Welding element and welding electrode for resistance spot welding of dissimilar metals

Abstract

The present invention provides a welding element and a welding electrode for resistance spot welding of dissimilar metals. The welding element welds first and second metals having a melting point difference greater than 700°C. The shaft of the welding element pierces the first metal with a lower melting point and forms a weld nugget with the second metal, thereby firmly welding the first metal. During welding, the auxiliary deformation zone of the cap structure preferentially undergoes plastic deformation, allowing the cap structure to maintain a thin-walled cavity structure and thereby fully accommodate the molten first metal discharged from the weld point. The provided welding electrode further facilitates the formation of the cap structure of the welding element, controls the height of the cap structure, and improves the forming quality of the weld point.

Description

Technical Field

[0001] The invention belongs to the field of dissimilar metal welding, and in particular relates to a welding element and a welding electrode thereof for dissimilar metal resistance spot welding. Background Art

[0002] In order to achieve energy conservation and emission reduction, the automotive industry is moving towards lightweight development. The use of mixed dissimilar metal components (such as aluminum / steel and magnesium / steel, etc.) to manufacture the car body can effectively reduce the weight of the car body while ensuring the safety performance of the car, reduce the car's energy consumption and harmful exhaust emissions. Therefore, the welding of dissimilar metal components has a wide range of application needs in car body manufacturing. However, due to the huge differences in physical and chemical properties between dissimilar metals, brittle intermetallic compounds, cracks and large residual stresses are easily formed in the welds of dissimilar metals, resulting in severe deformation and other problems. The extremely poor welding performance makes it difficult to obtain high-quality welds by direct fusion welding between dissimilar metals.

[0003] In order to improve the welding strength of dissimilar metal welded joints, patent document 1CN114211104B proposes a resistance spot welding method, which utilizes the huge differences in physical properties between dissimilar metals (such as material melting point, thermal conductivity and expansion coefficient, etc.). First, a current pulse that actively induces spattering of low-melting-point aluminum alloys is introduced into a stack of, for example, steel / aluminum / steel. By controlling the heat input, only the low-melting-point aluminum alloy is allowed to quickly melt and expand. Under the action of thermal-mechanical coupling, the molten aluminum alloy is discharged from the weld at a high speed through the spattering process. Subsequently, a welding current mainly used for nucleation is introduced into the weld forming the steel / steel contact, thereby achieving a firm connection between the steel / steel, and the aluminum alloy is firmly welded-riveted in the weld, thereby obtaining a high-performance aluminum / steel dissimilar metal welded joint. This method has an efficient and reliable effect of connecting dissimilar metals. However, the problem of actively inducing the discharge of spattered metal outside the weld point in this method must be taken seriously, because the discharged spattered metal will contaminate surrounding components and equipment; in addition, in order to better meet the needs of actual application scenarios of dissimilar metal connection components, this field needs a welding element that, in addition to realizing the function of accommodating spattered metal, can also achieve efficient and high-quality welding effects, and also has a reasonable structural setting and lighter weight.

[0004] Patent document 2CN115570251A discloses a welding element structure for welding dissimilar metals. The welding element can accommodate spattering metal, but the cap structure has a large wall thickness, making it difficult for the cap structure to deform during welding, resulting in certain difficulties for the cap structure to pierce the low-melting-point metal with the shaft. Patent document 3CN115780980A also discloses a welding element structure for welding dissimilar metals. Although the welding element solves the problem of the cap structure affecting the piercing of the low-melting-point metal with the shaft of the welding element, the cap structure needs to provide a riveting effect on the metal workpiece. Therefore, the cap structure needs to be designed with a larger wall thickness. However, as the wall thickness of the cap structure increases, in order to ensure that the cap structure has sufficient volume to accommodate spattering metal, the size of the welding element needs to be larger, resulting in poor surface flatness of the weld and increased joint weight, which is not conducive to the lightweight design of the weld. Patent document 4CN217316508U discloses a welding element for joining dissimilar metals. While this welding element can control metal spatter and features a thin-walled cap, the thin-walled structure of the receiving cavity lacks a preferred deformation zone, which can easily cause the entire cavity to collapse and deform during welding, resulting in the cavity losing its ability to contain metal spatter. The present invention aims to provide a welding element that balances weight and size considerations while achieving both good welding quality and effective metal spatter containment. Summary of the Invention

[0005] The purpose of the present invention is to provide a welding element and a welding electrode for resistance spot welding of dissimilar metals, so as to solve the problem of spattering metal discharged from the weld point during resistance spot welding of dissimilar metals, and at the same time reduce the problems of weld point indentation depth and severe joint deformation, thereby improving the strength of the weld joint.

[0006] A welding element for resistance spot welding of dissimilar metals, wherein the welding element is used for resistance spot welding a laminated structure of a first metal and a second metal with a melting point difference greater than 700°C. During welding, the welding electrode of the resistance spot welding welds the welding element from the side of the first metal with a low melting point to the second metal, thereby achieving welding of the dissimilar metal laminated structure; the welding element is made of the same material as the second metal, and includes a central shaft and a top cover on one side of the shaft, characterized in that: an annular cap structure extends from the edge of the top cover, the cap structure is bent from the top cover side in the same direction as the shaft and extends at least to the horizontal plane where the end face of the shaft is located; the cap structure is a thin-walled cavity structure, and the maximum wall thickness T1 range is 0.1m m to 0.8mm; an auxiliary deformation zone is provided in the connection area between the cap structure and the top cover, the minimum wall thickness of the auxiliary deformation zone is less than the wall thickness of any other area of ​​the cap structure, and one or more concave structures are presented on the cross section of the auxiliary deformation zone to thin its wall thickness; during the welding process, the auxiliary deformation zone undergoes plastic deformation first, so that the auxiliary deformation zone is elongated and deformed, so as to facilitate the piercing of the shaft into the first metal, and at the same time ensure that the cap structure always maintains an annular cavity structure during the welding process to fully accommodate the molten first metal discharged from the welding point; the minimum thickness T2 of the top cover is greater than the maximum wall thickness T1 of the cap structure, and the minimum thickness T2 of the top cover is 0.35mm to 1.5mm.

[0007] Furthermore, the side wall of the cap is provided with "V"-shaped grooves distributed at equal intervals, the "V"-shaped grooves are recessed toward the center of the welding element and extend in the axial direction, and the overall height H1 of the "V"-shaped grooves satisfies the range: 0.3×H≤H1<H

[0008] Optionally, the wall thickness of the cap structure gradually increases as it extends from the edge of the top cover to the end of the cap structure.

[0009] Furthermore, the cap structure is bent in an inverted "U" shape in the axial direction, so that a local area of ​​the cap structure is raised away from the shaft and the top cover side, so that the raised area is higher than the top cover, and the minimum protruding height H0 between the cap and the top cover satisfies the relationship: 0<H0≤2×H.

[0010] Furthermore, the ratio between the end radius R of the shaft portion and the radius R2 of the top cover satisfies the relationship: 1.1 < R2 / R < 2.2. Preferably, the radius R of the end face of the shaft portion ranges from 2.5 mm to 6 mm, and the radius R2 of the top cover ranges from 3 mm to 9 mm.

[0011] Furthermore, the edge of the top cover is provided with a plurality of protrusion structures which are distributed in a ring shape at equal intervals and in the same direction as the shaft portion.

[0012] Furthermore, the top cover is tilted toward the shaft as a whole, and the auxiliary deformation zone on the cap structure forms a positive "V" shape with the top cover. On a cross section passing through the center line of the welding element, the top cover forms an inclination angle α with the center line of the welding element, and the auxiliary deformation zone forms an angle β with the top cover. Preferably, the inclination angle α ranges from 60° to 85°, and the angle β ranges from 80° to 120°.

[0013] Furthermore, the shaft is provided with 2 to 5 radially distributed pressure relief grooves spaced at the same angle, the pressure relief grooves extending from the end face of the shaft to the side of the shaft, and the ratio between the circular radius R1 formed by the pressure relief grooves at the position of the minimum distance from the center line of the welding element on the end face of the shaft and the radius R of the end face of the shaft satisfies the range: 1<R / R1<1.25.

[0014] Furthermore, the end surface of the shaft is a spherical structure, and the spherical radius ranges from 30 mm to 150 mm.

[0015] According to another aspect of the present disclosure, a welding electrode is provided for performing resistance spot welding of dissimilar metals on the welding element, characterized in that a ring-shaped limiting structure is provided on the periphery of the welding end face of the upper welding electrode used on the welding element side, the limiting structure is used to assist in deformation of the cap structure of the welding element and limit the height of the cap structure after welding, and the minimum vertical distance H2 between the limiting structure and the welding end face satisfies the range: 0.5×T≤H2≤2.5×T, where T is the first metal thickness.

[0016] Technical effects of the present invention:

[0017] (1) The welding element of the present invention has a simple structure, is easy to manufacture, is light in weight, adds little weight to the welding point, and has a low welding cost.

[0018] (2) The weld joints connected by the present invention have little deformation and high flatness, which can effectively avoid excessive warping and deformation of the joints.

[0019] (3) The cap structure of the welding element and the auxiliary deformation zone of the edge of the top cover are prone to tensile plastic deformation during the welding process. During the process of piercing the first metal of the central axis of the welding element, the auxiliary deformation zone can be deformed first. On the one hand, it prevents the cap structure from hindering the piercing of the first metal by the axis of the welding element. On the other hand, it ensures that the side wall of the cap structure is not collapsed during the welding process, thereby maintaining a sufficient volume of the cap structure to accommodate the molten first metal discharged from the welding point.

[0020] (4) Because the cap structure is thin-walled, it not only reduces the weight of the welded component but also effectively reduces the size of the welded component while ensuring that it can accommodate the molten first metal discharged from the weld. Furthermore, after welding, the cap structure can be easily compressed and flattened, further reducing the height between the cap structure and the first metal surface and improving the flatness of the weld.

[0021] (5) A "V"-shaped groove is provided on the side wall of the cap structure, which is recessed toward the center of the welding element and extends in the axial direction. This enhances the supporting capacity of the side wall of the cap structure, so that the deformation of the cap structure during the welding process almost occurs in the auxiliary deformation zone, which is beneficial for the cap structure to maintain its cavity structure, thereby ensuring that the cap structure can accommodate the molten first metal discharged from the welding point.

[0022] (6) Since the top cover is designed to be tilted toward the shaft at an angle α, the warping deformation of the top cover caused by heat and resistance heat after welding is compensated. On the one hand, it ensures that the top cover has better flatness after welding, and on the other hand, it avoids the top cover from reducing the riveting strength to the first metal due to the warping deformation during welding.

[0023] (7) The auxiliary deformation zone and the top cover are designed to be a positive "V"-shaped structure, so that an angle β is formed between the cap structure and the top cover. This is beneficial for the cap structure to always maintain the cavity structure and enhance the plastic deformation capacity of the auxiliary deformation zone during welding, and on the other hand, it avoids fracture in the auxiliary deformation zone.

[0024] (8) Since 2 to 4 radially distributed pressure relief grooves with the same angle interval are provided on the shaft, on the one hand, the first metal discharge efficiency in the weld spot is improved and the energy required to input in the first metal removal stage is reduced; on the other hand, the molten first metal discharged from the weld spot can be discharged into the cap structure from multiple directions at the same time, so that the first metal is filled more evenly in each direction of the cap structure, avoiding the discharged molten first metal from being excessively discharged in a single direction and breaking through the barrier of the cap structure, causing the cap structure to deform. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a perspective view of a welding element from a top cover perspective according to one embodiment of the present disclosure.

[0026] Figure 2 is an axial cross-sectional view of a welding element according to one embodiment of the present disclosure.

[0027] Figure 3 FIG. 1 is a perspective view of a welding element according to another embodiment of the present disclosure from an axial perspective.

[0028] Figure 4 is a schematic diagram of the dimensions of a cross-section of a welding element according to one embodiment of the present disclosure.

[0029] Figure 5 FIG. 4 is a schematic cross-sectional view of a cap structure according to another embodiment of the present disclosure.

[0030] Figure 6 is a schematic diagram of a cap structure according to yet another embodiment of the present disclosure.

[0031] Figure 7 is a schematic diagram of a cross-section of a welding element according to yet another embodiment of the present disclosure.

[0032] Figure 8 is a schematic diagram of a cross-section of a welding element according to yet another embodiment of the present disclosure.

[0033] Figure 9 is a schematic cross-sectional view of an upper welding electrode according to one embodiment of the present disclosure.

[0034] Figure 10 is a schematic diagram of the relationship between welding current, electrode pressure and time in resistance welding of dissimilar metals according to the present disclosure;

[0035] Figure 11 FIG. 1 is a schematic cross-sectional view of a joint during the first metal removal stage of welding according to an embodiment of the present disclosure.

[0036] Figure 12 Schematic diagram of the shape change process of the cap structure during the welding process in one embodiment of the present disclosure.

[0037] Figure 13 FIG. 1 is a schematic diagram of a top cover change process of a welding component during welding in one embodiment of the present disclosure.

[0038] Figure 14 FIG. 1 is a schematic cross-sectional view of a joint after the aluminum removal stage during welding in one embodiment of the present disclosure.

[0039] Figure 15 FIG. 1 is a schematic cross-sectional view of a joint during welding in an embodiment of the present disclosure. FIG.

[0040] Figure 16 Schematic diagram of the cross section of a joint obtained after welding in one embodiment of the present disclosure. DETAILED DESCRIPTION

[0041] The embodiments of the present invention are further described in detail below through specific examples with reference to the accompanying drawings.

[0042] According to one aspect of an embodiment of the present invention, there is provided a welding element such as Figure 1 and Figure 2As shown, the welding element 100 includes a plate-shaped top cover 110 and a shaft portion 101 extending from the top cover, and a curved cap structure 105 is formed by extending radially and then axially at the edge of the top cover 110. The cap structure 105 is a thin-walled cavity structure, and its end portion extends at least to the plane where the end face 103 of the shaft portion is located. An annular auxiliary deformation zone 104 is provided near the area where the cap structure 105 is connected to the edge of the top cover 110. The minimum wall thickness of the auxiliary deformation zone 104 is less than the wall thickness of any other area of ​​the cap structure 105, and one or more concave structures are present on the cross section of the auxiliary deformation zone 104 to reduce its wall thickness. During the welding process of the welding element 100, the auxiliary deformation zone 104 undergoes plastic deformation first, and can be gradually stretched without breaking during the deformation process, so as to facilitate the shaft portion 101 to penetrate the first metal, while ensuring that the cap structure 105 always maintains a ring-shaped cavity structure during the welding process to fully accommodate the molten first metal discharged from the weld point. When the side surface 108 of the shaft portion 101 extends from the edge of the shaft portion end face to the top cover 110 of the welding element, the diameter of the shaft portion gradually increases. Preferably, the profile of the shaft portion side surface 108 on the axial cross section of the welding element is an arc shape, which is conducive to the shaft portion penetrating the first metal on the one hand, and the arc-shaped shaft portion side surface 108 can also provide a partial mechanical locking effect to the first metal on the other hand.

[0043] Another embodiment of the present invention is Figure 3 As shown, the provided welding element 100 is provided with a plurality of raised structures 107 distributed in a ring shape with equal spacing in the same direction as the shaft portion 101 on the edge of the top cover. Generally, in order to prevent the raised structure 107 from weakening the first metal, the height of the raised structure is less than 0.3T (where T is the thickness of the first metal). 2 to 4 pressure relief grooves 106 spaced at the same angle are provided on the shaft portion of the welding element 100, and preferably the number of pressure relief grooves is 3. The pressure relief grooves 106 extend from the shaft end face 103 to the shaft side circumference 108, and the pressure relief grooves 106 are distributed radially between the gaps of the raised structures 107. Since 2 to 5 radially distributed pressure relief grooves with equal angles are provided on the shaft, on the one hand, the first metal discharge efficiency in the weld spot is improved and the energy required in the first metal removal stage is reduced; on the other hand, the molten first metal discharged from the weld spot can be discharged into the cap structure from multiple directions at the same time, so that the first metal is filled more evenly in each direction of the cap structure, and the discharged molten first metal is prevented from being excessively discharged in a single direction and breaking through the barrier of the cap structure, causing deformation of the cap structure.

[0044] Figure 4The following is a schematic diagram of the cross-sectional dimensions of a welding element 100 in one embodiment. The minimum thickness T2 of the top cover 110 of the welding element 100 is greater than the maximum wall thickness T1 of the cap structure 105, and the minimum thickness ranges from 0.35 mm to 1.2 mm, preferably from 0.4 mm to 0.8 mm. Generally, the minimum thickness (T2) of the top cover 110 can be selected based on the thickness (T) of the first metal being welded. As the thickness T of the first metal increases, the minimum thickness T2 of the top cover is also appropriately increased to improve the locking strength of the top cover 110 to the first metal. For example, when T is less than 1.5 mm, the thickness range of T2 is between 0.35 mm and 0.45 mm; when T is greater than 1.5 mm and less than 2.5 mm, the thickness range of T2 is between 0.45 mm and 0.8 mm. The maximum wall thickness T1 of the cap structure ranges from 0.1 mm to 0.8 mm, preferably from 0.2 mm to 0.5 mm.

[0045] According to another aspect of the embodiment of the present invention, the maximum height difference H between the outer surface 102 of the top cover of the welding element 100 and the end surface 103 of the shaft portion satisfies: H≤2.5×T and H<5mm, and there is a relationship between H and T2: 0.3×T<H-T2<T (where T is the first metal thickness), such as Figure 4As shown. Setting H≤2.5×T and H<5mm can better balance the relationship between the welding effect of the welding element and its own weight; and setting 0.3×T<H-T2<T can ensure that the shaft 101 of the welding element can penetrate the first metal to a certain depth, while preventing the shaft 101 from completely penetrating the first metal, and avoiding the problem of a large gap between the top cover 110 and the first metal and tilting and twisting of the welding element 100 due to the excessive length of the shaft 101. Because the length of the shaft 101 cannot completely penetrate the first metal, the second metal is forced to produce a local concave deformation in the weld area and then contact the shaft end face 103, thereby improving the effect of the welding element 100 riveting the first metal. The radius R of the shaft end face 103 of the welding element 100 is set to 2.5mm to 6mm. In order to make it more convenient for the shaft 101 to penetrate the first metal, the preferred range of R is 3mm to 4.5mm. The radius R2 of the top cover 110 of the welding element 100 ranges from 3 mm to 9 mm. To balance the top cover 110's ability to lock the first metal with the overall size of the welding element 100, it is preferably 4.5 mm to 7 mm. Furthermore, the radius R of the shaft end surface 103 and the radius R2 of the top cover 110 satisfy the following relationship: 1.1 < R2 / R < 2.2, thereby ensuring that the top cover 110 is sufficiently large to rivet the first metal. The ratio between the radius R1 of the circular shape formed by the pressure relief groove 106 on the shaft 101 at the minimum distance from the welding element centerline 120 and the radius R of the shaft end surface 103 satisfies the following relationship: 1 < R / R1 < 1.25. Furthermore, the width of the pressure relief groove is 1 mm to 2.5 mm. The shaft end surface 103 of the welding element is spherical, with a radius ranging from 30 mm to 150 mm, preferably from 60 mm to 100 mm. The shaft end surface 103 is configured as a spherical structure, which further enhances the effect of discharging the first metal from the welding spot.

[0046] In order to keep the cap structure 105 in the shape of the accommodating cavity during the welding process and to prevent the cap structure 105 from hindering the shaft portion 101 from piercing the first metal, the cap structure auxiliary deformation zone 104 needs to have excellent plastic deformation ability. In another embodiment, the auxiliary deformation zone 104 is a plurality of closely arranged "arc" groove structures in its cross section, such as Figure 5 As shown, these "arc"-shaped groove structures are more likely to be stretched and deformed during welding. However, during welding, the sidewalls of the cap structure 105 need to have sufficient support to prevent the cap structure from collapsing, thereby reducing its ability to contain the molten first metal. In another embodiment, the cap structure 105 is provided with "V"-shaped grooves 109 distributed at equal intervals on the sidewalls, as shown in FIG. Figure 6As shown. The "V"-shaped groove 109 is recessed toward the center of the welding element 100 and extends in the axial direction. The overall height H1 of the "V"-shaped groove 109 satisfies the range: 0.3×H≤H1<H. Optionally, in order to improve the side wall support capacity of the cap structure 105, the thickness of the cap structure 105 gradually increases as it extends from the edge of the top cover 110 to the end of the cap structure. Since the side walls of the cap structure 105 have a good supporting effect, the deformation of the cap structure 105 during the welding process almost occurs in the auxiliary deformation zone, which is beneficial for the cap structure to maintain its cavity structure, thereby ensuring that the cap structure 105 can accommodate the molten first metal discharged from the weld point.

[0047] In yet another embodiment, the cross-sectional view of the welding element 100 is shown in FIG. Figure 7 As shown, the welding element 100 of this structure is typically used for welding a first metal having a relatively large thickness, such as a 2.5mm magnesium alloy or a 3mm aluminum alloy. The thicker the first metal, the greater the volume of molten first metal discharged from the weld. To fully accommodate the first metal discharged from the weld, the cap structure 105 of the welding element is bent axially into an inverted "U" shape, protruding from the outer surface 102 of the top cover. The protruding height H0 satisfies the relationship: 0<H0≤2×H.

[0048] In yet another embodiment, the cross-sectional view of the welding element 100 is as follows Figure 8 As shown, in order to enhance the riveting effect of the top cover 110 on the first metal, the top cover 110 is tilted toward the axis as a whole, and the top cover forms an inclination angle α with the center line 120 of the welding element on the cross section passing through the center line of the welding element. Usually, the inclination angle α is 60° to 85°. In addition, an auxiliary deformation zone 104 on the cap structure is provided to form a positive "V"-shaped structure with the top cover 110, so that an angle β is formed between the auxiliary deformation zone 104 and the top cover 110. Usually, the angle β ranges from 80° to 120°. By designing the angle β between the auxiliary deformation zone 104 and the top cover 110, on the one hand, it is beneficial for the cap structure to always maintain the cavity structure and enhance the plastic deformation capacity of the auxiliary deformation zone during welding, and on the other hand, it avoids fracture of the auxiliary deformation zone.

[0049] like Figure 8As shown, an electrode positioning groove 111 is provided in the center of the outer surface 102 of the top cover of the welding element 100. The depth of the electrode positioning groove 111 ranges from 0.5 mm to 1.5 mm, and its radius R4 ranges from 2 mm to 5 mm. The relationship between the radius R4 of the electrode positioning groove 111 and the radius R of the shaft end surface 103 is as follows: 1 < R / R4 < 1.5. The electrode positioning groove 111 facilitates rapid alignment of the welding electrode with the axis of the welding element 100, preventing the welding element 100 from tilting during welding. When welding a thicker first metal, such as a 3.0 mm thick cast aluminum alloy, the welding element 100, under a process that matches a relatively high electrode pressure and welding current, and under the combined effects of the high heat input and electrode pressure, causes the top cover 110 surrounding the electrode positioning groove 111 to bend and deform upward as a whole. The tilt angle α of the top cover 110 toward the shaft portion 101 can offset the upward warping deformation of the top cover 110 during welding, ensuring the mechanical locking effect of the top cover 110 to the first metal after welding. The sidewalls of the cap structure 105 surrounding the welding element extend in the axial direction and exceed the horizontal plane of the shaft end face 103, so that the end of the cap structure 105 contacts the surface of the first metal, forming a certain pressure. This prevents the end of the cap structure 105 from separating from the first metal surface due to the upward warping of the top cover 110 during welding, resulting in the molten first metal not being fully contained by the cap structure 105.

[0050] According to another aspect of the embodiment of the present invention, a welding electrode is provided for performing resistance spot welding of dissimilar metals on the welding element 100. The structure of the welding electrode is as follows: Figure 9 As shown, a ring-shaped limiting structure is provided on the periphery of the welding end surface of the welding electrode. The upper welding electrode 200 (such as Figure 9 As shown), the surface of the limiting structure 202 is a plane or an arc surface, which is used to assist the deformation of the cap structure of the welding element and limit the height of the cap structure after welding. The minimum vertical distance H2 between the limiting structure of the upper welding electrode 200 and the welding end face 201 satisfies the range: 0.5×T≤H2≤2.5×T, preferably the range of H2 is T≤H2≤1.8×T, where T is the first metal thickness.

[0051] When welding a laminated structure of a low-melting-point first metal and a high-melting-point second metal with a melting point difference greater than 700°C, such as aluminum / steel, magnesium / steel, and aluminum / titanium laminated structures, it is difficult to achieve a reliable welding effect due to the huge differences in the physical and chemical properties of the two materials. In order to improve the welding strength of dissimilar metals, the material of the welding element 100 is the same as the second metal material with a high melting point. For example, when welding aluminum / steel dissimilar metals, the welding element 100 is made of, for example, low-alloy high-strength steel. During welding, the upper welding electrode 200 of the resistance spot welding welds the welding element 100 from the first metal side to the second metal. When the shaft of the welding element 100 pierces the first metal and welds to the second metal, the first metal is firmly welded in the joint, achieving reliable welding of the first and second metal laminated structures.

[0052] In one welding embodiment, the first metal 400 is 2 mm thick AA6061-T4 aluminum alloy; the second metal 500 is 1.8 mm thick and 980 MPa strength grade quenched and partitioned steel (Q&P 980). Figure 10 As shown, it includes a first metal cleaning stage and a welding stage. The total duration of the first metal cleaning stage does not exceed 350ms, and the total duration of the welding stage does not exceed 1200ms. In the first metal cleaning stage, 2 to 6 current pulses are usually set to melt at high speed and induce the first metal 400 to splash (sputter). During the splashing process, the first metal in the area covered by the shaft portion 101 of the welding element 100 is expelled into the cap structure 105 (as shown in FIG. Figure 11 During the welding phase, 1 to 2 current pulses are set to form a common nugget between the shaft 101 and the second metal 500. The specific welding process is shown in FIG. Figures 11 to 15 Provide a detailed description.

[0053] like Figure 11The diagram shows the first metal removal stage during dissimilar metal welding. During this stage, the welding end face 201 of the upper welding electrode 200 contacts the electrode positioning groove 111 of the welding element 100, thereby pressing the welding element 100 against the weld spot of the first metal 400. At this point, the upper welding electrode's retaining structure 202 has not yet contacted the welding element 100. Because the end of the cap structure 105 extends at least to the level of the welding element's shaft 103, the electrode compresses the end of the cap structure 105 tightly against the surface of the first metal 400, forming a closed annular cavity surrounding the shaft 101. The welding end face 301 of the lower welding electrode 300 presses against the weld spot of the second metal 500. A welding current is applied to the weld spot to remove the first metal. For example, three 18kA current pulses, each lasting 60ms with a 15ms interval between pulses, are applied. The lower-melting-point first metal 400 is heated and preferentially melts, forming molten first metal 601. Because each pulse of the welding current used to remove the first metal is maintained for an extremely short duration, the resistive heat generated in the weld is insufficient to cause extensive melting of the second metal 500, resulting in only a small, closed melt zone 501 within the second metal 500. Consequently, the molten first metal 601 contacts the surface of the solid second metal 500 and the shaft end face 103. Under the influence of electrode pressure and the liquid pressure of the molten first metal 601, the molten first metal 601 rapidly splashes out of the area covered by the shaft 101. The rapidly dissipated splashing metal 603 is blocked and fully contained by the cap structure 105. In another aspect of the present invention, pressure relief grooves 106 are provided on the sides of the shaft 101 of the welding element 100. During the first metal removal phase, as the molten first metal 601 expands outward, the pressure of the molten first metal 601 upon encountering the pressure relief grooves 106 causes the liquid to splash even more rapidly, thereby enhancing the first metal removal effect in the weld. In addition, the pressure relief groove 106 can also reduce the energy required to remove the first metal, thereby achieving the effect of energy saving in welding.

[0054] As the first metal 400 in the weld spot is discharged to the cap structure 105 through the splashing process, the shaft 101 of the welding element 100 quickly sinks and penetrates the first metal 400. In the process of the shaft 101 quickly penetrating the first metal 400, the deformation process of the cap structure 105 is as follows: Figure 12As shown, during stage A1, the welding element is subjected to pressure F1 from the upper welding electrode 200, causing the top cap 110 to move downward. The end of the cap structure 105 presses against the surface of the first metal 400, causing the cap structure 105 to withstand a force F2 from the first metal 400, thereby supporting the sidewalls of the cap structure 105. During stage B1, the welding element top cap 110 rapidly descends. During this time, the auxiliary deformation zone 104 undergoes plastic deformation to accommodate the descent of the welding element top cap 110. Supported by the sidewalls of the cap structure 105, the cap structure 105 maintains its cavity shape. During stage C1, the welding element top cap 110 fully descends onto the surface of the first metal 400. At this point, the retaining structure 202 of the upper welding electrode 200 contacts the cap structure 105, both assisting in its deformation, allowing it to maintain its cavity shape to fully accommodate the spattered metal, and limiting the height of the cap structure 105 after welding.

[0055] The deformation process of the top cover 110 of the welding element during welding is as follows: Figure 13 As shown. Before welding, Figure 13 In the A2 stage, since the top cover 110 and the center line 120 have an angle α, for example, the angle α is set to 75°, the top cover 101 is tilted toward the shaft 101. During welding, as the shaft 101 penetrates the first metal 400, Figure 13 In stage B2, the electrode positioning groove 111 on the welding element is subjected to pressure F1 from the electrode, while the side of the welding element shaft 101 and the top cover 110 are subjected to force F2 from the first metal 400. Furthermore, due to the resistance heat, the welding element softens. Under the combined action of heat and force, the top cover 110 warps upward, causing the original angle α to expand to α'. Depending on the electrode pressure and welding process, the post-weld angle α' can approach or even exceed 90°, tightly pressing the welding element top cover 110 against the surface of the first metal 400, thereby providing sufficient mechanical locking strength to the weld.

[0056] like Figure 14 The figure shows the weld after the first metal removal stage. The cap structure 105 maintains its intact cavity structure under the pressure of the upper welding electrode's retaining structure 202, fully absorbing the spattered metal 603 ejected from the weld. The shaft 101 of the welding element penetrates the interior of the first metal 400. Under the pressure of the welding end surface 301 of the lower welding electrode 300, the weld area of ​​the second metal 500 is deformed concavely toward the first metal 400, forming a weld interface 602 with the end surface of the welding element's shaft. This weld interface 602 is distributed within the upper and lower surfaces of the first metal, which enhances the weld's adhesion and avoids large gaps between the weld's bonding surfaces. Re-solidified regions 604 of the molten first metal exist in localized areas on both sides of the weld interface 602.

[0057] like Figure 15 The figure shows a cross-sectional view of the joint under the action of current during the welding phase. A welding current, such as a single pulse current with a duration of 400ms and a current intensity of 14kA, is applied to the weld. As the resistive heat in the weld increases, the central region of the weld interface 602 melts, forming a weld nugget 605 with a size of at least 3.5√T (where T is the thickness of the first metal), thereby firmly connecting the shaft portion 101 of the welded component to the second metal 500. Furthermore, as the significant resistive heat generated in the weld during the welding phase further melts the aluminum alloy near the sides of the shaft portion 101, subsequently forming a resolidified region 604. This resolidified region 604 forms an iron-aluminum intermetallic compound layer at the interface between the sides of the shaft portion 101 and the second metal 500, achieving a metallurgical connection and further enhancing the joint strength and sealing performance. Furthermore, after the first metal 400 near the weld melts, the partially molten aluminum alloy is again expelled into the cavity of the cap structure 105 due to the expansion of the liquid aluminum and the further compression of the electrode on the weld.

[0058] like Figure 16 The schematic diagram shows a joint obtained by welding dissimilar metals using the welding element of the present invention. The cap structure 105 receives a large amount of molten first metal discharged from the weld point, successfully preventing the first metal from escaping the weld point. Because the first metal in the weld point is discharged, a direct weld between the welding element shaft 101 and the second metal 500 is achieved, resulting in a weld nugget 605 free of the influence of brittle intermetallic compounds. This avoids the problem of brittle intermetallic compounds seriously affecting the mechanical properties of the joint during dissimilar metal connection, significantly improving the reliability of the dissimilar metal connection. Furthermore, the welding element top cap 110 is firmly pressed against the surface of the first metal 400, achieving a mechanical locking effect on the first metal.

[0059] 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 welding element for resistance spot welding of dissimilar metals, wherein the welding element is used for resistance spot welding a laminated structure of a first metal and a second metal having a melting point difference greater than 700°C. During welding, the welding electrode of the resistance spot welding welds the welding element from the side of the first metal with the lower melting point to the second metal, thereby achieving welding of the dissimilar metal laminated structure. The welding element is made of the same material as the second metal and includes a central shaft and a top cover on one side of the shaft. The welding element is characterized by: An annular cap structure extending from the edge of the top cover, wherein the cap structure bends from the top cover side toward the same direction as the shaft portion and extends at least to the horizontal plane where the end surface of the shaft portion is located; The cap structure is a thin-walled cavity structure with a maximum wall thickness T1 ranging from 0.1 mm to 0.8 mm. An auxiliary deformation zone is provided at the connection area between the cap structure and the top cover. The minimum wall thickness of the auxiliary deformation zone is less than the wall thickness of any other area of ​​the cap structure. One or more concave structures are present on the cross section of the auxiliary deformation zone to reduce the wall thickness. During the welding process, the auxiliary deformation zone undergoes plastic deformation first, causing the auxiliary deformation zone to be elongated and deformed, thereby facilitating the shaft portion to penetrate the first metal. At the same time, the cap structure is ensured to always maintain an annular cavity structure during the welding process to fully accommodate the molten first metal discharged from the weld point. The minimum thickness T2 of the top cover is greater than the maximum wall thickness T1 of the cap structure, and the minimum thickness T2 of the top cover is 0.35 mm to 1.5 mm.

2. A welding element for resistance spot welding of dissimilar metals according to claim 1, characterized in that: The side wall of the cap is provided with "V"-shaped grooves distributed at equal intervals. The "V"-shaped grooves are recessed toward the center of the welding element and extend in the axial direction. The overall height H1 of the "V"-shaped grooves satisfies the range: 0.3×H≤H1<H, where H is the maximum height difference between the outer surface of the top cover of the welding element and the end face of the shaft.

3. The welding element for resistance spot welding of dissimilar metals according to claim 1, characterized in that: The wall thickness of the cap structure gradually increases as it extends from the edge of the top cover to the end of the cap structure.

4. The welding element for resistance spot welding of dissimilar metals according to claim 1, characterized in that: The cap structure is bent in an inverted "U" shape in the axial direction, so that a local area of ​​the cap structure is raised away from the shaft and the top cover side, so that the raised area is higher than the top cover, wherein the minimum protruding height H0 between the top cover and the top cover satisfies the relationship: 0<H0≤2×H, where H is the maximum height difference between the outer surface of the top cover of the welding element and the end face of the shaft.

5. The welding element for resistance spot welding of dissimilar metals according to claim 1, characterized in that: The ratio of the radius R of the end surface of the shaft portion to the radius R2 of the top cover satisfies the relationship: 1.1<R2 / R<2.

2.

6. The welding element for resistance spot welding of dissimilar metals according to claim 1, characterized in that: The edge of the top cover is provided with a plurality of protrusion structures which are distributed in a ring shape with equal intervals and are in the same direction as the shaft portion.

7. The welding element for resistance spot welding of dissimilar metals according to claim 1, characterized in that: The top cover is tilted toward the shaft as a whole, and the auxiliary deformation zone provided on the cap structure forms a positive "V"-shaped structure with the top cover. On a cross section passing through the center line of the welding element, the top cover forms an inclination angle α with the center line of the welding element, and an angle β is formed between the auxiliary deformation zone and the top cover.

8. The welding element for resistance spot welding of dissimilar metals according to claim 1, characterized in that: The shaft is provided with 2 to 5 radially distributed pressure relief grooves spaced at the same angle, the pressure relief grooves extending from the end face of the shaft to the side of the shaft, and the ratio between the circular radius R1 formed by the pressure relief grooves at the position of the minimum distance from the center line of the welding element on the end face of the shaft and the radius R of the end face of the shaft satisfies the range of: 1<R / R1<1.

25.

9. The welding element for resistance spot welding of dissimilar metals according to claim 1, characterized in that: The end surface of the shaft is a spherical structure, and the spherical radius ranges from 30 mm to 150 mm.

10. A welding electrode used for resistance spot welding of dissimilar metals using the welding element according to any one of claims 1 to 9, characterized in that: A ring-shaped limiting structure is arranged on the periphery of the welding end face of the upper welding electrode used on the welding element side. The limiting structure is used to assist the deformation of the cap structure of the welding element and limit the height of the cap structure after welding. The minimum vertical distance H2 between the limiting structure and the welding end face satisfies the range: 0.5×T≤H2≤2.5×T, where T is the first metal thickness.

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