RU2590429C1 - Production of boron-bearing metal-matrix composite based on aluminium sheet - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: this process comprises preparation of aluminium melt containing the following elements in wt %: manganese - 0.5-2, magnesium - 0.5-4, silicon - 0.1-0.3, scandium - 0.15-0.3. Boron-bearing particles are formed in aluminium melt by adding of foundry alloy containing the mix of powders TiB₂ and salts NaCl₂, MgCl₂ and KCl. Melt temperature in foundry alloy mixing is kept equal to 720-800°C for 30-45 minutes. Ingot is made by melt crystallisation and homogenization. Sheet is produced by ingot deformation while strained semi-finished product is annealed at 250-350°C. Produced sheets feature composite structure including the particles of TiB₂ in amount of 4 to 8%.

EFFECT: higher strength without homogenization and quenching.

2 cl, 2 ex, 2 tbl

Description

Technical field

The present invention relates to the field of metallurgy, in particular to deformed boron-containing aluminomatrix composite materials in the form of sheets, which are required to absorb neutron radiation in combination with a low specific gravity.

State of the art

Aluminomatric composite materials (AKM) containing boron have a unique combination of physical and mechanical properties, in particular low density and good absorption of neutron radiation, so 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 AKMs have been in operation for a long time, their use is limited due to a number of problems, in particular, this is due to the technology for their preparation. Such a difficulty in producing boron-containing alloys by classical casting technology is determined by: 1) a significant increase in the liquidus line with an increase in boron concentration, and as a result, the low solubility of boron in liquid aluminum (at traditional temperatures for producing aluminum alloys); 2) low wettability of some boron-containing particles by aluminum melt; 3) the inevitable interaction of boron with a number of basic alloying elements with the formation of the corresponding boron-containing intermetallic compounds. These main factors determine the need to use special methods for producing boron-containing AKM.

Numerous methods are known for producing boron-containing AKM using powder metallurgy methods. In particular, there is a known method for producing AKM, 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 patent 6602314 B1, publ. 05.08.2003). This method of manufacturing AKM involves sintering under pressure (with preliminary evacuation). The disadvantage of this method 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 physicochemical properties, which determines a wide range of physicomechanical characteristics achieved in AKM.

Another known method of preparing boron-containing ATM, developed by Alcan Aluminum Corporation, liquid phase process which comprises mixing boron-compound particles _B4C in liquid melt (US Patent 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 that the resulting sheets have low strength (σ _in <100 MPa).

Disclosure of invention

The basis of the invention is the task of creating a new boron-containing AKM in the form of sheets, hardened without hardening, characterized by sufficient strength (σ _in > 280 MPa), high adaptability to the production of ingots and their subsequent deformation into a sheet (without using homogenization) with the structure of an aluminum matrix, which uniformly distributed particles of the compound TiB ₂ with an average size of not more than 30 microns and a mass fraction of from 4 to 8 mass. %

The problem is solved by creating a method for producing sheets from a boron-containing metal matrix composite material based on aluminum, including the preparation of a melt containing manganese, magnesium, silicon, scandium, the formation of boron-containing particles in an aluminum melt, the production of an ingot by crystallization of the melt, the production of a sheet by deformation of the ingot and its thermal processing, characterized in that they prepare an aluminum melt containing

manganese from 0.5 to 2 mass. % magnesium from 0.5 to 4 mass. % silicon from 0.1 to 0.3 mass. % scandium` from 0.15 to 0.3 mass. %

the formation of boron-containing particles is carried out by introducing a ligature consisting of a mixture of TiB ₂ powder and salts of NaCl ₂ , MgCl ₂ and KCl, the melt temperature during mixing of the ligature is maintained in the range from 720 to 800 ° C for 30-45 minutes, and the annealing of the deformed semi-finished product is carried out at a temperature of 250-350 ° C to give sheets with the structure of a composite material comprising TiB ₂ particles in an amount of from 4 to 8%. In a private embodiment, the ligature additionally contains paraffin in the following ratio of components: TiB ₂ from 60 to 70 mass. %, NaCl ₂ from 3 to 5 wt. %, MgCl ₂ from 10 to 12 mass. %, KCl from 5 to 7 mass. %, paraffin - the rest.

The technical result achieved from the invention is the achievement of a high level of strength characteristics: temporary tensile strength (σ _in ) - not less than 280 MPa, high adaptability to pressure treatment in combination with low density and the possibility of its use as protection against neutron radiation.

SUMMARY OF THE INVENTION

The essence of the invention is to realize in the sheets of boron-containing AKM a structure based on an aluminum matrix hardened by secondary precipitates of the Al ₆ Mn and Al ₃ Sc phases and with TiB ₂ compound particles uniformly distributed in it with an average size of not more than 30 μm and mass fraction from 4 to 8 mass. % Such a structure makes it possible to ensure the best combination of mechanical properties (more than 280 MPa) and the ability to absorb neutron radiation (the calculated boron content for such a structure is from 2 to 3.5 mass%). The justification of the claimed amounts of alloying components in this alloy is given below.

Manganese in the claimed amounts is necessary for the formation of secondary precipitates (dispersoids) of Al ₆ Mn and solid-solution hardening. Lower concentrations will not provide the required strength, and with large quantities the processability characteristics during pressure treatment will be reduced due to the formation of primary crystals of the Μn-containing phase.

Magnesium in the claimed amounts is necessary for solid solution hardening. Lower concentrations will not provide the required level of strength, and with large quantities, the processability characteristics of the pressure treatment will be reduced due to the high strain hardening.

Scandium in the claimed amounts is necessary for the formation of secondary nanoparticles of the Al ₃ Sc phase (crystal lattice L1 ₂ ) having an average size of not more than 10 nm. At lower concentrations, the amount of the latter will be insufficient to achieve the required strength, and at large quantities there is a danger of the appearance of primary crystals, which negatively affects the mechanical properties and manufacturability.

Silicon in the claimed amounts is necessary to neutralize the harmful effects of iron impurities (permissible iron content up to 0.5%), in particular for the formation of eutectic inclusions (phases Al ₁₅ (Fe, Mn) ₃ Si ₂ ), which contribute to a more uniform deformation in microvolumes in the process pressure treatment.

The lower limit on the mass fraction of particles of the TiB ₂ phase is chosen in order to achieve the necessary level of absorption of neutron radiation, and the upper limit in order to achieve the required level of manufacturability, in particular, during rolling. The upper limit on the average size of the TiB ₂ phase is chosen in order to achieve the required level of mechanical properties.

The justification of the claimed technological parameters of the method for producing deformed from this alloy is given below.

A decrease in the temperature of the melt below 720 ° C may lead to a decrease in manufacturability when producing ingots. The consequence of this is the appearance of liquids and other defects on the surface of the ingot. An increase in the melt temperature above 800 ° C and a holding time of more than 45 minutes can adversely affect the particle size of TiB ₂ in the aluminum melt due to their coarsening.

If the annealing temperature of the sheet is below 250 ° C and above 350 ° C, the required level of hardening will not be achieved, which is associated with the underdevelopment of the aluminum solid solution in the first case and the formation of coarse secondary precipitates of Al ₃ Sc in the second.

Execution examples

EXAMPLE 1

For experimental substantiation of the proposed invention, 5 variants of obtaining boron-containing AKM, which are given in table. 1. Melt preparation and the formation of boron-containing TiB ₂ particles in it were carried out in a RELTEC induction furnace in a graphite chamotte crucible. Boron was introduced as a specially prepared by mixing ligatures containing TiB ₂ and a mixture (18 wt.% NaCl ₂ , 54 wt.% MgCl ₂ and 28 wt.% KCl). The number of TiB ₂ particles was different in order to obtain a different amount of boron-containing particles (Q) in the final structure.

Table 1 Compositions of AKM melts, mechanical properties and structure parameters of rolled sheets No. Concentrations, mass. % σ _in , MPa Q, mass. % Μn Mg Si Sc Al one 0.1 0.4 0.3 0.35 The basis 244 2,4 2 0.5 four 0.1 0.15 The basis 289 6.5 3 2 0.5 0.2 0.3 The basis 287 7.8 four one four 0.1 0.25 The basis 324 5.5 5 2.5 four 0.1 0.35 The basis Rolling cracks 10.1

The melt temperature was maintained at about 770 ° C. for 30 minutes. Pouring was carried out in a metal mold, receiving flat ingots with dimensions of 40 × 120 × 200 mm. Next, the ingots were rolled (first hot. And then cold), receiving sheets of a thickness of 2 mm The sheets were heat treated according to the regime: heating at 300 ° C for 3 hours.

Mechanical properties of the sheets (tensile strength (σ _c)) in uniaxial tension was measured at room temperature on a universal testing machine in accordance with GOST 1497-84. The test speed was 10 mm / min, the estimated length of 50 mm.

The mass fraction of boron-containing particles (Q) and their identification were determined by x-ray phase analysis (on a DRON-4.0-07 diffractometer).

As can be seen from the table. 1, only the proposed method for producing boron-containing AKM (No. 2-4) provides a given level of mechanical properties.

EXAMPLE 2

To justify the temperature of the melt, 5 options for producing boron-containing AKM (Table 2) were performed with reference to composition No. 4 (Table 1). The average size (d) of boron-containing TiB ₂ particles in the sheet was estimated using a metallographic analysis using a JEOL JSM-6610 scanning microscope.

The amount of magnesium, silicon, copper, and boron-containing ligatures introduced into the melt was the same in all cases and corresponded to option 3 from example 1 (see table 1). The melt temperature ranged from 800 to 1000 ° C. The remaining experimental conditions were the same as in example 1.

As can be seen from the table. 2, only the proposed method for producing AKM (No. 2-4) provides the specified structure parameters.

table 2 Melt temperatures for preparing experimental AKM and structure parameters of rolled sheets No. Melt temperature, ° С Melt holding time, min d, μm one 710 twenty uneven particle distribution 2 720 45 21 3 770 thirty 25 four 800 thirty 26 5 850 60 41

In the method No. 5 for a long exposure time and temperature increase above 800 ° C led to the formation of coarse particles of compound TiB ₂ with an average size of about 41 microns.

Claims (2)

1. A method of producing sheets from a boron-containing metal matrix composite material based on aluminum, including the preparation of a melt containing manganese, magnesium, silicon and scandium, the formation of boron-containing particles in an aluminum melt, the production of an ingot by crystallization of the melt, the production of a sheet by deformation of the ingot and its heat treatment, characterized in that an aluminum melt is prepared containing
manganese from 0.5 to 2 wt. % magnesium from 0.5 to 4 wt. % silicon from 0.1 to 0.3 wt. % scandium from 0.15 to 0.3 wt. %
formation of boron-containing particles is conducted by introducing into the master alloy melt comprising a mixture of TiB ₂ powder and salts NaCl _2, MgCl ₂ and KCl, the melt temperature during mixing is maintained within the ligature from 720 to 800 ° C for 30-45 minutes, and heat treatment carried out by annealing the deformed semifinished product at a temperature of 250-350 ° C, while receiving sheets with the structure of a composite material containing particles of TiB ₂ in an amount of from 4 to 8%. 2. The method according to p. 1, characterized in that the ligature further comprises paraffin in the following ratio of components: TiB ₂ from 60 to 70 wt. %, NaCl ₂ from 3 to 5 wt. %, MgCl ₂ from 10 to 12 wt. %, KCl from 5 to 7 wt. %, paraffin - the rest.