Manufacturing method of internal thread aluminum alloy pipe with corrosion-resistant zinc impregnation layer

Abstract

The invention discloses a manufacturing method of an internal thread aluminum alloy pipe with a corrosion-resistant zincizing layer, which comprises the following steps of: treating and forming an aluminum alloy blank into an aluminum alloy mother pipe, firstly performing electric arc zinc spraying on the aluminum alloy mother pipe, forming a zinc layer on the surface of the aluminum alloy mother pipe, and immediately performing primary permeation on the zinc layer; performing internal thread forming on the aluminum alloy mother pipe subjected to electric arc zinc spraying, so that secondary permeation of a zinc layer is synchronously realized under the action of heat generated by working of an internal thread forming mechanism and deformation of the aluminum alloy mother pipe in the internal thread forming process, then performing finishing coiling and heat treatment on the internal thread aluminum alloy pipe, and performing tertiary permeation on the zinc layer; therefore, in the overall manufacturing process of the internal thread aluminum alloy pipe, the zinc layer is permeated for three times, so that effective permeation of the zinc layer is guaranteed, a zinc permeation layer is formed, the combination tightness of the zinc layer and the pipe is improved, the corrosion resistance and reliability of the internal thread aluminum alloy pipe are guaranteed, and the service life is prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of aluminum alloy pipes, in particular to an internally threaded aluminum alloy pipe with a corrosion-resistant zinc-plated layer. Background Art

[0002] Internally threaded aluminum alloy tubes have the same pressure resistance and heat exchange capacity as copper tubes, but the cost is much lower than that of copper tubes. Therefore, internally threaded aluminum alloy tubes are usually used as air-conditioning pipes in the air-conditioning field. However, internally threaded aluminum alloy tubes have poor corrosion resistance and are easily corroded by moisture, oxygen, etc. in the air, resulting in failure of the internally threaded aluminum alloy tubes and leakage of air-conditioning pipes, thereby reducing the service life of the air-conditioning.

[0003] Zinc (Zn) is a metal with moderate activity. Its natural corrosion resistance is not high. However, due to the relatively negative standard electrode potential of zinc, when zinc comes into contact with other metals (such as aluminum and copper) and is exposed to electrolytes (such as seawater or humid air), zinc will preferentially undergo oxidation reactions, thereby protecting other metals from corrosion, which makes it a commonly used sacrificial anode material. In addition, a thin and dense layer of oxides and hydroxides will form on the surface of zinc when it comes into contact with air. This film can effectively prevent further oxidation reactions.

[0004] The Chinese patent application with the publication number CN 117066296 A discloses a method for preparing a zinc-sprayed internal spiral tooth tube, wherein the tube is first subjected to an internal thread forming process, and after the internal thread of the tube is spirally formed, the tube is reduced in diameter and subjected to arc zinc spraying, and finally the zinc layer is subjected to a penetration treatment.

[0005] However, the preparation method provided by the above scheme is not only cumbersome in steps, but also can only achieve one-time penetration treatment of the zinc layer, which cannot ensure the effective penetration of the zinc layer, easily causing the zinc layer to be loosely bonded to the pipe, unable to form an effective anti-corrosion barrier, and making the pipe more susceptible to corrosion.

[0006] Therefore, the art urgently needs a method for manufacturing the zinc layer of an internally threaded aluminum alloy pipe with simple steps, which can effectively improve the bonding tightness between the zinc layer and the pipe, ensure the corrosion resistance and reliability of the internally threaded aluminum alloy pipe, and extend the service life. Summary of the invention

[0007] In view of the defects of the prior art, the purpose of the present invention is to provide a method for manufacturing an internally threaded aluminum alloy tube with a corrosion-resistant zinc-diffused layer. The manufacturing method is simple, and can also ensure the effective penetration of the zinc layer, improve the bonding tightness between the zinc layer and the pipe, ensure the corrosion resistance and reliability of the internally threaded aluminum alloy tube, and extend the service life.

[0008] In order to achieve the above object, the present invention provides a method for manufacturing an internally threaded aluminum alloy tube with a corrosion-resistant zinc-plated layer, the manufacturing method comprising:

[0009] The aluminum alloy billet is hot extruded and coiled to be formed into an aluminum alloy mother tube;

[0010] The formed aluminum alloy mother tube is subjected to arc zinc spraying. First, the aluminum alloy mother tube is laid out, straightened, and the outer surface is cleaned and dried online. Then, the zinc spraying device is evenly distributed around the aluminum alloy mother tube. The zinc wire in the zinc spraying device is melted by the arc generated by the zinc wire and the aluminum alloy mother tube. At the same time, the zinc spraying device is used to spray atomized air to spray the molten zinc wire onto the surface of the aluminum alloy mother tube. The voltage of zinc spraying is 25-30V, the current is 100-130A, the pressure of the atomized gas is 3-5bar, and the passing speed of the aluminum alloy mother tube is 200-250m / min. Then, the aluminum alloy mother tube after arc zinc spraying is subjected to online annealing treatment to perform initial penetration of the zinc layer.

[0011] The aluminum alloy mother tube after arc zinc spraying is subjected to internal thread forming, and the aluminum alloy mother tube is reduced in diameter and deformed by an internal thread forming mechanism to form an internal thread aluminum alloy tube. During the forming process, the heat generated by the operation of the internal thread forming mechanism and the deformation of the aluminum alloy mother tube acts on the zinc layer, and the zinc layer is simultaneously penetrated for a second time;

[0012] After the internal thread aluminum alloy tube is finished and coiled, it is heat treated and the zinc layer is infiltrated three times.

[0013] Furthermore, in the hot extrusion process, the aluminum alloy mother tube is gradient heated to 400∽450°C or 430∽470°C, and then extruded through a die with an extrusion ratio of ≥150, and the extruded aluminum alloy mother tube is cooled in a water tank.

[0014] Furthermore, in the coiling process, when the aluminum alloy mother tube is stretched, the stretching passes are adapted to the size of the aluminum alloy mother tube, and the elongation coefficient of each pass is 1.1 to 1.8, and the total deformation rate of the stretching is configured to be 35% to 85%.

[0015] Furthermore, the zinc spraying device is configured with three arc zinc spraying guns evenly distributed around the aluminum alloy mother pipe at an angle of 120 degrees.

[0016] Furthermore, in the internal thread forming process, the internal thread forming mechanism includes a diameter reducing mechanism and a tooth spinning mechanism. The diameter of the aluminum alloy mother tube is first reduced by the diameter reducing mechanism, and then the surface of the aluminum alloy mother tube is rotated and rolled by the tooth spinning mechanism to press the aluminum alloy mother tube into the tooth groove of the thread core head, so that the aluminum alloy mother tube is deformed and formed into an internally threaded aluminum alloy tube, and the heat generated by the rotation of the tooth spinning mechanism and the deformation of the aluminum alloy mother tube is simultaneously applied to the zinc layer.

[0017] Furthermore, the diameter reducing mechanism includes an external die arranged outside the aluminum alloy mother tube and a movable core head built into the aluminum alloy mother tube, and the spinning gear mechanism includes a steel ring arranged outside the aluminum alloy mother tube, a steel ball arranged in the steel ring and a threaded core head built into the aluminum alloy mother tube, and the steel ball and the threaded core head rotate in opposite directions.

[0018] Furthermore, in the heat treatment process, the internally threaded aluminum alloy pipe is placed in an annealing heating furnace, the temperature of the annealing heating furnace is set to 450-570°C, and the internally threaded aluminum alloy pipe is heat treated for 30-90 minutes to apply heat to the zinc layer.

[0019] The method for manufacturing an internally threaded aluminum alloy tube with a corrosion-resistant zinc-diffused layer provided by the present invention comprises the following steps: after the aluminum alloy billet is processed and formed into an aluminum alloy mother tube, the aluminum alloy mother tube is firstly subjected to arc zinc spraying to form a zinc layer on the surface of the aluminum alloy mother tube, and then the zinc layer is initially infiltrated, and then the aluminum alloy mother tube after the arc zinc spraying is subjected to internal thread forming, so that during the internal thread forming process, the zinc layer is simultaneously infiltrated for a second time under the action of heat generated by the operation of the internal thread forming mechanism and the deformation of the aluminum alloy mother tube, and then the internally threaded aluminum alloy tube is finely coiled and heat-treated, and the zinc layer is infiltrated for a third time. Thus, in the overall manufacturing process of the internally threaded aluminum alloy tube, the zinc layer is infiltrated for a third time to ensure effective infiltration of the zinc layer, form a reliable zinc-diffused layer, improve the bonding tightness between the zinc layer and the tube, and ensure the corrosion resistance and reliability of the internally threaded aluminum alloy tube.

[0020] At the same time, the heat generated during the internal thread forming process can simultaneously achieve secondary penetration of the zinc layer, which can effectively improve manufacturing efficiency and reduce manufacturing costs.

[0021] Furthermore, the present invention also sets the voltage, current, pressure of atomizing gas and passing speed of the aluminum alloy mother tube of the arc zinc spraying within a certain range, thereby accurately controlling the process flow of the arc zinc spraying so that the formed zinc layer can be tightly combined with the aluminum alloy tube and is not easy to fall off. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0023] Figure 1 A flow chart of a method for manufacturing an internally threaded aluminum alloy tube with a corrosion-resistant zinc-plated layer provided by the present invention;

[0024] Figure 2 This is a schematic diagram of the internal thread forming principle in the present invention;

[0025] Figure 3 This is a comparison chart of the performance test results of the internally threaded aluminum alloy pipe under the manufacturing method of the present invention and the traditional manufacturing method;

[0026] Figure 4 This is a comparison chart of SWAAT test results of internally threaded aluminum alloy tubes under the manufacturing method of the present invention and the traditional manufacturing method.

[0027] Figure 5 and Figure 6 The following is a comparison chart of the performance and SWAAT test data of internally threaded aluminum alloy pipes with different zinc layer thicknesses. DETAILED DESCRIPTION

[0028] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further described below with reference to specific diagrams.

[0029] The method for manufacturing an internally threaded aluminum alloy pipe with a corrosion-resistant zinc-diffused layer provided by the present invention comprises the following steps: before the internal thread of the aluminum alloy pipe is formed, arc zinc spraying is first performed on the aluminum alloy pipe to form a zinc layer on the surface of the aluminum alloy pipe and perform initial penetration; internal thread forming is then performed on the aluminum alloy pipe after arc zinc spraying, so that the zinc layer is simultaneously penetrated for a second time during the internal thread forming process; finally, heat treatment is performed on the formed internally threaded aluminum alloy pipe, so that the zinc layer is penetrated for a third time, thereby ensuring effective penetration of the zinc layer, improving the bonding tightness between the zinc layer and the pipe, ensuring the corrosion resistance and reliability of the internally threaded aluminum alloy pipe, and extending the service life.

[0030] Combination Figure 1 , this manufacturing method mainly includes:

[0031] First, the aluminum alloy billet is hot extruded to be formed into an aluminum alloy mother tube.

[0032] In the hot extrusion process, aluminum alloy round bars of specified grades are selected as aluminum alloy billets, and the aluminum alloy billets are gradient heated so that there is a temperature difference from the core to the surface of the aluminum alloy mother tube. This can effectively control the temperature distribution of the material during the extrusion process, improve the fluidity of the aluminum alloy mother tube, and facilitate forming.

[0033] At the same time, the aluminum alloy billet is gradient heated to 400∽450℃, and in winter when the temperature is lower, it is heated to 430∽470℃ to reduce the deformation resistance of the aluminum alloy billet and improve the plasticity, thereby reducing the extrusion force, making it easier for the aluminum alloy billet to fill the mold and improving production efficiency.

[0034] Furthermore, the heated aluminum alloy billet is extruded through a die, and the die specification of the aluminum alloy billet is adapted to the tonnage of the extrusion equipment and the selected extrusion ratio (ratio of the cross-sectional area of ​​the aluminum alloy billet to the aluminum alloy mother tube after forming).

[0035] Specifically, in order to ensure that the zinc layer of the formed aluminum alloy mother tube can be firmly bonded to the surface of the aluminum alloy mother tube in the subsequent arc zinc spraying process, the hot extrusion process in the present manufacturing method has a stricter extrusion ratio than the traditional hot extrusion process. Preferably, the extrusion ratio is configured to be ≥150, so that the aluminum alloy billet undergoes greater deformation in the die, which helps to refine the grains, so that the hot-extruded aluminum alloy mother tube is dense and defect-free, with a smooth surface, and has improved mechanical properties, while also improving the processing effect of subsequent arc zinc spraying.

[0036] Next, the high-temperature aluminum alloy mother tube extruded by the die is cooled in a water tank.

[0037] Next, the formed aluminum alloy mother tube is coiled to make the aluminum alloy mother tube reach a predetermined geometric size, while reducing surface defects of the aluminum alloy mother tube so that it can be better combined with the zinc layer.

[0038] In the coiling process, the aluminum alloy mother tube is first paid out and the moving path of the aluminum alloy mother tube is preset. The pay-out device can guide the aluminum alloy mother tube to move along the predetermined path to avoid deviation or entanglement of the aluminum alloy mother tube during processing, so as to ensure the straightness and flatness of the aluminum alloy mother tube.

[0039] Next, the aluminum alloy mother tube is stretched, and the aluminum alloy mother tube is plastically deformed by external force under the action of the tensile force, thereby reducing the cross section and extending the length. During the stretching process, the stretching passes are adapted to the size of the aluminum alloy mother tube.

[0040] Specifically, in order to avoid cracking and breaking of the aluminum alloy mother tube during the coiling process, reduce the tightness of the bonding between the aluminum alloy mother tube and the zinc layer, and cause the zinc layer to fall off, the coiling process of the present manufacturing method has a smaller elongation coefficient and total deformation rate compared to the traditional coiling process. Preferably, the elongation coefficient of each pass (the multiple of the increase in length of the aluminum alloy mother tube after one stretching or the ratio of the cross-sectional area before and after stretching) is configured to be 1.1∽1.8, and the total deformation rate of stretching is configured to be 35%∽85%. By setting the elongation coefficient and total deformation rate within a smaller range, the processing rate of each pass can be determined, the processing process can be optimized, and cracking or breaking of the aluminum alloy mother tube caused by excessive processing can be avoided, thereby ensuring the stability and safety of the stretching process and ensuring that the aluminum alloy mother tube has a good metallurgical bond with the zinc layer.

[0041] Next, arc zinc spraying is performed on the aluminum alloy mother tube after coiling to form a zinc layer on the surface of the aluminum alloy mother tube.

[0042] In the arc zinc spraying process, the aluminum alloy mother tube is first laid out to preset the arc zinc spraying trajectory to ensure that the aluminum alloy mother tube maintains a stable position and angle during the zinc spraying process. Through the pre-set lines, the zinc spray can be guided to move along the predetermined trajectory, thereby achieving zinc spraying on specific areas on the surface of the aluminum alloy mother tube, thereby improving the quality and efficiency of zinc spraying.

[0043] Furthermore, the aluminum alloy mother tube needs to be straightened to ensure that the aluminum alloy mother tube will not be deformed due to the thermal stress generated by the arc zinc spraying, so that the aluminum alloy mother tube maintains a stable geometric shape before and after the arc zinc spraying. At the same time, the outer surface of the aluminum alloy mother tube is cleaned, for example, oil, dust, oxides and other pollutants on the outer surface of the aluminum alloy mother tube are removed to ensure the purity and suitable environment of the zinc spraying area, so that the aluminum alloy mother tube can form a good metallurgical bond with the zinc layer.

[0044] Next, the zinc spraying device is evenly distributed around the aluminum alloy mother tube and zinc spraying is performed corresponding to the wire laying trajectory. Preferably, the zinc spraying device is configured with three arc zinc spraying guns evenly distributed around the aluminum alloy mother tube at an angle of 120° to improve the uniformity of zinc spraying on the aluminum alloy mother tube and reduce thermal stress concentration, so as to form a uniform zinc layer and surface quality on the surface of the aluminum alloy mother tube.

[0045] During the arc zinc spraying process, three arc zinc spraying guns work synchronously, the arc zinc spraying guns are fixed, and the aluminum alloy mother tube makes axial linear motion, so that the zinc wire can act evenly on the surface of the aluminum alloy mother tube, forming a zinc layer on the entire surface of the aluminum alloy mother tube.

[0046] Specifically, two zinc wires are provided in the zinc spraying device, and the zinc wires are uniformly and continuously fed into two conductive nozzles in the zinc spraying device through a wire feeding device. The conductive nozzles are respectively connected to the positive and negative poles of the power supply, and ensure that the two zinc wires are insulated before they come into contact.

[0047] Furthermore, when the ends of two zinc wires contact each other, a short circuit is generated to form an electric arc. The electric arc serves as a heat source to instantly melt the ends of the zinc wires. At the same time, atomizing air is sprayed through the zinc spraying device, so that the molten zinc wire is atomized into tiny molten droplets under the action of the high-speed atomizing air flow, and is accelerated under the action of the high-speed atomizing air flow, and sprayed onto the surface of the aluminum alloy mother tube at a higher speed, forming a zinc layer on the surface of the aluminum alloy mother tube.

[0048] In order to improve the effective combination of the zinc layer and the aluminum alloy mother tube and prevent the zinc layer from falling off easily, during the arc zinc spraying process, the zinc spraying voltage is controlled to a lower 25-30V to control the power of the arc so that the zinc wire can be fully and quickly melted. At the same time, the zinc spraying current is configured to 100-130A, and the current will increase with the increase of the wire feeding speed, so that the melting efficiency of the zinc wire is adapted to the wire feeding speed, thereby improving the melting speed of the zinc wire.

[0049] Furthermore, the pressure of the atomizing gas will affect the atomization degree and injection speed of the molten zinc wire. If the pressure is too low, the molten zinc wire will be insufficiently atomized and the particles will be coarse, affecting the quality of the zinc layer. If the pressure is too high, it will interfere with the arc heat source, reduce the heat source temperature and affect the stability of the heat source. Therefore, the pressure of the atomizing gas is configured to 3-5 bar, so that the pressure of the atomizing gas is within an appropriate range, which can fully atomize the molten zinc wire to improve the density and uniformity of the zinc layer. At the same time, the oxidation of the zinc layer will not be caused by excessive atomizing gas pressure.

[0050] Furthermore, the passing speed of the aluminum alloy mother tube determines the thickness and uniformity of the zinc layer. If the passing speed is too fast, the zinc layer may be too thin. If the passing speed is too slow, the zinc layer may be too thick or local overheating may occur. Therefore, the passing speed of the aluminum alloy mother tube is configured to 200-250m / min, so that the passing speed of the aluminum alloy mother tube is compatible with the melting and spraying speed of the zinc wire, so that the zinc wire can be evenly sprayed on the surface of the aluminum alloy mother tube and is not easy to fall off.

[0051] Therefore, by controlling the voltage, current, pressure of atomizing gas and the passing speed of the aluminum alloy mother tube during arc zinc spraying, the zinc wire and the atomizing gas cooperate with each other to form a uniform, non-detachable zinc layer on the surface of the aluminum alloy mother tube.

[0052] Furthermore, the zinc layer can protect the aluminum alloy mother tube. When the zinc layer on the surface of the aluminum alloy mother tube is exposed to an electrolyte (such as seawater or humid air), the zinc layer will preferentially undergo an oxidation reaction to form a thin and dense oxide and hydroxide layer on the surface of the aluminum alloy mother tube, thereby protecting the aluminum alloy mother tube from corrosion to improve the corrosion resistance and reliability of the aluminum alloy mother tube. At the same time, the oxide and hydroxide layer can effectively prevent further oxidation reactions to increase the service life.

[0053] After the zinc layer is formed, the aluminum alloy mother tube is immediately subjected to online annealing treatment to perform the initial penetration of the zinc layer. The aluminum alloy mother tube is placed in an induction heating chamber for heat penetration and stress relief annealing. The atoms on the zinc layer and the surface of the aluminum alloy mother tube have a high ability under high temperature conditions, so that the zinc layer atoms diffuse into the interior of the aluminum alloy mother tube. At the same time, the iron atoms inside the aluminum alloy mother tube will also diffuse to the surface, forming a uniform zinc-iron compound layer on the surface of the aluminum alloy mother tube, namely the zincizing layer, to achieve the initial penetration of the zinc layer.

[0054] At the same time, it can also form a closer combination between the zinc layer and the aluminum alloy mother tube to improve the adhesion of the zinc layer, so that the zinc layer is firmly attached to the surface of the aluminum alloy mother tube.

[0055] Finally, the aluminum alloy mother tube after online annealing is cooled in a water tank.

[0056] Next, combine Figure 2The aluminum alloy mother tube with a zinc layer formed on the surface is internally threaded, and the aluminum alloy mother tube 200 is reduced in diameter by the internal thread forming mechanism 100 to be formed into an internally threaded aluminum alloy tube. During the forming process, the heat generated by the operation of the internal thread forming mechanism 100 and the deformation of the aluminum alloy mother tube 200 acts on the zinc layer, and the zinc layer is simultaneously penetrated for a second time to ensure effective penetration of the zinc layer, while improving manufacturing efficiency and reducing manufacturing costs.

[0057] Furthermore, the internal thread forming mechanism 100 includes a diameter reducing mechanism 110 and a tooth spinning mechanism 120. The aluminum alloy mother tube 200 is first reduced in diameter by the diameter reducing mechanism 110, and then the internal thread is formed by the tooth spinning mechanism 120.

[0058] Specifically, the diameter reducing mechanism 110 includes an outer die 111 arranged outside the aluminum alloy mother tube 200 and a movable core head 112 built into the aluminum alloy mother tube 200. The aluminum alloy mother tube 200 is reduced in diameter under the extrusion action of the outer die 111 and the movable core head 112, and then enters the spinning tooth forming mechanism 120 for internal thread forming.

[0059] Furthermore, the spinning tooth mechanism 120 includes a steel ring 121 arranged outside the aluminum alloy mother tube 200, a steel ball 122 arranged in the steel ring 121 and a threaded core head 123 built into the aluminum alloy mother tube 200. The steel ball 122 rotates and rolls around the aluminum alloy mother tube 200 driven by a high-speed motor, pressing the aluminum alloy mother tube 200 into the tooth groove of the threaded core head 123, so that a tooth body is generated inside the aluminum alloy mother tube 200. Then, the threaded core head 123 rotates in the opposite direction to the steel ball 122 under the action of the pulling force, so that the threaded core head 123 is separated from the formed tooth body, thereby forming a continuous tooth shape with a certain spiral angle in the inner cavity of the aluminum alloy mother tube 200. The aluminum alloy mother tube 200 after separation is further sized by a sizing die 130 to be formed into an internally threaded aluminum alloy tube that meets the size requirements.

[0060] Here, the tooth height, top angle and overall helix angle of the internally threaded aluminum alloy tube can be adaptively adjusted through the thread core head according to the specific application, and the speed of the high-speed motor is preferably 15,000∽50,000rpm to improve the tooth forming quality.

[0061] During the internal thread forming process, the high-speed rotation and rolling of the steel ball 122 on the surface of the aluminum alloy mother tube will generate heat acting on the surface of the aluminum alloy mother tube. At the same time, the deformation of the aluminum alloy mother tube itself will also generate heat, which causes the heat to act on the surface of the aluminum alloy mother tube, and simultaneously performs secondary penetration of the zinc layer on the surface of the aluminum alloy mother tube to improve the uniformity and penetration effect of the zinc layer.

[0062] Therefore, in the internal thread forming process, the aluminum alloy mother tube is formed into an internal thread aluminum alloy tube, and the heat generated in the forming process is used to act on the zinc layer, and the secondary penetration of the zinc layer is simultaneously achieved, thereby improving manufacturing efficiency and eliminating the need for additional heat treatment, thereby improving energy utilization and reducing manufacturing costs.

[0063] The next step is to perform finishing coiling on the internally threaded aluminum alloy tube. After the internally threaded aluminum alloy tube is straightened, cleaned on the outer surface, and inspected online, it is wound and cut into the required coils according to a regular pattern to reduce damage to the internally threaded aluminum alloy tube during transportation and storage, and to facilitate subsequent processing and use.

[0064] Next, the coiled internally threaded aluminum alloy tube is heat treated to achieve three penetrations of the zinc layer, thereby improving the penetration effect and increasing the thickness of the zinc diffusion layer.

[0065] During the heat treatment, the internally threaded aluminum alloy tube is firstly coiled and placed in an annealing heating furnace for heat treatment to promote the diffusion process inside the internally threaded aluminum alloy tube, thereby increasing the thickness of the zinc diffusion layer.

[0066] Specifically, during the arc zinc spraying and internal thread forming process, due to the fast cooling rate, the zinc layer may be incompletely fused or have microscopic holes, which will limit the increase in the thickness of the zinc diffusion layer. Through heat treatment, the diffusion between atoms can be reactivated under a lower stress state, which will promote the further fusion of the powder particles that are not fully fused, thereby increasing the overall thickness of the zinc layer.

[0067] Furthermore, heat treatment can also improve the mechanical properties of the internally threaded aluminum alloy tube. For example, through solution treatment and aging treatment (such as T6 heat treatment), high-density nano-scale strengthening phases such as MgZn2 and Al2Mg3Zn3 can be precipitated in the internally threaded aluminum alloy tube, and these strengthening phases can effectively improve the yield strength and hardness of the internally threaded aluminum alloy tube. In addition, heat treatment can also reduce the residual stress in the zinc layer and the internally threaded aluminum alloy tube, and transform the tensile stress into compressive stress, thereby improving the toughness and fatigue life of the internally threaded aluminum alloy tube.

[0068] In order to effectively increase the overall thickness of the zinc layer and improve the mechanical properties of the internally threaded aluminum alloy tube, the temperature of the annealing heating furnace is set to 450∽570℃, and the internally threaded aluminum alloy tube is heat treated for 30∽90 minutes, so that the zinc in the zinc layer further diffuses into the internally threaded aluminum alloy tube at high temperature, so that the thickness of the zinc layer on the surface of the internally threaded aluminum alloy tube after heat treatment reaches 150∽500μm, which effectively protects the internally threaded aluminum alloy tube and improves the corrosion resistance of the internally threaded aluminum alloy tube. At the same time, the mechanical properties of the internally threaded aluminum alloy tube reach the O state, so that the internally threaded aluminum alloy tube achieves the best strength and toughness combination.

[0069] Here, by adjusting the temperature or holding time of the annealing heating furnace, the mechanical properties of the internally threaded aluminum alloy tube can also be adjusted to meet the state requirements required for other specific applications.

[0070] Finally, the internal thread aluminum alloy tubes are packaged and stored for easy storage, and the zinc layer is not prone to failure.

[0071] Therefore, the internally threaded aluminum alloy tube with a corrosion-resistant zinc-diffused layer provided by the present invention processes the aluminum alloy mother tube through multiple processes, and accurately controls the specific implementation parameters of each process, so as to form the aluminum alloy mother tube into an internally threaded aluminum alloy tube, and at the same time, the zinc layer is penetrated three times during the manufacturing process to ensure the effective penetration of the zinc layer, improve the tightness of the combination of the zinc layer and the internally threaded aluminum alloy tube, make the zinc layer not easy to fall off, and at the same time, increase the thickness of the zinc layer, which can effectively protect the internally threaded aluminum alloy tube, improve the corrosion resistance and reliability of the internally threaded aluminum alloy tube, and extend the service life.

[0072] In order to specifically illustrate the technical effect of the present manufacturing method, in this example, the internal threaded aluminum alloy tube manufacturing method with a corrosion-resistant zinc-diffusion layer provided by the present invention and the traditional internal threaded aluminum alloy tube manufacturing method are used to process and form three types of internal threaded aluminum alloy tubes made of 3003 material, namely 7*0.50+0.18, 7*0.50+0.25, and 6.35*0.50+0.20.

[0073] For example, an internally threaded aluminum alloy tube with a specification of 7*0.50+0.18 refers to an internally threaded aluminum alloy tube with an outer diameter of 7 mm, a wall thickness of 0.50 mm, and a thread tooth height of 0.18 mm.

[0074] Furthermore, performance tests were conducted on the internally threaded aluminum alloy tubes formed by the present manufacturing method and the traditional manufacturing method to obtain the corresponding strengths of the internally threaded aluminum alloy tubes under different manufacturing methods.

[0075] Combination Figure 3 , which shows the comparison of performance test results of internally threaded aluminum alloy pipes.

[0076] As can be seen from the figure, the average tensile strength of the internally threaded aluminum alloy tube formed by the manufacturing method is 114.7MPa, the average yield strength is 71.7MPa, and the average elongation is 35.3%. Compared with the internally threaded aluminum alloy tube formed by the traditional manufacturing method, the tensile strength of the internally threaded aluminum alloy tube formed by the manufacturing method is increased by 4.3MPa, and the yield strength is increased by 6MPa. The higher tensile strength and yield strength can effectively improve the pressure resistance of the internally threaded aluminum alloy tube.

[0077] Furthermore, the internally threaded aluminum alloy tubes formed by the present manufacturing method and the traditional manufacturing method were subjected to SWAAT test. The SWAAT test simulates a salt spray test containing gases such as ammonia, which can reflect the corrosion resistance of the internally threaded aluminum alloy tubes, so as to obtain the corresponding corrosion resistance and service life of the internally threaded aluminum alloy tubes under different manufacturing methods.

[0078] Combination Figure 3 and Figure 4 , which shows the comparison of SWAAT test results of internally threaded aluminum alloy pipes.

[0079] As can be seen from the figure, the average failure days of the internally threaded aluminum alloy tube formed by the present manufacturing method is 44 days, which is much higher than the average failure days of 7.7 days of the internally threaded aluminum alloy tube formed by the traditional manufacturing method, and is about 6 times that of the traditional process. This fully demonstrates that the present manufacturing method can effectively improve the corrosion resistance and reliability of the internally threaded aluminum alloy tube and extend its service life.

[0080] Furthermore, the method for manufacturing an internally threaded aluminum alloy tube with a corrosion-resistant zinc-diffused layer provided by the present invention controls the gradient heating temperature and extrusion ratio of the hot extrusion process, the elongation coefficient and total deformation rate of the coil drawing process, the voltage, current, atomizing air pressure, and passing speed of the aluminum alloy mother tube in the arc zinc spraying process, and the heating temperature of the heat treatment within a certain parameter range, so that each process cooperates with each other, and the thickness of the zinc layer obtained by the manufacturing method of the present invention can reach 150∽500μm.

[0081] However, in the existing manufacturing method, each process does not control the processing parameters within the parameter range provided by the manufacturing method of the present invention during the specific processing and manufacturing process, so that the zinc layer obtained by the existing manufacturing method is thinner (<150μm) or thicker (>500μm).

[0082] Combination Figure 5 and Figure 6 , which shows the comparison of the strength and corrosion resistance test results of the zinc layer with a thickness of 150∽500μm obtained by the present manufacturing method and the zinc layer with a thickness of <150μm and a zinc layer with a thickness of >500μm obtained by the existing manufacturing method.

[0083] As can be seen from the figure, for the internally threaded aluminum alloy tube with a zinc layer thickness of <150 μm, the average corrosion failure days are 40 days, which is significantly lower than the average corrosion failure days of 44 days for the zinc layer with a thickness of 150∽500 μm obtained by this manufacturing method.

[0084] Furthermore, for the internally threaded aluminum alloy tube with a zinc layer thickness of >500μm, the average corrosion failure days is 43 days, which is slightly lower than the average corrosion failure days of 44 days for the zinc layer with a thickness of 150∽500μm obtained by the present manufacturing method; this is because when a thicker zinc layer is to be obtained, the aluminum alloy mother tube passes through at a slower speed, and the molten high-temperature zinc layer is exposed to the air for a long time to cool, which is prone to produce tiny pores and other defects, thereby affecting the overall corrosion resistance of the zinc layer.

[0085] Therefore, the manufacturing method controls the processing parameters of each process within a certain range, so that each process can cooperate with each other to obtain the optimal zinc layer with a thickness of 150∽500μm, effectively improving the overall strength and corrosion resistance of the internally threaded aluminum alloy tube.

[0086] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for manufacturing an internally threaded aluminum alloy tube having a corrosion-resistant zinc-plated layer, characterized in that: The manufacturing method comprises: The aluminum alloy billet is hot extruded and coiled to be formed into an aluminum alloy mother tube; The formed aluminum alloy mother tube is subjected to arc zinc spraying. First, the aluminum alloy mother tube is laid out, straightened, cleaned on the outer surface and dried online. Then, the zinc spraying device is evenly distributed around the aluminum alloy mother tube. The zinc wire in the zinc spraying device is melted by the arc generated by the zinc wire and the aluminum alloy mother tube. At the same time, the zinc spraying device sprays atomized air to spray the molten zinc wire onto the surface of the aluminum alloy mother tube to form a zinc layer on the surface of the aluminum alloy mother tube. The voltage of the zinc spraying is 25-30V, the current is 100-130A, the pressure of the atomized gas is 3-5bar, and the passing speed of the aluminum alloy mother tube is 200-250m / min. Then, the aluminum alloy mother tube after the arc zinc spraying is subjected to online annealing treatment to perform initial penetration of the zinc layer. The aluminum alloy mother tube after arc zinc spraying is subjected to internal thread forming, and the aluminum alloy mother tube is reduced in diameter and deformed by an internal thread forming mechanism to form an internal thread aluminum alloy tube. During the forming process, the heat generated by the operation of the internal thread forming mechanism and the deformation of the aluminum alloy mother tube acts on the zinc layer, and the zinc layer is simultaneously penetrated for a second time; After the internal thread aluminum alloy tube is finished and coiled, it is heat treated and the zinc layer is infiltrated three times.

2. The method for manufacturing an internally threaded aluminum alloy tube having a corrosion-resistant zinc-plated layer according to claim 1, characterized in that: In the hot extrusion process, the aluminum alloy mother tube is gradient heated to 400∽450℃ or 430∽470℃, and then extruded through a die with an extrusion ratio of ≥150. The extruded aluminum alloy mother tube is cooled in a water tank.

3. The method for manufacturing an internally threaded aluminum alloy tube having a corrosion-resistant zinc-plated layer according to claim 1, characterized in that: In the coiling process, when the aluminum alloy mother tube is stretched, the stretching passes are adapted to the size of the aluminum alloy mother tube, and the elongation coefficient of each pass is 1.1∽1.8, and the total deformation rate of the stretching is configured to be 35%∽85%.

4. The method for manufacturing an internally threaded aluminum alloy tube having a corrosion-resistant zinc-plated layer according to claim 1, characterized in that: The zinc spraying device is configured with three arc zinc spraying guns evenly distributed around the aluminum alloy mother pipe at an angle of 120 degrees.

5. The method for manufacturing an internally threaded aluminum alloy tube having a corrosion-resistant zinc-plated layer according to claim 1, characterized in that: In the internal thread forming process, the internal thread forming mechanism includes a diameter reducing mechanism and a spinning gear mechanism. The diameter of the aluminum alloy mother tube is first reduced by the diameter reducing mechanism, and then the surface of the aluminum alloy mother tube is rotated and rolled by the spinning gear mechanism to press the aluminum alloy mother tube into the tooth groove of the thread core head, so that the aluminum alloy mother tube is deformed and formed into an internally threaded aluminum alloy tube, and the heat generated by the rotation of the spinning gear mechanism and the deformation of the aluminum alloy mother tube is simultaneously applied to the zinc layer.

6. The method for manufacturing an internally threaded aluminum alloy tube having a corrosion-resistant zinc-plated layer according to claim 5, characterized in that: The diameter reducing mechanism includes an external mold arranged outside the aluminum alloy mother tube and a movable core head built into the aluminum alloy mother tube. The spinning gear mechanism includes a steel ring arranged outside the aluminum alloy mother tube, a steel ball arranged in the steel ring and a threaded core head built into the aluminum alloy mother tube. The steel ball and the threaded core head rotate in opposite directions.

7. The method for manufacturing an internally threaded aluminum alloy tube having a corrosion-resistant zinc-plated layer according to claim 1, characterized in that: In the heat treatment process, the internally threaded aluminum alloy pipe is placed in an annealing heating furnace, the temperature of the annealing heating furnace is set to 450-570°C, and the internally threaded aluminum alloy pipe is heat treated for 30-90 minutes to apply heat to the zinc layer.

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