Modelling the Structures and Melting of Mg-Zn Alloys using Molecular Dynamics with Lennard-Jones Potentials

Molecular dynamics modelling has been used to study the Mg-Zn alloys in solid and molten states. GULP and DL_POLY simulation software simulated the crystal structure of Mg-Zn alloys at room temperature and highly disordered structures at melting temperatures.

The GULP has been used to validate the Lennard-Jones potential for the simulation. The GULP output energy minimisation showed almost the same values of cell parameters which are then used for input of the DL_POLY simulations. The Substitutional alloys have been simulated by creating a 4×4×4 supercell of 128 atoms of pure Mg using CrystalMaker, and substituting some Mg atoms with Zn atoms. The compression lattice strain caused by the substitution of dissimilar sizes of Mg and Zn has been studied.

The DL_POLY simulation is run in an NPT ensemble with varying temperatures. It was obtained that the simulated melting temperatures of Pure Mg, α - Mg, Pure Zn, Mg51Zn20, Mg21Zn25, Mg4Zn7, MgZn2, and Mg2Zn11 are obtained at 1860K, 1820K, 1520K, 1740K, 1780K, 1860K, 1480K, and 1380K respectively. The experimental melting points of Pure Mg, α - Mg, Pure Zn, Mg51Zn20, Mg21Zn25, Mg4Zn7, MgZn2, and Mg2Zn11 are 923K, 910.87K, 692.58K, 621.4K, 822.47K, 851.93K, 862.93K, and 727.13K respectively.

The investigation of cell parameters (a, b, c) for different Mg-Zn compounds have been done from 300K to 2300K. The simulated and computational values of densities at the molten state of Pure Mg, α - Mg, Pure Zn, Mg51Zn20, Mg21Zn25, Mg4Zn7, MgZn2, and Mg2Zn11 are calculated.

The simulation of metal glass is studied by heating the alloys to 2500K using DL_POLY "bath" and quenching at the rate of 1013 K/s using DL_POLY "quench" in NPT. The study of the simulated metal glass showed the amorphous glassy atomic structure at room temperature for Pure Mg, α - Mg, Pure Zn, Mg51Zn20, Mg21Zn25, Mg4Zn7, MgZn2, and Mg2Zn11.

The surface melting of the alloys is investigated using DL_POLY in the NVT ensemble. The surface melting temperatures of Pure Mg, α - Mg, Pure Zn, Mg21Zn25, Mg4Zn7, MgZn2, Mg2Zn11 and Mg51Zn20 are obtained at 760K, 765K, 910K, 850K, 930K, 1000K,730K, and 500K respectively.