National University of Science and Technology MISiS, Moscow, Russia:
V. V. Doroshenko, Engineer of a Chair “Metal Forming”
E. A. Naumova, Assistant Professor of a Chair “Metal Forming”, e-mail: jan73@mail.ru
T. A. Bazlova, Assistant Professor of a Chair “Casting Technologies and Art Material Treatment”
M. E. Samoshina, Senior Researcher of a Chair “Metal Forming”

Al – Ca – Zn and quaternary Al – Ca – Zn – Mg systems were studied. Experimental alloys containing 2.5% Mg, 4–10% Ca and 1–12% Zn were melted in an induction furnace by RELTEC, using the aluminum A99. Four  portions of metallic calcium were introduced at an aluminum melt temperature of about 780 ^оC in an aluminum foil. At a melt temperature of 730–740 ^оC, zinc and magnesium were added as two portions wrapped in aluminum foil. The metal was cast into a steel mold at a temperature of 710–720 ^оC, obtaining flat castings with dimensions of 15×30×180 mm. The microstructure of the samples was studied with an Olympus GX51 (OM) optical microscope and a scanning electron microscope TESCAN VEGA 3 (SEM). The program Thermo-Calc (database TTAL5) was used to calculate the phase composition of the Al – Ca – Mg – Zn system. Fragments of the phase diagrams of Al – Ca – Mg, Al – Ca – Zn, and Al – Ca – Zn – Mg in the aluminum-rich region were constructed using the calculated and experimental methods: projections of the liquidus and solidus surfaces of the Al – Ca – Zn – Mg system, as well as polythermal sections at 2.5% Mg and variable amounts of calcium and zinc. The calculated and experimental data agree well with each other. The pre-eutectic alloys consist of dendrites (Al) and eutectics (Al) + Al₄Ca. Additions of magnesium and zinc significantly reduce the concentration of calcium at which the primary crystals of the Al₄Ca phase appear. The structure of the eutectic in the ternary alloys of the Al – Ca – Mg system is much coarser than in the Al – Ca system alloys, and the structure of the eutectic of the Al – Ca – Zn ternary alloys is coarser than in the Al – Ca alloys, but thinner than in the Al – Ca – Mg ones. Using the MRSA method, it was found that magnesium, when its content in the alloy is 2.5%, does not dissolve in the Al₄Ca phase, and zinc dissolves in it. As the zinc content increases, the proportion of primary crystals increases. According to MRSA, the percentage of zinc in primary crystals varies depending on its content in the alloy from 5.5% (Al – 10 Ca – 1 Zn – 2.5 Mg) to 23% (Al – 10 Ca – 8 Zn – 2.5 Mg). The more zinc are present in the primary crystals, the more they look more fragmented.

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