Method for directly carrying out micro-arc oxidation on aluminum alloy common anodic oxide film

Abstract

The invention discloses a method for directly carrying out micro-arc oxidation on an aluminum alloy common anodic oxidation film, which comprises the following steps: S1, surface cleaning: carrying out water washing treatment on an aluminum alloy common anodic oxidation workpiece to obtain a treated anodic oxidation workpiece; s2, preparing a working solution, and placing the working solution in an electrolytic bath; and S3, micro-arc oxidation treatment is conducted, specifically, the anodic oxidation workpiece in the S1 serves as an anode, a stainless steel plate serves as a cathode counter electrode, the anodic oxidation workpiece is immersed in a working solution, then bipolar pulse electricity 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 anodic oxidation workpiece. According to the method, on the basis that an original common anodic oxidation film layer of the workpiece to be repaired is not removed, the micro-arc oxidation film layer is generated on the surface of the workpiece in situ through direct micro-arc oxidation discharge, and removal of a base material is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum alloy material surface processing, and more particularly to a method for directly performing micro-arc oxidation on a common anodic oxide film of an aluminum alloy. Background Art

[0002] Aluminum alloys have received widespread attention due to their excellent comprehensive performance. Components of different types and working conditions have different requirements for the use of aluminum alloy materials. For some friction pairs, in order to avoid the possibility of part failure due to wear and corrosion, the parts need to be anodized. However, ordinary anodized films are thin and have low hardness. After a period of use, friction pairs will generally experience local wear. In order to reduce losses caused by part failure and reduce the replacement of parts, such anodized parts need to be repaired. The traditional method is to completely remove the anodized film layer by mechanical means (including turning, milling, grinding, etc.) before anodizing. This will not only reduce the size of the aluminum alloy substrate, but also make the process cumbersome, and increase the repair cycle and cost. 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.

[0003] Anodizing is an electrochemical process in which an oxide film forms on the surface of aluminum and its alloys using an applied electric field in an appropriate electrolyte and under specific process conditions. Currently, sulfuric acid anodizing and chromate anodizing are the most commonly used methods for anodizing aluminum alloys. The resulting film is porous and has a two-layer structure: a thin, dense barrier layer adjacent to the aluminum substrate, and a thick, loose porous layer above it. 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 is 5-20 μm thick, with a surface microhardness of 250-350 Hv, and can withstand salt spray tests for over 96 hours.

[0004] 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 to 100 μm, surface microhardnesses of 600 to 1600 Hv, and salt spray tests of 240 to 300 hours.

[0005] In summary, when the working fluid meets the discharge conditions, micro-arc oxidation discharge can use the barrier layer at the bottom of the anodized film to continue discharging, forming a new micro-arc oxidation film with better mechanical properties. This provides the possibility of developing a method for micro-arc oxidation directly on ordinary anodized films of aluminum alloys by leveraging each other's strengths. Summary of the Invention

[0006] In view of this, the present invention provides a method for micro-arc oxidation directly on an ordinary anodized film of an aluminum alloy. The purpose of the present invention is to solve the problem that when using the existing anodizing method to repair an anodized workpiece with locally damaged surfaces, the anodized film layer needs to be removed by mechanical means (including turning, milling, planing, grinding, etc.), resulting in a reduction in the size of the substrate and increasing the difficulty of size recovery. A method for directly performing micro-arc oxidation on the surface of an ordinary anodized aluminum alloy is proposed. This method generates a micro-arc oxidation film layer in situ on the surface of the workpiece by direct micro-arc oxidation discharge without removing the original ordinary anodized film layer of the workpiece to be repaired, thereby avoiding the removal of the substrate. Compared with the original ordinary anodized film layer, the micro-arc oxidation film layer generated by this method has better bonding with the substrate, a lower friction coefficient, and improved surface hardness, wear resistance, corrosion resistance and other properties.

[0007] The film layer generated by anodization is a porous film layer with a double-layer structure. The thin and dense barrier layer is close to the aluminum substrate, and the thick and loose porous layer is above the barrier layer. The micropores in the porous layer are nearly circular, closely arranged, and evenly distributed with almost the same size. The micropores have a surface that directly reaches the junction between the film layer and the aluminum alloy, which allows the working fluid to pass through the micropores directly to the barrier layer. The micro-arc oxidation discharge process is a succession of electrochemical discharge and plasma discharge. The former is the basis of the latter. The latter is organically combined with the former through microporous gas breakdown discharge, ultimately completing the micro-arc oxidation process and generating a micro-arc oxidation ceramic film layer in situ. The prerequisite for micro-arc oxidation to discharge is the barrier layer produced in the anodizing stage, which happens to be possessed by ordinary anodized workpieces. Therefore, this favorable condition can be utilized. When the working fluid meets the discharge conditions, the micro-arc oxidation discharge can continue to discharge using the barrier layer at the bottom of the anodized film layer to form a new micro-arc oxidation film layer with better mechanical properties. This provides the possibility of developing a method for micro-arc oxidation directly on ordinary anodized film of aluminum alloy.

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

[0009] A method for directly micro-arc oxidation on a common anodic oxide film of an aluminum alloy comprises the following steps:

[0010] S1. Surface cleaning

[0011] Performing water washing treatment on the common anodized aluminum alloy workpiece to obtain the treated anodized workpiece;

[0012] S2. Prepare working fluid

[0013] A mixed solution of one or more of potassium hydroxide, sodium hydroxide, barium hydroxide, sodium phosphate, sodium silicate, sodium tungstate, sodium tetraborate, sodium hexametaphosphate and sodium metaaluminate is prepared as a working solution and placed in an electrolytic cell;

[0014] S3, micro-arc oxidation treatment

[0015] The anodized workpiece in S1 is used as the anode, and the stainless steel plate is used as the cathode counter electrode. The anodized workpiece is immersed in the working fluid, and then bipolar pulse electricity is applied on both sides of the cathode and the anode. The surface of the anodized workpiece obtains a micro-arc oxidation ceramic film layer with high surface hardness, high wear resistance, low friction coefficient and high corrosion resistance.

[0016] Preferably, the water washing in step S1 is performed using deionized water.

[0017] Preferably, the aluminum alloy ordinary anodized workpiece described in step S1 does not need to undergo mechanical removal treatment (including turning, milling, planing, grinding, etc.) of its original ordinary anodized film, and can directly undergo micro-arc oxidation reaction with the anodized film layer.

[0018] Preferably, the original common anodized film includes a sulfate film and / or a chromate film, and the film thickness is 5-20 μm.

[0019] Preferably, in the working solution of step S2, the content of potassium hydroxide is 1g / L~10g / L, the content of sodium hydroxide is 1g / L~20g / L, the content of barium hydroxide is 5g / L~15g / L, the content of sodium phosphate is 3g / L~20g / L, the content of sodium silicate is 5g / L~30g / L, the content of sodium tungstate is 5g / L~20g / L, the content of sodium tetraborate is 1g / L~50g / L, the content of sodium hexametaphosphate is 5g / L~100g / L, the content of sodium metaaluminate is 5g / L~15g / L, and the content of glycerol is 3-25mL / L.

[0020] Preferably, the bipolar pulse electrical parameters in step S3 are: forward voltage of 250V to 600V, reverse voltage of 50V to 120V, and current density of 5A / dm 2 ~25A / dm 2 The positive and negative pulse frequencies are 500Hz to 2500Hz, the duty cycle is 10% to 40%, the working fluid temperature is 20℃ to 60℃, and the processing time is 10min to 60min.

[0021] It can be seen from the above technical solutions that, compared with the prior art, the present invention has the following technical effects:

[0022] 1. The starting voltage of the micro-arc oxidation ceramic film prepared by the present invention is 250V~600V, and the time taken to increase from 0V to 250V~600V is only 5-10 seconds, and the total processing time is 10-60min. Compared with anodizing treatment, there is no mechanical removal time of the anodized film layer, which reduces processing time and saves costs;

[0023] 2. Although the micro-arc oxidation ceramic film prepared by 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, and 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 anodized film layer, the generated micro-arc oxidation film layer has better bonding strength with the substrate, higher surface hardness, lower friction coefficient, and improved wear resistance, corrosion resistance and other properties;

[0024] 3. The thickness of the micro-arc oxidation ceramic film prepared by the present invention is 30 μm to 80 μm, and the surface quality of the micro-arc oxidation film is good, without ablation spots and powdery loose layers. DETAILED DESCRIPTION

[0025] 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.

[0026] Example 1

[0027] This embodiment provides a method for micro-arc oxidation directly on a common anodic oxide film of an aluminum alloy, comprising the following steps:

[0028] The aluminum alloy common anodized sample was used as the anode and the stainless steel plate of the electrolytic cell was used as the cathode counter electrode. The anodized sample was immersed in the working solution, and then a bipolar pulse power supply was applied on both sides of the cathode and the anode. The forward voltage was 350V, the reverse voltage was 50V, and the current density was 10A / dm 2 , frequency is 1000 Hz, duty cycle is 10%, temperature is below 60 ℃, treatment time is 55 minutes, and a micro-arc oxidation ceramic film with high surface hardness, high wear resistance, low friction coefficient and high corrosion resistance is directly generated on the anodized sample.

[0029] The anodized workpiece substrate is aluminum alloy 6061, the sample size is a cylinder with a bottom diameter of 30 mm and a height of 15 mm, the anodized film layer is a sulfate film, and the film thickness is 5 μm.

[0030] The initial water temperature in this embodiment is 25°C.

[0031] The specific components of the working solution are: potassium hydroxide 3g / L, sodium tetraborate 1.5g / L, glycerol 3mL / L, and sodium tungstate 5g / L.

[0032] In this embodiment, the detection method is as follows (the detection methods of the following embodiments are the same):

[0033] The film thickness is measured by using a high-precision eddy current thickness gauge to perform multi-point measurements. When measuring, avoid edges, select a representative plane position, and perform repeated measurements.

[0034] Microhardness: Use a microhardness tester to measure. When measuring, avoid the edge and take a uniformly distributed area of the film layer for repeated measurement.

[0035] Roughness: Use a surface roughness meter (stylus type Ra measuring instrument) to measure. Before measurement, make sure the surface is clean and free of oil.

[0036] Friction coefficient: Measured using a friction coefficient tester (such as a reciprocating or rotary friction tester) under constant load (50g, 100g), speed and environmental conditions, record the friction coefficient in the stable stage and take the average value.

[0037] Salt spray test: According to the standard (such as ASTM B117 or GB / T 10125), 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.

[0038] The thickness of the micro-arc oxidation ceramic film directly prepared on the anodized sample in this embodiment is 32μm to 41μm, its surface microhardness is 1387HV, its surface roughness Ra is 0.095, its friction coefficient is 0.4, and its salt spray test can reach more than 240 hours.

[0039] Example 2

[0040] This embodiment provides a method for micro-arc oxidation directly on a common anodic oxide film of an aluminum alloy, comprising the following steps:

[0041] The aluminum alloy common anodized sample was used as the anode and the stainless steel plate of the electrolytic cell was used as the cathode counter electrode. The anodized sample was immersed in the working solution, and then a bipolar pulse power supply was applied on both sides of the cathode and the anode. The forward voltage was 458V, the reverse voltage was 69V, and the current density was 16A / dm 2 Under the conditions of a frequency of 1300 Hz, a duty cycle of 15% and a temperature below 60°C, the treatment lasts for 45 minutes, and a micro-arc oxidation ceramic film with high surface hardness, high wear resistance, low friction coefficient and high corrosion resistance is directly generated on the anodized sample.

[0042] The anodized workpiece substrate is aluminum alloy 2024, the sample size is a cylinder with a bottom diameter of 30 mm and a height of 15 mm, the anodized film layer is a chromate film, and the film thickness is 8 μm.

[0043] In this embodiment, the initial water temperature is 30°C.

[0044] The specific components of the working solution are: potassium hydroxide 3g / L, sodium tetraborate 1.5g / L, glycerol 3mL / L, and sodium tungstate 5g / L.

[0045] The thickness of the micro-arc oxidation ceramic film directly prepared on the anodized sample in this embodiment is 45μm to 53μm, its surface microhardness is 1426HV, its surface roughness Ra is 0.089, its friction coefficient is 0.3, and its salt spray test can reach more than 260 hours.

[0046] Example 3

[0047] This embodiment provides a method for micro-arc oxidation directly on a common anodic oxide film of an aluminum alloy, comprising the following steps:

[0048] The aluminum alloy common anodized sample was used as the anode and the stainless steel plate of the electrolytic cell was used as the cathode counter electrode. The anodized sample was immersed in the working solution, and then a bipolar pulse power supply was applied on both sides of the cathode and the anode. The forward voltage was 525V, the reverse voltage was 90V, and the current density was 18A / dm 2 Under the conditions of a frequency of 1500 Hz, a duty cycle of 20% and a temperature below 20°C, the treatment lasts for 60 minutes, and a micro-arc oxidation ceramic film with high surface hardness, high wear resistance, low friction coefficient and high corrosion resistance is directly generated on the anodized sample.

[0049] The anodized workpiece substrate is aluminum alloy 4A01, the sample size is a cylinder with a bottom diameter of 30 mm and a height of 15 mm, the anodized film layer is an oxalate film, and the film thickness is 11 μm.

[0050] In this embodiment, the initial water temperature is 40°C.

[0051] The specific components of the working solution are: potassium hydroxide 3g / L, sodium tetraborate 1.5g / L, glycerol 3mL / L, and sodium tungstate 5g / L.

[0052] The thickness of the micro-arc oxidation ceramic film directly prepared on the anodized sample in this embodiment is 50μm to 58μm, its surface microhardness is 1524HV, its surface roughness Ra is 0.104, its friction coefficient is 0.3, and its salt spray test can reach more than 290 hours.

[0053] Example 4

[0054] This embodiment provides a method for micro-arc oxidation directly on a common anodic oxide film of an aluminum alloy, comprising the following steps:

[0055] The aluminum alloy common anodized sample was used as the anode and the stainless steel plate of the electrolytic cell was used as the cathode counter electrode. The anodized sample was immersed in the working solution, and then a bipolar pulse power supply was applied on both sides of the cathode and the anode. The forward voltage was 600V, the reverse voltage was 150V, and the current density was 25A / dm 2 Under the conditions of a frequency of 2000 Hz, a duty cycle of 40% and a temperature below 60°C, the treatment lasts for 80 minutes, and a micro-arc oxidation ceramic film with high surface hardness, high wear resistance, low friction coefficient and high corrosion resistance is directly generated on the anodized sample.

[0056] The anodized workpiece substrate is aluminum alloy 7075, the sample size is a cylinder with a bottom diameter of 30 mm and a height of 15 mm, the anodized film layer is a mixed acid salt film, and the film thickness is 20 μm.

[0057] In this embodiment, the initial water temperature is 30°C.

[0058] The specific components of the working solution are: potassium hydroxide 3g / L, sodium tetraborate 1.5g / L, glycerol 3mL / L, and sodium tungstate 5g / L.

[0059] The thickness of the micro-arc oxidation ceramic film directly prepared on the anodized sample in this embodiment is 60μm to 80μm, its surface microhardness is 1659HV, its surface roughness Ra is 0.083, its friction coefficient is 0.3, and its salt spray test can reach more than 300 hours.

[0060] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method description.

[0061] 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 micro-arc oxidation directly on an ordinary anodic oxide film of an aluminum alloy, characterized in that: The following steps are involved: S1. Surface cleaning Performing water washing treatment on the common anodized aluminum alloy workpiece to obtain the treated anodized workpiece; S2. Prepare working fluid A mixed solution of one or more of potassium hydroxide, sodium hydroxide, barium hydroxide, sodium phosphate, sodium silicate, sodium tungstate, sodium tetraborate, sodium hexametaphosphate and sodium metaaluminate is prepared as a working solution and placed in an electrolytic cell; S3, micro-arc oxidation treatment The anodized workpiece in S1 is used as the anode, and the stainless steel plate is used as the cathode counter electrode. The anodized workpiece is immersed in the working fluid, and then a bipolar pulse current is applied on both sides of the cathode and the anode. The forward voltage is 250V~600V, the reverse voltage is 50V~120V, and the current density is 5A / dm 2 ~25A / dm 2 The positive and negative pulse frequencies are 500Hz to 2500Hz, the duty cycle is 10% to 40%, the working fluid temperature is 20℃ to 60℃, and the processing time is 10min to 60min, and a micro-arc oxidation ceramic film layer can be obtained on the surface of the anodized workpiece.

2. The method for micro-arc oxidation directly on an ordinary anodic oxide film of an aluminum alloy according to claim 1, characterized in that: The water washing in step S1 is performed using deionized water.

3. The method for micro-arc oxidation directly on an ordinary anodic oxide film of an aluminum alloy according to claim 1, characterized in that: The aluminum alloy common anodized workpiece described in step S1 does not need to have its original common anodized film mechanically removed.

4. The method for micro-arc oxidation directly on an ordinary anodic oxide film of an aluminum alloy according to claim 3, characterized in that: The original common anodized film includes a sulfate film and / or a chromate film, and the film thickness is 5-20 μm.

5. The method for micro-arc oxidation directly on an ordinary anodic oxide film of an aluminum alloy according to claim 1, characterized in that: In the working solution of step S2, the content of potassium hydroxide is 1g / L~10g / L, the content of sodium hydroxide is 1g / L~20g / L, the content of barium hydroxide is 5g / L~15g / L, the content of sodium phosphate is 3g / L~20g / L, the content of sodium silicate is 5g / L~30g / L, the content of sodium tungstate is 5g / L~20g / L, the content of sodium tetraborate is 1g / L~50g / L, the content of sodium hexametaphosphate is 5g / L~100g / L, the content of sodium metaaluminate is 5g / L~15g / L, and the content of glycerol is 3-25mL / L.