Preparation method of aluminum alloy micro-arc oxidation coating

Abstract

The invention discloses a preparation method of an aluminum alloy micro-arc oxidation coating, which specifically comprises the following steps: step 1, pouring deionized water into an oxidation tank, adding a quantitative reagent at room temperature, and uniformly stirring to form an electrolyte; 2, an aluminum alloy plate is selected, and ultrasonic cleaning and distilled water cleaning are sequentially conducted on the aluminum alloy plate; 3, the aluminum alloy plate cleaned through distilled water is put into an oxidation tank to be subjected to a micro-arc oxidation reaction, and a micro-arc oxidation film layer is formed on the surface of the aluminum alloy plate; 4, the aluminum alloy plate is taken out and immersed in distilled water for sealing treatment; and 5, the aluminum alloy plate is taken out of the distilled water and air-dried. The problem that in the prior art, due to the fact that a large number of holes and micro cracks exist in a loose layer, the corrosion resistance and the wear resistance of a micro-arc oxidation film layer are poor is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of surface engineering of aluminum alloys, and particularly relates to a preparation method of a micro-arc oxidation coating for aluminum alloys. Background Art

[0002] The principle of the micro-arc oxidation process is to place valve metals such as aluminum, magnesium, and titanium as anodes in an electrolyte. After energization, a very thin high-resistance antioxidant film will first form on the metal surface. Subsequently, the thinner part of the film layer is broken down under the electric field to generate plasma discharge. The discharge area generates molten alumina under the combined action of electrochemistry, plasma chemistry, and thermochemistry, and rapidly solidifies on the surface of the film layer under the cooling of the electrolyte, thereby continuously and uniformly thickening the micro-arc oxidation film layer. At the same time, due to the extremely high instantaneous temperature in the plasma discharge area, up to 7000K, the surface Al 2 O 3 film layer undergoes a crystalline structure transformation. Also, because the reaction is in-situ generation, the bonding strength between the ceramic layer and the substrate is relatively high. This ceramic layer has high hardness, high wear resistance, corrosion resistance, outstanding oxidation resistance, and good insulation, and is particularly suitable for light metal alloy parts that move at high speeds and require high wear resistance, corrosion resistance, and high-temperature shock resistance. It is widely used in the fields of aviation, aerospace, weapons, automobiles, ships, etc.

[0003] However, the traditional micro-arc oxidation film layer consists of a dense layer and a porous layer. Among them, the porous layer accounts for about 20% - 25% of the total thickness of the film layer. The porous layer is located on the surface of the film layer and there are a large number of pores and microcracks inside. The porous layer on the surface of the film layer will seriously reduce the density of the micro-arc oxidation film layer, greatly reducing the corrosion resistance and wear resistance of the micro-arc oxidation, and at the same time also causing a significant decrease in the surface roughness of the film layer. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method of a micro-arc oxidation coating for aluminum alloys, which solves the problem that the corrosion resistance and wear resistance of the micro-arc oxidation film layer are poor due to the existence of a large number of pores and microcracks inside the porous layer in the prior art.

[0005] The technical solution adopted by the present invention is a preparation method of a micro-arc oxidation coating for aluminum alloys, which specifically includes the following steps: Step 1, pour deionized water into the oxidation tank, add a certain amount of reagent at room temperature, and stir evenly to form an electrolyte; Step 2, select an aluminum alloy plate, and sequentially perform ultrasonic cleaning and distilled water cleaning on the aluminum alloy plate; Step 3, put the aluminum alloy plate cleaned with distilled water into the oxidation tank for micro-arc oxidation reaction to form a micro-arc oxidation film layer on the surface of the aluminum alloy; Step 4, take out the aluminum alloy plate and immerse it in distilled water for sealing treatment; Step 5: Take out the aluminum alloy plate from the distilled water and air-dry it.

[0006] The features of the present invention also lie in that In Step 1, the reagent includes a main film-forming agent, a film-forming auxiliary agent and a pH regulator. The main film-forming agent is sodium hexametaphosphate with a concentration of 4 g / L to 25 g / L; the film-forming auxiliary agent is sodium silicate with a concentration of 1 g / L to 3 g / L and sodium tetraborate with a concentration of 0.5 g / L to 3 g / L, and the pH regulator is sodium hydroxide with a concentration of 0.6 g / L to 3 g / L.

[0007] The addition order of the main film-forming agent, the film-forming auxiliary agent and the pH regulator is to add them in descending order according to the amount added.

[0008] The addition ratio of the main film-forming agent, the film-forming auxiliary agent and the pH regulator is: 6 - 9: 1.5 - 2: 0.5 - 1.2: 0.5 - 1.2.

[0009] In Step 2, the ultrasonic cleaning is carried out in a sodium hydroxide solution with a concentration of 5 g / L to 20 g / L. The temperature of the ultrasonic cleaning is 20°C to 40°C, and the time of the ultrasonic cleaning is 10 min to 30 min.

[0010] In Step 2, the temperature of the distilled water cleaning is 20°C to 40°C.

[0011] In Step 3, the current density of the micro-arc oxidation reaction is 0.2 A / dm 2 ~20 A / dm 2 ; the frequency is 100 Hz to 800 Hz; the duty cycle is 20% to 50%, and the reaction time is 20 min to 80 min; during the micro-arc oxidation reaction, the temperature of the electrolyte is 1°C to 5°C.

[0012] In Step 4, when carrying out the sealing treatment by immersion in distilled water, the temperature of the distilled water is 90°C to 100°C, and the treatment time is 20 min.

[0013] The beneficial effects of the present invention are: (1) The preparation method of the aluminum alloy micro-arc oxidation coating of the present invention adopts a low-temperature micro-arc oxidation treatment method to increase the undercooling degree of the micro-arc oxidation reaction process, promote the large generation of γ-Al 2 O 3 , effectively improve the density of the loose layer in the film layer, and improve the corrosion resistance of the aluminum alloy micro-arc oxidation film layer; the film layer obtained by the low-temperature micro-arc oxidation treatment has the corrosion resistance increased by more than 2 times, the wear resistance is greatly enhanced, and the surface roughness of the film layer is also greatly improved.

[0014] (2) The preparation method of the aluminum alloy micro-arc oxidation coating of the present invention is affected by factors such as the solution composition and process parameters. Under the condition of rapid cooling, it can reduce γ-Al2 O 3 The free energy of the phase, α-Al 2 O 3 phase and γ-Al 2 O 3 There is a thermodynamic equilibrium point in the free energy. Below the equilibrium point, it is beneficial to generate γ-Al 2 O 3 , the greater the cooling rate, the longer the time maintained below the equilibrium point, and the more beneficial it is to improve γ-Al 2 O 3 The nucleation rate of the phase, γ-Al 2 O 3 The high nucleation rate of the phase can promote the dense growth of the film layer and effectively improve the density of the loose layer in the film layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a schematic flow chart of the method for preparing an aluminum alloy micro-arc oxidation coating of the present invention; Figure 2 is a phase composition analysis diagram of the micro-arc oxidation film layer prepared by the method for preparing an aluminum alloy micro-arc oxidation coating of the present invention; Figure 3 is a microscopic morphology diagram of the interface of the micro-arc oxidation film layer prepared in the embodiment of the present invention; Figure 4 is a microscopic morphology diagram of the interface of the micro-arc oxidation film layer prepared in the comparative example of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0016] Hereinafter, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0017] Example 1 The method for preparing an aluminum alloy micro-arc oxidation coating of the present invention, as Figure 1 shown, specifically includes the following steps: Step 1, pour deionized water into the oxidation tank, add a certain amount of reagent at room temperature, and stir evenly to form an electrolyte; Step 2, select an aluminum alloy plate, and perform ultrasonic cleaning and distilled water cleaning on the aluminum alloy plate in sequence; Step 3, put the aluminum alloy plate cleaned with distilled water into the oxidation tank for micro-arc oxidation reaction to form a micro-arc oxidation film layer on the surface of the aluminum alloy; Step 4, take out the aluminum alloy plate and immerse it in distilled water for sealing treatment; Step 5: Take out the aluminum alloy plate from the distilled water and air-dry it.

[0018] Example 2 The preparation method of the micro-arc oxidation coating for aluminum alloy of the present invention is as shown in Figure 1 and specifically includes the following steps: Step 1: Pour deionized water into the oxidation tank, add a certain amount of reagents at room temperature, and stir evenly to form an electrolyte solution; The reagents in Step 1 include a main film-forming agent, a film-forming auxiliary agent, and a pH regulator.

[0019] The main film-forming agent is sodium hexametaphosphate with a concentration of 4 g / L to 25 g / L; The film-forming auxiliary agent is sodium silicate with a concentration of 1 g / L to 3 g / L and sodium tetraborate with a concentration of 0.5 g / L to 3 g / L; The pH regulator is sodium hydroxide with a concentration of 0.6 g / L to 3 g / L.

[0020] Step 2: Select an aluminum alloy plate and sequentially perform ultrasonic cleaning and distilled water cleaning on the aluminum alloy plate; The ultrasonic cleaning is carried out in a sodium hydroxide solution with a concentration of 5 g / L to 20 g / L, the temperature of the ultrasonic cleaning is 20°C to 40°C, and the time of the ultrasonic cleaning is 10 min to 30 min.

[0021] The temperature of the distilled water cleaning is 20°C to 40°C.

[0022] Step 3: Put the aluminum alloy plate that has been cleaned with distilled water into the oxidation tank for micro-arc oxidation reaction to form a micro-arc oxidation film layer on the surface of the aluminum alloy; The current density of the micro-arc oxidation reaction is 0.2 A / dm 2 ~20 A / dm 2 ; the frequency is 100 Hz to 800 Hz; the duty cycle is 20% to 50%; the reaction time is 20 min to 80 min; during the micro-arc oxidation reaction, the temperature of the electrolyte solution is 1°C to 5°C.

[0023] Step 4: Take out the aluminum alloy plate and immerse it in distilled water for sealing treatment; Step 5: Take out the aluminum alloy plate from the distilled water and air-dry it.

[0024] Example 3 Based on Example 2, in this example, there are requirements for the addition order of the main film-forming agent, the film-forming auxiliary agent, and the pH regulator in Step 1 of the preparation method of the micro-arc oxidation coating for aluminum alloy of the present invention. Specifically, according to the amounts of the main film-forming agent, the film-forming auxiliary agent, and the pH regulator added, they are added in descending order.

[0025] Meanwhile, the addition ratio among the main film-forming agent, film-forming auxiliary agent and pH regulator is: 6 - 9: 1.5 - 2: 0.5 - 1.2: 0.5 - 1.2.

[0026] Furthermore, when performing the sealing treatment by immersion in distilled water in step 4, the temperature of the distilled water is 90°C - 100°C, and the treatment time is 20 min.

[0027] Perform component analysis on the micro-arc oxidation coating prepared in this example, as Figure 2 shown. It can be seen that the content of γ-Al 2 O 3 phase in the micro-arc oxidation layer prepared in this example is much higher than that of the α-Al 2 O 3 phase. Furthermore, it shows that when the preparation method of the present invention is used to prepare the micro-arc oxidation layer, the nucleation rate of its γ-Al 2 O 3 phase is significantly increased, thereby promoting the growth of the film layer to be denser and effectively improving the density of the loose layer in the film layer.

[0028] Example 4 The preparation method of the aluminum alloy micro-arc oxidation coating in this example specifically includes the following steps: Step 1, Pour deionized water into the oxidation tank, add a certain amount of reagents at room temperature, and stir and mix evenly. The mass / volume concentration of the reagents is as follows: Main film-forming agent: Sodium hexametaphosphate 25 g / L; Film-forming auxiliary agent: Sodium silicate 1 g / L, Sodium tetraborate 0.5 / L; PH regulator: Sodium hydroxide 0.6 g / L.

[0029] Step 2, Ultrasonically clean the aluminum alloy plate in a sodium hydroxide solution with a concentration of 20 g / L, the solution temperature is 20°C, and the cleaning time is 10 min.

[0030] Clean the aluminum alloy plate with distilled water, and the water temperature is 20°C.

[0031] Step 3, Connect the aluminum alloy plate to the electrode and place it in the electrolyte. The process parameters of micro-arc oxidation are: Current density: 20 A / dm². An appropriate current density can provide sufficient energy to initiate micro-arc discharge, prompting the metal atoms on the surface of the aluminum alloy to be oxidized to form an oxide film. If the current density is too low, the oxidation reaction is slow and the growth thickness of the film layer is insufficient; if the current density is too high, it may cause defects such as overheating and cracking of the film layer.

[0032] Frequency: 800 Hz. The selection of the frequency affects the stability and uniformity of micro-arc discharge. At this frequency, the micro-arc discharge can be evenly distributed on the surface of the aluminum alloy plate, enabling the uniform growth of the oxide film and avoiding the situation of local over-thickness or under-thickness.

[0033] Duty cycle: 20%. The duty cycle determines the time interval of micro-arc discharge. An appropriate duty cycle can control the growth rate and quality of the oxide film, preventing the film layer from being damaged due to excessive discharge.

[0034] Electrolyte temperature: 1 - 2 °C. A lower electrolyte temperature helps to reduce the thermal effect during micro-arc oxidation, avoid structural changes in the film layer due to high temperature, and ensure the stability and performance of the film layer.

[0035] Oxidation time: 30 min. Within this time, a micro-arc oxidation film with a certain thickness and performance can be formed on the surface of the aluminum alloy. If the time is too short, the film layer thickness is insufficient, and the corrosion resistance and other properties cannot be effectively improved; if the time is too long, not only energy and time are wasted, but also adverse phenomena such as film layer looseness may occur.

[0036] Step 4, take out the treated aluminum alloy plate from the oxidation tank and immerse it in distilled water for sealing treatment. The water temperature is 90 °C and the treatment time is 20 min.

[0037] The principle of the sealing treatment is to use high-temperature distilled water to cause a hydration reaction in the micropores of the micro-arc oxidation film layer, generating hydroxides, thereby filling the micropores of the film layer and reducing the porosity of the film layer. This can effectively improve the corrosion resistance and insulation of the film layer, preventing external corrosive media from entering the interior of the film layer through the micropores and eroding the aluminum alloy substrate.

[0038] Step 5, take out the aluminum alloy plate from the distilled water and let it air dry naturally or dry it with a hair dryer. Remove the residual moisture on the surface to enable the aluminum alloy micro-arc oxidation coating to maintain stable performance.

[0039] After testing, the corrosion resistance of the aluminum alloy micro-arc oxidation film layer has been improved from 1058 hours to 2589 hours.

[0040] Example 5 The preparation method of the aluminum alloy micro-arc oxidation coating in this example specifically includes the following steps: Step 1, pour deionized water into the oxidation tank, add a certain amount of reagents at room temperature, and stir and mix evenly. The mass / volume concentration of the reagents is as follows: Main film-forming agent: Sodium hexametaphosphate 7 g / L; Film-forming auxiliary agent: Sodium silicate 2.5 g / L, Sodium tetraborate 2 / L; PH regulator: Sodium hydroxide 1 g / L.

[0041] Step 2, ultrasonically clean the aluminum alloy plate in a sodium hydroxide solution with a concentration of 16 g / L, the solution temperature is 25 °C, and the cleaning time is 20 min.

[0042] Clean the aluminum alloy plate with distilled water, and the water temperature is 25 °C.

[0043] Step 3, connect the aluminum alloy plate to the electrode and place it in the electrolyte. The process parameters of micro-arc oxidation are as follows: Current density: 10 A / dm2; frequency: 500 Hz; duty cycle: 50%; electrolyte temperature: 2 - 3 °C; oxidation time: 30 min.

[0044] Step 4, take out the treated aluminum alloy plate from the oxidation tank and immerse it in distilled water for sealing treatment. The water temperature is 95 °C and the treatment time is 20 min.

[0045] Step 5, take out the aluminum alloy plate from the distilled water and let it air dry naturally or dry it with a hair dryer.

[0046] After testing, the corrosion resistance of the micro-arc oxidation film layer on the aluminum alloy is increased from 1147 hours to 2649 hours.

[0047] Example 6 The preparation method of the micro-arc oxidation coating on the aluminum alloy in this example specifically includes the following steps: Step 1, pour deionized water into the oxidation tank, add a certain amount of reagents at room temperature, and stir and mix evenly. The mass / volume concentration of the reagents is as follows: Main film-forming agent: sodium hexametaphosphate 13 g / L; Film-forming auxiliary agent: sodium silicate 3 g / L, sodium tetraborate 2 / L; PH regulator: sodium hydroxide 1 g / L.

[0048] Step 2, ultrasonically clean the aluminum alloy plate in a sodium hydroxide solution with a concentration of 5 g / L, the solution temperature is 40 °C, and the cleaning time is 30 min.

[0049] Clean the aluminum alloy plate with distilled water, and the water temperature is 40 °C.

[0050] Step 3, connect the aluminum alloy plate to the electrode and place it in the electrolyte. The process parameters of micro-arc oxidation are as follows: Current density: 9 A / dm2; frequency: 500 Hz; duty cycle: 50%; electrolyte temperature: 3 - 4 °C; oxidation time: 40 min.

[0051] Step 4, take out the treated aluminum alloy plate from the oxidation tank and immerse it in distilled water for sealing treatment. The water temperature is 95 °C and the treatment time is 20 min.

[0052] Step 5: Take out the aluminum alloy plate from distilled water and let it air dry naturally or dry it with a hair dryer.

[0053] After testing, the corrosion resistance of the micro-arc oxidation film layer on the aluminum alloy has been increased from 1147 hours to 2751 hours.

[0054] Comparative Example In this comparative example, the micro-arc oxidation coating was prepared with reference to the existing traditional micro-arc oxidation film layer. As Figure 3 shown, the microscopic morphology of the prepared micro-arc oxidation layer was observed.

[0055] At the same time, the microscopic morphology of the micro-arc oxidation layer prepared in Example 6 was observed. As Figure 4 shown, for Figure 3 and Figure 4 a comparison was made. It can be seen from the figure that there are a large number of holes and cracks in the loose layer of the traditional micro-arc oxidation film layer, while the holes and cracks in the micro-arc oxidation film layer treated by the low-temperature micro-arc oxidation method of the preparation method of the present invention are significantly reduced, greatly improving the density of the loose layer on the micro-arc oxidation surface.

[0056] In this specification, each embodiment is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. The same or similar parts among the embodiments can be referred to each other.

[0057] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing an aluminum alloy micro-arc oxidation coating, characterized in that: The specific steps include: Step 1, pour deionized water into an oxidation tank, add a certain amount of reagent at room temperature, and stir evenly to form an electrolyte; Step 2, selecting an aluminum alloy plate, and performing ultrasonic cleaning and distilled water cleaning on the aluminum alloy plate in sequence; Step 3, placing the aluminum alloy plate washed with distilled water into an oxidation tank for micro-arc oxidation reaction to form a micro-arc oxidation film layer on the surface of the aluminum alloy; Step 4, taking out the aluminum alloy plate and immersing it in distilled water for sealing treatment; Step 5, take the aluminum alloy plate out of the distilled water and air dry it.

2. The method for preparing an aluminum alloy micro-arc oxidation coating according to claim 1, characterized in that: The reagents in step 1 include a main film-forming agent, a film-forming auxiliary agent and a pH adjuster, wherein the main film-forming agent is sodium hexametaphosphate with a concentration of 4 g / L to 25 g / L; The film-forming auxiliary agent is sodium silicate with a concentration of 1 g / L to 3 g / L and sodium tetraborate with a concentration of 0.5 g / L to 3 g / L, and the pH regulator is sodium hydroxide with a concentration of 0.6 g / L to 3 g / L.

3. The method for preparing an aluminum alloy micro-arc oxidation coating according to claim 2, characterized in that: The main film-forming agent, the film-forming auxiliary agent and the pH adjuster are added in the order from large to small according to the amount added.

4. The method for preparing an aluminum alloy micro-arc oxidation coating according to claim 1, characterized in that: The addition ratio of the main film-forming agent, the film-forming auxiliary agent and the pH regulator is: 6~9: 1.5~2: 0.5~1.2: 0.5~1.

2.

5. The method for preparing an aluminum alloy micro-arc oxidation coating according to claim 1, characterized in that: In the step 2, the ultrasonic cleaning is carried out in a sodium hydroxide solution with a concentration of 5 g / L to 20 g / L, the temperature of the ultrasonic cleaning is 20° C. to 40° C., and the time of the ultrasonic cleaning is 10 min to 30 min.

6. The method for preparing an aluminum alloy micro-arc oxidation coating according to claim 1, characterized in that: The temperature of the distilled water washing in step 2 is 20°C to 40°C.

7. The method for preparing an aluminum alloy micro-arc oxidation coating according to claim 1, characterized in that: The current density of the micro-arc oxidation reaction in step 3 is 0.2A / dm 2 ~20A / dm 2 ; The frequency is 100Hz~800Hz; the duty cycle is 20%~50%, and the reaction time is 20min~80min; during the micro-arc oxidation reaction, the electrolyte temperature is 1℃~5℃.

8. The method for preparing an aluminum alloy micro-arc oxidation coating according to claim 1, characterized in that: When the sealing treatment is performed by immersing in distilled water in step 4, the temperature of the distilled water is 90° C. to 100° C., and the treatment time is 20 minutes.

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