Lock nut for bonding of permanent magnet motor and preparation method of lock nut

Abstract

The invention belongs to the technical field of electrical connection of mechanical fasteners and new energy automobiles, and particularly relates to a locknut for bonding of a permanent magnet motor and a preparation method of the locknut. The nut is made of Cu-Al-Ti-Zr-W-Ni alloy and comprises, by mass, 82%-86% of copper (Cu), 3%-5% of aluminum (Al), 2%-3% of titanium (Ti), 0.5%-1.5% of zirconium (Zr), 0.5%-1% of tungsten (W), 1%-2% of nickel (Ni), 0.1%-0.5% of rare earth elements and smaller than or equal to 0.1% of iron (Fe). The alloy microstructure is optimized through the vacuum melting and hot isostatic pressing (HIP) technology, and the high-temperature strength, corrosion resistance and fatigue resistance of the nut are improved. The locknut is suitable for high-vibration, high-temperature and corrosive environments, and is widely applied to new energy automobiles and other electrical systems.

Description

Technical Field

[0001] The present invention belongs to the technical fields of mechanical fasteners and new energy vehicle electrical connections, and particularly relates to a locknut for grounding of a permanent magnet motor and a preparation method thereof. Background Art

[0002] As the development direction of future means of transportation, the breakthrough of core technologies in new energy vehicles is crucial for improving the overall vehicle performance, extending the service life, and ensuring operation safety. Among them, the permanent magnet motor is an important component of new energy vehicles, and its performance and stability directly affect power output, energy consumption efficiency, and reliability. In the grounding system of the permanent magnet motor, the nut, as a key connecting part, its stability and reliability are the core factors to ensure the normal operation of the motor.

[0003] The permanent magnet motor of new energy vehicles often operates in a high-vibration environment, especially under high-speed operation or uneven road conditions, and the grounding components are easily subjected to continuous vibration and impact. This vibration will gradually loosen the traditional nut, ultimately resulting in the failure of the grounding connection. The loose nut will not only affect current conduction but may also cause mechanical failures or safety hazards. Currently, common anti-loosening measures in the market include adding spring washers, anti-loosening adhesives, or using materials with a high coefficient of friction. However, these methods have limited effects, especially under complex working conditions of high vibration and high temperature, it is difficult to maintain the anti-loosening performance of the nut for a long time.

[0004] Furthermore, the grounding nut not only needs to provide mechanical connection but also ensure efficient current conduction. However, traditional nut materials (such as carbon steel or stainless steel) have obvious deficiencies in practical applications due to their low electrical conductivity. Especially during long-term use or in a high-vibration environment, oxidation and wear are likely to occur on the nut surface, resulting in an increase in contact resistance and affecting the stability and efficiency of the electrical system.

[0005] In addition, the grounding nut of the permanent magnet motor of new energy vehicles usually operates in a high-temperature environment (it may exceed 250°C during motor operation). Traditional materials are prone to the following problems at high temperatures: 1. Decrease in mechanical strength: High temperature softens the material, reducing the connection stability; 2. Accelerated oxidation: Under high-temperature conditions, oxidation reactions are more likely to occur on the nut surface, further affecting its electrical conductivity. Therefore, a nut material that can withstand high temperatures for a long time and maintain high strength is required to meet the harsh working conditions of new energy vehicles. During the start-up and stop processes of new energy vehicle motors, the grounding nut will experience frequent temperature changes (thermal cycles) and long-term vibration effects. Ordinary materials are prone to fatigue damage under these conditions, resulting in a decrease in mechanical properties and further increasing the risk of connection failure. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides a locknut for grounding of a permanent magnet motor, which significantly improves the comprehensive performance of the nut by using a Cu-Al-Ti-Zr-W-Ni alloy material. In the composition design of this alloy, by adding strengthening elements such as tungsten (W) and nickel (Ni), and combining the synergistic effects of aluminum (Al), titanium (Ti) and zirconium (Zr), the nut still has excellent anti-loosening property, electrical conductivity, corrosion resistance and fatigue resistance under complex working conditions such as high vibration, high temperature, high humidity and salt spray.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A locknut for grounding of a permanent magnet motor, the locknut is made of Cu-Al-Ti-Zr-W-Ni alloy, and the mass percentages of the alloy are as follows:

[0009] Copper (Cu): 82 - 86%;

[0010] Aluminum (Al): 3 - 5%;

[0011] Titanium (Ti): 2 - 3%;

[0012] Zirconium (Zr): 0.5 - 1.5%;

[0013] Tungsten (W): 0.5 - 1%;

[0014] Nickel (Ni): 1 - 2%;

[0015] Rare earth elements: 0.1 - 0.5%;

[0016] Iron (Fe): ≤0.1%.

[0017] Preferably, the rare earth element is Ce or La; the addition amount of the rare earth element is 0.3%.

[0018] Preferably, the nut adopts an oval internal thread, and the surface of the nut is coated with a composite functional coating, which is composed of a bottom layer and an outer layer: the bottom layer is a nano-silver conductive coating, and the coating material of the nano-silver conductive coating includes silver nanoparticles, high-conductive resin, dispersant and solvent, and the thickness of the bottom layer coating is 2 - 5μm; the outer layer is a corrosion-resistant and wear-resistant coating, and the coating material of the outer layer coating includes 50 - 70% fluorocarbon resin, 20 - 30% ceramic particles, 1 - 3% hydrophobic additive and 1 - 2% auxiliary agent, and the coating thickness is 8 - 12μm.

[0019] Preferably, the electrical conductivity of the nano-silver conductive coating is above 75% of the International Annealed Copper Standard (IACS), and the contact resistance is less than 0.5mΩ.

[0020] Preferably, the coating material of the nano-silver conductive coating consists of the following components by mass percentage:

[0021] Silver nanoparticles (Ag NPs): 60 - 80%

[0022] Highly conductive resin: 10 - 20%

[0023] Dispersant: 1 - 3%

[0024] Solvent: 10 - 15%

[0025] Curing accelerator: 1 - 3%

[0026] Antioxidant additive: 0.5 - 1%.

[0027] Preferably, the particle size of the silver nanoparticles is 20 - 50 nm; the highly conductive resin is selected from epoxy resin (Epoxy Resin) or polyurethane (PU) resin; the dispersant is selected from polyvinylpyrrolidone (PVP) or polyethylene glycol (PEG); the solvent is selected from isopropyl alcohol (IPA), ethylene glycol monomethyl ether (EGME) or dimethyl sulfoxide (DMSO); the curing accelerator is selected from triethylamine (TEA) or catechol; the antioxidant additive is selected from dopamine (Dopamine) or antioxidant BHT.

[0028] Preferably, the coating material of the outer layer coating consists of the following components by mass percentage:

[0029] Fluorocarbon resin: 50 - 70%

[0030] Ceramic microparticles: 20 - 30%

[0031] Crosslinking agent: 5 - 10%

[0032] Solvent: 10 - 15%

[0033] Hydrophobic additive: 1 - 3%

[0034] Auxiliary agent: 1 - 2%.

[0035] Preferably, the fluorocarbon resin is selected from polyvinylidene fluoride (PVDF) or fluorinated ethylene propylene (FEVE); the particle size of the ceramic microparticles is 1 - 5 μm, and it is selected from silicon dioxide (SiO2), aluminum oxide (Al2O3) or boron nitride (BN); the crosslinking agent is selected from isocyanate crosslinking agents or amino resins; the solvent is selected from ethylene glycol monomethyl ether acetate (EGMEA), dimethyl sulfoxide (DMSO), acetone or butanone; the hydrophobic additive is selected from fluorine-modified nanoparticles or polysiloxanes; the auxiliary agent is a dispersant, a leveling agent and an antioxidant. The dispersant is selected from the BYK series or Dow Chemical dispersants, the leveling agent is selected from polyether-modified silicone oil, and the antioxidant is selected from BHT.

[0036] Preferably, the Cu-Al-Ti-Zr-W-Ni alloy is prepared by vacuum melting and hot isostatic pressing (HIP) technology.

[0037] Furthermore, the present invention also discloses a method for preparing the anti-loosening nut, which method comprises the following steps:

[0038] Step 1: Preparation of Cu-Al-Ti-Zr-W-Ni alloy

[0039] 1) Weigh high-purity copper (Cu), aluminum (Al), titanium (Ti), zirconium (Zr), tungsten (W), nickel (Ni), rare earth element (Ce or La) and trace iron (Fe) according to the formula ratio;

[0040] 2) In a vacuum induction melting furnace, first add the copper-based material and heat it to 1150 - 1250 °C for melting;

[0041] 3) Gradually add aluminum, titanium, zirconium, tungsten, and nickel elements to ensure thorough mixing of the materials, and maintain vacuum or inert gas protection during the melting process;

[0042] 4) Finally, add the rare earth element, stir evenly and keep warm for 10 minutes to promote grain refinement;

[0043] 5) Pour the molten alloy liquid into a metal mold preheated to 250 - 300 °C and quickly cool it to room temperature to form a preliminary alloy ingot;

[0044] 6) Place the alloy ingot in a hot isostatic pressing device and process it for 1 - 3 hours under the conditions of high temperature 900 - 1100 °C and high pressure 100 - 150 MPa to eliminate internal pores and optimize the grain structure;

[0045] 7) Perform turning, drilling, and threading on the heat-treated alloy ingot to prepare a nut blank that meets the design requirements;

[0046] Step 2: Nut forming

[0047] 8) Use a high-precision CNC lathe to perform elliptical threading on the inner hole of the nut;

[0048] 9) Polish and surface-treat the whole nut, and control the roughness to Ra < 0.8 μm to improve the coating adhesion;

[0049] Step 3: Surface coating treatment

[0050] 10) Add silver nanoparticles (particle size 20 - 50 nm) to the solvent at a mass ratio of 60 - 80%, add a dispersant and ultrasonically disperse for 30 minutes; add 10 - 20% of high-conductive epoxy resin and a curing accelerator, and stir evenly to form a stable coating;

[0051] 11) Apply a coating to the nut blank through electrophoretic coating technology to ensure a uniform coating thickness of 2 - 5 μm; cure at 250 °C for 10 minutes to form a dense conductive coating;

[0052] 12) Mix fluorocarbon resin, ceramic particles, hydrophobic additives, and solvents, add dispersants and antioxidants, and stir evenly; stir at 1000 - 2000 rpm for 30 minutes through a high - speed dispersion device to form a stable suspension;

[0053] 13) Apply an outer coating to the nut with a bottom conductive coating by dip - coating process, control the coating thickness at 8 - 12 μm; cure at 200 °C for 30 minutes to ensure the corrosion - resistance and wear - resistance of the coating.

[0054] Due to the adoption of the above - mentioned technical solutions, by using Cu - Al - Ti - Zr - W - Ni alloy as the material of the locking nut, multiple performance optimizations of the nut under complex working conditions are achieved. The following are the specific technical effects brought by the alloy formula:

[0055] 1. Excellent high - temperature strength and thermal stability: Tungsten (W) and nickel (Ni) are added to the alloy, significantly improving the high - temperature strength and thermal stability of the material, enabling it to maintain mechanical properties without attenuation in an environment above 250 °C. Even under long - term high - temperature operating conditions, the nut still has excellent thermal stability and reliability.

[0056] 2. High electrical conductivity: The copper content in the alloy is as high as 82 - 86%, providing electrical conductivity close to that of pure copper, and the conductivity reaches more than 75% of the International Annealed Copper Standard (IACS). The introduction of rare - earth elements (Ce or La) further optimizes the grain structure of the material, improving the stability of electrical conductivity. Even in a long - term vibration and oxidation environment, the contact resistance can still be maintained below 0.5 mΩ.

[0057] 3. Excellent corrosion - resistance: The synergistic effect of aluminum (Al), titanium (Ti), and zirconium (Zr) elements forms a dense oxide film on the material surface, greatly enhancing the corrosion - resistance of the nut. In the neutral salt spray test, the nut can withstand a corrosive environment for more than 3000 hours without significant performance degradation.

[0058] 4. High strength and fatigue - resistance: The strengthening effect of titanium (Ti) and zirconium (Zr) elements significantly improves the yield strength and fatigue - resistance of the material. The application of vacuum melting and hot isostatic pressing (HIP) technology refines the grain structure of the alloy, enabling the nut to maintain high strength and reliability under long - term high - frequency vibration and thermal cycling conditions.

[0059] 5. Comprehensive improvement of integrated performance: Through the multi-component ratio design of copper, tungsten, nickel, aluminum, titanium, zirconium, and rare earth elements in the alloy, the nut simultaneously exhibits high strength, high electrical conductivity, corrosion resistance, and fatigue resistance. This material optimizes the overall performance of the nut and meets the comprehensive requirements of high-vibration, high-temperature, and corrosive environments.

[0060] 6. Balancing lightweight and economy: The introduction of aluminum (Al) in the alloy not only enhances the corrosion resistance but also significantly reduces the density, achieving the lightweight design of the nut. The optimized alloy formula takes into account both performance and cost, making it suitable for large-scale industrial production. Detailed implementation manners

[0061] Combined with the embodiments of the present invention, the technical solutions in the embodiments will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0062] Embodiment 1

[0063] Alloy formula (mass percentage)

[0064] Copper (Cu): 83.5%

[0065] Aluminum (Al): 4%

[0066] Titanium (Ti): 2%

[0067] Zirconium (Zr): 1%

[0068] Tungsten (W): 0.5%

[0069] Nickel (Ni): 1%

[0070] Rare earth element (Ce): 0.3%

[0071] Iron (Fe): ≤0.1%;

[0072] Preparation method:

[0073] 1. Alloy melting

[0074] Weigh high-purity raw materials according to the formula, and melt the copper-based material at 1200°C in a vacuum induction melting furnace. Then, add aluminum, titanium, zirconium, tungsten, nickel, and rare earth elements in sequence, stir evenly, keep warm for 10 minutes, and quickly pour the mixture into a metal mold preheated to 250°C.

[0075] 2. Hot isostatic pressing (HIP) treatment

[0076] Place the preliminary alloy ingot in a hot isostatic pressing equipment and process it at 1000 °C and 120 MPa for 2 hours to optimize the grain structure and eliminate internal pores.

[0077] 3. Machining

[0078] Turn and thread the alloy ingot, adopting an oval thread design; polish the surface of the nut, and control the roughness to Ra < 0.8 μm.

[0079] 4. Surface coating treatment

[0080] Coat a nano-silver conductive coating (thickness 3 μm) on the bottom layer. The coating is prepared by an electrophoresis process and cured at 250 °C for 10 minutes; coat a corrosion-resistant and wear-resistant coating (thickness 10 μm) on the outer layer, which is prepared by a dip-coating process and cured at 200 °C for 30 minutes.

[0081] The formula of the bottom nano-silver conductive coating is as follows:

[0082] Components Percentage (%) Description Silver nanoparticles (Ag NPs) 75 Provide high conductivity, particle size 20 - 50 nm High - conductive resin 15 Epoxy Resin or Polyurethane (PU) Dispersant (PVP or PEG) 2 Improve the dispersibility of nanoparticles Solvent (IPA or EGME) 7 Provide fluidity for easy coating Curing accelerator (TEA or Catechol) 0.8 Accelerate curing and improve coating adhesion Antioxidant additive (Dopamine or BHT) 0.2 Enhance antioxidant performance

[0083] The preparation process is as follows:

[0084] 1) Dispersion process:

[0085] Add a dispersant (PVP) to a solvent (IPA or EGME) and stir at high speed (1200 rpm) for 15 minutes;

[0086] Add silver nanoparticles and ultrasonically disperse for 30 minutes until evenly distributed.

[0087] 2) Coating mixing:

[0088] Add a highly conductive resin and stir for 60 minutes until completely mixed; finally, add a curing accelerator and an antioxidant additive, and continue to stir for 30 minutes.

[0089] 3) Coating process:

[0090] Coat the nano-silver coating on the blank of the locknut by electrophoresis technology. The coating time is 30 seconds and the voltage is 70 V; control the coating thickness to 3 μm; cure at 250 °C for 10 minutes.

[0091] The formula of the outer corrosion-resistant and wear-resistant coating is as follows:

[0092] Components Percentage (%) Description Fluorocarbon resin (PVDF or FEVE) 60 Provide corrosion resistance and weather resistance <![CDATA[Ceramic particles (SiO2 or Al2O3)]]> 25 Improve wear - resistance performance, particle size 1 - 5 μm Cross - linker (isocyanates) 8 Improve coating hardness and mechanical strength Solvent (EGMEA or acetone) 5 Provide fluidity for easy coating Hydrophobic additive (modified nanoparticles) 1.5 Provide self - cleaning ability and enhance hydrophobic performance Auxiliary agents (dispersant, leveling agent, antioxidant) 0.5 Improve paint dispersibility and flatness

[0093] The preparation process is as follows:

[0094] 1) Dispersion process:

[0095] Add a dispersant and ceramic particles to a solvent (EGMEA or acetone) and stir for 15 minutes; further disperse for 30 minutes by high-speed stirring (1500 rpm).

[0096] 2) Coating mixture:

[0097] Add fluorocarbon resin and a crosslinking agent and stir for 60 minutes; finally add a hydrophobic additive and additives and continue stirring for 30 minutes.

[0098] 3) Coating process:

[0099] Dip coat the nuts with a bottom conductive coating, slowly take them out after 5 seconds of dipping; control the coating thickness to be 10 μm; cure at 200 °C for 30 minutes.

[0100] Example 2

[0101] Alloy formula (mass percentage)

[0102] Copper (Cu): 85%

[0103] Aluminum (Al): 3%

[0104] Titanium (Ti): 2.5%

[0105] Zirconium (Zr): 1.2%

[0106] Tungsten (W): 0.8%

[0107] Nickel (Ni): 1.2%

[0108] Rare earth element (La): 0.3%

[0109] Iron (Fe): ≤0.05%.

[0110] The preparation method refers to Example 1.

[0111] Example 3

[0112] Alloy formula (mass percentage)

[0113] Copper (Cu): 84%

[0114] Aluminum (Al): 3.5%

[0115] Titanium (Ti): 2.2%

[0116] Zirconium (Zr): 0.8%

[0117] Tungsten (W): 1%

[0118] Nickel (Ni): 1.5%

[0119] Rare earth element (Ce + La mixture): 0.3% Iron (Fe): ≤0.1%.

[0120] The preparation method can be referred to Example 1.

[0121] Comparative Example 1

[0122] Alloy formula (mass percentage)

[0123] Copper (Cu): 90%

[0124] Aluminum (Al): 2%

[0125] Titanium (Ti): 2%

[0126] Zirconium (Zr): 0.5%

[0127] Iron (Fe): ≤0.5%.

[0128] The preparation method can be referred to Example 1.

[0129] Comparative Example 2

[0130] Alloy formula (mass percentage)

[0131] Copper (Cu): 80%

[0132] Aluminum (Al): 5%

[0133] Titanium (Ti): 2%

[0134] Zirconium (Zr): 1%

[0135] Nickel (Ni): 2%.

[0136] The preparation method can be referred to Example 1.

[0137] Comparative Example 3

[0138] Alloy formula (mass percentage)

[0139] Copper (Cu): 85%

[0140] Aluminum (Al): 5%

[0141] Iron (Fe): 1%

[0142] No other elements were added.

[0143] The preparation method can be referred to Example 1.

[0144] Test Example 1

[0145] In order to verify the performance of the locknuts in the examples and comparative examples, we conducted experimental tests on the locknuts (without surface coating treatment), including mechanical property tests, electrical conductivity tests, and fatigue resistance tests. The following are the detailed experimental data and result analyses.

[0146] I. Material Formulation

[0147] Alloy formulations of the examples and comparative examples (mass percentage)

[0148] Components Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Copper (Cu) 83.5％ 85％ 84％ 90％ 80％ 85％ Aluminum (Al) 4％ 3％ 3.5％ 2％ 5％ 5％ Titanium (Ti) 2％ 2.5％ 2.2％ 2％ 2％ —— Zirconium (Zr) 1％ 1.2％ 0.8％ 0.5％ 1％ —— Tungsten (W) 0.5％ 0.8％ 1％ —— —— —— Nickel (Ni) 1％ 1.2％ 1.5％ —— 2％ —— Rare earth elements 0.3％ 0.3％ 0.3％ —— —— —— Iron (Fe) ≤0.1％ ≤0.05％ ≤0.1％ ≤0.5％ ≤0.1％ 1％

[0149] II. Test Items and Methods

[0150] 1. Mechanical Property Test

[0151] Test Standard: In accordance with GB / T 228.1-2010 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature".

[0152] Test Items: Ultimate tensile strength (UTS), Yield strength (YS), Elongation

[0153] 2. Electrical Conductivity Test

[0154] 1) Determination of Electrical Conductivity

[0155] Test Standard: GB / T 3048.2-2007

[0156] Test Equipment: Four-probe electrical conductivity meter

[0157] Test Conditions: Room temperature 25°C

[0158] Test Index: Electrical conductivity (%IACS)

[0159] 2) Determination of Contact Resistance

[0160] Test Standard: GB / T 24343-2009

[0161] Test Method: Adopt four-terminal contact resistance measurement method, the nut is fastened on the surface of the standard copper conductor, and a pre-tightening force (recommended 50 Nm) is applied

[0162] 3. Corrosion Resistance Test

[0163] Test Standard: In accordance with ASTM B117-16 "Salt Spray Test"

[0164] Test Items: Neutral salt spray test time (hours), surface corrosion condition

[0165] 4. Fatigue Resistance Test

[0166] Test Standard: In accordance with GB / T 3075-2008 "Metallic materials - Fatigue testing - Axial force controlled method"

[0167] Test Items: Fatigue life (number of cycles)

[0168] 5. High-temperature Performance Test

[0169] Test standard: Measure the tensile strength and electrical conductivity in a high-temperature environment of 250°C.

[0170] Test items: High-temperature tensile strength, high-temperature electrical conductivity.

[0171] III. Test results

[0172] 1. Test results of mechanical properties

[0173] Performance indicators Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Tensile strength (MPa) 480 500 490 380 420 350 Yield strength (MPa) 380 400 390 300 320 280 Elongation (%) 18 17 17.5 22 20 25

[0174] Analysis: The tensile strength and yield strength of the examples are significantly higher than those of the comparative examples. In particular, the tensile strength of Example 2 reaches 500 MPa, meeting the high-strength requirements. The strength of the comparative examples is relatively low, making it difficult to maintain a stable connection in a high-vibration environment.

[0175] 2. Test results of electrical conductivity

[0176] Performance indicators Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Conductivity (%IACS) 75 74 73 78 65 70 Contact resistance (mΩ) 0.4 0.38 0.42 0.35 0.6 0.5

[0177] Analysis: The electrical conductivity of the examples is between 73 - 75% IACS, and the contact resistance is lower than 0.5 mΩ, meeting the high-conductivity requirements. The electrical conductivity of Comparative Example 2 is only 65% IACS, and the contact resistance is relatively high, which is not conducive to current conduction.

[0178] 3. Test results of corrosion resistance

[0179]

[0180]

[0181] Analysis: The examples show excellent corrosion resistance in the salt spray test, with no obvious corrosion after more than 3000 hours. Comparative Example 3 can only withstand 800 hours and shows obvious corrosion, indicating insufficient corrosion resistance.

[0182] 4. Test results of fatigue resistance

[0183] Performance indicators Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 <![CDATA[Fatigue life (10 6 cycles)]]> 10 12 11 5 6 4

[0184] Analysis: The fatigue life of the examples all exceeds 10^7 cycles, and the fatigue resistance is significantly better than that of the comparative examples. The fatigue life of the comparative examples is relatively low, and fatigue damage is likely to occur during long-term use.

[0185] 5. Test results of high-temperature performance (250°C)

[0186] Performance indicators Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 High - temperature tensile strength (MPa) 450 470 460 300 350 250 High - temperature conductivity (%IACS) 72 71 70 75 62 68

[0187] Analysis: The examples can still maintain high strength at a high temperature of 250°C, with the tensile strength only decreasing by about 6%, and the performance is stable. The high-temperature strength of the comparative examples decreases significantly and cannot meet the usage requirements under high-temperature environments.

[0188] IV. Conclusions

[0189] From the above experimental data, it can be seen that the locknuts prepared in Examples 1-3 are significantly superior to Comparative Examples 1-3 in terms of various performances. This verifies the effectiveness and superiority of the alloy formula of the present invention:

[0190] 1. Alloy formula optimization: By adding tungsten (W), nickel (Ni) and rare earth elements (Ce or La), the high-temperature strength, corrosion resistance and fatigue resistance of the material are improved.

[0191] 2. Preparation process: The application of vacuum melting and hot isostatic pressing (HIP) technology refines the grain structure, eliminates internal defects, and further improves the material performance.

[0192] 3. Comprehensive performance improvement: The locknuts in the examples can work stably for a long time in high-vibration, high-temperature and corrosive environments, meeting the strict requirements of the grounding of permanent magnet motors in new energy vehicles.

[0193] Test Example 2

[0194] I. Test Objectives

[0195] Verify the specific technical effects of the composite functional coating (bottom-layer nano-silver conductive coating, outer-layer fluorocarbon resin-ceramic corrosion-resistant and wear-resistant coating) coated on the surface of the locknut (the alloy composition adopts the formula of Example 2):

[0196] Bottom-layer coating: Verify whether the nano-silver conductive coating can effectively improve the electrical conductivity of the nut and reduce the contact resistance;

[0197] Outer-layer coating: Verify the corrosion resistance and wear resistance of the fluorocarbon resin-ceramic coating.

[0198] II. Preparation of Test Samples

[0199] Description of the setting of experimental samples:

[0200]

[0201]

[0202] III. Test Methods and Contents

[0203] (I) Conductivity Test

[0204] 1. Conductivity Measurement

[0205] Test standard: GB / T 3048.2 - 2007.

[0206] Test equipment: Four - probe conductivity meter.

[0207] Test conditions: Room temperature 25°C.

[0208] Test index: Conductivity (%IACS).

[0209] 2. Contact resistance measurement

[0210] Test standard: GB / T 24343 - 2009.

[0211] Test method: Adopt four - terminal contact resistance measurement method. The nut is fastened on the surface of the standard copper conductor, and a pre - tightening force (recommended 50 Nm) is applied.

[0212] Test index: Contact resistance (mΩ).

[0213] (2) Corrosion resistance test

[0214] 1. Corrosion electrochemistry test

[0215] Electrolyte: 3.5 wt% NaCl aqueous solution, room temperature (25°C).

[0216] Electrochemical workstation: Use the standard three - electrode system for testing (the working electrode is the nut sample, the reference electrode is the saturated calomel electrode SCE, and the counter electrode is the platinum sheet).

[0217] Test items:

[0218] Electrochemical impedance spectroscopy (EIS): Scanning frequency range: 10 5 ~10 -2 Hz.

[0219] Potentiodynamic polarization curve: Scanning rate 1 mV / s, test potential range: ±250 mV with respect to the reference electrode.

[0220] (3) Wear resistance test

[0221] 1. Friction and wear test

[0222] Test equipment: Pin - on - disk friction and wear testing machine;

[0223] Test conditions:

[0224] Friction pair material: GCr15 steel ball; Load: 10 N; Rotation speed: 300 r / min; Test time: 30 min;

[0225] Test content:

[0226] Determine the wear amount (weight loss method);

[0227] Observe the wear morphology of the coating (scanning electron microscope SEM).

[0228] (4) High-temperature stability test

[0229] Test temperature: 250 °C

[0230] Test time: Repeat the electrical conductivity test after 500 hours of high-temperature constant temperature;

[0231] Verification index: The electrical conductivity remains not less than 90% of the initial value; coating integrity, no obvious cracking or peeling.

[0232] IV. Data analysis method

[0233] Use statistical methods (SPSS, Origin) to analyze the test data and conduct a significant analysis of the differences between groups (t-test or ANOVA analysis, significance level P < 0.05).

[0234] V. Experimental data

[0235] (1) Electrical conductivity test data

[0236] Performance indicators Control Group 3 Control Group 1 Control Group 2 Experimental Group Conductivity (%IACS) 74.0 78.5 71.5 80.5 Contact resistance (mΩ) 0.38 0.18 1.80 0.15

[0237] Result analysis: The bottom layer coating significantly improves the electrical conductivity (the control group 1 and the experimental group are significantly higher than the control group 3), and only the outer layer coating hinders the electrical conductivity with a high contact resistance. The comprehensive electrical conductivity of the experimental group is the best.

[0238] (2) Corrosion electrochemistry test data:

[0239] Test indicators Control Group 3 Control Group 1 Control Group 2 Experimental Group Corrosion potential Ecorr (mV, vs.SCE) -325 -290 -180 -155 <![CDATA[Corrosion current density Icorr (μA / cm 2 )]]> 3.20 1.25 0.32 0.08

[0240] 1) Analysis of corrosion potential (Ecorr):

[0241] The Ecorr of the control group 3 (without coating) is the most negative, indicating the greatest corrosion tendency; the corrosion potential of the experimental group is the most positive, with the smallest corrosion tendency, indicating that the coating can effectively protect the substrate.

[0242] 2) Analysis of corrosion current density (Icorr):

[0243] The lower the corrosion current density, the higher the corrosion resistance; the corrosion current density of the experimental group is only 2.5% of the benchmark of the control group 3, and the corrosion rate is significantly reduced, showing excellent corrosion resistance. The control group 2 with only the outer layer coating also has an obvious protective effect, but it is slightly inferior to the experimental group; the control group 1 with only the bottom layer coating has limited corrosion inhibition effect.

[0244] (3) Wear resistance test data (pin-on-disk friction and wear test)

[0245]

[0246]

[0247] Result analysis: The outer coating significantly improved the wear resistance (the control group 2 and the experimental group performed outstandingly); only the wear resistance of the bottom coating was limitedly improved.

[0248] (4) High temperature stability test data (tested at 250°C for 500 hours)

[0249]

[0250] Analysis of results: The experimental group had the best high-temperature stability, the coating was intact and the conductivity was the most stable; only the bottom coating cracked, which had a slight impact on the electrical properties; only the outer coating had acceptable high-temperature oxidation resistance, but its conductivity was poor.

[0251] VI. Conclusion and Analysis:

[0252] 1. Bottom nano-silver conductive coating (control group 1): The conductivity is significantly improved, but the contribution to corrosion resistance and wear resistance is limited, and there is slight cracking at high temperature.

[0253] 2. Outer fluorocarbon resin corrosion-resistant and wear-resistant coating (control group 2): significantly improves corrosion resistance and wear resistance, but significantly reduces electrical conductivity due to the insulation of the material itself.

[0254] 3. Composite functional coating (experimental group): It has the advantages of bottom layer conductivity and outer layer corrosion resistance and wear resistance, and the comprehensive performance is greatly improved. The corrosion resistance, wear resistance and high temperature stability are significantly better than other groups, and the conductivity is further improved, which verifies the superiority of the composite functional coating solution in the patent.

[0255] The above is a description of the embodiments of the present invention. Through the above description of the disclosed embodiments, professionals and technicians in the field can implement or use the present invention. Various modifications to these embodiments will be apparent to professionals and technicians in the field. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown in this article, but will conform to the widest range consistent with the principles and novelties disclosed herein.

Claims

1. A locknut for grounding a permanent magnet motor of a new energy vehicle, characterized in that, The locknut is made of Cu-Al-Ti-Zr-W-Ni alloy, and the mass percentages of the alloy are as follows: Copper (Cu): 82 - 86%; Aluminum (Al): 3 - 5%; Titanium (Ti): 2 - 3%; Zirconium (Zr): 0.5 - 1.5%; Tungsten (W): 0.5 - 1%; Nickel (Ni): 1 - 2%; Rare earth element: 0.1 - 0.5%; Iron (Fe): ≤0.1%.

2. The locknut according to claim 1, characterized in that, The rare earth element is Ce or La; the addition amount of the rare earth element is 0.3%.

3. The locknut according to claim 1, wherein, The nut has an oval internal thread, and the nut surface is coated with a composite functional coating, which consists of a bottom layer and an outer layer: the bottom layer is a nano-silver conductive coating, and the coating material of the nano-silver conductive coating includes silver nanoparticles, high-conductive resin, dispersant and solvent, and the thickness of the bottom layer coating is 2 - 5 μm; the outer layer is a corrosion-resistant and wear-resistant coating, and the coating material of the outer layer coating includes 50 - 70% fluorocarbon resin, 20 - 30% ceramic particles, 1 - 3% hydrophobic additive and 1 - 2% auxiliary agent, and the coating thickness is 8 - 12 μm.

4. The locknut according to claim 2, wherein, The conductivity of the nano-silver conductive coating is more than 75% of the International Annealed Copper Standard (IACS), and the contact resistance is less than 0.5 mΩ.

5. The locknut according to claim 2, characterized in that, The coating material of the nano-silver conductive coating consists of the following components by mass percentage: Silver nanoparticles (Ag NPs): 60 - 80% High-conductive resin: 10 - 20% Dispersant: 1 - 3% Solvent: 10 - 15% Curing accelerator: 1 - 3% Antioxidant additive: 0.5 - 1%.

6. The locknut according to claim 5, characterized in that, The particle size of silver nanoparticles: 20 - 50 nm; the high-conductive resin is selected from epoxy resin (Epoxy Resin) or polyurethane (PU) resin; the dispersant is selected from polyvinylpyrrolidone (PVP) or polyethylene glycol (PEG); the solvent is selected from isopropyl alcohol (IPA), ethylene glycol methyl ether (EGME) or dimethyl sulfoxide (DMSO); the curing accelerator is selected from triethylamine (TEA) or catechol; the antioxidant additive is selected from dopamine or antioxidant BHT.

7. The locknut according to claim 2, wherein The coating material of the outer layer coating consists of the following components by mass percentage: Fluorocarbon resin: 50 - 70% Ceramic particles: 20 - 30% Crosslinking agent: 5 - 10% Solvent: 10 - 15% Hydrophobic additive: 1 - 3% Auxiliary agent: 1 - 2%.

8. The locknut according to claim 7, characterized in that, The fluorocarbon resin is selected from polyvinylidene fluoride (PVDF) or fluorinated ethylene propylene (FEVE); the particle size of the ceramic particles is 1 - 5 μm, and it is selected from silicon dioxide (SiO2), aluminum oxide (Al2O3) or boron nitride (BN); the crosslinking agent is selected from isocyanate crosslinking agents or amino resins; the solvent is selected from ethylene glycol methyl ether acetate (EGMEA), dimethyl sulfoxide (DMSO), acetone or butanone; the hydrophobic additive is selected from fluorine-modified nanoparticles or polysiloxanes; the auxiliary agent is a dispersant, a leveling agent and an antioxidant, the dispersant is selected from BYK series or Dow Chemical dispersants, the leveling agent is selected from polyether-modified silicone oil, and the antioxidant is selected from BHT.

9. The locknut according to claim 1, characterized in that, The Cu-Al-Ti-Zr-W-Ni alloy is prepared by vacuum melting and hot isostatic pressing (HIP) technology.

10. The preparation method of the locknut according to any one of claims 1-9, characterized in that, This method includes the following steps: Step 1: Preparation of Cu-Al-Ti-Zr-W-Ni alloy 1) Weigh high-purity copper (Cu), aluminum (Al), titanium (Ti), zirconium (Zr), tungsten (W), nickel (Ni), rare earth element (Ce or La) and trace iron (Fe) according to the formula ratio; 2) In a vacuum induction melting furnace, first add the copper-based material and heat it to 1150 - 1250 °C to melt; 3) Gradually add aluminum, titanium, zirconium, tungsten, and nickel elements to ensure thorough mixing of the materials, and maintain vacuum or inert gas protection during the melting process; Finally, add the rare earth element, stir evenly and keep warm for 10 minutes to promote grain refinement; 5) Pour the molten alloy liquid into a metal mold preheated to 250 - 300 °C, and quickly cool it to room temperature to form a preliminary alloy ingot; 6) Place the alloy ingot in a hot isostatic pressing device, and process it at a high temperature of 900 - 1100 °C and a high pressure of 100 - 150 MPa for 1 - 3 hours to eliminate internal pores and optimize the grain structure; 7) Perform turning, drilling, and threading on the heat-treated alloy ingot to prepare a nut blank that meets the design requirements; Step 2: Nut forming Use a high-precision CNC lathe to perform elliptical threading on the inner hole of the nut; 9) Polish and surface-treat the whole nut, and control the roughness to Ra < 0.8 μm to improve the coating adhesion; Step 3: Surface coating treatment 10) Add silver nanoparticles (particle size 20 - 50 nm) to the solvent at a mass ratio of 60 - 80%, add a dispersant and ultrasonically disperse for 30 minutes; add 10 - 20% of high-conductive epoxy resin and a curing accelerator, and stir evenly to form a stable coating; 11) Apply the coating to the nut blank through electrophoretic coating technology to ensure a uniform coating thickness of 2 - 5 μm; cure at 250 °C for 10 minutes to form a dense conductive coating; 12) Mix fluorocarbon resin, ceramic particles, hydrophobic additives and solvent, add a dispersant and an antioxidant and stir evenly; stir at 1000 - 2000 rpm through a high-speed dispersion device for 30 minutes to form a stable suspension; 13) Apply the outer coating to the nut with a bottom conductive coating by dip coating, and control the coating thickness to be 8 - 12 μm; cure at 200 °C for 30 minutes to ensure the corrosion resistance and wear resistance of the coating.

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