PFC 법에 의한 광폭 Al-Ni 다결정 리본의 제조 및 응고특성

이상목,홍준표 ( Sang Mok Lee,Chun Pyo Hong ) 한국주조공학회 1995 한국주조공학회지 Vol.15 No.1

N/A Wide Al-Ni polycrystalline ribbons were produced continuously via the planar flow casting(PFC) process. The influence of the process variables on the ribbon geometry has been investigated. The empirical correlation t_c=0.835^(0.32)/V_s^(0.76) was proposed for the variation of ribbon thickness with melt flow reate and wheel velocity. The propagation rate(V) of the solid/liquid interface varies with the ribbon thickness(t), i.e. decreased with increasing the distance from the chilled surface of the ribbon, as V=9.16t^(-1). In accordance with the absolute stability criterion, the solid/liquid interface stability decreases as the solidification rate decreases toward the top surface of the ribbon, leading to the observed morphological degeneration, cellular to branched dendrite.

논문 : 응고 ; Al-Cu다결정 리본의 두께방향으로의 미세조직 천이기구

이상목 ( Sang Mok Lee ),홍준표 ( Chun Pyo Hong ) 대한금속재료학회 ( 구 대한금속학회 ) 1996 대한금속·재료학회지 Vol.34 No.11

Morphological characteristics of Al-4.3wt.%Cu and Al-15wt.%Cu ribbons spun by planar flow casting were analyzed using an optical microscope, SEM and TEM. The local solidification velocity within the Al-4.3wt.% Cu ribbon was found to be a function of ribbon thickness as V = 34.78 S-1. The absolute stability velocity of an Al-4.3wt.%Cu alloy was estimated as 2,460mm/s. Segregation free zone with the planar interface was developed from the bottom layer of the ribbon, where relevant solidification velocity was higher than the critical value of 2, 460mm/s. Following this zone, cellular/dendritic transitions occurred as the velocity decreased across the ribbon thickness. In the Al-15wt.%Cu ribbon, however, no segregation free zone was found and only cellular/dendritic region was developed due to its lower velocity compared to the absolute velocity for an Al-15wt.%Cu alloy throughout the entire ribbon thickness. Solidification sequences during ribbon formation were proposed for Al-Cu hypoeutetic alloy systems.

Al-Cu 다결정 리본의 응고거동에 미치는 휠조건의 영향

김주형,이상목,홍준표 ( Ju Hyung Kim,Sang Mok Lee,Chun Pyo Hong ) 한국주조공학회 1997 한국주조공학회지 Vol.17 No.3

N/A The effect of wheel surface condition on solidification behavior of Al-Cu ribbon was investigated in order to establish extreme levels of heat extraction. The condition of wheel surface was changed either by heating the wheel surface up to 200℃ or by coating boron nitride(BN) onto the rim of a wheel. Heating the wheel surface up to 200℃ improved the wetting behavior between the molten metal and the rotating wheel, leading to an increase in the ratio of columnar structure to the entire thickness of Al-4.3wt%Cu and Al-33.2wt%Cu ribbons. For Al-4.3wt%Cu ribbon, assuming one grain as a single heterogeneous nucleation event at the contact point, the nucleation density with the wheel surface heated to 200℃, was 4×10^6/㎟, and in the cases of BN coating with thin and thick layers, 10^5/㎟ and 5×10⁴/㎟, respectively. The largest cooling capacity of the wheel corresponded to the heated wheel surface, and as the thickness of BN coating layer increased, the cooling capacity of the wheel gradually decreased.

PFC 법에 있어서의 Al-Cu 다결정리본의 응고특성

이경구,이상목,홍준표 ( Kyung Ku Lee,Sang Mok Lee,Chun Pyo Hong ) 한국주조공학회 1995 한국주조공학회지 Vol.15 No.4

N/A Polycrystalline Al-Cu ribbons were produced by planar flow casting(PFC). Solidification behavior and microstructual changes of the ribbons have been investigated as a function of ribbon thickness and processing parameters. The solidification front velocity, V varies within the ribbon, decreasing with increasing the distance, S from the wheel-contact surface, as V=17.6S^(-1). In Al-4.5wt%Cu alloy, rapid decrease in solidification velocity toward the free surface causes a change in solidification morphology from planar to cellular, and finally, to dendritic. The length and inclination of columnar grains solidified with planar front were related to the wheel velocity. The transition from particulate degenerate eutectic structure to regular lamellar eutectic structure was observed to be caused by a difference of the relative growth velocites of α-Al and θ during solidification in the Al-Cu eutectic alloy.

반복 금형주조용 자동 금형냉각장치 개발 및 적용 1 : 용탕충진거동 및 응고해석

이영철,이상목,최정길,홍준표 ( Young Chul Lee,Sang Mok Lee,Jeong Kil Choi,Chun Pyo Hong ) 한국주조공학회 1998 한국주조공학회지 Vol.18 No.2

N/A A three dimensional simulation program based on the SOLA-VOF technique was developed for the modeling of mold filling and solidification sequences of the AC4B alloy in the cyclic permanent mold casting process. The geometries and mesh diagrams of the casting and the mold were automatically generated using a pre-processor based on the commercial Auto-CAD system. The solidification time of the casting and the temperature variation of the mold with cyclic casting were evaluated using the present scheme. The effects of the local water cooling of the metal mold on the cyclic casting process were also examined in order to control the temperature variation in the mold and to improve the soundness of the castings. The minimization of the casting cycle time was also confirmed by the present program for an improved productivity. It can be concluded that the present program can be used for obtaining the optimum casting parameters and the local cooling condition for obtaining sound castings without shrinkage defects in the cyclic mold casting process. (Received March 2, 1998)

반복 금형주조용 자동 금형냉각장치 개발 및 적용 2 : 실험적 검증

이상목,이영철,최정길,홍준표 ( Sang Mok Lee,Young Chul Lee,Jeong Kil Choi,Chun Pyo Hong ) 한국주조공학회 1998 한국주조공학회지 Vol.18 No.2

N/A The effects of water cooling channels in the metal mold on the cyclic casting process were examined experimentally in order to control the temperature variation in the mold and to improve the soundness of castings. An automatic control system for the water cooling channels was developed based on the computer simulation. Optimum cooling water can be supplied to maintain a quasi-steady state of the mold temperature during the cyclic casting process, leading to the prevention of hot spots and resultant casting defects. Various water cooling conditions were examined for obtaining better quality castings and reduced casting cycle time, and the results were compared with the computational results which was reported in paper I. It was found that the calculated results were in good agreement with those obtained experimentally. Microstructure and hardness variations were also investigated as a function of the distance from the casting center line. (Received March 2, 1998)

고 - 액 공존영역에서 교반후 가압에 의해 제조된 Al-7wt%Si 합금의 응고 특성

노동훈(Dong Hoon Rho),이상목(Sang Mok Lee),홍준표(Chun Pyo Hong) 한국주조공학회 1999 한국주조공학회지 Vol.19 No.2

N/A Fabrication of an Al-7wt%Si alloy was conducted by pressurization in the semi-solid state after mechanical stirring. Effects of the various process parameters on microstructure, macrostructure and mechanical properties of an Al-7wt%Si alloy ingot were investigated. The solidification structure and mechanical properties of the as-cast specimen were compared with the ones which were produced by conventional gravity casting and gravity casting after mechanical stirring. No solidification shrinkage was observed with an applied pressure over 50 MPa in this process. There was a less temperature difference between the center and the surface of the casting during squeeze casting after stirring, compared to the other casting methods. Higher cooling rate and finer solidification structure were also observed during squeeze casting after stirring. This is considered to be caused by the effective stirring and higher interfacial heat transfer behavior between mold and casting. As the stirring temperature decreased, the primary solid particle size and the aspect ratio of the particle gradually decreased. The tensile properties were improved with the decrease of the stirring temperature. With the decrease of the pouring and mold temperatures, the primary particle size decreased, leading to the better mechanical properties. As the pressurization temperature increased, the primary solid particle size gradually decreased. It is suggested that better quality casting can be fabricated by the pressurization in the semi-solid state after mechanical stirring. (Received December 3, 1998)

PFC 법에 의한 광폭 Sn 다결정리본의 제조

이상목,홍준표,명로훈 대한금속재료학회(대한금속학회) 1994 대한금속·재료학회지 Vol.32 No.10

Planar Flow Casting has been carried out so as to develop the continuous process which can produce the wide polycrystalline ribbons up to 50㎜ width with reliability. The material used in this investigation was tin for the sake of ease in processing. A series of experiments have been performed with 50㎜ width graphite nozzle, using argon gas to eject the molten tin onto a rotating steel substrate. The process conditions have been varied in order to determine the optimun casting parameters for the apparatus used. The basic relationships between the process parameters and ribbon geometry were exanined by measuring the thickness, surface roughness test, optical microscopy, SEM and XRD analysis. Polyscrystalline ribbons of several hundred ㎛ thick and 50㎜ wide have been cast continuously exceeding 30m in length for one batch procedure. The empirical relationship t.=8.785(Q^(0.17)/V^(0.84)) was proposed for the description of the dependence of ribbon thickness on melt flow rate and substrate velocity.

경사진 동판 위를 흐르는 Al-Cu 합금 용탕으로부터의 주상적 조직의 성장방향 편향에 관한 수치해석

이상목,홍준표,이성윤 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.5

A two-dimensional coupled cellular automaton-continuum model was developed to predict the solidification grain structures and the deflection behavior of columnar grains solidified in a flowing melt. Al-Cu alloys were solidified on an inclined Cu chill in order to investigate the deflection behavior of columnar grains in the upstream flow. The growth velocity of a dendrite was determined by the KGT model based on the calculated temperature and solute profiles around a dendrite tip during solidification. The effects of flow velocity and solute content on the deflection angle of the columnar grains were investigated through experiments, and the results were compared with computer simulations. It was found that the present model could predict the deflection behavior of the columnar grains solidified in a flowing melt.

연속주조 빌렛의 3 차원 열 및 유동해석

이상목,홍준표,박중길,이성윤 한국주조공학회 2000 한국주조공학회지 Vol.20 No.5

A three-dimensional model was developed in order to simulate heat and fluid flow of a continuous casting billet. The model was coded with the general-purpose CFD program FIDAP, using the finite element method. The present model consists of 2 individual calculation schemes, named model 1 and model 2. Mold region only was calculated to check the pouring stream through submerged nozzle with model 1. Entire region, which consists of mold, secondary cooling, radiation cooling was calculated to predict crater end position, temperature profile and solid shell profile(model 2). Standard k-A^ turbulence model has been applied to simulate the turbulent flow induced by submerged nozzle. Enthalpy method was adopted for the latent heat of solidification. Fluid flow in mushy zone was treated using variable viscosity approach. The more casting speed and superheat increased, the more metallurgical length increased. The shell thickness at the mold exit is proved to be mainly controlled by superheat by the present simulation. It may be concluded that the present model can be successfully applied far the prediction of heat and fluid flow behavior in the continuous casting process.