RU2630186C1 - Method for producing thin sheet rolled product of boron-containing aluminium alloy - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method for producing thin sheet rolled products from a boron-containing aluminium alloy with boron content of not less than 2 wt % and includes preparation of aluminium melt containing copper and boride particles, ingot preparation by melt crystallisation, homogenizing the ingot, hot rolling, cold rolling and hardening heat treatment, aluminium melt is from 5.5 to 6.5 wt % of copper, hot rolling is carried out at a temperature of 400-450°C with total reduction ratio of 85 to 90%, and cold rolling is carried out with total reduction ratio of 92 to 96%. The invention is directed to the production of aluminium alloy with boron content of not less than 2 wt %, having high and stable mechanical properties. In particular, the method makes it possible to obtain rolled products of thickness less than 0.3 mm, tensile resistance at σ>420 MPa and elongation δ>8%.

EFFECT: low specific gravity and high strength of rolled products.

2 cl, 2 ex, 2 tbl, 3 dwg

Description

Technical field

The present invention relates to the field of metallurgy, in particular to boron-containing aluminum alloys, which are required to absorb neutron radiation in combination with low specific gravity and high strength.

State of the art

Aluminum-based materials (alloys and composites) containing boron have a unique combination of physical and mechanical properties. Since boron tends to absorb neutron radiation well, they are widely used in nuclear energy [W.K. Barney, G.A. Shemel, W.E. Seymour, Nucl. Sci. Eng. 1 (1958) 439-448]. Despite the fact that boron-containing composites have been in operation for quite some time, their use is associated with a number of problems, in particular, with the technology for their preparation. Since boron has low solubility in liquid aluminum, the classical technologies associated with obtaining a homogeneous melt (without the presence of any solid phases) and the formation of boron-containing compounds during crystallization cannot be practically implemented.

Numerous methods are known for producing aluminum-based boron-containing materials using powder metallurgy methods. In particular, there is a known method of producing a material in which alloys of different systems (1xxx, 3xxx, 6xxx, etc.) are used as an aluminum matrix, and boron carbide (B ₄ C) in the form of a powder 1-60 μm in size is used as a boron-containing filler ( US Pat. No. 6,602,314 B1, publ. 08/05/2003). This method of production of materials involves sintering under pressure (with preliminary evacuation). The disadvantage of this and all methods associated with powder metallurgy is the difficulty of obtaining large billets intended for rolling. Another disadvantage of this method is that the proposed matrix alloys have a different combination of physico-chemical properties, which determines a wide range of characteristics achieved in the final product.

A known method for producing boron-containing material described in US 2008/0050270A1 (2008), according to which titanium is introduced into an aluminum melt obtained by melting an industrial aluminum-boron master alloy so as to form a melt whose temperature is maintained in the range from 700 to 850 ° C, particles of titanium diboride (TiB ₂ ), after which crystallization is carried out by casting. In the private claims of this patent, it is proposed to introduce gadolinium and samarium supplements. This method allows to obtain in the material a microstructure with dispersed particles of the TiB ₂ phase, which are formed during the mixing process as a result of phase transformations. However, the full course of these phase transformations requires a long time, which leads to a relatively high cost of this process. The presence of gadolinium and samarium additives makes the process even more expensive.

Known multicomponent alloy based on aluminum containing titanium diboride in an amount of 0.5-20 mass%, intended for castings and disclosed in patent RU 2556247 (publ. 10.07.2015, bull. No. 19). The disadvantage of this alloy is that it is not intended to produce deformed semi-finished products, in particular sheets.

There is also a method for producing boron-containing material developed by Alcan Aluminum Corporation, which includes a liquid-phase process of mixing boron-containing particles of compound B ₄ C into a liquid melt (US Pat. No. 5,531,425 (1996)). According to this method, ingots are obtained in crystallizers, then hot rolling is used to produce plates and sheets. The disadvantage of this method is the difficulty of preventing the clustering of non-metallic particles during the mixing process, which can lead to the formation of an inhomogeneous structure. A significant disadvantage of this method is that the resulting sheets have low strength (σ _in <100 MPa).

Closest to the claimed invention is a method for producing sheets of boron-containing material based on aluminum, which is disclosed in the patent of the Russian Federation 2538789 (publ. 10.01.2015, bull. No. 1). This method involves the preparation of an aluminum melt containing from 0.5 to 0.9% silicon, from 1.3 to 1.9% magnesium and from 0.2 to 0.4% copper, the formation of boron-containing particles in it with a mass fraction of 4 to 8% at a temperature of from 850 to 930 ° C for 30-45 min, casting of the ingots and their homogenization, obtaining sheets by rolling the ingot and their heat treatment.

The sheets with a thickness of 2 mm obtained by this method have the following mechanical properties: σ _in > 320 MPa, σ _0.2 > 300 MPa and δ> 4%. The disadvantage of this method is that the alloying system of the aluminum matrix (type AD33, GOST 4784-97), does not allow to obtain a strength above 350 MPa in deformed semi-finished products. In addition, the ingots obtained by this method are not intended for the manufacture of sheet metal (less than 0.3 mm). Another disadvantage is the presence of magnesium in the alloy, which interacts with boron. This leads to a decrease in its concentration in the aluminum matrix and, as a consequence, to a decrease in strength properties. Since the distribution of magnesium between boride particles and the aluminum matrix strongly depends on the melting parameters (in particular, on the temperature and the exposure time of the melt), in the known method the temperature and time of the melt are limited to narrow limits, which complicates its use in an industrial environment.

Disclosure of invention

The technical result is the creation of a method for producing thin-rolled aluminum alloy containing at least 2% boron and having high and stable mechanical properties.

In a private embodiment, this method allows to obtain rolled products with a thickness of less than 0.3 mm, a temporary tensile strength σ _of > 420 MPa and a relative elongation of δ> 8%.

The technical result is achieved by creating a method for producing thin-sheet rolled metal boron-containing aluminum alloy, including the preparation of an aluminum melt containing copper and boride particles in an amount of from 2.8 to 3.5 vol. %, production of an ingot by crystallization of the melt, homogenization of the ingot, hot and cold rolling and hardening heat treatment, characterized in that from 5.5 to 6.5 masses are introduced into the aluminum melt. % copper, hot rolling is carried out at 400-450 ° C with a total degree of compression from 85 to 90%, and cold rolling is carried out with a total degree of compression from 92 to 96%.

The invention is illustrated in the drawing, where in FIG. 1 shows the appearance of a sheet of rolled metal from boron-containing material based on aluminum, obtained according to option No. 3 (see table. 1);

in FIG. 2. shows the microstructure of thin-sheet rolled metal of boron-containing material based on aluminum, obtained by option No. 3 (see table. 1), and in FIG. Figure 3 shows a fractogram of thin-sheet rolled metal of boron-containing material based on aluminum, obtained according to option No. 3 (see table. 1).

The essence of the invention is to provide high technological ductility of the ingots and to realize in thin-sheet products a structure consisting of an aluminum matrix capable of strain-hardening to dispersion hardening due to the formation of secondary precipitates of the θ 'phase (metastable modification of the θ-Al ₂ phase Cu), and boron-containing particles evenly distributed in it with an average size of not more than 25 microns and a volume fraction of from 2.8 to 3.5 vol. % This structure allows you to provide the best combination of the operational properties of sheet products (in particular, strength, ductility and absorption of neutron radiation). The presence of boride particles (mainly in the form of AlB ₁₂ compound) in an amount of not less than 2.8 vol.% Allows to provide the necessary level of absorption of neutron radiation (the calculated boron content for such a structure is not less than 2 wt.%). Since copper does not interact with boron during the preparation of the melt, this method allows to ensure the stability of mechanical properties when changing the melting parameters in a wide range. The lower limit for copper is chosen in order to achieve the required level of strength properties, and the upper one in order to achieve the required level of manufacturability, in particular when producing sheet products.

Execution examples

EXAMPLE 1

For experimental substantiation of the proposed invention, 3 options for producing thin-sheet rolled metal of boron-containing aluminum alloy by the present method (2-4) and 3 options for producing rolled products by the known method (6-8) were made.

Melt preparation and the formation of boron-containing particles in it were carried out in a RELTEC induction furnace in a graphite chamotte crucible. Boron was introduced in the form of a specially prepared ligature. The melt temperature (Т) varied from 900 to 1050 ° С, and the melt holding time before casting ingots (τ) varied from 30 to 120 minutes (Table 1). Pouring was carried out in a metal mold, receiving flat ingots with dimensions of 40 × 80 × 200 mm. Next, the ingots were homogenized at 540 ° С, and then hot rolling was carried out at 430 ° С to a thickness (h) of 4 mm (total compression ratio of 90%), intermediate annealing, cold rolling to 0.28 mm (total compression ratio of 93%). In the known method (options 6-8), cold rolling was carried out up to 2 mm (total compression ratio of 50%)

The volume fraction of boron-containing inclusions (Qv) and their average size (d) were determined by metallographic analysis using microstructure images obtained using a TESCAN VEGA 3 scanning electron microscope.

The cold-rolled sheets were subjected to hardening heat treatment, including heating at 540 ° C, quenching in cold water, and artificial aging. The mechanical properties of the sheets are presented in table. 1 (tensile strength - σ _in and elongation - δ), uniaxial tension was determined at room temperature on a universal testing machine Zwick Z250 in accordance with GOST 1497-84. The test speed was 10 mm / min, the estimated length of 50 mm.

As can be seen from the table. 1, only the proposed method for producing sheet products (No. 2-4, see) provides high technological ductility (Fig. 1) and a given level of mechanical properties of the sheets. In this case, the spread in the values of the temporary resistance is only 7 MPa (i.e., less than 1 rel.%). In the structure of sheet rolling, boride particles with an average size of less than 25 μm and a small number of inclusions of the Al ° Cu phase are detected (Fig. 2a). The bulk of the copper is in the aluminum matrix in the form of hardening precipitates of the θ 'phase. The compact form of borides leads to a small-hole fracture mechanism, as can be seen from the fractogram (Fig. 2b). This type of failure is most favorable for mechanical properties.

In option No. 1, the copper content in the aluminum melt is lower than the declared level, so the strength of cold-rolled sheets is less than required. In the method No. 5, the concentration of copper and boron in the aluminum melt is higher than the declared limits. This led to a decrease in technological plasticity, as a result, the sheets cracked during the cold rolling process, so their mechanical properties were not determined.

In the known method of expanding the range of the temperature of the melt and the time of its exposure led to a strong dispersion of mechanical properties. In particular, the spread in the values of the temporary resistance is 80 MPa (i.e., more than 20 rel.%).

EXAMPLE 2

For the experimental substantiation of the parameters of the deformation processing of a boron-containing aluminum alloy, 5 options for producing sheet metal were made (Table 2). The amount of copper and boron introduced into the melt, its temperature, and the exposure time were the same in all cases and corresponded to option 3 of Example 1 (see Table 1).

In method No. 1, the temperature of hot rolling is lower than the declared limit, which did not provide sufficient technological ductility. As a result, the ingots cracked during the rolling process, so their mechanical properties were not determined. In the method No. 5, the combination of a high temperature of hot deformation and a small degree of compression during cold deformation led to a decrease in mechanical properties during tensile testing. Only the proposed method for producing sheet products (No. 2-4) provides high mechanical properties (σ _in > 420 MPa and δ> 8%).

table 2

The parameters for producing sheet products and its mechanical properties (h ₁ is the sheet thickness obtained after hot rolling; h ₂ is the sheet thickness obtained after cold rolling; ε ₁ is the total degree of compression during hot rolling; ε ₂ is the total degree of compression during cold rolling )

Claims (2)

1. A method of producing a sheet of rolled metal from a boron-containing aluminum alloy with a boron content of at least 2 wt. %, including the preparation of an aluminum melt containing copper and boride particles, obtaining an ingot by crystallization of the melt, homogenization of the ingot, hot rolling, cold rolling and hardening heat treatment, characterized in that from 5.5 to 6.5 wt. % copper, hot rolling of the ingot is carried out at a temperature of 400-450 ° C with a total degree of compression from 85 to 90%, and cold rolling is carried out with a total degree of compression from 92 to 96%. 2. The method according to p. 1, characterized in that the sheet metal has a thickness of less than 0.3 mm, a tensile strength of more than 420 MPa and elongation of more than 8%.

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