Method for recovering size of cover type aluminum alloy workpiece through micro-arc oxidation technology

Abstract

The invention discloses a method for recovering the size of a cover type aluminum alloy workpiece through a micro-arc oxidation technology, and belongs to the technical field of aluminum alloy friction piece surface pairs. The method comprises the following steps: (1) surface cleaning: cleaning a common anodic oxide film on the surface of the cover type aluminum alloy friction piece; (2) preparing a working solution: preparing the working solution from at least one of potassium hydroxide, sodium hydroxide, barium hydroxide, sodium phosphate, sodium silicate, sodium tungstate, sodium tetraborate, sodium hexametaphosphate, glycerol and sodium metaaluminate; and (3) micro-arc oxidation treatment is conducted, specifically, the working solution is placed in an electrolytic bath, the treated cover type aluminum alloy friction piece serves as an anode to be immersed in the working solution, a stainless steel plate serves as a cathode counter electrode, then a bipolar pulse power source is applied to the two sides of the cathode and the anode, and a micro-arc oxidation ceramic film layer can be obtained on the surface of the cover type aluminum alloy friction piece. According to the method, the removal of the base material is avoided, the loss of the base material is avoided, and the process steps can be simplified.

Description

Technical Field

[0001] The present invention relates to the technical field of surface auxiliary technology of aluminum alloy friction parts, and more particularly to a method for restoring the dimensions of a cover-type aluminum alloy workpiece by utilizing a micro-arc oxidation technology. Background Art

[0002] Aluminum alloys have garnered widespread attention for their excellent overall performance. Components of different types and locations have varying requirements for the use of aluminum alloy materials. A shaft-and-hole friction pair typically consists of two components: a rod and a cover. Typically, the friction surface of the rod-type aluminum alloy component is hard anodized for a high surface hardness, while the friction surface of the cover-type aluminum alloy component is conventionally anodized for a lower surface hardness, ensuring their compatibility as a friction pair. Both components wear out over time, with the cover-type aluminum alloy friction component typically exhibiting partial or complete wear, which can lead to significant size reduction during repair. Repairing localized surface damage to an anodized aluminum alloy component requires mechanical removal of the original conventional anodized film, followed by re-anodization. Removal of the original conventional anodized film inevitably results in the removal of the component's base material. This ultimately results in a reduction in the repaired component's size after re-anodization, making it difficult to restore the original dimensions.

[0003] Conventional anodizing is an electrochemical process in which an oxide film forms on the surface of aluminum and its alloys in an appropriate electrolyte and under specific process conditions, using an applied electric field. Currently, sulfuric acid anodizing and chromate anodizing are the most commonly used methods for anodizing aluminum alloys. The film produced by anodizing is porous and has a double-layer structure: a thin, dense barrier layer adjacent to the aluminum substrate, and a thick, loose, porous layer above the barrier layer. The micropores in the porous layer are nearly circular, closely arranged, and uniformly distributed in size. These micropores extend directly to the junction between the film and the aluminum alloy, allowing the working fluid to penetrate the micropores and reach the barrier layer. Typically, the film thickness is 5-20 μm, with a surface microhardness of 250-350 Hv, and can withstand salt spray tests for over 96 hours.

[0004] Micro-arc oxidation technology can generate a ceramic film layer on the surface of aluminum alloy with higher hardness and corrosion resistance than ordinary anodizing. Moreover, due to its high inter-electrode voltage and strong discharge breakdown ability, micro-arc oxidation discharge can be directly performed without removing the original anodized film layer. This not only simplifies the repair process and retains the size of the workpiece aluminum alloy substrate, but also enables the repaired film layer to have better friction resistance and corrosion resistance, thereby enhancing the mechanical properties of the repaired workpiece.

[0005] The micro-arc oxidation (MAO) discharge process involves sequential electrochemical and plasma discharges. The former is the foundation of the latter, and the latter is organically integrated with the former through microporous gas breakdown discharge, ultimately completing the MAO process and forming an in-situ MAO ceramic film. At the start of discharge, the interelectrode voltage increases from 0, first satisfying the electrochemical passivation reaction conditions, resulting in the formation of a thin barrier layer and tiny bubbles on the anode surface. As the barrier layer and bubbles increase the interelectrode resistance, they hinder the increase in current, causing the interelectrode voltage to continuously rise. Gradually, the electrochemical anodic oxidation conditions are met, and the anodic oxidation reaction rapidly thickens the barrier layer, forming micropores within it. The substrate and working fluid maintain contact at the bottom of the micropores, enabling continuous anodic oxidation. Simultaneously, a large number of bubbles are generated and escape, forming gas capacitance. This further causes the interelectrode voltage to rise rapidly, reaching over 250V in a very short period of time. After breaking through the Faraday discharge region, a plasma reaction occurs on the anode surface, generating a discharge spark. At the moment of plasma discharge, the temperature is extremely high, and heat is locally concentrated within the micropores, causing some of the less hard γ-Al2O3 phase to transform into the harder α-Al2O3 phase. Externally, the working fluid's rapid cooling effect causes the molten oxide to form a loose layer structure dominated by γ-Al2O3, while internally, a dense layer structure dominated by α-Al2O3 forms. At the boundary between the micromolten pool and the substrate, the high-temperature active particles chemically react with the substrate, forming a thin barrier layer that separates the substrate from the micromolten pool. This completes the micro-arc oxidation discharge and film formation process. When the electric field is re-established, the micro-arc oxidation process repeats. Micro-arc oxidation films can reach thicknesses of 20-100μm, surface microhardnesses of 600-1600Hv, and salt spray test resistance of 240-300h.

[0006] Therefore, how to develop a method for restoring the size of cover-type aluminum alloy workpieces using micro-arc oxidation technology is an urgent problem that technicians in this field need to solve. Summary of the Invention

[0007] In view of this, the purpose of the present invention is to provide a method for restoring the size of a cover-type aluminum alloy workpiece using micro-arc oxidation technology to address the shortcomings of the prior art.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A method for restoring the dimensions of a cover-type aluminum alloy workpiece using micro-arc oxidation technology specifically comprises the following steps:

[0010] (1) Surface cleaning

[0011] Cleaning the common anodic oxide film on the surface of the cover-type aluminum alloy friction part to obtain a treated cover-type aluminum alloy friction part;

[0012] (2) Preparation of working fluid

[0013] The working fluid is prepared by using at least one of potassium hydroxide, sodium hydroxide, barium hydroxide, sodium phosphate, sodium silicate, sodium tungstate, sodium tetraborate, sodium hexametaphosphate, glycerol and sodium metaaluminate;

[0014] (3) Micro-arc oxidation treatment

[0015] The working liquid is placed in the electrolytic cell, the treated aluminum alloy friction parts of the cover are immersed in the working liquid as the anode, and the stainless steel plate is used as the cathode counter electrode. Then, a bipolar pulse power supply is applied on both sides of the cathode and the anode. The bidirectional working mode is adopted, with a forward voltage of 250-600V, a reverse voltage of 50-120V, and a current density of 5-25A / dm 2 The positive and negative pulse frequency is 500-2500Hz, the duty cycle is 10%-40%, the working fluid temperature is 20-60℃, and the treatment time is 10-60min to obtain a micro-arc oxidation ceramic film layer on the surface of the cover-type aluminum alloy friction parts.

[0016] Furthermore, in the above step (1), the common anodized film includes a sulfate film and a chromate film, and the film thickness is 5-20 μm.

[0017] Furthermore, in the above step (1), the surface cleaning reagent is deionized water.

[0018] Furthermore, in the above step (2), the content of potassium hydroxide in the working solution is 1-10 g / L.

[0019] Furthermore, in the above step (2), the content of sodium hydroxide in the working solution is 1-20 g / L.

[0020] Furthermore, in the above step (2), the content of barium hydroxide in the working solution is 5-15 g / L.

[0021] Furthermore, in the above step (2), the content of sodium phosphate in the working solution is 3-20 g / L.

[0022] Furthermore, in the above step (2), the content of sodium silicate in the working solution is 5-30 g / L.

[0023] Furthermore, in the above step (2), the content of sodium tungstate in the working solution is 5-20 g / L.

[0024] Furthermore, in the above step (2), the content of sodium tetraborate in the working solution is 1-50 g / L.

[0025] Furthermore, in the above step (2), the content of sodium hexametaphosphate in the working solution is 15-100 g / L.

[0026] Furthermore, in the above step (2), the content of glycerol in the working solution is 3-25 mL / L.

[0027] Furthermore, in the above step (2), the content of sodium metaaluminate in the working solution is 5-15 g / L.

[0028] It can be seen from the above technical solution that compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] 1. The process of micro-arc oxidation discharge is that electrochemical discharge and plasma discharge are sequential. The former is the basis of the latter. The latter and the former are organically combined through microporous gas breakdown discharge, and finally the micro-arc oxidation process is completed, and a micro-arc oxidation ceramic film layer is generated in situ. The premise of micro-arc oxidation discharge is the barrier layer generated in the anodic oxidation stage. This premise happens to be possessed by hard anodized workpieces. Therefore, this favorable condition can be utilized. Under the condition that the working fluid meets the discharge conditions, the micro-arc oxidation discharge can use the barrier layer at the bottom of the anodized film layer to continue to discharge, forming a new micro-arc oxidation film layer with better mechanical properties. This provides the possibility of developing a method for recovering the size of cover-type aluminum alloy workpieces using micro-arc oxidation technology by leveraging strengths and weaknesses.

[0030] 2. Although the micro-arc oxidation ceramic film layer generated by the method of the present invention is directly generated by reaction on the anodized sample, the anodized sample substrate and the working fluid remain in contact at the bottom of the micropores. The conditions for the micro-arc oxidation discharge reaction are all met. The discharge breaks through the anodized film layer, and the film layer grows directly on the surface of the aluminum alloy substrate. Compared with the original ordinary anodized film layer, it has better bonding strength with the substrate and has the advantages of high surface hardness, high wear resistance, low friction coefficient, and high corrosion resistance.

[0031] 3. The thickness of the micro-arc oxidation ceramic film layer generated by the method of the present invention is about 30-80 μm, and the surface quality is good, without ablation spots and powdery loose layers.

[0032] 4. The method of the present invention generates a micro-arc oxidation film layer on the surface of the friction part of the cover-type aluminum alloy part in situ through direct micro-arc oxidation discharge without removing the original ordinary anodic oxidation film layer of the cover-type aluminum alloy friction part, thereby avoiding the removal of the substrate, without the loss of the substrate, and simplifying the process steps.

[0033] 5. The initial voltage applied to the treated cover-type aluminum alloy friction parts of the present invention is 250V. The time taken to increase from 0V to 250V is only 5-10s, and the total treatment time is 10-60min. There is no time for mechanically removing the anodized film layer. Compared with ordinary anodizing treatment, it can reduce processing time and save costs. DETAILED DESCRIPTION

[0034] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0035] Example 1

[0036] The method for restoring the size of a cover-type aluminum alloy workpiece using micro-arc oxidation technology specifically includes the following steps:

[0037] (1) Surface cleaning

[0038] cleaning the common anodic oxide film on the surface of the cover-type aluminum alloy friction part with deionized water to obtain a treated cover-type aluminum alloy friction part;

[0039] Among them, the material of the cover aluminum alloy friction part is aluminum alloy 2024, and the friction surface size of the sample is a cylindrical inner wall with a bottom inner diameter of 45mm and a width of 4mm;

[0040] The common anodic oxide film is a chromate film with a thickness of 10 μm;

[0041] (2) Preparation of working fluid

[0042] Prepare the working solution using 3 g / L potassium hydroxide, 5 g / L sodium tungstate, 1.5 g / L sodium tetraborate and 3 mL / L glycerol;

[0043] (3) Micro-arc oxidation treatment

[0044] The working fluid is placed in the electrolytic cell, the treated aluminum alloy friction parts of the cover are immersed in the working fluid as the anode, and the stainless steel plate is used as the cathode counter electrode. Then, a bipolar pulse power supply is applied on both sides of the cathode and the anode. The bidirectional working mode is adopted, with a forward voltage of 458V, a reverse voltage of 69V, and a current density of 16A / dm 2 The positive and negative pulse frequency is 1300Hz, the duty cycle is 15%, the working fluid temperature is 30℃, and the treatment time is 45min. Then, a micro-arc oxidation ceramic film layer can be obtained on the surface of the cover-type aluminum alloy friction parts.

[0045] Performance Testing

[0046] The micro-arc oxidation ceramic film layer produced by the method of Example 1 was taken, and its film thickness, surface microhardness HV, surface roughness Ra and friction coefficient were measured respectively, and a salt spray test was performed.

[0047] The film thickness is measured by using a high-precision eddy current thickness gauge to perform multi-point measurements. When measuring, avoid sharp edges, select a representative plane position, and perform repeated measurements.

[0048] The method for determining the surface microhardness HV is: use a microhardness tester to measure, avoid the edge during measurement, and take repeated measurements on an area with uniform distribution of the film layer.

[0049] The surface roughness Ra is measured using a surface roughness meter (stylus Ra measuring instrument). Before measurement, ensure that the surface is clean and free of oil.

[0050] The friction coefficient is determined by using a friction coefficient tester (such as a reciprocating or rotary friction tester) under constant load (50 g, 100 g), speed and environmental conditions, recording the friction coefficient in the stable stage and taking the average value.

[0051] The salt spray test is carried out in accordance with the standard (such as ASTM B117 or GB / T 10125), and the sample is placed in the salt spray test chamber for a specified time, and the corrosion condition and film changes are observed and recorded.

[0052] The results are shown in Table 1.

[0053] Table 1 Performance test results of micro-arc oxidation ceramic film layer in Example 1

[0054]

[0055] It can be seen from Table 1 that the micro-arc oxidation ceramic film prepared in Example 1 performs well in various performance indicators. The film thickness is uniform, ranging from 45-53μm, indicating that the process is stable and good. The surface microhardness reaches 1426HV (100g), showing a high hardness, which helps to improve wear resistance. The surface roughness Ra is 0.089, indicating that the surface of the film is relatively smooth after polishing, which is beneficial to reducing friction resistance. The friction coefficient is 0.3, which is at a relatively low level, further verifying its good wear resistance. The salt spray test time exceeds 260h, and no obvious signs of corrosion are seen, indicating that the film has good corrosion resistance. Based on the above results, the micro-arc oxidation ceramic film of Example 1 has good comprehensive performance.

[0056] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for restoring the dimensions of a cover-type aluminum alloy workpiece using micro-arc oxidation technology, characterized in that: The specific steps include: (1) Surface cleaning Cleaning the common anodic oxide film on the surface of the cover-type aluminum alloy friction part to obtain a treated cover-type aluminum alloy friction part; (2) Preparation of working fluid The working fluid is prepared by using at least one of potassium hydroxide, sodium hydroxide, barium hydroxide, sodium phosphate, sodium silicate, sodium tungstate, sodium tetraborate, sodium hexametaphosphate, glycerol and sodium metaaluminate; (3) Micro-arc oxidation treatment The working liquid is placed in the electrolytic cell, the treated aluminum alloy friction parts of the cover are immersed in the working liquid as the anode, and the stainless steel plate is used as the cathode counter electrode. Then, a bipolar pulse power supply is applied on both sides of the cathode and the anode. The bidirectional working mode is adopted, with a forward voltage of 250-600V, a reverse voltage of 50-120V, and a current density of 5-25A / dm 2 The positive and negative pulse frequency is 500-2500Hz, the duty cycle is 10%-40%, the working fluid temperature is 20-60℃, and the treatment time is 10-60min to obtain a micro-arc oxidation ceramic film layer on the surface of the cover-type aluminum alloy friction parts.

2. The method for restoring the dimensions of a cover-type aluminum alloy workpiece using micro-arc oxidation technology according to claim 1, characterized in that: In step (1), the common anodized film includes a sulfate film and a chromate film, and the film thickness is 5-20 μm.

3. The method for restoring the dimensions of a cover-type aluminum alloy workpiece using micro-arc oxidation technology according to claim 1, characterized in that: In step (1), the surface cleaning reagent is deionized water.

4. The method for restoring the dimensions of a cover-type aluminum alloy workpiece using micro-arc oxidation technology according to claim 1, characterized in that: In step (2), the content of potassium hydroxide in the working solution is 1-10 g / L.

5. The method for restoring the dimensions of a cover-type aluminum alloy workpiece using micro-arc oxidation technology according to claim 1, characterized in that: In step (2), the content of sodium hydroxide in the working solution is 1-20 g / L.

6. The method for restoring the dimensions of a cover-type aluminum alloy workpiece using micro-arc oxidation technology according to claim 1, characterized in that: In step (2), the content of barium hydroxide in the working solution is 5-15 g / L.

7. The method for restoring the dimensions of a cover-type aluminum alloy workpiece using micro-arc oxidation technology according to claim 1, characterized in that: In step (2), the content of sodium phosphate in the working solution is 3-20 g / L.

8. The method for restoring the dimensions of a cover-type aluminum alloy workpiece using micro-arc oxidation technology according to claim 1, characterized in that: In step (2), the content of sodium silicate in the working solution is 5-30 g / L.

9. The method for restoring the dimensions of a cover-type aluminum alloy workpiece using micro-arc oxidation technology according to claim 1, characterized in that: In step (2), the content of sodium tungstate in the working solution is 5-20 g / L.

10. The method for restoring the dimensions of a cover-type aluminum alloy workpiece using micro-arc oxidation technology according to claim 1, characterized in that: In step (2), in the working solution, the content of sodium tetraborate is 1-50 g / L, the content of sodium hexametaphosphate is 15-100 g / L, the content of glycerol is 3-25 mL / L, and the content of sodium metaaluminate is 5-15 g / L.

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