Mechanistic Origin of Orientation-Dependent Substructure Evolution in Aluminum and Aluminum-Magnesium Alloys

Role of magnesium (Mg) solute and deformation temperature on the orientation-dependent substructure evolution in aluminum (Al) was investigated experimentally. The mechanistic origin of the experimental orientation dependence was then explored with numerical modelling. In experiments, the Al-Mg showed more geometrically necessary dislocation density and residual strain but had insignificant differences between hard and soft crystallographic orientations. Increased Mg-content led to the conversion of dislocation cell structures to dislocation tangles. On the other hand, an increase in deformation temperature appeared to nullify the role of solute, and irrespective of Mg content, the substructures were not orientation dependent. Molecular dynamics (MD) simulations provided temperature and solute dependence of dislocation drag coefficient and probability of cross slip. These appeared to be orientations independent. Discrete dislocation dynamics (DDD) simulations were then conducted by incorporating relevant parameters from MD and fitting DDD simulated stress-strain behavior with experimental data. Further, the solute was modelled as static obstacles to dislocation movement, hindering easy glide and short-range dislocation-dislocation interactions. Dislocation interactions at the slip plane intersections generated dynamic obstacles and sources-their ratio being determined by the probability of cross-slip. The DDD simulations indicated that evolving density of dynamic obstacles and sources determined the orientation dependence of substructure evolution.