Method for achieving metal surface shrinkage cavity sealing repair through double-beam laser remelting

Abstract

The invention provides a method for achieving metal surface shrinkage cavity sealing repair through double-beam laser remelting. The method comprises the steps that in an inert atmosphere, continuous laser is used for melting a metal surface shrinkage cavity and metal around the shrinkage cavity, a molten pool is formed, meanwhile, pulse laser is used for conducting accelerated stirring on the molten pool, and repairing is achieved after solidification. The method comprises the following steps: placing metal to be repaired in an inert atmosphere, firstly melting a shrinkage cavity and a surrounding area on the surface of the metal by using continuous laser, and simultaneously introducing pulse laser to carry out accelerated stirring on a formed molten pool; the Marangoni convection formed by the combined action of liquid gravity, viscous force and surface tension in the molten pool is changed, liquid metal in the molten pool is promoted to flow back, metal self-backfilling is achieved after the molten pool is solidified, finally, the size of a shrinkage cavity in the surface of the metal is reduced, and therefore repairing is completed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laser repair, in particular to a method for realizing metal surface shrinkage hole sealing repair by using double-beam laser remelting. BACKGROUND

[0002] Shrinkage hole defect is one of the common defects in metal processing. Shrinkage hole is caused by the influence of environmental factors, temperature gradient, internal gas, etc. on liquid metal, which cannot flow back or flow back in time during the solidification process. Among them, as one of the main ways of metal forming processing, the traditional casting technology has the characteristics of high maturity, strong applicability and high efficiency; but the traditional casting technology may still produce shrinkage holes, shrinkage porosity and other defects on the surface of the casting, which affects the normal use of the material. For example, in the process of automobile surface painting, shrinkage hole caused by casting is one of the common defects, and due to its difficulty in online repair, it often leads to vehicle rework, which not only increases the cost of rework, but also wastes time and effort, and the problem is difficult to solve. In addition, in the field of aviation, for the widely used aluminum alloy welded components, there are strict regulations: the number of crack and shrinkage hole joint defects allowed for repair is not more than 5% for first-class important parts and not more than 10% for second-class important parts; in the field of medical oral repair, the shrinkage hole produced by the casting bridge due to its large thickness often increases the difficulty of subsequent production, seriously affects the strength and appearance of the denture, and even leads to the failure of the denture. In summary, timely repair of shrinkage hole defects can effectively reduce the scrap rate and avoid accidents caused by defects.

[0003] Laser technology has been widely used in aviation, aerospace, industrial processing and other fields due to its strong directivity, high energy density and convenient control. Among them, the technology can be divided into continuous laser processing technology and pulse laser processing technology according to the type of laser. Continuous laser processing technology is a processing method that uses continuous laser to continuously output laser and act on the metal surface, and the heat generated by the laser on the metal surface makes the metal surface melt, and finally realizes the surface remelting. This method has been widely used in 3D printing, laser cladding and other processing fields; pulse laser processing technology is to use pulse laser to act on the metal surface in pulse mode (millisecond, microsecond, nanosecond, picosecond). Compared with continuous laser processing, the action time of pulse laser on the metal surface is shorter, and the average temperature rise is small, which is not easy to cause deformation of the workpiece; in addition, due to the high peak energy density of pulse laser, it can cause instantaneous phase change of the metal surface, so it is widely used in laser nitriding, laser carbonization and other fields.

[0004] At present, laser cladding is to act high-energy beam laser on metal surface, make metal surface re-melt, and supplement material through wire feeding or powder laying, finally realize the repair of metal surface shrinkage. The characteristics of this technology are large laser energy, accurate positioning, strong technical specification, and deep repair depth. However, this method mainly uses continuous or millisecond laser to continuously melt the workpiece (the action time is more than minutes), which will introduce a large amount of heat energy and have a great influence on the deformation of the workpiece; at the same time, it needs to introduce additional elements, which leads to insufficient bonding force and pure organization of the repaired layer. Although this method can remove part of the surface shrinkage, for larger shrinkage, or for workpieces with high requirements for bonding force and surface flatness, and do not allow the introduction of impurities, the processing effect will be limited. SUMMARY

[0005] The present application provides a method for repairing metal surface shrinkage by using double-beam laser remelting.

[0006] The technical method of the present application is as follows: A method for repairing metal surface shrinkage by using double-beam laser remelting, the method comprising: in an inert atmosphere, using continuous laser to melt the metal surface shrinkage and the metal around the shrinkage to form a molten pool, and using pulse laser to accelerate the stirring of the molten pool to realize repair after solidification. Specifically, the continuous laser is used to heat the metal around the shrinkage to form a molten pool at the shrinkage, and the pulse laser is used to impact the molten pool metal to make the liquid metal in the molten pool flow back to form shrinkage repair. The size of the shrinkage is millimeter level.

[0007] The laser power of the continuous laser is 10-1000W, the focal length is 300-700m, the scanning speed is 500-1000mm / min, and the scanning times are 1-5 times. The laser power of the pulse laser is 10-100W, the laser frequency is 1-20kHz, the pulse width is 20-200ns, the focal length is 200-300mm, the scanning speed is 500-1000mm / min, and the scanning times are 1-5 times. The scanning path and filling type of the continuous laser and the pulse laser are one of back type, type and bow type.

[0008] Before melting the metal surface shrinkage and the metal around the shrinkage, the method of the present application further comprises: activating the oxide layer inside and around the shrinkage by using pulse laser. During the activation, the laser power is 10-100W, the laser frequency is 1-20kHz, the pulse width is 20-200ns, the focal length is 200-300mm, the scanning speed is 500-1000mm / min, and the scanning times are 1-5 times.

[0009] The method of the present application further comprises activating the oxide layer inside and around the shrinkage hole by using an acidic solution or an alkaline solution before melting the shrinkage hole and the metal around the shrinkage hole; wherein the acidic solution comprises phosphoric acid and / or hydrochloric acid, and the alkaline solution is sodium hydroxide.

[0010] The method of the present application further comprises performing a shaping treatment on the metal surface by using a pulsed laser after the repair.

[0011] The present application has the following beneficial effects: The present application places the metal to be repaired in an inert atmosphere, melts the shrinkage hole and the surrounding area of the metal surface by using a continuous laser, and simultaneously introduces a pulsed laser to accelerate the stirring of the molten pool; by changing the Marangoni convection formed by the combined action of liquid gravity, viscous force and surface tension in the molten pool, the liquid metal in the molten pool is promoted to flow back, and after the molten pool solidifies, the metal is self-refilled, finally the size of the shrinkage hole on the metal surface is reduced, thereby completing the repair. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 A schematic diagram of a method for repairing a shrinkage hole on a metal surface by using double-beam laser remelting; Figure 2 An XRD diagram of a uranium substrate before and after repair (also referred to as before and after treatment); Figure 3 A topography diagram of a micro shrinkage hole on a first metal surface; Figure 4 A topography diagram of the first metal surface after repair; Figure 5 A topography diagram of a micro shrinkage hole on a second metal surface; Figure 6 A topography diagram of the second metal surface after remelting by double-beam laser; Figure 7 A depth change diagram of the micro shrinkage hole on the second metal surface before and after repair; Figure 8 A depth change diagram of the micro shrinkage hole on the first metal surface before and after repair; Figure 9 A roughness change diagram of the micro shrinkage hole on the first metal surface before and after repair. DETAILED DESCRIPTION

[0013] The technical solutions of the present application will be described below in a clear and complete manner. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0014] In the present application, all the preparation raw materials are commercially available products well known to those skilled in the art unless otherwise specified.

[0015] The present application is described in detail below by way of examples and experimental examples. However, these are only examples and do not limit the present application in any form.

[0016] The present application provides a method for repairing metal surface shrinkage cavity by using double-beam laser remelting, as shown in the formula (I). Figure 1 As shown in the formula (I), the method comprises: in an inert atmosphere, using continuous laser to melt the metal surface shrinkage cavity and the metal around the shrinkage cavity to form a molten pool, and using pulsed laser to accelerate and stir the molten pool, and realizing repair after solidification. Specifically, the continuous laser is used to heat the metal around the shrinkage cavity to form a molten pool at the shrinkage cavity, and the pulsed laser is used to impact the molten pool metal to make the liquid metal in the molten pool backflow to form shrinkage cavity repair. Here, the continuous laser only needs to heat the shrinkage cavity metal, which has little thermal impact on the substrate, and only needs to provide low laser power, fast scanning speed and small step length, so the requirement for laser power is low (hundred watts). The pulsed laser has high peak power density and needs to have single-pulse energy of mJ level. The pulsed laser is not limited to nanosecond pulsed laser, and picosecond pulsed laser can also act on the molten pool.

[0017] In an embodiment, the size of the shrinkage cavity is millimeter level. For example, the continuous laser is used to heat the shrinkage cavity and the surrounding metal by high collimation and continuous heat input to form a millimeter-level molten pool at the shrinkage cavity, and then the pulsed laser is used to impact the molten pool metal by high peak power density, and finally make the liquid metal in the molten pool backflow to form shrinkage cavity repair.

[0018] The continuous laser of the present application acts on the metal surface to melt the shrinkage cavity to form a molten pool. The liquid metal after melting is subjected to the action of gravity, surface tension, viscous force and the like in the molten pool to form solution backfilling the shrinkage cavity. The pulsed laser of the present application acts on the metal surface to accelerate the flow of liquid in the molten pool by the impact effect of the pulsed laser to promote the liquid backfilling the shrinkage cavity.

[0019] Specifically, the method of the present application comprises the following steps: Step 1: The scanning path and filling type of the continuous laser and the pulsed laser are one of back type, Z type and arch type, and the scanning interval is set to 0.01-1 mm. For example, the scanning interval is 0.05 mm, 0.1 mm, 0.5 mm or 0.7 mm.

[0020] Step 2: Set the red light mode of the continuous laser and the pulsed laser respectively. Adjust the scanning pattern position and machine position to center and focus the two lasers.

[0021] Step 3: Selecting continuous laser mode, setting appropriate laser parameters according to material properties: laser power is 10-1000W, scanning speed is 500-1000mm / min, focal length is 300-700mm, scanning times is 1-5 times. For example, laser power is 5W, 100W, 500W, 700W. Scanning speed is 700mm / min, 800mm / min, 900mm / min. Scanning times is 3 times, 4 times. Focal length is 400mm, 500mm, 600mm.

[0022] Step 4: Selecting pulse laser mode, setting appropriate laser parameters according to material properties: laser power is 30-100W, laser frequency is 1-20kHz, pulse width is 20-200ns, scanning speed is 500-1000mm / min, focal length is 200-300mm, scanning times is 1-5 times. For example, laser power is 10W, 20W, 50W, 70W. Laser frequency is 5kHz, 10kHz, 15kHz. Pulse width is 50ns, 70ns, 100ns, 150ns. Scanning speed is 700mm / min, 800mm / min, 900mm / min. Focal length is 230mm, 270mm, 290mm. Scanning times is 3 times, 4 times.

[0023] Step 5: Turning on double-beam laser to process surface shrinkage.

[0024] In addition to using continuous laser, it is not limited to millisecond pulse laser, which can also achieve metal melting and stable maintenance of molten pool state for a period of time.

[0025] In an embodiment, the method further comprises, before melting the metal surface shrinkage and the metal around the shrinkage, activating the oxide layer inside and around the shrinkage by using pulse laser. The activation is performed by laser power of 10-100W, laser frequency of 1-20kHz, pulse width of 20-200ns, focal length of 200-300mm, scanning speed of 500-1000mm / min, and scanning times of 1-5 times. For example, laser power is 10W, 20W, 50W, 70W. Laser frequency is 5kHz, 10kHz, 15kHz. Pulse width is 50ns, 70ns, 100ns, 150ns. Scanning speed is 700mm / min, 800mm / min, 900mm / min. Focal length is 230mm, 270mm, 290mm. Scanning times is 3 times, 4 times.

[0026] In an embodiment, the method further comprises, before melting the metal surface shrinkage and the metal around the shrinkage, activating the oxide layer inside and around the shrinkage by using acid solution or alkaline solution; wherein the acid solution comprises phosphoric acid and / or hydrochloric acid, and the alkaline solution is sodium hydroxide.

[0027] In one embodiment, before activation, the metal surface and the area around the shrinkage cavity can be wiped with a lint-free cloth and alcohol. Here, the alcohol ensures that the stains on the substrate surface are cleaned, and the lint-free cloth prevents paper scraps from falling into the shrinkage cavity. Then, the dimensions such as the depth and diameter of the shrinkage cavity are measured using a roughness measuring instrument and vernier calipers. Finally, the measured dimensional data is input into laser processing software to draw a laser scanning pattern.

[0028] In one embodiment, after repair, the process further includes: shaping the metal surface using a pulsed laser. Appropriate laser parameters are set according to the material properties: laser power 10-100W, laser frequency 1-20kHz, pulse width 20-200ns, scanning speed 500-1000mm / min, focal length 200-300mm, and number of scans 1-5. For example, laser power of 10W, 20W, 50W, and 70W; laser frequency of 5kHz, 10kHz, and 15kHz; pulse width of 50ns, 70ns, 100ns, and 150ns; scanning speed of 700mm / min, 800mm / min, and 900mm / min; focal length of 230mm, 270mm, and 290mm; and number of scans of 3 or 4.

[0029] The method of this invention, after the shaping process, further includes: placing the repaired metal in an inert atmosphere for cooling to prevent surface oxidation. The sample surface can then be wiped with a lint-free cloth and alcohol. The process is then complete.

[0030] The metals used in this invention may include one or more of titanium alloys, stainless steel, and uranium alloys.

[0031] like Figure 2 As shown, the surface of depleted uranium after dual-beam laser treatment mainly consists of α phase and a small amount of UO2, indicating that it has little impact on the matrix phase composition and the oxide content on the sample surface is low.

[0032] like Figure 3 and Figure 4 As shown, the micro-holes (approximately 20 μm in size) on the first metal surface disappeared after repair, the pits became shallower, and laser scanning traces were visible.

[0033] like Figure 5 , Figure 6 and Figure 7 As shown, the deep micro-cavities (around 800 in size) on the second metal surface disappeared after repair, the pits became shallower, and laser scanning traces were visible.

[0034] like Figure 8 and Figure 9 As shown, the pits on the first metal surface become shallower and the roughness decreases after repair.

[0035] Example 1: Repair of surface shrinkage of TC4 titanium alloy The present example provides a method for repairing surface shrinkage by using double-beam laser remelting, comprising the following steps: 1) Spray alcohol (about 20 ml) on the surface of the titanium alloy, and wipe the surface shrinkage with a dust-free cloth, and change the angle to ensure that the stains on the substrate surface and around the shrinkage are cleaned; 2) Measure the diameter of the shrinkage with a vernier caliper. The average value of three measurement results is 330 μm; 3) Turn on the roughness measuring instrument, and ensure that the measured plane and the roughness measuring instrument are in the same plane. Set the measurement parameters: scanning step 2.5 mm, scanning range +400 μm. Measure three times and take the average value, and measure the measurement depth 80 μm; 4) Input the measured parameters into the software to draw a circular pattern with a diameter of 330 μm; 5) Turn on the pulse laser, select the circular pattern, and set the filling mode to arch reciprocating with a step of 0.1 mm; 6) Set the laser parameters: power 5 W, frequency 10 kHz, scanning speed 1000 mm / s, pulse width 20 ns, and focal length 600 mm; 7) Turn on the laser to activate the shrinkage once; 8) Select the circular pattern, and set the scanning interval to 0.1 mm for the continuous laser filling type of return type; 9) Select the circular pattern, and set the scanning interval to 0.08 mm for the pulse laser filling type of return type; 10) Turn on the red light of the continuous laser and the pulse laser respectively. Set the machine position to (X0, Y0), the continuous laser scanning pattern position to (X-32.3, Y31.8), and the pulse laser scanning pattern position to (X33.3, Y-15.7); 11) Select the continuous laser mode, and set the laser parameters and scanning times: laser power 400 W, scanning speed 1000 mm / min, focal length 602 mm, and scanning times 1; 12) Select the pulse laser mode, and set the laser parameters and scanning times: laser power 30 W, laser frequency 20 kHz, pulse width 200 ns, scanning speed 1000 mm / min, focal length 280 mm, and scanning times 1; 13) Turn on the double-beam laser to process the surface shrinkage; 14) Turn on the pulse laser to shape the surface. Set the laser parameters: laser power 10 W, laser frequency 20 kHz, pulse width 20 ns, scanning speed 1000 mm / min, focal length 300 mm, and scanning times 1.

[0036] 15) The processed sample is placed in a nitrogen atmosphere to cool to room temperature; the surface of the sample is wiped with a dust-free cloth and alcohol.

[0037] The size of the shrinkage cavity before repair is 900 pm, and the shrinkage cavity is obviously closed after repair. The surface roughness after repair is relatively low.

[0038] Example 2: Repair of shrinkage cavity on surface of 316L stainless steel The present example provides a method for repairing shrinkage cavity on metal surface by double-beam laser remelting, comprising the following steps: 1) Spray alcohol (about 20 ml) on the surface of the titanium alloy, and wipe the surface shrinkage cavity with a dust-free cloth, change the angle to ensure that the stains on the substrate surface and around the shrinkage cavity are cleaned; 2) Measure the diameter of the shrinkage cavity with a vernier caliper. The average value of three measurement results is 410 pm; 3) Turn on the roughness measuring instrument, and ensure that the measured plane and the roughness measuring instrument are in the same plane. Set the measurement parameters: scanning step 2.5 mm, scanning range +400 pm. Take the average value of three measurements, and measure the measurement depth of 140 pm; 4) Input the measured parameters into the software to draw a circular pattern with a diameter of 410 pm; 5) Turn on the pulsed laser, select the circular pattern, and set the filling mode to arch reciprocating with a step of 0.1 mm; 6) Set the laser parameters: power 5 W, frequency 10 kHz, scanning speed 1000 mm / s, pulse width 20 ns, and focal length 600 mm; 7) Turn on the laser to activate the shrinkage cavity once; 8) Select the circular pattern, and set the scanning interval to 0.1 mm for the continuous laser filling type of return type; 9) Select the circular pattern, and set the scanning interval to 0.08 mm for the pulsed laser filling type of return type; 10) Turn on the red light of the continuous laser and the pulsed laser respectively. Set the machine position to (X0, Y0), the continuous laser scanning pattern position to (X-30.0, Y31.0), and the pulsed laser scanning pattern position to (X30.0, Y-15.1); 11) Select the continuous laser mode, and set the laser parameters and scanning times: laser power 400 W, scanning speed 1000 mm / min, focal length 602 mm, and scanning times 2; 12) Select the pulsed laser mode, and set the laser parameters and scanning times: laser power 30 W, laser frequency 20 kHz, pulse width 200 ns, scanning speed 1000 mm / min, focal length 280 mm, and scanning times 2; 13) Turn on the double-beam laser to treat the surface shrinkage hole; 14) Turn on the pulse laser to shape the surface. Set the laser parameters: laser power 10 W, laser frequency 20 kHz, pulse width 20 ns, scanning speed 1000 mm / min, focal length 300 mm. Scanning times 1.

[0039] 15) Place the treated sample in a nitrogen atmosphere to cool to room temperature; wipe the surface of the sample with a dust-free cloth and alcohol.

[0040] The size of the shrinkage hole before repair is 100 μm, and the shrinkage hole is closed after repair. There is also a "back-type" laser scanning trace.

[0041] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for sealing and repairing shrinkage cavities on a metal surface using dual-beam laser remelting, characterized in that, The method includes: In an inert atmosphere, a continuous laser is used to melt the shrinkage cavities on the metal surface and the metal around the shrinkage cavities to form a molten pool. At the same time, a pulsed laser is used to accelerate the stirring of the molten pool, and the repair is achieved after solidification.

2. The method according to claim 1, characterized in that, The method involves using continuous laser to heat the shrinkage cavity and the metal around it, forming a molten pool at the shrinkage cavity. Then, pulsed laser is used to impact the molten pool metal, causing the liquid metal in the molten pool to flow back, thus repairing the shrinkage cavity.

3. The method according to claim 1, characterized in that, The continuous laser has a laser power of 10~1000W, a focal length of 300~700m, a scanning speed of 500~1000mm / min, and a scanning number of 1~5 times.

4. The method according to claim 1, characterized in that, The pulsed laser has a laser power of 10~100W, a laser frequency of 1~20kHz, a pulse width of 20~200ns, a focal length of 200~300mm, a scanning speed of 500~1000mm / min, and 1~5 scans.

5. The method according to claim 1, characterized in that, The scanning path and filling type of the continuous laser and pulsed laser are one of the following: loop, zigzag, and bow.

6. The method according to claim 1, characterized in that, Before melting the shrinkage cavity and the metal surrounding the shrinkage cavity on the metal surface, the method further includes: Pulsed lasers are used to activate the oxide layer inside and around the shrinkage cavity.

7. The method according to claim 6, characterized in that, During activation, the laser power is 10~100W, the laser frequency is 1~20kHz, the pulse width is 20~200ns, the focal length is 200~300mm, the scanning speed is 500~1000mm / min, and the number of scans is 1~5.

8. The method according to claim 1, characterized in that, Before melting the shrinkage cavity and the metal surrounding the shrinkage cavity on the metal surface, the method further includes: The oxide layer inside and around the shrinkage cavities is activated using an acidic or alkaline solution; wherein the acidic solution includes phosphoric acid and / or hydrochloric acid, and the alkaline solution is sodium hydroxide.

9. The method according to claim 1, characterized in that, After the repair, the method further includes: Pulsed lasers are used to shape metal surfaces.

10. The method according to claim 1, characterized in that, The size of the shrinkage cavity is on the order of millimeters.

Images