A strain-following welding method for chassis welding

Abstract

The present application provides a strain-following welding method for chassis welding, which belongs to the field of welding. The method includes: pre-treating at least two pieces of base materials to be welded; determining the relative distance between the welding point and the application point of plastic deformation according to the time required for the temperature of the coarse-grained heat-affected zone of the weld to cool down from the peak temperature to the set temperature, and the average speed of the welding, so that the application temperature of the plastic deformation is ≥ the set temperature; welding the pre-treated base materials to be welded to form a weld, and at the relative distance, simultaneously applying plastic deformation to the base material adjacent to the weld to form a plastic deformation zone inside the base material. During the welding process, the present application simultaneously introduces plastic deformation based on the principle of dynamic recrystallization of metal materials, and through the coupling of heat and force, it can achieve the refinement of the grains and structure of the coarse-grained heat-affected zone.

Description

Technical Field

[0001] The present application relates to the technical field of chassis welding, and in particular to a strain-following welding method for chassis welding. Background Art

[0002] Arc welding is a welding process that uses an arc generated between an electrode and a substrate to melt the base metal and filler metal, thereby achieving a metallurgical bond and a non-detachable joint. The heat-affected zone (HEZ) of a weld is the area of ​​the base metal where significant changes in structure and properties occur due to heat during welding. The coarse-grained heat-affected zone (CGHAZ) is the heat-affected zone closest to the weld. During welding, this area is heated to high temperatures, causing severe grain growth. After cooling, a coarse-grained, overheated structure is obtained, resulting in a severe decrease in toughness. Therefore, how to effectively refine the grains in the CGHAZ to achieve high toughness in this area has always been a major concern for scholars and welding engineers.

[0003] Arc welding is widely used in automobile chassis structures (base material thickness ≤ 6mm). During the research and development and testing process, it was found that fatigue cracks often initiated in the coarse-grained heat-affected zone of the chassis welding structure, and in severe cases, it led to failure. Surface defects near the coarse-grained heat-affected zone (unsmooth transition between weld and base material, undercut) and coarse grain structure in the coarse-grained heat-affected zone are important causes of fatigue failure. At present, conventional methods for optimizing the toughness of the coarse-grained heat-affected zone mainly include: adjusting welding parameters (line energy) and adding preheating and post-heating processes. Among them, the adjustment of welding parameters directly affects the grain size and toughness of the heat-affected zone, but it is subject to practical limitations of the engineering. For example, thin plates are not suitable for high line energy welding. Increasing preheating and post-heating can effectively regulate the heating and cooling speed of the welding thermal cycle, but it undoubtedly increases the cost and construction difficulty. Summary of the Invention

[0004] The present application provides a strain-following welding method for chassis welding to solve the following technical problem: how to refine the grain size of the coarse-grained heat-affected zone of chassis welding.

[0005] The present application provides a welding strain method for chassis welding, the method comprising:

[0006] Pre-treat at least two pieces of base metal to be welded;

[0007] Determining the relative distance between the welding point and the point where the plastic deformation is applied based on the time required for the temperature of the coarse-grained heat-affected zone of the weld to cool from the peak temperature to the set temperature and the average welding speed, so that the temperature where the plastic deformation is applied is greater than or equal to the set temperature;

[0008] The pre-treated base metal to be welded is welded to form a weld, and at the relative distance, plastic deformation is simultaneously applied to the base metal adjacent to the weld to form a plastic deformation zone inside the base metal.

[0009] Optionally, the relative distance satisfies the following relationship:

[0010] s≤vt

[0011] Wherein, v represents the average welding speed, and t represents the time required for the temperature of the coarse-grained heat-affected zone of the weld to drop from the peak temperature to the set temperature.

[0012] Optionally, the set temperature is the dynamic recrystallization temperature of the base material, so that dynamic recrystallization can occur in the coarse-grained heat-affected zone while applying plastic deformation.

[0013] Optionally, the dynamic recrystallization temperature of the base material is 950°C.

[0014] Optionally, t satisfies the following relationship:

[0015]

[0016] Where E represents the welding heat input, and the unit of E is J / cm; b represents the thickness of the base material to be welded, and the unit of b is cm; λ represents the thermal conductivity, and the unit of λ is w / (cm·℃), and the value of λ is 0.29; c represents the mass specific heat capacity, and the unit of c is J / (g·℃), and the value of c is 0.85; ρ represents the density, and the unit of ρ is g / cm 3 , the value of ρ is 7.9.

[0017] Optionally, the plastic deformation method includes: hammering, shot peening, ultrasonic treatment, electromagnetic plastic deformation and roller deformation.

[0018] Optionally, the curvature radius of the hammer head when struck by the small hammer satisfies the following relationship:

[0019] 0.05cm≤a≤0.5b

[0020] Wherein, a represents the radius of curvature of the hammer head, and the unit of a is cm; b represents the thickness of the base material to be welded, and the unit of b is cm.

[0021] Optionally, the hammering frequency of the small hammer is 100HZ~200HZ, and the maximum hammering force of the small hammer is 500N~1000N.

[0022] Optionally, the plastic deformation zone is the area from the weld toe to the coarse-grained heat-affected zone.

[0023] Optionally, the plastic deformation starts from the arc starting point of the welding and ends at the arc ending point of the welding, and the total distance of the plastic deformation is the same as the length of the weld.

[0024] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0025] An embodiment of the present application provides a strain-with-welding method for chassis welding. During the welding process, this method simultaneously introduces plastic deformation based on the principle of dynamic recrystallization of metal materials, and through the thermal-mechanical coupling effect, it can achieve the refinement of grains and structure in the coarse-grained heat-affected zone, surface modification, and pre-implanted compressive stress, thereby significantly improving the toughness and fatigue performance of the metal material. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0027] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0028] Figure 1 A flow chart of a strain-following welding method for chassis welding provided in an embodiment of the present application;

[0029] Figure 2 A schematic diagram of a strain-following welding method for chassis welding provided in an embodiment of the present application;

[0030] Figure 3 The metallographic structure diagram of the welded joint provided in Example 1 of the present application;

[0031] Figure 4 The metallographic structure diagram of the welded joint provided in Example 2 of the present application;

[0032] Figure 5 The metallographic structure diagram of the welded joint provided in Example 3 of the present application;

[0033] Figure 6 The metallographic structure diagram of the welded joint provided in Comparative Example 1 of this application;

[0034] Figure 7 The metallographic structure diagram of the welded joint provided in Comparative Example 2 of this application;

[0035] Figure 8 The metallographic structure diagram of the welded joint provided in Comparative Example 3 of this application;

[0036] Figure 9 This is a comparison chart of the -20°C impact toughness of the welded joints provided in Example 3 of the present application and Comparative Example 3. DETAILED DESCRIPTION

[0037] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0038] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be understood as a hard limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numbers within the range. For example, the description of a range from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which applies regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0039] In addition, in the description of the specification of this application, the terms "including", "comprising", etc. mean "including but not limited to". In this article, relational terms such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this article, "and / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. Wherein A and B can be singular or plural. In this article, "at least one" refers to one or more, and "plurality" refers to two or more. "At least one", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c", or "at least one of a, b and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, c can be single or multiple.

[0040] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0041] Figure 1 A flow chart of a strain-following welding method for chassis welding provided in an embodiment of the present application; Figure 2 A schematic diagram of a strain-following welding method for chassis welding provided in an embodiment of the present application.

[0042] See Figure 1 and Figure 2 The present application provides a welding strain method for chassis welding, the method comprising the following steps:

[0043] S1. Pre-treat at least two pieces of base metal to be welded;

[0044] S2. Determining the relative distance between the welding point and the point where the plastic deformation is applied based on the time required for the temperature of the coarse-grained heat-affected zone of the weld to cool from the peak temperature to the set temperature and the average welding speed, so that the temperature where the plastic deformation is applied is greater than or equal to the set temperature;

[0045] S3. Welding the pretreated base metal to be welded to form a weld, and simultaneously applying plastic deformation to the base metal adjacent to the weld at the relative distance to form a plastic deformation zone inside the base metal.

[0046] The heat affected zone (HAZ) in the welding process refers to the area caused by the heating of the surrounding materials during the welding process. In this area, the organizational structure and properties of the material will change. Among them, the coarse grain zone (CGZ) is an important area in the welding process, which refers to the area formed by the change of the grain structure of the welding zone. During the welding process, the temperature of the welding area will change, thereby affecting the growth and arrangement of the grains. If the temperature is too high or the welding speed is too fast, the grains in the welding area will become coarse, thereby forming a coarse grain zone. The key to step S3 is to ensure that the applied temperature of the plastic deformation of the spliced ​​base material is not lower than the set temperature, so as to introduce plastic deformation to the spliced ​​base material when the temperature of the heat affected zone is high, thereby refining the grain size of the coarse grain heat affected zone during the welding process.

[0047] In some embodiments, the relative distance satisfies the following relationship:

[0048] s≤vt

[0049] Wherein, v represents the average welding speed, and t represents the time required for the temperature of the coarse-grained heat-affected zone of the weld to drop from the peak temperature to the set temperature.

[0050] In some embodiments, the set temperature is the dynamic recrystallization temperature of the base material, so that dynamic recrystallization can occur in the coarse-grained heat-affected zone while plastic deformation is applied.

[0051] In some embodiments, the dynamic recrystallization temperature of the parent material is 950°C.

[0052] By controlling s≤vt, the temperature of high-temperature plastic deformation is ensured to be ≥950°C during the welding process, and dynamic recrystallization of the coarse-grained heat-affected zone is simultaneously achieved, thereby achieving grain refinement and improving toughness. At the same time, applying high-temperature plastic deformation can simultaneously optimize the surface morphology and pre-applied compressive stress of the weldment, achieving a significant improvement in fatigue performance. If s>vt, the temperature of the hammer point will be lower than the dynamic recrystallization temperature, and the effect of dynamic recrystallization and grain refinement cannot be achieved. At the same time, too low a temperature will make it difficult to plastically deform the steel, and it will be difficult to shape the hammer head and implant compressive stress.

[0053] In some embodiments, t satisfies the following relationship:

[0054]

[0055] Where E represents the welding heat input, and the unit of E is J / cm; b represents the thickness of the base material to be welded, and the unit of b is cm; λ represents the thermal conductivity, and the unit of λ is w / (cm·℃), and the value of λ is 0.29; c represents the mass specific heat capacity, and the unit of c is J / (g·℃), and the value of c is 0.85; ρ represents the density, and the unit of ρ is g / cm 3 , the value of ρ is 7.9.

[0056] The thickness of automobile chassis steel is relatively thin, so the calculation formula of t is reasonably designed.

[0057] In some embodiments, the plastic deformation method includes: hammering, shot peening, ultrasonic treatment, electromagnetic plastic deformation and roller deformation.

[0058] The introduction of plastic deformation will generate residual compressive stress inside the spliced ​​base material, which helps to refine the grain size of the coarse-grained heat-affected zone during welding and improve the microstructure of the weld joint.

[0059] Preferably, the plastic deformation is performed by hammering with a small hammer.

[0060] Description and principle of the plastic deformation method using a hammer: An electric hammer (deformation device) is synchronously followed by the welding torch. The steel heated by the welding torch (corresponding to the coarse-grained heat-affected zone) has excellent plasticity, and the hammer can cause large plastic deformation in this area with relatively small force. The hammer's striking action implants surface compressive stress on the surface of the welded steel and modifies the surface, which can significantly increase the fatigue life of this area. Due to the hammering at high temperature, dynamic recrystallization occurs in the heated area, significantly refining the austenite grains and microstructure, thereby significantly improving strength and plastic toughness.

[0061] The purpose of hammering is to create compressive stress on the surface of the weld toe. It also reduces the sharpness of existing notches, thereby reducing stress concentration and significantly improving the fatigue strength of the joint. Fatigue failure tends to initiate on the component surface. Traditionally, mechanical methods (such as extrusion and hammering) or shot peening have been used to treat the weld surface and transition zone, offering two benefits: creating favorable surface compressive stress and locally hardening the material, thereby increasing fatigue strength. This demonstrates the theoretical possibility of improving the fatigue performance of welded structures through hammering during welding.

[0062] The applicant of this application has proved through multiple rounds of experiments that this solution can effectively refine the grains and structure of the coarse-grained heat-affected zone. At the same time, it has also been verified that this application solution can effectively improve the toughness of the coarse-grained heat-affected zone.

[0063] In some embodiments, the radius of curvature of the hammer head when struck by the small hammer satisfies the following relationship:

[0064] 0.05cm≤a≤0.5b

[0065] Wherein, a represents the radius of curvature of the hammer head, and the unit of a is cm; b represents the thickness of the base material to be welded, and the unit of b is cm.

[0066] Determine the width of the coarse-grained heat-affected zone (generally 1mm to 3mm) based on the welding heat input and the type and specifications of the base material. Select a hammer head of appropriate size, limiting the radius of curvature of the hammer head to 0.05cm to 1 / 2 the plate thickness, to ensure that the hammer mark can completely cover the area from the weld toe to the coarse-grained heat-affected zone.

[0067] In some embodiments, the hammering frequency of the small hammer is 100 Hz to 200 Hz, and the maximum hammering force of the small hammer is 500N to 1000N.

[0068] The hammering frequency is limited to 100Hz to 200Hz, and the maximum hammering force is limited to 500N to 1000N. This allows strain to be introduced simultaneously during the same weld pass, achieving dynamic recrystallization and grain refinement without the need for additional heating. If the hammering frequency is lower than 100Hz, or the maximum hammering force is lower than 500N, the strain will be insufficient and the grain size will not be significantly refined. For example, the hammering frequency of the small hammer can be 100HZ, 110HZ, 120HZ, 130HZ, 140HZ, 150HZ, 160HZ, 180HZ, 200HZ, etc., and the maximum hammering force of the small hammer can be 500N, 550N, 600N, 650N, 700N, 750N, 800N, 850N, 900N, 950N, 1000N, etc.

[0069] In some embodiments, the plastic deformation zone is a region from the weld toe to the coarse-grained heat-affected zone.

[0070] In some embodiments, the plastic deformation starts at the arc starting point of the welding and ends at the arc ending point of the welding, and the total distance of the plastic deformation is the same as the length of the weld.

[0071] Specifically, fix the relative position of the welding gun and hammer head and start welding. The hammering starts at the arc starting point and ends at the arc ending point. The hammering distance is equal to the weld length.

[0072] This application applies hammering during the welding process, which not only improves the surface morphology and stress distribution of the weld toe, but also achieves dynamic recrystallization at the hammered area through the coupling of welding thermal cycle and hammering, refining the grain size and microstructure. This not only improves the fatigue life of the welded structure, but also significantly enhances toughness.

[0073] In summary, in the present application, during the welding process, the metal material is subjected to the combined action of thermal stress and mechanical stress, resulting in plastic deformation. In order to more effectively refine the grains and structure, the present application applies additional plastic deformation on the welding path (such as through auxiliary rolling, vibration, striking and other devices), or pre-treats the material before welding (such as shot peening), thereby simultaneously introducing greater plastic deformation during the welding process. Additional plastic deformation can further promote the dynamic recrystallization process and refine the grain structure. At the same time, the present application precisely controls the thermal-mechanical coupling effect, so that under the combined action of high temperature and stress, the grains in the coarse-grained heat-affected zone are refined, and a more uniform and dense microstructure is formed. In addition, the thermal stress and mechanical stress generated during the welding process can not only refine the grains, but also modify the metal surface. Therefore, the present application is based on the principle of dynamic recrystallization of metal materials and simultaneously introduces plastic strain during the welding process. By utilizing the thermal-mechanical coupling effect, the grain and structure refinement, surface modification and pre-stressing of the coarse-grained heat-affected zone are achieved simultaneously, achieving a significant improvement in toughness and fatigue performance.

[0074] This application provides a strain-following welding method for chassis welding, the technical advantages of which include:

[0075] 1. Grain refinement: By applying plastic deformation during welding, the grain size of the coarse-grained heat-affected zone can be significantly refined, thereby improving the mechanical properties and crack resistance of the weld joint.

[0076] 2. Improve microstructure: The introduction of plastic deformation can also improve the microstructure of the weld joint and reduce welding defects such as pores and cracks.

[0077] 3. Improve welding quality: This method helps to improve the overall quality of chassis welding, making the welded joints more solid and reliable, and meeting the chassis structure's requirements for strength, rigidity, and durability.

[0078] With the continuous development of the automotive industry, the requirements for chassis welding quality are becoming increasingly stringent. This strain-with-weld method provides an effective technical means to address the coarse grain problem in chassis welding and has broad application prospects. In the future, with the continuous improvement and widespread application of the technology, this method is expected to be applied in more fields, contributing to improving the overall performance of welded structural components.

[0079] The present application will be further described below in conjunction with specific examples. It should be understood that these examples are intended to illustrate the present application only and are not intended to limit the scope of the present application. The experimental methods in the following examples where specific conditions are not specified are generally measured according to industry standards. If there are no corresponding industry standards, then the methods are carried out according to general international standards, conventional conditions, or the conditions recommended by the manufacturer.

[0080] Example 1

[0081] This embodiment provides a welding strain method for chassis welding, the method comprising:

[0082] S11. Clean the oil, dirt, rust, scale, protective layer and oxide film on the surface of the weld or the surface within 20 mm to 30 mm on both sides of the groove of at least two pieces of base metal to be welded to ensure welding quality; wherein, the chemical composition of the base metal to be welded, by mass fraction, is as follows: C: 0.06%, Si: 0.13%, Mn: 1.26%, Ni: 4.0%, Cr: 0.53%, Mo: 0.53%, V: 0.02%, Nb: 0.05%, Ti: 0.03% and Fe: 93.39%;

[0083] S21. Determine the distance s between the welding gun and the hammer tip based on the time t required for the temperature of the coarse-grained heat-affected zone to cool from the peak temperature to the set temperature and the average speed v of the welding gun during welding. Where v is 0.8 cm / s, and t is determined using the following empirical formula: Where E is 3800 J / cm; b is 0.4 cm; λ is 0.29 w / (cm·℃); c is 0.85 J / (g·℃); ρ is 7.9 g / cm 3 , t is calculated to be 5s. Therefore, it is determined that the relative distance s is set to 4cm, at which time the temperature of the hammer hitting point is about 1100℃;

[0084] S31. Fix the relative positions of the welding gun and hammer head, weld the pretreated base metal to be welded, and form a joint base metal with a weld seam. Then, strike the base metal adjacent to the weld seam with an electric hammer, starting at the arc start and ending at the arc end. The hammering distance is equal to the weld seam length to form a plastic deformation zone and obtain the welded joint. The hammering frequency is 100 Hz and the hammering force is 500 N.

[0085] The impact toughness of the welded joint at -20℃ is 101J, the impact toughness at room temperature is 113J, and the fatigue strength is 83MPa.

[0086] Figure 3 This is the metallographic structure diagram of the welded joint provided in Example 1 of the present application. Figure 3 It can be seen that the grain boundaries in the heat-affected zone are deformed by hammering, and the grain size is slightly refined.

[0087] Example 2

[0088] The difference between this embodiment and embodiment 1 is that the distance s between the welding gun and the hammer is 6 cm, the temperature of the hammer striking point is about 950° C., the hammering frequency is 200 Hz, and the hammering force is 1000 N.

[0089] The impact toughness of the welded joint at -20℃ is 115J, the impact toughness at room temperature is 132J, and the fatigue strength is 94MPa.

[0090] Figure 4 The metallographic structure diagram of the welded joint provided in Example 2 of this application. Figure 4 It can be seen that the grain boundaries in the heat-affected zone are deformed by hammering, and the grain size is slightly refined.

[0091] Example 3

[0092] The difference between this embodiment and embodiment 1 is that the distance s between the welding gun and the hammer is 4 cm, the temperature of the hammer striking point is about 1100° C., the hammer striking frequency is 150 Hz, and the hammer striking force is 800N.

[0093] The impact toughness of the welded joint at -20℃ is 165J, the impact toughness at room temperature is 173J, and the fatigue strength is 133MPa.

[0094] Figure 5 This is the metallographic structure diagram of the welded joint provided in Example 3 of the present application. Figure 5 It can be seen that the grain boundaries in the heat-affected zone were deformed by hammering, but became smooth after sufficient recrystallization, and the grain size was significantly refined.

[0095] A comparison of Examples 1 to 3 shows that the striking force and frequency of Example 1 are insufficient, and the striking temperature of Example 2 is too low, resulting in insufficient recrystallization. This results in insufficient grain refinement in Examples 1 and 2, and only limited impact toughness and fatigue strength. Example 3 is the optimal example, with significantly refined grain size in the heat-affected zone, and significantly improved impact toughness and fatigue strength of the welded joint.

[0096] Comparative Example 1

[0097] The difference between this comparative example and Example 1 is that the distance s between the welding gun and the hammer is 8 cm, the temperature of the hammer striking point is about 900° C., the hammer striking frequency is 80 Hz, and the hammer striking force is 400 N.

[0098] The impact toughness of the welded joint at -20℃ is 78J, the impact toughness at room temperature is 92J, and the fatigue strength is 71MPa.

[0099] Figure 6 The metallographic structure diagram of the welded joint provided in comparative example 1 of this application. Figure 6 It can be seen that the grain boundaries in the heat-affected zone did not deform after hammering (the hammering force and frequency were insufficient, and the hammering temperature was too low). The grain size did not change.

[0100] Comparative Example 2

[0101] The difference between this comparative example and Example 1 is that the distance s between the welding gun and the hammer is 8 cm, the temperature of the hammer striking point is about 900° C., the hammer striking frequency is 300 Hz, and the hammer striking force is 1200 N.

[0102] The impact toughness of the welded joint at -20℃ is 38J, the impact toughness at room temperature is 49J, and the fatigue strength is 55MPa.

[0103] Figure 7 The metallographic structure diagram of the welded joint provided in Comparative Example 2 of this application is as follows: Figure 7 It can be seen that the grain boundaries in the heat-affected zone are not deformed by hammering (the hammering force and hammering frequency are too high, causing large internal stress), and the grain size does not change.

[0104] Comparative Example 3

[0105] The difference between this comparative example and Example 1 is that the welding is conventional welding without hammering.

[0106] The -20℃ impact toughness of the welded joint is 60J.

[0107] Figure 8 The metallographic structure diagram of the welded joint provided in comparative example 3 of this application. Figure 8 It can be seen that the grain boundaries are not deformed (not hammered) and the grain size does not change.

[0108] Figure 9 This is a comparison chart of the impact toughness of the welded joints provided in Example 3 and Comparative Example 3 at -20°C. Figure 9 It can be seen that by adopting the strain-following welding method of Example 3, the -20°C impact toughness of the coarse-grained heat-affected zone can be increased from 60 J to 165 J.

[0109] In addition, it should be noted that the fatigue tests of the welded joints under five different welding parameters were carried out on an INSTRON 880 fatigue testing machine in the examples and comparative examples. The fatigue tests of 10 samples in each batch were carried out under the stress ratio R = 0.2 (R = σ min / σ max ) and a load variation frequency of 20 Hz under several stress ranges until failure. The SN curve is determined and the fatigue category FAT value is calculated according to the International Institute of Welding (IIW) regulations.

[0110] In addition, one or more technical solutions in the embodiments of the present application have at least the following technical effects or advantages:

[0111] In the embodiments of the present application, during the welding process, the coarse-grained heat-affected zone behind the welding heat source is plastically deformed (without limitation to methods and means), and the heating of the welding heat source and the coupling effect of deformation are used to form dynamic recrystallization in the deformation area, thereby achieving grain refinement and improving toughness; and a method of using the high temperature of the thermal cycle to achieve surface modification and pre-implanted compressive stress of the weld joint with a small external force to achieve improved fatigue life.

[0112] In the embodiment of the present application, the equipment modification is simple, hardly affects the welding rhythm, and is low in cost.

[0113] In the embodiment of the present application, welding and forming are achieved simultaneously, and integrated control of structure and performance is achieved simultaneously.

[0114] In the embodiments of the present application, multiple mechanical properties (strength, plasticity, toughness, and fatigue performance) of the welded structure can be significantly improved simultaneously. The welded joint has a -20°C impact toughness of ≥100J, a room temperature impact toughness of ≥110J, and a fatigue strength of ≥80MPa.

[0115] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features of the present application.

Claims

1. A welding strain method for chassis welding, characterized in that: The method comprises: Pre-treat at least two pieces of base metal to be welded; Determine the relative distance between the welding point and the point where the plastic deformation is applied based on the time required for the temperature of the coarse-grained heat-affected zone of the weld to cool from the peak temperature to the set temperature, and the average welding speed, so that the temperature where the plastic deformation is applied is greater than or equal to the set temperature; Welding the pretreated parent metal to be welded to form a weld, and simultaneously applying plastic deformation to the parent metal adjacent to the weld at the relative distance to form a plastic deformation zone inside the parent metal; The relative distance satisfies the following relationship: s≤vt Wherein, v represents the average welding speed, and t represents the time required for the temperature of the coarse-grained heat-affected zone of the weld to cool from the peak temperature to the set temperature; The set temperature is the dynamic recrystallization temperature of the base material, so that dynamic recrystallization can occur in the coarse-grained heat-affected zone while plastic deformation is applied.

2. The method according to claim 1, characterized in that The dynamic recrystallization temperature of the base material is 950°C.

3. The method according to claim 1, characterized in that The plastic deformation methods include: hammering, shot peening, ultrasonic treatment, electromagnetic plastic deformation and roller deformation.

4. The method according to claim 3, characterized in that The curvature radius of the hammer head struck by the small hammer satisfies the following relationship: 0.05cm≤a≤0.5b Wherein, a represents the radius of curvature of the hammer head, and the unit of a is cm; b represents the thickness of the base material to be welded, and the unit of b is cm.

5. The method according to claim 4, characterized in that The hammering frequency of the small hammer is 100HZ to 200HZ, and the maximum hammering force of the small hammer is 500N to 1000N.

6. The method according to claim 1, characterized in that The plastic deformation zone is the area from the weld toe of the spliced ​​base material to the coarse-grained heat-affected zone.

7. The method according to claim 1, characterized in that The plastic deformation starts from the arc starting point of the welding and ends at the arc ending point of the welding, and the total distance of the plastic deformation is the same as the length of the weld.

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