The effects of a pulsed magnetic field on the solidified microstructure of an AZ31 magnesium alloy were investigated.The experimental results show that the remarkable microstructural refinement is achieved when the pu...The effects of a pulsed magnetic field on the solidified microstructure of an AZ31 magnesium alloy were investigated.The experimental results show that the remarkable microstructural refinement is achieved when the pulsed magnetic field is applied to the solidification of the AZ31 alloy.The average grain size of the as-cast microstructure of the AZ31 alloy is refined to 107 μm.By quenching the AZ31 alloy, the different primary α-Mg microstructures are preserved during the course of solidification.The microstructure evolution reveals that the primary α-Mg generates and grows in globular shape with pulsed magnetic field, contrast with the dendritic shape without pulsed magnetic field.The pulsed magnetic field causes melt convection during solidification, which makes the temperature of the whole melt homogenized, and produces an undercooling zone in front of the liquid/solid interface, which makes the nucleation rate increased and big dendrites prohibited.In addition, the Joule heat effect induced in the melt also strengthens the grain refinement effect and spheroidization of dendrite arms.展开更多
The effects of pulsed magnetic field on the solidified microstructure of an AZ91D magnesium alloy were investigated. The experimental results show that the remarkable microstructural refinement is achieved when the pu...The effects of pulsed magnetic field on the solidified microstructure of an AZ91D magnesium alloy were investigated. The experimental results show that the remarkable microstructural refinement is achieved when the pulsed magnetic field is applied in the solidification of AZ91D alloy. The average grain size of the as-cast microstructure of AZ91D alloy is refined to 104 μm. Besides the grain refinement, the morphology of the primary α-Mg is changed from dendritic to rosette, then to globular shape with changing the parameters of the pulsed magnetic field. The pulsed magnetic field causes melt convection during solidification, which makes the temperature of the whole melt homogenized, and produces an undercooling zone in front of the liquid/solid interface by the magnetic pressure, which makes the nucleation rate increased and big dendrites prohibited. In addition, primary α-Mg dendrites break into fine crystals, resulting in a refined solidification structure of the AZ91D alloy. The Joule heat effect induced in the melt also strengthens the grain refinement effect and spheroidization of dendrite arms.展开更多
The structures and macro-segregation of 2124 Al-alloy were studied when a pulsed magnetic field (PMF) was applied during solidification. It is found through experi-ments that a remarkable change occurs in the solidifi...The structures and macro-segregation of 2124 Al-alloy were studied when a pulsed magnetic field (PMF) was applied during solidification. It is found through experi-ments that a remarkable change occurs in the solidification structures of 2124 Al-alloy under pulsed magnetic field. The eutectic phase at grain boundaries change from thick continuous eutectic network to thin discontinuous one, and the distribution of solute elements was also homogenized. The typical negative segregation phenomenon of Cu in common solidification condition was restrained, and the segregation of Mg decreased.展开更多
Effect of a low-voltage pulsed magnetic field(LVPMF)on the solidified microstructure and mechanical properties of Mg-Al-Zn alloy was studied.When the LVPMF is applied during solidification,the as-cast microstructure i...Effect of a low-voltage pulsed magnetic field(LVPMF)on the solidified microstructure and mechanical properties of Mg-Al-Zn alloy was studied.When the LVPMF is applied during solidification,the as-cast microstructure is significantly refined and a-Mg is modified from developed dendrite to fine rosette.This morphology modification is caused by the accumulation of Joule heat on dendrite tip.Accumulation of Joule heat on dendrite tip melts the dendrite tip and increases the radius of curvature.The increased radius of curvature at the dendrite tip lowers the growth rate and results in the formation of rosette a-Mg.With the application of the LVPMF,β precipitates,formed in the interdendritic liquid region,are connected to each other due to the smaller dimension of the primary and secondary arms and larger volume fraction of the β precipitates between the dendrites.Experimental results indicate that the yield strength and ultimate tensile strength are both increased under with the application of the LVPMF.However,elongation is slightly decreased with the application of the LVPMF due to the continuous β precipitates.展开更多
The effects of pulsed magnetic field on the solidified microstructure of Mg-Gd-Y-Zr alloy were investigated. Fine uniform equiaxed grains are acquired in the whole ingot by the pulsed magnetic field treatment,and the ...The effects of pulsed magnetic field on the solidified microstructure of Mg-Gd-Y-Zr alloy were investigated. Fine uniform equiaxed grains are acquired in the whole ingot by the pulsed magnetic field treatment,and the average grain size of the as-cast φ50 mm and φ100 mm ingots is refined to 37 μm and 47 μm with the pulsed magnetic field.The macrosegregation of solute elements of Mg-Gd-Y-Zr alloy is also reduced by the pulsed magnetic field treatment. Structure refinement is due to the electromagnetic undercooling zone in front of the solid/liquid interface by the magnetic pressure,and reduction of temperature gradient by the vibration of melt resulted from the pulsed magnetic field,which increases the nucleation rate and prohibits dendrite growth.In addition,primary α-Mg dendrites break into fine crystals, resulting in a refined solidification structure of the magnesium alloys.The Joule heat effect induced in the melt also strengthens the grain refinement effect and the spheroidization of dendrite arms.展开更多
An experiment on the directional solidification of A1-7Si alloys under the influence of a pulsed magnetic field(PMF)is performed.Maximal peak value of PMF intensity up to 0.226 T between two iron cores was generated w...An experiment on the directional solidification of A1-7Si alloys under the influence of a pulsed magnetic field(PMF)is performed.Maximal peak value of PMF intensity up to 0.226 T between two iron cores was generated when a capacitor bank of 120 μF capacitance with initial voltage of 1000 V was triggered to a pair of solenoids.The PMF decreases the temperature gradient ahead of the liquidus front and increases the width of the mushy zone.In this paper, using Darcy's permeability law and Lehrnann's model,the order of magnitude of the interdendritic liquid flow velocities with the application of PMF is evaluated.展开更多
基金Project(ZC304009103) supported by the Doctoral Fund of Zhejiang Normal University,ChinaProject(KYJ06Y09157) supported by School-level Project of Zhejiang Normal University,China
文摘The effects of a pulsed magnetic field on the solidified microstructure of an AZ31 magnesium alloy were investigated.The experimental results show that the remarkable microstructural refinement is achieved when the pulsed magnetic field is applied to the solidification of the AZ31 alloy.The average grain size of the as-cast microstructure of the AZ31 alloy is refined to 107 μm.By quenching the AZ31 alloy, the different primary α-Mg microstructures are preserved during the course of solidification.The microstructure evolution reveals that the primary α-Mg generates and grows in globular shape with pulsed magnetic field, contrast with the dendritic shape without pulsed magnetic field.The pulsed magnetic field causes melt convection during solidification, which makes the temperature of the whole melt homogenized, and produces an undercooling zone in front of the liquid/solid interface, which makes the nucleation rate increased and big dendrites prohibited.In addition, the Joule heat effect induced in the melt also strengthens the grain refinement effect and spheroidization of dendrite arms.
基金Project(50774075) supported by the National Natural Science Foundation of ChinaProject(2006BAE04B01-4) supported by the Key Technologies R&D Program of Ministry of Science and Technology of China
文摘The effects of pulsed magnetic field on the solidified microstructure of an AZ91D magnesium alloy were investigated. The experimental results show that the remarkable microstructural refinement is achieved when the pulsed magnetic field is applied in the solidification of AZ91D alloy. The average grain size of the as-cast microstructure of AZ91D alloy is refined to 104 μm. Besides the grain refinement, the morphology of the primary α-Mg is changed from dendritic to rosette, then to globular shape with changing the parameters of the pulsed magnetic field. The pulsed magnetic field causes melt convection during solidification, which makes the temperature of the whole melt homogenized, and produces an undercooling zone in front of the liquid/solid interface by the magnetic pressure, which makes the nucleation rate increased and big dendrites prohibited. In addition, primary α-Mg dendrites break into fine crystals, resulting in a refined solidification structure of the AZ91D alloy. The Joule heat effect induced in the melt also strengthens the grain refinement effect and spheroidization of dendrite arms.
基金This research was supported by National Key Basic Research and Development Programme of China "973" (No. G19990649051).
文摘The structures and macro-segregation of 2124 Al-alloy were studied when a pulsed magnetic field (PMF) was applied during solidification. It is found through experi-ments that a remarkable change occurs in the solidification structures of 2124 Al-alloy under pulsed magnetic field. The eutectic phase at grain boundaries change from thick continuous eutectic network to thin discontinuous one, and the distribution of solute elements was also homogenized. The typical negative segregation phenomenon of Cu in common solidification condition was restrained, and the segregation of Mg decreased.
基金Item Sponsored by National Natural Science Foundation of China[No.50774075 and 51034012]
文摘Effect of a low-voltage pulsed magnetic field(LVPMF)on the solidified microstructure and mechanical properties of Mg-Al-Zn alloy was studied.When the LVPMF is applied during solidification,the as-cast microstructure is significantly refined and a-Mg is modified from developed dendrite to fine rosette.This morphology modification is caused by the accumulation of Joule heat on dendrite tip.Accumulation of Joule heat on dendrite tip melts the dendrite tip and increases the radius of curvature.The increased radius of curvature at the dendrite tip lowers the growth rate and results in the formation of rosette a-Mg.With the application of the LVPMF,β precipitates,formed in the interdendritic liquid region,are connected to each other due to the smaller dimension of the primary and secondary arms and larger volume fraction of the β precipitates between the dendrites.Experimental results indicate that the yield strength and ultimate tensile strength are both increased under with the application of the LVPMF.However,elongation is slightly decreased with the application of the LVPMF due to the continuous β precipitates.
基金Item Sponsored by Zhejiang Province Science Foundation of China[No.LQ12E05006]
文摘The effects of pulsed magnetic field on the solidified microstructure of Mg-Gd-Y-Zr alloy were investigated. Fine uniform equiaxed grains are acquired in the whole ingot by the pulsed magnetic field treatment,and the average grain size of the as-cast φ50 mm and φ100 mm ingots is refined to 37 μm and 47 μm with the pulsed magnetic field.The macrosegregation of solute elements of Mg-Gd-Y-Zr alloy is also reduced by the pulsed magnetic field treatment. Structure refinement is due to the electromagnetic undercooling zone in front of the solid/liquid interface by the magnetic pressure,and reduction of temperature gradient by the vibration of melt resulted from the pulsed magnetic field,which increases the nucleation rate and prohibits dendrite growth.In addition,primary α-Mg dendrites break into fine crystals, resulting in a refined solidification structure of the magnesium alloys.The Joule heat effect induced in the melt also strengthens the grain refinement effect and the spheroidization of dendrite arms.
基金Item Sponsored by National Natural Science Foundation of China (No.50874093 and 51054007)
文摘An experiment on the directional solidification of A1-7Si alloys under the influence of a pulsed magnetic field(PMF)is performed.Maximal peak value of PMF intensity up to 0.226 T between two iron cores was generated when a capacitor bank of 120 μF capacitance with initial voltage of 1000 V was triggered to a pair of solenoids.The PMF decreases the temperature gradient ahead of the liquidus front and increases the width of the mushy zone.In this paper, using Darcy's permeability law and Lehrnann's model,the order of magnitude of the interdendritic liquid flow velocities with the application of PMF is evaluated.