Surface corrosion-resistant coating for die-cast magnesium alloys and method for its production and use

Abstract

The application discloses a preparation method of a die-casting magnesium alloy surface corrosion-resistant coating, and the die-casting magnesium alloy substrate is immersed into a sodium silicate aqueous solution to perform a hydrothermal reaction, so that the die-casting magnesium alloy with the corrosion-resistant coating is obtained. The sodium silicate aqueous solution is used as an in-situ growth solution, the corrosion-resistant coating prepared through one-step hydrothermal reaction has excellent bonding force with the die-casting magnesium alloy substrate, the corrosion-resistant coating is formed by a large number of particles with small particle size, uniform distribution and close combination, has excellent compactness and barrier performance, can effectively prevent the corrosion of corrosive ions in the outside world on the magnesium alloy, and then effectively improves the corrosion resistance of the die-casting magnesium alloy, and further promotes the wide application of the magnesium alloy in the fields of aviation, aerospace, automobiles, electronics and the like. In the whole preparation process, no reagent is involved, only the sodium silicate aqueous solution is used, and the cost is low and the environment is not polluted.

Description

Technical Field

[0001] This invention belongs to the field of metal surface treatment technology, specifically relating to a corrosion-resistant coating for die-cast magnesium alloy surfaces, its preparation method, and its application. Background Technology

[0002] Magnesium alloys are among the lightest known metallic structural materials, with a density approximately two-thirds that of aluminum alloys and far lower than that of steel. Magnesium is abundant in the Earth's crust, and its mining and smelting processes are relatively energy-efficient, meeting the requirements for environmentally friendly materials. Although the absolute strength of magnesium alloys is not as high as that of steel, their high specific strength and specific stiffness make them stand out in lightweight structural applications. Furthermore, magnesium alloys possess excellent vibration reduction and damping properties, effectively reducing vibration and noise, giving them a significant advantage in fields requiring high dynamic stability, such as automobiles, aerospace, and electronic equipment. In particular, magnesium alloys have excellent machinability; through processes such as die casting, extrusion, and forging, complex-shaped workpieces can be manufactured, and modern processing technologies (such as laser processing and CNC machining) ensure the precision of magnesium alloy components.

[0003] Die-cast magnesium alloys are produced using a high-pressure die-casting process, where molten metal is injected into a mold under high pressure and rapidly solidified into a magnesium alloy. Compared to deformation and casting processes, die casting offers advantages such as high production efficiency, precision casting capabilities, and superior alloy surface quality. Therefore, die-cast magnesium alloys can achieve rapid prototyping of high-precision and complex structural parts, meeting the requirements of high-end applications and enabling large-scale industrial production.

[0004] However, die-cast magnesium alloys are no exception to the common problem of poor corrosion resistance. Especially in harsh service environments containing water or chlorine, magnesium alloys are highly susceptible to pitting corrosion, galvanic corrosion, and stress corrosion, severely hindering their widespread application in practical engineering. Therefore, slowing down or even inhibiting the corrosion rate of magnesium alloys and improving their corrosion resistance is a research hotspot in this field.

[0005] Alloying, optimizing the die-casting process, and surface coating are three main methods to improve the corrosion resistance of die-cast magnesium alloys. Alloying involves adding one or more alloying elements and some rare earth elements to magnesium to regulate the microstructure and the formation and distribution of the second phase, thereby refining the grain structure, reducing the internal defect rate, and effectively improving the overall uniformity and corrosion protection of the material. However, alloying often involves the addition of rare earth elements (such as Y and Nd), which are expensive, increasing alloy costs and hindering large-scale industrial production. Furthermore, the addition of certain elements may reduce the alloy's fluidity and filling capacity, increasing casting defects during the die-casting process and directly affecting product quality.

[0006] Optimizing die-casting parameters, such as melt temperature, mold temperature, injection speed, and pressure, can help reduce defects like porosity and shrinkage in die-cast parts, improve their density, and thus enhance the corrosion resistance of magnesium alloys. However, improving process parameters places stricter demands on equipment, requiring more precise control systems and advanced equipment, which increases initial investment and maintenance costs. Furthermore, while optimizing the die-casting process can improve the density and surface quality of die-cast magnesium alloys to some extent, the high chemical reactivity of magnesium alloys means that simply optimizing the process cannot fundamentally solve the problem of poor corrosion resistance.

[0007] Surface coating is one of the most common and effective methods for improving the corrosion resistance of metals in engineering practice. Coatings form a protective layer on the metal surface, preventing direct contact between oxygen, moisture, and corrosive media and the metal substrate, thereby reducing or preventing corrosion reactions. Furthermore, there are many types of surface coating technologies, including micro-arc oxidation, chemical conversion, and electrophoretic coating, suitable for die-cast parts of different shapes and sizes. Coating processes can be rationally selected according to specific needs, demonstrating strong applicability. In particular, compared with alloying and optimized die-casting processes, surface coating technology is simpler to operate and requires less skilled workers. However, some coating processes use chemical reagents that are not environmentally friendly, causing pollution and failing to meet the requirements of green manufacturing. In addition, some coatings have poor adhesion to the magnesium alloy substrate and insufficient mechanical durability, making them prone to peeling during use and unable to provide continuous protection. Summary of the Invention

[0008] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, the main objective of this invention is to provide a method for preparing a low-cost, easy-to-operate, environmentally friendly, easily industrialized, and in-situ-grown anti-corrosion coating for die-cast magnesium alloy surfaces.

[0009] The objective of this invention is achieved through the following technical solution: A method for preparing a corrosion-resistant coating on the surface of a die-cast magnesium alloy involves immersing a die-cast magnesium alloy substrate in an in-situ growth solution for a hydrothermal reaction to obtain a die-cast magnesium alloy with a corrosion-resistant coating, wherein the in-situ growth solution is an aqueous solution of sodium silicate.

[0010] This invention utilizes a one-step hydrothermal method to construct a dense protective coating with excellent corrosion resistance on the surface of die-cast magnesium alloys in situ.

[0011] In some specific embodiments, the concentration of the sodium silicate aqueous solution is 0.01-0.1 M.

[0012] In some specific embodiments, the process parameters for the hydrothermal reaction are: hydrothermal reaction at 100-150 ºC for 2-7 hours.

[0013] Furthermore, the process parameters for the hydrothermal reaction are: hydrothermal reaction at 120-140 ºC for 3-6 hours.

[0014] Furthermore, the process parameters for the hydrothermal reaction are: hydrothermal reaction at 150 ºC for 2 hours.

[0015] In some specific embodiments, the die-cast magnesium alloy matrix before hydrothermal reaction is further subjected to water grinding.

[0016] As part of the same inventive concept, the present invention also provides a corrosion-resistant coating for the surface of die-cast magnesium alloys.

[0017] As part of the same inventive concept, this invention also provides the application of the method for preparing the anti-corrosion coating on the surface of the die-cast magnesium alloy in the surface treatment of magnesium alloys.

[0018] Furthermore, the method for preparing the anti-corrosion coating of the present invention is also applicable to wrought magnesium alloys, aluminum alloys, titanium alloys, steel, etc., and has good versatility.

[0019] As part of the same inventive concept, this invention also provides the application of the anti-corrosion coating on the surface of the die-cast magnesium alloy in the fields of aerospace, automotive, and electronics.

[0020] Compared with the prior art, the present invention has at least the following advantages: 1) The preparation method of the present invention uses sodium silicate aqueous solution as in-situ growth liquid to prepare a corrosion-resistant coating in one step of hydrothermal reaction. The corrosion-resistant coating is composed of a large number of small, uniformly distributed and tightly bonded particles, which are firmly bonded to the die-cast magnesium alloy matrix and have a compact structure. This effectively blocks the erosion of corrosive ions and significantly improves the corrosion resistance of the die-cast magnesium alloy.

[0021] 2) The preparation method of the present invention does not involve any reagents in the entire preparation process, and only uses pure water and sodium silicate. No harmful reagents are added, the cost is low, and there is no pollution to the environment. The whole process is simple, safe and pollution-free, which meets the requirements of sustainable development and large-scale industrial production. This technology is expected to further promote the widespread application of magnesium alloys in many research fields such as aerospace, automobile manufacturing, and electronic devices. Attached Figure Description

[0022] To more clearly illustrate the specific embodiments of the present invention, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below.

[0023] Figure 1This is a scanning electron microscope image of the anti-corrosion coating (120ºC, 1 hour) on the surface of the die-cast magnesium alloy in Example 1; Figure 2 The X-ray diffraction pattern is the anti-corrosion coating (120ºC, 1 hour) on the surface of the die-cast magnesium alloy in Example 1. Figure 3 The infrared spectrum of the anti-corrosion coating (120ºC, 1 hour) on the surface of the die-cast magnesium alloy in Example 1 is shown. Figure 4 These are the Tafel polarization curves of AM50 die-cast magnesium alloy and corrosion-resistant coated (120ºC, 1 hour) magnesium alloy in Example 1 on the same coordinate system. Figure 5 This is a scanning electron microscope image of the anti-corrosion coating (120ºC, 5 hours) on the surface of the die-cast magnesium alloy in Example 2; Figure 6 This is the X-ray diffraction pattern of the anti-corrosion coating (120ºC, 5 hours) on the surface of the die-cast magnesium alloy in Example 2; Figure 7 This is the infrared spectrum of the anti-corrosion coating (120ºC, 5 hours) on the surface of the die-cast magnesium alloy in Example 2; Figure 8 These are the Tafel polarization curves of AM50 die-cast magnesium alloy and corrosion-resistant coated (120ºC, 5 hours) magnesium alloy in Example 2 on the same coordinate system. Figure 9 This is a scanning electron microscope image of the anti-corrosion coating (150ºC, 2 hours) on the surface of the die-cast magnesium alloy in Example 3; Figure 10 The X-ray diffraction pattern is the anti-corrosion coating (150ºC, 2 hours) on the surface of the die-cast magnesium alloy in Example 3; Figure 11 The infrared spectrum of the anti-corrosion coating (150ºC, 2 hours) on the surface of the die-cast magnesium alloy in Example 3 is shown. Figure 12 These are the Tafel polarization curves of AM50 die-cast magnesium alloy and anti-corrosion coated (150ºC, 2 hours) magnesium alloy in Example 3 on the same coordinate system. Figure 13 This is an adhesion test diagram of the anti-corrosion coating (150ºC, 2 hours) on the surface of the die-cast magnesium alloy in Example 3. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The following embodiments are merely descriptive and not limiting, and should not be construed as limiting the scope of protection of the present invention.

[0025] When a quantity, concentration, or other value or parameter is described as a range, preferred range, or preferred upper and lower limits, it should be understood that it is equivalent to specifically disclosing any range by combining any pair of upper or preferred values ​​with any lower or preferred values, regardless of whether the range is specifically disclosed. Unless otherwise stated, the numerical range values ​​listed herein include the endpoints of the range and all integers and fractions within that range.

[0026] Unless otherwise stated, all percentages, parts, ratios, etc. in this document are by weight.

[0027] The materials, methods, and embodiments described herein are exemplary and should not be construed as limiting unless otherwise stated.

[0028] In the following embodiments, the die-cast magnesium alloy substrate is subjected to a water-grinding process as follows: the die-cast magnesium alloy substrate is ground with 150, 600, 800, 1200 and 2000# sandpaper respectively, then ultrasonically cleaned with alcohol for 5 minutes and dried to obtain the water-grinded die-cast magnesium alloy substrate.

[0029] Example 1 This embodiment provides a method for preparing an anti-corrosion coating on the surface of a die-cast magnesium alloy, which includes the following steps: A 0.01 M sodium silicate aqueous solution was poured into the inner liner of the reactor, and then the water-milled die-cast magnesium alloy AM50 sample was placed into the sodium silicate aqueous solution. After sealing the reactor, it was placed in an electric oven for in-situ growth at a reaction temperature of 120ºC and a constant temperature reaction time of 1 hour to obtain a die-cast magnesium alloy with an anti-corrosion coating on its surface.

[0030] This application conducts performance tests on the die-cast magnesium alloy with a corrosion-resistant coating grown on its surface, prepared in this embodiment, specifically as follows: 1) Microscopic morphology The die-cast magnesium alloy with an anti-corrosion coating grown on its surface in this embodiment was observed using a scanning electron microscope (SEM), and the SEM image is shown below. Figure 1 As shown, observations revealed that the sample surface was uniformly covered with a large number of tiny particles, exhibiting typical granular structure characteristics. These particles are small in size and densely distributed, and may be oxides, deposits, or crystal particles generated during the reaction process, indicating significant nucleation and growth behavior on the material surface. However, obvious cracks were still visible in some areas. These cracks mostly extended along the interparticle gaps or interfaces, indicating that the bonding between particles was not dense enough, or that thermal stress concentration and uneven shrinkage occurred during cooling and drying.

[0031] The die-cast magnesium alloy with an anti-corrosion coating grown on its surface in this embodiment was characterized by XRD and infrared spectroscopy. Its X-ray diffraction pattern is shown below. Figure 2 As shown in the figure, the coating is mainly composed of the Mg(OH)2 phase. Characteristic diffraction peaks of Mg(OH)2 can be observed at 2θ ≈ 18.5°, 38.0°, and 50.8° in the XRD pattern, indicating that magnesium hydroxide products are generated during the coating growth process.

[0032] Its infrared spectrum is as follows Figure 3 As shown in the figure, the range is 3200–3600 cm. -1 O–H stretching vibration peaks appeared in the range of 1000–1100 cm⁻¹, which is related to adsorbed water or crystalline water present in the anti-corrosion coating; -1 The presence of Si–O stretching vibration peaks is mainly attributed to sodium silicate in the in-situ growth solution. In a hydrothermal environment, sodium silicate hydrolyzes to Si(OH)4, which then undergoes a condensation reaction to form a Si–O–Si network, which is deposited and solidified into a film on the surface of the die-cast magnesium alloy substrate.

[0033] 2) Electrochemical performance This embodiment also tested the electrochemical performance of AM50 die-cast magnesium alloy and anti-corrosion coated die-cast magnesium alloy. Specifically, the polarization curves of the die-cast magnesium alloy sample and the magnesium alloy sample with anti-corrosion coating on its surface were tested in 3.5 wt.% sodium chloride solution using an electrochemical workstation (Princeton 4000A).

[0034] The Tafel polarization curves of AM50 die-cast magnesium alloy and corrosion-resistant coated die-cast magnesium alloy (film) in this application are shown in the following figures. Figure 4 As shown in the figure, the corrosion voltage of the exposed AM50 die-cast magnesium alloy is -1.47 V, while the corrosion voltage of the die-cast magnesium alloy with the anti-corrosion coating is -1.41 V. Therefore, compared with the exposed die-cast magnesium alloy substrate, the preparation of the anti-corrosion coating significantly increases its corrosion voltage, and from a thermodynamic point of view, the corrosion tendency of the magnesium alloy substrate decreases.

[0035] From a kinetic perspective, corrosion rate and corrosion resistance are directly related to corrosion current density. The corrosion current density of exposed AM50 die-cast magnesium alloy is 1.52 × 10⁻⁶. -5 A cm -2 The corrosion current density of the anti-corrosion coated die-cast magnesium alloy is 1.39 × 10⁻⁶. -6 A cm -2Compared to the exposed die-cast magnesium alloy substrate, the corrosion current density of the sample with the anti-corrosion coating was reduced by an order of magnitude. This indicates that the anti-corrosion coating constructed on the surface of AM50 die-cast magnesium alloy by this invention can achieve excellent anti-corrosion protection, effectively preventing the intrusion of corrosive media, thereby significantly improving the corrosion resistance of the substrate material. In summary, the anti-corrosion coating on the surface of die-cast magnesium alloy involved in this invention has excellent anti-corrosion performance and can continuously and effectively protect the magnesium alloy substrate under harsh service environments, preventing it from corrosion damage.

[0036] Example 2 This embodiment provides a method for preparing an anti-corrosion coating on the surface of a die-cast magnesium alloy, which includes the following steps: A 0.01 M sodium silicate aqueous solution was poured into the inner liner of the reactor, and then the water-milled die-cast magnesium alloy AM50 sample was placed into the sodium silicate aqueous solution. After sealing the reactor, it was placed in an electric oven for in-situ growth at a reaction temperature of 120 ºC and a constant temperature reaction time of 5 hours to obtain a die-cast magnesium alloy with an anti-corrosion coating on its surface.

[0037] This application conducts performance tests on the die-cast magnesium alloy with a corrosion-resistant coating grown on its surface, prepared in this embodiment, specifically as follows: 1) Microscopic morphology The die-cast magnesium alloy with an anti-corrosion coating grown on its surface in this embodiment was observed using a scanning electron microscope (SEM), and the SEM image is shown below. Figure 5 As shown in the figure, with the extension of reaction time, the coating surface is still uniformly covered with a large number of tiny particles, and the particle structure remains well maintained and is tightly arranged; compared with Figure 1 In contrast, the previously noticeable cracks in the coating have largely disappeared with the extension of hydrothermal time, and the surface has become more continuous and smooth, with no signs of through cracks or interface peeling. The particles still have a spherical or polyhedral structure, are small in size, and are densely distributed, indicating that the coating has undergone a more complete growth, crystallization, and rearrangement process during the longer hydrothermal reaction, thus effectively alleviating the cracking phenomenon caused by local stress concentration and structural voids.

[0038] The die-cast magnesium alloy with an anti-corrosion coating grown on its surface in this embodiment was characterized by XRD and infrared spectroscopy. Its X-ray diffraction pattern is shown below. Figure 6 As shown in the figure, the coating is mainly composed of the Mg(OH)2 phase. Characteristic diffraction peaks of Mg(OH)2 can be observed at 2θ ≈ 18.5°, 38.0°, and 50.8° in the XRD pattern, indicating that magnesium hydroxide products are generated during the coating growth process.

[0039] Its infrared spectrum is as follows Figure 7As shown in the figure, the range is 3200–3600 cm. -1 O–H stretching vibration peaks appeared in the range of 1000–1100 cm⁻¹, which is related to adsorbed water or crystalline water present in the anti-corrosion coating; -1 The presence of Si–O stretching vibration peaks is mainly attributed to sodium silicate in the in-situ growth solution. In a hydrothermal environment, sodium silicate hydrolyzes to Si(OH)4, which then undergoes a condensation reaction to form a Si–O–Si network, which is deposited and solidified into a film on the surface of the die-cast magnesium alloy substrate.

[0040] 2) Electrochemical performance This embodiment also tested the electrochemical performance of AM50 die-cast magnesium alloy and anti-corrosion coated die-cast magnesium alloy. Specifically, the polarization curves of the die-cast magnesium alloy sample and the magnesium alloy sample with anti-corrosion coating on its surface were tested in 3.5 wt.% sodium chloride solution using an electrochemical workstation (Princeton 4000A).

[0041] The Tafel polarization curves of AM50 die-cast magnesium alloy and corrosion-resistant coated die-cast magnesium alloy (film) in this application are shown in the following figures. Figure 8 As shown in the figure, the corrosion voltage of the exposed AM50 die-cast magnesium alloy is -1.47 V, while the corrosion voltage of the die-cast magnesium alloy with the anti-corrosion coating is -1.34 V. Therefore, compared with the exposed die-cast magnesium alloy substrate, the preparation of the anti-corrosion coating significantly increases its corrosion voltage, and from a thermodynamic point of view, the corrosion tendency of the magnesium alloy substrate decreases.

[0042] From a kinetic perspective, corrosion rate and corrosion resistance are directly related to corrosion current density. The corrosion current density of exposed AM50 die-cast magnesium alloy is 1.52 × 10⁻⁶. -5 A cm -2 The corrosion current density of the anti-corrosion coated die-cast magnesium alloy is 1.35 × 10⁻⁶. -7 A cm -2 Compared to the exposed die-cast magnesium alloy substrate, the corrosion current density of the sample with the anti-corrosion coating was reduced by two orders of magnitude. This indicates that the anti-corrosion coating constructed on the surface of AM50 die-cast magnesium alloy by this invention can achieve a significant anti-corrosion protection effect, effectively preventing the intrusion of corrosive media, thereby significantly improving the corrosion resistance of the substrate material. In summary, the anti-corrosion coating on the surface of die-cast magnesium alloy involved in this invention has excellent anti-corrosion performance and can continuously and effectively protect the magnesium alloy substrate under harsh service environments, preventing it from corrosion damage.

[0043] Example 3 This embodiment provides a method for preparing an anti-corrosion coating on the surface of a die-cast magnesium alloy, which includes the following steps: A 0.01 M sodium silicate aqueous solution was poured into the inner liner of the reactor, and then the water-milled die-cast magnesium alloy AM50 sample was placed into the sodium silicate aqueous solution. After sealing the reactor, it was placed in an electric oven for in-situ growth at a reaction temperature of 150 ºC and a constant temperature reaction time of 2 hours to obtain a die-cast magnesium alloy with an anti-corrosion coating on its surface.

[0044] This application conducts performance tests on the die-cast magnesium alloy with a corrosion-resistant coating grown on its surface, prepared in this embodiment, specifically as follows: 1) Microscopic morphology The die-cast magnesium alloy with an anti-corrosion coating grown on its surface in this embodiment was observed using a scanning electron microscope (SEM), and the SEM image is shown below. Figure 9 As shown in the figure, with the increase of hydrothermal reaction temperature, the coating surface is still uniformly covered with a large number of granular structures, but the particle size is significantly smaller than that under low temperature (120 ºC) conditions, exhibiting a finer and denser distribution. Meanwhile, the entire coating surface structure remains intact, with no cracks or peeling observed, indicating that even with a shorter reaction time, a higher reaction temperature helps to obtain a denser, more uniform, and structurally stable coating. The reduction in particle size may be related to the following factors: 1) Enhanced nucleation rate: Under higher temperatures, the precursor hydrolysis and nucleation rates accelerate, leading to the generation of a large number of tiny nuclei, limiting the growth of single particles and promoting the evolution of the structure towards "fine grains"; 2) Limited grain growth: Although the temperature is high, the reaction time is shortened, preventing the grains from growing sufficiently after rapid nucleation, thus forming fine particles; 3) Enhanced kinetic control: High temperatures are beneficial for increasing ion migration and diffusion rates, resulting in a more uniform deposition process and a tighter arrangement between particles.

[0045] The die-cast magnesium alloy with an anti-corrosion coating grown on its surface in this embodiment was characterized by XRD and infrared spectroscopy. Its X-ray diffraction pattern is shown below. Figure 10 As shown in the figure, the coating is mainly composed of the Mg(OH)2 phase. Characteristic diffraction peaks of Mg(OH)2 can be observed at 2θ ≈ 18.5°, 38.0°, and 50.8° in the XRD pattern, indicating that magnesium hydroxide products are generated during the coating growth process.

[0046] Its infrared spectrum is as follows Figure 11 As shown in the figure, the range is 3200–3600 cm. -1 O–H stretching vibration peaks appeared in the range of 1000–1100 cm⁻¹, which is related to adsorbed water or crystalline water present in the anti-corrosion coating; -1The presence of Si–O stretching vibration peaks is mainly attributed to sodium silicate in the in-situ growth solution. In a hydrothermal environment, sodium silicate hydrolyzes to Si(OH)4, which then undergoes a condensation reaction to form a Si–O–Si network, which is deposited and solidified into a film on the surface of the die-cast magnesium alloy substrate.

[0047] 2) Electrochemical performance This embodiment also tested the electrochemical performance of AM50 die-cast magnesium alloy and anti-corrosion coated die-cast magnesium alloy. Specifically, the polarization curves of the die-cast magnesium alloy sample and the magnesium alloy sample with anti-corrosion coating on its surface were tested in 3.5 wt.% sodium chloride solution using an electrochemical workstation (Princeton 4000A).

[0048] The Tafel polarization curves of AM50 die-cast magnesium alloy and corrosion-resistant coated die-cast magnesium alloy (film) in this application are shown in the following figures. Figure 12 As shown in the figure, the corrosion voltage of the exposed AM50 die-cast magnesium alloy is -1.47 V, while the corrosion voltage of the die-cast magnesium alloy with the anti-corrosion coating is -1.32 V. Therefore, compared with the exposed die-cast magnesium alloy substrate, the preparation of the anti-corrosion coating significantly increases its corrosion voltage, and from a thermodynamic point of view, the corrosion tendency of the magnesium alloy substrate decreases.

[0049] From a kinetic perspective, corrosion rate and corrosion resistance are directly related to corrosion current density. The corrosion current density of exposed AM50 die-cast magnesium alloy is 1.52 × 10⁻⁶. -5 A cm -2 The corrosion current density of the anti-corrosion coated die-cast magnesium alloy is 3.31 × 10⁻⁶. -8 A cm -2 Compared to the exposed die-cast magnesium alloy substrate, the corrosion current density of the sample with the anti-corrosion coating was reduced by three orders of magnitude. This indicates that constructing an anti-corrosion coating on the surface of AM50 die-cast magnesium alloy can achieve a significant anti-corrosion protection effect, effectively preventing the intrusion of corrosive media, thereby significantly improving the corrosion resistance of the substrate material. In summary, the anti-corrosion coating on the surface of die-cast magnesium alloy involved in this invention has excellent anti-corrosion performance and can continuously and effectively protect the magnesium alloy substrate under harsh service environments, preventing it from corrosion damage.

[0050] 3) Bonding strength test results To evaluate the bonding strength between the coating and the substrate, this embodiment uses the cross-cut adhesion test to examine the corrosion-resistant coating on the surface of die-cast magnesium alloy according to the national standard GB / T 9286. During the test, a grid of intersecting lines was etched at 1 mm intervals on the coating surface, and the coating peeled off in the gridded areas using standard adhesive tape.

[0051] like Figure 13 As shown, there is no obvious peeling or flaking within the scribed area, the scribed line boundaries are clear, and the rating is 0, indicating excellent adhesion between the coating and the substrate. Good adhesion not only helps improve the structural stability of the coating but also ensures its long-term corrosion resistance and service reliability.

[0052] In summary, the anti-corrosion coating on the surface of die-cast magnesium alloy prepared by this invention exhibits excellent corrosion resistance and has broad application prospects. Using a one-step hydrothermal method with 0.01 M sodium silicate as the reaction medium, a coating composed of a large number of small, uniformly distributed, and tightly bonded particles can be grown in situ on the surface of AM50 die-cast magnesium alloy. This coating possesses excellent density and barrier properties, significantly improving its structural stability and corrosion resistance.

[0053] Therefore, by growing a dense, non-porous protective coating in situ on the surface of die-cast magnesium alloys, the corrosion of the substrate by external corrosive media can be effectively blocked, thereby significantly improving the corrosion resistance of die-cast magnesium alloys. Compared with the superhydrophobic coatings previously studied by our team, this method can achieve a fairly excellent protective effect without the need for low surface energy modification treatment.

[0054] In addition, the process uses environmentally friendly and pollution-free sodium silicate aqueous solution, eliminating the need for expensive chemical additives. It also has a shorter reaction time and a simpler process, giving it significant cost advantages and green and sustainable characteristics, demonstrating good potential for engineering applications and industrial promotion.

[0055] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A method for preparing an anti-corrosion coating on the surface of a die-cast magnesium alloy, characterized in that, A die-cast magnesium alloy substrate is immersed in an in-situ growth solution for hydrothermal reaction to obtain a die-cast magnesium alloy with an anti-corrosion coating. The in-situ growth solution is composed of an aqueous sodium silicate solution, the coating is mainly composed of the Mg(OH)2 phase, and the coating contains a Si-O-Si network.

2. The method for preparing the anti-corrosion coating on the surface of die-cast magnesium alloy according to claim 1, characterized in that, The process parameters for the hydrothermal reaction are: hydrothermal reaction at 100-150 ºC for 2-7 hours.

3. The method for preparing the anti-corrosion coating on the surface of die-cast magnesium alloy according to claim 1, characterized in that, The process parameters for the hydrothermal reaction are: hydrothermal reaction at 120-140 ºC for 3-6 hours.

4. The method for preparing the anti-corrosion coating on the surface of die-cast magnesium alloy according to claim 1, characterized in that, The process parameters for the hydrothermal reaction are: hydrothermal reaction at 150 ºC for 2 hours.

5. The method for preparing the anti-corrosion coating on the surface of die-cast magnesium alloy according to claim 1, characterized in that, It also includes water grinding of the die-cast magnesium alloy matrix before hydrothermal reaction.

6. A corrosion-resistant coating on the surface of a die-cast magnesium alloy obtained by the preparation method according to any one of claims 1-5.

7. The application of the anti-corrosion coating on the surface of die-cast magnesium alloy according to claim 6 in the fields of aerospace, automobile and electronic products.

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