A magnesium alloy material for aerospace liquid ammonia heat pipes and its preparation method

Abstract

The present invention discloses a magnesium alloy material for aerospace liquid ammonia heat pipes and a preparation method thereof, belonging to the technical field of alloy materials. The magnesium alloy material comprises, by mass percentage, 6% - 11% of Al, 0.1% - 1% of Mn, 0.1% - 0.5% of Zn, 0.05% - 0.5% of Y, 0.1% - 3.0% of Nd, 0.1% - 2.0% of Gd, and the balance of Mg and inevitable impurities. By adding Al and rare earth elements such as Y, Nd, and Gd, the magnesium alloy with this specific composition ratio can spontaneously form a magnesium nitride protective film in a liquid ammonia environment, and this protective film can effectively prevent the corrosion of the liquid ammonia on the magnesium alloy matrix, significantly improving the service life of the material in extreme environments.

Description

Technical Field

[0001] The present invention belongs to the technical field of alloy materials, and particularly relates to a magnesium alloy material for aerospace liquid ammonia heat pipes and a preparation method thereof. Background Art

[0002] With the large-scale development of high-power spacecraft such as Internet satellites and civilian mobile electronic devices, the usage of heat pipes in the thermal management system has increased dramatically. A heat pipe is an efficient heat conduction device, and its performance depends not only on the design of the internal structure but also on the materials used. Heat pipes are classified into copper alloy heat pipes, aluminum alloy heat pipes, stainless steel heat pipes, magnesium alloy heat pipes, and heat pipes made of other materials according to the materials. Among them, copper in the copper alloy heat pipe has a very high thermal conductivity, which makes the copper alloy heat pipe very suitable for applications that require rapid heat transfer. In addition, copper has good corrosion resistance and can maintain a long service life in many environments. Copper alloy heat pipes are often used in fields such as electronic device heat dissipation and precision instrument cooling. The aluminum in the aluminum alloy heat pipe has a lower density than copper, which means that the aluminum alloy heat pipe is lighter than the copper heat pipe. Although the thermal conductivity of aluminum is slightly lower than that of copper, it is still efficient enough and has a relatively low cost. Aluminum alloy heat pipes are widely used in portable electronic devices such as laptop computers and smartphones. The stainless steel material in the stainless steel heat pipe has excellent corrosion resistance and can be used in harsh environments without being easily damaged, making it suitable for use in environments with strong corrosion such as the chemical industry and marine engineering. Magnesium in the magnesium alloy heat pipe is the lightest among all common metals, which makes the magnesium alloy heat pipe an ideal choice for pursuing the ultimate lightweight design. However, magnesium alloys are prone to corrosion under certain environmental conditions, so special surface treatment or alloy formulations are required to enhance their durability. Magnesium alloy heat pipes are mainly used in application scenarios that require strict weight control such as aerospace and high-end electronic devices.

[0003] To solve the problem of poor corrosion resistance of magnesium alloy heat pipes, the main methods include surface treatment, designing composite materials, nanotechnology, etc. Or starting from the materials added to the heat pipes, using non-corrosive organic liquids instead of liquid ammonia. Among them, surface treatment mainly uses methods such as anodic oxidation or chemical conversion coatings to form a protective film on the surface of the magnesium alloy, thereby improving its corrosion resistance. However, this makes the preparation method of the magnesium alloy more complex, and the original coating will be damaged during the subsequent welding process of the heat pipe, reducing the service life of the heat pipe. Designing composite materials mainly combines magnesium alloy with other materials (such as carbon fiber) to form composite materials to utilize their respective advantages while making up for their respective deficiencies. However, in composite materials, the interfacial strength between the matrix and the reinforcing phase directly affects the overall performance of the material, and poor interfaces may lead to a decline in material performance. Modifying magnesium-based materials using nanotechnology can not only improve their strength and toughness but also improve their thermal conductivity and corrosion resistance. However, synthesizing nanomaterials usually requires the use of special equipment and technologies, such as chemical vapor deposition (CVD), atomic layer deposition (ALD), etc. These technologies are costly and face challenges in large-scale production. In addition, the nanoparticles prepared by nanotechnology are extremely prone to agglomeration, and agglomeration will cause the material performance to fail to reach the expected level. Replacing the internal working medium with organic liquids such as ethanol and acetone that do not corrode metals, but the thermal conductivity of such heat pipes is not as high as that of heat pipes using liquid ammonia as the working medium.

[0004] To solve the problem of poor corrosion resistance of magnesium alloy heat pipes, there is another method, which is alloying. By adding other elements to change the basic composition of the magnesium alloy to enhance its physical and chemical properties. Through alloying, the plasticity, toughness and other properties of the material can be adjusted, making the material easier to process and form, and the preparation method is simple and easy to operate. However, not all elements can be compatible with each other during the alloying process. There may be complex interactions between elements, and chemical reactions may occur between some elements, resulting in unstable or even ineffective alloy properties.

[0005] Therefore, there is an urgent need for a method to improve the liquid ammonia corrosion resistance of magnesium alloys through alloying. Summary of the Invention

[0006] The purpose of the present invention is to provide a magnesium alloy material and its preparation method for aerospace liquid ammonia heat pipes to solve the problems of the relatively complex magnesium alloy element design process and the poor liquid ammonia corrosion resistance of magnesium alloys. By adding Al and rare earth elements such as Y, Nd, Gd, this magnesium alloy with a specific composition ratio can spontaneously form a magnesium nitride protective film in a liquid ammonia environment. This protective film can effectively prevent the corrosion of the magnesium alloy matrix by liquid ammonia, significantly improving the service life of the material in extreme environments.

[0007] To achieve the above object, a first aspect of the present invention provides a magnesium alloy material for aerospace liquid ammonia heat pipes. The magnesium alloy material comprises, by mass percentage, 6% - 11% of Al, 0.1% - 1% of Mn, 0.1% - 0.5% of Zn, 0.05% - 0.5% of Y, 0.1% - 3% of Nd, 0.1% - 2.0% of Gd, and the balance of Mg and inevitable impurities.

[0008] Preferably, the crystal structure of the magnesium alloy material is a close-packed hexagonal crystal structure.

[0009] The magnesium alloy material can be used to prepare magnesium alloy heat pipes for aerospace. Its density is reduced by 1 / 3 compared with traditional aluminum alloy liquid ammonia heat pipes, which can achieve the lightweight of aerospace components. However, liquid ammonia needs to be filled in the magnesium alloy heat pipe, and the corrosion resistance of magnesium alloy to liquid ammonia is relatively low. To solve this problem, in the prior art, an anti-corrosion coating is generally set on the surface of the magnesium alloy heat pipe to improve the service life of the magnesium alloy heat pipe. However, this method will damage the original anti-corrosion coating during the subsequent processing of the heat pipe, and the preparation process of the anti-corrosion coating is also relatively complex. Therefore, it is necessary to study a material that can improve the corrosion resistance of magnesium alloy to liquid ammonia without replacing the liquid ammonia in the heat pipe. The present invention designs the material composition of the magnesium alloy. By adding Al and rare earth elements such as Y, Nd, and Gd, the addition of this specific composition enables the magnesium alloy to spontaneously form a layer of magnesium nitride protective film in a liquid ammonia environment. This protective film can effectively prevent the corrosion of the liquid ammonia on the magnesium alloy matrix, and significantly improve the service life of the material in extreme environments.

[0010] The present invention has specific limitations on the addition amount of each element. Once the addition amount exceeds this value, it will have an adverse effect on the liquid ammonia corrosion resistance of the magnesium alloy material. Among them, aluminum element is one of the most commonly used strengthening elements in magnesium alloy materials. If the addition amount of aluminum element is too high, it will not only increase the cost of the material, but also may form brittle phases, resulting in the decrease of the plasticity of the material, affecting the ductility and corrosion resistance of the material. Manganese element can improve the thermal stability and corrosion resistance of magnesium alloy materials, but if the content of manganese element is too high, the liquid ammonia corrosion resistance of magnesium alloy materials will decrease. Zinc element can improve the strength of magnesium alloy, but too much zinc will lead to the decrease of the plasticity of the alloy, thus reducing its processing performance; in addition, the volatilization of zinc at high temperature may also affect the stability and uniformity of the alloy. These rare earth elements such as Y (yttrium), Nd (neodymium), and Gd (gadolinium) can improve the mechanical properties and thermal stability of magnesium alloys, but if the content is too high, too many strengthening phases may be formed, resulting in the embrittlement of the material, and the cost of rare earth elements is relatively high, and excessive use will increase the material cost.

[0011] A second aspect of the present invention provides a preparation method of a magnesium alloy material for aerospace liquid ammonia heat pipes, comprising the following steps:

[0012] (1)Weigh pure magnesium, pure aluminum, magnesium-aluminum alloy, magnesium-manganese alloy, manganese chloride, aluminum-manganese alloy, pure zinc, magnesium-zinc alloy, magnesium-yttrium master alloy, magnesium-neodymium master alloy, and magnesium-gadolinium master alloy according to the mass percentage of the magnesium alloy material.

[0013] (2)Melt pure magnesium. After the pure magnesium melts, add pure aluminum, magnesium-aluminum alloy, magnesium-manganese alloy, manganese chloride, aluminum-manganese alloy, pure zinc, magnesium-zinc alloy, magnesium-yttrium master alloy, magnesium-neodymium master alloy, and magnesium-gadolinium master alloy, and continue melting until all the materials are melted to obtain a melt.

[0014] (3)Refine the melt and then cast it to obtain an ingot.

[0015] (4)Perform heat treatment on the ingot and cool it to room temperature to obtain the magnesium alloy material.

[0016] Preferably, the melting temperature of pure magnesium is 650 °C.

[0017] Preferably, the temperature for continued melting is 750 °C.

[0018] Preferably, the casting method is one of gravity casting, high-pressure casting, low-pressure casting, differential pressure casting, or semi-continuous casting.

[0019] Gravity casting is a casting method that uses the weight of the metal itself to inject the molten metal into the mold. The specific process of gravity casting is as follows:

[0020] Under an argon protection atmosphere, use a container coated with sodium silicate coating to take out the magnesium alloy melt (melt) from the melting crucible, and pour the melt into a preheated ingot mold at 200 °C by gravity. Then, wait for the melt to cool and solidify to obtain a as-cast ingot blank.

[0021] High-pressure casting, also known as high-pressure die casting, is a casting method that uses high pressure to inject the metal melt into the mold cavity. The specific process of high-pressure casting is as follows:

[0022] Transfer the magnesium alloy melt to the injection chamber of the die-casting machine. Keep the melt temperature between 620 and 680 °C, control the injection specific pressure between 40 and 70 MPa, keep the mold temperature between 180 and 250 °C, and take out the casting after die-casting.

[0023] Low-pressure casting is a casting method in which the mold is placed above a sealed crucible, compressed inert gas is introduced into the crucible, a low pressure is created on the surface of the molten metal, and the molten metal rises through the riser tube to fill the mold and control solidification. The specific process of low-pressure casting is as follows:

[0024] Cover and seal the melting crucible with a cover plate equipped with a riser pipe. Place the mold directly above the riser pipe and align the mold pouring gate. Cast at a temperature between 680 and 720 °C. Introduce compressed inert gas with a pressure of 0.02 to 0.05 MPa into the sealed crucible to lift the magnesium alloy melt in the crucible into the mold. Then, hold the pressure at 0.05 to 0.08 MPa for 120 s. After the melt in the mold solidifies, release the pressure and remove the mold.

[0025] Differential pressure casting is an improved casting process of low-pressure casting. The difference is that in differential pressure casting, a sealed cover is placed outside the mold and filled with compressed gas to keep the mold under a certain pressure of the gas. The specific process of differential pressure casting is as follows:

[0026] The process of differential pressure casting is basically the same as that of low-pressure casting. The difference is that in differential pressure casting, compressed gas needs to be introduced into both the sealed cover and the inside of the crucible simultaneously, and the pressure inside the crucible is slightly higher than that inside the sealed cover, with the pressure difference controlled between 0.03 and 0.06 MPa.

[0027] Semi-continuous casting is a casting method in which the metal melt is evenly introduced into a crystallizer whose outer wall is cooled by water, and rapidly solidifies and crystallizes under the combined action of the crystallizer wall and the crystallizer base to finally form an ingot. The specific process of semi-continuous casting is as follows:

[0028] Directly transport the magnesium alloy melt to the semi-continuous casting crystallizer. The crystallizer is made of copper alloy, with a height of 180 to 220 mm and a water hole diameter of 2 to 3 mm. Semi-continuous casting is carried out under the conditions of a casting temperature of 700 to 720 °C, a casting speed of 25 to 45 mm / min, a cooling water temperature of 10 to 30 °C, a cooling water pressure of 0.1 to 0.3 MPa, and a cooling water intensity of 250 to 350 L / min.

[0029] Preferably, the heat treatment includes at least one of solution heat treatment and aging heat treatment.

[0030] Preferably, the solution heat treatment method is to hold for 8 to 12 h at 350 to 420 °C and quench with cold water.

[0031] Preferably, the aging heat treatment method is to hold for 24 to 48 h at 200 to 300 °C and cool in the furnace.

[0032] Therefore, the present invention adopts the above-mentioned magnesium alloy material for aerospace liquid ammonia heat pipes and its preparation method, and has the following beneficial effects:

[0033] 1. By adding Al and rare earth elements such as Y, Nd, and Gd, the magnesium alloy with this specific composition ratio can spontaneously form a magnesium nitride protective film in the liquid ammonia environment. This protective film can effectively prevent the corrosion of the magnesium alloy matrix by liquid ammonia, significantly improving the service life of the material in extreme environments.

[0034] 2. The magnesium alloy composition designed in the present invention not only enhances the corrosion resistance of the material, but also ensures good processing performance. This alloy can be processed and formed by conventional processes such as extrusion, and is suitable for manufacturing complex aerospace liquid ammonia heat pipe components.

[0035] 3. By adopting specific heat treatment processes (such as solution treatment and / or aging treatment), the present invention can make the second-phase particles inside the alloy be evenly distributed, avoiding the risk of local corrosion caused by the aggregation of second-phase particles, and further improving the overall corrosion resistance and mechanical properties of the material.

[0036] 4. The magnesium alloy of the present invention itself has a relatively low density, combined with excellent mechanical properties, making the heat pipe manufactured using this material both light and strong, and very suitable for applications on spacecraft with strict weight restrictions.

[0037] 5. Compared with other high-performance alloys, the magnesium alloy of the present invention has better cost-effectiveness and relatively less environmental pollution during the production process; in addition, magnesium is a renewable resource, which makes the magnesium alloy a sustainable choice and meets the current demand for green and environmentally friendly materials.

[0038] The following further describes the technical solution of the present invention through examples. Description of the Drawings

[0039] Figure 1 It is the structural diagram for liquid ammonia corrosion test;

[0040] Figure 2 It is the liquid ammonia corrosion test device at room temperature;

[0041] Figure 3 It is the liquid ammonia corrosion test device at 80 °C;

[0042] Figure 4 It is the SEM image of the magnesium alloy material prepared in Example 1 after 3 months of corrosion;

[0043] Figure 5 It is the EDS image of the magnesium alloy material prepared in Example 1 after 3 months of corrosion;

[0044] Figure 6 It is the SEM image of the conventional AZ31B magnesium alloy after 3 months of corrosion. Detailed Embodiments

[0045] The following will further describe the present invention. It should be noted that this embodiment is based on the present technical solution and gives detailed implementation manners and specific operation processes, but the present invention is not limited to this embodiment.

[0046] The compositions of the magnesium alloy materials in Examples 1 to 5 are shown in Table 1.

[0047] Table 1 Compositions of the magnesium alloy materials in Examples 1 to 5

[0048]

[0049] A preparation method of the magnesium alloy material for aerospace liquid ammonia heat pipes in the above embodiments includes the following steps:

[0050] (1) Weigh pure magnesium, pure aluminum, magnesium-aluminum alloy, magnesium-manganese alloy, manganese chloride, aluminum-manganese alloy, pure zinc, magnesium-zinc alloy, magnesium-yttrium master alloy, magnesium-neodymium master alloy, and magnesium-gadolinium master alloy according to the mass percentages of the magnesium alloy material;

[0051] (2) Melt pure magnesium. After the pure magnesium melts, add pure aluminum, magnesium-aluminum alloy, magnesium-manganese alloy, manganese chloride, aluminum-manganese alloy, pure zinc, magnesium-zinc alloy, magnesium-yttrium master alloy, magnesium-neodymium master alloy, and magnesium-gadolinium master alloy, and continue melting until all the materials are melted to obtain a melt;

[0052] (3) Refine the melt and then cast it to obtain an ingot;

[0053] The casting method is gravity casting, and the specific process is as follows:

[0054] Under an argon protection atmosphere, use a container coated with sodium silicate coating to take out the magnesium alloy melt (melt) from the melting crucible, and pour the melt into a preheated ingot mold at 200 °C by gravity. Then, wait for the melt to cool and solidify to obtain a as-cast ingot blank;

[0055] (4) Heat-treat the ingot and cool it to room temperature to obtain the magnesium alloy material;

[0056] The heat treatment is solution heat treatment. The solution heat treatment method is to hold at 400 °C for 10 h and quench with cold water.

[0057] Comparative Example 1

[0058] The difference between this comparative example and Example 1 is that the addition amount of Al is increased. The specific composition and content of the magnesium alloy material are as follows:

[0059] The magnesium alloy material includes 15% Al, 0.3% Mn, 0.3% Zn, 0.08% Y, 2.5% Nd, 0.5% Gd, and the balance of Mg and unavoidable impurities by mass percentage.

[0060] Comparative Example 2

[0061] The difference between this comparative example and Example 1 is that the addition amount of Mn is increased. The specific composition and content of the magnesium alloy material are as follows:

[0062] The magnesium alloy material comprises, by mass percentage, 7% of Al, 2% of Mn, 0.3% of Zn, 0.08% of Y, 2.5% of Nd, 0.5% of Gd, the balance of Mg, and inevitable impurities.

[0063] Comparative Example 3

[0064] The difference between this comparative example and Example 1 is that the addition amount of Zn is increased. The specific composition and content of the magnesium alloy material are as follows:

[0065] The magnesium alloy material comprises, by mass percentage, 7% of Al, 0.3% of Mn, 1% of Zn, 0.08% of Y, 2.5% of Nd, 0.5% of Gd, the balance of Mg, and inevitable impurities.

[0066] Comparative Example 4

[0067] The difference between this comparative example and Example 1 is that the addition amount of Y is increased. The specific composition and content of the magnesium alloy material are as follows:

[0068] The magnesium alloy material comprises, by mass percentage, 7% of Al, 0.3% of Mn, 0.3% of Zn, 1% of Y, 2.5% of Nd, 0.5% of Gd, the balance of Mg, and inevitable impurities.

[0069] Comparative Example 5

[0070] The difference between this comparative example and Example 1 is that the addition amount of Nd is increased. The specific composition and content of the magnesium alloy material are as follows:

[0071] The magnesium alloy material comprises, by mass percentage, 7% of Al, 0.3% of Mn, 0.3% of Zn, 0.08% of Y, 4% of Nd, 0.5% of Gd, the balance of Mg, and inevitable impurities.

[0072] Comparative Example 6

[0073] The difference between this comparative example and Example 1 is that the addition amount of Gd is increased. The specific composition and content of the magnesium alloy material are as follows:

[0074] The magnesium alloy material comprises, by mass percentage, 7% of Al, 0.3% of Mn, 0.3% of Zn, 0.08% of Y, 2.5% of Nd, 5% of Gd, the balance of Mg, and inevitable impurities.

[0075] Comparative Example 7

[0076] The difference between this comparative example and Example 1 is that the Y element is not added. The specific composition and content of the magnesium alloy material are as follows:

[0077] The magnesium alloy material comprises, by mass percentage, 7% of Al, 0.3% of Mn, 0.3% of Zn, 2.5% of Nd, 0.5% of Gd, the balance of Mg, and inevitable impurities.

[0078] Comparative Example 8

[0079] The difference between this comparative example and Example 1 is that no Nd element is added. The specific composition and content of the magnesium alloy material are as follows:

[0080] The magnesium alloy material comprises, by mass percentage, 7% of Al, 0.3% of Mn, 0.3% of Zn, 0.08% of Y, 0.5% of Gd, the balance of Mg, and inevitable impurities.

[0081] Comparative Example 9

[0082] The difference between this comparative example and Example 1 is that no Gd element is added. The specific composition and content of the magnesium alloy material are as follows:

[0083] The magnesium alloy material comprises, by mass percentage, 7% of Al, 0.3% of Mn, 0.3% of Zn, 0.08% of Y, 2.5% of Nd, the balance of Mg, and inevitable impurities.

[0084] Comparative Example 10

[0085] The difference between this comparative example and Example 1 is that the magnesium alloy material is a conventional AZ31B magnesium alloy.

[0086] The composition of the AZ31B magnesium alloy is, by mass percentage, Al: 2.5 - 3.5%, Zn: 0.6 - 1.4%, Mn: 0.2 - 1%, the balance of Mg and trace impurities.

[0087] Performance Test

[0088] (1) Since liquid ammonia is extremely easy to vaporize and its vapor pressure is as high as 20 atmospheres, liquid ammonia corrosion must be carried out in a sealed pressure vessel. The magnesium alloys prepared in the examples and comparative examples are processed into round bars with a diameter of 5 mm and a length of 35 mm, and placed in a stainless steel gravity heat pipe filled with liquid ammonia. The temperatures at the upper, middle, and lower measurement points of the gravity heat pipe are measured respectively under the conditions of room temperature and an 80°C oil bath. If the magnesium alloy corrodes in liquid ammonia, hydrogen gas will be generated and accumulate in the upper part of the gravity heat pipe, resulting in a measurable temperature difference between the upper and lower temperature measurement points; if no corrosion reaction occurs, the temperature difference between the upper, middle, and lower temperature measurement points is relatively small (within 0.5 degrees Celsius). The structure of the temperature measurement points, gravity heat pipe, heating sheet, and magnesium alloy specimen is shown in Figure 1 .

[0089] (2)The corrosion tests of the magnesium alloy material prepared in Example 1 were carried out under the above-mentioned room temperature and 80 °C oil bath conditions, and the test results are shown in Table 2-3. Three parallel samples were tested at each temperature, and the average value was taken.

[0090] Test at room temperature:

[0091] After testing for three months at room temperature (from November 2023 to February 2024), the temperature records of the upper, middle, and lower temperature measurement points of the gravity heat pipe containing the magnesium alloy are shown in Table 2 below. It can be seen from Table 2 that the temperature difference between the upper measurement point and the lower measurement point is less than 0.5 degrees Celsius, indicating that the magnesium alloy has not corroded with liquid ammonia. The room temperature test device is shown in Figure 2 .

[0092] Table 2 Corrosion resistance test results of the magnesium alloy material prepared in Example 1 at room temperature in liquid ammonia

[0093]

[0094] Test at 80 °C:

[0095] The part of the gravity heat pipe containing the magnesium alloy described above was placed in an 80-degree Celsius oil bath for heating to evaluate the corrosion resistance of the magnesium alloy in liquid ammonia after heating. The test results are shown in Table 3. The device is as shown in Figure 3 shown.

[0096] Table 3 Corrosion resistance test results of the magnesium alloy material prepared in Example 1 at 80 °C in liquid ammonia

[0097]

[0098] (3)The surface morphology of the magnesium alloy material in Example 1 after three months of corrosion in heated liquid ammonia was tested by SEM. It can be seen from Figure 4 that the surface of the magnesium alloy is still relatively smooth, and the knife marks left on the machined surface are still clearly visible, and no corrosion products are found to cover it. This shows that the magnesium alloy material prepared by the present invention has excellent corrosion resistance in liquid ammonia. The surface layer composition was analyzed by an energy dispersive spectrometer (EDS), and the results are as shown in Figure 5 and Table 4. The main component is magnesium oxide (MgO), which is due to the rapid conversion of magnesium nitride to magnesium oxide (MgO) after contacting with moisture in the air.

[0099] Table 4 Analysis results of surface layer element content

[0100]

[0101] (4)The gravity heat pipes with the conventional AZ31B magnesium alloy (Comparative Example 10) placed inside and without any magnesium alloy specimens were tested for 1 month in a high-temperature environment of 80 °C, and the temperatures at the upper, middle, and lower temperature points were measured. The results are shown in Table 5 below. It can be seen from Table 5 that excessive hydrogen was generated due to the reaction of the ordinary magnesium alloy with liquid ammonia and accumulated at the uppermost end of the gravity heat pipe, resulting in the heat pipe being unable to effectively transfer heat through ammonia, and obvious temperature differences appeared at the upper and lower temperature measurement points. After taking out the corroded AZ31B magnesium alloy, SEM characterization was carried out as follows Figure 6 As shown, it can be seen from the figure that its surface has been covered by corrosion products, indicating that the AZ31B magnesium alloy is not resistant to liquid ammonia corrosion.

[0102] Table 5 Liquid ammonia corrosion resistance test results of the conventional AZ31B magnesium alloy in Comparative Example 7 at 80 °C

[0103]

[0104] (5)The magnesium alloy materials prepared in the examples and comparative examples were all processed into round bars with a diameter of 5 mm and a length of 35 mm, placed in a stainless-steel gravity heat pipe filled with liquid ammonia, and the temperatures at the upper, middle, and lower measurement points of the gravity heat pipe were measured at room temperature, and the temperature difference between the lower measurement point and the upper measurement point was calculated. The test results are shown in Table 6.

[0105] Table 6 Liquid ammonia corrosion resistance performance test results

[0106]

[0107] From the above performance test results, it can be seen that the liquid ammonia corrosion resistance of Examples 1-5 is better, especially the comprehensive performance of Example 1 is the most prominent. This is mainly because Al and rare earth elements such as Y, Nd, and Gd are added to the magnesium alloy material in the present invention. The magnesium alloy with this specific composition ratio can spontaneously form a magnesium nitride protective film in the liquid ammonia environment, and this protective film can effectively prevent the corrosion of the magnesium alloy matrix by liquid ammonia.

[0108] In the comparative examples, since the necessary technical solutions were not adopted, their performance in the corresponding performance tests was significantly worse than that of the examples. In Comparative Example 1, the content of aluminum element was changed, and the content of aluminum element exceeded the range defined in the present invention. It can be seen from the results that the temperature difference between the upper temperature measurement point and the lower temperature measurement point became larger, and the liquid ammonia corrosion resistance of the magnesium alloy material decreased, which proved that the addition amount of aluminum element had an important influence on the corrosion resistance of the magnesium alloy material. In Comparative Examples 2-6, the contents of manganese element, zinc element, yttrium element, neodymium element and gadolinium element were respectively increased, exceeding the range defined in the present invention. It can be seen from the results that the temperature difference between the upper temperature measurement point and the lower temperature measurement point increased to varying degrees compared with Examples 1-5, which proved that the addition amounts of manganese element, zinc element, yttrium element, neodymium element and gadolinium element had a very important influence on the corrosion resistance of the magnesium alloy material. In Comparative Examples 7-9, rare earth elements yttrium, neodymium and gadolinium were not added respectively. It can be seen from the results that the temperature difference between the upper temperature measurement point and the lower temperature measurement point increased further, indicating that the addition of the three rare earth elements in the present invention was very important for improving the corrosion resistance of the magnesium alloy material, and it could also prove that the simultaneous addition of the three rare earth elements had a synergistic effect. Comparative Example 10 used a conventional AZ31B magnesium alloy, the components of which included Mg, Al, Zn, Mn, Si, Fe, Cu and Ni, and did not contain the three rare earth elements Y, Nd and Gd in the present invention. It can be seen from the results that the temperature difference between the upper temperature measurement point and the lower temperature measurement point increased to 19.3 °C, indicating that the magnesium alloy was severely corroded, further proving the importance of adding the three rare earth elements Y, Nd and Gd in the present invention. The above experimental results further proved the importance of the technical solutions defined in the present invention for its technical effects.

[0109] Therefore, the present invention adopts a magnesium alloy material for a spaceborne liquid ammonia heat pipe and its preparation method with the above structure. By adding Al and rare earth elements such as Y, Nd, Gd, the magnesium alloy with this specific composition ratio can spontaneously form a magnesium nitride protective film in a liquid ammonia environment, and this protective film can effectively prevent the corrosion of the liquid ammonia on the magnesium alloy matrix, significantly improving the service life of the material in extreme environments.

[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A magnesium alloy material for aerospace liquid ammonia heat pipes, characterized in that, The magnesium alloy material comprises, by mass percentage, 6% - 11% of Al, 0.1% - 1% of Mn, 0.1% - 0.5% of Zn, 0.05% - 0.5% of Y, 0.1% - 3% of Nd, 0.1% - 2.0% of Gd, the balance being Mg and inevitable impurities; The preparation method of the magnesium alloy material comprises the following steps: (1) Weigh pure magnesium, pure aluminum, magnesium-aluminum alloy, magnesium-manganese alloy, manganese chloride, aluminum-manganese alloy, pure zinc, magnesium-zinc alloy, magnesium-yttrium master alloy, magnesium-neodymium master alloy, and magnesium-gadolinium master alloy according to the mass percentages of the magnesium alloy material; (2) Melting pure magnesium, and after the pure magnesium is melted, adding pure aluminum, magnesium-aluminum alloy, magnesium-manganese alloy, manganese chloride, aluminum-manganese alloy, pure zinc, magnesium-zinc alloy, magnesium-yttrium master alloy, magnesium-neodymium master alloy, and magnesium-gadolinium master alloy, and continuing melting until all the materials are melted to obtain a molten solution; (3) Refining the molten solution and then casting to obtain an ingot; (4) Performing heat treatment on the ingot and cooling to room temperature to obtain the magnesium alloy material; The heat treatment includes at least one of solution heat treatment and aging heat treatment; The aging heat treatment method is heat preservation treatment at 200 - 300 °C for 24 - 48 h, followed by furnace cooling.

2. The magnesium alloy material for an aerospace liquid ammonia heat pipe according to claim 1, wherein The crystal structure of the magnesium alloy material is a close-packed hexagonal crystal structure.

3. The preparation method of a magnesium alloy material for a spaceborne liquid ammonia heat pipe according to claim 2, characterized in that, The casting method is one of gravity casting, high-pressure casting, low-pressure casting, differential pressure casting, or semi-continuous casting.

4. The preparation method of a magnesium alloy material for a spaceborne liquid ammonia heat pipe according to claim 3, characterized in that The solution heat treatment method is heat preservation treatment at 350 - 420 °C for 8 - 12 h, followed by quenching with cold water.

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