Institute of Light Materials and Technologies Ltd., Moscow, Russia:

S. V. Matveev, Director of the department for Foundry Alloys1, Candidate of Technical Sciences, e-mail: Sergey.Matveev4@rusal.com
D. O. Fokin, Project Manager
D. K. Ryabov, Director of Science

The phase composition and the mechanical properties of the AZ5NF with various contents of silicon impurities alloy were investigated by both calculation and experimental methods. For evaluation of the alloy phase composition and the effect of the chemical composition, CALPHAD method integrated in Thermo-Calc software was applied. Further scanning electron microscopy technique a significant increase of the volume fraction of Mg2Si phase with an increase of silicon content from 0.1% to 0.3%. It is shown that in case of silicon content higher than 0,2 wt.% Mg2Si phase starts forming during equilibrium crystallization. This phase forms as the thin layers at the grain boundaries. This leads to brittle intergranular fracture and significant reduction of the alloy ductility both in the as-cast state and in T6 temper. Based on this limits for the silicon content in AZ5NF have been proven. It is shown that dissolution of Mg2Si phase (full or partial depending on silicon content) requires solid solution treatment. Following quenching and artificial ageing provide high strength and ductility.

1. GOST 1583–93. Aluminium casting alloys. Specifications. Introduced: 01.01.1997. Мoscow : Izdatelstvo standartov, 1993.

2. Mondal C., Mukhopadhyay A. K., Raghu T., Varma V. K. Tensile properties of peak aged 7055 aluminum alloy extrusions. Materials Science and Engineering A. 2007. Vol. 454–455. pp. 673–678.
3. Senatorova O. G., Bronz A. V., Cheverikin V. V., Somov A. V., Blinova N. E. Study of the structure and properties of especially strong aluminum alloys of the Al – Zn – Mg – Cu system. Metallurgist. 2017. Vol. 60, No. 9–10. pp. 978–982.
4. Chen Z., Mo Y., Nie Z. Effect of Zn content on the microstructure and properties of sSuper-high strength Al – Zn – Mg – Cu alloys. Metallurgical and Materials Transactions A. 2013. Vol. 44, No. 8. pp. 3910–3920.
5. Vojtch D., Šerák J., Eckert O., Kubatík T., Barta . et al. High strength Al – Zn – Mg – Cu – Ni –Si alloy with improved casting properties. Materials Science and Technology. 2003. Vol. 19, No. 6. pp. 757–761.
6. Gong B. S., Liu Z. J., Wang Y. L., Zhang Z. J., Zhang P., Jiang H.C. et al. Improving the fatigue strength of A7N01 aluminum alloy by adjusting Si content. Materials Science and Engineering A. 2019. Vol. 19. pp. 15–22.
7. Hatch J. Aluminium: Properties and Physical Metallurgy. Translated from English. Moscow : Metallurgiya, 1989. 324 p.
8. Belov N. А. Phase composition of industrial and promising aluminum alloys. Moscow : MISiS, 2010. 511 p.
9. Zou X., Yan H., Chen X. Evolution of second phases and mechanical properties of 7075 Al alloy processed by solution heat treatment. Transactions of Nonferrous Metals Society of China. 2017. Vol. 27, No. 10. pp. 2146–2155.
10. Shurkin P. К., Belov N. А., Musin А. F., Samoshina М. Е. Influence of calcium and silicon on the nature of crystallization and hardening of Al – 8% Zn – 3% Mg alloy. Fizika metallov i metallovedenie. 2020. No. 2. pp. 149–156.
11. Belov N. A., Akopyan T. K., Mishirov S. S., Korotkova N. O. Effect of Fe and Si on the microstructure and phase composition of the aluminiumcalcium eutectic alloys. Non-ferrous Metals. 2017. No. 2. pp. 37–42.
12. Belov N. A., Naumova E. A., Doroshenko V. V., Bazlova T. A. Effect of scandium on the phase composition and hardening of casting aluminum alloys of the Al– Ca – Si system. Russian Journal of Non-Ferrous Metals. 2016. Vol. 57, No. 7. pp. 695–702.
13. Thermo-Calc Software TTAL8 Al-Alloys. Available at: https://www.thermocalc.com/content/uploads/Documentation/Databases/ThermoTech/ttal8.pdf (accessed: 27.08.2020).
14. Pelton D., Eriksson G., Bale C. W. Scheil-Gulliver constituent diagrams. Metallurgical and Materials Transactions A. 2017. Vol. 48, No. 6. pp. 3113–3129.
15. Bryantsev P. Yu. Study and optimization of heat treatment modes of Al – Mg – Si system alloys. thesis of inaugaration of Dissertation … of Candidate of Engineering Sciences. Moscow : MISiS, 2005. 25 p.
16. GOST 1497–84. Metals. Methods of tension test. Introduced: 01.01.1986. Moscow : Izdatelstvo standartov, 1984.
17. GOST R 8.736–2011. State system for ensuring the uniformity of measurements. Multiple direct measurements. Methods of measurement results processing. Main positions. Introduced; 01.01.2013. Moscow : Izdatelstvo standartov, 2011.
18. Zolotorevskiy V. S., Belov N. А. Metallurgy of foundry aluminum alloys. Moscow : MISiS, 2005. 376 p.