WO2022127942A1

WO2022127942A1 - Methods for laser-integrated additive manufacturing and connecting based on control of molten pool flow by pulsed laser

Info

Publication number: WO2022127942A1
Application number: PCT/CN2022/076048
Authority: WO
Inventors: 胡耀武; 赵树森; 林学春; 刘胜; 张臣; 刘健; 张啸寒
Original assignee: 武汉大学
Priority date: 2020-12-14
Filing date: 2022-02-11
Publication date: 2022-06-23

Abstract

Methods for laser-integrated additive manufacturing and connecting based on control of molten pool flow by a pulsed laser. At the same time that a continuous laser (2) is used to cause the surface of a substrate to be processed (7) and an alloy powder (4) to melt to form a molten pool area (3), a pulsed laser (1) is introduced to perform synchronous shock processing on the molten pool area (3), and a laser-integrated connection and additive manufacturing process using pulsed laser (1) control of the molten pool is executed. In the manufacturing process, molten pool morphology and molten pool flow are controlled by using a pulsed laser, thus improving the flatness of a cladding surface or a weld, adjusting the residual stress in the cladding layer, and reducing anisotropy in cladding layer and weld performance. At the same time that laser forming precision and laser connection quality improvement and residual stress improvement are achieved, the flatness and mechanical performance of cladding layers and welds are improved, helping to improve production efficiency. The invention is suitable for continuous laser additive manufacturing work for multi-pass lap joining or multi-layer stacking, and is suitable for the field of laser additive manufacturing for surface remanufacturing repair, dissimilar metal welding, or direct 3D printing forming.

Description

A laser composite additive manufacturing and joining method based on pulsed laser control of molten pool flow

technical field

The invention relates to the technical fields of welding, additive manufacturing and surface modification, in particular to a laser composite additive manufacturing and connecting method based on pulsed laser control of molten pool flow.

Background technique

Laser additive manufacturing technology is a comprehensive integration of material science, mechanical engineering and laser technology. It forms a molten pool by focusing a high-energy laser beam on a substrate. Metal powder is fed into the molten pool by prefabrication or coaxial powder feeding. It is fused with the matrix solution in the molten pool, and with the movement of the laser beam, the molten pool moves in the direction of the movement of the laser beam under the action of the surface tension of the liquid, thereby gradually forming a deposition layer. This technology is of great significance for the remanufacturing of parts and the direct molding of complex parts, and is the main research direction of advanced manufacturing technology.

Laser additive manufacturing technology is based on the principle of discrete-stacking. While this technology can realize the direct forming of complex structural parts, it also has the following three limitations: (1) Continuous multi-pass lap laser additive manufacturing process This leads to large undulations on the deposition surface, which increases the workload of subsequent processing; (2) The continuous multi-pass laser additive manufacturing process leads to uneven cyclic heating and cooling processes in the deposited part, and the deposition layer memory Under complex thermal stress, the cladding layer is prone to defects such as cracks and pores; (3) The directional characteristics of heat flow diffusion in the molten pool promote the directional growth of dendrites, resulting in anisotropy in the properties of the deposited layer. In addition, in order to meet the engineering requirements of different functional characteristics of different areas of the same structural part of the new type of power, the structural parts need to be welded by dissimilar metals. However, compared with metal weldments with the same material properties, there are often more complex multi-physics coupling mechanisms in the welding process of dissimilar metals, such as material phase transition, pinhole effect and plasma effect. In addition, due to the differences in the thermal expansion coefficients of different metal materials, there is often an excessive thermal mismatch between dissimilar metals during welding, which will lead to asymmetric distribution of the three-dimensional morphology of the weld pool in the weld joint and asymmetric distribution of the element medium of the weld pool. The uniform distribution is bound to generate large thermal stress and residual stress during the welding process and after the weldment is cooled, which will affect the heat transfer, mass transfer and solidification evolution mechanism of the molten pool, and form an intermetallic at the position of the weldment joint. Compounds, which in turn affect the defect distribution, microscopic properties and mechanical properties of the weld, and ultimately affect the working reliability of the new type of power.

In view of the above problems, most of the existing laser-thermal composite additive manufacturing or joining methods with controllable internal stress are to heat the cladding layer to between the recrystallization temperature and the melting point after the laser processing is completed, and then use the laser shock process to The cladding layer is impact-strengthened to eliminate the tensile stress formed during the hot-melting process. The method can effectively improve the stress distribution in the cladding layer and improve the mechanical properties of the cladding layer. However, the three processes of cladding-heating-impacting included in this method are essentially carried out separately and independently, which is not conducive to the improvement of production efficiency. The existing dual-laser beam cladding forming and impact forging composite additive manufacturing method uses a continuous laser to perform the cladding work, and simultaneously uses a short-pulse laser to forge the cladding surface within the forging temperature range. The method can effectively eliminate defects such as pores in the cladding layer and improve thermal stress. However, in the laser additive manufacturing process, the cooling rate is fast, it is difficult to accurately control the forging temperature of the cladding layer, and it is difficult to accurately realize the forging of the cladding layer within the forging temperature range. Homogeneous and chill phenomenon. In addition, the above methods all use the laser shock process to impact or forge the cladding layer after the cladding is completed. Effectively reduce the workload of subsequent processing on the surface of the cladding layer and improve production efficiency. Therefore, how to improve the flatness of the surface of the cladding layer while ensuring the molding quality and performance of the cladding layer is still a technical problem to be solved urgently by those skilled in the art.

SUMMARY OF THE INVENTION

One of the objectives of the present invention is to overcome the shortcomings and deficiencies of the prior art, and to provide a laser composite additive manufacturing method based on pulsed laser control of molten pool flow, which can improve the thermal stress of the cladding layer and reduce the grain size. It can significantly improve the flatness of the surface of the cladding layer while ensuring the quality and performance of the cladding layer, which is conducive to improving the quality and production efficiency of the cladding layer. In material manufacturing work, it is suitable for surface remanufacturing repair or 3D printing direct forming in the field of laser additive manufacturing.

One of the objects of the present invention is achieved through the following technical solutions:

A laser composite additive manufacturing method based on pulsed laser control of molten pool flow: comprising the following steps: a continuous laser beam acts on the surface of a substrate after collimated and focused optical path transformation, so that the surface of the substrate and the preset alloy powder are transported synchronously. The alloy powder melts rapidly at the same time, forming a molten pool. At the same time, the plasma shock wave generated by the pulsed laser beam is used to act on the molten pool area, and the laser composite additive manufacturing process that uses the pulsed laser to control the molten pool is performed, and the deposition surface is formed continuously or layer by layer. Pulsed laser beams are used to control the melt pool morphology and melt pool flow during the manufacturing process.

Further, the use of the pulsed laser beam to control the morphology of the molten pool is to use the impact pressure generated by the pulsed laser to extrude part of the liquid alloy in the molten pool out of the molten pool, improve the aspect ratio of the cladding layer, and obtain a flat cladding. layer, thereby improving the flatness of the surface of the continuous multi-pass continuous lap or multi-layer accumulation cladding layer, and reducing the subsequent processing workload of the additive surface.

Further, the use of the pulsed laser beam to control the flow of the molten pool is to use the surface force field generated by the thermal action of the pulsed laser beam to control the flow of the molten pool, improve the uniformity of temperature distribution, reduce the temperature gradient in the molten pool, improve residual stress, and damage. The normal solidification process of dendrites growing in the opposite direction of heat flow diffusion inhibits the formation of cracks and dendrites, realizes grain refinement, and reduces the anisotropy of cladding properties.

Further, the spatial distribution characteristics of the pulsed laser beam can be adjusted by beam shaping or spatial light modulator.

Further, in the laser composite additive manufacturing process using the pulsed laser to control the molten pool, a high-speed camera real-time monitoring device can be installed to realize the real-time monitoring and control of the action position of the continuous laser beam and the pulsed laser beam and the impact effect.

Further, in the laser composite additive manufacturing method, the distance between the continuous laser beam acting on the surface of the substrate and the spot of the pulsed laser beam can be adjusted. When the distance between the two spots is smaller than the difference between the spot radius of the continuous laser beam and the spot radius of the pulsed laser beam, the spot of the pulsed laser beam is completely inside the spot of the continuous laser beam, and the pulsed laser acts on the molten pool in the form of thermal action, generating a force that can regulate the flow of the molten pool. When the distance between the two spots is greater than the sum of the continuous laser beam spot and the pulsed laser beam spot radius, the two spots are completely separated, and the pulsed laser acts on the solidified cladding layer, increasing the pulsed laser beam energy, and causing the cladding layer to produce plastic deformation. , resulting in a certain residual compressive stress; when the distance between the two spots is between the above two distances, the pulsed laser beam spot and the continuous laser beam spot partially intersect, and the pulsed laser acts on the edge of the molten pool in a semi-solidified state, which can cause the cladding layer to form plastic deformation. , increasing the residual compressive stress, while controlling the molten pool morphology and internal flow.

Further, in the laser composite additive manufacturing method, the control effect of the pulsed laser on the flow of the molten pool and the morphology of the molten pool can be adjusted by adjusting the energy of the pulsed laser, and the greater the energy, the more obvious the effect.

The second purpose of the present invention is to solve the technical bottleneck of the current dissimilar metal composite heat source welding seam joints with low flatness, poor symmetry and poor mechanical properties.

In order to achieve the second above-mentioned purpose, a laser composite connection method based on pulsed laser control of molten pool flow provided by the present invention comprises the following steps:

1) During the welding of dissimilar metals, place the first base metal and the second base metal according to the positional relationship of lap, butt or plug, open the heating platform, and heat the welding material to the ideal working temperature;

2) The angle between the first welding heat source and the high-frequency pulsed laser heat source ranges from 0 to 90 degrees, and the center of the first welding heat source and the center of the pulsed laser spot are concentric or 0 to 5 mm apart from the center of the heat source. The interface of the two metals or one of the base metal surfaces at a distance of 0 to 5 mm from the interface:

During the welding operation, the first welding heat source is turned on to melt the two base metals. After the molten pool is formed, the high-frequency pulsed laser heat source is turned on, so that the high-frequency pulsed laser heat source and the first welding heat source simultaneously act on the area to be processed. With the movement of the first welding heat source and the high-frequency pulsed laser heat source, a weld joint is formed at the bonding interface of the first base metal and the second base metal;

The difference between the first base metal and the second base metal is reflected in the fact that the two base metals belong to different types of welding materials, rather than different heat treatment states or structural forms of the same welding material; they can be selected according to actual engineering needs. Appropriate heat treatment methods and structural forms, including annealing, tempering, normalizing or quenching, and structural forms are the geometric dimensions or special structural forms of components (such as grooves, stress relief grooves or heat dissipation support blocks).

As a preferred solution, in the step 1), the heating platform (6) is turned on to heat up to an ideal operating temperature, which can realize the controllability of the parameters, and the parameters include the heating rate, the temperature control time and the cooling rate. Heat treatment reduces the harmful residual stress of the weldment; the ideal operating temperature is set accordingly due to the different materials of the weldment, generally not higher than the critical temperature at which the mechanical properties of the metal material are reduced, and the difference between the critical temperatures of the two base metals is taken. minimum value.

Further, in the step 2), the first welding heat source can select different heat source forms according to the actual needs of the project, and the heat source forms are any one, two or both of laser, TIG, MIG or pulsed laser. The combination of more than one type of heat source; the high-frequency pulsed laser heat source is the form of heat source generated by different types of pulsed lasers obtained by Q-switching or mode-locking, and can be selected according to actual engineering needs; the high-frequency pulsed laser heat source The size of the pulse frequency is a relative value, which is selected according to the actual welding material;

The angle relationship and positional relationship between the first welding heat source and the high-frequency pulsed laser heat source can be changed according to the actual engineering, so as to realize the change of the overlap ratio of the action area of the first welding heat source and the high-frequency pulsed laser heat source, so that high The frequency pulse laser heat source can act on both the molten pool area and the molten or semi-melted area 0-5mm behind the molten pool;

The interaction interface acting on dissimilar metals, due to the differences in the thermophysical performance parameters of dissimilar metal materials, makes the range of the heat affected zone different during the welding operation of dissimilar metals, so the center of the heat source is not necessarily located in the first place. The positional relationship between the intersection interface of the first base metal and the second base metal, the heat source center and the intersection interface of the dissimilar metals can be changed according to the actual welding material and the action position of the integrated pulsed laser.

Further, in the step 2), the to-be-processed area under the action of the high-frequency pulsed laser heat source can be the molten pool area heated and melted by the first welding heat source, or it can be the molten or semi-melted area 0-5 mm behind the molten pool. area; the special structural form is a groove, a stress relief groove, a heat dissipation support block or a combination of two or more of them.

An application of the above-mentioned laser composite additive manufacturing method based on pulsed laser-based control of molten pool flow in additive manufacturing or part remanufacturing or 3D printing.

An application of the above-mentioned laser composite joining method based on pulsed laser control of molten pool flow in welding of the same or dissimilar materials.

The advantages and beneficial effects of the present invention are as follows:

1. The laser composite additive manufacturing method in the present invention is coupled with the laser additive process by laser shock, and the shape of the molten pool and the flow control of the molten pool are realized by the pulse laser beam acting on the molten pool. The control method of molten pool flow is simple and effective, with high reliability, and can simultaneously improve the flatness of the cladding layer, improve thermal stress and grain refinement.

2. The laser composite additive manufacturing method in the present invention controls the morphology of the molten pool through pulsed lasers, improves the aspect ratio of the cladding layer, can significantly improve the surface flatness of the cladding layer, reduces the workload of subsequent processing of the additive surface, and improves production. It is more suitable for continuous multi-pass lamination or multi-layer stacking laser additive manufacturing work.

3. The laser composite additive manufacturing method in the present invention controls the flow of the molten pool by pulsed laser, destroys the normal growth process of dendrites, refines the crystal grains, realizes the uniformity of the isotropic properties of the cladding layer, and can significantly improve the cladding. The strength and plasticity of the cladding layer are improved; the residual stress in the cladding layer is improved by controlling the flow of the molten pool, which can improve the fatigue strength of the cladding layer and inhibit the occurrence of cracks; in addition, the flow of the molten pool is controlled by pulsed laser shock, which is beneficial to inhibit the solidification process. The generation of defects such as pores in the cladding layer not only improves the molding quality and performance of the cladding layer, but also improves the flatness of the surface of the cladding layer, enabling efficient and high-quality continuous laser additive manufacturing.

4. In the present invention, a pulsed laser is added to the original laser additive equipment to build a pulsed laser head that moves synchronously with the continuous laser head, so as to realize the laser composite additive manufacturing in which the laser shock and the laser additive process are coupled. The additive equipment is simple, and there is no need to modify the original laser additive equipment to a large extent.

5. The laser composite additive manufacturing method in the present invention is equipped with a high-speed camera real-time monitoring device and cooperates with the feedback signal of the molten pool position, so that the action position and impact effect of the continuous laser beam and the pulsed laser beam can be observed in real time, and the processing can be realized in the process. On-line regulation and closed-loop control of the laser beam action position.

6. The laser composite connection method in the present invention can increase the disturbance force inside the molten pool, enhance the Marangoni convection effect, accelerate the heat and mass transfer inside the molten pool, and realize the elements inside the molten pool through the intervention of the high-frequency pulsed laser beam. uniform distribution;

7. The laser composite connection method in the present invention reshapes the weld joint by directly or indirectly intervening in the weld pool by a high-frequency pulsed laser beam, which can refine the weld grains and obtain a smooth and symmetrical distribution along the center line of the weld. The shape of the weld joint;

8. The laser composite connection method in the present invention can compensate for the reason by changing the relative distance between the pulsed laser beam and the welding heat source, and comprehensively considering the relative position of the centerline of the pulsed laser beam and the welding heat source and the boundary line of the dissimilar metal base material. The deformation imbalance caused by the difference in the thermophysical performance parameters of dissimilar metal materials realizes the intervention effect of different time scales and spatial scales of weldments, and improves the reliability of dissimilar metal welding weld joints.

9. The laser composite connection method in the present invention, through the intervention of high-frequency pulsed laser beams, can not only reduce the initiation probability of weld pores, micro-cracks and harmful phase defects, but also realize the symmetrical distribution of micro-defects in the molten pool, preventing The stress concentration phenomenon induced by the asymmetric distribution of defect morphology can effectively improve the comprehensive mechanical properties of dissimilar metal weld joints.

Description of drawings

Fig. 1 is a process diagram of the laser composite additive manufacturing method based on pulsed laser control of molten pool flow according to the present invention; in the figure, 1-pulse laser, 2-continuous laser, 3-melt pool region, 4-alloy powder, 5-pulse The distance between the two spots of the laser and the continuous laser, 6-cladding surface, 7-substrate to be processed.

Figure 2 is a schematic diagram of different spot spacings: (a) the spot spacing is 0mm, (b) the spot spacing is 1mm, (c) the spot spacing is 3mm; in the figure, 1-pulse laser, 2-continuous laser.

Figure 3 shows the 2D profile of the cladding layer before (a) and after laser impact with different spot spacings (b), (c), (d), and the corresponding spot spacings of (b), (c), and (d) are 0mm, respectively. , 1mm, 3mm.

Figure 4 shows the residual stress distribution of the cladding layer after laser shock with different spot spacings.

Figure 5 is the metallographic diagram of the cladding layer before (a) and after (b) laser shock with a spot spacing of 0 mm.

Figure 6 shows the metallographic images of the molten pool area (a) and the solidified area (b) of the cladding layer after laser shock with a spot spacing of 1 mm.

Figure 7 is a metallographic diagram of the cladding layer after laser shock with a spot spacing of 3 mm.

Fig. 8 shows the microstructure of the high-entropy alloy coating by laser additive manufacturing before and after laser shock treatment: (a) the metallographic image of the high-entropy alloy coating without laser shock treatment, (b) the high-entropy alloy coating without laser shock treatment SEM image of the alloy coating, (c) metallographic image of the high-entropy alloy coating subjected to laser shock treatment, (d) SEM image of the high-entropy alloy coating subjected to laser shock treatment.

Figure 9 shows the nanoindentation test results along the depth direction of the laser additively manufactured high-entropy alloy coating before and after laser shock treatment: (a) the nanoindentation curve of the top of the coating before and after laser shock, (b) the middle of the coating before and after laser shock The nanoindentation curve of (c) the nanoindentation curve of the lower part of the coating before and after laser shock, (d) the hardness comparison of the coating before and after laser shock.

FIG. 10 is a schematic diagram of the effect comparison of the laser composite connection method in the present invention.

In the figure: without pulsed laser intervention (a); with pulsed laser intervention (b).

Figure 11 is a live image of the molten pool evolution with and without a pulsed laser heat source captured by a high-speed camera.

In the figure: without pulsed laser intervention (a~c); with pulsed laser intervention (d~f).

Detailed ways

The present invention will be described in further detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

Example 1

(1) Set the process parameters. In this embodiment, as shown in Figure 1, the energy of pulsed laser 1 is 2J, the power of continuous laser 2 is 1500W, the spot diameter of continuous laser beam 2 is 3 mm, the spot diameter of pulsed laser beam is 1.3 mm, the pulsed laser beam 1 and the continuous laser beam are The scanning speed of 2 is 4 mm/s, and the pulse laser frequency is 5 Hz. The positional relationship between the spots of pulsed laser 1 and continuous laser 2 is shown in Figure 2(a).

(2) Call the CNC worktable system to move the substrate to the processing station and perform laser composite additive manufacturing. Turn on the CW and pulsed lasers. After collimated and focused optical path transformation, the continuous laser beam acts on the surface of the substrate 7 to be processed, so that the surface of the substrate and the preset alloy powder/synchronously conveyed alloy powder 4 are rapidly melted at the same time to form a molten pool 3 . At the same time, the plasma shock wave generated by another pulsed laser is used to act on the molten pool 3 area, and the laser composite additive manufacturing process using the pulsed laser to control the molten pool is performed, and the cladding surface 6 is formed by cladding one by one. The base material selected in this embodiment is U71Mn rail steel, and the alloy powder is Fe901 iron-based alloy.

(3) Compare the geometric morphology, microstructure and residual stress of the cladding layer before and after the pulsed laser beam impact, to verify the effect of the pulsed laser impact, the results are shown in Figure 3-5.

Comparing the 2D profile of the cladding layer before (a) and after (b) the impact of the pulsed laser beam in Fig. 3, it can be seen that when the pulsed laser beam completely acts on the molten pool, the thickness of the cladding layer without the action of the pulsed laser beam is 633.4 μm, the thickness of the cladding layer after the impact of the pulsed laser beam is 362.6 μm, and the thickness of the cladding layer is reduced by about 48%, indicating that the impact pressure generated by the pulsed laser beam can extrude part of the liquid alloy in the molten pool out of the molten pool, changing the molten pool. The shape of the cladding layer is obtained, and the flatness of the cladding surface is improved. In addition, it can be seen from Fig. 4 that the residual stress of the unimpacted cladding layer is -332MPa, while the residual stress of the cladding layer after pulsed laser beam impact is -220MPa, and the residual stress of the cladding layer is reduced by about 33.7% . In addition, comparing the microstructure of the cladding layer before and after the pulsed laser beam in Fig. 5, it can be seen that the cladding layer without the pulsed laser beam has directional growth of dendrites, while the cladding layer after the pulsed laser beam has the presence of dendrites. Pronounced dendrite-refined dendrite interface. It shows that the pulsed laser beam can effectively control the flow of the molten pool, reduce the temperature gradient during the solidification of the molten pool, reduce the residual stress of the coating, destroy the directional growth process of dendrites, and refine the grains.

Example 2

In this embodiment, the distance between the two light spots is 1 mm, and the pulsed laser beam partially acts on the molten pool area and partially acts on the solidification area, as shown in Figure 2(b). The rest of the implementation process is the same as that of Example 1.

From the 2D profile of the cladding layer section in Figure 3(c), it can be seen that when the pulsed laser beam partially acts on the molten pool, the thickness of the cladding layer after the impact of the pulsed laser beam is 441.8 μm, and the thickness of the cladding layer is reduced by approximately 30.2%. The residual stress of the cladding layer impacted by the pulsed laser beam does not change significantly from that of the cladding layer without the pulsed laser effect. This is because the part of the pulsed laser beam acting on the molten pool area can reduce the residual stress of the cladding layer, and the part of the pulsed laser beam acting on the solidification area causes plastic deformation through pressure to increase the residual compressive stress, and the pulses acting on different areas The effect of the residual stress induced by the laser beam is offset, resulting in no significant change in the final average residual stress of the cladding layer. In addition, it can be seen from Figure 6(a) that the microstructure of the pulsed laser beam acting on the molten pool area is similar to the microstructure characteristics of the pulsed laser beam acting on the molten pool area in Example 1. The pulsed laser beam acts on the molten pool area. It can effectively destroy the directional growth process of dendrites and refine the grains. From Fig. 6(b), it can be seen that the pulsed laser beam acts on the solidified part, causing plastic deformation of the cladding layer, so the cladding layer presents refined dendrites.

Example 3

In this embodiment, the distance between the two light spots is 3 mm, and the pulsed laser beam completely acts on the coagulation area as shown in Fig. 2(c). The rest of the implementation process is the same as that of Example 1.

From the 2D profile of the cladding layer section in Figure 3(d), it can be seen that when the pulsed laser beam fully acts on the solidification region, the thickness of the cladding layer is 558.2 μm, and the thickness of the cladding layer is reduced by about 11.8%. The residual stress of the cladding layer is -381MPa, and the residual stress of the cladding layer is increased by about 14.7%. In addition, it can be seen from Fig. 7 that the microstructure of the pulsed laser beam acting on the solidification region is similar to the microstructure characteristics of the pulsed laser beam acting on the solidification region in Example 2, showing refined equiaxed grains. It shows that the pulsed laser beam acting completely on the solidification zone causes plastic deformation through the impact pressure to increase the residual compressive stress and achieve grain refinement at the same time.

Example 4

In order to prove the universality of the laser composite additive manufacturing process based on laser shock control of molten pool flow proposed in the present invention, Example 4 is performed on the laser additive manufacturing high-entropy alloy coating.

(1) Set the process parameters. In this embodiment, the energy of pulsed laser 1 is 2J, the power of continuous laser 2 is 800W, the spot diameter of continuous laser beam 2 is 3 mm, the spot diameter of pulsed laser beam is 1 mm, and the scanning speeds of pulsed laser beam 1 and continuous laser beam 2 are both 4 mm /s, the pulsed laser frequency is 10Hz. The spot spacing 5 between the pulsed laser 1 and continuous laser 2 spots is 0 mm, and the pulsed laser beam completely acts on the molten pool area.

(2) Invoke the CNC worktable system to move the substrate to the processing station and execute the laser composite additive manufacturing process. The rest of the operations are exactly the same as in Example 1. The base material selected in this embodiment is 45 steel, and the alloy powder is CoCrFeNi high-entropy alloy.

(3) Build a high-speed camera system to observe the morphology change of the molten pool before and after laser shock in real time.

(4) The geometric morphology, microstructure and mechanical differences of the cladding layer before and after pulsed laser beam impact were compared to verify the effect of pulsed laser impacting. The results are shown in Figures 8 and 9.

It can be seen from the microstructure comparison results of the laser additively manufactured high-entropy alloy coating before and after laser shock in Fig. 8 that the high-entropy alloy without laser shock treatment presents coarse polygonal grains (Fig. 8(a)), and There are columnar subgrains inside it (Fig. 8(b)), while the grain size in the high-entropy alloy coating after synchronous laser shock treatment is significantly reduced (Fig. 8(c)), and the columnar subgrains within the grains The grains are transformed into equiaxed crystal morphology (Fig. 8(d)). The above microstructure analysis results prove that laser shock can effectively control the flow and heat and mass transfer behavior of the molten pool, affect the solidification process, and achieve microstructure refinement.

The nanoindentation test results in Fig. 9 show that the mechanical properties of the coating in the depth direction after laser shock treatment are better than those of the coating without laser shock treatment, which proves that the laser composite method based on the laser shock to control the flow of the molten pool proposed by the present invention Joining and additive manufacturing methods can improve the mechanical properties by effectively modulating the flow and heat and mass transfer behavior of the molten pool and refining the microstructure.

Example 5:

The Nd:YAG solid-state continuous laser is used as the welding heat source, and the nanosecond pulse laser is used as the high-frequency pulsed laser heat source. The CW laser power is 1500W, the spot diameter is 3mm, the traveling speed is 4mm/s, the pulse energy of the nanosecond pulse laser is 2J, the pulse spot diameter is 1.3mm, the pulse frequency is 5Hz, and the center of the pulsed laser spot coincides with the spot center of the CW laser. FIG. 10 is a schematic diagram of the effect comparison of the present invention. A white light interferometer was used to characterize the three-dimensional morphology of the weld joint with or without the action of the pulsed laser: without the intervention of the pulsed laser, under the irradiation of the high-energy-density laser, the material melted to form a molten pool, and the melt fluctuated inside the molten pool , with the movement of the laser heat source, the molten pool melt condenses to form a weld with a convex morphology; under the action of the pulsed laser shock wave, the melt in the molten pool is squeezed to the edge of the molten pool, and the molten pool in the molten pool melts. The body is greatly reduced, and the resulting weld is flat. Figure 11 is a live image of the molten pool evolution with and without a pulsed laser heat source captured by a high-speed camera. Through observation, it can be found that the pulsed laser heat source acts on the surface of the base metal to generate obvious plasma, and at the same time of the welding operation, compared with a single continuous laser welding heat source, due to the compound action of the pulsed laser, plasma is generated behind the molten pool. A smoother weld profile.

The above-described embodiments with reference to the accompanying drawings are preferred embodiments of the present invention. Those skilled in the art to which the present invention pertains can also make changes and modifications to the above-mentioned embodiments. Therefore, the present invention is not limited to the above-mentioned embodiments, without departing from the essence of the present invention. In any case, any obvious improvement, replacement or modification that can be made by those skilled in the art of the present invention belongs to the protection scope of the present invention.

Claims

A laser composite additive manufacturing method based on pulsed laser to control the flow of molten pool, which is characterized in that: the surface of the substrate and the alloy powder are melted by using a continuous laser beam to form a molten pool, and a pulsed laser beam is introduced to synchronously impact the molten pool. Treatment, the laser composite additive manufacturing process using pulsed laser to control the molten pool; during the manufacturing process, the pulsed laser beam is used to control the molten pool morphology and flow, improve the flatness of the cladding surface, and adjust the residual stress in the cladding layer, Reduce the anisotropy of cladding properties;

The distance between the spot of the continuous laser beam and the spot of the pulsed laser beam is smaller than the difference between the spot of the continuous laser beam and the spot radius of the pulsed laser beam, the spot of the pulsed laser beam is completely located inside the spot of the continuous laser beam, and the pulsed laser acts on the spot in the form of thermal action. The molten pool generates a force field that can regulate the flow of the molten pool.
The laser composite additive manufacturing method based on pulsed laser to control the flow of molten pool according to claim 1, characterized in that: using the pulsed laser beam to control the morphology of the molten pool is: using the impact pressure generated by the pulsed laser beam to make a part of the molten pool liquid The alloy is extruded from the molten pool, the aspect ratio of the cladding layer is increased, the flat cladding layer is obtained, and the flatness of the cladding surface is improved.
The laser composite additive manufacturing method based on pulsed laser to control the flow of molten pool according to claim 1, wherein: using the pulsed laser beam to control the flow of the molten pool is: using the surface force field generated by the thermal action of the pulsed laser beam to increase the temperature Uniform distribution, reduce the temperature gradient in the molten pool, adjust the residual stress in the cladding layer, destroy the directional growth process of dendrites, inhibit the formation of cracks and dendrites, achieve grain refinement, and reduce the anisotropy of the cladding layer performance .
The laser composite additive manufacturing method based on pulsed laser controlling molten pool flow according to claim 1, wherein the spatial distribution characteristics of the pulsed laser beam are adjusted by beam shaping or spatial light modulator.
The laser composite additive manufacturing method based on pulsed laser control of molten pool flow according to claim 1, characterized in that: a high-speed camera real-time monitoring device is installed in the laser composite additive manufacturing process using pulsed laser to control molten pool.
A laser composite connection method based on pulsed laser control of molten pool flow, characterized in that it comprises the following steps:

1) During the dissimilar metal welding operation, place the first base metal and the second base metal according to the positional relationship of lap, butt or plug, open the heating platform, and heat the dissimilar metal welding material to the ideal working temperature;

2) The angle between the first welding heat source and the high-frequency pulsed laser heat source ranges from 0 to 90 degrees, and the center of the action area of the first welding heat source and the center of the pulsed laser spot act on the dissimilar metals at a concentric or 0-5mm distance. The surface of one of the base metals at the intersection interface or 0 to 5 mm from the intersection interface: During welding, firstly turn on the first welding heat source to melt the first and second base metals, and after the molten pool is formed, turn on the high frequency The pulse laser heat source makes the high frequency pulse laser heat source and the first welding heat source act on the area to be processed at the same time. With the movement of the first welding heat source and the high frequency pulse laser heat source, the first base metal and the second base metal Weld joints are formed at the bonding interface of the materials;

The difference between the first base metal and the second base metal is reflected in the fact that the two base metals belong to different types of welding materials, rather than different heat treatment states or structural forms of the same welding material; they can be selected according to actual engineering needs. Appropriate heat treatment method and structural form, the heat treatment state includes annealing, tempering, normalizing or quenching, and the structural form is the geometric size or special structural form of the component.
The laser composite connection method based on pulsed laser controlling molten pool flow according to claim 6, is characterized in that:

In the step 1), the heating platform is turned on and heated to an ideal operating temperature, which can realize the controllability of parameters, including the heating rate, the temperature control time and the cooling rate. Harmful residual stress; the ideal operating temperature is set correspondingly due to the different materials of the weldment, the heating temperature cannot be higher than the critical temperature at which the mechanical properties of the metal material are reduced, and the minimum value of the critical temperature of the two base metals is taken;

In the step 2), the first welding heat source can select different heat source forms according to the actual needs of the project, and the heat source form is any one, two or more heat sources in laser, TIG, MIG or pulsed laser. The high-frequency pulsed laser heat source is the form of heat source generated by different types of pulsed lasers obtained by Q-switching or mode locking, and can be selected according to actual engineering needs; the pulse frequency of the high-frequency pulsed laser heat source The size is a relative value and is selected according to the actual welding material;

The angle relationship and positional relationship between the first welding heat source and the high-frequency pulsed laser heat source can be changed according to the actual needs of the project, so as to realize the change of the overlap ratio of the action area of the first welding heat source and the high-frequency pulsed laser heat source, so that the The high-frequency pulsed laser heat source can act not only on the molten pool area, but also on the molten or semi-melted area 0-5mm behind the molten pool;

The interaction interface acting on dissimilar metals, due to the differences in the thermophysical performance parameters of dissimilar metal materials, makes the range of the heat affected zone different during the welding operation of dissimilar metals, so the center of the heat source is not necessarily located in the first place. The intersection interface between the first base metal and the second base metal, the positional relationship between the heat source center and the intersection interface of the dissimilar metals can be changed according to the actual welding material and the action position of the integrated pulsed laser;

In the step 2), the to-be-processed area under the action of the high-frequency pulsed laser heat source can be not only the molten pool area heated and melted by the first welding heat source, but also the molten or semi-melted area at 0-5 mm behind the molten pool; The special structural form is a groove, a stress relief groove, a heat dissipation support block, or a combination of two or more of them.
An application of the laser composite additive manufacturing method based on pulsed laser controlling molten pool flow according to any one of claims 1 to 5 in additive manufacturing or parts remanufacturing or 3D printing.
The application of the laser composite joining method based on pulsed laser controlling the flow of molten pool according to any one of claims 6 to 7 in the welding of the same or dissimilar materials.