• Title/Summary/Keyword: Solidification.

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A study on Production of Al Foam by Using of Al Return Scrap for Sound and Vibration Absorption Materials

  • Hur, Bo-Young;Kim, Sang-Youl;Park, Dae-Chol;Jeon, Sung-Hwan;Park, Chan-Ho;Yoon, Ik-Sub
    • Proceedings of the IEEK Conference
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    • 2001.10a
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    • pp.198-201
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    • 2001
  • Porous structures of aluminum foam have been studied by using return aluminum scrap. The apparent foam shape, foam height, density, pore size and their distributions in various section areas of the experimental samples have been investigated. The sample have been cast into metallic mold, using aluminum foam prepared from a precursor based on pure Al ingot and return aluminum scrap mixed with various amounts of 1-2wt% increasing viscosity and foam agent materials. The process provides for flexibility in design of foam structures via relatively easy control over the amount of hydrogen evolution and the drainage processes which occur during foam formation. This is facilitated by manipulating parameters such as the foaming agent, thermal histories during solidification and mix melt viscosities. A metal for producing the foamed are decomposing a foaming agent in a molten metal such that there is an initial and a subsequent expansion due to foaming agent. It has been found that the Al porous foaming with variation amount of 1∼2wt% foam agent and at 2min holding time, which melting temperature has appeared homogeneous pore size at 650∼700$^{\circ}C$. The compression strength were 10-13 kg/min at 125ppi, and increased by higher pore density. The acoustical performance of the panel made with the foamed aluminum is considerably improved; its absorption coefficient shows NRC 0.6-0.8. It has been found that the Al foam is very preferable for the compactness of the thermal system.

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Orientation Measurement and Related Mechanical Properties of Directionally Solidified NiAl/$Ni_3Al$ Two-Phase Alloys (일방향응고된 NiAl/$Ni_3Al$ 2상합금의 방향성 측정 및 기계적 특성 평가)

  • Lee, Hye-Jung;Park, No-Jin;Choi, Hwan;Lee, Je-Hyun;Oh, Myung-Hoon
    • Journal of the Korean Society for Heat Treatment
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    • v.23 no.2
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    • pp.96-103
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    • 2010
  • $Ni_3Al$ is known as a good high temperature structural material because of high yield strength at ambient temperature. However, it is too brittle to use as a structural material because of their weak grain boundary. In this work, orientation measurement and related mechanical properties of directionally solidified NiAl/$Ni_3Al$ two-phase alloys with various compositions (Ni-23~27 at.%Al) were investigated for developing multi-phase DS-processed alloys with the growth rates of 10, 50 and 100 ${\mu}m/s$ in a modified Bridgeman type furnace. It was found that the multi-phase microstructures such as the $\gamma$ dendrite +${\gamma}'$ matrix duplex microstructure was formed in the hypoeutectic composition of 23 at.%Al, $\beta$ dendrite +${\gamma}'$ matrix duplex microstructure in the hypereutectic composition of 26 and 27 at.%Al. And ${\gamma}'$ single phase was formed in the composition of 24.5 and 25 at.%Al. The hypoeutectic alloy including $\gamma$ dendrites with ${\gamma}'$ matrix showed a large elongation of over 70% at room temperature. However, the room-temperature tensile elongation decreased with increasing Al contents because the volume fraction of brittle $\beta$ dendrites in the ductile ${\gamma}'$ matrix increased.

Microstructures and Mechanical Properties of Extruded Al 7050 Billet and Ring Forged One with Large Scale

  • Bae, Dong-Su;Joo, Kyung-Hwan;Lee, Jin-Kyung;Lee, Sang-Pill;Chang, Chang-Beom;Hong, Sung-Seop;Park, Tae-Won
    • Journal of Power System Engineering
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    • v.20 no.6
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    • pp.40-45
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    • 2016
  • The manufacturing process of large scaled Al 7050 alloy is difficult for the occurrence of solidification crack during casting. The aims of this study are the evaluations of microstructure and mechanical properties of extruded Al 7050 billet and ring forged one with large scale. Large scaled Al 7050 billet was casted by direct-chill casting process. The extruded and ring forged specimens were prepared from the casted ingot after residual stress relief and homogenization heat treatment, respectively. Microstructures, hardness and tensile test of the surface, middle and center part of each specimen were performed at room temperature. Sheared and elongated type grains were observed at the edge parts of surface and center area and its aspect ratios of grains were low and similar as 0.21 while that of middle area was closed to 0.92 value in ring forged Al 7050 alloy. The mechanical properties of extruded Al 7050 alloy were superior than those of ring forged one. The hardness values of surface and center part were slightly higher than that of middle part in ring forged Al 7050 alloy.

Development of Variable Deposition manufacturing for Ethylene Vinyl Acettecopolymer (EVA를 이용한 가변 용착 쾌속 조형 공정의 개발)

  • Lee, Sang-Ho;Sin, Bo-Seong;Jeong, Jun-Ho;An, Dong-Gyu;Yang, Dong-Yeol
    • Journal of the Korean Society for Precision Engineering
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    • v.17 no.9
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    • pp.189-195
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    • 2000
  • RP techniques have their unique characteristics according to the working principles : star-stepped surface of parts due to layer-by-layer stacking low build speed caused by line-by-line solidification to fish one layer and post processing to improve surface finish etc The objective of this study is to propose a new RP technique Variable Deposition Mnanufacturing (VDM) which can make up for the disadvantages of the existing RP techniques and to develop an apparatus to implement the technique. The proposed process can greatly reduce the build time and improve the surface finish of parts generated. Experiments are carried out to obtain the range of temperature of molten material to maintain its fluidity and to investigate the effect of gas cooling on the preservation of the slopes. Some simple shapes such as a line-shape an S-shape and a circle-shape are fabricated from Ethylene Vinyl Acetatecopolymer(EVA) In order to examine the applicability of VDM to more general shapes a tensile specimen and a yo-yo shape were manufactured by the proposed RP method using EVA material as a trial approach. The current basic study shows a high potential of practical use of the proposed VDM process to prototyping of a general three-dimensional shape.

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The effect of sigma phases formation depending on Cr/Ni equivalent ratio in AISI 316L austenitic stainless steel weldments. (AISI 316L 용접부의 시그마상 형성에 영향을 미치는 크롬/니켈 당량비)

  • Kim, Y.H.;Jang, A.Y.;Choi, C.H.;Kang, D.H.;Jeon, J.H.;Byun, J.C.;Jung, G.H.;Lee, S.H.;Lee, H.W.
    • Proceedings of the KWS Conference
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    • 2010.05a
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    • pp.21-21
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    • 2010
  • AISI 316L 용접금속의 크롬/니켈 당량비에 따른 시그마상의 영향을 알아보기 위하여 응고모드가 다른 3종류의 플럭스 코어드 와이어를 제작하였다. AISI 316L 시편에 FCAW 프로세스를 적용한 용접재를 $650^{\circ}C$, $750^{\circ}C$, $850^{\circ}C$, $950^{\circ}C$에서 각 각 1H, 5H, 24H, 72H동안 열처리하였다. 크롬/니켈 당량비가 높을수록 즉, 크롬의 함량이 높아질수록 $\delta$-페라이트 함량은 증가하였으며, $\delta$-페라이트는 고온에서 시그마상으로 변태되었다. $\delta$-페라이트는 $650^{\circ}C$에서 가장 느리게 분해되었으며 $850^{\circ}C$에서 가장 활발히 분해되었다. 용접부의 특성상 크롬과 니켈 등의 합금원소에 의하여 응고온도범위가 넓어져 $950^{\circ}C$에서도 시그마상이 석출되었으며, 5시간 이상 유지 시 구형으로 존재하였다. 충격시험 시 시그마상에 의해 취약해진 inter-dendrite 를 따라 파면이 형성되었으며, $-100^{\circ}C$이하의 극저온에서는 시그마상의 양과 무관하게 충격흡수에너지는 0에 가까워졌다. 하지만 3%미만의 $\delta$-페라이트를 함유하는 AF모드에서 발생한 DDC와 미량의 시그마상은 충격흡수에너지에 결정적인 영향을 미치지 않았다.

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Experimental study on nano silica modified cement base grouting reinforcement materials

  • Zhou, Fei;Sun, Wenbin;Shao, Jianli;Kong, Lingjun;Geng, Xueyu
    • Geomechanics and Engineering
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    • v.20 no.1
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    • pp.67-73
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    • 2020
  • With the increasing number of underground projects, the problem of rock-water coupling catastrophe has increasingly become the focus of safety. Grouting reinforcement is gradually applied in subway, tunnel, bridge reinforcement, coal mine floor and other construction projects. At present, cement-based grouting materials are easy to shrink and have low strength after solidification. In order to overcome the special problems of high water pressure and high in-situ stress in deep part and improve the reinforcement effect. In view of the mining conditions of deep surrounding rock, a new type of cement-based reinforcement material was developed. We analyses the principle and main indexes of floor strengthening, and tests and optimizes the indexes and proportions of the two materials through laboratory tests. Then, observes and compares the microstructures of the optimized floor strengthening materials with those of the traditional strengthening materials through scanning electron microscopy. The test results show that 42.5 Portland cement-based grouting reinforcement material has the advantages of slight expansion, anti-dry-shrinkage, high compressive strength and high density when the water-cement ratio is 0.4, the content of bentonite is 4%, and the content of Nano Silica is 2.5%. The reinforcement effect is better than other traditional grouting reinforcement materials.

Current Issues and Future Considerations in Undergraduate Medical Education from the Perspective of the Korean Medical Doctor Development System (우리나라 의사양성체제의 관점에서 본 의과대학 교육의 문제점과 개선방향)

  • Han, Jae Jin
    • Korean Medical Education Review
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    • v.20 no.2
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    • pp.72-77
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    • 2018
  • Observation of the current Korean medical education and training system shows that certain negative traits of unchangeable solidification engraft themselves so deeply into the overarching system that they are now hampering the state of the national health welfare. Focusing only on undergraduate medical education, we can point out some glaring side-effects that should be of concern to any stakeholder. For instance, a graduate can legally begin his career as an independent practitioner immediately after passing the licensing exam and return to the old stuck school-year system of 2-year-premedical and 4-year-medical programs where outcome-based and integrated curricula are incomplete and unsatisfactory. In terms of learning opportunities, the balance between patient care and public health, as well as that between in-hospital highly specialized practice and community-based general practice, has worsened. Every stakeholder should be aware of these considerations in order to obtain the insight to forge a new direction. Moreover, our medical schools must prepare our students to take on the global roles of patient care within the Fourth Industrial Revolution, health advocacy for the imminent super-aged society, and education and research in the bio-health industry, by building and applying the concept of academic medicine. We will need to invest more resources, including educational specialists, into the current undergraduate medical education system in order to produce proper outcomes, smart curriculum, innovative methods of teaching and learning, and valid and reliable monitoring and evaluation. The improved quality of undergraduate medical education is the starting point for the success of the national system for public health and medical care as a whole, and therefore its urgency and significance should be emphasized to the public. The medical society should go beyond fixing what is broken and usher in a new era of cooperation and collaboration that invites other health professionals, governmental partners, law-makers, opinion leaders, and the general public in its steps toward the future.

A Study on Fabrication Conditions of Al-SiCp Composites by Squeeze Casting (Squeeze Casting에 의한 Al-SiCp 복합재료의 제조 조건에 관한 연구)

  • Kim, Sug-Won;Woo, Kee-Do;Han, Sang-Won
    • Journal of Korea Foundry Society
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    • v.14 no.5
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    • pp.471-479
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    • 1994
  • Al-2%Si-2%Mg alloy containing SiC particle in 20, $70{\mu}m$ were prepared by mean of squeeze casting with various pressure 50, 100, 150 and 220MPa respectively. The specimens were made by casting into $50{\Phi}{\times}100{\ell}$ mold under various squeeze conditions(pressures, pressurizing temperature, particle sizes). Mechanical properties(hardness, tensile strength, elongation and wear characteristics) were evaluated at room temperature with those various fabrication factors. It became feasible to make favorable Al-SiCp composite free from casting defects by the injection of Ar gas during melting and 100MPa pressure squeeze casting. However, pressure of 50MPa was not sufficient to avoid completely porosity formation as a result of precessing and shrinkage during solidification. As the particle size is smaller and the squeeze pressure is higher, the hardness and tensile strength at room temperature are higher. Cell size became smaller gradually with increase of squeeze pressure. With increase of squeeze pressure(MPa), wear behaviors of those composites were changed from adhesive into abrasive wear, and the tendency of above behavior became outstanding with increasing sliding speed. The chemical reaction(4Al+3SiC${\rightarrow}$$Al_4C_3+3Si$) is more accelerated at interface between SiCp and matrix with increase of squeeze pressure. Therefore $Al_4C_3$ intercompound and Si peak intensity is increased at interface.

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Microstructure of Squeeze-cast Aluminum Matrix Composite Reinforced by Fine Steel Wires (용탕단조한 미세강선 보강 알루미늄 복합재료의 미세조직에 대한 고찰)

  • Jeong, Bong-Yong;Lee, In-Woo;Park, Heung-Il;Kim, Jun-Su;Kim, Myung-Ho
    • Journal of Korea Foundry Society
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    • v.14 no.5
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    • pp.455-463
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    • 1994
  • Aluminum matrix composites reinforced by fine steel wires were fabricated by squeeze casting process. Preforms made of fine steel wires were prepared with different surface conditions, namely uncoated(TN), carbo-nitriding treated(TT), and brass coated(TA). Squeeze casting were performed under the pressure of $1500kg/cm^2$ for 3min. during solidification, and pouring temp. of the melt being $750^{\circ}C$ and the steel mold being preheated at $250^{\circ}C$. Microstructural characteristics were evaluated, particularly concerned with the effect of the surface conditions of the preforms. The results obtained from this study are like these. TN specimens show partially non-wetted regions, due to easy formation of oxides on the surface of the fine steel wires. TT specimens show no interfacial reaction between the steel wires and the aluminum alloy matrix, possibly due to the formation of carbo-nitrided zone on the surface of the steel wires. TA specimens show excellent wettabillity between the reinforced steel wires and the aluminum alloy matrix and very thin interfacial zone is formed between them. During the solution hardening treatment of TA specimens, thickness of the interfacial reaction zones were increased with the solution treating time. TA specimens show typical ductile fracture in tensile test, but TT specimens show brittle fracture possibly due to the formation of the brittle hard surface on the steel wires during carbo-nitriding treatments. TA specimens which were reinforced with 40 vol.% of the fine steel wires exhibit high tensile strength of $77.1kgf/mm^2$ and impact value of $8.1kgf-m/cm^2$.

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Effect of Alloying Elements on the Microstructure and Texture of the Secondary Ingots made by Al Used Beverage Cans (알루미늄 폐캔을 이용한 2차지금의 미세조직 및 집합조직에 미치는 합금원소의 영향)

  • 박차용;고흥석;강석봉
    • Resources Recycling
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    • v.9 no.2
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    • pp.46-52
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    • 2000
  • Aluminum can to can recycling was divided into two stpes. The first step was composed of the processes such as collection of used beverage cans (UBC), shredding, magnetic separation, De-laquiring, melting and casting. The second one was remelting and casting, heat treating, hot and cold rolling, annealing, and can making. In this study, the effect of alloying elements on the microstructure and texture of the secondary ingots made by Al UBC was investigated. In aluminum can to can recycling, the second phase particles appeared in the solidification stage must be controlled by heat treatment. The optimum heat treatment condition was $615^{\circ}C$ for 5hrs. the texture in hot rolled sheet was depressed with increasing Mn content, on the other hand, Si and Fe elements promoted the texture development. The textures of can-body sheet should be controlled in the hot rolling and annealing stage because can was formed from cold rolled sheet without heat treatment.

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