Engineering Center «Innovation Casting Technologies and Materials», Moscow, MISiS, Russia:

M. E. Samoshina, Senior Researcher

Chair of Casting Processes Technology, MISiS, Moscow, Russia:

N. A. Belov, Professor, e-mail: nikolay-belov@yandex.ru

Vsevolozhsk plant of aluminium alloys, Vsevolozhsk, Russia:

S. V. Savchenko, Deputy Chief Executive Officer of Production

Piston alloys are a special group of aluminum-silicon alloys. A distinctive feature of their composition is high silicon content (10 to 27%). The main application of these alloys is the production of pistons for a variety of engines, compressors, etc. Piston alloys have a complicated phase composition, which requires the analysis of multicomponent phase diagrams. The systematic analysis of phase composition for piston alloys AlSi12CuMgNi and AlSi12Cu2MgNi based on the thermodynamic calculations of multicomponent phase diagrams in the Thermocalc software was performed. To analyze the effect of composition and temperature the isothermal and polythermal sections were constructed. It is shown that the presence of manganese and higher concentration of copper in the alloy AlSi12Cu2MgNi affects the phase composition. In the alloy AlSi12CuMgNi eutectic (Al)+(Si) is primary crystallizing, but in the alloy AlSi12Cu2MgNi the primary crystals are the particles of Al₁₅(FeMn)₃Si₂ phase. The effect of crystallization rate and cooling rate after annealing on the microstructure and phase composition of piston alloys was studied. To simulate different cooling conditions the initial industrial ingot was melted and then casted at 800 ^оС into a graphite mold (cooling rate is about 10 K/s) or cooled in the crucible with the same temperature in air (cooling rate is about 1 K/s). Heating for quenching was performed at 500, 520 and 540 ^оC. The heating time was 6 h. The specimens were quenched after annealing in water. The agreement between the results of phase compositiondetermining by microstructure analysis and by the method of thermodynamic calculations is found. In the alloy AlSi12Cu2MgNi structure after annealing at 540 ^оC identified obvious signs of overburning, while they were not found in structure of the alloy AlSi12CuMgNi. It can be explained by lower solidus temperature of the alloy AlSi12Cu2MgNi due to higher content of copper

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