Method for improving mechanical property of high-strength aluminum alloy laser welding joint

Abstract

The invention relates to the technical field of laser welding, in particular to a high-strength aluminum alloy laser welding joint mechanical property improving method which comprises the steps that in the high-strength aluminum alloy laser welding process, a cooling device and a smoke dust recycling device are sequentially and additionally arranged behind a molten pool of a welding plane; inert gas with high water vapor content is sprayed to weld metal which is solidified and still in a high-temperature state behind a molten pool through the cooling device, and smoke steam or water vapor generated by heat absorption is sucked away from a welding area through the smoke dust recycling device; and the high-strength aluminum alloy is subjected to low-temperature aging treatment, and precipitation of an aging strengthening phase is promoted. The mechanical property of a welded joint can be remarkably improved, the welding piece shape correction difficulty is reduced, and the welding piece size precision and the operation efficiency are improved.

Description

Technical Field

[0001] The present application relates to the field of laser welding technology, and in particular to a method for improving the mechanical properties of high-strength aluminum alloy laser welded joints. Background Art

[0002] High-strength aluminum alloys are increasingly being used in aircraft fuselage structures within the aviation sector. To further improve material utilization or reduce structural weight, some thin-walled shells, pipelines, and other structures made of high-strength aluminum alloys are using welding instead of riveting to achieve metallurgical connections. Conventional arc welding, with its high heat input, results in significant weld deformation and severe joint softening. Compared to conventional arc welding, laser welding or laser arc hybrid welding not only significantly reduces welding heat input, facilitating grain refinement and improving joint performance, but also allows for further control of joint structure and performance through the addition of filler wire during the welding process, offering broader application prospects.

[0003] Typical examples of high-strength aluminum alloys are 7XXX and 2XXX aluminum alloys. Both 7XXX and 2XXX aluminum alloys are heat-treatable and hardened aluminum alloys. After the base metal undergoes melt welding, the strengthening phase in the original base metal dissolves into the molten pool and cannot be fully precipitated during the subsequent cooling process, resulting in a certain softening of the welded joints. Existing research shows that compared with conventional arc welding, the softening degree of laser welding or laser arc hybrid welding joints is relatively mild. However, it sometimes still cannot meet the service requirements of some specific structures. Post-weld solution aging heat treatment is one of the effective measures to restore or improve the strength of high-strength aluminum alloys. For some complex welded structures such as boxes, shells, and pipes, post-weld heat treatment may cause relatively large secondary deformation, which is difficult to correct. Therefore, in addition to conventional stress relief annealing, solution aging heat treatment is not allowed for such welds. This requires the welded joints to have relatively high strength and plasticity. Summary of the Invention

[0004] This application provides a method for improving the mechanical properties of high-strength aluminum alloy laser welded joints, which can significantly improve the mechanical properties of welded joints.

[0005] The method for improving the mechanical properties of high-strength aluminum alloy laser welded joints comprises: During the laser welding of high-strength aluminum alloys, a cooling device and a fume recovery device are sequentially installed behind the molten pool of the welding plane; The cooling device sprays an inert gas with a high water vapor content toward the weld metal that has solidified and is still in a high temperature state behind the molten pool, and the fume recovery device absorbs the fume or water vapor generated by heat absorption away from the welding area; The high-strength aluminum alloy is subjected to low-temperature aging treatment to promote the precipitation of aging-strengthening phase.

[0006] Furthermore, in the high-strength aluminum alloy laser welding process, before sequentially adding a cooling device and a smoke recovery device behind the molten pool of the welding plane, the method further includes: The high-strength aluminum alloy to be welded is cleaned, and the oil stains and oxide film on the surface of the high-strength aluminum alloy are completely removed, and then assembled and fixed after cleaning.

[0007] Furthermore, the high-strength aluminum alloy to be welded is cleaned, and the oil and oxide film on the surface of the high-strength aluminum alloy are completely removed. After cleaning, the assembly and fixing are performed, and the following steps are further included: The central axis of the laser beam is deflected in the opposite direction of the welding direction by a first angle, wherein the range of the first angle is 5° to 10°, and optimized welding process parameters are set.

[0008] Furthermore, the cooling device includes a mold cavity, an air inlet and a porous plate. The inert gas enters the mold cavity through the air inlet and is then blown toward the weld metal through the porous plate. The porous plate is densely covered with ventilation holes.

[0009] Furthermore, the ventilation holes include array arrangement and non-array arrangement. The apertures of the ventilation holes in the array arrangement are all equal, and the apertures of the ventilation holes in the non-array arrangement gradually decrease from bottom to top.

[0010] Furthermore, the included angle between the porous plate and the surface of the high-strength aluminum alloy is a second angle, and the range of the second angle is 30° to 60°.

[0011] Furthermore, the vertical distance between the cooling device and the surface of the high-strength aluminum alloy is 2 mm to 4 mm, and the horizontal distance between the cooling device and the molten pool is 2 mm to 8 mm.

[0012] Furthermore, the inert gas includes argon, high-purity argon or helium, and the humidity of the water vapor is not less than 80%.

[0013] Furthermore, the angle between the central axis of the welding gun and the normal of the surface of the high-strength aluminum alloy is a third angle, and the range of the third angle is 30° to 60°.

[0014] Furthermore, the aging temperature of the low-temperature aging treatment is 120° C. to 170° C., and the aging holding time is 5 h to 10 h.

[0015] The above technical solution of this application has the following advantages: The present application provides a method for improving the mechanical properties of high-strength aluminum alloy laser welded joints. During the high-strength aluminum alloy laser welding process, a cooling device and a smoke recovery device are sequentially arranged behind the molten pool of the welding plane. The cooling device sprays an inert gas with a high water vapor content toward the weld metal that has solidified and is still in a high-temperature state behind the molten pool. The smoke recovery device absorbs the smoke or water vapor generated by heat absorption from the welding area, and performs low-temperature aging treatment on the high-strength aluminum alloy to promote the precipitation of aging-strengthening phases. This can significantly improve the mechanical properties of the welded joint, reduce the difficulty of weldment correction, and improve the dimensional accuracy and operating efficiency of the weldment. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific implementation methods or the description of the prior art. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0017] Figure 1 Schematic diagram of laser-MIG arc hybrid welding provided for this application; Figure 2 A schematic diagram of the structure of the cooling device provided in this application; Figure 3 Schematic diagram of the porous plate structure with array-type ventilation holes provided in this application; Figure 4 Schematic diagram of the porous plate structure with non-arrayed ventilation holes provided in this application; Figure 5 Schematic diagram of laser-TIG arc hybrid welding provided for this application; Figure 6 Schematic diagram of laser wire welding provided for this application.

[0018] Figure numerals: 1-laser head; 2-laser beam; 3-MIG welding gun; 4-cooling device; 41-mold cavity; 42-air inlet; 43-porous plate; 44-vent; 5-smoke recovery device; 6-molten pool; 7-keyhole; 8-base material; 9-solidified metal; 10-TIG welding gun; 11-wire feeding device; 12-welding wire. DETAILED DESCRIPTION

[0019] In the following description, specific details such as specific system structures and techniques are provided for purposes of illustration rather than limitation to facilitate a thorough understanding of the embodiments of the present application. However, it will be apparent to those skilled in the art that the present application may be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to avoid obscuring the description of the present application with unnecessary detail.

[0020] It should be understood that when used in the present specification and the appended claims, the term "comprising" indicates the presence of described features, integers, steps, operations, elements and / or components, but does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or collections thereof.

[0021] In addition, in the description of the present application specification and the appended claims, the terms "first", "second", "third", etc. are only used to distinguish the descriptions and cannot be understood as indicating or implying relative importance.

[0022] References to "one embodiment" or "some embodiments" in this specification mean that one or more embodiments of the present application include a particular feature, structure, or characteristic described in conjunction with that embodiment. Thus, phrases such as "in one embodiment," "in some embodiments," "in other embodiments," and "in other embodiments" appearing in various places in this specification do not necessarily refer to the same embodiment, but rather mean "one or more but not all embodiments," unless otherwise specifically emphasized. The terms "including," "comprising," "having," and variations thereof all mean "including but not limited to," unless otherwise specifically emphasized. "Multiple" means "two or more."

[0023] In addition to solution aging heat treatment, methods for improving the strength and ductility of welded joints include adding trace amounts of rare earth elements (such as Sc and Zr) to the filler wire and optimizing welding process parameters. However, while adding trace elements can further refine the grain size, the improvement in weld joint performance is very limited, at approximately 2% to 8%. Optimizing welding process parameters to improve weld formation and, in turn, improve the performance of the as-welded joint is also limited, generally not exceeding 10%. To further address this issue, this application proposes a method for improving the mechanical properties of high-strength aluminum alloy laser welded joints.

[0024] The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0025] The method for improving the mechanical properties of high-strength aluminum alloy laser welded joints provided in an embodiment of the present application includes: during the high-strength aluminum alloy laser welding process, a cooling device and a smoke recovery device are sequentially arranged behind the molten pool of the welding plane; an inert gas with a high water vapor content is sprayed toward the weld metal that has solidified and is still in a high-temperature state behind the molten pool through the cooling device, and the smoke recovery device absorbs the smoke or water vapor generated by heat absorption from the welding area; and a low-temperature aging treatment is performed on the high-strength aluminum alloy to promote the precipitation of aging-strengthening phases.

[0026] In some embodiments, during the laser welding process of high-strength aluminum alloy, before sequentially adding a cooling device and a smoke recovery device behind the molten pool of the welding plane, it also includes: cleaning the high-strength aluminum alloy to be welded, thoroughly removing the oil and oxide film on the surface of the high-strength aluminum alloy, and assembling and fixing it after cleaning.

[0027] In some embodiments, the high-strength aluminum alloy to be welded is cleaned, and the oil and oxide film on the surface of the high-strength aluminum alloy are completely removed. After cleaning and assembly and fixation, it also includes: deflecting the central axis of the laser beam in the opposite welding direction by a first angle, the first angle range is 5° to 10°, and setting optimized welding process parameters.

[0028] In some embodiments, the cooling device includes a mold cavity, an air inlet and a porous plate. The inert gas enters the mold cavity through the air inlet and is then blown toward the weld metal through the porous plate. The porous plate is densely covered with ventilation holes.

[0029] In some embodiments, the ventilation holes include an array arrangement and a non-array arrangement. The apertures of the ventilation holes in the array arrangement are all equal, and the apertures of the ventilation holes in the non-array arrangement gradually decrease from bottom to top.

[0030] In some embodiments, the angle between the porous plate and the surface of the high-strength aluminum alloy is a second angle, and the range of the second angle is 30° to 60°.

[0031] In some embodiments, the vertical distance between the cooling device and the surface of the high-strength aluminum alloy is 2 mm to 4 mm, and the horizontal distance between the cooling device and the molten pool is 2 mm to 8 mm.

[0032] In some embodiments, the inert gas includes argon, high-purity argon or helium, and the humidity of the water vapor is not less than 80%.

[0033] In some embodiments, the angle between the central axis of the welding gun and the normal of the surface of the high-strength aluminum alloy is a third angle, and the range of the third angle is 30° to 60°.

[0034] In some embodiments, the aging temperature of the low-temperature aging treatment is 120° C. to 170° C., and the aging holding time is 5 h to 10 h.

[0035] The method for improving the mechanical properties of high-strength aluminum alloy laser welded joints proposed in this application embodiment sprays an inert gas with a high water vapor content into a high-temperature area lagging behind the molten pool by a certain distance during the welding process to accelerate the cooling of the weld metal. A low-temperature aging treatment is then performed to promote the precipitation of age-hardening phases, thereby significantly improving the mechanical properties of the welded joint. The method mainly includes the following steps: Parts cleaning and assembly: Clean the parts to be welded (e.g. 7050-T7451 aluminum alloy, wall thickness 3mm) to thoroughly remove the oil and oxide film on the surface of the parts; after cleaning, assemble and fix the parts with equal thickness, and the maximum local gap shall not exceed 0.5mm.

[0036] Robot instruction: The central axis of the laser beam is deflected in the opposite direction of the welding direction by a first angle α, ranging from 5° to 10°, with a specific value of 8°. Fiber laser-MIG paraxial hybrid welding is used, with optimized welding process parameters selected: welding speed 0.9 m / min, laser power 2400 W, defocus 0 mm, welding current 50 A, welding voltage 15.9 V, and arc spacing 4 ± 0.5 mm.

[0037] Laser welding is used to weld high-strength aluminum alloys: Figure 1 As shown, during the laser welding process, a cooling device 4 and a smoke recovery device 5 are sequentially arranged behind the molten pool of the welding plane. The cooling device 4 sprays an inert gas with a high water vapor content toward the weld metal that has solidified and is still in a high-temperature state behind the molten pool to achieve accelerated cooling of the weld metal. The smoke recovery device 5 absorbs the smoke or water vapor generated by heat absorption away from the welding area in a timely manner.

[0038] Carry out low temperature aging treatment on high strength aluminum alloy.

[0039] Parts are made of 7XXX and 2XXX high-strength aluminum alloys, with wall thicknesses ranging from 1mm to 6mm. When welding plates of unequal thickness, the thickness difference must not exceed 30% of the thinner wall thickness. When butt-jointing parts, the maximum local gap must not exceed 30% of the thinner wall thickness or 0.5mm, whichever is less.

[0040] like Figures 2 to 4As shown, the cooling device 4 includes a cavity 41, an air inlet 42 and a porous plate 43. Inert gas enters the cavity 41 through the air inlet 42 and is then blown toward the weld metal through the porous plate 43. The porous plate 43 is densely covered with vents 44. The vents 44 include array-type arrangements and non-array-type arrangements. The apertures of the vents 44 arranged in an array are all equal. The apertures of the vents 44 arranged in a non-array gradually decrease from the bottom to the top, so that the bottom of the cooling device 4 has a larger air flow function, that is, a better accelerated cooling function of the solid weld metal close to the molten pool is achieved.

[0041] The angle between the porous plate 43 and the surface of the parent material is a second angle γ, which ranges from 30° to 60°, with a specific value of 45°. The vertical distance between the cooling device 4 and the surface of the parent material is 2 mm to 4 mm, and the horizontal distance between the cooling device 4 and the molten pool 6 is approximately 2 mm to 8 mm. The temperature of the solidified but still high-temperature weld metal ranges from approximately 350°C to 530°C. The inert gas with a high water vapor content includes argon, high-purity argon, or helium, and the humidity of the high water vapor content is not less than 80%.

[0042] Laser welding methods include Figure 1 The laser-MIG paraxial hybrid welding shown in Figure 5 The laser-TIG paraxial hybrid welding shown and Figure 6 Laser welding with filler wire shown. When laser-MIG paraxial hybrid welding is used, the welding process parameters include welding speed, laser power, defocus, welding current, welding voltage, arc spacing, etc.; when laser-TIG paraxial hybrid welding is used, the welding process parameters include welding speed, laser power, defocus, welding current, welding voltage, wire feed speed, arc spacing, etc.; when laser welding with filler wire is used, the welding process parameters include welding speed, laser power, defocus, wire feed speed, wire spacing, etc.

[0043] In laser-MIG paraxial hybrid welding, the angle between the center axis of the MIG welding torch and the normal to the parent material surface is a third angle, β, which ranges from 30° to 60°, with a specific value of 45°. In laser-TIG paraxial hybrid welding, the angle between the center axis of the TIG welding torch and the normal to the parent material surface is also β, which ranges from 30° to 60°. The filler wire used in laser welding is ER5356 wire rich in Mg. Alternatively, ER5356 wire with a certain amount of strengthening elements added may be used. Strengthening elements include, but are not limited to, Er, Zr, and Sc.

[0044] The smoke recovery device 5, under the action of external power, has a certain suction force. The angle between the suction port and the surface of the base metal is 30° to 60°. The smoke recovery device 5 can promptly draw away the large amount of smoke or water vapor generated by the absorption of heat when the inert gas with high water vapor content contacts the high-temperature solid metal. The aging temperature of the low-temperature aging treatment is 120°C to 170°C, specifically 165°C ± 10°C, and the aging holding time is 5h to 10h, specifically 6h to 8h.

[0045] The method for improving the mechanical properties of high-strength aluminum alloy laser welded joints proposed in the embodiments of this application involves spraying an inert gas with a high water vapor content into a high-temperature region within a certain temperature range that lags behind the molten pool by a certain distance during the welding process. This accelerates the cooling rate of the weld metal, achieves a certain water quenching effect, and enhances the supersaturation state of the solid solution in the weld metal. A low-temperature aging process is then used to promote the precipitation of age-strengthening phases, achieving a significant improvement in the mechanical properties of the welded joint. This method replaces the welding + solid solution + water quenching + aging process with a welding + low-temperature aging process, which can minimize the effects of heat treatment deformation caused by the water quenching process, reduce the difficulty of weldment correction, and improve weldment dimensional accuracy and operating efficiency.

[0046] The cooling device's porous plates are angled relative to the base metal surface, and the orientation of the plate's vents mirrors the direction of the smoke recovery device's intake port. This facilitates the timely removal of smoke and water vapor generated during the cooling process from the weld zone, preventing it from affecting the weld pool and nearby areas. When the vents are arranged in a non-array pattern, the apertures gradually decrease from bottom to top, allowing the bottom of the cooling device to have a greater cooling airflow, effectively accelerating the cooling of the solid weld metal near the weld pool.

[0047] This solution can achieve 7050-T7451 high-strength aluminum alloy welded joints with strengths reaching 80% to 90% of the parent material, while also increasing elongation by over 20%. Compared to the existing welding, solutionizing, water quenching, and aging process, this solution minimizes the effects of heat treatment deformation caused by the water quenching process, reduces weld correction difficulty, improves weld dimensional accuracy, and boosts operational efficiency by over 30%.

[0048] It should be noted that the various embodiments in this specification are described in a progressive manner. Reference can be made to the same or similar parts between the various embodiments. Each embodiment focuses on the differences from other embodiments. This application is not limited to the specific structures described above and shown in the figures. Furthermore, for the sake of brevity, detailed descriptions of known methods and technologies are omitted here.

[0049] The above-described embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present application, and should all be included in the scope of protection of the present application.

Claims

1. A method for improving the mechanical properties of high-strength aluminum alloy laser welded joints, characterized in that: include: During the laser welding of high-strength aluminum alloys, a cooling device and a fume recovery device are sequentially installed behind the molten pool of the welding plane; The cooling device sprays an inert gas with a high water vapor content toward the weld metal that has solidified and is still at a high temperature behind the molten pool, and the fume recovery device absorbs the fume or water vapor generated by heat absorption away from the welding area; The high-strength aluminum alloy is subjected to low-temperature aging treatment to promote the precipitation of aging-strengthening phase.

2. The method for improving the mechanical properties of a high-strength aluminum alloy laser welded joint according to claim 1, characterized in that: The method further includes: before sequentially installing a cooling device and a fume recovery device behind the molten pool of the welding plane during the high-strength aluminum alloy laser welding process; The high-strength aluminum alloy to be welded is cleaned, and the oil stains and oxide film on the surface of the high-strength aluminum alloy are completely removed, and then assembled and fixed after cleaning.

3. The method for improving the mechanical properties of a high-strength aluminum alloy laser welded joint according to claim 2, characterized in that: The high-strength aluminum alloy to be welded is cleaned, and the oil and oxide film on the surface of the high-strength aluminum alloy are completely removed. After cleaning, the assembly and fixing are performed, and the following steps are further included: The central axis of the laser beam is deflected in the opposite direction of the welding direction by a first angle, wherein the range of the first angle is 5° to 10°, and optimized welding process parameters are set.

4. The method for improving the mechanical properties of a high-strength aluminum alloy laser welded joint according to claim 1, wherein: The cooling device includes a mold cavity, an air inlet and a porous plate. Inert gas enters the mold cavity through the air inlet and is then blown toward the weld metal through the porous plate. The porous plate is densely covered with ventilation holes.

5. The method for improving the mechanical properties of a high-strength aluminum alloy laser welded joint according to claim 4, characterized in that: The vent holes include array arrangement and non-array arrangement. The apertures of the vent holes in the array arrangement are all equal, while the apertures of the vent holes in the non-array arrangement gradually decrease from bottom to top.

6. The method for improving the mechanical properties of a high-strength aluminum alloy laser welded joint according to claim 4, characterized in that: The included angle between the porous plate and the surface of the high-strength aluminum alloy is a second angle, and the range of the second angle is 30° to 60°.

7. The method for improving the mechanical properties of a high-strength aluminum alloy laser welded joint according to claim 1, wherein: The vertical distance between the cooling device and the surface of the high-strength aluminum alloy is 2 mm to 4 mm, and the horizontal distance between the cooling device and the molten pool is 2 mm to 8 mm.

8. The method for improving the mechanical properties of a high-strength aluminum alloy laser welded joint according to claim 1, wherein: The inert gas includes argon, high-purity argon or helium, and the humidity of the water vapor is not less than 80%.

9. The method for improving the mechanical properties of a high-strength aluminum alloy laser welded joint according to claim 1, wherein: The angle between the central axis of the welding gun and the normal direction of the surface of the high-strength aluminum alloy is a third angle, and the range of the third angle is 30° to 60°.

10. The method for improving mechanical properties of high-strength aluminum alloy laser welded joints according to claim 1, characterized in that: The aging temperature of the low-temperature aging treatment is 120° C. to 170° C., and the aging holding time is 5 h to 10 h.

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