OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 1 2024 Fig. 3. Dependence of grain size on the amount of alloying components (on specimens cast into a steel and copper chill molds) (fi gure 2, f). With the addition of 0.1 % Er and 0.16 % Hf, the grain sharply refi nes to 69 μm; most of the observed grains become equiaxed (although individual dendrites remain) (fi gure 2, g). With 0.16 % Er and 0.05 % Hf, the average grain size is 172 μm (fi gure 2, h). In general, in this case, the grain structure pattern corresponds to the pattern observed in 1590 Er0.03-Hf0.05 alloys. With 0.16 % Er and 0.1 % Hf, the grain size is 168 μm (fi gure 2, i), and the grain structure resembles the structure observed in 1590 Er0.03-Hf0.05 and 1590 Er0.16-Hf0.05 alloys. The alloy 1590 Er0.16-Hf0.16 demonstrates a notable average grain size drop to 64 μm, and the structure acquires the equiaxed shape, as shown in fi gure 2, j. The analysis of the results leads to the conclusion that hafnium primarily presents the primary grain modifi er. For instance, when alloy contains 0.05 %, 0.1 %, and 0.16 % Hf, increasing the Er content from 0.03 % to 0.16 % reduces the grain size by only 191, 76, and 36 μm, respectively. At the same time, Hf content growth from 0.05 % to 0.16 % enables decreasing the average grain size from 181 to 64 μm. However, most importantly, hafnium transforms the grain structure into an equiaxed type. This is the eff ect of Al3Sc intermetallic compounds, containing both zirconium and hafnium, which are capable of modifying the as-cast structure (fi g. 1d). The following factors explain its capability to refi ne grain: fi rstly, unlike other detected intermetallic compounds, it is formed in the liquid phase prior to aluminum solid solution crystallization; secondly, it has crystalline lattice parameters close to aluminum matrix parameters. This ultimately gives it the opportunity to act as nuclei of new grains consisting of an aluminum solid solution. Note that such intermetallic compounds were detected only in alloy 1590 Er0.16-Hf0.16, due to its reasonably small size (about 1 μm). Therefore, it is rather diffi cult to detect and identify it using SEM. Thus, only indirect evidence of its presence is used, i.e., dendritic structure becomes equiaxed. It should also be noted that grain refi nement without dendritic structure conversion to equiaxed structure occurs as hafnium concentration increases from 0.05 to 0.1 % and erbium concentration increases from 0.03 to 0.16 %. This can be explained by the fact that an increase in the concentration of transition elements, especially hafnium, can also promote grain refi nement due to increased supercooling between the liquid and solid phase nuclei. Figure 3 demonstrates that when casting into a steel chill mold, the grain size is half as large as when casting into a copper chill mold. This is explained by the fact that with an increase in the crystallization rate,
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