Atomic structure evolutions and mechanisms of the crystallization pathway of liquid Al during rapid cooling

The solidification of pure aluminum has been studied by a large-scale molecular dynamic simulation. The potential energy, positionD, heightH, and widthWof the first peak and valley of PDF curves, and the local structures were investigated. It was found that the FCC-crystallization ability of pure Al is so strong that still local crystal regions exist in the amorphized solid. As the temperature decreases, besides the counter-intuitive increase inDp(Dof the first peak),Hpincreases monotonically;Wp,Dv, andHvdecrease monotonically; onlyWvfirst decreases and then increases. They all change critically when phase transition happens. After the nucleation, orientation-disordered HCP-regions, as the grain boundaries or defects of FCC crystals, rapidly transform into FCC structures, and then the surviving HCP-regions regularize into few parallel layers or orientation-disordered HCP-regions. If parallel layers result in dislocation pinning, structural evolution terminates; otherwise, it continues. These findings will have a positive impact on the development of the solidification and nucleation theory.