CN-120877984-B - Numerical simulation method for particle dispersion in molten pool of laser surface remelting particle reinforced magnesium-based composite material

CN120877984BCN 120877984 BCN120877984 BCN 120877984BCN-120877984-B

Abstract

A numerical simulation method for particle dispersion in a laser surface remelting particle reinforced magnesium-based composite material molten pool belongs to the technical field of numerical simulation of particle dispersion in a composite material molten pool. The invention solves the problem that the particle dispersion in the process of particle reinforced magnesium matrix composite LSR can not be predicted accurately at present. According to the invention, firstly, the temperature gradient and primary dendrite spacing in a molten pool are obtained based on experimental characterization, so that the liquidus and eutectic reaction temperature of unbalanced solidification are calculated. The liquidus and eutectic reaction temperature of unbalanced solidification are adopted to calculate molten pool evolution in the laser surface remelting process of the magnesium-based composite material, the formation characteristics of the molten pool of the composite material and migration behaviors of particles in the molten pool can be predicted more accurately, so that particle dispersion in the formation process of the molten pool of the particle-reinforced magnesium-based composite material can be predicted accurately, and theoretical guidance is provided for deep understanding of the molten pool evolution process and process parameter optimization in the laser forming process of the composite material. The method can be applied to prediction of particle dispersion in a composite material molten pool.

Inventors

LIU DONGRONG
PU ZHENPENG
ZHAO SICONG
GUO ERJUN

Assignees

哈尔滨理工大学

Dates

Publication Date: 20260508
Application Date: 20250715

Claims (9)

1. The numerical simulation method for particle dispersion in a molten pool of the laser surface remelting particle reinforced magnesium-based composite material is characterized by specifically comprising the following steps of: Step one, taking the prepared as-cast sample as a substrate, carrying out sand blasting treatment on the surface of the substrate, carrying out laser surface remelting on the treated substrate, and measuring the depth L molten-pool of a molten pool and the primary dendrite spacing lambda PDAS ; Calculating liquidus temperature T ' l in the unbalanced solidification process, and then calculating eutectic reaction temperature T ' e in the unbalanced solidification process according to T ' l , molten pool depth L molten-pool and primary dendrite spacing lambda PDAS ; step two, determining the corresponding relation between the melt viscosity and the temperature of the particle reinforced magnesium-based composite material; Dividing cube grids of the molten pool area and the air layer, wherein the size of each cube grid obtained by division is delta x; Square grid division is carried out on the substrate layer, and the size of each square grid obtained through division is Deltax o ×Δx o ×Δx o ,Δx＜Δx o ; Step four, calculating flow fields of an air layer and a molten pool area according to the corresponding relation between liquidus temperature T ' l , eutectic reaction temperature T' e and melt viscosity and temperature in the unbalanced solidification process, and solving the average density and the flowing speed of molten metal; step five, calculating a temperature field for the air layer, the molten pool area and the substrate area according to the average density and the metal liquid flowing speed obtained in the step four; Step six, for a molten pool area, calculating the resultant force born by the particles according to the molten metal flow speed solved in the step four, and solving the motion equation of the particles according to the resultant force born by the particles and the molten metal flow speed solved in the step four to obtain a particle motion speed field; step seven, judging whether the laser scanning process is finished; If the laser scanning process is finished, stopping calculation, and outputting a temperature field, a liquid flow velocity field and a particle movement velocity field of a local area of the lower molten pool at different moments; If the laser scanning process is not finished, adding 1 to the time step, and returning to execute the fourth step by utilizing the resultant force of the particles calculated in the sixth step.
2. The numerical simulation method for particle dispersion in a molten pool of a laser surface remelting particle reinforced magnesium-based composite material according to claim 1, wherein the calculating of liquidus temperature T ' l in the unbalanced solidification process, and calculating of eutectic reaction temperature T ' e in the unbalanced solidification process according to T ' l , molten pool depth L molten-pool and primary dendrite spacing λ PDAS are as follows: T′ l ＝(T l -ΔT R ) (6) ΔT ls ＝(T l -ΔT R )-T′ e (7) Wherein R tip is dendrite tip radius, V scan is laser scanning speed, D L is diffusion coefficient of solute in liquid phase, m lv is liquidus slope in unbalanced solidification process, k v is liquid solute distribution coefficient in unbalanced solidification process, C o is alloy initial component, Γ is gibbs coefficient, m le is liquidus slope in balanced solidification process, k e is solute distribution coefficient in balanced solidification process, Δt R is curvature supercooling, Δt ls is crystallization temperature range in unbalanced solidification process, G T is temperature gradient between bath surface and substrate, T l is liquidus temperature corresponding to equilibrium phase diagram, T ' e is eutectic reaction temperature in unbalanced solidification process, T' l is liquidus temperature in unbalanced solidification process, l is atomic spacing at solid-liquid interface.
3. The numerical simulation method of particle dispersion in a molten pool of a laser surface remelting particle-reinforced magnesium-based composite material according to claim 2, wherein a temperature gradient G T between the molten pool surface and the substrate is: G T ＝(T surface -T substrate )/(0.827·L molten-pool ) (8) Where T substrate denotes the initial temperature of the substrate, T surface denotes the maximum bath surface temperature, and L molten-pool denotes the bath depth.
4. The numerical simulation method for particle dispersion in a molten pool of the laser surface remelting particle-reinforced magnesium-based composite material according to claim 3, wherein the specific process of the second step is as follows: Step two, under the condition of known particle content, carrying out a mold filling experiment of a composite material melt thin-wall part by adopting a sand mold gravity casting process, obtaining a stepped thin-wall casting after the casting is completely solidified, and measuring the mold filling length of the melt; Step two, under the experimental parameters of the sand mould gravity casting process of step two, based on the change curve of the viscosity of the magnesium alloy melt along with the temperature Performing ProCAST numerical simulation calculation to obtain the melt filling length obtained through simulation; Wherein μ represents the melt viscosity of the magnesium alloy, T represents the temperature, and a o and b o are coefficients of the curve; step two, the melt filling length measured in the step two is subjected to difference with the melt filling length obtained through simulation, and a difference result is obtained; If the absolute value of the difference result is not more than 1mm, obtaining a curve of the viscosity changing along with the temperature, and marking the obtained curve of the viscosity changing along with the temperature as mu=aT -b , wherein a and b are coefficients of the curve; If the absolute value of the difference result exceeds 1mm, the melt viscosity value is adjusted up by 0.1 Pa.s, and then the second step is continuously executed; Step two, performing ProCAST numerical simulation calculation by using the adjusted melt viscosity value to obtain a melt filling length obtained through simulation; and returning to the second step and executing the third step.
5. The numerical simulation method for particle dispersion in a molten pool of the laser surface remelting particle-reinforced magnesium-based composite material according to claim 4, wherein the specific process of the fourth step is as follows: For grids with temperature T less than T ' e in the air layer and molten pool area, i.e. for grids with T' e > T, no flow field calculation is required; For grids with temperature T greater than or equal to T ' e in the air layer and molten pool area, namely for grids with T' e less than or equal to T, the flow field needs to be calculated, and the calculation equation is as follows: Wherein, the In order to achieve an average density of the particles, Is the flowing speed of the molten metal, t is the time, The gradient is calculated, p is the pressure, eta is the dynamic viscosity calculated according to the corresponding relation between the viscosity and the temperature, The acceleration of the gravity is that, Is the volumetric force caused by the solid phase particles, For the buoyancy force, the water is pumped, In order to provide a recoil pressure, In the form of a surface tension force, For Ma Rige Ni shear force, alpha 1 is the volume fraction of metal phase, 1-alpha 1 is the volume fraction of gas, ρ Mg-9Al is metal density, ρ gas is gas density, β T is thermal expansion coefficient, P 0 is standard atmospheric pressure, L v is metal latent heat of evaporation, M is molar mass, T v is metal evaporation temperature, R is gas constant, T is molten bath metal temperature, The gradient of alpha 1 is that of alpha 1 , K 1 is the surface curvature of the molten pool, sigma 0 is the surface tension coefficient corresponding to liquidus temperature T' l , dsigma/dT is the slope of the curve of the surface tension coefficient with temperature T, V c is the volume of the split grid, and I represent absolute values and temperature gradients for the resultant force of particle motion Gradient of normal vector of bath surface
6. The numerical simulation method for particle dispersion in a molten pool of the laser surface remelting particle-reinforced magnesium-based composite material according to claim 5, wherein the specific process of the fifth step is as follows: H=c pMg-9Al T+(1-f s-mico )L latent (20) Wherein H is enthalpy change, lambda is the heat conductivity coefficient of the magnesium-based composite material, Q laser is heat input from laser, Q v is heat loss caused by evaporation, Q rad is heat loss caused by radiation, c pMg-9Al is specific heat of magnesium alloy, f s-mico is solid phase fraction, L latent is latent heat of magnesium alloy, Q 0 is coefficient required for calculation of laser heat input, χ is energy density ratio, Z e is the position of the upper surface of the conical laser heat source along the Z axis, Z i is the position of the lower surface of the conical laser heat source along the Z axis, r 0 (Z) is the radius of the conical laser heat source at the Z axis of the device, c pgas is specific heat of gas, eta l is laser absorptivity, Q l is laser power, r e is the radius of the upper surface of the conical laser heat source, r i is the radius of the lower surface of the conical laser heat source, gamma is Stefan-Boltmann constant, tau is radiation heat dissipation, T 0 is room temperature, (x, y, Z) is the coordinate value of the center in three-dimensional space, E is the base of natural logarithm, which is the mixed specific heat of magnesium alloy and gas.
7. The numerical simulation method for particle dispersion in a molten pool of the laser surface remelting particle-reinforced magnesium-based composite material according to claim 6, wherein the specific process of the step six is as follows: step six, for grids with T ' e being more than or equal to T in the molten pool area, no calculation of particle stress is needed; For a grid of T ' e < T in the region of the bath, the forces to which the particles are subjected include gravity, buoyancy, pressure, drag and mass forces, the resultant forces to which the particles are subjected The method comprises the following steps: Wherein, the For the buoyancy force, the water is pumped, In the case of a pressure force, the pressure, In order for the drag force to be a drag force, For mass force, d is particle diameter, ρ SiC is particle density, R e is Reynolds number, The movement speed of the particles in the molten metal is represented by m add , and the mass coefficient is represented by m add ; And step six, predicting particle movement based on the resultant force of the particles and the instantaneous flow field of the particles obtained in the step four, and if at least A particles move to the same position in the current time step, forming agglomerates by the particles moving to the same position.
8. The numerical simulation method for particle dispersion in a molten pool of a laser surface remelting particle-reinforced magnesium-based composite material of claim 7, wherein the method is characterized in that the particle motion is predicted based on resultant force of particles and the instantaneous flow field of the particles obtained in the step four, and a Lagrange method is adopted.
9. The numerical simulation method of particle dispersion in a molten pool of laser surface remelting particle-reinforced magnesium-based composite material of claim 8 wherein the value of a is 5.

Description

Numerical simulation method for particle dispersion in molten pool of laser surface remelting particle reinforced magnesium-based composite material Technical Field The invention belongs to the technical field of numerical simulation of particle dispersion in a composite material molten pool, and particularly relates to a numerical simulation method of particle dispersion in a laser surface remelting particle reinforced magnesium-based composite material molten pool. Background The magnesium alloy has the advantages of low density, high specific strength, high specific stiffness, good electromagnetic shielding property, good machining property and the like, and is the lightest weight engineering material applicable at present. However, the magnesium alloy has lower strength and hardness, and poorer wear resistance and corrosion resistance, and limits the development of the magnesium alloy to a certain extent. The magnesium alloy can obtain extraordinary physical, chemical and mechanical properties by introducing ceramic particle components. The particle reinforced magnesium-based composite material not only inherits the advantages of magnesium alloy, but also obviously enhances absolute strength, high-temperature mechanical property, friction property and hardness, and is one of the most advantageous ways for improving the mechanical property of magnesium alloy and realizing industrial application at present. However, an important factor limiting the rapid development of as-cast magnesium-based composites is that the added particulate reinforcement agglomerates at the grain boundaries, reducing the corrosion resistance of the material, resulting in a composite that is more susceptible to corrosion than the matrix alloy. Surface modification studies of magnesium-based composites are particularly important because the corrosion behavior begins at the surface of the component. The Laser Surface Remelting (LSR) process irradiates the metal surface with laser beam with high energy density to make the surface layer with certain thickness melt instantaneously, and then the heat transfer and cooling of the base member itself are used to solidify the molten pool fast, so as to improve the surface structure of the material and the toughness and corrosion resistance of the material surface. However, the effect of different LSR processes on the dispersion of particles in the molten pool is different, so that the effect on the mechanical properties is also different, and finally the use of the product is affected. The quantitative relation between the LSR technology and the physical phenomenon in the LSR process is blindly found by experimental means, a large number of experiments mean a large number of trial and error, a large number of manpower, material resources and financial resources are consumed, energy conservation and emission reduction can not be achieved, and the concept is not consistent with the concept of green manufacturing. With the development of computer technology, numerical simulation is becoming important as an effective means for researching the solidification process of metals. The quantitative or qualitative analysis of a series of physical phenomena such as heat, mass, momentum and particle transmission in the nonlinear unsteady state solidification process can be carried out through numerical simulation, and the obtained simulation result has a key guiding effect on process development and optimization. The quantitative relation between the process parameters and the formation of the molten pool can be established in a short time through numerical simulation, so that the research and development period is shortened. Although a great deal of numerical modeling research has focused on the evolution of the molten pool during LSR, there are still some problems. The main reason is that LSR processes involve high temperature gradients and high cold speeds, which are typical non-equilibrium solidification processes, and the description of which cannot use equilibrium phase diagram data, whereas phase diagram data (liquidus and eutectic reaction temperatures) for non-equilibrium solidification processes are scarce. The viscosity of the magnesium alloy molten metal added with the particles is obviously changed, but the change curve of the viscosity of the composite material with temperature is lacking at present. Therefore, the developed numerical simulation method for particle dispersion in a molten pool of the laser surface remelting particle reinforced magnesium-based composite material is necessary to be closely related with experimental characterization data. In summary, the particle dispersion in the process of the particle reinforced magnesium matrix composite LSR cannot be predicted accurately at present, so that the method has important significance for the research on particle dispersion prediction of the laser surface remelting particle reinforced magnesium matrix composite, and can provide n