RU2677196C1 - Method of obtaining sheet from aluminum-magnetic alloys - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to the field of metallurgy of alloys, in particular to the technology of processing aluminum alloys of the Al-Mg-Mn system, and may be used to produce high strength sheets, used in aerospace, transporting and shipbuilding industry. Method includes the homogenization of cast alloy Al-Mg-Mn in the temperature range 340–355 °C for 7–8 hours, followed by cooling in a furnace to a temperature not higher than 60 °C, cutting the blank of the desired size, deformation-heat treatment followed by cooling in water at room temperature. While deformation-heat treatment is carried out in three stages: in the first stage, the workpiece is heated to 340–355 °C, rolled with a total reduction of 80–90 % at a deformation rate of 100–150 mm/s; in the second stage, the workpiece is rolled with a reduction of 55–65 % at a temperature of 180–195 °C and a deformation rate of 100–150 mm/s, in the third stage, the workpiece is rolled with a reduction of 40–50 % at a temperature of 205–220 °C and a deformation rate of 200–300 mm/s, in the second and third stages, the rolling is carried out in two rolls with the ratio of peripheral speeds determined by the proposed formula.

EFFECT: method allows to obtain sheets with a fine-grained structure and enhanced mechanical properties.

1 cl, 1 ex, 2 tbl

Description

The invention relates to the field of metallurgy of alloys, and in particular to the processing technology of aluminum alloys of the Al-Mg-Mn system and can be used to produce high strength sheets used in the aerospace, transport and shipbuilding industries.

A known method of manufacturing products from aluminum or magnesium alloys with nano- and submicrocrystalline structure and products made from these alloys (RU No. 2467090, C22F 1/04). In the method, for example, the alloy AMg6 of the Al-Mg-Mn system, equal-channel angular pressing is carried out in the temperature range 150-275 ° C at a strain rate of 0.4 mm / s and the total number of cycles is six. After equal-channel angular pressing, it is possible to conduct annealing at a temperature of 100-300 ° C.

A disadvantage of the known invention is the low strength characteristics of the resulting products due to insufficient shear deformation.

The closest analogue to the claimed object is a method of deformation-heat treatment of aluminum-magnesium alloys, including the homogenization of the cast alloy Al-Mg-Mn in the temperature range 340-355 ° C for 7-8 hours, followed by cooling in the furnace to a temperature of no higher than 60 ° C, cutting a workpiece of the desired size, heat-treating, followed by cooling in room temperature water. At the same time, equal-channel angular pressing is carried out as a deformation-thermal treatment in the temperature range 280-295 ° C with a total number of passes corresponding to the true degree of deformation from 8 to 12, and the deformation rate from 5 to 10 mm / s (see RF patent No. 2566107, C22F 1/047).

A disadvantage of the known invention is the low strength characteristics of the resulting products due to insufficient shear deformation. Another disadvantage is the low productivity of the process, due to the required large number of processing cycles and the limited size of the workpieces.

The problem solved by the invention is to increase the strength properties of sheets made of aluminum-magnesium alloys by obtaining a fragmented metal structure with a high dislocation density as a result of creating a complex stress-strain state in the metal while maintaining a sufficient ductility resource.

The technical result, which provides a solution to the problem, is to create conditions that ensure rational temperature, deformation and speed treatment in the deformation zone during asymmetric rolling with large shear deformations.

The problem is achieved in that in a method for producing a sheet of aluminum-magnesium alloys, comprising the homogenization of a cast alloy Al-Mg-Mn in the temperature range 340-355 ° C for 7-8 hours, followed by cooling in a furnace to a temperature not exceeding 60 ° C, cutting the workpiece of the desired size, heat-treating, followed by cooling in water at room temperature, according to the invention, heat-treating is carried out in three stages, and at the first stage, the workpiece is heated to 340-355 ° C, rolled with a total compression 80-90% at a strain rate of 100-150 mm / s, in the second stage, the workpiece is rolled with compression 55-65% at a temperature of 180-195 ° C and a strain rate of 100-150 mm / s, in the third stage, the workpiece is rolled with compression of 40-50% at a temperature of 205-220 ° C and a strain rate of 200-300 mm / s, while in the second and third stages, rolling is carried out in two rolls with a ratio of peripheral speeds, determined by the formula:

,

,

where V ₁ is the peripheral speed of the first roll, mm / s;

V ₂ - peripheral speed of the second roll, mm / s;

H ₀ is the thickness of the sheet before the second or third stage of the heat-treatment, mm;

H ₁ is the thickness of the sheet after the second or third stage of deformation-heat treatment, mm

A known method of manufacturing products from aluminum or magnesium alloys with nano- and submicrocrystalline structure, including preliminary equal-channel angular pressing of alloys, carried out with a strain rate of 0.4 mm / s and a strain temperature selected in the range of 150-275 ° C (see RF patent No. 2467090, C22F 1/04, C22F 1/06, B82B 3/00, B21J 5/00).

Both in the known and in the claimed method, the regulated temperature and speed conditions of deformation-heat treatment are designed to increase the strength and plastic properties of manufactured products.

Known cold rolling strips with a total degree of deformation of 75-95% to increase the strength properties of sheets (see. A. Tselikov. Theory of rolling. Reference. - M .: Metallurgy, 1982. - S. 128-131).

Both in the known and in the claimed method, high total degrees of compression during rolling are used to increase the strength properties of the manufactured sheets.

A known method of sheet rolling aluminum alloys (see RF patent No. 2622195, B21B 1/28), where the cold rolling of the strip is carried out in two rolls with a mismatch of their peripheral speeds with a total degree of deformation of 75-95%.

In the inventive method, the mismatch of velocities, as well as in the known method, is intended to create rational temperature conditions in the deformation zone while at the same time forming a complex stress-strain state circuit therein, including high compression and shear stresses. This will allow to obtain a stable fragmented metal structure with a high dislocation density, as a result of which the strength properties of manufactured thin strips and sheets of aluminum alloys are significantly increased.

A known method of deformation-heat treatment of aluminum-magnesium alloys (see RF patent No. 2566107, C22F 1/047), where the workpiece is heated in a furnace to a temperature of 280-295 ° C and conduct equal-channel angular pressing with a total number of passes corresponding to the true degree of deformation from 8 to 12, and a deformation rate of 5 to 10 mm / s in the temperature range 280-295 ° C.

In the inventive method, the use of preheating before deformation, a given degree of deformation and deformation rate, but already in the process of asymmetric rolling as well as in the known method, allows to reduce the stress during processing, and also to exclude subsequent annealing to stabilize the structure, resulting in an alloy a gradient ultrafine-grained structure is formed and the strength properties of the alloy increase.

It is known that the asymmetric rolling scheme allows you to create a complex stress state in the sample, where the intense shear is combined with the reduction of the sample characteristic of traditional rolling. With this deformation scheme, a superposition of the translational and rotational modes arises directly during the rolling process. An additional channel for the propagation of dislocations is included, which can significantly increase the concentration of defects that take part in the structure formation. In this case, an ultrafine-grained metal structure is formed (see Gogaev K.A., Voropaev V.S., Podrezov Yu.N. et al. Obtaining high-strength titanium ribbons by powder consolidation using asymmetric rolling technology // High Pressure Physics and Technology. 2016 Volume 26, No. 3-4, pp. 5-18).

In the claimed method also provides the formation of ultrafine metal structure.

However, along with the aforementioned known properties, in the claimed method, the set of distinctive features of the claimed invention exhibits a new technical result, which consists in creating rational temperature and speed conditions in the deformation zone while at the same time forming a complex stress-strain state circuit therein, including large stresses of comprehensive compression and deformation shear. As a result, a synergistic effect arises from the superposition of two deformation schemes — pure and simple shears in asymmetric rolling, while using high deformation rates. This provides a large angular rotation of the grains and, as a result, large shear deformations, leading to grain refinement and an increase in strength and plastic properties.

Based on the foregoing, we can conclude that the inventive method for producing a sheet of aluminum-magnesium alloys does not follow explicitly from the prior art and, therefore, meets the patentability condition "inventive step".

A method of obtaining a sheet of aluminum-magnesium alloys is as follows.

A method of obtaining a sheet of aluminum-magnesium alloys involves the homogenization of a cast Al-Mg-Mn alloy in the temperature range of 340-355 ° C for 7-8 hours, followed by cooling in an oven to a temperature not exceeding 60 ° C. This will eliminate dendritic segregation, which leads to the production of an inhomogeneous solid solution and the release of brittle nonequilibrium eutectic inclusions along the grain boundaries and between the branches of the dendrites. In the process of homogenization, the composition of the crystallites of the solid solution is leveled, and the intermetallic compounds dissolve. In the process of subsequent cooling, the intermetallic compounds are released in the form of uniformly distributed small secondary inclusions. As a result, the ductility of the cast alloy is increased, which allows to increase the degree of compression and the rate of deformation during hot processing, as well as reduce process waste. Next, from the homogenized ingot, blanks of the desired size are cut out. Then carry out the deformation-heat treatment in three stages. At the first stage, the billet is heated in an oven to 340-355 ° C, rolled with a total compression of 80-90% at a deformation rate of 100-150 mm / s. This will allow to compact the cast structure of the alloy and achieve the effect of structural hardening, thereby increasing the strength characteristics of the alloy. At the second stage, the workpiece is rolled with compression of 55-65% at a temperature of 180-195 ° C and a strain rate of 100-150 mm / s. This ensures the creation of a complex stress-strain state diagram in the deformation zone, including large stresses of comprehensive compression and shear deformation. At the third stage, the billet is rolled with compression of 40-50% at a temperature of 205-220 ° C and a deformation rate of 200-300 mm / s. This will also make it possible to obtain a fragmented metal structure with a high dislocation density. The peripheral speeds of the rolls in the second and third stages are set according to the ratio:

,

,

where V ₁ is the peripheral speed of the first roll, mm / s;

V ₂ - peripheral speed of the second roll, mm / s;

H ₀ is the thickness of the sheet before the second or third stage of the heat-treatment, mm;

H ₁ is the thickness of the sheet after the second or third stages of the heat-treatment, mm.

After rolling in the third processing step, the sheet is cooled in room temperature water, for example in a bath.

The set of distinctive features of the proposed method will allow to obtain a stable fragmented metal structure with a high dislocation density and, accordingly, to increase the strength properties of sheets made of aluminum-magnesium alloys while maintaining a sufficient plasticity resource.

In addition, the process of asymmetric rolling at the second and third stages of deformation-heat treatment is carried out with sufficiently large single reductions, as a result of which the deformable metal is significantly heated, so preheating can be carried out to lower temperatures.

If the temperature of the deformation processing at the first stage is higher than 355 ° C, then the recrystallization process will occur, which will lead to a decrease in strength and an increase in the plastic characteristics of the manufactured sheets.

If the temperature of deformation processing at the first stage is below 340 ° C, then the process of hardening of the metal occurs, which leads to a decrease in the plastic characteristics of the manufactured sheets and the possible appearance of cracks.

If the total compression at the first stage is more than 90%, then the metal hardens, which leads to a sharp decrease in the plastic characteristics of the manufactured sheets.

If the total compression at the first stage is less than 80%, then the metal is not uniformly deformed, which leads to insufficient grain refinement, and, consequently, a decrease in the strength and plastic characteristics of the sheets being produced.

If the speed of deformation of the workpiece at the first stage is more than 150 mm / s, then the metal hardens, which will lead to a decrease in the plastic characteristics of the manufactured sheets.

If the deformation rate at the first stage is less than 100 mm / s, then the hardening of the metal due to its insufficient heating during processing will lead to a decrease in the plastic characteristics of the manufactured sheets.

Carry out sheet rolling of aluminum-magnesium alloys at the second and third stages with a ratio of peripheral speeds:

или

or

impractical, since this reduces shear deformation, and therefore, decreases the strength and plastic characteristics of the manufactured sheets.

If the temperatures of deformation treatments are greater than 195 ° C and 220 ° C, respectively, at the second and third stages of processing, the return processes are intensified, which leads to a decrease in strength and an increase in the plastic characteristics of the sheets being manufactured.

If the temperature of the deformation treatments is less than 180 ° C and 205 ° C, respectively, at the second and third stages of processing, then the return process does not occur, which leads to a slight change in the strength characteristics and a decrease in the ductility of the manufactured sheets.

If the degree of deformation is more than 65% and 50%, respectively, at the second and third stages of processing, then an increase in strength characteristics and a decrease in the ductility of the manufactured sheets are observed.

If the degree of deformation is less than 55% and 40%, respectively, at the second and third stages of processing, then a decrease in the strength characteristics of the manufactured sheets is observed.

If the deformation rate is greater than 150 mm / s and 300 mm / s, respectively, at the second and third stages of processing, then an increase in strength and a decrease in the plastic characteristics of the manufactured sheets are observed.

If the deformation rate is less than 100 mm / s and 200 mm / s, respectively, at the second and third stages of processing, then a decrease in the strength and plastic characteristics of the produced sheets will be observed, since the deformation rate does not allow the grain to be crushed to the desired size.

An example implementation of the method.

To justify the advantages of the proposed method for producing a sheet of aluminum-magnesium alloys, 15 experiments were carried out in the first stage of processing and 19 experiments in the second and third stages of processing. Alloy 1561 (OST 5P.9466-88), belonging to the Al-Mg-Mn system, was homogenized at a temperature of 355 ° C for 7 hours, followed by cooling in an oven to a temperature of 40 ° C. Next, blanks were cut from a homogenized ingot and heated in a furnace to a post-treatment temperature of 340-355 ° C. After that, the billets were rolled with a total compression of 80-90% at a strain rate of 100-150 mm / s. Then, the obtained sheet blank 100 × 2 mm was rolled with compression of 50–70% at a temperature of 175–200 ° C and a deformation rate of 95–155 mm / s. The ratio of speeds on the rolls was selected from the interval of 1.95-3.25. In the third stage, the tape was rolled at a temperature of 205-225 ° C with a compression of 35-55% at a strain rate of 190-310 mm / s. The ratio of speeds on the rolls was selected from the interval 1.58-2.17. After rolling, the tape was cooled in room temperature water. As a result, an ultrafine-grained structure with an average grain size of about 800–900 nm was formed in the blanks. Thus obtained alloy structure 1561 provides a significant increase in its mechanical properties.

Experiments: 2-4, 7-9, 12-14, 17-18 were carried out in accordance with the claimed modes specified in the claims; experiments: 1, 5-6, 10-11, 15-16, 19 - according to modes that go beyond the minimum and maximum declared limits. The rolling modes are shown in table 1, the obtained mechanical properties are shown in table 2.

The test results showed that the strip of aluminum-magnesium alloy made by the present method (experiments: 2-4, 7-9, 12-14, 17-18), has strength properties 18% higher compared to the prototype.

It is impractical to produce a strip of aluminum-magnesium alloy according to regimes that go beyond the declared limits (experiments: 1, 5-6, 10-11, 15-16, 19), since the strength properties of the sheet are significantly reduced.

Thus, the proposed method allows to obtain a sheet of alloys of the Al-Mg-Mn system with a fine-grained structure and an increased set of mechanical properties for the manufacture of various semi-finished products for the aerospace, transport, shipbuilding industries.

Claims (6)

A method of obtaining a sheet of aluminum-magnesium alloys, including the homogenization of a cast alloy Al-Mg-Mn in the temperature range 340-355 ° C for 7-8 hours, followed by cooling in a furnace to a temperature not exceeding 60 ° C, cutting the workpiece of the desired size, deformation-heat treatment followed by cooling in water at room temperature, characterized in that the deformation-heat treatment is carried out in three stages, and in the first stage, the workpiece is heated to 340-355 ° C, rolled with a total compression of 80-90% at a speed of deformed I am 100-150 mm / s, at the second stage the workpiece is rolled with compression of 55-65% at a temperature of 180-195 ° C and a deformation rate of 100-150 mm / s, at the third stage the workpiece is rolled with compression of 40-50% at a temperature of 205 -220 ° C and a strain rate of 200-300 mm / s, while in the second and third stages, rolling is carried out in two rolls with a ratio of peripheral speeds, determined by the formula:

, where V ₁ is the peripheral speed of the first roll, mm / s; V ₂ - peripheral speed of the second roll, mm / s; H ₀ is the thickness of the sheet before the second or third stage of the heat-treatment, mm; H ₁ is the thickness of the sheet after the second or third stage of deformation-heat treatment, mm