A welding method for a thin-walled aluminum alloy frame of an electric bicycle

Abstract

This invention relates to the field of welding equipment technology and provides a welding method for thin-walled aluminum alloy frames of electric bicycles. An activator located in the high-temperature region participates in the arc plasma process, influencing the electron density distribution and local conductivity distribution in the outer region of the arc column, thereby causing the welding current to concentrate in the center region of the arc column to increase the concentration of welding heat. Anhydrous aluminum trichloride in the activator located in the low-temperature region sublimates and forms a transient endothermic process during the temperature rise in the heat-affected zone, regulating the local temperature field distribution. This results in the same activator system creating a deep penetration strengthening effect in the weld center region and a heat accumulation inhibition effect at the edge region of the heat-affected zone, achieving synergistic optimization of weld penetration improvement and heat-affected zone control.

Description

Technical Field

[0001] This invention relates to the field of welding equipment technology, and specifically to a welding method for thin-walled aluminum alloy frames of electric bicycles. Background Technology

[0002] With the increasing demand for lightweight electric bicycles, aluminum alloy frames have gradually become the mainstream structural form. Among them, 6061-T6 aluminum alloy is widely used in the main beam, rear top fork, rear bottom fork and head tube connection structure of electric bicycles due to its high specific strength, good corrosion resistance and excellent processing performance.

[0003] Electric bicycle frames are typically made of thin-walled aluminum alloy tubing, and different tubing components need to be welded together to form an integral frame structure. Due to the characteristics of thin-walled aluminum alloy, such as high thermal conductivity, low heat capacity, and easy deformation, problems such as insufficient weld penetration and excessively wide heat-affected zone are prone to occur simultaneously during the welding process.

[0004] To ensure the strength of the frame connection, it is usually necessary to increase the welding heat input to obtain sufficient penetration depth. However, with the increase of heat input, the range of the heat-affected zone on both sides of the weld will also expand, which can easily lead to coarsening of the strengthening phase and softening of the joint, thereby affecting the fatigue life of the key stress nodes of the frame and the overall structural strength.

[0005] While existing activator welding techniques can improve weld penetration, their main effect is concentrated in the weld area, with limited control over the heat-affected zone (HAZ). This can easily lead to a situation where the weld penetration increases while the HAZ expands simultaneously. Therefore, how to improve the weld penetration of thin-walled aluminum alloy frames for electric bicycles while suppressing excessive heating of the HAZ, and achieving coordinated control between the weld center and the edge of the HAZ, has become a pressing technical problem for those skilled in the art. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a welding method for thin-walled aluminum alloy frames of electric bicycles, which overcomes the deficiencies of existing technologies, has a reasonable design, a compact structure, and solves the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A welding method for a thin-walled aluminum alloy frame of an electric bicycle, characterized by comprising the following steps:

[0009] S1. Prepare an active agent suspension, which includes anhydrous aluminum trichloride, fluorine-containing active components, and anhydrous organic solvents.

[0010] S2. Spray the activator suspension onto the weld area of ​​the workpiece to be welded, and form an activator film covering the center of the weld and the areas on both sides of the weld.

[0011] S3. Use a welding heat source to weld the workpiece, move the welding heat source along the weld direction, and form a temperature gradient that gradually decreases from the center to both sides in the transverse direction of the weld.

[0012] S4. Utilizing a temperature gradient, the activator film covering the weld area generates a spatially partitioned response in different temperature regions, wherein:

[0013] The activator located in the high-temperature region participates in the arc plasma process, affecting the electron density distribution and local conductivity distribution in the outer region of the arc column, thereby causing the welding current to concentrate in the central region of the arc column to increase the concentration of welding heat.

[0014] Anhydrous aluminum trichloride in the surfactant located in the low-temperature region sublimates and forms a transient endothermic process during the temperature rise in the heat-affected zone, which has a regulating effect on the local temperature field distribution.

[0015] This allows the same activator system to create a deep penetration strengthening effect in the center region of the weld and a heat accumulation inhibition effect at the edge of the heat-affected zone, thus achieving synergistic optimization of weld penetration improvement and heat-affected zone control.

[0016] Preferably, the fluorine-containing active component includes one or both of aluminum fluoride and sodium hexafluoroaluminate.

[0017] Preferably, the mass ratio of anhydrous aluminum trichloride, aluminum fluoride and sodium hexafluoroaluminate is (4-8):(2-5):(0.5-2).

[0018] Preferably, the anhydrous organic solvent is one or more of anhydrous isopropanol, anhydrous ethanol, and perfluoropolyether.

[0019] Preferably, the solid content of the surfactant suspension is 15% to 35%.

[0020] Preferably, the thickness of the surfactant film is 3μm to 20μm.

[0021] Preferably, the activator film covers 2mm to 8mm on both sides along the center line of the weld.

[0022] Preferably, the surfactant suspension is prepared under a dry protective environment with a dew point not higher than -30°C.

[0023] Preferably, the surfactant suspension is stored in a sealed liquid storage container filled with inert protective gas and transported to the spraying device through a sealed delivery pipeline.

[0024] Preferably, the welding heat source is a TIG welding heat source, a MIG welding heat source, a laser welding heat source, or a laser-arc hybrid welding heat source.

[0025] This invention provides a welding method for thin-walled aluminum alloy frames of electric bicycles. It has the following beneficial effects:

[0026] 1. By setting an activator film containing anhydrous aluminum trichloride and fluorine-containing active components in the weld area, and utilizing the transverse temperature gradient formed by the welding heat source, the activator system can trigger spatial partition responses in different temperature regions, thereby constructing a dual-region synergistic regulation mechanism for the same activator system.

[0027] 2. By having the activator in the high-temperature zone participate in the arc plasma process, it affects the electron density distribution and local conductivity distribution in the outer region of the arc column, causing the welding current to concentrate in the central region of the arc column, increasing the degree of welding heat concentration, thereby forming a deep penetration strengthening effect and improving the weld penetration depth and weld penetration ability.

[0028] 3. Through the synergistic effect between the fluorine-containing active components and the molten pool, the obstruction effect of the oxide film on the flow of the molten pool is weakened, the flow capacity of molten metal to the bottom of the molten pool is improved, and heat is transferred to the thickness direction of the plate, thereby improving the weld depth-to-width ratio.

[0029] 4. Anhydrous aluminum trichloride in the low-temperature region sublimates during the temperature rise in the heat-affected zone, forming a transient endothermic process. This process regulates the local temperature field distribution, thereby helping to reduce the peak temperature of the heat-affected zone and shorten the high-temperature residence time, thus mitigating the coarsening phenomenon of the strengthening phase.

[0030] 5. By using the same activator system to form a deep penetration strengthening effect in the center area of ​​the weld and a heat accumulation inhibition effect in the edge area of ​​the heat-affected zone, the weld penetration depth and heat-affected zone control are synergistically optimized, thereby improving the load-bearing capacity, fatigue life and structural reliability of the welded joint of the thin-walled aluminum alloy frame of electric bicycle. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, what is described is only a part of this invention, not all of it. All other methods of invention derived by those skilled in the art without inventive effort based on this invention are within the scope of protection of this invention.

[0032] This embodiment provides a welding method for thin-walled aluminum alloy frames of electric bicycles. Its core lies in utilizing the transverse temperature gradient formed by the welding heat source itself to cause the same activator system covering the weld area to produce differentiated responses in different temperature regions, thereby constructing a dual-region collaborative control mechanism between the weld center region and the edge region of the heat-affected zone.

[0033] The inventors have discovered that anhydrous aluminum trichloride can not only participate in the welding arc process, but also utilize its sublimation properties to create a transient endothermic process at the edge of the heat-affected zone. Simultaneously, the fluorine-containing active component can participate in the arc and molten pool regulation processes. Therefore, during welding, the same activator system can create a deep penetration strengthening effect in the weld center region and a heat accumulation inhibition effect at the edge of the heat-affected zone.

[0034] Unlike traditional activators that only regulate weld penetration, this embodiment utilizes the temperature gradient formed by the welding heat source to trigger the spatial partitioning response of the activator, thereby achieving synergistic optimization of weld penetration enhancement and heat-affected zone control.

[0035] I. Preparation of Aqueous Suspension Surfactants

[0036] Because anhydrous aluminum trichloride (AlCl3) has strong hygroscopic properties, it easily undergoes a hydrolysis reaction upon contact with moisture:

[0037] AlCl3 + 3H2O → Al(OH)3 + 3HCl

[0038] The generated hydroxides and acidic substances can affect the stability of the welding process. Therefore, this embodiment uses an anhydrous environment for activator preparation.

[0039] First, in a dry nitrogen-protected environment with a dew point not higher than -50°C, anhydrous aluminum trichloride micro powder, anhydrous aluminum fluoride nano powder, and anhydrous sodium hexafluoroaluminate powder were weighed and mixed in a mass ratio of 6:3:1.

[0040] The powder was then placed in a ball mill for mixing and milling to uniformly disperse the components and obtain a composite active powder with an average particle size of 1–3 μm.

[0041] Then, the composite active powder was added to anhydrous isopropanol that had been dehydrated by molecular sieves, and the solid content of the suspension was controlled to be 25%.

[0042] The suspension was then dispersed using an ultrasonic dispersion device for 30 minutes, so that the composite active powder was uniformly suspended in anhydrous isopropanol to form a stable anhydrous surfactant suspension.

[0043] After the surfactant is prepared, it is transferred to a sealed storage tank, and nitrogen gas with a purity of 99.999% is continuously introduced into the storage tank for protection to prevent moisture in the air from entering the storage tank and causing the surfactant to become ineffective.

[0044] The storage tank is connected to the automatic spraying device through a sealed delivery pipeline, realizing the closed delivery of the surfactant from preparation and storage to spraying.

[0045] II. Pre-welding treatment and activator coating

[0046] This embodiment uses the automatic welding of 6061-T6 aluminum alloy pipe as an example for illustration.

[0047] The aluminum alloy tube has a wall thickness of 1.5mm.

[0048] Before welding, the area to be welded is first degreased with acetone to remove oil and impurities from the workpiece surface.

[0049] Then, a stainless steel wire brush is used to mechanically grind the area to be welded in order to remove the aluminum oxide film on the surface of the aluminum alloy and expose the metallic luster on the surface of the base material.

[0050] After the surface treatment is completed, start the automatic spraying device.

[0051] The automatic spraying device extracts anhydrous surfactant suspension from a sealed storage tank and sprays the surfactant evenly onto the center of the weld and the areas on both sides through an atomizing nozzle.

[0052] Using the weld centerline as a reference, the activator covers a 3mm wide area on both sides.

[0053] After the anhydrous isopropanol evaporates, a continuous and uniform surfactant film is formed on the surface of the workpiece.

[0054] Preferably, the thickness of the surfactant film is controlled within the range of 5 to 10 μm.

[0055] After conversion, the amount of activator adhering to each millimeter of weld length is approximately 0.1 to 0.15 mg.

[0056] III. Welding Process

[0057] After the surfactant coating is completed, the workpiece is fixed on the welding fixture.

[0058] This embodiment uses TIG welding equipment for welding.

[0059] The welding process uses DC positive polarity, with a welding current of 120A and a welding speed of 1.5m / min.

[0060] The protective gas used is argon gas with a purity of 99.99% and a gas flow rate of 15 L / min.

[0061] During welding, the electric arc moves continuously along the weld direction, and a temperature distribution that gradually decreases from the center to both sides is formed in the transverse direction of the weld.

[0062] Since the temperature is highest at the center of the electric arc and relatively low at the edge of the heat-affected zone, the same surfactant film covering the workpiece surface will be heated to different degrees in different areas.

[0063] IV. Spatial Partition Response Mechanism of Surfactants

[0064] When the electric arc moves to a certain welding position, the transverse temperature gradient formed by the welding heat source causes the activator film covering the weld area to produce differentiated responses in different temperature regions.

[0065] Under high-temperature conditions, anhydrous aluminum trichloride preferentially vaporizes and enters the electric arc region, while some aluminum fluoride and sodium hexafluoroaluminate particles participate in the electric arc plasma reaction process.

[0066] An electric arc is essentially a high-temperature conductive channel composed of electrons, ions, and neutral particles, with current mainly transmitted through charged particles.

[0067] When chlorine-containing and fluorine-containing components enter the outer region of the arc column, the high electronegativity of chlorine and fluorine elements will affect the electron density distribution in the outer region of the arc column.

[0068] Under this effect, the local conductivity of the outer region of the arc column decreases, while the central region of the arc column still maintains a high conductivity.

[0069] When chlorine-containing and fluorine-containing components enter the outer region of the arc column, they may affect the electron density distribution and local conductivity distribution, thereby causing the welding current to concentrate in the central region of the arc column and forming an arc contraction trend.

[0070] As the electric arc contracts, the heat flux density per unit area increases, causing the welding heat to be more concentrated in the central area of ​​the weld, thereby increasing the weld penetration.

[0071] At the same time, the fluorine-containing active components in aluminum fluoride and sodium hexafluoroaluminate can also weaken the obstruction effect of residual oxide film on the flow of molten pool and improve the flowability of molten metal.

[0072] With improved molten pool flow capacity, liquid metal flows from the edge of the molten pool to the bottom center, thereby promoting the transfer of welding heat in the direction of plate thickness.

[0073] Therefore, under the combined influence of arc contraction and molten pool flow strengthening, the weld depth-to-width ratio is improved, achieving deep penetration welding of thin-walled aluminum alloys.

[0074] Unlike the central area of ​​the weld, the activator located near the heat-affected zones on both sides of the weld is subjected to relatively lower temperatures.

[0075] The temperature at the edge of the heat-affected zone is lower than the temperature at the center of the weld.

[0076] When the temperature reaches the sublimation temperature of anhydrous aluminum trichloride, the anhydrous aluminum trichloride adhering to the surface of the workpiece gradually changes from a solid state to a gaseous state.

[0077] During the sublimation process, anhydrous aluminum trichloride absorbs a certain amount of latent heat of sublimation, thereby inhibiting the accumulation of local heat.

[0078] Because the activator film is thin, its total heat absorption is not dominant relative to the overall welding heat input. However, it acts during the rapid temperature rise phase of the heat-affected zone, thus reducing the peak temperature in the local area and shortening the high-temperature dwell time.

[0079] For 6061-T6 aluminum alloy, its strengthening effect mainly comes from the strengthening phase particles dispersed within the matrix.

[0080] When the heat-affected zone is at a high temperature for a long time, the strengthening phase is prone to aggregation and coarsening, which in turn leads to softening of the joint area.

[0081] Comparative Example 1

[0082] Welding was performed using the same 6061-T6 aluminum alloy tubing, welding equipment, welding parameters, and pre-weld treatment methods as in this embodiment, with the only difference being:

[0083] The surfactant system used in Comparative Example 1 only included aluminum fluoride and sodium hexafluoroaluminate, without adding anhydrous aluminum trichloride.

[0084] The mass ratio of aluminum fluoride to sodium hexafluoroaluminate is 3:1, and the suspension is prepared using anhydrous isopropanol with a solid content of 25%.

[0085] The thickness of the activator coating, the coverage width, and the welding process parameters were kept consistent with those in the embodiment. After welding, the weld penetration, the width of the heat-affected zone, and the weld hardness were tested and compared with those in the embodiment of the present invention.

[0086] The test results of Comparative Example 1 and the embodiments of the present invention are shown in the table below: (Each group of samples was tested 5 times, and the average value was taken as the final result.)

[0087] Melting depth 1.45mm 1.82mm HAZ 4.6mm 3.9mm hardness 72HV 78HV

[0088] This embodiment reduces the coarsening of the strengthening phase and improves the microstructure stability and mechanical properties of the weld joint by slowing down the temperature rise rate of the heat-affected zone and shortening the high-temperature dwell time.

[0089] Therefore, throughout the welding process, the same activator system mainly plays a role in arc contraction and deep penetration strengthening in the central region of the weld, and mainly plays a role in inhibiting heat accumulation in the edge region of the weld.

[0090] By utilizing the temperature gradient formed by the welding heat source itself, the activator can achieve spatial partitioned response, thereby achieving the goal of synergistic optimization of deep penetration and heat-affected zone control.

[0091] It should be noted that, in this document, relational terms such as "first" and "second" are used merely 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, article, 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 a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0092] The above description is only used to illustrate the technical solutions of the present invention, and is not intended to limit them. Although the present invention has been described in detail with reference to the foregoing, those skilled in the art should understand that modifications can still be made to the foregoing technical solutions, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A welding method for a thin-walled aluminum alloy frame of an electric bicycle, characterized in that, Includes the following steps: S1. Prepare an active agent suspension, which includes anhydrous aluminum trichloride, fluorine-containing active components, and anhydrous organic solvents. S2. Spray the activator suspension onto the weld area of ​​the workpiece to be welded, and form an activator film covering the center of the weld and the areas on both sides of the weld. S3. Use a welding heat source to weld the workpiece, move the welding heat source along the weld direction, and form a temperature gradient that gradually decreases from the center to both sides in the transverse direction of the weld. S4. Utilizing a temperature gradient, the activator film covering the weld area generates a spatially partitioned response in different temperature regions, wherein: The activator located in the high-temperature region participates in the arc plasma process, affecting the electron density distribution and local conductivity distribution in the outer region of the arc column, thereby causing the welding current to concentrate in the central region of the arc column to increase the concentration of welding heat. Anhydrous aluminum trichloride in the surfactant located in the low-temperature region sublimates and forms a transient endothermic process during the temperature rise in the heat-affected zone, which has a regulating effect on the local temperature field distribution. This allows the same activator system to create a deep penetration strengthening effect in the center region of the weld and a heat accumulation inhibition effect at the edge of the heat-affected zone, thus achieving synergistic optimization of weld penetration improvement and heat-affected zone control.

2. The welding method according to claim 1, characterized in that: The fluorine-containing active components include one or both of aluminum fluoride and sodium hexafluoroaluminate.

3. The welding method according to claim 1, characterized in that: The mass ratio of anhydrous aluminum trichloride, aluminum fluoride and sodium hexafluoroaluminate is (4-8):(2-5):(0.5-2).

4. The welding method according to claim 1, characterized in that: The anhydrous organic solvent is one or more of anhydrous isopropanol, anhydrous ethanol, and perfluoropolyether.

5. The welding method according to claim 1, characterized in that: The solid content of the surfactant suspension is 15% to 35%.

6. The welding method according to claim 1, characterized in that: The thickness of the surfactant film is 3μm to 20μm.

7. The welding method according to claim 1, characterized in that: The activator film covers 2mm to 8mm on both sides along the center line of the weld.

8. The welding method according to claim 1, characterized in that: The surfactant suspension was prepared under a dry and protected environment with a dew point not higher than -30°C.

9. The welding method according to claim 1, characterized in that: The surfactant suspension is stored in a sealed liquid storage container filled with inert protective gas and transported to the spraying device through a sealed delivery pipeline.

10. The welding method according to claim 1, characterized in that: The welding heat source is a TIG welding heat source, a MIG welding heat source, a laser welding heat source, or a laser-arc hybrid welding heat source.