Method for preparing aluminum-based wear-resistant ceramic coatings

Abstract

The present invention discloses a method for preparing an aluminum-based wear-resistant ceramic coating, so that the surface of the aluminum substrate is coated, and the coating process is performed in a double plating cell, with a bidirectional pulse power supply used to perform periodic coating, and such intermittent coating greatly improves the thickness of the ceramic coating and the proportion of α-Al2O3 therein to 90%, which is much higher than the proportion of α-Al2O3 that can be achieved by existing micro-arc oxidation. Here, the proportion of α-Al2O3 in micro-arc oxidation is 15%-25%, and the α-Al2O3 with a high proportion is a corundum structure, so it is an important indicator that affects the wear resistance, friction reduction and self-lubrication of the wear-resistant interface, and therefore, polishing is completed until the coating with the highest proportion of α-Al2O3 is measured, and the polished coating is used as the processed layer, which optimizes the wear resistance of the entire processed layer and also saves energy consumption.

Description

[Technical field]

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

[0002] The ceramic coating prepared on the surface of light metals such as aluminum, magnesium, titanium and their alloys by micro-arc oxidation surface treatment technology has good bonding force with the substrate, can greatly increase the surface hardness, and can improve the wear resistance, corrosion resistance, insulation and heat insulation of the substrate. In addition, the working fluid is environmentally friendly and the reaction is carried out at normal temperature and pressure, so the technology has better application prospects. At present, the main obstacle limiting the application of micro-arc oxidation technology is the large energy consumption of the process, which is particularly prominent when preparing coatings with high surface hardness. Most of the micro-arc oxidation process is carried out in the micro-arc discharge stage, for example, the micro-arc discharge voltage of aluminum alloy materials is usually between 380V-550V, and the current density is 8A / dm. 2 ~20A / dm 2 Meanwhile, the processing time of hard coating is usually more than 90 minutes, and the micro-arc oxidation by long-term high-voltage discharge process consumes a lot of energy, which leads to high costs; and the outer side of the coating is left with a large number of discharge channels, which forms a porous structure. Moreover, the inner dense layer is mainly composed of amorphous matrix oxide, and has better wear resistance and corrosion resistance. However, the dense layer usually accounts for a small proportion of the whole coating, and the thicker the dense layer, the higher the processing time and energy consumption. Therefore, the coating performance and energy consumption are contradictory, which limits the engineering application of micro-arc oxidation technology.

[0003] At the same time, after treating an existing aluminum substrate with micro-arc oxidation or thermoelectrochemical oxidation, the ceramic coating formed on the surface can be used as a wear-resistant interface layer after the porous layer is polished away, but no conclusion has been reached at this time regarding the optimal degree of polishing of the ceramic coating. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing an aluminum-based wear-resistant ceramic coating so that the surface of the aluminum substrate is coated, and the coating process is performed in a double plating cell using a bidirectional pulse power supply to perform periodic coating, and such intermittent coating can greatly improve the thickness of the ceramic coating and the proportion of α-Al2O3 therein to 90%, which is much higher than the proportion of α-Al2O3 that can be achieved by existing micro-arc oxidation. Here, the proportion of α-Al2O3 in micro-arc oxidation is 15%-25%, and the α-Al2O3 with a high proportion is a corundum structure, so it is an important indicator that affects the wear resistance, friction reduction and self-lubrication of the wear-resistant interface, and therefore, polishing is completed until the coating with the highest proportion of α-Al2O3 is measured, and the polished coating is used as the processed layer, so that the wear resistance of the entire processed layer is optimized and energy consumption is also saved.

[0005] The object of the present invention is to provide a method for preparing an aluminum-based wear-resistant ceramic coating, which comprises the following steps: Step 1, the aluminum substrate is immersed in the electrolyte and a ceramic coating is grown in situ on the surface by thermo-electrochemical oxidation treatment, where the thermo-electrochemical oxidation treatment is to carry out cyclic coating using a bidirectional pulse power supply in a dual plating cell.

[0006] Step 2: While grinding the ceramic coating, measure and record the percentage of α-Al2O3 on the coatings with different thicknesses, complete grinding until the coating with the highest percentage of α-Al2O3 is measured, and the ground coating is used as the processing layer, which is the wear-resistant interface layer. Here, the thickness refers to the distance from the aluminum substrate based on the aluminum substrate, and the percentage refers to the content of α-Al2O3 in α-Al2O3 and γ-Al2O3 at the same thickness.

[0007] In step 1, the aluminum substrate includes pure aluminum or an aluminum alloy.

[0008] Furthermore, in step 1, the aluminum substrate is a 2024 aluminum alloy, which has high hardness.

[0009] In addition, in step 1, the method further includes the steps of placing the same molded workpiece in a double plating cell, connecting the two molded workpieces with a wire, and connecting the double plating cell to a bidirectional pulse power source to form a periodic coating, so that the coated workpieces are alternately anode and cathode, and the coated workpieces are intermittently and discontinuously coated.

[0010] More specifically, a dual plating cell is used, where the dual plating cell is composed of two independent cylindrical electrodes, the cylindrical electrodes are filled with an electrolyte, and each cylindrical electrode is connected to an independent electrolyte circulation system, the same formed workpiece is placed on each of the two cylindrical electrodes, the two formed workpieces are respectively connected by wires, and the two cylindrical electrodes are respectively connected to a bidirectional pulse power supply, so that the objects to be coated alternately become anodes and cathodes, specifically, when the object to be coated is the anode, a thermoelectrochemical oxidation reaction is carried out, and when the object to be coated is the anode, the thermoelectrochemical oxidation reaction is stopped, thereby enabling the object to be coated intermittently and discontinuously coated.

[0011] In step 1, the pulse frequency of the bidirectional pulse power supply is 400-900Hz, the voltage is 400-800V, the operation mode is constant current mode, the voltage fluctuates, and the current density is 10-20A / dm 2 It is.

[0012] Furthermore, the bidirectional pulse power supply is a bidirectional high frequency pulse power supply, and the pulse frequency of the bidirectional high frequency pulse power supply is 500 Hz.

[0013] The coating time is 20 to 90 minutes.

[0014] Also, in step 1, the electrolyte is a silicate-based electrolyte.

[0015] In step 1, the temperature range of the electrolyte is 20 to 30°C.

[0016] As a result, it was found that the proportion of α-Al2O3 at different thicknesses on the same ceramic coating was positively correlated with its wear resistance, and the proportion of α-Al2O3 could be used as an index parameter for polishing to obtain the wear-resistant interface layer with the best performance.

[0017] In addition, in step 2, the thickness of the wear-resistant interface layer accounts for 30% to 60% of the total coating thickness, and the thickness of the sparse layer is thin, so the thickness of the self-densified layer is thick.

[0018] Furthermore, in step 2, the thickness of the entire coating is 100-300 μm, and the thickness of the wear-resistant interface layer is 50-160 μm.

[0019] The method specifically includes the following steps: Step 1, the aluminum substrate is immersed in the electrolyte and a ceramic coating is grown in situ on the surface by thermo-electrochemical oxidation treatment, where the thermo-electrochemical oxidation treatment is to perform cyclic coating using a bidirectional pulse power supply in a dual plating cell, and the α-Al2O3 content from near the aluminum substrate layer to near the surface shows a tendency to increase at first and then decrease.

[0020] Step 2, while polishing the ceramic coating, measure and record the percentage of α-Al2O3 on coatings with different thicknesses, complete the polishing until the coating with the highest percentage of α-Al2O3 is measured, and the polished coating is used as the machined layer, which is the wear-resistant interface layer, where the thickness of the wear-resistant interface layer accounts for 30%-60% of the total coating thickness.

[0021] A friction pair, comprising a working layer prepared by the method for preparing an aluminum-based wear-resistant ceramic coating.

[0022] Furthermore, the friction pair includes an internal combustion engine cylinder, the inner wall of the cylinder using a worked layer prepared by the method for preparing an aluminum-based wear-resistant ceramic coating.

[0023] The cylinder body of the cylinder is an aluminum-based cylinder liner.

[0024] The beneficial effects of the present invention are as follows: The present invention provides a method for preparing an aluminum-based wear-resistant ceramic coating, so that the surface of an aluminum substrate is coated. The coating process is performed in a double plating cell, and periodic coating is performed using a bidirectional pulse power supply. Such intermittent coating can greatly improve the thickness of the ceramic coating and the proportion of α-Al2O3 therein to 90%, which is much higher than the proportion of α-Al2O3 that can be achieved by existing micro-arc oxidation. Here, the proportion of α-Al2O3 in micro-arc oxidation is 15%-25%, and the α-Al2O3 with a high proportion has a corundum structure, which is an important indicator that affects the wear resistance, friction reduction and self-lubrication of the wear-resistant interface. Therefore, polishing is completed until the coating with the highest proportion of α-Al2O3 is measured, and the polished coating is used as the processed layer, so that the wear resistance of the entire processed layer is optimized and energy consumption is also saved. [Brief description of the drawings]

[0025] The above and other features of the present application will be further explained in conjunction with the following attached drawings, which are understood to illustrate only some embodiments of the present application and therefore should not be considered as limiting the scope of the present application, and the attached drawings will explain the contents of the present application more clearly and in detail. [Figure 1] 1 is an XRD pattern of a TECO coating (i.e., thermo-electrochemical oxidation coating) sample in Example 1 of the present application. [Diagram 2] XRD pattern of MAO (Micro Arc Oxidation) coating. [Diagram 3] XRD pattern of MAO (Micro Arc Oxidation) coating. [Figure 4] 1 is a line graph showing the α:γ phase ratio of different thicknesses of TECO coatings (i.e., thermo-electrochemical oxidation coatings) on the same aluminum substrate. [Diagram 5] 1 is a line graph showing the hardness of TECO coatings (i.e., thermo-electrochemical oxidation coatings) of different thicknesses on different aluminum substrates. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] The following examples are provided to aid in the understanding of this application, and these examples do not limit, and should not be construed as limiting, the scope of protection of this application.

[0027] Example 1 Step 1, the 2024 alloy substrate is immersed in an electrolyte to carry out a thermo-electrochemical oxidation treatment, the electrolyte is silicate-based, the temperature range of the electrolyte is 20-30°C, and a ceramic coating is grown in situ on the surface of the 2024 alloy substrate, where a dual-plating cell is used, the dual-plating cell is composed of two independent cylindrical electrodes, the cylindrical electrodes are filled with electrolyte, each cylindrical electrode is connected to an independent electrolyte circulation system, the same forming workpiece is placed on each of the two cylindrical electrodes, the two forming workpieces are respectively connected by wires, and 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 operation mode is constant current mode, the voltage is fluctuating, and the current density is 10-20A / dm 2 As a result, the object to be coated alternately becomes an anode and a cathode; specifically, when the object to be coated is an anode, a thermoelectrochemical oxidation reaction is carried out, and when the object to be coated is an anode, the thermoelectrochemical oxidation reaction is stopped, so that the object to be coated can be intermittently and discontinuously coated, and the coating time is 20 to 90 minutes.

[0028] The present test sample is the α-Al2O3 content in α-Al2O3 and γ-Al2O3 of a TECO coating (i.e., a thermoelectrochemical oxidation coating) on ​​a 2024 alloy with a thickness of 260–270 μm.

[0029] Test conditions: Rigaku Smartlab Cu Kβ / 40kV 40mA Angle of incidence: 2 / 3° Scan range: 3-100°Scan Scan interval: 0.02° Scan speed: 5.00° / min Detector: D / teX Ultra 250 Scan angle: θ / 2θ As shown in FIG. 1, this is the XRD pattern of the TECO coating (ie, thermo-electrochemical oxidation coating) sample in Example 1 of the present application.

[0030] From FIG. 1, the following Table 1 is obtained: Relative intensities of Al2O3 crystal structure reflection peaks measured by X-ray diffraction TIFF2025501852000002.tif85170

[0031] According to Figure 1 and Table 1, it can be seen that the reflection intensities of γ-Al2O3 crystal structure due to lattice planes are around 66.9, 45.9, and 39.5 degrees, and the reflection intensities of α-Al2O3 crystal structure due to lattice planes are around 35.2, 43.4, 57.5, 25.6, 52.6, and 68.2 degrees, where, for ease of identification, each reflection spectrum curve starting from 2# of the obtained data is shifted up by 2000 units from the previous sample.

[0032] As shown in Fig. 2 and Fig. 3, the XRD patterns of MAO (micro-arc oxidation) coatings, the XRD patterns consisting of MAO (micro-arc oxidation) coatings show that in most cases, the α peak signal is much weaker than that of γ, and in some cases, the α peak is not obvious (the γ crystal structure of Al2O3 is very close to the δ and η crystal structures, and the positions of the reflection peaks are almost consistent).

[0033] Therefore, it can be seen that the α peaks in the XRD patterns of the TECO coatings (i.e., thermoelectrochemical oxidation coatings) and MAO (microarc oxidation) coatings tested here are weak and the γ peak intensities are different, with the α peaks in the XRD patterns tested here being much stronger than the γ peaks.

[0034] Therefore, the α-Al2O3 content in the coating formed by the above method is much higher than that of the coating formed by micro-arc oxidation coating, and since α-Al2O3 has a corundum structure, it is an important indicator that affects the wear resistance, friction reduction and self-lubrication of the wear-resistant interface, and therefore the coating formed by the above method has high hardness and excellent wear resistance.

[0035] Step 2, while polishing the ceramic coating, measure and record the percentage of α-Al2O3 on the coating with different thicknesses, where the thickness refers to the distance from the aluminum substrate relative to the aluminum substrate, and the percentage refers to the content of α-Al2O3 in α-Al2O3 and γ-Al2O3 at the same thickness.

[0036] According to literature reports and related databases, the peaks at ~43.34° and ~57.48° of α-Al2O3 and the peaks at ~39.46°, ~45.90°, and ~66.90° of γ-Al2O3 are relatively far away from other peaks and have high relative reflection intensities, so the peak area integral ratio (S 43.3 +S 57.5 ) / (S 39.5 +S 45.9 +S 66.9 )=α:γ, which allows a relative comparison of the amounts of both in different coatings.

[0037] The α:γ content can be obtained by integrating the peak areas and the ratio at the above positions, as shown in Figure 4, which is a line graph showing the α:γ ratio of TECO coatings (i.e., thermo-electrochemical oxidation coatings) of different thicknesses on the same aluminum substrate. As can be seen from Figure 4, in the TECO coatings on the same aluminum substrate, the α-Al2O3 content from near the substrate layer to near the surface tends to increase at first and then decrease.

[0038] By replacing different aluminum substrates and repeating the above steps, the ratio of α-Al2O3 on the coatings of different thicknesses was measured and recorded while polishing the ceramic coating, as shown in Figure 5, which is a line graph showing the hardness of TECO coatings (i.e., thermo-electrochemical oxidation coatings) of different thicknesses on different aluminum substrates. As can be seen from Figure 5, the α:γ ratio of the TECO coating on 2024 alloy is much higher than that of the TECO coating on other aluminum alloy substrates, by several times to even ten times. This is also consistent with the experimentally measured hardness of 2024 aluminum alloy is much higher than that of cast aluminum alloy, which is the reason why 2024 aluminum alloy substrate is recommended as much as possible in practice.

[0039] Since the α:γ peak area ratio is the XRD reflection peak intensity ratio, not the ratio of the actual contents of the two, the α:γ values ​​obtained by peak area integration in Figures 4 and 5 are in the range of 0.13 to 1.57, and the calculated relative ratios of α:γ contents of different thicknesses of TECO coatings on different aluminum substrates are shown in Table 2 below.

[0040] TIFF2025501852000003.tif77170

[0041] According to the XRD patterns of MAO (micro-arc oxidation) coating in Figure 2 and Figure 3, five peaks were obtained at the same positions in the figures, and the peak areas were obtained using the open software ImageJ, and the peak areas were integrated according to Figure 4 and Figure 5, and the above (S 43.3 +S 57.5 ) / (S 39.5 +S 45.9 +S 66.9 The ratio was calculated by α:γ = α, and the value of α:γ was between 0.13 and 1.57. Therefore, the relative ratio of α:γ content at different thicknesses of MAO (Micro Arc Oxidation) coating was calculated, as shown in Table 3 below: TIFF2025501852000004.tif45170

[0042] Comparing Tables 2 and 3, from the corresponding ratios, it can be seen that the α:γ value of the TECO machined layer in Table 2 is much higher than that of the MAO coating in Table 3, especially the machined layer on 2024 aluminum alloy is about one order of magnitude higher, and the α-Al2O3 content of the hardest part of the TECO coating on 2024 aluminum alloy can reach as much as 90%.

[0043] Abstract: The content of α-Al2O3 in the TECO coating shows a pattern of first increasing and then decreasing, so the TECO coating can be polished until the coating with the highest percentage of α-Al2O3 is measured, and the polished coating is used as the working layer, which is the wear-resistant interface layer.

[0044] Although the present application has disclosed several aspects and embodiments, other aspects and embodiments are obvious to those skilled in the art, and some variations and improvements can be made without departing from the concept of the present application, all of which are included in the scope of protection of the present application. The various aspects and embodiments disclosed in the present application are for illustrative purposes only and do not limit the present application, and the actual scope of protection of the present application shall be determined by the claims.

Claims

1. A method for preparing an aluminum-based wear-resistant ceramic coating comprising the steps of: The aluminum substrate is immersed in an electrolyte and an electrochemical oxidation process is used to grow an in-situ ceramic coating on the surface, where the electrochemical oxidation process is performed using a bidirectional pulsed power supply in a dual plating cell to form an α-Al layer from near the aluminum substrate layer to near the surface. ２ O ３ Step 1, the content shows a tendency to initially increase and then decrease; While polishing the ceramic coating, α-Al on coatings of different thicknesses ２ O ３ The ratio of α-Al was measured and recorded. ２ O ３ Step 2: polishing is completed until the coating having the highest ratio of is measured, and the polished coating is used as a working layer, which is a wear-resistant interface layer, and the thickness of the wear-resistant interface layer accounts for 30% to 60% of the total thickness of the coating before polishing; 13. A method for preparing an aluminum-based wear-resistant ceramic coating comprising:

2. In step 1, the aluminum substrate contains pure aluminum or an aluminum alloy. A method for preparing the aluminum-based wear-resistant ceramic coating of claim 1.

3. The method further includes the steps of: placing the same molded workpiece in a double plating cell in step 1; connecting the two molded workpieces with a wire; and connecting the double plating cell to a bidirectional pulse power source to form a coating, so that the coated workpieces are alternately anode and cathode, and the coated workpieces are intermittently and discontinuously coated. A method for preparing the aluminum-based wear-resistant ceramic coating of claim 1.

4. In step 1, the pulse frequency of the bidirectional pulse power supply is 400-900 Hz, the voltage is 400-800 V, the operation mode is constant current mode, the voltage fluctuates, and the current density is 10-20 A / dm ２ characterized in that A method for preparing the aluminum-based wear-resistant ceramic coating of claim 1.

5. The bidirectional pulse power supply is a bidirectional high frequency pulse power supply, and the pulse frequency of the bidirectional high frequency pulse power supply is 500 Hz. A method for preparing the aluminum-based wear-resistant ceramic coating of claim 1.

6. In step 1, the electrolyte is a silicate-based electrolyte, and the temperature range of the electrolyte is 20 to 30° C. A method for preparing the aluminum-based wear-resistant ceramic coating of claim 1.

7. 1. A method for manufacturing a friction pair, comprising the steps of: A process for preparing an aluminum-based wear-resistant ceramic coating according to any one of claims 1 to 6, comprising a processed layer prepared by the process for preparing an aluminum-based wear-resistant ceramic coating according to any one of claims 1 to 6. method.

8. The friction pair includes an internal combustion engine cylinder, and the inner wall of the cylinder is characterized in that it uses a processed layer prepared by the above-mentioned method for preparing an aluminum-based wear-resistant ceramic coating. The method of claim 7.

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