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金完哲,金圭石 홍익대학교 산업기술연구소 2006 産業技術 Vol.16 No.-
In this study the effects of Ca addition on the rollability, microstructures and tensile properties of hot rolled Mg alloys were evaluated. In Ca containing alloys, reduction ratio and preheating temperature are the most important variables to make good sheet without any crack. The number and length of side crack increased with increasing Ca content. With increasing the reduction ratio per pass and decreasing the preheating temperature, crack initiates easily at the side. The dendritic grains were changed to fine equiaxed grains through hot rolling by dynamic recrystallization. The Al_(2)Ca Precipitates which were segregated to grain boundaries during solidification were rearranged parallel to the rolling direction. The tensile properties of hot-rolled Mg Alloys were decreased slightly by addition of Ca.
급냉응고된 Mg-9Al-xCa 합금의 시효특성에 관한 연구
金完哲,朴祉河 홍익대학교 산업기술연구소 1999 産業技術 Vol.9 No.-
Mg-Al-Si-Ca alloys were fabricated into the ribbons by rapid solidification using a single-roll melt spinner. The time and temperature effect on age-hardening was investigated for the ribbons with varying Ca contents of 1, 3, 6 and 10 wt%. The behavior of precipitates, phase transitions, and mechanical properties were examined by measurements of micro-hardness, XRD analysis, and transmission electron microscopy. For the case of 1 hour's isochronal heat treatment, the temperature of 200℃ gave the most significant age hardening effect and the increase in Ca content caused enhanced hardening. In the aging treatment at 200℃, the hardness decreased with the increase in aging time from 1 up to 81 hour. The microstructural analysis for Ca-added sample showed uniformly distributed compounds of Al_4Ca and Al_2Ca, forming coherent precipitates with matrix. When the alloy contains more Ca than the solubility limit, the excess Ca precipitates as Mg_2Ca and an increased hardness is observed.
기계적 합금화에 의한 급속냉각된 Al 분말의 조직과 기계적성질의 개선
金完哲 홍익대학교 산업기술연구소 1996 産業技術 Vol.6 No.-
Severe working of splats produced a very fine grain size and substructural strengthening. The dispersed particles were spherical and much finer then those obtained by conventional SAP. MA-AI splats extruded bars had the recrystallized grains when isothermally aged for 100 hours at 450℃. At higher temperature, hower, only the Al_2O_3 patricles pinned the grain boundaries. Accordingly grain size become smaller and grain boundary sliding was retarded, providing a superior high temperature hardness as the amount of Al_2O_3 increased.
급속 냉각한 Al-5Cr-2Zr 합금의 시효경화에 미치는 기계적 합금화 처리효과
金完哲 홍익대학교 산업기술연구소 1994 産業技術 Vol.4 No.-
The microstructual refinement process of Al - 5Cr - 2Zr alloys mechanical alloying 30h can be divided in five stages : initial stage welding predominance stage spherical partical formation stage convolution welding predominance stage and steady state. The rate of structural of aluminium splats was roughly logarithmic with processing time : ∈ = k/0.78 In (1+0.028t) The age hadening in rapidly solidified Al - 5Cr - 2Zr alloys is ascribed to the coherency and dispersion hardening Coherency hardening is occurred by matastable cubic Al_3Zr precipitates in Al - Cr - Zr alloys. Dispersion hardening after machanical alloying is attributed to the finely-dispersed Al_2O_3 and Al_4C_3 in Al - 5Cr - 2Zr alloys.
金完哲 弘益大學校 産業技術硏究所 2004 産業技術 Vol.14 No.-
The effects of homogenization on hot rolling properties of gravity cast AZ31-xCa (x=0~2.0wt.%) alloys were evaluated by examination of surface and microstructures of sheets. The side cracking during hot rolling was decreased by homogenization by the elimination of local inhomogeneity and dissolution of brittle precipitate into matrix. The coarse grains in raw materials were changed to fine grains with the average particle size of 5~10μm by the dynamic recrystallization during repeated hot rolling . A deformation twinning was more favorably formed in the hot-rolled sheets after homogenization. It is considered that the grains grow and the precipitates are solved into the matrix during homogenization heat treatment, which results in increasing the possibility of formation of deformation twinning during hot rolling.
프린지 필드에 의해 구동되는 하이브리드형 네마틱 액정 셀에서 러빙방향에 따른 전기광학 특성
김완철,안명환,이승희 한국전기전자재료학회 2004 전기전자재료학회논문지 Vol.17 No.1
We have studied the influence of rubbing directions on electro-optic characteristics of the fringe field driven hybrid aligned nematic liquid crystal (LC) cell by computer simulation. When a LC with positive dielectric anisotropy is used, the results show that the driving voltage and transmittance decreases as the rubbing direction with respect to horizontal electric field direction increases. The reason for decrease in light transmission is the increase of tilt angle on the center of common electrode. In this paper, we have studied how the rubbing angle effects on the transmittance of the cell by investigating a distribution of electric field and LC director.
급냉 응고된 Mg-Al-Si 합금의 미세조직에 관한 연구
金完哲 홍익대학교 산업기술연구소 2002 産業技術 Vol.12 No.-
Effects of Si and Ca addition on the microstructural refinement of Mg based alloys were studied. The melt-spun ribbons were aged at the temperature between 100 and 400℃ for 1h. The effect of additional elements on microstructure and precipitation hardening after heat treatment was investigated using TEM, XRD and a Vickers microhardness tester. Age hardening occurred after aging at 200℃ in the Mg-Al-Si-Ca alloys mainly due to the formation of Al2Ca and Mg2Ca Phase, whereas in the Mg-Zn-Ca alloys mostly due to the distribution of Mg2Ca. TEM results revealed that spherical Al2Ca precipitate had the coherent interface with the matrix. Considering the total amount of additional elements, Mg-Zn-Ca alloy showed higher hardness and smaller size of precipitates than Mg-Al-Si-Ca alloys. Mg-6Zn-5Ca alloys showed the maximum value of age hardening peak after aging at 200℃for 1h.