A method for simultaneously improving the corrosion resistance of magnesium alloys by laser-microarc oxidation composite

Abstract

The present invention discloses a method for simultaneously improving the corrosion resistance of magnesium alloys by laser-microarc oxidation composite, which includes: polishing the magnesium alloy substrate, followed by ultrasonic cleaning and then drying for standby; placing the pretreated magnesium alloy specimen in a stainless steel tank, configuring an electrolyte in the tank, and setting the laser processing technology for treatment; using the magnesium alloy specimen as the anode and the stainless steel tank as the cathode, irradiating the surface of the substrate with a laser beam while performing microarc oxidation treatment; after the treatment, performing ultrasonic cleaning and drying; the main creativity of the present invention lies in: it can prepare a high-performance corrosion-resistant film layer for magnesium alloys by a one-step method, and can improve the film formation quality and density of MAO by adjusting the laser parameters.

Description

Technical Field

[0001] The present invention belongs to the technical field of surface corrosion protection of magnesium alloys, and mainly relates to a method for surface treatment of magnesium alloys by synchronous laser-microarc oxidation to improve the long-term corrosion resistance of the substrate surface. Background Technique

[0002] Due to the advantages of magnesium and its alloys such as low density, high specific strength and specific stiffness, and good plasticity, they have important status and application value in the national defense fields such as machinery, aerospace, and ships. However, the chemical properties of magnesium are relatively active, and serious corrosion often occurs in humid atmospheres, land, and marine salt spray environments, which will ultimately lead to the premature failure of components, severely restricting the development of magnesium alloys to a wider range of fields. Therefore, from the perspective of the common requirements for magnesium alloy corrosion protection, improving the long-term corrosion resistance has become the research focus of magnesium and its alloy corrosion protection.

[0003] Laser surface modification technology is a method for local surface modification of metal materials. By using a high-energy density laser beam to directly melt and solidify the surface of the material or form a treatment layer with a certain thickness on the surface of the material, and relying on the extremely high cooling rate of the laser, the mechanical properties, metallurgical properties, and physical properties of the material surface are improved, thereby improving the wear resistance, corrosion resistance, etc. of the material surface. This method can effectively enhance the corrosion resistance of magnesium alloys by changing their microstructure and surface composition.

[0004] Microarc oxidation (MAO) is a process that, through the combination of an electrolyte and corresponding electrical parameters, in-situ grows a ceramic film layer mainly composed of the matrix metal oxide on the surface of metals such as aluminum, magnesium, titanium and their alloys under the action of the instantaneous high temperature and high pressure generated by arc discharge. The microarc oxidation film layer has a firm bond with the substrate, a dense structure, high toughness, and good wear resistance, corrosion resistance, high temperature impact resistance, and electrical insulation properties. Therefore, this method can be used to prepare a ceramic film layer on the surface of magnesium alloys, thereby improving the corrosion resistance of magnesium alloys.

[0005] The method of combining the above two technologies can, to a certain extent, more effectively improve the corrosion resistance of magnesium alloys compared to one of them. And the asynchronous combination of these two technologies has problems such as cumbersome preparation processes and high costs. For this reason, based on these two technologies, the present invention proposes a method for synchronously laser-microarc oxidation composite preparation of a corrosion-resistant film layer for magnesium alloys. Summary of the Invention

[0006] Based on the above-mentioned disadvantages and deficiencies existing in the prior art, the present invention provides a method for preparing a high-performance corrosion-resistant film layer for magnesium alloys, that is, a method for synchronously laser-microarc oxidation composite to improve the corrosion resistance of magnesium alloys.

[0007] The technical solution of the present invention is as follows:

[0008] A laser-microarc oxidation synchronous composite device includes: a power supply, a workpiece to be processed, a cathode electrolyte tank, an electrolyte, a galvanometer laser, and a laser beam; the positive electrode of the power supply is connected to the workpiece to be processed, and the negative electrode of the power supply is connected to the cathode electrolyte tank; the workpiece to be processed is placed parallel to the bottom of the cathode electrolyte tank and is 30 mm below the liquid level of the electrolyte; the galvanometer laser is arranged 293 mm above the surface of the workpiece to be processed; the laser beam is perpendicular to the surface of the workpiece to be processed, and the scanning mode of the laser beam is linear short-side reciprocating scanning, and the irradiation area of the laser beam is adjustable.

[0009] A method for improving the corrosion resistance of magnesium alloys by laser-microarc oxidation synchronization includes the following steps:

[0010] (1) Grind and polish the substrate magnesium alloy, then ultrasonically clean it and dry it for later use;

[0011] The magnesium alloy is, for example, AZ31B magnesium alloy;

[0012] Specifically, grind and polish it successively with 80-1000# SiC sandpaper;

[0013] (2) Configure the electrolyte in a stainless steel tank, and place the magnesium alloy sample pretreated in step (1) 30 mm below the liquid level of the electrolyte in the tank. Use the magnesium alloy sample as the anode and the stainless steel tank as the cathode, and irradiate the surface of the magnesium alloy sample with a laser beam while performing microarc oxidation treatment to prepare a corrosion-resistant and corrosion-resistant film layer on the magnesium alloy;

[0014] The composition of the electrolyte is: Na2SiO3: 20 g / L, Na2HPO4: 4 g / L, NaOH: 3 g / L, Na2WO4: 0.5-1 g / L, and the solvent is deionized water;

[0015] The laser processing process is: the control mode of laser movement is galvanometer scanning, the laser power is 30-150 W, the laser scanning speed is 5000 mm / s, the laser frequency is 20 kHz, the scanning pitch is 0.08 mm, and the focal length of the laser emission point from the surface of the sample is 293 mm;

[0016] The microarc oxidation electrical parameters are: using a constant current mode, the current is 1 A, the frequency is 800 Hz, the duty cycle is 10%, and the oxidation time is 5 min.

[0017] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in:

[0018] 1. The present invention synchronously combines two surface modification technologies of laser and micro-arc oxidation, which can effectively eliminate the deficiencies existing in the asynchronous combination of these two technologies, and further improve the surface corrosion resistance of magnesium alloys with high performance. At the same time, during the micro-arc oxidation treatment, the high-energy laser beam can, to a certain extent, eliminate the inherent micro-defects and micro-cracks in the micro-arc oxidation process, thereby improving the film formation quality and density of MAO, and further enhancing the corrosion resistance of magnesium alloys.

[0019] 2. Compared with the single laser surface modification treatment, by introducing the micro-arc oxidation technology, the present invention does not require blackening the surface to improve the absorption ability of the laser, which simplifies the operation process and saves costs; moreover, the process method of the present invention is environmentally friendly and pollution-free, belonging to the category of green manufacturing.

[0020] 3. Compared with the single micro-arc oxidation treatment, the present invention can improve the film formation quality and density of MAO by adjusting the laser process parameters, eliminate the defects of the MAO film layer with the characteristics of porosity and micro-cracks, thereby enhancing the corrosion resistance of the magnesium alloy surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 : Schematic diagram of the laser-micro-arc oxidation synchronous composite device, where 1 - power supply, 2 - workpiece to be processed, 3 - cathode electrolyte tank, 4 - electrolyte, 5 - galvanometer laser, 6 - laser beam.

[0022] Figure 2 : Polarization curves of AZ31B magnesium alloy, micro-arc oxidation, and laser-micro-arc oxidation synchronous composite in 3.5% NaCl solution.

[0023] Figure 3 : EIS diagrams of micro-arc oxidation and laser-micro-arc oxidation synchronous composite after soaking in 3.5% NaCl solution for 24 h; where (a): equivalent circuit diagram, (b): Nyquist diagram, (c)-(d): bode diagrams. DETAILED DESCRIPTION OF THE INVENTION

[0024] The present invention will be further described below with reference to the drawings through specific embodiments, but the protection scope of the present invention is not limited thereto.

[0025] Such as Figure 1As shown in the figure, a laser-microarc oxidation synchronous composite device includes: a power supply 1, a workpiece to be processed 2, a cathode electrolyte tank 3, an electrolyte 4, a galvanometer laser 5, and a laser beam 6. The positive electrode of the power supply 1 is connected to the workpiece to be processed 2, and the negative electrode of the power supply 1 is connected to the cathode electrolyte tank 3. The workpiece to be processed 2 is placed parallel to the bottom of the cathode electrolyte tank 3, 30 mm below the liquid level of the electrolyte 4. The galvanometer laser 5 is arranged 293 mm above the surface of the workpiece to be processed 2. The laser beam 6 is perpendicular to the surface of the workpiece to be processed 2, and the scanning mode of the laser beam 6 is linear short-side reciprocating scanning, and the irradiation area of the laser beam 6 is adjustable.

[0026] Example 1

[0027] In the following examples, the magnesium alloy used is AZ31B magnesium alloy, and the size of the specimen is 30×30×2 mm.

[0028] The control mode of the laser movement is galvanometer scanning, and the scanning area is 25×29 mm.

[0029] The method for improving the corrosion resistance of magnesium alloy by laser-microarc oxidation synchronization in the embodiments of the present invention is carried out according to the following steps:

[0030] 1) The magnesium alloy substrate is polished successively with 80-1000# SiC sandpaper, and then ultrasonically cleaned with alcohol and dried for use.

[0031] 2) Prepare the electrolyte in a stainless steel tank, and place the magnesium alloy specimen treated in step 1) 30 mm below the liquid level of the electrolyte in the tank. That is, add Na2SiO3: 20 g / L, Na2HPO4: 4 g / L, NaOH: 3 g / L, and Na2WO4: 0.5 g / L to deionized water in sequence and stir evenly. At the same time, set the laser processing process parameters: laser power 60 W, laser scanning speed 5000 mm / s, laser frequency 20 kHz, scanning pitch 0.08 mm, and the distance from the laser beam emission point to the specimen surface 293 mm. Microarc oxidation electrical parameters: use the constant current mode, current 1 A, frequency 800 Hz, duty cycle 10%, and oxidation time 5 min.

[0032] Using the magnesium alloy specimen as the anode and the stainless steel tank as the cathode, irradiate the surface of the substrate with a laser beam while performing microarc oxidation treatment. After the treatment, ultrasonically clean with alcohol and dry.

[0033] Results of the prepared composite film layer: Electrochemical performance tests were carried out in 3.5% NaCl solution, and the polarization curves of three specimens were obtained (as Figure 2 shown). The corrosion potential of AZ31B magnesium alloy (substrate) is -1.293 V, and the corrosion current density is 2.54×10 -4A / cm 2 ; Compared with the substrate, the corrosion potential of the micro-arc oxidation treated magnesium alloy (MAO) increased to -1.227 V, and the corrosion current density decreased to 4.07×10 -6 A / cm 2 , and its corrosion resistance was improved to a certain extent. The corrosion current density of the laser-micro-arc oxidation synchronous composite treated magnesium alloy (Laser-MAO) decreased to 2.44×10 -6 A / cm 2 , indicating that the corrosion resistance of the magnesium alloy surface was further improved.

[0034] To further explore the long-term electrochemical performance of the composite film layer on the magnesium alloy surface, impedance spectroscopy analysis was carried out on the composite film layer on the magnesium alloy surface after soaking in 3.5% NaCl solution for 24 h (as Figure 3 shown). By constructing the equivalent circuit diagram of the film layer (as shown in a in Figure 3 ), it was found that the fitting effect of the relevant impedance spectroscopy data of the MAO and Laser-MAO specimens was good. Compared with the single micro-arc oxidation treatment (MAO), in Figure 3 b (Nyquist diagram), it was shown that the Laser-MAO specimen had a larger capacitive reactance arc, indicating that the Laser-MAO specimen had better long-term corrosion resistance. At the same time, Figure 3 c-d in showed that the Laser-MAO specimen had higher impedance values in both the low-frequency and high-frequency regions, indicating that the quality of the dense layer and the loose layer of the MAO film layer had been improved to a certain extent. This was because the high-energy density laser beam could eliminate the micro-defects formed during the entire micro-arc oxidation process to a certain extent, thereby improving the film-forming quality and density of the MAO film layer and further enhancing the corrosion resistance of the magnesium alloy surface.

[0035] Based on the above research foundation and analysis, the results showed that the laser could further effectively improve the long-term corrosion resistance of the composite film layer on the magnesium alloy surface by improving the film layer quality during the micro-arc oxidation reaction process.

[0036] In addition, the electrolyte configuration: Na2SiO3: 20 g / L, Na2HPO4: 4 g / L, NaOH: 3 g / L, Na2WO4: 0.5 - 1 g / L, and the solvent was deionized water, and it needed to be stirred evenly; the electrolyte composition could be selected within this range, and since the effects were similar, it would not be described here.

[0037] The above only describes the specific preferred embodiments of the present invention in detail. It should be noted that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various deformations or modifications within the scope of the claims, which does not affect the essence of the present invention.

Claims

1. A method for simultaneously improving the corrosion resistance of magnesium alloys by laser-microarc oxidation composite, characterized in that, It includes the following steps: (1) Grind and polish the substrate magnesium alloy, then ultrasonically clean it and dry it for later use; (2) Prepare the electrolyte in a stainless-steel tank, and place the magnesium alloy specimen pretreated in step (1) 30 mm below the liquid level of the electrolyte in the tank. Use the magnesium alloy specimen as the anode and the stainless-steel tank as the cathode. While performing micro-arc oxidation treatment, irradiate the surface of the magnesium alloy specimen with a laser beam to prepare a corrosion-resistant film layer on the magnesium alloy; The composition of the electrolyte is: Na2SiO3: 20 g / L, Na2HPO4: 4 g / L, NaOH: 3 g / L, Na2WO4: 0.5 - 1 g / L, and the solvent is deionized water; The laser processing technology is: the control mode of laser movement is galvanometer scanning, the laser power is 30 - 150 W, the laser scanning speed is 5000 mm / s, the laser frequency is 20 kHz, the scanning pitch is 0.08 mm, and the focal length of the laser emission point from the specimen surface is 293 mm; The micro-arc oxidation electrical parameters are: using a constant current mode, the current is 1 A, the frequency is 800 Hz, the duty cycle is 10%, and the oxidation time is 5 min.

2. The method for improving the corrosion resistance of magnesium alloy by laser-microarc oxidation synchronous composite as claimed in claim 1, characterized in that The magnesium alloy is AZ31B magnesium alloy.

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