Effect Of Second Phase Particles On Grain Growth On ZK60 Mg Alloy Under Applied Stress By Phase Field Simulation

Magnesium alloy,which is the lightest metal structure material and has good mechanical properties,electromagnetic shielding ability,easy to recycle,and many other advantages,is widely used in the automotive,aerospace and 3C industry.However,lower strength is one of the key in the limitation of alloy application.One of the effective way to increase the strength is the grain size refinement caused by the pinning effect by the second phase particles in the alloy system.It is hard to study the effect of the stress and the second phase particles on the grain size and distribution quantitatively by traditional experimental method.In order to explore the mechanism of microstructure evolution,computational simulation is carried out for this study.In this study,based on the grain size refinement theory,ZK60,which is the high strength magnesium alloy,is chosen as the target alloy.In the industrial scale and real time-space condition,the effect of stress and second phase on the grain size and distribution has been studied.Meanwhile the ZK60 alloy system features has also been studied through the comparison of AZ31and ZK60 alloy system.In this study a phase field model suitable for ZK60 system grain growth has been set up,meanwhile stress and second phase items are coupled into the model.With the parameters choosing rules and partial experimental data;the simulation of microstructure evolution of ZK60 alloy system has been realized in real industrial scale and time-space condition.The grain size and distribution have been studied at 300? within 0-150 min when the second phase particles Mg3Zn6Y is 0%?2.5%and size is 0?0.6?m under stress range of 0?1000MPa.The simulation shows that the stress has a promoting effect on the increase of average grainsize.In ZK60 system,when the stress increases from 0MPa to 1000MPa,the grain size has a 63.8%increase which is from 11.28?m to 18.48?m.Under the same condition in AZ31 system,the average grain size increases from 24?m to 35?m,which has an increase of 45.8%.The difference of grain size variation means that stress has a more important effect in ZK60 system.The content of second phases also has a promoting effect on the refinement of grain size in ZK60 system.When the second phase particles increases from 0%to 2.5%and annealing time is 90min,the average grain size,which decreases from15.0?m to 9.9?m,has a 34.0%decrease.Compared with the AZ31 system whose grain size decreases from 12.8?m to 10.7?m in the same condition,it can be concluded that the second phase particles has a more important effect on the ZK60 system.When the second phase is 1.25%and the size changes from 0.1?m to 0.6?m,annealing time is 50 minutes,the average grain size increases first and then decreases and reaches the best level with a critical particle size of 0.2?m to 0.5?m.The critical particle size in AZ31 system is 0.5?m to 0.8p,m,which means ZK60 is more sensitive to the second phase particles compared with AZ31 system.The increase of second particles has the promoting effect on the refinement of grain size under stress.In the ZK60 system,the average grain size under stress of 200Mpa decreased from 24.1 ?m to 13.?m,which decreased by 42.3%compared with 36.1%when the stress is 0MPaThis indicates that the stress is more important on the grain refinement.Furthermore effect of the second particles size is carried on in this study.It is found that average grain size increases first and then decreases when the size of second particles increase from 0.1?m to 0.6?m under a stress of 200MPa and 150 min annealing time.The results show that the best refining effect occurred when the second phase size is 0.2?m to 0.5?m,which is same as the condition without stress.Above all,at 300?,when the second phase particles Mg3Zn6Y content is 1%?2.5%,whoses size is 0.2?0.5?m,external stress is 200MPa,annealing time is 100?120minutes,ZK60 magnesium alloy with Y adding has the optimal grain size and distribution.