Corrosion-resistant high strength and toughness magnesium alloy suitable for complex structure die castings and preparation method thereof

Abstract

The application discloses a corrosion-resistant high-strength and high-toughness magnesium alloy suitable for complex structure die castings and a preparation method thereof. The magnesium alloy is cast and synthesized by the following components in percentage by mass: Al: 6.0-10.0%, Mn: 0.3-0.8%, Ca: 0.1-0.6%, Zn: 0-1%, rare earth RE: 0.4-1.5%, unavoidable impurities: ≤0.02%, and the balance of Mg. The corrosion-resistant high-strength and high-toughness magnesium alloy is obtained by a die casting method. The obtained alloy has high strength and plasticity and corrosion resistance, is suitable for integrated die casting of large, medium and small complex components, and has a tensile strength of 242-288 MPa and an elongation of 10.2%-15.8%, and a corrosion rate of 0.03-0.109 mg / cm 2 / day after immersion in 3.5% NaCl solution for 7 days, thereby widening the application and promotion of magnesium alloy in the fields of electronics, transportation, aviation, aerospace and the like in terms of lightweight and integrated efficient forming of components.

Description

Technical Field

[0001] This invention relates to the field of magnesium alloy materials, and particularly to a corrosion-resistant, high-strength and high-toughness magnesium alloy suitable for die castings with complex structures and its preparation method. Background Technology

[0002] The lightweight development of aerospace, automotive, and military equipment industries urgently requires advanced lightweight metallic materials. Magnesium alloys, with their high specific strength, high specific stiffness, good damping and vibration reduction, and heat dissipation properties, are considered the lightest engineering structural metal materials. However, magnesium alloys with excellent comprehensive mechanical properties often require complex plastic deformation processes such as forging, extrusion, and rolling, resulting in high production costs and making them difficult to use for producing large and complex structural components. Furthermore, existing technologies struggle to simultaneously improve the strength and ductility, or the strength and corrosion resistance, or the ductility and corrosion resistance of magnesium alloys. In addition, cast magnesium alloys, due to their simple manufacturing process and low cost, are often used to produce large and complex structural components; however, the comprehensive mechanical properties of cast magnesium alloys are significantly inferior to those of aluminum / copper / zinc alloys, exhibiting lower strength and ductility, and poorer corrosion resistance. Therefore, how to reduce costs and develop cast magnesium alloys with high strength, ductility, corrosion resistance, and controllable dimensions is a pressing technical challenge that needs to be addressed. Summary of the Invention

[0003] To address the aforementioned challenges, this invention provides a corrosion-resistant, high-strength, and high-toughness magnesium alloy suitable for die-casting parts with complex structures. The alloy, by mass percentage, comprises the following components: Al: 6.0–10.0%, Mn: 0.3–0.8%, Ca: 0.1–0.6%, Zn: 0–1%, rare earth elements (RE): 0.4–1.5%, unavoidable impurities ≤0.02%, and the balance being Mg. The rare earth elements (RE) are any one or a combination of Ce, La, Nd, Pr, Sm, or Y. Its preparation method includes the following steps:

[0004] (1) Raw material preparation: Prepare Mg, Al, Zn, Mg-Ca, Mg-Mn and Mg-RE master alloy raw materials in the specified mass percentages;

[0005] (2) Melting: Under the protection of inert gas Ar or a mixed protective gas of SF6 and CO2, the volume ratio of SF6 and CO2 is 1-10:90-99; Mg is heated to 670-710℃ to melt; then the temperature is raised to 720-760℃, and the Al, Zn, Mg-Mn, Mg-RE, and Mg-Ca master alloys are added in sequence; after all the raw materials are completely melted, the temperature is lowered to 670-720℃, and the mixture is stirred thoroughly for 10-40 minutes and then allowed to stand for 10-70 minutes to obtain the alloy melt; the alloy melt is then poured into a mold to obtain corrosion-resistant high-strength and high-toughness magnesium alloy rods or ingots;

[0006] (3) Die casting: The magnesium alloy rod or ingot prepared in step (2) is heated to 680-760℃ and completely melted, then held at that temperature for 30-60 minutes; then cooled to 660-720℃ and die-cast for 1-10 seconds to obtain a corrosion-resistant, high-strength, and tough magnesium alloy. The die casting process is as follows: die casting mold temperature 150-300℃, injection pressure 100-200MPa, and injection speed 1.0-2.5m / s; the tensile strength of the corrosion-resistant, high-strength, and tough magnesium alloy is >240MPa and the elongation is >10%; the corrosion rate after immersion in 3.5% NaCl solution for 7 days is <0.11mg / cm. 2 / day.

[0007] Further, in step (2), after heating Mg to 680-700℃ to melt it, the temperature is then raised to 725-740℃, and the Al, Zn, Mg-Mn, Mg-RE, and Mg-Ca master alloys are added in sequence. After all the raw materials are completely melted, the temperature is lowered to 690-700℃, and the mixture is stirred thoroughly for 15-30 minutes and then allowed to stand for 20-60 minutes to obtain the alloy melt. The alloy melt is then poured into a mold to obtain a corrosion-resistant, high-strength, and tough magnesium alloy rod or ingot.

[0008] Further, in step (3), the magnesium alloy casting rod or ingot is heated to 690-730℃, completely melted, and held at that temperature for 35-50 minutes; then cooled to 680-700℃ and subjected to die casting for 2-5 seconds to obtain a corrosion-resistant, high-strength and tough magnesium alloy. The die casting process is as follows: die casting mold temperature 200-250℃, injection pressure 120-160MPa, and injection speed 1.3-2.2m / s.

[0009] Furthermore, the corrosion-resistant, high-strength, and high-toughness magnesium alloy obtained after the die-casting treatment in step (3) has the following properties: tensile strength ≤ 242 MPa < 300 MPa, elongation ≤ 10.2% < 16%; corrosion rate after immersion in 3.5% NaCl solution for 7 days: 0.03 mg / cm³. 2 / day ≤ corrosion rate ≤ 0.109mg / cm 2 / day.

[0010] This invention also provides the application of corrosion-resistant, high-strength, and high-toughness magnesium alloys suitable for complex die-cast parts in the fields of new energy vehicles, 3C electronics, high-speed rail, and aviation for the integrated application of large, medium, or small complex components.

[0011] Compared with the prior art, the advantages of the present invention are:

[0012] Compared with existing technologies, this invention simplifies the process and reduces production costs by synergistically controlling alloy composition, component interactions, proportions, processes, and process parameters, thereby eliminating rolling deformation and long-term high-temperature heat treatment, while simultaneously improving the alloy's strength, plasticity, and corrosion resistance.

[0013] The magnesium alloy obtained by this invention has a tensile strength ≥242MPa and an elongation ≥10.2%; the corrosion rate of the magnesium alloy obtained by this invention after immersion in 3.5% NaCl solution for 7 days is ≤0.109mg / cm. 2 / day. The magnesium alloy obtained by this invention is suitable for both integrated die casting of large and complex components weighing 30-50kg and die casting of medium and small-sized complex components. Specific advantages are as follows:

[0014] (1) The magnesium alloy obtained by the present invention has a wide solidification range and excellent die casting filling ability. It is suitable for integrated die casting of large, medium or small components, and is therefore suitable for industrial production.

[0015] (2) The magnesium alloy obtained by this invention achieves the following new breakthroughs in terms of internal structure, size distribution, and uniformity: the cooling rate is much higher than the sub-rapid solidification rate of the prior art, resulting in a more uniform internal structure and finer equiaxed crystals, with an average crystal size of ~3.3 μm; the grain size and eutectic phase in the internal structure are significantly refined; the volume fraction of the Mg-Al eutectic phase is reduced. According to calculations, the volume fraction of the eutectic phase in this invention is equivalent to ~1 / 2 of that in commercial AZ91 alloy, and a dispersed and uniform distribution is achieved, as well as the addition of Al and other elements in the Mg matrix. The high solid solution content significantly improves the density of the corrosion film and the strength of the matrix, reducing galvanic corrosion. At the same time, the present invention also forms a large number of uniformly distributed, fine, near-spherical or passivated small-particle second phases (~1-2 μm), which can achieve good dispersion in the matrix and significantly reduce the susceptibility to hot cracking. In contrast, existing commercial magnesium alloys contain a large number of irregular, large-sized rod-shaped second phases (~5-10 μm). The synergistic effect of the above advantages of the present invention makes the alloy stronger, more ductile, and more corrosion-resistant than alloys obtained by existing technologies, achieving a simultaneous improvement in various comprehensive properties. Attached Figure Description

[0016] Figure 1 EBSD microstructure of die-cast magnesium alloy in Example 5 of this invention;

[0017] Figure 2 EBSD microstructure of commercial die-cast AZ91D magnesium alloy. Detailed Implementation

[0018] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. It is obvious that the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the protection scope of the present invention.

[0019] In a specific embodiment, the raw materials used are as follows:

[0020] Mg: 99.5% purity. Al: 99.7% purity. Zn: 99.7% purity. Mg-5Mn master alloy. Mg-30Ca master alloy. Mg-RE master alloys: Mg-30Ce, Mg-30La, Mg-30Nd, Mg-30Pr, Mg-30Sm, Mg-30Y alloy.

[0021] The following detailed description is based on specific embodiments.

[0022] Example 1

[0023] Corrosion-resistant, high-strength and tough Mg-6Al-0.5Ca-0.5Mn-0.5Ce magnesium alloy die-cast components

[0024] In this embodiment, the components and their mass percentages of the component are: Al: 6.0%, Ca: 0.5%, Mn: 0.5%, Ce: 0.5%, with the balance being Mg and unavoidable impurities, wherein unavoidable impurities are ≤0.02%. The preparation method is as follows:

[0025] (1) Raw material preparation: Prepare Mg, Al, Mg-5Mn, Mg-30Ca and Mg-30Ce master alloy raw materials in the mass percentages described above;

[0026] (2) Melting: Under the protection of SF6+CO2 (volume ratio 2.5:97.5) mixed protective gas, Mg is heated to 680℃ and melted; then the temperature is raised to 720℃, and Al, Mg-5Mn, Mg-30Ce and Mg-30Ca intermediate alloy are added in sequence; after all raw materials are completely melted, the temperature is lowered to 690℃, stirred thoroughly for 10 minutes and then allowed to stand for 12 minutes to obtain alloy melt; the alloy melt is then poured into a mold to obtain corrosion-resistant high-strength and tough magnesium alloy rods or ingots.

[0027] (3) Die casting: The magnesium alloy rod or ingot prepared in step (2) is heated to 730℃ and completely melted, then held at that temperature for 60 minutes; then cooled to 700℃ and die-cast for 1-3 seconds to obtain a corrosion-resistant, high-strength and tough Mg-6Al-0.5Ca-0.5Mn-0.5Ce magnesium alloy. The die casting process is as follows: die casting mold: 250℃, injection pressure 120MPa and injection speed 1.2m / s. The tensile strength and elongation of the magnesium alloy are 288MPa and 15.8%, respectively. The corrosion rate after immersion in 3.5% NaCl solution for 7 days at room temperature is 0.030mg / cm. 2 / day.

[0028] Example 2

[0029] Corrosion-resistant, high-strength and tough Mg-7.5Al-0.5Ca-0.5Mn-0.5Y magnesium alloy die-cast components

[0030] In this embodiment, the components and their mass percentages of the component are: Al: 7.5%, Ca: 0.5%, Mn: 0.5%, Y: 0.5%, with the balance being Mg and unavoidable impurities ≤0.02%. Its preparation method includes the following steps:

[0031] (1) Raw material preparation: Prepare Mg, Al, Mg-5Mn, Mg-30Ca and Mg-30Y master alloy raw materials in the mass percentages described above;

[0032] (2) Melting: Under the protection of inert gas Ar, Mg is heated to 685℃ and melted; then the temperature is raised to 725℃, and Al, Mg-5Mn, Mg-30Y and Mg-30Ca intermediate alloy are added in sequence; after all raw materials are completely melted, the temperature is lowered to 695℃, and the mixture is stirred thoroughly for 16 minutes and then allowed to stand for 20 minutes to obtain the alloy melt; the alloy melt is then poured into a mold to obtain corrosion-resistant high-strength and tough magnesium alloy rods or ingots.

[0033] (3) Die casting: The magnesium alloy rod or ingot prepared in step (2) is heated to 720℃ and completely melted, then held at that temperature for 55 minutes; then cooled to 690℃ and die-cast for 1-3 seconds to obtain a corrosion-resistant, high-strength and tough Mg-7.5Al-0.5Ca-0.5Mn-0.5Y magnesium alloy. The die casting process is as follows: die casting mold: 260℃, injection pressure 125MPa and injection speed 1.3m / s. The tensile strength, elongation and corrosion rate of the magnesium alloy are 242MPa, 11.4% and 0.051mg / cm, respectively. 2 / day.

[0034] Example 3

[0035] Corrosion-resistant, high-strength and tough Mg-8.3Al-0.4Ca-0.5Mn-0.75Sm magnesium alloy

[0036] In this embodiment, the composition and mass percentage of the magnesium alloy material are: Al: 8.3%, Ca: 0.4%, Mn: 0.5%, Sm: 0.75%, with the balance being Mg and unavoidable impurities ≤0.02%. Its preparation method includes the following steps:

[0037] (1) Raw material preparation: Prepare Mg, Al, Mg-5Mn, Mg-30Ca and Mg-30Sm master alloy raw materials in the mass percentages described above;

[0038] (2) Melting: Under the protection of SF6+CO2 (volume ratio 2:98) mixed protective gas, Mg is heated to 690℃ and melted; then the temperature is raised to 735℃, and Al, Mg-5Mn, Mg-30Sm and Mg-30Ca intermediate alloy are added in sequence; after all raw materials are completely melted, the temperature is lowered to 693℃, stirred thoroughly for 18 minutes and then allowed to stand for 25 minutes to obtain alloy melt; the alloy melt is then poured into a mold to obtain corrosion-resistant high strength and toughness magnesium alloy rods or ingots;

[0039] (3) Die casting: The magnesium alloy rod or ingot prepared in step (2) is heated to 725℃ and completely melted, then held at that temperature for 52 minutes; then cooled to 693℃ and die-cast for 1-3 seconds to obtain a corrosion-resistant, high-strength and tough Mg-8.3Al-0.4Ca-0.5Mn-0.75Sm magnesium alloy. The die casting process is as follows: die casting mold: 240℃, injection pressure 130MPa and injection speed 1.4m / s. The tensile strength, elongation and corrosion rate of this magnesium alloy are 268MPa, 13.5% and 0.072mg / cm, respectively. 2 / day.

[0040] Example 4

[0041] Corrosion-resistant, high-strength and tough Mg-8.2Al-0.3Ca-0.3Mn-0.6Ce-0.3Sm magnesium alloy

[0042] In this embodiment, the composition and mass percentage of the magnesium alloy material are: Al: 8.2%, Ca: 0.3%, Mn: 0.3%, Ce: 0.6%, Sm: 0.3%, with the balance being Mg and unavoidable impurities ≤0.02%. Its preparation method includes the following steps:

[0043] (1) Raw material preparation: Prepare Mg, Al, Mg-5Mn, Mg-30Ca, Mg-30Ce and Mg-30Sm master alloy raw materials in the mass percentages described above;

[0044] (2) Melting: Under the protection of SF6+CO2 (volume ratio 3:97) mixed protective gas, Mg is heated to 694℃ and melted; then the temperature is raised to 720℃, and Al, Mg-5Mn, Mg-30Ce, Mg-30Sm and Mg-30Ca master alloys are added in sequence; after all raw materials are completely melted, the temperature is lowered to 695℃, and the mixture is stirred thoroughly for 20 minutes and then allowed to stand for 30 minutes to obtain the alloy melt; the alloy melt is then poured into a mold to obtain corrosion-resistant high-strength and tough magnesium alloy rods or ingots;

[0045] (3) Die casting: The magnesium alloy rod or ingot prepared in step (2) is heated to 722℃ and completely melted, then held at that temperature for 50 minutes; then cooled to 695℃ and die-cast for 1-3 seconds to obtain Mg-8.2Al-0.3Ca-0.3Mn-0.6Ce-0.3Sm magnesium alloy. The die casting process is as follows: die casting mold: 235℃, injection pressure 135MPa and injection speed 1.5m / s. The tensile strength, elongation and corrosion rate of this magnesium alloy are 255MPa, 10.3% and 0.088mg / cm, respectively. 2 / day.

[0046] Example 5

[0047] Corrosion-resistant, high-strength and tough Mg-8.2Al-0.4Ca-0.5Mn-0.2Ce-0.7Sm magnesium alloy

[0048] In this embodiment, the composition and mass percentage of the magnesium alloy material are: Al: 8.2%, Ca: 0.4%, Mn: 0.5%, Ce: 0.2%, Sm: 0.7%, with the balance being Mg and unavoidable impurities ≤0.02%. Its preparation method includes the following steps:

[0049] (1) Raw material preparation: Prepare Mg, Al, Mg-5Mn, Mg-30Ca, Mg-30Ce and Mg-30Sm master alloy raw materials in the mass percentages described above;

[0050] (2) Melting: Under the protection of a mixed protective gas of SF6+CO2 (volume ratio 3.5:96.5), Mg is heated to 700℃ and melted; then the temperature is raised to 725℃, and Al, Mg-5Mn, Mg-30Ce, Mg-30Sm and Mg-30Ca master alloys are added in sequence; after all raw materials are completely melted, the temperature is lowered to 698℃, and the mixture is stirred thoroughly for 25 minutes and then allowed to stand for 34 minutes to obtain the alloy melt; the alloy melt is then poured into a mold to obtain corrosion-resistant high-strength and tough magnesium alloy rods or ingots;

[0051] (3) Die casting: The magnesium alloy rod or ingot prepared in step (2) is heated to 714℃ and completely melted, and then held for 48 minutes; then cooled to 685℃ and die-cast for 1-3 seconds to obtain corrosion-resistant, high-strength and tough Mg-8.2Al-0.4Ca-0.5Mn-0.2Ce-0.7Sm magnesium alloy. The die casting process is as follows: die casting mold: 220℃, injection ratio 140MPa and injection speed 1.6m / s.

[0052] Figure 1 and Figure 2 The images show the EBSD microstructures of the magnesium alloy obtained in Example 5 and the commercially available die-cast AZ91 alloy, respectively. It can be observed that, compared to the AZ91 alloy, the alloy obtained in Example 5 exhibits a more uniform and finer equiaxed grain structure, with an average grain size of ~3.3 μm. Compared to the AZ91 alloy, the eutectic phase structure in the microstructure obtained in Example 5 is significantly refined and more dispersed. Calculations show that the volume fraction of the eutectic phase in this example alloy (12.8%) is significantly lower than that in the AZ91 alloy (22.3%). Furthermore, the AZ91 alloy contains a non-uniformly distributed, large-sized rod-shaped second phase (~5-10 μm), while the alloy in this example contains a uniformly fine, dispersed granular second phase (~1-2 μm) with a uniform distribution. Compared to the commercially available AZ91 alloy, this invention significantly reduces the potential difference between the second phase and the matrix, reduces localized corrosion, and simultaneously improves the alloy's strength, plasticity, and corrosion resistance. Therefore, the magnesium alloy obtained in this embodiment has a tensile strength of 262 MPa, an elongation of 11.2%, and a corrosion rate of 0.096 mg / cm². 2 / day.

[0053] Example 6

[0054] Corrosion-resistant, high-strength and tough magnesium alloy with a matrix structure of Mg-7.9Al-0.4Ca-0.5Mn-0.2Ce-0.7Sm-0.5Zn.

[0055] In this embodiment, the composition and weight percentage of the magnesium alloy material are: Al: 7.9%, Ca: 0.4%, Mn: 0.5%, Ce: 0.2%, Sm: 0.7%, Zn: 0.5%, with the balance being Mg and unavoidable impurities ≤0.02%. Its preparation method includes the following steps:

[0056] (1) Raw material preparation: Prepare Mg, Al, Zn, Mg-5Mn, Mg-30Ca, Mg-30Ce and Mg-30Sm master alloy raw materials in the mass percentages mentioned above;

[0057] (2) Melting: Under the protection of SF6+CO2 (volume ratio 4:96) mixed protective gas, Mg is heated to 710℃ and melted; then the temperature is raised to 735℃, and Al, Zn, Mg-5Mn, Mg-30Ce, Mg-30Sm and Mg-30Ca intermediate alloy are added in sequence; after all raw materials are completely melted, the temperature is lowered to 693℃, and the mixture is stirred thoroughly for 26 minutes and then allowed to stand for 40 minutes to obtain the alloy melt; the alloy melt is then poured into a mold to obtain corrosion-resistant high-strength and tough magnesium alloy rods or ingots;

[0058] (3) Die casting: The magnesium alloy rod or ingot prepared in step (2) is heated to 728℃ and completely melted, then held at that temperature for 45 minutes; then cooled to 683℃ and die-cast for 1-3 seconds to obtain Mg-7.9Al-0.4Ca-0.5Mn-0.2Ce-0.7Sm-0.5Zn magnesium alloy. The die casting process is as follows: die casting mold: 200℃, injection pressure 150MPa and injection speed 1.8m / s. The tensile strength, elongation and corrosion rate of the magnesium alloy die-cast component are 256MPa, 10.8% and 0.098mg / cm, respectively. 2 / day.

[0059] Example 7

[0060] Corrosion-resistant, high-strength and tough magnesium alloy with a matrix structure of Mg-7.8Al-0.4Ca-0.5Mn-0.6Ce-0.25Sm-0.5Zn.

[0061] In this embodiment, the composition and mass percentage of the magnesium alloy material are: Al: 7.8%, Ca: 0.4%, Mn: 0.5%, Ce: 0.6%, Sm: 0.25%, Zn: 0.5%, with the balance being Mg and unavoidable impurities ≤0.02%. Its preparation method includes the following steps:

[0062] (1) Raw material preparation: Prepare Mg, Al, Zn, Mg-5Mn, Mg-30Ca, Mg-30Ce and Mg-30Sm master alloy raw materials in the mass percentages mentioned above;

[0063] (2) Melting: Under the protection of a mixed protective gas of SF6+CO2 (volume ratio 4.5:95.5), Mg is heated to 705℃ and melted; then the temperature is raised to 728℃, and Al, Zn, Mg-5Mn, Mg-30Ce, Mg-30Sm, and Mg-30Ca master alloys are added in sequence; after all raw materials are completely melted, the temperature is lowered to 691℃, and the mixture is stirred thoroughly for 27 minutes and then allowed to stand for 45 minutes to obtain the alloy melt; the alloy melt is then poured into a mold to obtain corrosion-resistant high-strength and high-toughness magnesium alloy rods or ingots;

[0064] (3) Die casting: The magnesium alloy rod or ingot prepared in step (2) is heated to 730℃ and completely melted, then held at that temperature for 40 minutes; then cooled to 687℃ and subjected to die casting for 1-3 seconds to obtain Mg-7.8Al-0.4Ca-0.5Mn-0.6Ce-0.25Sm-0.5Zn magnesium alloy. The die casting process is as follows: die casting mold: 210℃, injection pressure 152MPa and injection speed 1.7m / s. The tensile strength, elongation and corrosion rate of this magnesium alloy are 254MPa, 10.2% and 0.109mg / cm, respectively. 2 / day.

[0065] Example 8

[0066] Corrosion-resistant, high-strength and tough Mg-7.2Al-0.3Ca-0.5Mn-0.5Nd magnesium alloy die-cast thin-walled components

[0067] In this embodiment, the components and weight percentages of the component are: Al: 7.2%, Ca: 0.3%, Mn: 0.5%, Nd: 0.5%, with the balance being Mg and unavoidable impurities ≤0.02%. Its preparation method includes the following steps:

[0068] (1) Raw material preparation: Prepare Mg, Al, Mg-5Mn, Mg-30Ca and Mg-30Nd master alloy raw materials in the mass percentages described above;

[0069] (2) Melting: Under the protection of inert gas Ar, Mg is heated to 695℃ and melted; then the temperature is raised to 730℃, and Al, Mg-5Mn, Mg-30Nd and Mg-30Ca intermediate alloy are added in sequence; after all raw materials are completely melted, the temperature is lowered to 693℃, stirred thoroughly for 28 minutes and then allowed to stand for 55 minutes to obtain alloy melt; the alloy melt is then poured into a mold to obtain corrosion-resistant high-strength and tough magnesium alloy rods or ingots;

[0070] (3) Die casting: The magnesium alloy rod or ingot prepared in step (2) is heated to 726℃ and completely melted, then held at that temperature for 35 minutes; then cooled to 684℃ and die-cast for 1-3 seconds to obtain Mg-7.2Al-0.3Ca-0.5Mn-0.5Nd magnesium alloy. The die casting process is as follows: die casting mold: 280℃, injection pressure 158MPa and injection speed 2.0m / s. The tensile strength, elongation and corrosion rate of this magnesium alloy are 280MPa, 14.5% and 0.092mg / cm, respectively. 2 / day.

[0071] Example 9

[0072] Corrosion-resistant, high-strength and tough Mg-7.5Al-0.3Ca-0.5Mn-0.2Pr-0.5Nd magnesium alloy die-cast thin-walled components

[0073] In this embodiment, the components and their mass percentages of the component are: Al: 7.5%, Ca: 0.3%, Mn: 0.5%, Pr: 0.2%, Nd: 0.3%, with the balance being Mg and unavoidable impurities ≤0.02%. Its preparation method includes the following steps:

[0074] (1) Raw material preparation: Prepare Mg, Al, Mg-5Mn, Mg-30Ca, Mg-30Pr and Mg-30Nd master alloy raw materials in the mass percentages described above;

[0075] (2) Melting: Under the protection of inert gas Ar, Mg is heated to 705℃ and melted; then the temperature is raised to 735℃, and Al, Mg-5Mn, Mg-30Pr, Mg-30Nd and Mg-30Ca master alloys are added in sequence; after all raw materials are completely melted, the temperature is lowered to 700℃, and the mixture is stirred thoroughly for 30 minutes and then allowed to stand for 60 minutes to obtain the alloy melt; the alloy melt is then poured into a mold to obtain corrosion-resistant high-strength and high-toughness magnesium alloy rods or ingots;

[0076] (3) Die casting: The magnesium alloy rod or ingot prepared in step (2) is heated to 730℃ and completely melted, then held at that temperature for 30 minutes; then cooled to 680℃ and die-cast for 1-3 seconds to obtain Mg-7.5Al-0.3Ca-0.5Mn-0.2Pr-0.5Nd magnesium alloy. The die casting process is as follows: die casting mold: 296℃, injection pressure 160MPa and injection speed 2.2m / s. The tensile strength, elongation and corrosion rate of this magnesium alloy are 276MPa, 14.9% and 0.083mg / cm, respectively. 2 / day.

[0077] Comparative Example 1

[0078] Sun et al. published a paper in the Journal of Alloys and Compounds 964(2023)171205 entitled "Improving the corrosion resistance of Mg-8Li-3Al-2Zn alloy by combining Gd alloying and hot extrusion." This comparative example discloses a Mg-8Li-3Al-2Zn-1Gd alloy. First, under pure argon protection, the alloy was melted and stirred in a tantalum crucible at 730°C. The melt was then allowed to stand for 10 minutes before being cast into an ingot. The ingot was then subjected to homogenization heat treatment at 300°C for 24 hours. Finally, it was extruded at 250°C with an extrusion ratio of 23:1. The average corrosion rate of this comparative example after immersion in a 3.5% NaCl solution for 15 days at room temperature was 0.27 mg / cm³. 2 / day.

[0079] Comparative Example 2

[0080] Dai et al. published a journal article in Materials & Design 221(2022)110980: "Insight into the role of Y addition in the microstructures, mechanical and corrosion properties of as-cast Mg-Gd-Y-Zn-Ca-Zr alloys". This comparative example discloses that after melting a Mg-4Gd-5Y-1Zn-0.5Ca-1Zr alloy at 780℃, mechanically stirring for 5 min to obtain a homogeneous melt; the melt was then cooled to 720℃ and held for 20 min before being poured into a preheated low-carbon steel mold, followed by water quenching at room temperature. The resulting alloy ingot had a tensile strength of 215.3 MPa and an elongation of 8.4%, respectively. The average corrosion rate of this comparative example after immersion in 3.5% NaCl solution for 60 h at room temperature was converted to 5.03 mg / cm². 2 / day.

[0081] In summary:

[0082] Compared with all embodiments of the present invention, Comparative Example 1 uses a higher amount of alloy components and rare earth elements. Furthermore, the Comparative Example 1 employs additional high-temperature, long-term heat treatment and high-temperature extrusion deformation treatment, resulting in higher raw material costs. Additionally, the process of Comparative Example 1 is more complex than that of the present invention. However, the highest corrosion resistance of the alloy obtained in Comparative Example 1 is lower than the lowest corrosion resistance of the alloy obtained in the present invention. Therefore, compared with the Comparative Example 1, the present invention achieves a significantly improved technical effect. Compared with all embodiments of the present invention, Comparative Example 2 uses a higher amount of alloy components and rare earth elements. The rare earth content of the alloy obtained in Comparative Example 2 is as high as 9%, far exceeding the main additive elements (non-rare earth elements) of the embodiments of the present invention. Therefore, compared with Comparative Example 2, the present invention saves on raw material costs. However, the highest strength, plasticity, and corrosion resistance of the alloy obtained in Comparative Example 2 are all lower than the lowest strength, plasticity, and corrosion resistance of the alloy obtained in the embodiments of the present invention. Therefore, compared with Comparative Example 2, the present invention achieves a significantly improved technical effect. Therefore, compared with the prior art, the components and process parameters used in this invention are different. The components used in this invention have lower content. Furthermore, compared with the comparative example, this invention omits complex processes such as plastic deformation, high-temperature long-term solution treatment, aging heat treatment, and high-temperature hot extrusion, thus simplifying the process. In addition, the prior art does not provide technical guidance on simultaneously achieving high strength, plasticity, and corrosion resistance in die-cast alloys, and the alloy obtained by this invention has significantly higher strength, plasticity, and corrosion resistance than the alloy obtained in the comparative example. Therefore, compared with the comparative example and the prior art, this invention has lower component content, reduces raw material costs, omits complex processes such as plastic deformation, high-temperature long-term solution treatment, aging heat treatment, and high-temperature hot extrusion, and achieves a short process (with advantages such as high-speed solidification, far exceeding the sub-rapid solidification rate of the prior art). The alloy obtained by this invention has higher strength, plasticity, and corrosion resistance than the alloys obtained in the comparative example and the prior art, simultaneously improving the alloy's strength, plasticity, and corrosion resistance. Therefore, compared with the prior art, this invention breaks through the technical bottleneck that it is difficult to improve the strength and corrosion resistance of magnesium alloys at the same time. It achieves simultaneous improvement in the three aspects of strength, plasticity and corrosion resistance of magnesium alloys. In addition, the casting alloys achieved by the prior art are only small-sized casting components, and it is difficult to obtain large-sized components. However, the magnesium alloy obtained by this invention is suitable for integrated die casting of large and complex components weighing 30-50kg, as well as for die casting of medium and small-sized complex components. Therefore, compared with the prior art, this invention has achieved significantly improved technical effects.Furthermore, in all embodiments of the present invention, the components, proportions, and process parameters used in each embodiment are different. Among them, the alloy obtained in Example 1 has the highest strength, plasticity, and corrosion resistance, but the content of each component and the total alloy content are not the highest. This indicates that the significant improvement effect achieved by the present invention is not determined by a certain element, process, or parameter, but is achieved by the synergistic regulation of components, component proportions, component interactions, processes, and process parameters. Moreover, only within the scope of protection of the claims of the present invention can the simultaneous improvement of alloy strength, plasticity, and corrosion resistance, as well as the die casting of large, medium, and small complex components, be achieved. In addition, compared with the prior art, the magnesium alloy obtained by the present invention has achieved the following new breakthroughs in terms of internal structure, size distribution, and uniformity: the present invention has a more uniform internal structure and finer equiaxed crystals (the main... (Irregularly shaped, large-sized grains), the equiaxed grains obtained by this invention have an average grain size of ~3.3 μm, and the eutectic phase structure in the internal microstructure is significantly refined. Calculations show that the volume fraction of the eutectic phase is approximately half that of commercial AZ91 alloy, and it is uniformly dispersed. Simultaneously, this invention also forms a large number of uniformly distributed granular second phases (~1-2 μm) (existing magnesium alloys mainly contain large, non-uniformly dispersed rod-shaped second phases with a size of ~5-10 μm). This invention reduces the potential difference between the second phase and the matrix, significantly improving the alloy's strength, plasticity, and corrosion resistance. After immersion in 3.5% NaCl solution for 7 days, the magnesium alloy obtained by this invention showed no significant hydrogen evolution on the alloy surface, and no obvious pitting corrosion was observed, indicating that the magnesium alloy obtained by this invention has excellent corrosion resistance. These superior effects ultimately enable the magnesium alloy obtained by this invention to simultaneously improve its strength, plasticity, and corrosion resistance, and to be suitable for die casting large, medium, and small complex components. In summary, this invention achieves superior technical effects through the interaction between components, proportions, processes, and synergistic control of process parameters. Furthermore, only within the scope of protection of the claims of this invention can the corrosion resistance and toughness of the alloy be improved simultaneously.

[0083] Table 1. Comparison of alloy properties obtained in Examples 1-9 and Comparative Examples 1-2

[0084]

Claims

1. A corrosion resistant high strength and toughness magnesium alloy suitable for complex structural die castings, characterized in that, The alloy is composed of the following components in percentage by mass: Al: 6.0-10.0%, Mn: 0.3-0.8%, Ca: 0.1-0.6%, rare earth RE: 0.4-1.5%, unavoidable impurities ≤0.02%, the balance being Mg, the rare earth RE being any one or combination of Ce, La, Nd, Pr, Sm or Y; its preparation method comprises the following steps: (1) raw material preparation: quantitatively configure Mg, Al, Mg-Ca, Mg-Mn and Mg-RE intermediate alloy raw materials according to the mass percentage; (2) melting: under the protection of inert gas Ar or mixed SF6 and CO2 protective gas, the volume ratio of SF6 and CO2 being 1-10:90-99, heat Mg to 670-710 ℃ to melt, then heat to 720-760 ℃, and then add the Al, Mg-Mn, Mg-RE and Mg-Ca intermediate alloys in sequence; after all the raw materials are completely melted, cool to 670-720 ℃, fully stir for 10-40 min, then stand for 10-70 min to obtain alloy melt; then pour the alloy melt into a mold to obtain a corrosion-resistant high-strength and high-toughness magnesium alloy cast rod or ingot; (3) die casting: heat the magnesium alloy cast rod or ingot prepared in step (2) to 680-760 ℃, completely melt, then heat for 30-60 min, cool to 660-720 ℃, and then perform 1-10 s die casting treatment to obtain a corrosion-resistant high-strength and high-toughness magnesium alloy, the die casting treatment being: die mold temperature 150-300 ℃, injection specific pressure 100-200 MPa and injection speed 1.0-2.5 m / s; In step (2), heat Mg to 680-700 ℃ to melt, then heat to 725-740 ℃, and then add the Al, Mg-Mn, Mg-RE and Mg-Ca intermediate alloys in sequence; after all the raw materials are completely melted, cool to 690-700 ℃, fully stir for 15-30 min, then stand for 20-60 min to obtain alloy melt; then pour the alloy melt into a mold to obtain a corrosion-resistant high-strength and high-toughness magnesium alloy cast rod or ingot. The corrosion-resistant high-toughness magnesium alloy has a tensile strength of > 240 MPa and an elongation of > 10%, and a corrosion rate of < 0.11 mg / cm 2 / day after being soaked in 3.5% NaCl solution for 7 days.

2. The corrosion resistant high strength and ductility magnesium alloy suitable for complex structural die castings as claimed in claim 1, wherein, In step (3), heat the magnesium alloy cast rod or ingot to 690-730 ℃, completely melt, then heat for 35-50 min, cool to 680-700 ℃, and then perform 2-5 s die casting treatment to obtain a corrosion-resistant high-strength and high-toughness magnesium alloy, the die casting treatment being: die mold temperature 200-250 ℃, injection specific pressure 120-160 MPa and injection speed 1.3-2.2 m / s.

3. The corrosion resistant high strength and ductility magnesium alloy suitable for complex structural die castings as claimed in claim 1, wherein, 5. Application of the corrosion-resistant high-strength and high-toughness magnesium alloy suitable for complex structure die castings according to any one of claims 1-4 in the field of large, medium or small complex components integration for new energy vehicles, 3C electronics, high-speed rail and aviation.

4. The corrosion resistant high strength and ductility magnesium alloy suitable for complex structural die castings as claimed in claim 1, wherein, The corrosion-resistant high-toughness magnesium alloy has a tensile strength of 242 MPa to less than 300 MPa and an elongation of 10.2 to less than 16%, and a corrosion rate of 0.03 mg / cm 2 / day to less than 0.11 mg / cm 2 / day after being soaked in a 3.5% NaCl solution for 7 days. ​

Images