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Mg-5wt%Al-0.6wt%Zr 합금의 용탕단조시 주조결함의 형성 및 방지
황영하,허승호,홍준표 ( Young Ha Hwang,Seung Ho Huh,Chun Pyo Hong ) 한국주조공학회 1998 한국주조공학회지 Vol.18 No.3
N/A The squeeze casting of a Mg-5wt%Al-0.6wt%Zr alloy was carried out to investigate the conditions for the formation and the prevention of macrodefects, such as macrosegregation and shrinkage defects. The effects of the process parameters, the applied pressure, the die temperature, and the pouring temperature on the formation of macrodefcts were investigated in correlation with the evolution of macrostructure. Three types of macrodefects were found; macrosegregation only, shrinkage defects only, both macrosegregation and shrinkage defects. It was found that the pouring temperature, the die temperature, and the applied pressure are closely related to the formation of macrodefects. Sound castings without macrosegregation and shrinkage defects can be obtained under the conditions of 80 MPa < P < 110 MPa, 730˚C < Tp < 760˚C, and 180˚C < Tp < 250˚C. (Received April 15, 1998)
열분석법에 의한 Mg-8.5Li-4.5Al합금의 시효거동 연구
김영우,황영하,박태원,김도향,홍준표 ( Y . W . Kim,Y . H . Hwang,T . W . Park,D . H . Kim,C . P . Hong ) 한국열처리공학회 1997 熱處理工學會誌 Vol.10 No.4
Precipitation and strengthening mechanisms in squeeze cast Mg-8.5wt%Li-4.5wt%Al have been investigated by differential scanning calorimetry(DSC), scanning electron microscopy(SEM), in-situ and ex-situ X-ray diffraction analysis and hardness measurement. Special emphasis was placed on the investigation of the precipitation behavior by the DSC technique. Microstructural and calorimetric analysis showed that θ and δ precipitates in the b.c.c. β phase matrix, forming two exothermic peaks at the temperature ranges of 130℃∼180℃ and 236℃∼280℃. θ and δ dissolve into the matrix forming an endothermic peak at the temperature range of 280℃∼352℃. The as-cast microstructure consists of α, β and δ. Peak strength was obtained after aging for 1 hour at 50℃. The aging time required for the peak strength decreased as the aging temperature increases. The hardness decrease during overaging was due to the coarsening of θ precipitates. Microhardness measurement showed that variation of the hardness of β matrix was more pronounced than that of the α phase, indicating that the β phase is more responsible for the strengthening of the Mg-8.5wt%Li-4.5wt%Al alloy.
한창화,황영하,김영우,김도향,홍준표 ( Chang Hwa Han,Yong Ha Hwang,Yong Woo Kim,Do Hyang Kim,Chun Pyo Hong ) 한국주조공학회 1997 한국주조공학회지 Vol.17 No.3
N/A Fabrication of high strength Mg-Li-Al alloys by squeeze casting was established by the stabilization of melt and mold temperatures, applied pressure and the refining method. The entrapment of inclusions during pouring was prevented using 30ppi alumina foam filter. The as-cast microstructure consists of a mixture of α and β phases including AlLi and MgLi₂Al particles, which are distributed in the β matrix. The grain sizes of gravity and squeeze casting alloys were 288㎛ and 207㎛ respectively. The addition of Al in Mg-Li alloys promoted the formation of second phase particles, which were adjusted to optimize the properties of Mg-Li-Al alloys. The Mg-10wt%Li-5wt%Al alloy after heat treatment at 350℃ for 1 hour showed the maximum hardness value. This is due to the facts that the amounts of α and β phases and their distributions are dependent upon the solution treatment temperature, and that the amounts of AlLi and MgLi₂Al particles are dependent upon the Al content.
김송희,윤여범,황영화,최창우,홍준표,이응조,Kim, Song-Hui,Yun, Yeo-Beom,Hwang, Yeong-Hwa,Choe, Chang-U,Hong, Jun-Pyo,Lee, Eung-Jo 한국재료학회 1993 한국재료학회지 Vol.3 No.3
High strength and fracture toughness of Al-Li-Cu alloy(2090 Al alloy) have been achieved by the improvement of melting and casting, extrusion and heat treatment techniques. To establish the sucessful process for semi-industrial scale ingot(20Kg) the following areas have been investigated: (1) Improvement of melting and casting techniques for ingot by introducing atmospheric modifications, vacuum and rotary degassing, and deslagging. (2) The effect of heat treatment on mechanical properties (3) Mechanical characterization by tensile test, fracture toughness test and fatigue crack propagation test. High mechanical properties were found to be intimately related with ingot soundness. Tensile strength of final products varied from 534MPa to 566MPa in peak aged condition while elongation/ductility ranged from 9.0% to 11.9%. From the fracture toughness test with using compact tensile specimen, plane strain fracture toughness($K_{Ic}$) appeared to be 39MPa${\surd}$m in peak aged condition and 23MPa${\surd}$ m in underaged condition. When load ratios of 0.1, 0.3 and 0.5 were given ${\Delta}K_{th}$ was 6.0MPa${\surd}$ m, 5.3MPa${\surd}$ m and 4.3MPa${\surd}$ m respectively. 용해와 주조, 압출과 열처리 기술의개선으로 고강도, 고파괴인성의 AI-Li-Cu 합금(2090 AI합금)을 제조하였다. 또한 준 산업용 규모(20kg)의 잉고트 제조공정을 확립하기 위해서 (1)선 (2)기계적 성질들에 미치는 열처리 영향 (3) 인장시험, 파괴인성 시험($K_{Ic}$) 및 피로균열 전파시계를 갖고 있으며 최종 제품의 인장강도는 최대시효 조건에서 534MPa부터 566MPa이었고 연신율은 9%에서 11.9%정도였다. C-T 시편을 이용한 파괴인성 시험 결과 최대시효 조건에서 평면변형 파괴인성 ($K_{Ic}$)값은 39MPa$\surd$m였고 미시효 조건에서는 23MPa$\surd$m였다. 또한 0.1, 0.3, 0.5의 하중비에서 피로균열 전파시험을 행하였을때 임계응력 확대계수(${\Delta}K_{th}$)는 각각 6.0, 5.3, 4.3 MPa$\surd$m이었다.
오상섭(Sang Sub Oh),황영하(Young Ha Hwang),김도향(Do Hyang Kim),홍준표(Chun Pyo Hong),박익민(Ik Min Park) 한국주조공학회 1999 한국주조공학회지 Vol.19 No.1
N/A Microstructural characteristics and strengthening behavior in Mg-5wt%Zn-0.6wtZr alloys have been investigated by a combination of optical, secondary electron and transmission electron microscopy, differential thermal analysis, and hardness and tensile, creep property measurements. The result have been compared with those of Mg-5wt%Zn alloys. The as-squeeze cast microstructure consisted of dendrite α-Mg, interdendrite or intergranular Mg_7Zn₃ and fine dispersoids of ZnZr₂. The size of secondary solidification phases in Mg-5wt%Zn-0.6wtZr alloys was significantly smaller than that of the Mg-5wt%Zn alloys due to the existence of fine dispersoid of ZnZr₂ which also effected the refinement of grain size. TEM study showed that the main cause of age hardening is formation of fine rodlike β₁` precipitates as well as fine ZnZr₂ dispersoids. Due to the observed microstructural characteristics mechanical propeties of Mg-5wt%Zn-0.6wtZr alloys was found to be superior to those of Mg-5wt%Zn alloys. (Received June 22, 1998)
경제 · 생활권 광역화에 따른 농어촌 경제 활성화 방안 (2/2차연도)
이동필(Dong-phil Lee),황의식(Eui-sik Hwang),송미령(Mee-ryong Song),김정섭(Jeong-seop Kim),홍준표(Jun-pyo Hong),김영단(Young-dan Kim),김광수(Kwang-soo Kim),김선배,홍진기,정강환,박천수 한국농촌경제연구원 2010 한국농촌경제연구원 기본연구보고서 Vol.- No.-
The purpose of this study is to suggest strategies how to stimulate the rural economy under the current mega-regionalization of economy and lifestyle in rural areas. We have five specific research topics in this study. First, we will investigate the existing state of mega-regionalization in rural areas. Second, we will analyze a positive (or negative) impact of mega-regionalization depending on rural areas" conditions. Third, we will examine case studies relating mega-regionalization and derive political implications. Fourth, we will analyze Korean governmental policies relating megaregionalization. Last, we will derive how to revitalize rural areas under the context of mega-regionalization. The findings of these research topics are provided as the following. First, an investigation of the existing state of mega-regionalization in rural areas led us to a conclusion that rural areas need to adopt regional development plan depending on their geographic and economic situations. Second, agro-food nurturing policies need to include two facets: differentiation and cooperation. Differentiation is to focus quality of agricultural products yielded in a small area. Cooperation is to develop mega-region"s brand through which neighboring areas should cooperate with. Third, it is required to revise industry-location policies in rural areas. A future agro-engineering complex needs to connect diverse industry complexes over rural areas in order to foster regional industry. Korean government should consider a regional development plan to revitalize rural areas such as a revised blanket subsidies and a so-called rural areas" industry development plan to reflect regional conditions.