• 한국주조공학회지
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• 제18권5호
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• pp.450-461
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• 1998

The optimal reheating conditions to apply the thixoforging and semi-solid die casting process were investigated by changing the reheating time, the holding time, the reheating temperatures, the capacity of the induction heating system, and the adiabatic material size. In the case of solid fraction fs=50% (for semi-solid die casting), the microstructure of SSM (specimen size:$d76{\times}l90$) at the condition of the first elevating time of 4 min, holding time of 1 min and holding temperature of $350^{\circ}C$, the second elevating time of 3 min, holding time of 3 min and holding temperature of $575^{\circ}C$, the third elevating time of 1 min, holding time of 2 min and holding temperature of $584^{\circ}C$, capacity of Q=8.398KW is obtained with globular microstructure and finest. In addition, in the case of solid fraction fs=55% (for thixoforging), the SSM (specimen size:$d76{\times}l90$) at the condition of the first elevating time of 4 min, holding time of 1 min and holding temperature of $350^{\circ}C$, the second elevating time of 3 min, holding time of 3 min and holding temperature of $570^{\circ}C$, the third elevating time of 1 min, holding time of 2 min and holding temperature of $576^{\circ}C$, capacity of Q=12.04KW is obtained with the finest globular microstructure. We saw that the most important factor in a three-step reheating process is the final holding time.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2009년 추계학술발표대회
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• pp.8-8
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• 2009

알루미늄 합금 Al 6082-T6는 최근에 개발되어 북유럽 등의 선진국에서는 그 뛰어난 해양 내식성과 우수한 강도로 인하여 해양구조물의 헬리데크(Helideck), 타워 갱웨이(Tower gangway), 알루미늄 피팅류(Aluminium fitting)등의 해양구조물과 플랫폼(Flatform), 알루미늄 래더(Aluminium ladder)등의 선박부품, 차량, 기계부품 분야에서 전 세계적으로 널리 사용되기 시작하였다. 그러나 전통적으로 용접금속의 기공은 결함으로 분류 되고, Rakesh Kumar 등의 논문에 따르면 용접 시 용접금속 내에 발생되어진 미세기공이 기계적 성질에 악영향을 미치는 것으로 보고되어졌다. 따라서 용접금속내의 발생하는 기공을 방지하는 용접공정의 개발이 반드시 필요하다. 본 연구의 목적은 Al 6082-T6 고속 MIG용접에서 기공방지를 위한 용접공정을 개발하는 것이다. Al 6082-T6의 7t 플레이트에 Al 5356의 와이어를 사용하여 아크길이 변경 및 용접속도를 60cpm과 120cpm으로 변경하여 실험하였고, 용접속도 120cpm의 고속 MIG용접에서 토치 진행각을 변경하여 실험을 진행하였다. 용접공정 파라메터 변경에 따른 기공율 측정은 이미지 분석 소프트웨어를 사용하여 정량적으로 분석하였다.

• 한국주조공학회지
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• 제32권2호
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• pp.65-74
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• 2012

In this paper, we present the results of our studies on optimal die design towards development of a vacuum die casting process to fabricate fuel cell bipolar plate with micro-channel array. Cavity and overflow shape is designed by computational filling analysis of MAGMA soft. Optimal die design consists of seven overflows at the end of cavity and three overflows at each side wall of cavity. The molten metal that passed the gate and reached the side wall flowed into the side overflow, no turbulent flow occurred, and the filling behavior and velocity distribution were uniform. In addition, partially solidified molten metal passing through the channel was perfectly eliminated by overflow without back-flow. When vacuum pressure, injection speed of low and high region was 300 mbar, 0.3 m/s and 2.5 m/s respectively with Silafont 36 die casting alloy, sound sample without casting defects was obtained. The experimental results are nearly consistent with simulation results.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2006년도 전기학술대회논문집
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• pp.265-266
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• 2006

The chemical conversion coating formed on magnesium alloy investigated for low cost and harmless in environment by using the colloidal silica as the main component. The film formed in 298 K is thick, the film, which was thought combination of Si-O, was formed. The film formed in 313 K is thinner than that in 298 K. The quantity of film formed at high temperature such as 333 K and 353 K is smaller than dissolved quantity. At the anodic polarization experiment, corrosion resistance in sealing by hot water after chemical conversion treatment in basic solution condition get worse than that in comparison with basic solution condition. In salt spray test, the ratio of black rust on specimen that did not conducted chemical conversion treatment was five times or more compared with those of chemical conversion treated specimen. The film thickness of chemical conversion coating produced by alkali treatment process is thinner than in comparison with that of specimen produced in basic chemical conversion treatment solution condition. It is thought, however, that it showed good corrosion resistance during salt spray test because the area of microcracks is small.

• Applied Microscopy
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• 제43권3호
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• pp.122-126
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• 2013

The heterogeneous nucleation of the ${\Theta}^{\prime}$ phase on nanoscale precipitates has been investigated using a combination of three-dimensional atom probe tomography and high-resolution transmission electron microscopy. Two types of ${\Theta}^{\prime}$ phases were observed, namely small (~2 nm thick) cylindrical precipitates and larger (~100 nm) globular precipitates and both appear to be heterogeneously nucleated on the nanoscale precipitates. The composition and crystal structure of precipitates were directly analyzed by combination of two advanced characterization techniques.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1999년도 춘계학술대회논문집
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• pp.165-168
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• 1999

The coil design of induction heating systems and their optimization are of paramount importance for semi-solid processing(SSP) The authors of this paper present the coil design and optimization of a 60 Hz induction heating system for ALTHIX 86S (Al-6%_Si-3%Cu-0.3%Mg) alloy. An objective function on the basis of the optimization process for the coil design is proposed by introducing an optimization technique. Finally the results of the optimal coil design are also applied to the induction heating process to obtain a fine globular microstructure. The proposed new objective function based on the computational techniques would contribute to obtaining the thixoformed components with good mechanical properties and reducing lead time.

• 한국표면공학회지
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• 제53권6호
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• pp.322-329
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• 2020

The utilization of aluminum scrap is a subject of great importance in terms of reducing energy consumption and environmental protection. However, aluminum scrap contains impurities, which can degrade the properties of aluminum alloy, especially corrosion resistance. This study examines the effect of scrap charge rate of aluminum alloys about microstructures and corrosion characteristics. According to the metallographic examinations, Mg2Si tended to become coarser and its uniformity was decreased by increasing aluminum scrap charge rate. The immersion test exhibited corrosion progressed through the eutectic areas due to micro-galvanic interactions. Electrochemical measurements revealed that excess aluminum scrap could reduce the intergranular corrosion resistance of aluminum alloys. Results showed that the scrap charge rate is important factor in the design of corrosion resistance of aluminum die casting alloys.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.505-510
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• 2002

The Friction Stir Welding (FSW) is a new joining method that was developed at The Welding Institute (TWI) in England in 1991. It applied heating by the rotational friction and material plastic flow. It was developed as a new joining method to solve the problems of epochally in the welding of Al alloys. In the study, 6000series of Alloy composed of AI-Mg-Si, one of the Al alloys that are utilized for shipbuilding and construction, is selected as a specimen and the numerical is executed against the welded zone of FSW. The material used in this study had the unique properties of strength and anti-corrosion, but since the welded joint of this material is easily softened by the welding heat, FSW is executed and the numerical analysis is carried out around the joint. To examine the mechanical behaviors and properties, F.E.M analysis is executed and the developed thermal-elastic-plastic [mite analysis are used.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2004년도 학술대회지
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• pp.66-74
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• 2004

The sliding wear behavior of $ZrO_2-22wt\%MgO\;(MZ)\;and\;ZrO_2-8wt\%Y_2O_3\;(YZ)$ deposited on a casting aluminum alloy with bond layer (NiCrCoAlY) by plasma spray against an SiC ball was investigated under dry test conditions at room temperature. At all load conditions, the wear mechanisms of the MZ and the YZ coatings were almost the same. The wear mechanisms involved the forming of a smooth film by material transferred on the sliding surface and pullout. The wear rate of the MZ coating was less than that of the YZ coating. With an increase normal load the wear rate of the studied coatings increased. The SEM was used to examine the sliding surfaces and elucidate likely wear mechanisms. The EDX analysis of the worn surface indicated that material transfer was occurred from the SiC ball to the disk. It was suggested that the material transfer played an important role in the wear performance.

• 한국산학기술학회논문지
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• 제21권7호
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• pp.270-276
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• 2020

3D 프린팅은 고분자, 세라믹, 금속 등 다양한 소재를 대상으로 복합적인 형상을 한 번의 공정으로 제작할 수 있는 적층 기반 제작 기술이다. 최근의 3D 프린팅 기술은 프린팅 속도의 향상과 적용 가능 소재의 지속적인 개발에 의해 양산형 제품 생산이 가능한 수준으로 발전하였다. 본 연구에서는 레이저를 활용한 3D 프린팅 기술을 적용하여 철도 차량용 공기 압축기에 쓰이는 열교환기 제작을 진행하였다. 먼저 3D 프린팅에 적합한 형상으로 경량화 및 컴팩트화를 주안점으로 열교환기의 최적 설계를 진행하였다. 그로부터 도출된 설계안을 기반으로 SLM 기법을 적용하여 AlSi10Mg 합금 소재로 열교환기 시작품을 제작하였다. 다음으로, 제작된 시작품을 기존 공기 압축기에 부착하여, 압축공기의 열교환 성능을 시험하였다. 3D 프린팅 시작품의 시험 결과는 기존 열교환기 대비하여 저압부와 고압부에서 열교환 성능은 각각 약 80% 및 85% 수준을 보였다, 하지만 외부 냉각공기 조건을 기존 열교환기와 유사한 조건으로 가정하였을 때 𝓔-NTU 법을 활용하여 계산한 열전달량은 기존 열교환기 대비하여 유사한 성능을 보여 주었다. 결과적으로, 3D 프린팅 제작 열교환기의 성능 효과 및 경량화 등의 장점을 확인할 수 있었다.