• 한국주조공학회지
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• 제21권4호
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• pp.246-252
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• 2001

Variation in the microstructure of Mg-5%Al semi-solid slurry during isothermal heating was investigated in relation to initial microstructure, holding time, and holding temperature. Specimens with three different initial microstructures were isothermally heated. Dendritic structure in as-cast ingot was decomposed into solid globules in the semi-solid slurry during isothermal holding, while in the recrystallized specimens prepared by extrusion or rolling the size of solid particles was continuously increased during the heating. Effects of mold temperature and liquid fraction of slurry on the mold filling ability were also studied. Very thin section (0.4 mm) could be successfully filled up to 50 mm by 60% liquid slurry when the mold was heated to $600^{\circ}C$.

• 한국정밀공학회지
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• 제14권9호
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• pp.45-51
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• 1997

For semi-solid forging, it is necessarily required to prepare a workpiece with globular microstructure. Among several processes to obtain golbular microstructure, SIMA process is very simple and advantageous with respect to equipment. This paper presents the influence of effective strain on the globularization with aluminium 2024 alloy in cold working stage by SIMA process. Upsetting and forward extrusion are tested for cold working and induction heating is also carried out for reheating to obtain golbular microstructure. Microstructure is observed with an optical microscope. And finite element simulations to obtain effective strain in cold working stage are performed by using commercial finite element code, DEFORM.

• 한국주조공학회지
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• 제29권5호
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• pp.213-219
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• 2009

Optimum conditions for production of semi-solid Al-Zn-Mg alloy billets was carried out by the Taguchi design method. And, Al-Zn-Mg alloy billets contained Sc (free, 0.1 and 0.3 mass %) were fabricated at optimum conditions. Evolution of microstructure in semi-solid state was investigated through various liquid fractions, holding times and holding temperatures. The Al-Zn-Mg alloy billets reheated at $615^{\circ}C$ during 30min are grain growth and it was fractured due to increasing liquid fraction before quenching. And, during reheating up to $600^{\circ}C$, grain growth of Al-Zn-Mg alloy billets contained Sc (0.1 and 0.3 mass %) was not occurred in comparison with those of Al-Zn-Mg alloy without Sc. It was thought that $Al_3Sc$ phases have a pinning effect in grain boundary and Sc content of 0.1 mass% is able to inhibit grain growth effectively through reheating process.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2001년도 추계 학술발표강연 및 논문개요집
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• pp.113-113
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• 2001

• 한국주조공학회지
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• 제37권2호
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• pp.38-44
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• 2017

Given that the conventional extrusion of high-strength Al alloys such as 7075 aluminum alloys is difficult due to their very low extrudability as compared to that of 6061 aluminum alloys, thixo-extrusion can be used to obtain a high-strength material easily at a lower extrusion pressure as compared to conventional extrusion. In this study, hot- and thixo-extruded 7075 aluminum alloys are prepared by a vertical forward extrusion process and their microstructures, hardness levels, and compressive properties are investigated. Hot-extruded alloy bars are assessed to obtain a microstructure elongated in the extrusion direction, whereas with thixo-extruded alloy bars, it was possible to obtain a microstructure having fine and equiaxed grains by dynamic recrystallization. The resulting isotropy and improved formability at the hot deformation temperature of the thixo-extruded alloy were attributed to the fine and equiaxed grains formed by the thixo-extrusion process.

• 열처리공학회지
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• 제26권4호
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• pp.165-172
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• 2013

In the present study, the microstructure and solution treatment response of Al-Zn-Mg alloys bars by thixo-extrusion was investigated. The alloy bars were solution treated at 400, 430, 460 and $490^{\circ}C$ for various times. In order to examine the microstructures and phase analysis of the samples after solution treatment, it was performed by optical and scanning electron microscopy. And, Vickers hardness and electrical conductivity was measured on the solution treated samples for each condition to investigate the solution treatment response of extruded bars during solution treatment. The results show that the optimum solution heat treatment conditions of thixo-extruded Al-Zn-Mg alloy for minimization of the grain growth and degradation promotion of the second phase is a temperature of $460^{\circ}C$ and holding time of 0.5 to 2 h.

• 한국주조공학회지
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• 제31권6호
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• pp.347-353
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• 2011

There is thixo-extrusion to form high strength aluminum alloy. But, it is a problem that grains become grain coarsening during reheating process because the alloy was exposed at high temperature. In order to solve grain growth during reheating process, calcium was added in Al-Zn-Mg alloys. Primary a grain sizes of semi-solid Al-Zn-Mg-(0, 0.4, 0.6 and 0.9, wt.%)Ca were measured with image analyzer after reheating. Measured primary a grain sizes were applied to LSW(Lifshitz-Slyozov and Wagner) equation to check the effect of Ca on grain coarsening. Coarsening rate constant K values of semi-solid Al-Zn-Mg-(0, 0.4, 0.6 and 0.9, wt.%)Ca alloys were $371\;mm^3s^{-1}$, $247\;mm^3s^{-1}$, $198\;mm^3s^{-1}$ and $166 mm^3s^{-1}$, respectively. As increasing calcium content, K value decreased which means grains are refined. Also, grains of calcium addition were more spherical than that of calcium free.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2001년도 추계학술대회(한국공작기계학회)
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• pp.387-392
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• 2001

Fused deposition(FD) modeling by Stratasys Inc., is one of the material deposition subfamilies of solid freeform fabrication(SFF) technologies. In this process, build material in the form of a flexible filament, is heated to a semi-liquid state and extruded from a robotically controlled deposition head onto a fixtureless table in a temperature controlled environment. The position of nozzle is computer controlled relative to the base, which allows geometric complex models to be made to precise dimensions. FDM provide what the part was directly tested by the worker. It provide believable data. This study is experiment on surface roughness of part at FDM

• 한국식품과학회지
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• 제27권4호
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• pp.582-592
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• 1995

옥수수전분과 찰옥수수전분을 사용하여 중간 수분계의 수분함량으로 반죽을 제조하고 수분함량과 가열온도, 가열시간에 따른 전분 반죽의 물성 변화와 호화양상을 밝혀보고자 하였다. 이를 위하여 먼저 전분반죽과 같은 반고체(semi-solid) 물질의 물성을 측정할 수 있는 Extrusion Capillary Viscometer(ECV)를 자체 제작하였다. ECV를 사용하여 수분함량 $36{\sim}52%$ 범위로 제조된 옥수수전분과 찰옥수수전분 반죽의 물성측정 시 반죽의 열전달 특성은 가열온도 $60{\sim}100^{\circ}C$ 범위에서 수분함량이 36%에서 52%로 증가할수록 반죽의 중심온도가 원하는 가열온도에 도달하는데 걸리는 시간이 220초에서 140초로 크게 단축되었다. 가열 후 ECV로 물성을 측정한 결과, 수분함량과 가열온도의 모든 범위에서 반죽은 의가소성 유체의 흐름 특성을 나타내었다. 동일한 전단속도에서는 반죽 수분함량이 증가할수록 전단응력과 전단점도가 전체적으로 감소하여 수분함량 증가에 따른 반죽의 유동성(flowability) 증가 영향이 매우 큰 것으로 나타났다. 그러나 44% 이상의 동일 수분함량 내에서는 $80^{\circ}C$ 이상의 가열온도부터는 동일한 전단속도에서 $80^{\circ}C$ 이하로 가열한 반죽에 비해 전단응력과 전단점도가 증가하는 경향을 보여 주었다. 반죽의 점도에 미치는 수분함량의 영향은 수분함량이 증가할수록 반죽의 유동성의 크기가 증가하여 전체적으로 전단응력이나 점도가 감소하는 것으로 나타나지만, 가열온도가 호화온도 이상인 $80^{\circ}C$부터는 전분호화에 의한 점도 증가에 의하여 수분함량에 따른 농도 의존성지수(B)값이 크게 감소하고 $60^{\circ}C$나 $70^{\circ}C$ 가열온도보다도 수분함량의 영향이 적게 미치는 것으로 나타났다.