Study On Solidification Behavior And Active Mechanism Of Al-Pb Monotectic Alloys Under Magnetic Field

Al-Pb monotectic alloy material with high wear resistance,reliable bearing capacity and good self lubrication,and the metal material reserve is rich in resources,low price,is a kind of potential bearing material,and has high application value in industrial applications.But the physical and mechanical properties of this material is excellent only in the second phase of uniform distribution of alloy solidification structure in order to reflect the microstructure morphology of the alloy depends largely on the area of immiscible liquid-liquid phase separation and decomposition process.Therefore,controlling the solidification process of the alloy has become an important way to improve the properties of materials and develop new materials.Therefore,this paper selected the typical two element partial Al-Pb alloy as the research object,studied with and without gravity by means of numerical simulation and experimental study of the combination,with and without magnetic field,the magnetic field strength,alloy composition and temperature on the solidification zone of immiscible liquid-liquid phase separation and decomposition process and realize continuous observation of the phenomenon of dissolving area difficult to mix macro transport,from the point of view of dynamics analysis of solidification microstructure evolution.This paper establishes the mathematical model which can describe the second phase nucleation in the solidification process of difficult mixing zone,diffusional growth,Ostwald ripening,Marangoni migration,Stokes motion and Lorentz force and magnetizing force to suppress convection and other complex physical processes by the Euler-Euler method.Based on the computational fluid dynamics software CFD(Computational Fluid Dynamic),compiled calculation procedure through C++ mathematical linguistics,the second phase droplet density conservation equations and two-phase solute transport conservation equations.Proceed to the secondary development of partial differential equation and physical quantity,defined droplet density conservation equations and two-phase solute transport equations as the user defined scalar UDS(User Define Salar),defined U,Q,M,C,I,FL,Fs,FM1 and FM2 in momentum conservation equation,heat conservation equation,mass conservation equation,solute conservation equation and density conservation equations,as source item,defined all above source items in respective source macros and adopt C++ mathematical linguistics to compile through user-defined function UDF(User Define Function),based on the computational fluid dynamics software CFD(Computational Fluid Dynamic).Calculate and store the correlated variable needed call repeatedly in the numerical procedure and correlated variable needed to put out through user-defined memory UDM(UDM,User Define Memory).Make the second phase droplet density conservation equations,the unsteady state two phase heat transfer conservation equation,the momentum conservation equation,the mass transfer conservation equation and the solute transport conservation equation get the coupled solution in specific order,load the defined source item to respective conservation equation in counting process,get the distribution of temperature field,velocity field,concentration field,second phase volume fraction and second droplet size in difficult miscible area at different solidification time.Adopt the established comprehensive mathematical model and according to the specific numerical calculation procedure,study evolution process and distribution condition of temperature field,velocity field,concentration field,the second phase volume fraction and the mean diameter distribution in the solidification process of Al-Pb monotectic alloy miscibility gap at different conditions of gravity field,gravity free condition,IT magnetic field,10T magnetic field,different alloy composition and ambient temperature,analyzed the existing influence of solidification organization macro segregation in different physical field.The results show that the largest migration velocity of droplet reduced to 1.12%of the gravity condition and the largest average diameter of droplet reduced to 10.51%of the gravity condition after applying 1T steady-state magnetic field,1T steady-state magnetic field lower the movement velocity of droplet,minish the size of second phase droplet effectively,control the macrosegregation of solidification in certain degree.After applying 10T high magnetic fields,the movement velocity of second phase droplet reduced to 0.11%of the gravity condition,the largest average diameter of droplet reduced t0 19.1%,the largest average diameter of droplet is 32.55-39.6?m in the whole solidification,the respective physical field distribution present as more homogeneous centrosymmetric distribution in the whole solidification.Apply l0T high magnetic fields,control the variety of convection existing in melt obviously,change the force condition of second phase droplet,reduce the movement rate of the droplet,control the migration of second phase,impede the collision ripening between droplet,control the gravity settling of second phase droplet,minish the droplet size while minish distribution range of mean droplet diameters,improves the uniformity of droplet distribution in the matrix phase,and the effect of strong magnetic field is better than that of 1T magnetic field.Solidification experiment of Al-Pb monotectic alloy under the condition of with or without strong magnetic field was carried out in this paper.The results indicate that after the exertion of 10T superconducting strong magnetic field,the average diameter distribution of Pb-rich phase particles reduce from 2-25?m to 2-18?m.The frequency,that Pb-rich phase particles with the average diameter of 2-4?m appeared at the top of the sample,increased from 170 to over 4100.The frequency,that Pb-rich phase particles with the average diameter of 2-4?m appeared at the bottom of the sample,increased from 1700 to over 4100.The simulation results are compared and analyzed with the experimental results and the simulation results verified by others to verify the correctness of the numerical results and the mathematical model.The experimental results and simulation results show that 10T superconducting strong magnetic field has improved the nucleation of Pb-rich phase,effected the migration of Pb-rich phase particles,refined the size of Pb-rich phase particles,narrowed the distribution of average diameter of Pb-rich phase particles,and improved the macroscopic segregation of solidification effectively.