Resistance spot welding method for dissimilar metal

Abstract

The invention discloses a resistance spot welding method for dissimilar metal. The invention relates to the technical field of dissimilar metal welding, in particular to a resistance spot welding method which comprises the following steps: preparing welding base materials including a first base material and a second base material; the first base material and the second base material are welded in a lap joint mode, and a containing groove is formed in the side, facing the second base material, of the first 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 high-entropy alloy powder interlayer is arranged between the first base material and the second base material, and the molten high-entropy alloy powder serves as the connecting layer of the first base material and the second base material, so that the defects of a welding joint can be reduced, the connecting strength of the first base material and the second base material is improved, and the mechanical property and reliability of the welding joint are improved.

Description

Technical Field

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

[0002] With the continuous improvement of requirements for automobile energy saving, emission reduction, safety performance and driving performance, automobile lightweighting has become the mainstream trend of development. The use of lightweight materials is one of the main ways to achieve automobile lightweighting. Aluminum alloy, magnesium alloy, high-strength steel and composite materials are the main lightweight materials for automobiles. Aluminum alloy has the advantages of low density, high specific strength, good corrosion resistance and easy recycling, making it a promising lightweight material for automobiles. Therefore, increasing the use of lightweight materials such as aluminum alloy and high-strength steel in automobile design and production, and using aluminum / steel composite structure in the car body are the most direct and effective ways to achieve lightweighting. 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 materials, the weldability of aluminum / steel dissimilar metals is seriously deteriorated, and the joint performance cannot meet the requirements of automobile performance.

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

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

[0005] In view of this, the present invention provides a method for resistance spot welding of dissimilar metals, wherein a high entropy alloy powder interlayer is arranged between a first base material and a second base material, and the melted high entropy alloy powder is used as a connecting layer between the first base material and the second base material, thereby reducing defects in the weld joint and improving the connection strength between the first base material and the second base material, that is, improving the mechanical properties and reliability of the weld joint.

[0006] Specifically, the following technical solutions are included: The present invention provides a resistance spot welding method for dissimilar metals, the resistance spot welding method comprising the following steps: Prepare welding parent metals, including first parent metal and second parent metal; The first parent material and the second parent material are overlap-welded, and a receiving groove is provided on a side of the first parent material facing the second parent material; Placing high entropy alloy powder in a containing tank; The first parent material and the second parent material are welded by resistance spot welding.

[0007] Optionally, welding the first parent material and the second parent material by resistance spot welding includes: The resistance spot welding comprises a first electrode and a second electrode, wherein the first electrode is located on a side of the first parent material away from the second parent material, and the second electrode is located on a side of the second parent material away from the first parent material; A first electrode belt is provided between the first matrix and the first electrode, and a second electrode belt is provided between the second matrix and the second electrode.

[0008] Optionally, when the first parent material is an aluminum alloy, the main component of the first electrode band is stainless steel; when the second parent material is high-strength steel, the main component of the second electrode band is low-carbon steel.

[0009] Optionally, the containing groove is a circular groove, and the high entropy alloy powder is arranged in the circular groove.

[0010] Optionally, the diameter of the circular groove is 6 mm to 10 mm, and the depth of the circular groove is 0.1 mm to 0.3 mm.

[0011] Optionally, the receiving groove includes a plurality of annular grooves, and the high entropy alloy powder is arranged in the plurality of annular grooves.

[0012] Optionally, the maximum outer diameter of the plurality of annular grooves is 6 mm to 10 mm, the width of the annular groove is 1 mm, the interval between two adjacent annular grooves is 1 mm, and the depth of the annular groove is 0.1 mm to 0.3 mm.

[0013] Optionally, the high entropy alloy powder includes Fe, Al, Cr, Si, Co and Ni, with the mass percentage being 16% Fe, 10.7% Al, 20.5% Cr, 14% Si, (15%-17%) Co, and (21.8%-23.8%) Ni.

[0014] Optionally, during the resistance spot welding, spot welding parameters are obtained by an orthogonal test method, and the spot welding parameters include: spot welding current of 13kA to 16kA, welding time of 300ms to 450ms, and electrode pressure of 3kN to 4.5kN.

[0015] Optionally, the thickness of the first mother material is 1.5 mm to 2 mm, and the thickness of the second mother material is 1 mm to 1.5 mm.

[0016] The resistance spot welding method of dissimilar metals provided by an embodiment of the present invention includes preparing a first base material and a second base material, processing a receiving groove on the first base material, and arranging a high entropy alloy powder in the receiving groove, and 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, metallurgical defects can be reduced, and the connection strength of the interface between the first base material and the second base material can be improved. At the same time, the high entropy alloy powder can effectively improve the structure of the intermetallic compound at the interface of the spot welding joint, reduce the possibility of cracking of the intermetallic compound along the interface during the tensile test, and thus improve the tensile strength of the welded joint.

[0017] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0019] Figure 1 A flowchart of the steps of a resistance spot welding method for dissimilar metals according to an embodiment of the present invention; Figure 2 A schematic diagram of the operation of resistance spot welding of dissimilar metals according to an embodiment of the present invention; Figure 3 is a schematic diagram of a containing tank according to an embodiment of the present invention; Figure 4 FIG. 4 is a schematic diagram of another receiving groove according to an embodiment of the present invention.

[0020] in, Figures 2 to 4 The corresponding relationship between the reference numerals and the component names is as follows: 101 first electrode, 102 first electrode belt, 103 first base material, 104 high entropy alloy powder, 105 second base material, 106 second electrode belt, 107 second electrode, 108 circular groove, 109 annular groove. DETAILED DESCRIPTION

[0021] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] Before further describing the embodiments of the present invention in detail, the directional nouns involved in the embodiments of the present invention, such as "upper part", "lower part" and "side part", do not have the meaning of limiting the protection scope of the present invention.

[0023] To make the technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0024] Figure 1 The present invention is a flowchart of a method for resistance spot welding of dissimilar metals according to an embodiment of the present invention.

[0025] like Figure 1 As shown, a resistance spot welding method of dissimilar metals of the present invention comprises the following steps: Step 1, preparing welding base materials, including a first base material and a second base material; Step 2: The first parent material and the second parent material are overlap-welded, and a receiving groove is provided on a side of the first parent material facing the second parent material; Step 3, placing high entropy alloy powder in the containing tank; Step 4: welding the first base material and the second base material by resistance spot welding.

[0026] The resistance spot welding method includes preparing a first mother material 103 and a second mother material 105, processing a receiving groove on the first mother material 103, and arranging a high entropy alloy powder 104 in the receiving groove, and then overlapping the first mother material 103 and the second mother material 105, and making the high entropy alloy powder 104 located between the first mother material 103 and the second mother material 105, and welding by resistance spot welding. By fusing the high entropy alloy powder 104 between the first mother material 103 and the second mother material 105, the reliability and stability of the connection between the dissimilar metals can be improved, the metallurgical defects are reduced, and the connection strength of the interface between the first mother material 103 and the second mother material 105 is improved. 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 of the intermetallic compound along the interface during the tensile test, and thus improve the tensile strength of the welded joint.

[0027] Specifically, the first parent material 103 and the second parent material 105 are made of different materials. In this embodiment, the first parent material 103 is an aluminum alloy, and the second parent material 105 is a 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 parent material 103 and the second parent material 105, and a high entropy alloy powder 104 interlayer is added between the contact surfaces of the first parent material 103 and the second parent material 105. Due to the high entropy effect and hysteresis diffusion effect of the high entropy alloy powder 104, the generation of intermetallic (between the first parent material 103 and the second parent material 105) compounds is suppressed, and the reaction system is easy to form a simple disordered solid solution structure, so it can effectively improve the organizational structure, reduce welding defects, and thus improve the welding quality of the welded joint, thereby ensuring the reliability of the connection between the first parent material 103 and the second parent 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 joints of the aluminum alloy (first base material 103) and the high-strength steel (second base material 105), the composition of the intermediate layer compound can be improved, the brittleness of the spot welding joint can be reduced, and the connection quality of the joint can be improved.

[0028] For example, in the first mother material 103 and the second mother material 105, the receiving groove is usually processed on the mother material with lower hardness to reduce the processing difficulty and improve the processing efficiency.

[0029] Figure 2 FIG. 1 is a schematic diagram of the operation of resistance spot welding of dissimilar metals according to an embodiment of the present invention.

[0030] In a possible implementation, Figure 2 As shown, welding the first parent material 103 and the second parent material 105 by resistance spot welding includes: The resistance spot welding comprises a first electrode and a second electrode, wherein the first electrode is located on a side of the first parent material away from the second parent material, and the second electrode is located on a side of the second parent material away from the first parent material; A first electrode belt is provided between the first base material and the first electrode, and a second electrode belt is provided between the second base material and the second electrode.

[0031] Among them, the first base material 103 of the present application is aluminum alloy, and the second base material 105 is high-strength steel. Therefore, the main component of the material of the first electrode band 102 of the present application is stainless steel, and the main component of the material of the second electrode band 106 is low-carbon steel. Different electrode bands are selected according to different base materials, which can increase resistance heat and realize heat compensation for the spot welding process. It can also reduce metal splashing in resistance spot welding of dissimilar metals, 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.

[0032] It can be understood that the main component of the electrode belt refers to a component whose metal element mass ratio is close to that of stainless steel or low-carbon steel, and a small amount of copper is mixed into the composition of the electrode belt, which can improve the conductivity and anti-corrosion effect of the electrode belt and increase the service life of the electrode belt.

[0033] Specifically, when the first parent material 103 is an aluminum alloy, since the aluminum alloy has good heat dissipation performance, it is not conducive to conduct the current heat of the first electrode 101 to the middle high entropy alloy powder 104 layer. Therefore, a first electrode belt 102 whose main component is stainless steel is set between the first electrode 101 and the aluminum alloy (first parent material 103). Since the stainless steel material has a high resistivity, it can generate resistance heat when the current passes through, so it can make up for the heat loss during welding caused by the heat dissipation performance of the aluminum alloy, that is, it can increase resistance heat and ensure the welding effect. A second electrode belt 106 whose main component is low carbon steel is set between the second electrode 107 and the high-strength steel (second parent material 105). The addition of the second electrode belt 106 not only generates additional resistance heat, but also can effectively prevent the adhesion of the second electrode 107 and the second parent material 105, so that the surface of the weld is well formed. At the same time, by arranging a first electrode belt 102 of stainless steel between the first electrode 101 and the aluminum alloy, and arranging a second electrode belt 106 of low carbon steel between the second electrode 107 and the high-strength steel, the first electrode 101 and the second electrode 107 are prevented from being contaminated with metal particle impurities. On the one hand, it can avoid the generation of spatter, reduce the metal vapor and waste slag generated during the welding process, reduce the impact of welding on the environment, and meet the production requirements for environmental protection and energy saving. On the other hand, it can also protect the electrodes, increase the service life of the first electrode 101 and the second electrode 107, and extend the maintenance time of the first electrode 101 and the second electrode 107.

[0034] Among them, Figure 2 As shown, the first electrode band 102 and the second electrode band 106 are U-shaped, and the first electrode band 102 is wrapped on the first electrode 101 so that the first electrode band 102 is located between the first electrode 101 and the first mother material 103. Similarly, the second electrode band 106 is wrapped on the second electrode 107 so that the second electrode band 106 is located between the second electrode 107 and the second mother material 105.

[0035] Figure 3 It is a schematic diagram of a containing tank according to an embodiment of the present invention.

[0036] In a possible implementation, Figure 3 As shown, the receiving groove is a circular groove 108 , and the high entropy alloy powder is arranged in the circular groove 108 .

[0037] The diameter of the circular groove 108 is 6 mm to 10 mm, and the depth of the circular groove 108 is 0.1 mm to 0.3 mm.

[0038] It should be noted that the aluminum alloy (first base material 103) and the high-strength steel (second base material 105) are overlap-welded, and a circular groove 108 is processed by milling on the side of the aluminum alloy facing the high-strength steel. By adding high-entropy alloy powder 104 into the circular groove 108, during resistance spot welding, the high-entropy alloy powder 104 is fused between the aluminum alloy and the high-strength steel, thereby realizing the connection of dissimilar metals.

[0039] Specifically, the diameter of the circular groove 108 in this embodiment is 6 mm to 10 mm, and the depth of the circular groove 108 is 0.1 mm to 0.3 mm. The diameter of the circular groove 108 mainly depends on the current during spot welding. When the current is large, the spot weld diameter produced by welding is large, and the diameter of the circular groove 108 also increases accordingly. If the diameter of the circular groove 108 is less than 6 mm, the area of ​​the high entropy alloy powder 104 added in the middle will be insufficient to cover the molten core area. If the diameter of the circular groove 108 is greater than 10 mm, that is, the area of ​​the high entropy alloy powder 104 added in the middle is greater than the spot welding molten core diameter, the high entropy alloy powder 104 will cause splashing and residue. When the depth of the circular groove 108 is less than 0.1 mm, the amount of high entropy alloy powder 104 added is small, which has little effect on the formation of the intermetallic compound layer at the interface of the spot welding joint, and the welding connection strength is almost unchanged compared with when the high entropy alloy powder 104 is not added. When the depth of the circular groove 108 is greater than 0.3 mm, due to the excessive amount of high entropy alloy powder 104 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 bond with the base material, resulting in a large number of pores and spatter.

[0040] In this embodiment, the diameter of the circular groove 108 is 6 mm, and the depth of the circular groove 108 is 0.2 mm.

[0041] It should be noted that when the receiving groove is a circular groove 108, the circular groove 108 is easy to process and has good matching with the shape of the circular electrode end surface. In addition, adding powder into the circular groove 108 can reduce powder loss and splashing during welding.

[0042] Figure 4 FIG. 4 is a schematic diagram of another receiving groove according to an embodiment of the present invention.

[0043] In a possible implementation, Figure 4 As shown, the receiving groove includes a plurality of annular grooves 109 , and high entropy alloy powder 104 is arranged in the plurality of annular grooves 109 .

[0044] Among them, the largest outer diameter of the plurality of annular grooves 109 is 6 mm to 10 mm, the groove width of the annular groove 109 is 1 mm, the interval between two adjacent annular grooves 109 is 1 mm, and the depth of the annular groove 109 is 0.1 mm to 0.3 mm.

[0045] It should be noted that the aluminum alloy (first base material 103) and the high-strength steel (second base material 105) are overlap-welded, and concentric annular grooves 109 are milled on the side of the aluminum alloy facing the high-strength steel. A plurality of concentric annular grooves 109 are machined, and high-entropy alloy powder 104 is added into the annular grooves 109. 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.

[0046] Specifically, in this embodiment, the largest outer diameter of the annular groove 109 is 6mm to 10mm, the groove width of the annular groove 109 is 1mm, and the depth of the annular groove 109 is 0.1mm to 0.3mm. The outer diameter of the annular groove 109 mainly depends on the current during spot welding. When the current is large, the spot welding diameter produced by welding is large, and the outer diameter of the annular groove 109 also needs to be increased accordingly. If the diameter of the annular groove 109 is less than 6mm, the area of ​​the high entropy alloy powder 104 added in the middle will be insufficient to cover the molten core area. If the diameter of the annular groove 109 is greater than 10mm, that is, the area of ​​the high entropy alloy powder 104 added in the middle is greater than the spot welding molten core diameter, the high entropy alloy powder 104 will cause splashing and residue. When the depth of the annular groove 109 is less than 0.1 mm, the amount of high entropy alloy powder 104 added is small, which has little effect on the formation of the intermetallic compound layer at the spot welding joint interface, and the welding connection strength is almost unchanged compared with when the high entropy alloy powder 104 is not added. When the depth of the annular groove 109 is greater than 0.3 mm, due to the excessive high entropy alloy powder 104 added between the two parent materials, part of the high entropy alloy powder 104 cannot be fully combined with the parent material, resulting in a large number of pores and splashes. The distance between two adjacent annular grooves 109 is 1 mm.

[0047] In this embodiment, the outer diameter of the annular groove 109 is 6 mm, the width of the annular groove 109 is 1 mm, the depth of the annular groove 109 is 0.2 mm, and the interval between two adjacent annular grooves 109 is 1 mm, that is, the annular groove 109 gradually shrinks inward. Figure 4 As shown, concentric rings are formed, and high entropy alloy powder 104 is added into the annular groove 109 .

[0048] It should be noted that, by comparison, the circular groove 108 is simple in shape and easy to process, and has good matching properties with the circular electrode end surface shape, and adding powder in the circular groove 108 can reduce powder loss and splashing during welding, but when the circular groove 108 is spot welded, a circular nugget is first generated in the central area of ​​the weld, and as the heat input increases, the nugget gradually grows around, resulting in a high amount of heat accumulation in the central area, and there is no time to diffuse, resulting in insufficient interface reaction. When the accommodating groove is a plurality of annular grooves 109, when the annular groove 109 is spot welded, since the contact conductivity of the annular area of ​​the first parent material 103 and the surface of the second parent material 105 is higher than that of the high entropy alloy powder 104, an annular nugget is first generated in the interface contact area, and as the heat input increases, the annular nugget grows to both inside and outside, so that the heat diffusion speed is accelerated, and the high entropy alloy powder 104 melts and combines with the parent material, which can make the interface temperature distribution more uniform and reduce the probability of defects. It can effectively increase the resistance heat of resistance spot welding and improve the efficiency of resistance spot welding, which can reduce energy consumption on the one hand and further improve welding quality on the other hand, making the connection between the first parent material 103 and the second parent material 105 more reliable. Different forms of receiving grooves can be selected according to needs.

[0049] In a feasible embodiment, 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, and (21.8%-23.8%) Ni. During welding, the high entropy alloy powder 104 tends to form a solid solution with a relatively simple phase structure. This is because the high entropy alloy powder 104 increases the compatibility between the main elements and avoids the formation of intermetallic compounds due to phase separation. Among them, the two elements Fe and Al can increase the wettability of the high entropy alloy powder 104 with the first parent material 103 and the second parent material 105, and enhance the tolerance of the high entropy alloy powder 104 to the parent material. The Cr element can reduce the hardness and strength of the material, and improve a certain plasticity, which is beneficial to improve the quality of the spot welding joint. The Si element occupies the Fe during spot welding. x Al y The vacancies on the C axis in the lattice hinder the diffusion of Al atoms into high-strength steel. The Si element plays an important role in inhibiting the diffusion of Fe x Al yPhase growth, it can also effectively inhibit the interface reaction between the first parent material 103 and the second parent material 105, and reduce the thickness of the brittle intermetallic compound. The Co element has ferromagnetism, promotes the formation of the FCC phase, improves the plastic toughness of the material, can be miscible with the Fe element, and plays a certain bonding role in the alloy. The Ni element can make the material exhibit paramagnetism and promote the formation of the FCC phase. At the same time, the Ni element can be miscible 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 during welding. Both Co and Ni elements can promote the formation of the FCC phase. The mass ratio of Co and Ni needs to be adjusted according to the thickness of the parent material and the spot welding parameters to ensure that the optimal number of FCC phases is obtained, thereby ensuring that the spot welding joint has good strength, plasticity and corrosion resistance.

[0050] Among them, the purpose of selecting the ratio 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 the formation of a simple solid solution structure during the spot welding process, and secondly, since the base material itself contains the four elements of Fe, Al, Cr, and Si, the mutual solubility between the intermediate layer and the base material can be increased. At present, the ratio of the four elements of Fe, Al, Cr, and Si is optimized and selected through relevant literature and preliminary experiments. Therefore, on this basis, the composition of Co and Ni elements is adjusted to adapt to different spot welding parameter conditions.

[0051] It should be noted that the high entropy alloy powder 104 of the present application is prepared by a mechanical alloying method, in which different metal powders are evenly mixed by a high-energy ball mill without a melting process, and alloy powders that are difficult to melt can be prepared.

[0052] In a feasible implementation, during resistance spot welding, spot welding parameters are obtained by an orthogonal test method, and the spot welding parameters include: spot welding current of 13kA to 16kA, welding time of 300ms to 450ms, and electrode pressure of 3kN to 4.5kN.

[0053] Among them, the welding parameters are obtained by orthogonal experiment method to determine the influence of each parameter on welding quality. The three main factors of welding parameters are welding current I, welding time t and electrode pressure F, so the orthogonal experiment is three factors. According to the previous experiment, four different levels of each factor are selected, as follows: welding current is I 1 =13kA, I 2 =14kA, I 3 =15kA and I 4 =16kA, welding time is t 1 =300ms, t 2 =350ms, t 3 =400ms and t 4 =450ms, electrode pressure is F1 =3kN, F 2 =3.5kN, F 3 =4kN and F 4 =4.5kN. The test selected the tensile shear force of aluminum / steel resistance spot welding joint as the test evaluation index, and the orthogonal table was L16 (4 3 ), the orthogonal table includes 16 groups of experiments, and each experimental combination corresponds to a different combination of factor levels. The selection of an orthogonal scheme can represent a comprehensive experiment that has both dispersion and representativeness. At least three repetitive experiments are carried out for each set of parameters to ensure experimental stability. Through experiments, it was found that when the high entropy alloy is added, the tensile shear force of the spot welding joint using an annular groove under the condition of optimized welding parameters is higher than that of the circular groove. In other words, the addition of high entropy alloy powder 104 to the circular groove 108 can achieve the connection effect between the first parent material 103 and the second parent material 105, and the addition of high entropy alloy powder 104 to the annular groove 109 can further increase the tensile shear force of the connection between the first parent material 103 and the second parent material 105, thereby improving the welding effect.

[0054] 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, the three influencing factors of welding current, welding time and electrode pressure are set, and the welding quality is evaluated by the joint shear force to obtain the best combination of welding process parameters.

[0055] For example, the thickness of the aluminum alloy (first parent material 103) is 1.5 mm and the thickness of the high-strength steel (second parent material 105) is 1.0 mm. A circular groove 108 is opened on the bonding surface of the aluminum alloy. 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, an orthogonal test is carried out according to Table 1.

[0056] Table 1 L16 (4 3 ) Three-factor four-level orthogonal test table

[0057] According to Table 1, an orthogonal test is carried out. By obtaining the tensile shear strength of the spot welding joint and combining the microstructure morphology of the spot welding nugget, the optimal resistance spot welding process parameter combination is calculated by the formula. The three-factor four-level orthogonal test table should have 64 sets of data. This comparative example selects a part of them as an illustration. Under the above example conditions (64 sets of data), the optimal process parameter combination is analyzed as follows: welding current 15kA, welding time 400ms, electrode pressure 4kN. In the same way, the optimal process parameters when the receiving groove is a circular ring groove 109 can be obtained. The method is the same and will not be repeated. In the future, large-scale welding can be carried out according to this parameter to improve welding efficiency and welding quality.

[0058] It should be noted that by optimizing the welding parameters, spot welding current, welding time and electrode pressure, the spot welding process can be optimized and the reliability and stability of welding can be improved.

[0059] In a feasible implementation manner, the thickness of the first mother material 103 is 1.5 mm to 2 mm, and the thickness of the second mother material 105 is 1 mm to 1.5 mm.

[0060] It should be noted that the thickness of the first parent material 103 and the second parent material 105 selected in this design is based on the actual thickness of the automobile body panel used. The thickness of the automobile body material is mainly selected considering factors such as lightweight, strength, safety, manufacturing process and cost. It is a conventional choice in this field and will not be elaborated on.

[0061] Comparative Example 1 At present, there are reports on the use of AlCu28 and AlSi12 as intermediate layers to complete the resistance spot welding of steel / aluminum alloy dissimilar metals, proving that the use of intermediate layers for dissimilar metal spot welding is effective. However, there are still limitations: the maximum tensile shear load of the aluminum alloy / low-carbon steel spot welding joint with the addition of the AlCu28 intermediate layer is 3.2kN due to the influence of the size of the molten core and the thickness of the intermetallic compound formed at the welding interface. When using AlSi12 as the intermediate transition layer to spot weld aluminum alloy and low-carbon steel, the intermetallic compound layer formed at the interface is thinner, which inhibits the growth of the interface IMC. However, the intermediate layer uses AlSi12 metal foil, so only the thickness of the intermediate layer can be changed, which is not convenient for flexible adjustment of the composition.

[0062] Table 2 Comparison of relevant data of different middle layers

[0063] By comparing Table 2, it can be seen that the high entropy alloy powder 104 used in the present application as an intermediate layer can reduce the welding current, achieve high efficiency and energy saving, reduce the power requirements for equipment, and save costs; at the same time, the reduction in the thickness of the intermetallic compound layer and the reduction in defects improve the tensile shear force of the spot welding joint.

[0064] Comparative Example 2 The parent materials of the present application are high-strength steel and aluminum alloy. The physical and chemical properties of the two parent metals are significantly different, and it is difficult to form an effective resistance spot welding joint. Therefore, the present invention reduces the thickness of the interface brittle metal compounds, changes the metallurgical properties of the weld metal, improves the bonding strength of the spot welding joint, and forms relatively small conductive channels between the powder particles in the middle layer, which greatly increases the current density through the material to be welded area, saves energy and forms a firm and reliable spot welding connection.

[0065] Table 3 Comparison of high entropy alloy intermediate layers with different compositions

[0066] By comparing Table 3, it can be seen that under the condition of basically the same welding current, adding the high entropy alloy powder 104 selected in this application as an intermediate layer makes the weld joint have fewer defects, and the fracture form of the interface is a button fracture of the aluminum alloy and the base material, and its strength is better than the interface fracture, so the tensile shear force of the weld joint is also effectively improved.

[0067] In the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance. The term "plurality" refers to two or more than two, unless otherwise clearly defined.

[0068] Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. The present invention is intended to cover any variations, uses or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art that are not disclosed by the present invention. The description and examples are to be considered exemplary only.

[0069] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for resistance spot welding of dissimilar metals, characterized in that: The resistance spot welding method comprises the following steps: Prepare welding parent metals, including first parent metal and second parent metal; The first parent material and the second parent material are overlap-welded, and a receiving groove is provided on a side of the first parent material facing the second parent material; Placing high entropy alloy powder in a containing tank; The first parent material and the second parent material are welded by resistance spot welding.

2. The method for resistance spot welding of dissimilar metals according to claim 1, characterized in that: The welding of the first parent material and the second parent material by resistance spot welding comprises: The resistance spot welding comprises a first electrode and a second electrode, wherein the first electrode is located on a side of the first parent material away from the second parent material, and the second electrode is located on a side of the second parent material away from the first parent material; A first electrode belt is provided between the first matrix and the first electrode, and a second electrode belt is provided between the second matrix and the second electrode.

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

4. The method for resistance spot welding of dissimilar metals according to claim 1, characterized in that: The containing groove is a circular groove, and the high entropy alloy powder is arranged in the circular groove.

5. The resistance spot welding method of dissimilar metals according to claim 4, characterized in that: The diameter of the circular groove is 6 mm to 10 mm, and the depth of the circular groove is 0.1 mm to 0.3 mm.

6. The method for resistance spot welding of dissimilar metals according to claim 1, characterized in that: The containing groove comprises a plurality of annular grooves, and the high entropy alloy powder is arranged in the plurality of annular grooves.

7. The resistance spot welding method of dissimilar metals according to claim 6, characterized in that: The maximum outer diameter of the plurality of annular grooves is 6 mm to 10 mm, the groove width of the annular groove is 1 mm, the interval between two adjacent annular grooves is 1 mm, and the depth of the annular groove is 0.1 mm to 0.3 mm.

8. The method for resistance spot welding of dissimilar metals according to claim 1, characterized in that: The high entropy alloy powder comprises Fe, Al, Cr, Si, Co and Ni, with the mass percentage being 16% Fe, 10.7% Al, 20.5% Cr, 14% Si, (15%-17%) Co, and (21.8%-23.8%) Ni.

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

10. The resistance spot welding method of dissimilar metals according to any one of claims 1 to 9, characterized in that: The thickness of the first mother material is 1.5 mm to 2 mm, and the thickness of the second mother material is 1 mm to 1.5 mm.

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