National University of Science and Technology MISIS, Moscow, Russia

E. A. Naumova, Associate Professor, Chair for Metal Forming, Candidate of Engineering Sciences, e-mail: jan73@mail.ru

Moscow Polytechnic University, Moscow, Russia
A. N. Koshmin, Associate Professor, Research Sector, Candidate of Engineering Sciences

IMET RAS, Moscow, Russia
S. G. Bochvar, Leading Researcher, Doctor of Technical Sciences
P. Yu. Predko, Researcher

The possibility of strengthening hypereutectic aluminum-calcium alloys with scandium additives was studied. Experimental alloys were prepared in a Graficarbo resistance electric furnace based on high-purity aluminum A99. Calcium and cerium were introduced in pure form, and nickel, manganese, zirconium and scandium were introduced as aluminum-based ligatures Al – 20% Ni, Al – 10% Mn, Al – 10% Sc and Al – 10% Zr, respectively. The structure of the Al – 6 Ca – 3 Mn – 2 Ce – 0.3 Sc alloy contains primary crystals of the Al₁₀(Ca,Ce)Mn₂ phases and the nonequilibrium transition phase Al₁₁(Ca,Ce)Mn_1,5 in the form of coarse plates, which is undesirable for further deformation processing. The structure of the Al – 8 Ca – 2 Mn – 1 Ni – 0.3 Sc alloy contains compact small (no more than 25 μm) primary crystals of the Al₁₀Ca(Mn,Ni)₂ phase, uniformly distributed in a multicomponent highly dispersed eutectic matrix. This structure implies higher deformation plasticity. At the same time, both alloys showed the same behavior during hot upsetting. During step annealing of ingots, the hardening of both alloys was about 40 HV at a temperature of 350 ^oC, which corresponds to the level of hardening of hypoeutectic alloys alloyed with scandium. However, in hypoeutectic alloys, maximum hardening is achieved at a temperature of 300 ^oC. In the Al – 8 Ca – 2 Mn – 1 Ni – 0.3 Sc alloy, softening does not yet occur at a temperature of 400 ^oC, which indicates its high thermal stability. The experimental alloys contain a high fraction of intermetallics (more than 40 % (wt.)) therefore, the temperature of their hot deformation should be at least 500 ^oC. However, at a temperature of 500 ^oC, the hardening from dispersed Al₃Sc particles is completely lost due to their coarsening. In addition, at such a temperature, fragmentation and spheroidization of eutectic intermetallics occurs, which contributes to softening. It is shown that the Al – 6 Ca – 3 Mn – 2 Ce – 0.3 Sc and Al – 8 Ca – 2 Mn – 1 Ni – 0.3 Sc alloys can be deformed at a temperature of 450 ^oC with a total reduction of no more than 50%. The level of hardening in this case is maintained at more than 60% (the combined effect of precipitation hardening and strain hardening). It is shown that in the Al – 8 Ca – 2 Mn – 1 Ni – 0.2 Sc – 0.1 Zr alloy, a hardness increase of 35–37 HV is achieved at a temperature of 350 oC, which demonstrates the possibility of obtaining economically alloyed hypereutectic alloys that are hardened by heating without preliminary quenching.

The work was supported by the grant of the Russian Science Foundation 20-19-00746-P (23-19-45018).
The authors thank postgraduate student M. A. Barykina and Candidate of Engineering Sciences, associate professor M. B. Savonkina for assistance in conducting the experiments.

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