A method for processing large-diameter thin-walled high-precision aluminum tubes

Abstract

This invention belongs to the field of aerospace tubing technology and discloses a method for processing large-diameter, thin-walled, high-precision aluminum tubes. First, 2024 aluminum alloy is prepared, and the aluminum tube is manufactured using a vertical hot extrusion forming method. Then, solution treatment and cold deformation are performed within an aging period, followed by natural aging. The cold deformation treatment includes core drawing before solution treatment, diameter straightening after solution treatment, and tension straightening. The specific sequence of cold deformation and solution treatment is as follows: the manufactured aluminum tube undergoes core drawing, roller straightening, solution treatment, diameter straightening, and tension straightening in sequence. This invention determines the optimal content of the main strengthening elements in the alloy through content analysis and experimentation. By analyzing the difficulties in straightening and rounding large-diameter, thin-walled, high-precision aluminum alloy tubes, it solves the deformation defects generated during straightening and rounding of large-diameter, thin-walled aluminum alloy tubes, establishes a new process technology, avoids surface defects in the aluminum tubes during the inspection process, and significantly improves the pass rate of aluminum tubes.

Description

Technical Field

[0001] This invention belongs to the field of aviation tubing technology, and relates to a method for manufacturing high-precision aluminum alloy tubing for helicopter tail drive shafts, specifically a method for processing large-diameter thin-walled high-precision aluminum tubing. Background Technology

[0002] Currently, among the high-precision aluminum alloy tubes used in helicopter tail drive shafts, there are no large-diameter thin-walled aluminum alloy tubes with a diameter greater than 130mm and a diameter-to-thickness ratio greater than 70. The processing difficulty level is level one. During the development of the test piece, similar high-precision aluminum alloy tubes are prone to problems such as core pull-out cracks, severe deformation during heat treatment, residual indentations on the tube wall after straightening, and failure of ultrasonic flaw detection.

[0003] Therefore, thicker tube walls are generally preferred to improve manufacturing precision, but this increases the overall weight of the machine. Currently, there is no suitable manufacturing method for large-diameter, thin-walled, high-precision aluminum tubes that can simultaneously achieve the required manufacturing precision and thin wall thickness. Summary of the Invention

[0004] To address the aforementioned issues, this invention provides a method for processing large-diameter thin-walled high-precision aluminum tubes. This method can be used for lightweight, high-strength, and stable large-diameter thin-walled high-precision aluminum alloy tubes with a diameter greater than 130mm and a diameter-to-thickness ratio greater than 70. The dimensional accuracy and mechanical properties of these tubes exceed national military standards, and the ultrasonic non-destructive testing pass rate is higher than 80%. This method is advanced, stable, and easy to promote and apply.

[0005] The technical solution of the present invention is as follows:

[0006] A method for processing large-diameter, thin-walled, high-precision aluminum tubes involves first preparing 2024 aluminum alloy, manufacturing the aluminum tube using a vertical hot extrusion forming method, then performing solution treatment and cold deformation treatment within an aging period, and finally performing natural aging treatment. The cold deformation treatment includes core drawing before solution treatment, diameter adjustment after solution treatment, and tension straightening treatment. The specific order of cold deformation treatment and solution treatment is as follows: the manufactured aluminum tube is subjected to core drawing, roller straightening, solution treatment, diameter adjustment, and tension straightening treatment in sequence.

[0007] Furthermore, all heat treatments must be followed by annealing, polishing, and water cleaning; except for tension straightening, all cold deformation treatments must be followed by degreasing and cleaning.

[0008] Furthermore, during the material preparation process, the Cu content of the 2024 aluminum alloy was adjusted to 4.40%.

[0009] Furthermore, the diameter adjustment process is as follows: using a pull rod, the mandrel for mandrel extraction is pulled into the aluminum tube from one end. The mandrel consists of two O-rings arranged axially, with the outer diameter of the O-rings being the required inner diameter of the aluminum tube. After the mandrel is pulled in, plugs supporting the inner diameter are inserted into both ends of the aluminum tube, and clamps for fixing the outer diameter are installed. Then, the mandrel is pulled out from the other end of the aluminum tube.

[0010] Furthermore, tension straightening processes include: tension straightening, bending straightening, measurement, multi-point rounding, and static imbalance correction.

[0011] Furthermore, in the multi-point rounding process, a quarter of the pipe is used as a three-dimensional finite element analysis model to simulate the deformation of the pipe during the rounding process and obtain the roundness correction parameters.

[0012] Furthermore, tension straightening treatment was performed 48 hours after solution treatment.

[0013] Furthermore, during the solution treatment process, the holding time is 90 minutes, the solution temperature is 465°C, and the cooling method is water quenching within T seconds.

[0014] Furthermore, in the natural aging treatment, two samples were cut from the same aluminum alloy tube and subjected to natural aging under constant temperature conditions of 20℃ and 40℃ respectively, and the hardness and electrical conductivity were measured every 20 hours.

[0015] The beneficial effects of this invention are as follows:

[0016] 1. Through content analysis and experiments of alloy strengthening elements, the optimal content of the main strengthening elements of the alloy was determined, the chemical composition of 2024 aluminum alloy was optimized, and new raw material control standards were established.

[0017] 2. By analyzing the difficulties in straightening and rounding large-diameter thin-walled high-precision aluminum alloy pipes, the finite element model analysis technology was selected for the first time, and a finite element model analysis method for straightening and rounding large-diameter thin-walled high-precision aluminum alloy pipes was established.

[0018] 3. To improve the mechanical properties of high-precision aluminum alloy tubing, research was conducted on two aspects: the microstructure and properties of raw materials and the tubing forming and processing technology. More precise control requirements were proposed for the chemical composition of raw materials, laying the foundation for improving the performance and strength of the final finished tubing. The tubing forming process was optimized, breaking through the upper limit of mechanical strength for large-diameter, thin-walled aluminum alloy tubing. The research on solution treatment + cold deformation + aging process technology was improved, resulting in a significant improvement in the mechanical properties of the tubing.

[0019] 4. Research on raw material metallurgical quality control technology was completed, and the quality control standard for pipe blanks was optimized and formed. The defect control and repair technology capabilities during pipe processing were improved, the deformation defects caused by straightening and rounding of large-diameter thin-walled aluminum alloy pipes were solved, and new detection process technology methods were established to avoid surface defects of pipes during the detection process, thus achieving a significant increase in the overall pass rate of pipes. Attached Figure Description

[0020] Figure 1 This is a flowchart of the aluminum tube processing method of the present invention;

[0021] Figure 2 This is a schematic diagram of the as-cast microstructure of 2024 aluminum alloys with different Cu mass fractions;

[0022] Figure 3 This is a schematic diagram showing the volume fraction of solidified crystalline phases in the as-cast microstructure of 2024 aluminum alloys with different Cu mass fractions.

[0023] Figure 4 These are hardness curves for room temperature aging with different Cu contents;

[0024] Figure 5 It is a diagram showing the changes in microstructure during the hot extrusion deformation process;

[0025] Figure 6 This is a schematic diagram of the diameter adjustment of the present invention. Figure 1 ;

[0026] Figure 7 This is a schematic diagram of the diameter adjustment of the present invention. Figure 2 ;

[0027] Figure 8 It is a ternary phase diagram of Al-Cu-Mg aluminum alloys;

[0028] Figure 9 This is a schematic diagram of pipe bending and straightening. Detailed Implementation

[0029] This section describes embodiments of the present invention, used to explain and illustrate the technical solutions of the present invention. Unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0030] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating directions or positional relationships, are given in the accompanying drawings and are used only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or device referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include more than one of those features. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0031] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integrated connections; they can refer to mechanical connections or point connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0032] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0033] Figure 1 This is a schematic diagram of the processing method provided by the present invention, with reference to... Figure 1 The processing method provided by this invention includes:

[0034] First, one group of Cu mass fractions was set at 3.7%, which is lower than the lower limit of the 2024 aluminum alloy composition (Cu mass fraction range of 3.8% to 4.9%). The purpose of this study is to further reveal the influence of Cu content on the residual crystalline phase of the alloy and to provide guidance for optimizing the composition of the 2024 alloy.

[0035] The ingots underwent homogenization heat treatment in a heat treatment furnace. The homogenization heat treatment process involved holding at 495℃ for 24 hours followed by air cooling. Samples were taken to observe the size and type of the second phase in the as-cast, homogenized, and solution-aged microstructures of the 2024 aluminum alloy. Figure 2 The as-cast microstructures of 2024 aluminum alloys with different Cu mass fractions are shown.

[0036] from Figure 2As can be seen from the figure, most of the solidified crystalline phases precipitate along the grain boundaries in a network pattern, while a small amount is distributed in granular form within the grains. Simultaneously, the figure shows that with increasing Cu mass fraction, the number of dendritic networks increases, as does the number of Al2Cu and AlCuMg phases distributed along the grain boundaries.

[0037] The volume fraction of the solidified crystalline phase was calculated using ImageJ software, as follows: Figure 3 As shown, with the increase of Cu mass fraction, the volume fraction of solidified crystalline phase in the as-cast microstructure increases from 3.96% to 5.36%.

[0038] Statistical analysis was conducted on the measured values ​​of the pipe's mechanical properties before and after optimization. Detailed data are shown in the table below, along with the distribution of data indicators:

[0039] Before optimization Optimized version 1 Optimized version 2 Optimized version 3 Cu element content 4.28％ 4.40％ 4.40％ 4.40％ tensile strength 442-447MPa 461-469MPa 462-467MPa 463-467MPa

[0040] II. Hot extrusion is a type of thermoplastic forming, its purpose being to ensure the metal successfully completes the recrystallization process to meet operational requirements. During hot extrusion, work hardening and softening mechanisms occur simultaneously. The hardening caused by large metal deformation is continuously offset by recovery and recrystallization, leaving the metal in a softened state with good plasticity and low deformation resistance. Based on the different properties of the softening process, thermoplastic softening processes are classified as dynamic recovery and dynamic recrystallization, static recovery and static recrystallization, and sub-dynamic recrystallization. During thermoplastic deformation, dynamic recovery and dynamic recrystallization gradually occur with varying degrees of deformation. Static recovery and static recrystallization occur during the intervals of hot deformation or from the residual heat after hot deformation. The effects of hot forming on the properties and microstructure of the metal are shown below: This invention uses vertical extrusion, which is commonly used in China to manufacture small pipes. Vertical extrusion offers better uniformity in wall thickness. This processing method is low-cost and generally not used for large pipes. The microstructure changes of the material during extrusion are as follows... Figure 5 As shown.

[0041] ① The grain structure is improved;

[0042] ② Internal defects are forged together;

[0043] ③ Improve and break down the distribution of non-metallic inclusions and carbides in metals;

[0044] ④ Generates and forms microstructures;

[0045] ⑤ Segregation has been improved.

[0046] Third, "solution treatment + cold deformation + aging treatment" is the main strengthening method for high-precision aluminum alloy tubes. However, different cold deformation mechanisms introduce dislocations in different ways, resulting in significant differences in the dislocation density that the alloy can accommodate and the aging precipitation behavior.

[0047] Cold deformation strengthening refers to the method of increasing alloy strength by increasing dislocation density during cold deformation, which makes dislocation movement more difficult. After solution heat treatment of aluminum alloy tubes, cold working deformation methods such as diameter expansion and tension straightening are used to improve the strength of the aluminum alloy. In addition, diameter adjustment and tension straightening can improve the dimensional accuracy of the tube, such as roundness and straightness. After solution treatment, aluminum alloys undergo natural aging at room temperature. During this period, the strength of the tube is unstable. Therefore, the time and amount of cold deformation are studied to carry out cold working within a reasonable aging period.

[0048] The sizing of the tubes in this invention is performed within 48 hours after solution treatment. The optimized and improved structure of the drawing fixture during sizing ensures greater stability in the drawing operation and improves the quality of the drawn tubes. Through comparative measurements, the straightness of the tubes drawn using the original drawing fixture was 20-45 mm / m, with a drawing defect rate of 7.9%. Using the optimized drawing fixture, the straightness of the drawn tubes was 5-30 mm / m, with a drawing defect rate of 0.7%, demonstrating a significant improvement in tube quality. Figure 6 As shown.

[0049] The tension straightening of the present invention is performed 48 hours after solution treatment. The effect is to improve straightness and roundness through this stretching, and on the other hand, to increase the unit strength by increasing the dislocation rate.

[0050] IV. Heat-treatable aluminum alloys contain a large number of alloying elements that can dissolve into the Al matrix, such as Cu, Mg, Zn, and Si. The solubility of these alloying elements in the Al matrix varies significantly at different temperatures. Therefore, solution quenching can be used to dissolve these alloying elements into the Al matrix, preparing for subsequent age hardening. The degree of solution hardening has a significant impact on the effect of age hardening. However, while ensuring a high concentration of supersaturated solid solution, it is also necessary to avoid overheating and grain growth. Therefore, when formulating the solution hardening process, the solution temperature, holding time, and cooling method must be appropriately selected: holding time 90 minutes, solution temperature 465°C, and water quenching within T seconds.

[0051] The supersaturated solid solution obtained from quenching is unstable and has a tendency to spontaneously decompose. When placed at a certain temperature and maintained for a period of time, the supersaturated solid solution decomposes, leading to a significant increase in the alloy's strength and hardness. This process is called aging. The aging process begins with quenching to obtain double-supersaturated vacancies and a solid solution. In the early stages of aging, due to the effect of vacancies, solute atoms aggregate at a very high rate to form GPB regions. As the aging temperature and aging time increase, the GPB regions transform into a transition phase, eventually forming a stable phase, such as... Figure 7 As shown.

[0052] V. Regarding the control of melt defects, processing defects and dimensional accuracy in raw materials, after multiple coordination and communication with Northeast Light Alloy Plant, it was clearly required that hydrogen content testing equipment be installed, and that there be no tailing, cracks, pores and foreign inclusions, etc., and that the wall thickness dimensional deviation be increased from ±10% to ±6%.

[0053] VI. The main process flow for pipe forming is as follows: inner diameter polishing—outer diameter polishing—water cleaning—narrowing—core drawing—incomplete annealing—polishing—measurement—deviation correction—solution treatment—diameter expansion—tension straightening—bending straightening—measurement—multi-point rounding—static imbalance correction—polishing—measurement—finished product polishing—fitting—ultrasonic testing—natural aging

[0054] VII. Straightening is a process or step that eliminates or reduces bending deformation of parts during processing, ensuring the parts meet usage requirements. Commonly used pipe straightening machines include chain straighteners, oblique-mark straighteners, rotor straighteners, and three-point bending hydraulic straighteners. Because the aluminum alloy pipes used for tail shafts require high dimensional accuracy and surface quality, straighteners with high control precision and minimal impact on surface quality are needed. The pressure head of a three-point bending hydraulic straightener can control accuracy within 0.1mm within its stroke range, and has almost no impact on the surface quality of the pipe during processing. Figure 8 As shown.

[0055] 8. A three-dimensional finite element analysis model is adopted. Due to symmetry, a quarter of the pipe can be used as the analysis model, which greatly reduces the amount of calculation and improves the analysis efficiency. In the model, the pipe is an elasto-plastic deformable body, and the element type selected for the deformable body in this model is a three-dimensional 8-node hexahedral reduced integral element. The mold is a discrete rigid body. Symmetry plane constraints are applied to the symmetry plane of the pipe, and the relative positions of the pipe and the mold are as follows. Figure 9 As shown.

[0056] IX. The main purpose of the polishing process is to remove defects on the inner and outer surfaces of the pipe to achieve a good inner and outer surface condition. When defects that can be felt on the inner surface of the pipe require increased grinding to remove, black oxide scale often remains on the inner surface after processing. To control the quality of pipe processing, a secondary polishing process is often necessary. During production follow-up, it was found that the pipe generates significant heat when using a large grinding amount to process the inner surface. Therefore, it was initially determined that the black oxide scale remaining after using a large grinding amount is caused by grinding heat.

[0057] 10. Control and repair processes for defects such as porosity and slag inclusions in smelting, combined with OTD full-process production protection, to improve the quality of pipe manufacturing and the pass rate of ultrasonic non-destructive testing.

Claims

1. A method for processing large-diameter, thin-walled, high-precision aluminum tubes, characterized in that, First, 2024 aluminum alloy is prepared, and aluminum tubes are manufactured using vertical hot extrusion forming. Then, solution treatment and cold deformation treatment are carried out within the aging time, and finally, natural aging treatment is performed. The cold deformation treatment includes core drawing before solution treatment, diameter adjustment after solution treatment, and tension straightening treatment. The specific order of cold deformation treatment and solution treatment is as follows: the manufactured aluminum tubes are subjected to core drawing, roller straightening, solution treatment, diameter adjustment, and tension straightening treatment in sequence. During the material preparation process, the Cu content of the 2024 aluminum alloy was adjusted to 4.40%. The diameter adjustment process should be carried out within 48 hours after solution treatment; Tension straightening is performed 48 hours after solution treatment. Tension straightening includes: tension straightening, bending straightening, measurement, multi-point rounding, and static imbalance correction.

2. The method for processing large-diameter thin-walled high-precision aluminum tubes according to claim 1, characterized in that, All heat treatments require annealing, polishing, and water cleaning; except for tension straightening, all cold deformation treatments require degreasing and cleaning.

3. The method for processing large-diameter thin-walled high-precision aluminum tubes according to claim 1, characterized in that, The diameter adjustment process is as follows: a pull rod is used to pull the core head for core pulling into the aluminum tube from one end. The core head consists of two O-rings arranged axially, and the outer diameter of the O-rings is the required inner diameter of the aluminum tube. After the core is pulled in, insert plugs to support the inner diameter at both ends of the aluminum tube, and install clamps to fix the outer diameter. Then pull the core out from the other end of the aluminum tube.

4. The method for processing large-diameter thin-walled high-precision aluminum tubes according to claim 1, characterized in that, In multi-point rounding, a quarter of the pipe is used as a three-dimensional finite element analysis model to simulate the deformation of the pipe during the rounding process and obtain the roundness correction parameters.

5. The method for processing large-diameter thin-walled high-precision aluminum tubes according to claim 1, characterized in that, During the solution treatment process, the holding time is 90 minutes, the solution temperature is 465°C, and the cooling method is water quenching within T seconds.

6. The method for processing large-diameter thin-walled high-precision aluminum tubes according to claim 1, characterized in that, In the natural aging treatment, two samples were cut from the same aluminum alloy tube and subjected to natural aging under constant temperature conditions of 20℃ and 40℃ respectively, and the hardness and electrical conductivity were measured every 20 hours.

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