A Process Design Method for Suppressing Segregation of Aluminum Alloy in Twin-Roll Strip Casting

Abstract

The present invention relates to a process design method for suppressing segregation in twin-roll thin strip continuous casting of aluminum alloy. Specifically: 1) Establish transient heat conduction equations for the casting roll zone and the solid phase zone; 2) Establish a solidification model; 3) Suggest the casting and rolling speed and the cooling water flow rate combination that can suppress segregation by applying the generalized stability applicable to solidification. The present invention follows the large driving force - large generalized stability criterion, and designs the optimal process parameters with the casting and rolling speed of 2 m / min and the cooling water flow rate of 0.068 m / s. Through twin-roll thin strip continuous casting experiments, it is verified that the process parameter combination designed by the present invention can reduce the Si element concentration at the center position to 1.2 at.%, and reduce the Si element concentration at the edge position to 1.7 at.%. The process design strategy proposed by the present invention can optimize the process controlled by two parameters simultaneously, find the optimal combination between the two process parameters, and optimize the actual production efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal and alloy preparation, and relates to a process design method for suppressing segregation in twin-roll strip casting of aluminum alloys. Background Art

[0002] As a near-net-shape forming process, the main advantages of twin-roll strip casting are the combination of sub-rapid solidification, solid-state phase transformation, and plastic deformation, significantly shortening the processing time, reducing production costs and energy consumption, and being widely used in the aviation and automotive fields. However, due to the high cooling rate (10 2 -10 3 K / s), the thin strips prepared by twin-roll strip casting not only have centerline segregation that is prone to occur in traditional solidification, but also have edge segregation located on both sides of the thin plate, thus restricting the popularization of twin-roll strip casting technology.

[0003] Generally, with the increase of the casting and rolling speed and the cooling water flow rate, the center segregation can be reduced, but the edge segregation is increased. In order to suppress both segregations simultaneously, extensive research has been carried out on solidification models such as dendrite growth model, complete transformation kinetics, and dendrite fragmentation theory. By relaxing the assumptions of local equilibrium diffusion, linear liquid / solidus line, etc. existing in classical solidification models, the formation mechanisms of the two segregations are elaborated; both segregations originate from solute redistribution at the liquid / solid interface. Edge segregation is formed by the solidification of the interfacial liquid phase where solutes are not fully diffused, and center segregation is formed by the solidification of the bulk liquid phase where solutes diffuse to the center. However, due to the lack of direct coupling of process parameters and quantitative criteria in the solidification model, it is impossible to achieve the quantitative design of the optimal combination of the casting and rolling speed and the cooling water flow rate.

[0004] Therefore, based on the dendrite growth model and the complete transformation kinetics model, coupling the process parameters of twin-roll strip casting, the present invention proposes a thermal-kinetic criterion of large driving force - large generalized stability to achieve the quantitative design of the optimal process parameter combination, suppress center segregation and edge segregation, and contribute to the popularization of twin-roll strip casting technology. Summary of the Invention

[0005] Technical Problems to be Solved

[0006] In order to avoid the deficiencies of the prior art, the present invention proposes a process design method for suppressing segregation in twin-roll strip casting of aluminum alloys, a quantitative process design method, coupling two process parameters of the casting and rolling speed and the cooling water flow rate with the solidification model, and according to the thermal-kinetic criterion of large driving force - large generalized stability, finding the process parameters that can suppress both segregations simultaneously, and using this result to guide the preparation of twin-roll strip casting aluminum alloy sheets on site.

[0007] Technical Solution

[0008] A process design method for suppressing segregation in twin-roll thin strip continuous casting of aluminum alloy, characterized by the following steps:

[0009] Step 1: Calculate the solid / liquidus temperature gradient at the interface: For the coupling of process parameters, establish transient heat conduction equations for the roll zone and the solid phase zone. Substitute the twin-roll thin strip continuous casting speed and the cooling water flow speed into the heat transfer boundary conditions, solve the numerical values at both ends of the heat transfer boundary conditions, and use the finite difference method with the numerical values at both ends to solve the transient heat conduction equations for the roll zone and the solid phase zone, obtaining the solid phase temperature gradient as:

[0010]

[0011] In the formula: is the temperature at point m at the solid / liquid interface, Δx is the finite difference spatial step size in the solid phase zone, is the temperature extending two finite difference spatial step sizes from point m into the solid phase zone;

[0012] Substitute the solid phase temperature gradient into the heat conservation equation at the solid / liquidus interface to obtain the temperature gradient at the phase interface in the mushy zone:

[0013]

[0014] In the formula: v is the interface migration velocity, K s and are the thermal conductivities of the solid phase zone and the mushy zone respectively, and ΔH f is the latent heat of solidification;

[0015] Step 2: Solve the edge segregation and center segregation parameters during the solidification process: For the solidification process of twin-roll thin strip continuous casting, establish a solidification model to describe the microscopic evolution and macroscopic evolution respectively, and solve the edge segregation and center segregation:

[0016] For microscopic evolution: Substitute the solid phase temperature gradient and the temperature gradient at the phase interface in the mushy zone obtained in Step 1 into the steady-state microscopic dendrite growth model, and solve the steady-state microscopic dendrite growth model to obtain microscopic parameters; The microscopic parameters include: interface migration velocity, interface solid phase concentration, and interface liquid phase concentration;

[0017] For macroscopic evolution: Substitute the microscopic parameters into the full transformation kinetics model to solve for the transient macroscopic solute field and temperature field parameters; The full transformation kinetics model includes solute field and temperature field conservation models for three phase zones: the solid phase zone, the mushy zone, and the liquid phase zone;

[0018] For the segregation problem: Based on the interface liquid phase concentration and the average liquid phase concentration in the transient macroscopic solute field, establish dimensionless edge segregation and center segregation index equations respectively, and solve the edge segregation and center segregation;

[0019]

[0020] In the formula: is the transient microscopic interface liquid phase concentration after the steady-state microscopic interface liquid phase concentration is iterated through the coupled transient equation, is the initial concentration of the alloy, is the average liquid phase concentration;

[0021] Step 3: Solve the driving force and generalized stability of the solidification process: For the thermo-kinetics in the solidification process, establish a generalized stability applicable to solidification, and solve the driving force and generalized stability of the solidification process;

[0022] For the steady-state process, establish the driving force and energy barrier equations for steady-state interface migration according to the thermodynamic extremum principle:

[0023] For the transient process, combine the driving force and energy barrier equations for steady-state interface migration and the macroscopic transient parameters obtained in Step 2 to establish the driving force and energy barrier equations for transient interface migration, and solve the transient driving force and energy barrier:

[0024] For the transient process, establish an analytical formula for generalized stability based on the transient interface migration driving force and energy barrier, and solve the numerical value of generalized stability;

[0025] Step 4: Change the casting and rolling speed and the cooling water flow rate, and use different combinations of casting and rolling speed and cooling water flow rate parameters to repeat Steps 1 to 3, continuously iterate Steps 1 to 3, solve the transient driving force and the numerical value of generalized stability in Step 3 under different parameters, and obtain two surfaces with the transient driving force and the numerical value of generalized stability. The process parameters corresponding to the intersection of the two surfaces are the designed process parameter combinations.

[0026] The transient heat conduction equations for the roll zone and the solid phase zone are:

[0027]

[0028] In the formula: T R and T s are the temperature evolutions of the roll zone and the solid phase zone respectively, a R and a s are the thermal diffusion coefficients of the roll zone and the solid phase zone respectively, and x is the one-dimensional spatial length.

[0029] The heat transfer boundary conditions are:

[0030]

[0031] T = T i

[0032] where: q0 and q1 are the heat fluxes at the interface between the roll zone and the cooling water and the interface between the roll zone and the solid phase zone respectively, and T is the temperature value at the interface between the solid phase zone and the mushy zone, is the temperature on the roll side at the interface between the casting roll and the cooling water, T w is the temperature of the cooling water, is the temperature on the roll side at the interface between the casting roll and the solid phase, is the temperature on the solid phase side at the interface between the casting roll and the solid phase, T i is the average temperature of the mushy zone, h1 is the heat transfer coefficient at the boundary between the casting roll zone and the solid phase zone, h0 = N uw (K w / d) is the heat transfer coefficient at the boundary between the casting roll zone and the cooling water zone;

[0033] The value of the heat transfer coefficient h1 is 5500 W / m2 / K;

[0034] Among the heat transfer coefficients where K w is the thermal conductivity of the cooling water, d is the diameter of the cooling water pipe, l is the width of the casting roll, μ w , ρ and C p are the dynamic viscosity, density and specific heat capacity of the cooling water respectively, ω is the casting and rolling speed, v w is the cooling water flow velocity.

[0035] The dendritic growth model adopts the model disclosed in "J.Mater.Sci.Technol.44(2020)209-222". When using the model, the interface solid / mush temperature gradient in the model is the solid phase temperature gradient obtained in step 1 and the temperature gradient at the phase interface of the mushy zone.

[0036] The solute field model in the full transformation kinetics three-phase zone is as follows:

[0037]

[0038] where: g s , and g l are the volume fractions of the solid phase zone, mushy zone and liquid phase zone respectively, and are the average concentrations in the three-phase zone, k v is the interface non-equilibrium solute distribution coefficient, is the liquid phase concentration at the interface, and are the concentrations of elements k and j in the dendritic envelope respectively, A e is the interfacial region concentration at the paste / liquid interface, is the diffusion coefficient of element k in the liquid phase under the influence of element j, is the bulk non-equilibrium solute diffusion factor, is the solute diffusion length in the liquid phase zone.

[0039] The temperature field conservation model in the three-phase zone is as follows:

[0040]

[0041] Wherein: <T s > s , T i and <T l > l are respectively the average temperature in the three-phase region, A s is the interfacial region concentration at the solid / paste interface, K l is the thermal conductivity in the liquid phase region, and are respectively the thermal diffusion lengths in the mushy zone and the liquid phase, C p2 is the specific heat capacity of the liquid metal.

[0042] The driving force for steady-state interface migration and the energy barrier equation derived according to the principle of thermodynamic extremum are respectively:

[0043]

[0044] In the formula: and are respectively the chemical potentials of element k at the solid / paste interface, calculated by Thermo-Calc software, v is the interface migration velocity, is the diffusion velocity of element k in the liquid phase, is the solid-phase concentration at the interface, R g is the gas constant, a0 is the interfacial non-equilibrium solute diffusion coefficient, is the diffusion coefficient of element k in the mushy zone, v0 is the maximum interface migration velocity, approximately equal to the sound velocity in the liquid phase, and M0 is the interface velocity mobility.

[0045] The transient energy barrier equation is:

[0046]

[0047] Where

[0048]

[0049] In the formula: and v 0 are respectively the initial interfacial liquid-phase side concentration, solid-phase side concentration and velocity, is the initial solid-liquid chemical potential difference, and v t are respectively the interfacial liquid-phase side concentration, solid-phase side concentration and velocity at time t during the iteration process, is the solid-liquid chemical potential difference at time t during the iteration process.

[0050] The transient energy barrier equation is:

[0051]

[0052] Among them

[0053]

[0054] In the formula: T i t is the temperature of the mushy zone at time t during the iterative process, and T i 0 is the temperature of the mushy zone at the initial time.

[0055] The generalized stability equation is:

[0056]

[0057] Beneficial effects

[0058] A process design method for suppressing segregation in twin-roll thin strip continuous casting of aluminum alloy proposed by the present invention solves the problem that the thin strip prepared by the existing twin-roll thin strip continuous casting is prone to center segregation and edge segregation. Specifically, it includes: 1) establishing transient heat conduction equations for the casting roll zone and the solid phase zone, 2) establishing a solidification model, and 3) suggesting a generalized stability applicable to solidification to obtain the matching of the casting and rolling speed and the cooling water flow rate for suppressing segregation. The present invention follows the large driving force - large generalized stability criterion and designs the optimal process parameters with a casting and rolling speed of 2 m / min and a cooling water flow rate of 0.068 m / s. Through twin-roll thin strip continuous casting experiments, it is verified that the process parameter combination designed by the present invention can reduce the Si element concentration at the center position to 1.2 at.%, and reduce the Si element concentration at the edge position to 1.7 at.%. The process design strategy proposed by the present invention can optimize the process with simultaneous control of two parameters, find the optimal matching between the two process parameters, and optimize the actual production efficiency.

[0059] The advantages of the present invention are:

[0060] 1. By connecting the process parameters with the solidification model theory, the present invention can perform quantitative control on twin-roll thin strip continuous casting compared with the traditional solidification model.

[0061] 2. The present invention follows the large driving force - large generalized stability criterion and proposes a new strategy to simultaneously suppress center segregation and edge segregation: the large driving force at the initial state of solidification corresponds to a high casting and rolling speed to suppress center segregation, and the large generalized stability at the final state of solidification corresponds to a low cooling water flow rate to suppress edge segregation.

[0062] 3. The process design strategy proposed by the present invention can optimize the process with simultaneous control of two parameters: the casting and rolling speed and the cooling water flow rate, find the optimal matching between the two process parameters, and optimize the actual production efficiency. Description of the drawings

[0063] Figure 1 This is the flow chart of the process design method for suppressing segregation in twin-roll strip casting proposed by the present invention.

[0064] Figure 2 These are two process parameters designed in the embodiments of the present invention, which can suppress both central segregation and edge segregation simultaneously.

[0065] Figure 3 This is the verification of the process design method of the present invention through the specific implementation of the twin-roll strip casting technology in the embodiments of the present invention.

[0066] Figure 4 This is the microstructure and composition characterization of the edge position of the sheet prepared with the optimal process parameters in the embodiments of the present invention.

[0067] Figure 5 This is the microstructure and composition characterization of the center position of the sheet prepared with the optimal process parameters in the embodiments of the present invention. Detailed implementation manners

[0068] The present invention will be further described below in conjunction with the embodiments and the accompanying drawings:

[0069] See Figure 1 , in order to find the best combination of two twin-roll strip casting process parameters and suppress both central segregation and edge segregation in twin-roll casting simultaneously, taking the Al-1.72Mg-1.67Si (in at.%) alloy as an example, the present invention proposes a process design method, including the following steps:

[0070] 1) Substitute the casting speed ω = 2 - 6 m / min and the cooling water flow rate v w = 0.043 - 0.068 m / s into the temperature field model:

[0071]

[0072] where a R and a s are the thermal diffusion coefficients of the roll zone and the solid phase zone. The process parameters, the casting speed (ω) and the cooling water flow rate (v w ) are coupled through the heat transfer boundary conditions:

[0073]

[0074] where q0 is the heat flux of the roll zone and the cooling water, is the temperature on the roll side of the interface between the roll and the cooling water, T w is the temperature of the cooling water, h0 = N uw (K w / d) is the heat transfer coefficient at the boundary between the roll zone and the cooling water zone, where:

[0075]

[0076] where K w is the thermal conductivity of the cooling water, d is the diameter of the cooling water pipe, l is the width of the casting roll, μ w , ρ and C p are the dynamic viscosity, density and specific heat capacity of the cooling water respectively, ω is the casting and rolling speed, v w is the cooling water flow velocity. By solving Equation (1) through the finite difference method, the solid and liquid temperature gradients at the dendrite tip can be obtained:

[0077]

[0078] where is the temperature at the m-th point of the solid / liquid interface, is the temperature from the m-th point to the third point in the solid phase region, Δx is the spatial step of the finite difference method, v is the velocity of the dendrite tip, ΔH f is the latent heat of solidification, K s and K l are the thermal conductivities of the solid phase region and the liquid phase region respectively.

[0079] 2) Substitute the solid and liquid temperature gradients obtained in step 1) into the steady-state microscopic dendrite growth model. The dendrite growth model uses the model described in "J.Mater.Sci.Technol.44(2020)209-222", and solve to obtain the dendrite tip velocity (v), the concentration on the solid side of the dendrite interface the concentration on the liquid side and the microscopic parameters of the dendrite tip radius (R). Substitute the obtained microscopic parameters into the full transformation model obtained by the volume averaging method to solve the transient macroscopic parameters. The full transformation model includes the concentration and temperature conservation equations in the solid phase region, the mushy zone and the liquid phase region. The concentration conservation equation is:

[0080]

[0081] where g s , and g l are the volume fractions of the solid phase region, the mushy zone and the liquid phase region respectively, and are the average concentrations in the three-phase region respectively, is the concentration of the dendrite envelope, A e is the interfacial region concentration at the mush / solid interface, is the solute diffusion length in the liquid phase region. The temperature conservation equation for the three-phase region of the full transformation is:

[0082]

[0083] where <Ts > s , T i and <T l > l are the average temperatures of the three-phase regions, and are the thermal diffusion lengths of the mushy region and the liquid phase, respectively. According to the full transformation model, it can be solved <T s > s , T i , <T l > l , and And other macro parameters. and The center segregation and edge segregation can be solved separately:

[0084]

[0085] in is the initial concentration of the alloy.

[0086] 3) Substitute the macroscopic parameters obtained in step 2) into the driving force and energy barrier equations for interface migration to solve the driving force and energy barrier. The driving force equation is:

[0087]

[0088] in

[0089]

[0090] in and v 0 are the initial interface liquid side concentration, solid side concentration and velocity, is the initial chemical potential difference between solid and liquid.

[0091] The energy barrier equation is:

[0092]

[0093] in

[0094]

[0095] According to equations (11) and (12), the driving force and energy barrier of interface migration can be solved and substituted into the generalized stability equation:

[0096]

[0097] The generalized stability of interface migration can be solved.

[0098] The driving force, generalized stability, central segregation, and edge segregation calculated for each pair of casting and rolling speeds and cooling water flow rates were compared. The results are as Figure 2 shown. As the casting and rolling speed increases, increasing the interface speed increases the initial driving force, decreases the final generalized stability, inhibits central segregation, and enhances edge segregation. Similarly, as the cooling water flow rate decreases, decreasing the interface speed decreases the initial driving force, increases the final generalized stability, enhances central segregation, and inhibits edge segregation. To simultaneously inhibit central segregation and edge segregation, a compromise intersection of the casting and rolling speed and the cooling water flow rate must be satisfied. Before this point, decreasing the casting and rolling speed reduces the driving force and enhances central segregation, while increasing the cooling water flow rate reduces the generalized stability and enhances edge segregation. After this point, increasing the casting and rolling speed reduces the generalized stability and edge segregation, while decreasing the cooling water flow rate reduces the driving force and enhances central segregation. When following the large driving force - large generalized stability criterion, ω = 6 m / min and v w = 0.043 m / s, central segregation and edge segregation are simultaneously inhibited.

[0099] According to the above process design method, this embodiment also operated specific examples, selecting three groups of process parameters: ω = 2 m / min and v w = 0.068 m / s, ω = 6 m / min and v w = 0.068 m / s, ω = 6 m / min and v w = 0.043 m / s to conduct thin strip continuous casting experiments, comparing the degrees of central segregation and edge segregation under the three groups of processes to verify the effectiveness of the method of the present invention, specifically as follows:

[0100] Prepare the melt, and roll the plates using the three groups of process parameters respectively. The equipment parameters of the twin-roll thin strip continuous casting are shown in Table 2:

[0101] Table 2 Twin-roll thin strip continuous casting process table

[0102]

[0103] * The pressure of the cooling water corresponds to the flow rate of the cooling water and can be measured through experiments.

[0104] Using high-purity aluminum ingots (99.99%), magnesium ingots (99.9%), and aluminum-silicon alloy (20 wt.%) as raw materials, they are melted in a resistance furnace protected by argon using a 0.4 AlTiB refiner. First, the aluminum ingots are placed in the resistance furnace, and the furnace is heated to 750 °C until they are completely melted. Then, the Al-Si alloy (20 wt.%) and the AlTiB master alloy are added to the melt. After the added alloying elements are completely melted, the temperature is reduced to 680 °C, and the magnesium ingot (99.9%) is pressed into the melt through a titanium cover coated with a BN coating. After degassing and slag removal, the 30% LiF - 70% LiCl molten salt is first dried and then sprinkled into the melt. After the alloy is fully melted, the casting and rolling mill is started. First, the casting and rolling speed and the cooling water flow rate are set to 2 m / min and 0.068 m / s respectively, and the melt is introduced into the roll gap between the upper and lower rolls through a refractory fiber insulation pouring port to prepare thin strips.

[0105] Prepare thin strips with ω = 6 m / min and v w = 0.068 m / s and ω = 6 m / min and v w = 0.043 m / s in sequence according to the above steps.

[0106] The as-cast specimens of thin strip continuous casting are taken from the plates manufactured by the stop method. The microstructure is characterized on a scanning electron microscope (SEM), and the composition test is carried out on an energy dispersive spectrometer (EDS). On the as-cast specimens, EDS area scans are taken every 170 μm in units of 30 * 30 μm 2 to represent the average concentration of each area scan range with the atomic mass ratio of Si and Mg.

[0107] The composition distributions under three process parameter combinations are as Figure 3 shown, where 0 mm represents the edge position and 5 mm represents the center position; when ω = 2 m / min and v w = 0.068 m / s, the Si element concentration at the edge is relatively high, and severe edge segregation occurs ( Figure 3 (a)); when ω = 6 m / min and v w = 0.068 m / s, the Si element concentration at the center is relatively high, and severe center segregation occurs ( Figure 3 (b)); when ω = 6 m / min and v w = 0.043 m / s, both center segregation and edge segregation are alleviated ( Figure 3 (c)); which conforms to the parameters designed by the process design method proposed in the present invention.

[0108] When ω = 6 m / min and v w = 0.043 m / s, the morphology and composition distribution at the edge position of the as-cast structure are as Figure 4 shown. The grain distribution at the edge position is uneven, and the average size is about 20 μm ( Figure 4(a)); There are white and gray strip-shaped distributions at the grain boundaries ( Figure 4 (b)), which are AlSi phase ( Figure 4 (c)) and Mg2Si phase ( Figure 4 (d) and (e)); It can be seen from the surface scan that the segregation of Si element at the grain boundary is more serious than that of Mg element.

[0109] When ω = 6 m / min and v w = 0.043 m / s, the morphology and composition distribution at the center of the as-cast structure are as Figure 5 shown. The grain distribution at the center is more uniform than that at the edge, and the grain size is slightly larger than that at the edge, about 30 μm ( Figure 5 (a)); There are still white AlSi phase and gray Mg2Si phase at the grain boundaries (( Figure 5 (b - e)); It can also be seen from the surface scan that the segregation of Si element at the center is more serious than that of Mg element.

[0110] Through the method of the present invention, it can provide an important reference basis for experimental work, avoid the large-scale repetition of experimental work, greatly reduce the expenditure, improve the research efficiency, and has strong practical value.

Claims

1. A process design method for suppressing segregation in continuously cast aluminum alloy thin strips by twin-roll casting, characterized in that The steps are as follows: Step 1: Calculate the solid / pasty temperature gradient at the interface: For the coupling of process parameters, establish the transient heat conduction equations for the casting roll zone and the solid phase zone. Substitute the twin-roll strip casting speed and the cooling water flow rate into the heat transfer boundary conditions, solve the numerical values at both ends of the heat transfer boundary conditions, and use the finite difference method to solve the transient heat conduction equations for the casting roll zone and the solid phase zone with the numerical values at both ends to obtain the solid phase temperature gradient as: where is the temperature at point m at the solid / liquid interface, and Δx is the finite-difference spatial step in the solid phase region, is the temperature extending two finite-difference spatial steps from point m into the solid phase region; Substitute the solid phase temperature gradient into the heat conservation equation at the solid / pasty interface to obtain the temperature gradient at the phase interface in the mushy zone: where v is the interface migration velocity, K s and are the thermal conductivities of the solid phase region and the mushy zone respectively, and ΔH f is the latent heat of solidification; Step 2: Solve the edge segregation and center segregation parameters during the solidification process: For the solidification process of twin-roll strip casting, establish a solidification model to describe the microevolution and macroevolution respectively, and solve the edge segregation and center segregation: For microevolution: Substitute the solid phase temperature gradient obtained in Step 1 and the temperature gradient at the phase interface in the mushy zone into the steady-state microscale dendrite growth model, and solve the steady-state microscale dendrite growth model to obtain the microscale parameters; The microscale parameters include: the interface migration velocity, the interface solid phase concentration, and the interface liquid phase concentration; For macroevolution: Substitute the microscale parameters into the full transformation kinetics model to solve for the transient macroscale solute field and temperature field parameters; the full transformation kinetics model includes the solute field and temperature field conservation models for three phase zones, namely the solid phase zone, the mushy zone, and the liquid phase zone; For the segregation problem: According to the interface liquid phase concentration and the average liquid phase concentration in the transient macroscale solute field, establish dimensionless edge segregation and center segregation index equations respectively, and solve the edge segregation and center segregation; where is the transient microscopic interface liquid phase concentration after iteration of the steady-state microscopic interface liquid phase concentration through the coupled transient equation, is the initial concentration of the alloy, is the average liquid phase concentration; Step 3: Solve the driving force and generalized stability during the solidification process: For the thermodynamics during the solidification process, establish a generalized stability applicable to solidification, and solve the driving force and generalized stability during the solidification process; For the steady-state process, establish the driving force and energy barrier equations for steady-state interface migration based on the principle of thermodynamic extremum: For the transient process, combine the driving force and energy barrier equations for steady-state interface migration and the macroscale transient parameters obtained in Step 2 to establish the driving force and energy barrier equations for transient interface migration, and solve the transient driving force and energy barrier: For the transient process, establish an analytical formula for generalized stability based on the transient interface migration driving force and energy barrier, and solve the numerical value of generalized stability; Step 4: Change the casting and rolling speed and the cooling water flow rate, and use different combinations of casting and rolling speed and cooling water flow rate parameters to repeat Steps 1 to 3, continuously iterate Steps 1 to 3, solve the transient driving force and the numerical value of generalized stability in Step 3 under different parameters, and obtain two surfaces with the transient driving force and the numerical value of generalized stability. The process parameter combination corresponding to the intersection point of the two surfaces is the designed process parameter combination.

2. The process design method for suppressing segregation of aluminum alloy in twin-roll strip casting according to claim 1, wherein: The transient heat conduction equations for the casting roll zone and the solid phase zone are: where: T R and T s are the temperature evolutions in the casting roll zone and the solid phase zone respectively, a R and a s are the thermal diffusivities in the casting roll zone and the solid phase zone respectively, and x is the one-dimensional spatial length.

3. The process design method for suppressing segregation of aluminum alloy in twin-roll strip casting according to claim 1, wherein: The heat transfer boundary conditions are: Where: q0 and q1 are the heat fluxes at the interfaces between the casting roll zone and the cooling water, and between the casting roll zone and the solid phase zone respectively, T is the temperature at the interface between the solid phase zone and the mushy zone. is the temperature on the casting roll side at the interface between the casting roll and the cooling water, T w is the temperature of the cooling water. is the temperature on the casting roll side at the interface between the casting roll and the solid phase. is the temperature on the solid phase side at the interface between the casting roll and the solid phase, T i is the average temperature of the mushy zone, h1 is the heat transfer coefficient at the boundary between the casting roll zone and the solid phase zone, h0 = N uw (K w / d) is the heat transfer coefficient at the boundary between the casting roll zone and the cooling water zone. The value of the heat transfer coefficient h1 is 5500 W / m2 / K; In the heat transfer coefficient where K w is the thermal conductivity of the cooling water, d is the diameter of the cooling water pipe, l is the width of the casting roll, μ w , ρ and C p are the dynamic viscosity, density and specific heat capacity of the cooling water respectively, ω is the casting and rolling speed, v w is the cooling water flow velocity.

4. The process design method for suppressing segregation of aluminum alloy in twin-roll strip casting according to claim 1, characterized in that: The dendrite growth model uses the model disclosed in "J.Mater.Sci.Technol.44(2020)209-222". When using the model, the interface solid / pasty temperature gradient in the model is the solid phase temperature gradient obtained in Step 1 and the temperature gradient at the phase interface in the mushy zone.

5. The process design method for suppressing segregation of aluminum alloy in twin-roll strip casting according to claim 1, wherein: The solute field model for the three-phase zone of the full transformation kinetics is: where: g s , and g l are the volume fractions of the solid phase region, the mushy zone, and the liquid phase region, respectively, and are the average concentrations in the three-phase region, k v is the interfacial non-equilibrium solute partition coefficient, is the liquid-phase concentration at the interface, and are the concentrations of elements k and j in the dendrite envelope, respectively, A e is the interfacial region concentration at the mush / liquid interface, is the diffusion coefficient of element k in the liquid phase under the influence of element j, is the bulk non-equilibrium solute diffusion factor, is the solute diffusion length in the liquid phase region.

6. The process design method for suppressing segregation of aluminum alloy in twin-roll strip casting according to claim 1, characterized in that: The temperature field conservation model for the three-phase zone is: Wherein: <T s > s , T i and <T l > l are respectively the average temperature in the three-phase region, A s is the interfacial region concentration at the solid / paste interface, K l is the thermal conductivity in the liquid phase region, and are respectively the thermal diffusion lengths in the mushy zone and the liquid phase, C p2 is the specific heat capacity of the liquid metal.

7. The process design method for suppressing segregation of aluminum alloy in twin-roll strip casting according to claim 1, wherein: The driving force for steady-state interface migration and the energy barrier equation derived according to the principle of thermodynamic extremum are respectively as follows: Wherein: and are the chemical potentials of element k at the solid / paste interface, respectively calculated by the Thermo-Calc software, v is the interface migration velocity, is the diffusion velocity of element k in the liquid phase, is the solid-phase concentration at the interface, R g is the gas constant, a0 is the interfacial non-equilibrium solute diffusion coefficient, is the diffusion coefficient of element k in the mushy zone, v0 is the maximum migration velocity at the interface, equal to the speed of sound in the liquid phase, and M0 is the interface velocity mobility.

8. The process design method for suppressing segregation of aluminum alloy in twin-roll strip casting according to claim 1, wherein: The transient energy barrier equation is as follows: where Where: and v 0 are the initial concentration on the liquid side of the interface, the concentration on the solid side, and the velocity, respectively, is the initial chemical potential difference between the solid and the liquid, and v t are the concentration on the liquid side of the interface, the concentration on the solid side, and the velocity at time t during the iteration process, respectively, is the chemical potential difference between the solid and the liquid at time t during the iteration process; The transient energy barrier equation is as follows: where Where: is the temperature of the mushy zone at time t during the iterative process, is the temperature of the mushy zone at the initial time.

9. The process design method for suppressing segregation of aluminum alloy in twin-roll strip casting according to claim 1, characterized in that: The generalized stability equation is as follows:

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