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ArticleName Eutectic alloys, based on Al – Ca system with scandium addition as a possible alternative to thermally reinforced silumins
DOI 10.17580/tsm.2015.10.05
ArticleAuthor Naumova E. A., Bazlova T. A., Alekseeva E. V.

Bauman Moscow State Technical University, Material Science Chair, Moscow, Russia:

E. A. Naumova, Assistant Professor


National University of Science and Technology “MISiS”, Casting Process Technology Chair, Moscow, Russia:
T. A. Bazlova, Assistant Professor
E. V. Alekseeva, Student (Undergraduate)


The structure and properties of Al – Ca – Sc alloy in cast and heat-treated state were researched in comparison with AK7pch (АК7пч) silumin. Both alloys were obtained on the basis of high purity aluminium A99 (State Standard 11069–2001). Calcium was added in pure metallic form while scandium was added as an Al – 2 % Sc master alloy. Flat ingots (15x30x180 mm) were obtained by casting into graphite mould (the cooling rate during crystallization was near 10 K/s). Ingots were annealed according to the multistage modes in the temperature range of 200–600 °C for experimental alloy (initial state is cast) and in the temperature range of 200–400 °C for silumin (initial state is heat treatment according to the T6 mode) with a step of 50 °C and 3-hour holding at each stage. Microstructure of cast and heat-treated samples was studied using optical microscope Olympus GX51 (OM) and scanning electron microscope TESCAN VEGA 3 (SEM). The microscope TESCAN, equipped with energydispersion microanalyzer-attachment (Oxford Instruments) and Aztec software were also used for micro-X-ray-spectral analysis. The Thermo-Calc software (TTAL5 database) was used for the calculations of the phase composition of Al – Ca – Sc system. According to the calculations, only binary system phases (Al4Ca and Al3Sc) may be in equilibrium with solid aluminium solution. It was found that the (Al) + Al4Ca eutectic has a much disperse structure than (Al) + + (Si) eutectic: the average thickness of dendritic branches of Al4Ca phase is near 0.5 μm. The scandium content in (Al) + Al4Ca eutectic colonies corresponds to its content in alloy. There were found no primary crystals of Al4Ca phase. The Ca-containing alloy has the same hot tearing value as silumin, which suggests a possibility to produce the complicated castings. Maximum hardness in new alloy can be obtained without quenching by annealing after casting at the temperature of 300 °C. Calcium-containing alloy is more thermally resistant than silumin. There was substantiated the possibility of aluminium alloys use with calcium instead of traditional silumins for complex casting obtaining.
This work was carried out with the support of the grant of Russian Science Foundation 14-19-00632.

keywords Al – Ca – Sc system, Al3Sc nanoparticles, heat treatment, phase composition, microstructure, eutectic, hot tearing

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