Resistance spot welding method for dissimilar metals

Abstract

The application discloses a resistance spot welding method for dissimilar metals. The application relates to the technical field of dissimilar metal welding, and the resistance spot welding method comprises the following steps: preparing base materials for welding, including a first base material and a second base material; the first base material and the second base material are lap welded, and the first base material is provided with a containing groove on one side facing the second base material; high-entropy alloy powder is arranged in the containing groove; and the first base material and the second base material are welded through resistance spot welding. By arranging the high-entropy alloy powder interlayer between the first base material and the second base material, the high-entropy alloy powder in a molten state is used as a connecting layer of the first base material and the second base material, so that the defects of a welded joint can be reduced, the connecting strength of the first base material and the second base material can be improved, and the mechanical properties and reliability of the welded joint are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of dissimilar metal welding, in particular to a dissimilar metal resistance spot welding method. BACKGROUND

[0002] With the increasing requirements of energy saving, emission reduction, safety performance and driving performance of automobiles, lightweight of automobiles has become the mainstream trend. The use of lightweight materials is one of the main ways to achieve lightweight of automobiles. Aluminum alloy, magnesium alloy, high-strength steel and composite material are the main lightweight materials of automobiles. Since aluminum alloy has the advantages of low density, high specific strength, good corrosion resistance and easy recycling, it has become a potential lightweight material for automobiles. Therefore, in the design and production of automobiles, the use of lightweight materials such as aluminum alloy and high-strength steel, and the use of aluminum / steel composite structure in the vehicle body are the most direct and effective methods to achieve lightweight. This makes the reliability of high-strength steel / aluminum alloy dissimilar metal connection an urgent problem to be solved. Due to the significant differences in physical and chemical properties between aluminum alloy and high-strength steel, the weldability of aluminum / steel dissimilar metal is severely deteriorated, and the joint performance cannot meet the requirements of automobile performance.

[0003] In the related art, friction stir spot welding, laser brazing, diffusion welding and ultrasonic spot welding can realize the connection of aluminum / steel dissimilar metal, but have the disadvantages of poor connection strength, low production efficiency and difficulty in automation, and cannot be used on a large scale in the vehicle body production line. SUMMARY

[0004] The present application aims to at least solve one of the problems in the prior art or related art.

[0005] In view of this, the present application provides a dissimilar metal resistance spot welding method, wherein by setting a high-entropy alloy powder interlayer between the first base material and the second base material, and using the melted high-entropy alloy powder as a connecting layer of the first base material and the second base material, the defects of the welded joint can be reduced, the connection strength of the first base material and the second base material can be improved, and the mechanical properties and reliability of the welded joint are improved.

[0006] Specifically, the technical scheme comprises the following:

[0007] The present application provides a dissimilar metal resistance spot welding method, which comprises the following steps:

[0008] Preparation of welding base material, including first base material and second base material;

[0009] The first base material and the second base material are lap welded, and the first base material is provided with a containing groove on one side facing the second base material;

[0010] A high-entropy alloy powder is arranged in the containing groove;

[0011] welding the first base material and the second base material by resistance spot welding.

[0012] Optionally, the welding the first base material and the second base material by resistance spot welding comprises:

[0013] The resistance spot welding comprises a first electrode and a second electrode, the first electrode is located on the side of the first base material away from the second base material, and the second electrode is located on the side of the second base material away from the first base material.

[0014] A first electrode strip is arranged between the first base material and the first electrode, and a second electrode strip is arranged between the second base material and the second electrode.

[0015] Optionally, when the first base material is an aluminum alloy, the main component of the first electrode strip is stainless steel; and when the second base material is a high-strength steel, the main component of the second electrode strip is low-carbon steel.

[0016] Optionally, the accommodation groove is a circular groove, and the high-entropy alloy powder is arranged in the circular groove.

[0017] Optionally, the diameter of the circular groove is 6mm to 10mm, and the depth of the circular groove is 0.1mm to 0.3mm.

[0018] Optionally, the accommodation groove comprises a plurality of circular ring grooves, and the high-entropy alloy powder is arranged in the plurality of circular ring grooves.

[0019] Optionally, the maximum outer circle diameter of the plurality of circular ring grooves is 6mm to 10mm, the groove width of the circular ring groove is 1mm, the interval between adjacent two circular ring grooves is 1mm, and the depth of the circular ring groove is 0.1mm to 0.3mm.

[0020] Optionally, the high-entropy alloy powder comprises Fe, Al, Cr, Si, Co and Ni, and the mass percentage is 16%Fe, 10.7%Al, 20.5%Cr, 14%Si, (15%-17%)Co, (21.8%-23.8%)Ni.

[0021] Optionally, during the resistance spot welding, the spot welding parameters are obtained by an orthogonal test method, and the spot welding parameters comprise: a spot welding current of 13kA to 16kA, a welding time of 300ms to 450ms, and an electrode pressure of 3kN to 4.5kN.

[0022] Optionally, the thickness of the first base material is 1.5mm to 2mm, and the thickness of the second base material is 1mm to 1.5mm.

[0023] The resistance spot welding method of dissimilar metals provided by the embodiment of the present application, wherein the resistance spot welding method comprises preparing a first base material and a second base material, machining a containing groove on the first base material, and setting high-entropy alloy powder in the containing groove, then overlapping the first base material and the second base material, and making the high-entropy alloy powder located between the first base material and the second base material, and welding by resistance spot welding. By fusing the high-entropy alloy powder between the first base material and the second base material, the reliability and stability of the connection between the dissimilar metals can be improved, the metallurgical defects are reduced, the connection strength of the interface of the first base material and the second base material is improved, and at the same time, the high-entropy alloy powder can effectively improve the structure of the intermetallic compound of the spot welding joint interface, reduce the possibility of cracking along the intermetallic compound of the interface during the tensile test, and further improve the tensile strength of the welded joint.

[0024] The above description is only a summary of the technical solutions of the present application. In order to more clearly understand the technical means of the present application, the embodiments can be implemented according to the content of the specification, and in order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the following specific embodiments of the present application are described. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0026] Figure 1 The step flow chart of the resistance spot welding method of dissimilar metals according to an embodiment of the present application;

[0027] Figure 2 The working schematic diagram of the resistance spot welding of dissimilar metals according to an embodiment of the present application;

[0028] Figure 3 The schematic diagram of a containing groove according to an embodiment of the present application;

[0029] Figure 4 The schematic diagram of another containing groove according to an embodiment of the present application.

[0030] Wherein, Figures 2 to 4 The correspondence between the reference signs and the component names in the drawings is as follows:

[0031] 101 first electrode, 102 first electrode strip, 103 first base material, 104 high-entropy alloy powder, 105 second base material, 106 second electrode strip, 107 second electrode, 108 circular groove, 109 annular groove. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0033] Before the embodiments of the present application are described in further detail, it should be understood that the directional terms such as "upper", "lower", "side" in the embodiments of the present application do not limit the protection scope of the present application.

[0034] In order to make the technical solutions and advantages of the present application clearer, the embodiments of the present application will be described in further detail below with reference to the drawings.

[0035] Figure 1 A flowchart of steps of a resistance spot welding method of dissimilar metals according to an embodiment of the present application.

[0036] As shown in Figure 1 A resistance spot welding method of dissimilar metals according to an embodiment of the present application, the resistance spot welding method comprises the following steps:

[0037] Step 1, preparing base materials for welding, including a first base material and a second base material;

[0038] Step 2, the first base material and the second base material are lap welded, and the first base material is provided with a containing groove on the side facing the second base material;

[0039] Step 3, setting high-entropy alloy powder in the containing groove;

[0040] Step 4, welding the first base material and the second base material by resistance spot welding.

[0041] Among them, the resistance spot welding method includes preparing the first base material 103 and the second base material 105, machining the containing groove on the first base material 103, and setting the high-entropy alloy powder 104 in the containing groove, then lap joining the first base material 103 and the second base material 105, and making the high-entropy alloy powder 104 located between the first base material 103 and the second base material 105, and welding by resistance spot welding. By fusing the high-entropy alloy powder 104 between the first base material 103 and the second base material 105, the reliability and stability of the connection between the dissimilar metals can be improved, the metallurgical defects are reduced, the connection strength of the interface of the first base material 103 and the second base material 105 is improved, and at the same time, the high-entropy alloy powder 104 can effectively improve the structure of the intermetallic compound at the interface of the spot welding joint, reduce the possibility of cracking along the intermetallic compound at the interface during the tensile test, and thus improve the tensile strength of the welded joint.

[0042] Specifically, the first base material 103 and the second base material 105 are made of different materials. In this embodiment, the first base material 103 is aluminum alloy, and the second base material 105 is high-strength steel, both of which are commonly used materials for automobile bodies. Resistance spot welding equipment is used to complete the resistance spot welding connection of the first base material 103 and the second base material 105. A high-entropy alloy powder 104 interlayer is added between the contact surfaces of the first base material 103 and the second base material 105. Due to the high-entropy effect and retarded diffusion effect of the high-entropy alloy powder 104, the formation of compounds between the metals (between the first base material 103 and the second base material 105) is suppressed, and the reaction system easily forms a simple disordered solid solution structure. Therefore, it can effectively improve the microstructure, reduce welding defects, and thus improve the welding quality of the welded joint, thereby ensuring the reliability of the connection between the first base material 103 and the second base material 105. When high-strength steel and aluminum alloy are welded, a brittle intermetallic compound intermediate layer exists in the joint, resulting in low connection strength. By adding high-entropy alloy powder between the lap joint of aluminum alloy (first base material 103) and high-strength steel (second base material 105), the composition of the intermediate layer compound can be improved, the brittleness of the spot weld joint can be reduced, and the connection quality of the joint can be improved.

[0043] For example, in the first base material 103 and the second base material 105, the receiving groove is usually processed on the base material with poor hardness to reduce processing difficulty and improve processing efficiency.

[0044] Figure 2 This is a schematic diagram of resistance spot welding of dissimilar metals according to an embodiment of the present invention.

[0045] In one feasible implementation, such as Figure 2 As shown, welding the first base material 103 and the second base material 105 by resistance spot welding includes:

[0046] Resistance spot welding includes a first electrode and a second electrode. The first electrode is located on the side of the first base material away from the second base material, and the second electrode is located on the side of the second base material away from the first base material.

[0047] A first electrode strip is provided between the first base material and the first electrode, and a second electrode strip is provided between the second base material and the second electrode.

[0048] In this application, the first base material 103 is aluminum alloy and the second base material 105 is high-strength steel. Therefore, the main component of the material of the first electrode strip 102 is stainless steel, and the main component of the material of the second electrode strip 106 is low-carbon steel. Selecting different electrode strips according to different base materials can increase resistance heat, realize heat compensation in the spot welding process, reduce metal spatter in dissimilar metal resistance spot welding, protect the first electrode 101 and the second electrode 107, and improve the service life of the first electrode 101 and the second electrode 107.

[0049] It can be understood that the main component of the electrode strip refers to the mass ratio of metal elements close to the composition of stainless steel or low carbon steel, and a small amount of copper is mixed and added in the composition of the electrode strip, so that the electrical conductivity and corrosion resistance of the electrode strip can be improved, and the service life of the electrode strip can be improved.

[0050] Specifically, when the first base material 103 is an aluminum alloy, since the aluminum alloy has good heat dissipation performance, it is not conducive to conduct the heat of the current of the first electrode 101 into the layer of the intermediate high-entropy alloy powder 104, therefore, the first electrode strip 102 with the main component of stainless steel is arranged between the first electrode 101 and the aluminum alloy (the first base material 103), since the stainless steel material has a high resistivity, resistance heat can be generated when the current passes through, therefore, the heat loss during welding caused by the heat dissipation performance of the aluminum alloy can be compensated, that is, the resistance heat can be increased, and the welding effect can be ensured. The second electrode strip 106 with the main component of low carbon steel is arranged between the second electrode 107 and the high-strength steel (the second base material 105), the addition of the second electrode strip 106 not only generates additional resistance heat, but also effectively prevents the adhesion of the second electrode 107 to the second base material 105, so that the surface of the welding point is well shaped. At the same time, by arranging the first electrode strip 102 of stainless steel between the first electrode 101 and the aluminum alloy, and arranging the second electrode strip 106 of low carbon steel between the second electrode 107 and the high-strength steel, the metal particle impurities adhered to the first electrode 101 and the second electrode 107 are avoided, on the one hand, the generation of spatter can be avoided, the metal vapor and waste slag generated during welding are reduced, the influence of welding on the environment is reduced, the requirements of production on environmental protection and energy saving are met, on the other hand, the service life of the first electrode 101 and the second electrode 107 can be improved, and the maintenance time of the first electrode 101 and the second electrode 107 can be prolonged.

[0051] As shown in Figure 2 , the first electrode strip 102 and the second electrode strip 106 are in U shape, the first electrode strip 102 is wrapped on the first electrode 101, so that the first electrode strip 102 is located between the first electrode 101 and the first base material 103, and similarly, the second electrode strip 106 is wrapped on the second electrode 107, so that the second electrode strip 106 is located between the second electrode 107 and the second base material 105.

[0052] Figure 3 A schematic view of a containing groove according to an embodiment of the present application.

[0053] In a feasible implementation manner, as shown in Figure 3 , the containing groove is a circular groove 108, and the high-entropy alloy powder is arranged in the circular groove 108.

[0054] The diameter of the circular groove 108 is 6mm to 10mm, and the depth of the circular groove 108 is 0.1mm to 0.3mm.

[0055] It should be noted that the aluminum alloy (first base material 103) and the high-strength steel (second base material 105) are lap welded, a circular groove 108 is processed on the side of the aluminum alloy facing the high-strength steel by milling, and the high-entropy alloy powder 104 is added in the circular groove 108. When resistance spot welding is performed, the high-entropy alloy powder 104 is fused between the aluminum alloy and the high-strength steel, thereby achieving the connection of dissimilar metals.

[0056] Specifically, the diameter of the circular groove 108 in the embodiment is 6 mm to 10 mm, the depth of the circular groove 108 is 0.1 mm to 0.3 mm, and the diameter of the circular groove 108 mainly depends on the current during spot welding. When the current is large, the spot welding diameter generated by welding is large, and the diameter of the circular groove 108 also increases. If the diameter of the circular groove 108 is less than 6 mm, the area of the added high-entropy alloy powder 104 in the middle will not be enough to cover the fusion zone. If the diameter of the circular groove 108 is greater than 10 mm, that is, the area of the added high-entropy alloy powder 104 in the middle is greater than the spot welding fusion zone diameter, it will cause the high-entropy alloy powder 104 to splash and remain. When the depth of the circular groove 108 is less than 0.1 mm, the amount of added high-entropy alloy powder 104 is small, and the influence on the formation of the intermetallic compound layer of the spot welding joint interface is small. The welding connection strength is almost unchanged compared to when the high-entropy alloy powder 104 is not added. When the depth of the circular groove 108 is greater than 0.3 mm, since excessive high-entropy alloy powder 104 is added between the aluminum alloy (first base material 103) and the high-strength steel (second base material 105), the partially melted high-entropy alloy powder 104 cannot fully contact and combine with the base material, resulting in a large number of pores and splashes.

[0057] In the embodiment, the diameter of the circular groove 108 is 6 mm, and the depth of the circular groove 108 is 0.2 mm.

[0058] It should be noted that when the accommodation groove is a circular groove 108, the circular groove 108 is easy to process, has good matching with the shape of the end face of the circular electrode, and adding powder in the circular groove 108 can reduce powder loss and splashing during welding.

[0059] Figure 4 A schematic view of another accommodation groove according to an embodiment of the present application.

[0060] In a possible implementation manner, as shown in Figure 4 the accommodation groove includes a plurality of circular ring grooves 109, and the high-entropy alloy powder 104 is arranged in the plurality of circular ring grooves 109.

[0061] Among them, the maximum outer circle diameter of the plurality of circular ring grooves 109 is 6 mm to 10 mm, the groove width of the circular ring groove 109 is 1 mm, the interval between adjacent two circular ring grooves 109 is 1 mm, and the depth of the circular ring groove 109 is 0.1 mm to 0.3 mm.

[0062] It should be noted that the aluminum alloy (first base material 103) and the high-strength steel (second base material 105) are lap welded, and a concentric circular groove 109 is processed on the side of the aluminum alloy facing the high-strength steel by milling. A plurality of concentric circular grooves 109 are processed, and by adding high-entropy alloy powder 104 in the circular groove 109, the high-entropy alloy powder 104 is fused between the aluminum alloy and the high-strength steel during resistance spot welding, thereby achieving the connection of dissimilar metals.

[0063] Specifically, in the present embodiment, the outer diameter of the largest circular groove 109 is 6-10 mm, the groove width of the circular groove 109 is 1 mm, and the depth of the circular groove 109 is 0.1-0.3 mm. The outer diameter of the circular groove 109 mainly depends on the current during spot welding. When the current is large, the spot welding diameter generated by welding is large, and the outer diameter of the circular groove 109 also needs to increase accordingly. If the diameter of the circular groove 109 is less than 6 mm, the area of the added high-entropy alloy powder 104 in the middle will not be enough to cover the fusion zone. If the diameter of the circular groove 109 is greater than 10 mm, that is, the area of the added high-entropy alloy powder 104 in the middle is greater than the spot welding fusion zone diameter, it will cause the high-entropy alloy powder 104 to splash and remain. When the depth of the circular groove 109 is less than 0.1 mm, the amount of added high-entropy alloy powder 104 is small, and the influence on the formation of the intermetallic compound layer of the spot welding joint interface is small. The welding connection strength is almost unchanged compared to when no high-entropy alloy powder 104 is added. When the depth of the circular groove 109 is greater than 0.3 mm, since excessive high-entropy alloy powder 104 is added between the two base materials, it will cause part of the high-entropy alloy powder 104 to not be fully combined with the base material, resulting in a large number of pores and splashes. The distance between adjacent two circular grooves 109 is 1 mm.

[0064] In the present embodiment, the outer diameter of the circular groove 109 is 6 mm, the width of the circular groove 109 is 1 mm, the depth of the circular groove 109 is 0.2 mm, and the distance between adjacent two circular grooves 109 is 1 mm, that is, the circular grooves 109 gradually shrink inward, as shown in Figure 4 The high-entropy alloy powder 104 is added in the circular groove 109.

[0065] It should be noted that by comparison, the circular groove 108 is simple in shape and easy to process, and has good matching with the shape of the circular electrode end face, and adding powder in the circular groove 108 can reduce powder loss and spatter during welding, but when spot welding the circular groove 108, a circular nugget is first generated in the center area of the welding spot, and with the increase of heat input, the nugget gradually grows to the surrounding, causing the center area to accumulate high heat, which is not enough to diffuse, resulting in insufficient interface reaction. When the containing groove is a plurality of circular ring grooves 109, when spot welding the circular ring groove 109, since the contact conductivity between the first base material 103 ring-shaped area and the second base material 105 surface is higher than that of the high-entropy alloy powder 104, a ring-shaped nugget is first generated in the interface contact area, and with the increase of heat input, the ring-shaped nugget grows to the inside and outside, so that the heat diffusion speed is accelerated, the high-entropy alloy powder 104 is melted and combined with the base material, which can make the interface temperature distribution more uniform, and can reduce the probability of defect generation. It can effectively increase the resistance heat of resistance spot welding and improve the efficiency of resistance spot welding, on the one hand, it can reduce energy consumption, on the other hand, it can further improve the welding quality, so that the first base material 103 and the second base material 105 are connected more reliably. Different forms of containing grooves can be selected as needed.

[0066] In a feasible implementation, the high-entropy alloy powder 104 includes Fe, Al, Cr, Si, Co, and Ni, with a mass percentage of 16% Fe, 10.7% Al, 20.5% Cr, 14% Si, (15%-17%) Co, (21.8%-23.8%) Ni. When welding, the high-entropy alloy powder 104 tends to form a solid solution with relatively simple phase structure, because the high-entropy alloy powder 104 increases the compatibility between the main elements, avoiding the formation of intermetallic compounds due to phase separation. Among them, the two elements of Fe and Al can increase the wettability of the high-entropy alloy powder 104 with the first base material 103 and the second base material 105, and improve the inclusion of the high-entropy alloy powder 104 to the base material. The Cr element can reduce the hardness and strength of the material and improve the plasticity, which is beneficial to improve the quality of the spot welding joint. The Si element occupies the Fe x Al y The vacancies on the C axis in the lattice hinder the diffusion of Al atoms into the high-strength steel, and the Si element can inhibit the Fe x Al yThe growth can also effectively inhibit the interface reaction between the first base material 103 and the second base material 105, and reduce the thickness of brittle intermetallic compounds. The Co element has ferromagnetism, promotes the generation of FCC phase, improves the plasticity and toughness of the material, can be mutually soluble with the Fe element, and plays a certain adhesive role in the alloy. The Ni element can make the material exhibit paramagnetism and promote the generation of the FCC phase, and the Ni element can be mutually soluble with the Fe element and will not produce brittle intermetallic compounds with the Al element. The Ni element has good toughness and can avoid defects in the welding process. The Co and Ni elements can both promote the generation of the FCC phase, and the mass ratio of Co and Ni needs to be adjusted according to the base material thickness and the spot welding parameters to ensure that the optimal FCC phase quantity is obtained, thereby ensuring that the spot welding joint has good strength, plasticity and corrosion resistance.

[0067] The purpose of selecting the proportion of each element in the high-entropy alloy powder 104 is firstly to meet the design requirements of the high-entropy alloy powder 104 to ensure that a simple solid solution structure is formed in the spot welding process, and secondly to increase the mutual solubility of the intermediate interlayer and the base material because the base material itself contains Fe, Al, Cr and Si. The proportion of the four elements Fe, Al, Cr and Si is selected and optimized through related literature and previous tests, and therefore the composition of Co and Ni elements is adjusted on this basis to adapt to different spot welding parameters.

[0068] It should be noted that the high-entropy alloy powder 104 of the present application is prepared by a mechanical alloying method, different metal powders are mixed uniformly by a high-energy ball mill, and no melting process is required, so that alloy powders that are difficult to smelt can be prepared.

[0069] In a feasible implementation, during resistance spot welding, the spot welding parameters are obtained by an orthogonal test method, and the spot welding parameters include: a spot welding current of 13kA to 16kA, a welding time of 300ms to 450ms, and an electrode pressure of 3kN to 4.5kN.

[0070] The welding parameters are obtained by an orthogonal test method, and the influence degree of each parameter on the welding quality is determined. The three main factors of the welding parameters are the welding current I, the welding time t and the electrode pressure F, so the orthogonal test is three factors. According to the previous test, each factor is selected to have four different levels, as follows: the welding current is I1=13kA, I2=14kA, I3=15kA and I4=16kA, the welding time is t1=300ms, t2=350ms, t3=400ms and t4=450ms, and the electrode pressure is F1=3kN, F2=3.5kN, F3=4kN and F4=4.5kN. The tensile shear force of the aluminum / steel resistance spot welding joint is selected as the test evaluation index, and the orthogonal table adopts L16(43 3), the orthogonal table includes 16 test groups, and each test group corresponds to a different combination of factor levels. The selection of the orthogonal scheme can represent comprehensive tests with dispersion and representativeness, and at least three repeated experiments are performed for each group of parameters to ensure experimental stability. Through the test, it is found that the lap shear force of the spot welded joint under the optimized welding parameter condition is higher when the high-entropy alloy is added in the circular ring groove. That is, the connection effect of the first base material 103 and the second base material 105 can be achieved by adding the high-entropy alloy powder 104 in the circular groove 108, and the lap shear force between the first base material 103 and the second base material 105 can be further improved by adding the high-entropy alloy powder 104 in the circular ring groove 109, thereby improving the welding effect.

[0071] It can be understood that the design and use of the orthogonal table are explained below with a specific example. In the orthogonal test, the base material thickness is first selected, the test conditions are fixed, three influencing factors of welding current, welding time and electrode pressure are set, the lap shear force of the joint is used to evaluate the welding quality, and the best welding process parameter combination is obtained.

[0072] For example, the thickness of the aluminum alloy (first base material 103) is 1.5 mm and the thickness of the high-strength steel (second base material 105) is 1.0 mm, a circular groove 108 is opened on the aluminum alloy bonding surface, the diameter of the circular groove 108 is 6 mm, and the depth of the circular groove 108 is 0.2 mm. Under this condition, the orthogonal test according to Table 1 is performed.

[0073] Table 1 L16 (4 3 ) three-factor four-level orthogonal test table

[0074]

[0075] According to Table 1, the lap shear strength of the spot welded joint is obtained, the microstructure morphology of the spot welding nugget is combined, the best resistance spot welding process parameter combination is calculated by formula, and the three-factor four-level orthogonal test table should have 64 groups of data. In the above example condition (64 groups of data), the best process parameter combination is obtained by analysis, which is: welding current 15 kA, welding time 400 ms, and electrode pressure 4 kN. In the same way, the best process parameters when the containing groove is a circular ring groove 109 can be obtained. The method is the same and will not be repeated. Subsequently, a large number of welding can be carried out according to the parameters to improve the welding efficiency and welding quality.

[0076] It should be noted that by optimizing the welding parameters, the spot welding current, the welding time and the electrode pressure, the spot welding process can be optimized, and the reliability and stability of the welding can be improved.

[0077] In a feasible implementation manner, the thickness of the first base material 103 is 1.5 mm to 2 mm, and the thickness of the second base material 105 is 1 mm to 1.5 mm.

[0078] It should be noted that the thickness of the first base material 103 and the second base material 105 is based on the actual thickness of the automobile body panel, and the thickness of the automobile body material is mainly considered in the selection of lightweight, strength, safety, manufacturing process and cost, which is a conventional choice in the art and will not be described again.

[0079] Comparative Example 1

[0080] It has been reported that AlCu28 and AlSi12 are used as intermediate layers to complete the resistance spot welding of steel / aluminum alloy dissimilar metals, and it is proved that the spot welding of dissimilar metals using an intermediate layer is effective. However, there are still limitations: the maximum tensile shear load of the aluminum alloy / low carbon steel spot welded joint with AlCu28 intermediate layer is 3.2kN due to the influence of nugget size and the thickness of intermetallic compound formed at the welding interface. When AlSi12 is used as an intermediate transition layer to spot weld aluminum alloy and low carbon steel, the intermetallic compound layer formed at the interface is relatively thin, which inhibits the growth of the interfacial IMC, but the intermediate layer uses AlSi12 metal foil, which can only change the thickness of the intermediate layer, and it is not convenient to adjust the composition.

[0081] Table 2 Comparison of different intermediate layer related data

[0082]

[0083] As can be seen from Table 2, the high-entropy alloy powder 104 used as an intermediate layer can reduce the welding current, save energy, reduce the power requirement of the equipment, and save costs; at the same time, the reduction of the thickness of the intermetallic compound layer and the reduction of defects improve the tensile shear force of the spot welded joint.

[0084] Comparative Example 2

[0085] The base materials of the present application are high-strength steel and aluminum alloy, and the physical and chemical properties of the two base materials are significantly different, making it difficult to form an effective resistance spot welded joint. Therefore, the present application adds different proportions of FeAlCrNiCoSi high-entropy alloy powder between the aluminum alloy (first base material 103) and the high-strength steel (second base material 105), reduces the thickness of the interfacial brittle intermetallic compound, changes the metallurgical properties of the weld metal, improves the bonding strength of the spot welded joint, and forms relatively small conductive channels between the intermediate layer powder particles, greatly improving the current density through the material to be welded. region, saving energy while forming a firm and reliable spot welding connection.

[0086] Table 3 Comparison of different compositions of high-entropy alloy intermediate layers

[0087]

[0088] It can be seen from Table 3 that under the condition of basically the same welding current, adding the high-entropy alloy powder 104 selected in the application as the intermediate layer makes the welding joint have less defects, the fracture form of the interface is the fracture of the aluminum alloy base material button, the strength is better than that of the interface fracture, and therefore the tensile shear force of the welding joint is effectively improved.

[0089] In the present application, the terms "first" and "second" are used only for descriptive purposes and are not to be construed as indicating or implying relative importance. The term "a plurality" refers to two or more, unless otherwise expressly specified.

[0090] Other embodiments of the present application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. It is intended that the present application cover any and all variations of the present application comprising modifications, alterations, substitutions, and equivalents within the scope and spirit of the present application. The specification and examples are illustrative only.

[0091] The above only is the preferred embodiment of the present application, and does not limit the present application, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method of resistance spot welding of dissimilar metals, characterized by, The resistance spot welding method comprises the following steps: Preparation of welding base material, including first base material and second base material; The first base material and the second base material are lap welded, and the first base material is provided with a containing groove on one side facing the second base material; High-entropy alloy powder is arranged in the containing groove; The first base material and the second base material are welded by resistance spot welding; The containing groove comprises a plurality of circular groove slots, and the high-entropy alloy powder is arranged in the plurality of circular groove slots; The maximum outer circle diameter of the plurality of circular groove slots is 6mm to 10mm, the groove width of the circular groove slot is 1mm, the interval between adjacent two circular groove slots is 1mm, and the depth of the circular groove slot is 0.1mm to 0.3mm; The high-entropy alloy powder comprises Fe, Al, Cr, Si, Co and Ni, and the mass percentage is 16%Fe, 10.7%Al, 20.5%Cr, 14%Si, (15%-17%)Co, (21.8%-23.8%)Ni.

2. The resistance spot welding method of dissimilar metals according to claim 1, characterized by, The welding of the first base material and the second base material by resistance spot welding comprises: The resistance spot welding comprises a first electrode and a second electrode, the first electrode is located on one side of the first base material away from the second base material, and the second electrode is located on one side of the second base material away from the first base material; A first electrode strip is arranged between the first base material and the first electrode, and a second electrode strip is arranged between the second base material and the second electrode.

3. The resistance spot welding method of dissimilar metals according to claim 2, characterized by, When the first base material is an aluminum alloy, the main component of the first electrode strip is stainless steel; when the second base material is a high-strength steel, the main component of the second electrode strip is low-carbon steel.

4. The resistance spot welding method of dissimilar metals according to claim 1, characterized by, During the resistance spot welding, the spot welding parameters are obtained by an orthogonal test method, and the spot welding parameters include: spot welding current is 13kA to 16kA, welding time is 300ms to 450ms, and electrode pressure is 3kN to 4.5kN.

5. The resistance spot welding method of dissimilar metals according to any one of claims 1 to 4, characterized by, The thickness of the first base material is 1.5mm to 2mm, and the thickness of the second base material is 1mm to 1.5mm.

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