THERMEC 2006 Supplement

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Authors: Y. Abe, Takehiko Watanabe, H. Tanabe, K. Kagiya
Abstract: Authors tried to butt-weld a mild steel plate to a magnesium alloy plate by the solid state welding using a rotating pin. This study investigated the effects of a pin rotating speed, the position for the pin axis to be plunged (pin offset) on the strength and the microstructure of the joint. The main results obtained are as follows. Butt-welding of a steel plate to a magnesium alloy plate was easily and successfully achieved. The maximum tensile strength of a joint reached about 70% of the magnesium base metal tensile strength and the fracture path was along the joint interface. When a pin rotating speed was slow, some defects appeared in the magnesium matrix due to the insufficient plasticization of the magnesium. The joint strength increased with the pin rotating speed. This seems to be because the plasticization of the magnesium was increased and the pressure for pushing the plasticized magnesium onto an activated faying surface of the steel increased. However, the excessive increase of the pin rotating speed caused the ignition of the magnesium, resulting in the decrease of a joint strength. At the pin offset of 0.1mm toward steel, steel fragments scattered in the magnesium matrix in the form of a small piece that had no influence to the joint strength. By contrast, larger offsets over 0.2mm produced the steel fragment continuous and parallel to the weld interface in the magnesium matrix, and the joint strength decreased.
Authors: Jee Hoon Choi, Dong Bok Lee
Abstract: L12-type Al65.5Ti24.4Cr10.1 alloys were prepared by induction melting followed by thermomechanical treatment. Corrosion tests were performed between 1173 and 1373 K in a flowing Ar-1% SO2 atmosphere for up to 150 hr. The corrosion proceeded mainly via the oxidation reaction. The oxide scale was primarily composed of Al2O3, together with a small amount of TiO2 that appeared mainly in the lower part of the oxide scale during the latter stages of corrosion. The formation of the highly stoichiometric, slowly growing alumina scale on the surface significantly improved the corrosion resistance of the alloys. Neither internal corrosion products nor sulfides were detected.
Authors: Wang Kee Min, Sung Doo Hwang, Chang Ho Lee, Young Do Park, Yang Do Kim, Young Seok Kim, Ik Min Park, Yong Ho Park
Abstract: The n-type Bi2(Te0.94Se0.06)3 thermoelectric compound was prepared by the direct extrusion process using the powder as raw materials. Hot extruded specimens were annealed at 200°C and 350°C for 2hrs. The electrical conductivity, thermoelectric power and thermal conductivity of hot extruded and annealed specimens were measured at room temperature. The fractographs of the specimens showed that the grain size became coarser and a lot of porosities were generated during annealing process. The power factor value (PF) decreased with increasing the annealing temperature. The electric conductivity and thermal conductivity of the specimens also decreased with the increase of annealing temperature. This may be reasoned that the generated porosities affect the thermal conductivity of the specimens prepared in this study. The figure of merit (Z) value of the annealed specimens at 350°C was improved about 10%. The highest Z value of the specimens annealed at 350°C was 2.0 x 10-3/K among the prepared specimens.
Authors: Masataka Hakamada, Yasuo Yamada, Tetsumune Kuromura, Yuuki Asao, Y. Chen, Hiromu Kusuda, Mamoru Mabuchi
Abstract: Porous metals, or metallic foams, are emerging ecomaterials that can be applied to structural use, shock absorber, filter, heat exchanger, etc. Their very low densities and peculiar deformation behaviors will facilitate the application. The control of pore characteristics such as porosity and pore size distribution can be successfully achieved by spacer method. In this paper, fabrication of porous aluminum via the spacer method is introduced and their excellent properties due to homogeneous pore characteristics are exhibited
Authors: Tetsumune Kuromura, Masataka Hakamada, Y. Chen, Hiromu Kusuda, Mamoru Mabuchi
Abstract: Porous Al specimens with a pore size range from 212-300 to 610-700 μm, a porosity from 85 to 95% and a specimen thickness from 2 to 20 mm were produced by the spacer method, and their sound absorption capacity was investigated. For these specimens, sound absorption coefficient increased with increasing porosity. On the other hand, sound absorption coefficient varied inconsistently with the variation of pore sizes. The latter may be attributed to variation of aperture sizes of each specimen because the porous Al specimens with differerent pore sizes produced by the spacer method should have different aperture sizes. Sound absorption coefficient increased at the frequency below 2000 Hz with increasing specimen thickness.
Authors: I.Ch. Konstantinidis, D.P. Papadopoulos, M. Gavaises, D.N. Tsipas
Abstract: In this paper we present some simple methods for the fabrication of closed and open cell Al metal foams. The closed cell Al metal foams were fabricated using liquid metallurgy. Their microstructure and morphological characteristics were studied using optical and electron microscopy techniques. The mechanical properties and their relationship to microstructure were established. A three dimensional model was developed relating the cell geometry to the mechanical behavior of Al closed cell foam material. The open cell Al foams were fabricated using sodium chloride powder sinters and liquid Al metal infiltration techniques. The potential of using these cellular structures in various systems is discussed.
Authors: Yoon S. Oh, Jung G. Lee, Choong Nyun Paul Kim, Nack J. Kim
Abstract: Solidification behavior of two Fe-base amorphous alloys during twin-roll strip casting has been investigated in the present study. Continuous cooling transformation (CCT) diagrams of both alloys were calculated using the heterogeneous nucleation theory coupled with thermal data obtained during cooling. Cooling sequence during twin-roll strip casting was also simulated. These were used for the determination of the optimum twin-roll strip casting conditions at which desirable solidification behavior could be achieved. It shows that twin-roll strip casting can continuously fabricate sheet product of Fe-base bulk amorphous alloys, despite their higher liquidus temperatures and larger differences between liquidus and glass transition temperatures (Tg) than those of other easier glass-forming bulk amorphous alloys.
Authors: Jessica Hiscocks, Lan Jiang, John J. Jonas
Abstract: Research is currently being conducted on the feasibility of hydroforming extruded magnesium tubes to integrate multiple parts into a single hydroformed section. Among other applications, such sections would reduce the weight of both cars and planes, particularly when used in the vehicle frame. This would lead to either reduced fuel costs, or the ability to carry an increased payload. Magnesium generally has limited ductility, which in the case of the current extruded tubes is even further reduced at the extrusion seams. These are locations where the material flow separates and rejoins during extrusion and are unavoidable when a hollow profile die is used. When the tubes were stressed in a circumferential direction, tube ruptures consistently occurred along the extrusion seams of the tubes. This led to the current project, an inquiry into the exact cause of failure at these locations. The creation of irregularities at the seams, such as precipitate dispersions, local texture changes, grain size changes and entrained material, is discussed. These irregularities are considered together with their roles in producing the failures. The results are summarized and the most fruitful directions for future work are outlined.
Authors: Toshiyuki Matsuno, Tokimasa Kawabata, Kenji Matsuda, Shigeharu Kamado, Yo Kojima, Susumu Ikeno
Abstract: The TEM observation was performed to investigate the precipitation hardening in Mg-Gd-Zr alloy. Both the β’ and the β” phase coexist in the specimen aged at 473K for 16h. In the specimen aged at 523K, the β’ phase which has base centered orthorhombic (bco) structure was observed at early stage during aging. The β’ phase has a globular shape and four atomic layer periodicity in the [1100]Mg. The β’ phase grew with increasing aging time mainly along the [0001]Mg and the [1100]Mg.

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