Initial structural transformation of Mg-Sm binary alloys during early isothermal aging.

The initial structural transformation of Mg-Sm binary alloys on early isothermal aging is investigated by first-principles calculations. There are three typical precipitate structures in this period, namely hexagonal structure, continuous zigzag structure, and discontinuous zigzag structure (˅˄ structure), which are the main transition state structures formed. The formation of clusters is a dynamic process needing to combine vacancy formation and migrations. Among these structures, the lower vacancy formation energy and dilute mixing energy (byproducts of the solute-vacancy binding energy calculation) make hexagonal clusters more possible to form and explain experimental observation of hexagonal structure abundant existing in the matrix, although its formation energy is slightly higher. Furthermore, vacancy-assisted diffusion in doped Mg lattices is calculated using the nudge elastic band method to investigate the kinetics of the cluster formation. [ABSTRACT FROM AUTHOR]