RU2647070C2 - Aluminium alloy - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, particularly to aluminum alloys, and can be used for manufacturing high-loaded brazed structures. Aluminum alloy contains, % by weight: 0.5–0.8 of silicon, 0.5–0.9 of magnesium, 0.05–0.3 of copper, 0.05–0.2 of chromium, 0.15–0.25 of iron, 0.005–0.02 of titanium, 0.1–0.2 of zirconium, 0.05–0.35 of molybdenum, aluminum is the remainder, while copper is completely bound to secondary precipitates of Al₅Cu₂Mg₈Si₆ phase, the material solidus temperature is not less than 600 °C.

EFFECT: invention is aimed at increasing the strength of brazed structures and blanks, which leads to increased service life of products.

4 cl, 4 ex, 3 tbl

Description

The invention relates to the field of metallurgy, in particular to deformable aluminum-based alloys, and can be used for the manufacture of highly loaded brazed structures.

To date, for the manufacture of soldered structures for various purposes, the most common among deformed alloys are alloys of the Al-Mn-Fe system (type AMts, GOST 4784-97). Alloys of this group are characterized by high manufacturability during casting, deformation processing, and are characterized by high corrosion resistance and thermal conductivity. However, the typical level of their strength properties in the annealed state usually does not exceed 150 MPa, which limits their use in highly loaded structures.

Relatively wide application in soldered structures also find more durable thermally hardened alloys of the Al-Mg-Si system (type AD31, GOST 4784-97). Alloys of type AD31 in their technological properties are similar to alloys of the Al-Mn-Fe system, however, the level of their strength properties usually does not exceed 240 MPa, which also limits their use for highly loaded structures. In addition, the low solidus temperature of the alloy (not exceeding 595 ° C) makes it necessary to carry out the high-temperature brazing process at extreme conditions typical of the minimum melting point of the solder, which can lead to incomplete melting of the solder and, as a result, to poor-quality formation of the compound.

Known corrosion-resistant aluminum alloy containing (in wt.%): 0.6 ÷ 1.15 Si, 0.6 ÷ 1.0 Cu, 0.8 ÷ 1.2 Mg, 0.55 ÷ 0.86 Zn, 0.1 Mn, 0.2 ÷ 0.3 Cr, the rest is aluminum (US patent No. 6537392). The alloy is characterized by a high level of strength properties. The disadvantage of this alloy is the low hardenability during air cooling, which makes it difficult to use it to obtain soldered structures, as well as the relatively low solidus, the values of which in some cases do not exceed 560 ° C.

Higher strength properties in comparison with alloys of the AMts and AD31 types can be realized on thermally hardened alloys of the Al-Mg-Si-Cu system. Known industrial aluminum alloy AD33 (GOST 4784-97), containing (in wt.%): 0.4 ÷ 1.8 Si, 0.7 Fe, 0.15 ÷ 0.4 Cu, 0.8 ÷ 1.2 Mg, 0.15 Mn, 0.25 Zn, 0.04 ÷ 0.35 Cr, 0.15 Ti, the rest is aluminum. This alloy is taken as a prototype. The alloy is characterized by a high level of strength properties, and in the state after artificial aging (T1), the values of temporary tensile strength are at least 300 MPa. Among the disadvantages of this alloy, it is worth noting the low solidus with the content of alloying elements at the upper limit of the concentration range, as well as the use of mandatory quenching operations in water to obtain high mechanical properties.

The objectives of the invention are the creation of a deformable aluminum alloy with a high level of strength properties for use in highly loaded brazed structures, as well as expanding the range of applied brazed structures.

Technical results include increasing the strength (not lower than 300 MPa) of brazed structures and preforms, as well as increasing the service life of products.

These technical results are achieved by the fact that it is proposed an aluminum alloy containing silicon, magnesium, copper, chromium, iron, zirconium, titanium, molybdenum and aluminum, with the following ratio of components (wt.%): Silicon 0.5 ÷ 0.8, magnesium 0.5 ÷ 0.9, copper 0.05 ÷ 0.3, chromium 0.05 ÷ 0.2, iron 0.15 ÷ 0.25, titanium 0.005 ÷ 0.02, zirconium 0.1 ÷ 0.2 , molybdenum 0.05 ÷ 0.35, aluminum - the rest, while copper is completely connected to the secondary precipitates of the Al ₅ Cu ₂ Mg ₈ Si ₆ phase, the solidus temperature of the material is at least 600 ° C.

Moreover, the total content of silicon and magnesium in the alloy can be no more than 1.5 mass. %, as well as the total content of titanium, chromium and zirconium can be no more than 0.25 mass. %

The alloy may also optionally contain cobalt, while the total content of cobalt and molybdenum should be no more than 0.35 mass. %

The main alloying elements of the proposed alloy are silicon and magnesium. These alloying elements in the claimed amounts are necessary for the formation of secondary precipitates of metastable phases of Mg ₂ Si. At lower concentrations of magnesium and silicon, the amount of secondary precipitates will not be sufficient to achieve the required strength, and with large quantities manufacturability will be reduced, the solidus of the alloy will be reduced. The main effect of the influence of these elements is due to their dissolution in an aluminum solution upon heating under quenching and the release of metastable phases β 'and β''in the form of secondary precipitates during subsequent aging.

Copper additives are necessary to increase the effect of dispersion hardening (due to the formation of metastable modifications of the Q phase of Al ₅ Cu ₂ Mg ₈ Si ₆ ). When the copper content is above the upper limit, processability during deformation and heat treatment, solidus of the alloy will significantly decrease, and the alloy itself will be characterized by lower values of corrosion resistance. At lower copper concentrations, the amount of secondary precipitates of the Q phase of Al ₅ Cu ₂ Mg ₈ Si ₆ will be insufficient to achieve the required level of strength properties.

Additives of titanium in the proposed alloy serve as modifiers of the grain of the aluminum solution (in the form of Al ₃ Ti particles), which improve the processability of the alloy during casting, in particular by reducing the tendency to form hot cracks. With large amounts of titanium in the alloy, there is a risk of conglomerates that can degrade processability during deformation and the general level of strength properties.

Zirconium in the claimed amounts is necessary to maintain strain hardening during high-temperature heating. The effect is achieved due to the formation of nanoparticles of the Al ₃ (Zr) phase (crystal lattice L1 ₂ ) having an average size of not more than 20 nm. At lower concentrations, the amount of the latter will be insufficient to maintain the required strength, and at large quantities there is a danger of the appearance of primary crystals (crystal lattice D0 ₂₃ ), which negatively affects the mechanical properties and manufacturability.

Iron in general is a harmful impurity in aluminum alloys. In this regard, to prevent harmful effects (primarily on the structure and, as a consequence, on the mechanical properties) of this element, the upper level is limited. The lower boundary is justified by the positive influence of this element on manufacturability when casting in a semi-continuous method using graphite crystallizers. Moreover, with the joint introduction of iron and silicon in the claimed amounts, they are necessary for the formation of eutectic inclusions (in particular, the Al ₈ FeSi phase), which contribute to more uniform deformation in microvolumes during pressure treatment. The presence of these elements has a positive effect on the formation of the final structure.

Chromium in the declared amounts forms Al ₇ Cr phase dispersoids, which also have a positive effect on the preservation of strain hardening at elevated temperatures, in particular during high-temperature soldering.

Additives of cobalt and molybdenum improve the hardenability of the aluminum alloy, stabilizing the solid solution at high temperatures. As a result, when exposed to the thermal soldering cycle, these components can slow down the decomposition of the solid solution and increase the mechanical properties of the soldered structure. Based on the extremely limited solubility of these components in aluminum, their total content in the alloy should be limited to 0.35 mass. % At a higher percentage, cobalt and molybdenum can interact with other components of the solder with the formation of coarse intermetallic phases. When the content in the alloy in an amount less than 0.05 mass. %, these elements do not significantly affect the structure of the material.

At present, for the manufacture of highly loaded structures from aluminum alloys, the most widespread use is high-temperature brazing, which allows us to obtain sufficiently extended joints in one heating cycle. At the same time, obtaining soldered structures with high strength and corrosion properties is complicated by the need to use solders based on eutectic silumin having a melting point of about 580 ° C. In this regard, the temperature of soldering with such solders should be above 600 ° C, and the solidus temperature should also be above 600 ° C. The use of alloys with a solidus temperature below 600 ° C when brazing with silumin-based solders will lead to the melting of grain boundaries in the alloy structure and the appearance of a burn-out defect, which can significantly reduce the mechanical properties of the alloy and, in particular, ductility. To predict the temperature characteristics at the stage of preparation for the production of semi-finished alloys using mathematical complexes, the temperature of solidus is calculated, based on which the final composition of the alloy is approved.

Example 1

In accordance with the proposed concentration range of alloying elements, 4 alloys were prepared. The compositions of the alloys, solidus temperatures are given in table. 1. The manufacture of alloys was carried out by adding double and triple ligatures with the main alloying components to the melt. The cross section of the obtained preform was 120 × 40 mm. The alloy composition of the claimed material corresponded to compositions No. 2 and 3 in the table. 1. The content of cobalt and molybdenum was controlled by the composition of the charge, the remaining elements using an ARL4460 emission spectrometer. The solidus temperature (T _sol ) for each composition was calculated using the Thermo-Calc program (TTAL5 database).

As follows from the table. 1, the proposed alloys (compositions No. 2 and 3) are characterized by permissible solidus temperatures (not lower than 600 ° C). Alloys No. 1 and No. 4 have an estimated solidus temperature below the required value.

According to the calculated phase composition of the alloys (see Table 2), it was determined that in alloy No. 1, precipitations of a separate Al ₂ Cu phase will be observed, which may cause a decrease in corrosion resistance.

Example 2

Sheets were made from the obtained ingots to determine the mechanical properties. For this, the alloy ingots of compositions No. 2 and 3 (table. 1) were processed according to the following scheme:

a) homogenization of ingots;

b) rolling (including hot and subsequent cold rolling) to a thickness of 3 ÷ 5 mm;

c) heat treatment of the obtained sheets according to the T1 mode.

Simultaneously with these alloys, for comparative studies, industrially produced sheets of AD33 alloy (prototype) 3 mm thick were used.

Samples for mechanical testing were cut from sheets of the studied alloys on a milling machine. Tests for mechanical properties were carried out on an Instron brand test machine. The test results are presented in table. 3 (presents the average test values of 5 samples).

* Note: the composition number of the alloy according to the table. one

Example 3

The following composition (in wt.%) Was obtained by semi-continuous casting in a laboratory setup: 0.5 silicon, 0.85 magnesium, 0.2 copper, 0.1 chromium, 0.18 iron, 0.025 titanium, 0.1 zirconium , 0.15 molybdenum, the rest is aluminum. After this, the ingot was cut into flat billets and then rolled to a thickness of 5 mm. After that, the standard heat treatment of the obtained sheets was carried out (hardening, artificial aging). Samples for mechanical testing were cut from the sheets obtained on a milling machine.

Tests for mechanical properties were carried out on an Instron brand test machine. The test results showed that the tensile strength is 310 MPa, the conditional yield strength is 269 MPa, the elongation is 8.6%.

Example 4

To conduct research on the possibility of obtaining soldered structures from the proposed alloys, alloy No. 2 was selected (Table 1), which has the highest solidus temperature. From the sheets with a thickness of 3 mm, 10 flat samples 40 × 100 mm in size were obtained. The soldering of the samples was carried out with an overlap in an air furnace at a temperature of 595 ± 5 ° C, the exposure time was 5 min using FPA-1 flux. After soldering, a study was made of the mechanical properties of the tensile samples on an Instron brand testing machine. As a result of testing 5 soldered samples, it was found that the average value of mechanical strength is 304 MPa, and the conditional yield strength is 275 MPa.

Thus, it was found that the invention allows to provide a level of structural strength of more than 300 MPa.

Claims (6)

1. Aluminum alloy containing silicon, magnesium, copper, chromium, iron, titanium and aluminum, characterized in that it additionally contains zirconium and molybdenum in the following ratio of components, wt. %: Silicon 0.5-0.8 Magnesium 0.5-0.9 Copper 0.05-0.3 Chromium 0.05-0.2 Iron 0.15-0.25 Titanium 0.005-0.02 Zirconium 0.1-0.2 Molybdenum 0.05-0.35 Aluminum rest, in this case, copper is completely bound into the secondary precipitates of the Al ₅ Cu ₂ Mg ₈ Si ₆ phase, and the solidus temperature of the material is at least 600 ° C. 2. The alloy according to claim 1, characterized in that the total content of silicon and magnesium is not more than 1.5 wt. % 3. The alloy according to claim 1, characterized in that the total content of titanium, chromium and zirconium is not more than 0.25 wt. % 4. The alloy according to claim 1, characterized in that it further comprises cobalt, while the total content of cobalt and molybdenum is not more than 0.35 wt. %