Aluminum alloy surface crystallized nanocomposite film layer and preparation method

Abstract

The application discloses an aluminum alloy surface crystalline nano-composite film layer and a preparation method thereof. The preparation method comprises the following steps: preparing a Cr plating layer on the surface of a substrate, then preparing a CrAlN plating layer on the Cr plating layer to obtain a substrate plated with a CrAlN film layer; and preparing a TiO2 plating layer on the surface of the substrate plated with the CrAlN film layer to form a nano-composite film layer on the surface of the aluminum alloy. The CrAlN plating layer provides structural support and oxidation resistance, and the crystalline TiO2 plating layer enhances the anti-coking ability and self-cleaning characteristics of the surface. The multilayer design can significantly improve the overall anti-coking effect and slow down the coke deposition rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of surface engineering, and specifically relates to a crystalline nano-composite film layer on the surface of an aluminum alloy and a preparation method thereof. Background Art

[0002] Coking occurs primarily when carbon generated by the thermal decomposition of hydrocarbons under high temperature conditions is deposited on the surface of equipment, gradually forming a hard coke layer. As coking increases, heat conduction is hindered, and the heat transfer efficiency of the equipment gradually decreases. Furthermore, the formation of a coke layer exacerbates corrosion, threatening the integrity of the equipment. The basic principle of anti-coking coatings is to prevent carbon deposition by forming a smooth, high-temperature, and corrosion-resistant coating on the surface of the equipment. Typically, anti-coking coatings have low surface energy, high hardness, and excellent chemical inertness to reduce the adsorption of hydrocarbons on the surface and prevent their further decomposition and accumulation.

[0003] CrAlN / TiO2 composite coatings offer significant advantages in the field of anti-coking, primarily in terms of oxidation resistance, high-temperature resistance, anti-coking, and corrosion resistance. CrAlN boasts excellent thermal stability, remaining stable at temperatures exceeding 800°C and resisting decomposition. The combination of Cr and Al gives the coating a high melting point, which is particularly critical for the high-temperature environments found in anti-coking applications. Furthermore, the chromium in CrAlN forms a dense Cr2O3 oxide layer at high temperatures. This film acts as a barrier, preventing further oxidation, improving the coating's oxidation resistance and delaying coke deposition. TiO2 has a low surface energy, significantly reducing the adsorption of hydrocarbon molecules on the surface, thereby inhibiting the formation of carbon deposits. This low surface energy property helps reduce coking. The composite structure of CrAlN and TiO2 can be achieved by controlling the thickness and microstructure of the coating. Generally, CrAlN provides structural support and oxidation resistance, while TiO2 enhances the surface's anti-coking and self-cleaning properties. This multilayer design significantly improves overall anti-coking performance and slows the rate of coke deposition. Due to these advantages, CrAlN / TiO2 composite coatings are widely used for anti-coking in high-temperature environments such as petrochemicals and cracking units. Practical applications have demonstrated that this composite coating not only significantly extends equipment cleaning cycles, but also reduces maintenance costs and improves production efficiency. Furthermore, its self-cleaning and corrosion-resistant properties further reduce equipment downtime and maintenance workload, thereby achieving greater economic benefits.

[0004] Currently, this composite coating structure has been applied to carbon steel and stainless steel with strong adsorption capacity (such as engine combustion chamber pipes, nozzles, and the inner and outer walls of high-temperature equipment such as industrial furnaces). However, since the adsorption capacity of aluminum alloy surfaces is weaker than that of carbon steel and stainless steel, and the formation of a passivation layer on the aluminum alloy surface makes it difficult to form a functional layer with excellent bonding and a dense internal structure, which brings difficulties to the preparation of the coating, its application on aluminum alloy parts is still a blank. Moreover, aluminum alloy parts such as pistons are also very prone to coking during operation, which affects the high efficiency of the combustion chamber. Summary of the Invention

[0005] In order to overcome the problems in the prior art that aluminum alloys are easily deformed at higher deposition temperatures and the film quality is poor due to the presence of an oxide layer, the purpose of the present invention is to provide a crystalline nano-composite film layer on the surface of an aluminum alloy and a preparation method. The method realizes the preparation of a CrAlN / TiO2 composite coating with anti-coking function on the surface of an aluminum alloy component. The composite coating is not easy to deform, thereby extending the cleaning cycle of the equipment, reducing maintenance costs, and improving production efficiency, thereby achieving higher economic benefits.

[0006] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0007] A method for preparing a crystalline nanocomposite film layer on the surface of an aluminum alloy comprises the following steps:

[0008] A Cr coating is prepared on the surface of a substrate, and then a CrAlN coating is prepared on the Cr coating to obtain a substrate coated with a CrAlN film layer;

[0009] A TiO2 coating is prepared on the surface of a substrate coated with a CrAlN film layer, and a nano-composite film layer is formed on the surface of the aluminum alloy.

[0010] Furthermore, the substrate is an aluminum alloy substrate;

[0011] Before preparing the Cr coating on the substrate surface, the substrate is roughened.

[0012] Furthermore, the Cr coating is prepared by a multi-arc ion plating method.

[0013] Furthermore, the preparation process parameters of the Cr coating include: Cr target arc current of 80-120A, bias voltage of 80-120V, deposition temperature of room temperature to 100°C, and Cr coating thickness of 0.1-0.5μm.

[0014] Furthermore, the preparation process parameters of the CrAlN coating include: CrAl alloy target arc current of 80-120A, bias voltage of 80-120V, nitrogen flow rate of 300-600sccm, and deposition temperature of room temperature to 100°C.

[0015] Furthermore, the atomic percentage of Al in the CrAl alloy target is 25 to 50%.

[0016] Furthermore, the TiO2 coating is prepared by atomic layer deposition.

[0017] Furthermore, the preparation process parameters of the TiO2 coating include: nitrogen is used as the purge gas in a single cycle during the atomic layer deposition process, and the passage time of the titanium source precursor, nitrogen, oxygen source, and nitrogen are 1-2s, 25-35s, 0.2-0.4s, and 75-85s, respectively; the total number of cycles is 1500-2500 times, and the thickness of the TiO2 coating is 0.1-0.3μm.

[0018] A nanocomposite film prepared according to the method of any one of claims 1 to 8, comprising a Cr coating, a CrAlN coating and a TiO2 coating arranged on a substrate from bottom to top.

[0019] Furthermore, the nanocomposite coating was subjected to a coking resistance test at 600-800° C., and the coking adhesion area was 8.707%.

[0020] Compared with the prior art, the beneficial effects of the present invention are embodied in:

[0021] 1) The present invention achieves the preparation of composite coatings at relatively low temperatures. By appropriately increasing the bias voltage from 40-70V to 100V and the target arc current from 60-90A to 100A, the deposition temperature is reduced from 350-400°C to 100°C without affecting the coating preparation speed. This is conducive to improving the uniformity of the surface coating, thereby optimizing the surface quality of the coating, reducing residual stress, and improving the coating's anti-coking performance. At the same time, excessively high temperatures can cause deformation of the aluminum alloy substrate, which may weaken the bonding between the composite coating and the substrate or even cause peeling, thus filling the gap in the anti-coking film layer for aluminum alloy components in engine combustion chambers.

[0022] 2) The present invention realizes the preparation of anatase crystalline TiO2 coating. The benefit of film crystallization is that the crystalline film structure is denser, which can better achieve the purpose of anti-coking.

[0023] 3) CrAlN / TiO2 composite coatings offer significant advantages in the hot-end components of engine combustion chambers, primarily in terms of coking resistance. CrAlN provides structural support and oxidation resistance, while TiO2 enhances the surface's coking resistance and self-cleaning properties. This multi-layer design significantly improves overall coking resistance and slows the rate of coke deposition. This composite coating not only significantly extends equipment cleaning cycles, but also reduces maintenance costs and improves production efficiency. Furthermore, its self-cleaning and corrosion-resistant properties further reduce equipment downtime and maintenance workload, resulting in greater economic benefits.

[0024] Furthermore, through roughening, the passivation layer is broken and the surface area of ​​the film layer is increased, so that the film layer can adhere better and the interlayer bonding force between the coating and the substrate is enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] Figure 1 Schematic diagram of piston components;

[0027] Figure 2 Schematic diagram of the composite coating structure;

[0028] Figure 3 is the SEM photo of the composite coating;

[0029] Figure 4 XRD results of TiO2 coating;

[0030] Figure 5 These are the test results of anti-coking performance, where (a) is the original state of the metal substrate surface; (b) is the coked state of the metal substrate surface; (c) is the original state of the composite coating surface; and (d) is the coked state of the composite coating surface. DETAILED DESCRIPTION

[0031] To facilitate understanding of the present invention, the present invention will be described more fully below with reference to the accompanying drawings. The accompanying drawings illustrate preferred embodiments of the present invention. However, the present invention may be implemented in a variety of different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the disclosure of the present invention.

[0032] The aluminum alloy substrate in the present invention is a cast aluminum piston component, and the cast aluminum piston component and an aluminum sheet are used as examples for description.

[0033] The method for preparing a crystalline nanocomposite film layer on an aluminum alloy surface of the present invention comprises the following steps:

[0034] A Cr coating is prepared on the surface of an aluminum alloy substrate by a multi-arc ion plating method as a base layer, and then a CrAlN coating is prepared to obtain a substrate coated with a CrAlN film layer.

[0035] The obtained substrate coated with the CrAlN film was ultrasonically cleaned and blown clean with N2, and finally placed in an oven for drying;

[0036] An atomic layer deposition method is used to prepare a TiO2 coating with anti-coking function on the surface of a dried CrAlN film-coated substrate, and a nano-composite film layer is formed on the surface of the aluminum alloy.

[0037] The specific steps are as follows: (1) grinding, polishing, cleaning and drying the surface of the cast aluminum piston component. The cast aluminum piston component is ground and polished, and after the grinding and polishing process, the cast aluminum piston component is ultrasonically cleaned with alcohol, and then placed in an 80°C oven to dry to obtain a clean and dry cast aluminum piston component. Then, a multi-arc ion plating process is used to sequentially plate a Cr coating and a CrAlN coating on the piston surface to obtain a cast aluminum piston component plated with a CrAlN composite layer. The preparation process parameters of the Cr coating include: a Cr target arc current of 80-120A, a bias voltage of 80-120V, a deposition temperature of room temperature to 100°C, and a Cr coating thickness of 0.1-0.5μm. The preparation process parameters of the CrAlN coating include: a CrAl alloy target arc current of 80-120A, a bias voltage of 80-120V, a nitrogen flow rate of 300-600sccm, and a deposition temperature of room temperature to 100°C. The atomic percentage of Al in the CrAl alloy target is 25-50%.

[0038] (2) The cast aluminum piston component coated with the CrAlN composite layer was ultrasonically cleaned with alcohol, and then placed in an oven at 80° C. for drying to obtain a clean and dry cast aluminum piston component coated with the CrAlN composite layer.

[0039] (3) A TiO2 coating is prepared on the surface of the cast aluminum piston component coated with the CrAlN composite layer obtained in step (2) using an atomic layer deposition process, thereby obtaining a cast aluminum piston component coated with a CrAlN / TiO2 composite layer.

[0040] Among them, the preparation process parameters of the TiO2 coating include: nitrogen is used as the purge gas in a single cycle during the atomic layer deposition process, and the passage time of the titanium source precursor, nitrogen, oxygen source, and nitrogen are 1-2s, 25-35s, 0.2-0.4s, and 75-85s respectively; the total number of cycles is 1500-2500 times, and the thickness of the TiO2 coating is 0.1-0.3μm.

[0041] The nanocomposite film layer prepared by the above method includes a Cr coating, a CrAlN coating and a TiO2 coating.

[0042] The nanocomposite coating was subjected to an anti-coking test at 600-800°C, and it was found that the coking adhesion area was reduced from 48.4% of the uncoated layer to 8.707%.

[0043] Example 1

[0044] A method for preparing a crystalline nanocomposite film layer on the surface of an aluminum alloy comprises the following steps:

[0045] (1) Roughening of cast aluminum piston parts: Roughening of cast aluminum piston parts (such as Figure 1The structure of the cast aluminum piston component includes a top portion 1, a ring groove portion 2 and a skirt portion 3 connected in sequence. The component is polished using sandpaper with mesh sizes of 80, 200, 600, 1000 and 2000 in sequence, and then polished using a handheld polisher. The polished component is ultrasonically cleaned using anhydrous ethanol for 20 min, dried using N2, and then placed in an oven at 80°C for 30 min.

[0046] (2) The cast aluminum piston component roughened in step (1) is placed in a vacuum chamber of a multi-arc ion plating device, and vacuumized to a vacuum degree less than 8x10 -3 Pa, and heated to 100°C for 30 min. The gas inlet valve is opened, 180 sccm of Ar is filled, the bias voltage is adjusted to 600 V, and the ion source is turned on for 20 min for cleaning. Then, the bias voltage is adjusted to 300 V and 100 V for 10 min respectively to clean the surface of the cast aluminum piston component.

[0047] (3) The current of the Cr target is adjusted to 100 A, the bias voltage is adjusted to 100 V, the deposition temperature is adjusted to 100°C, the cavity pressure is adjusted to 0.7 Pa, and the Cr coating is deposited for 32 min to obtain a Cr coating with a thickness of 0.2 μm.

[0048] (4) The arc current of the CrAl alloy target is adjusted to 100 A, the bias voltage is adjusted to 100 V, the nitrogen flow is adjusted to 300 sccm, the deposition temperature is adjusted to 100°C, the cavity pressure is adjusted to 0.7 Pa, and the CrAlN coating is deposited for 80 min to obtain a CrAlN coating with a thickness of 1.2 μm.

[0049] (5) The component coated with the CrAlN coating is ultrasonically cleaned using anhydrous ethanol for 20 min, dried using N2, and then placed in an oven at 80°C for 30 min.

[0050] (6) The component coated with the CrAlN coating is transferred to a coating cavity of an atomic layer deposition device, vacuumized to a cavity pressure of 40 mtorr, and heated to 200°C for 30 min. Then, titanium isopropoxide (temperature 60°C) is used as a titanium source precursor, hydrogen peroxide (30% H2O2 aqueous solution) is used as an oxygen source, and high-purity nitrogen (99.999% N2) is used as a purge gas. The flow of the high-purity nitrogen is adjusted by a needle valve, the working pressure is 400 mtor during the high-purity nitrogen purging, and in a single cycle of the atomic layer deposition process, the titanium source precursor, the high-purity nitrogen, the hydrogen peroxide, and the high-purity nitrogen are sequentially introduced for 1.5 s, 30 s, 0.3 s, and 80 s respectively. The total cycle number is 2500, so that a TiO2 coating with a thickness of 250 nm is prepared on the surface of the component coated with the CrAlN coating, and a final nano-composite film layer is formed on the surface of the cast aluminum piston component.

[0051] The structure of the composite film layer is shown in Figure 2The cast aluminum piston component is coated with Cr, the Cr coating is coated with CrAlN, and the CrAlN coating is coated with TiO2.

[0052] Example 2

[0053] A method for preparing a crystalline nanocomposite film layer on the surface of an aluminum alloy comprises the following steps:

[0054] (1) Roughening of aluminum sheet: The aluminum sheet (diameter 25.4 mm, thickness 1 mm) was polished with 80, 200, 600, 1000, and 2000 grit sandpaper in sequence, and then polished with a handheld polisher. The polished parts were then ultrasonically cleaned with anhydrous ethanol for 20 min, blown dry with N2, and finally dried in an oven at 80°C for 30 min.

[0055] (2) Place the aluminum sheet roughened in step (1) into the vacuum chamber of the multi-arc ion plating equipment and evacuate the vacuum chamber to a vacuum degree of less than 8×10 -3 Pa, heated to 100 ° C and kept warm for 30 minutes. Open the gas inlet valve, fill with 180 sccm of Ar, adjust the bias voltage to 600 V, turn on the ion source for 20 minutes, then adjust the bias voltage to 300 V and 100 V, respectively, for 10 minutes to clean the aluminum surface.

[0056] (3) The current of the Cr target was adjusted to 100 A, the bias voltage was adjusted to 100 V, the deposition temperature was adjusted to 100 ° C, the pressure in the chamber was adjusted to 0.7 Pa, and the deposition time was adjusted to 32 min. The Cr coating thickness was adjusted to 0.2 μm.

[0057] (4) Adjust the CrAl alloy target arc current to 100 A, the bias voltage to 100 V, the nitrogen flow rate to 300 sccm, the deposition temperature to 100 °C, the chamber pressure to 0.7 Pa, the deposition time to 80 min, and the CrAlN coating thickness to 1.2 μm.

[0058] (5) The aluminum sheet coated with CrAlN was ultrasonically cleaned with anhydrous ethanol for 20 min, then dried with N2, and finally dried in an oven at 80 °C for 30 min.

[0059] (6) The aluminum sheet plated with CrAlN plating layer is transferred to a plating cavity of an atomic layer deposition device, vacuumed to a cavity pressure equal to 40mtorr, and heated to 200℃ and kept for 30min. Then, titanium isopropoxide is used as a titanium source precursor (temperature is 60℃), hydrogen peroxide (30% H2O2 aqueous solution) is used as an oxygen source, and high-purity nitrogen (purity is 99.999%) is used as a purging gas. The flow of the high-purity nitrogen is adjusted by a needle valve. The working gas pressure is 400mtor when the high-purity nitrogen is purged. In a single cycle of the atomic layer deposition process, the titanium source precursor, the high-purity nitrogen, the hydrogen peroxide, and the high-purity nitrogen are sequentially introduced for 1.5s, 30s, 0.3s, and 80s, respectively. The total cycle number is 2500, so that a TiO2 plating layer with a thickness of 250nm is prepared on the surface of the substrate plated with CrAlN, and a final nano-composite film layer is formed on the surface of the aluminum sheet.

[0060] The structure of the composite film layer is shown in Figure 2 . The aluminum sheet substrate is plated with Cr, the Cr plating layer is plated with CrAlN, and the CrAlN plating layer is plated with TiO2.

[0061] The SEM photo of the composite film layer is shown in Figure 3 . It can be seen that the plating layer is divided into three layers from top to bottom, which are the TiO2 plating layer, the CrAlN plating layer, and the Cr plating layer. The TiO2 plating layer and the Cr plating layer are about 0.2μm, the thickness of the CrAlN plating layer is about 1.2μm, the total thickness of the plating layer is about 1.6μm, the plating layer is uniform and continuous, the interlayer bonding is good, and the internal structure is dense.

[0062] The XRD analysis of the phase composition of the film layer is shown in Figure 4 . It is found that the phase is anatase and is preferentially oriented along the 101 crystal face.

[0063] (7) Anti-coking test: The original aluminum sheet and the aluminum sheet with the nano-composite film layer in Example 2 are fixed in front of a diesel flame spray gun, the flame spray gun is ignited, and the surface temperature of the sample is controlled to be 800℃ by adjusting the oxygen amount. The test is performed for 30min. After the test, the macroscopic photo of the sample is taken and is binarized by image software to obtain the coking adhesion area.

[0064] Figure 5 (a) is the original state of the surface of the metal substrate; (b) is the coking state of the surface of the metal substrate; (c) is the original state of the surface of the composite plating layer; and (d) is the coking state of the surface of the composite plating layer. It can be seen that, compared with the original Al sample, the coking adhesion area of the sample with the composite plating layer prepared on the surface is reduced from 48.4% to 8.707%, which indicates that the present application plays an important role in the anti-coking function of aluminum alloy.

[0065] Example 3

[0066] A method for preparing a crystalline nanocomposite film layer on the surface of an aluminum alloy comprises the following steps:

[0067] (1) Roughening of cast aluminum piston parts: The cast aluminum piston parts were polished with 80-mesh, 200-mesh, 600-mesh, 1000-mesh, and 2000-mesh sandpaper in sequence, and then polished with a handheld polisher. The polished parts were then ultrasonically cleaned with anhydrous ethanol for 20 minutes, blown dry with N2, and finally dried in an oven at 80°C for 30 minutes.

[0068] (2) Place the cast aluminum piston component roughened in step (1) into the vacuum chamber of the multi-arc ion plating equipment and evacuate the vacuum chamber to a vacuum degree of less than 8×10 -3 Pa, heated to 100°C and kept warm for 30 minutes. Open the inlet valve, fill with 180 sccm of Ar, adjust the bias voltage to 600 V, turn on the ion source for 20 minutes of cleaning, then adjust the bias voltage to 300 V and 100 V, respectively, for 10 minutes to clean the surface of the cast aluminum piston component.

[0069] (3) The current of the Cr target was adjusted to 80 A, the bias voltage was adjusted to 120 V, the deposition temperature was adjusted to 100 ° C, and the pressure in the chamber was adjusted to 0.7 Pa. Deposition was carried out for 40 minutes to obtain a Cr coating with a thickness of 0.3 μm.

[0070] (4) The CrAl alloy target arc current was adjusted to 80 A, the bias voltage was 120 V, the nitrogen flow rate was 400 sccm, the deposition temperature was room temperature, the chamber pressure was 0.7 Pa, and deposition was carried out for 120 min to obtain a CrAlN coating with a thickness of 1.5 μm.

[0071] (5) Ultrasonic cleaning of the CrAlN-plated parts was performed using anhydrous ethanol for 20 min, followed by drying with N2, and finally drying in an oven at 80 °C for 30 min.

[0072] (6) The CrAlN-plated component was transferred to the coating chamber of the atomic layer deposition equipment, and the chamber pressure was evacuated to 40 mtorr. At the same time, the temperature was raised to 200°C and kept at this temperature for 30 minutes. Then, titanium isopropoxide was used as the titanium source precursor (temperature was 60°C), hydrogen peroxide (30% H2O2 aqueous solution by mass) was used as the oxygen source, and high-purity nitrogen (99.999% purity N2) was used as the purge gas. The flow rate of high-purity nitrogen was adjusted by a needle valve. The working pressure during the high-purity nitrogen purge was 400 mtorr. In a single cycle of the atomic layer deposition process, the introduction time of the titanium source precursor, high-purity nitrogen, hydrogen peroxide, and high-purity nitrogen was 1s, 25s, 0.4s, and 85s, respectively. The total number of cycles was 2500 times, thereby preparing a TiO2 coating layer with a thickness of 250 nm on the surface of the CrAlN-plated component, and forming the final nanocomposite film layer on the surface of the above-mentioned cast aluminum piston component.

[0073] Example 4

[0074] A method for preparing a crystalline nanocomposite film layer on the surface of an aluminum alloy comprises the following steps:

[0075] (1) Roughening of cast aluminum piston parts: Roughening of cast aluminum piston parts (such as Figure 1 As shown in FIG, the structure of the cast aluminum piston component includes: the top, the ring groove and the skirt) which are polished with 80 mesh, 200 mesh, 600 mesh, 1000 mesh and 2000 mesh sandpaper in sequence, and then polished with a handheld polisher. The polished components are then ultrasonically cleaned with anhydrous ethanol for 20 minutes, blown dry with N2, and finally dried in an 80°C oven for 30 minutes.

[0076] (2) Place the cast aluminum piston component roughened in step (1) into the vacuum chamber of the multi-arc ion plating equipment and evacuate the vacuum chamber to a vacuum degree of less than 8×10 -3 Pa, heated to 100°C and kept warm for 30 minutes. Open the inlet valve, fill with 180 sccm of Ar, adjust the bias voltage to 600 V, turn on the ion source for 20 minutes of cleaning, then adjust the bias voltage to 300 V and 100 V, respectively, for 10 minutes to clean the surface of the cast aluminum piston component.

[0077] (3) The current of the Cr target was adjusted to 120 A, the bias voltage was adjusted to 100 V, the deposition temperature was adjusted to 100 ° C, the pressure in the chamber was adjusted to 0.7 Pa, and the deposition time was adjusted to 60 min to obtain a Cr coating with a thickness of 0.5 μm.

[0078] (4) The CrAl alloy target arc current was adjusted to 120 A, the bias voltage was 100 V, the nitrogen flow rate was 500 sccm, the deposition temperature was 50 ° C, the chamber pressure was 0.7 Pa, and the deposition time was 80 min to obtain a CrAlN coating with a thickness of 1.2 μm.

[0079] (5) Ultrasonic cleaning of the CrAlN-plated parts was performed using anhydrous ethanol for 20 min, followed by drying with N2, and finally drying in an oven at 80 °C for 30 min.

[0080] (6) The CrAlN-plated component was transferred to the coating chamber of the atomic layer deposition equipment, and the chamber pressure was evacuated to 40 mtorr. At the same time, the temperature was raised to 200°C and kept at this temperature for 30 minutes. Then, titanium isopropoxide was used as the titanium source precursor (temperature was 60°C), hydrogen peroxide (30% H2O2 aqueous solution by mass) was used as the oxygen source, and high-purity nitrogen (99.999% purity N2) was used as the purge gas. The flow rate of high-purity nitrogen was adjusted by a needle valve. The working pressure during the high-purity nitrogen purge was 400 mtorr. In a single cycle of the atomic layer deposition process, the introduction time of the titanium source precursor, high-purity nitrogen, hydrogen peroxide, and high-purity nitrogen was 2s, 35s, 0.2s, and 75s, respectively. The total number of cycles was 1500 times, thereby preparing a TiO2 coating layer with a thickness of 200 nm on the surface of the CrAlN-plated component, and forming the final nanocomposite film layer on the surface of the above-mentioned cast aluminum piston component.

[0081] Example 5

[0082] A method for preparing a crystalline nanocomposite film layer on the surface of an aluminum alloy comprises the following steps:

[0083] (1) Roughening of cast aluminum piston parts: Roughening of cast aluminum piston parts (such as Figure 1 As shown in FIG, the structure of the cast aluminum piston component includes: the top, the ring groove and the skirt) which are polished with 80 mesh, 200 mesh, 600 mesh, 1000 mesh and 2000 mesh sandpaper in sequence, and then polished with a handheld polisher. The polished components are then ultrasonically cleaned with anhydrous ethanol for 20 minutes, blown dry with N2, and finally dried in an 80°C oven for 30 minutes.

[0084] (2) Place the cast aluminum piston component roughened in step (1) into the vacuum chamber of the multi-arc ion plating equipment and evacuate the vacuum chamber to a vacuum degree of less than 8×10 -3 Pa, heated to 100°C and kept warm for 30 minutes. Open the inlet valve, fill with 180 sccm of Ar, adjust the bias voltage to 600 V, turn on the ion source for 20 minutes of cleaning, then adjust the bias voltage to 300 V and 100 V, respectively, for 10 minutes to clean the surface of the cast aluminum piston component.

[0085] (3) The current of the Cr target was adjusted to 110 A, the bias voltage was adjusted to 80 V, the deposition temperature was adjusted to 100 ° C, the pressure in the chamber was adjusted to 0.7 Pa, and the deposition time was adjusted to 16 min to obtain a Cr coating with a thickness of 0.1 μm.

[0086] (4) The CrAl alloy target arc current was adjusted to 90 A, the bias voltage was 80 V, the nitrogen flow rate was 600 sccm, the deposition temperature was 70 ° C, the chamber pressure was 0.7 Pa, and the deposition time was 80 min to obtain a CrAlN coating with a thickness of 1.2 μm.

[0087] (5) Ultrasonic cleaning of the CrAlN-plated parts was performed using anhydrous ethanol for 20 min, followed by drying with N2, and finally drying in an oven at 80 °C for 30 min.

[0088] (6) The CrAIN-coated parts were transferred to the coating chamber of the atomic layer deposition equipment, evacuated to a chamber pressure of 40 mtorr, and the temperature was raised to 200 °C and kept at this temperature for 30 min. Then, titanium isopropoxide was used as the titanium source precursor (temperature of 60°C), hydrogen peroxide (30% by mass H2O2 aqueous solution) as the oxygen source, and high-purity nitrogen (99.999% purity N2) as the purge gas. The flow rate of high-purity nitrogen was adjusted by a needle valve. The working pressure during the high-purity nitrogen purge was 400 mtor. In a single cycle of the atomic layer deposition process, the introduction time of the titanium source precursor, high-purity nitrogen, hydrogen peroxide, and high-purity nitrogen was 1.5s, 30s, 0.3s, and 80s, respectively, and the total number of cycles was 3000, thereby preparing a TiO2 coating with a thickness of 300 nm on the surface of the CrAlN-plated component, and forming a final nano-composite film layer on the surface of the above-mentioned cast aluminum piston component.

[0089] Compared to patent CN113584440B (High-temperature and anti-coking chromium-aluminum-nitrogen and titanium dioxide composite coating and its preparation method), this method achieves the production of composite coatings at lower temperatures. By appropriately increasing the bias voltage from 40-70V to 100V and the target arc current from 60-90A to 100A, the deposition temperature can be reduced from 350-400°C to 100°C without affecting the coating preparation speed. This helps improve the uniformity of the surface coating, thereby optimizing the surface quality of the coating, reducing residual stress, and improving the coating's anti-coking properties. At the same time, excessively high temperatures can cause deformation of the aluminum alloy substrate, which may weaken the bonding between the composite coating and the substrate and even cause peeling.

[0090] Compared with patent: CN113584440B (high temperature resistant and anti-coking chromium aluminum nitrogen, titanium dioxide composite coating and its preparation method), the preparation of anatase crystalline TiO2 coating is achieved. The benefit of film crystallization is that the crystalline film structure is denser, which can better achieve the purpose of anti-coking.

[0091] The above description is merely a description of the preferred embodiment of the present invention and is not to be construed as limiting the claims. The present invention is not limited to the above embodiment, and variations in the specific structure are permitted. Any variations made within the scope of the independent claims of the present invention are also within the scope of protection of the present invention.

[0092] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

Claims

1. A method for preparing a crystalline nanocomposite film layer on the surface of an aluminum alloy, characterized in that: The steps include: A Cr coating is prepared on the surface of an aluminum alloy substrate, and then a CrAlN coating is prepared on the Cr coating to obtain a substrate coated with a CrAlN film layer; A TiO2 coating is prepared on the surface of a substrate coated with a CrAlN film layer, and a nanocomposite film layer is formed on the surface of an aluminum alloy substrate; The Cr coating and CrAlN coating were prepared by multi-arc ion plating method; The preparation process parameters of the Cr coating include: Cr target arc current of 80-120A, bias voltage of 80-120V, deposition temperature of room temperature to 100°C, and Cr coating thickness of 0.1-0.5μm; The preparation process parameters of the CrAlN coating include: CrAl alloy target arc current of 80-120A, bias voltage of 80-120V, nitrogen flow rate of 300-600 sccm, and deposition temperature of room temperature to 100°C; The TiO2 coating was prepared by atomic layer deposition.

2. The method for preparing a crystalline nanocomposite film layer on an aluminum alloy surface according to claim 1, characterized in that: Before preparing the Cr coating on the substrate surface, the substrate is roughened.

3. The method for preparing a crystalline nanocomposite film on an aluminum alloy surface according to claim 1, characterized in that: The atomic percentage of Al in the CrAl alloy target is 25~50%.

4. The method for preparing a crystalline nanocomposite film on an aluminum alloy surface according to claim 1, wherein: The preparation process parameters of the TiO2 coating include: nitrogen is used as the purge gas in a single cycle during the atomic layer deposition process, and the passage time of the titanium source precursor, nitrogen, oxygen source, and nitrogen are 1-2s, 25-35s, 0.2-0.4s, and 75-85s respectively; the total number of cycles is 1500-2500 times, and the TiO2 coating thickness is 0.1-0.3μm.

5. A nanocomposite film prepared according to any one of claims 1 to 4, characterized in that: It includes a Cr coating, a CrAlN coating and a TiO2 coating on the substrate from bottom to top.

6. The nanocomposite film layer according to claim 5, characterized in that: The nanocomposite film layer was subjected to an anti-coking test at 600-800° C., and the coking adhesion area was 8.707%.

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