抗大变形管线钢加热并保温一段时间后,钢管力学性能将发生变化,通常屈服强度、屈强比升高,均匀延伸率降低,应力-应变曲线形状改变等,这些性能变化将降低钢管的抵抗变形的能力。利用扫描电镜等设备研究了冷却工艺对21 mm X70HD抗大变形...抗大变形管线钢加热并保温一段时间后,钢管力学性能将发生变化,通常屈服强度、屈强比升高,均匀延伸率降低,应力-应变曲线形状改变等,这些性能变化将降低钢管的抵抗变形的能力。利用扫描电镜等设备研究了冷却工艺对21 mm X70HD抗大变形管线钢组织、性能和应变时效硬化的影响。结果表明,随开始冷却温度的降低,先共析铁素体含量逐渐增加,贝氏体含量逐渐降低,贝氏体由粒状逐渐向板条状转变,当开始冷却温度在700℃时,钢板具有最佳的综合力学性能,试验钢板通过制成1016 mm钢管,钢管在200℃时效保温5 min下,纵向屈服强度Rt0.5为509 MPa,抗拉强度Rm为692 MPa,延伸率为42%,屈强比Rt0.5/Rm为0.73,Rt1.5/Rt0.5为1.19、Rt2.0/Rt1.0为1.10,均匀变形伸长率达到9.5%。展开更多
Process of warm tube hydroforming was experimentally investigated for forming an AZ31B magnesium alloy tubular part with a large expansion ratio. Effects of temperature on the mechanical properties and formability wer...Process of warm tube hydroforming was experimentally investigated for forming an AZ31B magnesium alloy tubular part with a large expansion ratio. Effects of temperature on the mechanical properties and formability were studied by uniaxial tensile test and hydraulic bulge test. Total elongation increases with temperature up to 250℃, but uniform elongation and maximum expansion ratio get the highest value at 175℃. Different axial feeding amounts were applied in experiments to determine the reasonable loading path. A preform with useful wrinkles was then realized and the tubular part with an expansion ratio of 50% was formed. Finally, mechanical condition to produce useful wrinkles is deduced and the result illustrates that useful wrinkles are easier to be obtained for tube with higher strain hardening coefficient value and tubular part with smaller expansion ratio.展开更多
How an individual constituent zone behaves during the deformation of a heterostructured metallic material is a fundamental issue for understanding heterostructure deformation, but it remains a challenge to experimenta...How an individual constituent zone behaves during the deformation of a heterostructured metallic material is a fundamental issue for understanding heterostructure deformation, but it remains a challenge to experimentally observe it. Here we report a study on the stress-strain behavior of the nanostructured gradient layer(NGL) in an integrated gradient specimen that consists of a coarse-grained(CG)central layer sandwiched between two NGLs. Constraint from the CG central layer led to the formation of dense and dispersed stable strain bands(SBs) in the NGL, which regained dislocation hardening after initial recovery and grain coarsening. Consequently, the NGL exhibited a transient plateau of flow stress after yielding, and then regained extra strain hardening to achieve excellent uniform elongation. These unique behaviors are dramatically different from those of a freestanding NGL, indicating a fundamentally different deformation principle that is intrinsic to heterostructures, i.e.,inter-zone constraint modifies the constitutive behavior of constituent zones.展开更多
The ultrafine grained(UFG)1050 aluminum alloy was prepared by equal channel angular pressing at cryogenic temperature,namely cryoECAP process.The tensile behavior and microstructures of UFG 1050 aluminum alloy after a...The ultrafine grained(UFG)1050 aluminum alloy was prepared by equal channel angular pressing at cryogenic temperature,namely cryoECAP process.The tensile behavior and microstructures of UFG 1050 aluminum alloy after annealing at 90-210°C for 4 h without and with high magnetic field of 12 T were investigated by tensile tests,transmission electron microscope,and electron backscattered diffraction analyses.After cryoECAP and annealing treatments,the 1050 aluminum alloy has ultrafine grains with 0.7-1.28μm in size,the ratio of ultimate tensile strength to yield strength is less than 1.24,and the uniform elongation is less than 2.3%.With increasing the annealing temperature from 90°C to 210°C,the yield-drop phenomenon becomes more obvious due to the decrease in mobile dislocations to maintain the applied strain rate during tensile deformation.The uniform elongation decreases from 1.55%to 0.55%,the dislocation density reduces from 5.6×10^(14)m^(−2)to 4.2×10^(13)m^(−2),and the fraction of high-angle grain boundaries(HABs)increases from 63.8%to 70.8%.These phenomena cause the higher annihilation rate of dislocations,thereby leading to the degradation of strain hardening effect.During annealing under high magnetic field at 90-210°C,the low fraction of HABs(61.7%-66.2%)can provide a slower annihilation rate of dislocations,therefore resulting in the higher uniform elongation(0.64%-1.60%)and slower decrease in the flow stress after the yield peak.展开更多
基金Project(NCET-07-0237) supported by New Century Excellent Talents Program in Chinese University
文摘Process of warm tube hydroforming was experimentally investigated for forming an AZ31B magnesium alloy tubular part with a large expansion ratio. Effects of temperature on the mechanical properties and formability were studied by uniaxial tensile test and hydraulic bulge test. Total elongation increases with temperature up to 250℃, but uniform elongation and maximum expansion ratio get the highest value at 175℃. Different axial feeding amounts were applied in experiments to determine the reasonable loading path. A preform with useful wrinkles was then realized and the tubular part with an expansion ratio of 50% was formed. Finally, mechanical condition to produce useful wrinkles is deduced and the result illustrates that useful wrinkles are easier to be obtained for tube with higher strain hardening coefficient value and tubular part with smaller expansion ratio.
基金supported by the National Natural Science Foundation of China (NSFC, 51931003)China Postdoctoral Science Foundation (2020M680223)+2 种基金the NSFC Basic Science Center Program for "Multiscale Problems in Nonlinear Mechanics" (11988102)the Chinese Academy of Sciences (XDB22040503)the National Key R&D Program of China (2017YFA0204403)。
文摘How an individual constituent zone behaves during the deformation of a heterostructured metallic material is a fundamental issue for understanding heterostructure deformation, but it remains a challenge to experimentally observe it. Here we report a study on the stress-strain behavior of the nanostructured gradient layer(NGL) in an integrated gradient specimen that consists of a coarse-grained(CG)central layer sandwiched between two NGLs. Constraint from the CG central layer led to the formation of dense and dispersed stable strain bands(SBs) in the NGL, which regained dislocation hardening after initial recovery and grain coarsening. Consequently, the NGL exhibited a transient plateau of flow stress after yielding, and then regained extra strain hardening to achieve excellent uniform elongation. These unique behaviors are dramatically different from those of a freestanding NGL, indicating a fundamentally different deformation principle that is intrinsic to heterostructures, i.e.,inter-zone constraint modifies the constitutive behavior of constituent zones.
基金National Natural Science Foundation of China(51574076)。
文摘The ultrafine grained(UFG)1050 aluminum alloy was prepared by equal channel angular pressing at cryogenic temperature,namely cryoECAP process.The tensile behavior and microstructures of UFG 1050 aluminum alloy after annealing at 90-210°C for 4 h without and with high magnetic field of 12 T were investigated by tensile tests,transmission electron microscope,and electron backscattered diffraction analyses.After cryoECAP and annealing treatments,the 1050 aluminum alloy has ultrafine grains with 0.7-1.28μm in size,the ratio of ultimate tensile strength to yield strength is less than 1.24,and the uniform elongation is less than 2.3%.With increasing the annealing temperature from 90°C to 210°C,the yield-drop phenomenon becomes more obvious due to the decrease in mobile dislocations to maintain the applied strain rate during tensile deformation.The uniform elongation decreases from 1.55%to 0.55%,the dislocation density reduces from 5.6×10^(14)m^(−2)to 4.2×10^(13)m^(−2),and the fraction of high-angle grain boundaries(HABs)increases from 63.8%to 70.8%.These phenomena cause the higher annihilation rate of dislocations,thereby leading to the degradation of strain hardening effect.During annealing under high magnetic field at 90-210°C,the low fraction of HABs(61.7%-66.2%)can provide a slower annihilation rate of dislocations,therefore resulting in the higher uniform elongation(0.64%-1.60%)and slower decrease in the flow stress after the yield peak.
