Aluminum / steel dissimilar metal brazing method based on semi-circular rod-shaped wire

Abstract

A method for aluminum / steel dissimilar metal brazing based on semi-circular rod-shaped wire includes butting and fixing a stainless steel plate and an aluminum alloy plate to form a workpiece to be welded, wherein the thickness of the plates is p; the workpiece to be welded is welded using a rotating laser-MIG arc hybrid welding method, wherein the welding wire of the MIG arc is a semi-circular rod-shaped wire, and the wide side length of the semi-circular rod-shaped wire is dw; during the welding process, the rotating laser beam is in front and the MIG arc is in the back, and the angle between the straight surface of the semi-circular rod-shaped wire and the normal is 40°-5 0°, with the straight surface at the bottom and the arc surface at the top; the laser spot of the laser beam is circular with a radius of r, the rotation diameter of the laser spot is dl, the rotation center of the laser spot is biased toward the aluminum alloy side, and the distance from the center line of the workpiece to be welded is s. The distance between the rotation center of the laser spot and the midpoint of the straight edge of the cross section of the semicircular rod-shaped wire is A, A = 2dw + 1 / 2dl + r, dl / dw = 1 / 2, dl / 2 + r < s, p + 2r = 2dw, 1mm ≤ p ≤ 4mm. The welding method of the present invention can obtain an aluminum alloy / stainless steel dissimilar metal joint with excellent welding quality and high joint strength.

Description

Technical Field

[0001] The invention provides an aluminum / steel dissimilar metal brazing method based on semi-circular rod-shaped wires, belonging to the field of welding processing. Background Art

[0002] Faced with increasingly severe energy shortages, lightweight design concepts have gained widespread attention and adoption within the transportation industry. In vehicle manufacturing, based on modular and integrated structural design concepts, a more diverse material system is used to manufacture vehicle body components to achieve equal strength design, effectively minimizing the impact of lightweighting on vehicle performance, such as structural strength, rigidity, and airtightness. Alstom of France uses an aluminum / steel composite structural design on its high-speed trains, connecting the steel end frame and aluminum alloy floor through welding technology. The steel end frame, due to its high rigidity and strength, serves as the primary load-bearing structure of the vehicle body, ensuring train safety. The aluminum alloy floor, as a secondary load-bearing structure, reduces axle weight and reduces vehicle weight.

[0003] However, due to the large differences in thermal physical properties, aluminum / steel dissimilar metal welding is often affected by the complex interactions of materials, heat and structure during conventional welding. There are problems such as poor joint forming, insufficient spread of cladding metal, obvious differences in interface brittle metal compounds and excessive growth. As a result, the performance of the welded joint is significantly reduced and it is difficult to meet actual service requirements, which seriously restricts the application of aluminum / steel dissimilar metals in vehicle body structure design.

[0004] Laser brazing has the advantages of high production efficiency, high energy density, and narrow heat-affected zone. It can effectively and accurately control the heat input of the welding interface, improve the joint forming, and inhibit the excessive growth of the interface layer. It has great potential in optimizing the performance of aluminum / steel dissimilar metal joints. However, the reflectivity of aluminum alloy to laser is as high as over 90%, and most of the laser energy is reflected, making it difficult to form a stable keyhole, affecting the welding quality. At the same time, this high reflection phenomenon not only leads to the risk of damaging the laser, but also greatly reduces the utilization rate of laser energy, resulting in waste of resources and increased production costs. On the other hand, due to the small diameter of the laser spot and poor bridging ability, high requirements are placed on the alignment flatness and precision of the joint, which also increases the difficulty and cost of welding. Summary of the Invention

[0005] The purpose of the present invention is to provide an aluminum / steel dissimilar metal brazing method based on semi-circular rod-shaped wire, which can obtain an aluminum alloy / stainless steel dissimilar metal joint with excellent welding quality and high joint strength without beveling.

[0006] The technical solution adopted by the present invention to achieve its invention object is: a method for aluminum / steel dissimilar metal brazing based on semi-circular rod-shaped wire, comprising: butting and fixing a stainless steel plate and an aluminum alloy plate to form a workpiece to be welded, wherein the stainless steel plate and the aluminum alloy plate have the same thickness, and the plate thickness of the stainless steel plate and the aluminum alloy plate is denoted as p; welding the workpiece to be welded by rotating laser-MIG arc hybrid welding, wherein the welding wire of the MIG arc is a semi-circular rod-shaped wire, wherein the plane where the long side and the wide side of the semi-circular rod-shaped wire lie is a straight plane, the plane where the long side and the arc side lie is an arc surface, the plane where the wide side and the arc side lie is a cross section, and the length of the wide side of the semi-circular rod-shaped wire is denoted as dw;

[0007] During the welding process, the rotating laser beam is in front and the MIG arc is behind. The angle between the straight surface of the semicircular rod-shaped wire and the normal is 40°-50°, and the straight surface is at the bottom and the arc surface is at the top. The laser beam adopts negative defocus. The laser spot on the workpiece to be welded is circular with a radius of r. The rotation diameter of the laser spot on the workpiece to be welded is dl. The rotation center of the laser spot on the workpiece to be welded is biased toward the aluminum alloy side, and the distance from the butt center line of the workpiece to be welded is s. The line connecting the rotation center of the laser spot on the workpiece to be welded and the midpoint of the straight side of the cross section of the semicircular rod-shaped wire is parallel to the butt center line of the workpiece to be welded. The distance between the rotation center of the laser spot on the workpiece to be welded and the midpoint of the straight side of the cross section of the semicircular rod-shaped wire is A.

[0008] The relationship between the plate thickness p, the wide side length dw of the semicircular rod-shaped wire, the laser spot radius r, the rotation diameter dl of the laser spot on the workpiece to be welded, the distance s between the rotation center of the laser spot on the workpiece to be welded and the butt center line of the workpiece to be welded, and the distance A between the rotation center of the laser spot on the workpiece to be welded and the midpoint of the straight side of the semicircular rod-shaped wire cross section is as follows:

[0009] A=2dw+1 / 2dl+r, dl / dw=1 / 2, dl / 2+r<s, p+2r=2dw, 1mm≤p≤4mm.

[0010] Furthermore, the rotary laser power of the rotary laser-MIG arc hybrid welding of the present invention is 1500-2200W, and the rotary frequency is 60-100HZ.

[0011] Furthermore, the MIG arc of the rotary laser-MIG arc hybrid welding of the present invention adopts a pulsed arc, and the pulsed arc power is 1000-2000W.

[0012] Furthermore, the welding speed of the rotary laser-MIG arc hybrid welding of the present invention is 1-1.4 m / min, and the wire feeding speed is 3.5-5.5 m / min.

[0013] Furthermore, the welding process of the present invention uses high-purity argon gas protection with a gas flow rate of 25L / min.

[0014] Furthermore, the distance between the rotation center of the laser spot on the workpiece to be welded and the butt center line of the workpiece to be welded is s=0.5-1 mm.

[0015] Furthermore, the laser spot radius r of the present invention is 0.2-0.3 mm.

[0016] Furthermore, the width length dw of the semi-circular rod-shaped wire of the present invention is 0.8-2.4 mm, and the rotation diameter dl of the laser spot on the workpiece to be welded is 0.4-1.2 mm.

[0017] Furthermore, the present invention cuts the cross section of the semicircular rod-shaped wire obliquely before welding, so that the sharp corner of the cut wire is located on the side away from the butt center line of the parent material.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] Compared with conventional laser-arc hybrid welding of aluminum / steel dissimilar metals, the present invention has beautiful weld formation, without defects such as cracks, pores, and unfused parts; it expands the welding process parameter window, which is conducive to adapting to diverse actual production conditions; it reduces the step of adding alloy layers before welding aluminum / steel dissimilar metals, further reduces assembly precision requirements, and reduces production time and costs; it breaks through the tensile strength of aluminum / steel fusion brazing joints, and effectively improves the flexibility of multi-material structure design in the field of lightweighting.

[0020] The present invention solves the shortcomings of difficult-to-control interface heat distribution and excessive growth of intermetallic compounds at the interface during aluminum / steel brazing. The laser rotation method is used to effectively reduce the interface temperature gradient and peak temperature, so that the composition and thickness of the intermetallic compounds growing along the interface tend to be consistent, and the overall thickness is significantly reduced. On the other hand, due to the improved temperature distribution in the welding heat-affected zone, the brazing flux burning phenomenon on the steel surface is greatly alleviated, and the wetting of the aluminum alloy melt on the steel surface is enhanced, which together promotes the increase in spreading distance. By improving the wire morphology and controlling the matching relationship between the droplet transition amount and the welding heat distribution, the stability of the welding process and the quality of the weld are further improved. By obliquely cutting the end of the semi-circular rod-shaped wire, the arc starting point is deviated from the steel side, the spattering phenomenon during the welding process is reduced, and the quality of the weld is guaranteed.

[0021] The principles and advantages of selecting rotating lasers in the present invention are as follows:

[0022] For the welding of dissimilar metal sheets targeted by this application, high-power laser composite welding can form a deeper keyhole and bring heat to the bottom of the joint, which is very important for promoting uniform distribution of heat in the thickness direction. However, blindly increasing the laser power will also bring higher heat input, causing the interface layer to thicken. It is necessary to take corresponding measures to not only suppress the excessive growth of the interface layer but also take into account the uniformity of the interface layer. Molten pool stirring can make the strengthening phase more evenly dispersed and the grain refinement obvious, which is beneficial to the dilution and alloying element homogenization of the melt and inhibit the diffusion of Fe at the interface. Therefore, in order to improve the metallurgical bonding of the interface, reduce the thickness of the interface layer, and improve the uniformity of the intermetallic compounds along the interface direction, a laser rotation method is adopted.

[0023] The principle of the semi-circular rod-shaped wire material used in the present invention is as follows:

[0024] For dissimilar metals with large differences in thermophysical properties, the key to improving the strength of their welded joints is: ① the joint is complete and beautiful; ② the intermetallic compound generated at the interface of the dissimilar materials has an appropriate thickness, and its composition and distribution along the interface direction have a certain degree of uniformity.

[0025] First, consider the weld formation factor when selecting the wire shape. Wider wires melt more metal during welding, resulting in a wider weld. Therefore, choosing a wider wire helps increase weld bridging capacity, achieve better weld formation, and ensure joint strength. However, thicker wires also increase heat input, which can lead to a decrease in the uniformity of intermetallic compounds at the interface, inevitably significantly weakening joint performance. Figure 1 This is a schematic diagram of the energy distribution of the rotating laser-MIG composite heat source of the present invention. The composite heat source energy distribution characteristics indicate that the upper portion of the weld pool comprises a large, shallow arc active zone, while the lower portion comprises a narrow, deep laser active zone. Heat accumulates in the upper portion of the joint, a situation exacerbated by the absence of a groove, as is the case with this application. Therefore, increasing the arc heat input at the wire end undoubtedly increases the non-uniformity of the temperature distribution along the interface, resulting in high peak temperatures, large temperature gradients, and prolonged high-temperature duration in the upper portion. This contrasts significantly with the lower portion, leading to significant differences in the interface growth state. If fine-wire welding is chosen to reduce upper heat input and improve joint temperature uniformity, insufficient droplet transfer makes it difficult to achieve the desired, complete, and aesthetically pleasing dissimilar weld joint formation under high-speed welding conditions. Therefore, a wire material should be selected that balances both bridging capability and heat input control.

[0026] Next, consider the inherent temperature distribution characteristics of the welding process to further determine the shape of the welding wire. When the welding heat source acts on the base metal, the temperature is highest around the heat source and decreases with distance, forming a distinct temperature gradient, with the edges being the lowest. This temperature distribution characteristic causes the center of the wire to be subject to higher temperatures, resulting in a greater amount of melting, while the surrounding areas, due to lower temperatures, melt less. This affects the size and shape of the resulting molten pool, resulting in poor joint formation. To avoid this, a wire with less material at the ends and more in the middle should be used, based on the welding temperature distribution characteristics. This ensures that the amount of filler material melted during welding is dynamically balanced at the horizontal ends.

[0027] For these two reasons, a wire with a semicircular cross-section is used. The symmetry of the semicircular wire cross-section allows for relatively uniform droplet transfer, resulting in a nearly spherical or hemispherical droplet shape, good fluidity, and efficient weld filling. Furthermore, the semicircular rod-shaped wire offers stable arc transfer and a low spatter rate, making the welding process more stable and easier to control. Process experiments have demonstrated that this wire can simultaneously reduce heat input and increase bridging capacity within a controllable range.

[0028] The principles and advantages of matching the size of the semi-circular rod-shaped wire with the laser position and parameters of the present invention are as follows:

[0029] In order to ensure that the combined effect of wire shape and laser rotation can improve the strength of dissimilar metal welding joints and enhance the performance of joints, it is necessary to clarify their matching range. It is known that the welding temperature field has changed accordingly after the introduction of rotating laser, such as the temperature gradient and peak temperature have both decreased. Based on this, according to the matching principle of temperature field and welding wire shape described in the first point, a matching relationship between welding wire shape characteristics and rotating laser parameters was proposed based on a large number of experimental analyses: dl / dw=1 / 2, p+2r=2dw, where the plate thickness is p, the wide side length of the semi-circular rod-shaped wire is dw, the laser spot radius is r, and the rotating diameter of the laser spot on the workpiece to be welded is dl. In addition, this combination helps to improve the stability of the molten droplet transition at the end of the wire and ensure the quality of the welded joint. This is because the center of gravity of the cross-sectional shape of the semi-circular rod-shaped wire is low. The wire feeding angle and position described in this application ensure that the filler material is fed into the molten pool at a lower center of gravity, reducing spatter.

[0030] Finally, considering that excessive offset can cause excessive melting of the base metal, resulting in weld-through defects, while insufficient heating of the steel base metal can hinder liquid metal spreading, while too small offset can dramatically increase heat input on the steel side, causing the base metal to melt and mix with the liquid aluminum, generating a large amount of intermetallic compounds and leading to joint failure. The distance between the laser rotation center and the center of the wire's wide side should also be controlled to minimize heat insufficiency or heat concentration, thereby avoiding incomplete penetration or burn-through. Therefore, based on extensive experimental analysis, the relationship between the offset, the distance between the laser rotation center and the center of the wire's wide side, and the laser rotation parameters was established: dl / 2 + r < s, A = 2dw + 1 / 2dl + r, where r is the laser spot radius, dl is the rotation diameter of the laser spot on the workpiece, s is the distance between the laser spot's rotation center on the workpiece and the butt centerline of the workpiece, A is the distance between the laser spot's rotation center on the workpiece and the midpoint of the wide side of the semicircular rod-shaped wire, and dw is the wide side length of the semicircular rod-shaped wire. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of energy distribution of the laser-MIG composite heat source of the present invention.

[0032] Figure 2 Schematic diagram of the laser rotation welding path according to an embodiment of the present invention.

[0033] Figure 3 Schematic diagram of rotary laser-MIG arc hybrid welding according to an embodiment of the present invention.

[0034] Figure 4 Schematic diagram of the curved surface of the semi-circular rod-shaped wire according to an embodiment of the present invention. DETAILED DESCRIPTION

[0035] Example

[0036] A method for aluminum / steel dissimilar metal brazing based on semi-circular rod-shaped wire includes butting, mounting, and fixing a stainless steel plate and an aluminum alloy plate to form a workpiece to be welded, wherein the stainless steel plate and the aluminum alloy plate have the same thickness, and the plate thickness is denoted as p; welding the workpiece to be welded using a rotary laser-MIG arc hybrid welding method, wherein the welding wire of the MIG arc is a semi-circular rod-shaped wire, wherein the plane where the long side and the wide side of the semi-circular rod-shaped wire lie is a straight plane, the plane where the long side and the arc side lie is an arc surface, the plane where the wide side and the arc side lie is a cross section, and the wide side length of the semi-circular rod-shaped wire is denoted as dw;

[0037] During the welding process, the rotating laser beam is in front and the MIG arc is behind. The angle between the straight surface of the semicircular rod-shaped wire and the normal is 40°-50°, and the straight surface is at the bottom and the arc surface is at the top. The laser beam adopts negative defocus. The laser spot on the workpiece to be welded is circular with a radius of r. The rotation diameter of the laser spot on the workpiece to be welded is dl. The rotation center of the laser spot on the workpiece to be welded is biased toward the aluminum alloy side, and the distance from the butt center line of the workpiece to be welded is s. The line connecting the rotation center of the laser spot on the workpiece to be welded and the midpoint of the straight side of the cross section of the semicircular rod-shaped wire is parallel to the butt center line of the workpiece to be welded. The distance between the rotation center of the laser spot on the workpiece to be welded and the midpoint of the straight side of the cross section of the semicircular rod-shaped wire is A.

[0038] The relationship between the plate thickness p, the wide side length dw of the semicircular rod-shaped wire, the laser spot radius r, the rotation diameter dl of the laser spot on the workpiece to be welded, the distance s between the rotation center of the laser spot on the workpiece to be welded and the butt center line of the workpiece to be welded, and the distance A between the rotation center of the laser spot on the workpiece to be welded and the midpoint of the straight side of the semicircular rod-shaped wire cross section is as follows:

[0039] A=2dw+1 / 2dl+r, dl / dw=1 / 2, dl / 2+r<s, p+2r=2dw, 1mm≤p≤4mm.

[0040] Figure 2 This is a schematic diagram of the laser rotation welding path in this embodiment. Figure 3 Schematic diagram of rotary laser-MIG arc hybrid welding in this embodiment.

[0041] The rotary laser power of the rotary laser-MIG arc hybrid welding described in this example is 1500-2200W, and the rotation frequency is 60-100HZ.

[0042] The MIG arc of the rotary laser-MIG arc hybrid welding described in this example adopts a pulsed arc, and the pulsed arc power is 1000-2000W.

[0043] The welding speed of the rotary laser-MIG arc hybrid welding described in this example is 1-1.4 m / min, and the wire feeding speed is 3.5-5.5 m / min.

[0044] The welding process described in this example uses high-purity argon gas protection with a gas flow rate of 25L / min.

[0045] In this example, the distance s between the rotation center of the laser spot on the workpiece to be welded and the center line of the workpiece to be welded is 0.5-1 mm.

[0046] The laser spot radius r in this example is 0.2-0.3 mm.

[0047] The width length of the semi-circular rod-shaped wire in this example is dw = 0.8-2.4 mm, and the rotation diameter of the laser spot on the workpiece to be welded is dl = 0.4-1.2 mm.

[0048] In this example, before welding, the cross section of the semi-circular rod-shaped wire is cut obliquely so that the tip of the cut wire is located on the side away from the center line of the base material. Figure 4 As shown, Figure 4 Schematic diagram of the curved plane of the semicircular rod-shaped wire.

Claims

1. A method for brazing dissimilar aluminum and steel metals based on semi-circular rod-shaped wire, comprising butting and fixing a stainless steel plate and an aluminum alloy plate to form a workpiece to be welded, characterized in that: The stainless steel plate and the aluminum alloy plate have the same thickness, and the plate thickness is denoted as p; the workpiece is welded by rotary laser-MIG arc hybrid welding, and the welding wire of the MIG arc is a semi-circular rod-shaped wire. The plane where the long side and the wide side of the semi-circular rod-shaped wire are located is a straight surface, the surface where the long side and the arc side are located is an arc surface, and the plane where the wide side and the arc side are located is a cross section, and the length of the wide side of the semi-circular rod-shaped wire is dw; During the welding process, the rotating laser beam is in front and the MIG arc is behind. The angle between the straight surface of the semicircular rod-shaped wire and the normal is 40°-50°, with the straight surface at the bottom and the arc surface at the top. The laser beam adopts negative defocus. The laser spot on the workpiece to be welded is circular with a radius of r. The rotation diameter of the laser spot on the workpiece to be welded is dl. The rotation center of the laser spot on the workpiece to be welded is biased toward the aluminum alloy side, and the distance from the midline of the workpiece to be welded is s. The line connecting the rotation center of the laser spot on the workpiece to be welded and the midpoint of the straight side of the semicircular rod-shaped wire section is parallel to the midline of the workpiece to be welded. The distance between the midpoint of the straight side of the semicircular rod-shaped wire section and the rotation center of the laser spot on the workpiece to be welded is A. The relationship between the plate thickness p, the wide side length dw of the semicircular rod-shaped wire, the laser spot radius r, the rotation diameter dl of the laser spot on the workpiece to be welded, the distance s between the rotation center of the laser spot on the workpiece to be welded and the butt center line of the workpiece to be welded, and the distance A between the rotation center of the laser spot on the workpiece to be welded and the midpoint of the straight side of the semicircular rod-shaped wire cross section is as follows: A=2dw+1 / 2dl+r, dl / dw=1 / 2, dl / 2+r<s, p+2r=2dw, 1mm≤p≤4mm.

2. The aluminum / steel dissimilar metal brazing method based on semi-circular rod-shaped wire according to claim 1, characterized in that: The rotary laser power of the rotary laser-MIG arc hybrid welding is 1500-2200W, and the rotary frequency is 60-100HZ.

3. The aluminum / steel dissimilar metal brazing method based on semi-circular rod-shaped wire according to claim 1, characterized in that: The MIG arc of the rotary laser-MIG arc hybrid welding adopts a pulse arc, and the pulse arc power is 1000-2000W.

4. The aluminum / steel dissimilar metal brazing method based on semi-circular rod-shaped wire according to claim 1, characterized in that: The welding speed of the rotary laser-MIG arc hybrid welding is 1-1.4 m / min, and the wire feeding speed is 3.5-5.5 m / min.

5. The aluminum / steel dissimilar metal brazing method based on semi-circular rod-shaped wire according to claim 1, characterized in that: The welding process is protected by high-purity argon gas with a gas flow rate of 25 L / min.

6. The aluminum / steel dissimilar metal brazing method based on semi-circular rod-shaped wire according to claim 1, characterized in that: The distance s between the rotation center of the laser spot on the workpiece to be welded and the center line of the workpiece to be welded is 0.5-1 mm.

7. A method for aluminum / steel dissimilar metal brazing based on semi-circular rod-shaped wire according to claim 1 or 6, characterized in that: The laser spot radius r=0.2-0.3 mm.

8. The aluminum / steel dissimilar metal brazing method based on semi-circular rod-shaped wire according to claim 1, characterized in that: The width length dw of the semicircular rod-shaped wire is 0.8-2.4 mm, and the rotation diameter dl of the laser spot on the workpiece to be welded is 0.4-1.2 mm.

9. The aluminum / steel dissimilar metal brazing method based on semi-circular rod-shaped wire according to claim 7, characterized in that: The width length dw of the semicircular rod-shaped wire is 0.8-2.4 mm, and the rotation diameter dl of the laser spot on the workpiece to be welded is 0.4-1.2 mm.

10. The aluminum / steel dissimilar metal brazing method based on semi-circular rod-shaped wire according to claim 1, characterized in that: Before welding, the cross section of the semi-circular rod-shaped wire is cut obliquely so that the sharp corner of the cut wire is located on the side away from the center line of the base material.

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