Preparation method of large-cylinder-diameter air-cooled diesel engine piston

Abstract

The invention discloses a preparation method of a piston of a large-cylinder-diameter air-cooled diesel engine. The preparation method specifically comprises the following steps: S1, modeling and zoning; s2, gradient printing; s3, adding a coating; the invention relates to the technical field of diesel engine pistons. According to the preparation method of the large-cylinder-diameter air-cooled diesel engine piston, collaborative optimization of the overall performance of the piston is achieved through gradient printing of the piston, light weight of the piston is achieved in cooperation with a honeycomb lattice structure, the abrasion loss is reduced through silicon carbide, the abrasion resistance of a top area is improved, a zirconium trialuminum nano precipitated phase is formed through zirconium, grains are refined, and the piston is obtained. Scandium, zirconium and aluminum are used for forming a composite precipitated phase, the high-temperature strength is improved, an efficient heat conduction network is constructed through graphene nanosheets, the heat conductivity of a middle area is improved, a three-dimensional network is constructed through carbon nanotubes, the toughness of a skirt area is improved, and by spraying a wear-resistant and corrosion-resistant coating on the surface of the piston, high interface bonding strength is achieved, friction force is reduced, and the service life of the piston is prolonged. The service life of the piston is prolonged and the maintenance cost is effectively reduced.

Description

Technical Field

[0001] The invention relates to the technical field of diesel engine pistons, in particular to a method for preparing a large-cylinder-diameter air-cooled diesel engine piston. Background Art

[0002] Pistons in large-bore, air-cooled diesel engines are typically made of aluminum alloy or cast iron. Aluminum alloys are suitable for high-speed diesel engines due to their light weight and excellent thermal conductivity, helping to reduce inertia and improve heat transfer efficiency. Cast iron, particularly pearlitic cast iron, offers advantages such as high mechanical strength, low thermal expansion coefficient, and excellent wear and corrosion resistance. It is therefore more suitable for low-speed diesel engines, especially air-cooled ones, due to its excellent wear resistance and strength, making it more suitable for air-cooled environments.

[0003] As engine technology develops towards high power density, low emissions, and intelligence, the performance requirements for large-bore air-cooled diesel engine pistons are becoming increasingly stringent. Traditional piston materials such as cast iron and conventional aluminum alloys have problems such as high density, poor thermal conductivity, and low thermal fatigue life, making it difficult to meet the stringent requirements of modern engines for lightweight, durability, and thermal efficiency. For example, although cast iron pistons have high strength, they have a high density of approximately 7.8g / cm 3 , which leads to an increase in the engine inertia load and a decrease in fuel economy; although conventional aluminum alloy pistons such as ZL108 can reduce weight, their high-temperature strength is insufficient and they are prone to creep or thermal cracking under the scouring of high-temperature combustion gas in the combustion chamber, and their service life is limited. Therefore, a preparation method for a large-cylinder air-cooled diesel engine piston is proposed. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the present invention provides a method for preparing a large-cylinder air-cooled diesel engine piston, which solves the problem that traditional piston materials are difficult to meet the requirements of lightweight, durability and thermal efficiency.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solutions: A method for preparing a large-cylinder air-cooled diesel engine piston, specifically comprising the following steps: S1. Modeling and Zoning: Build a piston simulation model and divide the piston into the top area, middle area, and skirt area from top to bottom; S2. Gradient printing: using 3D printing technology to sequentially print a hypereutectic alloy layer, a eutectic alloy layer, and a hypoeutectic alloy layer as the top region, the middle region, and the skirt region, respectively, to obtain a piston; S3. Coating addition: After post-processing the piston, spray a wear-resistant and corrosion-resistant coating on the piston surface to complete the piston preparation.

[0006] The present invention is further configured as follows: the interior of the top area is configured as a honeycomb lattice structure, wherein the side length of the lattice unit is 1.9 to 2.1 mm, the wall thickness is 0.45 to 0.55 mm, and the filling rate is 38% to 42%.

[0007] The present invention is further configured as follows: the raw materials for the hypereutectic alloy layer include, by mass percentage: Silicon: 21.5% to 22.5%; Copper: 2.8%-3.2%; Magnesium: 1.9% to 2.1%; Zirconium: 0.5%; Scandium: 0.3%; Strontium: 0.05%; Nano silicon carbide: 15%; The balance is aluminum.

[0008] The present invention is further configured as follows: the raw materials for the eutectic alloy layer include, by mass percentage: Silicon: 11.7% to 12.3%; Copper: 2.8%-3.2%; Magnesium: 1.9% to 2.1%; Zirconium: 0.3%; Scandium: 0.2%; Manganese: 0.2%; Graphene nanosheets: 7%; The balance is aluminum.

[0009] The present invention is further configured as follows: the raw materials for the hypoeutectic alloy layer include, by mass percentage: Silicon: 7.8% to 8.2%; Iron: 0.4% to 0.6%; Manganese: 0.2% to 0.4%; Zirconium: 0.2%; Titanium: 0.1%; Carbon nanotubes: 3%; The balance is aluminum.

[0010] The present invention is further configured such that the thickness ratio of the hypereutectic alloy layer, the eutectic alloy layer and the hypoeutectic alloy layer is preferably 15:25:10.

[0011] The present invention is further configured as follows: the post-processing method in S3 includes: Keep at 600℃ for 3-5h under 150MPa pressure; Keep warm at -196℃ for 24 to 48 hours.

[0012] The present invention is further configured as follows: the method of spraying the wear-resistant and corrosion-resistant coating on the piston surface in S3 includes: After alkali washing and pickling, the piston is sandblasted to a surface roughness of Ra3.2-6.3μm; The 12-cobalt tungsten carbide powder was accelerated to 600-800 m / s with 3.5 MPa nitrogen, and sprayed on the piston surface according to a spiral scanning path at 590-610 ° C to obtain a dense coating with a thickness of 45-55 μm. Soak the piston in acetone solution and ultrasonically clean it for 10 minutes; The piston was removed and preheated to 150°C. Stellite 6 powder was laser clad on the dense coating using a spiral scanning path. During the process, the laser power was 1500W and the scanning speed was 8mm / s to obtain a wear-resistant and corrosion-resistant coating with a thickness of 290-310μm.

[0013] The present invention provides a method for preparing a large-cylinder air-cooled diesel engine piston. The method has the following beneficial effects: (1) The present invention provides support for gradient printing of the piston by dividing the top area, the middle area and the skirt area, and realizes piston lightweighting by combining with a honeycomb lattice structure. Silicon carbide is used to reduce wear and improve the wear resistance of the top area. Zirconium is used to form a zirconium-aluminum nano-precipitate phase to refine the grains. Scandium, zirconium and aluminum are used to form a composite precipitation phase to improve high-temperature strength. Graphene nanosheets are used to construct an efficient thermal conductivity network to improve the thermal conductivity of the middle area. Carbon nanotubes are used to form a three-dimensional network to improve the toughness of the skirt area, thereby achieving synergistic optimization of the overall performance of the piston. In addition, by spraying a wear-resistant and corrosion-resistant coating on the piston surface, the piston has a high interface bonding strength, reduces friction, increases the service life of the piston, and effectively reduces maintenance costs. (2) The present invention forms micron-scale protrusions at the interface through silicon carbide, which is embedded in the aluminum matrix in the middle area to form a mechanical interlocking structure, effectively preventing interlayer slippage and improving the interface shear strength. In addition, under the high temperature of 3D printing, a tetraaluminum carbide phase is generated. This phase has a hexagonal crystal structure and is needle-shaped. It forms a coherent interface with the aluminum matrix, strengthens the bonding force through chemical bonding, and further improves the peeling strength.

[0014] (3) Graphene nanosheets form a two-dimensional network at the interface, which enhances mechanical interlocking through friction resistance between sheets and interlayer slip resistance. Its high specific surface area provides more contact points, increasing the interface bonding area. The oxygen-containing functional groups on the graphene surface form Al-OC bonds with the aluminum atoms in the aluminum matrix. In addition, the sp 2 The hybrid orbital undergoes orbital hybridization with the d orbital of aluminum to form a covalent bond, further enhancing the bonding strength.

[0015] (4) The carbon nanotubes form a three-dimensional entangled network at the interface, which enhances mechanical interlocking through the van der Waals force between the tubes and the friction between the tubes and the matrix. Their high aspect ratio provides excellent load transfer capability and reduces stress concentration. The carbon nanotubes form Al-C bonds with aluminum atoms, achieving strong chemical bonding. In addition, the π electrons of the carbon nanotubes and the d electrons of the aluminum undergo charge transfer, forming ionic bonds, which further enhances the interfacial binding energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of the method of the present invention. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

[0018] See also Figure 1 , the embodiment of the present invention provides the following technical solutions: Example 1: A method for preparing a large-cylinder air-cooled diesel engine piston, comprising the following steps: S1. Modeling and Zoning: Build a piston simulation model and divide the piston into the top area, middle area and skirt area from top to bottom. The thickness ratio of the top area, middle area and skirt area is 14:26:9. The top area is the uppermost end of the piston and is directly exposed to the combustion chamber. The top area directly faces the high-temperature and high-pressure combustion gas in the combustion chamber and is the main stress-bearing area of ​​the piston. A lightweight design is achieved by setting a honeycomb lattice structure in the top area. The side length of the lattice unit is 1.9 mm, the wall thickness is 0.45 mm, and the filling rate is 42%. The honeycomb lattice structure increases the surface area and facilitates heat conduction.

[0019] The middle area serves as the transition section of the piston, evenly transferring the high-temperature and high-pressure gas pressure borne by the top area to the skirt area. At the same time, the plastic deformation ability of the eutectic alloy layer is used to relieve the thermal stress concentration. The skirt area is the lowest end of the piston and contacts the cylinder wall, playing a guiding and supporting role. The skirt area ensures the linear motion of the piston in the cylinder through precise cooperation with the cylinder wall, reducing eccentric wear and knocking.

[0020] S2. Gradient printing: Using 3D printing technology, a hypereutectic alloy layer, a eutectic alloy layer, and a hypoeutectic alloy layer are sequentially printed as the top region, the middle region, and the skirt region, respectively, to obtain a piston. The specific steps include: S21. Ingredients The hypereutectic alloy layer is prepared by raw materials in percentage by mass: silicon: 21.5%; copper: 2.8%; magnesium: 1.9%; zirconium: 0.5%; scandium: 0.3%; strontium: 0.05%; nano-silicon carbide: 15%; and the balance is aluminum, wherein silicon, copper, magnesium, zirconium, scandium, strontium and aluminum are provided in powder form with a particle size of 15-45 μm and D50=30 μm; The eutectic alloy layer comprises the following raw materials by mass percentage: silicon: 11.7%; copper: 2.8%; magnesium: 1.9%; zirconium: 0.3%; scandium: 0.2%; manganese: 0.2%; graphene nanosheets: 7%; and the balance aluminum, wherein the silicon, copper, magnesium, zirconium, scandium, manganese, and aluminum are provided in powder form with a particle size of 15-45 μm and a D50 of 30 μm. The hypoeutectic alloy layer is prepared by raw materials in percentage by mass: silicon: 7.8%; iron: 0.4%; manganese: 0.2%; zirconium: 0.2%; titanium: 0.1%; carbon nanotubes: 3%; and the balance aluminum. Silicon, iron, manganese, zirconium, titanium, and aluminum are provided in powder form with a particle size of 15-45 μm and a D50 of 30 μm. The carbon nanotubes have a diameter of 10 nm and a length of 15 μm. S22, grinding The hypereutectic alloy layer ingredients were injected into a high-energy ball mill and ground at a speed of 500 rpm for 4 h to obtain a hypereutectic layer powder; The eutectic alloy layer ingredients were injected into a high-energy ball mill and ground at a speed of 500 rpm for 4 h to obtain eutectic layer powder; The hypoeutectic alloy layer ingredients were injected into a high-energy ball mill and ground at a speed of 500 rpm for 4 h to obtain hypoeutectic layer powder; S33, 3D printing Hypereutectic alloy layer printing was performed using hypereutectic layer powder with a layer thickness of 30 μm and a scanning speed of 1200 mm / s; The hypereutectic alloy layer was printed using eutectic layer powder with a layer thickness of 40 μm and a scanning speed of 1350 mm / s. Hypoeutectic alloy layers were printed using hypoeutectic layer powder with a layer thickness of 50 μm and a scanning speed of 1500 mm / s. Get the piston.

[0021] S3. Coating addition: In order to further reduce the porosity and improve the strength and toughness of the piston, the piston is post-processed. The post-processing methods include: Keep the temperature at 600℃ for 3h under 150MPa pressure to reduce the porosity; Keeping at -196℃ for 24h promotes the uniform distribution of Al3(Zr, Sc) nanocomposite precipitation phase and improves strength and toughness.

[0022] Spraying a wear-resistant and corrosion-resistant coating on the piston surface to complete piston preparation. The methods of spraying a wear-resistant and corrosion-resistant coating on the piston surface include: After alkali washing and pickling, the piston was sandblasted to a surface roughness of Ra3.2μm; The 12-cobalt tungsten carbide powder was accelerated to 800 m / s with 3.5 MPa nitrogen and sprayed on the piston surface according to a spiral scanning path at 590 ° C to obtain a dense coating with a thickness of 45 μm. Soak the piston in acetone solution and ultrasonically clean it for 10 minutes; The piston was removed and preheated to 150°C. Stellite 6 powder was laser clad on the dense coating using a spiral scanning path. During the process, the laser power was 1500 W and the scanning speed was 8 mm / s to obtain a wear-resistant and corrosion-resistant coating with a thickness of 290 μm.

[0023] Example 2: The difference between this example and Example 1 is that: The thickness ratio of the top region, the middle region and the skirt region is: 15:25:10.

[0024] The side length of the lattice unit is 2 mm, the wall thickness is 0.5 mm, and the filling rate is 40%.

[0025] The hypereutectic alloy layer is prepared by mass percentages of the following raw materials: silicon: 22.0%; copper: 3.0%; magnesium: 2.0%; zirconium: 0.5%; scandium: 0.3%; strontium: 0.05%; nano-silicon carbide: 15%; and the balance aluminum. The eutectic alloy layer ingredients include the following raw materials by mass percentage: silicon: 12.0%; copper: 3.0%; magnesium: 2.0%; zirconium: 0.3%; scandium: 0.2%; manganese: 0.2%; graphene nanosheets: 7%; and the balance aluminum. The hypoeutectic alloy layer is prepared from raw materials in percentage by mass including: silicon: 8.0%; iron: 0.5%; manganese: 0.3%; zirconium: 0.2%; titanium: 0.1%; carbon nanotubes: 3%; and the balance being aluminum.

[0026] The piston is post-processed, and the post-processing methods include: Keep the temperature at 600℃ for 4h under 150MPa pressure to reduce the porosity; Keeping at -196℃ for 36h promotes the uniform distribution of Al3(Zr, Sc) nanocomposite precipitation phase and improves strength and toughness.

[0027] The methods of spraying wear-resistant and corrosion-resistant coating on the piston surface include: After alkali washing and pickling, the piston was sandblasted to a surface roughness of Ra5.1μm; The 12-cobalt tungsten carbide powder was accelerated to 700 m / s with 3.5 MPa nitrogen and sprayed on the piston surface at 600 ° C according to a spiral scanning path to obtain a dense coating with a thickness of 50 μm. Soak the piston in acetone solution and ultrasonically clean it for 10 minutes; The piston was removed and preheated to 150°C. Stellite 6 powder was laser clad on the dense coating using a spiral scanning path. During the process, the laser power was 1500 W and the scanning speed was 8 mm / s to obtain a wear-resistant and corrosion-resistant coating with a thickness of 300 μm.

[0028] Example 3: The difference between this example and Example 1 is that: The thickness ratio of the top region, the middle region and the skirt region is: 16:24:11.

[0029] The side length of the lattice unit is 2.1 mm, the wall thickness is 0.55 mm, and the filling rate is 38%.

[0030] The hypereutectic alloy layer is prepared by mass percentages of the following raw materials: silicon: 22.5%; copper: 3.2%; magnesium: 2.1%; zirconium: 0.5%; scandium: 0.3%; strontium: 0.05%; nano-silicon carbide: 15%; and the balance aluminum. The eutectic alloy layer ingredients include the following raw materials by mass percentage: silicon: 12.3%; copper: 3.2%; magnesium: 2.1%; zirconium: 0.3%; scandium: 0.2%; manganese: 0.2%; graphene nanosheets: 7%; and the balance aluminum. The hypoeutectic alloy layer is prepared from raw materials in percentage by mass including: silicon: 8.2%; iron: 0.6%; manganese: 0.4%; zirconium: 0.2%; titanium: 0.1%; carbon nanotubes: 3%; and the balance being aluminum.

[0031] The piston is post-processed, and the post-processing methods include: Keep the temperature at 600℃ for 5h under 150MPa pressure to reduce the porosity; Keeping at -196℃ for 48h promotes the uniform distribution of Al3(Zr, Sc) nanocomposite precipitation phase and improves strength and toughness.

[0032] The methods of spraying wear-resistant and corrosion-resistant coating on the piston surface include: After alkali washing and pickling, the piston was sandblasted to a surface roughness of Ra6.3μm; The 12-cobalt tungsten carbide powder was accelerated to 600 m / s with 3.5 MPa nitrogen and sprayed on the piston surface according to a spiral scanning path at 610 ° C to obtain a dense coating with a thickness of 55 μm. Soak the piston in acetone solution and ultrasonically clean it for 10 minutes; The piston was removed and preheated to 150°C. Stellite 6 powder was laser clad on the dense coating using a spiral scanning path. During the process, the laser power was 1500 W and the scanning speed was 8 mm / s to obtain a wear-resistant and corrosion-resistant coating with a thickness of 310 μm.

[0033] Transmission electron microscopy test: needle-shaped Al4C3 phase was observed at the interface between the top region and the middle region, Al-OC bonds with a bond length of 0.19nm were observed at the interface between the top region and the middle region, and between the middle region and the skirt region, and Al-C bonds with a bond length of 0.21nm were observed at the interface between the middle region and the skirt region, confirming the existence of chemical bonding.

[0034] Simulation experiment The conventional cast piston Mahle MS15319 and the aluminum alloy-based composite piston Federal Mogul 5741M were used as comparison pistons. The thermal expansion coefficient CTE and thermal stress level tests were conducted to verify the thermal compatibility and thermal shock resistance of the piston provided by the present invention.

[0035] The temperature range of 25°C to 300°C covers the actual operating temperature range of the engine. The heating and cooling process of the engine is simulated at a heating and cooling rate of 5°C / min. The CTE is tested using the ejector rod method. The test results are shown in Table 1: Table 1 index Mahle MS15319 Federal Mogul 5741M The present invention <![CDATA[CTE / 10 -6 / ℃]]> 24.0 21.5 19.0 Maximum thermal stress 180MPa 150MPa 120MPa As can be seen from Table 1, the CTE of the conventional cast piston Mahle MS15319 is consistent with the properties of gray cast iron, and the CTE of the aluminum alloy composite piston Federal Mogul 5741M is close to the typical value of SiC particle reinforced aluminum composite. The piston provided by the present invention has the lowest CTE, which is closest to the 10×10 -6 / ℃, it can be judged that its thermal compatibility has been improved. Using the product of the elastic modulus, thermal expansion coefficient and temperature difference as the thermal stress calculation result, it was found that the traditional cast piston MahleMS15319 is close to the aluminum alloy thermal stress limit of 200MPa, which poses a risk of thermal cracking. The piston provided by the present invention has a lower CTE and thermal stress reduced to 120MPa. Its thermal shock resistance is better than that of the traditional cast piston Mahle MS15319 and the aluminum alloy-based composite piston Federal Mogul 5741M.

[0036] In summary, the present invention forms a complete thermal management chain through heat dissipation in the top area → heat conduction in the middle area → temperature control in the skirt area, ensuring the stability of the piston under high-temperature conditions. The high rigidity of the top area, the force transmission in the middle area and the toughness of the skirt area jointly improve the service life of the piston.

[0037] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a large-cylinder air-cooled diesel engine piston, characterized in that: The specific steps include: S1. Modeling and Zoning: Build a piston simulation model and divide the piston into the top area, middle area, and skirt area from top to bottom; S2. Gradient printing: using 3D printing technology to sequentially print a hypereutectic alloy layer, a eutectic alloy layer, and a hypoeutectic alloy layer as the top region, the middle region, and the skirt region, respectively, to obtain a piston; S3. Coating addition: After post-processing the piston, spray a wear-resistant and corrosion-resistant coating on the piston surface to complete the piston preparation.

2. The method for preparing a large-cylinder air-cooled diesel engine piston according to claim 1, characterized in that: The interior of the top area is configured as a honeycomb lattice structure, wherein the side length of the lattice unit is 1.9 to 2.1 mm, the wall thickness is 0.45 to 0.55 mm, and the filling rate is 38% to 42%.

3. The method for preparing a large-cylinder air-cooled diesel engine piston according to claim 1, characterized in that: The raw materials of the hypereutectic alloy layer include, by mass percentage: Silicon: 21.5% to 22.5%; Copper: 2.8%-3.2%; Magnesium: 1.9% to 2.1%; Zirconium: 0.5%; Scandium: 0.3%; Strontium: 0.05%; Nano silicon carbide: 15%; The balance is aluminum.

4. The method for preparing a large-cylinder air-cooled diesel engine piston according to claim 1, characterized in that: The raw materials of the eutectic alloy layer include, by mass percentage: Silicon: 11.7% to 12.3%; Copper: 2.8%-3.2%; Magnesium: 1.9% to 2.1%; Zirconium: 0.3%; Scandium: 0.2%; Manganese: 0.2%; Graphene nanosheets: 7%; The balance is aluminum.

5. The method for preparing a large-cylinder air-cooled diesel engine piston according to claim 1, characterized in that: The raw materials of the hypoeutectic alloy layer include, by mass percentage: Silicon: 7.8% to 8.2%; Iron: 0.4% to 0.6%; Manganese: 0.2% to 0.4%; Zirconium: 0.2%; Titanium: 0.1%; Carbon nanotubes: 3%; The balance is aluminum.

6. The method for preparing a large-cylinder air-cooled diesel engine piston according to claim 1, characterized in that: The thickness ratio of the hypereutectic alloy layer, the eutectic alloy layer and the hypoeutectic alloy layer is: 14-16:24-26:9-11.

7. The method for preparing a large-cylinder air-cooled diesel engine piston according to claim 1, characterized in that: The post-processing methods in S3 include: Keep at 600℃ for 3-5h under 150MPa pressure; Keep warm at -196℃ for 24 to 48 hours.

8. The method for preparing a large-cylinder air-cooled diesel engine piston according to claim 1, characterized in that: The method of spraying the wear-resistant and corrosion-resistant coating on the piston surface in S3 includes: After alkali washing and pickling, the piston is sandblasted to a surface roughness of Ra3.2-6.3μm; The 12-cobalt tungsten carbide powder was accelerated to 600-800 m / s with 3.5 MPa nitrogen, and sprayed on the piston surface according to a spiral scanning path at 590-610 ° C to obtain a dense coating with a thickness of 45-55 μm. Soak the piston in acetone solution and ultrasonically clean it for 10 minutes; The piston was removed and preheated to 150°C. Stellite 6 powder was laser clad on the dense coating using a spiral scanning path. During the process, the laser power was 1500W and the scanning speed was 8mm / s to obtain a wear-resistant and corrosion-resistant coating with a thickness of 290-310μm.

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