Study And Calculation On Stacking Fault Energy Of Magnesium Alloys Based On Molecular Dynamics

Magnesium alloys are the lightweight structural metal materials with superior potential.However,magnesium and its alloys exbit low ductility at room temperature due to close-packed hexagonal structure and insufficience of slip systems limit the application in more fields.The capability of plastic deformation in magnesium alloy is related to microscopic deformation mechanism such as dislocation glide,twinning and so on.Therefore,understanding the deformation mechanism can provide new insights into improving ductility of magnesium alloys.Stacking fault energy is a fundamental property to explain the shear behavior in metal crystal,which has long been a question of great interest in microscopic deformation of magnesium alloy.Moreover,the change of temperature and solute concentration are important parameters in the actual processing and composition design,but were less studied in previous research because of limited calculation method.This study uses molecular dynamics to measure the generalized stacking fault energy in Mg-Al,Mg-Zn and Mg-Y alloys crystal models with random solute concentrations are 0³ at.%,and the interaction between the atoms is described by 2NN MEAM?the second nearest neighbor modified embedded-atom method?.The results of four slip systems,which are{0001}<112?0>,{0001}<101?0>,{101?0}<112?0>and{112?2}<112?3>respectively,have been linear fitting to search the effect of composition and temperature on stacking fault energy,as well as the contact between microscopic plastic deformation and stacking fault energy.Moreover,in the present study?₁,?₂,?₁^T and?₂^T are defined to reflect the activation trendency of prismatic and pyramidal slip compared to basal slip.The calculation results of the generalized stacking fault energy at 0 K are basically consistent with the previous report by first-principle method,in addition,the error and correlation coefficient of the results at each temperature are within a reasonable range.Therefore,it can be considered that the calculation by molecular dynamics method can appropriately reflect the variation of the stacking energy of magnesium alloy with temperature and solute concentration.The addition of Al,Zn and Y can decrease the stacking fault energy in{0001}<112?0>and{101?0}<112?0>slip systems at each temperature.With the increasing of Al solute concentration,the I₂ stable stacking fault energy decrease,while the Zn and Y can increase I₂ stable stacking fault energy,and the influence of Zn is more effective.The addition of Al and Zn in magnesium can decrease the unstable stacking fault energy in second order pyramidal plane while the addition of Y can increase it slightly.Elevated temperature can decrease unstable stacking fault energy in different slip systems strongly,but it has little effect on stable stacking fault energy.Based on the previous literatures on the plastic deformation behavior of Mg-Al,Mg-Zn and Mg-Y alloys and the calculation results of generalized stacking fault energy,it is considered that the micropic deformation mode of magnesium alloy is not depend on individual slip system solely.The tendency of the non-base slip is determined by the ratio of between stable and unstable stack fault energy of different slip systems.By calculating the newly defined parameters?₁,?₂,?₁^T and?₂^T,which are used to reflect effects of the change of solute concentration or temperature on non-basal slip activity in magnesium alloys,we can found that elevated Y or Zn solute concentration would improve the possibility of activationg non-basal slip,and the rising temperature is the most effective in promoting non-basal slip.The Mg-Y alloy has a higher non-basal dislocation glide tendency among the three alloys,and Mg-Zn alloy is slightly lower than the Mg-Y alloy,but stronger than Mg-Al alloy.