Browsing by Author "Bajilane, Isam Jabbar Ibrahim"

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Application of a novel friction stir spot welding process on dissimilar aluminum joints
(Elsevier, 2018-10) Bajilane, Isam Jabbar Ibrahim; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Bajilane, Isam Jabbar Ibrahim
Intermediate layer friction stir spot welding (IL-FSSW) is introduced in this study as a novel spot welding technique to eliminate the keyhole associated with the conventional friction stir spot welding (FSSW). This process is utilized for fabricating a joint of 6061-T6 and 2024-T3 aluminum alloys. The welding process is based on preventing the keyhole occurrence owing to the addition of an intermediate layer (IL), rendering additional post-treatments unnecessary. Results indicated a decent joint appearance without a keyhole along with improved mechanical performance yielding a lap shear force over 4.5 kN. The microstructure of the weld cross-section indicated that the IL contributed to the nugget zone and revealed its influence on the formation of a hooked structure. The fracture surface showed ductile features within the IL boundary, whereas mixed failure was prevalent outside it.
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Development of a solid state spot welding technique for the manufacturing of detect free joints
(2019-06) Bajilane, Isam Jabbar Ibrahim; Yapıcı, Güney Güven; Yapıcı, Güney Güven; Başol, Altuğ; Şendur, Polat; Tezel, Y. Ş.; İpekoğlu, M.; Department of Mechanical Engineering; Bajilane, Isam Jabbar Ibrahim
Development of a Solid State Spot Welding Technique for the Manufacturing of Defect Free Joints.--Friction stir spot welding (FSSW) processing is a recently developed process for joining hard weldability materials, which has expanded into automotive applications by using the concept of light alloys. Thus, by reducing its fuel consumption, FSSW as a solid-state welding method does not need to melt the workpieces used, which has attracted the attention of automotive manufacturing companies around the world. Although considerable research has been conducted to observe the advantages of the FSSW process, rather more attention has been paid to solving the probe hole (keyhole) defect, which appears at the weld spot center in the welds as a result of the pin of the welding tool after joining process is complete. This study investigates the fabrication of flat friction stir spot welds without the keyhole by using a newly developed FSSW process, which uses the intermediate layer (IL) part, and tracks the mechanical properties of the fabricated welds. The welds produced by the Intermediate Layer FSSW (IL-FSSW) process showed an excellent appearance with no large distortion resulting from the welded sheets. The top surface of the spot weld showed a smooth, flat surface. Regardless of the use of different welding parameters, the appearances of all the spot welds were comparable. It is considerable that no keyhole is formed in comparison with the conventional FSSW welds. It was shown that using the IL part improved the lap shear failure force (LSFF). Some of the welded samples, which were about two folds relative to the maximum value of the American Welding Society (AWS) welds quality requirements. In order to understand the effect of the welding parameters on the tensile behavior, design of experiment (DOE) were utilized to optimize the results of the tensile test. The optimization work indicated that the LSFF increases linearly with the increasing plunging depth. The analysis of the variance (ANOVA) statistical method in respect to LSFF indicates that the tool rotation speed was the most significant parameter, whereas the plunging feed rate was the lower one in this regard. The fatigue tests were conducted under T6 and annealing (O) conditions and over Nf of the lap welded samples of the dissimilar Al 6061/Al 2024 and similar Al 6061/Al 2024 alloys, which were determined for all the conditions. In all the samples, the annealing treatment was observed to have a negative effect on the Nf under high applied loads. However, no heat treatment effect was clearly observed under the low load levels, except in Al 2024, in which the annealing treatment had a positive effect on the Nf. In terms of the Al/Cu welds, the flat weld spots without the keyhole were produced successfully. The results revealed that there was very little difference in the LSFF achieved with the IL-FSSW using the pinless tool when compared to the welds conducted with the conventional FSSW using a tool with a pin. The X-ray diffraction (XRD) analyses showed that the Al2Cu and Al4Cu9 phases formed as a result of the peritectic reactions at the interface of the sheets within the weld nugget. The Vickers examination showed distinctly different microhardness levels up to 575 Hv, which are superior to that of the base metal corresponding to the hard intermetallic compounds formed in the weld nugget. Two finite element models were built to simulate the IL-FSSW process, i.e. thermal and mechanical. The temperature distributions obtained from the thermal model were compared with the experimental measurements with decent agreement. The mechanical model is utilized to predict the strength of the joints in conjunction with the experimental values from shear-tensile tests, providing satisfactory results for demonstrating the trends in the mechanical behavior of various joints.
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Effect of processing parameters on the strength of keyhole free friction stir spot aluminum welds
(American Institute of Physics Inc., 2019) Bajilane, Isam Jabbar Ibrahim; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Bajilane, Isam Jabbar Ibrahim
Intermediate layer friction stir spot welding (IL-FSSW) is a new solid-state welding method appropriate for making spot joints, particularly in light-weight materials, especially notable on account of the weight saving opportunity. Using a welding tool consisting of a non-consumable flat rotating pin, joint between overlapped sheets are fabricated, including an intermediate layer in the middle that eliminates keyhole formation. This study investigates the effect of IL-FSSW parameters on the lap shear strength of 1 mm thick 6061 aluminum alloy joints. Parameter optimization was performed via experimental design based on the Taguchi method and the analysis of variance method was used to identify the importance of each process parameter on the resulting joint strength. The outcome of this work demonstrated that the tool rotational speed has the major effect followed by the tool descending depth and the welding feed rate.
Open Access
On the fatigue and fracture behavior of keyhole-free friction stir spot welded joints in an aluminum alloy
(Elsevier, 2021-03) Yapıcı, Güney Güven; Bajilane, Isam Jabbar Ibrahim; Mechanical Engineering; YAPICI, Güney Güven; Bajilane, Isam Jabbar Ibrahim
The target of this research study was to evaluate the shear-tensile and fatigue behavior of aluminum 6061 alloy welds, in two different heat treatment conditions, joined by the recently developed intermediate layer friction stir spot welding (FSSW) technique. The keyhole, which is the disadvantage of the conventional FSSW process, was avoided using an additional intermediate layer (IL) accompanied by a simple tooling. Shear-tensile experiments demonstrated acceptable mechanical performance of IL-FSSW joints in comparison with that obtained using alternative methods. Fatigue behavior of the joints revealed a dependency to pre-processing temper especially at high cyclic load levels with improved life for the aged condition. Observations on the failure regions under shear-tensile experiments exhibited plug type and shear-plug type fracture modes for the aged and annealed conditions, respectively. In contrast, the fracture mode showed variation with respect to the load level but not to the type of temper during cyclic loading.
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Optimization of the intermediate layer friction stir spot welding process
(Springer Nature, 2019-09) Bajilane, Isam Jabbar Ibrahim; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Bajilane, Isam Jabbar Ibrahim
Friction stir spot welding was performed for joining sheets of 2024 and 6061 aluminum alloys, which is otherwise difficult using conventional welding techniques. The presented approach utilizes an intermediate layer to avoid the keyhole problem. Design of experiment analysis was carried out to evaluate the influence of process parameters. The optimized set of parameters led to the fabrication of sound joints with strength properties exceeding twice the applicable standard requirements as discussed with the evidence of branched hook formations with extensive penetration. Tool rotational speed was determined to be the most significant parameter influencing the mechanical performance. The failure mode revealed itself as sheet tearing-nugget pull out in the joints produced under optimum conditions with various sized dimples apparent on the fracture surface.