Model Construction And Evolution Law Of Voids In Uniaxial Compression Of Single Crystal Magnesium

Magnesium alloy has good lightweight,machinability,corrosion resistance,shock absorption,dimensional stability and impact resistance.In the fields of computer,consumer electronic products,high-speed rail,medical rehabilitation equipment and so on,the application prospect is good and the potential is great.The crystal structure of magnesium alloy is a typical close packed hexagonal crystal,with few slip systems.The grains are not easy to yield macroscopically,but easy to produce large stress concentration at the grain boundary.On the macro level,it shows poor plastic deformation ability.On the micro level,the existence of micro defects(shrinkage cavity,micro crack)caused by the production or processing process is closely related to the main plastic deformation of the actual metal diffusion and fracture,and the strong crack affects many physical properties of the metal crystal.Therefore,it is necessary to study the effect of nano voids defects on the mechanical properties of magnesium alloy.With the continuous development and maturity of computer simulation technology,scientific research has made new breakthroughs in the micro field.Molecular dynamics(MD),as one of the most important simulation techniques,can simulate at the atomic scale,output the movement track data of atoms,and realize the dynamic tracking of material microstructure,which is very beneficial to the study of the effect of nano voids on the plastic deformation mechanism of magnesium alloy.Because the plastic mechanical behavior of single crystal of magnesium alloy is similar to that of single crystal of pure magnesium,a micro single crystal model of magnesium alloy is proposed to study the evolution of internal voids.In this paper,the molecular dynamics method is used to study the microstructure of single void and double voids single crystal models with different radius and size under c-axis compression,and the microstructure of double voids single crystal under different loading directions.The law of void change during the forming process is revealed and the deformation mechanismof the micro single crystal model is studied.Using ovito software to visualize different atomic structures,vacancy and gap atoms,dislocation and defect structures under different strains,and calculate the number of different atomic structures,radial distribution function and dislocation length under different strains.After statistical analysis of the data,the relevant discussion is carried out.The results show that:(1)To some extent,the existence of spherical voids can enhance the plasticity of magnesium single crystal.The size of the spherical void does not affect the properties of the compression model,but only the numerical value.The smaller the radius of the preformed spherical single void is,the larger the yield strength is,the less time and the less the deformation are required for the complete closure under c-axial compression.In the process of deformation,the atom energy around the void is high and the atom structure is easy to change.(2)The effect of the double voids arrangement on the plastic behavior,especially the yield strength,is obvious.When the double voids arrangement is parallel to the loading direction,the yield strength and the corresponding strain degree are the largest;when the double voids arrangement is perpendicular to the loading direction,the yield strength and the corresponding strain degree are the second;when the arrangement is 45° with the loading direction,the yield strength and the corresponding strain degree are the smallest.The analysis of radial distribution function and dislocation extraction algorithm also shows that the single crystal model with 45° arrangement with c axis has the strongest plastic deformation ability,and the single crystal model with 0° arrangement with c axis has the worst plastic deformation ability.(3)When the angle between the two voids and the three axes is 45°,the effect of the loading direction on the plastic behavior of the single crystal is obvious.The yield strength and the corresponding strain degree of the double voids magnesium single crystal are the largest when it is compressed along the[-12-10] crystal direction;the yield strength and the corresponding strain degree are the second when it is compressed along the [-1010] crystal direction,and the yield strength and the corresponding strain degree are the smallest along the[0001] crystal direction.The analysis of radial distribution function and dislocation extraction algorithm also shows that the plastic deformation ability of magnesium single crystal model is the strongest when it is compressed along the [-1010] crystal direction,and the worst when it is compressed along the[-12-10] crystal direction.