High-strength heat-resistant cast magnesium alloy suitable for aeronautical casings and method for producing same

Abstract

The application belongs to the field of magnesium alloy material and casting technology, and particularly relates to a high-strength heat-resistant cast magnesium alloy suitable for an aeroengine case and a preparation method thereof. The magnesium alloy components and their weight percentages are as follows: Gd: 10.0-11.5%, Y: 0-1.0%, Zn: 0-0.3%, Zr: 0.3-1.0%, impurity elements Si<=0.01%, Fe<=0.01%, Cu<=0.01%, Ni<=0.005%, and the rest is Mg.

Description

Technical Field

[0001] This invention belongs to the field of magnesium alloy materials and casting technology, specifically relating to a high-strength heat-resistant cast magnesium alloy suitable for aircraft casings and its preparation method. Background Technology

[0002] With the development of high-speed heavy-load helicopters and hypersonic aircraft, my country has increasingly higher requirements for the load-bearing capacity and service temperature of structural materials used in aircraft gearboxes, and the demand for lightweight equipment is becoming more and more urgent. High-strength heat-resistant cast magnesium alloys have become an inevitable development trend for the selection of materials for the new generation of high-performance helicopter transmission gearboxes and aircraft engine accessory transmission gearboxes.

[0003] Currently, the main high-strength heat-resistant magnesium alloys used in domestic aircraft casings are ZM6 alloy, WE43 alloy, and EV31 alloy. These magnesium alloys either have insufficient comprehensive mechanical properties and heat resistance, or poor casting process performance. In particular, WE43 alloy is prone to oxidation during melting, casting, and mold filling, and the resulting yttrium oxide inclusion defects are difficult to overcome. Therefore, the existing magnesium alloys cannot meet the development requirements of high-speed heavy-load helicopters and hypersonic aircraft, and there is an urgent need to develop new high-strength heat-resistant magnesium alloys.

[0004] Aircraft transmission housings are characterized by large dimensions, significant wall thickness variations, and complex structures, and are primarily manufactured using sand casting. Sand casting suffers from slow solidification rates and a strong tendency for core gas generation. If the selected magnesium alloy has a wide crystallization temperature range and a high content of easily oxidized rare earth elements, metallurgical defects such as porosity and oxide inclusions often occur, resulting in lower mechanical properties. This makes it difficult to meet the technical requirements of magnesium alloy castings for next-generation high-performance helicopter and aircraft transmission housings. Therefore, developing new high-strength, heat-resistant cast magnesium alloys suitable for aircraft housings has become a major research and development issue for high-performance helicopter and aircraft transmission housings.

[0005] The solid solubility of Gd in Mg exhibits a high-temperature, low-temperature solubility pattern, with a relatively high limiting solubility (approximately 23.49 wt.%). This limiting solubility decreases rapidly with decreasing temperature, promoting the formation of numerous nano-precipitates during aging, thus giving Mg-Gd alloys excellent age-hardening properties. A literature search revealed that Chinese invention patent CN105483485B discloses a Mg-Gd high-strength cast magnesium alloy. After solution treatment and aging, this alloy achieves yield strength and tensile strength of 330 MPa and 430 MPa, respectively, but its elongation is low, only about 2.5%, failing to meet the mechanical performance requirements of aerospace transmission housings. Furthermore, excessive addition of rare earth Gd leads to high production costs, poor alloy fluidity, and severe segregation in castings, hindering large-scale engineering applications. Chinese invention patents with publication numbers CN107858575A, CN107090558A, CN106086563A, and CN104928548A each disclose a cast magnesium alloy with a moderate Gd content and its preparation method. Although these magnesium alloys can obtain relatively excellent strength and plasticity after sand casting and corresponding heat treatment, they all contain a large amount of Y element. This means that there is a risk of yttrium oxide inclusion defects in the castings, which will not only greatly increase the difficulty of the casting process, but also seriously affect the fatigue performance of the castings. They are also unsuitable for the development and application of high-performance aerospace casing castings. Summary of the Invention

[0006] Purpose of the invention: To address the shortcomings of existing technologies, this invention provides a high-strength, heat-resistant cast magnesium alloy suitable for aircraft transmission housings and its preparation method, thereby solving the urgent problems of insufficient room-temperature mechanical properties and heat resistance of existing magnesium alloys, poor casting process performance, and failure to meet the development requirements of next-generation aircraft transmission housings.

[0007] The technical solution of this invention is:

[0008] The present invention provides a high-strength heat-resistant cast magnesium alloy suitable for aircraft casings, wherein the high-strength heat-resistant magnesium alloy comprises the following components in weight percentage: Gd: 10.0-11.5%, Y: 0-1.0%, Zn: 0-0.3%, Zr: 0.3-1.0%, impurity elements Si≤0.01%, Fe≤0.01%, Cu≤0.01%, Ni≤0.005%, and the remainder is Mg.

[0009] Preferably, the magnesium alloy composition and its weight percentage are as follows: Gd: 10.2-11.4%, Y: 0.1-0.6%, Zn: 0.1-0.3%, Zr: 0.4-0.8%, impurity elements Si≤0.01%, Fe≤0.01%, Cu≤0.01%, Ni≤0.005%, and the remainder is Mg.

[0010] In another aspect, the present invention provides a method for melting and casting a high-strength, heat-resistant cast magnesium alloy suitable for aircraft casings. The melting and casting method for melting and casting the magnesium alloy includes the following steps:

[0011] Step 1: Batching: Weigh the Mg-Gd master alloy, Mg-Y master alloy, Mg-Zr master alloy, pure Zn ingot, and pure Mg ingot according to the weight percentage of the chemical composition of the magnesium alloy, and dry them.

[0012] Step 2, Melting: Preheat the crucible. In a preheated crucible protected by SF6+CO2 mixed gas or RJ-2 flux, add Mg-Gd master alloy, Mg-Y master alloy, Mg-Zr master alloy, pure Zn ingot and pure Mg ingot, and heat up to melt.

[0013] Step 3, Refining: Reduce the melt temperature to the refining temperature range, use a refining agent to refine the melt, and after refining for a specified time, clean the slag from the surface of the melt and the crucible wall; heat the melt to 800-820℃ and let it stand for 20-30 minutes.

[0014] Step 4: Casting: Lower the temperature of the melt to 750-770℃ and pour the melt into the sand mold filled with a protective atmosphere of SF6+CO2 mixture. After complete solidification, it forms a sand casting or ingot.

[0015] Preferably, in step one, the surfaces of the Mg-Gd master alloy, Mg-Y master alloy, Mg-Zr master alloy, pure Zn ingot, and pure Mg ingot are pre-cleaned using sandblasting or grinding methods; the drying temperature is 200–300°C, and the drying time is 1–2 hours; the mass percentage of Gd in the Mg-Gd master alloy is 30%; the mass percentage of Y in the Mg-Y master alloy is 30%; and the mass percentage of Zr in the Mg-Zr master alloy is 30%.

[0016] Preferably, in step two, a crucible resistance furnace is used for melting, and the specific melting process is as follows: First, preheat the crucible to 400-500°C, then place the pure Mg ingot into the preheated crucible protected by SF6+CO2 mixed gas or RJ-2 flux, and raise the furnace temperature to 720-740°C; after all the pure Mg ingot has melted, raise the melt temperature to 740-760°C and add the pure Zn ingot; continue to raise the melt temperature to 760-780°C and add the Mg-Gd master alloy; after the Mg-Gd master alloy has completely melted, when the melt temperature rises back to 760-780°C, add the Mg-Y master alloy; after the Mg-Y master alloy has melted, raise the melt temperature to 780-800°C and add the Mg-Zr master alloy; after all the furnace charge has completely melted, stir along the crucible wall for 5-10 minutes without disrupting the melt surface.

[0017] Preferably, in step three, the refining temperature range is 750–760°C; the refining agent is RJ-5 flux; the refining process specifically involves: submerging the refining stirrer to 2 / 3 depth of the melt for stirring, while continuously sprinkling RJ-5 flux at the crests of the melt flow, with the total amount of RJ-5 flux accounting for 1.5–2.5% of the total weight of the furnace charge; and the refining time is limited to 10–15 minutes.

[0018] In another aspect, the present invention provides a heat treatment method for high-strength, heat-resistant cast magnesium alloy suitable for aircraft casings. The heat treatment method is used to treat the magnesium alloy or to treat magnesium alloy castings obtained by the melting and casting method. The heat treatment method includes the following steps:

[0019] Step A, Solution treatment: Place the magnesium alloy casting or ingot in a heat treatment furnace and perform a two-stage solution treatment. First, hold at 340-360℃ for 2-2.5 hours, then heat to 515-525℃ and hold for 9-11 hours. After holding at the solution treatment time, cool to room temperature.

[0020] Step B, Aging Treatment: Place the solution-treated castings or ingots into a heat treatment furnace filled with a protective atmosphere, raise the furnace temperature to 220-230℃, hold for 20-40 hours, remove and air-cool to room temperature to obtain high-strength heat-resistant magnesium alloy castings or ingots.

[0021] Preferably, in steps A and B of the heat treatment method, the heat treatment furnace is a pit-type resistance furnace equipped with a fan; the heat treatment furnace needs to be filled with a CO2 protective atmosphere, or a mixture of pyrite and sulfur powder with a mass ratio of 12:1 is placed in advance.

[0022] Preferably, in step A of the heat treatment method, after solution treatment, the cooling method is: quenching in water at 20-30°C or air cooling.

[0023] In another aspect, the present invention provides a method for preparing a high-strength, heat-resistant cast magnesium alloy suitable for aircraft casings. The method is used to prepare the magnesium alloy and includes the melting and casting method and the heat treatment method.

[0024] The advantages of this invention are:

[0025] 1. The high-strength heat-resistant cast magnesium alloy provided by this invention improves the room temperature mechanical properties and heat resistance of the alloy by optimizing the content of Gd and Y elements in the Mg-Gd-Y system alloy, and improves its casting process performance. While ensuring high strength, it reduces its segregation tendency, yttrium oxide inclusion tendency, casting difficulty and production cost, and is suitable for large-scale industrial production of sand casting of aerospace transmission casings.

[0026] 2. The method for preparing high-strength, heat-resistant cast magnesium alloy provided by this invention, through optimization and improvement of the melt purification process, greatly reduces the impurity content in the melt, reduces oxide inclusion defects in the alloy casting, and effectively improves the plasticity and fatigue performance of the alloy casting; through optimization of the solution aging process parameters, the room temperature mechanical properties and heat resistance of the alloy are further improved. The mechanical properties of the casting body are: room temperature tensile strength σ b ≥320MPa, yield strength σ 0.2 ≥210MPa, elongation δ5≥5.5%; tensile strength σ at 250℃ b ≥255MPa, yield strength σ 0.2 ≥180MPa, elongation δ5≥12%; tensile strength σ at 280℃ b ≥225MPa, yield strength σ 0.2 ≥175MPa, elongation δ5≥8%.

[0027] 3. The high-strength heat-resistant cast magnesium alloy and its preparation method for aviation transmission casings provided by this invention can produce magnesium alloy sand castings for direct transmission casings with high metallurgical quality and excellent mechanical properties at both room temperature and high temperature. This solves the technical problem that the comprehensive mechanical properties and heat resistance of commonly used commercial high-strength heat-resistant magnesium alloys (such as ZM6 alloy, WE43 alloy and EV31 alloy) are not good enough. It also solves the bottleneck problems of poor casting processability, serious tendency of segregation and oxide inclusions, and high production cost of existing Mg-Gd-Y series alloys. This is of great significance to the research and development of high-speed heavy-load helicopters and hypersonic aircraft in my country. Attached Figure Description

[0028] Figure 1 Metallographic photograph of the high-strength heat-resistant magnesium alloy casting prepared in Example 1;

[0029] Figure 2Metallographic photograph of the high-strength heat-resistant magnesium alloy casting prepared in Example 3;

[0030] Figure 3 A schematic diagram of the octagonal gas refiner used in Comparative Example 5;

[0031] Figure 4 This is a stereomicroscopic photograph of the tensile fracture surface of the high-strength heat-resistant magnesium alloy casting prepared in Comparative Example 5. Detailed Implementation

[0032] This section describes embodiments of the present invention, used to explain and illustrate the technical solutions of the present invention.

[0033] The present invention will now be described in detail with reference to specific embodiments and accompanying drawings. The following embodiments are implemented under the premise of the technical solution of the present invention and will help those skilled in the art to further understand the present invention. The following embodiments are only a part of the embodiments of the present invention, and not all of them; the present invention is not limited to these embodiments.

[0034] A high-strength, heat-resistant cast magnesium alloy suitable for aircraft casings, wherein the magnesium alloy composition and its weight percentage are as follows: Gd: 10.0-11.5%, Y: 0-1.0%, Zn: 0-0.3%, Zr: 0.3-1.0%, impurity elements Si≤0.01%, Fe≤0.01%, Cu≤0.01%, Ni≤0.005%, and the remainder is Mg.

[0035] A melting and casting method for a high-strength, heat-resistant cast magnesium alloy suitable for aircraft casings includes the following steps:

[0036] Step 1, Batching: Clean the surfaces of the Mg-Gd master alloy, Mg-Y master alloy, Mg-Zr master alloy, pure Zn ingot, and pure Mg ingot by sandblasting or grinding. Weigh the Mg-Gd master alloy, Mg-Y master alloy, Mg-Zr master alloy, pure Zn ingot, and pure Mg ingot according to the weight percentage of the magnesium alloy chemical composition, and dry them. The mass percentage of Gd in the Mg-Gd master alloy is 30%; the mass percentage of Y in the Mg-Y master alloy is 30%; and the mass percentage of Zr in the Mg-Zr master alloy is 30%. The drying temperature is 200-300℃, and the drying time is 1-2 hours.

[0037] Step 2, Melting: Using a crucible resistance furnace, preheat the crucible to 400-500℃. Place the pure Mg ingot into the preheated crucible protected by SF6+CO2 mixed gas or RJ-2 flux, and raise the furnace temperature to 720-740℃. After the pure Mg ingot has completely melted, raise the melt temperature to 740-760℃ and add the pure Zn ingot. Continue to raise the melt temperature to 760-780℃ and add the Mg-Gd master alloy. After the Mg-Gd master alloy has completely melted, when the melt temperature returns to 760-780℃, add the Mg-Y master alloy. After the Mg-Y master alloy has melted, raise the melt temperature to 780-800℃ and add the Mg-Zr master alloy. After all the furnace charge has completely melted, stir along the crucible wall for 5-10 minutes without disrupting the melt surface.

[0038] Step 3, Refining: Reduce the melt temperature to the refining temperature range of 750-760℃. Use RJ-5 flux as a refining agent to refine the melt. Submerge the refining stirrer to 2 / 3 depth of the melt and stir continuously. Simultaneously, sprinkle RJ-5 flux at the crests of the melt flow. The total amount of RJ-5 flux should be 1.5-2.5% of the total weight of the furnace charge. The refining time is limited to 10-15 minutes. After the refining time is completed, clean the slag from the surface of the melt and the crucible wall. Heat the melt to 800-820℃ and let it stand for 20-30 minutes.

[0039] Step 4: Casting: Lower the temperature of the melt to 750-770℃ and pour the melt into the sand mold filled with a protective atmosphere of SF6+CO2 mixture. After complete solidification, it forms a sand casting or ingot.

[0040] A heat treatment method for high-strength, heat-resistant cast magnesium alloy suitable for aircraft casings includes the following steps:

[0041] Step A, Solution Treatment: Place the magnesium alloy sand casting or ingot into a heat treatment furnace and perform a two-stage solution treatment. First, hold at 340-360℃ for 2-2.5 hours, then heat to 515-525℃ and hold for 9-11 hours. After holding at the solution treatment time, cool to room temperature. The cooling method is quenching in water at 20-30℃ or air cooling.

[0042] Step B, Aging Treatment: Place the solution-treated castings or ingots into a heat treatment furnace filled with a protective atmosphere, raise the furnace temperature to 220-230℃, hold for 20-40 hours, remove and air-cool to room temperature to obtain high-strength heat-resistant magnesium alloy castings or ingots.

[0043] The above heat treatment process is carried out in a pit-type resistance furnace equipped with a fan; the furnace must be filled with a CO2 protective atmosphere, or a mixture of pyrite and sulfur powder with a mass ratio of 12:1 must be placed in advance.

[0044] Example 1

[0045] This embodiment provides a high-strength, heat-resistant cast magnesium alloy suitable for aircraft casings. The alloy's chemical composition by weight percentage is: 10.2 wt.% Gd, 0.55 wt.% Y, 0.12 wt.% Zn, 0.52 wt.% Zr, with impurity elements Si, Fe, and Cu all less than 0.01 wt.%, impurity element Ni less than 0.005 wt.%, and the remainder being Mg.

[0046] The preparation method of this high-strength heat-resistant magnesium alloy sand casting includes a melting and casting method and a heat treatment method.

[0047] The specific steps of the smelting and casting method are as follows:

[0048] (1) Batching: First, grind the surface of the raw material ingots required for batching clean. Then, according to the above alloy chemical composition, weigh the corresponding weights of Mg-30wt.%Gd master alloy, Mg-30wt.%Y master alloy, Mg-30wt.%Zr master alloy, pure Zn ingot and pure Mg ingot for batching. Next, place the weighed raw material ingots at 260℃ and dry them for 2 hours.

[0049] (2) Melting: First, preheat the crucible to 450°C, put the pure Mg ingot into the preheated crucible protected by RJ-2 flux, and raise the furnace temperature to 725°C; after the pure Mg ingot has completely melted, raise the melt temperature to 750°C and add the pure Zn ingot; continue to raise the melt temperature to 770°C and add the Mg-Gd master alloy; after the Mg-Gd master alloy has completely melted, when the melt temperature rises back to 770°C, add the Mg-Y master alloy; after the Mg-Y master alloy has melted, raise the melt temperature to 780°C and add the Mg-Zr master alloy; after all the furnace charge has completely melted, stir along the crucible wall for 6 minutes without damaging the melt surface;

[0050] (3) Refining: Reduce the temperature of the melt to 750℃, submerge the refining stirrer to 2 / 3 depth of the melt and stir for 15 minutes. At the same time, continuously sprinkle 2% of the total weight of RJ-5 flux at the crest of the melt flow for refining treatment. Then clean the slag on the surface of the melt and the crucible wall, raise the temperature of the melt to 800℃ and let it stand for 25 minutes.

[0051] (4) Casting: Reduce the temperature of the melt to 760°C and pour the melt into the sand mold filled with a protective atmosphere of SF6+CO2. After it is completely solidified, a sand casting is formed.

[0052] The heat treatment method includes the following steps:

[0053] (1) Solution treatment: The magnesium alloy sand casting is placed in a heat treatment furnace filled with CO2 protective atmosphere. Then the furnace temperature is raised to 350℃ for primary solution treatment. After holding for 2 hours, it is heated to 520℃ for secondary solution treatment. After holding for 10 hours, it is quenched in water at 25℃.

[0054] (2) Aging treatment: The solution-treated casting is placed in a heat treatment furnace filled with a protective atmosphere. The furnace temperature is then raised to 225°C and held for 20 hours. The casting is then taken out and air-cooled to room temperature to obtain the high-strength heat-resistant magnesium alloy casting.

[0055] Metallographic photographs of the high-strength, heat-resistant magnesium alloy sand casting are shown below. Figure 1 The grain size is approximately 73 μm.

[0056] The mechanical properties of this high-strength, heat-resistant magnesium alloy sand casting are as follows:

[0057] The tensile strength at room temperature is 328 MPa, the yield strength is 223 MPa, and the elongation is 5.5%; the tensile strength at 250℃ is 268 MPa, the yield strength is 212 MPa, and the elongation is 12%; the tensile strength at 280℃ is 225 MPa, the yield strength is 194 MPa, and the elongation is 23%; and the tensile strength at 300℃ is 178 MPa, the yield strength is 143 MPa, and the elongation is 29%.

[0058] Example 2

[0059] This embodiment provides a high-strength, heat-resistant cast magnesium alloy suitable for aircraft casings. Its chemical composition is identical to that of Example 1, differing only in the aging treatment parameters. The aging treatment parameters for this embodiment are: aging temperature of 225°C and aging time of 40 hours.

[0060] The mechanical properties of this high-strength, heat-resistant magnesium alloy sand casting are as follows:

[0061] The tensile strength at room temperature is 330 MPa, the yield strength is 220 MPa, and the elongation is 5.0%; the tensile strength at 250℃ is 265 MPa, the yield strength is 207 MPa, and the elongation is 11%; the tensile strength at 280℃ is 228 MPa, the yield strength is 198 MPa, and the elongation is 17%; and the tensile strength at 300℃ is 180 MPa, the yield strength is 144 MPa, and the elongation is 26%.

[0062] Example 3

[0063] This embodiment provides a high-strength, heat-resistant cast magnesium alloy suitable for aircraft casings. The alloy's chemical composition by weight percentage is: 11.4 wt.% Gd, 0.11 wt.% Y, 0.03 wt.% Zn, 0.46 wt.% Zr, with impurity elements Si, Fe, and Cu all less than 0.01 wt.%, impurity element Ni less than 0.005 wt.%, and the remainder being Mg.

[0064] The preparation method of this high-strength heat-resistant magnesium alloy sand casting is exactly the same as that of Example 1, the main difference being that the Gd content in its alloy chemical composition is relatively high.

[0065] Metallographic photographs of the high-strength, heat-resistant magnesium alloy sand casting are shown below. Figure 2 The grain size is approximately 60 μm.

[0066] The mechanical properties of this high-strength, heat-resistant magnesium alloy sand casting are as follows:

[0067] The tensile strength at room temperature is 353 MPa, the yield strength is 217 MPa, and the elongation is 7.5%; the tensile strength at 250℃ is 289 MPa, the yield strength is 221 MPa, and the elongation is 10.5%; the tensile strength at 280℃ is 235 MPa, the yield strength is 198 MPa, and the elongation is 16%; and the tensile strength at 300℃ is 185 MPa, the yield strength is 146 MPa, and the elongation is 25%.

[0068] Comparative Example 1

[0069] This comparative example relates to a high-strength, heat-resistant magnesium alloy with the same chemical composition as Example 1, differing only in the aging treatment parameters. The aging treatment parameters for this comparative example are: aging temperature of 225°C and aging time of 60 hours.

[0070] The mechanical properties of this high-strength heat-resistant magnesium alloy sand casting are as follows: room temperature tensile strength of 314 MPa, yield strength of 210 MPa, and elongation of 4.0%.

[0071] The main difference between this comparative example and Example 1 is the aging time; everything else is exactly the same. The strength and elongation of this comparative example are both lower than those of Example 1.

[0072] Comparative Example 2

[0073] This comparative example relates to a high-strength, heat-resistant magnesium alloy with the same chemical composition as Example 1, differing only in the aging treatment parameters. The aging treatment parameters for this comparative example are: aging temperature of 200℃ and aging time of 20 hours.

[0074] The mechanical properties of this high-strength, heat-resistant magnesium alloy sand casting are as follows: room temperature tensile strength of 311 MPa, yield strength of 208 MPa, and elongation of 4.5%.

[0075] The main difference between this comparative example and Example 1 is the aging temperature; everything else is exactly the same. The strength and elongation of this comparative example are both lower than those of Example 1.

[0076] Comparative Example 3

[0077] This comparative example relates to a high-strength, heat-resistant magnesium alloy with the same chemical composition as Example 2, differing only in the aging treatment parameters. The aging treatment parameters for this comparative example are: aging temperature of 250°C and aging time of 40 hours.

[0078] The mechanical properties of this high-strength heat-resistant magnesium alloy sand casting are as follows: room temperature tensile strength of 283 MPa, yield strength of 196 MPa, and elongation of 8%.

[0079] The main difference between this comparative example and Example 2 is the aging temperature; everything else is exactly the same. The strength of this comparative example is significantly lower than that of Example 2.

[0080] Comparative Example 4

[0081] This comparative example relates to a high-strength heat-resistant magnesium alloy, whose chemical composition by weight percentage is: 9.1 wt.% Gd, 0.96 wt.% Y, 0.14 wt.% Zn, 0.50 wt.% Zr, with impurity elements Si, Fe and Cu each containing less than 0.01 wt.%, impurity element Ni containing less than 0.005 wt.%, and the remainder being Mg.

[0082] The preparation method of this high-strength heat-resistant magnesium alloy sand casting is exactly the same as that of Example 1, the main difference being that the Gd content in its alloy chemical composition is relatively low.

[0083] The mechanical properties of this high-strength heat-resistant magnesium alloy sand casting are as follows: room temperature tensile strength of 197 MPa, yield strength of 284 MPa, and elongation of 9.5%.

[0084] The main difference between this comparative example and Example 1 is the chemical composition; everything else is completely identical. The strength of this comparative example is significantly lower than that of Example 1.

[0085] Comparative Example 5

[0086] This comparative example relates to a high-strength, heat-resistant magnesium alloy with the same chemical composition as Example 1, differing only in the refining treatment method used in the melting and casting process. Specifically, the refining treatment in this comparative example involves lowering the melt temperature to 750°C, followed by preheating the melt in an octagonal disc gas refiner (at 200°C). Figure 3After introducing argon gas, place it at the bottom of the crucible. The argon gas flow rate is 20 L / min, and the refining time is 15 min. After refining, clean the liquid surface and the slag on the crucible wall.

[0087] The mechanical properties of this high-strength heat-resistant magnesium alloy sand casting are as follows: room temperature tensile strength of 261 MPa, yield strength of 203 MPa, and elongation of 3%.

[0088] The main difference between this comparative example and Example 1 is the refining treatment; everything else is identical. The strength and elongation of this comparative example are significantly lower than those of Example 1. A stereomicroscopic photograph of the tensile fracture surface of the alloy casting in this comparative example can be found [link to stereomicroscopic image]. Figure 4 .

Claims

1. A high-strength, heat-resistant cast magnesium alloy suitable for aircraft casings, characterized in that: The magnesium alloy composition and its weight percentage are as follows: Gd: 10.0~11.5%, Y: 0.1~1.0%, Zn: 0.1~0.3%, Zr: 0.3~1.0%, impurity elements Si≤0.01%, Fe≤0.01%, Cu≤0.01%, Ni≤0.005%, and the remainder is Mg.

2. The high-strength, heat-resistant cast magnesium alloy suitable for aircraft casings according to claim 1, characterized in that: The magnesium alloy composition and its weight percentage are as follows: Gd: 10.2~11.4%, Y: 0.1~0.6%, Zn: 0.1~0.3%, Zr: 0.4~0.8%, impurity elements Si≤0.01%, Fe≤0.01%, Cu≤0.01%, Ni≤0.005%, and the remainder is Mg.

3. A method for melting and casting a high-strength, heat-resistant cast magnesium alloy suitable for aircraft casings, wherein the melting and casting method is used for melting and casting the magnesium alloy as described in claim 1 or 2, characterized in that: The method includes the following steps: Step 1: Batching: Weigh the Mg-Gd master alloy, Mg-Y master alloy, Mg-Zr master alloy, pure Zn ingot, and pure Mg ingot according to the weight percentage of the chemical composition of the magnesium alloy, and dry them. Step 2, Melting: Preheat the crucible. In a preheated crucible protected by SF6+CO2 mixed gas or RJ-2 flux, place pure Mg ingots into the crucible and raise the furnace temperature to 720~740℃. After the pure Mg ingots have completely melted, raise the melt temperature to 740~760℃ and add pure Zn ingots. Continue to raise the melt temperature to 760~780℃ and add Mg-Gd master alloy. After the Mg-Gd master alloy has completely melted, raise the melt temperature back to 760~780℃ and add Mg-Y master alloy. After the Mg-Y master alloy has melted, raise the melt temperature to 780~800℃ and add Mg-Zr master alloy. After all the furnace charge has completely melted, stir along the crucible wall for 5~10 minutes without disturbing the melt surface. Step 3, Refining: Reduce the melt temperature to the refining temperature range, use a refining agent to refine the melt, and after the refining time is limited, clean the slag on the surface of the melt and the crucible wall; heat the melt to 800~820℃ and let it stand for 20~30 minutes. Step 4: Casting: Lower the temperature of the melt to 750~770℃ and pour the melt into the sand mold filled with a protective atmosphere of SF6+CO2 mixture. After complete solidification, it forms a sand casting or ingot.

4. The method according to claim 3, characterized in that: In step one, the surfaces of the Mg-Gd master alloy, Mg-Y master alloy, Mg-Zr master alloy, pure Zn ingot, and pure Mg ingot need to be cleaned beforehand by sandblasting or grinding; the drying temperature is 200~300℃, and the drying time is 1~2h; the mass percentage of Gd in the Mg-Gd master alloy is 30%; the mass percentage of Y in the Mg-Y master alloy is 30%; and the mass percentage of Zr in the Mg-Zr master alloy is 30%.

5. The method according to claim 3, characterized in that: In step two, the crucible is preheated to 400~500℃.

6. The method according to claim 3, characterized in that: In step three, the refining temperature range is 750~760℃; the refining agent is RJ-5 flux; the refining process specifically involves: submerging the refining stirrer to 2 / 3 depth of the melt for stirring, while continuously sprinkling RJ-5 flux at the crests of the melt flow, with the total amount of RJ-5 flux accounting for 1.5~2.5% of the total weight of the furnace charge; the refining time is limited to 10~15 minutes.

7. A heat treatment method for high-strength, heat-resistant cast magnesium alloy suitable for aircraft casings, the method being used to treat the magnesium alloy as described in claim 1 or 2, or to treat magnesium alloy castings obtained by any one of the melting and casting methods in claims 3 to 6, characterized in that: The heat treatment method includes the following steps: Step A, Solution treatment: Place the magnesium alloy casting or ingot in a heat treatment furnace and perform a two-stage solution treatment. First, hold at 340~360℃ for 2~2.5h, then heat to 515~525℃ and hold for 9~11h. After holding for the solution treatment time, cool to room temperature. Step B, Aging Treatment: Place the solution-treated castings or ingots into a heat treatment furnace filled with a protective atmosphere, raise the furnace temperature to 220~230℃, hold for 20~40h, remove and air cool to room temperature to obtain high-strength heat-resistant magnesium alloy castings or ingots.

8. The method according to claim 7, characterized in that: In steps A and B of the heat treatment method, the heat treatment furnace is a pit-type resistance furnace equipped with a fan; the heat treatment furnace must be filled with a CO2 protective atmosphere, or a mixture of pyrite and sulfur powder with a mass ratio of 12:1 must be placed in advance.

9. The method according to claim 7, characterized in that: In step A of the heat treatment method, after solution treatment, the cooling method is: quenching in water at 20~30℃ or air cooling.

10. A method for preparing a high-strength, heat-resistant cast magnesium alloy suitable for aircraft casings, the method being used to prepare the magnesium alloy as described in claim 1 or 2, characterized in that: The method includes the smelting and casting method according to any one of claims 3-6 and the heat treatment method according to any one of claims 7-9.

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