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        • KCI등재

          수직 연속주조 공정으로 제조된 Al-8Zn-2Mg-2Cu 빌렛의 표면 결함 형성에 미치는 주조 온도와 주조 속도의 영향

          이윤호 ( Yoon-ho Lee ),김용유 ( Yong-You Kim ),이상화 ( Sang-hwa Lee ),김민석 ( Min-seok Kim ),어광준 ( Kwangjun Euh ),이동근 ( Dong-geun Lee ) 한국주조공학회 2021 한국주조공학회지 Vol.41 No.3

          7000계 알루미늄 합금은 다른 Al 합금에 비해 강도가 우수하여 주목을 받고있으며, 7000계 알루미늄 빌렛은 일반적으로 Direct-Chill (DC) 주조 공정을 통해 제조된다. DC 주조 공정으로 제조된 알루미늄 빌렛의 표면 결함은 주로 Exudation과 Meniscus freezing 현상과 관련이 있으며, 이는 합금 성분, 주조 속도 및 주조 온도의 영향을 받는다. 특히, 7000계 알루미늄 합금은 응고 과정에서 응고 온도 범위가 넓어 주조 결함이 발생하기 쉽다. 본 연구에서는 DC 주조 공정에 의해 제조된 Al-8Zn-2Mg-2Cu 합금 빌렛에 대한 표면 결함 변화에 대하여 조사하였다. 빌렛의 표면은 "Wavy" 또는 "Dot" 표면으로 관찰되었다. Wavy 표면은 낮은 주조 속도(200mm/min)와 온도(655℃)에서 Meniscus freezing 현상에 의해 형성되었으며, Concave 영역에서 Meniscus freezing 현상으로 인한 조성작 과냉으로 인해 미세한 수지상 조직이 관찰되었다. 반면에, 주조 온도가 높은 조건(675℃)에서는 Dot 표면이 기공 형성에 의해 형성되었으며, 높은 주조 속도(230mm/min)에서 제조된 Dot 표면을 갖는 빌렛에서는 높은 금속 수두압에 의해 Exudation 층이 형성되었다. Exudation 층의 Dot 영역과 Smooth 영역은 각각 미세한 수지상 형태와 주상정 형태의 조직이 관찰되었으며 이는 Dot 영역에서 가스 기공의 형성에 의한 결과이다. 7000-series aluminum alloys are noted for their superior strength compared with other Al alloys, and their billets are generally fabricated by direct-chill (DC) casting. Surface defects in a DC-cast aluminum billet are mainly related to exudation and the meniscus freezing phenomenon, which are influenced by alloy compositions, casting speed, and casting temperature. 7000-series aluminum alloys have a wide freezing range during solidification, which makes it easy for casting defects to occur. In this study, we investigated surface defect evolution in casting billets of Al-8Zn-2Mg-2Cu alloy fabricated by a DC casting process. The billets showed “wavy” or “dotted” surfaces. The wavy surface was formed by meniscus freezing at a lower casting speed (200 mm/min) and temperature (655 ℃). In the wavy surface, refined dendritic cells were observed in a concave region due to the constitutional supercooling caused by meniscus freezing. Meanwhile, at a higher casting temperature (675 ℃), the dotted surface was formed by pore formation. In the dotted surfaces in the billet formed at a high casting speed (230 mm/min), an exudation layer was formed by the high metallostatic head pressure. The dotted region and the smooth region had a refined dendritic morphology and a columnar morphology at the exudation layer, respectively. This is attributed to the formation of gas pores in the dotted region.

        • KCI등재

          대기 플라즈마 용사법으로 제조된 SiCp/Al 복합재료의 열전도도 특성

          어광준,강석봉,Gui, Manchang 대한금속재료학회 2005 대한금속·재료학회지 Vol.43 No.1

          Feedstock for plasma spraying was prepared by ball milling with A1-55 vol.%SiC and Al-75 vol.%SiC powder mixtures in different conditions. The average size of SiC particles was varied from 8 to 30 gm. Freestanding SiC_(p)/Al composites were fabricated by atmospheric plasma spraying onto a graphite substrate. Thermal conductivity of the plasma-sprayed composites was measured at room temperature of 25℃ by the laser flash method. Thermal conductivity of the sprayed composites was significantly lower than that of conventionally cast SiCp/Al composites. Thermal conductivity was varied considerably with respect to the SiC size and feedstock preparation method. The deterioration mechanism of thermal conductivity in the sprayed composites was elucidated, and numerical analyses based on theories of Maxwell and thermal boundary resistance were carried out. (Received September 30, 2004)

        • KCI등재

          플라즈마 spray forming법으로 제조된 Al-SiCp 복합재료의 후속공정에 의한 물성 향상

          어광준,강석봉 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.3

          In order to fabricate aluminum matrix composites reinforced by SiC particulates, atmospheric plasma spray forming method was adopted. Aluminum and SiC powders were mechanically mixed for plasma spraying feedstock. The feedstock was deposited into freestanding bulk composite on a graphite substrate. As-sprayed composites had a great amount of porosity, which reduced thermal properties, especially in thermal conductivity. The spray-formed Al-SiCp composites were rolled at the room and elevated temperature and hot isostatic pressed (HIPped) at 500℃ under 100 MPa. By rolling, the amount of porosity decreased and consequently thermal conductivity increased. Although, the amount of porosity hardly decreased by HIP, thermal conductivity increased due to the precipitation of solid solution elements such as Fe and Si. Coefficients of thermal expansion (CTEs) of the composites were affected less significantly by post treatment.

        • KCI등재

          대기 플라즈마 용사에 의한 Al-SiC 복합재료 판재의 제조에 미치는 공정변수의 영향

          어광준,강석봉,양병모 대한금속재료학회 2003 대한금속·재료학회지 Vol.41 No.6

          Increased electronic packaging density requires thermal management materials with high thermal conductivities and low coefficients of thermal expansion (CTEs) matching those of ceramic substrates or semiconductors. Recently, metal matrix composites (MMCs) have been developed, which provide unique combination of properties that make them candidates for thermal management materials. Most of conventional processes to fabricate MMCs have complicated steps that reduce the cost effectiveness, such as the infiltration process requiring a preform preparation and long process time. Plasma spraying can be adopted to produce MMCs in a flexible and cost effective manner. In this study, SiC particles reinforced Al matrix composites were fabricated by atmospheric plasma spraying method. Al and SiC powders were blended and sprayed with plasma arc power. SiC were uniformly dispersed in the Al matrix with a volume fraction of up to 46%. There were also pores in the composite with a range of 1.8∼12 vol.%, which could be tailored by process parameters. The experimental CTEs showed 13.5∼17.6×10^-6/℃ for the Al-SiC composite containing about 40 vol.% SiC, which were matched well with the predicted ones.

        • KCI등재

          가스-용탕 in-situ 반응에 의한 AIN/Al 복합재료의 제조

          김재덕,어광준,이정무,강석봉 대한금속재료학회 2003 대한금속·재료학회지 Vol.41 No.5

          Fabrication method of aluminum nitride reinforced aluminum composites using gas-melt in-situ reaction was investigated. AA 5083 aluminum alloy was melted in vacuum and nitrogen atmosphere, and then nitrogen gas bearing 12.5% ammonia gas was injected in the molten alloy through alumina and graphite tube for 4 hours at the temperature of 1100℃. The melt was divided into the upper and lower parts. There were many AlN particles in the upper part and no AlN in the lower part. In order to mix the upper and lower part, an impeller was introduced to the melt. There was also two parts with decreased thickness of the upper part and small amount of AlN in the lower part. Formation of AlN has been identified by optical and transmission electron microscopy, X-ray diffraction, and electrolytic extraction method. AlN was evolved in the form of a cluster with hexagonal particles of 1 μm and a rod of about 3 μm length.

        • KCI등재

          가스/용탕의 in-situ반응에 의한 Al-Mg/AIN 복합재료 제조

          김재덕,어광준,이정무,강석봉 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.8

          Effects of fabrication condition on the formation of A1N by means of gas/melt in-situ reactions were investigated through injection of mixture gas of 95% N₂+5%H₂into the commercial grade A5083 alloys. In this investigation, the fabrication was performed in the temperature range of 1000 to 1200℃ for up to 4 hours. The fabricated composites were characterized using X-ray diffraction, scanning electron microscopy with dispersive X-ray microanalysis and transmission electron microscopy. The volume fraction of MN formed in the specimens increased with increasing reaction time and reaction temperature as well, while the trend of increment of volume fraction of AIN per hour is different with the reaction temperature. The formation of A1N by means of gas/melt in-situ reactions was examined through the thermodynamic and kinetic considerations.

        • 고에너지 전자빔 투사를 이용한 표면합금화 재료의 미세조직 연구

          유정훈,신기삼,윤재홍,이찬규,허성강,오준철,이성학,어광준 국립7개대학공동논문집간행위원회 2002 공업기술연구 Vol.2 No.-

          For determination of the mechanism of microstructural modification by surface alloying technique using high energy electron beam (HEEB), surface alloys of carbon steel with TiC, TiB_2 and VC were fabricated and their microstructures were analyzed using optical microscope, XRD (X-ray diffractometer), and SEM (scanning electron microscope). The surface regions of TiC and VC surface alloy consists of 1) melted, 2) interface, and 3) heat affected regions. In the TiC surface alloy precipitates of large primary and fine eutectic TiC were observed. In TiB_2 surface alloy, neither fine precipitates were present nor the TiB_2 shape was changed from the original particles, which was attributed to the high melting temperature of TiB_2. Among the three surface alloys studied, the melted region hardness of VC surface alloy was the highest.

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