Method for prolonging service life of aluminum alloy piston and prepared piston part

Abstract

The invention discloses a method for prolonging the service life of an aluminum alloy piston and a prepared piston part, and belongs to the technical field of machine manufacturing. According to the technical scheme, in order to solve the problem of performance mismatch between an aluminum alloy piston and a high-performance coating, a PVD process combining reactive sputtering and co-sputtering is adopted, and the ternary composite coating composed of an AlZrCr transition layer, an AlZrCrB middle layer and an AlZrCrC surface layer is sequentially constructed on a piston base body. According to the structure, strong interface bonding is achieved through the transition layer, high hardness and strength are provided through the boride middle layer, and a low friction coefficient is given through the carbide surface layer, so that the wear resistance, fatigue resistance and high-temperature stability of the piston are cooperatively improved. The process temperature is low, a base body is not damaged, the service life of the piston can be prolonged by 3-4 times, and the method is suitable for various aluminum alloy pistons such as ZL108, ZL109 and A390.

Description

Technical Field

[0001] This invention belongs to the field of mechanical manufacturing technology, specifically relating to a method for extending the service life of aluminum alloy pistons and the piston parts prepared therefrom. Background Technology

[0002] As the core moving component of an engine, the piston undergoes continuous high-speed reciprocating motion under high temperature and high pressure, bearing immense mechanical stress and thermal load. To reduce the overall weight of the engine and improve fuel efficiency and power response, aluminum alloys, with their low density and excellent thermal conductivity, have become the mainstream choice for piston manufacturing. However, aluminum alloys have relatively low hardness and insufficient wear resistance. Under increasingly demanding engine operating conditions (such as high boost and high speed), critical areas such as the piston skirt and ring grooves are prone to premature wear, which in turn affects the overall reliability, efficiency, and service life of the engine.

[0003] Surface strengthening treatment technology is widely used to enhance the wear resistance of pistons. Carbide and oxide coatings have attracted widespread attention due to their high hardness, good strength, excellent chemical stability, high temperature resistance, and wear resistance. In particular, multi-component carbide and oxide systems exhibit outstanding comprehensive performance and are therefore highly valued. Currently, the main methods for preparing such coatings include spraying technology and chemical vapor deposition.

[0004] Although the spraying process is highly efficient, the bonding strength between the coating and the aluminum alloy piston substrate is usually insufficient, and the coating surface is relatively rough, making it difficult to meet the engine's strict requirements for piston surface precision and smoothness, which can easily lead to cylinder scoring or abnormal wear problems during operation.

[0005] Physical vapor deposition (PVD) technology, as a surface treatment process with great potential, can be implemented at relatively low temperatures (e.g., not exceeding 400°C), avoiding adverse effects on the microstructure of the aluminum alloy piston substrate or causing dimensional deformation. PVD coatings themselves possess extremely high hardness, good strength, and excellent wear resistance and thermal stability. However, directly applying this technology to the surface of aluminum alloy pistons still faces key challenges: the aluminum alloy substrate and high-performance PVD coating materials (such as carbides, borides, nitrides, or oxide ceramics) differ significantly in key physical properties such as hardness, elastic modulus, and coefficient of thermal expansion. This performance mismatch leads to insufficient interfacial adhesion between the coating and the substrate. Under harsh conditions of high temperature, high speed, and alternating loads, large stress concentrations easily occur inside the coating, which can induce cracks and cause premature spalling failure.

[0006] Existing patented technologies also reflect similar problems. For example, Chinese patent CN101058870A proposes preparing a single PVD coating on the surface of a mold, but this approach also faces limitations such as weak adhesion between the coating and the substrate and mismatch in mechanical properties. Another Chinese patent CN103727180A attempts to directly deposit an ultra-hard ceramic coating on a carbon steel surface, but due to the relatively soft substrate failing to provide effective support, coupled with significant performance differences, the coating fails rapidly under harsh operating conditions. These examples illustrate that directly depositing hard coatings on soft substrates is difficult to achieve ideal results, and this problem is particularly significant for engine aluminum alloy pistons operating under extremely complex conditions.

[0007] In summary, there is currently a lack of a durable coating method that can specifically address the characteristics of aluminum alloy pistons in engines, creating a coating on their surface that possesses excellent friction reduction and wear resistance, achieves high bonding strength with the substrate, and can withstand the complex stress states brought about by high-temperature, high-speed reciprocating motion. Therefore, developing a novel surface treatment technology that can effectively solve the problems of mechanical property matching and interfacial bonding between the coating and the substrate is of significant practical importance for improving the overall performance, operational reliability, and service life of engines. Summary of the Invention

[0008] This invention provides a method for extending the service life of aluminum alloy pistons and the piston parts manufactured using this method. The method focuses on solving the problem of performance mismatch between the aluminum alloy piston substrate and the high-performance coating. It enhances the adhesion between the coating and the substrate and alleviates internal stress by constructing a functionally graded coating structure. The key lies in using a functionally graded coating structure to mitigate the physical property mismatch caused by differences in thermal expansion coefficients, elastic moduli, etc., between the coating and the substrate. Therefore, this method can effectively improve the friction reduction and wear resistance characteristics of aluminum alloy pistons under high-temperature and high-load conditions, thereby significantly improving their overall performance and service durability.

[0009] The technical solution of this invention is as follows: In the first aspect, a method for extending the service life of aluminum alloy pistons is disclosed. After the engine aluminum alloy piston blank is smelted, cast, heat treated, rough machined, fine machined, deburred and cleaned, an AlZrCr / AlZrCrB / AlZrCrC composite coating is prepared by a composite method of reactive sputtering and co-sputtering. During deposition, one Al sputtering target, one Zr sputtering target, one Cr sputtering target and one C sputtering target are used. Specifically, the following steps are included: (1) Casting of engine piston parts blanks: piston blank melting → casting → solidification and demolding → heat treatment; (2) Machining of engine piston parts: rough machining of piston blank → semi-finishing → finishing → deburring → cleaning to remove surface oil stains; (3) Surface treatment of engine piston parts: The piston parts are ultrasonically immersed in alcohol and acetone respectively to remove surface impurities and deposits. After drying, they are placed in a PVD composite coating machine and vacuumed to 6.0×10 -3 Pa, heat to 300℃, and hold for 40-50 minutes; (4) Ion cleaning of piston parts surface: pulse bias voltage adjusted to 415V, duty cycle 0.45, Ar gas pressure 1.3-1.7Pa; (5) Deposition of AlZrCr layer: Ar gas pressure is adjusted to 0.7-0.75 Pa, flow rate is 50-55 sccm, pulse bias voltage is 275 V, deposition temperature is 260-265 ℃, Al target power is 90 W, Zr target power is 75 W, Cr target power is 60 W, and AlZrCr coating is deposited for 10-15 min. (6) Reactive sputtering of AlZrCrB layer: Ar flow rate is 95-100 sccm, pulse bias voltage is 240V, deposition temperature is 245-250℃, Al target power is 95W, Zr target power is 80W, Cr target power is 65W, B2H6 gas flow rate is 13-16 sccm, and AlZrCrB coating is deposited by reactive sputtering for 15-20 min. (7) Co-sputtering AlZrCrC layer: B2H6 gas is turned off, Ar flow rate is 70-75 sccm, pulse bias voltage is 225V, deposition temperature is 220-230℃, Al target power is 85W, Zr target power is 70W, Cr target power is 60W, C target power is 65W, and AlZrCrC coating is co-sputtered for 15-20 min; (8) Post-processing: Turn off the power supply and gas source of each target, reduce the room temperature to below 70°C, take out the sample, the coating is completed, and the aluminum alloy engine piston part with AlZrCr / AlZrCrB / AlZrCrC composite coating is obtained.

[0010] Preferably, the base material of the engine piston part is one of ZL108, ZL109 and A390.

[0011] Preferably, in step (3), the mixture is sonicated for 40-50 minutes in both alcohol and acetone.

[0012] Preferably, in step (4), the cleaning temperature is 275℃, Ar + Ion cleaning for 30-35 minutes.

[0013] Preferably, in step (6), the boron atom content introduced by the reaction of B2H6 gas in the AlZrCrB layer accounts for 8-12 at.% of the total metal atoms.

[0014] Preferably, in step (7), the carbon atom content introduced by co-sputtering in the AlZrCrC layer accounts for 16-20 at.% of the total metal atoms.

[0015] Secondly, the piston part prepared by the method is disclosed, which has a composite coating of AlZrCr layer, AlZrCrB layer and AlZrCrC layer sequentially outward from the surface of the part substrate.

[0016] Compared with the prior art, the present invention has the following advantages: This invention proposes a composite process combining reactive sputtering and co-sputtering to construct a multilayer protective coating on the surface of aluminum alloy pistons, thereby significantly extending their service life. This method integrates the technical advantages of reactive sputtering and co-sputtering, utilizing the characteristics of boride and carbide coatings to design a multilayer composite coating system. Specifically, an AlZrCr transition layer is deposited between the substrate and the boride coating via sputtering to alleviate internal stress caused by differences in physical properties between the coating and the substrate, enhancing the bonding force between them and providing a stable support and good bonding interface for the subsequent construction of the AlZrCrB / AlZrCrC composite coating. Simultaneously, the interlayer interface formed by the AlZrCr / AlZrCrB / AlZrCrC multilayer structure effectively inhibits the growth of columnar crystals in the coating, blocking the propagation path of cracks and defects, thereby improving the overall hardness, toughness, and impact resistance of the coating. The AlZrCrB coating primarily enhances the surface hardness, strength, and wear resistance of the material; while the surface AlZrCrC coating helps reduce the coefficient of friction, improving friction reduction and wear resistance. This composite coating structure comprehensively improves the overall performance of engine aluminum alloy pistons, effectively enhancing the workpiece's performance and service life.

[0017] Compared to traditional aluminum alloy piston substrates, this method can increase the bonding strength between the coating and the substrate by approximately four times, significantly reducing friction and material adhesion during operation, and increasing the surface hardness by ten times compared to traditional MoS2 lubricating coatings. Based on the composite process of reactive sputtering and co-sputtering, the service life of engine pistons can be extended, while maintenance and upkeep costs are reduced. Furthermore, the processing temperature can be controlled below 300℃, preventing degradation of the substrate's microstructure and preserving the dimensional and shape accuracy of the workpiece. No finishing or reprocessing is required after processing, making it a suitable final surface treatment process for aluminum alloy piston parts. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the surface structure of the aluminum alloy piston obtained in Embodiment 1 of the present invention.

[0019] In the figure: 1. Part substrate; 2. AlZrCr layer; 3. AlZrCrB layer; 4. AlZrCrC layer.

[0020] Figure 2 This is a morphological image of the AlZrCr / AlZrCrB / AlZrCrC composite coated part prepared in Example 1 of the present invention.

[0021] Figure 3 This is a scratch morphology diagram of the bonding force of the AlZrCr / AlZrCrB / AlZrCrC composite coated part prepared in Example 1 of the present invention.

[0022] Figure 4 This is a surface wear mark morphology image of the AlZrCr / AlZrCrB / AlZrCrC composite coated part prepared in Example 1 of the present invention. Detailed Implementation

[0023] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions will be clearly and completely described below in conjunction with the embodiments of this invention.

[0024] Example 1 Using ZL108 aluminum alloy as the substrate material, the method for extending the service life of the aluminum alloy piston involves preparing an AlZrCr / AlZrCrB / AlZrCrC composite coating by a combination of reactive sputtering and co-sputtering after the aluminum alloy piston blank undergoes melting, casting, heat treatment, rough machining, fine machining, deburring, and cleaning. During deposition, one Al sputtering target, one Zr sputtering target, one Cr sputtering target, and one C sputtering target are used.

[0025] Specifically, the following steps are included: (1) Casting of engine aluminum alloy piston parts blanks: The ZL108 aluminum alloy ingot is heated to a molten state (approximately 725°C) in a melting furnace. Add hexachloroethane refining agent at a rate of 0.4% of the aluminum alloy ingot mass. Introduce argon gas to degas and remove slag, thereby removing hydrogen and oxide inclusions from the molten metal and preventing porosity and shrinkage in the casting. The molten aluminum is poured into a preheated metal mold at a preheating temperature of 290°C. The molten aluminum cools and solidifies in the mold, and the piston blank is removed. The piston blank is heated to about 450℃, held for 6 hours, and then quickly quenched in water. The quenched piston was kept at 150℃ for 4 hours until the material reached a stable state.

[0026] (2) Machining of aluminum alloy pistons: Rough datum machining (using the top of the piston inner cavity as the rough datum, machining the fine datum—stop and end face, roughness Ra 3.2μm) → Rough machining of the outer circle (clamping with the stop and end face as the datum, rough turning the piston outer circle, ring land, and ring groove, leaving a machining allowance of 1.0mm) → Pin hole machining (tolerance grade H7, Ra 0.8μm) → Ring groove machining (tolerance grade H7, Ra 1.6μm) → Skirt profile machining (Ra 0.8μm) → Weight removal and dynamic balancing → Deburring and cleaning.

[0027] (3) Surface treatment of engine piston parts: The piston parts were placed in alcohol and acetone respectively, and ultrasonically cleaned for 40 minutes each to remove surface impurities and deposits. After drying, they were quickly loaded into a PVD composite coating machine and vacuumed to 6.0×10 -3 Pa, heat to 300℃, and hold for 40 minutes; (4) Ion cleaning of piston surface: Pulse bias voltage adjusted to 415V, duty cycle 0.45, Ar gas pressure 1.3Pa, temperature 275℃, Ar + Ion cleaning for 30 minutes; (5) Deposition of AlZrCr layer 2: Ar gas pressure is adjusted to 0.7-0.75 Pa, flow rate is 50 sccm, pulse bias voltage is 275 V, deposition temperature is 260 ℃, Al target power is 90 W, Zr target power is 75 W, Cr target power is 60 W, and AlZrCr coating is deposited for 10 min. (6) Reactive sputtering of AlZrCrB layer 3: Ar flow rate 95 sccm, pulse bias 240 V, deposition temperature 245 °C, Al target power 95 W, Zr target power 80 W, Cr target power 65 W, B2H6 gas flow rate 13 sccm, reactive sputtering deposition of AlZrCrB coating for 15 min; In AlZrCrB layer, the boron atom content introduced by B2H6 gas reaction accounts for 9 at.% of the total metal atom content. (7) Co-sputtering of AlZrCrC layer 4: B2H6 gas was turned off, Ar flow rate was 70 sccm, pulse bias voltage was 225 V, deposition temperature was 220 °C, Al target power was 85 W, Zr target power was 70 W, Cr target power was 60 W, C target power was 65 W, and AlZrCrC coating was co-sputtered for 15 min; in the AlZrCrC layer, the carbon atom content introduced by co-sputtering accounted for 17 at.% of the total metal atoms. (8) Post-treatment: Turn off the power supply and gas source of each target, let the room temperature drop to below 70°C, take out the sample, and the coating is finished.

[0028] like Figure 1 The wear-resistant aluminum alloy piston obtained in this embodiment has the following structure: a composite coating consisting of an AlZrCr layer, an AlZrCrB layer, and an AlZrCrC layer, which are sequentially applied outward from the surface of the part substrate.

[0029] In this embodiment, the prepared AlZrCr / AlZrCrB / AlZrCrC composite coating exhibits excellent mechanical and tribological properties on the surface of the part. The coating surface has a microhardness as high as HV2540, which is more than ten times higher than the hardness achieved by a traditional aluminum alloy piston using a MoS2 lubricating coating (approximately HV210). Simultaneously, the coating thickness is approximately 1.01 μm, and the surface roughness is controlled at Ra 43 nm. Its specific morphological characteristics are as follows: Figure 2 As shown. Regarding bonding strength, the test values ​​for this composite coating range from 83N to 87N, approximately four times higher than the MoS2 anti-friction lubricating coating used in traditional pistons (bonding strength of 22N to 30N), demonstrating superior interfacial bonding performance. Figure 3 As shown in the adhesion scratch morphology, even in the scratch end region with higher loading force, some coating residue remains, further indicating a significantly enhanced adhesion between the coating and the substrate. Under the set friction test conditions (using an HRT multi-functional friction tester, reciprocating linear motion mode, bearing steel with a hardness of HRC50-56 as the grinding ball, a loading load of 60N, a sliding speed of 10mm / s, and a test time of 30min), the friction coefficient of this composite coating remained stable between 0.34 and 0.37, a decrease of nearly 30% compared to the uncoated aluminum alloy sample (friction coefficient approximately 0.56 to 0.64). Furthermore, the wear rate of the coating was approximately 2.01 × 10⁻⁻⁻⁶. 6 mm 3 / (N·m) to 2.07×10⁻ 6 mm 3 In the range of / (N·m), the wear rate was significantly reduced by 91% to 93% compared to uncoated parts. Figure 4 As can be seen from the surface wear morphology of the coating, even after a long period of friction testing, the coating still retains residual structure, indicating that it has excellent overall performance and durability.

[0030] Example 2 A method for extending the service life of aluminum alloy pistons, wherein the substrate material of the aluminum alloy piston part 1 is A390, and the aluminum alloy piston blank is smelted, cast, heat treated, rough machined, fine machined, deburred and cleaned, and then an AlZrCr / AlZrCrB / AlZrCrC composite coating is prepared by a composite method of reactive sputtering and co-sputtering. During deposition, one Al sputtering target, one Zr sputtering target, one Cr sputtering target and one C sputtering target are used.

[0031] Specifically, the following steps are included: (1) Casting of aluminum alloy piston blanks: The A390 aluminum alloy ingot is heated to a molten state (approximately 770°C) in a melting furnace. Add hexachloroethane refining agent at a rate of 0.5% of the aluminum alloy ingot mass. Introduce argon gas to degas and remove slag, thereby removing hydrogen and oxide inclusions from the molten metal and preventing porosity and shrinkage in the casting. The molten aluminum is poured into a preheated metal mold at a preheating temperature of 330°C. The molten aluminum cools and solidifies in the mold, and the piston blank is removed. The piston blank is heated to about 530℃, held for 8 hours, and then quickly quenched in water. The quenched piston was kept at 210℃ for 5 hours until the material reached a stable state.

[0032] (2) Machining of aluminum alloy pistons: Rough datum machining (using the top of the piston inner cavity as the rough datum, machining the fine datum—stop and end face, roughness Ra 6.4μm) → Rough machining of the outer circle (clamping with the stop and end face as the datum, rough turning the piston outer circle, ring land, ring groove, etc., leaving a machining allowance of 1.0mm) → Pin hole machining (tolerance grade H7, Ra 0.4 μm) → Ring groove machining (tolerance grade H7, Ra 0.8 μm) → Skirt profile machining (Ra 0.8 μm) → Weight removal and dynamic balancing → Deburring and cleaning.

[0033] (3) Surface treatment of engine piston parts: The piston parts were placed in alcohol and acetone respectively, and ultrasonically cleaned for 50 minutes each to remove surface impurities and other attachments. After drying, they were quickly loaded into a PVD composite coating machine and vacuumed to 6.0×10 - 3 Pa, heat to 300℃, and hold for 50 minutes; (4) Ion cleaning of piston surface: Pulse bias voltage adjusted to 415V, duty cycle 0.45, Ar gas pressure 1.7Pa, temperature 275℃, Ar + Ion cleaning for 35 minutes; (5) Deposition of AlZrCr layer 2: Ar gas pressure is adjusted to 0.75 Pa, flow rate is 55 sccm, pulse bias voltage is 275 V, deposition temperature is 265 °C, Al target power is 90 W, Zr target power is 75 W, Cr target power is 60 W, and AlZrCr coating is deposited for 15 min. (6) Reactive sputtering of AlZrCrB layer 3: Ar flow rate 100 sccm, pulse bias 240 V, deposition temperature 250 °C, Al target power 95 W, Zr target power 80 W, Cr target power 65 W, B2H6 gas flow rate 16 sccm, reactive sputtering deposition of AlZrCrB coating for 20 min; In AlZrCrB layer, the boron atom content introduced by B2H6 gas reaction accounts for 11 at.% of the total metal atom content. (7) Co-sputtering of AlZrCrC layer 4: B2H6 gas was turned off, Ar flow rate was 75 sccm, pulse bias voltage was 225 V, deposition temperature was 230 °C, Al target power was 85 W, Zr target power was 70 W, Cr target power was 60 W, C target power was 65 W, and AlZrCrC coating was co-sputtered for 20 min; in the AlZrCrC layer, the carbon atom content introduced by co-sputtering accounted for 19 at.% of the total metal atoms. (8) Post-treatment: Turn off the power supply and gas source of each target, let the room temperature drop to below 70°C, take out the sample, and the coating is finished.

[0034] The AlZrCr / AlZrCrB / AlZrCrC composite coating prepared in this embodiment exhibits excellent comprehensive performance on the surface of the part. The coating surface microhardness reaches HV2570, which is more than ten times higher than the MoS2 lubricating coating commonly used in traditional aluminum pistons (whose surface hardness is approximately HV210), demonstrating a significant material strengthening effect. In terms of bonding strength, the composite coating measured values ​​of 81N to 86N, while the bonding strength of the traditional MoS2 lubricating coating is only 22N to 30N, with the former being approximately four times stronger, showing superior interfacial adhesion. Furthermore, the composite coating has a uniform thickness of approximately 1.12μm, while the surface roughness is controlled at the Ra 42nm level, exhibiting good surface quality and structural consistency.

[0035] Although the present invention has been described in detail by way of preferred embodiments, the invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method of extending the service life of an aluminum alloy piston, characterized by, After the engine aluminum alloy piston blank is smelted, cast, heat treated, roughly machined, finely machined, deburred and cleaned, an AlZrCr / AlZrCrB / AlZrCrC composite coating is prepared by a composite method of reactive sputtering and co-sputtering, and 1 Al sputtering target, 1 Zr sputtering target, 1 Cr sputtering target and 1 C sputtering target are used during deposition. Specifically comprising the following steps: (1) Engine piston part blank casting: piston blank smelting → casting → solidification and demolding → heat treatment; (2) Engine piston part machining: piston blank rough machining → semi-finishing → finishing → deburring → cleaning to remove surface oil stains; (3) Surface treatment of engine piston parts: Put the piston parts into alcohol and acetone respectively for ultrasonic, remove surface impurities and attachments, blow dry and load into PVD composite plating film machine, vacuum to 6.0 x 10 -3 Pa, heat to 300°C, keep warm for 40-50 min; (4) Piston part surface ion cleaning: pulse bias is adjusted to 415V, duty cycle is 0.45, and Ar gas pressure is 1.3-1.7Pa; (5) Depositing AlZrCr layer: Ar gas pressure is adjusted to 0.7-0.75Pa, flow rate is 50-55sccm, pulse bias is 275V, deposition temperature is 260-265℃, Al target power is 90W, Zr target power is 75W, Cr target power is 60W, and AlZrCr coating is deposited for 10-15min; (6) Reactive sputtering AlZrCrB layer: Ar flow rate is 95-100sccm, pulse bias is 240V, deposition temperature is 245-250℃, Al target power is 95W, Zr target power is 80W, Cr target power is 65W, B2H6 gas flow rate is 13-16sccm, and AlZrCrB coating is deposited by reactive sputtering for 15-20min; (7) Co-sputtering AlZrCrC layer: B2H6 gas is turned off, Ar flow rate is 70-75sccm, pulse bias is 225V, deposition temperature is 220-230℃, Al target power is 85W, Zr target power is 70W, Cr target power is 60W, C target power is 65W, and AlZrCrC coating is deposited by co-sputtering for 15-20min; (8) Post-processing: each target power supply and gas source are turned off, chamber temperature is reduced to below 70℃, the sample is taken out, coating is completed, and an aluminum alloy engine piston part with AlZrCr / AlZrCrB / AlZrCrC composite coating is obtained.

2. The method of extending the service life of an aluminum alloy piston of claim 1 wherein, The engine piston part base material is one of ZL108, ZL109 and A390.

3. The method of extending the service life of an aluminum alloy piston of claim 1 wherein, In step (3), each is ultrasonically treated in alcohol and acetone for 40-50min.

4. The method of extending the service life of an aluminum alloy piston of claim 1 wherein, In step (4), the cleaning temperature was 275°C, Ar + Ion cleaning for 30-35 min.

5. The method of extending the service life of an aluminum alloy piston of claim 1 wherein, In step (6), the content of boron atoms introduced by B2H6 gas reaction in the AlZrCrB layer accounts for 8-12at.% of the total amount of metal atoms.

6. The method of extending the service life of an aluminum alloy piston of claim 1 wherein, In step (7), the content of carbon atoms introduced by co-sputtering in the AlZrCrC layer accounts for 16-20at.% of the total amount of metal atoms.

7. A piston part prepared according to the method of any one of claims 1 to 6, characterized in that The part base surface has the composite coating of AlZrCr layer, AlZrCrB layer and AlZrCrC layer in turn from outside.

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