Study On The Change Law Of Microstructure And Properties Of Magnesium Single Crystal Based On Molecular Dynamics

Magnesium,as a kind of high quality metal material,is widely used in various fields.However,due to its dense hexagonal structure,its application scope is greatly limited.Therefore,it has become an important project to study the properties of magnesium.At present,most researchers used experimental methods to study the mechanical properties of the magnesium alloy,which can only study magnesium alloys from a macro perspective,but fail to study the changes of internal microstructure and properties of magnesium single crystal under different loading conditions from a nano-perspective.Even if the experiment can be realized,it is difficult and costly due to various reasons.Therefore,it is very necessary to use computer simulation technology to simulate the single crystal of magnesium,and it is also a method to conform to the research trend.Among them,molecular dynamics simulation is a more practical method.In this paper,the molecular dynamics simulation method was used to carry out the simulation experiment of the tensile rate of magnesium single crystal at 0.01s^-1at different temperatures,simulation experiment of tensile strength of magnesium single crystal at 300K under different tensile rates and0.01s^-1rate under different loading directions.Through the analysis of stress change,potential energy change,crystal structure transformation,dislocation line change,etc.,the influence of different loading conditions on the properties of magnesium single crystal is discussed.The results are as follows:(1)When magnesium single crystal is loaded at different temperatures,with the increase of temperature,the peak value of tensile strength of magnesium single crystal decreases,and the corresponding strain value when the peak point is generated gradually decreases with the increase of temperature.Before the stress peak,HCP first transforms into other structure without dislocation.After the stress peak,FCC and BCC structures appear and dislocation occurs at the same time.Among them,the main dislocations are1/3<-1100>dislocation and unknown structure dislocation.The transformation of crystal structure and the generation of dislocation are about 0.45%of the strain value of the hysteresis stress peak point.The transformation of crystal structure and the generation of dislocation also occur in advance with the rise of temperature.(2)At different tensile rates,the elastic modulus of magnesium single crystal does not change.With the increase of tensile rate,the corresponding stress peak value gradually increases,and the corresponding strain value also increases.The emergence of the dislocation line generally lags behind the peak stress point.With the increase of the tensile rate,the lag strain becomes larger and larger.The first and dominant dislocations are 1/3<-1100>incomplete dislocation and unknown dislocation,followed by 1/3<11-20>full dislocation.At the peak point,the crystal structure begins to transform from HCP structure to other structure,and after the peak point,BCC and FCC structures begin to appear.With the increase of tensile rate,the corresponding strain when BCC and FCC appear gradually increases.(3)Under different loading directions,where X[-12-10]crystal orientation,Y[-1010]crystal orientation and Z[0001]crystal orientation,the corresponding strain values when generating dislocation lines are different.When the loading direction of X,the corresponding strain value is the smallest,followed by the loading direction of Y,and the strain value corresponding to Z direction loading is the largest.The distribution law of the generated dislocation lines is also different from the conversion and distribution of the crystal structure.When loading in the X direction,the distribution of the dislocation lines is regular and the majority of the crystal structure is transformed from HCP structure to BCC structure,accompanied by some FCC structure and unknown structure.In the Y loading direction,the overall distribution of dislocation lines is irregular and the local distribution is regular.The crystal structure of HCP is mainly converted to BCC structure and unknown structure,accompanied by a small amount of FCC structure.When loading in Z direction,the overall distribution of dislocation lines is irregular,while the distribution of a few local dislocations is regular.The crystal structure is mainly transformed from HCP structure to unknown structure,accompanied by a small number of BCC structure and FCC structure.The number and length of dislocation lines are different.When loading in the direction of X,the number of dislocation lines is small but short.In the Y loading direction,the number of dislocation lines is large and the length is long,accompanied by a small amount of interleavings.In the loading direction of Z,the number of dislocation lines is large and the length becomes longer.Meanwhile,a large number of dislocation lines are interwoven together.The types generated by dislocation lines are basically the same.The dominant role is1/3<-1100>dislocation and unknown structure dislocation,and the number of1/3<-1100>slocation is greater than the number of unknown structure dislocation.