Phase Field Simulation Of Dendrite Growth In Solidification Process Of Aluminum Alloy Welding Pool

The advantages of aluminum alloy include its high specific strength,good formability and corrosion resistance.It is widely used in high-speed trains,aerospace,ships and other fields.Most aluminum alloy structures need to be welded in production,and the properties of welded joints are often lower than that of base metal,especially for aluminum alloy fusion welding process.It is very important to study the solidification process and microstructure evolution of aluminum alloy weld pool.Acquiring knowledge regarding these aspects can help to reveal the cause of weld inhomogeneity and control the microstructure.The study of microstructure is beneficial in cost saving and the provision of the theoretical basis for the actual welding process,which is facilitated by computer simulation.In this research,the phase field method was used to simulate the growth process of columnar and equiaxed grains in Al-Mg alloy under different conditions by calculating the ordered parameter concentration field and disordered parameter phase field.This research simulated the effects of different pulling speeds,temperature gradients and anisotropy coefficients on the morphology of columnar dendrite growth and solute concentration distribution of Al-Mg alloy.It also analyzed the distributions of concentration field under three kinds of dendrite growth modes.The results show that the pulling speed affects the width of primary dendrites and the number of primary dendrites in a given area,and the solute concentration in the liquid phase is changed.The faster the pulling speed,the higher the solute concentration.The temperature gradient has an important influence on the growth distance of the primary dendrite and enrichment degree of the corresponding concentration when grown to the same position.The anisotropy coefficient changes the morphology of the primary dendrite but it does not change the final solute concentration value,nor does it affect the growth rate of dendrites.Different dendrite growth methods cause different degrees of solute segregation.The solubility of dendrites is higher,the concentration of cellular dendrites is second,and the concentration of planar crystals is the lowest,which is at the growth interface.It can be seen that the concentration values of the three of them are arranged in the order of the lowest dendritic crystals,followed by cellular dendrites,and the highest concentration values of planar crystals.This research also simulated the growth of equiaxed crystals and observed the morphology and solute concentration distribution.The influencing factors were the anisotropy coefficient,the initial crystal nucleus position,the number of nuclei,and the cooling rate.The results show that the anisotropy coefficient affects the number and development degree of secondary dendrites.The position of initial crystal nucleus changes the dendrite profile and solute enrichment degree.The number of initial crystal nuclei affects the morphology of primary dendrites and the time of coarsening and fusion between secondary dendrites.The cooling rate not only changes the growth rate of dendrite but also affects the inhomogeneity of solute in dendrite.