Michigan Technological University Digital Commons @ Michigan Tech Dissertations, Master's Theses and Master's Reports 2016 Thermomechanical Processing of Aluminum Micro-alloyed with Sc, Zr, Ti, B, and C Cameron McNamara Michigan Technological University, [email protected] Copyright 2016 Cameron McNamara Recommended Citation McNamara, Cameron, "Thermomechanical Processing of Aluminum Micro-alloyed with Sc, Zr, Ti, B, and C", Open Access Dissertation, Michigan Technological University, 2016. http://digitalcommons.mtu.edu/etdr/240 Follow this and additional works at:http://digitalcommons.mtu.edu/etdr Part of theMetallurgy Commons THERMOMECHANICAL PROCESSING OF ALUMINUM MICRO-ALLOYED WITH Sc, Zr, Ti, B, AND C By Cameron T McNamara A DISSERTATION Submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY In Materials Science and Engineering MICHIGAN TECHNOLOGICAL UNIVERSITY 2016 ©2016 CT McNamara This dissertation has been approved in partial fulfillment of the requirements for the Degree of DOCTOR OF PHILOSOPHY in Materials Science and Engineering. Department of Materials Science and Engineering Dissertation Advisor: Professor Stephen Kampe Committee Member: Assoc. Professor Doug Swenson Committee Member: Assoc. Professor Paul Sanders Committee Member: Asst. Professor Scott Wagner Department Chair: Professor Stephen Kampe To Ms. Bailey K. Ross and our daughter Sawyer Sofia Table of Contents Preface………………………………….……………………………………….…………………………...…………………………ix Acknowledgments.…………………….…………………………………………………………………………….…………..xi Abstract…………………………………………………………………………..……………………………………….…………..xiii Introduction: The Case for HSLA-Al ………………………………………………………….......………………..…1 Chapter I: Precipitation Strengthening of Dilute Al-TM alloys………….……………..………..…….3 1 Introduction...............................................................................................................................3 1.1 Diffusion and Characteristics of Trialuminides………………………………………….……..…....3 1.2 Strengthening Mechanisms……………………………………………………………………………………5 1.2.1 Precipitation, Dislocation, and Solute Strengthening…………………………….6 1.3 Existing Alloys…………………………………………………………………………………….………………..10 1.4 HSLA-Al Alloys sans Scandium………………………………………………………………………………10 1.5 Scope of the Current Study..………….…………………………………………………………………….11 2 Methods...................................................................................................................................12 2.1 Casting…………………………………………………………………………………………………………………12 2.2 Thermomechanical Processing…………………………………………………………………………….14 2.3 Macroscale Imaging and Compositional Analysis…………………………………………………16 2.4 Microhardness, Conductivity, and Tensile Testing……..………………………………………..16 2.5 Electron Microscopy………………………………..……………………………...………………………….17 3 Results…………………………………………………………………………………………………………………………………17 3.1 Cooling Rates and Compositions………………………………………………………………………….17 3.2 As-cast Grain Structures and Porosity……………………..…………………………………………..19 3.3 Multi-step and Two-step Isothermal Aging Curves……………………..……………………….20 3.4 Comparison of Peak Microhardness for Al-Sc-Zr and Al-Zr Alloys………………...………25 3.5 Tensile Stress-Strain Curves for Al-Sc-Zr and Al-Mg-Sc-Zr………..…………………………..27 3.6 Post-mortem TEM Imaging of Nanoscale Precipitates and SEM Fractography……..29 4 Discussion……………………………………………………………………………………………………………………………30 4.1 Quality of Castings……………………………………………………………………………………………….30 4.1.1 Grain Refinement…………………………………………………………………………………31 4.2 Hardness Increases from Mg, Ti, Ti-B, and Ti-C Additions…………………………………….32 4.3 Increase of Hardness and Yield Strength and Hardness through Precipitation....…34 4.3.1 Effect of Mg, Ti, Ti-B, and Ti-C on Aging………………………………………………..38 4.3.2 Effect of Cold Work on Aging………………………………………………………………..38 4.4 Challenges………………………………………………………………………………..………………………...41 5 Conclusions………………………………………………………………………………………………………………………….44 Chapter II: Recrystallization Resistance in Grain Refined Dilute Al-Zr Alloys…………………47 1 Introduction…………………………………………………………………………………………………………………………47 1.1 Use of Zr in Combination with Al-Ti-B, Al-Ti-C………..…………………………………….………47 1.2 Recrystallization Resistance…………………………………………………………………………………49 1.2.1 Optimizing the Precipitate Distribution………………………………………………..49 1.2.2 Mechanisms of Recrystallization……………………..…………………………………..51 vii 1.2.3 Particle Stimulated Nucleation………………..…………………………………………..52 1.2.4 Predicting Recrystallized Grain Size during Static Annealing…………………53 1.3 Mitigation of Dendritic Segregation……………………………………………………………………..55 1.4 Scope of this Contribution……………………………………………………………………………………56 2 Methods……………………………………………………………………………………………………………….……………..57 2.1 Casting………………………………………………………..………..…………………………………………....57 2.2 Thermomechanical Processing………………….….……………………………………………………..58 2.3 Optical and Electron Microscopy………………..…...……………………………………………….…59 3 Results.…………………………………………………………………………………………………………….………………….60 3.1 Alloying Levels……………………………………………………………………………………………………60 3.2 Optical and Electron Microscopy……………………………….……………………………………….61 3.2.1 As-cast Microstructures…………………………………………………………………..…61 3.2.2 Thermomechanically Processed Microstructures……………………………....65 4 Discussion…………………………………………………………………………………………………………………………...71 4.1 Grain Size Determination and As-cast Observations…………………………………………….71 4.2 Changes in Hardness and Conductivity during TMP…………………………….……………….75 4.3 Low- and High-Angle Grain Boundaries…………………….………………………………………….77 4.4 Theoretical vs. Observed Recrystallized Grain Size……………………………………………….81 4.5 Other Factors and Limitations………………………………………………………………………………82 5 Conclusions………………………………………………………………………………………………………………………….83 List of References………………………………………………………………………………………………….…………….85 Appendix I: Metallographic Preparation…………………………………………………………………………..91 Appendix II: Multi-step Aging Conductivity Curves………………………………………………………….93 Appendix III: Casting X-Ray Images…………………………………………………………..……………………….95 Appendix IV: All Available Raw Material Certification Sheets..……………..……………………….99 viii Preface This dissertation is written in two chapters, each intended to be published in part or wholly as journal articles. In terms of contributions to this work, Professor Steve Kampe clarified the discussion of strengthening mechanisms in Sections 1.2 and 4.3 and provided valuable feedback during the entire data collection and writing process. Many useful recommendations for additional analysis were also given by Assoc. Prof. Paul Sanders, Assoc. Prof. Doug Swenson, and Asst. Prof. Scott Wagner throughout. Brian Milligan, an undergraduate research assistant, collected the second series of isothermal aging data presented in Figure 12. Owen Mills, Director of the Applied Chemical and Morphological Analysis Laboratory (ACMAL), provided training and expertise in SEM and TEM data collection. A great friend, colleague, and talented microscopist, Jerome Cornu, enabled quality electron backscattered diffraction data collection for Chapter II, and Dr. Thomas Dorin assisted with the analysis thereof; both of these researchers reside at the Institute for Frontier Materials at Deakin University in Victoria, Australia. All other data was collected and analyzed by the author. Both chapters were written in toto by the author, other than the aforementioned edits. ix