Formation of the eutecticum with multilayer structure during solidification in as-cast Al–Mg alloy containing a high level of Sc

• EBSD analyses explain the reason of Sc can cause a potent grain refinement effect.
• AFM was employed to investigate the inner structure of the Sc-rich particles.
• The Sc-rich particles are identified as the eutectics.
• The Sc-rich particles exhibit an ‘Al3Sc+α-Al+Al3Sc’ layer by layer structure.

An addition of a high level of 0.6 wt% Sc imposed a remarkable grain refining effect on Al-5Mg alloy for as-cast condition, changing typical dendritic microstructure into fine equiaxed grains. Such effect was found to be related to the extensively formed Sc-rich particles. Electron back-scatter diffraction (EBSD), Atomic force microscopy (AFM) and SEM-elemental mapping were employed to investigate the inner structure of these particles and their role in grain refining. They could be identified as some eutectic structure consist of multilayer of ‘Al3Sc+α-Al+Al3Sc····’, which shows good consistency in orientation both in the particle and matrix.