Abstract: A solid solution 6063 aluminium alloy features an exceptional combination of strength and ductility at 77 K. Here, the deformation mechanisms responsible for superior strength-ductility synergy and excellent strain hardening capacity at a cryogenic temperature of the alloy were comparatively investigated by in-situ electron backscatter diffraction (EBSD) observations coupled with transmission electron microscopy (TEM) characterization and fracture morphologies at both 298 and 77 K. It is found that kernel average misorientation (KAM) mappings and quantified KAM in degree suggest a higher proportion of geometrically necessary dislocations (GNDs) at 77 K. The existence of orientation scatter partitions at 77 K implies the activation of multiple slip systems, which is consistent with the results of potential slip systems calculated by Taylor axes. Furthermore, dislocation tangles characterized by brief and curved dislocation cells and abundant small dimples have been observed at 77 K. This temperature-mediated activation of dislocations facilitates the increased dislocations, thus enhancing the strain hardening capacity and ductility of the alloy. This research enriches cryogenic deformation theory and provides valuable insights into the design of high-performance aluminium alloys that are suitable for cryogenic applications.

Key words: Aluminium alloy, Cryogenic temperature, Strength-ductility synergy, In-situ EBSD, Deformation mechanisms