Atomic cluster structures, phase stability and physicochemical properties of binary Mg-X (X= Ag, Al, Ba, Ca, Gd, Sn, Y and Zn) alloys from ab-initio calculations

Both structural and physicochemical properties of binary Mg-X (X = Ag, Al, Ba, Ca, Gd, Sn, Y, Zn) intermetallics were studied by performing ab-initio calculations. It was shown that except for Mg-Zn and Mg-Ba alloys, the mass density of the other Mg-X intermetallics changed linearly as the X-content. The local atomic structural features of Mg-X alloys could be well represented by the characteristic principal clusters, which denote the short-range-order structure of the Mg-X alloys. The coordination number (CN) of these atomic clusters changed in-between 8 and 16, and most were 12 and 14. The structural stability of Mg-Al, Mg-Ba, Mg-Ag, Mg-Ca, Mg-Sn, Mg-Y and Mg-Gd intermetallics increased as the solute content, while that of Mg-Zn intermetallics decreased as the Zn-content. For each Mg-X alloy system, MgAl2, MgAg3, Mg17Ba2, Mg2Zn11, MgGd and MgY intermetallics had larger elastic moduli and higher hardness than the others. Besides, MgAg3 and MgZn2 exhibited better plasticity among these Mg-X intermetallics, as reflected by the Poisson ratio and Pugh ratio. All of these Mg-X intermetallics were both thermodynamically and mechanically stable phases, and exhibited conductive metallic features based on the band structures and density of states.