RU2468114C1 - Method to produce superplastic sheet from aluminium alloy of aluminium-lithium-magnesium system - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: from an ingot a stock of rectangular section is produced, which is square in plan, with the ratio of thickness and width equal to 0.17-0.33, stock deformation is carried out with equal channel angular pressing at the angle of channels crossing 90°, temperature of 320-330°C, a number of stages corresponding to true deformation 4, with back pressure, equal to 40-50% of the applied pressure, and rotation of the stock after each stage by the angle of 90° around the normal line to the largest area of stock section and additionally by 180° around the longitudinal axis, the pressed stock is exposed to isothermal rolling in the range of temperatures 320-330°C, then tempering is carried out with 450±10°C after soaking for 2 hours, and repeatedly heated to 120°C, soaked for 5 hours and cooled with the furnace.

EFFECT: method makes it possible to superplastic sheets from an aluminium alloy of a system of Al-Mg-Li with high isotropy of mechanical properties and higher indices of superplasticity under lower temperatures and high speeds of deformation due to preservation of homaxonic ultra-fine-grain structure.

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Description

The invention relates to the field of metallurgy, and in particular to methods for producing superplastic sheets from an aluminum alloy of an aluminum-magnesium-lithium system, used for superplastic molding of products of complex shape, as well as for the production of extruded profiles as a structural material.

A known method of producing a thin sheet for superplastic forming from alloys of the Al-Mg-Li system (RU No. 1529750, publ. 03/27/1996), including ingot homogenization, hot rolling, quenching, heterogeneous annealing and cold rolling with intermediate annealing.

The technological process includes:

- homogenization annealing of ingots at 475-520 ° C for 3-8 hours;

- hot rolling;

- quenching from 490-520 ° C;

- heterogenization annealing at 385-410 ° C for 1-2 hours;

- cold rolling with intermediate annealing at 385-410 ° C for 5-30 minutes after every 30-55% deformation, and cooling after heterogenization and intermediate annealing is carried out at a rate of 350-750 ° C / s.

The main disadvantage of this method is the low level of mechanical properties, with a final sheet thickness of 6 mm, respectively, characterized by an increased weight of the structural part and makes it economically unprofitable. The disadvantage of this method is also the multi-stage thermomechanical processing, resulting in increased cost of the final product.

The closest in technical essence and the achieved result to the proposed invention is a method for producing superplastic sheets from aluminum alloys of the aluminum-magnesium-lithium system (RU No. 2345173, publ. January 27, 2009), which includes the preparation of an ingot in the form of a cylinder from the ingot, which is subjected to hardening with 460 ± 10 ° C for 0.5 h, then the workpiece is pressed in intersecting channels with a diameter corresponding to the diameter of the workpiece deformed by shear in the temperature range 300-400 ° C with the degree of accumulated deformation e = 10, then proca ku at 330-370 ° C. In this method, with a grain size of 1 μm, the sheet showed at a temperature of 400 ° C and a strain rate of 10 ^-2 s ^{-1 the} effect of superplasticity with a relative elongation of 530%.

The main disadvantage of this method is that it does not achieve the maximum (limit) effect of superplasticity required to obtain defect-free products of complex shape by the superplastic molding method. In addition, the method is not economically effective, since an additional operation is necessary to redistribute the production after the control gear from a cylindrical shape to a rectangular shape for rolling the sheet.

The technical result is the creation of a method for producing a superplastic sheet from an aluminum alloy of the Al-Mg-Li system with high isotropic mechanical properties and increased superplasticity at low temperatures and high strain rates by maintaining equiaxed ultrafine-grained structure.

The technical result is achieved using the proposed method for producing a superplastic sheet from an aluminum alloy of the Al-Mg-Li system, which includes obtaining a workpiece from an ingot, pressing it in intersecting channels, rolling, and a rectangular workpiece with a square section in relation to thickness to width equal to 0.17-0.33, deformation of the workpiece by equal channel angular pressing at an angle of intersection of channels 90 ° is carried out at a temperature of 320-330 ° C with the number of passes corresponding to the true deformation, 4, with with a pressure equal to 40-50% of the applied pressure, with the workpiece turning after each pass through an angle of 90 ° around the normal to the largest cross-sectional area of the workpiece and an additional 180 ° around the longitudinal axis, after which the pressed workpiece is subjected to isothermal rolling in the temperature range 320-330 ° C, then quenching is carried out from 450 ± 10 ° C for 2 hours and reheated to 120 ° C with holding for 5 hours, cooling with the oven.

Significant differences of the present invention consist in the fact that a rectangular preform is obtained from the ingot, square in plan, with a ratio of thickness to width equal to 0.17-0.33, deformation by equal channel angular pressing at an angle of intersection of channels of 90 ° is carried out at a temperature of 320 -330 ° C with the number of passes corresponding to the true deformation, 4, with a back pressure equal to 40-50% of the applied pressure, with the workpiece turning after each pass at an angle of 90 ° around the normal to the largest cross-sectional area of the workpiece and tively by 180 ° about the longitudinal axis, whereby when the proposed compression modes provided forming ultrafine structures (1.0-1.2 microns). Integrated processing with a reduced number of ECAP cycles makes the method cost-effective for a batch of products.

, которая практически совпадает с максимально возможной по техническим условиям скоростью сверхпластической пневмоформовки, относительное удлинение составляет 1500%, в отличие от прототипа. Способ обеспечивает минимальную разнотолщинность детали сложной формы при пневмоформовке.In addition, a two-stage treatment consisting of ECAP, followed by isothermal rolling, allows one to obtain sheets from Al-Mg-Li alloys with high superplastic properties, characterized by a combination of strength and ductility at room temperature due to the formation of a recrystallized homogeneous structure with a weak crystallographic texture. Thin sheets with a homogeneous ultrafine-grained structure exhibit high superplasticity at a fairly low temperature of 350 ° C and strain rate

, which almost coincides with the maximum possible technical specifications for the speed of superplastic pneumoforming, the elongation is 1500%, in contrast to the prototype. The method provides minimal thickness variation of a part of complex shape during pneumoforming.

An example implementation of the method.

A method of obtaining a superplastic sheet is as follows. A rectangular billet with a size of 180 × 180 × 40 mm is cut from the obtained ingot, pressed into channels intersecting at an angle of 90 ° with a cross section corresponding to the cross section of the deformable billet, by a simple shift at a temperature of 325 ° C to the degree of accumulated deformation 4 with a back pressure of 40- 50% of the applied pressure, then a workpiece with dimensions of 175 × 175 × 35 mm is rolled under isothermal conditions to a final thickness of 1.8 mm at a temperature of 325 ° C, after which it is quenched at a temperature of 450 ± 10 ° C for 2 hours with cooling, for example, in oil and re-heating is carried out - aging 120 ° C with holding for 5 hours and cooling with the oven.

The ultrafine-grained structure obtained by equal channel angular pressing remains stable during isothermal rolling, and the preserved equiaxiality of the grain structure leads to an increase in the uniformity of mechanical properties and to an improvement in their operational characteristics.

The proposed method allows to obtain superplastic sheets from an aluminum alloy of the Al-Mg-Li system with high isotropic mechanical properties and increased superplasticity at low temperatures and high strain rates due to the preservation of equiaxed ultrafine-grained structure.

The method is more economical and practicable in industrial production, can reduce the total duration of the main operations of the process.

Claims (1)

A method of producing a superplastic sheet of an aluminum alloy of an Al-Mg-Li system, including producing a preform from an ingot, equal channel angular pressing in intersecting channels, rolling, characterized in that a rectangular preform is obtained from the ingot, square in plan, with a ratio of thickness to width equal to 0.17-0.33, equal-channel angular pressing is carried out at an angle of intersection of the channels 90 ° and a temperature of 320-330 ° C with the number of passes corresponding to the true deformation, 4, with a backpressure equal to 40-50% of the applied phenomenon, and by turning the workpiece after each pass through an angle of 90 ° around the normal to the largest cross-sectional area of the workpiece and an additional 180 ° around the longitudinal axis, after which the pressed workpiece is subjected to isothermal rolling in the temperature range 320-330 ° C, then quenching is performed with 450 ± 10 ° C for 2 hours and reheated to 120 ° C with holding for 5 hours and cooled with the oven.