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대한금속재료학회(구 대한금속학회)> 대한금속재료학회지> 유한요소해석을 이용한 AA1100의 변형 불균일성에 미치는 다축 단조 유형의 영향 연구

KCI등재SCISCOUPUS

유한요소해석을 이용한 AA1100의 변형 불균일성에 미치는 다축 단조 유형의 영향 연구

A Study on the Effect of Multi-Axial Forging Type on the Deformation Heterogeneity of AA1100 Using Finite Element Analysis

김민성 ( Min-seong Kim ) , 김정균 ( Jeong Gyun Kim ) , 유태현 ( Tae Hyun Yoo ) , 조유연 ( You Yeon Jo ) , 이성 ( Seong Lee ) , 정효태 ( Hyo-tae Jeong ) , 최시훈 ( Shi-hoon Choi )
  • : 대한금속재료학회
  • : 대한금속재료학회지 59권9호
  • : 연속간행물
  • : 2021년 09월
  • : 624-639(16pages)
대한금속재료학회지

DOI


목차

1. 서 론
2. 실험 방법
3. 결과 및 고찰
4. 결 론
감사의 글
REFERENCES

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초록 보기

The effect of 3 forging routes (Route A - 1~12 passes by plane forging (PF) and reverse-plane forging (R-PF), Route B - 1~6 passes by PF and R-PF, 7~12 passes by diagonal forging (DF) and reverse-diagonal forging (R-DF), Route C - 1~12 passes by DF and R-DF) on maximum load to produce the workpiece, deformation heterogeneity and hydrostatic pressure distribution in AA1100 was theoretically investigated using finite element analysis (FEA). The maximum load per pass required to complete 1 cycle of the SPD process was different depending on the forging routes. Route A was relatively higher than Route B and C. From the results of effective strain, the deformation heterogeneity was predicted at the center, edge, and corner regions of the AA1100 workpiece produced by Route A and B. However, the distribution of effective strain in Route C was relatively more homogeneous than Route A and B. The average hydrostatic pressure, which is closely related to the suppression of crack formation in the workpiece under multi-axial forging, was predicted to be relatively bigger in Route C than Route A and B.
(Received December 1, 2020; Accepted March 2, 2021)

UCI(KEPA)

간행물정보

  • : 공학분야  > 금속공학
  • : KCI등재
  • : SCI,SCOPUS
  • : 월간
  • : 1738-8228
  • : 2288-8241
  • : 학술지
  • : 연속간행물
  • : 1963-2021
  • : 6970


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59권12호(2021년 12월) 수록논문
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KCI등재 SCI SCOPUS

1강유전성 플루오라이트 구조 기반 나노라미네이트 리뷰

저자 : 양건 ( Kun Yang ) , 박주용 ( Ju Yong Park ) , 이동현 ( Dong Hyun Lee ) , 김세현 ( Se Hyun Kim ) , 유근택 ( Geun Hyeong Park ) , 박근형 ( Eun Been Lee ) , 이은빈 ( Je In Lee ) , 이제인 ( Min Hyuk Park ) , 박민혁

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 12호 발행 연도 : 2021 페이지 : pp. 849-856 (8 pages)

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Ferroelectricity can be induced in fluorite-structured oxides such as HfO2 and ZrO2, a feature of increasing interest in both academia and industry. Initially, most research focused on solid solution films, but recently, it has been suggested that nanolaminates with independent HfO2 and ZrO2 layers may show electrical and physical properties superior to those of solid solution samples. It was reported that the nanolaminate samples could have remanent polarization higher than that of solid solution film or a wider composition window for robust ferroelectricity compared to the solid solution films. In this review, the existing literature on fluorite-structured nanolaminates is comprehensively reviewed.
(Received August 12 2021; Accepted September 1, 2021)

KCI등재 SCI SCOPUS

2고비강도와 고연신을 가지는 다중변형기구 하이엔트로피 합금 개발

저자 : 윤국노 ( Kook Noh Yoon ) , 오현석 ( Hyun Seok Oh ) , 이제인 ( Je In Lee ) , 박은수 ( Eun Soo Park )

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 12호 발행 연도 : 2021 페이지 : pp. 857-869 (13 pages)

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In this study we developed a novel (TRIP+TWIP) high entropy alloy (HEA) with high specific strength and large ductility. First, by controlling the atomic constitution of the 3d transition metals (Cr, Mn, Fe, Co, and Ni), we designed a light-weight TRIP-assisted dual-phase HEA with a non-equiatomic composition of Cr22Mn6Fe40Co26Ni6, which exhibited 5% lighter density than the Cantor HEA. Secondly, we systematically added Al (a lightweight element (2.7 g/㎤), which has a large atomic size misfit with 3d transition metals, and Ferrite stabilizer) up to 5 at.% in Cr22Mn6Fe40Co26Ni6 HEA. With increasing Al content, the phase constitution of the alloy changed from a dual-phase of FCC and HCP (0 to 2.0 at.%) to a FCC single-phase (2.5 to 3.5 at.%), to a dual-phase of FCC and BCC (4.0 to 5.0 at.%). In particular, the (Cr22Mn6Fe40Co26Ni6)97.5Al2.5 HEA with the FCC single-phase exhibited a large Hall-Petch coefficient and relatively lower thermal conductivity due to its three times larger atomic size mismatch (δ) than the Cantor HEA, which causes the superior solid solution strengthening effect. Furthermore, the (Cr22Mn6Fe40Co26Ni6)96Al4.0 HEA, a boundary composition of BCC precipitation in the FCC phase, exhibited a 10% higher specific strength than the Cantor HEA as well as 50% larger strain, due to the unique TRIP and TWIP complex deformation mechanism. This result shows that the addition of Al in Cr22Mn6Fe40Co26Ni6 HEA can result not only in greater chemical complexity due to the multicomponent high entropy compositions, but also microstructural complexity due to the increase in competing crystalline phases. The confusion effect caused by both complexities lets the alloy overcome the trade-off relationship among conflicting intrinsic properties, such as strength versus ductility (or density). Consequently, these results pave the way for a new design strategy of a novel (TRIP+TWIP) HEA with high specific strength and large ductility.
(Received August 19 2021; Accepted September 8, 2021)

KCI등재 SCI SCOPUS

3Twin-Roll Strip Casting 공정으로 제조된 Al 7075 합금의 미세조직 및 마모 특성

저자 : 김경욱 ( Kyoung-wook Kim ) , 백민석 ( Min-seok Baek ) , 어광준 ( Kwangjun Euh ) , 이기안 ( Kee-ahn Lee )

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 12호 발행 연도 : 2021 페이지 : pp. 870-879 (10 pages)

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Al 7075 alloy was manufactured using the twin-roll strip casting (TRC) process, and the mechanical and wear properties of the fabricated TRC process were investigated. To compare the properties of the alloy manufactured by TRC, another Al 7075 alloy was fabricated by conventional direct chill (DC) casting as a comparative material. Based on initial microstructure observations, the Al 7075 alloy manufactured by the DC process showed relatively elongated grains compared to the Al 7075 alloy by TRC process. In both alloys, η(MgZn2) phases were present at the grain and grain boundaries. In the Al 7075 alloy manufactured by the DC process, the η(MgZn2) phases were coarse with a size of ~86 nm and were mainly concentrated in the local area. However, the Al 7075 alloy manufactured by TRC had relatively fine η(MgZn2) phases size of ~40 nm, and they were evenly distributed throughout the matrix. When the mechanical properties of the two alloys were compared, the TRC process showed higher hardness and strength properties than the DC process. In room temperature wear test results, the TRC process exhibited lower weight loss and wear rates compared to the DC process at all wear loads. In other words, the TRC process resulted in relatively superior wear resistance properties compared to the conventional DC process. The wear behavior of both alloys changed from abrasive wear to adhesive wear as the wear load increased. However, the TRC process maintained abrasive wear up to higher loads. Based on the above results, a correlation between the microstructure and wear mechanism of the Al 7075 alloy manufactured by TRC is also suggested.
(Received May 24 2021; Accepted September 17, 2021)

KCI등재 SCI SCOPUS

4열보조 나노 전사 프린팅을 통한 금속 박막의 표면 주름 나노패턴 형성 방법

저자 : 박태완 ( Tae Wan Park ) , 박운익 ( Woon Ik Park )

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 12호 발행 연도 : 2021 페이지 : pp. 880-885 (6 pages)

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Nanopatterning methods for pattern formation of high-resolution nanostructures are essential for the fabrication of various electronic devices, including wearable displays, high-performance semiconductor devices, and smart biosensor systems. Among advanced nanopatterning methods, nanotransfer printing (nTP) has attracted considerable attention due to its process simplicity, low cost, and great pattern resolution. However, to diversify the pattern geometries for wide device applications, more effective and useful nTP based patterning methods must be developed. Here, we introduce a facile and practical nanofabrication method to obtain various three-dimensional (3D) ultra-thin metallic films via thermally assisted nTP (T-nTP). We show how to generate surface-wrinkled 3D nanostructures, such as angular line, concave-valley, and convex-hill structures. We also demonstrate the principle for effectively forming 3D nanosheets by T-nTP, using Si master molds with a low aspect ratio (A/R ≤ 1). In addition, we explain how to obtain a 3D wavy structure when using a mold with high A/R (≥ 3), based on the isotropic deposition process. We also produced a highly ordered 3D Au nanosheet on flexible PET over a large area (> 15 μm). We expect that this T-nTP approach using various Si mold shapes will be applied for the useful fabrication of various metal/oxide nanostructured devices with high surface area.
(Received September 10, 2021; Accepted September 24, 2021)

KCI등재 SCI SCOPUS

5Ti/Cu 이종 마찰 교반 용접 시 미세조직과 기계적 특성에 미치는 회전속도의 영향

저자 : 이용재 ( Yong-jae Lee ) , 정원기 ( Won-ki Jung ) , 신세은 ( Se-eun Shin ) , 이동근 ( Dong-geun Lee )

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 12호 발행 연도 : 2021 페이지 : pp. 886-892 (7 pages)

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The dissimilar welding of titanium and copper by fusion welding is very difficult because the melting points of the materials are very highly different and strong brittle intermetallic compounds (IMCs) can be easily produced in welded zone and heat-affected zone, etc. Friction stir welding was employed as a type of solid-state welding for Ti/Cu dissimilar welding to obtain a sound welded zone and reduce the total process cost. This study investigated how the metal flow of the welded zone changes according to the variation in the rotational speed of the tool, from 450 rpm to 600 rpm. When the rotational speed was too high, the plastic flow of the softened material increased and intermetallic compounds such as TiCu, Ti2Cu3, and Ti2Cu, were generated in the Cu region of the welded zone. The microstructural evolution of AS (Advancing Side) and RS (Retreating Side) were investigated and the soundness of the welded zone and its mechanical properties were evaluated through the microstructural evolution. A high hardness value of 200 Hv or more was exhibited in some points, due to the formation of intermetallic compounds in the RS (Cu) region. Ti/Cu dissimilar friction stir welding at a welding speed of 50 mm/min and an appropriate rotation speed of 500 rpm showed a good welded zone and mechanical properties.
(Received June 11 2021; Accepted August 27, 2021)

KCI등재 SCI SCOPUS

6Al-Si 도금된 핫스탬핑 보론강의 볼트 프로젝션 용접시 예열 통전이 용융 거동에 미치는 영향

저자 : 김재훈 ( Jae-hun Kim ) , 전현욱 ( Hyun-uk Jun ) , 천주용 ( Joo-yong Cheon ) , 김재원 ( Jae-won Kim ) , 김재득 ( Jae-deuk Kim ) , 지창욱 ( Changwook Ji )

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 12호 발행 연도 : 2021 페이지 : pp. 893-903 (11 pages)

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This study evaluated the effect of preheating on early stage melting behavior of a Al-Si coated hot stamped boron steel bolt during projection welding. A large amount of heat was generated in the early stage of projection welding. Because of the large heat generation, a rapid collapse of the projection occurred and a molten coating layer remained on the interface of the welded part. This caused welding defects such as expulsion and porosity. However, preheating helped remove the molten Al-Si coating layer by pushing it out toward the outer edge of the molten pool. This suggests that preheating can effectively minimize or remove the molten coating layer within the weld. Preheating also prevented the rapid collapse of the projection by partially melting the projection, and thus improving the contact area. These phenomena can prevent the concentration of current density at the weld interface and hence decrease heat generation. Finally, the preheating current improved nugget quality by promoting the stable growth of the melted metal and by preventing expulsion and porosity.
(Received July 23 2021; Accepted August 25, 2021)

KCI등재 SCI SCOPUS

7Synthesis of Nb0.8Hf0.2FeSb0.98Sn0.02 and Hf0.25Zr0.25Ti0.5NiSn0.98Sb0.02 Half-Heusler Materials and Fabrication of Thermoelectric Generators

저자 : Sung-jae Joo , Ji-hee Son , Jeongin Jang , Bong-seo Kim , Bok-ki Min

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 12호 발행 연도 : 2021 페이지 : pp. 904-910 (7 pages)

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In this study, half-Heusler (HH) thermoelectric materials Nb0.8Hf0.2FeSb0.98Sn0.02 (p-type) and Hf0.25Zr0.25Ti0.5NiSn0.98Sb0.02 (n-type) were synthesized using induction melting and spark plasma sintering. For alloying, a conventional induction melting technique was employed rather than arc melting, for mass production compatibility, and the thermoelectric properties of the materials were analyzed. The maximum dimensionless figures of merit (zTmax) were 0.75 and 0.82 for the p- and n-type material at 650 ℃ and 600 ℃, respectively. These materials were then used to fabricate generator modules, wherein two pairs of p- and nlegs without interfacial metal layers were brazed on direct bonded copper (DBC)/Al2O3 substrates using a Zrbased alloy. A maximum power of 0.57 W was obtained from the module by applying a temperature gradient of 476 ℃, which corresponds to a maximum power density of 1.58W cm -2 when normalized by the area of the material. The maximum electrical conversion efficiency of the module was 3.22% at 476 ℃ temperature gradient. This value was negatively affected by the non-negligible contact resistivity of the brazed interfaces, which ranged from 6.63 × 10 -9 Ω ㎡ to 7.54 × 10 -9 Ω ㎡ at hot-side temperatures of 190 ℃ and 517 ℃, respectively. The low electrical resistivity of the HH materials makes it especially important to develop a brazing technique for ultralow resistance contacts.
(Received August 11 2021; Accepted August 31, 2021)

KCI등재 SCI SCOPUS

8슈퍼커패시터 전극 제조시 Indium-Tin-Oxide기판 위 활성탄 증착에 적합한 바인더와 용매 소재

저자 : 최영묵 ( Young Mook Choi ) , 전상은 ( Sang-eun Chun )

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 12호 발행 연도 : 2021 페이지 : pp. 911-920 (10 pages)

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Supercapacitor electrode slurry is prepared for mass production by mixing activated carbon powder, conductive agent, and binder, which is then deposited on a substrate using the doctor-blade method. Polyvinylidene fluoride (PVDF) and 1-methyl-2-pyrrolidone (NMP) are used as binder and solvent, respectively, to form the electrode slurry on a metal substrate. In this study, ethyl cellulose (EC) is evaluated as a binder to prepare an electrode on an indium-tin-oxide (ITO) substrate obtaining transparent supercapacitors. Terpineol and isopropyl alcohol (IPA) are compared as suitable solvents for the EC binder. When terpineol is employed as a solvent, the conductive agent is uniformly deposited around the activated carbon powder. An electrode prepared using EC and terpineol exhibits slightly lower specific capacitance and rate performance than that using conventional PVDF and NMP. However, the electrode prepared using EC and terpineol securely adheres to the electrode components, resulting in a robust electrode. In contrast, an electrode prepared using EC and IPA exhibits high charge transfer resistance at the interface of the electrode/electrolyte, leading to a low specific capacitance and rate performance. Thus, ecofriendly EC and terpineol can substitute the conventional PVDF and NMP for depositing activated carbon powder on an ITO substrate, while improving the specific capacitance of manufactured electrodes.
(Received September 1 2021; Accepted September 17, 2021)

KCI등재 SCI SCOPUS

9Shielding Analysis of Metal Hydride-based Materials for Both Neutron and Gamma Rays Using Monte Carlo Simulation

저자 : Jeongkwon Kwak , Boravy Muth , Hyeon-woo Yang , Chang Je Park , Woo Seung Kang , Sun-jae Kim

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 12호 발행 연도 : 2021 페이지 : pp. 921-925 (5 pages)

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Radiation causes damage to the human body, the environment, and electronic equipment. Shielding against neutron and gamma rays is particularly difficult because of their strong ability to penetrate materials. Conventional gamma ray shields are typically made of materials containing Pb. However, they pose problems in that Pb is a heavy metal, and human poisoning and/or pollution can result from the manufacturing, use, and disposal of these materials. In addition, neutron rays are shielded by materials rich in H2 or concrete. In the case of the latter, the manufacturing cost is high. Thus, it is necessary to develop a new multilayer structure that can shield against both neutron and gamma rays. We set up a simulation model of a multilayered structure consisting of metal hydrides and heavy metals, and then evaluated the simulations using Monte Carlo N-Particle Transport Code. Monte Carlo simulation is an accurate method for simulating the interaction between radiation and materials, and can be applied to the transport of radiation particles to predict values such as flux, energy spectrum, and energy deposition. The results of the study indicated the multilayer structure of ZrH2, U, and W could shield both neutron and gamma rays, thus showing potential as a new shielding material to replace Pb and concrete.
(Received July 6 2021; Accepted September 15, 2021)

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KCI등재SCISCOUPUS

1압력 용기 재료 SA508에서 열적 처리에 따른 입계 파괴의 원인

저자 : 김성수 ( Sung Soo Kim ) , 정종엽 ( Jung Jong Yeob ) , 김영석 ( Young Suk Kim )

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 9호 발행 연도 : 2021 페이지 : pp. 589-601 (13 pages)

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Intergranular(IG) fracture due to thermal treatment has been reported in a reactor pressure vessel(RPV) steel of Russian light water reactor in last decade. This is attributed to grain boundary segregation of phosphorus (P) or precipitation of carbide, etc.. This is a finding a difference in microstructure before and after IG cracking; this cannot explain the cause of the IG embrittlement. This old paradigm follows only correlation. Recently, a mechanism in which IG embrittlement occurs due to a decrease in entropy of a material has been reported at a temperature where atomic diffusion is possible. It is anticipated that new paradigm can explain the IG embrittlement of RPV based on a causal relationship. Thus, the thermal treatment at 350-420 ℃ was applied to RPV steel of SA508 and IG cracking was confirmed. DSC analysis was applied to confirm whether a decrease in entropy due to a short range ordering reaction occurs in SA508. It was possible to quantify the entropy change(ΔS= Q/T) through DSC measurement. A lattice changes due to thermal treatment were confirmed using XRD analysis in aged specimens. The results showed that lattice contraction by aging causes a reduction of fracture toughness. The internal stress formed inside the material due to entropy reduction can be calculated by multiplying the exothermic energy per unit mass by the density. This relationship is expressed by a equation of stress(σ) = exothermic heat(ΔQ) x density(ρ).
(Received May 21, 2021; Accepted June 28, 2021)

KCI등재SCISCOUPUS

2Si 및 Al 함량과 항온열처리조건이 초고강도 마르텐사이트-베이나이트 Fe-0.2C-2.0Mn 복합조직강의 미세조직과 인장특성에 미치는 영향

저자 : 이응혁 ( Eung Hyuk Lee ) , 유창재 ( Chang Jae Yu ) , 이홍범 ( Hong-bum Lee ) , 김지훈 ( Ji-hoon Kim ) , 서동우 ( Dong-woo Suh )

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 9호 발행 연도 : 2021 페이지 : pp. 602-612 (11 pages)

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This study investigated the influence of partial replacement of Si by Al on the microstructure and tensile properties of ultra-high strength steels with martensite-bainite complex microstructure produced by austenitization and subsequent isothermal heat treatment around Ms temperature. When the isothermal heat treatment was done below the Ms temperature, the fraction of martensite increased with the lower isothermal temperature, but the fractions of constituent phases in the final microstructure were not significantly affected by the partial replacement of Si by Al. Nevertheless, the increase in Al content in the complex phase steel accelerated the bainite transformation, which is thought to be associated with the increase of the free energy difference between FCC and BCC. The enhancement of the bainite transformation not only effectively suppressed the martensite formation upon final cooling when the isothermal temperature was above the Ms temperature but also helped refine the final microstructure when subjected to isothermal heat treatment below the Ms temperature. The yield strengths of the investigated complex phase steels were little influenced by the partial replacement of Si with Al, as long as the fractions of the constituent phases were comparable. This possibly originates with the solid solution hardening and the microstructure refinement with Al addition.
(Received June 8, 2021; Accepted June 30, 2021)

KCI등재SCISCOUPUS

3고내식 합금도금 PosMAC® 강판의 개발과 응용 특성

저자 : 손일령 ( Il-ryoung Sohn ) , 김태철 ( Tae-chul Kim ) , 주광일 ( Gwang-il Ju ) , 김명수 ( Myung-soo Kim ) , 김종상 ( Jong-sang Kim )

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 9호 발행 연도 : 2021 페이지 : pp. 613-623 (11 pages)

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PosMAC® is a hot dipping Zn-Mg-Al coated steel sheet developed by POSCO. PosMAC®3.0 shows excellent anti-corrosion performance and is suitable for construction and solar energy systems in severe corrosive environments. PosMAC®1.5 has a superior surface quality and is preferred for automotive and home appliances. The advanced anti-corrosion properties of PosMAC® comes from a dense corroded layer which forms on coated surfaces, compared with traditional Zn coatings such as GI, GA and EG. PosMAC® steels show superior corrosion protection compared to GI coatings in cyclic corrosion tests, despite an approximate 30% reduction in coating weight. The PosMAC® has excellent application properties for the arc welding of automotive chassis. It has a heat resistance that is more robust than the GI coating, and maintains excellent corrosion protection near the welds of the chassis. Zn-Mg-Al coatings, whose chemical compositions are similar to PosMAC® coatings, have very low surface friction properties compared to the GI coating. The friction coefficient of PosMAC® is stabilized to 0.09~0.11. In contrast, the GI coating showed higher friction coefficients of 0.2~0.3 in the repeated friction test. PosMAC® would be appropriate for complex forming parts with less galling, given these low friction resistance properties. It is expected that the industrial demand for PosMAC® steel will increase in the near future, thanks to its Zn saving and high anti-corrosion performance.
(Received October 9, 2020; Accepted May 24, 2021)

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4유한요소해석을 이용한 AA1100의 변형 불균일성에 미치는 다축 단조 유형의 영향 연구

저자 : 김민성 ( Min-seong Kim ) , 김정균 ( Jeong Gyun Kim ) , 유태현 ( Tae Hyun Yoo ) , 조유연 ( You Yeon Jo ) , 이성 ( Seong Lee ) , 정효태 ( Hyo-tae Jeong ) , 최시훈 ( Shi-hoon Choi )

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 9호 발행 연도 : 2021 페이지 : pp. 624-639 (16 pages)

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The effect of 3 forging routes (Route A - 1~12 passes by plane forging (PF) and reverse-plane forging (R-PF), Route B - 1~6 passes by PF and R-PF, 7~12 passes by diagonal forging (DF) and reverse-diagonal forging (R-DF), Route C - 1~12 passes by DF and R-DF) on maximum load to produce the workpiece, deformation heterogeneity and hydrostatic pressure distribution in AA1100 was theoretically investigated using finite element analysis (FEA). The maximum load per pass required to complete 1 cycle of the SPD process was different depending on the forging routes. Route A was relatively higher than Route B and C. From the results of effective strain, the deformation heterogeneity was predicted at the center, edge, and corner regions of the AA1100 workpiece produced by Route A and B. However, the distribution of effective strain in Route C was relatively more homogeneous than Route A and B. The average hydrostatic pressure, which is closely related to the suppression of crack formation in the workpiece under multi-axial forging, was predicted to be relatively bigger in Route C than Route A and B.
(Received December 1, 2020; Accepted March 2, 2021)

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5Effect of Interfacial Intermetallic Compounds Morphology on Mechanical Properties of Laser Brazing of Aluminum to Steel

저자 : Kwang-hyeon Lee , Su-jin Lee , In-duck Park , Kwang-deok Choi , Chung-yun Kang , Jeong Suh , Tae-jin Yoon

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 9호 발행 연도 : 2021 페이지 : pp. 640-651 (12 pages)

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The paper provides experimental details of the welding and specific examples of welding aluminum welding battery cans and conductive tabs for battery pack manufacture. In this study, we provide experimental details of a process for joining dissimilar materials used in sealing battery parts. A laser brazing technique was used for the lap joining of aluminum alloy and a deep drawing quality stainless steel, with an Al-Si filler metal. These materials are commonly used in battery applications, as materials for the cap plate, tab plate and can. The relationships among the width of the brazed zone, formation of intermetallic compounds (IMCs), shape of the joint interface, and joint strength were systematically investigated with respect to the laser power and filler wire feeding rate. When a low and medium laser power (1.2-2.0 kW) was applied, the joint strength was very low, and fracture occurred across the band-shaped IMC layer. With a further increase in the applied laser power (2.2-2.8 kW), a new needle-like IMC composed of Al13Fe5 with a monoclinic crystal structure was formed, and it penetrated the brazed zone. In addition, the width of the brazed zone increased due to the partial melting of the aluminum. The joint efficiency under a high laser power condition was 70% compared to that of the base material. Fractures occurred alternately along the needle-shaped IMC and filler metal zone. Since the fracture propagated along the needle-like IMCs inside the brazed zone, the peak load was higher than that of the band-shaped IMCs.
(Received April 21 2021; Accepted June 17, 2021)

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6적층제조 공정으로 구현된 형상 적응형 냉각채널 적용 다이캐스팅 금형의 냉각성능 평가

저자 : 박유진 ( Yu Jin Park ) , 김억수 ( Eok Soo Kim ) , 이정훈 ( Jeong Hun Lee ) , 최지환 ( Ji Hwan Choi ) , 윤필환 ( Pil Hwan Yoon ) , 강호정 ( Ho Jeong Kang ) , 김동현 ( Dong Hyun Kim ) , 박용호 ( Yong Ho Park ) , 고종완 ( Jong Wan Ko )

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 9호 발행 연도 : 2021 페이지 : pp. 652-663 (12 pages)

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A cooling channel with an optimized design provides not only high throughput with gravity die casting, but also guarantees product quality. A conformal cooling channel (CC) whose structure follows the shapes or surfaces of the mold cavity has attracted great attention in the die casting industry, because it allows rapid and uniform cooling. However, implementing conformal cooling remains highly challenging, because the complicated geometries of CC are difficult to form using conventional fabrication methods such as drilling and milling. In recent years, advances in additive manufacturing (AM) technology have made it possible to fabricate products with complex and elaborate structures. In this paper, a gravity die casting mold with CC was designed and built using AM technology. The cooling channel performance was estimated and evaluated using an Al-Si-Cu alloy casting simulation and die casting experiments, respectively. The casting simulation results showed that the cooling performance of the CC was enhanced by ca. 10% compared with that of a conventional cooling channel. The experimental cooling performance of the CC improved by ca. 8% compared to that of a conventional cooling channel, and the increment in performance was consistent with the simulation results. In addition, microstructural evidence clarified that the effective cooling performance of CC could be attributed to the decrement (ca. 17%) of the secondary dendrite arm spacing (SDAS) of the Al-Si-Cu alloy. In this research, AM technology provides a novel way to fabricate functionally superior CC molds that are hardly producible with traditional methods.
(Received May 14, 2021; Accepted June 4, 2021)

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7텅스텐 나노박막의 상변태를 이용한 반투명 면상발열체 형성 연구

저자 : 최지윤 ( Jiyun Choi ) , 최두호 ( Dooho Choi )

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 9호 발행 연도 : 2021 페이지 : pp. 664-669 (6 pages)

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In this study, we prepared highly thermostable semi-transparent heaters composed of W layers with thicknesses of 1-20 nm, on which a 30 nm-thick ZnO layer was deposited to serve as an anti-oxidation barrier. The optical transmittance and sheet resistance of the heaters could be greatly modulated by varying the W layer thickness. For layer thicknesses up to 10 nm, the initial Joule heating above 100 ℃ significantly reduced the sheet resistance, by 300% for a 6 nm-thick W layer at a fixed voltage for a duration of 400 s. During the test period, heater current and heating capability continuously increased. In subsequent heater operations, the heaters exhibited highly reproducible heating capability. In contrast, for films thicker than 10 nm, the Joule heating process resulted in only a marginal reduction in sheet resistance, i.e., by 4% for a 20 nm-thick W layer. In order to investigate the sharp dependence of heater characteristics on thickness, we performed x-ray diffraction analyses, which revealed that the films thinner than 10 nm were composed of both the equilibrium low-resistivity α-phase and metastable high-resistivity β-phase, and films thicker than 10 nm contained mostly α-phase. The Joule heating process for the thinner films was found to transform the β-phase into α-phase at temperatures above 100 ℃, which resulted in significant improvement in the heating capability of the 6 nm-thick W layer. For films thicker than 10 nm, the W layers contained mostly α-phase and no such transformation-induced effects were observed. Finally, W heaters composed of α-phase exhibited highly thermostable and reproducible heater properties, which make the heaters suitable for applications with semi-transparent heaters.
(Received April 29, 2021; Accepted June 1, 2021)

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8Porous MnO2/ carbon Hybrid Material with Improved Electrochemical Performance

저자 : Venugopal Nulu

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 9호 발행 연도 : 2021 페이지 : pp. 670-676 (7 pages)

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In this work, MnO2 nanoparticles were embedded in a carbon matrix as a porous composite, fabricated using a simple chemical route followed by low-temperature annealing, with activated carbon (AC) as the carbon source in the composite preparation. The porous MnO2/carbon structures contained some selective nanoparticles coated with carbon. The structural feature was identified by transmission electron microscopy (TEM). The surface area and pore size distribution of the materials were investigated by N2 adsorption/desorption isotherms, and demonstrated a high surface area of about 80 ㎡ g-1. AC is a readily available carbon source that can easily form a composite with MnO2 nanoparticles, forming a distinctive porous morphology. When employed as an anode material for lithium-ion batteries (LIB), the composite electrode demonstrated high specific capacities with an initial discharge capacity of 2500 mAh g-1 and maintained about 1391 mAh g-1 after fifty cycles. It also demonstrated excellent high rate performance, delivering more than 500 mAh g-1 of specific capacity at 3000 mA g-1, which is a higher capacity than a conventional graphite anode. Overall, the MnO2/ carbon composite electrode delivered superior anode performance, which was attributed to the improved surface area of the carbon hybridized MnO2 nanoparticles. The porous composite has benefits for lithium storage performance.
(Received April 29 2021; Accepted June 21, 2021)

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9Al과 SnO2 혼합 분말을 사용한 일차원 Al과 Al2O3 나노/마이크로구조의 저온 성장

저자 : 이근형 ( Geun-hyoung Lee )

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 9호 발행 연도 : 2021 페이지 : pp. 677-681 (5 pages)

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One-dimensional Al and Al2O3 nano/microstructures were fabricated via thermal oxidation of Al and SnO2 powder mixtures at temperatures below the melting point of Al (660 ℃). Furthermore, the synthesis process was carried out in air at atmospheric pressure, which made the process very simple and easy. Sn metal particles with spherical shape were observed on the tips of the Al and Al2O3 nano/microstructures, suggesting that the nano/microstructures were grown via a catalyst-assisted growth mechanism. The Sn acted as a catalyst for growing the Al and Al2O3 nano/microstructures. The Sn with low melting point (232 ℃) was produced via the reduction of SnO2 by Al, and formed catalyst droplets at the growth temperatures. Al atoms diffused and dissolved into the Sn liquid droplets, leading to the nucleation and then the growth of the Al and Al2O3 nano/microstructures. At 400 ℃, the diffusion of Al atoms into the Sn liquid droplets was associated with high stress generated at the Al2O3/Al interface. At 600 ℃ close to the melting point of Al, Al atoms were diffused from the thin Al liquid layer, which was formed on the surface of the Al powder, to the Sn liquid droplets. Simultaneously, the Al atoms reacted with oxygen in air and formed solid Al2O3 nuclei. A relatively strong ultraviolet emission band centered at 330 nm was observed in the sample prepared at 600 ℃.
(Received May 5, 2021; Accepted June 2, 2021)

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