7.1. Anaerobic Bacteria......Page 276 6.7.3. Co-action of Anaerobic and Aerobic Bacteria......Page 277 6.8.3. Cyanobacteria and Algae (Polluted Freshwater)......Page 279 6.8.5. SRB (Industrial and Seawater)......Page 280 6.9.1. Corrosion Mechanisms......Page 281 6.9.3. Corrosion Inhibition by Microorganisms......Page 283 6.10. MIC Prevention and Control......Page 284 References......Page 285 Overview......Page 288 7.1. Impingement with Liquid-Containing Solid Particles......Page 289 7.2. Corrosion by Cavitation......Page 293 7.3. Water Drop Impingement Corrosion......Page 294 7.5. Fretting Fatigue Corrosion......Page 296 7.7. General Considerations and Morphology......Page 297 7.8.1. Environmental Considerations......Page 298 7.8.2. Cyclic Stresses......Page 299 7.9. Mechanisms of Corrosion Fatigue......Page 302 7.10. Corrosion Fatigue of Aluminum Alloys......Page 303 7.10.1. Corrosion Fatigue of AA7017-T651......Page 304 7.10.3. Corrosion Fatigue of Al–Mg–Si Compared to Al–Mg Alloys......Page 306 7.10.4. Modeling of the Propagation of Fatigue Cracks in Aluminum Alloys......Page 310 7.11. Prevention of Corrosion Fatigue......Page 312 References......Page 313 8.1. Introduction and Definition of SCC......Page 314 8.2.1. Stress......Page 316 8.2.2. Environment......Page 317 8.3.1. Influence of Stress......Page 319 8.3.2. Role of Environment......Page 320 8.4.1. Overlapping of Cracking Phenomena......Page 322 8.4.2. Significance of the Magnitude of Strain Rates......Page 324 8.4.3. Cracking Initiation and Propagation......Page 325 8.5. SCC of Aluminum Alloys......Page 326 8.5.1. SCC Resistance of Aluminum Alloys......Page 327 8.5.2. Influence of Heat Treatments on Corrosion Forms......Page 329 8.6.1. Galvanic Corrosion and SCC of Welded Assemblies......Page 331 8.6.2. SCC Knife-Line Attack......Page 332 8.6.3. Localized Corrosion and SCC of LBW AA6013......Page 333 8.6.5. Corrosion Fatigue of Friction Stir Welding White Zone......Page 335 8.6.6. SCC of Friction Stir Welded 7075 and 6056 Alloys......Page 336 8.6.7. SCC of FSW of 7075-T651 and 7050-T451 Alloys......Page 337 8.7.2. Environmental Considerations......Page 338 8.7.3. Metallurgical Considerations......Page 339 8.7.4. Surface Modification......Page 340 References......Page 341 Part Three Performance and Corrosion Forms of Magnesium and Its Alloys......Page 344 Overview......Page 346 9.1. Physical and General Properties of Magnesium......Page 347 9.2.1. Designation of Cast Magnesium Alloys......Page 348 9.2.2. Alloying Elements......Page 349 9.2.3. Cast Magnesium Alloys Series......Page 350 9.3. Properties of Wrought Magnesium Alloys......Page 353 9.5. Magnesium Composites......Page 358 9.6.2. Mg(2)Si......Page 359 9.7. Applications of Cast Magnesium Alloys......Page 360 9.7.2. Application as Refractory Material......Page 361 9.8. Applications of Wrought Magnesium Alloys......Page 362 9.9. Resistance of Magnesium Alloys to Atmospheric Corrosion......Page 363 9.11. Water Corrosion......Page 365 9.12. Salt Solutions......Page 366 9.15. Dry Organic Compounds......Page 368 9.17. Magnesium High-Temperature Corrosion......Page 369 References......Page 371 A. General Corrosion......Page 373 10.1.1. E(corr) and Corrosion Rates in Natural and Aqueous Media......Page 374 10.1.2. Corrosion Rate Methods of Mg–Al Alloys......Page 376 10.1.3. Critical Evaluation of the Passive Properties of Magnesium Alloys......Page 377 10.2. The Negative Difference Effect (NDE)......Page 378 10.3.1. Electrochemical Noise Studies......Page 383 10.4. Corrosion Prevention......Page 386 B. Galvanic Corrosion......Page 387 10.5. Hydrogen Overpotentials......Page 388 10.6. Galvanic Corrosion of Pure and Alloyed Magnesium......Page 389 10.6.1. Cathodic Corrosion of Aluminum......Page 390 10.7. Composite Coat for Molten Magnesium......Page 391 10.9. Prevention of Galvanic Corrosion......Page 392 10.9.1. Joining Magnesium to Dissimilar Metal Assemblies......Page 393 10.10. Pitting Corrosion......Page 394 10.10.1. The Pitting Potential Determination......Page 395 10.10.2. Polarization Curves and Pitting Potential of AXJ Alloy......Page 397 10.11. Crevice Corrosion......Page 399 10.12.1. Initiation and Kinetics Parameters......Page 400 10.12.2. Mechanism of Propagation......Page 401 References......Page 402 Overview......Page 405 11.1.1. Casting Alloys......Page 406 11.1.3. Alloying Elements and Tolerance Limit......Page 407 11.2.1. Galvanic Corrosion and Secondary Phases......Page 413 11.2.2. Intergranular Corrosion......Page 416 11.2.3. Exfoliation Corrosion......Page 417 11.2.5. Microstructure and Corrosion Creep of Magnesium Die-Cast Alloys......Page 418 11.2.6. The OCP, i(corr), and Corrosion Creep......Page 420 11.2.7. Corrosion Creep and Aging......Page 421 11.3.1. Influence of Heat Treatments......Page 422 11.3.2. Effect of Rapid Solidification......Page 424 11.3.3. Influence of the Microstructure of Some Mg Alloys......Page 426 11.3.4. Influence of Joining and Welding......Page 433 11.3.5. Cold Chamber Processes......Page 436 11.3.6. Hot Chamber Processes and Corrosion Resistance of Thin Plates......Page 443 B. MIC of Magnesium and Magnesium Alloys......Page 446 11.4.1. Behavior of Sacrificial Magnesium......Page 447 11.4.2. Rational Biocorrosion of Mg and Its Alloys in the Human Body......Page 448 11.6.1. Alloying......Page 449 11.6.3. Magnesium Implants and Bone Surgery......Page 451 References......Page 454 12.1.1. Erosion Corrosion......Page 458 12.2. Corrosion Fatigue of Magnesium Alloys......Page 460 12.2.1. Corrosion Fatigue of Cast Magnesium Alloys......Page 461 12.2.3. Crack Propagation of Wrought Extruded Alloys......Page 465 12.2.4. Welding and Corrosion Fatigue of AZ31......Page 471 12.2.5. Mechanisms of Corrosion Fatigue: Initiation and Propagation......Page 473 12.2.6. Prevention of Corrosion Fatigue......Page 474 References......Page 475 13.1. Use of Magnesium Alloys and Stress-Corrosion Cracking Failures......Page 477 13.2.1. Alloy Composition and Magnesium Impurities......Page 478 13.2.2. Microstructure and Crack Morphology......Page 479 13.2.4. Effect of the Environment......Page 481 13.3.3. Pitting and Localized Corrosion......Page 484 13.3.4. Welded Material and SCC......Page 485 13.3.5. Environment-Enhanced Creep and SCC of Mg Alloys......Page 486 13.4.1. Electrochemical Dissolution Models......Page 488 13.4.2. Hydrogen Embrittlement......Page 489 13.5. SCC–HE of Some Magnesium Alloys......Page 492 References......Page 498 Part Four Coating and Testing......Page 502 Overview......Page 504 14.2. Metallic Coatings......Page 506 14.2.2. Surface Preparation for Thermal Spraying......Page 507 14.2.3. Sacrificial Protection by Aluminum Alloys......Page 508 14.2.5. Cathodic Protection of Aluminum Alloys......Page 510 14.3. Conversion Coating......Page 511 14.3.1. Phosphates and/or Chromates......Page 512 14.3.2. Chromate–Phosphate Treatments......Page 515 14.3.3. Chromate Alternatives......Page 516 14.4. Anodization......Page 521 14.5.2. Converted Coating During or After Application......Page 528 14.5.3. Coatings Containing Metals More Active than Aluminum......Page 530 14.5.4. Electrodeposited Coatings......Page 531 14.6.1. Electrochemical Testing of Coatings......Page 532 14.6.3. Corrosion Fatigue of Thermal Spraying of Aluminum as a Coating......Page 533 References......Page 534 15.1. General Approach and Surface Preparation......Page 537 15.2.1. Metallic Coatings......Page 539 15.2.2. Chemical Conversion Surface Treatments......Page 541 15.3.1. Anodizing Description and Approaches......Page 546 15.3.2. Formation of Anodized Coatings......Page 548 15.3.4. Some Industrial and Developing Anodizing Processes......Page 551 15.3.5. Forms of Surface Corrosion: Anodized or with Conversion Treatments......Page 558 15.4.1. Chemical and Physical Vapor Deposition......Page 564 15.4.2. The H-Coat and Magnesium Hydrides......Page 566 15.5.1. OCP and Polarization Studies of the Metal–Oxide Interface......Page 574 15.5.2. Impedance Measurements......Page 575 15.6.1. Organic Coatings......Page 579 15.6.2. Conventional Corrosion Testing of Coated Metal......Page 581 References......Page 586 Part Five Evaluation and Testing......Page 590 Overview......Page 592 16.1.2. Categories of Corrosion Testing......Page 593 16.1.3. Testing Duration......Page 594 16.1.5. Removal of Corrosion Products......Page 595 16.2.1. Visual and Microscopic Techniques of Testing......Page 596 16.2.2. Nondestructive Evaluation Techniques......Page 598 16.2.4. Chemical Analysis......Page 600 16.2.6. Published Data of Performance and Corrosion Resistance......Page 602 16.3. Electrochemical Polarization Studies......Page 604 16.3.2. Potentiodynamic Methods......Page 605 16.3.4. Potentiostatic, Galvanostatic, and Galvanodynamic Methods......Page 608 16.4.1. Introduction......Page 609 16.4.2. EIS Terms and Equivalent Circuits......Page 610 16.4.3. Impedance Plots......Page 614 16.5.1. Historical and Electrochemical Noise Definition......Page 619 16.5.2. EN Generation and Data Acquisition Systems......Page 621 16.5.3. Analysis of ENM Data......Page 625 16.5.4. Potentiodynamic, Potentiostatic, and Galvanostatic EN Studies......Page 637 16.6. Scanning Reference Electrode Technique......Page 638 16.7.1. Microsystems and Atomic Force Microscopy......Page 641 16.7.2. Wire Beam Electrode......Page 642 References......Page 643 Overview......Page 646 17.1. General Corrosion of Aluminum and Its Alloys......Page 649 17.2.1. General Considerations......Page 650 17.2.3. Electrochemical Testing......Page 652 17.3.1. Pitting Corrosion......Page 653 17.3.2. Crevice Corrosion......Page 665 17.4.1. Intergranular Corrosion Testing......Page 666 17.4.2. Exfoliation Testing......Page 667 17.5. MIC and Biodegradation Evaluation......Page 668 17.6.1. Erosion Corrosion Testing......Page 671 17.6.2. Corrosion Fatigue Testing......Page 672 17.7. Environmentally Influenced Corrosion......Page 675 17.7.1. SCC Testing Procedures of Aluminum Alloys......Page 676 17.7.2. Test Specimens......Page 678 17.7.3. Stressors......Page 679 17.7.4. Fracture Morphology and SCC of Aluminum Alloys......Page 682 References......Page 684 Overview......Page 688 18.1.1. Hydroxide Solutions......Page 689 18.1.4. Buffered Solutions......Page 690 18.2.1. Immersion Testing and Corrosion Rate......Page 691 18.2.2. Salt Spray Corrosion Test......Page 694 18.2.3. Some Electrochemical Methods of Investigation......Page 696 18.3. Galvanic or Bimetallic Corrosion of Magnesium and Its Alloys......Page 702 18.4.1. Open Circuit Potential and Pitting Corrosion Studies......Page 703 18.4.2. Electrochemical Noise Measurements......Page 705 18.4.3. Magnesium SRET Studies......Page 709 18.6. MIC and Biodegradation of Magnesium and Its Alloys......Page 713 18.7. Corrosion Fatigue......Page 714 18.8.1. Static Loading of Smooth Specimens and General Considerations......Page 715 18.8.3. Solutions and Operational Conditions......Page 716 18.8.4. Constant Extension Rate and Linearly Increasing Stress Tests......Page 718 18.8.5. SCC CERT Versus LIST Techniques......Page 720 References......Page 721 Part Six Bibliography, International Units, and Abbreviations......Page 724 A1.2. Bibliography of Corrosion Data for Performance of Materials......Page 726 A1.3. ASTM Standards......Page 727 A2.1.1. Constants......Page 728 A2.1.3. Key Equations......Page 729 A2.3. Electrochemical Cells and Their Potentials......Page 731 A2.4. Standard Electrode Potential of Cations (T=25 °C)......Page 732 A2.5. The Periodic Table......Page 733 Appendix 3. Abbreviations and Symbols......Page 734 Index......Page 738

Valuable information on corrosion fundamentals and applications of aluminum and magnesium

Aluminum and magnesium alloys are receiving increased attention due to their light weight, abundance, and resistance to corrosion. In particular, when used in automobile manufacturing, these alloys promise reduced car weights, lower fuel consumption, and resulting environmental benefits.

Meeting the need for a single source on this subject, Corrosion Resistance of Aluminum and Magnesium Alloys gives scientists, engineers, and students a one-stop reference for understanding both the corrosion fundamentals and applications relevant to these important light metals. Written by a world leader in the field, the text considers corrosion phenomena for the two metals in a systematic and parallel fashion. The coverage includes:

• The essentials of corrosion for aqueous, high temperature corrosion, and active-passive behavior of aluminum and magnesium alloys


• The performance and corrosion forms of aluminum alloys


• The performance and corrosion forms of magnesium alloys


• Corrosion prevention methods such as coatings for aluminum and magnesium


• Electrochemical methods of corrosion investigation and their application to aluminum and magnesium alloys

Offering case studies and detailed references, Corrosion Resistance of Aluminum and Magnesium Alloys provides an essential, up-to-date resource for graduate-level study, as well as a working reference for professionals using aluminum, magnesium, and their alloys.