• 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.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 추계학술대회논문집
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• pp.103-106
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• 2004

The new rheology fabrication process has been developed to rheo die casting and rheo forming process. Thixoforming process has disadvantages in terms of induction reheating process, scrap recycling, loss of raw material and cycle time. Therefore, to reduce the number of process, new rheology fabrication process with specially designed the rotational barrel type equipment has been proposed to apply in various part productions. The barrel type equipment, which could continuously fabricate the rheology materil, was specially designed to have a function to control cooling rate, shear rate and temperature. During the continuous rotation of barrel with a constant temperature, the shear rate is controlled with the rotation speed. The barrel surface has both the induction heating system and the cooling system to control the temperature of molten metal. By using this system, the effect of the rotation speed and the rotation time on the microstructure was widely examined. The possibility for the rheoforming process was investigated with microstructural characteristic.

• 한국정밀공학회지
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• 제20권2호
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• pp.58-65
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• 2003

The conventional forming process such as squeeze casting or die casting for fabricating metal matrix composites products have a disadvantage such as non homogenous distribution of reinforcement, weak bonding between matrix and reinforcement and cost increase in parts fabrication. Thixoforming process has been accepted as a new method for fabricating the net shaped metal matrix composites with lightweight and wear resistance. In this paper, the effect of volume fraction and reinforcement sizes on mechanical properties in cylinder liner part of metal matrix composites has been investigated with processes parameters such as pressure and velocity. Moreover, the methods to obtain the thixoforged composites cylinder liner with high quality has been proposed. To evaluate the composites cylinder linear fabricated at the conditions proposed in this study, mechanical properties of fabricated composites cylinder linear were compared with those of commercial composites cylinder linear.

• 한국주조공학회지
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• 제28권3호
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• pp.129-135
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• 2008

The reheating stage of electromagnetically stirred Al billet is a critical factor in the thixoforming process. When reheated to the solid-liquid state, the microstructure evolves to a more globular and more homogeneous structure by a coarsening mechanism, the kinetics depending on the initial microstructure. Microstructural evolution has been characterized by conventional parameters (mean size of particle and shape factor) as a function of holding time in the solid-liquid state. The aim of this study is to report experimental results concerning microstructural evolution in the solid-liquid state of electromagnetically stirred Al billet. The material was elaborated in the form of continuously cast bars solidified with electromagnetic stirring to degenerate the dendritic structure. The choice of the reheating conditions is determined by a dendritic ripening and coalescence mechanism, involving variations of both the shape and size of the particles. The reheating time has to be long enough to allow a minimum degree of spheroidizing, but has to be limited as much as possible in order to avoid excessive ripening. The optimum microstructure was obtained at the reheating temperature of near $584^{\circ}C$ and the holding time of 5 min. The only means of combining high productivity with good casting quality was to use feedstock billets whose microstructure showed rapid transformation characteristics.

• Composites Research
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• 제14권5호
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• pp.1-11
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• 2001

본 논문은 금속복합재료를 반용융상태로 재가열하여 Thixoforming을 하는데 필요한 소재를 제공하기 위한 장비 설계와 제조방법 등에 관한 내용을 소개하고 있다. 장비 설계에서 기지재내에 강화재가 균일하게 분산되도록 하기 위하여 강화재의 연속주입 방법과 강화재의 온도를 제어하는 방법을 소개하고 있다. 일정한 양의 강화재를 기지재료 내에 분산시키는 것은 균일 혼합을 위하여 필요한 기술이다. 또한 분산시 강화재의 수분제거를 위하여 강화재의 온도를 제어하면서 연속적으로 강제분산시키는 것은 균일분산을 위하여 필요하다. 기지재의 초정 $\alpha$의 크기가 강화재의 분산성에 크게 영향을 미치기 때문에 기지재의 초기 온도가 초정$\alpha$의 크기에 미치는 영향 등을 검토하여 복합재료 빌렛트의 제조조건에 이용하였다.

• 한국재료학회지
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• 제10권1호
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• pp.69-76
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• 2000

반응고 금속의 반응용 성형법은 그 우수한 성형성으로 생산공정에 있어 주조나 단조와 같은 일반 성형법에 비해 많은 장점을 가지고 있는 반면, 정밀한 공정 변수 제어가 요구되므로 실용화에 있어 크게 제한 받고 있다. 본 연구에서는 반응고 금속인 A356합금을 사용하여 밀폐형 가압 성형 전후의 기계적 특성의 변화를 관찰하여, 가압 성형시의 정확한 공정 변수 제어가 이루어지지 않았을 경우에 일어날 수 있는 기계적 특성의 감소 원인이 가압 성형에 의한 미세조직의 응집과 조대화에 있음을 미세조직과 파단면 관찰을 통하여 규명하였다. 또한 가압 성형 후 본 연구에서 \`반응고 열처리\`라 명명한 후 처리 공정을 적용하여 인장 특성을 향상시킬수 있었다.