Influence of Precipitation on Geometrically Necessary Dislocations Distribution and Fracture Behavior in an Al-Cu-Li Alloy

Abstract

This study investigates the mesoscale plastic deformation behavior and factors affecting fracture toughness in Al-Cu-Li alloys with a medium Li/Cu ratio using high-resolution electron backscatter diffraction (HR-EBSD) and transmission electron microscopy (TEM). It is found that fine δ'/GPⅠ/δ' composite precipitates are readily sheared, leading to dislocation planar slip and pile-up at the grain boundaries. Conversely, T₁ precipitates inhibit planar slip and promote cross-slip, resulting in increased geometrically necessary dislocation (GND) storage capacity in samples exhibiting wavy slip. Brittle intergranular fracture is not solely caused by dislocation planar slip due to composite precipitates; rather, it is significantly influenced by interactions with intermetallic compounds at the grain boundaries. For samples dominated by T₁ precipitates, Cu-rich precipitates along grain boundaries are primarily responsible for decreasing fracture toughness, with the negative effect of coarse grain boundary precipitates being more detrimental than that of dislocation planar slip. This research provides valuable insights into the mechanical properties of Al-Cu-Li alloys at the mesoscale level.