High-performance die-casting magnesium-rare earth alloy and preparation method thereof

Abstract

The invention provides a high-performance die-casting magnesium-rare earth alloy and a preparation method thereof. The die-casting magnesium rare earth alloy comprises the following components in percentage by weight: 5-15% of RE (rare earth); 0.5 to 3 wt.% of X; the balance is Mg; wherein RE comprises at least one of Gd, Y, La, Nd and Sm; and X comprises at least one of Zn, Mn and Zr. The die-casting magnesium rare earth alloy is prepared through smelting, pressure casting and heat treatment. According to the method, the problem that in a traditional casting process, grains are thick easily is solved, a structure with fine grains is obtained through a die casting technology, the structure is further optimized through a proper heat treatment process, strength and plasticity are synergistically improved, and the Mg-RE-X magnesium rare earth alloy material with the fine grains, high strength and high plasticity is successfully prepared; the urgent requirements of the fields of aerospace, rail transit and the like on light, high-strength and high-plasticity magnesium rare earth materials can be met.

Description

Technical Field

[0001] This invention relates to the field of magnesium alloy pressure casting technology, specifically to a high-performance die-cast magnesium rare earth alloy and its preparation method. More particularly, it relates to a high-performance magnesium rare earth alloy material prepared by adding rare earth alloying elements and other non-rare earth elements, including Mn and Zn, and subsequent heat treatment processes. Background Technology

[0002] Magnesium is the lightest structural material. Magnesium alloys are widely used in aerospace, automotive, electronics, and other high-performance engineering fields due to their low density and good mechanical properties. However, traditional magnesium alloys are limited in application due to their low strength and low plasticity. Gravity casting technology, during the solidification of molten magnesium alloys, has a slow cooling rate and long cooling time, facing a series of problems such as coarse grains and compositional segregation, making it difficult to improve both strength and plasticity, thus limiting the application range of magnesium alloy materials.

[0003] Die casting technology is primarily used to address the challenges of mass production of automotive parts and complex-shaped components. It rapidly injects molten magnesium alloy into a mold cavity under pressure, causing it to solidify quickly. The biggest advantage of this technology is its ability to achieve rapid cooling and solidification of the molten metal, resulting in fine grains and a uniform microstructure. Die casting also allows for precise control of the casting temperature of magnesium alloys. Currently, commercially available die-cast magnesium alloys mostly use the AZ (Mg-Al-Zn) system. The main advantage of this system is its good plasticity, but its strength is limited, and compared to the Mg-RE system, its strengthening methods are insufficient. For example, patent CN118241091A is a typical AZ system alloy, but its tensile strength in various examples does not exceed 260 MPa, making it difficult to meet higher strength requirements.

[0004] Rare earth elements are commonly used alloying elements in magnesium alloys. The addition of rare earth elements is beneficial for solid solution strengthening and age hardening of magnesium alloys, increasing their strength and forming reinforcing phases that enhance strength and plasticity. Adding elements such as Zn to rare earth magnesium alloys can reduce stacking fault energy, which is conducive to the formation of long-period stacking-ordered (LPSO) and other strengthening structures. However, we have noticed that the addition of rare earth elements in some die-cast magnesium alloys is often insufficient. This is because the addition of rare earth elements often increases the brittleness of magnesium alloys and affects the fluidity during the casting process, requiring certain technical means to mitigate these effects. For example, in patent CN118345290A, the rare earth element addition is less than 1.5%, but the final strength is still not high. Summary of the Invention

[0005] This invention aims to comprehensively utilize the advantages of die casting technology and magnesium rare earth alloys to provide a high-performance die-cast magnesium rare earth alloy and its preparation method. Specifically, this invention develops a Mg-RE-X magnesium rare earth alloy material with high strength and plasticity. Using alloying methods and die casting technology, a fine-grained as-cast magnesium alloy microstructure is obtained, and the grain size does not significantly increase after heat treatment. This solves the problems of coarse grains and low strength and plasticity in traditional casting processes for Mg-RE materials, significantly improving the overall performance of the material and meeting the urgent needs of aerospace, rail transportation, and other fields for high-performance lightweight materials.

[0006] The Mg-RE-X magnesium rare earth alloy material prepared by the method of this invention has excellent comprehensive mechanical properties. Moreover, it is easy to manufacture and has a simple heat treatment process, which can meet the urgent needs of aerospace, rail transportation and other fields for lightweight and high-strength magnesium alloy materials. Among them, the Mg-Gd-Y-Zn-Mn system magnesium alloy with significant performance advantages is also used for the first time in the die casting process.

[0007] This invention adds X elements (such as Mn, Zn, Zr, etc.) to die-cast magnesium rare earth alloys, which improves the microstructure of the alloys and thus significantly enhances the mechanical and comprehensive properties of magnesium rare earth alloy materials, especially tensile strength and elongation.

[0008] This invention is achieved through the following technical solution:

[0009] In a first aspect, the present invention provides a high-performance die-cast magnesium rare earth alloy, wherein the die-cast magnesium rare earth alloy comprises the following components in the following amounts: RE: 5-15 wt.%; X: 0.5-3 wt.%; balance Mg;

[0010] RE includes at least one of Gd, Y, La, Nd, and Sm; X includes at least one of Zn, Mn, and Zr.

[0011] As a preferred embodiment, the die-cast magnesium rare earth alloy comprises the following components with the following contents: RE: 9-13 wt.%; X: 1-2 wt.%; balance Mg.

[0012] As a preferred embodiment, the RE is at least one of Gd and Y.

[0013] As a preferred embodiment, X is Zn or Mn.

[0014] As a further preferred embodiment, the RE is Gd and Y, and the mass ratio of Gd to Y is 2 to 3.5:1.

[0015] As a further preferred embodiment, the mass ratio of Zn to Mn is 2 to 10:1, more preferably 2:1.

[0016] As a preferred embodiment, the die-cast magnesium rare earth alloy is a Mg-Gd-Y-Zn-Mn alloy.

[0017] Secondly, the present invention provides a method for preparing a high-performance die-cast magnesium rare earth alloy, the method comprising the following steps:

[0018] A. Based on the design composition of the magnesium rare earth alloy, select the intermediate alloy and / or single metal and weigh them;

[0019] B. Place the batched intermediate alloy and / or single metal in a die-casting equipment for melting, and homogenize and purify it by removing slag, stirring and settling.

[0020] C. Using the magnesium rare earth alloy molten liquid formed after melting in step B as raw material, die casting is performed to obtain die castings;

[0021] D. Heat treatment of the die-cast parts yields high-performance die-cast magnesium rare earth alloy.

[0022] As a preferred embodiment, in step A, the intermediate alloy is a binary alloy or a single metal.

[0023] As a preferred option, in step B, the smelting process must ensure a dry environment, the molten liquid must be protected by an inert gas, and the total smelting time must not exceed 5 hours.

[0024] As a preferred embodiment, the temperature during the smelting process shall not exceed 780°C and shall be at least higher than the melting point of all intermediate alloys and / or single metals.

[0025] As a preferred embodiment, in step C, the magnesium rare earth alloy molten liquid must be the upper-middle layer molten liquid in the furnace; the temperature range for die casting the magnesium rare earth alloy molten liquid is 680-740℃; and the pressure value used for die casting is 80-100MPa.

[0026] As a preferred embodiment, the temperature of the mold used for die casting is 240–260°C.

[0027] As a preferred embodiment, in step D, the heat treatment includes solution treatment and aging treatment.

[0028] As a preferred embodiment, the solution treatment temperature is 480–530°C and the time is 0–30 h; the aging treatment temperature is 150–250°C and the time is 0–256 h.

[0029] As a further preferred embodiment, the solution treatment temperature is 515–520℃, and the time is 8–16 hours; the aging treatment temperature is 200℃, and the time is 20 minutes to 2 hours. Under these solution and aging treatment conditions, the performance of the magnesium rare earth alloy can be further improved. The most preferred solution treatment temperature is 515–520℃, and the time is 12–16 hours; the aging treatment temperature is 200℃, and the time is 20–30 minutes.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. The die-cast magnesium rare earth alloy prepared by this invention combines high yield strength, high tensile strength, and high elongation. In particular, by using Mg-9~13wt.%RE-1~2wt.% X-series magnesium alloys, specifically selecting RE as Y or RE as Gd and Y, and X as Zn and Mn, die-cast magnesium rare earth alloys with a T6 yield strength ≥170MPa, a T6 tensile strength ≥290MPa, and a T6 elongation ≥10% can be prepared. The magnesium rare earth alloy of this invention incorporates a higher rare earth content, resulting in more significant solid solution strengthening and age-hardening effects, while also overcoming, to some extent, the problem of high brittleness caused by high rare earth content.

[0032] 2. The die-casting process used in this invention is short, which is beneficial for mass production of finished products. Attached Figure Description

[0033] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0034] Figure 1 The microstructure of Example 1, which was prepared by pressure casting, is compared with that of Comparative Example 1, which was prepared by gravity casting.

[0035] Figure 2 The image shows the microstructure of the Mg-8wt.%Gd-3wt.%Y-1wt.%Zn-0.5wt.%Mn alloy described in Example 1 after T6 treatment. Detailed Implementation

[0036] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0037] The raw materials used in the following embodiments are all obtained through conventional means, and the present invention does not impose any special limitations.

[0038] The die casting method used in the following embodiments is cold chamber die casting. This invention does not impose any special limitations on the specific preparation process conditions.

[0039] The specific heat treatment methods used in the following embodiments are high-temperature furnace solution treatment and oil bath furnace aging treatment, followed by quenching after solution treatment and aging treatment. This invention does not impose specific limitations on the specific preparation process conditions.

[0040] The performance tests conducted in the following examples are performed using the methods specified in GB / T 228.1-2010 "Metallic materials, tensile testing - Part 1: Test at room temperature".

[0041] Example 1

[0042] This embodiment provides a method for preparing high-performance magnesium rare earth alloys using pressure casting technology. The specific steps are as follows:

[0043] 1) Select an alloy of Mg-8wt.%Gd-3wt.%Y-1wt.%Zn-0.5wt.%Mn. Calculate and weigh the intermediate alloys (Mg-Gd, Mg-Y, Mg-Mn) and single metals (pure magnesium and pure zinc) to determine their proportions. The selected raw materials should contain as few impurities as possible. The raw materials should be dried before die casting.

[0044] 2) Clean the furnace to minimize waste. Place the pure magnesium block in the furnace, heat it, and continuously introduce a protective gas mixture of CO2 and SF6. Once the temperature reaches 720℃, wait for the magnesium block to completely melt.

[0045] 3) Add other intermediate alloys to the furnace, raise the furnace temperature to melt them, and the melting time shall not exceed 5 hours. Then hold at 780℃ for 20 minutes.

[0046] 4) Cool down and add refining agent (MgCl2 47.6%, KCl 37.4%, NaCl 12.5%, CaF2 2.5%, the total weight of refining agent is 2% of the total weight of alloy raw materials, unless otherwise specified, the refining agent in other examples and comparative examples is of this type), stir thoroughly and scrape off the oxide slag on the upper surface.

[0047] 5) Cool down to 730℃ and let stand at that temperature. The total time for this process is about 30 minutes.

[0048] 6) Pour the molten metal from the upper and middle layers of the furnace into the pressure chamber of the cold chamber die casting machine (die casting temperature controlled at 730℃). Operate the machine to force the molten metal into the mold at a temperature of 250℃ under a pressure of 90MPa.

[0049] 7) Open the mold to obtain the die-cast part. The as-cast OM structure of the die-cast part is as follows: Figure 1As shown in the middle right figure.

[0050] 8) The die-cast parts were solution-treated in a high-temperature furnace at 515℃ for 12 hours, followed by water quenching. They were then aged in an oil bath at 200℃ for 20 minutes, again followed by water quenching. The SEM image of the microstructure after T6 treatment is shown below. Figure 2 As shown.

[0051] The final performance test results of the Mg-8wt.%Gd-3wt.%Y-1wt.%Zn-0.5wt.%Mn alloy prepared by the above steps are as follows:

[0052] Die-cast yield strength (σ) 0.2 ): 192MPa, tensile strength (σ) b σ0: 289 MPa, elongation (δ): 8.9%; T6 state yield strength (σ0): ... 0.2 ): 185MPa, tensile strength (σ) b 310 MPa, elongation (δ): 14.5%.

[0053] Example 2

[0054] This embodiment provides a method for preparing high-performance magnesium rare earth alloys using pressure casting technology. The specific steps are as follows:

[0055] 1) Select a Mg-6wt.%Y-1wt.%Zn-1wt.%Zr alloy. Calculate and weigh the intermediate alloys (Mg-Y, Mg-Zr) and single metals (pure magnesium and pure zinc) to determine their proportions. The selected raw materials should contain as few impurities as possible. Dry the raw materials before die casting.

[0056] 2) Clean the furnace to minimize waste. Place the pure magnesium block in the furnace, heat it, and continuously introduce a protective gas mixture of CO2 and SF6. Once the temperature reaches 720℃, wait for the magnesium block to completely melt.

[0057] 3) Add other intermediate alloys to the furnace, raise the furnace temperature to melt them, and the melting time shall not exceed 5 hours. Then hold at 780℃ for 20 minutes.

[0058] 4) Cool down, add refining agent at 750℃-760℃, stir thoroughly and scrape off the oxide slag on the upper surface.

[0059] 5) Cool down to 680℃ and let stand at that temperature. The total time for this process is about 30 minutes.

[0060] 6) Pour the molten metal from the upper and middle layers of the furnace into the pressure chamber of the cold chamber die casting machine, and operate the machine to press the molten metal into the mold at a temperature of 250℃ under a pressure of 90MPa.

[0061] 7) Open the mold to obtain the die-cast part.

[0062] 8) The die castings were solution treated in a high-temperature furnace at 480°C for 8 hours. After the solution treatment, the samples were water-quenched. Then, they were placed in an oil bath furnace for aging treatment at 200°C for 0 hours. After the aging treatment, the samples were water-quenched.

[0063] The final performance test results of the Mg-6wt.%Y-1wt.%Zn-1wt.%Zr alloy prepared by the above steps are as follows:

[0064] Die-cast yield strength (σ) 0.2 ): 165MPa, tensile strength (σ) b σ0: 272 MPa, elongation (δ): 15%; T6 state yield strength (σ0): 272 MPa 0.2 ): 160MPa, tensile strength (σ) b 287 MPa, elongation (δ): 23%.

[0065] Example 3

[0066] This embodiment provides a method for preparing high-performance magnesium rare earth alloys using pressure casting technology. The specific steps are as follows:

[0067] 1) Select a Mg-14wt.%Gd-1wt.%La-1.5wt.%Mn alloy. Calculate and weigh the intermediate alloys (Mg-Gd, Mg-La, Mg-Mn) and the single metal (pure magnesium) to determine their proportions. The selected raw materials should contain as few impurities as possible. Dry the raw materials before die casting.

[0068] 2) Clean the furnace to minimize waste. Place the pure magnesium block in the furnace, heat it, and continuously introduce a protective gas mixture of CO2 and SF6. Once the temperature reaches 720℃, wait for the magnesium block to completely melt.

[0069] 3) Add other intermediate alloys to the furnace, raise the furnace temperature to melt them, and the melting time shall not exceed 5 hours. Then hold at 780℃ for 20 minutes.

[0070] 4) Cool down, add refining agent at 750℃-760℃, stir thoroughly and scrape off the oxide slag on the upper surface.

[0071] 5) Cool down to 740℃ and let stand at that temperature. The total time for this process is about 30 minutes.

[0072] 6) Pour the molten metal from the upper and middle layers of the furnace into the pressure chamber of the cold chamber die casting machine, and operate the machine to press the molten metal into the mold at a temperature of 250℃ under a pressure of 90MPa.

[0073] 7) Open the mold to obtain the die-cast part.

[0074] 8) The die-cast parts were solution-treated in a high-temperature furnace at 525°C for 30 hours, followed by water quenching. They were then placed in an oil bath furnace for aging treatment at 225°C for 32 hours. After aging, the parts were water quenched again.

[0075] The final performance test results of the Mg-14wt.%Gd-1wt.%La-1.5wt.%Mn alloy prepared by the above steps are as follows:

[0076] Die-cast yield strength (σ) 0.2 ): 223MPa, tensile strength (σ) b σ0: 276 MPa, elongation (δ): 3.4%; T6 state yield strength (σ0): ...%. 0.2 ): 210MPa, tensile strength (σ) b 340 MPa, elongation (δ): 8.5%.

[0077] Example 4

[0078] This embodiment provides a method for preparing high-performance magnesium rare earth alloys using pressure casting technology. The specific steps are as follows:

[0079] 1) Select a Mg-5wt.%Nd-3wt.%Zr alloy. Calculate and weigh the intermediate alloys (Mg-Nd, Mg-Zr) and the single metal (pure magnesium) to determine their proportions. The selected raw materials should contain as few impurities as possible. Dry the raw materials before die casting.

[0080] 2) Clean the furnace to minimize waste. Place the pure magnesium block in the furnace, heat it, and continuously introduce a protective gas mixture of CO2 and SF6. Once the temperature reaches 720℃, wait for the magnesium block to completely melt.

[0081] 3) Add other intermediate alloys to the furnace, raise the furnace temperature to melt them, and the melting time shall not exceed 5 hours. Then hold at 780℃ for 20 minutes.

[0082] 4) Cool down, add refining agent at 750℃-760℃, stir thoroughly and scrape off the oxide slag on the upper surface.

[0083] 5) Cool down to 700℃ and let stand at that temperature. The total time for this process is about 30 minutes.

[0084] 6) Pour the molten metal from the upper and middle layers of the furnace into the pressure chamber of the cold chamber die casting machine, and operate the machine to press the molten metal into the mold at a temperature of 250℃ under a pressure of 90MPa.

[0085] 7) Open the mold to obtain the die-cast part.

[0086] 8) The die castings were solution treated in a high-temperature furnace at 530°C for 20 hours. After the solution treatment, the samples were water-quenched. Then, they were placed in an oil bath furnace for aging treatment at 150°C for 256 hours. After the aging treatment, the samples were water-quenched.

[0087] The final performance test results of the Mg-5wt.%Nd-3wt.%Zr alloy prepared by the above steps are as follows:

[0088] Die-cast yield strength (σ) 0.2 ): 175MPa, tensile strength (σ) b σ0: 274 MPa, elongation (δ): 15%; T6 state yield strength (σ0): 274 MPa 0.2 ): 167MPa, tensile strength (σ) b 290 MPa, elongation (δ): 7.3%.

[0089] Example 5

[0090] This embodiment provides a method for preparing high-performance magnesium rare earth alloys using pressure casting technology. The specific steps are as follows:

[0091] 1) Select a Mg-8wt.%Sm-0.5wt.%Mn alloy. Calculate and weigh the intermediate alloys (Mg-Sm, Mg-Mn) and the single metal (pure magnesium) to determine their proportions. The selected raw materials should contain as few impurities as possible. Dry the raw materials before die casting.

[0092] 2) Clean the furnace to minimize waste. Place the pure magnesium block in the furnace, heat it, and continuously introduce a protective gas mixture of CO2 and SF6. Once the temperature reaches 720℃, wait for the magnesium block to completely melt.

[0093] 3) Add other intermediate alloys to the furnace, raise the furnace temperature to melt them, and the melting time shall not exceed 5 hours. Then hold at 780℃ for 20 minutes.

[0094] 4) Cool down, add refining agent at 750℃-760℃, stir thoroughly and scrape off the oxide slag on the upper surface.

[0095] 5) Cool down to 720℃ and let stand at that temperature. The total time for this process is about 30 minutes.

[0096] 6) Pour the molten metal from the upper and middle layers of the furnace into the pressure chamber of the cold chamber die casting machine, and operate the machine to press the molten metal into the mold at a temperature of 250℃ under a pressure of 90MPa.

[0097] 7) Open the mold to obtain the die-cast part.

[0098] 8) The die castings were solution treated in a high-temperature furnace at 500°C for 0 hours. After the solution treatment, the samples were water-quenched. Then, they were placed in an oil bath furnace for aging treatment at 175°C for 128 hours. After the aging treatment, the samples were water-quenched.

[0099] The final performance test results of the Mg-8wt.%Sm-0.5wt.%Mn alloy prepared by the above steps are as follows: Die-cast yield strength (σ 0.2 ): 183MPa, tensile strength (σ) b σ0: 280 MPa, elongation (δ): 7.8%; T6 state yield strength (σ0): ... 0.2 ): 213MPa, tensile strength (σ) b 324 MPa, elongation (δ): 5.4%.

[0100] Example 6

[0101] This embodiment provides a method for preparing high-performance magnesium rare earth alloys using pressure casting technology. The specific steps are basically the same as those in Embodiment 1, except that: in step 1), the alloy selected is Mg-6wt.%Gd-3wt.%Y-1wt.%Zn-0.5wt.%Mn; and in step 8), the aging treatment time is 2 hours.

[0102] The final performance test results of the Mg-6wt.%Gd-3wt.%Y-1wt.%Zn-0.5wt.%Mn alloy prepared by the above steps are as follows:

[0103] Die-cast yield strength (σ) 0.2 ): 188MPa, tensile strength (σ) b σ6: 274 MPa, elongation (δ): 11%; T6 state yield strength (σ6): ... 0.2 ): 172MPa, tensile strength (σ) b 292 MPa, elongation (δ): 16%.

[0104] Example 7

[0105] This embodiment provides a method for preparing high-performance magnesium rare earth alloys using pressure casting technology. The specific steps are basically the same as in Embodiment 1, except that: in step 1), the selected alloy is Mg-10wt.%Gd-3wt.%Y-1wt.%Zn-0.5wt.%Mn; in step 8), the solution treatment temperature is 520℃ and the time is 16h; the aging treatment temperature is 200℃ and the time is 30min.

[0106] The final performance test results of the Mg-10wt.%Gd-3wt.%Y-1wt.%Zn-0.5wt.%Mn alloy prepared by the above steps are as follows:

[0107] Die-cast yield strength (σ) 0.2 ): 204MPa, tensile strength (σ) b σ0: 256 MPa, elongation (δ): 5.3%; T6 state yield strength (σ0): ... 0.2 ): 192MPa, tensile strength (σ) b 307 MPa, elongation (δ): 11%.

[0108] Example 8

[0109] This embodiment provides a method for preparing high-performance magnesium rare earth alloys using pressure casting technology. The specific steps are basically the same as in Embodiment 1, except that: in step 1), the selected alloy is Mg-9wt.%Gd-3.5wt.%Y-1wt.%Zn-0.5wt.%Mn. In step 8), the solution treatment temperature is 515℃ and the time is 16h; the aging treatment temperature is 200℃ and the time is 30min.

[0110] The final performance test results of the Mg-9wt.%Gd-3.5wt.%Y-1wt.%Zn-0.5wt.%Mn alloy prepared by the above steps are as follows:

[0111] Die-cast yield strength (σ) 0.2 ): 202MPa, tensile strength (σ) b σ0: 261 MPa, elongation (δ): 6.0%; T6 state yield strength (σ0): ...%. 0.2 ): 189MPa, tensile strength (σ) b 304 MPa, elongation (δ): 12%.

[0112] Example 9

[0113] This embodiment provides a method for preparing high-performance magnesium rare earth alloys using pressure casting technology. The specific steps are basically the same as those in Embodiment 1, except that: in step 1), the alloy selected is Mg-11wt.%Y-1wt.%Zn-0.5wt.%Mn; and in step 8), the aging treatment time is 40 min.

[0114] The final performance test results of the Mg-11wt.%Y-1wt.%Zn-0.5wt.%Mn alloy prepared by the above steps are as follows:

[0115] Die-cast yield strength (σ) 0.2 ): 182MPa, tensile strength (σ)b σ0: 270 MPa, elongation (δ): 13.5%; T6 state yield strength (σ0): ...%. 0.2 ): 174MPa, tensile strength (σ) b 297 MPa, elongation (δ): 18.5%.

[0116] Example 10

[0117] This embodiment provides a method for preparing high-performance magnesium rare earth alloys using pressure casting technology. The specific steps are basically the same as those in Example 8, except that: in step 1), the selected alloy is Mg-9wt.%Gd-3.5wt.%Y-1.3wt.%Zn-0.2wt.%Mn.

[0118] The final performance test results of the Mg-9wt.%Gd-3.5wt.%Y-1.3wt.%Zn-0.2wt.%Mn alloy prepared by the above steps are as follows:

[0119] Die-cast yield strength (σ) 0.2 ): 201MPa, tensile strength (σ) b σ0: 259 MPa, elongation (δ): 6.7%; T6 state yield strength (σ0): ... 0.2 ): 179MPa, tensile strength (σ) b 299 MPa, elongation (δ): 12.7%.

[0120] Example 11

[0121] This embodiment provides a method for preparing high-performance magnesium rare earth alloys using pressure casting technology. The specific steps are basically the same as those in Embodiment 8, except that: in step 1), the selected alloy is Mg-9wt.%Gd-3.5wt.%Y-0.7wt.%Zn-0.8wt.%Mn.

[0122] The final performance test results of the Mg-9wt.%Gd-3.5wt.%Y-0.7wt.%Zn-0.8wt.%Mn alloy prepared by the above steps are as follows:

[0123] Die-cast yield strength (σ) 0.2 ): 201MPa, tensile strength (σ) b σ0: 262 MPa, elongation (δ): 7.2%; T6 state yield strength (σ0): 262 MPa 0.2 ): 178MPa, tensile strength (σ) b 300 MPa, elongation (δ): 13.1%.

[0124] Example 12

[0125] This embodiment provides a method for preparing high-performance magnesium rare earth alloys using pressure casting technology. The specific steps are basically the same as those in Embodiment 8, except that: in step 1), the selected alloy is Mg-9wt.%Gd-3.5wt.%Y-1wt.%Zn-0.5wt.%Zr.

[0126] The final performance test results of the Mg-9wt.%Gd-3.5wt.%Y-1wt.%Zn-0.5wt.%Zr alloy prepared by the above steps are as follows:

[0127] Die-cast yield strength (σ) 0.2 ): 202MPa, tensile strength (σ) b σ0: 254 MPa, elongation (δ): 5.9%; T6 state yield strength (σ0): ... 0.2 ): 169MPa, tensile strength (σ) b 281 MPa, elongation (δ): 9.3%.

[0128] Example 13

[0129] This embodiment provides a method for preparing high-performance magnesium rare earth alloys using pressure casting technology. The specific steps are basically the same as those in Example 8, except that: in step 1), the selected alloy is Mg-9wt.%Gd-3.5wt.%Y-1wt.%Al-0.5wt.%Mn.

[0130] The final performance test results of the Mg-9wt.%Gd-3.5wt.%Y-1wt.%Al-0.5wt.%Mn alloy prepared by the above steps are as follows:

[0131] Die-cast yield strength (σ) 0.2 ): 201MPa, tensile strength (σ) b σ0: 259 MPa, elongation (δ): 6.2%; T6 state yield strength (σ0): ... 0.2 ): 181MPa, tensile strength (σ) b 295 MPa, elongation (δ): 11.7%.

[0132] Example 14

[0133] This embodiment provides a method for preparing high-performance magnesium rare earth alloys using pressure casting technology. The specific steps are basically the same as those in Embodiment 1, except that: in step 1), the selected alloy is Mg-7wt.%Gd-4wt.%Y-1wt.%Al-0.5wt.%Mn.

[0134] The final performance test results of the Mg-7wt.%Gd-4wt.%Y-1wt.%Al-0.5wt.%Mn alloy prepared by the above steps are as follows:

[0135] Die-cast yield strength (σ) 0.2 ): 199MPa, tensile strength (σ) b σ0: 261 MPa, elongation (δ): 7.3%; T6 state yield strength (σ0): 261 MPa 0.2 ): 176MPa, tensile strength (σ) b 294 MPa, elongation (δ): 13.6%.

[0136] Example 15

[0137] This embodiment provides a method for preparing high-performance magnesium rare earth alloys using pressure casting technology. The specific steps are basically the same as those in Embodiment 1, except that: in step 1), the selected alloy is Mg-9wt.%Gd-2wt.%Y-1wt.%Al-0.5wt.%Mn.

[0138] The final performance test results of the 9wt.%Gd-2wt.%Y-1wt.%Al-0.5wt.%Mn alloy prepared by the above steps are as follows:

[0139] Die-cast yield strength (σ) 0.2 ): 206MPa, tensile strength (σ) b σ0: 257 MPa, elongation (δ): 5.7%; T6 state yield strength (σ0): ... 0.2 ): 181MPa, tensile strength (σ) b 292 MPa, elongation (δ): 11.2%.

[0140] Example 16

[0141] This embodiment provides a method for preparing high-performance magnesium rare earth alloys using pressure casting technology, which is basically the same as that in Embodiment 1, except that the die casting temperature is controlled at 670°C, which is lower than 730°C in Embodiment 1.

[0142] Observation of the prepared material revealed that the as-cast structure obtained by die casting contained a large amount of pre-crystallization, with a large average grain size and a high content of casting defects, resulting in insufficient filling capacity and thus affecting the mechanical properties of the material.

[0143] The performance test results of the Mg-8wt.%Gd-3wt.%Y-1wt.%Zn-0.5wt.%Mn material prepared by the above steps are as follows:

[0144] Die-cast yield strength (σ) 0.2): 183MPa, tensile strength (σ) b σ0: 256 MPa, elongation (δ): 2.6%; T6 state yield strength (σ0): 256 MPa 0.2 ): 161MPa, tensile strength (σ) b ): 268 MPa, elongation (δ): 8.2%. Determination of mechanical properties is often influenced by casting defects.

[0145] Comparative Example 1

[0146] This comparative example provides a method for preparing high-performance magnesium rare earth alloys using gravity casting technology, which is basically the same as Example 1, except that step 6) uses gravity casting, specifically:

[0147] 1) Select an alloy of Mg-8wt.%Gd-3wt.%Y-1wt.%Zn-0.5wt.%Mn. Calculate and weigh the intermediate alloys (Mg-Gd, Mg-Y, Mg-Mn) and single metals (pure magnesium and pure zinc) to determine their proportions. The selected raw materials should contain as few impurities as possible. The raw materials should be dried before die casting.

[0148] 2) Clean the surface of the gravity casting iron mold required for casting with a brush, scrape off oxides and other residues, and evenly apply a viscous mixture of graphite and water to the outer surface of the mold, and then keep it in a 200℃ oven to dry.

[0149] 3) Clean the furnace to minimize waste. Place the pure magnesium block in the furnace, heat it, and continuously introduce a protective gas mixture of CO2 and SF6. Wait for the temperature to reach 720℃ and allow the magnesium block to melt completely.

[0150] 4) Add other intermediate alloys to the furnace, raise the furnace temperature to melt them, and the melting time shall not exceed 5 hours. Then hold at 780℃ for 20 minutes.

[0151] 5) Cool down, add refining agent at 750℃-760℃, stir thoroughly and scrape off the oxide slag on the upper surface.

[0152] 6) Cool down to 730℃ and let stand at that temperature. The total time for this process is about 30 minutes.

[0153] 7) Take the molten metal from the middle and upper layers of the furnace and quickly pour it into the gravity casting mold after step 2) through the gating system.

[0154] 8) After the molten metal in the mold cools and solidifies at room temperature, open the mold to obtain the gravity casting.

[0155] 9) The gravity castings were solution treated in a high-temperature furnace at 515°C for 12 hours. After the treatment, the samples were water-quenched. Then, they were placed in an oil bath furnace for aging treatment at 200°C for 20 minutes. After the treatment, the samples were water-quenched.

[0156] The as-cast OM structure of the die-cast part obtained in this comparative example is as follows: Figure 1 As shown in the middle left figure. (By...) Figure 1 It is evident that the as-cast OM structure of the die casting obtained by gravity casting in Comparative Example 1 has coarse grains, which is detrimental to strength and plasticity; while the die casting prepared by Example 1 has significantly finer grain size, which conforms to the principle of fine grain strengthening.

[0157] The performance test results of the gravity-cast Mg-8wt.%Gd-3wt.%Y-1wt.%Zn-0.5wt.%Mn material prepared by the above steps are as follows:

[0158] As-cast yield strength (σ 0.2 ): 162MPa, tensile strength (σ) b σ0: 233 MPa, elongation (δ): 6.7%; T6 state yield strength (σ0): ... 0.2 ): 155MPa, tensile strength (σ) b 262 MPa, elongation (δ): 10.3%.

[0159] Comparative Example 2

[0160] This comparative example provides a method for preparing high-performance magnesium rare earth alloys using pressure casting technology, which is basically the same as Example 2, except that its composition contains only rare earth elements, and the actual composition is Mg-6wt%Y.

[0161] Observation of the prepared material revealed that the grains of the as-cast structure obtained by die casting were not fine enough, and the strengthening phases such as LPSO failed to form after heat treatment, resulting in low overall strength.

[0162] The performance test results of the Mg-6wt%Y material prepared by the above steps are as follows:

[0163] Die-cast yield strength (σ) 0.2 ): 160MPa, tensile strength (σ) b σ6: 234 MPa, elongation (δ): 15%; yield strength in T6 state (σ6) 0.2 ): 150MPa, tensile strength (σ) b 252 MPa, elongation (δ): 18%.

[0164] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A high-performance die-cast magnesium rare earth alloy, characterized in that, The die-cast magnesium rare earth alloy comprises the following components in the following proportions: RE: 5-15 wt.%; X: 0.5-3 wt.%; balance Mg; RE includes at least one of Gd, Y, La, Nd, and Sm; X includes at least one of Zn, Mn, and Zr.

2. The high-performance die-cast magnesium rare earth alloy according to claim 1, characterized in that, The die-cast magnesium rare earth alloy comprises the following components with the following contents: RE: 9-13 wt.%; X: 1-2 wt.%; balance Mg.

3. The high-performance die-cast magnesium rare earth alloy according to claim 1 or 2, characterized in that, The RE is at least one of Gd and Y; X is Zn or Mn.

4. The high-performance die-cast magnesium rare earth alloy according to claim 3, characterized in that, The RE is Gd and Y, and the mass ratio of Gd to Y is 2 to 3.5:

1.

5. The high-performance die-cast magnesium rare earth alloy according to claim 3, characterized in that, The mass ratio of Zn to Mn is 2 to 10:

1.

6. A method for preparing a high-performance die-cast magnesium rare earth alloy according to any one of claims 1 to 5, characterized in that, The method includes the following steps: A. Based on the design composition of the magnesium rare earth alloy, select the intermediate alloy and / or single metal and weigh them; B. Place the batched intermediate alloy and / or single metal in a die-casting equipment for melting, and homogenize and purify it by stirring, removing slag and letting it stand. C. Using the magnesium rare earth alloy molten liquid formed after melting in step B as raw material, die casting is performed to obtain die castings; D. Heat treatment of the die-cast parts yields high-performance die-cast magnesium rare earth alloy.

7. The method for preparing high-performance die-cast magnesium rare earth alloy according to claim 6, characterized in that, In step A, the intermediate alloy is a binary alloy or a single metal.

8. The method for preparing high-performance die-cast magnesium rare earth alloy according to claim 6, characterized in that, In step B, the smelting process must ensure a dry environment, the molten liquid must be protected by an inert gas, and the total smelting time must not exceed 5 hours; The temperature during the smelting process shall not exceed 780°C and shall be at least higher than the melting point of all intermediate alloys and / or single metals.

9. The method for preparing high-performance die-cast magnesium rare earth alloy according to claim 6, characterized in that, In step C, the magnesium rare earth alloy molten liquid must be the upper-middle layer molten liquid in the furnace; the temperature range for die casting the magnesium rare earth alloy molten liquid is 680-740℃; and the pressure value used for die casting is 80-100MPa. The temperature of the mold used for die casting is 240–260°C.

10. The method for preparing high-performance die-cast magnesium rare earth alloy according to claim 6, characterized in that, In step D, the heat treatment includes solution treatment and aging treatment; The solution treatment is performed at a temperature of 480–530°C for 0–30 h; the aging treatment is performed at a temperature of 150–250°C for 0–256 h.

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