• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1048-1049
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• 2006

Rapidly solidified ribbon-consolidation processing was applied for preparation of high strength bulk Mg-Zn-Gd alloys. Mg alloys have been used in automotive and aerospace industries. Rapid solidification (RS) process is suitable for the development of high strength Mg alloys, because the process realizes grain-refinement, increase in homogeneity, and so on. Recently, several nanocrystalline Mg-Zn-Y alloys with high specific tensile strength and large elongation have been developed by rapidly solidified powder metallurgy (RS P/M) process. Mg-Zn-Y RS P/M alloys are characterized by long period ordered (LPO) structure and sub-micron fine grains. The both additions of rare earth elements and zinc remarkably improved the mechanical properties of RS Mg alloys. Mg-Zn-Gd alloy also forms LPO structure in -Mg matrix coherently, therefore, it is expected that the RS Mg-Zn-Gd alloys have excellent mechanical properties. In this study, we have developed high strength RS Mg-Zn-Gd alloys with LPO structure and nanometer-scale precipitates by RS ribbon-consolidation processing. $Mg_{97}Zn_1Gd_2$ and $Mg_{95.5}Zn_{1.5}Gd_3$ and $Mg_{94}Zn_2Gd_4$ bulk alloys exhibited high tensile yield strength (470 MPa and 525 MPa and 566 MPa) and large elongation (5.5% and 2.8% and 2.4%).

• Journal of Korea Foundry Society
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• v.7 no.4
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• pp.358-365
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• 1987

To investigate the grain refining mechanism of Al by the addition of Ti-B, the unidirectional solidifications of 99.9%Al and 99.7%Al were performed under the condition of varing the pouring temperature. The solidification modes of Al were studied by the cooling curve analyses, metallographic and microprobe examinations. The results were as follows: 1) Grains were most refined with an addition of 0.15wt.%Ti-0.021wt.%B but the grain size with 0.2wt.%Ti-0.028wt.%B was increased. 2) The grain size of 99.7wt.%Al was even more refined than that of 99.9wt.%Al with the same amount of Ti-B. 3) As the pouring temperature increased, the grain size of pure Al and an alloy with 0.lwt.%Ti-0.014wt.%B was increased. However, an alloy with 0.2wt.%Ti-0.028wt.%B did not show any effects of temperature. 4) TiC(Al-Ti) and (Al-Ti-C) were identified as nucleants for Al.

• Journal of Korea Foundry Society
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• v.21 no.6
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• pp.343-349
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• 2001

The effect of cooling rate on the solidification microstructure and segregation behavior of 7075 and 7050 aluminum alloy was investigated. Samples were solidified with cooling rates from 0.3 to $17^{\circ}K/sec$. Using the cooling curves of each sample, liquidus, eutectic and intermetallic reaction temperatures were estimated. The microstructures were characterized in terms of dendrite arm spacing and eutectic volume fraction. The segregation behavior of each alloying element of these alloys in various cooling rates was discussed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.4
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• pp.485-495
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• 2001

This paper presents a similarity solution for the directional casting of binary peritectic alloys in the presence of shrinkage-induced flow. The present model retains essential ingredients of alloy solidification, such as temperature-solute coupling, macrosegregation, solid-liquid property differences, and finite back diffusion in the primary phase. An algorithm for simultaneously determining the peritectic and liquidus positions is newly developed, which proves to be more efficient and stable than the existing scheme. Sample calculations are performed for both hypo- and hyper-peritectic compositions. The results show that the present analysis is capable of properly resolving the solidification characteristics of peritectic alloys so that it can be used for validating numerical models as a test solution.

• Applied Microscopy
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• v.45 no.2
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• pp.58-62
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• 2015

Formation of an icosahedral phase in the bulk glass forming $Ti_{40}Zr_{29}Be_{14}Cu_9Ni_8$ alloy during crystallization from amorphous phase and solidification from melt is investigated. The icosahedral phase with a size of 10 to 15 nm forms as a thermodynamically stable phase at intermediate temperature during the transformation from amorphous to crystalline phases such as Laves and ${\beta}$-(Ti-Zr) phases, indicating that the existence of the icosahedral cluster in the undercooled liquid. On the other hand, the icosahedral phase forms as a primary solidification phase even though the Laves phase is stable at high temperature, which is can be explained based on the high nucleation rate of icosahedral phase relative to that of competing crystalline Laves phase due to lower interfacial energy between icosahedral and liquid phases.

• Journal of Powder Materials
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• v.16 no.6
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• pp.438-441
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• 2009

Mg-Cu composites were successively fabricated using a combination of rapid solidification and extrusion processes. In addition, the microstructural variation of the composite was investigated by performing the extrusion repeatedly. It resulted that the composite formed an uniform and dense structure by the extrusion, and the microstructure became fine as the extrusion conducted repeatedly. The microstructural variation was known to be dependent on the number of extrusion and the area reduction ratio. The tensile strength was also measured as a function of the microstructural variation.

• Journal of Korea Foundry Society
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• v.11 no.1
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• pp.63-70
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• 1991

Aluminium alloy castings, which can be not only manufactured in larger geometrically complex shapes, but also show good mechanical properties in addition to light weight, have kept their potential use as structures in the field of automotives, industrial machines and aircrafts. The variations of eutectic Si size a great effect on the elongation, impact value, fracture toughness and fatigue crack propagation rate without changes in the tensile strength or yield strength. The cooling curves with the solidification rate between $1.4^{\circ}C\;/min$ and $19.1^{\circ}C\;/min$ were obtained. With the increase of solidification rate, DAS, eutectic Si size and grain size were all decreased, which enhanced the mechanical properties. The tensile strength and yield strength were the most greatly influenced by DAS, and the elongation and impact value by eutectic Si size.

• Journal of applied mathematics & informatics
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• v.12 no.1_2
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• pp.419-427
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• 2003

We have developed and analyzed numerically a simple ordinary differential equation for a mush. Numerical solutions illustrate that the solid fraction at the bottom of the mush increases and the depth of the mush decreases when convection increases. The results are consistent to those observed in experiments with aqueous solutions of ammonium chloride（Loper ＆ Roberts［11］, Chen & Chen［2］, Tait ＆ Jaupart［11］）and in experiments with lead-tin alloys（Hellawell etc.［6］）.

• Proceedings of the KWS Conference
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• v.43
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• pp.85-87
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• 2004

• Proceedings of the KWS Conference
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• 2003.11a
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• pp.98-100
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• 2003