3D elastic-plastic FE model for simulating the force controlled stretch-bending process of double-cavity aluminum profile was established using hybrid explicit−implicit solvent method.Considering the computational acc...3D elastic-plastic FE model for simulating the force controlled stretch-bending process of double-cavity aluminum profile was established using hybrid explicit−implicit solvent method.Considering the computational accuracy and efficiency,the optimal choices of numerical parameters and algorithms in FE modelling were determined.The formation mechanisms of cross-section distortion and springback were revealed.The effects of pre-stretching,post-stretching,friction,and the addition of internal fillers on forming quality were investigated.The results show that the stress state of profile in stretch-bending is uniaxial with only a circumferential stress.The stress distribution along the length direction of profile is non-uniform and the maximum tensile stress is located at a certain distance away from the center of profile.As aluminum profile is gradually attached to bending die,the distribution characteristic of cross-section distortion along the length direction of profile changes from V-shape to W-shape.After unloading the forming tools,cross-section distortion decreases obviously due to the stress relaxation,with a maximum distortion difference of 13%before and after unloading.As pre-stretching and post-stretching forces increase,cross-section distortion increases gradually,while springback first decreases and then remains unchanged.With increasing friction between bending die and profile,cross-section distortion slightly decreases,while springback increases.Cross-section distortion decreases by 83%with adding PVC fillers into the cavities of profile,while springback increases by 192.2%.展开更多
The automobile suspension parts of a high strength 6xxx aluminum alloy were produced using a novel technique known as near net shape casting for forging stock preparation. Based on the outline dimension of the forging...The automobile suspension parts of a high strength 6xxx aluminum alloy were produced using a novel technique known as near net shape casting for forging stock preparation. Based on the outline dimension of the forging stock, the shape of the ingot was designed as the near net shape and its casting process was studied by the numerical simulation and experimental investigation. The results show that the shrinkage of the ingot was highly correlated to its shape parameters and could be successfully forecast by the stimulation model. The casting parameters of the near net shape ingot were optimized and the near net shape 6xxx aluminum alloy ingots free of defects were cast in the laboratory. In order to obtain high performance forged suspension parts, the hot compression tests of the ingot were carried out. The results show that the subgrain fraction of the forged ingot was strongly affected by Zener-Hollomon parameters （Z parameters）. The intermediate Z parameters, 1.09×10^16 s^-1, will contribute to the larger number fraction of subgrains inside the forged ingot, which contributes to the high performance of the forged products.展开更多
Asymmetric rolling （ASR）, as one of severe plastic deformation （SPD） methods to make ultra-fine materials with enhanced performance is mainly used to prepare foil and thin strip. The asymmetrical rolling was achie...Asymmetric rolling （ASR）, as one of severe plastic deformation （SPD） methods to make ultra-fine materials with enhanced performance is mainly used to prepare foil and thin strip. The asymmetrical rolling was achieved by adjusting the diameters of the upper roll and the bottom roll and was used to prepare hot-rolled thick plate of 5182 aluminium alloy. The shear deformation and plate shape control were experimentally studied. The experimental results show that asymmetrical rolling has a significant effect on metal deformation stream and can somehow refine microstructure and improve the uniformity of microstructure and properties. The asymmetrical rolling process can also reduce the rolling force. However, bending of rolling plate often happens during asymmetrical rolling process. The factors affecting the bending were discussed.展开更多
Wurtzite aluminum nitride（AlN） films were deposited on Si（100） wafers under various sputtering pressures by radio-frequency（RF） reactive magnetron sputtering. The film properties were investigated by XRD, SEM, A...Wurtzite aluminum nitride（AlN） films were deposited on Si（100） wafers under various sputtering pressures by radio-frequency（RF） reactive magnetron sputtering. The film properties were investigated by XRD, SEM, AFM, XPS and nanoindenter techniques. It is suggested from the XRD patterns that highly c-axis oriented films grow preferentially at low pressures and the growth of（100） planes are preferred at higher pressures. The SEM and AFM images both reveal that the deposition rate and the surface roughness decrease while the average grain size increases with increasing the sputtering pressure. XPS results show that lowering the sputtering pressure is a useful way to minimize the incorporation of oxygen atoms into the AlN films and hence a film with closer stoichiometric composition is obtained. From the measurement of nanomechanical properties of AlN thin films, the largest hardness and elastic modulus are obtained at 0.30 Pa.展开更多
Pure Al coating was deposited on sintered NdFeB magnet by direct current（DC） magnetron sputtering to improve the corrosion resistance of magnet. The influences of coating thickness and sputtering power on microstruc...Pure Al coating was deposited on sintered NdFeB magnet by direct current（DC） magnetron sputtering to improve the corrosion resistance of magnet. The influences of coating thickness and sputtering power on microstructure and corrosion resistance of Al coating were investigated. The surface morphology of Al coating was characterized by scanning electron microscopy（SEM）. The corrosion properties were investigated by potentiodynamic polarization curves and neutral salt spray（NSS） test. The formation of the uniform and compact Al coating is a necessary condition to achieve excellent corrosion resistance. And the optimal corrosion resistance can be obtained in the sample with 6.69 μm thick Al coating deposited at 51-82 W.展开更多
A new process of hydroforming with controllable radial pressure was proposed to overcome difficulties in the forming of low plastic materials and large height-to-diameter ratio workpieces. A typical 5A06 aluminum allo...A new process of hydroforming with controllable radial pressure was proposed to overcome difficulties in the forming of low plastic materials and large height-to-diameter ratio workpieces. A typical 5A06 aluminum alloy dome was numerically and experimentally investigated. The reasons for typical defects were analyzed under different radial pressures. Effects of radial pressure on the thickness distribution were discussed and optimal radial pressure was determined. It is shown by numerical simulations and experiment that a cup with a drawing ratio of 2.4 is formed by the new process of hydroforming with controllable radial pressure. It is significantly effective for the forming of low plastic materials and large height-to-diameter ratio workpieees. Two typical thinning points exit along the dome wall. With the radial pressure, thinning is decreased effectively at the two points, the dome forming is achieved and thickness distribution is more uniform.展开更多
In order to improve the activity and eliminate some impurities, pretreatment was used before hydrothermal synthesis. The fly ash was mixed with an aqueous NaOH solution, the alkali melted fly ash was also adopted, whi...In order to improve the activity and eliminate some impurities, pretreatment was used before hydrothermal synthesis. The fly ash was mixed with an aqueous NaOH solution, the alkali melted fly ash was also adopted, which is hydrothermally treated at about 104 ℃, and the liquid/solid ratio was controlled at 6：1. In order to control Si/Al molar ratio, SiO2 or Al2O3 powers were added to the fly ash. The results of XRD and SEM show that the alkali melted can activate fly ash and eliminate its quartz and mullite, along with the improvement of Si/Al molar ratio and alkalinity. In addition, zeolite Na-A changes into sodalite gradually, and nepheline is the synthesized intermediate product. Those results were discussed on the basis of a formation mechanism of zeolite from fly ash.展开更多
The main objective of this study is to enhance the strength of CNTs （carbon nanotubes） which reinforced AI matrix composites by introducing an appropriate amount of Copper（Cu） into the composite material. AI-Cu/MW...The main objective of this study is to enhance the strength of CNTs （carbon nanotubes） which reinforced AI matrix composites by introducing an appropriate amount of Copper（Cu） into the composite material. AI-Cu/MWCNTs （multi-walled carbon nanotubes） nanocomposites were produced via compaction, sintering and hot extrusion process of AI-Cu/MWCNTs powders, which were fabricated by a conventional ball mill process with AI powders and Cu-MWCNTs composite powders which were synthesized by molecular level mixing technique. Also the change of mechanical properties with different content ratio of Cu/MWCNT composite powders in A1 matrix is analyzed. It is found that the addition of the proper Cu/MWCNTs powders which are well distributed in AI matrix leads to high mechanical stiffness. The 2 wt% Cu/MWCNTs reinforced A1 composites which exhibited 3.2 times higher tensile strength and 4.4 times higher yield strength than pure AI.展开更多
基金the National Natural Science Foundation of China(Nos.52005244,U20A20275)the Natural Science Foundation of Hunan Province,China(Nos.2021JJ30573,2023JJ60193)the Open Fund of State Key Laboratory of Advanced Design and Manufacture for Vehicle Body,China(No.31715011)。
文摘3D elastic-plastic FE model for simulating the force controlled stretch-bending process of double-cavity aluminum profile was established using hybrid explicit−implicit solvent method.Considering the computational accuracy and efficiency,the optimal choices of numerical parameters and algorithms in FE modelling were determined.The formation mechanisms of cross-section distortion and springback were revealed.The effects of pre-stretching,post-stretching,friction,and the addition of internal fillers on forming quality were investigated.The results show that the stress state of profile in stretch-bending is uniaxial with only a circumferential stress.The stress distribution along the length direction of profile is non-uniform and the maximum tensile stress is located at a certain distance away from the center of profile.As aluminum profile is gradually attached to bending die,the distribution characteristic of cross-section distortion along the length direction of profile changes from V-shape to W-shape.After unloading the forming tools,cross-section distortion decreases obviously due to the stress relaxation,with a maximum distortion difference of 13%before and after unloading.As pre-stretching and post-stretching forces increase,cross-section distortion increases gradually,while springback first decreases and then remains unchanged.With increasing friction between bending die and profile,cross-section distortion slightly decreases,while springback increases.Cross-section distortion decreases by 83%with adding PVC fillers into the cavities of profile,while springback increases by 192.2%.
文摘The automobile suspension parts of a high strength 6xxx aluminum alloy were produced using a novel technique known as near net shape casting for forging stock preparation. Based on the outline dimension of the forging stock, the shape of the ingot was designed as the near net shape and its casting process was studied by the numerical simulation and experimental investigation. The results show that the shrinkage of the ingot was highly correlated to its shape parameters and could be successfully forecast by the stimulation model. The casting parameters of the near net shape ingot were optimized and the near net shape 6xxx aluminum alloy ingots free of defects were cast in the laboratory. In order to obtain high performance forged suspension parts, the hot compression tests of the ingot were carried out. The results show that the subgrain fraction of the forged ingot was strongly affected by Zener-Hollomon parameters （Z parameters）. The intermediate Z parameters, 1.09×10^16 s^-1, will contribute to the larger number fraction of subgrains inside the forged ingot, which contributes to the high performance of the forged products.
基金Projects(51104043,51374067)supported by the National Natural Science Foundation of ChinaProject(2012CB619506)supported by the National Basic Research Program of ChinaProject(N120409002)supported by the Fundamental Research Funds for the Central Universities,China
文摘Asymmetric rolling （ASR）, as one of severe plastic deformation （SPD） methods to make ultra-fine materials with enhanced performance is mainly used to prepare foil and thin strip. The asymmetrical rolling was achieved by adjusting the diameters of the upper roll and the bottom roll and was used to prepare hot-rolled thick plate of 5182 aluminium alloy. The shear deformation and plate shape control were experimentally studied. The experimental results show that asymmetrical rolling has a significant effect on metal deformation stream and can somehow refine microstructure and improve the uniformity of microstructure and properties. The asymmetrical rolling process can also reduce the rolling force. However, bending of rolling plate often happens during asymmetrical rolling process. The factors affecting the bending were discussed.
基金Project(21271188)supported by the National Natural Science Foundation of ChinaProject(2012M521541)supported by the China Postdoctoral Science Foundation+2 种基金Project(2012QNZT002)supported by the Fundamental Research Funds for the Central South Universities,ChinaProject(20110933K)supported by the State Key Laboratory of Powder Metallurgy,ChinaProject(CSU2012024)supported by the Open-End Fund for Valuable and Precision Instruments of Central South University,China
文摘Wurtzite aluminum nitride（AlN） films were deposited on Si（100） wafers under various sputtering pressures by radio-frequency（RF） reactive magnetron sputtering. The film properties were investigated by XRD, SEM, AFM, XPS and nanoindenter techniques. It is suggested from the XRD patterns that highly c-axis oriented films grow preferentially at low pressures and the growth of（100） planes are preferred at higher pressures. The SEM and AFM images both reveal that the deposition rate and the surface roughness decrease while the average grain size increases with increasing the sputtering pressure. XPS results show that lowering the sputtering pressure is a useful way to minimize the incorporation of oxygen atoms into the AlN films and hence a film with closer stoichiometric composition is obtained. From the measurement of nanomechanical properties of AlN thin films, the largest hardness and elastic modulus are obtained at 0.30 Pa.
基金Project(NCET-11-0127)supported by Program for New Century Excellent Talents in University,ChinaProject(K1306063-11)supported by the Key Project for Science and Technology of Changsha,China
文摘Pure Al coating was deposited on sintered NdFeB magnet by direct current（DC） magnetron sputtering to improve the corrosion resistance of magnet. The influences of coating thickness and sputtering power on microstructure and corrosion resistance of Al coating were investigated. The surface morphology of Al coating was characterized by scanning electron microscopy（SEM）. The corrosion properties were investigated by potentiodynamic polarization curves and neutral salt spray（NSS） test. The formation of the uniform and compact Al coating is a necessary condition to achieve excellent corrosion resistance. And the optimal corrosion resistance can be obtained in the sample with 6.69 μm thick Al coating deposited at 51-82 W.
基金Projects(50525516, 50875062 ) supported by the National Natural Science Foundation of China
文摘A new process of hydroforming with controllable radial pressure was proposed to overcome difficulties in the forming of low plastic materials and large height-to-diameter ratio workpieces. A typical 5A06 aluminum alloy dome was numerically and experimentally investigated. The reasons for typical defects were analyzed under different radial pressures. Effects of radial pressure on the thickness distribution were discussed and optimal radial pressure was determined. It is shown by numerical simulations and experiment that a cup with a drawing ratio of 2.4 is formed by the new process of hydroforming with controllable radial pressure. It is significantly effective for the forming of low plastic materials and large height-to-diameter ratio workpieees. Two typical thinning points exit along the dome wall. With the radial pressure, thinning is decreased effectively at the two points, the dome forming is achieved and thickness distribution is more uniform.
基金Supported by the Henan Outstanding Youth Science Fund (0612002400)
文摘In order to improve the activity and eliminate some impurities, pretreatment was used before hydrothermal synthesis. The fly ash was mixed with an aqueous NaOH solution, the alkali melted fly ash was also adopted, which is hydrothermally treated at about 104 ℃, and the liquid/solid ratio was controlled at 6：1. In order to control Si/Al molar ratio, SiO2 or Al2O3 powers were added to the fly ash. The results of XRD and SEM show that the alkali melted can activate fly ash and eliminate its quartz and mullite, along with the improvement of Si/Al molar ratio and alkalinity. In addition, zeolite Na-A changes into sodalite gradually, and nepheline is the synthesized intermediate product. Those results were discussed on the basis of a formation mechanism of zeolite from fly ash.
文摘The main objective of this study is to enhance the strength of CNTs （carbon nanotubes） which reinforced AI matrix composites by introducing an appropriate amount of Copper（Cu） into the composite material. AI-Cu/MWCNTs （multi-walled carbon nanotubes） nanocomposites were produced via compaction, sintering and hot extrusion process of AI-Cu/MWCNTs powders, which were fabricated by a conventional ball mill process with AI powders and Cu-MWCNTs composite powders which were synthesized by molecular level mixing technique. Also the change of mechanical properties with different content ratio of Cu/MWCNT composite powders in A1 matrix is analyzed. It is found that the addition of the proper Cu/MWCNTs powders which are well distributed in AI matrix leads to high mechanical stiffness. The 2 wt% Cu/MWCNTs reinforced A1 composites which exhibited 3.2 times higher tensile strength and 4.4 times higher yield strength than pure AI.
