Thermal stability of the microstructure of rapidly solidified ribbon-consolidated Mg97.94Zn0.56Y1.5 alloy
Abstract
The present study deals with the thermal stability of the microstructure of the rapidly solidified ribbon-consolidated Mg97.94Zn0.56Y1.5 alloy. In the consolidated state, the material has a very fine-grained microstructure with an average grain size of similar to 790 nm and contains Zn- and Y-rich stacking faults (SFs) in basal planes.
SFs are dispersed in an individual manner or organized in the blocks forming a Mille-feuille structure (MFS). The alloy is characterized by a weak basal texture with a more pronounced intensity at the (10 (1) over bar0) pole.
In order to study the thermal stability of the microstructure, isothermal annealing in a temperature range of 300-500 degrees C was applied. The microstructure is thermally stable up to 400 degrees C, which is exceptionally high compared to conventional ultra-fine grained magnesium alloys.
At higher temperatures, the growth of the grain size and redistribution of the texture intensity is related to the recrystallization process. The order of dispersion of the solute-segregated SFs is independent of the annealing temperatures.
However, there is a change in the arrangement of SFs in the grains: the thickness of the SFs blocks increases with increasing temperature, i.e., the stacking faults became more agglomerated. Nevertheless, even after annealing at 500 degrees C, there is still a mixture of several polytypes of the long-period stacking ordered (LPSO) phase rather than a single-ordered LPSO phase.