Laser welding method for improving forming quality of medium-thickness aluminum alloy lock bottom connector

Abstract

The invention discloses a laser welding method for improving the forming quality of a medium-thickness aluminum alloy lock bottom connector, and belongs to the technical field of laser machining. The problems that the quality of a welding seam formed by swing laser welding of a medium-thickness aluminum alloy lock bottom connector is insufficient, and the air hole defect is difficult to restrain are solved. The method comprises the following steps: 1, assembling a medium-thickness aluminum alloy lock bottom joint; and secondly, swing point ring laser welding is conducted. The laser welding method is used for improving the forming quality of the medium-thickness aluminum alloy lock bottom connector.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser processing. Background Art

[0002] Due to its advantages such as high strength, good plasticity, and excellent corrosion resistance, aluminum alloy is widely used in important national fields such as aerospace and national defense. Using medium-thickness aluminum alloy as the pressure-bearing structural material is an effective way to meet the lightweight development needs of key components of aerospace equipment such as missile compartments and fuel tanks. For the convenience of assembly and sealing requirements, the connection adopts the form of a lock-bottom joint; in addition, due to the continuous improvement of equipment technical indicators, more stringent requirements are put forward for the welding quality of medium-thickness aluminum alloy lock-bottom butt joints.

[0003] Laser welding technology has the advantages of a small heat-affected zone, good joint quality, and easy automation. In recent years, with the continuous improvement of laser welding technology, the laser power has been continuously increased and the beam quality has been continuously improved. Therefore, laser welding can achieve rapid welding with large penetration depth and high energy density, and has become one of the important technical means for equipment production in fields such as aerospace. Oscillating laser can improve the adaptability of joint gap and refine the weld microstructure by regularly stirring the molten pool. Based on the above advantages, oscillating laser welding is the commonly used welding method for medium-thickness aluminum alloy butt joints at present.

[0004] However, there are still some deficiencies in the oscillating laser welding of medium-thickness aluminum alloy lock-bottom joints at present: during the oscillating laser welding process, due to the large fluctuations in the shape of the molten pool edge over time, it is easy to cause undercut defects, which limits the further improvement of the weld forming quality; compared with thin-sheet aluminum alloy structures, during the laser welding of medium-thickness aluminum alloy, the keyhole stability decreases, and it is difficult to suppress the porosity defects due to the frequent collapse and closure of the keyhole. Therefore, it is urgent to develop a new laser energy field control method to improve the deficiencies existing in the oscillating laser welding of medium-thickness aluminum alloy lock-bottom joints. Summary of the Invention

[0005] The present invention aims to solve the problems of insufficient weld quality and difficulty in suppressing porosity defects in the oscillating laser welding of medium-thickness aluminum alloy lock-bottom joints, and further provides a laser welding method for improving the forming quality of medium-thickness aluminum alloy lock-bottom joints.

[0006] A laser welding method for improving the forming quality of a lock-bottom joint is carried out according to the following steps:

[0007] I. Assembly of medium-thickness aluminum alloy lock-bottom joint:

[0008] Assemble the aluminum alloy lock-bottom joint, then perform laser tack welding, and finally fix it with a tooling fixture to form a specimen to be welded;

[0009] II. Perform oscillating spot-ring laser welding:

[0010] Using a point-ring laser and a swing mode, under the conditions that the total power of the point-ring laser is 4000W - 5500W, the welding speed is 1.5m / min - 3m / min, the swing amplitude is 1.5mm - 2.5mm, and the swing frequency is 50Hz - 250Hz, center the point-ring laser on the weld center line of the lock-bottom joint of the specimen to be welded, and move along the welding path according to the swing path, then the laser welding method for improving the forming quality of the medium-thickness aluminum alloy lock-bottom joint is completed;

[0011] The total power of the point-ring laser mentioned above is the sum of the point light power and the ring light power, and the point light power accounts for 50% - 90% of the total power of the point-ring laser.

[0012] The beneficial effects of the present invention are:

[0013] 1. The method of the present invention makes up for the deficiencies of the traditional swing laser welding technology, combines the swing laser with the energy field control method of the point-ring laser, changes the thermal field distribution during the welding process by introducing an annular light spot, suppresses the violent flow of liquid metal during the laser welding process, suppresses the generation of forming defects such as spatter and undercut, and improves the weld forming quality of the medium-thickness aluminum alloy lock-bottom joint;

[0014] 2. For the laser welding method of the present invention for improving the forming quality of the medium-thickness aluminum alloy lock-bottom joint, the introduction of the point-ring laser mode can effectively improve the stability of the keyhole during the laser welding process, reduce the occurrence frequency of keyhole collapse and closure, thereby effectively suppressing the process porosity defects that are difficult to avoid in the laser welding of medium-thickness aluminum alloys, and a high-quality medium-thickness aluminum alloy lock-bottom joint weld with good surface forming and no obvious porosity defects can be obtained.

[0015] 3. For the laser welding method of the present invention for improving the forming quality of the medium-thickness aluminum alloy lock-bottom joint, the stability of the penetration depth is improved. During the conventional laser welding process of medium-thick aluminum alloy plates, due to the increase in penetration depth, there are large fluctuations in the keyhole morphology, and it is difficult to maintain the keyhole depth at a stable level, resulting in large fluctuations in the weld penetration depth and incomplete penetration phenomena occurring in part of the length of the joint, making the medium-thickness aluminum alloy laser welding components unusable and increasing production costs. By introducing the point-ring laser mode, the stability degree of the keyhole depth is significantly improved, ensuring complete penetration of the lock-bottom joint, avoiding rework due to incomplete penetration of the joint, and achieving the effect of reducing costs and increasing efficiency. Description of the Drawings

[0016] Figure 1 Schematic diagram of the laser welding method for improving the forming quality of the medium-thickness aluminum alloy lock-bottom joint in Example 1; where 1 is a solid-state laser, 2 is the internal core of the two-in-one optical fiber, 3 is the external ring core of the two-in-one optical fiber, 4 is the two-in-one optical fiber, 5 is a swing welding head, 6 is a medium-thickness aluminum alloy lock-bottom joint, and 7 is a swing laser welding path;

[0017] Figure 2 Schematic diagram of the bottom-locking joint structure in Step 1 of the embodiment, where H is the thickness at the butt joint position, h is the bottom-locking thickness, d1 is the butt joint gap, and d2 is the butt joint misalignment width;

[0018] Figure 3 Surface morphology diagram of the weld seam obtained by single laser welding in Comparative Experiment 1;

[0019] Figure 4 Longitudinal section metallographic diagram of the weld seam obtained by single laser welding in Comparative Experiment 1;

[0020] Figure 5 Radiographic inspection diagram of the joint porosity defect obtained by single laser welding in Comparative Experiment 1;

[0021] Figure 6 Surface morphology diagram of the weld seam obtained by oscillating single laser welding in Comparative Experiment 2;

[0022] Figure 7 Longitudinal section metallographic diagram of the weld seam obtained by oscillating single laser welding in Comparative Experiment 2;

[0023] Figure 8 Radiographic inspection diagram of the joint porosity defect obtained by oscillating single laser welding in Comparative Experiment 2;

[0024] Figure 9 Surface morphology diagram of the weld seam obtained by oscillating spot-ring laser welding in Embodiment 1;

[0025] Figure 10 Longitudinal section metallographic diagram of the weld seam obtained by oscillating spot-ring laser welding in Embodiment 1;

[0026] Figure 11 Schematic diagram of radiographic inspection of joint porosity defect obtained by oscillating spot-ring laser welding in Embodiment 1. Specific implementation method

[0027] Specific implementation method 1: A laser welding method for improving the forming quality of medium-thickness aluminum alloy bottom-locking joints in this implementation method is carried out according to the following steps:

[0028] I. Assembly of medium-thickness aluminum alloy bottom-locking joints:

[0029] Assemble the aluminum alloy bottom-locking joints, then perform laser tack welding, and finally fix them with tooling fixtures to form a specimen to be welded;

[0030] II. Perform oscillating spot-ring laser welding:

[0031] Using a point-ring laser and a swing mode, under the conditions that the total power of the point-ring laser is 4000W - 5500W, the welding speed is 1.5m / min - 3m / min, the swing amplitude is 1.5mm - 2.5mm, and the swing frequency is 50Hz - 250Hz, center the point-ring laser on the weld center line of the bottom-lock joint of the specimen to be welded, and move along the welding path according to the swing path, then the laser welding method for improving the forming quality of the medium-thickness aluminum alloy bottom-lock joint is completed;

[0032] The total power of the point-ring laser mentioned above is the sum of the point light power and the ring light power, and the point light power accounts for 50% - 90% of the total power of the point-ring laser.

[0033] In this embodiment, through the coupling of the swing laser mode and the point-ring laser mode, combining the advantages of the two laser energy field control means, on the basis of the swing laser improving the gap adaptability of the bottom-lock joint and suppressing the porosity defects to a certain extent, the point-ring laser is introduced to optimize the laser energy field distribution, improve the keyhole stability during the laser welding process, suppress forming defects such as spatter and undercut, and further suppress the porosity defects, and finally obtain a high-quality medium-thickness aluminum alloy bottom-lock joint weld with excellent surface forming quality and no obvious porosity defects.

[0034] The beneficial effects of this embodiment are as follows:

[0035] 1. The method of this embodiment makes up for the deficiencies of the traditional swing laser welding technology, combines the swing laser and the point-ring laser energy field control methods, changes the heat field distribution during the welding process by introducing an annular light spot, suppresses the violent flow of liquid metal during the laser welding process, suppresses the generation of forming defects such as spatter and undercut, and improves the weld forming quality of the medium-thickness aluminum alloy bottom-lock joint;

[0036] 2. For the laser welding method for improving the forming quality of the medium-thickness aluminum alloy bottom-lock joint of this embodiment, the introduction of the point-ring laser mode can effectively improve the keyhole stability during the laser welding process, reduce the occurrence frequency of keyhole collapse and closure, thereby effectively suppressing the process porosity defects that are inevitable in the laser welding of medium-thickness aluminum alloy, and a high-quality medium-thickness aluminum alloy bottom-lock joint weld with good surface forming and no obvious porosity defects can be obtained.

[0037] 3. For the laser welding method for improving the forming quality of the medium-thickness aluminum alloy bottom-lock joint of this embodiment, the penetration stability is improved. During the conventional laser welding process of medium-thick aluminum alloy plates, due to the increase in penetration, there are large fluctuations in the keyhole morphology, and it is difficult to maintain the keyhole depth at a stable level, resulting in large fluctuations in the weld penetration and incomplete penetration in part of the joint length, making the medium-thickness aluminum alloy laser welding components unusable and increasing production costs. By introducing the point-ring laser mode, the stability degree of the keyhole depth is significantly improved, ensuring complete penetration of the bottom-lock joint, avoiding rework due to incomplete penetration of the joint, and achieving the effect of reducing costs and increasing efficiency.

[0038] Embodiment 2: The difference between this embodiment and Embodiment 1 is that the aluminum alloy lock bottom joint described in Step 1 is a lock bottom joint after acid-base cleaning. Others are the same as Embodiment 1.

[0039] Embodiment 3: The difference between this embodiment and either Embodiment 1 or 2 is that the aluminum alloy described in Step 1 is 5-series aluminum alloy or 6-series aluminum alloy. Others are the same as Embodiment 1 or 2.

[0040] Embodiment 4: The difference between this embodiment and any one of Embodiments 1 to 3 is that the thickness of the docking position of the lock bottom joint described in Step 1 is 8 mm to 10 mm. Others are the same as Embodiment 3.

[0041] Embodiment 5: The difference between this embodiment and any one of Embodiments 1 to 4 is that the lock bottom thickness of the lock bottom joint described in Step 1 is 4 mm to 5 mm. Others are the same as Embodiments 1 to 4.

[0042] Embodiment 6: The difference between this embodiment and any one of Embodiments 1 to 5 is that the docking gap of the lock bottom joint described in Step 1 is 0 mm to 0.2 mm. Others are the same as Embodiments 1 to 5.

[0043] Embodiment 7: The difference between this embodiment and any one of Embodiments 1 to 6 is that the docking misalignment width of the lock bottom joint described in Step 1 is 0 mm to 0.2 mm. Others are the same as Embodiments 1 to 6.

[0044] Embodiment 8: The difference between this embodiment and any one of Embodiments 1 to 7 is that the swing mode described in Step 2 is circular swing, linear swing, figure-eight swing or infinity swing. Others are the same as Embodiments 1 to 7.

[0045] Embodiment 9: The difference between this embodiment and any one of Embodiments 1 to 8 is that the dot-ring laser described in Step 2 is output by a two-in-one optical fiber. Others are the same as Embodiments 1 to 8.

[0046] Embodiment 10: The difference between this embodiment and any one of Embodiments 1 to 9 is that the two-in-one optical fiber consists of an internal core and an external ring core. The diameter of the internal core is 50 μm to 200 μm, the diameter of the external ring core is 200 μm to 700 μm, and the width of the external ring core is 50 μm to 100 μm. Others are the same as Embodiments 1 to 9.

[0047] The following examples are used to verify the beneficial effects of the present invention:

[0048] Example 1, in combination withFigure 1 and 2 Detailed description:

[0049] A laser welding method for improving the forming quality of medium-thickness aluminum alloy bottom-locked joints, which is carried out according to the following steps:

[0050] I. Assembly of medium-thickness aluminum alloy bottom-locked joints:

[0051] Assemble the aluminum alloy bottom-locked joints so that the butt surfaces fit tightly, then carry out laser tack welding, and finally fix them with tooling fixtures to form a specimen to be welded;

[0052] II. Carry out oscillating spot-ring laser welding:

[0053] Using spot-ring laser and oscillating mode, under the conditions that the total power of the spot-ring laser is 5250 W, the welding speed is 2.5 m / min, the oscillating amplitude is 2 mm, and the oscillating frequency is 100 Hz, align the spot-ring laser with the center line of the weld of the specimen to be welded at the bottom-locked joint, and move along the welding path according to the oscillating path, then the laser welding method for improving the forming quality of medium-thickness aluminum alloy bottom-locked joints is completed;

[0054] The total power of the said spot-ring laser is the sum of the spot light power and the ring light power, and the spot light power is 4200 W, the ring light power is 1050 W, and the spot light power accounts for 80% of the total power of the spot-ring laser;

[0055] The aluminum alloy bottom-locked joint mentioned in step I is the bottom-locked joint after being cleaned with acid and alkali.

[0056] The specific acid and alkali cleaning is carried out according to the following steps: Immerse the bottom-locked joint in a NaOH solution with a mass concentration of 10% for 5 minutes, then take it out and rinse it with water at 60 °C, then clean it with industrial pure alcohol and dry it; Then immerse it in a HNO3 solution with a mass concentration of 30% for 1 minute, take it out and rinse it with water, then clean it with industrial pure alcohol and dry it.

[0057] The aluminum alloy mentioned in step I is 5A06 aluminum alloy.

[0058] The thickness of the butt joint position of the bottom-locked joint mentioned in step I is 8 mm, the bottom-locked thickness is 4 mm, the butt joint gap is 0 mm, and the butt joint misalignment width is 0 mm.

[0059] The specific laser tack welding mentioned in step I is carried out according to the following steps: Under the conditions of being in focus and the laser power being 2 kW, apply the pure spot laser to both ends of the weld for 150 ms respectively.

[0060] The oscillating mode mentioned in step II is figure-eight oscillation.

[0061] The spot-ring laser mentioned in step II is output by a two-in-one optical fiber.

[0062] The described two-in-one optical fiber consists of an internal core and an external ring core. The diameter of the internal core is 100μm, the diameter of the external ring core is 400μm, and the width of the external ring core is 100μm.

[0063] This embodiment utilizes a solid-state laser and a swing welding head.

[0064] Comparative Experiment 1: The difference between this comparative experiment and Embodiment 1 is as follows: In Step 2, no ring light is added and there is no swing mode. Using a pure point laser, with a laser power of 3000W and a welding speed of 2.5m / min, the laser is centered on the weld center line of the bottom-lock joint of the specimen to be welded and moves along the welding path. Other conditions are the same as those in Embodiment 1.

[0065] Comparative Experiment 2: The difference between this comparative experiment and Embodiment 1 is as follows: In Step 2, no ring light is added. Using a pure point laser and a swing mode, with a laser power of 4500W, a welding speed of 2.5m / min, a swing amplitude of 2mm, and a swing frequency of 100Hz, the laser is centered on the weld center line of the bottom-lock joint of the specimen to be welded and moves along the welding path according to the swing path. Other conditions are the same as those in Embodiment 1.

[0066] Figure 3 It is the surface morphology diagram of the weld obtained by single-laser welding in Comparative Experiment 1; under the single-laser condition, the forming quality of the weld obtained by laser welding of the medium-thickness aluminum alloy bottom-lock joint is poor, there are frequent undercut defects in the weld, and at the same time, there is severe welding spatter.

[0067] Figure 4 It is the longitudinal section metallographic diagram of the weld obtained by single-laser welding in Comparative Experiment 1; under the single-laser condition, the penetration depth of the medium-thickness aluminum alloy bottom-lock joint fluctuates violently, and some areas of the joint are not welded through.

[0068] Figure 5 It is the radiographic inspection diagram of the joint porosity defect obtained by single-laser welding in Comparative Experiment 1; under the single-laser condition, a large number of process porosity defects appear inside the joint, randomly distributed in the melting area. In summary, for the medium-thickness aluminum alloy bottom-lock joint under the single-laser condition, the weld forming quality is poor, the penetration depth fluctuates violently, and the porosity defect is serious.

[0069] Figure 6 It is the surface morphology diagram of the weld obtained by swing single-laser welding in Comparative Experiment 2; under the swing-laser condition, the forming quality of the weld of the medium-thickness aluminum alloy bottom-lock joint has been improved to a certain extent, but due to the large fluctuation of the molten pool edge shape over time, there are still undercut defects in the weld.

[0070] Figure 7The longitudinal section metallographic diagram of the weld obtained by single laser oscillating welding in Comparative Experiment 2; under the condition of oscillating laser, the stability of the keyhole at the bottom of medium-thickness aluminum alloy locks is improved to a certain extent, and the fluctuation degree of the penetration depth decreases.

[0071] Figure 8 The radiographic inspection diagram of the joint porosity defect obtained by single laser oscillating welding in Comparative Experiment 2; under the condition of oscillating laser, process porosity defects appear inside the joint, mainly concentrated at the bottom of the lock, but the porosity defects are still relatively serious. Although oscillating laser welding can improve the forming quality of the bottom-lock joint of medium-thickness aluminum alloy, it is still difficult to suppress the porosity defects.

[0072] Figure 9 The surface morphology diagram of the weld obtained by oscillating spot-ring laser welding in Example 1; under the condition of oscillating spot-ring laser, the introduction of the ring laser changes the thermal field distribution during the welding process, suppresses the violent flow of the liquid metal during the laser welding process, and inhibits the generation of forming defects such as spatter and undercut. The weld forming quality is significantly improved.

[0073] Figure 10 The longitudinal section metallographic diagram of the weld obtained by oscillating spot-ring laser welding in Example 1; under the condition of oscillating spot-ring laser, the penetration stability of the bottom-lock joint of medium-thickness aluminum alloy is improved, and no partial lack of penetration occurs in the bottom-lock joint.

[0074] Figure 11 The schematic radiographic inspection diagram of the joint porosity defect obtained by oscillating spot-ring laser welding in Example 1; under the condition of oscillating spot-ring laser, the occurrence frequency of keyhole collapse and closure is significantly reduced, the porosity defects inside the bottom-lock joint of medium-thickness aluminum alloy are significantly suppressed, and a high-quality weld of the bottom-lock joint of medium-thickness aluminum alloy with good surface forming and no obvious porosity defects is obtained.

Claims

1. A laser welding method for improving the forming quality of medium-thickness aluminum alloy lock bottom joints, characterized in that It is carried out in the following steps:

1. Assembly of medium thickness aluminum alloy lock bottom joint: The aluminum alloy lock bottom joint is assembled, then laser spot fixed, and finally fixed with a fixture to form a sample to be welded; 2. Perform swing point ring laser welding: Using the spot ring laser and the swing mode, under the conditions of the spot ring laser total power of 4000W to 5500W, the welding speed of 1.5m / min to 3m / min, the swing amplitude of 1.5mm to 2.5mm and the swing frequency of 50Hz to 250Hz, the spot ring laser is centered on the center line of the weld of the lock bottom joint of the sample to be welded, and moves along the welding path according to the swing path, thus completing the laser welding method for improving the forming quality of the medium-thickness aluminum alloy lock bottom joint; The total power of the spot ring laser is the sum of the spot light power and the ring light power, and the spot light power accounts for 50% to 90% of the total power of the spot ring laser.

2. A laser welding method for improving the forming quality of a mid-thickness aluminum alloy lock bottom joint according to claim 1, characterized in that The aluminum alloy bottom lock joint described in step 1 is a bottom lock joint that has been cleaned with acid or alkali.

3. A laser welding method for improving the forming quality of a medium-thickness aluminum alloy lock bottom joint according to claim 1, characterized in that The aluminum alloy described in step 1 is a 5 series aluminum alloy or a 6 series aluminum alloy.

4. A laser welding method for improving the forming quality of a medium-thickness aluminum alloy lock bottom joint according to claim 1, characterized in that The thickness of the joint at the bottom lock joint described in step 1 is 8 mm to 10 mm.

5. The laser welding method for improving the forming quality of the mid-thickness aluminum alloy lock bottom joint according to claim 1 is characterized in that The lock bottom thickness of the lock bottom joint described in step 1 is 4 mm to 5 mm.

6. A laser welding method for improving the forming quality of a mid-thickness aluminum alloy lock bottom joint according to claim 1, characterized in that The butt clearance of the lock bottom joint described in step 1 is 0 mm to 0.2 mm.

7. The laser welding method for improving the forming quality of the mid-thickness aluminum alloy lock bottom joint according to claim 1 is characterized in that The docking misalignment width of the lock bottom joint described in step 1 is 0 mm to 0.2 mm.

8. The laser welding method for improving the forming quality of medium-thickness aluminum alloy lock bottom joints according to claim 1 is characterized in that The swing mode described in step 2 is circular swing, linear swing, figure-8 swing or infinite swing.

9. The laser welding method for improving the forming quality of the mid-thickness aluminum alloy lock bottom joint according to claim 1 is characterized in that The dot ring laser described in step 2 is output by a two-in-one optical fiber.

10. A laser welding method for improving the forming quality of a mid-thickness aluminum alloy lock bottom joint according to claim 9, characterized in that The two-in-one optical fiber consists of an inner fiber core and an outer ring core, the inner fiber core has a diameter of 50 μm to 200 μm, the outer ring core has a diameter of 200 μm to 700 μm, and the outer ring core has a width of 50 μm to 100 μm.

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