Continuous bending (CB) process along rolling direction was performed to improve the formability of AZ31 magnesium alloy sheets. The microstructure and texture evolutions were characterized by optical microscopy (OM) ...Continuous bending (CB) process along rolling direction was performed to improve the formability of AZ31 magnesium alloy sheets. The microstructure and texture evolutions were characterized by optical microscopy (OM) and electronic backscatter diffraction (EBSD). The results reveal that the basal texture intensity of continuously bent and annealed (CBA) sample is drastically weakened. A large number of twins are induced on the concave surface by the 1st pass bending and the density of twins obviously declines during the 2nd pass bending owing to the occurrence of detwinning. Due to the asymmetric tension?compression strain states between the outer and inner regions during V-bending, twinning and detwinning are generated alternatively during the CB process. The Erichsen value is 5.2 mm which increases by 41% compared with that of as-received sample. This obvious improvement of formability can be attributed to the weakened basal texture, which leads to a smaller plastic strain ratio (r-value)together with a larger strain-hardening exponent (n-value).展开更多
Mg-3Al-lZn alloy sheets have been deformed by continuous bending（CB）to investigate the effects of pro-cessing parameters（bending angle and repetitive passes）on the texture and formability.The samples exhibited a b...Mg-3Al-lZn alloy sheets have been deformed by continuous bending（CB）to investigate the effects of pro-cessing parameters（bending angle and repetitive passes）on the texture and formability.The samples exhibited a bimodal microstructure with abnormal growth grains in the surface region and fine grains distributed in the center after CB process followed by annealing.The texture evolution measured by XRD indicated that the basal poles were rotated from ND toward RD,and the texture intensity decreased with the bending angle decreasing and repetitive passes increasing.Compared with the as-received sample,the yield strength of CBA-120-2 sample significantly decreased from 183 to 112 MPa,and a smaller r-value and a larger n-value were obtained.The formability of CB processed samples in annealing condition was significantly enhanced with the highest of Erichsen value of 5.4 mm,increased by about 135%.The improvement of formability was likely attributed to the weakened and RD-tilt basal texture and coarse grains in the surface part.展开更多
The upper reach of the Yellow River from Daliushu to Shapotou consists of five bends and has complex topography. A two-dimensional Re-Normalisation Group （RNG） k-ε model was developed to simulate the flow in the re...The upper reach of the Yellow River from Daliushu to Shapotou consists of five bends and has complex topography. A two-dimensional Re-Normalisation Group （RNG） k-ε model was developed to simulate the flow in the reach. In order to take the circulation currents in the bends into account, the momentum equations were improved by adding an additional source term. Comparison of the numerical simulation with field measurements indicates that the improved two-dimensional depth-averaged RNG k-e model can improve the accuracy of the numerical simulation. A rapid adaptive algorithm was constructed, which can automatically adjust Manning＇s roughness coefficient in different parts of the study river reach. As a result, not only can the trial computation time be significantly shortened, but the accuracy of the numerical simulation can also be greatly improved. Comparison of the simulated and measured water surface slopes for four typical cases shows that the longitudinal and transverse slopes of the water surface increase with the average velocity upstream. In addition, comparison was made between the positions of the talweg and the main streamline, which coincide for most of the study river reach. However, deviations between the positions of the talweg and the main streamline were found at the junction of two bends, at the position where the river width suddenly decreases or increases.展开更多
基金Project(CDJZR13130081)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(CSCT2014FAZKTJCSF50004)supported by the Chongqing Science and Technology Commission,China
文摘Continuous bending (CB) process along rolling direction was performed to improve the formability of AZ31 magnesium alloy sheets. The microstructure and texture evolutions were characterized by optical microscopy (OM) and electronic backscatter diffraction (EBSD). The results reveal that the basal texture intensity of continuously bent and annealed (CBA) sample is drastically weakened. A large number of twins are induced on the concave surface by the 1st pass bending and the density of twins obviously declines during the 2nd pass bending owing to the occurrence of detwinning. Due to the asymmetric tension?compression strain states between the outer and inner regions during V-bending, twinning and detwinning are generated alternatively during the CB process. The Erichsen value is 5.2 mm which increases by 41% compared with that of as-received sample. This obvious improvement of formability can be attributed to the weakened basal texture, which leads to a smaller plastic strain ratio (r-value)together with a larger strain-hardening exponent (n-value).
基金financially supported by the National Natural Science Foundation of China (Nos. 51671041 and 51531002)the National Key Research and Development Plan (No. 2016YFB0301104)+1 种基金Demonstrative Project of Chongqing Science and Technology Commission (No. CSCT2014FAZKTJCSF50004)Fundamental Research Funds for the Central Universities (No. 106112017CDJPT280001)
文摘Mg-3Al-lZn alloy sheets have been deformed by continuous bending（CB）to investigate the effects of pro-cessing parameters（bending angle and repetitive passes）on the texture and formability.The samples exhibited a bimodal microstructure with abnormal growth grains in the surface region and fine grains distributed in the center after CB process followed by annealing.The texture evolution measured by XRD indicated that the basal poles were rotated from ND toward RD,and the texture intensity decreased with the bending angle decreasing and repetitive passes increasing.Compared with the as-received sample,the yield strength of CBA-120-2 sample significantly decreased from 183 to 112 MPa,and a smaller r-value and a larger n-value were obtained.The formability of CB processed samples in annealing condition was significantly enhanced with the highest of Erichsen value of 5.4 mm,increased by about 135%.The improvement of formability was likely attributed to the weakened and RD-tilt basal texture and coarse grains in the surface part.
基金supported by the National Natural Science Foundation of China(Grants No.11361002 and 91230111)the Natural Science Foundation of Ningxia,China(Grant No.NZ13086)+1 种基金the Project of Beifang University of Nationalities,China(Grant No.2012XZK05)the Foreign Expert Project of Beifang University of Nationalities,China,and the Visiting Scholar Foundation of State Key Laboratory of Water Resources and Hydropower Engineering Science,Wuhan University,China(Grant No.2013A011)
文摘The upper reach of the Yellow River from Daliushu to Shapotou consists of five bends and has complex topography. A two-dimensional Re-Normalisation Group （RNG） k-ε model was developed to simulate the flow in the reach. In order to take the circulation currents in the bends into account, the momentum equations were improved by adding an additional source term. Comparison of the numerical simulation with field measurements indicates that the improved two-dimensional depth-averaged RNG k-e model can improve the accuracy of the numerical simulation. A rapid adaptive algorithm was constructed, which can automatically adjust Manning＇s roughness coefficient in different parts of the study river reach. As a result, not only can the trial computation time be significantly shortened, but the accuracy of the numerical simulation can also be greatly improved. Comparison of the simulated and measured water surface slopes for four typical cases shows that the longitudinal and transverse slopes of the water surface increase with the average velocity upstream. In addition, comparison was made between the positions of the talweg and the main streamline, which coincide for most of the study river reach. However, deviations between the positions of the talweg and the main streamline were found at the junction of two bends, at the position where the river width suddenly decreases or increases.
