Al-zn-mg high-strength aluminum alloy laser-mig hybrid welding method based on adjustable oscillation frequency

Abstract

A kind of Al-Zn-Mg high-strength aluminum alloy laser-MIG composite welding method based on adjustable swing frequency, the method comprises the following steps: welding preparation, the surface of Al-Zn-Mg high-strength aluminum alloy to be welded workpiece needs to be polished, cleaned and dried to remove oxide film, dirt and other impurities;Welding process parameter setting and execution, the swing frequency of laser beam is adjusted during welding, and the synergistic effect of MIG arc is used to realize the precise control of molten pool flow behavior;Welding post-processing, artificial aging or natural aging method is used for post-welding treatment to eliminate welding residual stress and improve joint mechanical properties.The invention optimizes the swing frequency parameter, effectively suppresses the defects such as hot crack and porosity that easily occur during welding of Al-Zn-Mg high-strength aluminum alloy, significantly improves the strength and corrosion resistance of the welded joint, and is suitable for the welding requirements of high-performance aluminum alloy components in the fields of aerospace, rail transportation, etc.

Description

Technical Field

[0001] This invention belongs to the field of laser composite welding technology, specifically relating to a laser-MIG composite welding method for Al-Zn-Mg high-strength aluminum alloys, which is particularly suitable for high-precision welding of key components such as rail transit vehicle bodies and bogies. Background Technology

[0002] Under the trend of lightweight development in rail transit, Al-Zn-Mg series high-strength aluminum alloys have become the core material for vehicle body structures due to their low density, high specific strength, and excellent fatigue resistance. However, the welding process of this type of alloy faces many technical challenges: traditional MIG welding has a large heat input, resulting in severe welding deformation and obvious joint softening; although conventional laser-MIG hybrid welding can improve efficiency, it is prone to porosity defects due to keyhole instability, and the coarse grains of the weld seam affect the mechanical properties.

[0003] Among existing aluminum alloy welding technologies, MIG welding offers flexibility but suffers from significant thermal deformation, while laser welding boasts high energy density but exhibits high reflectivity and a pronounced tendency for porosity. A single process cannot simultaneously achieve both welding quality and efficiency. Research indicates that laser oscillation can promote molten pool flow and refine grain size; however, there is insufficient research on optimizing the oscillation frequency for Al-Zn-Mg alloys, and a lack of clear process parameter matching schemes leads to significant fluctuations in weld joint performance, hindering the large-scale application of this material in the rail transportation sector.

[0004] Therefore, this invention optimizes the laser-MIG composite welding process by adjusting the laser oscillation frequency, thereby solving problems such as excessive porosity, coarse grains, and insufficient mechanical properties in Al-Zn-Mg alloy welding, and meeting the dual requirements of lightweight and high strength for rail transit. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a laser-MIG composite welding method for Al-Zn-Mg high-strength aluminum alloys based on adjustable oscillation frequency. The specific technical solution is as follows: Step 1: Preparation before welding Turn on the main power switch to connect the main power supply of the equipment. Then, start the KUKA welding robot system in sequence according to the standard operating procedures. The system includes an RFL-C6000 fiber laser, a TPS400i welding power supply, a KRC-60 six-axis linkage industrial robot, and a HansLaser WWH100 scanning galvanometer system. During the startup process, pay attention to the initialization status of each device, confirm that the communication connection between the control system and the execution unit is normal, and that all status indicator lights show the ready state. Correctly install the 1.2mm diameter ER5356 aluminum alloy welding wire into the welding machine's wire feeding mechanism, ensuring that the wire feeding wheel has appropriate clamping force and the wire feeding pipeline is unobstructed. At the same time, carefully check the cleanliness of the protective lens of the laser output port. If there is any contamination, clean it with special lens cleaning paper. Also, check each connection part of the protective gas pipeline one by one to confirm that there are no leaks and ensure good gas sealing. The surface of the 4mm thick Al-Zn-Mg aluminum alloy sheet to be welded was treated using an angle grinder to thoroughly remove oxide film, oil, and other impurities until a metallic luster was exposed. After grinding, the surface was wiped with a lint-free cloth moistened with anhydrous ethanol to remove residual dust, and then allowed to air dry to allow the ethanol to completely evaporate. The processed aluminum alloy sheet is precisely mounted on a special welding fixture. The positioning mechanism of the fixture is adjusted to ensure that the workpiece assembly gap is no more than 0.3mm. This step is crucial to ensuring the quality of the weld formation and can effectively avoid welding defects such as incomplete penetration caused by excessive assembly gap or burn-through caused by excessive gap. Step 2: Welding process control The preset basic process parameters include: laser power set to 3.6 kW, welding speed controlled at 30 mm / s (equivalent to 1.8 m / min), arc current set to 150 amperes, filament spacing maintained at 3 mm, laser beam oscillation amplitude set to 1.8 mm, and the oscillation trajectory adopting a circular pattern; high-purity argon gas is selected as the shielding gas, with a purity requirement of not less than 99.99%. The flow rate is maintained at 20 liters per minute; the core adjustment parameter is the laser oscillation frequency, which can be adjusted between 160 and 240 Hz; after selecting the corresponding welding program, the start and end positions of the welding are precisely calibrated through robot teaching, and the program reset operation is executed after confirmation; the air compressor and protective gas cylinder are started, and after confirming that the gas flow output is stable, the laser galvanometer system is turned on and the operation mode is switched to automatic welding state; when welding begins, the system will synchronously trigger the laser and the MIG welding machine to work together, the laser beam is quickly focused on the area to be welded, effectively breaking the surface oxide film and forming an initial molten pool, while the electric arc completes the metal filling, and the laser oscillation further promotes the internal flow of the molten pool, thereby achieving a smooth transition of the molten droplets and ensuring that the final weld is uniform and consistent; Step 3: Post-welding treatment After all welding operations are completed, the shielding gas must be continuously purged for at least 30 seconds to ensure that the weld seam is adequately protected at high temperatures and to prevent oxidation from contact with air. After the weld seam has cooled to room temperature naturally, use a special wire brush to carefully clean the surface of the weld seam to remove metal spatter, dust, and other residual impurities, ensuring that the weld seam area is clean and free of contamination. Then, shut down all equipment in the following order according to the standard operating procedure: first, shut down the welding machine; then, shut down the laser; then, shut down the galvanometer controller; then, shut down the robot system; then, shut down the air compressor; and finally, close the valve of the shielding gas cylinder. Only after all the above equipment shutdown operations are completed can the main power switch be turned off. At this point, the entire welding process is complete.

[0006] Furthermore, the Al-Zn-Mg high-strength aluminum alloy sheet used has a specification of 100mm×50mm×4mm, and the composition range (mass fraction %) is: Zn: 2.75%, Mg: 7.96%, Cu≤0.0077%, Si: 0.22%, with the remainder being Al; the composition (mass fraction %) of the ER5356 welding wire used is: Si≤0.04%, Fe≤0.09%, Cu≤0.001%, Mn: 0.15%, Mg: 4.8%, Cr: 0.12%, Zn≤0.002%, Ti: 0.09%, other ≤0.05%, with the remainder being Al.

[0007] Furthermore, the laser oscillation frequency is preferably 200Hz, at which the weld porosity is the lowest (1.42%), the grain refinement effect is the best, and the mechanical properties are optimal.

[0008] Furthermore, the oxygen content is controlled below 100ppm during the welding process, and the filament spacing deviation is ≤±0.2mm to ensure energy coupling stability.

[0009] The advantages and beneficial effects of this invention are as follows: 1. This invention significantly improves weld quality by optimizing the laser oscillation frequency (preferably 200Hz): compared with welding without oscillation (0Hz), the porosity is reduced from 8.98% to 1.42%, effectively solving the problem of porosity defects in Al-Zn-Mg alloy welding, while suppressing crack formation.

[0010] 2. Laser oscillation promotes molten pool flow and grain refinement, forming uniform equiaxed grains in the weld center and reducing the width of the fusion zone. According to the Hall-Page equation, fine grains significantly improve the hardness and strength of the joint. At 200Hz, the microhardness of the joint reaches 91.28HV (12.8% higher than 0Hz), and the tensile strength reaches 277.91MPa (more than 35% higher than 0Hz).

[0011] 3. By employing the synergistic effect of laser and MIG arc, the laser rapidly breaks down the oxide film while the arc stably fills the metal, balancing welding efficiency and forming quality. This avoids the defects of large thermal deformation in traditional MIG welding and high reflectivity in laser welding, making it suitable for high-precision welding of key components in rail transit.

[0012] The process parameters are clear and easy to control. Good joint performance can be obtained in the range of laser oscillation frequency from 160 to 240 Hz, with 200 Hz being the optimal parameter, which is convenient for industrial mass production applications. Attached Figure Description

[0013] Figure 1 This is a flowchart illustrating a laser-MIG composite welding method for Al-Zn-Mg high-strength aluminum alloys based on adjustable oscillation frequency, as proposed in an embodiment of this application.

[0014] Figure 2 This is a schematic diagram of the welding equipment.

[0015] Figure 3 This is a schematic diagram of the dimensions of a tensile specimen.

[0016] Figure 4 These are the results of tensile property tests.

[0017] Figure 5 This refers to the microscopic morphology of the weld.

[0018] For those skilled in the art, other related figures can be obtained from the above figures without any creative effort. Detailed Implementation

[0019] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0020] The following disclosure provides many different embodiments or examples for implementing different structures of this application. To simplify the disclosure, specific examples of components and arrangements are described below. Of course, these are merely examples and are not intended to limit the scope of this application. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, various specific examples of processes and materials are provided in this application, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0021] The embodiments of this application will be further described below with reference to the accompanying drawings.

[0022] Please see Figures 1 to 5 All embodiments and comparative examples adopt the welding process of steps one to three above, only changing the laser oscillation frequency parameter, while keeping the other parameters the same: laser power 3.6KW, welding speed 30mm / s, arc current 150A, filament spacing 3mm, oscillation amplitude 1.8mm, and shielding gas flow rate 20L / min.

[0023] Example 1 The laser oscillation frequency was set to 200Hz; the Al-Zn-Mg aluminum alloy sheet and ER5356 welding wire used conformed to the specifications of claim 2; the assembly gap was controlled at 0.2mm; the protective gas purity was 99.995%, and the oxygen content was 80ppm. During welding, standardized operations should be followed to ensure the welding plate is clean and dry, avoiding interference from oxides; attention should also be paid to the proper release of the protective gas to prevent oxidation after welding; operators should work in a well-ventilated environment to avoid inhaling metal vapors and causing poisoning.

[0024] The welded joint prepared in this embodiment has no obvious defects in the cross-section of the weld, with a porosity of 1.42%; the weld center is composed of uniform equiaxed crystals with an average grain size of 28.12 μm; the microhardness reaches 91.28 HV, the tensile strength is 277.91 MPa, the tensile fracture is characterized by ductile fracture, and the dimples are fine and uniform, resulting in the best joint performance.

[0025] Example 2 The laser oscillation frequency was set to 180Hz; the composition of the Al-Zn-Mg aluminum alloy sheet and ER5356 welding wire used conformed to the requirements of claim 2; the assembly gap was controlled at 0.2mm; the purity of the shielding gas was 99.995%, and the oxygen content was 80ppm. During welding, standardized operations should be followed to ensure the welding plate is clean and dry, avoiding interference from oxides; attention should also be paid to the proper release of the shielding gas to prevent oxidation after welding; operators should work in a well-ventilated environment to avoid inhaling metal vapors and causing poisoning.

[0026] The welded joint prepared in this embodiment has a porosity of 1.83%, an average grain size of 27.5 μm, a microhardness of 89.6 HV, and a tensile strength of 251 MPa. Its performance is slightly lower than that of Example 1, but better than that of non-wobbling welding.

[0027] Example 3 The laser oscillation frequency was set to 220Hz; the composition of the Al-Zn-Mg aluminum alloy sheet and ER5356 welding wire used conformed to the requirements of claim 2; the assembly gap was controlled at 0.2mm; the purity of the shielding gas was 99.995%, and the oxygen content was 80ppm. During welding, standardized operations should be followed to ensure the welding plate is clean and dry, avoiding interference from oxides; attention should also be paid to the proper release of the shielding gas to prevent oxidation after welding; operators should work in a well-ventilated environment to avoid inhaling metal vapors and causing poisoning.

[0028] The welded joint prepared in this embodiment has a porosity of 2.15%, an average grain size of 28.8 μm, a microhardness of 88.9 HV, and a tensile strength of 260 MPa. Due to the high frequency, the flow of the molten pool intensifies, and the number of pores increases slightly, resulting in slightly lower performance than in Example 1.

[0029] Comparative Example 1 The laser oscillation frequency was set to 0Hz (no oscillation); the Al-Zn-Mg aluminum alloy sheet and ER5356 welding wire used conformed to the specifications of claim 2; the assembly gap was controlled at 0.2mm; the protective gas purity was 99.995%, and the oxygen content was 80ppm. During welding, standardized operations should be followed to ensure the welding plate is clean and dry, avoiding interference from oxides; attention should also be paid to the proper release of the protective gas to prevent oxidation after welding; operators should work in a well-ventilated environment to avoid inhaling metal vapors and causing poisoning.

[0030] The welded joint prepared in this comparative example has a porosity of 8.98%, with obvious coarse large pores; the weld grains are coarse, with an average size of 35.2 μm; the microhardness is 80.73 HV, the tensile strength is 204 MPa, the joint softens significantly, and has the worst mechanical properties.

[0031] Comparative Example 2 The laser oscillation frequency was set to 240Hz; the composition of the Al-Zn-Mg aluminum alloy sheet and ER5356 welding wire used conformed to the requirements of claim 2; the assembly gap was controlled at 0.2mm; the purity of the shielding gas was 99.995%, and the oxygen content was 80ppm. During welding, standardized operations should be followed to ensure the welding plate is clean and dry, avoiding interference from oxides; attention should also be paid to the proper release of the shielding gas to prevent oxidation after welding; operators should work in a well-ventilated environment to avoid inhaling metal vapors and causing poisoning.

[0032] The welded joint prepared in this comparative example had a porosity of 3.49%, with metallurgical pores; an average grain size of 29.19 μm; a microhardness of 87.3 HV; and a tensile strength of 245 MPa. The keyhole stability decreased due to the excessively high oscillation frequency, resulting in an increase in weld defects.

[0033] The above experimental results show that the laser oscillation frequency has a significant impact on the performance of the laser-MIG composite welded joint of Al-Zn-Mg aluminum alloy. 200Hz is the optimal frequency, which can obtain the lowest porosity and the highest mechanical properties, fully meeting the welding requirements of lightweight structures for rail transit.

[0034] This invention significantly improves weld quality by adjusting the laser oscillation frequency: compared to welding without oscillation (0Hz), the porosity is reduced from 8.98% to 1.42%, effectively solving the problem of porosity defects in Al-Zn-Mg alloy welding and helping to suppress crack formation. This invention provides a reliable welding technology solution for the manufacture of key components in the rail transit field at a lower cost, and has significant industrial application value.

[0035] It will be apparent to those skilled in the art that this application is not limited to the details of the exemplary embodiments described above, and that this application can be implemented in other specific forms without departing from the spirit or essential characteristics of this application. Therefore, the embodiments should be regarded as exemplary and non-limiting in all respects, and the scope of this application is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be embraced within this application.

[0036] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the spirit and scope of the technical solutions of this application.

Claims

1. A laser-MIG composite welding method for Al-Zn-Mg high-strength aluminum alloys based on adjustable oscillation frequency, characterized in that, Includes the following steps: Step 1: Preparation before welding Turn on the main power switch to connect the main power supply of the equipment. Then, start the KUKA welding robot system in sequence according to the standard operating procedures. The system includes an RFL-C6000 fiber laser, a TPS400i welding power supply, a KRC-60 six-axis linkage industrial robot, and a HansLaser WWH100 scanning galvanometer system. During the startup process, pay attention to the initialization status of each device, confirm that the communication connection between the control system and the execution unit is normal, and that all status indicator lights show the ready state. Correctly install the 1.2mm diameter ER5356 aluminum alloy welding wire into the welding machine's wire feeding mechanism, ensuring that the wire feeding wheel has appropriate clamping force and the wire feeding pipeline is unobstructed. At the same time, carefully check the cleanliness of the protective lens of the laser output port. If there is any contamination, clean it with special lens cleaning paper. Also, check each connection part of the protective gas pipeline one by one to confirm that there are no leaks and ensure good gas sealing. Use an angle grinder to treat the surface of the 4mm thick Al-Zn-Mg aluminum alloy sheet to be welded, thoroughly remove oxide film, oil and other impurities until the metal luster is exposed. After grinding, wipe the surface with a lint-free cloth soaked in anhydrous ethanol to remove residual dust, and let it stand to dry so that the ethanol can completely evaporate. The processed aluminum alloy sheet is precisely mounted on a special welding fixture. The positioning mechanism of the fixture is adjusted to ensure that the workpiece assembly gap is no more than 0.3mm. This step is crucial to ensuring the quality of the weld formation and can effectively avoid welding defects such as incomplete penetration caused by excessive assembly gap or burn-through caused by excessive gap. Step 2: Welding process control The preset basic process parameters include: laser power set to 3.6 kW, welding speed controlled at 30 mm / s (equivalent to 1.8 m / min), arc current set to 150 amperes, filament spacing maintained at 3 mm, laser beam oscillation amplitude set to 1.8 mm, and the oscillation trajectory adopting a circular pattern; high-purity argon gas is selected as the shielding gas, with a purity requirement of not less than 99.99%. The flow rate is maintained at 20 liters per minute; the core adjustment parameter is the laser oscillation frequency, which can be adjusted between 160 and 240 Hz; after selecting the corresponding welding program, the start and end positions of the welding are precisely calibrated through robot teaching, and the program reset operation is executed after confirmation; the air compressor and protective gas cylinder are started, and after confirming that the gas flow output is stable, the laser galvanometer system is turned on and the operation mode is switched to automatic welding state; when welding begins, the system will synchronously trigger the laser and the MIG welding machine to work together, the laser beam is quickly focused on the area to be welded, effectively breaking the surface oxide film and forming an initial molten pool, while the electric arc completes the metal filling, and the laser oscillation further promotes the internal flow of the molten pool, thereby achieving a smooth transition of the molten droplets and ensuring that the final weld is uniform and consistent; Step 3: Post-welding treatment After all welding operations are completed, the shielding gas must be continuously purged for at least 30 seconds to ensure that the weld seam is adequately protected at high temperatures and to prevent oxidation from contact with air. After the weld seam has cooled to room temperature naturally, use a special wire brush to carefully clean the surface of the weld seam to remove metal spatter, dust, and other residual impurities, ensuring that the weld seam area is clean and free of contamination. Then, shut down all equipment in the following order according to the standard operating procedure: first, shut down the welding machine; then, shut down the laser; then, shut down the galvanometer controller; then, shut down the robot system; then, shut down the air compressor; and finally, close the valve of the shielding gas cylinder. Only after all the above equipment shutdown operations are completed can the main power switch be turned off. At this point, the entire welding process is complete.

2. The method according to claim 1, characterized in that: The Al-Zn-Mg high-strength aluminum alloy sheet used has a size of 100mm×50mm×4mm and a composition range (mass fraction %) of: Zn: 2.75%, Mg: 7.96%, Cu≤0.0077%, Si: 0.22%, with the remainder being Al. The filler wire used is ER5356 with a diameter of 1.2mm and a composition range (mass fraction %) of: Si≤0.04%, Fe≤0.09%, Cu≤0.001%, Mn: 0.15%, Mg: 4.8%, Cr: 0.12%, Zn≤0.002%, Ti: 0.09%, other ≤0.05%, with the remainder being Al.

3. The method according to claim 1, characterized in that: After the plates are fixed in step one, the assembly gap should be ≤0.3mm to avoid incomplete penetration defects during the welding process.

4. The method according to claim 1, characterized in that: In step two, the laser oscillation frequency is preferably 200Hz, at which the weld porosity is lowest and the mechanical properties are optimal.

5. The method according to claim 1, characterized in that: The protective gas is pure argon with a purity of ≥99.99%, and the oxygen content is controlled below 100ppm during welding to prevent weld oxidation.

6. The method according to claim 1, characterized in that: During the welding process, the coupling distance between the laser beam and the electric arc remains stable, and the filament spacing deviation is ≤±0.2mm to ensure energy synergy.

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