TEM Observation of Precipitates in a Mg-Gd-Sc Alloy with High Content of Sc

Precipitates in a Mg–Gd–Sc alloy with high Sc content (up to 13mass%) were examined by means of transmission electron microscopy. Plate-like precipitates appeared during the early stages of aging of specimens aged at 573 K. The plate-like precipitates lay on the { } magnesium matrix planes, and were similar to the β1 phase and β phase in the counterpart Mg–Gd–Zr alloy aged at 523 K. These precipitates had a high Sc content. Particle-shaped precipitate were observed alongside the plate-like precipitates, unlike the case in Mg–Gd alloys. The contrasts of the plate-like precipitates became longer and the number density of precipitate contrasts increased with increasing aging time at 573 K up to the point where the maximum hardness was attained. We suggest that the plate-like precipitates contribute to the increased hardness of Mg–Gd–Sc alloys with a high content of Sc.