The Al−Mg alloy with high Mg addition(Al−9.2Mg−0.8Mn−0.2Zr-0.15Ti,in wt.%)was subjected to different passes(1,2 and 4)of high strain rate rolling(HSRR),with the total thickness reduction of 72%,the rolling temperature...The Al−Mg alloy with high Mg addition(Al−9.2Mg−0.8Mn−0.2Zr-0.15Ti,in wt.%)was subjected to different passes(1,2 and 4)of high strain rate rolling(HSRR),with the total thickness reduction of 72%,the rolling temperature of 400℃and strain rate of 8.6 s^(−1).The microstructure evolution was studied by optical microscope(OM),scanning electron microscope(SEM),electron backscattered diffraction(EBSD)and transmission electron microscope(TEM).The alloy that undergoes 2 passes of HSRR exhibits an obvious bimodal grain structure,in which the average grain sizes of the fine dynamic recrystallization(DRX)grains and the coarse non-DRX regions are 6.4 and 47.7mm,respectively.The high strength((507±9)MPa)and the large ductility((24.9±1.3)%)are obtained in the alloy containing the bimodal grain distribution.The discontinuous dynamic recrystallization(DDRX)mechanism is the prominent grain refinement mechanism in the alloy subjected to 2 passes of HSRR.展开更多
A flow stress equation was proposed to compute the roll force in the finishing stands of an actual rod mill where the strain rate and the temperature of the material range from 100 to 400 s-1 and from 900 to 1050 ℃,r...A flow stress equation was proposed to compute the roll force in the finishing stands of an actual rod mill where the strain rate and the temperature of the material range from 100 to 400 s-1 and from 900 to 1050 ℃,respectively.The underlying idea is to modify the Shida model and Misaka model,which provide flow stress equations（constitutive equations） frequently used to depict deformation behavior of high temperature material at different strain rates.The modified model was coupled with finite element method to compute the roll force during four-pass continuous rod rolling,where strain rates are in the range of 100-400 s-1 at high temperatures（900-1050 ℃）.The roll forces and the surface temperatures of the material at each stand were measured,and the measured data were compared with the computed values.Results reveal that the Misaka model is better than the Shida model for high temperatures and intermediate strain rates.The roll force error was-5.7 % when the Misaka model was used at 900 ℃.However,the error increased by-15.2% at 1050 ℃.When the modified Misaka model was used,the error was reduced to 1.8% on average.It can consequently be deduced that the modified Misaka model can be used to depict the deformation resistance behavior in intermediate ranges of strain rate and high temperature ranges in continuous rod rolling process.展开更多
The high strain rate superplastic deformation properties and characteristics of a rolled AZ91 magnesium alloy at temperatures ranging from 623 to 698 K（0.67Tm-0.76Tm） and high strain rates ranging from 10^-3 to 1 s^...The high strain rate superplastic deformation properties and characteristics of a rolled AZ91 magnesium alloy at temperatures ranging from 623 to 698 K（0.67Tm-0.76Tm） and high strain rates ranging from 10^-3 to 1 s^-1 were investigated.The rolled AZ91 magnesium alloy possesses excellent superplasticity with the maximum elongation of 455% at 623 K and a strain rate of 10-3 s-1,and its strain rate sensitivity m is high up to 0.64.The dominant deformation mechanism responsible for the high strain rate superplasticity is still grain boundary sliding（GBS）,and the dislocation creep mechanism is considered as the main accommodation mechanism.展开更多
Considering roll elastic flattening, new equations were proposed to calculate the average strain ε and average strain rate ε- in the hot strip rolling process. By comparing the proposed equations with currently used...Considering roll elastic flattening, new equations were proposed to calculate the average strain ε and average strain rate ε- in the hot strip rolling process. By comparing the proposed equations with currently used equations ,it was observed that the strain rate of thick strip and strain are not sensitive to roll elastic flattening. However,for thin strip, a noticeable calculated difference in the strain rate occurred when roll elastic flattening was considered.展开更多
Effects of calcium( Ca) and yttrium( Y) on microstructure and mechanical properties of high strain-rate rolled AZ91 D magnesium alloy were studied. High strain-rate rolling can improve the strength and plasticity of m...Effects of calcium( Ca) and yttrium( Y) on microstructure and mechanical properties of high strain-rate rolled AZ91 D magnesium alloy were studied. High strain-rate rolling can improve the strength and plasticity of magnesium alloy sheets.Additions of Ca and Y into AZ91 D can refine grains and modify the size and the distribution of the precipitated phases. After solution treatment( 418 ℃ and 20 h) and high strain-rate rolling( heating at420 ℃ for 10 min firstly and then rolling from 10 mm to 2 mm in thickness via a single pass),the tensile strength of the AZ91 D-0. 2%Ca alloy was 1. 3% higher than that of the AZ91 D-0. 4 D%Y alloy,and the tensile strength of the AZ91 D-0. 2%Ca-0. 4%Y alloy was about 8. 3% and 6. 9% higher than those of the AZ91 D-0. 4%Y and the AZ91 D-0. 2%Ca alloys respectively.展开更多
TiN_p/1N90Al composite was fabricated by powder metallurgy method with a reinforcement volume fraction of 15%. The tensile experiment, DSC and SEM were used to study the high strain rate superplasticity of the TiN_p/1...TiN_p/1N90Al composite was fabricated by powder metallurgy method with a reinforcement volume fraction of 15%. The tensile experiment, DSC and SEM were used to study the high strain rate superplasticity of the TiN_p/1N90Al composite. The DSC result shows that the incipient melting temperature of the TiN_p/1N90Al composite is 906K. The tensile tests were carried out over a range of deformation temperature from 918 to 928K and strain rate from 1.7 to 1.7×10 -3 s -1. The maximum elongation of 201% is realized at 923K with a strain rate of 1.7×10 -1 s -1. Otherwise all the elongations are higher than 100% in the strain rate range of 3.3×10 -2-6.7×10 -1 s -1 at the three deformation temperatures. The curves of m value of the TiN_p/1N90Al composite can be divided into two stages with the variation of strain rate at different deformation temperatures and the critical strain rate of 10 -1 s -1. When the strain rate is higher than 10 -1 s -1, the m values of the three curves are smaller than 0.3, but the m values of the three curves are about 0.37 when the strain rate is higher than 10 -1 s -1.展开更多
A two-phase Mg-9Li-2Zn alloy sheet is made by cold-rolling at room temperature, and the formability of it at room temperature is investigated in this study. Uniaxial tension tests are carried out for various strain ra...A two-phase Mg-9Li-2Zn alloy sheet is made by cold-rolling at room temperature, and the formability of it at room temperature is investigated in this study. Uniaxial tension tests are carried out for various strain rates between 0.5 mm/min and 250 mm/min, and the microstructural changes during the tests are observed. The sheet has high formability at comparatively low strain rates. Maximum elongation amounts to 40%. However, ductility decreases with the increase of strain rate. Even at room temperature, the stress is also sensitive to the strain rate. There are many large dimples at comparatively low strain rates, and small dimples occur at high strain rates, it shows fine sub-grains come into being.展开更多
The dual-stream function velocity field is reduced in order to analyze two-dimensional plate broadside roll- ing in roughing. The strain rate vector inner product and integral mean value theorem, as well as coqine vec...The dual-stream function velocity field is reduced in order to analyze two-dimensional plate broadside roll- ing in roughing. The strain rate vector inner product and integral mean value theorem, as well as coqine vector inner product are used respectively in plastic deformation power, friction losses and shear power. A theoretical solution of roll torque and separating force for the rolling is obtained and the calculated results by the solution are compared with those measured in broadside rolling on-line. It shows that both the force and torque calculated are higher than those of measured, but the maximum relative error between them is no more than 11%.展开更多
A new linear integral method for bar hot rolling on roughing train was obtained. First, for plastic deformation energy rate, equivalent strain rate about Kobayashi＇s three-dimensional velocity field was expressed by ...A new linear integral method for bar hot rolling on roughing train was obtained. First, for plastic deformation energy rate, equivalent strain rate about Kobayashi＇s three-dimensional velocity field was expressed by two-dimensional strain rate vector; then, the two-dimensional strain rate vector was inverted into inner product and was integrated term by term. During those processes, boundary equation and mean value theorem were introduced; for friction and shear energy dissipation rate, definite integral was applied to the solution process. Sequentially, the total upper bound power was minimized, and the analytical expressions of rolling torque, separating force, and stress state factor were obtained. The calculated results by these expressions were compared with those of experimental values. The results show that the new linear integral method is available for bar rough rolling analysis and the calculated results by this method are a little higher than those of experimental ones. However, the maximum error between them is less than 10%.展开更多
By observing the microstructure evolution of Mg-Ga alloy during tensile deformation, it is found that the prismatic slip and the pyramidal <c+a> slip occur during the tensile process at room temperature, which ...By observing the microstructure evolution of Mg-Ga alloy during tensile deformation, it is found that the prismatic slip and the pyramidal <c+a> slip occur during the tensile process at room temperature, which finally leads to the plenty of dislocation accumulation. After 8% tensile deformation,the {1012} extension twin is the main way to coordinate the strain in the c-axis direction for the alloy with the Ga content lower than 2 wt.%, but the pyramidal <c+a> slip is the main way to coordinate the strain along the c-axis direction for the alloy with the Ga content higher than 2 wt.%. The Ga addition can promote the activation of the non-basal slip, which is beneficial to the work-hardening of the alloy to achieve better plasticity. Dynamic precipitation can slightly reduce the increment of dislocations.The preparation method of high strain rate rolling(HSRR) is another important reason for the plasticity of magnesium alloy sheets, and it is an important embodiment of the application of the dislocation engineering concept in magnesium alloy. The non-basal dislocations derived from the HSRR deformation can provide the non-basal dislocation sources when magnesium alloy is deformed at room temperature,resulting in good ductility. This study can be used as a reference for preparing wrought magnesium alloy with high strength and high plasticity by Ga alloying and hot deformation.展开更多
文摘The Al−Mg alloy with high Mg addition(Al−9.2Mg−0.8Mn−0.2Zr-0.15Ti,in wt.%)was subjected to different passes(1,2 and 4)of high strain rate rolling(HSRR),with the total thickness reduction of 72%,the rolling temperature of 400℃and strain rate of 8.6 s^(−1).The microstructure evolution was studied by optical microscope(OM),scanning electron microscope(SEM),electron backscattered diffraction(EBSD)and transmission electron microscope(TEM).The alloy that undergoes 2 passes of HSRR exhibits an obvious bimodal grain structure,in which the average grain sizes of the fine dynamic recrystallization(DRX)grains and the coarse non-DRX regions are 6.4 and 47.7mm,respectively.The high strength((507±9)MPa)and the large ductility((24.9±1.3)%)are obtained in the alloy containing the bimodal grain distribution.The discontinuous dynamic recrystallization(DDRX)mechanism is the prominent grain refinement mechanism in the alloy subjected to 2 passes of HSRR.
基金supported by the Dong-A University research fund
文摘A flow stress equation was proposed to compute the roll force in the finishing stands of an actual rod mill where the strain rate and the temperature of the material range from 100 to 400 s-1 and from 900 to 1050 ℃,respectively.The underlying idea is to modify the Shida model and Misaka model,which provide flow stress equations（constitutive equations） frequently used to depict deformation behavior of high temperature material at different strain rates.The modified model was coupled with finite element method to compute the roll force during four-pass continuous rod rolling,where strain rates are in the range of 100-400 s-1 at high temperatures（900-1050 ℃）.The roll forces and the surface temperatures of the material at each stand were measured,and the measured data were compared with the computed values.Results reveal that the Misaka model is better than the Shida model for high temperatures and intermediate strain rates.The roll force error was-5.7 % when the Misaka model was used at 900 ℃.However,the error increased by-15.2% at 1050 ℃.When the modified Misaka model was used,the error was reduced to 1.8% on average.It can consequently be deduced that the modified Misaka model can be used to depict the deformation resistance behavior in intermediate ranges of strain rate and high temperature ranges in continuous rod rolling process.
基金supported by the National Natural Science Foundation of China(No.50674067).
文摘The high strain rate superplastic deformation properties and characteristics of a rolled AZ91 magnesium alloy at temperatures ranging from 623 to 698 K（0.67Tm-0.76Tm） and high strain rates ranging from 10^-3 to 1 s^-1 were investigated.The rolled AZ91 magnesium alloy possesses excellent superplasticity with the maximum elongation of 455% at 623 K and a strain rate of 10-3 s-1,and its strain rate sensitivity m is high up to 0.64.The dominant deformation mechanism responsible for the high strain rate superplasticity is still grain boundary sliding（GBS）,and the dislocation creep mechanism is considered as the main accommodation mechanism.
文摘Considering roll elastic flattening, new equations were proposed to calculate the average strain ε and average strain rate ε- in the hot strip rolling process. By comparing the proposed equations with currently used equations ,it was observed that the strain rate of thick strip and strain are not sensitive to roll elastic flattening. However,for thin strip, a noticeable calculated difference in the strain rate occurred when roll elastic flattening was considered.
基金Natural Science Foundation of Hunan Province,China(No.2017JJ5032)
文摘Effects of calcium( Ca) and yttrium( Y) on microstructure and mechanical properties of high strain-rate rolled AZ91 D magnesium alloy were studied. High strain-rate rolling can improve the strength and plasticity of magnesium alloy sheets.Additions of Ca and Y into AZ91 D can refine grains and modify the size and the distribution of the precipitated phases. After solution treatment( 418 ℃ and 20 h) and high strain-rate rolling( heating at420 ℃ for 10 min firstly and then rolling from 10 mm to 2 mm in thickness via a single pass),the tensile strength of the AZ91 D-0. 2%Ca alloy was 1. 3% higher than that of the AZ91 D-0. 4 D%Y alloy,and the tensile strength of the AZ91 D-0. 2%Ca-0. 4%Y alloy was about 8. 3% and 6. 9% higher than those of the AZ91 D-0. 4%Y and the AZ91 D-0. 2%Ca alloys respectively.
文摘TiN_p/1N90Al composite was fabricated by powder metallurgy method with a reinforcement volume fraction of 15%. The tensile experiment, DSC and SEM were used to study the high strain rate superplasticity of the TiN_p/1N90Al composite. The DSC result shows that the incipient melting temperature of the TiN_p/1N90Al composite is 906K. The tensile tests were carried out over a range of deformation temperature from 918 to 928K and strain rate from 1.7 to 1.7×10 -3 s -1. The maximum elongation of 201% is realized at 923K with a strain rate of 1.7×10 -1 s -1. Otherwise all the elongations are higher than 100% in the strain rate range of 3.3×10 -2-6.7×10 -1 s -1 at the three deformation temperatures. The curves of m value of the TiN_p/1N90Al composite can be divided into two stages with the variation of strain rate at different deformation temperatures and the critical strain rate of 10 -1 s -1. When the strain rate is higher than 10 -1 s -1, the m values of the three curves are smaller than 0.3, but the m values of the three curves are about 0.37 when the strain rate is higher than 10 -1 s -1.
基金Project supported by National High Tech Research Programof China (2001AA335010)
文摘A two-phase Mg-9Li-2Zn alloy sheet is made by cold-rolling at room temperature, and the formability of it at room temperature is investigated in this study. Uniaxial tension tests are carried out for various strain rates between 0.5 mm/min and 250 mm/min, and the microstructural changes during the tests are observed. The sheet has high formability at comparatively low strain rates. Maximum elongation amounts to 40%. However, ductility decreases with the increase of strain rate. Even at room temperature, the stress is also sensitive to the strain rate. There are many large dimples at comparatively low strain rates, and small dimples occur at high strain rates, it shows fine sub-grains come into being.
基金Sponsored by National Natural Science Foundation of China (51074052,50734002)
文摘The dual-stream function velocity field is reduced in order to analyze two-dimensional plate broadside roll- ing in roughing. The strain rate vector inner product and integral mean value theorem, as well as coqine vector inner product are used respectively in plastic deformation power, friction losses and shear power. A theoretical solution of roll torque and separating force for the rolling is obtained and the calculated results by the solution are compared with those measured in broadside rolling on-line. It shows that both the force and torque calculated are higher than those of measured, but the maximum relative error between them is no more than 11%.
基金Item Sponsored by National Natural Science Foundation of China (50474015)
文摘A new linear integral method for bar hot rolling on roughing train was obtained. First, for plastic deformation energy rate, equivalent strain rate about Kobayashi＇s three-dimensional velocity field was expressed by two-dimensional strain rate vector; then, the two-dimensional strain rate vector was inverted into inner product and was integrated term by term. During those processes, boundary equation and mean value theorem were introduced; for friction and shear energy dissipation rate, definite integral was applied to the solution process. Sequentially, the total upper bound power was minimized, and the analytical expressions of rolling torque, separating force, and stress state factor were obtained. The calculated results by these expressions were compared with those of experimental values. The results show that the new linear integral method is available for bar rough rolling analysis and the calculated results by this method are a little higher than those of experimental ones. However, the maximum error between them is less than 10%.
基金financially supported by the National Natural Science Foundation of China (no. 51871093)the Natural Science Foundation of Hunan Province, China (no. 2019JJ40044)。
文摘By observing the microstructure evolution of Mg-Ga alloy during tensile deformation, it is found that the prismatic slip and the pyramidal <c+a> slip occur during the tensile process at room temperature, which finally leads to the plenty of dislocation accumulation. After 8% tensile deformation,the {1012} extension twin is the main way to coordinate the strain in the c-axis direction for the alloy with the Ga content lower than 2 wt.%, but the pyramidal <c+a> slip is the main way to coordinate the strain along the c-axis direction for the alloy with the Ga content higher than 2 wt.%. The Ga addition can promote the activation of the non-basal slip, which is beneficial to the work-hardening of the alloy to achieve better plasticity. Dynamic precipitation can slightly reduce the increment of dislocations.The preparation method of high strain rate rolling(HSRR) is another important reason for the plasticity of magnesium alloy sheets, and it is an important embodiment of the application of the dislocation engineering concept in magnesium alloy. The non-basal dislocations derived from the HSRR deformation can provide the non-basal dislocation sources when magnesium alloy is deformed at room temperature,resulting in good ductility. This study can be used as a reference for preparing wrought magnesium alloy with high strength and high plasticity by Ga alloying and hot deformation.
