Journal
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
Volume 846, Issue -, Pages -Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.msea.2022.143280
Keywords
Aluminum alloys; Atom probe tomography (APT); Transmission electron microscopy (TEM); Cyclic ageing; Natural ageing
Categories
Funding
- Research Council of Norway (RCN) through the Norwegian Laboratory for Mineral and Materials Characterization (MiMaC) [269842]
- NTNU Digital Transformation initiative 'AllDesign'
- RCN through the 'SumAl' project [NFR: 294933]
- Hydro
- Benteler Automotive Raufoss AS
- Neuman Aluminium
- Norwegian Micro-and NanoFabrication Facility, NorFab
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Cyclic ageing at room temperature enhances the mechanical properties of aluminum alloys by continuously injecting vacancies and enabling the dynamic precipitation of fine solute clusters. These clusters, uniformly distributed throughout the material, exhibit structural similarities to GPI zones observed after low temperature ageing. The strengthening effect of solute clusters is accelerated during cyclic ageing compared to natural ageing.
The cyclic application of mechanical stress to aluminum alloys at room temperature, referred to as cyclic ageing, continuously injects vacancies, enabling dynamic precipitation of a fine distribution of solute clusters. These are uniformly distributed throughout the bulk and are responsible for enhancing the mechanical properties to comparable values as T6 conditions obtained by conventional artificial aging. The atomic structure of the clusters in two Al-Zn-Mg (-Cu) alloys is studied using atomically resolved transmission electron microscopy, and their size, volume density and chemistry are investigated using atom probe tomography. It was found that cyclic ageing yields a high number density of solute clusters exhibiting structural similarities to the GPI zones commonly observed after low temperature ageing in such alloys. A subsequent 10-day natural ageing allows both cluster nucleation and further cluster growth, without altering their atomic structure. As compared to natural ageing, the strengthening caused by the solute clusters is accelerated during cyclic ageing, due to dynamic precipitation. The copper containing alloy also had higher amounts of Mg and Zn. Still, a slightly lower number density of smaller clusters with lower Zn/Mg ratio formed in this alloy, both after cyclic aging and after natural aging. The higher strength of this alloy is attributed to a higher strength contribution from each cluster.
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