Interface Characteristics Of Element Doped Mg Matrix And Its Precipitated Phase

Magnesium alloys are widely used in aerospace,automotive,electronics and other fields because of their light weight,good casting properties and heat resistance.Mg-Sn alloy has excellent precipitation hardening effect,significant high temperature creep resistance,and the aging strengthening effect.Mg-Zn-Sn alloy changes the fatigue limit,enhances the creep resistance and corrosion resistance of magnesium alloy.These two alloys are favored because of their low price and good performance.The interfaces doped with element of Mg-Sn alloy and Mg-Sn-Zn alloy were studied by first-principles method.The bonding strength and electronic structure characteristics of interface doped with different group elements of Mg-Sn alloy and Mg-Sn-Zn alloy were discussed.For the most stable interface,the electronic structural characteristics of the interface were analyzed by the density of states,the crystal orbital hamilton populations and the differential charge density,and the mechanism of stability improvement of Mg（0001）/Mg₂Sn（022）interface,Mg Zn（001）/Mg（0001）/Mg₂Sn（001）interface and Mg Zn（001）/Mg（0001）-Al/Mg₂Sn（001）interface were investigated.The effect of element doping on the properties of the alloy was explained from the atomic scale and electronic level.The interface adhesion energy is discussed for the interface with Al element doped of Mg/Mg₂Sn with different orientations.The stability of the interface was enhanced with Al element doped at the Mg termination position V,Sn termination position IV and V of Mg（0001）/Mg₂Sn（001）interface,the Mg termination position V,Sn termination position IV and V of Mg（0001）/Mg₂Sn（001）interface,and the Mg termination position VI,Sn termination position III,V,VI and VII.It is worth noting that position IV is easier to be doped than others for Mg（0001）/Mg₂Sn（022）doping Al element,and the interface energy of Al element doped to this position is reduced by 0.007e V/?².The electronic structure analysis shows that there is a significant interaction between the s orbital of Al and p orbital of Sn with doping Al element at position IV.The interface adhesion energy was discussed for the Mg（0001）/Mg₂Sn（022）interface with doping 3d and 4d transition group elements at the position IV of the Mg layer.It is found that the adhesion energies of interface with 3d group Fe element and 4d group Ru element doped to the position IV are higher than that with other 3d and 4d group elements doped.In addition,the change of bond length between atoms at the interface shows that the shorter the bond length between atoms,the more stable the interface.The Bader charge analysis of the atoms at the interface shows that Mg loses charge,while Sn and 20 transition elements obtained charge.The results of differential charge density analysis show that Mg atoms transfer more charge to Fe and Ru atoms at the interface,and part of the charge is transferred from Fe and Ru to Sn atoms,thus forms a charge sharing area at the interface and enhances the interaction between atoms,which leads to the higher stability of Fe and Ru atom doped interface.After convergence test,the optimal interface structure of Mg Zn（001）/Mg（0001）/Mg₂Sn（001）interface and Mg Zn（001）/Mg（0001）-Al/Mg₂Sn（001）were obtained.The interface bonding strength and the electronic structure characteristics at the interface with transition group elements were analyzed.The results show that the doping of 3d Cu,Zn and 4d Pd,Ag,Cd is not conducive to improving the stability of Mg Zn（001）/Mg（0001）/Mg₂Sn（001）interface.Ti and Zr element doping can significantly improve the bonding strength of Mg Zn（001）/Mg（0001）-Al/Mg₂Sn（001）interface,but Cr element doping is not conducive to improving the stability of the interface.The smaller the atomic bond length of the interface of Mg Zn（001）/Mg（0001）/Mg₂Sn（001）and Mg Zn（001）/Mg（0001）-Al/Mg₂Sn（001）,the more stable the interface.By comparing the changes of the adhesion energy of the Mg Zn（001）/Mg（0001）-Al/Mg₂Sn（001）interface and Mg Zn（001）/Mg（0001）-Al/Mg₂Sn（001）interfaces before and after Pd element doping,it is found that when Pd element is doped to the Mg Zn（001）/Mg（0001）-Al/Mg₂Sn（001）interface,this element becomes an element beneficial to the interface stability,which is mainly due to the enhanced covalent interaction between Al-Mg and Pd elements and surrounding atoms.The hybridization between Al-s orbital and Pd-s orbital strengthens the bonding strength of the interface.