A friction stir welding apparatus and method for improving the strength and corrosion resistance of aluminum / steel lap joints

Abstract

The application discloses a friction stir welding device and method for improving the strength and corrosion resistance of an aluminum / steel ring joint, and relates to a friction stir welding device and method. The application is used to solve the problems of low strength, insufficient corrosion resistance and large design difficulty of a tooling of an aluminum / steel ring joint caused by surface thinning, weak root connection and large potential difference. The friction stir welding device comprises a welding tool and a radial support heating device. The welding tool is arranged on the outer surface of a workpiece, and the radial support heating device is arranged on the back of the workpiece. The welding tool comprises a screw rod and a water-cooled static shoulder sleeve, the screw rod is inserted into the water-cooled static shoulder sleeve, and the screw rod and the water-cooled static shoulder sleeve are coaxially and fixedly arranged through positioning installation holes. A wire feeding port is arranged on the side wall of the water-cooled static shoulder sleeve, and a cooling water channel is arranged in the water-cooled static shoulder sleeve. A screw groove is arranged on the lower side wall of the screw rod, and a stirring needle is arranged at the lower end of the shoulder of the screw rod. The radial support heating device comprises a sliding block, a sliding rail and a control assembly, is arranged on the back of the workpiece, the sliding rail is annular, the sliding block can freely slide along the sliding rail, and the outer surface of the sliding block is in close contact with the inner surface of the workpiece. The application belongs to the technical field of solid-phase welding.

Description

Technical Field

[0001] This invention relates to a friction stir welding apparatus and method, belonging to the field of solid-state welding technology. Background Technology

[0002] Driven by the dual demands of lightweight equipment and high-performance manufacturing, "replacing steel with aluminum" has become a core approach for reducing structural weight and increasing efficiency in fields such as aerospace, marine engineering, and automotive industry. The mechanical reliability and environmental durability of aluminum / steel ring joints directly determine the service safety and lifespan of the structure. Friction stir welding (FSW) has become the mainstream technology for welding dissimilar materials like aluminum and steel due to its advantages such as high weld quality and absence of fusion defects. However, for highly corrosive service environments such as marine and chemical plants, aluminum / steel annular friction stir welded joints still have the following core problems: 1. The shoulder pressing into the surface of the workpiece results in weld thinning, reducing the joint's load-bearing capacity; 2. The stirring pin usually does not penetrate the workpiece, and insufficient heat generation and mechanical stirring at the root of the aluminum / steel interface easily lead to poor metallurgical bonding, resulting in weak connection defects. This not only reduces the interface bonding strength but also easily forms concentration cells due to the crevice effect, inducing local crevice corrosion; 3. The standard electrode potentials of aluminum and steel differ significantly, easily forming galvanic cells in an electrolyte environment, causing structural failure; 4. The thermal expansion coefficients of aluminum and steel differ greatly. For annular joints, the heat gradient in the circumferential direction during welding easily leads to elliptical deformation of the structure, making tooling back support difficult.

[0003] A search revealed that existing technologies mostly attempt to solve the above problems from the perspectives of process optimization and welding tool improvement, but all of them have certain limitations.

[0004] A patent application (CN119703315A, filed on December 12, 2024) discloses a method for preparing a carbon nanotube-reinforced aluminum / steel composite plate using friction stir welding, and the composite plate itself. The method involves welding an aluminum alloy base material and a steel base material using friction stir welding. Before friction stir welding, steps are pre-machined on the upper and lower end faces of the mating surfaces of the aluminum alloy and steel base materials, forming a serrated shape to create complete steps and achieve tight engagement between the mating surfaces. Furthermore, carbon nanotube coatings are pre-laid on the upper and lower complete steps formed by the aluminum alloy and steel base materials. The stirring pin of the friction stir welding tool is pre-machined into a serrated shape matching the mating surfaces. However, this method requires extremely high precision in coating preparation, processing consistency, and assembly gap control, resulting in poor adaptability for large-scale production.

[0005] A patent application (CN119747839B, filed March 10, 2025) discloses a penetrating double-shoulder friction stir welding device and method. The welding device includes a headstock, a tailstock, an outer clamp, an inner support fixture, an outer welding head, and a retractable lower shoulder system. The headstock and tailstock are mounted on a machine bed and positioned on opposite sides of the workpiece to be welded, both used to clamp the workpiece. The inner support fixture is positioned between the headstock and tailstock to expand the workpiece from within. The outer clamp is arranged circumferentially around the workpiece and clamps it. The outer welding head and the retractable lower shoulder system jointly perform circumferential penetrating double-shoulder friction stir welding on the workpiece. However, this technology uses complex fixture structures and has high manufacturing costs. Furthermore, the excessively long stirring pin is prone to breakage due to excessive torque during welding, making it unsuitable for welding thick structures.

[0006] Therefore, developing a friction stir welding method that can solve problems such as surface thinning, weak root connection, and insufficient corrosion resistance in aluminum / steel ring joints, and that has simple tooling and strong versatility, has important scientific value and broad engineering application prospects. Summary of the Invention

[0007] This invention addresses the problems of low strength, insufficient corrosion resistance, and high tooling design difficulty in aluminum / steel ring joints caused by surface thinning, weak root connection, and large potential difference. It proposes a friction stir welding device and method to improve the strength and corrosion resistance of aluminum / steel ring joints.

[0008] The technical solution adopted by the present invention to solve the above problems is as follows: The friction stir welding device for improving the strength and corrosion resistance of aluminum / steel annular joints according to the present invention includes a welding tool and a radial support heating device.

[0009] Furthermore, the welding tool includes a screw and a water cooling shaft shoulder sleeve. The screw is inserted into the water cooling shaft shoulder sleeve, and the screw and the water cooling shaft shoulder sleeve are coaxially fitted through positioning mounting holes. The side wall of the water cooling shaft shoulder sleeve is provided with a wire feeding port, and the interior is provided with cooling water channels.

[0010] Furthermore, the lower side wall of the screw is provided with a screw groove, and the lower end of the screw shoulder is provided with a stirring needle.

[0011] Furthermore, the pitch of the screw groove is 0.3~1.5mm, and the depth of the screw groove is 0.5~3mm; the stirring pin is cylindrical or conical, and its length is equal to the wall thickness of the workpiece to be welded, and the number can be adjusted according to the wall thickness of the workpiece to be welded.

[0012] Furthermore, the radial support heating device includes a slider, a slide rail, and a control assembly, which is located on the back of the workpiece to be welded. The slide rail is annular, and the slider can slide freely along the slide rail. The outer surface of the slider is in close contact with the inner surface of the workpiece to be welded.

[0013] The steps of the friction stir welding method for improving the strength and corrosion resistance of aluminum / steel ring joints according to the present invention include: Step 1: Install the screw and the water cooler shaft shoulder sleeve coaxially in the welding machine clamping part, ensuring that the end faces of the screw shaft shoulder and the water cooler shaft shoulder sleeve are flush; debug the wire feeder and water pump, connect the wire feed guide tube, introduce cooling water, and confirm that all components are operating normally; Step 2: Clean the workpiece to be welded, removing surface oil, oxide film and burrs; use special tooling for docking and assembly, install the radial support heating device on the back of the workpiece to be welded, adjust the cylinder support force to the preset value, start the ceramic heating plate of the slider, and heat up to the preset temperature. Step 3: Start the welding machine spindle. The welding tool slowly rotates and penetrates to the preset depth. There is a gap between the end face of the water cooler shaft shoulder sleeve and the upper surface of the workpiece to be welded, i.e., negative pressure is applied. Turn on the wire feeder and water pump. The welding wire is continuously fed in and, after being sheared and plasticized by the screw inside the water cooler shaft shoulder sleeve, is squeezed to the surface of the workpiece to be welded, forming a high layer on the weld surface. The slider moves synchronously along the slide rail with the welding machine spindle, and the radial position and support force are adjusted in real time by the cylinder. Step 4: After welding is completed, turn off the ceramic heating plate, wire feeder and water pump in sequence. After the joint cools to room temperature, remove the tooling and radial support heating device.

[0014] The beneficial effects of this invention are: 1. The filler wire welding proposed in this invention avoids the reduction in interfacial load-bearing capacity caused by weld thinning due to the high aluminum excess layer on the weld surface; the standard electrode potential of the aluminum-silicon alloy welding wire is lower than that of the aluminum base material, and corrosion occurs preferentially in the corrosive environment, forming a cathodic protection mechanism of sacrificial anode, which effectively inhibits galvanic corrosion at the aluminum / steel interface; at the same time, silicon element has an inhibitory effect on the growth of intermetallic compounds, and the formation of aluminum-iron-silicon compounds replaces aluminum-iron compounds, which is beneficial to improving the strength and toughness of the joint.

[0015] 2. The negative pressure feed method used in the filler wire welding of this invention reduces the axial force of welding, reduces the power consumption of the welding machine and the wear of the welding tool, and helps to increase the service life of the welding machine and the welding tool.

[0016] 3. In the welding fixture proposed in this invention, the water-cooled shoulder controls the temperature of the plasticized layer through cooling water, which effectively avoids the blockage of the feeding channel caused by welding wire adhesion, and can realize long-distance continuous high-quality welding, which is conducive to improving production efficiency.

[0017] 4. The radial support heating device in this invention is suitable for all-position welding. The adjustable radial position of the slider and the rigid back support solve the problem of poor support that may exist when the annular joint is deformed into an ellipse. Back heating can enhance the fluidity of the material at the root of the weld. Through the combination of mechanical stirring action of the stirring pin and heat conduction, the weak connection defects common at the root of the butt joint are avoided, which is conducive to increasing the joint strength and eliminating the risk of crevice corrosion. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the friction stir welding process; Figure 2 This is a cross-sectional view showing the positional relationship of each component during the friction stir welding process; Figure 3 This is a schematic diagram of the screw structure; Figure 4 This is a structural schematic diagram of the water cooling shaft shoulder; Figure 5 This is a schematic diagram of the radial support heating device; Figures 1 to 5 In the middle, 1-aluminum ring, 2-steel ring, 3-welding tool, 301-screw, 30101-screw groove, 30102-stirring needle, 302-water cooling shaft shoulder sleeve, 30201-mounting positioning hole, 30202-wire feed port, 4-welding wire, 5-radial support heating device, 501-slider, 502-slide rail. Detailed Implementation

[0019] Specific implementation method one: as follows Figures 1 to 5As shown, the friction stir welding apparatus for improving the strength and corrosion resistance of aluminum / steel annular joints according to this embodiment includes a welding fixture 3 and a mirror support heating device 5. The welding fixture 3 consists of a screw 301 and a water-cooled shoulder sleeve 302, which are coaxially fitted together through a mounting positioning hole 30201. The screw groove 30101 is used for shearing, plasticizing, migrating, and depositing the welding wire 4, and the stirring pin 30102 at the end is used for stirring the welding wire 4 and the base material. The water-cooled shoulder sleeve 302 is provided with a wire feed port 30202 and a cooling water channel. The wire feed port 30202 is used to guide the welding wire 4 into the internal cavity of the sleeve 302, and the cooling water channel is used to introduce cooling water to control the temperature of the plasticized layer in the cavity. Through filler wire welding, the excess layer formed on the weld surface avoids thinning, and the welding wire 4 preferentially corrodes in the corrosive environment, forming a sacrificial anode cathodic protection mechanism, which effectively inhibits galvanic corrosion at the aluminum / steel interface. The radial support heating device 5 includes a slider 501, a slide rail 502, and a control component. The slider 501 is modified from an adjustable temperature ceramic heating plate, which has the dual functions of rigid support and uniform heating, promoting root material flow and metallurgical bonding, and eliminating weak connections at the root. The slider 501 can slide freely along the slide rail 502. The control component includes a built-in position sensor, a controller, a pressure sensor, and a cylinder. The position sensor collects the position signal of the welding machine spindle in real time, and the controller drives the slider 501 to move synchronously with the welding machine spindle along the slide rail 502. The pressure sensor collects the pressure signal in real time, and the cylinder adjusts the radial position and support force of the slider in real time to ensure that the upper surface of the slider 501 is in close contact with the back of the workpiece to be welded throughout the welding process.

[0020] Among them, the wall thickness of aluminum ring 1 and steel ring 2 is 3~100mm, and the docking method can be selected according to the requirements: planar docking, beveled docking that can increase the interface bonding length, or sawtooth docking that can enhance the mechanical interlocking of the interface.

[0021] The screw 301 has a single or double thread on its outer surface, the screw groove 30101 has a pitch of 0.3~1.5mm and a depth of 0.5~3mm; the stirring pin 30102 is cylindrical or conical with a taper of 1:5~1:10, with a diameter of 3~10mm and a length equal to the wall thickness of the workpiece to be welded. The quantity can be adjusted according to the wall thickness of the workpiece to be welded (0 for thin parts less than 1mm, 1~3 for conventional parts, and 4~6 for thick parts greater than 5mm).

[0022] Among them, welding wire 4 can be 4XXX, 6XXX aluminum alloy or other artificially synthesized aluminum-silicon alloy welding wire. The diameter of welding wire 4 is 0.5~3mm. Welding wire 4 is matched with wire feed port 30202. The wire feed speed is 10~200mm / min, which can be dynamically adjusted according to other welding parameters.

[0023] Among them, the speed difference between the slider 501 and the main shaft is ≤1mm / min, the preset temperature of the ceramic heating plate is 0.5~1 times the peak welding temperature, and the cylinder support force is 100~1000N.

[0024] Specific implementation method two: such as Figures 1 to 5 As shown, the steps of the friction stir welding method for improving the strength and corrosion resistance of aluminum / steel annular joints according to this embodiment include: Step 1: Install the screw 301 and the water cooling shaft shoulder sleeve 302 coaxially in the welding machine clamping part, ensuring that the end faces of the screw 301 shoulder and the water cooling shaft shoulder sleeve 302 are flush; debug the wire feeder and water pump, connect the wire feed guide tube, introduce cooling water, and confirm that all components are operating normally; Step 2: Clean the workpiece to be welded, removing surface oil, oxide film and burrs; use special tooling for docking and assembly, install radial support heating device 5 on the back of the workpiece to be welded, adjust the cylinder support force to the preset value, start the ceramic heating plate of slider 501 and heat it to the preset temperature. Step 3: Start the welding machine spindle. The welding tool 3 slowly rotates and penetrates to the preset depth. There is a gap between the end face of the water cooler shaft shoulder sleeve 302 and the upper surface of the workpiece to be welded, i.e., negative pressure is applied. Turn on the wire feeder and water pump. The welding wire 4 is continuously fed in and is sheared and plasticized by the screw 301 inside the water cooler shaft shoulder sleeve 302 before being squeezed to the surface of the workpiece to be welded, forming an excess layer on the weld surface. The slider 501 moves synchronously with the welding machine spindle along the slide rail 502, and the radial position and support force are adjusted in real time by the cylinder. Step 4: After welding is completed, turn off the ceramic heating plate, wire feeder and water pump in sequence. After the joint cools to room temperature, remove the tooling and radial support heating device 5.

[0025] The spindle speed is 300~3000rpm, the welding speed is 20~1000mm / min, the negative pressure infeed is 0.05~0.5mm, and the welding tilt angle is 0°~5°. The parameters can be optimized and matched according to the material and wall thickness of the workpiece to be welded in order to obtain the best performance.

[0026] Working principle This invention includes a welding fixture and a radial support heating device. The welding fixture consists of a screw and a water-cooled cooling shoulder sleeve, which are coaxially fitted together through mounting positioning holes. The screw groove is used for shearing, plasticizing, migrating, and depositing the welding wire, and the stirring pin at the end is used for stirring the welding wire and the base material. The water-cooled cooling shoulder sleeve is provided with a wire feed port and a cooling water channel. The wire feed port is used to guide the welding wire into the internal cavity of the sleeve, and the cooling water channel is used to introduce cooling water to control the temperature of the plasticized layer in the cavity. Through filler wire welding, the excess layer formed on the weld surface avoids thinning, and the welding wire preferentially corrodes in the corrosive environment, forming a sacrificial anode cathodic protection mechanism, effectively inhibiting galvanic corrosion at the aluminum / steel interface. The radial support heating device includes a slider, a slide rail, and a control assembly. The slider is modified from an adjustable temperature ceramic heating plate, which has the dual functions of rigid support and uniform heating, promoting root material flow and metallurgical bonding, eliminating weak connections at the root, and the slider can slide freely along the slide rail. The control assembly includes a built-in position sensor, a controller, a pressure sensor, and a cylinder. The position sensor collects the welding machine spindle position signal in real time, and the controller drives the slider to move synchronously with the welding machine spindle along the slide rail. The pressure sensor collects the pressure signal in real time, and the cylinder adjusts the radial position and support force of the slider in real time to ensure that the upper surface of the slider is in close contact with the back of the workpiece to be welded throughout the welding process.

[0027] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent substitutions, and improvements made to the above embodiments without departing from the scope of the present invention, based on the technical essence of the present invention and within the spirit and principles of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. A friction stir welding apparatus for improving the strength and corrosion resistance of aluminum / steel annular joints, characterized in that, It includes a welding tool (3) and a radial support heating device (5). The welding tool (3) is set on the outer surface of the workpiece to be welded, and the radial support heating device (5) is set on the back of the workpiece to be welded.

2. The friction stir welding apparatus for improving the strength and corrosion resistance of aluminum / steel annular joints according to claim 1, characterized in that, The welding tool (3) includes a screw (301) and a water cooling shaft shoulder sleeve (302). The screw (301) is inserted into the water cooling shaft shoulder sleeve (302), and the screw (301) and the water cooling shaft shoulder sleeve (302) are coaxially fitted through the positioning mounting hole (30201). The side wall of the water cooling shaft shoulder sleeve (302) is provided with a wire feeding port (30202), and the interior is provided with a cooling water channel.

3. The friction stir welding apparatus for improving the strength and corrosion resistance of aluminum / steel annular joints according to claim 2, characterized in that, The lower side wall of the screw (301) is provided with a screw groove (30101), and the lower end of the shoulder of the screw (301) is provided with a stirring needle (30102).

4. The friction stir welding apparatus for improving the strength and corrosion resistance of aluminum / steel annular joints according to claim 3, characterized in that, The screw (301) has a pitch of 0.3~1.5mm and a groove (30101) depth of 0.5~3mm; the stirring needle (30102) is cylindrical or conical, with a length equal to the wall thickness of the workpiece to be welded, and the number can be adjusted according to the wall thickness of the workpiece to be welded.

5. The friction stir welding apparatus for improving the strength and corrosion resistance of aluminum / steel annular joints according to claim 1, characterized in that, The radial support heating device (5) includes a slider (501), a slide rail (502) and a control component, which is set on the back of the workpiece to be welded. The slide rail (502) is annular, and the slider (501) can slide freely along the slide rail (502). The outer surface of the slider (501) is in close contact with the inner surface of the workpiece to be welded.

6. A welding method based on the friction stir welding apparatus according to any one of claims 1 to 5, characterized in that, The specific steps include: Step 1: Install the screw (301) and the water cooler shaft shoulder sleeve (302) coaxially in the welding machine clamping part, ensuring that the end face of the screw (301) shaft shoulder and the water cooler shaft shoulder sleeve (302) are flush; debug the wire feeder and water pump, connect the wire feed guide pipe, introduce cooling water, and confirm that all components are operating normally; Step 2: Clean the workpiece to be welded, remove surface oil, oxide film and burrs; use special tooling for docking and assembly, install the mirror support heating device (5) on the back of the workpiece to be welded, adjust the cylinder support force to the preset value, start the ceramic heating plate of the slider (501) and heat it to the preset temperature. Step 3: Start the welding machine spindle, and the welding tool (3) slowly rotates and penetrates to the preset depth. There is a gap between the end face of the water cooling shaft shoulder sleeve (302) and the upper surface of the workpiece to be welded, i.e., negative pressure is applied. Turn on the wire feeder and water pump, and the welding wire (4) is continuously fed in. After being sheared and plasticized by the screw (301) inside the water cooling shaft shoulder sleeve (302), it is squeezed to the surface of the workpiece to be welded, and a high layer is formed on the surface of the weld. The slider (501) moves synchronously with the welding machine spindle along the slide rail (502), and the radial position and support force are adjusted in real time by the cylinder. Step 4: After welding is completed, turn off the ceramic heating plate, wire feeder and water pump in sequence. After the joint cools to room temperature, remove the tooling and radial support heating device (5).

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