A first-principles computational tensile test was performed on an Al grain boundary with a Ga layer. The tensile strength, the toughness and the Griffith energy for the Ga-layer segregated grain boundary were, respectively, 17%, 19% and 23% lower than those of the clean grain boundary, which indicated that the grain boundary was weakened. A closely-packed Ga cluster was formed following the breaking of some Ga–Ga bonds at a certain tensile strain, leading to the formation of a void-like structure in the grain boundary. It was suggested that the grain boundary weakening was directly associated with the formed void-like structure, which made the applied stress concentrate mainly on the Ga cluster. The final fracture occurred inside the Ga layer. The weakened grain boundary could contribute to the Ga-induced Al grain boundary embrittlement. Investigating the Effects of a Ga Layer on an Al Grain Boundary by a First-Principles Computational Tensile Test. Y.Zhang, G.H.Lu, M.Kohyama, T.Wang: Modelling and Simulation in Materials Science and Engineering, 2009, 17[1], 015003 (9pp)