Local Microstructural Environments Govern Evolution of Precipitate–Dislocation Interactions in an Al-Sc Alloy: Plasticity Regulation and Crack-Path Selection

Nanoscale Al3Sc precipitates strongly influence dislocation transport and heterogeneous plastic deformation in Al-Sc alloys. Here, the environment-dependent evolution of precipitate–dislocation interactions in an Al–0.3 wt.% Sc alloy was investigated by in-situ TEM tensile testing, assisted by EBSD, TEM, EDS, and atomic-resolution HAADF-STEM. The ordered Al3Sc precipitates exhibit an average equivalent diameter of 27.0 ± 6.3 nm, an areal number density of ~27.5 μm−2, and an average center-to-center spacing of ~102 nm, corresponding to an effective obstacle spacing of ~75 nm. The modified Orowan model gives a critical shear-stress increment of ~67 MPa and a macroscopic strengthening contribution of ~205 MPa. During intragranular deformation, dislocations undergo repeated bowing, pinning, depinning, and renewed glide. Near grain boundaries, precipitate arrangements promote directional dislocation transport and heterogeneous strain accommodation. At the crack tip, selective pinning redistributes plastic flow, promotes crack-tip blunting, and activates alternative slip paths, contributing to crack-path deflection. These observations establish a continuous mechanistic link between nanoscale precipitate characteristics, dislocation transport, heterogeneous plasticity, and crack propagation in Al-Sc alloys.