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주조용 B390 알루미늄합금의 조직과 기계적 성질에 대한 각종 주조법의 영향
한요섭,이호인,김성수,김정식 ( Yo Sub Han,Ho In Lee,Sung Su Kim,Jung Sik Kim ) 한국주조공학회 1993 한국주조공학회지 Vol.13 No.3
N/A The effects of casting processes-direct and indirect squeeze casting, permanent mold casting and die casting on the microstructure and mechanical properties were studied for the hypereutectic B390 aluminium alloy. The effects of T5 and T6 heat treatment were also examined. The direct and indirect squeeze casting showed no casting defects such as porosity and shrinkage were observed in permanent mold castings and die castings. The primary silicon phase was refined and homogeneously distributed in the order of indirect squeeze casting, deicasting, direct squeeze casting and permanent mold casting. Depletion of primary silicon phase in die casting surface was disappeared in indirect squeeze casting. Tensile strength of cast and heat treated specimens were increased in the order of direct squeeze casting, permanent mold casting, indirect squeeze casting and die casting. Hardness of indirect squeeze castings was larger than that of other castings. As indirect squeeze casting of B390 aluminium alloy, the time of T6 heat treatment to achieve high strength can be reduced.
고강도 황동 , 알루미늄 청동 및 인청동합금의 용탕단조 조직과 기계적 성질에 관한 연구
한요섭(Yo Sub Han),이호인(Ho In Lee) 한국주조공학회 1999 한국주조공학회지 Vol.19 No.6
The microstructures and mechanical properties of high strength yellow brass, Al bronze and Sn bronze alloys fabricated by gravity die casting and squeeze casting were investigated. A rapid cooling of casting was enhanced by pressure applied during solidification of Cu alloys, the cooling rate of casting was more great for high strength yellow brass alloy than other Cu alloys. Grain size and phases of the squeeze cast products become refined to 1/2 level compared to gravity die castings. Squeeze cast Al bronze and high strength yellow brass has about 10-20% higher yield and tensile strength and slighter decreased or nearly same elongation, compared to gravity die cast ones. Sn bronze has nearly same strength and hardness, but shows increased in elongation, compared to gravity die cast ones. (Received November 1, 1999)
AlSi7Mg 알루미늄 합금의 초정 구형화에 대한 주조조건의 영향
한요섭 ( Yo Sub Han ),이호인 ( Ho In Lee ),이재철 ( Jae Chul Lee ) 한국주조공학회 2003 한국주조공학회지 Vol.23 No.1
N/A Semisolid forming requires alloys with non-dendritic microstructure of the thixotropy. Recently, low pouring temperture method without stirring, i.e. liquidus casting has been found out new fabrication method of the semisolid metals. Effects of melt superheat and mold conditions on the globulization of primary Al of AlSi_7Mg alloy were investigated in gravity casting process without stirring. The microstructures of primary Al as function of melt superheat and mold temperature show globular, rosette and dendritic shapes. The conditions for globular microstructure of primary Al were low melt superheat < 35 K and low mold temperature < 500 K. The thermal conditions for globular microstructure of primary Al were undercooled melt at early solidification stages and slow cooling < 0.6 K/s. It was found that the initial microstructure was maintained throughout the solidification and the globules of primary Al can be obtained by high nucleation of fine and spherical nuclei due to enhanced undercooling of melt.
유승목,한요섭,이호인,홍준표 ( Seung Mok Yoo,Yo Sub Han,Ho In Lee,Chun Pyo Hong ) 한국주조공학회 1990 한국주조공학회지 Vol.10 No.6
N/A A basic heat flow model has been developed to estimate the heat transfer coefficient at the casting/mold interface during squeeze casting. Based on the measured temperature profiles in squeeze casting of Al-4.5%Si alloy, heat transfer coefficients which vary with time were calculated by numerical method. The influences of the load and the amount of fraction solid on the heat transfer coefficient have also been studied. Using the calculated heat transfer coefficient two dimensional solidification analysis in the squeeze casting process was carried out by the finite difference method, and the results were in good agreement with the experiments. It may be concluded that heat flow analysis in the squeeze casting process with accurate heat transfer coefficient at the casting /mold interface is important for a proper design of cooling in die and finally for improving productivity and die life as well.
김진수,안재영,한요섭,이호인,홍준표 ( Jin Soo Kim,Jae Young Ahn,Yo Sub Han,Ho In Lee,Chun Pyo Hong ) 한국주조공학회 1994 한국주조공학회지 Vol.14 No.3
N/A Research in heat transfer and solidification commonly involves experimentation and mathematical modeling with associated numerical analysis and computation. Inverse problems in heat transfer are part of this paradigm. During the solidification of metal casting, an interfacial heat transfer resistance exists at the boundary between the casting and the mold, and this heat transfer resistance usually varies with time. In the case of the squeeze casting the contact heat transfer resistance is decreased by pressure and ideal contact is almost accomplished. In the present work, heat transfer coefficient, which is inverse value of the heat transfer resistance, was used for convenience. A numerical technique, Non-Linear Estimation has been adopted for calculation of the casting/mold interfacial heat transfer coefficient during the squeeze casting process. In this method, the measured temperature data from experiment were used. The computational results were applied to the analysis of heat transfer and solidification.
용탕단조 Al-Cu-Si-Mg 합금의 열처리시 제2응고상의 분해거동
김유찬,김도향,한요섭,이호인 ( Yu Chan Kim,Do Hyang Kim,Yo Sub Han,Ho In Lee ) 한국주조공학회 1997 한국주조공학회지 Vol.17 No.6
N/A The dissolution behavior of secondary solidification phases in squeeze cast Al-3.9wt%Cu-1.5wt%Si-1.0wt%Mg has been studied using a combination of optical microscope, image analyzer, scanning electron microscope(SEM), energy dispersive spectrometer(EDS), X-ray diffractometer(XRD) and differential thermal analyzer (DTA). Special emphasis was placed on the investigation of the effects of the nonequilibrium heat treatment on the dissolution of the second solidification phases. Ascast microstructure consisted of primary solidification product of α-Al and secondary solidification products of Al₂Cu, Mg₂Si and Al₂CuMg. Equilibrium and non-equilibrium solution treatments were carried out at the temperatures of 495˚C, 502˚C and 515˚C for 3 to 5 hours. The amount of the dissolved secondary phases increased with increasing solution treatment temperature, for example, area fractions of Al₂Cu, Mg₂Si and Al₂CuMg were approximately 0%, 1.6% and 4.2% after solution treatment at 495˚C for 5 hours, and were approximately 0%, 0.36% and 2% after solution treatment at 515˚C for 5hours. The best combination of tensile properties was obtained when the as-cast alloy was solution treated at 515˚C for 3hours followed by aging at 180˚C for 10 hours. Detailed DTA and TEM study showed that the strengthening behavior during aging was due to enhanced precipitation of the platelet type fine θ` phase. (Received August 23, 1997)
Finite-state 오토마타로부터 짧은 정규 표현식을 구하기
안재희(Jae-Hee Ahn),한요섭(Yo-Sub Han) 한국정보과학회 2008 한국정보과학회 학술발표논문집 Vol.35 No.2
State 제거법은 주어진 finite-state 오토마타로부터 정규 표현식을 구하는 매우 직관적이며 구현이 쉬운 효율적 방법이다. 이 방법의 한 가지 특성은 state 제거 순서에 따라 같은 오토마타(즉 같은 정규 언어)에 대해 길이가 다른 정규 표현식이 만들어진다는 점이다. 우리는 주어진 오토마타의 구조적 특성을 살펴보고 이를 이용해 state 제거 법을 통한 짧은 정규 표현식을 구하는 알고리즘을 개발하고 이를 구현한다. 좋은 state 제거 순서를 찾기 위해 bridge state를 정의하고 이를 이용한 vertical chopping, 오토마타 내 state의 독립된 그룹을 찾아내는 horizontal chopping 그리고 각 state의 transition 복잡도를 바탕으로 하는 state weight 이 세 가지 state 제거 방법을 이용한다. 이 세 가지 방법은 개별적으로 적용되었을 때 보다는 서로 함께 사용될 때 더 나은 state 제거 순서를 찾을 수 있다.