Anti-fatigue automobile accessory bolt and heat treatment process thereof

Abstract

The application discloses an anti-fatigue steam fitting bolt and a heat treatment processing technology thereof, and relates to the technical field of bolt production. The anti-fatigue steam fitting bolt to be processed is cleaned and dried; the cleaned anti-fatigue steam fitting bolt to be processed is heated and kept warm through a heating box, and then is rapidly cooled; during the heating and keeping warm process, the position of the anti-fatigue steam fitting bolt to be processed is continuously changed; the anti-fatigue steam fitting bolt to be processed is cleaned and dried again; the anti-fatigue steam fitting bolt to be processed is quenched, and then is rapidly immersed into a quenching oil pool for cooling; the quenched anti-fatigue steam fitting bolt to be processed is tempered, and finally is naturally cooled to obtain an anti-fatigue steam fitting bolt product. During the heating process of the bolt, the bolt is kept moving, the positions of the bolts are exchanged, the heating uniformity of the bolt is improved, and the problem of uneven heating caused by the heating equipment itself and the bolt position is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of bolt production, in particular to an anti-fatigue automobile accessory bolt and a heat treatment processing technology thereof. BACKGROUND

[0002] Bolt heat treatment is a key process for improving its performance, generally including quenching and tempering two steps. Quenching is to heat the bolt above the critical temperature, and after holding, it is rapidly cooled to make the internal organization into high-hardness martensite, which greatly improves the strength and hardness. But the bolt is brittle after quenching, and needs to be tempered. It is heated to an appropriate temperature and cooled after holding for a period of time, which can eliminate internal stress, adjust hardness and toughness, so that the bolt has sufficient strength and good toughness to meet the needs of different working conditions.

[0003] The process of heat treatment is different, and the improvement of bolt performance will be different. For example, a bolt heat treatment device and process disclosed in patent publication No. CN119372438A, which includes a heat treatment box, the inner wall of the heat treatment box is symmetrically provided with two bidirectional drive rods, two heat insulation plates are threadedly sleeved between the two bidirectional drive rods, and two heat insulation plates are movably inserted into the left and right sides of the heat treatment box. When the bolt holder moves, the guide rod slides along the inner wall of the guide groove, so as to make the bolt holder shake left and right, and make the bolt shake to shake off the debris on its surface. At the same time, the debris is collected by the heat insulation plate, and the possibility of affecting the heat treatment effect of the bolt by the debris is reduced. Through the toothed plate, the bidirectional drive rod is rotated, and the heat insulation plate is moved, so as to open the heat treatment box, and make the bolt holder move to the lower side of the heat insulation plate, and make the heat insulation plate reset by continuing to move the toothed plate, so as to seal the heat treatment box and reduce the possibility of heat loss.

[0004] The bolt needs to be uniformly heated during the heat treatment process to ensure the heat treatment effect of the bolt. However, the above process and the existing heat treatment process do not move the bolt relatively during the heating process of the bolt, which is difficult to improve the problem of uneven heating caused by the heating equipment itself and the position of the bolt, and the heat treatment effect is poor. SUMMARY

[0005] The purpose of the present application is to provide an anti-fatigue automobile accessory bolt heat treatment processing technology to solve the problems raised in the background art.

[0006] To achieve the above purpose, the present application provides the following technical scheme: an anti-fatigue automobile accessory bolt heat treatment processing technology, comprising:

[0007] S1: washing and drying the anti-fatigue automobile accessory bolt to be processed;

[0008] S2: heat the cleaned anti-fatigue steam fitting bolt to be processed to 870-890 ℃ by heating box and keep for 60-75 min, then quickly cool down, keep the position of the anti-fatigue steam fitting bolt to be processed changing during heating and keeping;

[0009] S3: clean and dry the anti-fatigue steam fitting bolt to be processed again, then heat to 560-580 ℃, keep for 80-90 min, then cool down;

[0010] S4: quench the anti-fatigue steam fitting bolt to be processed, the quenching temperature is 860-880 ℃, the heating time is 30-45 min, then quickly immerse in quenching oil pool to cool down;

[0011] S5: temper the quenched anti-fatigue steam fitting bolt to be processed, the tempering temperature is 330-350 ℃, the heating time is 100-120 min, then naturally cool down to obtain the finished anti-fatigue steam fitting bolt.

[0012] Preferably, the heating box comprises a box body, a cylindrical heating cavity is arranged in the box body, heating resistance wires are arranged in the side wall of the box body, a cover body is arranged at the upper end of the box body, a bottom disc is rotatably arranged at the bottom of the cylindrical heating cavity, a driving motor for driving the rotation of the bottom disc is mounted at the bottom of the box body, a support base is arranged in the box body, the support base is placed above the bottom disc, a positioning mechanism is arranged on the support base, a plurality of circumferentially distributed storage shelves are arranged above the support base, and a plurality of storage discs for placing bolts are arranged on the storage shelves.

[0013] Preferably, the positioning mechanism comprises a plurality of positioning rods fixed on the bottom disc, the positioning rods are circumferentially distributed, a plurality of positioning grooves are formed in the edge of the support base and correspond to the positioning rods, and the positioning rods are respectively located on the inner side of the corresponding positioning grooves.

[0014] Preferably, the storage shelves are composed of a plurality of short rods stacked together, the upper end of each short rod is provided with a positioning sleeve, the bottom of each short rod can be inserted into the positioning sleeve, the storage disc is fixed on the short rod, a plurality of circumferentially distributed round holes are formed in the upper surface of the support base, the bottom of the lowermost short rod is rotatably inserted into the round hole, the cover body is located on the inner side of the cylindrical heating cavity, and the heating resistance wires can be controlled by layer-by-layer on-off.

[0015] Preferably, a tooth ring is fixed at the center position of the lower surface of the cover body, a plug rod is inserted into the uppermost positioning sleeve, the upper end of the plug rod is fixed with a gear, the gear is engaged with the tooth ring, a vertical groove is formed in the inner wall of the box body, a protrusion is arranged at the edge of the cover body, and the protrusion is located on the inner side of the vertical groove.

[0016] Preferably, a center hole is formed at the middle position of the cover body, and a center rod is arranged at the upper end of the support base and penetrates the center hole.

[0017] Preferably, the upper end of the cover is provided with a handle.

[0018] Based on the same inventive concept, an anti-fatigue automobile accessory bolt is also provided, which is prepared by the anti-fatigue automobile accessory bolt heat treatment process described above, and the anti-fatigue automobile accessory bolt to be processed is a low-alloy high-strength steel, and the components thereof include, by mass percentage, C 0.18-0.23%, Si 0.15-0.35%, Mn 1.2-1.6%, Cr 0.8-1.2%, Mo 0.15-0.25%, V 0.05-0.12%, B 0.001-0.005%, and the balance is Fe.

[0019] After the anti-fatigue automobile accessory bolt to be processed is subjected to quenching + low-temperature tempering treatment, the core hardness is 38-42 HRC, and the surface compressive stress is greater than or equal to 500 MPa.

[0020] Preferably, the surface of the anti-fatigue automobile accessory bolt to be processed is sequentially covered from inside to outside with:

[0021] A nanocrystallized nickel-phosphorus alloy plating layer, the thickness of which is 3-8 microns, the grain size of which is less than or equal to 50 nanometers, and the hardness of which is greater than or equal to 600 HV;

[0022] A rare earth modified zinc-nickel alloy plating layer, the rare earth element content of which is 0.5-2 wt%, and the thickness of which is 10-15 microns;

[0023] A composite lubricating plating layer containing graphite-like carbon, the thickness of which is 1-3 microns, and the friction coefficient of which is less than or equal to 0.12;

[0024] The nanocrystallized nickel-phosphorus alloy plating layer, the rare earth modified zinc-nickel alloy plating layer, and the composite lubricating plating layer are formed by a pulse electrodeposition process, the total thickness of which is not more than 25 microns, and the interlayer bonding strength of which is greater than or equal to 35 MPa.

[0025] Preferably, the composite lubricating plating layer also contains nanometer titanium dioxide particles, the particle size of which is 20-50 nanometers, and the content of which is 0.5-1.5 wt%;

[0026] The fluctuation value of the friction coefficient of the composite lubricating plating layer is not more than 0.03 within the temperature range of -40 DEG C to 150 DEG C, and the salt spray corrosion resistance time is greater than or equal to 1000 hours.

[0027] Compared with the prior art, the anti-fatigue automobile accessory bolt has the following beneficial effects:

[0028] By heating the box, the bolts are kept moving and exchanging positions during heating, heat preservation and natural cooling, the heating uniformity of the bolts is improved, and the problem of uneven heating caused by the heating equipment itself and the bolt position is reduced.

[0029] Meanwhile, the cover body cannot rotate due to the limiting effect of the protrusions and the vertical grooves, and the gear will roll along the tooth ring while the support base rotates, and the multiple short rods stacked below are driven to rotate through the insertion rod, so that the rotation of the storage disc is realized, and further combined with multiple rotation modes, the movement track of the bolt is changed, and the heating uniformity is further improved.

[0030] In addition, different numbers of short rods can be stacked according to the number of bolts, and then the cover body is covered on the upper ends of the multiple short rods, the heating space of the cylindrical heating cavity is reduced, and the heating resistance wire of the appropriate height at the bottom is turned on, so that the heat treatment effect is ensured while the energy consumption is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 It is a structure schematic view of the heating box in the application;

[0032] Figure 2 It is a structure schematic view of the bottom structure of the heating box in the application;

[0033] Figure 3 It is a structure schematic view of the bottom structure of the cover body in the application;

[0034] Figure 4 It is a structure schematic view of the support base and the bottom disc in the application;

[0035] Figure 5 It is a structure schematic view of the short rod and the gear in the application;

[0036] Figure 6 It is a structure schematic view of the anti-fatigue automobile accessory bolt in the application.

[0037] In the figure:

[0038] 1, box body; 2, bottom disc; 3, driving motor; 4, support base; 5, storage disc; 6, positioning groove; 7, positioning rod; 8, short rod; 9, positioning sleeve; 10, round hole; 11, cover body; 12, gear; 13, insertion rod; 14, tooth ring; 15, protrusion; 16, vertical groove; 17, center rod; 18, center hole; 19, handle; 20, automobile accessory bolt to be processed. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the application.

[0040] As Figures 1-3As shown, the present application provides a kind of anti-fatigue steam fitting bolt heat treatment processing technology, comprising:

[0041] S1: the anti-fatigue steam fitting bolt 20 to be processed is washed and dried;

[0042] S2: the anti-fatigue steam fitting bolt 20 to be processed is heated to 870-890 ℃ by heating box and is kept for 60-75 min, then is rapidly cooled down, and in the process of heating and keeping, the position of the anti-fatigue steam fitting bolt 20 to be processed is kept changing;

[0043] S3: the anti-fatigue steam fitting bolt 20 to be processed is washed and dried again, then heated to 560-580 ℃, and after keeping for 80-90 min, it is cooled down;

[0044] S4: the anti-fatigue steam fitting bolt 20 to be processed is quenched, the quenching temperature is 860-880 ℃, the heating time is 30-45 min, then it is rapidly immersed in quenching oil pool for cooling;

[0045] S5: the anti-fatigue steam fitting bolt 20 to be processed after quenching is tempered, the tempering temperature is 330-350 ℃, the heating time is 100-120 min, and finally it is naturally cooled down to obtain the anti-fatigue steam fitting bolt product.

[0046] It should be noted that the following heating box is used in the embodiment, and in the process of heating, keeping and natural cooling, the bolt is kept moving, the position between the bolts is exchanged, the heating uniformity of the bolt is improved, and the problem of uneven heating caused by the heating equipment itself and the bolt position is reduced.

[0047] As shown in the figure, Figures 1-6 The heating box comprises a box body 1, a cylindrical heating cavity (not marked in the figure) is arranged inside the box body 1, heating resistance wires (not shown in the figure) are arranged inside the side wall of the box body 1, a cover body 11 is arranged at the upper end of the box body 1, a bottom disc 2 is rotatably arranged at the bottom of the cylindrical heating cavity, a driving motor 3 for driving the bottom disc 2 to rotate is installed at the bottom of the box body 1, a support base 4 is arranged inside the box body 1, the support base 4 is placed above the bottom disc 2, a positioning mechanism is arranged on the support base 4, a plurality of circumferentially distributed storage shelves are arranged above the support base 4, and a plurality of storage discs 5 for placing bolts are arranged on the storage shelves.

[0048] It should be noted that, inside the box 1 is also provided with temperature sensor (not shown), in use, the bolt is placed in the storage tray 5, then the bracket base 4 is placed on the bottom tray 2, and is connected through the positioning mechanism, heated by the heating resistance wire, the driving motor 3 drives the bottom tray 2 to rotate, and then adjusts the rotation of several storage trays 5, so that the bolt rotates in the box 1, improves the heating uniformity of the bolt, and improves the heat treatment effect.

[0049] As shown in Figure 4 , the positioning mechanism comprises a plurality of positioning rods 7 fixed on the bottom tray 2, and the positioning rods 7 are circumferentially distributed, and the edges of the bracket base 4 are provided with positioning grooves 6 which are the same as the number of the positioning rods 7, and the positioning rods 7 are respectively located inside the corresponding positioning grooves 6.

[0050] It should be noted that the position of the bracket base 4 is limited by the positioning grooves 6 and the positioning rods 7, and the bracket base 4 can also be ensured to rotate with the bottom tray 2 at all times. When the bracket base 4 is put in and taken out, the bracket base 4 can be directly moved upward, which is convenient to use.

[0051] As shown in Figure 4 and Figure 5 , the storage rack is composed of a plurality of short rods 8 stacked together, the upper end of the short rod 8 is provided with a positioning sleeve 9, and the bottom of the short rod 8 can be inserted into the positioning sleeve 9, the storage tray 5 is fixed on the short rod 8, the upper surface of the bracket base 4 is provided with a plurality of circumferentially distributed round holes 10, and the bottom of the lowermost short rod 8 is rotatably inserted into the round hole 10, the cover body 11 is located inside the cylindrical heating cavity, and the heating resistance wire can be controlled by layering.

[0052] It should be noted that the number of short rods 8 stacked can be selected according to the number of bolts, and then the cover body 11 is placed on the upper end of the plurality of short rods 8, which reduces the heating space of the cylindrical heating cavity, and the heating resistance wire with appropriate height at the bottom is turned on, which ensures the heat treatment effect while reducing energy consumption.

[0053] As shown in Figure 1 , Figure 3 and Figure 5 , the lower surface of the cover body 11 is fixed with a tooth ring 14 at the center position, the upper end of the plug rod 13 is fixed with a gear 12, and the gear 12 is engaged with the tooth ring 14, the inner wall of the box 1 is provided with a vertical groove 16, and the edge of the cover body 11 is provided with a lug 15, and the lug 15 is located inside the vertical groove 16.

[0054] It should be noted that, under the limiting action of the bump 15 and the vertical groove 16, the cover body 11 cannot rotate, and the gear 12 will roll along the tooth ring 14 while the support base 4 rotates, driving the multiple short rods 8 stacked below to rotate through the insertion rod 13, so as to realize the rotation of the storage disc 5, and further combine multiple rotation modes to change the movement trajectory of the bolt, thereby further improving the heating uniformity.

[0055] As shown in Figure 1 , Figure 3 and Figure 4 , a center hole 18 is formed in the middle position of the cover body 11, and a center rod 17 is arranged at the upper end of the support base 4, which penetrates the center hole 18.

[0056] It should be noted that, in use, the bolt is placed in the storage disc 5 outside the box body 1, and then the support base 4 is placed into the box body 1 through the center rod 17, and after heating, the support base 4 and the bolt are also taken out through the center rod 17, which is convenient and practical.

[0057] As shown in Figure 1 , a handle 19 is arranged at the upper end of the cover body 11.

[0058] It should be noted that the handle 19 is more convenient for taking and placing the cover body 11, and is more convenient to use.

[0059] Referring to Figure 6 , an anti-fatigue automotive hardware bolt is also provided, which is prepared by the anti-fatigue automotive hardware bolt heat treatment process described above. The anti-fatigue automotive hardware bolt 20 to be processed is made of low-alloy high-strength steel, and its components include, by mass percentage: C 0.18-0.23%, Si 0.15-0.35%, Mn 1.2-1.6%, Cr 0.8-1.2%, Mo 0.15-0.25%, V 0.05-0.12%, B 0.001-0.005%, and the balance is Fe.

[0060] After quenching + low-temperature tempering treatment, the core hardness of the anti-fatigue automotive hardware bolt 20 to be processed is 38-42HRC, and the surface compressive stress is greater than or equal to 500MPa.

[0061] In the scheme, Cr, Mo, V micro-alloying can form fine carbides such as Cr7C3, Mo2C, VC, hinder dislocation movement, and inhibit fatigue crack initiation; B element addition will segregate at grain boundaries, improve grain boundary bonding, and delay crack propagation along grain boundaries; the effect of Mn, Si solid solution strengthening is to improve the yield strength of the base material by the interaction of solid solution atoms and dislocations, which can be ≥900MPa. After two quenching, martensite organization is obtained, surface compressive stress is generated, tensile stress in external load is offset, and fatigue crack propagation rate is reduced; after low temperature tempering, quenching stress is eliminated, toughness is improved while high hardness is retained, and brittle fracture is avoided.

[0062] The surface of the anti-fatigue bolt 20 to be processed is covered from inside to outside with:

[0063] The nanocrystalline nickel-phosphorus alloy plating layer has a thickness of 3-8 μm, a grain size of ≤50 nm, and a hardness of ≥600 HV;

[0064] The rare earth modified zinc-nickel alloy plating layer has a rare earth element content of 0.5-2 wt%, and a thickness of 10-15 μm;

[0065] The graphite-like carbon-containing composite lubricating plating layer has a thickness of 1-3 μm, and a friction coefficient of ≤0.12;

[0066] The nanocrystalline nickel-phosphorus alloy plating layer, the rare earth modified zinc-nickel alloy plating layer, and the composite lubricating plating layer are formed by pulse electrodeposition process, and the total thickness is not more than 25 μm, and the interlayer bonding strength is ≥35 MPa.

[0067] The nanocrystalline nickel-phosphorus alloy plating layer has a nanocrystalline structure of ≤50 nm, a high grain boundary density, hindered dislocation movement, a hardness of ≥600 HV, and effectively disperses stress concentration on the bolt surface. And through high-frequency pulse current, the grain is refined, and the metallurgical bonding between the plating layer and the base material is enhanced, and the bonding strength can be ≥35 MPa.

[0068] The rare earth modified zinc-nickel alloy plating layer has a rare earth element content of 0.5-2 wt%, and a thickness of 10-15 μm;

[0069] The graphite-like carbon-containing composite lubricating plating layer can be graphite-like carbon + nano TiO2 composite lubricating plating layer. The graphite-like carbon provides self-lubricating properties and reduces fretting wear during bolt assembly and service. The nano TiO2 particle size can be 20-50 nm: stable structure at high temperature, inhibits oxidation of the lubricating film, ensures that the friction coefficient fluctuation is ≤0.03 within the range of -40℃ to 150℃, and the salt spray corrosion resistance time is ≥1000 hours.

[0070] The base material of the anti-fatigue bolt is micro-alloyed and coated with nanocrystalline layer, which can increase the fatigue limit by about 25%, and the surface compressive stress and high-hardness coating can work together to prolong the fatigue life by 1.8-2.5 times. The friction coefficient is reduced to below 0.12, and the fretting wear volume is reduced by more than 60%. At 150℃ high temperature, it still maintains low friction to avoid seizure or looseness caused by lubrication failure. It can meet the long-term service requirements of automobile chassis bolts in salt spray and moisture environment.

[0071] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A heat treatment process for fatigue-resistant automotive bolts, characterized in that, include: S1: Clean and dry the fatigue-resistant automotive bolts (20) to be processed; S2: Heat the cleaned anti-fatigue auto parts bolts (20) to 870℃-890℃ in a heating box and keep them warm for 60min-75min, then cool them down quickly. During the heating and warming process, keep the position of the anti-fatigue auto parts bolts (20) constantly changing. The heating box includes a box body (1), a cylindrical heating chamber is provided inside the box body (1), and a heating resistance wire is provided inside the side wall of the box body (1). A cover (11) is provided at the upper end of the box body (1). A chassis (2) is rotatably provided at the bottom of the cylindrical heating chamber. A drive motor (3) for driving the chassis (2) to rotate is installed at the bottom of the box body (1). A support base (4) is provided inside the box body (1). The support base (4) is placed above the chassis (2), and a positioning mechanism is provided on the support base (4). Several storage racks are evenly distributed around the circumference above the support base (4), and several storage trays (5) for placing bolts are provided on the storage racks. The positioning mechanism includes several positioning rods (7) fixed on the chassis (2). The several positioning rods (7) are evenly distributed around the circumference. The edge of the support base (4) is provided with positioning grooves (6) in the same number as the positioning rods (7), and the positioning rods (7) are respectively located inside the positioning grooves (6) at the corresponding positions. S3: Clean and dry the fatigue-resistant auto parts bolts (20) to be processed again, then heat them to 560℃-580℃, keep them warm for 80min-90min and then cool them; S4: Quench the fatigue-resistant auto parts bolts (20) to be processed at a quenching temperature of 860℃-880℃ and a heating time of 30min-45min, and then quickly immerse them in a quenching oil bath for cooling. S5: Temper the quenched fatigue-resistant auto parts bolts (20) at a temperature of 330℃-350℃ and a heating time of 100min-120min. Finally, allow them to cool naturally to obtain the finished fatigue-resistant auto parts bolts.

2. The fatigue-resistant automotive bolt heat treatment process according to claim 1, characterized in that: The storage rack is composed of multiple short rods (8) stacked together. The upper end of the short rod (8) is provided with a positioning sleeve (9), and the bottom of the short rod (8) can be inserted into the positioning sleeve (9). The storage tray (5) is fixed on the short rod (8). The upper surface of the support base (4) is provided with several circumferentially distributed circular holes (10), and the bottom of the lowest short rod (8) is rotatably inserted into the circular hole (10). The cover (11) is located inside the cylindrical heating cavity, and the heating resistance wire can be controlled to turn on and off in layers.

3. The fatigue-resistant automotive bolt heat treatment process according to claim 2, characterized in that: A toothed ring (14) is fixed at the center of the lower surface of the cover (11), and a rod (13) is inserted into the uppermost positioning sleeve (9). A gear (12) is fixed at the upper end of the rod (13), and the gear (12) meshes with the toothed ring (14). A vertical groove (16) is opened on the inner wall of the box (1), and a protrusion (15) is provided on the edge of the cover (11), and the protrusion (15) is located inside the vertical groove (16).

4. The fatigue-resistant automotive bolt heat treatment process according to claim 1, characterized in that: The cover (11) has a central hole (18) in the middle position, and the upper end of the support base (4) is provided with a central rod (17), which passes through the central hole (18).

5. The heat treatment process for fatigue-resistant automotive bolts according to claim 1, characterized in that: The upper end of the cover (11) is provided with a handle (19).

6. A fatigue-resistant automotive bolt, prepared using the heat treatment process for a fatigue-resistant automotive bolt as described in claim 1, characterized in that: The fatigue-resistant automotive bolt (20) to be processed is a low-alloy high-strength steel, and its composition by mass percentage includes: C 0.18-0.23%, Si 0.15-0.35%, Mn 1.2-1.6%, Cr 0.8-1.2%, Mo 0.15-0.25%, V 0.05-0.12%, B 0.001-0.005%, with the balance being Fe; The fatigue-resistant automotive bolt (20) to be processed has a core hardness of 38-42HRC and a surface compressive stress of ≥500MPa after quenching and low-temperature tempering.

7. The fatigue-resistant automotive bolt according to claim 6, characterized in that: The surface of the fatigue-resistant automotive bolt (20) to be processed is covered from the inside out with the following: Nanocrystalline nickel-phosphorus alloy coating, with a thickness of 3-8μm, grain size ≤50nm, and hardness ≥600HV; Rare earth modified zinc-nickel alloy coating, with a rare earth element content of 0.5-2wt% and a thickness of 10-15μm; A composite lubricating coating containing graphite-like carbon, with a thickness of 1-3 μm and a friction coefficient ≤0.12; The nanocrystalline nickel-phosphorus alloy coating, rare earth modified zinc-nickel alloy coating, and composite lubricating coating are formed by pulse electrodeposition process, with a total thickness not exceeding 25 μm and an interlayer bonding strength ≥35 MPa.

8. The fatigue-resistant automotive bolt according to claim 7, characterized in that: The composite lubricating coating also contains nano-titanium dioxide particles with a particle size of 20-50 nm, accounting for 0.5-1.5 wt%. The composite lubricating coating exhibits a friction coefficient fluctuation of no more than 0.03 within a temperature range of -40℃ to 150℃, and a salt spray corrosion resistance time of ≥1000 hours.

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