A creep-resistant die casting rare earth magnesium alloy with high strength and high fluidity, a preparation method and application thereof

Abstract

The application discloses a creep-resistant die-casting rare earth magnesium alloy with high strength and high fluidity, and a preparation method and application thereof. The application belongs to the field of die-casting magnesium alloys. The magnesium alloy comprises, in percentage by mass, Al: 4.8-7.2%, La: 3.0-4.2%, Sm: 1.2-2.0%, Y: 0.4-1.2%, Mn: 0.1-0.6%, Te: 0.01-0.1%, Bi: 0.01-0.5%, and the balance of Mg and inevitable impurity elements. The application significantly refines the structure of the magnesium alloy by optimizing the alloy composition, changes the composition, distribution and morphology of intermetallic compounds in the alloy, simultaneously generates Al-Te phases stable at high temperatures, improves the mechanical properties and creep resistance of the magnesium alloy, and further improves the die-casting fluidity of the magnesium alloy, so as to meet the requirements of large-scale integrated design automobile parts.

Description

A creep-resistant die-cast rare earth magnesium alloy with both high strength and high fluidity, its preparation method and application Technical Field

[0001] This invention belongs to the field of die-cast magnesium alloys, specifically relating to a creep-resistant die-cast rare earth magnesium alloy with both high strength and high fluidity, its preparation method, and its application. Background Technology

[0002] Magnesium and its alloys have several advantages, such as low density (the density of pure magnesium is 1.74 g / cm³). 3 Magnesium alloys are currently the lightest practically applicable metal structural material. They possess high specific strength and specific stiffness (magnesium alloys have significantly higher specific strength than aluminum alloys and steel, while their specific stiffness is comparable to aluminum alloys and steel, and far exceeds that of engineering plastics, being 10 times that of ordinary plastics). They also exhibit excellent damping and vibration reduction properties (under the same load, their vibration reduction is 100 times that of aluminum and 300-500 times that of titanium alloys). Furthermore, they offer good electromagnetic shielding (magnesium alloy shells can completely absorb electromagnetic interference with frequencies exceeding 100dB). They are also relatively easy to die-cast (under good structural conditions, magnesium alloys allow for castings with a minimum wall thickness of 0.6mm, which is unattainable for plastics at the same strength. Aluminum alloys require a die-casting thickness of 1.2-1.5mm or more to compare with magnesium alloys. Magnesium alloys are suitable for mass die-casting production, and mold wear is lower than that of aluminum). With the increasing demand for lightweight materials in many fields, magnesium alloys are gradually receiving widespread attention, especially in the automotive sector, where the demand for casting alloys is enormous.

[0003] Currently, the most widely used magnesium alloys in the die-casting field are Mg-Al-Mn alloys such as AZ91D (Mg-9Al-1Zn-Mn) and AM60B (Mg-6Al-Mn). However, these alloys encounter the following problems when die-casting larger parts: 1. Low mechanical properties: Generally, the die-casting tensile strength of these magnesium alloys is about 230MPa, the yield strength is 140MPa, and the elongation is 3%; 2. Poor flow properties: Insufficient filling and insufficient feeding often result in casting defects in the die-cast parts, which cannot be remedied by process adjustments alone; 3. Poor creep resistance: When the operating temperature reaches 150℃ (the common temperature for engine parts), and the stress reaches 50MPa, AZ91D alloy can no longer suppress creep deformation and produce continuous strain elongation. In actual application environments, this stress level is often reached or even exceeded. Such problems can cause irreversible damage to parts such as cylinder heads under these stress conditions after about 100 hours of service, resulting in problems such as air leakage. The aforementioned problems have severely limited the application of magnesium alloys in the automotive field, hindering the industry's lightweighting process. With technological advancements, the automotive industry's demands for large, integrated design parts are becoming increasingly urgent, and conventional magnesium alloys can no longer meet these requirements. There is an urgent need to develop new high-strength, high-fluidity, creep-resistant die-casting magnesium alloys.

[0004] CN 111155012 B discloses a high-fluidity, high-thermal-conductivity rare-earth magnesium alloy suitable for die-casting ultra-thin parts and its preparation method. This high-fluidity, high-thermal-conductivity rare-earth magnesium alloy, suitable for die-casting ultra-thin parts, comprises the following components by mass percentage: Al 1.0–5.0%, RE 1.0–5.0%, Si 0.1–1.0%, Ca 0.1–1.0%, Mn 0.01–0.5%, with the remainder being Mg. It can be seen that the Al content is relatively low, belonging to the AE44 alloy system. The rare-earth RE is selected from La, Ce, or a mixture of La and Ce. Simultaneously, the addition of Si generates the highly stable intermetallic compound Mg2Si, which strengthens the alloy and significantly improves its microstructure and fluidity. However, generally speaking, the Mg2Si formed by adding Si to magnesium alloys is relatively coarse and cannot effectively achieve dispersion strengthening, resulting in only a limited improvement in fluidity. Furthermore, it significantly reduces the corrosion resistance of the magnesium alloy. CN 104630584 A discloses a high-fluidity, high-strength ultra-thin-walled magnesium alloy and its preparation method, solving the problem of poor performance affecting the yield of thin-walled parts made from AZ91 magnesium alloy. The high-fluidity, high-strength ultra-thin-walled magnesium alloy is composed of the following raw materials by mass percentage: aluminum 9-11%, zinc 0.3-0.9%, manganese 0.15-0.50%, antimony 0.1-0.8%, rare earth elements 0.2-1.0%, with the balance being magnesium and impurities. Through improvements to the magnesium alloy formulation, its performance is effectively enhanced, achieving a tensile strength of 300-310 MPa and a yield strength of 200-210 MPa. Fluidity properties are also significantly improved, ensuring a high die-casting cost rate. However, the RE element in this patent is a mixed rare earth element composed of four metallic elements: cerium, lanthanum, praseodymium, and neodymium, with cerium accounting for more than or equal to 55% by mass. Praseodymium and neodymium are currently extremely expensive due to their large-scale application in neodymium-iron-boron magnetic materials. Therefore, their application in magnesium alloys would significantly increase costs, making them uneconomical. Furthermore, the low RE content limits the strengthening effect of this addition in Mg-Al alloys. CN 100497696 C discloses a high-fluidity magnesium alloy with the following weight percentage composition: Al: 4.5-5.5%, Mn: 0.28-0.40%, Zn: 5.5-6.5%, Si: ≤0.08%, Fe: ≤0.004%, Cu: ≤0.025%, Ni: ≤0.002%, Be: ≤0.0005-0.0015%, with the balance being Mg.This invention primarily improves the tensile and yield strength of AM50A magnesium alloy in the die-cast state by increasing the zinc content in its composition. The average tensile strength is 290 MPa, yield strength is 160 MPa, and elongation after fracture is 3%, effectively compensating for the insufficient filling capacity of existing AM50A magnesium alloys in the die-cast state, thus meeting higher technical requirements for die-casting production. Simultaneously, the increased zinc content enhances its electroplating performance and significantly improves its corrosion resistance. Furthermore, the addition of beryllium further increases the magnesium alloy's oxidation resistance. However, adding large amounts of zinc drastically reduces the alloy's die-castability; within the zinc content range of 5.5-6.5%, the yield and elongation after fracture of die-casting decrease significantly. Moreover, while beryllium is effective as an antioxidant, it is classified as a Group 1 carcinogen by the International Agency for Research on Cancer (IARC) of the World Health Organization and has systemic toxicity. CN 100432259 C discloses a high-fluidity die-cast magnesium alloy and its preparation method. The alloy is characterized by the following mass percentage composition: Al: 9.0-10.5%, Ca: 0.1-2.0%, Sr: 0.1-2.0%, Ce: 0.1-1.0%, La: 0.05-0.5%, Nd: 0.02-0.5%, Zn: 0.2-1.0%, Mn: 0.2-0.4%, impurities ≤0.2%, and the balance being Mg. The preparation method involves first batching the alloy according to its mass percentage composition, then melting it under a CO2+SF6 mixed atmosphere at a melting temperature of 720-740℃, and finally casting it at a pouring temperature of 700-720℃. The alloy provided by this invention has a fluidity that is more than 40% higher than that of AZ91 magnesium alloy. This alloy is suitable not only for die casting but also for semi-solid forming casting, sand or metal mold heavy casting, or low-pressure casting. However, Nd was chosen as the rare earth element, which is too expensive and has poor mechanical properties. CN 106676354 A discloses a magnesium alloy with good fluidity, heat resistance, creep resistance, and corrosion resistance, and its preparation method. The magnesium alloy is composed of the following raw materials in the following mass percentages: aluminum 5.0-8.0 wt.%; rare earth elements 0.5-5.5 wt.%; manganese 0.1-0.9 wt.%; zinc 0.1-0.9 wt.%; the rare earth elements are composed of one or more of lanthanum, cerium, praseodymium, neodymium, and yttrium, with the remainder being magnesium and unavoidable impurity elements. Although this patent solves the problems of poor strength and toughness, poor fluidity, and poor corrosion resistance of existing magnesium alloys to some extent, the use of expensive rare earth elements such as praseodymium and neodymium has low practical application value, and the claimed effect is not supported by data. In summary, existing technologies generally use the addition of expensive rare earth elements to improve the mechanical properties of magnesium alloys; however, the high cost directly leads to poor practicality, and none of the existing technologies involve research on creep resistance. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, this invention provides a creep-resistant die-cast rare earth magnesium alloy with both high strength and high fluidity, as well as its preparation method and application.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] One objective of this invention is to provide a creep-resistant die-cast rare-earth magnesium alloy that combines high strength and high fluidity. The magnesium alloy, by mass percentage, comprises Al: 4.8-7.2%, La: 3.0-4.2%, Sm: 1.2-2.0%, Y: 0.4-1.2%, Mn: 0.1-0.6%, Te: 0.01-0.1%, Bi: 0.01-0.5%, with the balance being Mg and unavoidable impurity elements, and the mass ratio of (La+Sm+Y) / Al is greater than 0.7 and less than 1.5.

[0008] Preferably, the magnesium alloy comprises, by mass percentage, Al: 5.6-6.4%, La: 3.2-3.8%, Sm: 1.4-1.7%, Y: 0.6-0.9%, Mn: 0.2-0.4%, Te: 0.02-0.08%, Bi: 0.1-0.3%, with the balance being Mg and unavoidable impurity elements, and the mass ratio of (La+Sm+Y) / Al is greater than 0.9 and less than 1.1.

[0009] Preferably, the magnesium alloy comprises, by mass percentage, Al: 5.8%, La: 3.6%, Sm: 1.6%, Y: 0.8%, Mn: 0.3%, Te: 0.05%, Bi: 0.2%, with the balance being Mg and unavoidable impurity elements.

[0010] The second objective of this invention is to provide a method for preparing a creep-resistant die-cast rare-earth magnesium alloy that combines high strength and high fluidity, the method comprising the following steps:

[0011] First, the raw materials are preheated, and then they are added and smelted in the order of magnesium source, aluminum source, lanthanum source, samarium source, tellurium source, bismuth source, yttrium source and manganese source. After all the raw materials are melted, they are refined by argon gas. Finally, they are die-cast under high pressure to obtain a creep-resistant die-cast rare earth magnesium alloy with both high strength and high fluidity.

[0012] Preferably, the magnesium source and aluminum source are added in the form of metal ingots, the lanthanum source, samarium source, yttrium source and manganese source are added in the form of Mg-La, Mg-Sm, Mg-Y and Mg-Mn master alloys, and the tellurium source and bismuth source are added in the form of particles.

[0013] Preferably, the preheating temperature is 160-200℃.

[0014] Preferably, the melting temperature is 730-735℃.

[0015] Preferably, the refining temperature is 700-710℃ and the time is 5-10 minutes.

[0016] Preferably, the sample is held at 690-710℃ for 20-40 minutes before die casting.

[0017] Preferably, the injection pressure of die casting is 65-95MPa, the injection speed is 1-8m / s, the casting temperature is 690-710℃, the mold temperature is 230-270℃, the holding pressure is 30-60MPa, and the holding time is 12-20s.

[0018] The third objective of this invention is to provide an application of a high-strength, high-fluidity, creep-resistant die-casting rare-earth magnesium alloy in the molding of large-size die-cast parts in the automotive field.

[0019] The significant advantages of this invention compared to existing technologies are:

[0020] (1) This invention significantly refines the microstructure of magnesium alloys by optimizing the alloy composition, altering the composition, distribution, and morphology of intermetallic compounds in the alloy, thus improving the microstructure of Mg alloys. 17 Al 12 Phase transformation to Al 11 The alloy contains RE3 phase and a small amount of Al3RE phase, while simultaneously generating a high-temperature stable Al-Te phase. Furthermore, the addition of Bi accelerates the diffusion rate of Al and rare earth elements (La, Sm, Y) in the alloy, thus accelerating the formation of the Al-RE phase and acting as a carrier. Bi itself also participates in phase formation. Through the synergistic effect of Bi with Al and RE, the dispersion distribution of precipitated phases is optimized, avoiding segregation and the formation of coarse, blocky, and continuous precipitated phases. These mechanisms and compositional optimizations collectively improve the mechanical properties and creep resistance of the magnesium alloy, increasing the tensile strength from approximately 230 MPa to over 270 MPa, while also exhibiting excellent fluidity and significant creep resistance.

[0021] (2) The present invention improves the oxidation of magnesium alloy melt and reduces the viscosity of melt by optimizing rare earth and trace elements. In addition, the surface tension of magnesium melt is reduced by optimizing rare earth. Using die casting fluidity mold test, the fluidity under the same die casting conditions can be improved by up to 40% or more, which meets the requirements of large integrated design automotive parts. Attached Figure Description

[0022] Figure 1 shows the microstructure of the rare earth magnesium alloy obtained in Example 1;

[0023] Figure 2 shows the microstructure of the rare earth magnesium alloy obtained in Example 3;

[0024] Figure 3 shows the effect of the die-casting fluidity test in Example 1;

[0025] Figure 4 shows the effect of the die-casting fluidity test in Example 3;

[0026] Figure 5 shows the microstructure of the rare earth magnesium alloy obtained in Comparative Example 1. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0028] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0029] Example 1: The preparation method of the creep-resistant die-cast rare earth magnesium alloy with high strength and high fluidity in this example is carried out according to the following steps:

[0030] (1) The magnesium alloy is weighed according to the following composition: by mass percentage, it includes Al: 5.8%, La: 3.6%, Sm: 1.6%, Y: 0.8%, Mn: 0.3%, Te: 0.05%, Bi: 0.2%, with the balance being Mg. The total weight of the raw materials is 600 kg. The rare earth elements lanthanum, samarium, and yttrium are added by Mg-La, Mg-Sm, and Mg-Y master alloys, respectively. Manganese is added by Mg-Mn master alloys. Tellurium is added by high-purity Te particles, and bismuth (Bi) is added by high-purity Bi particles.

[0031] (2) Preheat all raw materials and tools required for the experiment to 180°C, add Mg ingots and Al ingots into the crucible, heat up, and pass in a mixture of SF6 and CO2 (volume ratio of 1:100) for protection.

[0032] (3) After the Mg ingot has melted, add the Mg-La master alloy and stir until melted;

[0033] (4) When the melt temperature reaches 730℃, add Mg-Sm master alloy, Te particles and Bi particles in batches and stir until melted.

[0034] (5) When the melt temperature reaches 735℃ again, add Mg-Y master alloy and Mg-Mn master alloy and stir until melted;

[0035] (6) When the melt temperature is reduced to 705℃, argon gas is introduced for refining for 5 minutes, and the composition is determined using an Ultima2 inductively coupled plasma spectrometer (ICP).

[0036] (7) Hold the melt at 700℃ for 0.5h;

[0037] (8) The melt temperature was lowered to 690℃, the oxide scale on the melt surface was scraped off, and high-pressure die casting was performed using a die casting machine. The injection pressure was 75MPa, the injection speed was 5m / s, the casting temperature was 700℃, the mold temperature was 250℃, the holding pressure was 50MPa, and the holding time was 16s. This yielded a creep-resistant die-cast rare earth magnesium alloy with both high strength and high fluidity. The properties are shown in Table 1, and the microstructure is shown in Figure 1. The figure shows that the alloy has fine and uniform grains with a size of about 3-7μm. The precipitates at the grain boundaries are uniform and fine, with no large precipitates present. The die casting fluidity is shown in Figure 3, which shows that it has excellent fluidity.

[0038] Example 2: The preparation method of the creep-resistant die-cast rare earth magnesium alloy with both high strength and high fluidity in this example is carried out according to the following steps:

[0039] (1) The magnesium alloy is weighed according to the following composition: by mass percentage, it includes Al: 6.4%, La: 3.2%, Sm: 1.4%, Y: 0.6%, Mn: 0.4%, Te: 0.08%, Bi: 0.3%, with the balance being Mg. The total weight of the raw materials is 600 kg. The rare earth elements lanthanum, samarium, and yttrium are added by Mg-La, Mg-Sm, and Mg-Y master alloys, respectively. Manganese is added by Mg-Mn master alloys. Tellurium is added by high-purity Te particles, and bismuth (Bi) is added by high-purity Bi particles.

[0040] (2) Preheat all raw materials and tools required for the experiment to 180°C, add Mg ingots and Al ingots into the crucible, heat up, and pass in a mixture of SF6 and CO2 (volume ratio of 1:100) for protection.

[0041] (3) After the Mg ingot has melted, add the Mg-La master alloy and stir until melted;

[0042] (4) When the melt temperature reaches 730℃, add Mg-Sm master alloy, Te particles and Bi particles in batches and stir until melted.

[0043] (5) When the melt temperature reaches 735℃ again, add Mg-Y master alloy and Mg-Mn master alloy and stir until melted;

[0044] (6) When the melt temperature is reduced to 705℃, argon gas is introduced for refining for 5 minutes, and the composition is determined using an Ultima2 inductively coupled plasma spectrometer (ICP).

[0045] (7) Hold the melt at 700℃ for 0.5h;

[0046] (8) The melt temperature is reduced to 690℃, the oxide scale on the surface of the melt is scraped off, and high pressure die casting is performed using a die casting machine. The injection pressure is 70MPa, the injection speed is 3m / s, the casting temperature is 695℃, the mold temperature is 235℃, the holding pressure is 35MPa, and the holding time is 14s. Thus, a creep-resistant die-cast rare earth magnesium alloy with high strength and high fluidity is obtained. The properties are shown in Table 1.

[0047] Example 3: The preparation method of the creep-resistant die-cast rare earth magnesium alloy with both high strength and high fluidity in this example is carried out according to the following steps:

[0048] (1) The magnesium alloy is weighed according to the following composition: by mass percentage, it includes Al: 5.6%, La: 3.8%, Sm: 1.7%, Y: 0.9%, Mn: 0.2%, Te: 0.02%, Bi: 0.1%, with the balance being Mg. The total weight of the raw materials is 600 kg. The rare earth elements lanthanum, samarium, and yttrium are added by Mg-La, Mg-Sm, and Mg-Y master alloys, respectively. Manganese is added by Mg-Mn master alloys. Tellurium is added by high-purity Te particles, and bismuth (Bi) is added by high-purity Bi particles.

[0049] (2) Preheat all raw materials and tools required for the experiment to 180°C, add Mg ingots and Al ingots into the crucible, heat up, and pass in a mixture of SF6 and CO2 (volume ratio of 1:100) for protection.

[0050] (3) After the Mg ingot has melted, add the Mg-La master alloy and stir until melted;

[0051] (4) When the melt temperature reaches 730℃, add Mg-Sm master alloy, Te particles and Bi particles in batches and stir until melted.

[0052] (5) When the melt temperature reaches 735℃ again, add Mg-Y master alloy and Mg-Mn master alloy and stir until melted;

[0053] (6) When the melt temperature is reduced to 705℃, argon gas is introduced for refining for 5 minutes, and the composition is determined using an Ultima2 inductively coupled plasma spectrometer (ICP).

[0054] (7) Hold the melt at 700℃ for 0.5h;

[0055] (8) The melt temperature was lowered to 690℃, the oxide scale on the melt surface was scraped off, and high-pressure die casting was performed using a die casting machine. The injection pressure was 75MPa, the injection speed was 5m / s, the casting temperature was 700℃, the mold temperature was 250℃, the holding pressure was 50MPa, and the holding time was 16s. This yielded a creep-resistant die-cast rare earth magnesium alloy with both high strength and high fluidity. The properties are shown in Table 1, and the microstructure is shown in Figure 2. The figure shows that the grains in the alloy microstructure are slightly larger than those in Example 1, with a size of about 6-17μm. Due to the decrease in Bi content, the precipitates at the grain boundaries are slightly coarser, and the uniformity is slightly worse than that in Example 1. The die casting fluidity is shown in Figure 4, which shows that the fluidity is second only to Example 1.

[0056] Example 4: The preparation method of the creep-resistant die-cast rare earth magnesium alloy with high strength and high fluidity in this example is carried out according to the following steps:

[0057] (1) The magnesium alloy is weighed according to the following composition: by mass percentage, it includes Al: 7.2%, La: 3.0%, Sm: 1.2%, Y: 0.4%, Mn: 0.6%, Te: 0.1%, Bi: 0.5%, with the balance being Mg. The total weight of the raw materials is 600 kg. The rare earth elements lanthanum, samarium, and yttrium are added by Mg-La, Mg-Sm, and Mg-Y master alloys, respectively. Manganese is added by Mg-Mn master alloys. Tellurium is added by high-purity Te particles, and bismuth (Bi) is added by high-purity Bi particles.

[0058] (2) Preheat all raw materials and tools required for the experiment to 180°C, add Mg ingots and Al ingots into the crucible, heat up, and pass in a mixture of SF6 and CO2 (volume ratio of 1:100) for protection.

[0059] (3) After the Mg ingot has melted, add the Mg-La master alloy and stir until melted;

[0060] (4) When the melt temperature reaches 730℃, add Mg-Sm master alloy, Te particles and Bi particles in batches and stir until melted.

[0061] (5) When the melt temperature reaches 735℃ again, add Mg-Y master alloy and Mg-Mn master alloy and stir until melted;

[0062] (6) When the melt temperature is reduced to 705℃, argon gas is introduced for refining for 5 minutes, and the composition is determined using an Ultima2 inductively coupled plasma spectrometer (ICP).

[0063] (7) Hold the melt at 700℃ for 0.5h;

[0064] (8) The melt temperature is reduced to 690℃, the oxide scale on the surface of the melt is scraped off, and high pressure die casting is performed using a die casting machine. The injection pressure is 65MPa, the injection speed is 1m / s, the casting temperature is 690℃, the mold temperature is 230℃, the holding pressure is 30MPa, and the holding time is 12s. Thus, a creep-resistant die-cast rare earth magnesium alloy with high strength and high fluidity is obtained. The properties are shown in Table 1.

[0065] Example 5: The preparation method of the creep-resistant die-cast rare earth magnesium alloy with both high strength and high fluidity in this example is carried out according to the following steps:

[0066] (1) The magnesium alloy is weighed according to the following composition: by mass percentage, it includes Al: 4.8%, La: 4.2%, Sm: 2.0%, Y: 1.2%, Mn: 0.1%, Te: 0.01%, Bi: 0.01%, with the balance being Mg. The total weight of the raw materials is 600 kg. The rare earth elements lanthanum, samarium, and yttrium are added by Mg-La, Mg-Sm, and Mg-Y master alloys, respectively. Manganese is added by Mg-Mn master alloys. Tellurium is added by high-purity Te particles, and bismuth (Bi) is added by high-purity Bi particles.

[0067] (2) Preheat all raw materials and tools required for the experiment to 180°C, add Mg ingots and Al ingots into the crucible, heat up, and pass in a mixture of SF6 and CO2 (volume ratio of 1:100) for protection.

[0068] (3) After the Mg ingot has melted, add the Mg-La master alloy and stir until melted;

[0069] (4) When the melt temperature reaches 730℃, add Mg-Sm master alloy, Te particles and Bi particles in batches and stir until melted.

[0070] (5) When the melt temperature reaches 735℃ again, add Mg-Y master alloy and Mg-Mn master alloy and stir until melted;

[0071] (6) When the melt temperature is reduced to 705℃, argon gas is introduced for refining for 5 minutes, and the composition is determined using an Ultima2 inductively coupled plasma spectrometer (ICP).

[0072] (7) Hold the melt at 700℃ for 0.5h;

[0073] (8) The melt temperature is reduced to 690℃, the oxide scale on the surface of the melt is scraped off, and high pressure die casting is performed using a die casting machine. The injection pressure is 95MPa, the injection speed is 8m / s, the casting temperature is 710℃, the mold temperature is 270℃, the holding pressure is 60MPa, and the holding time is 20s. Thus, a creep-resistant die-cast rare earth magnesium alloy with high strength and high fluidity is obtained. The properties are shown in Table 1.

[0074] Comparative Example 1

[0075] (1) The raw materials were prepared according to the alloy element composition ratio of Al: 6%, Mn: 0.2%, and the balance being Mg, with a total weight of 600 kg. The manganese was added using a Mg-Mn master alloy.

[0076] (2) Preheat all raw materials and tools required for the experiment to 180°C, add Mg ingots and Al ingots into the crucible, heat up, and pass in a mixture of SF6 and CO2 (volume ratio of 1:100) for protection.

[0077] (3) When the melt temperature reaches 735℃, add the Mg-Mn master alloy and stir until melted.

[0078] (4) When the melt temperature is reduced to 705℃, argon gas is introduced for refining for 5 minutes, and the composition is determined using an Ultima2 inductively coupled plasma spectrometer (ICP).

[0079] (5) Keep the melt at 700℃ for 0.5h;

[0080] (6) The melt temperature is reduced to 690℃, the oxide scale on the surface of the melt is scraped off, and high pressure die casting is performed using a die casting machine. The injection pressure of the die casting is 75MPa, the injection speed is 5m / s, the casting temperature is 700℃, the mold temperature is 250℃, the holding pressure is 50MPa, and the holding time is 16s. The required comparative magnesium alloy is obtained. The properties are shown in Table 1. The die casting fluidity is shown in Figure 5. It can be seen from the figure that the fluidity effect is poor.

[0081] Comparative Example 2

[0082] (1) The raw materials were prepared according to the following alloy element composition by mass ratio: Al: 8.8%, La: 1.2%, Sm: 1.0%, Y: 0.2%, Mn: 0.7%, Te: 0.008%, Bi: 0.006%, with the balance being Mg, and the total weight was 600 kg. The rare earth elements lanthanum, samarium, and yttrium were added using Mg-La, Mg-Sm, and Mg-Y master alloys, manganese was added using a Mg-Mn master alloy, tellurium was added using high-purity Te particles, and bismuth (Bi) was added using high-purity Bi particles.

[0083] (2) Preheat all raw materials and tools required for the experiment to 180°C, add Mg ingots and Al ingots into the crucible, heat up, and pass in a mixture of SF6 and CO2 (volume ratio of 1:100) for protection.

[0084] (3) After the Mg ingot has melted, add the Mg-La master alloy and stir until melted;

[0085] (4) When the melt temperature reaches 730℃, add Mg-Sm master alloy, Te particles and Bi particles in batches and stir until melted.

[0086] (5) When the melt temperature reaches 735℃ again, add the Mg-Y master alloy and Mg-Mn master alloy, and stir until melted.

[0087] (6) When the melt temperature is reduced to 705℃, argon gas is introduced for refining for 5 minutes, and the composition is determined using an Ultima2 inductively coupled plasma spectrometer (ICP).

[0088] (7) Hold the melt at 700℃ for 0.5h;

[0089] (8) Reduce the temperature of the melt to 690℃, scrape off the oxide scale on the surface of the melt, and use a die casting machine to perform high-pressure die casting. The injection pressure of the die casting is 75MPa, the injection speed is 5m / s, the casting temperature is 700℃, the mold temperature is 250℃, the holding pressure is 50MPa, and the holding time is 16s. The required comparative magnesium alloy is obtained, and its properties are shown in Table 1.

[0090] Comparative Example 3

[0091] (1) The raw materials were prepared according to the following alloy element composition by mass ratio: Al: 4.0%, La: 4.8%, Sm: 2.5%, Y: 1.6%, Mn: 0.01%, Te: 0.12%, Bi: 0.6%, with the balance being Mg, and the total weight was 600 kg. The rare earth elements lanthanum, samarium, and yttrium were added using Mg-La, Mg-Sm, and Mg-Y master alloys, respectively; manganese was added using Mg-Mn master alloys; tellurium was added using high-purity Te particles; and bismuth (Bi) was added using high-purity Bi particles.

[0092] (2) Preheat all raw materials and tools required for the experiment to 180°C, add Mg ingots and Al ingots into the crucible, heat up, and pass in a mixture of SF6 and CO2 (volume ratio of 1:100) for protection.

[0093] (3) After the Mg ingot has melted, add the Mg-La master alloy and stir until melted;

[0094] (4) When the melt temperature reaches 730℃, add Mg-Sm master alloy, Te particles and Bi particles in batches and stir until melted.

[0095] (5) When the melt temperature reaches 735℃ again, add the Mg-Y master alloy and Mg-Mn master alloy, and stir until melted.

[0096] (6) When the melt temperature is reduced to 705℃, argon gas is introduced for refining for 5 minutes, and the composition is determined using an Ultima2 inductively coupled plasma spectrometer (ICP).

[0097] (7) Hold the melt at 700℃ for 0.5h;

[0098] (8) Reduce the temperature of the melt to 690℃, scrape off the oxide scale on the surface of the melt, and use a die casting machine to perform high-pressure die casting. The injection pressure of the die casting is 75MPa, the injection speed is 5m / s, the casting temperature is 700℃, the mold temperature is 250℃, the holding pressure is 50MPa, and the holding time is 16s. The required comparative magnesium alloy is obtained, and its properties are shown in Table 1.

[0099] Table 1. Alloy properties of examples and comparative examples

[0100]

[0101] The above description is merely a preferred embodiment of the present invention. These specific embodiments are different implementations based on the overall concept of the present invention, and the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A creep-resistant die-cast rare-earth magnesium alloy with both high strength and high fluidity, characterized in that, The magnesium alloy, by mass percentage, comprises Al: 5.6-6.4%, La: 3.2-3.8%, Sm: 1.4-1.7%, Y: 0.6-0.9%, Mn: 0.2-0.4%, Te: 0.02-0.08%, Bi: 0.1-0.3%, with the balance being Mg and unavoidable impurity elements, and the mass ratio of (La+Sm+Y) / Al is greater than 0.9 and less than 1.

1.

2. The magnesium alloy according to claim 1, characterized in that, The composition by mass percentage includes Al: 5.8%, La: 3.6%, Sm: 1.6%, Y: 0.8%, Mn: 0.3%, Te: 0.05%, Bi: 0.2%, with the balance being Mg and unavoidable impurity elements.

3. The method for preparing the magnesium alloy according to claim 1 or 2, characterized in that, The method involves preheating each raw material, then sequentially adding and melting the magnesium source, aluminum source, lanthanum source, samarium source, tellurium source, bismuth source, yttrium source, and manganese source. After all raw materials are melted, they are refined by passing argon gas through them. Finally, they are die-cast under high pressure to obtain a creep-resistant die-cast rare earth magnesium alloy with both high strength and high fluidity.

4. The method according to claim 3, characterized in that, Magnesium and aluminum sources are added in the form of metal ingots, while lanthanum, samarium, yttrium, and manganese sources are added in the form of Mg-La, Mg-Sm, Mg-Y, and Mg-Mn master alloys. Tellurium and bismuth sources are added in the form of particles.

5. The method according to claim 3, characterized in that, The preheating temperature is 160-200℃.

6. The method according to claim 3, characterized in that, The melting temperature is 730-735℃.

7. The method according to claim 3, characterized in that, The refining temperature is 700-710℃, and the time is 5-10 minutes.

8. The method according to claim 3, characterized in that, Before die casting, keep the temperature at 690-710℃ for 20-40 minutes.

9. The application of the magnesium alloy according to claim 1 or 2 in the molding of large die-cast parts in the automotive industry.

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