Magnesium steel dissimilar material mechanical-metallurgical composite connection method and connection structure

Abstract

The invention relates to the field of dissimilar metal resistance rivet welding, and discloses a magnesium steel dissimilar material mechanical-metallurgical composite connection method and a connection structure, and the method comprises the following steps: placing a magnesium alloy plate above a steel plate, and placing a semi-tubular hollow steel rivet on the upper surface of the magnesium alloy plate; pressing force F is applied to the rivet-magnesium alloy plate-steel plate laminated layer through an electrode, and pre-pressing is carried out; the pressing force F is kept, puncture current is applied, the rivet penetrates through the magnesium alloy plate and makes contact with the steel plate, and meanwhile the magnesium alloy material is intercepted in the rivet; keeping the pressing force F, stopping electrifying, and cooling; the pressing force F is kept, and welding current is applied to enable the rivet, the steel plate and the intercepted magnesium alloy material to be melted to form nuggets; and after welding is finished, the pressing force F is kept, and after cooling, a double-layer nugget structure with the steel nugget on the outer layer and the magnesium nugget on the inner layer is formed. According to the magnesium / steel rivet welding method, by forming the double-layer steel ladle magnesium nugget, interface brittle intermetallic compound layer connection is avoided, and the strength and toughness of a connector are improved.

Description

Technical Field

[0001] This invention relates to the field of resistance riveting of dissimilar metals, and more particularly to a mechanical-metallurgical composite connection method and connection structure for magnesium-steel dissimilar materials. Background Technology

[0002] Magnesium alloys have attracted widespread attention in the automotive manufacturing industry due to their excellent specific strength and specific stiffness, which is close to that of aluminum alloys and steel. Using magnesium alloy shells in conjunction with steel reinforcements can not only effectively improve the body strength but also significantly reduce the overall vehicle weight, thus achieving lightweighting. However, joining magnesium alloys and steel presents significant technical challenges. Because magnesium alloys and steel have extremely low solid solubility, lack matching crystal planes, and significantly different thermophysical properties, they are inherently unweldable. Furthermore, the low ductility of magnesium alloys makes direct bonding between them impossible using common mechanical joining methods.

[0003] Currently, the main joining technologies between magnesium alloys and steel include intermetallic compound (IMC) bonding at the magnesium / steel interface and mechanical bonding via pre-drilling holes in the magnesium alloy sheet. However, each of these methods has its limitations. For example, IMC bonding may lead to increased brittleness of the interface layer, while pre-drilling bonding processes may affect the integrity and strength of the magnesium alloy material.

[0004] Therefore, there is an urgent need for a new joining method to overcome the shortcomings of existing technologies and achieve a reliable connection between magnesium alloys and steel without compromising material properties. Summary of the Invention

[0005] The main objective of this invention is to solve the technical problem of how process technology affects the integrity and strength of magnesium alloy materials. A mechanical-metallurgical composite joining method for dissimilar magnesium and steel materials includes the following steps: Place the magnesium alloy plate on top of the steel plate, and place the semi-tubular hollow steel rivets on the upper surface of the magnesium alloy plate. Pre-compression is achieved by applying a clamping force F to the rivet-magnesium alloy plate-steel plate stack using electrodes; Maintain the clamping force F, apply a piercing current to make the rivet penetrate the magnesium alloy plate and contact the steel plate, while simultaneously trapping magnesium alloy material inside the rivet; Maintain the clamping force F, stop the power supply, and allow it to cool. Maintain the clamping force F, and apply welding current to melt the rivet, steel plate, and cut-off magnesium alloy material to form a weld nugget; After welding, the clamping force F is maintained, and after cooling, a double-layer fusion core structure is formed with a steel fusion core on the outer layer and a magnesium fusion core on the inner layer.

[0006] In a preferred embodiment, the length of the rivet leg is set to 1.0-2.0 times the thickness of the magnesium alloy plate.

[0007] In a preferred embodiment, the clamping force F ranges from 1500 to 4000 N.

[0008] In a preferred embodiment, the pre-compression time T1 is 50-300ms.

[0009] In a preferred embodiment, the puncture current I1 is 7-12kA.

[0010] In a preferred embodiment, the duration T2 of the puncture current is 15-100 ms.

[0011] In a preferred embodiment, the cooling time T3 is 5-50 ms.

[0012] In a preferred embodiment, the welding current I2 is 5-12kA and the duration T4 is 100-300ms.

[0013] In a preferred embodiment, the pressure holding time T5 is 100-300ms.

[0014] The second aspect of the present invention provides a mechanical-metallurgical composite connection structure for dissimilar materials of magnesium and steel. The connection structure connects a magnesium alloy plate and a steel plate by rivets. The magnesium alloy plate, the steel plate, and the rivets form a double-layer fusion core structure with an outer steel fusion core and an inner magnesium fusion core.

[0015] The present invention has the following beneficial effects: This invention proposes a novel magnesium / steel joining process that enables mechanical-metallurgical composite joining between magnesium alloys and steel without the need for pre-drilling holes.

[0016] This invention enables the welding of magnesium alloy and steel in a single process, eliminating the need for additional pre- or post-processing steps, such as drilling holes in the magnesium alloy plate, thus simplifying the production process. Compared to the "pre-drilled connection process," it saves processing steps and reduces costs. This invention innovatively proposes a magnesium / steel riveting method, which forms a double-layer "steel-clad magnesium" weld nugget, so that the magnesium alloy and the steel plate are connected by the steel-steel welding weld nugget, resulting in a high-strength magnesium-steel welded joint, avoiding the brittle intermetallic compound layer connection at the interface, and improving the joint strength and toughness. Attached Figure Description

[0017] Figure 1 The structural diagram of the magnesium-steel dissimilar material mechanical-metallurgical composite structure provided in the embodiment of the present invention is shown.

[0018] Figure 2The figure shows the experimental results of the mechanical-metallurgical composite joining method for dissimilar magnesium and steel materials provided in the embodiments of the present invention.

[0019] Figure 3 The figure shows the experimental results for control group 5.

[0020] Figure 4 The figure shows the experimental results for control group 8.

[0021] Figure 5 This is a schematic diagram of the riveting and welding method of the present invention. Detailed Implementation

[0022] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms “comprising” or “having,” and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0023] For ease of understanding, the specific process of the embodiments of the present invention is described below. Please refer to [link / reference]. Figure 1 The first embodiment of the mechanical-metallurgical composite joining method for magnesium-steel dissimilar materials in this invention includes: Place the magnesium alloy plate on top of the steel plate, and place the semi-tubular hollow steel rivets on the upper surface of the magnesium alloy plate. Pre-compression is achieved by applying a clamping force F to the rivet-magnesium alloy plate-steel plate stack using electrodes; Maintain the clamping force F, apply a piercing current to make the rivet penetrate the magnesium alloy plate and contact the steel plate, while simultaneously trapping magnesium alloy material inside the rivet; Maintain the clamping force F, stop the power supply, and allow it to cool. Maintain the clamping force F, and apply welding current to melt the rivet, steel plate, and cut-off magnesium alloy material to form a weld nugget; After welding, the clamping force F is maintained, and after cooling, a double-layer fusion core structure is formed with a steel fusion core on the outer layer and a magnesium fusion core on the inner layer.

[0024] In a preferred embodiment, the rivet leg length is set to 1.0-2.0 times the thickness of the magnesium alloy plate. Specifically, the rivet leg length is set to 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2 times the thickness of the magnesium alloy plate.

[0025] In a preferred embodiment, the clamping force F ranges from 1500 to 4000 N. Specifically, the clamping force F is 1500 N, 1600 N, 1700 N, 1800 N, 1900 N, 2000 N, 2100 N, 2200 N, 2300 N, 2400 N, 2500 N, 2600 N, 2700 N, 2800 N, 2900 N, 3000 N, 3100 N, 3200 N, 3300 N, 3400 N, 3500 N, 3600 N, 3700 N, 3800 N, 3900 N, or 4000 N.

[0026] In a preferred embodiment, the pre-compression time T1 is 50-300ms. Specifically, the compression time T1 is 50ms, 60ms, 70ms, 80ms, 90ms, 100ms, 110ms, 120ms, 130ms, 140ms, 150ms, 160ms, 170ms, 180ms, 190ms, 200ms, 210ms, 220ms, 230ms, 240ms, 250ms, 260ms, 270ms, 280ms, 290ms, or 300ms.

[0027] In a preferred embodiment, the puncture current I1 is 7-12kA. Specifically, the puncture current I1 is 7kA, 7.5kA, 8kA, 8.5kA, 9kA, 9.5kA, 10kA, 10.5kA, 11kA, 11.5kA, or 12kA.

[0028] In a preferred embodiment, the duration T2 of the puncture current is 15-100 ms. Specifically, the duration T2 is 15 ms, 20 ms, 250 ms, 30 ms, 35 ms, 40 ms, 45 ms, 50 ms, 60 ms, 70 ms, 80 ms, 90 ms, or 100 ms.

[0029] In a preferred embodiment, the cooling time T3 is 5-50ms. Specifically, the cooling time T3 is 5ms, 6ms, 7ms, 8ms, 9ms, 10ms, 11ms, 12ms, 13ms, 14ms, 15ms, 16ms, 17ms, 18ms, 19ms, 20ms, 21ms, 22ms, 23ms, 24ms, 25ms, 26ms, 27ms, 28ms, 29ms, 30ms, 31ms, 32ms, 33ms, 34ms, 35ms, 36ms, 37ms, 38ms, 39ms, 40ms, 41ms, 42ms, 43ms, 44ms, 45ms, 46ms, 47ms, 48ms, 49ms, or 50ms.

[0030] In a preferred embodiment, the welding current I2 is 5-12kA, and the duration T4 is 100-300ms. Specifically, the welding current I2 is 5kA, 5.5kA, 6kA, 6.5kA, 7kA, 7.5kA, 8kA, 8.5kA, 9kA, 9.5kA, 10kA, 10.5kA, 11kA, 11.5kA, or 12kA. The duration T4 is 100ms, 110ms, 120ms, 130ms, 140ms, 150ms, 160ms, 170ms, 180ms, 190ms, 200ms, 210ms, 220ms, 230ms, 240ms, 250ms, 260ms, 270ms, 280ms, 290ms, or 300ms.

[0031] In a preferred embodiment, the pressure holding time T5 is 100-300ms. Specifically, the pressure holding time T5 is 100ms, 110ms, 120ms, 130ms, 140ms, 150ms, 160ms, 170ms, 180ms, 190ms, 200ms, 210ms, 220ms, 230ms, 240ms, 250ms, 260ms, 270ms, 280ms, 290ms, or 300ms.

[0032] The mechanical-metallurgical composite joining method for dissimilar magnesium and steel materials in the embodiments of the present invention has been described above. The following describes a mechanical-metallurgical composite joining structure for dissimilar magnesium and steel materials in the embodiments of the present invention: like Figure 1 The connecting structure connects the magnesium alloy plate and the steel plate with rivets, and the magnesium alloy plate, the steel plate and the rivets form a double-layer fusion core structure with an outer steel fusion core and an inner magnesium fusion core.

[0033] See Figure 5 In this example, the workpieces to be welded are a 2.0 mm magnesium alloy plate and a 2.0 mm steel plate, and the rivet leg length is 3.0 mm.

[0034] 1) When performing step 1, the materials to be connected should be arranged in the order of magnesium alloy plate on top and steel plate on the bottom. Place the semi-tubular hollow steel rivet on top of the magnesium alloy plate so that the rivet leg is in contact with the surface of the magnesium alloy plate. 2) Perform step 2, apply a clamping force to the rivet-magnesium alloy plate-steel plate composite material using the electrode, ensuring that the electrode is aligned with the rivet. The electrode clamping force is F, which is 2.5kN here. The clamping time before the next process is T1, which is 200ms here. 3) Execute step 3, continue to maintain the electrode clamping force F, apply the puncture current I1, and the duration is T1. Here, I1 is selected as 9kA and T1 is 40ms. 4) Execute step 4, continue to maintain the electrode clamping force F, do not apply current, and allow it to cool for a period of time T3, here T3 is selected as 20ms; 5) Execute step 5, continue to maintain the electrode clamping force F, and apply welding current I2 for a duration of T5. Here, I2 is selected as 9kA and T5 as 140ms.

[0035] 6) Execute step 6 and continue to maintain the electrode clamping force F for a duration of T5, where I5 ​​is selected as 200ms.

[0036] 7) Perform step 7, raise the electrode cap, and obtain the magnesium-steel mechanical-metallurgical composite connection joint. Experimental results are shown below. Figure 2 .

[0037] Control experiment: Control group 1: In this example, the workpieces to be welded are a 2.0 mm magnesium alloy plate and a 2.0 mm steel plate, with rivet legs of 3.0 mm. A standard self-piercing riveting process is used. Holes are pre-punched in the magnesium plate, and then solid steel rivets are used to rivet the magnesium and steel plates together.

[0038] Control group 2: In this example, the workpieces to be welded are a 2.0 mm magnesium alloy plate and a 2.0 mm steel plate. Traditional resistance spot welding is used to directly connect the magnesium plate and the steel plate.

[0039] By comparing experimental data, it can be found that the magnesium alloy plate, steel plate and rivet obtained by the present invention form a double-layer fusion core structure with an outer steel fusion core and an inner magnesium fusion core, which has stronger mechanical properties, reaching 4.5KN, while control groups 1 and 2 are 2.5KN and 2KN respectively.

[0040] Experiment with double-layer molten core structure Magnesium plate thickness: 2.0 mm; Steel plate thickness: 2.0 mm; Pre-compression time T1: 200 ms; Holding time T5: 200 ms; Electrode pressure F: 2500 N; Other parameters are shown in the table below: Experiments show that the solution of this invention can successfully form an ideal double-layer weld nugget structure. Control group 3 uses solid rivets, which cannot achieve the function of "intercepting magnesium alloy," and the inner magnesium weld nugget cannot be formed. It forms a purely mechanically interlocked or single steel-steel weld nugget without an internal magnesium weld nugget. Control group 4 uses the traditional single high-current spot welding mode, resulting in heat runaway and material mixing to form a brittle phase. This produces spatter and porosity, forming a single, brittle mixed weld nugget without a layered structure. Control group 5, see... Figure 3 Excessive heat input caused severe spattering, resulting in a hole forming in the center of the molten core. In control group 7, the rivet penetration depth was insufficient, leaving too little magnesium alloy, and the inner magnesium molten core was incomplete or missing. In control group 8, see... Figure 4 The outer steel fusion core is small or discontinuous, unable to completely encapsulate the inner magnesium fusion core, resulting in low connection strength. In the control group, the 9-pin legs are upset, deeply pressed in, and have severe surface indentations.

[0041] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for mechanical-metallurgical composite joining of magnesium-steel dissimilar materials, characterized in that, Includes the following steps: Place the magnesium alloy plate on top of the steel plate, and place the semi-tubular hollow steel rivets on the upper surface of the magnesium alloy plate. Pre-compression is achieved by applying a clamping force F to the rivet-magnesium alloy plate-steel plate stack using electrodes; Maintain the clamping force F, apply a piercing current to make the rivet penetrate the magnesium alloy plate and contact the steel plate, while simultaneously trapping magnesium alloy material inside the rivet; Maintain the clamping force F, stop the power supply, and allow it to cool. Maintain the clamping force F, and apply welding current to melt the rivet, steel plate, and cut-off magnesium alloy material to form a weld nugget; After welding, the clamping force F is maintained, and after cooling, a double-layer fusion core structure is formed with a steel fusion core on the outer layer and a magnesium fusion core on the inner layer.

2. The mechanical-metallurgical composite joining method for magnesium-steel dissimilar materials according to claim 1, characterized in that, The length of the rivet leg is set to 1.0-2.0 times the thickness of the magnesium alloy plate.

3. The mechanical-metallurgical composite joining method for magnesium-steel dissimilar materials according to claim 1, characterized in that, The clamping force F ranges from 1500 to 4000 N.

4. The mechanical-metallurgical composite joining method for magnesium-steel dissimilar materials according to claim 1, characterized in that, The pre-compression time T1 is 50-300ms.

5. The mechanical-metallurgical composite joining method for magnesium-steel dissimilar materials according to claim 1, characterized in that, The breakdown current I1 is 7-12kA.

6. The mechanical-metallurgical composite joining method for magnesium-steel dissimilar materials according to claim 1, characterized in that, The duration T2 of the puncture current is 15-100ms.

7. The mechanical-metallurgical composite joining method for magnesium-steel dissimilar materials according to claim 1, characterized in that, The cooling time T3 is 5-50ms.

8. The mechanical-metallurgical composite joining method for magnesium-steel dissimilar materials according to claim 1, characterized in that, The welding current I2 is 5-12kA, and the duration T4 is 100-300ms.

9. The mechanical-metallurgical composite joining method for magnesium-steel dissimilar materials according to claim 1, characterized in that, The pressure holding time T5 is 100-300ms.

10. A mechanical-metallurgical composite connection structure for dissimilar magnesium and steel materials, characterized in that, The connection structure connects the magnesium alloy plate and the steel plate with rivets, and the magnesium alloy plate, the steel plate, and the rivets form a double-layer fusion core structure with an outer steel fusion core and an inner magnesium fusion core.

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