Splicing fastener for welding dissimilar alloy and welding method thereof

Abstract

The invention provides a splicing fastener for dissimilar alloy welding and a welding method. The fastener is composed of a cap and a core part, the cap is formed by punching a thin blank, the wall thickness is uniform, the range of the wall thickness T is 0.85 Tm to Tm, the Tm is the maximum wall thickness of the cap, the machining process is effectively simplified, and the cost is reduced. The bulging structure on the cap can be used for stably anchoring the core part during assembly and is adaptive to fast-beat stamping manufacturing; in the welding process, the bulging structure loses efficacy in time, the core portion can conveniently puncture the first alloy to form a high-quality connector, the upper end face of the cap can be fully deformed, the cavity volume is enlarged to contain discharged metal, and the welding spot forming quality is improved. In addition, the flange structure on the lower end face of the cap enhances axial support, and deformation of the cap and damage to the first alloy are prevented. According to the matched welding method, welding parameters are accurately controlled, the structural advantages of the fastener are fully played, and an efficient and reliable solution is provided for dissimilar alloy welding.

Description

Technical Field

[0001] The invention belongs to the field of welding of dissimilar alloys, and particularly relates to a spliced ​​fastener for welding dissimilar alloys and a welding method thereof. Background Art

[0002] In the field of automobile manufacturing, the welding technology of dissimilar alloy components is the key to achieving lightweight and high-performance car bodies. However, due to the significant differences in physical properties (such as melting point, thermal expansion coefficient) and chemical properties of dissimilar alloys, traditional welding processes can easily generate brittle intermetallic compounds in the weld area and cause defects such as cracks, resulting in insufficient weld quality stability and mechanical properties that are difficult to meet the stringent requirements of the car body structure. In order to overcome this technical bottleneck, the welding-riveting composite welding process has become an effective solution to improve the reliability of dissimilar alloy welding. This process combines the metallurgical bonding of welding with the mechanical locking advantages of riveting by introducing special fasteners at each weld point, but this also makes the structural design of the fasteners a core factor affecting welding quality, manufacturing costs and production efficiency.

[0003] The fastener manufacturing method proposed in the existing patent CN118595755A uses thin and thick blanks to form a cap-shaped thin-walled structure and a center frustum structure, respectively, which reduces the difficulty of stamping processing to a certain extent. However, there is still room for optimization in this solution: the wall thickness parameters of the cap-shaped thin-walled structure and the geometric configuration of the mounting portion need to be further refined. Through the systematic optimization of structural and dimensional parameters, the number of steps in the stamping process during the fastener forming process can be significantly reduced. This can not only significantly reduce manufacturing complexity and cost, but also effectively improve the forming accuracy of the fastener and the reliability during the welding process, thereby promoting the industrial application of dissimilar alloy welding technology. Summary of the Invention

[0004] In order to overcome the above-mentioned deficiencies in the prior art, the present invention aims to provide a spliced ​​fastener for welding dissimilar alloys and a welding method thereof, thereby reducing the number of stamping times in the manufacture of cap parts and fasteners, thereby reducing the manufacturing cost of the fasteners, and improving the riveting quality of the core and the cap. At the same time, it is ensured that during the welding process of the spliced ​​fastener of the present invention, the riveted positions of the core and the cap can be smoothly separated, ensuring the deformation ability of the cap during welding and the effect of the core piercing the first alloy layer, thereby improving the forming quality of the weld point.

[0005] In order to achieve the above object, a spliced ​​fastener for welding dissimilar alloys is provided, which is used for resistance spot welding a laminated component of a first alloy and a second alloy, wherein the first alloy is a light metal, and the spliced ​​fastener comprises: a bowl-shaped thin-walled cap having a hollow structure with a single-side opening, the open end of which forms the lower end face of the cap, and the side periphery transitions to the upper end face through an arc-shaped area; a solid core coaxially arranged in the central area inside the cap, having a shaft portion and a flange portion extending outward from the upper end of the shaft portion; wherein the bottom surface of the core portion is aligned with the lower end face of the cap Coplanar or indented with the plane where the lower end face is located; the wall thickness T of the cap ranges from 0.85Tm to Tm, and Tm is the maximum wall thickness of the cap; the cap is provided with a plurality of bulging structures distributed at equal angles in the circumferential direction, and the bulging structure forms a convex area by plastically deforming a local area of ​​the cap by stamping, and the local convex area of ​​the bulging structure is squeezed to the core to produce a mechanical anchoring effect; the bulging structure is separated from the core during the welding process, so that the mechanical anchoring function of the bulging structure on the core is completely lost.

[0006] Preferably, the shaft height H3 is no greater than 1.5 times the thickness of the first alloy; the shaft bottom diameter φ3 and the shaft top diameter φ4 are in the following relationship: 1.4×φ3≤φ4≤2×φ4; the flange maximum diameter φ5 and φ4 are in the following relationship: φ4<φ5≤1.5×φ4; and the shaft sidewall has an arc-shaped cross-section, connecting the core bottom and the top flange.

[0007] Furthermore, the maximum wall thickness Tm of the cap is in the range of 0.2 mm to 0.5 mm.

[0008] Preferably, the cap is made of cold-rolled carbon steel having a yield strength of less than 300 MPa, including IF steel (Interstitial-Free Steel), SPCC steel (Steel Plate Cold Coiled), DC steel (Deep Drawing Cold Rolled Steel), etc.

[0009] Preferably, the core is one of stainless steel, advanced high strength steel and ultra-high strength steel, wherein the advanced high strength steel includes dual phase steel (DP steel), transformation induced plasticity steel (TRIP steel), complex phase steel (CP steel) and hot formed steel (HF steel).

[0010] Furthermore, the bulging structure is a supplementary extrusion and concave forming of a local area of ​​the cap after the cap and the core are assembled, and the minimum wall thickness Tb of the local area of ​​the bulging structure is greater than 0.25Tm, where Tm is the maximum wall thickness of the cap.

[0011] Furthermore, the cap is provided with a positioning ladder groove which is recessed inward from the outer surface and distributed in a circumferential ring shape, and its longitudinal side wall is clearance-matched with the outer side wall of the flange portion to accurately define the installation position of the core portion.

[0012] Furthermore, the bulging structure is provided in the positioning ladder groove area, so that the longitudinal side wall of the positioning ladder groove is partially deformed to form a convex area to mechanically anchor the core.

[0013] Preferably, the axial height H1 of the positioning ladder groove is 0.8 mm to 1.2 mm.

[0014] Furthermore, the lower end surface of the cap is provided with a flange structure extending radially outward, and the transverse width Lf of the flange structure and the maximum wall thickness Tm of the cap satisfy: 3×Tm≤Lf≤6×Tm.

[0015] Furthermore, the cap includes a cap side and an arc-shaped area; the arc-shaped area extends in an arc from the upper end of the cap side to the upper end surface of the cap, and forms a bend structure when expanding radially inward, so that a local area of ​​the arc-shaped area is higher than the upper end surface of the cap, thereby forming an inwardly concave contour on the upper end surface of the cap.

[0016] Furthermore, the upper end surface of the cap has an inwardly concave profile and is only partially in contact with the top surface (208) of the core.

[0017] Preferably, the outer edge of the core flange abuts against the side of the cap, and mechanical clamping is achieved by squeezing the bulging structure onto the side.

[0018] Furthermore, the height H1 of the outer side wall H2 of the flange portion and the positioning ladder groove satisfies: H2

[0019] Furthermore, after the spliced ​​fastener is welded, at least a portion of the contact interface between the upper end surface of the cap and the top surface of the core is firmly connected through a metallurgical bonding process.

[0020] Furthermore, after the core and the cap are assembled and installed, the bulging structure produces a mechanical anchoring effect on the outer edge of the flange portion of the cap, and the upper surface of the core fits tightly with the upper end surface of the cap, and the gap between the two does not exceed 0.1 mm.

[0021] Furthermore, the arc-shaped area forms a bend structure, the highest point of which protrudes 0.3-1.0 mm from the upper end surface of the cap; the side wall of the core shaft portion is an arc transition surface, connecting the bottom surface of the core portion and the flange portion.

[0022] Preferably, the surface of the spliced ​​fastener is coated with a corrosion-resistant coating, and the corrosion-resistant coating is not limited to zinc coating, zinc-nickel alloy, chromium coating, aluminum-silicon coating, and the like.

[0023] ​According to another aspect of the present invention, a method for welding dissimilar metals is provided, wherein resistance welding is performed on dissimilar metals comprising a first alloy having a melting point not exceeding 700°C and a second alloy having a melting point greater than 1300°C, wherein the welding method uses a split fastener as described in any one of claims 1 to 13, wherein the split fastener is welded from the first alloy side, wherein during the welding process, the core of the split fastener pierces the first alloy layer and forms a molten core with the second alloy layer to achieve connection, and the cap of the split fastener stays on the surface of the first alloy layer to form a sealed cap-like structure to accommodate the first alloy extruded from the weld point.

[0024] Furthermore, during welding, electrode pressure and preheating current I1 are applied to the spliced ​​fastener and the first and second alloys, so that the upper end surface of the cap squeezed by the welding electrode is in close contact with the top surface of the core, and the lower end surface of the cap and the bottom surface of the core are in close contact with the surface of the first alloy.

[0025] Furthermore, it also includes a puncture stage and a nucleation stage. In the puncture stage, several puncture currents I2 are applied, and the maintenance time of each puncture current is ΔT. a In the range of 50 milliseconds to 65 milliseconds, a nucleation current I3 is applied during the nucleation phase, wherein the nucleation current is maintained for a time ΔT b and ΔT a There is a relationship: 2×ΔT a ≤ΔT b ≤4×ΔT a , and the current difference ΔI of the nucleation current I3 minus the puncture current I2 ranges from 1 kiloampere to 6 kiloamperes.

[0026] Furthermore, the resistance heat generated during the puncture stage causes part of the first alloy in the weld to melt and be discharged into the cap of the split fastener, and the mechanical anchoring effect between the bulging structure of the split fastener and the core fails, causing the core to penetrate the first alloy layer and contact the second alloy layer.

[0027] Preferably, the first alloy is an aluminum alloy and a magnesium alloy, and the thickness of the first alloy is greater than 3 mm; the second alloy is an advanced high-strength steel and an ultra-high-strength steel with a coating (including a zinc coating and an aluminum-silicon coating) on ​​the surface, and the thickness of the second alloy is greater than 1 mm.

[0028] Beneficial effects of the present invention:

[0029] (1) The control range of the wall thickness T of the thin-walled cap is 0.85Tm to Tm (Tm is the maximum cap wall thickness), which ensures the uniformity of the wall thickness of the thin-walled cap. In the manufacturing process of the cap, there is no need to significantly thicken or thin the blank, so that the cap can be directly stretched or bent from the thin blank. This greatly improves the production efficiency of the cap, significantly improves the molding quality, and effectively reduces the manufacturing cost of the thin-walled cap.

[0030] (2) After the cap and the core are assembled, the mechanical locking effect formed by the bulging structure extruded from the thin-walled cap can well adapt to the fast-paced stamping manufacturing process, enabling the cap and the core to be quickly assembled and firmly locked, while ensuring assembly efficiency and structural stability.

[0031] (3) During the welding process, the bulging structure will separate from the core. This feature helps the core to penetrate the first alloy smoothly and form a reliable joint. On the other hand, it causes the deformation of the upper end face of the cap to be as close as possible to the outer edge of the electrode contact area, thereby effectively expanding the cavity volume of the cap after welding, significantly improving the cap's ability to accommodate the discharged liquid first alloy, and ensuring welding quality.

[0032] (4) The flange structure provided on the lower end face of the cap has a dual function. First, it can significantly enhance the axial support strength of the cap and prevent the cap side from excessive collapse and deformation; second, it can effectively prevent the thin-walled lower end face of the cap from penetrating into the surface of the first alloy, thereby preventing the strength of the first alloy from being damaged and ensuring the integrity and reliability of the entire joint structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a three-dimensional schematic diagram of the outer surface of the cap in one embodiment;

[0034] Figure 2 is a schematic diagram of the inner surface of a cap in one embodiment;

[0035] Figure 3 for Figure 1 A schematic cross-sectional view of the cap in FIG.

[0036] Figure 4 is a schematic cross-sectional view of a core portion in one embodiment;

[0037] Figure 5 is a schematic cross-sectional view of a spliced ​​fastener in one embodiment;

[0038] Figure 6 is a schematic diagram of the inner surface of a split fastener in one embodiment;

[0039] Figure 7 Schematic diagram of the core shape in another embodiment

[0040] Figure 8 is a schematic diagram of the inner surface of a split fastener in another embodiment;

[0041] Figure 9 is a schematic diagram of the structure of a spliced ​​fastener in yet another embodiment;

[0042] Figure 10is a cross-sectional schematic diagram of a split fastener in yet another embodiment;

[0043] Figure 11 for Figure 10 Schematic diagram of the welding process of the spliced ​​fastener A;

[0044] Figure 12 for Figure 10 Schematic diagram of the welding process of the spliced ​​fastener B;

[0045] Figure 13 is a schematic cross-sectional view of a split fastener in yet another embodiment;

[0046] Figure 14 is a schematic cross-sectional view of a split fastener in yet another embodiment;

[0047] Figure 15 3D topography and cross-sectional schematic diagram of a spliced ​​fastener in yet another embodiment;

[0048] Figure 16 A schematic diagram of welding a spliced ​​fastener in yet another embodiment;

[0049] Figure 17 is a graph showing the relationship between welding current, electrode pressure and time in one embodiment;

[0050] Figure 18 Schematic diagram of the preheating stage and the puncture stage of the welding process in one embodiment;

[0051] Figure 19 Schematic diagram of the nucleation stage and the end of welding during the welding process in one embodiment;

[0052] Figure 20 This is an optical microscope image of the outer surface of the spliced ​​fastener in Example 1;

[0053] Figure 21 This is an optical microscope image of the inner surface of the spliced ​​fastener in Example 1;

[0054] Figure 22 This is an optical microscope image of the outer surface of the split fastener in Example 1 after being welded to a dissimilar alloy;

[0055] Figure 23 This is an optical microscope image of the weld cross-section of the split fastener in Example 1 after welding to a dissimilar alloy.

[0056] Comparison table of numbers and names in the attached drawings:

[0057]

[0058] DETAILED DESCRIPTION

[0059] The following detailed description of the device of the present invention is provided through specific embodiments and in conjunction with the accompanying drawings. It should be understood that the dimensions mentioned herein are not limited by the dimensions or proportions of the schematic diagrams, and that descriptions of the positions of the split fasteners, such as the terms "upper," "lower," "left," "right," and "outer," are merely intended to illustrate the relative positional relationships of the various regions in relation to the placement of the split fasteners in the accompanying drawings. Descriptive terms such as "first..." and "second..." are merely used to distinguish one region (or object) from another, and do not necessarily require or imply any actual progressive or ordered relationship between these regions (or objects).

[0060] like Figure 1 and Figure 2 As shown, the cap 100 in this embodiment is an open, hollow, bowl-shaped structure. Its open end forms the cap lower end surface 101, and the side surface is a circular cylinder with a maximum diameter of Φ2. The cap side surface 102 extends upward and smoothly transitions to the cap upper end surface 104 through an arc-shaped area 103.

[0061] Three positioning grooves 105 are recessed inward from the outer surface of the cap's curved region 103. These grooves are arranged at equal angles of 120° from the center point. Each groove has a longitudinal sidewall 106. On the inner upper surface of the cap, the longitudinal sidewalls 106 of the three grooves are evenly spaced along a circle with a diameter of Φ1.

[0062] like Figure 3 As shown in the figure, Figure 1 Schematic diagram of the cross section of the middle cap. The cap is made of thin blanks of equal thickness and is formed through stamping processes such as drawing and bending. In order to achieve efficient forming of the cap, the wall thickness of the cap is controlled to be evenly distributed, so that the range of the wall thickness T of the cap is controlled between 0.85T and T, thereby ensuring the consistency and stability of the performance of various parts of the cap. On the other hand, thanks to the fact that the stamping process does not involve a significant thickening process of the blank, the processing complexity of the cap is reduced. The axial height H1 of the longitudinal side wall 106 on the positioning ladder groove 105 is preferably in the range of 0.8 to 1.2 mm. In addition, the specific size of H1 can be flexibly adjusted according to the outermost height H2 of the core flange. In order to achieve the longitudinal side wall 106 firmly fixing the core through the bulging structure, and at the same time avoid the waste of space caused by the excessive size of the positioning ladder groove 105, H1 and H2 need to satisfy the following relationship: H2

[0063] Figure 4 ​The cross-sectional structure of the core is shown, which is mainly composed of a shaft portion 201 and a flange portion 202. The bottom surface 203 of the core is preferably designed as a circular plane with a diameter of Φ3, and the side wall 204 of the shaft portion adopts an arc profile to achieve a smooth transition connection between the bottom surface of the core and the upper flange portion 202. The design of the shaft height H3 needs to be strictly controlled. If the size is too high, the shaft portion will easily pierce the first alloy layer and contact the surface of the second alloy during welding, causing significant roughening deformation. Therefore, the shaft height H3 needs to be customized according to the thickness of the first alloy to be welded, generally not exceeding 1.5 times the thickness of the first alloy, and the ideal value range is 0.8 to 0.9 times the thickness of the first alloy. At the same time, the diameter Φ3 of the bottom surface of the shaft and the diameter Φ4 of the upper end of the shaft satisfy the dimensional relationship of 1.4×Φ3≤Φ4≤2×Φ3.

[0064] The flange portion 202 is formed by extending outward from the upper end of the shaft portion. In order to optimize the extrusion molding effect, the bottom surface 205 of the flange portion is at an angle α to the horizontal plane. In a preferred embodiment, the angle α is controlled in the range of 20° to 45°. The recommended value of the side wall height H2 of the flange portion is 0.4 to 0.7 mm, and it needs to be designed in coordination with the height H1 of the cap positioning ladder groove, and the two satisfy the matching relationship of H2

[0065] like Figure 5 As shown in Figure A, the core is precisely installed in the center of the cap, with the top surface 208 of the core fitting tightly against the upper end surface 104 of the cap, and the bottom surface 203 of the core flush with the lower end surface 101 of the cap. Thus, an annular accommodating cavity with an initial volume of V is formed between the cap side 102, the arc-shaped area 103 and the core side. Figure 5 As shown in B, the cap positioning ladder groove 105 is extruded and recessed through a supplementary molding process to form a bulging structure 107. After the structure is formed, on the one hand, the longitudinal side wall 106 is driven to move toward the outer side wall 206 of the flange portion, generating pressure F1 acting on the flange portion; on the other hand, an outward convex area 108 is generated on the side of the bulging structure 107, covering the flange portion from below and achieving a firm riveting to the core portion. In the process of supplementary extrusion and recessing, the local minimum wall thickness Tb of the bulging structure is strictly controlled to ensure that it is greater than 0.25Tm (Tm is the maximum wall thickness of the cap). This design not only ensures the firm anchoring of the bulging structure to the core portion, but also effectively avoids the risk of cracking during welding. Also refer to Figure 5 ​In middle B, the transverse width L of the convex area 108 formed by the bulging structure 107 is less than 1 mm, and the recommended value range is 0.2 to 0.5 mm. This size design can make the anchoring effect of the bulging structure on the core invalid during the welding process, thereby ensuring stable deformation of the cap.

[0066] like Figure 6 As shown, three bulging structures 107 are respectively arranged on three positioning ladder grooves 105, and through three-way symmetrical distribution, a stable mechanical riveting constraint is formed on the core. According to different processing characteristics, the cross-sectional shape of the bulging structure 107 can be flexibly designed into geometric shapes such as circular, square or prismatic, or can be uniformly extruded using a ring mold. In order to ensure the precise assembly of the core and the positioning ladder groove, the maximum diameter of the core flange is Φ5 (see Figure 4 ) must be smaller than the diameter Φ1 enclosed by the longitudinal sidewall 106 of the positioning ladder groove (see Figure 2 ), the size difference between the two is strictly controlled within the tolerance range of 0.04 to 0.15 mm.

[0067] Figure 7 Another design scheme of the core of the spliced ​​fastener is shown. This scheme adds three convex tooth structures 209 on the side wall 206 of the flange portion, and processes a number of ratchet grooves 210 in the flange portion area. Figure 8 As shown in A, when the core 200 is assembled, the protruding tooth structure 209 avoids the positioning ladder groove 105 and is embedded in the cap along a specific angle. Figure 8 As shown in Figure B, by applying rotational torque to the ratchet groove 210, the protruding tooth structure 209 is precisely rotated to engage with the longitudinal sidewall 106 of the positioning ladder groove, forming a reliable mechanical interlocking connection. In addition, the re-molding and bulging structure (not shown) on the positioning ladder groove 105 can further enhance the mechanical locking performance of the core and the cap, achieving a double fastening effect.

[0068] like Figure 9 As shown in Figure A, in another embodiment of the spliced ​​fastener design, the positioning ladder groove 105 adopts an annular integrated structure, and a continuous surrounding longitudinal side wall 106 is formed by a molding process that is integrally recessed from the outer surface of the cap, thereby achieving 360° circumferential positioning of the flange portion 202 of the core. Figure 9 As shown in Figure B, the core is firmly anchored in the cap, relying on the bulging structure 107 and the convex area 108 formed by the supplementary extrusion and concave process on the positioning ladder groove 105. Due to the annular nature of the positioning ladder groove 105, the arcuate area 103 of the cap naturally becomes the transition area between the side wall 102 and the positioning ladder groove 105. In order to facilitate the formation of the positioning ladder groove 105, a rounded chamfer 109 can be provided between the upper end surface 104 of the cap and the longitudinal side wall 106, as shown in FIG. Figure 10 As shown in A.

[0069] During the welding process, as the core penetrates the first alloy material, the upper end surface 104 of the cap moves downward toward the plane where the lower end surface 101 of the cap is located, causing the arc-shaped area 103 to undergo bending plastic deformation (see Figure 11 By precisely adjusting the height dimension H4 from the lower end face 101 of the cap to the positioning ladder groove 105, and the height dimension H5 from the positioning ladder groove 105 to the upper end face 104 of the cap (such as Figure 10 As shown in A in the figure, it can effectively control the height of the cap protruding from the first alloy surface after welding, and at the same time adjust the volume of the cap to accommodate the discharged metal. In application scenarios with special requirements for the protruding height of the cap (such as Figure 10 (As shown in B in the figure), the height dimension H4 can be reduced from 4 mm to 3 mm (H4→H4'), and H5 can be increased from 1 mm to 2.5 mm (H5→H5') to meet the needs of specific working conditions.

[0070] In addition, in order to enhance the axial support performance of the thin-walled cap, prevent the cap side from excessive collapse and deformation, and avoid the cap lower end surface from damaging the first alloy material, a flange structure 101' ( Figure 10 The transverse width Lf of the flange structure is related to the maximum wall thickness Tm of the cap: 3×Tm≤Lf≤6×Tm. Through the above design, the structural strength and compactness are improved at the same time.

[0071] In special application scenarios involving the welding of thick cast aluminum alloys and cast magnesium alloys, for example, when the first alloy is a 4.5 mm thick cast magnesium alloy and the second alloy is a 2.0 mm thick hot-formed steel, due to the high expansion coefficient and large thickness of the cast magnesium alloy, a large amount of discharged metal will be generated during the welding process, thus placing higher requirements on the volume of the cap receiving cavity. For such working conditions, please refer to Figure 10 In the design scheme shown in A and B, the height dimension H4 is kept unchanged (i.e., H4=H4'=5 mm), while H5 is increased to H5'=2.5 mm (original H5 is 1 mm). Accordingly, the height of the outer side wall 206 of the core flange portion also needs to be increased synchronously to adapt to the structural changes. Figure 11 and Figure 12 The comparison of welding effects of the above-mentioned spliced ​​fastener specifications is presented intuitively. Figure 11 In the conventional design shown, when the height of the outer sidewall of the flange is relatively low (e.g., 0.8 mm), under the extrusion of the upper and lower welding electrodes 500, 600, the core shaft completely penetrates the first alloy 300, and the core top surface 208 approaches or even falls below the upper surface of the first alloy. This phenomenon causes the upper end surface 104 of the cap to deform downward under the action of welding pressure, driving the arc-shaped area 103 and the positioning ladder groove 105 to undergo plastic bending, ultimately reducing the volume V0 of the cap housing cavity. Figure 11 As shown in A2, there is a height difference H6 between the center area of ​​the weld and the highest point of the spliced ​​fastener after welding.

[0072] In contrast, Figure 12 The welding effect after the optimized design is demonstrated. When the height of the outer side wall of the flange is increased to 2.5 mm, the shaft of the core is also completely penetrated into the first alloy 300 during the welding process, but sufficient space is retained between the top surface 208 of the core and the upper surface of the first alloy, effectively limiting the downward deformation of the upper end surface of the cap. Figure 12 As can be seen from B2, the height difference H6' between the center area of ​​the weld and the highest point of the spliced ​​fastener is significantly reduced. At the same time, the deformation degree of the arc area of ​​the cap and the positioning ladder groove is greatly reduced, so that the volume V0' of the accommodating cavity formed by the cap after welding is significantly increased compared with V0, thereby achieving comprehensive storage of the discharged metal 302.

[0073] like Figure 13 As shown, when the upper end of the cap side 102 bends and extends toward the cap upper end surface 104, the arc section 103 forms a unique back-bend structure. This structure makes part of the arc section protrude outward from the cap upper end surface, thereby making the cap upper end surface appear inwardly concave. According to actual application requirements, the outer contour of the arc section 103 can also be optimized to a smoother curve. The specific shape can be referred to Figure 14 At the same time, the diameter Φ6 of the upper end surface 104 of the cap is adapted and designed to be slightly smaller than the end surface diameter of the welding electrode, so as to ensure that the welding electrode can accurately and stably contact the upper end surface of the cap.

[0074] In terms of the core structure, the shaft sidewall 204 can be flexibly adjusted to a configuration vertical or inclined to the horizontal plane according to different working conditions. In order to achieve a stable assembly with the cap, the flange 202 is specially enlarged in outer diameter so that it can directly abut the side of the cap, and a bulging structure 107 is provided on the cap side 102 to achieve mechanical clamping and fixing (see Figure 13 、 Figure 14 ). In addition, the bulging structure 107 can also be designed as Figure 15 The longitudinal bulging structure 110 shown in Figure A is distributed along the longitudinal side wall 106 and also enhances the lateral support performance of the cap side wall during the welding process.

[0075] It is worth noting that since the flange part directly abuts against the side of the cap, the cap receiving chamber is divided into two parts, the upper and lower parts, whose volumes are V1 and V2 respectively. In order to realize the connection between the upper and lower cavities, a connecting notch structure 211 is specially provided on the flange part 202 (see Figure 15 During welding, when the core shaft 201 penetrates the first alloy, the flange 202 is pressed down to fit the surface of the first alloy. At this time, the discharged metal 302 generated by the weld will flow smoothly into the cap receiving cavity through the connecting notch structure 211. The specific flow pattern can be referred to Figure 16 .

[0076] Figure 17 The figure shows the relationship between welding current and electrode pressure over time in one embodiment. Throughout the welding process, the welding electrode maintains a constant pressure output, while the welding current is sequentially divided into three key stages: preheating, penetration, and nucleation. These stages correspond to inputs for preheating current I1, penetration current I2, and nucleation current I3, respectively. To precisely control the heat input at each stage, a cooling window of 10 to 30 milliseconds is set between adjacent stages. This design effectively promotes uniform resistance heat dissipation, ensuring that the heat input parameters meet optimal process requirements.

[0077] like Figure 18 As shown in Figure A, during the preheating phase, a preheating current I1 is applied. Combined with the electrode pressure, the upper welding electrode 500 exerts a moderate pressure on the upper end face of the cap and the top surface of the core, ensuring a close fit between them and significantly reducing contact resistance. Simultaneously, the lower end face 101 of the cap and the bottom surface 203 of the core also form close contact with the surface of the first alloy 300, thereby establishing an annular, sealed containment structure around the core, creating a stable physical environment for the subsequent welding process.

[0078] During the puncture phase, Figure 17 The welding parameters shown are set to input piercing current I2 to the welding spot in batches. The duration of each piercing current pulse ΔT a Strictly controlled within the range of 50 to 65 milliseconds. With the high heat released instantly by the current, the first alloy (due to its low melting point) quickly forms a molten zone 301 at the weld point. Under the synergistic effect of the welding electrode pressure, the molten first alloy is pressed into the cap of the spliced ​​fastener in the form of a high-speed spray. Thanks to the pre-constructed sealed containment cavity structure of the cap, these discharged metals 302 can be efficiently collected and stored, such as Figure 18 As shown in B.

[0079] Further integration Figure 18 Analysis of the structural changes in B shows that when the welding electrode drive shaft 201 penetrates the first alloy, the upper end face of the cap is displaced downward by the electrode pressure, causing the arc area to undergo plastic bending deformation along the direction 701. At the same time, in the peripheral area of ​​the upper end face of the cap that is not in direct contact with the upper welding electrode 500, reverse bending occurs along the direction 703. This double deformation effect causes the longitudinal side wall 106 of the positioning ladder groove to undergo plastic deformation in the direction 702, thereby releasing the mechanical constraint of the bulging structure on the flange part 202, creating conditions for the core to smoothly penetrate the first alloy. At the end of this stage, the core has completely penetrated the first alloy layer, forming a close contact interface with the second alloy, and the remaining first alloy on the contact surface is maintained at only a trace level, creating conditions for nucleation in the next stage.

[0080] During the nucleation stage, Figure 10As shown in Figure 1, a stable welding nugget is constructed by inputting the nucleation current I3. The duration of the nucleation current ΔT b The current maintenance time ΔT during the puncture phase a There is a relationship: 2×ΔT a ≤ΔT b ≤4×ΔT a At the same time, the nucleation current I3 is greater than the puncture current I2, and there is a current difference ΔI of 1 to 6 kiloamperes between the two.

[0081] like Figure 19 As shown in center C, under the action of the nucleation current, the metal at the interface between the shaft and the second alloy rapidly melts, forming a critical nugget 401, laying the foundation for a secure connection between the dissimilar materials. During this stage, the resistive heating effect continues to intensify, further expanding the molten zone 301 of the first alloy surrounding the core. A large amount of molten discharged metal 302 is squeezed into the sealed containment cavity formed by the cap, with some metal also filling the gap 303 between the upper end surface of the cap and the top surface of the core.

[0082] After welding is completed, Figure 19 As shown in center D, the melt zone 301 solidifies synchronously with the discharged metal within the cap, forming an integrated structure that achieves both mechanical and metallurgical bonding with the core of the split fastener, thus completing a reliable connection between the first and second alloys. Within the weld electrode contact area (a circular area with a diameter of Φ7), a metallurgical reaction occurs within the internal contact region 402 between the cap's upper end surface and the core's top surface due to resistive heating, forming an atomic-level bond and ultimately achieving a permanent connection between the cap and the core.

[0083] Example 1:

[0084] In this embodiment, the structure of the spliced ​​fastener is as follows Figure 20 and 21 As shown. The cap is made of 0.3 mm thick DC06 steel, and the core is made of dual-phase steel DP590. The core is positioned and installed through the positioning ladder groove 105 on the cap, and the bulging structure 107 is formed on the positioning ladder groove by extrusion and concave process, so as to firmly rivet the flange part 202 (see Figure 21 During welding, the first alloy material 300 is a 4.3 mm thick cast magnesium alloy, and the second alloy material 400 is a 2.0 mm thick ultra-high strength hot-formed steel. The welding process uses Figure 17 The specifications shown are: in the preheating stage, a preheating current of 4kA with a duration of 150 milliseconds is input; in the puncture stage, a puncture current of 16kA with a duration of 53 milliseconds each is input three times; in the nucleation stage, a nucleation current of 17.5kA with a duration of 160 milliseconds is input.

[0085] After welding, the surface morphology of the fastener is as follows Figure 22 As shown, there is no crack defect on the surface and the quality is good. Figure 23 The cross-sectional morphology of the weld joint shown shows that the fastener core successfully pierces the first alloy layer 300 and forms a weld nugget 401 with the second alloy 400, achieving a reliable connection. Simultaneously, the positioning ladder groove 105 on the cap is smoothly separated from the flange portion 208, effectively expanding the volume of the cap's accommodating cavity. The cap completely accommodates the discharged metal 302 generated during the welding process, and the discharged metal fully fills the gap area 303 between the cap's upper end surface and the core's top surface. Furthermore, the cap's upper end surface 104 forms a metallurgical connection with the internal contact area 402 of the core's top surface 208, ensuring a secure bond between the two.

[0086] It should be understood that the purpose of the above-described embodiments is merely to illustrate the technical concepts of the present invention to facilitate understanding by those skilled in the art, and is not intended to limit the scope of protection of the present invention. Within the scope of the claims of the present invention, any improvement or equivalent replacement of the parts, structures, or method steps involved in the above-described embodiments, especially any combination of different embodiments without causing any structural or theoretical conflicts, falls within the scope of protection of the present invention.

Claims

1. A spliced ​​fastener for welding dissimilar alloys, used for resistance spot welding a laminated component of a first alloy and a second alloy, wherein the first alloy is a light metal, characterized in that: include: A bowl-shaped thin-walled cap (100) has a hollow structure with a single-side opening, wherein the open end forms the cap lower end surface (101), and the side circumference (102) transitions to the upper end surface through an arc-shaped area (103); A solid core (200) is coaxially arranged in the central area of ​​the cap (100), and comprises a shaft (201) and a flange (202) extending outward from the upper end of the shaft; Wherein, the bottom surface (203) of the core (200) is coplanar with the lower end surface (101) of the cap (100) or is retracted into the plane where the lower end surface (101) is located; The wall thickness T of the cap (100) ranges from 0.85Tm to Tm, where Tm is the maximum wall thickness of the cap; the cap (100) is provided with a plurality of bulging structures (107) distributed at equal angles in the circumferential direction, the bulging structures forming convex regions (108) by performing plastic deformation by stamping on local regions of the cap, and the local convex regions of the bulging structures are squeezed onto the core to produce a mechanical anchoring effect; The bulging structure separates from the core during the welding process, so that the mechanical anchoring function of the bulging structure on the core is completely lost.

2. The split fastener according to claim 1, wherein: The maximum wall thickness Tm of the cap is in the range of 0.2 mm to 0.5 mm.

3. The split fastener according to claim 1, wherein: The bulging structure is a supplementary extrusion and concave forming of a local area of ​​the cap after the cap and the core are spliced ​​together. The minimum wall thickness Tb of the local area of ​​the bulging structure is greater than 0.25Tm, where Tm is the maximum wall thickness of the cap.

4. The split fastener according to claim 1, wherein: The cap is provided with a positioning ladder groove (105) which is recessed inward from the outer surface and distributed in a circumferential annular pattern. Its longitudinal side wall (106) is clearance-matched with the outer side wall (206) of the flange portion (202) to accurately define the installation position of the core portion.

5. The split fastener according to claim 1 or 4, characterized in that: The bulging structure is arranged in the positioning ladder groove area, so that the longitudinal side wall (106) of the positioning ladder groove is locally deformed to form an outward convex area to mechanically anchor the core.

6. The split fastener according to claim 1, wherein: The lower end surface of the cap is provided with a flange structure extending radially outward, and the transverse width Lf of the flange structure and the maximum wall thickness Tm of the cap satisfy: 3×Tm≤Lf≤6×Tm.

7. The split fastener according to claim 1, wherein: The cap includes a cap side and an arc-shaped area; the arc-shaped area extends in an arc from the upper end of the cap side to the upper end surface of the cap, and forms a bend structure when expanding radially inward, so that a local area of ​​the arc-shaped area is higher than the upper end surface of the cap, thereby forming an inwardly concave contour on the upper end surface of the cap.

8. The split fastener according to claim 9, wherein: The upper end surface of the cap has an inwardly concave profile and is only partially in contact with the top surface (208) of the core.

9. The split fastener according to claim 4 or 7, characterized in that: The outer side wall H2 of the flange portion and the height H1 of the positioning ladder groove satisfy: H2<H1≤3×H2.

10. The split fastener according to claim 1, wherein: After the spliced ​​fastener is welded, at least a portion of the contact interface between the upper end surface of the cap and the top surface of the core is firmly connected through a metallurgical bonding process.

11. The split fastener according to any one of claims 1 to 10, characterized in that: After the core and the cap are assembled, the bulging structure produces a mechanical anchoring effect on the outer edge of the flange of the cap, and the upper surface of the core fits tightly with the upper end surface of the cap, with a gap between the two not exceeding 0.1 mm.

12. The split fastener according to claim 11, wherein: The arc-shaped area (103) forms a bent structure, with its highest point protruding from the upper end surface (104) of the cap by 0.3-1.0 mm; The side wall (204) of the core shaft portion (201) is an arc transition surface, connecting the core bottom surface (203) and the flange portion (202).

13. A method for welding dissimilar metals, comprising resistance welding a first alloy having a melting point not exceeding 700°C and a second alloy having a melting point greater than 1300°C, using the split fastener according to any one of claims 1 to 12, wherein: Welding is performed from the first alloy side. During the welding process, the core of the split fastener pierces the first alloy layer and forms a molten core with the second alloy layer to achieve connection. The cap of the split fastener stays on the surface of the first alloy layer to form a sealed cap-like structure to accommodate the first alloy extruded from the weld point.

14. The welding method according to claim 13, characterized in that: During welding, electrode pressure and preheating current I1 are applied to the spliced ​​fastener and the first and second alloys, so that the upper end surface of the cap squeezed by the welding electrode is in close contact with the top surface of the core, and the lower end surface of the cap and the bottom surface of the core are in close contact with the surface of the first alloy.

15. The welding method according to claim 13, characterized in that: It also includes a puncture stage and a nucleation stage. In the puncture stage, several puncture currents I2 are applied, and the maintenance time of each puncture current is ΔT. a In the range of 50 milliseconds to 65 milliseconds, a nucleation current I3 is applied during the nucleation phase, wherein the nucleation current is maintained for a time ΔT b and ΔT a There is a relationship: 2×ΔT a ≤ΔT b ≤4×ΔT a , and the current difference ΔI of the nucleation current I3 minus the puncture current I2 ranges from 1 kiloampere to 6 kiloamperes.

16. The welding method according to claim 15, characterized in that The resistance heat generated during the piercing stage causes a portion of the first alloy in the weld to melt and be discharged into the cap of the split fastener, causing the mechanical anchoring effect between the bulging structure of the split fastener and the core to fail, causing the core to penetrate the first alloy layer and contact the second alloy layer.

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