Effect Of Second Phase Particles On Grain Growth In AZ31 Studied By Three-Dimensional Phase-Field Simulations

Magnesium Alloy as the light-weight structural materials has been paid much attention in recent years because of their excellent properties such as high strength rate and excellent castability.AZ31 alloy which is one of the widely used commercial deformation magnesium alloys has been chosen as simulation sample in the research.For the solubility of A1 and other elements in magnesium alloy is low,the effect of solution and aging strengthening is not good.Therefore,we explore a potential way to improve mechanical properties of AZ31 alloy by refining grain size through introducing second-phase particles.A phase field model method is a convenient and flexible approach to explore this problem.However,there is subtle differences between two-dimensional and three-dimensional phase field model to simulate the process of grain growth,and there were few reports about this distinction.Therefore based on the previous 2D code,the simulation of grain growth with second-phase particle effect in three dimensions has been implemented by parallel programming in a high-performance computer cluster.We found that the 2-D simulation and 3-D simulation reach the same conclusions with an acceptable fluctuation,and the particles strongly affect the mobility of grain boundaries.The relationship of steady grain radius and average particle radius and particle fraction obeyed the Zener pinning low Rlim/r = b/fn at n=0.467,b=1.44 in 2D case and at n=0.398,b=0.584 in 3D case,which indicates 3-D grain structures,the pinning effect is a bit different from that observed in 2-D simulations.This results were in agreement with the theoretical results.The grain size distribution agrees with lognormal distribution in two case.For the grain size statistics method,we compared the sections method with volume method,then we found that sections method results in fluctuant date,and volume method sections method is more accurate.Therefore,we suggest using volume method to statistic analysis.The simulation results show that the rod-shaped particles exhibit the better ability to hinder growth than spherical particles,and the one orientation distribution rod-shaped particles exhibit the better pinning effect than random orientation distribution.At a constant particle volume fraction,there is a critical size of 1.2?m of second-phase particles during the grain growth of AZ31 Mg alloy.If the particle size is smaller than the critical size,large particles will strongly hinder grain growth;in contrast,if the size is larger than the critical size,large particles will exhibit a weaker hindering effect than small particles.The grain growth rate is affected by the volume fraction of second-phase particle and the facet number of this grain.The grain growth rate is faster when the facet number is more at low fraction of the second-phase particles,whereas it is slower when the facet is more at high fraction of the particles.The possibility of the five-facet grain is the highest at low fraction of the second-phase particles,while the possibility of the four-facet grain is the highest at high fraction of the particles.