Method for resistance spot welding of steel parts

Abstract

The application relates to the technical field of resistance spot welding, and discloses a resistance spot welding method for steel parts, which comprises the following steps: obtaining a part to be welded, the part to be welded comprising a first part and a second part; performing local heat treatment on at least one welding position of the part to be welded, so that metal elements in a metal plating layer and iron elements in the part are subjected to an alloying reaction, and an alloy layer is formed at the welding position; and making the welding position of the first part and the welding position of the second part contact, and welding the welding positions by using a resistance spot welding device to form a nugget. The technical scheme disclosed by the application can solve the problem that a steel part plated with a low-melting-point plating layer material is prone to zinc stacking defects during resistance spot welding, and can avoid the need for polishing treatment after the zinc stacking defects are formed.

Description

Technical Field

[0001] This application relates to the field of resistance spot welding technology and discloses a resistance spot welding method for steel parts. Background Technology

[0002] Resistance spot welding is a method of locally heating the materials to be welded by passing an electric current through them under pressure, using the resulting resistance heat as a heat source to ultimately form a connection. Currently, resistance spot welding is widely used for joining metallic materials and has become a primary welding method in the automotive industry.

[0003] Due to continuous improvements in corrosion resistance, low-melting-point coating materials are increasingly widely used in automobile manufacturing. GI plates with pure zinc coatings have a melting point of 420℃; ZM plates, composed of Zn-Al-Mg elements, have a melting point of 380-390℃. Because of the low melting point of GI and ZM coatings, their weldability deteriorates compared to continuously annealed products. This deterioration primarily includes: ① After melting, the coating is squeezed out of the welding area under electrode pressure. Under the influence of a magnetic field, zinc buildup defects easily form around the weld point. For visible weld points with appearance quality requirements, grinding is necessary before electrophoretic coating. This grinding process increases labor costs and affects the corrosion resistance of the area around the weld point, potentially endangering vehicle safety; ② The zinc in the coating reacts with the copper in the electrode, causing premature electrode failure and reducing service life; ③ Due to the low melting point of the coating, melting during resistance spot welding reduces the current density, requiring an increase in welding current. The lower the melting point of the coating, the more significant the reduction in current density.

[0004] Therefore, there is an urgent need to develop a resistance spot welding method to solve the welding problem of low melting point coating materials and form welds with good weld appearance quality. Summary of the Invention

[0005] The embodiments of this application provide a resistance spot welding method for steel parts. This method can solve the problem of zinc buildup defects occurring when steel parts coated with low-melting-point plating materials are subjected to resistance spot welding, and avoids the need for grinding after zinc buildup defects form.

[0006] Other features and advantages of this application will become apparent from the following detailed description, or may be learned in part from practice of this application.

[0007] According to one aspect of the embodiments of this application, a resistance spot welding method for steel parts is provided, wherein the surface of the steel parts is coated with a low-melting-point metal coating, the method comprising: obtaining parts to be welded, the parts to be welded including a first part and a second part; performing local heat treatment on at least one position of the parts to be welded, so that the metal elements in the metal coating react with the iron elements in the parts to form an alloy layer at the position to be welded; bringing the positions to be welded of the first part and the second part into contact, and welding the positions to be welded using a resistance spot welding device to form a weld nugget.

[0008] In one embodiment of this application, based on the foregoing scheme, after performing local heat treatment on at least one welding position of the part to be welded, the method further includes: detecting whether the iron content in the metal coating of the welding position after local heat treatment is less than the iron content threshold; if the iron content in the metal coating of the welding position after local heat treatment is less than the iron content threshold, then performing local heat treatment again on the welding position after local heat treatment.

[0009] In one embodiment of this application, based on the aforementioned scheme, the iron content threshold is 8%.

[0010] In one embodiment of this application, based on the aforementioned scheme, during the process of performing local heat treatment on at least one position of the part to be welded, the diameter of the heat treatment area is controlled to be 8mm to 50mm.

[0011] In one embodiment of this application, based on the aforementioned scheme, during the process of performing local heat treatment on at least one position of the part to be welded, the temperature of the metal coating surface is controlled at 400°C to 907°C.

[0012] In one embodiment of this application, at least one position of the part to be welded is subjected to local heat treatment by a heating device, wherein the heating device includes any one of an induction heating device, a laser heating device, a resistance heating device, and an electric arc heating device.

[0013] In one embodiment of this application, based on the aforementioned scheme, when the heating device is a laser heating device, the step of performing local heat treatment on at least one welding position of the part to be welded by the heating device includes: performing local heat treatment on at least one welding position of the part to be welded according to the laser spot diameter of the laser heating device being 15mm, the laser output power being 500W, the pulse mode being used, the frequency being 3.3Hz, the duty cycle being 50%, the heating time being 20 seconds, and the temperature of the metal coating surface being controlled at 700℃.

[0014] In one embodiment of this application, based on the aforementioned scheme, the resistance spot welding device includes a first electrode and a second electrode, which are disposed opposite to each other. The first electrode includes a first electrode substrate, a first electrode end face, and a first electrode transition region, which is used to connect the first electrode substrate and the first electrode end face. The second electrode includes a second electrode substrate, a second electrode end face, and a second electrode transition region, which is used to connect the second electrode substrate and the second electrode end face. During welding, the welding position of the part to be welded after local heat treatment comes into contact with the first electrode.

[0015] In one embodiment of this application, based on the aforementioned scheme, the diameter of the first electrode end face is greater than or equal to the diameter of the second electrode end face, and the radius of curvature of the first electrode end face is greater than or equal to the radius of curvature of the second electrode end face.

[0016] In one embodiment of this application, based on the foregoing scheme, the diameter of the weld nugget satisfies the following formula:

[0017]

[0018] Where d represents the diameter of the weld nugget; t represents the thickness of the part to be welded at the welding position.

[0019] In some embodiments of this application, the parts to be welded are obtained, and at least one welding location of the parts is subjected to local heat treatment, causing the metal elements in the metal plating to undergo an alloying reaction with the iron elements in the parts, forming an alloy layer at the welding location. The welding locations of the first part and the second part are then brought into contact, and the welding is performed using a resistance spot welding device to form a weld nugget. By performing local heat treatment on the welding locations of the parts to be welded, the melting point of the plating is increased, thereby significantly reducing the area of ​​the plating melting on the weld surface during subsequent welding, avoiding or suppressing the occurrence of zinc buildup defects, and avoiding the need for grinding after zinc buildup defects have formed.

[0020] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0021] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. It is obvious that the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. In the drawings:

[0022] Figure 1 A flowchart of a resistance spot welding method for steel parts according to an embodiment of this application is shown;

[0023] Figure 2 A schematic diagram of the local heat treatment of the first part according to the first embodiment of the present invention is shown;

[0024] Figure 3 A schematic diagram of the local heat treatment of the first part according to the second embodiment of the present invention is shown;

[0025] Figure 4 A schematic diagram of the local heat treatment of the first part according to the third embodiment of the present invention is shown;

[0026] Figure 5 The diagram shows the resistance spot welding process of the first and third embodiments of the present invention;

[0027] Figure 6 A schematic diagram of the resistance spot welding process in the second embodiment of the present invention is shown;

[0028] Figure 7 A photograph of the appearance of the resistance spot weld after resistance spot welding in the first embodiment of the present invention is shown;

[0029] Figure 8 A photograph of the appearance of the resistance spot weld after resistance spot welding according to the second embodiment of the present invention is shown;

[0030] Figure 9 A photograph of the appearance of the resistance spot weld after resistance spot welding according to the third embodiment of the present invention is shown;

[0031] Figure 10 A photograph of the weld joint appearance after resistance spot welding in the comparative example of the present invention is shown. Detailed Implementation

[0032] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided to make this application more comprehensive and complete, and to fully convey the concept of the exemplary embodiments to those skilled in the art.

[0033] Furthermore, the described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Numerous specific details are provided in the following description to give a thorough understanding of embodiments of this application. However, those skilled in the art will recognize that the technical solutions of this application can be practiced without one or more of the specific details, or other methods, components, apparatuses, steps, etc., can be employed. In other instances, well-known methods, apparatuses, implementations, or operations are not shown or described in detail to avoid obscuring various aspects of this application.

[0034] The flowcharts shown in the accompanying drawings are merely illustrative and do not necessarily include all content and operations / steps, nor do they necessarily have to be performed in the described order. For example, some operations / steps can be broken down, while others can be combined or partially combined; therefore, the actual execution order may change depending on the specific circumstances.

[0035] The schematic diagrams shown in the attached figures are only general descriptions or representations of the shape, relative size, and relationships between objects. Actual objects do not necessarily have the same shape, relative size, or relationships as shown in the figures.

[0036] It should be noted that "multiple" in this article refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0037] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such uses of these terms can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described.

[0038] The implementation details of the technical solutions in the embodiments of this application are described in detail below:

[0039] Figure 1 A flowchart of a resistance spot welding method for steel parts according to an embodiment of this application is shown.

[0040] like Figure 1 As shown, the resistance spot welding method for the steel part includes at least steps 110 to 150.

[0041] The following will be about Figure 1 Steps 110 to 150 are described in detail below:

[0042] In step 110, the parts to be welded are obtained, including a first part and a second part.

[0043] In this application, the surface of the part to be welded is coated with a low-melting-point metal coating. The metal coating can be a pure zinc coating with a melting point of 420°C, or a zinc-magnesium-aluminum coating composed of zinc, magnesium, and aluminum elements with a melting point of 380°C-390°C.

[0044] Continue to refer to Figure 1In step 130, at least one welding position of the part to be welded is subjected to local heat treatment, so that the metal elements in the metal coating react with the iron elements in the part to form an alloy layer at the welding position.

[0045] In this application, it should be noted that the number of the locations to be welded can be one or more.

[0046] In this application, one or more locations of the parts to be welded are subjected to local heat treatment, which causes the metal elements in the metal plating to undergo an alloying reaction with the iron elements in the parts, forming an alloy layer at the location to be welded. The melting point of the alloy layer is significantly higher than that of the metal plating before the local heat treatment, which greatly reduces the area of ​​plating melting in the subsequent welding steps.

[0047] For example, the surface of the part to be welded is coated with a pure zinc plating layer with a melting point of 420°C. Local heat treatment is performed on one of the welding positions of the part to be welded, so that the zinc element in the pure zinc plating layer and the iron element in the part undergo an alloying reaction, so that the heated part forms a zinc-iron alloy, thereby increasing the melting point of the plating layer from less than or equal to 420°C to greater than 600°C.

[0048] Continue to refer to Figure 1 In step 150, the welding positions of the first part and the second part are brought into contact, and the welding positions are welded by a resistance spot welding device to form a weld nugget.

[0049] In some embodiments of this application, such as Figure 1 During step 130, i.e. after performing local heat treatment on at least one welding position of the part to be welded, the method further includes: detecting whether the iron content in the metal coating of the welding position after local heat treatment is less than the iron content threshold; if the iron content in the metal coating of the welding position after local heat treatment is less than the iron content threshold, then the welding position after local heat treatment is re-performed with local heat treatment.

[0050] In this application, after performing local heat treatment on the welding position of the part to be welded, a glow discharge spectrometer is used to detect whether the iron content in the metal coating of the welding position after local heat treatment is less than the iron content threshold. If the iron content in the metal coating of the welding position after local heat treatment is less than the iron content threshold, the welding position after local heat treatment is re-performed with local heat treatment. If the iron content in the metal coating of the welding position after local heat treatment is greater than or equal to the iron content threshold, the local heat treatment of the welding position of the part to be welded is successful and no further local heat treatment is required.

[0051] In some embodiments of this application, the iron content threshold is 8%.

[0052] In some embodiments of this application, during the process of performing local heat treatment on at least one position of the part to be welded, the diameter of the heat treatment area is controlled to be 8mm to 50mm.

[0053] In this application, it should be noted that if the diameter of the heat treatment area is greater than 50 mm, the parts subjected to local heat treatment will deform due to the excessive heating area.

[0054] In some embodiments of this application, during the local heat treatment of at least one position of the part to be welded, the temperature of the metal coating surface is controlled to be 400°C to 907°C.

[0055] In this application, it should be noted that when the metal coating of the part to be welded is a pure zinc coating or a zinc-magnesium-aluminum coating, during the local heat treatment process, because the melting point of the pure zinc coating is 420℃, the melting point of the zinc-magnesium-aluminum coating is 380℃-390℃, and the boiling point of zinc is 906℃, the local heat treatment temperature needs to exceed 400℃ to allow the metal elements in the metal coating to undergo an alloying reaction with the iron elements in the part, forming an alloy layer at the welding location. When the local heat treatment temperature exceeds 907℃, which exceeds the boiling point of zinc, the zinc in the pure zinc coating or zinc-magnesium-aluminum coating will evaporate due to the excessively high temperature. Therefore, during the local heat treatment process, the surface temperature of the metal coating must be controlled below 907℃.

[0056] In some embodiments of this application, at least one welding position of the part to be welded is subjected to local heat treatment by a heating device, wherein the heating device includes any one of an induction heating device, a laser heating device, a resistance heating device, and an electric arc heating device.

[0057] In some embodiments of this application, when the heating device is a laser heating device, the step of performing local heat treatment on at least one welding position of the part to be welded by the heating device includes: performing local heat treatment on at least one welding position of the part to be welded according to the laser spot diameter of the laser heating device being 15mm, the laser output power being 500W, the pulse mode being used, the frequency being 3.3Hz, the duty cycle being 50%, the heating time being 20 seconds, and the temperature of the metal coating surface being controlled at 700℃.

[0058] In some embodiments of this application, the resistance spot welding device includes a first electrode and a second electrode, which are disposed opposite to each other. The first electrode includes a first electrode substrate, a first electrode end face, and a first electrode transition region, which connects the first electrode substrate and the first electrode end face. The second electrode includes a second electrode substrate, a second electrode end face, and a second electrode transition region, which connects the second electrode substrate and the second electrode end face. During welding, the welding position of the part to be welded after local heat treatment comes into contact with the first electrode.

[0059] In some embodiments of this application, the diameter of the first electrode end face is greater than or equal to the diameter of the second electrode end face, and the radius of curvature of the first electrode end face is greater than or equal to the radius of curvature of the second electrode end face.

[0060] In this application, when the diameter or radius of curvature of the first electrode end face is greater than that of the second electrode end face, the current density and pressure on the contact side between the metal plating layer of the part to be welded and the first electrode end face can be reduced, thereby reducing the surface temperature and pressure of the part to be welded, suppressing the occurrence of zinc build-up defects, and reducing the indentation depth of the weld joint.

[0061] In some embodiments of this application, the diameter of the weld nugget satisfies the following formula:

[0062]

[0063] Where d represents the diameter of the weld nugget; t represents the thickness of the part to be welded at the welding position.

[0064] To enable those skilled in the art to more easily understand this application, specific embodiments will be used to illustrate this application below.

[0065] Reference Figure 2 , Figure 5 and Figure 7 The diagrams show a partial heat treatment schematic of the first part according to the first embodiment of the present invention, a resistance spot welding process schematic, and a resistance spot weld appearance image after resistance spot welding.

[0066] First embodiment:

[0067] Specifically, in this embodiment of the invention, the first test plate 1 includes a first test plate substrate 11, a first plating layer 12, and a second plating layer 13. The first test plate substrate 11 is made of IF steel with a thickness of 1.4 mm; both the first plating layer 12 and the second plating layer 13 are GI plating layers with a Zn content > 99%, a melting point of 420°C, and a single-sided plating weight of 50 g / m². 2The second test plate 3 includes a second test plate substrate 31, a second test plate first coating 32, and a second test plate second coating 33. The second test plate substrate 31 is made of IF steel with a thickness of 1.4 mm; both the second test plate first coating 32 and the second test plate second coating 33 are GI coatings with a Zn content >99%, a melting point of 420℃, and a single-sided coating weight of 50 g / m². 2 .

[0068] First, the first test plate 1 and the second test plate 2 are stamped to prepare the first part and the second part, respectively.

[0069] Then, local heating is applied to the welding position of the first part. In this embodiment, the heating device 2 is a high-frequency induction heating device, such as... Figure 2 As shown. The area to be welded on the first part is heated, and the heated area is a circular region with a diameter of 40 mm. In this embodiment, the metal plating of the area to be welded on the first part is heated to 600°C for 5 minutes, and then allowed to cool naturally to room temperature in air after heating is stopped. In this embodiment, there is only one area to be welded. For multiple areas to be welded, multiple areas can be heated simultaneously to improve efficiency. The Fe content in the plating of the local heat treatment area is ≥8%.

[0070] Next, the area to be welded on the second part is locally heated as described above.

[0071] Finally, the first and second parts are assembled together, with their corresponding welding positions in contact. Resistance spot welding is then performed under the action of the first electrode 4 and the second electrode 5, as follows: Figure 5 As shown. In this embodiment, the first electrode 4 and the second electrode 5 are identical, both made of chromium-zirconium-copper material. The first electrode 4 includes a first electrode substrate 41, a first electrode end face 42, and a first electrode transition region 43, which connects the first electrode substrate 41 and the first electrode end face 42. The first electrode end face 42 is a curved surface with a diameter of 6 mm and a radius of curvature of 40 mm. The second electrode 5 includes a second electrode substrate 51, a second electrode end face 52, and a second electrode transition region 53, which connects the second electrode substrate 51 and the second electrode end face 52. The second electrode end face 52 is a curved surface with a diameter of 6 mm and a radius of curvature of 40 mm. The first electrode 4 and the second electrode 5 are arranged opposite each other. During welding, the metal plating at the welding position of the first part contacts the first electrode 4, and the metal plating at the welding position of the second part contacts the second electrode 5. The parameters of the resistance spot welding device are: electrode pressure 3 kN, welding current 8 kA, and welding time 200 ms. Finally, weld nugget 6 is formed between the first and second parts, with a diameter of 5.9 mm, satisfying the requirement that the weld nugget diameter is greater than or equal to... The requirement is that t is the plate thickness.

[0072] like Figure 7 As shown, after welding, the weld indentation still exists, but the zinc buildup defects around the indentation are significantly improved, with no obvious protrusions. Furthermore, continuous welding tests were conducted on the electrodes at a spot welding frequency of 30 points / minute, increasing the electrode life from 2200 points without heat treatment to 3500 points after local heat treatment.

[0073] Reference Figure 3 , Figure 6 and Figure 8 The diagrams show a partial heat treatment schematic of the first part according to the second embodiment of the present invention, a resistance spot welding process schematic, and a resistance spot weld appearance image after resistance spot welding.

[0074] Second embodiment:

[0075] The first test plate 1 includes a first test plate substrate 11, a first coating 12, and a second coating 13. The first test plate substrate 11 is made of IF steel with a thickness of 1.4 mm; both the first coating 12 and the second coating 13 are GI coatings with a Zn content >99%, a melting point of 420℃, and a single-sided coating weight of 50 g / m². 2 The second test plate 3 includes a second test plate substrate 31, a second test plate first coating 32, and a second test plate second coating 33. The second test plate substrate 31 is made of IF steel with a thickness of 1.4 mm; both the second test plate first coating 32 and the second test plate second coating 33 are GI coatings with a Zn content >99%, a melting point of 420℃, and a single-sided coating weight of 50 g / m². 2 .

[0076] First, the first test plate 1 and the second test plate 2 are stamped to prepare the first part and the second part, respectively.

[0077] Then, local heating is applied to the welding position of the first part. In this embodiment, the heating device 2 is a laser heat source, such as... Figure 3 As shown, the laser spot diameter is 15mm, used to heat the metal plating at the location to be welded on the first part. In this embodiment, the laser output power is 500W, using pulse mode, frequency 3.3Hz, duty cycle 50%, heating time 20 seconds, and the surface temperature of the plating is approximately 700℃. After heating is stopped, it is allowed to cool naturally to room temperature in air. The Fe content in the metal plating of the local heat treatment area is ≥8%.

[0078] Finally, the first and second parts are assembled together, with their corresponding welding positions in contact. Resistance spot welding is then performed under the action of the first electrode 4 and the second electrode 5, as follows: Figure 6As shown. In this embodiment, both the first electrode 4 and the second electrode 5 are made of chromium-zirconium-copper material. The first electrode 4 includes a first electrode substrate 41, a first electrode end face 42, and a first electrode transition region 43, which connects the first electrode substrate 41 and the first electrode end face 42. The first electrode end face 42 is a plane with a diameter of 10 mm (radius of curvature is ∞). The second electrode 5 includes a second electrode substrate 51, a second electrode end face 52, and a second electrode transition region 53, which connects the second electrode substrate 51 and the second electrode end face 52. The second electrode end face 52 is a curved surface with a diameter of 6 mm and a radius of curvature of 40 mm. The first electrode 4 and the second electrode 5 are arranged opposite each other. During welding, the metal plating at the welding position of the first part contacts the first electrode 4, and the metal plating at the welding position of the second part contacts the second electrode 5. The parameters of the resistance spot welding device are: electrode pressure 3 kN, welding current 9.5 kA, and welding time 200 ms. Finally, weld nugget 6 is formed between the first and second parts, with a diameter of 5.9 mm, satisfying the requirement that the weld nugget diameter is greater than or equal to... The requirement is that t is the plate thickness.

[0079] like Figure 8 As shown, after welding, due to the further reduction in pressure and weld surface temperature, the weld surface of the first part located on the first electrode 4 side is almost flat, with only a color change at the weld point; zinc buildup defects at the weld point are further reduced, with no obvious protrusions. Ultimately, a significant improvement in the appearance quality of the weld point is achieved on the first electrode 4 side.

[0080] Reference Figure 4 , Figure 5 and Figure 9 The diagrams show a partial heat treatment schematic of the first part according to the third embodiment of the present invention, a resistance spot welding process schematic, and a resistance spot weld appearance image after resistance spot welding.

[0081] Third embodiment:

[0082] Specifically, in this embodiment of the invention, the first test plate 1 includes a first test plate substrate 11, a first test plate first coating 12, and a first test plate second coating 13. The first test plate substrate 11 is made of IF steel with a thickness of 1.8 mm; both the first coating 12 and the second coating 13 are GI coatings with a Zn content >99%, a melting point of 420°C, and a single-sided coating weight of 50 g / m². 2 The second test plate 3 includes a second test plate substrate 31, a second test plate first coating 32, and a second test plate second coating 33. The second test plate substrate 31 is made of IF steel with a thickness of 1.8 mm; both the second test plate first coating 32 and the second test plate second coating 33 are GI coatings with a Zn content >99%, a melting point of 420℃, and a single-sided coating weight of 50 g / m². 2 .

[0083] First, the first test plate 1 and the second test plate 2 are stamped to prepare the first part and the second part, respectively.

[0084] Then, local heating is applied to the area of ​​the first part to be welded. In this embodiment, the heating device 2 is a resistance heating device, such as... Figure 4 As shown. The heating device 2 includes a first electrode 21 and a second electrode 22. The first electrode 21 and the second electrode 22 clamp the first part, and the distance between the first electrode 21 and the second electrode 22 is 20 mm. By passing a heating current between the first electrode 21 and the second electrode 22, the metal plating at the welding location of the first part is heated to 750°C. The heating is maintained for 3 seconds and then stopped, allowing it to cool naturally to room temperature. In this embodiment, there is only one welding location. For multiple welding locations, multiple locations can be heated simultaneously to improve efficiency. The Fe content in the plating of the local heat treatment area is ≥8%.

[0085] Finally, the first and second parts are assembled together, with their corresponding welding positions in contact. Resistance spot welding is then performed under the action of the first electrode 4 and the second electrode 5, as follows: Figure 5 As shown. In this embodiment, the first electrode 4 and the second electrode 5 are identical, both made of chromium-zirconium-copper material. The first electrode 4 includes a first electrode substrate 41, a first electrode end face 42, and a first electrode transition region 43, which connects the first electrode substrate 41 and the first electrode end face 42. The first electrode end face 42 is a curved surface with a diameter of 6 mm and a radius of curvature of 40 mm. The second electrode 5 includes a second electrode substrate 51, a second electrode end face 52, and a second electrode transition region 53, which connects the second electrode substrate 51 and the second electrode end face 52. The second electrode end face 52 is a curved surface with a diameter of 6 mm and a radius of curvature of 40 mm. The first electrode 4 and the second electrode 5 are arranged opposite each other. During welding, the metal plating at the welding position of the first part contacts the first electrode 4, and the metal plating at the welding position of the second part contacts the second electrode 5. The parameters of the resistance spot welding device are: electrode pressure 3.5 kN, welding current 8.7 kA, and welding time 400 ms. Finally, a weld nugget 6 is formed between the first and second parts, with a diameter of 6.1 mm, satisfying the requirement that the weld nugget diameter is greater than or equal to... The requirement is that t is the plate thickness.

[0086] like Figure 9 As shown, after welding, the weld indentation still exists, but the zinc buildup defects around the indentation are significantly improved, with no obvious protrusions.

[0087] Comparative example:

[0088] Using conventional methods, the first test plate 1, the second test plate 3, the first electrode 4, and the second electrode 5 are the same as in the first embodiment. The first test plate 1 and the second test plate 2 are respectively stamped to prepare a first part and a second part. No local heat treatment is performed on the welding positions of the first and second parts. The welding assembly consisting of the first and second parts is resistance-spot welded using the first electrode 4 and the second electrode 5. The parameters of the resistance spot welding device are the same as in the first embodiment.

[0089] The effect of resistance spot welding is as follows Figure 10 As shown, the weld joint has a significant indentation, and there is a significant protrusion around the indentation, which is a zinc buildup defect.

[0090] The one or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages:

[0091] Before resistance spot welding, the welding position of the parts to be welded is heated to a temperature between 400°C and 907°C by a heating device, so that the Zn element in the metal coating and the Fe element in the matrix can undergo an alloying reaction, and the resulting zinc-iron alloy phase has a higher melting point.

[0092] After localized heat treatment and cooling, the surfaces requiring aesthetic quality undergo a significant reduction in the melting point of the plating during subsequent resistance spot welding. This is because the localized heat treatment raises the melting point of the plating from below 420°C to above 600°C, drastically reducing the area of ​​plating melting on the weld joint surface and thus preventing or suppressing zinc buildup defects. Simultaneously, the increased melting point of the plating slows the reaction rate between Zn in the plating and Cu in the electrode, extending the electrode's lifespan.

[0093] When the radius of curvature or diameter of the first electrode face of the resistance spot welding device is greater than that of the second electrode face, the current density and pressure on the contact side between the metal plating layer of the part to be welded and the first electrode face can be reduced, thereby reducing the surface temperature and pressure of the part to be welded, further suppressing the occurrence of zinc build-up defects, and significantly reducing the indentation depth of the weld point, thus improving the surface quality of the weld point.

[0094] Since the welding position of the parts to be welded is subjected to local heat treatment, and the heat treatment process is after the material stamping and deformation process, it will not affect the stamping process, and the zinc powder peeling phenomenon during the stamping process will not increase due to the increase in iron content and hardness in the coating.

[0095] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the embodiments disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein.

[0096] Furthermore, the above figures are merely illustrative of the processes included in the method according to exemplary embodiments of this application, and are not intended to be limiting. It is readily understood that the processes shown in the above figures do not indicate or limit the temporal order of these processes. Additionally, it is readily understood that these processes may be executed synchronously or asynchronously, for example, in multiple modules.

[0097] It should be understood that this application is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A method for resistance spot welding of steel parts, characterized in that, The steel part is coated with a low-melting-point metallic coating, and the method includes: Obtain the parts to be welded, which include a first part and a second part; At least one welding position of the part to be welded is subjected to local heat treatment, so that the metal elements in the metal coating react with the iron elements in the part to form an alloy layer at the welding position; wherein, during the local heat treatment of at least one welding position of the part to be welded, the diameter of the heat treatment area is controlled to be 8mm~50mm. The welding positions of the first part and the second part are brought into contact, and a resistance spot welding device is used to weld the welding positions to form a weld nugget; wherein, After performing local heat treatment on at least one weldable location of the part to be welded, the method further includes: The iron content in the metal coating at the welding location after local heat treatment is checked to see if it is less than a threshold value. If the iron content in the metal coating at the welding location after local heat treatment is less than the threshold value, the welding location is re-heat treated locally, wherein the iron content threshold value is 8%. When the heating device is a laser heating device, local heat treatment is performed on at least one welding location of the part to be welded by the heating device, including: The laser heating device has a laser spot diameter of 15mm, a laser output power of 500W, uses a pulse mode, a frequency of 3.3Hz, a duty cycle of 50%, a heating time of 20 seconds, and a metal coating surface temperature control of 700℃. At least one welding position of the part to be welded is subjected to local heat treatment.

2. The method according to claim 1, characterized in that, The resistance spot welding device includes a first electrode and a second electrode, which are disposed opposite to each other. The first electrode includes a first electrode substrate, a first electrode end face, and a first electrode transition region, which connects the first electrode substrate and the first electrode end face. The second electrode includes a second electrode substrate, a second electrode end face, and a second electrode transition region, which connects the second electrode substrate and the second electrode end face. During welding, the welding position of the part to be welded after local heat treatment comes into contact with the first electrode.

3. The method according to claim 2, characterized in that, The diameter of the first electrode end face is greater than or equal to the diameter of the second electrode end face, and the radius of curvature of the first electrode end face is greater than or equal to the radius of curvature of the second electrode end face.

4. The method according to claim 1, characterized in that, The diameter of the weld nugget satisfies the following formula: in, Indicates the diameter of the weld nugget; This indicates the thickness of the part to be welded at the location where it is to be welded.

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