• 한국안광학회지
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• 제16권1호
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• pp.13-19
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• 2011

목적: 본 연구는 국외에서 판매중인 셀룰로오스 아세테이트 안경테용 판재(수입 CA판재, overseas company's cellulose acetate glasses frame sheet)의 특성을 평가하고 안경테용 CA 판재로서 적합한 공업용 셀룰로오스 아세테이트 레진(공업용 CA레진, industrial cellulose acetate resin)을 선정하여 그 소재의 최적 용융 압출 조건을 도출하는 데 목적이 있다. 방법: 수입 CA판재의 특성을 고찰하기 위해 $^1H$-NMR, GPC, TGA 분석을 실시하고, 공업용 CA레진의 최적 배합 조건 및 용융 압출 조건을 도출한다. 또한 hot press에 의해 제조 된 3개국의 수입 CA판재와 공업용 CA레진 성형체의 물성을 비교 평가를 실시하였다. 결과: 수입 CA판재의 특성 분석 결과, virgin CA를 가소화시키기 위해 사용된 가소제는 diethyl phthalate이며 가소제의 함량은 30 wt% 내외임을 확인하였다. 용융 압출 시험 결과, 압출온도는 190~200${^{\circ}C}$에서 공업용 CA레진의 충분한 용융거동 및 압출성을 보였으며 성형체 또한 안경테용 물성을 만족하는 수준인 2.3 kgf/$mm^2$임을 확인하였다. 결론: 30 wt%의 가소제 함량을 가진 공업용 CA레진의 경우, 중국의 CA판재를 대체하여 안경테용 셀룰로오스 아세테이트 판재 제조에 적합한 소재로 판단된다.

• 한국재료학회지
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• 제30권10호
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• pp.542-549
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• 2020

Effects of Sc addition on microstructure, electrical conductivity, thermal conductivity and mechanical properties of the as-cast and as-extruded Al-2Zn-1Cu-0.3Mg-xSc (x = 0, 0.25, 0.5 wt%) alloys are investigated. The average grain size of the as-cast Al-2Zn-1Cu-0.3Mg alloy is 2,334 ㎛; however, this value drops to 914 and 529 ㎛ with addition of Sc element at 0.25 wt% and 0.5 wt%, respectively. This grain refinement is due to primary Al₃Sc phase forming during solidification. The as-extruded Al-2Zn-1Cu-0.3Mg alloy has a recrystallization structure consisting of almost equiaxed grains. However, the as-extruded Sc-containing alloys consist of grains that are extremely elongated in the extrusion direction. In addition, it is found that the proportion of low-angle grain boundaries below 15 degree is dominant. This is because the addition of Sc results in the formation of coherent and nano-scale Al₃Sc phases during hot extrusion, inhibiting the process of recrystallization and improving the strength by pinning of dislocations and the formation of subgrain boundaries. The maximum values of the yield and tensile strength are 126 MPa and 215 MPa for the as-extruded Al-2Zn-1Cu-0.3Mg-0.25Sc alloy, respectively. The increase in strength is probably due to the existence of nano-scale Al₃Sc precipitates and dense Al₂Cu phases. Thermal conductivity of the as-cast Al-2Zn-1Cu-0.3Mg-xSc alloy is reduced to 204, 187 and 183 W/MK by additions of elemental Sc of 0, 0.25 and 0.5 wt%, respectively. On the other hand, the thermal conductivity of the as-extruded Al-2Zn-1Cu-0.3Mg-xSc alloy is about 200 W/Mk regardless of the content of Sc. This is because of the formation of coherent Al₃Sc phase, which decreases Sc content and causes extremely high electrical resistivity.

• 한국분말재료학회지
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• 제3권4호
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• pp.227-232
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• 1996

(i) The development of a metallurgical bond during the spray forming of clad products has offered the possibility of manufacturing large rolls, including those used in hot and cold strip mills. Small rolls are already being produced in Japan. (ii) Technical developments, including the use-of-multi-atomizers have resulted in the elimination of porosity from the internal bore of a sprayed tube. Bimetallic tubing can also be manufactured and the installation of a 4.5 ton tube plant in the USA should provide low operation costs. (iii) Spray forming offers a potentially low cost manufacturing route for superalloy ring/casing components in high strength superalloys. (iv) A large pilot plant has been built for the spray forming of ultra-clean superalloys for turbine disc applications. (v) Using twin-atomizing technology, special steel billets have been spray formed up to 400mm diameter with deposition yields in excess of 90%. (vi) Al/Si alloy extrusion billets with excellent dimensional tolerances are being manufactured for large scale automotive applications. Several new aluminum alloys have also been developed, including high strength, low density and low cocfficient of expansion materials. (vii) New copper alloys have been developed and pilot plants are in operation to produce these alloys once markets have become established.

• 한국분말재료학회지
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• 제10권1호
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• pp.15-20
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• 2003

Hybrid $A1_2O_3-TiC$ ceramic particle reinforced 6061 and 5083 Al composite powders were prepared by the combination of twin rolling and stone mill crushing process, followed by consolidating processes of cold compaction, degassing and hot extrusion. The composite bar consists of lamellar structure of ceramic particle rich area and matrix area, in which the hybrid was decomposed into each TiC of about $3-4\mutextrm{m}$ and $AI_2O_3$ particles of about $1-2\mutextrm{m}$ in diameter. It also found that fine $Mg_2Si$ precipitates of about 30 nm were embedded in the matrix, which have grains of about 3 $\mutextrm{m}$. Higher UTS was measured at the 5083 composite bar compared to the conventionally fabricated composite, due to again refinement effect by the rapid solidification. No particle was shown to form in the interface between the matrix and reinforcement, whereas carbon was diffused into the matrix.

• Advances in materials Research
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• 제1권3호
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• pp.169-182
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• 2012

In this paper the intrinsic influence of micron-sized nickel particle reinforcements on microstructure, micro-hardness tensile properties and tensile fracture behavior of nano-alumina particle reinforced magnesium alloy AZ31 composite is presented and discussed. The unreinforced magnesium alloy (AZ31) and the reinforced nanocomposite counterpart (AZ31/1.5 vol.% $Al_2O_3$/1.5 vol.% Ni] were manufactured by solidification processing followed by hot extrusion. The elastic modulus and yield strength of the nickel particle-reinforced magnesium alloy nano-composite was higher than both the unreinforced magnesium alloy and the unreinforced magnesium alloy nanocomposite (AZ31/1.5 vol.% $Al_2O_3$). The ultimate tensile strength of the nickel particle reinforced composite was noticeably lower than both the unreinforced nano-composite and the monolithic alloy (AZ31). The ductility, quantified by elongation-to-failure, of the reinforced nanocomposite was noticeably higher than both the unreinforced nano-composite and the monolithic alloy. Tensile fracture behavior of this novel material was essentially normal to the far-field stress axis and revealed microscopic features reminiscent of the occurrence of locally ductile failure mechanisms at the fine microscopic level.

• 한국분말재료학회지
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• 제27권1호
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• pp.8-13
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• 2020

In this study, we investigated the effects of precipitates and oxide dispersoids on the high-temperature mechanical properties of oxide dispersion-strengthened (ODS) Ni-based super alloys. Two ODS Ni-based super alloy rods with different chemical compositions were fabricated by high-energy milling and hot extrusion process at 1150 ℃ to investigate the effects of precipitates on high-temperature mechanical properties. Further, the MA6000N alloy is an improvement over the commercial MA6000 alloy, and the KS6000 alloy has the same chemical composition as the MA6000 alloy. The phase and microstructure of Ni-based super alloys were investigated by X-ray diffraction and scanning electron microscopy. It was found that MC carbide precipitates and oxide dispersoids in the ODS Ni-based super alloys developed in this study may effectively improve high-temperature hardness and creep resistance.

• 한국주조공학회지
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• 제26권3호
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• pp.123-128
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• 2006

Mechanical and thermal properties of spray-cast hypereutectic Al-20wt.%Si-xwt.%Fe alloys (x=0, 1, 3, 5) were investigated. After the spray-casting, hot extrusion was performed at $400^{\circ}C$. Intermetallic compound (${\beta}-Al_5FeSi$) and primary Si are observed in the spray-cast aluminum alloys. The size of primary Si and intermetallic compound of the spray-aluminum alloys became finer and more uniformly distributed than that of the permanent mold cast ones. Ultimate tensile strength of the spray-cast aluminum alloys increased by increasing Fe contents, but that of the permanent mold cast aluminum alloys decreased by increasing Fe contents possibly due to increased amount of coarse intermatallic compound. The coefficient of thermal expansion (CTEs) of the aluminum alloys became lower with finer primary Si and intermetallic compound, and this is attributed to the increased amount of interfacial area between the aluminum matrix and the phases of finer Si and intermetallic compound.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1999년도 압출 및 인발 심포지엄
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• pp.38-46
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• 1999

Dispersion strengthened Cu alloys have been manufactured by spray forming and also by reactive spray forming, followed by hot extrusion of the spray deposited billets. The size of dispersed particles in the reactive spray formed alloy was much finer than that in the spray formed alloy. That was because the dominant chemical reaction between Ti and B had occurred in Cu-Ti-B alloy melt in spray forming while it had occurred after deposition of droplets in reactive spray forming. The yield strength of the reactive spray formed alloy was greater than that of the spray formed alloy. To understand the mechanism responsible for this observed strengthening, the yield strength of two Cu alloys were analyzed using the dislocation pile-up model and Orowan mechanism, which were fairly consistent with the experimental results. Increase in yield strength of reactive spray formed alloy relative to spray formed alloy was largely attributed to nano-scale TiB dispersoids.

• Journal of Advanced Marine Engineering and Technology
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• 제34권2호
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• pp.303-309
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• 2010

유한요소법을 통하여 유성압연기(planetary rolling mill)에 의한 동관 압연공정을 연구하였다. 이 압연은 3개의 롤에 의해 만네스만 공법으로 동관을 성형하는 공정이고, 냉간가공으로 시작하여 열간가공으로 종료되며, 기존의 압출방식에 비해 공정의 단축과 원가 절감의 장점을 갖고 있다. 압연공정은 다양하고 복합적인 공정변수 들을 포함하고 있고, 각각의 변수들은 성형결과에 영향을 미친다. 그러므로 동관압연의 모든 공정변수가 고려되어져야 한다. 동관 압연공정은 성공적으로 시뮬레이션 되었고 최적의 압연조건을 결정하는데 유용할 것이다.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 1997년도 특별강연 및 추계학술발표 개요집
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• pp.184-193
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• 1997

Aluminium and aluminium alloys have the high electrical and heat conductivity. It gives rise to difficulties for a choice of electrodes material for their contact electric welding. This paper describes the investigations performed to solve the above problem. The purpose of this investigation was to obtain dispersion-hardening alloys by the internal oxidation method, to optimize their contents and treatment modes, to produce electrodes of these alloys and to test them. The strengthing effect of alloys with oxide particles depends on their size stability at high temperatures. Despite of the fact, that oxides are the most stable of all the non-metallic phases their coagulation takes place. Based on the early results, we chose two types of alloys, first No. 1 Cu - 0,4%Al and second No. 2 Cu - 0,2%Be for production of electrodes. These alloys had not additional alloying elements. These alloys were prepared as 1 mm plates and flake-formed 200 m thick, and also No. 1 as a powder of size 100 mkm (received from Korea). The large samples for electrodes were produced by three methods : explosive welding method, dynamic one including the explosion compression of electrode blank and the quasi-dynamic method including the high-speed compression of dense briquest and the further hot extrusion of a rod.