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MATERIALS SCIENCE
ArticleName The technology of synthesis of a master alloy with nickel and rare earth aluminides and its influence on the structure formation, segregation processes and properties of aluminum alloys
DOI 10.17580/tsm.2018.05.08
ArticleAuthor Ri E. H., Ri Khosen, Deev V. B., Goncharov A. V.
ArticleAuthorData

Pacific National University, Khabarovsk, Russia:

E. H. Ri, Head, Chair of Foundry and Process Metallurgy
Khosen Ri, Professor, Chair of Foundry and Process Metallurgy
A. V. Goncharov, Post-Graduate Student, Chair of Foundry and Process Metallurgy


National University of Science and Technology “MISiS”, Moscow, Russia:

V. B. Deev, Professor, Chair of Foundry Technologies and Artistic Processing of Materials, e-mail: deev.vb@mail.ru

Abstract

This paper describes the developed technology for obtaining master alloys based on nickel and rare earth (REM) aluminides. There were used a complex modifier AKTse (АКЦе) (composition, % (wt.): 30–33 Al, 28–30 REM, 3–4 Ca, reminder — Ni), produced by Complex Modifiers Ltd, and A7 grade aluminum (impurities sum of Si and Fe <0.3% (wt.)) for master alloys creation. Two methods are proposed for obtaining master alloys. The first one is the saturation of liquid aluminum with a complex AKTse modifier at 1400 оC to a content of 60% (wt.) in increments of 10% (wt.). The second one is the saturation of molten complex modifier AKTse with aluminum at 1400 оC to a content of 60% (wt.) in increments of 10% (wt.). Regardless of the method for master alloys obtaining with additives of 60% (wt.) AKTse or A7, the content of the main alloying elements which are Al, Ni, REM practically does not vary. The average chemical composition of the master alloy, % (wt.), is the following: 68.1 Al; 1.15 Ca; 20.0 Ni; 12.25 REM (3.82 La, 8.43 Ce). The first method of master alloys A7 — AKTse obtaining can be considered more rational. Intermetallic compounds such as nickel aluminides (Al3Ni) and REM (Al11REM3) crystallize in pure argon atmosphere with the addition of 50–60% (wt.) AKTse in liquid aluminum at 1400 оC. With the help of electron microscopy and X-ray spectrum analysis, nickel and REM aluminides were identified, their microhardness is determined. It was found that increase of a master alloy (A7 + 60% AKTse (wt.)) addition in molten aluminum leads to increase of the crystallization start temperature to ~825 оC, and intermetallic phases τcr crystallization time increases in accordance with expansion of the crystallization temperature range. In this case, eutectic crystallization start temperature te and the duration of this processe decrease dramatically. Also the synthesized alloying composition influence with Ni and REM aluminides on the structure formation, the character of elements distribution and the microhardness of the structural components of the solid α-solution and eutectic in the AK7ch (AK7ч) alloy was studied in this paper. The increase in the addition of a master alloy leads to an increase in the microhardness of the solid α -solution and the eutectic. The formation features of four types of various chemical compositions of quasi-eutectics are determined:
1) solid α -solution + Si;
2) solid α -solution + Si + Fe + Mn;
3) solid α -solution + Si + Fe, but without Mn;
4) modified eutectic, contains all the components of the master alloy.
The crystallization of Ni and REM aluminides, which have a high microhardness, is possible in the modified eutectic 4. The total eutectic microhardness depends on: the ratio of 1–4 eutectic distribution as well as the amount and dispersity intermetallic compounds.

The research was carried out with the sponsorship of the Ministry of Education and Science of the Russian Federation within the fulfilment of government assignments (No. 11.7208.2017 / 7.8, 11.3014.2017 / 4.6 and 11.7213.2017 / 7.8) on the equipment of the Chair of Foundry and Process Metallurgy and the Centre of Collective Usage for Applied Materials Science, Pacific National University.

keywords Alloying composition, synthesis, aluminum alloys, nickel aluminides, rare earth aluminides, crystallization, modification
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