A method for preparing a hard coating for improving fatigue of an automatic tilt guide cylinder

Abstract

The present invention discloses a method for preparing a hard coating for improving fatigue of an automatic tilting device guide tube, the method comprising: 1. cleaning and pre-treating the automatic tilting device guide tube; 2. sequentially performing surface treatments of sandblasting and shot peening on the automatic tilting device guide tube after cleaning and pre-treating; 3. using supersonic flame spraying of NiCrAl coating and WC‑Co coating on the surface of the automatic tilting device guide tube after surface treatment to form a hard coating. The present invention combines sandblasting and shot peening for surface treatment to obtain a roughened surface with both good roughness and compressive stress, while removing the sharp corners obtained by the sandblasting surface, and spraying a NiCrAl coating with a hardness between the substrate and the WC‑Co coating to prevent fatigue cracks from extending into the substrate, thereby improving the fatigue performance of the automatic tilting device guide tube substrate. The method has high reliability, does not require additional equipment, and is suitable for promotion.

Description

Technical Field

[0001] The invention belongs to the technical field of aluminum and aluminum alloy surface hardening, and in particular relates to a method for preparing a hard coating for improving fatigue of an automatic tilting device guide cylinder. Background Art

[0002] Aluminum and aluminum alloys have the advantages of low density and high specific strength. As the preferred lightweight structural material for the guide tube of the automatic tilter, 7075 high-strength aluminum alloy in particular has been widely used in this field. The hardness of this alloy generally does not exceed 200HV, but this hardness value still cannot meet the demand for wear resistance, and it needs to be surface hardened. Supersonic flame spraying of tungsten carbide coating is one of the commonly used methods to improve surface wear resistance. The tungsten carbide wear-resistant coating sprayed by supersonic flame spraying is mainly mechanically bonded to the substrate. The commonly used treatment process requires the substrate to be sandblasted and roughened first. Sandblasting increases the specific surface area of ​​the substrate and improves the bonding performance between the substrate and the sprayed coating; at the same time, the sharp angle introduced by sandblasting brings a notch effect, which affects the fatigue performance of the substrate. After the substrate is sandblasted, the tungsten carbide wear-resistant coating is sprayed by supersonic flame spraying. A single tungsten carbide hard coating will reduce the fatigue performance of the guide tube. The preparation of tungsten carbide coating on such a sandblasted substrate will greatly reduce the fatigue life and affect the safety of related components.

[0003] The guide cylinder of the automatic tilt gear is a key component of the helicopter. As recorded in the patent "Guide cylinder of automatic tilt gear" with application number 201220149023.5 and the patent "Guide cylinder of automatic tilt gear assembly and main reducer" with application number 201710404799.4, the guide cylinder of the automatic tilt gear has high requirements on the fatigue life of the guide cylinder when working with the assembly, and the surface quality of the guide cylinder substrate has a significant impact on its fatigue performance. While the single sandblasting roughens the substrate, it will bring a large number of defects to the substrate surface, introduce a large number of sharp angles, destroy the integrity of the substrate surface, and then affect the fatigue performance of the substrate.

[0004] Shot peening can form a residual compressive stress layer on the material surface, which is a common and effective means to improve the fatigue performance of materials. However, single shot peening is difficult to obtain the roughness required by HVOF spraying.

[0005] The patent "Surface Strengthening Method of Aluminum Alloy and Its Composite Materials" with application number 201310629089.3 adopts sandblasting first, then soaking in sodium hydroxide aqueous solution and nitric acid solution to remove the surface sandblasting marks, and finally using glass shot to obtain the surface compressive stress layer. The purpose of this method is to use shot blasting to obtain a hardened layer with compressive stress, but because of concerns that shot blasting cannot remove impurities and defects introduced during plastic forming, sand blasting is first used to remove lubricants such as graphite remaining on the plastic forming part, impurities such as iron filings introduced, and defects such as folds and pits. According to the patent drawings, there are a large number of granular corrosion products on the surface after corrosion, and these particles are pressed into the matrix after shot blasting, introducing defects. The patent "A Method for Improving the Surface Quality of Aluminum-based Composite Materials" with application number 201811312997.9 uses a dry sandblasting machine to sandblast aluminum-based composite parts to clean surface lubricants, scratches, microcracks, etc., and then removes the sandblasted surface by grinding, and then performs shot blasting to form a compressive stress layer. The above patents all use sandblasting to remove the surface layer such as oxide scale, then remove the layer by grinding or corrosion, and then perform shot peening to obtain a hardened layer with compressive stress.

[0006] The patent "Preparation Method of Wear-Resistant Self-Lubricating Coating of Aluminum and Aluminum Alloy" with application number 201811208479.2 uses single sandblasting, shot peening, shot blasting and other methods to roughen the surface. There is no order of priority for these methods. They only roughen the surface. The roughened surface obtained has large sharp angles, which will reduce fatigue performance; nor does it use shot to trim the roughened surface to obtain a roughened surface with both compressive stress and sharp angles, which is beneficial to the fatigue performance of the substrate. The patent "Preparation Method of a High Fatigue Performance Titanium Alloy Spring" with application number 201810546610.X and the patent "A High Strength Fatigue Resistant Titanium Alloy Rod and Wire and Its Preparation Method" with application number 201810546639.8 use solid solution, aging and other methods to treat titanium materials, followed by sandblasting and / or shot peening to obtain a strengthening layer with compressive stress on the surface of the titanium part. The above two patents both utilize the pressure of sandblasting or shot peening to obtain a strengthening layer with compressive stress. This utilizes the basic physical properties of sandblasting and shot peening, that is, under the drive of highly compressed gas, high-speed shots (sand) hit the surface of the substrate to obtain a strengthening layer with pressure. These two patents do not involve roughening the surface, nor do they involve trimming the roughening surface to obtain a roughening surface without sharp corners.

[0007] The hardness of tungsten carbide sprayed by supersonic flame is about 1000HV, while the substrate of the guide tube is aluminum, and the hardness of aluminum does not exceed 200HV. When the hard coating is directly sprayed on the soft substrate, there is an "eggshell effect" due to the large hardness difference between the two, which causes the risk of crushing the tungsten carbide coating sprayed on the guide tube during operation; at the same time, the hard tungsten carbide coating is prone to cracks, and under the action of force, the cracks extend to the substrate and cause the guide tube to fail. Therefore, studying the preparation of a transition layer between the soft substrate and the hard coating is one of the methods to solve the above problems. Summary of the invention

[0008] The technical problem to be solved by the present invention is to provide a method for preparing a hard coating that improves the fatigue performance of an automatic tilt guide tube in view of the deficiencies of the above-mentioned prior art. The method combines sandblasting and shot peening to sequentially treat the surface of the automatic tilt guide tube, thereby obtaining a roughened surface with both good roughness and compressive stress, while removing the sharp corners obtained by the sandblasting surface, thereby avoiding the notch effect that causes the fatigue performance of the substrate to decrease; a NiCrAl coating with a hardness between the substrate and the WC-Co coating is prepared between the substrate and the WC-Co coating, and the NiCrAl coating serves as an adhesive layer to improve the bonding performance between the coating and the substrate, and as a metal layer to prevent the fatigue cracks generated in the WC-Co coating from extending into the substrate, thereby improving the fatigue performance of the automatic tilt guide tube substrate, and solving the problem that fatigue performance is greatly reduced after traditional sandblasting and then spraying tungsten carbide coating.

[0009] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing a hard coating for improving the fatigue of an automatic tilting device guide cylinder, characterized in that the method comprises the following steps:

[0010] Step 1: Clean and pretreat the guide cylinder of the automatic tilter;

[0011] Step 2: placing the automatic tilting device guide tube that has been cleaned and pretreated in step 1 in a sandblasting machine equipped with sandblasting material, spraying the sandblasting material onto the surface of the automatic tilting device guide tube through a spray gun using air pressure for sandblasting treatment, and then placing the automatic tilting device guide tube that has been roughened by sandblasting in a sandblasting machine equipped with shot peening material, spraying the shot peening material onto the surface of the automatic tilting device guide tube through a spray gun using air pressure for shot peening treatment, thereby obtaining a surface-treated automatic tilting device guide tube;

[0012] Step 3: Fix the surface-treated automatic tilt guide tube obtained in step 2 on a rotating table of supersonic flame spraying, then use supersonic flame spraying to coat NiCrAl coating, and then use supersonic flame spraying to coat WC-Co coating to form a hard coating on the surface of the automatic tilt guide tube.

[0013] The present invention firstly performs cleaning pretreatment on the guide tube of the automatic tilting device to remove impurities and oil stains on the surface thereof, and then performs sandblasting and shot peening, and uses sandblasting to roughen the surface of the guide tube of the automatic tilting device to obtain a sandblasting surface with relatively large roughness, and then uses shot peening to trim the sandblasting surface, and adjusts the roughness and compressive stress of the sandblasting surface to obtain a roughened surface with both good roughness and compressive stress, and removes the sharp angle obtained by the sandblasting surface, so that the surface of the guide tube of the automatic tilting device meets the requirements of the roughened surface required by subsequent supersonic flame spraying, and avoids the problem that a single sandblasting simultaneously brings a large number of defects on the roughened surface and destroys the surface integrity, thereby improving the fatigue performance of the guide tube substrate of the automatic tilting device; and then, supersonic flame spraying is sequentially used on the roughened surface of the guide tube of the automatic tilting device after the surface treatment. Sonic flame spraying NiCrAl coating and WC-Co coating, on the one hand, uses NiCrAl coating as a bonding layer to form good adhesion with the surface of the automatic tilt guide tube and WC-Co coating, thereby improving the bonding force between the hard coating and the substrate; on the other hand, NiCrAl coating with a hardness of about 500HV acts as a hardness transition layer, playing a transitional role between the substrate with lower hardness and the hard coating with higher hardness, thereby reducing the risk of crushing during operation caused by the large hardness difference between the substrate and the hard coating; at the same time, NiCrAl coating has good bearing capacity for hardness, and can prevent tungsten carbide cracks in the hard coating from extending into the substrate, thereby reducing the adverse effects of the hard coating on the fatigue performance of the automatic tilt guide tube, thereby further improving its fatigue performance.

[0014] The above-mentioned method for preparing a hard coating for improving fatigue of an automatic recliner guide sleeve is characterized in that the automatic recliner guide sleeve in step 1 is made of aluminum alloy.

[0015] The above-mentioned method for preparing a hard coating for improving the fatigue resistance of an automatic tilt guide tube is characterized in that the cleaning pretreatment process described in step one is: first immerse the automatic tilt guide tube in a container containing a metal cleaning agent solution at 20°C to 30°C and a mass concentration of 0.5% to 1%, and place it in an ultrasonic generator for ultrasonic cleaning for 5min to 20min, then rinse it under running water after removal, then immerse it in a container containing anhydrous ethanol, place it in an ultrasonic generator for ultrasonic cleaning for 5min to 10min, and blow it dry with a hair dryer.

[0016] The above-mentioned method for preparing a hard coating for improving the fatigue resistance of an automatic tilting device guide sleeve is characterized in that the air pressure of the sandblasting treatment in step 2 is 0.1MPa~0.6MPa, and the distance between the spray gun and the workpiece is 50mm~150mm; the air pressure of the shot peening treatment is 0.1MPa~0.5MPa, and the distance between the spray gun and the workpiece is 50mm~150mm.

[0017] The above-mentioned method for preparing a hard coating for improving fatigue of the guide tube of an automatic tilting device is characterized in that the process parameters of the supersonic flame spraying NiCrAl coating in step 3 are: oxygen flow rate 18m 3 / h~24m 3 / h, kerosene flow rate 16L / h~24L / h, powder feeding amount 1kg / h~10kg / h, spray distance 150mm~350mm, spray gun moving speed 100mm / min~600mm / min, spray gun step distance 1mm~6mm; the process parameters of the supersonic flame spraying WC-Co coating are: oxygen flow rate 18m 3 / h~24m 3 / h, kerosene flow rate 16L / h~24L / h, powder feeding amount 1kg / h~10kg / h, spray distance 150mm~350mm, spray gun moving speed 100mm / min~600mm / min, spray gun step distance 1mm~6mm.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] 1. The present invention combines sandblasting and shot peening to sequentially perform surface treatment on the guide tube of the automatic tilter, thereby obtaining a roughened surface with both good roughness and compressive stress, while removing the sharp corners obtained by the sandblasting surface, solving the problem that a single sandblasting will cause a large number of defects and damage the surface integrity when roughening the surface, avoiding the notch effect, and improving the fatigue performance of the guide tube substrate of the automatic tilter.

[0020] 2. The present invention adopts supersonic flame spraying to add a NiCrAl coating as a bonding layer and a transition layer between the automatic tilt guide tube substrate and the WC-Co coating, thereby improving the bonding strength between the hard coating and the substrate, reducing the risk of crushing during operation, and preventing the tungsten carbide cracks in the hard coating from extending into the substrate, thereby reducing the adverse effects of the hard coating on the fatigue performance of the automatic tilt guide tube and further improving its fatigue performance.

[0021] 3. The sandblasting and shot peening surface treatment of the present invention has simple equipment requirements, rich selection of corresponding sandblasting materials and shot peening materials, high reliability, low preparation cost and short preparation time, and is suitable for promotion.

[0022] 4. The present invention adopts supersonic flame spraying of NiCrAl coating and WC-Co coating, which can be completed on the same supersonic flame spraying equipment, with high processing efficiency, high operating cost, strong applicability, and suitable for batch industrial production.

[0023] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1This is a 3D topography of the surface of the guide cylinder of the automatic tilter after sandblasting in Example 1 of the present invention.

[0025] Figure 2 This is a 3D topography of the surface of the guide cylinder of the automatic tilter after surface treatment in Example 1 of the present invention.

[0026] Figure 3 This is a cross-sectional SEM image of the hard coating prepared in Example 1 of the present invention.

[0027] Figure 4 It is a high cycle fatigue data curve diagram of the hard coating prepared in Example 1 of the present invention and Comparative Examples 1 to 3. DETAILED DESCRIPTION

[0028] Example 1

[0029] This embodiment includes the following steps:

[0030] Step 1, cleaning and pre-treating the guide tube of the automatic tilter made of 7075 aluminum; the cleaning and pre-treating process is: first immersing the guide tube of the automatic tilter in a container containing a metal cleaning agent solution of 20°C to 30°C and a mass concentration of 0.5%, and placing it in an ultrasonic generator for ultrasonic cleaning for 20 minutes, then rinsing it under running water after removal, and then immersing it in a container containing anhydrous ethanol, and placing it in an ultrasonic generator for ultrasonic cleaning for 5 minutes, and drying it with a hair dryer;

[0031] Step 2: Place the automatic tilting device guide tube that has been cleaned and pre-treated in step 1 in a sandblasting machine equipped with sandblasting material, and use air pressure to spray the sandblasting material 24# brown corundum through a spray gun onto the surface of the automatic tilting device guide tube for sandblasting treatment. The air pressure for sandblasting treatment is 0.6MPa, and the distance between the spray gun and the workpiece is 150mm, until the sandblasting surface is matte, uniform, and the roughness is 10μm~13μm, and compressed air is used to blow to remove surface sand and floating dust, and then place the automatic tilting device guide tube that has been roughened by sandblasting in a sandblasting machine equipped with shot peening material, and use air pressure to spray the shot peening material 300# zirconium oxide through a spray gun onto the surface of the automatic tilting device guide tube for shot peening treatment. The air pressure for shot peening treatment is 0.1MPa, and the distance between the spray gun and the workpiece is 50mm, until the shot peening surface is matte, uniform, and the roughness is 8μm~11μm, and compressed air is used to blow to remove the shot and floating dust on the blasting surface, so as to obtain the automatic tilting device guide tube after surface treatment;

[0032] Step 3: Use the tooling to fix the surface treated automatic tilting device guide tube obtained in step 2 on the rotating table of the supersonic flame spraying. Then the ABB manipulator holds the supersonic flame spraying gun and uses supersonic flame spraying to spray NiCrAl coating on the surface of the automatic tilting device guide tube. The process parameters are: oxygen flow rate 24m 3 / h, kerosene flow rate 16L / h, powder feeding rate 10kg / h, spray distance 350mm, spray gun moving speed 600mm / min, spray gun step distance 1mm, spray 3 times, after the automatic tilter guide tube cools to room temperature, continue to use the spray gun to spray WC-12Co coating with supersonic flame. The process parameters are: oxygen flow rate 18m 3 / h, kerosene flow rate 24L / h, powder feeding amount 10kg / h, spray distance 350mm, spray gun moving speed 600mm / min, spray gun step 1mm, spray 6 times, form a hard coating on the surface of the automatic tilter guide cylinder, and remove the automatic tilter guide cylinder after it cools to room temperature.

[0033] The mechanical properties of the guide cylinder of the automatic recliner in this embodiment and the guide cylinder of the automatic recliner after surface treatment were tested, and the results are shown in Table 1.

[0034] Table 1

[0035]

[0036] As can be seen from Table 1, the mechanical properties of the automatic tilt guide tube substrate after surface treatment are comparable to those of the automatic tilt guide tube substrate.

[0037] The surface of the guide cylinder of the automatic tilter after each treatment process in this embodiment is subjected to 3D morphology analysis. The detection equipment is a VHX-950 digital microscope system of KEYNCE Company. The results are as follows: Figure 1-2 shown.

[0038] Figure 1 The 3D topography of the surface of the guide cylinder of the automatic tilting device after sandblasting in this embodiment is shown in FIG. Figure 1 It can be seen that the surface of the automatic tilter guide cylinder after sandblasting has greater roughness and a large number of sharp corners.

[0039] Figure 2 The surface 3D topography of the guide sleeve of the automatic tilting device after surface treatment in this embodiment is shown in FIG. Figure 2 It can be seen that the surface of the automatic tilter guide cylinder after the sandblasting and shot peening surface treatments still has a large roughness, but no sharp corners.

[0040] Will Figure 1 and Figure 2 By comparison, it can be seen that the present invention combines sandblasting and shot peening to obtain a roughened surface with both good roughness and compressive stress, while removing the sharp corners obtained by the sandblasting surface.

[0041] Figure 3 This is a cross-sectional SEM image of the hard coating prepared in this example. Figure 3It can be seen that the NiCrAl coating in the middle is well bonded to the automatic tilt guide tube substrate and the WC-12Co coating.

[0042] Comparative Example 1

[0043] The difference between this comparative example and Example 1 is that in step 2, the guide tube of the automatic tilter is only sandblasted; in step 3, the surface of the guide tube of the automatic tilter after surface treatment is only coated with WC-12Co coating by supersonic flame spraying.

[0044] Comparative Example 2

[0045] The difference between this comparative example and Example 1 is that in step 2, the guide cylinder of the automatic tilter is only subjected to sandblasting.

[0046] Comparative Example 3

[0047] The difference between this comparative example and Example 1 is that in step 3, only the surface of the automatic tilter guide cylinder after surface treatment is subjected to supersonic flame spraying of WC-12Co coating.

[0048] Figure 4 The high cycle fatigue data curve of the hard coating prepared in Example 1 of the present invention and Comparative Examples 1 to 3 is shown in FIG. Figure 4 It can be seen that the fatigue performance of the hard coating prepared in Comparative Example 1 by using a single sandblasting treatment combined with supersonic flame spraying of WC-12Co coating is the lowest, the fatigue performance of the hard coating prepared in Comparative Example 2 by using a single sandblasting treatment combined with supersonic flame spraying of NiCrAl coating and supersonic flame spraying of WC-12Co coating is better than that of Comparative Example 1, the fatigue performance of the hard coating prepared in Comparative Example 3 by using sandblasting and shot peening treatment combined with supersonic flame spraying of WC-12Co coating is significantly better than that of Comparative Example 1, and the fatigue performance of the hard coating prepared in Example 1 by using sand and shot peening treatment combined with supersonic flame spraying of NiCrAl coating and supersonic flame spraying of WC-12Co coating is the best, which is better than the hard coatings prepared in Comparative Examples 1 to 3.

[0049] In summary, the superhard coating prepared on the surface of the automatic tilt guide cylinder made of 7075 aluminum by the method of the present invention has excellent high-cycle fatigue performance while maintaining good mechanical properties, and its surface hardness and wear resistance are greatly improved.

[0050] Example 2

[0051] This embodiment includes the following steps:

[0052] Step 1, pre-cleaning the guide tube of the automatic tilter made of 7075 aluminum; the process of the pre-cleaning is as follows: first, immerse the guide tube of the automatic tilter in a container containing a metal cleaning agent solution at 20°C to 30°C and a mass concentration of 1%, and place it in an ultrasonic generator for ultrasonic cleaning for 5 minutes, then rinse it under running water after removal, and then immerse it in a container containing anhydrous ethanol, place it in an ultrasonic generator for ultrasonic cleaning for 10 minutes, and blow it dry with a hair dryer;

[0053] Step 2: Place the automatic tilting device guide tube that has been cleaned and pre-treated in step 1 in a sandblasting machine equipped with sandblasting material, and use air pressure to spray the sandblasting material 24# brown corundum through a spray gun onto the surface of the automatic tilting device guide tube for sandblasting treatment. The air pressure for sandblasting treatment is 0.1MPa, and the distance between the spray gun and the workpiece is 50mm, until the sandblasting surface is matte, uniform, and the roughness is 9μm~12μm, and compressed air is used to blow to remove surface sand and floating dust, and then place the automatic tilting device guide tube that has been roughened by sandblasting in a sandblasting machine equipped with shot peening material, and use air pressure to spray the shot peening material 300# zirconium oxide through a spray gun onto the surface of the automatic tilting device guide tube for shot peening treatment. The air pressure for shot peening treatment is 0.5MPa, and the distance between the spray gun and the workpiece is 150mm, until the shot peening surface is matte, uniform, and the roughness is 8μm~11μm, and compressed air is used to blow to remove the shot and floating dust on the blasting surface, so as to obtain the automatic tilting device guide tube after surface treatment;

[0054] Step 3: Use the tooling to fix the surface treated automatic tilting device guide tube obtained in step 2 on the rotating table of the supersonic flame spraying. Then the ABB manipulator holds the supersonic flame spraying gun and uses supersonic flame spraying to spray NiCrAl coating on the surface of the automatic tilting device guide tube. The process parameters are: oxygen flow rate 18m 3 / h, kerosene flow rate 24L / h, powder feeding rate 1kg / h, spray distance 300mm, spray gun moving speed 100mm / min, spray gun step distance 6mm, spray 3 times, after the automatic tilter guide tube cools to room temperature, continue to use the spray gun to spray WC-12Co coating with supersonic flame. The process parameters are: oxygen flow rate 24m 3 / h, kerosene flow rate 16L / h, powder feeding amount 1kg / h, spray distance 150mm, spray gun moving speed 100mm / min, spray gun step 6mm, spray 6 times, form a hard coating on the surface of the automatic tilter guide cylinder, and remove the automatic tilter guide cylinder after it cools to room temperature.

[0055] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiment according to the technical essence of the invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a hard coating for improving fatigue of an automatic tilt guide cylinder, characterized in that: The method comprises the following steps: Step 1: Clean and pretreat the guide cylinder of the automatic tilter; Step 2, placing the automatic tilting device guide tube that has been cleaned and pretreated in step 1 in a sandblasting machine equipped with sandblasting material, using air pressure to spray the sandblasting material onto the surface of the automatic tilting device guide tube through a spray gun for sandblasting treatment, and then placing the automatic tilting device guide tube that has been roughened by sandblasting in a sandblasting machine equipped with shot peening material, using air pressure to spray the shot peening material onto the surface of the automatic tilting device guide tube through a spray gun for shot peening treatment, to obtain the automatic tilting device guide tube after surface treatment; the air pressure of the sandblasting treatment is 0.1MPa-0.6MPa, and the distance between the spray gun and the workpiece is 50mm-150mm; the air pressure of the shot peening treatment is 0.1MPa-0.5MPa, and the distance between the spray gun and the workpiece is 50mm-150mm; Step 3: Fix the surface-treated guide tube of the automatic tilter obtained in step 2 on a rotating table of supersonic flame spraying, and then use supersonic flame spraying to apply NiCrAl coating, and then use supersonic flame spraying to apply WC-Co coating to form a hard coating on the surface of the guide tube of the automatic tilter; the process parameters of the supersonic flame spraying of NiCrAl coating are: oxygen flow rate 18m 3 / h~24m 3 / h, kerosene flow rate 16L / h~24L / h, powder feeding amount 1kg / h~10kg / h, spray distance 150mm~350mm, spray gun moving speed 100mm / min~600mm / min, spray gun step distance 1mm~6mm; the process parameters of the supersonic flame spraying WC-Co coating are: oxygen flow rate 18m 3 / h~24m 3 / h, kerosene flow rate 16L / h~24L / h, powder feeding amount 1kg / h~10kg / h, spray distance 150mm~350mm, spray gun moving speed 100mm / min~600mm / min, spray gun step distance 1mm~6mm.

2. The method for preparing a hard coating for improving fatigue of an automatic tilting device guide sleeve according to claim 1, characterized in that: The guide cylinder of the automatic tilter described in step 1 is made of aluminum alloy.

3. The method for preparing a hard coating for improving fatigue of an automatic tilting device guide sleeve according to claim 1, characterized in that: The cleaning pretreatment process described in step 1 is: first immerse the automatic tilter guide tube in a container containing a metal cleaning agent solution at 20°C to 30°C and a mass concentration of 0.5% to 1%, and place it in an ultrasonic generator for ultrasonic cleaning for 5min to 20min. After removal, rinse it under running water, then immerse it in a container filled with anhydrous ethanol, place it in an ultrasonic generator for ultrasonic cleaning for 5min to 10min, and blow dry it with a hair dryer.

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