P, Mastanaiah and Sharma, Abhay
(2018)
Electron Beam Welding and Friction Stir Welding of Dissimilar Aluminium Alloys (AA2219 and AA5083).
PhD thesis, Indian Institute of Technology Hyderabad.
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Abstract
Certain critical and high performance applications require distinct attributes in the either sides of the weld, e.g. load bearing capability in one side and corrosion resistance in the other. In order to meet these requirements, such systems are designed with a high strength aluminium alloy and a medium strength aluminium alloy with good corrosion resistance. However, in some stringent scenario, the weldment need to be used in as-welded condition as one of the alloys may be non-heat treatable (e.g. AA5083) and further machining of the weld is not possible because of inevitable reasons. On the other hand, another alloy may be heat treatable (e.g. AA2219) which may impose a limitation on use of filler wire as it may reduce the resulting mechanical properties of the weld joint. The development in welding technologies such as friction stir welding (FSW) and electron beam welding (EBW) have made it possible to weld aforementioned dissimilar materials that are otherwise difficult to weld with conventional arc welding processes. FSW (solid state) and EBW (fusion) processes are considered in this study as both the processes are autogenous welding processes result in minimum possible heat input, better joint quality and mechanical properties among the respective category of welding processes.
Many more investigations are required to exploit the best of the aforementioned developments. The thesis presents such an effort and primarily focuses on establishment of friction stir and electron beam welding technology for dissimilar aluminium alloys AA2219 and AA5083, considering two different thicknesses, by developing a detailed understanding on the effect of process parameters on material intermixing in weld/nugget zone, defect formation, mechanical properties, and tensile failure location. The problem definition of the investigation in this thesis reads as “An experimental investigation through parametric study, tool and process development, and mechanical and microstructural characterization with a direction to produce high performance low- and high- thick section weld joints in dissimilar aluminium alloys (AA2219 and AA5083) using election beam welding and friction stir welding”.
The work innovatively brings out a hybrid tool pin profile for welding thick section aluminum alloys, which has improved joint strength even at welding speeds seven times more than that is generally possible with conventional tool. The thesis also presents new models that can predict relation between weld bead geometry and weld strength in EBW and the prediction of defects in FSW. The outcome of this research is envisaged to provide a better
insight into metallurgical understanding and its correlation with mechanical properties of EBW and FSW joints of dissimilar aluminium alloys.
The research work reported in this thesis establishes An industry friendly comprehensive technology for welding of low- and high- thick dissimilar aluminum alloys (AA2219 and AA5083), both by fusion and solid state welding processes has been developed over a wide range of workable welding parameters. In low-thick welds produced, either by EBW or FSW, very good joint strengths are achievable and the failure location of tensile specimen is always located in HAZ or fusion line AA5083 alloy depending upon the type welding process employed. However, at a higher thickness of weld joint, the friction stir welding scores better in terms of joint strengths, %elongation and quality, with a failure location located in TMAZ of AA2219 alloy. The electron beam welding produces dissimilar weld joint with relatively lower tensile properties and quality with failure location at PMZ of AA2219 alloy.
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