Method for improving elongation of high-strength aluminum alloy medium plate welded joint and welding device

Abstract

The application provides a method for improving the elongation of a high-strength aluminum alloy medium plate welded joint, which comprises the following steps: butting and assembling two welding workpieces with equal thickness to form a flat plate-shaped workpiece to be welded; determining first optimized process parameters of a laser-arc hybrid welding device and second optimized process parameters of a laser heat conduction welding device, wherein the second optimized process parameters are determined according to the front surface fusion width FW and the back surface fusion width BW of the welded joint formed according to the first optimized process parameters; using the first optimized process parameters to perform laser-arc hybrid welding on the front surface welding area of the flat plate-shaped workpiece to be welded, and simultaneously using the second optimized process parameters to perform laser heat conduction welding on the back surface welding area of the workpiece to be welded. The laser heat conduction welding acts on the back surface welding area, so that the back surface fusion zone and the corner part of the base material surface realize smooth transition, the stress concentration at the weld toe is relieved, and the post-weld elongation of the welded joint is improved under the premise that the strength of the welded joint meets the design standard.

Description

Technical Field

[0001] This invention relates to the field of welding technology, and more specifically, to a method for improving the elongation of welded joints in high-strength aluminum alloy medium-thick plates. Background Technology

[0002] High-strength aluminum alloys are widely used in aircraft airframe structures in the aerospace field, primarily through machining or riveting processes. To improve material utilization or achieve structural weight reduction, argon arc welding is employed in a few non-load-bearing areas to achieve metallurgical connections in thin-walled structures. However, argon arc welding suffers from high heat input, leading to significant deformation and severe joint softening. Compared to argon arc welding, laser-arc hybrid welding technology not only significantly reduces welding heat input, which is beneficial for grain refinement and improved joint performance, but also allows for further control of joint microstructure and properties through filler wire during the welding process, thus offering broader application prospects.

[0003] When laser-arc hybrid welding is used for penetration welding, the laser and arc couple energy. The strong penetrating power of the laser significantly affects the weld width on the back side; the arc mainly acts on the weld front side, thus having a greater impact on the weld width on the front side. The weld back width ratio, which is dimensionless and represents the ratio of the weld width on the back side to the weld width on the front side, characterizes the full penetration of the weld and the strength of the heat source, while also reflecting the stability of keyhole formation. When the weld back width ratio is small, uneven weld width on the back side of the aluminum alloy weld is prone to occur, leading to defects such as porosity within the weld, severely affecting weld quality. When the weld back width ratio is large, over-penetration is likely to occur, exacerbating joint softening or ablation. Therefore, the weld back width ratio should be controlled within a reasonable range.

[0004] 7050 aluminum alloy is a heat-treatable aluminum alloy. After welding, the strength of machined parts can be restored through solution aging heat treatment. However, for some complex box and shell welded structures, post-weld heat treatment may lead to significant secondary deformation that is difficult to correct. Therefore, such weldments are not allowed to undergo solution aging heat treatment except for conventional stress-relieving annealing. This requires welded joints to possess relatively high strength and ductility. The elongation after fracture of a welded joint is an important indicator for evaluating its ductility and is of great significance for engineering design and application.

[0005] During laser-MIG arc cross-axis hybrid welding of 7050-T7451 aluminum alloy medium-thick plates, it was found that the welded joint could suppress or eliminate defects such as welding cracks and porosity, meeting the Class I quality requirements of relevant standards. While conventional adjustments to welding process parameters, optimization of the filler wire's chemical composition, or adjustment of the weld back width ratio resulted in tensile mechanical property tests showing that the welded joint strength could reach over 350 MPa (strength coefficient over 70%), its elongation after fracture remained consistently within the range of 1.5%-2.5%, making it difficult to achieve above 2.5%.

[0006] Therefore, the current 7050 high-strength aluminum alloy medium-thick plate welded joints have the problem of low elongation after fracture. Summary of the Invention

[0007] (a) Technical problems to be solved

[0008] The technical problem to be solved by the present invention is that the existing 7050 high-strength aluminum alloy medium-thick plate welded joints have low elongation after fracture.

[0009] (II) Technical Solution

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] This invention provides a method for improving the elongation of welded joints in high-strength aluminum alloy medium-thick plates, used to increase the tensile elongation after fracture of welded joints formed by laser-arc hybrid welding, comprising the following steps:

[0012] S100. Two welding workpieces of equal thickness are butted together to form a flat workpiece to be welded.

[0013] S200. Determine the first optimized process parameters of the laser-arc hybrid welding equipment and the second optimized process parameters of the laser heat-conducting welding equipment, wherein the second optimized process parameters are determined based on the front weld width FW and the back weld width BW of the weld joint formed by the first optimized process parameters.

[0014] S300. Laser-arc hybrid welding is performed on the front welding area of ​​the flat workpiece using the first optimized process parameters, and laser thermal conductive welding is performed on the back welding area of ​​the flat workpiece using the second optimized process parameters.

[0015] Preferably, the laser-arc hybrid welding equipment performs laser-arc hybrid welding on the front welding area using a first laser beam and an arc beam, and the laser heat-conducting welding equipment performs laser heat-conducting welding on the back welding area using a second laser beam, wherein the first center of action of the first laser beam in the front welding area is located in front of the second center of action of the second laser beam in the back welding area along the welding direction.

[0016] Preferably, the relative distance between the first center of action and the second center of action in the welding direction is d, where d is (0.5~0.75) BW.

[0017] Preferably, the first optimized process parameters include the arc spacing S between the first laser beam and the arc beam, the defocusing amount Δf1 of the first laser beam relative to the welding surface, and the focal spot diameter of the first laser beam. And the angle range θ1 between the first laser beam and the normal to the welding surface; where S is 2.0mm~5.0mm, and Δf1 is ±2mm. The value is 0.15mm to 0.6mm, and θ1 is ±10°.

[0018] Preferably, the second optimized process parameters include the scanning frequency f of the second laser beam, the defocusing amount Δf2 of the second laser beam relative to the welding surface, and the focal spot diameter of the second laser beam. And the range θ2 of the angle between the second laser beam and the normal to the welding surface; where f is 30~200Hz, and Δf2 is 0. The value is 0.15mm to 0.6mm, and θ2 is ±10°.

[0019] Preferably, the welding speed of the first laser beam is the same as the welding speed of the second laser beam.

[0020] Preferably, the laser heat-conducting welding equipment performs laser heat-conducting welding on the back welding area using a second laser beam. The second laser beam scans along the welding direction along a preset trajectory, and the second optimized process parameters include the focal spot diameter of the second laser beam. and the scanning amplitude of the second laser beam in,

[0021] Preferably, the first optimized process parameters are determined through the following steps:

[0022] Establish the correlation between the process parameters of the laser-arc hybrid welding and the front weld width FW and back weld width BW of the weld joint formed by them;

[0023] Based on the aforementioned correlation, the first optimized process parameters are determined according to the appropriate value ranges of the front melt width FW and the back melt width BW.

[0024] Preferably, when two welded workpieces of equal thickness are butt-assembled to form a flat workpiece to be welded, the local assembly gap of the workpiece to be welded is not greater than Δx, where Δx is the smaller of 0.3δ and 0.5mm; the misalignment is not greater than Δy, where Δy is the smaller of 0.2δ and 0.5mm; where δ is the minimum thickness of the two welded workpieces.

[0025] Secondly, the present invention also provides a welding apparatus for implementing the method for improving the elongation of high-strength aluminum alloy medium-thick plate welded joints as described in any of the above technical solutions, comprising a laser-arc hybrid welding device and a laser heat-conducting welding device. The laser-arc hybrid welding device includes a first laser head and an arc welding gun, wherein the first laser head is used to generate a first laser beam and the arc welding gun is used to generate an arc beam; the laser heat-conducting welding device includes a second laser head, wherein the second laser head is used to generate a second laser beam.

[0026] (III) Beneficial Effects

[0027] The above-described technical solution of the present invention has at least the following advantages:

[0028] 1. Laser-arc hybrid welding is performed on the front welding area of ​​the flat workpiece using the first optimized process parameters. Simultaneously, laser heat conduction welding is performed on the back welding area of ​​the flat workpiece using the second optimized process parameters. The two heat sources on the front and back are positioned one after the other, and the second laser beam is applied to the back of the molten pool or the high-temperature zone of the weld, increasing the energy absorption rate of the scanning laser on the back surface of the weld. This achieves a smooth transition between the weld back fusion zone and the corner of the base material surface, effectively alleviating stress concentration at the weld toe on the back of the weld joint. While ensuring that the current weld joint strength meets design requirements, the tensile elongation after fracture of the weld joint is further improved, thereby enhancing the plasticity of the material. The scanning laser also appropriately widens and modifies the weld width on the back, further improving the forming quality of the back of the weld.

[0029] 2. This invention can improve the metallurgical bonding interface formed by the solidification of the molten pool after it flows to the solid surface of the base material, while keeping the weld back width ratio basically unchanged, into a metallurgical bonding interface formed in the fusion zone of the weld joint (laser-arc hybrid welding is performed in the front welding area, forming a molten pool in the front welding area; laser heat conduction welding is performed in the back welding area, forming a molten pool in the back welding area as well; through the connection and solidification of the two molten pools, a metallurgical bonding interface with higher strength is formed at the weld joint), significantly increasing the degree of metallurgical bonding at the weld toe, thereby increasing the strength and plasticity of the weld joint. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of the welding device provided in an embodiment of the present invention.

[0032] Figure 2 This is a schematic diagram of the working state of the welding device provided in an embodiment of the present invention.

[0033] Figure 3 This is a cross-sectional schematic diagram of a welded joint of 7050 high-strength aluminum alloy medium-thick plate in the prior art.

[0034] Figure 4 This is a cross-sectional schematic diagram of a 7050 high-strength aluminum alloy medium-thick plate welded joint provided in an embodiment of the present invention.

[0035] Figure 5 It is a metallographic image of the macroscopic morphology of the cross-section of a welded joint in the prior art.

[0036] Figure 6 yes Figure 5 A magnified metallographic image of the first corner in the middle.

[0037] Figure 7 yes Figure 5 A magnified metallographic image of the second corner in the middle section.

[0038] Figure 8 This is a metallographic image of the macroscopic morphology of the cross-section of the welded joint provided in an embodiment of the present invention.

[0039] Figure 9 yes Figure 8 A magnified metallographic image of the first corner in the middle.

[0040] Figure 10 yes Figure 9 A magnified metallographic image of the second corner in the middle section.

[0041] The labels for the attached figures are as follows:

[0042] 1. First laser beam; 2. Arc welding torch; 3. Second laser beam; 4. Weld seam; 5. Molten pool; 6. Penetrating pinhole; 7. Weld zone; 8. Heat-affected zone; 9. Base metal zone; 10. Fusion line; 11. First corner; 12. Second corner. Detailed Implementation

[0043] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0044] It should be noted that when a component is referred to as "fixed to" or "set on" another component, it can be located directly on or indirectly on the other component. When a component is referred to as "connected to" another component, it can be directly or indirectly connected to the other component.

[0045] It should be understood that the terms "length", "width", "up", "down", "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, and are only for the convenience of describing the present invention, and do not indicate that the device or element must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0046] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating relative importance or the number of technical features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. The specific implementation of this invention will be described in more detail below with reference to specific embodiments:

[0047] like Figure 1 and Figure 2 As shown, this embodiment of the invention provides a welding apparatus, including a laser-arc hybrid welding device and a laser heat-conducting welding device. The laser-arc hybrid welding device includes a first laser head and an arc welding gun. The first laser head is used to generate a first laser beam 1, and the arc welding gun 2 is used to generate an arc beam. The laser heat-conducting welding device includes a second laser head, which is used to generate a second laser beam 3. The laser-arc hybrid welding device performs laser-arc hybrid welding on the front welding area using the first laser beam 1 and the arc beam, and the laser heat-conducting welding device performs laser heat-conducting welding on the back welding area using the second laser beam 3. That is, the first laser beam 1 acts on the front of the molten pool 5, forming a penetrating hole 6 in the molten pool 5, and the second laser beam 3 acts on the back of the molten pool 5, ultimately forming a weld 4.

[0048] This invention also provides a method for improving the elongation of welded joints in high-strength aluminum alloy medium-thick plates, used to increase the tensile elongation after fracture of welded joints formed by laser-arc hybrid welding, comprising the following steps:

[0049] S100. Two welding workpieces of equal thickness are butted together to form a flat workpiece to be welded.

[0050] S200. Determine the first optimized process parameters of the laser-arc hybrid welding equipment and the second optimized process parameters of the laser heat-conducting welding equipment. The second optimized process parameters are determined based on the front weld width FW and the back weld width BW of the weld joint formed by the first optimized process parameters.

[0051] S300: Laser-arc hybrid welding is performed on the front welding area of ​​the flat workpiece using the first optimized process parameters. Simultaneously, laser heat-conducting welding is performed on the back welding area of ​​the flat workpiece using the second optimized process parameters. During heat-conducting welding, laser radiation energy acts on the material surface, and the laser radiation energy is converted into heat on the surface. The surface heat diffuses inward through heat conduction, melting the material and forming a molten pool at the junction of the two materials. Using laser heat-conducting welding for the back welding area does not significantly change the back width ratio of the weld, thus keeping the back width ratio of the weld within a suitable range.

[0052] Specifically, the laser-arc hybrid welding described in this embodiment includes, but is not limited to, laser-MIG hybrid welding and laser-TIG hybrid welding.

[0053] In one embodiment, the laser-arc hybrid welding equipment performs laser-arc hybrid welding on the front welding area using a first laser beam and an arc beam, and the laser heat-conducting welding equipment performs laser heat-conducting welding on the back welding area using a second laser beam. The first center of action of the first laser beam on the front welding area is located in front of the second center of action of the second laser beam on the back welding area along the welding direction.

[0054] In one embodiment, the relative distance between the first and second action centers in the welding direction is d, where d is (0.5–0.75) BW. In existing technologies, dual-beam laser synchronous welding requires high precision in the positioning of the heat sources on both sides, generally needing to ensure that the positions of the two laser beams acting on the weld are essentially coincident. However, in this embodiment, the precision requirements for the positions of the front heat source (the first laser beam and the arc welding heat source) and the back heat source (the second laser beam) are not very high, which reduces the precision requirements on the process, thereby reducing equipment setup time and accuracy, and ultimately improving welding efficiency.

[0055] In one embodiment, the first optimized process parameters include the arc spacing S between the first laser beam and the arc beam, the defocusing amount Δf1 of the first laser beam relative to the welding surface, and the focal spot diameter of the first laser beam. And the angle range θ1 between the first laser beam and the normal to the welding surface; where S is 2.0mm~5.0mm, and Δf1 is ±2mm. The value is 0.15mm to 0.6mm, and θ1 is ±10°.

[0056] In one embodiment, the second optimized process parameters include the scanning frequency f of the second laser beam, the defocusing amount Δf2 of the second laser beam relative to the welding surface, and the focal spot diameter of the second laser beam. And the range θ2 of the angle between the second laser beam and the normal to the welding surface; where f is 30~200Hz, and Δf2 is 0. The value is 0.15mm to 0.6mm, and θ2 is ±10°.

[0057] In one embodiment, the welding speed of the first laser beam is the same as that of the second laser beam.

[0058] In one embodiment, the laser heat-conducting welding equipment performs laser heat-conducting welding on the back welding area using a second laser beam. The second laser beam scans along the welding direction along a preset trajectory, and the second optimized process parameters include the focal spot diameter of the second laser beam. and the scanning amplitude of the second laser beam in,

[0059] In one embodiment, the first optimized process parameter is determined through the following steps:

[0060] Establish the correlation between the process parameters of laser-arc hybrid welding and the front weld width (FW) and back weld width (BW) of the weld joint formed by them;

[0061] Based on the correlation, the first optimized process parameters are determined according to the appropriate range of values ​​for the front melt width FW and the back melt width BW.

[0062] In one embodiment, when two weldable workpieces of equal thickness are butt-assembled to form a flat workpiece to be welded, the local assembly gap of the workpiece to be welded is not greater than Δx, where Δx is the smaller of 0.3δ and 0.5mm; the misalignment is not greater than Δy, where Δy is the smaller of 0.2δ and 0.5mm; where δ is the minimum thickness of the two weldable workpieces.

[0063] In one embodiment, both workpieces to be welded are made of 7050 aluminum alloy or 7075 aluminum alloy. The method provided in this embodiment is applicable to the welding of high-strength aluminum alloys, and is particularly suitable for 7XXX series aluminum alloys, such as 7050 aluminum alloy and 7075 aluminum alloy.

[0064] like Figure 3 , Figure 5 , Figure 6 as well as Figure 7 As shown, Figure 3 This is a schematic diagram showing the fracture location of the cross-section of a welded joint formed by laser-arc hybrid welding using only laser-arc hybrid welding equipment in the prior art. Figure 5 , Figure 6 as well as Figure 7 This is the metallographic image of the welded joint.

[0065] Analysis of the tensile fracture location revealed that the fracture originated at the weld toe on the back side of the weld joint and extended towards the weld's positive surface in an approximately perpendicular direction. Microstructural analysis of the weld joint's cross-section showed that although a metallurgical interface was formed during welding due to the molten pool flowing to the solid surface of the base metal, its strength was significantly weaker than that formed in the weld joint's fusion zone. Furthermore, compared to the positive surface, the angle between the weld's fusion zone and the base metal surface on the back side is abrupt, exhibiting an approximate angle α (90°–100°), which is smaller than the approximate angle β formed between the weld's fusion zone and the base metal surface on the positive side (β ≥ 120°). Therefore, the tensile fracture actually originated at the abrupt transition point between the weld's fusion zone and the base metal on the back side (where stress concentration is most severe) and extended upwards and downwards. This abrupt transition between the weld's fusion zone and the base metal on the back side is the primary reason for the low elongation after fracture in the 7050-T7451 aluminum alloy weld joint.

[0066] The following is a specific embodiment provided in this application:

[0067] In this embodiment, both welding workpieces are made of 3mm thick 7050-T7451 high-strength aluminum alloy. The welding workpieces are butt-assembled to form a flat workpiece to be welded. The front welding area is welded using laser-MIG arc hybrid welding technology. The specific welding process is as follows:

[0068] Step 1: Establish the correlation between the process parameters of the laser-MIG arc hybrid welding and the front weld width (FW) and back weld width (BW) of the resulting weld joint. The optimized process parameters for laser-MIG arc hybrid welding include: welding speed of 0.9 m / min, laser power of 2100 W, MIG welding current of 50 A, arc spacing S of 4.0 mm, the first laser beam 1 and the arc welding torch 2 being on the same welding plane, the defocusing amount Δf1 between the focal point of the first laser beam 1 and the welding surface being 0 mm, and the focal spot diameter... The diameter is 0.525 mm, and the angle θ1 between the first laser beam 1 and the normal of the welding surface is 8°. When welding with these optimized process parameters, the weld formation is full and the process is stable. The weld width on the front side is FW≈6.15 mm, the weld width on the back side is BW≈3.83 mm, and the weld back width ratio is BW / FW≈0.62. Therefore, this set of process parameters is taken as the first optimized process parameters.

[0069] Step 2: Keep the right-angle welding edges of the two welded workpieces of equal thickness, that is, there is no need to open the welding bevel. Degrease and remove oxide film from the welding edge and the area near the seam.

[0070] Step 3: Assemble the two welding workpieces to form a flat workpiece to be welded. Ensure that the local assembly gap is no greater than △x, where △x is 0.5mm; and that the assembly misalignment is no greater than △y, where △y is 0.3mm.

[0071] Step 4: Set the second optimized process parameters for the second laser beam 3. The second laser beam 3 is a scanning laser beam with a circular scanning trajectory and a scanning amplitude of... The value is 4mm, the scanning frequency is 100Hz, the second laser beam 3 uses zero defocus, that is, Δf2 is zero, and the focal spot diameter is... The diameter of the second laser beam 3 is 0.525 mm, and the angle θ2 between the second laser beam 3 and the normal to the welding surface is 8°. The center of action of the second laser beam 3 on one side of the base material is located behind the center of action of the first laser beam 1 on the other side of the base material, and the relative distance d between the two in the welding direction is 2.5 mm. The welding speed of the second laser beam 3 is the same as that of the first laser beam 1. The laser welding mode of the second laser beam 3 is heat-conducting welding, that is, the laser power should not be too high, and the laser power is set to 1600W.

[0072] Step 5: Double-sided welding is performed (i.e., laser-arc hybrid welding equipment performs laser-arc hybrid welding on the front welding area through the first laser beam and the arc beam, and laser heat conduction welding equipment performs laser heat conduction welding on the back welding area through the second laser beam). In other words, laser-MIG off-axis hybrid welding is used on one side of the base material to obtain deep penetration welding, and on the other side of the weld pool and high temperature zone, the second laser beam 3 is asymmetrically set to achieve scanning welding in the heat conduction welding mode.

[0073] Please see Figure 4 ,as well as Figure 8 , Figure 9 and Figure 10 The metallographic image is shown. The second laser beam 3 scans the back side of the molten pool or the high-temperature zone of the weld. The molten pool or the high-temperature zone of the weld has a high energy absorption rate of the second laser beam 3. The second laser beam 3 can effectively alleviate the abrupt transition between the fusion zone on the back side of the weld and the surface of the base material, that is, it can expand the approximate angle α formed by the fusion zone on the back side of the weld and the surface of the base material to ≥120°, effectively alleviating the stress concentration of the weld joint, modifying the back side of the weld, and further improving the weld back-side formation. Under the premise that the weld back width ratio remains basically unchanged, the metallurgical bonding interface formed by the solidification of the molten pool after flowing to the solid surface of the base material can be improved into a metallurgical bonding interface formed by the fusion zone of the weld joint, significantly increasing the metallurgical bonding degree of the weld toe. After adopting the method for improving the elongation of high-strength aluminum alloy medium-thick plate welded joints provided in this embodiment, the elongation after fracture of the 7050-T7451 high-strength aluminum alloy medium-thick plate welded joint can reach the range of 2.5%-5.0%, and the tensile strength can also be further improved, with an improvement of about 5%-20%.

[0074] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for improving the elongation of welded joints in high-strength aluminum alloy medium-thick plates, used to improve the tensile elongation after fracture of welded joints formed by laser-arc hybrid welding, characterized in that, Includes the following steps: S100. Two welded workpieces of equal thickness are butt-assembled to form a flat workpiece to be welded, such that the local assembly gap of the workpiece to be welded is no greater than Δx, where Δx is the smaller of 0.3δ and 0.5mm; the assembly misalignment is no greater than Δy, where Δy is the smaller of 0.2δ and 0.5mm; where δ is the minimum thickness of the two welded workpieces. S200. Determine the first optimized process parameters of the laser-arc hybrid welding equipment and the second optimized process parameters of the laser heat-conducting welding equipment. The second optimized process parameters are determined based on the front weld width (FW) and back weld width (BW) of the weld joint formed by the first optimized process parameters. The laser heat-conducting welding equipment performs laser heat-conducting welding on the back welding area using a second laser beam. The second laser beam scans along the welding direction using a preset trajectory. The second optimized process parameters include the focal spot diameter (Ø) of the second laser beam. L2 and the scanning amplitude of the second laser beam Ø SL ;in, The first optimized process parameter is determined through the following steps: Establish the correlation between the process parameters of the laser-arc hybrid welding and the front weld width FW and back weld width BW of the weld joint formed by them; Based on the aforementioned correlation, the first optimized process parameters are determined according to the appropriate value range of the front melt width FW and the back melt width BW. S300. Laser-arc hybrid welding is performed on the front welding area of ​​the flat workpiece using the first optimized process parameters, and laser thermal conductive welding is performed on the back welding area of ​​the flat workpiece using the second optimized process parameters.

2. The method for improving the elongation of welded joints in high-strength aluminum alloy medium-thick plates as described in claim 1, characterized in that, The laser-arc hybrid welding equipment performs laser-arc hybrid welding on the front welding area using a first laser beam and an arc beam, and the laser heat-conducting welding equipment performs laser heat-conducting welding on the back welding area using a second laser beam. The first center of action of the first laser beam in the front welding area is located in front of the second center of action of the second laser beam in the back welding area along the welding direction.

3. The method for improving the elongation of welded joints in high-strength aluminum alloy medium-thick plates as described in claim 2, characterized in that, The relative distance between the first center of action and the second center of action in the welding direction is d, where d is (0.5~0.75) BW.

4. The method for improving the elongation of welded joints in high-strength aluminum alloy medium-thick plates as described in claim 2, characterized in that, The first optimized process parameters include the arc distance S between the first laser beam and the arc beam, the defocusing amount Δf1 of the first laser beam relative to the welding surface, and the focal spot diameter Ø of the first laser beam. L1 And the range θ1 of the angle between the first laser beam and the normal to the welding surface; where S is 2.0mm~5.0mm, △f1 is ±2mm, Ø L1 The value is 0.15mm to 0.6mm, and θ1 is ±10°.

5. The method for improving the elongation of welded joints in high-strength aluminum alloy medium-thick plates as described in claim 2, characterized in that, The second optimized process parameters include the scanning frequency f of the second laser beam, the defocusing amount Δf2 of the second laser beam relative to the welding surface, and the focal spot diameter Ø of the second laser beam. L2 And the range of the angle between the second laser beam and the normal to the welding surface, θ2; where f is 30~200Hz, Δf2 is 0, Ø L2 The value is 0.15mm to 0.6mm, and θ2 is ±10°.

6. The method for improving the elongation of welded joints in high-strength aluminum alloy medium-thick plates as described in claim 2, characterized in that, The welding speed of the first laser beam is the same as that of the second laser beam.

7. A welding apparatus for implementing the method for improving the elongation of welded joints of high-strength aluminum alloy medium-thick plates as described in any one of claims 1-6, characterized in that, include: A laser-arc hybrid welding device includes a first laser head and an arc welding gun, wherein the first laser head is used to generate a first laser beam and the arc welding gun is used to generate an arc beam; A laser thermal conductive welding device includes a second laser head, which is used to generate a second laser beam.

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