Spot welding method for aluminum alloy material based on cooperative control of pressure and current and aluminum alloy welding part

Abstract

The invention discloses a spot welding method of an aluminum alloy material based on cooperative control of pressure and current and an aluminum alloy weldment, aluminum alloy plates are overlapped up and down, and the overlapped aluminum alloy plates are welded by adopting a method of cooperative control of electrode pressure and current. According to the heat-force requirements of nugget formation in different stages, a method of electrode pressure and current cooperative control is adopted, heat-force input in the welding process is precisely regulated and controlled, welding spatter is avoided, the defects of internal cracks, shrinkage cavities and the like of the nugget are restrained, the strength and stability of a connector are improved, and therefore the high-quality aluminum alloy nugget is obtained.

Description

Technical Field

[0001] This invention relates to the field of welding technology, and more specifically, to a spot welding method for aluminum alloy materials and aluminum alloy welded parts based on pressure and current coordinated control. It is mainly applicable to the resistance spot welding process of aluminum alloy plates with an overlap thickness of 2mm or more in applications such as automobiles, high-speed rail, and ships. Background Technology

[0002] Aluminum alloys, based on aluminum, exhibit excellent lightweight properties through the addition of various alloying elements, making them widely used in the transportation sector. However, the low resistivity, high thermal conductivity, large coefficient of linear expansion, and dense oxide film on the surface of aluminum alloys make spot welding difficult and unstable, hindering their application in lightweight vehicle bodies. In most industrial manufacturing scenarios, aluminum alloy plate welding employs constant pressure and constant current control methods. This process parameter transfer is based on experience in steel spot welding, making the welding operation relatively easy to implement. More importantly, the continuous high current can accumulate high heat in a very short time, ensuring the melting of the aluminum alloy and the formation of the weld nugget. However, aluminum alloy spot welding is a multi-field coupling process, particularly sensitive to heat and pressure input. The aforementioned simple current or pressure control methods have poor stability, easily leading to spatter, cracks, shrinkage cavities, and other defects, reducing the internal quality of the weld nugget and deteriorating the joint's mechanical properties, especially dynamic impact resistance and fatigue performance. The characteristics of aluminum alloys make these problems difficult to identify on the production site, posing service safety hazards. Therefore, precise control of heat and pressure input is necessary.

[0003] Papers such as "A Method for Improving Joint Strength of Resistance Spot Welds of AA 5182-O Aluminum Alloy," "Effect of process parameters on the strength of resistance spot welds in 6082-T6 aluminum alloy," and "Improving mechanical properties and electrode life for joining aluminum alloys within innovatively designated Newton ring electrode" all employ current parameters, combined with appropriate electrode caps and constant pressure control, effectively ensuring the requirements for weld nugget formation and achieving a generally acceptable weld nugget appearance. However, the evaluation of spot weld nugget quality is not only about a good appearance, but more importantly, its internal quality. In actual production, this current control method leads to concentrated heating in the welding zone, frequently causing spatter problems. Furthermore, the internal temperature gradient of the weld nugget is very large, and defects such as cracks and shrinkage cavities are common during the solidification of the liquid metal, reducing the joint's mechanical properties, especially its dynamic impact resistance and fatigue performance. The characteristics of aluminum alloys make these problems difficult to identify on the production site, affecting service safety and requiring control.

[0004] Existing technologies also involve spot welding of aluminum alloy materials. For example, Chinese patent application CN202210169336.5 discloses an aluminum alloy resistance spot welding equipment and method; Chinese patent publication CN112548295A discloses an automotive aluminum alloy resistance spot welding method; Chinese patent publication CN112570867A discloses a method for suppressing the generation of internal defects in the weld nugget of aluminum alloy resistance spot welding; and Chinese patent publication CN104084686A discloses an electrode for suppressing the generation of cracks in aluminum alloy resistance spot welding. These technologies improve the welding quality of aluminum alloy materials by optimizing electrode morphology and welding methods. To a certain extent, they introduce problems such as stress concentration. The pulsed welding current used in these technologies does not take into account the heat-force synergy input during the welding process, as well as the synergistic improvement of the internal quality of the weld nugget by current and pressure. Chinese Patent Publication No. CN116493722A discloses a resistance spot welding method for ultra-high strength aluminum alloy plates with an intermediate zinc layer. By adding a zinc layer between the aluminum alloy plates, the internal quality of the joint is improved. However, it does not pay attention to the precise control of the heat input on the weld quality during the welding process.

[0005] In view of the above, there is an urgent need to develop a new spot welding technology for aluminum alloy materials that can precisely control the heat input during the welding process according to the heat and force requirements of the weld nugget formation at different stages, thereby obtaining a high-quality aluminum alloy weld nugget. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a spot welding method for aluminum alloy materials and aluminum alloy welded parts based on the coordinated control of pressure and current. According to the heat and force requirements for the formation of the weld nugget at different stages, the heat and force input during the welding process is precisely controlled, which avoids welding spatter, suppresses defects such as internal cracks and shrinkage cavities in the weld nugget, and improves the joint strength and stability, thereby obtaining a high-quality aluminum alloy weld nugget.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] The first aspect of the present invention provides a spot welding method for aluminum alloy materials based on pressure and current coordinated control, wherein aluminum alloy plates are overlapped one above the other, and the overlapped aluminum alloy plates are welded by a method of electrode pressure and current coordinated control.

[0009] Preferably, when the aluminum alloy plates are overlapped, the gap between the plates does not exceed 1mm.

[0010] Preferably, the surface of the aluminum alloy sheets is cleaned and the oxide film is polished before the aluminum alloy sheets are overlapped.

[0011] Preferably, the overlap thickness of the aluminum alloy sheet is 2.0 to 8.0 mm, and the number of overlap layers is 2 or 3.

[0012] Preferably, the method for coordinated control of electrode pressure and current includes the following stages:

[0013] In stage T1, an electrode pressure of N1 is applied to press the two overlapping aluminum alloy plates together and keep them in a non-energized state.

[0014] In stage T2, while keeping the electrode pressure N1 constant, a pulsed current I1 is applied to rapidly generate heat, causing the aluminum alloy interface material to melt and form a melt nucleus.

[0015] In the T3 stage, the electrode pressure N1 is kept constant, and a pulse current I2 is applied to bring the welding heat generation and the heat dissipation of the molten pool into equilibrium.

[0016] In the T4 stage, apply pulsed current I3 or pause the application of pulsed current to make the heat dissipation of the molten pool exceed the heat generated during welding, so that the molten pool metal gradually solidifies. At the same time, apply electrode pressure N2, which is greater than N1.

[0017] During stage T5, the electrode pressure N2 is kept constant, and a pulsed current I4 is applied for reheating.

[0018] In stage T6, stop applying current, maintain electrode pressure N2 constant, and welding ends after the weld nugget cools naturally.

[0019] The pulse currents I1, I2, I3, and I4 satisfy the following relationship: I1 > I2 > I4 > I3.

[0020] Preferably, the relationship between the electrode pressures N1 and N2 is as follows: N2 = 1.2N1 ~ 1.4N1.

[0021] Preferably, the electrode pressure N1 is 3kN to 7kN.

[0022] Preferably, the pulse currents I1, I2, I3, and I4 satisfy the following relationship: 1 / 3I1≤I2≤1 / 2I1, 0≤I3≤1 / 3I2, I4≤2I3.

[0023] Preferably, the pulse current I1 is 15kA to 45kA.

[0024] Preferably, the time for stage T1 is 100-500ms, the time for stage T2 is 50-200ms, the time for stage T3 is 50-200ms, the time for stage T4 is 50-200ms, the time for stage T5 is 50-200ms, and the time for stage T6 is 100-500ms.

[0025] The second aspect of the present invention provides an aluminum alloy welded part, obtained by the spot welding method of aluminum alloy material based on pressure and current coordinated control according to the first aspect of the present invention, wherein the weld nugget diameter of the aluminum alloy welded part is 5-14 mm and the joint tensile shear strength is ≥2.5 kN.

[0026] The beneficial effects of this invention are as follows:

[0027] 1. This invention precisely adjusts the heat and force input of the welding process by synergistically controlling pressure-current parameters. This effectively improves the internal quality of the weld nugget while ensuring its appearance quality, preventing welding spatter, suppressing defects such as internal cracks and shrinkage cavities, and improving joint strength and stability, resulting in high-quality aluminum alloy weld nuggets. Furthermore, since this invention provides empirical formulas for process parameter settings and employs automated welding processes and parameterized process settings, it has low dependence on the qualifications and experience of relevant production personnel, thus exhibiting good scalability. In addition, the method of this invention does not require electrodes with specific morphologies or compositions; it can be implemented using commercially available conventional electrodes, making it more widely accepted.

[0028] 2. In the initial stage of welding, this invention uses a high current to generate heat rapidly, combined with appropriate pressure, to quickly melt the aluminum alloy material at the interface, ensuring the rapid formation of the weld nugget. Then, while maintaining constant pressure, the current is reduced to achieve a balance between welding heat generation and molten pool heat dissipation, resulting in a more uniform temperature gradient. This ensures the weld nugget extends and grows without spatter, with a stable increase in volume. Next, the current is further reduced so that molten pool heat dissipation exceeds welding heat generation, causing the liquid metal to gradually solidify under a uniform temperature gradient. Simultaneously, a slight increase in electrode pressure suppresses shrinkage cavities or cracks during solidification. Finally, a slight increase in current is used for reheating, resulting in a more uniform microstructure and further eliminating microscopic defects. Pressure is maintained until the weld nugget is completely cooled, ultimately forming a high-quality weld nugget with excellent appearance and internal structure. Attached Figure Description

[0029] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0030] Figure 1 This is an implementation diagram of the spot welding method for aluminum alloy materials based on the coordinated control of pressure and current of the present invention;

[0031] Figure 2 This is a metallographic image of the spot welded joint obtained in Embodiment 1 of the present invention;

[0032] Figure 3 This is a metallographic image of the spot welded joint obtained in Embodiment 2 of the present invention;

[0033] Figure 4 This is a metallographic image of the spot welded joint obtained in Embodiment 3 of the present invention. Detailed Implementation

[0034] To better understand the above-mentioned technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0035] The spot welding method for aluminum alloy materials based on pressure and current coordinated control of the present invention adopts electrode pressure and current coordinated control, and effectively regulates the heat and force input during the welding process according to the heat and force requirements of the weld nugget formation at different stages, thus ensuring the formation of high-quality aluminum alloy weld nuggets.

[0036] Combination Figure 1 As shown, the spot welding method for aluminum alloy materials based on pressure and current coordinated control of the present invention involves overlapping aluminum alloy plates and welding the overlapping aluminum alloy plates using a method of coordinated control of electrode pressure and current. The specific process is as follows:

[0037] S1: Clean the oil stains on the surface of the aluminum alloy sheet and polish the oxide film. Overlap the aluminum alloy sheet to ensure that the gap between the sheets does not exceed 1mm. Place it on the spot welding fixture for welding. The overlap thickness of the aluminum alloy sheet is 2.0 to 8.0mm, and the number of overlap layers is 2 or 3.

[0038] S2 uses a medium-frequency DC welding machine and employs a method of coordinated control of electrode pressure and current to weld lapped aluminum alloy plates. By controlling the heat-force input at different stages of welding through the coordinated control of electrode pressure and current, high-quality aluminum alloy weld nuggets can be formed.

[0039] The method for coordinated control of electrode pressure and current includes six stages: T1, T2, T3, T4, T5, and T6. Specifically, it involves two pressures (Pressure I and Pressure II) and four current pulses (Pulse I, Pulse II, Pulse III, and Pulse IV), and includes the following stages:

[0040] In stage T1, an electrode pressure of N1 is applied to press the two overlapping aluminum alloy plates together and keep them in a non-energized state.

[0041] In stage T2, while keeping the electrode pressure N1 constant, a pulsed current I1 is applied to rapidly generate heat, causing the aluminum alloy interface material to melt and quickly form a melt nucleus.

[0042] This stage is the initial stage of welding. By using a large current to generate heat quickly, and with appropriate electrode pressure, the aluminum alloy material at the interface is melted quickly, ensuring that the weld nugget is formed rapidly.

[0043] In the T3 stage, the electrode pressure N1 is kept constant, and a pulse current I2 is applied to achieve a balance between welding heat generation and molten pool heat dissipation, thereby obtaining a more uniform temperature gradient and ensuring that the molten nugget extends and grows to the surrounding area without splashing, so that the volume of the molten nugget increases steadily.

[0044] During the T4 stage, apply pulsed current I3 or pause the application of pulsed current to make the heat dissipation of the molten pool exceed the heat generated during welding, so that the molten pool metal gradually solidifies, while applying an electrode pressure N2 greater than N1.

[0045] During this stage, the current is further reduced so that the heat dissipation of the molten pool exceeds the heat generated during welding. The liquid metal gradually solidifies under a uniform temperature gradient. At the same time, by slightly increasing the electrode pressure, shrinkage cavities or cracks are suppressed during the solidification process.

[0046] During stage T5, the electrode pressure N2 is kept constant, and a pulsed current I4 is applied for reheating.

[0047] During this stage, the molten core that has not yet fully solidified is reheated by slightly increasing the current, which makes the structure more uniform, further eliminates the internal stress of the weld core, and avoids micro-defects such as keyholes and cracks.

[0048] In the T6 stage, the current is stopped, the electrode pressure N2 is kept constant, and the welding is completed after the weld nugget cools naturally.

[0049] During this process, pressure is maintained, and the welding torch is released after the nucleus cools naturally, ultimately forming a high-quality weld nucleus with excellent appearance and internal structure.

[0050] In the above process, the relationship between electrode pressures N1 and N2 is as follows: N2 = 1.2N1 ~ 1.4N1. In a specific embodiment, the electrode pressure N1 is 3kN ~ 7kN.

[0051] In pulses I, II, III, and IV, the pulse currents I1, I2, I3, and I4 satisfy the following relationships: I1 > I2 > I4 > I3, 1 / 3I1 ≤ I2 ≤ 1 / 2I1, 0 ≤ I3 ≤ 1 / 3I2, and I4 ≤ 2I3. In a specific embodiment, the pulse current I1 is 15kA to 45kA.

[0052] In the above process, the time of stage T1 is 100-500ms, the time of stage T2 is 50-200ms, the time of stage T3 is 50-200ms, the time of stage T4 is 50-200ms, the time of stage T5 is 50-200ms, and the time of stage T6 is 100-500ms.

[0053] The aluminum alloy welded parts obtained by the above spot welding method have a weld nugget diameter of 5-14mm and a joint tensile-shear strength ≥2.5kN, for example: joint tensile-shear strength ≥3kN.

[0054] The following section provides a further introduction to the spot welding method for aluminum alloy materials based on the coordinated control of pressure and current, and to aluminum alloy welded parts, using specific examples.

[0055] Example 1

[0056] High-strength aluminum alloy 6056 was selected as the research object. The plate size was 138*60*3mm. After cleaning and grinding the surface, the two layers were overlapped and placed on the welding fixture. At this time, the gap between the plates was about 0.3mm. Spot welding tests were carried out using the electrode pressure-current coordinated control method. The specific process parameters for stages T1-T6 are listed in Table 1.

[0057] Table 1 Process parameters for stages T1-T6

[0058]

[0059] During the welding process, precise control of the heat and force input through the above parameters can achieve the following effects: the weld nugget of the aluminum alloy weldment is as follows: Figure 2 As shown, its appearance quality is good, no spatter occurred during the welding process, and no obvious defects such as cracks or shrinkage cavities were observed inside the weld nugget. The diameter of the weld nugget A reached 9.6 mm, and the tensile shear strength of the joint reached 12.2 kN, which is about 13.6% higher than that of constant pressure and constant current control methods. The welding stability and fatigue performance are also improved.

[0060] Example 2

[0061] Automotive-grade 5182 aluminum alloy was selected as the research object. The plate size was 105*45*1mm. After cleaning and polishing the surface, the two layers were overlapped and placed on the welding fixture. At this time, the gap between the plates was approximately 0.1mm. Spot welding tests were carried out using an electrode pressure-current coordinated control method. The specific process parameters for stages T1-T6 are listed in Table 2.

[0062] Table 2 Process parameters for stages T1-T6

[0063]

[0064]

[0065] During the welding process, precise control of the heat and force input through the above parameters can achieve the following effects: the weld nugget of the aluminum alloy weldment is as follows: Figure 3 As shown, its appearance quality is good, no spatter occurred during the welding process, and no obvious defects such as cracks or shrinkage cavities were observed inside the weld nugget. The diameter of the weld nugget B reached 5.4 mm, and the tensile shear strength of the joint reached 3.0 kN, which is about 16.7% higher than that of constant pressure and constant current control methods. The welding stability and fatigue performance are also improved.

[0066] Example 3

[0067] Aerospace-grade 2219 aluminum alloy was selected as the research object. The plate size was 138*60mm, and the thicknesses were 2.0mm and 6.0mm respectively. After cleaning and grinding the surface, the two layers were overlapped and placed on the welding fixture. At this time, the gap between the plates was approximately 0.1mm. Spot welding tests were carried out using an electrode pressure-current coordinated control method. The specific process parameters for stages T1-T6 are listed in Table 3.

[0068] Table 3 Process parameters for stages T1-T6

[0069]

[0070] During the welding process, precise control of the heat and force input through the above parameters can achieve the following effects: the weld nugget of the aluminum alloy weldment is as follows: Figure 4As shown, its appearance quality is good, no spatter occurred during the welding process, and no obvious defects such as cracks or shrinkage cavities were observed inside the weld nugget. The diameter of the weld nugget C reached 10.2 mm, and the tensile shear strength of the joint reached 9.6 kN, which is about 11.4% higher than that of constant pressure and constant current control methods. The welding stability and fatigue performance are also improved.

[0071] In summary, applying the spot welding method for aluminum alloys based on pressure and current coordinated control of this invention to the welding of aluminum alloys under conventional production conditions in the automotive, high-speed rail, and shipbuilding industries can effectively improve the heat and force input during the melting and solidification of aluminum alloys by precisely controlling the current and pressure settings throughout the spot welding process, while ensuring high welding efficiency and versatility. This suppresses defects such as welding spatter, cracks, and shrinkage cavities, achieving high-quality and stable connections from appearance morphology to internal quality and mechanical properties. Furthermore, since this invention provides empirical formulas for process parameter settings and employs automated welding technology processes and parameterized process settings, it has low dependence on the professional qualifications and experience of relevant production personnel, thus possessing good scalability.

[0072] Those skilled in the art should recognize that the above embodiments are merely illustrative of the present invention and are not intended to limit the present invention. Any variations or modifications to the above embodiments that are within the spirit and essence of the present invention will fall within the scope of the claims of the present invention.

Claims

1. A spot welding method for aluminum alloy materials based on pressure and current coordinated control, characterized in that: The aluminum alloy sheets are overlapped and welded using a method that combines electrode pressure and current control.

2. The spot welding method for aluminum alloy materials based on pressure and current coordinated control according to claim 1, characterized in that: When the aluminum alloy plates are overlapped, the gap between the plates shall not exceed 1mm.

3. The spot welding method for aluminum alloy materials based on pressure and current coordinated control according to claim 1, characterized in that: Before overlapping the aluminum alloy sheets, the surface of the aluminum alloy sheets should be cleaned and the oxide film should be polished off.

4. The spot welding method for aluminum alloy materials based on pressure and current coordinated control according to claim 1, characterized in that, The overlap thickness of the aluminum alloy sheet is 2.0 to 8.0 mm, and the number of overlap layers is 2 or 3.

5. The spot welding method for aluminum alloy materials based on pressure and current coordinated control according to claim 1, characterized in that, The method for coordinated control of electrode pressure and current includes the following stages: In stage T1, an electrode pressure of N1 is applied to press the two overlapping aluminum alloy plates together and keep them in a non-energized state. In stage T2, while keeping the electrode pressure N1 constant, a pulsed current I1 is applied to rapidly generate heat, causing the aluminum alloy interface material to melt and form a melt nucleus. In the T3 stage, the electrode pressure N1 is kept constant, and a pulse current I2 is applied to bring the welding heat generation and the heat dissipation of the molten pool into equilibrium. In the T4 stage, apply pulsed current I3 or pause the application of pulsed current to make the heat dissipation of the molten pool exceed the heat generated during welding, so that the molten pool metal gradually solidifies. At the same time, apply electrode pressure N2, which is greater than N1. During stage T5, the electrode pressure N2 is kept constant, and a pulsed current I4 is applied for reheating. In stage T6, stop applying current, maintain electrode pressure N2 constant, and welding ends after the weld nugget cools naturally. The pulse currents I1, I2, I3, and I4 satisfy the following relationship: I1 > I2 > I4 > I3.

6. The spot welding method for aluminum alloy materials based on pressure and current coordinated control according to claim 5, characterized in that: The relationship between the electrode pressures N1 and N2 is as follows: N2 = 1.2N1 ~ 1.4N1.

7. The spot welding method for aluminum alloy materials based on pressure and current coordinated control according to claim 5, characterized in that: The electrode pressure N1 is 3kN to 7kN.

8. The spot welding method for aluminum alloy materials based on pressure and current coordinated control according to claim 5, characterized in that: The pulse currents I1, I2, I3, and I4 satisfy the following relationships: 1 / 3I1≤I2≤1 / 2I1, 0≤I3≤1 / 3I2, I4≤2I3.

9. The spot welding method for aluminum alloy materials based on pressure and current coordinated control according to claim 5, characterized in that: The pulse current I1 is 15kA to 45kA.

10. The spot welding method for aluminum alloy materials based on pressure and current coordinated control according to claim 5, characterized in that: The duration of stage T1 is 100–500 ms, the duration of stage T2 is 50–200 ms, the duration of stage T3 is 50–200 ms, the duration of stage T4 is 50–200 ms, the duration of stage T5 is 50–200 ms, and the duration of stage T6 is 100–500 ms.

11. An aluminum alloy welded part, obtained by the spot welding method for aluminum alloy materials based on pressure and current coordinated control according to any one of claims 1 to 10, characterized in that: The diameter of the weld nugget of the aluminum alloy welded part is 5-14 mm, and the tensile and shear strength of the joint is ≥2.5 kN.

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