ABSTRACT
Reversion after ageing was observed at first in the investigation of solid solution decom-
position in the M g - 8 . 7 mass % Y alloy [254]. In these experiments the heat treatment
regime 260°C, 1 h resulted in a decrease of the hardness produced after ageing at a lower
temperature, 200°C. Addit ional ageing at 200°C restored the hardness of the alloy actually
to the same value. Indication of the reversion was obtained also in [255] where the same
alloy M g - 8 . 7 mass % Y was firstly aged at 260°C for 192 h and then annealed at 315°C
for 2 h. The visible precipitates of the Y - r i c h phase after ageing at 260°C for 192 h then
disappeared. In [288, 292, 293] the reversion process was studied in more detail in M g - Y
alloy and, moreover, M g - G d was also studied for comparison.
