First-Principles Investigation Of Mg Segregation At Sigma=11(113) Grain Boundaries In Al

The preferred site of Mg segregation at Sigma = 11 (113) grain boundaries in Al and the effects of Mg segregation on grain boundary cohesion have been investigated through first-principle pseudopotential total energy calculations. The results show that the Mg atom prefers to occupy the 'looser' site at the grain boundary of Al but not the 'tighter' site. Furthermore, on basis of the thermodynamic theory of Rice and Wang, we have studied the effect of Mg segregation on the grain boundary cohesion of Al. Our total energy calculations show that Mg behaves as an embrittler. Additionally, the cohesive energies for a pure Al boundary and an Al boundary with Mg segregation have been calculated in this paper. The calculated results indicate that the cohesion of an Al grain boundary with Mg segregation is weaker than that of a pure Al grain boundary. The total charge density of the gain boundary also demonstrates that the Mg atom forms weaker metallic bonds with neighbouring Al atoms in the grain boundary region.