Preparation and spraying process of stable, difficult-to-crack and controllable-thickness aluminum-silicon diffusion coating

Abstract

The invention discloses a preparation and spraying process for a stable, difficult-to-crack and thickness-controllable aluminum-silicon diffusion coating, which comprises the following steps: firstly, preparing slurry, then sequentially carrying out a series of early-stage preparation work of sieving, hot degreasing, sanding and cleaning and shielding before spraying, then selecting proper spraying equipment and spraying environment, carrying out trial spraying by using a spray gun to face a suction opening before spraying, and finally, carrying out spray coating on the aluminum-silicon diffusion coating. And after the spraying state is stable, the gun is moved in sequence, after spraying, a workpiece needs to be subjected to coating curing treatment, then vacuum diffusion heat treatment is conducted, and finally sanding cleaning is conducted. According to the process, an AI-Si and AI-Cr multi-element co-permeation technology is adopted. A nickel-based component is coated with the aluminum-silicon slurry, and an aluminum-silicon compound coating is formed after diffusion heat treatment, so that the aluminum-silicon compound coating has high-temperature oxidation resistance, vulcanization or erosion resistance and thermal shock resistance. The process can be applied to partial blades of gas turbines and aero-engines.

Description

Technical Field

[0001] The invention relates to a spraying process for preparing a stable, crack-resistant, thickness-controllable aluminum-silicon diffusion coating, and belongs to the technical field of coating preparation processes. Background Art

[0002] Heavy-duty gas turbines (heavy-duty gas turbines) are the heavy equipment of a great country. They are important strategic high-end technical equipment to ensure national defense security, energy security and industrial competitiveness. They are widely used in power generation, ship propulsion and other fields. High-temperature turbine blades are used in harsh working conditions such as high temperature, high load and high corrosion, which far exceeds the use limit of the current high-temperature alloy substrate. A thick and uniform functional coating must be sprayed on the surface of the substrate.

[0003] In order to improve the efficiency and power of heavy-duty gas turbines, turbine blades are usually designed into complex structures with twists, bends, and widths. There are many key problems in uniformly spraying coatings on large blades with complex shapes. First of all, the current coating spraying method is mainly manual spraying. The operator's technical level and working conditions will seriously affect the stability of thermal barrier coating spraying, resulting in excessive defective rate and low efficiency. Secondly, complex high-temperature alloy blades have high technical requirements for spraying. The existing spraying process leads to uneven coating thickness, which seriously affects the quality of spraying and ultimately affects the service life of high-temperature blades and the life cycle of heavy-duty gas turbines. Therefore, it is necessary to design a process method to reduce problems such as cracking, cracking after diffusion heat treatment, and uncontrollable thickness. Summary of the invention

[0004] In view of the problems existing in the above-mentioned prior art, the present invention provides a spraying process for preparing a stable, crack-resistant, thickness-controllable aluminum-silicon diffusion coating, thereby providing a coating with high-temperature oxidation, sulfurization or erosion resistance and thermal shock resistance.

[0005] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a spraying process for preparing a stable, crack-resistant, thickness-controllable aluminum-silicon diffusion coating, comprising the following steps: Step S1: slurry preparation, prepare slurry components including 40%-60% 5μm Al powder, 5%-10% 5μm silicon powder, 3%-8% glycerol, 3%-8% phosphoric acid, 20%-28% water, 3%-8% chromium trioxide, and 0.5%-1.5% chromium hydroxide, place the above components in a container and stir them regularly; Step S2: Preparatory work before operation: the spray gun needs to be cleaned with alcohol to ensure that it is clean and free of foreign matter, the slurry is placed in a mixing box and stirred for at least 24 hours, and the slurry is screened through 50, 100, and 150 mesh screens in sequence to remove all agglomerated materials; Step S3: thermally degrease the required spraying parts to remove surface oil stains, use an air circulation drying furnace for treatment, the treatment time is 0.8-1.2 hours, and the treatment temperature is controlled to operate at 330±5°C; Step S4: sandblasting and cleaning, sandblasting and cleaning the parts before spraying; Step S5: Visually inspect the spraying area to see if there is any abnormality. If there is still a lot of oil or foreign matter; or a lot of sand particles remain, repeat steps S2-S4; Step S6: Masking before spraying: Use Japanese paper protective film and masking tape to mask the non-spraying area before spraying. Check whether the protective film is intact. If it is broken, it needs to be masked again. During the masking process, be careful not to touch the area to be sprayed, which will cause quality problems in the subsequent spraying. After masking, dry to remove moisture; Step S7: Select appropriate spraying equipment and spraying environment; Step S8: Loading aluminum paint, adding slurry into the spray gun tank. Before loading the paint, the spray gun tank must be cleaned to prevent other impurities from mixing into it. After loading, the aluminum slurry sealing tank must be immediately covered and placed back on the agitator; Step S9: Before painting, use a spray gun to test spray at the exhaust port, and close the spray gun after the paint spraying state is stable and the atomization degree is appropriate; the distance between the spray gun nozzle and the workpiece surface is 80-120 mm, and the gun is moved in sequence, and 2-3 layers of paint are sprayed each time; if the part has an arc or a bridge area, only one layer of spraying is required; dip a brush in the paint, and use the brush to evenly apply the paint to the position that cannot be sprayed; after spraying, remove the mask; after spraying, the workpiece needs to be cured by coating; S10: Visually inspect the coating of the component and perform post-processing if any abnormality is found; S11: Measuring paint thickness Use German Fisher high-precision coating thickness gauge to measure the thickness of the spray paint; S12: After the abnormal state is processed, the steps S3 to S7 are circulated, and the number of cycles is determined according to the thickness of the diffusion coating to be prepared. The thickness of each layer of spray paint cannot exceed 30 μm; S13: performing vacuum diffusion heat treatment on the component after the cycle execution is completed; S14: Sand blasting cleaning. After diffusion heat treatment, the parts need to be sprayed with glass sand to remove surface powder and scum.

[0006] Furthermore, the storage temperature of the slurry prepared in step S1 is 5-10°C, and it is stirred regularly for 24 hours, once a month. The slurry is stored in a closed container and has a shelf life of 3-6 months.

[0007] Furthermore, the sandblasting cleaning conditions in step S4 are as follows: medium: #220 alumina; pressure: 1-3 bar; angle: 60°-90°; distance from the workpiece: 10-20 cm.

[0008] Furthermore, in step S6, after shielding, the workpiece is placed under a short-wave infrared paint lamp for drying for 5-10 minutes to remove surface moisture of the workpiece, and the surface temperature of the component is maintained below 35° C. before painting.

[0009] Furthermore, in step S7, SATA Jet 1000 or ANEST IWATA 77-21G gravity manual spray gun is used for spraying, and the spraying pressure is 35psi. Parts that cannot be sprayed with a spray gun can be locally painted with camel hair or squirrel hair brushes; spray booth: dry back or wet back spray booth; check whether the aluminum paint has been stirred for more than 24 hours, and ensure that it has been stirred on the mixer after being taken to the spray booth.

[0010] Furthermore, in step S8, no impurities such as water and dust shall touch the workpiece during the spraying process; the appropriate air pressure, oil volume and atomization size shall be adjusted; the distance between the spray gun and the workpiece shall always be controlled at about 10 cm; when spraying to the bridge position, it can be wiped with non-woven fabric or pure cotton gloves; when spraying, the angle between the spray gun and the workpiece should be between 60° and 90°; after spraying, the unused paint in the spray gun should be immediately put into the original packaging can; after spraying, the brush and spray gun should be cleaned immediately; during the spraying process, the ventilation system should be ensured to work normally.

[0011] Furthermore, in step S9, after spraying, the workpiece needs to be subjected to coating curing treatment, specifically, the sprayed stator blades are subjected to paint surface drying treatment, and are baked at 80°C for 15 minutes using an infrared paint baking lamp; and then heat treated at 330°C for 1 hour using an air circulation furnace.

[0012] Furthermore, in step S10, the post-processing steps are specifically as follows: if the paint surface is rough and uneven; the painted surface is obviously uneven; there are protruding particles on the paint surface, sandpaper can be used to polish and repair the abnormal area; if there are cracks in the coating, the state of the workpiece needs to be evaluated according to the size and depth of the cracks. If the cracks are not penetrating, they can be polished and removed with a sanding machine and then sprayed. If the cracks penetrate the body, rework is required.

[0013] Furthermore, in step S13, the temperature is raised to 870 degrees Celsius and then kept for two hours, and then cooled to below 200 degrees Celsius in an argon environment, and then taken out of the furnace and cooled to room temperature. The diffusion furnace is a controlled atmosphere furnace, using pure argon with a dew point not higher than -40 degrees Celsius. The furnace should be able to maintain a temperature of up to 1065 ± 15 degrees Celsius, and the argon inert gas partial pressure standard is 0.05 TORR (6.6661 Pa).

[0014] Furthermore, in step S13, 180# glass sand is used for sand blasting; pressure: 1-2 bar (low pressure); angle: 60°-90° distance: 10-20 cm.

[0015] The beneficial effects of the present invention are as follows: the process adopts Al-Si and Al-Cr multi-element co-penetration technology. Aluminum-silicon slurry is coated on nickel-based components, and after diffusion heat treatment, an aluminum-silicon compound coating is formed, thereby having high-temperature oxidation resistance, sulfurization or erosion resistance, and thermal shock resistance. This process can be applied to gas turbines and some blades of aircraft engines. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagrams of four abnormal states in an embodiment of the present invention; Figure 2 A schematic diagram of using sandpaper to polish an abnormal area in an embodiment of the present invention; Figure 3 Schematic diagram of surface changes during the spraying process in an embodiment of the present invention; Figure 4 This is a microscopic metallographic structure test piece of the aluminum silicon diffusion coating prepared in an embodiment of the present invention. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solution and advantages of the present invention more clear, the present invention is further described in detail below through the accompanying drawings and embodiments. However, it should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0018] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which the present invention belongs. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0019] The present invention mainly uses the slurry method to spray the improved aluminum diffusion coating (chromium aluminum silicon coating) on ​​the parts. This process adopts AI-Si and AI-Cr multi-element co-penetration technology. The aluminum silicon slurry is coated on the nickel-based parts, and after diffusion heat treatment, an aluminum silicon compound coating is formed, which has high temperature oxidation resistance, sulfurization or erosion resistance, and thermal shock resistance. This process can be applied to some blades of gas turbines and aircraft engines.

[0020] The preparation of aluminum-silicon compound coatings is prone to cracking during the preparation process, cracking after diffusion heat treatment, and uncontrollable thickness. This process introduces how to stably prepare thickened aluminum-silicon diffusion coatings that are not prone to cracking and have controllable thickness.

[0021] The slurry method is to mix the metal powder to be infiltrated with a binder and an activator in a certain proportion and grind it into a suspension, also called "slurry", which is then brushed on the surface of the workpiece, dried and then subjected to high-temperature diffusion treatment under vacuum or argon protection. The proportioned slurry is a substance with a heavy pigment, which delaminates quickly and the pigment is easy to clump, so it needs to be stirred regularly during storage; it needs to be stirred continuously during use.

[0022] Step S1: Composition and analysis of slurry 1. Ingredients: 5μm Al powder 50%, 5μm silicon powder 10%, glycerol 5%, phosphoric acid 5%, water 24%, chromium trioxide 5%, chromium hydroxide 1% 2. Component Analysis Aluminide coatings have good resistance to high-temperature oxidation, but the nickel-rich NiAl phase is prone to martensitic transformation and is not resistant to sulfidation and hot corrosion.

[0023] Cr is an excellent element for high temperature hot corrosion resistance, so the introduction of chromium into a simple aluminized coating can improve the mutual diffusion of elements between the coating and the substrate and extend the service life. Aluminum-chromium co-diffusion prepared on the surface of nickel-based alloy can also prevent the nickel-rich β-NiAl phase from undergoing martensitic transformation during high temperature oxidation. The presence of chromium can promote the selective oxidation of aluminum on the coating surface and reduce the critical aluminum content required to form a protective aluminum oxide film.

[0024] Al-Si co-penetration has good high temperature oxidation resistance, and its hot corrosion resistance can be improved after co-penetration. The co-penetration coating has less brittleness and is not easy to crack and fall off. The coating structure is mainly β-NiAl phase, and the silicon element is distributed in the coating as silicon-rich second phase particles. However, the silicon content in the coating should not be too high, otherwise the silicon and the nickel in the matrix will form a harmful low melting point phase at high temperature, and make the coating brittle and easy to fall off during the oxidation process. Therefore, the silicon content in the slurry shall not be higher than 10%.

[0025] Step S2: Preparatory work before operation: the spray gun needs to be cleaned with alcohol to ensure that it is clean and free of foreign matter, the slurry is placed in a mixing box and stirred for at least 24 hours, and the slurry is screened through 50, 100, and 150 mesh screens in sequence to remove all agglomerated materials; Step S3: thermally degrease the required spraying parts to remove surface oil stains, use an air circulation drying furnace for treatment, the treatment time is 0.8-1.2 hours, and the treatment temperature is controlled to operate at 330±5°C; Step S4: sandblasting and cleaning, sandblasting and cleaning the parts before spraying; Step S5: Visually inspect the spraying area to see if there is any abnormality. If there is still a lot of oil or foreign matter; or a lot of sand particles remain, repeat steps S2-S4; Step S6: Masking before spraying: Use Japanese paper protective film and masking tape to mask the non-spraying area before spraying. Check whether the protective film is intact. If it is broken, it needs to be masked again. During the masking process, be careful not to touch the area to be sprayed, which will cause quality problems in the subsequent spraying. After masking, dry to remove moisture; Step S7: Select appropriate spraying equipment and spraying environment; Step S8: Loading aluminum paint, adding slurry into the spray gun tank. Before loading the paint, the spray gun tank must be cleaned to prevent other impurities from mixing into it. After loading, the aluminum slurry sealing tank must be immediately covered and placed back on the agitator; Step S9: Before painting, use a spray gun to test spray at the exhaust port, and close the spray gun after the paint spraying state is stable and the atomization degree is appropriate; the distance between the spray gun nozzle and the workpiece surface is 80-120 mm, and the gun is moved in sequence, and 2-3 layers of paint are sprayed each time; if the part has an arc or a bridge area, only one layer of spraying is required; dip a brush in the paint, and use the brush to evenly apply the paint to the position that cannot be sprayed; after spraying, remove the mask; after spraying, the workpiece needs to be cured by coating; S10: Visually inspect the coating of the component and perform post-processing if any abnormality is found; S11: Measuring paint thickness Use German Fisher high-precision coating thickness gauge to measure the thickness of the spray paint; S12: After the abnormal state is processed, the steps S3 to S7 are circulated, and the number of cycles is determined according to the thickness of the diffusion coating to be prepared. The thickness of each layer of spray paint cannot exceed 30 μm; S13: performing vacuum diffusion heat treatment on the component after the cycle execution is completed; S14: Sand blasting cleaning. After diffusion heat treatment, the parts need to be sprayed with glass sand to remove surface powder and scum.

[0026] Preferably, in this embodiment, the storage temperature of the slurry prepared in step S1 is 5-10°C, and it is stirred regularly for 24 hours once a month. The slurry is stored in a closed container and has a shelf life of 3-6 months.

[0027] In this embodiment, preferably, the sandblasting cleaning conditions in step S4 are as follows: medium: #220 alumina; pressure: 1-3 bar; angle: 60°-90°; distance from the workpiece: 10-20 cm.

[0028] Preferably, in step S6 of this embodiment, after shielding, the workpiece is placed under a short-wave infrared paint lamp for drying for 5-10 minutes to remove surface moisture of the workpiece, and the surface temperature of the component is maintained below 35° C. before painting.

[0029] Preferably, in step S7, a gravity-type manual spray gun is used for spraying paint, and the spraying pressure is 35 psi. Parts that cannot be sprayed with a spray gun can be locally painted with a camel hair or squirrel hair brush; spray paint room: dry back or wet back spray paint room; check whether the aluminum paint has been stirred for more than 24 hours, and ensure that it has been stirred on the mixer after being taken to the spray paint room.

[0030] Preferably, in step S8, no impurities such as water and dust shall touch the workpiece during the spraying process; the air pressure, oil volume and atomization size shall be adjusted appropriately; the distance between the spray gun and the workpiece shall always be controlled at about 10 cm; when spraying to the bridging position, it can be wiped with non-woven fabric or pure cotton gloves; when spraying, the angle between the spray gun and the workpiece should be between 60° and 90°; after spraying, the unused paint in the spray gun should be immediately put into the original packaging can; after spraying, the brush and spray gun should be cleaned immediately; during spraying, the ventilation system should be ensured to work normally.

[0031] Preferably, in step S9 of the present embodiment, after spraying, the workpiece needs to be subjected to coating curing treatment, specifically, the sprayed stator blades are subjected to paint surface drying treatment, and are baked at 80°C for 15 minutes using an infrared paint baking lamp; followed by heat treatment at 330°C for 1 hour using an air circulation furnace.

[0032] In this embodiment, in step S10, the post-processing steps are as follows: if the paint surface is rough and uneven; the painted surface is obviously uneven; there are protruding particles on the paint surface, sandpaper can be used to polish and repair the abnormal area; if there are cracks in the coating, the state of the workpiece needs to be evaluated according to the size and depth of the cracks. If the cracks are not penetrating, they can be polished and removed with a sanding machine and then sprayed. If the cracks penetrate the body, rework is required.

[0033] In this embodiment, preferably, in step S13, the temperature is raised to 870 degrees Celsius and then kept for two hours, and then cooled to below 200 degrees Celsius in an argon environment, and then taken out of the furnace and cooled to room temperature. The diffusion furnace is a controlled atmosphere furnace, using pure argon with a dew point not higher than -40 degrees Celsius. The furnace should be able to maintain a temperature of up to 1065 ± 15 degrees Celsius, and the argon inert gas partial pressure standard is 0.05 TORR (6.6661 Pa).

[0034] In this embodiment, preferably, in step S13, 180# glass sand is used for sand blasting; pressure: 1-2 bar (low pressure); angle: 60°-90°; distance: 10-20 cm.

[0035] This process uses AI-Si and AI-Cr multi-element co-penetration technology. Aluminum-silicon slurry is coated on nickel-based components, and after diffusion heat treatment, an aluminum-silicon compound coating is formed, which has high-temperature oxidation, sulfurization or erosion resistance and thermal shock resistance. This process can be applied to some blades of gas turbines and aircraft engines.

[0036] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A spraying process for preparing a stable, crack-resistant, thickness-controllable aluminum-silicon diffusion coating, characterized in that: The following steps are involved: Step S1: slurry preparation, prepare slurry components including 40%-60% 5μm Al powder, 5%-10% 5μm silicon powder, 3%-8% glycerol, 3%-8% phosphoric acid, 20%-28% water, 3%-8% chromium trioxide, and 0.5%-1.5% chromium hydroxide, place the above components in a container and stir them regularly; Step S2: Preparatory work before operation: the spray gun needs to be cleaned with alcohol to ensure that it is clean and free of foreign matter, the slurry is placed in a mixing box and stirred for at least 24 hours, and the slurry is screened through 50, 100, and 150 mesh screens in sequence to remove all agglomerated materials; Step S3: thermally degrease the required spraying parts to remove surface oil stains, use an air circulation drying furnace for treatment, the treatment time is 0.8-1.2 hours, and the treatment temperature is controlled to operate at 330±5°C; Step S4: sandblasting and cleaning, sandblasting and cleaning the parts before spraying; Step S5: Visually inspect the spraying area to see if there is any abnormality. If there is still a lot of oil or foreign matter; or a lot of sand particles remain, repeat steps S2-S4; Step S6: Masking before spraying: Use Japanese paper protective film and masking tape to mask the non-spraying area before spraying. Check whether the protective film is intact. If it is broken, it needs to be masked again. During the masking process, be careful not to touch the area to be sprayed, which will cause quality problems in the subsequent spraying. After masking, dry to remove moisture; Step S7: Select appropriate spraying equipment and spraying environment; Step S8: Loading aluminum paint, adding slurry into the spray gun tank. Before loading the paint, the spray gun tank must be cleaned to prevent other impurities from mixing into it. After loading, the aluminum slurry sealing tank must be immediately covered and placed back on the agitator; Step S9: Before painting, use a spray gun to test spray at the exhaust port, and close the spray gun after the paint spraying state is stable and the atomization degree is appropriate; the distance between the spray gun nozzle and the workpiece surface is 80-120 mm, and the gun is moved in sequence, and 2-3 layers of paint are sprayed each time; if the part has an arc or a bridge area, only one layer of spraying is required; dip a brush in the paint, and use the brush to evenly apply the paint to the position that cannot be sprayed; after spraying, remove the mask; after spraying, the workpiece needs to be cured by coating; S10: Visually inspect the coating of the component and perform post-processing if any abnormality is found; S11: Measuring paint thickness Use German Fisher high-precision coating thickness gauge to measure the thickness of the spray paint; S12: After the abnormal state is processed, the steps S3 to S7 are circulated, and the number of cycles is determined according to the thickness of the diffusion coating to be prepared. The thickness of each layer of spray paint cannot exceed 30 μm; S13: performing vacuum diffusion heat treatment on the component after the cycle execution is completed; S14: Sand blasting cleaning. After diffusion heat treatment, the parts need to be sprayed with glass sand to remove surface powder and scum.

2. The spraying process for preparing a stable, crack-resistant, thickness-controllable aluminum-silicon diffusion coating according to claim 1 is characterized in that: The storage temperature of the slurry prepared in step S1 is 5-10° C., and it is stirred regularly and continuously for more than 24 hours, once a month. The slurry is stored in a closed container and has a shelf life of 3-6 months.

3. The spraying process for preparing a stable, crack-resistant, thickness-controllable aluminum-silicon diffusion coating according to claim 1 is characterized in that: The sandblasting cleaning conditions in step S4 are as follows: medium: #220 alumina; Pressure: 1-3 bar; Angle: 60°-90°; Distance from workpiece: 10-20cm.

4. The spraying process for preparing a stable, crack-resistant, thickness-controllable aluminum-silicon diffusion coating according to claim 1 is characterized in that: In step S6, after shielding, the workpiece is placed in a short-wave infrared paint lamp or an air circulation oven for drying for 5-10 minutes to remove surface moisture of the workpiece, and the surface temperature of the component is maintained below 35° C. before painting.

5. The spraying process for preparing a stable, crack-resistant, thickness-controllable aluminum-silicon diffusion coating according to claim 1, characterized in that: In the step S7, a gravity-type manual spray gun is used for spraying paint, and the spraying pressure is 35 psi. Parts that cannot be sprayed with a spray gun can be partially painted with a camel hair or squirrel hair brush; spray booth: dry back or wet back spray booth; check whether the aluminum paint has been stirred for more than 24 hours, and ensure that it has been stirred on the mixer after being taken to the spray booth.

6. The spraying process for preparing a stable, crack-resistant, thickness-controllable aluminum-silicon diffusion coating according to claim 1, characterized in that: In the step S8, no impurities such as water and dust should touch the workpiece during the spraying process; the appropriate air pressure, oil volume, and atomization size should be adjusted; the distance between the spray gun and the workpiece should always be controlled at about 10 cm; when spraying to the bridge position, it can be wiped with non-woven fabric or pure cotton gloves; when spraying, the angle between the spray gun and the workpiece should be between 60° and 90°; after spraying, the unused paint in the spray gun should be immediately put into the original packaging can; after spraying, the brush and spray gun should be cleaned immediately; During spraying, ensure that the ventilation system is operating normally.

7. The spraying process for preparing a stable, crack-resistant, thickness-controllable aluminum-silicon diffusion coating according to claim 1, characterized in that: In step S9, after spraying, the workpiece needs to be subjected to coating curing treatment, specifically, the sprayed stator blades are subjected to paint surface drying treatment, and are baked at 80°C for 15 minutes using an infrared paint lamp or an air circulation oven; and then heat treated at 330°C for 1 hour using an air circulation oven.

8. The spraying process for preparing a stable, crack-resistant, thickness-controllable aluminum-silicon diffusion coating according to claim 1, characterized in that: In step S10, the post-processing steps are specifically as follows: if the paint surface is rough and uneven; the painted surface is obviously uneven; there are protruding particles on the paint surface, sandpaper can be used to polish and repair the abnormal area; if there are cracks in the coating, the state of the workpiece needs to be evaluated according to the size and depth of the cracks. If it is not a penetrating crack, it can be polished and removed with a sanding machine and then sprayed. If the crack is penetrating, rework is required.

9. The spraying process for preparing a stable, crack-resistant, thickness-controllable aluminum-silicon diffusion coating according to claim 1, characterized in that: In step S13, the temperature is raised to 870 degrees Celsius and then kept for two hours, and then cooled to below 200 degrees Celsius in an argon environment, and then taken out of the furnace and cooled to room temperature. The diffusion furnace is a controlled atmosphere furnace, using pure argon with a dew point not higher than -40 degrees Celsius. The furnace should be able to maintain a temperature of up to 1065 ± 15 degrees Celsius, and the argon inert gas partial pressure standard is 0.05 TORR (6.6661Pa).

10. The spraying process for preparing a stable, crack-resistant, thickness-controllable aluminum-silicon diffusion coating according to claim 1, characterized in that: In step S13, 180# glass sand is used for sand blasting; Pressure: 1-2 bar (low pressure); Angle: 60°-90° Distance: 10-20cm.

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