Concurrent substitutional and displacive phase transformations in Al-Mg-Si nanoclusters

Al-Mg-Si nanoclusters embedded in aluminum transform through a delicate interplay of two characteristically distinct phase transformations: a diffusion-controlled substitutional transformation associated with solute enrichment and a swift displacive transformation involving collective shifts of columns of atoms once a critical enrichment has been reached. Through first-principles calculations, we show that these transformations are inseparable. Moreover, we show in atomistic detail how precipitates that are not superstructures of the matrix form from a supersaturated solid solution.