An ultra-high strength rare earth magnesium alloy and its high temperature single phase zone forging forming process

Abstract

The invention discloses an ultra-high strength rare earth magnesium alloy and a high temperature single phase zone forging forming process thereof, and relates to the technical field of non-ferrous metal materials and processing thereof. The mass percentage components are as follows: Gd 12.8-13.4wt.%, Fe≤0.05%, Cu≤0.05%, Si≤0.05%, Ni≤0.005%, and the balance is Mg; the single phase zone high temperature forging is carried out in the range of 500-450 DEG C, the 500 DEG C forging ratio is about 1.18, and annealing treatment is carried out at 450 DEG C for 40 minutes after forging; the 450 DEG C forging ratio is about 2.64, and cold water quenching is carried out after final forging; the invention makes full use of the high solid solubility and strong precipitation hardening characteristics of Gd in magnesium, avoids the formation of coarse dynamic precipitation phase through high temperature single phase forging processing, improves the forging forming performance of the alloy, and successfully prepares large-size, ultra-high strength magnesium forgings in combination with subsequent isothermal aging treatment, which is of great significance for promoting the application of magnesium forgings in high technology fields such as aerospace, national defense and military industry.

Description

Technical Field

[0001] The invention belongs to the technical field of nonferrous metal structural materials and processing thereof, and specifically relates to magnesium alloy forging technology and a design and preparation method of ultra-high strength magnesium alloy. Background Art

[0002] As the lightest metal structural material currently available, magnesium alloy has high specific strength, specific stiffness, good cutting performance, electromagnetic shielding performance, damping and shock absorption performance, and is abundant in resources and easy to recycle. Therefore, it has broad application prospects in aerospace, automobile, consumer electronics, military industry and other fields; however, compared with traditional steel, aluminum, titanium and other alloys, the low absolute strength seriously hinders the widespread application of magnesium alloys, especially in high-tech fields such as aerospace and military industry.

[0003] At present, the main solutions to the technical problem of low strength of magnesium alloys are: (1) optimizing alloy composition design, (2) using plastic processing technology. A large number of studies have proved that rare earth magnesium alloys are the most promising ultra-high strength magnesium alloy systems, such as WE43 / 54 and Mg-Gd-Y(-Zn)-Zr(GW) magnesium alloys; in addition, the main plastic processing technologies currently include extrusion, rolling and forging, which can be used to produce magnesium profiles, bars, plates and strips.

[0004] During the forging process of magnesium alloy, especially during free forging or open die forging, the free surface of the magnesium billet is easily cracked under the action of impact load, resulting in a low yield of forged magnesium alloy; secondly, due to the poor plastic deformation ability of magnesium alloy, its forging process is usually carried out at high temperature, which makes it difficult to obtain fine-grained structure during forging; on the other hand, although the composite addition of a large amount of rare earth elements such as Gd, Y, Nd, etc. can significantly increase the strength of the alloy, it also increases the deformation resistance of the alloy, resulting in a narrow processing temperature window, which has also become a technical bottleneck restricting the development of high-performance rare earth magnesium alloy forgings.

[0005] Up to now, there is no report on the preparation technology of large-size, high-performance rare earth magnesium alloy forgings with yield strength ≥450MPa.

[0006] In response to the urgent demand for ultra-high strength and large-size magnesium forgings in my country's high-tech fields such as aerospace, the present invention abandons the traditional method of designing high-performance magnesium alloys by multi-component rare earth composite strengthening, and for the first time proposes to use the high solid solubility Gd element to design an aging-strengthened Mg-13Gd binary alloy, combined with a high-temperature single-phase zone forging forming process, to achieve "shape control and property control" of magnesium forgings, and to prepare large-size, ultra-high strength magnesium forgings. Summary of the invention

[0007] In view of the deficiencies in the prior art, the purpose of the present invention is to provide an aging-strengthened Mg-13Gd binary alloy designed using the high solid solubility Gd element, and combined with a high-temperature single-phase zone forging forming process, to achieve "shape control and property control" of high-strength magnesium forgings, which is of great significance to further promote the application of large-size high-strength magnesium forgings in my country's aerospace and other high-tech fields.

[0008] In order to achieve the above technical objectives, the technical solution adopted by the present invention is as follows.

[0009] The mass percentage composition of an ultra-high strength rare earth magnesium alloy is Gd12.8-13.4%, Fe≤0.05%, Cu≤0.05%, Si≤0.05%, Ni≤0.005%, and the balance is Mg.

[0010] A high temperature single phase zone forging process for an ultra-high strength rare earth magnesium alloy, the steps of which are as follows:

[0011] (a) Semi-continuous casting technology is used to prepare large-sized high-quality ingots: the casting temperature is 720-740°C, the casting speed is 40-50 mm / min, and the cooling water pressure is 0.02-0.03 MPa.

[0012] (b) High temperature and long time solution treatment: solution temperature is 520-530℃, time is 20-30 hours, after solution treatment, slowly immerse in 80-100℃ hot water for quenching.

[0013] (c) Use a drop hammer forging machine to roughen the forging blank with a small deformation, and the roughing reduction is about 5-8%; then stretch forging is performed in the radial direction, with the two mutually perpendicular radial directions of the cylindrical forging blank as the equivalent forging direction, and the axial direction of the forging blank as the stretching direction. The upper and lower anvils are preheated to 250-300℃, the forging hammer impact frequency is about 60-100 times / minute, the average strain rate is about 13-15s-1, and the annealing time between passes before forging is about 30-40 minutes; the forging ratio of the first or second pass of 500℃ forging is maintained between 1.17 and 2.64, the annealing temperature between passes is 500℃, but the annealing temperature after the final forging at 500℃ is 450℃; then forge one pass at 450℃, the forging ratio is about 2.25-2.65, and cold water quenching is performed after the final forging at 450℃.

[0014] (d) Isothermal aging treatment: Isothermal aging treatment is carried out at 200°C for 40 to 45 hours.

[0015] As a further improvement, the inter-pass annealing temperature in step (c) corresponds to the forging temperature of the next pass.

[0016] Further optimization and improvement of the above technical solution, in step (c), first forging at 500 ° C for the first time, the forging ratio is about 1.18, and annealing at 450 ° C for 40 minutes after forging; then forging at 450 ° C for the second time, the forging ratio is about 2.64, and cold water quenching is performed after forging.

[0017] Further optimization and improvement of the above technical solutions,

[0018] In step (c), the forging blank is kept at 500°C for 40 minutes, and then forged at 500°C for 2 passes, the forging ratio of the first pass is 1.18, the forging ratio of the second pass is 2.64, the annealing temperature between passes is 450°C, the annealing time between passes is 40 minutes, and the final forging at 450°C is followed by cold water quenching.

[0019] Isothermal aging treatment was carried out at 200°C for 40 hours;

[0020] The yield strength of the forging in the drawing direction is ≥458MPa, the tensile strength is ≥493MPa, and the elongation is ≥3.5%.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] The ultra-high strength rare earth magnesium alloy of the present invention uses heavy rare earth Gd with high solid solubility as the only alloying element. After high-temperature solid solution, it can form a quasi-single-phase solid solution structure, which is beneficial to high-temperature forging and forming; at the same time, because Gd can reduce the stacking fault energy of the magnesium alloy, promote non-basal slip, and improve its plasticity. The high-temperature single-phase zone forging and forming process adopted effectively suppresses the dynamic precipitation of coarse Mg5Gd phase during the forging process. At the same time, high-temperature forging makes the Gd solute diffuse evenly, avoids solute segregation, and thus promotes the formation of basal texture. Therefore, the structure of the forged alloy is a near-single-phase solid solution structure, similar to the cast solid solution alloy. But unlike the cast solid solution alloy, the structure of the forged alloy also has a strong basal texture. Therefore, the supersaturated Gd solute in the forging structure provides good organizational conditions for subsequent maximum precipitation and precipitation. After aging treatment, the high-density columnar precipitation phase is dispersed in the magnesium matrix, which can effectively hinder dislocation slip and mechanical twinning, thereby contributing to ultra-high strength.

[0023] The test results show that the mechanical properties of the ultra-high strength Mg-13Gd forging alloy prepared by the high temperature single-phase zone forging forming process of the present invention are: yield strength of 426-458MPa, tensile strength of 431-493MPa, and elongation of 0.93-3.5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0025] Figure 1 This is the metallographic structure of the ultra-high strength forged magnesium-gadolinium alloy prepared in Example 2 of the present invention.

[0026] Figure 2 This is the stress-strain curve of the ultra-high strength forged magnesium-gadolinium alloy prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0028] Example 1

[0029] The mass percentage composition of the ultra-high strength rare earth magnesium alloy is Gd12.8%, Fe≤0.05%, Cu≤0.05%, Si≤0.05%, Ni≤0.005%, and the balance is Mg.

[0030] The high temperature single phase zone forging process of ultra-high strength rare earth magnesium alloy comprises the following steps:

[0031] (1) Mg-12.8Gd (wt.%) ingots were prepared by semi-continuous casting technology, with a casting temperature of 720-740°C, a casting speed of 40-50 mm / min, and a cooling water pressure of 0.02-0.03 MPa;

[0032] (2) Then keep at 520℃ for 24 hours and quench in hot water at 80-100℃;

[0033] (3) Processing into forging blanks with a height of 100 mm and a diameter of 80 mm;

[0034] Specifically, a drop hammer forging machine is used to roughen the forging blank with a small deformation amount, and the roughing reduction is about 5-8%; then, the forging is stretched in the radial direction, with the two mutually perpendicular radial directions of the cylindrical forging blank as the equivalent forging directions, and the axial direction of the forging blank as the stretching direction; the upper and lower anvils are preheated to 250-300°C, the forging hammer impact frequency is about 60-100 times / min, and the average strain rate is about 13-15s -1 , the annealing time between passes is about 30 to 40 minutes;

[0035] The forging billet was kept at 500℃ for 40min, then forged at 500℃ for 2 passes, the forging ratio of the first pass was 1.18, the forging ratio of the second pass was 1.69, the total forging ratio was 2.01, the annealing temperature between passes was 500℃, the annealing time between passes was 40min, and cold water quenching was performed after final forging at 450℃;

[0036] (4) Isothermal aging treatment: isothermal aging treatment is carried out at 200°C for 45 hours.

[0037] According to the standard of GBT-228.1-2021 "Metallic Materials-Tensile Test-Part 1: Room Temperature Test Method", the Mg-12.8Gd forging prepared in Example 1 of the present invention was tested for room temperature mechanical properties. The tensile direction was parallel to the drawing direction of the forging. The test results are listed in Table 1.

[0038] Example 2

[0039] The mass percentage composition of the ultra-high strength rare earth magnesium alloy is Gd13.2%, Fe≤0.05%, Cu≤0.05%, Si≤0.05%, Ni≤0.005%, and the balance is Mg.

[0040] The high temperature single phase zone forging process of ultra-high strength rare earth magnesium alloy comprises the following steps:

[0041] (1) Mg-13.2Gd (wt.%) ingots were prepared by semi-continuous casting technology, with a casting temperature of 720-740°C, a casting speed of 40-50 mm / min, and a cooling water pressure of 0.02-0.03 MPa;

[0042] (2) Then keep at 520℃ for 28 hours and quench in hot water at 80-100℃;

[0043] (3) Processing into forging blanks with a height of 100 mm and a diameter of 80 mm;

[0044] Specifically, a drop hammer forging machine is used to roughen the forging blank with a small deformation amount, and the roughing reduction is about 5-8%; then, the forging is stretched in the radial direction, with the two mutually perpendicular radial directions of the cylindrical forging blank as the equivalent forging directions, and the axial direction of the forging blank as the stretching direction; the upper and lower anvils are preheated to 250-300°C, the forging hammer impact frequency is about 60-100 times / min, and the average strain rate is about 13-15s -1 , the annealing time between passes is about 30 to 40 minutes;

[0045] The forging blank is kept at 500℃ for 40min, then forged at 500℃ for 2 passes, the forging ratio of the first pass is 1.18, the forging ratio of the second pass is 2.64, the annealing temperature between passes is 450℃, the annealing time between passes is 40min, and after final forging at 450℃, cold water quenching is performed; (4) isothermal aging treatment is performed at 200℃ for 40 hours.

[0046] According to the standard of GBT-228.1-2021 "Metallic Materials-Tensile Test-Part 1: Room Temperature Test Method", the Mg-13.2Gd forging prepared in Example 2 of the present invention was tested for room temperature mechanical properties. The tensile direction was parallel to the drawing direction of the forging. The test results are listed in Table 1.

[0047] Example 3

[0048] The mass percentage composition of the ultra-high strength rare earth magnesium alloy is Gd13.4%, Fe≤0.05%, Cu≤0.05%, Si≤0.05%, Ni≤0.005%, and the balance is Mg.

[0049] The high temperature single phase zone forging process of ultra-high strength rare earth magnesium alloy comprises the following steps:

[0050] (1) Mg-13.2Gd (wt.%) ingots were prepared by semi-continuous casting technology, with a casting temperature of 720-740°C, a casting speed of 40-50 mm / min, and a cooling water pressure of 0.02-0.03 MPa;

[0051] (2) Then keep at 525℃ for 25 hours and quench in hot water at 80-100℃;

[0052] (3) Processing into forging blanks with a height of 100 mm and a diameter of 80 mm;

[0053] Specifically, a drop hammer forging machine is used to roughen the forging blank with a small deformation amount, and the roughing reduction is about 5-8%; then, the forging is stretched in the radial direction, with the two mutually perpendicular radial directions of the cylindrical forging blank as the equivalent forging directions, and the axial direction of the forging blank as the stretching direction; the upper and lower anvils are preheated to 250-300°C, the forging hammer impact frequency is about 80-120 times / min, and the average strain rate is about 13-15s -1 , the annealing time between passes is about 30 to 40 minutes;

[0054] The first forging was performed at 500℃, with a forging ratio of about 1.18, followed by annealing at 500℃ for 35min; the second forging was performed at 500℃, with a forging ratio of about 1.17, followed by annealing at 450℃ for 40min; the third forging was performed at 450℃, with a forging ratio of about 1.42, followed by cold water quenching;

[0055] (4) Isothermal aging treatment: isothermal aging treatment is carried out at 200°C for 45 hours.

[0056] According to the standard of GBT-228.1-2021 "Metallic Materials-Tensile Test-Part 1: Room Temperature Test Method", the Mg-13.4Gd forging prepared in Example 3 of the present invention was tested for room temperature mechanical properties. The tensile direction was parallel to the drawing direction of the forging. The test results are listed in Table 1.

[0057] Table 1. Room temperature mechanical properties of forgings prepared in Examples 1 to 3 in the drawing direction:

[0058]

[0059] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. The high temperature single phase zone forging process of ultra-high strength rare earth magnesium alloy has the following steps: (a) Take a target rare earth magnesium alloy ingot, whose mass percentage composition is Gd: 13.2~13.4%, Fe≤0.05%, Cu≤0.05%, Si≤0.05%, Ni≤0.005%, and the balance is Mg; (b) Semi-continuous casting technology is used to prepare large-sized high-quality ingots: the casting temperature is 720~740ºC, the casting speed is 40~50mm / min, and the cooling water pressure is 0.02~0.03 MPa; (c) High temperature and long time solution treatment: solution temperature 520~530ºC, time 20~30 hours, after solution treatment, slowly immerse in 80~100 ºC hot water for quenching; (d) Use a drop hammer forging machine to roughen the forging billet with a small deformation amount, and the roughing reduction is 5~8%; then stretch forging is performed in the radial direction, with the two mutually perpendicular radial directions of the cylindrical forging billet as the equivalent forging direction, and the axial direction of the forging billet as the stretching direction; the upper and lower anvils are preheated to 250-300ºC, the forging hammer impact frequency is 60~100 times / minute, the average strain rate is 13~15 s-1, and the annealing time between passes before forging is 30~40 minutes; the forging ratio of the first or second pass of 500ºC forging is maintained between 1.17~2.64, the annealing temperature between passes is 500ºC, but the annealing temperature after 500ºC final forging is 450ºC; then forge one pass at 450ºC, the forging ratio is 2.25~2.65, and cold water quenching is performed after final forging at 450ºC; (e) Isothermal aging treatment: Isothermal aging treatment is carried out at 200°C for 40 to 45 hours.

2. According to the high temperature single phase zone forging forming process of an ultra-high strength rare earth magnesium alloy as described in claim 1, the inter-pass annealing temperature in step (d) corresponds to the forging temperature of the next pass.

3. According to the high temperature single-phase zone forging forming process of an ultra-high strength rare earth magnesium alloy according to claim 1, first forging the first pass at 500ºC with a forging ratio of 1.18, and annealing at 450ºC for 40 minutes after forging; then forging the second pass at 450ºC with a forging ratio of 2.64, and cold quenching after forging.

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