In-situ quenching friction stir welding device and method

Abstract

The invention provides an in-situ quenching friction stir welding device and method. The device comprises a stirring head assembly, an in-situ quenching mechanism is arranged behind the stirring head assembly, and the in-situ quenching mechanism is used for quenching the friction stir welding seam while scraping the flash on the surface of the friction stir welding seam; the method comprises the steps that the in-situ quenching friction stir welding device is started, the stirring head is driven to rotate and press downwards, the stirring head stays for a set time after being pressed downwards to a target depth, and the main shaft of the friction stir welding machine drives the in-situ quenching friction stir welding device and the rotating stirring head to synchronously move in the welding direction until welding is completed. The method realizes better precipitation of the precipitation strengthening phase in the heat affected zone of the friction stir welding seam, effectively solves the technical problem that homogenization aging treatment is difficult to perform on the friction stir welding seam in the existing scheme, directly quench the welding seam in the friction stir welding process, and remarkably improves the mechanical property and aging stability of the welding seam.

Description

Technical Field

[0001] This invention belongs to the field of friction stir welding technology, specifically relating to an in-situ quenching friction stir welding apparatus and method. Background Technology

[0002] Existing literature CN114799514A discloses a laser oscillation scanning welding method for magnesium-lithium alloys. This method achieves good welding quality by adjusting process parameters such as welding speed, laser power, and shielding gas flow rate, and ensures the stability of the magnesium-lithium alloy weld performance through subsequent solution treatment. However, this method is equivalent to accelerating the aging process of the weld using solution heating, causing the weld to reach the stable state after aging softening prematurely, without actually suppressing the aging softening behavior of the weld. Existing literature CN117483925A discloses a TIG welding process for magnesium-lithium alloys. This method uses TIG welding and post-weld cryogenic treatment to refine the grain structure and promote the precipitation of precipitates during the transition between room temperature and liquid nitrogen temperature, resulting in magnesium-lithium alloy joints with good mechanical properties. However, this method is complex, and it is impossible to predict whether it will suppress the aging softening behavior of the joint.

[0003] Studies have shown that direct quenching on the surface of friction stir welds can improve the mechanical properties of the joint to some extent. However, the existing technical approach to quenching the surface of friction stir welds involves spraying coolant through nozzles, which presents the problem of uneven quenching, and the performance of the welded joint needs further improvement. Summary of the Invention

[0004] At least in order to solve the technical problems mentioned in the background art, the present invention aims to provide an in-situ quenching friction stir welding device and method.

[0005] The present invention adopts the following technical solution.

[0006] An in-situ quenching friction stir welding device includes a stirring head assembly and an in-situ quenching mechanism arranged behind the stirring head assembly. The in-situ quenching mechanism scrapes off the flash on the surface of the friction stir weld while quenching the friction stir weld.

[0007] In this invention, the in-situ quenching mechanism includes a scraper, with a flow channel inside the scraper. The inlet of the flow channel is connected to a coolant supply system via a pipeline, and several flow channel outlets are arranged at intervals on the blade of the scraper.

[0008] In one preferred embodiment of the present invention, the scraper includes a scraper blade, the flow channel outlet is located on the slope behind the blade of the scraper, and two sets of steel rollers are provided on the scraper. The lowest points of the two sets of rollers are at the same horizontal plane as the blade of the scraper, and the distance between the two sets of rollers is 5-10 mm. This design is suitable not only for processing welds in thinned areas but also for processing welds without thinned areas, and it can effectively prevent weld deformation.

[0009] In a second preferred embodiment of the present invention, the scraper includes a scraper blade and a support plate. The scraper blade and the support plate together form a flow channel. The scraper blade is located above the support plate, and the flow channel outlet is located at the bottom of the support plate. A ballpoint pen tip assembly is provided at each flow channel outlet. The diameter of the steel ball in the ballpoint pen tip assembly is 1.2~2mm. When the blade of the scraper moves against the workpiece surface, the steel ball adheres to the workpiece surface and rolls, while the coolant flows from the surface of the steel ball in the ballpoint pen tip assembly to the workpiece surface. This solution effectively solves the technical problem of the existing solution's difficulty in homogenizing the aging treatment of friction stir welds.

[0010] Furthermore, the width of the flow channel outlet is not less than the width of the friction stir weld.

[0011] The method of using the aforementioned in-situ quenching friction stir welding device includes the following steps: Step 1: Prepare the board material to be welded, mechanically grind to remove the oxide film on the surface of the board material, and wipe the surface of the board material with chemical reagents to remove surface oil stains; Step 2: Fix the sheet metal onto the worktable using tooling fixtures, and assemble the in-situ quenching friction stir welding device onto the friction stir welding machine. Step 3: Start the in-situ quenching friction stir welding device, drive the stirring head to rotate and press down, and hold for a set time after pressing down to the target depth. At this time, the blade of the scraper is just in contact with the surface of the plate. The main shaft of the friction stir welding machine drives the in-situ quenching friction stir welding device and the rotating stirring head to move synchronously along the welding direction until the welding is completed. Step 4: Turn off the friction stir welding machine and the in-situ quenching friction stir welding device, remove the welded workpiece and clean it.

[0012] Preferably, during the welding process, the stirring head rotates at a speed of 500-800 rpm, the welding speed is 100-300 mm / min, the shoulder pressure is 0.1-0.2 mm, and the pressure in the flow channel is controlled at 0.2-0.3 MPa.

[0013] Preferably, an airflow nozzle is provided in front of the stirring head assembly, and the airflow nozzle is connected to the compressed air supply system.

[0014] Beneficial effects: This invention not only achieves better precipitation of precipitated strengthening phases in the heat-affected zone of friction stir welds, but also effectively solves the technical problem of difficulty in homogenizing the aging treatment of friction stir welds using existing methods. Furthermore, it enables direct quenching of the weld during the friction stir welding process, significantly improving its mechanical properties and aging stability. Using this invention, in-situ quenching of the weld can be achieved, shortening the residence time of the weld during high-temperature cooling and refining the weld grain structure. On the one hand, this promotes further precipitation of precipitated strengthening phases during welding; on the other hand, the refined grains provide more grain boundaries. These grain boundaries act as a barrier, preventing the metastable precipitated strengthening phases from coarsening and transforming into stable softening phases during aging, thus preserving more of the precipitation strengthening effect introduced by friction stir welding and suppressing softening during aging. When using this invention for friction stir welding, it prevents the coolant from flowing to the front of the stirring head and affecting the unwelded base material, avoiding immediate oxidation of the stirred metal and the phenomenon of incomplete weld formation and filamentous metal distribution. It also acts as a protective gas, reducing weld oxidation. Attached Figure Description

[0015] Figure 1 This is a partial structural diagram of the in-situ quenching friction stir welding device in Example 1; Figure 2 This is a partial structural diagram of the in-situ quenching friction stir welding device in Example 2; Figure 3 for Figure 2 A side view diagram. Detailed Implementation

[0016] The technical solutions 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example 1

[0017] Combination Figure 1As shown, an in-situ quenching friction stir welding device includes a stirring head assembly 1. An in-situ quenching mechanism 2 is arranged behind the stirring head assembly 1. The in-situ quenching mechanism 2 scrapes off the flash on the surface of the friction stir weld while quenching the friction stir weld. In this embodiment, the in-situ quenching mechanism 2 includes a scraper 10. A flow channel 16 is arranged inside the scraper 10. The inlet of the flow channel 16 is connected to a coolant supply system through a pipeline. Several flow channel outlets 11 are arranged at intervals on the blade of the scraper 10. The distance between adjacent flow channel outlets 11 is 5 mm. The width of the flow channel outlet 11 (i.e., the width with the flow channel outlet 11) is not less than the width of the friction stir weld, specifically 30 mm. The flow channel outlet 11 is located on the slope 12 behind the blade of the scraper 10. Two sets of steel rollers 12 are installed on the scraper 10, with the lowest point of the two sets of rollers 12 at the same horizontal plane as the blade of the scraper 10, and the distance between the two sets of rollers 12 is 8mm. An airflow nozzle 3 is also installed in front of the stirring head assembly 1, with the axis of the airflow nozzle 3 intersecting the axis of the stirring head assembly 1, and the airflow nozzle 3 is connected to the compressed air supply system.

[0018] The method of using the in-situ quenching friction stir welding device in this embodiment includes the following steps: Step 1: Prepare the board material to be welded (LAZ933 magnesium-lithium alloy, 4mm thick, 350mm long), remove the oxide film on the surface of the board material by mechanical grinding, and wipe the surface of the board material with chemical reagent (anhydrous ethanol) to remove surface oil. Step 2: Fix the sheet metal onto the worktable using tooling fixtures, and assemble the in-situ quenching friction stir welding device onto the friction stir welding machine. Step 3: Start the in-situ quenching friction stir welding device, set the friction stir welding process parameters (stirring head rotation speed of 600 rpm, welding speed of 150 mm / min, shoulder pressing amount of 0.15 mm, and liquid pressure in the flow channel controlled at 0.25 MPa), drive the stirring head to rotate and press down, and hold for a set time after pressing down to the target depth. At this time, the blade of scraper 10 is just in contact with the surface of the plate. The main shaft of the friction stir welding machine drives the in-situ quenching friction stir welding device and the rotating stirring head to move synchronously along the welding direction until the welding is completed. In this step, turn on the compressed air supply system, and control the compressed air pressure at 0.4 MPa. The compressed air is continuously blown onto the stirring head to prevent the coolant from flowing to the edge of the stirring head. Step 4: Turn off the friction stir welding machine and the in-situ quenching friction stir welding device, remove the welded workpiece 4 and clean it.

[0019] In the friction stir welding process, the blade of the scraper 10 scrapes away the weld flash in time, and the weld flash moves along the top surface of the scraper 10. At the same time, the small liquid particles (droplets formed by coolant) flowing out through the flow channel outlet 11 directly act on the surface of the workpiece 4 behind the stirring head assembly 1, and also directly act on the surface of the workpiece 4 at the location of the weld flash, so as to perform in-situ quenching of the welding area in time, effectively avoiding the droplets directly acting on the surface of the weld flash and affecting the strengthening of the heat-affected zone of the friction stir weld. Example 2

[0020] Combination Figure 2 and Figure 3 As shown, an in-situ quenching friction stir welding device includes a stirring head assembly 1. An in-situ quenching mechanism 2 is located behind the stirring head assembly 1. The in-situ quenching mechanism 2 scrapes away the flash on the surface of the friction stir weld while simultaneously quenching the weld. In this embodiment, the in-situ quenching mechanism 2 includes a scraper 10. A flow channel is provided inside the scraper 10. The flow channel inlet is connected to a coolant supply system via a pipeline. Several flow channel outlets 11 are spaced apart on the blade of the scraper 10. The distance between adjacent flow channel outlets 11 is 2 mm. The width of the flow channel outlets 11 (i.e., the width with flow channel outlets 11) is not less than the width of the friction stir weld, specifically 30 mm. The scraper 10 includes a scraper blade 14 and a support plate 15. The scraper blade 14 and the support plate 15 together form a flow channel 16. The scraper blade 14 is located above the support plate 15, and the flow channel outlet 11 is located at the bottom of the support plate 15. A ballpoint pen tip assembly 13 is provided at each flow channel outlet 11. The diameter of the steel ball 13 in the ballpoint pen tip assembly is 2mm. When the blade of the scraper 10 moves against the surface of the workpiece 4, the steel ball 13 adheres to the surface of the workpiece 4 and rolls, and the coolant flows from the surface of the steel ball 13 of the ballpoint pen tip assembly to the surface of the workpiece 4. An airflow nozzle 3 is also provided in front of the stirring head assembly 1. The airflow nozzle 3 is connected to the compressed air supply system.

[0021] The method of using the in-situ quenching friction stir welding device in this embodiment includes the following steps: Step 1: Prepare the board material to be welded (LAZ933 magnesium-lithium alloy, 4mm thick, 350mm long), remove the oxide film on the surface of the board material by mechanical grinding, and wipe the surface of the board material with chemical reagent (anhydrous ethanol) to remove surface oil. Step 2: Fix the sheet metal onto the worktable using tooling fixtures, and assemble the in-situ quenching friction stir welding device onto the friction stir welding machine. Step 3: Start the in-situ quenching friction stir welding device, set the friction stir welding process parameters (stirring head rotation speed of 600 rpm, welding speed of 150 mm / min, shoulder pressing amount of 0.15 mm, and liquid pressure in the flow channel controlled at 0.25 MPa), drive the stirring head to rotate and press down, and hold for a set time after pressing down to the target depth. At this time, the blade of scraper 10 is just in contact with the surface of the plate. The main shaft of the friction stir welding machine drives the in-situ quenching friction stir welding device and the rotating stirring head to move synchronously along the welding direction until the welding is completed. In this step, turn on the compressed air supply system, and control the compressed air pressure at 0.4 MPa. The compressed air is continuously blown onto the stirring head to prevent the coolant from flowing to the edge of the stirring head. Step 4: Turn off the friction stir welding machine and the in-situ quenching friction stir welding device, remove the welded workpiece 4 and clean it.

[0022] In the friction stir welding process, the blade of the scraper 10 scrapes away the weld flash in time, and the weld flash moves along the top surface of the scraper 10. At the same time, the coolant overflowing from the flow channel outlet 11 directly scratches the surface of the workpiece 4 behind the stirring head assembly 1 (similar to the action of writing with a pen), and also directly scratches the surface of the workpiece 4 at the location of the weld flash, so as to perform in-situ quenching of the welding area in time, and avoid the coolant directly acting on the surface of the weld flash, which would affect the strengthening of the heat-affected zone of the friction stir weld.

[0023] In the schemes of Embodiments 1 and 2, one of the inventive concepts is that while scraping off the weld burrs online with a scraper, the coolant is precisely applied to the workpiece surface near the stirring head assembly in a splash-free manner. This not only achieves better precipitation of the strengthening phase in the weld area, but also achieves better precipitation of the strengthening phase in the heat-affected zone of the friction stir weld. At the same time, it can effectively prevent the coolant from flowing along the weld towards the front of the stirring head assembly, effectively solving the technical problem that the existing scheme is difficult to perform homogenization aging treatment on the friction stir weld.

[0024] Compared to Example 1, the difference lies in the following: a six-hole nozzle is directly used instead of the in-situ quenching mechanism 2 in Example 1. The six-hole nozzle is connected to an external coolant supply system. During the welding process, the distance between the six-hole nozzle and the surface of the workpiece 4 is controlled at 3mm. In step 3, the compressed air supply system is simultaneously turned on, and the pressure of the compressed air is controlled at 0.4MPa. During the welding process, on the one hand, coolant is sprayed onto the weld surface through the six-hole nozzle, and on the other hand, compressed air is continuously blown onto the stirring head to prevent coolant from flowing to the edge of the stirring head. Example 3

[0025] Referring to Embodiment 2, the difference from Embodiment 2 is that: the plate thickness is 3mm; the stirring head rotation speed is 700rpm, the welding speed is 200mm / min, the shoulder pressing amount is 0.1mm, and the liquid pressure in the flow channel is controlled at 0.25Mpa; in step 3, the compressed air supply system is kept closed.

[0026] The weld samples from Examples 1, 2, and the comparative examples were tested, and the results are as follows.

[0027] The weld interior of the sample in Example 1: α phase size 4.8 μm, maximum grain size 7.1 μm, minimum grain size 2.0 μm; β phase size 6.64 μm, maximum grain size 9.8 μm, minimum grain size 4.5 μm; Heat-affected zone of sample in Example 1: α phase size 13.1 μm, maximum grain size 15.3 μm, minimum grain size 11.1 μm; β phase size 11.3 μm, maximum grain size 14.2 μm, minimum grain size 8.7 μm; The post-weld strength of the sample in Example 1 was 258.2 MPa, and the strength after aging stabilization was 239.6 MPa. The weld interior of the sample in Example 2: α phase size 3.9 μm, maximum grain size 5.1 μm, minimum grain size 1.7 μm; β phase size 5.5 μm, maximum grain size 6.8 μm, minimum grain size 3.9 μm; Heat-affected zone of sample in Example 2: α phase size 12.0 μm, maximum grain size 12.9 μm, minimum grain size 9.1 μm; β phase size 9.8 μm, maximum grain size 11.3 μm, minimum grain size 9.0 μm; The post-weld strength of the sample in Example 1 was 264.8 MPa, and the strength after aging stabilization was 253.0 MPa. The weld interior of the sample in Comparative Example 1: α phase size 5.3 μm, maximum grain size 7.5 μm, minimum grain size 3.3 μm; β phase size 7.2 μm, maximum grain size 9.8 μm, minimum grain size 4.8 μm; The heat-affected zone of the sample in Comparative Example 1: α phase size 18.6 μm, maximum grain size 23.7 μm, minimum grain size 14.8 μm; β phase size 15.7 μm, maximum grain size 19.3 μm, minimum grain size 11.2 μm; The post-weld strength of the sample in Comparative Example 1 was 245.0 MPa, and the strength after aging stabilization was 202.6 MPa.

[0028] The results show that Example 2 has the best quenching uniformity and homogenization aging treatment effect for friction stir welds (including their heat-affected zones). Example 1 also has a relatively good quenching uniformity and homogenization aging treatment effect for friction stir welds. However, in comparison, only the weld itself has a relatively good aging treatment effect for friction stir welds in Example 1, while the aging treatment effect of the heat-affected zone of the weld, especially the uniformity, is poor.

[0029] Using the schemes of Examples 1-3, the weld can be directly quenched during the friction stir welding process, significantly improving its mechanical properties and aging stability. This enables online quenching of the weld, shortening the residence time of the weld during high-temperature cooling, and refining the weld grain structure. On the one hand, this promotes further precipitation of the strengthening phase during welding; on the other hand, the refined grains provide more grain boundaries. These grain boundaries act as a barrier, preventing the metastable strengthening phase from coarsening and transforming into a stable softening phase during aging. This preserves more of the precipitation strengthening effect introduced by friction stir welding and suppresses softening during aging. When using the schemes of Examples 1-3 for friction stir welding, the coolant flow to the front of the stirring head can be prevented from affecting the unwelded base material. This avoids immediate oxidation of the stirred metal and the phenomenon of an incomplete weld with a filamentous metal distribution. Simultaneously, it can also act as a protective gas, reducing weld oxidation. Example 4

[0030] The method of using the in-situ quenching friction stir welding device in Example 2 includes the following steps: Step 1: Prepare the plate to be welded (AZ91D magnesium alloy, 4mm thick, 350mm long), remove the oxide film on the surface of the plate by mechanical grinding, and wipe the surface of the plate with chemical reagent (anhydrous ethanol) to remove surface oil. Step 2: Fix the sheet metal onto the worktable using tooling fixtures, and assemble the in-situ quenching friction stir welding device onto the friction stir welding machine. Step 3: Start the in-situ quenching friction stir welding device, set the friction stir welding process parameters (stirring head rotation speed of 550 rpm, welding speed of 180 mm / min, shoulder pressing amount of 0.1 mm, and liquid pressure in the flow channel controlled at 0.25 MPa), drive the stirring head to rotate and press down, and hold for a set time after pressing down to the target depth. At this time, the blade of scraper 10 is just in contact with the surface of the plate. The main shaft of the friction stir welding machine drives the in-situ quenching friction stir welding device and the rotating stirring head to move synchronously along the welding direction until the welding is completed. In this step, turn on the compressed air supply system, and control the pressure of the compressed air at 0.4 MPa. The compressed air is continuously blown onto the stirring head to prevent the coolant from flowing to the edge of the stirring head. Step 4: Turn off the friction stir welding machine and the in-situ quenching friction stir welding device, remove the welded workpiece 4 and clean it.

[0031] The weld samples in Example 4 were tested, and the results were as follows: the average grain size inside the weld was 1.7 μm, the maximum grain size was 2.5 μm, and the minimum grain size was 0.4 μm; the average grain size in the heat-affected zone of the weld was 8.9 μm, the maximum grain size was 10.3 μm, and the minimum grain size was 7.5 μm; and the tensile strength of the joint sample was 279.6 MPa.

[0032] The method of using the in-situ quenching friction stir welding device in Example 2 differs from that in Example 2 in that: for 6061 aluminum alloy, the plate thickness is 3.5mm; the stirring head rotation speed is 720rpm, the welding speed is 160mm / min, the shoulder pressing amount is 0.1mm, and the liquid pressure in the flow channel is controlled at 0.25Mpa.

Claims

1. An in-situ quenching friction stir welding device, comprising a stirring head assembly (1), characterized in that: An in-situ quenching mechanism (2) is provided behind the stirring head assembly (1). The in-situ quenching mechanism (2) scrapes off the flash on the surface of the friction stir weld while quenching the friction stir weld.

2. The in-situ quenching friction stir welding device according to claim 1, characterized in that: The in-situ quenching mechanism (2) includes a scraper (10), and a flow channel (16) is provided inside the scraper (10). The inlet of the flow channel (16) is connected to the coolant supply system through a pipeline. Several flow channel outlets (11) are arranged at intervals on the blade of the scraper (10).

3. The in-situ quenching friction stir welding apparatus according to claim 2, characterized in that: The scraper (10) includes a scraper blade (14), and the flow channel outlet (11) is located on the slope (12) behind the blade of the scraper (10). Two sets of steel rollers (12) are provided on the scraper (10). The low point of the two sets of rollers (12) is on the same horizontal plane as the blade of the scraper (10), and the distance between the two sets of rollers (12) is 5-10mm.

4. The in-situ quenching friction stir welding apparatus according to claim 2, characterized in that: The scraper (10) includes a scraper blade (14) and a support plate (15). The scraper blade (14) and the support plate (15) together form a flow channel (16). The scraper blade (14) is located above the support plate (15), and the flow channel outlet (11) is located at the bottom of the support plate (15). A ballpoint pen tip assembly (13) is provided at each flow channel outlet (11). The diameter of the steel ball (13) of the ballpoint pen tip assembly is 1.2~2mm. When the blade of the scraper (10) moves against the surface of the workpiece (4), the steel ball (13) is against the surface of the workpiece (4) and rolls. The coolant flows from the surface of the steel ball (13) of the ballpoint pen tip assembly to the surface of the workpiece (4).

5. The in-situ quenching friction stir welding apparatus according to any one of claims 2-4, characterized in that: The width of the flow channel outlet (11) is not less than the width of the friction stir weld.

6. The method of using the in-situ quenching friction stir welding apparatus as described in any one of claims 2-5, characterized in that, step include: Step 1: Prepare the board material to be welded, mechanically grind to remove the oxide film on the surface of the board material, and wipe the surface of the board material with chemical reagents to remove surface oil stains; Step 2: Fix the sheet metal onto the worktable using tooling fixtures, and assemble the in-situ quenching friction stir welding device onto the friction stir welding machine. Step 3: Start the in-situ quenching friction stir welding device, drive the stirring head to rotate and press down, press down to the target depth and stay for a set time. At this time, the blade of the scraper (10) is just touching the surface of the plate. The main shaft of the friction stir welding machine drives the in-situ quenching friction stir welding device and the rotating stirring head to move synchronously along the welding direction until the welding is completed. Step 4: Turn off the friction stir welding machine and the in-situ quenching friction stir welding device, remove the welded workpiece and clean it.

7. The method of use according to claim 6, characterized in that: During the welding process, the stirring head rotates at 500-800 rpm, the welding speed is 100-300 mm / min, the shoulder pressure is 0.1-0.2 mm, and the pressure in the flow channel is controlled at 0.2~0.3 MPa.

8. The method of use according to claim 7, characterized in that: An airflow nozzle (3) is also provided in front of the stirring head assembly (1), and the airflow nozzle (3) is connected to the compressed air supply system.

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