First-principles computational tensile test on a Na-segregated Al grain boundary with an Si additive and an intergranular embrittlement suppression mechanism

We have performed a first-principles computational tensile test (FPCTT) on an Na-segregated Al grain boundary (GB) with an Si additive. We show that the Si additive in the GB greatly increases both the tensile strength and the toughness of the Na-segregated Al GB. We demonstrate that the final GB fracture is dominated by the breaking of interfacial stronger Al-Si bonds according to the bond evolution with increasing strain. Based on the Na-induced Al intergranular embrittlement mechanism explored before and the present calculation results, we propose a GB-strengthening mechanism by adding a strengthening element such as Si for Al alloy to suppress the intergranular embrittlement by an Na impurity. Such an intergranular embrittlement suppression mechanism can explain the experimental observations.