Icosahedron-forming ability of MgZn alloys studied by molecular dynamics simulations

A molecular dynamics simulation is performed to investigate the icosahedron in MgxZn(100-x) alloys during solidification at the cooling rate of 1 × 1011 K/s. It is found that with x increase the icosahedron-forming ability (IFA) of MgxZn(100-x) increases first, and then decrease as x > 50; and Mg90Zn10 can crystallize at this cooling rate. Consistent with the geometry, the smaller Zn atoms are usually at the centre of icosahedra, and the maximal fraction of Mg atoms in neighbours of Zn-centred icosahedra is just the critical value with which such icosahedra get the highest packing density. Further analysis reveals that the stronger IFA of Zn-rich alloys is closely related to the forming ability of GE9IS-ICOs (clusters composed of more than 8 icosahedra that are interconnected by IS-linkages) that still grow at low temperatures where all other smaller icosahedral clusters stop grow.