Minimum energy path of a solute atom diffusing to an edge dislocation core in Al-Mg alloys based on empirical atomic potential

Al-Mg alloys are widely used in manufacturing. But at specific temperatures and strain rates, their plastic instability is not conducive to processing applications. The microscopic mechanism of plastic instability is the interaction between solute atoms and dislocations which induce a pinning-unpinnning effect. This effect, reflected on the microscopic scale, is also called dynamic strain aging (DSA). The DSA phenomenon causes negative strain-rate sensitivity and leads to plastic instability, which is harmful to its production. In this paper, the climbing image nudged elastic band method was adopted to explore the transition states along the minimum potential energy path, revealing a detailed evolution of atomic structures. The interaction range relies on the relative position and energy barrier of the transition, when a substitutional solute diffuses to an edge dislocation core in its stress field. Both substitution and vacancy-assisted migration are considered. The thermal activation time required for diffusion was estimated using transition state theory. The results indicate that there is no obvious law of solute atom migration in the compressive stress field. However, with the distance of the solute atom and the dislocation shortening, the migration potential energy barrier and the total energy of the system were gradually reduced. The present widespread empirical atomic potential can well estimate the phenomenon that the solute atom is prone to gathering in the tensile stress field. The transition states of migration confirmed the microstructure changes, depending on the position of the solute atom. The interaction region was no more than 2 nm. The migration energy was significantly reduced by vacancy mechanism, and the corresponding thermal activation time was shortened to microseconds. When the solute atoms finally migrated and stabilized near the dislocation core, there existed a maximum linear density. That is to say a dense arrangement along the dislocation line was not energetically preferred.