Pacific National University, Khabarovsk, Russia:

E. H. Ri, Head of the Department of Foundry Engineering and Metal Technology, erikri999@mail.ru
H. Ri, Professor of the Department of Foundry Engineering and Metal Technology

M. V. Kolisova, Post-graduate student of the direction “Foundry Engineering”, laboratory technician of the Department of Foundry Engineering and Metal Technology

National University of Science and Technology “MISiS”, Moscow, Russia:
V. B. Deev, Professor of the Department of Foundry Technology and Art Processing of Materials

Using the methods of optical and electronic scanning microscopy and micro X-ray analysis, the features of the formation of the structural components of the AM4.5Kd alloy and their properties under the influence of cerium and lanthanum as modifiers were studied. The amount of modifiers varied from 0.05 to 0.3 wt.% at the variation interval of 0.05 wt.%. When modifying the AM4,5K alloy with cerium (up to 0.1 wt.%) and lanthanum (0.15 wt.%) a sharp grinding of structural components — α-solid solution and eutectic, followed by a slight enlargement of Ce and La up to 0.3 wt.% took place. The regularities of changes in composition and microhardness of α-solid solution and eutectic of various origins depending on the amount of cerium and lanthanum were established. The presence of two types of α-solid solution (α₁ and α₂) due to intradendritic segregation of copper and five types of eutectic components in the modified and unmodified AM4.5Kd alloy was revealed:
1. α₁-solid solution with the decreased content of copper (0.5–0.7 at.%).
2. α₂-solid solution with the increased content of copper (1.5–2.0 at.%) located on the periphery of the α-solid solution dendrites and having a higher nanohardness (1419 MPa) than the α₁ solid solution (939 MPa). In contrast to the initial and lanthanum alloys AM4.5Cd, the intradendritic segregation of copper is weakened in cerium, which indicates its partial homogenization in the process of alloy crystallization.
3. Eutectic without Cadmium with the decreased (<10 at.%Cu) and the increased (>10 at.% Cu) content of copper.
4. Eutectic containing Cadmium with the decreased (<1.0 at.% Cd) and increased (>1.0 at.% Cd) content of cadmium. The modified Ce and La eutectic.
Regularities of modifications in the composition of α-solid solutions (α₁ and α₂) and eutectic components and their microhardness depending on the amount of Ce and La additives were established. An increase in the copper content in the above mentioned eutectics should contribute to the formation of highly hard Al₂Cu particles and the increase in the eutectic microhardness. Additions of large amount of cerium might lead to the decrease of the eutectic microhardness due to the crystallization of a large amount of high solid particles of Al₂Cu, causing the embrittlement of the eutectic. The influence of these two factors contributes to the leveling of microhardness in the range of cerium addition of 0.1–0.3 wt.%. Established dependences of the change in the nature of distribution of elements in the structural components of the AM4.5Kd alloy and their microhardness depending on the amount of lanthanum additive were also justified.
The work was done with financial support from the Ministry of Science and Higher Education of the Russian Federation as a part of the state assignment number 11.3014.2017 / 4.6 “Study of the possibilities for obtaining REM-containing ligatures for the modification of metal alloys”. The studies were carried out on the equipment of the Joint Center for “Applied Materials Science” at Pacific National University with the financial support of the Ministry of Science and Higher Education of the Russian Federation with in the framework of the state program assignments (state registration number 11.7208.2017 / 7.8 and 11.7213.2017 / 7.8).

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