Study On The Influence Of Differential Phase Electromagnetic Field And Mould Structure On Macroscopic Physical Fields

Magnesium alloys have wide application prospects in aerospace,military,3C products and other fields due to their some advantages,for example,low density,high specific strength,and recyclability.The preparation of fine-grained and homogeneous billets is the prerequisite largescale application of wrought magnesium alloy.However,magnesium alloy itself have some disadvantages,such as poor thermal conductivity,easily oxidized combustion and so on,the magnesium alloy billets produced by conventional semi-continuous casting have some disadvantages,such as coarse grains,serious segregation and poor surface quality,which seriously affect subsequent deformation and materials properties.Based on electromagnetic induction principle,Lorentz force generated by low frequency electromagnetic casting technology promotes forced convection of melt,change the flow state,uniform the temperature field and solute field,which significantly refine solidification structure of magnesium alloy billets and decrease their difference,macrosegregation are suppressed and the surface quality is remarkably improved.But so far,some researches of low frequency electromagnetic casting mainly focuses on the influence of electromagnetic conditions,there is no systematic studies on the effects of mould and excitation coils structure and their combinations and matching relationships with electromagnetic fields types on macroscopic physical field and solidification behavior,which restrict precision design of hardware equipment and further optimization and improvement of action effect.Therefore,this paper carried out the numerical simulation studies of electromagnetic mould,excitation coils structure and their combinations,as well as electromagnetic types and parameters on macro-physical field of magnesium alloy electromagnetic casting,which provide some basic data for optimized design of magnesium alloy electromagnetic casting mould and improvement of technological effects.This paper takes the AZ80 magnesium alloy billets with a diameter of 300 mm as the object,study the effect laws of electromagnetic mould,excitation coils structure and their combination,and single-phase pulsed magnetic field and differential phase pulsed magnetic field on macro-physical field such as electromagnetic field,flow field and temperature field by the method of numerical simulation.Through the numerical simulation of electromagnetic mould structure on magnetic field distribution,the magnetic flux density and Lorentz force distribution laws of different widththickness ratio of coil cross-section,coil turns,internal sleeve thickness and distance between internal sleeve and coil under single pulsed magnetic field,different coils spacing under differential phase pulsed magnetic field were obtained.The research results indicate that the maximum magnetic flux and Lorentz force occur when the coil cross-section is square.Magnetic flux density and Lorentz force increase linearly when coil turns increase,and the two increase when the internal sleeve thickness and distance between internal sleeve and coil decrease,the best case of axial magnetic field distribution uniformity is 20 mm?30 mm under differential phase pulsed magnetic field.By studying the Lorentz force,melt flow and temperature field under conventional semicontinuous casting,single phase and differential phase electromagnetic casting,the research results indicates that compared with conventional semi-continuous casting,the appearance of single-phase and differential phase pulsed magnetic field can enhance the forced convection,change the flow state of melt,and the melt velocity increases significantly and exhibits periodic changes to produce an oscillating effect.At the same time,the cooling rate of melt accelerate,the temperature field distribution become more uniform and sump depth reduces.The maximum z component of Lorentz force,melt velocity and fluctuation amplitudes under differential phase pulsed magnetic field are 10 times higher than these under single-phase pulsed magnetic field,and the melt circulation is larger and forced convection action is stronger,temperature field of liquid sump become more homogeneous.The results of numerical simulations of macro-physics field under different current intensities,frequencies and duty cycles of differential phase pulsed magnetic field show that in the range of electromagnetic parameters of this study,when current intensity increases,magnetic flux density and Lorentz force increase linear,melt velocity and fluctuation amplitude also increase linear.In addition,the temperature field become more homogeneous and cooling rate become larger,at the same time,the liquid zone decrease and mushy zone increase.As the electromagnetic frequency increases,the maximum magnetic flux density,melt velocity and fluctuation amplitude decrease first and then increase,the temperature of melt center gradually increases with the increasing of frequency.When the duty cycle increases,the maximum magnetic flux density increases linear.On the contrary,Lorentz force decreases slightly,however,due to the increasing of pulsed action time,and melt velocity,fluctuation amplitude and temperature distribution are consistent with the changes under current intensity.