Differential friction stir welding connection method based on metal polymer sandwich structure

Abstract

The invention discloses a differential friction stir welding connection method based on a metal polymer sandwich structure, which comprises the following steps: carrying out surface treatment on a metal plate to form a microstructure with nanoscale micropores, pits or grooves on the inner wall of the metal plate; the polymer plate is embedded in an inner cavity of the metal plate, and the upper-layer plate and the lower-layer plate of the metal plate and the polymer plate jointly form a sandwich structure; and friction stir welding is conducted on the obtained sandwich structure, and the metal / polymer plate composite component is obtained. According to the method, efficient, effective and lossless connection of the metal structure and the finished polymer plate is achieved, particularly, the effectiveness of the connection structure is guaranteed under the condition that the main body structure of the polymer plate is not damaged, the high efficiency of the connection mode is considered, and meanwhile the method has the advantage of being convenient to operate; and the connection strength, the stability and the anti-seismic property of the metal / FRP plate interface of the structure are enhanced.

Description

Technical Field

[0001] The invention relates to the technical field of heterogeneous sandwich composite structure connection, and in particular to a differential friction stir welding connection method based on a metal-polymer sandwich structure. Background Art

[0002] Metal / polymer (FRP) sandwich composite structures are mainly composed of alternating metal sheets and fiber-reinforced composite materials. They combine the advantages of metal materials and fiber-reinforced composite materials, can greatly improve the strength, fatigue resistance, impact toughness and other properties of a single material, enhance structural stability, and can greatly reduce the weight of structural parts, reduce energy consumption, and achieve the goal of energy conservation and emission reduction. They are important materials in the fields of aerospace and shipbuilding. However, due to the large differences in the physical and chemical properties of metal materials and FRP materials, it is difficult to achieve a stable and high-strength connection between the two.

[0003] At present, the commonly used methods for manufacturing metal / FRP sandwich composite structures mainly include gluing, mechanical connection and hot pressing. Among them, the gluing method often uses epoxy resin as an adhesive, but the long curing time of the adhesive layer leads to low production efficiency, and the adhesive layer is easily affected by the environment; mechanical connection (including riveting and bolting, etc.) requires prefabricated holes on the FRP plate, which is easy to destroy the fiber continuity of the FRP composite plate. At the same time, due to the need to add additional structural parts, it may cause the weight of the structure and stress concentration, affecting the service life of the composite plate. The hot pressing method mainly heats and presses both sides of the composite structure at the same time, so that the FRP matrix is ​​softened by heat and contacts with the metal plate. However, due to the great difference in the physical properties of the two materials, it is difficult to coordinate the formation under the action of the thermal and mechanical composite energy field, and it is easy to produce interface stratification and fracture.

[0004] In the prior art, document CN2007100289261 provides a metal-polyurethane-metal sandwich panel and a manufacturing method thereof, wherein the sandwich panel is obtained by casting and curing, but its essence is still a bonding method, and there are problems such as long curing time and the need to improve production efficiency; document CN111231375A discloses a hot forming and co-curing integrated forming method for CFRP / aluminum alloy composite structures, wherein the aluminum alloy is surface treated to make it rough, and prepreg is laid on the treated surface, and a CFRP / aluminum alloy composite structure is prepared through subsequent heating, heat preservation, aging, and air cooling steps. This method increases the interface microscopic interlocking structure and curing molding, but the required preparation time is also relatively long, and the production efficiency still needs to be improved.

[0005] In addition, since the mechanical properties of most finished polymer sheets are far superior to those of the aforementioned casting and curing molding and prepreg laying and curing molding, a relatively more ideal heterogeneous sandwich composite structure should utilize the effective connection between the finished polymer sheet and the metal structure, and the main structure of the polymer sheet should not be destroyed during the connection process (defined as lossless connection), while the only existing method that does not destroy the main structure of the polymer sheet during the connection process is bonding. Therefore, how to achieve efficient, effective, and lossless connection between metal structures and finished polymer sheets is a problem that needs to be further solved. More importantly, for a certain aircraft panel with a weight-reducing structure (a metal / polymer sandwich composite structure), its stability and seismic resistance during use need to be further improved, and a new connection technology needs to be developed to improve the connection stability and seismic resistance of such aircraft panels. Summary of the invention

[0006] At least in view of the problems mentioned in the background technology, the present invention aims to provide a differential friction stir welding connection method based on a metal-polymer sandwich structure.

[0007] The present invention adopts the following technical solution.

[0008] A differential friction stir welding connection method based on a metal-polymer sandwich structure, comprising the following steps: Step 1, performing surface treatment on the metal sheet so that a microstructure having nano-scale micropores, pits or grooves is formed on the inner wall of the metal sheet; Step 2, embedding the polymer sheet in the inner cavity of the metal sheet, and forming a sandwich structure with the upper and lower plates of the metal sheet and the polymer sheet; Step 3, performing friction stir welding on the obtained sandwich structure to obtain a metal / polymer plate composite component; Step 4: Cooling the obtained metal / polymer plate composite component to room temperature.

[0009] In the present invention, the metal plate comprises an upper plate, a lower plate and a connecting portion, and the longitudinal section of the metal plate is formed into a plurality of continuously arranged “I” shapes.

[0010] Furthermore, in step 2, the connection part is formed by connecting the boss arranged on the lower wall of the upper plate and the boss arranged on the upper wall of the lower plate, the two side walls of the polymer plate are against the side walls of the connection part, the top surface of the polymer plate is against the lower wall of the upper plate, and the bottom surface of the polymer plate is against the upper wall of the lower plate. Such a solution can greatly improve the connection efficiency of the metal-polymer sandwich structure while ensuring the overall strength of the metal plate, and is more convenient to operate.

[0011] Preferably, the width of the connecting portion is 2-5 mm larger than the diameter of the stirring needle of the friction stir welding equipment.

[0012] Preferably, in step 2, the polymer sheet and the metal sheet are fitted in an interference fit.

[0013] In order to better connect the metal-polymer sandwich structure efficiently, effectively and losslessly, and to be suitable for connecting the metal-polymer sandwich structure with upper and lower plates of different thicknesses, in step 3, the friction stir welding equipment used includes an upper shoulder, a lower shoulder and a stirring needle, the stirring needle penetrates the upper shoulder and is fixedly connected to the lower shoulder, the upper shoulder is connected to motor one, the lower shoulder is connected to motor two, the upper shoulder is used to cooperate with the top surface of the upper plate and stir friction welding at a speed of one, the lower shoulder is connected to motor two, the lower shoulder is used to cooperate with the bottom surface of the lower plate and stir friction welding at a speed of two; or; In step 3, the stir friction welding equipment used includes an upper shoulder, a lower shoulder and a stirring needle. The stirring needle is fixedly connected to the upper shoulder, and the upper shoulder is connected to motor one. Through holes are provided on the stirring needle and the upper shoulder. The connecting rod on the lower shoulder penetrates and fits in the through hole and is connected to motor two. The upper shoulder is used to cooperate with the top surface of the upper plate and perform stir friction welding at a speed of one. The lower shoulder is connected to motor two. The lower shoulder is used to cooperate with the bottom surface of the lower plate and perform stir friction welding at a speed of two.

[0014] Furthermore, the diameters of the upper shoulder and the lower shoulder are substantially equal to the inner width of the metal sheet; and the spacing between the upper shoulder and the lower shoulder is 0.5-3 mm smaller than the thickness of the metal sheet.

[0015] Preferably, in step 3, the rotation speed of the shoulder is 500rpm-3000rpm, and the welding speed is 500mm / min-3000mm / min.

[0016] In a preferred embodiment of the present invention, during the friction stir welding process, the connecting portion is completely reshaped, and the material of the connecting portion and the remelted material of the side wall of the polymer plate are interlocked with each other; the remelted material of the top wall of the polymer plate is embedded in the microstructure of the upper plate, and the remelted material of the bottom wall of the polymer plate is embedded in the microstructure of the lower plate.

[0017] Furthermore, the metal sheet is a panel of an aircraft.

[0018] Beneficial effects: The present invention realizes efficient, effective and lossless connection between the metal structure and the finished polymer plate, especially ensures the effectiveness of the connection structure without destroying the main structure of the polymer plate, takes into account the efficiency of the connection method, and has the advantage of convenient operation; the scheme of the present invention can be used for the preparation of metal / FRP sandwich composite plates with different materials and different thicknesses of upper and lower metal skins according to actual needs, and can flexibly realize indirect control of heat input of the metal / FRP interface with different materials and different metal skin thicknesses, thereby enhancing the connection strength, stability and seismic resistance of the metal / FRP plate interface of such structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a partial schematic diagram of the metal plate in Example 1; Figure 2 This is a lateral schematic diagram of the connection process of the metal-polymer sandwich structure in Example 1; Figure 3 This is a three-dimensional schematic diagram of the connection process of the metal-polymer sandwich structure in Example 1. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Example 1

[0021] A differential friction stir welding connection method based on a metal-polymer sandwich structure, comprising the following steps: Step 1, surface treatment of the metal sheet is performed to form a microstructure with nano-scale micropores, pits or grooves on the inner wall of the metal sheet; Figure 1 and Figure 3 As shown, the metal plate (a certain aircraft cover) includes an upper plate 3 with a thickness of 6 mm, a lower plate 4 with a thickness of 2 mm, and a connecting portion 7 with a width of 5 mm and a height of 3.5-4 mm, and the longitudinal section of the metal plate is formed into a plurality of continuously arranged "I" shapes, and the connecting portion 7 is formed by butting a boss arranged on the lower wall of the upper plate 3 with a boss arranged on the upper wall of the lower plate 4; First, prepare an aluminum alloy single-layer plate (i.e., an upper plate 3 and a lower plate 4 with a boss), and sandpaper polish and clean the aluminum alloy single-layer plate to remove scratches and oil stains on the surface, then perform surface pretreatment on the aluminum alloy single-layer plate, specifically, anodizing and silane coupling treatment methods can be used; connect the aluminum alloy single-layer plate to the positive electrode of the power supply, and immerse it in an anodizing electrolyte, the anodizing electrolyte uses a phosphoric acid electrolyte with a mass fraction of 10% (10g of phosphoric acid and 90g of water are configured to form a phosphoric acid electrolyte with a mass fraction of 10%), according to the width and length of the aluminum alloy single-layer plate, adjust the electrolysis voltage to 30V, the current to 15A, and the treatment time to 10min, so that a uniform micro-nano pore structure is formed on the surface of the aluminum alloy single-layer plate after anodizing treatment; the treated aluminum alloy single-layer plate is then immersed in a KH560 silane treatment agent (silane treatment agent ratio: 3g KH560, 45g ethanol, 2g deionized water, acetic acid to adjust the pH to 5-6, configuration: 3g KH560, 45g ethanol, 2g deionized water are fully mixed, and acetic acid is added dropwise at room temperature to adjust the solution pH to 5-6); after the surface of the aluminum alloy single-layer plate is covered with a uniform silane film, it is heated to 120°C in air with a humidity of 20%-30% for drying and curing for 40 minutes; in the present invention, the main function of the surface treatment is to form a micro-nano scale mechanical structure on the surface of the metal plate, and at the same time cover the chemical film layer, so that a microscopic mechanical interlocking structure and a chemical bond can be formed between the metal material and the FRP matrix material, such as a silane coupling agent can be used as an intermediate medium, and a C-…-Si-O-Al chemical bond can be formed with the FRP matrix at a certain temperature, so that the FRP matrix and the metal plate have a good bonding strength; Step 2, prepare a polymer sheet (i.e., FRP sheet) with a width of 10 mm and a thickness of 4 mm, embed the polymer sheet (FRP sheet) in the inner cavity 8 of the metal sheet (first lay the lower plate 4 flat, then put the FRP sheet on the top of the lower plate 4 and press it, then clamp the upper plate 3 on the lower plate 4 and the FRP sheet and press it; the width of the inner cavity 8 of the metal sheet is 9.5 mm), and the upper plate 3 and the lower plate 4 of the metal sheet and the polymer sheet 6 together form a sandwich structure; in this structure, the two side walls of the polymer sheet are against the side walls of the connecting part 7, the top surface of the polymer sheet is against the lower wall of the upper plate 3, and the bottom surface of the polymer sheet is against the upper wall of the lower plate 4, and the polymer sheet 6 and the metal sheet are matched in an interference fit manner (for example, when the height of the inner cavity 8 of the metal sheet is 3.5 mm, the thickness of the polymer sheet is 4 mm); Step 3, fixing the obtained sandwich structure with a fixture and then performing friction stir welding to obtain a metal / polymer plate composite component; Combination Figure 2 and Figure 3As shown, the friction stir welding equipment used includes an upper shoulder 1, a lower shoulder 2 and a stirring needle 5, the stirring needle 5 penetrates the upper shoulder 1 and is fixedly connected to the lower shoulder 2, the upper shoulder 1 is connected to motor 1, the lower shoulder 2 is connected to motor 2, the upper shoulder 1 is used to cooperate with the top surface of the upper plate 3 and stir friction welding at a speed of one, the lower shoulder 2 is connected to motor 2, and the lower shoulder 2 is used to cooperate with the bottom surface of the lower plate 4 and stir friction welding at a speed of two; Before welding, adjust the motor parameters, control the speed of the upper shoulder 1 to 800rpm, control the speed of the lower shoulder 2 and the stirring needle 5 to 500rpm, adjust the spacing between the upper and lower shoulders to 11~11.5mm (0.5-1mm lower than the total thickness of the grid plate) to ensure that the shoulder provides sufficient pressure on the metal / FRP interface during welding; adjust the welding speed to 600mm / min (the welding path is as follows Figure 3 As shown by the arrow in the middle, along the length direction of the connection part 7); then adjust the position of the welding tool to weld the assembled aluminum alloy / FRP plate. During the welding process, the aluminum alloy single-layer plate and the FRP plate are in contact with each other. Under the welding heat of the stir friction welding, the thermoplastic resin matrix of the FRP plate softens and fits tightly with the interface of the aluminum alloy single-layer plate to form a mechanical interlocking structure and chemical bonding to achieve a firm connection; through multiple welding (one welding for each connection part 7), the aluminum alloy single-layer plate and the FRP plate are tightly bonded at the interface to form an aluminum / FRP sandwich composite component; During the friction stir welding process, the connection part 7 is completely reshaped, and the material of the connection part 7 and the remelted material of the side wall of the polymer sheet (i.e., the surface material of the polymer sheet) are interlocked with each other; the remelted material of the top wall of the polymer sheet is embedded in the microstructure of the upper plate 3, and the remelted material of the bottom wall of the polymer sheet is embedded in the microstructure of the lower plate 4.

[0022] Step 4, placing the obtained aluminum / FRP sandwich composite component in air for cooling, controlling the humidity of the air to 20% to 30% to prevent part of the FRP matrix material from absorbing moisture at high temperature, and cooling to solidify the interface resin material.

[0023] Comparative Scheme 1: The metal plate (the cover of a certain aircraft) includes an upper plate 3 with a thickness of 6 mm, a lower plate 4 with a thickness of 2 mm and a connecting portion 7 with a width of 6 mm, and the longitudinal cross-section of the metal plate is a plurality of continuously arranged "I" shapes, and the upper plate 3, the lower plate 4 and the connecting portion 7 are integrally formed; a polymer plate (i.e., FRP plate) with a width of 10 mm and a thickness of 4 mm is prepared, and the polymer plate (FRP plate) is embedded in the inner cavity 8 of the metal plate (firstly an adhesive is coated on the polymer plate, and the inner cavity 8 of the metal plate is provided with a microstructure in the corresponding manner of Example 1, and then the polymer plate is inserted / stuck into the inner cavity 8 of the metal plate, and the width of the inner cavity 8 of the metal plate is 9.5 mm), and the upper plate 3 and the lower plate 4 of the metal plate and the polymer plate 6 together form a sandwich structure.

[0024] Comparative Scheme 2: The metal plate (the cover of a certain aircraft) includes an upper plate 3 with a thickness of 6 mm, a lower plate 4 with a thickness of 2 mm and a connecting portion 7 with a width of 6 mm, and the longitudinal cross-section of the metal plate is formed into a plurality of continuously arranged "I" shapes, the upper plate 3, the lower plate 4 and the connecting portion 7 are integrally formed, and the inner cavity 8 of the metal plate is provided with a microstructure in a corresponding manner with reference to Example 1, and the reaction material of the polymer plate is directly injected into the inner cavity 8 of the metal plate. After curing, the upper plate 3 and the lower plate 4 of the metal plate and the cured polymer together form a sandwich structure.

[0025] Comparative Scheme 3: Referring to Example 1, the difference between it and Example 1 is that the stirring needle is omitted, the welding path is along the length direction of the inner cavity 8 of the metal plate, the upper shoulder 1 is located directly above the inner cavity 8 of the metal plate, and the lower shoulder 2 is located directly below the inner cavity 8 of the metal plate.

[0026] The performance (connection strength and seismic performance) of the aluminum / FRP sandwich composite components prepared in Example 1 and the comparative scheme was tested. The connection strength refers to the bonding strength of the connection interface between the metal plate and the polymer plate (the sample was taken from the area where the inner cavity 8 of the metal plate was located during the test, and the metal plate and the polymer plate after the sample were pulled, excluding the influence of the connection part 5 on the test result). The vibration frequency of the seismic performance test was 50HZ and the vibration time was 500 hours. The results showed that the connection strength of the sample in Example 1 was 24.5MPa, the connection strength of the sample in Comparative Scheme 1 was 9.5MPa, the connection strength of the sample in Comparative Scheme 2 was 14MPa, and the connection strength of the sample in Comparative Scheme 3 was 11.2MPa; there was no peeling / separation at the connection interface of the sample in Example 1 after the vibration test; there were five peeling / separation areas at the connection interface after the vibration test of the sample in Comparative Scheme 1, one peeling / separation area at the connection interface after the vibration test of the sample in Comparative Scheme 2, and eleven peeling / separation areas at the connection interface after the vibration test of the sample in Comparative Scheme 3, and the metal plate was deformed inward.

[0027] In the present invention, one of the core technical points is that the stirring needle and shoulder of the aforementioned specific structure are used to stir friction weld the metal-polymer sandwich structure of the specific structure. During the welding process, the connection part is completely reshaped, and the material of the connection part and the remelted material of the polymer plate side wall (i.e., the surface material of the polymer plate) are interlocked with each other, which can not only avoid the occurrence of concave and convex deformation structures on the top and bottom surfaces of the metal plate (because the connection part is plasticized during the welding process, which can make the upper plate as a whole adaptively move downward and the lower plate as a whole adaptively move upward), but also ensure the strength of the metal plate itself and the connection strength between the metal plate and the polymer plate.

[0028] This embodiment realizes efficient, effective and lossless connection between the metal structure and the finished polymer sheet, especially ensures the effectiveness of the connection structure without destroying the main structure of the polymer sheet, takes into account the efficiency of the connection method, and has the advantage of convenient operation; adopting this scheme, it can be used for the preparation of metal / FRP sandwich composite sheets with different materials and different thicknesses of upper and lower metal skins according to actual needs, and can flexibly realize indirect control of heat input of metal / FRP interfaces with different materials and different metal skin thicknesses, thereby enhancing the connection strength, stability and seismic resistance of the metal / FRP sheet interface of such structures. Example 2

[0029] A differential friction stir welding connection method based on a metal-polymer sandwich structure, referring to Example 1, the main difference between it and Example 1 is that the friction stir welding equipment used includes an upper shoulder 1, a lower shoulder 2 and a stirring needle 5, the stirring needle 5 is fixedly connected to the upper shoulder 1, the upper shoulder 1 is connected to motor one, through holes are provided on the stirring needle 5 and the upper shoulder 1, the connecting rod on the lower shoulder 2 is penetrated and fitted in the through hole and connected to motor two, the upper shoulder 1 is used to cooperate with the top surface of the upper plate 3 and stir friction welding at a speed of one, the lower shoulder 2 is connected to motor two, and the lower shoulder 2 is used to cooperate with the bottom surface of the lower plate 4 and stir friction welding at a speed of two.

Claims

1. A differential friction stir welding connection method based on a metal-polymer sandwich structure, characterized in that the steps include: Step 1, performing surface treatment on the metal sheet so that a microstructure having nano-scale micropores, pits or grooves is formed on the inner wall of the metal sheet; Step 2, embedding the polymer sheet in the inner cavity (8) of the metal sheet, and forming a sandwich structure with the upper plate (3) and the lower plate (4) of the metal sheet and the polymer sheet (6); Step 3, performing friction stir welding on the obtained sandwich structure to obtain a metal / polymer plate composite component; Step 4: Cooling the obtained metal / polymer plate composite component to room temperature.

2. The differential friction stir welding connection method according to claim 1, characterized in that: The metal plate comprises an upper plate (3), a lower plate (4) and a connecting portion (7), and a longitudinal cross section of the metal plate is in the form of a plurality of continuously arranged "I" shapes.

3. The differential friction stir welding connection method according to claim 2, characterized in that: In step 2, the connecting portion (7) is formed by connecting a boss provided on the lower wall of the upper plate (3) and a boss provided on the upper wall of the lower plate (4), the two side walls of the polymer sheet are abutted against the side walls of the connecting portion (7), the top surface of the polymer sheet is abutted against the lower wall of the upper plate (3), and the bottom surface of the polymer sheet is abutted against the upper wall of the lower plate (4).

4. The differential friction stir welding connection method according to claim 3, characterized in that: The width of the connecting portion (7) is 2 to 5 mm greater than the diameter of the stirring needle (5) of the friction stir welding device.

5. The differential friction stir welding connection method according to claim 3, characterized in that: In step 2, the polymer sheet (6) and the metal sheet are fitted in an interference fit.

6. The differential friction stir welding connection method according to any one of claims 1 to 5, characterized in that: In step 3, the friction stir welding equipment used comprises an upper shoulder (1), a lower shoulder (2) and a stirring needle (5), the stirring needle (5) penetrates the upper shoulder (1) and is fixedly connected to the lower shoulder (2), the upper shoulder (1) is connected to motor one, the lower shoulder (2) is connected to motor two, the upper shoulder (1) is used to cooperate with the top surface of the upper plate (3) and stir friction welding at a speed of one, the lower shoulder (2) is connected to motor two, and the lower shoulder (2) is used to cooperate with the bottom surface of the lower plate (4) and stir friction welding at a speed of two; or; In step 3, the friction stir welding equipment used includes an upper shoulder (1), a lower shoulder (2) and a stirring needle (5), the stirring needle (5) is fixedly connected to the upper shoulder (1), the upper shoulder (1) is connected to motor one, through holes are provided on the stirring needle (5) and the upper shoulder (1), a connecting rod on the lower shoulder (2) is inserted into the through hole and connected to motor two, the upper shoulder (1) is used to cooperate with the top surface of the upper plate (3) and stir friction welding at a speed of one, the lower shoulder (2) is connected to motor two, and the lower shoulder (2) is used to cooperate with the bottom surface of the lower plate (4) and stir friction welding at a speed of two.

7. The differential friction stir welding connection method according to claim 6, characterized in that: The diameters of the upper shoulder (1) and the lower shoulder (2) are substantially equal to the width of the inner cavity (8) of the metal plate; and the distance between the upper shoulder (1) and the lower shoulder (2) is 2-3 mm smaller than the thickness of the metal plate.

8. The differential friction stir welding connection method according to claim 7, characterized in that: In step 3, the rotation speed of the shoulder is 500rpm-3000rpm, and the welding speed is 500mm / min-3000mm / min.

9. The differential friction stir welding connection method according to claim 6, characterized in that: During the friction stir welding process, the connection portion (7) is completely reshaped, and the material of the connection portion (7) and the remelted material of the side wall of the polymer plate are interlocked with each other; the remelted material of the top wall of the polymer plate is embedded in the microstructure of the upper plate (3), and the remelted material of the bottom wall of the polymer plate is embedded in the microstructure of the lower plate (4).

10. The differential friction stir welding connection method according to claim 9, characterized in that: The metal sheet is a cover plate of an aircraft.

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