Special welding method for aluminum alloy

Abstract

The invention relates to a special welding method for aluminum alloy. The special welding method comprises the steps that S1, preparation before welding is conducted; s2, MIG welding bottoming is carried out; s3, the groove is filled through TIG welding, and surface covering is conducted; and S4, post-welding treatment is carried out. The composite technology of MIG welding bottoming and TIG welding capping filling is adopted, the method is used for thick plate aluminum alloy welding, deformation is small, the porosity is low, preheating is not needed, and the requirement for welding of complex structures and dissimilar materials is met. The welding speed is increased by 3 times, and the porosity is reduced from 2.1% to 0.5%; and the flaw detection qualification rate is increased from 85% to 98%. The shrinkage amount is reduced by 60-80%; and the workload of the correction process is reduced by 50%. The method is suitable for the fields of aerospace, automobile manufacturing, rail transit and the like.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy welding, specifically relating to a special welding method for aluminum alloys, and in particular a welding method for thick aluminum alloy plates, which is adapted to the welding needs of complex structures and dissimilar materials. Background Technology

[0002] Traditional methods for welding aluminum alloys have the following problems:

[0003] 1. TIG welding: When welding thick plates, the large heat input leads to significant shrinkage deformation (2-5mm), which can easily penetrate the base material and requires subsequent correction.

[0004] 2. MIG welding: Although the welding speed is relatively fast, the porosity is high, and the welding of thick plates requires preheating to 80-150℃, which is difficult to achieve in on-site construction;

[0005] 3. Poor adaptability to complex structures: The argon arc welding torch has difficulty penetrating into narrow grooves, making wire feeding difficult and easily resulting in incomplete fusion or cracks;

[0006] 4. Welding of dissimilar aluminum alloys: When welding 5 series aluminum alloys with 6 series and 7 series aluminum alloys, heat input control is difficult, which can easily lead to uneven microstructure and properties.

[0007] 5. Industry Needs and Challenges:

[0008] The aerospace, automotive manufacturing and other fields have increasingly higher requirements for the welding quality of aluminum alloys, which need to take into account high strength, low deformation and high efficiency.

[0009] Existing methods are insufficient to meet the requirements of complex structures (such as large components and welding of dissimilar aluminum alloys).

[0010] 6. Necessity of Technological Improvement

[0011] Existing welding methods cannot simultaneously solve problems such as heat input control, deformation suppression, and porosity reduction, and there is an urgent need for a new welding method to meet the needs of high-end manufacturing. Summary of the Invention

[0012] This invention provides a special welding method for aluminum alloys, which has small deformation, low porosity, and requires no preheating, and is suitable for welding complex structures and dissimilar materials.

[0013] To address the above technical problems, this invention provides a special welding method for aluminum alloys, characterized by the following specific steps:

[0014] S1. Pre-welding preparation:

[0015] Clean the surface of the base material of oil stains and oxide film; bevel the edges of boards with a thickness of ≥5mm;

[0016] S2. MIG soldering for root pass:

[0017] Using jet transition or pulse transition mode, one-time filling of the groove root;

[0018] Parameters: current 150-250A, voltage 19-24V, welding speed 5-60m / h;

[0019] S3. Fill the groove with TIG welding and cover:

[0020] Parameters: starting arc current 120-180A, welding current 200-300A, arc current 10%-20% of welding current, welding frequency 110-150Hz;

[0021] During filling, a small amount of wire feeding is used to promote the overflow of the base layer pores;

[0022] S4. Post-weld treatment.

[0023] Beneficial effects: The present application adopts the composite process of MIG welding backing + TIG welding filling and covering, which is used for thick plate aluminum alloy welding, and has the following specific advantages:

[0024] 1. High efficiency:

[0025] MIG welding backing speed is fast, which shortens the production cycle;

[0026] Suitable for mass production.

[0027] 2. Low deformation:

[0028] MIG welding low heat input reduces shrinkage (0.5-1mm vs. 2-5mm of traditional TIG welding);

[0029] Reduce the cost of correction process.

[0030] 3. High quality:

[0031] Meet the requirements of radiographic inspection secondary film, porosity rate ≤0.5%;

[0032] High weld strength (such as tensile strength ≥310MPa).

[0033] 4. Strong adaptability:

[0034] Suitable for complex structures (such as narrow groove, dissimilar aluminum alloy welding);

[0035] Reduce the dependence on the technical level of workers.

[0036] 5. Significant economic benefits:

[0037] Reduce the rework rate, save raw materials and energy;

[0038] Enhance the market competitiveness of enterprises. DETAILED DESCRIPTION

[0039] In order to make the purpose, content and advantages of the present application more clear, the specific embodiments of the present application are described in further detail below.

[0040] The present application proposes a special welding method for aluminum alloy. The present application adopts the composite process of MIG welding backing + TIG welding filling and covering, and the specific steps are as follows:

[0041] S1. Preparation before welding:

[0042] Surface cleaning: use chemical cleaning agent or mechanical polishing method to clean the oil stains and oxide film on the surface of the base material to ensure the cleanliness of the welding area. For the surface with heavy oil stains, first wipe it with organic solvent (such as acetone), and then polish it with sandpaper or steel wire brush to expose the metal luster.

[0043] Groove machining: groove (such as 60° V-type groove) is opened for plate with thickness ≥5mm. The machining accuracy of the groove has important influence on the welding quality. The error of the groove angle is controlled within ±2°, and the thickness of the blunt edge is controlled within 0.5-1mm, so as to ensure good fusion during welding and avoid defects such as incomplete penetration.

[0044] S2. MIG welding backing:

[0045] Welding mode: jet transition or pulse transition mode is adopted to fill the groove root at one time. Under jet transition mode, the arc is stable, the droplet transition frequency is high, and high-efficiency welding can be realized; under pulse transition mode, the heat input can be better controlled, which is suitable for the area sensitive to heat input.

[0046] Heat input advantage: low heat input, compared with the traditional welding method, can effectively reduce the deformation, especially suitable for the welding of complex structures (such as narrow groove, horn corner and corner area), and avoid the deformation problem caused by excessive heat input.

[0047] Ensure the stability of the molten pool and avoid defects such as incomplete fusion and slag inclusion. Low heat input reduces deformation and adapts to complex structures (such as narrow groove, horn corner and corner area).

[0048] Welding parameters:

[0049] Current: 150-250A, which is appropriately adjusted according to the thickness and material of the plate. For thinner thick plate aluminum alloy (such as 5-8mm), the current can be set at 150-180A; for thicker plate (such as 8-12mm), the current can be adjusted to 200-250A.

[0050] Voltage: 19-24V, which is matched with the current to ensure the stability of the arc and the smoothness of the droplet transition. Generally, as the current increases, the voltage also increases accordingly to maintain a suitable arc length.

[0051] Welding speed: 5-60 m / h, the welding speed is selected according to the groove shape, weld position and the number of backing. For simple groove and single layer backing, the welding speed can be appropriately increased to 40-60 m / h; for complex groove or multi-layer backing, the speed is controlled at 5-30 m / h to ensure the backing quality.

[0052] Wire feed speed: adjust according to the selected current, voltage and welding speed, ensure that the welding wire can be timely supplemented to the molten pool, and ensure the formation of the weld. The wire feed speed range is usually 3-10 m / min, and the specific value needs to be determined through test to achieve the best fusion effect.

[0053] Gas flow: the protective gas uses argon with purity ≥ 99.99%, and the flow is controlled at 15-25 L / min. Suitable gas flow can effectively protect the welding area and prevent air from entering to cause porosity and other defects. In windy environment, the gas flow needs to be appropriately increased.

[0054] Special four-step operation:

[0055] First step: arc striking: the arc striking current is set to 20%-50% of the welding current. For example, if the welding current is set to 200 A, the arc striking current is between 40-100 A. When striking the arc, first aim the welding gun at the arc starting point, press the welding gun switch, and smoothly ignite the arc with a lower arc striking current, the duration is about 1-2 seconds, which locally heats the surface of the base material, and prepares for normal welding.

[0056] Second step: welding: after the arc striking is completed, quickly increase the current to the normal welding current, and perform the welding operation according to the set welding speed, voltage and other parameters. During the welding process, closely observe the molten pool state to ensure that the shape and size of the molten pool are stable, the droplet transfer is smooth, and the fusion of the weld is good.

[0057] Third step: adjustment before arc stopping: 2-3 seconds before reaching the end of the weld, gradually reduce the welding current to the arc stopping current, which is 10%-20% of the welding current. For example, when the welding current is 200 A, the arc stopping current is between 20-40 A. This can reduce the heat input of the molten pool and avoid defects such as shrinkage and cracks at the arc stopping position.

[0058] Fourth step: arc stopping: when welding to the end of the weld, release the welding gun switch, stop the wire feeding and arc, and complete the arc stopping operation. After arc stopping, keep the welding gun at the arc stopping position for 1-2 seconds to ensure that the protective gas continues to protect the molten pool until it cools and solidifies.

[0059] Set the welding parameters for the MIG welding root pass as described above. During the welding process, closely observe the state of the molten pool to ensure its stability and avoid defects such as incomplete fusion and slag inclusions.

[0060] Key operating points: Maintain a 70-80° angle between the welding torch and the workpiece surface to ensure that the shielding gas effectively covers the welding area. During welding, pay attention to the extension length of the welding wire, generally keeping it at 10-15mm to ensure normal melting of the welding wire and proper transfer of molten droplets.

[0061] S3, TIG welding filler capping:

[0062] Gas protection: High-purity argon gas is used for protection, with an argon purity of ≥99.999%, which reduces the generation of porosity and provides a good protective atmosphere for the weld.

[0063] Weld quality optimization: By optimizing welding parameters and operating methods, the requirements of radiographic testing level 2 are met, thereby improving the surface and internal quality of the weld.

[0064] Welding parameters:

[0065] Arc ignition current: 120~180A. A lower current is used when igniting the arc to ignite it smoothly and avoid impacting the base material and causing defects due to excessive arc ignition current.

[0066] Welding current: 200-300A. This current range is used for filling and capping processes to ensure the weld penetration and width, allowing the weld metal to fully fuse with the base metal. For thicker filler layers, the current can be appropriately increased to 250-300A; for capping layers, the current should be controlled at 200-230A to obtain good surface finish.

[0067] Frequency: 110~150Hz. By adjusting the frequency of the current, the heat input of the weld and the stirring effect of the molten pool can be controlled, the grains can be refined, and the mechanical properties of the weld can be improved.

[0068] Interpass temperature: A special four-step method is used to strictly control the interpass temperature to ≤150℃. This helps reduce welding stress and prevent defects such as weld cracks.

[0069] Wire feed rate: Feed wire in small amounts, controlling the amount of wire fed each time to 0.2-0.5 g / cm, to promote the overflow of porosity in the root pass and ensure the uniform chemical composition of the weld. By precisely controlling the wire feed rate, weld quality problems caused by too much or too little wire can be avoided.

[0070] During the cover weld, perform normal welding.

[0071] Special four-step operation:

[0072] Step 1: Arc Ignition: The arc ignition current is 20% to 50% of the welding current. Assuming the welding current is 250A, the arc ignition current should be between 50 and 125A. When igniting the arc, maintain a suitable distance between the tungsten electrode and the workpiece (approximately 2-3 mm), gently press the welding torch switch, and ignite the arc with a low ignition current. The ignition time is approximately 1-2 seconds, allowing the surface of the workpiece to begin melting and forming a molten pool.

[0073] Step 2: Welding: After successful arc ignition, quickly adjust the current to the set welding current and begin fill or cover welding. During welding, maintain a stable angle between the tungsten electrode and the workpiece (generally 70-80°), move the welding torch at a uniform speed, and feed the wire according to the set wire feed amount to ensure that the welding wire melts evenly and fills the molten pool, thus guaranteeing the formation and quality of the weld.

[0074] Step 3: Pre-arc termination adjustment: 3-4 seconds before the weld is finished, gradually reduce the welding current to the arc termination current, which should be 10%-20% of the welding current. For example, if the welding current is 250A, the arc termination current should be between 25-50A. By reducing the current, the heat in the molten pool is reduced, preventing defects such as shrinkage cavities and arc craters at the arc termination point.

[0075] Step 4: Arc Termination: When welding reaches the end of the weld, release the welding torch switch to stop wire feeding, and simultaneously gradually lengthen the arc until it extinguishes, completing the arc termination. After arc termination, maintain argon protection for 3-5 seconds to ensure the molten pool cools sufficiently under argon protection and prevents oxidation of the molten pool.

[0076] Welding parameters for TIG welding filler and cover passes were strictly set, and a special four-step welding method was used. During the welding process, the wire feed rate was strictly controlled, with each feed rate controlled at 0.2–0.5 g / cm to ensure that the porosity of the root pass could be smoothly expelled, while also ensuring the uniform chemical composition of the weld.

[0077] Cover welding technique: When welding the cover layer, adjust the oscillation amplitude and speed of the welding torch appropriately to make the weld surface smoother and more aesthetically pleasing. The oscillation amplitude is generally 1.2 to 1.5 times the weld width, and the welding speed is slightly slower than that of the filler layer to obtain a good surface finish.

[0078] S4. Post-welding treatment:

[0079] Non-destructive testing: Conduct non-destructive testing (such as radiographic testing and ultrasonic testing) to comprehensively inspect the welds according to relevant standards to ensure that the weld quality meets the requirements. Radiographic testing should meet the Class II standard, and the size and number of defects detected by ultrasonic testing must be within the allowable range.

[0080] Defect Handling: Detected defects should be addressed promptly. Smaller defects such as porosity and slag inclusions can be repaired by grinding or welding. Larger defects require complete removal of the defective area before re-welding. After handling, non-destructive testing should be performed again until the weld quality is acceptable.

[0081] Effects of the present invention

[0082] 1. Increased production efficiency:

[0083] Welding speed is increased by 3 times (e.g., 12m / h vs. traditional TIG welding 4m / h).

[0084] 2. Welding quality optimization:

[0085] The porosity decreased from 2.1% to 0.5%;

[0086] The flaw detection pass rate increased from 85% to 98%.

[0087] 3. Excellent deformation control:

[0088] Shrinkage is reduced by 60% to 80%;

[0089] The workload of the calibration process is reduced by 50%.

[0090] 4. Wide range of applications:

[0091] Suitable for aerospace, automotive manufacturing, rail transportation and other fields;

[0092] The deformation was reduced from 5mm to 1.2mm.

[0093] Experimental data and validation:

[0094] Test conditions

[0095] Test plate material: Prepare 3 sets of dissimilar aluminum alloy test pieces of 5A06 and 6061, with a thickness of 10mm;

[0096] Bevel design: Single-sided V-shape (55° angle, 1.5mm blunt edge);

[0097] Equipment: Furniture TPS 5000MIG welding machine, Lincoln V205-T AC / DC TIG welding machine;

[0098] Environment: constant temperature 25℃, humidity ≤40%, argon flow rate 20L / min for MIG welding and 15L / min for TIG welding.

[0099] Test piece 1 (using pure MIG welding): Current 200A, voltage 22V, pulse transfer, welding speed 20m / h (root pass).

[0100] Current 250A, voltage 24V, pulse transfer, welding speed 22m / h (filler and cover weld)

[0101] Test piece 2 (using pure TIG welding): welding current 250A, frequency 120Hz, interpass temperature controlled at 120℃ (root pass).

[0102] Welding current 240A, frequency 120Hz, interpass temperature controlled at 120℃ (fill and cover welds)

[0103] Specimen 3 (using the MIG+TIG welding of this invention):

[0104] MIG welding root pass: current 200A, voltage 22V, pulse transfer, welding speed 20m / h;

[0105] TIG welding filler:

[0106] Segmented wire feeding (speed reduced to 30% of MIG);

[0107] Welding current 250A, frequency 120Hz, interpass temperature controlled at 120℃;

[0108] TIG welding cover pass: multi-pass welding (each pass covers 1 / 2 the width of the previous pass), shielding gas flow rate 20L / min;

[0109] Post-weld data comparison:

[0110] Index Pure MIG welding Pure TIG welding The invention (MIG+TIG) Shrinkage (mm) 0.5～1 2～5 0.3～0.8 Porosity (%) (vol) 2.5 1.2 0.8 Flaw detection pass rate 85％ |90％ 98％ Tensile strength (MPa) 275 300 310

[0111] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A special welding method for aluminum alloys, characterized in that, The specific steps are as follows: S1. Pre-welding preparation: Clean the surface of the base material of oil stains and oxide film; bevel the edges of boards with a thickness of ≥5mm; S2. MIG soldering for root pass: The root of the bevel is filled in one go using either jet or pulse transition mode. Parameters: Current 150~250A, Voltage 19~24V, Welding speed 5~60m / h; S3. Fill the bevel with TIG welding and cover the surface: Parameters: Arc starting current 120-180A, welding current 200-300A, arc ending current 10%-20% of welding current, welding frequency 110-150Hz; During the filling process, a small amount of wire is used to promote the overflow of air pores in the bottom layer; S4. Post-weld treatment.

2. The special welding method for aluminum alloys according to claim 1, characterized in that: In S1, the bevel angle error is controlled within ±2°, and the blunt edge thickness is controlled within 0.5 to 1 mm.

3. The special welding method for aluminum alloys according to claim 1, characterized in that: In S2, for simple bevels and single-layer root passes, the welding speed is 40–60 m / h; for complex bevels or multi-layer root passes, the welding speed is controlled at 5–30 m / h.

4. The special welding method for aluminum alloys according to claim 1, characterized in that: In S2, the protective gas is argon with a purity of ≥99.99%, and the flow rate is controlled at 15-25 L / min.

5. A special welding method for aluminum alloys according to claim 1, characterized in that: MIG soldering root pass uses a special four-step process: Step 1: Arc ignition: Set the arc ignition current to 20% to 50% of the welding current; Step 2: Welding: After the arc is struck, quickly increase the current to the normal welding current and perform the welding operation according to the set welding speed and voltage parameters; Step 3: Pre-arc adjustment: 2-3 seconds before the end of the weld, gradually reduce the welding current to the arc-ending current, which is 10%-20% of the welding current. Step 4: Arc termination: When welding reaches the end of the weld, release the welding torch switch, stop wire feeding and arc, and complete the arc termination operation. After arc termination, keep the welding torch in the arc termination position for 1 to 2 seconds to ensure that the shielding gas continues to protect the molten pool until the molten pool cools and solidifies.

6. A special welding method for aluminum alloys according to claim 1, characterized in that: In S2, the welding torch is kept at a 70-80° angle to the surface of the workpiece to ensure that the shielding gas can effectively cover the welding area. During welding, the extension length of the welding wire is kept at 10-15 mm to ensure that the melting of the welding wire and the transfer of molten droplets are normal.

7. A special welding method for aluminum alloys according to claim 1, characterized in that: In S3, high-purity argon gas is used for protection, with an argon purity of ≥99.999%.

8. A special welding method for aluminum alloys according to claim 1, characterized in that: In S3, the interlayer temperature is strictly controlled to be ≤150℃.

9. A special welding method for aluminum alloys according to claim 1, characterized in that: In S3, a small amount of silk is fed, with each feeding amount controlled at 0.2–0.5 g / cm.

10. A special welding method for aluminum alloys according to claim 1, characterized in that: When welding the cover layer, adjust the oscillation amplitude and speed of the welding torch. The oscillation amplitude should be 1.2 to 1.5 times the width of the weld, and the welding speed should be slightly slower than that of the filler layer.