Effect of Cu and Mg co-segregation on the strength of the Al grain boundaries: A molecular dynamics simulation

Molecular dynamics simulations employing machine learning potential functions of Al-Cu-Mg ternary alloys, were performed to elucidate the segregation behavior of Cu and Mg solutes and study their effects on the mechanical properties of Al grain boundaries. The calculation results show that Cu segregation enhances the strength of the Al Σ5 (2 1 0)[0 0 1] grain boundary, while the Mg instead weakens the Al Σ5 (2 1 0)[0 0 1] grain boundary. Cu and Mg solutes lead to the Al Σ41 (5 4 0)[0 0 1] grain boundary embrittlement. Dislocation plays a crucial role in the analysis of plastic deformation. We found that the reinforcing effect of the Cu solutes lies in the dislocation pile-up in plastic deformation, and the stair-rod dislocations inhibited the movement of the Shockley dislocations. The embrittlement cause of Mg solutes is that Mg solutes inhibit dislocation emission and shorten the dislocation nucleation cycle. This work illustrates the relationship between solute strengthening mechanism and dislocation evolution at the atomic scale.