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
Central region coarse grains and centerline segregation are common defects in aluminum ingots fabricated by direct chill(DC)casting.A double cooling field was introduced into the DC casting process to reduce these def...Central region coarse grains and centerline segregation are common defects in aluminum ingots fabricated by direct chill(DC)casting.A double cooling field was introduced into the DC casting process to reduce these defects,whereby the external cooling was supplied by the mold and water jets,and intercooling was achieved by inserting a rod of the same alloy into the molten pool along the central axis of the ingot.Rather than forming a good metallurgical interface during solid-liquid compound casting,in the present work,the purpose of inserting the rod is to enforce internal cooling and consequently decrease the sump depth.Moreover,the insertion provides more nucleation sites with the unmoltenα-Al particles.The structure and the macrosegregation of 2024 Al alloy ingots prepared by DC casting with and without the inserts were investigated.Results show that when the inserting position is 50 mm above the upper edge of the graphite ring,significant grain refinement in the central region of the ingot and a reduced centerline segregation are achieved.展开更多
The ingot was prepared by direct-chill(DC)casting technology with different casting speeds under the influence of intensive melt shearing to explore the effect of casting speed and intensive melt shearing on the float...The ingot was prepared by direct-chill(DC)casting technology with different casting speeds under the influence of intensive melt shearing to explore the effect of casting speed and intensive melt shearing on the floating grains and negative centerline segregation.The results indicate that the application of intensive melt shearing in DC casting process can distribute the floating grains uniformly,reduce the area fraction of the floating grains,alleviate the negative centerline segregation,and improve the uniformity of temperature field in the sump.It is also suggested that under the influence of intensive melt shearing,the casting speed plays a crucial role in the amounts and distribution of floating grains.At low casting speed,the intensive melt shearing can significantly reduce the area fraction of the floating grains and distribute them uniformly throughout the ingot.However,this effect gradually disappears with the increase of casting speed.展开更多
Effects of cooling rates on the morphology, sizes and species of primary vanadium-containing phases in Al-10V master alloys were investigated. The results show that the primary vanadium-containing phases with differen...Effects of cooling rates on the morphology, sizes and species of primary vanadium-containing phases in Al-10V master alloys were investigated. The results show that the primary vanadium-containing phases with different morphologies and compositions present in Al-10V master alloys at different cooling rates with the pouring temperature of 1,170 °C. When the Al-10V master alloy is solidified in the refractory mold at a cooling rate of 2 °C·s-1, the vanadium-containing phases are mainly plate-like Al10V phases, with the average size of 100.0 μm in the center and 93.2 μm at the edge of the ingot. When the master alloy is solidified in the graphite mold at a cooling rate of 24.3 °C·s-1, the primary vanadium-containing phases are dendritic Al3V phases, with the average length of 297.0 μm for the first dendrite in the center and 275.0 μm at the edge of the ingot. The secondary dendrite arm spacing (SDAS) is 9.5 μm in the center and 9.3 μm at the edge of the ingot, respectively. When the solidification is carried out in the copper mould at a cooling rate of 45.7 °C·s-1, the primary vanadium-containing phases are also Al3V phases but with smaller size, compared with that prepared at the cooling rate of 24.3 °C·s-1. As a result, the average length is 190.0 μm for the first dendrite in the center and 150.0 μm at the edge of the ingot. The SDAS is 9.8 μm in the center and 4.4 μm at the edge of the ingot, respectively.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
Degassing is very important for aluminum alloys especially for 7xxx series alloys. In the present study, a high shear technology was used to degas 7032 aluminum alloy in order to study its degassing efficiency. The ex...Degassing is very important for aluminum alloys especially for 7xxx series alloys. In the present study, a high shear technology was used to degas 7032 aluminum alloy in order to study its degassing efficiency. The experimental results showed that the high shear technology can significantly degas 7032 aluminum alloy. By applying intensive melt shearing and an Ar injection of 60 seconds, the density index, D,, was reduced from 13.25% to 0.28% and the hydrogen concentration was significantly i＇educed from 0.31 to 0.10 mL/100g AI. Compared with the conventional rotary degassing, high shear technology showed a much higher degassing efficiency, achieving a lower concentration of hydrogen in a shorter time. The water simulation experiment was used to study the mechanism of the high degassing efficiency. The small bubble size and the uniform distribution of Ar bubbles with the application of high shear technology are believed to be the main cause for the high degassing efficiency.展开更多
A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid （Pb）/ liquid （Sn） diffusion couples were investigated under various static magnetic fields. Results show that the...A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid （Pb）/ liquid （Sn） diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field （〈0.3 T）. When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level （0.8-5 T）, the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.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financially supported by the Natural Science Foundation of Liaoning Province(Nos.2019-ZD-0002,2019KF-0503)the Fundamental Research Funds for the Central Universities(Nos.N2002025,N2109006)the National Natural Science Foundation of China(No.51674078)。
文摘Central region coarse grains and centerline segregation are common defects in aluminum ingots fabricated by direct chill(DC)casting.A double cooling field was introduced into the DC casting process to reduce these defects,whereby the external cooling was supplied by the mold and water jets,and intercooling was achieved by inserting a rod of the same alloy into the molten pool along the central axis of the ingot.Rather than forming a good metallurgical interface during solid-liquid compound casting,in the present work,the purpose of inserting the rod is to enforce internal cooling and consequently decrease the sump depth.Moreover,the insertion provides more nucleation sites with the unmoltenα-Al particles.The structure and the macrosegregation of 2024 Al alloy ingots prepared by DC casting with and without the inserts were investigated.Results show that when the inserting position is 50 mm above the upper edge of the graphite ring,significant grain refinement in the central region of the ingot and a reduced centerline segregation are achieved.
基金the financial supports from the National Natural Science Foundation of China (51674078, 51374067)
文摘The ingot was prepared by direct-chill(DC)casting technology with different casting speeds under the influence of intensive melt shearing to explore the effect of casting speed and intensive melt shearing on the floating grains and negative centerline segregation.The results indicate that the application of intensive melt shearing in DC casting process can distribute the floating grains uniformly,reduce the area fraction of the floating grains,alleviate the negative centerline segregation,and improve the uniformity of temperature field in the sump.It is also suggested that under the influence of intensive melt shearing,the casting speed plays a crucial role in the amounts and distribution of floating grains.At low casting speed,the intensive melt shearing can significantly reduce the area fraction of the floating grains and distribute them uniformly throughout the ingot.However,this effect gradually disappears with the increase of casting speed.
基金financially supported by the Electromagnetic Processing of Materials (EPM) Lab Foundation in Northeastern University in China(No.NEU-EPM-005)the National Natural Science Foundation of China(Nos.51374067 and 51804010)the Training Program Foundation for the Talents by Beijing(No.2015000020124G023)
文摘Effects of cooling rates on the morphology, sizes and species of primary vanadium-containing phases in Al-10V master alloys were investigated. The results show that the primary vanadium-containing phases with different morphologies and compositions present in Al-10V master alloys at different cooling rates with the pouring temperature of 1,170 °C. When the Al-10V master alloy is solidified in the refractory mold at a cooling rate of 2 °C·s-1, the vanadium-containing phases are mainly plate-like Al10V phases, with the average size of 100.0 μm in the center and 93.2 μm at the edge of the ingot. When the master alloy is solidified in the graphite mold at a cooling rate of 24.3 °C·s-1, the primary vanadium-containing phases are dendritic Al3V phases, with the average length of 297.0 μm for the first dendrite in the center and 275.0 μm at the edge of the ingot. The secondary dendrite arm spacing (SDAS) is 9.5 μm in the center and 9.3 μm at the edge of the ingot, respectively. When the solidification is carried out in the copper mould at a cooling rate of 45.7 °C·s-1, the primary vanadium-containing phases are also Al3V phases but with smaller size, compared with that prepared at the cooling rate of 24.3 °C·s-1. As a result, the average length is 190.0 μm for the first dendrite in the center and 150.0 μm at the edge of the ingot. The SDAS is 9.8 μm in the center and 4.4 μm at the edge of the ingot, respectively.
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financially supported by the National Natural Science Foundation of China(51104043 and 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Degassing is very important for aluminum alloys especially for 7xxx series alloys. In the present study, a high shear technology was used to degas 7032 aluminum alloy in order to study its degassing efficiency. The experimental results showed that the high shear technology can significantly degas 7032 aluminum alloy. By applying intensive melt shearing and an Ar injection of 60 seconds, the density index, D,, was reduced from 13.25% to 0.28% and the hydrogen concentration was significantly i＇educed from 0.31 to 0.10 mL/100g AI. Compared with the conventional rotary degassing, high shear technology showed a much higher degassing efficiency, achieving a lower concentration of hydrogen in a shorter time. The water simulation experiment was used to study the mechanism of the high degassing efficiency. The small bubble size and the uniform distribution of Ar bubbles with the application of high shear technology are believed to be the main cause for the high degassing efficiency.
基金financially supported by the National Natural Science Foundation of China (Nos. 51201029, 51071042 and 51374067)the Fundamental Research Funds for the Central Universities (Nos. N130409002, N130209001 and N130709001)+1 种基金the China Postdoctoral Science Foundation (No. 2012M520637)the National Basic Research Program of China (No. 2012CB619506)
文摘A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid （Pb）/ liquid （Sn） diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field （〈0.3 T）. When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level （0.8-5 T）, the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.
