Energetics of {10-12} twin nucleation and growth in magnesium alloys

Deformation twinning strongly affects the mechanical properties of magnesium and other alloys with hexagonal close-packed structures. But how solute atoms in magnesium alloys influence {10-12} twin nucleation and growth remains unclear. In this work, we performed energetics calculations for {10-12} twin nucleation and growth using molecular dynamic (MD) simulations and Density Functional Theory (DFT). For the MD simulations, the embedded atom method (EAM) potential and modified embedded atom method (MEAM) potential were used. The result shows that the energy barrier for {10-12} twin nucleation was about 40 meV/atom by using EAM potential, which was close to 30 meV/atom from DFT, as compared to about 70 meV/atom by the MEAM potential. The energy barrier for twin growth was about 13 meV/atom (EAM) and 24 meV/atom (MEAM), both energies are about one third of the twin nucleation energy. Addition of Al or Zn atoms will decrease the energy barrier for twin nucleation at low concentration. At 12 wt% Al concentration, no twins were observed in the simulation. However, the twin growth energy was 16 meV/atom (EAM) for a pre-existed twin boundary simulation. It appears that high Al concentrations will suppress both twin nucleation and growth. Zn in solid solution will promote twin nucleation.