OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 1 2024 of 0.5 % is ideal for refi ning the fi nished aluminum alloy structure. Scandium is an expensive metal, so attempts are continuously made to reduce its content by adding zirconium and hafnium. These elements stimulate the thermal stability of Al3Sc particles, and erbium precipitates as Al3Er nano-particles, increasing its total amount. The 1570 alloy is a conventional commercial high-magnesium aluminum alloy with combined scandium-zirconium additions. However, attempts are being made to further reduce the expensive scandium content in the alloys. For example, in the recently designed 1590 alloy, the scandium content varies in the range 0.06–0.16 %. Hafnium and erbium are added along with zirconium to reduce the scandium content in the alloy. The study aims to investigate the eff ect of erbium and hafnium concentrations on the modifi cation of the cast structure in 1590 aluminum alloy under fast crystallization conditions. The study will evaluate the grain structure formation when casting 1590 alloy into a copper chill mold and assess the eff ect of hafnium and erbium content on its size and type. It will also study the eff ect of erbium and hafnium on the formation of intermetallic particles, emerging during crystallization of 1590 alloy cast into a copper chill mold, and the relationship between intermetallic particles and grain structure size and type. Methods For the purpose of the study, ten melts were cast into a copper chill mold with diff erent chemical compositions as shown in Table 1. The melts contained Er and Hf in the range of 0.03–0.16 wt. % and 0.05–0.16 wt. %, respectively. These ranges are close to the minimal and maximal allowed concentrations of these elements in the 1590 alloy. The chemical compositions were previously analyzed in [21] as part of the study of 1590 alloy casting into a steel mold. Using the same compositions enables the comparison of the eff ects of crystallization rate on grain size in alloys with identical chemical compositions. Other elements in the melts corresponded to the chemical composition of the 1590 alloy, which was studied in [15, 16] from the perspective of heat treatment eff ect on microstructure and mechanical properties. Thus, this chemical composition allows the investigation of the eff ect of changes in Er and Hf concentrations on microstructure formation during casting and heat treatment. The charge stock used for experimental alloy design consisted of primary aluminum A85 grade, primary magnesium Mg90 grade, primary zinc TS1, and alloying compounds Al-Mn10, Al-Zr5, Al-Sc2, Al-Er5, and Al-Hf2. All materials were weighed using high-precision measurement devices before being charged into the furnace. The “MECHELECTRON-M VR4900” electronic scales, with a 5 g error, were used for materials weighing up to 15 kg, while the “MIDLENA 251” electronic scales were used for materials weighing up to 500 g, ensuring an accuracy level of plus/minus 0.1 g. The furnace was charged manually following the sequence below: 1. Primary aluminum was charged and melted fi rst. 2. Once the temperature reached 730 °C, slag was removed from the molten metal surface. 3. The molten metal was then heated to a temperature range of 770–790 °C. 4. Portions of 300 g of Al-Sc2, Al-Hf2, Al-Zr5, Al-Mn10 alloying compounds were sequentially introduced. 5. After each component was introduced, the molten metal was carefully stirred and soaked for 5 minutes. 6. After introducing all the calculated alloying components, the molten metal was cooled down to 740 °C. 7. Magnesium and zinc were then added to the molten metal. 8. The molten metal was stirred for 3 minutes using a titanium spoon. 9. The molten metal was reheated to 740°C. After casting, the chemical composition of all aluminum alloys was comprehensively studied using atomic emission spectroscopy with an ARL 3460 detector. The detector operates in the 0–10 keV energy range and has an energy resolution of 122 eV, which ensures accurate analysis. The analysis was carried out in accordance with the standards established by GOST 25086. Permissible concentration limits for key elements have been strictly established as follows: – Sc and Zn: 0.009 % – Hf, Zr, Er, Si, and Fe: 0.0053 %
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