• 한국산업융합학회 논문집
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• 제4권1호
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• pp.3-9
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• 2001

Many products related to automobile and airplane have been manufactured by semi-solid process. There are many parameters in semi-solid process such as punch velocity, die temperature, and solid fraction of material. Among these parameters, solid fraction of material is one of the most important factors to determine quality of product. To obtain solid fraction of a certain semi-solid product is very necessary and useful for inspecting and analyzing the product. In this paper, image analysis program for microstructure by semi-solid forming process has been developed with the simple apparatus such as a personal computer and scanner, instead of expensive image analyzer.

• 한국주조공학회지
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• 제15권2호
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• pp.184-193
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• 1995

Effects of process parameters during thixocasting, such as solid volume fraction, mold temperature and extrusion ratio, on the mold filling behaviour and fluidity of Mg alloy(AZ91D) have been investigated. The semi-solid ingot held for 60 minutes at the semi-solid temperature range did not contain the equilibrium volume fraction of solid as expected from the phase diagram. Therefore, in order to obtain the desired solid fractions, and to suppress the exaggerated grain growth during heating, it was required to heat the ingot rapidly up to the temperature $10^{\circ}C$ higher than the semi-solid temperature suggested from the phase diagram for a specific volume fraction of solid. The experimental results show that mold filling behaviour and fluidity can be improved with the use of the higher mold temperature and the lower volume fraction of solid, but remain nearly unaffected by the change of extrusion ratio.

• 소성∙가공
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• 제8권4호
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• pp.399-406
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• 1999

It is more appropriate to treat that the semi-solid mixture as a single phase material that obeys incompressibility in the global sense and to analyze the liquid flow only locally than the approach based on compressible yield criteria. In the present study, a numerical algorithm of updating the solid volume fraction based on mixture theory has been developed. Finite element analysis of simple upsetting was carried out using the proposed algorithm to investigate the degree of macro-segregation according to friction conditions and compressive strain rates under the isothermal condition. The simulation results were compared to experimental results available in reference to test the validity of the currently proposed algorithm. Since the comparison results show a good agreement it is construed that the proposed algorithm can contribute to the development of numerical analysis of determining the solid volume fraction semi-solid processing.

• 한국주조공학회지
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• 제14권5호
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• pp.438-446
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• 1994

The effect of various thermomechanical treatments on the structure and rheological behaviour of Al-6.2wt%Si alloy in its solidification range were investigated using a Searle type high temperature viscometer. During continuous cooling, the viscosity increases gradually with increasing fraction of solidified alloy, until a critical fraction of solidified alloy is reached above which the viscosity sharply increases. The viscosity of the slurry, at a given volume fraction wolid, decreased with increasing shear rate. The size and morphology of primary solid particles during stirring is influenced strongly by shear rates, cooling rates, volume fraction and stirring time of solid. Morphological changes during stirring as a function of solid volume fractions, shear rate and processing time were also reported. In this study, the size of primary solid particles in these alloys consistently increases and the it`s aspect ratio decrease with the increase in fraction solid and decrease in shear rate. Crystal morphology changes from rosette type to spheroid type with the increase in shear rate and solid fraction.

• 대한기계학회논문집
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• 제15권2호
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• pp.584-595
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• 1991

In the direct rolling processes for the mushy state alloy, a mushy state material which simultaneously contains liquid-solid phase is obtained from the exit port of stirring apparatus with a given solid fraction. This solid fraction is dependent on the temperature of within the solid-liquid range which shows to be controlled accurately by the experimental conditions for a given stirring apparatus. Rolling conditions for fabrication the fine surface strip were obtained from direct rolling experiment with mushy state alloys of Sn-75%Pb and aluminum alloy. Influence of solid fraction, rolling speed and initial roller gap on the state of strip surface and solidified structure was observed. We proposed theoretical model for prediction of rolling force, and we compared calculation result and experimental value measured with load cell.

• 한국주조공학회지
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• 제10권4호
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• pp.309-315
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• 1990

Aluminum alloy matrix composites reinforced by SiC particles were prepared by rheocompocasting, a process which consists of the incoporation and distribution of reinforcement by stirring within a semi-solid alloy. When the volume fraction of SiCp and stirring speed were fixed, the dispersion of SiCp in Al-matrix alloy depended on stirring time and solid volume fraction in slurry. The results were as follows : 1) As a dispersed SiCp during stirring at $647^{\circ}C$ in 6063-Al alloy, SiC was better dispersed than that other temperature, where solid volume fraction was 43% in slurry. 2) When increased solid fraction in slurry, rate of dispersing SiC increased during stirring and porosities decreased in matrix alloy after casting. 3) Inspite of stirring with 800rpm, since solid particles of matrix alloy in slurry joined each other and occured joining growth, so that SiC was not dispersed into solid particle.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 춘계학술대회 논문집
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• pp.777-781
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• 1997

In this study, the effect of strain-rate and inital solid fraction on the deformation behaviour of semi-solid material is investigated, when semi-solid forging is performed by the process of closed-die compression using A356 alloy of which the above results can be practically applied for industrical purpose. In order to simulate densification in the deformation of semi-solid material, the semi-solid material is assumed to be composed of solid region following rigid visco-plastic material, the liquid region following Darcy's law for the liquid flow saturated in the interstitial space. Simulation results of closed-die compression and simple upsetting under different strain-rate and initial solid fraction are compared.

• 소성∙가공
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• 제6권4호
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• pp.338-345
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• 1997

The behaviour of alloys in the semi-solid state strongly depends on the imposed stress stage and on the morphology of the phase which can vary from dendritic to globular. To optimal net shape forging of semi-solid materials, it is important to investigate for material behaviour for variation of strain rate. Therefore, to investigate the effect of compression speed on deformation of aluminum alloy with globular microstructure, the compression test for semi-solid aluminum alloy with controlled solid fraction is perform by material test system which is attracted with furance. The behavior of semi-solid aluminum alloy were discussed for the various solid fraction and die speed. The material constants in stress-strain were are also proposed.

• International Journal of Precision Engineering and Manufacturing
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• 제4권2호
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• pp.49-56
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• 2003

As semi-solid forging (SSF) is compared with conventional casting such as gravity die-casting and squeeze casting, the product without inner defects can be obtained from semi-solid forming and globular microstructure as well. Generally, SSF consists of reheating, forging, and ejecting processes. In the reheating process, the materials are heated up to the temperature between the solidus and liquidus line at which the materials exists in the form of liquid-solid mixture. The process variables such as reheating time, reheating temperature, reheating holding time, and induction heating power has large effect on the quality of the reheated billets. It is difficult to consider all the variables at the same time for predicting the quality. In this paper, Taguchi method, regression analysis and neural network were applied to analyze the relationship between processing conditions and solid fraction. A356 alloy was used for the present study, and the learning data were extracted from the reheating experiments. Results by neural network were in good agreement with those by experiment. Polynominal regression analysis was formulated using the test data from neural network. Optimum processing condition was calculated to minimize the grain size and solid fraction standard deviation or to maximize the specimen temperature average. Discussion is given about reheating process of row material and results are presented with regard to accurate process variables fur proper solid fraction, specimen temperature and grain size.

• 소성∙가공
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• 제7권4호
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• pp.364-374
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• 1998

It is the objective of this study to analyze the effect of various process variables on the quality of extruded product and extrusion force for semi-solid extrusion of Al2024 with solid phase structure of globular type by the finite element method. Process variables are initial solid fraction, ram speed, semi-angle of die, and reduction in area. The results of experiment are compared with those of simulation in order to verify the usefulness of the developed finite element program. The flow and deformation of semi-solid alloy are analyzed by coupling by coupling the deformation of porous skeleton and the flow of liquid phase. It is also assumed that initial solid fraction is homogeneous.