Secondary phase engineering to enhanced recyclability of aluminium from low-grade scrap

Aluminium manufacturing is directly responsible for 2% of global CO₂ emissions and increasing recycling rates is urgently needed to accelerate its decarbonization. However, current aluminium recycling processes are not capable of dealing with low-grade ‘dirty’ scrap and heavily rely on energy intensive primary metal to tightly constrain impurity levels. Impurity elements have the tendency to segregate during solidification and precipitate into harmful intermetallic compounds (IMCs) which compromise the material performance even at small volume fractions. A radical alternative, is to shift from composition tuning to microstructure tuning, wherein properties are engineered using designed solidification conditions to manipulate impurities into forming benign and finely dispersed IMCs, rather than the ‘naturally’ occurring plate-like detrimental compounds. However, practical applications of this concept are still underexploited because the methodologies to promote these more benign IMC morphologies are not known. Within the group we have developed an experimental methodology, which combines in-situ X-ray imaging with ex-situ electron microscopy and XCT, to investigate the role of impurities on the formation of IMCs and how to manipulate them. Our initial work has demonstrated that IMC morphologies can be significantly manipulated by controlling their nucleation and growth through the use of ‘inoculants’ and ‘modifiers’ additions.

This project will develop the necessary science and understanding to design new inoculants and modifiers for the most problematic IMCs present in automotive and aerospace aluminium alloys. A methodology will be developed to accelerate the selection of potential additions tailored to specific IMCs and experimentally asses their effectiveness via electron microscopy and thermal analysis. Time-resolved X-ray imaging, both in laboratory and at the synchrotron, will be utilised to investigate the performance of the additions under industrial relevant solidification conditions. Additionally, if time allows, the research will explore scalable processing routes for effectively introducing these additions into the liquid metal during the casting process.