Welding-following strain method for chassis welding

Abstract

The invention provides a welding-following strain method for chassis welding, and belongs to the field of welding. The method comprises the steps that at least two pieces of base metal to be welded are pretreated; according to the time required for reducing the temperature of a coarse grain heat affected zone of welding from the peak temperature to the set temperature and the average speed of welding, the relative distance between a welding point of welding and an application point of plastic deformation is determined, so that the application temperature of the plastic deformation is larger than or equal to the set temperature; and the pretreated to-be-welded base metal is welded to form a weld joint, and plastic deformation is synchronously applied to the base metal close to the weld joint under the relative distance, so that a plastic deformation area is formed in the base metal. In the welding process, based on the principle of dynamic recrystallization of metal materials, plastic deformation is introduced synchronously, and refining of grains and structures in a coarse grain heat affected zone can be achieved through the heat-force coupling effect.

Description

Technical Field

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

[0002] Arc welding is a welding process that uses the arc generated between the electrode and the substrate to melt the base metal and the filler metal, thereby obtaining a non-detachable joint with metallurgical bonding characteristics. The welding heat affected zone refers to the area where the base metal undergoes obvious changes in structure and properties 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 a high temperature, causing severe grain growth. After cooling, a coarse-grained overheated structure is obtained, and the toughness is severely reduced. Therefore, how to effectively refine the grains in the coarse-grained heat affected zone to achieve high toughness in this area has always been a major concern of scholars and welding engineers.

[0003] Arc welding is widely used in automobile chassis structures (parent 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, which led to failure in severe cases. Surface defects near the coarse-grained heat-affected zone (unsmooth transition between weld and parent 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 (wire 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 the actual limitations of the project. For example, thin plates are not suitable for high wire 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-with-welding method for chassis welding to solve the following technical problem: how to refine the grain size of a 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] According to 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, and the average speed of the weld, the relative distance between the welding point and the application point of the plastic deformation is determined so that the application temperature of the plastic deformation is ≥ 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 welding 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 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 thermal conductivity, and the unit of λ is w / (cm·℃), and the value of λ is 0.29; c represents mass specific heat capacity, and the unit of c is J / (g·℃), and the value of c is 0.85; ρ represents 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 radius of curvature of the hammer head 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 a region 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] The embodiment of the present application provides a strain-on-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 coupling of heat and force, 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 drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

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

[0029] Figure 2 A schematic diagram of a strain-with-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 the present application;

[0034] Figure 7 The metallographic structure diagram of the welded joint provided for comparative example 2 of the present application;

[0035] Figure 8 The metallographic structure diagram of the welded joint provided for comparative example 3 of the present application;

[0036] Fig. 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] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work 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 rigid 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 numerical values ​​within the range. For example, the range description 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 apply 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 the present application, the terms "including", "comprising", etc. mean "including but not limited to". In this article, relational terms such as "first" and "second", etc. are only 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" means one or more, and "plurality" means two or more. "At least one", "the following at least one item (items)" or similar expressions refer to any combination of these items, including any combination of single items (items) or plural items (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 plural, respectively.

[0040] Unless otherwise specified, various 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-with-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 also 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 base materials to be welded;

[0044] S2. Determine the relative distance between the welding point and the application point of the plastic deformation according to the time required for the temperature of the coarse-grained heat-affected zone of the welding to drop 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;

[0045] S3, 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.

[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, thus 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 welding 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 applying plastic deformation.

[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℃ 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-stress of the weldment, thereby significantly improving 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 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 thermal conductivity, and the unit of λ is w / (cm·℃), and the value of λ is 0.29; c represents mass specific heat capacity, and the unit of c is J / (g·℃), and the value of c is 0.85; ρ represents 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, therefore, 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 welded joint.

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

[0060] Description and principle of the scheme of plastic deformation by hammering: An electric hammer (deformation device) is synchronously followed behind the welding gun. The steel heated by the welding gun (corresponding to the coarse-grained heat-affected zone) has good plasticity, and the hammer can cause large plastic deformation in this area with a small force. The striking action of the hammer implants surface compressive stress on the surface of the welded steel and modifies the surface, which can greatly improve the fatigue life of this area. Due to the hammering at high temperature, dynamic recrystallization will occur in the heated part, which greatly refines the austenite grains and structure, thereby greatly improving the strength and plastic toughness.

[0061] The role of hammering is to create compressive stress on the surface of the joint weld toe; at the same time, hammering can also reduce the sharpness of the existing notch, thereby reducing stress concentration, which is also the reason for significantly improving the fatigue strength of the joint. Fatigue damage is easy to start from the surface of the component. Traditionally, mechanical methods (extrusion and hammering, etc.) or shot peening are used to treat the weld surface and transition zone, which can bring two benefits: forming favorable surface compressive stress and causing local work hardening of the material, thereby improving fatigue strength. These show in principle the possibility of improving the fatigue performance of welded structures by hammering during welding.

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

[0063] In some embodiments, the radius of curvature of the hammer head 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] According to the welding heat input and the specifications of the base material, the width of the coarse-grained heat-affected zone (generally 1mm to 3mm) is determined. The hammer head of appropriate size is selected, and the radius of curvature of the hammer head should be limited to 0.05cm to 1 / 2 of the plate thickness, so as 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 of the small hammer is limited to 100HZ~200HZ, and the maximum hammering force of the small hammer is 500N~1000N, so that strain can be introduced simultaneously in the same welding pass, and dynamic recrystallization and grain refinement can be achieved without additional heating. If the hammering frequency of the small hammer is lower than 100HZ, or the maximum hammering force of the small hammer is lower than 500N, the strain force is insufficient and the grain size will not be significantly refined. Exemplarily, 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 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.

[0071] Specifically, fix the relative position of the welding gun and the 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 length of the weld.

[0072] The present invention performs hammering during the welding process, which can not only improve the surface morphology and stress distribution of the weld toe, but also realize dynamic recrystallization of the hammered part under the coupling effect of welding thermal cycle and hammering, and refine the grains and structure. It can not only improve the fatigue life of the welded structure, but also greatly improve the toughness.

[0073] In summary, in the welding process of the present application, the metal material will be subjected to the combined action of thermal stress and mechanical stress, resulting in plastic deformation. In order to more effectively refine the grains and organization, 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), so as to simultaneously introduce 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 accurately 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 can be 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 coupling effect of heat and force, 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] The present application provides a welding strain 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 welded joint.

[0076] 2. Improve microstructure: The introduction of plastic deformation can also improve the microstructure of the welded 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 welding joints more firm and reliable, and meeting the chassis structure's requirements for strength, rigidity and durability.

[0078] With the continuous development of the automobile industry, the requirements for chassis welding quality are becoming higher and higher. This welding strain method provides an effective technical means to solve the coarse grain problem in chassis welding and has broad application prospects. In the future, with the continuous improvement and promotion of technology, this method is expected to be applied in more fields and contribute to improving the overall performance of welded structural parts.

[0079] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are intended only to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are usually measured according to industry standards. If there is no corresponding industry standard, then the conditions recommended by the manufacturer are followed.

[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 welding place or the surface within 20mm to 30mm on both sides of the groove of at least two pieces of base materials to be welded to ensure the welding quality; wherein, the chemical composition of the base materials to be welded is, by mass fraction, 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 head according to the time t required for the temperature of the coarse-grained heat-affected zone of welding to drop 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 by 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 position of the welding gun and the hammer head, weld the pre-treated base material to be welded, form a spliced ​​base material with a weld, and strike the spliced ​​base material adjacent to the weld with an electric hammer, starting from the arc starting point and ending at the arc closing point. The hammering distance is equal to the weld length to form a plastic deformation zone and obtain a welded joint after welding; wherein the hammering frequency is 100Hz with welding strain, and the hammering force is 500N.

[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 were deformed by hammering, and the grain size was 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, and the temperature of the hammer striking point is about 950° C. The hammer striking frequency is 200 Hz and the hammer striking force is 1000N.

[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 This is the metallographic structure diagram of the welded joint provided in Example 2 of the present application. Figure 4 It can be seen that the grain boundaries in the heat-affected zone were deformed by hammering, and the grain size was 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, and 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 -20℃ impact toughness of the welded joint is 165J, the room temperature impact toughness 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 are deformed by hammering, but become smooth after sufficient recrystallization, and the grain size is significantly refined.

[0095] From the comparison of Examples 1 to 3, it can be seen that the knocking force and frequency of Example 1 are insufficient, the knocking temperature of Example 2 is too low, and the recrystallization is insufficient, resulting in insufficient grain refinement in Examples 1 and 2, and only impact toughness and fatigue strength can be improved to a certain extent. Example 3 is the best example, the grain size of the heat-affected zone is significantly refined, and the impact toughness and fatigue strength of the welded joint are significantly improved.

[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, and the temperature of the hammer striking point is about 900° C. The hammer striking frequency is 80 Hz and the hammer striking force is 400N.

[0098] The -20℃ impact toughness of the welded joint is 78J, the room temperature impact toughness 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 the present 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, and the temperature of the hammer striking point is about 900° C. The hammer striking frequency is 300 Hz, and the hammer striking force is 1200N.

[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 for comparative example 2 of the present application is as follows: Figure 7 It can be seen that the grain boundaries in the heat-affected zone were not deformed after hammering (the hammering force and hammering frequency were too high, causing large internal stress), and the grain size did 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 the present application. Figure 8 It can be seen that the grain boundaries are not deformed (not hammered) and the grain size does not change.

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

[0109] In addition, it should be noted that the fatigue tests of welded joints under five different welding parameters were carried out on an INSTRON 880 fatigue testing machine in the embodiments 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 several stress ranges with a load change frequency of 20 Hz until failure. The SN curve is determined and the fatigue category FAT value is calculated according to the provisions of the International Institute of Welding (IIW).

[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 dynamic recrystallization is formed in the deformation area by utilizing the heating of the welding heat source and the coupling effect of deformation, thereby achieving grain refinement and improving toughness; and utilizing the high temperature of the thermal cycle to achieve surface modification and pre-implanted compressive stress of the weld joint with a relatively small external force, thereby improving fatigue life.

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

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

[0114] In the embodiment of the present application, it is possible to simultaneously achieve a substantial improvement in multiple mechanical properties (strength, plasticity, toughness, fatigue performance) of the welded structure. The impact toughness of the welded joint after welding is ≥100J at -20°C, ≥110J at room temperature, and the fatigue strength is ≥80MPa.

[0115] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

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; According to 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, and the average speed of the weld, the relative distance between the welding point and the application point of the plastic deformation is determined so that the application temperature of the plastic deformation is ≥ the set temperature; 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.

2. The method according to claim 1, characterized in that 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 welding to drop from the peak temperature to the set temperature.

3. The method according to claim 2, characterized in that The set temperature is the dynamic recrystallization temperature of the base material, so that the coarse-grained heat affected zone can undergo dynamic recrystallization while plastic deformation is applied.

4. The method according to claim 3, characterized in that The dynamic recrystallization temperature of the base material is 950°C.

5. The method according to claim 2, characterized in that: t satisfies the following relationship: Where, E represents 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 thermal conductivity, and the unit of λ is w / (cm·℃), and the value of λ is 0.29; c represents mass specific heat capacity, and the unit of c is J / (g·℃), and the value of c is 0.85; ρ represents density, and the unit of ρ is g / cm 3 , the value of ρ is 7.

9.

6. 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.

7. The method according to claim 6, characterized in that The radius of curvature 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.

8. The method according to claim 7, characterized in that The hammering frequency of the small hammer is 100HZ-200HZ, and the maximum hammering force of the small hammer is 500N-1000N.

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

10. 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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