Casting speed,casting temperature and secondary cooling water flow rate are the main process parameters affecting the DC casting process.These parameters significantly influence the flow and temperature fields during ...Casting speed,casting temperature and secondary cooling water flow rate are the main process parameters affecting the DC casting process.These parameters significantly influence the flow and temperature fields during casting,which are crucial for the quality of the ingot and can determine the success or failure of the casting operation.Numerical simulation,with the advantages of low cost,rapid execution,and visualized results,is an important method to study and optimize the DC casting process.In the present work,a simulation model of DC casting 2024 aluminum alloy was established,and the reliability of the model was verified.Then,the influence of casting parameters on flow field and temperature field was studied in detail by numerical simulation method.Results show that with the increase of casting speed,the melt flow becomes faster,the depths of slurry zone and mushy zone increase,and the variation of slurry zone depth is greater than that of mushy zone.With an increase in casting temperature,the melt flow rate increases,the depth of the slurry zone becomes shallower,and the depth of the mushy zone experiences only minor changes.The simulation results further indicate that the increase of the flow rate of the secondary cooling water slightly reduces the depths of both slurry and mushy zone.展开更多
A mathematical model of the direct chill(DC)casting process for AZ31magnesium slab has been developed to predict the temperature evolution in the slab.The temperature fields at different casting speeds were compared a...A mathematical model of the direct chill(DC)casting process for AZ31magnesium slab has been developed to predict the temperature evolution in the slab.The temperature fields at different casting speeds were compared and the optimum casting speed of 300 mm×800 mm magnesium slab in the certain pouring temperature and cooling-water flow rate was obtained.The casting speed during the plant trial was consistent with the calculation.展开更多
The working principle of LFEC（Low frequency electromagnetic casting） process developed in Northeastern University, China was introduced and the metallurgical results of LFEC were discussed according to the casting p...The working principle of LFEC（Low frequency electromagnetic casting） process developed in Northeastern University, China was introduced and the metallurgical results of LFEC were discussed according to the casting practices. The low frequency field around the mold produces Lorenz force, which can be divided into two parts： one is the potential force which will be balanced by a pressure gradient of the liquid and results in the formation of a convex surface meniscus and improves the surface quality; the other is the rotary force which stirs the liquid in the mold to refine the microstructures and homogenize the distribution of alloying elements. LFEC can refine microstructures remarkably, improve surface quality of the ingots, depress macrosegregation and eliminate cracks. Some new technologies, such as horizontal direct chill casting under low-frequency electromagnetic field （HLEC）, DC casting of hollow billets under electromagnetic fields （HBEC）, electromagnetic modifying of hypereutectic A1-Si alloys（EMM）, air film casting under static magnetic field （AFCM）, and multi-ingots casting under low-frequency magnetic field （MLFEC） were developed based on LFEC.展开更多
Based on multi-physical field coupling numerical simulation method,magnetic field distribution,melt flow,and heat transfer behavior of aΦ300 mm AZ80 alloy billet during differential phase electromagnetic DC casting(D...Based on multi-physical field coupling numerical simulation method,magnetic field distribution,melt flow,and heat transfer behavior of aΦ300 mm AZ80 alloy billet during differential phase electromagnetic DC casting(DP-EMC)with different electromagnetic parameters were studied.The results demonstrate that the increase in current intensity only changes the magnitude but does not change the Lorentz force's distribution characteristics.The maximum value of the Lorentz force increases linearly followed by an increase in current intensity.As the frequency increases,the Lorentz force's r component remains constant,and the z component decreases slightly.The change in current intensity correlates with the melt oscillation and convection intensity positively,as well as the liquid sump temperature uniformity.It does not mean that the higher the electric current,the better the metallurgical quality of the billet.A lower frequency is beneficial to generate a more significant melt flow and velocity fluctuation,which is helpful to create a more uniform temperature field.Appropriate DP-EMC parameters for aΦ300 mm AZ80 Mg alloy are 10-20 Hz frequency and 80-100 A current intensity.展开更多
A comprehensive mathematical model has been developed to describe the interaction of the multiple physics fields during the conventional DC casting and LFEC (low frequency electromagnetic casting) process. The model i...A comprehensive mathematical model has been developed to describe the interaction of the multiple physics fields during the conventional DC casting and LFEC (low frequency electromagnetic casting) process. The model is based on a combination of the commercial finite element package ANSYS and the commercial finite volume package FLUENT, with the former for the calculation of the electromagnetic field and the latter for the calculation of the magnetic driven fluid flow, heat transfer and solidification. Moreover, the model has been verified against the temperature measurements obtained from two 7XXX aluminum alloy billets of 200mm diameter, cast during the conventional DC casting and the LFEC casting processes. In addition, a measurement of the sump shape of the billets were carried out by using addition melting metal of Al-30%Cu alloy into the billets during casting process. There was a good agreement between the calculated results and the measured results. Further, comparison of the calculated results during the LFEC process with that during the conventional DC casting process indicated that velocity patterns, temperature profiles and the sump depth are strongly modified by the application of a low frequency electromagnetic field during the DC casting.展开更多
The effects of a low-voltage pulsed magnetic field on the solidified structure and mechanical properties of DC casting AZ80 magnesium alloy were investigated.The results showed that the solidified structure of the DC ...The effects of a low-voltage pulsed magnetic field on the solidified structure and mechanical properties of DC casting AZ80 magnesium alloy were investigated.The results showed that the solidified structure of the DC casting AZ80 magnesium alloy was refined obviously by the low-voltage pulsed magnetic field and significant grain refinement in the DC casting ingot of AZ80 magnesium alloy was achieved.Meanwhile,the morphology of the dentritic in the DC casting ingot was transformed from coarse dentritic to fine rosette with the application of low-voltage pulsed magnetic field.The ability of deformation of the ingot was enhanced and especially the plasticity of the ingot center after upsetting was improved greatly by more than 80%after deformation.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
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
The effects of low frequency electromagnetic (LFEC) field and ultrasonic (US) field on the microstructures, macrosegregation of alloying elements and the mechanical properties of DC cast AZ80 alloy were studied. The r...The effects of low frequency electromagnetic (LFEC) field and ultrasonic (US) field on the microstructures, macrosegregation of alloying elements and the mechanical properties of DC cast AZ80 alloy were studied. The results show that both LFEC and US fields can refine the grains of the billets, which results in the increase in mechanical properties and uniformity of alloying element distribution. The effective refinement takes place on the edge of ingots when LFEC field is applied, while in the center of billets when field US is adopted. Combined the characteristics of LFEC and US fields, a new process for direct-chilling (DC) casting of Mg-electromagnetic-ultrasonic (ECUS) casting is developed, by which the grains are refined significantly and are more uniform in the whole ingots, and the mechanical properties of the ingots are improved.展开更多
Based on the heat transfer analysis of Air-Slip DC mold, a numerical model was presented to study the quantitative relationships between critical solidification layer and casting rate, pouring temperature and mold coo...Based on the heat transfer analysis of Air-Slip DC mold, a numerical model was presented to study the quantitative relationships between critical solidification layer and casting rate, pouring temperature and mold cooling ability etc. The analytical results show that the Air-Slip mold heat transfer condition plays important roles on choices of a casting rate and the pouring temperature, and that the product of billet diameter and casting rate is a certain constant under a certain condition of the mold.展开更多
The combined electromagnetic fields were achieved by the application of an alternating magnetic field and a stationary magnetic field and were used during direct chill(DC) casting process to control the microstructure...The combined electromagnetic fields were achieved by the application of an alternating magnetic field and a stationary magnetic field and were used during direct chill(DC) casting process to control the microstructure and macrosegregation of an Al-Zn-Mg-Cu alloy. Ingot microstructures were analyzed under an optical microscope(Leica DMR). The composition at different locations in the ingots was measured with inductively coupled plasma mass spectrometry(ICP) method. The results showed that the grain structure is transformed from dendrite to equiaxed structure and significantly refined with the application of combined electromagnetic fields. The uniformity of microstructure is also greatly improved. The combined electromagnetic fields show a significant effect on the distribution of elements. The negative macrosegregation in the centre area of the ingot is obviously reduced.展开更多
Ingots of a new super-high strength Al-Zn-Mg-Cu-Zr alloy were produced respectively by low frequency electromagnetic casting(LFEC)and by conventional direct chill(DC)casting process.Microstructure and constituents of ...Ingots of a new super-high strength Al-Zn-Mg-Cu-Zr alloy were produced respectively by low frequency electromagnetic casting(LFEC)and by conventional direct chill(DC)casting process.Microstructure and constituents of the ingots were studied.The results indicated that the LFEC process significantly refines microstructure and constituents of the alloy,and to some extent,decreases the area(or volume)fraction of constituents and eutectic structure precipitated at grain boundaries.But,no difference in the type of constituents was observed between LFEC and DC ingots.The results also showed LFEC process can improve the as-cast mechanical properties.展开更多
The effects of a low frequency electromagnetic field and a low frequency electromagnetic vibration field applied during DC casting of AZ80 Mg on microstructures and alloying element distribution in ingots were investi...The effects of a low frequency electromagnetic field and a low frequency electromagnetic vibration field applied during DC casting of AZ80 Mg on microstructures and alloying element distribution in ingots were investigated.The experiments were performed both in absence and in the presence of the magnetic fields.In DC casting,the ingot exhibited coarse microstructure and severe segregation of Al.In the presence of solo low frequency alternating magnetic field,namely LFEC,the grains of the ingot was effectively refined and the segregation of Al was significantly decreased.In LFEVC,namely low frequency electromagnetic vibration casting,the ingot were significantly refined and the segregation was suppressed.With increasing the vibration intensities,the grain refinement and segregation suppression were increased.展开更多
Microstructure evolutions of an AZ80 magnesium alloy ingot with 300 mm in diameter cast with and without the electromagnetic vibration was investigated. The microstructures of the ingot cast with the conventional DC e...Microstructure evolutions of an AZ80 magnesium alloy ingot with 300 mm in diameter cast with and without the electromagnetic vibration was investigated. The microstructures of the ingot cast with the conventional DC exhibited relatively fine dendritic grains at the surface area, but coarse dendritic grains at the 1/2 radius and large equiaxed dendritic grains at the center. However, under the electromagnetic vibration casting condition, the microstructures of the ingot is significantly refined, especially those at the surface and at the center.展开更多
Microstructure inhomogeneity and negative segregation have long been challenges for large-size alloy ingots,directly affecting the downstream processing and final performance of products.Here,we used2024 aluminum allo...Microstructure inhomogeneity and negative segregation have long been challenges for large-size alloy ingots,directly affecting the downstream processing and final performance of products.Here,we used2024 aluminum alloy as a model alloy to propose a technique,named double-cooling field casting,i.e.,one 2024 Al alloy rod(Φ20 mm)at room temperature was introduced into the melt along the central axis of the hot-top with the protection of a thermal-insulation tube during the direct chill(DC)casting process of aΦ300 mm 2024 Al alloy ingot.The results show that the introduction of the same alloy solid insert has a remarkable influence on refining grains in the center region of the ingot,reducing negative centerline segregation and decreasing the depth of the center part of the sump.With the application of the 2024 Al insert,the mean size of equiaxed grains at the center part of the ingot decreased from1204±132μm to 721±69μm.The relative deviation of the Cu and Mg main solutes reduced from-0.062 and-0.054 to-0.03 and-0.024,respectively,and the sump depth decreased from 280 mm to242 mm.Moreover,the shape of the solidification front was changed from‘V’-shaped to‘W’-shaped.The ingot quality was thus improved,mainly arising from the dissolution of the cold 2024 Al insert at a proper position of the hot-top counteracting some latent heat of solidification of the ingot,dissipating the heat of the central part of the hot-top by conducting the 2024 Al insert to the outside,and providing extra-nuclei from the unmoltenα-Al particles of the insert.展开更多
Low frequency electromagnetic casting(LFEC)process has been developed for years with the application of an induction coil outside the conventional direct chill(DC)casting mould.It has been demonstrated that the LFEC p...Low frequency electromagnetic casting(LFEC)process has been developed for years with the application of an induction coil outside the conventional direct chill(DC)casting mould.It has been demonstrated that the LFEC process has a significant grain refining effect on aluminium alloys.However,how it refines the microstructure is still not clearly understood.In the present work,the temperature measurement were carried out to study the temperature field during casting and to understand the mechanism of the grain refining effect of the LFEC process.The results showed that in contrast to the conventional DC casting process,during the LFEC process,the liquid melt flowing from the launder into the mould is cooled with very high cooling rate directly to 3-6 ℃ below the liquidus and the temperature field of the entire melt in the mould and the hot top is quite uniform,which results in enhanced heterogeneous nucleation and improved survival rate of the nuclei.This is believed to be the main reason why the LFEC process can significantly refine the grain size of aluminium alloys.展开更多
基金financially supported by the National Natural Science Foundation of China(No.51674078)。
文摘Casting speed,casting temperature and secondary cooling water flow rate are the main process parameters affecting the DC casting process.These parameters significantly influence the flow and temperature fields during casting,which are crucial for the quality of the ingot and can determine the success or failure of the casting operation.Numerical simulation,with the advantages of low cost,rapid execution,and visualized results,is an important method to study and optimize the DC casting process.In the present work,a simulation model of DC casting 2024 aluminum alloy was established,and the reliability of the model was verified.Then,the influence of casting parameters on flow field and temperature field was studied in detail by numerical simulation method.Results show that with the increase of casting speed,the melt flow becomes faster,the depths of slurry zone and mushy zone increase,and the variation of slurry zone depth is greater than that of mushy zone.With an increase in casting temperature,the melt flow rate increases,the depth of the slurry zone becomes shallower,and the depth of the mushy zone experiences only minor changes.The simulation results further indicate that the increase of the flow rate of the secondary cooling water slightly reduces the depths of both slurry and mushy zone.
基金This work is supported by National Key Technology R&D Program of China(2011BAE22B03)National Key Technology R&D Program of China(2012BAF09B01)+1 种基金National Basic Research Program of China(2013CB632203)National Natural Science Foundation of China(51074207).
文摘A mathematical model of the direct chill(DC)casting process for AZ31magnesium slab has been developed to predict the temperature evolution in the slab.The temperature fields at different casting speeds were compared and the optimum casting speed of 300 mm×800 mm magnesium slab in the certain pouring temperature and cooling-water flow rate was obtained.The casting speed during the plant trial was consistent with the calculation.
基金Project(2005CB623707) supported by the National Basic Research Program of China Projects(2007CB613701 and 2007CB613702) supported by the National Key Basic Research Program of China+2 种基金Projects(50974037,51004032 and 50904018) supported by the National Natural Science Foundation of ChinaProject(NCET-08-0098) supported by the New Century Excellent Talents in University,Ministry of Education,ChinaProject(20100471468) supported by China Postdoctoral Science Foundation
文摘The working principle of LFEC（Low frequency electromagnetic casting） process developed in Northeastern University, China was introduced and the metallurgical results of LFEC were discussed according to the casting practices. The low frequency field around the mold produces Lorenz force, which can be divided into two parts： one is the potential force which will be balanced by a pressure gradient of the liquid and results in the formation of a convex surface meniscus and improves the surface quality; the other is the rotary force which stirs the liquid in the mold to refine the microstructures and homogenize the distribution of alloying elements. LFEC can refine microstructures remarkably, improve surface quality of the ingots, depress macrosegregation and eliminate cracks. Some new technologies, such as horizontal direct chill casting under low-frequency electromagnetic field （HLEC）, DC casting of hollow billets under electromagnetic fields （HBEC）, electromagnetic modifying of hypereutectic A1-Si alloys（EMM）, air film casting under static magnetic field （AFCM）, and multi-ingots casting under low-frequency magnetic field （MLFEC） were developed based on LFEC.
基金the Fundamental Research Funds for the Central Universities(Grant No.N2009003)the National Natural Science Foundation of China(Grant No.51904151).
文摘Based on multi-physical field coupling numerical simulation method,magnetic field distribution,melt flow,and heat transfer behavior of aΦ300 mm AZ80 alloy billet during differential phase electromagnetic DC casting(DP-EMC)with different electromagnetic parameters were studied.The results demonstrate that the increase in current intensity only changes the magnitude but does not change the Lorentz force's distribution characteristics.The maximum value of the Lorentz force increases linearly followed by an increase in current intensity.As the frequency increases,the Lorentz force's r component remains constant,and the z component decreases slightly.The change in current intensity correlates with the melt oscillation and convection intensity positively,as well as the liquid sump temperature uniformity.It does not mean that the higher the electric current,the better the metallurgical quality of the billet.A lower frequency is beneficial to generate a more significant melt flow and velocity fluctuation,which is helpful to create a more uniform temperature field.Appropriate DP-EMC parameters for aΦ300 mm AZ80 Mg alloy are 10-20 Hz frequency and 80-100 A current intensity.
文摘A comprehensive mathematical model has been developed to describe the interaction of the multiple physics fields during the conventional DC casting and LFEC (low frequency electromagnetic casting) process. The model is based on a combination of the commercial finite element package ANSYS and the commercial finite volume package FLUENT, with the former for the calculation of the electromagnetic field and the latter for the calculation of the magnetic driven fluid flow, heat transfer and solidification. Moreover, the model has been verified against the temperature measurements obtained from two 7XXX aluminum alloy billets of 200mm diameter, cast during the conventional DC casting and the LFEC casting processes. In addition, a measurement of the sump shape of the billets were carried out by using addition melting metal of Al-30%Cu alloy into the billets during casting process. There was a good agreement between the calculated results and the measured results. Further, comparison of the calculated results during the LFEC process with that during the conventional DC casting process indicated that velocity patterns, temperature profiles and the sump depth are strongly modified by the application of a low frequency electromagnetic field during the DC casting.
基金Project(51034012)supported by the the National Natural Science Foundation of ChinaProject(2013CB632205)supported by the National Basic Research Program of China
文摘The effects of a low-voltage pulsed magnetic field on the solidified structure and mechanical properties of DC casting AZ80 magnesium alloy were investigated.The results showed that the solidified structure of the DC casting AZ80 magnesium alloy was refined obviously by the low-voltage pulsed magnetic field and significant grain refinement in the DC casting ingot of AZ80 magnesium alloy was achieved.Meanwhile,the morphology of the dentritic in the DC casting ingot was transformed from coarse dentritic to fine rosette with the application of low-voltage pulsed magnetic field.The ability of deformation of the ingot was enhanced and especially the plasticity of the ingot center after upsetting was improved greatly by more than 80%after deformation.
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.
基金Projects(2007CB613701, 2007CB613702) supported by the National Basic Research Program of ChinaProjects(50974037, 50904018) supported by the National Natural Science Foundation of China+1 种基金Project(NCET-08-0098) supported by New Century Excellent Talents in Chinese UniversityProject(N90209002) supported by the Special Foundation for Basic Scientific Research of Central Colleges
文摘The effects of low frequency electromagnetic (LFEC) field and ultrasonic (US) field on the microstructures, macrosegregation of alloying elements and the mechanical properties of DC cast AZ80 alloy were studied. The results show that both LFEC and US fields can refine the grains of the billets, which results in the increase in mechanical properties and uniformity of alloying element distribution. The effective refinement takes place on the edge of ingots when LFEC field is applied, while in the center of billets when field US is adopted. Combined the characteristics of LFEC and US fields, a new process for direct-chilling (DC) casting of Mg-electromagnetic-ultrasonic (ECUS) casting is developed, by which the grains are refined significantly and are more uniform in the whole ingots, and the mechanical properties of the ingots are improved.
文摘Based on the heat transfer analysis of Air-Slip DC mold, a numerical model was presented to study the quantitative relationships between critical solidification layer and casting rate, pouring temperature and mold cooling ability etc. The analytical results show that the Air-Slip mold heat transfer condition plays important roles on choices of a casting rate and the pouring temperature, and that the product of billet diameter and casting rate is a certain constant under a certain condition of the mold.
基金supported by the National Natural Science Foundation of China(51374067)the Outstanding Young Scholars'Growth Plan in the Colleges and Universities of Liaoning Province(LJQ2014032)the National Basic Research Program of China(2012CB619506)
文摘The combined electromagnetic fields were achieved by the application of an alternating magnetic field and a stationary magnetic field and were used during direct chill(DC) casting process to control the microstructure and macrosegregation of an Al-Zn-Mg-Cu alloy. Ingot microstructures were analyzed under an optical microscope(Leica DMR). The composition at different locations in the ingots was measured with inductively coupled plasma mass spectrometry(ICP) method. The results showed that the grain structure is transformed from dendrite to equiaxed structure and significantly refined with the application of combined electromagnetic fields. The uniformity of microstructure is also greatly improved. The combined electromagnetic fields show a significant effect on the distribution of elements. The negative macrosegregation in the centre area of the ingot is obviously reduced.
基金This study was supported by the National "973" Foundation of China(No.:2005CB623707).
文摘Ingots of a new super-high strength Al-Zn-Mg-Cu-Zr alloy were produced respectively by low frequency electromagnetic casting(LFEC)and by conventional direct chill(DC)casting process.Microstructure and constituents of the ingots were studied.The results indicated that the LFEC process significantly refines microstructure and constituents of the alloy,and to some extent,decreases the area(or volume)fraction of constituents and eutectic structure precipitated at grain boundaries.But,no difference in the type of constituents was observed between LFEC and DC ingots.The results also showed LFEC process can improve the as-cast mechanical properties.
基金This work is financially supported by the Emphasis Project Fund of National Eleven Five-Year Scientific and Technical Support Plans ( No 2006BAE04B02)the National Natural Science Foundation of Chi-na ( No 50574028)+1 种基金the Programme of Introducing Talents of Discipline to Universities(No B07015) the Cultivation Fund of the Key Scientific and Technical Innovation Project,Ministry of Education of China(No 704015)
文摘The effects of a low frequency electromagnetic field and a low frequency electromagnetic vibration field applied during DC casting of AZ80 Mg on microstructures and alloying element distribution in ingots were investigated.The experiments were performed both in absence and in the presence of the magnetic fields.In DC casting,the ingot exhibited coarse microstructure and severe segregation of Al.In the presence of solo low frequency alternating magnetic field,namely LFEC,the grains of the ingot was effectively refined and the segregation of Al was significantly decreased.In LFEVC,namely low frequency electromagnetic vibration casting,the ingot were significantly refined and the segregation was suppressed.With increasing the vibration intensities,the grain refinement and segregation suppression were increased.
文摘Microstructure evolutions of an AZ80 magnesium alloy ingot with 300 mm in diameter cast with and without the electromagnetic vibration was investigated. The microstructures of the ingot cast with the conventional DC exhibited relatively fine dendritic grains at the surface area, but coarse dendritic grains at the 1/2 radius and large equiaxed dendritic grains at the center. However, under the electromagnetic vibration casting condition, the microstructures of the ingot is significantly refined, especially those at the surface and at the center.
基金financially supported by the Fundamental Research Funds for the Central Universities(Nos.N2002025,N2109006 and N2109007)the Project of Promoting Talents in Liaoning Province(No.XLYC1808038)。
文摘Microstructure inhomogeneity and negative segregation have long been challenges for large-size alloy ingots,directly affecting the downstream processing and final performance of products.Here,we used2024 aluminum alloy as a model alloy to propose a technique,named double-cooling field casting,i.e.,one 2024 Al alloy rod(Φ20 mm)at room temperature was introduced into the melt along the central axis of the hot-top with the protection of a thermal-insulation tube during the direct chill(DC)casting process of aΦ300 mm 2024 Al alloy ingot.The results show that the introduction of the same alloy solid insert has a remarkable influence on refining grains in the center region of the ingot,reducing negative centerline segregation and decreasing the depth of the center part of the sump.With the application of the 2024 Al insert,the mean size of equiaxed grains at the center part of the ingot decreased from1204±132μm to 721±69μm.The relative deviation of the Cu and Mg main solutes reduced from-0.062 and-0.054 to-0.03 and-0.024,respectively,and the sump depth decreased from 280 mm to242 mm.Moreover,the shape of the solidification front was changed from‘V’-shaped to‘W’-shaped.The ingot quality was thus improved,mainly arising from the dissolution of the cold 2024 Al insert at a proper position of the hot-top counteracting some latent heat of solidification of the ingot,dissipating the heat of the central part of the hot-top by conducting the 2024 Al insert to the outside,and providing extra-nuclei from the unmoltenα-Al particles of the insert.
基金Items Sponsored by National Natural Science Foundation of China[No.51104043]National Basic Research Program of China[No.2012CB619506]
文摘Low frequency electromagnetic casting(LFEC)process has been developed for years with the application of an induction coil outside the conventional direct chill(DC)casting mould.It has been demonstrated that the LFEC process has a significant grain refining effect on aluminium alloys.However,how it refines the microstructure is still not clearly understood.In the present work,the temperature measurement were carried out to study the temperature field during casting and to understand the mechanism of the grain refining effect of the LFEC process.The results showed that in contrast to the conventional DC casting process,during the LFEC process,the liquid melt flowing from the launder into the mould is cooled with very high cooling rate directly to 3-6 ℃ below the liquidus and the temperature field of the entire melt in the mould and the hot top is quite uniform,which results in enhanced heterogeneous nucleation and improved survival rate of the nuclei.This is believed to be the main reason why the LFEC process can significantly refine the grain size of aluminium alloys.
