Aluminum alloy pump wheel low temperature brazing method

Abstract

This invention discloses a low-temperature brazing method for aluminum alloy pump impellers, comprising the following steps: S1: Precision pretreatment of the surfaces to be welded; taking an aluminum alloy pump impeller, and sequentially performing mechanical grinding, alkaline washing, neutralization, aviation-grade gasoline cleaning, distilled alcohol cleaning, and drying on the surfaces to be welded of the blades and hub of the aluminum alloy pump impeller; S2: Preparation and coating of alloy brazing filler metal; S3: Argon-protected gradient temperature brazing; S4: Segmented isothermal cooling; S5: Post-weld integrated treatment. 1. Low-temperature welding ensures pump impeller precision and performance: The brazing temperature is controlled at 290~310℃ to avoid coarsening of aluminum alloy grains. The overall deformation of the pump impeller is ≤0.02mm, and no secondary shaping is required after welding, directly meeting assembly requirements; 2. Overall performance fully meets standards: The combination of a special Al-Si based composite brazing filler metal and gradient temperature control process results in a weld shear strength ≥300MPa, far exceeding traditional methods. Furthermore, post-weld anodizing treatment reduces the corrosion rate to ≤0.01mm / a, making it suitable for harsh operating environments in engineering machinery.

Description

Technical Field

[0001] This invention belongs to the field of brazing technology for high-pressure turbine pump components of spacecraft engines, specifically involving a low-temperature brazing method for the three core components of hydraulic torque converters in engineering machinery: pump impeller, guide impeller, and turbine. It is applicable to the connection between the blades and hub of pump impellers made of commonly used aluminum alloys such as 6061 / 2A12. Background Technology

[0002] Aluminum alloy pump impellers are core rotating components of hydraulic torque converters in engineering machinery, comprising the pump impeller, guide wheel, and turbine. They are widely used due to their advantages such as lightweight, high strength, and good thermal conductivity. During manufacturing, the connection quality between the blades and the hub directly determines the pump impeller's working efficiency, pressure resistance, and service life; brazing is a crucial process for this connection. Current brazing technologies for aluminum alloy pump impellers mostly employ medium-to-high temperature brazing (temperature ≥480℃), which presents the following significant problems: 1. High temperature leads to deterioration of pump wheel performance: Aluminum alloys are prone to grain coarsening at medium and high temperatures, which leads to a decrease in mechanical properties. In addition, the pump wheel has a complex structure (multi-blade, thin-walled structure), and high temperature can easily cause irregular deformation (deformation amount is usually >0.05mm), which affects the flow stability and sealing performance of the hydraulic system. 2. Insufficient joint strength and corrosion resistance: Traditional brazing filler metals have poor metallurgical compatibility with aluminum alloy base materials, and brittle phases are easily generated at high temperatures, resulting in low joint shear strength (usually <250MPa). In addition, high-temperature brazing is prone to defects such as joint oxidation and porosity. Aluminum alloys themselves have weak corrosion resistance, and the joint area is prone to corrosion weak points. It is prone to failure in the harsh operating environment of engineering machinery, especially in spacecraft, where failure during operation can cause major accidents. 3. Poor adaptability: Existing brazing methods are not optimized for the structural characteristics of aluminum alloy pump impellers (small angle between blades and hub, narrow joint space), resulting in uneven filler metal filling, easy incomplete penetration defects, and complex shaping processing required after welding, leading to low production efficiency.

[0003] While existing technologies have addressed the aforementioned problems, some shortcomings still remain: For example, Chinese patent CN101406977B discloses a vacuum brazing method for pump impellers. The brazing temperature is as high as 850-860℃. It adopts single-stage heating and heat preservation and simple air cooling. It does not involve low-temperature brazing, alloy brazing material composition and gradient temperature control process. There is also no stress relief and anodizing treatment after welding. The high-temperature brazing of this technology is prone to pump impeller deformation and grain coarsening.

[0004] Chinese patent CN118106573A discloses an aluminum alloy atmospheric pressure brazing method. It uses traditional Zl-102 brazing filler metal in an atmospheric pressure air atmosphere of 680-700℃, with a holding time of only 25-30 seconds. The temperature control accuracy is low, and no protective atmosphere or gradient cooling is used, resulting in limited brazed joint performance. Summary of the Invention

[0005] The purpose of this invention is to provide a low-temperature brazing method for aluminum alloy pump wheels, addressing the deficiencies and shortcomings in the prior art.

[0006] The technical solution of the present invention: A low-temperature brazing method for aluminum alloy pump impellers includes the following steps: S1: Precision pretreatment of the surfaces to be welded. Take an aluminum alloy pump wheel and sequentially perform mechanical grinding, alkaline washing, neutralization, aviation-grade gasoline cleaning, distilled alcohol cleaning, and drying on the surfaces to be welded, ensuring that the surface roughness Ra is ≤0.6μm, the oxide film thickness is ≤5nm, and the oil residue is ≤3mg / m². 2 ; S2: Preparation and coating of alloy brazing filler metal. The alloy brazing filler metal is prepared with the following mass percentage composition: Al 88%~92%, Si 6%~8%, Cu 1%~2%, Zn 0.5%~1%, rare earth element Ce 0.3%~0.5%, and Ti 0.2%~0.4%. The alloy brazing filler metal is made into powder and mixed with an organic binder to form a paste-like brazing filler metal. The paste is then uniformly coated onto the surface to be soldered, with a coating thickness of 0.3~0.4mm. S3: Argon-protected gradient heating brazing. The assembled and fixed aluminum alloy pump wheel is placed in a vacuum brazing furnace. Argon gas with a purity of ≥99.995% is introduced to make the oxygen content in the furnace ≤30ppm. The gradient heating mode is used to heat to the brazing temperature of 290~310℃ and hold for 40~50 minutes. The pressure in the furnace is controlled at 0.12~0.15MPa and the argon gas flow rate is 12~18L / min. S4: Segmented isothermal cooling. After the heat preservation is completed, the furnace is first isothermally cooled at 210-230℃ for 25-35 minutes, then cooled at a rate of 2-4℃ / min to below 80℃, and finally cooled to ambient temperature with the furnace. Argon gas is kept running throughout the process. S5: Post-weld integrated treatment, removal of residues and cleaning, followed by stress relief treatment, and finally anodizing of the entire aluminum alloy pump wheel to form an oxide film with a thickness of 5-8 μm.

[0007] In step S1, the mechanical polishing uses 1500-2000 grit sandpaper, the alkaline washing uses a 5-7 wt% sodium hydroxide aqueous solution at 40-45°C for 5-8 minutes, the neutralization uses a 10-15 wt% nitric acid aqueous solution for 30-60 seconds, the aviation washing gasoline is mainly composed of C9-C12 straight-chain alkanes and isoalkanes, accounting for more than 90%, the distilled alcohol purity is 99.5%, and the drying is carried out at 90-100°C for 20-30 minutes.

[0008] In step S1, after mechanical grinding, the surface to be welded is subjected to laser inspection to ensure that there are no scratches, cracks and inclusions with a depth greater than 0.05mm.

[0009] In step S2, the particle size of the alloy brazing powder is 30-80 μm, and the organic binder is made by mixing ethyl cellulose, turpentine oil, and ethanol in a mass ratio of 4:10:86.

[0010] In step S2, the mass ratio of the alloy brazing powder to the organic binder is 10:1. In step S3, the gradient heating mode is specifically as follows: from room temperature to 120°C, the heating rate is 6-8°C / min; from 120°C to 220°C, the heating rate is 4-6°C / min; from 220°C to the brazing temperature, the heating rate is 1-1.5°C / min.

[0011] In step S3, the vacuum degree of the vacuum brazing furnace is ≤5×10⁻⁶. -3 Pa, during the heating process, the oxygen content and temperature uniformity in the furnace are monitored in real time, and the temperature uniformity error in the front, middle and rear zones of the brazing furnace is ≤±2℃.

[0012] In step S5, the residue is removed manually by rinsing under tap water for at least 10 minutes.

[0013] In step S5, the stress-relief treatment temperature is 130–160°C, and the holding time is 80–100 minutes; the electrolyte for the anodizing treatment is a 15–20 wt% sulfuric acid solution, the temperature is 18–22°C, and the current density is 1–2 A / dm³. 2 The time is 20 to 30 minutes.

[0014] In step S5, after the anodizing treatment, the aluminum alloy pump wheel is dissected and inspected to check whether the internal microstructure of the aluminum alloy pump wheel is overburned.

[0015] The beneficial effects of this invention are: 1. Low-temperature welding ensures pump wheel precision and performance: The brazing temperature is controlled at 290~310℃ to avoid coarsening of aluminum alloy grains. The overall deformation of the pump wheel is ≤0.02mm. No secondary shaping is required after welding, and it directly meets the assembly requirements. 2. Overall performance fully meets standards: The combination of special Al-Si based composite brazing filler and gradient temperature control process results in a shear strength of ≥300MPa for the welded parts, far exceeding traditional methods. Furthermore, the post-weld anodizing treatment reduces the corrosion rate to ≤0.01mm / a, making it suitable for the harsh operating environment of engineering machinery. 3. Strong adaptability: The brazing filler coating method and gap control are optimized for the structural characteristics of aluminum alloy pump impellers, solving the problem of brazing filler filling in the narrow space between the blades and the hub, and reducing the incomplete penetration defect rate to below 0.5%; 4. High production efficiency: The post-weld processing is simplified, and the overall production cycle is shortened by more than 60% compared with traditional medium and high temperature brazing, making it suitable for mass production needs. Detailed Implementation

[0016] Example 1 A low-temperature brazing method for aluminum alloy pump impellers includes the following steps: S1: Precision pretreatment of the surfaces to be welded. Take an aluminum alloy pump wheel and sequentially perform mechanical grinding, alkaline washing, neutralization, aviation-grade gasoline cleaning, distilled alcohol cleaning, and drying on the surfaces to be welded, ensuring that the surface roughness Ra is ≤0.6μm, the oxide film thickness is ≤5nm, and the oil residue is ≤3mg / m². 2 ; Mechanical polishing uses 1500-2000 grit sandpaper; alkaline washing uses a 5-7 wt% sodium hydroxide aqueous solution at 40-45°C for 5-8 minutes; neutralization uses a 10-15 wt% nitric acid aqueous solution for 30-60 seconds; aviation washing gasoline is mainly composed of C9-C12 straight-chain alkanes and isoalkanes, accounting for more than 90%; distilled alcohol purity is 99.5%; and drying is carried out at 90-100°C for 20-30 minutes.

[0017] After mechanical grinding, the surface to be welded is subjected to laser inspection to ensure that there are no scratches, cracks or inclusions with a depth greater than 0.05mm.

[0018] Specifically, this step involves a combination of processes: mechanical polishing, alkaline washing, aviation cleaning with gasoline, and distilled alcohol cleaning, taking advantage of the characteristic that aluminum alloy surfaces are prone to forming a dense oxide film.

[0019] First, remove the oxide film using 1500-2000 grit sandpaper. Finely grind the surfaces of the blades (6061 aluminum alloy) and hubs (2A12 aluminum alloy) to remove surface oxide scale and impurities. Then, immerse them in a 5-7 wt% sodium hydroxide aqueous solution (40-45℃) for 3-5 minutes to dissolve the oxide film and activate the surface. Immediately neutralize with a 10-15 wt% nitric acid aqueous solution for 30-60 seconds to avoid excessive corrosion. Next, clean with aviation cleaning gasoline, primarily composed of C9-C12 straight-chain alkanes and isoalkanes (over 90%), supplemented with a small amount of aromatics (such as toluene, usually ≤5%) and trace detergents. Finally, clean with 99.5% distilled alcohol. Dry in a 90-100℃ drying oven for 20-30 minutes, ensuring a surface roughness Ra ≤ 0.6 μm, oxide film thickness ≤ 5 nm, and oil residue ≤ 3 mg / m³. 2 Furthermore, laser inspection confirmed the absence of scratches or cracks with a depth greater than 0.05 mm. S2: Preparation and coating of alloy brazing filler metal. The alloy brazing filler metal is prepared with the following mass percentage composition: Al 88%~92%, Si 6%~8%, Cu 1%~2%, Zn 0.5%~1%, rare earth element Ce 0.3%~0.5%, and Ti 0.2%~0.4%. The alloy brazing filler metal is made into powder and mixed with an organic binder to form a paste-like brazing filler metal. The paste is then uniformly coated onto the surface to be soldered, with a coating thickness of 0.3~0.4mm. The alloy brazing powder has a particle size of 30-80 μm, and the organic binder is made by mixing ethyl cellulose, turpentine oil and ethanol in a mass ratio of 4:10:86.

[0020] The mass ratio of alloy brazing powder to organic binder is 10:1. This step specifically involves designing an Al-Si based cryogenic alloy brazing filler metal suitable for aluminum alloy pump impellers. The mass percentage composition is as follows: Al 88%–92%, Si 6%–8%, Cu 1%–2%, Zn 0.5%–1%, rare earth element Ce 0.3%–0.5%, and Ti 0.2%–0.4%. Si lowers the filler metal's melting point to approximately 290℃, Cu increases welding strength, Zn improves wettability, Ce refines the filler metal microstructure and inhibits the formation of brittle phases, and Ti promotes metallurgical bonding between the filler metal and the base metal. The components are melted and mixed at 700–750℃ under argon protection, and then atomized into a 30–80 μm powder. This powder is then mixed with an organic binder (ethyl cellulose: turpentine: ethanol = 4:10:86) at a mass ratio of 10:1 to form a paste-like filler metal.

[0021] Considering the narrow space between the pump impeller blades and the hub, the solder paste is evenly applied to the surface to be soldered and the gap of 0.1 to 0.2 mm, with a coating thickness of 0.3 to 0.4 mm, to ensure that the solder fills the gap fully and does not interfere with the internal flow channel of the pump impeller.

[0022] S3: Argon-protected gradient heating brazing. The assembled and fixed aluminum alloy pump wheel is placed in a vacuum brazing furnace. Argon gas with a purity of ≥99.995% is introduced to make the oxygen content in the furnace ≤30ppm. The gradient heating mode is used to heat to the brazing temperature of 290~310℃ and hold for 40~50 minutes. The pressure in the furnace is controlled at 0.12~0.15MPa and the argon gas flow rate is 12~18L / min. The gradient heating mode is as follows: from room temperature to 120℃, the heating rate is 6~8℃ / min; from 120 to 220℃, the heating rate is 4~6℃ / min; from 220℃ to the brazing temperature, the heating rate is 1~1.5℃ / min.

[0023] The vacuum degree of the vacuum brazing furnace is ≤5×10 -3 Pa, during the heating process, the oxygen content and temperature uniformity in the furnace are monitored in real time, and the temperature uniformity error in the front, middle and rear zones of the brazing furnace is ≤±2℃.

[0024] This step specifically involves placing the assembled and fixed aluminum alloy pump wheel into a vacuum brazing furnace (vacuum degree ≤ 5×10). - 3 Argon gas with a purity ≥99.995% was introduced into the furnace to purge the air for at least 20 minutes, ensuring the oxygen content inside the furnace was ≤30ppm to prevent aluminum alloy oxidation during brazing. A precise gradient heating mode was used to control thermal stress: from room temperature to 120℃, the temperature was increased at a rate of 6–8℃ / min to quickly remove moisture from the binder; from 120–220℃, the temperature was increased at a rate of 4–6℃ / min to allow the binder to slowly decompose and be expelled; from 220℃ to 290–310℃, the brazing temperature was increased at a rate of 1–1.5℃ / min to ensure uniform melting of the brazing filler metal and prevent localized overheating. After reaching the brazing temperature, the furnace was held for 40–50 minutes to allow the brazing filler metal to fully wet and diffuse with the aluminum alloy base material, forming a strong metallurgical bond layer. During brazing, the furnace pressure was controlled at 0.12–0.15MPa, the argon gas flow rate at 12–18L / min, and the temperature uniformity was monitored in real time, with the error in the front, middle, and rear zones controlled within ±2℃.

[0025] S4: Segmented isothermal cooling. After the heat preservation is completed, the furnace is first isothermally cooled at 210-230℃ for 25-35 minutes, then cooled at a rate of 2-4℃ / min to below 80℃, and finally cooled to ambient temperature with the furnace. Argon gas is kept running throughout the process. The specific steps are as follows: After the heat preservation is completed, in order to avoid thermal stress cracking or pump wheel deformation caused by rapid cooling, the furnace is first isothermally cooled at 210-230℃ for 25-35 minutes to promote the homogenization of the brazing filler metal structure and stress release; then it is cooled to below 80℃ at a rate of 2-4℃ / min to further reduce residual stress; finally, it is cooled to ambient temperature with the furnace, and argon gas is continuously introduced throughout the process to prevent oxidation of the joint surface during the cooling process.

[0026] S5: Post-weld integrated treatment, removal of residues and cleaning, followed by stress relief treatment, and finally anodizing of the entire aluminum alloy pump wheel to form an oxide film with a thickness of 5-8 μm.

[0027] Residues are removed manually, followed by rinsing under tap water for at least 10 minutes.

[0028] The stress-relief treatment temperature is 130–160℃, and the holding time is 80–100 minutes; the electrolyte for anodizing is a 15–20 wt% sulfuric acid solution, the temperature is 18–22℃, and the current density is 1–2 A / dm³. 2 The time is 20 to 30 minutes.

[0029] After anodizing, the aluminum alloy pump wheel is dissected and inspected to check whether the internal microstructure of the aluminum alloy pump wheel has been overburned.

[0030] This step specifically involves: manually removing residual flux and oxide scale, and rinsing under tap water for at least 10 minutes; followed by stress relief treatment (temperature 130–160℃, holding for 80–100 minutes); finally, anodizing the entire pump impeller (electrolyte: 15–20 wt% sulfuric acid solution, temperature 18–22℃, current density 1–2 A / dm³). 2 (The time is 20 to 30 minutes) to form an oxide film with a thickness of 5 to 8 μm.

[0031] Example 2 Take the brazing of 6061 aluminum alloy pump wheel (blade) and 2A12 aluminum alloy hub as an example.

[0032] Pretreatment: The surface to be welded was sanded with 1800-grit sandpaper, then alkaline washed with 5wt% NaOH at 42℃ for 4 min, neutralized with 12wt% HNO3 for 38 s, cleaned with aviation cleaning gasoline (C9~C12 alkanes ≥92%), cleaned with 99.5% ethanol, and dried at 95℃ for 25 min. Laser inspection showed no defects >0.05mm, Ra≈0.5μm, and oxide film thickness ≤4nm.

[0033] Solder preparation: The solder was prepared by mixing Al 90%, Si 7%, Cu 1.5%, Zn 0.8%, Ce 0.4%, and Ti 0.3% in an argon atmosphere at 730℃, and then atomizing it to obtain a powder with a particle size of 50μm. A binder (ethyl cellulose: turpentine: ethanol = 4:10:86) was mixed with the powder at a ratio of 1:10 to form a paste, and a coating thickness of 0.35mm was applied.

[0034] Brazing: Place in a vacuum furnace (vacuum degree 3×10) -3(Pa), purge with argon gas for 20 min until oxygen content reaches 25 ppm. Gradient heating: room temperature to 120℃ (7℃ / min), 120~220℃ (5℃ / min), 220~300℃ (1.2℃ / min); hold at 300℃ for 45 min, furnace pressure 0.13MPa, argon gas flow rate 15L / min. Temperature difference between zones ±1.5℃.

[0035] Cooling: Isothermal at 220℃ for 30 minutes, then cool to 80℃ at 3℃ / min, and then cool to room temperature with the furnace, with argon flowing through the furnace throughout the process.

[0036] Post-treatment: Manual slag removal, rinsing with tap water for 12 min; stress relief at 150℃ for 90 min; anodizing (18wt% H2SO4, 20℃, 1.5A / dm). 2 (25 min), oxide film thickness 6.5 μm.

[0037] Test results: shear strength 312MPa, corrosion rate 0.008mm / a, deformation 0.015mm, production efficiency increased by 62%, and incomplete penetration rate 0.3%.

[0038] Example 3 The procedure was basically the same as in Example 1, except that the brazing temperature was adjusted to 290℃ for 50 minutes and the stress relief temperature was adjusted to 130℃ for 100 minutes. The shear strength was measured to be 305 MPa, the corrosion rate to be 0.009 mm / a, and the deformation to be 0.018 mm.

Claims

1. A low-temperature brazing method for aluminum alloy pump impellers, characterized in that: Includes the following steps: S1: Precision pretreatment of the surfaces to be welded. Take an aluminum alloy pump wheel and sequentially perform mechanical grinding, alkaline washing, neutralization, aviation-grade gasoline cleaning, distilled alcohol cleaning, and drying on the surfaces to be welded, ensuring that the surface roughness Ra is ≤0.6μm, the oxide film thickness is ≤5nm, and the oil residue is ≤3mg / m². 2 ; S2: Preparation and coating of alloy brazing filler metal. The alloy brazing filler metal is prepared with the following mass percentage composition: Al 88%~92%, Si 6%~8%, Cu 1%~2%, Zn 0.5%~1%, rare earth element Ce 0.3%~0.5%, and Ti 0.2%~0.4%. The alloy brazing filler metal is made into powder and mixed with an organic binder to form a paste-like brazing filler metal. The paste is then uniformly coated onto the surface to be soldered, with a coating thickness of 0.3~0.4mm. S3: Argon-protected gradient heating brazing. The assembled and fixed aluminum alloy pump wheel is placed in a vacuum brazing furnace. Argon gas with a purity of ≥99.995% is introduced to make the oxygen content in the furnace ≤30ppm. The gradient heating mode is used to heat to the brazing temperature of 290~310℃ and hold for 40~50 minutes. The pressure in the furnace is controlled at 0.12~0.15MPa and the argon gas flow rate is 12~18L / min. S4: Segmented isothermal cooling. After the heat preservation is completed, the furnace is first isothermally cooled at 210-230℃ for 25-35 minutes, then cooled at a rate of 2-4℃ / min to below 80℃, and finally cooled to ambient temperature with the furnace. Argon gas is kept running throughout the process. S5: Post-weld integrated treatment, removal of residues and cleaning, followed by stress relief treatment, and finally anodizing of the entire aluminum alloy pump wheel to form an oxide film with a thickness of 5-8 μm.

2. The low-temperature brazing method for aluminum alloy pump impellers according to claim 1, characterized in that: In step S1, the mechanical polishing uses 1500-2000 grit sandpaper, the alkaline washing uses a 5-7 wt% sodium hydroxide aqueous solution at 40-45°C for 5-8 minutes, the neutralization uses a 10-15 wt% nitric acid aqueous solution for 30-60 seconds, the aviation washing gasoline is mainly composed of C9-C12 straight-chain alkanes and isoalkanes, accounting for more than 90%, the distilled alcohol purity is 99.5%, and the drying is carried out at 90-100°C for 20-30 minutes.

3. The low-temperature brazing method for aluminum alloy pump impellers according to claim 1, characterized in that: In step S1, after mechanical grinding, the surface to be welded is subjected to laser inspection to ensure that there are no scratches, cracks and inclusions with a depth greater than 0.05mm.

4. The low-temperature brazing method for aluminum alloy pump impellers according to claim 1, characterized in that: In step S2, the particle size of the alloy brazing powder is 30-80 μm, and the organic binder is made by mixing ethyl cellulose, turpentine oil, and ethanol in a mass ratio of 4:10:

86.

5. The low-temperature brazing method for aluminum alloy pump impellers according to claim 1, characterized in that: In step S2, the mass ratio of the alloy brazing powder to the organic binder is 10:

1.

6. The low-temperature brazing method for aluminum alloy pump impellers according to claim 1, characterized in that: In step S3, the gradient heating mode is specifically as follows: from room temperature to 120°C, the heating rate is 6-8°C / min; from 120°C to 220°C, the heating rate is 4-6°C / min; from 220°C to the brazing temperature, the heating rate is 1-1.5°C / min.

7. The low-temperature brazing method for aluminum alloy pump impellers according to claim 1, characterized in that: In step S3, the vacuum degree of the vacuum brazing furnace is ≤5×10⁻⁶. -3 Pa, during the heating process, the oxygen content and temperature uniformity in the furnace are monitored in real time, and the temperature uniformity error in the front, middle and rear zones of the brazing furnace is ≤±2℃.

8. The low-temperature brazing method for aluminum alloy pump impellers according to claim 1, characterized in that: In step S5, the residue is removed manually by rinsing under tap water for at least 10 minutes.

9. The low-temperature brazing method for aluminum alloy pump impellers according to claim 1, characterized in that: In step S5, the stress-relief treatment temperature is 130–160°C, and the holding time is 80–100 minutes; the electrolyte for the anodizing treatment is a 15–20 wt% sulfuric acid solution, the temperature is 18–22°C, and the current density is 1–2 A / dm³. 2 The time is 20 to 30 minutes.

10. The low-temperature brazing method for aluminum alloy pump impellers according to claim 1, characterized in that: In step S5, after the anodizing treatment, the aluminum alloy pump wheel is dissected and inspected to check whether the internal microstructure of the aluminum alloy pump wheel is overburned.