First Principles Calculation On Several Kinds Of Binary Phases Of Mg-Al Alloy

The structural stability, electronic structures, elastic properties of Mg17Al12, Mg2Sn,Al2Y, Al3Zr and Al2Sc phases have been investigated by Castep program based on thedensity functional theory, and compared toγ-Mg17Al12.The crystal structure parameters and lattice constants of Mg17Al12, Mg2Sn, Al2Y,Al3Zr and Al2Sc are very consistent with the literature values after geometry optimization.The results of heat of formation and cohesive energy show that the alloying capability andstructural stability of Mg2Sn, Al2Y, Al3Zr and Al2Sc phases are stronger than Mg17Al12phase.Various degrees of covalent hybrid are found in the density of states of Mg17Al12,Mg2Sn, Al2Y, Al3Zr and Al2Sc, and the covalent hybrid of Al3Zr is the strongest amongthese five phases. Electronic charge density difference contour plots show that the bondingbehaviors of Mg17Al12, Mg2Sn, Al2Y, Al3Zr and Al2Sc compounds are the combinations ofmetallic, covalent and ionic bonds, which lead to the structural stability. The results ofmulliken electronic populations show that the pecking order of ionic bonds is Al3Zr <Al2Sc<Mg17Al12<Al2Y <Mg2Sn. Mg17Al12has the strongest metallicity, and the Mg2Sn has theweakest metallicity.The three independent crystal elastic constants of Mg17Al12、Mg2Sn、Al2Y、Al3Zr andAl2Sc phases are calculated, bulk modulus, shear modulus, Young’s modulus, andPoisson’s ratio are predicted.The larger the B, G value,The ascending sequence of hardnessis Al3Zr> Al2Sc> Al2Y> Mg17Al12> Mg2Sn, which is found from the the B,G value analysisresult. The analysis results of G/B and Cauchy pressure jointly indicated that Mg2Sn, Al2Y,Al3Zr and Al2Sc phases are more brittle than Mg17Al12The conclusion which Mg17Al12hasthe best lateral deformation capacity and Al2Sc has the worst lateral deformation capacitycan be drawn after analyzing the Poisson ratio of Mg17Al12, Mg2Sn, Al2Y, Al3Zr and Al2Sc.