Method for restraining aluminum alloy laser wire filling welding air holes through welding wire ultrasonic excitation

Abstract

The invention discloses a method for restraining aluminum alloy laser wire filling welding air holes through welding wire ultrasonic excitation, and belongs to the technical field of metal welding. According to the method, a welding system comprising a laser, a wire feeding device, an ultrasonic impact device, a movable platform and a control cabinet is adopted. The method is characterized in that welding wires on a conveying path are directly excited through an ultrasonic impact device, so that the welding wires vibrate at ultrasonic frequency and enter a molten pool. The method has double effects of'source hydrogen control 'and'process intervention', on one hand, ultrasonic vibration can effectively clean the surface of the welding wire, and a hydrogen source is reduced; and on the other hand, a molten pool inlet disturbance effect is generated when the vibration welding wire enters a molten pool, dendritic crystals are broken through micromechanical stirring, and bubble escape is promoted. According to the method, on-line continuous treatment without interrupting welding and polluting a molten pool is achieved, keyhole type and metallurgical type air holes are remarkably inhibited, the method is particularly suitable for automatic welding of two-series and six-series aluminum alloys, and the welding seam quality and the production efficiency can be effectively improved.

Description

A method for suppressing porosity in laser filler wire welding of aluminum alloys using ultrasonic excitation of welding wire. Technical Field

[0001] This invention relates to the field of metal welding technology, and specifically to a method for suppressing porosity in laser filler wire welding of aluminum alloys by ultrasonic excitation of welding wire. Background Technology

[0002] Aluminum alloys, with their comprehensive advantages of being lightweight, high-strength, and corrosion-resistant, have become an indispensable basic material in modern industry. Laser welding of aluminum alloys, with its advantages of high energy density, low heat input, and minimal deformation, has been widely applied. However, the high reflectivity, high thermal conductivity, and easy oxidation of aluminum alloys make them highly susceptible to porosity defects during the welding process, severely affecting weld quality and structural safety.

[0003] There are two main types of porosity generated during aluminum alloy welding: keyhole porosity and metallurgical porosity. Keyhole porosity is a unique problem in laser deep penetration welding of aluminum alloys. Under laser action, local evaporation of the molten pool forms a keyhole. When the keyhole collapses due to instability caused by molten pool flow or changes in vapor pressure, the residual gas cannot escape in time and is trapped by the solidified metal, forming a porosity. An excessively high ratio of keyhole depth to width (depth-to-width ratio) is a key factor leading to its instability; deep and narrow keyholes are more prone to collapse. Metallurgical porosity is mainly related to hydrogen. Hydrogen may originate from the oxide film (Al2O3) on the aluminum surface, oil, moisture, or the material itself. Aluminum can dissolve a large amount of hydrogen in its liquid state, but during solidification, the solubility of hydrogen decreases sharply. Supersaturated hydrogen precipitates out to form bubbles, which, if unable to escape, become porosity.

[0004] In the existing technology, the methods for suppressing porosity mainly revolve around the following three paths: (1) reducing the source of hydrogen by strictly cleaning the base material and welding wire, and using high-purity protective gas. This method has a certain effect on metallurgical porosity, but it is ineffective for process porosity, and it has strict requirements on the production environment and is costly.

[0005] (2) By modulating the laser waveform and oscillating the beam, etc., we attempt to stabilize the keyhole and promote the escape of bubbles. This method is highly flexible, but the process window is narrow, the universality is poor, and the effect is limited.

[0006] (3) Introducing external energy fields such as ultrasound and electromagnetic fields to act on the molten pool. Among them, ultrasonic impact technology has significant effects. However, traditional interlayer ultrasonic impact requires interrupting the welding process, which is inefficient; while in-weld ultrasonic impact directly acts the impact head near the molten pool, which has problems such as contaminating the molten pool, complex equipment, poor accessibility, and severe attenuation of the effect on the inside of thick-walled components.

[0007] Therefore, there is an urgent need in this field for a novel method that can effectively suppress porosity formation by enabling real-time, online intervention of the molten pool without interrupting the welding process or contaminating the molten pool. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a method for suppressing porosity in laser filler wire welding of aluminum alloys by ultrasonic excitation of welding wire. This method achieves the dual effects of "hydrogen control at the source" and "process intervention" by directly applying ultrasonic excitation to the fed welding wire, thereby suppressing the generation of porosity in laser filler wire welding and reducing porosity defects in laser filler wire welding.

[0009] The core mechanism of this invention is the molten pool inlet disturbance effect. When the vibrating welding wire tip enters the liquid-solid interface of the molten pool, its kinetic energy directly acts on the interface, generating continuous micro-mechanical stirring. This disturbance can break up dendrites at the solidification front, promote the merging and escape of bubbles, and improve solute distribution. The core of this invention lies in using the welding wire as a "vibration transmission medium" to exert influence during its critical stage of entering the molten pool, rather than conducting long-distance acoustic energy transmission.

[0010] To achieve the above objectives, the specific solution adopted by the present invention is as follows: a method for suppressing porosity in laser-filled aluminum alloy welding using ultrasonic excitation of welding wire, employing a welding system, the system including a laser, a wire feeding device, an ultrasonic impact device, a moving platform, a gas protection device, and a control cabinet for controlling the above devices; wherein, the moving platform is placed on a guide rail and can move along the guide rail, the ultrasonic impact device is set independently of the wire feeding device, and it transmits ultrasonic vibration to the welding wire on the conveying path through an ultrasonic impact needle; the method for suppressing porosity in laser-filled aluminum alloy welding using ultrasonic excitation of welding wire includes the following steps: (1) Material preparation: preparing the aluminum alloy base material to be welded and the welding wire; (2) Beveling and cleaning: opening a bevel at the welding joint of the aluminum alloy base material and cleaning the bevel to remove oil and oxide film; (3) Fixing the base material: fixing the cleaned aluminum alloy base material on the moving platform; (4) Setting welding parameters: setting the power of the laser, the laser focus position, the travel speed of the moving platform, and the wire feeding speed of the wire feeding device through the control cabinet; wherein, the laser focus is set at the bottom of the bevel. (5) Adjust the welding wire position: feed the welding wire into the center of the laser spot through the wire feeding device, adjust the angle and height of the wire feeding nozzle so that the end of the welding wire is 2-3mm above the bottom of the bevel, and ensure that the distance between the laser spot center and the end of the welding wire is 1mm; (6) Start the welding process: start the gas protection device through the control cabinet to provide protective gas, start the laser to generate a laser beam, and start the wire feeding. The device feeds the welding wire and simultaneously starts the ultrasonic impact device, so that the welding wire is continuously fed into the molten pool under ultrasonic excitation; wherein, the vibration frequency of the ultrasonic impact device is 18.5KHz±2KHz and the amplitude is 20~40μm; (7) Welding: the moving platform is controlled by the control cabinet to move along the guide rail, so that the aluminum alloy base material to be welded moves relative to the laser beam. The laser beam melts the welding wire and the aluminum alloy base material to form a molten pool. The ultrasonic excitation of the welding wire acts on the molten pool, promotes the escape of pores, and realizes the continuous laser filler wire welding until the weld is completed.

[0011] Furthermore, the wire feeding device has holes through which the ultrasonic impact needle passes.

[0012] Furthermore, the aluminum alloy base material is a B2 series aluminum alloy or a 6 series aluminum alloy.

[0013] Furthermore, the welding wire is made of aluminum alloy and has a diameter of 1.0~1.6mm.

[0014] Furthermore, the diameter of the welding wire is 1.2 mm.

[0015] Furthermore, in step (4), the power of the laser is 3.0~3.5kW.

[0016] Furthermore, the protective gas is argon, with a flow rate of 20 L / min.

[0017] Furthermore, the movement trajectory of the mobile platform is a straight line.

[0018] Furthermore, in step (2), the bevel is a Y-shaped bevel.

[0019] The principle of auxiliary strengthening of aluminum alloy laser filler wire weld in this invention is as follows: (1) High-frequency ultrasonic vibration can effectively break and peel off the trace water molecule film and weak oxide layer adsorbed on the surface of the welding wire, significantly reducing the amount of hydrogen input from the material source and inhibiting the formation of metallurgical pores. (2) When the end of the welding wire carrying vibration enters the liquid-solid interface of the molten pool, its kinetic energy directly acts on the interface, generating continuous micro-mechanical stirring. This disturbance can break the dendrites at the solidification front, promote the merging and escape of bubbles, and improve the solute distribution. The core of this invention is to use the welding wire as a "vibration transmission medium" to exert influence at the critical stage of its entry into the molten pool, rather than to carry out long-distance acoustic energy transmission.

[0020] The beneficial effects of the present invention are as follows: (1) The present invention applies the ultrasonic energy that is traditionally applied to the molten pool or solidified weld to the welding wire being fed in, thereby achieving "non-contact" intervention of the molten pool and fundamentally avoiding the risk of ultrasonic head contamination of the molten pool.

[0021] (2) The present invention seamlessly integrates the porosity suppression function into the main welding process, eliminating the pause, movement and repositioning required for interlayer ultrasonic impact, significantly improving production efficiency and realizing true online continuous processing.

[0022] (3) In this invention, on the one hand, high-frequency ultrasonic vibration can effectively break up and peel off the trace water molecule film and thin oxide layer adsorbed on the surface of the welding wire, significantly reducing the amount of hydrogen input from the material source and inhibiting the formation of metallurgical pores. On the other hand, when the vibrating end of the welding wire enters the liquid-solid interface of the molten pool, its kinetic energy directly acts on the interface, generating continuous micro-mechanical stirring. This disturbance can break up dendrites at the solidification front, promote the merging and escape of bubbles, and improve the solute distribution. Thus, the dual effects of "hydrogen control at the source" and "process intervention" are achieved.

[0023] (4) The welding system has a compact structure, is easy to modify, and is easy to integrate with existing automated laser welding equipment. It is especially suitable for robotic automated welding scenarios.

[0024] (5) While effectively reducing porosity, the present invention can also refine weld grains and improve microstructure uniformity, thereby simultaneously improving the static strength and dynamic fatigue performance of the joint. Attached Figure Description

[0025] Figure 1 is a schematic diagram of the Y-shaped bevel of the aluminum alloy base material in Example 1.

[0026] Figure 2 is a schematic diagram of a specific embodiment of the present invention.

[0027] The diagram shows: 1. Wire feeding device, 2. Laser, 3. Ultrasonic impact device, 4. Aluminum alloy base material, 5. Moving platform, 6. Guide rail. Detailed Implementation

[0028] The technical solution of the present invention will be clearly and completely described below from the following aspects.

[0029] First aspect, welding method. This invention discloses a method for suppressing porosity in laser filler wire welding of aluminum alloy by ultrasonic excitation of welding wire. A welding system is used, which includes a laser 2, a wire feeding device 1, an ultrasonic impact device 3, a moving platform 5, a gas protection device (not shown in the figure), and a control cabinet (not shown in the figure) for controlling the above devices. The moving platform 5 is placed on a guide rail 6 and can move along the guide rail 6. The ultrasonic impact device 3 is set independently of the wire feeding device 1 and transmits ultrasonic vibration to the welding wire on the conveying path through an ultrasonic impact needle.

[0030] The method includes the following steps: (1) Material preparation: Prepare the aluminum alloy base material 4 to be welded and the welding wire; (2) Beveling and cleaning: Open a beveling at the welding joint of the aluminum alloy base material 4, wipe the beveling with alcohol or acetone, and polish it evenly with fine sandpaper along the beveling direction until it has a metallic luster, removing the oil and oxide film from the Y-shaped beveling of the base material; this step can ensure the weld fusion quality by cleaning the beveling and reduce the source of hydrogen from the base material end; (3) Fixing the base material: Fix the cleaned aluminum alloy base material 4 on the moving platform 5 to ensure stability during the welding process. (4) Setting welding parameters: This step mainly sets the key process parameters for forming a stable molten pool and achieving good filling. Specifically, the power of the laser 2, the laser focus position, the travel speed of the moving platform 5 and the wire feeding speed of the wire feeding device 1 are set through the control cabinet. The laser focus is set 1~2mm below the bottom of the bevel (negative defocus), the travel speed of the moving platform 5 is 7~9m / min, and the wire feeding speed of the wire feeding device 1 is 6~8m / min. (5) Adjusting the welding wire position: The welding wire is fed into the laser through the wire feeding device 1. At the center of the laser spot, adjust the angle and height of the wire feed nozzle so that the end of the welding wire is 2-3mm above the bottom of the bevel, and ensure that the distance between the laser spot center and the end of the welding wire is 1mm, so as to achieve the best energy coupling of laser-welding wire-base material and ensure the stability of the welding process; (6) Start the welding process: start the gas protection device through the control cabinet to provide protective gas, start the laser 2 to generate a laser beam, start the wire feed device 1 to transport the welding wire, and start the ultrasonic impact device 3 at the same time so that the welding wire is continuously fed into the molten pool under ultrasonic excitation; wherein, the ultrasonic impact device 3 is activated. The vibration frequency of the impact device 3 is 18.5KHz±2KHz, and the amplitude is 20~40μm. This step synchronously starts all functional units, so that ultrasonic excitation, laser melting, and filler delivery are carried out synchronously. This is the core of realizing online continuous processing. (7) Welding: The control cabinet controls the moving platform 5 to move along the guide rail 6, so that the aluminum alloy base material 4 to be welded moves relative to the laser beam. The laser beam melts the welding wire and the aluminum alloy base material 4 to form a molten pool. The ultrasonic excitation of the welding wire acts on the molten pool, promotes the escape of pores, and realizes the continuous laser filler welding until the weld is completed. In the entire single-pass or multi-pass welding process, the laser melting, filler and welding wire ultrasonic excitation are carried out synchronously and continuously without any form of interlayer pause or post-processing.

[0031] Preferably, the wire feeding device 1 has a hole through which the ultrasonic impact needle passes. Before welding, the ultrasonic impact needle is placed in the pre-drilled hole in the wire feeding device 1 to vibrate the welding wire with appropriate pressure without affecting the stability of the wire feeding. The advantages of this arrangement are: it ensures stable contact between the ultrasonic impact needle and the welding wire, achieving efficient transmission of vibration energy, while minimizing interference and obstruction to the wire feeding path, ensuring the smoothness and continuity of the wire feeding process, thereby maintaining the stability of the welding process.

[0032] The aluminum alloy base material 4 can be any series of aluminum alloys, preferably bi-series aluminum alloys (such as 2A14) and hexagonal aluminum alloys (such as 6061 and 6082). The advantage of preferring bi-series and hexagonal aluminum alloys is that these two series are widely used in aerospace, transportation, and other fields, and are highly sensitive to porosity issues in laser welding. The method of this invention exhibits a more significant porosity suppression effect and practical value for these materials, helping to improve the welding quality and reliability of core components in related fields.

[0033] Preferably, the welding wire is an aluminum alloy welding wire with a diameter of 1.0~1.6mm. This diameter range ensures that the welding wire has sufficient rigidity for stable feeding, while its heat capacity matches the laser energy input, which is beneficial for forming a stable molten pool. A diameter of 1.2mm is further preferred, as this specification achieves the best balance between wire feeding stability, deposition efficiency, and ultrasonic vibration transmission effect, making it the optimal choice for overall performance.

[0034] Preferably, in step (4), the power of laser 2 is 3.0~3.5kW. This power range is crucial for achieving stable deep penetration welding and ensuring good fusion of the bevel sidewalls, given the plate thickness and bevel size. At this power, a keyhole of moderate depth and relative stability can be formed and maintained, creating favorable conditions for the escape of gas from the molten pool, while avoiding violent fluctuations in the keyhole or spatter caused by excessive energy.

[0035] Preferably, the protective gas is argon with a flow rate of 20 L / min. Argon, as an inert gas, effectively isolates the molten pool from air, preventing oxidation of the molten metal at high temperatures. Setting the gas flow rate to 20 L / min ensures a stable and adequately covered gas curtain at the welding torch nozzle outlet, providing reliable protection and preventing turbulence caused by excessive flow, which could interfere with the stability of the molten pool.

[0036] Preferably, the moving trajectory of the mobile platform 5 is a straight line. Welding using a straight trajectory is the simplest and most reliable process, and it is easy to achieve precise path control and speed stability. This helps to maintain a constant welding heat input and molten pool behavior, thereby ensuring that the effect of ultrasonic excitation in suppressing porosity is uniform throughout the entire weld length, which is particularly suitable for the automated production of long straight welds.

[0037] Preferably, in step (2), the bevel is a Y-shaped bevel. The Y-shaped bevel is easy to process, provides good accessibility for the laser beam and filler, and facilitates uniform filling from the bottom to the top of the bevel. Its bevel angle helps reflect and absorb laser energy, promotes sidewall fusion, and provides favorable geometric conditions for molten pool flow and bubble rising. In synergy with the method of this invention, it further reduces the risk of porosity.

[0038] Second, Examples and Comparative Examples Example 1 (1) Raw material preparation 10mm thick 6061 aluminum alloy plate with size of 200mm×100mm was selected as aluminum alloy base material 4. The butt edge was machined to form a Y-shaped bevel with α=60° (as shown in Figure 1), and acetone was used to chemically degrease the bevel and the 20mm area on both sides. Then, the surface oxide film was removed immediately with a stainless steel wire brush, and finally wiped with anhydrous ethanol and dried. 6061 aluminum alloy welding wire with a diameter of 1.2 mm was selected. (2) Equipment and parameter settings The laser 2 has a power parameter of 3kW, the wire feeding device 1 has a wire feeding speed of 7m / min, and the moving platform 5 moves along a straight track at a speed of 8mm / s. The protective gas of the gas protection device is high-purity argon with a gas flow rate of 20L / min. The parameters of the ultrasonic impact device 3 are as follows: rated power 650W, frequency 18.5KHz±2 KHz, amplitude 20μm; (3) During the welding process, the workpiece to be welded is clamped on the welding fixture to ensure that the butt gap is about 2mm; the laser 2, wire feeding device 1 and gas protection device are started according to the set parameters; after the laser melts the welding wire and forms a stable molten pool, the ultrasonic impact device 3 is started at the same time so that the welding wire is continuously fed into the molten pool under ultrasonic excitation; a 3-layer multi-pass welding strategy is adopted, and the above process is repeated for each layer until the groove is completely filled.

[0039] Example 2 The difference between Example 2 and Example 1 is that in step (2), the amplitude of the ultrasonic impact device 3 is set to 30μm.

[0040] Example 3 The difference between Example 3 and Example 1 is that in step (2), the amplitude of the ultrasonic impact device 3 is set to 40μm.

[0041] The difference between Comparative Example 1 and Example 1 is that in step (3), the ultrasonic impact device 3 is not activated.

[0042] Third, performance testing methods and test result analysis (1) Metallographic sample preparation After welding, metallographic samples were cut from the welds of each embodiment and comparative example using wire electrical discharge machining. The sampling position was at least 3cm away from the start and end of the weld to ensure that the center of the weld was located at the center of the sample. 2 to 3 samples were taken from each weld, with a sampling interval of more than 10mm. After grinding and polishing (polishing to a mirror finish using 3.5 to 0.5μm polishing paste), the samples were etched with an etching solution.

[0043] (2) Porosity observation and results: The morphology and distribution of pores in the weld cross section were observed using an optical microscope. The observation results showed that: Comparative example (without ultrasonic excitation): A large number of large pores could be observed in the weld cross section, mainly distributed in the center of the weld and near the fusion line.

[0044] Examples 1-3 (with ultrasonic excitation): In the welds of the three examples, the number and size of pores were significantly smaller than those in the comparative example. As the ultrasonic amplitude increased from 20 μm (Example 1) to 40 μm (Example 3), the pore suppression effect showed a further enhanced trend, and almost no obvious pores were observed in the weld of Example 3.

[0045] (3) Results Analysis Based on the principle shown in Figure 2, the reason why this invention can effectively suppress porosity is that: ultrasonic vibration is transmitted to the welding wire through the impact needle. At the moment the welding wire enters the molten pool, its kinetic energy directly acts on the liquid-solid interface, generating a disturbance effect at the molten pool inlet. This micro-stirring action breaks up dendrites, disrupts the attachment points of bubbles, and promotes the merging and floating of small bubbles. Simultaneously, ultrasonic vibration activates and cleans the surface of the welding wire during the wire transport process, breaking up the surface water molecule film and weak oxide layer, reducing hydrogen input from the source. Therefore, as shown in Figure 2, the vibrating welding wire acts like a "micro-oscillator" continuously acting on the inlet area of ​​the molten pool, achieving dual suppression of keyhole-type and metallurgical-type porosity. The test results fully confirm the effectiveness of this method.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention in any way. All equivalent transformations or modifications made in accordance with the essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for suppressing porosity in laser-welded aluminum alloys using ultrasonic excitation of welding wire, characterized in that, A welding system is adopted, which includes a laser, a wire feeding device, an ultrasonic impact device, a moving platform, a gas protection device, and a control cabinet for controlling the above devices; wherein, the moving platform is placed on a guide rail and can move along the guide rail, and the ultrasonic impact device is set independently of the wire feeding device, which transmits ultrasonic vibration to the welding wire on the conveying path through an ultrasonic impact needle; the method of suppressing porosity in aluminum alloy laser filler welding by ultrasonic excitation of welding wire includes the following steps: (1) Material preparation: prepare the aluminum alloy base material to be welded and the welding wire; (2) Beveling and cleaning: open a bevel at the welding joint of the aluminum alloy base material and clean the bevel to remove oil and oxide film; (3) Fixing the base material: fix the cleaned aluminum alloy base material on the moving platform; (4) Setting welding parameters: set the power of the laser, the laser focus position, the travel speed of the moving platform, and the wire feeding speed of the wire feeding device through the control cabinet; wherein, the laser focus is set 1~2mm below the bottom of the bevel, and the travel speed of the moving platform is 7~9 m / min, the wire feeding speed of the wire feeding device is 6~8m / min; (5) Adjust the position of the welding wire: feed the welding wire into the center of the laser spot through the wire feeding device, adjust the angle and height of the wire feeding nozzle so that the end of the welding wire is 2~3mm above the bottom of the bevel, and ensure that the wire spacing between the center of the laser spot and the end of the welding wire is 1mm; (6) Start the welding process: start the gas protection device through the control cabinet to provide protective gas, start the laser to generate a laser beam, start the wire feeding device to transport the welding wire, and start the welding process at the same time. The ultrasonic impact device continuously feeds the welding wire into the molten pool under ultrasonic excitation; wherein, the vibration frequency of the ultrasonic impact device is 18.5KHz±2KHz and the amplitude is 20~40μm; (7) Welding: The control cabinet controls the moving platform to move along the guide rail, so that the aluminum alloy base material to be welded moves relative to the laser beam. The laser beam melts the welding wire and the aluminum alloy base material to form a molten pool. The ultrasonic excitation of the welding wire acts on the molten pool, promotes the escape of pores, and realizes the continuous laser filler wire welding until the weld is completed.

2. The method according to claim 1, characterized in that, The wire feeding device has holes through which the ultrasonic impact needle passes.

3. The method according to claim 1, characterized in that, The aluminum alloy base material is a 2-series aluminum alloy or a 6-series aluminum alloy.

4. The method according to claim 3, characterized in that, The welding wire is made of aluminum alloy and has a diameter of 1.0~1.6mm.

5. The method according to claim 4, characterized in that, The diameter of the welding wire is 1.2 mm.

6. The method according to claim 1, characterized in that, In step (4), the power of the laser is 3.0~3.5kW.

7. The method according to claim 1, characterized in that, The protective gas is argon, with a flow rate of 20 L / min.

8. The method according to claim 1, characterized in that, The movement trajectory of the mobile platform is a straight line.

9. The method according to claim 1, characterized in that, In step (2), the bevel is a Y-shaped bevel.

Images