First-principles Study On The Effect Of Alloying Elements On The Properties Of Aluminum Alloy Materials

Because of its excellent performance,aluminum alloy is widely used in aviation,aerospace,automobile,machinery manufacturing,shipbuilding and chemical industry.But the heat resistance of aluminum alloys is unstable.At the same time,it is difficult to produce twins in aluminum alloy materials due to the high fault energy internal reasons,making,which largely limited their wider applications.It is difficult to obtain the thermal performance parameters of aluminum alloy through experiments,and obtain the twin structures in aluminum alloys under conventional experimental conditions.Therefore,it is difficult to study the thermodynamic and plastic deformation properties of aluminum alloy through experiments.With the development of Computational Materials Science and computing technology,we can solve this kind of problem well by computing means.With the development of Computing Materials Science and computing technology,we could solve this kind of problem well by computing means.In this paper,the effects of alloying elements on L12 phase,and the stacking fault and twin structures of bulk aluminum alloys are systematically studied by first-principles method based on density functional theory.First-principles calculations based on density functional theory(DFT)are used to calculate the thermodynamic properties(including the formation enthalpy H,Gibbs free energy F,entropy S,heat capacity Cv,thermal expansion coefficient a and Gruneisen parameter γ)of L12-Al3M(M=Er,Hf,Lu,Sc,Ti,Tm,Yb,Li,Mg,Zr)compounds systematically.The results show that the enthalpy of L12-A13M structure compounds is negative,and they are highly coherent with Al matrix(the maximum lattice mismatch is 6.27%),which indicates that L12-Al3M structure compounds can exist stably in Al matrix.The value of the note is,four kinds of big atoms Yb,Lu,Er and Tm(the atomic radius is 1.2 times more than that of Al atom)have positive effects on the thermal stability of Al alloy,the order of thermal stability is:A13Yb>Al3Lu>Al3Er>A13Tm>Al.The differential charge density diagram and Bader charge analysis show that the covalent bond between M atom and Al is easy to form,and the strong bond cooperation between Al-M bond provides a solid internal foundation for the thermal stability of Al3M structure.The effects of 11 kinds of binary clusters Er-Er,Hf-Hf,Li-Li,Mg-Mg,Sc-Sc,Si-Si,SrSr,Ti-Ti,Tm-Tm,Yb-Yb and Zr-Zr on stacking fault energy and twin boundary energy of aluminum alloys are studied by first-principles calculations.It is found that the second nearest neighbor occupation is the dominant occupation distribution of these clusters in the aluminum matrix.We calculate the interaction energies between the clusters and stacking faults/twin boundaries(SFs/TBs),and the relationship of the stacking fault energy(SFE)and twin boundary energy(TBE)with temperature and clusters’ concentration are obtained.It is found that due to the strong interaction energy between the binary clusters and SFs/TBs,the Sr-Sr,Er-Er,Tm-Tm,Yb-Yb,Zr-Zr clusters significantly reduce the SFEs and TBEs of aluminum alloys.At the same time,it is found that the interaction energies between the clusters and SFs/TBs show a quadratic polynomial relationship with doping atom radius.From the microscopic point of view,the differential charge density shows that Sr-Sr,Er-Er,Tm-Tm,Yb-Yb and Zr-Zr clusters produce obvious charge delocalization,which shows that these atoms are easy to bond with Al atoms.As a result,there is a large mutual attraction between clusters and the SFs/TBs,which lead the clusters to segregate near the SFs/TBs easily,and then reduce the SFE/TBE.In this paper,the effects of alloying elements on thermal stability of L12 phase,and the effects of clusters on SFs/TBs of bulk aluminum alloys have been systematically studied.It shows that some alloy elements can improve the thermal stability of aluminum alloy,which predicts a new way to improve the thermal stability of aluminum alloy theoretically,and the possibility of introducing twins into aluminum alloy.Our research provides a theoretical basis for optimizing alloy composition and selecting reasonable heat treatment,which have important practical significance in saving cost and reduce the period of experiment.