Raw material composition proportion of 7-series aluminum alloy material gas cylinder and production and manufacturing process of 7-series aluminum alloy material gas cylinder

Abstract

The invention relates to the technical field of gas cylinder pressure vessel manufacturing, in particular to a 7-series aluminum alloy material gas cylinder which comprises the following chemical components in percentage by mass: less than or equal to 0.11% of Si, less than or equal to 0.12% of Fe, 1.8-2.6% of Cu, less than or equal to 0.13% of Mn, 1.3-2.1% of Mg, 0.15-0.25% of Cr, 6.1-7.5% of Zn, less than or equal to 0.05% of Ti, less than or equal to 0.05% of Zr and the balance of Al. The content of other single impurities is less than or equal to 0.05%, and the total content is less than or equal to 0.15%. The contents of key elements silicon, iron and manganese forming an impurity phase in the 7-series aluminum alloy are strictly limited, the contents of the impurity elements are controlled within an extremely low range, generation of harmful intermetallic compound impurities is directly reduced, and then the content of the impurity phase in the 7-series aluminum alloy is accurately controlled, so that the content of the impurity phase in the 7-series aluminum alloy is greatly reduced. A good material basis is created for the subsequent heat treatment process, excessive aggregation of impurity phases in the grain boundary or in the grain is avoided, and the overall mechanical performance of the material is remarkably improved through the synergistic effect of a pure matrix and a controlled microstructure.

Description

Technical Field

[0001] This invention relates to the field of gas cylinder and pressure vessel manufacturing technology, and more specifically, to a raw material composition ratio and manufacturing process for a 7-series aluminum alloy gas cylinder. Background Technology

[0002] In recent years, with the rapid development of aerospace, special equipment and high-end civilian equipment, the market demand for lightweight, high-strength and high-safety high-pressure gas cylinders has become increasingly urgent. Traditional gas cylinders are mostly made of 6-series aluminum alloy. Although the process is mature, its strength is limited and it is difficult to meet the comprehensive requirements of high-end equipment for higher pressure and lighter weight. Therefore, seeking higher performance material alternatives has become an inevitable trend in the industry.

[0003] 7-series aluminum alloys are considered ideal materials for the next generation of high-pressure metal gas cylinders due to their excellent specific strength, good resistance to stress corrosion and heat treatability. While ensuring safety, they can significantly reduce the cylinder wall thickness, achieve structural lightweighting, and thus improve the overall performance and energy efficiency of the equipment. However, the application of 7-series aluminum alloys in gas cylinder manufacturing still faces many technical challenges, such as composition control, heat treatment process optimization and internal surface strengthening, which urgently require systematic research and process breakthroughs.

[0004] Currently, although some research in related fields has focused on the application of 7-series aluminum alloys in pressure vessels, there are still problems in actual production, such as large fluctuations in composition, poor control of impurity phases, mismatched heat treatment regimes, and insufficient fatigue performance. These problems lead to unstable product performance and difficulty in guaranteeing product life. In addition, traditional processes also have room for improvement in terms of energy conservation, environmental protection, and production efficiency, and are difficult to fully meet the requirements of modern industry for green manufacturing and efficient production. Summary of the Invention

[0005] To overcome the above deficiencies, the present invention provides a solution that overcomes or at least partially solves the above technical problems.

[0006] This invention provides a gas cylinder made of 7-series aluminum alloy, wherein the chemical composition of the gas cylinder, by mass percentage, includes: Si: ≤0.11%, Fe: ≤0.12%, Cu: 1.8-2.6%, Mn: ≤0.13%, Mg: 1.3-2.1%, Cr: 0.15-0.25%, Zn: 6.1-7.5%, Ti: ≤0.05%, Zr: ≤0.05%; Other individual impurities are ≤0.05%, the total is ≤0.15%, and the balance is Al.

[0007] Preferably, the aluminum alloy raw material is high-purity aluminum, wherein the Si content is 0-0.10%, the Fe content is 0-0.12%, and the Mn content is 0-0.13%.

[0008] A preferred manufacturing process for a 7-series aluminum alloy gas cylinder includes the following steps: a. Raw material customization and cutting; b. Clean the material block and apply lubricating oil; c. Dry and extrude to form an aluminum cylinder 600-610mm long; d. Flatten the aluminum cylinder to 520mm; e. Gas cylinders are formed using a heat-sealing process; f. Heat-treat the gas cylinder; g. Conduct performance testing on the heat-treated gas cylinders; h. Perform machining and internal surface strengthening treatment; i. Conduct hydrostatic tests, airtightness tests, and volumetric weight measurements; j. Perform surface treatment and final inspection.

[0009] Preferably, the heat treatment in step f includes solution treatment and two-stage aging treatment. The solution treatment is carried out at 460-470℃ for 1-3 hours. The two-stage aging treatment includes: a first-stage aging at 90-120℃ for 5-12 hours and a second-stage aging at 130-150℃ for 2-4 hours.

[0010] Preferably, the two-stage aging treatment is as follows: the first stage of aging is performed at 90-110℃ for 5-8 hours, and the second stage of aging is performed at 130-140℃ for 2-4 hours.

[0011] Preferably, the inner surface strengthening treatment in step h is carried out by shot blasting, using steel shot with a particle size of 0.5-1.5 mm, and treating the inner surface of the gas cylinder for 5-20 minutes under a pressure of 0.5-1 MPa.

[0012] Preferably, the internal surface strengthening treatment takes 5-15 minutes.

[0013] Preferably, the performance inspection in step g includes hardness testing, strength testing, metallographic observation, and cold bending test. Only after all inspections are passed can the process proceed to the machining process.

[0014] Preferably, a gas cylinder made of 7-series aluminum alloy has the following mechanical properties: specified non-proportional elongation strength Rp0.2≥430MPa, tensile strength Rm≥506MPa, and elongation after fracture A≥12%.

[0015] Preferably, in the metallographic structure of the gas cylinder, the precipitated phases are fine, uniform, and diffusely distributed, mainly including GP regions, transition phase and Equilibrium phase.

[0016] The targeted solution provided by this invention has the following beneficial effects: 1. This invention strictly limits the content of silicon, iron, and manganese, the key elements that form impurity phases in 7-series aluminum alloys. By controlling the content of these impurity elements to an extremely low range, the generation of harmful intermetallic compound impurities is directly reduced. Secondly, this precise control of chemical composition creates a good material basis for subsequent heat treatment processes, avoiding excessive aggregation of impurity phases at grain boundaries or within grains. The synergistic effect of a pure matrix and controlled microstructure significantly improves the overall mechanical properties of the material, especially its toughness, fracture resistance, and fatigue resistance to cyclic loads, thereby ensuring the long-term reliability of the gas cylinder from the material source. 2. This invention performs solution treatment at a set temperature to ensure that the strengthening elements are fully dissolved in the matrix while avoiding overheating of the alloy. Then, a two-step aging treatment is performed: first, low-temperature first-stage aging is performed to form a large number of uniform, dispersed and stable nanoscale strengthening core regions in the matrix; then, high-temperature second-stage aging is performed to gradually transform these core regions into more stable strengthening phases. The gradual aging process makes the strengthening phases fine and extremely uniformly distributed, thereby achieving uniform stress transmission within the grains. Therefore, the final material not only obtains yield strength and tensile strength far exceeding those of traditional 6-series aluminum alloys, but also maintains excellent elongation, that is, it has both high strength and high plasticity, meeting the stringent requirements of high-pressure vessels for the comprehensive mechanical properties of materials. 3. This invention utilizes high-speed jets of fine steel shot to impact the inner wall surface of the gas cylinder. This process introduces a uniform residual compressive stress layer on the material surface. When the gas cylinder is subjected to cyclic loads under internal pressure, this pre-existing compressive stress layer can effectively offset part of the working tensile stress. Its direct effect is to greatly inhibit the initiation of fatigue microcracks in stress concentration areas. At the same time, even if microcracks are generated, the compressive stress layer will hinder their further propagation. This active strengthening mechanism fundamentally improves the fatigue performance of the gas cylinder and its fatigue performance in a notched state, making the product more prone to leakage rather than sudden explosion before reaching the burst pressure, thus significantly improving the safety and durability of the gas cylinder in actual use. Attached Figure Description

[0017] Figure 1 The metallographic structure of the 7-series aluminum alloy gas cylinder after heat treatment is magnified 100 times. Figure 2 This is a SEM image of the matrix of the 7-series material after heat treatment according to the present invention; Figure 3 This is a SEM image of the fracture surface of the 7-series material after tensile testing according to the present invention; Figure 4 This is a SEM image of the fracture surface of the 7-series material after tensile testing according to the present invention; Figure 5 This is a shape diagram of the 7-series aluminum alloy gas cylinder of the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Example 1

[0020] Reference Figures 1-5 This invention provides a technical solution: a gas cylinder made of 7-series aluminum alloy, wherein the chemical composition of the gas cylinder, by mass percentage, includes: Si: ≤0.11%, Fe: ≤0.12%, Cu: 1.8-2.6%, Mn: ≤0.13%, Mg: 1.3-2.1%, Cr: 0.15-0.25%, Zn: 6.1-7.5%, Ti: ≤0.05%, Zr: ≤0.05%; Other individual impurities are ≤0.05%, the total is ≤0.15%, and the balance is Al.

[0021] The aluminum alloy raw material is made of high-purity aluminum, with a Si content of 0-0.10%, an Fe content of 0-0.12%, and a Mn content of 0-0.13%.

[0022] One of the manufacturing processes for a 7-series aluminum alloy gas cylinder includes the following steps: a. Raw material customization and cutting; b. Clean the material block and apply lubricating oil; c. Dry and extrude to form an aluminum cylinder 600-610mm long; d. Flatten the aluminum cylinder to 520mm; e. Gas cylinders are formed using a heat-sealing process; f. Heat-treat the gas cylinder; g. Conduct performance testing on the heat-treated gas cylinders; h. Perform machining and internal surface strengthening treatment; i. Conduct hydrostatic tests, airtightness tests, and volumetric weight measurements; j. Perform surface treatment and final inspection.

[0023] The heat treatment in step f includes solution treatment and two-stage aging treatment. Solution treatment is carried out at 460-470℃ for 1-3 hours. Two-stage aging treatment includes: first-stage aging at 90-120℃ for 5-12 hours and second-stage aging at 130-150℃ for 2-4 hours.

[0024] The preferred method for the two-stage aging treatment is as follows: the first stage of aging is carried out at 90-110℃ for 5-8 hours, and the second stage of aging is carried out at 130-140℃ for 2-4 hours.

[0025] In step h, the inner surface strengthening treatment adopts shot blasting, using steel shot with a particle size of 0.5-1.5mm, and treating the inner surface of the gas cylinder for 5-20 minutes under a pressure of 0.5-1MPa.

[0026] The preferred time for internal surface strengthening treatment is 5-15 minutes.

[0027] Among them, the performance inspection in step g includes hardness testing, strength testing, metallographic observation and cold bending test. Only after all inspections are qualified can the process proceed to the machining process.

[0028] One type of gas cylinder made of 7-series aluminum alloy has the following mechanical properties: specified non-proportional elongation strength Rp0.2≥430MPa, tensile strength Rm≥506MPa, and elongation after fracture A≥12%.

[0029] In the metallographic structure of the gas cylinder, the precipitated phases are fine, uniform, and diffusely distributed, mainly including GP regions, transition phase and Equilibrium phase.

[0030] Example 2

[0031] The preparation of the standard 7-series aluminum alloy gas cylinder is as follows: Raw material composition (mass percentage): Si: 0.10%, Fe: 0.10%, Cu: 2.2%, Mn: 0.10%, Mg: 1.8%, Cr: 0.20%, Zn: 6.8%, Ti: 0.04%, Zr: 0.04%, other impurities: ≤0.05%, Al: balance; Production process flow: Customized raw materials, using high-purity aluminum as the base material, and smelting and casting according to the above composition ratio; After being extruded and cleaned and coated with lubricating oil, it is extruded into an aluminum cylinder 600mm long; Flatten the end of the aluminum cylinder to 520mm. Heat sealing: The gas cylinder shape is formed by heat sealing in a specified mold. Heat treatment: Solution treatment: Hold at 465℃ for 2 hours; Level 1 aging: 100℃ for 7 hours; Level 2 aging: Keep warm at 135℃ for 3 hours.

[0032] Inner surface strengthening treatment: Use 1.0mm steel shot to shot blast the inner surface of the gas cylinder for 10 minutes under a pressure of 0.8MPa.

[0033] Inspection and subsequent processing include metallographic inspection, mechanical property testing, hydrostatic testing, airtightness testing, and stamping.

[0034] Performance indicators: Yield strength: ≥435MPa, tensile strength: ≥515MPa, elongation: ≥13%, weight is reduced by about 33% compared with the same specification 6 series gas cylinder.

[0035] Example 3

[0036] The preparation of high-strength and high-toughness 7-series aluminum alloy gas cylinders is as follows: Raw material composition (mass percentage): Si: 0.05%, Fe: 0.08%, Cu: 2.5%, Mn: 0.05%, Mg: 2.0%, Cr: 0.22%, Zn: 7.2%, Ti: 0.03%, Zr: 0.03%, other impurities: ≤0.05%, Al: balance; Production process flow: Similar to Example 1, the key difference lies in the adjustment of heat treatment parameters; Solution treatment: Hold at 468℃ for 2 hours; Level 1 aging: 110℃ for 6 hours; Level 2 aging: Keep warm at 140℃ for 3 hours.

[0037] Inner surface treatment to enhance strength: using 1.2mm steel shot, pressure 1.0MPa, treatment for 12 minutes; Performance indicators: Yield strength: ≥450MPa, tensile strength: ≥520MPa, elongation: ≥12.5%, notch fatigue performance is significantly improved, and the number of notch fatigue and premature leakage cycles is increased.

[0038] Example 4

[0039] The preparation of lightweight, high-toughness 7-series aluminum alloy gas cylinders is as follows: Raw material composition (mass percentage): Si: 0.08%, Fe: 0.06%, Cu: 1.9%, Mn: 0.03%, Mg: 1.4%, Cr: 0.18%, Zn: 6.3%, Ti: 0.02%, Zr: 0.02%, other impurities: ≤0.05%, Al: balance; Production process flow and heat treatment parameter optimization: Solution treatment: Hold at 462℃ for 1.5 hours; Level 1 aging: 95℃ for 8 hours; Level 2 aging: 132℃ for 2.5 hours.

[0040] Inner surface treatment: Use 0.8mm steel shot, 0.6MPa pressure, for 8 minutes.

[0041] Performance indicators: Yield strength: ≥430MPa, tensile strength: ≥506MPa, elongation: ≥14%, outstanding toughness, suitable for high impact load environments, and the weight is only 65% ​​of that of 6-series gas cylinders of the same pressure rating.

[0042] Comparative Example 1

[0043] Based on 6061 aluminum alloy gas cylinders - conventional process, specifically: Composition (mass percentage): Si: 0.4-0.8%, Fe: ≤0.7%, Cu: 0.15-0.4%, Mn: ≤0.15%, Mg: 0.8-1.2%, Cr: 0.04-0.35%, Zn: ≤0.25%, Ti: ≤0.15%, Al: balance; Process Overview: Conventional melting, extrusion molding, and heat treatment – ​​namely T6 state: solution treatment + single-stage aging, simple cleaning of the inner surface or no strengthening treatment; Performance indicators: Yield strength ≈ 240-270MPa, tensile strength Rm ≈ 290-320MPa, elongation A ≈ 12-14%, and the wall thickness is about 50% greater than that of the 7-series gas cylinders under the same volumetric pressure. Weight comparison: The weight of the gas cylinder of the present invention is approximately 130-135% of that of the 7-series gas cylinder of the same specifications.

[0044] Comparative Example 2

[0045] 7-series aluminum alloy gas cylinders - standard heat treatment process: Composition: Same as the four embodiments of the present invention, Zn 6.1-7.5%, but the contents of Si, Fe, and Mn are not strictly controlled, such as Si ≤ 0.2% and Fe ≤ 0.3%; Process Overview: Conventional single-stage aging is adopted, such as 120-130℃, heat preservation for 8-16 hours, without internal surface shot blasting strengthening; Performance indicators: yield strength ≈ 480-510MPa, tensile strength ≈ 500-570MPa, elongation ≈ 12-15%, poor notched fatigue performance, prone to fatigue cracks, fatigue cycles less than 8000.

[0046] Experimental Example 1

[0047] Fatigue life comparison test Sample grouping: Group 1: Embodiment 2 of the present invention (standard type); Group 2: Comparative Example 1 (6061 conventional); Group 3: Comparative Example 2 (7-series conventional); Test conditions: Water pressure circulation test, pressure range: 0-30MPa, frequency: 8 times / min Medium: hydraulic oil; result: Group 1: No failure after ≥21,000 cycles; Group 2: Failed after approximately 18,000 cycles; Group 3: Failed after ≤8000 cycles; Conclusion: The present invention improves the fatigue life of gas cylinders by more than 40%, and has a significant effect on strengthening the inner surface.

[0048] Experimental Example 2

[0049] Notch fatigue and pre-explosion leakage test Sample grouping: Group A: Embodiment 3 of the present invention (high strength and toughness type); Group B: Comparative Example 2 (7-series conventional); Test method: A notch is pre-made on the outer wall of the gas cylinder, with a depth of 10% of the measured wall thickness, and a pulse pressure test is carried out; result: Group A: The crack propagation rate was significantly slowed down, and the number of cracks leaking before they burst increased by 2 times; Group B: Cracks propagate rapidly, with a low number of failures, and the failure is in the form of cracking.

[0050] Experimental Example 3

[0051] Weight vs. Wall Thickness Comparison Comparison: Example 4 of the present invention (lightweight type) vs. Comparative Example 1 (6061 gas cylinder); Same volume and pressure rating: Volume: 5L; Working pressure: 20MPa; Measurement results: Example 4: Wall thickness: 8.9 mm, weight: 6.4 kg; Comparative Example 1: Wall thickness: 6.1 mm, weight: 4.5 kg; Weight reduction percentage: approximately 29% reduction in weight and approximately 31% reduction in wall thickness.

[0052] The features of this invention: This invention involves the refined design and control of the chemical composition of 7-series aluminum alloy gas cylinder materials. Specifically, it effectively controls the formation of impurity phases, such as Mg2Si, AlMnFeSi, and (FeMn)Al6, by strictly limiting the content ranges of alloying elements silicon (Si), iron (Fe), and manganese (Mn). Excessive presence of these impurity phases significantly impairs the toughness and fatigue performance of the material. By controlling the Si content to 0% to 0.11% by mass, the Fe content to 0% to 0.12%, and the Mn content to 0% to 0.13%, not only is the proportion of brittle impurity phases reduced, but also... The purity of the matrix was improved, and the contents of the main strengthening elements, copper (Cu), magnesium (Mg), chromium (Cr), and zinc (Zn), were precisely controlled, such as Cu: 1.8%-2.6%, Mg: 1.3%-2.1%, Cr: 0.15%-0.25%, and Zn: 6.1%-7.5%. This laid the compositional foundation for the uniform formation of the strengthening phase during subsequent heat treatment. This compositional design aims to achieve homogenization of the internal structure of the grains and reduce stress concentration sources, thereby synergistically improving the static strength and dynamic toughness of the gas cylinder from the material's origin, so as to meet the requirements of high specific strength and good crack propagation resistance of the material under high pressure. The special heat treatment process employed, namely solution treatment followed by two-stage aging, involves solution treatment within a temperature range of 460°C to 470°C. The purpose of this solution treatment is to fully dissolve the alloying elements into the aluminum matrix, forming a supersaturated solid solution, and to dissolve as much of the coarse residual second phase as possible. The subsequent two-stage aging treatment is crucial. The first stage of aging is performed at a lower temperature, such as 90°C to 110°C or 90°C to 120°C, depending on the specific version, to promote the formation of numerous fine, uniform, and dispersed GP regions. These GP regions, acting as nanoscale precipitate precursors, effectively pin dislocations and initially strengthen the material. The second stage of aging is performed at a higher temperature, such as 130°C to 140°C or 130°C to 150°C, to gradually transform the GP regions into a transition phase. The phase eventually forms a more stable, finer, and more uniformly distributed equilibrium phase. This stepwise precipitation process avoids the coarsening or uneven distribution of the precipitated phase that may occur under a single high-temperature aging, ensuring that the precipitation strengthening effect is maximized. As a result, the material achieves high strength, such as yield strength ≥430MPa and tensile strength ≥506MPa, while maintaining good plasticity and elongation ≥12%, achieving the best match between strength and toughness. Shot peening technology introduces a beneficial residual compressive stress layer on the inner surface of gas cylinders, significantly improving their fatigue life. The specific operation involves using steel shot with a diameter of 0.5 mm to 1.5 mm to impact the inner wall of the gas cylinder for 5 to 15 minutes, or 5 to 20 minutes, under a pressure of 0.5 MPa to 1 MPa. The working principle is that a large number of high-speed shot particles impact the metal surface, causing localized plastic deformation of the surface material. Because this deformation is constrained by the underlying elastic matrix, macroscopic residual compressive stress is generated in the surface area after the shot is removed. This residual compressive stress field interacts with the gas... When the cylinder is in operation, the tensile stress fields generated by the internal pressure superimpose each other, which can effectively offset part of the working tensile stress and reduce the actual stress level on the inner wall surface. More importantly, fatigue cracks usually initiate and propagate under tensile stress. The residual compressive stress layer on the inner surface can significantly inhibit the initiation of microcracks and close or slow down the propagation of existing microcracks. Therefore, this treatment directly improves the fatigue performance, notch sensitivity, and pre-explosion leakage safety mode of the gas cylinder under cyclic pressure load. It is a key post-treatment step to improve the long-term safety and reliability of the gas cylinder.

[0053] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A gas cylinder made of 7-series aluminum alloy, characterized in that, The chemical composition of the gas cylinder, by mass percentage, includes: Si: ≤0.11%, Fe: ≤0.12%, Cu: 1.8-2.6%, Mn: ≤0.13%, Mg: 1.3-2.1%, Cr: 0.15-0.25%, Zn: 6.1-7.5%, Ti: ≤0.05%, Zr: ≤0.05%; Other individual impurities are ≤0.05%, the total is ≤0.15%, and the balance is Al.

2. A gas cylinder made of 7-series aluminum alloy according to claim 1, characterized in that: The aluminum alloy raw material is selected from high-purity aluminum, wherein the Si content is 0-0.10%, the Fe content is 0-0.12%, and the Mn content is 0-0.13%.

3. The manufacturing process for a 7-series aluminum alloy gas cylinder according to any one of claims 1-2, characterized in that, Includes the following steps: a. Raw material customization and cutting; b. Clean the material block and apply lubricating oil; c. Dry and extrude to form an aluminum cylinder 600-610mm long; d. Flatten the aluminum cylinder to 520mm; e. Gas cylinders are formed using a heat-sealing process; f. Heat-treat the gas cylinder; g. Conduct performance testing on the heat-treated gas cylinders; h. Perform machining and internal surface strengthening treatment; i. Conduct hydrostatic tests, airtightness tests, and volumetric weight measurements; j. Perform surface treatment and final inspection.

4. The manufacturing process for a 7-series aluminum alloy gas cylinder according to claim 3, characterized in that, The heat treatment in step f includes solution treatment and two-stage aging treatment. The solution treatment is held at 460-470℃ for 1-3 hours. The two-stage aging treatment includes: a first-stage aging at 90-120℃ for 5-12 hours and a second-stage aging at 130-150℃ for 2-4 hours.

5. The manufacturing process for a 7-series aluminum alloy gas cylinder according to claim 4, characterized in that: The preferred method for the two-stage aging process is as follows: the first stage of aging is performed at 90-110℃ for 5-8 hours, and the second stage of aging is performed at 130-140℃ for 2-4 hours.

6. The manufacturing process for a 7-series aluminum alloy gas cylinder according to claim 5, characterized in that, The inner surface strengthening treatment in step h adopts shot blasting process, using steel shot with a particle size of 0.5-1.5mm, and treating the inner surface of the gas cylinder for 5-20 minutes under a pressure of 0.5-1MPa.

7. The manufacturing process for a 7-series aluminum alloy gas cylinder according to claim 6, characterized in that: The preferred time for the internal surface strengthening treatment is 5-15 minutes.

8. The manufacturing process for a 7-series aluminum alloy gas cylinder according to claim 7, characterized in that, The performance inspection described in step g includes hardness testing, strength testing, metallographic observation, and cold bending test. Only after all inspections are passed can the process proceed to the machining process.

9. A gas cylinder made of 7-series aluminum alloy, characterized in that, The product is manufactured by any one of the production processes described in claims 3-8, and its mechanical properties meet the following requirements: specified non-proportional elongation strength Rp0.2≥430MPa, tensile strength Rm≥506MPa, and elongation after fracture A≥12%.

10. A gas cylinder made of 7-series aluminum alloy according to claim 1 or 9, characterized in that, In the metallographic structure of the gas cylinder, the precipitated phases are fine, uniform, and diffusely distributed, mainly including GP regions. transition phase and Equilibrium phase.

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