• Title/Summary/Keyword: Superplasticity

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Finite Element Analysis of Superplastic Forming Considering Grain Growth-II. Superplastic Behavior of AZ31 Alloy (결정립 성장을 고려한 초소성 성형공정의 유한요소해석-II. AZ31 합금의초소성 거동)

  • Kim, Y.G.;Kim, S.H.;Kwon, Y.N.;Kim, Y.H.
    • Transactions of Materials Processing
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    • v.21 no.7
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    • pp.403-411
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    • 2012
  • The aim of this study was to predict the results of superplastic forming on magnesium alloy, by considering the grain growth using numerical simulations. Superplastic behavior of AZ31 alloy was investigated through a set of uniaxial tensile tests that cover the forming temperatures ranges from 375 to $450^{\circ}C$. All the material parameters in the model, which consists of a constitutive equation and a grain growth equation, were determined. The model was used in the finite element analysis for uniaxial tensile tests and superplastic blow forming, through a user-subroutine available within ABAQUS. From this study, the effect of grain growth during forming was evaluated. The results show that it is essential to include the effect of grain growth in predicting the behavior during superplastic forming of this magnesium alloy.

Micro-mechanical Modeling of the Consolidation Processes in Titanium Metal Matrix Composites (티타늄금속기 복합재료의 강화공정에 관한 미시역학적 모델링)

  • 김준완;김태원
    • Proceedings of the Korean Society For Composite Materials Conference
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    • 2002.05a
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    • pp.207-210
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    • 2002
  • Metal matrix composites(MMCs) are increasingly attractive for high technology components such as aerospace applications and transportations due to their high strength, stiffness, and toughness. Many processes for fabricating MMCs have been developed, and relatively simple Foil-Fiber-Foil method is usually employed in solid state consolidation processes. During the consolidation processes at high temperature, densification occurs by the inelastic flow of the matrix materials, and the process is coupled with the conditions of pressure, temperature and volume fraction of fiber and matrix materials. This is particularly important in titanium matrix composites, and thus a generic model based on micro-mechanical approaches enabling the evolution of density over time to be predicted has been developed. The mode developed is then implemented into FEM so that practical process simulation has been carried out. Further the experimental investigation of the consolidation behavior of SiC/Ti-6Al-4V composites using vacuum hot pressing has been performed, and the results obtained are compared with the model predictions.

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Development of Friction Welding Process of Zr-based Bulk Metallic Glasses (Zr-기 벌크 금속 유리의 마찰 접합 공정 개발)

  • Shin, Hyung-Seop;Jeong, Young-Jin;Kim, Ki-Hyun
    • Proceedings of the KSME Conference
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    • 2004.11a
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    • pp.337-341
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    • 2004
  • Bulk metallic glasses(BMG) with good mechanical properties have problems that engineering application fields have been limited because of limitation of the alloy size. In order to solving this problem, the friction welding of BMG has been tried using the superplastic-like deformation behavior under the supercooled liquid region. The apparatus for friction welding test was designed and constructed using pneumatic cylinder and gripper based on a conventional lathe. Friction welding have been tried to combination of same BMG alloy and crystalline alloys. The results of welding test were evaluated by X-ray diffraction, measurement of hardness and mechanical properties test. In order to obtain the optimized welding test conditions the temperature of friction interface was measured using Infrared thermal imager.

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Finite Element Analysis of Superplastic Forming Processes Considering Grain Growth (I) (결정립 성장을 고려한 초소성 성형공정의 유한요소해석(I))

  • Kim, Y.G.;Song, J.S.;Kim, Y.H.
    • Transactions of Materials Processing
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    • v.21 no.3
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    • pp.151-159
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    • 2012
  • Finite element simulations were conducted to investigate the influence of grain growth in the superplastic blow forming process. A microstructure-based constitutive model considering grain growth effects is proposed and used in the simulations. Also, a grain growth rate equation accounting for both static and dynamic grain growth is implemented. The simulations were made using a 2D plane-strain model for constrained blow forming and an axisymmetric model for free bulging. These two models showed different features during the forming stages. However, the forming pressure-time curve and the thickness distribution obtained by both simulations explained well the deformation hardening induced by the grain growth during superplastic forming. This study shows that grain growth is an important factor in determining the material behavior during superplastic deformation.

A study on optimization of AZ31 alloy sheet by blow forming (AZ31 합금 부풀림 성형의 최적화 연구)

  • Kim, S.D.;Kwon, Y.N.;Lee, Y.S.;Kim, B.M.;Lee, J.H.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2006.05a
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    • pp.67-69
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    • 2006
  • Since magnesium alloy has a limited formability at room temperature, forming should be carried out at the elevated temperature. If the initial grain size is small, superplasticity could be expected over $400^{\circ}C$. Using superplastic behavior, blow forming can be used to overcome the low formability of Mg alloys. In the present study, the optimization of blow forming of AZ31 alloy at the elevated temperature was investigated. Finite element simulation was carried out and verified with the blow forming experiments.

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A Study on the Effect of Back Pressure on the Superplastic Bulge Forming of Ti-6Al-4V Alloy (Ti-6Al-4V 합금의 초소성 벌지성형에 미치는 배압력의 영향)

  • 송유준;이종수
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 1997.03a
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    • pp.175-178
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    • 1997
  • A modified Mukerjee's model considering the microstructural evolution was developed to study the superplastic bulge forming process of Ti-6Al-4V alloy. Through the microstructual observation after deformation, it was found that the grain growth rate of uniaxially tested specimens was different from that of biaxially deformed specimens. From this result, bulge forming experiments with and without back pressure were performed to examine the grain growth behavior and to compare the results of biaxial test with those of triaxial test. Good agreement between the prediction by a modified Mukerjee's model and the experimental measurements was obtained for bulge profile and thickness distribution.

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Cavitation Behavior of AZ31 Sheet during Gas Blow Forming (AZ31 합금의 부풀림 성형시 공공의 거동)

  • Kim, S.H.;Kang, N.H.;Kwon, Y.N.
    • Transactions of Materials Processing
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    • v.20 no.8
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    • pp.601-610
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    • 2011
  • Based on the facts that AZ31 magnesium alloy can be blow formed just like superplastic aluminum alloys and that most superplastic alloys fail by cavitation, the present study was undertaken to investigate the cavitation behavior of a fine-grained AZ31 sheet during blow forming at the elevated temperature. Other points of interest included the much lower strain rate and temperature dependencies of the magnesium alloy compared with conventional superplastic alloys. It was also aimed to find if cavitation in the AZ31 alloy can be suppressed by hydrostatic pressure, as is the case in most superplastic alloys. Interestingly, the application of hydrostatic pressure did not increase the blow formability of AZ31 sheet, even though it reduced the degree of cavitation. A possible reason for this behavior is discussed.

Fabrication of Ultrafine Grained Structure Materials by Equal Channel Angular Pressing (ECAP 강소성 가공에 의한 구조재료 초미세립화)

  • Kim W. G.;Ahn Y. J.;Shin D. H.;Park K. T.;Ko Y. G.;Lee J. S.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2005.10a
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    • pp.126-129
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    • 2005
  • Microstructures and tensile properties of low carbon steels, 5083 Al alloy and Ti-6Al-4V alloy fabricated by equal channel angular pressing (ECAP) were examined in order to understand their deformation response associated with a formation of an ultrafine grained (UFG) structure. Room temperature tensile properties of UFG low carbon ferrite/pearlite steels and UFG ferrite/martensite dual phase steel were compared for exploring a feasibility enhancing the strain hardening capability of UFG materials. In addition, low temperature and high strain rate superplasticity of the two grades of the UFG 5083 Al alloy, and Ti-6Al-4V alloy were presented. From the analysis of a series of experiments, it was found that UFG materials exhibited the enhanced mechanical properties compared to coarse grained counterparts.

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Non-uniform Failure in Superplastic Ti-6Al-4V Alloy (초소성 Ti-6Al-4V 합금에서의 불균일 파손)

  • 김태원
    • Transactions of Materials Processing
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    • v.9 no.6
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    • pp.663-669
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    • 2000
  • A material model has been presented, at the continuum level, for the representation of superplastic deformation coupled with microstructural evolution. The model presented enables the effects of the spatial variation of distributions of grain size to be predicted at the process level. The model has been tested under conditions of both homogeneous and inhomogeneous stress and strain by carrying out detailed comparison of predicted distributions of grain size and their evolutions with experimentally obtained data. Experimental measurements have shown the extent of the spatial variation of the distribution of grain size that exists in the titanium alloy, Ti-6Al-4V. It is shown that whilst not large, the variations in grain size distributions are sufficient to lead to the development of inhomogeneous deformation in test pieces, which ultimately result in localisation of strain and failure.

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Rapidly Solidified Powder Metallurgy Mg-Zn-RE Alloys with Long Period Order Structure

  • Kawamura, Yoshihito
    • Proceedings of the Korean Powder Metallurgy Institute Conference
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    • 2006.09b
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    • pp.1269-1270
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    • 2006
  • Mg-Zn-RE alloys had a novel lond period stacking ordered (LPO) structure. Their rapidly solidified powder metallurgy (RS P/M) alloys exhibited a combination of high strength and god ductility (tensile yield strength above 550 MPa and elongation above 5%). The LPO Mg-Zn-RE RS P/M alloys had high elevated temperature strength (tensile yield strength above 380 MPa at 473 K) and exhibited a high-strain-rate superplasticity at higher temperatures. In Japan, a national project for developing high strength LPO Mg-Zn-RE RS P/M alloys has started at 2003 for 5 years, which is founded by the Ministry of Economy, Trade and Industry (METI) of Japan. In the national project, project targets in materials performances have been achieved. The developed LPO Mg-Zn-RE RS P/M alloys exhibited higher tensile yield strength, fatigue strength and corrosion resistance than high strength aluminum alloys of extra-super-duralumin (7075-T6).

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