Lap welding method for thin aluminum row

Abstract

The invention relates to the technical field of copper-aluminum composite welding, in particular to a thin aluminum bar lap welding method. The method comprises the following steps: firstly, carrying out microstructure regulation and control on a welding surface by adopting a mechanical directional polishing technology, effectively removing a surface oxide layer and forming a uniform rough surface; secondly, accurate management of heat input is achieved through a gradient temperature control strategy, and heat damage to the thin-wall material is avoided; and meanwhile, mutual diffusion of copper atoms and aluminum atoms is promoted by combining a metallurgical transition layer technology, and stable metallurgical bonding is formed. In terms of structural design, a unique positioning system ensures the assembly precision, and the process stability is remarkably improved in cooperation with an optimized welding process. According to the method, the welding quality of the thin aluminum row is improved in a breakthrough mode, meanwhile, the good industrial production adaptability is achieved, and a reliable solution is provided for the connection technology in the fields of power batteries, energy storage equipment and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of copper-aluminum composite welding, and more particularly to a thin aluminum bar lap welding method. BACKGROUND

[0002] Under the background of rapid development in the new energy field, thin aluminum bars (0.3-2.0mm) are widely used in the fields of power batteries, energy storage devices, etc. as key connecting components with lightweight and high conductivity. However, the existing welding technology faces three major technical bottlenecks: first, in terms of material properties, the high thermal conductivity of aluminum makes it difficult to control heat input, which easily leads to burn-through defects; the surface oxide film is difficult to completely remove, causing problems such as weld slag and incomplete fusion; the poor rigidity of thin aluminum bars easily leads to deformation due to welding thermal stress. Second, in terms of process, the heat input precision of traditional arc welding is insufficient, and the cost of laser welding equipment is high and requires strict assembly precision, which is difficult to meet the needs of industrial production. Finally, in the scenario of copper-aluminum dissimilar metal welding, high polymer diffusion welding easily causes problems such as material melting and poor interface bonding, which directly affects the reliability and service life of the product. SUMMARY

[0003] In view of the deficiencies of the prior art, the present application aims to provide a thin aluminum bar lap welding method to solve at least one of the technical problems of thin aluminum bar welding process, such as thermal melting, copper-aluminum interface bonding and unstable quality in industrial production.

[0004] To achieve the above-mentioned purpose, the present application realizes the following scheme:

[0005] A thin aluminum bar lap welding method, comprising the following steps:

[0006] (1) Pre-welding treatment: two positioning holes are processed on the lap welding area of the thin aluminum bar and the copper bar; a nylon polishing wheel is used to polish along the length direction of the thin aluminum bar to expose the metal luster, and remove the oxide film and oil stains;

[0007] (2) Welding preparation: uniformly apply copper-aluminum solder paste on the lap welding surface of the thin aluminum bar; through the copper nails passing through the positioning holes, the copper bar and the thin aluminum bar are assembled;

[0008] (3) Welding process: using a high polymer diffusion welding device, first preheat the graphite to 520±10℃ with a current of 100-120A; adjust the current to 50-60A to make the device in a welding state; place the lap welding part in the middle of the graphite, apply a pressure of 7.5-8.5KN at 530-550℃ for 6-10s to complete the welding;

[0009] (4) Post-welding treatment: immediately immerse in cold water for rapid cooling; use a nylon polishing wheel to polish the welding area.

[0010] Preferably, the model of the nylon polishing wheel in step (1) and step (4) is 7P-120#.

[0011] Preferably, the polishing direction of step (1) is parallel to the length direction of the aluminum bar.

[0012] Preferably, the viscosity of the copper-aluminum solder paste ranges from 500-800 cP, and the coating thickness is 0.05-0.1 mm.

[0013] Preferably, the thickness of the thin aluminum bar is 0.3-2.0 mm.

[0014] Preferably, when the thickness of the thin aluminum bar is 0.8 mm, and the overlap area is 30x30 mm 2 , the welding parameters are: current 55A±5%, temperature 540±10℃, and holding time 8s.

[0015] Preferably, the water temperature of the cold water in step (4) is 20-25℃, and the immersion time is no more than 30s.

[0016] Preferably, the fitting gap between the positioning hole and the copper pin is 0.05-0.1 mm.

[0017] Preferably, during the welding process in step (3), the position of the lap joint is clamped in the middle of the graphite using tweezers.

[0018] The thin aluminum bar lap welding method provided by the present application has the following beneficial effects: The thin aluminum bar lap welding method provided by the present application realizes multiple technical breakthroughs through innovative process design. In terms of heat management, the gradient temperature control strategy is adopted, and through the synergistic effect of 520±10℃ preheating, 530-550℃ welding, and 10-25℃ rapid cooling, the problem of thin aluminum bar hot melting perforation is completely solved. In terms of interface bonding, the combination scheme of mechanical directional polishing and metallurgical solder paste coating is combined, which significantly improves the strength of the copper-aluminum joint and breaks through the technical bottleneck of poor interface bonding. In terms of industrial application, the new positioning system design ((Φ3.05mm positioning hole / Φ3.00mm copper pin)) realizes a ±0.05mm assembly accuracy, and cooperates with a 6-10s single-point welding time program, which ensures the stability and consistency of large-scale production. DETAILED DESCRIPTION

[0019] The present application will be further described below in conjunction with examples, but the scope of protection required by the present application is not limited to the scope expressed in the examples.

[0020] Example 1

[0021] Take a 3.0mm thick soft copper bar, a 0.8mm thick thin aluminum bar (model: AL1060), and a 30x30mm 2 lap area as an example. A method for lap welding of a thin aluminum bar includes the following steps:

[0022] 1. Pre-welding preparation:

[0023] (1) Positioning hole processing: In the lap welding area of the thin aluminum row and the copper row, two positioning holes with a diameter of 3.05 mm are punched as the precise positioning reference for lap welding to ensure assembly accuracy.

[0024] (2) Surface treatment: Before lap welding, the lap welding area of the thin aluminum row and the copper row is polished and sanded: using a 7P-120# nylon polishing wheel, uniform speed and uniform polishing along the length direction of the thin aluminum row until the fresh metal luster is exposed, completely removing the oxide film, oil stains and appearance defects, and improving the bonding quality of the welding surface.

[0025] 2. Welding preparation:

[0026] (1) Solder paste coating: On the surface of the lap welding area of the thin aluminum row, evenly (screen printing principle) coat the appropriate copper-aluminum solder paste (viscosity range 500-800 cP, coating thickness 0.05-0.1 mm) to provide a metallurgical bonding basis for dissimilar metal welding.

[0027] (2) Assembly connection: The copper row and the thin aluminum row are connected by two copper nails with a diameter of 3.00 mm to ensure the alignment of the lap welding edges and control the assembly gap within 0.05-0.1 mm to create conditions for stable welding.

[0028] 3. Welding process:

[0029] Using a high polymer diffusion welding equipment, the process of (preheating-parameter adjustment-product welding) is executed, and the parameters and operation specifications are as follows:

[0030] (1) Welding parameters: welding current 50-60 A, welding pressure 7.5-8.5 KN, welding temperature 530-550℃; operation mode is manual welding.

[0031] (2) Operation steps:

[0032] ① Graphite preheating: turn on the equipment, adjust the welding current to 100-120 A, preheat the graphite, and stop heating when the graphite temperature reaches 520±10℃.

[0033] ② Parameter switching: manually adjust the equipment current to 55 A±5%, ensuring that the equipment is in a welding-ready state.

[0034] ③ Product clamping and welding: place the lap welding part of the product to be welded in the middle of the graphite through tweezers, start the welding program; when the welding temperature reaches the preset value of 540±10℃, maintain the welding pressure of 8.0 KN±5% for 8 seconds to complete the welding action.

[0035] 4. Post-welding treatment:

[0036] (1) Fast water cooling: After welding, the product is immediately put into clean cold water for water cooling treatment (directly immersed in cold water with a water temperature of 20-25℃, the time is not more than 30s), through fast cooling to stabilize the weld structure, avoid excessive oxidation of the heat affected zone.

[0037] (2) Polishing and grinding: 7P-120# nylon polishing wheel is used to polish and grind the welding area and the surrounding area: uniform speed is moved along the weld direction, remove the welding spatter, oxide layer, make the welding surface smooth and clean, meet the appearance and subsequent process requirements.

[0038] Comparative Example 1

[0039] The difference from Example 1 is only that the thin aluminum row and the copper row are treated and pretreated by degreasing soaking process.

[0040] Comparative Example 2

[0041] The difference from Example 1 is only that the thin aluminum row is not coated with copper aluminum solder paste on the welding surface.

[0042] Comparative Example 3

[0043] The difference from Example 1 is only that the graphite temperature is not preheated to 520±10℃, and then the welding is started.

[0044] Comparative Example 4

[0045] The difference from Example 1 is only that natural air cooling process is used for cooling after welding.

[0046] Three batches of copper-aluminum composite rows are produced by using the method provided in Example 1 and Comparative Examples 1-4 respectively, and the number of each batch is 30PCS. The copper-aluminum composite rows are detected for the following indexes, and the data in Table 1 is obtained.

[0047] (1) Hot melting perforation detection: CT equipment is used to perform three-dimensional tomography on each welding sample, VGStudio MAX software is used to automatically identify and mark the through holes with a diameter of >0.2mm, record the number, position and maximum diameter of the perforation; During the detection process, the environmental temperature is maintained at 23±2℃, 30 samples are detected for each batch, and non-process defects such as transportation damage are excluded during final statistics, and the average value of each batch is calculated in "perforation number per piece" as the measurement unit.

[0048] (2) Shear strength detection: A universal material testing machine was used for testing. The copper-aluminum composite row sample was fixed with a clamping interval of 30±0.5 mm, and a constant shear force of 1 mm / min was applied. The load-displacement curve was collected in real time until the sample was broken. Ten samples were randomly selected from each batch, and the shear strength was calculated by the formula τ=F / (L×T) (F is the maximum shear force, L is the 30 mm overlap length, and T is the actual thickness of the thin aluminum row). After excluding invalid data such as clamp slipping, the arithmetic mean was taken as the representative value of the batch strength.

[0049] (3) Good rate detection: Full number of appearance detection was carried out, and the weld forming quality was checked by visual and magnifying glass. Samples with obvious defects such as cracks and undercut were excluded, and the good rate was calculated.

[0050] Table 1 Performance detection table

[0051]

[0052]

[0053] Compared with Example 1, the average shear strength and good rate of Comparative Example 1 (degreasing immersion) were reduced, indicating that mechanical polishing could make the welding surface microscopically rough and uniform, increasing the bonding force, compared with degreasing immersion. Degreasing immersion removes impurities and oxidation layer as a whole, and has relatively insufficient effect on promoting welding in the lap joint area.

[0054] The shear strength of Comparative Example 2 (without solder paste) was much lower than that of other groups, indicating that mechanical polishing or gradient temperature control process alone could not achieve ideal bonding strength. Only by combining precise impurity removal, gradient temperature control and metallurgical transition as in Example 1, can high strength, low defect and high yield be achieved simultaneously.

[0055] The number of perforations in Comparative Example 3 (without preheating) was much higher than 0.33 pieces / batch in Example 1, indicating that thin aluminum row could be easily thinned or hot melt perforated due to heating and pressure. The 88-92% yield further proves that the absence of preheating has an important impact on quality stability. In high polymer diffusion welding, preheating of graphite not only shortens the welding time, but also effectively solves the hot melt problem of thin aluminum row, helping to improve product efficiency and quality.

[0056] The average shear strength of the batch of the comparative example 4 (air cooling) is close to that of the example 1, and is 77.8 MPa, and the batch yield is slightly lower than that of the example 1, and is 96.7%. The reason is that the air cooling is similar to the product tempering process in essence. The air cooling is not only time-consuming, but also easy to cause the product to be over-oxidized and deformed. The welding area is affected by the continuous heat, and the texture is soft, which affects the structural stability. The water cooling process in the application is equivalent to the quenching process, which can promote the hardening of the welding area. It is verified by the actual production that the application risk is not found at present, and the product performance can be better protected.

[0057] The above only describes the preferred embodiments of the application, and the protection scope of the application is not limited to the above-described embodiments. Any technical solution falling within the idea of the application shall fall within the protection scope of the application. It should be noted that, for ordinary skilled persons in the art, some improvements and refinements without departing from the principles of the application shall also be considered as the protection scope of the application.

Claims

1. A method of lap welding thin aluminum strips, characterized by, The method comprises the following steps: (1) Pre-welding treatment: two positioning holes are processed on the lap welding area of the thin aluminum bar and the copper bar; A nylon polishing wheel is used to polish the thin aluminum bar along the length direction until the metal luster is exposed, and the oxide film and oil stains are removed; (2) Welding preparation: the copper-aluminum solder paste is uniformly coated on the lap welding surface of the thin aluminum bar; the copper pin is passed through the positioning hole to assemble the copper bar and the thin aluminum bar; (3) Welding process: the high polymer diffusion welding equipment is used, the graphite is preheated to 520±10℃ by 100-120A current, the current is adjusted to 50-60A to make the equipment in the state of waiting for welding, the lap welding part is placed in the middle of the graphite, and the welding is completed by applying 7.5-8.5KN pressure for 6-10s at 530-550℃; (4) Post-welding treatment: immediately immersed in cold water for rapid cooling; the nylon polishing wheel is used to polish the welding area.

2. The method of claim 1, wherein, The model of the nylon polishing wheel in steps (1) and (4) is 7P-120#.

3. The method of claim 1, wherein, The polishing direction of step (1) is parallel to the length direction of the aluminum bar.

4. The method of claim 1, wherein, The viscosity of the copper-aluminum solder paste is 500-800cP, and the coating thickness is 0.05-0.1mm.

5. The method of claim 1, wherein, The thickness of the thin aluminum bar is 0.3-2.0mm.

6. The method of claim 5, wherein, When the thickness of the thin aluminum row is 0.8 mm, the overlap area is 30 x 30 mm 2 , and the welding parameters are: current 55 A ± 5%, temperature 540 ± 10℃, and pressure maintaining time 8 s.

7. The method of claim 1, wherein, The water temperature of the cold water in step (4) is 20-25℃, and the immersion time is not more than 30s.

8. The method of claim 1, wherein, The gap between the positioning hole and the copper pin is 0.05-0.1mm.

9. The method of claim 1, wherein, In the welding process of step (3), the lap welding part is clamped in the middle of the graphite by using tweezers.

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