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대한금속재료학회(구 대한금속학회)> 대한금속재료학회지> 고내식 합금도금 PosMAC® 강판의 개발과 응용 특성

KCI등재SCISCOUPUS

고내식 합금도금 PosMAC® 강판의 개발과 응용 특성

Development of PosMAC® Steel and Its Application Properties

손일령 ( Il-ryoung Sohn ) , 김태철 ( Tae-chul Kim ) , 주광일 ( Gwang-il Ju ) , 김명수 ( Myung-soo Kim ) , 김종상 ( Jong-sang Kim )
  • : 대한금속재료학회
  • : 대한금속재료학회지 59권9호
  • : 연속간행물
  • : 2021년 09월
  • : 613-623(11pages)
대한금속재료학회지

DOI


목차

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

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초록 보기

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)

UCI(KEPA)

간행물정보

  • : 공학분야  > 금속공학
  • : KCI등재
  • : SCI,SCOPUS
  • : 월간
  • : 1738-8228
  • : 2288-8241
  • : 학술지
  • : 연속간행물
  • : 1963-2021
  • : 6961


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KCI등재 SCI SCOPUS

1영구자석 재료의 개발현황 및 향후 발전방향

저자 : 최철진 ( Chul-jin Choi ) , 박지훈 ( Jihoon Park ) , 임정태 ( Jung Tae Lim ) , 김종우 ( Jong-woo Kim )

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 11호 발행 연도 : 2021 페이지 : pp. 761-768 (8 pages)

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Permanent magnetic materials are essential for converting mechanical and electric energy, and are needed in electric vehicles, electronics, wind turbines, and etc. However, high performance rare-earth element based magnets have many limitations, including critical materials problems and the degradation of magnetic properties at elevated temperatures. There has been increasing international demand to solve these problems, and to develop new magnets with reduced rare earth materials, or free magnets based on metallic alloys. This paper describes current research trends, and state of art and future research directions for next generation permanent magnetic materials, to accelerate their research and rapid industrialization.
(Received July 26 2021; Accepted August 19, 2021)

KCI등재 SCI SCOPUS

21.25Cr-0.5Mo과 2.25Cr-1Mo 강의 동적 변형시효 거동에 미치는 합금원소 및 미세조직의 영향

저자 : 이요섭 ( Yo Seob Lee ) , 이호중 ( Ho Jung Lee ) , 이종현 ( Jong Hyeon Lee )

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 11호 발행 연도 : 2021 페이지 : pp. 769-780 (12 pages)

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The effect of alloying elements and microstructure on the dynamic strain aging (DSA) behavior of 1.25Cr-0.5Mo (P11, ASTM 335Gr.P11) and 2.25Cr-1Mo (P22, ASTM 335Gr.P22) steels was investigated. For both steels, different cooling conditions such as air-cooling (AC) and oil-quenching (OQ) were applied. Tensile tests were conducted in the temperature range of 20-450 ℃ and a strain rate in the range of 6 × 10-5- 6 × 10-3 s-1 for the steels with different cooling conditions. The P11AC steel showed serration behavior over a wider temperature range and exhibited higher ultimate tensile strength (UTS) than for the P22AC steel. This is attributed to the effects of alloying elements (Cr, Mo and Si) due to dissolved C, and the ferrite fraction on mechanical behavior. Meanwhile, the P11AC and P11OQ steels also showed different behaviors for DSA starting temperature, DSA temperature range, and serration type. The AC condition showed higher UTS from the interaction solid solution hardening (ISSH) effect due to substitutional Cr, Mo, and interstitial C elements. The calculated activation energy value (Q) for the P11 steel was around 94-103 kJ/mol-1, similar to that of ferritic steels, and it was higher for the P22 steel, with a Q value of 233 kJ/mol-1 from the ISSH effect.
(Received July 21, 2021; Accepted August 23, 2021)

KCI등재 SCI SCOPUS

3Effect of Cooling Rate on The Microstructure And Cryogenic Impact Toughness of HAZ in 9% Ni Steel

저자 : Hae Won Eom , Joo Yeon Won , Sang Yong Shin

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 11호 발행 연도 : 2021 페이지 : pp. 781-795 (15 pages)

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The effects of cooling rate on the microstructure and cryogenic impact toughness of coarse-grained heat-affected zone (CGHAZ) and inter-critically reheated coarse-grained HAZ (IC CGHAZ) in 9% Ni steel were investigated. CGHAZ and IC CGHAZ specimens were prepared from 9% Ni steel by controlling the cooling rate of the simulated welding process. The microstructure of the CGHAZ specimens consisted of auto-tempered martensite and lath martensite. As the cooling rate increased, the volume fraction of the auto-tempered martensite and the effective grain size decreased. A large amount of fine carbides was distributed inside the auto-tempered martensite, the dislocation density was low, and high angle grain boundaries were not observed. The microstructure of the IC CGHAZ specimens consisted of tempered martensite and lath martensite. As the cooling rate increased, the volume fraction of the tempered martensite and effective grain size decreased. Finer carbides were distributed inside the tempered martensite than in the auto-tempered martensite, the dislocation density was low, and high angle grain boundaries were not observed. Cryogenic fracture revealed that ductile fracture occurred in the auto-tempered martensite and tempered martensite, and brittle fracture occurred in the lath martensite. The crack propagation path was zig-zag in the high angle grain boundaries of the lath martensite. The volume fraction of auto-tempered martensite and tempered martensite and the effective grain size in the HAZ specimens had a significant effect on cryogenic impact toughness. In the IC CGHAZ specimens, cryogenic impact toughness decreased and then became constant as the cooling rate increased, due to a decrease in the volume fraction of the tempered martensite and effective grain size.
(Received July 14 2021; Accepted August 13, 2021)

KCI등재 SCI SCOPUS

4Effect of Joule-Heating Treatment on the Microstructure and Physical Properties of 16-Stranded Compressed Copper Wires

저자 : Jin-ju Choi , Byoungyong Im , Yubin Kang , Dae-geun Kim

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 11호 발행 연도 : 2021 페이지 : pp. 796-801 (6 pages)

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Compressed wires are produced by cross-sectionally compressing stranded conductors, which results in a smaller conductor diameter. This also leads to a lower weight wire, because a thinner external insulated coating can be used, compared to the low-voltage wires typically used in automobiles. However, a post production heat treatment of the compressed wires is required because plastic deformation occurs during compression after drawing the wires. In this study, the work hardening of stranded compressed copper wires was controlled by Joule-heating, and the resulting changes in microstructure, mechanical, and electrical properties after various annealing voltages (0, 25, 27, 31, 35, and 39 V) were observed. The results confirmed that as the annealing voltage increased from 0 to 31 V, the anisotropic deformation texture with a <111> orientation as the main component was reduced, and micrograins were generated throughout the stranded wires via recrystallization. At an annealing voltage above 31 V, the grains grew to be more than twice as large as those before heat treatment. At an annealing voltage of 31 V these structural changes contribute to the elongation increase of the compressed wires to 28.34%, and an improvement in electrical resistance to 145.85 mΩ.
(Received July 7 2021; Accepted August 23, 2021)

KCI등재 SCI SCOPUS

5Nano Silicon Composite with Gelatin/Melamine Derived N-doped Carbon as an Efficient Anode Material for Li-ion Batteries

저자 : Venugopal Nulu

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 11호 발행 연도 : 2021 페이지 : pp. 802-812 (11 pages)

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Silicon (Si) has a high theoretical capacity and low working potential vs. Li/Li+, and has been investigated as the most capable negative electrode material for lithium-ion batteries (LIBs). However, Si undergoes significant volume changes during the Li+ alloying/ dealloying processes, leading to unstable cycle life and limiting its practical applicability in anodes. Introducing carbon into the Si anodes can effectively address the Si drawbacks, while providing advantages of improved conductivity and structural stability. In this study we choose gelatin/ melamine combination as an eco-friendly and cost-effective source for nitrogen-doped carbon to make a Si composite. The prepared composite was studied as an anode material for LIBs, and it delivered excellent cyclability with 2175 mAh g-1 capacity after 50 cycles with 86% capacity retention at 200 mA g-1. The composite exhibited superior rate capability and improved Li+ diffusion properties compared with bare Si nanoparticles (Si NP). The significant enhancement could be attributed to the structural stability and conductivity provided by the nitrogen-doped carbon matrix. This work promotes emerging batteries with low-cost materials as a promising solution for increasing energy storage requirements.
(Received June 29, 2021; Accepted August 20, 2021)

KCI등재 SCI SCOPUS

6높은 전류밀도에서 리튬이온배터리의 사이클 성능 향상을 위한 세라믹 코팅 분리막 연구

저자 : 조규상 ( Kyusang Cho ) , 찬드란발라무루간 ( Chandran Balamurugan ) , 임하나 ( Hana Im ) , 김형진 ( Hyeong-jin Kim )

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 11호 발행 연도 : 2021 페이지 : pp. 813-820 (8 pages)

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Given the global demand for green energy, the battery industry is positioned to be an important future technology. Lithium-ion batteries (LIBs), which are the most widely used battery in the market, are the focus of various research and development efforts, from materials to systems, that seek to improve their performance. The separator is one of the core materials in LIBs and is a significant factor in the lifespan of high-performance batteries. To improve the performance of present LIBs, electrochemical testing and related surface analyses of the separator is essential. In this paper, we prepared a ceramic (Boehmite, γ-AlOOH) coated polypropylene separator and a porous polyimide separator to compare their electrochemical properties with a commercialized polypropylene (PP) separator. The prepared separators were assembled into nickel-manganese-cobalt (NMC) cathode half-cell and full-cell lithium-ion batteries. Their cycling performances were evaluated using differential capacity and electrochemical impedance spectroscopy with ethylene carbonate:dimethylcarbonate (EC:DMC) electrolyte. The ceramic coated polypropylene separator exhibited the best cycle performance at a high 5 C rate, with high ionic conductivity and less resistive solid electrolyte interphase. Also, it was confirmed that a separator solid electrolyte interface (SSEI) layer formed on the separator with cycle repetition, and it was also confirmed that this phenomenon determined the cycle life of the battery depending on the electrolyte.
(Received July 13, 2021; Accepted August 20, 2021)

KCI등재 SCI SCOPUS

7Electrochemical Corrosion Resistance and Electrical Conductivity of Three-Dimensionally Interconnected Graphene-Reinforced Cu Composites

저자 : Xue Li , Ateeq Ahmed , Byung-sang Choi

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 11호 발행 연도 : 2021 페이지 : pp. 821-828 (8 pages)

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A three-dimensionally interconnected graphene-reinforced Cu (3Di Gr-Cu) composite was synthesized using a simple two-step process technique which involves the mechanical compaction of micron-sized Cu particles followed by chemical vapor deposition (CVD) at 995 ℃. The microstructural properties of pure Cu and the 3Di Gr-Cu composite were investigated by optical microscope, scanning electron microscope, and X-ray diffractometer. The electrical and corrosion behaviors of the 3Di Gr-Cu composite and Cu only, prepared by powder metallurgy (PM Cu), were studied and compared. The electrical conductivity (EC) of the 3Di Gr-Cu composites was found to be 38.8 MSm-1 at a carbon content of 73 ppm, and exhibited a 12% higher EC than the PM Cu. Due to the interconnected graphene around the Cu grains, the corrosion current density and corrosion rate of the 3Di Gr-Cu composite decreased by 29% and 40%, respectively, compared to the PM Cu. The EC of the 3Di Gr-Cu composite depended on the carbon content. The improvement in the EC of the 3Di Gr-Cu composite is attributed to the electron-carrying ability of the three-dimensionally interconnected graphene network (3DIGN) formed at the grain boundaries in the composite. The enhancement in corrosion resistance is due to the impermeability of graphene to various chemical species.
(Received May 17, 2021; Accepted August 11, 2021)

KCI등재 SCI SCOPUS

8기계학습에 의한 Al-Si 주조 합금 미세조직 이미지 생성

저자 : 황인규 ( In-kyu Hwang ) , 이현지 ( Hyun-ji Lee ) , 정상준 ( Sang-jun Jeong ) , 조인성 ( In-sung Cho ) , 김희수 ( Hee-soo Kim )

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 11호 발행 연도 : 2021 페이지 : pp. 828-837 (10 pages)

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In this study, we constructed a deep convolutional generative adversarial network (DCGAN) to generate the microstructural images that imitate the real microstructures of binary Al-Si cast alloys. We prepared four combinations of alloys, Al-6wt%Si, Al-9wt%Si, Al-12wt%Si and Al-15wt%Si for machine learning. DCGAN is composed of a generator and a discriminator. The discriminator has a typical convolutional neural network (CNN), and the generator has an inverse shaped CNN. The fake images generated using DCGAN were similar to real microstructural images. However, they showed some strange morphology, including dendrites without directionality, and deformed Si crystals. Verification with Inception V3 revealed that the fake images generated using DCGAN were well classified into the target categories. Even the visually imperfect images in the initial training iterations showed high similarity to the target. It seems that the imperfect images had enough microstructural characteristics to satisfy the classification, even though human cannot recognize the images. Cross validation was carried out using real, fake and other test images. When the training dataset had the fake images only, the real and test images showed high similarities to the target categories. When the training dataset contained both the real and fake images, the similarity at the target categories were high enough to meet the right answers. We concluded that the DCGAN developed for microstructural images in this study is highly useful for data augmentation for rare microstructures.
(Received July 22, 2021; Accepted August 24, 2021)

KCI등재 SCI SCOPUS

9매트랩/시뮬링크 simulation model을 이용한 열전 모듈의 효율 예측

저자 : 이나영 ( Nayoung Lee ) , 예성욱 ( Sungwook Ye ) , Rahman Jamil Ur , 탁장렬 ( Jang-yeul Tak ) , 조중영 ( Jung Young Cho ) , 서원선 ( Won Seon Seo ) , 신원호 ( Weon Ho Shin ) , Walter Commerell , 남우현 ( Woo Hyun Nam ) , 노종욱 ( Jong Wook Roh )

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 11호 발행 연도 : 2021 페이지 : pp. 829-837 (9 pages)

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Development new high-performance thermoelectric materials for more efficient power generation systems and eco-friendly refrigerating systems has been challenging. Over the past few decades, thermoelectric studies have been focused on increasing the thermoelectric properties of materials. However, for conventional applications, developing of thermoelectric devices or modules with lower cost and simpler fabrication processes is also important. Simulation models that can predict the thermoelectric efficiency of modules using the thermoelectric properties of materials are needed for this purpose. In this study, we developed a simple model for calculating the efficiency of thermoelectric modules using MATLAB/Simulink. In this model, the temperature difference between the hot source and heat sink was fixed to ensure the precise comparisons of thermoelectric efficiency. The electric resistivity and Seebeck coefficient of thermoelectric materials was used in order to predict the efficiency of the thermoelectric modules. Then, the efficiency of the thermoelectric modules was verified using measured values which had been reported in prior experimental works. In this study, the simulated values were higher than the real thermoelectric effiency values. To address this, the simulations should consider the thermal resistance or electric contact resistance between the thermoelectric materials and electrodes.
(Received July 16, 2021; Accepted August 24, 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)

KCI등재SCISCOUPUS

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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