The possible transition mechanism for the meta-stable phase in the 7xxx aluminium

Abstract

Metastable phases in aluminium alloys are the primary nano-scale precipitates which have the biggest contribution to the increase in the tangible mechanical properties. The continuous increase in hardness in the 7xxx aluminium alloys is associated with the phase transformation from clusters or GP-zones to the metastable η′ phase. The high-resolution electron imaging is used to observe the precipitates and reconstruct a kinetic model that might explain the transformation. This work is an attempt to gain insight into how the structural transformation may occur based on the shortest route of diffusion for the eventual structure to result in that of the η′ phase.

KEYWORDS:

• Aluminum alloy
• Al-Zn-Mg-Cu alloy
• Ageing
• Precipitation
• Phase transformation
• TEM
• STEM
• High resolution imaging

Acknowledgements

The HAADF-STEM electron microscopy work was done using instruments of the NORTEM infrastructure by C.D. Marioara and A. Lervik (NFR 197405) at the TEM Gemini Centre at NTNU, Trondheim, Norway.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The authors acknowledge JST (Japan Science and Technology Agency) under collaborative research based on industrial demand ‘Heterogeneous Structure Control’: Toward innovative development of metallic structural materials [grant number #20100114], Light Metal Educational Foundation, President description and the University of Toyama (2019).