RU2714564C1 - Cast aluminum alloy - Google Patents

Abstract

FIELD: metallurgy.SUBSTANCE: invention relates to metallurgy, namely to alloys based on aluminum, and can be used in production of thin-walled castings of complex shape, mainly by injection molding, and can be used for casting parts for automotive industry, housings of electronic devices, etc. From the material there can be obtained parts of critical purpose, capable to work, including at high temperatures up to 300 °C. Foundry alloy based on aluminum contains, wt.%: calcium 1.1–2.7, iron 0.05–0.25, manganese 1.2–2.4, silicon 0.06–0.22, at least one element selected from a group comprising zinc to 1.0, chromium 0.05–0.2, titanium 0.05–0.2, zirconium 0.05–0.18, vanadium to 0.15, scandium to 0.14, aluminum and unavoidable impurities – the rest.EFFECT: invention is aimed at production of cast aluminum alloys having the required combination of technological and mechanical properties.6 cl, 5 ex, 8 tbl, 1 dwg

Description

Technical field

The invention relates to the field of metallurgy, in particular, to aluminum-based alloys, and can be used in the preparation of complex castings by casting into a metal mold, mainly by injection molding.

State of the art

It is known that castings of complex shape, depending on the purpose, are made of thermally unstrengthened and hardened alloys of the Al-Si and Al-Mg systems. Castings intended for the most critical parts are usually used after heat treatment of type T6 and T5, including quenching in water or in air, respectively, with subsequent aging to increase the strength properties, see http://metalurgu.ru/termoobrabotka- metallov-i-splavov / termicheskaya-obrabotka-alyuminievyih-i-magnievyih-splavov.html

Thermally unstrengthened alloys used for injection molding based on the Al-Si system, for example, A413.2 or AK12pch (GOST 1583-93), are characterized by high processability during casting and a relatively low level of strength properties, in particular, yield strength, not exceeds 60-80 MPa, depending on the thickness of the casting. A higher level of strength properties of castings already in the cast state is ensured by the addition of copper, in particular, alloys of the type AA383.1 or AK12M2 are known. The increase in mechanical properties in this case is accompanied by a significant decrease in elongation and deterioration of corrosion resistance.

Among thermally non-hardened alloys, alloys based on a solid solution based on the Al-Mg system are known, for example, AMg6l, AMg5K, AMg5Mts (GOST 1583-93), Magsimal ^® 59 (Rheinfelden Alloys), etc., characterized by satisfactory castability, good corrosion resistance, a good level of strength properties and elongation. Among the disadvantages of the alloys of this system, high linear shrinkage and insufficiently good tightness of thin-walled castings should be highlighted.

The combination of a high level of strength properties, with respect to elongation and corrosion resistance is realized in Al-Si alloys with the addition of 0.2-0.5 mass. % of magnesium, in particular, AK9 alloys (GOST 1583-93), Silafont ^® 36 (Rheinfelden Alloys), trimal ^® 37 (Trimet) and others are known. Quenching significantly complicates the casting production cycle, since casting can warp ( especially when using quenching in water), a change in overall dimensions and the appearance of cracks.

Known cast alloy system Al-Ni-Mn, designed to obtain structural components for automotive and aerospace applications, which is an alternative to branded silumin, developed by Alcoa and disclosed in US patent 6783730 B2 (publ. 08/31/2004). From this alloy it is possible to obtain castings with a good combination of casting and mechanical properties at a content (wt.%): Ni - 2-6, Mn - 1-3, Fe - 1, Si - less than 1, as well as with a low content of other unavoidable impurities . Among the disadvantages of the known alloy, it should be noted that a high level of casting and mechanical properties is ensured by the use of high purity aluminum grades and a high nickel content, which significantly increases the cost of the obtained castings. In addition, the material is thermally unstrengthened in the entire concentration range, which limits its use. Moreover, in the region of high nickel concentrations, the corrosion resistance of castings is significantly reduced.

Known cast aluminum alloys based on Al-Ni and Al-Ni-Mn systems and a method for producing molded parts from them are described in Alcoa's invention according to US 8349462 B2 (publ. 08.01.2013) and EP 2011055318 from Rheinfelden Alloys GmbH & Co. KG. Alloy compositions are proposed for cast applications. Common in the proposed alloys is a high nickel content of 1-6 mass. %, which determines the main disadvantage is a significant decrease in corrosion resistance. With a relatively low nickel and manganese content, cast alloys have a low level of strength characteristics.

Known material based on the Al-Ni-Mn system proposed by NUST "MISiS" and disclosed in patent RU 2478131 (publ. 03/27/2013). The material contains (wt.%): 1.5-2.5 Ni, 0.3-0.7 Fe, 1-2 Mn, 0.02-0.2 Zr, 0.02-0.12 Sc and 0.002 -0.1 Ce. Castings obtained from the alloy after annealing (without using the hardening operation) are characterized by a temporary resistance of at least 250 MPa with a relative elongation of at least 4%. One of the disadvantages of this alloy is its increased tendency to form concentrated porosity, which makes it difficult to obtain high-quality relatively large castings. Another drawback is the need to use elevated casting temperatures, which cannot always be realized in foundry conditions.

Closest to the proposed is the invention NITU MISiS disclosed in the patent RU 2660492 (publ. 06.07.2018). Material for use in the molten state contains (wt.%): 5.4-6.4 Ca, 0.3-0.6 Si and 0.8-1.2 Fe. Among the disadvantages of this invention should be highlighted low elongation, which did not exceed 2.6%, which limits the use of the material in critical cast parts.

Disclosure of Invention

The objective of the proposed invention is the creation of a new aluminum alloy designed to produce castings mainly by casting under high pressure, but not limited to, meeting specified requirements for a set of technological and mechanical characteristics, especially relative elongation, which also determines the advantages of the invention.

The choice of alloying elements to create a new casting alloy was carried out on the basis that the following conditions must be met during alloying:

1) the presence of a eutectic component;

2) the presence of elements capable of providing solid solution hardening without a significant increase in the crystallization interval.

To fulfill these conditions, phase diagrams of the state were analyzed. In this case, the selection of elements capable of providing the required level of manufacturability and the ability to harden in the cast state was carried out on the basis of direct measurement of casting characteristics and determination of mechanical properties.

Since the relative elongation depends primarily on the size of the structural components, to ensure a high elongation, the concentration range of alloying elements was additionally selected from the condition of the ability to form crystallization phases with a relatively favorable morphology in the molten structure.

The technical result is also the provision of the required combination of technological and mechanical properties of the alloy during casting.

The problem is solved, and the technical result is achieved by the fact that the proposed casting alloy based on aluminum contains calcium, iron, manganese, silicon, at least one element selected from the group, zinc, chromium, titanium, zirconium, vanadium and scandium, with the following concentrations of alloying elements, mass. %:

Calcium 1.1-2.7 Iron 0.05-0.25 Manganese 1.2-2.4 Silicon 0.06-0.22 Zinc up to 1.0 Chromium 0.05-0.2 Titanium 0.05-0.2 Zirconium 0.05-0.18 Vanadium up to 0.15 Scandium 0.05-0.14 Aluminum and inevitable impurities rest.

In this case, the following conditions must be fulfilled: calcium and / or iron should be presented mainly in the form of eutectic particles with a size of not more than 3 μm, and the total content of titanium, zirconium, vanadium and scandium in the alloy should not exceed 0.3 mass. %

Various modifications and improvements are allowed that do not go beyond the scope of the legal protection of an invention defined by the claims.

SUMMARY OF THE INVENTION

It has been experimentally established that the concentration of calcium and iron within the stated limits provides the necessary amount of eutectic particles, which ensures the required combination of manufacturability during casting (primarily in terms of heat resistance). Provided that the transverse size of the eutectic particles is not more than 3 μm, within the stated chemical composition, an elongation of at least 7% is achieved. The content of calcium and iron less than the declared level will lead to a decrease in casting characteristics. The content of calcium and iron above the declared level will lead to a decrease in the values of elongation.

Manganese within the stated limits is necessary to provide solid solution hardening in the cast state. A lower manganese content will not be enough to achieve the required level of strength characteristics, in particular, a yield strength of at least 100 MPa, and with large quantities, primary crystals of the Al ₆ (Fe, Mn) phase are formed, which reduce the mechanical characteristics.

Silicon in the declared amount is redistributed between the solid solution and the eutectic, which provides, first of all, additional solid solution hardening in the cast state. At a higher content, silicon partially interacts with manganese, which reduces the concentration of manganese in the solid solution and reduces the strength characteristics.

Zinc in the declared concentrations is mainly located in solid solution, providing an increase in strength characteristics.

Chrome within the stated limits is necessary to ensure solid-solution hardening. A lower chromium concentration will not provide the required level of strength properties, and at a higher concentration the probability of the formation of primary crystals of the Al ₇ Cr phase will prevail, which will lead to a decrease in the level of mechanical properties.

Zirconium, vanadium and scandium in the claimed amounts are necessary for solid solution hardening. At lower concentrations, the specified level of strength characteristics is not achieved, and for large quantities, it will be necessary to increase the casting temperature above a typical level, which will reduce the resistance of casting molds.

Titanium in the claimed range is necessary for the modification of aluminum solid solution. With a higher titanium content in the structure, primary crystals may appear that will reduce the overall level of mechanical properties, and with a lower one, the required positive effect from the influence of this element on the general characteristics of the alloy will not be realized.

In the case of the introduction of titanium in the form of a multicomponent diagram of Al-Ti-B or Al-Ti-C in the alloy, its presence in amounts proportional to the content in the ligature is possible. In this case, boron and carbon, as independent elements, as applied to the range under consideration, did not significantly affect the mechanical and casting properties.

Examples of carrying out the invention

EXAMPLE 1

The alloy compositions shown in Table 1 were prepared in laboratory conditions. The alloys were prepared in an induction furnace in graphite crucibles using aluminum grades A85 and A99 and alloys: Al-10Са, Al-10Fe, Al-20Mn, Al-10Si, Al-5Ti. The zinc content was at the level of impurities of 0.02 mass. % The sum of the remaining elements did not exceed 0.05 mass. %

The resulting alloys were poured into a metal mold “separately cast cylindrical sample” with a diameter of the working part of 10 mm The mold was heated to a temperature of 150 ° C. The casting properties of the alloys were evaluated by the heat resistance (GH) using a "ring test", where the best indicator is a ring with a minimum wall thickness, crystallized without crack. The mechanical properties were evaluated under uniaxial tension of separately cast samples (Table 2). Test speed 10 mm / mm, length of the working part 50 mm.

An analysis of the results of tables 1 and 2 shows that alloys 2-6 in the claimed concentration range provide a good level of casting characteristics. The alloy of composition 1 is characterized by an unsatisfactory level of mechanical properties (primarily in terms of yield strength) and in terms of heat resistance. In the structure of alloy 7, the primary crystals of the glandular phase were revealed, which negatively affected the mechanical properties.

For use in the molten state, composition 3 is most preferred due to the best ratio of yield strength and elongation. The most optimal alloy structure of composition 3 of the table. 1 is shown in FIG. 1.

EXAMPLE 2

To assess the level of hardening in the cast state due to small additives, 4 alloys were prepared using an example of an alloy of composition 3 of the table 1. An assessment of the level of hardening in the cast state was evaluated by the values of the mechanical properties of the tensile strength of separately cast samples.

For use in the molten state, the most preferred is composition 3 (table. 3)

EXAMPLE 3

In laboratory conditions, from an alloy of composition 3 of the table. 3, flat samples were obtained by injection molding. The results of tensile tests are given in table. 5. The thickness of the samples was 2.4 mm. Estimated length 50 mm.

EXAMPLE 4

The impact of the transition elements of zirconium, scandium, vanadium and titanium, as well as their sum on the level of mechanical properties of the inventive alloy, was evaluated by uniaxial tensile tests. The composition of the alloy and the values of the mechanical properties are shown in table 6 and 7, respectively.

The mechanical properties were evaluated under uniaxial tension of separately cast samples. Test speed 10 mm / mm, length of the working part 50 mm.

An analysis of the results of tables 6 and 7 shows that compositions 1-5 in the claimed concentration range provide a good combination of strength properties and elongation. In the alloy of composition 7, a low level of elongation is noted, which is due to the presence in the structure of primary crystals containing titanium, zirconium, vanadium and scandium.

In the case of alloying with zirconium, scandium, vanadium and titanium additives (for example, for casting large castings) for use in the cast state, composition 1 is most preferred (Table 6).

EXAMPLE 5

The effect of the size of the structural components, in particular, the transverse size of the eutectic components of the cast structure on the level of mechanical properties, was assessed (Table 8). Changing the transverse size of the eutectic components was carried out by crystallization of the alloy with different cooling rates. The change in the cooling rate was carried out by changing the section of the casting on the example of composition 3 of table 1.

From an analysis of the results of Table 8 it follows that the level of mechanical properties measured in the cast state depends on the size of the structural components of the alloy, in particular, with an increase in the transverse size of the eutectic phases, a decrease in the level of strength characteristics is observed.

Thus, embodiments of the proposed invention confirm the indicated advantages of the new alloy.

Claims (7)

1. Cast aluminum alloy based on calcium, iron, manganese, silicon and at least one element selected from the group consisting of zinc, chromium, titanium, zirconium, vanadium and scandium, in the following ratio, wt.%: Calcium 1.1-2.7 Iron 0.05-0.25 Manganese 1.2-2.4 Silicon 0.06-0.22 at least one element selected from the group containing Zinc up to 1.0 Chromium 0.05-0.2 Titanium 0.05-0.2 Zirconium 0.05-0.18 Vanadium up to 0.15 Scandium up to 0.14 Aluminum and inevitable impurities Rest 2. The alloy according to claim 1, characterized in that calcium and / or iron are present in the alloy mainly in the form of eutectic particles with a transverse size of not more than 3 microns. 3. The alloy according to claim 1, characterized in that the total content of titanium, zirconium, vanadium and scandium does not exceed 0.3 wt.%. 4. The alloy according to claim 1, characterized in that it preferably contains calcium in an amount of 1.5-2.0 wt.% And manganese in an amount of 1.8-2.2 wt.%. 5. The alloy according to any one of paragraphs. 1-3, characterized in that it is made in the form of a casting having the following tensile properties in a molten state: yield strength (σ _0.2 ) of at least 110 MPa and elongation (δ) of at least 7%. 6. Casting from a cast alloy based on aluminum, characterized in that it is made of an alloy according to any one of paragraphs. 1-4.

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