Ultra-short pulse laser welding method for YAG crystal and metal heat sink

Abstract

The invention discloses an ultra-short pulse laser welding method for a YAG crystal and a metal heat sink, and belongs to the field of ultra-short pulse laser welding. The invention aims to overcome the defect that the existing YAG crystal and metal heat sink connection process cannot integrate effective heat transfer of an interface, low connection stress and high production efficiency at the same time. The method comprises the steps of 1, pretreatment; 2, assembling a to-be-welded part; and thirdly, ultrashort pulse laser welding is conducted. The ultra-short pulse laser welding method is used for ultra-short pulse laser welding of the YAG crystal and the metal heat sink.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of ultra-short pulse laser welding. BACKGROUND

[0002] Yttrium aluminum garnet (Y3Al5O 12 12) crystal has excellent optical and thermodynamic properties, and is a new type of ultraviolet and infrared optical device substrate and window material. At the same time, it is the most widely used laser gain medium material in laser. In the working process of the solid laser made of YAG crystal as gain medium, the heat effect generated in the crystal will affect the beam transmission quality of the laser crystal, which is an important factor limiting the development of high-power laser system. In current practical applications, metal heat sink materials are usually used as heat conduction medium to contact with YAG crystal and realize heat dissipation of the crystal component.

[0003] Mechanical connection is a commonly used method to connect YAG crystal and metal heat sink, but mechanical connection is difficult to realize tight contact of the two materials in microscale, resulting in limited actual contact area, which is not conducive to interface heat transfer. If YAG crystal and metal heat sink are welded, it is beneficial to reduce the interface thermal resistance between YAG crystal and metal heat sink in laser, improve the heat conduction performance, and realize the integration of laser components.

[0004] Vacuum brazing is a method that can realize the connection of YAG crystal and metal heat sink, but due to the large difference in thermal expansion coefficient between YAG crystal and brazing alloy and metal heat sink, obvious residual stress is easily generated after brazing, which has adverse effect on the optical transmission performance of YAG crystal. Under some brazing parameters, YAG crystal may directly crack and fail after brazing. At the same time, vacuum brazing method needs to be welded in non-air atmosphere, and the brazing heating and cooling process often takes several hours, which greatly limits the connection conditions and production efficiency. SUMMARY

[0005] The present application solves the defects that the existing connection process of YAG crystal and metal heat sink cannot have effective interface heat transfer and low connection stress, high production efficiency, and further provides a method for ultra-short pulse laser welding of YAG crystal and metal heat sink.

[0006] A method for ultra-short pulse laser welding of YAG crystal and metal heat sink, which is carried out according to the following steps:

[0007] I. The upper and lower surfaces of YAG crystal and the surface to be connected of metal heat sink are pretreated respectively to obtain YAG crystal to be welded and metal heat sink to be welded;

[0008] II. The YAG crystal to be welded and the metal heat sink to be welded are stacked in order from top to bottom, and then the stacked parts are pressed and fixed to obtain the welding assembly;

[0009] III. The welding assembly is placed on the ultra-short pulse laser processing platform, the YAG crystal on the upper surface of the welding assembly is adjusted to pass through the ultra-short pulse laser, and the focal point is located near the welding interface, then the ultra-short pulse laser welding is carried out under the conditions of room temperature, air atmosphere, laser pulse width of 5fs-50ps, laser average power of 10mW-500W and laser processing speed of 0.01mm / s-25mm / s, and the ultra-short pulse laser welding of the YAG crystal and the metal heat sink is completed.

[0010] The beneficial effects of the present application are:

[0011] The present application provides a kind of YAG crystal and the ultra-short pulse laser welding method of metal heat sink, by ultra-short pulse laser processing, realize YAG crystal and metal heat sink connection under the condition of room temperature and air atmosphere, its main connection mechanism is that ultra-short pulse laser induces transparent YAG crystal nonlinear absorption laser energy and metal heat sink linear absorption laser energy in micron size processing area, and then causes YAG crystal surface micron size area to be modified into amorphous state and form micro-scale mixing with metal heat sink, to realize welding. Because of the extremely high peak power density of ultra-short pulse laser and the direct action area of extremely small size, the size of welding and heat affected zone can be controlled in the micron range, and the total average laser power is very small, which minimizes the heat input of the joint during welding, and is beneficial to obtain a low connection stress welded joint.

[0012] Compared with the existing YAG crystal and metal heat sink connection technology, the ultra-short pulse laser welding method of YAG crystal and metal heat sink of the present application mainly includes the following beneficial effects:

[0013] 1. Low joint stress: Because the total heat input and the size of the affected area during welding are small, the generation of large thermal stress is avoided, thereby avoiding the direct impact on the optical application performance of YAG crystal.

[0014] 2. High interface heat transfer efficiency: The direct welding of YAG crystal and metal heat sink ensures the close combination of the two materials at the microscale, thereby avoiding the adverse effects of microscale gaps on interface heat transfer efficiency.

[0015] 3. High production efficiency: The connection process can be carried out at room temperature and in air atmosphere, and the laser processing speed is high, which can effectively improve the production efficiency of the welded joint of YAG crystal and metal heat sink.

[0016] 4. The connection process is simple and easy to operate, without adding filler metal and intermediate layer materials, and has broad application prospects and practical value. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 Figure (1) is a schematic diagram of an ultrashort pulse laser processing system; (2) is a schematic diagram of an ultrashort pulse laser welding jig; and (3) is a schematic diagram of an ultrashort pulse laser welding routing mode;

[0018] Figure 2 Figure (1) is a schematic diagram of an ultrashort pulse laser processing system; (2) is a schematic diagram of an ultrashort pulse laser welding jig; and (3) is a schematic diagram of an ultrashort pulse laser welding routing mode;

[0019] Figure 3 Figure (1) is a schematic diagram of an ultrashort pulse laser processing system; (2) is a schematic diagram of an ultrashort pulse laser welding jig; and (3) is a schematic diagram of an ultrashort pulse laser welding routing mode;

[0020] Figure 4 Figure (1) is a schematic diagram of an ultrashort pulse laser processing system; (2) is a schematic diagram of an ultrashort pulse laser welding jig; and (3) is a schematic diagram of an ultrashort pulse laser welding routing mode;

[0021] Figure 5 Figure (1) is a schematic diagram of an ultrashort pulse laser processing system; (2) is a schematic diagram of an ultrashort pulse laser welding jig; and (3) is a schematic diagram of an ultrashort pulse laser welding routing mode. DETAILED DESCRIPTION

[0022] Specific embodiment one: a method for ultrashort pulse laser welding of a YAG crystal and a metal heat sink, which is carried out according to the following steps:

[0023] I. The upper and lower surfaces of the YAG crystal and the surface to be connected of the metal heat sink are pretreated respectively to obtain a YAG crystal to be welded and a metal heat sink to be welded;

[0024] II. The YAG crystal to be welded and the metal heat sink to be welded are stacked in the order of the YAG crystal to be welded and the metal heat sink to be welded from top to bottom to obtain a stacked part, and then the stacked part is pressed and fixed to obtain a welding assembly;

[0025] III. The welding assembly is placed on an ultrashort pulse laser processing platform, the ultrashort pulse laser is adjusted to pass through the YAG crystal on the upper surface of the welding assembly, and the focal point is located near the welding interface, and then ultrashort pulse laser welding is carried out under the conditions of room temperature, air atmosphere, laser pulse width of 5 fs to 50 ps, laser average power of 10 mW to 500 W, and laser processing speed of 0.01 mm / s to 25 mm / s, thereby completing the ultrashort pulse laser welding of the YAG crystal and the metal heat sink.

[0026] The beneficial effects of the present embodiment are:

[0027] The application provides a YAG crystal and metal heat sink ultra-short pulse laser welding method, which realizes the connection of the YAG crystal and the metal heat sink at room temperature and in an air atmosphere through ultra-short pulse laser processing. The main connection mechanism is that the ultra-short pulse laser induces the nonlinear absorption of the YAG crystal and the linear absorption of the metal heat sink in the micron-sized processing area, and then causes the micron-sized area on the surface of the YAG crystal to be modified into an amorphous state and form a micro-scale mixture with the metal heat sink, so that the welding is realized. Due to the extremely high peak power density of the ultra-short pulse laser and the extremely small direct action area, the size of the welding and heat affected zone can be controlled in the micron range, and the total average laser power is very small, which maximally reduces the heat input of the joint in the welding process, and is beneficial to obtain a low-stress welded joint.

[0028] Compared with the existing YAG crystal and metal heat sink connection technology, the YAG crystal and metal heat sink ultra-short pulse laser welding method has the following beneficial effects:

[0029] 1. Low joint stress: due to the small total heat input and affected zone size in the welding process, the generation of large thermal stress is avoided, so that the direct influence on the optical application performance of the YAG crystal is avoided.

[0030] 2. High interface heat transfer efficiency: the direct welding of the YAG crystal and the metal heat sink ensures the close combination of the two materials at the microscale, so that the adverse influence of the microscale gap on the interface heat transfer efficiency is avoided.

[0031] 3. High production efficiency: the connection process can be carried out at room temperature and in an air atmosphere, and the laser processing speed is high, so that the production efficiency of the YAG crystal and metal heat sink welded joint can be effectively improved.

[0032] 4. The connection process is simple and easy to operate, and does not need to add brazing filler metal and intermediate layer materials, and has wide application prospect and practical value.

[0033] Specific implementation method two: different from the specific implementation method one is that the pretreatment in step one is to mechanically polish by using SiC sandpaper with numbers of 800#, 1500#, 2000# and 3000# in sequence, then polish by using diamond polishing agent, and finally clean by using anhydrous ethanol ultrasonic cleaning. The others are the same as the specific implementation method one.

[0034] Specific implementation method three: different from the specific implementation method one or two is that the metal heat sink in step one is copper, aluminum, molybdenum, molybdenum copper alloy, tungsten copper alloy or tungsten molybdenum alloy. The others are the same as the specific implementation method one or two.

[0035] Specific embodiment four: the difference between this embodiment and one of the specific embodiments one to three is that the stacked parts are fixed and pressed by a clamp with a through hole in step two; the clamp with a through hole is specifically composed of an upper fixed plate, a lower fixed plate and a bolt, and a through hole is arranged at the center of the upper fixed plate. The others are the same as specific embodiments one to three.

[0036] Specific embodiment five: the difference between this embodiment and one of the specific embodiments one to four is that the stacked parts are fixed and pressed by a clamp with a through hole, which is specifically performed by the following steps: placing the stacked parts on the lower fixed plate, with the metal heat sink in contact with the lower fixed plate, then placing the upper fixed plate on the surface of the YAG crystal, with the through hole of the upper fixed plate corresponding to the position of the YAG crystal, and finally applying pressure by screwing, until the Newton's ring of light and shade is observed near the interface. The others are the same as specific embodiments one to four.

[0037] Specific embodiment six: the difference between this embodiment and one of the specific embodiments one to five is that the wavelength of the ultra-short pulse laser in step three is 200nm~2000nm. The others are the same as specific embodiments one to five.

[0038] Specific embodiment seven: the difference between this embodiment and one of the specific embodiments one to six is that the repetition frequency of the ultra-short pulse laser in step three is 0.1kHz~100MHz. The others are the same as specific embodiments one to six.

[0039] Specific embodiment eight: the difference between this embodiment and one of the specific embodiments one to seven is that the ultra-short pulse laser is adjusted to pass through the YAG crystal on the upper surface of the assembly to be welded in step three, and the focal point is located near the interface to be welded, which is specifically performed by the following steps: setting a CCD camera, with its phase plane and center point coinciding with the focal plane and focal point center of the laser respectively, then adjusting the horizontal position of the ultra-short pulse laser processing platform through the computer control end, until the assembly to be welded is located directly below the laser light path, and then adjusting the height of the ultra-short pulse laser processing platform through the computer control end, until the clear phase of the interface can be seen in the CCD image, that is, the laser focal point is located near the interface. The others are the same as specific embodiments one to seven.

[0040] Specific embodiment nine: the difference between this embodiment and one of the specific embodiments one to eight is that the processing path of the ultra-short pulse laser welding in step three is a snake-shaped processing path. The others are the same as specific embodiments one to eight.

[0041] Specific embodiment ten: the difference between this embodiment and one of the specific embodiments one to nine is that the welding line spacing between the processing paths is 0.01mm~1mm. The others are the same as specific embodiments one to nine.

[0042] The beneficial effects of the present application are verified by the following examples:

[0043] Example 1

[0044] A method for YAG crystal and metal heat sink ultra-short pulse laser welding, which is carried out according to the following steps:

[0045] I. The upper and lower surfaces of the YAG crystal and the surfaces to be connected of the metal heat sink are pretreated respectively to obtain the YAG crystal to be welded and the metal heat sink to be welded;

[0046] II. The YAG crystal to be welded and the metal heat sink to be welded are stacked in order from top to bottom to obtain a stacked part, and then the stacked part is pressed and fixed to obtain a welding assembly;

[0047] III. The welding assembly is placed on an ultra-short pulse laser processing platform, the ultra-short pulse laser is adjusted to pass through the YAG crystal on the upper surface of the welding assembly, and the focal point is located near the welding interface, then the ultra-short pulse laser welding is carried out under the conditions of room temperature, air atmosphere, laser pulse width of 37 fs, laser average power of 100 mW, and laser processing speed of 0.05 mm / s, thereby completing the ultra-short pulse laser welding of the YAG crystal and the metal heat sink.

[0048] The pretreatment in step I is mechanical polishing using SiC sandpaper with grits of 800#, 1500#, 2000# and 3000# in sequence, and then polishing with diamond polishing agent, and finally ultrasonic cleaning with anhydrous ethanol for 10 min under the condition of a power of 480 W.

[0049] The YAG crystal in step I has a thickness of 2 mm; and the metal heat sink is pure Cu.

[0050] In step II, the stacked part is pressed and fixed by using a fixture with a through hole; the fixture with a through hole specifically consists of an upper fixed plate, a lower fixed plate and a bolt, and the upper fixed plate is provided with a through hole at the center.

[0051] The stacked part is pressed and fixed by using the fixture with a through hole, which is specifically carried out according to the following steps: placing the stacked part on the lower fixed plate, with the metal heat sink in contact with the lower fixed plate, then placing the upper fixed plate on the surface of the YAG crystal, with the through hole of the upper fixed plate corresponding to the position of the YAG crystal, and finally applying pressure by screwing, until the Newton's rings with light and dark alternating are observed near the interface by naked eye.

[0052] The wavelength of the ultra-short pulse laser in step III is 800 nm.

[0053] The repetition frequency of the ultra-short pulse laser in step III is 1 kHz.

[0054] In step three, the ultrashort pulse laser is adjusted to pass through the YAG crystal on the upper surface of the assembly to be welded, and the focus is located near the interface to be welded. Specifically, the following steps are performed: a CCD camera is set so that its phase plane and center point coincide with the focal plane and focal center of the laser respectively, and then the horizontal position of the ultrashort pulse laser processing platform is adjusted through the computer control end until the assembly to be welded is located directly below the laser optical path, and then the height of the ultrashort pulse laser processing platform is adjusted through the computer control end until a clear physical phase at the interface is visible in the CCD image, that is, the laser focus is located near the interface.

[0055] The processing path of the ultrashort pulse laser welding described in step 3 is a serpentine processing path.

[0056] The welding line spacing between the processing paths is 0.05mm.

[0057] Figure 1 Schematic diagram of the ultrashort pulse laser welding process of Example 1, (1) is a schematic diagram of the ultrashort pulse laser processing system; (2) is a schematic diagram of the ultrashort pulse laser welding fixture; (3) is a schematic diagram of the ultrashort pulse laser welding routing method;

[0058] In order to directly characterize the quality of the ultrashort pulse laser welded joint between the YAG crystal and the metal heat sink in this embodiment, the interface structure of the joint after connection was observed. The low-magnification and high-magnification backscattered scanning electron microscope photos of the typical interface structure between the YAG crystal and the copper were obtained. Figure 2 and Figure 3 shown. Figure 2 This is a low-magnification scanning electron microscope photograph of the weld line position at the interface of the ultrashort pulse laser welded joint between the YAG crystal and the metal heat sink in Example 1; Figure 3 This is a high-magnification scanning electron microscope image of the weld line at the interface of the ultrashort pulse laser welded joint between the YAG crystal and the metal heat sink in Example 1. As can be seen, the YAG crystal and Cu were successfully bonded together by the ultrashort pulse laser. No obvious defects were observed at the weld line irradiated by the ultrashort pulse laser or in the untreated area between the weld lines. An uneven interface formed between the YAG crystal and Cu at the weld line. Furthermore, a laser-modified region approximately 10 μm wide appeared near the YAG ceramic interface.

[0059] In order to further determine the interfacial reaction during the femtosecond laser welding process, the YAG / Cu interface in the weld line area was analyzed by transmission electron microscopy. Figure 4 shown. Figure 4 This is a transmission electron microscope bright-field image of the weld line position at the interface of the ultrashort pulse laser welded joint between the YAG crystal and the metal heat sink in Example 1. As can be seen from the figure, the two materials at the interface undergo intense stirring and mixing, forming a chimeric structure on a microscopic scale.

[0060] Figure 5 The selected area electron diffraction photograph of the laser modified zone on the YAG crystal side of the weld line position of the YAG crystal and metal heat sink ultrashort pulse laser welded joint in Example 1. As can be seen from the figure, the YAG crystal in the modified zone is transformed into an amorphous structure under the action of ultrashort pulse laser. Therefore, ultrashort pulse laser realizes the defect-free connection of YAG crystal and metal heat sink copper by modifying and microscale mixing of the materials at the interface.

[0061] In order to characterize the mechanical properties of the YAG crystal and metal heat sink ultrashort pulse laser welded joint in this embodiment, a universal testing machine was used to test the shear strength of the joint at a loading speed of 0.5 mm / s. According to the shear strength formula P=F / S, F is the maximum load before the joint breaks, unit is N, S is the total area of the weld line, unit is mm 2 , the average strength of the joint is 50.6 MPa, which is basically equivalent to the strength of the YAG crystal parent material used, indicating that ultrashort pulse laser welding realizes high-quality connection of YAG crystal and metal heat sink copper.

Claims

1. A method for ultrashort pulse laser welding of a YAG crystal and a metal heat sink, characterized in that It is carried out in the following steps:

1. Pre-treating the upper and lower surfaces of the YAG crystal and the surface to be joined of the metal heat sink respectively to obtain the YAG crystal to be welded and the metal heat sink to be welded; 2. Stack the YAG crystal to be welded and the metal heat sink to be welded in order from top to bottom to obtain a stacked part, and then press and fix the stacked parts to obtain an assembly to be welded; 3. Place the assembly to be welded on the ultrashort pulse laser processing platform, adjust the ultrashort pulse laser to pass through the YAG crystal on the upper surface of the assembly to be welded, and focus it near the interface to be welded. Then, perform ultrashort pulse laser welding under the conditions of room temperature, air atmosphere, laser pulse width of 5fs~50ps, laser average power of 10mW~500W and laser processing speed of 0.01mm / s~25mm / s to complete the ultrashort pulse laser welding of the YAG crystal and the metal heat sink.

2. The method for ultrashort pulse laser welding of a YAG crystal and a metal heat sink according to claim 1, characterized in that The pretreatment described in step 1 is to mechanically polish using 800#, 1500#, 2000# and 3000# SiC sandpaper in sequence, then polish with diamond polishing agent, and finally ultrasonically clean with anhydrous ethanol.

3. The method for ultrashort pulse laser welding of a YAG crystal and a metal heat sink according to claim 1, characterized in that The metal heat sink described in step 1 is copper, aluminum, molybdenum, molybdenum-copper alloy, tungsten-copper alloy or tungsten-rhenium alloy.

4. The method for ultrashort pulse laser welding of a YAG crystal and a metal heat sink according to claim 1, characterized in that In step 2, the stacked parts are pressed and fixed using a fixture with a through hole; the fixture with a through hole is specifically composed of an upper fixing plate, a lower fixing plate and bolts, and a through hole is set in the center of the upper fixing plate.

5. The method for ultrashort pulse laser welding of a YAG crystal and a metal heat sink according to claim 4, characterized in that The stacked parts are pressed and fixed using a fixture with through holes. Specifically, the following steps are followed: the stacked parts are placed on the lower fixed plate with the metal heat sink in contact with the lower fixed plate, and then the upper fixed plate is placed on the surface of the YAG crystal, with the through holes of the upper fixed plate corresponding to the position of the YAG crystal. Finally, pressure is applied by tightening with bolts until alternating light and dark Newton rings are observed near the interface.

6. The method for ultrashort pulse laser welding of a YAG crystal and a metal heat sink according to claim 1, characterized in that The wavelength of the ultrashort pulse laser described in step 3 is 200nm~2000nm.

7. The method for ultrashort pulse laser welding of a YAG crystal and a metal heat sink according to claim 1, characterized in that The repetition frequency of the ultrashort pulse laser described in step 3 is 0.1kHz~100MHz.

8. The method for ultrashort pulse laser welding of a YAG crystal and a metal heat sink according to claim 1, characterized in that In step three, the ultrashort pulse laser is adjusted to pass through the YAG crystal on the upper surface of the assembly to be welded, and the focus is located near the interface to be welded. Specifically, the following steps are performed: a CCD camera is set so that its phase plane and center point coincide with the focal plane and focal center of the laser respectively, and then the horizontal position of the ultrashort pulse laser processing platform is adjusted through the computer control end until the assembly to be welded is located directly below the laser optical path, and then the height of the ultrashort pulse laser processing platform is adjusted through the computer control end until a clear physical phase at the interface is visible in the CCD image, that is, the laser focus is located near the interface.

9. The method for ultrashort pulse laser welding of a YAG crystal and a metal heat sink according to claim 1, characterized in that The processing path of the ultrashort pulse laser welding described in step 3 is a serpentine processing path.

10. The method for ultrashort pulse laser welding of a YAG crystal and a metal heat sink according to claim 9, characterized in that The welding line spacing between the processing paths is 0.01mm~1mm.

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