National University of Science and Technology MISiS, Moscow, Russia:

N. A. Belov, Professor of the Department of Metal Forming, e-mail: nikolay-belov@yandex.ru
V. V. Doroshenko, Post-Graduate Student of the Department of Metal Forming

Bauman Moscow State Technical University, Moscow, Russia:

K. A. Batyshev, Professor

Using both thermodynamic calculations and experimental analyses, the Al – Ca – Mn – Fe – Zr – Sc phase diagram near the aluminum corner has been studied. Based on the obtained results, the optimal concentrations of calcium (about 4%) and manganese (about 0.7%) at an allowable iron content of up to 0.3–0.4% were chosen. According to the thermodynamic calculations, during solidification of the Al4Ca0.7Mn0.4Fe alloy, after formation of a the (Al) primary crystals, the eutectic reaction L → (Al) + Al₆(Fe, Mn) should occur. Solidification of this alloy should be completed via the ternary eutectic reaction L → (Al) + Al₆(Fe, Mn) + Al₄Ca. The addition of 0.2–0.4% zirconium should leads to the formation of primary crystals of the Al₃Zr aluminide. However, it is known that at the cooling rates typical for the casting in metal moulds (5–20 ^oC/s), the concentration boundary is shifted toward higher zirconium concentrations. Therefore, it was assumed that the total amount of Zr should enter into the (Al) composition and consequently have no influence on the phase composition of the alloy. When zirconium addition is present, the casting temperature should be higher than for the base alloy. The microstructure of two alloys with different content of zirconium and scandium: Al4Ca0.7Mn0.4Fe0.2Zr0.1Sc and Al4Ca0.7Mn0.4Fe0.4Zr was examined by means of optical microscopy, scanning electron microscopy and by electron microprobe analysis. The obtained results have revealed that for both alloys microstructure consists of the (Al) primary crystals and eutectic colonies with a fine structure. Calcium and iron are concentrated in the eutectic, while scandium, zirconium and manganese were detected in the both eutectic composition and (Al) primary crystals. Analysis of the hardness and specific electrical conductivity together with transmission electron microscopy has revealed that joint alloying with zirconium and scandium (0.20% Zr and 0.1% Sc) leads to the precipitation hardening due to the decomposition of (Al) and further precipitation of the coherent L1₂ – Al₃(Zr, Sc) phase nanoparticles. The highest hardness is observed after step annealing at 250 ^oC, 3 h plus 300 ^oC, 3 h.

The work was supported by the Russian Science Foundation grant 14-19-00632P.

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