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.

1. Anthony U. U., Ellyott F. R., Boll M. D. Alyuminiy : svoystva i fizicheskoe metallovedenie : spravochnik (Aluminium : properties of physical metallurgy : reference book). Under the editorship of G. E. Hatch. Translated from English. Moscow : Metallurgiya, 1989. 324 p.
2. Zolotorevskiy V. S., Belov N. A. Metallovedenie liteynykh aluminievykh splavov (Physical metallurgy of casting aluminium alloys). Moscow : MISiS, 2005. 376 p.
3. Hengcheng Liao, Yuna Wu. Ke Ding, Hardening response and precipitation behavior of Al – 7 % Si – 0.3 % Mg alloy in a pre-aging process. Materials Science and Engineering: A. 2013. Vol. 560. pp. 811–816.
4. Mondolfo L. F. Struktura i svoystva splavov (Structure and properties of alloys). Translated from English. Moscow : Metallurgiya, 1979. 640 p.
5. Polmear I. J., John St. D. Light Alloys : From Traditional Alloys to Nanocrystals. Forth edition. Elsevier, 2005. 416 p.
6. Svoystva elementov : spravochnoe izdanie Kniga 1 (Properties of elements : reference book. Book 1). Under the editorship of M. E. Drits. Second edition. Moscow : Metallurgiya, 1997. 432 p.
7. Janz A., Gröbner J., Cao H., Zhu J., Chang Y. A., Schmid-Fetzer R. Thermodynamic modeling of the Mg – Al –Ca system. Acta Materialia. 2009. Vol. 57, iss. 3, February. pp. 682–694.
8. Aljarrah M., Medraj M., Wanga X., Essadiqi E., Muntasar A., Denes G. Experimental investigation of the Mg – Al – Ca system. Journal of Alloys and Compounds. 2007. Vol. 436. pp. 131–141.
9. Xu S. W., Oh-ishi K., Kamado S., Uchida F., Homma T., Hono K. Highstrength extruded Mg – Al – Ca – Mn alloy. Scripta Materialia. 2011. Vol. 65. pp. 269–272.
10. Kim W. J., Lee Y. G. High-strength Mg – Al – Ca alloy with ultrafine grain size sensitive to strain rate. Materials Science and Engineering: A. 2011. Vol. 528. pp. 2062–2066.
11. Toropova L. S., Eskin D. G., Kharakterova M. L., Dobatkina T. V. Advanced Aluminum Alloys Containing Scandium: Structure and Properties. Amsterdam : Gordon and Breach Science Publishers, 1998. 175 p.
12. Marquis E. A., Seidman D. N. Nanoscale structural evolution of Al3Sc precipitates in Al (Sc) alloys. Acta Materialia. 2001. Vol. 49. pp. 1909–1919.
13. Costa S., Puga H., Barbosa J., Pinto A. M. P. The effect of Sc additions on the microstructure and age hardening behaviour of as cast Al – Sc alloys. Materials and Design. 2012. Vol. 42. pp. 347–352.
14. Knipling K. E., Karnesky R. A., Lee C. P., Dunand D. C., Seidman D. N. Precipitation evolution in Al–0.1Sc, Al–0.1Zr and Al–0.1Sc–0.1Zr (at.%) alloys during isochronal ageing. Acta Materialia. 2010. Vol. 58. pp. 5184–5195.
15. Belov N. A., Belov V. D., Alabin A. N., Mishurov S. S. Termostoykiy liteynyy alyuminievyy splav (Heat-resistant casting aluminium alloy). Patent RF, No. 2478131. Published : March 27, 2013.
16. GOST 1583–93. Splavy alyuminievye liteynye. Tekhnicheskie usloviya (State Standard 1583–93. Aluminium casting alloys. Specifications). Introduced : January 01, 1997. (in Russian).
17. GOST 11069–2001. Alyuminiy pervichnyy. Marki (State Standard 11069-2001. Primary aluminium. Grades). Introduced : January 01, 2003. (in Russian).
18. GOST 9012–59. Metally. Metod izmereniya tverdosti po Brinellyu (State Standard 9012–59. Metals. Method of Brinell hardness measurement). Introduced : January 01, 1960. (in Russian).
19. Andersson J. O., Helander T., Hoglud T. THERMO-CALC & DICTRA, Computation Tools For Materials Science. CALPHAD. 2002. Vol. 26, No. 2. pp. 273–312.
20. Belov N. A., Sannikov A., Mishurov S. S., Belov V. D. Vliyanie kremniya na kharakter kristallizatsii i goryachelomkost zharoprochnogo liteynogo alyuminievogo splava AN2ZhMts (Influence of silicon on the type of crystallization and hot-shortness of heat resistant casting aluminium alloy AN2ZhMts (АН2ЖМЦ)). Tsvetnye Metally = Non-ferrous metals. 2011. No. 7. pp. 68–71.