First Principle Study On Structure And Properties Of Al, Zn And Cd Doping Mg-Li Phase Interface

To date, because of the remarkable lightweight characteristics of Mg-Li alloy, a superior performance of Mg-Li alloy such as low-density and good quality, has been paid attention to and a vast amount of research work have been done to improve it, with the development of science and technology. Low intensity and corrosion resistance of Mg-Li alloy limit its widespread applications. As is well-known, alloying is one of the effective methods to improve the performance of alloys. The first principle calculation, based on the density functional theory (DFT) quantum mechanics, absolutely depends on the material, quantity and spatial arrangement and discuss the energetics and structural properties on the electron level, without any empirical parameters. So the materials simulation and development is more directional, forward-looking, to help original innovation and research efficiency. In terms of these advantages, the first principle calculation based on the density functional theory (DFT) and ultrasoft pseudopotential plane wave method has been applied on the research of the rupture strength of single-phase and multiphase Al, Zn and Cd doping Mg-Li phase interface and the twinning energy of Al existing in β-Li twinning structure. The main contents are as follows.(1) The structural optimization and thermodynamic performance analysis show that the structural stability of a-Mg/β-Li, a-Mg(Al), a-Mg(Zn), a-Mg(Cd), P-Li(Al), β-Li(Zn) and β-Li(Cd), the system with Al, Zn and Cd solid solution, is more stable.(2) The calculation results of density of rupture strength suggest that Al more easily dissolved into a-Mg phase, and enhancement of the rupture strength is superior than that of a-Mg/β-Li phase interface. Zn and Cd can improve rupture strength by dissolving in grain and phase interface. Al and Zn/Zn and Cd co-doping can further improve the stability of the system and rupture strength.(3) The environment-sensitive embedding energy calculation results show that Zn and Cd can more easily segregate to the phase interface than Al.(4) Analyses of the density of states reveal that the properties modify mainly attribute to the contribution by3p and3s states of Al, the new peak of3d states of Zn, Cd and the hybridization between Mg-2p and Li-2s at the Fermi level.(5) Al solid solution in the β-Li twinning structure results in the increase of twinning energy. The twinning energy of Al substituting a Mg atom is larger than that of substituting a Li atom. The more Al substitute Mg, the larger twin energy, the replacement of the same number of different atoms, twin energy can be changed the single Mg atoms than substitution of Mg and Li atom largely.