  Grain boundary (GB) segregation of solute atoms plays an important role in
the microstructure and macroscopic mechanical properties of materials. The
study of GB segregation of solute atoms using computational simulation has
become one of the hot spots in recent years. However, most studies mainly focus
on ground-state GB structures with the lowest energy, and the impact of GB
metastability with higher energy on solute segregation remains poorly
understood. In this work, the first-principles method based on the density
functional theory was adopted to investigate the effect of solute atoms Mg and
Cu segregation on ground-state {\Sigma}5(210) GB (GB-I) and metastable
GBs(GB-II, GB-III) in Al. GB energy, segregation energy, and theoretical
tensile strength of Mg and Cu segregation at three GBs were calculated. The
results show that both Mg and Cu have a large driving force to segregate to Al
GBs, which reduces the GB energy and improves improve GB stability. The
segregation of Mg and Cu on GB-III induces the transformation of the GB
structural unit and the GB structural phase transformations. For the above
three GBs, Cu segregation increases the theoretical tensile strength of GBs to
varying degrees. The segregation of Mg would reduce the resistance of GB-I and
GB-II, but enhances the strength of GB-III. The effect of solute atoms
segregation on the mechanical properties of GBs was investigated by charge
density distribution and density of states.
