A method for strengthening the interface of a steel-aluminum composite plate

Abstract

This invention discloses a method for strengthening the interface of steel-aluminum composite plates, belonging to the field of dissimilar metal welding technology. The invention first fixes the steel-aluminum composite plate with an aluminum alloy layer on top and a steel plate layer on the bottom. A high-speed rotating steel rivet penetrates the aluminum layer and rubs against the steel layer, forming a metallurgical bonding zone at the rivet-steel interface. Simultaneously, a mechanical interlocking structure is formed at the bottom of the rivet. During the process, by precisely controlling parameters such as the rivet rotation speed, pressing speed, and pressing depth, the formation of brittle intermetallic compounds is suppressed, ultimately achieving a reliable connection of high-strength and high-toughness steel-aluminum composite plates. This technology can be widely applied in the preparation of steel-aluminum transition joints in industries such as shipbuilding, aviation, aerospace, and electrolytic aluminum, and is particularly suitable for components with stringent requirements for lightweighting and connection reliability.

Description

Technical Field

[0001] This invention belongs to the field of dissimilar metal welding technology, specifically relating to a method for strengthening the interface of steel-aluminum composite plates. It is applicable to steel-aluminum composite components in fields such as transportation, aerospace, and shipbuilding that require lightweight, high-strength, and high-reliability connections. Background Technology

[0002] Steel-aluminum composite panels are often used as steel / aluminum transition components or composite load-bearing components, combining the strength of steel with the lightweight advantages of aluminum alloys in the same structure. However, during the fabrication and subsequent processing / service of composite panels, defects such as brittle intermetallic compound layers, weak bonding bands, or microcracks may still exist at the steel-aluminum interface. When the component is subjected to alternating loads, impact loads, or thermal stress, cracks are prone to propagate along the interface and induce delamination failure, leading to a decrease in connection strength and service reliability.

[0003] For the interface strengthening problem of steel-aluminum composite plates, domestic and international research mainly focuses on optimizing process parameters, adding alloying elements, and using intermediate layers to suppress interface defects. Developing novel steel-aluminum welding technologies is also an important approach. Currently, common interface strengthening schemes mainly include the following categories: First, during rolling or explosive bonding processes, strictly controlling the heating temperature, deformation amount, and heat treatment regime to reduce the thickness of brittle Fe-Al intermetallic compounds (such as FeAl3 and Fe2Al5) at the interface; second, introducing intermediate transition metals (such as Cu, Ni, Ag, and Zn) or multilayer composite sandwiches between steel and aluminum to alleviate interface brittleness by blocking direct contact between Fe and Al or generating new phases with better toughness; third, using advanced joining processes such as friction welding, diffusion welding, and laser brazing, utilizing their controllable heat input or pressure-assisted characteristics to obtain fine-grained structures or amorphous transition layers to improve interface bonding performance.

[0004] While these methods improve interfacial bonding strength to some extent, they still cannot completely prevent the formation of brittle phases. For example, under improper heat input control, a continuous brittle intermetallic compound layer is easily formed at the Fe-Al interface; and if the interlayer is not well-matched with the base material, new brittle phases or defects may also form after the introduction of an intermediate layer, thus affecting the reliability of the joint. In addition, existing welding processes often suffer from problems such as narrow process windows, high requirements for assembly accuracy, and difficulty in achieving efficient connections of thick or complex structures when dealing with complex working conditions. Nevertheless, the improvement in interfacial fracture toughness is still relatively limited, and the mechanical stability and reliability of the joint still need to be improved, especially under alternating loads or thermal cycling service environments, where microcracks are still prone to initiation at the interface, leading to delamination failure.

[0005] Therefore, how to fundamentally suppress the continuous generation of brittle phases at the steel-aluminum interface, while optimizing the stress distribution and microstructure of the interface region and improving the interface's crack resistance under complex stress conditions, is a key issue that urgently needs to be addressed in the current steel-aluminum composite plate connection technology field. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a method for strengthening the connection of steel-aluminum composite panels at the interface, achieving a reliable connection between steel-aluminum composite panel components, resulting in joints with high strength and high reliability, and applicable to components of different sizes and specifications.

[0007] The present invention achieves the above objectives through the following technical solutions: A method for strengthening the connection of steel-aluminum composite panels involves first fixing the steel-aluminum composite panels with an aluminum alloy layer on top and a steel plate layer on the bottom. High-speed rotating steel rivets penetrate the aluminum layer and rub against the steel layer, forming a metallurgical bonding zone at the rivet-steel interface. Simultaneously, a mechanical interlocking structure is formed at the bottom of the rivet. During the process, precise control of parameters such as rivet rotation speed, pressing speed, and pressing depth suppresses the formation of brittle intermetallic compounds, ultimately achieving a reliable connection of the high-strength, high-toughness steel-aluminum composite panels.

[0008] Specifically, the following steps are included: 1) Pretreatment of steel-aluminum composite panels The surface of the aluminum alloy layer of the steel-aluminum composite panel is cleaned, and blind holes are machined on the surface of the aluminum alloy layer of the steel-aluminum composite panel. The diameter of the blind holes is not less than the diameter of the rivet head, and the depth of the blind holes is greater than the height of the rivet head.

[0009] 2) Rivet positioning and staged welding

[0010] Steel rivets are used as connecting elements. The outer circumference of the rivet shank is provided with external threads. The rivets are driven to rotate at high speed by a continuous friction welding device, so that the rivets are aligned with the pre-set blind hole position of the aluminum alloy layer of the steel-aluminum composite plate and pressed down to realize the connection. The connection process includes the aluminum layer penetration stage, the friction welding stage and the upsetting stage in sequence.

[0011] Aluminum layer penetration stage: The rivet penetrates the remaining aluminum alloy layer at a rotation speed of 1000-8000rpm and a pressing speed of 1.0-5.0mm / s. The pressing amount is the distance from the bottom of the aluminum alloy blind hole to the interface of the composite plate. Frictional heat puts the aluminum layer in a thermoplastic state. The aluminum material is extruded along the side wall of the rivet and fills the annular gap below the rivet head. Friction welding stage: After the rivet tip contacts the steel plate, adjust the rotation speed to 2000-10000 rpm, keep the pressing speed at 1.0-5 mm / s, and the pressing amount is 1-2 times the thickness of the remaining aluminum layer. The friction heat causes the rivet to form a metallurgical bond with the steel plate. Upsetting stage: Stop rotation, apply upsetting pressure of 100-350MPa along the axial direction, hold pressure for 0-3s, so that the bottom of the rivet forms a mechanically interlocking "hook" structure, and the connection is completed.

[0012] 3) Embedded welding of rivet holes

[0013] After completing step 2), a welding wire of the same or similar type as the aluminum alloy base material is used to fill and weld the periphery / orifice area of ​​the rivet head to form a buried weld layer. The buried weld layer forms a metallurgical connection with the aluminum alloy layer and the rivet head to further enhance the joint.

[0014] Further, the steel-aluminum composite plate mentioned in step 1) includes explosively welded composite plate, rolled composite plate and friction stir welded composite plate.

[0015] Furthermore, the aluminum alloy layer of the steel-aluminum composite plate mentioned in step 1) is an aluminum alloy series suitable for making steel-aluminum composite plates, such as aluminum-magnesium, aluminum-magnesium-silicon, or aluminum-zinc-magnesium-copper.

[0016] Furthermore, the steel plate layer of the steel-aluminum composite plate mentioned in step 1) is a series of steel plates suitable for making steel-aluminum composite plates, such as low-carbon steel, high-strength steel, and stainless steel.

[0017] Furthermore, the continuous drive friction welding equipment described in step 2) includes a rotary drive module and an axial feed module.

[0018] Furthermore, the surface of the rivet described in step 2) is plated with a ZnNi coating or passivated to improve corrosion resistance.

[0019] Furthermore, the head of the rivet described in step 2) is designed with a tapered tip and a cap structure, with a tapered angle of 100-150°, a rivet head diameter of 1.5-2.5 times the diameter of the rivet shaft, and the volume of the annular gap below the rivet head is 1.2-1.5 times the volume of the rivet inserted into the aluminum plate.

[0020] Further, the remaining aluminum layer thickness mentioned in step 2) refers to the axial distance from the bottom of the prefabricated blind hole to the connection interface of the steel-aluminum composite plate.

[0021] Furthermore, the welding methods used for rivet hole embedding welding in step 3) include, but are not limited to, electric arc welding and laser welding.

[0022] Furthermore, this method is applicable to the preparation of steel-aluminum composite plate components in the fields of shipbuilding, aviation, and aerospace.

[0023] Compared with the prior art, the present invention has the following advantages: 1. By using friction plug-riveting composite spot welding technology, steel rivets are introduced as an intermediate medium, and pre-drilled holes and embedded welding methods are combined. On the one hand, a stable metallurgical bond is formed on the steel side, and on the other hand, a reliable mechanical anchor is formed on the aluminum side, achieving dense filling and sealing of the orifice. This transforms the dissimilar metal connection of steel / aluminum into a metallurgical bond of the same metal between the rivet and the steel plate, effectively suppressing the formation of brittle intermetallic compounds at the interface.

[0024] 2. High-speed rotating rivets are used to directly penetrate the aluminum layer, simplifying the processing steps. Furthermore, the control system enables precise control of axial displacement accuracy to ±0.005mm and pressure accuracy to ±10N, improving process stability and reliability.

[0025] 3. It combines the thermo-mechanical coupling effect of friction welding, the filling characteristics of plug welding, and the mechanical interlocking effect of riveting. It not only significantly improves the interface strength, but also forms a "hook-shaped" mechanical interlocking structure with the aluminum plate through the flash structure at the bottom of the rivet and the thread structure on the rivet rod, which significantly improves the joint strength.

[0026] 4. The joint area simultaneously contains a rivet-steel metallurgical bonding zone, a rivet-aluminum mechanical interlocking zone, and a submerged weld layer metallurgical bonding zone. This triple connection mechanism enhances the mechanical properties of the joint.

[0027] This invention can be widely applied to the preparation of steel-aluminum transition joints in industrial fields such as shipbuilding, aviation, aerospace and electrolytic aluminum, and is especially suitable for components with stringent requirements for lightweighting and connection reliability. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the interface enhancement method of the present invention.

[0029] Among them, (a) pre-drilled holes, (b) penetrating aluminum layers, (c) friction welding, (d) upsetting, (e) submerged welding, and (f) smoothing weld points.

[0030] Figure 2 This is a schematic diagram of the joint section of the interface-strengthened steel-aluminum composite plate.

[0031] Among them, 1—embedded welding layer, 2—aluminum side metal of steel-aluminum composite plate, 3—steel rivet, 4—steel side metal of steel-aluminum composite plate, 5—annular gap below the rivet head. Detailed Implementation

[0032] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0033] For the pretreatment of steel-aluminum composite panels, the surface of the aluminum alloy layer of the steel-aluminum composite panel is cleaned by mechanical or chemical cleaning methods to remove the oxide film, oil and impurities on the surface. For steel-aluminum composite panels, blind holes are machined on the surface of the aluminum alloy layer. The diameter of the blind hole is not less than the diameter of the rivet head, and the depth of the blind hole is greater than the height of the rivet head. After the blind holes are machined, they are deburred by milling.

[0034] Steel rivets are used as connecting elements. A continuous-drive friction welding machine drives the rivets to rotate at high speed, aligning them with pre-drilled holes in the aluminum alloy layer of the steel-aluminum composite plate for connection. The connection process sequentially includes a penetration stage, a friction welding stage, and an upsetting stage, followed by rivet hole embedding welding. The process is as follows: Figure 1 As shown.

[0035] Example 1

[0036] In this embodiment, an AA5083 aluminum / Q235 steel rolled composite plate is used, with an aluminum layer thickness of 5.0 mm. A tapered medium carbon steel rivet with a ZnNi coating is selected, with a rivet diameter of 6.0 mm, a length of 7.8 mm, a cone angle of 120°, and a national standard ordinary metric coarse external thread M6×1. The rivet head diameter is twice the diameter of the rivet shaft.

[0037] Step 1: Surface treatment, clamping and positioning, and closed-loop control parameter setting of composite plate and rivets before welding.

[0038] Step 1-1: Mechanically grind the aluminum alloy side surface until it is smooth, focusing on removing oxide film, indentations and attached oil stains. Then, wipe it thoroughly with alcohol and blow it dry to ensure that the surface of the connection area is clean, dry and free of visible contamination.

[0039] Step 1-2: Clean the contact surface between the clamp and the steel side of the composite plate to ensure that there are no impurities on the contact surface; place the steel side of the composite plate below and reliably support and fix it so that the plate surfaces in the connection area fit together without obvious warping, and mark the center position of the connection point at the work station.

[0040] Steps 1-3: Activate the closed-loop control system and complete the calibration of the spindle zero point, displacement reference point, and pressure sensor zero point.

[0041] Step 2 involves pre-drilling blind holes in the aluminum alloy layer and completing coaxial alignment with the rivets to improve penetration stability.

[0042] Step 2-1: Machine blind holes in the aluminum alloy layer. The diameter of the blind holes should not be less than the diameter of the rivet head. After machining, remove burrs from the hole opening to prevent the rivet from scratching the hole wall or causing eccentric friction when it enters the hole. In this embodiment, the depth of the blind hole is 3.0 mm and the diameter is 13 mm.

[0043] Step 2-2: Clean and dry the walls and bottom of the blind hole with alcohol; after clamping, adjust the rivet axis to be coaxial with the blind hole axis to ensure stable guidance of the rivet during the initial pressing stage, and tighten the clamp to prevent centering drift. Figure 1 As shown in (a).

[0044] Step 3: Press down the rivet at the set rotation speed and pressing speed to complete the penetration of the aluminum layer and accurately reach the vicinity of the steel-aluminum connection interface.

[0045] Step 3-1: Set the first stage rotation speed to 1000-8000 rpm and the first stage pressing speed to 1.0-5.0 mm / s. In this embodiment, the first stage rotation speed is 3500 rpm, the pressing speed is 1.8 mm / s, and the pressing depth (measured from the bottom of the blind hole) is 2 mm, so that the aluminum enters a controllable thermoplastic state under the action of frictional heat.

[0046] Step 3-2: The first stage of the downward pressure is set to the distance from the bottom of the blind hole to the interface of the steel-aluminum composite plate. During the downward pressure process, the axis is kept stable and the displacement curve is monitored to ensure that the rivet reaches the vicinity of the interface after penetrating the aluminum layer without overshooting. The state of the weld point after penetrating the aluminum plate is as follows: Figure 1 As shown in (b).

[0047] Step 4 involves friction welding after the rivet contacts the steel and then performing metallurgical bonding densification during upsetting at a stop.

[0048] Step 4-1: After the rivet tip contacts the steel layer, the second stage begins. The rotation speed for the second stage is set to 2000–10000 rpm, the pressing speed to 1.0–5.0 mm / s, and the pressing amount to be 1–2 times the thickness of the penetrated aluminum plate. In this embodiment, the rotation speed is 3600 rpm, the pressing speed is 3.4 mm / s, the pressing depth is 2.2 mm, and the pressing amount is controlled to be 1.1 times the thickness of the remaining penetrated aluminum layer. This allows the rivet and steel plate to form a stable metallurgical bond under frictional heat and axial pressure.

[0049] After reaching the set displacement in step 4-2, rotation is stopped and downward pressure continues to complete the upsetting. The additional upsetting depth after stopping rotation is 0.4 mm. The axial upsetting pressure is set to 200 MPa. In this embodiment, the total pressing depth is approximately 4.6 mm. During the upsetting process, displacement / pressure is kept under control to further densify the interface and form a structure at the bottom of the rivet. Figure 1 (d) shows a continuous and stable "hook-shaped" interlocking structure.

[0050] Step 5 involves post-weld treatment and quality inspection of the weld joint appearance and cross-sectional structure to confirm the interface strengthening effect. Remove any burrs on the aluminum side and clean the weld joint surface. If necessary, make minor adjustments to the perimeter of the weld joint to ensure the surface morphology meets subsequent assembly or inspection requirements.

[0051] Step 6: Embedding and welding the rivet holes and shaping the surface.

[0052] Step 6-1: Clean the upper hole area of ​​the rivet after friction welding to confirm that there is a gap between the upper part of the rivet and the aluminum alloy.

[0053] Step 6-2 uses the same welding wire as the aluminum alloy base material to fill the gaps using gas metal arc welding. After the filling welding, a structure is formed above the aluminum plate as shown in the image. Figure 1 The protrusion shown in (e) was smoothed by machining after the filler welding. The cross-sectional morphology of the finished weld point is as follows: Figure 2 As shown.

[0054] Under the above parameters, the tensile and shear strength of the joint was tested to be approximately 11.43 kN.

[0055] Example 2

[0056] This embodiment uses a 6061 aluminum / Q235 steel explosion-proof composite plate with an aluminum layer thickness of 4.5mm; a tapered medium carbon steel rivet with a ZnNi coating is selected, with a rivet diameter of 6mm, a length of 7.5mm, a cone angle of 120°, and a national standard ordinary metric coarse external thread M6×1. The rivet head diameter is twice the diameter of the rivet shaft.

[0057] Step 1: Surface treatment, clamping and positioning, and closed-loop control parameter setting of the exploded composite plate and rivets before welding.

[0058] Step 1-1: Mechanically grind the aluminum alloy side surface until it is flat, perform chemical cleaning, acid pickling, rinse the aluminum alloy layer surface with clean water, and dry it to avoid residual acid from corroding the substrate and to ensure that the surface of the connection area is clean.

[0059] Steps 1-2: Place the composite steel plate side down and reliably support and fix it. Clean the contact surface between the support surface and the clamp. Ensure there is no warping near the connection area and maintain clamping rigidity. Mark the center of the connection point.

[0060] Steps 1-3 initiate displacement / pressure dual closed-loop control and process acquisition, and complete displacement zero point and pressure zero point calibration.

[0061] Step 2 involves pre-drilling blind holes in the aluminum alloy layer and completing coaxial alignment with the rivets to improve penetration stability.

[0062] Step 2-1: Machine blind holes in the aluminum alloy layer. The diameter of the blind holes should not be less than the diameter of the rivet head. After machining, remove burrs from the hole opening to prevent the rivet from scratching the hole wall or causing eccentric friction when it enters the hole. In this embodiment, the depth of the blind hole is 3mm and the diameter is 13mm.

[0063] Step 2-2: Clean and dry the walls and bottom of the blind hole with alcohol; after clamping, adjust the rivet axis to be coaxial with the blind hole axis to ensure stable guidance of the rivet during the initial pressing stage, and tighten the clamp to prevent centering drift. Figure 1 As shown in (a).

[0064] Step 3: Complete aluminum layer penetration within the specified first-stage parameter range.

[0065] Step 3-1 sets the rotation speed of the first stage to 1000-8000 rpm and the pressing speed of the first stage to 1.0-5.0 mm / s. In this embodiment, the rotation speed of the first stage is 5000 rpm, the pressing speed is 3.5 mm / s, and the pressing displacement of the first stage is 1.5 mm (same as the aluminum layer thickness).

[0066] During step 3-2, monitor displacement and pressure changes during the pressing process, maintain the rivet axis stability, and ensure that the aluminum material flows symmetrically along the rivet circumference, forming a relatively uniform backfilling trend. The state of the weld point after penetrating the aluminum plate is as follows: Figure 1 As shown in (b).

[0067] Step 4 involves friction welding after the rivet contacts the steel and then performing metallurgical bonding densification during upsetting at a stop.

[0068] After entering the second stage in step 4-1, set the rotation speed of the second stage to 2000-10000 rpm, the pressing speed of the second stage to 1.0-5.0 mm / s, and the pressing amount of the second stage to 1-2 times the thickness of the aluminum plate being penetrated, so that the rivet and the steel plate form a metallurgical bond. In this embodiment, the rotation speed of the second stage is 5200 rpm, the pressing speed is 4.0 mm / s, the pressing displacement of the second stage is 2.0 mm, and the pressing amount is controlled to 4 / 3 times the thickness of the remaining aluminum layer being penetrated.

[0069] Step 4-2: Stop rotation and continue pressing to complete the upsetting. After stopping rotation, the additional upsetting amount is 0.4mm. The axial upsetting pressure is set to 230MPa. In this embodiment, the total displacement of the two-stage setting is approximately 3.9mm. Based on this, the stop-rotation upsetting ensures the overall density of the weld joint, forming a structure like... Figure 1 (d) shows a continuous and stable "hook-shaped" interlocking structure.

[0070] Step 5: Post-weld cleaning, appearance consistency inspection, and cross-sectional microstructure confirmation.

[0071] Step 5-1: Clean the burrs and solder joint surface, check for surface defects, and verify the appearance and dimensions if necessary.

[0072] Step 5-2 cross-sectional inspection confirmed the coexistence of the metallurgical bonding zone and the mechanical interlocking zone, with the bottom interlocking exhibiting a continuous "hook-like" structure and no obvious pores.

[0073] Step 6: Rivet Hole Embedding and Surface Shaping. After friction welding, clean the area around the rivet head / hole opening. Use welding wire of the same or similar type as the aluminum alloy base material to embed and weld the rivet hole area, forming an embedded weld layer. This embedded weld layer forms a metallurgical bond between the rivet head and the aluminum alloy layer. After embedding and welding, a layer is formed on top of the aluminum plate, resembling... Figure 1 The protrusion shown in (e) was smoothed by machining after the filler welding. The cross-sectional morphology of the finished weld point is as follows: Figure 2 As shown.

[0074] Under the above parameters, the tensile and shear strength of the joint was tested to be approximately 10.24 kN.

[0075] Example 3

[0076] This embodiment uses a 7075-T6 aluminum / DP980 steel friction stir welded composite plate with an aluminum layer thickness of 3.5mm; a tapered medium carbon steel rivet with a ZnNi coating is selected, with a rivet diameter of 5mm, a length of 7.0mm, a cone angle of 120°, and a rivet head diameter that is twice the diameter of the rivet shaft. The outer circumference of the rivet shank is provided with a standard metric coarse thread with a thread specification of M5×0.8.

[0077] Step 1: Surface treatment, clamping and positioning, and closed-loop control parameter setting of friction stir welding composite plate and rivet before welding.

[0078] Step 1-1 involves lightly mechanically polishing the aluminum alloy side surface and then cleaning and drying it with alcohol to avoid excessive polishing that could cause localized thinning of the aluminum layer and to ensure the cleanliness of the connection area.

[0079] Steps 1-2: Clean the contact surfaces of the support and the fixture to ensure clamping rigidity and prevent the composite plate from deflecting during the pressing process.

[0080] Steps 1-3 enable displacement / pressure dual closed-loop control and process acquisition, and complete displacement zero point and pressure zero point calibration.

[0081] Step 2 involves pre-drilling blind holes in the aluminum alloy layer and completing coaxial alignment with the rivets to improve penetration stability.

[0082] Step 2-1: Machine blind holes in the aluminum alloy layer. The diameter of the blind holes should not be less than the diameter of the rivet head. After machining, remove burrs from the hole openings. In this embodiment, the depth of the blind hole is 2.0 mm and the diameter is 13 mm.

[0083] Step 2-2: Clean and dry the walls and bottom of the blind hole with alcohol; after clamping, adjust the rivet axis to be coaxial with the blind hole axis, and tighten the clamp to prevent centering drift. Figure 1 As shown in (a).

[0084] Step 3 involves setting the rotation speed and pressing speed to complete the aluminum layer penetration and precisely reach the vicinity of the steel-aluminum interface.

[0085] Step 3-1 sets the first stage rotation speed to 1000-8000 rpm and the first stage pressing speed to 1.0-5.0 mm / s. In this embodiment, the first stage rotation speed is 2700 rpm, the pressing speed is 2.2 mm / s, and the pressing depth is 1.5 mm, so that the aluminum enters a controllable thermoplastic state under the action of frictional heat.

[0086] Step 3-2: The first stage pressing amount is set to the distance from the bottom of the blind hole to the interface of the steel-aluminum composite plate; during the pressing process, the displacement curve is monitored to ensure that it reaches the vicinity of the interface without overshooting, and the state of the weld point after penetrating the aluminum plate is as follows. Figure 1 As shown in (b).

[0087] Step 4 involves friction welding after the rivet contacts the steel and then performing metallurgical bonding densification during upsetting at a stop.

[0088] Step 4-1 sets the second stage rotation speed to 2000-10000 rpm, the second stage pressing speed to 1.0-5.0 mm / s, and the second stage pressing amount to be approximately 1.47 times the thickness of the remaining aluminum layer that has been penetrated. In this embodiment, the second stage rotation speed is 5500 rpm, the pressing speed is 3.8 mm / s, and the second stage pressing displacement is 2.2 mm.

[0089] Step 4-2: Stop rotation and continue pressing to complete the upsetting. The additional upsetting amount after stopping rotation is 0.4mm. The axial upsetting pressure is set to 280MPa. In this embodiment, the total displacement of the two-stage setting is approximately 4.1mm, forming as shown... Figure 1 The weld joint structure shown in (d).

[0090] Step 5: Post-weld cleaning, visual consistency inspection, and cross-sectional microstructure confirmation. Clean up any burrs and the surface of the weld joints, and perform visual finishing if necessary.

[0091] Step 6: Embedding and welding the rivet holes and shaping the surface.

[0092] Step 6-1 Clean the periphery / hole area of ​​the rivet head after friction welding to ensure the hole area is clean.

[0093] Step 6-2 uses welding wire of the same or similar type as the aluminum alloy base material to perform embedded welding in the orifice area to form an embedded weld layer. This embedded weld layer forms a metallurgical connection with the rivet head and the aluminum alloy layer. After the embedded welding, a layer is formed on top of the aluminum plate as shown in the image. Figure 1 The protrusion shown in (e) was smoothed by machining after the filler welding. The cross-sectional morphology of the finished weld point is as follows: Figure 2 As shown.

[0094] Under the above parameters, the tensile and shear strength of the joint was tested to be approximately 10.59 kN.

[0095] The above description is merely a preferred embodiment of the present invention and an explanation of the technical principles employed, and is not intended to limit the scope of the claimed invention, but merely to illustrate preferred embodiments of the invention. Those skilled in the art should understand that the scope of the invention is not limited to the specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for strengthening the interface of a steel-aluminum composite plate, characterized in that, Specifically, the following steps are included: 1) Pretreatment of steel-aluminum composite panels The surface of the aluminum alloy layer of the steel-aluminum composite panel is cleaned, and blind holes are machined on the surface of the aluminum alloy layer of the steel-aluminum composite panel. The diameter of the blind holes is not less than the diameter of the rivet head, and the depth of the blind holes is greater than the height of the rivet head. 2) Rivet positioning and staged welding Steel rivets are used as connecting elements. The outer circumference of the rivet shank is provided with external threads. The rivets are driven to rotate at high speed by a continuous friction welding device, so that the rivets are aligned with the pre-set blind hole position of the aluminum alloy layer of the steel-aluminum composite plate and pressed down to realize the connection. The connection process includes the aluminum layer penetration stage, the friction welding stage and the upsetting stage in sequence. Aluminum layer penetration stage: The rivet penetrates the remaining aluminum alloy layer at a rotation speed of 1000-8000rpm and a pressing speed of 1.0-5.0mm / s. The pressing amount is the distance from the bottom of the aluminum alloy blind hole to the interface of the composite plate. Frictional heat puts the aluminum layer in a thermoplastic state. The aluminum material is extruded along the side wall of the rivet and fills the annular gap below the rivet head. Friction welding stage: After the rivet tip contacts the steel plate, adjust the rotation speed to 2000-10000 rpm, keep the pressing speed at 1.0-5 mm / s, and the pressing amount is 1-2 times the thickness of the remaining aluminum layer. The friction heat causes the rivet to form a metallurgical bond with the steel plate. Upsetting stage: Stop rotation, apply upsetting pressure of 100-350MPa along the axial direction, hold pressure for 0-3s, so that the bottom of the rivet forms a mechanically interlocking "hook" structure, and the connection is completed; 3) Embedded welding of rivet holes After completing step 2), the periphery / orifice area of ​​the rivet head is filled and welded using welding wire that is the same as or similar to the aluminum alloy base material to form a weld layer. The weld layer forms a metallurgical connection with the aluminum alloy layer and the rivet head.

2. The steel-aluminum composite plate interface strengthening connection method as described in claim 1, characterized in that, The steel-aluminum composite plate mentioned in step 1) includes explosively welded composite plate, rolled composite plate and friction stir welded composite plate.

3. The steel-aluminum composite plate interface strengthening connection method as described in claim 1, characterized in that, The aluminum alloy layer of the steel-aluminum composite plate mentioned in step 1) is an aluminum-magnesium series, an aluminum-magnesium-silicon series, or an aluminum-zinc-magnesium-copper series aluminum alloy.

4. The steel-aluminum composite plate interface strengthening connection method as described in claim 1, characterized in that, The steel layer of the steel-aluminum composite plate mentioned in step 1) is made of low-carbon steel, high-strength steel, or stainless steel.

5. The steel-aluminum composite plate interface strengthening connection method as described in claim 1, characterized in that, The continuous drive friction welding equipment described in step 2) includes a rotary drive module and an axial feed module.

6. The steel-aluminum composite plate interface strengthening connection method as described in claim 1, characterized in that, The surface of the rivet described in step 2) is plated with a ZnNi coating or passivated.

7. The steel-aluminum composite plate interface strengthening connection method as described in claim 1, characterized in that, The head of the rivet described in step 2) is designed with a tapered tip and a cap structure, with a tapered angle of 100-150°, a rivet head diameter of 1.5-2.5 times the diameter of the rivet shaft, and an annular gap below the rivet head with a volume of 1.2-1.5 times the volume of the rivet inserted into the aluminum plate.

8. The steel-aluminum composite plate interface strengthening connection method as described in claim 1, characterized in that, The remaining aluminum layer thickness mentioned in step 2) refers to the distance from the bottom of the pre-made blind hole to the interface of the steel-aluminum composite plate along the rivet axis.

9. The steel-aluminum composite plate interface strengthening connection method as described in claim 1, characterized in that, The welding methods used for rivet hole embedding welding in step 3) include arc welding and laser welding.

10. The method for strengthening the interface connection of steel-aluminum composite plates according to any one of claims 1-8, characterized in that, Preparation of steel-aluminum composite plate components for shipbuilding, aviation, and aerospace applications.

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