Tungsten carbide coating and wear rate control method thereof

Abstract

The invention discloses a tungsten carbide coating and a wear rate control method thereof. The raw materials of the tungsten carbide coating comprise Ni45 powder and WC45 powder, and the WC45 powder comprises 0.3% of C, 2.2% of B, 3.3% of Si, 11% of Cr, 9% of Fe and 1t of Mn; 0.1%; the WC45 powder comprises the following components in percentage by weight: 1.83% of C, 0.1% of Cr, 1.24% of B, 1.76% of Si, 1.44% of Fe, 43.2% of W and the balance of Ni and inevitable impurities; the wear rate control method comprises the step of surfacing the Ni45 transition layer and the WC45 hard coating on the steel base material. The invention provides a brand-new method for regulating and controlling the wear rate of the coating, the wear rate of the tungsten carbide coating can be remarkably reduced, the high hardness of the tungsten carbide coating can be considered, and the coating has low friction coefficient and wear rate.

Description

Technical Field

[0001] The invention belongs to the technical field of tungsten carbide coatings, and in particular relates to a tungsten carbide coating and a wear rate control method thereof. Background Art

[0002] In the field of metallurgical industry, wear caused by friction has a significant impact on equipment and production efficiency, which is mainly reflected in shortened equipment life, reduced energy efficiency, reduced product quality, increased downtime and maintenance costs, increased accident risks and many other aspects. Seeking feasible and effective solutions has always been the goal of the metallurgical industry and the focus of tribology. Surface engineering technology can improve the wear resistance, corrosion resistance, fatigue resistance and other properties by modifying the metal surface. Common technologies include plasma surfacing, laser cladding, electroplating, etc. These technologies can form high-hardness, low-friction coatings on the substrate surface, reduce friction and wear, extend equipment life, improve the working efficiency of metallurgical equipment, and reduce maintenance costs. They have been widely used in metallurgy, machinery, aviation and other fields.

[0003] 45# steel is a commonly used high-strength medium-carbon steel, which is widely used in the fields of machinery manufacturing and metallurgical industry due to its good plasticity, toughness and machinability. However, due to its low hardness and load-bearing capacity, 45# steel is prone to abrasive wear during operation as a metal substrate, resulting in low wear resistance, which greatly shortens its service life. Therefore, surfacing high-hardness wear-resistant coating on 45# steel to improve wear resistance has a positive effect on giving full play to the advantages of 45# steel and extending its service life.

[0004] Research shows that tungsten carbide is known for its extremely high hardness, wear resistance close to diamond, and excellent high temperature resistance. Under high temperature conditions, it can maintain hardness and strength, so it is widely used in cutting tools, wear-resistant coatings, drill bits and mold manufacturing, and is also widely used in friction pairs, bearings and other components to reduce friction and extend service life.

[0005] It is well known in the art that the wear resistance of a coating material is inversely proportional to its wear rate. The smaller the wear rate, the better the corresponding wear resistance. Therefore, the wear resistance of the coating material can be changed by regulating the wear rate of the coating material. At present, the traditional ways to regulate the wear rate of materials mainly include optimizing the composition ratio of materials, nitriding treatment, and reducing the surface roughness of materials. With the development of surface treatment technology, it is necessary to continue to develop new technologies for regulating the wear rate of materials. Summary of the invention

[0006] The present invention aims to provide a tungsten carbide coating and a wear rate control method thereof.

[0007] The present invention adopts the following technical solution.

[0008] A tungsten carbide coating adopts Ni45-WC45 alloy, and its raw materials include, by weight percentage: Ni45 powder: C: 0.2-0.6%, B: 2-3%, Si: 3-4.5%, Cr: 7-12%, Fe: <15%, Mn: <0.1%, the balance is Ni and unavoidable impurities; WC45 powder: C: 1.83%, Cr: 0.1%, B: 1.24%, Si: 1.76%, Fe: 1.44%, W: 43.2%, and the balance is Ni and unavoidable impurities.

[0009] As a preferred embodiment, the raw materials of the tungsten carbide coating in the present invention include: Ni45 powder: C: 0.3%, B: 2.2%, Si: 3.3%, Cr: 11%, Fe: 9%, Mn: < 0.1%, the balance is Ni and unavoidable impurities; WC45 powder: C: 1.83%, Cr: 0.1%, B: 1.24%, Si: 1.76%, Fe: 1.44%, W: 43.2%, and the balance is Ni and unavoidable impurities.

[0010] One of the wear rate control methods of the tungsten carbide coating of the present invention comprises the following steps: Step 1, placing the Ni45 powder and WC45 powder of the aforementioned proportion in a hot oven, drying them at 100±2°C for 3.5-4.5 hours for standby use; wherein the particle size distribution is about 44-150 μm; Step 2, polishing the surface of the 45# steel substrate, then placing it in anhydrous ethanol, cleaning it with an ultrasonic cleaner, and drying it for later use after cleaning; Step 3, using plasma surfacing equipment, first surfacing two layers of Ni45 transition layer on the 45# steel substrate treated in step 2, and then surfacing a layer of WC45 hard coating on the surface of the transition layer. After surfacing is completed, the workpiece is naturally cooled in the air; Step 4, grinding and polishing the coating surface obtained in step 3, and then washing it in anhydrous ethanol; Step 5, using aqua regia to corrode the coating surface of the workpiece treated in step 4, the corrosion time is controlled to be 5 to 10 seconds, and then cleaning and drying; Step 6, molding a coating melt on the coating surface of the workpiece treated in step 5, wherein the powder raw materials used in the coating melt are, by weight percentage, C: 2%, Cr: 0.2%, B: 1%, Si: 1.5%, Fe: 0.5%, Ti: 12%, and the balance is Ni and unavoidable impurities; Step 7, placing the workpiece processed in step 6 into a muffle furnace for tempering treatment, controlling the temperature to 400±5°C, setting the holding time to 30±2min, and placing it in the air for natural cooling after tempering treatment.

[0011] The second method for controlling the wear rate of the tungsten carbide coating in the present invention comprises the following steps: Step 11, placing the Ni45 powder and WC45 powder of the above proportion in a hot oven, drying them at 100±2°C for 3.5-4.5 hours for standby use; wherein the particle size distribution is about 44-150 μm; Step 12, polishing the surface of the 45# steel substrate, then placing it in anhydrous ethanol, cleaning it with an ultrasonic cleaner, and drying it for later use after cleaning; Step 13, using plasma surfacing equipment, first surfacing two layers of Ni45 transition layer on the 45# steel substrate treated in step 2, and then surfacing a layer of WC45 hard coating on the surface of the transition layer. After surfacing is completed, the workpiece is naturally cooled in the air; Step 14, using aqua regia to corrode the coating surface of the workpiece treated in step 13, the corrosion time is controlled to be 5 seconds, and then cleaning and drying are performed; Step 15, grinding and polishing the coating surface obtained in step 14 (the sandpaper specifications used for polishing are 600 mesh, 1200 mesh and 2000 mesh, respectively, and finally polishing to a mirror surface using a polishing paste with a particle size of W1), and then washing in anhydrous ethanol; Step 16, placing the workpiece processed in step 15 into a muffle furnace for tempering treatment, controlling the temperature to 400° C., setting the heat preservation time to 30 min, and placing it in the air for natural cooling after the tempering treatment.

[0012] As a preferred solution, in step 3: First, preheat the 45# steel substrate to 300℃, and control the surfacing process conditions as follows: adjust the distance between the plasma spray gun and the 45# steel substrate to 10mm, set the plasma surfacing machine current to 140A, the powder feeding amount to 15.5g / min, the welding speed to 220min / min, and surfacing two layers of Ni45 transition layer; Then, the 45# steel substrate was preheated to 550°C, the powder feeding rate was adjusted to 16.5g / min, the welding speed was adjusted to 200mm / min, and the WC45 hard surface layer was surfacing; During the cladding process, the powder feeding gas flow rate of the ion cladding machine is controlled at 4L / min, the ion gas flow rate is controlled at 2L / min, and the shielding gas flow rate is controlled at 10L / min.

[0013] As a preferred solution, the sandpaper used for polishing has specifications of 600 mesh, 1200 mesh and 2000 mesh, respectively, and finally a polishing paste with a particle size of W1 is used to polish to a mirror surface.

[0014] As a preferred embodiment, the step of molding the coating melt in step 6 is: first pouring the coating melt into the concave mold, and then immersing the coating surface of the workpiece treated in step 5 into the coating melt and extruding it, the extrusion pressure is controlled to be 20 to 30 MPa, the extrusion direction is perpendicular to the coating surface of the workpiece, the extrusion time is controlled to be 3 to 5 seconds, and the excess material on the edge of the workpiece is scraped off immediately after the extrusion is completed.

[0015] Beneficial effects: The present invention provides a new method for regulating the wear rate of the coating, which can not only significantly reduce the wear rate of the tungsten carbide coating, but also take into account the high hardness of the tungsten carbide coating; the coating prepared by the present invention is uniformly distributed with γ-(Fe, Ni), WC, and W2C phase structures, and the C element generated by the decomposition of WC combines with the W element, Cr element, Fe element, etc. in the material to generate W2C and M7C3 (M: Fe, Co, Cr, etc.) and other phase structures, and there is good metallurgical bonding between the coating and the substrate, and there are no defects such as cracks on the surface; the hardness of the coating prepared by the present invention can reach about 750Hv, and it has a low friction coefficient and wear rate, which plays an important role in extending the stability and safety of 45# steel under long-term working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the coating morphology image in Example 1 (after processing in step 5); Figure 2 This is the coating morphology image in Example 2 (after processing in step 7). DETAILED DESCRIPTION

[0017] The technical solution of the present invention is described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Example 1

[0018] A tungsten carbide coating adopts a Ni45-WC45 alloy. Its raw materials include, by weight percentage: Ni45 powder: C: 0.3%, B: 2.2%, Si: 3.3%, Cr: 11%, Fe: 9%, Mn: < 0.1%, the balance is Ni and inevitable impurities; WC45 powder: C: 1.83%, Cr: 0.1%, B: 1.24%, Si: 1.76%, Fe: 1.44%, W: 43.2%, the balance is Ni and inevitable impurities; titanium alloy powder: C: 2%, Cr: 0.2%, B: 1%, Si: 1.5%, Fe: 0.5%, Ti: 12%, the balance is Ni and inevitable impurities.

[0019] The wear rate control method of the tungsten carbide coating in this embodiment comprises the following steps: Step 1, placing the Ni45 powder and WC45 powder of the above proportion in a hot oven, drying at 100° C. for 4 hours, and setting aside; wherein the particle size distribution is about 44-150 μm; Step 2: Grind the surface of the 45# steel substrate (use 600 mesh and 1200 mesh to polish the surface to remove the surface iron oxide), then put it into anhydrous ethanol, clean it with an ultrasonic cleaner, and dry it after cleaning; Step 3, using plasma surfacing equipment, first surfacing two layers of Ni45 transition layer on the 45# steel substrate treated in step 2, and then surfacing a layer of WC45 hard coating on the surface of the transition layer. After surfacing, the workpiece is naturally cooled in the air; specifically: First, preheat the 45# steel substrate to 300℃, and control the surfacing process conditions as follows: adjust the distance between the plasma spray gun and the 45# steel substrate to 10mm, set the plasma surfacing machine current to 140A, the powder feeding amount to 15.5g / min, the welding speed to 220min / min, and surfacing two layers of Ni45 transition layer; Then, the 45# steel substrate was preheated to 550°C, the powder feeding rate was adjusted to 16.5g / min, the welding speed was adjusted to 200mm / min, and the WC45 hard surface layer was surfacing; During the cladding process, the powder feeding gas flow rate of the ion cladding machine is controlled at 4L / min, the ion gas flow rate is controlled at 2L / min, and the shielding gas flow rate is controlled at 10L / min; Step 4, grinding and polishing the coating surface obtained in step 3 (the sandpaper specifications used for polishing are 600 mesh, 1200 mesh and 2000 mesh, respectively, and finally polishing to a mirror surface using a polishing paste with a particle size of W1), and then washing in anhydrous ethanol; Step 5, using aqua regia to corrode the surface of the workpiece coating treated in step 4, the corrosion time is controlled to 8 seconds, and then cleaned and dried after the end; after step 5, the coating morphology obtained by sampling and testing is as follows Figure 1 As shown, it can be clearly seen that the coating surface has a large number of fishbone structures; Step 6, molding a coating melt on the coating surface of the workpiece after the treatment in step 5, wherein the powder raw materials used in the coating melt are, by weight percentage, C: 2%, Cr: 0.2%, B: 1%, Si: 1.5%, Fe: 0.5%, Ti: 12%, and the remainder is Ni and unavoidable impurities, and the particle size distribution is not greater than 20 μm; specifically: In an inert environment, first prepare the powder material according to the ratio in step 6 and melt it to obtain a coating melt, then pour the coating melt into a concave mold, and then immerse the coating surface of the workpiece treated in step 5 into the coating melt and extrude it, the extrusion pressure is controlled to be 24 MPa, the extrusion direction is perpendicular to the coating surface of the workpiece, the extrusion time is controlled to be 3 seconds, and the excess material on the edge of the workpiece is scraped off immediately after the extrusion is completed; In this embodiment, the cooperation of steps 4 to 7 includes shaping the fishbone structure, embedding the coating melt into the gap of the fishbone structure and metallurgically bonding it, so as to take into account the wear rate, hardness and friction coefficient of the coating; Step 7, the workpiece treated in step 6 is placed in a muffle furnace for tempering treatment, the temperature is controlled at 200°C, the holding time is set to 30 minutes, and after tempering treatment, it is placed in the air for natural cooling; after step 7, the coating morphology obtained by sampling and testing is as follows Figure 2 As shown, it can be clearly seen that the fishbone structure on the coating surface is basically filled with new materials and has basically formed a metallurgical bond with the WC45 hard surface layer. In this embodiment, the role of step 7 is to better control the wear rate of the coating. Comparative Example 1

[0020] A tungsten carbide coating and a wear rate control method thereof, referring to Example 1, the difference between the embodiment 1 and Example 1 is that the titanium alloy powder and steps 4 to 7 are omitted. Example 2

[0021] A tungsten carbide coating adopts a Ni45-WC45 alloy. Its raw materials include, by weight percentage: Ni45 powder: C: 0.3%, B: 2.2%, Si: 3.3%, Cr: 11%, Fe: 9%, Mn: < 0.1%, the balance is Ni and inevitable impurities; WC45 powder: C: 1.83%, Cr: 0.1%, B: 1.24%, Si: 1.76%, Fe: 1.44%, W: 43.2%, the balance is Ni and inevitable impurities.

[0022] The wear rate control method of the tungsten carbide coating in this embodiment comprises the following steps: Step 11, placing the Ni45 powder and WC45 powder of the above proportion in a hot oven, drying at 100° C. for 4 hours for standby use; wherein the particle size distribution is about 44-150 μm; Step 12, polish the surface of the 45# steel substrate (use 600 mesh and 1200 mesh to polish the surface to remove the surface iron oxide), then put it into anhydrous ethanol, clean it with an ultrasonic cleaner, and dry it after cleaning; Step 13, using plasma surfacing equipment, first surfacing two layers of Ni45 transition layer on the 45# steel substrate treated in step 2, and then surfacing a layer of WC45 hard coating on the surface of the transition layer. After surfacing, the workpiece is naturally cooled in the air; specifically: First, preheat the 45# steel substrate to 300℃, and control the surfacing process conditions as follows: adjust the distance between the plasma spray gun and the 45# steel substrate to 10mm, set the plasma surfacing machine current to 140A, the powder feeding amount to 15.5g / min, the welding speed to 220min / min, and surfacing two layers of Ni45 transition layer; Then, the 45# steel substrate was preheated to 550°C, the powder feeding rate was adjusted to 16.5g / min, the welding speed was adjusted to 200mm / min, and the WC45 hard surface layer was surfacing; During the cladding process, the powder feeding gas flow rate of the ion cladding machine is controlled at 4L / min, the ion gas flow rate is controlled at 2L / min, and the shielding gas flow rate is controlled at 10L / min; Step 14, using aqua regia to corrode the coating surface of the workpiece treated in step 13, the corrosion time is controlled to be 5 seconds, and then cleaning and drying are performed after the corrosion is completed; after step 5, the coating surface obtained by sampling and testing also has a large number of fishbone structures; Step 15, grinding and polishing the coating surface obtained in step 14 (the sandpaper specifications used for polishing are 600 mesh, 1200 mesh and 2000 mesh, respectively, and finally polishing to a mirror surface using a polishing paste with a particle size of W1), and then washing in anhydrous ethanol; Step 16, placing the workpiece processed in step 15 into a muffle furnace for tempering treatment, controlling the temperature to 200° C., setting the heat preservation time to 30 min, and placing it in the air for natural cooling after the tempering treatment. Example 3

[0023] A tungsten carbide coating and a wear rate control method thereof, referring to Example 1, the difference between the embodiment 1 and Example 1 is that step 7 is omitted. Comparative Example 2

[0024] A tungsten carbide coating and a wear rate control method thereof, referring to Example 1, the difference between the embodiment 1 and Example 1 is that step 7 is omitted. Comparative Example 3

[0025] A tungsten carbide coating and a wear rate control method thereof, referring to Example 1, the difference between the embodiment 1 and Example 1 is that the tempering treatment temperature is controlled to 400°C.

[0026] The coating samples in the examples and comparative examples were subjected to friction and wear tests and hardness tests. The results showed that the friction coefficient of the coating sample in Example 1 was finally maintained between 0.40 and 0.43, and the corresponding wear rate was 0.0274×10 -5 mm 3 / (N·m), the average hardness of the coating at three random points was 767.19 Hv; the friction coefficient of the coating sample in Example 2 was finally maintained between 0.58 and 0.62, and the corresponding wear rate was 0.0524×10 -5 mm 3 / (N·m), the average hardness of the coating at three random points was 744.06Hv; the friction coefficient of the coating sample in Example 3 was finally maintained between 0.70 and 0.73, and the corresponding wear rate was 0.0937×10 -5 mm 3 / (N·m), the average hardness of the coating at three random points was 780.61Hv; the friction coefficient of the coating sample in Example 1 was finally maintained between 0.78 and 0.83, and the corresponding wear rate was 1.5760×10 -5 mm 3 / (N·m), the average hardness of the coating at three random points was 789.49Hv; the friction coefficient of the coating sample in Example 2 was finally maintained between 0.43. and 0.47, and the corresponding wear rate was 0.0363×10 - 5 mm 3 / (N·m), the average hardness of the coating at three random points was 771.48Hv; the friction coefficient of the coating sample in Example 3 was finally maintained between 0.33 and 0.42, and the corresponding wear rate was 0.0508×10 -5 mm 3 / (N·m), the average hardness of the coating at three random test points is 714.55Hv.

[0027] On the whole, the coating performance obtained by the scheme in Example 1 is the best, and the wear rate, hardness and friction coefficient after adjustment can be well taken into account; the coating performance obtained by the scheme in Example 2 is slightly inferior to that of the coating performance in Example 1.

[0028] The new method for regulating the wear rate of the coating provided can not only significantly reduce the wear rate of the tungsten carbide coating, but also take into account the high hardness of the tungsten carbide coating; the prepared coating has uniformly distributed γ-(Fe, Ni), WC, and W2C phase structures, and the C element produced by the decomposition of WC combines with the W element, Cr element, Fe element, etc. in the material to generate W2C and M7C3 (M: Fe, Co, Cr, etc.) and other phase structures. There is good metallurgical bonding between the coating and the substrate, and there are no defects such as cracks on the surface; the hardness of the prepared coating can reach about 750Hv, with a low friction coefficient and wear rate, which plays an important role in extending the stability and safety of 45# steel under long-term working conditions.

Claims

1. A tungsten carbide coating, using Ni45-WC45 alloy, characterized in that: In terms of weight percentage, its raw materials include: Ni45 powder: C: 0.2-0.6%, B: 2-3%, Si: 3-4.5%, Cr: 7-12%, Fe: <15%, Mn: <0.1%, the balance is Ni and unavoidable impurities; WC45 powder: C: 1.83%, Cr: 0.1%, B: 1.24%, Si: 1.76%, Fe: 1.44%, W: 43.2%, the balance is Ni and unavoidable impurities.

2. The tungsten carbide coating according to claim 1, characterized in that: Its raw materials include: Ni45 powder: C: 0.3%, B: 2.2%, Si: 3.3%, Cr: 11%, Fe: 9%, Mn: < 0.1%, the balance is Ni and unavoidable impurities; WC45 powder: C: 1.83%, Cr: 0.1%, B: 1.24%, Si: 1.76%, Fe: 1.44%, W: 43.2%, the balance is Ni and unavoidable impurities.

3. The wear rate control method of tungsten carbide coating according to claim 2, characterized in that the steps include: Step 1, placing the Ni45 powder and WC45 powder of the above proportion in a hot oven, drying them at 100±2°C for 3.5-4.5 hours for standby use; wherein the particle size distribution is about 44-150 μm; Step 2, polishing the surface of the 45# steel substrate, then placing it in anhydrous ethanol, cleaning it with an ultrasonic cleaner, and drying it for later use after cleaning; Step 3, using plasma surfacing equipment, first surfacing two layers of Ni45 transition layer on the 45# steel substrate treated in step 2, and then surfacing a layer of WC45 hard coating on the surface of the transition layer. After surfacing is completed, the workpiece is naturally cooled in the air; Step 4, grinding and polishing the coating surface obtained in step 3, and then washing it in anhydrous ethanol; Step 5, using aqua regia to corrode the coating surface of the workpiece treated in step 4, the corrosion time is controlled to be 5 to 10 seconds, and then cleaning and drying; Step 6, molding a coating melt on the coating surface of the workpiece treated in step 5, wherein the powder raw materials used in the coating melt are, by weight percentage, C: 2%, Cr: 0.2%, B: 1%, Si: 1.5%, Fe: 0.5%, Ti: 12%, and the balance is Ni and unavoidable impurities; Step 7, placing the workpiece processed in step 6 into a muffle furnace for tempering treatment, controlling the temperature to 400±5°C, setting the holding time to 30±2min, and placing it in the air for natural cooling after tempering treatment.

4. The wear rate control method of tungsten carbide coating according to claim 2, characterized in that the step include: Step 11, placing the Ni45 powder and WC45 powder of the above proportion in a hot oven, drying them at 100±2°C for 3.5-4.5 hours for standby use; wherein the particle size distribution is about 44-150 μm; Step 12, polishing the surface of the 45# steel substrate, then placing it in anhydrous ethanol, cleaning it with an ultrasonic cleaner, and drying it for later use after cleaning; Step 13, using plasma surfacing equipment, first surfacing two layers of Ni45 transition layer on the 45# steel substrate treated in step 2, and then surfacing a layer of WC45 hard coating on the surface of the transition layer. After surfacing is completed, the workpiece is naturally cooled in the air; Step 14, using aqua regia to corrode the coating surface of the workpiece treated in step 13, the corrosion time is controlled to be 5 seconds, and then cleaning and drying are performed; Step 15, grinding and polishing the coating surface obtained in step 14, and then washing it in anhydrous ethanol; Step 16, placing the workpiece processed in step 15 into a muffle furnace for tempering treatment, controlling the temperature to 400° C., setting the heat preservation time to 30 min, and placing it in the air for natural cooling after the tempering treatment.

5. The wear rate control method of tungsten carbide coating according to claim 3 or 4, characterized in that: In step 3: First, preheat the 45# steel substrate to 300℃, and control the surfacing process conditions as follows: adjust the distance between the plasma spray gun and the 45# steel substrate to 10mm, set the plasma surfacing machine current to 140A, the powder feeding amount to 15.5g / min, the welding speed to 220min / min, and surfacing two layers of Ni45 transition layer; Then, the 45# steel substrate was preheated to 550°C, the powder feeding rate was adjusted to 16.5g / min, the welding speed was adjusted to 200mm / min, and the WC45 hard surface layer was surfacing; During the cladding process, the powder feeding gas flow rate of the ion cladding machine is controlled at 4L / min, the ion gas flow rate is controlled at 2L / min, and the shielding gas flow rate is controlled at 10L / min.

6. The wear rate control method of tungsten carbide coating according to claim 3, characterized in that: The sandpaper specifications used for polishing are 600 mesh, 1200 mesh and 2000 mesh, respectively, and finally polishing to a mirror surface is performed using polishing paste with a particle size of W1.

7. The wear rate control method of tungsten carbide coating according to claim 3, characterized in that: The step of molding the coating melt in step 6 is: first pour the coating melt into the concave mold, then immerse the coating surface of the workpiece processed in step 5 into the coating melt and extrude it, the extrusion pressure is controlled to be 20-30Mpa, the extrusion direction is perpendicular to the coating surface of the workpiece, the extrusion time is controlled to be 3-5 seconds, and the excess material on the edge of the workpiece is scraped off immediately after the extrusion is completed.

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