  In magnesium alloys with multiple substitutional elements, solute segregation
at grain boundaries (GBs) has a strong impact on many important material
characteristics, such as GB energy and mobility, and therefore, texture.
Although it is well established that GB segregation is inhomogeneous, the
variation of GB solute composition for random boundaries is still not
understood. In the current study, atomic-scale experimental and simulation
techniques were used to investigate the compositional inhomogeneity of six
different GBs. Three-dimensional atom probe tomography results revealed that GB
solute concentration of Nd in Mg varies between 2 to 5 at.%. This variation was
not only seen for different GB orientations but also within the GB plane.
Correlated atomistic simulations suggest that the inhomogeneous segregation
behavior observed experimentally stems from local atomic rearrangements within
the GBs and introduce the notion of potential excess free volume in the context
of improving the prediction of per-site segregation energies.
