Composite connecting method of thick plate titanium alloy, thick plate titanium alloy structural member

Abstract

The application provides a thick plate titanium alloy composite connection method, and belongs to the technical field of metal material welding and additive manufacturing. The technical scheme of the application comprises the following steps: processing symmetric X-shaped grooves on thick plate titanium alloy workpieces to be connected; using a laser-arc composite welding system to perform double-sided backing welding on the X-shaped grooves to form double-sided backing welds; and using a powder feeding type laser cladding system to perform multi-layer and multi-pass additive filling in the X-shaped grooves above the double-sided backing welds. The application separates the efficient laser-arc composite backing from the low heat input laser cladding additive filling, first ensures high-quality root penetration, then significantly reduces welding deformation and residual stress through low heat input filling, and optimizes the microstructure of the filling area, so as to obtain a welded joint with excellent comprehensive performance.

Description

Technical Field

[0001] This invention relates to the field of advanced manufacturing technology for metallic materials, specifically to a composite connection method for thick plate titanium alloys and a thick plate titanium alloy structural component. Background Technology

[0002] With the trend towards lightweight and high-strength structural materials, the application of titanium alloys in aerospace manufacturing has rapidly developed. High-performance titanium alloys have become indispensable structural materials in aircraft and engines. The high thrust-to-weight ratio and high reliability of modern aircraft have created a demand for large, integral titanium alloy components. Rivets and bolts are often used instead of assemblies for these components, resulting in lightweight, high-reliability, and short-life components. As difficult-to-deform titanium alloy components become larger, traditional forging processes are insufficient for direct forming. Efficient joining of high-quality titanium alloy components relies on advanced joining technologies, including narrow-gap tungsten inert gas welding, vacuum electron beam welding, laser welding, and linear friction welding. The welding quality of titanium alloy forgings thicker than 50mm directly determines the structural safety and service reliability of core equipment. However, the welding process for these forgings faces two major technological challenges that urgently need to be overcome. These two challenges are interconnected and have a cumulative effect, further increasing the difficulty of implementing the welding process.

[0003] Titanium alloys possess extremely high chemical reactivity, a characteristic amplified dramatically, especially under high-temperature welding conditions. When heated to above 600°C, titanium alloys rapidly undergo violent chemical reactions with gaseous elements such as oxygen, nitrogen, and hydrogen in the air: combination with oxygen forms highly hard titanium oxide inclusions, disrupting the continuity of the weld metal; the reaction with nitrogen produces titanium nitride, significantly increasing weld brittleness and reducing impact toughness and fatigue performance; hydrogen intrusion leads to hydrogen embrittlement, making the weld prone to microcracks under stress, and in severe cases, causing weld fracture failure. More critically, for forgings thicker than 50mm, the weld pool depth is greater and the high-temperature residence time is longer during welding, significantly increasing the area and time of contact between the molten metal and air. The risk of gaseous element intrusion is far higher than for thin-walled titanium alloy components. Inadequate protection can easily lead to a severe degradation of weld performance, failing to meet the service requirements of high-end equipment.

[0004] The unique physical properties of titanium alloys lead to welding deformation and heat-affected zone (HAZ) quality issues. The thermal conductivity of titanium alloys is only about one-fifth that of low-carbon steel. During welding, the large amount of heat input is difficult to conduct and diffuse quickly, easily leading to localized high-temperature concentrations in the weld and surrounding areas. While its coefficient of linear expansion is slightly lower than that of steel, the large thickness and high rigidity of forgings mean that the thermal expansion and contraction effects caused by the high heat input during welding are constrained by the component itself, resulting in significant welding deformation and residual stress. This residual stress not only reduces the load-bearing capacity of the welded joint but may also induce cracks during subsequent processing or service. Furthermore, the high-temperature concentration areas form coarse-grained HAZs. These HAZs exhibit significantly lower plasticity and toughness than the base metal, becoming weak points in the welded joint. This is especially true for forgings thicker than 50 mm, where the welding heat input is typically higher, the HAZ is wider, and grain growth is more pronounced, severely impacting the overall performance of the welded joint. Summary of the Invention

[0005] In view of the deficiencies in the prior art, the purpose of this invention is to provide a composite connection method for thick plate titanium alloys and a thick plate titanium alloy structural component.

[0006] A composite joining method for thick plate titanium alloys according to the present invention includes the following steps:

[0007] An X-shaped bevel is machined at the joint of the thick titanium alloy workpieces to be joined.

[0008] A laser-arc hybrid welding system was used to perform double-sided root pass welding on the X-shaped groove to form a double-sided root pass weld. This results in a root pass weld with full penetration and a well-formed back side, providing a geometrically precise, thinner, and cleaner "base" for subsequent additive filling. Compared to the potential for incomplete penetration, undercut, or spatter in traditional arc welding, the smooth surface formed by laser-arc welding significantly improves the wetting and spreading properties of the first layer of cladding powder, reducing the risk of incomplete fusion. Simultaneously, the double-sided root pass process generates a uniform preheating and slow cooling effect on the base material. This "pre-tempering" effect not only optimizes the microstructure but also partially releases restraint stress. When subsequent low-heat-input laser cladding is performed, the stress caused by the thermal expansion and contraction of the cladding layer acts on a base material already in a better thermomechanical state, thereby inhibiting the propagation of welding deformation to the overall component.

[0009] A powder-feed laser cladding system is used to perform multi-layer, multi-pass additive filling within the X-shaped groove above the double-sided root pass weld. During the powder-feed laser cladding filling stage, precise matching of energy density and powder feed rate ensures the powder fully melts and forms a good metallurgical bond with the groove sidewall and the previous metal layer. Simultaneously, high-purity inert gas is used for continuous protection to prevent high-temperature oxidation of the titanium alloy. Leveraging the inherent advantage of low heat input in laser cladding, an intermittent, skip-scanning strategy avoids localized overheating and strictly controls heat accumulation, keeping the interpass temperature below the critical value of 150℃. For the X-shaped groove, a symmetrical, alternating, and staggered multi-layer, multi-pass filling strategy is employed, filling simultaneously from both sides of the bottom of the groove upwards while staggering the start and end positions of each pass. This homogenizes heat distribution, balances welding stress, and ultimately achieves efficient, low-stress, and defect-free additive filling of large, thick sections.

[0010] Furthermore, the double-sided root pass welding step includes:

[0011] The first root pass welding is performed on one side of the X-shaped bevel to form the first root pass weld.

[0012] The back side of the first root pass weld is cleaned; and

[0013] A second root pass is performed on the other side of the X-shaped bevel, thereby forming the double-sided root pass weld together with the first root pass weld.

[0014] Furthermore, after processing the X-shaped bevel, the process also includes cleaning the X-shaped bevel and its surrounding area to remove oil, oxide layer and impurities, and wiping with acetone or alcohol.

[0015] Furthermore, before performing the first root pass welding, the process also includes assembling the thick titanium alloy workpieces to be joined into the welding fixture, with a butt gap of no more than 0.5 mm.

[0016] Furthermore, the laser-arc hybrid welding system has a laser power of 2~4kW, an arc current of 180~250A, a voltage of 20~28V, uses argon as the shielding gas with a flow rate of 20~30L / min, and the welding wire material is matched with the material of the thick plate titanium alloy workpiece.

[0017] Furthermore, the bevel angle of the X-shaped bevel is 55 to 65 degrees, and a blunt edge with a thickness of 2 mm to 3 mm is retained at the root of the X-shaped bevel.

[0018] Furthermore, in the multi-layer, multi-pass additive filling process, the thickness of each layer is 1~2mm, and the interlayer temperature is not higher than 150℃;

[0019] Repeat filling until the X-shaped bevel is completely filled, with the cladding surface of the last layer being 0.5~1mm higher than the surface of the thick titanium alloy workpiece.

[0020] Furthermore, after completing the multi-layer, multi-pass additive filling, the connected thick plate titanium alloy workpiece is subjected to stress-relief annealing treatment. The stress-relief annealing treatment includes heating to 600°C to 700°C under argon protection, holding at that temperature for 1 hour to 2 hours, and then cooling in the furnace.

[0021] Furthermore, it also includes using machining to grind the weld seam excess height until it is flush with the thick titanium alloy workpiece.

[0022] According to the present invention, a thick plate titanium alloy structural component is provided, which adopts the composite connection method described above.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] This application employs a two-step process that separates "laser-arc composite root pass" and "laser cladding additive filler," breaking away from the traditional thick plate welding approach of "completing all processes in one step" and relying on a single heat source and filler metal for connection, which is "path-dependent." First, the deep-penetrating capability of the laser-arc composite heat source and the arc-stabilizing effect of the electric arc ensure high-quality penetration at the root of the thick plate. Then, laser cladding with extremely low heat input is used for filling, effectively avoiding the huge heat input associated with traditional one-time filling methods. This significantly reduces overall welding deformation and residual stress, resolving the contradiction between root quality and efficient, low-deformation filling.

[0025] Laser cladding is an additive manufacturing process with high energy density and fast cooling rate, which can form fine crystalline structures and effectively inhibit grain growth in the heat-affected zone. At the same time, by precisely controlling the interlayer temperature and layer-by-layer deposition, the joint quality is improved at three scales: macroscopic (controlling deformation), mesoscopic (optimizing molten pool flow and bonding), and microscopic (refining grains and regulating phase composition), thus obtaining a high-performance welded joint.

[0026] Whether it's the initial welding or additive filler, the entire process is carried out under inert gas protection, which effectively isolates the high-temperature molten pool from air, preventing oxidation and gas absorption of the titanium alloy from the source, ensuring the chemical purity of the weld, and avoiding performance degradation caused by contamination. Attached Figure Description

[0027] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0028] Figure 1 This is a schematic diagram of the overall cross-section of the welded joint provided in an embodiment of this application;

[0029] Figure 2This is a schematic diagram of the micro-region division of the welded joint provided in the embodiments of this application;

[0030] Figure 3 This is a schematic diagram illustrating the principle of the laser-arc hybrid welding process provided in the embodiments of this application;

[0031] Figure 4 This is a schematic diagram illustrating the principle of the coaxial powder feeding laser cladding process provided in an embodiment of this application.

[0032] Figure 5 This is a schematic flowchart illustrating a thick plate titanium alloy composite connection method provided in an embodiment of this application.

[0033] The main reference numerals in the attached drawings are explained as follows: 10-Base material area; 20-Welding area; 21-Laser-arc hybrid welding area; 22-Laser cladding filling area; 23-Heat-affected zone; 24-Fusion zone; 31-Laser beam; 32-Arc welding torch; 33-Molten pool; 34-Molten droplet; 35-Keyhole; 36-Shielding gas; 41-Coaxial powder feeding cladding head; 43-Powder flow; 45-Clad layer; 46-Powder feeding gas. Detailed Implementation

[0034] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0035] Example 1

[0036] This application provides a method for composite joining of thick titanium alloy plates. Please refer to... Figure 5 This is a complete flowchart illustrating a method for composite joining of thick titanium alloy plates provided in this application. Specifically, the method includes steps such as beveling preparation (S100), front-side root pass welding (S200), weld back-side root cleaning (S300), back-side root pass welding (S400), laser cladding filler (S500), stress-relief annealing (S600), and post-processing and inspection (S700). By combining high-efficiency laser-arc composite root pass welding with low-heat-input powder-feeding laser cladding additive filler, this method achieves high-quality, low-deformation joining of thick titanium alloy plates.

[0037] In one embodiment of this application, the detailed process steps of the method may include:

[0038] First, perform beveling step S100. Two TC4 titanium alloy plates, each measuring 300mm × 150mm × 60mm, are selected as the workpieces to be joined. The mating edges of the two plates are machined using a CNC milling machine to form a symmetrical X-shaped bevel with a bevel angle of 60 degrees. This symmetrical X-shaped bevel design helps to distribute welding heat input and shrinkage deformation more evenly along the workpiece thickness during subsequent double-sided welding, effectively controlling and reducing overall angular and bending deformation. At the root of the bevel, a 2.5mm thick blunt edge is retained. This blunt edge is designed to provide sufficient support material for the first root pass to prevent burn-through during high-energy-density welding, while its thickness is sufficient for complete penetration by subsequent double-sided root passes, ensuring the integrity of the root connection. After beveling, the bevel surface and an area within at least 20mm of it are thoroughly cleaned using organic solvents such as acetone or alcohol to remove oil, cutting fluid, and other impurities. Then, use a stainless steel wire brush or abrasive disc to remove the oxide film from the surface until a fresh, bright metallic luster is revealed. It should be noted that thorough cleaning is a crucial prerequisite for ensuring the quality of subsequent welding and preventing defects such as porosity or inclusions.

[0039] The two cleaned titanium alloy workpieces were then clamped onto a specialized welding platform. By adjusting the fixture, the butt joint gap between the bevel roots of the two workpieces was precisely controlled to 0.3 mm. This gap helps the laser beam energy penetrate the blunt edge to promote root penetration, but it should not be too large to avoid molten metal collapse. The workpieces were securely fixed to prevent misalignment due to thermal expansion during welding.

[0040] Next, the front root pass welding step S200 is performed. This step uses a laser-arc hybrid welding system, which integrates a high-power fiber laser and a gas metal arc welding (GMAW) arc device. (Refer to...) Figure 3 This diagram illustrates the principle of laser-arc hybrid welding. During welding, the laser beam 31 and the arc welding torch 32 work together on the workpiece. The laser spot leads the arc center in the welding direction, employing a laser-fronted arrangement. This arrangement utilizes the high energy density of the laser beam 31 to first form a deep and narrow metal vapor aperture, or keyhole 35, on the blunt edge of the workpiece. The formation of the keyhole 35 greatly enhances the energy transfer efficiency into the workpiece, which is key to achieving a large weld penetration. The subsequent arc becomes more stable under laser preheating and plasma assistance, and its molten welding wire transitions into the molten pool 33, maintained by both the laser and the arc, in the form of molten droplets 34, serving to fill the metal and stabilize the molten pool morphology.

[0041] As a specific implementation method, the process parameters can be set as follows: the laser power of the laser is 3kW, the welding current of the arc power supply is 220A, and the welding voltage is 24V. Argon gas with a purity of 99.99% is used as the shielding gas 36, and is delivered to the welding area through the nozzle on the welding head at a flow rate of 25L / min, forming a local inert atmosphere layer that completely isolates the high-temperature molten pool 33 and the nearby heat-affected zone from the air, thereby effectively preventing oxidation and nitriding of the titanium alloy at high temperatures. The welding robot drives the composite welding head to move at a uniform speed along the centerline of the groove, completing the first root pass welding on one side of the X-shaped groove, forming the first root pass weld.

[0042] Next, perform the back-side root cleaning step S300. Remove the welded workpiece from the fixture and rotate it 180 degrees. Using a handheld angle grinder, mechanically grind the back side of the first root pass weld. Root cleaning aims to thoroughly remove any incomplete fusion, oxide layer, and other welding defects that may exist at the weld root, thereby creating a clean, defect-free weld surface for subsequent back-side root passes. This is a crucial step in ensuring complete root penetration and internal quality of the final joint. The grinding depth should be sufficient to completely remove weld root defects and expose fresh metal.

[0043] Next, perform the back root pass welding step S400. The workpiece, after root cleaning, is re-clamped and fixed. Using the same laser-arc hybrid welding system and process parameters as the front root pass welding step S200, a second root pass welding is performed on the other side of the root-cleaned bevel. The second root pass weld is completely fused with the first root pass weld at the root, forming a double-sided root pass weld that extends through the entire thickness of the blunt edge. Figure 2 As shown, the double-sided root pass weld forms the central laser-arc hybrid welding zone 21 in the final joint cross-section. This step completes the reliable connection of the root of the thick titanium alloy plate.

[0044] Subsequently, laser cladding filling step S500 is performed. On the workpiece with completed double-sided root pass welding, a powder-feeding laser cladding system is used to additively fill the remaining space within the X-shaped groove. In this embodiment, a coaxial powder-feeding laser cladding system can be used. (Refer to...) Figure 4 This demonstrates the principle of coaxial powder-feed laser cladding. The coaxial powder-feed cladding head 41 in this system integrates a central laser channel and an annular powder channel. During operation, the laser beam 31 is emitted from the center, forming a molten pool 33 on the solidified root weld surface or the previous cladding layer. Simultaneously, spherical titanium alloy powder, matching the composition of the base material TC4, is carried by argon gas (46) and uniformly transported through the annular channel, converging into the molten pool 33 at the laser focal point. The powder stream 43 rapidly melts in the molten pool and solidifies as the coaxial powder-feed cladding head 41 moves, forming a new, dense cladding layer 45. The entire process is also carried out under the protection of the shielding gas 36.

[0045] The filling process employs a multi-layer, multi-pass method. The cladding head reciprocates and scans along the bevel width to form a complete filler layer, with each layer's thickness controlled to approximately 1.5 mm. Here, a crucial heat management measure is introduced: after each layer is completed, the next layer is not immediately started. Instead, the interpass temperature of the weld is monitored in real-time using a non-contact infrared thermometer. Only when the temperature has naturally cooled or been cooled to below 150°C by auxiliary air blowing is the next layer of cladding initiated. Strictly controlling the interpass temperature below 150°C serves two purposes: firstly, to limit heat accumulation in the workpiece, thereby significantly reducing the overall welding heat input, a core method for controlling welding deformation and residual stress; secondly, to avoid excessive thermal cycling and prolonged high-temperature residence on the underlying cladding layer and heat-affected zone 23, thus inhibiting grain coarsening and ensuring a fine solidification structure throughout the weld zone 20. This layer-by-layer deposition process is repeated until the filler metal height is slightly higher than the surface of the base metal zone 10 by approximately 0.8 mm, forming the weld reinforcement. Figure 2 In this process, the area formed by this step is the laser cladding filling area 22.

[0046] Subsequently, stress-relief annealing step S600 is performed. The welded workpiece is placed entirely into a vacuum heat treatment furnace. The furnace is first evacuated to a high vacuum state, and then filled with high-purity argon as a protective atmosphere. The workpiece is slowly heated to 650°C according to a preset program and held at this temperature for 1.5 hours. The purpose of holding the temperature is to allow atoms sufficient time and energy for diffusion and migration, thereby relaxing and releasing the internal residual stress generated during welding through microscopic plastic deformation. After holding, the heating power is turned off, and the workpiece is allowed to cool slowly to room temperature with the furnace. Cooling with the furnace avoids the generation of new thermal stress due to excessively rapid cooling.

[0047] Finally, the post-processing and inspection step S700 is executed. For the heat-treated workpiece, non-destructive testing is first performed, such as X-ray inspection, to check for volumetric defects inside the weld, such as porosity, cracks, lack of fusion, and slag inclusions. After confirming that the internal quality of the weld is acceptable, a milling machine is used to remove the excess weld surface, making the surface of the entire welding zone 20 flush with the surfaces of the base material zones 10 on both sides, thus obtaining the final welded joint. A schematic diagram of the overall cross-section of the final welded joint can be found in [reference needed]. Figure 1 The welding area 20 perfectly fills the original X-shaped groove, forming a smooth transition with the base material areas 10 on both sides.

[0048] The welded joint obtained by the above method, after mechanical property testing, showed that its tensile strength could reach more than 95% of that of the base material TC4 titanium alloy, demonstrating excellent connection strength. At the same time, due to the use of a step-by-step heat source and strict heat management, the overall welding deformation of the joint was minimal, the width of the heat-affected zone 23 was effectively controlled, and its internal grains were fine, avoiding the problems of microstructure coarsening and performance degradation caused by traditional high heat input welding methods.

[0049] Example 2

[0050] As an optional implementation, this embodiment provides a variant based on Embodiment 1, the main difference being the different types of arc heat sources used in the front root pass welding step S200 and the back root pass welding step S400. This embodiment illustrates that the composite connection method proposed in this application has good adaptability to different arc forms.

[0051] In this embodiment, the execution methods and parameters of steps such as bevel preparation step S100, weld back root cleaning step S300, laser cladding filling step S500, stress-relieving annealing step S600, and post-processing and inspection step S700 are basically the same as in embodiment 1.

[0052] The main difference lies in the root pass welding step: the arc equipment used in this embodiment of the laser-arc hybrid welding system is a tungsten inert gas (TIG) arc welding device, rather than the gas metal arc welding (GMAW) arc equipment in Embodiment 1. TIG welding uses a non-molten tungsten electrode to generate an arc, which has a more stable arc shape, more concentrated heat, and minimal spatter.

[0053] Accordingly, the process flow for performing the front root pass welding step S200 and the back root pass welding step S400 can be adjusted as follows: 1. Beveling and assembly: Considering the morphological characteristics of the tungsten inert gas (TIG) welding arc, the beveling angle of the X-shaped beveling can be adjusted to 55 degrees to appropriately reduce the amount of filler metal required while ensuring root accessibility. The remaining assembly requirements are the same as in Example 1. 2. Root pass welding: Double-sided root pass welding is performed using a laser-TIG hybrid welding system. The laser is also positioned in front, with the laser beam 31 providing the main penetration depth and forming a keyhole 35 on the blunt edge. The TIG welding arc stably covers the molten pool 33, providing auxiliary heating and improving the fluidity of the molten pool, which helps to form a smooth and aesthetically pleasing root pass weld. If filler metal is required, a TC4 welding wire matching the base metal can be fed into the molten pool through an independent wire feeding mechanism. In this embodiment, the process parameters are set as follows: laser power 2.5kW, tungsten inert gas (TIG) welding current 200A. The shielding gas is also high-purity argon. 3. Subsequent steps: After completing the double-sided root pass, the subsequent laser cladding and filling steps, such as S500, are completely consistent with those in Example 1.

[0054] Compared to Example 1, using a laser-tungsten inert gas (TIG) welding hybrid heat source for the root pass results in a smoother weld bead with finer internal quality, namely the laser-arc hybrid welding zone 21. This method is particularly suitable for applications with extreme requirements for root pass quality and surface roughness. The overall performance of the resulting weld joint is comparable to that of Example 1, and may even have a slight advantage in fatigue resistance due to the smoother root transition. Therefore, the laser-arc hybrid welding system in this application can be specifically implemented as a laser-gas metal arc welding (GMAW) hybrid system, or as a laser-tungsten inert gas (TIG) hybrid system.

[0055] Example 3

[0056] Alternatively, in another embodiment, this application also provides a variant based on Embodiment 1, the main difference of which lies in the powder feeding method used in the laser cladding filling step S500. This embodiment is used to illustrate that the additive filling step proposed in this application is not limited to a specific powder feeding technology and has good equipment compatibility.

[0057] In this embodiment, the execution methods and parameters of the following steps are exactly the same as those in Embodiment 1: bevel preparation step S100, front root welding step S200, weld back root cleaning step S300, back root welding step S400, stress-relieving annealing step S600, and post-processing and inspection step S700.

[0058] The main difference lies in the laser cladding filling step S500: This embodiment uses a side-mounted powder feeding system, or lateral powder feeding system, instead of the coaxial powder feeding system in Embodiment 1. In the side-mounted powder feeding system, the powder feeding nozzle is located on one side of the laser beam, forming a certain angle with both the workpiece surface and the welding direction, precisely blowing the powder flow 43 to the leading edge of the molten pool 33 formed by the laser beam 31 on the substrate.

[0059] Specifically, the filling process may include: 1. Double-sided root pass welding: This process is exactly the same as in Example 1, forming a solid laser-arc composite welding zone 21. 2. Laser cladding filling: Filling is performed using a side-axis powder feeding laser cladding system. The laser head moves along the centerline of the bevel, and the lateral powder feeding nozzle delivers TC4 powder into the molten pool. To ensure uniform filling across the entire bevel width, the scanning path of the cladding head can adopt a zigzag trajectory. It is understood that, due to the directionality of powder feeding, to ensure powder utilization and good overlap between molten pools, it may be necessary to dynamically fine-tune parameters such as laser power and scanning speed according to the direction of movement of the cladding head relative to the powder feeding nozzle. For example, when moving against the powder feeding direction, the speed can be appropriately reduced or the power increased to ensure that the powder is fully melted. 3. Thermal management and post-treatment: The remaining control measures, such as strictly controlling the interpass temperature below 150°C, and the final stress-relief annealing step S600 and post-processing and inspection step S700, can be consistent with Example 1.

[0060] The method described in this embodiment can also achieve low heat input and high-quality additive filling of X-shaped grooves, ultimately resulting in a high-performance welded joint. This embodiment shows that the powder-feeding laser cladding system in this application method can be either a coaxial powder-feeding laser cladding system or a side-axis powder-feeding laser cladding system, thereby significantly broadening the equipment applicability of this application method and enabling it to adapt to certain specific equipment configurations or application scenarios where coaxial heads cannot be used due to space constraints.

[0061] Example 4

[0062] Based on Example 1, this embodiment further illustrates a scheme to enhance thermal management and optimize intermediate processing steps, aiming to achieve more extreme control over the welding process in order to obtain the best joint structure and performance.

[0063] The process flow in this embodiment still follows... Figure 5 The framework shown is used, but the implementation of the specific steps has been optimized.

[0064] 1. Bevel preparation step S100 and front root pass welding step S200: Same as in Example 1.

[0065] 2. In the weld back root cleaning step S300, as an optional implementation method, this embodiment uses plasma arc gouging instead of mechanical grinding in Embodiment 1 for back root cleaning. Plasma arc gouging uses a high-temperature, high-speed plasma jet to melt and blow away the metal at the weld root. Its cleaning efficiency is much higher than that of mechanical grinding, which can significantly shorten auxiliary time. At the same time, its heat action range is relatively concentrated, and its thermal impact on the base material is smaller.

[0066] 3. Backside root pass welding step S400: On the bevel after plasma arc gouging, perform backside root pass welding, the method is the same as in Example 1.

[0067] 4. In the laser cladding filling step S500, this embodiment adds a forced cooling measure based on Embodiment 1. Specifically, during the waiting interval after each cladding layer 45 is filled, an additional argon gas nozzle is used to rapidly blow and cool the newly solidified weld surface. This measure can significantly improve the cooling rate, allowing the interlayer temperature to drop below the target value of 150°C more quickly. Its advantages are: on the one hand, it can further shorten the high-temperature dwell time of each layer, thereby more effectively suppressing grain growth and obtaining a finer microstructure in the filled area and heat-affected zone; on the other hand, it can also shorten the interlayer waiting time, thereby improving the overall production efficiency.

[0068] 5. In the stress-relief annealing step S600, this embodiment employs a two-stage heat treatment process to achieve in-depth optimization of the joint's mechanical properties. First stage: Stress-relief annealing. The workpiece is heated to 680°C, held at that temperature for 1 hour, and then cooled in the furnace. The main purpose of this step is the same as in Example 1, namely, to eliminate most of the residual welding stress. Second stage: Aging treatment. After stress-relief annealing, the workpiece is reheated to 550°C and held at this temperature for 4 hours, then air-cooled. It is understood that for α+β titanium alloys like TC4, aging treatment can promote the decomposition of the metastable β phase and precipitate finely dispersed α phases or intermetallic compounds, etc., as strengthening phases. These precipitated phases can effectively pin dislocations, thereby significantly improving the joint's strength and hardness.

[0069] 6. Post-processing and inspection steps S700: Same as in Example 1.

[0070] Through a series of strengthening processes described in this embodiment, the final welded joint exhibits superior performance. Metallographic analysis shows that the grain size of the weld and heat-affected zone 23 is further refined. Mechanical property tests indicate that the joint has a better balance between strength and toughness, with strength further improved while maintaining sufficient ductility. Simultaneously, due to more effective heat management and more thorough stress relief treatment, the residual stress level inside the joint is also reduced to a lower level.

[0071] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0072] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A composite joining method for thick plate titanium alloys, characterized in that, Includes the following steps: An X-shaped bevel is machined at the joint of the thick titanium alloy workpieces to be joined. The X-shaped groove is subjected to double-sided root pass welding using a laser-arc hybrid welding system to form a double-sided root pass weld. A powder-feeding laser cladding system is used to perform multi-layer, multi-pass additive filling in the X-shaped groove above the double-sided root weld. After completing the multi-layer, multi-pass additive filling, the connected thick plate titanium alloy workpiece is subjected to stress-relieving annealing treatment. The double-sided root pass welding step includes: performing a first root pass welding on one side of the X-shaped groove to form a first root pass weld. The back side of the first root pass weld is cleaned; and the other side of the X-shaped groove is welded with a second root pass, thereby forming the double-sided root pass weld together with the first root pass weld. The bevel angle of the X-shaped bevel is 55 to 65 degrees, and a blunt edge with a thickness of 2 mm to 3 mm is retained at the root of the X-shaped bevel. In the multi-layer, multi-pass additive filling process, the thickness of each layer is 1~2mm, and the interlayer temperature is not higher than 150℃; Repeat filling until the X-shaped bevel is completely filled, with the surface of the last cladding layer being 0.5~1mm higher than the surface of the thick titanium alloy workpiece; The coaxial powder-feeding cladding head in the powder-feeding laser cladding system integrates a central laser channel and an annular powder channel. During operation, the laser beam is emitted from the central laser channel, forming a molten pool on the solidified double-sided root pass weld surface or the previous cladding layer. Simultaneously, titanium alloy powder, matching the composition of the base material of the thick titanium alloy workpiece, is uniformly transported and converged into the molten pool at the laser focal point by argon gas, which serves as the powder-feeding gas. The powder melts in the molten pool and solidifies as the coaxial powder-feeding cladding head moves, forming a cladding layer. The entire process is also carried out under the protection of a shielding gas.

2. The method according to claim 1, characterized in that, After processing the X-shaped bevel, the process also includes cleaning the X-shaped bevel and its surrounding area to remove oil, oxide layer and impurities, and wiping with acetone or alcohol.

3. The method according to claim 1, characterized in that, Before the first root pass welding, the process also includes assembling the thick titanium alloy workpieces to be joined into the welding fixture, with a butt gap of no more than 0.5mm.

4. The method according to claim 1, characterized in that, The laser-arc hybrid welding system has a laser power of 2~4kW, an arc current of 180~250A, a voltage of 20~28V, uses argon as the shielding gas with a flow rate of 20~30L / min, and the welding wire material is matched with the material of the thick titanium alloy workpiece.

5. The method according to claim 4, characterized in that, The stress-relief annealing process includes heating to 600°C to 700°C under argon protection, holding at that temperature for 1 to 2 hours, and then cooling it in the furnace.

6. The method according to claim 5, characterized in that, It also includes using machining to grind the weld seam excess height until it is flush with the thick plate titanium alloy workpiece.

7. A thick plate titanium alloy structural component, characterized in that, The composite connection is made using the method described in any one of claims 1-6.

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