OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 1 2024 were heated back up to the initial rolling temperature. The overall reduction percentage was 88 %. It is worth mentioning that the hot rolling temperature was the same as the homogenization temperature. This is because a higher temperature may cause particle coagulation, at least in the alloy without hafnium content. Lower temperatures may result in a loss of plasticity [20]. Rolling a small ingot that has already been heated after homogenization, including its heating in the furnace, takes no more than 30 minutes. The microstructure and properties of the alloy were not examined after this operation since it was not a fi nishing operation, and short-term heating did not signifi cantly aff ect Al3Sc particles. After reaching a thickness of 5 mm, the tapes underwent cold rolling to 2 mm thick. The percentage of reduction during cold rolling was 95 %. Cold rolled tape annealing The cold-rolled tape from the tested alloys was annealed after rolling to examine how the hafnium content aff ects the recrystallization process. Furthermore, an additional series of annealing was conducted on the cold-rolled tape to investigate the mechanical properties of the alloy (Table 2). Ta b l e 2 Annealing modes of cold-rolled tape Annealing for recrystallization verifi cation Annealing for mechanical properties analysis 470 °C – 3 hours 340 °C – 3 hours 500 °C – 3 hours 440 °C – 3 hours 530 °C – 3 hours 470 °C – 3 hours 550 °C – 3 hours 530 °C – 3 hours It is worth noting that the annealing temperature for high-magnesium alloy can be chosen from a wide range of temperatures (340 to 530 °C), depending on the required mechanical properties level and the desired combination of strength and plastic properties, as well as the contents of scandium, zirconium, and hafnium. This is precisely why these temperature values were chosen for the present study. Methods for studying the microstructure and mechanical properties of specimens Transmission electron microscopy The fi ne structure of the specimens was analyzed using a JEOL analytical transmission electron microscope from Japan. The microscope had a 200 kV accelerating voltage and an INCA attachment for EDX analysis from Oxford Instruments in the UK. To achieve precision positioning of the foil specimen, a 2-axes rotation holder was used, allowing it to be tilted ±30° along each axis. For particle transmission electron microscopy (TEM) analysis, standard procedures were followed. This included preparing two 500 μm thick foil specimens, further thinning it mechanically to 120 μm, and electrolytic thinning [29]. A total of fi ve thin foil specimens were prepared for TEM analysis. For the examination of Al3Sc particles, a specimen was placed in the zone axis, and an electron diff raction pattern was taken. During the examination, a weak superstructure refl ection from the (011) α plane was detected. This method allowed the acquisition of dark-fi eld images (DF), which helped count the visible particles. To determine the particle size and density, we used a Digitizer software module. We assessed the average particle size and its fraction by studying fi ve diff erent fi elds of view for each condition. Optical microscopy Optical microscopy was performed using an Axiovert microscope, and the average grain size after recrystallization was determined using the secant method.
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