Dissimilar metal joint and resistance welding method therefor

Abstract

The present invention provides a method for resistance welding of dissimilar metal joints, the method comprising the steps of: an outer layer made of iron or an iron-based alloy; and an inner layer having a density of 5 g / cm 3 The present invention welds a laminated structure made of a metal having a melting point of less than 800°C or a light metal having a melting point of less than 800°C. The resistance welding method includes a sputtering step, in which the light metal or low melting point metal in the middle of the laminated structure is detached in the form of sputtering, and a direct joint structure of iron or iron-based alloy layers is formed in the weld interface to complete the welding. The present invention can avoid the formation of brittle intermetallic compounds in the weld interface of dissimilar joints, improve the mechanical performance of the joint, and realize reliable joint between dissimilar metals. The present invention further provides a dissimilar metal joint.

Description

[Technical Field]

[0001] The present invention relates to the field of welding, and more particularly to dissimilar metal joints and resistance welding methods thereof. [Background technology]

[0002] As demands for energy conservation and emission reduction continue to rise, lightweight design has become a key challenge facing the automotive industry. Design options such as all-aluminum bodies have already emerged in a few luxury brand products. However, all-aluminum bodies are expensive, difficult to maintain, and unaffordable for average consumers. Therefore, in mainstream products, the body structure, particularly structural components such as A-pillars, B-pillars, door reinforcement panels, and side members, is still primarily made of steel. High-strength steel, and even ultra-high-strength steel, are increasingly replacing traditional steel. Automotive companies and consumers are gradually discovering that the use of light alloy materials, including aluminum alloys and magnesium alloys, in parts such as shock absorbers, wheelhouse end panels, floors, engines, and exterior body components offers an acceptable solution in terms of both cost and performance. Therefore, automotive manufacturing methods incorporating steel and light metals are becoming increasingly popular. The importance of joining processes for steel and light metal dissimilar joints is becoming increasingly apparent.

[0003] Conventional body-in-white manufacturing processes often involve resistance welding to join steel plates. However, the physical properties of steel, especially high-strength steel, differ significantly from those of aluminum alloys and magnesium alloys. The melting point of steel generally exceeds 1,400°C, while the melting points of aluminum and magnesium alloys are often below 700°C. Therefore, conventional resistance welding processes often result in defects such as large amounts of porosity and cracks in the welded joints between steel and aluminum or magnesium alloys, and large amounts of brittle iron-aluminum or iron-magnesium intermetallic compounds are formed in the welded area, significantly affecting the mechanical strength of the joints.

[0004] Some prior art techniques use a three-layer composite structure of a steel workpiece, an aluminum workpiece, and a steel workpiece, or a steel part, an aluminum workpiece, and a steel workpiece. The steel part is typically a specially designed rivet, including specially designed solid, hollow, and semi-hollow rivets. When welding these together, the welding area is first heated or the steel part is driven and held in contact with and pressed against the aluminum part at high speed, softening or semi-molten the intermediate aluminum plate at high temperature. The welding equipment then applies greater pressure to force the softened or semi-molten aluminum alloy out of the welding area, completing a weld directly between the outermost steel plate or steel part and the steel workpiece. However, the inventors have discovered that prolonged contact between the heated aluminum alloy and the steel plate during this process results in the formation of a large amount of brittle intermetallic compounds, making it difficult for the high-temperature, plastic aluminum alloy to be efficiently forced out of the welding area, thereby affecting the quality of the weld. The reason for this is that when dissimilar metals such as aluminum and steel are welded, iron has a high solid solubility in aluminum, but aluminum is almost insoluble in iron, so a large amount of solid solution cannot be formed between iron and aluminum. As a result, a large amount of brittle iron-aluminum intermetallic compounds (e.g., FeAl3, Fe2Al5, FeAl2, FeAl, Fe3Al, etc.) is quickly formed at the weld seam during welding. These brittle intermetallic compounds usually form a layer structure and are distributed at the weld interface. When the compound layer is subjected to external stress, it is very easy for cracks to form and promote crack growth, which is thought to have a significant adverse effect on the final joint strength. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 7-328774 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-236673 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a resistance welding method for dissimilar metal joints that solves the problems of low weld strength when dissimilar metals are welded by resistance spot welding, the presence of a large amount of brittle intermetallic compounds at the weld interface, and the likelihood of cracks occurring. [Means for solving the problem]

[0007] Another object of the present invention is to provide a dissimilar metal joint having a secure bond.

[0008] According to one aspect of the present invention, there is provided a method for resistance welding a dissimilar metal joint, the method comprising: welding a dissimilar metal laminate structure, the laminate structure including a first metal plate and a second metal plate, the first metal plate being pure iron or an iron-based alloy, and the second metal plate having a density of 5 g / cm 3 The outer plates of the stack structure are first-class metal plates, and the second-class metal plates are located between the first-class metal plates. The resistance welding method includes a step of discharging the second-class metal plates from a welding area and a welding step, and the step of discharging the second-class metal plates includes a sputtering step. In the sputtering step, a sputtering current and an electrode pressure are applied to the stack structure to heat the stack structure in the welding area, the second-class metal melts and sputters away from the welding area under the action of pressure, and the first-class metals approach each other under the action of resistance heat and pressure, whereby the second-class metal plates are completely scattered in at least a portion of the welding area. In the welding step, a weld interface is formed in at least a portion of the welding area where only the first-class metal plates are in contact, and a metallurgical bond is generated at the weld interface.

[0009] Optionally, the sputtering current comprises one or more, preferably 2 to 5, current pulses, the duration of a single current pulse being 200 ms or less, preferably 50 ms to 120 ms.

[0010] Furthermore, the sputtering current intensity I1 = K1 * I0, where I0 is the current intensity when resistance welding is performed individually on the first class metal plates in the dissimilar metal joint to form a weld nugget cross-sectional diameter ≧ 4√t, t is the thickness of the thinner of the first class metal plates, and the range of values ​​that K1 can take is 0.8 to 3.5.

[0011] Optionally, in the sputtering step, after the second type metal plate is separated from the welding area in a sputtering manner, a welding interface is formed by contacting only the first type metal plate, and it is preferable that the thickness of the second type metal layer remaining at the welding interface is ≦0.15 mm, and the equivalent diameter of the welding interface is ≧0.5 times the diameter of the electrode end face, and the thickness of the second type metal layer remaining therein is ≦0.05 mm.

[0012] Optionally, during the welding step, a welding current and electrode pressure are applied to the laminate structure, the intensity of the welding current being less than or equal to the intensity of the sputtering current.

[0013] Furthermore, the welding current intensity I2 = K2 * I0, where I0 is the current intensity when resistance welding is performed individually on the first-class metal plates in the dissimilar metal joint to form a weld nugget cross-sectional diameter ≧ 4√t, t is the thickness of the thinner of the first-class metal plates, and K2 can range from 0.5 to 2.5. Controlling the welding current intensity can ensure the weld strength of the dissimilar joint obtained by the resistance welding method.

[0014] Optionally, the interval between the sputtering current and the welding current is between 0 ms and 200 ms.

[0015] Optionally, the method further comprises a tempering step after the welding step, wherein an electrode provides a tempering current to the weld area. The tempering process can improve the mechanical performance of the joint.

[0016] Furthermore, the tempering current intensity I3 = K3 * I0, where I0 is the current intensity when resistance welding is performed individually on the first class metal plates in the dissimilar metal joint to form a weld nugget cross-sectional diameter ≧ 4√t, t is the thickness of the thinner plate among the first class metal plates, and the range of values ​​that K3 can take is 0.4 to 1.8.

[0017] Optionally, the method further includes a preheating step before the sputtering step, in which an electrode provides a preheating current to the area to be welded. The preheating step can melt the aluminum alloy or magnesium alloy in the intermediate layer more quickly and promote the occurrence of the sputtering step.

[0018] Furthermore, the preheating current intensity I4 = K4 * I0, where I0 is the current intensity when resistance welding is performed individually on the first class metal plates in the dissimilar metal joint to form a weld nugget cross-sectional diameter ≧ 4√t, t is the thickness of the thinner plate among the first class metal plates, and the range of values ​​that K4 can take is 0.2 to 1.3.

[0019] Optionally, the welding method further includes a preheating step before the sputtering step, in which an electrode provides a preheating current to an area to be welded in the preheating step, and a tempering step after the welding step, in which an electrode provides a tempering current to the welded area in the tempering step, wherein a sputtering current intensity I1=K1*I0, a welding current intensity I2=K2*I0, a preheating current intensity I4=K4*I0, and a tempering current intensity I3=K3*I0, K1 having a range of possible values ​​from 0.8 to 3.5, K2 having a range of possible values ​​from 0.5 to 2.5, K4 having a range of possible values ​​from 0.2 to 1.3, and K3 having a range of possible values ​​from 0.4 to 1.8, and K1≧K2≧K3≧K4.

[0020] Furthermore, the welding current, the preheating current, and the tempering current each have at least one electric pulse, and the application time is 800 ms or less, preferably 200 to 700 ms.

[0021] Furthermore, the interval between the welding current or the preheating current and the sputtering current, and the interval between the tempering current and the welding current are 0 to 200 ms, preferably 5 to 80 ms.

[0022] Optionally, a plating layer is present on at least one surface of the first type metal plate, and the plating layer is a zinc-based plating layer or an aluminum-based plating layer.

[0023] Optionally, the structural form of the laminated structure is a three-layer group or a five-layer group, and two outer layer groups of the three-layer group are single layers or adjacent overlapping layers of the first-class metal plate, while the inner layer group is a single layer or adjacent overlapping layers of the second-class metal plate; and two outer layer groups and an intermediate layer group of the five-layer group are single layers or adjacent overlapping layers of the first-class metal plate, and another two layer groups are single layers or adjacent overlapping layers of the second-class metal plate, located respectively between the outer layer groups and the intermediate layer group, and in the welding step, adjacent first-class metal plates are welded by direct contact with each other under electrode pressure.

[0024] Furthermore, at least two layers of the first type metal plates in the laminated structure are formed by bending the same metal plate, and the bending position is outside the welding area.

[0025] Optionally, the second type metal plate is any one of aluminum, aluminum alloy, magnesium, and magnesium alloy, or a combination of at least two layers of aluminum, aluminum alloy, magnesium, magnesium alloy, and magnesium alloy.

[0026] Optionally, the first type metal plate has a tensile strength of 2500 MPa or less, a micro Vickers hardness of 650 Hv or less, and a single layer thickness range of 0.5 mm to 2.5 mm.

[0027] Optionally, the thickness of the single layer or adjacently overlapped second class metal plates between the adjacently spaced first class metal plates is ≦4.5 mm, and the total thickness of the single layer or adjacently overlapped first class metal plates is ≦5.5 mm.

[0028] Optionally, a single layer or adjacent superposed layers of the first type metal plate satisfy the condition that the product A of the plate thickness (unit: mm) and tensile strength (unit: MPa) satisfies 100≦A≦5000.

[0029] Optionally, one of the two outer plates of the laminate structure has a smaller value of the product of plate thickness (in mm) and tensile strength (in MPa) than the other.

[0030] According to another aspect of the present invention, there is provided a dissimilar metal joint, the dissimilar metal joint having a laminated structure and including a first type metal plate and a second type metal plate, the first type metal plate being pure iron or an iron-based alloy, and the second type metal plate having a density of 5.0 g / cm 3 the outer plate of the laminated structure is a Class 1 metal plate, and the Class 2 metal plate is located between the Class 1 metal plates. From the appearance of the dissimilar metal joint, the thickness of the indentation region on the electrode end surfaces of the dissimilar metal joint is less than the sum of the thicknesses of the Class 1 metal plates, and the thickness of the joint structure gradually increases from the edge of the indentation region on the electrode end surfaces to the outside, finally presenting the original combined stack structure. From the cross-section of the dissimilar metal joint, the indentation region on the electrode end surfaces and its surrounding material are characterized by a thin middle and thick sides, the middle indentation region on the electrode end surfaces is made only of the Class 1 metal plate, and interatomic bonds occur at the interface between the Class 1 metal plates to form a permanent bond, and the thickness of the stack structure gradually increases from the edge of the indentation region to the outside, and the Class 2 metal plate gradually increases from a small thickness between the Class 1 metal plates to the original thickness of the Class 2 metal plate.

[0031] Optionally, a "jet-like" solidification structure is present between the first type metal plates outside the indentation area due to molten sputtering of the second type metal plates.

[0032] Optionally, an intermetallic compound (IMC layer) is generated at the contact interface between the second type metal plate and the first type metal plate in an indented edge region of the electrode end surface.

[0033] Furthermore, at least two layers of the first type metal plates in the laminated structure are formed by bending the same metal plate, and the bending is located outside the welding area.

[0034] According to yet another aspect of the embodiment of the present invention, there is provided a dissimilar metal joint obtained by the resistance welding method of any of the above embodiments. [Effects of the Invention]

[0035] The beneficial effects of the embodiments of the present invention are as follows:

[0036] (1) The sputtering feature of the method of the present invention allows for effective removal of light metals from the stack structure, thereby avoiding the adverse effects of light metals on the joint. While it is generally recognized in the field that sputtering during resistance spot welding is a defect that should be avoided, the present invention utilizes the sputtering phenomenon. By applying a sputtering current to the weld area, the second-class metal located in the interlayer is rapidly melted. The molten liquid metal instantly breaks through the plastic deformation zone around the liquid zone through the combined action of electrode pressure and current heating, and leaves the weld area in the form of sputtering. This leaves only a small amount of second-class metal in the weld area, and thus no second-class metal at all. This ensures intimate contact between the first-class metals, avoids the formation of a large amount of brittle intermetallic compounds (IMCs) at the weld interface in subsequent welding steps, and effectively improves welding quality. The method of the present invention is simple, efficient, and widely applicable, with high joint quality.

[0037] (2) The sputtering step of the present invention can be carried out with multiple pulses, which can achieve the effect of heating and ejecting the light metal multiple times, thereby achieving maximum ejection of the light metal in the stack structure, and thereby satisfying the bond of the stack structure containing multiple layers of light metal.

[0038] (3) The method of the present invention can realize high-quality joining of light metals and steel plates in a stack structure with multiple layers spaced apart, and is not limited by the type, composition, or processing method of the light metal, or the strength of the steel plate, and can realize joining of magnesium alloys, aluminum alloy cold-rolled plates, aluminum alloy profiles, aluminum castings, and cases where ultra-high strength hot-formed steel is present in between.

[0039] (4) Compared with the conventional direct resistance spot welding method of steel and aluminum, the method of the present invention avoids direct contact between the electrode and the light metal, thereby significantly improving the service life of the electrode and the joining quality of the joint.

[0040] (5) Compared with the same type of conventional technology, the method of the present invention does not require specialized manufacturing of steel metal parts with locking features, does not require piercing of light metal or steel members, and has a very wide application market. [Brief explanation of the drawings]

[0041] [Figure 1] 1 is a schematic diagram of a laminated structure of an example of a dissimilar metal joint. FIG. [Figure 2a] FIG. 10 is a schematic diagram of a laminated structure of another embodiment of a dissimilar metal joint. [Figure 2b] FIG. 10 is a schematic diagram of a laminated structure of yet another example of a dissimilar metal joint. [Figure 3] FIG. 10 is a schematic diagram of a laminated structure of yet another example of a dissimilar metal joint. [Figure 4] FIG. 2 is a schematic diagram of current, electrode pressure, and time in an embodiment of a method for resistance welding a dissimilar metal joint. [Figure 5a] 1A-1C are schematic diagrams illustrating the evolution of a weld joint at different stages of welding in an embodiment of a method for resistance welding a dissimilar metal joint. [Figure 5b] 1A-1C are schematic diagrams illustrating the evolution of a weld joint at different stages of welding in an embodiment of a method for resistance welding a dissimilar metal joint. [Figure 5c] 1A-1C are schematic diagrams illustrating the evolution of a weld joint at different stages of welding in an embodiment of a method for resistance welding a dissimilar metal joint. [Figure 5d]1A-1C are schematic diagrams illustrating the evolution of a weld joint at different stages of welding in an embodiment of a method for resistance welding a dissimilar metal joint. [Figure 5e] 1A-1C are schematic diagrams illustrating the evolution of a weld joint at different stages of welding in an embodiment of a method for resistance welding a dissimilar metal joint. [Figure 6] 1 is a structural schematic diagram of a welded joint in one embodiment of a dissimilar metal joint. FIG. [Figure 7] FIG. 10 is a structural schematic diagram of a welded joint of another embodiment of a dissimilar metal joint. [Figure 8a] 10A to 10C are structural schematic diagrams of welded joints in two other different embodiments of dissimilar metal joints. [Figure 8b] 10A to 10C are structural schematic diagrams of welded joints in two other different embodiments of dissimilar metal joints. [Figure 9] FIG. 2 is a diagram showing the structure of a peel fracture surface of a welded joint in Example 1 of a resistance welding method for a dissimilar metal joint. [Figure 10] FIG. 10 is a cross-sectional metallographic diagram of a welded joint in Example 2 of the resistance welding method for a dissimilar metal joint. [Figure 11] FIG. 10 is a tensile shear load-displacement curve diagram of a welded joint in Example 2 of the resistance welding method for a dissimilar metal joint. [Figure 12] FIG. 10 is a cross-sectional metallographic diagram of a welded joint in Example 4 of the resistance welding method for a dissimilar metal joint. [Figure 13] FIG. 10 is a tensile shear load-displacement curve diagram of a welded joint in Example 4 of the resistance welding method for a dissimilar metal joint. [Figure 14] FIG. 10 is a cross-sectional metallographic diagram of a welded joint in Example 5 of the resistance welding method for a dissimilar metal joint. [Figure 15] FIG. 10 is a tensile shear load-displacement curve diagram of a welded joint in Example 5 of the resistance welding method for a dissimilar metal joint. [Figure 16] FIG. 10 is a cross-sectional metallographic diagram of a welded joint in Example 7 of the resistance welding method for a dissimilar metal joint. [Figure 17] FIG. 10 is a tensile shear load-displacement curve diagram of a welded joint in Example 7 of the resistance welding method for a dissimilar metal joint. [Figure 18] FIG. 10 is a cross-sectional metallographic diagram of a welded joint in Example 8 of the resistance welding method for a dissimilar metal joint. [Figure 19]FIG. 10 is a tensile shear load-displacement curve diagram of a welded joint in Example 8 of the resistance welding method for a dissimilar metal joint. [Figure 20] 1 is a cross-sectional metallographic diagram of a welded joint in an embodiment of a resistance welding method for a dissimilar metal joint. FIG. [Figure 21] FIG. 16 is a cross-sectional metallographic diagram of a welded joint in Example 10 of the resistance welding method for dissimilar metal joints. [Figure 22] FIG. 11 is a cross-sectional metallographic diagram of a welded joint in Example 11 of the resistance welding method for dissimilar metal joints. [Figure 23] FIG. 12 is a cross-sectional metallographic diagram of a welded joint in Example 12 of the resistance welding method for dissimilar metal joints. [Figure 24] FIG. 1 is a cross-sectional metallographic diagram of a welded joint according to a comparative example of a resistance welding method for a dissimilar metal joint. [Figure 25] FIG. 10 is a tensile shear load-displacement curve diagram of a welded joint according to a comparative example of a resistance welding method for a dissimilar metal joint. [Figure 26] 1 is a schematic diagram of each region of a dissimilar metal joint. The purpose of the above drawings is to explain the technical idea of ​​the present invention so as to facilitate the understanding of those skilled in the art, and the drawings only include parts related to the technical features of the present invention, and do not show the whole or all details of the invention. DETAILED DESCRIPTION OF THE INVENTION

[0042] Hereinafter, the embodiments of the present invention will be described in more detail with reference to the drawings using specific examples.

[0043] The present invention will be further described below with reference to specific examples. It should be understood that these examples are merely illustrative of the present invention and do not limit the scope of the present invention. Furthermore, the drawings are schematic, and therefore, the relevant dimensions of the method and joint of the present invention are not limited to the dimensions or proportions of the schematic. In the claims and specification of this patent, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any actual relationship or order between these entities or operations. Furthermore, the terms "comprise," "include," "includes," or any other variant thereof are intended to include a non-exclusive inclusion, whereby a process, method, article, or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent in such process, method, article, or device. Terms such as "upper," "lower," "outer," and "inner" are merely used to describe relative positions and do not imply specific internal or external limitations. Absent more limitations, an element qualified by the phrase "comprising one ..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0044] The dissimilar metal joint has a laminated structure as shown in Figure 1, and this laminated structure includes first-class metal plates 3 and 5 and a second-class metal plate 4. The first-class metal plates 3 and 5 may be referred to as the upper plate 3 and the lower plate 5, respectively, and the second-class metal plate 4 may be referred to as the inner plate 4. The upper plate 3 is made of the first-class metal, the inner plate 4 is made of the second-class metal, and the lower plate 5 is made of the first-class metal. The first-class metal from which the upper and lower plates 3 and 5 are manufactured is pure iron or an iron-based alloy. The specific plate material can be selected from a variety of factors. For example, in terms of mechanical properties, the tensile strength is 2500 MPa or less, the micro-Vickers hardness is 650 Hv or less, and in terms of dimensions, the thickness of the single layer is in the range of 0.5 mm to 2.5 mm. Alternatively, the product of the thickness (unit: mm) and the tensile strength (unit: MPa), A, is in the range of 100 to 5000. Taking all these factors into consideration, in a preferred embodiment, the values ​​A of the upper and lower plates 3 and 5 are unequal. Either surface of either of the first-class metal plates may be bare, or may have an aluminum- or zinc-based plating layer, such as a zinc-plated layer, an aluminum-silicon plating layer, a zinc-aluminum plating layer, or a zinc-nickel plating layer, or a lead-tin plating layer. For the inner plate 4, the second-class metal from which the plate is manufactured is selected from a material with a density of 5 g / cm. 3 The specific plate material can be selected from a number of factors, for example, in terms of composition, any one of aluminum, aluminum alloy, magnesium, and magnesium alloy, or a combination of at least two layers, and in terms of dimensions, the thickness must be 4 mm or less.

[0045] The upper plate 3, inner plate 4, and lower plate 5 are each a single-layer plate structure, or in other embodiments, a composite structure in which multiple layers are adjacently stacked, and such a composite structure in which multiple layers are adjacently stacked may be made of different plate materials that meet the above-mentioned constraints. To help improve welding quality, regardless of the type of laminated structure, it is preferable that the total thickness of the first-class metal plates be 5 mm or less, and the total thickness of the second-class metal plates be 4 mm or less.

[0046] The upper plate 3, inner plate 4, and lower plate 5 of a dissimilar metal joint can all be installed as a multi-layer structure. In the dissimilar metal joint (before welding) shown in FIG. 2a, the upper plate 3 has a three-layer structure, and the lower plate 5 has a two-layer structure. In the dissimilar metal joint (before welding) shown in FIG. 2b, the inner plate 4 has a two-layer structure. Here, the multi-layer structures of the upper plate 3, inner plate 4, and lower plate 5 may be made of the same type of material, or may be a combination of multiple different types of materials that satisfy the parameter restrictions in the above-mentioned embodiments. For example, the multi-layer structures of the upper plate 3 and lower plate 5 may be a combination of laminations of low-carbon steel and pure iron, and the multi-layer structure of the inner plate 4 may be a combination of laminations of one or at least two of aluminum, aluminum alloy, magnesium, and magnesium alloy.

[0047] As shown in Figure 3, another type of dissimilar metal joint may be a five-layer composite structure consisting of upper plate 3 and lower plate 5 made of a Class 1 metal, inner plate 4 made of a Class 2 metal, and inner plate 13 made of a Class 1 metal, where each layer may be a single plate or a composite structure in which multiple layers of plate material are adjacently superimposed. For such a structure, in the welding step, the adjacent, spaced-apart Class 1 metal plates, i.e., upper plate 3 and inner plate 13, and inner plate 13 and lower plate 5, are respectively in contact and welded.

[0048] The following describes the welding process of an embodiment of a resistance welding method for dissimilar metal joints, taking the three-layer laminate structure shown in FIG. 1 as an example. Referring to FIG. 5, during the resistance welding process, the upper electrode 1 and the lower electrode 2 apply current and electrode pressure to the laminate structure. In FIG. 5, the horizontal axis represents time (ms), and the vertical axis represents electrode pressure (N) or current (kA). Here, the dashed line represents the change in pressure over time, and the solid line represents the change in current over time. The resistance welding process includes a preheating stage from t1 to t2, a sputtering stage from t3 to t4, a welding stage from t5 to t6, and a tempering stage from t6 to t7. In each stage, the upper electrode 1 and the lower electrode 2 apply a corresponding preheating current I4, sputtering current I1, welding current I2, and tempering current I3 to the laminate structure, respectively. In FIG. 4, the electrode pressure changes stepwise over time. In the sputtering step, a sputtering current and an electrode pressure are applied to the stack structure to heat the stack structure in the welding area, the second type metal melts and is sputtered away from the welding area under the action of pressure, and the first type metals approach each other under the action of resistance heat and pressure, whereby the second type metal sheets are completely scattered in at least a portion of the welding area. In the welding step, a welding interface is formed in which only the first type metal sheets are in contact in at least a portion of the welding area, and a metallurgical bond is generated at the welding interface. In another embodiment, the electrode pressure shown in Table 1 can be maintained constant throughout the entire welding process.

[0049] Here, the sputtering current and electrode pressure are applied by a welding electrode, and the welding electrode has an electrode end surface. The complete sputtering of the second-class metal sheet during the sputtering process includes a situation in which a trace amount of the second-class metal remains at the weld interface formed by the contact of the first-class metal sheet, and the trace amount of the second-class metal is mixed with the plating layer or base element on the surface of the first-class metal, so that when the cross section of the weld is observed with the naked eye, only a stack structure made of the first-class metal is seen, and during subsequent welding, the trace amount of the second-class metal is completely fused and incorporated into the weld nugget formed by the first-class metal sheet, without affecting the quality of the weld, i.e., the trace amount of the second-class metal sheet does not form a brittle intermetallic compound with the first-class metal sheet and does not affect the performance of the weld nugget.

[0050] The occurrence of metallurgical bonding is the mixing of the first-class metal and the second-class metal elements at the weld interface, and the situation in which the original contact surface is fused and disappears due to the joining of only the first-class metal. Metallurgical bonding includes diffusion bonding and weld nugget bonding in the examples described below.

[0051] First, the reference current intensity I0 is defined. I0 is the current intensity when single-pulse resistance welding is performed individually on the upper sheet 3 and the lower sheet 5 to form a weld nugget with a cross-sectional diameter ≧4√t, where t is the thickness of the thinner sheet.

[0052] An optional pre-pressure step is applied before the electrode applies current to the laminated structure. The pre-pressure step brings the stacked workpieces into intimate contact and reduces the resistance between the sheets. The pre-pressure pressure, as shown in Figure 5, can be lower than the electrode pressure used in the sputtering and welding steps described below.

[0053] During the preheating stage, as shown in FIG. 5a, the electrode applies a preheating current to the laminated structure, forcing the stacked workpieces into closer contact and reducing the resistance between the sheets. The preheating current has at least one electrical pulse, and its duration is typically 800 ms or less, preferably 200-700 ms. The preheating current is preferably such that sputtering does not occur. The preheating current intensity I4 numerically satisfies I4 = K4 * I0, with K4 ranging from 0.2 to 1.3. In some embodiments, welding of the laminated structure can still be completed even if the preheating stage is omitted.

[0054] In the sputtering step, as shown in Figures 5b and 5c, the electrodes apply a sputtering current to the laminated structure. The sputtering current melts the inner sheet 4 material within the weld zone into liquid metal 6, some of which leaves the weld zone to form spatters 7, creating a region between the first-class metal sheets 3 and 5 where no second-class metal is present. The current softens the first-class metal sheets 3 and 5, forcing them together under the pressure of the upper electrode 1 and the lower electrode 2. The second-class metal sheets 4 are pressed and deformed, and the thickness of the second-class metal remaining at the weld zone 8 is typically ≤ 0.15 mm, preferably ≤ 0.05 mm. The equivalent diameter of the weld zone 8 is typically 0.5 times the diameter of the end face of the upper electrode 1 or the lower electrode 2. The sputtering current intensity I1 numerically satisfies I1=K1*I0, and the range of possible values ​​for K1 is 0.8 to 3.5. The sputtering current may be a single pulse or multiple pulses, with the number of pulses preferably being 2 to 5, and the duration of a single pulse being 200 ms or less, preferably 50 ms to 120 ms.

[0055] In the welding stage, as shown in FIG. 5d, the electrode applies a welding current to the laminated structure. The welding current intensity is lower than in the sputtering stage, but the electrode pressure is higher. The welding current may be single-pulse or multi-pulse, and its application time is generally 800 ms or less, preferably 200-700 ms. The welding current intensity I2 satisfies I2 = K2 * I0, and the range of possible values ​​for K2 is 0.5-2.5. The first-class metal sheets 3 and 5 continue to heat under the action of the welding current, and the metal at the contact surface 8 melts, forming a steel weld nugget 9 with a diameter reaching 3.5√t, further achieving a metallurgical bond between the first-class metal sheets 3 and 5. A small amount of intermetallic compound (IMC) layer is formed at the interface where a portion of the liquid metal remaining around the weld interface of the inner sheet 4 comes into contact with the adjacent steel. To bring the upper sheet 3 and the lower sheet 5 into sufficient contact after sputtering occurs, an interval of 0 to 200 ms can be set between the sputtering current and the welding current, and preferably 10 to 70 ms.

[0056] During the tempering step, as shown in FIG. 5e, the electrode applies a tempering current to the laminate structure to warm and temper the weld interface, achieving a uniform weld structure and removing residual stress. The tempering current has at least one electrical pulse, and its application time is typically 800 ms or less, preferably 200-700 ms. The tempering current does not preferentially cause sputtering, and the tempering current intensity I3 numerically satisfies I3 = K3 * I0, with K3 ranging from 0.4 to 1.8. In some embodiments, welding of the laminate structure can be completed even if the tempering step is omitted. The tempering current I3 is typically 15 kA or less, preferably 4-12 kA.

[0057] In the above process, K1, K2, K3, and K4 should satisfy K1≧K2≧K3≧K4.

[0058] The current is provided by the welding electrode, and its specific value may be an effective current, a peak current, or an average current, which is readily understood in the art. The welding electrode functions as part of resistance welding equipment. Resistance spot welding equipment can be realized by commercial frequency welding machines, intermediate frequency welding machines, or AC welding machines, which are widely used in industry. Here, the resistance spot welding equipment may be a stationary spot welding equipment or a robot-driven automated equipment, which generally includes welding clamps of C-shaped, X-shaped, and other structural shapes, and is usually realized by a robot or automated member. The welding electrode may be made of any material having electrical and thermal conductivity, such as a copper alloy including a copper chromium (CuCr) alloy, a copper chromium zirconium (CuCrZr) alloy, a copper alloy with aluminum oxide particles, or various other copper alloys that can be used as an electrode material. The welding surface may be spherical, cross-sectional, or have other special shapes, such as an electrode cap with a protruding or concave end face.

[0059] According to the specific circumstances of different embodiments, a time interval can be set between the preheating current and the sputtering current, between the sputtering current and the welding current, and between the welding current and the tempering current, and the setting range of the interval is 0 to 200 ms, preferably 5 to 80 ms. During the interval period, the welding electrode maintains a pressure holding state.

[0060] In some other embodiments, for example, if the upper and lower plates 3 and 5 are made of thick, hot-formed steel and the inner plate 4 is made of a very thin aluminum plate, the sputtering stage of the resistance welding process is very short, allowing the aluminum material constituting the inner plate 4 to quickly separate from the weld interface in a short time. In this case, the sputtering current I1 and the welding current I2 can be maintained at the same value. Furthermore, the duration of the welding stage is short, and the upper and lower plates 3 and 5 made of hot-formed steel are bonded together in the form of a diffusion weld without melting in the weld area. In such embodiments, no weld nugget is formed in the joint structure.

[0061] The resistance welding method described above is not limited to three-layer stacked structures, but can also be applied to the stacked structures shown in Figures 2a, 2b, and 3, where I0 is the current strength when single-pulse resistance welding is performed on individual Class 1 metal plates to form a weld nugget with a cross-sectional diameter of ≥ 4√t, t is the thickness of the thinner of the Class 1 metal plates, as shown in Figure 2a for example, t is the thickness of the thinner of the three-layer plate in upper plate 3 and the two-layer plate in lower plate 5, and Figure 3 is the thickness of the thinner of the upper plate 3, inner plate 13, and lower plate 5.

[0062] According to the above embodiment, a dissimilar metal joint provided in another aspect of the present invention can be obtained. A typical joint structure is as shown in Figure 6, where the dissimilar metal joint has a laminated structure and includes a first metal plate and a second metal plate, of which the first metal plate is pure iron or an iron-based alloy and includes an upper plate 3 and a lower plate 5, and the second metal plate has a density of 5.0 g / cm 3 The dissimilar metal joint is composed of an element or alloy with a melting point of less than 800°C or less, including an inner plate 4. From the outside, the thickness between the indentation regions 10, 11 on the electrode end surfaces of the dissimilar metal joint is less than the sum of the thicknesses of the first-class metal plates 3, 5, and the thickness of the joint structure gradually increases from the edges of the indentation regions 10, 11 on the electrode end surfaces outward, finally resuming the original stack structure. From the cross-section of the dissimilar metal joint, the indentation regions 10, 11 on the electrode end surfaces and the surrounding material are characterized by a thin middle and thick sides. The middle indentation region of the indentation region on the electrode end surfaces consists only of the first-class metal plate, and the first-class metal plate has atomic bonding at the interface to form a permanent bond. This permanent bond may be a solidified weld nugget 9 or a metal interface where solid-state diffusion bonding has occurred. The thickness of the laminated structure gradually increases from the edge of the indentation outward, with the outer first-class metal sheet exhibiting a V-shape, and the second-class metal sheet gradually increasing from a smaller thickness to the original thickness of the second-class metal sheet between the V-shaped structures formed by the first-class metal sheets. The second-class metal sheet deformed during the sputtering process typically meets the characteristic of a joint structure in which the equivalent diameter of the region with a thickness of ≦0.15 mm within the indentation regions 10 and 11 on the electrode end surface is at least 0.5 times the diameter of the end surface of the upper electrode 1 or the lower electrode 2.

[0063] Typically, between the inner plate 4 and the upper plate 3 or lower plate 5, there is a jet-like solidified structure formed when the inner plate 4, which is a second-class metal plate, melts during the sputtering process and the sputtering 7 solidifies.

[0064] As shown in Figure 6, in the indented edge region of the electrode end face, the surface of the area where the inner sheet 4 made of Class 2 metal meets the upper sheet 3 and lower sheet 5 made of Class 1 metal melts, forming an intermetallic compound (IMC) layer 12. Outside the intermetallic compound 12, the pressed and deformed Class 2 metal sheet has an equivalent diameter of the area of ​​the Class 2 metal sheet (including the weld nugget) with a thickness of ≤ 0.15 mm, which is typically 0.5 times or more the end face diameter of the upper electrode 1 or lower electrode 2. In some embodiments, the IMC layer may be formed by diffusion between the Class 2 metal sheet and the Class 1 metal sheet.

[0065] In other embodiments, the upper plate 3, inner plate 4, and lower plate 5 in the dissimilar metal joint may be single-layer or multi-layer, and may have a three-layer structure as shown in Figure 6, or may have a five-layer structure as shown in Figure 7, in which an intermediate layer 13 made of a Class 1 metal is added between the inner plate 4 made of multiple layers of Class 2 metal plates.

[0066] As shown in Figures 8a and 8b, another type of dissimilar metal joint may be one in which one folded Class 1 metal plate constitutes at least two layers of the stack structure, and the folded portion 14 is located outside the welding area. Such a stack structure may be a three-layer structure as shown in Figure 8a, in which the outer side of the stack structure is made of Class 1 metal plate 5 with a folded portion 14, and an inner plate 4 made of Class 2 metal plate is inserted into the folded overlap area. Alternatively, it may be a five-layer structure as shown in Figure 8b, in which the stack structure includes an upper plate 3 and a lower plate 5 made of Class 1 metal, of which the lower plate 5 has a folded portion 14, and two inner plates 4 made of Class 2 metal are inserted between the upper plate 3 and the lower plate 5 and into the space formed by the folded structure of the lower plate 5, respectively.

[0067] 26 to more easily understand the various regions of the welded joint described above. Welded joint a is a structure including a first-class metal sheet and a second-class metal sheet, forming a spot joint. Welded region b includes the region where the welding electrode welds the stack structure and achieves the joint through the effect of resistance heat. Indentation region c on the electrode end surface is a pressure-receiving region formed when the end surface of the welding electrode directly contacts and presses the dissimilar metal joint during the welding process. Weld interface region d is a region where only the first-class metal sheets are in contact with each other after the second-class metal sheet has separated. The welded joint also includes a light-metal thinning region e, which is a region where the original thickness of the second-class metal sheet gradually thins adjacent to the weld interface region.

[0003] An embodiment of a resistance welding method for dissimilar metal joints will now be described with reference to examples.

[0068] Example 1 The upper plate 3 is made of CR210 cold-rolled steel with a thickness of 0.8 mm and a tensile strength of less than 400 MPa, the inner plate 4 is made of AA6016 aluminum alloy with a thickness of 0.8 mm, and the lower plate 5 is made of CR420 cold-rolled steel with a thickness of 1.0 mm and a tensile strength of less than 600 MPa. The first welding electrode 1 and the second welding electrode 2 are both ordinary spherical electrodes, and the welding end faces of the electrodes are 6 mm. The specific welding process parameters are as shown in Table 1. After welding was completed, the peeling fracture surface was as shown in Figure 9, with solidified light metal spatter 7 present at the interface between the inner plate 4 and the lower plate 5, circling the weld point and distributing radially outwards. The results of the tensile shear load test of the welded joint were as shown in Table 2. Because a strong steel-to-steel weld nugget was formed between the Class 1 metal plates 3, 5 and the Class 2 metal plate 4, the tensile shear load test showed that the joint had an extremely high tensile shear strength of approximately 3775 N.

[0069] Example 2 The upper plate 3 was made of 1.0 mm thick CR210 cold-rolled steel with a tensile strength of less than 400 MPa, and the inner plate 4 was made of 1.2 mm thick AA5754 aluminum alloy. Unlike the materials used in Example 1, the inner plate 4 was a 5 series aluminum alloy, and the lower plate 5 was made of 1.0 mm thick CR420 cold-rolled steel with a tensile strength of less than 600 MPa. The first and second welding electrodes 1 and 2 were both conventional spherical electrodes, with a 6 mm weld end face. The specific welding process parameters are listed in Table 1, and the cross-sectional metallography of the joint is shown in Figure 10. After welding, a tensile shear load test was performed on the joint, and the tensile shear load-displacement curve is shown in Figure 11. The tensile shear load test showed that the joint had an extremely high tensile shear strength of 7292.4 N during the significant plastic deformation stage of the shear-tensile process. Table 2 shows the results of the tensile shear peak load test.

[0070] Example 3 The upper plate 3 is made of 1.0 mm thick Q&P980 cold-rolled steel, which generally has a tensile strength of 1000 MPa or more. The inner plate 4 is made of 1.5 mm thick AA5754 aluminum alloy. The lower plate 5 is made of 1.2 mm thick Q&P1180 cold-rolled high-strength steel, which generally has a tensile strength of 1200 MPa or more. The first welding electrode 1 and the second welding electrode 2 are both ordinary spherical electrodes, and the welding end faces of the electrodes are 6 mm. The specific welding process parameters are as shown in Table 1. After welding, a tensile shear load test was conducted on the joint. The test showed that the joint also had an extremely high tensile shear strength of about 7557.6 N. The peak tensile shear load test results are shown in Table 2.

[0071] Example 4 The upper plate 3 was a 1.0 mm thick CR420 cold-rolled steel with a tensile strength of 600 MPa or less. The inner plate 4 was a 1.6 mm thick AA6016 aluminum alloy. The lower plate 5 was a 1.2 mm thick Q&P1180 cold-rolled high-strength steel with a tensile strength of typically 1200 MPa or more. The first and second welding electrodes 1 and 2 were both conventional spherical electrodes, with a 6 mm weld end face. The specific welding process parameters are shown in Table 1. The cross-sectional metallographic diagram of the joint is shown in Figure 12. After welding, a tensile shear load test was performed on the joint, and the tensile shear load-displacement curve was shown in Figure 13. The tensile shear load test showed significant plastic deformation in the joint, with an extremely high strength of approximately 8995.0 N. The peak tensile shear load test results are shown in Table 2.

[0072] Example 5 The upper plate 3 was a 1.0 mm thick CR420 cold-rolled steel with a tensile strength of less than 600 MPa. The inner plate 4 was a 2.0 mm thick AA6016 aluminum alloy. The lower plate 5 was a 1.2 mm thick Q&P1180 cold-rolled high-strength steel with a tensile strength typically greater than 1200 MPa. The first and second welding electrodes 1 and 2 were both conventional spherical electrodes, with a 6 mm weld end face. The specific welding process parameters are shown in Table 1. The metallographic diagram of the joint cross section is shown in Figure 14. After welding, a tensile shear load test was performed on the joint, and the tensile shear load-displacement curve is shown in Figure 15. The tensile shear load test showed that the joint had an extremely high tensile shear strength of approximately 9508.4 N. The peak tensile shear load test results are shown in Table 2.

[0073] Example 6 The upper plate 3 is a 1.0 mm thick Q&P980 cold-rolled high-strength steel sheet with a tensile strength typically exceeding 1000 MPa. The inner plate 4 is a 2.0 mm thick AA6061 aluminum alloy sheet. The lower plate 5 is a 1.4 mm thick CR420 cold-rolled steel sheet with a tensile strength of less than 600 MPa, with a galvanized surface. The first and second welding electrodes 1 and 2 are both conventional spherical electrodes, with a 6 mm weld end face. The specific welding process parameters are listed in Table 1. After welding, a tensile shear load test was conducted on the joint. The test results showed that the joint had an extremely high tensile shear strength of approximately 10,437.8 N. The peak tensile shear load test results are shown in Table 2.

[0074] Example 7 The upper plate 3 was a 1.0 mm thick CR420 steel with a tensile strength of less than 600 MPa. The inner plate 4 was a 2.0 mm thick AZ31 magnesium alloy. The lower plate 5 was a 1.2 mm thick, hot-formed ultra-high-strength steel with a tensile strength typically exceeding 1300 MPa. The first and second welding electrodes 1 and 2 were both conventional spherical electrodes, with a 6 mm weld end face. The specific welding process parameters are listed in Table 1. The cross-sectional metallographic diagram of the joint is shown in Figure 16. After welding, a tensile shear load test was performed on the joint, and the tensile shear load-displacement curve was shown in Figure 17. The tensile shear load test revealed that the joint had an extremely high tensile shear strength of approximately 6970.0 N. The peak tensile shear load test results are listed in Table 2.

[0075] Example 8 A 1.0 mm thick Q&P980 steel plate with a tensile strength typically exceeding 1000 MPa was used as the upper plate 3, a 2.4 mm thick 6061 aluminum alloy section was used as the inner plate 4, and a 1.4 mm thick hot-formed ultra-high-strength steel plate was used as the lower plate 5. The specific welding process parameters are shown in Table 1, and the joint cross-sectional metallography is shown in Figure 18. After welding, a tensile shear load test was conducted on the joint, and the tensile shear load-displacement curve is shown in Figure 19. The tensile shear load test showed that the joint had an extremely high tensile shear strength of approximately 9883.4 N. The peak load results of the tensile shear test are shown in Table 2.

[0076] Example 9 A 1.0 mm thick Q&P980 steel plate was used as the upper plate 3, a 1.6 mm thick AA6061 aluminum alloy plate was used as the inner plate 4, and a 1.2 mm thick combination of hot-formed steel with a tensile strength of 2000 MPa and hardened Q&P1180 steel with a tensile strength of 1180 MPa was selected as the lower plate 5. The hot-formed steel plate was used as the upper layer of the lower plate 5, and the Q&P1180 steel plate was used as the lower layer of the lower plate 5. Welding was performed using three 16 kA sputtering current I1 pulses, each lasting 80 ms and spaced 20 ms apart. After the sputtering current, a 30 ms cooling period was allowed. A 13 kA welding current I2 was applied and lasted for 300 ms. The metallographic diagram of the resulting joint is shown in Figure 20. In this example, I0 was 8.2 kA (welding time: 280 ms). The weld nugget structure 9 consisted entirely of steel and contained no bright intermetallic compounds.

[0077] Example 10 A 1.0 mm thick DP780 steel was used as the upper plate 3, a 2.0 mm thick AZ31 magnesium alloy was used as the inner plate 4, and a 1.4 mm thick hot-formed steel with a tensile strength of 2000 MPa and a 1.2 mm thick Q&P1180 hardened steel with a tensile strength of 1180 MPa were combined to form the lower plate 5. Of these, the hot-formed steel was used as the upper layer of the upper plate 5, and the Q&P1180 steel was used as the lower layer of the lower plate 5. Welding was performed using three 19 kA sputtering current I1 pulses, each lasting 80 ms and spaced 20 ms apart. The sputtering current I1 was followed by a 30 ms cooling period. A 13 kA welding current I2 was applied and lasted for 400 ms. The metallographic diagram of the resulting joint is shown in Figure 21. In this example, I0 was 8.7 kA (welding time: 280 ms). The weld nugget structure 9 consisted entirely of steel and contained no bright intermetallic compounds.

[0078] Example 11 A 1mm thick DP780 steel plate was used as the upper plate 3, a 0.8mm thick 5754 aluminum alloy plate and a 1.6mm thick AA6061 aluminum alloy plate were used as the inner plate 4, and a 1.2mm thick Q&P1180 hardened steel plate with a tensile strength of 1200MPa was inserted between them as the inner plate 13. A 1mm thick DP780 steel plate was used as the lower plate 5 to form a five-layer composite structure, of which the 5754 aluminum alloy was placed above the inner plate 13 and the AA6061 aluminum alloy was placed below the inner plate 13. A 6 kA preheating current I4 was used for 100 ms preheating, followed by three 20 kA pulses as the sputtering current I1, each lasting 85 ms and spaced 20 ms apart. The sputtering current I1 was followed by a 30 ms cooling period. A 15 kA welding current I2 was applied, lasting 400 ms. The resulting joint metallography is shown in Figure 22. In this example, I0 was 8.6 kA (300 ms welding time). The weld nugget structure 9 consisted entirely of steel and contained no bright intermetallic compounds.

[0079] Example 12 The upper plate 3 was a 1 mm thick DP780 steel, the inner plate 4 was a composite of a 0.8 mm thick 5754 aluminum alloy and a 1.6 mm thick AA6061 aluminum alloy, and the lower plate 5 was a 1.2 mm thick, 1200 MPa tensile strength Q&P1180 hardened steel. A 6 kA preheating current (I4) was used for 100 ms preheating, followed by three 21 kA pulses (I1), each lasting 80 ms and spaced 20 ms apart. The sputtering current (I2) was then applied, with a 30 ms cooling period. A 15 kA welding current (I2) was applied, lasting 380 ms. The resulting joint metallography is shown in Figure 23. In this example, I0 was 8.5 kA (welding time 280 ms). The weld nugget structure (9) consisted entirely of steel and contained no bright intermetallic compounds.

[0080] (Comparative Example) For comparison with the examples of the present invention, this example uses a conventional resistance spot welding method to weld aluminum and steel dissimilar metals. During welding, the first and second welding electrodes are both spherical, with a spherical radius of 100 mm and a welding surface diameter of 10 mm. Optimized welding parameters were selected for welding, including a welding pressure of 5600 N, a welding current of 17 kA, a welding time of 100 ms, five pulse currents, a pulse current interval of 20 ms, and a post-weld hold time of 300 ms. The joint metallography is shown in Figure 24. For welding, a 1.2 mm thick Q&P1180 steel was selected as the first metal plate 5, and a 1.6 mm thick AA6016 was selected as the second metal plate 4. After welding, a tensile shear load test was carried out on the joint. The test results are shown in Table 2 and Figure 25. The peak tensile shear load of the joint was only 3265.8 N, which was much lower than the peak load of the joint of the present invention. As can be seen from the load-displacement curve, the joint displacement was very small, about 0.3 mm, which showed significant brittleness and was much smaller than the joint provided by the present invention.

[0081] [Table 1]

[0082] [Table 2]

[0083] It should be understood that the above examples, combined with the drawings, are intended to allow those skilled in the art to better understand the technical idea of ​​the present invention, and do not specifically limit the embodiments and protection scope of the present invention. Within the scope of the claims of the present invention, modifying or substituting related parts, materials, and method steps, and combining different embodiments when no conflict occurs, all fall within the protection scope of the present invention.

Claims

1. A resistance welding method for a dissimilar metal joint for welding a dissimilar metal laminate structure, the laminate structure including a first-class metal plate and a second-class metal plate, the first-class metal plate being pure iron or an iron-based alloy, and the second-class metal plate being a metal having a density of 5 g / cm ３ a metal alloy having a melting point of less than 800°C or less than 800°C, an outer plate of the laminated structure is a first class metal plate, the second class metal plate is located between the first class metal plates, and the resistance welding method includes a step of removing the second class metal plate from a welding area and a welding step, The step of discharging the second type metal plate includes a sputtering step, In the sputtering step, a sputtering current and an electrode pressure are applied to the stack structure to heat the stack structure in the welding area, the second type metal melts and separates from the welding area in the form of sputtering under the action of pressure, and the first type metals approach each other under the action of resistance heat and pressure, whereby the second type metal plate is completely scattered in at least a part of the welding area, forming a welding interface constituted by only the first type metal plate in contact, and the thickness of the second type metal layer remaining at the welding interface is ≦0.15 mm; In the welding step, a welding interface is formed in which only the first type metal plate is in contact with the at least a portion of the welding region, and a metallurgical bond is generated at the welding interface. The sputtering current intensity I1 = K1 * I0, where I0 is the current intensity when resistance welding is performed individually on the first class metal plates in the dissimilar metal joint to form a weld nugget cross-sectional diameter ≧ 4√t, t is the thickness of the thinner plate among the first class metal plates, and the range of values ​​that K1 can take is 0.8 to 3.

5.

1. A resistance welding method for dissimilar metal joints, comprising:

2. 2. The method of resistance welding of dissimilar metal joints according to claim 1, wherein the sputtering current includes one or more current pulses, and the duration of a single current pulse is 200 ms or less.

3. 2. The resistance welding method for dissimilar metal joints according to claim 1, wherein in the sputtering step, the thickness of the second type metal layer left at the weld interface is ≦0.05 mm, and the equivalent diameter of the weld interface is ≧0.5 times the diameter of the electrode end surface of the welding electrode.

4. 2. The resistance welding method for a dissimilar metal joint according to claim 1, wherein in the welding step, a welding current and an electrode pressure are applied to the laminated structure, and the intensity of the welding current is equal to or less than the intensity of the sputtering current.

5. A resistance welding method for a dissimilar metal joint for welding a dissimilar metal laminate structure, wherein the laminate structure includes a first class metal plate and a second class metal plate, the first class metal plate is pure iron or an iron-based alloy, the second class metal plate is a simple substance or alloy having a density of less than 5 g / cm 3 or a melting point of less than 800°C, the outer plate of the laminate structure is a first class metal plate, and the second class metal plate is located between the first class metal plates, the resistance welding method comprising a step of discharging the second class metal plate from a welding area and a welding step, The step of discharging the second type metal plate includes a sputtering step, In the sputtering step, a sputtering current and an electrode pressure are applied to the stack structure to heat the stack structure in the welding area, the second type metal melts and separates from the welding area in the form of sputtering under the action of pressure, and the first type metals approach each other under the action of resistance heat and pressure, whereby the second type metal plate is completely scattered in at least a part of the welding area, forming a welding interface constituted by only the first type metal plate in contact, and the thickness of the second type metal layer remaining at the welding interface is ≦0.15 mm; In the welding step, a welding interface is formed in which only the first type metal plate is in contact with the at least a portion of the welding region, and a metallurgical bond is generated at the welding interface. a resistance welding method for a dissimilar metal joint, characterized in that I2=K2*I0, where I2 is the intensity of the welding current, I0 is the current intensity when single-pulse resistance welding is performed individually on the first class metal plates in the dissimilar metal joint to form a weld nugget with a cross-sectional diameter of ≧4√t, t is the thickness of the thinner of the first class metal plates, and K2 can have a value in the range of 0.5 to 2.

5.

6. A resistance welding method for a dissimilar metal joint for welding a dissimilar metal laminate structure, wherein the laminate structure includes a first class metal plate and a second class metal plate, the first class metal plate is pure iron or an iron-based alloy, the second class metal plate is a simple substance or alloy having a density of less than 5 g / cm 3 or a melting point of less than 800°C, the outer plate of the laminate structure is a first class metal plate, and the second class metal plate is located between the first class metal plates, the resistance welding method comprising a step of discharging the second class metal plate from a welding area and a welding step, The step of discharging the second type metal plate includes a sputtering step, In the sputtering step, a sputtering current and an electrode pressure are applied to the stack structure to heat the stack structure in the welding area, the second type metal melts and separates from the welding area in the form of sputtering under the action of pressure, and the first type metals approach each other under the action of resistance heat and pressure, whereby the second type metal plate is completely scattered in at least a part of the welding area, forming a welding interface constituted by only the first type metal plate in contact, and the thickness of the second type metal layer remaining at the welding interface is ≦0.15 mm; In the welding step, a welding interface is formed in which only the first type metal plate is in contact with the at least a portion of the welding region, and a metallurgical bond is generated at the welding interface.

2. The method for resistance welding a dissimilar metal joint according to claim 1, wherein an interval between the sputtering current and the welding current is 0 ms to 200 ms.

7. The method of claim 1, further comprising a tempering step after the welding step, wherein an electrode applies a tempering current to the weld area during the tempering step.

8. A resistance welding method for a dissimilar metal joint for welding a dissimilar metal laminate structure, wherein the laminate structure includes a first class metal plate and a second class metal plate, the first class metal plate is pure iron or an iron-based alloy, the second class metal plate is a simple substance or alloy having a density of less than 5 g / cm 3 or a melting point of less than 800°C, the outer plate of the laminate structure is a first class metal plate, and the second class metal plate is located between the first class metal plates, the resistance welding method comprising a step of discharging the second class metal plate from a welding area and a welding step, The step of discharging the second type metal plate includes a sputtering step, In the sputtering step, a sputtering current and an electrode pressure are applied to the stack structure to heat the stack structure in the welding area, the second type metal melts and separates from the welding area in the form of sputtering under the action of pressure, and the first type metals approach each other under the action of resistance heat and pressure, whereby the second type metal plate is completely scattered in at least a part of the welding area, forming a welding interface constituted by only the first type metal plate in contact, and the thickness of the second type metal layer remaining at the welding interface is ≦0.15 mm; In the welding step, a welding interface is formed in which only the first type metal plate is in contact with the at least a portion of the welding region, and a metallurgical bond is generated at the welding interface. a tempering step after the welding step, wherein the electrode provides a tempering current to the weld area; A resistance welding method for a dissimilar metal joint, characterized in that tempering current intensity I3 = K3 * I0, where I0 is the current intensity when single-pulse resistance welding is performed individually on the first class metal plates in the dissimilar metal joint to form a weld nugget with a cross-sectional diameter of ≧ 4√t, t is the thickness of the thinner plate among the first class metal plates, and the range of possible values ​​for K3 is 0.4 to 1.

8.

9. The method of claim 1, further comprising a preheating step before the sputtering step, wherein an electrode provides a preheating current to the area to be welded.

10. A resistance welding method for a dissimilar metal joint for welding a dissimilar metal laminate structure, wherein the laminate structure includes a first class metal plate and a second class metal plate, the first class metal plate is pure iron or an iron-based alloy, the second class metal plate is a simple substance or alloy having a density of less than 5 g / cm 3 or a melting point of less than 800°C, the outer plate of the laminate structure is a first class metal plate, and the second class metal plate is located between the first class metal plates, the resistance welding method comprising a step of discharging the second class metal plate from a welding area and a welding step, The step of discharging the second type metal plate includes a sputtering step, In the sputtering step, a sputtering current and an electrode pressure are applied to the stack structure to heat the stack structure in the welding area, the second type metal melts and separates from the welding area in the form of sputtering under the action of pressure, and the first type metals approach each other under the action of resistance heat and pressure, whereby the second type metal plate is completely scattered in at least a part of the welding area, forming a welding interface constituted by only the first type metal plate in contact, and the thickness of the second type metal layer remaining at the welding interface is ≦0.15 mm; In the welding step, a welding interface is formed in which only the first type metal plate is in contact with the at least a portion of the welding region, and a metallurgical bond is generated at the welding interface. a preheating step prior to the sputtering step, wherein an electrode provides a preheating current to an area to be welded; A resistance welding method for a dissimilar metal joint, characterized in that preheating current intensity I4 = K4 * I0, where I0 is the current intensity when single-pulse resistance welding is performed individually on the first class metal plates in the dissimilar metal joint to form a weld nugget cross-sectional diameter ≧ 4√t, t is the thickness of the thinner plate among the first class metal plates, and the range of possible values ​​for K4 is 0.2 to 1.

3.

11. A resistance welding method for a dissimilar metal joint for welding a dissimilar metal laminate structure, wherein the laminate structure includes a first class metal plate and a second class metal plate, the first class metal plate is pure iron or an iron-based alloy, the second class metal plate is a simple substance or alloy having a density of less than 5 g / cm 3 or a melting point of less than 800°C, the outer plate of the laminate structure is a first class metal plate, and the second class metal plate is located between the first class metal plates, the resistance welding method comprising a step of discharging the second class metal plate from a welding area and a welding step, The step of discharging the second type metal plate includes a sputtering step, In the sputtering step, a sputtering current and an electrode pressure are applied to the stack structure to heat the stack structure in the welding area, the second type metal melts and separates from the welding area in the form of sputtering under the action of pressure, and the first type metals approach each other under the action of resistance heat and pressure, whereby the second type metal plate is completely scattered in at least a part of the welding area, forming a welding interface constituted by only the first type metal plate in contact, and the thickness of the second type metal layer remaining at the welding interface is ≦0.15 mm; In the welding step, a welding interface is formed in which only the first type metal plate is in contact with the at least a portion of the welding region, and a metallurgical bond is generated at the welding interface. The resistance welding method further includes a preheating step before the sputtering step, in which an electrode provides a preheating current to an area to be welded in the preheating step, a welding step after the sputtering step, and a tempering step after the welding step, in which an electrode provides a tempering current to the weld area in the tempering step, wherein a sputtering current intensity I1=K1*I0, a welding current intensity I2=K2*I0, a preheating current intensity I4=K4*I0, and a tempering current intensity I3=K3*I0, where I0 is the difference and K1≧K2≧K3≧K4.

12. A resistance welding method for dissimilar metal joints as described in Claim 11, characterized in that the welding current, the preheating current, and the tempering current have at least one electric pulse, and the action time is 800 ms or less.

13. The resistance welding method for a dissimilar metal joint according to claim 11, characterized in that there is an interval of 0 to 200 ms between the welding current or the preheating current and the sputtering current, and between the tempering current and the welding current.

14. 2. The resistance welding method for a dissimilar metal joint according to claim 1, wherein a plating layer is present on at least one surface of the first type metal plate, and the plating layer is a zinc-based plating layer or an aluminum-based plating layer.

15. 2. The resistance welding method for dissimilar metal joints according to claim 1, wherein the structural form of the laminated structure is a three-layer group or a five-layer group, and the two outer layer groups of the three-layer group are single layers or adjacent overlapping layers of the first class metal plate, while the inner layer group is a single layer or adjacent overlapping layers of the second class metal plate, and the two outer layer groups and the middle layer group of the five-layer group are single layers or adjacent overlapping layers of the first class metal plate, and the other two layer groups are single layers or adjacent overlapping layers of the second class metal plate, and are located between the outer layer groups and the middle layer group, respectively.

16. 16. The resistance welding method for a dissimilar metal joint according to claim 1 or 15, wherein at least two layers of the first type metal plate in the laminated structure are formed by bending the same metal plate, and the bending position is outside the welding area.

17. 16. The resistance welding method for a dissimilar metal joint according to claim 1 or 15, wherein the second type metal plate is any one of aluminum, aluminum alloy, magnesium, and magnesium alloy, or a combination of at least two layers of these.

18. 2. The method for resistance welding a dissimilar metal joint according to claim 1, wherein the thickness of the single layer or adjacently overlapped second class metal plates between the adjacently spaced first class metal plates is ≦4.5 mm, and the total thickness of the single layer or adjacently overlapped first class metal plates is ≦5.5 mm.

19. 2. The resistance welding method for a dissimilar metal joint according to claim 1, wherein one of the two outer plates of the laminate structure has a smaller value of the product of the plate thickness (unit: mm) and the tensile strength (unit: MPa) than the other.

20. The laminated structure includes a first-class metal plate and a second-class metal plate, the first-class metal plate being pure iron or an iron-based alloy, and the second-class metal plate having a density of 5.0 g / cm ３ a metal alloy having a melting point of less than 800°C or less than 800°C, an outer plate of the laminated structure is a first class metal plate, and the second class metal plate is located between the first class metal plates, When viewed from the cross section of the dissimilar metal joint, the indentation area of ​​the electrode end surface and its surrounding material are characterized by being thin in the middle and thick on both sides, the thickness of the indentation area of ​​the electrode end surface of the dissimilar metal joint is less than the sum of the thicknesses of the first-class metal plates, the intermediate indentation area of ​​the indentation area of ​​the electrode end surface is made only of the first-class metal plate, and interatomic bonds occur at the interface between the first-class metal plates to form a bond, the thickness of the stack structure gradually increases from the edge of the indentation area to the outside, and the second-class metal plate gradually increases from a small thickness between the first-class metal plates to the original thickness of the second-class metal plate, A dissimilar metal joint, characterized in that at least two layers of the first type metal plates in the laminated structure are formed by bending the same metal plate, and the bending is located outside the welding area.

21. A dissimilar metal joint as described in claim 20, characterized in that a ``jet-like'' solidification structure caused by molten sputtering of the second type metal plate is present between the first type metal plate and the second type metal plate outside the indentation area.

22. 21. The dissimilar metal joint according to claim 20, wherein an intermetallic compound (IMC layer) is generated at the contact interface between the second type metal plate and the first type metal plate in the indentation edge region of the electrode end surface.

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