Welding method and joint capable of eliminating bubble defects in dissimilar material joint

Abstract

The application provides a welding method and joint capable of eliminating bubble defects in a dissimilar material joint. The welding method comprises the following steps: a through hole processing step, in which a through hole is processed on a metal plate, the through hole being located in a welding overlap area of the metal plate and a resin-based composite material plate and outside a tool shoulder influence area of a welding tool; a cleaning and drying step, in which the metal plate, the resin-based composite material plate and a thermoplastic resin interlayer are cleaned and dried; a clamping and positioning step, in which the resin-based composite material plate, the thermoplastic resin interlayer and the metal plate are stacked from bottom to top and positioned on a workbench, wherein the thermoplastic resin interlayer is located in the welding overlap area of the resin-based composite material plate and the metal plate; and a friction stir welding step, in which the metal plate is subjected to friction stir welding from one side of the metal plate by using the welding tool. The application can transfer the bubble defects easily existing in the interface of the dissimilar material joint to the through hole, increase the close combination of the interface, and improve the tensile strength of the dissimilar joint through the mechanical interlocking formed in the through hole.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of material welding and processing, and particularly relates to a welding method capable of eliminating bubble defects in a dissimilar material joint and the joint. BACKGROUND

[0002] As an important part of sustainable development strategy, innovative lightweight design is not only an important measure to achieve energy saving and emission reduction, but also has important significance for improving the performance of structural parts. The main strategies of lightweight design are material replacement, structure optimization and process innovation. Resin and its composite materials have been gradually paid more and more attention due to their excellent properties such as light weight, high specific strength, corrosion resistance, wear resistance and fatigue resistance.

[0003] In engineering applications, structural parts often need to have excellent properties of both resin and its composite materials and metals. Therefore, following the concept of lightweight design, combining the excellent properties of dissimilar materials, expanding the application range of composite structural materials, and obtaining composite structures between various lightweight materials through welding method are of great significance to the development of aerospace and automotive fields.

[0004] Friction stir welding is a solid-phase joining technology, which can provide heat and force simultaneously during welding. Various welding tools can be used to connect most dissimilar materials, and long-distance and large-area welding of the welded materials can also be achieved. Friction stir welding has the characteristics of low welding temperature, severe plastic deformation, and axial downward pressure during simultaneous welding, which is beneficial to the discharge of bubbles in resin materials, so that high-quality dissimilar joints can be obtained. The aforementioned bubbles are produced by the decomposition of resin and other substrates during heating and melting, and by the expansion of air in the gap between the overlapped dissimilar materials or the vaporization of residual water in the resin. However, there are still bubbles in the dissimilar material joints formed by friction stir welding that are difficult to discharge. The existence of bubbles can easily cause a large stress concentration at the bubble during deformation, which becomes the preferred location for crack initiation and propagation, thereby greatly reducing the performance of the joint, especially the fatigue performance, and thus reducing the service performance of the dissimilar joint, greatly limiting the engineering application of metal / resin-based composite material joints. SUMMARY

[0005] Therefore, the present application provides a welding method capable of eliminating bubble defects in a dissimilar material joint and the joint to solve the problem of insufficient joint performance caused by incomplete bubble discharge in the dissimilar material joint formed by friction stir welding in the related art, and the low quality and service performance of the dissimilar joint.

[0006] In order to solve the above problems, the present application provides a welding method capable of eliminating bubble defects in a dissimilar material joint, comprising the following steps:

[0007] A through hole processing step, processing a through hole on the metal plate, the through hole being in a welding overlap area of the metal plate and the resin matrix composite plate, when a friction stir welding tool is used to weld the welding overlap area, a track area formed by a shaft shoulder of the friction stir welding tool in the welding overlap area is a shaft shoulder influence area, the through hole is also outside the shaft shoulder influence area;

[0008] A cleaning and drying step, cleaning and drying the metal plate, the resin matrix composite plate and the thermoplastic resin interlayer;

[0009] A clamping and positioning step, stacking and positioning the resin matrix composite plate, the thermoplastic resin interlayer and the metal plate from bottom to top on a workbench, wherein the thermoplastic resin interlayer corresponds to the welding overlap area of the resin matrix composite plate and the metal plate;

[0010] A friction stir welding step, using the friction stir welding tool to friction stir weld the metal plate from one side of the metal plate.

[0011] In some embodiments, in the friction stir welding step,

[0012] The metal plate is friction stir welded by spot welding.

[0013] In some embodiments,

[0014] The through hole is in a spot welding overlap area, preferably, the through hole is symmetrically distributed along the shaft shoulder hole. Symmetrically distributed through holes facilitate the flow of bubbles from the through holes on both sides.

[0015] In some embodiments,

[0016] The shaft shoulder diameter of the friction stir welding tool is 6-20 mm, the through hole can be a square hole, a round hole and a special-shaped hole, but preferably a round hole, and the diameter of the round hole is 1-10 mm. The shaft shoulder diameter directly determines the heat production during welding. If the shaft shoulder is too small, the heat production is insufficient to melt the resin, and effective connection cannot be achieved. If the shaft shoulder is too large, the heat production is too high, which will cause a large amount of resin to decompose, resulting in poor joint connection quality. When the exhaust hole is of different shapes, the material can be discharged from the through hole of the metal plate, but the square hole and the special-shaped hole are more difficult to make the material flow freely compared with the round hole without edges and with the same radius at each position. Therefore, in order to improve the effect of bubble discharge, a round through hole is preferred, and the diameter of the round through hole is 1-10 mm. If it is too small, the effect of bubble discharge cannot be achieved, and if it is too large, the discharged material cannot fill the metal through hole, resulting in a decrease in joint stiffness and other properties. In addition, in order to reduce the weight, the overlap area of the material should not be too large, so the size of the through hole is limited.

[0017] In some embodiments,

[0018] The shoulder diameter of the friction stir welding tool is D, the through hole is a circular hole with a diameter of D0, the hole corresponding to the shoulder diameter formed by spot welding is a shoulder hole, the center distance between the shoulder hole and the through hole is d, (D+D0) / 2+0.5mm≤d≤D+D0 / 2. The through hole should not be too close to the shoulder boundary, otherwise the surrounding material will soften during the tool friction stir welding process, the hole will collapse, and the bubble removal effect will be poor. The distance between the through hole and the shoulder should also not be too far from the shoulder, otherwise the material cannot be discharged from the too far through hole, the air hole still remains in the joint, and cannot play the role of guiding bubble removal. In some embodiments,

[0019] The friction stir welding tool adopts the following process parameters when spot welding:

[0020] The rotation speed of the welding tool is 600-2000 revolutions per minute, the pressing amount is 0.3-2.0 millimeters, the holding time is 3-15 seconds, and the tool inclination angle is 0°-5°.

[0021] The rotation speed in this range mainly considers to ensure that the upper metal plate can have enough heat to flow and enough heat to conduct to the lower resin-based material, thereby achieving good connection. Too low or too high rotation speed or due to too low heat input cannot achieve good connection or too high heat input causes excessive decomposition of resin and leads to too low joint performance. The pressing amount must be within a certain range, too large pressing amount leads to heat accumulation of the metal plate and causes bubbles to accumulate too early, and too small pressing amount leads to insufficient heat of the metal plate and makes the joint interface unable to effectively combine. The holding time within a certain range can ensure that the tool generates enough heat to make the dissimilar interfaces have enough contact and connection time, and can discharge bubbles within a certain holding time, but too low holding time will lead to insufficient connection time and poor connection effect, and too high holding time will produce new thermal decomposition and cause bubbles in the joint. The tool inclination angle needs to be kept within this range to ensure that the bubbles flow out smoothly with the outflow of the melted resin.

[0022] In some embodiments,

[0023] The thermoplastic resin interlayer has a thickness of 0.1-0.4 mm. The thermoplastic resin interlayer has the same base material as the resin-based composite plate, and can effectively supplement the same base material in the resin-based composite plate, thereby avoiding the defects of holes caused by the loss of the ductile resin base and the ineffective bonding of the fibers. The thickness of the thermoplastic resin interlayer must be within a certain range. If the thickness is too small, it cannot effectively supplement the resin matrix in the resin-based composite plate. If the thickness is too large, the resin interlayer cannot be completely melted and cannot be effectively connected with the lower resin-based composite.

[0024] In some embodiments,

[0025] The thermoplastic resin interlayer is made of a thermoplastic polar resin. The advantage of using a thermoplastic polar resin is that the material has good thermoforming properties. During the welding thermoforming process, the material can flow well, so that during the welding process, the material can be well filled between the metal and the resin-based composite plate under the action of tool pressure, thus serving as an intermediate layer to well lubricate and connect the two. Further, the material contains polar functional groups, which can easily form hydrogen bonds or chemical bonds with metals, thereby increasing the close combination of dissimilar materials and improving the performance of the joint.

[0026] In some embodiments,

[0027] The resin-based composite material is a continuous fiber reinforced resin-based composite material. When the resin-based composite material is a continuous fiber reinforced resin-based composite material, the continuous fibers have poor flowability and high fiber content. When directly connected with the metal, the base material melts and flows out during the welding process, resulting in insufficient base material and direct exposure of the fibers, thus poor direct connection. The use of thermoplastic polar resin can supplement the lost resin material and connect with the metal, so this measure is especially suitable for improving the welding quality of metal and continuous fiber reinforced resin-based composite material.

[0028] In some embodiments, the cleaning and drying step specifically includes:

[0029] The metal plate, the resin-based composite material plate and the thermoplastic resin interlayer are cleaned by using dustproof cloth and alcohol, and then dried by blowing with a hair dryer. If there are oil stains or other dirt in the metal plate, the resin-based composite material plate and the thermoplastic resin interlayer to be welded, the dirt is easy to form holes and other defects due to heating and volatilization during welding, which reduces the joint connection quality. In addition, after cleaning, drying is performed, and residual moisture is easy to vaporize and form bubbles during welding, thereby reducing the joint connection quality and performance. Therefore, this step is mainly to remove oil stains and other dirt, and dry, thereby improving the joint connection quality and performance.

[0030] The application also provides a dissimilar material joint, wherein the bubble volume fraction of the dissimilar joint is 0-5%, and the joint is prepared by using the welding method for eliminating bubble defects in a dissimilar material joint.

[0031] Compared with the prior art, in the welding method for eliminating bubble defects in a dissimilar material joint, the welding tool applies pressure to the metal plate and is heated due to friction, and then the part of the matrix of the thermoplastic resin interlayer and the resin-based composite material plate is melted and flows. Under the action of stirring and pressure of the welding tool, the bubbles generated in the shoulder influence area are transferred to the through hole along the fluid of the melted flow without accumulating in the welding joint, so that the design purpose of eliminating the bubble defects in the dissimilar material joint is achieved, and mechanical interlocking between the dissimilar materials can be formed after solidification in the through hole, thereby improving the tensile strength of the joint. In addition, the weight of the metal plate is reduced due to the pre-prepared through hole in the metal plate, which further plays a lightweight purpose. In addition, it should be particularly emphasized that the thermoplastic resin interlayer is pre-placed between the metal plate and the resin-based composite material plate in the application, which can be heated and melted to form a fluid, thereby facilitating the elimination of the aforementioned bubbles in the application, and can also form an effective supplement to the matrix content in the resin-based composite material plate, thereby reducing the connection difficulty between the dissimilar materials.

[0032] The stirring friction welding tool in the application directly acts on the metal plate, and can quickly transfer the heat generated by friction between the welding tool and the metal to the connection interface between the dissimilar materials by utilizing the excellent heat conduction performance of the metal plate, thereby improving the welding efficiency and welding effect. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 A step schematic diagram of a welding method for eliminating bubble defects in a dissimilar material joint according to an embodiment of the application;

[0034] Figure 2Figure 1 is a schematic diagram of the state of the metal plate, resin matrix composite plate and thermoplastic resin interlayer before welding in Examples 1-4, in which the metal plate is at the top layer, the thermoplastic resin interlayer is in the middle, and the resin matrix composite plate is at the bottom layer, and the friction stir welding tool is at the top region of the metal plate;

[0035] Figure 3 Figure 2 is a macroscopic morphology of the interface of a 5052 aluminum alloy and a carbon fiber reinforced polyether ether ketone (CF-PEEK) joint prepared by the welding method of the present application (Example 1), from which it can be seen that bubbles accumulate in the through hole, no bubbles are found at the connection interface, and the thermoplastic resin interlayer and the matrix (i.e., PEEK) in the CF-PEEK melt and solidify in the through hole, forming macroscopic mechanical interlocking;

[0036] Figure 4 Figure 3 is a cross-sectional morphology of the main connection region interface of a 5052 aluminum alloy and a carbon fiber reinforced polyether ether ketone (CF-PEEK) after direct friction stir welding (Comparative Example 1), from which it can be seen that when the dissimilar materials are directly welded, there are large pores at the interface of the connection region-shoulder affected zone, and the connection effect is relatively poor.

[0037] Figure 5 Figure 4 is an SEM morphology of the main connection region interface of a 5052 aluminum alloy and a carbon fiber reinforced polyether ether ketone (CF-PEEK) joint prepared by the welding method of the present application (Example 1), from which it can be seen that there are no bubbles at the main connection region interface of the present application, and the intermediate resin layer connects the metal and the resin matrix composite material well.

[0038] Figure 6 Figure 5 is an SEM morphology of the main connection region interface of a 5052 aluminum alloy and a carbon fiber reinforced polyether ether ketone (CF-PEEK) joint prepared by the welding method of the present application (a, Example 1) and direct connection (b, without using the welding method of the present application, Comparative Example 1), from which it can be seen that the present application eliminates the bubbles at the interface of the main connection region-shoulder affected zone in direct connection.

[0039] Figure 7 Figure 6 is a comparison of the tensile shear force of a 5052 aluminum alloy and a carbon fiber reinforced polyether ether ketone joint prepared by the method of the present application (Example 1) and direct connection (Comparative Example 1) and pre-thermoplastic resin interlayer treatment (Comparative Example 2), from which it can be seen that the present application improves the strength of the joint. DETAILED DESCRIPTION

[0040] For a better understanding of the present application, reference will be made to Figures 1 to 7 According to the embodiments of the present application, a welding method capable of eliminating bubble defects in dissimilar material joints is provided, which comprises the following steps:

[0041] The through hole processing step is to process a through hole on the metal plate, the through hole being in the welding overlap area of the metal plate and the resin matrix composite plate, when a friction stir welding tool (referred to as a tool) is used to weld the welding overlap area, a track area formed by a shaft shoulder of the friction stir welding tool in the welding overlap area is a shaft shoulder affected area, and the through hole is also outside the shaft shoulder affected area;

[0042] The cleaning and drying step is to clean and dry the metal plate, the resin matrix composite plate, and the thermoplastic resin interlayer.

[0043] The clamping and positioning step is to stack and position the resin matrix composite plate, the thermoplastic resin interlayer, and the metal plate from bottom to top on a workbench, wherein the thermoplastic resin interlayer corresponds to the welding overlap area of the resin matrix composite plate and the metal plate.

[0044] The friction stir welding step is to use a friction stir welding tool to friction stir weld the metal plate from one side of the metal plate, in the process of the friction stir welding, the welding tool applies pressure to the metal plate and is heated due to friction, thereby causing the thermoplastic resin interlayer and part of the matrix of the resin matrix composite plate to melt and flow, under the action of the welding tool stirring and applying pressure, the bubbles generated in the shaft shoulder affected area are transferred to the through hole without accumulating in the welded joint, thereby achieving the design purpose of eliminating the bubble defects in the joint of dissimilar materials, and after solidification in the through hole, mechanical interlocking between dissimilar materials is formed, which improves the tensile strength of the joint. In addition, it should be particularly emphasized that the thermoplastic resin interlayer is pre-placed between the metal plate and the resin matrix composite plate in the present application, which can be heated and melted to form a fluid, thereby facilitating the elimination of the aforementioned bubbles in the present application, and it can also form an effective supplement to the matrix content in the resin matrix composite plate, thereby reducing the connection difficulty between dissimilar materials.

[0045] It can be clearly seen that the friction stir welding tool in the present application directly acts on the metal plate, which can utilize the excellent heat conduction performance of the metal plate to quickly transfer the heat generated by the friction between the welding tool and the metal to the connection interface between dissimilar materials, thereby improving the welding efficiency and welding effect.

[0046] In some embodiments, in the friction stir welding step,

[0047] The metal plate can be welded by using a friction stir welding method such as line welding or spot welding. In a preferred embodiment, the metal plate is welded by using the spot welding method. The reason for using the spot welding method is that the tool pressing amount and the holding time can be accurately controlled, so that the pressure can be accurately controlled, thereby accurately controlling the effective discharge of the bubbles, and even no bubbles can exist in the final joint. In the line welding process, the tool pressing amount and the holding time cannot be accurately controlled, and the discharge of the bubbles cannot be accurately controlled, resulting in a poor bubble discharge effect than that of the spot welding.

[0048] In some embodiments,

[0049] The through hole is in the spot welding lap area and is symmetrically distributed outside the shoulder influence area with respect to the shoulder hole. The symmetric distribution is more conducive to the effective discharge of the bubbles.

[0050] In a preferred embodiment,

[0051] The shoulder diameter of the friction stir welding tool is D, D is 6-20 mm, and the through hole is a circular hole with a diameter of D0, D0 is 1-10 mm. The shoulder diameter directly determines the heat generation during welding. If the shoulder is too small, the heat generation is insufficient to melt the resin, and effective connection cannot be achieved. If the shoulder is too large, the heat generation is too high, which will cause a large amount of resin to decompose, resulting in poor joint connection quality. When the exhaust hole has different shapes, the material can be discharged from the through hole of the metal plate. However, compared with the circular hole without edges and with the same radius at each position, the square hole and the special-shaped hole are more difficult to make the material flow freely. Therefore, in order to improve the bubble discharge effect, a circular through hole is preferred, and the diameter of the circular through hole is 1-10 mm. If the diameter is too small, the bubble discharge effect cannot be achieved, and if the diameter is too large, the discharged material cannot fill the metal through hole, resulting in a decrease in the joint stiffness and other properties. In addition, in order to reduce the weight, the lap area of the material should not be too large, so the size of the through hole is limited.

[0052] The hole corresponding to the shoulder diameter formed by spot welding is the shoulder hole, and the center distance between the through hole and the shoulder hole is d, (D+D0) / 2+0.5mm≤d≤D+D0 / 2. The through hole should not be too close to the shoulder boundary. If it is too close, the surrounding material will soften during the tool friction stir welding process, and the hole will collapse, resulting in poor bubble discharge effect. The distance between the through hole and the shoulder should not be too far from the shoulder. If it is too far, the material cannot be discharged from the through hole that is too far away, and the air hole still exists in the joint, which cannot play a role in guiding the bubble discharge.

[0053] In some embodiments,

[0054] The friction stir welding tool uses the following process parameters when spot welding:

[0055] The tool rotation speed is 600-2000 rpm, the pressing amount is 0.3-2.0 mm, the holding time is 3-15 seconds, and the tool inclination angle is 0-5°.

[0056] The rotation speed in the range mainly considers that sufficient heat can ensure that the upper metal plate can have sufficient heat to flow and sufficient heat can be conducted to the lower resin-based material, thereby achieving good connection. Too low or too high rotation speed cannot achieve good connection due to too low heat input or too high heat input leading to excessive decomposition of the resin and too low joint performance. The pressing rate and the pressing amount must be within a certain range. Too high pressing amount leads to heat accumulation of the metal plate and causes bubbles to accumulate too early, while too low pressing amount leads to insufficient heat of the metal plate and makes the joint interface unable to effectively combine. The holding time within a certain range can ensure that the tool generates sufficient heat to make the dissimilar interfaces have sufficient contact and connection time, and can discharge bubbles within a certain holding time, but too low holding time will lead to insufficient connection time and poor connection effect, and too high holding time will produce new thermal decomposition and cause bubbles in the joint. The tool inclination angle needs to be kept within the range to ensure that the bubbles flow out smoothly with the melted resin.

[0057] In some embodiments,

[0058] The base material of the thermoplastic resin interlayer is consistent with the base material of the resin-based composite plate, and the thickness of the thermoplastic resin interlayer is 0.1-0.4 mm. For example, when the resin-based composite plate is a carbon fiber reinforced polyether ether ketone (CF-PEEK), the base material of the thermoplastic resin interlayer is also polyether ether ketone (PEEK), and the best thermoplastic resin interlayer is a polyether ether ketone interlayer, and the thickness of the resin interlayer is controlled to be 0.1-0.4 mm. In this way, the content of the same base material in the resin-based composite plate can be effectively supplemented, thereby reducing the connection difficulty between dissimilar materials.

[0059] In some embodiments,

[0060] The material of the thermoplastic resin interlayer is a thermoplastic polar resin. The advantage of using a thermoplastic polar resin is that the material has good thermal forming performance. In the thermal forming process of welding, the material can flow well, so that in the welding process, the material can be well filled between the metal and the resin-based composite plate under the action of tool pressure after melting, thereby achieving good lubrication and connection as an intermediate layer. Further, the material contains polar functional groups, which can easily form hydrogen bonds or chemical bonds with metals, thereby increasing the close combination of dissimilar materials and improving the performance of the joint.

[0061] In some embodiments,

[0062] The resin-based composite material is a continuous fiber reinforced resin-based composite material. When the resin-based composite material is a continuous fiber reinforced resin-based composite material, due to poor flowability of the continuous fibers and high fiber content, direct connection with the metal is poor because the matrix material is insufficient due to melting and flowing out during the welding process of the matrix material, and the fibers are directly exposed. The use of a thermoplastic polar resin can supplement the lost resin material and connect with the metal, so this measure is particularly suitable for improving the welding quality of the metal and the continuous fiber reinforced resin-based composite material.

[0063] In some embodiments, the cleaning and drying steps specifically include:

[0064] After cleaning the metal plate, the resin-based composite material plate, and the thermoplastic resin interlayer, drying is performed to achieve the cleaning and drying level of the materials of the plates before welding. Specifically, a duster and alcohol are used to clean the metal plate, the resin-based composite material plate, and the thermoplastic resin interlayer, and a hair dryer is used to dry them. Finally, the materials of the plates dried by the hair dryer are preferably placed in a vacuum drying box to maintain their dry state, and are taken out for welding processing. It should be noted that the resin-based composite material and the thermoplastic resin interlayer in the present application contain hydrophilic groups, and the water absorbed therein will evaporate and vaporize during friction stir welding to form bubbles. The use of the aforementioned means can effectively reduce the water content in the material, and further reduce the amount of bubbles in the welded joint.

[0065] According to the embodiments of the present application, a dissimilar material joint is also provided, which is prepared by using the above-mentioned welding method capable of eliminating bubble defects in the dissimilar material joint.

[0066] The aforementioned welding method capable of eliminating bubble defects in the dissimilar material joint of the present application is described below in combination with examples and comparative examples.

[0067] Example 1:

[0068] A 2 mm thick 5052 aluminum alloy plate and a 2.5 mm thick carbon fiber reinforced polyether ether ketone (CF-PEEK, carbon content: 50%-55%, i.e., one of the aforementioned resin-based composite material plates, and the same below) are used. Before welding, two through holes with a diameter of 2.5 mm are pre-placed in the lap area outside the welding area of the 5052 aluminum alloy; the distance between the center of the through hole and the center of the shoulder hole (welding center) is 8.0 mm; during assembly, a 0.2 mm thick polyether ether ketone interlayer (i.e., one of the aforementioned thermoplastic resin interlayers, and the same below) is pre-placed in the dissimilar materials; the dissimilar materials are connected by using friction stir spot welding, as shown in Figure 2The thread-shaped welding tool (i.e., the friction stir welding tool as mentioned above, hereinafter the same) with a shoulder diameter of 12 mm, a pin tip diameter of 4.1 mm, a pin root diameter of 4.8 mm, and a pin length of 0.93 mm made of H13 steel was selected to connect the 5052 aluminum alloy and the CF-PEEK. In order to meet the lightweight design requirements and reduce the overlap area as much as possible, the overlap width of the 5052 aluminum alloy and the CF-PEEK was 20 mm. The rotation speed was 1400 rpm, the pressing amount was 1.6 mm, the dwell time was 8 s, and the tool tilt angle was 0 degrees. The macroscopic morphology of the joint interface after welding is shown in Figure 3 As shown, the bubbles accumulated in the through hole, and the molten interlayer and the polyether ether ketone matrix in the carbon fiber reinforced composite material accumulated in the through hole and solidified to form macroscopic mechanical interlocking. The SEM morphology of the joint pin affected area and the shoulder affected area interface is shown in Figure 5 and Figure 6 As shown in (a), no bubble defects were found in the main joint area-shoulder affected area of the joint, and the tensile shear force of the joint was Figure 7 As shown, the maximum was 2.92 kN.

[0069] Comparative Example 1:

[0070] The 5052 aluminum alloy plate with a thickness of 2 mm and the carbon fiber reinforced polyether ether ketone (CF-PEEK, carbon content: 50%-55%) with a thickness of 2.5 mm were directly connected by friction stir spot welding. The thread-shaped welding tool with a shoulder diameter of 12 mm, a pin tip diameter of 4.1 mm, a pin root diameter of 4.8 mm, and a pin length of 0.93 mm made of H13 steel was selected to connect the 5052 aluminum alloy and the CF-PEEK. In order to meet the lightweight design requirements and reduce the overlap area as much as possible, the overlap width of the 5052 aluminum alloy and the CF-PEEK was 20 mm. The rotation speed was 1400 rpm, the pressing amount was 1.6 mm, the dwell time was 8 s, and the tool tilt angle was 0 degrees. The joint macroscopic cross-sectional view and the interface SEM morphology are shown in Figure 4 and Figure 6 As shown in (b), there are a large number of pores at the joint interface, and a large number of bubble defects are found in the main joint area-shoulder affected area. The bubble volume fraction can reach more than 10% of the joint, and the tensile shear force of the joint is Figure 7 As shown, the maximum was 2.68 kN.

[0071] Comparative Example 2:

[0072] A 2mm-thick 5052 aluminum alloy sheet and a 2.5mm-thick carbon fiber reinforced polyether ether ketone (carbon content: 50%-55%) were used. During assembly, a 0.2mm-thick polyether ether ketone interlayer was pre-positioned between the dissimilar materials. A threaded friction stir welding tool with a shoulder diameter, a pin tip diameter, and a pin root diameter of 12mm, 4.1mm, and 4.8mm, respectively, and a pin length of 0.93mm was selected for connection. The welding tool was made of H13 steel. To meet the requirements of lightweight design, the overlap area was minimized as much as possible. The overlap width of the 5052 aluminum alloy and the CF-PEEK was 20mm. A rotation speed of 1400rpm, a pressing amount of 1.6mm, a holding time of 8s, and a tool tilt angle of 0 degrees were used. The tensile shear force of the joint was 1.29kN, as shown in Figure 7

[0073] Technical effects: According to Example 1, Comparative Example 1, and Comparative Example 2, the present application eliminates the bubble defect at the joint interface formed by welding the metal plate and the resin-based composite material plate by pre-positioning the through hole on the metal plate and pre-positioning the thermoplastic resin interlayer between the metal plate and the resin-based composite material plate. This effectively prevents the stress concentration phenomenon caused by the residual bubbles in the joint in the prior art, thereby improving the joint performance and the service performance of the dissimilar joint, greatly expanding the engineering application range of the metal / resin-based composite material joint. In addition, the aforementioned molten thermoplastic resin and part of the matrix of the resin-based composite material plate flow into the through hole and solidify, forming a mechanical interlock between the metal plate and the resin-based composite material plate, which further improves the joint strength.

[0074] Example 2:

[0075] A 4mm-thick 5052 aluminum alloy sheet and a 3mm-thick continuous carbon fiber reinforced polyether ether ketone (CF-PEEK, carbon content: 40%-45%) were used. Two 2mm-diameter through holes were pre-positioned in the overlap area outside the welding area of the 5052 aluminum alloy before welding. The distance between the center of the through hole and the center of the shoulder hole (welding center) was 11.5mm. During assembly, a 0.4mm-thick polyether ether ketone interlayer was pre-positioned between the dissimilar materials. The dissimilar materials were connected by friction stir spot welding, as shown in Figure 2 ​The threaded welding tool with a shoulder diameter of 20 mm, a pin tip diameter of 8 mm, a pin root diameter of 9 mm, and a pin length of 2.9 mm made of H13 steel was used to connect the 4-mm-thick 5052 aluminum alloy plate and the 3-mm-thick continuous carbon fiber reinforced polyether ether ketone (CF-PEEK, carbon content: 40%-45%) with a lap width of 28 mm. The rotation speed was 2000 rpm, the pressing amount was 0.3 mm, the pressure maintaining time was 15 s, and the tool tilt angle was 0 degrees.

[0076] Comparative Example 3:

[0077] The 4-mm-thick 5052 aluminum alloy plate and the 3-mm-thick continuous carbon fiber reinforced polyether ether ketone (CF-PEEK, carbon content: 40%-45%) were connected by friction stir spot welding. Before welding, a through hole with a diameter of 2 mm was pre-placed in the lap area outside the welding area of the 5052 aluminum alloy. The distance between the center of the through hole and the center of the shoulder hole (welding center) was 10 mm, i.e., part of the through hole was located in the shoulder affected area. During assembly, a 0.4-mm-thick polyether ether ketone interlayer was pre-placed in the intermediate heterogeneous material. A threaded welding tool with a shoulder diameter of 20 mm, a pin tip diameter of 8 mm, a pin root diameter of 9 mm, and a pin length of 2.9 mm made of H13 steel was used to connect the 4-mm-thick 5052 aluminum alloy plate and the 3-mm-thick continuous carbon fiber reinforced polyether ether ketone (CF-PEEK, carbon content: 40%-45%) with a lap width of 28 mm. The rotation speed was 2000 rpm, the pressing amount was 0.3 mm, the pressure maintaining time was 15 s, and the tool tilt angle was 0 degrees.

[0078] Technical effect: There are still about 10% of bubbles at the interface of the main connection area of the welded joint-the shoulder affected area, indicating that the bubble discharge effect is poor when the through hole is located in the shoulder affected area.

[0079] Comparative Example 4:

[0080] A 4 mm thick 5052 aluminum alloy plate and a 3 mm thick continuous carbon fiber reinforced polyether ether ketone (CF-PEEK, carbon content: 40%-45%) were used. Before welding, a through hole with a diameter of 2 mm was pre-installed in the lap area outside the 5052 aluminum alloy welding area. The distance between the center of the through hole and the center of the shoulder hole (welding center) was 11.5 mm. During assembly, a 0.4 mm thick polyether ether ketone interlayer was pre-installed in the middle of the dissimilar materials. The dissimilar materials were connected by friction stir spot welding. A threaded welding tool with a shoulder diameter, a stirring needle tip diameter, and a needle root diameter of 20 mm, 8 mm, and 9 mm, respectively, and a needle length of 2.9 mm was selected for connection. The welding tool was made of H13 steel, and the lap width of the 5052 aluminum alloy and the CF-PEEK was 28 mm. A rotation speed of 3000 rpm, a pressing amount of 1 mm, a holding time of 20 s, and a tool inclination angle of 0 degrees were used.

[0081] Technical effect: There are still about 13% of bubbles in the main connection area-shoulder affected area of the welded joint, which indicates that the rotation speed is too fast, the holding time is too long, and the heat input is too large, resulting in excessive thermal decomposition of the resin in the joint and excessive bubbles. Even if a suitable through hole is drilled in the appropriate position, the bubbles cannot be completely removed, which affects the joint connection quality and joint performance.

[0082] Example 3:

[0083] A 3 mm thick 5052 aluminum alloy plate and a 3 mm thick carbon fiber reinforced polyether ether ketone (CF-PEEK, carbon content: 40%-45%) were used. Before welding, a through hole with a diameter of 1 mm was pre-installed in the lap area outside the 5052 aluminum alloy welding area. The distance between the center of the through hole and the center of the shoulder hole (welding center) was 6.5 mm. During assembly, a 0.1 mm thick polyether ether ketone interlayer was pre-installed in the middle of the dissimilar materials. The dissimilar materials were connected by friction stir spot welding, as shown in Figure 2 The welding tool had a shoulder diameter of 6 mm and no stirring needle. The welding tool was made of H13 steel, and the lap width of the 5052 aluminum alloy and the CF-PEEK was 20 mm. A rotation speed of 600 rpm, a pressing amount of 2 mm, a holding time of 3 s, and a tool inclination angle of 0 degrees were used. After welding, most of the bubbles in the joint accumulated in the through hole, and the molten interlayer and the polyether ether ketone matrix in the carbon fiber reinforced composite material accumulated in the through hole and solidified, forming a macroscopic mechanical interlock. The bubble volume fraction in the main connection area-shoulder affected area of the joint was less than 5%, and the maximum tensile shear force of the joint was 2.4 kN.

[0084] Comparative Example 5:

[0085] A 3 mm thick 5052 aluminum alloy sheet and a 3 mm thick carbon fiber reinforced polyether ether ketone (CF-PEEK, carbon content: 40%-45%) were used. Before welding, a through hole with a diameter of 1 mm was pre-placed in the lap area outside the 5052 aluminum alloy welding area. The distance between the center of the through hole and the center of the shoulder hole (welding center) was 6.5 mm. During assembly, a 0.1 mm thick polyether ether ketone interlayer was pre-placed in the middle of the dissimilar materials. The dissimilar materials were connected by friction stir spot welding. A welding tool with a shoulder diameter of 6 mm and no stirring needle was selected for connection. The welding tool was made of H13 steel. The lap width of the 5052 aluminum alloy and the CF-PEEK was 20 mm. A rotation speed of 400 rpm, a pressing amount of 2 mm, a holding time of 3 s, and a tool inclination angle of 0 degrees were used. After welding, the joint was directly separated from the metal and resin interface. Due to the excessively low heat input, the metal and resin-based materials could not be effectively connected.

[0086] Example 4:

[0087] A 3 mm thick 5052 aluminum alloy sheet and a 3 mm thick carbon fiber reinforced polyamide-based composite plate (CF-PA6, carbon content: 50%-55%) were used. Before welding, a through hole with a diameter of 10 mm was pre-placed in the lap area outside the 5052 aluminum alloy welding area. The distance between the center of the through hole and the center of the shoulder hole (welding center) was 17 mm. During assembly, a 0.2 mm thick polyamide (PA6) interlayer was pre-placed in the middle of the dissimilar materials. The dissimilar materials were connected by friction stir spot welding, as shown in FIG. 1. A threaded welding tool with a shoulder diameter, a stirring needle tip diameter, and a needle root diameter of 12 mm, 5 mm, and 5.4 mm, respectively, and a needle length of 1.8 mm was selected for connection. The welding tool was made of H13 steel. The lap width of the 5052 aluminum alloy and the CF-PEEK was 50 mm. A rotation speed of 1000 rpm, a pressing amount of 1.2 mm, a holding time of 10 s, and a tool inclination angle of 5 degrees were used. Figure 2 After welding, the joint interface bubbles accumulated in the through hole, and the molten interlayer and the polyamide matrix in the carbon fiber reinforced composite material accumulated in the through hole and solidified, forming a macroscopic mechanical interlock. No bubble defects were found in the main connection area of the joint-the shoulder affected area. The maximum tensile shear force of the joint was 3.2 kN.

[0088] Comparative Example 6:

[0089] A 3mm-thick 5052 aluminum alloy plate and a 3mm-thick carbon fiber reinforced polyamide-based composite plate (CF-PA6, carbon content: 50%-55%) are used, a through hole with a diameter of 10mm is pre-placed in the lap area outside the 5052 aluminum alloy welding area before welding; the distance between the center of the through hole and the center of the shoulder hole (welding center) is 19mm; a 0.2mm-thick polyamide (PA6) interlayer is pre-placed in the intermediate area of the dissimilar materials during assembly; the dissimilar materials are connected by friction stir spot welding, a threaded welding tool with a shoulder diameter, a pin tip diameter and a pin root diameter of 12mm, 5mm and 5.4mm respectively, and a pin length of 1.8mm is selected for connection, the welding tool is made of H13 steel, and the lap width of the 5052 aluminum alloy and the CF-PEEK is 50mm. The rotation speed is 1000rpm, the pressing amount is 1.2mm, the holding time is 10s, and the tool inclination angle is 5 degrees. After welding, the bubbles accumulate at the joint interface, so the maximum tensile shear force of the joint is only 1.8kN.

[0090] From the above examples and comparative examples, it can be concluded that the present application eliminates the bubble defects in the joint formed by welding the metal plate and the resin-based composite plate by pre-placing a through hole on the metal plate and pre-placing a thermoplastic resin interlayer between the metal plate and the resin-based composite plate, which can effectively prevent the stress concentration phenomenon caused by the residual bubbles in the joint in the prior art, thereby improving the joint strength and improving the service performance of the dissimilar joint, greatly widening the engineering application range of the metal / resin-based composite joint, and at the same time, the aforementioned molten thermoplastic resin and part of the matrix of the resin-based composite plate flow into the through hole and solidify, forming a mechanical interlock between the metal plate and the resin-based composite plate, which further improves the joint strength; in addition, the pre-made hole can reduce the weight of the metal plate, thereby further achieving lightweight design; the welding method of the present application is particularly suitable for preparing high-strength metal / carbon fiber reinforced resin-based composite structural parts.

[0091] It is easily understood by those skilled in the art that the advantageous technical features of each of the above methods can be freely combined and superimposed without conflict.

[0092] The above is only a preferred embodiment of the present application and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principles of the present application shall be included in the protection scope of the present application. The above is only a preferred embodiment of the present application, and it should be noted that those skilled in the art can make several improvements and modifications without departing from the technical principles of the present application, and these improvements and modifications shall be regarded as the protection scope of the present application.

Claims

1. A welding method capable of eliminating a blister defect in a dissimilar material joint, characterized by, It comprises the following steps: A through hole processing step, processing a through hole on the metal plate, the through hole is in the welding overlap area of the metal plate and the resin-based composite plate, when the welding overlap area is welded by using a friction stir welding tool, the track area formed by the shaft shoulder of the friction stir welding tool in the welding overlap area is the shaft shoulder affected area, the through hole is also outside the shaft shoulder affected area, so that the bubbles generated in the shaft shoulder affected area are transferred to the through hole following the molten flowing fluid without accumulating in the welded joint, thereby achieving the design purpose of eliminating the bubble defects in the dissimilar material joint; A cleaning and drying step, cleaning and drying the metal plate, the resin-based composite plate and the thermoplastic resin interlayer; A clamping and positioning step, stacking and positioning the resin-based composite plate, the thermoplastic resin interlayer and the metal plate from bottom to top on the workbench, wherein the thermoplastic resin interlayer corresponds to the welding overlap area of the resin-based composite plate and the metal plate, and the thermoplastic resin interlayer can be heated and molten to form a fluid, thereby facilitating the elimination of the bubbles; A friction stir welding step, using the friction stir welding tool to perform friction stir welding on the metal plate from one side of the metal plate.

2. The welding method according to claim 1, characterized in that, In the friction stir welding step, the metal plate is welded by spot welding.

3. The welding method according to claim 2, wherein The shaft shoulder diameter of the friction stir welding tool is 6-20 mm, and the through hole is a circular hole with a diameter of 1-10 mm.

4. The welding method according to claim 2, wherein The shaft shoulder diameter of the friction stir welding tool is D, the through hole is a circular hole with a diameter of D0, the hole corresponding to the shaft shoulder diameter formed by spot welding is a shaft shoulder hole, the center distance between the shaft shoulder hole and the through hole is d, and (D+D0) / 2+0.5 mm≤d≤D+D0 / 2.

5. The welding method according to claim 2, wherein The following process parameters are used when the friction stir welding tool performs spot welding: The rotation speed of the welding tool is 600-2000 rpm, the pressing amount is 0.3-2.0 mm, the holding time is 3-15 seconds, and the tool inclination angle is 0°-5°.

6. The welding method according to claim 1, wherein The base material of the thermoplastic resin interlayer is consistent with that of the resin-based composite plate, and the thickness of the thermoplastic resin interlayer is 0.1-0.4 mm.

7. The welding method according to claim 1, wherein The material of the thermoplastic resin interlayer is a thermoplastic polar resin.

8. The welding method according to claim 1, wherein The resin-based composite material is a continuous fiber reinforced resin-based composite material.

9. The welding method of claim 1, wherein, The cleaning and drying step specifically comprises: Using a dust cloth and alcohol to clean the metal plate, the resin-based composite plate and the thermoplastic resin interlayer, and then using a hair dryer to dry.

10. A dissimilar material joint, characterized by, The volume content of the bubbles at the interface of the dissimilar material joint is 0-5% when the welding method capable of eliminating the bubble defects in the dissimilar material joint according to any one of claims 1-9 is used to prepare the dissimilar material joint.

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