Friction plug welding stopper rod based on friction stir additive and preparation method and application thereof

Abstract

The invention discloses a friction plug welding stopper rod based on friction stir additive and a preparation method and application thereof.The friction plug welding stopper rod comprises a connecting section, a transition section and a welding section, the connecting section, the transition section and the welding section are sequentially connected, and the friction plug welding stopper rod is manufactured through a friction stir additive manufacturing method; the connecting section, the transition section and the welding section are respectively formed by a substrate used in the friction stir additive manufacturing method, the formed multi-layer composite material deposition layer and the formed multi-layer aluminum alloy deposition layer. The base plate, the multiple composite material deposition layers and the multiple aluminum alloy deposition layers can be in metallurgical bonding in sequence from bottom to top to form a deposition component, and after solid solution-aging composite heat treatment is conducted on the deposition component, the friction plug welding stopper rod is obtained through machining. According to the method, the structure of the friction plug welding stopper rod can be strengthened, so that the friction plug welding stopper rod has higher strength and heat stability in a geometric mutation area, and the fracture resistance and fatigue resistance are remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of friction plug welding technology, specifically relating to a method for preparing friction plug welding plug rods based on friction stir additive manufacturing. Background Technology

[0002] As a core pressure-bearing component of a liquid propulsion system, the rocket propellant tank plays a crucial role in storing cryogenic propellants such as liquid oxygen and liquid hydrogen. Its structural integrity and sealing performance directly affect the safety and reliable operation of the spacecraft. To simultaneously achieve lightweight and high strength requirements, the main body of the tank is mostly made of aluminum alloy, and welding processes are used to assemble complex structural components such as the cylinder section, end caps, and connecting rings. Currently, electron beam welding, friction stir welding, and tungsten inert gas welding have become the main technical means for manufacturing aluminum alloy propellant tanks.

[0003] However, in actual manufacturing processes, due to factors such as the high thermal conductivity and narrow thermoplastic range of aluminum alloys, as well as the complex geometry of the propellant tank, typical defects such as incomplete welding, porosity, and cracks are still prone to form in the welded joints. The presence of these defects weakens the mechanical load-bearing capacity of the joints, damages sealing performance, and in severe cases, even affects the service safety of the entire tank. Therefore, efficient repair of welding defects has become a key technical requirement in the manufacturing and maintenance of rocket propellant tanks.

[0004] Pull-out friction plug repair welding technology is a solid-state welding process with advantages such as low heat input, dense joint structure, and minimal post-weld deformation. It is particularly suitable for local repair of thin-walled, high-precision structures such as aluminum alloy tanks. The basic principle of this method is: after removing local defects through machining, a plug hole is formed in the plate wall. Then, a rotatable metal plug rod is used to achieve dense filling and metallurgical bonding of the hole under the combined action of pull-out force and frictional heat.

[0005] However, when aluminum alloys are welded under conditions of high thermal conductivity and high load, the welding process places extremely high demands on the thermo-mechanical properties of the stopper rods used. To obtain sufficient plasticizing zone temperature and fluidity, friction plug welding requires high rotational speeds (typically exceeding 7000 rpm) and large axial forces (exceeding 30 kN). This subjects the stopper rod to intense torque and tensile stress during welding. Currently, commonly used stopper rods are mostly machined from a single aluminum alloy bar, making it difficult to balance strength and toughness under the coupled high stress and high temperature environment. This fails to meet the high-reliability welding repair requirements of aluminum alloy rocket propellant tanks under severe welding conditions. The stopper rod is also highly susceptible to fracture in areas of abrupt geometric changes. Figure 1 As shown, traditionally machined plug bars have a connecting section, a transition section, and a welding section. The transition section is the area where the plug bar's geometry changes abruptly, and it is prone to fracture during the welding process. This problem has become a key bottleneck restricting the improvement of the reliability of friction plug welding technology. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this invention is to provide a friction plug welding rod based on friction stir additive manufacturing.

[0007] Another object of the present invention is to provide a method for preparing the above-mentioned friction plug welding rod based on friction stir additive manufacturing;

[0008] Another object of the present invention is to provide the use of the above-mentioned friction plug welding rod based on friction stir additive manufacturing in friction plug welding.

[0009] The objective of this invention is achieved through the following technical solutions.

[0010] A friction plug welding rod based on friction stir additive manufacturing includes: a connecting section, a transition section, and a welding section, which are connected sequentially. The friction plug welding rod is manufactured by a friction stir additive manufacturing method. The connecting section is formed by a substrate used in the friction stir additive manufacturing method, the transition section is formed by a multilayer composite material deposition layer formed in the friction stir additive manufacturing method, and the welding section is formed by a multilayer aluminum alloy deposition layer formed in the friction stir additive manufacturing method.

[0011] The substrate has the same composition as the workpiece to be soldered;

[0012] The material of the rod used in the friction stir additive manufacturing method for forming the composite material deposition layer is aluminum-based composite material rod;

[0013] The composition of the bar stock used in the friction stir additive manufacturing method for forming the aluminum alloy deposit layer is the same as that of the workpiece to be welded;

[0014] In the above technical solution, the parameters of the friction stir additive manufacturing method for forming the composite material deposition layer are: the shoulder rotation speed is 400-500 rpm, the stirring head travel speed is 300-500 mm / min, the axial force is 40-50 kN, and the single-layer deposition thickness of the composite material deposition layer is 1-1.5 mm.

[0015] In the above technical solution, the parameters of the friction stir additive manufacturing method for forming the aluminum alloy deposit layer are: the shoulder rotation speed is 200-400 rpm, the stirring head travel speed is 200-300 mm / min, the axial force is 20-30 kN, and the single-layer deposition thickness of the aluminum alloy deposit layer is 1-1.5 mm.

[0016] In the above technical solution, the thickness of the substrate is 90-100 mm.

[0017] In the above technical solution, the length of the transition section is 40-50 mm, and the length of the welding section is 40-50 mm.

[0018] The above-mentioned method for preparing friction plug welding rods based on friction stir additive manufacturing includes the following steps:

[0019] Step 1: Perform friction stir additive deposition on the substrate surface to form an M-layer composite material deposition layer;

[0020] Step 2: Stir-friction additive deposition is performed on the surface of the composite material deposition layer to form an N-layer aluminum alloy deposition layer. The substrate, the M-layer composite material deposition layer and the N-layer aluminum alloy deposition layer are metallurgically bonded from bottom to top to form a deposition component.

[0021] Step 3: Perform a solution-aging composite heat treatment on the deposited component;

[0022] In step 3, the solution-aging composite heat treatment includes: solution treatment at 500-535°C for 1 hour, followed by water cooling to room temperature, and then aging heat treatment at 160-170°C for 24-26 hours.

[0023] Step 4: Process the deposited component into a friction plug welding rod with the target geometry.

[0024] In step 4, the machining method is CNC turning or milling.

[0025] Application of friction plug welding stoppers based on friction stir additive manufacturing in friction plug welding.

[0026] The beneficial effects of this invention are as follows:

[0027] 1. Compared with existing friction plug welding rods produced by integral bar turning, this invention uses friction stir additive manufacturing technology to sequentially deposit a composite material deposition layer and an aluminum alloy deposition layer on a substrate, forming a gradient structure with a gradually decreasing cross-sectional diameter from the welding section to the transition section. This achieves structural strengthening of the friction plug welding rod while giving it higher strength and thermal stability in the geometric change region. It can effectively withstand stress concentration caused by high rotation speed and large axial tensile force during welding. The multi-layer metallurgical bonding interface formed by the additive manufacturing process has a dense structure and fine grains, which significantly improves the comprehensive mechanical properties of the friction plug welding rod.

[0028] 2. In this invention, the deposited components formed by the substrate, composite material deposited layer and aluminum alloy deposited layer are subjected to solution-aging composite heat treatment before being processed into friction plug weld rods. The solution-aging composite heat treatment operation can eliminate the residual stress inside the deposited components, further improve the hardness and tensile strength of the formed friction plug weld rods, effectively release the internal residual stress, and make the overall structure more stable.

[0029] 3. The friction plug welding rod prepared by this invention exhibits excellent fracture resistance and fatigue performance during friction plug welding, significantly reducing the welding failure rate and improving the forming quality and reliability of the welded joint. The preparation method offers high process controllability and a wide range of material adaptability, allowing for flexible adjustment of the thickness and composition of the composite material deposition layer and the aluminum alloy deposition layer according to different welding requirements, thus achieving personalized friction plug welding rod design. This invention provides an efficient and reliable solution for defect repair of large thin-walled aluminum alloy structures such as rocket propellant tanks, and has broad engineering application prospects. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the stopper rod structure;

[0031] Figure 2 This is a schematic flowchart of the method for preparing the friction plug welding rod based on friction stir additive manufacturing according to the present invention.

[0032] Figure 3 (a) is a schematic diagram of the dimensions of the friction plug welded plug prepared by the friction stir additive manufacturing method of Example 4 of the present invention and the turning plug prepared by the turning machining method of Comparative Example 1. Figure 3 (b) is a schematic diagram of the stopper rod structure;

[0033] Figure 4 (a) is a comparison diagram of the tensile strength of the friction-welded plug rod and the machined plug rod; (b) is a comparison diagram of the hardness of the friction-welded plug rod and the machined plug rod; (c) is a schematic diagram of the microstructure of the interface between the composite material deposit layer and the matrix in the friction-welded plug rod; and (d) is a schematic diagram of the microstructure of the interface between the composite material deposit layer and the aluminum alloy deposit layer in the friction-welded plug rod.

[0034] Figure 5 This is a photograph of the joint after the friction plug welding rod and the aluminum alloy plate are welded in Example 4.

[0035] Figure 6 A photograph of the transition section fracture during a pull-out friction plug welding test of the machined plug rod in Comparative Example 1. Detailed Implementation

[0036] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0037] Example 1

[0038] A friction plug welding rod based on friction stir additive manufacturing includes: a connecting section, a transition section, and a welding section, which are connected sequentially (one end of the connecting section is connected to one end of the transition section, and the other end of the transition section is connected to one end of the welding section; the welding section includes a tapered section whose cross-sectional diameter gradually decreases from the welding section towards the connecting section). The friction plug welding rod is manufactured by a friction stir additive manufacturing method, wherein the connecting section is formed from a substrate used in the friction stir additive manufacturing method, the transition section is formed from a multilayer composite material deposition layer formed in the friction stir additive manufacturing method, and the welding section is formed from a multilayer aluminum alloy deposition layer formed in the friction stir additive manufacturing method.

[0039] The composition of the substrate is the same as that of the workpiece to be welded. In this embodiment, the workpiece to be welded is a rocket propellant tank, and the material of the rocket propellant tank is a high-strength aluminum alloy, such as 2219-T87 aluminum alloy or 6061-T6 aluminum alloy.

[0040] The material of the rod used in the friction stir additive manufacturing method for forming the composite material deposition layer is aluminum-based composite material rod. Using aluminum-based composite material rod to prepare the transition section can effectively improve the fracture resistance of the friction plug welding rod under high load conditions. The material of the aluminum-based composite material rod can be, for example, silicon carbide (SiC) reinforced aluminum-based composite material, alumina (Al2O3) reinforced aluminum-based composite material, titanium diboride (TiB2) reinforced aluminum-based composite material, boron carbide (B4C) reinforced aluminum-based composite material, aluminum nitride (AlN) reinforced aluminum-based composite material, etc.

[0041] The composition of the bar stock used in the friction stir additive manufacturing method for forming the aluminum alloy deposit layer is the same as that of the workpiece to be welded;

[0042] In the above technical solution, the parameters of the friction stir additive manufacturing method for forming the composite material deposition layer are: the shoulder rotation speed is 400-500 rpm, the stirring head travel speed is 300-500 mm / min, the axial force is 40-50 kN, and the single-layer deposition thickness of the composite material deposition layer is 1-1.5 mm.

[0043] In the above technical solution, the parameters of the friction stir additive manufacturing method for forming the aluminum alloy deposit layer are: the shoulder rotation speed is 200-400 rpm, the stirring head travel speed is 200-300 mm / min, the axial force is 20-30 kN, and the single-layer deposition thickness of the aluminum alloy deposit layer is 1-1.5 mm.

[0044] In the above technical solution, the thickness of the substrate is 90-100 mm.

[0045] In the above technical solution, the length of the transition section is 40-50mm, and the length of the welding section is 40-50mm.

[0046] Example 2

[0047] A method for preparing friction plug welding rods based on friction stir additive manufacturing, such as... Figure 2 As shown, it includes the following steps:

[0048] Step 1, place the substrate (i.e. Figure 2 A medium-aluminum alloy substrate is fixed on the worktable. The friction stir additive manufacturing device is started to perform friction stir additive deposition on the substrate surface (the upper surface of the substrate needs to be polished and cleaned before friction stir additive deposition; keeping the surface clean and flat ensures the bonding quality with the composite material deposition layer), to form the M-layer composite material deposition layer (i.e., Figure 2 The composite material has a uniform structure and fine particle distribution, which can significantly improve the load-bearing capacity of the transition section of the stopper rod. Preferably, the parameters of the friction stir additive manufacturing method for forming the composite material deposition layer are: shoulder rotation speed of 400 rpm, stirring head travel speed of 400 mm / min, axial force of 45 kN, single-layer deposition thickness of the composite material deposition layer of 1.1 mm, and the rod material used is aluminum-based composite material rod (brand and model: ZL101-20%SiC).

[0049] Step 2: Continue friction stir additive deposition on the surface of the composite material deposit to form an N-layer aluminum alloy deposit (i.e., Figure 2 The parameters of the friction stir additive manufacturing method for forming the aluminum alloy deposition layer are as follows: the shoulder rotation speed is 300 rpm, the stirring head travel speed is 200 mm / min, the axial force is 20 kN, the single-layer deposition thickness of the aluminum alloy deposition layer is 1.3 mm, the rod material used is aluminum alloy rod (brand model 2219-T6), and the substrate, the M-layer composite material deposition layer and the N-layer aluminum alloy deposition layer are metallurgically bonded from bottom to top to form the deposition component;

[0050] Step 3: Perform a solution-aging composite heat treatment on the deposited component to eliminate residual stress and improve overall hardness. The solution-aging composite heat treatment includes: solution treatment at 500-535°C for 1 hour followed by rapid water cooling to room temperature, and then aging heat treatment at 160-170°C for 24-26 hours.

[0051] Step 4: Machining the deposited component into a friction plug welding rod of the target geometry. The machining method is CNC turning or milling or other mechanical machining methods.

[0052] In this embodiment, to ensure the quality of interlayer bonding, before each layer is deposited in the friction stir additive deposition process, the surface of the layer to be deposited needs to be lightly mechanically removed to remove the oxide film on the surface to be deposited and improve the interlayer metallurgical bonding.

[0053] Example 3

[0054] A method for preparing a friction plug welding rod based on friction stir additive manufacturing, in addition to Example 2, uses 2219-T87 aluminum alloy for both the rocket propellant tank and the substrate. The solution-aging composite heat treatment includes: solution treatment at 520°C for 1 hour followed by rapid water cooling to room temperature, and then aging heat treatment at 165°C for 24 hours.

[0055] Example 4

[0056] A method for preparing a friction plug weld rod based on friction stir additive manufacturing, building upon Example 3, involves machining the friction plug weld rod. The process is as follows: The deposited component is clamped and positioned; the tool movement coordinates corresponding to the target geometry of the friction plug weld rod are input to the lathe control system; and then, the friction plug weld rod is obtained after roughing and finishing turning. The roughing turning parameters are as follows: rotation speed 800 rpm, depth of cut 4 mm, feed rate 0.2 mm / r; the finishing turning parameters are as follows: rotation speed 1000 rpm, depth of cut 0.2 mm, feed rate 0.06 mm / r. The final friction plug weld rod has a surface roughness <1.6. .

[0057] Comparative Example 1

[0058] A method for machining a stopper rod is basically the same as the method for preparing a friction-welded stopper rod based on friction stir additive manufacturing described in Example 4. The only difference is that an aluminum alloy cylindrical part is used for machining to obtain the machined stopper rod. The aluminum alloy cylindrical part is a cylinder with a diameter of 80 mm and a height of 200 mm. The material of the aluminum alloy cylindrical part is 2219-T6 aluminum alloy.

[0059] In the invention, the specific structure of the stopper rod is not limited. The stopper rod can also be the same as that in the literature "Zhao Huihui, Gao Han, Hu Lan, et al. Pull-out friction plug welding process and mechanical property optimization of 2219 aluminum alloy thin plate [J]. Welding, 2021(6):48-55". Figure 1 Middle stopper rod structure.

[0060] In this embodiment, friction-welded plugs and machined plugs are prepared based on the friction stir additive manufacturing method described in Example 4 and the machining method described in Comparative Example 1, respectively. The dimensions of the friction-welded plugs and the machined plugs are as follows: Figure 3 As shown in (a) (the length of the transition section is 40 mm, and the length of the welded section is 47.5 mm), the three-dimensional structural schematic diagram is as follows. Figure 3 As shown in (b), the mechanical properties of the friction-welded stopper rod and the machined stopper rod were tested respectively, and the test results are as follows. Figure 4 (a) and Figure 4 As shown in (b), the tensile strength of the friction-welded plug prepared in Example 4 is about 15% higher than that of the machined plug prepared in Comparative Example 1, and the microhardness ( Figure 4 The hardness of (b) increases by approximately 15% to 25%.

[0061] like Figure 4 (c) and Figure 4 As shown in (d), the deposited component prepared by the friction plug welding rod preparation method based on friction stir additive manufacturing in Example 4 of the present invention has a composite material deposited layer and a substrate (i.e., Figure 4 In (c), a defect-free metallurgical bond was formed between the aluminum alloy matrix and the aluminum alloy deposited layer, as well as between the aluminum alloy deposited layer and the composite material deposited layer (i.e., the aluminum alloy deposited layer). Figure 4 (d) deposited aluminum alloy).

[0062] A 10mm thick 2219-T87 aluminum alloy plate was used as the workpiece to be welded. A 44mm diameter plug hole was formed on the workpiece. Pull-out friction plug welding tests were conducted on the friction plug welding rod prepared in Example 4 and the machined plug rod prepared in Comparative Example 1, respectively. The connecting section of the plug rod (i.e., the friction plug welding rod or the machined plug rod) was passed through the plug hole, such that the welded section of the plug rod was located on one side of the 2219-T87 aluminum alloy plate, and the connecting section of the plug rod was located on the other side of the 2219-T87 aluminum alloy plate and connected to the tool holder (if the workpiece to be welded is a rocket propellant tank, then the welded section of the plug rod is located on the other side of the 2219-T87 aluminum alloy plate). Inside the rocket propellant tank, the connecting section of the stopper rod is located outside the rocket propellant tank. The tool holder is fixed coaxially with the main shaft of the friction plug welding machine. The main shaft of the friction plug welding machine drives the stopper rod to rotate at high speed at 7000 rpm. The friction plug welding machine pulls the stopper rod away from the 2219-T87 aluminum alloy plate to complete the axial feed (50kN axial force). The axial feed amount is 11mm, which causes frictional heat to be generated at the interface between the stopper rod and the plug hole to the thermoplastic state of the metal. After the feed is in place, the main shaft of the friction plug welding machine stops rotating and applies a forging force of 50kN for 5s. The forging time is 5s. The flash is extruded through the pulling action to promote the metallurgical bonding of the interface.

[0063] The friction plug welding rod prepared in Example 4 exhibited stable welding process with no torque fluctuations or rod breakage. A photograph of the completed friction plug welding is shown below. Figure 5 As shown in the figure, the friction-welded plug prepared in Example 4, after being welded to the aluminum alloy plate, exhibits a complete joint formation without any incomplete welds or cracks, significantly improving the welding success rate. In contrast, the machined plug in Comparative Example 1 fractured during the transition section of the friction-welded process. Figure 6 As shown.

[0064] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. A friction plug welding rod based on friction stir additive manufacturing, comprising: The connecting section, transition section and welding section are connected in sequence. The characteristic is that the friction plug welding rod is manufactured by the friction stir additive manufacturing method. The connecting section is formed by a substrate used in the friction stir additive manufacturing method, the transition section is formed by a multilayer composite material deposition layer formed in the friction stir additive manufacturing method, and the welding section is formed by a multilayer aluminum alloy deposition layer formed in the friction stir additive manufacturing method. The substrate has the same composition as the workpiece to be soldered; The material of the rod used in the friction stir additive manufacturing method for forming the composite material deposition layer is aluminum-based composite material rod; The composition of the bar stock used in the friction stir additive manufacturing method for forming the aluminum alloy deposit layer is the same as that of the workpiece to be welded.

2. The friction plug welding rod according to claim 1, characterized in that, The parameters for the friction stir additive manufacturing method for forming composite material deposits are: shoulder rotation speed of 400–500 rpm, stirring head travel speed of 300–500 mm / min, axial force of 40–50 kN, and single-layer deposition thickness of the composite material deposits of 1–1.5 mm.

3. The friction plug welding rod according to claim 1, characterized in that, The parameters for the friction stir additive manufacturing method for forming aluminum alloy deposits are: shoulder rotation speed of 200–400 rpm, stirring head travel speed of 200–300 mm / min, axial force of 20–30 kN, and single-layer deposition thickness of aluminum alloy deposits of 1–1.5 mm.

4. The friction plug welding rod according to claim 1, characterized in that, The thickness of the substrate is 90–100 mm.

5. The friction plug welding rod according to claim 1, characterized in that, The length of the transition section is 40–50 mm, and the length of the welding section is 40–50 mm.

6. A method for preparing a friction plug welding rod based on friction stir additive manufacturing, characterized in that, Includes the following steps: Step 1: Perform friction stir additive deposition on the substrate surface to form an M-layer composite material deposition layer; Step 2: Stir-friction additive deposition is performed on the surface of the composite material deposition layer to form an N-layer aluminum alloy deposition layer. The substrate, the M-layer composite material deposition layer and the N-layer aluminum alloy deposition layer are metallurgically bonded from bottom to top to form a deposition component. Step 3: Perform a solution-aging composite heat treatment on the deposited component; Step 4: Process the deposited component into a friction plug welding rod with the target geometry.

7. The method for preparing a friction plug welding rod according to claim 6, characterized in that, In step 3, the solution-aging composite heat treatment includes: solution treatment at 500-535°C for 1 hour followed by water cooling to room temperature, and aging heat treatment at 160-170°C for 24-26 hours.

8. The method for preparing a friction plug welding rod according to claim 6, characterized in that, In step 4, the machining method is CNC turning or milling.

9. The use of the friction plug welding rod as described in claim 1 in friction plug welding.

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