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Öğe Effect of welding parameters on microstructure and mechanical properties of AA7075/AA5182 alloys joined by TIG and MIG welding methods(SpringerLink, 2020) Çelik, Yahya Hışman; Temiz, Şemsettin; Çetkin, EdipIn this study, V and X welding grooves were opened to the forehead positions of the AA5182 and AA7075 aluminum alloy pairs and these alloy pairs were joined with tungsten inert gas (TIG) and metal inert gas (MIG) methods. Three diferent welding currents were used in joints. Gas fow rates of 12 and 17 l/min at the TIG welding and wire feed rates of 38 and 45 cm/min at MIG welding were selected. The efect of the welding grooves, welding current, gas fow rate and wire feed rate on microstructure and mechanical properties were investigated. Microstructures of welding zones were analyzed by an optical microscope and a scanning electron microscope (SEM). Vickers hardness of these zones was also measured. In addition, tensile and fatigue tests were carried out. Fracture mechanisms of failed specimens were conducted after the tensile tests were examined by using SEM. The highest hardness, tensile and fatigue strengths were obtained from the alloy pairs joined by opening X welding groove with TIG welding method. These values were 89 HV, 262.87 MPa, and 131.5 MPa, respectively. Similarly, the lowest tensile and fatigue strengths were obtained from the alloy pairs joined by opening V welding groove in the TIG welding method. These values were, respectively, 94.48 MPa and 19.1 MPa. However, the minimum hardness value was measured as 58 HV from the alloy pairs joined by opening V welding groove with MIG welding methods. In addition, it was observed on the fracture surfaces that the grain distributions and mechanisms difered depending on the welding methods, welding groove, and welding parameters.Öğe Investigation of wear behaviours of Al matrix composites reinforced with different B4C rate produced by powder metallurgy method(Elsevier, 2017-09) Çelik, Yahya Hışman; Seçilmiş, KübraIn this study, the effects of wear behaviours of Al matrix composites reinforced with different B4C rate produced by powder metallurgy method were investigated. Al and B4C powders with purity of 99.9% and sizes of 25–44 µm were prepared as pure Al, 4% B4C/Al, 8% B4C/Al, 12% B4C/Al and 16% B4C/Al. After these prepared mixtures were pressed under 350 MPa, they were sintered for 90 min at 580 °C in atmospheric environment. Microhardness and wear tests of the produced samples were carried out. Wear experiments of these composites were performed with specially manufactured test equipment at different application loads (5 N, 10 N and 15 N), different sliding distances (250 m, 500 m, 750 m and 1000 m) and a constant speed of 0.46 m/s. In addition, optical microscope, SEM, EDS analyses were used to determine the microstructural changes in the worn and unworn surface of the manufactured composite materials. The results of experimental studies show that the increasing the B4C reinforced rate in composites with Al matrix has led to increase of the hardness and to reduce of the wear loss.Öğe Mesogenic properties of PAA/6BA binary liquid crystal complexes(Elsevier, 2018-09-19) Okumuş, Mustafa; Eskalen, Hasan; Sünkür, Murat; Özgan , ŞükrüA novel supramolecular liquid crystal complex has been designed and formed from pure liquid crystalspara-azoxyanisole (PAA) and 4-hexylbenzoic acid (6BA). Thermal and microstructural properties offormed PAA/6BA binary liquid crystal complex system are investigated by differential scanning calo-rimeter (DSC), polarized optical microscopy (POM) and X-ray diffractometer (XRD). Fourier transformedinfrared spectroscopy (FTIR) is used to confirm the formation of hydrogen bond between the PAA and6BA molecules. The XRD results show that the molecular ordering of the hydrogen bonded PAA/6BAcomplex is arranged in the orthorhombic structure. The DSC and POM results clearly indicate that thePAA/6BA binary complex exhibits liquid crystalline properties due to the hydrogen bonds formed be-tween the PAA and 6BA molecules. The PAA/6BA complex shows the phase transition peaks indicatingCr/N/I and I/N/SmA/Cr phase sequence during continuous heating and cooling, respectively, byDSC. These phase sequences have also been confirmed by POM observations. Furthermore, the effect ofthe heating rate on the phase transition temperature values is investigated. As the heating rate increases,the phase transition temperature values increase as well. Moreover, the activation energies for the phasetransitions of the PAA/6BA liquid crystal complex are calculated by using Kissinger, Ozawa and Takhormethods. The calculated results clearly show that the phase transitions are regular.Öğe Microstructure and mechanical properties of AA7075/AA5182 jointed by FSW(Journals & Books, 2019-06) Çelik, Yahya Hışman; Çetkin, Edip; Temiz, ŞemsettinIn this study, AA7075 and AA5182 aluminium alloys were joined using different rotation speeds (980, 1325 and 1800 rpm), feed rates (108 and 233 mm/min) and stirred pins having two different geometries (conical helical and triangular). Microstructures of welding joints were examined by an optical microscope and a scanning electron microscope (SEM). Vickers hardness measurements were performed in the welding zone of samples removed from each welded plate. Tensile and fatigue tests were also applied to the test specimens taken from the welded plates. After the tensile tests, the surface fractures and possible welding defects were scanned via SEM. The best mechanical properties were obtained when conical helical shape stirrer pins were used. The values were 265 MPa for tensile test and 159 MPa for fatigue test. The hardness value was very close to each other and varied depending on the rotation speed. The highest hardness value was determined as 87 HV in the weld center at 1325-rpm rotation speed.Öğe Microstructure and mechanical properties of AA7075/AA5182 jointed byFSW(Elsevier, 2019-06) Çetkin, Edip; Çelik, Yahya Hışman; Temiz, ŞemsettinIn this study, AA7075 and AA5182 aluminium alloys were joined using different rotation speeds (980, 1325 and 1800 rpm), feed rates (108 and 233 mm/min) and stirred pins having two different geometries (conical helical and triangular). Microstructures of welding joints were examined by an optical microscope and a scanning electron microscope (SEM). Vickers hardness measurements were performed in the welding zone of samples removed from each welded plate. Tensile and fatigue tests were also applied to the test specimens taken from the welded plates. After the tensile tests, the surface fractures and possible welding defects were scanned via SEM. The best mechanical properties were obtained when conical helical shape stirrer pins were used. The values were 265 MPa for tensile test and 159 MPa for fatigue test. The hardness value was very close to each other and varied depending on the rotation speed. The highest hardness value was determined as 87 HV in the weld center at 1325-rpm rotation speed.
