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Experimental Investigations on Friction Stir Welded Joint of Dissimilar Aluminium Alloys

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Experimental Investigations on Friction Stir Welded Joint of Dissimilar Aluminium Alloys EXPERIMENTAL INVESTIGATIONS ON FRICTION STIR WELDED JOINT OF DISSIMILAR ALUMINIUM ALLOYS Thesis Submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY by ANIL KUMAR K. S. DEPARTMENT OF MECHANICAL ENGINEERING NATIONAL INSTITUTE OF TECHNOLOGY KARNATAKA, SURATHKAL, MANGALORE – 575025 SEPTEMBER, 2019 D E C L A R A T I O N I hereby declare that the Research Thesis entitled “EXPERIMENTAL INVESTIGATIONS ON FRICTION STIR WELDED JOINT OF DISSIMILAR ALUMINIUM ALLOYS” which is being submitted to the National Institute of Technology Karnataka, Surathkal in partial fulfillment of the requirements for the award of the Degree of Doctor of Philosophy in Department of Mechanical Engineering is a bonafide report of the research work carried out by me. The material contained in this Research Thesis has not been submitted to any University or Institution for the award of any degree. Register Number : 145020ME14P01 Name of the Research Scholar : ANIL KUMAR K.S. Signature of the Research Scholar : Department of Mechanical Engineering Place : NITK, Surathkal Date : CERTIFICATE This is to certify that the Research Thesis entitled “EXPERIMENTAL INVESTIGATIONS ON FRICTION STIR WELDED JOINT OF DISSIMILAR ALUMINIUM ALLOYS” submitted by Mr. ANIL KUMAR K.S. (Register Number: 145020ME14P01) as the record of the research work carried out by him, is accepted as the Research Thesis submission in partial fulfillment of the requirements for the award of degree of Doctor of Philosophy. Research Guide(s) Prof. S.M. Murigendrappa Dr. Hemantha Kumar Professor Associate Professor Department of Mechanical Engineering Department of Mechanical Engineering NITK, Surathkal. NITK, Surathkal. Chairman-DRPC Date: Place: NITK, Surathkal. Date: ACKNOWLEDGEMENTS With a deep sense of gratitude, I wish to express my sincere thanks to my supervisors Prof. S.M. Murigendrappa and Dr. Hemantha Kumar, Department of Mechanical Engineering, National Institute of Technology Karnataka (NITK), Surathkal, for their excellent guidance and support throughout the work. I received very useful, encouraging and excellent academic feedback from them, which has stood in good stead while writing this thesis. Their constant encouragement, help and review of the entire work during the course of the investigation were invaluable. I profoundly thank them. I take this opportunity to acknowledge my thanks to Prof. Shrikantha S. Rao, Head of the Department of Mechanical Engineering and Chairman, DRPC for his continuous and timely suggestions. I express my heartfelt thanks to the Director, NITK, Surathkal. I wish to thank all the members of the Research Program Assessment Committee including Dr. Srikanth Bontha, Associate Professor, Department of Mechanical Engineering and Dr. Basavaraju Manu, Associate Professor, Department of Civil Engineering for their appreciation and criticism all through this research work. I gratefully acknowledge the help for providing the lab facilities and support received from Prof. Sathish V Kailas, Professor, Department of Mechanical Engineering, Indian Institute of Science (IISc.), Bangalore, Karnataka. I also acknowledge help rendered by Prof. Narayanaprabhu, Professor, Department of Metallurgical and Materials Engineering, NITK, Surathkal, Karnataka. I acknowledge the support from scanning electron microscopy (SEM) lab and experimental facility provided by A Centre of excellence at NITK, Surathkal. I wish to express my sincere gratitude to all the faculty members of the Department of Mechanical Engineering, NITK, Surathkal, for their help, encouragement and support all through this research work. My sincere thanks to my friends Dr. Madhusudana C. K., Dr. Gurubasavaraju T. M., Dr. Gangadhar, Dr. Hemanth K, Dr. Gopi K.R, Mr. Bala Narasimha G., Mr. Suman M.L.J., Mr. Vipin Allien J., Mr. Ravikumar K.N., and Mr. Subhash Acharya of Department of Mechanical Engineering, NITK Surathkal, for their help and support to carry out this dissertation work. I am grateful to my dearest friends Dr. Madhu H.C., Dr. Amlan kar, Dr. Anbukkarasi R., Mr. Rajaneesh H., and Mr. Himanshu Shekar of Department of Mechanical Engineering, IISc., Bangalore, for extending their support whenever I required. Finally, my sincere gratitude to my parents, wife and son who have trusted me throughout my life. I would like to share this moment of happiness with my mother Mrs. Jayasheela, my son Mr. Pranav. A., my wife Mrs. Rohini C., and her family, my sister Mrs. Araunashree K.S., my nephew Mr. Srujan Shaiva for their constant encouragement. I would like to dedicate my dissertation work to my father late Sri. K.P. Shivamurthy, without his dedication to provide me the best education and facilities throughout my carrier, I would not have reached this position in my life. The list goes on and there are many others I should mention. There are people who have helped me all the way and provided me support when I didn’t even realize I needed it, or needed it now, or needed it constantly. Listing all of them would fill a book itself, so I merely will have to limit myself to a few words: I THANK YOU ALL…………..! (Anil Kumar K.S.) ABSTRACT Friction stir welding (FSW) is solid-state joining process for producing similar or dissimilar joints of plates. Joining process carried out by means of a non-consumable rotating tool passed along the joining edges of plates, after developing sufficient amount of heat. The joints may prone to have defects such as pin-hole, cracks, tunnel defects, worm-hole defects, sharp boundary defects, etc. lead to influence the mechanical properties and microstructures. Main motivation of the present study is to produce defect-free joints and, improve the mechanical properties and microstructures of the friction stir welded dissimilar aluminium alloys joint. To achieve these, it is necessary to choose the optimum FSW parameters such as tool plunge depth, tool rotational speed, tool traverse speed, tool tilt angle, etc. The present study focuses on selection of an optimum FSW parameters using a bottom-up optimization experimental approach for joining dissimilar aluminium alloys. Further focuses on the combined effect of tool probe offset and the tool traverse speed on the properties of welded joint. Study also focuses on the fabrication of metal matrix nano composite (MMNC) at the weld nugget zone (WNZ) of the FSW dissimilar aluminium alloys joint. The bottom-up experimental approach has been successfully adopted for joining two dissimilar aluminium alloys of AA2024-T351 and AA7075-T651 in butt-joint configuration for optimizing the FSW parameters such as tool plunge depth (TPD), tool rotation speed (TRS) and tool travel speed (TTS). Optimized FSW parameters for taper threaded cylindrical tool are TPD, 6.20 mm, TRS, 650 rpm and TTS, 150 mm/min yields higher tensile properties such as ultimate tensile strength (UTS) of 435 MPa, yield strength (YS) of 290 MPa, percentage elongation (% EL) of 13, and maximum weld joint efficiency ( ) of 92% with defect-free microstructures of weld region. Similarly, for taper triangle tool the TPD, 6.20 mm, TRS, 950 rpm and TTS, 90 mm/min yields a higher UTS, 440 MPa, YS, 350 MPa, % EL, 17.5 and of 93% with enhanced microstructure characteristics at the weld region. The tool probe offset of 1 mm towards AA7075-T651 favours the flow characteristics of AA7075-T651 towards WNZ. In addition, increase in the TTS ranging from 20-120 mm/min has revealed higher tensile properties. Higher UTS of 435 MPa, YS of 375 MPa, % EL of 13.6 and of 92% obtained for tool probe offset of 1 mm towards AA7075-T651 and TTS of 110 mm/min with constant TPD of 6.20, and TRS of 650 rpm. For the fabrication of MMNC at the WNZ produced with varying % vol. fractions (5, 8 and 13) of SiCNP revealed a higher tensile properties of UTS of 418 MPa, YS of 247 MPa and % EL of 14.5 for 5% vol. fraction SiCNP with FSW second pass. The decrease in the grain size range 2-4 µm observed at the WNZ of the MMNC compared to the WNZ without SiCNP having grain size range 6-8 µm. The novelty of this work lies in the demonstration of friction stir welded joint of dissimilar aluminium alloys. Keywords: Friction stir welding; Bottom-up approach; Optimization technique; Dissimilar aluminium alloys; Composites; Nano silicon carbide particles; Microstructure; Mechanical properties; CONTENTS Declaration Certificate Acknowledgements Abstract Contents……………………………………………………………………….. i List of figures …………………………………………………………………. viii List of tables ………………………………………………………………….. xviii Abbreviations ……………………………………………………………….... xx Nomenclature ……………………………………………………………….... xxii 1. INTRODUCTION 1.1 Overview................................................................................................. 01 1.2 Aluminium alloys of 2000 and 7000 series.............................................. 03 1.3 Friction stir welding (FSW)...................................................................... 04 1.3.1 Terminologies used in the FSW.................................................... 06 1.3.1.1 FSW parameters and its significance.................................... 06 1.3.1.2 Tool geometry........................................................................ 08 1.3.1.3 Microstructure....................................................................... 08 1.3.2 Temperature distribution in the weld region................................ 10 1.3.3 Mechanical properties, microstructure evaluation of the FSW joints and its significance……………………………………….. 11 1.3.3.1 Tensile strength ...................................................................
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