Preparation method of corrosion-resistant coating of aluminum alloy pipe

Abstract

The invention discloses a preparation method of a corrosion-resistant coating of an aluminum alloy pipe, a weakly alkaline electrolyte system (NaSiO3) is adopted for surface modification, and compared with an acidic or strongly alkaline electrolyte system commonly used in the prior art, the preparation method has the remarkable advantages that the environmental protection property is high, harmful waste liquid is not generated, and pollutant emission is reduced. The pulse laser is used for replacing a traditional high-voltage discharge technology (such as 400-800 V high voltage in MAO), energy consumption can be remarkably reduced, meanwhile, the machining efficiency is improved, and energy is saved. The generated oxide layer is compact, uniform and stable, contains a gamma-Al2O3 crystal phase, obviously improves the corrosion resistance and mechanical strength of the surface, and shows an excellent corrosion resistance effect especially in a high-chlorine environment.

Description

Technical Field

[0001] The invention relates to the field of material surface modification, and in particular to a method for preparing a corrosion-resistant coating of an aluminum alloy pipe. Background Art

[0002] In actual practical use, aluminum alloy pipes are prone to serious corrosion problems, especially when in contact with chloride media (such as seawater), which in turn damages the integrity of the structure and significantly increases maintenance costs. Specifically, aluminum alloys are prone to local corrosion, stress corrosion cracking and pitting in chloride environments, especially under conditions of high temperature, high humidity and high flow rate. The root cause is that the natural oxide film (Al2O3) formed on the surface of aluminum alloys usually has problems such as poor uniformity, strong porosity and amorphous state, resulting in poor integrity of the protective layer. Therefore, the oxide layer is easily affected by the penetration of chloride ions, further destroying the protective effect of the metal matrix and causing corrosion to intensify. In addition, the chemical stability of aluminum alloys themselves is poor. Under extreme environmental conditions (such as seawater or industrial coolants containing chlorides), electrochemical corrosion may occur, and even perforations may be formed on the pipe wall, resulting in reduced heat exchange performance and equipment failure. As the corrosion deepens, the mechanical properties of aluminum alloy pipes will also be significantly affected, resulting in embrittlement and reduced strength of the material, which may eventually lead to premature failure of aluminum alloy pipes. Therefore, how to effectively improve the corrosion resistance of aluminum alloy pipes in chloride environments has become an important research topic.

[0003] The prior art of manufacturing corrosion-resistant coatings for aluminum alloy pipes requires a large amount of energy input and expensive reinforcing materials. The corrosion-resistant coatings for aluminum alloy pipes provide insufficient corrosion resistance in chlorine-rich environments. The surfaces of the corrosion-resistant coatings for aluminum alloy pipes often lack strength and durability, thereby limiting their anti-corrosion capabilities.

[0004] Therefore, there is an urgent need to develop a method for preparing a corrosion-resistant coating for aluminum alloy pipes. Summary of the invention

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] A method for preparing a corrosion-resistant coating for an aluminum alloy pipe comprises the following steps:

[0007] (1) Grind the aluminum alloy pipe to be coated with 250 mesh, 500 mesh, and 800 mesh metallographic sandpaper in sequence;

[0008] (2) Using an electronic balance, weigh solid sodium silicate and dissolve it in deionized water to a concentration of 14-16 g / L, and then add a hydrogen peroxide solution to the water to a concentration of 2.0-2.5 g / L; then place the aluminum alloy pipe in a flat-bottomed container and pour the prepared solution into the container until the liquid level is 2-4 mm above the upper surface of the aluminum alloy.

[0009] (3) Adjust the parameters of the pulse laser beam modulation equipment: power is 80-90W, pulse width is 200-220ns, frequency is 500-510kHz, moving speed is 100-110mm / min, adjust the distance between the laser output device and the aluminum alloy pipe to the optimal focal length and scan back and forth 20-25 times.

[0010] (4) After the laser treatment, cool in the prepared solution for 1-2 hours. After cooling, take out from the solution and dry at room temperature for 24-30 hours.

[0011] Preferably, in step (2), the concentration of sodium silicate in the prepared solution is 16 g / L.

[0012] Preferably, in step (2), the concentration of hydrogen peroxide in the prepared solution is 2.5 g / L.

[0013] Preferably, the solution prepared in step (2) covers the upper surface of the aluminum alloy pipe by 2 mm.

[0014] Furthermore, the optimal focal length of the laser output device is 26 cm.

[0015] Furthermore, in step (3), the parameters of the pulse laser beam modulation equipment are adjusted: the power is 80 W, the pulse width is 220 ns, the frequency is 500 kHz, the moving speed is 100 mm / min, and the distance between the laser output device and the aluminum alloy pipe is adjusted to the optimal focal length and scanned back and forth 20 times.

[0016] Furthermore, in step (4), after the laser treatment is completed, the mixture is cooled in the prepared solution for 1 hour, and after cooling, it is taken out of the solution and dried at room temperature for 24 hours.

[0017] Due to the adoption of the above technical solution, the present invention has the following technical advances compared with the prior art:

[0018] 1. The present invention adopts a weak alkaline electrolyte system (NaSiO3) for surface modification. Compared with the acidic or strong alkaline electrolyte system commonly used in the prior art, it has the significant advantages of being highly environmentally friendly, not generating harmful waste liquid, and reducing pollutant emissions.

[0019] 2. The present invention replaces the traditional high-voltage discharge technology (such as 400-800V high voltage in MAO) with pulsed laser, which can significantly reduce energy consumption, improve processing efficiency and save energy.

[0020] 3. The oxide layer generated by the present invention is dense, uniform and stable, and contains γ-Al2O3 crystal phase, which significantly improves the corrosion resistance and mechanical strength of the surface, especially in a high-chlorine environment, showing excellent corrosion resistance.

[0021] 4. The present invention can be implemented under normal pressure or low pressure conditions, without the need for high-voltage discharge equipment or additional cooling systems, thereby significantly reducing equipment costs and overall process costs.

[0022] 5. The present invention realizes the grain refinement and mechanical strength optimization of the aluminum alloy surface through laser processing, improves the corrosion resistance and hardness of the surface, and enhances the density and uniformity of the coating.

[0023] 6. The process of the present invention is simple and applicable to a variety of aluminum alloy materials, especially the modification effect on aluminum alloy substrates is particularly significant, and can be widely used in aviation, shipbuilding, automobile and other industrial fields.

[0024] 7. The NaSiO3 electrolyte raw material used in the present invention is cheap and easily available, and the process flow is simple, which significantly reduces the production cost and has the potential for large-scale industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0026] Figure 1 This is a comparison group of electrochemical polarization curves of the samples obtained in Example 1 and Comparative Examples 1-2.

[0027] Figure 2 This is a group of SEM comparison images of samples obtained in Example 1 and Comparative Examples 1-2, wherein images ac are original surface morphologies. DETAILED DESCRIPTION

[0028] The following embodiments may help those skilled in the art to more fully understand the present invention, but shall not limit the present invention in any way.

[0029] Example

[0030] A method for preparing a corrosion-resistant coating for an aluminum alloy pipe comprises the following steps:

[0031] (1) Grind the aluminum alloy pipe to be coated with 250 mesh, 500 mesh, and 800 mesh metallographic sandpaper in sequence;

[0032] (2) Using an electronic balance, weigh solid sodium silicate and dissolve it in deionized water to a concentration of 14-16 g / L, and then add a hydrogen peroxide solution to the water to a concentration of 2.0-2.5 g / L; then place the aluminum alloy pipe in a flat-bottomed container and pour the prepared solution into the container until the liquid level is 2-4 mm above the upper surface of the aluminum alloy.

[0033] (3) Adjust the parameters of the pulse laser beam modulation equipment: power is 80-90W, pulse width is 200-220ns, frequency is 500-510kHz, moving speed is 100-110mm / min, adjust the distance between the laser output device and the aluminum alloy pipe to the optimal focal length and scan back and forth 20-25 times.

[0034] (4) After the laser treatment, cool in the prepared solution for 1-2 hours. After cooling, take out from the solution and dry at room temperature for 24-30 hours.

[0035] In one embodiment of the present invention, in step (2), the concentration of sodium silicate in the prepared solution is 16 g / L.

[0036] In one embodiment of the present invention, in step (2), the concentration of hydrogen peroxide in the prepared solution is 2.5 g / L.

[0037] Too high a concentration of sodium silicate or hydrogen peroxide will increase the corrosion current density, while too low a concentration will reduce the content of γ-Al2O3 crystal phase on the surface.

[0038] In one embodiment of the present invention, the solution prepared in step (2) covers the upper surface of the aluminum alloy tube by 2 mm.

[0039] Furthermore, the optimal focal length of the laser output device is 26 cm.

[0040] In one embodiment of the present invention, the model of the pulse laser beam modulation device is HGTECH LSF200C.

[0041] Furthermore, in step (3), the parameters of the pulse laser beam modulation equipment are adjusted: the power is 80 W, the pulse width is 220 ns, the frequency is 5000 kHz, the moving speed is 100 mm / min, and the distance between the laser output device and the aluminum alloy pipe is adjusted to the optimal focal length and scanned back and forth 20 times.

[0042] Furthermore, in step (4), after the laser treatment is completed, the mixture is cooled in the prepared solution for 1 hour, and after cooling, it is taken out of the solution and dried at room temperature for 24 hours.

[0043] Example 1

[0044] (1) Wire EDM processing: Place the aluminum alloy pipe on the fixed table of the wire EDM machine, and then set the wire EDM machine parameters to pulse width 60, pulse interval c, power amplifier c, and cut at a speed of 250 steps per minute to 30×15×10cm 3 Then, the cut aluminum alloy pipes were polished with 250 mesh, 500 mesh, and 800 mesh metallographic sandpapers in turn.

[0045] (2) Solution preparation: 2.605 g of solid sodium silicate was weighed using an electronic balance and dissolved in 140 mL of deionized water to a concentration of 16 g / L, followed by the addition of 6 mL of hydrogen peroxide to a concentration of 2.5 g / L. The aluminum alloy pipe was then placed in a flat-bottomed glass container, and the prepared solution was poured in until the liquid level was 2 mm above the upper surface of the aluminum alloy pipe.

[0046] (3) Adjust the parameters of the pulse laser beam modulation equipment: power is 80 W, pulse width is 220 ns, frequency is 500 kHz, moving speed is 100 mm / min, adjust the distance between the laser output device and the aluminum alloy pipe to the optimal focal length and control the programmable logic controller to scan back and forth 20 times.

[0047] (4) Cooling, waiting and drying: After the laser treatment, the aluminum alloy pipe is cooled in the prepared solution for 1 hour. After cooling, it is taken out of the solution and dried at room temperature for 24 hours.

[0048] Comparative Example 1

[0049] (1) Wire EDM processing: Place the aluminum alloy pipe or aluminum alloy block on the fixed table of the wire EDM machine, and then set the parameters of the wire EDM machine to pulse width 60, pulse interval c, power amplifier c, and cut at a speed of 250 steps per minute to 30×15×10cm 3 Then, the cut aluminum alloy pipes were polished with 250 mesh, 500 mesh, and 800 mesh metallographic sandpapers in turn.

[0050] Comparative Example 2

[0051] (1) Wire EDM processing: Place the aluminum alloy pipe or aluminum alloy block on the fixed table of the wire EDM machine, and then set the parameters of the wire EDM machine to pulse width 60, pulse interval c, power amplifier c, and cut at a speed of 250 steps per minute to 30×15×10cm 3 Then, the cut aluminum alloy pipes were polished with 250 mesh, 500 mesh, and 800 mesh metallographic sandpapers in turn.

[0052] (2) Adjust the parameters of the pulse laser beam modulation equipment: power is 80 W, pulse width is 220 ns, frequency is 500 kHz, moving speed is 100 mm / min, adjust the distance between the laser output device and the aluminum alloy pipe to the optimal focal length and control the programmable logic controller to scan back and forth 20 times.

[0053] Electrochemical corrosion testing

[0054] To evaluate the corrosion resistance of the oxide layer of each sample, a potentiodynamic polarization test was performed using an electrochemical workstation. Before the test, all samples were cleaned with ethanol and acetone in sequence and dried thoroughly. The test used a three-electrode system, in which the sample was used as the working electrode, the saturated calomel electrode (SCE) was used as the reference electrode, and the platinum electrode was used as the counter electrode.

[0055] During the experiment, the sample was first immersed in a 3.5wt.% NaCl solution, left to stand for 40 minutes to ensure that the open circuit potential (OCP) was stable, and then the electrochemical test was performed. The dynamic potential polarization curve was scanned at a rate of 0.33mV / s, a sampling frequency of 1Hz, and a potential range of -0.25V to 0.5V. The EIS test applied a sinusoidal signal with an amplitude of 50mV and a frequency range from 10-2Hz to 105Hz. The data analysis used the Taaffe extrapolation method. In order to ensure the reliability of the results, each sample was tested three times and the average value was taken as the final result. The data is organized into a table as follows:

[0056] Table 1 Polarization curve data and Nyquist data table of each sample

[0057] Sample corrosion potential (V) Corrosion current density (Acm -2 ) Charge transfer resistance (Ωcm -2 )

[0058] Example 1 -0.6104 5.64×10-9 6.97×105

[0059] Comparative Example 1 -0.9392 4.70×10-6 4.10×104

[0060] Comparative Example 2 -0.7568 5.75×10-7 9.69×104

[0061] When the corrosion potential is more positive and the corrosion current density is lower, it often indicates that it is easier to form an effective protective layer or passivation film on the coating surface, thereby improving its corrosion resistance. By combining these two parameters, the corrosion resistance of the coating can be evaluated as a whole. As can be seen from Table 1, Example 1 has the lowest corrosion current density and the most positive corrosion potential, indicating that the NaSiO3 electrolyte solution can effectively block the entry of corrosive media during the coating preparation process, thereby giving the coating more excellent corrosion resistance. Table 1 lists the Tafel fitting results of the potentiodynamic polarization curves of the three samples. Among them, the corrosion potential of Example 1 is -0.6104V, and the corrosion current density is only 5.64×10-9A cm -2 ,and Figure 1 The polarization curves shown are consistent. Compared with the comparative examples, the corrosion current density of Example 1 is 3 orders of magnitude lower than that of Comparative Example 1 and 2 orders of magnitude lower than that of Comparative Example 2, highlighting its excellent corrosion resistance.

[0062] Surface morphology

[0063] Scanning electron microscopy was used to analyze the surface morphology of each sample coating. Figure 2 (ac) show the microstructures of Example 1, Comparative Example 1 and Comparative Example 2 (magnification is 300 times). The results show that the surface of Example 1 has a porous structure with different pore sizes and significant metal remelting and accumulation characteristics. The formation of the porous structure is mainly attributed to the ablation process under the action of the pulsed laser and the bubble formation in the metal remelting stage. These bubbles come from the rise of the internal gas and the reaction in the plasma zone. The metal remelting and accumulation are related to the rapid melting caused by the pulsed laser heating and the rapid cooling promoted by the electrolyte. These holes are small shallow pits rather than through holes. In Comparative Example 2, due to the extremely poor thermal conductivity of the air, the heat inside the substrate is difficult to dissipate in time, resulting in the molten substrate covering the laser-induced small pits, and the subsequent plasma plume and the overflow of the internal gas will cause larger channels to form on the molten surface.

[0064] The above generally describes the present invention in detail, but it is obvious to a person skilled in the art that some modifications or improvements can be made to the present invention. Therefore, modifications or improvements that do not depart from the spirit of the present invention are within the scope of protection of the present invention.

Claims

1. A method for preparing a corrosion-resistant coating for an aluminum alloy pipe, characterized in that: The following steps are involved: (1) Grind the aluminum alloy pipe to be coated with 250 mesh, 500 mesh, and 800 mesh metallographic sandpaper in sequence; (2) using an electronic balance to weigh solid sodium silicate and dissolve it in deionized water to a concentration of 14-16 g / L, and then adding a hydrogen peroxide solution to the deionized water to a concentration of 2.0-2.5 g / L; then placing the aluminum alloy pipe in a flat-bottomed container, and pouring the prepared solution into the container until the liquid level is 2-4 mm above the upper surface of the aluminum alloy; (3) Adjust the parameters of the pulse laser beam modulation equipment: power is 80-90W, pulse width is 200-220ns, frequency is 500-510kHz, moving speed is 100-110mm / min, adjust the distance between the laser output device and the aluminum alloy pipe to the optimal focal length and scan back and forth 20-25 times; (4) After the laser treatment, cool in the prepared solution for 1-2 hours. After cooling, take out from the solution and dry at room temperature for 24-30 hours.

2. The method for preparing the corrosion-resistant coating of the aluminum alloy pipe according to claim 1, characterized in that: In step (2), the sodium silicate concentration in the prepared solution is 16 g / L.

3. The method for preparing the corrosion-resistant coating of the aluminum alloy pipe according to claim 1, characterized in that: In step (2), the concentration of hydrogen peroxide in the prepared solution is 2.5 g / L.

4. The method for preparing the corrosion-resistant coating of the aluminum alloy pipe according to claim 1, characterized in that: Step (2) The solution is prepared to cover the upper surface of the aluminum alloy pipe by 2 mm.

5. The method for preparing the corrosion-resistant coating of the aluminum alloy pipe according to claim 1, characterized in that: In step (3), the parameters of the pulse laser beam modulation equipment are adjusted: the power is 80 W, the pulse width is 220 ns, the frequency is 500 kHz, the moving speed is 100 mm / min, the distance between the laser output device and the aluminum alloy pipe is adjusted to the optimal focal length and scan back and forth 20 times.

6. The method for preparing the corrosion-resistant coating of the aluminum alloy pipe according to claim 4, characterized in that: In step (4), after the laser treatment is completed, the sample is cooled in the prepared solution for 1 hour. After cooling, the sample is taken out of the solution and dried at room temperature for 24 hours.

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