NELSON MANDELA METROPOLITAN UNIVERSITY CHARACTERISATION OF DISSIMILAR FRICTION STIR WELDS BETWEEN 5754 ALUMINIUM ALLOY AND C11000 COPPER AKINLABI, Esther Titilayo i COPYRIGHT STATEMENT The copy of this thesis has been supplied on condition that anyone who consults it is understood to recognise that its copyright rests with the Nelson Mandela Metropolitan University, and that no information derived from it may be published without the author’s prior consent, unless correctly referenced. ii CHARACTERISATION OF DISSIMILAR FRICTION STIR WELDS BETWEEN 5754 ALUMINIUM ALLOY AND C11000 COPPER A thesis submitted in compliance with the full requirements for the degree of Doctor Technologiae: Engineering: Mechanical Akinlabi, Esther Titilayo Submitted to the Faculty of Engineering, The Built Environment and Information Technology Nelson Mandela Metropolitan University Port Elizabeth, South Africa December, 2010 Promoters Prof. Annelize Els-Botes Prof. Patrick McGrath iii AUTHOR’S DECLARATION I, Akinlabi Esther Titilayo hereby declare that: The work done in this thesis is my own; All sources used or referred to have been documented and recognized; and This thesis has not been previously submitted in full or partial fulfilment of the requirements for an equivalent qualification at any other educational institution. Author’s Signature Date: December, 2010 iv ACKNOWLEDGEMENT Unto the Lord be the glory, honour, and adoration for his infinite mercies and favour upon my life. Sincere gratitude and appreciation goes to my promoter, Prof Annelize Els-Botes, for her guidance and support throughout the period of study. I am grateful to Prof Andre Venter of the Physics Department for his assistance with the electrical resistance measurements; Dr Ernst Ferg of the Chemistry Department for his assistance with the X-Ray Diffraction analysis; Dr Petersen Jacques for the statistical analysis; and Mr G. C. Erasmus for his assistance in the Metallurgy lab. In addition, I would like to express my appreciation to Dr T. Hua and Mr L. Von Wielligh for operating the Friction Stir Welding platform; and to members of the staff of the Mechanical Engineering workshop for their ceaseless support in the use of equipment. Furthermore, the input of the Head Of Department and my Co-Promoter - Prof P. J. McGrath, Director of Automotive Components Technology Station (ACTS) Prof D. G. Hattingh, and members of staff. These people are all noted and appreciated. Special thanks must go to Dr H. Lombard for her input at the preliminary stages of the research work, and to Dr S. Krishnan for her technical advice. I would also like to thank my fellow researchers – the currently registered Masters’ and Doctoral students for their moral support. Special gratitude also goes to my parents, Chief Dare Olorunfemi (1945-2006), who was a source of inspiration to me in my academic career. You encouraged me to be an engineer like you, I miss you dad. To my mum – Mrs Felicia Olorunfemi and my parents-in-law - Mr and Mrs S.O. Akinlabi, I say a big “Thank you”, for your support and prayers. Also, my appreciation goes to my uncle Barr J. F. Olorunfemi, my siblings and their spouses, - Dr and Mrs Gbenga Olorunfemi, Mr and Mrs Peter Oloba and Mr and Mrs Abraham Ilugbuhi- for their moral support. As anticipated, my spiritual mentors Rev and Pastor Mrs Alfred Oladapo and Pastor and Mrs Kunle Oyeniyi of the Divine Grace Baptist Church Woji, Port Harcourt v Nigeria, and Pastors Vic and Lathicia Klackers of Church on the Way, Summerstrand. My humble thanks for your prayers and support. I remain grateful to family friends – Dr and Mrs K. A. Olowu, Dr and Mrs A. A. Ogungbire, Dr and Mrs Oluwatobi Oluwafemi, Mr and Mrs F. A. Emuze, Prof and Dr (Mrs) A. A. Olufayo, Dr and Mrs P. A. Olubambi, Dr and Mrs Kutu, Engr and Mrs E. I. Obieje, Mr and Mrs D. R. Pienaar, Mr and Mrs Toba Dada, Mr and Mrs A. O. Aiyetan, Mr and Mrs A. B. Taiwo, Mr and Mrs E.A Taiwo, Mr and Mrs O.F. Inegbedion, Mr and Mrs A. Adelakun, Mr and Mrs R.A. Jimoh, Oluwole Olufayo, Bukola Makinwa, Seun Oshoniyi, Kayode Oyedemi, and Manka Kariuki for supporting me whenever the need has arisen. I would like to thank the National Research Foundation (NRF) of South Africa, Research Capacity Development (RCD) unit and the Automotive Components Technology Station (ACTS) of NMMU for their financial support. Finally, and most importantly, to the most significant adviser, supporter, and financier in my life, my love and husband, Mr Stephen Akinlabi, who is always there to encourage and shower me with love when the going gets tough. I sincerely appreciate you for all your financial support to enable me attend the 8th International Conference on Trends in Welding Research organized by ASM International at Georgia, the United States of America; between June 1-6, 2008; and the 8th International Friction Stir Welding Symposium organized by The Welding Institute (TWI) at Hamburg, Germany between May 18-20, 2010. To my lovely kids - Stephen Akinkunmi and Stephanie Omolabake, I thank you for your understanding. From the very depth of my heart, I say that I am truly fortunate to have you, I am highly humbled by your co-operation; and you remain my pride and joy. I love you all. vi ABSTRACT Characterisation of Dissimilar Friction Stir Welds Between 5754 Aluminium Alloy and C11000 Copper Akinlabi, E.T. Faculty of Engineering, the Built Environment and Information Technology P.O. Box 77000, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa December, 2010 Friction Stir Welding (FSW) is a solid state welding process invented and patented by The Welding Institute (TWI) in 1991, for joining ferrous and non-ferrous materials1. The FSW of Aluminium and its alloys has been commercialised; and recent interest is focused on joining dissimilar materials. However, in order to commercialise the process, research studies are required to characterise and establish process windows. This research work through material characterisation of the welded joints establishes a process window for the Friction Stir welding of 5754 Aluminium Alloy and C11000 Copper. Furthermore, preliminary studies83,85 on the FSW of aluminium and copper have revealed the presence of intermetallic compounds which are detrimental to the weld qualities. This research work is also aimed at establishing process parameters that will result in limited or no intermetallic formation in the weld. The joint integrity of the resulting welds will also be correlated with the input process parameters. Based on the preliminary investigations conducted, a final weld matrix consisting of twenty seven welds was produced by varying the rotational speed between 600 and 1200 rpm, and the feed rate between 50 and 300 mm/min using three different shoulder diameter tools – 15, 18 and 25 mm to compare the heat input into the welds and to achieve the best results. The welds were characterised through microstructural evaluation, tensile testing, microhardness profiling, X-Ray Diffraction analysis, electrical resistivity and statistical analysis – in order to establish the inter- relationship between the process parameters and the weld qualities. vii Microstructural evaluation of the weld samples revealed that the interfacial regions are characterised by mixture layers of aluminium and copper; while 33 % of the tensile samples are within the acceptable range (> 75 % joint efficiency). High Vickers microhardness values were measured at the joint interfaces, which corresponded with the intermetallic compounds. The Energy Dispersive Spectroscopy analysis revealed the presence of thin layers of intermetallics in nanoscale at the interfacial regions. The diffractograms of the X-Ray Diffraction analysis showed small peaks for intermetallics in some of the welds. Low electrical resistivities were measured at the joint interfaces. The statistical analysis showed that the downward vertical force, (Fz) can significantly influence the resulting weld qualities. An overall summary of the analysis of the weld qualities - with respect to the shoulder diameter tools employed showed that the 18 mm shoulder diameter tool is most appropriate among the three shoulder diameters considered, and a process window of medium spindle speed of 950 rpm and low-to-medium feed rate between 50 and 150 mm/min is established for FSW of Aluminium and Copper. Welds produced at 1200 rpm and 300 mm/min with low heat input did not have intermetallics formed at the joint interface. viii TABLE OF CONTENTS Copyright Statement ii Author’s Declaration iv Acknowledgement v Abstract vii Abbreviations xiii Nomenclature xiv List of Figures xv List of Tables xxi Glossary of Terms xxiii CHAPTER 1 INTRODUCTION 1 1.1 Introduction ................................................................................................. 1 1.2 Problem Statement ..................................................................................... 2 1.3 Aim ............................................................................................................. 2 1.4 Objectives ................................................................................................... 3 1.5 The Hypothesis Statement.......................................................................... 3 1.6 Research Methods ...................................................................................... 3 1.7 Delimitation ................................................................................................. 4 1.8 Significance of the Research .....................................................................