• 한국주조공학회지
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• 제27권1호
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• pp.31-35
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• 2007

본 연구에서는 Mg합금의 반응고성형 공정기술을 개발하기 위하여 여러 가지 전단속도와 냉각속도에 따른 Mg합금의 점도와 딕소트러픽 거동을 분석하였으며, 이를 전산모사연구와 비교 검토하였다. 전산모사연구에서는 미세조직과 공정변수를 고려한 반응고 슬러리의 유변학적 거동을 분석하였다. 반응고 온도영역에서의 Mg합금(AZ91D) 슬러리의 점도는 고상율에 따라 지수함수적으로 증가하였으며, 전단속도가 증가하면 감소하는 경향을 나타났다. Mg합금 슬러리의 유변학적 거동을 정확하게 분석하기 위하여 Carreau 모델을 사용하여 ANYCAST 프로그램에서 고압다이캐스팅용 금형으로의 Mg합금 반응고 슬러리의 충진거동을 모사하였다. 전산모사된 결과는 동일한 조건에서의 실제 실험결과와 잘 일치하였다.

• 소성∙가공
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• 제16권6호
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• pp.443-446
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• 2007

The semi-solid process has been developed near net-shape components for kinds of methods. Thixo-forming with reheating prepared billet and rheo-forming with cooled melt until semi-solid state. Material is applied electromagnetic stirring system to slurry with aluminum 6061 alloy. An experiment has variation factors which are pressure, solid-fraction, stirring current and stirring time. The mechanical properties are compared to forge sample with to apply heat treatment T6. This study is researched function a virtual pressure and fine shape zone. Optimum pressure is found to prevent defect of porosity.

• 한국주조공학회지
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• 제22권2호
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• pp.82-88
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• 2002

Al-5.5Zn-2.5Mg-l.5Cu semi-solid slurry was prepared by cooling the liquid metal with a low superheat to a solid and liquid co-existing temperature. Relatively round solid particles could be obtained in the slurry through the simple process. The prepared slurry was deformed into the metallic mold by a press and the mechanical properties of obtained specimens were investigated. Mold filling ability of the alloy slurry was also investigated and compared with that of A356 alloy. Al-Zn-Mg-Cu alloy showed lower mold filling ability than A356 alloy probably because small amount of eutectic phase is present and the heat of fusion generated during solidification is smaller than that of A356 alloy.

• 열처리공학회지
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• 제25권3호
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• pp.126-133
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• 2012

Semi-solid forming of the high melting point alloys such as steel is a promising near-net shape forming process for decreasing manufacturing costs and increasing the quality of the final products. This paper presents the microstructure characteristics of SKH51 (high speed tool steel) during heating and holding in the mushy zone between $1233^{\circ}C$ and $1453^{\circ}C$, which has been measured by differential scanning calorimetry (DSC). The results of heating/holding experiments showed that the grain size and the liquid fraction increased gradually with temperature up to $1350^{\circ}C$. The drastic grain growth occurred at heating above $1380^{\circ}C$. The strain-induced melt-activated (SIMA) process has been applied to obtain globular grains in the billet materials. Working by mechanical upsetting and successive heating of SKH51 into the temperatures in the mushy zone resulted in globular grains due to recrystallization and partial melting.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.649-652
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• 2005

It is reported that semi-solid forming process takes many advantages over the conventional forming process, such as long die lift, good mechanical properties and energy saves. Rheology material has a thixotropic, pseudo-plastic and shear-thinning characteristic. Therefore, general plastic or fluid dynamic analysis is not suitable for the behavior of rheology material. So it is difficult for a numerical simulation of the rheology process to be performed because complicated processes such as the filling to include the state of the free surface and solidification in the phase transformation must be considered. Moreover, it is important to predict the deformation behavior for optimization of net shape forging process with semi-solid materials and to control liquid segregation for mechanical properties of materials. In this study, so, molecular dynamics simulation was performed for the control of liquid segregation in compression experiment as a part of study on analysis of rheology forming process.

• 한국산업융합학회 논문집
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• 제23권4_1호
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• pp.541-547
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• 2020

This paper relates a rheo die casting using electromagnetic force, which is one of the representative semi-solid methods for aluminum. The most important factors in electromagnetic stirring would be the melt temperature, sleeve temperature, electromagnetic force, and input time. The effect of the temperature of molten alloy on the direct rheo-casting is assessed in this study. The temperature of the molten alloy is set to 590 ℃ with a solidification of 40%, 600 ℃ with 30%, and 610℃ with less than 20%. Under the condition of 590 ℃ with a solidification of 40%, the whole molten alloy is solidified, causing non-forming during forming process. Meanwhile, under the condition of 600 ℃, where the solidification was 30%, appropriate amount of molten alloy is solidified, filled well into the mold, resulting in good forming, while at 610 ℃ with the solidification of 20%, the molten alloy is not sufficiently solidified and scattered away. The investigation of the defects inside the product with the help of the X-ray equipment shows that the electromagnetic stirring at 590 ℃ with a solidification of 30% produces many air-pores inside the product.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 춘계학술대회 논문집
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• pp.397-400
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• 2007

Recently, rheology forming technology has been interested in industrial and academic for light weight materials and to solve environmental issues. In this study, the rheology material production equipments were used to be made spiral shape by special design. And the experiment variables established stirring time 0 $\sim$ 1200 sec, stirring velocity 0 $\sim$ 100 rpm and several material temperature of semi - solid states. The rheology materials were made for established experiment conditions then measured mechanical properties. Sequence-production equipments were appended to fabrication system of rheology material for make rheology materials continually. Therefore, the development of sequence-production equipments were demanded for fine grains and for uniform globule shape rheology materials by a specially designed spiral stirrer machine.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 추계학술대회 논문집
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• pp.240-243
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• 2001

Recently, many automobile parts produced by semi-solid forming(SSF) process has been applied for improved weight reduction, better environmental protection and energy savings. SSF process was well developed for high volume production of light weight aluminum components. In this paper, knuckle has been manufactured with A357 by SSF and thor investigated for microstructures and mechanical properties followed by various heat-treatment conditions. It was found that the examined microstructure was equiaxed at the whole cross-section area and as a result, the mechanical properties were satisfied by 100MPa YS, 260MPa UTS and $14\%$ elongation.

• 열처리공학회지
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• 제16권1호
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• pp.16-25
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• 2003

Recently, semi-solid forming (SSF) Process has been applied in many automobile parts for improved weight reduction, better environmental protection and energy savings. SSF process was well developed for high volume production of light weight aluminum components. In this paper, knuckle has been manufactured by SSF and then the microstructures and mechanical properties were investigated followed by various heat-treatment conditions. It was found that the examined microstructure was equiaxed at the whole cross-section area.

• 소성∙가공
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• 제17권1호
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• pp.5-8
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• 2008

As the semi-solid forming technology has a lot of advantages compared to the die casting, squeeze casting and hot/cold forging, it has been studied actively. This paper focuses on the thixoforging of the rheological materials fabricated by the spiral mechanical stirring equipment with A356 casting aluminum alloy and A6061 wrought aluminum alloy. Formability tests of rheological materials fabricated by spiral mechanical stirring were carried out and the microstructures of forged sample were observed. After thixoforging experiment, the heat-treated conditions of forged samples are investigated to improve the mechanical properties. These results are able to suggest the possibility of commercialization for rheological materials fabricated by spiral mechanical stirring.