First Principles Study Of The Effect Of Doping Element X On The Properties Of Al-Sc Alloys

Aluminum-based alloys are widely used in the nuclear,aerospace,automotive,and microelectronics industries due to their low density,high strength ratio,good toughness,and excellent electrical and thermal conductivity.Among the various alloying elements used in aluminum alloys,scandium stands out as an excellent microalloying element because of its beneficial effects of both specific rare earth metals and transition group metals,which can improve the overall strength,toughness,high temperature properties,corrosion resistance and weldability of aluminum alloys.However,scandium has a small maximum solid solution in α-Al and is brittle at room temperature in L1₂-Al₃ Sc.Scandium is reactive and not easy to prepare,and the high cost and difficulty of preparation directly affects the application of aluminumscandium alloys in structural materials and components.Therefore,it is important to explore other elements that can replace scandium.In this thesis,the effect of the doping element X on the solid solution degree of Sc in α-Al matrix is investigated using a first-principles calculation method based on density generalized function theory,and the structural stability,thermomechanical properties,elastomechanical properties and electronic structure of randomly structured Al-Sc-X alloys are systematically analyzed in this study,and the interfacial energy,adhesion work,fracture energy and electronic structure characteristics of Al/Al₃ Sc,Al/Al₃ Zr,Al₃Sc/ Al₃Sc/Al₃ Zr composite interfacial structures were investigated for their interfacial energy,adhesion work,fracture energy and electronic structure characteristics.The main contents are as follows:（1）The cell energies and lattice distortion rates of all metallic elements were calculated,from which nine doping elements X were selected: Li,Mg,Ti,V,Zr,Y,Hf,Nb and Ta.The interaction forces between the doping elements X and Sc atoms in the α-Al matrix were also calculated when the two atoms were at different proximity distances from each other.It is deduced that Ti,Li,Y,Hf,Zr and Ta as doping elements decrease the solid solution of Sc in α-Al matrix,and V,Nb and Mg as doping elements increase the solid solution of Sc in Al matrix.（2）The structural stability,thermodynamic properties,elastodynamic properties and electronic structure of nine random disordered structures of Al-Sc-X（X=Li,Mg,Ti,V,Zr,Y,Hf,Nb,Ta）were calculated.The results of the enthalpy of formation calculations show that the structures have good stability,the thermodynamic calculations show that the properties of the nine alloy systems have high dependence on temperature,and the elastodynamic calculations show that the ductility,modulus and anisotropy of these nine alloy structures have improved to different degrees compared with the Al-Sc binary structure.The electronic structure analysis also shows the bonding behavior between the atoms in the alloy system,and among the nine doping elements,Zr has the most obvious effect on the properties.（3）The three interfacial structures of Al/Al₃ Sc,Al/Al₃ Zr and Al₃Sc/Al₃ Zr were calculated.The interfacial energy,adhesion energy and fracture work were investigated,and the calculation results showed that the cracks would preferentially appear at the interface under the applied load.Analysis of the electronic structure of the interfacial bodies shows that the electronic contribution of Sc atoms near the interfacial layer plays an important role in bonding with Al atoms during the formation of the interface,and the metal bonds formed enhance the stability of the interfacial structure.