Friction welding stirring head structure with adjustable friction coefficient and preparation method thereof

Abstract

The invention belongs to the technical field of friction stir welding, and relates to a friction welding stir head structure with an adjustable friction coefficient and a preparation method thereof. The friction welding stirring head structure comprises a shaft shoulder and a stirring needle connected to the lower portion of the shaft shoulder. The exterior of the stirring needle is plated with a thin film to form a plurality of composite friction units; each composite friction unit comprises a high-friction-coefficient area and a low-friction-coefficient area, and the high-friction-coefficient areas and the low-friction-coefficient areas alternate with each other. Under the conditions of the same or similar rotating speed, pressure and feeding speed, a proper composite friction coefficient stirring head is made according to different welding materials, the situation that welding parameters need to be greatly adjusted when the welding materials are replaced every time is avoided, equipment stably works within a certain range to a certain extent, and the stability and the working efficiency of the equipment are improved. The low-friction-coefficient area has high hardness, good wear resistance and a smooth surface, adhesion is prevented, the welding quality is improved, and meanwhile the phenomena that the temperature is too high and distribution is not uniform in the welding process are reduced.

Description

Technical Field

[0001] This invention belongs to the field of friction stir welding technology, specifically relating to a friction welding stirring head structure with adjustable friction coefficient and its preparation method. Background Technology

[0002] Unlike traditional fusion welding methods, friction stir welding keeps the material in a solid state throughout the welding process and does not undergo a melting process. Therefore, it fundamentally avoids common welding defects in fusion welding, such as porosity, cracks, slag inclusions and other metallurgical problems.

[0003] This technology involves inserting a high-speed rotating stirring head into the workpiece to be welded. The frictional heat between the stirring head and the workpiece softens the material to a plastic state, and the metallurgical bonding is achieved under the mechanical stirring action of the stirring pins. Because the welding temperature is below the material's melting point, it is particularly suitable for joining lightweight, high-strength materials such as aluminum alloys and magnesium alloys, which are difficult to weld using traditional fusion welding methods, as well as for joining dissimilar materials.

[0004] In the aerospace field, friction stir welding has been successfully applied to the manufacture of critical load-bearing structures such as rocket fuel tanks, aircraft skin panels, and fuselage frames. In the automotive industry, this technology is used for lightweight vehicle body design, chassis structural component connections, and the manufacture of battery pack housings for new energy vehicles. Furthermore, it shows broad application prospects in rail transportation, shipbuilding, and electronic packaging.

[0005] However, friction stir welding (FSW) technology still faces many challenges in practical applications. During FSW, the coefficient of friction of the stirring head varies relatively little within a certain temperature range, and different welding materials require different process parameters. Changing welding materials during the welding process necessitates adjusting parameters such as rotation speed, feed rate, and downward pressure to obtain optimized process parameters for the new material, thereby optimizing the temperature distribution during stirring and achieving a high-quality joint. Furthermore, once the coefficient of friction reaches a certain value, severe welding material adhesion occurs during stirring, which also affects the joint quality. These factors limit the efficiency and quality of FSW. Summary of the Invention

[0006] The purpose of this invention is to provide a friction welding stirring head structure with adjustable friction coefficient and its preparation method, which solves the problem that existing friction welding stirring heads require parameter readjustment after changing welding materials, resulting in low efficiency and limitations.

[0007] This invention is achieved through the following technical solution: This invention discloses a friction welding stirring head structure with adjustable friction coefficient, including a shoulder and a stirring pin connected below the shoulder; The stirring needle is coated with a thin film to form multiple composite friction units; Each composite friction unit includes a high friction coefficient region and a low friction coefficient region, which alternate with each other.

[0008] Furthermore, two adjacent compound friction units are separated by threads, and the number of cycles of the compound friction unit is N, where N≥1.

[0009] Furthermore, the thin film deposited in the low friction coefficient region is a tetrahedral amorphous carbon thin film; The high friction coefficient region is the substrate or other film layer with a friction coefficient greater than that of tetrahedral amorphous carbon film.

[0010] This invention also discloses a method for preparing a friction welding stirring head structure with an adjustable friction coefficient, comprising the following steps: S1. Polish the stirring head. During the polishing process, with the end face of the stirring needle facing the direction of abrasive spray, the surface finish of the front area of ​​the thread top is higher than that of the back area. S2. With the head of the stirring needle facing the ion deposition direction, a bias voltage is applied. The film layer will be deposited more on the front side of the threaded top of the stirring needle and less on the back side, resulting in film layer B. The friction coefficient of film layer B is f2. S3. After removing the stirring head, peel it in the stripping liquid. The film layer B on the front area of ​​the thread top is retained, while the film layer B on the back area is detached, thus exposing the substrate on the back area of ​​the thread top, resulting in alternating high friction coefficient areas and low friction coefficient areas.

[0011] Furthermore, prior to S1, a film A with a friction coefficient of f1 is deposited on the surface of the stirring head; Polishing the stirring head, with the end face of the stirring needle facing the direction of abrasive spraying during the polishing process, results in a surface finish of film layer A on the front side of the thread top being higher than that on the back side. In S3, the film layer B on the front area of ​​the thread top is retained, while the film layer B on the back area is detached, thus exposing the film layer A on the back area of ​​the thread top, resulting in a stirring head structure with alternating friction coefficients f1 and f2.

[0012] Furthermore, before S1, the stirring head is ultrasonically cleaned with deionized water, cleaning solution, and alcohol, and then dried.

[0013] Further, after polishing S1, the parts are cleaned and dried.

[0014] Furthermore, the drying process specifically involves maintaining the temperature at 50-150℃ for 1-20 hours.

[0015] Furthermore, the coating methods for the film include magnetron sputtering, pulsed laser deposition, multi-arc ion plating or filtered cathode vacuum arc, and chemical vapor deposition.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects: This invention discloses a friction welding stirring head structure with adjustable friction coefficient. A composite friction coefficient is obtained by depositing thin films with different friction coefficients in different areas of the stirring head. This composite friction coefficient can be adjusted by changing the coating material. This allows for the creation of a suitable composite friction coefficient stirring head based on different welding materials under similar or identical rotational speed, pressure, and feed rate conditions. This avoids significant adjustments to welding parameters each time welding materials are changed, enabling the equipment to operate stably within a certain range and improving equipment stability and efficiency. The stirring head has high and low friction coefficient regions. The low friction coefficient region has a high hardness, good wear resistance, and a smooth surface, preventing adhesion and improving welding quality. It also reduces excessively high temperatures and uneven temperature distribution during welding. The high friction coefficient region is mainly used for frictional heat generation. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the stirring head structure; Figure 2 SEM image of the prepared stirring head after welding; Figure 1 In the middle: 01, shoulder; 02, stirring pin; 1, low friction coefficient area; 2, thread top; 3, high friction coefficient area. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the present invention clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of the present invention, and not all of them.

[0019] The detailed description of the embodiments of the present invention provided in the following drawings is not intended to limit the scope of the claimed invention, but merely to illustrate one selected embodiment. All other embodiments obtained by those skilled in the art based on the drawings and embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0020] This invention provides a friction welding stirring head structure with an adjustable friction coefficient. By adjusting the composite friction coefficient of the stirring head, stirring head products can be obtained for different welding material conditions. Under the same or similar process parameters, optimized welding conditions can be achieved simply by changing the corresponding stirring head. Simultaneously, in the composite friction coefficient stirring head, the low friction coefficient region 1 exhibits less welding material adhesion, further improving welding quality.

[0021] This invention provides a friction welding stirring head structure with an adjustable coefficient of friction, such as... Figure 1 As shown, the stirring head is divided into a shoulder 01 and a stirring pin 02. A thin film with a certain coefficient of friction is deposited on the surfaces of the shoulder 01 and the stirring pin 02 through a coating process. The surface of the stirring pin 02 has multiple composite friction units with alternating coefficients of friction from its tip to its tail.

[0022] like Figure 1 and Figure 2 As shown, each composite friction unit includes a high friction coefficient region 3 and a low friction coefficient region 1. By adjusting the friction coefficients and width ratio of the high friction coefficient region 3 and the low friction coefficient region 1, a stirring head with a certain composite friction coefficient is obtained. The adjustment is mainly based on the melting point, thermal conductivity, and adhesion of the welding material to the stirring head. Furthermore, the adjustment is also based on the quality of the weld joint.

[0023] The outer surface of the stirring pin 02 is pre-machined with threads, and adjacent composite friction units are separated by the threads. The number of cycles of the composite friction unit is N, where N≥1. The thread width of the stirring pin 02 affects the area width of the composite friction unit.

[0024] The present invention also provides a method for preparing the friction welding stirring head structure with adjustable friction coefficient, comprising the following steps: Polishing: Polishing is carried out perpendicular to the end face of the stirring needle 02 by means of sandblasting, abrasive flow, etc., to produce different polishing effects on the front and back areas of the thread top 2, that is, the surface of the film layer A on the front side has a high smoothness, while the surface of the film layer A on the back side has a low smoothness.

[0025] After polishing, clean with alcohol, deionized water, etc., and then keep warm in an oven at 50-150℃ for 1-20 hours.

[0026] Coating: With the head of the stirring pin 02 facing the ion deposition direction, a certain bias voltage is applied. Due to the difference in electric field line distribution between the front and back sides of the thread tip 2, more film is deposited on the front side and less on the back side. This further forms regions with different friction coefficients. By adjusting the process parameters, the film thickness is controlled to obtain film B. After removing the stirring head, it is left to stand in a certain stripping solution for a certain period of time or subjected to ultrasonic treatment. The film layer on the front side of the stirring head is retained and has a friction coefficient f2. Due to the action of the stripping solution, the film layer B on the back side is detached, thus exposing the substrate.

[0027] To control the coefficient of friction more flexibly, the present invention also designed a first coating before polishing: through the coating process, a film layer A with a friction coefficient of f1 is coated on the surface of the stirring head, and finally a stirring head structure with alternating friction coefficients of f1 and f2 is obtained.

[0028] The coating methods for films include magnetron sputtering, pulsed laser deposition (PLD), multi-arc ion plating, filtered cathode vacuum arc (FCVA), and chemical vapor deposition.

[0029] During the second coating process, the difference in smoothness between the front and back sides leads to differences in the quality and adhesion of the film layer B deposited on the front and back sides, so the film layer B on the back side is prone to peeling off.

[0030] Using the top 2 of the thread as the dividing line, the area facing the direction of abrasive spraying is the front area, and the area on the other side facing away from the direction of abrasive spraying is the back area.

[0031] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0032] Example 1 Select a static shaft shoulder stirring head. The stirring needle 02 is 5mm long, 5mm in diameter at the tail, and 4mm in diameter at the tip. The stirring needle 02 has threads on its side, with a height difference of 1.5mm between the bottom and top of the threads.

[0033] Step 1: Polish the mixing head using a sandblasting and polishing equipment. During the polishing process, the end face of the mixing needle 02 should be directly facing the direction of abrasive spraying, and the angle between the normal direction of the end face and the direction of abrasive spraying should be less than 30°. Polishing time is 5 minutes. The second step involves ultrasonic cleaning with acetone, alcohol, and deionized water for 10 minutes, followed by incubation at 80°C in a drying oven for 5 hours. Step 3: Place the stirring head into the FCVA coating equipment, with the end face of the stirring pin 02 facing the ion incident direction, and coat a tetrahedral amorphous carbon (ta-C) thin film for 1 hour.

[0034] Step 4: After coating is completed, remove the stirring head and let it stand in the stripping solution for 1 hour. The ta-C film layer on the front area of ​​the thread top 2 and the ta-C film layer on the back area will fall off, thereby exposing the substrate on the back area of ​​the thread top 2, and obtaining a composite friction coefficient stirring head with alternating areas of high friction coefficient (substrate) and low friction coefficient (ta-C).

[0035] Example 2 Select a moving shoulder stirring head. The diameter of the shoulder 01 of the stirring head is 9mm, the length of the stirring needle 02 is 4mm, the diameter of the tail is 4mm, the diameter of the tip is 3mm, and the side of the stirring needle 02 has threads with a height difference of 1mm between the bottom and top of the thread.

[0036] Step 1: Clean the stirring head with deionized water using ultrasonic cleaning for 10 minutes, and then keep it at 80℃ in a drying oven for 1 hour; The second step is to use a sandblasting and polishing device to polish the mixing head for 5 minutes. The third step is to ultrasonically clean the product with acetone, alcohol and deionized water for 10 minutes, and then keep it at 80°C in a drying oven for 5 hours. Step 4: Deposit a CrN thin film in a magnetron sputtering coating equipment for 60 minutes with a nitrogen flow rate of 1 sccm, so that the entire O2 area of ​​the stirring needle is coated with a CrN thin film with a coating thickness of 2 μm.

[0037] Step 5: Use sandblasting and polishing equipment to polish the stirring head after the CrN film is coated. During the polishing process, the end face of the stirring needle 02 is facing the direction of the abrasive spray, and the angle between the normal direction of the end face and the direction of the abrasive spray is less than 30°. The polishing time is 5 minutes. Then the surface smoothness of the CrN film on the front area of ​​the thread top 2 is higher than that of the CrN film on the back area. Step 6: Place the stirring head into the FCVA device, with the end face of the stirring pin 02 facing the ion incident direction, and deposit a ta-C thin film. The deposition time is 1 hour and the bias voltage is 200V. The film layer will be deposited more on the front side of the thread top 2 of the stirring pin 02 and less on the back side, thus obtaining a ta-C thin film. Step 7: After coating is completed, remove the stirring head and perform ultrasonic peeling in the stripping solution. The ta-C film on the front side of the thread top 2 is retained, while the ta-C film on the back side is detached, thereby exposing the CrN film on the back side of the thread top 2, and obtaining a composite friction coefficient stirring head with alternating regions of high friction coefficient (CrN) and low friction coefficient (ta-C).

[0038] SEM analysis was performed on the composite friction coefficient stirring head prepared in this embodiment after welding and use, and the results were as follows: Figure 2 The SEM image shown shows that region 1, with a low coefficient of friction, is located on the front side of the thread tip 2, while region 3, with a high coefficient of friction, is located on the back side of the thread tip 2. Region 1 has a relatively smooth surface with no adhesion, while region 3 has adhesion. Figure 2 The white substance on region 3, which has a medium to high coefficient of friction, is adhesive welding material.

[0039] Example 3 Select a moving shoulder stirring head. The diameter of the shoulder 01 of the stirring head is 9mm, the length of the stirring needle 02 is 4mm, the diameter of the tail is 4mm, the diameter of the tip is 3mm, and the side of the stirring needle 02 has threads with a height difference of 1mm between the bottom and top of the thread.

[0040] Step 1: Clean the stirring head with deionized water using ultrasonic cleaning for 10 minutes, and then keep it at 80℃ in a drying oven for 1 hour; The second step is to use a sandblasting and polishing device to polish the mixing head for 5 minutes. The third step is to ultrasonically clean the product with acetone, alcohol and deionized water for 10 minutes, and then keep it at 80°C in a drying oven for 5 hours. Step 4: Deposit a CrN thin film in the FCVA coating equipment for 30 minutes with a nitrogen flow rate of 2 sccm. The stirring head is mounted on a support of a rotating disk. The disk revolves around the center of the disk, while the stirring head rotates along its own axis. This ensures that the entire O2 area of ​​the stirring pin is coated with a CrN thin film with a thickness of 2 μm. The bias voltage is 500V.

[0041] Step 5: Use polishing equipment to polish the stirring head after the CrN film is deposited. During the polishing process, polish the end face of the stirring pin 02 directly. The angle between the normal direction of the end face and the polishing direction is less than 30°. The polishing time is 5 minutes. Then the surface smoothness of the CrN film on the front area of ​​the thread top 2 is higher than that of the CrN film on the back area. Step 6: Change the position of the stirring head in the FCVA equipment so that the end face of the stirring pin 02 faces the ion incident direction, and deposit a ta-C thin film. The deposition time is 1 hour and the bias voltage is 200V. The film layer will be deposited more on the front area of ​​the thread top 2 of the stirring pin 02 and less on the back area, thus obtaining a ta-C thin film. Step 7: After the final coating is completed, remove the stirring head and perform ultrasonic peeling in the stripping solution. The ta-C film on the front side of the thread top 2 is retained, while the ta-C film on the back side is detached, thereby exposing the CrN film on the back side of the thread top 2, and obtaining a composite friction coefficient stirring head with alternating regions of high friction coefficient (CrN) and low friction coefficient (ta-C).

[0042] CrN films can also be replaced by other films with a friction coefficient greater than that of ta-C films.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the present invention.

Claims

1. A friction welding stirring head structure with adjustable friction coefficient, characterized in that, Includes a shoulder (01) and a stirring needle (02) connected below the shoulder (01); The stirring needle (02) is coated with a thin film to form multiple composite friction units; Each composite friction unit includes a high friction coefficient region (3) and a low friction coefficient region (1), which alternate with each other.

2. The friction welding stirring head structure with adjustable friction coefficient according to claim 1, characterized in that, Two adjacent compound friction units are separated by threads, and the number of cycles of the compound friction unit is N, where N≥1.

3. The friction welding stirring head structure with adjustable friction coefficient according to claim 1, characterized in that, The film deposited in the low friction coefficient region (1) is a tetrahedral amorphous carbon film; The high friction coefficient region (3) is a substrate or other film layer with a friction coefficient greater than that of tetrahedral amorphous carbon film.

4. A method for preparing a friction welding stirring head structure with an adjustable friction coefficient as described in any one of claims 1-3, characterized in that, Includes the following steps: S1. Polish the stirring head. During the polishing process, the end face of the stirring needle (02) is facing the direction of the abrasive spray. The surface finish of the front area of ​​the thread top (2) is higher than that of the back area. S2. With the head of the stirring needle (02) facing the ion deposition direction, a bias voltage is applied. The film layer will be deposited more in the front area of ​​the thread top (2) of the stirring needle (02) and less in the back area, resulting in film layer B. The friction coefficient of film layer B is f2. S3. After removing the stirring head, peel it in the stripping liquid. The film layer B in the front area of ​​the thread top (2) is retained, and the film layer B in the back area is detached, thereby exposing the substrate in the back area of ​​the thread top (2), thus obtaining the alternating high friction coefficient area (3) and low friction coefficient area (1).

5. The method for preparing a friction welding stirring head structure with adjustable friction coefficient according to claim 4, characterized in that, Before S1, a film layer A with a friction coefficient of f1 is deposited on the surface of the stirring head; Polishing the stirring head, with the end face of the stirring needle (02) facing the direction of abrasive spraying during the polishing process, the surface finish of the film layer A in the front area of ​​the thread top (2) is higher than that of the film layer A in the back area. In S3, the film layer B in the front area of ​​the thread top (2) is retained, while the film layer B in the back area is detached, thereby exposing the film layer A in the back area of ​​the thread top (2), resulting in a stirring head structure with alternating friction coefficients f1 and f2.

6. The method for preparing a friction welding stirring head structure with adjustable friction coefficient according to claim 4, characterized in that, Before S1, the stirring head is ultrasonically cleaned with deionized water, cleaning solution, and alcohol, and then dried.

7. The method for preparing a friction welding stirring head structure with adjustable friction coefficient according to claim 4, characterized in that, After polishing with S1, the surface is cleaned and dried.

8. The method for preparing a friction welding stirring head structure with adjustable friction coefficient according to claim 7, characterized in that, The drying process specifically involves maintaining the temperature at 50-150℃ for 1-20 hours.

9. The method for preparing a friction welding stirring head structure with adjustable friction coefficient according to claim 4, characterized in that, The coating methods for the film include magnetron sputtering, pulsed laser deposition, multi-arc ion plating or filtered cathode vacuum arc, and chemical vapor deposition.

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