A method for improving the strength of a welded joint of a 2000-series aluminium alloy heat-insulated pipe

Abstract

The application relates to a method for improving the strength of a welded joint of a 2000 series aluminum alloy heat-insulating pipeline, and belongs to the technical field of material welding. The method comprises the following steps: 1) processing the welding bevels at the two ends of the 2000 series aluminum alloy heat-insulating pipeline into V-U composite shapes, the bevel angle is 50-90 DEG, the blunt edge is 0-0.7 mm, and the pipeline surface is cleaned; 2) performing low-temperature short-time aging treatment on the aluminum alloy heat-insulating pipeline before welding; 3) performing welding on the aluminum alloy heat-insulating pipeline by adopting a MIG welding process; 4) performing solid solution heat treatment after welding: the solid solution heat treatment temperature is 480-600 DEG C, and the heat preservation time is 0.5-4 h; 5) performing low-temperature long-time aging treatment after the solid solution heat treatment: the aging treatment temperature is 160-200 DEG C, and the heat preservation time is 1-10 h; and 6) cooling to 20-25 DEG C after the aging treatment. The application improves the tensile strength, yield strength, elongation, hardness and corrosion resistance of the welded joint of the 2000 series aluminum alloy heat-insulating pipeline.

Description

Technical Field

[0001] This invention belongs to the field of material welding technology, specifically relating to a method for improving the strength of welded joints of 2000 series aluminum alloy thermal insulation pipes. Background Technology

[0002] 2000 series aluminum alloys are made primarily of copper (Cu) and are heat-treatable aluminum alloys. They are characterized by high strength, often referred to as hard aluminum alloys, good heat resistance and machinability, and excellent weldability.

[0003] Oil well casing is a widely used pipe in oil pumping unit production technology, and steel, as one of the specialized materials for downhole oil casing, is the most widely used. Although steel oil and gas pipelines possess excellent physical and mechanical properties, their high density results in high weight, making assembly difficult and drastically increasing collection costs when transporting oil and gas from deep wells. Furthermore, they cannot withstand their own weight at certain depths and become unusable. Use in harsh environments, such as Antarctic glaciers, can severely impact the performance of steel pipelines. This places higher demands on oil and gas pipelines.

[0004] 2000 series aluminum alloys, as an emerging material for oil and gas pipelines, have a density approximately one-third that of traditional steel. Using aluminum alloys as the material for oil and gas pipelines significantly reduces pipeline weight while still meeting strength requirements, thereby reducing the overall load on the pipeline and enabling deeper oil and gas extraction. It also reduces energy consumption associated with transportation pipelines.

[0005] However, oil and gas pipelines mostly rely on welding connections, and argon arc welding is widely used in the welding of aluminum alloy insulated pipelines due to its low cost and high efficiency. Because aluminum alloys have good thermal conductivity, and the argon arc welding process involves excessively high temperatures, the weld joint experiences varying temperature changes and strains, resulting in a wide heat-affected zone (HAZ) and significant differences between the HAZ and the weld joint itself. This leads to significant softening of the aluminum alloy weld joint, with its strength reaching only 50% or even less of the base material. This fails to meet the strength requirements of oil and gas pipelines. Therefore, inventing a method to improve the tensile strength, yield strength, elongation, hardness, and corrosion resistance of weld joints in 2000 series aluminum alloy insulated pipelines is both an urgent need to ensure the safety of oil and gas transportation and resolve existing technological contradictions, and a key measure to support industry development and control transportation costs. Improving the strength of weld joints in 2000 series aluminum alloy insulated pipelines is of irreplaceable importance for promoting technological progress in oil and gas pipelines and enhancing industry safety and economic benefits.

[0006] The Chinese invention patent entitled "A welding method for improving the electrical conductivity of welded joints of aluminum alloy tubular busbars" (publication number CN106735765A) optimizes the electrical conductivity of welded joints of 6063 aluminum alloy tubular busbars. However, its post-weld heat treatment cannot activate the Cu strengthening phase of 2000 series aluminum alloys, resulting in low joint strength that cannot meet the pressure resistance requirements of oil and gas pipelines. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for improving the strength of welded joints of 2000 series aluminum alloy thermal insulation pipes. This application improves the tensile strength, yield strength, elongation, hardness and corrosion resistance of welded joints of 2000 series aluminum alloy thermal insulation pipes.

[0008] To achieve the above objectives, the present invention provides a method for improving the strength of welded joints in 2000 series aluminum alloy thermal insulation pipes, comprising the following steps: (1) The welding bevels at both ends of the 2000 series aluminum alloy heat insulation pipe are processed into VU composite shape, with a bevel angle of 50 to 90° and a blunt edge of 0 to 0.7 mm. The surface is cleaned before welding. (2) Before welding, the 2000 series aluminum alloy thermal insulation pipes are subjected to low temperature short-time aging treatment at a temperature of 100~200℃ for 5~10min. (3) The aluminum alloy heat-insulating pipe is welded using the MIG welding process; (4) Solution heat treatment after welding: After welding, the weldment is placed in a heat treatment furnace. The solution heat treatment temperature is 480~600℃ and the holding time is 0.5~4h; the quenching transfer time is 10~30s. (5) Low-temperature long-term aging treatment after solution heat treatment: The aluminum alloy pipe welded parts are subjected to low-temperature long-term aging treatment in a heat treatment furnace. The low-temperature long-term aging treatment temperature is 160~200℃ and the holding time is 1~10h. (6) After the low-temperature long-term aging is completed, cool to 20~25℃.

[0009] In step (1), the welding bevels at both ends of the 2000 series aluminum alloy thermal insulation pipe are machined by milling. Before welding, the surface of the 2000 series aluminum alloy thermal insulation pipe is treated by plasma cleaning (vacuum cleaning for 15~60s) or laser cleaning to remove oxides and oil stains from the surface of the 2000 series aluminum alloy thermal insulation pipe.

[0010] The VU composite shape described in step (1) is formed by adding a U-shaped transition area at the bottom of the V-groove; optimizing the weld penetration and joint strength.

[0011] Preferably, the bevel angle in step (1) is 60-80°, with a blunt edge of 0mm. Using a 60-80° VU composite bevel angle can significantly improve weld penetration, reduce incomplete penetration defects, increase welding efficiency, reduce filler metal usage, reduce welding deformation and heat-affected zone size, and simultaneously improve weld quality and crack resistance. It is suitable for thick plate welding and high-strength aluminum alloy welding, helping to reduce welding costs and improve production efficiency. A 60-80° VU composite bevel angle can improve weld penetration, reduce incomplete penetration defects, increase welding efficiency, reduce filler metal usage, reduce welding deformation and heat-affected zone size, and simultaneously improve weld quality and crack resistance. It is suitable for thick plate welding and high-strength aluminum alloy welding, helping to reduce welding costs and improve production efficiency.

[0012] The 2000 series aluminum alloy insulated pipe described in step (1) has an outer diameter of 30~100mm and a wall thickness of 2~10mm. The outer diameter of 30~100mm can meet the needs of mainstream pipes, and the wall thickness of 2~10mm, combined with VU composite beveling and subsequent processes, can optimize the penetration and reduce welding defects. At the same time, relying on the low density characteristics of aluminum alloy, it can reduce the assembly and transportation costs of deep well mining and is suitable for use in harsh environments.

[0013] The process parameters for the low-temperature short-time aging treatment in step (2) are: temperature 100~200℃, heating time 5~10min; rotating the aluminum alloy pipe during heating to ensure uniform heating. Under 100~200℃ conditions, a short-time heat treatment is performed to partially precipitate the solute atoms in the aluminum alloy, forming fine second-phase particles. These particles can pin dislocations, improving the yield strength and crack resistance of the material. This treatment method differs from preheating, which primarily aims to reduce thermal stress and cracking tendency during welding. The short-time aging in this application, however, is more about optimizing the microstructure of the material and improving the strength and toughness of the welded joint.

[0014] A heating temperature of 100-200℃ for 5-10 minutes can reduce welding stress, improve penetration, reduce hydrogen porosity, promote uniform temperature distribution, increase welding efficiency, and prevent cracking, thereby improving the quality and performance of the welded joint, reducing welding defects, and ensuring a smooth welding process. However, excessively high temperatures can cause grain coarsening, leading to decreased weld joint toughness, poor heat-affected zone performance, increased welding deformation, excessive surface oxidation and impurity introduction, reduced welding efficiency, and increased crack sensitivity. Conversely, excessively low temperatures cannot completely remove surface moisture, resulting in numerous hydrogen pores and hydrogen-induced cracks that significantly reduce joint strength. Therefore, it is necessary to control the temperature of the pre-weld low-temperature short-time aging treatment to ensure welding quality and efficiency. Too short a treatment time will result in uneven heating of the material, while too long a time will lead to grain coarsening.

[0015] Preferably, the process parameters for the low-temperature short-time aging treatment in step (2) are: temperature of 140~180℃ and heating time of 7~9min; which can obtain better quality and performance of the welded joint.

[0016] The process parameters for the MIG welding process in step (3) are as follows: the shielding gas is 95-98% argon and 2-5% helium, the shielding gas flow rate is 12-50 L / min, the welding current is 160-200 A, the arc voltage is 18-22 V, and the welding speed is 35-45 cm / min. The welding wire used in step (3) has a diameter of 1-5 mm and a wire extension of 10-15 mm. ER2319 and ER2519 welding wires with compositions similar to those of 2000 series aluminum alloy thermal insulation pipes are used in the welding process. The welding speed is controlled to promote more complete welding, and the welding wire and base material exhibit better compatibility, which improves the welding cladding rate, increases the flow of the molten pool, and promotes penetration.

[0017] Preferably, the process parameters of the MIG welding process in step (3) are as follows: the shielding gas is 96-97% argon and 3-4% helium, and the purity of both argon and helium is higher than 99.999%, the shielding gas flow rate is 16-19 L / min, the welding wire is ER2319 or ER2519, the welding wire diameter is 1-3 mm, the welding wire extension is 10-13 mm, the welding current is 170-190 A, the arc voltage is 18-20 V, and the welding speed is 30-40 cm / min.

[0018] The post-weld solution heat treatment temperature is 480~600℃, held for 0.5~4h; the quenching transfer time is 10~30s, and the quenching medium is ice water. When the temperature is too low, it cannot promote the complete precipitation and uniform distribution of the precipitated phases; when the temperature is too high, overheating causes grain boundary melting and irreversible property degradation. Through solution heat treatment and quenching, the strengthening phases in the aluminum alloy are uniformly distributed in the matrix, such as CuAl2 and Mg2Si, while inhibiting grain growth, thereby improving the strength and toughness of the welded joint. During the solution heat treatment process, Cu, Mg, and Si atoms dissolve in large quantities into the α-Al matrix, forming a uniform supersaturated solid solution (without precipitation). The rapid annealing cooling rate of ≥100℃ / s inhibits the nucleation of the second phase, causing the supersaturated solute atoms to be instantly "frozen" in the crystal lattice, avoiding preferential grain boundary nucleation and providing a uniform solute field for subsequent aging.

[0019] Preferably, the solution heat treatment temperature in step (4) is 500~560℃, and the holding time is 1~3h. The preferred solution heat treatment parameters can ensure that the main reinforcing phase is completely dissolved in the matrix, providing a highly supersaturated solid solution for subsequent aging precipitation, while strictly preventing grain boundary overheating that could lead to permanent performance degradation; and the sufficient holding time can eliminate component segregation in the weld area, making the entire joint form a uniform structure, laying a decisive foundation for comprehensively improving strength, plasticity and corrosion resistance.

[0020] Preferably, the quenching transfer time in step (4) is 11~20s, which can maximize the quenching quality of the workpiece, avoid defects, and thus obtain uniform and excellent mechanical properties.

[0021] The specific operation of the solution heat treatment followed by low-temperature long-term aging treatment in step (5) is as follows: after solution heat treatment, the transfer time of the aluminum alloy pipe welded parts to the heat treatment furnace is 5~30min; the aluminum alloy pipe welded parts are subjected to low-temperature long-term aging treatment in the heat treatment furnace, the low-temperature long-term aging treatment temperature is 160~200℃, and the heat preservation time is 1~10h.

[0022] The temperature of the low-temperature long-term aging treatment in step (5) is 170~190℃, and the holding time is 2~5h. After welding, the solution heat treatment process is carried out. The solution heat treatment and low-temperature long-term aging treatment can control the precipitation and dissolution of the strengthening phase at the weld, and inhibit the growth of recrystallized grains and the softening of the weld joint, promote the uniformity of strength in the heat-affected zone and the weld joint, greatly improve the strength and hardness of the weld joint, and reduce the softening range of the heat-affected zone.

[0023] Compared with the prior art, the beneficial effects of this invention are: 1. This application improves the tensile strength, yield strength, elongation, hardness, and corrosion resistance of welded joints in 2000 series aluminum alloy thermal insulation pipes. This invention removes moisture from the pipe surface through pre-weld surface treatment and short-term aging, avoiding weld defects and cracks; during welding, ER2319 or ER2519 welding wire is selected and the welding speed is controlled to improve weld sufficiency, wire-base material compatibility, and penetration depth; post-weld solution treatment and aging treatment control the precipitation and dissolution of strengthening phases, inhibit grain growth and joint softening, and promote uniform strength.

[0024] The welded joints for 2000 series aluminum alloy thermal insulation pipes prepared by the method of this invention exhibit significantly improved comprehensive performance. The welded joints of this invention possess tensile strength of 325.5~383.2 MPa, yield strength of 233.6~301.8 MPa, elongation of 12.7%~21.2%, hardness of 105~126 HV, and corrosion current density of -6.2~-6.0 A / cm². In particular, under the preferred parameters, Example 3 achieves a tensile strength exceeding 383.2 MPa, surpassing the strength of the base material, while also possessing excellent plasticity, hardness, and corrosion resistance. Attached Figure Description

[0025] Figure 1 A schematic diagram of the temperature-time curve for a method to improve the strength of welded joints in 2000 series aluminum alloy thermal insulation pipes.

[0026] Figure 2 SEM image of the welded joint of 2000 series aluminum alloy thermal insulation pipe after heat treatment.

[0027] Figure 3 EDS image of the welded joint of 2000 series aluminum alloy thermal insulation pipe after heat treatment.

[0028] Figure 4 These are comparison diagrams of the tensile strength and yield strength of the base material and the welded joint in Examples 1-3. Detailed Implementation

[0029] Example 3 is the preferred embodiment of the present invention. The present invention will be further described below with reference to specific embodiments and comparative examples.

[0030] Example 1 This embodiment describes a method for improving the strength of welded joints in 2000 series aluminum alloy thermal insulation pipes, which uses MIG welding technology to weld 2A12 aluminum alloy thermal insulation pipes with specifications of 60×5.5mm. The preparation method in this embodiment adopts the following steps: (1) The welding bevels at both ends of the 2A12 aluminum alloy heat insulation pipe are processed into VU composite shape by milling process. The bevel angle is 60° and the blunt edge is 0.7mm. Before welding, the surface is cleaned by laser cleaning method to remove oxides and oil stains from the pipe surface. (2) Before welding, the 2000 series aluminum alloy heat insulation pipe is subjected to low temperature short-time aging treatment at a temperature of 160℃ for 8 minutes. During heating, the aluminum alloy heat insulation pipe is rotated continuously to ensure uniform heating. (3) The aluminum alloy heat-insulating pipe is welded using the MIG welding process; the shielding gas is 98% argon + 2% helium, the purity of argon and helium is higher than 99.999%, the shielding gas flow rate is 18L / min, the welding wire is ER2319, the welding wire diameter is 2mm, the dry extension is 13mm, the welding current is 170A, the arc voltage is 18V, and the welding speed is 30cm / min. (4) Solution heat treatment after welding: After welding, the weldment is placed in a heat treatment furnace. The solution heat treatment temperature is 560℃ and the temperature is held for 1 hour. The quenching transfer time is 20 seconds and the quenching medium is ice water. (5) Low-temperature long-term aging treatment after solution heat treatment: After solution heat treatment, the aluminum alloy pipe weldment is transferred to the heat treatment furnace in 30 minutes. The aluminum alloy pipe weldment is subjected to low-temperature long-term aging treatment in the heat treatment furnace. The low-temperature long-term aging treatment temperature is 175℃ and the holding time is 2h. (6) After the low-temperature long-term aging is completed, cool to 20~25℃.

[0031] Example 2 This embodiment describes a method for improving the strength of welded joints in 2000 series aluminum alloy thermal insulation pipes, which uses MIG welding technology to weld 2A12 aluminum alloy thermal insulation pipes with specifications of 60×5.5mm. The preparation method in this embodiment adopts the following steps: (1) The welding bevels at both ends of the 2A12 aluminum alloy heat insulation pipe are processed into VU composite shape by milling process. The bevel angle is 80° and the blunt edge is 0.5mm. Before welding, the surface is cleaned by laser cleaning method to remove oxides and oil stains from the pipe surface. (2) Before welding, the 2000 series aluminum alloy heat insulation pipe is subjected to low temperature short-time aging treatment at a temperature of 170℃ for 10 minutes. During heating, the aluminum alloy heat insulation pipe is rotated continuously to ensure uniform heating. (3) The aluminum alloy heat insulation pipe was welded using the MIG welding process. The shielding gas was 97% argon + 3% helium. The purity of both argon and helium was higher than 99.999%. The shielding gas flow rate was 18L / min. The welding wire was ER2519 with a diameter of 2mm and a dry extension of 12mm. The welding current was 190A, the arc voltage was 19V, and the welding speed was 40cm / min. (4) Solution heat treatment after welding: After welding, the weldment is placed in a heat treatment furnace. The solution heat treatment temperature is 530℃ and the temperature is held for 3 hours. The quenching transfer time is 15 seconds. The quenching medium is ice water. (5) Low-temperature long-term aging treatment after solution heat treatment: After solution heat treatment, the aluminum alloy pipe weldment is transferred to the heat treatment furnace in 5 minutes. The aluminum alloy pipe weldment is subjected to low-temperature long-term aging treatment in the heat treatment furnace. The low-temperature long-term aging treatment temperature is 170℃ and the holding time is 5h. (6) After the low-temperature long-term aging is completed, cool to 20~25℃.

[0032] Example 3 This embodiment describes a method for improving the strength of welded joints in 2000 series aluminum alloy thermal insulation pipes, which uses MIG welding technology to weld 2A12 aluminum alloy thermal insulation pipes with specifications of 60×5.5mm. The preparation method in this embodiment adopts the following steps: (1) The welding bevels at both ends of the 2A12 aluminum alloy heat insulation pipe are processed by milling process into VU composite shape with a bevel angle of 70° and a blunt edge of 0mm. Before welding, the surface is cleaned by laser cleaning to remove oxides and oil stains from the pipe surface. (2) Before welding, the 2000 series aluminum alloy heat insulation pipe is subjected to low temperature short-time aging treatment at a temperature of 150℃ for 10 minutes. During heating, the aluminum alloy heat insulation pipe is rotated continuously to ensure uniform heating. (3) The aluminum alloy heat insulation pipe was welded using the MIG welding process. The shielding gas was 98% argon + 2% helium. The purity of both argon and helium was higher than 99.999%. The shielding gas flow rate was 19L / min. The welding wire was ER2319 with a diameter of 2mm and a dry extension of 11mm. The welding current was 180A, the arc voltage was 20V, and the welding speed was 30cm / min. (4) Solution heat treatment after welding: After welding, the weldment is placed in a heat treatment furnace. The solution heat treatment temperature is 500℃ and the temperature is held for 1 hour. The quenching transfer time is 11 seconds. The quenching medium is ice water. (5) Low-temperature long-term aging treatment after solution heat treatment: After solution heat treatment, the aluminum alloy pipe weldment is transferred to the heat treatment furnace in 10 minutes. The aluminum alloy pipe weldment is subjected to low-temperature long-term aging treatment in the heat treatment furnace. The low-temperature long-term aging treatment temperature is 190℃ and the holding time is 3h. (6) After the low-temperature long-term aging is completed, cool to 20~25℃.

[0033] Comparative Example 1 This comparative example uses the traditional aluminum alloy MIG welding process, omitting the pre-weld low-temperature short-time aging and post-weld solution and aging heat treatment; The preparation method includes the following steps: (1) The welding bevel is processed by milling. The bevel is a traditional V-shaped bevel with a bevel angle of 80° and a blunt edge of 3mm. The oxide on the pipe surface is removed by sanding with sandpaper, and then soaked in acetone solution for 5 minutes to remove oil stains. After taking it out, it is dried. (2) Conventional MIG welding was performed on 2A12 aluminum alloy thermal insulation pipes with an outer diameter of 90 mm and a wall thickness of 5.5 mm. The shielding gas was selected as pure argon with a purity of more than 99% and a flow rate of 18 L / min. The welding wire was selected as general-purpose ER4043 (Al-Si system) with a diameter of 2.5 mm and a dry extension of 11 mm. The welding current was 180 A, the arc voltage was 19 V, and the welding speed was 60 cm / min. (3) Allow to cool naturally after welding; Samples were taken from the welded joints of the pipe to test its performance.

[0034] Comparative Example 2 This comparative example omits post-weld solution heat treatment and low-temperature long-term aging treatment: The preparation method includes the following steps: (1) The welding bevel is processed by milling. The bevel is a VU composite bevel with a bevel angle of 60° and a blunt edge of 0mm. The oxide on the pipe surface is removed by sandblasting, and then the pipe is immersed in acetone solution for 5 minutes to remove oil stains. After removal, the pipe is dried. (2) Low temperature short-time aging treatment before welding: The temperature is 150℃ and the heat is kept for 10 minutes. During heating, the aluminum alloy heat insulation pipe is rotated continuously to ensure uniform heating. (3) MIG welding was performed on 2A12 aluminum alloy thermal insulation pipes with an outer diameter of 60 mm and a wall thickness of 5.0 mm. The shielding gas was 99.999% high-purity argon with a flow rate of 18 L / min. The welding wire was ER2319 with a diameter of 2 mm and a dry extension of 11 mm, which matched the composition of the base metal. The welding current was 180 A, the arc voltage was 19 V, and the welding speed was 30 cm / min. (4) Allow to cool naturally after welding; Samples were taken from the welded joints of the pipe to test its performance.

[0035] Comparative Example 3 The preparation method of the method for improving the strength of the welded joint of the 2000 series aluminum alloy thermal insulation pipe described in this comparative example is the same as that in Example 3, except that the bevel angle in step (1) is 48°.

[0036] Comparative Example 4 The preparation method of the method for improving the strength of the welded joint of the 2000 series aluminum alloy thermal insulation pipe described in this comparative example is the same as that in Example 3, except that the bevel angle in step (1) is 92°.

[0037] Comparative Example 5 The preparation method of the method for improving the strength of the welded joint of the 2000 series aluminum alloy thermal insulation pipe described in this comparative example is the same as that in Example 3, except that the low temperature short-time aging treatment temperature in step (2) is 95°C and the time is 15 min.

[0038] Comparative Example 6 The preparation method of the method for improving the strength of the welded joint of the 2000 series aluminum alloy thermal insulation pipe described in this comparative example is the same as that in Example 3, except that the low temperature short-time aging treatment temperature in step (2) is 205°C and the time is 3 min.

[0039] Comparative Example 7 The preparation method of the method for improving the strength of the welded joint of the 2000 series aluminum alloy thermal insulation pipe described in this comparative example is the same as that in Example 3, except that the solution heat treatment temperature in step (4) is 450℃ and the heat treatment time is 4.5h.

[0040] Comparative Example 8 The preparation method of the method for improving the strength of the welded joint of the 2000 series aluminum alloy thermal insulation pipe described in this comparative example is the same as that in Example 3, except that the solution heat treatment temperature in step (4) is 620℃ and the heat treatment time is 0.4h.

[0041] Comparative Example 9 The preparation method of the method for improving the strength of the welded joint of the 2000 series aluminum alloy thermal insulation pipe described in this comparative example is the same as that in Example 3, except that the quenching transfer time in step (4) is 8s.

[0042] Comparative Example 10 The preparation method of the method for improving the strength of the welded joint of the 2000 series aluminum alloy thermal insulation pipe described in this comparative example is the same as that in Example 3, except that the quenching transfer time in step (4) is 32s.

[0043] Comparative Example 11 The preparation method of the method for improving the strength of the welded joint of the 2000 series aluminum alloy thermal insulation pipe described in this comparative example is the same as that in Example 3, except that the temperature of the low temperature long-term aging treatment in step (5) is 150°C and the heat preservation time is 15h.

[0044] Comparative Example 12 The preparation method of the method for improving the strength of the welded joint of the 2000 series aluminum alloy thermal insulation pipe described in this comparative example is the same as that in Example 3, except that the temperature of the low temperature long-term aging treatment in step (5) is 210°C and the heat preservation time is 0.8h.

[0045] Performance testing The performance of the welded joints prepared in the examples and comparative examples was tested, and the specific test results are shown in Table 1.

[0046] Tensile strength was tested in accordance with GB / T228.1-2010; Yield strength was tested in accordance with GB / T228.1-2010; Elongation was tested in accordance with GB / T228.1-2010; Hardness was tested according to GB / T27552-2021; The corrosion current density was tested in accordance with GB / T19746-2018.

[0047] Table 1 Performance test results of the examples and comparative examples .

[0048] Comparative Example 1 employed traditional MIG welding technology, lacking pre-weld low-temperature short-time aging, post-weld solution treatment, and aging treatment. It also used a traditional V-groove, pure argon shielding gas, and ER4043 universal welding wire, resulting in severe softening of the welded joint. The tensile strength was only 199.8 MPa, representing 57.8% of the base metal, and the yield strength, elongation, hardness, and corrosion resistance were all significantly lower than in Example 3. Comparative Example 2 used a VU composite groove, 150℃ pre-weld short-time aging, and ER2319 matching welding wire. No post-weld solution treatment or aging treatment was applied; only natural cooling was used. The welded joint had a tensile strength of 269.8 MPa and a yield strength of 173.4 MPa. The overall mechanical properties were significantly lower than in the examples. The results of Comparative Example 2 indicate that post-weld solution heat treatment and low-temperature long-time aging treatment are the decisive factors for achieving higher welded joint strength.

[0049] Comparative Example 3, with a bevel angle of 48°, showed lower tensile strength, elongation, and hardness of the welded joint compared to Example 3, indicating that a small bevel angle negatively impacts penetration and joint strength. Comparative Example 4, with a bevel angle of 92°, also exhibited lower performance than Example 3, demonstrating that an excessively large bevel angle cannot achieve optimal welding results. Comparative Example 5, with a pre-weld low-temperature short-time aging temperature of 95°C for 15 minutes, resulted in decreased tensile strength and elongation of the joint, failing to effectively optimize the material's microstructure. Comparative Example 6, with a pre-weld low-temperature short-time aging temperature of 205°C for 3 minutes, experienced grain coarsening, resulting in welded joint performance lower than Example 3 and affecting welding quality. Comparative Example 7, with a solution heat treatment temperature of 450°C and a holding time of 4.5 hours, failed to allow the reinforcing phase to fully dissolve into the matrix, leading to poor welded joint strength and overall performance. Comparative Example 8, with a solution heat treatment temperature of 620°C and a holding time of 0.4 hours, exhibited grain boundary overheating, significantly reducing joint tensile strength and elongation, resulting in performance degradation. Comparative Example 9: Quenching transfer time of 8s affected quenching quality, resulting in lower mechanical properties of the welded joint compared to Example 3, and an inability to obtain a uniform and excellent microstructure. Comparative Example 10: Quenching transfer time of 32s resulted in insufficient cooling, leading to poor microstructure uniformity and reduced tensile and yield strength. Comparative Example 11: Low-temperature long-term aging at 150℃ for 15h resulted in insufficient precipitation of the strengthening phase, leading to joint performance lower than Example 3. Comparative Example 12: Low-temperature long-term aging at 210℃ for 0.8h disrupted the conditions for sufficient and uniform precipitation of the strengthening phase, failing to effectively inhibit recrystallization grain growth and softening of the heat-affected zone in the welded joint. It also weakened the strength uniformity of the heat-affected zone and the welded joint, resulting in reduced overall mechanical properties and corrosion resistance of the joint.

[0050] Example 3: Through the synergistic effect of optimized parameters such as 70° VU composite groove, 150° short-term aging before welding, and 190° long-term aging after welding, the strengthening phase of the welded joint is fully and uniformly precipitated, the softening of the heat-affected zone is suppressed, and the tensile strength of the welded joint exceeds 110% of the strength of the base material.

[0051] Depend on Figure 1 It can be seen that the temperature and time changes in each process of this application are as follows; Figure 2 and Figure 3 It can be seen that solution heat treatment and quenching result in a uniform distribution of the strengthening phase in the aluminum alloy, and the precipitation of relevant strengthening phases. In the comparative example, the lack of a VU composite beveling, the absence of pre-weld short-term aging treatment, and the absence of post-weld heat treatment led to lower tensile and yield strengths in the welded joints of the 2000 series aluminum alloy thermal insulation pipes compared to the example, and the tensile strength of the comparative example was less than 75% of that of the base material. Figure 4 It can be seen that the tensile strength of the aluminum alloy thermal insulation pipe welded joint obtained by the present invention reaches more than 95% of that of the base material, and the comprehensive performance of the 2000 series aluminum alloy thermal insulation pipe welded joint obtained by the present invention is better than that of the 2000 series aluminum alloy thermal insulation pipe welded joint obtained by the traditional welding process.

[0052] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for improving the strength of welded joints in 2000 series aluminum alloy thermal insulation pipes, characterized in that, Includes the following steps: (1) The welding bevels at both ends of the 2000 series aluminum alloy heat insulation pipe are processed into VU composite shape, with a bevel angle of 50 to 90° and a blunt edge of 0 to 0.7 mm. The surface is cleaned before welding. (2) Before welding, the 2000 series aluminum alloy thermal insulation pipes are subjected to low temperature short-time aging treatment at a temperature of 100~200℃ for 5~10min. (3) The aluminum alloy heat-insulating pipe is welded using the MIG welding process; (4) Solution heat treatment after welding: After welding, the weldment is placed in a heat treatment furnace. The solution heat treatment temperature is 480~600℃ and the holding time is 0.5~4h; the quenching transfer time is 10~30s. (5) Low-temperature long-term aging treatment after solution heat treatment: The aluminum alloy pipe welded parts are subjected to low-temperature long-term aging treatment in a heat treatment furnace. The temperature of the low-temperature long-term aging treatment is 160~200℃ and the holding time is 1~10h. (6) After the low-temperature long-term aging is completed, cool to 20~25℃; The VU composite shape described in step (1) is formed by adding a U-shaped transition area at the bottom of the V-shaped bevel; The temperature of the low-temperature long-term aging treatment in step (5) is 170~190℃, and the holding time of the aging treatment is 2~5 h.

2. The method for improving the strength of welded joints in 2000 series aluminum alloy thermal insulation pipes according to claim 1, characterized in that, The bevel angle mentioned in step (1) is 60 to 80°.

3. The method for improving the strength of welded joints in 2000 series aluminum alloy thermal insulation pipes according to claim 1, characterized in that, The outer diameter of the 2000 series aluminum alloy heat-insulating pipe in step (1) is 30~100mm and the wall thickness is 2~10mm.

4. The method for improving the strength of welded joints in 2000 series aluminum alloy thermal insulation pipes according to claim 1, characterized in that, The temperature of the low-temperature short-time aging treatment in step (2) is 140~180℃ and the time is 7~9min.

5. The method for improving the strength of welded joints in 2000 series aluminum alloy thermal insulation pipes according to claim 1, characterized in that, The process parameters of the MIG welding process in step (3) are as follows: the gas used is 95~98% argon and 2~5% helium as protective gas, the protective gas flow rate is 12~50L / min, the welding current is 160~200A, the arc voltage is 18~22V, and the welding speed is 35~45cm / min.

6. The method for improving the strength of welded joints in 2000 series aluminum alloy thermal insulation pipes according to claim 1, characterized in that, In step (3), the welding wire used has a diameter of 1~5mm and a wire extension of 10~15mm.

7. The method for improving the strength of welded joints in 2000 series aluminum alloy thermal insulation pipes according to claim 1, characterized in that, The solution heat treatment temperature in step (4) is 500~560℃, and the heat treatment holding time is 1~3h.

8. The method for improving the strength of welded joints in 2000 series aluminum alloy thermal insulation pipes according to claim 1, characterized in that, The quenching transfer time in step (4) is 11~20s.

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