The rapid development of magnetic materials provides the possibility for the application of permanent magnet stirring(PMS).Numerical and experimental investigations were employed with respect to the solidification pro...The rapid development of magnetic materials provides the possibility for the application of permanent magnet stirring(PMS).Numerical and experimental investigations were employed with respect to the solidification process of the Al—2Sc alloy controlled by a novel PMS using NdFeB permanent magnets under various rotation speeds(0,50,100 and 150 r/min).The simulated results reveal that the maximum electromagnetic force increases proportionally from 4.14 to 12.39 kN/m^(3)and the maximum tangential velocity increases from 0.13 to 0.36 m/s when the rotation speed of PMS enhances from 50 to 150 r/min in the ingot melt.Besides,the experimental results demonstrate that PMS can achieve a uniform distribution of blocky Al_(3)Sc precipitated phase in the longitudinal direction under the impact of a forced fluid flow.Moreover,increasing rotation speed of PMS is beneficial to refining aluminum grain size significantly and decreasing the texture intensity in the alloy.In addition,the Brinell hardness of Al-2Sc alloy is increased by 33%to 27.8 HB and the tensile strength is enhanced by 34%-128.2 MPa,due to the improved distribution of the strengthening Al_(3)SC phase and the grain refinement of Al matrix under the impact of PMS.This work provides an effective application of NdFeB permanent magnets in the metal cast field.展开更多
Thermal analyses on squeeze cast aluminum alloy A380(SC A380) solidified under 90MPa were carried out to study the microstructure development of the alloy, in which a differential scanning calorimeter(DSC) was employe...Thermal analyses on squeeze cast aluminum alloy A380(SC A380) solidified under 90MPa were carried out to study the microstructure development of the alloy, in which a differential scanning calorimeter(DSC) was employed. During the DSC runs, heating and cooling rates of 1, 3, 10, and 20 °C·min^(-1) were applied to investigate the heating and cooling effects on dissolution of secondary eutectic phases and microstructure evolution. Various reactions corresponding to troughs and peaks of the DSC curves were identified as corresponding to phase transformations taking place during dissolution or precipitation suggested by the principles of thermodynamics and kinetics. The comparison of the identified characteristic temperatures in the measured heating and cooling curves are generally in good agreement with the computed equilibrium temperatures. The microstructure analyses by scanning electron microscopy(SEM) with energy dispersive X-ray spectroscopy(EDS) indicate that the distribution and morphology of secondary phases present in the microstructure of the annealed sample are similar to the as-cast A380, i.e., strip β(Si), buck bone like or dot distributed θ(Al_2Cu), β(Al_5Fe Si) and Al_(15)(FeMn)_3Si_2. Two kinetic methods are employed to calculate the activation energies of the three common troughs and three common peaks in DSC curves of SC A380. The activation energies of the identified reaction θ_(CuAl_2) = α(Al)+β(Si) is 188.7 and 187.1 k J?mol^(-1) when the activation energies of reaction α(Al)+β(Si)→θCu Al_2 is^(-1)22.7 and^(-1)21.8 k J?mol^(-1), by the Kissinger and Starink methods, respectively.展开更多
Using seismic shear phases from 47 Tonga-Fiji and its adjacent region events recorded by the CENC and IRIS, and from 26 northeast Asia and north Pacific events recorded by IRIS, we studied the shear wave anisotropy i...Using seismic shear phases from 47 Tonga-Fiji and its adjacent region events recorded by the CENC and IRIS, and from 26 northeast Asia and north Pacific events recorded by IRIS, we studied the shear wave anisotropy in D＂ region beneath the western Pacific utilizing the ScS-S differential travel time method and obtained the splitting time values between the radial and transverse components of each ScS wave corresponding to each core-mantle boundary （CMB） reflection point. We found that most shear waves involved horizontally polarized shear wave components traveling faster than vertically polarized shear wave components through the D＂ region. The splitting time values of ScS wave range from -0.91 s to 3.21 s with an average value of 1.1 s. The strength of anisotropy varies from -0.45% to 1.56% with an average value of 0.52%. The observations and analyses show that in the D＂ region beneath the western Pacific the lateral flow is expected to be dominant and the vertical transverse isotropy may be the main anisotropic structure. This structure feature may be explained by the shape preferred orientation of the CMB chemical reaction products or partial melt and the lattice preferred orientation of the lower mantle materials caused by the lateral flow at lowermost mantle.展开更多
The static recrystallization behavior of 7075 aluminum alloy containing Al_(3)(Sc,Zr)phase prepared by casting and the relationship between recrystallization behavior and mechanical properties were studied.The additio...The static recrystallization behavior of 7075 aluminum alloy containing Al_(3)(Sc,Zr)phase prepared by casting and the relationship between recrystallization behavior and mechanical properties were studied.The addition of Sc and Zr made the Sc−Zr−7075 aluminum alloy remain the most of fibrous structure and high-density dislocations formed in the extrusion process,resulting in the recrystallization fraction of the alloy decreasing from 35%to 22%,and the corresponding fraction of substructure increasing from 59%to 67%.The Sc and Zr effectively inhibited the recrystallization behavior of 7075 aluminum alloy mainly,which was attributed to the fact that the existence of fine and coherent Al_(3)(Sc,Zr)phase(r=35 nm,f=1.8×10^(−3))strongly pined the dislocations and grain boundaries,preventing the dislocations from rearranging into sub-grain boundaries and from developing into high angle grain boundaries,and further hindering the formation and growth of recrystallized core of the alloy.展开更多
基金Project supported by the Natural Science Foundation of Hunan Province(2024JJ4056)the Key Project of Guangxi Zhuang Autonomous Region(AB22080089)the Government of Chongzuo,Guangxi Zhuang Autonomous Region(FA20210716)。
文摘The rapid development of magnetic materials provides the possibility for the application of permanent magnet stirring(PMS).Numerical and experimental investigations were employed with respect to the solidification process of the Al—2Sc alloy controlled by a novel PMS using NdFeB permanent magnets under various rotation speeds(0,50,100 and 150 r/min).The simulated results reveal that the maximum electromagnetic force increases proportionally from 4.14 to 12.39 kN/m^(3)and the maximum tangential velocity increases from 0.13 to 0.36 m/s when the rotation speed of PMS enhances from 50 to 150 r/min in the ingot melt.Besides,the experimental results demonstrate that PMS can achieve a uniform distribution of blocky Al_(3)Sc precipitated phase in the longitudinal direction under the impact of a forced fluid flow.Moreover,increasing rotation speed of PMS is beneficial to refining aluminum grain size significantly and decreasing the texture intensity in the alloy.In addition,the Brinell hardness of Al-2Sc alloy is increased by 33%to 27.8 HB and the tensile strength is enhanced by 34%-128.2 MPa,due to the improved distribution of the strengthening Al_(3)SC phase and the grain refinement of Al matrix under the impact of PMS.This work provides an effective application of NdFeB permanent magnets in the metal cast field.
基金supported by the Natural Sciences and Engineering Research Council of Canada(NSERC)Discovery(No239080-2010)the project of Shandong science and technology development plan(No2014GGX103035),China
文摘Thermal analyses on squeeze cast aluminum alloy A380(SC A380) solidified under 90MPa were carried out to study the microstructure development of the alloy, in which a differential scanning calorimeter(DSC) was employed. During the DSC runs, heating and cooling rates of 1, 3, 10, and 20 °C·min^(-1) were applied to investigate the heating and cooling effects on dissolution of secondary eutectic phases and microstructure evolution. Various reactions corresponding to troughs and peaks of the DSC curves were identified as corresponding to phase transformations taking place during dissolution or precipitation suggested by the principles of thermodynamics and kinetics. The comparison of the identified characteristic temperatures in the measured heating and cooling curves are generally in good agreement with the computed equilibrium temperatures. The microstructure analyses by scanning electron microscopy(SEM) with energy dispersive X-ray spectroscopy(EDS) indicate that the distribution and morphology of secondary phases present in the microstructure of the annealed sample are similar to the as-cast A380, i.e., strip β(Si), buck bone like or dot distributed θ(Al_2Cu), β(Al_5Fe Si) and Al_(15)(FeMn)_3Si_2. Two kinetic methods are employed to calculate the activation energies of the three common troughs and three common peaks in DSC curves of SC A380. The activation energies of the identified reaction θ_(CuAl_2) = α(Al)+β(Si) is 188.7 and 187.1 k J?mol^(-1) when the activation energies of reaction α(Al)+β(Si)→θCu Al_2 is^(-1)22.7 and^(-1)21.8 k J?mol^(-1), by the Kissinger and Starink methods, respectively.
基金National Natural Science Foundation of China (40474016).
文摘Using seismic shear phases from 47 Tonga-Fiji and its adjacent region events recorded by the CENC and IRIS, and from 26 northeast Asia and north Pacific events recorded by IRIS, we studied the shear wave anisotropy in D＂ region beneath the western Pacific utilizing the ScS-S differential travel time method and obtained the splitting time values between the radial and transverse components of each ScS wave corresponding to each core-mantle boundary （CMB） reflection point. We found that most shear waves involved horizontally polarized shear wave components traveling faster than vertically polarized shear wave components through the D＂ region. The splitting time values of ScS wave range from -0.91 s to 3.21 s with an average value of 1.1 s. The strength of anisotropy varies from -0.45% to 1.56% with an average value of 0.52%. The observations and analyses show that in the D＂ region beneath the western Pacific the lateral flow is expected to be dominant and the vertical transverse isotropy may be the main anisotropic structure. This structure feature may be explained by the shape preferred orientation of the CMB chemical reaction products or partial melt and the lattice preferred orientation of the lower mantle materials caused by the lateral flow at lowermost mantle.
基金The authors are grateful for the financial supports from the National Natural Science Foundation of China(No.51871111)the Natural Science Foundation of Shandong Province,China(No.ZR2018LE001)+1 种基金the Science and Technology Program of University of Ji’nan,China(Nos.XKY2036,XKY1713)the Key Research and Development Program of Shandong Province,China(No.2019GGX102008).
文摘The static recrystallization behavior of 7075 aluminum alloy containing Al_(3)(Sc,Zr)phase prepared by casting and the relationship between recrystallization behavior and mechanical properties were studied.The addition of Sc and Zr made the Sc−Zr−7075 aluminum alloy remain the most of fibrous structure and high-density dislocations formed in the extrusion process,resulting in the recrystallization fraction of the alloy decreasing from 35%to 22%,and the corresponding fraction of substructure increasing from 59%to 67%.The Sc and Zr effectively inhibited the recrystallization behavior of 7075 aluminum alloy mainly,which was attributed to the fact that the existence of fine and coherent Al_(3)(Sc,Zr)phase(r=35 nm,f=1.8×10^(−3))strongly pined the dislocations and grain boundaries,preventing the dislocations from rearranging into sub-grain boundaries and from developing into high angle grain boundaries,and further hindering the formation and growth of recrystallized core of the alloy.
