First‐Principles Modeling of Solid Solution Softening and Hardening Effects in Al–Mg–Zr–Si Aluminum Alloys

Solid solution hardening and softening effects in aluminum alloys by substitutional foreign atoms are studied using quantum‐mechanical first‐principles modeling of periodically repeated supercells, with full density functional theory (DFT) calculations in the generalized gradient approximation, employing a plane wave basis set and pseudopotentials. In supercell models of the Shockley partial dislocation, the electronic and steric interactions of the alloying atoms are investigated within the dislocation core and the surrounding Cottrell atmosphere. The DFT‐derived energy barrier toward dislocation motion is most strongly modified for substitutional sites located close to the dislocation core. The influence of the different substituents increases with the propensity to form binary aluminum compounds, but with an element‐specific variation: Si lowers the barrier, indicating a potential solid solution softening effect, whereas Zr increases the barrier, which correlates with an impeded dislocation motion. On the quantum scale, Mg is of little influence with a slight tendency toward a barrier increase, although its classical alloying parameters are identical to those of Zr. Thus, calculating from first principles the additional electronic contributions to the still commonly applied classical size‐stress theory is indispensable for alloying near dislocation cores. This indicates that electronic interactions need to be included for refining the classical model.