A method for connecting a lightweight composite automobile luggage rack rod member

Abstract

This invention discloses a method for butt-joining lightweight composite automotive roof rack rods, belonging to the field of automotive parts processing technology. This invention aims to solve the problems of low connection strength, poor impact resistance, and low processing efficiency in existing metal-to-CFRP (carbon fiber reinforced resin) rod butt joints. The method includes: setting an inner groove, an inner annular groove, an end face groove, and an outer groove at the metal rod joint and performing surface treatment; preparing a CFRP rod with a three-stage stepped structure; heating the metal connecting section to induce a viscous flow state in the CFRP matrix, inserting it, and axially pressurizing and curing it; then wrapping the connecting section with carbon fiber prepreg tape and coating it with homogeneous thermoplastic resin before curing. This invention significantly improves the axial and radial load-bearing capacity, impact toughness, and connection efficiency of the metal-to-CFRP rod butt joint through the synergistic effect of mechanical interlocking, surface chemical bonding, and prepreg tape reinforcement, making it suitable for lightweight manufacturing of automotive roof rack rods.

Description

Technical Field

[0001] This invention relates to the field of automotive parts processing technology, specifically to a method for connecting lightweight composite automotive luggage rack rods. Background Technology

[0002] With the increasing popularity of energy conservation, emission reduction, and green manufacturing concepts, lightweighting has gradually become the mainstream design philosophy for vehicle body structures. The development of new materials has brought greater opportunities for lightweight vehicle manufacturing. Vehicle body structures have evolved from traditional high-strength steel to lightweight high-strength aluminum and magnesium alloys, and then to carbon fiber reinforced resin (CFRP) composites. Metal materials such as aluminum alloys and titanium alloys possess advantages such as lightweight, high strength, good ductility, heat resistance, and corrosion resistance, making them the mainstream load-bearing components of current vehicle bodies. CFRP has advantages such as low density, high specific strength, good corrosion resistance, strong energy absorption and impact resistance, and easy recyclability, showing broad application prospects in vehicle body structures, especially in weight reduction for new energy vehicles. The combination of metal materials and CFRP can maximize the performance advantages of both materials while further meeting the technical requirements of lightweighting, improving overall vehicle performance while further reducing emissions and energy consumption. Currently, the lightweighting demand for automotive roof rack components, as exterior trim and load-bearing parts, is increasingly urgent. Roof rack components using a metal-CFRP composite structure can ensure strength while significantly reducing weight.

[0003] Currently, some high-end vehicles have adopted a combination of aluminum alloy and CFRP materials in their roof rack components, achieving both improved vehicle performance and weight reduction. However, for the metal / CFRP butt joint connection of roof rack components, existing processes still primarily employ riveting or adhesive bonding. Riveting introduces rivets, leading to increased weight and stress concentration; adhesive bonding suffers from long curing times and aging failure. Furthermore, the commonly used adhesive bonding method for metal / CFRP also faces challenges in actual production, including long curing times and aging failure due to temperature and humidity variations. While some researchers have used thermal joining methods such as laser welding, resistance welding, and friction stir welding to achieve metal-CFRP sheet metal connections, research on metal / CFRP butt joints is relatively limited, especially for automotive roof rack components. This is mainly due to the differences in material properties and the limitations of welding methods. Direct connection methods also result in limited actual connection dimensions at the joint, making it difficult to achieve a robust and reliable connection between the metal and CFRP components, and the mechanical properties may not meet the requirements of practical engineering applications.

[0004] Existing luggage rack rod connection technologies mostly employ mechanical fastening or adhesive bonding, which struggles to meet the requirements of lightweight design and high reliability. Therefore, this invention aims to overcome the technical bottleneck of achieving butt joint connections between metal and CFRP rods in automotive luggage racks, further improving the connection strength, impact resistance, and fatigue toughness at the joint through structural design or surface treatment, while also shortening connection time, improving engineering efficiency, and meeting the service requirements of metal-CFRP structural components under various operating conditions. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, this invention provides a method for connecting lightweight composite automotive luggage rack rods, which enhances the impact resistance and fatigue resistance of the joints, making them more adaptable to actual engineering requirements.

[0006] The technical solution adopted by this invention is as follows: The method for connecting lightweight composite automotive roof rack rods proposed in this solution specifically includes the following steps: Step 1: Fabrication of the metal rod joint structure: A small inner groove structure is provided at the center of the cross-section of the metal rod joint. An inner annular groove structure is arranged on the side of the inner groove. A grid-like groove structure is arranged at the end of the metal rod. An outer groove is machined on the outer surface of the metal rod at a depth equidistant from the inner groove. The joint area of ​​the metal rod is surface-treated, and the surface of the inner groove is covered with a surface-treated layer after treatment. Step 2: Fabrication of CFRP rod joint structure: CFRP rods are fabricated by injection molding, wherein the section to be connected is processed into a three-step structure so that the CFRP rod connection section can fit with the metal rod connection section; Step 3: CFRP to Metal Rod Connection Process: Using auxiliary clamps, fix the metal rod joint structure to one side and the CFRP rod joint structure to the opposite side. The connection process begins by heating the metal rod connection section to between the viscous flow temperature and thermal decomposition temperature of the CFRP matrix material. Then, insert the CFRP rod connection section into the groove within the metal rod connection section and hold it for a period of time, allowing the CFRP matrix to enter a viscous flow state upon heating. Subsequently, using a clamping mechanism, press the metal connection section and the CFRP connection section together and hold them under axial forging force for a period of time to allow the CFRP to solidify within the groove and end face of the metal joint. Step 4: Reinforcement with carbon fiber prepreg tape: Wrap carbon fiber prepreg tape around the metal and CFRP connection section, embedding the prepreg tape into the outer groove of the metal rod connection section, and tightly wrapping the outer surface of the second CFRP step section. Step 5: Prepreg Resin Coating and Curing: The prepreg tape wrapped in the previous step is impregnated and coated with viscous thermoplastic resin, and then cooled and cured to form a joint. This yields a metal / CFRP butt joint structure.

[0007] Preferably, in step one, the metal rod material includes, but is not limited to, aluminum alloy, magnesium alloy, titanium alloy, and steel, and the cross-section of the metal rod and CFRP rod is circular, square, or trapezoidal.

[0008] Preferably, in step one, when the cross-section of the metal rod and the CFRP rod is circular, the length of the groove in the metal connecting section is 3 to 5 times the diameter of its cross-section; when the cross-section of the metal rod and the CFRP rod is square or trapezoidal, the length of the groove in the metal connecting section is 3 to 5 times the diagonal distance.

[0009] Preferably, in step one, before surface treatment of the metal rod connection section, the transition joint needs to be cleaned with an organic solvent or cleaning agent to remove surface oxides and oil stains. The organic solvent is alcohol or acetone.

[0010] Preferably, in step one, the surface treatment method for the metal rod connection section includes silane coupling agent treatment, anodizing, and micro-arc oxidation.

[0011] Preferably, in step one, the geometry of the inner groove structure is set to be wider on the outside and narrower on the inside, the connection between the inner groove and the edge of the rod is a rounded transition, and the spacing between adjacent inner annular grooves in the inner groove is equal.

[0012] Preferably, in step one, the area of ​​the annular structure at the end of the metal connecting section should not be less than 1 / 3 of the cross-sectional area of ​​the rod, the depth of the outer groove of the metal connecting section is 5~8mm, and the depth and width of the mesh groove at the end of the metal rod are the same, and the width is 1 / 2 of the distance between adjacent grooves.

[0013] Preferably, in step two, the geometry and dimensions of the first stepped structure in the CFRP rod connection segment are the same as the groove inside the metal connection segment; the length of the first stepped structure is slightly less than or equal to the length of the groove inside the metal rod connection segment.

[0014] Preferably, in step two, the cross-sectional dimensions of the second stepped structure in the CFRP rod connection segment are the same as the diameter (circular) or diagonal (square or trapezoidal) of the end section of the metal rod connection segment; the axial length of the second stepped structure is equal to the distance from the end face of the metal connection segment to the outer edge of the outer groove.

[0015] Preferably, in step two, the geometry and dimensions of the third stepped structure are the same as the overall shape and dimensions of the metal rod. The heating method of the metal connecting section is resistance heating or induction heating. The axial upsetting force during the connection process should be such that the CFRP completely fills the groove structure of the metal connecting section without excessive extrusion and overflow.

[0016] Preferably, in step four, the width of the carbon fiber prepreg tape should be equal to the sum of the axial length of the outer groove of the metal connecting section and the axial length of the second step of the CFRP rod.

[0017] Preferably, in step five, the viscous flow thermoplastic resin material used should be the same as the thermoplastic resin matrix material of the CFRP rod, the cooling and curing temperature gradient is 10℃ / min, and the air humidity is 20~30%.

[0018] The beneficial effects achieved by the present invention using the above structure are as follows: 1. Through the structural design of the inner groove, inner annular groove and end arc transition of the metal rod connection section, and in combination with the viscous flow characteristics of CFRP material at high temperature, the mechanical interlock between the metal / CFRP rods at the connection section is fully realized through the axial force extrusion process; effectively improving the axial and radial load-bearing capacity of the metal / CFRP joint, making it more suitable for practical engineering applications.

[0019] 2. By surface treating the metal rod connection section, the surface treatment layer is evenly covered in the groove of the rod, thereby achieving an effective connection with the CFRP matrix, further improving the bonding strength between the metal and the CFRP material. The resulting butt joint has better mechanical properties and can be applied to more complex working conditions.

[0020] 3. By wrapping the metal / CFRP joint with carbon fiber prepreg tape, the joint of the metal / CFRP rod is reinforced, further improving the connection strength. Simultaneously, due to the good toughness of the carbon fiber prepreg tape, the radial load-bearing capacity of the joint is further improved, enhancing the energy absorption and impact resistance of the joint area.

[0021] 4. By using the same thermoplastic viscous resin material as the CFRP matrix for coating and curing, the carbon fiber prepreg tape is wrapped and reinforced to ensure the uniformity of material properties between the joint and the CFRP rod, thereby ensuring the connection strength of the joint. Attached Figure Description

[0022] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic diagram of the metal rod joint connection section structure in this invention; Figure 2 This is a schematic diagram of the CFRP rod joint connection section structure in this invention; Figure 3 This is a schematic diagram of the cross-section of the metal or CFRP rod in this invention; Figure 4 This is a schematic diagram of the connection effect between the metal and the CFRP rod in Embodiment 1 of the present invention.

[0023] The reference numerals in the attached figures are explained as follows: 1. Inner groove of metal connecting section; 2. Inner annular groove of metal connecting section; 3. Outer groove of metal connecting section; 4. End face of metal connecting section; 5. First stepped structure of CFRP connecting section; 6. Second stepped structure of CFRP connecting section; 7. Third stepped structure of CFRP connecting section; 8. Carbon fiber prepreg tape. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention. Example

[0025] This embodiment provides a method for butt-joining metal and CFRP rods of an automotive roof rack. The metal rod connecting section is provided with an inner groove 1, an inner annular groove 2, and an outer groove 3. An arc transition is provided between the end face 4 of the metal rod connecting section and the inner groove 1, and the end face 4 of the metal rod connecting section is arranged with equidistant grooves. This structural design effectively enhances the mechanical fit between the CFRP and the metal rod connecting section, thereby improving the axial and radial load-bearing capacity of the joint.

[0026] The specific steps are as follows: (1) Preparation of metal rod joint structure: Circular cross-section aluminum alloy rods are selected. The connecting section of the aluminum alloy rod is cleaned using organic solvents such as alcohol or acetone to remove surface oxides and oil stains. Subsequently, the inner groove and inner annular groove of the aluminum alloy connecting section are surface treated to uniformly cover the surface with a surface treatment layer. The surface treatment methods include, but are not limited to, anodizing, micro-arc oxidation, and silane coupling agent treatment.

[0027] (2) Preparation and clamping of CFRP rod joint structure: The aluminum alloy rod connecting section is clamped and fixed by a clamp, and the CFRP rod connecting section is clamped and fixed directly opposite the aluminum alloy rod connecting section, so that the first stepped structure 5 of the CFRP rod is directly opposite the inner groove structure 1 of the aluminum alloy rod connecting section, ensuring that the first stepped structure of the CFRP rod can extend into the inner groove of the aluminum alloy rod connecting section during the subsequent connection process; The dimensions of the second stepped structure 6 of the CFRP rod correspond to the end face 4 of the aluminum alloy rod connecting section.

[0028] (3) Heating and Curing: The aluminum alloy connecting section is heated to 260℃~290℃ using induction heating. Then, the double-sided fixing clamps are moved so that the first stepped structure 5 of the CFRP rod is inserted into the groove 1 of the connecting section of the aluminum alloy rod. The temperature is maintained for 10 minutes, and the heat of the aluminum alloy connecting section is used to soften the CFRP rod matrix and bring it into a viscous flow state. Then, the clamps are used to move the aluminum alloy rod connecting section and the CFRP rod connecting section toward each other. Under the action of axial force, the softened CFRP fully fills the groove 1 and inner annular groove 2 of the aluminum alloy rod connecting section. After the groove structure of the aluminum alloy connecting section is fully filled, the axial pressure is maintained to fully press the second stepped section 6 of the CFRP rod with the end face 4 of the aluminum alloy connecting section. The softened CFRP material matrix flows into the groove structure of the end face 4 of the aluminum alloy connecting section. After holding for 3-5 minutes, perform a gradient cooling at a rate of 10℃ / min to fully cure the CFRP matrix at the joint, thus completing the initial connection between the aluminum alloy rod and the CFRP rod.

[0029] (4) Reinforcement with carbon fiber prepreg tape: Carbon fiber prepreg tape 8 is used to reinforce the connection section between the aluminum alloy and CFRP rods that has been initially connected. The width of the carbon fiber prepreg tape is equal to the sum of the axial length 3 of the outer groove of the aluminum alloy connection section and the axial length 6 of the second step of the CFRP. The winding thickness is slightly less than the depth of the outer groove 3 of the aluminum alloy connection section.

[0030] (5) Prepreg resin coating and curing: The carbon fiber prepreg tape 8 is coated with viscous thermoplastic resin material. The outer diameter of the joint connection section after coating with thermoplastic resin should be consistent with the main body size of aluminum alloy or CFRP rod.

[0031] (6) Cooling: Place the connected aluminum alloy / CFRP composite rod in an air environment with a relative humidity of 20%~30% to cool to room temperature to obtain aluminum alloy / CFRP butt rod structure. Example

[0032] The difference between this embodiment and Embodiment 1 is that a square-section magnesium alloy rod is used for the metal rod, in order to further verify the applicability of the method of the present invention to different cross-sectional shapes and metal materials.

[0033] The specific steps are as follows: (1) Preparation of metal rod joint structure: A square cross-section magnesium alloy rod is selected. The connecting section of the magnesium alloy rod is cleaned with organic solvent alcohol or acetone to remove surface oxides and oil stains. Then, the inner groove and inner annular groove of the magnesium alloy connecting section are subjected to micro-arc oxidation surface treatment to make the surface uniformly covered with a surface treatment layer. In this embodiment, the length of the inner groove of the metal connecting section is 4 times the diagonal distance of the cross-section of the magnesium alloy rod; the geometry of the inner groove structure is set to be wider on the outside and narrower on the inside, and the connection between the inner groove and the edge of the rod is a circular arc transition connection. The spacing between adjacent inner annular grooves in the inner groove is equal; the area of ​​the annular structure at the end of the metal connecting section is not less than 1 / 3 of the cross-sectional area of ​​the rod; the depth of the outer groove of the metal connecting section is 6mm; the depth and width of the grid groove at the end of the metal rod are the same, and the width is 1 / 2 of the spacing between adjacent grooves.

[0034] (2) Fabrication and clamping of CFRP rod joint structure: CFRP rods are fabricated by injection molding, and the sections to be connected are processed into three stepped structures. The geometry and dimensions of the first stepped structure in the CFRP rod connection section are the same as the inner groove of the metal connection section, and the length of the first stepped structure is equal to the length of the inner groove of the metal rod connection section; the cross-sectional dimensions of the second stepped structure are the same as the diagonal distance at the end of the metal rod connection section, and the axial length of the second stepped structure is equal to the distance from the end face of the metal connection section to the outer edge of the outer groove; the geometry and dimensions of the third stepped structure are the same as the shape and dimensions of the main body of the magnesium alloy rod. The magnesium alloy rod connection section is clamped and fixed by a clamp, and the CFRP rod connection section is clamped and fixed directly opposite the magnesium alloy rod connection section, so that the first stepped structure 5 of the CFRP rod is directly opposite the inner groove structure 1 of the magnesium alloy rod connection section, ensuring that it can extend into the inner groove of the magnesium alloy rod connection section; the dimensions of the second stepped structure 6 of the CFRP rod correspond to the end face 4 of the magnesium alloy rod connection section.

[0035] (3) Heating and Curing: The magnesium alloy connecting section is heated to 250℃~280℃ using resistance heating (between the viscous flow temperature and thermal decomposition temperature of the CFRP matrix material). Then, the double-sided fixing clamps are moved so that the first stepped structure 5 of the CFRP rod is inserted into the groove 1 of the connecting section of the magnesium alloy rod. The temperature is maintained for 8 minutes while continuing to heat the material. The heat from the magnesium alloy connecting section softens the CFRP matrix and induces it to enter a viscous flow state. Then, the clamps are used to move the magnesium alloy rod connecting section and the CFRP rod connecting section toward each other. Under the action of axial forging force, the softened CFRP fully fills the groove 1 and inner annular groove 2 of the magnesium alloy rod connecting section. The axial forging force should be such that the CFRP completely fills the groove structure of the metal connecting section without excessive extrusion. After the groove structure of the magnesium alloy connecting section is fully filled, the axial pressure is maintained to fully press the second stepped section 6 of the CFRP rod against the end face 4 of the magnesium alloy connecting section. The softened CFRP matrix flows into the grid-like groove structure of the end face 4 of the magnesium alloy connecting section. After holding for 3-5 minutes, perform a gradient cooling at a rate of 10℃ / min to fully solidify the CFRP matrix at the joint, thus completing the initial connection between the magnesium alloy rod and the CFRP rod.

[0036] (4) Reinforcement with carbon fiber prepreg tape: Carbon fiber prepreg tape 8 is used to reinforce the connection section between the magnesium alloy and CFRP rods that has been initially connected. The width of the carbon fiber prepreg tape is equal to the sum of the axial length of the outer groove of the magnesium alloy connection section and the axial length of the second step of the CFRP; the winding thickness is slightly less than the depth of the outer groove 3 of the magnesium alloy connection section. During winding, the prepreg tape is embedded in the outer groove of the magnesium alloy rod connection section and tightly wrapped around the outer surface of the second step of the CFRP.

[0037] (5) Prepreg resin coating and curing: The carbon fiber prepreg tape 8 is impregnated and coated with the same viscous thermoplastic resin matrix material as the CFRP rod. The outer diameter of the joint connection section after coating with thermoplastic resin is ensured to be consistent with the main body size of the magnesium alloy or CFRP rod. Subsequently, under the condition of relative humidity of 25%, it is cooled and cured at a temperature gradient of 10℃ / min to form a joint, thus obtaining the magnesium alloy / CFRP butt rod structure.

[0038] The magnesium alloy / CFRP butt joint structure prepared in this embodiment achieves full mechanical interlocking and chemical bonding between the metal and CFRP material at the joint position, exhibiting good axial and radial load-bearing capacity. This further verifies the wide applicability of the method of the present invention to different cross-sectional shapes and different metal materials.

[0039] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, material, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, material, or apparatus.

[0040] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for butt-connecting lightweight composite automotive roof rack rods, characterized in that, Includes the following steps: S1. Preparation of metal rod joint structure: A small section of inner groove structure is provided at the center of the cross section of the metal rod joint, an inner annular groove structure is arranged on the side of the inner groove, a grid-like groove structure is arranged at the end of the metal rod, and an outer groove is machined on the outer surface of the metal rod at the same depth as the inner groove; the metal rod joint position is surface treated, and the surface of the inner groove is covered with a surface treatment layer after treatment. S2. Fabrication of CFRP rod joint structure: CFRP rods are fabricated by injection molding. The section to be connected in the rod is processed into a three-step structure so that the CFRP rod connection section can fit with the metal rod connection section. S3. CFRP to Metal Rod Connection Process: Using an auxiliary clamp, the metal rod connector section is fixed to one side, and the CFRP connector section is fixed to the opposite side. The connection process begins by heating the metal rod connector section to between the viscous flow temperature and thermal decomposition temperature of the CFRP matrix material. Then, the CFRP connector section is inserted into the groove within the metal rod connector section and held for a period of time, allowing the CFRP matrix to enter a viscous flow state upon heating. Subsequently, the metal connector section and the CFRP connector section are pressed together using a clamping mechanism and held for a period of time under axial upsetting force, allowing the CFRP to solidify within the groove and end face of the metal connector. S4. Carbon fiber prepreg tape reinforcement: Carbon fiber prepreg tape is used to wrap around the metal and CFRP connection section, and the prepreg tape is embedded in the outer groove of the metal rod connection section and tightly wrapped around the outer surface of the second step section of CFRP. S5. Prepreg tape resin coating and curing: The prepreg tape wrapped in the previous step is impregnated and coated with viscous thermoplastic resin and then cooled and cured to form a joint, resulting in a metal / CFRP butt rod structure.

2. The method for butt connection of lightweight composite car roof rack rods according to claim 1, characterized in that: The cross-section of the metal rod and CFRP rod is circular, square, or trapezoidal. When the cross-section of the metal rod and CFRP rod is circular, the length of the groove in the metal connecting section is 3 to 5 times the diameter of its cross-section. When the cross-section of the metal rod and CFRP rod is square or trapezoidal, the length of the groove in the metal connecting section is 3 to 5 times the diagonal distance.

3. The method for butt connection of lightweight composite car roof rack rods according to claim 1, characterized in that: In step S1, before surface treatment of the metal rod connection section, the transition joint needs to be cleaned with an organic solvent or cleaning agent to remove surface oxides and oil stains. The organic solvent is alcohol or acetone. The surface treatment methods for the metal rod connection section include silane coupling agent treatment, anodizing, and micro-arc oxidation.

4. The method for butt connection of lightweight composite car roof rack rods according to claim 1, characterized in that: In S1, the geometry of the inner groove structure is set to be wider on the outside and narrower on the inside, and the connection between the inner groove and the edge of the rod is a rounded transition connection; the spacing between adjacent inner annular grooves in the inner groove is equal. The area of ​​the annular structure at the end of the metal connecting section should not be less than 1 / 3 of the cross-sectional area of ​​the rod; The depth of the outer groove of the metal connecting section is 5~8mm; the depth and width of the grid groove at the end of the metal rod are the same, and the width is 1 / 2 of the distance between adjacent grooves.

5. The method for butt connection of lightweight composite car roof rack rods according to claim 1, characterized in that: In S1, the metal rod material includes, but is not limited to, aluminum alloy, magnesium alloy, titanium alloy, and steel.

6. The method for butt connection of lightweight composite car roof rack rods according to claim 1, characterized in that: In S2, the geometry and dimensions of the first stepped structure in the CFRP rod connection segment are the same as the inner groove of the metal connection segment, and the length of the first stepped structure is slightly less than or equal to the length of the inner groove of the metal rod connection segment; the cross-sectional dimensions of the second stepped structure in the CFRP rod connection segment are the same as the diameter (circular) or diagonal (square or trapezoidal) distance of the end section of the metal rod connection segment, and the axial length of the second stepped structure is equal to the distance from the end face of the metal connection segment to the outer edge of the outer groove; the geometry and dimensions of the third stepped structure are the same as the overall shape and dimensions of the metal rod.

7. The method for butt connection of lightweight composite car roof rack rods according to claim 1, characterized in that: In step S3, the heating method for the metal connecting section is resistance heating or induction heating; the magnitude of the axial upsetting force during the connecting process should be such that the CFRP completely fills the groove structure of the metal connecting section without excessive extrusion and overflow.

8. The method for butt connection of lightweight composite car roof rack rods according to claim 1, characterized in that: In S4, the width of the carbon fiber prepreg tape should be equal to the sum of the axial length of the outer groove of the metal connecting section and the axial length of the second step of the CFRP rod.

9. The method for butt connection of lightweight composite car roof rack rods according to claim 1, characterized in that: In step S5, the viscous flow thermoplastic resin material used should be the same as the thermoplastic resin matrix material of the CFRP rod; the cooling and curing temperature gradient is 10℃ / min, and the air humidity is 20~30%.

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