Aluminium-based alloys are in the focus of intensive research owing to their exceptional mechanical properties and microstructure stability at high temperatures. The primary reason for the co-alloying of Al alloys with Sc and Zr is their synergistic effects on the stabilization of the nano-sized precipitates. These alloying elements form highly ordered phases, which are isomorphic having the L12 structure. The cube-on-cube orientation relationship (OR) with the Al matrix has been accepted as the orientation relationship for the coherent nano-scaled Al₃Sc-based particles in Al.

The formation of nanoprecipitates in Al alloys can be achieved by dedicated annealing treatments at ambient pressure. We have shown that finite-temperature thermodynamics in combination with elasticity theory can be used to predict an upper limit for the size of Al₃Sc nanoprecipitates needed to maintain coherency with the host matrix. These findings can be exploited to fine-tune the microstructure of Al-Sc-based alloys for optimum mechanical properties. Another study on these alloys addressed the effect of precipitates and the associated coherency/semicoherency strain fields onto the solute diffusion. Recently, in a severely cold-rolled and subsequently annealed Al-Sc-Zr-Ti alloy, atomic-scale investigations using high resolution scanning transmission electron microscopy (HRSTEM) reveals a novel type of precipitate/matrix coherency.

We performed density functional theory (DFT) based total energy calculations to understand the mechanism of formation of this new type of precipitate/matrix coherency between Al₃Sc and Al matrix and to compare it with the established interfaces. Our DFT results reveal that the newly observed interface corresponds to a local minimum of energy and there is an energy penalty for the interface boundary to ‘escape’ the particle. We also studied segregation behavior of Sc atoms to probe the initial stage of formation of the observed novel Al₃Sc/Al interface.