A method for using t-ZrO2-reinforced micro-arc oxidation ceramic film on aluminum alloy drill pipes

Abstract

This invention relates to the field of metal surface modification technology and provides a method for strengthening aluminum alloy drill pipes with a micro-arc oxidation ceramic film based on t-ZrO2. The method includes the following steps: cleaning the surface of the aluminum alloy drill pipe; subjecting the cleaned aluminum alloy drill pipe to MAO treatment to form an Al2O3 ceramic film; preparing superhydrophobic t-ZrO2 powder; mixing the superhydrophobic t-ZrO2 powder with epoxy resin, curing agent, and solvent to prepare a coating solution; and spraying the coating solution onto the surface of the micro-arc oxidation-treated aluminum alloy drill pipe, followed by curing to form a composite coating. This composite coating not only effectively seals micropores and microcracks, significantly improving the corrosion resistance of the aluminum alloy drill pipe, but also utilizes the phase transformation toughening effect of t-ZrO2 to significantly improve the toughness and crack propagation resistance of the ceramic film, making it suitable for harsh working conditions such as deep-sea oil and gas exploration.

Description

Technical Field

[0001] This invention belongs to the field of metal surface modification technology, and particularly relates to a method for using a micro-arc oxidation ceramic film based on t-ZrO2 to strengthen aluminum alloy drill rods. Background Technology

[0002] As deep-sea oil and gas exploration moves towards extreme environments, drill pipes require higher overall performance. Aluminum alloys, due to their high specific strength and low density, are gradually becoming an important material for deep-sea drill pipes. To improve their surface properties, a micro-arc oxidation (MAO) process is often used to prepare an Al2O3 ceramic film on the surface, thereby enhancing hardness, wear resistance, and corrosion resistance.

[0003] However, the ceramic membrane has inherent micropores and microcracks, which not only provide a permeation channel for corrosive media (such as drilling fluid and H2S), affecting its long-term protective capability, but also the ceramic itself is brittle and has poor toughness. Under complex alternating loads downhole, it is prone to crack propagation, leading to early coating failure or drill pipe breakage risk.

[0004] To address the aforementioned issues, existing improvement methods mainly involve adding a reinforcing phase to the electrolyte or applying an organic coating to the oxide film surface for pore sealing. The former is difficult to completely seal the pores and has limited toughening effect; the latter, while improving corrosion resistance, often neglects the fundamental improvement of the underlying ceramic film's brittleness and lacks synergistic toughness with the substrate. Currently, a technology that incorporates superhydrophobic tetragonal zirconium dioxide (t-ZrO2), which exhibits significant phase transformation toughening effects, as a functional component into the organic-inorganic composite coating system of aluminum alloy micro-arc oxide films to achieve the dual effects of "superhydrophobic sealing" and "phase transformation toughening" has not yet been publicly disclosed. Summary of the Invention

[0005] The purpose of this invention is to provide a method for using a micro-arc oxidation ceramic film based on t-ZrO2 to strengthen aluminum alloy drill pipes, thereby addressing the problems mentioned in the background art.

[0006] The present invention is implemented as follows: a method for using a micro-arc oxidation ceramic film based on t-ZrO2 to strengthen aluminum alloy drill pipes includes the following steps:

[0007] Step 1: Clean the surface of the aluminum alloy drill rod;

[0008] Step 2: Perform MAO treatment on the cleaned aluminum alloy drill rod to form an Al2O3 ceramic film;

[0009] Step 3: Prepare superhydrophobic t-ZrO2 powder;

[0010] Step 4: Mix the superhydrophobic t-ZrO2 powder with epoxy resin, curing agent and solvent to prepare a coating solution;

[0011] Step 5: Spray the coating solution onto the surface of the aluminum alloy drill rod after micro-arc oxidation treatment, and cure it to form a composite coating.

[0012] A further technical solution, the specific steps of step 3 are as follows:

[0013] 1 g of t-ZrO2 (with 5 mol% Y2O3 doping) was weighed and added to a mixture of 50 mL EtOH and 6 mL ammonia (NH3·H2O) for ultrasonic dispersion. Under magnetic stirring, 0.8 mL of tetraethyl orthosilicate (TEOS) was added dropwise to the solution, and the mixture was stirred for 2 h. Then, 0.4 mL of 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PFAS) was added dropwise, and stirring continued for 6 h. Finally, the mixture was filtered to obtain a filter cake, which was then dried in an oven at 60 °C to obtain powdered superhydrophobic t-ZrO2.

[0014] A further technical solution, the specific steps of step 4 are as follows:

[0015] 1 g of epoxy resin (EP) and 10 mL of EtOH were mixed and stirred for 60 min, then 0.3 g of curing agent was added and stirred for another 10 min to obtain an epoxy resin coating solution; then 1.5 g of superhydrophobic t-ZrO2 was added and stirred for another 30 min to obtain an epoxy resin coating solution containing superhydrophobic t-ZrO2.

[0016] A further technical solution, the specific steps of step 5 are as follows:

[0017] The surface of the MAO-treated aluminum alloy drill rod was cleaned with deionized water for 2 min; a spraying process was adopted, and the coating solution was the epoxy resin coating solution containing superhydrophobic t-ZrO2 prepared in step 4. After spraying, the sample was cured in an oven at 60°C for 6 h to obtain the coating sample.

[0018] In a further technical solution, in step 5, the spraying distance is 15 cm, the spraying pressure is 0.6 MPa, and the spraying time is 5 s.

[0019] The present invention provides a method for strengthening aluminum alloy drill pipes with micro-arc oxidation ceramic film based on t-ZrO2, the beneficial effects of which are as follows:

[0020] (1) Synergistic improvement of corrosion resistance and long-term protection: The superhydrophobic composite coating constructed in this invention can effectively seal the pores and cracks of the micro-arc oxide film through epoxy resin, blocking the corrosion channel; and it can also actively repel corrosive media by utilizing its superhydrophobic properties (contact angle greater than 150°). This dual effect of "physical sealing" and "surface superhydrophobicity" significantly improves the corrosion resistance life of the drill pipe in harsh environments.

[0021] (2) Fundamentally improve the toughness of the film and enhance its resistance to damage: By introducing t-ZrO2 particles with phase transformation toughening effect, when the coating is subjected to stress and microcracks are generated, t-ZrO2 undergoes phase transformation and volume expansion, which can effectively inhibit crack propagation, greatly improve the fracture toughness and impact resistance of the ceramic film, and overcome its inherent brittleness.

[0022] (3) Constructing a strong and tough integrated composite structure with superior comprehensive performance: The technical solution forms a synergistic system of "micro-arc oxidation hard base layer - epoxy resin sealing layer - t-ZrO2 functional enhancement phase". This structure has high strength, high toughness, strong bonding force and superhydrophobicity, which simultaneously and significantly improves the hardness, toughness and corrosion resistance of the drill pipe surface.

[0023] (4) Simple process and easy to promote: This method adds a spray curing step to the mature micro-arc oxidation process. The process is simple and stable, and easy to implement and scale up. The design concept of this coating system also has the potential to be extended to other high-performance light alloy parts. Attached Figure Description

[0024] Figure 1 A flowchart of a method for strengthening aluminum alloy drill pipes with micro-arc oxidation ceramic film based on t-ZrO2 is provided for embodiments of the present invention;

[0025] Figure 2 The wettability results of t-ZrO2 powder surface are shown (where a is unmodified t-ZrO2 powder, b is modified t-ZrO2 powder, and c is the contact angle measurement diagram of b).

[0026] Figure 3 The image shows a physical sample of an epoxy resin coating solution containing superhydrophobic t-ZrO2 (where a is a front view of the solution and b is a top view of the solution).

[0027] Figure 4 The dynamic contact process of water droplets on the surface of a 7075 aluminum alloy drill rod after spraying (where a is the uncoated 7075 aluminum alloy drill rod, b is the coated 7075 aluminum alloy drill rod, and c is the dynamic contact process of water droplets on the surface of the coated 7075 aluminum alloy drill rod).

[0028] Figure 5 The surface wettability of 7075 aluminum alloy is shown in Figure 1 (where a is a surface image of 7075 aluminum alloy, b is an image of a water droplet on 7075 aluminum alloy, and c is a contact angle measurement diagram of b).

[0029] Figure 6The surface wettability of 7075 aluminum alloy coated with epoxy resin is shown in Figure 1 (where a is a surface image of 7075 aluminum alloy coated with epoxy resin, b is an image of water droplets on 7075 aluminum alloy coated with epoxy resin, and c is a contact angle measurement diagram of b).

[0030] Figure 7 The surface wettability of 7075 aluminum alloy coated with superhydrophobic t-ZrO2 epoxy resin is shown in Figure 1 (where a is an image of the surface of 7075 aluminum alloy coated with superhydrophobic t-ZrO2 epoxy resin, b is an image of water droplets on 7075 aluminum alloy coated with superhydrophobic t-ZrO2 epoxy resin, and c is a contact angle measurement diagram of b).

[0031] Figure 8 The dynamic contact process of water droplets on 7075 aluminum alloy coated with superhydrophobic t-ZrO2 epoxy resin is shown.

[0032] Figure 9 Microscopic images of 7075 aluminum alloy coated with superhydrophobic t-ZrO2 epoxy resin (where a, b, c and d are microscopic images at different magnifications). Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0034] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0035] like Figure 1 As shown, a method for producing a micro-arc oxidation ceramic film for strengthening aluminum alloy drill pipes based on t-ZrO2, according to an embodiment of the present invention, includes the following steps:

[0036] Step 1: Aluminum alloy surface preparation;

[0037] First, the 7075 aluminum alloy drill rod is cleaned to remove oil, oxide layers, and impurities, ensuring a clean and smooth surface. This step is essential for the subsequent MAO process to achieve optimal results.

[0038] Step 2: MAO treatment;

[0039] The aluminum alloy drill pipe from step 1 is placed in an electrolytic cell, and its surface is oxidized by applying a high voltage to generate an Al2O3 ceramic film. This film possesses high hardness, corrosion resistance, and wear resistance, effectively improving the surface properties of the aluminum alloy. During this process, the thickness and density of the Al2O3 ceramic film are adjusted according to the process conditions to meet the requirements of different drilling conditions.

[0040] Step 3: Preparation of superhydrophobic t-ZrO2;

[0041] 1 g of t-ZrO2 (with 5 mol% Y2O3 doping) was weighed and added to a mixture of 50 mL EtOH and 6 mL NH3·H2O for ultrasonic dispersion. Under magnetic stirring, 0.8 mL of TEOS was added dropwise to the solution, and the mixture was stirred for 2 h. Then, 0.4 mL of PFAS was added dropwise, and stirring continued for 6 h. Finally, the mixture was filtered to obtain a filter cake, which was then dried in an oven at 60 °C to obtain powdered superhydrophobic t-ZrO2.

[0042] Step 4: Preparation of epoxy resin coating solution containing superhydrophobic t-ZrO2;

[0043] 1 g of EP and 10 mL of EtOH were mixed and stirred for 60 min, followed by the addition of 0.3 g of curing agent and stirring for another 10 min to obtain an epoxy resin coating solution. Then, 1.5 g of superhydrophobic t-ZrO2 was added, and the mixture was stirred for another 30 min to obtain an epoxy resin coating solution containing superhydrophobic t-ZrO2.

[0044] Step 5: Spray coating process;

[0045] The surface of the MAO-treated aluminum alloy drill rod was cleaned with deionized water for 2 min. A spray coating process was then employed, using the epoxy resin coating solution containing superhydrophobic t-ZrO2 prepared in step 4. The spraying distance was 15 cm, the spraying pressure was 0.6 MPa, and the spraying time was 5 s. After spraying, the sample was cured in an oven at 60°C for 6 h to obtain the coated sample.

[0046] Appendix Figure 2 The wettability of water droplets (the ultrapure water in the examples was treated with methylene blue) on the surface of superhydrophobic t-ZrO2 powder. From Figure 2 As can be seen, water droplets easily wet the unmodified t-ZrO2 powder, indicating that it exhibits hydrophilicity; however, as Figure 2 b and Figure 2 As shown in c, after modification, water droplets cannot wet the modified t-ZrO2 powder and appear as spherical shapes on its surface. The contact angle is measured to be 154°, indicating that its surface exhibits superhydrophobicity.

[0047] The prepared epoxy resin coating solution containing superhydrophobic t-ZrO2 is as follows: Figure 3 As shown, the prepared superhydrophobic coating solution is milky white, and t-ZrO2 is well dispersed and evenly distributed in it.

[0048] The dynamic contact process between the 7075 aluminum alloy drill rod after spraying and water droplets on its surface is as follows: Figure 4 As shown, from Figure 4 As can be seen from a, the surface of the 7075 aluminum alloy drill rod is very smooth; from Figure 4 As can be seen from b, after spraying the epoxy resin coating solution containing superhydrophobic t-ZrO2, a milky white coating is loaded on the surface; due to the superhydrophobic properties of the coating, it is difficult for water droplets to remain stable on the arc-shaped drill rod surface. Therefore, this invention only tests the dynamic wettability of water droplets on the drill rod surface. Figure 4 c represents the dynamic contact wettability test of the 7075 aluminum alloy drill rod surface after spraying. It can be found that the interfacial adhesion between water droplets and the coating surface is extremely low, and water droplets are difficult to adhere to its surface. This indicates that after spraying the epoxy resin coating solution containing superhydrophobic t-ZrO2, the 7075 aluminum alloy drill rod also has superhydrophobic properties.

[0049] To measure the contact angle of the coating surface of the 7075 aluminum alloy drill rod, a flat 7075 aluminum alloy block was used instead of the 7075 aluminum alloy drill rod for ease of measurement in subsequent processes.

[0050] Appendix Figure 5 The wettability of water droplets on the surface of 7075 aluminum alloy is shown. It can be seen that water droplets spread easily on the surface of 7075 aluminum alloy, and the contact angle is measured to be 40°, indicating that the surface is hydrophilic.

[0051] An epoxy resin coating was sprayed onto the surface of 7075 aluminum alloy, with... Figure 6 The figure shows the wettability of water droplets on the 7075 aluminum alloy surface after spraying. As can be seen from the figure, there is a transparent epoxy resin film on the aluminum alloy surface. The water droplets on the surface are spherical, and the contact angle is measured to be 68°, indicating that the hydrophobicity is further improved after epoxy resin spraying.

[0052] An epoxy resin coating solution containing superhydrophobic t-ZrO2 was sprayed onto the surface of 7075 aluminum alloy, with... Figure 7 The figure shows the wettability of water droplets on the 7075 aluminum alloy surface after coating. As can be seen from the figure, there is a milky white epoxy resin film containing superhydrophobic t-ZrO2 on the aluminum alloy surface. Water droplets on this surface appear spherical, and the contact angle is measured to be 151°. This indicates that after coating modification, the hydrophobicity of the 7075 aluminum alloy surface is greatly improved, changing from a hydrophilic state to a superhydrophobic state.

[0053] As attached Figure 8 As shown, the dynamic contact process of a water droplet on a 7075 aluminum alloy surface coated with a superhydrophobic t-ZrO2 epoxy resin is recorded. As the water droplet gradually moves downwards and approaches the coating (red arrow pointing downwards), its overall shape remains approximately spherical, with only slight flattening deformation at the bottom during the initial contact. Subsequently, as the droplet moves upwards, it quickly returns to its original shape and exhibits a clear rebound / detachment trend (red arrow pointing upwards), with almost no residual water or dripping appearing on the coating surface. These dynamic contact characteristics indicate that the superhydrophobic t-ZrO2 epoxy resin coating has extremely low interfacial adhesion to water droplets, making it difficult to form a stable liquid-solid adhesion state.

[0054] Microscopic observation was performed on 7075 aluminum alloy coated with a superhydrophobic t-ZrO2 epoxy resin coating (attached). Figure 9 As can be seen, t-ZrO2 is uniformly distributed in the epoxy resin, and some of t-ZrO2 is exposed, which greatly improves the surface roughness of the coating and provides the necessary conditions for the superhydrophobicity of the surface.

[0055] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for using a micro-arc oxidation ceramic film based on t-ZrO2 to strengthen aluminum alloy drill pipes, characterized in that, Includes the following steps: Step 1: Clean the surface of the aluminum alloy drill rod; Step 2: Perform MAO treatment on the cleaned aluminum alloy drill rod to form an Al2O3 ceramic film; Step 3: Prepare superhydrophobic t-ZrO2 powder; Step 4: Mix the superhydrophobic t-ZrO2 powder with epoxy resin, curing agent and solvent to prepare a coating solution; Step 5: Spray the coating solution onto the surface of the aluminum alloy drill rod after micro-arc oxidation treatment, and cure it to form a composite coating; The specific steps of step 3 are as follows: Weigh 1 g of t-ZrO2 and add it to a mixture of 50 mL EtOH and 6 mL NH3·H2O for ultrasonic dispersion; under magnetic stirring, add 0.8 mL TEOS dropwise to the above solution and stir for 2 h; then add 0.4 mL PFAS dropwise and continue stirring for 6 h; finally, filter the mixed solution to obtain a filter cake and dry it in an oven at 60 °C to obtain powdered superhydrophobic t-ZrO2.

2. The method for using a micro-arc oxidation ceramic film based on t-ZrO2-reinforced aluminum alloy drill pipe according to claim 1, characterized in that, The doping amount of Y2O3 in the t-ZrO2 is 5 mol.

3. The method for using a micro-arc oxidation ceramic film based on t-ZrO2-reinforced aluminum alloy drill pipe according to claim 1, characterized in that, The specific steps of step 4 are as follows: 1 g of EP and 10 mL of EtOH were mixed and stirred for 60 min, then 0.3 g of curing agent was added and stirred for another 10 min to obtain an epoxy resin coating solution; then 1.5 g of superhydrophobic t-ZrO2 was added and stirred for another 30 min to obtain an epoxy resin coating solution containing superhydrophobic t-ZrO2.

4. The method for using a micro-arc oxidation ceramic film based on t-ZrO2-reinforced aluminum alloy drill pipe according to claim 3, characterized in that, The specific steps of step 5 are as follows: The surface of the MAO-treated aluminum alloy drill rod was cleaned with deionized water for 2 min; a spraying process was adopted, and the coating solution was the epoxy resin coating solution containing superhydrophobic t-ZrO2 prepared in step 4. After spraying, the sample was cured in an oven at 60°C for 6 h to obtain the coating sample.

5. The method for using a micro-arc oxidation ceramic film based on t-ZrO2-reinforced aluminum alloy drill pipe according to claim 4, characterized in that, In step 5, the spraying distance is 15 cm, the spraying pressure is 0.6 MPa, and the spraying time is 5 s.

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