Friction stir welding device and metal plate friction stir welding method adopting same

Abstract

The invention provides a friction stir welding device and a metal plate friction stir welding method adopting the friction stir welding device. The friction stir welding device comprises a welding machine head and a welding-following in-situ heating device, and the welding machine head is provided with a stirring head used for forming friction stir welding on a metal plate; the welding-following in-situ heating device comprises an induction heating main body and an induction coil arranged in the induction heating main body, and further comprises a first electrode connecting column and a second electrode connecting column which are electrically connected with the induction coil, the first electrode connecting column and the second electrode connecting column are arranged in a spaced mode in the welding advancing direction of the welding machine head, and the spacing distance between the first electrode connecting column and the second electrode connecting column can be adjusted so as to adjust the effective heating length of the induction coil. According to the friction stir welding device, the heating and heat preservation time of welding seams formed by welding metal plates of different materials or sizes can be adjusted, and the universality of the friction stir welding device is improved.

Description

Technical Field

[0001] This invention belongs to the field of friction stir welding technology, specifically relating to a friction stir welding apparatus and a friction stir welding method for metal plates using the same. Background Technology

[0002] Medium-manganese steel (containing 3-12 wt.% manganese) is a typical representative of third-generation advanced high-strength steel. Leveraging the transformation-induced plasticity (TRIP) effect generated by metastable austenite, it exhibits excellent synergistic effects of strength and toughness, making it an ideal candidate material for manufacturing high-performance components in vehicles, energy equipment, and other applications. Welding is a critical process in component manufacturing, and high-performance component manufacturing requires high-quality welding technology. While fusion welding techniques, such as argon arc welding, are widely used, they suffer from high heat input, large residual stress, and are prone to solidification defects such as porosity, hot cracks, and cold cracks. Friction stir welding, as a solid-state joining technology, features low heat input and can effectively avoid solidification defects such as hot cracks in the weld. However, due to the high alloy content and severe hardenability of medium-manganese steel, the austenite-to-martensite transformation cannot be avoided during friction stir welding. The joint is highly susceptible to losing the TRIP effect and generating significant phase transformation stress, leading to a decrease in toughness and plasticity. When friction stir welding parameters are not properly selected, the weld's toughness and plasticity decrease significantly, and cold cracks, such as hardening embrittlement cracks, may even form. The problem of reduced weld toughness has severely hampered the engineering application of medium manganese steel.

[0003] Currently, the main method to address the reduced plasticity and toughness of friction stir welds in medium manganese steel is to perform off-site heat treatment. This involves transferring the cooled welded component as a whole to an annealing furnace for heating and holding, causing the joint microstructure to undergo austenitic inverse transformation and martensitic tempering. This increases the austenite content and reduces the martensitic hardness, thereby improving the plasticity and toughness of the weld microstructure and eliminating residual stress. However, post-weld heat treatment not only requires post-weld cooling but also involves transferring the workpiece to the furnace for heating and holding, extending the welding process and cycle, and significantly increasing production costs. Furthermore, for some large or complex components, post-weld annealing can easily lead to overall workpiece deformation and performance degradation, and is also easily limited by the furnace volume. Since hardening embrittlement cracks can form during the welding cooling process, off-site heat treatment cannot solve the problem of weld crack formation. Therefore, existing off-site heat treatment methods cannot effectively solve the bottleneck problem of reduced plasticity and toughness in friction stir welds of medium manganese steel, which is not conducive to cost reduction and efficiency improvement in the welding production process.

[0004] Based on the aforementioned shortcomings of manganese steel and other metal plates in friction stir welding, related technologies have proposed using in-situ heating to simultaneously heat the weld after its formation, achieving online heat treatment of the weld (also known as in-situ heat treatment during welding). Specifically, during the friction stir process, an electromagnetic heating coil is placed above the weld to electromagnetically heat and maintain its temperature, thereby overcoming the aforementioned shortcomings. However, different sizes of electromagnetic heating coils need to be configured for welding different materials and different models (sizes) of metal plates to ensure that different heating times correspond to different metal plates, thus ensuring the performance of the welded joint. This makes the electromagnetic heating components configured for friction stir welding not very versatile. Summary of the Invention

[0005] Therefore, the present invention provides a friction stir welding apparatus and a friction stir welding method for metal plates using the same, which can overcome the shortcomings of the electromagnetic heating components in friction stir welding configurations in related technologies, which lack versatility.

[0006] To address the aforementioned problems, the present invention provides a friction stir welding apparatus, comprising a welding machine head and an in-situ heating device. The welding machine head has a stirring head for forming friction stir welding on a metal plate. The in-situ heating device includes an induction heating body and an induction coil disposed within the induction heating body. The in-situ heating device further includes a first electrode connecting post and a second electrode connecting post electrically connected to the induction coil. The first electrode connecting post and the second electrode connecting post are spaced apart along the welding travel direction of the welding machine head, and the distance between the first electrode connecting post and the second electrode connecting post can be adjusted to adjust the effective heating length of the induction coil.

[0007] In some embodiments, with reference to the orientation of the in-situ heating device in use, the first electrode connecting post is located on the side of the second electrode connecting post closer to the stirring head, the first electrode connecting post is fixedly connected to the induction coil, the second electrode connecting post is slidably connected to the induction coil, and the sliding direction of the second electrode connecting post is parallel to the welding travel direction; and / or, it also includes a bracket, the in-situ heating device is assembled on the bracket and the bracket is connected to the welding machine head, and the distance between the in-situ heating device and the welding body in the welding travel direction can be adjusted.

[0008] In some embodiments, the induction coil includes a plurality of parallel segments spaced apart perpendicular to the welding direction and a connecting segment connecting the ends of two adjacent parallel segments, wherein each connecting segment and each parallel segment form a bent shape.

[0009] In some embodiments, an electrical connector is formed at the bottom end of the second electrode connecting post, and the bottom surface of the electrical connector facing the induction heating body is arc-shaped.

[0010] In some embodiments, an insulating slide is formed on the top surface of the induction heating body, and a slide rail extending along the welding travel direction is formed on the top surface of the slide rail. A plurality of conductive contacts are provided in the slide rail at intervals along the welding travel direction. The bottom end of each conductive contact is electrically connected to a different parallel segment, and the electrical connector can contact the top end of each conductive contact.

[0011] In some embodiments, the conductive contact is a conductive ball, each of which is embedded in the sliding surface of the slide and can be rotated by the electrical connector.

[0012] In some embodiments, the area corresponding to the electrical connector and the conductive ball has a limiting groove.

[0013] The present invention also provides a method for friction stir welding of metal plates using the above-mentioned friction stir welding apparatus, comprising the following steps:

[0014] The distance between the second electrode connecting post and the first electrode connecting post is adjusted to d6, and the distance between the induction heating body and the stirring head in the welding travel direction is adjusted to d4. The weld temperature formed by the welding head when welding the metal plate is cooled to below the phase transformation point temperature A of the metal plate. c1 The distance between the weld position and the stirring head in the welding travel direction is d7, where d4 > d7;

[0015] The welding machine head is controlled to operate after the in-situ heating device is operated, thereby realizing the friction stir welding of two metal plates positioned on the welding worktable.

[0016] In some embodiments, the metal plate is a medium manganese steel plate, and the operation of the in-situ heating device during welding causes the surface temperature of the weld to be at A. c1 To A c3 Between these two points, the heating time for the same location of the weld is t, where 50s≤t≤200s.

[0017] In some embodiments, the metal plate is a medium manganese steel plate, the rotational speed of the stirring head is ω, the welding travel speed of the welding machine head is v, and the downward pressure of the shoulder of the stirring head is p. , , .

[0018] The friction stir welding apparatus and the friction stir welding method for metal plates using the present invention have the following beneficial effects:

[0019] The spacing between the first and second electrode connecting posts in the welding head's welding travel direction can be adjusted, thereby allowing for adjustment of the actual heating length of the induction heating body over the weld area. This enables the heating and holding time of the weld formed by the friction stir welding device for metal plates of different materials or sizes to be adjustable, improving the versatility of the friction stir welding device and allowing for precise control of heating time at different welding speeds. Furthermore, because this invention employs in-situ heat treatment of the weld during friction stir welding, compared to traditional off-site heat treatment methods in the prior art, it eliminates the need to wait for the workpiece to cool before transferring it to the furnace for heat treatment. This significantly shortens the welding process and cycle, reduces production costs, and is not limited by the matching of workpiece size and furnace volume, making heat treatment more convenient and contributing to cost reduction and efficiency improvement in the welding production process. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the accompanying drawings used in the description of the embodiments or related technologies will be briefly introduced below. The drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the structure of the friction stir welding device in an embodiment of the present invention;

[0022] Figure 2 yes Figure 1 A front view of the friction stir welding apparatus in the image;

[0023] Figure 3 yes Figure 1 A top-down view of the structure of the induction heating element;

[0024] Figure 4 This is a temperature curve of the bottom of the weld when in-situ heat treatment is performed using the friction stir welding device in this embodiment of the invention.

[0025] Figure 5 The figures are microstructure diagrams of welded joints (including base metal). In the figures, (a) is the microstructure diagram of the base metal, (b) is the microstructure diagram of the weld nugget of a conventional welded joint (i.e., a welded joint not obtained by the in-situ heat treatment method of the present invention), and (c) is the microstructure diagram of the weld nugget of a welded joint obtained by the in-situ heat treatment method of the present invention.

[0026] Figure 6 The mechanical properties of the welded joint obtained by the in-situ heat treatment method of the present invention are as follows:

[0027] Figure 7 This is a comparison diagram of the impact energy of the base material, conventional welded joint, and welded joint obtained by the present invention.

[0028] The attached figures are labeled as follows:

[0029] 11. Stirring head; 2. In-situ heating device for welding; 21. Induction heating body; 211. Insulated slide; 221. Parallel section; 222. Connecting section; 223. Slide rail; 224. Conductive ball; 231. First electrode connecting post; 232. Second electrode connecting post; 2321. Electrical connector; 3. Welding workbench; 4. Heat-insulating pad; 5. Clamping block; 100. Metal plate. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. 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.

[0031] In the description of this invention, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is generally based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this invention; the directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0032] For ease of description, spatial relative terms such as "above," "on top of," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation beyond the orientation of the device as described in the figures. For example, if the device in the figures were inverted, a device described as "above" or "on top of" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90° or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0033] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0034] See also Figures 1 to 7 As shown in the figure, according to an embodiment of the present invention, a friction stir welding apparatus is provided, including a welding machine head (not shown in the figure) and an in-situ heating device 2. The welding machine head has a stirring head 11 for forming friction stir welding on a metal plate 100. The in-situ heating device 2 includes an induction heating body 21 and an induction coil (not labeled in the figure) disposed in the induction heating body 21. The in-situ heating device 2 also includes a first electrode connecting post 231 and a second electrode connecting post 232 electrically connected to the induction coil. The first electrode connecting post 231 and the second electrode connecting post 232 are along the welding travel direction of the welding machine head (e.g., ...). Figure 2 The electrodes are spaced apart in the left and right directions (as shown), and the distance between the first electrode connecting post 231 and the second electrode connecting post 232 can be adjusted to adjust the effective heating length of the induction coil (e.g., in the left and right directions). Figure 2As indicated by d6 in the figure, it can be understood that the first electrode connecting post 231 and the second electrode connecting post 232 are specifically connected to the power supply in a controllable manner via a current commutator (e.g., an electronic oscillator), thereby causing the current in the induction coil to be reversed, thereby generating a pulsating magnetic field that alternates at high frequency, thus forming eddy currents in the weld area, thereby achieving its heating purpose. As a conventional design for electromagnetic heating, this application will not elaborate on the electromagnetic heating principle. In addition, when one of the first electrode connecting post 231 and the second electrode connecting post 232 is a positive pole, the other is a negative pole, and the two alternately supply power to the induction coil. The heating temperature of the induction heating body 21 is specifically determined by the induction heating frequency f and the heating power P. As a conventional technical means of electromagnetic heating, this invention will not elaborate on it.

[0035] In this technical solution, the spacing between the first electrode connecting post 231 and the second electrode connecting post 232 in the welding travel direction of the welding machine head can be adjusted, thereby allowing the actual heating length of the induction heating body 21 on the weld area to be adjusted. This enables the heating and holding time of the weld formed by the friction stir welding device for welding metal plates of different materials or models to be adjustable, improving the versatility of the friction stir welding device and enabling precise control of the heating time at different welding speeds. Furthermore, it is understood that because this invention employs in-situ heat treatment of the weld simultaneously with friction stir welding, compared with the traditional off-site heat treatment method in the prior art, there is no need to wait for the workpiece to cool before transferring it to the furnace for heat treatment. This significantly shortens the welding process and welding cycle, reduces production costs, and is not limited by the matching of workpiece size and furnace volume, making heat treatment more convenient and contributing to cost reduction and efficiency improvement in the welding production process.

[0036] In some embodiments, with reference to the orientation of the in-situ heating device in use, the first electrode connecting post 231 is located on the side of the second electrode connecting post 232 closer to the stirring head 11. Figure 2 (On the left side of the indicated position), the first electrode connecting post 231 is fixedly connected to the induction coil, that is, the relative position between the first electrode connecting post 231 and the induction coil remains unchanged, the second electrode connecting post 232 is slidably connected to the induction coil, and the sliding direction of the second electrode connecting post 232 is parallel to the welding travel direction.

[0037] In this technical solution, one of the two electrode connecting posts is designed to remain in a fixed position relative to the induction coil, while the other is designed to be driven to slide. This not only achieves matching between the heating length of the induction coil and the material and specifications of the metal plate 100, but also significantly reduces the difficulty of adjustment. Furthermore, the first electrode connecting post 231 near the stirring head 11 is fixedly connected, which allows the starting point of the heating length to be determined, thus facilitating the adjustment of the relative interval between the induction heating body 21 and the stirring head 11 (i.e., Figure 2 The accurate adjustment of d4 in the middle.

[0038] In some embodiments, the friction stir welding device further includes a bracket (not shown in the figure), the in-situ heating device 2 is assembled on the bracket and the bracket is connected to the welding machine head, and the distance between the in-situ heating device 2 and the welding body in the welding travel direction can be adjusted. Specifically, the first electrode connecting post 231 and the second electrode connecting post 232 are both connected to the aforementioned bracket through corresponding support rods, wherein the top end of the support rod of the first electrode connecting post 231 is fixedly connected to the bracket, while the top end of the support rod of the second electrode connecting post 232 is slidably connected to the aforementioned bracket. In this way, the relative electrical connection position between the second electrode connecting post 232 and the induction coil can be adjusted by changing the relative position of the support rod of the second electrode connecting post 232 and the bracket. For example, a groove parallel to the welding travel direction is provided on the bracket, and the top end of the support rod of the second electrode connecting post 232 is inserted into the groove and the position of the support rod can be detachably fixed by corresponding set nuts. The structure is simple and the manufacturing cost is low. The distance between the aforementioned support frame and the welding machine head in the welding travel direction can be adjusted, so that the heating area of ​​the induction heating body 21 is set on the weld formed after the corresponding metal plate 100 is welded and cooled to its phase transformation point A. c1 The position after the welding process is adjusted to effectively restore the TRIP effect through in-situ heat treatment. It is understood that the bracket connects the aforementioned in-situ heating device 2 to the welding machine head as a whole. The moving speed of the induction heating body 21 is consistent with the welding travel speed of the welding machine head. Thus, when using different welding travel speeds (for metal plates 100 of different materials or specifications), the heating time can be adjusted by changing the position of the second electrode connecting post 232.

[0039] In some implementation methods, see details. Figure 3As shown, the induction coil includes multiple parallel segments 221 spaced apart perpendicular to the welding direction and connecting segments 222 connecting the ends of adjacent parallel segments 221. Each connecting segment 222 forms a bend with each parallel segment 221. It should be noted that the aforementioned parallel segments 221 and connecting segments 222 are not necessarily straight lines in practical applications; they can also be spiral, arc-shaped, or other shapes to improve the battery induction heating performance of the induction coil. To ensure the uniformity of induction heating, the spacing between each parallel segment 222 is equal.

[0040] In this technical solution, by designing the induction coil as a bent shape, a large induction magnetic field can be formed within the relatively limited area of ​​the induction heating body 21, thereby ensuring the full utilization of the electromagnetic heating performance.

[0041] In some embodiments, an electrical connector 2321 is formed at the bottom end of the second electrode connecting post 232, and the bottom surface of the electrical connector 2321 facing the induction heating body 21 is arc-shaped.

[0042] In this technical solution, the bottom surface of the electrical connector 2321 facing the induction heating body 21 is designed as an arc shape, which can improve the smoothness of sliding and friction of the second electrode connecting post 232 and prevent the electrical connector 2321 from getting stuck during movement.

[0043] In some embodiments, an insulating slide 211 (e.g., made of ceramic) is formed on the top surface of the induction heating body 21. A slide rail 223 extending along the welding direction is formed on the top surface of the slide rail 211. A plurality of conductive contacts are provided in the slide rail 223 at intervals along the welding direction. The bottom end of each conductive contact is electrically connected to a different parallel segment 221. The electrical connector 2321 can contact the top end of each conductive contact, that is, the electrical connector 2321 is electrically connected to each conductive contact.

[0044] In this technical solution, an insulating slide 211 is provided on the top surface of the induction heating body 21, and a slide rail 223 is provided on the insulating slide 211 to form a reliable guide for the sliding of the second electrode connecting post 232. At the same time, conductive contacts are provided on the slide rail 223 to realize the indirect electrical connection between each parallel segment 221 of the induction coil and the electrical connector 2321. This can prevent the wear caused by direct contact between the electrical connector 2321 and the induction coil, thereby improving the service life of the induction coil and reducing the failure rate.

[0045] In some embodiments, the conductive contact is a conductive ball 224, each of which is embedded in the sliding surface of the slide rail 223 and can be rotated by the electrical connector 2321. In this way, the rotation of the conductive ball 224 can be used to transform sliding friction into rolling friction, further reducing the contact wear between the aforementioned electrical connectors 2321. In this case, as a more preferred embodiment, a corresponding conductive spring is provided between the conductive ball 224 and the parallel segment 221 of the corresponding induction coil. The conductive spring has a certain elastic compensation capability, which can ensure the reliability of the contact between the conductive ball 224 and the electrical connector 2321. At the same time, the bottom end of the conductive spring is welded to the parallel segment 221 of the induction coil and the top end abuts against the conductive ball 224. Its elastic compensation function can ensure the reliable electrical connection between the two while ensuring the rotation of the conductive ball 224.

[0046] In some embodiments, the area of ​​the electrical connector 2321 corresponding to the conductive ball 224 has a limiting groove (not shown in the figure), so that a portion of the protrusion (minor arc area) of the conductive ball 224 at the corresponding position can be accommodated in the limiting groove, thereby ensuring the accuracy of the position adjustment of the second electrode connection 232.

[0047] See Figure 1 As shown, the friction stir welding apparatus also includes a welding worktable 3 and a heat-resistant pad 4 placed on the welding worktable 3. The thermal conductivity of the heat-resistant pad 4 is no greater than half that of the metal plate 100, and the mechanical strength of the heat-resistant pad 4 is no less than that of the metal plate 100. Specifically, the material can be one of the following low thermal conductivity materials: high-temperature alloy, oxide ceramic, granite, titanium alloy, etc. If the strength of the heat-resistant pad 4 is lower than that of the metal plate 100, it cannot effectively support the welding pressure, and weld collapse is likely to occur. If the thermal conductivity of the heat-resistant pad 4 is greater than half that of the metal plate 100, it cannot effectively prevent heat loss from the bottom of the weld, requiring higher welding heat input and heating power to achieve welding and heat treatment, increasing the probability of welding cold cracks and energy consumption. To ensure the positional stability of the metal plate 100 during welding, corresponding clamping blocks 5 are provided on the aforementioned welding worktable 3.

[0048] In a preferred embodiment, the aforementioned induction heating body 21 is rectangular in plan view when in use, so as to match the shape of the weld and thus ensure accurate and effective heating of the weld. It is understood that if the induction heating body 21 is cylindrical or disc-shaped, the shape of the heating area does not match the shape of the weld, and the weld cannot be accurately and effectively heated, resulting in a new and larger heat-affected zone, and the weld structure and properties cannot be accurately controlled.

[0049] In some embodiments, the aforementioned induction heating body 21 can be formed by wrapping it with high-temperature resistant insulating tape. Of course, other materials (such as ceramic) can also be used to form the corresponding body to facilitate the reliable arrangement and assembly of the components. The induction heating body 21 objectively wraps around the outer periphery of the induction coil, forming a reliable protection for the induction coil and preventing the weld seam burrs from scratching the induction coil and causing a short circuit.

[0050] In practical applications, the induction heating body 21 should be positioned directly behind the stirring head 11, and the center line of the width of the induction heating body 21 (assuming it is rectangular) should be aligned with the weld joint of the two welded metal plates 100 to ensure the accuracy and timeliness of the induction heating body 21 in heating the weld joint, and to avoid uneven heating caused by the heating position being biased to one side of the weld joint.

[0051] See details Figure 1 As shown, the shoulder diameter of the stirring head 11 is d1, and the width of the induction heating body 21 is d2 (the dimension in the horizontal direction perpendicular to the welding travel direction), d1≤d2≤1.5d1, to ensure that the heating width of the induction heating body 21 covers the entire weld width and effectively heats the weld. It should be noted that the width of the induction coil inside should be as close as possible to d2. For ease of description, the width d2 of the induction heating body 21 in this invention is the same as the width of the induction coil.

[0052] See details Figure 2 As shown, the minimum distance between the induction heating body 21 and the stirring head 11 in the welding travel direction is d4, and the distance between the bottom surface of the induction heating body 21 and the top surface of the metal plate 100 is d5. In some embodiments, 0.5d1≤d4≤2d1, 2 mm≤d5≤10 mm If the distance between the induction heating body 21 and the stirring head 11 is too small, the induction heating body 21 is prone to misheating the stirring head 11, increasing the risk of wear and deformation of the stirring head 11. If the distance between the induction heating body 21 and the stirring head 11 is too large, the weld will cool to a lower temperature before induction heating, which cannot effectively suppress austenite decomposition and martensitic phase transformation, and cannot avoid the generation of hardening embrittlement cracks. If the distance between the induction heating body 21 and the test plate to be welded (i.e., the aforementioned metal plate 100) is too small, the induction heating body 21 is easily scratched and disturbed by the weld burrs, reducing process stability. If the distance between the induction heating body 21 and the test plate to be welded is too large, the induction eddy current penetration depth is insufficient, the heating efficiency is reduced, and the test plate to be welded cannot be effectively heated.

[0053] According to an embodiment of the present invention, a method for friction stir welding of metal plates using the above-described friction stir welding apparatus is also provided, comprising the following steps:

[0054] The distance between the second electrode connecting post 232 and the first electrode connecting post 231 is adjusted to d6, and the distance between the induction heating body 21 and the stirring head 11 in the welding travel direction is adjusted to d4. The weld temperature formed by the welding head when welding the metal plate 100 is cooled to below the phase transformation point temperature A of the metal plate 100. c1 At that time, the distance between the weld position and the stirring head 11 in the welding travel direction is d7 (not marked in the figure), d4 > d7, see details. Figure 4 The spacing corresponding to point B is to ensure that the weld nugget structure recovers the TRIP effect. The aforementioned d4 and d7 can be obtained through theoretical derivation or by conducting trial welding tests after the material and specifications of metal plate 100 are determined.

[0055] After controlling the operation of the in-situ heating device 2, the welding machine head is then controlled to perform friction stir welding on two metal plates 100 positioned on the welding workbench 3. The heating is stopped when the induction heating body 21 is completely removed from above the weld. This ensures that the heating time is consistent at different positions along the weld length, avoiding uneven weld structure and properties caused by different heating times.

[0056] In one specific embodiment, the metal plate 100 is a medium manganese steel plate, and the operation of the in-situ heating device 2 during welding ensures that the heating temperature of the weld surface is at A. c1 To A c3 Between, the aforementioned A c1 A is the phase transformation temperature corresponding to the start of the austenite transformation. c3 Let t be the phase transformation point temperature at which the austenite transformation is complete, and t be the heating time for the same location in the weld. If the heating temperature is lower than A c1 The microstructure does not undergo austenitic reverse phase transformation, and the weld nugget microstructure cannot recover the TRIP effect or improve toughness and plasticity. If the heating temperature is higher than A... c3 The inverted austenite undergoes grain coarsening, resulting in decreased stability and a tendency to undergo martensitic transformation upon cooling, failing to effectively recover the TRIP effect and improve toughness and plasticity. If the residence time (i.e., heating time) is less than 50 seconds, austenite-stabilizing elements such as C and Mn cannot fully diffuse into the inverted austenite, leading to decreased stability. If the residence time is greater than 200 seconds, the inverted austenite is prone to grain coarsening, further reducing stability. Correspondingly, the rotational speed of the stirring head 11 is ω, the welding travel speed of the welding machine head is v, and the shoulder pressing amount of the stirring head 11 is p. , , If the rotation speed is too high, the welding speed is too low, or the shoulder pressure is too high, the welding heat input will be too large, resulting in severe weld burrs, increasing the risk of cold cracking, accelerating the thermal wear rate of the stirring head, and increasing the risk of burrs scratching and disturbing the heating end. If the rotation speed is too low, the welding speed is too high, or the shoulder pressure is too low, the welding heat input will be too small, making it easy for welding defects such as tunnels and holes to appear in the weld, reducing the weld formation quality, and increasing the mechanical wear rate and damage risk of the stirring head.

[0057] In a specific embodiment, for medium manganese steel with a plate thickness of d0, the penetration range of the induced eddy current needs to be... The thickness of the cover plate, i.e. ,but In the formula, ρ is the material resistivity and μ is the magnetic permeability. The induction heating frequency f is calculated from this, the heating power P is adjusted, and a non-contact infrared thermometer is used to measure the heating temperature T on the weld surface below the induction heating body 21, so that A... c1 <T<A c3 .

[0058] In this embodiment, the microstructure of the medium-manganese steel friction stir welded joint after the in-situ heat treatment has the following characteristics: the average grain size of the weld nugget zone is not larger than that of the base metal, and the volume content of austenite in the weld nugget zone is not less than 90% of that in the base metal. The mechanical properties of the medium-manganese steel friction stir welded joint after the in-situ heat treatment have the following characteristics: the tensile strength of the welded joint is not less than 95% of that of the base metal, and the impact energy of the weld nugget zone is not less than 80% of that of the base metal.

[0059] The technical solution of the present invention will be further illustrated below with reference to several embodiments and comparative examples.

[0060] Example 1:

[0061] This embodiment selects chemical components as follows: The plate thickness is 3 mm, A c1 A c3 Medium-manganese steel plates with phase transformation temperatures of 523℃ and 730℃ were used as the base material for welding. The austenite volume content in the base material was 9%, and the average grain size was 0.47±0.67 μm. A tungsten-rhenium alloy with a shoulder diameter of 12 mm was selected as the stirring head for friction stir welding. In-situ heat treatment was performed using a rectangular induction heating coil with a width of 15 mm (i.e., the aforementioned induction heating body 21). The main implementation steps are as follows:

[0062] 1) Workpiece clamping: First, place the high-temperature alloy heat-insulating pad on the welding worktable, then place the medium manganese steel plate to be welded (i.e., the aforementioned metal plate 100) on the heat-insulating pad (i.e., the aforementioned heat-insulating pad 4, the same below) in a butt joint manner, and use a clamping fixture (i.e., the aforementioned clamping block 5, the same below) to rigidly fix it to the pad. Figure 1 (As shown).

[0063] 2) Equipment debugging: The heating end (i.e., the aforementioned induction heating body 21, hereinafter the same) is set directly behind the stirring head (i.e., the aforementioned stirring head 11), and is integrated with the welding machine head and moves synchronously. Adjust the position and direction of the heating device (i.e., the aforementioned in-situ heating device 2) so that the center plane of the width of the heating end is aligned with the butt joint of the weld. The distances between the heating device and the stirring head and the test plate to be welded are 15 mm and 3 mm, respectively. Figure 2 (As shown).

[0064] 3) Welding parameter settings: Set the stirring head rotation speed to 500 r / min, the welding speed to 200 mm / min, and the stirring head shoulder downward pressure to 0.15 mm.

[0065] 4) Setting parameters for heat treatment during welding: induction heating frequency (in The heating temperature is 650℃. Measured by an infrared thermometer, when the temperature of the weld surface below the heating tip is 650℃, the heating power is 30 kW, and the dwell time of the heating tip above the weld is 120 s. Figure 4 Adjust the position of the sliding contact (i.e., the aforementioned electrical connector 2321) on the slide rail (i.e., the slide 223 on the aforementioned insulating slide table 211) so that the effective heating length is 400 mm.

[0066] 5) Start the friction stir welding equipment to carry out welding. When the heating end passes over the weld, start the induction heating device to carry out heating until the induction heating end completely leaves the weld. Then turn off the induction heating device to stop heating.

[0067] The average grain size of the weld nugget zone of the medium-manganese steel friction stir welded joint after the aforementioned in-situ heat treatment is 0.42 ± 0.56 μm, which is not larger than that of the base metal. The volume content of austenite in the weld nugget zone is 10.5%, which is 117% of that in the base metal. Figure 5 The tensile strength of the welded joint is 1043±3 MPa. Figure 6 The weld nugget microstructure has an impact toughness of 23 J, which is 99.6% of that of the base metal, and is 104.5% of that of the base metal microstructure. Figure 7 ).

[0068] Comparative Example 1:

[0069] Medium manganese steel plate, the same as in Example 1, was selected as the base material for friction stir welding. The stirring head used was the same as in Example 1. The difference in implementation steps compared to Example 1 was that in-situ heat treatment was not used. After friction stir welding, the average grain size of the weld nugget was 0.81 ± 1.37 μm, which was larger than that of the base material, and the volume content of austenite was 0%. Figure 5 (b) Through-type cold cracks appear in the weld nugget along the length of the weld.

[0070] Comparative Example 2:

[0071] Medium manganese steel plate, the same as in Example 1, was selected as the base material for friction stir welding. The stirring head used was the same as in Example 1. The difference in implementation steps compared to Example 1 was that the heating temperature of the heating device was too high, at 750℃; and the dwell time of the heating device on the upper part of the weld was too long, at 250 s. After the in-situ heat treatment, the average grain size of the weld nugget of the medium manganese steel friction stir welded joint was 0.56±0.33 μm, which was larger than that of the base material. The volume content of austenite in the weld nugget was 3%, which was 33% of that in the base material. The tensile strength of the welded joint was 1041±6 MPa, which was 99.4% of that of the base material, and the impact toughness of the weld nugget was 16 J, which was 72.7% of that of the base material.

[0072] Comparative Example 3:

[0073] The same medium-manganese steel plate as in Example 1 was selected as the base material for friction stir welding. The stirring head used was the same as in Example 1. The differences in the implementation steps compared to Example 1 were: the distance between the heating device and the stirring head and the test plate was too large, 30 mm and 12 mm respectively; the heating temperature of the heating device was too low, at 500℃. After the in-situ heat treatment, the average grain size of the weld nugget of the medium-manganese steel friction stir welded joint was 0.62 ± 0.51 μm, larger than that of the base material, and the austenite volume content was 0%. Local cold cracking defects appeared in the weld nugget.

[0074] Example 2:

[0075] The same medium-manganese steel plate as in Example 1 was selected as the base material for welding. A tungsten-rhenium alloy with a shoulder diameter of 12 mm was selected as the stirring head for friction stir welding, and in-situ heat treatment was performed using a rectangular induction heating coil with a width of 15 mm. The main implementation steps are as follows:

[0076] 1) Workpiece clamping: First, place the granite heat-insulating pad on the welding workbench, then place the medium manganese steel plate to be welded on the heat-insulating pad in a butt joint manner, and use a clamping fixture to rigidly fix it to the pad.

[0077] 2) Equipment Debugging: The online heating device is located directly behind the stirring head and is integrated with the welding machine head for synchronous movement. Adjust the position and direction of the heating device so that the center plane of the heating end is aligned with the weld butt joint. The distances between the heating device and the stirring head and the test plate to be welded are 6 mm and 2 mm, respectively.

[0078] 3) Welding and heat treatment during welding: The stirring head speed is set to 300 r / min, the welding speed is 100 mm / min, and the downward pressure of the stirring head shoulder is 0.2 mm.

[0079] 4) Welding heat treatment parameter settings: Induction heating frequency f = 336 Hz, heating temperature 700℃. Infrared thermometer measurement showed that when the temperature of the weld surface below the heating tip was 700℃, the heating power was 35 kW. The dwell time of the heating tip above the weld was 60 s, and the position of the sliding contact on the slide rail was adjusted to achieve an effective heating length of 100 mm.

[0080] 5) Start the friction stir welding equipment to carry out welding. When the heating end passes over the weld, start the induction heating device to carry out heating until the induction heating end completely leaves the weld. Then turn off the induction heating device to stop heating.

[0081] The average grain size of the weld nugget zone of the medium-manganese steel friction stir welded joint after the aforementioned in-situ heat treatment is 0.40±0.41 μm, which is not larger than that of the base metal. The volume content of austenite in the weld nugget zone is 12%, which is 133% of that in the base metal. The tensile strength of the welded joint is 1045±5 MPa, which is 99.8% of that in the base metal, and the impact toughness of the weld nugget zone is 25 J, which is 114% of that in the base metal.

[0082] Example 3:

[0083] The same medium-manganese steel plate as in Example 1 was selected as the base material to be welded. A tungsten-rhenium alloy with a shoulder diameter of 15 mm was selected as the stirring head for friction stir welding, and in-situ heat treatment was performed using a rectangular induction heating coil with a width of 20 mm. The main implementation steps are as follows:

[0084] 1) Workpiece clamping: First, place the high-temperature alloy heat-insulating pad on the welding worktable, then place the medium manganese steel plate to be welded on the heat-insulating pad in a butt joint manner, and use a clamping fixture to rigidly fix it to the pad.

[0085] 2) Equipment Debugging: The online heating device is located directly behind the stirring head and is integrated with the welding machine head for synchronous movement. Adjust the position and direction of the heating device so that the center plane of the heating end is aligned with the butt joint of the weld. The distances between the heating device and the stirring head and the test plate to be welded are 20 mm and 5 mm, respectively.

[0086] 3) Welding and heat treatment during welding: The stirring head speed is set to 100 r / min, the welding speed is 50 mm / min, and the downward pressure of the stirring head shoulder is 0.2 mm.

[0087] The heating temperature of the heating device is 550℃. Start the friction stir welding equipment and the power supply to the heating device to begin welding. The heating device remains on the upper part of the weld for 180 seconds.

[0088] 4) Welding heat treatment parameter settings: Induction heating frequency f = 336 Hz, heating temperature 550℃. Infrared thermometer measurement showed that when the temperature of the weld surface below the heating tip was 700℃, the heating power was 35 kW. The dwell time of the heating tip above the weld was 180 s, and the position of the sliding contact on the slide rail was adjusted to achieve an effective heating length of 150 mm.

[0089] 5) Start the friction stir welding equipment to carry out welding. When the heating end passes over the weld, start the induction heating device to carry out heating until the induction heating end completely leaves the weld. Then turn off the induction heating device to stop heating.

[0090] The average grain size of the weld nugget zone of the medium-manganese steel friction stir welded joint after the aforementioned in-situ heat treatment is 0.38±0.32 μm, which is no larger than that of the base metal. The volume content of austenite in the weld nugget zone is 8.5%, which is 94.4% of that in the base metal. The tensile strength of the welded joint is 1046±2 MPa, which is 99.9% of that in the base metal, and the impact toughness of the weld nugget zone is 19 J, which is 86.4% of that in the base metal.

[0091] It will be readily understood by those skilled in the art that, without conflict, the advantageous technical features of the above-mentioned methods can be freely combined and superimposed.

[0092] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention. The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the protection scope of the present invention.

Claims

1. A friction stir welding apparatus, characterized in that, The device includes a welding machine head and an in-situ heating device (2). The welding machine head has a stirring head (11) for forming friction stir welding on a metal plate (100). The in-situ heating device (2) includes an induction heating body (21) and an induction coil disposed in the induction heating body (21). The in-situ heating device (2) also includes a first electrode connecting post (231) and a second electrode connecting post (232) electrically connected to the induction coil. The first electrode connecting post (231) and the second electrode connecting post (232) are spaced apart along the welding travel direction of the welding machine head, and the spacing between the first electrode connecting post (231) and the second electrode connecting post (232) can be adjusted to adjust the effective heating length of the induction coil.

2. The friction stir welding apparatus according to claim 1, characterized in that, With reference to the orientation of the in-situ heating device in use, the first electrode connecting post (231) is located on the side of the second electrode connecting post (232) near the stirring head (11), the first electrode connecting post (231) is fixedly connected to the induction coil, the second electrode connecting post (232) is slidably connected to the induction coil, and the sliding direction of the second electrode connecting post (232) is parallel to the welding travel direction; and / or, it also includes a bracket, the in-situ heating device (2) is assembled on the bracket and the bracket is connected to the welding machine head, and the distance between the in-situ heating device (2) and the welding machine head in the welding travel direction can be adjusted.

3. The friction stir welding apparatus according to claim 2, characterized in that, The induction coil includes multiple parallel segments (221) spaced apart perpendicular to the welding direction and connecting segments (222) connecting the ends of two adjacent parallel segments (221), with each connecting segment (222) forming a bent shape with each parallel segment (221).

4. The friction stir welding apparatus according to claim 3, characterized in that, An electrical connector (2321) is formed at the bottom end of the second electrode connecting post (232), and the bottom surface of the electrical connector (2321) facing the induction heating body (21) is arc-shaped.

5. The friction stir welding apparatus according to claim 4, characterized in that, An insulating slide (211) is formed on the top surface of the induction heating body (21). A slide rail (223) extending along the welding direction is formed on the top surface of the slide rail (211). A plurality of conductive contacts are provided in the slide rail (223) at intervals along the welding direction. The bottom end of each conductive contact is electrically connected to a different parallel segment (221). The electrical connector (2321) can contact the top end of each conductive contact.

6. The friction stir welding apparatus according to claim 5, characterized in that, The conductive contact is a conductive ball (224), each of which is embedded in the sliding surface of the slide (223) and can be rotated by the electrical connector (2321).

7. The friction stir welding apparatus according to claim 6, characterized in that, The area corresponding to the electrical connector (2321) and the conductive ball (224) has a limiting groove.

8. A method for friction stir welding of metal plates using the friction stir welding apparatus according to any one of claims 1 to 7, characterized in that, Includes the following steps: The distance between the second electrode connecting post (232) and the first electrode connecting post (231) is adjusted to d6, and the distance between the induction heating body (21) and the stirring head (11) in the welding travel direction is adjusted to d4. The weld temperature formed by the welding head when welding the metal plate (100) is cooled to below the phase transformation point temperature A of the metal plate (100). c1 The distance between the weld position and the stirring head (11) in the welding travel direction is d7, d4 > d7; After controlling the operation of the in-situ heating device (2) and then controlling the operation of the welding machine head, the two metal plates (100) positioned on the welding workbench (3) are subjected to friction stir welding.

9. The method for friction stir welding of metal plates according to claim 8, characterized in that, The metal plate (100) is a medium manganese steel plate. The operation of the in-situ heating device (2) ensures that the heating temperature of the weld surface is at A. c1 To A c3 Between these two points, the heating time for the same location of the weld is t, where 50s≤t≤200s.

10. The method for friction stir welding of metal plates according to claim 8, characterized in that, The metal plate (100) is a medium manganese steel plate, the rotation speed of the stirring head (11) is ω, the welding travel speed of the welding machine head is v, the shoulder pressing amount of the stirring head (11) is p, 50 r / min≤ω≤500 r / min, 50 mm / min≤v≤200 mm / min, 0.1 mm≤p≤0.2 mm.

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