FRICTION STIR WELDING OF 5083-H131 ALUMINUM ALLOY USING A2 AND H13 TOOL STEELS OR 420 STAINLESS STEEL TOOLING by Justin Michael Evans A thesis submitted to the Graduate Faculty of Auburn University in partial fulfillment of the requirements for the Degree of Master of Science Auburn, Alabama December 13, 2014 Copyright 2014 by Justin Evans Approved by Lewis N. Payton, Associate Research Professor, Mechanical Engineering Robert E. Thomas, Professor Emeritus, Industrial and Systems Engineering Robert L. Jackson, Associate Professor, Mechanical Engineering Abstract Friction Stir Welding (FSW) is a solid state welding method developed by The Welding Institute. The process is environmentally friendly, highly repetitive and easily adapted to manufacturing geometries. New welding schedules are being continuously developed for materials that are traditionally difficult to join by fusion welding methods (e.g. TIG/MIG/Stick). This experiment develops the welding schedule and process parameters for acceptable welds in 5083-H131 aluminum using three different tool materials (A2 and H13 tool steel along with 420 Stainless Steel). The mechanical properties of all friction stir welds were compared against standard MIG welds (from a qualified industrial facility) and the as-delivered parent material. All of the friction stir welds greatly outperformed the MIG welds. The welds produced by the H13 tool were statistically identical in bending to the original parent material. None of the friction stir welds performed more poorly than the MIG during ultimate tensile testing. The friction stir weld produced by the 420 SS tool was by far the best weld in terms of tensile strength. Equipment limitations (motor horsepower) may have prevented achieving a friction stir weld equal to or better than the parent material. All friction stir welds exhibited uniform hardness results across the weld that was much higher than the MIG welds hardness. None of the friction stir welds exhibited the porosity of the MIG welds when cross-sectioned. i i The FSW machine used was actually a CNC mill that lacked the horsepower to extend the test to higher RPM/Feeds. Technical guidelines were developed (as an Appendix) from the lessons learned for the university research technician attempting to develop a welding schedule with a three-axis CNC machine not intended for friction stir welding. iii Acknowledgments I would like to dedicate this thesis to my family and friends who have supported me throughout my college career. Foremost, I would like to thank my beautiful wife, Stephanie, for your unconditional love and support as I complete my Master’s. I cannot imagine my college years without you and look forward to many more years together. I want to thank my parents, Mike and Tana, for always being there for me and supporting me in all the decisions I have made in my life. To my little brother, Austin, I am happy to have experienced college with you and proud of you for your accomplishments in life. Next, I want to thank the many professionals outside the University (Brian Thompson, Don Hendry, Cale McGraw, Michael Peterson, Phillip Howell, and Kyle Williams) who provided services and technical support in completing my thesis research. Finally, I would like to thank Dr. Payton for giving me the opportunity to work in the Design and Manufacturing Laboratory (DML) and providing guidance to complete my graduate degree. I would also like to thank my colleagues, Vishnu Chandrasekaran, Chase Wortman, Wesley Hunko, Drew Sherer, Michael Carter, and Jordan Roberts for all your help completing this thesis. I most especially would like to thank Wesley Hunko for giving me a place to stay and helping me on long nights of research. iv Table of Contents ABSTRACT ........................................................................................................................ II ACKNOWLEDGMENTS ................................................................................................ IV TABLE OF CONTENTS ................................................................................................... V LIST OF TABLES ......................................................................................................... VIII LIST OF FIGURES .......................................................................................................... IX LIST OF ABBREVIATIONS AND SYMBOLS ............................................................. XI I. INTRODUCTION .......................................................................................................... 1 II. SCOPE AND OBJECTIVES ........................................................................................ 3 III. LITERATURE REVIEW ............................................................................................ 5 BASIC REVIEW OF THE FRICTION STIR WELDING PROCESS .......................... 5 TOOL GEOMETRY ....................................................................................................... 6 TOOL MATERIAL ........................................................................................................ 9 MICROSTRUCTURE AND MECHANICAL PROPERTIES .................................... 10 DEFECTS IN FRICTION STIR WELDING ............................................................... 12 PROCESS PARAMETERS .......................................................................................... 15 CONCLUSIONS OF THE LITERATURE REVIEW ................................................. 21 IV. MATERIALS AND EQUIPMENT ........................................................................... 22 v V. METHODOLOGY...................................................................................................... 30 TOOL SELECTION AND PREPARATION ............................................................... 30 WORKPIECE HOLDER .............................................................................................. 32 MATERIAL PREPARATION ..................................................................................... 32 WELDING PROGRAM SCHEDULES ....................................................................... 33 WELDING PARAMETER SELECTION .................................................................... 33 STATISTICAL COMPARISON .................................................................................. 35 MACROSCOPIC AND MICROSCOPIC EVALUATION ......................................... 35 HARDNESS TESTING ................................................................................................ 36 BEND TESTING .......................................................................................................... 37 TENSILE TESTING ..................................................................................................... 38 VI. RESULTS OF THE EXPERIMENT ......................................................................... 40 BEND TESTING .......................................................................................................... 40 TENSILE TESTING ..................................................................................................... 43 HARDNESS TESTING ................................................................................................ 46 VII. DISCUSSION .......................................................................................................... 48 BEND TESTS ............................................................................................................... 48 TENSILE TESTS.......................................................................................................... 49 HARDNESS TESTS ..................................................................................................... 50 PROCEDURAL WELD RESULTS ............................................................................. 51 VIII. CONCLUSIONS AND FUTURE WORK .............................................................. 54 IX. REFERENCES .......................................................................................................... 57 vi APPENDIX 1: WELD PROCEDURE ............................................................................. 60 APPENDIX 2: LESSONS LEARNED ............................................................................. 67 APPENDIX 3: BEND RESULTS DATA ........................................................................ 71 APPENDIX 4: TENSILE TEST RESULTS DATA ........................................................ 78 APPENDIX 5: HARDNESS TEST RESULTS DATA ................................................. 115 APPENDIX 6: VISUAL EXAMINATION RESULTS ................................................. 121 APPENDIX 7: PROCEDURAL WELD RESULTS ...................................................... 128 vi i List of Tables TABLE 1: WELDING PARAMETERS ............................................................................ 9 TABLE 2: TENSILE STRENGTH OF PARENT AND JOINT MATERIAL ................ 11 TABLE 3: SUMMERY OF THE MECHANICAL TESTING EXPERIMENTS ........... 12 TABLE 4: PROCESS PARAMETERS ............................................................................ 16 TABLE 5: BISADI TESTING RESULTS ....................................................................... 19 TABLE 6: PROCESS PARAMETER COMBINATIONS .............................................. 20 TABLE 7: PARENT MATERIAL COMPARISON ........................................................ 20 TABLE 8: FATIGUE LIFE .............................................................................................. 21 TABLE 9: MATERIALS USED IN EXPERIMENTS .................................................... 22 TABLE 10: OPTIMAL PROCESS PARAMETERS ....................................................... 35 TABLE 11: EXPERIMENTAL FACTORS ..................................................................... 35 TABLE 12: BEND TEST ANOVA .................................................................................. 41 TABLE 13: INDIVIDUAL BEND TEST COMPARISON ............................................. 42 TABLE 14: TENSILE TEST ANOVA ............................................................................ 44 TABLE 15: INDIVIDUAL TENSILE TESTING COMPARISON ................................. 45 TABLE 16: HARDNESS TESTS ANOVA ..................................................................... 47 TABLE 17: HARDNESS TESTING COMPARISON..................................................... 47 TABLE 18: BEND TESTING DATA .............................................................................. 49 TABLE 19: CUMULATIVE TENSILE TESTING DATA ............................................. 50 viii List of Figures FIGURE 1: FRICTION STIR WELDING PROCESS[1] .................................................. 2 FIGURE 2: SIDE VIEW OF THE TOOL[1] ..................................................................... 6 FIGURE 3: SKEW STIR TOOL ........................................................................................ 7 FIGURE 4: TOOL GEOMETRY: (A) SMOOTH PIN, (B) THREADED PIN, (C) TRIANGULAR PRISM.............................................................................................. 8 FIGURE 5: TOOL WEAR WITH CORRESPONDING LOCATIONS. (A) MMC FSW AT 500 RPM, (B) MMC FSW AT 1000 RPM, (C) COMMERCIAL 6061 FSW AT 1000 RPM ................................................................................................................. 10 FIGURE 6: FLOW-PARTITIONED DEFORMATION ZONE MODEL[7] .................. 13 FIGURE 7: MICROSTRUCTURE OF THE STIR ZONES ............................................ 16 FIGURE 8: SURFACE NOTCHES (ONION RINGS) ASSOCIATION WITH CRACK INITIATION ............................................................................................................. 17 FIGURE 9: HARDNESS OF STIR ZONE IN 5083-O .................................................... 18 FIGURE 10: GRAIN SIZE OF STIR ZONE IN 5083-O FSW’S .................................... 18 FIGURE 11: CINCINNATI CNC VERTICAL MILLING MACHINE .......................... 23 FIGURE 12: SOUTHBEND LATHE ............................................................................... 23 FIGURE 13: FRICTION STIR TOOLING ...................................................................... 24 FIGURE 14: CAT-40 ¾” SHANK TOOL HOLDER WITH PIN TOOL ........................ 24 FIGURE 15: BRIDGEPORT VERTICAL MILLING MACHINE.................................. 25 ix FIGURE 16: WORKPIECE HOLDER ............................................................................ 25 FIGURE 17: WILTON BELT SANDER ......................................................................... 26 FIGURE 18: TINIUS OLSEN 1000 ................................................................................. 26 FIGURE 19: INSTRON 5569 TENSILE TESTER .......................................................... 27 FIGURE 20: KEYENCE MICROSCOPE ........................................................................ 28 FIGURE 21: AVEN MIGHTY SCOPE ........................................................................... 28 FIGURE 22: NEWAGE INDENTRON ROCKWELL B HARDNESS TESTER ........... 29 FIGURE 23: MTM SCALE .............................................................................................. 29 FIGURE 24: FRICTION STIR TOOL GEOMETRY ...................................................... 31 FIGURE 25: PIN AND SHOULDER DETAIL ............................................................... 31 FIGURE 26: WORKPIECE HOLDER DETAIL ............................................................. 32 FIGURE 27: PROCESS PARAMETER SELECTION USING A2 TOOLS ................... 34 FIGURE 28: BEND TESTS FOR KISSING BONDS ..................................................... 34 FIGURE 29: VISUAL EXAMINATION OF FINAL WELDS ....................................... 36 FIGURE 30: HARDNESS TESTING LOCATIONS....................................................... 37 FIGURE 31: BEND SAMPLE ......................................................................................... 38 FIGURE 32: BEND TESTING CONFIGURATION....................................................... 38 FIGURE 33: TENSILE TEST SPECIMENS ................................................................... 39 FIGURE 34: MEAN BEND RESULTS ........................................................................... 41 FIGURE 35: MEAN TENSILE RESULTS ...................................................................... 43 FIGURE 36: MEAN HARDNESS RESULTS ................................................................. 46 FIGURE 37: SPEED SELECTION SAMPLE 3 .............................................................. 52 x