Preparation method of large-bore air-cooled diesel engine piston

Abstract

The application discloses a preparation method of a large-bore air-cooled diesel engine piston and specifically comprises the following steps: S1, modeling and dividing regions; S2, gradient printing; and S3, coating addition; and relates to the technical field of diesel engine pistons. The preparation method of the large-bore air-cooled diesel engine piston realizes the synergistic optimization of the overall performance of the piston through gradient printing of the piston, realizes the lightweight of the piston in cooperation with the honeycomb lattice structure, reduces the abrasion amount by using silicon carbide, improves the wear resistance of the top region, forms zirconium tri-aluminum nano precipitated phases by zirconium, refines the grains, forms a composite precipitated phase by using scandium, zirconium and aluminum, improves the high-temperature strength, constructs an efficient heat conduction network by using graphene nanosheets, improves the heat conductivity of the middle region, forms a three-dimensional network by using carbon nanotubes, improves the toughness of the skirt region, and has high interfacial bonding strength by spraying a wear-resistant and corrosion-resistant coating on the surface of the piston, reduces the friction, improves the service life of the piston and effectively reduces the maintenance cost.

Description

Technical Field

[0001] This invention relates to the field of diesel engine piston technology, specifically to a method for manufacturing a large-bore air-cooled diesel engine piston. Background Technology

[0002] Pistons for large-bore air-cooled diesel engines are typically made of aluminum alloy or cast iron. Aluminum alloys, due to their light weight and good thermal conductivity, are suitable for high-speed diesel engines, helping to reduce inertial forces and improve heat transfer efficiency. Cast iron, especially pearlitic cast iron, has advantages such as high mechanical strength, low coefficient of thermal expansion, and wear and corrosion resistance, making it more suitable for low-speed diesel engines, especially air-cooled diesel engines, as its good wear resistance and strength are better suited to the air-cooled environment.

[0003] As engine technology advances towards higher power density, lower emissions, and greater intelligence, the performance requirements for pistons in large-bore air-cooled diesel engines are becoming increasingly stringent. Traditional piston materials such as cast iron and conventional aluminum alloys suffer from high density, poor thermal conductivity, and low thermal fatigue life, making it difficult to meet the demanding requirements of modern engines for lightweight design, durability, and thermal efficiency. For example, while cast iron pistons have high strength, they also have a high density, approximately 7.8 g / cm³. 3 This leads to increased engine inertial load and decreased 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 gases in the combustion chamber, resulting in a limited service life. Therefore, a method for manufacturing large-bore air-cooled diesel engine pistons is proposed. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for manufacturing large-bore air-cooled diesel engine pistons, solving 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 provides the following technical solution: a method for manufacturing a large-bore air-cooled diesel engine piston, specifically comprising the following steps:

[0006] S1. Modeling and Zoning: Build a piston simulation model and divide the piston into a top region, a middle region, and a skirt region from top to bottom;

[0007] S2. Gradient printing: Using 3D printing technology, a eutectic alloy layer, a eutectic alloy layer, and a hypoeutectic alloy layer are printed sequentially to serve as the top region, middle region, and skirt region, respectively, to obtain the piston;

[0008] S3. Coating addition: After post-treatment of the piston, a wear-resistant and corrosion-resistant coating is sprayed onto the piston surface to complete the piston preparation.

[0009] The present invention is further configured such that the interior of the top region is configured with 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%.

[0010] The present invention is further configured such that the raw material for the hypereutectic alloy layer comprises, by mass percentage:

[0011] Silicon: 21.5%–22.5%;

[0012] Copper: 2.8%–3.2%;

[0013] Magnesium: 1.9%–2.1%;

[0014] Zirconium: 0.5%;

[0015] Scandium: 0.3%;

[0016] Strontium: 0.05%;

[0017] Nano silicon carbide: 15%;

[0018] Balance of aluminum.

[0019] The present invention is further configured such that the raw material of the eutectic alloy layer comprises, by mass percentage:

[0020] Silicon: 11.7%–12.3%;

[0021] Copper: 2.8%–3.2%;

[0022] Magnesium: 1.9%–2.1%;

[0023] Zirconium: 0.3%;

[0024] Scandium: 0.2%;

[0025] Manganese: 0.2%;

[0026] Graphene nanosheets: 7%;

[0027] Balance of aluminum.

[0028] The present invention is further configured such that the hypoeutectic alloy layer raw material comprises, by mass percentage:

[0029] Silicon: 7.8%–8.2%;

[0030] Iron: 0.4%–0.6%;

[0031] Manganese: 0.2%–0.4%;

[0032] Zirconium: 0.2%;

[0033] Titanium: 0.1%;

[0034] Carbon nanotubes: 3%;

[0035] Balance of aluminum.

[0036] 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.

[0037] The present invention is further configured such that the post-processing method in S3 includes:

[0038] Hold at 600℃ for 3–5 hours under 150 MPa pressure;

[0039] Keep warm at -196℃ for 24 to 48 hours.

[0040] The present invention is further configured such that: the method of spraying a wear-resistant and corrosion-resistant coating on the piston surface in step S3 includes:

[0041] After the piston is subjected to alkaline washing and acid washing, it is roughened by sandblasting to a surface roughness of Ra3.2-6.3μm;

[0042] Tungsten carbide powder with cobalt 12 was accelerated to 600-800 m / s with nitrogen gas at 3.5 MPa and deposited on the piston surface by spraying along a spiral scanning path at 590-610 °C to obtain a dense coating with a thickness of 45-55 μm.

[0043] Immerse the piston in acetone solution and ultrasonically clean it for 10 minutes;

[0044] Remove the piston, preheat to 150°C, and laser clad Stellite 6 powder onto the dense coating using a spiral scanning path. During the process, the laser power is 1500W and the scanning speed is 8mm / s to obtain a wear-resistant and corrosion-resistant coating with a thickness of 290-310μm.

[0045] This invention provides a method for manufacturing a large-bore air-cooled diesel engine piston. It has the following beneficial effects:

[0046] (1) This invention provides support for the gradient printing of pistons by dividing them into top, middle and skirt regions. It achieves piston lightweighting by combining honeycomb lattice structure, reduces wear by using silicon carbide, improves wear resistance of the top region, refines grains by forming zirconium trialuminum nanoprecipitates, enhances high-temperature strength by forming composite precipitates of scandium, zirconium and aluminum, improves thermal conductivity of the middle region by constructing an efficient thermally conductive network by graphene nanosheets, and improves toughness of the skirt region by using carbon nanotubes to form a three-dimensional network. This achieves synergistic optimization of the overall performance of the piston. Furthermore, by spraying a wear-resistant and corrosion-resistant coating on the piston surface, it has high interfacial bonding strength, reduces friction, improves piston service life, and effectively reduces maintenance costs.

[0047] (2) In this invention, silicon carbide forms micron-level protrusions at the interface and is embedded in the aluminum matrix in the middle region to form a mechanical interlocking structure, which effectively prevents interlayer slippage and improves the shear strength of the interface. Furthermore, 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 and enhances the bonding force through chemical bonding, further improving the peel strength.

[0048] (3) Graphene nanosheets form a two-dimensional network at the interface, enhancing mechanical interlocking through interlayer frictional resistance and interlayer slip resistance. Their high specific surface area provides more contact points, increasing the interfacial bonding area. The oxygen-containing functional groups on the graphene surface form Al-OC bonds with aluminum atoms in the aluminum matrix. Furthermore, the sp... 2 The hybrid orbitals undergo orbital hybridization with the d orbitals of aluminum, forming covalent bonds and further enhancing the bonding strength.

[0049] (4) Carbon nanotubes form a three-dimensional entangled network at the interface, and enhance mechanical interlocking through van der Waals forces between tubes and friction between tubes and the matrix. Its high aspect ratio provides excellent load transfer capability and reduces stress concentration. Carbon nanotubes form Al-C bonds with aluminum atoms, achieving strong chemical bonding. In addition, the π electrons of carbon nanotubes and the d electrons of aluminum undergo charge transfer to form ionic bonds, further enhancing the interfacial bonding energy. Attached Figure Description

[0050] Figure 1 This is a schematic diagram of the method flow of the present invention. Detailed Implementation

[0051] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0052] Please see Figure 1 The present invention provides the following technical solutions:

[0053] Example 1: A method for manufacturing a large-bore air-cooled diesel engine piston, specifically including the following steps:

[0054] S1. Modeling and Zoning: Build a piston simulation model and divide the piston into a top region, a middle region, and a skirt region from top to bottom. The thickness ratio of the top, middle, and skirt regions is 14:26:9. The top region is the uppermost part of the piston, directly exposed to the combustion chamber. The top region directly faces the high-temperature and high-pressure combustion gases in the combustion chamber and is the main stress area of ​​the piston. By setting a honeycomb lattice structure in the top region, a lightweight design is achieved. The side length of the lattice unit is 1.9mm, the wall thickness is 0.45mm, and the filling rate is 42%. The honeycomb lattice structure increases the surface area and facilitates heat conduction.

[0055] The central region, serving as the transition section of the piston, evenly transfers the high-temperature, high-pressure combustion gas experienced by the top region to the skirt region. Simultaneously, the plastic deformation capability of the eutectic alloy layer alleviates thermal stress concentration.

[0056] The skirt area is the lowest part of the piston, which contacts the cylinder wall and serves as a guide and support. Through precise matching with the cylinder wall, the skirt area ensures the linear movement of the piston within the cylinder, reducing uneven wear and knocking.

[0057] S2. Gradient Printing: Using 3D printing technology, a eutectic alloy layer, a eutectic alloy layer, and a hypoeutectic alloy layer are sequentially printed to serve as the top region, middle region, and skirt region, respectively, to obtain the piston. Specific steps include:

[0058] S21, Ingredients

[0059] The hypereutectic alloy layer is formulated with the following raw materials by mass percentage: 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 being aluminum. The silicon, copper, magnesium, zirconium, scandium, strontium, and aluminum are in powder form with a particle size of 15-45 μm and a D50 of 30 μm.

[0060] The eutectic alloy layer is formulated with 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 being aluminum. Among these, silicon, copper, magnesium, zirconium, scandium, manganese, and aluminum are in powder form with a particle size of 15-45 μm and a D50 of 30 μm.

[0061] The hypoeutectic alloy layer is formulated with the following raw materials by mass percentage: silicon: 7.8%; iron: 0.4%; manganese: 0.2%; zirconium: 0.2%; titanium: 0.1%; carbon nanotubes: 3%; and the balance being aluminum. Among these, silicon, iron, manganese, zirconium, titanium, and aluminum are 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.

[0062] S22, Grinding

[0063] The hypereutectic alloy layer material was injected into a high-energy ball mill and ground at 500 rpm for 4 hours to obtain hypereutectic layer powder.

[0064] The eutectic alloy layer material was injected into a high-energy ball mill and ground at 500 rpm for 4 hours to obtain eutectic layer powder.

[0065] The hypoeutectic alloy layer material was injected into a high-energy ball mill and ground at 500 rpm for 4 hours to obtain hypoeutectic layer powder.

[0066] S33, 3D printing

[0067] Hypereutectic alloy layers were printed using hypereutectic powder, with a layer thickness of 30 μm and a scanning speed of 1200 mm / s.

[0068] Hypereutectic alloy layers were printed using eutectic layer powder with a layer thickness of 40 μm and a scanning speed of 1350 mm / s.

[0069] Hypoeutectic alloy layers were printed using hypoeutectic powder with a layer thickness of 50 μm and a scanning speed of 1500 mm / s.

[0070] Get the piston.

[0071] S3. Coating Addition: To further reduce porosity and improve piston strength and toughness, the piston undergoes post-treatment. Post-treatment methods include:

[0072] Porosity was reduced by holding the material at 600℃ for 3 hours under 150MPa pressure.

[0073] Incubation at -196℃ for 24 hours promotes uniform distribution of Al3(Zr,Sc) nanocomposite precipitates, thereby improving strength and toughness.

[0074] The piston is manufactured by spraying a wear-resistant and corrosion-resistant coating onto its surface. Methods for spraying this coating include:

[0075] After the piston is subjected to alkaline washing and acid washing, it is roughened by sandblasting to a surface roughness of Ra3.2μm;

[0076] Tungsten carbide powder of cobalt 12 was accelerated to 800 m / s with nitrogen gas at 3.5 MPa and deposited on the piston surface by spraying along a spiral scanning path at 590 °C to obtain a dense coating with a thickness of 45 μm.

[0077] Immerse the piston in acetone solution and ultrasonically clean it for 10 minutes;

[0078] Remove the piston, preheat to 150°C, and laser clad Stellite 6 powder onto the dense coating using a spiral scanning path. During the process, the laser power is 1500W and the scanning speed is 8mm / s to obtain a wear-resistant and corrosion-resistant coating with a thickness of 290μm.

[0079] Example 2: The difference between this example and Example 1 is as follows:

[0080] The thickness ratio of the top area, middle area, and skirt area is 15:25:10.

[0081] The lattice unit has a side length of 2 mm, a wall thickness of 0.5 mm, and a fill rate of 40%.

[0082] The hypereutectic alloy layer is formulated with the following raw materials by weight percentage: silicon: 22.0%; copper: 3.0%; magnesium: 2.0%; zirconium: 0.5%; scandium: 0.3%; strontium: 0.05%; nano-silicon carbide: 15%; balance aluminum;

[0083] The eutectic alloy layer is formulated with the following raw materials by weight percentage: silicon: 12.0%; copper: 3.0%; magnesium: 2.0%; zirconium: 0.3%; scandium: 0.2%; manganese: 0.2%; graphene nanosheets: 7%; balance aluminum;

[0084] The hypoeutectic alloy layer is formulated with the following raw materials by weight percentage: silicon: 8.0%; iron: 0.5%; manganese: 0.3%; zirconium: 0.2%; titanium: 0.1%; carbon nanotubes: 3%; and the balance being aluminum.

[0085] The piston undergoes post-processing, including the following methods:

[0086] Porosity was reduced by holding the material at 600℃ for 4 hours under 150MPa pressure.

[0087] Incubation at -196℃ for 36 hours promotes uniform distribution of Al3(Zr,Sc) nanocomposite precipitates, thereby improving strength and toughness.

[0088] Methods for applying a wear-resistant and corrosion-resistant coating to the piston surface include:

[0089] After the piston is subjected to alkaline washing and acid washing, it is roughened by sandblasting to a surface roughness of Ra5.1μm;

[0090] Tungsten carbide powder of cobalt 12 was accelerated to 700 m / s with nitrogen gas at 3.5 MPa and deposited on the piston surface by spraying along a spiral scanning path at 600 °C to obtain a dense coating with a thickness of 50 μm.

[0091] Immerse the piston in acetone solution and ultrasonically clean it for 10 minutes;

[0092] Remove the piston, preheat to 150°C, and laser clad Stellite 6 powder onto the dense coating using a spiral scanning path. During the process, the laser power is 1500W and the scanning speed is 8mm / s to obtain a wear-resistant and corrosion-resistant coating with a thickness of 300μm.

[0093] Example 3: The difference between this example and Example 1 is as follows:

[0094] The thickness ratio of the top region, middle region, and skirt region is 16:24:11.

[0095] The lattice unit has a side length of 2.1 mm, a wall thickness of 0.55 mm, and a fill rate of 38%.

[0096] The hypereutectic alloy layer is formulated with the following raw materials by weight percentage: silicon: 22.5%; copper: 3.2%; magnesium: 2.1%; zirconium: 0.5%; scandium: 0.3%; strontium: 0.05%; nano-silicon carbide: 15%; balance aluminum;

[0097] The eutectic alloy layer is formulated with the following raw materials by weight percentage: silicon: 12.3%; copper: 3.2%; magnesium: 2.1%; zirconium: 0.3%; scandium: 0.2%; manganese: 0.2%; graphene nanosheets: 7%; balance aluminum;

[0098] The hypoeutectic alloy layer is formulated with the following raw materials by weight percentage: silicon: 8.2%; iron: 0.6%; manganese: 0.4%; zirconium: 0.2%; titanium: 0.1%; carbon nanotubes: 3%; and the balance being aluminum.

[0099] The piston undergoes post-processing, including the following methods:

[0100] Porosity was reduced by holding the material at 600℃ for 5 hours under 150MPa pressure.

[0101] Incubation at -196℃ for 48 hours promotes uniform distribution of Al3(Zr,Sc) nanocomposite precipitates, thereby improving strength and toughness.

[0102] Methods for applying a wear-resistant and corrosion-resistant coating to the piston surface include:

[0103] After the piston is subjected to alkaline washing and acid washing, it is roughened by sandblasting to a surface roughness of Ra6.3μm;

[0104] Tungsten carbide powder of cobalt 12 was accelerated to 600 m / s with nitrogen gas at 3.5 MPa and deposited on the piston surface by spraying along a spiral scanning path at 610 °C to obtain a dense coating with a thickness of 55 μm.

[0105] Immerse the piston in acetone solution and ultrasonically clean it for 10 minutes;

[0106] Remove the piston, preheat to 150°C, and laser clad Stellite 6 powder onto the dense coating using a spiral scanning path. During the process, the laser power is 1500W and the scanning speed is 8mm / s to obtain a wear-resistant and corrosion-resistant coating with a thickness of 310μm.

[0107] Transmission electron microscopy (TEM) revealed needle-like Al4C3 phases at the interface between the top and middle regions, Al-OC bonds with a bond length of 0.19 nm at the interfaces between the top and middle regions, and between the middle and skirt regions, and Al-C bonds with a bond length of 0.21 nm at the interface between the middle and skirt regions, confirming the existence of chemical bonding.

[0108] Simulation Experiment

[0109] Using the conventional cast piston Mahle MS15319 and the aluminum alloy-based composite piston Federal Mogul 5741M as comparative pistons, the thermal matching and thermal shock resistance performance of the piston provided by the present invention were verified by testing the coefficient of thermal expansion (CTE) and thermal stress level.

[0110] The actual operating temperature range of the engine was covered by a temperature range of 25℃-300℃. The heating and cooling processes of the engine were simulated with a heating and cooling rate of 5℃ / min. The CTE was tested using the pushrod method. The test results are shown in Table 1.

[0111] Table 1

[0112] index Mahle MS15319 Federal Mogul 5741M This invention <![CDATA[CTE / 10 -6 / ℃]]> 24.0 21.5 19.0 Maximum thermal stress 180MPa 150MPa 120MPa

[0113] As shown in Table 1, the CTE of the conventional cast piston Mahle MS15319 conforms to the characteristics of gray cast iron, while the CTE of the aluminum alloy matrix composite piston Federal Mogul 5741M is close to the typical value of SiC particle-reinforced aluminum matrix composites. The piston provided by this invention has the lowest CTE, closest to the 10×10 CTE of conventional cast iron cylinder walls. -6 The temperature of / ℃ indicates that its thermal matching has been improved. Using the product of elastic modulus, coefficient of thermal expansion and temperature difference as the result of thermal stress calculation, it was found that the traditional cast piston MahleMS15319 is close to the thermal stress limit of aluminum alloy 200MPa, and there is a risk of thermal cracking. The piston provided by the present invention has a lower CTE and the thermal stress is 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.

[0114] In summary, this 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 together improve the service life of the piston.

[0115] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for manufacturing a piston for a large-bore air-cooled diesel engine, characterized in that, Specifically, the following steps are included: S1. Modeling and Division: Build a piston simulation model and divide the piston into a top region, a middle region, and a skirt region from top to bottom; S2. Gradient printing: Using 3D printing technology, a eutectic alloy layer, a eutectic alloy layer, and a hypoeutectic alloy layer are printed sequentially to serve as the top region, middle region, and skirt region, respectively, to obtain the piston; S3. Coating addition: After post-treatment of the piston, a wear-resistant and corrosion-resistant coating is sprayed onto the piston surface to complete the piston preparation; The hypereutectic alloy layer raw materials comprise, by mass percentage: Silicon: 21.5%–22.5%; Copper: 2.8%–3.2%; Magnesium: 1.9%–2.1%; Zirconium: 0.5%; Scandium: 0.3%; Strontium: 0.05%; Nano silicon carbide: 15%; Balance aluminum; The raw materials for the eutectic alloy layer include, by mass percentage: Silicon: 11.7%–12.3%; Copper: 2.8%–3.2%; Magnesium: 1.9%–2.1%; Zirconium: 0.3%; Scandium: 0.2%; Manganese: 0.2%; Graphene nanosheets: 7%; Balance aluminum; The hypoeutectic alloy layer raw materials include, by mass percentage: Silicon: 7.8%–8.2%; Iron: 0.4%–0.6%; Manganese: 0.2%–0.4%; Zirconium: 0.2%; Titanium: 0.1%; Carbon nanotubes: 3%; Balance of aluminum.

2. The method for manufacturing a large-bore air-cooled diesel engine piston according to claim 1, characterized in that, The top region is internally configured with a honeycomb lattice structure, wherein the side length of the lattice unit is 1.9–2.1 mm, the wall thickness is 0.45–0.55 mm, and the filling rate is 38%–42%.

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

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

5. The method for manufacturing a large-bore air-cooled diesel engine piston according to claim 1, characterized in that, The method of spraying a wear-resistant and corrosion-resistant coating on the piston surface in S3 includes: After the piston is subjected to alkaline washing and acid washing, it is roughened by sandblasting to a surface roughness of Ra3.2-6.3μm; Tungsten carbide powder with cobalt 12 was accelerated to 600-800 m / s with nitrogen gas at 3.5 MPa and deposited on the piston surface by spraying along a spiral scanning path at 590-610 °C to obtain a dense coating with a thickness of 45-55 μm. Immerse the piston in acetone solution and ultrasonically clean it for 10 minutes; Remove the piston, preheat to 150℃, and laser clad Stellite 6 powder onto the dense coating using a spiral scanning path. During the process, the laser power is 1500W and the scanning speed is 8mm / s to obtain a wear-resistant and corrosion-resistant coating with a thickness of 290-310μm.

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