Abstract: A simulation study on the formation characteristics of cluster structures during rapid cooling process in a liquid metal system consisting of 100 000 Al atoms has been performed by molecular dynamics method. A cluster-type index method (CTIM) has been used to describe the structural configurations of various clusters. The results demonstrate that, during the solidification process of liquid metal Al, only the icosahedral clusters (12 0 12 0) related to the 1551 bond-types and various cluster structures formed by their combination play the key and critical role for the microstructure evolution; the cluster structures of various levels formed by different numbers and different types of basic clusters would present the peak values in a certain section of atomic number, namely the magic numbers; the magic number order in the system is 13(13); 19(21); 25～28(27); 31～33(29～30); 37,39;…(the numbers in the brackets are the corresponding values in liquid state) as shown in detail in Table 1 and Fig.4, this is quite in agreement with the experimental results obtained by Harris et al. The method used here to research the magic numbers from the cluster structures according to the level order and sections will give these experimental results a rather scientific and reasonable model explanation.

Key words: Liquid metal, Solidification process, Cluster configuration, Magic number, Computer simulation