A non-contact controllable alternating magnetic field - eddy current coupling assisted laser shock peening device and method for improving hydrogen embrittlement resistance

Abstract

This invention provides a non-contact, adjustable alternating magnetic field-eddy current coupled laser shock strengthening device and method for improving hydrogen embrittlement resistance. The device includes a laser shock strengthening unit, a magnetic field generating unit, a driving unit, and a position adjustment unit. The magnetic field generating unit has alternating N and S pole permanent magnets, which are driven to rotate by the driving unit. This induces an alternating magnetic field and closed eddy currents within the metal workpiece. The magnetic field strength, eddy current density, and temperature rise are synergistically controlled by adjusting the air gap and rotation speed. This invention couples a multi-directional alternating electromagnetic field during laser shock, promoting the activation of multiple slip systems and dislocation dispinning, improving the surface microstructure uniformity and residual compressive stress distribution, effectively inhibiting hydrogen intrusion and enrichment, delaying the initiation and propagation of hydrogen-induced cracks, and improving the workpiece's resistance to hydrogen embrittlement. The device has no contact electrodes and is suitable for complex curved surfaces and large-area workpieces.

Description

Technical Field

[0001] This invention belongs to the field of surface strengthening technology of metallic materials, specifically involving the intersection of laser shock strengthening and hydrogen embrittlement resistant material preparation, and particularly relates to a non-contact adjustable alternating magnetic field-eddy current coupling assisted laser shock strengthening device and method for improving hydrogen embrittlement resistance. Background Technology

[0002] With the global energy structure transformation and the rapid development of marine engineering equipment, the metal structural components of key equipment such as hydrogen energy storage and transportation containers, hydrogen pipelines, deep-sea oil production platforms, and petroleum refining reactors are increasingly facing harsh service conditions in hydrogen-containing environments, such as high-pressure hydrogen, wet hydrogen sulfide, or electrochemical hydrogen charging. Hydrogen atoms have extremely small radii and readily penetrate into the metal lattice as interstitial atoms, segregating and enriching in dislocations, grain boundaries, phase boundaries, inclusions, and stress concentration areas. This hydrogen intrusion and localized enrichment significantly reduces the plasticity, fracture toughness, and fatigue life of metallic materials, triggering a series of hydrogen embrittlement failure phenomena such as hydrogen-induced cracking, hydrogen-induced delayed fracture, hydrogen blistering, and hydrogen-induced plasticity loss, seriously threatening the operational safety and long-term reliability of equipment.

[0003] Given that hydrogen embrittlement failure typically initiates at or near the material surface and propagates inward, surface strengthening techniques—introducing residual compressive stress, refining grain structure, and increasing hydrogen trap density on the surface of metal workpieces—are widely recognized as effective ways to improve the material's resistance to hydrogen embrittlement. Among numerous surface strengthening techniques, laser shock peening (LSP) has attracted considerable attention due to its ability to generate a residual compressive stress layer hundreds of micrometers to millimeters deep on the material surface, along with good surface integrity and high process flexibility. Its basic principle involves the interaction of a high-power-density short-pulse laser with the material surface, generating a high-temperature, high-pressure plasma explosion shock wave through a confinement layer and an absorption layer. This causes ultra-high strain rate plastic deformation in the material surface, thereby introducing residual compressive stress and refining the surface grains. The residual compressive stress can counteract applied tensile stress or welding residual stress, reduce the stress intensity factor at the crack tip, and inhibit the initiation and propagation of hydrogen-induced cracks. The refined grains and increased grain boundaries provide more hydrogen trapping sites, helping to disperse hydrogen concentration and reduce the tendency for local hydrogen enrichment.

[0004] However, conventional laser shock peening technology still has several inherent limitations in its application against hydrogen embrittlement. First, the propagation of the laser shock wave decays exponentially with depth, limiting the depth of plastic deformation. Furthermore, the surface microstructure after shock peening often exhibits significant anisotropy, meaning that plastic deformation and dislocation movement are mainly concentrated on a few favorable-orientation slip systems, leading to localized strain concentration. This non-uniform microstructure provides sensitive areas for preferential hydrogen intrusion and local enrichment. Second, the ability to control dislocation configuration solely through mechanical shock waves is limited. It is difficult to actively intervene in the binding and unlocking, multiplication and annihilation of dislocations during the peening process, and the effects of grain refinement and optimization of residual compressive stress distribution have reached a bottleneck. Third, the residual compressive stress field formed after laser shock peening is susceptible to thermal relaxation and hydrogen-induced relaxation under thermo-mechanical-hydrogen coupled service environments, and its long-term stability directly affects the durability of the hydrogen embrittlement resistance.

[0005] To overcome these bottlenecks, researchers have attempted to introduce external physical fields for auxiliary strengthening during laser shock blasting. Existing technologies propose a combined laser shock and ultrasonic shock strengthening method, which superimposes ultrasonic mechanical vibrations onto high-strain-rate laser shock to form a deep gradient nanostructure. This technology essentially still belongs to a defect accumulation mode driven by strong plastic deformation. Although it can increase the number of hydrogen traps, its deformation mechanism is still dominated by a few slip systems, unable to actively achieve the synergistic activation of multiple slip systems, and lacks the ability to control the decomplication and unlocking of dislocation binding states. Dislocations are prone to directional transport, leading to the formation of anisotropic strengthening layers. Another example is a composite treatment technology based on laser cladding and laser shock strengthening, which improves resistance to hydrogen embrittlement by constructing a carbide hydrogen barrier and a gradient transition layer. This method focuses on the reconstruction of surface structure and composition, and for the original matrix, there is a risk of insufficient interfacial bonding. It also lacks the ability to intervene in dislocation behavior and stress state in situ, continuously, and controllably during the strengthening process.

[0006] In addition, some scholars have attempted to introduce a single steady magnetic field to assist laser shock irradiation, utilizing the magnetoplastic effect to promote dislocation movement. However, this magnetic field has a single direction and can only activate slip systems with specific orientations, resulting in limited improvement in tissue uniformity. Furthermore, it cannot induce eddy currents and the accompanying thermal effects. If contact electrodes are used to introduce current assistance, practical engineering problems such as unstable contact resistance, electrode wear, localized arcing, and uneven heat input are encountered, making it particularly difficult to apply to the uniform processing of complex curved surfaces and large-area workpieces.

[0007] In summary, there is an urgent need to develop a laser shock strengthening auxiliary method and device that can achieve non-contact, multi-field coupling and continuous control of process parameters, so as to actively modulate dislocation behavior, promote the synergistic activation of multiple slip systems, and suppress directional dislocation transport during the strengthening process, thereby obtaining a metal workpiece surface with uniform structure, stable residual compressive stress, and significantly improved resistance to hydrogen embrittlement. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a non-contact, adjustable alternating magnetic field-eddy current coupled assisted laser shock strengthening device and method for improving hydrogen embrittlement resistance. By inducing an alternating magnetic field and closed eddy currents within a metal workpiece through a rotating permanent magnet rotor, a non-contact, integrated electromagnetic field loading is achieved. The alternating magnetic field and induced eddy currents create a coupled electric-magnetic-temperature field within the material, promoting plastic deformation and improving the surface microstructure. The surface eddy currents generate a skin effect, concentrating the electromagnetic effect in the surface region, thereby improving the surface microstructure and residual compressive stress distribution, increasing the material's resistance to hydrogen intrusion, reducing the tendency for local hydrogen enrichment, and delaying the initiation and propagation of hydrogen-induced cracks. By adjusting the rotation speed and air gap distance, the magnetic field strength, eddy current density, frequency characteristics, and temperature level can be continuously controlled, achieving synergistic control of the skin effect, magnetostrictive, and electrostrictive plastic softening, thus coordinating the regulation of surface microstructure evolution, stress distribution, and hydrogen embrittlement resistance strengthening effect. The device requires no electrode contact, has a simple structure, is suitable for strengthening complex curved surfaces and large-area workpieces, and exhibits high engineering stability.

[0009] The present invention achieves the above-mentioned technical objectives through the following technical means.

[0010] A non-contact adjustable alternating magnetic field-eddy current coupled assisted laser shock strengthening device for improving resistance to hydrogen embrittlement is characterized by comprising a laser shock strengthening unit, a magnetic field generating unit, a driving unit, and a position adjustment unit.

[0011] The laser shock strengthening unit is used to emit pulsed laser light onto the surface of a metal workpiece to form a shock wave on the surface of the metal workpiece.

[0012] The magnetic field generating unit is disposed on one side of the metal workpiece in a non-contact manner, and there is an adjustable gap between the magnetic field generating unit and the metal workpiece; the magnetic field generating unit includes alternating N-pole permanent magnets and S-pole permanent magnets, and the magnetic field generating unit is driven to rotate around an axis to induce an alternating magnetic field inside the metal workpiece and to induce the formation of closed eddy currents; the driving unit is connected to the magnetic field generating unit for driving the magnetic field generating unit to rotate.

[0013] The position adjustment unit is used to adjust the relative position between the magnetic field generating unit and the metal workpiece, so as to change the size of the air gap between the magnetic field generating unit and the metal workpiece and / or the part of the metal workpiece facing the magnetic field generating unit.

[0014] Furthermore, the magnetic field generating unit includes a permanent magnet yoke disk and a retainer fixed thereon. The N-pole permanent magnets and S-pole permanent magnets are alternately arranged in the retainer along the circumferential direction, and the magnetization direction of both is axial. The magnetization directions of adjacent N-pole permanent magnets and S-pole permanent magnets are opposite.

[0015] Furthermore, the position adjustment unit includes a first sliding track for adjusting the air gap and a second sliding track for adjusting the position of the metal workpiece facing the magnetic field generating unit.

[0016] Furthermore, the laser shock strengthening unit includes a laser, a confinement layer, and an absorption layer. The laser is used to generate pulsed laser light. The confinement layer is disposed above the surface of the metal workpiece to limit plasma expansion. The absorption layer is disposed between the confinement layer and the surface of the metal workpiece to absorb laser energy and generate plasma.

[0017] Furthermore, the air gap can be adjusted from 2 to 20 mm, and the rotational speed at which the driving unit drives the magnetic field generating unit to rotate can be adjusted from 50 to 5000 rpm.

[0018] A strengthening method for a non-contact, tunable alternating magnetic field-eddy current coupled laser shock strengthening device aimed at improving resistance to hydrogen embrittlement includes the following steps:

[0019] Pre-treatment of the surface of metal workpieces;

[0020] Place the metal workpiece in the processing position, adjust the air gap between the magnetic field generating unit and the metal workpiece, and adjust the position of the metal workpiece facing the magnetic field generating unit.

[0021] The driving unit drives the magnetic field generating unit to rotate, inducing an alternating magnetic field inside the metal workpiece and forming a closed eddy current.

[0022] An absorption layer and a constraint layer are set on the surface of the area to be strengthened of the metal workpiece, and the surface of the metal workpiece is strengthened by laser shock through the laser shock strengthening unit.

[0023] Furthermore, by adjusting the size of the air gap and / or changing the rotational speed of the drive unit, at least one of the magnetic field strength, induced eddy current density, and temperature state of the surface of the metal workpiece can be controlled.

[0024] Furthermore, regulation satisfies the following relationship:

[0025] The relationship between the magnetic induction intensity B on the surface of a metal workpiece and the air gap distance g is as follows:

[0026] ,

[0027] In the formula: B is the magnetic induction intensity; Ф is the magnetic flux; A is the cross-sectional area of ​​the magnetic circuit; H c For the coercivity of permanent magnets; l m R is the equivalent length of the permanent magnet along the magnetization direction; pm ρ is the magnetic reluctance of the permanent magnet; g is the air gap distance; μ0 is the permeability of free space; A g The effective cross-sectional area of ​​the air gap; l y μ is the length of the magnetic circuit of the metal workpiece. y A represents the magnetic permeability of the metal workpiece. y R is the cross-sectional area traversed by the total magnetic flux path; 𝜎 Total leakage magnetic resistance;

[0028] Average induced eddy current density J on the surface of a metal workpiece av With the rotational speed n of the drive unit s The magnetic field strength B satisfies the following relationship:

[0029] ,

[0030] In the formula: J av σ is the average induced current density; c n represents the electrical conductivity of the metal workpiece material. s r is the rotational speed of the drive unit. av S is the equivalent average radius of the region to be strengthened in the metal workpiece; S is the total area of ​​the electromagnetic interaction region.

[0031] Furthermore, under the action of the alternating magnetic field, the distribution of the induced current density on the surface of the metal workpiece along the depth direction satisfies:

[0032]

[0033] In the formula: J(x) is the current density at a depth x from the surface, and f is the frequency of the alternating magnetic field;

[0034] The temperature rise response of the metal workpiece satisfies:

[0035] ,

[0036] ,

[0037] In the formula, P e K represents the power loss generated by the electromagnetic field. sis the three-dimensional end effect correction coefficient; J is the induced current density vector in the volume region under the action of alternating magnetic field; B is the magnetic induction intensity vector; V is the electromagnetic action volume region; C is the equivalent heat capacity; ΔT is the temperature rise; G is the system thermal conductivity matrix; G0 is the thermal conductivity matrix between the environmental node and the system node.

[0038] Furthermore, the parameters of the pulsed laser are: a circular flat-topped spot, a spot diameter of 1-5 mm, a pulse width of 10-25 ns, a single pulse energy of 1-11 J, and a spot overlap rate of 20%-80%.

[0039] The beneficial effects of this invention are as follows:

[0040] 1. The non-contact adjustable alternating magnetic field-eddy current coupled assisted laser shock strengthening device and method for improving hydrogen embrittlement resistance, as described in this invention, achieves in-situ integrated loading of magnetic field, electric field, and thermal field by non-contactly inducing alternating magnetic field and closed eddy current inside the metal workpiece using a rotating permanent magnet rotor. Because the alternating magnetic field forms a multi-directional magnetic field line distribution inside the material, and the induced eddy current forms a multi-directional closed loop within the workpiece plane, the coupling effect of these two forces enables slip systems with different grain orientations to obtain the driving force required for activation. This effectively alleviates the strain concentration caused by single-direction loading, thereby significantly improving the uniformity of surface microstructure and residual compressive stress distribution, and reducing the tendency for hydrogen-sensitive regions to form.

[0041] 2. The non-contact, tunable alternating magnetic field-eddy current coupling assisted laser shock strengthening device and method for improving hydrogen embrittlement resistance, as described in this invention, repeatedly modulates the dislocation binding state through periodic changes in the alternating magnetic field, reducing the critical stress for dislocation unlocking. Combined with the electron wind effect generated by induced eddy currents, it promotes dislocation slip, multiplication, and rearrangement, achieving active intervention in dislocation behavior during laser shock. This mechanism not only accelerates the grain refinement process but, more importantly, suppresses the directional transport of dislocations along specific directions, avoiding the preferred orientation strengthening layer that easily occurs in conventional laser shock strengthening, thus obtaining a more uniform and stable surface nanogradient structure.

[0042] 3. The non-contact adjustable alternating magnetic field-eddy current coupling assisted laser shock strengthening device and method for improving hydrogen embrittlement resistance described in this invention can change the frequency of the alternating magnetic field by adjusting the speed of the drive motor, thereby enhancing the skin effect under high-frequency conditions and concentrating the energy of induced eddy currents and electromagnetic interactions highly on the surface of the metal workpiece. This characteristic allows this invention to precisely strengthen the surface area most susceptible to hydrogen intrusion, constructing a denser microstructure barrier and a higher amplitude residual compressive stress barrier near the material surface, effectively improving the resistance of the material surface to hydrogen intrusion and delaying the initiation and propagation of hydrogen-induced cracks.

[0043] 4. The non-contact adjustable alternating magnetic field-eddy current coupling assisted laser shock strengthening device and method for improving hydrogen embrittlement resistance described in this invention, by using the air gap distance between the permanent magnet rotor and the metal workpiece and the rotor speed as independently adjustable process parameters, combined with the revealed quantitative relationship between magnetic induction intensity, eddy current density, frequency characteristics and temperature rise, achieves continuous and synergistic control of electromagnetic effect intensity, thermal effect and plastic softening degree. This adjustability allows this invention to specifically optimize the hydrogen barrier effect, hydrogen trapping site distribution and crack arrest capability according to the specific hydrogen embrittlement resistance requirements of different material systems and service conditions, flexibly adjust the surface microstructure and stress field characteristics, and provide a broad process optimization window.

[0044] 5. The non-contact adjustable alternating magnetic field-eddy current coupled assisted laser shock strengthening device for improving hydrogen embrittlement resistance described in this invention abandons the contact electrodes in traditional electro-assisted strengthening and adopts a non-contact loading method using a rotating permanent magnet. This fundamentally avoids problems such as contact resistance fluctuations, electrode ablation, and uneven local heat input, resulting in high system operational stability. Furthermore, the structure is simple and compact, highly adaptable to workpiece shapes, and can meet the engineering application requirements of complex curved surfaces and large-area workpieces. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are some embodiments of the present invention. For those skilled in the art, it is obvious that other drawings can be obtained from these drawings without creative effort.

[0046] Figure 1 This is a schematic diagram of the non-contact adjustable alternating magnetic field-eddy current coupling assisted laser shock strengthening device for improving resistance to hydrogen embrittlement as described in this invention.

[0047] Figure 2 This is a schematic diagram of the spatial distribution of magnetic flux paths and eddy current paths corresponding to adjacent pole pairs under the action of an alternating magnetic field.

[0048] Figure 3 This is a schematic diagram showing the distribution of magnetic flux paths and eddy current paths along the thickness section of a metal workpiece under the action of an alternating magnetic field.

[0049] Figure 4 This is a schematic diagram showing the distribution of magnetic flux paths and eddy current paths along the surface section of a metal workpiece under the action of an alternating magnetic field.

[0050] Figure 5 The graph shows a comparison of the maximum residual compressive stress and hydrogen-induced plasticity loss rate under the conditions of no impact, single laser impact, and the treatment of this invention.

[0051] In the picture:

[0052] 1-Laser; 2-Constraint layer; 3-Absorption layer; 4-Metal workpiece; 5-Copper support platform; 6-N-pole permanent magnet; 7-S-pole permanent magnet; 8-Aluminum cage; 9-Permanent magnet yoke; 10-Rotating shaft; 11-Drive motor; 12-Horizontal sliding rail; 13-Horizontal sliding rail drive power supply; 14-Permanent magnet rotor assembly support platform; 15-Laser assembly support platform; 16-Vertical sliding rail drive power supply; 17-Vertical sliding rail; 18-Water storage platform. Detailed Implementation

[0053] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0054] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "axial," "radial," "vertical," "horizontal," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0055] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0056] like Figure 1As shown, the non-contact adjustable alternating magnetic field-eddy current coupled assisted laser shock strengthening device for improving hydrogen embrittlement resistance, as described in this invention, includes a laser shock strengthening unit, a magnetic field generating unit, a driving unit, and a position adjustment unit. The laser shock strengthening unit generates a high-power pulsed laser and acts on the surface of the metal workpiece to form a shock wave; the magnetic field generating unit generates an alternating magnetic field inside the metal workpiece and induces eddy currents; the position adjustment unit adjusts the air gap distance and facing position between the magnetic field generating unit and the metal workpiece; the driving unit drives the magnetic field generating unit to rotate, thereby forming an adjustable frequency alternating magnetic field, achieving a synergistic strengthening effect of magnetic field-current-Joule heating-laser shock.

[0057] The laser shock peening unit emits pulsed laser light onto the surface of a metal workpiece 4, creating a shock wave on its surface. The unit includes a laser 1, a constraint layer 2, an absorption layer 3, a copper support platform 5, and a water storage platform 18. The metal workpiece 4 is fixed to the copper support platform 5, which is mounted on top of the water storage platform 18 to provide stable support and enhance thermal induction efficiency. The absorption layer 3 and constraint layer 2 are sequentially laid on the surface of the metal workpiece 4 to be strengthened. The pulsed laser beam emitted by the laser 1 passes through the constraint layer 2 and the absorption layer 3 before acting on the surface of the metal workpiece 4. The absorption layer 3 can be made of black tape with a thickness of approximately 80 μm, used to absorb laser energy and generate high-temperature, high-pressure plasma. The constraint layer 2 is a flowing deionized water layer with a thickness controlled at approximately 3 mm; its function is to limit the instantaneous expansion of the plasma and guide the shock wave pressure into the workpiece. The copper support platform 5 serves to stably support the metal workpiece 4 and, due to its high electrical and thermal conductivity, enhances thermal induction efficiency and makes the workpiece temperature rise more uniform under the action of an alternating magnetic field. The thickness of the copper support platform 5 is generally selected between 5 and 30 mm. The water storage platform 18 is located below the support platform 5 and is responsible for providing a continuous water flow to the constraint layer 2 and recycling the returned water.

[0058] The magnetic field generating unit is disposed on one side of the metal workpiece 4 in a non-contact manner, maintaining an adjustable air gap between them. The magnetic field generating unit includes several N-pole permanent magnets 6, S-pole permanent magnets 7, an aluminum retainer 8, and a permanent magnet yoke disk 9. The N-pole permanent magnets 6 and S-pole permanent magnets 7 are arranged alternately along the circumference within the aluminum retainer 8 and fixed to the permanent magnet yoke disk 9. The magnetization direction of each permanent magnet is axial, with adjacent N-pole permanent magnets 6 and S-pole permanent magnets 7 magnetized in opposite directions. The permanent magnets can be made of N35 neodymium iron boron material to provide a stable, uniform, and non-demagnetizing permanent magnetic field. When the magnetic field generating unit is driven to rotate around its axis, an alternating magnetic field can be induced inside the metal workpiece 4, and closed eddy currents can be formed. Figure 2As shown, alternating N-pole and S-pole permanent magnets generate a periodically changing alternating magnetic field during rotation. Magnetic lines of force enter the copper support platform through the air gap and then into the metal workpiece, forming a closed magnetic circuit. Short dashed lines with thin arrows represent the magnetic flux path, while long dashed lines with thick arrows represent the induced eddy current path. Under the influence of the changing magnetic field, the metal workpiece cuts the magnetic lines of force and generates closed-loop induced alternating eddy currents inside. These eddy currents are mainly distributed along the plane of the workpiece and form an alternating coupling field with the magnetic flux path, thus providing conditions for modulating material dislocation behavior, coordinating plastic deformation, and homogenizing the structure of the strengthening layer.

[0059] The drive unit is connected to the magnetic field generating unit for driving the latter to rotate. The drive unit includes a drive motor 11 and a rotating shaft 10. One end of the rotating shaft 10 is connected to the output shaft of the drive motor 11, and the other end is coaxially fixedly connected to the permanent magnet yoke disk 9. The rotational speed of the drive motor 11 can be continuously adjusted within the range of 50 to 5000 rpm, thereby forming an alternating magnetic field with adjustable frequency.

[0060] The position adjustment unit is used to adjust the relative spatial position between the magnetic field generating unit and the metal workpiece 4. It includes a horizontal sliding rail 12, a horizontal sliding rail drive power supply 13, a permanent magnet rotor assembly support platform 14, a laser assembly support platform 15, a vertical sliding rail drive power supply 16, and a vertical sliding rail 17. The horizontal sliding rail 12 is mounted on the permanent magnet rotor assembly support platform 14. The magnetic field generating unit and drive motor 11 are mounted on the horizontal sliding rail 12 and can move horizontally to adjust the air gap distance between the magnetic field generating unit and the metal workpiece 4. The vertical sliding rail 17 is mounted on the laser assembly support platform 15. The laser shock strengthening unit is mounted entirely on the vertical sliding rail 17 and can move vertically to adjust the specific position of the metal workpiece 4 facing the magnetic field generating unit. Both the horizontal sliding rail 12 and the vertical sliding rail 17 can be position-adjusted via screw motors and are powered and controlled by the horizontal sliding rail drive power supply 13 and the vertical sliding rail drive power supply 16, respectively.

[0061] A motion control system (not shown in the figure) can also be set up. The motion control system is electrically connected to the laser 1, the drive motor 11, the horizontal sliding rail drive power supply 13 and the vertical sliding rail drive power supply 16 respectively, and is used to coordinate and control the emission of laser pulses, the motor speed and the position of each slide rail to realize the synchronous operation of laser impact and magnetic field modulation.

[0062] This invention generates a non-contact alternating magnetic field inside a metal workpiece by rotating a permanent magnet rotor, inducing closed eddy currents within the material. This places the workpiece in a multi-field coupled state of magneto-electric-thermal interaction before and during laser shock peening. By controlling dislocation behavior, skin effect, and workpiece temperature through the coupling of the alternating magnetic field and eddy currents, it achieves uniform and refined surface microstructure and stable strengthening, thereby increasing the material's resistance to hydrogen intrusion, reducing the tendency for local hydrogen enrichment, and delaying the initiation and propagation of hydrogen-induced cracks. Furthermore, all strengthening effects are controllable, the non-contact structure is simple, it has wide applicability, and high engineering stability. Figure 3 As shown, the magnetic flux path penetrates the surface of the metal workpiece along the thickness direction, forming a vertically continuous magnetic flux channel. Simultaneously, it induces closed eddy current loops along the planar direction within the material, placing different crystal orientations in a controlled environment. This facilitates the synergistic activation of multiple slip systems and reduces local strain concentration. As the permanent magnet rotor speed increases, the magnetic field variation frequency increases, and the eddy currents gradually concentrate in the material surface region, exhibiting a significant skin effect, thereby improving the surface strengthening effect. This is beneficial for establishing a more stable structural reinforcement layer and residual compressive stress barrier on the surface where hydrogen is most easily penetrated, increasing the material surface's resistance to hydrogen intrusion. Figure 4 As shown, within the surface plane, induced eddy currents form multi-directional closed loops. Because the magnetic field direction changes periodically with time, the eddy current direction also alternates accordingly, thus avoiding directional strengthening defects caused by unidirectional current. This helps suppress directional dislocation transport and improves the uniformity of the strengthened layer microstructure and stress distribution. Consequently, the tendency for localized hydrogen-sensitive regions to form can be reduced, lowering the risk of preferential hydrogen enrichment in localized high-defect and high-strain regions.

[0063] Example 1

[0064] The strengthening method of the non-contact adjustable alternating magnetic field-eddy current coupling assisted laser shock strengthening device for improving hydrogen embrittlement resistance, as described in this invention, is particularly suitable for thicker workpieces or applications requiring deep microstructure control. The specific steps are as follows:

[0065] S01: Pre-treatment of the surface of the metal workpiece 4 to be strengthened. The workpiece surface is progressively polished using sandpaper of varying grits, from coarse to fine, followed by mechanical polishing. Finally, the workpiece is ultrasonically cleaned in anhydrous ethanol and dried. The surface roughness Ra after treatment should be controlled below 50 μm. The thickness of the metal workpiece 4 is generally between 1 and 10 mm.

[0066] S02: Place and fix the pre-treated metal workpiece 4 in front of the copper support platform 5. Drive the vertical sliding rail 17 via the control system to adjust the vertical position of the copper support platform 5 so that the area to be strengthened on the metal workpiece 4 faces the magnetic field generating unit behind it. Simultaneously, drive the horizontal sliding rail 12 to move the magnetic field generating unit horizontally, adjusting the air gap distance between it and the metal workpiece 4. The air gap distance is 2–20 mm; in this embodiment, the air gap distance is set to 4 mm.

[0067] S03: Start the drive motor 11, causing it to drive the magnetic field generating unit to rotate stably at a speed of 200 rpm. At this time, the rotor formed by the alternating arrangement of N-pole permanent magnets 6 and S-pole permanent magnets 7 generates a periodically changing alternating magnetic field in space. The alternating magnetic field passes through the air gap, through the copper support platform 5, and acts on the interior of the metal workpiece 4. On the one hand, multi-directional magnetic lines of force distributed along the thickness direction are formed inside the metal workpiece 4; on the other hand, when the metal workpiece 4, as a conductor, cuts the changing magnetic lines of force, closed alternating eddy currents are induced inside it. Figures 2-4 The spatial distribution of magnetic flux paths and eddy current paths is shown from different perspectives. At a low frequency of 200 rpm, the magnetic field penetrates to a greater depth, and the magnetoplastic softening effect is more significant, making it suitable for thick-walled materials or deep strengthening.

[0068] S04: Laser shock peening is performed based on a stable electromagnetic field loading. First, black tape is applied as an absorption layer 3 to the surface of the area to be strengthened on the metal workpiece 4. Then, the water circulation system of the water storage platform 18 is activated, forming a uniformly thick, continuously flowing deionized water layer as a constraint layer 2 on the surface of the absorption layer 3. Subsequently, the laser 1 is activated, and its emitted pulsed laser beam is perpendicularly irradiated onto the surface of the constraint layer 2, passing through the water layer and the absorption layer 3 before acting on the surface of the workpiece 4. In this embodiment, the laser parameters are set as follows: circular flat-topped spot, spot diameter 3mm, pulse width 15ns, single pulse energy 5J, and spot overlap rate 50%. Under high-energy laser shock, the surface layer of the workpiece undergoes severe plastic deformation. Simultaneously, the previously loaded low-frequency alternating magnetic field continues to act on the dislocation structure inside the material, promoting dislocation unlocking and synergistic activation of multiple slip systems; the electron wind generated by the induced eddy current also assists dislocation movement, promoting dislocation rearrangement and grain refinement. This combined effect helps improve the uniformity of the microstructure over a greater depth range and establishes a more stable residual compressive stress field.

[0069] S05: After the laser impact in the preset area is completed, first turn off the laser 1, then stop the operation of the drive motor 11. After the metal workpiece 4 has cooled naturally to room temperature, remove it from the support platform, peel off the black adhesive tape on the surface, and rinse it with clean water. This yields a metal workpiece with optimized surface microstructure and residual compressive stress distribution, and improved resistance to hydrogen embrittlement.

[0070] Example 2

[0071] Based on Example 1, the rotational speed of the drive motor 11 was changed to demonstrate the adjustable characteristics of the process parameters of the present invention and its adaptability in different application scenarios.

[0072] The steps of Example 2 are basically the same as those of Example 1, except that in S03, the speed of the drive motor 11 is increased from 200 rpm to 3000 rpm, while the air gap distance and other parameters remain unchanged.

[0073] When the drive motor 11 operates at a high speed of 3000 rpm, a high-frequency alternating magnetic field is induced inside the metal workpiece 4. Under these conditions, the skin effect is significantly enhanced, and the induced eddy currents are highly concentrated in the very shallow surface layer of the workpiece 4. The accompanying Joule heating effect also causes a significant increase in the surface temperature. The depth of both electromagnetic and thermal effects converges towards the surface.

[0074] In step S04, during laser shock peening, the high-frequency electromagnetic field has a more intense effect on the evolution of the surface microstructure. The concentrated eddy currents and temperature rise, in synergy with the laser shock wave, greatly promote dislocation proliferation, slip, and annihilation in the near-surface region of the material, achieving further refinement and hardening of the surface microstructure. This mode of action is more effective in improving the surface hardness, fatigue resistance, and inhibiting microcrack initiation of materials, and is particularly suitable for hydrogen embrittlement resistance treatment scenarios where surface strengthening is the primary objective.

[0075] Figure 5 The maximum residual compressive stress and hydrogen-induced plasticity loss rate were compared under the following conditions: no impact, single laser shock, and the two embodiments of the present invention. It is evident that the method of the present invention achieved higher maximum residual compressive stress on the surface while significantly reducing the hydrogen-induced plasticity loss rate, verifying its superior effect in improving the material's resistance to hydrogen embrittlement.

[0076] The principle of parameter control in this invention:

[0077] In this invention, the electromagnetic parameters exhibit excellent controllability. First, by adjusting the air gap distance between the magnetic field generating unit and the metal workpiece 4, or by adjusting the rotational speed of the drive motor 11, the surface magnetic field strength, induced eddy current density, and skin effect intensity of the metal workpiece can be altered, thereby enabling the control of the temperature state of the metal workpiece 4. When the air gap is reduced, or the rotational speed is appropriately increased below the critical speed for mechanical properties, the eddy current density increases, generating more Joule heat and raising the temperature of the metal workpiece. The magnitude of this temperature rise can be determined in advance through electromagnetic field-temperature field coupling simulation or theoretical calculations using the equivalent magnetic circuit method and equivalent thermal network method to determine the corresponding air gap value or rotational speed range. Second, increasing the rotational speed of the drive motor 11 increases the frequency of the alternating magnetic field, making the skin effect on the material surface more pronounced, thus enhancing the surface electromagnetic field strength and surface temperature. Next, magnetoplastic softening can be controlled by adjusting the air gap size; reducing the air gap reduces magnetic leakage and increases the number of magnetic lines of force passing through the substrate, thereby enhancing the magnetic field's control over dislocation motion. Finally, the electron wind effect generated by the induced eddy currents can also be controlled by adjusting the eddy current density. By coordinating the above parameters, comprehensive control can be achieved over the material's temperature field, electromagnetic field strength, and dislocation activation behavior, thus providing a basis for parameter control to improve the material's resistance to hydrogen embrittlement.

[0078] The parameter control principle in this invention is as follows:

[0079] The process parameters involved in this invention have good continuous controllability, and their physical basis lies in the quantitative relationship between the interaction between the electromagnetic field and the conductive and magnetic materials. By synergistically adjusting the air gap distance and the drive motor speed, the magnetic field strength, eddy current density, frequency characteristics, and temperature rise of the surface layer of the metal workpiece can be controlled.

[0080] There is a quantitative relationship between the magnetic induction intensity B on the surface of the metal workpiece 4 and the air gap distance g, determined by the equivalent magnetic circuit model. The expression is as follows:

[0081]

[0082] In the formula: B is the magnetic flux density, measured in Tesla (T); Ф is the magnetic flux, measured in Weber (Wb); A is the cross-sectional area of ​​the magnetic circuit, measured in square meters; H c The coercivity of a permanent magnet is expressed in amperes per meter (A / m); m R is the equivalent length of the permanent magnet along the magnetization direction, expressed in meters (m). pm The reluctance of a permanent magnet is expressed in henry (H). -1 g is the air gap distance, in meters (m); μ0 is the free permeability, with a value of 4π × 10⁻⁶. -7 Henry per meter (H / m); A g The effective cross-sectional area of ​​the air gap is expressed in square meters (m²). 2); l y The length of the magnetic circuit of the metal workpiece is expressed in meters (m); μ y A represents the magnetic permeability of the metal workpiece 4, expressed in Henry per meter (H / m); y The total cross-sectional area traversed by the magnetic flux path is expressed in square meters (m²). 2 ); R 𝜎 Total leakage magnetic resistance, expressed in henry (H). -1 ).

[0083] Therefore, reducing the air gap distance can reduce the air gap magnetic reluctance and increase the main magnetic flux, thereby improving the magnetic field strength on the surface of the metal workpiece.

[0084] Under the action of an alternating magnetic field, the average induced eddy current density J on the surface layer of the metal workpiece 4 av With the rotational speed n of the drive unit s The magnetic field strength B satisfies the following relationship:

[0085] ,

[0086] In the formula: J av The average induced current density is expressed in amperes per square meter (A / m²). 2 ); σ c The electrical conductivity of the metal workpiece material, expressed in Siemens units per meter (S / m); n s This refers to the rotational speed of the drive unit, measured in revolutions per minute (r / min); r av S is the equivalent average radius of the region to be strengthened in the metal workpiece, in meters (m); S is the total area of ​​the electromagnetic effect region, in square meters (m²). 2 ); dS is the area element within this region;

[0087] Under the influence of the alternating magnetic field, high-frequency conditions will induce a significant skin effect. At this time, the induced current density decreases exponentially along the depth direction of the workpiece, and its distribution satisfies:

[0088]

[0089] In the formula: J(x) is the current density at a depth x from the surface, in amperes per square meter (A / m²). 2 x is the depth from the surface, in meters (m); f is the frequency of the alternating magnetic field, in Hertz (Hz), which is related to the rotational speed n. s The relationship between f and the number of pole pairs p of a permanent magnet is f=n s p / 60; μ y σ is the magnetic permeability of a metallic workpiece, expressed in Henry per meter (H / m); c The value represents electrical conductivity, measured in Siemens units per meter (S / m).

[0090] Therefore, reducing the air gap distance g and increasing the permanent magnet rotor speed n s It can increase the average induced current density J av Furthermore, increasing the rotational speed of the permanent magnet rotor also increases the magnetic field frequency, thereby enhancing the skin effect and achieving coordinated control of the induced eddy current density and the intensity of surface electromagnetic interaction.

[0091] The Joule heat generated during electromagnetic induction serves as an internal heat source, causing a temperature rise in the metal workpiece 4. Its thermal equilibrium relationship is described by the following set of equations:

[0092] ,

[0093] ,

[0094] In the formula, P e K represents the power loss generated by the electromagnetic field, measured in watts (W). s is the three-dimensional end effect correction coefficient, dimensionless; J is the induced current density vector within the volume region subjected to the alternating magnetic field, in amperes per square meter (A / m²). 2 B represents the magnetic flux density vector, measured in Tesla (T); V represents the volume of the electromagnetic field, measured in cubic meters (m³). 3 C represents the equivalent heat capacity in joules per kelvin (J / K); ΔT represents the temperature rise in kelvin (K); t represents time in seconds (s); G represents the system thermal conductivity matrix in watts per kelvin (W / K); G0 represents the thermal conductivity matrix between the environmental node and the system node in watts per kelvin (W / K).

[0095] As can be seen from the above relationship, by coordinating the adjustment of the air gap distance g and the drive motor speed n s It can precisely control the magnetic field strength, eddy current density, electromagnetic field frequency characteristics, and temperature rise response caused by Joule heating on the metal workpiece 4 within a continuous range. This multi-parameter coordinated adjustability provides a scientific basis for process optimization and flexible control methods for the present invention to meet the requirements of hydrogen embrittlement resistance for different material systems, different workpiece sizes, and different service environments.

[0096] It should be understood that although this specification is described according to various embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0097] The detailed descriptions listed above are merely specific illustrations of feasible embodiments of the present invention and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A non-contact, tunable alternating magnetic field-eddy current coupled assisted laser shock strengthening device for improving resistance to hydrogen embrittlement, characterized in that, It includes a laser shock enhancement unit, a magnetic field generating unit, a driving unit, and a position adjustment unit; The laser shock strengthening unit is used to emit pulsed laser to the surface of the metal workpiece (4) to form a shock wave on the surface of the metal workpiece (4); The magnetic field generating unit is disposed on one side of the metal workpiece (4) in a non-contact manner, and there is an adjustable gap between the magnetic field generating unit and the metal workpiece (4); the magnetic field generating unit includes alternating N-pole permanent magnets (6) and S-pole permanent magnets (7), and the magnetic field generating unit is driven to rotate around an axis to induce an alternating magnetic field inside the metal workpiece (4) and to induce the formation of closed eddy currents; the driving unit is connected to the magnetic field generating unit for driving the magnetic field generating unit to rotate; The position adjustment unit is used to adjust the relative position between the magnetic field generating unit and the metal workpiece (4) to change the size of the air gap between the magnetic field generating unit and the metal workpiece (4) and / or the part of the metal workpiece (4) facing the magnetic field generating unit.

2. The non-contact adjustable alternating magnetic field-eddy current coupling assisted laser shock strengthening device for improving hydrogen embrittlement resistance according to claim 1, characterized in that, The magnetic field generating unit includes a permanent magnet yoke disk (9) and a retainer (8) fixed thereon. The N-pole permanent magnet (6) and the S-pole permanent magnet (7) are arranged alternately in the retainer (8) along the circumferential direction, and the magnetization direction is axial. The magnetization directions of adjacent N-pole permanent magnets (6) and S-pole permanent magnets (7) are opposite.

3. The non-contact adjustable alternating magnetic field-eddy current coupled assisted laser shock strengthening device for improving hydrogen embrittlement resistance according to claim 1, characterized in that, The position adjustment unit includes a first sliding track for adjusting the air gap and a second sliding track for adjusting the position of the metal workpiece (4) facing the magnetic field generating unit.

4. The non-contact adjustable alternating magnetic field-eddy current coupling assisted laser shock strengthening device for improving hydrogen embrittlement resistance according to claim 1, characterized in that, The laser shock enhancement unit includes a laser (1), a confinement layer (2) and an absorption layer (3). The laser (1) is used to generate pulsed laser. The confinement layer (2) is disposed above the surface of the metal workpiece (4) to restrict plasma expansion. The absorption layer (3) is disposed between the confinement layer (2) and the surface of the metal workpiece (4) to absorb laser energy and generate plasma.

5. The non-contact adjustable alternating magnetic field-eddy current coupling assisted laser shock strengthening device for improving hydrogen embrittlement resistance according to claim 1, characterized in that, The air gap can be adjusted from 2 to 20 mm, and the rotational speed at which the driving unit drives the magnetic field generating unit to rotate can be adjusted from 50 to 5000 rpm.

6. A strengthening method for a non-contact tunable alternating magnetic field-eddy current coupled assisted laser shock strengthening device for improving hydrogen embrittlement resistance according to any one of claims 1-5, characterized in that, Includes the following steps: The surface of the metal workpiece (4) is pretreated; Place the metal workpiece (4) in the processing position, adjust the air gap between the magnetic field generating unit and the metal workpiece (4), and adjust the position of the metal workpiece (4) facing the magnetic field generating unit. The driving unit drives the magnetic field generator to rotate, inducing an alternating magnetic field inside the metal workpiece (4) and forming a closed eddy current. An absorption layer (3) and a constraint layer (2) are provided on the surface of the area to be strengthened in the metal workpiece (4), and the surface of the metal workpiece (4) is subjected to laser shock strengthening by the laser shock strengthening unit.

7. The strengthening method according to claim 6, characterized in that, By adjusting the size of the air gap and / or changing the rotation speed of the drive unit, at least one of the magnetic field strength, induced eddy current density, and temperature state of the surface of the metal workpiece (4) can be controlled.

8. The strengthening method according to claim 6, characterized in that, Regulation satisfies the following relationship: The relationship between the magnetic induction intensity B on the surface of the metal workpiece (4) and the air gap distance g is as follows: ， In the formula: B is the magnetic induction intensity; Ф is the magnetic flux; A is the cross-sectional area of ​​the magnetic circuit; H c For the coercivity of permanent magnets; l m R is the equivalent length of the permanent magnet along the magnetization direction; pm ρ is the magnetic reluctance of the permanent magnet; g is the air gap distance; μ0 is the permeability of free space; A g The effective cross-sectional area of ​​the air gap; l y For the magnetic circuit length of the metal workpiece (4); μ y A is the magnetic permeability of the metal workpiece (4); y R is the cross-sectional area traversed by the total magnetic flux path; 𝜎 Total leakage magnetic resistance; The average induced eddy current density J on the surface of the metal workpiece (4) av With the rotational speed n of the drive unit s The magnetic field strength B satisfies the following relationship: ， In the formula: J av σ is the average induced current density; c n represents the electrical conductivity of the metal workpiece material. s r is the rotational speed of the drive unit. av S is the equivalent average radius of the region to be strengthened in the metal workpiece; S is the total area of ​​the electromagnetic interaction region.

9. The strengthening method according to claim 8, characterized in that, Under the action of the alternating magnetic field, the distribution of the induced current density on the surface of the metal workpiece (4) along the depth direction satisfies: , In the formula: J(x) is the current density at a depth x from the surface, and f is the frequency of the alternating magnetic field; The temperature rise response of the metal workpiece (4) satisfies: ， ， In the formula, P e K represents the power loss generated by the electromagnetic field. s is the three-dimensional end effect correction coefficient; J is the induced current density vector in the volume region under the action of alternating magnetic field; B is the magnetic induction intensity vector; V is the electromagnetic action volume region; C is the equivalent heat capacity; ΔT is the temperature rise; G is the system thermal conductivity matrix; G0 is the thermal conductivity matrix between the environmental node and the system node.

10. The strengthening method according to claim 6, characterized in that, The parameters of the pulsed laser are: circular flat-topped spot, spot diameter 1-5 mm, pulse width 10-25 ns, single pulse energy 1-11 J, and spot overlap rate 20%-80%.

Images