Pacific National University, Khabarovsk, Russia:

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

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

V. B. Deev, Professor of a Chair “Foundry Technologies and Art Material Treatment”

A new technology for obtaining ligature alloys that consist of third group transition metal (Ce, La and Y) aluminides was developed. The technology is based on adding cerium, lanthanum and yttrium into an A95 aluminium alloy at a temperature of 900 ^оC in argon atmosphere. The ratio of elements is as follows: cerium 7…10; lanthanum 3.5…5.0; yttrium 15…20; the rest is aluminium. The optimal ratio of Y, Ce and La is 2 : 1 : 0.5. The features of microstructure of the new Al – Ce – La – Y ligature alloy system were studied with optical and electron microscopy, X-ray crystallography, measurements of micro- and nanohardness. The new ligature alloy consisted of pure aluminium crystals, Al₃Y-type intermetallic compounds – yttrium aluminide with REM and Al₁₁REM = Al_3,66REM (Ce and La) with Y and Al + Al_xREM_yY_z eutectic. REM aluminide crystals with Y are brighter in colour, whilst Y crystals with REM are darker. By systematically studying the character of the distribution of elements into different structural components of the Al – Ce – La – Y alloy, we identified the following phases:
1. Yttrium aluminide with REM has the following stoichiometry, different from the standard Al₃Y compound: Al_xY_yREM_z, where x = 3.08…3.15 (arithmetic mean x = 3.11); y + z = 1.0. Microhardness of yttrium aluminide REM equals 6547 MPa (min 5233 MPa, max 8176 MPa), whilst nanohardness equals 9627 MPa (min 9410 MPa, max 9730 MPa).
2. REM aluminide with Y has a stoichiometric formula, different from the standard Al₁₁REM₃ = Al_3,66REM (Al_3,6Ce, Al_3,66La) compound: Al_xREM_yY_z, where x = 3.5…3.7 (arithmetic mean х = 3.6); y + z = 1.0. Microhardness is 4695 MPa (min 3230 MPa, max 854 MPa), whilst nanohardness equals 8560 MPa (min 8350 MPa and max 8710 MPa). 3. Eutectical REM aluminide with Y has an AlxREMyYz stoichiometry, where x = 3.51…3.9 (arithmetical mean х = 3.71); y + z = 1.0. Eutectic microhardness equals 423 MPa, whilst nanohardness equals 4580 MPa (min 4120 MPa and
max 5930 MPa).
4. Microhardness of pure aluminium amounts to 254 MPa.
The application area of the Al – Ce – La – Y ligature alloy:
1. The ligature alloy is added into a liquid cast iron (wt.%: 3.0–3.6% C; 1.5–2.0% Si; 0.5–1.0% Mn; 0.1–0.15% P; 0.05–0,07% S) by the dip method in quantity of 1.0–1.25 % of the liquid metal’s weight. The melting point of the ligature is 720–760 ^оС. The ligature is well absorbed into the cast iron. When adding the ligature into the liquid cast iron (at a 1300–1600 ^оС), no pyroeffect was observed, whilst the obtainment of spherical graphite was stable. There was no chilling effect in the case of V-sample. The structural robustness and plasticity of the cast iron with a spherical graphite are growing simultaneously.
2. The ligature alloy may be used for casting aluminium alloys to increase their mechanical properties through REM radically grinding the structural components (α-solid solution, primary and eutectical silicium) and changing the morphology of iron and silicon compounds.
Our investigations were carried out using the equipment of a chair “Foundry and Process Metallurgy” and multiple-access center “Applied Material Science” (Pacific National University) with the financial support of the Ministry of Education and Science of Russian Federation (state task No. 11.7208.2017/7.8, 11.3014.2017/4.6 and 11.7213.2017/7.8).

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