Method for preparing copper-tin alloy coating on surface of steel through ultrahigh-speed laser cladding

Abstract

The invention discloses a method for preparing a copper-tin alloy coating on the surface of steel through ultrahigh-speed laser cladding, which comprises the following steps of: S1, pretreating a steel substrate, and controlling the surface roughness Ra to be 2.5-3.2 microns; s2, spherical copper powder and flaky tin powder with the particle size of 15-53 microns are taken, and the copper powder is treated through microwave plasma, so that a nanoscale copper oxide layer is formed on the surface of the copper powder; s3, tin powder and the activated copper powder serve as coating raw materials, an airborne double-barrel powder feeder is adopted, laser is in a flat-top type circular light spot mode, a steel substrate moves relative to a laser cladding device according to a set track, the laser power is 3.5-4.5 kW, the laser scanning speed is 50-80 m / min, and the copper powder is molten into a liquid state to wrap the tin powder; and the temperature of the molten pool is monitored in real time, so that the temperature is stabilized at 1300-1400 DEG C, and finally the copper-tin alloy coating is prepared on the surface of the steel substrate. According to the method, efficient, high-precision and low-defect manufacturing of the copper-tin alloy coating is achieved through a light-powder-matrix coordinated regulation and control mechanism.

Description

Technical Field

[0001] The present invention relates to the technical field of steel manufacturing, in particular to a method for preparing a copper-tin alloy coating on a steel surface by ultra-high-speed laser cladding. Background Art

[0002] Sliding bearings are bearings that work under sliding friction. Traditional sliding bearings face the severe challenges of high speed, heavy load, long life and low maintenance. Steel is the core base material of sliding bearings (accounting for more than 80%), and the performance of its surface coating directly determines the tribological performance and service reliability of the bearing. Copper-tin alloy (such as CuSn10) is one of the best material systems for surface modification of high-end sliding bearings due to its high thermal conductivity, anti-seizure and self-lubricating properties. At present, the industrial preparation of copper-tin alloy coating on steel surface still relies on electroplating process, but it has two major bottlenecks: (1) Performance defects: the thickness of the electroplated layer is usually less than 50μm, and it is mechanically bonded (bonding strength <150MPa), which is prone to peeling under high-speed shear force, leading to sudden failure of the bearing; (2) Environmental constraints: the electroplating process requires the use of cyanide complexing agent, and the waste liquid treatment cost accounts for more than 30% of the total production cost.

[0003] Although laser cladding technology can achieve metallurgical bonding between the coating and steel (bonding strength > 400 MPa), conventional laser cladding (scanning speed < 10 m / min) has inherent defects when applied to copper-tin alloys: (1) Uncontrolled tin burnout: The low-melting-point tin (232°C) stays in the high-temperature zone of the molten pool (> 2000°C) for too long, resulting in a burnout rate of up to 40%-50%, resulting in the actual composition of the coating being a copper-rich phase (CuSn6-CuSn8), and the friction coefficient surges from the designed 0.12 to over 0.25. (2) Thermal stress accumulation: Low-speed scanning leads to excessive heat input to the substrate, and the depth of the heat-affected zone (HAZ) of the steel substrate exceeds 200 μm, causing the substrate hardness to decrease (loss of 15%-20%). At the same time, the residual stress inside the copper-tin coating exceeds 600 MPa, and the risk of interface crack initiation is significant.

[0004] (3) Imbalance between efficiency and precision: In order to reduce the tendency of cracks, the traditional process needs to adopt a multi-layer thin coating strategy (single layer thickness <30μm), but the cumulative processing efficiency is less than 0.2m 2 / h, which makes it difficult to meet the industrial demand for large-scale aviation bearings (such as diameter > 500mm).

[0005] Ultra-high-speed laser cladding (scanning speed > 50 m / min) has demonstrated the advantages of "low heat input-high efficiency" in nickel-based and iron-based alloys, but faces new challenges when directly transplanted to copper-tin alloy systems: (1) Instability in cladding layer formation: The high reflectivity of copper (> 90%) and the rapid vaporization of tin result in a laser energy absorption rate of less than 20%, making it difficult for the molten pool to spread stably, and the coating exhibits intermittent spheroidization; (2) Loss of control of composition gradient: The ultra-high-speed cooling rate exacerbates the microsegregation of tin elements, forming a brittle SnO2 inclusion phase, which causes the coating toughness to decrease by more than 50%; (3) Narrow process window: Existing equipment parameters (such as spot shaping mode and carrier gas flow) cannot match the ultra-high-speed transportation requirements of copper-tin powder, and the powder feeding stability (fluctuation > ± 15%) directly causes the coating thickness deviation to exceed ± 30 μm.

[0006] Therefore, developing a method for preparing ultra-high-speed laser cladding copper-tin alloy coatings on steel substrates to achieve coordinated control of "high speed-low defects-stable composition" has become a core technology proposition for promoting high-end bearing manufacturing. Summary of the Invention

[0007] In response to the problems existing in the existing copper-tin alloy laser cladding technology on the surface of steel, such as high tin element burnout rate, prominent contradiction between interface bonding strength and processing efficiency, and uncontrolled coating formation under ultra-high-speed conditions, the present invention provides a method for preparing copper-tin alloy coating on the surface of steel by ultra-high-speed laser cladding.

[0008] The method for preparing a copper-tin alloy coating on a steel surface by ultra-high-speed laser cladding provided by the present invention comprises the following steps:

[0009] S1. Pretreatment of steel substrate: The surface of the steel substrate is sandblasted to 200 mesh and then ultrasonically cleaned with anhydrous ethanol to control the surface roughness to Ra 2.5-3.2μm to enhance laser absorption rate.

[0010] S2. Raw material pretreatment: Take spherical copper powder (Cu≥99.9%) with a particle size of 15-53μm and flaky tin powder (Sn≥99.95%), according to the target composition ratio of CuSn10, of which flaky tin powder accounts for 10-12wt% and the rest is copper powder, totaling 100%. Copper powder and tin powder are respectively ultrasonically cleaned (ethanol, 30min) to remove surface organic matter and impurities, and then dried. The dried copper powder is treated with microwave plasma to form a nano-scale copper oxide layer on its surface to improve powder fluidity and laser absorption rate. The thickness of the copper oxide layer is 50-80nm.

[0011] The microwave plasma treatment method is: copper powder is placed in a reaction chamber containing an O2 / Ar mixed gas (O2 accounts for 30%) for microwave plasma activation treatment. The cavity pressure is 50Pa, the radio frequency power is 30-50W, the treatment time is 20min, and the temperature is room temperature, so that a nano-scale copper oxide layer is formed on the surface of the copper powder.

[0012] S3, using tin powder and plasma-treated copper powder as coating raw materials, an airborne double-barrel powder feeder was used, and the laser was in a flat-top circular spot mode with a spot diameter of 0.8 mm. The spot was focused approximately 1-2 mm above the steel substrate, causing the steel substrate to move along a set trajectory relative to the laser cladding device. The laser power was 3.5-4.5 kW, and the laser scanning speed was 50-80 m / min. This melted the copper powder into a liquid that encapsulated the tin powder, inhibiting tin vaporization. During the laser cladding process, a spectral feedback module pre-installed on the laser cladding equipment was used to monitor the intensity of the Sn characteristic spectrum line (wavelength 450 nm) in the molten pool in real time to monitor the molten pool temperature. The laser power was then adjusted in real time to stabilize the molten pool temperature at 1300-1400°C (above the melting point of copper and below the boiling point of tin). Finally, a copper-tin alloy coating was produced on the surface of the steel substrate.

[0013] Among them, the air-borne double-drum powder feeder mixes the copper powder and tin powder after plasma treatment, and the powder feeding method is coaxial powder feeding. Through the coupling of ultrasonic vibration (frequency 28kHz) and Venturi effect, the powder feeding accuracy fluctuation is achieved at a scanning speed of 50-80m / min. ≤3%; the spot overlap rate (60-80%) and the melt channel overlap strategy are optimized to control the coating thickness tolerance within ±8μm.

[0014] Preferably, when adjusting the laser power in real time, the laser power fluctuation needs to be ≤2% to ensure the composition stability within CuSn9.5-10.2.

[0015] Compared with the prior art, the present invention is beneficial in that:

[0016] (1) The method of the present invention improves the laser absorption rate of the copper powder surface through plasma activation treatment, and adopts relatively low power (3.5-4.5kW) ultra-fast laser cladding to shorten the high temperature residence time of the molten pool, thereby reducing the tin burnout rate from 40% in conventional processes to 10% or even lower. During the laser cladding process, the intensity of the Sn characteristic spectrum line of the molten pool is monitored in real time, and the laser power fluctuation is automatically adjusted to ≤2%, thereby ensuring the stability of the composition (CuSn9.5-10.2). An airborne double-barrel powder feeder is used, and ultrasonic vibration (frequency 28kHz) is coupled with the Venturi effect to achieve a powder feeding accuracy fluctuation of ≤3% at a scanning speed of 50-80m / min; at the same time, the spot overlap rate of 60-80% and the melt channel overlap strategy are optimized to control the coating thickness tolerance within ±8μm.

[0017] (2) The coating prepared by the present invention has uniform composition, the tin content deviation of the CuSn10 alloy is ≤0.5wt%, the hardness is 190-220HV, the interface bonding strength is improved to ≥250MPa, and the interface shear strength is ≥380MPa, which is more than 1 times higher than that of the traditional electroplating process; moreover, the results of non-destructive penetration testing show that the porosity is less than or equal to 0.2%.

[0018] (3) The coating processing efficiency of the method of the present invention is high. The cladding time of a single aviation bearing (diameter 500 mm) is ≤40 minutes, which is 80% shorter than that of conventional laser cladding. In addition, the comprehensive energy consumption cost is reduced by 65% compared with the imported electroplating process, completely avoiding the cost of cyanide pollution control.

[0019] In summary, the method for preparing copper-tin alloy coating by ultra-high-speed laser cladding on steel surface provided by the present invention realizes efficient, high-precision and low-defect manufacturing of copper-tin alloy coating through the light-powder-substrate coordinated control mechanism, overcomes the technical problems existing in the existing copper-tin alloy laser cladding technology on steel surface, such as high tin element burnout rate, prominent contradiction between interface bonding strength and processing efficiency, and uncontrolled coating formation under ultra-high-speed working conditions, and meets the dual requirements of high-end sliding bearings for coating performance and industrialization cost.

[0020] Other advantages, objectives and features of the present invention will be reflected in part from the following description and will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the ultra-high-speed laser cladding process. Reference numbers: 1-laser spot, 2-copper-tin alloy coating, 3-GCr15 bearing steel substrate, 4-coaxial annular nozzle, 5-powder feed tube, 6-cooling tube, 7-dynamic spectrum feedback system, 8-laser interface, 9-optical fiber.

[0022] Figure 2 Schematic diagram of the macroscopic morphology of the copper-tin alloy coating prepared in Example 1.

[0023] Figure 3 Schematic diagram of the macroscopic morphology of the copper-tin alloy coating prepared in Example 2.

[0024] Figure 4 Schematic diagram of the macroscopic morphology of the copper-tin alloy coating prepared in Example 3.

[0025] Figure 5 Schematic diagram of the macroscopic morphology of the copper-tin alloy coating prepared in Comparative Example 1.

[0026] Figure 6 Schematic diagram of the cross-sectional morphology of the copper-tin alloy coating prepared in Example 1.

[0027] Figure 7 Schematic diagram of the cross-sectional morphology of the copper-tin alloy coating prepared in Example 2.

[0028] Figure 8 Schematic diagram of the cross-sectional morphology of the copper-tin alloy coating prepared in Example 3.

[0029] Figure 9 Schematic diagram of the cross-sectional morphology of the copper-tin alloy coating prepared in Comparative Example 1.

[0030] Figure 10 This is a cross-sectional microstructural diagram of the copper-tin alloy coating prepared in Example 1.

[0031] Figure 11 This is a cross-sectional microstructural diagram of the copper-tin alloy coating prepared in Example 2.

[0032] Figure 12 This is a cross-sectional microstructural diagram of the copper-tin alloy coating prepared in Example 3.

[0033] Figure 13 This is a cross-sectional microstructural diagram of the copper-tin alloy coating prepared in Comparative Example 1.

[0034] Figure 14 This is the microhardness result diagram of the copper-tin alloy coating prepared in Example 1.

[0035] Figure 15 This is the microhardness result diagram of the copper-tin alloy coating prepared in Example 2.

[0036] Figure 16 This is the microhardness result diagram of the copper-tin alloy coating prepared in Example 3.

[0037] Figure 17 This is the microhardness result diagram of the copper-tin alloy coating prepared in Comparative Example 1.

[0038] Figure 18 This is a graph showing the test results of the bonding strength between the GCr15 bearing steel substrate and the copper-tin alloy coating interface of Examples 1-3 and Comparative Example 1.

[0039] Figure 19 Graph showing the shear strength test results of the interface between the GCr15 bearing steel substrate and the copper-tin alloy coating of Examples 1-3 and Comparative Example 1. DETAILED DESCRIPTION

[0040] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0041] Example 1

[0042] A method for preparing a copper-tin alloy coating on a steel surface by ultra-high-speed laser cladding, comprising the following steps:

[0043] (1) GCr15 bearing steel was selected as the substrate, and the surface of the GCr15 bearing steel was sandblasted to 200 mesh. The sandblasting process was performed by spraying the surface of the GCr15 bearing steel with sand particles, wherein the sand particles were aluminum oxide particles. The spraying angle of the sandblasting process was 45 degrees, and the spraying pressure was 0.5 MPa. The sandblasting process was stopped after the surface roughness of the bearing steel surface reached 3 μm. Ultrasonic cleaning was then performed, using anhydrous ethanol as the cleaning medium, the ultrasonic cleaning power was 30 W, and the time was 5 minutes, to obtain the pretreated GCr15 bearing steel substrate.

[0044] (2) Pretreatment of laser cladding raw materials: The raw materials used are spherical copper powder (Cu≥99.9%) with a particle size of 15-53 μm and flaky tin powder (Sn≥99.95%), which are mixed according to the target composition of CuSn10, of which the flaky tin powder accounts for 10 wt%. A nano-scale copper oxide layer (thickness 50 nm) is formed on the powder surface through plasma activation treatment to improve the powder fluidity and laser absorption rate.

[0045] (3) According to Figure 1 The processing method shown is to perform ultra-high-speed laser cladding on the surface of the GCr15 bearing steel substrate pretreated in step (1). Coaxial powder feeding is used to spray copper powder and tin powder. The total laser power during high-speed laser cladding is 3.5kW, the scanning speed is set to 80m / min, the distance between the laser focus and the substrate is 1mm, the laser spot diameter is 0.8mm, the powder feeding rate is 90g / min, and the overlap rate is 60%. The carrier gas (argon) pressure is 0.8MPa, and the power is adjusted by real-time monitoring of the molten pool radiation spectrum (characteristic wavelength 450nm) to stabilize the molten pool temperature at 1300℃ (above the melting point of copper and below the boiling point of tin). After the laser cladding is completed, it is placed in the air to cool naturally to obtain a copper-tin alloy coating with a cladding layer thickness of 600μm.

[0046] Figure 1 The dynamic spectral feedback system 7, as described in the preceding text, refers to a spectral feedback module pre-installed on the laser cladding equipment. This module includes a MER2-041-302GM / P camera (hardware) and a real-time monitoring and data feedback system (software) from Nanjing Huirui Optoelectronics Technology Co., Ltd. This system monitors the melt pool temperature by real-time monitoring of the intensity of the Sn characteristic spectral line (wavelength 450nm). The laser cladding equipment used in the industry can be used.

[0047] Example 2

[0048] A method for preparing a copper-tin alloy coating on a steel surface by ultra-high-speed laser cladding, comprising the following steps:

[0049] (1) GCr15 bearing steel was selected as the substrate, and the surface of the GCr15 bearing steel was sandblasted to 300 mesh. The sandblasting process was performed by spraying the surface of the GCr15 bearing steel with sand particles, wherein the sand particles were aluminum oxide particles. The spraying angle of the sandblasting process was 30 degrees, and the spraying pressure was 0.4 MPa. The sandblasting process was stopped after the surface roughness of the bearing steel surface reached 2 μm. Ultrasonic cleaning was then performed, using anhydrous ethanol as the cleaning medium, the ultrasonic cleaning power was 35 W, and the time was 10 minutes, to obtain a pretreated GCr15 bearing steel substrate.

[0050] (2) Pretreatment of laser cladding raw materials: The raw materials used are spherical copper powder (Cu≥99.9%) with a particle size of 15-53 μm and flaky tin powder (Sn≥99.95%), which are mixed according to the target composition of CuSn10, of which the flaky tin powder accounts for 11 wt%. A nano-scale copper oxide layer (thickness 60 nm) is formed on the powder surface through plasma activation treatment to improve the powder fluidity and laser absorption rate.

[0051] (3) According to Figure 1 The processing method shown is to perform ultra-high-speed laser cladding on the surface of the GCr15 bearing steel substrate pretreated in step (1). Coaxial powder feeding is used to spray copper powder and tin powder. The total laser power during high-speed laser cladding is 4.0kW, the scanning speed is set to 65m / min, the distance between the laser focus and the substrate is 1.5mm, the laser spot diameter is 0.8mm, the powder feeding rate is 80g / min, and the overlap rate is 70%. The carrier gas (argon) pressure is 0.7MPa, and the power is adjusted by real-time monitoring of the molten pool radiation spectrum (characteristic wavelength 450nm) to stabilize the molten pool temperature at 1350℃ (above the melting point of copper and below the boiling point of tin). After the laser cladding is completed, it is placed in the air for natural cooling to obtain a copper-tin alloy coating with a cladding layer thickness of 600μm.

[0052] Example 3

[0053] A method for preparing a copper-tin alloy coating on a steel surface by ultra-high-speed laser cladding, comprising the following steps:

[0054] (1) GCr15 bearing steel was selected as the substrate, and the surface of the GCr15 bearing steel was sandblasted to 400 mesh. The sandblasting process was performed by spraying the surface of the GCr15 bearing steel with sand particles, wherein the sand particles were aluminum oxide particles. The spraying angle of the sandblasting process was 60 degrees, and the spraying pressure was 0.3 MPa. The sandblasting process was stopped after the surface roughness of the bearing steel surface reached 1.5 μm. Ultrasonic cleaning was then performed, using anhydrous ethanol as the cleaning medium, the ultrasonic cleaning power was 40 W, and the time was 15 minutes, to obtain a pretreated GCr15 bearing steel substrate.

[0055] (2) Pretreatment of laser cladding raw materials: The raw materials used are spherical copper powder (Cu≥99.9%) with a particle size of 15-53 μm and flaky tin powder (Sn≥99.95%), which are mixed according to the target composition of CuSn10, of which the flaky tin powder accounts for 12 wt%. A nano-scale copper oxide layer (thickness 80 nm) is formed on the powder surface through plasma activation treatment to improve the powder fluidity and laser absorption rate.

[0056] (3) According to Figure 1 The processing method shown is to perform ultra-high-speed laser cladding on the surface of the GCr15 bearing steel substrate pretreated in step (1). Coaxial powder feeding is used to spray copper powder and tin powder. The total laser power during high-speed laser cladding is 4.5kW, the scanning speed is set to 50m / min, the distance between the laser focus and the substrate is 1.5mm, the laser spot diameter is 0.8mm, the powder feeding rate is 70g / min, and the overlap rate is 80%. The carrier gas (argon) pressure is 0.6MPa, and the power is adjusted by real-time monitoring of the molten pool radiation spectrum (characteristic wavelength 450nm) to stabilize the molten pool temperature at 1400℃ (above the melting point of copper and below the boiling point of tin). After the laser cladding is completed, it is placed in the air to cool naturally to obtain a copper-tin alloy coating with a cladding layer thickness of 600μm.

[0057] Comparative Example 1

[0058] In the copper-tin alloy coating method, the copper powder was not plasma activated, and the laser cladding process did not monitor the molten pool radiation spectrum (characteristic wavelength 450nm) in real time to provide feedback and adjust the power. The specific method is as follows:

[0059] (1) GCr15 bearing steel was selected as the substrate, and the surface of the GCr15 bearing steel was sandblasted to 400 mesh. The sandblasting process was performed by spraying the surface of the GCr15 bearing steel with sand particles, wherein the sand particles were aluminum oxide particles. The spraying angle of the sandblasting process was 60 degrees, and the spraying pressure was 0.3 MPa. The sandblasting process was stopped after the surface roughness of the bearing steel surface reached 1.5 μm. Ultrasonic cleaning was then performed, using anhydrous ethanol as the cleaning medium, the ultrasonic cleaning power was 40 W, and the time was 15 minutes, to obtain a pretreated GCr15 bearing steel substrate.

[0060] (2) Ultra-high-speed laser cladding is performed on the surface of the GCr15 bearing steel substrate pretreated in step (1). The raw materials used in the ultra-high-speed laser cladding are spherical copper powder (Cu≥99.9%) with a particle size of 15-53μm and flake tin powder (Sn≥99.95%), which are mixed according to the target composition of CuSn10, wherein the flake tin powder accounts for 12wt%. Coaxial powder feeding is used to spray the copper powder and tin powder. The total laser power during high-speed laser cladding is 4.5kW, the scanning speed is set to 50m / min, the distance between the laser focus and the substrate is 1.5mm, the laser spot diameter is 0.8mm, the powder feeding rate is 70g / min, and the overlap rate is 80%; the carrier gas (argon) pressure is 0.6MPa. After the laser cladding is completed, it is placed in the air for natural cooling to obtain a copper-tin alloy coating.

[0061] The copper-tin alloy coating samples prepared in Examples 1-3 and Comparative Example 1 were numbered 1#-1, 1#-2, 1#-3, and 1#-4, respectively, and the following performance tests were performed.

[0062] (1) The copper-tin alloy coatings prepared in Examples 1-3 and Comparative Example 1 were characterized by morphology. The macroscopic morphology is shown in FIG. Figure 2-5 Its cross-sectional morphology is shown in Figure 6-9 Its cross-sectional microstructure is shown in Figure 10-13 shown.

[0063] (2) An X-ray fluorescence element analyzer (XRF) was used to detect the element content of the copper-tin alloy coatings of Examples 1-3 and Comparative Example 1. The test conditions of the X-ray fluorescence element analyzer were: voltage 40 kV, test time 300 s. The results are shown in Tables 1-4.

[0064] Table 1. Element content results of the copper-tin alloy coating of Example 1

[0065]

[0066] Table 2. Element content results of the copper-tin alloy coating of Example 2

[0067]

[0068] Table 3. Element content results of the copper-tin alloy coating of Example 3

[0069]

[0070] Table 4. Element content results of the copper-tin alloy coating of Comparative Example 1

[0071]

[0072] (3) The microhardness of the GCr15 bearing steel substrate and the copper-tin alloy coating in Examples 1-3 and Comparative Example 1 was measured using a micro Vickers hardness tester (SHIMADZU, HMV-G-XY-S). The test conditions of the micro Vickers hardness tester were: load 1.96 N, loading time 15 s. The results are shown in Figure 2. Figure 14-17 shown.

[0073] (4) The destructive test of the bonding strength between the GCr15 bearing steel substrate and the copper-tin alloy coating was carried out according to the standard ISO 4386-2:2019. The results are as follows: Figure 18 shown.

[0074] (5) Shear strength test of GCr15 bearing steel substrate and copper-tin alloy coating was carried out according to standard YS / T 485. The results are as follows: Figure 19 shown.

[0075] (6) Image pro software was used to measure the pore diameter in the cross-sectional microstructure.

[0076] It can be seen that the copper-tin alloy coating prepared by the method of the present invention has a uniform composition, with a tin content deviation of ≤0.5 wt% in the CuSn10 alloy. The microhardness of the copper-tin alloy coating prepared in Example 1 is in the range of 205-220 HV, the bonding strength is 255 MPa, the shear strength is 387 MPa, and the pore diameter is less than 1 μm. The microhardness of the copper-tin alloy coating prepared in Example 2 is in the range of 204-218 HV, the bonding strength is 251 MPa, the shear strength is 385 MPa, and the pore diameter is less than 2 μm. The microhardness of the copper-tin alloy coating prepared in Example 3 is in the range of 198-222 HV, the bonding strength is 264 MPa, the shear strength is 393 MPa, and the pore diameter is less than 3 μm. The copper-tin alloy coating prepared in Comparative Example 1 has a porosity of ≥5% and contains unfused pores (size >150 μm). The microhardness is reduced by 30 to 40 HV, the bonding strength is reduced by 53 MPa, and the shear strength is reduced by 92 MPa. The results show that the interfacial bonding strength of the copper-tin alloy coating prepared by the method of the present invention is increased to ≥250 MPa, and the interfacial shear strength is ≥380 MPa, which is more than double that of the traditional electroplating process. Furthermore, non-destructive penetrant testing conducted according to the standard ISO 4386-3:2018(E) shows that the porosity of the copper-tin alloy coating prepared by the method of the present invention does not exceed 0.2%.

[0077] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a copper-tin alloy coating on a steel surface by ultra-high-speed laser cladding, characterized in that: The following steps are involved: S1, steel substrate pretreatment; S2. Raw material pretreatment: Spherical copper powder and flaky tin powder with a particle size of 15-53 μm are taken, and the copper powder is treated by microwave plasma to form a nano-scale copper oxide layer on its surface; S3. Tin powder and activated copper powder are used as coating raw materials. An airborne double-barrel powder feeder is used. The laser adopts a flat-top circular spot mode. The steel substrate is moved relative to the laser cladding device according to the set trajectory. The laser power is 3.5-4.5kW and the laser scanning speed is 50-80m / min. The copper powder is melted into liquid and coated with tin powder. The molten pool temperature is monitored in real time to stabilize the molten pool temperature at 1300-1400℃. Finally, a copper-tin alloy coating is obtained on the surface of the steel substrate.

2. The method for preparing a copper-tin alloy coating by ultra-high-speed laser cladding on a steel surface according to claim 1, characterized in that: In step S3, the diameter of the light spot is 0.8 mm, and the light spot is focused about 1-2 mm above the steel substrate.

3. The method for preparing a copper-tin alloy coating on a steel surface by ultra-high-speed laser cladding according to claim 1, characterized in that: In step S3, the method for real-time monitoring of the molten pool temperature is: using a spectral feedback module pre-installed on the laser cladding equipment to monitor the intensity of the Sn characteristic spectrum line of the molten pool in real time to achieve the purpose of measuring the molten pool temperature, and by real-time adjusting the laser power to stabilize the molten pool temperature in the range of 1300-1400℃.

4. The method for preparing a copper-tin alloy coating by ultra-high-speed laser cladding on a steel surface according to claim 3, characterized in that: In step S3, the fluctuation of the laser power is adjusted in real time to be ≤2%.

5. The method for preparing a copper-tin alloy coating on a steel surface by ultra-high-speed laser cladding according to claim 1, characterized in that: In step S2, the amount of tin powder used accounts for 10-12 wt %, and the rest is copper powder, totaling 100%.

6. The method for preparing a copper-tin alloy coating on a steel surface by ultra-high-speed laser cladding according to claim 1, characterized in that: In step S2, the microwave plasma treatment method is: copper powder is placed in a reaction chamber containing an O2 / Ar mixed gas for microwave plasma activation treatment, the chamber pressure is 50Pa, the radio frequency power is 30-50W, the treatment time is 20min, and the temperature is room temperature, so that a nano-scale copper oxide layer is formed on the surface of the copper powder.

7. The method for preparing a copper-tin alloy coating on a steel surface by ultra-high-speed laser cladding according to claim 5, characterized in that: The thickness of the nano-scale copper oxide layer formed on the surface of the copper powder is 50-80nm.

8. The method for preparing a copper-tin alloy coating on a steel surface by ultra-high-speed laser cladding according to claim 1, wherein: In step S1 , the pretreatment method of the steel substrate is: the surface of the steel substrate is sandblasted to 200 mesh and then ultrasonically cleaned, and the surface roughness is controlled to be Ra 2.5-3.2 μm.

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