A method for forging a low directionally sensitive 7085-series aluminum alloy forging

Abstract

The present application belongs to the field of metal material processing, and relates to a forging method and application of high-strength low-direction-sensitive large-size 7085 series aluminum alloy. The forging method comprises the combination of medium-temperature forging and differential-temperature forging. The present application proposes a forging method for reducing the direction sensitivity of 7085 aluminum alloy forgings and providing high tensile properties, which can improve the rheological properties of the center part of the forging and greatly improve the recrystallization rate to improve the uniformity of the large-section forging in all directions, improve the comprehensive performance, and reduce the direction sensitivity of the forging. The process designed in the present application is particularly suitable for manufacturing large-thickness-section aluminum alloy materials with a forging blank size of 200 mm.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of metal material processing and relates to a forging method of a 7085 aluminum alloy forge piece with high yield strength and extremely low direction sensitivity. BACKGROUND

[0002] The 7085 high-strength aluminum alloy is widely used in the fields of aerospace, military industry and transportation. In order to reduce weight, it is urgently needed to support the overall manufacturing of large complex parts by using large-thickness-section 7085 aluminum alloy forge pieces. The large-thickness-section 7085 alloy forge pieces generally adopt high-temperature forging process, and the center part is prone to have insufficient flow properties, so that sufficient deformation cannot be generated in the forging, resulting in that the alloy forge piece has strong direction sensitivity, mainly manifested as that the elongation anisotropy index is more than 50%, the fracture toughness in different directions is more than 30% different, and the high direction stress corrosion performance is significantly lower than that in other directions, which limits the advantages of longitudinal and transverse performance and restricts the improvement of comprehensive weight reduction benefit. In order to solve the problem of strong direction sensitivity, some researches have been made in the prior art. For example, in the patent 2023104747198, the 7085 aluminum alloy is taken as a processing object, and a multi-direction forging process is adopted. For example, a 7085 aluminum alloy blank with a size of 100*100*100mm is taken as an untreated object. The blank is heated to 460℃ and kept for 1h, and then is placed at 340℃ and kept for 0.5h. The multi-direction forging is carried out at 340℃, the single-direction deformation amount in the single upsetting and elongation process is 30%, after the forging, the L direction is forged from 100mm to 70mm to obtain a first forge piece. Then, the forge piece is heated to 460℃ and kept for 0.5h, and the multi-direction forging is carried out at 460℃, the temperature difference between the surface and the center is 20℃, the single-direction deformation amount in the single upsetting and elongation process is 30%, after the forging, the T direction is forged from 70mm to 50mm, and then is air-cooled. The T74 state forge piece obtained by the technology has a tensile strength of 563MPa, a yield strength of 486MPa and an elongation of 13.4% in the L direction of the center part, a tensile strength of 562MPa, a yield strength of 481MPa and an elongation of 15.0% in the LS direction, and a tensile strength of 548MPa, a yield strength of 458MPa and an elongation of 12.2% in the ST direction.

[0003] On the basis of the above research, in order to obtain a 7085 forge piece with higher yield strength and extremely low direction sensitivity, a series of explorations are carried out, and the application is formed. SUMMARY

[0004] In view of the deficiencies of the prior art, the application first obtains a forging method of a large-size 7085 aluminum alloy with a size of E*E*E mm (wherein E is in a range of 180-220), and an excellent product with high tensile strength, high yield strength, high elongation and extremely low anisotropy is obtained.

[0005] The application discloses a low direction-sensitive 7085 series aluminum alloy free forging piece, adopts a forging method combining medium-temperature forging and differential-temperature forging to control the structure of the forging piece, and the alloy material and the forging heat treatment comprise the following steps:

[0006] Step one: heating and heat preservation of the forging piece

[0007] The blank is heated to A ℃, heat preservation is performed until the temperature difference between the core and the surface of the blank is less than 5 ℃, then the temperature is lowered to B ℃, heat preservation is performed at B ℃ until the temperature difference between the core and the surface of the blank is less than 5 ℃, and a to-be-forged piece is obtained; the size of the blank is E×E×E mm, wherein the value range of E is 180-220,

[0008] The value of A is 440-480, and preferably 455-465; the value of B is 320-360, and preferably 335-345;

[0009] The material of the blank is a 7085 series aluminum alloy;

[0010] Step two: medium-temperature forging

[0011] The to-be-forged piece is subjected to medium-temperature forging; the initial forging temperature is controlled to be B ℃ during the medium-temperature forging, and the forging piece is forged from E mm to F mm; a first intermediate forging piece is obtained; the value of F is 0.65-0.75E, and preferably 0.7E;

[0012] Step three: heating and heat preservation after medium-temperature forging

[0013] The first intermediate forging piece obtained in step two is heated to C ℃, and heat preservation is performed until the temperature difference between the core and the surface is less than 5 ℃; a second intermediate forging piece is obtained; the value of C is 440-480, and preferably 455-465;

[0014] Step four: hot forging and differential-temperature forging

[0015] The second intermediate forging piece obtained in step three is subjected to hot forging and differential-temperature forging treatment; the hot forging and differential-temperature forging treatment is as follows: hot forging is started at C ℃, and hot forging is performed to 0.45-0.55E, and preferably 0.5E; during the hot forging process, a cooling agent is sprayed on the surface of the forging piece until the surface temperature reaches D ℃, and the temperature of the core of the forging piece is higher than that of the surface of the forging piece; the final forging temperature is greater than or equal to D ℃; after the forging is completed, air cooling is performed; a product is obtained; the value of D is 360-400, and preferably 375-385.

[0016] As preferred, the value range of E is 195-205, and more preferably 200.

[0017] The application discloses a low direction-sensitive 7085 series aluminum alloy free forging piece, adopts a forging method combining medium-temperature forging and differential-temperature forging to control the structure of the forging piece, and the alloy material and the forging heat treatment comprise the following steps:

[0018] The application discloses a forging method of a low direction-sensitive 7085 series aluminum alloy.

[0019] The application discloses a forging method of a low direction-sensitive 7085 series aluminum alloy.

[0020] As a preferred solution, the application discloses a forging method of a low direction-sensitive 7085 series aluminum alloy,

[0021] In step one, the blank is heated to 460 DEG C and kept for 2 hours, and then is placed at 340 DEG C and kept for 2 hours.

[0022] In step two, the initial forging temperature of the medium-temperature forging is 340 DEG C, and the forging piece is forged from 200 mm to 140 mm.

[0023] In step three, the medium-temperature forging is heated to 460 DEG C and kept for 2 hours.

[0024] In step four, the initial forging temperature of the hot forging is 460 DEG C, the forging piece is forged from 140 mm to 100 mm, and the upper and lower surfaces are sprayed with a cooling agent during the hot forging process until the surface temperature reaches 380 DEG C, so that the temperature of the central part is relatively high, the final forging temperature is not lower than 380 DEG C, and the forging is subjected to air cooling.

[0025] The application discloses a forging method of a low direction-sensitive 7085 series aluminum alloy; when the forging object is 7085 aluminum alloy, the product is obtained after T74 aging treatment after forging.

[0026] The difference between the tensile strengths of any two directions of the product L, LT and ST is less than or equal to 13 MPa, and the tensile strength of any one direction is greater than or equal to 535 MPa.

[0027] The difference between the yield strengths of any two directions of the product L, LT and ST is less than or equal to 12 MPa, and the yield strength of any one direction is greater than or equal to 510 MPa.

[0028] The difference between the elongations of any two directions of the product L, LT and ST is less than or equal to 2.1%, and the elongation of any one direction is greater than or equal to 13.1%.

[0029] This invention discloses a forging method for low-directionally sensitive 7085 series aluminum alloys; when the forging object is 7085 aluminum alloy, it is aged under T74 after forging; the product is obtained; after C-ring stress corrosion, only slight cracks are observed; the conditions for C-ring stress corrosion are: pressure 290MPa and time 20d.

[0030] Principles and advantages

[0031] This invention significantly improves the yield strength of the product and minimizes anisotropy by synergistically combining dimensional and forging process control during the forging process. The billets used in this invention fall within a specific size range; the method of first medium-temperature forging and then differential-temperature forging results in a more uniform microstructure and anisotropic properties in the forged parts. Furthermore, even after the temperature is reduced during hot forging, the surface temperature of the forging remains above D℃ (preferably greater than 380℃), ensuring that excessive recrystallization during subsequent processing prevents a decrease in surface material properties. If the process sequence of this invention is not followed, the anisotropy of the final product will be affected to some extent. Moreover, if the dimensions set by this invention are not followed, even with identical processes, the anisotropy of the product will significantly increase, and the product strength may even decrease.

[0032] The advantages of this invention are: 1. Improved uniformity of microstructure through recrystallization; 2. Simultaneous improvement of surface and core properties; 3. Improved deformation uniformity of various parts of the material, reduced directional sensitivity of the final material properties, and the forging does not exhibit lamellar grain structure with weak grain boundaries in the high direction; 4. Simple process combination operation, which can be realized in industrial production and has production application value; 5. The forging has significant advantages in directional sensitivity and toughness compared with similar forgings or thick plate aluminum alloy materials. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the process used in Example 1;

[0034] Figure 2 The grain boundary and grain orientation difference distribution of the T74 state forging obtained in Example 1.

[0035] from Figure 1 The basic process flow of the technology designed in this invention can be seen from the diagram.

[0036] from Figure 2 It can be seen that there is no lamellar grain structure with weak grain boundaries in the height direction of the forging. Detailed Implementation

[0037] The following comparative examples and embodiments are intended to further illustrate the present invention and not to limit the invention.

[0038] For room temperature tensile testing, relevant standard tensile specimens were prepared according to the national standard GB / T228-2002.

[0039] Comparative Example 1-1:

[0040] The alloy composition was Al-7.28Zn-1.49Mg-1.68Cu-0.11Zr (wt.%)

[0041] The blank was 7085 aluminum alloy with a size of 150x200x200mm. The blank was heated to 460℃ and held for 2h, and then was put into a 460℃ environment for multi-pass hot forging from 100mm to 70mm. Then the forged piece was heated to 460℃ and held for 2h, and then was forged from 70mm to 50mm, and was air cooled after forging.

[0042] Comparative Example 1-2:

[0043] The alloy composition was Al-7.28Zn-1.49Mg-1.68Cu-0.11Zr (wt.%)

[0044] The blank was 7085 aluminum alloy with a size of 300x300x300mm. The blank was heated to 460℃ and held for 2h, and then was put into a 340℃ environment for 2h, and then was pre-forged at 340℃ from 300mm to 210mm. Then the forged piece was heated to 460℃ and held for 2h, and then was forged from 210mm to 150mm, and was air cooled after forging.

[0045] Example 1:

[0046] The alloy composition was Al-7.28Zn-1.49Mg-1.68Cu-0.11Zr (wt.%)

[0047] The blank was 7085 aluminum alloy with a size of 200x200x200mm. The blank was heated to 460℃ and held for 2h, and then was put into a 340℃ environment for 2h, and then was pre-forged at 340℃ from 200mm to 140mm. Then the forged piece was heated to 460℃ and held for 2h, and then was hot forged at 460℃ from 140mm to 90mm, and was air cooled after hot forging.

[0048] The materials prepared in the comparative examples and the example were heat treated to a T74 state, and the heat treatment process parameters were 470℃ / 2h, water quenching, and then were subjected to a two-stage aging process of T74 aging system 120℃ / 7h+160℃ / 10h. The performance of the materials prepared according to the conventional forging process and the inventive process in three directions was compared, as shown in Table 1.

[0049] Table 1: Performance comparison of the comparative examples and the example in each direction

[0050]

Claims

1. A low directionally sensitive 7085-series aluminum alloy freeform forging, characterized by: The alloy composition is Al-7.28wt.%Zn-1.49wt.%Mg-1.68wt.%Cu-0.11wt.%Zr; the blank is 200*200*200mm of 7085 aluminum alloy; the blank is heated to 460 DEG C, and kept for 2h, and then placed to 340 DEG C, and kept for 2h, and multi-pass pre-forging is carried out at 340 DEG C, and forged from 200mm to 140mm; then the forgings are heated to 460 DEG C, kept for 2h, and hot-forged at 460 DEG C, forged from 140mm to 90mm, and the upper and lower surfaces are sprayed with cooling liquid during the hot-forging process until the surface temperature reaches 380 DEG C, and the forgings are air-cooled after the forging; The prepared material is heat treated to T74 state, and the heat treatment process parameters are 470 DEG C / 2h, water quenching, and after water quenching, T74 aging system 120 DEG C / 7h+160 DEG C / 10h is adopted for double-stage aging.

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