Papers by Author: Young Sup Lee

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Authors: Y.S. Shin, Young Sup Lee, C.H. Lee
Abstract: The purpose of this study is to introduce and discuss flux laminated strip. Flux laminated strip can be used for air atmosphere brazing. The new product is fabricated by four processes: embossing of strip; multi bending of embossed strip; flux injection; and resizing of the material. This flux laminated strip exhibits similar melting characteristics to flux cored and flux coated alloys. The flux laminated strip eliminates the need for a separate fluxing operation that is typically needed when using bulk alloy. The product ensures the correct amount of flux during the brazing process and reduces the post-braze clean time. The ability to produce a quality joint while reducing the amount of pre-braze and post-braze operations make flux laminated strip an innovative Eco-braze-materials.
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Authors: Young Sup Lee, Cheol Ho Lim, C.H. Lee, K.W. Seo, Seung Y. Shin, Chang Hee Lee
Abstract: In this study, a diffusion bonding of aluminium alloy A6061 was preformed using an Ag-28Cu filler metal in order to conduct eutectic brazing. Melting mechanism was surveyed. Interface behaviors of the brazed joints were observed after brazing and T6 solution treatment. Also, tensile property of the brazed joints was examined. During diffusion bonding of Al6061 alloys with Ag-28Cu filler metal, eutectic melts were formed by eutectic reaction between Al6061 and Ag-28Cu filler metal. It was found that the reaction layer consist of two phases formed at the interface between AA6061 and Ag-28Cu filler metal. EPMA analysis revealed that two phases in the reaction layers consist of Ag-rich phase and Cu-rich phase. Tensile strength was 300 MPa after ageing treatment at 175°C.
2772
Authors: Jong Won Yoon, Young Sup Lee, Kyoung Don Lee, Ki Young Park
Abstract: 2 mm thick 6061-T6 aluminum alloy sheets were I square butt welded using 3kW Nd:YAG laser. Filler wires of 1 mm diameter, 5183A(Al-4wt.%Mg), 4043A(Al-5wt.%Si) and 4047A (Al-12wt.%Si) were used. The welds made with 4047A wire showed the lowest solidification cracking among the welds investigated. Abundant amount of Al-12wt.%Si eutectic which was observed at the grain boundaries of the 4047A wire feed welds was closely related with the reduced solidification cracking susceptibility. Yield and tensile strength, and formability of the welds made with 4047A wire were improved compared to the welds made with other filler wires, which is attributed to the reduced cracking susceptibility in the welds.
2591
Authors: Taek Kyun Jung, Hyouk Chon Kwon, Sung Chul Lim, Young Sup Lee, Mok Soon Kim
Abstract: We investigated about the effects of core material(Pure Al, Al3003) on extrudability such as the maximum extrusion ratio and the bonding strength of Copper Clad Aluminum(CCA) by indirect extrusion. As a results of this experiment, the maximum extrusion ratio of Cu/Al3003 was 38, which was larger than 21.39 of Cu/Al(Cu/pure Al). It was because that the difference of flow stress between copper as the sheath material and Al3003 as the core material was smaller than that of between copper and pure aluminum under the same extrusion temperature of 623K. The bonding strength gradually increased when the extrusion ratio increased, on the other hand, the bonding strength of Cu/Al3003 was higher than that of Cu/Al under same extrusion conditions. The diffusion layer thickness that affected bonding strength was not affected by the kind of core material, but it gradually increased when the extrusion ratio increased. It was thought that Cu/Al3003 had a more intimate diffusion layer than Cu/Al had because the extrusion pressure of Cu/Al3003 was higher than that of Cu/Al under the same extrusion conditions.
967
Authors: Cheol Ho Lim, Ki Tae Kim, Yong Hwan Kim, Dong Choul Cho, Young Sup Lee, C.H. Lee
Abstract: P-type Bi0.5Sb1.5Te3 compounds doped with 3wt% Te were fabricated by spark plasma sintering and their mechanical and thermoelectric properties were investigated. The sintered compounds with the bending strength of more than 50MPa and the figure-of-merit 2.9×10-3/K were obtained by controlling the mixing ratio of large powders (PL) and small powders (PS). Compared with the conventionally prepared single crystal thermoelectric materials, the bending strength was increased up to more than three times and the figure-of-merit Z was similar those of single crystals. It is expected that the mechanical properties could be improved by using hybrid powders without degradation of thermoelectric properties.
875
Authors: Young Sup Lee, C.H. Lee, Cheol Ho Lim, Dong Choul Cho, Seung Y. Shin
Abstract: A diffusion brazing of aluminium alloy A6061 was preformed using a Ag-28Cu insert to conduct eutectic brazing. Interface behaviors of the brazed joints were observed after brazing at 450-560°C. The tensile property of the brazed joints was also examined. During diffusion brazing of Al6061 alloys with Ag-28Cu insert, eutectic melts were formed by eutectic reaction between Al6061 and Ag-28Cu insert. It was found that the reaction layers composed of two phases were formed at the interface between Al6061 and Ag-28Cu insert. EPMA analysis revealed that two phases in the reaction layers consist of Ag-rich phase and Cu-rich phase. The tensile strength of the joints brazed at 560°C for 30min was 160 MPa.
173
Authors: Chung Hyo Lee, Young Sup Lee, Dong Choul Cho, Chang Hee Lee
Abstract: The process of Direct Bonding Copper (DBC) is performed by a spinel reaction between CuO and Al2O3. In order to develop DBC on alumina substrate with high bonding strength, alumina substrate was preformed as follows: Cu was sputter-deposited on alumina substrate. Sputter-Deposited Cu (SDC) on alumina substrate was oxidized at 673K for 30min in air atmosphere and then stabilized at 1273K for 30min in N2 gas atmosphere to improve bonding strtrength between preformed alumina substrate and SDC layer. Subsequently, the Cu-foil (300µm) was bonded on preformed-alumina substrate in N2 gas atmosphere at 1342~1345K. It was found that optimum condition of DBC on preformed-alumina substrate could be successfully obtained at 1345K for 30min. Consequently, bonding strength of DBC on alumina substrate was the high value of 80N/cm. Observation and analysis of microstructure for Cu sputtered DBC showed that reaction compounds such as CuAlO2 and CuAl2O4 approved to be formed in the vicinity of interface between Cu and alumina substrate.
677
Authors: Ki Tae Kim, Cheol Ho Lim, Yong Hwan Kim, Dong Choul Cho, Young Sup Lee, C.H. Lee
Abstract: P-type Bi0.5Sb1.5Te3 compounds doped with 3wt.% Te were fabricated by spark plasma sintering after mixing large powders(PL) and small powders(PS). We could obtained the highest figure of merit(Zc) of 2.89×10-3/K in sintered compound mixed to PL:PS=80:20. This resulted from the increase of orientation by large powders(PS) and the reduce of pores by small powders. The figure of merit(Zc) of the sintered compound using only small powders(PS) showed lower value of 2.67×10-3/K compared with that of sintered compound mixed to PL:PS=80:20 due to the increase of electrical resistivity.
646
Authors: Dong Choul Cho, Cheol Ho Lim, Ki Tae Kim, Seung Y. Shin, D.M. Lee, Young Sup Lee, C.H. Lee
Abstract: Thermoelectric properties of the spark plasma sintered n-type Bi2Te2.7Se0.3 compounds were characterized with the sintering temperature, time and hydrogen reduction process. The Seebeck coefficient, electrical resistivity and thermal conductivity were dependent on hydrogen reduction process as well as sintering temperature. The Seebeck coefficient and electrical resistivity decreased and thermal conductivity increased with reduction treatment and sintering temperature. The results suggest that the carrier density varies with the dissolved oxygen and Te vacancies generated during the pulverization process. The highest figure of merit of 3.11×10-3/K was obtained for the compounds spark plasma sintered at 460°C for 16min by using the reduced powders.
654
Authors: Young Sup Lee, Kyoung Won Seo, C.H. Lee, Cheol Ho Lim, C.H. Lee
Abstract: In this study, we examined brazeability of Al5052 alloys using a Ag-28Cu insert metal in vacuum condition. A high frequency induction-heating vacuum hot press was used for the brazing. Under a static pressure of 0.5 MPa and a vacuum of 5×10-5 Torr, the temperature of hot press was raised up to brazing temperature (480-590°C) at a speed of 10°C/min and held at the brazing temperature for various times. Interface behaviors of the brazed joints were observed after brazing at 480-590°C by optical microscopy and Electron Probe Micro Analyzer (EPMA). Also, bonding strength of the brazed joints was examined. During vacuum brazing of Al5052 alloys with Ag-28Cu insert metal, eutectic melts were formed by eutectic reaction between Al5052 and Ag-28Cu insert metal at about 490°C. It was found that reaction layers of two phases are formed at the interface between Al5052 and Ag-28Cu insert. EPMA analysis revealed that two phases in the reaction layers consist of Ag-rich phase and Cu-rich phase. The bonding strength of the joints increased with brazing temperature and time. The highest bonding strength was 141 MPa at 580°C, 10min.
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