A method for laser helical spot welding of phosphating film coated steel by laser-ultrasonic combined surface pretreatment

Abstract

A kind of laser-ultrasonic composite surface pretreatment phosphating film coating steel laser spiral spot welding method, the present application relates to welding technical field, specifically to lap plating film steel workpiece laser spot welding method.The purpose of the present application is to solve the technical problem that phosphating film coating steel is prone to form crack in weld zone.Method: one, the phosphating film steel to be welded is pretreated;Two, laser and coaxial ultrasonic vibration auxiliary device are used to carry out spiral film removal pretreatment on phosphating film steel;Three, laser spiral spot welding is carried out.The present application can improve the impact performance of joint, reduce crack, realize the spot welding of phosphating film coating steel, increase the toughness of spot welding joint.The present application is used for spot welding phosphating film coating steel.

Description

Technical Field

[0001] This invention relates to the field of welding technology, and more specifically to a laser spot welding method for overlapping coated steel workpieces. Background Technology

[0002] After degreasing and rust removal, metal surfaces are usually chemically treated to prevent them from rusting again. This process creates a protective film on the metal surface, which is typically only a few micrometers thick. The main function of this film is to enhance the adhesion between the coating and the substrate. A thicker film can also enhance the rust prevention performance.

[0003] Phosphating is a high-efficiency and low-cost process, but it involves many steps, including degreasing, surface rust removal, surface activation, phosphating, sealing and passivation treatment, and drying. It also has drawbacks such as difficulty in removing the phosphating film and the tendency for cracks to appear after laser irradiation. These drawbacks limit the widespread application of phosphating.

[0004] During welding, the metal is heated and melted rapidly, then cooled at an extremely fast rate. The metal in the molten pool solidifies quickly, and phosphorus in the weld does not have enough time to diffuse, resulting in segregation at the grain boundaries. This segregation of phosphorus at the grain boundaries reduces the bonding force between grains. At the same time, the Fe3P formed by the combination of phosphorus and iron is both hard and brittle, leading to a decrease in the toughness of the weld joint and the formation of cracks in the weld zone. Summary of the Invention

[0005] The purpose of this invention is to solve the technical problem of easy crack formation in the weld zone of phosphated coated steel, and to provide a method for laser spiral spot welding of phosphated coated steel using laser-ultrasonic composite surface pretreatment.

[0006] A method for laser spiral spot welding of phosphated steel with laser-ultrasonic composite surface pretreatment is specifically carried out according to the following steps:

[0007] Step 1: Pre-treat the surfaces of the phosphated steel weldments to be welded, removing impurities and oil stains, and then stack and fix the two phosphated steel weldments together.

[0008] Step 2: Apply the laser and the coaxial ultrasonic vibration auxiliary device together to the phosphated steel weldment processed in Step 1 to perform a large-radius spiral decoction pretreatment. Control the laser power to be 500-1000W, the defocusing amount to be 0-+6mm, the spot diameter to be 2-3mm, the ultrasonic vibration amplitude to be 15-20μm, and the working frequency to be 50-100KHz.

[0009] Step 3: Turn off the ultrasonic device from Step 2 and reset the laser parameters. The laser power is 2000-4000W, the defocusing amount is +2mm-+8mm, and the spot diameter is 1-2mm. Perform small-radius spiral spot welding with laser to complete the process.

[0010] The method of the present invention uses a laser and a coaxial ultrasonic vibration auxiliary device for pretreatment before laser spot welding. Through the combined action of laser and ultrasound, a portion of the phosphide decomposes and vaporizes and escapes from the molten pool. The combined action of the large-radius ultrasonic laser causes another portion of the phosphide to distribute around the spot welding center, reducing the phosphorus content at the subsequent laser spot welding position, thereby improving the performance of the spot weld joint.

[0011] This invention improves the impact performance of joints, reduces cracking, enables spot welding of steel with phosphate coating, and increases the toughness of the welded joint. Tests showed that laser spiral spot welding of phosphate-coated steel treated with this invention, with ultrasonic-assisted laser spiral decoction, can remove a 0.5mm thick phosphate film from the bottom of the specimen surface. Furthermore, the laser spot welded joint has a good morphology, with the welded joint width smaller than the ultrasonic-assisted laser pretreatment width, and no obvious cracks or porosity are generated. Moreover, the laser spot welded joint pretreated with ultrasonic-assisted laser spiral decoction exhibits better impact toughness, with an impact absorption energy reaching 120J.

[0012] This invention is used for spot welding of phosphated coating steel. Attached Figure Description

[0013] Figure 1 Here is a cross-sectional view of a spot weld in an embodiment;

[0014] Figure 2 The image shows a comparison of the impact toughness of a spot weld joint and the impact toughness of a laser spot weld joint without ultrasonic-assisted laser spiral decoction pretreatment. Detailed Implementation

[0015] Specific Implementation Method 1: This implementation method describes a laser spiral spot welding method for steel with a phosphated film coating pretreated by laser-ultrasonic composite surface treatment, specifically carried out according to the following steps:

[0016] Step 1: Pre-treat the surfaces of the phosphated steel weldments to be welded, removing impurities and oil stains, and then stack and fix the two phosphated steel weldments together.

[0017] Step 2: Apply the laser and the coaxial ultrasonic vibration auxiliary device together to the phosphated steel weldment processed in Step 1 to perform a large-radius spiral decoction pretreatment. Control the laser power to be 500-1000W, the defocusing amount to be 0-+6mm, the spot diameter to be 2-3mm, the ultrasonic vibration amplitude to be 15-20μm, and the working frequency to be 50-100KHz.

[0018] Step 3: Turn off the ultrasonic device from Step 2 and reset the laser parameters. The laser power is 2000-4000W, the defocusing amount is +2mm-+8mm, and the spot diameter is 1-2mm. Perform small-radius spiral spot welding with laser to complete the process.

[0019] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that: in step one, the area to be welded is pretreated by wiping it with acetone before welding. Everything else is the same as in Specific Implementation Method One.

[0020] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the thickness of the upper phosphated steel weldment and the thickness of the lower phosphated steel weldment are both 3-10 mm in the two phosphated steel weldments mentioned in step one. Everything else is the same as in Specific Implementation Method One or Two.

[0021] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the combined action time of the laser and the coaxial ultrasonic vibration auxiliary device in step two is 3 to 5 seconds. Everything else is the same as in Specific Implementation Methods One to Three.

[0022] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that the spiral radius in step two is 3-5 mm. Everything else is the same as in Specific Implementation Methods One to Four.

[0023] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that argon gas is used as a protective gas in step two. Everything else is the same as in Specific Implementation Methods One to Five.

[0024] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One through Six in that: in step two, the ultrasonic vibration amplitude is controlled to be 20 μm, the working frequency to be 50 kHz, the laser power to be 750 W, the defocusing amount to be +4 mm, the spot diameter to be 3 mm, and the spiral radius to be 4 mm. Everything else is the same as in Specific Implementation Methods One through Six.

[0025] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that the radius of the spiral spot welding in step three is 1-3 mm. Everything else is the same as in Specific Implementation Methods One to Seven.

[0026] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that the spiral spot welding time in step three is 1 to 2 seconds. Everything else is the same as in Specific Implementation Methods One to Eight.

[0027] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One to Nine in that argon gas is used as the protective gas in step three. Everything else is the same as in Specific Implementation Methods One to Nine.

[0028] The scope of this invention is not limited to the above-described embodiments; a combination of one or more specific embodiments can also achieve the purpose of the invention.

[0029] Example 1:

[0030] A method for laser spiral spot welding of phosphated steel with laser-ultrasonic composite surface pretreatment is specifically carried out according to the following steps:

[0031] Step 1: Pre-treat the surfaces of the phosphated steel weldments to be welded. Before welding, wipe the area to be welded with acetone to remove impurities and oil. Then, stack and fix the two phosphated steel weldments together. The upper plate is 3mm thick and the lower plate is 4mm thick.

[0032] Step 2: Apply the laser and coaxial ultrasonic vibration-assisted device together to the phosphated steel weldment treated in Step 1 for large-radius spiral decoction pretreatment. Control the ultrasonic vibration amplitude to be 20μm, the working frequency to be 50KHz, the laser power to be 750W, the defocusing amount to be +4mm, the spot diameter to be 3mm, and the spiral radius to be 4mm. The combined action time of the laser and coaxial ultrasonic vibration-assisted device is 3s.

[0033] Step 3: Turn off the ultrasonic device from Step 2 and reset the laser parameters to 3000W, +6mm defocus, and 2mm spot diameter. Perform small-radius spiral spot welding with a radius of 2mm and an action time of 1s.

[0034] Figure 1 The example is a spot weld cross-section diagram. As can be seen from the morphology and width-to-depth ratio in the figure, the ultrasonic-assisted laser spiral decoction can remove the phosphate film up to 0.5 mm thick on the surface of the bottom specimen. The laser spot weld joint has a good morphology, the width of the laser spot weld joint is smaller than the width of the ultrasonic-assisted laser pretreatment, and there are no obvious cracks or pores.

[0035] Figure 2 The image shows a comparison of the impact toughness of a spot welded joint with that of a laser spot welded joint without ultrasonic-assisted laser spiral decoction pretreatment. It can be seen that the laser spot welded joint with ultrasonic-assisted laser spiral decoction pretreatment has better impact toughness, and the impact absorption energy reaches 120J.

Claims

1. A method for laser spiral spot welding of steel with phosphate film coating using laser-ultrasonic composite surface pretreatment, characterized in that... This method is specifically carried out in the following steps: Step 1: Pre-treat the surfaces of the phosphated steel weldments to be welded, removing impurities and oil stains, and then stack and fix the two phosphated steel weldments together. Step 2: Apply the laser and the coaxial ultrasonic vibration auxiliary device together to the phosphated steel weldment processed in Step 1 to perform a large-radius spiral decoction pretreatment. Control the laser power to be 500-1000W, the defocusing amount to be 0-+6mm, the spot diameter to be 2-3mm, the ultrasonic vibration amplitude to be 15-20μm, and the working frequency to be 50-100KHz. Step 3: Turn off the ultrasonic device from Step 2 and reset the laser parameters. The laser power is 2000-4000W, the defocusing amount is +2mm-+8mm, and the spot diameter is 1-2mm. Perform small-radius spiral spot welding with laser to complete the process.

2. The method for laser spiral spot welding of phosphated steel with laser-ultrasonic composite surface pretreatment as described in claim 1, characterized in that... Step 1: Before welding, wipe the area to be welded with acetone for pretreatment.

3. The method for laser spiral spot welding of phosphated steel with laser-ultrasonic composite surface pretreatment as described in claim 1, characterized in that... In step one, the thickness of the upper phosphated steel weldment is 3-10 mm, and the thickness of the lower phosphated steel weldment is 3-10 mm.

4. The method for laser spiral spot welding of phosphated steel with laser-ultrasonic composite surface pretreatment as described in claim 1, characterized in that... In step two, the combined action time of the laser and the coaxial ultrasonic vibration auxiliary device is 3 to 5 seconds.

5. The method for laser spiral spot welding of phosphated steel with laser-ultrasonic composite surface pretreatment according to claim 1, characterized in that... Step 2: The spiral radius is 3-5 mm.

6. The method for laser spiral spot welding of phosphated steel with laser-ultrasonic composite surface pretreatment as described in claim 1, characterized in that... Argon is used as a protective gas in step two.

7. The method for laser spiral spot welding of phosphated steel with laser-ultrasonic composite surface pretreatment according to claim 1, characterized in that... Step 2: Control the ultrasonic vibration amplitude to 20μm, the working frequency to 50KHz, the laser power to 750W, the defocusing amount to +4mm, the spot diameter to 3mm, and the spiral radius to 4mm.

8. The method for laser spiral spot welding of phosphated steel with laser-ultrasonic composite surface pretreatment according to claim 1, characterized in that... The radius of the spiral spot weld in step three is 1 to 3 mm.

9. A method for laser spiral spot welding of phosphated steel with laser-ultrasonic composite surface pretreatment according to claim 1, characterized in that... The spiral spot welding action time in step three is 1 to 2 seconds.

10. A method for laser spiral spot welding of phosphated steel with laser-ultrasonic composite surface pretreatment according to claim 1, characterized in that... Step 3 uses argon as a protective gas.

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