Multiscale characterization of dislocation processes in Al 5754

Abstract

Multiscale characterization was performed on an Al–Mg alloy, Al 5754 O-temper, including in situ mechanical deformation in both the scanning electron microscope and the transmission electron microscope. Scanning electron microscopy characterization showed corresponding inhomogeneity in the dislocation and Mg distribution, with higher levels of Mg correlating with elevated levels of dislocation density. At the nanoscale, in situ transmission electron microscopy straining experiments showed that dislocation propagation through the Al matrix is characterized by frequent interactions with obstacles smaller than the imaging resolution that resulted in the formation of dislocation debris in the form of dislocation loops. Post-mortem chemical characterization and comparison to dislocation loop behaviour in an Al–Cr alloy suggests that these obstacles are small Mg clusters. Previous theoretical work and indirect experimental evidence have suggested that these Mg nanoclusters are important factors contributing to strain instabilities in Al–Mg alloys. This study provides direct experimental characterization of the interaction of glissile dislocations with these nanoclusters and the stress needed for dislocations to overcome them.

Keywords:

• aluminium alloys
• electron microscopy
• EBSD
• dislocation interactions
• dislocation dynamics
• dislocation mechanics
• in situ electron microscopy
• mechanical behaviour

Acknowledgements

This work was supported by the National Science Foundation CMMI/MoM programme under GOALI Grant 1235610. Portions of this work were performed as a user project at the Molecular Foundry at Lawrence Berkeley National Laboratory, which is supported by the US Department of Energy under Contract # DE-AC02-05CH11231.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the National Science Foundation, Division of Civil, Mechanical and Manufacturing Innovation [GOALI Grant 1235610].