OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 1 2024 transition metals do not have time to precipitate in the form of primary intermetallic compounds and remain in a supersaturated solid solution, which is confi rmed in [31]. It shows that Al3Zr-type primary intermetallic compounds are not formed at a higher crystallization rate of aluminum alloy with zirconium addition. At the same time, zirconium itself remains in a supersaturated solid solution. In our case, the same eff ect is identifi ed in the alloys containing hafnium and erbium, except for 1590 Er0.16-Hf0.16, where close to Al3(Zr,Sc,Hf) primary intermetallic compounds [21]. In order to understand the phenomenon of transition elements migrating to the supersaturated solid solution at high casting rates, let us take the example of the aluminum-scandium phase diagram illustrated in fi gure 4. The fi gure shows the eutectic interaction in the aluminum-rich zone, which is identifi ed by point E. At a temperature of 655 °C and a scandium content of 0.55 wt % scandium, the equilibrium state Zh↔ ((Al) + Al3Sc) is achieved. When the cooling rate of the aluminum-based alloy increases to 10 °С/s, a marked shift in the eutectic interaction temperature from equilibrium conditions becomes apparent. The Sc content increases to 0.8 wt%, which enables the formation of primary intermetallic compounds, identifi ed as E’ in the diagram. Thus, with an increased rate of crystallization in alloys where a dendritic structure is observed, the concentration of scandium, zirconium, hafnium and erbium required for the formation of primary intermetallic compounds increases, so the content of these transition elements for the appearance of such particles becomes insuffi cient. Conclusions An increase in the content of erbium and, mainly, hafnium helps to refi ne the grain structure. However, only when the content of hafnium reaches 0.16 %, the dendritic structure is replaced by an equiaxed one. This is because the refi nement process begins due to supercooling between the nuclei of solid and liquid phases. When the hafnium content reaches 0.16 %, primary intermetallic compounds emerge in the liquid phase, thus facilitating refi nement and causing a modifi cation of the as-cast structure. Intermetallic compounds, which have no eff ect on the modifi cation of the as-cast structure, are identifi ed in all alloys close to Al8(Fe,Mn), Al12(Fe,Mn), and MgSi2 eutectic origin. Al3Sc-type primary intermetallic compounds were found only in the 1590 Er0.16-Hf0.16, and its presence in other alloys containing 0.16 % hafnium can be indicated only by indirect indicators, such as as-cast structure refi nement. The absence of these intermetallic compound traces can be explained by its relatively small sizes in such alloys, making its identifi cation and detection diffi cult using scanning microscopy. An increase in the crystallization rate of the 1590 alloy leads to grain size growth at any content of erbium and hafnium. This is mainly due to the fact that an increase in the casting rate leads to an increase in the concentration of transition elements required for the formation of primary intermetallic compounds that act as grain modifi ers in the liquid phase. Fig. 4. Aluminum-scandium phase diagram [32] References 1. Alattar A.L.A., Bazhin V.Yu. Kompozitsionnye materialy Al-Cu-B4C dlya polucheniya vysokoprochnykh zagotovok [Al-Cu-B4C composite materials for production of high-strength workpieces]. Metallurg = Metallurgist, 2020, no. 6, pp. 65–70. (In Russian).
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