A method for preparing a zinc-sprayed internal helical toothed tube

Abstract

This invention discloses a method for preparing a zinc-sprayed internally spiral toothed tube, comprising the following steps: The aluminum internally spiral toothed round tube is the zinc-sprayed HIG tube, which can be manufactured using extrusion tube blanking, drawing, spiral tooth forming, drawing, zinc spraying, and zinc infiltration processes. The blank tube is processed to a suitable size through continuous cold drawing, and then undergoes internal spiral tooth forming. After the incoming coil is drawn to its outer diameter, it is fed into the tooth forming machine by a feeding mechanism. During internal spiral tooth forming, steel balls rotate around the tube within a gearbox, driven by a motor at high speed. Simultaneously, after tooth forming, the tube is cooled and then coiled into an aluminum coil. This invention's method for preparing a zinc-sprayed internally spiral toothed tube combines arc zinc spraying with the processing of aluminum internally spiral tubes to produce an aluminum tube with controllable zinc layer thickness. Furthermore, through the development of the zinc infiltration process, the appropriate zinc layer penetration depth is studied to achieve optimal corrosion resistance in the zinc-sprayed internally spiral toothed aluminum tube.

Description

TECHNICAL FIELD

[0001] The present application is mainly used for processing aluminum alloy extrusion, drawing and other products, and the products are used in the field of household and commercial heat exchangers, and particularly relates to a preparation method of a zinc-sprayed inner spiral tooth pipe. BACKGROUND

[0002] The aluminum inner spiral tooth pipe is a kind of pipe material processed by aluminum alloy extrusion, drawing and other products and used in household and commercial heat exchangers, and the existing alloy of the aluminum inner spiral tooth pipe is 3003 or 3103 alloy in a conventional manner. With the continuous development of science and technology, people have higher and higher requirements for the manufacturing process of the aluminum inner spiral tooth pipe.

[0003] The existing aluminum inner spiral tooth pipe has certain disadvantages in use, the alloy inner spiral tooth pipe has poor corrosion resistance in the application process, and cannot meet the requirements of some customers for high corrosion resistance. Electric arc zinc spraying is a traditional process applied to micro-channel flat pipes to provide zinc layer protection and improve corrosion resistance, but this zinc spraying process has not been developed for the drawing-formed aluminum inner spiral tooth pipe, and the actual process and corrosion resistance need to be further studied, which brings certain adverse effects to the use of people. Therefore, we propose a preparation method of a zinc-sprayed inner spiral tooth pipe. SUMMARY

[0004] The technical problem solved by the present application is that, in view of the deficiencies of the prior art, the present application provides a preparation method of a zinc-sprayed inner spiral tooth pipe, which combines the electric arc zinc spraying and the processing method of the aluminum inner spiral pipe to produce an inner spiral tooth aluminum pipe with a controllable zinc layer thickness, and at the same time, the zinc penetration process is developed, the suitable zinc layer penetration depth is studied, and the zinc-sprayed inner spiral tooth aluminum pipe with the best corrosion resistance is obtained, which can effectively solve the problems in the background art.

[0005] The technical scheme is that, in order to achieve the above-mentioned purpose, the present application adopts the following technical scheme: a preparation method of a zinc-sprayed inner spiral tooth pipe, comprising the following operation steps:

[0006] S1: the aluminum inner spiral tooth pipe is a zinc-sprayed HIG pipe, which can be made by the processes of extrusion blank pipe, drawing, spiral tooth forming, drawing, zinc spraying and zinc penetration;

[0007] S2: the blank pipe is processed to a suitable size by continuous cold drawing, and then inner spiral tooth forming is performed, the incoming coil is drawn after the outer diameter is drawn, and then the pipe is sent into the tooth forming machine device through a feeding mechanism, during the inner spiral tooth forming, the steel ball rotates around the pipe in the gear box under the driving of the motor, the steel ball presses the aluminum into the groove with a spiral groove core head arranged inside the pipe, and then the spiral groove core head rotates under the action of the drawing force, so that the tooth shape with a spiral angle is pressed in the pipe, and the pipe after tooth forming is cooled and wound into an aluminum coil;

[0008] S3: After the inner spiral tooth tube is formed, the tube with ball marks needs to be further drawn and reduced in diameter. The tube after being reduced in diameter is straightened and then is annealed on line. The high-temperature tube is then arc zinc sprayed. The aluminum tube enters a water tank for cooling and is then wound up;

[0009] S4: The aluminum tube after being zinc sprayed needs to be finally subjected to special heat treatment so that zinc diffuses from the surface of the aluminum tube to the tube wall to form a zinc diffusion layer with a zinc concentration gradient. The zinc penetration annealing process can be selected from two kinds of low-temperature long holding time or high-temperature short holding time. After the zinc penetration heat treatment, the zinc penetration depth is generally between 80-300 μm at the position of the maximum thickness of the zinc spraying to provide sufficient corrosion protection;

[0010] S5: This process is also suitable for producing conventional round tubes without inner spiral teeth. The round tube can be directly zinc sprayed after being extruded and then subjected to the same penetration treatment. The conventional round tube can also be zinc sprayed after being cold drawn. The zinc penetration treatment is also carried out after the zinc spraying to obtain a zinc penetration layer with a suitable thickness.

[0011] As a preferred technical solution of the present application, the process flow in the S1 step is that the alloy aluminum ingot is extruded into a blank tube, is once drawn, is formed with inner spiral teeth, is twice drawn, is arc zinc sprayed, and is subjected to zinc penetration treatment.

[0012] As a preferred technical solution of the present application, the process flow in the S2 step is that the blank tube is unwound, is cold drawn and shaped in outer diameter, is fed by a feeding device, is formed with inner spiral teeth, is cooled, and is wound up.

[0013] As a preferred technical solution of the present application, the process flow in the S3 step is that the blank tube is unwound, is drawn and shaped in diameter, is straightened, is annealed on line, is zinc sprayed, is cooled, and is wound up.

[0014] As a preferred technical solution of the present application, the process flow in the S4 step is that the blank tube is heat treated, is arc zinc sprayed, is subjected to zinc penetration annealing process, and is provided with corrosion protection.

[0015] As a preferred technical solution of the present application, the process flow in the S5 step is that the alloy aluminum ingot is extruded into a round tube and is subjected to arc zinc spraying and zinc penetration treatment. The alloy aluminum ingot is extruded into a blank tube, is drawn, is arc zinc sprayed, and is subjected to zinc penetration treatment.

[0016] As a preferred technical solution of the present application, in the S1 step, the extruder extrudes the aluminum ingot heated to a temperature range of 450-510 ℃ through a die into a blank tube with a suitable size. The aluminum ingot is heated by gradient heating. The gradient is controlled to be 60-120 ℃ / m.

[0017] As a preferred technical solution of the present application, in the S1-S5 steps, the arc zinc spraying and the processing mode of the aluminum inner spiral tube are combined to produce the inner spiral tooth aluminum tube with a controllable zinc layer thickness. Meanwhile, the zinc penetration process is developed.

[0018] Beneficial effects: Compared with the prior art, the present application provides a preparation method of a zinc-sprayed internal spiral tooth pipe, which has the following beneficial effects: the preparation method of the zinc-sprayed internal spiral tooth pipe realizes the combination of electric arc zinc spraying and aluminum internal spiral pipe processing to produce an internal spiral tooth aluminum pipe with a controllable zinc layer thickness, and through the development of a zinc penetration process, a suitable zinc layer penetration depth is researched to obtain a zinc-sprayed internal spiral tooth aluminum pipe with optimal corrosion resistance. The entire aluminum internal spiral tooth pipe has a simple structure, is convenient to operate, and has a better use effect than traditional methods. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 It is a whole structure schematic diagram of the preparation method of the zinc-sprayed internal spiral tooth pipe of the present application.

[0020] Figure 2 It is a structure schematic diagram of the process flow of the S1 step in the preparation method of the zinc-sprayed internal spiral tooth pipe of the present application.

[0021] Figure 3 It is a structure schematic diagram of the process flow of the S2 step in the preparation method of the zinc-sprayed internal spiral tooth pipe of the present application.

[0022] Figure 4 It is a structure schematic diagram of the process flow of the S3 step in the preparation method of the zinc-sprayed internal spiral tooth pipe of the present application.

[0023] Figure 5 It is a structure schematic diagram of the process flow of the S5 step in the preparation method of the zinc-sprayed internal spiral tooth pipe of the present application.

[0024] Figure 6 It is a schematic diagram of a double-gun ZAS coating on the HIG pipe and a zinc penetration scanning electron microscope (SEM) diagram in the preparation method of the zinc-sprayed internal spiral tooth pipe of the present application.

[0025] Figure 7 It is a schematic diagram of a Zn penetration curve measured by SEM line scanning in the preparation method of the zinc-sprayed internal spiral tooth pipe of the present application.

[0026] Figure 8 It is an AA3003 HIG pipe sample after SWAAT testing in the preparation method of the zinc-sprayed internal spiral tooth pipe of the present application. It is a schematic diagram of the cross-sectional morphology of a zinc-sprayed HIG pipe sample and a non-zinc-sprayed HIG pipe sample.

[0027] Figure 9 It is a schematic diagram of the SWAAT life of an AA3003 HIG pipe sample with a zinc layer and an AA3003 HIG pipe sample without a zinc layer in the preparation method of the zinc-sprayed internal spiral tooth pipe of the present application. DETAILED DESCRIPTION

[0028] The technical solutions of the present application will be clearly and completely described below in combination with the drawings and specific embodiments, but those skilled in the art will understand that the following described embodiments are part of the embodiments of the present application, not all the embodiments, and are only used to illustrate the present application, and should not be regarded as limiting the scope of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application. If the specific conditions are not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are used. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased on the market.

[0029] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like indicate the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as limiting the devices or elements referred to have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second", "third" are only for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0030] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connecting" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the communication inside two elements. For those of ordinary skill in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0031] As shown in Figures 1-9 A method for manufacturing a zinc-sprayed inner spiral tooth pipe, comprising the following operation steps:

[0032] S1: The aluminum inner spiral tooth round pipe is a zinc-sprayed HIG pipe, which can be manufactured by the process of extruding a blank pipe, drawing, spiral tooth forming, drawing, zinc spraying and zinc penetration;

[0033] S2: The blank pipe is processed to a suitable size by continuous cold drawing, and then inner spiral tooth forming is performed. After the incoming coil is drawn in the outer diameter, the pipe is sent into the tooth forming machine device through the feeding mechanism. During the inner spiral tooth forming, the steel ball rotates around the pipe in the gear box under the drive of the motor. The steel ball presses the aluminum into the groove with a spiral groove core head placed inside the pipe, and then the spiral groove core head rotates under the action of the drawing force, so that the tooth shape with a spiral angle is pressed in the pipe. After the tooth forming, the pipe is cooled and wound into an aluminum coil;

[0034] S3: After the inner spiral pipe forming, the pipe with ball marks needs to be further drawn and reduced in diameter. The pipe after reducing in diameter is straightened and then annealed on line. The high temperature pipe is then arc sprayed with zinc. The aluminum pipe enters the water tank for cooling and then is wound up;

[0035] S4: The aluminum pipe after zinc spraying needs to be finally subjected to special heat treatment so that zinc diffuses from the surface of the aluminum pipe to the pipe wall to form a zinc diffusion layer with a zinc concentration gradient. The zinc penetration annealing process can be selected from two kinds of low temperature long holding time or high temperature short holding time. After the zinc penetration heat treatment, the zinc penetration depth is generally between 80-300 μm at the position of the maximum thickness of the zinc spraying to provide sufficient corrosion protection;

[0036] S5: This process is also suitable for producing conventional round pipes without inner spiral teeth. The round pipe can be directly sprayed with zinc after extrusion and then subjected to the same penetration treatment. The conventional round pipe can also be cold drawn and then sprayed with zinc. After the zinc spraying, the same zinc penetration treatment is carried out to obtain a zinc penetration layer with a suitable thickness.

[0037] Further, the process flow in S1 step is that the alloy aluminum ingot is extruded into a blank pipe, once drawn, inner spiral tooth forming, twice drawn, arc sprayed with zinc, and zinc penetration treatment.

[0038] Further, the process flow in S2 step is that the pipe is unwound, the outer diameter is shaped by cold drawing, the feeding device is used, the inner spiral tooth is formed, the pipe is cooled, and the pipe is wound up.

[0039] Further, the process flow in S3 step is that the pipe is unwound, the pipe is drawn and the diameter is shaped, the pipe is straightened, the pipe is annealed on line, the pipe is sprayed with zinc, the pipe is cooled, and the pipe is wound up.

[0040] Further, the process flow in S4 step is that the pipe is heat treated, the pipe is arc sprayed with zinc, the pipe is subjected to zinc penetration annealing process, and the pipe is provided with corrosion protection.

[0041] Further, the process flow in S5 step is that the alloy aluminum ingot is extruded into a round pipe and subjected to arc spraying with zinc and zinc penetration treatment. The alloy aluminum ingot is extruded into a blank pipe, drawn, arc sprayed with zinc, and subjected to zinc penetration treatment.

[0042] Further, in S1 step, the extruder extrudes the aluminum ingot heated to a temperature range of 450-510°C through a die into a blank pipe with a suitable size. When the aluminum ingot is heated, gradient heating is adopted. The gradient control is 60-120°C / m.

[0043] Further, in S1-S5 steps, the arc zinc spraying is combined with the processing mode of the aluminum inner spiral pipe to produce the inner spiral tooth aluminum pipe with a controllable zinc layer thickness. At the same time, the zinc penetration process is developed.

[0044] Embodiment:

[0045] Aluminum internally spiral toothed round tubes (hereinafter referred to as HIG tubes) are widely used in heat exchangers for HVAC&R (heating, ventilation, air conditioning, and refrigeration) applications to replace copper tubes. HIG tubes are made from standard 3003, 3103, or high-corrosion-resistant, long-life alloys developed by Hydro. For air conditioning units / systems used in harsh environments, a zinc (arc spraying) coating is applied to the surface of the heat exchanger tubes to provide additional corrosion protection.

[0046] Zinc-sprayed HIG tubes can be manufactured using processes such as extrusion tube blanks, drawing, spiral tooth forming, drawing, zinc spraying, and zinc penetration. The process flow diagram is shown below. Figure 2 .

[0047] The selected alloy aluminum ingots are cast and homogenized at the foundry. Then, an extruder heats the ingots to a temperature range of 450-510℃ and extrudes them through a die into preforms of suitable dimensions. Gradient heating is used during ingot heating, with the gradient controlled at 60-120℃ / m to achieve a uniform extruded preform temperature. The preform dimensions are set according to the drawing capacity of the equipment. After being extruded from the press, the high-temperature preforms are cooled in a water bath and then coiled for the cold drawing process.

[0048] The blank tube is processed to the appropriate size through continuous cold drawing, with the total cold drawing deformation controlled between 30% and 90%, and then undergoes internal helical tooth forming. The principle of internal helical tooth forming is as follows: Figure 1 As shown. After the outer diameter of the incoming coil is drawn, it is fed into the gear forming machine via a feeding mechanism. During the internal helical gear forming, steel balls rotate around the tube inside the gearbox at high speed driven by a motor. The steel balls press aluminum into the groove with a helical groove core placed inside the tube. Then, the helical groove core rotates under the action of the drawing force, thereby pressing a tooth shape with a helical angle inside the tube. The helical angle of HIG tubes can be 10°-45° with the tube axis. During the gear forming process, the tube's outlet temperature must be controlled not to exceed 250°. After gear forming, the tube must be cooled and then rolled into an aluminum coil. The process flow diagram is shown below. Figure 3 .

[0049] After the internal spiral toothed tube is formed, the tube with ball marks needs to be further air-stretched, with the diameter reduction controlled between 10-25% to more effectively remove the ball marks, making the outer surface of the tube smooth and obtaining the final tube size. After diameter reduction, the tube is straightened and then subjected to online annealing at a temperature controlled between 450-550℃. The high-temperature tube is then subjected to electric arc zinc spraying. Zinc spraying can be done with two guns at 180° angles or three guns at 120° angles. The zinc spraying process adopts the traditional electric arc zinc spraying principle. Each zinc spraying gun has two zinc wires with a diameter of 1.2mm or 1.6mm. When the two charged zinc wires approach each other at a certain angle inside the wire feeding copper tube, an electric arc is generated. The zinc wire near the arc melts, and a certain pressure of gas blows the molten zinc into powder, which adheres to the surface of the high-temperature aluminum tube, forming a zinc spray layer of a certain thickness. The aluminum tube is then cooled in a water bath and wound up. The process flow diagram is shown below. Figure 4 .

[0050] After zinc spraying, the aluminum tubes undergo a special heat treatment to allow zinc to diffuse from the tube surface to the tube wall, forming a zinc diffusion layer with a zinc concentration gradient. After arc zinc spraying, the average zinc adhesion on the aluminum tube surface is controlled at 3–10 g / m² to ensure sufficient zinc penetration. Two zinc penetration annealing processes can be used: low-temperature long holding time or high-temperature short holding time. Low-temperature zinc penetration annealing: 380–450℃, 3–9 hours. High-temperature zinc penetration annealing: 450–550℃, 1–3 hours. After zinc penetration heat treatment, the Zn penetration depth is generally measured at the location of maximum zinc spraying thickness, typically between 80 and 300 μm, to provide sufficient corrosion protection.

[0051] The geometric dimensions of HIG sprayed zinc pipe include: outer diameter (OD) 5-10mm, WT 0.3-0.8mm, FH 0.10-0.50mm, number of teeth 30-60, and helix angle 15-40°.

[0052] This process is also suitable for producing conventional round tubes without internal spiral teeth. These round tubes can be directly zinc-sprayed after extrusion, followed by the same zinc penetration treatment. Conventional round tubes can also be cold-drawn followed by zinc spraying, and then subjected to the same zinc penetration treatment to obtain a zinc penetration layer of suitable thickness. The specific process flow is as follows: Figure 5 .

[0053] Figure 6The diagram illustrates the application of two-gun arc zinc spraying on a HIG pipe, with the spray guns positioned at 12:00 and 18:00. When using a two-gun system, the zinc deposition is highest at the position directly opposite the spray guns, gradually decreasing towards the sides of the highest deposition point, reaching its lowest point, or even zero, at 15:00 and 21:00. During the zinc penetration treatment process, zinc diffuses into the pipe wall at high temperature, forming a zinc diffusion layer with a specific concentration gradient within a certain depth on the outer wall. The bright white area in the diagram represents this diffusion layer, thus creating a zinc-protected layer on the pipe surface.

[0054] Figure 7 The Zn permeation curves were measured at different locations on the cross-section of the HIG tube for SEM line scan analysis. It can be seen that the zinc diffusion depth is also the deepest at points A and D, where the zinc spraying amount is the highest, and the depth gradient is also the largest. At points B, C, E, and F, where the zinc spraying amount is relatively low, the zinc diffusion depth is shallower, and the concentration gradient is also smaller. In this case, the depth of the zinc permeation layer is between 170 and 210 μm.

[0055] Figure 8 The images show metallographic cross-sections of AA3003 alloy 7HIG pipe samples with a wall thickness of 0.47 mm, with and without a zinc coating, tested using SWAAT. SWAAT testing was conducted according to ASTM G85-A3. The pipe without the zinc coating was corroded through by pitting corrosion in less than 10 days during the SWAAT test. In contrast, the zinc-coated sample, even after 20 days of SWAAT testing, showed uniform corrosion across the entire circumference without pitting, thus improving the overall corrosion resistance of the pipe.

[0056] Figure 9 The SWAAT life of tube samples in the same condition is shown. It can be seen that the SWAAT life of the unzinc-coated AA3003 HIG tube is less than 10 days, while the SWAAT life of the zinc-coated tube sample can reach 46 days. Studies on standard AA3003 tube material show that, under the same wall thickness, the SWAAT life of tubes treated with zinc spraying and zinc penetration is 5 to 6 times that of unzinc-sprayed tubes. Therefore, zinc spraying can significantly improve the corrosion resistance and service life of pipes and heat exchangers, thus making the application of aluminum internally threaded tubes as a replacement for copper tubes more widespread.

[0057] It should be noted that, in this document, relational terms such as first and second (number one, number two), etc., are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0058] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A method of manufacturing a zinc-coated internally helically toothed tube, characterized in that: The method comprises the following steps: S1: the aluminum inner spiral tooth pipe is a HIG pipe for zinc spraying, which is manufactured by the processes of extruding a blank pipe, drawing, spiral tooth forming, drawing, zinc spraying and zinc penetration; S2: the blank pipe is processed to a proper size by continuous cold drawing, and then the inner spiral tooth is formed; after the incoming coil is drawn in the outer diameter, the pipe is sent into the tooth forming device by a feeding mechanism; when the inner spiral tooth is formed, a steel ball rotates at a high speed around the pipe in a gear box under the driving of a motor, and the steel ball presses the aluminum pipe into a groove with a spiral core head inside the pipe, and then the spiral core head rotates under the drawing force, so that the tooth shape with a spiral angle is pressed in the pipe; and the pipe after the tooth forming is cooled and then wound into a coil; S3: the pipe with the ball marks after the inner spiral tooth forming needs to be further drawn and reduced in diameter; the pipe after the reduction in diameter is straightened and then annealed on line; the high-temperature pipe is then arc zinc sprayed; and the aluminum pipe is cooled in a water tank and then wound; S4: the aluminum pipe after the zinc spraying needs to be finally treated by a special heat treatment, so that the zinc diffuses from the surface of the aluminum pipe to the pipe wall to form a zinc diffusion layer with a zinc concentration gradient; the zinc penetration annealing process adopts a low-temperature long holding time or a high-temperature short holding time; and after the zinc penetration heat treatment, the zinc penetration depth is measured at the position of the maximum thickness of the zinc spraying, and the zinc penetration depth is between 80-300 μm, so as to provide sufficient corrosion protection.

2. A method of manufacturing a zinc sprayed internal spiral fluted tube according to claim 1, characterised in that: The process flow in the S1 step is that an alloy aluminum ingot is extruded into a blank pipe, drawn once, formed with an inner spiral tooth, drawn twice, arc zinc sprayed and treated by zinc penetration.

3. The method of making a zinc-coated internally spiral- fluted tube of claim 1, wherein: The process flow in the S2 step is that a coil is unwound, the outer diameter is shaped by cold drawing, fed, formed with an inner spiral tooth, cooled and wound.

4. The method of making a zinc-coated internally spiral- fluted tube of claim 1, wherein: The process flow in the S3 step is that a coil is unwound, drawn and shaped in diameter, straightened, annealed on line, zinc sprayed, cooled and wound.

5. The method of making a zinc-coated internally spiral- fluted tube of claim 1, wherein: The process flow in the S4 step is that heat treated, arc zinc sprayed, treated by zinc penetration annealing process and provided with corrosion protection.

6. The method of making a zinc-coated internally spiral- fluted tube of claim 1, wherein: In the S1 step, the extruder extrudes the aluminum ingot heated to a temperature range of 450-510 ℃ through a die into a blank pipe with a proper size; when the aluminum ingot is heated, gradient heating is adopted, and the gradient is controlled to be 60-120 ℃ / m.

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