RU2478131C2 - Refractory castable aluminium alloy - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to casting critical parts to be operated at high loads at 300-350°C, e.g. ICE components, valves and accessories of hydraulic works, stages of borehole pumps, heating radiator parts, etc. Proposed composition contains the following substances, in wt %: 1.5-2.5 Ni; 1-2 Mn; 0.3-0.7 Fe, 0.2-0.6 Zr, 0.02-0.12 Sc, 0.002-0,1 Ce, at content of zirconium and scandium satisfying the condition 0.44<2·C_Zr+C_Sc<0.64. Note here that said zirconium and scandium exist in alloy structure as Al(Zr,Sc) phase with Ll₂ crystal lattice and mean size of nanoparticles not exceeding 20 nm.

EFFECT: new sparingly alloyed refractory alloy.

1 tbl, 4 ex, 3 dwg

Description

The invention relates to the field of metallurgy of aluminum-based materials and can be used for the manufacture of castings designed to produce critical parts operating under high loads at temperatures up to 300-350 ° C. Among them: automotive engine parts (cylinder heads, water pump housings, intake pipes, etc.), aviation parts (housings, covers, nozzles, valves, flanges, etc.), water intake fittings, submersible pump stages for oil and gas complex, details of heating radiators, etc.

One of the disadvantages of branded aluminum alloys, which prevents their wider use, is the limitation on operating temperatures. Even for the best alloys based on this characteristic, based on the Al-Cu system of the AM5 type [GOST 1583-93], operating temperatures do not exceed 250-300 ° С. At the same time, the minus of the latter is the fact that the technology for producing castings from them requires complete heat treatment, including the hardening operation. This increases their cost and often leads to the appearance of an unwanted marriage, in particular to size instability. It should also be noted that alloys of type AM5 have very low casting properties, which makes it difficult to obtain thin-walled castings of complex shape from them [Zolotorevsky B.C., Belov N.A. Metallurgy of foundry aluminum alloys. - M .: MISiS, 2005, 376 p.].

To eliminate the disadvantages inherent in AM5 alloys, see [Belov NA "Principles of Optimizing the Structure of Creep-Resisting Casting Aluminum Alloys Using Transition Metals". Journal of Advanced Materials, 1994 1 (4), p.321-329], it was proposed to create heat-resistant alloys based on the eutectic (Al) + Al ₃ Ni due to alloying with nickel and other transition metals (Mn, Zr, Cr, Sc, V etc.). Alloys constructed in this way are oriented to traditional foundry technologies and the available equipment, the technological cycle for producing finished parts from them is much shorter than alloy alloys based on the Al-Cu system (in particular, there is no hardening operation). This approach is reflected in a number of patents. In particular, in the patent of the Russian Federation No. 2001145 (bull. 37-38 dated 10/15/1993, MISiS) an aluminum-based alloy is claimed containing 3-6.5% Ni, 0.5-2% Mn, 0.2-0, 8% Sc and 0.05-0.3% Zr. This alloy has excellent casting properties and higher heat resistance at 300-350 ° C in comparison with alloys of the AM5 type. On the basis of the (Al) + Al ₃ Ni eutectic, several experimental alloys were developed (they were called nikalin), which successfully underwent pilot testing under the conditions of IL and VASO [Belov N.A., Zolotorevsky BC “ Casting alloys based on aluminum-nickel eutectic (nikalin) as a possible alternative to silumin ”. Non-ferrous metals, 2003, No. 2, S.99-105]. The disadvantage of these alloys is the high nickel content, which negatively affects the cost of castings. The second disadvantage is the strict restriction on the maximum permissible iron content, i.e. their production requires high-purity aluminum, which also leads to a rise in the cost of castings.

The closest alloy to the proposed one is the alloy disclosed in US 2004/0261916 F1 (publ. December 30, 2004, patent holder: Alcoa Inc.). This alloy, designed to produce shaped castings by various casting methods, contains, wt.%: 0.5-6% Ni, 1-3% Mn, up to 1% Zr, up to 0.6% Sc. In the private claims of this patent, the most preferred concentrations of alloying elements are claimed: ~ 4% Ni, ~ 2% Mn, ~ 0.6% Zr (or ~ 0.3% Sc). The main disadvantage of this alloy is its uneconomical composition: high nickel content and the absence of iron among the alloying components. This prevents the use of scrap waste for its production. It should also be noted that the increased nickel content negatively affects the overall corrosion. Under the influence of a medium-aggressive environment (for example, sea water), this leads to a strong darkening of the surface of the castings.

The objective of the invention is the creation of a new heat-resistant alloy based on aluminum (economically alloyed nikalin), designed to produce shaped castings of complex shape containing not more than 2.5% Ni and allowing at least 0.3% Fe.

The problem is solved in that the casting alloy based on aluminum, containing Nickel, manganese, zirconium and scandium, is characterized in that it additionally contains iron and cerium at the following concentrations of alloying components, wt.%:

Component The content in the alloy, wt.% Nickel 1.5-2.5 Iron 0.3-0.7 Manganese 1.0-2.0 Zirconium ¹ 0.2-0.6 Scandium ¹ 0.02-0.12 Cerium 0.002-0.1 ^{1 in} order to achieve the best combination of mechanical properties, the condition must be fulfilled: 0.44 <2 · C _Zr + C _Sc <0.64 (where C _Zr and C _Sc are the concentrations of zirconium and scandium in the alloy, wt.%).

Zirconium and scandium are present in its structure in the form of nanoparticles of the Al ₃ (Zr, Sc) phase (crystal lattice L1 ₂ ) having an average size of not more than 20 nm. This allows castings to achieve the following level of mechanical properties: temporary resistance (σ _in ) of at least 250 MPa, elongation (6) of at least 4%, 100-hour strength (σ ₁₀₀ ) at 350 ° C of at least 40 MPa, however, the strength properties do not decrease after heating at temperatures up to 400 ° C inclusive when holding for up to 10 hours.

The invention consists in the following. Nickel and iron concentrations within the stated limits provide high technological properties when producing thin-walled castings (in particular, mold filling and resistance to the formation of hot cracks). These elements are completely included in the phases Al ₃ Ni and Al ₉ FeNi of eutectic origin. To achieve the best mechanical properties, in particular ductility, the eutectic should have a sufficiently dispersed structure similar to that shown in figure 1. The concentration of manganese in the stated limits provides the necessary level of heat resistance. After heat treatment, manganese is present in the structure in the form of secondary precipitates of the Al ₆ Mn phase, the typical size of which is 100-500 μm (figure 2). The zirconium and scandium concentrations within the stated limits provide the necessary effect of dispersion hardening due to the formation of an Al ₃ Zr and / or Al ₃ (Zr, Sc) phase with an L1 ₂ lattice during annealing. The average size of these nanoparticles should not exceed 20 nm (figure 3). Cerium, within the declared limits, performs an auxiliary function, neutralizing the negative effect of silicon impurities on the heat resistance index.

EXAMPLE 1

Six alloys were prepared, the compositions of which are listed in Table 1. All alloys were prepared in an electric resistance furnace in graphite chamotte crucibles based on remelting waste of wire rod grade A5E (0.4% impurities, the rest is aluminum). Separately cast samples were obtained from experimental alloys according to GOST 1583-93. These samples were annealed in a muffle electric furnace according to the following regime: 350 ° C, 3 hours + 450 ° C, 3 hours. Mechanical properties (tensile strength - σ _in , conditional yield strength - σ _0.2 and elongation - δ) were determined by the results of uniaxial tensile tests on a Zwick Z250 machine. Tests at room temperature were carried out according to GOST 1497-84. Tests for 100-hour strength at 350 ° C were carried out according to GOST 10145-81.

Table 1 The compositions of experimental alloys and their properties after heat treatment No. Alloying components ¹ , wt.% Fur. tensile properties Ni Mn Fe Zr Sc Xie Ti σ _in , MPa σ _0.2 , MPa δ,% one one 0.5 0.1 0.1 0.01 0.001 135 75 14.5 2 1,5 2 0.7 0.2 0.12 0.1 250 160 6.5 3 2 1.4 0.5 0.4 0.05 0.01 260 170 7.5 four 2,5 one 0.3 0.6 0.02 0.002 255 165 6.0 5 3 2,5 one 0.8 0.2 0.2 190 185 0.5 6 four 2 0.3 0.15 0.1 205 155 3,5 ¹ aluminum base (with impurities)

From table 1 it is seen that only the inventive alloy (compositions 2-4) provides the best combination of temporary resistance (σ _in ), yield strength (σ _0.2 ) and elongation (δ): temporary resistance (σ _in ) not less than 250 MPa, yield strength (σ _0.2 ) of at least 160 MPa, elongation (δ) of at least 4%.

In alloy 1, the strength is less than the required level, which is associated with an insufficient amount of precipitation of the Al ₃ phase (Zr, Sc).

Alloy 5 has a low value of 5, which is associated with the presence of primary crystals of intermetallic compounds.

The prototype alloy (composition 6) is inferior to alloys 2-4 in mechanical properties. However, it contains more nickel.

EXAMPLE 2

Samples of the inventive alloy composition No. 3 were annealed at 400 ° C for 10 hours. After the tensile test, the following values were obtained: temporary resistance (σ _in ) - 265 MPa, yield strength (σ _0.2 ) - 170 MPa. Thus, a decrease in strength properties compared with the initial level (see table 1) did not occur, due to the high thermal stability of the alloy structure.

EXAMPLE 3

Samples of the inventive alloy composition No. 3 were tested for 100 hours at 350 ° C. The obtained value (σ ₁₀₀ ) was 43 MPa.

EXAMPLE 4

Samples of the inventive alloy composition No. 3 and prototype alloy No. 6 (see table 1) were tested for general corrosion in an aqueous solution of 5.7% NaCl + 0.3% H ₂ O ₂ . After aging for 24 hours, the inventive alloy had significantly less surface darkening compared to the prototype alloy. The increased corrosion resistance of the claimed alloy is due to the lower nickel content.

Claims (3)

1. Cast aluminum alloy based on nickel, manganese, zirconium and scandium, characterized in that it additionally contains iron and cerium in the following ratio, wt.%:
Nickel 1.5-2.5 Iron 0.3-0.7 Manganese 1.0-2.0 Zirconium 0.2-0.6 Scandium 0.02-0.12 Cerium 0.002-0.1
when the content of zirconium and scandium satisfies the following condition: 0.44 <2 · C _Zr + C _Sc <0.64, and zirconium and scandium are present in the alloy structure in the form of an Al (Zr, Sc) phase with a crystal lattice Ll ₂ and medium the size of the nanoparticles is not more than 20 nm. 2. The alloy according to claim 1, characterized in that it is made in the form of casting and after annealing has a temporary resistance (σ _in ) of at least 250 MPa, elongation (δ) of at least 4%. 3. The alloy according to claim 2, characterized in that its 100-hour strength (σ ₁₀₀ ) at 350 ° C is at least 40 MPa.

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