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

A. V. Koltygin, Assistant Professor, Casting Process Technology Chair, e-mail: misistlp@mail.ru
A. A. Nikitina, Post-Graduate Student, Casting Process Technology Chair
V. E. Bazhenov, Senior Lecturer, Junior Researcher, Casting Process Technology Chair

The process of crystallization of Mg – 6.3% Al – 3.7% Ca – 0.3% Mn and Mg – 4.5% Al – 2% Ca – 0.5% Mn alloys was considered with application of modeling of the state diagram Mg – Al – Ca – Mn in the Thermo-Calc program. Their phase content in equilibrium conditions was researched. There was made a definition that both alloys are crystallized in the area of formation of Al₂Ca compound, and there should be no calcium compounds, having such composition of researched alloys in equilibrium structure. According to the state diagrams, the equilibrium structure of both alloys is a magnesium solid solution with inclusions of manganous Al₄Mn phase and areas of eutectic isolations of intermetallic Al₂Ca phases and a small amount of -phase (Mg₁₇Al₁₂), placed along the grain boundaries. There was researched the influence of heat treatment on morphology of eutectic isolations of Al₂Ca phase in alloys. Cast alloy samples were annealed during 20, 30, 50 and 100 hours at the temperature of 490 °C for Mg – Al 6.3% – 3.7% Ca alloy and at the temperature of 500 °C for Mg – 4.5% Al – 2.0% Ca alloy with following air hardening at the room temperature. The morphology of isolations of Al₂Ca phase was defined by deep etching of samples with dissolution of solid magnesium solution (Mg), when the Al₂Ca phase was almost not etched. Research of samples by electron microscopy mehods defined that the as-cast microstructure of investigated alloys consists of primary crystals of magnesium solid solution and eutectic isolations of Al₂Ca phase, having the shapes of plates or hyeroglyphs. During the annealing of researched alloys, the shape of eutectic inclusions is changed from plate to compact, which should make a positive effect on mechanical properties of the alloys.
This work was carried out within the State work “Scientific-research works (basic research, applied research and experimental development)” of the State task of the Ministry of Education and Science of Russian Federation in the sphere of scientific activities for 2014–2016. (task No. 2014/113).

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