| Laminar metal composite material is an important branch of composite material,which is prepared by some advanced composite technology,achieving a good combination of two different alloys with different physical,chemical,and mechanical properties.Laminar metal composite materials are widely used in many fields,such as aerospace,petroleum,chemical,shipbuilding and automobile industries.For example,radiators and heat exchangers are manufactured with brazing sheets made from 4045 alloy clad onto 3003 alloy.Laminar metal composite material is conventionally manufactured by roll bonding,cast bonding,explosive welding,etc.Among them,continuous casting is an ideal method for producing laminar metal composite material because it realizes liquid state contact between two metals directly and avoids the problem of low bonding strength due to oxide,inclusion and greasy dirt.Therefore,this method has drawn great attention in recent years.However,in the continuous casting preparation process of laminar metal composite materials,how to avoid the mixed flow of molten metal to obtain smooth,continuous,stable and strong composite interface,is still the key to solve the problem of technology.In this paper,3xxx and 4xxx aluminum alloys,commonly used in industrial production,are choosed for the the typical alloys in the research of continuous casting process for preparing different shapes of laminar metal composites to study the problems of interface control and casting forming.This research will provide the theoretical guidance and research ideas for industrialization of the direct chilled continuous casting technology for preparing laminar aluminum composite materials.The main contents and conclusion of this paper are as follows:A comprehensive mathematic model is established to describe the direct chilled continuous casting process for preparing laminar aluminum composite materials.This model provides the theory basis for the numerical simulation of continuous casting progress for preparing laminar composites of aluminum alloys.By using this model,the effect of different casting parameters on the continuous casting process for preparing different shapes of laminar aluminum composites can be well simulated,the stability and integrity of the interface can be predicted and the preparation process of laminar aluminum composite ingots can be guided.First,simulation and experimental study on the direct chilled continuous casting process for preparing 3003/4004 circular clad ingots with outer diameter of 160 mm are done.Whether the calculated minimum solid fraction of 3003 alloy at the interface is greater than the solid fraction when the dendrite coherency is used as a criteria to determine the stability and integrity of the interface during the casting process for preparing 3003/4004 circular aluminum clad ingot.The simulation results show that,when the casting speed is 50-70 mm/min,the cooling water flow in annular baffle is 500-900 L/h,the pouring temperature of 3003 melt is 973-1013 K and the pouring temperature of 4004 is 873-933 K,the minimum solid fraction of 3003 alloy at the interface is always greater than the solid fraction when the dendrite coherency,that is to say,a sufficiently strong primary shell at the interface is provided to maintain the stability and integrity of the interface under these casting conditions.These casting parameters exhibit following effect degree for the minimum solid fraction at the interface in the order of Casting speed>Cooling water flow rate in annular baffle>3003 pouring temperature>4004 pouring temperature.According to the numerical simulation results,the 3003/4004 circular clad ingot with excellent metallurgical bonding is successfully prepared by direct chill casting process when the casting speed is 60 mm/min,the cooling water flow in annular baffle and mold are 700 L/h and 1200 L/h respectively,the pouring temperature of 3003 melt and 4004 melt are 720 ? and 630 ? respectively.Then,simulation and experimental study on the direct chilled continuous casting process for preparing 3003/4004 clad slab with cross section of 300 mm× 160 mm are done.The simulation results show that,when the cooling water flow in the dividing plate is 250-300 L/h,the cooled part height of the dividing plate is 20-30 mm,the casting speed is 60-70 mm/min,the pouring temperature of 3003 alloy is 963-1003 K,the pouring temperature of 4004 alloy is 943 K,the minimum solid fraction of 3003 alloy at the interface is greater than the solid fraction when the dendrite coherency.When the cooling water flow in the dividing plate is changed to 200 L/h,or the cooled part height of the dividing plate is changed to 10 mm,or the casting speed is changed to 80 mm/min,the minimum solid fraction of 3003 alloy at the interface is smaller than the solid fraction when the dendrite coherency.According to the numerical simulation results,a clad slab with excellent metallurgical bonding can be obtained when the cooling water flow of dividing plate is 250 L/h,the cooled part height of the dividing plate is 20 mm,the casting speed is 70 mm/min,the pouring temperature of 3003 alloy is 983 K and the pouring temperature of 4004 alloy is 943 K.However,some mixed flow occur at the interface in the continuous casting process when the cooling water flow in the dividing plate is changed to 200 L/h,or the casting speed is changed to 80 mm/min.This is in good agreement with the numerical simulation results.Finally,in order to solve the problem of the filling difficulty in the near-net shape continuous casting process for preparing thin-walled tubular ingot,the horizontal continuous casting process for preparing tubular aluminum clad ingot with the electromagnetic filling technology by using rotating electromagnetic stirring was developed,and the simulation and experimental study on the direct chilled continuous casting process for preparing 3003/4004 tubular clad ingot with outer diameter of 86 mm and wall thickness of 21 mm are done.The simulation results show that,when rotating electromagnetic stirring with 80 A and 50 Hz is applied,the maximum Lorenz force in the external and internal layers are 19000 N/m3 and 4000 N/m3,respectively,which can realize the successful stirring effect on the liquid melt of tubular clad ingot.The rotating electromagnetic stirring caused vigorous forced convection,the maximum velocity in the external and internal layers are increased from 0.002 m/s and 0.00371 m/s to 0.25 m/s and 0.35 m/s,respectively.Therefore,the electromagnetic filling technology can significantly enhance the flow and filling ability of the liquid melt in the external and internal layers,which is helpful to solve the problem of the filling difficulty in the near-net shape continuous casting process for preparing thin-walled tubular aluminum clad ingot.In present study,3003/4045 tubular aluminum clad ingots are prepared successfully when the casting speed is 120 mm/min,the mold cooling water flow is 1000 L/h,the casting temperature of 3003 melt and 4045 melt are 730 ? and 690 ? respectively.When the rotating electromagnetic stirring was not applied,the macrostructure of the tubular clad ingot was not uniform,and the inner grains were mostly columnar crystals.When the rotating electromagnetic stirring was applied,the axial depth of the mushy zone was increased by 27 mm for 4045 and 17 mm for 3003,and the axial temperature gradient of the mushy zone was decreased by 4.4 K/cm for 4045 and 38.1 K/cm for 3003,the macrostructure of the tubular clad ingot became fine and homogeneous,and the diffusion of the elements at the interface was promoted with the rotating electromagnetic stirring.The uniform temperature field,the low temperature gradient and the vigorous forced convection produced by electromagnetic stirring in the mushy zone are the main causes for the formation of the equiaxed grain in the tubular clad ingot with the rotating electromagnetic stirring. |
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