A stir head and a welding method for dissimilar material friction stir welding of unequal thicknesses

Abstract

The present application belongs to the technical field of welding, and specifically provides a stir head and a welding method for friction stir welding of dissimilar materials with different thicknesses. The stir head comprises coaxially arranged from top to bottom a large shoulder, a small shoulder and a stir pin. The diameters of the large shoulder, the small shoulder and the stir pin are sequentially reduced. The length of the stir pin is not greater than the thickness of the thin plate to be welded. The sum of the length of the small shoulder and the stir pin is not greater than the thickness of the thick plate to be welded. When welding by using the above stir head, a step is processed at the length edge of the thick plate, the height of the step is equal to the thickness of the thin plate, the thin plate is assembled on the step, and the friction welding is performed with the thick plate on the top and the thin plate on the bottom. The welding performance between dissimilar plates with different thicknesses can be improved by the present application.

Description

Technical Field

[0001] This invention mainly relates to the field of welding-related technologies, specifically a stirring head and welding method for friction stir welding of dissimilar materials of unequal thickness. Background Technology

[0002] Friction stir welding (FSW), as a solid-state joining technology, has gradually gained widespread attention and application in high-end manufacturing, especially in the field of lightweight intelligent manufacturing. Its welding principle is well-known. Compared to traditional fusion welding methods, FSW offers numerous advantages, including a green and environmentally friendly welding process, low energy consumption, minimal welding deformation, and high weld quality. It is particularly suitable for joining aluminum alloys, magnesium alloys, and other difficult-to-weld materials. In the FSW process, the shape, size, and other geometric characteristics of the welding tool (or stirring head) play a decisive role in the weld quality. A typical stirring head consists of a shoulder and a stirring head. The stirring head intensely rubs against the materials being welded, generating heat and driving the material to undergo plastic flow, forming a weld. Currently, FSW technology has been applied to some extent in aerospace, automotive manufacturing, and other fields.

[0003] Due to its unique advantages, FSW technology is also well-suited for efficient welding of dissimilar materials. Especially for materials with significant differences in properties, such as aluminum / steel, aluminum / copper, aluminum / titanium, magnesium / titanium, and magnesium / copper, the thickness of the sheet metal used in actual applications often varies. Typically, lower-strength sheets (such as light alloys like aluminum and magnesium) are thicker, while higher-strength sheets (such as steel, copper, and titanium) are thinner.

[0004] For dissimilar materials of unequal thickness, conventional butt welding for FSW is limited by the thickness of the thinner plate (such as steel, copper, titanium, etc.) and insufficient effective bonding area. Conventional lap welding for FSW typically places the thicker plate (such as aluminum, magnesium, etc., light alloys) on top of the thinner plate (such as steel, copper, titanium, etc.), resulting in a longer stirring pin (generally the same as or slightly less than the thickness of the thicker plate). During welding, the bottom of the stirring pin is subjected to intense friction from the high-strength plate (such as steel, copper, titanium, etc.), making it prone to wear or breakage. The final joint thickness is the sum of the thicknesses of the two plates, occupying too much longitudinal space and subject to large bending moments, resulting in poor overall performance. Summary of the Invention

[0005] To address the shortcomings of current technologies, this invention, based on existing technologies and practical applications, provides a stirring head and welding method for friction stir welding of dissimilar materials of unequal thickness, which can improve the welding performance between dissimilar plates of unequal thickness.

[0006] The technical solution of the present invention is as follows:

[0007] A stirring head for friction stir welding of dissimilar materials of unequal thickness includes a large shoulder, a small shoulder, and a stirring pin arranged coaxially from top to bottom, with the large and small shoulders made of different materials. The diameters of the large shoulder, small shoulder, and stirring pin decrease sequentially. The length of the stirring pin is not greater than the thickness of the thin plate to be welded; specifically, the length of the stirring pin is equal to or slightly less than the thickness of the thin plate to be welded. The sum of the lengths of the small shoulder and the stirring pin is not greater than the thickness of the thick plate to be welded; that is, the sum of the lengths of the small shoulder and the stirring pin is equal to or slightly less than the thickness of the thick plate to be welded. Preferably, the large shoulder is made of H13 tool steel, and the small shoulder is made of tungsten-rhenium alloy, thereby effectively controlling manufacturing costs while ensuring the performance of key components.

[0008] For friction stir welding of dissimilar materials of unequal thickness, a step is machined along the edge of the thick plate, with the step height equal to the thickness of the thin plate. The thin plate is then assembled onto the step, with the thick plate on top and the thin plate on the bottom. Welding is performed using the aforementioned stirring head. During welding, the small shoulder contacts and rubs against the overlapping surfaces of the two plates, while the side of the stirring pin contacts and rubs against the interface between the two plates.

[0009] Furthermore, the welding steps are as follows:

[0010] S1. For two different types of plates with different thicknesses, a step is machined along the edge of the thicker plate, with the step height being the same as that of the thinner plate. The two plates are then cleaned.

[0011] S2. Assemble the thin plate into the step of the thick plate, with the thick plate on top and the thin plate on the bottom, and clamp it. Assemble the stirring tool onto the friction stir welding machine and position it with the clamped plates so that the bottom of the stirring needle is tangent to the mating surface of the inner side of the two plates.

[0012] S3. Start the friction stir welding machine, control the stirring tool to rotate and press down. When the stirring needle has completely entered the material, it stays for a period of time. Heat is generated by friction between the bottom of the small shoulder and the plate, causing the thick plate to plasticize. Then control the stirring tool to continue pressing down so that the small shoulder enters the material until it is completely inside the material. At this time, the small shoulder contacts and rubs against the overlapping surface of the two plates, while the side of the stirring needle contacts and rubs against the interface of the two plates.

[0013] S4. Control the friction stir welding machine to weld according to the set path and parameters to achieve friction stir welding. During the welding process, always maintain the contact friction between the small shoulder and the lap surface and the contact friction between the side of the stirring pin and the mating surface.

[0014] S5. After processing is complete, remove the stirring tool, then turn off the friction stir welding machine, and place the processed plate in the air to cool to room temperature.

[0015] Furthermore, the width of the step processed on the thick plate is 20-30mm.

[0016] Furthermore, the thin plate has a higher hardness than the thick plate.

[0017] The beneficial effects of this invention are:

[0018] The stirring tool of this invention can simultaneously weld the butt joint and lap joint interfaces of dissimilar plates of different thicknesses, improving welding efficiency, eliminating the need for additional preparation and steps, saving time and labor costs, and simplifying the welding process.

[0019] Traditionally, lap joints and butt joints usually require different welding methods or additional process steps. This invention simplifies the entire welding process through a single welding process, reduces material waste, improves material utilization, reduces the weight of the weldment, and simultaneously completes the welding of butt joints and lap joints, thereby improving welding quality. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a stirring head for friction stir welding of dissimilar materials of unequal thickness, as disclosed in an embodiment of the present invention.

[0021] Figure 2 This is a flowchart of a friction stir welding method for dissimilar materials of unequal thickness disclosed in an embodiment of the present invention; Figure 2 Part (a) is a schematic diagram before welding, part (b) is a schematic diagram during welding, and part (c) is a schematic diagram after welding.

[0022] Figure 3 This is a physical schematic diagram of a stirring head suitable for friction stir welding of dissimilar materials of unequal thickness, as disclosed in an embodiment of the present invention.

[0023] Figure 4 This is a macroscopic weld morphology diagram after welding in Embodiment 1 of the present invention.

[0024] Figure 5 This is a macroscopic weld cross-sectional morphology diagram after welding in Embodiment 1 of the present invention.

[0025] Figure 6 This is a macroscopic weld morphology diagram after welding in Embodiment 2 of the present invention.

[0026] Figure 7 This is a macroscopic weld morphology diagram after welding in Embodiment 3 of the present invention.

[0027] Figure 8 This is a macroscopic weld morphology diagram after welding in Embodiment 4 of the present invention.

[0028] Figure 9 This is a macroscopic weld morphology diagram after welding at a rotation speed of 400 rpm, corresponding to Embodiment 5 of the present invention.

[0029] Figure 10This is a macroscopic weld morphology diagram after welding at a rotation speed of 600 rpm, corresponding to Embodiment 5 of the present invention.

[0030] Figure 11 This is a macroscopic weld morphology diagram after welding at a rotation speed of 800 rpm, corresponding to Embodiment 5 of the present invention.

[0031] The labels shown in the attached diagram are: 1. Large shoulder, 2. Small shoulder, 3. Stirring needle, 4. Thick plate, 5. Thin plate. Detailed Implementation

[0032] The present invention will be further described in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined in this application.

[0033] This embodiment provides a stirring head for friction stir welding of dissimilar materials of unequal thickness. For example... Figure 1 As shown, the stirring head adopts a unique three-section design, including a large shoulder 1, a small shoulder 2, and a stirring pin 3, which together constitute the stirring tool. The diameters of the large shoulder 1, small shoulder 2, and stirring pin 3 decrease sequentially, and the sum of the lengths of the small shoulder 2 and the stirring pin 3 is equal to the thickness of the thick plate 4 to be welded, while the length of the stirring pin 3 is equal to the thickness of the thin plate 5 to be welded. The large shoulder 1 and small shoulder 2 employ differentiated material designs: the large shoulder 1 uses H13 tool steel to reduce costs, while the small shoulder 2 uses a tungsten-rhenium alloy to enhance the high-temperature resistance and wear resistance of key components. This tungsten-rhenium alloy, by weight percentage, contains 24.0% to 26.0% rhenium (Re), with the balance being tungsten (W) and unavoidable trace impurities, wherein the total content of the trace impurities is less than 0.1%. Preferably, a W-25Re alloy conforming to ASTM F2885 is used, which ensures that the small shoulder maintains shape stability and excellent wear resistance when welding high-strength materials.

[0034] In this embodiment, this stirring tool can be used to weld dissimilar materials of different thicknesses (thicker plates are usually lightweight alloy materials such as aluminum and magnesium, while thinner plates are usually high-strength materials such as steel, titanium, and copper), while simultaneously welding the lap interface and the butt interface to form a butt-lap composite joint of dissimilar materials of different thicknesses.

[0035] This embodiment also provides a welding method for the above-mentioned stirring head, the process flow of which is as follows: Figure 2 As shown, the main steps include the following.

[0036] Step 1: Use two different types of boards of different thicknesses, with the softer board being the thicker board 4 and the harder board being the thinner board 5. Cut a 20-30mm wide step along the length edge of the thicker board 4, with the height being the same as the thickness of the thinner board 5. Clean the two boards.

[0037] Step 2: Assemble the thin plate 5 into the thick plate step, with the thick plate 4 on top and the thin plate 5 on the bottom; assemble the stirring tool onto the friction stir welding machine and position it with the clamped plate, so that the bottom of the stirring pin 3 is tangent to the mating interface.

[0038] Step 3: Start the friction stir welding machine, control the stirring tool to rotate and press down. After the stirring needle 3 has completely entered the material, it stays for a period of time. Heat is generated by the friction between the bottom of the small shoulder 2 and the plate, causing the thick plate 4 to be plasticized. Then control the stirring tool to continue pressing down so that the small shoulder 2 enters the material until it is completely inside the material. At this time, the small shoulder contacts and rubs against the overlapping surface of the dissimilar materials, while the side of the stirring needle contacts and rubs against the interface of the dissimilar materials.

[0039] Step 4: Achieve friction stir welding by controlling the friction stir welding machine to weld according to the set path and parameters. During the welding process, always maintain the contact friction between the small shaft shoulder and the lap surface and the contact friction between the side of the stirring pin and the mating surface.

[0040] Step 5: After processing is complete, remove the stirring tool, then turn off the friction stir welding equipment, and place the processed plate in the air to cool to room temperature.

[0041] The performance of the stirring head and welding method in the above embodiments was verified through specific examples, as follows.

[0042] Example 1:

[0043] A friction stir welding method applicable to dissimilar materials of unequal thickness is disclosed. The method described in the above embodiment is used to weld 6mm thick 6061-T6 aluminum alloy and 3mm thick 304 stainless steel. A step 25mm wide and 3mm high is cut into the 6061-T6 aluminum alloy. Before welding, both plates are cleaned. The 304 stainless steel is placed on the advancing side, and the 6061-T6 aluminum alloy is used as the upper plate. The stirring head is installed on the friction stir welding machine. The diameter of the large shoulder 1 is 30mm, the diameter of the small shoulder 2 is 15mm, and the stirring pin 3 is a 5mm cylinder. Preset welding parameters: rotation speed 400rpm, welding speed 50mm / min, dwell time of small shoulder 2 8s, dwell time of large shoulder 1 4s, downward pressure 0.15mm, and total weld length 160mm. After the workpiece is assembled, the friction stir welding machine is started. After the above welding steps are completed, the friction stir welding system is turned off, and the welded product is removed. The tensile strength of the sample is measured to be 792.94 N / mm² through a tensile test. Figure 4 and Figure 5These are the macroscopic weld morphology and macroscopic weld cross-sectional morphology of this example, respectively.

[0044] Example 2:

[0045] A friction stir welding method applicable to dissimilar materials of unequal thickness is disclosed. The method described in the above embodiment is used to weld 6mm thick 6061-T6 aluminum alloy and 3mm thick 304 stainless steel. A step 25mm wide and 3mm high is cut into the 6061-T6 aluminum alloy. Before welding, both plates are cleaned. The 304 stainless steel is placed on the advancing side, and the 6061-T6 aluminum alloy is used as the upper plate. The stirring head is installed on the friction stir welding machine. The diameter of the large shoulder 1 is 30mm, the diameter of the small shoulder 2 is 15mm, and the stirring pin 3 is a 5mm cylinder. The preset welding parameters are: rotation speed 200rpm, welding speed 50mm / min, dwell time of small shoulder 2 8s, dwell time of large shoulder 1 4s, downward pressure 0.15mm, and total weld length 160mm. After the workpiece is assembled, the friction stir welding machine is started. After the above welding steps are completed, the friction stir welding system is turned off, and the welded product is removed. The tensile strength of the sample is measured to be 917.11 N / mm² through a tensile test. Figure 6 These are the macroscopic weld morphologies of this example.

[0046] Example 3:

[0047] A friction stir welding method applicable to dissimilar materials of unequal thickness is disclosed. The method described in the above embodiment is used to weld 6mm thick 6061-T6 aluminum alloy and 2mm thick 304 stainless steel. A step 25mm wide and 3mm high is cut into the 6061-T6 aluminum alloy. Before welding, both plates are cleaned. The 304 stainless steel is placed on the advancing side, and the 6061-T6 aluminum alloy is used as the upper plate. The stirring head is installed on the friction stir welding machine. The large shoulder 1 has a diameter of 30mm, the small shoulder 2 has a diameter of 15mm, and the stirring pin 3 is a 5mm cylinder. The preset welding parameters are: rotation speed 600rpm, welding speed 50mm / min, dwell time of small shoulder 2 8s, dwell time of large shoulder 1 4s, downward pressure 0.15mm, and total weld length 160mm. After the workpiece is assembled, the friction stir welding machine is started. After the above welding steps are completed, the friction stir welding system is turned off, and the welded product is removed. The tensile strength of the sample is measured to be 616.50 N / mm² through a tensile test. Figure 7 These are the macroscopic weld morphologies of this example.

[0048] Example 4:

[0049] A friction stir welding method applicable to dissimilar materials of unequal thickness is disclosed. The method described in the above embodiment is used to weld 6mm thick 6061-T6 aluminum alloy and 3mm thick T2 pure copper. A step 25mm wide and 3mm high is cut into the 6061-T6 aluminum alloy. Before welding, both plates are cleaned, with the pure copper placed on the rear side and the 6061-T6 aluminum alloy as the upper plate. The stirring head is installed on the friction stir welding machine. The large shoulder 1 has a diameter of 30mm, the small shoulder 2 has a diameter of 15mm, and the stirring pin 3 is a 5mm cylinder. The preset welding parameters are: rotation speed 600rpm, welding speed 100mm / min, dwell time at small shoulder 2 7s, dwell time at large shoulder 1 3s, downward pressure 0.15mm, and total weld length 160mm. After the workpiece is assembled, the friction stir welding machine is started. After the above welding steps are completed, the friction stir welding system is turned off, and the welded product is removed. The tensile strength of the sample is measured to be 232.09 N / mm² through a tensile test. Figure 8 These are the macroscopic weld morphologies of this example.

[0050] Example 5:

[0051] A friction stir welding method applicable to dissimilar materials of unequal thickness is provided, wherein the method described in the above embodiment is used to weld 6mm thick 6061-T6 aluminum alloy and 3mm thick T2 pure copper. A 25mm wide and 3mm high step was cut into a 6061-T6 aluminum alloy plate. Before welding, both plates were cleaned, with the pure copper plate placed on the back side and the 6061-T6 aluminum alloy plate as the top plate. The stirring head was installed on the friction stir welding machine. The large shoulder 1 had a diameter of 30mm, the small shoulder 2 had a diameter of 15mm, and the stirring pin 3 was a 5mm cylinder. The preset welding parameters were: a constant welding speed of 50mm / min, rotation speeds of 400 rpm, 600 rpm, and 800 rpm, a dwell time of 7s for small shoulder 2 and 3s for large shoulder 1, a pressure of 0.15mm, and a total weld length of 160mm. After the workpiece assembly was completed, the friction stir welding machine was started. After the above welding steps were completed, the friction stir welding system was turned off, and the welded product was removed. Tensile tests were conducted, and the tensile strengths of the samples were measured to be 433.76 N / mm², 318.81 N / mm², and 202.83 N / mm², respectively. Figure 9 , Figure 10 , Figure 11 These are the macroscopic weld morphologies of this example.

[0052] It is evident that the stirring head and welding method provided by this invention can weld dissimilar materials of varying thicknesses, and simultaneously weld lap and butt joint interfaces to form butt-lap composite joints of dissimilar materials of varying thicknesses, thereby significantly increasing the effective bonding area between dissimilar materials and significantly improving the mechanical properties of the joint.

Claims

1. A method for friction stir welding of dissimilar materials of unequal thickness, wherein welding is performed using a stirring head, the stirring head comprising a large shoulder, a small shoulder, and a stirring pin arranged coaxially from top to bottom, the diameters of the large shoulder, the small shoulder, and the stirring pin decreasing sequentially, the length of the stirring pin not exceeding the thickness of the thin plate to be welded, and the sum of the lengths of the small shoulder and the stirring pin not exceeding the thickness of the thick plate to be welded, characterized in that... The specific welding steps are as follows: S1. For two different types of plates with different thicknesses, a step is machined along the edge of the thicker plate, with the step height being the same as that of the thinner plate. The two plates are then cleaned. S2. Assemble the thin plate into the step of the thick plate, with the thick plate on top and the thin plate on the bottom, and clamp it. Assemble the stirring tool onto the friction stir welding machine and position it with the clamped plates so that the bottom of the stirring needle is tangent to the mating surface of the inner side of the two plates. S3. Start the friction stir welding machine, control the stirring tool to rotate and press down. When the stirring needle has completely entered the material, it stays for a period of time. Heat is generated by friction between the bottom of the small shoulder and the plate, causing the thick plate to plasticize. Then control the stirring tool to continue pressing down so that the small shoulder enters the material until it is completely inside the material. At this time, the small shoulder contacts and rubs against the overlapping surface of the two plates, while the side of the stirring needle contacts and rubs against the interface of the two plates. S4. Control the friction stir welding machine to weld according to the set path and parameters to achieve friction stir welding. During the welding process, always maintain the contact friction between the small shoulder and the lap surface and the contact friction between the side of the stirring pin and the mating surface. S5. After processing, remove the stirring tool, then turn off the friction stir welding machine, and place the processed plate in the air to cool to room temperature.

2. The method for friction stir welding of dissimilar materials of unequal thickness according to claim 1, characterized in that, The width of the step machined on the thick plate is 20-30mm.

3. The method for friction stir welding of dissimilar materials of unequal thickness according to claim 1, characterized in that, The thinner plate has a higher hardness than the thicker plate.

4. The method for friction stir welding of dissimilar materials of unequal thickness according to claim 1, characterized in that, The large shoulder is made of H13 tool steel, and the small shoulder and stirring needle are made of tungsten-rhenium alloy.

Images