Atomistic analysis for grain size and pre-deformation controlled melting behavior of polycrystalline AlMg alloys under high temperatures

The melting behavior of aluminum alloy is crucial for spacecraft structure re-entry damage. This work performs the molecular dynamics simulations to investigate the amorphization behavior of polycrystalline AlMg alloys with different grain sizes and pre-deformations under high temperatures. The simulation results demonstrated that the melting rate slows down for the polycrystalline AlMg alloys with the larger grains. The melting process shifts from the grain-boundary-to-interior amorphization in small grains to both grain boundary and interior melting in large grains. Further simulations discovered that the elastic pre-deformation has little effect on melting behaviors of polycrystalline AlMg alloys, and the plastic pre-deformation leads to the significant impact on the amorphization process of the smaller grain size but less contribution for the larger grains. This is originated from the fact that the small grains experience grain-boundary sliding and the large grains generate dislocations when the pre-plastic deformation. Analysis of the differences between the pre-loading and non-pre-loading cases reveals that the difference under plastic pre-loading is more obvious than elastic pre-loading. Such difference first rises then falls with increasing the temperature. In addition, the relationship between the difference in amorphous-atom volume fraction (pre-loading vs non-pre-loading) and grain size is further discussed and the pre-stretched (pre-compressed) deformation makes the difference decrease (increase) with grain size. The findings in this work could be helpful to understand the melting process of Al alloys under the high temperature environment.