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    Effect of rotational speed and dwell time on mechanical properties of dissimilar AA1050-AA3105 friction stir spot welded joints
    (Carl Hanser Verlag, 2014) Aydin, Hakan; Tuncel, Oguz; Yuce, Celalettin; Tutar, Mumin; Yavuz, Nurettin; Bayram, Ali
    Friction stir spot welding is a newly developed joining technology which is expected to be used in the automotive industry for joining body parts made of aluminum sheets. The effect of the rotational speed and dwell time on the mechanical properties of dissimilar friction stir spot welded aluminum sheet alloys was investigated in this study. In the experimental studies, macro-structural characterization, micro-hardness tests and tensile shear tests were conducted. The experimental results showed that the tensile shear load and tensile deformation of the friction stir spot welded joints decreased roughly by 20 % and 25 %, respectively, when the rotational speed increased from 1000 rpm to 2000 rpm. On the other hand, when the dwell time increased from 3 s to 11 s, the tensile shear load increased roughly by 7 %, while the tensile deformation decreased roughly by 19 %, respectively. © Carl Hanser Verlag GmbH & Co.
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    Effect of tool pin profile on the hook geometry and mechanical properties of a friction stir spot welded AA6082-T6 aluminum alloy
    (Canadian Science Publishing, 2021) Aydin, Hakan; Tuncel, Oguz; Tutar, Mumin; Bayram, Ali
    AA6082-T6 alloy was joined by friction stir spot welding using five different pin profiles, namely cylindrical, conical, triangular, hexagonal, and cylindrical with two grooves, at different dwell time. The joints welded by cylindrical pins had larger effective weld width. However, grooves on the cylindrical pin decreased the effective weld width. In the weld made with the hexagonal pin, the hook was bent downward from the interface of the sheets and had the smallest effective weld width. When the conical pin was used, the effective weld width increased with increasing dwell time. In the case of using tools with cylindrical and conical pins, HAZ hardness was relatively lower. With increasing dwell time, HAZ hardness of the joints made with the conical pin decreased. Effective weld width determined the weld strength under the tensile shear loading condition: larger effective weld width resulted in higher weld strength. Weld strength of the joints made with cylindrical pins was higher. The joints fabricated with hexagonal pins had the lowest weld strength. In general, higher dwell time led to higher weld strength. The welds with the higher strength experienced both brittle and ductile fractures, while the joints with the lower strength exhibited completely brittle fracture.
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    EYM ile Üretilen YMK Yapılı Numunelerde Kenar Genişliğinin Basma Dayanımı Üzerine Etkisinin Araştırılması
    (2023) Tunçel, Oğuz; Tutar, Mumin
    Bu çalışmada, 3 boyutlu baskı (3D printing) kullanılarak üretilen farklı kenar genişliklerine sahip yüzey merkezli kübik YMK yapılı numunelerin basma dayanımı üzerindeki etkisi incelenmiştir. PLA malzemesi kullanılarak Eriyik Yığma Modellemesi (EYM) yöntemi ile numuneler üretilmiştir. Kenar genişliği arttıkça, maksimum basma yüklerinde ve basma dayanımlarında artışlar gözlenmiştir. En düşük yük 1,2 mm kenar genişliğinde 2849 N iken, en yüksek yük 2,4 mm kenar genişliğinde 6351 N olarak ölçülmüştür. Benzer şekilde, en düşük basma gerilimi 34,76 MPa ile 1,2 mm kenar genişliğinde, en yüksek basma gerilimi ise 40,15 MPa ile 2,4 mm kenar genişliğinde kaydedilmiştir. Kenar genişliğinin artmasıyla birlikte maksimum yük/kütle değeri %33,1 oranında artış göstermiştir. Sonuçlar, 3D baskı üretiminde kenar genişliğinin tasarım faktörü olarak önemini vurgularken, daha geniş kenar genişliklerinin ürünlerin mekanik dayanıklılığını artırabileceğini ve uygulama gereksinimlerine uygunluğunu sağlayabileceğini göstermiştir.
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    Friction Stir Spot Weldability of AA7075-T6 Sheets with a Pinless Tool Providing Enhanced Stirring Effect
    (Springer, 2024) Cakan, Betul Gulcimen; Tuncel, Oguz; Tutar, Mumin
    The automotive and aerospace industries have explored alternative welding methods, such as friction stir welding (FSW) and its derivation, friction stir spot welding (FSSW). Welding parameters and tool shoulder designs influence material flow dynamics and stirring during the FSSW process. The current study uses a newly manufactured pinless tool to focus on the FSSW of 3-mm-thick AA7075-T6 aluminum sheets, which were joined using a pinless tool with a concave shape of three grooves for improved flow characteristics. The experiments explore the impact of welding parameters on the weld quality. Tensile tests, macroscopic examination, fracture surface analysis, and microhardness tests were performed. The geometric characteristics of hook shape and effective weld width substantially affected the tensile shear load (TSL). Tensile test findings and changes in effective weld width with welding parameters reveal that low rotational speed, high penetration depth, and dwell time parameters can result in a high TSL. Microhardness profiles reveal that the stir zone (SZ) exhibits the highest hardness values, reaching 27% above the base material hardness. The heat-affected zone (HAZ) shows the lowest hardness values. Fracture surface morphology analysis reveals different fracture modes in high and low TSL specimens.