First-principles Study On Structure And Physical Properties Of Mg-Sn Based Alloys

Lightweight magnesium alloys have shock resistance,high specific strength,good heat transfer,good process performance and many other advantages?such as easy recycling?,so in the fields of aviation,aerospace,automotive industry,electronics,etc.,especially because of its light weight advantage.It is a material with ideal application prospects in the field of lightweight.At present,how to further improve the strength of magnesium alloys and develop high-performance heat-resistant magnesium alloys is a major task in the future,and alloying is the most effective and direct method to improve mechanical properties.In this paper,first-principles methods are used to study the effects of alloying elements Si,Ca,Sn,Sr,and La into magnesium on the structure,electronic structure,elastic properties and thermodynamic properties of magnesium.The structural,structural stability and elastic properties of Li_xMg₁₆Sn₈?x=0,1,2,3?phases.And the structure,electronic structure,elastic properties and thermodynamic properties of precipitated phases in Mg-Sn-Si-Ca?Sr?quaternary alloys are investigated,the structure,electronic structure,elastic properties and thermodynamic properties of lanthanum compounds precipitation in the Mg-Sn-Mn?Si?-La alloys are studied.Moreover,the effect of pressure on the structure,electronic structure,elasticity and thermal properties of Mg_xLa?x=1,2,3?compounds are investigated.The above parameters have important influences on the alloy properties,but it is difficult to explore their laws by experiments.The theoretical parameters can be obtained through this research,which will play a theoretical guiding role in the design,development and experiment of magnesium alloys.The conclusions of this study are as follows:?1?The structure,electronic structure,elastic properties and thermodynamic properties of magnesium-based solid solution Mg-R?R=Si,Ca,Sn,Sr,La?are calculated.When the alloy solid solubility is 2.77 at.%,Mg-R alloys are all metallic,ductile and stable.The solid solution of these alloy elements changes the ductility,the volume change resistance,shear deformation resistance and hardness of magnesium.The constant volume heat capacity and constant pressure heat capacity of each solid solution increase with increasing temperature,but the thermal conductivity of each solid solution decreases with the increase of temperature.?2?The crystal structure and elastic properties of Li_xMg₁₆Sn₈?x=0,1,2,3?are calculated.The alloying process of each phase of Li_xMg₁₆Sn₈?x=0,1,2,3?is easy to proceed and the structure is stable.The alloying ability and structural stability of Mg₂Sn are reduced due to the interstitial solid solution of Li,and the more the number of solid solution Li atoms,the weaker the alloying ability and structural stability.The volume deformation resistance,shear deformation resistance and hardness of Mg₂Sn continue to decrease with the increase in the number of Li solid solution atoms.Doping with Li makes Mg₂Sn change from brittleness to ductility,and the more Li atoms doped,the better the ductility of the alloy is.?3?The structure,electronic structure,mechanical properties and thermodynamic properties of the precipitated phases Mg₂Si,Mg₂Sn,Ca Mg Si and Mg Sn Sr in the Mg-Sn-Si-Ca?Sr?alloy system are calculated.The alloying ability increases in the order of Mg₂Si<Mg₂Sn<Ca Mg Si<Mg Sn Sr,the structural stability increases in the order of Mg₂Sn<Mg Sn Sr<Mg₂Si<Ca Mg Si.The physical nature of the four compounds with different properties was revealed by electronic structure.All compounds exhibit brittleness.Mg₂Sn,Ca Mg Si and Mg Sn Sr phases are all elastically anisotropic,while Mg₂Si phase is elastically isotropic.The entropy,constant volume heat capacity and constant pressure heat capacity of these four compounds increase with the increase of temperature.Thermal conductivity decreases with increasing temperature.The structure,electronic structure,mechanical properties and thermodynamic properties of Mg₁₇La₂,La₅Sn₃ and La₅Si₄ in the Mg-Sn-Mn?Si?-La alloy system are calculated.After adding Mn,Si and La elements to the Mg-Sn alloy,the structural stability of the alloy is improved because of the formation of intermetallic compounds La₅Si₄ and La₅Sn₃.The precipitation of La₅Si₄ hard reinforcing phase can improve the hardness of the alloy.Both La₅Si₄ and La₅Sn₃ exhibit ductility,while Mg₁₇La₂ is brittle.The volumetric deformation resistance and thermal conductivity of these three compounds decrease as the temperature increases,the thermal stability is better with increasing temperature.?4?The structural properties,density of states,elastic properties and thermodynamic properties of Mg_xLa?x=1,2,3?are calculated,and the effects of pressure on these properties are studied.These three compounds are mechanically stable at 0?30 GPa.All compounds are harder to compress with increasing pressure.The curves of total density of states under pressure illustrate the physical nature of the changes in the properties of the compounds.The volume deformation resistance of these compounds can be significantly improved with the increase of pressure,and the ductility of the compounds can be enhanced by increasing the pressure properly.At the same temperature,the bulk modulus,Gibbs free energy and Debye temperature of Mg_xLa?x=1,2,3?increase with the increase of pressure,and the heat capacity decreases with increasing pressure.