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Song K.H.,Korea Institute of Industrial Technology | Nakata K.,Joining and Welding Research Institute
Korean Journal of Materials Research | Year: 2011

This study was carried out to evaluate the microstructures and mechanical properties of a friction stir welded Ni based alloy. Inconel 600 (single phase type) alloy was selected as an experimental material. For this material, friction stir welding (FSW) was performed at a constant tool rotation speed of 400 rpm and a welding speed of 150~200 mm/min by a FSW machine, and argon shielding gas was utilized to prevent surface oxidation of the weld material. At all conditions, sound friction stir welds without any weld defects were obtained. The electron back-scattered diffraction (EBSD) method was used to analyze the grain boundary character distributions (GBCDs) of the welds. As a result, dynamic recrystallization was observed at all conditions. In addition, grain refinement was achieved in the stir zone, gradually accelerating from 19 μm in average grain size of the base material to 5.5 μm (150 mm/min) and 4.1 μm (200 mm/min) in the stir zone with increasing welding speed. Grain refinement also led to enhancement of the mechanical properties: the 200 mm/min friction stir welded zone showed 25% higher microhardness and 15% higher tensile strength relative to the base material. Source


Wahba M.,Central Metallurgical Research and Development Institute | Wahba M.,Osaka University | Wahba M.,Joining and Welding Research Institute | Kawahito Y.,Osaka University | Katayama S.,Osaka University
Journal of Materials Processing Technology | Year: 2011

Lap joints between AZ91D thixomolded Mg alloy and amorphous polyethylene terephthalate (PET) were produced by direct irradiation of high power diode laser beam from either plastic or metal side. Joints with strength higher than that of PET could be successfully produced. Joining mechanism involves the generation of gas bubbles in a narrow region inside PET specimen adjacent to the interface. The pressure induced by expansion of these bubbles secures tight bonding in the micro size between AZ91D and PET specimens. Discrete bubbles morphology associated with metal-side laser-irradiation promoted higher joint strength in comparison with networked wormhole morphology in the case of plastic-side laser-irradiation. The presence of pre-made pits on the AZ91D specimen surface proved to be effective to the improvement in the performance of plastic-side laser-irradiated joints. © 2011 Elsevier B.V. All rights reserved. Source


Song K.-H.,Korea Institute of Industrial Technology | Nakata K.,Joining and Welding Research Institute
Korean Journal of Materials Research | Year: 2012

The microstructures and mechanical properties of friction stir welded lap joints of Inconel 600 and SS 400 were evaluated; friction stir welding was carried out at a tool rotation speed of 200 rpm and welding speed of 100 mm/min. Electron back-scattering diffraction and transmission electron microscopy were introduced to analyze the grain boundary characteristics and the precipitates, respectively. Application of friction stir welding was notably effective at reducing the grain size of the stir zone. As a result, the reduced average grain size of Inconel 600 ranged from 20μm in the base material to 8.5μm in the stir zone. The joint interface between Inconel 600 and SS 400 showed a sound weld without voids and cracks, and MC carbides with a size of around 50 nm were partially formed at the Inconel 600 area of lap joint interface. However, the intermetallic compounds that lead to mechanical property degradation of the welds were not formed at the joint interface. Also, a hook, along the Inconel 600 alloy from SS 400, was formed at the advancing side, which directly brought about an increase in the peel strength. In this study, we systematically discussed the evolution of microstructures and mechanical properties of the friction stir lap joint between Inconel 600 and SS 400. Source


Song K.H.,Korea Institute of Industrial Technology | Kim W.Y.,Korea Institute of Industrial Technology | Nakata K.,Joining and Welding Research Institute
Materials and Design | Year: 2012

The microstructures and mechanical properties of friction stir welded Inconel 600 and SS 400 lap joints were evaluated in this study. Friction stir welding was carried out at a tool rotation speed of 200. rpm and a welding speed of 100. mm/min. Application of friction stir welding was notably effective in reducing the grain size of the stir zone, as a result, the average grain size of Inconel 600 was reduced from 20 μm in the base material to 8.5 μm in the stir zone. The joint interface between Inconel 600 and SS 400 was soundly welded without voids and cracks, and MC carbides with a size of 50. nm were partially formed in the region of the lap joint interface in Inconel 600. In addition, a hook from SS 400 was formed on the advancing side of the Inconel 600 alloy, which directly affected an increase in the peel strength of the weld. In this study, we systematically discussed the effect of friction stir welding on the evolution of the microstructures and mechanical properties of friction stir lap jointed Inconel 600 and SS 400. © 2011 Elsevier Ltd. Source


Song K.H.,Korea Institute of Industrial Technology | Chung Y.D.,Joining and Welding Research Institute | Nakata K.,Joining and Welding Research Institute
Metals and Materials International | Year: 2013

This study was conducted to investigate the microstructure and mechanical properties of friction stir lap joints. Monel 400 and Inconel 600 were selected as the experimental materials, and friction stir welding was carried out at a tool rotation speed of 200 rpm and welding speed of 100 mm/min. The application of friction stir welding to Monel 400 effectively reduced the grain size in the stir zone; the average grain size of Monel 400 was reduced from 11.9 μm in the base material to 4.2 μm in the stir zone, which resulted in an improvement in the mechanical properties of the stir zone. The joint interface between Monel 400 and Inconel 600 showed a relatively sound weld without grooves or cracks, and only a small amount of voids with a size of 0.5 μm; however, no intermetallic compounds were observed in the lap jointed interface. Moreover, the hook on the advancing side of Monel 400 was formed from Inconel 600, which contributed to maintenance of the tensile strength. The evolution of microstructures and mechanical properties of friction stir lap jointed Monel 400 and Inconel 600 are also discussed herein. © 2013 The Korean Institute of Metals and Materials and Springer Science+Business Media Dordrecht. Source

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