The Electronic Structure In The Dislocation Core And Magnetic Field Effect In The Al-Zn-Mg-Cu High Strength Aluminum Alloy

Al-Zn-Mg-Cu(7xxx series) high strength aluminum alloy is widely used in the fields of aerospace and transportation. The properties of dislocation and main reinforced phase have very important influences on the performance of the aluminum alloy. The quantum mechanics has been widely used in the researches on the material design and property. In this paper, the electronic structure of dislocation core in the Al-Zn-Mg-Cu high-strength aluminum alloy has been calculated by the first principles method based on density functional theory, and the influence of magnetic field on the electronic structure was investigated further. The results of calculation and analysis can be found as follows.When compared the dislocation-contained and the defect-free aluminum crystal, some results have been acquired. Firstly, as for the the density of states(DOS), the appearance of new peaks in DOS curve near the Fermi level indicates the rearrangement of electrons and the increment of electronic activity in dislocation core. Secondly, the electrons distribution in the dislocation-contained aluminum crystal is nonuniform. The nonuniform distribution of electrons will influence the distribution of alloying atoms in dislocation core. Thirdly, as for the spin polarization of electrons, the electron spin magnetic moment of adjacent atomic layers are opposite in the defect-free aluminum crystal at non-ground state, which demonstrates that the repulsive interaction between the adjacent atomic layers. While for the dislocation-contained aluminum crystal at nonground state, due to the same electron spin magnetic moment of atoms above the dislocation cores, the repulsive interaction will become stronger between the adjacent upper and lower atomic layers that are close to the dislocation cores. In the presence of magnetic field, the strong repulsive interaction between adjacent atomic layers will lead to the decrease of their interactions and the enhancement of mobility. In the macroscopic sense the plasticity of materials will be, therefore, increased.In defect-free aluminum crystal supercell that contains Mg Zn2, the bonding characteristic of main atoms was acquired on the basis of DOS and electrons distribution. The strongest bond between Mg Zn2 and Al is formed by the interaction of Mg Zn2 s, p, d hybrid state electrons with Al p state electrons. Moreover, for upper and lower adjacent Mg Zn2 and Al, the electron spin magnetic moment are opposite, which weaken the bond strength between them and facilitate the slip along the slipping plane in the presence of magnetic field. In the position of E=-0.6 e V, the ionic bond between Al and Mg Zn2 will transform from singlet state to triplet state, namely from stable to excited states. It further facilitates the slipping tendency of atomic layers and the enhancement of plasticity.In dislocation-contained aluminum crystal supercell that contains Mg Zn2, the bonding characteristic of main atoms was acquired on the basis of DOS. In the position of E=-0.6 e V, the chemical bond is formed between Mg Zn2 and Al, whose bonding way lie in the interaction of Mg Zn2 s, p, d hybrid state electrons with Al s or p state electrons. The p state electrons above fermi level cruise around of atoms and are not involved in bonding between atoms. As for the electrons distribution, it is found that electrons gather in dislocation core, and chemical bond is formed in there. Moreover, the electron spin magnetic moment tend to be same in dislocation core. This may be caused by p state electrons above fermi level. In the position of E=-0.6 e V, the strongest chemical bond between Mg Zn2 and Al will transform from singlet state to triplet state, namely from stable to excited states. These will also lead to easier sliding atomic layer.To sum up, in the dislocation core of Al-Zn-Mg-Cu high strength aluminum alloy, the electronic structure will change together with the enhancement of reactive activity of atoms. When the electrons spin is introduced to discuss the magnetic field effect, it is summarized that the electron spin magnetic moment will change towards the decrease of interaction between the adjacent atomic layers. The transformation is benefical to improve the slipping ability of atomic layers. The research result supports strongly the magentoplasticity in the quantum scale.