Corrosion-resistant magnesium alloy for marine atmospheric environment and preparation method thereof

Abstract

The application provides a kind of corrosion-resistant magnesium alloy for marine atmospheric environment and a preparation method thereof, and belongs to the field of magnesium alloy material preparation.The chemical composition of the magnesium alloy is as follows in terms of mass percentage: 6.0-6.5% of Al, 1.3-1.5% of Y, 0.3-0.5% of Zn, 0.05-0.1% of Mn, 0.1-0.12% of Sr, and the balance of magnesium and inevitable impurities.The application alloys the magnesium-aluminum alloy by the combined addition of Y, Zn, Mn and Sr elements, suppresses the micro-galvanic corrosion of the magnesium alloy, improves the protection ability of the surface film, and increases the corrosion resistance of the magnesium-aluminum alloy in the marine atmospheric environment.The preparation of the above magnesium alloy adopts semi-solid forming, the process is simple, suitable for industrial production, and the prepared product has a compact structure, reduced defects and excellent service performance.

Description

Technical Field

[0001] This invention relates to the field of magnesium alloy material preparation, specifically to a corrosion-resistant magnesium alloy for marine atmospheric environments and its preparation method. Background Technology

[0002] Magnesium alloys, as the lightest structural materials, possess advantages such as high specific strength and stiffness, high elastic modulus, good damping and vibration reduction properties, excellent castability, and superior electrical and thermal conductivity, making them widely used in aerospace, military, automotive, electronics, and biomaterials fields. However, due to their relatively active chemical properties, low corrosion potential, and poor protection of the substrate by the surface film they form, magnesium alloys inherently have poor corrosion resistance. With the implementation of a series of national strategies for strengthening the country, magnesium alloy materials are also gradually being applied to marine equipment—such as important marine instrument recovery devices, timing devices, nautical instruments, and hydrogen buoyancy devices. The harsh high humidity, high temperature, and high salinity environment of the marine atmosphere further accelerates the corrosion of magnesium alloys. Therefore, improving the corrosion resistance of magnesium alloys and developing corrosion-resistant magnesium alloys suitable for use in the marine atmospheric environment is of paramount importance.

[0003] Currently, measures to improve the corrosion resistance of magnesium alloys include: improving the corrosion resistance of magnesium alloys through alloying or microalloying; and improving the distribution and morphology of phases in the alloy by optimizing the preparation process to enhance the corrosion resistance of magnesium alloys. Among these, alloying and microalloying can fundamentally improve the corrosion resistance of magnesium alloys.

[0004] As is well known, Mg-Al magnesium alloys exhibit superior corrosion resistance compared to other magnesium alloy series, and due to their excellent casting properties, they have become the most widely used magnesium alloy series. Zn and Mn elements are typically added as trace elements to Mg-Al alloys to reduce the impact of impurity elements on the alloy's corrosion resistance. Utilizing the alloying effect of rare earth element Y, on the one hand, Y preferentially forms a high-melting-point Al-Y phase with Al in the Mg-Al alloy, suppressing the β phase (Mg... 17 Al 12 The generation and improvement of Mg 17 Al 12 The addition of rare earth element Y can significantly increase the Al content in the oxide layer on the surface of Mg-Al alloys, thereby reducing microgalvanic corrosion of the magnesium alloy itself. Conversely, the addition of Sr can refine the grain size of magnesium alloys and delay anodic activity. Furthermore, the combined addition of Sr and Y to Mg-Al alloys will further improve the corrosion resistance of the alloy.

[0005] Magnesium alloy forming processes include extrusion, rolling, die casting, rapid solidification, and semi-solid forming. Semi-solid forming is a novel processing technique that utilizes the semi-solid temperature range during the melting or solidification process to shape the alloy. Due to its unique characteristics, semi-solid forming combines the advantages of both solid forming and liquid forming (casting) technologies. Compared to liquid forming, semi-solid formed parts exhibit higher mechanical properties, denser internal structure, fewer defects such as porosity and segregation, lower forming temperatures, and can achieve near-net-shape forming. Furthermore, due to its uniform and dense microstructure, its corrosion resistance is superior to that of solid-formed metals. Summary of the Invention

[0006] The purpose of this invention is to address the problem of poor corrosion resistance of magnesium alloys in marine environments by providing a corrosion-resistant magnesium alloy for marine atmospheric environments and its preparation method. By alloying Mg-Al alloys with the addition of Y, Zn, Mn, and Sr elements, the corrosion resistance of the magnesium alloy is significantly improved. Simultaneously, a dense, non-dendritic microstructure is obtained using a semi-solid rheoforming method, further enhancing the corrosion resistance of the magnesium alloy.

[0007] To achieve the above technical objectives, the technical solution adopted in this application is as follows:

[0008] This invention provides a corrosion-resistant magnesium alloy for marine atmospheric environments, the chemical composition of which, by mass percentage, is: Al 6.0-6.5%, Y 1.3-1.5%, Zn 0.3-0.5%, Mn 0.05-0.1%, Sr 0.1-0.12%, with the balance being magnesium and unavoidable impurities; the total mass fraction of the unavoidable impurities is ≤0.02%.

[0009] This invention provides a method for preparing a corrosion-resistant magnesium alloy for marine atmospheric environments, the method comprising the following steps:

[0010] (1) Prepare pure magnesium, pure aluminum, pure zinc, Mg-Mn master alloy, Mg-Y master alloy and Mg-Sr master alloy by mixing materials according to the corrosion-resistant magnesium alloy composition ratio as described above.

[0011] (2) Introduce protective gas, put pure magnesium and pure aluminum ingots into the melting furnace and heat them to a molten state. Then, raise the temperature again and add pure zinc, Mg-Mn, Mg-Y and Mg-Sr master alloys in sequence and heat to obtain magnesium alloy melt.

[0012] (3) Introduce protective gas, stir the magnesium alloy melt obtained in step (2) and let it stand, prepare a semi-solid slurry in the form of rheological slurry preparation, and then inject it into a stainless steel mold. After cooling and solidification, obtain a semi-solid molded magnesium alloy material.

[0013] Further, in step (1), the mass fraction of Y in the Mg-Y master alloy is 30%, the mass fraction of Sr in the Mg-Sr master alloy is 10%, and the mass fraction of Mn in the Mg-Mn master alloy is 5%.

[0014] Furthermore, the smelting furnace described in step (2) needs to be preheated to a temperature of 200°C before smelting.

[0015] Further, in step (2), the heating temperature for pure magnesium and pure aluminum is 680-700℃; the heating temperature for pure zinc, Mg-Mn, Mg-Y and Mg-Sr master alloys is 730-750℃, and the heating time is 25-30 min.

[0016] Furthermore, the protective gas mentioned in steps (2) and (3) is a mixture of CO2 and SF6, with a volume ratio of CO2 to SF6 of 100:1.

[0017] Furthermore, the temperature of the magnesium alloy melt during stirring in step (3) is 700-720°C, and the settling time is 10-15 minutes.

[0018] Furthermore, the temperature for preparing the semi-solid slurry in step (3) is 570–590°C.

[0019] Furthermore, the rheological pulping method described in step (3) is one of two methods: pneumatic rheological pulping or mechanical rheological pulping.

[0020] Furthermore, the cooling and solidification process described in step (3) requires placing the cast mold in 20°C water to cool it to room temperature.

[0021] The beneficial effects of this invention are as follows:

[0022] First, this invention further enhances the corrosion resistance of Mg-Al alloys by adding Y and Sr elements, and the elements used are inexpensive and readily available. By utilizing the alloying effect of rare earth Y, the microstructure and surface film protection of the magnesium alloy are improved, significantly enhancing its corrosion resistance in alternating wet and dry marine atmospheric environments. The addition of Zn and Mn elements reduces the impact of impurity elements on the alloy's corrosion resistance, while the combined addition of Sr and rare earth Y effectively reduces the micro-galvanic corrosion of the magnesium alloy itself, significantly improving the chemical stability and protective properties of the magnesium alloy surface.

[0023] Second, the present invention uses a semi-solid isothermal heat treatment process to prepare magnesium alloys. The microstructure of the magnesium alloy is non-dendritic, and its matrix phase structure is uniform, fine, and nearly spherical granular, which gives the alloy excellent comprehensive properties. It reduces the potential difference between corrosion galvanic pairs inside the magnesium alloy and inhibits microgalvanic corrosion of the alloy. The internal structure of the semi-solid part is dense, and defects such as porosity and segregation are significantly reduced.

[0024] Third, the magnesium alloy and its preparation method described in this invention significantly improve the corrosion performance of existing alloys through alloying and optimized preparation processes, helping the alloy to transform pitting corrosion in marine atmospheric environments into shallow, uniform corrosion, and the alloy exhibits good corrosion resistance. Attached Figure Description

[0025] Figure 1 This is a schematic diagram illustrating the corrosion of the magnesium alloy described in this invention under marine atmospheric conditions.

[0026] Figure 2 This is a scanning electron microscope image of the magnesium alloy microstructure provided in Embodiment 5 of the present invention;

[0027] Figure 3 This is a scanning electron microscope image of the magnesium alloy microstructure provided in Embodiment 6 of the present invention. Detailed Implementation

[0028] In the description of this invention, it should be noted that unless specific conditions are specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0029] The magnesium alloy provided in this invention example will be tested for corrosion performance using an immersion test. A 10mm × 10mm magnesium alloy ingot sample is ground, cleaned, and dried, and its mass is taken as the initial mass. The sample is placed in a 3.5wt% NaCl solution and subjected to a corrosion test at room temperature for up to 5 days. Afterward, the sample is cleaned, dried, weighed, and the corrosion rate is calculated.

[0030] The following will further explain and illustrate the implementation scheme of the present invention with reference to specific embodiments. It should be understood that the specific embodiments herein are only used to explain the present invention and are not intended to limit the present invention.

[0031] Example 1

[0032] This embodiment relates to a corrosion-resistant magnesium alloy for marine atmospheric environments, wherein the chemical composition by mass percentage is: Al 6.0%, Y 1.3%, Zn 0.3%, Mn 0.05%, Sr 0.1%, with the balance being magnesium and unavoidable impurities; the total weight percentage of the unavoidable impurities is ≤0.02%.

[0033] A method for preparing a corrosion-resistant magnesium alloy for marine atmospheric environments, comprising the following specific steps:

[0034] (1) Prepare pure magnesium, pure aluminum, pure zinc, Mg-Mn master alloy, Mg-Y master alloy and Mg-Sr master alloy according to the above-mentioned chemical composition of magnesium alloy; wherein, the mass fraction of Y in Mg-Y master alloy is 30%, the mass fraction of Sr in Mg-Sr master alloy is 10%, and the mass fraction of Mn in Mg-Mn master alloy is 5%.

[0035] (2) First, put the graphite crucible into the resistance furnace and preheat it to 200°C. Then, put the pure magnesium and pure aluminum ingots into the melting furnace, set the furnace temperature to 690°C, and introduce a mixed protective gas of CO2 and SF6 (the volume ratio of CO2 and SF6 is 100:1) to heat the pure magnesium and pure aluminum to a molten state. Raise the temperature to 740°C, and add pure zinc, Mg-Mn, Mg-Y and Mg-Sr master alloys in sequence. Hold the temperature for 25 minutes to obtain magnesium alloy melt.

[0036] (3) Under a protective atmosphere, adjust the temperature to 710℃ and stir the magnesium alloy melt obtained in step (2) thoroughly; let it stand for 15 minutes to remove the surface slag. Under a continuous protective atmosphere, prepare a semi-solid slurry from the magnesium alloy melt at 570℃ using a mechanical rheological slurry preparation process, then pour the obtained semi-solid slurry into a stainless steel mold and quickly immerse it in water for rapid cooling to obtain a semi-solid molded magnesium alloy material.

[0037] Corrosion tests were conducted on the alloy in this example. The results showed that after 5 days, the average weight loss rate of the alloy placed in a 3.5 wt% NaCl solution was 1.96 mg·cm⁻¹. -2 ·d -1 .

[0038] Example 2

[0039] This embodiment relates to a corrosion-resistant magnesium alloy for marine atmospheric environments, wherein the chemical composition by mass percentage is: Al 6.2%, Y 1.3%, Zn 0.4%, Mn 0.1%, Sr 0.12%, with the balance being magnesium and unavoidable impurities; the total weight percentage of the unavoidable impurities is ≤0.02%.

[0040] A method for preparing a corrosion-resistant magnesium alloy for marine atmospheric environments differs from Example 1 in that:

[0041] In step (3), under a protective atmosphere, the temperature is adjusted to 710°C, and the magnesium alloy melt obtained in step (2) is thoroughly stirred; it is then allowed to stand for 15 minutes to remove surface slag. Under a continuous protective atmosphere, the magnesium alloy melt is heated to 575°C to prepare a semi-solid slurry using a mechanical rheological slurry preparation process. The obtained semi-solid slurry is then poured into a stainless steel mold and rapidly cooled in water to obtain a semi-solid molded magnesium alloy material.

[0042] Corrosion tests were conducted on the alloy in this example. The results showed that after 5 days, the average weight loss rate of the alloy placed in a 3.5 wt% NaCl solution was 1.76 mg·cm⁻¹. -2 ·d -1 .

[0043] Example 3

[0044] This embodiment relates to a corrosion-resistant magnesium alloy for marine atmospheric environments, wherein the chemical composition by mass percentage is: Al 6.5%, Y 1.3%, Zn 0.5%, Mn 0.1%, Sr 0.1%, with the balance being magnesium and unavoidable impurities; the total weight percentage of the unavoidable impurities is ≤0.02%.

[0045] A method for preparing a corrosion-resistant magnesium alloy for marine atmospheric environments differs from Example 1 in that:

[0046] In step (3), under a protective atmosphere, the temperature is adjusted to 710°C, and the magnesium alloy melt obtained in step (2) is thoroughly stirred; it is then allowed to stand for 15 minutes to remove surface slag. Under a continuous protective atmosphere, the magnesium alloy melt is heated to 580°C to prepare a semi-solid slurry using a mechanical rheology slurry preparation process. The obtained semi-solid slurry is then poured into a stainless steel mold and rapidly cooled in water to obtain a semi-solid molded magnesium alloy material.

[0047] Corrosion tests were conducted on the alloy in this example. The results showed that after 5 days, the average weight loss rate of the alloy placed in a 3.5 wt% NaCl solution was 1.71 mg·cm⁻¹. -2 ·d -1 .

[0048] Example 4

[0049] This embodiment relates to a corrosion-resistant magnesium alloy for marine atmospheric environments, wherein the chemical composition by mass percentage is: Al 6.2%, Y 1.4%, Zn 0.3%, Mn 0.05%, Sr 0.12%, with the balance being magnesium and unavoidable impurities; the total weight percentage of the unavoidable impurities is ≤0.02%.

[0050] A method for preparing a corrosion-resistant magnesium alloy for marine atmospheric environments differs from Example 1 in that:

[0051] In step (3), under a protective atmosphere, the temperature is adjusted to 710°C, and the magnesium alloy melt obtained in step (2) is thoroughly stirred; it is then allowed to stand for 15 minutes to remove surface slag. Under a continuous protective atmosphere, the magnesium alloy melt is heated to 585°C to prepare a semi-solid slurry using a pneumatic rheological slurry preparation process. The obtained semi-solid slurry is then poured into a stainless steel mold and rapidly cooled in water to obtain a semi-solid molded magnesium alloy material.

[0052] Corrosion tests were conducted on the alloy in this example. The results showed that after 5 days, the average weight loss rate of the alloy placed in a 3.5 wt% NaCl solution was 1.68 mg·cm⁻¹. -2 ·d -1

[0053] Example 5

[0054] This embodiment relates to a corrosion-resistant magnesium alloy for marine atmospheric environments, wherein the chemical composition by mass percentage is: Al 6.0%, Y 1.5%, Zn 0.5%, Mn 0.1%, Sr 0.12%, with the balance being magnesium and unavoidable impurities; the total weight percentage of the unavoidable impurities is ≤0.02%.

[0055] A method for preparing a corrosion-resistant magnesium alloy for marine atmospheric environments differs from Example 1 in that:

[0056] In step (3), under a protective atmosphere, the temperature is adjusted to 710°C, and the magnesium alloy melt obtained in step (2) is thoroughly stirred; it is then allowed to stand for 15 minutes to remove surface slag. Under a continuous protective atmosphere, the magnesium alloy melt is heated to 590°C to prepare a semi-solid slurry using a mechanical rheological slurry preparation process. The obtained semi-solid slurry is then poured into a stainless steel mold and rapidly cooled in water to obtain a semi-solid molded magnesium alloy material.

[0057] Corrosion tests were conducted on the alloy in this example. The results showed that after 5 days, the average weight loss rate of the alloy placed in a 3.5 wt% NaCl solution was 1.58 mg·cm⁻¹. -2 ·d -1 .

[0058] Example 6

[0059] This embodiment relates to a corrosion-resistant magnesium alloy for marine atmospheric environments, and the chemical composition is the same as that in Example 1.

[0060] A method for preparing a corrosion-resistant magnesium alloy for marine atmospheric environments differs from Example 1 in that:

[0061] In step (3), under a protective atmosphere, the temperature is adjusted to 710°C, and the magnesium alloy melt obtained in step (2) is thoroughly stirred; it is then allowed to stand for 15 minutes to remove surface slag. Under a continuous protective atmosphere, the magnesium alloy melt is heated to 590°C to prepare a semi-solid slurry using a mechanical rheological slurry preparation process. The obtained semi-solid slurry is then poured into a stainless steel mold and rapidly cooled in water to obtain a semi-solid molded magnesium alloy material.

[0062] Corrosion tests were conducted on the alloy in this example. The results showed that after 5 days, the average weight loss rate of the alloy placed in a 3.5 wt% NaCl solution was 1.62 mg·cm⁻¹. -2 ·d -1 .

[0063] Comparative Example

[0064] The chemical composition described in this comparative example, by mass percentage, is: Al 6.0%, Zn 0.5%, Mn 0.1%, with the balance being magnesium and unavoidable impurities; the total weight percentage of the unavoidable impurities is ≤0.02%.

[0065] The difference between the preparation method of the alloy described in this comparative example and that in Example 1 is:

[0066] In step (3), under a protective atmosphere, the temperature is adjusted to 710°C, and the magnesium alloy melt obtained in step (2) is stirred thoroughly; after standing for 15 minutes, the surface slag is removed, and finally the alloy melt is quickly poured into a metal mold to obtain the as-cast AZ61 alloy.

[0067] Corrosion tests were conducted on the alloy in this example. The results showed that after 5 days, the average weight loss rate of the alloy placed in a 3.5 wt% NaCl solution was 3.74 mg·cm⁻¹. -2 ·d -1 .

[0068] Table 1 Chemical composition design and corrosion rate of different alloys

[0069]

[0070] In this invention, the corrosion resistance of existing alloys is improved through alloying and optimized preparation processes, resulting in magnesium alloys with a weight loss rate of 1.58–1.96 mg·cm³. -2 ·d -1 According to Table 1, the optimal temperature for processing semi-solid slurry is 590℃. Figure 2 The microstructure of the alloy in Example 5 is shown. Figure 3The diagram shows the microstructure of the alloy in Example 6. The semi-solid process gives the alloy a typical non-dendritic structure, reducing the surface area ratio of galvanic pairs in the micro-galvanic corrosion of the magnesium alloy and decreasing the corrosion rate. Furthermore, the uniform microstructure and elemental distribution of the semi-solid-formed alloy provide stronger protection for the surface film. The addition of rare earth elements further inhibits micro-galvanic corrosion in the magnesium alloy, thus enhancing its corrosion resistance in simulated marine atmospheric environments. A schematic diagram of the corrosion of the magnesium alloy described in this invention in a marine atmospheric environment is shown below. Figure 1 As shown.

Claims

1. A method for producing a corrosion-resistant magnesium alloy for marine atmospheric environments, characterized by: The method includes the following steps: (1) Prepare pure magnesium, pure aluminum, pure zinc, Mg-Mn master alloy, Mg-Y master alloy and Mg-Sr master alloy according to the composition ratio of corrosion-resistant magnesium alloy; the chemical composition of the corrosion-resistant magnesium alloy by mass percentage is: Al 6.0~6.5%, Y 1.3~1.5%, Zn 0.3~0.5%, Mn 0.05~0.1%, Sr 0.1~0.12%, with the balance being magnesium and unavoidable impurities; the total mass fraction of the unavoidable impurities is ≤0.02%; (2) Introduce a protective gas, put pure magnesium and pure aluminum ingots into a melting furnace and heat them to a molten state, then raise the temperature again and add pure zinc, Mg-Mn, Mg-Y and Mg-Sr master alloys in sequence and heat to obtain magnesium alloy melt; the protective gas is a mixture of CO2 and SF6 with a volume ratio of 100:

1. (3) Introduce a protective gas, stir the magnesium alloy melt obtained in step (2) at 700~720℃ and let it stand for 10~15 minutes, prepare a semi-solid slurry at 570~590℃ by rheological slurry preparation, and then inject it into a stainless steel mold. After casting, place the mold in 20℃ water to cool and solidify to obtain a semi-solid molded magnesium alloy material; the protective gas is a mixture of CO2 and SF6 with a volume ratio of 100:

1.

2. The method of claim 1, wherein the corrosion-resistant magnesium alloy for marine atmospheric environment is prepared by the following steps. In step (1), the mass fraction of Y in the Mg-Y master alloy is 30%, the mass fraction of Sr in the Mg-Sr master alloy is 10%, and the mass fraction of Mn in the Mg-Mn master alloy is 5%.

3. The method for preparing a corrosion-resistant magnesium alloy for marine atmospheric environments according to claim 1, characterized in that: The smelting furnace described in step (2) needs to be preheated to a temperature of 200°C before smelting.

4. The method of claim 1, wherein the corrosion-resistant magnesium alloy for marine atmospheric environment is prepared by the following steps. In step (2), the heating temperature for pure magnesium and pure aluminum is 680~700℃; the heating temperature for pure zinc, Mg-Mn, Mg-Y and Mg-Sr master alloys is 730~750℃, and the heating time is 25~30min.

5. The method for preparing a corrosion-resistant magnesium alloy for marine atmospheric environments according to claim 1, characterized in that: The rheological pulping method described in step (3) is one of two methods: pneumatic rheological pulping or mechanical rheological pulping.

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