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Weiwen Zhang - One of the best experts on this subject based on the ideXlab platform.
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microstructure evolution during high strain rate tensile Deformation of a fine grained az91 magnesium alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2014Co-Authors: Fang Chai, Datong Zhang, Weiwen ZhangAbstract:Abstract A fine-grained AZ91 magnesium alloy prepared by submerged friction stir processing is subjected to high temperature tensile test at 623 K and 2×10 −2 s −1 to intermediate strains of 270%, 510%, 750% and failure strain of 990%, and microstructure evolution of the experimental material during tensile test is investigated. The initial grain size is about 1.2 μm. Microstructures within the gauge region are much finer than those of grip region, and the grain aspect ratios remain approximately 1.0 in the whole Superplastic Deformation. With the tensile strains increasing, the average size of β-Mg 17 Al 12 particles increases, and the density of the β-Mg 17 Al 12 particles decreases. Due to the pinning effect of β-Mg 17 Al 12 particles and the occurrence of DRX, the fine microstructures are maintained in the whole Superplastic Deformation process. Grain boundary sliding is the main Deformation mechanism, and cavities are formed in the triple junctions of grains and around the second phase particles during Deformation. The excellent high strain rate Superplasticity of the AZ91 magnesium alloy is mainly attributed to its initial fine microstructure and good thermal stability.
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high strain rate Superplasticity of a fine grained az91 magnesium alloy prepared by submerged friction stir processing
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2013Co-Authors: Fang Chai, Datong Zhang, Yuanyuan Li, Weiwen ZhangAbstract:Friction stir processing (FSP) is a novel severe plastic Deformation technique to prepare fine-grained metallic materials. Superplastic behaviors of FSP magnesium alloys have not been fully studied until now. In this study, microstructure and tensile behaviors of a fine-grained Mg-9Al-1Zn alloy prepared by FSP under water are investigated. It is found that the process results in significant grain refinement, and the second phase networks are broken into small particles. The FSP specimens exhibit excellent high strain rate Superplasticity, with an elongation of 990% at a strain rate of 2×10−2 s−1 and 623K. Microstructure evolution and Superplastic Deformation mechanism of the experimental materials during Superplastic tensile test are investigated. Grain boundary sliding is the main mechanism for the Superplastic Deformation of the specimens. The excellent Superplasticity of the FSP material is attributed to its fine grain structures, which contain a larger fraction of grain boundary.
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high strain rate Superplasticity of a fine grained az91 magnesium alloy prepared by submerged friction stir processing
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2013Co-Authors: Fang Chai, Datong Zhang, Weiwen ZhangAbstract:Abstract The as-cast AZ91 plate was subjected to normal friction stir processing (processed in air) and submerged friction stir processing (processed in water, SFSP), and microstructure and Superplastic tensile behavior of the experimental alloys were investigated. SFSP results in remarkable grain refinement due to the enhanced cooling rate compared with normal FSP, with an average grain size of 1.2 μm and 7.8 μm. The SFSP AZ91 specimen exhibits considerably enhanced Superplastic ductility with reduced flow stress and higher optimum strain rate, as compared to the normal FSP specimen. The optimum Superplastic Deformation temperature is found to be 623 K for both the normal FSP and SFSP AZ91 specimens. An elongation of 990% is obtained at 2×10−2 s−1 and 623 K for the SFSP specimen, indicating that excellent high strain rate Superplasticity could be achieved. By comparison, maximum ductility of the normal FSP specimen strained at high strain rate is 158%. Grain boundary sliding is the main mechanism for the Superplastic Deformation of the normal FSP and SFSP specimens. The excellent high strain rate Superplasticity of the SFSP alloy is attributed to its finer grain structure and higher fraction of grain boundary.
Yw Chang - One of the best experts on this subject based on the ideXlab platform.
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Effects of microstructural evolution on Superplastic Deformation characteristics of a rapidly solidified Al-Li alloy
'Indiana University Press (Project Muse)', 2019Co-Authors: Yn Kwon, Hj Koh, Lee S, Nj Kim, Yw ChangAbstract:This study is concerned with the effects of microstructural modification on Superplastic Deformation characteristics of a rapidly solidified (RS) Al-3Li-1Cu--.5Mg-0.5Zr (wt pct) alloy. This Al-Li alloy has a very fine grain structure desirable for improved Superplasticity. The results of Superplastic Deformation indicated that the alloy exhibited a high Superplastic ductility, e.g., elongation of approximately 800 pct, when deformed at temperatures above 500 degreesC and at the strain rates of 10(-2)/s to 10(-1)/s. Such a high strain rate is quite advantageous for the practical Superplastic forming application of the alloy. Stress-strain rate curves were obtained by performing a series of load relaxation tests in the temperature range from 460 degreesC to 520 degreesC in order to examine the Superplastic Deformation behavior and to establish its mechanisms. The stress-strain rate curves could be separated into two parts according to their respective physical mechanisms, i.e., grain matrix Deformation and grain boundary sliding, as was proposed in a new Superplasticity theory based on internal Deformation variables. The microstructural evolution during Superplastic Deformation was also analyzed by using transmission electron microscopy. During Superplastic Deformation, grains were kept fine and changed into equiaxed ones due to the presence of fine secondary phase particles and the continuous recrystallization due to the development of subgrains. Consequently, the rapidly solidified (RS) alloy showed much improved Superplasticity compared to the conventional ingot cast 8090 alloy.X1
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Effects of microstructural evolution on Superplastic Deformation characteristics of a rapidly solidified Al-Li alloy
'Springer Science and Business Media LLC', 2019Co-Authors: Yn Kwon, Hj Koh, Lee S, Nj Kim, Yw ChangAbstract:This study is concerned with the effects of microstructural modification on Superplastic Deformation characteristics of a rapidly solidified (RS) Al-3Li-1Cu--.5Mg-0.5Zr (wt pct) alloy. This Al-Li alloy has a very fine grain structure desirable for improved Superplasticity. The results of Superplastic Deformation indicated that the alloy exhibited a high Superplastic ductility, e.g., elongation of approximately 800 pct, when deformed at temperatures above 500 degreesC and at the strain rates of 10(-2)/s to 10(-1)/s. Such a high strain rate is quite advantageous for the practical Superplastic forming application of the alloy. Stress-strain rate curves were obtained by performing a series of load relaxation tests in the temperature range from 460 degreesC to 520 degreesC in order to examine the Superplastic Deformation behavior and to establish its mechanisms. The stress-strain rate curves could be separated into two parts according to their respective physical mechanisms, i.e., grain matrix Deformation and grain boundary sliding, as was proposed in a new Superplasticity theory based on internal Deformation variables. The microstructural evolution during Superplastic Deformation was also analyzed by using transmission electron microscopy. During Superplastic Deformation, grains were kept fine and changed into equiaxed ones due to the presence of fine secondary phase particles and the continuous recrystallization due to the development of subgrains. Consequently, the rapidly solidified (RS) alloy showed much improved Superplasticity compared to the conventional ingot cast 8090 alloy.X115sciescopu
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Microscopic observation of Superplastic Deformation in a 2-phase Ti3Al-Nb alloy
'Elsevier BV', 2019Co-Authors: Jh Kim, Cg Park, Yw ChangAbstract:Microscopic aspects of Superplastic Deformation in a 2-phase Ti3Al-Nb alloy were studied using transmission electron microscopy. A 5-kW radiant heating system capable of heating up 200 degrees C per min was used to minimize possible microstructural changes during heating and cooling stages. A Ti-24Al-11Nb alloy with the grain size of 3.6 mu m showed the maximum elongation of 1280% at 970 degrees C under an initial strain rate of 10(-3)/s, which is the largest elongation ever reported in open literature. Localized dislocation activity was observed mainly along alpha(2)/alpha(2) grain boundaries and/or alpha(2)/beta phase boundaries without noticeable dislocation activity inside the alpha(2) grains of the Superplastically deformed specimen. Severe Deformation was also observed in the soft beta phase. Adjacent alpha(2) grains, however, only contained some dislocations that were piled up at the region near the triple junctions. The observations on dislocation activities suggest that boundary sliding plays a major role in Superplastic Deformation of this alloy, together with a dominant accommodation mechanism via dislocation motion inside beta and alpha(2) grains. The effects of strain rate and grain size on deformed microstructure were also investigated, and finally, a possible Superplastic Deformation mechanism of 2-phase Ti3Al-Nb alloy is proposed. (C) 1999 Elsevier Science S.A. All rights reserved.X1112sciescopu
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Microstructural evolution of quasi-single phase alloy during Superplastic Deformation
'Trans Tech Publications Ltd.', 2019Co-Authors: Bang W, Yw ChangAbstract:Flow shifts and changes in microstructure were investigated for Superplastic Deformation of 7475 Al alloy. The recently proposed internal variable theory of structural Superplasticity has been applied to the results of mechanical test. Deformed microstructure was observed using a TEM to check the validity of the constitutive relations. Accommodation mechanism for grain boundary sliding was also examined through the microchemical analysis of deformed microstructures.X112sciescopu
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Internal variable approach to microstructural change in 7475 alumin-ium alloy during Superplastic Deformation
'Maney Publishing', 2019Co-Authors: Bang W, Yw ChangAbstract:Flow behaviour and microstructural changes in fine grained 7475 Al during Superplastic Deformation have been investigated. A series of mechanical tests and transmission electron micrography has been conducted at various temperatures ranging from 430 to 516degreesC. Quantitative constitutive parameters have been determined from load relaxation tests by applying the internal variable theory of structural Superplasticity proposed recently. The validity of the mechanical analysis is proved by the evolution of the microstructure (precipitate free zones PFZs) during the accommodation process. Additional information about the mechanism of PFZ formation was determined by microchemical analysis.X113sciescopu
Kaibyshev R. - One of the best experts on this subject based on the ideXlab platform.
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On the possibility of Superplasticity enhanced by dynamic recrystallization
'Trans Tech Publications Ltd.', 2020Co-Authors: Kaibyshev R., Galiyev A.Abstract:yesThe possibility of Superplastic Deformation of ultrafine-grained materials is discussed in terms of the influence of grain boundary structure on mechanisms of Superplastic flowBelgorod State Universit
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Superplastic behavior of an Al-Li-Cu-Mg alloy
2020Co-Authors: Kaibyshev R.Abstract:yesThe microstructural evolution during Superplastic Deformation of the Al-Li-Cu-Mg alloy has been studied quantitatively. The role of dispersoids in Superplasticity is consideredBelgorod State Universit
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Superplastic behavior in Al-Li-Mg-Cu-Sc alloy sheet
2020Co-Authors: Shagiev M., Kaibyshev R., Motohashi Y., Musin F., Itoh G.Abstract:yesIt was found that partially recrystallized microstructure evolved under the hot rolling resulting in slight anisotropy of Superplastic behavior. Microstructure evolution and cavitation during Superplastic Deformation were examinedBelgorod State Universit
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Grain refinement and Superplastic behaviour of a modified 6061 aluminium alloy
'Maney Publishing', 2020Co-Authors: Kaibyshev R., Musin F., Gromov D., Nieh T. G., Lesuer D. R.Abstract:yesThe microstructural evolution during Superplastic Deformation of the 6061 alloy has been studied quantitatively. The presence of a slight amount of liquid phase greatly promotes the Superplastic properties of the 6061 alloy, reducing the cavitation levelBelgorod State Universit
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Superplasticity in an 7475 aluminum alloy subjected to equal channel angular extrusion
'Trans Tech Publications Ltd.', 2020Co-Authors: Kaibyshev R., Sakai T., Musin F.Abstract:yesIt was shown that the main feature of Superplastic behavior of the equal-channel angular extrusion (ECAE) processed 7475 aluminum alloy is an extensive strain-hardening at initial stages of Superplastic Deformation attributed to instability of microstructureBelgorod State Universit
Fang Chai - One of the best experts on this subject based on the ideXlab platform.
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microstructure evolution during high strain rate tensile Deformation of a fine grained az91 magnesium alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2014Co-Authors: Fang Chai, Datong Zhang, Weiwen ZhangAbstract:Abstract A fine-grained AZ91 magnesium alloy prepared by submerged friction stir processing is subjected to high temperature tensile test at 623 K and 2×10 −2 s −1 to intermediate strains of 270%, 510%, 750% and failure strain of 990%, and microstructure evolution of the experimental material during tensile test is investigated. The initial grain size is about 1.2 μm. Microstructures within the gauge region are much finer than those of grip region, and the grain aspect ratios remain approximately 1.0 in the whole Superplastic Deformation. With the tensile strains increasing, the average size of β-Mg 17 Al 12 particles increases, and the density of the β-Mg 17 Al 12 particles decreases. Due to the pinning effect of β-Mg 17 Al 12 particles and the occurrence of DRX, the fine microstructures are maintained in the whole Superplastic Deformation process. Grain boundary sliding is the main Deformation mechanism, and cavities are formed in the triple junctions of grains and around the second phase particles during Deformation. The excellent high strain rate Superplasticity of the AZ91 magnesium alloy is mainly attributed to its initial fine microstructure and good thermal stability.
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high strain rate Superplasticity of a fine grained az91 magnesium alloy prepared by submerged friction stir processing
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2013Co-Authors: Fang Chai, Datong Zhang, Yuanyuan Li, Weiwen ZhangAbstract:Friction stir processing (FSP) is a novel severe plastic Deformation technique to prepare fine-grained metallic materials. Superplastic behaviors of FSP magnesium alloys have not been fully studied until now. In this study, microstructure and tensile behaviors of a fine-grained Mg-9Al-1Zn alloy prepared by FSP under water are investigated. It is found that the process results in significant grain refinement, and the second phase networks are broken into small particles. The FSP specimens exhibit excellent high strain rate Superplasticity, with an elongation of 990% at a strain rate of 2×10−2 s−1 and 623K. Microstructure evolution and Superplastic Deformation mechanism of the experimental materials during Superplastic tensile test are investigated. Grain boundary sliding is the main mechanism for the Superplastic Deformation of the specimens. The excellent Superplasticity of the FSP material is attributed to its fine grain structures, which contain a larger fraction of grain boundary.
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high strain rate Superplasticity of a fine grained az91 magnesium alloy prepared by submerged friction stir processing
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2013Co-Authors: Fang Chai, Datong Zhang, Weiwen ZhangAbstract:Abstract The as-cast AZ91 plate was subjected to normal friction stir processing (processed in air) and submerged friction stir processing (processed in water, SFSP), and microstructure and Superplastic tensile behavior of the experimental alloys were investigated. SFSP results in remarkable grain refinement due to the enhanced cooling rate compared with normal FSP, with an average grain size of 1.2 μm and 7.8 μm. The SFSP AZ91 specimen exhibits considerably enhanced Superplastic ductility with reduced flow stress and higher optimum strain rate, as compared to the normal FSP specimen. The optimum Superplastic Deformation temperature is found to be 623 K for both the normal FSP and SFSP AZ91 specimens. An elongation of 990% is obtained at 2×10−2 s−1 and 623 K for the SFSP specimen, indicating that excellent high strain rate Superplasticity could be achieved. By comparison, maximum ductility of the normal FSP specimen strained at high strain rate is 158%. Grain boundary sliding is the main mechanism for the Superplastic Deformation of the normal FSP and SFSP specimens. The excellent high strain rate Superplasticity of the SFSP alloy is attributed to its finer grain structure and higher fraction of grain boundary.
Z Y - One of the best experts on this subject based on the ideXlab platform.
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high strain rate Superplasticity in a micro grained al mg sc alloy with predominant high angle grain boundaries
Journal of Materials Science & Technology, 2012Co-Authors: Z Y, Fucheng ZhangAbstract:Friction stir processing (FSP) was applied to extruded Al-Mg-Sc alloy to produce fine-grained microstructure with a grain size of 2.2 mu m. Electron backscatter diffraction (EBSD) result showed that the grain boundary misorientation distribution was very close to a random grain assembly for randomly oriented cubes. Superplastic investigations in the temperature range of 425-500 degrees C and strain rate range of 1x10(-2)-1x1(0) s(-1) showed that a maximum elongation of 1500% was achieved at 475 degrees C and a high strain rate of 1x10(-1) s(-1). The FSP Al-Mg-Sc exhibited enhanced Superplastic Deformation kinetics compared to that predicted by the constitutive relationship for Superplasticity in fine-grained aluminum alloys. The origin for enhanced Superplastic Deformation kinetics in the FSP alloy can be attributed to its high fraction of high angle grain boundaries (HAGBs). The analyses of the Superplastic data and scanning electron microscopy (SEM) examinations on the surfaces of deformed specimens indicated that grain boundary sliding is the main Superplastic Deformation mechanism for the FSP Al-Mg-Sc alloy.
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Superplastic Deformation mechanism of an ultrafine grained aluminum alloy produced by friction stir processing
Acta Materialia, 2010Co-Authors: Z Y, F C Liu, Rajiv S MishraAbstract:An ultrafine-grained (UFG) Al-4Mg-1Zr alloy with a grain size of similar to 0.7 mu m with predominantly high-angle boundaries of 97% was produced by friction stir processing (FSP). The UFG Al-4Mg-1Zr retained submicrometer grains even after static annealing at 425 degrees C, and exhibited excellent Superplasticity at 175-425 degrees C. High strain rate and low-temperature Superplasticity of >1200% were observed at 1 x 10(-2)-1 x 10(-1) s(-1) and 300-350 degrees C. Even at 425 degrees C, a Superplasticity of 1400% was achieved at 1 s(-1). A linear relationship between log (epsilon) over dot(opti) and T was observed (where (epsilon) over dot(opti) is the optimum strain rate, and T is the temperature). The analyses on the Superplastic data revealed the presence of threshold stress, a stress exponent of 2, an inverse grain size dependence of 2, and an activation enemy of 142 kJ mol(-1). This indicated that the dominant Deformation mechanism was grain boundary sliding, which was controlled by lattice diffusion. Based on this notion, a constitutive equation has been developed. A new Superplastic Deformation mechanism map for FSP aluminum alloys is proposed. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All
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Superplastic Deformation behaviour of friction stir processed 7075al alloy
Acta Materialia, 2002Co-Authors: Z Y, Rajiv S Mishra, Murray W MahoneyAbstract:Commercial 7075Al rolled plates were subjected to friction stir processing (FSP) with different processing parameters, resulting in two fine-grained 7075Al alloys with a grain size of 3.8 and 7.5 µm. Heat treatment at 490 °C for 1 h showed that the fine grain microstructures were stable at high temperatures. Superplastic investigations in the temperature range of 420–530 °C and strain rate range of 1× 10 3 –1× 10 1 s 1 demonstrated that a decrease in grain size resulted in significantly enhanced Superplasticity and a shift to higher optimum strain rate and lower optimum Deformation temperature. For the 3.8 µm 7075Al alloy, Superplastic elongations of 1250% were obtained at 480 °C in the strain rate range of 3× 10 3 –3× 10 2 s 1 , whereas the 7.5 µm 7075Al alloy exhibited a maximum ductility of 1042% at 500 °C and 3× 10 3 s 1 . The analyses of the Superplastic data for the two alloys revealed a stress exponent of 2, an inverse grain size dependence of 2, and an activation energy close to that for grain boundary self-diffusion. This indicates that grain boundary sliding is the main Deformation mechanism for the FSP 7075Al. This was verified by SEM examinations on the surfaces of deformed specimens. 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.
