A manufacturing method for a thin-walled cylindrical part of TC18 titanium alloy

Abstract

A manufacturing method for a TC18 titanium alloy thin-walled cylindrical part, by changing the process route of the existing technology, implementing double annealing in stages, and performing double annealing on the rear cylinder body of the cylinder section welded with various external parts after the first stage. After the double annealing in the first stage, machining is carried out on the rear cylinder body of the cylinder section, and the front cylinder body of the head and the rear cylinder body of the cylinder section are welded. After the frame is completed, the second stage of double annealing is carried out on the cylindrical part, and during the subsequent post-welding heat treatment process, the deformation, aging, and parameter matching of double annealing heat treatment in the argon arc welding process of the thin-walled cylindrical part are comprehensively considered, and the heat treatment process is simple and efficient. The present invention solves the deficiency that the tensile strength of the matrix is weakened by the heat processes of argon arc welding and electron beam welding required for the structural connection of parts during the forming process of the TC18 titanium alloy thin-walled cylindrical part. The tensile strength of the manufactured TC18 titanium alloy thin-walled cylindrical part is greater than 1200 Mpa, and the elongation after fracture is greater than 6%.

Description

Technical Field

[0001] The present invention belongs to the field of processing and manufacturing, and specifically relates to a manufacturing method for thin-walled cylindrical parts made of TC18 titanium alloy. Background Art

[0002] The nominal composition of TC18 titanium alloy is Ti-5Al-5V-5Mo-1Cr-1Fe, belonging to the near-β type titanium alloy. It has the characteristics of low density, high strength, and high elongation after fracture, and is an ideal structural material in the fields of aviation and aerospace manufacturing. The thin-walled cylindrical part is the main structural form of the metal shell of a solid rocket motor. As the main power device of weapons, launch vehicles, etc., in recent years, with the continuous improvement of the combat performance indicators of new weapon systems, the comprehensive performance requirements of solid rocket motors have become higher and higher. The thin-walled cylindrical part is the largest negative mass in a solid rocket motor. When the density is constant, increasing the tensile strength of the thin-walled cylindrical part will directly affect the mass ratio of the motor. Compared with thin-walled cylindrical parts made of high-strength steel, titanium alloy thin-walled cylindrical parts of the same mass have obvious advantages in terms of performance. At present, thin-walled titanium alloy cylindrical parts are generally developed using TA15 titanium alloy, with a tensile strength of 930 Mpa to 1130 Mpa, while the tensile strength of TC18 titanium alloy is 1080 Mpa to 1280 Mpa, having the potential to manufacture thin-walled cylindrical parts with higher manufacturing performance. Since the thin-walled cylindrical part needs to be connected between structures by welding during manufacturing, mainly involving two welding methods: argon arc welding and electron beam welding. It has been proven by experiments that both of the above two welding methods have an impact on the material strength. The tensile strength of the electron beam welded joint of TC18 titanium alloy is 870 Mpa to 930 Mpa, and the tensile strength of the argon arc welded joint of TC18 titanium alloy is 680 Mpa to 710 Mpa. To improve the overall load-bearing capacity of the thin-walled cylindrical part, a reasonable heat treatment system is required to strengthen the weld area.

[0003] In view of the requirement for the material tensile strength to be greater than 1200 Mpa for the designed function of the thin-walled cylindrical part, and the low characteristic of the welding process in the manufacturing process of the TC18 thin-walled cylindrical part to reduce the material tensile strength, it is necessary to develop a manufacturing method for thin-walled cylindrical parts made of TC18 titanium alloy with a tensile strength greater than 1200 Mpa.

[0004] There is no information showing the manufacturing method of thin-walled cylindrical parts made of TC18 titanium alloy with a tensile strength greater than 1200 Mpa. Central South University disclosed a heat treatment method for TC18 titanium alloy in the patent application with the authorized publication number CN103924180A. This invention proposes a heat treatment method for TC18 titanium alloy. By selecting the holding temperature, time, and cooling method, the microstructure of the alloy can be effectively regulated, enabling TC18 titanium alloy to have high strength, good plasticity, and toughness, and solving the problems of low alloy strength in the double annealing process and difficulty in meeting the use requirements of alloy plasticity and toughness in the solution-aging process. Since this heat treatment method needs to use water quenching for performance strengthening, it is prone to large deformation and is more suitable for the treatment of raw material states and not suitable for the manufacture of thin-walled cylindrical parts. Shenyang Liming Aero Engine (Group) Co., Ltd. disclosed a self-weight hot forming process method for titanium alloy thin-walled cylindrical parts in the patent application with the authorized announcement number CN102107243B. This invention uses the self-weight of the hot forming fixture to act on the titanium alloy thin-walled cylindrical part of the part to generate pressure instead of power, and completes the forming of the thin-walled cylindrical part in a vacuum furnace. The process method and functional structure requirements involved in this invention are different from those of the present invention. Summary of the Invention

[0005] To overcome the deficiency in the prior art that the heat processes of argon arc welding and electron beam welding during the forming process of TC18 titanium alloy thin-walled cylindrical parts weaken the tensile strength of the base material and cannot meet the requirement of a tensile strength greater than 1200 Mpa, the present invention proposes a manufacturing method for TC18 titanium alloy thin-walled cylindrical parts.

[0006] The specific process of the present invention is as follows:

[0007] Step 1, machining of the front cylinder body of the cylinder section:

[0008] The machining of the front cylinder body of the cylinder section is divided into three stages: rough machining, semi-finishing machining, and finishing machining. Among them, 3 mm / single is reserved for the inner and outer diameters and the end face during rough machining; 1 mm / single is reserved for the inner and outer diameters and the end face during semi-finishing machining.

[0009] While machining the front cylinder body of the cylinder section, a specimen raw material is intercepted from the blank of the front cylinder body of the cylinder section and machined into a tensile specimen with threads at both ends.

[0010] Step 2, machining of the rear cylinder body of the cylinder section:

[0011] Step 3, welding of external components:

[0012] The external component 2 is welded to the rear cylinder body of the cylinder section by argon arc welding. The external component includes eight outer joints, four cable cover seats 4, and one slider 3.

[0013] Execute the Class II standard of QJ175-1993, and successively weld each of the said external joints, cable cover seats and sliders to the rear cylinder of the cylinder section. Obtain the rear cylinder of the cylinder section welded with each external component.

[0014] During welding, the arc voltage is 15-20V, the welding current is 40-80A, and the gas flow rate is 13-20L / min. The length of the weld is 4-5mm.

[0015] Step Four, the first-stage double annealing:

[0016] Carry out the first-stage double annealing on the obtained rear cylinder of the cylinder section welded with each external component.

[0017] The said double annealing process is implemented in stages. The annealing temperature in the first stage is a stepped temperature. First, heat the rear cylinder of the cylinder section in the furnace to 830±10°C and hold for 60±10min, then cool in the furnace to 760°C and hold for 60±10min, and then air-cool.

[0018] Place the rear cylinder of the cylinder section with a titanium alloy heat treatment protective coating and the said tensile specimen in the annealing furnace, and carry out heat treatment according to the determined heat treatment system in the first stage.

[0019] Obtain the rear cylinder of the cylinder section and the said tensile specimen after the first-stage heat treatment.

[0020] During the said first-stage double annealing, it is necessary to apply a titanium alloy heat treatment protective coating on the outer circumference of each of the said external components and at each weld; the number of coating applications is 3-5 times, and the interval time between each coating application is 15-20min. After the said titanium alloy heat treatment protective coating is applied, it is naturally dried for 30-60min.

[0021] During the said first-stage double annealing, spray a titanium alloy heat treatment protective coating on the said tensile specimen and dry it. The process of spraying the coating and drying is the same as the process of brushing and drying the titanium alloy heat treatment protective coating on the rear cylinder of the cylinder section.

[0022] Step Five, machining of the rear cylinder of the cylinder section:

[0023] The machining process of the said rear cylinder of the cylinder section includes semi-finishing and finishing stages.

[0024] Among them, during semi-finishing, a finishing allowance of 1mm is left for the inner diameter, outer diameter and end face of the said rear cylinder of the cylinder section.

[0025] Step Six, weld the front cylinder of the head and the rear cylinder of the cylinder section:

[0026] Weld the said front cylinder of the head and the rear cylinder of the cylinder section by electron beam welding. Obtain a thin-walled cylindrical part.

[0027] When welding the front cylinder and the rear cylinder of the head, pickling is performed on the area within 30 mm around the welding part of the front cylinder of the head and the rear cylinder of the head for 3 - 5 minutes; immediately after pickling, rinse with distilled water and then dry.

[0028] Use a vacuum electron beam welder to perform electron beam circumferential weld welding, and successively perform cleaning, backfilling, welding, and shaping. The cleaning focusing current is 1980 mA, the backfilling focusing current is 1960 mA, the welding focusing current is 1960 mA, the shaping is 2000 mA, the welding speed is 800 mm / min, the cleaning electron beam current is 8 mA, the backfilling electron beam current is 9 mA, the welding electron beam current is 12 mA, and the shaping electron beam current is 10 mA.

[0029] Step seven, second-stage double annealing:

[0030] Perform second-stage double annealing on the obtained TC18 titanium alloy thin-walled cylindrical parts and tensile specimens.

[0031] Place the TC18 titanium alloy thin-walled cylindrical parts with a titanium alloy heat treatment protective coating brushed on them and the tensile specimens in an annealing furnace for the heat treatment of the second stage of double annealing. During heat treatment, heat up with the furnace to 570 ± 10 °C, hold for 240 ± 10 minutes, and air cool.

[0032] Obtain the thin-walled cylindrical parts and the tensile specimens that have undergone the heat treatment of the second stage of double annealing.

[0033] Perform sandblasting on the thin-walled cylindrical parts that have undergone the heat treatment of the second stage of double annealing to remove the heat treatment protective coating. Complete the production of the TC18 titanium alloy thin-walled cylindrical parts.

[0034] During the second-stage double annealing, apply a titanium alloy heat treatment protective coating on the outer circumference and weld seams of the TC18 titanium alloy thin-walled cylindrical parts; the number of coating applications is 3 - 5 times, and the interval time between each coating application is 15 - 20 minutes. After the titanium alloy heat treatment protective coating is applied, let it dry naturally for 30 - 60 minutes.

[0035] Spray a titanium alloy heat treatment protective coating on the tensile specimens and dry it. The process of spraying the coating and drying is the same as the process of brushing and drying the titanium alloy heat treatment protective coating on the rear cylinder of the cylinder section.

[0036] Step eight, performance testing and flaw detection:

[0037] Perform sandblasting on the tensile specimens that have undergone the heat treatment of the second stage of double annealing respectively to remove the heat treatment protective coating.

[0038] The mechanical properties of the tensile specimen were tested. The test results were as follows: the tensile strength Rm of the specimen was ≥1200 Mpa, and the elongation after fracture A was ≥6%. The circumferential weld was subjected to 100% radiographic inspection, which was carried out according to the Class I standard of GJB1718A-2005.

[0039] The manufacturing method of the TC18 titanium alloy thin-walled cylindrical part proposed by the present invention enables the tensile strength of the manufactured TC18 titanium alloy thin-walled cylindrical part to be greater than 1200 Mpa, and the elongation after fracture to be greater than 6%.

[0040] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0041] 1. The manufacturing method of the TC18 titanium alloy thin-walled cylindrical part designed by the present invention enables the tensile strength of the base material and the weld position of the thin-walled cylindrical part to meet the requirements of being greater than 1200 Mpa and the elongation after fracture to be greater than 6%. Compared with the average tensile strength of the TA15 titanium alloy thin-walled cylindrical parts at the present stage, it is increased by more than 170 Mpa. Compared with the performance of this type of product at the present stage, the tensile strength is significantly improved.

[0042] 2. The manufacturing method of the TC18 titanium alloy thin-walled cylindrical part designed by the present invention solves the deficiency that the heat process of argon arc welding and electron beam welding required for the connection of the part structure weakens the tensile strength of the matrix during the forming process of the TC18 titanium alloy thin-walled cylindrical part. Through process tests, the conclusion is obtained that the weld after electron beam welding needs to be heat-treated and strengthened by aging, and the weld after argon arc welding needs to be heat-treated and strengthened by double annealing. During the design process of the subsequent post-weld heat treatment method, the deformation, aging and parameter matching of double annealing heat treatment during the argon arc welding process of the thin-walled cylindrical part are comprehensively considered, and the heat treatment process design is simple and efficient. Description of the Drawings

[0043] Figure 1 It is a schematic structural diagram of the rear section of the TC18 titanium alloy thin-walled cylindrical part; among them, Figure 1 a in it is the front view, Figure 1 b in it is Figure 1 the side view of a in it.

[0044] Figure 2 It is the process curve of the first stage of double annealing.

[0045] Figure 3 It is the process curve of the second stage of double annealing.

[0046] Figure 4 It is the performance change of the thin-walled cylindrical part before and after heat treatment.

[0047] Figure 5 It is the flow chart of the present invention.

[0048] In the figure: 1. Rear cylinder of the cylinder section; 2. External component; 3. Slide block; 4. Cable wire cover; 5. Front cylinder of the head; 6. Tensile strength curve at the welding position after heat treatment; 7. Tensile strength value curve at the welding position before heat treatment. Detailed implementation method

[0049] Example 1

[0050] This example is the process of manufacturing a certain TC18 titanium alloy thin-walled cylindrical part. The outer diameter of the TC18 thin-walled cylindrical part is 300 mm, the wall thickness is 2 mm, and the total length is 1250 mm. There is an external component welding reinforcement ring on the outer circumference of the TC18 thin-walled cylindrical part, and the outer diameter of the reinforcement ring is 301 mm.

[0051] The TC18 titanium alloy thin-walled cylindrical part is composed of a front section and a rear section, where the front section is the front cylinder of the head 2 and the rear section is the rear cylinder of the cylinder section 1.

[0052] The specific process of this example is as follows:

[0053] Step 1, machining of the front cylinder of the cylinder section:

[0054] The machining of the front cylinder of the cylinder section is divided into three stages: rough machining, semi-finishing machining, and finishing machining. During rough machining, 3 mm / single is left for the inner and outer diameters and the end face; during semi-finishing machining, 1 mm / single is left for the inner and outer diameters and the end face.

[0055] While machining the front cylinder of the cylinder section, a specimen raw material with a length of 70 mm is intercepted from the blank of the front cylinder of the cylinder section, and it is machined into a circular tensile specimen with a diameter of 5 mm, a length of 55 mm, and threads at both ends.

[0056] Step 2, machining of the rear cylinder of the cylinder section:

[0057] The rear cylinder of the cylinder section is machined into a thick-walled cylinder with a wall thickness of 10 mm through rough machining.

[0058] Step 3, welding of the external component:

[0059] The external component 2 is welded on the rear cylinder of the cylinder section by argon arc welding. The external component includes eight outer joints, four cable wire cover seats 4, and one slide block 3.

[0060] Sand the welding position with sandpaper, mount it on the dividing head, mark the dividing bus and the assembly position line of the installation position. Degrease the external components to be welded and the rear cylinder of the cylinder section. Sand the welding joints of each external component.

[0061] During welding, implement the QJ175-1993 Class II standard, and successively weld each of the outer joints, cable cover seats, and sliders to the rear cylinder of the cylinder section. The arc voltage is 15-20V, the welding current is 40-80A, and the gas flow rate is 13-20L / min.

[0062] The length of the weld is 4-5mm.

[0063] Inspection: Conduct penetrant inspection on the fillet welds, and evaluate the weld quality according to the requirements of the QJ175-1993 Class II standard.

[0064] Obtain the rear cylinder of the cylinder section with each external component welded.

[0065] Step Four, the first stage of double annealing:

[0066] Perform double annealing on the obtained rear cylinder of the cylinder section with each external component welded.

[0067] The double annealing process is implemented in stages. The annealing temperature in the first stage is a stepped temperature. First, heat the rear cylinder of the cylinder section in the furnace to 830±10°C and hold for 60±10 minutes, then cool in the furnace to 760°C and hold for 60±10 minutes, and then air cool.

[0068] The specific process is:

[0069] Coating protection: Clean the oil stains and colorants on the inner and outer surfaces of the rear cylinder of the cylinder section and the surface of the specimen with alcohol; apply titanium alloy heat treatment protection coating on the outer circumference of each external component and at each weld; the number of coating applications is 3-5 times, and the interval time between each coating application is 15-20 minutes. After the titanium alloy heat treatment protection coating is applied, it is naturally dried for 30-60 minutes.

[0070] Hang the threaded section of the circular tensile specimen on the specimen rack, spray titanium alloy heat treatment protection coating and dry it. The process of spraying the coating and drying is the same as the process of brushing and drying the titanium alloy heat treatment protection coating on the rear cylinder of the cylinder section.

[0071] Check the titanium alloy heat treatment protection coating on the rear cylinder of the cylinder section, and no leakage coating and scratch defects are allowed.

[0072] Place the rear cylinder of the cylinder section with the titanium alloy heat treatment protection coating and the circular tensile specimen in the annealing furnace, and perform heat treatment according to the determined heat treatment system in the first stage.

[0073] Obtain the rear cylinder of the cylinder section and the circular tensile specimen after the first stage of heat treatment.

[0074] Step Five, machining of the rear cylinder of the cylinder section:

[0075] The machining process of the rear cylinder of the cylinder section includes semi-finishing and finishing stages.

[0076] During semi-finishing, a 1-mm finishing allowance is left on the inner diameter, outer diameter, and end face of the rear cylinder body of this cylinder section.

[0077] Step Six, welding the front cylinder body of the head and the rear cylinder body of the cylinder section:

[0078] Weld the front cylinder body of the head and the rear cylinder body by electron beam welding. Specifically:

[0079] Degrease the surfaces of the front cylinder body of the head and the rear cylinder body respectively.

[0080] Pickle the area within 30 mm around the welding parts of the front cylinder body of the head and the rear cylinder body for 3 - 5 minutes respectively; immediately rinse with distilled water and then dry after pickling.

[0081] Clean the welding parts with acetone before welding to confirm there is no any oil stain.

[0082] Use a vacuum electron beam welding machine to carry out electron beam circumferential weld welding, and sequentially perform cleaning, backfilling, welding, and shaping. The cleaning focusing current is 1980 mA, the backfilling focusing current is 1960 mA, the welding focusing current is 1960 mA, the shaping is 2000 mA, the welding speed is 800 mm / min, the cleaning electron beam current is 8 mA, the backfilling electron beam current is 9 mA, the welding electron beam current is 12 mA, and the shaping electron beam current is 10 mA.

[0083] Obtain a thin-walled cylindrical part.

[0084] Step Seven, the second stage of double annealing:

[0085] Implement the second stage of double annealing on the obtained TC18 titanium alloy thin-walled cylindrical part. The specific process is as follows:

[0086] Coating protection: Clean the oil stain and colorant on the surface of this TC18 titanium alloy thin-walled cylindrical part with alcohol; apply titanium alloy heat treatment protection coating on the outer circumference and weld seam of the TC18 titanium alloy thin-walled cylindrical part; the number of coating applications is 3 - 5 times, and the interval time between each coating application is 15 - 20 minutes. After the titanium alloy heat treatment protection coating is applied, it is naturally dried for 30 - 60 minutes.

[0087] Hang the threaded section of the circular tensile specimen on the specimen rack, spray titanium alloy heat treatment protection coating and dry it. The process of spraying the coating and drying is the same as the process of brushing and drying the titanium alloy heat treatment protection coating on the rear cylinder body of the cylinder section.

[0088] Place the TC18 titanium alloy thin-walled cylindrical part with the titanium alloy heat treatment protective coating on the circular tensile specimen in an annealing furnace for the heat treatment of the second stage of double annealing. During the heat treatment, heat it in the furnace to 570±10°C, hold for 240±10 min, and air cool.

[0089] Obtain the thin-walled cylindrical part and the circular tensile specimen after the heat treatment of the second stage of double annealing.

[0090] Perform sandblasting on the thin-walled cylindrical part after the heat treatment of the second stage of double annealing to remove the heat treatment protective coating. Complete the production of the TC18 titanium alloy thin-walled cylindrical part.

[0091] Step eight, performance testing and flaw detection:

[0092] Perform sandblasting on the circular tensile specimen after the heat treatment of the second stage of double annealing to remove the heat treatment protective coating.

[0093] Conduct mechanical property testing on the circular tensile specimen. The test results are as follows: the tensile strength Rm of the specimen is ≥1200 Mpa, and the elongation after fracture A is ≥6%. Conduct 100% radiographic flaw detection on the circumferential weld, and implement it according to the GJB1718A-2005 Class I standard.

Claims

1. A manufacturing method for a thin-walled cylindrical part made of TC18 titanium alloy, characterized in that, The specific process is as follows: Step 1, machining the front cylinder body of the cylinder section; While machining the front cylinder body of the cylinder section, a specimen raw material is intercepted from the blank of the front cylinder body of the cylinder section and machined into a tensile specimen with threads at both ends; Step 2, machining the rear cylinder body of the cylinder section; Step 3, welding external components: Weld the external components on the rear cylinder body of the cylinder section by argon arc welding; the external components include eight outer connectors, four cable cover seats, and one slider; Execute the QJ175-1993 Class II standard, and successively weld each of the outer connectors, cable cover seats, and sliders to the rear cylinder body of the cylinder section; obtain the rear cylinder body of the cylinder section welded with each external component; Step 4, the first-stage double annealing: Conduct the first-stage double annealing on the obtained rear cylinder body of the cylinder section welded with each external component; The double annealing process is implemented in stages; the annealing temperature in the first stage is a stepped temperature. First, heat the rear cylinder body of the cylinder section in the furnace to 830±10°C and hold for 60±10 min, then cool in the furnace to 760°C and hold for 60±10 min, and then air-cool; Place the rear cylinder body of the cylinder section with a titanium alloy heat treatment protective coating and the tensile specimen in the annealing furnace, and conduct heat treatment according to the determined heat treatment system in the first stage; Obtain the rear cylinder body of the cylinder section and the tensile specimen after the first-stage heat treatment; Step 5, machining the rear cylinder body of the cylinder section: The machining process of the rear cylinder body of the cylinder section includes semi-finishing and finishing stages; Among them, during semi-finishing, a 1-mm finishing allowance is left for the inner diameter, outer diameter, and end face of the rear cylinder body of the cylinder section; Step 6, welding the front cylinder body of the head and the rear cylinder body of the cylinder section: Weld the front cylinder body of the head and the rear cylinder body of the cylinder section by electron beam welding; obtain a TC18 titanium alloy thin-walled cylindrical part; Perform electron beam circumferential weld welding using a vacuum electron beam welder, and successively execute cleaning, backfilling, welding, and shaping; the cleaning focusing current is 1980 mA, the backfilling focusing current is 1960 mA, the welding focusing current is 1960 mA, the shaping is 2000 mA, the welding speed is 800 mm / min, the cleaning electron beam current is 8 mA, the backfilling electron beam current is 9 mA, the welding electron beam current is 12 mA, and the shaping electron beam current is 10 mA; Step 7, the second-stage double annealing: Conduct the second-stage double annealing on the obtained TC18 titanium alloy thin-walled cylindrical part and the tensile specimen; Place the TC18 titanium alloy thin-walled cylindrical part with a titanium alloy heat treatment protective coating brushed on it and the tensile specimen in the annealing furnace, and conduct the heat treatment in the second stage of double annealing; during heat treatment, heat in the furnace to 570±10°C, hold for 240±10 min, and then air-cool; Obtain the thin-walled cylindrical part and the tensile specimen after the heat treatment in the second stage of double annealing; Perform sandblasting on the thin-walled cylindrical part after the heat treatment in the second stage of double annealing to remove the heat treatment protective coating; complete the production of the TC18 titanium alloy thin-walled cylindrical part; Step 8, performance testing and flaw detection: Perform sandblasting on the tensile specimen after the heat treatment in the second stage of double annealing respectively to remove the heat treatment protective coating; Perform mechanical property tests on the tensile test specimen; the test results are as follows: the tensile strength Rm of the specimen is ≥1200 Mpa, and the elongation after fracture A is ≥6%; perform 100% radiographic inspection on the circumferential weld, and execute according to the Class I standard of GJB1718A-2005.

2. The manufacturing method of the TC18 titanium alloy thin-walled cylindrical part according to claim 1, characterized in that, The machining of the front cylinder of the cylinder section is divided into three stages: rough machining, semi-finishing machining, and finishing machining. For rough machining, a 3-mm / side allowance is left for both the inner and outer diameters and the end face; for semi-finishing machining, a 1-mm / side allowance is left for both the inner and outer diameters and the end face.

3. The manufacturing method of the TC18 titanium alloy thin-walled cylindrical part as described in claim 1, characterized in that, During welding, the arc voltage is 15 - 20 V, the welding current is 40 - 80 A, the gas flow rate is 13 - 20 L / min; the length of the weld spot is 4 - 5 mm.

4. The manufacturing method of the TC18 titanium alloy thin-walled cylindrical part according to claim 1, characterized in that During the double annealing in the first stage, it is necessary to apply a titanium alloy heat treatment protective coating on the outer circumference of each of the external components and at each weld; the number of coating applications is 3 - 5 times, and the interval time between each coating application is 15 - 20 min; after the titanium alloy heat treatment protective coating is applied, it is naturally dried for 30 - 60 min.

5. The manufacturing method of the TC18 titanium alloy thin-walled cylindrical part according to claim 1, characterized in that, During the double annealing in the first stage, spray and dry a titanium alloy heat treatment protective coating on the tensile test specimen; the process of spraying and drying the coating is the same as the process of brushing and drying the titanium alloy heat treatment protective coating on the rear cylinder of the cylinder section.

6. The manufacturing method of the TC18 titanium alloy thin-walled cylindrical part according to claim 1, characterized in that When welding the front cylinder of the head and the rear cylinder of the cylinder, pickle the area within 30 mm around the welding part of the front cylinder of the head and the rear cylinder of the cylinder for 3 - 5 min, rinse, and then dry.

7. The manufacturing method of the TC18 titanium alloy thin-walled cylindrical part as described in claim 1, characterized in that, During the double annealing in the second stage, apply a titanium alloy heat treatment protective coating on the outer circumference and welds of the TC18 titanium alloy thin-walled cylindrical part; the number of coating applications is 3 - 5 times, and the interval time between each coating application is 15 - 20 min; after the titanium alloy heat treatment protective coating is applied, it is naturally dried for 30 - 60 min; Spray and dry a titanium alloy heat treatment protective coating on the tensile test specimen; the process of spraying and drying the coating is the same as the process of brushing and drying the titanium alloy heat treatment protective coating on the rear cylinder of the cylinder section.

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