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Abstract a Comparative Study of 2024-T3 and 7075-T6 ABSTRACT A COMPARATIVE STUDY OF 2024-T3 AND 7075-T6 ALUMINUM ALLOYS FRICTION STIR WELDED WITH BOBBIN AND CONVENTIONAL TOOLS by Paul Aaron Goetze Aluminum alloys 2024-T3 and 7075-T6 were joined by friction stir welding using bobbin and conventional tools types. The effectiveness of placing each alloy on the advancing and retreating side within the bobbin and conventional tool configurations was investigated, and comparisons were made between the welds of the two tool types. Microstructural imaging, micro-hardness mapping, tensile testing, and computational modeling were used to evaluate the weld quality of each tool and material configuration. Temperature data and simulation profiles indicated that the temperature distribution from both tools favored the advancing side with the bobbin tool reaching higher temperatures than the conventional tool. Higher mechanical properties were reported for conventional tool welds than those performed with the bobbin tool, and material placement affected the weld performance in the conventional tool configurations. All tensile specimens fractured on the 2024 side of the weld and specimens joined with the conventional tool were more consistent than those with the bobbin tool. Differential scanning calorimetry identified the precipitation behavior of the alloys which correlated well to the mechanical properties of the welds. Optical microscopy and EBSD analysis highlighted advanced stirring patterns through the weld thickness. Identical equiaxed grain structures observed in the stir zone of both alloys suggested complete recrystallization. A COMPARATIVE STUDY OF 2024-T3 AND 7075-T6 ALUMINUM ALLOYS FRICTION STIR WELDED WITH BOBBIN AND CONVENTIONAL TOOLS A Thesis Submitted to the Faculty of Miami University in partial fulfillment of the requirements for the degree of Master of Science by Paul Aaron Goetze Miami University Oxford, Ohio 2019 Advisor: Dr. Carter Hamilton Reader: Dr. Giancarlo Corti Reader: Dr. Fazeel Khan ©2019 Paul Aaron Goetze This Thesis titled A COMPARATIVE STUDY OF 2024-T3 AND 7075-T6 ALUMINUM ALLOYS FRICTION STIR WELDED WITH BOBBIN AND CONVENTIONAL TOOLS by Paul Aaron Goetze has been approved for publication by The College of Engineering and Computing and Department of Mechanical and Manufacturing Engineering ____________________________________________________ Dr. Carter Hamilton ______________________________________________________ Dr. Giancarlo Corti _______________________________________________________ Dr. Fazeel Khan Table of Contents 1. INTRODUCTION ..................................................................................................................... 1 2. LITERATURE SURVEY ......................................................................................................... 3 2.1 INFLUENCE OF TOOL GEOMETRY ............................................................................................ 3 2.1.1 Conventional Tooling Geometries ................................................................................ 3 2.1.2 Bobbin Tooling Geometries .......................................................................................... 4 2.2 INFLUENCE OF PROCESSING TEMPERATURE ............................................................................ 4 2.2.1 Precipitation Behavior of 2024 ..................................................................................... 5 2.2.2 Precipitation Behavior of 7075 ..................................................................................... 5 2.2.3 Heat Input, Process Temperature and Material Flow .................................................... 5 2.3 WELD CHARACTERIZATION ..................................................................................................... 8 2.3.1 Microscopy Methods ..................................................................................................... 8 2.3.2 Mechanical Methods ..................................................................................................... 9 3. EXPERIMENTAL PROCEDURE .........................................................................................12 4. COMPUTATIONAL MODELING APPROACH .................................................................14 4.1 GEOMETRY, MESHING, GENERAL PHYSICS, AND BOUNDARY CONDITIONS ............................14 4.1.1 Boundary Conditions for Heat Transfer .......................................................................16 4.1.2 Boundary Conditions for the Flow Capable Region ....................................................17 4.2 MATERIAL PROPERTIES ..........................................................................................................18 4.3 MODEL VERIFICATION ...........................................................................................................19 5. RESULTS AND DISCUSSION ...............................................................................................22 5.1 OPTICAL MICROSCOPY ...........................................................................................................22 5.2 ELECTRON BACKSCATTER DIFFRACTION ...............................................................................24 5.3 MICRO-HARDNESS DISTRIBUTIONS ........................................................................................24 5.4 TEMPERATURE ANALYSIS ......................................................................................................26 5.4.1 Base Material Calorimetry ...........................................................................................26 5.4.2 Simulation Results .......................................................................................................27 5.4.3 Time at Temperature Evaluation ..................................................................................34 5.5 TENSILE TESTING ...................................................................................................................36 6. CONCLUSIONS AND FUTURE WORK ..............................................................................38 7. APPENDICES ..........................................................................................................................40 7.1 APPENDIX A – TENSILE SPECIMEN PREPARATION ..................................................................40 7.2 APPENDIX B – FRACTURE TOUGHNESS SPECIMEN PREPARATION...........................................42 7.3 APPENDIX C – TEMPERATURE PROFILE EVALUATIONS OF WELDING CONFIGURATIONS ........46 7.3.1 AS-7075B Configuration .............................................................................................46 7.3.2 AS-2024B Configuration .............................................................................................46 7.3.3 AS-7075C Configuration .............................................................................................46 7.3.4 AS-2024C Configuration .............................................................................................47 7.4 APPENDIX D – SEM FRACTURE SURFACE MICROGRAPHS FOR ALL WELDING CONFIGURATIONS ......................................................................................................................................48 7.5 APPENDIX E – EXAMPLE WELDING ZONE DIAGRAM ......................................................................49 8. REFERENCES .........................................................................................................................51 iii List of Tables Table 1 Summary of experimental configurations and welding trial designations. ................................. 12 Table 2 Material constants used to calculate the dynamic viscosity of the material in the flow capable region of the simulation. ............................................................................................................... 19 Table 3 Tensile testing results for all material and tool configurations.................................................. 37 iv List of Figures Figure 1 Cross-section of FSW stir and surrounding zones. ...................................................................... 1 Figure 2 Representations of geometries for: a the conventional tool, b the bobbin tool. ........................ 3 Figure 3 Conventional tool simulation geometry and mesh. ................................................................. 15 Figure 4 Bobbin tool simulation geometry and mesh. ........................................................................... 15 Figure 5 The steady-state temperature comparison of conventional tool experiment and simulation. 19 Figure 6 Temperature as a function of distance away from the bobbin tool. A comparative plot between the simulation and experimental results. ....................................................................... 20 Figure 7 Optical Micrograph for, a the AS-2024B configuration and, b the AS-7075B configuration. ..... 22 Figure 8 Optical Micrographs for, a the AS-2024C configuration and, b the AS-7075C configuration ..... 23 Figure 9 Results of, a the SEM EBSD scan and, b the Mackenzie plot for the SZ in AS-7075C. ................ 24 Figure 10 Vickers Hardness Profiles for, a the AS-2024B configuration and, b the AS-7075B configuration. ............................................................................................................................... 25 Figure 11 Vickers Hardness Profiles for, a the AS-2024C configuration ad b the AS-7075C configuration. ....................................................................................................................................................
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