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First-Principles Research on the Electronic and Magnetic properties of MgZn_2 Phase

MgZn2 phase is the main reinforcement in the high strength-toughness aluminum alloy, such as Al-ZnMg-Cu(7××× series). These alloys can be strengthened by solution and aging heat treatment. The precipitation sequence is recognized as: supersaturated solute →GP area→metastable η′ phase→stable η(MgZn2) phase.Therefore, it is important to know the quantum behavior and phase formation mechanism of MgZn2. But till to now, the concerned research has been rarely reported. Besides, the magnetic property of MgZn2 is also important when the aluminum alloy is processed in the presence of magnetic field. By using the first principles method, the electronic and magnetic properties of MgZn2 were calculated and analyzd in detail. The computing results on the band structure and density of state demonstrates that Zn-Mgbond is generated through the interaction of two sp hybrid state, which are from Zn4s-4p hybridized orbit and Mg3s-3p hybridized orbit separately. Especially nearby the Fermi level an intense interaction takes place between the Zn4 p and Mg3 p orbits. The Mulliken population distribution computation illustrates that the overlapped population distribution of Zn1-Mgor Zn2-Mgalmost equals to zero. Here, it is noted that the Zn1 and Zn2just means the Zn atoms located individually at the edge and the interior of lattice. The calculation outcome of electron density shows that the electron density distribution of Mg-Zn has an obvious locality. Combining these results with the electronegativity difference of Mgand Zn, it is regarded that the Zn-Mgis polar covalent bond. The difference of Zn1-Mgbond and Zn2-Mgbond is that the contribution of Zn24 s orbit to the bond formation is higher than that of Zn14 s orbit in-10 ~-6 e V, the contribution of Zn14 s orbit to the bond formation is higher than that of Zn24 s orbit in 2 ~5 e V. The population distribution also demonstrates that the overlapped population of Zn1-Zn1is-1.15, which proves that the electrons are in the antibonding orbit; nevertheless, the population distribution of Zn2-Zn2 is 1.08 and the corresponding electrons are in the bonding orbital. The population distribution and electron density calculating results reveal that the Mg-Mgbond is covalent bond while the Zn1-Zn2 bond is metallic bond. Furthermore, the studies on the integrated spin density of state demonstrate that the MgZn2 phase shows paramagnetism, which stems mainly from the two unpaired electrons in the Zn1-Mgbond, and the paramagnetism of MgZn2 will make a magnetoplastic effect in Al-Zn-Mg-Cu(7××× series) high strength-toughness aluminum alloy in the presence of magnetic field.