СПОСОБ ПОЛУЧЕНИЯ ИЗНОСОСТОЙКОГО КЕРАМИЧЕСКОГО ПОКРЫТИЯ НА ОСНОВЕ АЛЮМИНИЯ

Abstract

Disclosed is a preparation method for an aluminum-based wear-resistant ceramic coating. The surface of an aluminum substrate is coated. The coating process is cyclic coating carried out in a double-coating bath system and by using a bidirectional pulse power supply. Such intermittent coating greatly increases the thickness of a ceramic film layer and the proportion of α-Al2O3 therein, which is up to 90%, far exceeding the proportion of α-Al2O3 that can be achieved by micro-arc oxidation in the prior art, wherein the proportion of α-Al2O3 by the micro-arc oxidation is 15%-25%. Since α-Al2O3 is a corundum structure, and the proportion thereof is a key indicator affecting the wear resistance, anti-friction performance, and self-lubricating performance of a wear-resistant interface. Therefore, polishing is carried out until the highest proportion of the α-Al2O3 in the film layer is measured, and the polished film layer is used as a working layer, thus optimizing the wear resistance of the entire working layer and reducing energy consumption.

Description

A method for preparing aluminum-based wear-resistant ceramic coating Technical Field

[0001] The present invention relates to the technical field of thermo-electrochemical oxidation, and in particular to a method for preparing an aluminum-based wear-resistant ceramic coating. Background Art

[0002] The ceramic film layer prepared by micro-arc oxidation surface treatment technology on the surface of light metals such as aluminum, magnesium, titanium and their alloys has good bonding force with the substrate, greatly improving the surface hardness, and can improve the wear resistance, corrosion resistance, insulation and heat insulation properties of the substrate. The working fluid is environmentally friendly and the reaction is carried out at room temperature and pressure. Therefore, this technology has good application prospects. At present, the main obstacle restricting the application of micro-arc oxidation technology is the high energy consumption of the process, especially in the preparation of films with high surface hardness. This problem is particularly prominent. Most of the time in the micro-arc oxidation process is the micro-arc discharge stage. For example, the micro-arc discharge voltage of aluminum alloy materials is usually between 380V and 550V, and the current density is between 8A / dm2 and 20A / dm2. The processing time of the hard film layer is usually more than 90 minutes. The long high-voltage discharge process makes the micro-arc oxidation energy consumption high, making its cost high. In addition, a large number of discharge channels are left on the outside of the film layer, forming a loose and porous structure, which is mainly composed of amorphous matrix oxides. The internal dense layer has good wear resistance and corrosion resistance, but the dense layer usually accounts for a low proportion of the entire film layer. The thicker the dense layer grows, the longer the processing time is, and the more energy it consumes. Therefore, the film performance and energy consumption become a contradiction, which restricts the engineering application of micro-arc oxidation technology.

[0003] At the same time, after the existing aluminum substrate is treated with micro-arc oxidation or thermo-electrochemical oxidation, the ceramic film layer formed on the surface can be used as a wear-resistant interface layer after the loose porous layer is polished off. However, the optimal degree of polishing of the ceramic film layer is still unclear.

[0004] Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method of an aluminum-based wear-resistant ceramic coating, so that the surface of the aluminum substrate is plated. The coating process is a cyclic coating in a dual-plating tank system using a bidirectional pulse power supply. This intermittent coating greatly improves the film thickness of the ceramic film layer and the proportion of α-Al2O3 therein, which can reach up to 90%, far exceeding the α-Al2O3 proportion that can be achieved by existing micro-arc oxidation; wherein, the proportion of α-Al2O3 in micro-arc oxidation is 15%-25%. Since a high proportion of α-Al2O3 is a corundum structure, it is a key indicator affecting the wear resistance, friction reduction and self-lubricating properties of the wear-resistant interface. Therefore, grinding is stopped until the film layer with the highest α-Al2O3 proportion is measured, and the polished film layer is used as the working layer, so that the wear resistance of the entire working layer is optimized, while also saving energy consumption.

[0006] The object of the present invention is to provide a method for preparing an aluminum-based wear-resistant ceramic coating, comprising the following steps:

[0007] Step 1: Immerse the aluminum substrate in an electrolyte for thermal electrochemical oxidation treatment to form an in-situ ceramic film layer on its surface. The thermal electrochemical oxidation treatment method uses a dual plating cell system and a bidirectional pulse power supply for cyclic coating.

[0008] Step 2: Polish the ceramic film layer while measuring and recording the α-Al2O3 ratio on film layers of different thicknesses. Continue polishing until the film layer with the highest α-Al2O3 ratio is found. The polished film layer is used as the working layer, i.e., the wear-resistant interface layer. Thickness refers to the distance from the aluminum substrate with the aluminum substrate as a reference, and ratio refers to the α-Al2O3 content in α-Al2O3 and γ-Al2O3 at the same film thickness.

[0009] Furthermore, in Step 1, the aluminum substrate includes: pure aluminum or aluminum alloy.

[0010] Furthermore, in Step 1, the aluminum substrate is 2024 aluminum alloy, and the 2024 aluminum alloy has high hardness.

[0011] Furthermore, in Step 1, the following steps are also included: placing a same formed workpiece in each of the dual plating pool systems, connecting the two formed workpieces through a wire, and connecting the dual plating pool system to a bidirectional pulse power supply to form a cyclic coating, so that the coated workpieces alternately become the anode and cathode, so that the coated workpieces can be intermittently and discontinuously coated.

[0012] More specifically, a dual plating cell system is adopted, which includes two independent cylindrical electrodes, each of which contains an electrolyte, and each cylindrical electrode is connected to an independent electrolyte circulation system. An identical formed workpiece is placed in each of the two cylindrical electrodes, and the two formed workpieces are connected by a wire. The two cylindrical electrodes are then connected to a bidirectional pulse power supply, so that the workpieces being plated alternately become anodes and cathodes. Specifically, when the workpiece being plated serves as an anode, a thermoelectrochemical oxidation reaction is carried out, and when the workpiece being plated serves as a cathode, the thermoelectrochemical oxidation reaction is stopped, so that the workpiece being plated can be intermittently and discontinuously plated.

[0013] Furthermore, in Step 1, the pulse frequency of the bidirectional pulse power supply is 400-900Hz, the voltage is 400-800V, the working mode is constant current mode, the voltage fluctuates, and the current density is 10-20A / dm 2 .

[0014] Furthermore, the bidirectional pulse power supply is a bidirectional high-frequency flow pulse power supply, and the pulse frequency of the bidirectional high-frequency flow pulse power supply is 500Hz.

[0015] Furthermore, the application time is 20 to 90 minutes.

[0016] Furthermore, in Step 1, the electrolyte is a silicate system.

[0017] Furthermore, in Step 1, the temperature range of the electrolyte is 20 to 30°C.

[0018] After research, it was found that the proportion of α-Al2O3 at different thicknesses of the same ceramic film layer is positively correlated with its wear resistance. The proportion of α-Al2O3 can be used as an indicator parameter for polishing to obtain a wear-resistant interface layer with optimal performance.

[0019] Furthermore, in Step 2, the thickness of the wear-resistant interface layer accounts for 30%-60% of the thickness of the entire coating film. Since the thickness of the loose layer is thinner, the thickness of the self-compacting layer is thicker.

[0020] Furthermore, in Step 2, the thickness of the entire coating layer is 100 to 300 μm, and the thickness of the wear-resistant interface layer is 50 to 160 μm.

[0021] Furthermore, the method specifically comprises the following steps:

[0022] Step 1: Immerse the aluminum substrate in an electrolyte for thermal electrochemical oxidation treatment to form an in-situ ceramic film on its surface. The thermal electrochemical oxidation treatment utilizes a dual-plating cell system and a bidirectional pulse power supply for cyclic coating. The α-Al2O3 content increases first and then decreases from near the aluminum substrate layer to near the surface.

[0023] Step 2: Polish the ceramic film layer while measuring and recording the α-Al2O3 ratio on film layers of varying thicknesses. Polishing is continued until the film layer with the highest α-Al2O3 ratio is found. The polished film layer serves as the working layer, or wear-resistant interface layer. The thickness of the wear-resistant interface layer accounts for 30% to 60% of the total coating thickness. A friction pair includes a working layer prepared using the aforementioned method for preparing an aluminum-based wear-resistant ceramic coating.

[0024] Furthermore, the friction pair includes an internal combustion engine cylinder, and the inner wall of the cylinder has a working layer prepared by the preparation method of the aluminum-based wear-resistant ceramic coating.

[0025] Furthermore, the cylinder body of the cylinder is an aluminum-based cylinder liner.

[0026] Beneficial effects of the present invention: The present invention provides a method for preparing an aluminum-based wear-resistant ceramic coating, which is used to coat the surface of an aluminum substrate. The coating process is to perform cyclic coating in a dual-plating pool system using a bidirectional pulse power supply. This intermittent coating greatly improves the film thickness of the ceramic film layer and the proportion of α-Al2O3 therein, which can reach up to 90%, far exceeding the α-Al2O3 proportion that can be achieved by existing micro-arc oxidation. Among them, the proportion of α-Al2O3 in micro-arc oxidation is 15%-25%. Since a high proportion of α-Al2O3 is a corundum structure, it is a key indicator affecting the wear resistance, friction reduction and self-lubricating properties of the wear-resistant interface. Therefore, grinding is stopped until the film layer with the highest α-Al2O3 proportion is measured, and the polished film layer is used as the working layer, so that the wear resistance of the entire working layer is optimized, and energy consumption is also saved. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The above and other features of the present application will be more fully described when read in conjunction with the following drawings. It should be understood that these drawings only depict certain embodiments of the present application and should not be considered to limit the scope of the present application. The present application will be more clearly and detailed through the use of the drawings.

[0028] FIG1 is an XRD pattern of the TECO film layer (ie, thermal electrochemical oxidation film layer) sample of Example 1 of the present application.

[0029] Figure 2 is the XRD pattern of the MAO (micro-arc oxidation) film.

[0030] Figure 3 is the XRD pattern of the MAO (micro-arc oxidation) film.

[0031] FIG4 is a line graph showing the α:γ phase ratio of the TECO film (ie, the thermal electrochemical oxidation film) at different thicknesses on the same aluminum substrate.

[0032] FIG5 is a line graph showing the hardness of TECO films (ie, thermoelectrochemical oxidation films) of different aluminum substrates at different thicknesses. DETAILED DESCRIPTION

[0033] The following examples are described to assist in understanding the present application, and the examples are not and should not be interpreted in any way as limiting the scope of protection of the present application.

[0034] Example 1

[0035] Step 1: Immerse the 2024 alloy substrate in an electrolyte for thermal electrochemical oxidation treatment. The electrolyte is a silicate system, and the temperature range of the electrolyte is 20-30°C, so that a ceramic film layer is grown in situ on its surface. A double plating cell system is used. The double plating cell system includes two independent cylindrical electrodes. The cylindrical electrodes contain electrolyte. Each cylindrical electrode is connected to an independent electrolyte circulation system. An identical formed workpiece is placed in each of the two cylindrical electrodes. The two formed workpieces are connected by a wire. The two cylindrical electrodes are respectively connected to a bidirectional pulse power supply. The pulse frequency of the bidirectional pulse power supply is 400-900Hz, the voltage is 400-800V, the working mode is a constant current mode, the voltage fluctuates, and the current density is 10-20A / dm 2 , so that the coated workpiece alternately becomes the anode and cathode. Specifically, when the coated workpiece serves as the anode, the thermo-electrochemical oxidation reaction is carried out, and when the coated workpiece serves as the cathode, the thermo-electrochemical oxidation reaction is stopped, so that the coated workpiece can be intermittently and discontinuously coated, and the application time is 20 to 90 minutes.

[0036] This sample study is about the α-Al2O3 content in α-Al2O3 and γ-Al2O3 of the TECO film (ie, thermo-electrochemical oxidation film) on the 2024 alloy with a thickness of 260-270um.

[0037] Test conditions:

[0038] Rigaku Smartlab

[0039] Cu Kβ / 40kV 40mA

[0040] incident 2 / 3°

[0041] Scan: 3-100°Scan

[0042] Step: 0.02°

[0043] Scan rate:5.00° / min

[0044] Dector:D / teX Ultra 250

[0045] Scan Axis:θ / 2θ

[0046] As shown in FIG1 , it is the XRD pattern of the TECO film layer (ie, thermal electrochemical oxidation film layer) sample of Example 1 of the present application.

[0047] The following Table 1 is obtained from Figure 1: Relative intensity of Al2O3 crystal phase reflection peak measured by X-ray diffraction

[0048] According to Figure 1 and Table 1, the reflection intensity of the γ-Al2O3 crystal according to the lattice plane is around 66.9, 45.9 and 39.5 degrees respectively; the reflection intensity of the α-Al2O3 crystal according to the lattice plane is around 35.2, 43.4, 57.5, 25.6, 52.6 and 68.2 degrees respectively. Among them, for the convenience of identification, the data obtained from sample 2# onwards are shifted 2000 units higher than the previous one.

[0049] As shown in Figures 2 and 3, these are the XRD patterns of the MAO (micro-arc oxidation) film. The XRD patterns of the MAO (micro-arc oxidation) film phase composition are mostly α-phase peak signals that are much weaker than the γ-phase. In some cases, the α-phase peak is not even obvious. (The γ-phase crystal form of Al2O3 is very close to the δ- and η-phase crystal forms, and the reflection peak positions almost overlap.

[0050] Therefore, it can be seen that the TECO film layer (i.e., thermoelectrochemical oxidation film layer) and the MAO (microarc oxidation) film layer measured this time have weak α peaks and strong γ peaks in the XRD patterns. In the XRD patterns measured this time, it is obvious that the α peak is much stronger than the γ peak.

[0051] Therefore, the α-Al2O3 content in the film layer formed by the above-mentioned coating method is much higher than the α-Al2O3 content in the film layer formed by micro-arc oxidation coating. Since α-Al2O3 is a corundum structure, it is a key indicator affecting the wear resistance, friction reduction and self-lubricating properties of the wear-resistant interface. Therefore, the film layer formed by the above-mentioned method has higher hardness and is more wear-resistant.

[0052] Step 2: Polish the ceramic film layer and measure and record the proportion of α-Al2O3 on the film layers of different thicknesses. The thickness refers to the distance from the aluminum substrate with the aluminum substrate as a reference, and the proportion refers to the α-Al2O3 content in α-Al2O3 and γ-Al2O3 at the same film thickness.

[0053] According to literature reports and related databases, the ~43.34° and ~57.48° peaks of α-Al2O3 and the ~39.46°, ~45.90° and ~66.90° peaks of γ-Al2O3 are relatively far away from other peaks, and have high relative reflection intensities. The peak area integral ratio can be calculated to obtain (S 43.3 +S 57.5 ) / (S 39.5 +S 45.9 +S 66.9 )=α:γ, which can be used as a relative comparison of the two-phase content in different film layers.

[0054] The ratio of the α:γ phase contents is obtained by integrating the peak areas at the above positions and calculating the ratio. FIG4 is a line graph of the α:γ phase ratio at different thicknesses of the TECO film layer (i.e., the thermoelectrochemical oxidation film layer) on the same aluminum substrate. As shown in FIG4 , in the TECO film layer on the same aluminum substrate, the α-Al2O3 content from the near-substrate layer to the near-surface layer first increases and then decreases.

[0055] Replace different aluminum substrates, repeat the above steps, polish the ceramic film layer, measure and record the proportion of α-Al2O3 on the film layers of different thicknesses. As shown in Figure 5, it is a line graph of the hardness of the TECO film layer (i.e., thermoelectrochemical oxidation film layer) of aluminum substrates with different aluminum substrates at different thicknesses. As shown in Figure 5, the α:γ ratio in the TECO film layer of the 2024 alloy is much higher than that of the TECO film layers of other aluminum alloy substrates, as high as several times to nearly ten times. This is consistent with the experimental measurement that the hardness of the 2024 aluminum alloy is much higher than that of the cast aluminum alloy. This is also the reason why the 2024 aluminum alloy substrate is recommended as much as possible in practice.

[0056] Since the α:γ peak area ratio is the ratio of the XRD reflection peak intensity, not the ratio of the actual content of the two phases, the α:γ value obtained by peak area integration in Figures 4 and 5 is between 0.13 and 1.57. The relative ratios of α:γ content at different thicknesses of TECO films on different aluminum substrates are calculated and shown in Table 2 below:

[0057] Table 2 shows the relative ratio of α:γ content of TECO film with different thickness on different aluminum substrates

[0058] According to the XRD patterns of the MAO (micro-arc oxidation) film in Figures 2 and 3, the five peaks at the same position in the figure were taken and the peak areas were calculated using the open software ImageJ. According to the peak area integration in Figures 4 and 5, the above (S 43.3 +S 57.5 ) / (S 39.5 +S 45.9 +S 66.9 )=α:γto calculate the ratio, and the α:γ value is between 0.13-1.57. Therefore, the relative ratio of α:γ content at different thicknesses of MAO (micro-arc oxidation) film is calculated, as shown in Table 3 below:

[0059] Table 3 shows the relative ratio of α:γ content in different thicknesses of MAO (micro-arc oxidation) films

[0060] Comparing Table 2 and Table 3, from the corresponding ratios, the α:γ value in the TECO working layer in Table 2 is much higher than that in the MAO film layer in Table 3, especially the working layer on 2024 aluminum alloy, which is about one order of magnitude higher. The α-Al2O3 phase content at the hardest part of the TECO film on 2024 aluminum alloy may be as high as 90%.

[0061] Summary: The α-Al2O3 content in the TECO film shows a pattern of first increasing and then decreasing. Therefore, the TECO film can be polished until the film layer with the highest α-Al2O3 content is measured and then polishing is stopped. The polished film layer is used as the working layer, that is, the wear-resistant interface layer.

[0062] Although this application has disclosed various aspects and embodiments, other aspects and embodiments will be readily apparent to those skilled in the art. Variations and modifications may be made without departing from the spirit of this application, and all such variations and modifications are within the scope of this application. The various aspects and embodiments disclosed in this application are provided for illustrative purposes only and are not intended to limit this application. The actual scope of this application is determined by the claims.

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