압연온도 및 어닐링 온도에 따른 5052합금의 미세조직 및 기계적 성질

강의구,남원종 대한금속·재료학회 2019 대한금속·재료학회지 Vol.57 No.10

The microstructural evolution and corresponding mechanical properties of 5052 Al alloys with different deformation temperatures and post-deformation annealing conditions were investigated. The warmrolled alloy showed higher strength and elongation than the cold-rolled and cryo-rolled alloys. The improved strength and ductility of warm rolled alloys is attributed to the formation of fine precipitates and a higher degree of recovery during rolling. The formation of precipitates and the occurrence of dynamic recovery during the warm-rolling process were confirmed by the absence of the first two peaks in DSC curves of warm-rolled alloys. In particular, it was found that the application of cryo-rolling combined with warm-rolling at 448K increased tensile strength and yield strength without a decrease of ductility. This notable increase of strength is attributed to the increased dislocation density during cryo-rolling and the subsequent formation of fine precipitates at dislocations during warm-rolling. The contribution of fine precipitates and fully recovered microstructures, during cryo-rolling, warm-rolling, and subsequent annealing enhances the effective combination of strength and elongation. The ultra-fine grained 5052 Al alloy with high strength (405 MPa) and ductility (11.4% elongation) could be achieved by a combination of cryo-rolling with warm-rolling (448 K) and subsequent static annealing at 448 K.

고강도강의 냉간 조질 압연 시 호일 압연이론을 이용한 압연하중의 예측

송길호(Gil Ho Song),정제숙(Jae Chook Jung) 대한기계학회 2013 大韓機械學會論文集A Vol.37 No.2

냉간압연 및 소둔공정에서의 조질압연 과정은 강종별로 적정 연신율을 부여함으로서 프레스 가공시 항복점 연신 현상을 제거해주는 중요한 공정이다. 적정 연신율 확보를 위해서는 강종별, 사이즈별 정확한 압연하중 예측이 필수이다. 열간 및 냉간압연과는 달리 조질압연에서는 2%이내의 연신율을 부과하는 공정이므로 압연하중 작용 시 롤 바이트 내 에서의 롤의 탄성변형 거동이 복잡하여 정확한 압연하중을 예측하기가 어려워 예측모델이 정립되어 있지 않다. 그럼에도 불구하고 최근 인장강도 590MPa 급 이상의 자동차용 고강도강 개발이 가속화 됨에 따라 조질압연시 정확한 압연하중의 예측은 더욱더 중요하게 되었다. 따라서 본 연구에서는 조질 압연 시 롤 바이트 내에서 롤의 변형거동이 유사하다고 알려져 있는 호일(foil)압연 이론 식을 이용해 조질 압연 시 전체 생산 강종을 대상으로 압연하중 예측 가능성에 대해 검토하였다. 그 결과 인장강도 350MPa 이상 980MPa 이하의 강종에 대해서는 non circular model 이 circular 모델보다 압연하중 예측 정도가 우수하며, 이 영역에서 압연하중 예측 모델로의 적용이 가능함을 확인하였다. Skin pass rolling is a very important process for applying a certain elongation to a strip in the cold rolling and annealing processes, which play an important role in preventing the stretching of the yield point when the material is processed. The exact prediction of the rolling force is essential for obtaining a given elongation with the steel grade and strip size. Unlike hot rolling and cold rolling, skin pass rolling is used to apply an elongation of within 2% to the strip. Under a small reduction, it is difficult to predict the rolling force because the elastic deformation behavior of the rolls is complicated and a model for predicting the rolling force has not yet been established. Nevertheless, the exact prediction of the rolling force in skin pass rolling has gained increasing importance in recent times with the rapid development of high-strength steels for use in automobiles. In this study, the possibility of predicting the rolling force in skin pass rolling for producing various steel grades was examined using foil rolling theory, which is known to have similar elastic deformation behavior of rolls in the roll bite. It was found that a noncircular arc model is more accurate than a circular model in predicting the roll force of high-strength steel below TS 980 MPa in skin pass rolling.

Influence of Shape Rolling on the Side Profile During Horizontal Rolling Process of Reed Wire Using LS-DYNA

김세종(Se Jong Kim),김진호(Jin Ho Kim) Korean Society for Precision Engineering 2019 한국정밀공학회지 Vol.36 No.2

The production method of round wire used in conventional high-grade fabric production requires an additional step of cutting the side portion after cold rolling. However, after the additional cutting process, the performance of the round side portion was not improved. To solve these problems, the shape of the side portion is improved by replacing the process of wire cutting by the shape rolling. The rolling is done six times in total, and four flat rolling and two shape rolling are performed. There are three types of shape rolling: square, box and oval. The total number of cases of rolling analysis was analyzed nine times according to the kind of 3,5th shape rolling. Efficient shape rolling was selected by comparing deformation of wire thickness and width after final rolling, residual stress of the wire and the shape of the side part. The above study was conducted through LS-DYNA, a simulation program that can analyze material behavior of materials.

EBSD에 의한 A1050 압연판재의 결정립 구조 분석

한준현,신명철,Han, Jun-Hyun,Shin, Myung-Chul 한국분석과학회 2001 분석과학 Vol.14 No.1

압연판재의 결정립 미세화를 위해 새롭게 도입된 극저온 강압연법을 극저온 압연법, 상온 강압연법과 비교 분석하였다. EBSD를 이용하여 결정립 구조를 분석하였으며, 결정립 크기를 측정하였다. 극저온 압연법과 상온 강압연법은 각각 39%와 87%의 결정립 크기 감소효과를 보였으며, 극저온 강압연법은 상온 강압연법과 비슷한 결정립 감소효과를 갖고 있었다. 따라서 강압연법이 극저온 압연법보다 결정립 미세화에 훨씬 더 효과적임을 알 수 있었다. The effect of cryogenic heavy rolling method on grain refinement has been studied and compared with those obtained by previous methods of cryogenic rolling and heavy rolling developed separately. Both grain structure and grain size were analyzed using electron back scattered diffraction (EBSD), which can distinguish grains each other by means of crystallographic misorientations between them. The cryogenic rolling and heavy rolling exhibit reduction in grain size of 39% and 87%, respectively, and the cryogenic heavy rolling shows reduced grain size similar to that observed in the heavy rolling. The heavy rolling was proved more effective in grain size refinement than the cryogenic rolling.

Process Design by FEM Simulation for Shape Ring Rolling of Large-Sized Ring

Y.S. Lee,M.W. Lee,S.S. Park,I. Lee,Y.H. Moon 한국소성가공학회 2010 기타자료 Vol.2010 No.6

Ring rolling process is usually used to fabricate large-sized ring, such as, tower flange for wind power electric generator. Many kinds of seamless ring are used in wind power electric generator and manufactured by ring rolling process. In general, final part is machined after forming with shape of plain square section. Since interests for near net shaping of seamless ring have been increased gradually because of green energy, it is necessary to develop the technology for shape ring rolling with respect to the market demands and cost. Therefore, we studied the process and die design for shape ring rolling of large sized ring over 3,500mm out diameter by experiment and FEM simulation. Ring rolling process is very difficult to solve by FEM method because of equilibrium state and size effect, etc. Moreover, shape ring rolling is more difficult to solve the problem that two plastic deformation zones are different each other, that is main roll and conical roll. Also since conical roll has a shape, deformation velocity field is very much complex and the deformed section passed axial roll is different section and velocity field. The FE simulations are performed to analyze process variables affected in forming of profiled ring. Therefore, the main features of used FE model are: (1) it adopts a transient or unsteady state full ring mesh to model the deformation processes and shape development; (2) the mandrel and conical rolls are modeled using coupled heat-transfer elements; (3) the model involves the full process from blank through perform to final profiled ring. From these calculated results, we have proposed the mechanisms of various tools, such as mandrel and conical roll. The calculated results are compared experimental results. Calculated results can predict the tilting of profiled ring and then process variables to form large sized ring.

Effect of the Reduction Ratio per Pass on the Microstructure of a Hot-Rolled AZ31 Magnesium Alloy Sheet

임창동,유봉선,서영명 대한금속·재료학회 2009 METALS AND MATERIALS International Vol.15 No.4

The effect of the reduction ratio per pass on the microstructural evolution of an AZ31 gravity cast plate during hot rolling was evaluated systematically. {1012} extension twinning was observed in large grains after an earlier rolling pass, but it disappeared upon a subsequent rolling pass due to the reorientation of the grains in an unfavorable direction caused by repetitive rolling. The finer grains were newly formed at the boundaries of the original large grains and twin boundaries by dynamic recrystallization. The grain size distribution was changed from a bimodal distribution upon a small total reduction to a homogeneous distribution upon a large total reduction due to the formation of finer grains that continued at the grain boundaries of large grains by repetitive hot rolling. The size and distribution of the grains were affected not only by the reduction ratio per pass but also by the total reduction (number of rolling passes). The effect of the reduction ratio per pass on the microstructural evolution of an AZ31 gravity cast plate during hot rolling was evaluated systematically. {1012} extension twinning was observed in large grains after an earlier rolling pass, but it disappeared upon a subsequent rolling pass due to the reorientation of the grains in an unfavorable direction caused by repetitive rolling. The finer grains were newly formed at the boundaries of the original large grains and twin boundaries by dynamic recrystallization. The grain size distribution was changed from a bimodal distribution upon a small total reduction to a homogeneous distribution upon a large total reduction due to the formation of finer grains that continued at the grain boundaries of large grains by repetitive hot rolling. The size and distribution of the grains were affected not only by the reduction ratio per pass but also by the total reduction (number of rolling passes).

유연 기판상 ITO 박막의 롤링변형에 따른 신뢰성 연구

설재근,이동준,김태욱,김병준,Seol, Jae-Geun,Lee, Dong-Jun,Kim, Tae-Wook,Kim, Byoung-Joon 한국마이크로전자및패키징학회 2018 마이크로전자 및 패키징학회지 Vol.25 No.1

미래의 전자 기기는 접고 굽히고 둘둘 마는 등 다양한 변형에도 전기적 안정성을 가지는 기기들로 발전할 것이며, 반복 기계적 변형 하에서 유연 전자 소자의 전기적 신뢰성 확보가 중요한 이슈로 부각되고 있다. 본 연구에서는 반복 롤링 변형이 가능한 장치를 개발하고 이를 이용해, 현재 유연 전자 소자용 투명 전극 소재로 가장 널리 사용 중인 ITO 박막의 반복 롤링 실험 중 전기적 특성 변화를 연구하였다. 전극과 기판의 상대적 위치에 의해 인장 응력과 압축 응력이 가해지므로, Outer rolling 및 Inner rolling의 두 조건에서 실험을 진행하여 응력 상태에 따른 전기적 신뢰성 차이를 연구하였다. 그 결과, inner rolling의 경우 outer rolling에 비해 더 우수한 전기적 안정성을 나타냈으며, 이는 inner bending에 의한 압축 응력 상태의 경우 crack closing 변형에 따라 전기저항이 상대적으로 낮게 증가하는 것으로 해석된다. 또한, 롤링 바퀴 수에 따른 피로 저항성을 실시간 전기저항 측정을 통해 연구하였으며, 그 결과, 롤링 바퀴 수가 증가할수록 피로 파괴 영역이 증가하므로 전기저항이 더욱 크게 증가하는 것으로 나타났다. 본 연구를 통해 롤링 조건에서 유연 전극의 신뢰성에 대해 이해하고, 이는 향후 유연 전자소자용 고신뢰성 전극 개발에 활용 될 수 있을 것으로 기대한다. Flexible electronics must be stable under various deformations such as bending, folding, and rolling. The reliability of ITO (Indium Tin Oxide) film used widely as a transparent electrode for flexible electronics has been studied using rolling fatigue test and bending test. During repeated rolling deformations, the electrical resistance was in-situ measured with different number of rotation. During rolling fatigue test, the electrical resistance of ITO film was significantly increased with increasing the number of rotation. As the stress state of ITO film is different according to the relative position of ITO and substrate, the rolling fatigue test was investigated under both outer and inner bending conditions. Inner rolling fatigue test showed superior electrical stability because the crack nucleation and propagation were retarded under compressive stress state.

고온 비대칭압연이 알루미늄 합금의 미세조직과 성형성에 미치는 영향

정무섭,이종범,한준현,Jeong, Museob,Lee, Jongbeom,Han, Jun Hyun 한국재료학회 2019 한국재료학회지 Vol.29 No.10

In order to analyze the effect of hot asymmetric rolling on the microstructure and texture of aluminum alloy and to investigate the effect of the texture on the formability and plastic anisotropy of aluminum alloy, aluminum 6061 alloy is asymmetrically rolled at room temperature, $200^{\circ}C$, $350^{\circ}C$, and $500^{\circ}C$, and the results are compared with symmetrically rolled results. In the case of asymmetric rolling, the equivalent strain (${\varepsilon}_{eq}$) is greatest in the upper roll part where the rotational speed of the roll is high and increases with increasing rolling temperature. The increase rate of the mean misorientation angle with increasing temperature is larger than that during symmetrical rolling, and dynamic recrystallization occurs the most when asymmetrical rolling is performed at $500^{\circ}C$. In the case of hot symmetric rolling, the {001}<110> rotated cube orientation mainly develops, but in the case of hot asymmetric rolling, the {111}<110> orientation develops along with the {001}<100> cube orientation. The hot asymmetric rolling improves the formability (${\bar{r}}$) of the aluminum 6061 alloy to 0.9 and reduces the plastic anisotropy (${\Delta}r$) to near zero due to the {111}<110> shear orientation that develops by asymmetric rolling.

Study on the improved accuracy of strip profile using numerical formula model in continuous cold rolling with 6-high mill

Sang-Ho Lee,Gil-Ho Song,Sung-Jin Lee,김병민 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.8

The quality requirements for thickness accuracy in cold rolling continue to become more stringent. In cold rolling mill, it is very important that the rolling force calculation considers rolling conditions. The rolled strip thickness was predicted using calculated rolling force. However, the prediction of strip thickness in cold rolling is very difficult; in particular, for 6-high mill with shifted intermediate roll (IMR), the accuracy of thickness is not good. In this study, to improve the accuracy of rolled strip thickness, the roll gap flattening can be given based on Hertz contact theory, with contact between rolls and the smooth cylindrical rolls for the rolling elastic deformation. Also,the distribution of the roll gap flattening may be calculated using the contact force of unit transverse length. The strip profile at the continuous cold rolling is calculated by using the numerical analysis model considering the initial strip profile before cold rolling. Hence, we propose that the numerical model can predict the rolled strip profile more quickly and accurately and be applicable to the field. The results of the proposed numerical model were verified by FE-simulation and cold rolling experiments of 6-high mill with five stands.

공형압연에서 롤의 비대칭 배치로 인한 소재단면형상의 변화

김성기,이동윤,이석의,정원태,남규한,나두현,이영석 대한기계학회 2024 大韓機械學會論文集A Vol.48 No.5

공형압연에서 롤을 지지하는 부품의 강성부족으로 발생한 롤의 비대칭 배치로 인해 압연된 소재의 FSP(free surface profile)가 대칭이 되지 않는다. 본 연구는 이런 점을 역이용하여 롤의 비대칭 배치가 압연된 소재단면의 FSP에 미치는 영향을 분석하였다. 롤의 비대칭 배치는 상/하부 롤이 수평방향으로 서로 어긋나 약간 평행 이동한 경우, 상/하부 롤의 좌/우측 롤 갭이 다른 경우 그리고 상/하부 롤이 압연방향으로 상반되게 약간 회전한 경우이다. 상기 세 가지 비대칭 압연조건에서 3종류의 티타늄 소재(Ti-Gr.4, Gr.19, Gr.23)를 압연하였다. 같은 압연조건에서 FE 해석을 수행하였고, 계산과 측정결과를 비교 분석하였다. 결과적으로 상기에서 언급된 3가지 비대칭 압연조건 중에서 상/하부 롤이 압연방향으로 상반되게 약간 회전한 경우가 FSP 변화에 가장 큰 영향을 주었다. In groove (or caliber) rolling, the free surface profile (FSP) of the rolled material is not symmetrical owing to the asymmetric arrangement of rolls caused by the insufficient stiffness of the components supporting the roll. This study utilizes this aspect to analyze the effect of the asymmetric arrangement of rolls on the FSP of materials departing from the rolls. The asymmetric arrangement of rolls is reflected in cases where the upper/lower rolls propagate parallel to the horizontal direction (x-direction), the left/right roll gaps of the upper/lower rolls are different, and the upper/lower rolls rotate in opposite directions along the rolling direction. Titanium of three grades (Ti-Gr.4, Gr.19, and Gr.23) are rolled under the abovementioned three asymmetric rolling conditions. We perform three-dimensional finite-element analysis under the asymmetric rolling conditions mentioned above and compare the predictions with the measurements. The results show that among the three asymmetric rolling conditions, the case where the upper/lower rolls rotate in opposite directions along the rolling direction exerts the most significant effect on variations in the FSP.