1. Ph.D Theses
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Item Welding of Dissimilar A5754-A5083 and A6061- A6082 Aluminium Alloys for Automotive Applications(National Institute of Technology Karnataka, Surathkal, 2021) Rajeshkumar, R.; Banerjee, Kumkum.; Devakumaran, K.In the present study, dissimilar aluminium alloy combinations A6061 T6-A6082 T6 and A5754 H111-A5083 H111 were welded using the cold metal transfer (CMT), tungsten inert gas (TIG) welding and friction stir welding (FSW) processes. Each dissimilar combination was welded by two different fillers, such as ER4043 and ER5356, in CMT and TIG. Since FSW is a solid-state welding process, no filler materials were used. The miniature tensile samples were extracted from the interface regions of the TIG and CMT welded joints and the stir zone (SZ) of the FSWed joint. The TIG and CMT welded alloys' individual interface microstructure has been correlated with mechanical properties. The SZ of FSWed parts is of prime importance because this zone primarily decides the resulting property of the welded joint. Therefore, the microstructural features and mechanical properties of the SZ in the FSWed joints have been investigated in detail. The tensile properties of the overall weld region samples have been determined using macro-tensile testing samples. The dissimilar A6061-T6 and A6082-T6 joints welded by CMT and TIG welding processes using two different fillers (ER5356 and ER4043) exhibited higher strength in the A6082 interface in comparison to the A6061 interface. When the dissimilar A5754 and A5083 alloys were welded by CMT and TIG welding processes using two different fillers (ER5356 and ER4043) fillers, the interface region of the A5083 side exhibited higher strength than the interface region of the A5754. In the FSWed joints, the refined grain structure in SZ increased the hardness and strength. The overall joint tensile properties of the dissimilar joints are essential for identifying a suitable welding process to join A6061-A6082 and A5754-A5083 dissimilar alloys. Among the A6061-A6082 dissimilar joints, the CMT joint produced by ER5356 filler and the FSW joint exhibited higher tensile properties than the other joints. The tensile properties of the A6061-A6082 dissimilar CMT joint produced by ER5356 filler and the FSW joint are nearly the same. However, the FSW process does not use any shielding gas, filler materials, and the surface preparation is also not critical for the process. These factors can play a vital role to reduce the cost of welding effectively. Also, the FSW process is environment friendly, due to the absence of fumes and shielding gases. In the case of A5754-A5083 dissimilar joints, the FSW joint shows higher tensile properties than the other joints. Therefore, the FSW process can be recommended as the preferable joining method among all the investigated processes.Item Experimental Investigations on Friction Stir Welded Joint of Dissimilar Aluminium Alloys(National Institute of Technology Karnataka, Surathkal, 2019) Anilkumar, K. S.; Murigendrappa, S. M.; Kumar, HemanthaFriction 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 ofMMNC 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.