Phase Field Method Simulation To Study The Effect Of Second Phase Particles On The Microstructure Of AZ31 Magnesium Alloy

With the growing demand for lightweight and high-strength structural materials,magnesium alloys have gradually become a focus of attention.It has been found that the comprehensive mechanical properties of magnesium alloys can be effectively improved by precise modulation of their microstructures.In view of the current commercial application context,AZ31 magnesium alloy was selected as the study material in this study.In order to improve the mechanical properties of AZ31 magnesium alloy,this study used simulations to explore fine grain strengthening through the introduction of second phase particles,which provided theoretical guidance on microstructure design for experimental studies in order to select the methods of external incorporation and in-situ synthesis of second phase particles.Compared with other methods,the phase field method shows significant superiority in investigating the problem of particle fine grain strengthening.Therefore,in this study,a modified multi-order parametric phase field model is used and the physical significance of each parameter is clarified to realize the simulation of AZ31 magnesium alloy in real time and space.The phase field model was used to simulate and analyze the microstructure change process of the material.By introducing different particle volume fraction,size,shape,arrangement direction,length-diameter ratio,and mixed particles,the effect on the microstructure of the matrix produced by annealing at 350°C for 100 min was simulated and studied.And the reliability of the model was proved against the experimental data.By analyzing the microstructure of AZ31 magnesium alloy containing second phase particles obtained from the simulation,it was concluded that:the higher the volume fraction of second phase particles with a certain size,the stronger the pinning effect on the grain boundaries,and the smaller the average grain size when the grains reach a stable state.It is also found that there is a critical value of the volume fraction of the second-phase particles in the nail-binding effect,as follows:when the volume fraction of the second-phase particles f=5%,the corresponding maximum critical size is r_max=6.5μm,and there is no minimum critical size.And the critical value increases with the increase of the second phase particle volume fraction.The larger the particle size,the weaker the pinning effect on the grain boundaries and the corresponding larger the average grain size when the grains reach a stable state,for a certain volume fraction of second phase particles with particle size at the micron level.Further study found that there is a critical value of the particle size on the nail-binding effect,as shown by the maximum critical volume fraction f_max=20%and the minimum critical volume fraction f_min=0.25%for the second phase particle size r=1.0μm.And the value of the maximum critical size value increases with the increase of the second phase particle volume fraction.When the volume fraction of the second phase particles is fixed,the effect on the grain growth is as follows:elliptical particles≈rod-shaped particles>round particles.It is also found that when the volume fraction,shape and size of the second phase particles are fixed,the arrangement direction of the non-equiaxial particles has no substantial effect on the grain growth.The larger the aspect ratio of non-equiaxial particles,the stronger the inhibitory effect on grain growth and the stronger the pinning effect on grain boundaries.The effect of mixed second-phase particles on AZ31 magnesium alloy is shown as follows:the same volume fraction of round particles f₁=f₂=5%,size r₁=2.0μm,r₂=1.0μm respectively mixed into AZ31 magnesium alloy,compared with round particles f=10%,r=1μm and round particles f=10%,r=2μm,in terms of grain refinement effect f=10%,r=2μm<mixed case<f=10%,r=1μm;the same volume fraction of round,elliptical,rod The same volume fraction of round,elliptical,and rod-shaped particles were mixed into AZ31 magnesium alloy,and the effect of grain refinement was elliptical+rod-shaped>elliptical+round≈rod-shaped+round.According to the comprehensive analysis,the microstructure evolution pattern of AZ31magnesium alloy obtained from the field simulation is consistent with the theoretical prediction of Zener’s formula.The simulation results of this study provide an important academic reference for the in-depth investigation of the mechanism and law of the influence of the second-phase particles on grain growth,as well as an important reference for the precise control of the second-phase particles to refine AZ31 grains and material properties in experiments.