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DISSERTATION O Attribution COPYRIGHT AND CITATION CONSIDERATIONS FOR THIS THESIS/ DISSERTATION o Attribution — You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use. o NonCommercial — You may not use the material for commercial purposes. o ShareAlike — If you remix, transform, or build upon the material, you must distribute your contributions under the same license as the original. How to cite this thesis Surname, Initial(s). (2012). Title of the thesis or dissertation (Doctoral Thesis / Master’s Dissertation). Johannesburg: University of Johannesburg. Available from: http://hdl.handle.net/102000/0002 (Accessed: 22 August 2017). RESEARCH DISSERTATION INVESTIGATING MECHANICAL PROPERTIES OF MIG REINFORCED STEEL SHEETS USING TITANIUM ALLOY POWDER By Odiaka, TN Submitted in partial fulfilment for the requirements of the degree Masters in Engineering In Mechanical Engineering Department of Mechanical Engineering Science Faculty of Engineering and the Built Environment Student Number: 218085764 At the UNIVERSITY OF JOHANNESBURG Supervisor: Dr S.A. Akinlabi Co-supervisor: Dr N. Madushele January 2020 DECLARATION I, Odiaka Timothy Nkemasom, hereby declare that this dissertation is wholly my own work and has not been submitted anywhere else for academic credit either by myself or another person. I understand what plagiarism implies and declare that this dissertation is my own ideas, words, phrases, arguments, graphics, figures, results and organization except where reference is explicitly made to another’s work. I understand that any unethical academic behaviour, which includes plagiarism, is seen in a serious light by the University of Johannesburg and is punishable by disciplinary action. Signed: Date: January, 2020 i | P a g e ACKNOWLEDGEMENT Special thanks go to my supervisor, Dr S.A. Akinlabi for conceptualizing this research study and providing all the research materials and for his immense patience, guidance and contribution to this research work. You were always readily available and eager to help in the accomplishment of this work. Heartfelt thanks also go to my co-supervisor, Dr N. Madushele for your frankness, immense contribution and priceless guidance. I’m grateful to the MAMS (Modern and Advanced Manufacturing System) research group leader, Prof. E.T. Akinlabi, for being a source of inspiration to me and the entire research team. I would like to acknowledge Mr Willie Williams at South Africa Institute of Welding, for his gracious help during the experimental phase of this work. I’m also grateful to my research colleagues, Mr Simeon Okwudili, Mr Pardon Baloyi, Mr Opeoluwa Dada, Mrs Cynthia Abima, Pastor Olatunji Abolusoro, Dr Olajide Abdulrahman, Mr Paul Adedeji, Mr Victor Aladesanmi, Dr Damilare Baruwa and all distinguished members of MAMS Research group. Your help and friendship made research fun. I remain indebted to my parents, Prof. and Dr (Mrs) Odiaka for their invaluable support and inspiration. Above all, I’m thankful to God. All we discover is only but a minute fraction of what you already know. ii | P a g e RESEARCH OUTPUT Journal Manuscripts Submitted 1. Investigating the Role of Titanium Alloy Powder Reinforcement in MIG Mild Steel Lap Joints 2. Effect of Titanium Alloy Powder Reinforcement on the Mechanical Properties and Microstructural Evolution of GMAW Mild Steel Butt Joints. Conference Paper - Published 3. Odiaka Timothy, Madushele Nkosinathi and Akinlabi Stephen. "Improvement of Joint Integrity in MIG Welded Steel: A Review." Proceedings of the ASME 2018 International Mechanical Engineering Congress and Exposition. Volume 2: Advanced Manufacturing. Pittsburgh, Pennsylvania, USA. November 9–15, 2018. V002T02A099. ASME. https://doi.org/10.1115/IMECE2018-86788 iii | P a g e ABSTRACT Mild steel is one of the commonest materials used in the metal industry due to its weldability, malleability and hardness properties. Consequently, there is always a need for joining processes of mild steel, with welding techniques such as Metal Inert Gas (MIG) welding being a popular choice. However, the complex physics involved in welding such as phase changes, metal deposition, and inhomogeneous heating and cooling rates across the weld zone often results in the compromise of structural integrity in mild steel welds. Improving weld integrity has since become an area of interest, with process parameter optimization and post-weld heat treatment being the most popular solutions as discovered in the literature. This study explores the prospects of titanium powders as weld reinforcements in improving the structural integrity of AISI 1008 mild steel welds. Using Taguchi’s design of experiment method, butt and lap joint weldments reinforced with titanium powders were optimized for tensile strength in the first welding phase. In the second welding phase, the optimum parameters obtained were used to make two sets of weldments for comparison; one with titanium reinforcement and the other without any reinforcement. The weldments were characterized using optical microscopy, x-ray diffraction (XRD) analysis, energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). Mechanical tests for tensile strength and for microhardness were carried out. A three-dimensional transient thermal numerical analysis was used to predict the temperature field and weld pool geometry of the reinforced and unreinforced weldments. The temperature histories obtained, and the simulated weld pool geometries were correlated with the microstructure evolution observed across the weld zones. The optimum parameters obtained from the optimization process were 24V and 220 A for butt joints and 26 V, 215 A for lap joints. Ti 6-2-2-2-2 alloy powder was also selected as the preferred titanium powder reinforcement. It was discovered that microhardness in the weld metal was higher in the reinforced weldments due to the formation of an iron-titanium intermetallic compound and martensite microphases. There was no significant improvement in the tensile strength of the reinforced joints. However, it was observed that acicular ferrite formation was more prominent in the titanium-reinforced weldments, suggesting an improvement of impact toughness. Failure analysis revealed that all reinforced welds underwent predominantly ductile failure. The temperature histories at selected points away from the weld centre were estimated for the iv | P a g e weldments using numerical analysis. These temperature histories correlated well with the microstructures observed across the weld zones. The weld pool geometry prediction obtained through the numerical analysis agreed with experimental results. It was concluded that the reinforcement of steel welds with titanium particles improved the hardness property of the weldments. It also promoted the dominance of acicular ferrite microstructure in the weld zone. Acicular ferrite is desired in mild steel welds to improve material toughness. v | P a g e TABLE OF CONTENT DECLARATION ............................................................................................................................. i ACKNOWLEDGEMENT .............................................................................................................. ii RESEARCH OUTPUT .................................................................................................................. iii ABSTRACT ................................................................................................................................... iv TABLE OF CONTENT ................................................................................................................. vi LIST OF FIGURES ........................................................................................................................ x LIST OF TABLES ....................................................................................................................... xiv GLOSSARY OF TERMS ............................................................................................................. xv ABBREVIATIONS ................................................................................................................... xviii 1. Introduction ................................................................................................................................. 1 Background ........................................................................................................................... 1 Keywords ........................................................................................................................ 3 Problem Statement ................................................................................................................ 3 Rationale and Motivation for the Study ................................................................................ 4 Aim of Research .................................................................................................................... 4 Objectives of Research .......................................................................................................... 4 Research Methodology .......................................................................................................... 5 Delimitation ........................................................................................................................... 6 Research Expectation ...........................................................................................................
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