OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 2 2024 Fig. 5. The dependences of the average size of structural elements of phases on the annealing temperature Fig. 6. Fragments of XRD patterns of extruded Mg-2.9Y-1.3Nd alloy and after annealing According to XRD patterns of the extruded Mg-2.9Y-1.3Nd alloy, high intensity peaks belong to the HCP α-Mg phase solid solution. After annealing at 100–450 ℃, XRD patterns do not change, whereas at a temperature of 525 ℃, the X-ray line width of the α-phase notably decreases and the intensity redistribution occurs in (100), (101) and (101) directions, indicating to intensive recrystallization processes accompanied by the grain growth. In addition to the major α-Mg phase, TEM investigations show the presence of fine-grained Mg24Y5 intermetallic particles and b-, b′-, and b1-phases precipitates in the alloy, which cannot be identified by the X-ray spectroscopy. Thus, we can conclude, that the bimodal microstructure of the Mg-2.9Y-1.3Nd alloy does not change after one hour annealing in the temperature range of 100–450 °С, although a slight growth is observed for fine-grained Mg24Y5 particles and b-, b′-, and b1-phases precipitates with its morphology transformation. Conclusions In conclusion, this study has shown the formation of the bimodal microstructure in the extruded Mg2.9Y-1.3Nd alloy. The microstructure consisted of a a-phase and textured bands with an average grain size of 17 µm and 1 µm, respectively. It was found that along with the major stable α-Mg phase, the alloy microstructure comprised Mg24Y5 intermetallic particles and precipitates of the of three types phases. Annealing within 100–450 °С for 1 hour had no effect on the general structure of the Mg-2.9Y-1.3Nd alloy, but promoted the growth in the linear dimensions of precipitates of b-, b′-, and b1-phases. It is shown that within 300–450 °С, the morphology of b-, b′-, and b1-phases changed while maintaining the average size of the α-phase. Annealing at 525 °С resulted in a significant transformation of the bimodal microstructure, conditioned by the recrystallization process and intensive grain growth of the major phase, Mg24Y5 intermetallic particles, and secondary precipitates of b-, b′-, and b1-phases.
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