Deep fusion variable polarity TIG welding method for AA7075 aluminum alloy

Abstract

The invention discloses a deep fusion variable polarity TIG welding method of an AA7075 aluminum alloy, which comprises the following steps of: surface treatment of a to-be-welded material of the AA7075 aluminum alloy: carrying out surface treatment on the to-be-welded material by combining mechanical polishing and chemical cleaning to remove an oxide layer, oil stains and impurities; and the to-be-welded AA7075 aluminum alloy material subjected to surface treatment is welded through DP-VPTIG welding, formation of air holes in AA7075 aluminum alloy welding seams is inhibited by regulating and controlling the frequency of three-frequency pulses composed of low-frequency pulses, intermediate-frequency pulses and high-frequency pulses and heat input, and the quality and performance of welding joints are improved. According to the method, DP-VPTIG welding is carried out through three-frequency pulse current coupling, the process flexibility is high, the stability of the welding process is improved, the air hole defect in the aluminum alloy welding process is effectively reduced, and the macroscopic forming and mechanical properties of a welded joint are good.

Description

Technical Field

[0001] The present invention belongs to the technical field of tungsten inert gas welding, and particularly relates to a method for deep penetration variable polarity TIG welding of AA7075 aluminum alloy. Background Art

[0002] AA7075 aluminum alloy is an alloy material with high strength, excellent mechanical properties and good corrosion resistance, and is widely used in high-performance structural fields such as aerospace and automotive manufacturing. However, AA7075 aluminum alloy is extremely prone to porosity during the welding process. This is because aluminum alloy has a high thermal conductivity and a large coefficient of thermal expansion during welding, and is extremely prone to absorbing hydrogen, oxygen and moisture during the welding process, thereby forming pores in the weld. These pores will seriously affect the mechanical properties of the welded joint, such as reducing the strength, toughness and corrosion resistance of the weld, and ultimately affecting the overall quality and service life of the product.

[0003] To suppress the formation of pores in the weld, traditional welding methods mainly focus on optimizing welding parameters, improving welding materials and the composition of shielding gas, and performing pre-treatment before welding (such as cleaning and preheating of welded parts), etc. These methods can suppress the generation of pores to a certain extent, but it is difficult to fundamentally solve this problem. Especially when welding complex structural parts or high-strength aluminum alloys, the control of pores is still a technical problem.

[0004] Pulsed TIG welding technology has gradually become an effective means to suppress the formation of pores in the weld because it can achieve precise control of the welding heat input by adjusting the frequency and amplitude of the pulsed current. During the pulsed welding process, the periodic change of the arc can cause dynamic stirring of the molten pool and effective discharge of gas, thereby significantly reducing the porosity in the weld. However, single-frequency pulsed welding may not provide sufficient flexibility and effect when dealing with complex welding conditions.

[0005] To solve this problem, the deep penetration variable polarity TIG (DP-VPTIG) welding technology has emerged. By combining low-frequency pulses, medium-frequency pulses, and high-frequency pulses, the size of the arc and the behavior of the molten pool are adjusted multi-dimensionally. Specifically, it includes: (1) Low-frequency pulses: mainly control the overall heat input during the welding process and the basic shape of the arc, and form a uniform and stable molten pool through appropriate low-frequency adjustment; (2) Medium-frequency pulses: further control the detailed changes of the arc and the subtle dynamics of the molten pool, enhance the effect of discharging bubbles, and inhibit the formation of pores; (3) High-frequency pulses: under the small-amplitude pulse current change of high frequency S, fine molten pool oscillations are generated, effectively stirring the liquid metal in the molten pool and further promoting the escape of gas. Through the combined action of the three-frequency pulse current coupling, the periodic contraction of the arc and the dynamic stirring effect of the molten pool are significantly enhanced, which not only helps the discharge of gas, but also can avoid excessive melting and the formation of pores through precise control of heat input. Therefore, it is of great significance to suppress the formation of pores during the welding process of AA7075 aluminum alloy by DP-VPTIG welding technology. Summary of the Invention

[0006] The object of the present invention is to provide a deep penetration variable polarity TIG welding method for AA7075 aluminum alloy. Based on DP-VPTIG welding technology, by regulating the pulse frequency and heat input, the formation of pores in the AA7075 aluminum alloy weld is effectively suppressed, thereby improving the quality and performance of the welded joint.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] In the first aspect of the present invention, a deep penetration variable polarity TIG welding method for AA7075 aluminum alloy is provided, including the following steps:

[0009] (1) The surface of the AA7075 aluminum alloy material to be welded is treated by combining mechanical grinding and chemical cleaning to remove the oxide layer, oil stain, and impurities;

[0010] (2) The surface-treated AA7075 aluminum alloy material to be welded is welded by DP-VPTIG welding, and the formation of pores in the AA7075 aluminum alloy weld is suppressed by regulating the three-frequency pulse frequency and heat input composed of low-frequency pulses, medium-frequency pulses, and high-frequency pulses.

[0011] Preferably, in step (1), the chemical composition of the AA7075 aluminum alloy material to be welded includes, by mass percentage: Si: 0.18%, Fe: 0.34%, Cu: 0.17%, Mn: 0.19%, Mg: 2.6%, Cr: 0.20%, Zn: 5.6%, Ti: 0.03%, and the balance is Al.

[0012] Preferably, in step (1), the AA7075 aluminum alloy material to be welded is an AA7075 aluminum alloy plate with a thickness of 8 mm.

[0013] More preferably, in step (1), the AA7075 aluminum alloy plate is a rectangular plate with a length of 250 mm and a width of 130 mm.

[0014] Preferably, in step (2), a low-frequency pulse is first applied to the AA7075 aluminum alloy material to be welded to generate a stable arc and molten pool; subsequently, a medium-frequency pulse is applied to regulate the arc to produce a slight arc contraction and molten pool oscillation; finally, a high-frequency pulse is applied to stir the molten pool through high-frequency small-amplitude oscillation to promote the escape of gas.

[0015] More preferably, in step (2), the three-frequency pulse frequencies include: the low-frequency pulse frequency is 80 Hz, the medium-frequency pulse frequency is 750 Hz, and the high-frequency pulse frequency is 20 kHz.

[0016] Preferably, in step (2), DP-VPTIG welding is used, the base welding current is 258 A, the peak welding current is 430 A, the welding speed is 350 mm / min, pure argon is used as the shielding gas, and the gas flow rate is 18 L / min.

[0017] Preferably, in step (2), the morphology of the arc and the dynamic changes of the molten pool are monitored in real time during the welding process.

[0018] In the second aspect of the present invention, a deep penetration variable polarity TIG welding device for AA7075 aluminum alloy is provided, including:

[0019] (a) A three-frequency pulse power supply module for generating low-frequency pulses, medium-frequency pulses and high-frequency pulses to respectively control the size of the arc, heat input and oscillation of the molten pool;

[0020] (b) A control unit for adjusting the frequency, width and amplitude of each pulse to achieve periodic contraction of the arc and effective stirring of the molten pool;

[0021] (c) A monitoring module for real-time monitoring of the arc morphology and dynamic changes of the molten pool, and dynamically adjusting the pulse parameters according to the monitoring data;

[0022] Wherein, the deep penetration variable polarity TIG welding method for AA7075 aluminum alloy as described in any one of the foregoing is realized by the deep penetration variable polarity TIG welding device for AA7075 aluminum alloy.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The present invention utilizes the DP-VPTIG welding technology to combine low-frequency, medium-frequency, and high-frequency pulses for multiple regulations of the arc and molten pool, significantly suppressing porosity in the welds of AA7075 aluminum alloy. Compared with the single-pulse technology, the present invention can flexibly control the heat input and molten pool stirring, suppress the formation of weld porosity, form high-quality welded joints, and improve the mechanical properties and reliability of the welded joints.

[0025] 2. The present invention conducts welding through the coupling of three-frequency pulsed currents in DP-VPTIG welding. The process has strong flexibility. The arc shows a higher energy density and more effective arc constriction. The arc oscillation improves the molten pool flow effect, enhances the stability of the welding process, effectively reduces porosity defects in aluminum alloy welding, and the macroscopic forming and mechanical properties of the welded joints are good. In addition, the impact and stirring effects of the arc refine the grains of the microstructure in the center of the weld. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is the pulsed electrical signal diagram at different medium frequencies in the embodiment.

[0027] Figure 2 It is the grain size characterization diagram at different medium frequencies in the embodiment.

[0028] Figure 3 It is the arc morphology and molten pool pictures in the embodiment.

[0029] Figure 4 It is the cross-sectional characterization diagram at different medium frequencies in the embodiment.

[0030] Figure 5 It is the CT photo of the internal pore distribution in the weld under conventional TIG welding in the embodiment.

[0031] Figure 6 It is the CT photo of the internal pore distribution in the weld under DP-VPTIG welding in the embodiment.

[0032] Figure 7 It is the schematic structural diagram of the DP-VPTIG welding device for AA7075 aluminum alloy in the embodiment. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] In order to more fully understand and demonstrate the technical solutions, objectives, and advantages of the present invention, the technical effects produced by the present invention will be further described in detail and completely below in conjunction with the drawings and specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. It should be noted that for those of ordinary skill in the art, other embodiments obtained without departing from the concept of the present invention all fall within the protection scope of the present invention.

[0034] As Figure 7As shown below, the following embodiments exemplarily describe a keyhole variable polarity TIG welding device for AA7075 aluminum alloy. The device includes:

[0035] 1.1 A welding power supply module for generating low-frequency pulses, medium-frequency pulses, and high-frequency pulses to respectively control the size of the arc, heat input, and oscillation of the molten pool;

[0036] 1.2 A control unit for adjusting the frequency, width, and amplitude of each pulse to achieve periodic contraction of the arc and effective stirring of the molten pool;

[0037] 1.3 A monitoring module for real-time monitoring of the arc shape and dynamic changes of the molten pool, and dynamically adjusting the pulse parameters according to the monitoring data.

[0038] The following embodiments propose a keyhole variable polarity TIG welding method for AA7075 aluminum alloy to suppress the formation of pores in the AA7075 aluminum alloy weld. The method includes the following steps:

[0039] (1) Surface treatment of the AA7075 aluminum alloy material to be welded, including: mechanically grinding and chemically cleaning the AA7075 aluminum alloy material to be welded to remove the oxide layer, oil stains, and impurities;

[0040] (2) Welding the surface-treated AA7075 aluminum alloy material to be welded using DP-VPTIG welding. In DP-VPTIG welding, the formation of pores in the AA7075 aluminum alloy weld is suppressed by regulating the frequency and heat input of the three-frequency pulse composed of low-frequency pulses, medium-frequency pulses, and high-frequency pulses. Specifically:

[0041] 2.1 Set the parameters of the low-frequency pulse, medium-frequency pulse, and high-frequency pulse, including frequency, width, and amplitude, to optimize the arc size and molten pool oscillation;

[0042] 2.2 During the welding process, change the arc size and stirring effect of the molten pool by coupling the three-frequency pulse current to suppress the formation of pores;

[0043] 2.3 Use the monitoring module to real-time monitor the state of the arc and molten pool, and adjust the pulse parameters according to the actual situation to further optimize the pore elimination effect;

[0044] 2.4 After welding is completed, check the weld quality to ensure that the porosity is reduced to the required range.

[0045] In some embodiments, in step (1), the chemical composition of the AA7075 aluminum alloy to-be-welded material by mass percentage includes: Si: 0.18%, Fe: 0.34%, Cu: 0.17%, Mn: 0.19%, Mg: 2.6%, Cr: 0.20%, Zn: 5.6%, Ti: 0.03%, and the balance is Al.

[0046] In some embodiments, in step (1), the AA7075 aluminum alloy to-be-welded material is an AA7075 aluminum alloy plate with a thickness of 8 mm.

[0047] In some embodiments, in step (1), the AA7075 aluminum alloy plate is a rectangular plate with a length of 250 mm and a width of 130 mm.

[0048] In some embodiments, in step (2), a low-frequency pulse is first applied to the AA7075 aluminum alloy to-be-welded material to generate a stable arc and molten pool; subsequently, a medium-frequency pulse is applied to regulate the arc to generate a fine arc contraction and molten pool oscillation; finally, a high-frequency pulse is applied to stir the molten pool through high-frequency small-amplitude oscillation to promote the escape of gas.

[0049] In some embodiments, in step (2), the three-frequency pulse includes: the low-frequency pulse frequency is 80 Hz, the medium-frequency pulse frequency is 750 Hz, and the high-frequency pulse frequency is 20 kHz.

[0050] In some embodiments, in step (2), DP-VPTIG welding is used, the welding base current is 258 A, the welding peak current is 430 A, the welding speed is 350 mm / min, pure argon is used as the shielding gas, and the gas flow rate is 18 L / min.

[0051] In some embodiments, in step (2), the morphology of the arc and the dynamic changes of the molten pool are monitored in real time during the welding process.

[0052] Example 1

[0053] This example provides a DP-VPTIG welding method for AA7075 aluminum alloy, and the steps are as follows:

[0054] 1. Welding specimen preparation

[0055] Specimen material: AA7075 aluminum alloy plate with a thickness of 8 mm.

[0056] Specimen size: The welding specimen is a rectangular plate with a length of 250 mm and a width of 130 mm.

[0057] Specimen surface treatment: Before welding, the surface of the specimen is treated by a combination of mechanical grinding and chemical cleaning to remove the oxide layer, oil stain and impurities, and ensure the cleanliness of the welding surface.

[0058] 2. Welding Equipment and Parameter Settings

[0059] Welding Equipment: DP-VPTIG welding is adopted, supporting multi-frequency pulsed current output.

[0060] Welding Current Setting: The base current is 258 A and the peak current is 430 A.

[0061] Welding Speed: The welding speed is set at 350 mm / min to ensure the formation of a stable molten pool.

[0062] Protecting Gas: Pure argon is used as the protecting gas, and the flow rate is set at 18 L / min.

[0063] 3. Welding Process

[0064] The current pulse electrical signal parameters are set through the control unit ( Figure 1 ): The low-frequency pulse is 80 Hz, the medium-frequency pulse is 250 - 1000 Hz, and the high-frequency pulse is 20 kHz. During welding, the low-frequency pulse is applied first to generate a stable arc and molten pool. Subsequently, the medium-frequency pulse modulates the arc to produce fine arc contraction and molten pool oscillation. Finally, the high-frequency small-amplitude oscillation effect of the high-frequency pulse further stirs the molten pool to promote the escape of gas. The impact and stirring effects of the arc can refine the microstructure grains at the center of the weld seam ( Figure 2 ). During the welding process, the arc shape and the dynamic changes of the molten pool are monitored in real time to ensure the effectiveness of the pulse parameters ( Figure 3 ).

[0065] 4. Weld Quality Inspection

[0066] Microstructure Analysis: Samples of the weld cross-section are taken and photographed by a scanning electron microscope to observe the pore distribution in the weld. The results are as Figure 4 shown. In the weld using DP-VPTIG welding technology, pores are significantly suppressed, and the weld density is significantly improved.

[0067] Mechanical Property Testing: Tensile and hardness tests are carried out on the weld. The results show that the tensile strength of the weld reaches more than 60% of the base metal strength, the hardness is uniform, there is no obvious softening zone, and the mechanical properties are excellent.

[0068] CT Industrial Scanning Detection: Non-destructive CT industrial scanning is carried out on the weld to further verify the presence of pores inside the weld. The detection results show that there are no obvious pore defects inside the weld, and the porosity is controlled below 0.5%, meeting the requirements of high-quality welding.

[0069] 5. Welding Effect Evaluation

[0070] Porosity Control: By CT industrial scanning of the welded part and comparing with traditional TIG welded joints (Figure 5 ) and DP-VPTIG welded joints Figure 6 ), it is found that DP-VPTIG welding has significant advantages in pore control. The coupling of three-frequency pulsed current effectively enhances the stirring effect of the molten pool, making it easier for gases in the weld to escape.

[0071] Weld density: The AA7075 aluminum alloy weld after welding is dense, without obvious welding defects, and the overall comprehensive performance of the welded joint is good.

[0072] The results show that by using the DP-VPTIG welding technology with low frequency of 80 Hz, medium frequency of 750 Hz and high frequency of 20 kHz, the porosity in the AA7075 aluminum alloy weld can be significantly reduced, the weld quality can be improved, the mechanical properties and reliability of the welded joint can be enhanced, and it is suitable for the welding of high-strength aluminum alloys, especially for aerospace and high-performance engineering structures with high requirements for weld quality.

[0073] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for deep penetration variable polarity TIG welding of AA7075 aluminum alloy, characterized in that, It includes the following steps: (1) The surface of the AA7075 aluminum alloy material to be welded is treated by combining mechanical grinding and chemical cleaning to remove the oxide layer, oil stain and impurities; (2) The surface-treated AA7075 aluminum alloy material to be welded is welded by DP-VPTIG welding. The formation of pores in the AA7075 aluminum alloy weld is suppressed by regulating the three-frequency pulse frequency and heat input composed of low-frequency pulse, medium-frequency pulse and high-frequency pulse.

2. The keyhole variable polarity TIG welding method for AA7075 aluminum alloy according to claim 1, characterized in that In step (1), the chemical composition of the AA7075 aluminum alloy material to be welded is calculated by mass percentage including: Si: 0.18%, Fe: 0.34%, Cu: 0.17%, Mn: 0.19%, Mg: 2.6%, Cr: 0.20%, Zn: 5.6%, Ti: 0.03%, and the balance is Al.

3. The deep penetration variable polarity TIG welding method for AA7075 aluminum alloy according to claim 1, characterized in that, In step (1), the AA7075 aluminum alloy material to be welded is an AA7075 aluminum alloy plate with a thickness of 8 mm.

4. The deep penetration variable polarity TIG welding method for AA7075 aluminum alloy according to claim 3, characterized in that, In step (1), the AA7075 aluminum alloy plate is a rectangular plate with a length of 250 mm and a width of 130 mm.

5. The method for deep penetration variable polarity TIG welding of AA7075 aluminum alloy according to claim 1, characterized in that, In step (2), a low-frequency pulse is first applied to the AA7075 aluminum alloy material to be welded to generate a stable arc and molten pool; subsequently, a medium-frequency pulse is applied to regulate the arc to generate a fine arc contraction and molten pool oscillation; finally, a high-frequency pulse is applied to stir the molten pool through high-frequency small-amplitude oscillation to promote the escape of gas.

6. The keyhole variable polarity TIG welding method for AA7075 aluminum alloy according to claim 5, characterized in that, In step (2), the three-frequency pulse frequencies include: the low-frequency pulse frequency is 80 Hz, the medium-frequency pulse frequency is 750 Hz, and the high-frequency pulse frequency is 20 kHz.

7. The keyhole variable polarity TIG welding method for AA7075 aluminum alloy according to claim 5, characterized in that, By using DP-VPTIG welding, the welding base current is 258 A, the welding peak current is 430 A, the welding speed is 350 mm / min, pure argon is used as the shielding gas, and the gas flow rate is 18 L / min.

8. The keyhole variable polarity TIG welding method for AA7075 aluminum alloy according to claim 1, characterized in that, In step (2), the morphology of the arc and the dynamic changes of the molten pool are monitored in real time during the welding process.

9. A deep penetration variable polarity TIG welding device for AA7075 aluminum alloy, characterized in that, The keyhole variable polarity TIG welding method for AA7075 aluminum alloy according to any one of claims 1 to 8 is realized by the keyhole variable polarity TIG welding device for AA7075 aluminum alloy, including: (a) A three-frequency pulse power supply module for generating low-frequency pulse, medium-frequency pulse and high-frequency pulse, and respectively controlling the arc size, heat input and molten pool oscillation; (b) A control unit for adjusting the frequency, width and amplitude of each pulse to realize the periodic contraction of the arc and the stirring of the molten pool; (c) A monitoring module for real-time monitoring of the morphology of the arc and the dynamic changes of the molten pool, and dynamically adjusting the pulse parameters according to the monitoring data.

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