Method for improving spinning formability of solid-solution-state barrel section with inner ribs through pretreatment

Abstract

The invention relates to the technical field of plastic processing of metal materials, and discloses a method for improving spinning formability of a solid-solution-state barrel section with inner ribs through pretreatment, which comprises the following steps: annealing a barrel section blank made of an aluminum alloy material, firstly placing the barrel section blank in a heat treatment furnace for heat preservation at 400-450 DEG C, and then carrying out water quenching and cooling to room temperature; the annealed barrel section blank is installed on a cylindrical core mold, and then thinning spinning is carried out; carrying out solution treatment on the thinned barrel section blank, firstly putting the thinned barrel section blank in a heat treatment furnace for heat preservation at 500-540 DEG C, and then carrying out water quenching and cooling to room temperature; and the barrel section blank obtained after solution treatment is installed on a cylindrical core mold with rib grooves, spinning forming is carried out, and the aluminum alloy barrel section with the inner ribs is obtained. According to the method, annealing-thinning pretreatment is adopted, the cracking risk in the solid solution state barrel section spinning forming process is effectively reduced, the aluminum alloy strip inner rib barrel section obtained through the method has the higher rib height wall thickness ratio, and the method is suitable for various aluminum alloy strip inner rib barrel sections in aerospace.

Description

Technical Field

[0001] The invention relates to the technical field of plastic processing of metal materials, and in particular to a method for improving the spinning formability of a solid solution barrel section with inner ribs through pretreatment. Background Art

[0002] Aluminum alloy internal ribbed barrel segments are widely used in the aerospace field due to their high specific strength, high load-bearing and weight-reducing advantages. However, the high-ribbed and thin-bellied structural characteristics of such components bring many challenges to the manufacturing process. The traditional sheet metal milling-ribbed plate bending-melon slice welding process not only has low material utilization, but also easily causes various defects during the welding process, which in turn affects the service reliability of the component. In contrast, high-power spinning technology can achieve the overall forming of such components, which is a manufacturing technology with significant advantages.

[0003] After the aluminum alloy components are plastically formed, they are usually required to be solution treated and then artificially aged to reach the T6 heat treatment state and improve their strength (a method for improving the mechanical properties of Al-Cu high-strength aluminum alloy rings, application number: CN201610194060.0). However, the formed material will undergo recrystallization during the solution process, and the high-density dislocations and a large number of substructures introduced into the component by the deformation process will disappear, resulting in the difficulty in retaining the work hardening effect, which is not conducive to improving the strength of the component. Therefore, the blank can be solution treated before plastic forming, and the component can be made to reach the T8 heat treatment state through the process path of solution treatment-plastic processing-artificial aging to further improve its strength (a method for strengthening aluminum alloys, application number: CN202311362273.6). However, for the aluminum alloy inner rib barrel section, the barrel blank directly treated with solution treatment has poor spinning formability and is prone to a variety of macro and micro defects after forming, which seriously affects the service performance of the component. At the same time, the direct solid solution blank has a large grain size and poor material fluidity, resulting in poor internal rib filling during spinning and difficulty in meeting design requirements. Therefore, it is urgent to develop a method that can improve the spinning formability of solid solution barrel segments with internal ribs. Summary of the invention

[0004] The purpose of the present invention is to provide a method for improving the spin forming property of a solid solution state barrel segment with internal ribs through pretreatment, so as to overcome the cracking problem during the spin forming process of the solid solution state barrel segment with internal ribs. The present invention significantly improves the spin forming property of the solid solution state barrel segment and increases the filling height of the internal ribs by performing an annealing-thinning spinning pretreatment process before the solid solution treatment, thereby promoting theoretical research on the solid solution forming manufacturing of aluminum alloys and laying a good foundation for practical applications.

[0005] To achieve the above object, the present invention provides a method for improving the spinning formability of a solid solution barrel segment with internal ribs by pretreatment, which comprises the following steps:

[0006] S1. Annealing

[0007] The barrel section blank made of aluminum alloy is placed in a heat treatment furnace, heated to 400-450°C at a rate of 10-20°C per minute, kept at this temperature for 1-2 hours, and then the barrel section blank is taken out of the heat treatment furnace and cooled to room temperature by water quenching;

[0008] S2, Thinning Spinning

[0009] The annealed barrel blank is mounted on a cylindrical core mold, and then thinned and spun, with a thinning rate of 20% to 40%;

[0010] S3. Solution treatment

[0011] The thinned barrel blank is placed in a heat treatment furnace, heated to 500-540°C at a rate of 10-20°C per minute, kept at this temperature for 1-2 hours, and then the barrel blank is taken out of the heat treatment furnace and cooled to room temperature by water quenching;

[0012] S4, Spinning

[0013] The barrel section blank after the solid solution treatment is installed on a cylindrical core mold with rib grooves and subjected to spin forming to obtain an aluminum alloy barrel section with internal ribs.

[0014] As a further preferred technical solution of the present invention, the barrel section blank in step S1 is manufactured by hot extrusion.

[0015] As a further preferred technical solution of the present invention, in step S2, the inner diameter of the cylindrical core mold is consistent with the inner diameter of the barrel section blank after annealing.

[0016] As a further preferred technical solution of the present invention, in step S2, lubricating oil is applied to the surface of the cylindrical core mold before the barrel section blank is installed on the cylindrical core mold; and lubricating oil is applied to the outer surface of the barrel section blank before thinning and spinning begins.

[0017] As a further preferred technical solution of the present invention, in step S2, multi-pass spinning is used to achieve thinning, and the reduction amount of each pass is one quarter to one fifth of the total reduction amount.

[0018] As a further preferred technical solution of the present invention, in step S4, the reinforcement grooves are in the form of one or more of longitudinal reinforcements, transverse reinforcements, oblique reinforcements, normal cross reinforcements, and oblique cross reinforcements.

[0019] As a further preferred technical solution of the present invention, in step S4, before the barrel section blank is installed on the cylindrical core mold, lubricating oil is applied to the surface of the cylindrical core mold; before spinning begins, lubricating oil is applied to the outer surface of the barrel section blank.

[0020] As a further preferred technical solution of the present invention, in step S4, the thinning rate of the spinning forming is 40% to 80%; and / or the forming is completed by a single-pass spinning.

[0021] As a further preferred technical solution of the present invention, in steps S2 and S4, the spinning process uses a double-conical spinning wheel.

[0022] Compared with the prior art, the present invention has the following beneficial technical effects:

[0023] The method of the present invention first anneals the initial tube blank to promote partial recrystallization of the material, thereby partially eliminating the dislocations and substructures introduced during the previous processing and reducing the risk of cracking during the thinning and spinning process. Through the thinning and spinning process, pre-deformation is introduced into the material, and the subsequent recrystallization process that occurs during the solution treatment can eliminate the banded grains generated during the hot forming process of the tube blank and replace them with fine equiaxed grain structures. This equiaxed structure can effectively disperse strain through multi-grain coordinated deformation; in contrast, the coarse banded structure obtained by direct solution treatment is prone to strain concentration at the grain boundary during deformation, resulting in poor microscopic deformation uniformity, thereby inducing cracking of the material during the spinning process with internal ribs. In addition, the fine equiaxed grain structure has better fluidity during the spinning process with internal ribs, which significantly increases the filling height of the internal ribs, thereby enhancing the bearing capacity of the final component. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0025] Figure 1 1 and 2 are comparison diagrams of the inner and outer surfaces of the aluminum alloy cylindrical spun parts with upright cross ribs obtained in Example 1 and Comparative Example 1, respectively. a1 and a2 are the outer and inner surface display structures of the sample in Example 1, and b1 and b2 are the outer and inner surface display structures of the sample in Comparative Example 1, respectively.

[0026] Figure 2 Comparative test curves of the cross-rib ...

[0027] Figure 3 These are the engineering stress test curves of the aluminum alloy cylindrical spun parts samples with positive cross ribs obtained in Example 1 and Comparative Example 1, respectively.

[0028] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings in conjunction with the embodiments. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. The terms such as "upper", "lower", "left", "right", "middle" and "one" cited in the preferred embodiments are only for the convenience of description, and are not used to limit the scope of the present invention. The change or adjustment of the relative relationship shall also be regarded as the scope of the present invention without substantially changing the technical content.

[0030] The present invention provides a method for improving the spinning formability of a heat-treatable strengthened aluminum alloy barrel section with internal ribs through pretreatment. The barrel section is annealed and thinned before solid solution, so that the coarse solid solution microstructure can be transformed into a fine equiaxed structure. After the initial barrel blank undergoes annealing-thinning spinning, the structure is broken, a large number of substructures represented by small-angle grain boundaries are generated, and the characteristic grain morphology and texture introduced by the previous hot working process are eliminated. Therefore, during the solid solution process, the material recrystallizes with a large number of substructures as nucleation sites to obtain a fine, equiaxed solid solution structure. The initial barrel blank is obtained by air cooling after hot working, and direct solid solution is transformed into a coarse strip-like structure. During the strong spinning process, the deformation of this type of structure is easily concentrated at the grain boundary, inducing premature cracking; and the fluidity is poor, and the internal rib filling height is insufficient. The solid solution microstructure composed of fine equiaxed grains can evenly disperse the strain to each grain through multi-grain coordinated deformation during high-power spinning, thereby reducing the possibility of cracking; and the small-grain equiaxed structure has good flow properties and better internal rib filling effect. This method effectively reduces the risk of cracking during the solid solution barrel spinning process, and the aluminum alloy barrel with internal ribs obtained by this method has a higher rib height to wall thickness ratio, which is suitable for various aluminum alloy barrels with internal ribs in aerospace.

[0031] The specific method is as follows:

[0032] The method of the present invention for improving the spinning formability of a solid solution barrel segment with internal ribs by pretreatment comprises the following steps:

[0033] (1) Preparation of tube blank

[0034] a The barrel section blank whose material is a heat-treatable aluminum alloy is prepared by multiple hot extrusion passes.

[0035] (2) Annealing process

[0036] a. Anneal the barrel blank described in (1) to allow the fiber structure formed after the heat treatment to recrystallize. Place the barrel blank in a heat treatment furnace in a vertical manner, heat it to 400-450°C at a rate of 10-20°C per minute, and keep it at that temperature for 1-2 hours.

[0037] b Take the tube blank in (2-a) out of the furnace, transfer it to the quenching pool within 3 seconds, and cool it to room temperature by water cooling.

[0038] (3) Thinning Spinning

[0039] a. Install the barrel segment obtained in (2) onto the cylindrical core mold. Apply lubricating oil to the core mold surface before installing the barrel segment, and apply lubricating oil to the outer surface of the barrel segment before each spinning process.

[0040] b After the spindle reaches the set speed, the roller first feeds radially along the barrel section, and then feeds radially along the barrel section. The total thinning rate is 20% to 40%, which is completed in multiple passes, with each pass reducing 10% to 20% of the total reduction.

[0041] (4) Solution process

[0042] a. The barrel blank obtained in (3) is subjected to a solid solution treatment, so that the cold-worked structure undergoes recrystallization and transforms into an equiaxed structure, and the second phase in the material structure dissolves into the matrix. The barrel blank is placed in a heat treatment furnace in a vertical manner, and the temperature is raised to 535°C at a rate of 10 to 20°C per minute, and kept at this temperature for 1 to 2 hours.

[0043] b Take the tube blank in (4-a) out of the furnace, transfer it to the quenching pool within 3 seconds, and cool it to room temperature by water cooling.

[0044] (5) Spinning

[0045] a. Install the solid solution barrel segment obtained in (4) onto the cylindrical core mold with rib grooves within 30 minutes. Apply lubricating oil to the surface of the core mold before installing the barrel segment. Apply lubricating oil to the outer surface of the barrel segment before spinning begins.

[0046] b After the spindle reaches the set speed, the rotary wheel first feeds radially along the barrel section to reach the preset downward pressure, and then feeds radially along the barrel section. The total thinning rate is 40% to 80%, which is completed in a single pass.

[0047] The following provides a specific embodiment of the method of the present invention for improving the spinning formability of a solid solution barrel segment with internal ribs through pretreatment.

[0048] Example 1

[0049] This embodiment provides a solution-spinning forming process for processing a 2219 aluminum alloy barrel section with a positive cross inner rib. The barrel section has an inner diameter of 200 mm, a wall thickness of 4 mm, a transverse rib spacing of 50 mm, six longitudinal ribs evenly distributed along the barrel section, and a root width of both longitudinal and transverse inner ribs of 6 mm. The demoulding slope is 2.5°. The specific processing process is:

[0050] (1) Preparation of tube blank

[0051] a The volume of the barrel blank is calculated using the structural diagram of the barrel with positive cross ribs. According to the principle of constant volume in plastic forming and the principle of nearly uniform plastic deformation, 2219 aluminum alloy is selected for hot extrusion to form a barrel with a size of 200 mm and a wall thickness of 10 mm, which is then cut into barrel segments with a height of 200 mm using a sawing machine.

[0052] (2) Annealing process

[0053] a. Place the tube blank vertically in the heat treatment furnace and close the furnace door. Set the heating program to increase the temperature to 450℃ at a heating rate of 20℃ per minute and keep it at this temperature for 1 hour.

[0054] b. After the insulation is completed, open the furnace door, use tongs to transfer the tube blank to the quenching pool within 3 seconds, and cool it to room temperature with water.

[0055] (3) Thinning Spinning

[0056] a. Install the cylindrical core mold with an outer diameter of 200mm and a height of 400mm on the main shaft of the double-wheel spinning machine, then apply lubricating oil on its surface, and then install the barrel blank on the cylindrical core mold and fix it with bolts. Apply lubricating oil on the outer surface of the barrel blank before spinning. Set the tool so that the starting position of the spinning wheels on both sides is located at a section of the barrel blank away from the main shaft, and the distance between the starting position and the top of the barrel segment is 20mm.

[0057] b Set the spinning program. In each pass, the spinning wheel first presses down along the radial direction of the barrel section, and then feeds along the axial direction of the barrel section toward the spindle after reaching the preset pressing amount. The total radial single-sided pressing amount is 3mm, which is completed in six passes. The starting position of the spinning wheel does not change, and the pressing amount increases by 0.5mm. The initial pressing amount is 0.5mm; the spindle speed is 60r / min, and a double-conical spinning wheel is used, with a front angle of 22.5°, a back angle of 27.5°, a fillet radius of R10mm, and a thickness of 43mm; the spinning feed ratio is 1.5mm / r. After spinning, the barrel section is removed from the core mold.

[0058] (4) Solution treatment

[0059] a. Place the spinning thinned tube blank in a vertical position in a heat treatment furnace and close the furnace door. Set the heating program to increase the temperature to 535°C at a heating rate of 20°C per minute and keep it at this temperature for 1 hour.

[0060] b. After the insulation is completed, open the furnace door, use tongs to transfer the tube blank to the quenching pool within 3 seconds, and cool it to room temperature with water.

[0061] (5) Spinning

[0062] a. Install a cylindrical split core mold with an outer diameter of 200mm and a height of 340mm with a positive cross rib groove on the main shaft of the double-wheel spinning machine, and then apply lubricating oil on its surface. The rib groove form is consistent with the internal rib form of the target barrel segment. The fillet radius of the rib groove edge is R2mm, the fillet radius of the intersection of the two internal ribs is R3mm, and the rib groove depth is 6mm. 20 minutes after the solution treatment is completed, install the barrel segment blank obtained in (4-b) on the core mold and fix it with bolts. Apply lubricating oil to the outer surface of the barrel blank before spinning. Adjust the tool so that the starting position of the spinning wheels on both sides is located at a section of the barrel blank away from the main shaft, and the distance between the starting position and the top of the barrel segment is 20mm.

[0063] b. Set the spinning program. In each pass, the spinning wheel first presses down along the radial direction of the barrel section. After reaching the preset pressing amount, it feeds along the axial direction of the barrel section toward the spindle. The radial single-side pressing amount is 4mm, and it is completed in a single pass. The spindle speed is 30r / min, and the same double-conical spinning wheel as in step (3-b) is used. The spinning feed ratio is 1.5mm / r. After the spinning is completed, remove the fixing bolts, remove the barrel section with internal ribs and the core mold petals together, and then separate the two.

[0064] Comparative Example 1

[0065] As a comparative experiment of Example 1, the only difference is that (2) the annealing process and (3) the pretreatment step of thinning and spinning are omitted, and the rest of the process is consistent with Example 1.

[0066] The inner and outer surfaces of the inner rib barrel segment obtained in Example 1 were compared with the barrel segment obtained by direct solid solution-spinning based on the same process parameters in Comparative Example 1 (e.g. Figure 1 As shown), it can be seen that cracks appear on both the inner and outer surfaces of the barrel section obtained in Comparative Example 1 ( Figure 1 The results show that the process of Example 1 inhibits the formation of fracture defects on the inner and outer surfaces during the existing direct solid solution-spinning process, and the spinning formability of the solid solution aluminum alloy with inner rib barrel section is significantly improved. The cross-rib section and longitudinal rib section of the component samples of Example 1 and Comparative Example 1 are further compared and tested, and the engineering stress is compared and tested. The results are as follows: Figure 2 and 3 As shown, by comparison, it can be seen that Example 1 can effectively increase the filling height of the internal reinforcement, thereby enhancing the bearing capacity of the component.

[0067] The present invention adopts a pretreatment strategy of annealing first and then thinning to solve a series of defects caused by the direct solid solution state with internal ribs in the barrel section spinning formability. Among them, the annealing process before thinning causes the material to partially recrystallize, which can improve the plasticity of the barrel section material and prevent it from cracking during the thinning and spinning process; and the role of thinning is to introduce deformation characteristics such as dislocations into the material through spinning, which provides driving force and nucleation sites for the subsequent solid solution process to completely recrystallize the material to form fine equiaxed crystals. In addition, based on the same experimental conditions as the above-mentioned Example 1, the present application has conducted a large number of experiments and found that: if the annealing process is omitted or the order of the two is reversed, the material will crack during the spinning process; and if the thinning is omitted, the structure after annealing-solid solution is not much different from the structure of direct solid solution, both of which are coarse banded grains.

[0068] In addition, the study found that too high or too low temperature in the solution treatment is not good. For example, if the solution temperature is as high as 550 degrees, overburning will occur, and below 490 degrees will affect the solution speed and the final workpiece performance. After a large number of experimental tests, the best solution temperature is 535℃.

[0069] Although specific embodiments of the present invention are described above, those skilled in the art should understand that these are merely examples and that various changes or modifications may be made to the embodiments without departing from the principles and essence of the present invention. The scope of protection of the present invention is limited only by the appended claims.

Claims

1. A method for improving the spinning formability of a solid solution-state inner rib barrel segment by pretreatment, characterized in that: The following steps are involved: S1. Annealing The barrel section blank made of aluminum alloy is placed in a heat treatment furnace, heated to 400-450°C, kept warm for 1-2 hours, and then the barrel section blank is taken out of the heat treatment furnace and cooled to room temperature by water quenching; S2, Thinning Spinning The annealed barrel blank is mounted on a cylindrical core mold, and then thinned and spun, with a thinning rate of 20% to 40%; S3. Solution treatment The thinned barrel blank is placed in a heat treatment furnace, heated to 500-540°C, kept warm for 1-2 hours, then the barrel blank is taken out of the heat treatment furnace and cooled to room temperature by water quenching; S4, Spinning The barrel section blank after the solid solution treatment is installed on a cylindrical core mold with rib grooves and subjected to spin forming to obtain an aluminum alloy barrel section with internal ribs.

2. The method for improving the spinning formability of a solid solution barrel segment with inner ribs by pretreatment according to claim 1, characterized in that: The barrel section blank in step S1 is manufactured by hot extrusion.

3. The method for improving the spinning formability of a solid solution barrel segment with inner ribs by pretreatment according to claim 1, characterized in that: In step S2, the inner diameter of the cylindrical core mold is consistent with the inner diameter of the barrel section blank after annealing.

4. The method for improving the spinning formability of a solid solution barrel segment with inner ribs by pretreatment according to claim 1, characterized in that: In step S2, before the barrel section blank is installed on the cylindrical core mold, lubricating oil is applied to the surface of the cylindrical core mold; before the thinning and spinning process begins, lubricating oil is applied to the outer surface of the barrel section blank.

5. The method for improving the spinning formability of a solid solution barrel segment with inner ribs by pretreatment according to claim 1, characterized in that: In step S2, thinning is achieved by multiple spinning passes, with the reduction amount in each pass being one quarter to one fifth of the total reduction amount.

6. The method for improving the spinning formability of a solid solution barrel segment with inner ribs by pretreatment according to claim 1, characterized in that: In step S4, the reinforcement grooves are in the form of one or more of longitudinal reinforcement, transverse reinforcement, oblique reinforcement, normal cross reinforcement, and oblique cross reinforcement.

7. The method for improving the spinning formability of a solid solution barrel segment with inner ribs by pretreatment according to claim 1, characterized in that: In step S4, before the barrel section blank is installed on the cylindrical core mold, lubricating oil is applied to the surface of the cylindrical core mold; before the spinning begins, lubricating oil is applied to the outer surface of the barrel section blank.

8. The method for improving the spinning formability of a solid solution barrel segment with inner ribs by pretreatment according to claim 1, characterized in that: In step S4, the thinning rate of the spinning forming is 40% to 80%; and / or the forming is completed by a single spinning pass.

9. The method for improving the spinning formability of a solid solution barrel segment with inner ribs by pretreatment according to claim 1, characterized in that: In step S1, the temperature is raised to 400-450°C at a rate of 10-20°C per minute; in step S3, the temperature is raised to 500-540°C at a rate of 10-20°C per minute.

10. The method for improving the spinning formability of a solid solution barrel segment with inner ribs by pretreatment according to any one of claims 1 to 9, characterized in that: In steps S2 and S4, the spinning process uses a double-conical spinning wheel.

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