The effects of low frequency electromagnetic field on the macro-physical fields in the semi-continuous casting process of aluminum alloys and the microstructure and crack in the billets were studied and analyzed by th...The effects of low frequency electromagnetic field on the macro-physical fields in the semi-continuous casting process of aluminum alloys and the microstructure and crack in the billets were studied and analyzed by the numerical and experimental methods.Comparison of the results for the macro-physical fields in the low frequency electromagnetic casting（LFEC） process with the conventional DC casting process indicates the following characters due to the application of electromagnetic field：an entirely changed direction and remarkably increased velocity of melt flow;a uniform distribution and a decreased gradient of temperature;elevated isothermal lines;a reduced sump depth;decreased stress and plastic deformation.Further,the microstructure of the billets is refined remarkably and the crack in the billets is eliminated in LFEC process because of modification of the macro-physical fields induced by the application of low frequency electromagnetic field.展开更多
Numerical analysis is critically important to understanding the complex deformation mechanics that occur during sheet forming processes.It has been widely used in simulation of sheet metal forming processes at room te...Numerical analysis is critically important to understanding the complex deformation mechanics that occur during sheet forming processes.It has been widely used in simulation of sheet metal forming processes at room temperature in the automotive industry.However,material at elevated temperature behaves more differently than at room temperature and specific material parameters and models need to be developed for the simulation of warm forming.Based on the experimental investigation of material behavior of high strength aluminum alloy 7075(AA7075),constitutive equations with strain rate sensitivity at 140,180 and 220 ℃ are developed.Anisotropic yield criterion Barlat 89 is used in the simulation.Warm forming of limit dome height tests and limit drawing ratio tests of AA7075 at 140,180 and 220℃are performed.Forming limit diagrams developed from experiment at several elevated temperatures in the previous study are used to predict the failure in the simulation results.Punch force and displacement predicted from simulation are compared with the experimental data.Simulation results agree with experimental results,so the developed material model can be used to accurately predict material behavior during isothermal warm forming of the AA7075-T6 alloy.展开更多
The elevated temperature performances of 2D70 Al alloy hot extrusion rods after two-stage homogenization and intensive deformation were studied by measuring the elevated temperature enduring strength and the creep ult...The elevated temperature performances of 2D70 Al alloy hot extrusion rods after two-stage homogenization and intensive deformation were studied by measuring the elevated temperature enduring strength and the creep ultimate strength. The fracture morphology of some selected samples after testing at different elevated temperatures was observed by scanning electron microscopy （SEM）. The results indicate that, as the test temperature increases, the elevated temperature enduring strength of 2D70 Al alloy decreases gradually. In a comparison between 150 C and 240 C, the notch enduring strength drops from 375 to 185 MPa and the smooth enduring strength drops from 337 to 130 MPa. Enduring strength is not sensitive to the notch. The notch sensitivity ratio （NSR） coefficient is in the range of 1.119 to 1.423 from 150 C to 240 C. The creep test results show that, as the test temperature increases from 150 C to 240 C, the creep ultimate strength of 2D70 Al alloy rods drops gradually from 312 to 117 MPa.展开更多
Al Li Cu合金TIG焊后接头软化较为严重,强度仅为母材的55%,为了解决这一问题,研究了焊后固溶+时效热处理对接头组织及力学性能的影响。结果表明,焊后热处理可提高接头的强度,焊态接头经520℃固溶1h+150℃时效10h后强度系数高于0.64。但...Al Li Cu合金TIG焊后接头软化较为严重,强度仅为母材的55%,为了解决这一问题,研究了焊后固溶+时效热处理对接头组织及力学性能的影响。结果表明,焊后热处理可提高接头的强度,焊态接头经520℃固溶1h+150℃时效10h后强度系数高于0.64。但在接头强化的同时,母材却受到了一定程度的弱化,试件经520℃固溶1h+176℃时效10h后,母材处的强度弱化到初始强度的31%,随着时效温度的提高和时效时间的延长,试件母材部位的弱化程度随之增大。展开更多
基金Project(2005CB623707)supported by National Basic Research Project of China
文摘The effects of low frequency electromagnetic field on the macro-physical fields in the semi-continuous casting process of aluminum alloys and the microstructure and crack in the billets were studied and analyzed by the numerical and experimental methods.Comparison of the results for the macro-physical fields in the low frequency electromagnetic casting（LFEC） process with the conventional DC casting process indicates the following characters due to the application of electromagnetic field：an entirely changed direction and remarkably increased velocity of melt flow;a uniform distribution and a decreased gradient of temperature;elevated isothermal lines;a reduced sump depth;decreased stress and plastic deformation.Further,the microstructure of the billets is refined remarkably and the crack in the billets is eliminated in LFEC process because of modification of the macro-physical fields induced by the application of low frequency electromagnetic field.
文摘Numerical analysis is critically important to understanding the complex deformation mechanics that occur during sheet forming processes.It has been widely used in simulation of sheet metal forming processes at room temperature in the automotive industry.However,material at elevated temperature behaves more differently than at room temperature and specific material parameters and models need to be developed for the simulation of warm forming.Based on the experimental investigation of material behavior of high strength aluminum alloy 7075(AA7075),constitutive equations with strain rate sensitivity at 140,180 and 220 ℃ are developed.Anisotropic yield criterion Barlat 89 is used in the simulation.Warm forming of limit dome height tests and limit drawing ratio tests of AA7075 at 140,180 and 220℃are performed.Forming limit diagrams developed from experiment at several elevated temperatures in the previous study are used to predict the failure in the simulation results.Punch force and displacement predicted from simulation are compared with the experimental data.Simulation results agree with experimental results,so the developed material model can be used to accurately predict material behavior during isothermal warm forming of the AA7075-T6 alloy.
基金support from the National Key Technology Research and Development Program of China (No.2007BAE38B06)Heilongjiang Province Science Fund for Distinguished Young Scholars(No. JC201013)
文摘The elevated temperature performances of 2D70 Al alloy hot extrusion rods after two-stage homogenization and intensive deformation were studied by measuring the elevated temperature enduring strength and the creep ultimate strength. The fracture morphology of some selected samples after testing at different elevated temperatures was observed by scanning electron microscopy （SEM）. The results indicate that, as the test temperature increases, the elevated temperature enduring strength of 2D70 Al alloy decreases gradually. In a comparison between 150 C and 240 C, the notch enduring strength drops from 375 to 185 MPa and the smooth enduring strength drops from 337 to 130 MPa. Enduring strength is not sensitive to the notch. The notch sensitivity ratio （NSR） coefficient is in the range of 1.119 to 1.423 from 150 C to 240 C. The creep test results show that, as the test temperature increases from 150 C to 240 C, the creep ultimate strength of 2D70 Al alloy rods drops gradually from 312 to 117 MPa.
文摘Al Li Cu合金TIG焊后接头软化较为严重,强度仅为母材的55%,为了解决这一问题,研究了焊后固溶+时效热处理对接头组织及力学性能的影响。结果表明,焊后热处理可提高接头的强度,焊态接头经520℃固溶1h+150℃时效10h后强度系数高于0.64。但在接头强化的同时,母材却受到了一定程度的弱化,试件经520℃固溶1h+176℃时效10h后,母材处的强度弱化到初始强度的31%,随着时效温度的提高和时效时间的延长,试件母材部位的弱化程度随之增大。
