Regulation and control method for grain refinement of surface metal of electron beam welding joint

Abstract

The invention relates to the technical field of electron beam welding, in particular to an electron beam welding joint surface layer metal grain refinement regulation and control method which comprises the following steps: carrying out modification welding and surface processing on a welded joint, designing single-side grain refinement treatment allowance, and designing scanning areas on the front and back surfaces of the joint to completely cover welding seams; designing a one-way translation snakelike scanning path for scanning areas on the front and back sides of the joint, and performing heating treatment by adopting a lower focusing pulse electron beam rapid motion scanning process; and an upper focusing electron beam one-way circulation scanning method is adopted, surface micromachining is assisted, residual stress is eliminated, tiny allowance is removed, and a grain refinement surface layer is obtained. The surface smoothness and flatness of a welded joint can be improved, grain refining treatment is achieved, and a grain refined surface layer is obtained.

Description

Technical Field

[0001] The present application relates to the technical field of electron beam welding, and in particular to a method for controlling the grain refinement of surface metal of an electron beam welded joint. Background Art

[0002] Currently, electron beam welding typically results in welds with excess height, a rough surface, and a coarse upper structure in the nail head weld. This presents challenges in controlling the grain refinement of the surface metal in the joint: The presence of excess height and a rough surface in the weld make it difficult to achieve uniform electron beam scanning of the weld surface; the coarse grains of the surface metal in the weld (nail head) make grain refinement difficult through heat input control; and conventional electron beam scanning makes it difficult to achieve a completely flat weld surface, making grain refinement difficult. The surface morphology and microstructure of the surface metal in welded structures significantly influence fatigue performance. A coarse weld surface structure, with its correspondingly low strength, is prone to fatigue cracking and fracture, while a rough weld surface often serves as a crack source, initiating fatigue fracture.

[0003] Therefore, surface and surface treatment of welded joints is an effective way to improve the fatigue performance of welded components, especially for aerospace structures, which have high demands on fatigue performance and lifespan. Electron beam scanning grain refinement is expected to effectively alter the compositional distribution and microstructure of the surface layer by instantaneously heating and cooling the material surface in a very short time, as well as physical and chemical phenomena such as stress impact and enhanced diffusion, thereby improving the fatigue performance of titanium alloy welded components. It is expected that the electron beam scanning process and related steps will enable the control of grain refinement of the metal surface layer of the joint. Summary of the Invention

[0004] The present application provides a method for regulating the crystallization refinement of the surface metal of an electron beam welded joint, which is suitable for regulating the crystallization refinement of the surface metal of a high-energy beam welded joint.

[0005] The method for controlling the grain refinement of the surface metal of an electron beam welded joint comprises: Perform finishing welding and surface processing on the welded joints, design a single-side grain refinement treatment allowance, and design scanning areas on both sides of the joints to completely cover the welds; A unidirectional serpentine scanning path is designed for the front and back scanning areas of the joint, and a downward focused pulsed electron beam rapid motion scanning process is used for heating treatment; The upper focused electron beam unidirectional cycle scanning method is adopted and assisted by surface micromachining to eliminate residual stress, remove tiny margins and obtain a grain-refined surface layer.

[0006] Furthermore, the post-weld joint is subjected to finishing welding and surface processing, including: After welding, defocused, high-current, high-speed electron beam is used to perform surface modification welding on the joint to make the weld surface smooth; Modify the surface of the weld by machining after welding, remove the excess height on the front and back sides of the weld and the back lock bottom.

[0007] Furthermore, the design of the single-side grain refinement processing allowance includes: A single-side 0.2~0.5mm grain refinement allowance is designed to keep the front and back sides of the weld smooth.

[0008] Furthermore, the scanning area on the front and back sides of the joint is designed to completely cover the weld, including: On the front and back sides of the joint, an 8 to 10 mm extension area on both sides of the weld and its edge is designed as the electron beam scanning area.

[0009] Furthermore, after the weld is completely covered in the scanning area on the front and back sides of the joint, the method further includes: A heat dissipation copper plate structure is arranged around the scanning area to absorb the heat conducted outward during the electron beam scanning process.

[0010] Furthermore, the heat dissipation copper plate has a length that is the same as the length of the weld, a width of 30-100 mm, and a thickness of 10-30 mm.

[0011] Furthermore, the parameters of the downward focused pulsed electron beam rapid motion scanning process include an acceleration voltage of 150 kV, a pulse beam current of 30 to 80 mA, a scanning beam spot diameter of 2 to 6 mm, a pulse duration of 1 to 20 μs, a repetition frequency of 500 to 1000 Hz, a scanning speed of 1500 to 1800 mm / min, and a cycle scanning time of 5 to 10 min.

[0012] Furthermore, the process parameters of the unidirectional cyclic scanning method of the upper focused electron beam include a defocused beam spot diameter of 25-40 mm, a beam current of 10-20 mA, a scanning speed of 600-800 mm / min, and a cyclic scanning time of 5-10 min.

[0013] The above technical solution of this application has the following advantages: The present application provides a method for regulating the grain refinement of the surface metal of an electron beam welded joint, which performs finishing welding and surface processing on the joint after welding, designs a single-side grain refinement treatment allowance, designs a scanning area on the front and back sides of the joint to completely cover the weld, designs a unidirectional translation serpentine scanning path for the scanning area on the front and back sides of the joint, adopts a lower focused pulsed electron beam rapid motion scanning process for heating treatment, adopts an upper focused electron beam unidirectional cycle scanning method and assists in surface micro-processing to eliminate residual stress, remove tiny allowances, and obtain a grain-refined surface layer, which can improve the surface finish and flatness of the welded joint, realize grain refinement treatment, and obtain a grain-refined surface layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific implementation methods or the description of the prior art. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0015] Figure 1 Schematic diagram of the scanning area design and heat dissipation copper plate setting provided for this application; Figure 2 Schematic diagram of pulsed electron beam scanning provided for this application; Figure 3 Schematic diagram of pulse scanning thermal effect provided for this application; Figure 4 Schematic diagram of the serpentine scanning path along the weld seam provided in this application; Figure 5 Schematic diagram of the serpentine scanning path along the longitudinal direction of the weld provided in this application; Figure 6 Schematic diagram of the electron beam scanning stress relief treatment provided in this application. DETAILED DESCRIPTION

[0016] In the following description, specific details such as specific system structures and techniques are provided for purposes of illustration rather than limitation to facilitate a thorough understanding of the embodiments of the present application. However, it will be apparent to those skilled in the art that the present application may be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to avoid obscuring the description of the present application with unnecessary detail.

[0017] It should be understood that when used in the present specification and the appended claims, the term "comprising" indicates the presence of described features, integers, steps, operations, elements and / or components, but does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or collections thereof.

[0018] In addition, in the description of the present application specification and the appended claims, the terms "first", "second", "third", etc. are only used to distinguish the descriptions and cannot be understood as indicating or implying relative importance.

[0019] References to "one embodiment" or "some embodiments" in this specification mean that one or more embodiments of the present application include a particular feature, structure, or characteristic described in conjunction with that embodiment. Thus, phrases such as "in one embodiment," "in some embodiments," "in other embodiments," and "in other embodiments" appearing in various places in this specification do not necessarily refer to the same embodiment, but rather mean "one or more but not all embodiments," unless otherwise specifically emphasized. The terms "including," "comprising," "having," and variations thereof all mean "including but not limited to," unless otherwise specifically emphasized. "Multiple" means "two or more."

[0020] The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0021] The embodiment of the present application provides a method for regulating the grain refinement of the surface metal of an electron beam welded joint, including: performing touch-up welding and surface processing on the joint after welding, designing a single-side grain refinement processing allowance, and designing a scanning area on the front and back sides of the joint to completely cover the weld; designing a unidirectional translation serpentine scanning path for the scanning area on the front and back sides of the joint, and using a lower focused pulsed electron beam rapid motion scanning process for heating treatment; using an upper focused electron beam unidirectional cycle scanning method and assisting surface micro-processing to eliminate residual stress, remove tiny allowances, and obtain a grain-refined surface.

[0022] In some embodiments, the post-weld joint modification welding and surface processing include: using a defocused, high-current, high-speed electron beam to perform joint surface modification welding after welding to make the weld surface smooth; and mechanically processing the weld surface after modification welding to remove excess height on the front and back sides of the weld and the back lock bottom.

[0023] In some embodiments, the designing of a single-sided grain refinement treatment allowance includes: designing a single-sided grain refinement treatment allowance of 0.2 to 0.5 mm to keep the front and back sides of the weld smooth.

[0024] In some embodiments, the scanning area designed on the front and back sides of the joint completely covers the weld, including: designing an 8-10 mm extension area on both sides of the weld and its edges on the front and back sides of the joint as the electron beam scanning area.

[0025] In some embodiments, after the scanning area on the front and back sides of the joint is designed to completely cover the weld, the method further includes: arranging a heat dissipation copper plate structure around the scanning area to absorb the heat conducted outward during the electron beam scanning process.

[0026] In some embodiments, the heat dissipation copper plate has a length equal to the length of the weld, a width of 30-100 mm, and a thickness of 10-30 mm.

[0027] In some embodiments, the parameters of the down-focused pulsed electron beam rapid motion scanning process include an acceleration voltage of 150 kV, a pulse beam current of 30 to 80 mA, a scanning beam spot diameter of 2 to 6 mm, a pulse duration of 1 to 20 μs, a repetition frequency of 500 to 1000 Hz, a scanning speed of 1500 to 1800 mm / min, and a cycle scanning time of 5 to 10 min.

[0028] In some embodiments, the process parameters of the unidirectional cyclic scanning method of the upper focused electron beam include a defocused beam spot diameter of 25-40 mm, a beam current of 10-20 mA, a scanning speed of 600-800 mm / min, and a cyclic scanning time of 5-10 min.

[0029] In response to the problem of grain refinement in the surface layer of joints, this application proposes a method for regulating the grain refinement of the surface metal of electron beam welded joints. Based on touch-up welding and surface processing, grain refinement processing allowances and scanning areas are designed on the front and back sides of the joints. A copper plate rapid cooling environment is set along the circumference of the scanning area to completely cover the weld and its heat-affected zone, thereby accelerating the rapid cooling of the metal in the scanning area. A unidirectional translational serpentine scanning path is designed, and a downward-focused pulsed electron beam rapid motion scanning process is adopted to ensure sufficient energy input and improve the heat dissipation and cooling effects. After processing, an upper-focused electron beam unidirectional circular scanning method is adopted and surface micro-machining is assisted to eliminate residual stress, improve surface smoothness and flatness, and obtain a grain-refined surface.

[0030] Taking the electron beam welding of TC4 titanium alloy with a thickness of 90~100mm as an example, the specific scheme for controlling the grain refinement of the surface metal of the joint is as follows: (1) Surface treatment and preparation of electron beam welded joints 1) Post-weld joint surface modification welding After welding, a defocused, high-current, high-speed electron beam is used to perform surface modification welding on the joint to make the weld surface smooth and increase the cooling rate of the modification weld.

[0031] 2) Joint surface preparation Modify the surface of the weld after post-weld machining, remove the excess height on the front and back sides of the weld and the back lock bottom, design a single-side 0.2~0.5mm reserve allowance for fine grain treatment, so that the front and back sides of the weld remain flat, preparing for the surface electron beam scanning fine grain treatment.

[0032] 3) Design of electron beam scanning area and rapid cooling environment conditions Based on the width of the weld surface, an 8~10mm extension area on both sides of the weld 1 and its edge is designed on the front and back sides of the joint as the electron beam scanning area 2, such as Figure 1 As shown, the weld and its heat-affected zone are fully covered while avoiding adding additional scanning processing areas.

[0033] At the same time, in order to increase the cooling rate of the surface metal, heat dissipation copper plate structures 3 are respectively arranged at the welding starting end, the ending end, and the upper and lower surfaces of the structure close to both sides of the scanning area. The length of the heat dissipation copper plate is the same as the length of the weld, the width is 30-100 mm, and the thickness is 10-30 mm. That is, by arranging the heat dissipation copper plate structure around the scanning area to absorb the heat conducted outward by the electron beam scanning process, the cooling of the surface metal is accelerated.

[0034] (2) Electron beam scanning grain refinement treatment In order to meet the requirements of grain refinement, electron beam scanning process method design, scanning trajectory design and rapid heating treatment are carried out for the front and back scanning areas of the joint.

[0035] 1) Electron beam scanning process design In order to reduce the heat input energy, a pulsed electron beam 4 is used to form a beam spot 5 for scanning processing, such as Figure 2 As shown, the depth of the direct heat effect layer 51 is 0.2~0.5mm, and the depth of the scanning treatment effect layer 52 is not less than 0.5mm ( Figure 3 The specific pulse electron beam scanning process adopts an acceleration voltage of 150kV, a pulse beam current of 30~80mA, a scanning beam spot diameter of 2mm~6mm, a pulse duration of 1~20μs, and a repetition frequency of 500~1000Hz, which ensures sufficient energy input at the beam spot position while taking into account rapid heat dissipation and cooling.

[0036] 2) Electron beam scanning trajectory design Based on the pulsed electron beam scanning processing method, two methods of serpentine scanning paths, namely the transverse and longitudinal ones along the weld seam, were designed6,7. Figure 4 、 5 As shown, heating, heat dissipation and cooling are performed along a single longitudinal direction, or heating, heat dissipation and cooling are performed along a single transverse direction, which respectively increases the heat dissipation effect and cooling speed along the transverse and longitudinal directions of the weld, and the scanning beam spots overlap with each other to cover the entire scanning area.

[0037] 3) Rapid heating and grain refinement treatment In order to improve the beam spot quality and energy state, the grain refinement treatment is performed by scanning the pulsed electron beam 4 in the lower focusing state. The numerical control programming method is used to set the workbench to scan along the serpentine path 6 or 7. The movement speed is selected from 1500 to 1800 mm / min, and the cycle scanning time is 5 to 10 minutes to obtain the surface recrystallization or micro-melting effect.

[0038] (3) Surface treatment planning 1) Electron beam scanning stress relief treatment In order to eliminate the surface residual stress of the scanning treatment, a conventional electron beam 8 in the upper focusing state is used to scan and perform stress relief heat treatment on the front and back surfaces of the joint after an interval of 5 to 10 minutes. The specific process is as follows: the diameter of the defocused beam spot 9 is adjusted to 25 to 40 mm to cover most of the scanning area containing the weld. The beam current is set to 10 to 20 mA and the scanning speed is 600 to 800 mm / min. The unidirectional cycle scanning and heating are carried out along the weld direction for 5 to 10 minutes. The scanning area is not melted to achieve the effect of removing residual stress.

[0039] 2) Surface micro-machining After stress relief scanning, the scanning areas on the front and back sides of the joint are machined, ground or milled to remove tiny allowances and improve the surface finish and flatness of the joint.

[0040] The following describes the invention through specific embodiments.

[0041] Example In combination with the method and drawings provided in this application, a TC4 titanium alloy joint with a thickness of 100 mm, a width of 200 mm, and a length of 300 mm ( Figure 1 ) as an example, the surface grain refinement treatment of the joint is carried out, and the specific embodiment is as follows: (1) Post-weld joint surface modification welding: For titanium alloy welded joints, electron beam surface modification welding is performed to make the weld surface smooth.

[0042] (2) Joint surface preparation: Remove the excess height of the weld on the front and back sides and the back lock bottom, leaving a processing allowance of 0.2mm on one side to keep the front and back sides of the weld 1 flat. The width of the weld on the front and back sides is 20mm and 2mm respectively.

[0043] (3) Setting of electron beam scanning area and rapid cooling environment conditions: According to the surface width of the weld, the dimensions of the front and back scanning areas 2 are designed to be 40mm wide × 300mm long and 25mm wide × 300mm long respectively. Figure 1 As shown, a heat dissipation copper plate 3 is installed in the circumference of the scanning area, with a length of 300 mm, a width of 100 mm, and a thickness of 15 mm.

[0044] (4) Determination of electron beam scanning process parameters: pulse scanning test was conducted to determine the scanning parameters such as high voltage 150kV, beam current 50mA, beam spot diameter 2~3mm, pulse duration 4μs, repetition frequency 500Hz. Pulsed electron beam scanning was used to treat the direct thermal effect layer 51 with a depth of 0.3mm and the affected layer 52 with a depth of 0.5mm. Figure 3 ).

[0045] (5) Scanning path selection: Use a serpentine scanning path along the longitudinal direction of the weld 7 ( Figure 5 ).

[0046] (6) Refinement and stress relief treatment of the upper surface of the joint: Based on the process parameters determined in step (4), the front scanning area of ​​the joint is refined by the down-focused pulsed electron beam 4. The scanning motion is realized along the serpentine path 7 by the numerical control programming method, and the motion speed is selected to be 1500 mm / min. After the refinement treatment, the stress relief heat treatment of the front surface of the joint is carried out by scanning with the up-focused conventional electron beam 8 for 8 minutes. The beam spot 9 is adjusted to 35 mm in diameter, the voltage is 150 kV, the beam current is 20 mA, the scanning speed is 800 mm / min, and the cyclic scanning heating is carried out for 8 minutes.

[0047] (7) Refinement and stress relief treatment of the lower surface of the joint: For the scanning area on the reverse side of the joint, the refinement treatment is performed with the same parameters as step (6), and then the beam spot diameter is adjusted to 25 mm and stress relief treatment is performed according to the parameters of step (6).

[0048] (8) The front and back scanning areas of the joint are milled and finished to remove 0.2mm of excess to improve the surface finish and flatness of the joint.

[0049] (9) After cutting the metallographic specimens, the surface finish of the joint was found to be 1.6 μm. Compared with the welding state, the depth of the grain refinement layer could reach 0.2 mm, and the grain size was refined by 10%.

[0050] The method for regulating the grain refinement of the surface metal of the electron beam welded joint provided in the embodiment of the present application is based on the surface modification welding and surface processing of the joint, proposes a reserved margin for the grain refinement treatment of one side of the joint, designs a scanning area range including the weld and the extended parts on both sides, completely covers the weld and its heat-affected zone, and arranges a copper plate fast cooling environment in its circumference to absorb the heat dissipated by the electron beam scanning, accelerates the rapid cooling of the metal in the scanning area, and provides basic conditions for regulating the grain refinement of the surface metal of the electron beam welded joint.

[0051] For the grain refinement scanning area, a pulsed electron beam scanning process is proposed to form a direct heat-affected layer and a scanning treatment-affected layer. A unidirectional, serpentine scanning path is designed, and rapid scanning with a downward-focused pulsed electron beam is employed. This ensures sufficient heating energy input while enhancing heat dissipation and cooling, resulting in a recrystallized or slightly melted surface layer. Following the pulsed scanning process, a unidirectional, cyclic scanning method with an upward-focused electron beam is employed, supplemented by surface micromachining to eliminate residual stress and improve the smoothness and flatness of the joint surface.

[0052] It should be noted that the various embodiments in this specification are described in a progressive manner. Reference can be made to the same or similar parts between the various embodiments. Each embodiment focuses on the differences from other embodiments. This application is not limited to the specific structures described above and shown in the figures. Furthermore, for the sake of brevity, detailed descriptions of known methods and technologies are omitted here.

[0053] The above-described embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present application, and should all be included in the scope of protection of the present application.

Claims

1. A method for controlling the grain refinement of the surface metal of an electron beam welded joint, characterized in that: include: Perform finishing welding and surface processing on the welded joints, design a single-side grain refinement treatment allowance, and design scanning areas on both sides of the joints to completely cover the welds; A unidirectional serpentine scanning path is designed for the front and back scanning areas of the joint, and a downward focused pulsed electron beam rapid motion scanning process is used for heating treatment; The upper focused electron beam unidirectional cycle scanning method is adopted and assisted by surface micromachining to eliminate residual stress, remove tiny margins and obtain a grain-refined surface layer.

2. The method for controlling the grain refinement of the surface metal of the electron beam welded joint according to claim 1, characterized in that: The post-weld joint is subjected to finishing welding and surface processing, including: After welding, defocused, high-current, high-speed electron beam is used to perform surface modification welding on the joint to make the weld surface smooth; Modify the surface of the weld by machining after welding, remove the excess height on the front and back sides of the weld and the back lock bottom.

3. The method for controlling the grain refinement of the surface metal of the electron beam welded joint according to claim 1, characterized in that: The designed single-side grain refinement treatment allowance includes: A single-side 0.2~0.5mm grain refinement allowance is designed to keep the front and back sides of the weld smooth.

4. The method for controlling the grain refinement of the surface metal of an electron beam welded joint according to claim 1, wherein: The scanning area designed on the front and back sides of the joint completely covers the weld, including: On the front and back sides of the joint, an 8 to 10 mm extension area on both sides of the weld and its edge is designed as the electron beam scanning area.

5. The method for controlling the grain refinement of the surface metal of an electron beam welded joint according to claim 1, wherein: After the weld is completely covered in the scanning area on the front and back sides of the joint, the following steps are also included: A heat dissipation copper plate structure is arranged around the scanning area to absorb the heat conducted outward during the electron beam scanning process.

6. The method for controlling the grain refinement of the surface metal of an electron beam welded joint according to claim 5, characterized in that: The heat dissipation copper plate has a length that is the same as the length of the weld, a width of 30 to 100 mm, and a thickness of 10 to 30 mm.

7. The method for controlling the grain refinement of the surface metal of an electron beam welded joint according to claim 1, wherein: The parameters of the down-focused pulsed electron beam rapid motion scanning process include an acceleration voltage of 150 kV, a pulse beam current of 30-80 mA, a scanning beam spot diameter of 2-6 mm, a pulse duration of 1-20 μs, a repetition frequency of 500-1000 Hz, a scanning speed of 1500-1800 mm / min, and a cycle scanning time of 5-10 min.

8. The method for controlling the grain refinement of the surface metal of an electron beam welded joint according to claim 1, wherein: The process parameters of the unidirectional cycle scanning method of the upper focused electron beam include a defocused beam spot diameter of 25-40 mm, a beam current of 10-20 mA, a scanning speed of 600-800 mm / min, and a cycle scanning time of 5-10 min.

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