• 한국주조공학회지
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• 제38권6호
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• pp.121-131
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• 2018

The effect of additives on the castability of the AC2BS aluminum alloy, which contains 35% recycled scrap, was investigated. For the wide utilization of the recycled scrap AC2BS aluminum alloy, the research results were compared to those with the AC2B virgin alloy, which is typical Al-Si-Cu alloy system. It was confirmed that the addition of Al-5%Ti-1%B increased the ${\alpha}$-Al nucleation temperature during solidification and decreased the grain size through cooling curve and microstructural observations of the recycled alloy. It was also found that an addition of Al-10%Sr decreased the eutectic Si growth temperature during the solidification process and modified the shape of the eutectic Si of the recycled alloy. The characteristics of fluidity, shrinkage and solidification crack strength were evaluated. For the AC2BS aluminum alloy containing 35% recycled scrap, both ${\alpha}$-Al grain refinement due to Ti-B and eutectic Si modifications due to Sr contributed to the improvement of the fluidity. The macro- shrinkage ratio increased with additions of both Al-10%Sr and Al-5%Ti-1%B and the micro-shrinkage ratio increased with the addition of Al-10%Sr but decreased with the addition of Al-5%Ti-1%B. The casting characteristics of TiB and Sr-treated AC2BS aluminum alloy containing 35% recycled scrap are similar to those of AC2B virgin alloy. The improvement of the solidification crack strength of the AC2BS aluminum alloy was possible by the reduction of the grain boundary the stress concentration through the enhancement by both ${\bullet}{\cdot}$-Al refinement and eutectic Si modification. More extensive use of the AC2BS aluminum alloy containing 35% recycled scrap can be expected in the future.

• 열처리공학회지
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• 제29권6호
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• pp.259-263
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• 2016

This study was carried out to investigate the effect of hot forging ratio on the microstructure and mechanical properties of incoloy 825 alloy. Hot forging was carried out at the forging ratio of 0%, 60% and 90% respectively in a range of $900^{\circ}C{\sim}1,140^{\circ}C$ and followed solution treatment was conducted at $1,000^{\circ}C$ for 1 hr. In all the specimens of hot forged of 0%, 60% and 90%, precipitates were not observed. The average grain size of 0% specimen is $82{\mu}m$ and that of 60% and 90% is $56{\mu}m$ and $31{\mu}m$, respectively. The range of grain size in the 0% specimen is uneven in $182{\mu}m$ to $31{\mu}m$, but the grain size of 90% specimen is uniform. With increasing hot forging ratio, the mechanical properties such as tensile strength, elongation, hardness increased and impact toughness increased by grain refinement.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 1998년도 특별강연 및 추계학술발표 개요집
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• pp.73-74
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• 1998

• 한국재료학회지
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• 제9권7호
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• pp.740-747
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• 1999

결정립 미세화는 강도와 인성을 동시에 향상시킬 수 있는 유일한 방법이다. 제어압연과 가속냉각은 공정 중에 재결정과 결정립 조대화 거동을 조절함으로써 기계적 성질을 향상시키는 효과적인 방법으로 알려져 있으며, 반복열처리에 의한 반복상변태는 결정립 미세화 방법 중의 하나이다. 본 연구에서는 제어압연과 반복열처리를 복합 적용하여 그 효과를 관찰하였다. Mo 첨가효과와 공정변수의 효과를 관찰하기 위해 Mo이 첨가된 저탄소강 시편을 준비하여 Gleeble로 가공열처리 모의실험을 하였다. Mo첨가는 결정립 조대화 온도를 상승시키고, 오스테나이트 재결정을 억제하는 효과를 나타내었다. 오스테나이트 결정립 미세화에 가장 효과적인 공정조건은 반복 열처리 제어압연을 두번 실시하는 것이고, 첫번째보다 두번째 압연율을 더 크게 하는 것이었다

• 소성∙가공
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• 제31권3호
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• pp.124-128
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• 2022

NdFeB magnets have been positioned as the core materials in advanced technologies such as MRI (magnetic resonance imaging), FA (factory automation system), robot, motors, and so on based on the highest magnetic properties. To effectively improve the refined microstructure, the plastic deformation has been known as the good alternatives by the recrystallization. However, it has been regarded as being impossible because of the few slip systems in the RE-Fe-B magnets at room temperature. The purpose of this study was to investigate the possibility of control of grain refinement and magnetic anisotropy of NdFeB alloy powder by the severe plastic deformation. The NdFeB magnet powder was fabricated by gas atomization process, and the powder was pre-compacted at high temperature. The pre-compacted billets were deformed by HPT (high pressure torsion), and then the deformed billets were observed microstructure and magnetic properties. After the HPT process at room temperature, the grain size decreased with increasing because of the melted Nd-rich phase, and the anisotropy of Nd₂Fe₁₄B phase was formed after the HPT process.

• 한국주조공학회지
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• 제19권5호
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• pp.403-409
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• 1999

Mg-Zn-Zr ternary alloys containing 6wt% Zn and (0, 0.4, 0.6)wt% Zr, which is added for grain refinement, can be cast into complex shape by squeeze casting. The influence of Zn and Zr as additional elements on microstructure and mechanical characteristics is investigated by OM, SEM, WDX, XRD and microvickers hardness measurement. The microstructure of Mg-Zn-Zr alloys consists of primary ${\alpha}-Mg$ and MgZn eutectic compound between dendrites. The grain size is decreased from $136{\mu}m$ to $97\;{\mu}m$ by Zr addition, resulting in that the hardness is increased from 42Hv to 59Hv. Furthermore, the grain size is changed to $83{\beta}$ and the hardness is increased to 65Hv by additional infiltration pressure. These results indicate that the Zr addition and additional infiltration pressure are effective for grain refinement acting as an important factor to increase the hardness. The increment in hardness by the Zr addition is slightly larger than that by the additional infiltration pressure.

• 한국주조공학회지
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• 제22권1호
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• pp.17-25
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• 2002

Recently, many studies have been carried out to process on the purpose of lightness in a transport parts because of the saving energy, the environmental problem. The cast-forging process can be expected to lower costs without decreasing the mechanical properties. So, the finest microstructure is needed to get for applying the cast-forging process with Al-Si alloy because the microstructure affects to the cast-forging process. For refinement treatment of eutectic Si and Al solid-solution phase, Sr and TiB were added in Al-Si alloys. The finest microstructure could be observed when 0.075 wt.%Sr and 0.1 wt.%TiB were added respectively. In this case, tensile strength and elongation much more increased than as casting. After high temperature deformation simulation test with grain refinement specimens was carried out, about 70N per unit $area(mm^2)$ of specimen was confirmed. After hot forging, tensile strength and elongation were increased. It was considered because casting defect was removed by compressive working.

• 한국재료학회지
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• 제21권10호
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• pp.556-562
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• 2011

We carried out this study to evaluate the grain refining in and the mechanical properties of alloys that undergo severe plastic deformation (SPD). Conventional rolling (CR) and cross-roll rolling (CRR) as SPD methods were used with Ni-20Cr alloy as the experimental material. The materials were cold rolled to a thickness reduction of 90% and subsequently annealed at $700^{\circ}C$ for 30 min to obtain a fully recrystallized microstructure. For the annealed materials after the cold rolling, electron back-scattered diffraction (EBSD) analysis was carried out to investigate the grain boundary characteristic distributions (GBCDs). The CRR process was more effective when used to develop the grain refinement relative to the CR process; as a result, the grain size was refined from $70{\mu}m$ in the initial material to $4.2{\mu}m$ (CR) and $2.4{\mu}m$ (CRR). These grain refinements have a direct effect on improving the mechanical properties; in this case, the microhardness, yield and tensile strength showed significant increases compared to the initial material. In particular, the CRR-processed material showed more effective values relative to the CR-processed materials. The different texture distributions in the CR (001//ND) and CRR (111//ND) were likely the cause of the increase in the mechanical properties. These findings suggest that CRR can result in materials with a smaller grain size, improved texture development and improved mechanical properties after recrystallization by a subsequent annealing process.

• 소성∙가공
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• 제15권7호
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• pp.524-528
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• 2006

Although equal channel angular pressing (ECAP), imposing large plastic shear strain deformation by moving a workpiece through two intersecting channels, is a promising severe plastic deformation method for grain refinement of metallic materials, its batch type characteristic makes ECAP inefficient for multiple-passing. Rotary-die ECAP (RDECAP) proposed by Nishida et al. can achieve high productivity by using continuous processing without taking out the samples from the channel. However, plastic deformation behavior during RD-ECAP has not been investigated. In this study, material plastic flow and strain hardening behavior of the workpiece during RD-ECAP was investigated using the finite element method. It was found that plastic deformation becomes inhomogeneous with the number of passes due to an end effect, which was not found seriously in ECAP. Especially, decreasing corner gap with increasing the number of passes was observed and explained by the strain hardening effect.

• 열처리공학회지
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• 제20권6호
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• pp.293-298
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• 2007

Influences of aluminum carbide ($Al_4C_3$) addition on microstructure and damping capacity of Mg-3%Al casting alloy have been investigated based on experimental results of optical micrography, scanning electron microscopy with energy-dispersive spectrometry analysis and damping capacity measurement at RT. The addition of $Al_4C_3$ particles results in an efficient grain refinement. The damping capacity shows an increasing tendency with an increase in $Al_4C_3$ content. The damping value associated with $Al_4C_3$ particles is linearly dependent on the volume fraction of $Al_4C_3$ particles to the 2/3 power, $f_{2/3}$, which corresponds to the total surface area of the particles.