A low-density high-modulus high-strength magnesium alloy and a preparation method thereof

Abstract

The application provides a preparation method of a low-density high-modulus high-strength magnesium alloy, comprising the following steps: a) according to the target alloy composition, magnesium ingot, intermediate alloy and pure metal are weighed and put into a smelting furnace, argon is introduced into the smelting furnace until the oxygen content is less than 200 ppm, and heating is performed; after the alloy is melted, when the temperature reaches 730-760 DEG C, degassing refining is started to obtain a degassed high-purity magnesium alloy melt; the target alloy composition is: 4-7 wt% of Gd, 1.5-4 wt% of Y, 1.5-3 wt% of Si, 2-6 wt% of Li, 3-8 wt% of Al, 1-3 wt% of Zn, 1.5-2.5 wt% of Nb, 0.3-0.8% of Zr, and the balance of Mg; b) the degassed high-purity magnesium alloy melt obtained in step a) is sequentially subjected to casting, homogenization, forging and aging to obtain a low-density high-modulus high-strength magnesium alloy. The low-density high-modulus high-strength magnesium alloy prepared by the preparation method has the performance indexes of: the elastic modulus is greater than or equal to 57 GPa, the tensile strength is greater than or equal to 390 MPa, the elongation after fracture is greater than or equal to 6%, and the density is less than or equal to 1.86 g / cm 3 , which meets the demand of lightweight of aerospace vehicles.

Description

Technical Field

[0001] This invention relates to the field of alloy materials technology, and more specifically, to a low-density, high-modulus, high-strength magnesium alloy and its preparation method. Background Technology

[0002] Magnesium alloys typically have a density of 1.8–1.95 g / cm³. 3 As a typical lightweight structural material, magnesium alloys have significant advantages and potential in structural weight reduction. However, due to their low elastic modulus (only around 40-45 GPa, far lower than conventional aluminum, titanium, and alloy steel), magnesium alloy structures require increased weight to meet structural stiffness requirements. This significantly reduces the weight reduction effect of magnesium alloys and greatly limits their application in the aerospace field.

[0003] The elastic modulus is not sensitive to changes in microstructure, and the main methods used both domestically and internationally are composite and alloying. Composites are problematic because poor bonding between the reinforcing phase and the matrix in magnesium-based composites often leads to poor strength and toughness. Furthermore, the preparation of magnesium-based composites is difficult, hindering large-scale industrial production. Alloying, on the other hand, is the most fundamental and effective way to improve the modulus of magnesium alloys, but currently, there is only limited research in China, and corresponding engineering preparation methods and practical applications have not been reported.

[0004] Chinese patent CN114574744A discloses a high-modulus magnesium alloy and its preparation method, which is prepared using rare earth elements, Al, Si, and other elements, and is melted and cast under the protection of a mixed gas of SF6 and CO2. This method achieves a magnesium alloy with a room temperature elastic modulus of 60.7 GPa, a tensile strength of 317.1 MPa, and an elongation after fracture of 0.8%. The modulus meets the requirements, but the strength and elongation are relatively low. Chinese patent CN109161770A discloses a high-modulus magnesium alloy and its preparation method, which uses vacuum melting and brine cooling to achieve an elastic modulus of 52–55 GPa and a strength of 248 MPa; however, the performance of the magnesium alloy prepared by this method does not meet the existing performance requirements. In addition, Chinese patent CN107641750A discloses an in-situ self-generated precipitate phase reinforced high-strength and high-modulus magnesium alloy and its preparation method, which achieves the preparation of magnesium alloy with tensile strength of 302 MPa, yield strength of 218 MPa, elongation of 3.2% and elastic modulus of 57 GPa; however, the performance of the magnesium alloy prepared by this method also cannot meet the existing requirements.

[0005] In summary, none of the aforementioned existing preparation methods achieve an elastic modulus ≥ 57 GPa, tensile strength ≥ 390 MPa, elongation after fracture ≥ 6%, and density ≤ 1.86 g / cm³. 3The development of high-performance magnesium alloys is in high demand. Therefore, providing a low-density, high-modulus, and high-strength magnesium alloy and its preparation method to meet the lightweight requirements of aerospace vehicles has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide a low-density, high-modulus, high-strength magnesium alloy and its preparation method. The low-density, high-modulus, high-strength magnesium alloy prepared by the method provided by this invention has the following performance indicators: elastic modulus ≥ 57 GPa, tensile strength ≥ 390 MPa, elongation after fracture ≥ 6%, and density ≤ 1.86 g / cm³. 3 .

[0007] This invention provides a method for preparing a low-density, high-modulus, high-strength magnesium alloy, comprising the following steps:

[0008] a) Weigh magnesium ingots, master alloys, and pure metals according to the target alloy composition and put them into a melting furnace. Introduce argon gas until the oxygen content in the melting furnace is less than 200 ppm and heat the furnace. After the alloy melts, when the temperature reaches 730℃~760℃, start degassing and refining to obtain a degassed high-purity magnesium alloy melt.

[0009] The target alloy composition is:

[0010] 4–7 wt% Gd, 1.5–4 wt% Y, 1.5–3 wt% Si, 2–6 wt% Li, 3–8 wt% Al, 1–3 wt% Zn, 1.5–2.5 wt% Nb, 0.3–0.8 wt% Zr, balance Mg;

[0011] b) The degassed high-purity magnesium alloy melt obtained in step a) is sequentially subjected to casting, homogenization, forging and aging to obtain a low-density, high-modulus and high-strength magnesium alloy.

[0012] Preferably, the master alloy in step a) includes magnesium-gadolinium master alloy, magnesium-yttrium master alloy, magnesium-silicon master alloy, magnesium-niobium master alloy, and magnesium-zirconium master alloy;

[0013] The pure metals include pure aluminum ingots, pure zinc ingots, and pure lithium ingots.

[0014] Preferably, the degassing and refining process in step a) uses argon gas with a flow rate of 40-60 In / min, an argon gas pressure of 4-7 barg, and a rotor speed of 720-850 rpm.

[0015] Preferably, the casting process described in step b) specifically includes:

[0016] Argon gas is introduced into the flow channel and the crystallizer. When the oxygen content in the flow channel and the crystallizer is less than 50 ppm, the degassed high-purity magnesium alloy melt is introduced into the crystallizer through the flow channel for semi-continuous direct cooling casting to obtain an ingot.

[0017] Preferably, the casting speed of the semi-continuous direct cooling casting is 25–55 mm / min, and the water flow rate is 90–140 m³ / min. 3 / h.

[0018] Preferably, the homogenization process described in step b) specifically includes:

[0019] The cast ingot is sent to a homogenizing furnace for homogenization to obtain a homogenized ingot; the homogenization temperature is 480-520℃ and the holding time is 20-32h.

[0020] Preferably, the forging process described in step b) specifically includes:

[0021] The homogenized ingot is heated to 440–480℃ and held for 8–12 hours before being sent to a forging press for forging. A multi-directional slow deformation process is adopted, with a forging speed of 0.5–3 mm / s, to obtain a forged sample.

[0022] Preferably, the multi-directional slow deformation process is a four-upsetting and four-drawing process.

[0023] Preferably, the aging temperature in step b) is 170–230°C, and the holding time is 45–65 h.

[0024] The present invention also provides a low-density, high-modulus, high-strength magnesium alloy, which is prepared by the preparation method described in the above technical solution.

[0025] This invention provides a low-density, high-modulus, high-strength magnesium alloy and its preparation method. The preparation method includes the following steps: a) Weighing magnesium ingots, intermediate alloys, and pure metals according to the target alloy composition and putting them into a melting furnace, introducing argon gas until the oxygen content in the melting furnace is less than 200 ppm, and heating the furnace; after the alloy melts, when the temperature reaches 730℃~760℃, degassing and refining are started to obtain a degassed high-purity magnesium alloy melt; the target alloy composition is: 4~7wt% Gd, 1.5~4wt% Y, 1.5~3wt% Si, 2~6wt% Li, 3~8wt% Al, 1~3wt% Zn, 1.5~2.5wt% Nb, 0.3~0.8% Zr, with the balance being Mg; b) The degassed high-purity magnesium alloy melt obtained in step a) is sequentially subjected to casting, homogenization, forging, and aging to obtain a low-density, high-modulus, high-strength magnesium alloy. Compared with existing technologies, the preparation method provided by this invention uses specific chemical components and specific process steps to achieve better overall interaction. The resulting low-density, high-modulus, high-strength magnesium alloy meets the following performance indicators: elastic modulus ≥ 57 GPa, tensile strength ≥ 390 MPa, elongation after fracture ≥ 6%, and density ≤ 1.86 g / cm³. 3 This meets the requirements for lightweight aerospace vehicles. Detailed Implementation

[0026] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0027] This invention provides a method for preparing a low-density, high-modulus, high-strength magnesium alloy, comprising the following steps:

[0028] a) Weigh magnesium ingots, master alloys, and pure metals according to the target alloy composition and put them into a melting furnace. Introduce argon gas until the oxygen content in the melting furnace is less than 200 ppm and heat the furnace. After the alloy melts, when the temperature reaches 730℃~760℃, start degassing and refining to obtain a degassed high-purity magnesium alloy melt.

[0029] The target alloy composition is:

[0030] 4–7 wt% Gd, 1.5–4 wt% Y, 1.5–3 wt% Si, 2–6 wt% Li, 3–8 wt% Al, 1–3 wt% Zn, 1.5–2.5 wt% Nb, 0.3–0.8 wt% Zr, balance Mg;

[0031] b) The degassed high-purity magnesium alloy melt obtained in step a) is sequentially subjected to casting, homogenization, forging and aging to obtain a low-density, high-modulus and high-strength magnesium alloy.

[0032] The present invention first weighs magnesium ingots, master alloys and pure metals according to the target alloy composition and puts them into a melting furnace. Argon gas is introduced into the melting furnace until the oxygen content is less than 200 ppm, and the temperature is raised. After the alloy melts, when the temperature reaches 730℃~760℃, degassing and refining are started to obtain a degassed high-purity magnesium alloy melt.

[0033] In this invention, the target alloy composition is:

[0034] 4–7 wt% Gd, 1.5–4 wt% Y, 1.5–3 wt% Si, 2–6 wt% Li, 3–8 wt% Al, 1–3 wt% Zn, 1.5–2.5 wt% Nb, 0.3–0.8 wt% Zr, balance Mg;

[0035] Preferred options are:

[0036] 5-6 wt% Gd, 2-3 wt% Y, 2 wt% Si, 3-4 wt% Li, 5 wt% Al, 2 wt% Zn, 2 wt% Nb, 0.5% Zr, balance Mg.

[0037] This invention uses magnesium ingots, master alloys, and pure metals as raw materials; the master alloys preferably include magnesium-gadolinium master alloys, magnesium-yttrium master alloys, magnesium-silicon master alloys, magnesium-niobium master alloys, and magnesium-zirconium master alloys; the pure metals preferably include pure aluminum ingots, pure zinc ingots, and pure lithium ingots. This invention does not impose any special restrictions on the source of the above raw materials; commercially available products well-known to those skilled in the art can be used.

[0038] In this invention, the degassing and refining process preferably uses argon gas, with an argon gas flow rate preferably of 40-60 In / min, more preferably 50-60 In / min, an argon gas pressure preferably of 4-7 barg, more preferably 4-5 barg, and a rotor speed preferably of 720-850 rpm, more preferably 750-770 rpm.

[0039] The present invention obtains a degassed high-purity magnesium alloy melt through the above-mentioned smelting process; then, the present invention sequentially processes the obtained degassed high-purity magnesium alloy melt through casting, homogenization, forging and aging to obtain a low-density, high-modulus and high-strength magnesium alloy.

[0040] In this invention, the casting process is preferably as follows:

[0041] Argon gas is introduced into the flow channel and the crystallizer. When the oxygen content in the flow channel and the crystallizer is less than 50 ppm, the degassed high-purity magnesium alloy melt is introduced into the crystallizer through the flow channel for semi-continuous direct cooling casting to obtain an ingot.

[0042] In this invention, the casting speed of the semi-continuous direct cooling casting is preferably 25-55 mm / min, more preferably 30-40 mm / min, and the water flow rate is preferably 90-140 m³ / min. 3 / h, more preferably 100-110m 3 / h.

[0043] In this invention, the homogenization process is preferably specifically as follows:

[0044] The cast ingot is sent to a homogenizing furnace for homogenization to obtain a homogenized ingot; the homogenization temperature is preferably 480-520℃, more preferably 490-510℃, and the holding time is preferably 20-32h, more preferably 24-26h.

[0045] In this invention, the forging process is preferably as follows:

[0046] The homogenized ingot is heated to 440-480℃ and held for 8-12 hours before being sent to a forging press for forging. A multi-directional slow deformation process is adopted, and the forging speed is 0.5-3 mm / s to obtain a forged sample.

[0047] More preferably:

[0048] The homogenized ingot is heated to 450-460℃ and held for 9-11 hours before being sent to a forging press for forging. A multi-directional slow deformation process is adopted, with a forging speed of 1.5-2.5 mm / s, to obtain a forged sample.

[0049] In this invention, the multi-directional slow deformation process is preferably a four-upsetting and four-drawing process.

[0050] In this invention, the aging temperature is preferably 170-230°C, more preferably 200-220°C, and the heat preservation time is preferably 45-65 hours, more preferably 50-60 hours.

[0051] This invention proposes a method for producing high-purity magnesium alloy ingots under full-process, fully enclosed inert gas protection by designing a multi-phase composite composition of "Gd and Y heavy rare earth elements enhancement + Mg2Si, Si3Gd5, Si2Y modulus increase + Al3Li density reduction modulus increase + Al3Nb enhancement modulus increase".

[0052] This invention also provides a low-density, high-modulus, high-strength magnesium alloy, prepared using the method described above. This invention optimizes the chemical composition by incorporating reinforcing, modulus-enhancing phases and low-density elements, resulting in a chemical composition scheme that meets the requirements. Combined with a fully enclosed argon-protected melting and casting method, along with a medium-temperature slow-deformation process and corresponding heat treatment, a low-density, high-modulus, high-strength magnesium alloy is prepared. The performance indicators meet the following requirements: elastic modulus ≥ 57 GPa, tensile strength ≥ 390 MPa, elongation after fracture ≥ 6%, and density ≤ 1.86 g / cm³. 3 It can be industrialized and has broad application prospects.

[0053] The present invention has the following beneficial effects:

[0054] (1) By employing specific chemical compositions and specific process steps, a better overall interaction is achieved, and the resulting low-density, high-modulus, high-strength magnesium alloy meets the following performance requirements: elastic modulus ≥ 57 GPa, tensile strength ≥ 390 MPa, elongation after fracture ≥ 6%, and density ≤ 1.86 g / cm³. 3 To meet the lightweight requirements of aerospace vehicles;

[0055] (2) The entire process of smelting and casting low-density, high-modulus, and high-strength magnesium alloys is protected by a fully enclosed argon gas system to control the generation of oxide inclusions and improve the purity of the melt, thereby solving the problem of reduced formability and plasticity caused by the addition of a large amount of high-strength and high-modulus phases.

[0056] (3) The low-density, high-modulus, high-strength magnesium alloy is plastically deformed by adopting a medium-temperature slow deformation process.

[0057] This invention provides a low-density, high-modulus, high-strength magnesium alloy and its preparation method. The preparation method includes the following steps: a) Weighing magnesium ingots, intermediate alloys, and pure metals according to the target alloy composition and putting them into a melting furnace, introducing argon gas until the oxygen content in the melting furnace is less than 200 ppm, and heating the furnace; after the alloy melts, when the temperature reaches 730℃~760℃, degassing and refining are started to obtain a degassed high-purity magnesium alloy melt; the target alloy composition is: 4~7wt% Gd, 1.5~4wt% Y, 1.5~3wt% Si, 2~6wt% Li, 3~8wt% Al, 1~3wt% Zn, 1.5~2.5wt% Nb, 0.3~0.8% Zr, with the balance being Mg; b) The degassed high-purity magnesium alloy melt obtained in step a) is sequentially subjected to casting, homogenization, forging, and aging to obtain a low-density, high-modulus, high-strength magnesium alloy. Compared with existing technologies, the preparation method provided by this invention uses specific chemical components and specific process steps to achieve better overall interaction. The resulting low-density, high-modulus, high-strength magnesium alloy meets the following performance indicators: elastic modulus ≥ 57 GPa, tensile strength ≥ 390 MPa, elongation after fracture ≥ 6%, and density ≤ 1.86 g / cm³. 3 This meets the requirements for lightweight aerospace vehicles.

[0058] To further illustrate the present invention, the following embodiments are provided for detailed description. All raw materials used in the following embodiments of the present invention are commercially available.

[0059] Example 1

[0060] A method for preparing a low-density, high-modulus, high-strength magnesium alloy, with an ingot diameter of Φ470mm, includes the following steps:

[0061] (1) The chemical composition of the magnesium alloy by mass percentage is: 5% Gd, 2% Y, 2% Si, 4% Li, 5% Al, 2% Zn, 2% Nb, 0.5% Zr, with the balance being Mg (a very small amount of impurities exist, which are ignored here); Magnesium ingots, master alloys, and pure metals are weighed as raw materials according to the composition of the target alloy. The above raw materials are put into the melting furnace, and argon gas is introduced into the melting furnace. When the oxygen content in the melting furnace is less than 200ppm, heating is started; After the alloy melts, when the temperature reaches 745℃, degassing and refining are started. Argon gas is used for refining, with an argon gas flow rate of 60In / min, an argon gas pressure of 4.8barg, and a rotor speed of 760rpm.

[0062] (2) Argon gas is introduced into the casting tank and crystallizer. When the oxygen content in the casting tank and crystallizer is less than 50 ppm, the degassed high-purity magnesium alloy melt is introduced into the crystallizer through the casting tank for semi-continuous direct cooling casting. The casting speed is 35 mm / min and the water flow rate is 105 m³ / min. 3 / h.

[0063] (3) The ingot is sent into a homogenizing furnace for homogenization. The homogenization temperature is 500℃ and the temperature is held for 25 hours.

[0064] (4) Heat the ingot to 455℃ and keep it at that temperature for 10 hours. Then send it to the forging press for forging. Use a four-upsetting and four-drawing process. The forging speed is 2mm / s. The sample size is 200mm×200mm×100mm.

[0065] (5) After forging, aging is carried out at 210℃ for 55 hours to obtain a low-density, high-modulus, high-strength magnesium alloy.

[0066] Example 2

[0067] A method for preparing a low-density, high-modulus, high-strength magnesium alloy, with an ingot diameter of Φ470mm, includes the following steps:

[0068] (1) The chemical composition of the magnesium alloy by mass percentage is: 6% Gd, 3% Y, 2% Si, 3% Li, 5% Al, 2% Zn, 2% Nb, 0.5% Zr, with the balance being Mg (a very small amount of impurities are present, which are ignored here); Magnesium ingots, master alloys, and pure metals are weighed as raw materials according to the composition of the target alloy. The above raw materials are put into the melting furnace, and argon gas is introduced into the melting furnace. When the oxygen content in the melting furnace is less than 200ppm, heating is started; After the alloy melts, when the temperature reaches 745℃, degassing and refining are started. Argon gas is used for refining, with an argon gas flow rate of 60In / min, an argon gas pressure of 4.8barg, and a rotor speed of 760rpm.

[0069] (2) Argon gas is introduced into the casting tank and crystallizer. When the oxygen content in the casting tank and crystallizer is less than 50 ppm, the degassed high-purity magnesium alloy melt is introduced into the crystallizer through the casting tank for semi-continuous direct cooling casting. The casting speed is 35 mm / min and the water flow rate is 105 m³ / min. 3 / h.

[0070] (3) The ingot is sent into a homogenizing furnace for homogenization. The homogenization temperature is 500℃ and the temperature is held for 25 hours.

[0071] (4) Heat the ingot to 455℃ and keep it at that temperature for 10 hours. Then send it to the forging press for forging. Use a four-upsetting and four-drawing process. The forging speed is 2mm / s. The sample size is 200mm×200mm×100mm.

[0072] (5) After forging, aging is carried out at 210℃ for 55 hours to obtain a low-density, high-modulus, high-strength magnesium alloy.

[0073] Comparative Example 1

[0074] The preparation method provided in Example 1 was used, except that Nb was not added; a magnesium alloy was obtained.

[0075] Comparative Example 2

[0076] The preparation method provided in Example 1 was used, except that the forging speed was 5 mm / s; a magnesium alloy was obtained.

[0077] The magnesium alloys prepared in the above embodiments and comparative examples were subjected to various performance tests, and the results are shown in Table 1.

[0078] Table 1. Performance data of magnesium alloys prepared in the examples and comparative examples.

[0079] Example 1 395 8.2 58.1 1.79 Example 2 407 6.7 57.5 1.82 Comparative Example 1 372 10.1 56.2 1.76 Comparative Example 2 392 4.9 58 1.8

[0080] As can be seen from Table 1, the magnesium alloy prepared by using the alloy composition ratio and corresponding melting, casting, forging and heat treatment processes of the present invention has better performance than the magnesium alloy technical indicators disclosed in the prior art and meets the application requirements of the corresponding aerospace field.

[0081] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a low-density, high-modulus, high-strength magnesium alloy, characterized in that, Includes the following steps: a) Weigh magnesium ingots, master alloys, and pure metals according to the target alloy composition and put them into a melting furnace. Introduce argon gas until the oxygen content in the melting furnace is less than 200 ppm and heat the furnace. After the alloy melts, when the temperature reaches 730℃~760℃, start degassing and refining to obtain a degassed high-purity magnesium alloy melt. The target alloy composition is: 4~7wt% Gd, 1.5~4wt% Y, 1.5~3wt% Si, 2~6wt% Li, 3~8wt% Al, 1~3wt% Zn, 1.5~2.5wt% Nb, 0.3~0.8wt% Zr, balance Mg; The degassing and refining process uses argon gas with a flow rate of 40-60 In / min, an argon gas pressure of 4-7 barg, and a rotor speed of 720-850 rpm. b) The degassed high-purity magnesium alloy melt obtained in step a) is sequentially subjected to casting, homogenization, forging and aging to obtain a low-density, high-modulus and high-strength magnesium alloy. The forging process is as follows: The homogenized ingot is heated to 440~480℃ and held for 8~12 hours. Then it is sent to a forging press for forging. A multi-directional slow deformation process is adopted, and the forging speed is 0.5~3mm / s to obtain a forging sample. The aging temperature described in step b) is 170~230℃, and the holding time is 45~65h; The casting process described in step b) is as follows: Argon gas is introduced into the flow channel and the crystallizer. When the oxygen content in the flow channel and the crystallizer is less than 50 ppm, the degassed high-purity magnesium alloy melt is introduced into the crystallizer through the flow channel for semi-continuous direct cooling casting to obtain an ingot. The semi-continuous direct cooling casting has a casting speed of 25~55 mm / min and a water flow rate of 90~140 m³ / min. 3 / h.

2. The preparation method according to claim 1, characterized in that, The master alloys mentioned in step a) include magnesium-gadolinium master alloys, magnesium-yttrium master alloys, magnesium-silicon master alloys, magnesium-niobium master alloys, and magnesium-zirconium master alloys; The pure metals include pure aluminum ingots, pure zinc ingots, and pure lithium ingots.

3. The preparation method according to claim 1, characterized in that, The homogenization process described in step b) is specifically as follows: The cast ingot is sent to a homogenizing furnace for homogenization to obtain a homogenized ingot; the homogenization temperature is 480~520℃ and the holding time is 20~32h.

4. The preparation method according to claim 1, characterized in that, The multi-directional slow deformation process is a four-upsetting and four-drawing process.

5. A low-density, high-modulus, high-strength magnesium alloy, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 4.