Resistance spot welding of dissimilar metal fasteners

Abstract

The present invention provides a fastener for resistance spot welding dissimilar metals. The fastener includes a shaft, a top cover, and a cap. The cap extends from the outer periphery of the top cover to the plane where the end of the shaft is located, sequentially forming a transition zone, an arc zone, and a straight wall zone. The straight wall zone vertically supports the cap during the welding process, forcing the cap deformation to concentrate in the arc zone, while preventing the cap from collapsing after welding and reducing the volume of the accommodating cavity. After welding, the straight wall zone is almost vertically squeezed onto the surface of the first workpiece, providing additional mechanical locking force for the weld joint. The wall thickness of the transition zone gradually decreases from the thickness of the outer periphery of the top cover to the wall thickness of the arc zone, avoiding stress concentration and cracking in the transition zone during manufacturing and welding, and ensuring that the plastic deformation of the cap is concentrated in the arc zone. Utilizing the fastener provided by the present invention, high-strength welding of dissimilar metals can be achieved.

Description

Technical Field

[0001] The invention belongs to the field of welding dissimilar metals, and in particular relates to a fastener for welding dissimilar metals by resistance spot welding. Background Art

[0002] In the automotive industry, the use of a variety of metal materials to manufacture the body is more conducive to achieving the goals of body safety performance and body lightweight at the same time. Among them, steel and aluminum alloys are widely used in body manufacturing, especially in the current popular new energy vehicle manufacturing, where a large number of large-scale integrated die-cast aluminum alloys are widely used to reduce the number and weight of body parts. In addition, in the body frame and key parts, multi-material advanced high-strength steel or even ultra-high-strength steel is used to ensure the safety performance of the body. For example, hot-formed steel with a strength of 1500MPa or even higher is used in parts such as A / B pillars and longitudinal beams. Therefore, reliable welding of dissimilar metals (such as aluminum / steel, magnesium / steel, etc.) is conducive to promoting the development of lightweight automobiles, and dissimilar metal welding technology has a wide range of application needs in the automotive field. However, when traditional welding processes connect dissimilar metals, they are easily affected by brittle intermetallic compounds and cracks, resulting in extremely poor mechanical properties of the weld. Therefore, current traditional welding processes cannot weld dissimilar metals with high quality.

[0003] To achieve efficient and reliable welding of dissimilar metals, patent document CN114211104B discloses a dissimilar metal joint and a resistance spot welding method thereof. This method induces low-melting-point metal to be ejected from the weld spot at high speed in the form of spatter, and then welds the steel plates on both sides, achieving a high-quality dissimilar metal connection. However, the spatter metal ejected at high speed from the weld spot can cause contamination of the weld spot surface and surrounding components. In addition, this method has difficulty achieving a good weld spot formation effect when welding thicker low-melting-point metals. Patent document CN115570251A discloses a dissimilar metal welding rivet that achieves dissimilar metal welding while effectively absorbing spatter metal ejected from the weld spot. However, the rivet does not have a carefully designed shape, structure, and size of the shaft and cap. During the welding process, the cap cannot adapt to the position change of the shaft and produce adaptive deformation. That is, after the edge (end) of the cap contacts the metal workpiece to be welded, the cap cannot undergo good plastic deformation, resulting in the central shaft being difficult to sink relative to the cap and pierce the low-melting-point metal to be welded at high speed. This is not conducive to welding low-melting-point metals with large thickness (for example, low-melting-point metals greater than 2.5mm). Since the shaft cannot effectively pierce the low-melting-point metal, the high-melting-point metal needs to produce a more significant concave deformation, resulting in a significant depth of electrode indentation at the weld, which increases the risk of cracks in the weld. In addition, the structure of the cap is bloated, and the cross-sectional wall thickness of the cap is large. When the cap forms the same accommodating cavity volume, a larger rivet needs to be designed, which results in increased weight of the joint and reduced flexibility in the joint structure design.

[0004] Patent document CN116810111A discloses a welding element for resistance spot welding of dissimilar metals. This element features a top cover structure around the shaft to contain metal spatter. Furthermore, one or more recessed auxiliary deformation zones are located at the junction of the cap and top cover. This allows the cap to deform preferentially in the auxiliary deformation zones during welding, improving the cap's plastic deformation capability. However, since the cap is thin-walled, further thinning the auxiliary deformation zones increases manufacturing complexity and costs. Furthermore, in complex welding environments, the auxiliary deformation zones present a risk of excessive plastic deformation, leading to cracking. This is particularly true when the welding electrode and the centerline of the welding element cannot be accurately aligned. Once cracks occur in the auxiliary deformation zones, metal spatter is expelled from the cracks, affecting the weld's quality and surface quality. Furthermore, the expelled metal spatter can contaminate the electrode surface, reducing the electrode's service life. Furthermore, the auxiliary deformation zones are susceptible to tensile deformation, while other areas deform less, resulting in a more pronounced protrusion of the cap from the workpiece surface after welding. Therefore, there is an urgent need in this field for a more reasonable structural design to ensure efficient collection of splash metal (metal discharge) and high-strength welding of dissimilar metals, while also ensuring that the height of the fastener protruding from the workpiece surface after welding is smaller. Summary of the Invention

[0005] The purpose of the present invention is to provide a fastener for resistance spot welding dissimilar metals, improve the welding quality of dissimilar metal resistance spot welding, improve the deformation ability of the fastener cap structure during the welding process, ensure that the fastener cap structure maintains the cavity structure during the welding process, improve the weld spot forming and realize low-cost and high-efficiency manufacturing of the fastener.

[0006] A fastener for resistance spot welding dissimilar metals, the fastener being used to resistance spot weld a first metal and a second metal laminate, the first metal having a lower melting point than the second metal, the melting point of the fastener metal being the same as or similar to the second metal, the fastener comprising a top cover, a shaft extending from the center of the top cover, and a cap disposed around the periphery of the top cover, the cap, the side edges of the shaft, and the horizontal plane containing the ends of the shaft forming a receiving cavity, the receiving cavity being used to collect the first metal extruded or ejected from the weld, and characterized in that:

[0007] The side wall of the shaft portion gradually expands as it extends from the end of the shaft portion toward the outer periphery of the top cover, which facilitates the shaft portion to penetrate the first metal at high speed and discharge the molten first metal from the weld point during welding, and provides the main mechanical locking force for the fastener to the first metal;

[0008] The cap extends from the outer periphery of the top cover to the horizontal plane where the end of the shaft portion is located, and sequentially forms a transition area, an arc area and a straight wall area; wherein,

[0009] The arc-shaped area has good plastic deformation ability and can adapt to the position of the shaft during welding to produce adaptive deformation, thereby preventing the cap from hindering the shaft from piercing the first metal;

[0010] The straight wall area supports the cap vertically during the welding process, forcing the cap to deform in the arc area, while preventing the cap from collapsing after welding and reducing the volume of the accommodating cavity;

[0011] After welding, the straight wall area is almost vertically pressed against the surface of the first workpiece, providing additional mechanical locking force for the weld joint;

[0012] The wall thickness of the transition zone gradually decreases from the thickness of the outer peripheral side of the top cover to the wall thickness of the arc zone, avoiding stress concentration and cracking in the transition zone during manufacturing and welding, and ensuring that the plastic deformation of the cap is concentrated in the arc zone.

[0013] Furthermore, the wall thickness of the arc area gradually decreases as it extends from the top cover side to the straight wall area, so that plastic deformation of the arc area occurs on the side close to the straight wall area during welding, thereby controlling the height of the cap protruding from the first metal surface after welding.

[0014] Furthermore, the wall thickness of the straight wall area gradually increases from one end close to the arc-shaped area to the other end in contact with the first metal, and the increase does not exceed 65%.

[0015] Furthermore, the wall thickness of the arc-shaped area gradually decreases when extending from the top cover side to the straight wall area, and the reduction does not exceed -50%.

[0016] Furthermore, the minimum height H2 of the shaft protruding from the top cover satisfies H2=K1×T, wherein T is the first metal thickness, K1 is a coefficient considering the first metal thickness, and the value range is K1=0.6~1.2.

[0017] The thickness H at the center of the fastener satisfies H=1.2×H2~2×H2,

[0018] The minimum horizontal width from the outer periphery of the top cover to the side wall of the shaft portion is L, and the minimum horizontal distance from the outer periphery of the top cover to the straight wall area is L1, where L1 is greater than 1.5×L.

[0019] The horizontal width L2 of the transition zone is less than 0.5×L1,

[0020] A line passing through the connection point of the arc-shaped area and the straight-wall area and being tangent to the arc-shaped area forms an angle δ with the straight-wall area, and the range of the angle δ is 0° to 40°.

[0021] The straight wall area is distributed around the axis of the fastener and forms an angle β with the center axis of the fastener, and β=0°~5°, and the height of the straight wall area H1<H,

[0022] The included angle Ω between the inner wall of the top cover and the horizontal plane satisfies Ω=10°~50°.

[0023] Furthermore, the angle γ between the side wall of the shaft portion and the horizontal plane ranges from 45° to 80°, and γ>Ω.

[0024] Furthermore, an angle α is formed between a line connecting one end of the cap close to the outer periphery of the top cover and one end of the arc-shaped area close to the straight wall area and a horizontal plane, and α=15° to 65°.

[0025] Furthermore, the height H1 of the straight wall area is smaller than the height H2.

[0026] Furthermore, the connection area between the arc-shaped area and the straight-wall area is in a tangent relationship.

[0027] Furthermore, the arc-shaped area is composed of an arc, and the arc radius ranges from 0.6 mm to 4 mm.

[0028] Preferably, the horizontal width of the transition zone Where L1 is the minimum horizontal distance from the outer periphery of the top cover to the straight wall area.

[0029] Furthermore, the wall thickness of the arc area and the straight wall area is 0.25mm to 0.6mm; the horizontal width L from the outer periphery of the top cover to the side wall of the shaft portion is 0.3mm to 1.6mm; the minimum horizontal distance L1 from the outer periphery of the top cover to the straight wall area ranges from 1.2mm to 3.2mm; and the end diameter D of the shaft portion ranges from 3mm to 6mm.

[0030] Preferably, when the thickness of the first metal is less than 1.5 mm, the value range of the coefficient K1 is 0.6 to 0.8; when the thickness of the first metal is greater than or equal to 1.5 mm and less than 2.5 mm, the value range of the coefficient K1 is 0.7 to 1.0; when the thickness of the first metal is greater than or equal to 2.5 mm, the value range of the coefficient K1 is 0.8 to 1.2.

[0031] Preferably, the angle β ranges from 2° to 4°.

[0032] Preferably, the angle Ω ranges from 25° to 40°.

[0033] Furthermore, the intersection of the outer periphery of the top cover and the inner wall of the top cover is connected by an arc R1, and the radius of the arc R1 is greater than 0.3mm. Preferably, the inner surface of the arc area and the top cover are connected by an arc R2, wherein the arc R2 is tangent to the inner surface of the arc area and the arc R1 respectively, and the radius of the arc R2 is greater than 0.5mm.

[0034] Furthermore, the melting point of the first metal is lower than 750°C, and the melting point of the second metal is higher than 1300°C.

[0035] Beneficial effects of the present invention:

[0036] (1) The side wall of the shaft gradually expands as it extends from the end of the shaft to the outer periphery of the top cover, which is beneficial for the shaft to penetrate the first metal at high speed and discharge the molten first metal from the weld point during welding, and provides the main mechanical locking force for the fastener to the first metal; the arc area has good plastic deformation ability, and can adapt to the position of the shaft to produce adaptive deformation during the welding process, avoiding the cap from hindering the ability of the shaft to penetrate the first metal; the wall thickness of the transition area gradually decreases from the thickness of the outer periphery of the top cover to the wall thickness of the arc area, avoiding stress concentration and cracking in the transition area during the manufacturing and welding process, ensuring that the plastic deformation of the cap is concentrated in the arc area; the effect of the straight wall area on the vertical support of the cap structure during the welding process forces the cap deformation to be concentrated in the arc area, avoiding collapse deformation in this area, ensuring that the cap structure maintains the cavity structure after welding, and at the same time, the straight wall area is almost vertically squeezed to the surface of the first workpiece after welding, providing additional mechanical locking force effect.

[0037] (2) According to a preferred embodiment of the present invention, the straight wall area provides vertical support for the cap structure during the welding process, thereby preventing the area from collapsing and deforming, and ensuring that the cap structure maintains the cavity structure after welding. At the same time, the straight wall area is almost vertically squeezed onto the surface of the first workpiece after welding, providing an additional mechanical locking force effect.

[0038] (3) According to a preferred embodiment of the present invention, the thickness of the straight wall area gradually increases as it extends from the arc area to the end, forming a trend in which the wall thickness first decreases and then increases. On the one hand, this is beneficial to controlling the plastic flow of the material of the cap and the bending forming of the cap during the manufacturing process, thereby reducing the difficulty of stamping manufacturing of the fastener; on the other hand, the wall thickness of the straight wall area gradually increases toward the end, thereby improving the vertical support effect of the straight wall area during the welding process and preventing it from being crushed.

[0039] (4) According to a preferred embodiment of the present invention, the angle Ω between the inner wall of the top cover of the fastener and the horizontal plane satisfies Ω=10°~50°, and the inner wall 1061 of the top cover extends upward from one side of the shaft portion toward the outer periphery of the top cover, which improves the compatibility of the fastener with welding first metals of different thicknesses.

[0040] (5) According to a preferred embodiment of the present invention, the fastener of the present invention has a simple structure and a more compact size, which ensures that it can efficiently collect spatter metal (discharge metal) and achieve high-strength welding of dissimilar metals, while also ensuring that the height of the fastener protruding from the workpiece surface and the diameter of the weld spot after welding are smaller. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is a schematic cross-sectional view of a fastener according to the present disclosure;

[0042] Figure 2is a schematic cross-sectional view of a transition region of a fastener according to the present disclosure;

[0043] Figure 3 Schematic diagram of the connection between the fastener transition area and the top cover of the present disclosure

[0044] Figure 4 It is a cross-sectional schematic diagram of the connection between the curved area and the straight wall area of ​​the fastener of the present disclosure;

[0045] Figure 5 A schematic cross-sectional view of a cap of a fastener according to an embodiment of the present disclosure;

[0046] Figure 6 FIG1 is a schematic diagram of deformation of a cap of a fastener during welding in yet another embodiment of the present disclosure;

[0047] Figure 7 FIG1 is a schematic diagram of deformation of a cap of a fastener during welding in another embodiment of the present disclosure;

[0048] Figure 8 FIG1 is a schematic diagram of deformation of a cap of a fastener during welding in yet another embodiment of the present disclosure;

[0049] Figure 9 FIG1 is a schematic diagram of deformation of a cap of a fastener during welding in yet another embodiment of the present disclosure;

[0050] Figure 10 This is a schematic diagram of deformation of a fastener when the fastener is welded to first metals of different thicknesses in yet another embodiment of the present disclosure;

[0051] Figure 11 This is a schematic diagram of the surface morphology of the arc-shaped area of ​​a fastener in yet another embodiment of the present disclosure;

[0052] Figure 12 Schematic diagram of the relationship between welding current, electrode pressure and time during resistance spot welding of dissimilar metals according to the present disclosure;

[0053] Figure 13 A schematic diagram of the pre-pressing stage of the welding electrode of the fastener of the present disclosure in welding dissimilar metals;

[0054] Figure 14 A schematic diagram of the preheating stage of the fastener of the present disclosure in welding dissimilar metals;

[0055] Figure 15 A schematic diagram of a fastener according to the present disclosure during the fastener penetration stage in welding dissimilar metals;

[0056] Figure 16 A schematic diagram of a fastener according to the present disclosure during a welding process of dissimilar metals;

[0057] Figure 17 is a schematic cross-sectional view of a fastener in Example 1 of the present disclosure;

[0058] Figure 18 is a cross-sectional metallographic image of the weld joint in Example 1 of the present disclosure;

[0059] Figure 19 Dimensional statistics of the weld joint in Example 1 of the present disclosure and the weld joint in the reference document;

[0060] Figure 20 is a schematic cross-sectional view of a fastener in Example 2 of the present disclosure;

[0061] Figure 21 is a cross-sectional metallographic image of the weld joint in Example 2 of the present disclosure;

[0062] Figure 22 Surface and cross-sectional views of the fastener in Example 3 of the present disclosure;

[0063] Figure 23 This is a diagram showing the distribution of discharged metal in the cap of the fastener after the fastener puncture stage during welding in Example 3 of the present disclosure;

[0064] Figure 24 is a cross-sectional metallographic image of the weld joint in Example 3 of the present disclosure;

[0065] Figure 25 Surface morphology and cross-sectional metallographic images of the welded joint in Example 4 of the present disclosure;

[0066] Figure 26 A metallographic image of a cross section of a fastener and a surface topography image of the joint after welding in Comparative Example 1 of the present disclosure;

[0067] Figure 27 Force-displacement curves obtained after cross tensile testing of the welded joints in Example 4 and Comparative Examples 1 and 2 of the present disclosure;

[0068] Figure 28 Fracture morphology of the welded joints in Example 4 and Comparative Examples 1 and 2 of the present disclosure after cross tensile testing;

[0069] Figure 29 A schematic diagram of the stress on the welded joint of the fastener disclosed in the present invention during a cross tensile test; DETAILED DESCRIPTION

[0070] The embodiments of the present invention are further described in detail below through specific examples with reference to the accompanying drawings.

[0071] The horizontal plane in the present invention refers to the plane where the end portion is located.

[0072] According to one aspect of the present invention, a fastener 100 for resistance spot welding of dissimilar metals is provided. Figure 1 As shown, fastener 100 has a rotationally symmetrical structure about its central axis, comprising a top cover 106, a shaft portion 102 extending from the center of top cover 106, and a cap 104 disposed around the outer periphery 1062 of the top cover. As cap 104 extends from the outer periphery 1062 of the top cover to the horizontal plane of the shaft portion's end 103, it forms a transition region 1043, an arcuate region 1041, and a straight-walled region 1042. The cross-sectional thickness of transition region 1043 gradually decreases from the thickness on the side of top cover outer periphery 1062 to the wall thickness of the arcuate region, which then curves to connect to the straight-walled region.

[0073] The minimum height H2 of the protruding top cover 106 of the shaft of the fastener 100 satisfies the relationship: H2 = K1 × T, where T is the thickness of the first metal, K1 is a coefficient considering the thickness of the first metal, and the value range of K1 is 0.6 to 1.2. For the thickness H of the center of the fastener 100, H = 1.2 × H2 to 2 × H2 is satisfied. The minimum horizontal width from the outer periphery 1062 of the top cover of the fastener to the side wall of the shaft is L, and the minimum horizontal distance from the outer periphery of the top cover to the straight wall area is L1, where L and L1 satisfy the relationship: L1 > 1.5 × L. The horizontal width L2 of the transition zone 1043 satisfies the relationship: L2 < 0.5 × L1. In this way, it can ensure that the fastener effectively pierces the first metal to form a high-quality weld, while making the fastener compact in size and able to effectively accommodate spattered metal during welding.

[0074] like Figure 2 The schematic cross-sectional view of the transition zone 1043 is shown. The arcuate zone 1041 extends from the top cover in the following forms: (1) The arcuate zone 1041 intersects with the top cover periphery 1062 or the top cover upper surface 101. The transition zone 1043 is designed to be filled from both the upper and lower sides, such as Figure 2 (2) The arc-shaped area 1041 is tangent to the upper surface of the top cover, and the transition area 1043 is mainly filled from the bottom, as shown in FIG. Figure 2 (3) The arc-shaped area 1041 is tangent to the outer periphery 1062 of the top cover, and the transition area 1043 is mainly filled from the top, as shown in FIG. Figure 2 As shown in C1. Since the curved section 1041 is a thin-walled structure, a transition zone 1043 is used to gradually reduce the wall thickness from the top cover 106 to the curved section. This prevents excessive plastic deformation in the transition zone during welding, which could lead to cracks. Furthermore, the horizontal width L2 of the transition zone 1043 is controlled to be less than 0.5 × L1 to prevent the excessive size of the transition zone from affecting the plastic deformation of the curved section during welding.

[0075] like Figure 3The figure shows the connection state of the transition zone and the top cover in a preferred embodiment. The arc-shaped area 1041 is an arc and intersects with the outer periphery of the top cover 106. On the upper surface, the arc-shaped area 1041 is connected to the top cover upper surface 101 by an arc R3, wherein the arc R3 is tangent to the arc-shaped area 1041 and the top cover upper surface 101. The arc R1 is connected at the intersection of the top cover outer periphery and the top cover inner wall 1061, and the arc R1 is tangent to the top cover outer periphery and the top cover inner wall 1061. The inner surface of the arc-shaped area 1041 is connected to the top cover by an arc R2, wherein the arc R2 is tangent to the inner surface of the arc-shaped area 1041 and the arc R1 respectively. The radius of the arc R1 is greater than 0.3mm, and the radius of the arc R2 is greater than 0.5mm.

[0076] like Figure 4 The figure shows a cross-sectional view of the connection between the curved area and the straight wall area of ​​the fastener. A line passing through the connection point between the curved area 1041 and the straight wall area 1042 and tangent to the curved area 1041 forms an angle δ with the straight wall area 1042, and the angle δ ranges from 0° to 40°. Preferably, the angle δ is set to 0°, that is, the curved area 1041 and the straight wall area 1042 are in a tangent relationship, as shown in FIG. Figure 4 According to different requirements of application scenarios, the connection between the arc area 1041 and the straight wall area 1042 can also be set to an intersection relationship, but the angle δ formed does not exceed 40°, such as Figure 4 As shown in B2, in this way, the cavity volume formed by the cap is guaranteed and the manufacturability of the cap is improved while maintaining the compact size of the compact fastener.

[0077] More specifically, the diameter D of the end portion 103 of the shaft portion of the fastener ranges from 3 mm to 6 mm, the horizontal width L from the outer periphery 1062 of the top cover to the side wall of the shaft portion 102 ranges from 0.3 mm to 1.6 mm, preferably from 0.5 mm to 1 mm, and the minimum horizontal distance L1 from the outer periphery of the top cover to the straight wall area 1042 ranges from 1.2 mm to 3.2 mm, preferably from 1.8 mm to 2.5 mm. In addition, the angle Ω between the inner wall 1061 of the top cover and the horizontal plane ranges from 10° to 50°. Preferably, when the first metal thickness range is less than 1.5mm, the diameter D ranges from 3mm to 4.5mm, the L ranges from 0.3mm to 0.6mm, the L1 ranges from 1.2mm to 2.0mm, and the Ω ranges from 10° to 25°; when the first metal thickness range is 1.5mm to 3mm, the diameter D ranges from 4.2mm to 5.2mm, the L ranges from 0.5mm to 1mm, the L1 ranges from 1.8mm to 2.5mm, and the Ω ranges from 20° to 40°; when the first metal thickness range is greater than 3mm, the diameter D ranges from 4.8mm to 6mm, the L ranges from 0.9mm to 1.6mm, the L1 ranges from 2.3mm to 3.2mm, and the Ω ranges from 30° to 50°. This ensures that the shaft can efficiently pierce the first metal and form a reliable weld under the premise of compact size of the fastener, and the cap structure can fully accommodate the molten metal discharged from the weld.

[0078] Figure 5 A schematic cross-sectional view of a fastener cap in one embodiment is shown. As the curved region 1041 extends from the transition region 1043 to the straight-wall region 1042, a thickness relationship t1 ≥ t4 > t3 > t2 exists, resulting in a trend in cap wall thickness that first decreases and then increases. T1 represents the wall thickness of the curved region near the transition region, t2 represents the wall thickness of the curved region near the straight-wall region, t3 represents the wall thickness of the straight-wall region near the curved region, and t4 represents the wall thickness of the straight-wall region away from the curved region. Furthermore, the wall thickness of the curved region 1041 decreases by no more than -50% as it extends from the top cap side to the straight-wall region. The wall thickness of the straight-wall region 1042 gradually increases from one end of the curved region to the end 105, with an increase of no more than 65%. This allows for better control of cap shape during manufacturing and prevents deformation of the curved region 1041 near the straight-wall region 1042 during welding, thus reducing the height of the cap protruding from the first metal surface after welding. In addition, the straight wall area 1042 gradually increases from top to bottom, which is more conducive to maintaining the vertical support effect.

[0079] like Figure 6 In another embodiment, a schematic diagram of the deformation process of the cap of the fastener during welding is shown. Figure 6 In the A3 stage), the electrode applies an electrode pressure F to the fastener. eThe fastener shaft 102 and the end of the straight wall region 1042 of the cap are pressed onto the surface of the first metal 200, and the first metal 200 forms a reaction force F on the straight wall region 1042 of the cap. s During the welding stage ( Figure 6 During stage B3, as shaft 102 rapidly penetrates first metal 200 and sinks downward, the top cover causes curved section 1041 on the cap to bend and deform downward. The upward support provided by straight wall section 1042 causes curved section 1041 to bend and deform around its upper end, thereby maintaining the cap's cavity structure. The rapid deformation of curved section 1041 during welding facilitates the fastener shaft's penetration of first metal 200. Furthermore, the vertical support provided by the straight wall section effectively ensures that the cap maintains a cavity volume sufficient to accommodate discharged metal during welding.

[0080] The straight wall area 1042 is distributed around the fastener shaft 102, as shown in FIG. Figure 1 As shown, the height H1 of the straight wall area is smaller than H. In addition, the straight wall area 1042 is designed to extend downward to form an angle β with the central axis, and the angle β is in the range of 0° to 5°. This ensures that the cap is easy to manufacture and compact in size, while achieving a better vertical support effect of the straight wall area on the curved area during the welding process, reducing the risk of the straight wall area tipping over, and at the same time causing the deformation of the cap during the welding process to be concentrated in the curved area. Figure 7 The angle β of the straight wall area 1042 shown in A4 is in the range of 0° to 5°, which can more effectively maintain the vertical support effect after welding, ensuring that the cap maintains a larger cavity volume V1 after welding (such as Figure 7 When the straight wall area 1042 is designed to extend downward and tilt inward, especially as the angle β' formed with the central axis increases, such as Figure 7 As shown in Figure C4, this increases the risk of the straight wall area tipping over during welding. A steep tilt further compresses the volume V1' of the post-weld cap cavity, reducing its effectiveness in accommodating and discharging metal. Furthermore, an excessively tilted straight wall area provides limited additional mechanical locking force to the workpiece.

[0081] When the fastener of the present invention is used to weld a thicker first metal, for example, the first metal thickness reaches 4mm to 7mm, the volume of the first metal discharged from the weld point increases significantly due to the large thickness of the first metal pierced by the shaft, which requires the volume of the accommodating cavity formed by the cap to be large enough. While ensuring the compactness of the lateral dimensions, if the cross-sectional length of the arc section is too short, excessive folding deformation (such as the deformation of the arc section) will occur between the straight wall section and the arc section during welding. Figure 8 A5 and B5), which will reduce the volume of the accommodating cavity (V2) formed by the cap, which is not conducive to the cap fully receiving and discharging metal. In another preferred embodiment, the cross-sectional shape of the arc area is designed as follows Figure 8 As shown in C5, the height H1 of the straight wall area 10421 is less than the minimum height H2 of the protruding top cover of the shaft, and the highest point of the arc area is set on the side close to the top cover 106, so that the cap forms a significant convex shape close to the top cover side, and the height of the arc area protruding from the top cover is H3, and H3 does not exceed H1, and there is a relationship between the cross-sectional length La of the arc area and the cross-sectional length Lb of the straight wall area: La ≥ 2 × Lb. With such a design, it is possible to increase the cross-sectional length (La) of the arc area 1041, and then the height design of H1 can be appropriately reduced. In addition, since the arc area close to the top cover side will be greatly reduced after welding, the horizontal distance L3 from the outer periphery 1062 of the top cover to the highest point of the arc area is designed to be: L3 ≤ 0.4 × L1, which is conducive to the arc area to produce a larger curvature deformation during welding, such as Figure 8 As shown in D5, after welding, the height of the cap protruding from the first metal surface is reduced while ensuring that the upper end of the cap has a larger horizontal width (such as Figure 8 D5), thereby forming a sufficient volume (V2') to accommodate the discharged metal.

[0082] like Figure 9 The figure shows a cross-sectional schematic diagram of a fastener and a deformation schematic diagram of its cap in yet another embodiment. When welding a thinner first metal, for example, the thickness of the first metal is 1mm to 2mm, the height H1 of the straight wall area 1042 of the fastener is set to be less than the minimum height H2 of the protruding top cover of the shaft portion, and the cross-sectional thickness of the transition zone is gradually reduced from the thickness of the outer peripheral side of the top cover to the wall thickness of the arc zone, and the arc zone 1041 is quickly bent downward from the transition zone to connect to the straight wall area, so that there is an angle α between the connecting line of the two ends of the arc zone and the horizontal line, and the value range of α is 15° to 65°. In addition, the wall thickness t1 of most areas of the arc zone 1041 is almost equal to the wall thickness t2 of the straight wall area 1042. The shape schematic diagrams of the caps before and after welding are shown as follows: Figure 9 As shown in A6 and B6 in FIG, since the thickness of the first metal to be welded is thin, the metal discharged from the weld point is relatively small. The height H1 of the straight wall area can be reduced to make the arc area 1041 produce a larger arc bending deformation, thereby reducing the height of the cap after welding while maintaining a sufficient volume of the accommodating cavity to accommodate the discharged metal.

[0083] The angle Ω between the top cover inner wall 1061 and the horizontal plane is set to a range of 10° to 50°, and the top cover inner wall 1061 extends upward from one side of the shaft portion to the outer periphery of the top cover, so that the top cover inner wall 1061 forms an obtuse angle with the shaft portion side wall 1021 (such as Figure 1 This design allows at least a portion of the top cover to be embedded in the first metal during welding, expanding the contact range of the fastener with the first metal and forming a strong locking effect. On the other hand, it is also conducive to draining the liquid first metal from the welding point. Figure 10The figure shows the deformation of the fastener when the fastener of the same size is welded to the first metal 200 of different thicknesses. Figure 10 As shown in A7 in the figure, due to the small thickness of the first metal, the shaft 102 can almost penetrate the first metal 200 and contact the second metal 300, so that the top cover 106 cannot continue to sink, resulting in only a small area of ​​the top cover inner wall 1061 contacting the surface of the first metal. When the first metal 200 is welded with a thickness of T1 (T1>T0) (as shown in the figure), the shaft 102 can almost penetrate the first metal 200 and contact the second metal 300, so that the top cover 106 cannot continue to sink, resulting in only a small area of ​​the top cover inner wall 1061 contacting the surface of the first metal. Figure 10 (As shown in B7 in the figure), due to the large thickness of the first metal 200 and the short size of the shaft, a large penetration distance of the first metal 200 cannot be generated. Therefore, under the combined action of the electrode pressure and the resistance heat, the top cover 106 produces a more significant bending deformation toward the central axis, which further promotes the top cover 106 to sink and embed into the first metal 200, resulting in the top cover inner wall 1061 being able to completely contact the first metal. Therefore, the same fastener is compatible with the welding of first metals with a larger thickness range. In addition, when welding first metals of the same thickness, by adjusting the welding process, such as increasing the electrode pressure and the welding current, the shaft 102 is plastically deformed and shortened, which also lifts the top cover inner wall 1061 to embed into the surface of the first metal.

[0084] like Figure 11 The fastener shown has radially distributed knurled indentations 1044 on the arc-shaped area in order to further enhance the plastic deformation capability of the arc-shaped area 1041 during welding. The knurled indentations can weaken the strength of the arc-shaped area 1041 to a certain extent, which is beneficial for improving the bending deformation of the arc-shaped area and the compression deformation of the circumferential material when the shaft penetrates the first metal, thereby enhancing the capability of the fastener shaft to penetrate the first metal.

[0085] In one embodiment of resistance spot welding of dissimilar metals using the disclosed fastener, the welding process is as follows: Figure 12 As shown. In the welding process, the current settings include the preheating stage current (I1), the fastener puncture stage current (I2) and the welding stage current (I3). The electrode pressures in the preheating stage, the fastener puncture stage and the welding stage are F1, F2 and F3 respectively, and the electrode pressure relationship is F1 ≥ F2 ≥ F3. The current in each stage is designed for different purposes and in combination with the thickness and strength of the first metal and the second metal to be welded. Combined with the welding process schematic diagram as shown Figures 13 to 16 FIG1 further describes the process of welding dissimilar metals using the fastener 100 of the present invention. First, the upper electrode 400 and the lower electrode 500 apply pressure F1 to the fastener 100, the first metal 200, and the second metal 300, so that the fastener and the workpiece are in close contact, and the end of the fastened shaft and the straight wall area of ​​the cap are completely pressed onto the surface of the first metal workpiece, as shown in FIG1. Figure 13 shown.

[0086] During the warm-up phase, Figure 14 As shown, in order to ensure closer contact between the fastener shaft and the end of the cap's straight-walled area and the surface of the first metal 200 to be welded, the preheating stage uses a low current I1 and maintains it for a relatively long time, for example, 4kA for 150ms. Furthermore, when welding a thicker first metal, such as an aluminum alloy with a first metal thickness greater than 4.0mm, the preheating stage can further squeeze the fastener shaft 102 into the first metal 200, reducing the remaining first metal thickness T2 between the fastener shaft end face 103 and the second metal 300. This creates more favorable conditions for the shaft 102 to quickly penetrate the first metal 200 during the subsequent fastener penetration stage. To this end, the electrode pressure is preferably set to satisfy the relationship: F1 > 1.5 × F2, and F2 = F3. At this point, the preheating current is appropriately increased. For example, I1 is increased to 6kA and the hold time is increased to 250mm, so that a portion of the first metal molten region 201 is squeezed into the cap, forming discharged metal (spatter) 202.

[0087] During the fastener penetration stage Figure 15As shown, an electrode pressure F2 is applied to the weld, and several relatively large and short current pulses I2 are applied to the weld. For example, four current pulses are applied, with the current I2 of a single pulse being 18kA and maintained for 50ms. This causes the first metal 200 in the weld to rapidly melt. Under the pressure of the fastener shaft and the expansion force of the liquid metal itself, the molten liquid metal forms discharged metal (splashed metal) 202, which rapidly enters the accommodation cavity formed by the fastener cap. Under the electrode pressure, the fastener shaft rapidly pierces the first metal 200 and comes into contact with the second metal 300. As the fastener shaft pierces the first metal, the straight wall region 1042 on the cap supports it upward, causing the curved region 1041 to bend downward as the fastener shaft sinks. This, in turn, causes a significant bending deformation near the straight wall region 1042 and the curved region 1041, ensuring that the cap can maintain the accommodation cavity structure. The fastener shaft rapidly penetrates the first metal until the shaft contacts the surface of the second metal 300, ending the penetration process. Furthermore, the weld area of ​​the second metal 300 is dented due to the resistance heat and the compression of the lower electrode 500, resulting in the formation of a raised area with a height of T3 on the surface of the second metal in the weld, which allows the raised area to come into direct contact with the end 103 of the fastener shaft. Because the current pulse duration during the fastener penetration phase is short, it facilitates the control of heat input, resulting in the formation of isolated localized melting zones 107 and 301 within the weld of the fastener shaft and the second metal, respectively, during this phase. The peripheries of these localized melting zones 107 and 301 remain in a solid state, avoiding contact with the first metal melting zone 201 and preventing the formation of large amounts of brittle intermetallic compounds in the weld. However, in some embodiments, due to excessive current pulses being set during the fastener penetration stage, or due to a single current pulse being maintained for too long, as the aluminum between the fastener shaft and the second metal is fully expelled to form a contact surface, excessive resistance heat may promote the formation of a local melting zone on the contact surface and form a smaller weld core 600, so that the fastener 100 can form a stronger connection effect with the second metal 300 at this stage.

[0088] Welding process as follows Figure 16 As shown, the electrode applies pressure F3 to the weld point and applies a relatively high welding current I3 that is maintained for a relatively long time, for example, 12 kA for 400 ms. Under the action of the continuous resistance heat input, the fastener shaft and the second metal contact surface melt, forming a solid weld nugget 600. The first metal surrounding the fastener shaft is further affected by the resistance heat, further expanding the first metal melt region 201. A metallurgical reaction occurs at the interface between the first metal melt region 201 and the fastener and second metal, forming a metallurgical connection. Furthermore, the partially melted first metal is again expelled into the receiving cavity formed by the fastener cap 104, filling the cavity with more expelled metal 202.

[0089] Example 1:

[0090] In this embodiment, the cross-sectional structure of the fastener used is as follows: Figure 17 As shown, the side wall of the shaft gradually expands as it extends from the end of the shaft to the outer periphery of the top cover, and the wall thickness of the transition zone gradually decreases from the thickness of the outer periphery of the top cover to the wall thickness of the arc zone. The dimensions of the fastener design are: L = 0.7mm, L1 = 1.71mm, L2 = 0.45mm, D = 5.0mm, Dmax = 12.0mm, H = 2.2mm, H1 = 1.45mm, H2 = 1.2mm, γ = 60°, Ω = 30°. The arc zone 1041 is a circular arc, and the straight wall zone is designed to be perpendicular to the horizontal plane. When welding, use Figure 12 The welding process shown is used to weld a first metal and a second metal, wherein the fastener is made of stainless steel, the first metal 200 is 1.6mm thick 6061 aluminum alloy, and the second metal 300 is 1.2mm thick QP1180 steel (the first and second metals are the same materials used in an embodiment of the patent publication CN115570251A). The cross-sectional metallographic structure of the joint after welding is as follows Figure 18 As shown, the shaft of the fastener effectively pierces the first metal 200 and forms a firm connection with the second metal 300 through the molten core 300. The straight wall area 1042 of the cap is vertically squeezed to the surface of the first metal 200 and cannot move downward, vertically supporting one end of the arc area 1041, while the other end of the arc area moves downward under the traction of the transition area, causing the arc area to bend and deform near the straight wall area, so that the cap maintains the cavity structure to fully accommodate the discharged metal 202. Compared with the joint in the embodiment of the comparative document CN115570251 A, as shown in FIG. Figure 19 As shown in the figure, the maximum diameter Dmax of the fastener after welding and the height H5 of the cap protruding from the first metal surface of the present invention are 12.18mm and 2.06mm, respectively, which are much smaller than the Dmax and H5 of the joint in the reference document. Furthermore, the electrode indentation depth H6 of the second metal surface of the fastener of the present invention is 0.38mm, which is much smaller than H6 of the joint in the reference document. This fully demonstrates that the fastener of the present invention is more compact, effectively reducing the indentation depth and the height of the cap protruding from the first metal surface while ensuring sufficient metal collection and discharge, while also achieving a secure connection.

[0091] Example 2:

[0092] In this embodiment, the cross section of the fastener used is as follows: Figure 20As shown, the sidewall of the shaft gradually expands as it extends from the end of the shaft toward the outer periphery of the top cover, while the wall thickness of the transition zone gradually decreases from the thickness of the outer periphery of the top cover to the wall thickness of the arcuate zone. The design dimensions of the fastener are: L = 0.68mm, L1 = 2.45mm, L2 = 1.0mm, D = 4.8mm, Dmax = 15.0mm, and H1 = 1.6mm. Arcuate zone 1041 is an arc with an outer wall radius of 2.5mm and a wall thickness of 0.4mm. Arc R1 connects the outer periphery 1062 of the top cover with the inner wall 1061 of the top cover at its intersection. Arc R1 is tangent to both the outer periphery of the top cover and the inner wall 1061 of the top cover. Arc R2 connects the inner surface of arcuate zone 1041 to the top cover, where arc R2 is tangent to both the inner surface of arcuate zone 1041 and arc R1, forming a transition zone. The radius of the arc R1 and the arc R2 are both 0.8mm. The wall thickness of the transition zone is gradually reduced from the thickness of the outer peripheral side of the top cover (greater than 1mm) to the wall thickness of the arc zone (0.4mm), so that the plastic deformation of the cap mainly occurs in the arc zone. In addition, the straight wall area 1042 is perpendicular to the horizontal plane. The fastener is welded to the first metal and the second metal. Figure 12 The welding process shown in the figure uses a fixed electrode pressure of 5.5 kN. The fastener is made of stainless steel, the first metal 200 is a 2.5 mm thick 6000 series aluminum alloy, and the second metal 300 is a 1.5 mm thick aluminum-silicon coated hot-formed steel with a strength of 1500 MPa. The metallographic cross section of the welded joint is shown in the figure below. Figure 21 As shown, the fastener successfully penetrates the first metal 200 and forms a common weld core 600 with the second metal 300 to achieve a firm connection. The arc area 1041 of the fastener is bent, and due to the upward support of the straight wall area 1042, the cap maintains the cavity structure to accommodate and discharge the metal 202. After welding, the height of the fastener cap protruding from the first metal surface is only 2.66mm, the maximum diameter Dmax is 15.28mm, and the indentation depth of the second metal side electrode is 0.61mm. It can be seen that the fastener of the present invention can not only achieve a firm connection when welding a thicker first metal, but also the height of the cap protruding from the first metal surface of the obtained joint is lower than that of the joint in the comparative document CN115570251 A; in addition, the indentation depth of the second metal side electrode is also much smaller than that of the comparative document (such as Figure 19 ), indicating that the shaft portion of the fastener of the present invention has a better ability to pierce the first metal.

[0093] Example 3:

[0094] In this embodiment, the surface morphology and cross-sectional schematic diagram of the fastener 100 are as follows: Figure 22As shown, the sidewall of the shaft gradually widens as it extends from the end of the shaft toward the outer periphery of the top cap. The wall thickness of the transition zone gradually decreases from the thickness on the outer periphery of the top cap to the thickness of the curved zone. The fastener is made of low-carbon steel. The curved zone 1041 of the fastener is a circular arc and is tangentially connected to the straight wall zone 1042. The wall thickness of the curved zone gradually decreases as it extends from the top cap to the straight wall zone. This causes plastic deformation of the curved zone during welding to occur closer to the straight wall zone, thereby controlling the height of the cap protruding from the first metal surface after welding. The dimensions of the fastener are: H = 3.2mm, H1 = 2.6mm, H2 = 2.0mm, L = 0.85mm, L1 = 2.22mm, L2 = 0.6mm, γ = 55°, Ω = 32°, and D = 5.1mm. The cap wall thickness decreases first and then increases, with t1 = 0.42mm, t2 = 0.31mm, t3 = 0.34mm, and t4 = 0.38mm. The straight wall area 1042 is designed to be inclined outward at an angle of β = 2°. The fastener is used to weld the first metal 200 and the second metal 300, wherein the first metal 200 is made of a 2.5mm thick 6000 series aluminum alloy and the second metal 300 is made of a 2.0mm thick advanced high strength steel (QP 980) with a strength of 980 MPa. Figure 12 The welding process shown in the figure has a fixed electrode pressure of 5.5 kN. First, a preheating current I1 and a fastener piercing current I2 are applied to the weld point. Figure 23 This is a topographical image of the fastener 100 being peeled from the weld after the fastener has penetrated the first metal. A large hole is visible in the first metal 200, indicating that the shaft has successfully penetrated the first metal 200. Furthermore, the ejected metal 202 ejected from the weld is completely contained within the cavity formed by the fastener cap, which is significantly larger than the volume of the ejected metal 202.

[0095] Figure 24A metallographic image of the cross-section of the joint obtained after welding is shown, showing that the fastener shaft pierces the first metal 200 and forms a common weld nugget 600 with the second metal 300, securely locking the first metal in the joint. Due to the thin thickness of the first metal 200, only a local area of ​​the inner wall 1061 of the top cap presses against the first metal surface. Furthermore, the straight wall region 1042 of the cap presses against the surface of the first metal 200 and supports it vertically upward, causing significant bending and deformation in the curved region 1041 and the area near the straight wall region 1042. This prevents the cap structure from collapsing and allows the cap to maintain its cavity shape and fully accommodate the discharged metal 202. As can be seen from this embodiment, due to the vertical support of the straight wall region 1042, the curved region 1041 bends and deforms near the upper end of the straight wall region. After welding, the height of the fastener cap protruding from the first metal surface is 3.23 mm, the indentation depth of the electrode on the second metal side is 0.62 mm, and the maximum diameter Dmax is 15.25 mm. Compared with the fastener in Example 2, since the height H1 of the straight wall area 1042 in this embodiment is larger, the height of the cap protruding from the first metal surface after welding is also higher, but the volume of the accommodating cavity formed by the cap after welding is also increased. Figure 24 It can be seen that the left cap is not filled with the discharged metal 202, which also shows that the fastener of the present invention can adjust the volume of the accommodating cavity formed by the cap after welding and the height of the cap protruding from the first metal surface by controlling the height of the straight wall area 1042.

[0096] Example 4:

[0097] In this embodiment, the same fastener 100 as in embodiment 3 is used. The first metal 200 to be welded is a 3 mm thick cast aluminum alloy, while the second metal is still a 1.5 mm thick aluminum-silicon coated hot-formed steel with a strength of 1500 MPa. The welding process is still the same. Figure 12 The process shown in the figure is to fix the electrode pressure during welding to 5.5kN. The surface and cross-sectional morphology of the joint obtained after welding are as follows: Figure 25As shown, it can be seen that the shaft portion of the fastener 100 can also pierce the thicker first metal 200 and form a common weld core 600 with the second metal 300, forming a secure connection between the fastener and the second metal. Because the shaft sidewall 1021 and the top cover inner wall 1061 gradually expand as they extend upward from the second metal side, the first metal is securely locked in the joint, forming a high-strength connection between the first and second metals. Compared to Example 3, since the thickness of the first metal 200 has increased by 0.5 mm, the penetration depth of the fastener shaft 102 must also be further increased while the fastener size remains unchanged. This causes the top cover 106 to sink further and embed into the first metal, resulting in a larger area on the top cover inner wall 1061 contacting the first metal. The fastener cap can also completely accommodate the discharged metal 202, and from the surface of the weld, no first metal overflows the cap. After welding, the height of the fastener cap protruding from the first metal surface was 3.04mm, the indentation depth of the electrode on the second metal side was 0.62mm, and the maximum diameter Dmax was 15.28mm. These results are similar to those measured in Example 3, indicating that the same fastener of the present invention achieves relatively stable joint structure dimensions even when welding first metals of varying thicknesses. Furthermore, the results of this example demonstrate that the fastener structure not only enables secure welding of thicker first metals, but also that the same fastener can be compatible with welding a wide range of first metal thicknesses.

[0098] Comparative Example 1:

[0099] In this comparative example, the fastener 100 used is the fastener in Example 3, and the cap of the fastener is as shown in FIG. Figure 26 The schematic diagram of A8 is cut to obtain a fastener without a cap for welding dissimilar metals. The welding parameters, the first metal and the second metal to be welded are exactly the same as those in Example 4. The surface morphology of the weld after welding is as follows Figure 26 As shown in Figure B8, because the fastener lacks a cap structure to contain the discharged metal 202, the discharged metal is distributed around the weld point. This not only affects the surface quality of the weld point, but also contaminates surrounding components with the high-speed metal splash. This comparative example 1 fully demonstrates the importance, necessity, and effectiveness of the cap of the fastener of the present invention in containing discharged metal.

[0100] Comparative Example 2:

[0101] The conventional resistance spot welding process is used to weld the same first metal, wherein the welded first metal is the 3.0 mm thick cast aluminum alloy in Example 4, and the welding parameters are the optimized resistance spot welding parameters. In this embodiment, welding of the same cast aluminum alloy is achieved.

[0102] The cross tensile mechanical properties test was carried out on the welded joints of Example 4, Comparative Example 1 and Comparative Example 2 (the cross tensile specimen size was 150 mm × 50 mm). The force-displacement curves obtained after the test were as follows: Figure 27 As shown, curve ① is the joint obtained in Example 4, curve ② is the joint obtained in Comparative Example 1, and curve ③ is the joint obtained in Comparative Example 2. The fracture morphology of the joint after stretching is as shown in FIG. Figure 28 As shown, A9 is the joint of Example 4 (curve ①), B9 is the joint of Comparative Example 1 (curve ②), and C9 is the joint of Comparative Example 2 (curve ③).

[0103] The load of the resistance spot welded joint of the same cast aluminum alloy is 3443.4N, and the joint is a button pull-out fracture, such as Figure 28 As shown in C9, it shows that the resistance spot welding joint of the same cast aluminum alloy has a higher connection performance. However, the cross tensile load of the dissimilar metal welding joint of the fastener 100 of the present invention is as high as 5424.6N, and has a larger displacement than curve ③ (as shown in FIG. Figure 27 Curve ① and curve ③ in FIG), which shows that the fastener of the present invention can achieve high-strength and reliable connection of dissimilar metals.

[0104] Compared with Example 4, the only difference of Comparative Example 1 is that the fastener used in this example does not have a cap structure, but there are great differences in the cross-tensile properties and fracture modes of the joints in Example 4 and Comparative Example 1. In terms of cross-tensile properties, the maximum loads of the joints are almost similar, indicating that the structural design of the shaft and the top cover of the fastener of the present invention can provide the joint with high-strength connection performance. However, curve ① of the joint in Example 4 has a larger displacement than curve ② of the joint in Comparative Example 1. In addition, after the load reaches the maximum value, curve ② suddenly drops, while curve ① continues to produce a displacement S, and then the load suddenly drops to a certain extent and then slowly decreases (such as Figure 27 As shown). In terms of joint failure, the cast aluminum alloy around the joint in Example 4 produced significant cracks, and the arc-shaped area 1041 of the fastener cap was broken, resulting in a straight wall area 1042 remaining on the aluminum side weld ( Figure 28 A9). The joint cast aluminum alloy in Comparative Example 1 did not produce cracks ( Figure 28 In B9), after breaking free from the mechanical lock between the fastener shaft and the top cover, a circular hole is left on the first metal weld. The reason for the difference in cross tensile load and fracture mode between Example 4 and Comparative Example 1 is that the straight wall area 1042 provided in the fastener 100 of the present invention can be vertically pressed onto the surface of the first metal 200 after welding, as shown in FIG. Figure 29 As shown in the figure, during the cross-stretching process, the straight wall area generates additional extrusion force Fc on the periphery of the joint, which provides additional mechanical locking force for the joint and thus improves the mechanical properties of the joint.

[0105] 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 fastener for resistance spot welding dissimilar metals, the fastener being used to resistance spot weld a first metal and a second metal laminate, the first metal having a lower melting point than the second metal, the melting point of the fastener being the same as or similar to that of the second metal, the fastener comprising a top cover, a shaft extending from the center of the top cover, and a cap disposed around the periphery of the top cover, the cap, the side edges of the shaft, and the horizontal plane containing the ends of the shaft forming a receiving cavity, the receiving cavity being used to collect the first metal extruded or ejected from the weld spot, and characterized in that: The side wall of the shaft portion gradually expands as it extends from the end of the shaft portion toward the outer periphery of the top cover, which facilitates the shaft portion to penetrate the first metal at high speed and discharge the molten first metal from the weld point during welding, and provides the main mechanical locking force for the fastener to the first metal; The cap extends from the outer periphery of the top cover to the horizontal plane where the end of the shaft portion is located, and sequentially forms a transition area, an arc area and a straight wall area; wherein, The arc-shaped area has good plastic deformation ability and can adapt to the position of the shaft during welding to produce adaptive deformation, thereby preventing the cap from hindering the shaft from piercing the first metal; The straight wall area supports the cap vertically during the welding process, forcing the cap to deform and concentrate in the arc area, while preventing the cap from collapsing after welding and reducing the volume of the accommodating cavity; After welding, the straight wall area is almost vertically pressed against the surface of the first workpiece, providing additional mechanical locking force for the weld joint; The wall thickness of the transition zone gradually decreases from the thickness of the outer peripheral side of the top cover to the wall thickness of the arc zone, thereby avoiding stress concentration and cracking in the transition zone during manufacturing and welding, and ensuring that the plastic deformation of the cap is concentrated in the arc zone; The minimum height H2 of the shaft protruding from the top cover satisfies H2=K1×T, wherein T is the first metal thickness, K1 is a coefficient considering the first metal thickness, and the value range is K1=0.6~1.

2. The thickness H at the center of the fastener satisfies H=1.2×H2~2×H2, The minimum horizontal width from the outer periphery of the top cover to the side wall of the shaft portion is L, and the minimum horizontal distance from the outer periphery of the top cover to the straight wall area is L1, where L1 is greater than 1.5×L. The horizontal width L2 of the transition zone is less than 0.5×L1, A line passing through a connection point between the arc-shaped area and the straight-wall area and being tangent to the arc-shaped area forms an angle δ with the straight-wall area, and the angle δ ranges from 0° to 40°.

2. The fastener according to claim 1, wherein: The wall thickness of the arc-shaped area gradually decreases as it extends from the top cover side to the straight wall area, so that the plastic deformation of the arc-shaped area occurs on the side close to the straight wall area during welding, thereby controlling the height of the cap protruding from the first metal surface after welding.

3. The fastener according to claim 1, wherein: The wall thickness of the straight wall area gradually increases from one end close to the arc-shaped area to the other end in contact with the first metal, and the increase does not exceed 65%.

4. The fastener according to claim 1 or 2, characterized in that: The wall thickness of the arc-shaped area gradually decreases when extending from the top cover side to the straight wall area, and the reduction does not exceed -50%.

5. The fastener according to claim 1, wherein: The straight wall area is distributed around the axis of the fastener and forms an angle β with the center axis of the fastener, and β=0°~5°, and the height of the straight wall area H1<H, The included angle Ω between the inner wall of the top cover and the horizontal plane satisfies Ω=10°~50°.

6. The fastener according to claim 1 or 5, characterized in that: The included angle γ between the side wall of the shaft portion and the horizontal plane ranges from 45° to 80°, and γ>Ω.

7. The fastener according to claim 1 or 5, characterized in that: An angle α is formed between a line connecting one end of the cap close to the outer periphery of the top cover and one end of the arc-shaped area close to the straight wall area and a horizontal plane, and α=15° to 65°.

8. The fastener according to claim 1 or 5, characterized in that: The height H1 of the straight wall area is smaller than the minimum height H2 of the protruding top cover of the shaft portion.

9. The fastener according to claim 1, wherein: The connection area between the arc-shaped area and the straight-wall area is in a tangent relationship.

10. The fastener according to claim 1, wherein The arc-shaped area is composed of an arc, and the arc radius ranges from 0.6 mm to 4 mm.

11. The fastener according to claim 1, wherein: The wall thickness of the arc area and the straight wall area is 0.25mm to 0.6mm; the horizontal width L from the outer periphery of the top cover to the side wall of the shaft portion is 0.3mm to 1.6mm; the minimum horizontal distance L1 from the outer periphery of the top cover to the straight wall area ranges from 1.2mm to 3.2mm; the end diameter D of the shaft portion ranges from 3mm to 6mm.

12. The fastener according to claim 1, wherein The intersection of the outer periphery of the top cover and the inner wall of the top cover is connected by an arc R1, and the radius of the arc R1 is greater than 0.3 mm.

13. The fastener according to any one of claims 1-5 or 9-12, characterized in that: The melting point of the first metal is lower than 750°C, and the melting point of the second metal is higher than 1300°C.

Images