Samara National Research University, Samara, Russia¹; Technische Universität Bergakademie Freiberg, Freiberg, Germany²:

E. V. Aryshnskii, Assistant Professor^1,2, ar-evgenii@ya.ru

Saint-Petersburg Mining University, St. Petersburg, Russia:
V. Yu. Bazhin, Professor, Bazhin-alfoil@mail.ru

Technische Universität Bergakademie Freiberg, Freiberg, Germany:
R. Kawalla, Professor, rudolf.kawalla@imf.tu-freiberg.de

T he article reviews the studies on the microalloying of aluminum alloys with such transition metals as Nb, Zr, Hf and Sc for the purpose of grain refinement. It has been shown that each of these elements is intrinsically able to refine the structure during casting. Peritectic reaction explains the capability of all above elements, except Sc, to modify structure during casting. Zr and Sc belong to the best grain refiners in aluminum alloys, while Nb is close second, and Hf is also a good grain modifier. However, using these elements in combination gives higher effect on grain refinement and lower concentration required for it. Analysis of Al – Zr – Hf, Al – Sc – Hf, Al – Sc – Nb and Al – Zr – Nb ternary diagrams shows that Nb, Zr, Hf and Sc reduce each other’s solid solubility in aluminum, which makes their combined use in grain refinement very effective. In addition, it has been analyzed how beneficial complex microalloying can be for grain refinement during hot deformation. It is especially evident in magnesium rich aluminum alloys. Such alloys contain large amount of the second phase coarse particles, which present potential new grains nuclei. Besides, due to small size of subgrains in such alloys, these particles specifically will be the major nucleation source during recrystallization. At the same time, the above transition elements facilitate formation of secondary fine (including nano-size) particles, retarding recrystallization, thus stimulating activation of maximum nuclei. To achieve the maximum effect, it is necessary to maintain the correct proportion of coarse intermetallic compounds capable to be potential nucleation sites and fine particles precipitated from supersaturated solid solution, which shall retard recrystallization without blocking it completely.
The article is published as a platform for discussion.

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