Method for in-line rapidly and synchronously improving strength and plasticity of weld seam

Abstract

In a method for in line rapidly and synchronously improving the strength and plasticity of a weld seam, electropulse generating devices are provided on two sides of the advancing direction of a welding gun (1). During welding, the welding gun (1) performs filler wire welding in a circular swinging mode, the electropulse generating devices and the welding gun (1) move synchronously, and simultaneously a protective gas is supplied to a welding position.

Description

Method for improving strength and plasticity of weld seam in line and quickly and synchronously TECHNICAL FIELD

[0001] The present application relates to a method for improving the strength and plasticity of a weld seam, in particular to a method for improving the strength and plasticity of a weld seam in line and quickly and synchronously, and belongs to the technical field of electric pulse processing. BACKGROUND

[0002] Since the advent of welding technology, it has been widely used in aerospace, shipbuilding, construction, pipeline containers and other industries, and plays a key role. So far, there are many mature welding methods, such as electric arc welding, laser welding, plasma welding, friction stir welding, etc. The performance of the weld after welding is the most critical factor in determining the quality of the welding. However, not all welds are excellent in performance from the beginning, and often need to be post-processed to improve the quality of the weld, such as heat treatment, laser quenching, carburizing treatment, etc. But the conventional heat treatment is difficult to consider both strength and plasticity, and cannot improve both strength and plasticity at the same time, and the processing time is relatively long, which cannot meet the current application.

[0003] Take CMT welding as an example, which belongs to a kind of electric arc welding. Cold metal transfer welding technology (Cold Metal Transfer, CMT) is a new type of welding process technology without slag spatter, which is evolved on the basis of short circuit transfer. Short circuit transfer, that is, the welding wire is sent into the molten drop, and the molten drop is in contact with the molten pool before it is separated from the welding wire, forming a liquid metal short circuit, and the short circuit bridge explodes, and the molten drop falls off, and then the welding wire is stretched out to restart the arc. The current CMT welding machine has two independent wire feeding systems, so that the welding wire is continuously withdrawn when feeding, that is, discontinuous wire feeding. When the welding wire is fed, the arc is started, and at the moment when the molten drop contacts the molten pool, the power supply automatically reduces the short circuit current to nearly zero, and the heat input at this time is also zero, then the welding wire is withdrawn to help the molten drop fall off, and the welding wire continues to feed in this way. Compared with traditional gas shielded welding MIG / MAG, it has the advantages of fast arc starting, low welding heat input, no spatter after welding, small welding deformation, etc., and is currently widely used in aluminum alloy plate, especially aluminum alloy thin plate welding. The performance of the weld during welding is the most critical factor in determining the quality of the welding. However, not all welds have excellent performance during the welding process of the existing CMT welding machine, and generally need to be heat treated after welding to improve the mechanical properties of the sample, but the conventional heat treatment is difficult to consider both strength and plasticity, and cannot improve both strength and plasticity at the same time, and the processing time is relatively long, which cannot meet the current application. SUMMARY

[0004] The technical problem to be solved by the present application is to overcome the defects of the prior art and provide a method for processing quickly and improving the strength and plasticity of CMT welds at the same time.

[0005] Electropulsing Treatment (EPT) can improve the plasticity of materials without reducing or even improving the strength, and it is short-time and high-efficiency. The electropulsing treatment is the result of the coupling of multiple physical fields. Part of the energy of the electric pulse is used to form thermal effect, which is the same as the thermal effect generated by direct current, and the essence is Joule heat effect. The electroplasticity is mainly caused by the non-thermal effect of the electric pulse. The non-thermal effect includes magnetic compression effect, skin effect, induced magnetic field effect and electron wind effect. The magnetic compression effect and the skin effect have little effect on the sample, and are not discussed. The induced magnetic field effect promotes the movement of dislocations by weakening the binding force between dislocations and dislocation pinning, thereby improving the plasticity of the material. The electron wind effect promotes the movement of dislocations by high-speed moving electrons to improve the plasticity of the material. The non-thermal effect of the electric pulse reduces the migration barrier of atoms, promotes the movement of dislocations, and opens the dislocation entanglement, thereby promoting the occurrence of recrystallization and phase change. However, the effect of the electric pulse cannot be simply understood as promoting the movement of dislocations, it also promotes the interaction between electrons and atoms, vacancies and second phases, such as refining grains, promoting the dissolution or precipitation of second phases. The electric pulse treatment can promote grain refinement. The finer the grain, the more the number of grains in a certain volume, and the more uniform the deformation under the same deformation, and the less the dislocation accumulation in each grain, the less the cracking opportunity caused by stress concentration, and it may be able to withstand a larger deformation before breaking, that is, it shows higher plasticity. In fine-grained metal, cracks are not easy to initiate and propagate, so more energy is absorbed during the fracture process, showing higher toughness.

[0006] The essence of grain refinement is the migration of grain boundaries / phase boundaries, which is driven by the difference in deformation energy or Gibbs energy between the new phase and the matrix. The driving force in the electric pulse treatment process is shown as formula 1:

[0007] In formula 1, ΔE is the additional driving force generated after electrification, which does not exist without electrification; E D is the driving force in the electric pulse treatment process (kJ); E Volume is the volume energy (kJ); E GB is the grain boundary energy (kJ); E TH is the thermal driving force (kJ); E ATH is the driving force provided by the current (kJ); 2a is the grain boundary thickness (nm); ΔS is the entropy difference between the grain boundary and the grain (J*mol -1 *K -1 ); gradT is the temperature gradient (k / m); E is the atomic volume (cm 3 / mol); e is the charge of an electron (C); n e is the electron density (kg / m3 J is the current density (A / m 2 ); p / N is the resistivity ratio per unit dislocation length (Ω / m). Thus E Volume and E GB are considered as the initial driving force (ΔW0), and E TH and E ATH are defined as the additional driving force (ΔW e ).

[0008] According to the classical nucleation theory, the grain size ratio of the untreated alloy and the electric pulse treated alloy is shown in formula 2:

[0009] In formula 2: d e and d0 are the grain sizes (mm) of the untreated alloy and the electric pulse treated alloy respectively; T is the temperature (K); K is a constant related to the material; and Exp is the exponential function with the natural constant e as the base.

[0010] To solve the above technical problems, the method for improving the strength and plasticity of a weld seam provided by the present application comprises the following steps: arranging an electric pulse generating device on both sides of the welding gun in the advancing direction of the welding gun; and moving the electric pulse generating device and the welding gun in the same direction synchronously during welding, and simultaneously delivering protective gas to the welding position.

[0011] In the present application, the electric pulse generating device and the welding gun move at the same speed.

[0012] In the present application, the welding gun performs the filler wire welding in the manner of clockwise circular swing.

[0013] In the present application, the voltage of the electric pulse generating device is 0.74-0.77 V, the current is 48-52 A, the duty cycle is 42-47%, and the frequency is 95-102 Hz.

[0014] In the present application, the protective gas is pure Ar with a purity of 99.999%.

[0015] The present application has the following beneficial effects: (1) the strength and plasticity of the weld seam after welding often cannot meet the use requirements, and by simultaneously adding electric pulse instantaneous treatment during welding, the strength and plasticity of the weld seam can be improved through the multi-physical field coupling effect of the electric pulse, the reduction of atomic migration barrier, the promotion of dislocation movement, and the opening of dislocation entanglement, thereby eliminating the complicated procedures such as post-weld heat treatment of the test piece, and achieving simplicity and high efficiency; (2) the electric pulse generating device and the welding gun move forward at the same speed, which can further improve the strength and plasticity of the weld seam; (3) the device used in the present method has a simple structure and is easy to operate, does not increase unnecessary processing steps, and is efficient and fast in the entire welding process. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced as follows. Obviously, the accompanying drawings in the following description only represent some embodiments of the present application, and all other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative effort belong to the protection scope of the present application.

[0017] Fig. 1 is a schematic diagram of the arrangement of a welding torch, a welding plate and an electric pulse generating device;

[0018] Fig. 2 is a schematic diagram of a circular oscillation trajectory of a welding torch;

[0019] Fig. 3 is a comparison diagram of tensile force-displacement curves of welding joints with and without electric pulse treatment;

[0020] Fig. 4 is a comparison of tensile DIC stress-strain cloud maps of welding joints with and without electric pulse treatment, (a) is without treatment, (b) is Example 1, (c) is Example 2, and (d) is Example 3.

[0021] Fig. 5 is a comparison diagram of tensile fracture micro-morphologies of welding joints with and without electric pulse treatment, (a) is without treatment, (b) is Example 1, (c) is Example 2, and (d) is Example 3.

[0022] Fig. 5 is a comparison diagram of tensile fracture micro-morphologies of welding joints with and without electric pulse treatment, (a) is without treatment, (b) is Example 1, (c) is Example 2, and (d) is Example 3.

[0023] In the figure: 1-welding torch, 2-welding workpiece, 3-guide frame, 31-sliding roller, 32-guide rod. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. The components of the embodiments of the present application described and shown in the accompanying drawings herein can be arranged and designed in various different configurations.

[0025] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative effort belong to the protection scope of the present application.

[0026] It should be noted that: similar reference numerals and letters represent similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0027] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship when the product of the present application is usually placed, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second", "third" and the like are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0028] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "arrangement", "installation", "connection", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0029] Some embodiments of the present application will be described in detail below with reference to the accompanying drawings. The following examples and features in the examples can be combined with each other without conflict.

[0030] As shown in FIG. 1, the technical scheme provided in Example 1 adopts a CMT welding head for the welding torch 1, and the welding torch 2 is arranged directly above the groove of the workpiece to be welded 2. The welding torch 2 includes a protective gas feeding mechanism, and the electric pulse generating device adopts a SOYI-368000M type. The electric pulse generating device is symmetrically arranged on both sides (i.e. left and right sides) of the welding torch in the direction of movement of the welding torch. When the welding torch moves, the electric pulse generating device moves at the same speed as the welding torch.

[0031] The wires in the electric pulse generating device are arranged inside the guide frame 3, which has a "U" shaped structure composed of two guide rods 31. Two sliding rollers 31 are arranged at the tail of the guide frame 3 to facilitate the synchronous movement of the guide frame 3 and the welding torch 1.

[0032] As shown in FIG. 2, the welding torch in this embodiment moves forward in a circular swing.

[0033] The specific welding steps are as follows:

[0034] Step one, processing a beveled groove with a blunt edge at the welding position of the workpiece to be welded: two Q355B steel plates with a thickness of 20 mm are respectively processed with a beveled groove with a blunt edge, the blunt edge thickness is 1-2 mm, the groove root width is 1-2 mm, the groove angle is 22.5°, and the workpiece to be welded is formed after butt jointing to form a 45° groove.

[0035] Step two, equipment fixation: fix the workpiece to be welded with the existing fixture, move the welding torch to the top of the welding plate groove, and move the sliding roller on the guide frame of the electric pulse generator to the two sides of the welding torch.

[0036] Step three, CMT parameter setting: first, fill the wire, and then start the welding machine and the electric pulse generator. The specific settings are as follows: when the filling pass is 1-2 times, the welding speed is 45-55 cm / min, the welding current is 250-280 A, the welding voltage is 15.5-17 V, and the wire feeding speed is 8.1-9.2 m / min; when the filling pass is ≥3, the welding speed is 35-45 cm / min, the welding current is 262-285 A, the welding voltage is 16.7-18.3 V, and the wire feeding speed is 8.5-10.2 m / min. The electric pulse parameters are as follows: voltage 0.74-0.77 V, current 48-52 A, duty cycle 42-47%, and frequency 95-102 Hz. The same electric pulse parameters are used for each pass. After each filling pass, the surface oxide film is cleaned.

[0037] During the welding process, the guide frame 3 and the welding torch move at the same speed in the same direction; the welding head of the welding torch forms an angle of 5-10° with the surface of the workpiece to be welded, and the dry extension of the welding wire is 10-15 mm; in this embodiment, the shielding gas is pure Ar with a purity of 99.999%, and the shielding gas flow rate is 13-18 L / min.

[0038] In Example 2, the electric pulse parameters are as follows: voltage 0.84-0.87 V, current 49-53 A, duty cycle 43-50%, and frequency 97-101 Hz. The other steps and parameters are the same as in Example 1.

[0039] In Example 3, the electric pulse parameters are as follows: voltage 0.95-0.99 V, current 50-55 A, duty cycle 48-52%, and frequency 99-108 Hz. The other steps and parameters are the same as in Example 1.

[0040] Fig. 3 is a tensile force-displacement curve of the sample treated by applying electric pulses in Examples 1, 2, and 3, respectively. As can be seen from Fig. 3, the tensile force that Examples 1, 2, and 3 can withstand during stretching is greater than that of the sample without electric pulse treatment. However, only the displacement of Example 1 is improved relative to that of the untreated sample, while the displacements of Examples 2 and 3 are reduced relative to that of the untreated sample. By dividing the force by the cross-sectional area of the tensile sample to obtain the stress and dividing the displacement by the total length of the sample to obtain the strain, it is found that the tensile strength of Example 1 is improved by 13.4% and the plasticity is improved by 8.8% relative to the untreated sample. Although the tensile strength of Examples 2 and 3 is improved, the plasticity is reduced.

[0041] Fig. 4 is a stress-strain cloud chart of the tensile sample of a, b, c, d corresponding to untreated, example 1, example 2, example 3 respectively. As can be seen from Fig. 4, during the stretching, the stress of the untreated sample is mainly concentrated in the middle part of the sample; the stress of the treated sample is mainly concentrated above or below the gauge section of the sample, that is, the place where the electric pulse is not treated, and the gauge section does not appear the phenomenon of stress concentration, indicating that the strength of the weld of example 1, 2, 3 is greatly improved after the electric pulse treatment.

[0042] Fig. 5a, b, c, d correspond to the fracture micrograph of the tensile sample of untreated, example 1, example 2, example 3 respectively. a1, b1, c1, d1 are micrographs of 500 times, a2, b2, c2, d2 are micrographs of 1200 times. As can be seen from Fig. 5, the fracture micrograph of the untreated sample has a large number of dimples, and the size of the dimples is relatively large, which is a typical ductile fracture; the fracture micrograph of the sample of example 1 also has a large number of dimples, and the size of the dimples is smaller than that of the untreated sample, indicating that the plasticity of the sample of example 1 is better than that of the untreated sample; the fracture micrograph of the sample of example 2 and example 3 both exist cleavage plane, and the number of dimples is less, which is a typical cleavage fracture, and its plasticity is worse than that of the untreated sample.

[0043] As can be seen from the above comparison, the present application can avoid post-welding treatment by simultaneously applying electric pulse instantaneous treatment in the CMT wire filling welding process, has the characteristics of instantaneous high efficiency, and can simultaneously improve the strength and plasticity of the weld. Through the coupling effect of the induced magnetic field effect and electron wind effect and other multi-physical fields, the atomic migration barrier is reduced, the dislocation movement is promoted, the dislocation entanglement is opened, the plasticity of the material is improved without reducing or even improving the strength, so as to ensure good welding effect.

[0044] The present embodiment takes CMT welding as an example to illustrate the technical scheme, and other welding methods such as laser welding can also achieve the purpose of the present application.

[0045] The above is only the preferred embodiment of the present application, and it should be pointed out that those skilled in the art can make some improvements without departing from the principle of the present application, and these improvements should also be regarded as the protection scope of the present application.

Claims

1. A method for on-line fast synchronization of weld strength and ductility, characterized in that It comprises the following steps: The electric pulse generating device is arranged on both sides of the welding gun in the direction of the welding gun movement; during welding, the electric pulse generating device moves synchronously with the welding gun in the same direction and simultaneously delivers protective gas to the welding position.

2. The method of online quick synchronous enhancement of weld strength and ductility as claimed in claim 1, wherein: The electric pulse generating device moves at the same speed as the welding gun.

3. The on-line quick synchronous method for increasing strength and plasticity of a weld seam according to claim 1 or 2, characterized in that: The welding gun fills the wire in a clockwise circular swing manner.

4. The method of online quick synchronous strength and ductility enhancement of welds as claimed in claim 3 wherein: The voltage of the electric pulse generating device is 0.74-0.77V, the current is 48A-52A, the duty cycle is 42-47%, and the frequency is 95-102Hz.

5. The on-line quick synchronous strength and ductility improvement of welds method according to claim 1 or 2, characterized in that: The voltage of the electric pulse generating device is 0.74-0.77V, the current is 48A-52A, the duty cycle is 42-47%, and the frequency is 95-102Hz.

6. The on-line quick synchronous strength and ductility improvement of welds method according to claim 1 or 2, characterized in that: The protective gas is pure Ar with a purity of 99.999%.

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