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

Yoo, Yung Suk Jeremy; Su, Yang; Das, Sazol; Hamerton, Richard; Kacher, Josh

Affiliations

¹School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA, USA

²Novelis Inc., Kennesaw, GA, USA

Abstract and keywords

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 and naturally aged (T4) and artificially aged (T6). Electron backscatter diffraction and cross-sectional scanning electron microscopy imaging showed that, prior to crack formation, grain boundary ledges formed. These ledges formed adjacent to grain boundaries whose surface traces were oriented parallel to the bend axis and their planes forming angles below 70° with the sample surface. The grain boundary misorientation angle did not show any correlation with grain boundary ledge or crack formation. The sub-surface deformation fields associated with the grain boundary ledges were strongly affected with the precipitate state, with grain refinement and ultrafine grain formation occurring in artificially aged samples in the precipitate free zone and more diffuse deformation structures forming in the non-aged samples. In both cases, constituent particles were not found to have a significant influence on damage nucleation processes.

Keywords: Aluminum alloy 6451; Transmission kikuchi diffraction; Grain boundary fracture; Ductile fracture; Crack initiation

Links

DOI: 10.1016/j.msea.2021.142572

WoS: 000761637100002

History

Received: 2021-09-30

Revised: 2021-12-20

Accepted: 2021-12-26

Online: 2021-12-29

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