SumAl: Solute cluster manipulation for optimized properties in Al-Mg-Si based Al alloys

Continuous weight reduction is a key to the development of a sustainable and greener transport sector. This represents a significant opportunity for the Norwegian aluminum industry, as market growth and increased profitability of lightweight Al solutions can be realized by further improving product properties. Precipitation is the most important mechanism the Al industry can use to be able to improve the performance of both AA6xxx wrought alloys and A3xx cast alloys. However, so far, the Al industry is unable to understand, control and manipulate nucleation and early-stage clustering of hardening precipitates. In the 5 years KPN project SumAl NTNU and SINTEF, together with key players in the Norwegian and European Al industry will try to change this by establishing detailed insight into the atomic scale of the early stage before aging. Through a combination of experiments and modelling, the project will develop a basic understanding of early clustering and arrangement of dissolved alloying element atoms in aluminum and how these structures are related to the development of hardening precipitates and material properties. A successful result of SumAl will provide the Norwegian Al industry with the tools needed to develop and design innovative Al-based products that are competitive and have an excellent balance of properties. Two PhD students and one postdoc are hired at NTNU, who have main activities in transmission electron microscopy (TEM), atom probe tomography (APT) and atomistic modelling, respectively. Here we use the national infrastructures NORTEM, MiMAC and SIGMA2. The project consist of three work packages, (1) to establish fundamental relations between the thermomechanical treatment prior to artificial aging and development of solute ordering and atomic clusters from a supersaturated solid solutes, (2) to establish knowledge on how atomic clusters develop into age hardening precipitates during subsequent artificial aging, and from these (3) establish the relationships between thermomechanical treatment, microstructure development and mechanical properties. The project has so far educated two MSc students and one more is in progress. We also work closely with other internally funded PhD students at NTNU. Due to the corona pandemic, it has been a somewhat slow start for the research fellows, but activities have now started. We study alloys that have been stored for a very long time (17 years) at room temperature and have received several types of aluminum alloys from industrial partners that we heat-treat and analyse. We build on the TEM and combine this with APT studies. Here we have established methods for studying the structure of clusters at an early stage. This is done by the GP1 phase in AlMgZn (7xxx) alloys to establish the method, and we now concentrate on AlMgSi (6xxx) alloys which are more challenging. On the modelling side, we have further developed the kinematic Monte-Carlo (KMC) calculation method and are now working on cluster models.

Continued weight reductions remain a key to the development of a sustainable and greener transportation sector. This represents a significant opportunity for Norwegian companies in the Aluminium (Al) value chain. Market growth and increased profitability of lightweight Al-solutions can be expected by further improving product properties. Precipitation hardening is the most important strategy for Al industry to improve performance of both AA6xxx wrought alloys and A3xx foundry alloys. However, the Al industry is still unable to control and manipulate nucleation and growth of hardening precipitates. A recent scientific break-through by NTNU and SINTEF now opens perspectives to change this, by establishing detailed insights in the early-stage microstructure prior to aging. Building on recent results obtained on atomistic scale through the national infrastructure NORTEM, NTNU and SINTEF have together with key actors in the Norwegian and European Al industry defined this 5-year KPN project SumAl. The project will through a combination of experiments and modelling, develop fundamental understanding of early stage clustering and ordering of solute atoms in aluminium and how these structures relate to the development of hardening precipitates and materials properties. A successful outcome of SumAl will give Norwegian Al actors the tools to develop and design innovative Al-based products with a competitive and superior balance of properties.