Component design and preparation method of high-strength heat-resistant rare earth magnesium alloy for aviation

Abstract

The invention aims to provide a component design and a preparation method of a high-strength heat-resistant Mg-Y-Nd series rare earth magnesium alloy for aviation, and the alloy comprises the following chemical components in percentage by mass: 3-5% of Y, 2.5-3.5% of Nd, 0.5-3% of Gd, 0.5-1.5% of Ce, 0.4-0.6% of Zr and 93.1-86.4% of Mg. The optimized components comprise the following elements in percentage by mass: 3%-5% of Y, 2.5%-3.5% of Nd, 1%-2.5% of Gd, 0.5%-1% of Ce, 0.4%-0.6% of Zr and 92.6%-87.4% of Mg. The preparation method is a gravity casting technology under a pulsed magnetic field, the heat treatment process is solid solution and aging heat treatment, the Gd and Ce elements are added into the Mg-Y-Nd series rare earth magnesium alloy with the high mechanical property, the pulsed magnetic field is applied in the alloy solidification process for treatment, then the solid solution and aging heat treatment is carried out, and the Gd and Ce rare earth magnesium alloy with the high mechanical property is obtained. The two treatment processes can achieve the purpose of further improving the mechanical property of the alloy, so that the alloy is expected to be widely applied to preparation of large complex thin-wall structural components of aircrafts.

Description

Technical Field

[0001] The present invention belongs to the field of composition design and preparation of aviation magnesium alloys, and specifically relates to a composition design and preparation method of a high-strength and heat-resistant rare earth magnesium alloy for aviation. Background Art

[0002] Traditional magnesium-yttrium-neodymium (Mg-Y-Nb) magnesium alloys are widely used in large, complex, thin-walled structural components of aircraft due to their good aging strengthening effect and excellent room temperature comprehensive mechanical properties. However, the development of new products and the upgrading of existing products have put forward higher requirements on the strength and plasticity of materials. The traditional MY-Nd magnesium alloy castings have a relatively coarse structure and can no longer fully meet the application requirements of different engineering fields. Therefore, it is necessary to find an effective strengthening and toughening method to improve the structure of magnesium-yttrium-neodymium rare earth magnesium alloys in order to improve their mechanical properties and break through their application bottlenecks. Literature search found that alloying, pulsed magnetic field treatment and heat treatment are all simple and effective methods to strengthen magnesium alloys.

[0003] In magnesium alloys, rare earth elements are the most effective elements in improving their performance. Adding rare earth elements to magnesium alloys will improve many physical and chemical properties of magnesium alloys, including deoxidation and dehydrogenation, improving creep resistance, and improving alloy strength. Compared with magnesium alloys without rare earth elements, magnesium alloys containing a small amount of one or several rare earth elements are more excellent in mechanical properties, and the improvement in high-temperature performance is particularly obvious. The atomic radius of most rare earth elements is similar to that of magnesium. Under high temperature conditions, most rare earth elements have a certain solid solubility in magnesium, and this solid solubility will decrease rapidly as the temperature decreases. In the process of lowering the temperature, the supersaturated rare earth atoms in the magnesium matrix will precipitate from the magnesium matrix in the form of precipitation phase, so rare earth magnesium alloys have a very good aging hardening effect.

[0004] Among the rare earth elements, Y and Gd are the most commonly used rare earth elements in magnesium alloys, and they are also the two most effective rare earth elements for strengthening magnesium alloys. At high temperatures, the solid solubility of Y in magnesium-based solid solutions is very high, and as the temperature decreases, this solid solubility will drop rapidly. When the temperature drops to about 200°C, the supersaturated Y element in the magnesium matrix will precipitate as a second phase and disperse in the interior and grain boundaries of the α-Mg matrix, preventing the movement of dislocations, and greatly improving the high-temperature and room-temperature mechanical properties of the alloy. At high temperatures, the solid solubility of Gd in magnesium-based solid solutions is also very high. When the temperature increases to 548°C, the solid solubility of Gd in the Mg matrix reaches a maximum value of 23.5wt.%, which is a value that is difficult for other elements to reach, and is higher than the solid solubility of Y. Therefore, in terms of aging hardening reaction, Mg-Gd alloy has a better effect than Mg-Y alloy. At the same time, this Gd easily forms compounds with Mg, which plays a role in grain refinement and second phase strengthening, thereby improving mechanical properties. Therefore, adding Gd elements to magnesium-yttrium-neodymium rare earth magnesium alloys is an effective method to improve their mechanical properties. However, if the heavy rare earth element Gd is added too much, the density of the magnesium alloy will increase, and the advantage of being lighter than aluminum alloys and steel materials will no longer exist, and the room temperature elongation will deteriorate accordingly, and the cost of the alloy will also be greatly increased, and it cannot be widely used in industrial applications. In order to reduce its density and cost, and further improve the performance of magnesium alloys, some relatively light and cheap alloying elements are usually added to Mg-Gd alloys to reduce the amount of Gd, such as Nd, Zr, Ce and other elements. The addition of these elements can greatly improve the high temperature and room temperature mechanical properties of Mg-Y-Gd magnesium alloys.

[0005] In recent years, the application of pulsed magnetic fields during the metal solidification process has been rapidly developed as a method to effectively control the solidification structure and properties of materials. Pulsed magnetic field treatment has the advantages of being pollution-free, easy to operate, and having significant effects, and has been highly valued. One of the main effects of the pulsed magnetic field on the alloy solidification process is that it can refine the metal solidification structure and improve its comprehensive mechanical properties. Many studies have shown that pulsed magnetic fields have the effect of refining the structure of pure metals, low-melting point alloys (aluminum alloys, copper alloys, magnesium alloys, etc.), composite materials, etc. Therefore, with regard to the preparation of the high-strength and heat-resistant Mg-Y-Nd rare earth magnesium alloy in the present invention, the pulsed magnetic field can improve the mechanical properties of the alloy through the effect of grain refinement strengthening, which is of great significance for its promotion and application in the preparation of large, complex, thin-walled structural parts for aircraft.

[0006] In addition, for the heat treatment of cast rare earth magnesium alloys, a solid solution + aging heat treatment process is often required. Solid solution heat treatment refers to a heat treatment process in which the alloy is heated to a high temperature single-phase region and maintained at a constant temperature, so that the second phase is fully dissolved into the solid solution and then rapidly cooled to obtain a supersaturated solid solution. It is suitable for alloys whose solid solubility changes greatly with temperature, and its function is to prepare the best conditions for subsequent aging heat treatment. Aging heat treatment is a process in which the supersaturated solid solution in the alloy decomposes to form a second phase at a certain temperature. Therefore, for heat treatments at different heating temperatures, holding times and cooling rates, the phase transformation laws in the alloy are different, resulting in large differences in the final mechanical properties. In view of the method for alloying Gd and Ce elements in Mg-Y-Nb alloys proposed in the present invention, it is necessary to optimize the process of solid solution aging heat treatment of this new rare earth magnesium alloy so that the precipitation phase strengthening effect of the alloy can be effectively exerted, thereby significantly improving the mechanical properties.

[0007] In summary, the use of alloying, pulsed magnetic field treatment and heat treatment methods to further improve the mechanical properties of rare earth magnesium alloys will help promote the lightweight development of aviation equipment, significantly reduce fuel consumption and increase range, and significantly improve the maneuverability and flexibility of helicopters, further improving the battlefield survivability of equipment, with significant economic and military benefits! Summary of the invention

[0008] The purpose of the present invention is to provide a composition design concept for a high-strength and heat-resistant rare earth magnesium alloy and a gravity casting forming method under pulsed magnetic field treatment.

[0009] The object of the present invention is achieved in that:

[0010] Step 1: Prepare raw materials: Use a cutting machine to cut an appropriate amount of pure magnesium, Mg-30Nd, Mg-30Y, Mg-30Gd, Mg-30Ce and Mg-30Zr master alloy according to the alloy composition, then use a grinder to remove impurities such as oxide scale on the surface, and then place it in an electric heated blast drying oven at 180°C to dry.

[0011] Step 2: Treat the crucible: After cleaning the 304 stainless steel crucible, evenly apply refractory coating (talcum powder: water: water glass = 3:2.5:2) on the inner surface of the crucible 4 times, with an interval of 30 minutes each time, to prevent the crucible from reacting with the metal and ensure the purity of the molten metal. Finally, put the crucible into the above-mentioned drying oven for drying.

[0012] Step 3: Melting: Place the treated stainless steel crucible in a resistance furnace for heating, and put the raw materials into the crucible in the order of pure Mg, Mg-30Y, Mg-30Gd, Mg-30Nd, Mg-30Ce, and Mg-30Zr master alloy. After melting, stir continuously and keep warm for 10 minutes to fully alloy the elements. When the temperature reaches above 750°C, add Mg-30Zr master alloy and stir for 3 to 5 minutes, and then keep warm for another 10 minutes.

[0013] The fourth step is: pouring. Before pouring, stir and slag the melt. When its temperature cools to 720℃, pour the melt into the graphite mold preheated to 200℃. The pulse magnetic field treatment experiment requires the graphite mold to be placed in the coil for pouring. The specific process is as follows: connect the coil to the magnetic field solidification device prepared in advance. After powering on, increase the magnetic field voltage and feel the coil vibrate significantly, indicating that the device is normal, and then return the voltage to zero. Take out the preheated graphite mold from the furnace and place it in the magnetic field coil. After the molten metal is poured into the mold, start the magnetic field immediately. Experiments are carried out under different magnetic field parameters. The pulse voltage range is 100-400V, and the pulse frequency range is 1-10Hz. After the molten metal in the graphite mold solidifies, turn off the device, take out the graphite mold, and take it out after the ingot cools down. The entire smelting and pouring process is carried out under the protection of a mixed gas with a volume fraction of 99.5% CO2+0.5% SF6. During the pouring process, since the pouring temperature of the alloy melt is high, in order to prevent accidents caused by splashing, the following measures should be taken to protect the pouring process: ① When pouring, the crucible mouth should be as close to the mold as possible, and the molten liquid should be poured into the mold slowly to avoid the danger caused by splashing of the molten liquid. The pouring process cannot be interrupted or discontinued; ② The tools in the pouring process need to be preheated first, then painted, and immediately placed in the furnace after use to continue preheating and drying to prevent moisture on the tools from entering the molten liquid and causing dangers such as solution explosion; ③ Wear lab coats, protective masks and gloves.

[0014] Step 5: subject the obtained casting to solution + aging heat treatment, the solution treatment temperature is 480°C-520°C, and the treatment time is 4 to 10 hours; the aging treatment temperature is 180°C-250°C, and the aging treatment time is 20 to 60 hours.

[0015] The characteristics of the present invention are:

[0016] 1) The present invention adopts alloying and solidification technology under a pulsed magnetic field and heat treatment to prepare a high-strength, heat-resistant rare earth magnesium alloy aviation material. This method has a more significant effect on improving the mechanical properties of the alloy.

[0017] 2) The present invention selects Gd and Ce as alloying elements, and the addition temperature is 700-730°C. These two elements can play a significant second phase strengthening effect; and adding Mg-30Zr master alloy above 750°C can make Zr fully melt into the magnesium liquid, and act as a modifier to refine the alloy grains, thereby improving the structure of the alloy and enhancing its strength and plasticity. The optimized alloy composition is (mass percentage): Y: 3-5%, Nd: 2.5-3.5%, Gd: 1-2.5%, Ce: 0.5-1%, Zr: 0.4-0.6%, and the rest is Mg.

[0018] 3) The material forming method of the present invention adopts casting forming technology under pulse magnetic field. Pulse magnetic field treatment has the advantages of no pollution, easy operation, significant effect, etc. It can refine the metal solidification structure and significantly improve the comprehensive mechanical properties of the alloy.

[0019] 4) The optimized pulse magnetic field treatment parameters of the present invention are: voltage range: 300-400V, pulse frequency range: 2.5-5Hz.

[0020] 5) The optimized heat treatment process parameters of the present invention are: solution treatment temperature is 490°C-510°C, and the treatment time is 4-10h; aging treatment temperature is 200°C-230°C, and the aging treatment time is 20-60h. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Phase analysis results of the magnesium alloys of the examples and comparative examples detected by X-ray diffraction analysis. Implementation

[0023] The following is a further description of the embodiments of the present invention in conjunction with specific examples:

[0024] Embodiments 1 to 8:

[0025] The specific data of the alloy composition, magnetic field treatment process parameters and heat treatment methods of Examples 1 to 8 are shown in Table 1.

[0026] Comparative Examples 1 to 10:

[0027] The specific data of the alloy composition, magnetic field treatment process parameters and heat treatment methods of Comparative Examples 1 to 10 are shown in Table 1.

[0028] Table 1 Main alloy components, pulse magnetic field treatment process and heat treatment process of magnesium alloys in Examples and Comparative Examples

[0029]

[0030]

[0031] 1. Hardness test

[0032] The hardness of the alloy was evaluated by Vickers microhardness tester (Hv). The hardness test was performed by loading 50N for 15s on the surface of the metallographically polished sample. Each group of alloy sample surfaces was tested 10 times, and the arithmetic average of the multiple measurement results was taken. The relevant results are shown in Table 2.

[0033] 2. Room temperature tensile mechanical properties test

[0034] The tensile test was carried out on a MTS810 tensile testing machine with a tensile speed of 0.5 mm / min and a test temperature of room temperature. The tensile samples were prepared according to the national standard GB / T228.1-2010. The relevant results are shown in Table 2.

[0035] Table 2 Mechanical properties of magnesium alloys

[0036]

[0037]

[0038] It can be seen from the mechanical properties test results in Table 2 that when the alloy element content is low (Comparative Example 1) or high (Comparative Examples 2 and 3), the magnetic field treatment voltage is low (Comparative Example 4), the magnetic field treatment frequency is low (Comparative Example 5) or high (Comparative Example 6), and the heat treatment temperature is low (Comparative Examples 7 and 8) or high (Comparative Examples 9 and 10), the yield strength, tensile strength, elongation and hardness of the alloy are all low. It can be obtained that the samples within the preferred composition range and the preferred magnetic field treatment and heat treatment process parameters (Examples 1 to 8) have better mechanical properties test results and can better meet the use requirements of large and complex thin-walled parts.

[0039] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A Mg-Y-Nd rare earth magnesium alloy having high room temperature strength and high temperature strength, characterized in that: Calculated by mass percentage, the chemical components of the alloy are: Y: 3-5%, Nd: 2.5-3.5%, Gd: 0.5-3%, Ce: 0.5-1.5%, Zr: 0.4-0.6%, Mg: 93.1-86.4%.

2. The Mg-Y-Nd rare earth magnesium alloy with high room temperature and high temperature strength according to claim 1, characterized in that: The optimized chemical composition of the alloy has the following mass percentages: Y: 3-5%, Nd: 2.5-3.5%, Gd: 1-2.5%, Ce: 0.5-1%, Zr: 0.4-0.6%, and Mg: 92.6-87.4%.

3. The method for preparing a Mg-Y-Nd rare earth magnesium alloy having high room temperature and high temperature strength according to claim 1, characterized in that: The preparation process includes two steps: smelting and heat treatment.

4. The method for preparing a Mg-Y-Nd rare earth magnesium alloy having high room temperature and high temperature strength according to claim 3, characterized in that: The first step of smelting is: heating the raw materials in sequence within the range of 700-800°C until they are melted. The order of adding the raw materials is pure Mg, Mg-30Y, Mg-30Gd, Mg-30Nd, Mg-30Ce, and Mg-30Zr master alloy. After melting, they need to be stirred continuously and kept warm for 10 minutes to fully alloy the elements. When the temperature reaches above 750°C, Mg-30Zr master alloy is added and stirred for 3-5 minutes, and then kept warm for 20 minutes. The second step is pouring. Before pouring, stir and remove the slag from the melt. When the temperature cools to 720°C, pour the melt into a graphite mold preheated to 200°C. The pulse magnetic field treatment experiment requires the graphite mold to be placed in a coil for pouring. The specific process is as follows: connect the coil to the pre-prepared magnetic field solidification device, take out the preheated graphite mold from the furnace and place it in the magnetic field coil. After the molten metal is poured into the mold, start the magnetic field immediately. Experiments are carried out under different magnetic field parameters. After the molten metal in the graphite mold solidifies, turn off the device, take out the graphite mold, and take it out after the ingot cools down. The entire smelting and pouring process is carried out under the protection of a mixed gas with a volume fraction of 99.5% CO2 + 0.5% SF6.

5. The method for preparing a Mg-Y-Nd rare earth magnesium alloy having high room temperature and high temperature strength according to claim 4, characterized in that: The pulse magnetic field coil consists of 3 layers of 6×2mm 2 The flat sandbag wire is wound with 60 turns and a total length of 100 mm, and is wound on a stainless steel cylinder, which is wrapped with asbestos cloth and has an inner diameter of 60 mm. When preparing Mg-Y-Nd rare earth magnesium alloy, the voltage range is 100-400V and the pulse frequency range is 1-10Hz.

6. The method for preparing a Mg-Y-Nd rare earth magnesium alloy having high room temperature and high temperature strength according to claim 5, characterized in that: The optimized pulse magnetic field treatment process parameters are: voltage range is 300-400V, pulse frequency range is 2.5-5Hz.

7. The method for preparing a Mg-Y-Nd rare earth magnesium alloy having high room temperature and high temperature strength according to claim 3, characterized in that: The heat treatment adopts the method of solid solution + aging. The solid solution treatment temperature is 480℃-520℃, and the treatment time is 4 to 10h; the aging treatment temperature is 180℃-250℃, and the aging treatment time is 20 to 60h.

8. The method for preparing a Mg-Y-Nd rare earth magnesium alloy having high room temperature and high temperature strength according to claim 7, characterized in that: Optimized solution treatment temperature The temperature of the aging treatment is 200℃-230℃, and the treatment time is 4-10h. The aging treatment time is 20 to 60 hours.

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