• Українська
  • English
ISSN 2664-2441 (Online)
ISSN 2073-9583 (Print)

Phase transformations during the crystallization of the AK7 alloy, neutralization of the harmful effect of iron by treating the melt with a pulsed electric current

Metalozn. obrobka met., 2020, vol. 26 (96), 17-29
https://doi.org/10.15407/mom2020.04.017

A.G. Prigunova, Doctor of Technical Science, Professor, Head of Department, аdel_nayka@ukr.net

UDC 669.2/.8.017 : 537.3.39
Download: PDF

Summary

The method of quenching-microstructural analysis, the so-called "stop-quenching", was used to study phase transformations during crystallization of the AK7 casting alloy of the Al-Si-Mg system. The alloy is smelted from scrap and waste, therefore it contains a large amount of impurities, including iron, copper. It was found that the formation of the structure of the AK7 alloy is carried out in the course of the following reactions: 1. Р → Аlα. 2. P → α-(Fe, Mn) 3Si2Al15 + Alα. 3. P → β-FeSiAl5 + Alα. 4. P + β-FeSiAl5 → α-(Fe, Mn, Cu)3Si2Al15. 5. P → β-FeSiAl5 + Si + Alα. 6. P → β-FeSiAl5 + α-(Fe, Mn, Cu)3Si2Al15 + Si + Alα. At the last stages of crystallization, eutectics are formed, which include phases with magnesium and copper: Mg2Si, π-FeMg3Si6Al8, W-Cu2Mg8Si6Al and  θ-CuAl2. The transformation P → β + Si + Alα is realized both by the mechanism of cooperative growth of the β, Si, and Alα phases, and by the formation of double eutectics: P → Si + Alα and P → β + Alα, which grow simultaneously in the same temperature range from various centers of crystallization. The four-phase eutectic transformation P → β + α + Si + Alα is carried out according to the type of double or triple eutectic reactions: P → Si + Alα; P → α + Alα; P → β + Alα; β + Si + Alα. The main iron-containing phase in the AK7 alloy is the needle-shaped intermetallic compound β-FeSiAl5 - a stress concentrator, which leads to a decrease in mechanical properties. In this work, the neutralization of the harmful effect of iron was carried out by treating the melt with a unipolar pulsed electric current, under the influence of which the cluster structure of the melt changes. During crystallization, instead of β, a branched phase α is formed. The ratio of intermetallic compounds β and α depends on the processing modes. With optimal parameters of density and current frequency, at which the volume fraction of the branched phase α is the largest, the strength of the AK7 alloy increases by 32.1%, the hardness by 16.7%, and the relative elongation by 2.5 times, bringing its mechanical properties closer to the primary alloy AK7h.
Keywords: aluminum-silicon alloys, phase transformations, iron-containing intermetallic compounds, growth forms, treatment of the melt with an electric current.

References

  1. Prigunova A.G., Belov N.A., Taran Yu.N., Zolotorevskiy V.S., Napalkov V.I., Petrov S.S. Siluminy. Atlas mikrostruktur i fraktogramm promyshlennykh splavov (Silumin. Atlas of microstructures and fractograms of industrial alloys): Sprav. izd., Moscow, MISiS, 1996, 175 p. [in Russsian].
  2. Bychkov Yu.B. Priroda vtorichnykh doevtekticheskikh siluminov, optimizatsiya ikh sostavov i svoystv (The nature of secondary hypoeutectic silumins, optimization of their compositions and properties): dis. na soisk. uchenoy stepeni dokt. tekhn. nauk, Moscow, MISiS, 1987, 354 р. [in Russsian].
  3. Kutsova V.Z., Ayupova T.A., Ambrazhey M.Yu. Stroitelstvo, materialovedeniye, mashinostroyeniye: sb. nauchn. Trudov, Dnepropetrovsk : PGAS, 2007, Vоl. 41,  Part 1, рр. 18-30 [in Russsian].
  4. Sínchuk A.V., Tsurkín V.M., Fedchenko N.A. Metaloznavstvo ta obrobka metalív, 2012, No. 34,  pp. 36-43 [in Ukrainian]. 
  5. Deyev V.B., Bashmakova N.V., Prikhodko O.G. Selyanin I.F. Polzunovskiy al'manakh, 2008, No. 3, рр. 77-81 [in Russsian].
  6. Taran Yu.N., Prigunova A.G., Kazimirova I.Ye. DAN SSSR, 1986,  T. 289, No. 3, рр. 668-670 [in Russsian].
  7. Patent No.101208 Ukraine, MPK S22V9/00. Sposib virobnitstva siluminiv [method of producing silumin], Petrov S.S., Prigunov S.V., Prigunova A.G., Klyuchnik D.N.; No. а201101616, zayavl. 11.02.2011, opubl. 11.03.2013, Byul. No. 5/2011, 10 p. [in Ukrainian]. 
  8. Borisov G.P., Tsurkin V.N., A.V. Sinchuk, Ivanov A.V. Metallurgiya mashinostroyeniya, 2010, No. 5, pp. 33-40 [in Russsian].
  9. Yakimov V.I., Marin B.N., Zelinskiy V.V. [i dr.] Metallurgiya mashinostroyetiya, 2003, No. 3, рр. 36-39 [in Russsian].
  10. Vernidub A.G., Volkov A.G., Grabovskiy V.M. [i dr.] Protsessy lit'ya, 2005, No. 1, рр. 64-67 [in Russsian].
  11. Patent No. 136173, Ukraine, MPK GO1N25. Sposib doslidzhennya fazovikh peretvoren i morfologii faz u protsesi kristalízatsii [Methods of continuous phase transformation and morphology of phases in the process of crystallization], Prigunova A.G., Shenevidko L.K., Sheygam V.Yu., Prigunov S.V., Koshelev M.V; zayavl. 11.02.2019; opubl. 12.08.2019; Byul. no. 5/2019, 4 p. [in Ukrainian]. 
  12. Prigunova A.G., Belik V.I., Shenevidko L.K., Koshelev M.V. Protsesi littya, 2020, No. 3 (141), pp. 27-41 [in Ukrainian]. https://doi.org/10.15407/plit2020.03.027
  13. Saltykov S.A. Stereometricheskaya metallografiya (Stereometric metallography), Moscow, Metallurgiia, 1976, 272 p. [in Russsian].
  14. Prigunova A.G. Zelinskaya G.M., Koshelev M.V., Protsessy lit'ya,  2019, No. 4 (136), pp. 20-34 [in Russsian].
  15. Taran Yu.N., Prigunova A.G., Gal'chak V.P., Petrov S.S. Rasplavy, 1987,  T.1,Vol. 4, pp. 111-116 [in Russsian].
  16. Kharkov Ye.I., Lysov V.I., Fodorov V.Ye. Fizika zhidkikh metallov (Physics of liquid metals), Kiev : Vishcha shkola, 1979, 248 p. [in Russsian].