Scanning electron micrographs showing the particles in Mg–20 wt% Dy alloy with T4 treatment. (a) Machined and polished in a dry environment [preparation method (ii)]. (b) Machined and polished with water [preparation method (i)]; cuboid particles are observed. (c) Cluster of cuboid particles with high Dy and O contents in a sample prepared using method (i). (d) Cuboid particle with a very high Dy content in a sample prepared using method (i). Numbers shown in the pictures are atomic percent.