Age-hardenable aluminium alloys - based on Al-Mg-Si, Al-Mg-Zn and Al-Cu - are important structural materials for construction and automotive applications due to properties like high strength/weight ratio and good formability, often combined with good corrosion resistance. Our overall objective is to improve the understanding of the fundamental physics, taking place at the atomic scale in these alloys – which decides nucleation, phase stabilization and precipitation [1]. The distribution, number density, morphology, structure and interfaces of age-hardening precipitates depend on the alloy composition and the thermo-mechanical history of the material, and to a large extent decide the material’s physical properties. If we are able to map the atomic structure of precipitates and predict how they develop, we can design new or optimize chemical compositions of existing alloys to get desired properties for given applications. Our research group at NTNU and SINTEF in Trondheim has over a long period worked together with the Norwegian light metal industry on nanoscale studies of these alloys. We are using several advanced (scanning) transmission electron microscopy ((S)TEM) based techniques to study the alloy precipitates and micro-structures. Atomic structure is determined using aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), often in combination with density functional theory calculations [1]. The scanning precession electron diffraction (SPED) technique, combined with effective machine learning approaches and digital post-processing [2] is a very useful methodology to get comprehensive information about precipitate morphology and phase compositions, as well as crystallite orientations, also in deformed materials.
The TEM work was conducted using the NORTEM infrastructure (NFR 197405) at the TEM Gemini Centre, Trondheim, Norway.