Mechanism Of Dislocation Slip And Phase Transition In Magnesium Alloy Based On Molecular Dynamics

Magnesium alloy is mainly used in aerospace,rail transit,electronic devices and medical services.It has a close packed hexagonal crystal structure and less slip system at room temperature.However,after mechanical deformation or temperature change,HCP → FCC phase transition will occur,which is considered to be one of the most important solid-solid phase transitions.In order to improve the strength and plasticity of magnesium alloys,it is necessary to study the nanostructure evolution during deformation.In particular,the specific dislocation evolution and phase transformation mechanism of magnesium alloys during compression have not been fully explored,and the dynamic evolution process of dislocation slip during phase transformation has not been fully solved.Therefore,the plastic deformation of magnesium alloy is studied based on molecular dynamics method.The evolution law of mechanical properties is obtained by combining molecular dynamics simulation and compression experiment.The changes of atomic structure are observed by Transmission Electron Microscope(TEM),and the dislocation slip and phase transformation mechanism are obtained.Through the molecular dynamics simulation of uniaxial compression of nano polycrystalline magnesium,the effects of temperature and strain rate were explored.The molecular dynamics simulation of uniaxial compression of block AZ31 magnesium alloy was carried out to explore the effects of solute atom,temperature,strain rate and loading direction on its uniaxial compression.The differences of mechanical behavior and micro evolution between Plane Strain Compression(PSC)and Uniaxial Compression(UC)are analyzed,and the effects of loading mode,temperature and strain rate on the compression behavior of AZ31 are explored.The molecular dynamics simulation of uniaxial compression of cylindrical AZ31 magnesium alloy was carried out,the corresponding uniaxial compression experiments were designed,the constitutive equations of magnesium alloy were fitted,the effects of temperature and strain rate on the mechanical behavior of cylindrical magnesium alloy were explored,and the solid-state phase transformation of magnesium alloy was deeply studied by TEM characterization experiment.By studying the evolution of mechanical behavior and microstructure of AZ31 Magnesium Alloy during dynamic compression,it is found that Shockley partial dislocation has an extremely important relationship with the solid-state phase transformation of magnesium alloy.The HCP → FCC phase transition of magnesium alloy occurs before the plastic stage.Shockley partial dislocation is accompanied by the whole phase transition process.One side of Shockley partial dislocation is the atom of HCP structure and the other side is the atom of FCC stacking fault.In the process of compression,the atoms of HCP structure first become the grain boundary of other structure,resulting in Shockley partial dislocation.When entering the yield stage,the other structure becomes FCC structure,forming FCC stacking fault.With the increase of temperature,the yield stress decreases and the grain refinement of magnesium alloy is restrained,which has no obvious effect on the phase transformation mechanism of magnesium alloy;With the increase of strain rate,the grain refinement of magnesium alloy intensifies and the atomic position changes violently.More dislocations are introduced to promote grain refinement,and the yield stress and yield strain increase.The increase of strain rate will change the phase transformation mechanism of AZ31 magnesium alloy.The sliding of Shockley partial dislocation at low strain rate will produce obvious HCP → FCC phase transformation,and the basal dislocation at high strain rate will make the amorphous phase transformation of HCP →OTHER more obvious,Cause continuous increase of stress.