Method for improving surface wear resistance and corrosion resistance of aluminum-lithium alloy with high magnesium content

Abstract

The invention belongs to the practical application of a surface treatment technology on a high-magnesium-content Al-Li alloy, and particularly provides a method for improving the surface wear resistance and corrosion resistance of a high-magnesium-content Al-Li alloy, which comprises the steps of pretreatment, electrolytic polishing, anodic oxidation, sealing treatment and the like. The Al-Li alloy surface subjected to electrolytic polishing shows silver metal luster, the surface roughness is remarkably reduced, the alloy surface quality is improved, and a high-quality surface foundation is provided for subsequent anodic oxidation; a hard anodic oxide film which is uniform in color and luster, high and continuous in density, 5-25 microns in thickness and has a specific structure and performance can be obtained on the surface of the alloy, the wear resistance and corrosion resistance of the material can be effectively improved, and the service life of the material can be effectively prolonged.

Description

Technical Field

[0001] This invention relates to surface treatment technology for aluminum alloy materials, specifically to surface polishing technology for Al-Li alloys and the preparation technology of films that improve the surface wear resistance and corrosion resistance of high magnesium content aluminum-lithium alloys. Background Technology

[0002] Aluminum and its alloys are widely used in aerospace, automotive, and weaponry due to their high strength-to-weight ratio, ease of processing and formability, excellent physical properties, and good corrosion resistance. Aluminum and its alloys spontaneously form an amorphous oxide film in air, giving them good atmospheric corrosion resistance. However, in some harsh environments, this film is relatively thin, has low hardness, poor wear resistance, insufficient mechanical strength, and high porosity, which cannot meet the requirements of practical applications.

[0003] Currently, surface protection treatments are commonly used to prevent abrasion and damage, extend service life, and meet environmental adaptability and safety requirements. Common protective processes include anodizing, which forms an oxide film on the surface of aluminum and aluminum alloys, giving the material surface certain corrosion resistance, wear resistance, heat resistance, sun resistance, insulation, and decorative properties, while also enhancing the material's strength and hardness. However, Al-Li alloys differ from other aluminum alloys in that they contain a wide variety of alloying elements, many of which are highly reactive, especially Li. During electrolytic polishing, Li easily reacts with the polishing solution, generating substances such as Li₂O / LiOH, which macroscopically manifest as tiny corrosion pits on the polished surface, resulting in surface roughness and affecting the workpiece's appearance quality. Secondly, the high concentration of Al-Li alloying elements and their segregation can lead to uneven dissolution on the material surface, resulting in streaks, black spots, or dark areas. Furthermore, Li segregation affects the subsequent oxide film formation rate, leading to localized unevenness in the oxide film. Embedded oxide films also decrease the electrochemical impedance of the oxide film, thus reducing its corrosion resistance. Meanwhile, the grain size and orientation of the alloy, the size and distribution of the second phase particles, and the deformation texture all have a certain impact on electrolysis and film formation.

[0004] Furthermore, magnesium atoms exist in solid solutions or as a second phase, such as hard intermetallic compounds like Al3Mg2 (β phase) or together with Li to form the Al2MgLi phase, increasing surface hardness. However, this phase is susceptible to damage in common electrolytes (such as those containing Cl). - In the environment, the potential is more negative than that of the aluminum matrix, so it preferentially dissolves as an anode, initiating pitting or intergranular corrosion. In addition, the presence of magnesium will destroy the density and self-healing ability of the original oxide film (Al2O3) on the aluminum surface, reduce the corrosion barrier effect, and at the same time, it will form an active phase with lithium, which will further aggravate the electrochemical inhomogeneity and accelerate corrosion. Therefore, high magnesium content will further weaken the corrosion resistance of aluminum-lithium alloys.

[0005] Therefore, it is urgent to conduct research on surface protection technology for Al-Li alloy materials, which is of great significance to the field of advanced metals. Summary of the Invention

[0006] The purpose of this invention is to provide a method for improving the wear resistance and corrosion resistance of high-magnesium-content aluminum-lithium alloys, addressing the problem of unsatisfactory wear resistance and corrosion resistance.

[0007] The technical solution of this invention: A method for improving the wear resistance and corrosion resistance of high-magnesium-content aluminum-lithium alloy surfaces includes the following steps: (a) Pretreatment: The high magnesium content aluminum-lithium alloy is mechanically polished to 2000# with sandpaper, and then cleaned with anhydrous ethanol, strong acid and deionized water in sequence. The high magnesium content aluminum-lithium alloy must be completely immersed in the cleaning solution for each cleaning, and the cleaning time is 1-10 minutes. (b) Electrolytic polishing: The cleaned high magnesium content aluminum-lithium alloy is immersed in an electrolytic polishing solution for polishing. The electrolyte temperature is controlled at 20-30℃, the electrolytic voltage is set at 15-25V, and the time is 120s-180s. (c) Anodizing: The polished high-magnesium-content aluminum-lithium alloy is immersed in an acidic anodizing solution for anodizing. The concentration of the acidic anodizing solution is 180~200 g / L, the oxidation voltage is set to 15~20 V, and the time is 15~25 min. (d) Sealing treatment: Immerse the anodized high magnesium content aluminum-lithium alloy in a hot water sealing solution at a temperature of 80~100℃ for 20~35 min.

[0008] In step (b), the electropolishing solution is composed of a weak acid and a strong acid in a volume ratio of weak acid: strong acid: water = (4~8):1:(1~5); the weak acid is an organic acid; and the strong acid is one or more of perchloric acid, hydrochloric acid, sulfuric acid, and nitric acid.

[0009] Furthermore, the organic acid is acetic acid.

[0010] In step (c), the acidic anodizing solution is a sulfuric acid solution.

[0011] The high-magnesium-content aluminum-lithium alloy has a Mg content of 3-10%.

[0012] The beneficial effects of this invention are: The method of this invention significantly improves the surface quality of Al-Li alloys. Electrolytic polishing can eliminate the micro-stress present during mechanical grinding of the material surface. The formation of the oxide film can block the erosion of the environmental medium, and the wear resistance and corrosion resistance are significantly improved.

[0013] Compared to surface treatment methods such as spraying and electroplating, the method of this invention is environmentally friendly, green, and economical. The combination of electropolishing and anodizing effectively improves the aesthetics of the aluminum-lithium alloy surface, solves the material protection problem of the high reactivity of Al-Li alloys, and gives the material a wider range of applications.

[0014] By strictly controlling process parameters, this invention can obtain a hard anodized film layer with uniform color, high density and continuity, and a film thickness of 5-25 μm, while also having excellent corrosion resistance and wear resistance. Attached Figure Description

[0015] Figure 1 Example 1 of the present invention demonstrates its effects. Figure 2 Example 1 of the present invention: thickness of the alloy surface film; Figure 3 Example 1 of this invention: Hardness comparison of alloy before and after surface treatment. Detailed Implementation

[0016] Example 1: A method for improving the wear resistance and corrosion resistance of high magnesium content aluminum-lithium alloy surfaces includes the following steps: (a) The Al-Li alloy sample with Mg content of 4.5% was polished with sandpaper from 240# to 2000# one by one. Then the surface was rinsed with deionized water, placed in a beaker containing analytical ethanol, ultrasonically cleaned for 5 min, and then cleaned with 15% HNO3 for 30 s. After rinsing with deionized water, the sample was immediately dried with air at a pressure not exceeding 200 kPa at a distance of about 300 mm from the sample surface. (b) High-purity CH3COOH:HClO4:H2O were prepared in a volume ratio of 5:1:4 and poured into a clean beaker. A stainless steel plate was inserted and connected to the cathode of the workstation with a copper wire. After connecting the sample to the anode, it was completely immersed in the prepared electrolytic polishing solution. The voltage was kept constant at 20V. The circuit was turned on and the sample was removed, cleaned and dried after 120 seconds. This process yielded an alloy sample with lower surface roughness, obvious metallic luster, no color difference, no streaks, and excellent texture. (c) The alloy sample after electrolytic polishing was immersed in a sulfuric acid solution of 185 g / L, the circuit was turned on and the voltage was controlled at 20 V, and the magnetic stirring was turned on to make the solutions of each part fully and evenly mixed. The reaction time was 25 min.

[0017] (d) Take out the fully anodized sample and immediately place it in 95°C hot water for 30 min to seal the reaction, then take it out and air dry.

[0018] The anodic oxide film obtained in Example 1 after pretreatment, electrolytic polishing, anodizing, and sealing treatment has a moist feel and matte texture, uniform color, and no defects such as uncoated areas, black spots, or black lines. The film thickness prepared in Example 1 is 12-14 μm, and the film hardness value is approximately 310-350 HV, which is 120% higher than the substrate hardness (140 HV) (calculated based on the lowest film hardness value), demonstrating significant improvement.

[0019] Example 2 A method for improving the wear resistance and corrosion resistance of high magnesium content aluminum-lithium alloy surfaces includes the following steps: (a) The Al-Li alloy sample with Mg content of 4.5% was polished with sandpaper from 240# to 2000# one by one. Then the surface was rinsed with deionized water, placed in a beaker containing analytical ethanol, ultrasonically cleaned for 5 min, and then cleaned with 15% HNO3 for 30 s. After rinsing with deionized water, the sample was immediately dried with air at a pressure not exceeding 200 kPa at a distance of about 300 mm from the sample surface. (b) High-purity CH3COOH:HClO4:H2O were prepared in a volume ratio of 4:1:5 and poured into a clean beaker. A stainless steel plate was inserted and connected to the cathode of the workstation with a copper wire. The sample was then connected to the anode and completely immersed in the prepared electrolytic polishing solution. The voltage was kept constant at 20V. The circuit was turned on and the sample was removed, cleaned and dried after 120 seconds. This process yielded an alloy sample with lower surface roughness, obvious metallic luster, no color difference, no streaks, and excellent texture. (c) The alloy sample after electrolytic polishing is immersed in a 180 g / L sulfuric acid solution, the circuit is turned on and the voltage is controlled at 15 V, and the magnetic stirring is turned on to make the solutions in each part fully and evenly mixed. The reaction time is 20 min.

[0020] (d) Take out the fully anodized sample and immediately place it in 95℃ hot water for 20 min to seal the reaction, then take it out and air dry.

[0021] The anodic oxide film obtained in Example 2 after pretreatment, electrolytic polishing, anodizing, and sealing treatment has a moist touch and matte texture, uniform color, and no defects such as uncoated areas, black spots, or black lines. The film thickness prepared in Example 2 is 10-12 μm, and the film hardness value is approximately 310-320 HV, which is 120% higher than the substrate hardness (140 HV) (calculated based on the lowest film hardness value), demonstrating significant improvement.

[0022] Example 3 A method for improving the wear resistance and corrosion resistance of high magnesium content aluminum-lithium alloy surfaces includes the following steps: (a) The Al-Li alloy sample with Mg content of 4.5% was polished with sandpaper from 240# to 2000# one by one. Then the surface was rinsed with deionized water, placed in a beaker containing analytical ethanol, ultrasonically cleaned for 5 min, and then cleaned with 15% HNO3 for 30 s. After rinsing with deionized water, the sample was immediately dried with air at a pressure not exceeding 200 kPa at a distance of about 300 mm from the sample surface. (b) High-purity CH3COOH:HClO4:H2O were prepared in a volume ratio of 6:1:3 and poured into a clean beaker. A stainless steel plate was inserted and connected to the cathode of the workstation with a copper wire. The sample was then connected to the anode and completely immersed in the prepared electrolytic polishing solution. The voltage was kept constant at 25V. The circuit was turned on and the sample was removed, cleaned, and dried after 180 seconds. This process yielded an alloy sample with lower surface roughness, obvious metallic luster, no color difference, no streaks, and excellent texture. (c) The alloy sample after electrolytic polishing was immersed in a 200 g / L sulfuric acid solution, the circuit was turned on and the voltage was controlled at 25 V, and the magnetic stirring was turned on to make the solutions fully and evenly mixed. The reaction time was 25 min.

[0023] (d) Take out the fully anodized sample and immediately place it in hot water at 95°C for 35 min to seal the reaction, then take it out and air dry.

[0024] The anodic oxide film obtained in Example 3 after pretreatment, electrolytic polishing, anodizing, and sealing treatment has a moist touch and matte texture, uniform color, and no defects such as uncoated areas, black spots, or black lines. The film thickness prepared in Example 3 is 10-15 μm, and the film hardness value is approximately 280-300 HV, which is 100% higher than the substrate hardness (140 HV) (calculated based on the lowest film hardness value), demonstrating significant improvement.

[0025] Example 4 A method for improving the wear resistance and corrosion resistance of high magnesium content aluminum-lithium alloy surfaces includes the following steps: (a) The Al-Li alloy sample with 5.5% Mg content was polished with sandpaper from 240# to 2000# one by one. Then the surface was rinsed with deionized water, placed in a beaker containing analytical ethanol, ultrasonically cleaned for 5 min, and then cleaned with 15% HNO3 for 30 s. After rinsing with deionized water, the sample was immediately dried with air at a pressure not exceeding 200 kPa at a distance of about 300 mm from the sample surface. (b) High-purity CH3COOH:HClO4:H2O were prepared in a volume ratio of 8:1:1 and poured into a clean beaker. A stainless steel plate was inserted and connected to the cathode of the workstation with a copper wire. The sample was then connected to the anode and completely immersed in the prepared electrolytic polishing solution. The voltage was kept constant at 22V. The circuit was turned on and the sample was removed, cleaned and dried after 135 seconds. This process yielded an alloy sample with lower surface roughness, obvious metallic luster, no color difference, no streaks, and excellent texture. (c) The alloy sample after electrolytic polishing was immersed in a 192 g / L sulfuric acid aqueous solution, the circuit was turned on and the voltage was controlled at 22 V, and the magnetic stirring was turned on to make the solutions fully and evenly mixed. The reaction time was 18 min.

[0026] (d) Take out the fully anodized sample and immediately place it in 95°C hot water for 30 min to seal the reaction, then take it out and air dry.

[0027] The anodic oxide film obtained in Example 4 after pretreatment, electrolytic polishing, anodizing, and sealing exhibits a moist feel and matte texture, uniform color, and is free from defects such as uncoated areas, black spots, or black lines. The film prepared in Example 4 has a thickness of 12-15 μm and a hardness value of approximately 330-350 HV, representing a 130% increase compared to the substrate hardness (143 HV) (calculated based on the lowest film hardness value), demonstrating significant improvement.

Claims

1. A method for improving the wear resistance and corrosion resistance of high-magnesium-content aluminum-lithium alloy surfaces, characterized in that, Includes the following steps: (a) Pretreatment: The high magnesium content aluminum-lithium alloy is mechanically polished to 2000# with sandpaper, and then cleaned with anhydrous ethanol, strong acid and deionized water in sequence. The high magnesium content aluminum-lithium alloy must be completely immersed in the cleaning solution for each cleaning, and the cleaning time is 1-10 minutes. (b) Electrolytic polishing: The cleaned high magnesium content aluminum-lithium alloy is immersed in an electrolytic polishing solution for polishing. The electrolyte temperature is controlled at 20-30℃, the electrolytic voltage is set at 15-25V, and the time is 120s-180s. (c) Anodizing: The polished high-magnesium-content aluminum-lithium alloy is immersed in an acidic anodizing solution for anodizing. The concentration of the acidic anodizing solution is 180~200 g / L, the oxidation voltage is set to 15~20 V, and the time is 15~25 min. (d) Sealing treatment: Immerse the anodized high magnesium content aluminum-lithium alloy in a hot water sealing solution at a temperature of 80~100℃ for 20~35 min.

2. The method for improving the wear resistance and corrosion resistance of high-magnesium-content aluminum-lithium alloy surfaces according to claim 1, characterized in that, In step (b), the electropolishing solution is composed of a weak acid and a strong acid in a volume ratio of weak acid: strong acid: water = (4~8):1:(1~5); the weak acid is an organic acid; and the strong acid is one or more of perchloric acid, hydrochloric acid, sulfuric acid, and nitric acid.

3. The method for improving the wear resistance and corrosion resistance of a high-magnesium-content aluminum-lithium alloy surface according to claim 1, characterized in that, In step (c), the acidic anodizing solution is a sulfuric acid solution.

4. The method for improving the wear resistance and corrosion resistance of high-magnesium-content aluminum-lithium alloy surfaces according to claim 1, characterized in that, The high-magnesium-content aluminum-lithium alloy has a Mg content of 3-10%.

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