Multiscale electron microscopy investigation of grain boundary-mediated crack initiation in AA6451 during three-point bending

The microstructural origins and early behavior of crack formation in AA6451 samples under three-point bending has been investigated using a multiscale electron microscopy-based approach. Two different heat treatments were investigated: solution treated naturally aged (T4) artificially (T6). Electron backscatter diffraction cross-sectional scanning microscopy imaging showed that, prior to formation, grain boundary ledges formed. These formed adjacent boundaries whose surface traces oriented parallel the bend axis their planes forming angles below 70° with sample surface. misorientation angle did not show any correlation ledge or formation. sub-surface deformation fields associated strongly affected precipitate state, refinement ultrafine occurring free zone more diffuse structures non-aged samples. In both cases, constituent particles found have significant influence on damage nucleation processes.