Microstructure evolutions of rapidly-solidified and conventionally-cast Mg97Zn1Y2 alloys

Microstructure evolutions of rapidly-solidified (RS) ribbon and conventionally cast bulk Mg-1 at%Zn-2 at%Y alloys have been studied by transmission electron microscopy (TEM), particularly focusing on formation process and phase stability of the long-period structures. It is found that there are significant differences in microstructural evolutions between the RS ribbon and the cast-bulk alloys, in terms of thermal stability of the long-period phases at temperatures higher than 673 K. For both the as-quench ribbon and the as-cast bulk specimens, 18R-type long-period phase is dominantly observed at grain boundaries. After annealing at temperatures higher than 673 K, the long-period phases at grain boundaries in the RS ribbon almost disappear to form Mg24Y5 and Mg3Zn3Y2 compounds within the grain interiors, while the long-period phases remained stable in the cast-bulk alloy even at temperatures higher than 673 K.