Backfilling friction stir spot welding method for realizing material reconfiguration regulation

Abstract

The application discloses a backfill type friction stir spot welding method for realizing material reconfiguration regulation, and belongs to the technical field of welding.The method comprises the following steps: firstly, rotating a sleeve and a stirring needle at a rotating speed of omega 1 to preheat the surface of a welding workpiece; keeping the sleeve and the stirring needle at the same rotating speed of omega 1, continuously lowering in stages, stopping rotating when the sleeve is lowered to a predetermined position; rotating the sleeve to draw back while the stirring needle is rotated and lowered at a speed of nu 2, the sleeve is drawn back at a speed of nu 3, the sleeve and the stirring needle are rotated and stopped at different depths in stages, and the backfill material in the cavity formed by the sleeve and the stirring needle is gradually backfilled to the welding spot area in stages; finally, the sleeve and the stirring needle are separated from the surface of the welded plate and return to the initial position.The method can improve the strength reduction and functional loss caused by the grain size and composition disorder in the welding joint of the heterogeneous structure material through the processing mode in stages.

Description

Technical Field

[0001] This invention relates to the field of welding technology, and in particular to a backfill-type friction stir spot welding method for achieving material reconfiguration control. Background Technology

[0002] Backfill friction stir spot welding offers advantages such as no spatter during welding, a smooth appearance, and high weld strength, making it highly promising for applications in lightweight alloy structural manufacturing in aerospace, shipbuilding, rail transit, and automotive industries. In recent years, heterogeneous materials, combining high strength and toughness, possess high specific strength and specific stiffness, showing great potential for lightweight applications in aerospace and other fields. During structural manufacturing, heterogeneous materials are often joined using traditional welding, riveting, or adhesive bonding methods. However, during backfill friction stir spot welding, the intense plastic flow of the material can disrupt the configuration, affecting the performance advantages of the heterogeneous material. The main reasons for this configuration disruption are: firstly, the rapid stirring of the stirring head causes significant changes in the grain size compared to the substrate; and secondly, the rapid stirring disrupts the compositional order within the material. Changes in grain size and composition create significant strain and stress gradients between different grain size regions of the joint, directly affecting the strength and stability of the welded joint. Disruptions in the compositional order can also greatly affect the strengthening effect inherent in the design principles of heterogeneous materials, reducing structural strength and, in severe cases, leading to component failure. Furthermore, for heterogeneous materials with more feasible designs, disordered changes in grain size and composition can cause the functional combinations within the joint to fail. Therefore, researchers have proposed many methods to control the ordered changes in grain size and composition of materials, thereby regulating the physical properties of heterogeneous materials.

[0003] Chinese invention patent CN109570933 discloses a method for preparing gradient materials via friction stir welding. This method involves spraying a coating onto the surface of a substrate material, with the coating thickness gradient along the substrate direction, followed by sequential rolling and friction stir welding to prepare the gradient material. However, this method prepares a material with a gradient coating thickness through a combination of multi-pass rolling and friction stir welding, without considering the changes in the material configuration within the joint after multiple passes of friction stir welding.

[0004] Chinese invention patent CN108188565 discloses an apparatus and method for preparing tissue-controllable gradient nanostructures. The apparatus includes a support region, a shoulder, and multiple stirring needles of different diameters below the shoulder, forming a stepped structure. The apparatus performs horizontal reciprocating multi-pass processing. However, this method is not suitable for point-connected structures. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a backfill-type friction stir spot welding method for achieving material reconstruction control, thereby improving the strength reduction and functional loss caused by the disorder of grain size and composition in the welded joint of heterogeneous materials.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A backfill-type friction stir spot welding method for achieving material remodeling control includes the following steps:

[0008] Step 1 Preheating Stage: The welding tools used in this method include a coaxially arranged clamping ring, sleeve, and stirring pin. The end faces of the stirring pin, sleeve, and clamping ring are placed on the same horizontal plane, with the stirring pin located in the sleeve and the clamping ring placed on the outside of the sleeve. The three components are pressed down onto the upper surface of the workpiece to be welded, and the workpiece is pressed and fixed. The sleeve and stirring pin begin to rotate at a rotational speed of ω1 to preheat the surface of the workpiece. The rotation directions of the sleeve and stirring pin are always the same.

[0009] Step Two: The insertion stage: Maintain the same rotational speed ω1 for both the sleeve and the stirring needle. The sleeve rotates and inserts into the workpiece, while the stirring needle rotates and retracts. The insertion speed of the sleeve is the same as the retraction speed of the stirring needle. In this stage, the insertion speed of the sleeve is ν1, and the dwell time after the insertion depth is h1 is t1. Change the sleeve rotational speed to ω2, and the dwell time of the sleeve is t2. Continue this staged insertion process, forcing the metal to be welded into the cavity of the sleeve. Continue this process until the sleeve rotational speed is finally changed to ω1. n The dwell time of the rear sleeve is t. n The sleeve stops rotating after it is lowered to the predetermined position;

[0010] Step 3: Backfilling Stage: While the sleeve is rotated and retracted, the stirring needle rotates downwards at a speed of ν2. The sleeve retraction speed is ν3. When the backfilling depth of the stirring needle is h1, the stirring needle and sleeve maintain the same rotation speed ω1 and residence time t1, thus obtaining the first layer of the reconstructed material. When the backfilling depth is h2, the stirring needle and sleeve maintain the same rotation speed ω2 and residence time t2, thus obtaining the second layer of the reconstructed material with a different structure. When the backfilling depth is h3, the stirring needle and sleeve maintain the same rotation speed ω3 and residence time t3, thus obtaining the third layer of the reconstructed material, and so on, until the final backfilling depth is h1. n At the same time, the stirring needle and the sleeve maintain the same rotational speed ω. n and stay time t n Thus, the configuration reconstruction material layer n is obtained, and the backfill material in the cavity formed by the sleeve and the stirring needle is gradually backfilled into the weld area in stages;

[0011] Step 4: Removal Phase: Keep the sleeve and stirring needle rotating at a speed of ω1, and remove the sleeve and stirring needle from the surface of the welded plate at a speed of ν4, returning them to their initial positions.

[0012] Furthermore, in this invention, the rotational speeds ω1-ω... n The range is 100 to 30,000 rpm.

[0013] Furthermore, in the second step of the insertion stage, the insertion speed of the sleeve is the same as the retraction speed of the stirring needle, and ν1 ranges from 1 to 30 mm / min.

[0014] Furthermore, in the backfilling stage of step three, the downward movement speed ν2 of the stirring needle ranges from 1 to 30 mm / min, and the retraction speed ν3 of the sleeve ranges from 1 to 30 mm / min.

[0015] Furthermore, in step four, the evacuation phase, the moving speed ν4 ranges from 1 to 50 mm / min.

[0016] Furthermore, the depth of the sleeve and stirring needle in this invention is the same as the backfill depth h1-h. n The range is 0 to 2.0 mm.

[0017] Furthermore, the residence time of the sleeve and stirring needle in this invention is t1-t n The range is 0 to 50 seconds.

[0018] Furthermore, the welding material used in this invention is a heterogeneous material or a graded functional material.

[0019] Furthermore, a cooling process is added during the backfilling stage in step three. Specifically, a liquid nitrogen or cooling water device is placed under the welding material pad, and a water circulation cooling device is installed inside the stirring needle or sleeve. During the backfilling stage... n When the speed is greater than 1500 rpm, the cooling process is activated to accelerate heat loss and control the heat input during the welding process.

[0020] The beneficial effects of this invention are:

[0021] 1. The backfill-type friction stir spot welding method of the present invention adopts a staged variable process parameter configuration backfilling method. Based on the control of the plunge depth, residence time, and rotation speed, the heat input and material flow in each plunge stage can be controlled. In the staged plunge process, the initial configuration of the heterogeneous material can be preserved, avoiding the loss of mechanical properties of the heterogeneous material in the weld joint and ensuring the quality of the weld joint. While ensuring sufficient material flow in the sleeve, the material flow velocity in the lower part of the stirring pin and the forging force on the material can be changed by changing the rotation speed of the sleeve and the stirring pin, thereby controlling the grain size in the high-speed flow region of the material in the lower part of the stirring pin, and thus achieving the purpose of grain size and composition reconstruction of the weld joint; at the same time, the strong impulsive flow generated by the material flow in the stirring zone can improve the metallurgical bonding of the interface between the stirring zone and the thermomechanical affected zone.

[0022] 2. For heterogeneous materials with a second phase, based on the intergranular distribution characteristics of the second phase, the stirring speed can be controlled to allow for ordered changes in grain size and composition, thereby effectively reconstructing the material's composition distribution and regulating the joint strength, toughness, and functionality of the heterogeneous material. Furthermore, the introduction of cooling processes can effectively suppress grain growth in the heat-affected zone and thermomechanically affected zone; moreover, the combination of controlled cooling and staged backfilling can achieve more precise structural reconstruction of the stirred zone. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the cross-sectional structure of the welding tool and the plate being welded in a backfill-type friction stir spot welding method for achieving material reconstruction control provided by the present invention.

[0024] Figure 2 This is a schematic diagram of the puncture stage process provided by the present invention;

[0025] Figure 3 This is a schematic diagram of the process of forming the first layer of reconfigurable material during backfilling provided by the present invention;

[0026] Figure 4 This is a schematic diagram of the process of forming a second-layer reconfiguration material layer during backfilling, provided by the present invention.

[0027] Figure 5 This is a schematic diagram of the cross-sectional structure of the welding tool and the plate being welded after the process of forming the third layer of the reconstructed material layer during the backfilling process and the withdrawal stage provided by the present invention.

[0028] The reference numerals in the accompanying drawings include:

[0029] 1-Pressure ring, 2-Sleeve, 3-Stirring needle, 4-Upper welded plate, 5-Lower welded plate, 6-Backing plate, 7-Backfill material, 8-Configuration reconstruction material layer. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0031] Example 1

[0032] like Figures 1 to 5 As shown, a backfill-type friction stir spot welding method for achieving material reconfiguration control includes the following steps:

[0033] Step 1: Preheating Stage: A schematic diagram of the cross-sectional structure of the welding tool and the plate being welded during the preheating stage is shown below. Figure 1 As shown, the welding objects are the upper weld plate 4 and the lower weld plate 5. The welding tools used in this method include a coaxially arranged clamping ring 1, sleeve 2, and stirring needle 3. The end faces of the stirring needle 3, sleeve 2, and clamping ring 1 are placed on the same horizontal plane. The stirring needle 3 is located in the sleeve 2, and the clamping ring 1 is set on the outside of the sleeve 2. The three are pressed down as a whole onto the upper surface of the upper weld plate 4, and the upper weld plate 4 is pressed and fixed. The lower weld plate 5 is placed below the upper weld plate 4, and a pad 6 is placed below the lower weld plate 5 for support. The sleeve 2 and the stirring needle 3 start to rotate at a rotation speed ω1 to preheat the upper surface of the upper weld plate 4. In this embodiment, the upper weld plate 4 and plate 5 are both aluminum-titanium layered plates with a thickness of 2mm and a depth of 2.7mm. The outer diameter of the sleeve 2 is 9mm, the diameter of the stirring needle 3 is 5mm, the outer diameter of the clamping ring 1 is 18mm, and ω1 is 1500rpm.

[0034] Step 2, the downward insertion stage: The sleeve 2 is alternately inserted downwards into the upper weld plate 4 at rotational speeds ω1 and ω2. When inserting into the aluminum layer of the upper weld plate 4, the rotational speed is ω1, and the dwell time is t1; when inserting into the titanium layer of the upper weld plate 4, the rotational speed is ω2, and the dwell time is t2. The insertion speed of the sleeve 2 is ν1, which is 9 mm / min. The sleeve 2 is inserted until it penetrates to a depth of 0.7 mm into the lower weld plate 5, and then stops. At the same time, the stirring needle 3 moves upwards at rotational speeds ω1 and ω2. The retraction speed of the stirring needle 3 is the same as the insertion speed of the sleeve 2. The metal in the weld plate is squeezed into the cavity inside the sleeve 2, forming backfill material 7. In this embodiment, t1 is 1 s, t2 is 1.5 s, ω1 is 1500 rpm, and ω2 is 3500 rpm.

[0035] Step 3 Backfilling Stage: A cooling water device is installed under the welding material pad 6, and a water circulation cooling device is set inside the sleeve 2. When the rotation speed is greater than 1500 rpm during the backfilling stage, the water circulation cooling device is activated to accelerate heat loss and control the heat input of the welding process. The sleeve 2 is rotated upward and pulled back. When the sleeve 2 is in the aluminum layer, the rotation speed is ω1 and it stays for 1 second to form the first configuration reconstruction material layer 8. When the sleeve 2 is in the titanium layer, the rotation speed is ω2 and it stays for 1.5 seconds to form the second configuration reconstruction material layer 8. While the sleeve 2 is retracted at a rotational speed ν3 of 9 mm / min, the stirring pin 3 rotates downwards at rotational speeds ω2 and ω1, with the downward pressing speed of the stirring pin 3 being ν2 of 10 mm / min. This gradually backfills the backfill material 7 within the cavity formed by the sleeve 2 and the stirring pin 3 into the weld area in stages. Due to the different rotational speeds and the certain dwell time, internal defects caused by the different flow properties of different metals during the backfilling welding process can be mitigated, ensuring the weld quality of the joint and improving the joint strength. Simultaneously, by using the high-speed downward pressing process parameters of the stirring pin 3, when there is sufficient material inside the sleeve 2, the internal pressure of the plastic metal inside the sleeve 2 can be increased, thereby reducing the formation of voids. In this embodiment, ω1 is 1500 rpm and ω2 is 3500 rpm.

[0036] Step 4: Removal phase: Sleeve 2 and stirring needle 3 move upward synchronously at a speed ν4 of 9 mm / min. When sleeve 2 and stirring needle 3 reach the upper surface of the upper welded plate 4, they stop rotating and are pulled away from the surface of the upper welded plate 4, returning to their initial positions. This completes the entire backfill friction stir spot welding process.

[0037] Example 2

[0038] like Figures 1 to 5 As shown, a backfill-type friction stir spot welding method for achieving material reconfiguration control includes the following steps:

[0039] Step 1: Preheating Stage: A schematic diagram of the cross-sectional structure of the welding tool and the plate being welded during the preheating stage is shown below. Figure 1As shown, the welding objects are the upper weld plate 4 and the lower weld plate 5. The welding tools used in this method include a coaxially arranged clamping ring 1, sleeve 2, and stirring pin 3. The end faces of the stirring pin 3, sleeve 2, and clamping ring 1 are placed on the same horizontal plane, with the stirring pin 3 located inside the sleeve 2. The clamping ring 1 is set on the outside of the sleeve 2. The three components are pressed down onto the upper surface of the upper weld plate 4, and the upper weld plate 4 is pressed and fixed. The lower weld plate 5 is placed below the upper weld plate 4. A support plate 6 is placed below to allow the sleeve 2 and stirring needle 3 to start rotating at a rotational speed ω1, preheating the upper surface of the upper weld plate 4. In this embodiment, the upper weld plate 4 is a SiC / 6061 aluminum plate with SiC gradient distribution, and the lower weld plate 5 is an aluminum plate. The thickness of the upper weld plate 4 and the lower weld plate 5 is 2mm, the depth is 2.3mm, the outer diameter of the sleeve 2 is 5mm, the diameter of the stirring needle 3 is 2.5mm, the outer diameter of the clamping ring 1 is 15mm, and ω1 is 1000rpm.

[0040] Step Two: Insertion Stage

[0041] The sleeve 2 is driven downwards into the upper weld plate 4 at a rotational speed ω1, with the downward speed ν1 being 10 mm / s. After driving in 0.5 mm, it pauses for 0.5 s. It continues to drive in 0.5 mm at a rotational speed ω2, pauses for 1 s, then drives in 0.5 mm at a rotational speed ω3, pauses for 1.5 s, and continues to drive in 0.5 mm at ω3, pauses for 2 s. Finally, it drives in 0.3 mm into the lower weld plate 5 at a rotational speed ω4 until it stops rotating. At the same time, the stirring needle 3 moves upwards at the same rotational speed as the sleeve 2. The retraction speed of the stirring needle 3 is the same as the downward speed of the sleeve 2. The metal in the weld plate is squeezed into the cavity inside the sleeve 2, forming backfill material 7. In this embodiment, ω1 is 1000 rpm, ω2 is 1200 rpm, ω3 is 1500 rpm, and ω4 is 1800 rpm.

[0042] Step 3: Backfilling Stage: A cooling water device is installed under the welding material backing plate 6. Simultaneously, a water circulation cooling device is installed inside the sleeve 2. When the rotation speed exceeds 1500 rpm during the backfilling stage, the water circulation cooling device is activated to accelerate heat loss and control the heat input during the welding process. The sleeve 2 is rotated upwards at a speed ω4-ω1 and pulled back. Simultaneously, while the sleeve 2 is pulled back at an upward rotation speed ν3 of 10 mm / min, the stirring needle 3 is rotated downwards at a speed ω4-ω1, with a downward pressing speed ν2 of 12 mm / min. n. Gradually fill the backfill material 7 in the cavity formed by the sleeve 2 and the stirring needle 3 into the welding area in stages. Fill 0.3mm at a rotation speed ω4 and hold for 2s to form the first layer of configuration reconstruction material 8. Then fill 0.5mm at a rotation speed ω4 and hold for 1.5s to form the second layer of configuration reconstruction material 8. Then fill 0.5mm at a rotation speed ω3 and hold for 1s to form the third layer of configuration reconstruction material 8. Finally fill 0.5mm at a rotation speed ω2 and hold for 0.5s to form the fourth layer of configuration reconstruction material 8. Finally, the rotation speed ω1 is maintained until backfilling is complete. Due to the different rotation speeds and the certain dwell time, internal defects caused by the different flow properties of different metals during backfilling welding can be mitigated, ensuring joint welding quality and improving joint strength. Simultaneously, by using the high-speed downward thrust of the stirring pin 3, the internal pressure of the plastic metal inside the sleeve 2 can be increased when there is sufficient material inside the sleeve 2, thereby reducing the formation of voids. In this embodiment, ω1 is 1000 rpm, ω2 is 1200 rpm, ω3 is 1500 rpm, and ω4 is 1800 rpm.

[0043] Step 4: Removal Stage: When sleeve 2 and stirring pin 3 reach the upper surface of the upper weld plate 4 at a speed of ν4 (10 mm / min), they stop rotating. Sleeve 2 and stirring pin 3 are then removed from the surface of the upper weld plate 4 and returned to their initial positions, thus completing the entire backfill friction stir spot welding process. Due to the variable-speed, staged backfilling and the cooling process introduced during welding, the SiC gradient distribution is maintained within the joint, and the grains are distributed from coarse to fine along the upper surface to the lap surface, thereby achieving improved joint mechanical properties. The low-speed backfilling process increases the internal pressure of the ductile metal, prolongs the atomic diffusion time at the interface between the stirring zone and the thermomechanical influence zone, improves the atomic diffusion effect, and enhances the metallurgical bonding quality, thereby controlling the quality of the welded joint.

Claims

1. A backfill-type friction stir spot welding method for achieving material reconfiguration control, characterized in that, Includes the following steps: Step 1 Preheating stage: The welding tools used in this method include a coaxial clamping ring, a sleeve, and a stirring pin. The end faces of the stirring pin, sleeve, and clamping ring are placed on the same horizontal plane. The stirring pin is located in the sleeve, and the clamping ring is set on the outside of the sleeve. The three components are pressed down onto the upper surface of the workpiece to be welded, and the workpiece is pressed and fixed. The sleeve and stirring pin start to rotate at ω1 to preheat the surface of the workpiece. The rotation direction of the sleeve and stirring pin is always the same. Step Two: The insertion stage: Maintain the same rotational speed ω1 for both the sleeve and the stirring needle. The sleeve rotates and inserts into the workpiece, while the stirring needle rotates and retracts. The insertion speed of the sleeve is the same as the retraction speed of the stirring needle. In this stage, the insertion speed of the sleeve is ν1, and the dwell time after the insertion depth is h1 is t1. After changing the sleeve rotational speed to ω2, the dwell time of the sleeve is t2. This process is repeated in stages until the workpiece is forced into the cavity of the sleeve. Finally, the sleeve rotational speed is changed to ω1. n The dwell time of the rear sleeve is t. n The sleeve stops rotating after it is lowered to the predetermined position; Step 3: Backfilling Stage: While the sleeve is rotated and retracted, the stirring needle rotates downwards at a speed of ν2. The sleeve retraction speed is ν3. When the backfilling depth of the stirring needle is h1, the stirring needle and sleeve maintain the same rotation speed ω1 and residence time t1, thus obtaining the first layer of the remodeling material. When the backfilling depth is h2, the stirring needle and sleeve maintain the same rotation speed ω2 and residence time t2, thus obtaining the second layer of the remodeling material with a different structure. When the backfilling depth is h3, the stirring needle and sleeve maintain the same rotation speed ω3 and residence time t3, thus obtaining the third layer of the remodeling material, and so on, until the final backfilling depth is h1. n At the same time, the stirring needle and the sleeve maintain the same rotational speed ω. n and stay time t n Thus, the configuration reconstruction material layer n is obtained, and the backfill material in the cavity formed by the sleeve and the stirring needle is gradually backfilled into the welding area in stages; Step 4: Removal phase: The sleeve and stirring needle maintain a rotation speed of ω1, and the stirring needle is withdrawn from the surface of the welded plate at a speed of ν4, returning to the initial position; In step three, during the backfilling stage, a cooling process is incorporated. Specifically, a liquid nitrogen or cooling water device is placed under the welding material backing plate, and a water circulation cooling device is installed inside the stirring needle or sleeve. During the backfilling stage... n When the speed is greater than 1500 rpm, the cooling process is activated to accelerate heat loss and control the heat input during the welding process.

2. The backfill-type friction stir spot welding method for achieving material remodeling control according to claim 1, characterized in that, In this method, the rotational speeds of the sleeve and the stirring needle are ω1-ω n The range is 100 to 30,000 rpm.

3. The backfill-type friction stir spot welding method for achieving material remodeling control according to claim 1, characterized in that, In step two, during the insertion stage, the insertion speed of the sleeve is the same as the withdrawal speed of the stirring needle, with ν1 ranging from 1 to 30 mm / min.

4. A backfill-type friction stir spot welding method for achieving material remodeling control according to claim 1, characterized in that, In step three, during the backfilling stage, the downward movement speed ν2 of the stirring needle ranges from 1 to 30 mm / min, and the retraction speed ν3 of the sleeve ranges from 1 to 30 mm / min.

5. A backfill-type friction stir spot welding method for achieving material remodeling control according to claim 1, characterized in that, During the evacuation phase in step four, the moving speed ν4 ranges from 1 to 50 mm / min.

6. The backfill-type friction stir spot welding method for achieving material reconfiguration control according to claim 1, characterized in that, In this method, the depth of the sleeve and stirring needle insertion is related to the backfill depth h1-h. n The range is 0 to 2.0 mm.

7. The backfill-type friction stir spot welding method for achieving material remodeling control according to claim 1, characterized in that, In this method, the residence time of the sleeve and stirring needle is t1-t. n The range is 0–50 s.

8. The backfill-type friction stir spot welding method for achieving material remodeling control according to claim 1, characterized in that, The welding materials used in this method are heterogeneous materials or graded functional materials.

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