The multi-pass hot compression test of 7055 aluminum alloy was performed at different temperatures and then the samples were heat treated by T6 heat treatment.The compressed samples were analyzed by OM and TEM.The res...The multi-pass hot compression test of 7055 aluminum alloy was performed at different temperatures and then the samples were heat treated by T6 heat treatment.The compressed samples were analyzed by OM and TEM.The results reveal that the average aspect ratio of the grains in the specimens compressed first decreases and then increases,the dislocation density decreases and subgrain diameter increases with the increase of deformation temperature.The effects of deformation temperature on the microstructure and mechanical properties of 7055 aluminum alloy after heat treatment were investigated by means of OM and mechanical property test.The results indicate that the deformation temperature significantly influences microstructure and mechanical property of 7055 aluminum alloy.The volume fraction of recrystallization grains presents a "fall-rise" pattern with the deformation temperature rising.The mechanical properties get better when the volume fraction of recrystallization grains decreases.Moreover,the volume fraction of recrystallization grain has a minimum value,appropriately 45%,and the sample exhibits the highest strength and elongation at the deformation temperature of 400 ℃.展开更多
In order to establish the rolling process parameters of grade-2 commercially pure titanium (CP-Ti), it is necessary to understand the transformation mechanism and mechanical properties of this material. The β→α t...In order to establish the rolling process parameters of grade-2 commercially pure titanium (CP-Ti), it is necessary to understand the transformation mechanism and mechanical properties of this material. The β→α transformation kinetics of the grade-2 CP-Ti during continuous cooling was measured and its hot compression behavior was investigated using Gleeble-1500 thermal mechanical simulator. Dynamic CCT diagram confirms that cooling rate has an obvious effect on the start and finishing transformation and microstructures at room temperature. The critical cooling rate for γ-phase transforms to a phase is about 15℃/s. When the cooling rate is higher than 15 ℃/s, some β phases with fine granular shape remain residually into plate-like structure. The plate-like a phase forms at cooling rate lower than 2 ℃/s, serrate a phase forms at medium cooling rates, about 5-15℃/s. The flow stress behavior of grade-2 CP-Ti was investigated in a temperature range of 700-900℃ and strain rate of 3.6-40 mm/min. The results show that dynamic recrystallization, dynamic recovery and work-hardening obviously occur during hot deformation. Constitutive equation of grade-2 CP-Ti was established by analyzing the relationship of the deformation temperature, strain rate, deformation degree and deformation resistance.展开更多
The dynamic recrystallization(DRX) process of hot compressed aluminium alloy 7050 was predicted using cellular automaton(CA) combined with topology deformation. The hot deformatation characteristics of aluminium alloy...The dynamic recrystallization(DRX) process of hot compressed aluminium alloy 7050 was predicted using cellular automaton(CA) combined with topology deformation. The hot deformatation characteristics of aluminium alloy 7050 were investigated by hot uniaxial compression tests in order to obtain the material parameters used in the CA model. The influences of process parameters(strain, strain rate and temperature) on the fraction of DRX and the average recrystallization grain(R-grain) size were investigated and discussed. It is found that larger stain, higher temperature and lower strain rate(less than 0.1 s^(–1)) are beneficial to the increasing fraction of DRX. And the deformation temperature affects the mean R-grain size much more greatly than other parameters. It is also noted that there is a critical strain for the occurrence of DRX which is related to strain rate and temperature. In addition, it is shown that the CA model with topology deformation is able to simulate the microstructural evolution and the flow behavior of aluminium alloy 7050 material under various deformation conditions.展开更多
The 6061 semi-solid aluminium alloy feedstocks prepared by near-liquidus casting were compressed in semi-solid state by means of Gleeble-3500 thermal-mechanical simulator.The relationship between the true stress and t...The 6061 semi-solid aluminium alloy feedstocks prepared by near-liquidus casting were compressed in semi-solid state by means of Gleeble-3500 thermal-mechanical simulator.The relationship between the true stress and the true strain at different temperatures and strain rates was studied with the deformation degree of 70%.The microstructures during the deformation process were characterized.The deformation mechanism and thixo-forming properties of the semi-solid alloys were analyzed.The results show that the homogeneous and non-dendrite microstructures of semi-solid 6061Al alloy manufactured by near-liquidus casting technology could be transformed into semi-solid state with the microstructure suitable for thixo-forming which are composed of near-spherical grains and liquid phase with eutectic composition through reheating process.The deformation temperature and strain rate affect the peak stress significantly rather than steady flow stress.The resistance to deformation in semi-solid state decreases with the increase of the deformation temperature and decrease of the strain rate.At steady thixotropic deformation stage, the thixotropic property is uniform, and the main deformation mechanism is the rotating or sliding between the solid particles and the plastic deformation of the solid particles.展开更多
Isothermal compression tests at temperatures from 1 273 to l 423 K and strain rates from 0.1 to 10 s-q were carried out to investigate the flow behaviors of Q420qE steel. Stress-strain data collected from the tests we...Isothermal compression tests at temperatures from 1 273 to l 423 K and strain rates from 0.1 to 10 s-q were carried out to investigate the flow behaviors of Q420qE steel. Stress-strain data collected from the tests were employed to establish the constitutive equation, in which the influence of strain was incorporated by considering the effect of strain on material constants Q, n, a, and lnA. The results show that the flow stress curves are dependent on the strain, strain rate and deformation temperature. They display typical dynamic recrystallization behavior and consist of three stages, i.e., hardening stage, softening stage and steady stage. The flow stress decreases with increasing the deformation temperature and decreasing the strain rate. In addition, the flow stress data predicted by the proposed constitutive model agree well with the corresponding experimental results, and the correlation coefficient and the average absolute relative error between them are 0.990 3 and 3.686%, respectively.展开更多
基金Project(CHALCO-2007-KJ-02) supported by the Technology Development Program of Aluminum Corporation of ChinaProject (2011BS0802) supported by the Natural Science Foundation of Inner Mongolia,ChinaProject(NJZY11075) supported by the Research Fund for the Higher Education of Inner Mongolia,China
文摘The multi-pass hot compression test of 7055 aluminum alloy was performed at different temperatures and then the samples were heat treated by T6 heat treatment.The compressed samples were analyzed by OM and TEM.The results reveal that the average aspect ratio of the grains in the specimens compressed first decreases and then increases,the dislocation density decreases and subgrain diameter increases with the increase of deformation temperature.The effects of deformation temperature on the microstructure and mechanical properties of 7055 aluminum alloy after heat treatment were investigated by means of OM and mechanical property test.The results indicate that the deformation temperature significantly influences microstructure and mechanical property of 7055 aluminum alloy.The volume fraction of recrystallization grains presents a "fall-rise" pattern with the deformation temperature rising.The mechanical properties get better when the volume fraction of recrystallization grains decreases.Moreover,the volume fraction of recrystallization grain has a minimum value,appropriately 45%,and the sample exhibits the highest strength and elongation at the deformation temperature of 400 ℃.
基金Project(J51504) supported by Shanghai Leading Academic Discipline Project,China
文摘In order to establish the rolling process parameters of grade-2 commercially pure titanium (CP-Ti), it is necessary to understand the transformation mechanism and mechanical properties of this material. The β→α transformation kinetics of the grade-2 CP-Ti during continuous cooling was measured and its hot compression behavior was investigated using Gleeble-1500 thermal mechanical simulator. Dynamic CCT diagram confirms that cooling rate has an obvious effect on the start and finishing transformation and microstructures at room temperature. The critical cooling rate for γ-phase transforms to a phase is about 15℃/s. When the cooling rate is higher than 15 ℃/s, some β phases with fine granular shape remain residually into plate-like structure. The plate-like a phase forms at cooling rate lower than 2 ℃/s, serrate a phase forms at medium cooling rates, about 5-15℃/s. The flow stress behavior of grade-2 CP-Ti was investigated in a temperature range of 700-900℃ and strain rate of 3.6-40 mm/min. The results show that dynamic recrystallization, dynamic recovery and work-hardening obviously occur during hot deformation. Constitutive equation of grade-2 CP-Ti was established by analyzing the relationship of the deformation temperature, strain rate, deformation degree and deformation resistance.
基金Project(2012ZX04010-8)supported by National Key Technology R&D Program of China
文摘The dynamic recrystallization(DRX) process of hot compressed aluminium alloy 7050 was predicted using cellular automaton(CA) combined with topology deformation. The hot deformatation characteristics of aluminium alloy 7050 were investigated by hot uniaxial compression tests in order to obtain the material parameters used in the CA model. The influences of process parameters(strain, strain rate and temperature) on the fraction of DRX and the average recrystallization grain(R-grain) size were investigated and discussed. It is found that larger stain, higher temperature and lower strain rate(less than 0.1 s^(–1)) are beneficial to the increasing fraction of DRX. And the deformation temperature affects the mean R-grain size much more greatly than other parameters. It is also noted that there is a critical strain for the occurrence of DRX which is related to strain rate and temperature. In addition, it is shown that the CA model with topology deformation is able to simulate the microstructural evolution and the flow behavior of aluminium alloy 7050 material under various deformation conditions.
基金Project(50874049) supported by the National Natural Science Foundation of ChinaProject(2008DFB50020) supported by International Science and Technology Cooperation of Ministry of Science and Technology of China
文摘The 6061 semi-solid aluminium alloy feedstocks prepared by near-liquidus casting were compressed in semi-solid state by means of Gleeble-3500 thermal-mechanical simulator.The relationship between the true stress and the true strain at different temperatures and strain rates was studied with the deformation degree of 70%.The microstructures during the deformation process were characterized.The deformation mechanism and thixo-forming properties of the semi-solid alloys were analyzed.The results show that the homogeneous and non-dendrite microstructures of semi-solid 6061Al alloy manufactured by near-liquidus casting technology could be transformed into semi-solid state with the microstructure suitable for thixo-forming which are composed of near-spherical grains and liquid phase with eutectic composition through reheating process.The deformation temperature and strain rate affect the peak stress significantly rather than steady flow stress.The resistance to deformation in semi-solid state decreases with the increase of the deformation temperature and decrease of the strain rate.At steady thixotropic deformation stage, the thixotropic property is uniform, and the main deformation mechanism is the rotating or sliding between the solid particles and the plastic deformation of the solid particles.
基金Project(200804220021) supported by the Specialized Research Fund for Doctoral Program of Higher Education of China Project (Y2007F06) supported by the Natural Science Foundation of Shandong Province,China
文摘Isothermal compression tests at temperatures from 1 273 to l 423 K and strain rates from 0.1 to 10 s-q were carried out to investigate the flow behaviors of Q420qE steel. Stress-strain data collected from the tests were employed to establish the constitutive equation, in which the influence of strain was incorporated by considering the effect of strain on material constants Q, n, a, and lnA. The results show that the flow stress curves are dependent on the strain, strain rate and deformation temperature. They display typical dynamic recrystallization behavior and consist of three stages, i.e., hardening stage, softening stage and steady stage. The flow stress decreases with increasing the deformation temperature and decreasing the strain rate. In addition, the flow stress data predicted by the proposed constitutive model agree well with the corresponding experimental results, and the correlation coefficient and the average absolute relative error between them are 0.990 3 and 3.686%, respectively.