Welding device and welding method for inhibiting loss of strengthening phase of al-mg-li alloy lap joint

Abstract

This invention discloses a welding apparatus and method for suppressing the loss of reinforcing phases in Al-Mg-Li alloy lap joints. The method includes: 1. Mechanically grinding, cleaning, and vacuum drying the Al-Mg-Li alloy base material; 2. Processing a serrated surface array on the lap joint surface of the Al-Mg-Li alloy base material; 3. Using a pulsed laser to press a pure copper film onto the serrated surface array of the Al-Mg-Li alloy base material; 4. Clamping two Al-Mg-Li alloy base materials on a welding worktable and preheating the worktable; 5. After preheating, using a defocused laser to cyclically heat the lap joint area of ​​the Al-Mg-Li alloy base material, while simultaneously applying synchronous cyclic pressure to the lap joint area using rollers; 6. After welding, removing the weldment to complete the Al-Mg-Li alloy lap welding. This welding method effectively solves the problem of deterioration of the joint's mechanical properties caused by the burning of light elements during the laser welding of Al-Mg-Li alloys.

Description

Technical Field

[0001] This invention relates to the field of metal material processing technology, specifically to a welding device and welding method for suppressing the loss of reinforcing phase in lightweight, high-strength Al-Mg-Li alloy lap joints. Background Technology

[0002] With the continuous development of my country's aerospace technology, lightweight and high-strength materials have become a key research focus. Due to the addition of lithium and magnesium, Al-Mg-Li alloys have a lower density than ordinary aluminum alloys, and due to the precipitation of reinforcing phases such as Al-Li, Al-Cu-Li, and Al-Mg-Cu, they possess higher strength. Therefore, Al-Mg-Li alloys are ideal materials for lightweight and high-strength components and have been widely used in the manufacture of various critical aerospace components, such as seat frames, instrument panel parts, and fuel tanks. Thus, achieving high-quality welding of Al-Mg-Li alloys is crucial.

[0003] Due to the high energy density at the weld seam during welding and the low melting and boiling points of lithium and magnesium in Al-Mg-Li alloys, lithium and magnesium elements evaporate easily during welding, leading to a reduction in the amount of lithium-containing reinforcing phase in the weld and a decrease in the strength and hardness of the joint. Currently, the main method used to address the problem of reinforcing phase loss during Al-Mg-Li alloy welding is to strictly control the welding heat input to avoid excessive evaporation of lithium and magnesium elements, resulting in insufficient precipitation of the reinforcing phase. However, since the lithium and magnesium content in Al-Mg-Li alloys is relatively low (not exceeding 1.0 wt%), even slight evaporation loss can lead to insufficient lithium and magnesium elements in the weld seam, thus limiting the welding process window for controlling element evaporation loss. Furthermore, a hot-press diffusion welding method has been proposed, which applies pressure to the weld seam while reducing the welding heat input, aiming to form a diffusion-like connection effect without melting, providing a new approach for welding lightweight, high-strength Al-Mg-Li alloys. However, due to the short heating and pressurization time, the diffusion effect at the butt joint is poor, making it difficult to form an effective connection. Furthermore, hot-press diffusion welding is generally limited to butt joints, and it is difficult to achieve simultaneous pressurization for lap joints. Therefore, how to achieve high-quality connections in lightweight, high-strength Al-Mg-Li alloy lap joints has become a critical issue that urgently needs to be addressed. Summary of the Invention

[0004] The purpose of this invention is to address the problems existing in the prior art by providing a welding device and welding method for suppressing the loss of reinforcing phase in Al-Mg-Li alloy lap joints, so as to effectively solve the problem of insufficient precipitation of reinforcing phase in Al-Mg-Li alloy lap joints caused by the evaporation and burning of lithium and magnesium elements in the weld, thereby improving the strength of the welded joint.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] On one hand, a welding apparatus for suppressing the loss of strengthening phase in Al-Mg-Li alloy lap joints is provided. The welding apparatus includes a heatable worktable base plate, a movable support on the worktable base plate, a movable laser on the support, and a pressure application component disposed near the laser. The pressure application component is provided with pressure rollers arranged toward the worktable base plate. The worktable base plate is also provided with a clamp for holding the base material to be welded. The laser is used to heat the base material to be welded. The pressure rollers move synchronously with the laser and roll the heated area.

[0007] This welding device is not only simple in structure, easy to manufacture and use, but also highly flexible, capable of meeting the lap welding operations of various Al-Mg-Li alloy base materials. It provides a reliable working platform for welding Al-Mg-Li alloy base materials, and facilitates the implementation of welding methods that suppress the loss of strengthening phases in Al-Mg-Li alloy lap joints, thereby improving the quality and efficiency of Al-Mg-Li alloy welding.

[0008] The support can move relative to the workbench substrate, and the laser and the pressure application component can also move relative to the support, so that the laser and the pressure application component can move freely in the longitudinal and lateral directions in the plane synchronously, so as to cover the entire overlapping area to be welded.

[0009] The pressure application component can provide downward pressure to the pressure roller, allowing the pressure roller to press on the base material to be welded, providing the pressure required for forming the overlapping surface of the base material, and forming a hot-pressing welding effect together with the heating of the laser; it can also appropriately adjust the height position of the pressure roller to adapt to welding base materials of different thicknesses, or lift the pressure roller during the longitudinal movement of the support.

[0010] Furthermore, the support includes a pair of longitudinally movable support rods, on which a workbench truss is provided, and on which a laterally movable mounting seat is provided, the mounting seat connecting the laser and the pressure application assembly.

[0011] Furthermore, the pressure application assembly includes a vertical connecting rod, below which is a hydraulic actuator, and below which is a pressure roller connected via a wheel frame; the pressure rollers are a pair arranged symmetrically.

[0012] On the other hand, a welding method for suppressing the loss of reinforcing phase in Al-Mg-Li alloy lap joints is provided. This welding method utilizes the aforementioned welding apparatus for suppressing the loss of reinforcing phase in Al-Mg-Li alloy lap joints, and includes the following steps:

[0013] Pre-welding pretreatment is carried out on the base material to be welded. The Al-Mg-Li alloy base material to be welded is mechanically ground, then cleaned in anhydrous ethanol, and then vacuum dried.

[0014] A sawtooth array is processed on the base material to be welded. A cutting machine is used to process the sawtooth array at the overlapping surface of the two Al-Mg-Li alloy base materials to be welded.

[0015] A tightly bonded copper film is stamped at the serrated array of the overlapping surfaces of two Al-Mg-Li alloy base materials to be welded using a pulsed laser.

[0016] The Al-Mg-Li alloy base material to be welded is clamped on the worktable substrate, and the heating switch on the worktable substrate is turned on to preheat the worktable substrate and the Al-Mg-Li alloy base material.

[0017] The laser generates a defocused laser to repeatedly heat the overlapping area of ​​the Al-Mg-Li alloy base material, while the pressure rollers simultaneously apply pressure to the overlapping area in a synchronous cycle.

[0018] After the heating and pressurization operations are completed, the welded Al-Mg-Li alloy base material is removed from the workbench substrate, thus completing the Al-Mg-Li alloy lap welding.

[0019] This welding method employs a combination of defocused laser scanning heating and synchronous roller pressure to perform hot-press composite treatment on the Al-Mg-Li alloy lap joint area. This significantly reduces the welding heat input, prevents the base material from melting, and avoids the problem of joint strengthening phase loss due to lithium and magnesium evaporation, thereby improving the strength of the welded joint. At the same time, the welding time of this invention is significantly reduced compared to traditional diffusion welding, which is beneficial to improving welding efficiency.

[0020] Furthermore, the Al-Mg-Li alloy base material is 2198 Al-Mg-Li alloy, and the thickness of the Al-Mg-Li alloy base material is 3mm to 10mm.

[0021] Furthermore, the overlapping surfaces and other surfaces of the Al-Mg-Li alloy base material are mechanically polished step by step using sandpaper of 80 mesh, 200 mesh, 400 mesh, 600 mesh, 800 mesh and 1000 mesh to remove the surface oxide layer and oil stain layer; the cleaning time with anhydrous ethanol is 5 to 10 minutes, the vacuum drying temperature is room temperature, and the vacuum drying time is 15 to 30 minutes.

[0022] Furthermore, the tooth tip height of the sawtooth array is 0.5-1.5mm, the tooth width is 0.5-1.5mm, the array length is 10-15cm, and the array width is 5-10cm.

[0023] Furthermore, the thickness of the copper thin film is 0.5 mm to 1 mm, and the wavelength of the pulsed laser is 1064 nm, the frequency is 6 kHz, the pulse width is 20 to 30 ns, the spot diameter is 0.6 to 1.0 mm, and the pulse energy is 20 to 50 mJ.

[0024] Furthermore, a heating plate or electric heating wire is pre-installed inside the workbench substrate, and the preheating temperature of the workbench substrate is 200-300°C.

[0025] Furthermore, the power of the defocused laser is 300W to 500W, the defocusing amount is 5mm to 10mm, the moving speed is 2mm / s to 4mm / s, the cyclic reciprocating direction is horizontal and vertical, until the heating area covers the entire overlapping area, the heating time is 3 to 6 minutes, and the pressure applied by the pressure roller is 50MPa to 100MPa.

[0026] Compared with the prior art, the beneficial effects of the present invention are: 1. This welding device is not only simple in structure, easy to manufacture and use, but also highly flexible, capable of meeting various Al-Mg-Li alloy base material lap welding operations, providing a reliable working platform for Al-Mg-Li alloy base material welding, and facilitating the implementation of welding methods that suppress the loss of strengthening phases in Al-Mg-Li alloy lap joints, thereby improving the quality and efficiency of Al-Mg-Li alloy welding; 2. The workbench base plate can not only be used to place the base material plate to be welded, but also to support the bracket. 1. To facilitate the installation of a laser and pressure application assembly for lap welding of the base material, and to enable heating to preheat the base material; 2. The support can move relative to the worktable base plate, and the laser and pressure application assembly can also move relative to the support, allowing the laser and pressure application assembly to move freely in the horizontal and vertical directions synchronously to cover the entire lap area to be welded; 3. The pressure application assembly can provide downward pressure to the pressure roller, allowing the pressure roller to press against the base material to be welded, providing the necessary pressure for forming the lap surface of the base material, and coordinating with the laser... The heating of the laser and the heat exchanger work together to create a hot-press welding effect; on the other hand, the height of the pressure roller can be adjusted appropriately, which can accommodate welding of base materials of different thicknesses and can also lift the pressure roller during the longitudinal movement of the support; 5. This welding method uses defocused laser scanning heating and synchronous pressure application of rollers to perform hot-press composite treatment on the Al-Mg-Li alloy lap area, which significantly reduces the welding heat input, prevents the base material from melting, avoids the problem of joint strengthening phase loss due to lithium and magnesium evaporation, thereby improving the strength of the welded joint. At the same time, the welding of this invention... The welding time is significantly reduced compared to traditional diffusion welding, which is beneficial to improving welding efficiency; 6. This invention abandons the diffusion connection approach where the lap surface does not melt at all, and achieves a more effective connection by forming a liquid film through micro-melting at the lap surface, while the base material does not melt, thus avoiding the evaporation of lithium and magnesium elements; 7. During the welding pressurization process of this invention, the mutual compression of the serrated array can form a larger local pressure at the lap surface, which is conducive to the dynamic recrystallization of the solidified liquid film under the combined action of heat and pressure, forming fine equiaxed crystals at the weld, thereby improving the joint strength and hardness. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the welding device for suppressing the loss of the reinforcing phase in Al-Mg-Li alloy lap joints according to the present invention.

[0028] Figure 2 This is a schematic diagram of the welding of the base material on the welding device according to the present invention;

[0029] Figure 3 This is a schematic diagram of the present invention, which involves setting a sawtooth array and a copper thin film on the overlapping surface of the base material;

[0030] Figure 4 This is a schematic diagram of the overlapping of two base materials in this invention;

[0031] In the figure: 1. Workbench base plate; 2. Support rod; 3. Workbench truss; 4. Laser; 5. Vertical connecting rod; 6. Hydraulic actuator; 7. Wheel frame; 8. Pressure roller; 9. Al-Mg-Li alloy base material; 10. Defocused laser; 11. Sawtooth array; 12. Copper thin film. Detailed Implementation

[0032] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] In the description of this invention, it should be noted that the terms "middle," "upper," "lower," "left," "right," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and for 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 invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Example 1

[0034] like Figure 1 As shown, this embodiment provides a welding apparatus for suppressing the loss of strengthening phase in Al-Mg-Li alloy lap joints. The welding apparatus includes a heatable worktable base plate 1, a movable support on the worktable base plate 1, a movable laser 4 on the support, and a pressure application component disposed near the laser 4. The pressure application component is provided with pressure rollers 8 arranged toward the worktable base plate 1. The worktable base plate 1 is also provided with a clamp for holding the base material to be welded. The laser 4 is used to heat the base material to be welded. The pressure rollers 8 move synchronously with the laser 4 and roll the heated area.

[0035] This welding device is not only simple in structure, easy to manufacture and use, but also highly flexible, capable of meeting the lap welding operations of various Al-Mg-Li alloy base materials. It provides a reliable working platform for welding Al-Mg-Li alloy base materials, and facilitates the implementation of welding methods that suppress the loss of strengthening phases in Al-Mg-Li alloy lap joints, thereby improving the quality and efficiency of Al-Mg-Li alloy welding.

[0036] The workbench base plate 1 can be used to place the base material plate to be welded and can be heated to preheat the base material; at the same time, it can also support the bracket, and the laser 4 and pressure application component for lap welding can be connected and installed through the bracket, so that the laser 4 and pressure application component can face the base material.

[0037] The support can move relative to the workbench substrate, and the laser 4 and the pressure application component can also move relative to the support, one moving longitudinally (e.g., in the Y direction) and the other moving laterally (e.g., in the X direction), so that the laser 4 and the pressure application component can move freely in the XY plane so that they can cover the entire overlapping area to be welded, and the two can move synchronously.

[0038] The pressure-applying component can provide downward pressure to the pressure roller 8, allowing the pressure roller 8 to press on the base material to be welded, providing the pressure required for forming the overlapping surface of the base material, and forming a hot-press welding effect together with the heating of the laser 4; on the other hand, it can also appropriately adjust the height position of the pressure roller 8, which can not only adapt to the welding of base materials of different thicknesses, but also lift the pressure roller 8 during the longitudinal movement of the support.

[0039] Furthermore, the support includes a pair of longitudinally movable support rods 2, a workbench truss 3 is provided on the pair of support rods 2, and a laterally movable mounting seat is provided on the workbench truss 3, the mounting seat connecting the laser 4 and the pressure application component.

[0040] The area between the pair of support rods 2 is the area for placing the base material, which is clamped and fixed in this area of ​​the workbench base plate by a clamp, such as a clamp or a gripper; a pair of slide rails are provided on both sides of the workbench base plate 1, and the support rods 2 are mounted on the slide rails so that they can move back and forth along the slide rails; the workbench truss 3 spans this area, allowing the laser and the pressure application component to move laterally in this area; the mounting base is provided to facilitate the connection and installation of the laser and the pressure application component.

[0041] The movement of both the support rod 2 and the mounting base can be achieved electrically. For example, an electric slider can be installed on the slide rail, and the support rod can be installed on the electric slider. A linear module can be installed on the workbench truss 3, and the slider of the linear module can be connected to the mounting base. Other electrically controlled movement methods, such as lead screw sliders, can also be used.

[0042] Furthermore, the pressure application assembly includes a vertical connecting rod 5 connected to the mounting, a hydraulic actuator 6 is provided below the vertical connecting rod 5, and the pressure roller 8 is connected below the hydraulic actuator 6 via a wheel frame 7; the pressure roller 8 is a pair arranged symmetrically.

[0043] The hydraulic actuator 6, such as a hydraulic cylinder, drives its piston rod to extend and retract, thereby raising and lowering the pressure roller 8 and providing appropriate downward pressure to the base material. The axis of the pressure roller 8 is perpendicular to the direction of horizontal movement of the pressure application assembly, that is, parallel to the direction of longitudinal movement of the support.

[0044] In some embodiments, the upper end of the vertical connecting rod 5 is rotatably connected to the mounting base. By setting a servo motor and a gear transmission assembly, the vertical connecting rod 5 can be driven to rotate, thereby changing the rolling direction of the pressure roller 8 and allowing it to apply pressure to the overlapping area of ​​the base material from multiple directions. Example 2

[0045] This embodiment provides a welding method for suppressing the loss of reinforcing phases in Al-Mg-Li alloy lap joints. The welding method uses the welding apparatus for suppressing the loss of reinforcing phases in Al-Mg-Li alloy lap joints described in Embodiment 1, combined with... Figures 2-4 As shown, the welding method includes the following steps:

[0046] Step 1: Pre-treatment of the base material to be welded. Select a base material of suitable size, such as two Al-Mg-Li alloy base materials 9 of similar size. Mechanically grind the Al-Mg-Li alloy base material 9 to be welded, then clean it in anhydrous ethanol, and vacuum dry it after cleaning.

[0047] Step 2: Perform serrated array processing on the base materials to be welded. Use a cutting machine to process serrated array 11 at the overlapping surface of the two Al-Mg-Li alloy base materials 9 to be welded.

[0048] Step 3, copper film stamping: A tightly bonded copper film 12 is stamped at the serrated array 11 of the overlapping surface of the two Al-Mg-Li alloy base materials 9 to be welded using a pulsed laser.

[0049] Step 4: Heating the workbench substrate 1 (preheating the base material): Clamp the Al-Mg-Li alloy base material 9 to be welded onto the workbench substrate 1, turn on the heating switch on the workbench substrate 1, and preheat the workbench substrate 1 and the Al-Mg-Li alloy base material 9.

[0050] Step 5, hot-press composite welding: The laser 4 generates a defocused laser 10 to repeatedly heat the overlapping area of ​​the Al-Mg-Li alloy base material 9, while the pressure roller 8 applies pressure to the overlapping area in a synchronous and repeated manner.

[0051] Step 6: Remove the welded parts: After the heating and pressurization operations are completed, remove the welded Al-Mg-Li alloy base material from the workbench substrate to complete the Al-Mg-Li alloy lap welding.

[0052] This welding method employs a combination of defocused laser scanning heating and synchronous roller pressure to perform hot-press composite treatment on the Al-Mg-Li alloy lap joint area. This significantly reduces the welding heat input, prevents the base material from melting, and avoids the loss of the joint strengthening phase due to the evaporation of lithium and magnesium elements, thereby improving the strength of the welded joint. At the same time, the welding time of this invention is significantly reduced compared to traditional diffusion welding, which is beneficial to improving welding efficiency.

[0053] Furthermore, addressing the issues of poor diffusion bonding or even bonding failure in current laser (or electron beam) thermopressing diffusion welding methods, this invention abandons the approach of achieving a completely non-melting diffusion bonding at the lap joint. Instead, it achieves a more effective bonding by micro-melting at the lap joint to form a liquid film, while preventing the base material from melting and thus avoiding the evaporation of lithium and magnesium. Specifically, before welding, the surface of the Al-Mg-Li alloy base material lap joint is modified by processing a sawtooth array and applying a copper thin film using a pulsed laser. During welding, the copper thin film undergoes a eutectic reaction with the base material at a temperature of 548°C, far below the melting point of the base material, to form a liquid film, thereby achieving an effective bonding at the mating surface. Compared to conventional mechanical inlay, the copper thin film applied by a pulsed laser is more tightly bonded to the Al-Mg-Li alloy base material, even forming a metallurgical bond, which is more conducive to the formation of a liquid film through a eutectic reaction at high temperatures, thus facilitating an effective bonding.

[0054] Moreover, during the welding pressurization process of this invention, compared with a flat lap surface, the mutual compression of the serrated array can form a greater local pressure at the lap surface, which is conducive to the dynamic recrystallization of the solidified liquid film under the combined action of heat and pressure, forming fine equiaxed crystals at the weld, thereby improving the joint strength and hardness.

[0055] Furthermore, the Al-Mg-Li alloy base material is 2198 Al-Mg-Li alloy, whose chemical composition includes Li: 0.8-1.1 wt%, Mg: 0.25-0.8 wt%, Cu: 2.9-3.5 wt%, Zr: 0.04-0.18 wt%, Zn: 0.4 wt%, Mn: 0.5 wt%, and Al: balance; the preferred composition is Li: 1.0 wt%, Mg: 0.5 wt%, Cu: 3.2 wt%, Zr: 0.1 wt%, Zn: 0.4 wt%, Mn: 0.5 wt%, and Al: balance.

[0056] Although this type of alloy has advantages such as being lightweight, high-strength, and corrosion-resistant, it is prone to problems such as porosity, hot cracking, and joint softening during welding. The welding method of this invention can effectively avoid these welding disadvantages.

[0057] Furthermore, the thickness of the Al-Mg-Li alloy base material 9 mentioned in step one is 3mm to 10mm.

[0058] Furthermore, in step one, the overlapping surfaces and other surfaces of the Al-Mg-Li alloy base material 9 are mechanically polished sequentially using sandpaper of 80 grit, 200 grit, 400 grit, 600 grit, 800 grit, and 1000 grit to remove the surface oxide layer and oil stain layer. Polishing with sandpaper of various grits can not only effectively remove oxides and impurities from the surface of the base material to prevent them from affecting the welding quality, but also increase the contact area and improve the surface roughness to enhance the adhesion during welding. Polishing can also make the surface of the base metal smoother and reduce problems such as porosity and cracks during the welding process.

[0059] After grinding and cleaning, perform a cleaning process using anhydrous ethanol for 5–10 minutes. Vacuum drying is performed at room temperature for 15–30 minutes.

[0060] Furthermore, in step two, the tooth tip height of the sawtooth array 11 is 0.5-1.5mm, the tooth width is 0.5-1.5mm, the array length is 10-15cm, and the array width is 5-10cm.

[0061] The sawtooth array 11 is a continuous wavy tooth structure arranged in the overlapping area. The sawtooth array 11 can further improve the surface condition of the overlapping area of ​​the base materials. On the one hand, it increases the surface area of ​​the overlapping area, which multiplies the actual overlapping area and increases the actual coverage area of ​​the subsequent copper film. On the other hand, the tooth structure can increase the local pressure. Under the same pressure, the sawtooth of the two base materials generates greater pressure during the mutual compression process, which allows the solidified liquid film to undergo dynamic recrystallization, so as to form equiaxed crystals at the weld joint, thereby improving the connection strength and hardness of the weld joint.

[0062] Furthermore, the thickness of the copper thin film 12 is 0.5 mm to 1 mm, and the wavelength of the pulsed laser is 1064 nm, the frequency is 6 kHz, the pulse width is 20 to 30 ns, the spot diameter is 0.6 to 1.0 mm, and the pulse energy is 20 to 50 mJ.

[0063] The pulsed laser, through the parameter settings of the aforementioned pulsed laser, uses the energy it generates to fix the copper film 12 in the area where the sawtooth array 11 is located, and to fit tightly with the sawtooth array 11. That is to say, the copper film 12 is also arranged in a sawtooth shape. For the base material, under the same projected area of ​​the overlapping area, a larger copper film area can be attached. The copper film 12 can generate the liquid film required for welding, which is beneficial to promoting the welding connection of the two base materials.

[0064] Furthermore, the workbench base plate 1 is pre-installed with a heating plate or electric heating wire. The preheating temperature of the workbench base plate 1 is 200-300°C. The workbench base plate 1 is equipped with a heating switch (temperature controller) for its heating plate or electric heating wire. The heating can be turned on or off, and the heating time and stability can be controlled by the heating switch.

[0065] Furthermore, in step five, the power of the defocused laser 10 is 300W to 500W, the defocusing amount is 5mm to 10mm, and its lateral or longitudinal moving speed is 2mm / s to 4mm / s. The cyclic reciprocating direction is lateral and longitudinal until the heating area covers the entire overlapping area. The heating time is 3 to 6 minutes. During this period, protective gas can be sprayed to protect the heating area. The pressure applied by the pressure roller is 50MPa to 100MPa. Since the pressure roller is symmetrically arranged on both sides of the defocused laser irradiation heating area, when it moves, the pressure roller can apply pressure to the heated area in real time to ensure that the overlapping area of ​​the pair of parent materials receives the required pressure and stress so that the metal material can recrystallize.

[0066] In some implementations, after adjusting the placement of the base material to be welded according to the actual situation, a defocused laser can be used to preheat the area of ​​the base material to be welded. The defocused laser power is 200W to 400W, the moving speed is 3mm / s to 6mm / s, the shielding gas flow rate is 15L / min to 25L / min, the defocusing amount is 5mm to 10mm, and the number of cycles of heating is 5 to 10. Example 3

[0067] Taking the welding process of an 8mm thick 2198 Al-Mg-Li alloy as an example, this welding method will be further explained in detail.

[0068] Step 1: Use sandpaper of 80 grit, 200 grit, 400 grit, 600 grit, 800 grit and 1000 grit to mechanically grind the lap surface and other surfaces of the 8mm thick 2198 Al-Mg-Li alloy base material to be welded in sequence. Then, clean it in anhydrous ethanol for 7 minutes. After cleaning, vacuum dry it for 30 minutes to obtain a clean and dry Al-Mg-Li alloy base material.

[0069] Step 2: Using an internal circular cutting machine, a serrated array with a length of 12cm and a width of 8cm is processed on the overlapping surface of the 8mm thick 2198 Al-Mg-Li alloy base material. The serrated array has a tooth tip height of 1.0mm and a tooth width of 1.0mm.

[0070] Step 3: A tightly bonded 0.8mm thick copper film is stamped onto the serrated array of the overlapping surface of the 8mm thick 2198 Al-Mg-Li alloy substrate using a pulsed laser. The pulsed laser wavelength is 1064nm, the frequency is 6kHz, the pulse width is 20ns, the spot diameter is 0.8mm, and the pulse energy is 40mJ. In this embodiment, the copper film is respectively applied to the overlapping surfaces of the two Al-Mg-Li alloy substrates to be welded.

[0071] Step 4: Clamp the 8mm thick 2198 Al-Mg-Li alloy base material onto the worktable substrate, turn on the heating switch of the worktable substrate, and preheat the worktable substrate to 300℃; wherein, the worktable substrate is equipped with components such as slide rails, support rods, worktable trusses, lasers, pressure rollers and their hydraulic actuators, the support rods and the worktable trusses can move longitudinally along the slide rails, the lasers and pressure components can move laterally along the worktable trusses, the lasers and the pressure rollers move synchronously, and the hydraulic actuators can apply pressure to the workpiece to be welded through the pressure rollers;

[0072] Step 5: After preheating, a defocused laser is used to cyclically heat the 8mm thick 2198 Al-Mg-Li alloy overlapping area. At the same time, the pressure roller applies pressure to the overlapping area in a synchronous cyclic manner. The defocused laser power is 500W, the moving speed is 3mm / s, the defocusing amount is 8mm, and the cyclic direction is horizontal and vertical until the heating area covers the entire overlapping area. The heating time is 5min, and the pressure applied by the pressure roller is 80MPa.

[0073] Step 6: Remove the weldment: Remove the weldment (the welded base material) from the workbench to complete the 8mm thick 2198 Al-Mg-Li alloy lap weld.

[0074] This example demonstrates a welding method for suppressing the loss of reinforcing phases in lightweight, high-strength Al-Mg-Li alloy lap joints. The resulting weld joint exhibits a lithium content of 1.0 wt% and a magnesium content of 0.5 wt%, comparable to the base metal content and higher than the 0.6 wt% and 0.2 wt% of conventional lap welding, respectively. The weld joint achieves a tensile strength of 368 MPa, significantly higher than the 306 MPa of conventional lap welding. Therefore, this invention effectively improves joint strength by suppressing the loss of reinforcing phases in lightweight, high-strength Al-Mg-Li alloy lap joints.

[0075] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A welding method for suppressing the loss of reinforcing phases in Al-Mg-Li alloy lap joints, characterized in that, The welding apparatus used in the welding method includes a heatable worktable base plate, a movable support on the worktable base plate, a movable laser on the support, and a pressure application assembly disposed near the laser. The pressure application assembly has pressure rollers arranged towards the worktable base plate. The worktable base plate also has a clamp for holding the base material to be welded. The laser is used to heat the base material to be welded. The pressure rollers move synchronously with the laser and roll over the heated area. The pressure application assembly includes a vertical connecting rod, and a hydraulic actuator is disposed below the vertical connecting rod. The pressure rollers are connected to the hydraulic actuator via a wheel frame. The pressure rollers are a pair arranged symmetrically. The welding method includes the following steps: Pre-welding pretreatment is carried out on the base material to be welded. The Al-Mg-Li alloy base material to be welded is mechanically ground, then cleaned in anhydrous ethanol, and then vacuum dried. A sawtooth array is processed on the base material to be welded. A cutting machine is used to process the sawtooth array at the overlapping surface of the two Al-Mg-Li alloy base materials to be welded. A tightly bonded copper film is stamped at the serrated array of the overlapping surfaces of two Al-Mg-Li alloy base materials to be welded using a pulsed laser. The Al-Mg-Li alloy base material to be welded is clamped on the worktable substrate, and the heating switch on the worktable substrate is turned on to preheat the worktable substrate and the Al-Mg-Li alloy base material. The laser generates a defocused laser to repeatedly heat the overlapping area of ​​the Al-Mg-Li alloy base material, while the pressure rollers simultaneously apply pressure to the overlapping area in a synchronous cycle. After the heating and pressurization operations are completed, the welded Al-Mg-Li alloy base material is removed from the workbench substrate, thus completing the Al-Mg-Li alloy lap welding. The copper thin film has a thickness of 0.5 mm to 1 mm, and the pulsed laser has a wavelength of 1064 nm, a frequency of 6 kHz, a pulse width of 20 to 30 ns, a spot diameter of 0.6 to 1.0 mm, and a pulse energy of 20 to 50 mJ.

2. The welding method for suppressing the loss of reinforcing phase in Al-Mg-Li alloy lap joints according to claim 1, characterized in that, The support includes a pair of longitudinally movable support rods, on which a workbench truss is provided. The workbench truss is provided with a laterally movable mounting seat, which connects the laser and the pressure application component.

3. The welding method for suppressing the loss of reinforcing phase in Al-Mg-Li alloy lap joints according to claim 1, characterized in that, The Al-Mg-Li alloy base material is 2198 Al-Mg-Li alloy, and the thickness of the Al-Mg-Li alloy base material is 3mm to 10mm.

4. The welding method for suppressing the loss of reinforcing phase in Al-Mg-Li alloy lap joints according to claim 1, characterized in that, The overlapping surfaces and other surfaces of the Al-Mg-Li alloy base material were mechanically polished sequentially using sandpaper of 80 mesh, 200 mesh, 400 mesh, 600 mesh, 800 mesh and 1000 mesh to remove the surface oxide layer and oil stain layer; the cleaning time with anhydrous ethanol was 5 to 10 minutes, the vacuum drying temperature was room temperature, and the vacuum drying time was 15 to 30 minutes.

5. The welding method for suppressing the loss of reinforcing phase in Al-Mg-Li alloy lap joints according to claim 1, characterized in that, The sawtooth array has a tooth tip height of 0.5–1.5 mm, a tooth width of 0.5–1.5 mm, an array length of 10–15 cm, and an array width of 5–10 cm.

6. The welding method for suppressing the loss of reinforcing phase in Al-Mg-Li alloy lap joints according to claim 1, characterized in that, The workbench substrate is pre-installed with a heating plate or electric heating wire, and the preheating temperature of the workbench substrate is 200-300℃.

7. The welding method for suppressing the loss of reinforcing phase in Al-Mg-Li alloy lap joints according to claim 1, characterized in that, The defocused laser has a power of 300W to 500W, a defocusing amount of 5mm to 10mm, a moving speed of 2mm / s to 4mm / s, and a reciprocating direction of both horizontal and vertical until the heating area covers the entire overlapping area. The heating time is 3 to 6 minutes, and the pressure applied by the pressure roller is 50MPa to 100MPa.

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