National University of science and technology “MISiS”, Moscow, Russia:

P. K. Shurkin, Engineer of the Department of Metal Forming, e-mail: pa.shurkin@yandex.ru
A. P. Dolbachev, Engineer of the Department of Metal Forming
E. A. Naumova, Associate professor of the Department of Metal Forming
V. V. Doroshenko, Engineer of the Department of Metal Forming

The theoretical and experimental investigation of the effect of iron content (1, 0.5 and 0.25%) on various Al – Zn – Mg – Ca based alloys containing Mg (3%), Zn (6 and 12%), Ca (0,1 and 2%) has been conducted. It is revealed that the crystallization process in all the studied alloys containing 1% Fe, regardless of the amount of calcium, begins with the formation of coarse Al3Fe phase. In the alloys containing 2% Ca and 0.5–0.25% Fe, the Al₁₀CaFe₂ ternary phase formed by the reaction L → (Al) + Al₁₀CaFe₂ + (AlZn)₄Ca at a temperature of 596 ^оC. This phase has a skeletal morphology similar to that of the Al15(Fe, Mn)₃Si₂ phase. Application of two-stage heat treatment at 450 ^оC, 3 h + 500 ^оC, 3 h allowed dissolving the T-phase, as well as spheroidizing the equilibrium intermetallics including the Al10CaFe2 phase. In the presence of 12% Zn, the temperature of the equilibrium solidus is reduced to 480 ^оC, thus causing the incipient melting during spheroidization heat treatment. The content of up to 0.5% Fe showed little effect on the density. The lowest density (2.7 g/cm³) is achieved in an alloy containing 6% Zn, 2% Ca and 0.5% Fe, which is lower than the values of other experimental alloys by 0.1–0.2 g/cm³. The values of the specific electrical conductivity and microhardness as a function of the aging temperature showed a positive effect of iron on hardening of the alloys of the Al – Zn – Mg – Ca system, which can be explained by the formation of a smaller amount of the (AlZn)₄Ca phase due to its formation in combination with the Al₁₀CaFe₂ phase. The values depend strongly on the amount of zinc. In the maximum hardening (T6) state, alloys with 12% Zn and 1% Fe have a microhardness of 218 units, with a content of 0.5% Fe – 201 units, 0.25% Fe — 196 units, and alloys containing 6 % Zn — 151 (1% Fe), 141 (0.5% Fe), and 119 (0.25% Fe) units. According to the results obtained, further research directions aimed to study the nature of the distribution of calcium between the intermetallic phases (AlZn)₄Ca and Al₁₀CaFe₂ have been substantiated. It is assumed that the composition Al – 3% Mg – (6–8%) Zn – 2% Ca – 0.5% Fe is capable of providing high hardening and workability not only in the casting state, but also upon metal forming.

The article was prepared within the framework of the AgreementNo. 14.578.21.0220 (the unique identifier of the RFMEFI57816X0220) for granting a subsidy from the Ministry of Education and Science of Russia within the framework of the federal program “Research and development in priority areas for the development of Russia's scientific and technological complex for 2014–2020”.

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