Moscow Aviation Institute (National Research University), Moscow, Russia:

M. V. Zharov, Associate Professor at the Department of Computer-Aided Design of Metallurgical Processes, Candidate of Technical Sciences, e-mail: MaximZharov@mail.ru

This paper describes the results of a study that looked at granulated materials produced from high-strength aluminium alloys of the Al – Zn – Mg – Cu system by meltspinning. The concept of Steam Jacket is introduced, which stands for a layer of vapour that forms between the particle and the coolant and inhibits heat dissipation while also hindering the crystallization rate due to lower heat conductivity of water vapour. It was established that the vapour layer forms when the coolant comes in contact with the melt and heats up to the boiling point resulting in its transition from liquid phase to vapour. This paper describes how the particle crystallization rate can be increased by the vapour layer being constantly removed. The steam jacket that forms around a droplet gets removed due to a high speed with which the droplet travels through the coolant. What is crucial for industrial implementation of this process is not so much the design of the meltspinning unit but the velocity of the spray crucible. The paper describes the results of theoretical calculations, as well as proven experimental data, which can help determine what velocity a perforated cup should have to ensure sufficient initial speed of the droplet and constant removal of the steam jacket. It was established that by rising the rate of heat dissipation from solidified granules and, consequently, the crystallization rate one can enhance the strength of the resulting granulated aluminium alloys of the Al – Zn – Mg – Cu system. Thus, when dealing with Al – Zn – Mg – Cu alloys (such as ‘B95’, ‘В96ц’) with additional zirconium doping up to 0.5% for making pressed semi-finished products, the resultant material can have an up to 15% higher strength compared with similar granulated materials that are made using conventional processes and industrial solidification rates. It is pointed out that the technique that involves removal of the vapour layer around a forming granule is the only possible way to further raise the cooling rate and, consequently, the solidification rate. Bringing the granule size to the size of little powder particles can disrupt the following granule consolidation process meaning that it is not a feasible technique that could enhance the granulation process.

1. Kolpashnikov A. I., Efremov A. V. Granulated materials. Moscow : Metal lurgiya, 1977. 240 p.
2. Dobatkin V. I. Aluminium alloy ingots. Sverdlovsk : Metallurgizdat, 1960. 176 p.
3. Dobatkin V. I., Elagin V. I. Granulated aluminium alloys. Moscow : Metallurgiya, 1981. 176 p.
4. Ankudinov V. B., Marukhin Yu. A. Method for producing globular granules. Patent RF, No. 2032498. Applied: 14.12.1992. Published: 10.04.1995.
5. Kolpashnikov A. I., Efremov A. V., Silin M. B. Device for meltspinning. Certificate of Authorship RF, No. 403445. Published: 26.10.1973. Bulletin No. 3.
6. Murr L. E., Gaytan S. M. Electron beam melting. Comprehensive Materials Processing. 2014. Vol. 10. pp. 135–161.
7. Samal S. Thermal plasma echnology: the prospective future in material processing. Journal of Cleaner Production. 2017. Vol. 142. pp. 3131–3150.
8. Angelo P. C., Subramanian R. Powder metallurgy: science, technology and applications. New Delhi : PHI Learning Private Limited, 2009. 312 p.
9. Mohanty T., Tripathi B., Mahata T., Sinha P. Arc plasma assisted rotating electrode process for preparation of metal pebbles. India : 2014 International Symposium on Discharges and Electrical Insulation in Vacuum, 2014. pp. 741–744.
10. Karlsson J., Snis A., Engqvist H., Lausmaa J. Characterization and comparison of materials produced by electron beam melting (EBM) of two different Ti – 6Al – 4V powder fractions. Journal of Materials Processing Technology. 2013. Vol. 213, No. 12. pp. 2109–2118.
11. Zhu H., Tong H., Yang F. Cheng C. Plasma-assisted preparation and characterization of spherical stainless steel powders. Journal of Materials Processing Technology. 2018. Vol. 252. pp. 559–566.
12. Sentyurina Zh. A. Production of NiAl-based globular powders for additive manufacturing : Candidate of technical sciences dissertation. Moscow : MISiS, 2016. 168 p.
13. Entezarian M., Allaire F., Tsantrizos P., Drew R. A. Plasma atomization: A new process for the production of fine, spherical powders. The Journal of the Minerals, Metals and Materials Society. 1996. Vol. 48. pp. 53–55.
14. Bojarevics V., Roy A., Pericleous K. Numerical model of electrode induction melting for gas atomization. The International Journal for Computation and Mathematics in Electrical and Electronic Engineering. 2011. Vol. 30. pp. 1455–1466.
15. Baskoro A. S., Supriadi S., Dharmanto D. Review on plasma atomizer technology for metal powder. MATEC Web of Conferences. 2019. Vol. 269. pp. 1–9.
16. Xia Y., Khezzar L., Alshehhi M., Hardalupas Y. Droplet size and velocity characteristics of water-air impinging jet atomizer. International Journal of Multiphase Flow. 2017. Vol. 94. pp. 31–43.
17. Skuratov A. P., Pianykh A. A. Water cooling rate of a molten aluminium droplet: Simulation study. Nauchnye problemy transporta Sibiri i Dalnego Vostoka. 2009. No. 1. pp. 233–235.
18. Skuratov A. P., Pianykh A. A. Heat exchange during wet granulation of lead-bearing aluminium alloys. Thermophysics and Aeromechanics. 2012. Vol. 19, No. 2. pp. 155–162.
19. Launder B. E., Spalding D. B. Lectures in mathematical models of turbulence. London : Academic Press, 1972. pp. 157–162.
20. Silin M. B., Zharov M. V. Method of producing metal granules. Patent RF, No. 2117556. Applied: 24.09.1997. Published: 20.08.1998.
21. GOST 4784–2019. Aluminium and wrought aluminium alloys. Grades. Introduced: 01.09.2019. Moscow : Standartinform, 2019.
22. GOST 21073.0–75. Non-ferrous metals. Determination of grain size. General requirements. Introduced: 01.07.1976. Moscow : Izdatelstvo standartov, 1983.
23. GOST 21073.1–75. Non-ferrous metals. Determination of grain size by comparison with microstructure scale. Introduced: 01.07.1976. Moscow : Izdatelstvo standartov, 1983.
24. GOST 21073.2–75. Non-ferrous metals. Determination of grain size by grain calculation method. Introduced: 01.07.1976. Moscow : Izdatelstvo standartov, 1983.
25. GOST 21073.3–75. Non-ferrous metals. Determination of grain size by calculation of grain intersections. Introduced: 01.07.1976. Moscow : Izdatelstvo standartov, 1983.
26. GOST 21073.4–75. Non-ferrous metals. Determination of grain size by planimetric method. Introduced: 01.07.1976. Moscow : Izdatelstvo standartov, 1983.
27. Konkevich V. Yu., Lebedeva T. I., Bochvar S. G. Method of making billets from fast-crystallised aluminium alloys. Patent RF, No. 2467830. Applied: 05.09.2011. Published: 27.11.2012.
28. GOST 1497–84. Metals. Methods of tension test. Introduced: 01.01.1986. Moscow : Izdatelstvo standartov, 1984.
29. Teleshov V. V. The fundamental law of changing structure during solidification of aluminium alloys at varying cooling rates. Tekhnologiya legkikh splavov. 2015. No. 2. pp. 13–18.
30. Eskin G. I. A new pattern behind crystallization of metallic materials (a scientific discovery by VILS). Tekhnologiya legkikh splavov. 2010. No. 1. pp. 7–10.
31. Dobatkin V. I., Eskin G. I., Borovikova S. I. On the subdendritic structure formed in an ingot during solidification under ultrasonic melt treatment. Tekhnologiya legkikh splavov. 1971. No. 6. pp. 9–17.
32. Semenov E. I. Forging and stamping: Reference book. Vol. 1. Materials and heat. Equipment. Forging. Moscow : Mashinostroenie, 1985. 568 p.
33. Kvasov F. I., Fridlyander I. N. Commercial aluminium alloys. Moscow : Metallurgiya, 1972. 552 p.
34. Belokopytov V. I. Developing a forging process for pre-compacted aluminium alloy granules. Vestnik of Nosov Magnitogorsk State Technical University. 2016. Vol. 14, No. 3. pp. 25–31.