The role of microalloying elements in the formation of precipitate plates in aluminium alloys

Rationally-oriented, plate-shaped precipitates of intermediate or equilibrium phases are key strengthening constituents in high strength aluminium alloys. The identity and distribution and these precipitate plates are often controlled by strategic additions of microalloying elements. It is demonstrated that the transformation strain defining the change in structure associated with formation of such precipitate plates may involve a large shear component and that the manner in which the shear strain energy is accommodated may be a critical factor in controlling their nucleation. One way in which this shear strain energy might be minimised during nucleation is if the nucleus forms in association with clusters combining relatively large solute atoms with a local excess of vacancies.