Papers by Author: Takuya Tsumura

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Authors: Takuya Tsumura, Taichi Murakami, Soong Keun Hyun, Hideo Nakajima, Kazuhiro Nakata
Abstract: Effects of pore directions on the profile of fusion zone for lotus-type porous magnesium by laser welding has been investigated by comparing the experimental observations and the results of numerical simulation. The three-dimensional finite element calculations were performed, which takes into account equivalent thermal properties and anisotropy of thermal conductivity. There is the pore anisotropy in the profile of fusion zone by laser beam irradiation and the good weldability was obtained when the growth direction of the original pore equaled to the direction of the laser beam irradiation. A good agreement was obtained between the calculated profile of the weld fusion zone and the experimental results.
Authors: Hyun Guen Kim, Kazuhiro Nakata, Takuya Tsumura, Masaharu Sugiyama, Takanori Igarashi, Masahiro Fukumoto, Hisamichi Kimura, Akihisa Inoue
Abstract: The Fe-based bulk metallic glass (Fe43Cr16Mo16C15B10) sprayed coating with the thickness about 220%m was successfully deposited on an aluminum alloy (A5052) metal substrate using an HVOF (High Velocity Oxygen Fuel) spraying process. All sprayed coating has still kept the amorphous state after spraying. The Fe-based bulk metallic glass coating shows good adhesion to the aluminum alloy metal substrate, and has a high hardness with HMV 913~1120. It has been found that better properties can be obtained in the sprayed coating by using finer powder.
Authors: Kazuhiro Nakata, Hirohisa Ikegami, Takuya Tsumura
Abstract: Lap joint of AZ31 Mg alloy extruded sheet can be successfully made by friction spot joining (FSJ) process. Joint strength was strongly affected by the probe thread, which increased the plastically deformed zone around a rotating probe and increased the tensile shear strength of the joint in comparison with the joint made by a thread-less probe.
Authors: Yuji Sakai, Kazuhiro Nakata, Takuya Tsumura, Mitsuji Ueda, Tomoyuki Ueyama, Katsuya Akamatsu
Abstract: Noncombustible magnesium alloy AMC602 (Mg-6mass%Al-2mass%Ca) extruded sheet of 2.0mm thickness was successfully welded using a fiber laser welding process at welding speed of 10m/min at 3kW laser power. Tensile strength of the welded joint was about 82 to 88% of that of the base metal. Vickers hardness, tensile strength and micro structural properties are also discussed.
Authors: Y.C. Chen, T. Komazaki, Y.G. Kim, Takuya Tsumura, Kazuhiro Nakata
Abstract: AC4C cast aluminum alloy and zinc-coated steel were friction stir lap welded, and the microstructures and mechanical properties of the joints were examined and analyzed. Experimental results show that the welding speeds have a significant effect on the tensile properties and fracture locations of the joints at a rotational speed of 1500 rpm. When the welding speed is higher than 60 mm/min, the joints fracture in the zinc-coated steel base material and the tensile strength is equal to that of the zinc-coated steel; when the welding speed is lower than 60 mm/min, the joints fracture in the interface and the shear strength is about 50 MPa. The change of the fracture locations is attributed to the presence of large quantity intermetallic compounds adjacent to the interface of the joints. The composition and formation mechanism of the intermetallic compounds and its effect on the mechanical properties of the joints were discussed.
Authors: Hidetoshi Fujii, Takahiro Tatsuno, Takuya Tsumura, Manabu Tanaka, Kazuhiro Nakata
Abstract: A new welding technique called hybrid FSW was developed to decrease the tool load and the defects during the FSW of high melting point materials. This method consists of FSW and a laser for preheating ahead of the tool. The hybrid FSW enables the proper welding conditions to be significantly expanded, and the joint characteristics are similar to those obtained by the normal FSW at the same welding speeds.
Authors: Souta Matsusaka, Toshiro Uezono, Takuya Tsumura, Manabu Tanaka, Takehiro Watanabe
Abstract: Galvanized steel sheets with a lap joint were welded by a laser-arc hybrid process. The hybrid system consisted of 2kW LD or YAG laser oscillator and frequency-modulated DC pulsed MAG welding machine. In this experiment, the arc traveled on the specimens, following the laser beam with the interval of 2 mm. The results showed that the hybrid process had some advantages, such as deep penetration depth, high welding speed and high gap-tolerance, in comparison with the conventional MAG welding. Observations from a high-speed digital video-camera suggested that the zinc and iron vapors induced by laser beam irradiation stabilized the arc plasma. Effects of the incidence angle between a welding head and a specimen on the weld bead formations were also discussed. As a result, the welding speed of 2.0 m/min was achieved at 1.0 mm of gap length condition when the incidence angle was 50 degree.
Authors: Takuya Tsumura, Fu Xing Ye, Taichi Murakami, Hideo Nakajima, Kazuhiro Nakata
Abstract: Lotus-type porous metals, whose pores are aligned in one direction by unidirectional solidification, have a unique combination of properties. These are expected as revolutionary engineering materials with anisotropy of the properties. For the industrial use of the lotus-type porous metals, a reliable joining technology is required. We already reported the melting property of a few lotus-type porous metals by laser welding. These results indicated that these materials possessed anisotropy of melting property with the pore direction perpendicular and parallel to the specimen surface, especially remarkable anisotropy was obtained for the copper specimen owing to the difference of the laser energy absorption to the specimen surface. In this report, the three-dimensional heat transfer analyses, which take into account the difference of the laser energy absorption comparing with the anisotropy of thermal conductivity inherent to lotus-type porous metals, were performed by commercial code with user-defined subroutine. Predicted profile of weld fusion zone is in good agreement with the cross-sectional view obtained by experiments.
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