OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 1 2024 Fig. 3. Mechanical properties of studied as-cast alloys after homogenization annealing at 440°C – 4 hours ticles in the 1570 alloy. In an alloy with hafnium additives, all particles are formed during heat treatment. However, fi nally, after thermal treatment, Al3Sc nanoparticles in both alloys generally have approximately equal size and number. The 1570 aluminum alloy and its modifi ed version with 0.5 % hafnium addition exhibit almost identical strength in a homogenized state (fi gure 3). After analyzing post-heat treatment strength properties and as-cast state data from the paper [33], it is evident that heating has minimal eff ect on ultimate strength (fi gure 3), showing only a slight increase. The infl uence of particles on the increase in yield stress is explained primarily by the degree of infl uence of dispersed phases. The greater the number of particles of the dispersed phase released, the more diffi cult it is for dislocations to move along planes and, as a consequence, when the movement of dislocations is diffi cult, the yield strength increases. On the other hand, several factors such as metal porosity, presence of coarse intermetallic compounds, etc., aff ect the ultimate strength. Therefore, the ultimate strength remains at the same level. The homogenized state of both alloys exhibits similar strength parameters primarily associated with similar particle numbers and sizes. Figure 4 shows the eff ects of cold rolling and annealing at diff erent temperatures on the alloys. During cold rolling, the alloys form a fi ber structure (as shown in fi gure 4), and black dots visible in the grain structure depict coarse intermetallic compounds. The size, chemical composition and morphology of these alloys have been already studied [32, 33]; therefore, its analysis by scanning microscopy methods was not carried out in the current paper. At temperatures up to 440 °С, cold-rolled sheets maintain a non-recrystallized structure. This shows that the Al3Sc particles effi ciently inhibit the recrystallization process [37]. In the 1570 alloy, new grain nuclei only appear during annealing at 500 °С for 3 hours, and only with an increase in annealing temperature to 530 °С, a mixed structure with an approximate ratio of 1:1 can be observed. The alloy with 0.5 % hafnium addition is more susceptible to recrystallization. After annealing at 500 °С and soaking for 3 hours, a mixed structure with predominantly recrystallized grains is observed in the 1570 alloy with 0.5 wt% Hf. If the annealing temperature is further increased to 530 °С, a fully recrystallized structure is observed in the alloy containing 0.5 % hafnium. It is worth noting that in hafnium-containing alloys, the resultant microstructure has a smaller grain size due to recrystallization than the as-cast state. The causes of accelerated recrystallization in the 1570 alloy with hafnium addition require further investigation.
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