A method for improving the spinning formability of solid solution inner rib barrel segments through pretreatment

Abstract

The present invention relates to the technical field of plastic processing of metal materials, and discloses a method for improving the spin forming properties of a solid solution barrel segment with internal ribs through pretreatment, comprising: annealing a barrel segment blank made of an aluminum alloy, first placing it in a heat treatment furnace at 400-450°C for insulation, and then water quenching it to room temperature; installing the annealed barrel segment blank on a cylindrical core mold, and then thinning and spinning it; solution treating the thinned barrel segment blank, first placing it in a heat treatment furnace at 500-540°C for insulation, and then water quenching it to room temperature; installing the solution treated barrel segment blank on a cylindrical core mold with rib grooves, and spinning it to obtain an aluminum alloy barrel segment with internal ribs. The present invention adopts annealing-thinning pretreatment, which effectively reduces the risk of cracking in the solid solution barrel segment spinning process, and the aluminum alloy barrel segment with internal ribs obtained by this method has a higher rib height-to-wall thickness ratio, and is suitable for various types of aluminum alloy barrel segments with internal ribs in aerospace.

Description

Technical Field

[0001] The present 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-state inner rib barrel segment through pretreatment. Background Art

[0002] Aluminum alloy internally ribbed tube segments are widely used in the aerospace field due to their high specific strength, high load-bearing capacity, and weight-saving structural advantages. However, the high-ribbed, thin-bellied structural characteristics of such components pose 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 is also prone to various defects during the welding process, which in turn affects the service reliability of the component. In contrast, high-pressure spinning technology can achieve the integral forming of such components and is a manufacturing technology with significant advantages.

[0003] After plastic forming, aluminum alloy components are usually required to undergo solution treatment and then artificial aging to achieve a 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 treatment process, and the high-density dislocations and a large number of substructures introduced into the component by the deformation process will disappear, making it difficult to retain 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. Through a process path of solution treatment-plastic forming-artificial aging, the component can be brought to a T8 heat treatment state to further improve its strength (A method for strengthening aluminum alloys, application number: CN202311362273.6). However, for aluminum alloy inner rib tube segments, the tube blanks that are directly solution treated have poor spin forming properties and are prone to various macroscopic and microscopic defects after forming, which seriously affect the service performance of the component. At the same time, due to the large grain size and poor material fluidity of the direct solid solution blank, the internal rib filling effect during the spinning process is poor, making it difficult to meet the design requirements. Therefore, it is urgent to develop a method to improve the spinning formability of the solid solution barrel segment with internal ribs. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for improving the spinning formability of solid solution state barrel segments with internal ribs through pretreatment, so as to overcome the cracking problem during the spinning process of solid solution state barrel segments with internal ribs. The present invention significantly improves the spinning formability of the solid solution state barrel segments and increases the filling height of the internal ribs by performing an annealing-thinning spinning pretreatment process before solid solution treatment, thereby promoting theoretical research on solid solution forming and 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-state inner rib barrel segment by pretreatment, which comprises the following steps:

[0006] S1. Annealing

[0007] The aluminum alloy barrel blank 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 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 taken out of the heat treatment furnace and cooled to room temperature by water quenching.

[0012] S4, Spinning

[0013] The barrel section blank after solid solution treatment is installed on a cylindrical core mold with rib grooves and is subjected to spinning 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, 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 ironing spinning begins, lubricating oil is applied to the outer surface of the barrel section blank.

[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, upright cross reinforcements, and oblique cross reinforcements.

[0019] As a further preferred technical solution of the present invention, in step S4, before the barrel segment 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 segment blank.

[0020] As a further preferred technical solution of the present invention, in step S4, the thinning rate of the spinning 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 spinning process. Through the thinning spinning process, pre-deformation is introduced into the material. 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 coordinated deformation of multiple grains; in contrast, the coarse banded structure obtained by direct solution treatment tends to concentrate strain at the grain boundaries during deformation, resulting in poor micro-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, significantly improving 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 with reference to 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, respectively. 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 with upright 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 and in conjunction with the embodiments. DETAILED DESCRIPTION

[0029] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Terms such as "upper," "lower," "left," "right," "center," and "one" used in the preferred embodiments are for ease of description and are not intended to limit the scope of the present invention. Changes or adjustments to these relative terms, without substantially altering the technical content, are also considered within the scope of the present invention.

[0030] The present invention provides a method for improving the spinning formability of heat-treatable strengthened aluminum alloy barrel segments with internal ribs through pretreatment. The barrel segments are 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, and a large number of substructures represented by small-angle grain boundaries are generated, and the characteristic grain morphology and texture introduced by the previous heat treatment 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 transforms it into a coarse strip-like structure. During the strong spinning process, the deformation of this type of structure is easily concentrated at the grain boundaries, 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, evenly distributes strain throughout the grains through multi-grain coordinated deformation during high-pressure spinning, reducing the potential for cracking. Furthermore, the small-grain equiaxed structure exhibits excellent flow properties and enhances internal rib filling. This method effectively reduces the risk of cracking during solid solution barrel spinning. The resulting aluminum alloy internally ribbed barrel segments exhibit a higher rib height-to-wall thickness ratio, making them suitable for various aluminum alloy internally ribbed barrel segments used in aerospace applications.

[0031] The specific method is as follows:

[0032] The method of the present invention for improving the spinning formability of a solid solution-state inner rib barrel segment through pretreatment comprises the following steps:

[0033] (1) Preparation of tube blank

[0034] a. A barrel section blank made of 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 vertical heat treatment furnace and 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 (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 and 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. 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 is first fed radially along the barrel section, and then fed 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 solution treatment to recrystallize the cold-worked structure 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 using a vertical method, and the temperature is raised to 535°C at a rate of 10-20°C per minute and kept at this temperature for 1-2 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 ribbed 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 starting spinning.

[0046] b After the spindle reaches the set speed, the roller 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 specific embodiments 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 process for processing a 2219 aluminum alloy barrel segment with an upright cross-ribbed inner rib. The barrel segment 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 circumference of the barrel segment, a root width of both longitudinal and transverse inner ribs of 6 mm, and a draft angle of 2.5°. The specific processing process is as follows:

[0050] (1) Preparation of tube blank

[0051] aThe volume of the barrel blank is calculated using the structural diagram of the barrel segment 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. It 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, close the furnace door, set the heating program, and heat it up to 450℃ at a heating rate of 20℃ per minute, and keep it at that temperature for 1 hour.

[0054] b. After the insulation is completed, open the furnace door and 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 and spinning

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

[0057] b. Set the spinning program. Each pass begins with radial reduction of the barrel. After reaching the preset reduction, the spinning wheel advances axially toward the spindle. A total radial reduction of 3 mm is achieved in six passes. Each pass increases the reduction by 0.5 mm while maintaining the starting position of the spinning wheel. The initial reduction is 0.5 mm. The spindle speed is 60 rpm. A bi-conical spinning wheel is used with a rake angle of 22.5°, a relief angle of 27.5°, a fillet radius of 10 mm, and a thickness of 43 mm. The spinning feed rate is 1.5 mm / r. After spinning, the barrel is removed from the core mold.

[0058] (4) Solution treatment

[0059] a. Place the 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 and 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 an upright 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 inner rib form of the target barrel segment. The fillet radius of the rib groove edge is R2mm, the fillet radius at the intersection of the two inner 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 begins. 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. Each pass of the spinning wheel first presses radially down the barrel. After reaching the preset reduction, it feeds the barrel axially toward the spindle. The radial reduction on each side is 4 mm, and this is completed in a single pass. The spindle speed is 30 rpm, and the same double-tapered spinning wheel as in step (3-b) is used. The spinning feed ratio is 1.5 mm / r. After spinning is completed, remove the fixing bolts, remove the barrel with internal ribs and the core mold petals together, and then separate them.

[0064] Comparative Example 1

[0065] As a comparative experiment of Example 1, the only difference is that the pretreatment steps of (2) annealing process and (3) thinning and spinning are omitted, and the rest of the process remains the same as 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 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 internal and external surface fracture defects 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. Further comparative tests were conducted on the transverse and longitudinal rib sections of the component samples of Example 1 and Comparative Example 1, as well as on the engineering stress. The results are as follows: Figure 2 and 3 As shown, by comparison, 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 ribbed 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 avoid 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 complete recrystallization of the material to form fine equiaxed crystals during the subsequent solid solution process. In addition, based on the same experimental conditions as the above-mentioned Example 1, the present application 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] Furthermore, research has found that both excessively high and low solution temperatures can be detrimental. For example, temperatures as high as 550°C can cause overheating, while temperatures below 490°C can affect the solution rate and final workpiece properties. Extensive experimental testing has determined that 535°C is the optimal solution temperature.

[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 inner rib barrel segment by pretreatment, characterized in that: The following steps are involved: S1. Annealing The aluminum alloy barrel blank is placed in a heat treatment furnace, heated to 400-450°C, 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. 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, and kept warm for 1-2 hours. The barrel blank is then taken out of the heat treatment furnace and cooled to room temperature by water quenching. S4, Spinning The barrel section blank after solid solution treatment is installed on a cylindrical core mold with rib grooves and is subjected to spinning forming to obtain an aluminum alloy barrel section with internal ribs.

2. The method for improving the spinning formability of the solid solution inner rib barrel segment 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 the solid solution inner rib barrel segment 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 the solid solution inner rib barrel segment 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 ironing spinning begins, lubricating oil is applied to the outer surface of the barrel section blank.

5. The method for improving the spinning formability of the solid solution inner rib barrel segment by pretreatment according to claim 1, characterized in that: In step S2, thinning is achieved by multi-pass spinning, 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 the solid solution inner rib barrel segment by pretreatment according to claim 1, characterized in that: In step S4, the reinforcement grooves may be in the form of one or more of longitudinal reinforcement, transverse reinforcement, oblique reinforcement, upright cross reinforcement, and oblique cross reinforcement.

7. The method for improving the spinning formability of the solid solution inner rib barrel segment by pretreatment according to claim 1, characterized in that: In step S4, before the barrel section blank is mounted 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.

8. The method for improving the spinning formability of the solid solution inner rib barrel segment by pretreatment according to claim 1, characterized in that: In step S4, the thinning rate of the spinning 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 inner rib barrel segment 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 inner rib barrel segment by pretreatment according to any one of claims 1 to 9, characterized in that: In steps S2 and S4, a double-conical spinning wheel is used in the spinning process.

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