WO2021068285A1

WO2021068285A1 - Ultrasonic assisted laser peening method for obtaining ultrafine grain surface layer

Info

Publication number: WO2021068285A1
Application number: PCT/CN2019/112637
Authority: WO
Inventors: 孟宪凯; 赵曜民; 周建忠; 许晓静; 黄舒; 盛杰; 李京
Original assignee: 江苏大学
Priority date: 2019-10-08
Filing date: 2019-10-23
Publication date: 2021-04-15
Also published as: CN110760668A; GB2598874A; GB2598874B; CN110760668B

Abstract

Provided is an ultrasonic assisted laser peening method for obtaining an ultrafine grain surface layer, comprising: using ultrasonic vibration waves emitted by an ultrasonic transducer to induce high-frequency vibration waves on a metal surface layer, and using laser shock waves and the ultrasonic vibration waves to jointly prepare a metal material having the ultrafine grain surface layer. The high-frequency vibration waves induced by the ultrasonic vibration waves may cause the atomic lattice to be periodically dense and loose, so as to promote rapid transition of microscopic structures, such as dislocation cells and dislocation walls, to a low energy state during the propagation of the laser shock waves, and to promote the formation of sub-grain boundaries and large angle grain boundaries, effectively increasing the dynamic recrystallization behavior induced by the laser peening, thereby improving the grain refinement ability of the traditional laser peening technology, obtaining a metal material having an ultrafine grain surface layer, and improving the fatigue strength and fracture toughness of a metal part; in addition, this technology has the characteristics of low pollution, low cost and high efficiency.

Description

Ultrasonic assisted laser shot peening method for obtaining superfine crystal surface layer

Technical field

The invention belongs to the field of laser processing technology, especially the field of laser surface strengthening, and specifically refers to an ultrasonic-assisted laser shot peening method for obtaining an ultra-fine crystal surface layer.

Background technique

Laser shot peening technology uses pulsed laser-induced high-pressure shock waves to produce plastic deformation on the surface of metal materials, inducing the formation of dislocation walls, dislocation cells, and other dislocation structures. Some of the dislocation structures are transformed into subcrystalline or subcrystalline through the dynamic recrystallization process. The large-angle grain boundary makes the material grain refinement, which has been widely used in the field of anti-fatigue manufacturing. For example, the Chinese invention patent with the patent number ZL201610695635.7 proposes a laser shock strengthening combination method to obtain the mixed distribution of metal surface grains. The laser shock strengthening is used to impact the surface of the metal workpiece according to the designed trajectory, which can form a specific surface layer on the metal workpiece. The grains distributed between the coarse and fine phases realize the mixed distribution of grains on the surface and the depth direction. However, the degree of grain refinement in laser shock strengthening technology is mainly related to the dynamic recrystallization process, and the degree of dynamic recrystallization is closely related to the ability of dislocation cells, dislocation walls and other microstructures to transform into sub-grain boundaries or large-angle grain boundaries. Related. Therefore, the traditional laser shock strengthening technology has the disadvantages of low dynamic recrystallization and low grain refinement.

The Chinese patent application with application number CN201810335784.1 proposes a surface strengthening method for vibration-assisted laser shock treatment of metal components. The laser shock strengthening technology is combined with vibration aging treatment to perform laser lap shock strengthening with the assistance of vibration aging treatment. Treatment to make the surface produce more serious plastic deformation, and induce high-amplitude residual compressive stress in the impact area, and further refine the surface grains to achieve the strengthening of the metal surface, thereby effectively improving the fatigue life of the metal component. This technology has the following shortcomings: (1) This method uses a vibration exciter to apply vibration to the entire sample while laser peening, which is not conducive to achieving local strengthening of large parts; (2) This method requires the use of high-power excitation The vibrator realizes vibration aging, and the energy utilization efficiency is low; (3) This method cannot realize the coupling of vibration wave and laser shock wave, and the degree of grain refinement is low.

Ultrasonic technology is mature and inexpensive, and has been widely used in laser processing technology. The Chinese invention patent application with the application number CN201810290661.0 discloses an ultrasonic-assisted laser spot welding device and method, which introduces high-frequency ultrasonic energy into the welding, effectively controls the interface reaction and strengthens the melt flow, and improves the interface wettability. The welding seam grains are reduced, and the subsequent ultrasonic vibration is more helpful to reduce or eliminate the residual stress of the welding seam and the connecting surface, and improve the connection strength. The Chinese invention patent with application number CN201711057771.4 discloses a dual ultrasonic-assisted laser additive manufacturing device, which enables flame-retardant titanium alloys to receive the dual effects of ultrasonic stirring and ultrasonic impact during the laser additive manufacturing process to achieve resistance The refinement and homogenization of the structure of the titanium-burning alloy realizes the effective control of the alloy structure and mechanical properties. The above method uses ultrasonic vibration to stir/impact the laser-induced molten pool to achieve microstructure refinement, but it has the following shortcomings: (1) There are many structural defects in the laser melting process, such as pores, cracks, etc.; (2) After laser melting Residual tensile stress appears on the surface of the material, which is not conducive to the improvement of fatigue strength.

Summary of the invention

In view of the shortcomings in the prior art, the present invention proposes an ultrasonic-assisted laser shot peening method for obtaining an ultra-fine crystal surface layer, which utilizes the interaction of vibration waves induced by ultrasound inside the material and laser-induced shock waves to promote the dynamic recrystallization process. The metal material of the ultra-fine grained surface layer greatly improves the fatigue strength and fracture toughness of metal parts. The defects of the prior art can be overcome, and the grain size of the material surface layer can be refined without changing the properties of the core material, and the efficiency is high and the cost is low.

The present invention achieves the above-mentioned technical objects through the following technical means.

An ultrasonic-assisted laser shot peening method for obtaining the superfine crystal surface layer, which is characterized in that the ultrasonic vibration wave emitted by the ultrasonic transducer induces high-frequency vibration waves on the metal surface, and the high-frequency vibration waves cause the atomic lattice to propagate in the vibration wave. Periodic atomic dense and loose areas appear along the path; then laser shock waves are loaded for laser peening. In the atomic dense areas, the ultrasonic vibration waves increase the potential energy of the material, and the laser shock waves induce higher potential during the laser peening process. Dislocation density; in the region of loose atoms, ultrasonic vibration waves increase the distance between atoms and intensify the movement of atoms, which promotes the rapid transformation of microstructures such as dislocation cells and dislocation walls induced by laser peening to low-energy states, forming sub-grain boundaries and large-angle crystals To promote the dynamic recrystallization behavior of materials, use laser shock waves and ultrasonic vibration waves to combine to obtain ultra-fine crystal surface metal materials.

Further, the ultrasonic transducer is in direct or indirect contact with the metal surface.

Further, the angle α between the ultrasonic vibration wave and the propagation direction of the laser shock wave satisfies 0-15°.

Further, when the angle between the ultrasonic vibration wave and the propagation direction of the laser shock wave is difficult to satisfy 0-15° and the thickness of the workpiece to be processed is less than 3mm, the angle α between the ultrasonic vibration wave and the propagation direction of the laser shock wave is 165-180 °.

Further, the start time of ultrasonic loading is ahead of the start time of laser loading by Δt, and Δt is related to the angle α between the propagation direction of the ultrasonic vibration wave and the laser shock wave;

When the angle α between the ultrasonic vibration wave and the propagation direction of the laser shock wave satisfies 0～15°:

When the angle α between the ultrasonic vibration wave and the propagation direction of the laser shock wave satisfies 165～180°:

z is the thickness of the laser peened metal part, v ₁ is the propagation speed of the laser-induced shock wave, v ₂ is the propagation speed of the ultrasonic-induced vibration wave, and α is the angle between the ultrasonic vibration wave and the propagation direction of the laser shock wave.

Furthermore, the ultrasonic vibration wave parameters need to meet the requirements that the ultrasonic frequency is higher than 20 kHz and the vibration amplitude is 1-10 μm.

Further, the laser parameters need to satisfy the laser pulse energy of 3-10J, the pulse width of 15-25ns, the overlap rate of 50-75%, the coverage rate of 200%, and the pulse frequency of 1-5 Hz.

Further, in the laser shot peening, running water is used as the constraining layer, and black tape is used as the absorbing layer.

Further, the workpiece to be processed by the laser shot peening is an aluminum alloy, a titanium alloy, a nickel-based alloy or a mold steel part.

The ultrasonic-assisted laser shot peening method for obtaining the superfine crystal surface layer of the present invention has the processing principle that: the high-frequency vibration wave induced by the ultrasonic transducer induces the periodic density and looseness of the atomic lattice, that is, the propagation of the high-frequency vibration wave There are periodic dense and loose areas along the path; in dense areas, vibration waves increase the potential energy of the material, which is conducive to the formation of dislocations during the laser peening process. Therefore, ultrasonic vibration waves can induce higher laser shock waves. Dislocation density; In the region of loose atoms, high-frequency vibration waves increase the distance between atoms and aggravate the movement, prompting the laser peening-induced dislocation cells, dislocation walls and other microstructures to quickly transform to low-energy states, forming sub-grain boundaries and large Angle the grain boundary, promote the dynamic recrystallization behavior of the material and obtain the ultra-fine grain structure.

The ultrasonic-assisted laser shot peening method for obtaining the superfine crystal surface layer of the present invention is suitable for aluminum alloy, titanium alloy, nickel-based alloy and die steel parts. Its technical advantages are:

1. The high-frequency vibration wave induced by ultrasound increases the dislocation density during the laser shock wave propagation process on the one hand, and on the other hand promotes the conversion of dislocation walls and dislocation cells into sub-grain boundaries or large-angle grain boundaries, effectively reducing the surface layer of the material The grain size.

2. In this method, the ultrasonic vibration wave and the laser shock wave have little effect on the performance of the core material of the part, and will not cause the performance of the core material to decrease.

3. The surface layer of the material will not produce defects such as pores, cracks, residual tensile stress, etc., which is conducive to the increase of fatigue strength.

4. Ultrasonic and laser parameters are precisely controllable, easy to operate and realize automation, high efficiency, low cost and environmentally friendly.

Description of the drawings

Fig. 1 is a schematic diagram of the ultrasonic-assisted laser shot peening method for obtaining the superfine crystal surface layer according to the present invention.

Fig. 2 is a schematic diagram of the ultrasonic-assisted laser shot peening method for obtaining the superfine crystal surface layer according to the present invention.

Fig. 3 is a schematic diagram of the angle α between the ultrasonic vibration wave and the propagation direction of the laser shock wave according to the present invention.

Among them, 1. Laser, 2. Ultrasonic transducer, 3. Flowing water, 4. Black tape, 5. Metal, 6. High frequency vibration wave, 7. Laser shock wave, 8. High temperature plasma.

Detailed ways

The present invention will be further described below in conjunction with the drawings and specific embodiments, but the protection scope of the present invention is not limited to this.

The ultrasonic-assisted laser shot peening method for obtaining the superfine crystal surface layer of the present invention, as shown in Fig. 1, uses the ultrasonic vibration wave emitted by the ultrasonic transducer 2 to induce the high-frequency vibration wave 6 on the surface of the metal 5, and then loads the laser 1. Laser shot peening is performed. The laser 1 excites a high-temperature plasma 8 on the metal surface to form a laser shock wave 7. The laser shock wave 7 and the ultrasonic vibration wave are combined to prepare the metal material of the ultra-fine crystal surface layer. In this process, the high-frequency vibration wave 6 induced by the ultrasonic transducer 2 induces periodic density and looseness of the atomic lattice, that is, periodic dense and loose areas of atoms appear on the propagation path of the high-frequency vibration wave 6, as shown in the figure. 2 shown. In the dense area of atoms, the vibration wave increases the potential energy of the material, which is conducive to the formation of dislocations in the laser peening process. Therefore, the ultrasonic vibration wave can induce a higher dislocation density in the laser shock wave 7; in the loose atom area, high frequency Vibration wave 6 increases the distance between atoms and intensifies the movement, which promotes the rapid transformation of microstructures such as dislocation cells and dislocation walls induced by laser peening to low-energy states, forming sub-grain boundaries and large-angle grain boundaries, and promoting the dynamic recrystallization behavior of materials In turn, ultra-fine crystal structure is obtained; the fatigue strength and fracture toughness of metal parts are greatly improved.

In the specific implementation process, the ultrasonic transducer 2 is in direct or indirect contact with the surface of the metal 5. As shown in Fig. 3, the angle α between the ultrasonic vibration wave and the propagation direction of the laser shock wave 7 satisfies 0-15°. When the angle α between the ultrasonic vibration wave and the propagation direction of the laser shock wave 7 is difficult to satisfy 0-15° and the thickness of the workpiece to be processed is less than 3mm, the angle α between the ultrasonic vibration wave and the propagation direction of the laser shock wave 7 is 165～180 °. The laser shot peening is suitable for metal parts of aluminum alloy, titanium alloy, nickel-based alloy or die steel.

According to the working principle of the ultrasonic-assisted laser peening of the present invention, the start time of the ultrasonic vibration wave loading is earlier than the start time of the laser 1 loading by the time Δt. After the ultrasonic vibration wave is loaded, periodic sparse and dense parts are formed on the surface of the material, and then the laser 1 is loaded. The laser shock wave 7 passes through the sparse and dense parts to produce different effects and promote the dynamic recrystallization behavior of the material.

The start time of the ultrasonic loading is earlier than the start time of the laser 1 loading by a time Δt related to the angle α between the ultrasonic vibration wave and the propagation direction of the laser shock wave 7.

When the angle α between the ultrasonic vibration wave and the propagation direction of the laser shock wave 7 satisfies 0～15°:

When the angle α between the ultrasonic vibration wave and the propagation direction of the laser shock wave 7 satisfies 165～180°:

z is the thickness of the laser shot peened metal 5 part, v ₁ is the propagation speed of the laser-induced shock wave, v ₂ is the propagation speed of the ultrasonic-induced vibration wave, and α is the angle between the ultrasonic vibration wave and the propagation direction of the laser shock wave 7.

Ultrasonic vibration wave parameters must meet the requirements of ultrasonic frequency higher than 20kHz, vibration amplitude 1-10μm; laser 1 parameters must meet laser 1 pulse energy 3-10J, pulse width 15-25ns, overlap rate 50-75%, coverage rate 200% , The pulse frequency is 1～5Hz.

Example 1

Taking the 2024-T351 aluminum alloy sheet with a thickness of 2mm as an example, the ultrasonic-assisted laser shot peening method for obtaining the superfine crystal surface layer of the present invention is used to strengthen the surface layer of the material, and the laser shock wave 7 and the ultrasonic vibration wave are combined to prepare the super Fine-grained surface material.

In the laser peening process, the flowing water 3 is used as the constraining layer, and the black tape 4 is used as the absorbing layer. The start time of the ultrasonic loading is 15 minutes ahead of the start time of the laser loading, and the angle between the ultrasonic vibration wave and the propagation direction of the laser shock wave 7 is 180°, that is, the ultrasonic vibration is applied from the back of the sheet. The ultrasonic frequency is 25kHz, and the vibration amplitude is 2μm. The laser pulse energy is 5J, the pulse width is 15ns, the overlap rate is 50%, the coverage rate is 200%, and the pulse frequency is 1Hz.

After grinding, polishing and metallographic corrosion, SEM is used to observe the metallographic structure of the material surface. After measurement, the average grain size of the 2024-T351 aluminum alloy surface layer after ultrasonic-assisted laser 1 shot peening is reduced by more than 15% compared with traditional laser shot peening, indicating that the method of the present invention can effectively reduce the grain size of metal materials and obtain an ultra-fine crystal surface layer.

The embodiments are the preferred embodiments of the present invention, but the present invention is not limited to the above-mentioned embodiments. Without departing from the essence of the present invention, any obvious improvements, substitutions or substitutions can be made by those skilled in the art. The variants all belong to the protection scope of the present invention.

Claims

An ultrasonic-assisted laser shot peening method for obtaining ultra-fine crystal surface layer, which is characterized in that: the ultrasonic vibration wave emitted by the ultrasonic transducer (2) induces the high-frequency vibration wave (6) on the surface of the metal (5), and the high-frequency vibration The wave (6) causes the atomic lattice to appear periodic atomic dense areas and loose areas on the vibration wave propagation path; then load the laser (1) for laser peening. In the atomic dense areas, the ultrasonic vibration wave increases the potential energy of the material. Promote the laser shock wave (7) in the process of laser peening to induce a higher dislocation density; in the area of loose atoms, ultrasonic vibration waves increase the distance between atoms and aggravate the movement of atoms, which promotes dislocation cells and dislocation walls induced by laser peening The microstructure quickly transforms to a low-energy state, forming sub-grain boundaries and large-angle grain boundaries to promote the dynamic recrystallization behavior of the material. The laser shock wave (7) is combined with the ultrasonic vibration wave to obtain the metal material of the ultra-fine crystal surface layer.
The ultrasonic-assisted laser shot peening method for obtaining the superfine crystal surface layer according to claim 1, wherein the ultrasonic transducer (2) is in direct or indirect contact with the surface of the metal (5).
The ultrasonic-assisted laser shot peening method for obtaining the superfine crystal surface layer according to claim 1, wherein the angle α between the ultrasonic vibration wave and the propagation direction of the laser shock wave (7) satisfies 0-15°.
The ultrasonic-assisted laser shot peening method for obtaining the superfine crystal surface layer according to claim 1, characterized in that: when the angle between the ultrasonic vibration wave and the propagation direction of the laser shock wave (7) is difficult to satisfy 0-15° and needs to be processed When the thickness of the workpiece is less than 3mm, the angle α between the ultrasonic vibration wave and the propagation direction of the laser shock wave (7) is 165-180°.
The ultrasonic-assisted laser shot peening method for obtaining the superfine crystal surface layer according to claim 3, characterized in that: when the angle between the ultrasonic vibration wave and the propagation direction of the laser shock wave (7) satisfies 0-15°, the ultrasonic vibration The start time of wave loading is ahead of the start time of laser (1) loading by Δt:

Among them, z is the thickness of the laser shot metal (5) part, v 1 is the propagation speed of the laser-induced shock wave, v 2 is the propagation speed of the ultrasonic-induced vibration wave, and α is the propagation direction of the ultrasonic vibration wave and the laser shock wave (7) The angle between.
The ultrasonic-assisted laser shot peening method for obtaining the superfine crystal surface layer according to claim 4, characterized in that: when the angle between the ultrasonic vibration wave and the propagation direction of the laser shock wave (7) satisfies 165-180°, the ultrasonic vibration The start time of wave loading is ahead of the start time of laser (1) loading by Δt:
The ultrasonic-assisted laser shot peening method for obtaining the superfine crystal surface layer according to claim 1, wherein the ultrasonic vibration wave parameters are: the ultrasonic frequency is higher than 20 kHz, and the vibration amplitude is 1-10 μm.
The ultrasonic-assisted laser shot peening method for obtaining the superfine crystal surface layer according to claim 1, wherein the laser parameters are: laser pulse energy 3-10J, pulse width 15-25ns, overlap rate 50%-75%, Coverage rate is 200%, pulse frequency is 1～5Hz.
The ultrasonic-assisted laser shot peening method for obtaining the superfine crystal surface layer according to claim 1, characterized in that: in the laser shot peening, running water (3) is used as the constraining layer, and black tape (4) is used as the absorption layer. Floor.
The ultrasonic-assisted laser shot peening method for obtaining an ultra-fine crystal surface layer according to claim 1, wherein the metal material processed by the laser shot peening is aluminum alloy, titanium alloy, nickel-based alloy or die steel parts.