Method for local micro-arc oxidation of magnesium alloy workpiece

Abstract

The invention relates to the technical field of magnesium alloy micro-arc oxidation, and discloses a local micro-arc oxidation method for a magnesium alloy workpiece. The method comprises the following steps: carrying out passivation, drying, dust removal and shielding protection treatment on a magnesium alloy workpiece, and reserving an area to be subjected to micro-arc oxidation; carrying out micro-arc oxidation and water washing treatment on the area to be subjected to micro-arc oxidation, and forming a micro-arc oxidation film layer in the area to be subjected to micro-arc oxidation; an electrolyte for micro-arc oxidation treatment is composed of sodium silicate with the concentration of 8-10 g / L, sodium hydroxide with the concentration of 4-6 g / L, potassium fluoride with the concentration of 2-3 g / L, sodium aluminate with the concentration of 2-4 g / L, potassium fluotitanate with the concentration of 0.2-0.4 g / L and silicon dioxide nanoparticles with the concentration of 0.1-0.3 g / L. By adopting a micro-arc oxidation process and controlling the content of each component, especially potassium fluotitanate and silicon dioxide nanoparticles, the compactness, wear resistance and corrosion resistance of a micro-arc oxidation film are improved. In addition, the electrolyte used for micro-arc oxidation is basically free of pollution to the environment.

Description

Technical Field

[0001] The invention relates to the technical field of micro-arc oxidation of magnesium alloys, and in particular to a method for local micro-arc oxidation of a magnesium alloy workpiece. Background Art

[0002] In the field of automobile manufacturing, lightweighting is one of the important ways to save energy and reduce consumption. Magnesium alloys are ideal lightweight materials due to their low density and good mechanical properties. However, magnesium alloys have poor corrosion resistance, especially in high temperature and humid environments, such as the water channel part of the automobile engine housing, which is directly installed on the engine and is more prone to corrosion.

[0003] Therefore, the prior art needs to be further improved and enhanced. Summary of the invention

[0004] In view of the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a method for local micro-arc oxidation of a magnesium alloy workpiece, aiming to solve the problem that the water channel part of the existing magnesium alloy engine casing is easily corroded.

[0005] The above object of the present invention is achieved through the following technical solution: a method for local micro-arc oxidation of a magnesium alloy workpiece, wherein the method comprises the following steps:

[0006] Passivate, dry, remove dust, and shield the magnesium alloy workpiece to leave an area for micro-arc oxidation;

[0007] Performing micro-arc oxidation on the area to be micro-arc oxidized, and washing with water to form a micro-arc oxidation film layer in the area to be micro-arc oxidized;

[0008] The electrolyte for micro-arc oxidation treatment is composed of 8-10 g / L sodium silicate, 4-6 g / L sodium hydroxide, 2-3 g / L potassium fluoride, 2-4 g / L sodium aluminate, 0.2-0.4 g / L potassium fluorotitanate, and 0.1-0.3 g / L silicon dioxide nanoparticles.

[0009] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the objectives and beneficial effects of the present invention can be better achieved and realized.

[0010] As a preferred technical solution, in the method for local micro-arc oxidation of a magnesium alloy workpiece, the pH value of the electrolyte is 10-12 and the temperature is 20-40°C.

[0011] As a preferred technical solution, the method for local micro-arc oxidation of a magnesium alloy workpiece is described, wherein the micro-arc oxidation treatment adopts a constant voltage double-pulse mode, wherein the positive pulse voltage is 300-410V, the negative pulse voltage is 80-100V, the frequency is 500-600Hz, the duty cycle is 15-20%, and the oxidation time is 10-15min.

[0012] As a preferred technical solution, in the method for local micro-arc oxidation of a magnesium alloy workpiece, the passivation treatment is selected from one of anodizing, ultrasonic treatment in an aluminum salt solution, and surface sandblasting.

[0013] As a preferred technical solution, in the method for local micro-arc oxidation of a magnesium alloy workpiece, the conductivity of the electrolyte is 4 to 6 S / m.

[0014] As a preferred technical solution, in the method for local micro-arc oxidation of a magnesium alloy workpiece, the passivation treatment is an anodic oxidation treatment, and the thickness of the oxide film is 20 to 35 μm.

[0015] As a preferred technical solution, the method for local micro-arc oxidation of magnesium alloy workpieces, wherein the passivation treatment is to use a 3 ) 3 The magnesium alloy workpiece is ultrasonically treated with a solution.

[0016] As a preferred technical solution, in the method for local micro-arc oxidation of a magnesium alloy workpiece, the water washing is performed using deionized water at a temperature of 15 to 25°C.

[0017] As a preferred technical solution, the method for local micro-arc oxidation of a magnesium alloy workpiece is described, wherein the magnesium alloy workpiece is an engine casing, and the micro-arc oxidation area is a water channel installed on the motor.

[0018] As a preferred technical solution, in the method for local micro-arc oxidation of a magnesium alloy workpiece, after the surface sandblasting treatment, the surface roughness of the magnesium alloy workpiece is 2 to 3.5 μm.

[0019] Beneficial effects: Compared with the prior art, the present invention adopts the micro-arc oxidation process and controls the content of each component, especially potassium fluorotitanate and silicon dioxide nanoparticles, to improve the compactness, wear resistance and corrosion resistance of the micro-arc oxidation film. In addition, the electrolyte used in micro-arc oxidation is basically pollution-free to the environment, and no harmful wastewater and waste gas are generated during the entire treatment process, which is green, environmentally friendly and sustainable. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the partial structure of the magnesium alloy engine casing, where the circled area is the water channel;

[0021] Figure 2 It is a schematic flow chart of a method for local micro-arc oxidation of a magnesium alloy workpiece provided by the present invention;

[0022] Figure 3 It is a SEM picture of the micro-arc oxidation film provided by the present invention. DETAILED DESCRIPTION

[0023] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0024] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings 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. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0026] Unless otherwise specifically stated, the relative arrangement of the components and steps, numerical expressions and numerical values ​​described in these embodiments do not limit the scope of the present invention. At the same time, it should be clear that for the convenience of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship. For the techniques, methods known to ordinary technicians in the relevant fields,

[0027] The techniques, methods and devices may not be discussed in detail, but where appropriate, the techniques, methods and devices should be considered part of the specification. In all examples shown and discussed herein, any specific value should be interpreted as merely exemplary and not as a limitation. Therefore, other examples of the exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following figures, so once an item is defined in one figure, it does not need to be further discussed in subsequent figures.

[0028] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below their position devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0029] The present invention provides a method for local micro-arc oxidation of a magnesium alloy workpiece, combined with Figure 2 , including the following steps:

[0030] S10. Passivate, dry, remove dust, and shield the magnesium alloy workpiece to leave an area for micro-arc oxidation.

[0031] Specifically, the magnesium alloy workpiece is the engine outer shell, and the area that needs to be micro-arc oxidized is the area where the water channel is located, such as Figure 1 As shown (marked by the gray arrow), because this area is directly installed on the engine, it is easily corroded during use. Although the existing process has wear-resistant and anti-corrosion treatment on the surface of magnesium alloy workpieces, due to process reasons, the cost is generally high and the corrosion resistance does not meet the requirements. Among them, the passivation process can be anodizing to form an anodized film on the surface of the magnesium alloy workpiece, or it can be using a material containing Al(NO 3 ) 3 Ultrasonic treatment is performed on the solution to change the surface structure of the magnesium alloy workpiece to improve the uniformity of the micro-arc oxidation film and enhance the corrosion resistance of the micro-arc oxidation film. Of course, passivation can also be performed by surface sandblasting to change the roughness of the magnesium alloy workpiece surface. By changing the roughness, the corrosion resistance of the micro-arc oxidation film can be improved.

[0032] After the passivation treatment is completed, deionized water is used for cleaning, and then drying and dust removal are carried out after cleaning. Then, a masking film is used to mask the areas that do not need micro-arc oxidation, leaving the micro-arc oxidation area.

[0033] S20, performing micro-arc oxidation on the area to be micro-arc oxidized, and washing with water to form a micro-arc oxidation film layer in the area to be micro-arc oxidized;

[0034] The electrolyte for micro-arc oxidation treatment is composed of 8-10 g / L sodium silicate, 4-6 g / L sodium hydroxide, 2-3 g / L potassium fluoride, 2-4 g / L sodium aluminate, 0.2-0.4 g / L potassium fluorotitanate, and 0.1-0.3 g / L silicon dioxide nanoparticles.

[0035] Specifically, the magnesium alloy workpiece after shielding and drying is placed in a tank containing an electrolyte composed of 10g / L sodium silicate, 6g / L sodium hydroxide, 3g / L potassium fluoride, 4g / L sodium aluminate, 0.4g / L potassium fluorotitanate, and 0.3g / L silicon dioxide nanoparticles. The magnesium alloy workpiece is used as the anode and micro-arc oxidation is performed using a constant voltage double pulse power supply, wherein the positive pulse voltage is 400V, the negative pulse voltage is 90V, the frequency is 500Hz, the duty cycle is 15%, and the oxidation time is 10min. After micro-arc oxidation, it is washed with deionized water at 20°C to form a micro-arc oxidation film in the waterway area.

[0036] In the present invention, sodium silicate, sodium hydroxide, sodium aluminate as the main film-forming agent and Mg 2+ The formation of a stable precipitate, potassium fluoride can reduce the arc starting voltage, make the breakdown more severe, and thus promote the formation of the film layer. The addition of potassium fluoride helps to generate MgF 2 and MgAl 2 O 4 The formation of these phases is beneficial to improve the corrosion resistance of the film. In addition, the participation of potassium fluoride also changes the phase composition of the coating, making the coating denser and reducing the porosity.

[0037] The addition of potassium fluorotitanate can significantly improve the corrosion resistance of micro-arc oxidation coatings. The ionization reaction of potassium fluorotitanate in the electrolyte generates TiO 2 and F - , these components help seal the micropores in the micro-arc oxidation coating, thereby improving the microstructure of the coating. This structural improvement not only improves the corrosion resistance of the coating, but also enhances its mechanical properties. Silica nanoparticles improve the corrosion resistance and wear resistance of the coating.

[0038] The present invention selects the above materials and controls the addition ratio of the above materials, and coordinates the setting parameters of the constant voltage power supply, so that the obtained micro-arc oxidation film has higher corrosion resistance.

[0039] The technical solution provided by the present invention is further explained below through specific preparation examples.

[0040] Example 1

[0041] The magnesium alloy workpiece is degreased and dusted, and then the surface is passivated by anodizing to form an oxide film with a thickness of 25 μm on the surface of the magnesium alloy workpiece. The passivated magnesium alloy workpiece is cleaned and dried, and then masked with a masking film, and a micro-arc oxidation area is reserved.

[0042] According to the formula concentration, 8g / L sodium silicate, 4g / L sodium hydroxide, 2g / L potassium fluoride, 2g / L sodium aluminate, 0.2g / L potassium fluorotitanate, 0.1g / L silicon dioxide nanoparticles, prepare the electrolyte, put the electrolyte in the tank, immerse the magnesium alloy workpiece in the electrolyte, adjust the pH value of the electrolyte to 10-12, the temperature is 20°C, and perform micro-arc oxidation. Among them, the constant voltage double pulse mode is adopted, the positive pulse voltage is 300V, the negative pulse voltage is 80V, the frequency is 500Hz, the duty cycle is 15%, and the oxidation time is 10min.

[0043] After washing with deionized water at 25°C and drying at 85°C, a micro-arc oxidation film was prepared on the surface of the magnesium alloy workpiece. The SEM image is shown in FIG. Figure 3 shown.

[0044] Example 2

[0045] The magnesium alloy workpiece is degreased and dusted, and then the Al(NO 3 ) 3 The magnesium alloy workpiece is ultrasonically treated with a solution of . The passivated magnesium alloy workpiece is cleaned and dried, and then shielded with a shielding film, while a micro-arc oxidation area is reserved.

[0046] According to the formula concentration, 9g / L sodium silicate, 5g / L sodium hydroxide, 3g / L potassium fluoride, 3g / L sodium aluminate, 0.3g / L potassium fluorotitanate, 0.2g / L silicon dioxide nanoparticles, prepare the electrolyte, put the electrolyte in the tank, immerse the magnesium alloy workpiece in the electrolyte, adjust the pH value of the electrolyte to 10-12, the temperature is 30°C, and perform micro-arc oxidation. Among them, the constant voltage double pulse mode is adopted, the positive pulse voltage is 350V, the negative pulse voltage is 90V, the frequency is 550Hz, the duty cycle is 15%, and the oxidation time is 15min.

[0047] The micro-arc oxidation film was prepared on the surface of the magnesium alloy workpiece after washing with deionized water at 20°C and drying at 85°C.

[0048] Example 3

[0049] The magnesium alloy workpiece is degreased and dusted, and then sandblasted to a surface roughness of 2 μm. The passivated magnesium alloy workpiece is cleaned and dried, and then masked with a masking film, while a micro-arc oxidation area is reserved.

[0050] According to the formula concentration, 10g / L sodium silicate, 6g / L sodium hydroxide, 3g / L potassium fluoride, 4g / L sodium aluminate, 0.4g / L potassium fluorotitanate, 0.3g / L silicon dioxide nanoparticles, prepare the electrolyte, put the electrolyte in the tank, immerse the magnesium alloy workpiece in the electrolyte, adjust the pH value of the electrolyte to 10-12, the temperature is 40°C, and perform micro-arc oxidation. Among them, the constant voltage double pulse mode is adopted, the positive pulse voltage is 400V, the negative pulse voltage is 100V, the frequency is 600Hz, the duty cycle is 20%, and the oxidation time is 15min.

[0051] The micro-arc oxidation film was prepared on the surface of the magnesium alloy workpiece after washing with deionized water at 20°C and drying at 85°C.

[0052] Example 4

[0053] The magnesium alloy workpiece is degreased and dusted, and then sandblasted to a surface roughness of 2.5 μm. The passivated magnesium alloy workpiece is cleaned and dried, and then masked with a masking film, while a micro-arc oxidation area is reserved.

[0054] According to the formula concentration, 10g / L sodium silicate, 6g / L sodium hydroxide, 3g / L potassium fluoride, 4g / L sodium aluminate, 0.4g / L potassium fluorotitanate, 0.3g / L silicon dioxide nanoparticles, prepare the electrolyte, put the electrolyte in the tank, immerse the magnesium alloy workpiece in the electrolyte, adjust the pH value of the electrolyte to 10-12, the temperature is 40°C, and perform micro-arc oxidation. Among them, the constant voltage double pulse mode is adopted, the positive pulse voltage is 400V, the negative pulse voltage is 100V, the frequency is 600Hz, the duty cycle is 20%, and the oxidation time is 15min.

[0055] The micro-arc oxidation film was prepared on the surface of the magnesium alloy workpiece after washing with deionized water at 20°C and drying at 85°C.

[0056] Example 5

[0057] The magnesium alloy workpiece is degreased and dusted, and then sandblasted to a surface roughness of 3.0 μm. The passivated magnesium alloy workpiece is cleaned and dried, and then masked with a masking film, while a micro-arc oxidation area is reserved.

[0058] According to the formula concentration, 10g / L sodium silicate, 6g / L sodium hydroxide, 3g / L potassium fluoride, 4g / L sodium aluminate, 0.4g / L potassium fluorotitanate, 0.3g / L silicon dioxide nanoparticles, prepare the electrolyte, put the electrolyte in the tank, immerse the magnesium alloy workpiece in the electrolyte, adjust the pH value of the electrolyte to 10-12, the temperature is 40°C, and perform micro-arc oxidation. Among them, the constant voltage double pulse mode is adopted, the positive pulse voltage is 400V, the negative pulse voltage is 100V, the frequency is 600Hz, the duty cycle is 20%, and the oxidation time is 15min.

[0059] The micro-arc oxidation film was prepared on the surface of the magnesium alloy workpiece after washing with deionized water at 20°C and drying at 85°C.

[0060] Example 6

[0061] The magnesium alloy workpiece is degreased and dusted, and then sandblasted to a surface roughness of 3.5 μm. The passivated magnesium alloy workpiece is cleaned and dried, and then masked with a masking film, while a micro-arc oxidation area is reserved.

[0062] According to the formula concentration, 10g / L sodium silicate, 6g / L sodium hydroxide, 3g / L potassium fluoride, 4g / L sodium aluminate, 0.4g / L potassium fluorotitanate, 0.3g / L silicon dioxide nanoparticles, prepare the electrolyte, put the electrolyte in the tank, immerse the magnesium alloy workpiece in the electrolyte, adjust the pH value of the electrolyte to 10-12, the temperature is 40°C, and perform micro-arc oxidation. Among them, the constant voltage double pulse mode is adopted, the positive pulse voltage is 400V, the negative pulse voltage is 100V, the frequency is 600Hz, the duty cycle is 20%, and the oxidation time is 15min.

[0063] The micro-arc oxidation film was prepared on the surface of the magnesium alloy workpiece after washing with deionized water at 20°C and drying at 85°C.

[0064] It should be understood that the application of the present invention is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for local micro-arc oxidation of a magnesium alloy workpiece, characterized in that: The method comprises the following steps: Passivate, dry, remove dust, and shield the magnesium alloy workpiece to leave an area for micro-arc oxidation; The area to be micro-arc oxidized is subjected to micro-arc oxidation and water washing treatment to form a micro-arc oxidation film layer in the area to be micro-arc oxidized; the electrolyte for the micro-arc oxidation treatment is composed of 8-10 g / L sodium silicate, 4-6 g / L sodium hydroxide, 2-3 g / L potassium fluoride, 2-4 g / L sodium aluminate, 0.2-0.4 g / L potassium fluorotitanate, and 0.1-0.3 g / L silicon dioxide nanoparticles.

2. The method for local micro-arc oxidation of a magnesium alloy workpiece according to claim 1, characterized in that: The pH value of the electrolyte is 10-12, and the temperature is 20-40°C.

3. The method for local micro-arc oxidation of a magnesium alloy workpiece according to claim 1, characterized in that: The micro-arc oxidation treatment adopts a constant voltage double pulse mode, wherein the positive pulse voltage is 300-410V, the negative pulse voltage is 80-100V, the frequency is 500-600Hz, the duty cycle is 15-20%, and the oxidation time is 10-15min.

4. The method for local micro-arc oxidation of a magnesium alloy workpiece according to claim 1, characterized in that: The passivation treatment is selected from one of anodizing, ultrasonic treatment in an aluminum salt solution, and surface sandblasting.

5. The method for local micro-arc oxidation of a magnesium alloy workpiece according to claim 1, characterized in that: The conductivity of the electrolyte is 4-6 S / m.

6. The method for local micro-arc oxidation of a magnesium alloy workpiece according to claim 4, characterized in that: The passivation treatment is an anodic oxidation treatment, and the thickness of the oxide film is 20 to 35 μm.

7. The method for local micro-arc oxidation of a magnesium alloy workpiece according to claim 4, characterized in that: The passivation treatment is to use a solution containing Al(NO3)3 to perform ultrasonic treatment on the magnesium alloy workpiece.

8. The method for local micro-arc oxidation of a magnesium alloy workpiece according to claim 1, characterized in that: The water washing is performed by using deionized water at 15-25°C.

9. The method for local micro-arc oxidation of a magnesium alloy workpiece according to claim 1, characterized in that: The magnesium alloy workpiece is an engine housing, and the micro-arc oxidation area is a water channel installed on the motor.

10. The method for local micro-arc oxidation of a magnesium alloy workpiece according to claim 4, characterized in that: After the surface sandblasting treatment, the surface roughness of the magnesium alloy workpiece is 2-3.5 μm.

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