Laser Cladding Method of Silver Layer on Copper Substrate and Its Use in Repair of High-Current Copper Bus of Hydroelectric Power Unit

Abstract

Regarding a laser cladding method for a silver layer on a copper substrate and its use in the repair of a large-current copper bus of a hydraulic power unit, a pretreatment step S1 is performed to polish the surface of the copper substrate to remove impurities and oxide layers, clean it thoroughly, and dry it. Then, a blue laser cladding device is used, with silver-copper alloy powder as the powder material, and the laser cladding of the silver layer on the copper substrate is carried out by a coaxial powder supply method. At this time, the laser output is 1100W - 1350W, the scanning speed of the laser cladding head is 6mm / s - 10mm / s, and the overlap rate is 45% - 65%. This includes a laser cladding step S2 and a step S3 of polishing the laser-cladded silver layer on the surface of the copper substrate.

Description

Technical Field

[0001] The present invention belongs to the field of laser cladding technology, and specifically relates to a method for laser cladding of a silver layer on a copper substrate and its use in the repair of large-current copper buses of a hydraulic power generation unit.

Background Art

[0002] As an important member for electrical connection, the copper bus of a hydraulic power generation unit plays a role in large-current conduction. To improve the conduction efficiency, the surface of the copper bus joint is usually plated with a silver layer. The silver plating layer on the surface of the copper bus is affected by the silver plating process and related standards, and the thickness of the silver plating layer is thin. After long-term operation, the silver plating layer on the surface of the copper bus may have poor adhesion, and a silver layer failure phenomenon of silver plating layer peeling off may occur.

[0003] Currently, laser cladding technology is a new laser additive manufacturing technology that emerged with the development of high-power lasers. At the same time, the technical advantages of laser cladding technology are more prominent. The substrate and the surface coating material are metallurgically combined, the adhesion strength is relatively high, the structure is dense and has few pores, so the dilution rate is low, and the thickness of the cladding coating layer can be controlled. These advantages also meet the needs of the silver layer on the surface of the copper bus.

[0004] However, the currently commonly used laser light source is an infrared laser light source (wavelength about 1000 nm), which is not suitable for laser cladding of the silver layer on the surface of the copper bus. Since copper and silver are metals with high reflectivity, the absorption rate in the infrared laser band is very low. Here, the absorption rate of copper in the infrared band is only about 5%, and the laser absorption rate of silver in the infrared band is even lower. Based on the good thermal conductivity of copper, the laser cladding means using an infrared laser light source has many scattering phenomena in copper surface treatment, and there are many pores and inclusions in the cladding coating layer. The quality of the cladding coating layer is poor, and it is difficult to achieve stable forming.

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present invention provides a laser cladding method for a silver layer on a copper substrate and its use in the repair of large-current copper buses of a hydraulic power generation unit. The method improves the absorption rate of the substrate and powder to the laser, and the cladding layer has no defects such as pores and inclusions.

Means for Solving the Problems

[0006] The technical solution of the present invention is a laser cladding method for a silver layer on a copper substrate. Specifically, Performing polishing to remove impurities and oxide layers on the surface of the copper substrate, cleaning it cleanly and drying it, the pre-treatment step S1 before cladding, and Using a blue laser cladding device, using silver-copper alloy powder as the powder material, performing laser cladding of the silver layer on the copper substrate by a coaxial powder feeding method. Here, the laser output is 1100W to 1350W, the scanning speed of the laser cladding head is 6mm / s to 10mm / s, and the lap rate is 45% to 65%. The laser cladding step S2, and Polishing the laser-clad silver layer on the surface of the copper substrate to meet the relevant requirements of the hydraulic power generation unit, step S3.

[0007] Furthermore, the copper substrate is T2 purple copper, the copper content (wt%) ≥ 99.9, and other impurities (wt%) ≤ 0.1.

[0008] Furthermore, in step S2, the silver-copper alloy powder, calculated by mass fraction, is Cu: 20 to 30%, Ni: 8 to 15%, Si: 0.5 to 2%, and the rest is silver and inevitable impurities.

[0009] Furthermore, the particle size of the silver-copper alloy powder is 75μm to 150μm and it is dried before use.

[0010] Furthermore, in step S2, the blue laser wavelength of the blue laser cladding device is 450 nm to 480 nm.

[0011] Furthermore, in step S2, when laser cladding is performed, the spot is circular and the diameter is 1.5 mm to 1.8 mm.

[0012] Furthermore, in step S2, the coaxial powder feeding method employs an annular powder feeding nozzle, and the powder feeding nozzle is coaxial with the circular spot.

[0013] Furthermore, in step S2, the flow rate of the powder feeding gas during laser cladding is 10 to 15 L / min, the powder feeding amount is 4 g / min to 8 g / min, the flow rate of the protective gas is 10 to 15 L / min, and both the powder feeding gas and the protective gas are inert gases, including but not limited to nitrogen, argon, or helium.

[0014] Furthermore, in step S3, the thickness of the silver layer on the surface of the copper substrate is required to exceed 0.1 mm after polishing, and the surface roughness is less than Ra0.8.

[0015] Furthermore, the surface of the copper bus can be clad with a multi-layer coating silver layer, and the thickness of the single-layer clad silver layer is 0.1 mm to 0.4 mm.

Advantages of the Invention

[0016] The present invention has the following beneficial effects.

[0017] 1. In the present invention, by using a blue laser light source, the absorption rate of the material for the laser can be significantly improved as compared with a red laser light source. Moreover, the laser cladding substrate and powder in the present invention are all materials with high reflectivity. In particular, the absorption rate of the silver powder material for the laser in the infrared band (less than 3%) is lower than that of the copper substrate (the absorption rate for the infrared band laser is less than 5%). Therefore, the process window for cladding the silver powder material on the copper substrate becomes narrow, making it difficult to find the balance point where the copper substrate and the silver powder material absorb the laser energy, completely melt, and bond. When using a short-wavelength blue laser to perform cladding on the copper substrate and silver powder, the absorption rate for the laser can be effectively improved.

[0018] 2. When cladding the silver powder material on the copper substrate with a blue laser, the absorption rate of the laser energy by the copper substrate and the silver powder increases. However, there is still a significant difference in the absorption rate of the laser energy between the copper substrate and the silver powder material. Also, the difference in the absorption rate of the laser energy by different materials results in the mismatch between the minimum energy threshold for each material to absorb the laser energy and open the melting pool and the maximum energy threshold for boiling and overburn in the melting pool. When the copper substrate absorbs the laser energy and reaches the minimum threshold to open the melting pool, but the silver powder material does not reach the melting threshold, defects such as aggregation and non-welding will appear in the manufactured cladding layer. When the silver powder material completely reaches the threshold for complete and sufficient melting, more laser energy is absorbed by the copper substrate, further causing overburn of the copper substrate and boiling of the melting pool. Since copper has good fluidity in the liquid state, it flows rapidly when the melting pool boils and closes immediately when solidifying, so the gas and impurities in the melting pool with insufficient overflow are trapped, forming defects such as pores and inclusions. The inventor creatively discovered that an output of 1100 - 1350W can better match the melting pool state of the copper substrate and the silver-copper alloy powder. At the same time, by controlling a low scanning speed and a high lap rate, a dense structure of the cladding layer can be realized without defects such as pores and inclusions.

[0019] 3. Using the method provided by the present invention, a silver alloy coating layer with high reflectivity and high thermal conductivity can be clad on the surface of the copper bus, and a metallurgical bond can be achieved between the copper bus and the surface clad silver layer, with high bond strength. The present invention can realize a single-layer clad silver layer with a thickness of 0.1 mm to 0.4 mm, and multilayer cladding can also be carried out as required.

[0020] 4. In the silver-copper alloy powder employed in the present invention, by doping a certain amount of Cu, the antioxidant performance can be improved and the mechanical properties can be enhanced. When the doping amount of Cu is large, Cu and Ag form a eutectic to strengthen its mechanical properties. However, when the Cu content increases, crystallization is likely to occur. In the present invention, by adding a certain amount of Ni, the crystal grains can be refined and the separation of the internal structure of the silver-based alloy can be reduced. Furthermore, by adding a certain amount of Si to the alloy material, the high-temperature oxidation resistance of the alloy material can be significantly improved due to the synergistic effect with Cu.

Brief Description of the Drawings

[0021]

Figure 1

Embodiments for Carrying Out the Invention

[0022] Next, in combination with the examples, the embodiments of the present invention will be described in detail. Those skilled in the art can understand that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention.

[0023] In the silver-copper alloy powder used in the following examples, calculated by mass fraction, Cu: 28%, Ni: 10%, Si is 1%, and the rest is Ag and inevitable impurities, and its particle size is 75 μm to 150 μm.

[0024] Example 1:

[0025] A method for laser cladding a silver layer on a copper substrate, wherein the copper substrate is subjected to single-layer cladding using a copper plate, and the thickness of the silver layer after cladding and polishing is required to be 0.1 mm or more and the surface roughness is less than Ra0.8.

[0026] Specifically, Step 1: Place the silver-copper alloy powder in an environment of 140 °C using a drying device and dry it for 30 minutes; Step 2: Turn on the protective gas (high-purity nitrogen) and keep the gas flow rate constant until the power of the device is turned off; Step 3: Keep the distance between the laser cladding head and the surface of the copper plate always at 12 - 14 mm; Step 4: Polish the copper plate using 800-mesh sandpaper, and use a duster cloth and industrial alcohol to wipe off metal dust, dust, oil stains, etc. on the surface of the copper plate, ensure that the surface of the copper plate is clean and dry, and keep the surface of the copper plate in a dry state; Step 5: The selected process parameters are as follows: the laser spot diameter is 1.6 mm, the laser output is 1300 W, the scanning speed of the laser cladding head is 6 mm / s, the cladding scanning overlap rate is 50%, the powder supply rate of the silver-copper alloy powder is 4.5 g / min, the flow rate of the powder supply gas is 11 L / min, and the flow rate of the laser cladding protective gas is 11 L / min; Step 6: After the laser cladding is completed, polish the cladded silver layer back and forth with 100-mesh and 400-mesh sandpaper, and detect the surface roughness and thickness of the front and back surfaces of the cladded silver layer. After polishing, as shown in Table 1, it meets the requirements of the copper bus of the hydraulic power unit, the surface roughness is less than Ra0.8, the thickness of the silver layer exceeds 0.1 mm, and there are no defects such as pores and inclusions.

[0027] Example 2-1

[0028] Based on Example 1, the difference is only that the laser output is 1100 W. Only when the laser energy density reaches the minimum energy threshold for opening the molten pool can the molten pool be formed, and further, laser cladding can be realized.

[0029] Example 2-2

[0030] Based on Example 1, the difference was only that the laser output was 1000 W. The melting pool could not be opened and cladding could not be achieved.

[0031] Example 2-3

[0032] Based on Example 1, the difference was only that the laser output was 1400 W. If the density of laser energy was too high, it would cause overburn of the copper substrate and boiling of the melting pool, resulting in a certain degree of deterioration of the fluidity of the melting pool. Also, it would close immediately after solidification, and finally defects such as pores and inclusions would appear in the cladding layer. Cu and Ag would form a eutectic and might cause tissue separation even in an unstable state of the melting pool.

[0033] Example 3-1

[0034] Based on Example 1, the difference was only that the scanning speed of the laser cladding head was 10 mm / s.

[0035] Example 3-2

[0036] Based on Example 1, the difference was only that the scanning speed of the laser cladding head was 20 mm / s. The heat input time of the laser for cladding within the unit dimension was shortened, the heat accumulation of the cladding within the unit dimension decreased, the melting pool became unstable and did not completely melt, resulting in an increase in the defects of unwelded parts in the cladding layer.

[0037] Example 4:

[0038] After performing single-layer cladding on the surface of the copper plate, a multi-layer silver coating layer is further clad on the surface of the silver layer on the copper plate.

[0039] It is the same as the operation process of Example 1.

[0040] After the second layer of the cyan laser cladding silver layer is completed, as shown in Table 1, the thickness and surface roughness of the cladding silver layer before and after polishing are detected.

[0041] After polishing the silver layer on the copper plate surface, to meet the basic requirements, the surface roughness is less than Ra0.8, the thickness of the silver layer exceeds 0.3 mm, and there are no defects such as pores and inclusions.

[0042] The results of the surface roughness and thickness detection of the cladding silver layer before and after polishing obtained in the above examples are shown in Table 1.

[0043]

Table 1

[0044] When the method of the present invention is applied to the laser cladding silver repair of the large current copper bus of the hydraulic power generation unit, the absorption rates of the copper bus and the cladding silver layer for the cyan laser light source are high. As shown in FIG. 1, a silver coating layer with a certain thickness without pores and inclusions can be formed on the copper bus, realizing metallurgical bonding.

[0045] (Appendix) (Appendix 1) A method for laser cladding a silver layer on a copper substrate, specifically, A pre-treatment step S1 before cladding, which performs polishing to remove impurities and oxide layers on the surface of the copper substrate, cleans it cleanly and dries it, and Using a cyan laser cladding device, with silver-copper alloy powder as the powder material, laser cladding of the silver layer on the copper substrate is performed by a coaxial powder feeding method. Here, the laser output is 1100W - 1350W, the scanning speed of the laser cladding head is 6mm / s - 10mm / s, and the overlap rate is 45% - 65%. A laser cladding step S2, and A step S3 of polishing the laser cladding silver layer on the surface of the copper substrate to meet the relevant requirements of the hydraulic power generation unit, characterized by including a method for laser cladding a silver layer on a copper substrate.

[0046] (Appendix 2) The copper substrate is T2 purple copper, with a copper content (wt%) ≥ 99.9 and other impurities (wt%) ≤ 0.1, and the method according to Appendix 1 is characterized in that.

[0047] (Appendix 3) In step S2, the silver-copper alloy powder, calculated by mass fraction, is Cu: 20 - 30%, Ni: 8 - 15%, Si: 0.5 - 2%, and the rest is silver and inevitable impurities, and the method according to Appendix 1 is characterized in that.

[0048] (Appendix 4) The particle size of the silver-copper alloy powder is 75 μm - 150 μm and it is dried before use, and the method according to Appendix 1 is characterized in that.

[0049] (Appendix 5) In step S2, the blue laser wavelength of the blue laser cladding device is 450 nm - 480 nm, and the method according to Appendix 1 is characterized in that.

[0050] (Appendix 6) In step S2, when laser cladding is performed, the spot is circular, with a diameter of 1.5 mm - 1.8 mm. The coaxial powder supply method adopts an annular powder supply nozzle, and the powder supply nozzle is coaxial with the circular spot, and the method according to Appendix 1 is characterized in that.

[0051] (Appendix 7) In step S2, the flow rate of the powder supply gas during laser cladding is 10 - 15 L / min, the powder supply amount is 4 g / min - 8 g / min, the flow rate of the protective gas is 10 - 15 L / min, and both the powder supply gas and the protective gas are inert gases, including but not limited to nitrogen, argon or helium, and the method according to Appendix 1 is characterized in that.

[0052] (Appendix 8) In step S3, the thickness of the silver layer on the surface of the copper substrate is required to exceed 0.1 mm after polishing, and the surface roughness is less than Ra 0.8. The method according to any one of appendices 1 to 8, characterized in that.

[0053] (Appendix 9) The surface of the copper bus can be clad with a multi-layer coated silver layer, and the thickness of the single-layer clad silver layer is 0.1 mm to 0.4 mm. The method according to appendix 1, characterized in that.

[0054] (Appendix 10) Use of the method according to any one of appendices 1 to 9 in the repair of large current copper buses of a hydroelectric power unit.

Claims

1. A method for laser cladding a silver layer on a copper substrate, specifically: A pre-treatment step S1 before cladding, which involves polishing to remove impurities and oxide layers on the surface of the copper substrate, cleaning it thoroughly, and drying it; Using a blue laser cladding device, with silver-copper alloy powder as the powder material, performing laser cladding of the silver layer on the copper substrate by means of a coaxial powder feeding method. Here, the laser output is 1100 W to 1350 W, the scanning speed of the laser cladding head is 6 mm / s to 10 mm / s, and the overlap rate is 45% to 65%. This is the laser cladding step S2; A method for laser cladding a silver layer on a copper substrate, characterized by including a step S3 of polishing the laser-clad silver layer on the surface of the copper substrate so as to meet the relevant requirements of a hydraulic power generation unit.

2. The method according to claim 1, wherein the copper substrate is T2 purple copper, the copper content (wt%) ≥ 99.9, and the content of other impurities (wt%) ≤ 0.

1.

3. In step S2, the silver-copper alloy powder, calculated by mass fraction, has Cu: 20 - 30%, Ni: 8 - 15%, Si: 0.5 - 2%, and the rest is silver and inevitable impurities. This is the method according to claim 1.

4. The method according to claim 1, wherein the particle size of the silver-copper alloy powder is 75 μm to 150 μm, and it is dried before use.

5. In step S2, the blue laser wavelength of the blue laser cladding device is 450 nm to 480 nm. This is the method according to claim 1.

6. In step S2, when laser cladding is performed, the spot is circular, with a diameter of 1.5 mm to 1.8 mm. The coaxial powder feeding method employs an annular powder feeding nozzle, and the powder feeding nozzle is coaxial with the circular spot. This is the method according to claim 1.

7. In step S2, the flow rate of the powder feeding gas during laser cladding is 10 - 15 L / min, the powder feeding amount is 4 g / min to 8 g / min, the flow rate of the protective gas is 10 - 15 L / min, and both the powder feeding gas and the protective gas are inert gases, including but not limited to nitrogen, argon, or helium. This is the method according to claim 1.

8. In step S3, the thickness of the silver layer on the surface of the copper substrate is required to exceed 0.1 mm after polishing, and the surface roughness is less than Ra 0.

8. The method according to any one of claims 1 to 8, characterized in that.

9. The surface of the copper bus can be clad with a multi-layer coating silver layer, and the thickness of the single-layer clad silver layer is 0.1 mm to 0.4 mm. The method according to claim 1, characterized in that.

10. Use of the method according to any one of claims 1 to 9 in the repair of the large current copper bus of a hydraulic power unit.

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