Formation characteristics of clusters during rapid solidification process of liquid metal Al

A simulation study on the formation characteristics of clusters in a large-scale liquid Al system consisting of 10(5) atoms has been performed by the molecular dynamics method. And a cluster-type index method (CTIM) has been used to describe the structural configurations of various clusters. The results demonstrate that the icosahedron clusters (12 0 12 0) and their combinations play the most important role in the microstructure transition. The nano-clusters (containing up to 104 atoms) have been formed by combining some middle clusters which have been formed by combining smaller basic clusters. The structures of these nano-clusters are very different from those of nano-clusters obtained by evaporation, ionic spray methods, and so on. The latter is formed by the multi-shell crystals accumulated with an atom as the center and the surrounding atoms arranged according to octahedron configuration. The center atoms of these basic clusters are bond-connected each other with the linear or twisting mode. The corners of the nano-cluster just could become the starting points of the dendrite growth in the solidification processes of liquid metals.