Atomic-scale TEM characterization of dislocation-precipitate interaction mechanisms in a cold-worked Al-Cu-Mg-Si alloy

This study examines dislocation structures and their interactions with nanoscale precipitates in an Al-Cu-Mg-Si alloy using transmission electron microscopy (TEM) and high-angle annular dark-field scanning TEM (HAADF-STEM). The alloy was subjected to solution heat treatment, quenching, 30% cold rolling, and artificial aging at 160 ᵒC. In the cold-rolled condition, a high density of dislocations arranged in cells and planar slip structures on {111} planes were observed, with Burger's vectors of 1/2〈11̅0〉 confirmed by atomic-resolution imaging and inverse fast Fourier transform analysis. After aging, dislocations were partially rearranged and acted as preferential sites for heterogeneous precipitation. Rod-shaped and lath-shaped precipitates were identified, exhibiting distinct interaction mechanisms with dislocations. Direct atomic-scale observations reveal that rod-shaped precipitates promote dislocation bypass, whereas lath-shaped precipitates, with semi-coherent interfaces, are sheared. The shearing process is evidenced by the continuity of the extra half-plane across the precipitate. These results provide direct nanoscale insight into the coexistence of dislocation-precipitate interaction mechanisms and their dependence on precipitate morphology and coherency.