A high-quality lap welding method for dissimilar materials based on laser surface treatment

Abstract

The present application relates to the technical field of metal and fiber reinforced plastic dissimilar material connection, and particularly relates to a high-quality lap welding method for dissimilar materials based on laser surface treatment, which comprises the following steps: S1: performing laser surface treatment on a metal plate to be welded, etching a target microstructure in the to-be-welded area, and introducing new polar functional groups; S2: performing friction stir lap welding on the processed metal plate and the fiber reinforced composite plate without processing. The present application has the following advantages: the microstructure of the present application is more compact in arrangement, improves the utilization rate of the to-be-welded area, further increases the connection area between dissimilar materials, secondly, the microstructure has more levels in space, can effectively reduce the welding internal stress of the to-be-welded area, and makes the stress distribution more uniform, greatly improves the strength and fatigue performance of the welded joint.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal and fiber reinforced plastic dissimilar material connection, and particularly relates to a high-quality lap welding method of dissimilar materials based on laser surface treatment. BACKGROUND

[0002] In order to pursue the vision of energy saving and emission reduction and environmental protection, in recent years, lightweight design is gradually considered in many fields such as automobiles, aerospace and medical devices. Lightweight metal materials (magnesium alloy, aluminum alloy, titanium alloy, etc.) have the characteristics of light weight, low density, high strength and strong weldability, and fiber (especially carbon fiber) reinforced composite materials have the characteristics of light weight, high specific strength, good corrosion resistance and excellent fatigue resistance, so they are widely used in the above fields.

[0003] Two materials each have their own advantages, and the use of both materials can not only meet the requirements of lightweight design, but also obtain high-quality structures by combining the excellent performance of the two materials. However, due to the huge differences in mechanical properties, physical properties and chemical properties, direct welding cannot be achieved, and the main problem is that the two materials cannot produce atomic or molecular bonding force, so it can only be achieved indirectly. One of the mainstream methods is to perform surface treatment on the material surface before welding to remove oil stains and impurities on the surface and provide new connection sites to achieve close contact between the two materials.

[0004] At present, the surface treatment methods that have been researched or applied to metal and fiber reinforced composite materials mainly include mechanical treatment (laser etching, sanding, shot blasting, etc.) and chemical treatment (chemical etching, anodizing, etc.), the former has the effect of increasing the connection area and forming a mechanical interlocking structure, and the latter can introduce new chemical bonds. However, chemical treatment will produce a large amount of wastewater, waste gas and waste, which not only pollutes the environment but also increases the cost. Most mechanical treatments will increase the loss of materials, and the dust and fine particles generated during the process will also pollute the environment, in addition, the noise problem caused by equipment vibration cannot be ignored. Compared with these methods, laser surface treatment technology has the advantages of environmental friendliness, low time cost, high dimensional accuracy and strong stability, and has been applied to etching different microstructures on the material surface to enhance the strength of the welded joint.

[0005] In the context of current technological development, patent CN113414496A proposes a method for enhancing the connection strength between composite materials and metals by ultrafast laser processing, aiming to significantly enhance the connection strength between fiber-reinforced composite materials and metals by removing the oxide film on the metal surface and precisely etching the microstructure. This method strengthens the mechanical anchoring effect of heterogeneous structural joints by expanding the actual contact area, thereby achieving a significant improvement in shear strength. However, although the introduction of microstructures effectively improves the connection performance, it is also accompanied by the problem of stress concentration, which to a certain extent limits the upper limit of strength improvement. Patent CN114571736A discloses a method for ultrasonically enhanced connection of metal / chopped carbon fiber composite materials. By electrolytic processing combined with silane coupling agent treatment, microstructures are constructed on the material surface and chemically active sites are introduced. Subsequently, ultrasonic welding technology is used to effectively promote the bonding between dissimilar materials. Although this method shows advantages in connection effect, its complex chemical treatment process reduces the overall production efficiency. Therefore, there is an urgent need to provide a high-quality lap welding method for metal and fiber-reinforced composite plates based on laser surface treatment. Summary of the Invention

[0006] Purpose of the Invention

[0007] In order to solve the current connection problem of metal and fiber-reinforced composite materials, the present invention provides a high-quality lap welding method for dissimilar materials based on laser surface treatment. The obtained microstructure is more compact in arrangement, which improves the utilization rate of the area to be welded and further increases the connection area between dissimilar materials. Secondly, the microstructure is more layered in space, which can effectively reduce the welding internal stress in the area to be welded and make the stress distribution more uniform, greatly improving the strength and fatigue performance of the welded joint.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] A high-quality lap welding method for dissimilar materials based on laser surface treatment comprises the following steps:

[0010] S1: Laser surface treatment of the metal sheet is performed to etch the target microstructure in the area to be welded and introduce a Schiff base polymer containing a Schiff base -RC=N- and a carbonyl group -C=O;

[0011] S2: Friction stir lap welding the treated metal sheet and the untreated fiber reinforced composite sheet.

[0012] As a further description of the above scheme, in step S2, the metal plate is made of magnesium alloy, aluminum alloy or titanium alloy; the fiber-reinforced composite plate is a carbon fiber reinforced thermoplastic resin plate; the thermoplastic resin can be PEEK, PA66 or PPS; the thickness of the metal plate and the fiber-reinforced composite plate are both 1.5-3 mm.

[0013] As a further description of the above scheme, in step S1, the central wavelength of the laser surface treatment of the metal plate is 1064nm; the pulse width of the laser surface treatment is 9-30ns; the laser frequency of the laser surface treatment is 450-600kHz; the laser power of the laser surface treatment is 15-25W; the scanning speed of the laser surface treatment is 10-30mm / s, and the number of scans is 3-5 times.

[0014] As a further description of the above scheme, in step S1, the metal sheet is laser surface treated twice. The first laser surface treatment is performed on the area to be welded to etch out the target microstructure, and then terephthalaldehyde C8H6O2 and aniline C6H5NH2 are introduced into the area to be welded; the second laser surface treatment is performed to heat the terephthalaldehyde C8H6O2 and aniline C6H5NH2 introduced into the area to be welded (3) to generate Schiff base polymers, which then react and bond with the metal ions of the metal sheet.

[0015] As a further description of the above scheme, the cross-section of the target microstructure etched from the metal plate is a triangle, the three sides of the triangle are provided with concave arcs, and the corners of the triangle adopt rounded transitions; a groove is formed between the etched target microstructure and the metal plate, the groove cross-section is an inverted trapezoid, the groove width is 200-400μm, the groove depth is 200-400μm, and the groove aspect ratio is 1-2.

[0016] As a further description of the above solution, in step S1, the width of the area to be welded is 10-12 mm.

[0017] As a further description of the above scheme, in step S2, the stirring head of the stir friction lap welding is perpendicular to the top of the area to be welded, and the metal plate is overlapped on the top and the fiber reinforced composite plate is overlapped on the bottom, with a lap width of 12-15 mm.

[0018] As a further description of the above scheme, in step S2, the stirring head rotation speed of the friction stir lap welding is 1000-1500 r / min, the welding speed of the friction stir lap welding is 150-300 mm / min, and the sinking depth of the stirring head of the friction stir lap welding is 0.2-0.4 mm.

[0019] As a further description of the above scheme, in step S2, the metal sheet after laser surface treatment is sealed and stored before welding, and the surface of the fiber reinforced composite sheet is cleaned with a detergent and a soft cloth before welding to remove oil, dust and impurities.

[0020] The beneficial effects of the present invention include the following:

[0021] 1. Compared with traditional microstructure morphologies (linear, lattice, grid, etc.), the microstructure of the present invention is more compact in arrangement, which improves the utilization rate of the area to be welded and further increases the connection area between dissimilar materials. Secondly, the microstructure is more spatially layered, which can effectively reduce the welding internal stress in the area to be welded and make the stress distribution more uniform, greatly improving the strength and fatigue performance of the welded joint.

[0022] 2. After using laser surface treatment technology to etch a microstructure on the surface of the metal plate, the process is directly used to introduce Schiff base polymer into the area to be welded. The spatial hierarchy of the microstructure makes the Schiff base polymer also have the characteristics of spatial distribution, providing a large number of reaction sites for metal and fiber-reinforced composites. While improving the mechanical properties of the joint, it also omits the tedious chemical treatment steps and improves processing efficiency.

[0023] 3. Compared with the use of adhesives, mechanical connections and other methods to connect metals and fiber-reinforced composites, welding processes can further reduce costs and do not need to consider issues such as adhesive aging and weight gain of mechanical fasteners. In addition, stir friction lap welding, as a solid-phase welding method, can effectively reduce the temperature of the connection area compared to the fusion welding method, and can control the plastic deformation and flow of fiber-reinforced composites.

[0024] 4. By synergistically controlling the laser surface treatment parameters and the friction stir lap welding parameters, and by finely adjusting key parameters such as laser power and scanning speed, as well as the friction stir lap welding head rotation speed and welding speed, the fiber-reinforced composite material can completely fill the grooves. This synergistic effect not only effectively reduces void defects in the joint but also significantly improves the overall load-bearing capacity and structural integrity of the joint.

[0025] 5. Since the process parameters of laser surface treatment and the geometric parameters of the microstructure (scanning spacing, geometric dimensions, etc.) can be flexibly adjusted, the present invention is not limited to the test materials and welding methods listed in the present invention and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the microstructure morphology of the laser surface treatment of the present invention;

[0027] Figure 2From left to right, Figure a is the first scanning path diagram, Figure b is the second scanning path diagram, and Figure c is a schematic diagram of the structure obtained by etching.

[0028] Metal sheet; 2-Laser beam; 3-Area to be welded; 4-Target microstructure. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. On the contrary, the present invention covers any substitutions, modifications, equivalent methods and solutions made on the spirit and scope of the present invention as defined by the claims. Furthermore, in order to enable the public to better understand the present invention, some specific details are described in detail in the detailed description of the present invention below, and those skilled in the art can fully understand the present invention without the description of these details.

[0030] In this embodiment, the laser surface treatment device used is a fiber nanosecond pulsed laser system (SP-050P-AEP-ZFY, SPI laser). The microstructure morphology can be precisely controlled by adjusting parameters such as pulse width, laser frequency, laser power, scanning speed, and number of scans. The welding device used is a friction stir lap welder (HT-JM16X8 / 1). Before welding, parameters such as the stirring head speed, stirring head travel speed, stirring head sinking depth, and stirring head dwell time can be set. The stirring head automatically completes the welding process according to a preset program on the moving mechanism.

[0031] A high-quality lap welding method for metal and fiber-reinforced composite plates based on laser surface treatment comprises the following steps:

[0032] S1: Laser surface treatment is performed on a metal sheet 1 using a laser beam 2 to etch a target microstructure 4 in the area to be welded 2 and introduce a Schiff base polymer containing a Schiff base (-RC=N-) and a carbonyl group (-C=O).

[0033] S2: Friction stir lap welding the treated metal sheet 1 to the untreated fiber-reinforced composite sheet. The advantage of this method is that the fiber-reinforced composite material undergoes plastic deformation during welding, reacting and bonding with new polar functional groups as it flows into the microstructure. After the joint cools, a stronger mechanical interlocking structure is formed. Furthermore, compared to traditional microstructure morphologies, this structure can further reduce the internal stress in the weld area and distribute it more evenly, effectively improving the strength and fatigue performance of the welded joint.

[0034] In step S2 of the present invention, the metal plate 1 is made of lightweight metal material, the metal plate 1 is made of magnesium alloy, aluminum alloy or titanium alloy, and the fiber-reinforced composite plate is a carbon fiber-reinforced thermoplastic resin plate. The thermoplastic resin can be selected from PEEK, PA66, PPS, etc., wherein the thickness of the metal plate 1 and the fiber-reinforced composite plate are both 1.5-3 mm.

[0035] In step S1 of the present invention, the metal plate 1 is subjected to laser surface treatment with a central wavelength of 1064 nm; a pulse width of 9-30 ns; a laser frequency of 450-600 kHz; a laser power of 15-25 W; and a scanning speed of 10-30 mm / s and 3-5 scanning times, in order to flexibly control the depth-to-width ratio of the target groove and ensure the stability of the etching effect.

[0036] This design uses a laser surface treatment process to etch a microstructure on the surface of the metal sheet, and then directly uses this process to introduce a Schiff base polymer into the area to be welded. The spatial hierarchy of the microstructure makes the Schiff base polymer also have the characteristics of spatial distribution, providing a large number of reaction sites for metal and fiber reinforced composites. While improving the mechanical properties of the joint, it also omits the tedious chemical treatment steps and improves processing efficiency. At the same time, compared with the use of adhesive bonding, mechanical connection and other methods to connect metal and fiber reinforced composites, the welding process can further reduce costs and does not need to consider problems such as adhesive aging and weight gain of mechanical fasteners. In addition, stir friction lap welding, as a solid-phase welding method, can effectively reduce the temperature of the connection area compared to the melting welding method, and can control the plastic deformation and flow of fiber reinforced composites.

[0037] In step S1 of the present invention, the metal plate 1 is subjected to laser surface treatment twice. The first laser surface treatment is performed on the area to be welded 3 to etch out the target microstructure 4, and then terephthalaldehyde C8H6O2 and aniline C6H5NH2 are introduced into the area to be welded (3). The second laser surface treatment heats the terephthalaldehyde C8H6O2 and aniline C6H5NH2 introduced into the area to be welded (3) to generate a Schiff base polymer, which then reacts and bonds with the metal ions of the metal plate 1.

[0038] The cross-section of the target microstructure 4 etched from the metal plate 1 of the present invention is a triangle, wherein the three sides of the triangle are provided with concave arcs, and the corners of the triangle adopt rounded transitions; a groove is formed between the etched target microstructure 4 and the metal plate 1, the groove cross-section is an inverted trapezoid, the groove width is 200-400μm, the groove depth is 200-400μm, and the groove aspect ratio is 1-2.

[0039] Compared with the traditional microstructure morphology (line, dot array, grid, etc.), the microstructure of the present design is more compact in arrangement, improves the utilization rate of the area of the to-be-welded region, further increases the connection area between the dissimilar materials, secondly, the microstructure has more levels in space, can effectively reduce the welding internal stress of the to-be-welded region, and makes the stress distribution more uniform, greatly improves the strength and fatigue performance of the welded joint; in addition, since the process parameters of laser surface treatment and the geometric parameters (scanning interval, geometric size, etc.) of the microstructure can be flexibly adjusted, therefore, it is not limited to the test materials and welding methods listed in the present application, and has broad application prospects.

[0040] In step S1 of the present application, the width of the to-be-welded region 3 is 10-12mm.

[0041] In step S2 of the present application, the stir welding head of the friction stir lap welding is vertically above the to-be-welded region 3, and the metal plate 1 is used in the upper lap mode and the fiber reinforced composite plate is used in the lower lap mode, and the lap width is 12-15mm.

[0042] In step S2 of the present application, the rotation speed of the stir welding head of the friction stir lap welding is 1000-1500 r / min, the welding speed of the friction stir lap welding is 150-300mm / min, and the sinking depth of the stir welding head of the friction stir lap welding is 0.2-0.4mm. Under the synergistic control of the laser surface treatment parameters and the welding parameters of the friction stir lap welding, by finely adjusting the key parameters such as the laser power and the scanning speed of the laser and the rotation speed and the welding speed of the stir welding head of the friction stir lap welding, the plastic deformation and flow of the fiber reinforced composite material can be realized, the groove can be completely filled after cooling, and good weld forming can be obtained. This synergistic effect not only effectively reduces the hole defects in the joint, but also significantly improves the overall carrying capacity and structural integrity of the joint.

[0043] In step S2 of the present application, the metal plate 1 after laser surface treatment is sealed and stored before welding, wherein the fiber reinforced composite plate 3 is cleaned with a cleaner and a soft cloth before welding to remove oil stains, dust and impurities.

[0044] As shown in Figure 1 The region of the metal plate welded with the fiber reinforced composite plate is defined as the to-be-welded region, and the region is sequentially subjected to twice laser surface treatment, and the first scanning path is as shown in Figure 2 The shadow area is the area not etched.

[0045] As shown in Figure 2As shown: Figure a is the first scanning path diagram, Figure b is the second scanning path diagram, and Figure c is a schematic diagram of the structure obtained by etching. The thin solid line in the figure is the laser scanning path before the array, and the direction indicated by the arrow on the solid line is the laser scanning direction. This is used as an array unit, and the first scanning and second scanning steps are performed in sequence in the array form to obtain the target microstructure 4 of the array. The number of thin solid lines contained in the array unit is only for reference and needs to be determined according to actual conditions.

[0046] Example 1

[0047] In this example, friction stir lap welding was used. The test materials used were a 75mm×50mm×2mm 6061 aluminum alloy sheet and a 65mm×50mm×2mm carbon fiber-reinforced PA66 sheet (with a carbon fiber content of 30%). Lap welding was performed with the aluminum alloy sheet on top and the fiber-reinforced composite sheet on the bottom. Prior to welding, laser surface treatment was used to create the target microstructure in the area to be welded on the surface of the aluminum alloy sheet.

[0048] Welding is carried out according to the following steps:

[0049] Step 1: Draw the laser scanning path. First, draw a closed line with the geometric parameters of an equilateral triangle with a side length of 520μm and a corner radius of 300μm. Then, based on this, process the inside and outside at an equal distance of 10μm to obtain the first scanning path.

[0050] Step 2: Copy and paste the first scan path, press Figure 2 As shown, redundant lines are removed to obtain the second scanning path.

[0051] Step 3: Set the laser processing parameters: central wavelength 1064nm; pulse width 9ns; laser frequency 600kHz; laser power 17.5W; scanning speed 25mm / s, scan number 3 times, use sandpaper to polish the area to be welded of the aluminum alloy plate to remove the surface oxide film, then start the laser and process the target microstructure 4 in the 10×60mm area to be welded on the surface of the aluminum alloy plate.

[0052] Step 4: Before welding, seal and store the laser-treated 6061 aluminum alloy sheet to avoid touching the surface treated area. Before welding, use a detergent and soft cloth to thoroughly clean the plastic surface of the carbon fiber reinforced PA66 sheet to remove oil, dust and other impurities, and then prepare for welding.

[0053] Step 5: Place the weldments in the fixture in sequence, with the 6061 aluminum alloy sheet on the upper layer and the carbon fiber reinforced PA66 sheet on the lower layer. The overlap width is 12 mm. After clamping, fix the fixture on the workbench of the friction stir lap welder to prevent the weldments from moving after welding.

[0054] Step 6: Adjust the positional relationship between the stirring head and the weldment, and set the welding parameters: stirring head speed 1200 r / min, welding speed 280mm / min, stirring head sinking depth 0.2mm. During the welding process, the welding parameters remain fixed. After welding is completed, remove the weldment.

[0055] The above description is merely an embodiment of the present application and does not constitute any form of limitation to the present application. Although the present application discloses the preferred embodiments as above, it is not intended to limit the present application. Any technical personnel familiar with the present profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A high-quality lap welding method for dissimilar materials based on laser surface treatment, characterized in that: The following steps are involved: S1: Laser surface treatment is performed on the metal sheet (1), a target microstructure (4) is etched in the area to be welded (3), and a Schiff base polymer containing a Schiff base -RC=N- and a carbonyl group -C=O is introduced; S2: Friction stir lap welding the treated metal sheet (1) and the untreated fiber reinforced composite sheet; In the step S1, the center wavelength of the laser surface treatment of the metal plate (1) is 1064 nm; the pulse width of the laser surface treatment is 9-30 ns; the laser frequency of the laser surface treatment is 450-600 kHz; the laser power of the laser surface treatment is 15-25 W; the scanning speed of the laser surface treatment is 10-30 mm / s, and the number of scanning times is 3-5 times; In step S1, the metal plate (1) is subjected to laser surface treatment twice. The first laser surface treatment is performed on the area to be welded (3) to etch out the target microstructure (4), and then terephthalaldehyde (C8H6O2) and aniline (C6H5NH2) are introduced into the area to be welded (3). The second laser surface treatment is performed to heat the terephthalaldehyde (C8H6O2) and aniline (C6H5NH2) introduced into the area to be welded (3) to generate a Schiff base polymer, which then reacts and bonds with the metal ions of the metal plate (1). The cross section of the target microstructure (4) etched from the metal plate (1) is triangular, the three sides of the triangle are provided with concave radians, and the corners of the triangle are rounded; a groove is formed between the etched target microstructure (4) and the metal plate (1), the groove cross section is an inverted trapezoid, the groove width is 200-400 μm, the groove depth is 200-400 μm, and the groove aspect ratio is 1-2.

2. The high-quality lap welding method for dissimilar materials based on laser surface treatment according to claim 1, characterized in that: In step S2, the metal plate (1) is made of a lightweight metal material, such as a magnesium alloy, an aluminum alloy or a titanium alloy; the fiber-reinforced composite plate is a carbon fiber-reinforced thermoplastic resin plate; the thermoplastic resin can be PEEK, PA66 or PPS; the thickness of the metal plate (1) and the fiber-reinforced composite plate are both 1.5-3 mm.

3. The high-quality lap welding method for dissimilar materials based on laser surface treatment according to claim 1, characterized in that: In step S1, the width of the area to be welded (3) is 10-12 mm.

4. The high-quality lap welding method for dissimilar materials based on laser surface treatment according to claim 1, characterized in that: In step S2, the stirring head of the friction stir lap welding is perpendicular to the top of the area to be welded (3), and a lap method is adopted in which the metal plate (1) is on top and the fiber reinforced composite plate is on the bottom, and the lap width is 12-15 mm.

5. The high-quality lap welding method for dissimilar materials based on laser surface treatment according to claim 4, characterized in that: In the step S2, the rotation speed of the stirring head of the friction stir lap welding is 1000-1500 r / min, the welding speed of the friction stir lap welding is 150-300 mm / min, and the sinking depth of the stirring head of the friction stir lap welding is 0.2-0.4 mm.

6. The high-quality lap welding method for dissimilar materials based on laser surface treatment according to claim 4, characterized in that: In the step S2, the metal plate (1) after the laser surface treatment is sealed and stored before welding, and the surface of the fiber reinforced composite plate is cleaned with a detergent and a soft cloth before welding to remove oil, dust and impurities.

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