A split-type friction stir welding tool and a welding method for weakening joint texture.

Abstract

This invention provides a split-type friction stir welding fixture and a welding method for weakening joint texture. It solves the technical problem in traditional friction stir welding of metallic materials where the concentrated grain orientation and high texture strength at the joint lead to inconsistent deformation in different areas of the joint during tensile testing, thus impairing the tensile performance of the joint. The invention provides a split-type friction stir welding fixture with an outer stirring head and an inner stirring head. The outer stirring head has a central stirring chamber, and the inner stirring head is located within the stirring chamber. The outer and inner stirring heads can move relatively independently. The lower end face of the inner stirring head has a concentric annular groove, and the outer stirring head has a concave lower end face with a vortex groove. Simultaneously, this invention provides a welding method for weakening joint texture using a split-type friction stir welding fixture. This invention can be widely applied in the field of friction stir welding technology.

Description

Technical Field

[0001] This invention belongs to the field of welding technology, and more specifically, relates to a split-type friction stir welding tool and a welding method for weakening joint texture. Background Technology

[0002] Friction stir welding (FSW) is a highly efficient solid-state welding technology invented by the Welding Institute in the UK in 1991. During the welding process, the welding machine drives the welding tool to rotate at high speed and penetrate into the material to be welded, and advance along a predetermined trajectory. During this process, the welding tool and the material to be welded undergo frictional shearing, generating a large amount of heat, which causes the material to reach a thermoplastic state and flow under the shearing action of the welding tool. Under the upsetting action of the shoulder, a continuous and dense weld is formed.

[0003] As a solid-state welding method, friction stir welding effectively avoids defects such as porosity, inclusions, and hot cracking that are prone to occur in fusion welding of materials such as aluminum alloys and magnesium alloys. Therefore, it has been widely used in aerospace, weaponry, and transportation fields. However, in the conventional friction stir welding of close-packed hexagonal metal materials such as magnesium alloys and α-type titanium alloys, the relatively simple and regular flow behavior of thermoplastic metals leads to a strong texture phenomenon in the stirring zone. In this process, the grain basal planes are distributed around the side surface of the stirring pin. This grain orientation causes uneven deformation in different areas of the joint during tensile testing, and the metal in some areas yields prematurely, resulting in strain concentration and thus impairing the tensile performance of the joint. Secondly, in conventional friction stir welding, due to the presence of shoulder pressure, some thermoplastic metal will overflow during welding, resulting in a certain amount of weld thinning. Especially for welding thin plates, the reduction in the thickness of the welded area will seriously impair the load-bearing capacity of the joint, thus exhibiting certain limitations.

[0004] Patent CN203003336 discloses a retractable friction stir welding spindle head with differential rotation of the stirring pin and the shoulder. It solves the technical problem of weld overheating affecting welding quality in the prior art by controlling the differential rotation of the shoulder and the stirring pin. However, when applied to welding close-packed hexagonal metal materials such as magnesium alloys and α-type titanium alloys, since the shoulder and the stirring pin rotate in the same direction, it does not fundamentally change the flow behavior of thermoplastic materials during welding. The concentrated distribution of grain orientation and strong texture phenomenon are not significantly improved, and the mechanical properties of the joint are still low.

[0005] Patent CN111618420A discloses a method and equipment for weakening the texture of magnesium alloy friction stir welded joints. It uses a static shoulder friction stir welding tool to improve the symmetry of the joint structure and uses pulsed current to promote the dynamic recrystallization process of the joint structure, thereby randomizing the grain orientation and weakening the joint texture strength. However, this method does not fundamentally change the metal flow behavior during the welding process, so the effect of weakening the texture strength is limited, and the process is complex and the equipment cost is high.

[0006] Patent CN101890572B discloses a friction stir welding method in which the stirring pin and the shoulder rotate in opposite directions. This method improves the asymmetry of the joint's microstructure and properties, thereby enhancing its mechanical properties, by applying opposing driving forces to the materials being welded. However, due to the presence of the stirring pin, the material flow at the bottom of the weld is primarily influenced by its rotation. The reverse rotation of the shoulder cannot effectively alter the material flow behavior at the bottom of the weld, thus limiting its effect on improving the texture strength at the weld bottom. Furthermore, this method reduces the weld thickness, thereby affecting the joint's load-bearing capacity. Summary of the Invention

[0007] This invention addresses the shortcomings of the aforementioned background technology by providing a split-type friction stir welding fixture and a welding method for weakening joint texture. The split-type friction stir welding fixture of this invention comprises an inner and outer stirring head that move relatively independently. Driven by different spindles, they rotate in opposite directions at differential speeds. Combined with the groove structure on their respective lower end faces, this design complicates the strain form of the thermoplastic metal and increases its strain rate, promoting the activation of non-basal surface slip systems and thus weakening the joint texture. Simultaneously, the concave lower end face edge of the outer stirring head forms a closed cavity with the metal plate surface and the sidewall of the inner stirring head, temporarily storing any overflowing thermoplastic metal. During welding, the thermoplastic metal stored in the closed space is refilled into the thinned area behind the inner stirring head by the upsetting action of the outer stirring head, preventing the overflow and loss of thermoplastic metal. Ultimately, a friction stir joint with the same thickness as the base material, randomized grain orientation, low texture strength, and excellent mechanical properties is obtained.

[0008] Therefore, the present invention provides a split friction stir welding tool, which is provided with an outer stirring head and an inner stirring head. The outer stirring head has a stirring chamber at its center, and the inner stirring head is disposed in the stirring chamber. The outer stirring head and the inner stirring head can move relatively independently. The lower end face of the inner stirring head is provided with a concentric annular groove, and the outer stirring head is provided with a concave lower end face, and the concave lower end face is provided with a vortex groove.

[0009] Preferably, the lower end face of the inner stirring head protrudes 0.3-0.5mm more than the concave lower end face of the outer stirring head.

[0010] Preferably, the depth of the concentric annular groove is 0.2-0.5 mm, and the width of the concentric annular groove is 0.6-1.0 mm.

[0011] Preferably, the concave angle of the concave lower end face is 5-15°, the depth of the vortex groove is 0.2-0.5mm, and the width of the vortex groove is 0.6-1.0mm.

[0012] Meanwhile, this invention provides a welding method for weakening joint texture, which utilizes the aforementioned split-type friction stir welding tool. The specific method steps are as follows:

[0013] The inner and outer stirring heads of the split-type friction stir welding fixture are connected to the two main shafts of the friction stir welding machine, respectively. This drives the split-type friction stir welding fixture to rotate and press into the metal plate. The weld metal reaches a thermoplastic state. The inner and outer stirring heads rotate in opposite directions at different speeds under the drive of the two main shafts. The thermoplastic metal flows in opposite directions at different speeds along the concentric annular groove of the inner stirring head and the vortex groove of the outer stirring head, respectively. The thermoplastic metal squeezed by the inner stirring head overflows into the concave lower end face of the outer stirring head, forming a closed cavity with the surface of the metal plate and the side wall of the inner stirring head. During the welding process, the thermoplastic metal stored in the closed cavity is refilled into the thinning area behind the inner stirring head until the welding is completed.

[0014] Preferably, the inner stirring head rotates at a speed of 400-800 rpm, the outer stirring head rotates at a speed of 200-600 rpm, the inner and outer stirring heads rotate in opposite directions, and their rotation speeds differ by 100-400 rpm.

[0015] Preferably, the lower end face of the inner stirring head is pressed into the metal plate by 0.3-0.5 mm, and the outer edge of the concave lower end face of the outer stirring head is in contact with the surface of the metal plate.

[0016] Preferably, before welding, the metal sheet needs to be mechanically ground and surface-treated with chemical reagents.

[0017] Preferably, the chemical reagent is anhydrous ethanol or acetone solution.

[0018] The beneficial effects of this invention are as follows:

[0019] (1) In the split-type friction stir welding fixture of the present invention, there are an inner stirring head and an outer stirring head that rotate independently. The lower end face of the inner stirring head is provided with a concentric annular groove, which promotes the flow of metal material along the direction of the concentric annular groove and reduces the amount of metal material overflowing. The concave lower end face of the outer stirring head is provided with a vortex groove, which promotes the flow of metal material along the direction of the vortex groove and prevents the metal material below the outer stirring head from overflowing and forming flash, causing thinning. The above-mentioned structural design of the inner and outer stirring heads, combined with their opposite differential rotation, can not only complicate the strain form of thermoplastic metals, but also increase the strain rate of thermoplastic metals to promote the activation of non-basal surface slip system, thereby weakening the joint texture and improving the overall mechanical properties of the joint. In addition, the protrusion distance of the lower end face of the inner stirring head compared with the concave lower end face of the outer stirring head makes the split-type friction stir welding fixture adaptable to the welding of metal plates of different thicknesses, with flexible replacement, strong adaptability, and high feasibility.

[0020] (2) In the welding method for weakening the joint texture of the present invention, the inner stirring head is pressed into the metal plate, and the thermoplastic metal overflows due to the pressure of the inner stirring head. The outer edge of the concave lower end face of the outer stirring head just fits against the surface of the metal plate. The concave lower end face, the surface of the metal plate, and the side wall of the inner stirring head form a closed cavity that can temporarily store the overflowed thermoplastic metal. During the welding process, the thermoplastic metal stored in the closed cavity is backfilled into the thinned area behind the inner stirring head under the forging action of the outer stirring head, avoiding the overflow and loss of thermoplastic metal, resulting in a thinning-free weld and improving the mechanical properties of the joint. The present invention further simplifies the process flow, improves efficiency, and saves costs, greatly increasing the breadth and depth of application of friction stir welding technology, and is suitable for large-scale industrial production. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the split-type friction stir welding fixture structure in this invention;

[0023] Figure 2 yes Figure 1 Schematic diagram of the internal stirring head structure;

[0024] Figure 3 yes Figure 1 Schematic diagram of the structure of the Chinese and foreign stirring heads;

[0025] Figure 4This is a schematic diagram of the friction stir welding process using a split-type friction stir welding tool in this invention;

[0026] Explanation of symbols in the diagram:

[0027] 1. Metal sheet; 2. External stirring head; 21. Vortex groove; 22. Concave lower end face; 23. Screw hole; 3. Internal stirring head; 31. Concentric annular groove; 32. External thread; 4. Screw. Detailed Implementation

[0028] To make the technical problems, technical solutions, and beneficial effects to be solved by this application 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 and are not intended to limit the scope of this application.

[0029] Example 1

[0030] A split-type friction stir welding tool, made of tool steel, cemented carbide, etc., with a hardness not lower than 1 of the metal sheet. For example... Figure 1 As shown, it is equipped with an outer stirring head 2 and an inner stirring head 3. The outer stirring head 2 has a stirring chamber at its center, and the inner stirring head 3 is located inside the stirring chamber. The outer stirring head 2 and the inner stirring head 3 can move relatively independently. The lower end face of the inner stirring head 3 is provided with a concentric annular groove 31, which promotes the flow of metal material along the direction of the concentric annular groove 31 and reduces the amount of metal material overflowing. The outer stirring head 2 is provided with a concave lower end face 22, and the concave lower end face 22 is provided with a vortex groove 21, which promotes the flow of metal material along the direction of the vortex groove 21 and prevents the metal material below the outer stirring head 2 from overflowing and forming flash, causing thinning. The above structural design of the inner stirring head 3 and the outer stirring head 2, combined with their opposite differential rotation, not only complicates the strain form of the thermoplastic metal, but also increases the strain rate of the thermoplastic metal to promote the activation of the non-basal surface slip system, thereby weakening the joint texture and improving the overall mechanical properties of the joint.

[0031] Specifically, such as Figure 1-2 As shown, the lower end face of the inner stirring head 2 protrudes 0.3-0.5mm more than the lower end face of the outer stirring head 3, allowing the split-type friction stir welding tool to adapt to welding metal plates 1 of different thicknesses. It offers flexible replacement, strong adaptability, and high feasibility. The concentric annular grooves 31 on the lower end face of the inner stirring head 3 are distributed concentrically along the central axis of the inner stirring head 3, with a depth of 0.2-0.5mm and a width of 0.6-1.0mm. The top of the inner stirring head 3 is provided with an external thread 32 for connection with the main shaft.

[0032] like Figure 1 and Figure 3As shown, the outer stirring head 2 has a concave lower end face 22 with a concave angle of 5-15°. The vortex grooves 21 of the concave lower end face 22 are distributed in a circular array along the central axis of the outer stirring head 2, with a depth of 0.2-0.5 mm and a width of 0.6-1.0 mm. Multiple screw holes 23 are evenly distributed around the outer stirring head 2, and the screws 4 are used to connect with the main shaft.

[0033] Example 2: A welding method for weakening joint texture, the specific steps of which are as follows:

[0034] In this embodiment, the lower end face of the inner stirring head 2 protrudes 0.4 mm from the concave lower end face 22 of the outer stirring head 3. The concentric annular groove 31 on the lower end face of the inner stirring head 3 has a depth of 0.4 mm and a width of 0.8 mm; the concave angle of the concave lower end face 22 of the outer stirring head 2 is 10°, and the depth of the concave lower end face 22 is 0.4 mm and the width is 0.8 mm.

[0035] like Figure 4 As shown, Figure 4 The direction of the middle arrow indicates the welding direction.

[0036] (1) Prepare a metal sheet 1 with a thickness of 1.0-3.0 mm. Use sandpaper and an angle grinder to mechanically polish the surface of the metal sheet 1 to remove the oxide film. Then use a chemical reagent to wipe the surface of the metal sheet 1 to remove surface oil and prevent re-oxidation. The chemical reagent used is anhydrous ethanol or acetone solution. The metal sheet 1 is a close-packed hexagonal structure metal sheet 1 such as magnesium alloy or α-type titanium alloy.

[0037] (2) Use appropriate tooling fixtures to fix the metal plate 1 on the horizontal worktable of the welding machine, connect the inner stirring head 2 and the outer stirring head 3 of the split friction stir welding tool to the two main shafts of the friction stir welding machine respectively, calibrate the spatial position of the split friction stir welding tool so that it is located directly above the starting point of the metal plate 1, and preset the movement trajectory of the split friction stir welding tool.

[0038] (3) Start the friction stir welding machine, and drive the split friction stir welding tool to rotate and press into the metal plate 1 from directly above the starting point of the welding, so that the weld metal reaches a thermoplastic state. The inner stirring head 3 and the outer stirring head 2 of the split friction stir welding tool rotate in opposite directions at different speeds, driving the thermoplastic metal below them to flow in opposite directions at different speeds along the concentric annular groove 31 of the inner stirring head 3 and the vortex groove 21 of the outer stirring head 2, thereby increasing the complexity of the metal material flow during the welding process. Specifically, the rotation speed of the inner stirring head 3 is 600 rpm, the rotation speed of the outer stirring head 2 is 200 rpm, the rotation direction of the inner stirring head 3 and the outer stirring head 2 are opposite, and the rotation speed difference is 400 rpm.

[0039] The split-type friction stir welding fixture is set to move along a preset trajectory at a speed of 50-200 mm / min to the welding end position. During the welding process, the inner stirring head 3 is pressed into the metal plate 1 by 0.4 mm. The thermoplastic metal overflows due to the compression of the inner stirring head 3. The outer edge of the concave lower end face 22 of the outer stirring head 2 just fits against the surface of the metal plate 1, forming a closed cavity with the surface of the metal plate 1 and the side wall of the inner stirring head 3 to temporarily store the overflowed thermoplastic metal. As the split-type friction stir welding fixture moves along the welding direction, the thermoplastic metal stored in the closed cavity is backfilled into the thinned area behind the inner stirring head 3 by the forging action of the concave lower end face 22 of the outer stirring head 2, avoiding the overflow and loss of thermoplastic metal, resulting in a weld without thinning. After being cooled to room temperature in air, a friction stir welded joint with the same thickness as the base material, randomized grain orientation, low texture strength, and excellent mechanical properties is finally obtained.

[0040] Example 3: A welding method for weakening joint texture, the specific steps of which are as follows:

[0041] Unlike Embodiment 2, in this embodiment, the lower end face of the inner stirring head 2 protrudes 0.3 mm from the concave lower end face 22 of the outer stirring head 3. The concentric annular groove 31 on the lower end face of the inner stirring head 3 has a depth of 0.2 mm and a width of 0.6 mm; the concave angle of the concave lower end face 22 of the outer stirring head 2 is 5°, and the depth of the concave lower end face 22 is 0.2 mm and the width is 0.6 mm.

[0042] The inner stirring head 2 rotates at 400 rpm, and the outer stirring head 3 rotates at 300 rpm. The inner stirring head 2 and the outer stirring head 3 rotate in opposite directions, and their rotation speeds differ by 100 rpm.

[0043] In addition, the lower end face of the inner stirring head 2 is pressed into the interior of the metal plate 1 by 0.5 mm. After welding, a friction stir welded joint with the same thickness as the base material, randomized grain orientation, low texture strength, and excellent mechanical properties is finally obtained.

[0044] Example 4: A welding method for weakening joint texture, the specific steps of which are as follows:

[0045] Unlike Embodiment 2, in this embodiment, the lower end face of the inner stirring head 2 protrudes 0.5 mm from the concave lower end face 22 of the outer stirring head 3. The concentric annular groove 31 on the lower end face of the inner stirring head 3 has a depth of 0.5 mm and a width of 1.0 mm; the concave angle of the concave lower end face 22 of the outer stirring head 2 is 15°, and the depth of the concave lower end face 22 is 0.5 mm and the width is 1.0 mm.

[0046] The inner stirring head 3 rotates at 800 rpm, and the outer stirring head 2 rotates at 600 rpm. The inner stirring head 3 and the outer stirring head 2 rotate in opposite directions, with a speed difference of 200 rpm. Additionally, the lower end face of the inner stirring head 3 is pressed into the metal plate 1 by 0.3 mm. After welding, a friction stir welded joint with the same thickness as the base material, randomized grain orientation, low texture strength, and excellent mechanical properties is obtained.

[0047] In summary, firstly, the split-type friction stir welding fixture of the present invention includes an inner stirring head 3 and an outer stirring head 2 that rotate independently. The lower end face of the inner stirring head 3 is provided with a concentric annular groove 31, which promotes the flow of metal material along the direction of the concentric annular groove 31 and reduces the amount of metal material overflowing. The concave lower end face 22 of the outer stirring head 2 is provided with a vortex groove 21, which promotes the flow of metal material along the direction of the vortex groove 21 and prevents the metal material below the outer stirring head 2 from overflowing and forming flash, causing thinning. The above-mentioned structural design of the inner stirring head 3 and the outer stirring head 2, combined with their opposite differential rotation, not only complicates the strain form of thermoplastic metals, but also increases the strain rate of thermoplastic metals to promote the activation of non-basal surface slip systems, thereby weakening the joint texture and improving the overall mechanical properties of the joint. In addition, the lower end face of the inner stirring head 3 protrudes further than the concave lower end face 22 of the outer stirring head 2, which allows the split-type friction stir welding tool to adapt to the welding of metal plates 1 of different thicknesses, making it flexible to replace, highly adaptable, and highly feasible.

[0048] Secondly, in the welding method for weakening the joint texture of the present invention, the inner stirring head 3 is pressed into the metal plate 1, and the thermoplastic metal overflows due to the pressure of the inner stirring head 3. The outer edge of the concave lower end face 22 of the outer stirring head 2 just fits against the surface of the metal plate 1. The concave lower end face 22, the surface of the metal plate 1, and the sidewall of the inner stirring head 3 form a closed cavity that can temporarily store the overflowed thermoplastic metal. During the welding process, the thermoplastic metal stored in the cavity is backfilled into the thinned area behind the inner stirring head 3 under the upsetting action of the outer stirring head 2, avoiding the overflow and loss of thermoplastic metal, resulting in a weld without thinning, and finally obtaining a friction stir welded joint with the same thickness as the base material, relatively randomized grain orientation, and excellent mechanical properties. The present invention further simplifies the process flow, improves efficiency, and saves costs, greatly increasing the breadth and depth of application of friction stir welding technology, and is suitable for large-scale industrial production.

[0049] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A welding method for weakening a joint texture, characterized by, The application discloses a split type friction stir welding tool, which is provided with an outer stirring head and an inner stirring head, the outer stirring head is provided with a stirring cavity in the center, the inner stirring head is arranged in the stirring cavity, the outer stirring head and the inner stirring head can be reversely differentially rotated, the lower end surface of the inner stirring head is provided with a concentric annular groove, the outer stirring head is provided with a concave lower end surface, and the concave lower end surface is provided with a vortex groove, so that the joint texture can be weakened. The welding method comprises the following steps: The inner stirring head and the outer stirring head of the split type friction stir welding tool are respectively connected with two main shafts of a friction stir welding machine, the split type friction stir welding tool is driven to rotate and press into a metal plate, the weld metal reaches a hot plastic state, the inner stirring head and the outer stirring head are reversely differentially rotated under the driving of the two main shafts, the hot plastic metal flows reversely and differentially along the concentric annular groove of the inner stirring head and the vortex groove of the outer stirring head, and the joint texture is weakened; meanwhile, the hot plastic metal extruded by the inner stirring head overflows into the concave lower end surface of the outer stirring head, the surface of the metal plate and the closed cavity formed by the side wall of the inner stirring head, the hot plastic metal stored in the closed cavity is refilled into the thinning area behind the inner stirring head during the welding process, and the welding process is ended.

2. The method of welding a weakened joint texture of claim 1, wherein, The lower end surface of the inner stirring head is protruded by 0.3-0.5 mm compared with the concave lower end surface of the outer stirring head.

3. The method of welding a weakened joint texture of claim 1, wherein, The depth of the concentric annular groove is 0.2-0.5 mm, and the width of the concentric annular groove is 0.6-1.0 mm.

4. The method of welding a weakened joint texture of claim 1, wherein, The concave angle of the concave lower end surface of the inner stirring head is 5-15°, the depth of the vortex groove is 0.2-0.5 mm, and the width of the vortex groove is 0.6-1.0 mm.

5. The method of welding a weakened joint texture according to any one of claims 1-4, wherein, The rotating speed of the inner stirring head is 400-800 rpm, the rotating speed of the outer stirring head is 200-600 rpm, the rotating directions of the inner stirring head and the outer stirring head are opposite, and the rotating speed difference is 100-400 rpm.

6. The method of welding a weakened joint texture according to any one of claims 1-4, wherein, The lower end surface of the inner stirring head is pressed into the inner part of the metal plate by 0.3-0.5 mm, and the outer edge of the concave lower end surface of the outer stirring head is in contact with the surface of the metal plate.

7. The method of welding a weakened joint texture according to any one of claims 1-4, wherein, Before welding, the metal plate needs to be mechanically polished and surface treated by using a chemical reagent.

8. The method of welding a weakened joint texture of claim 7, wherein, The chemical reagent is anhydrous ethanol or acetone solution.

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