Preparation method of high-strength Mg-Gd binary alloy rod

Abstract

The application discloses a preparation method of high-strength Mg-Gd binary alloy rod material, comprising the following steps: alloy smelting: preparing Mg-Gd alloy; solid solution treatment: carrying out solid solution treatment on the Mg-Gd alloy obtained by smelting; preliminary extrusion: extruding the Mg-Gd alloy blank after the solid solution treatment at 380-440 DEG C, the extrusion ratio is 6-12, the extrusion speed is 0.2-2 mm / s, and a preliminary extrusion rod material is obtained; secondary extrusion: extruding the preliminary extrusion rod material at 300-340 DEG C, the extrusion ratio is 4-9, the extrusion speed is 0.1-1 mm / s, and a secondary extrusion rod material is obtained; aging treatment: aging the secondary extrusion rod material to a peak aging state, and high-strength Mg-Gd binary alloy rod material is obtained. According to the preparation method, the aging type Mg-Gd binary alloy rod material with high strength and good plasticity is obtained.

Description

A method for preparing high-strength Mg-Gd binary alloy rods Technical Field

[0001] This invention relates to the field of metallic materials technology, specifically to a method for preparing high-strength Mg-Gd binary alloy rods. Background Technology

[0002] Magnesium alloys, as the lightest metallic structural materials currently used in engineering applications, meet the medium- and long-term weight reduction requirements of aerospace, defense, and rail transportation, and have broad application prospects. However, compared with traditional metallic materials such as steel and aluminum alloys, magnesium alloys have some obvious performance deficiencies, such as low absolute engineering strength, which greatly limits their large-scale application in these fields. To expand the practical application of magnesium alloys, the development of high-strength / ultra-high-strength magnesium alloy materials has become an urgent task. In recent years, the requirements for high-performance and large-scale components of lightweight magnesium alloys in my country's high-end equipment have become increasingly prominent. Researchers at home and abroad have conducted extensive and in-depth research using various preparation technologies and structural modification methods. The results show that rare-earth-containing aging magnesium alloys are the ultra-high-strength magnesium alloys with the greatest development potential.

[0003] In age-hardening extruded magnesium alloys, when extrusion is performed at relatively low temperatures (300℃-350℃) and small extrusion ratios (extrusion ratio less than 10), a mixed-grain structure is formed, consisting of fine recrystallized equiaxed grains and elongated deformed grains. The mixed-grain structure has a better strengthening effect than the fully dynamic recrystallized structure. However, in the mixed-grain structure obtained by one-step extrusion, the high proportion of non-uniform coarse elongated grains will cause the age-hardening magnesium alloy to have lower plasticity. Summary of the Invention

[0004] To address the issue of low plasticity in high-strength aging magnesium alloys, this invention provides a method for preparing Mg-Gd binary alloy rods that combine high strength and good plasticity.

[0005] A method for preparing high-strength Mg-Gd binary alloy rods, comprising:

[0006] Alloy smelting: Preparation of Mg-Gd alloys;

[0007] Solution treatment: The Mg-Gd alloy obtained by smelting is subjected to solution treatment;

[0008] Preliminary extrusion: The solution-treated Mg-Gd alloy billet is extruded at 380-440℃ with an extrusion ratio of 6-12 and an extrusion speed of 0.2-2 mm / s to obtain preliminary extruded bars;

[0009] Secondary extrusion: The initially extruded bar is extruded at 300-340℃, with an extrusion ratio of 4-9 and an extrusion speed of 0.1-1mm / s to obtain a secondary extruded bar;

[0010] Aging treatment: The secondary extruded bar is aged to the peak aging state to obtain a high-strength Mg-Gd binary alloy bar.

[0011] Furthermore, the alloy smelting is carried out by preparing Mg-Gd alloys with a diameter greater than 300 mm using a semi-continuous casting method.

[0012] Furthermore, the solution treatment is performed by holding the solution at 500-530℃ for 10-25 hours, followed by quenching with hot water at 80℃ or higher.

[0013] Furthermore, the preliminary extrusion also includes: rapidly induction heating the billet at 380-440°C for no more than 5 minutes before extrusion.

[0014] Furthermore, the preliminary extrusion also includes: quenching with cold water to cool to room temperature after extrusion.

[0015] Furthermore, the secondary extrusion also includes: rapidly induction heating the initially extruded bar at 300-340°C for no more than 5 minutes before extrusion.

[0016] Furthermore, the secondary extrusion also includes: quenching with cold water to cool to room temperature after extrusion.

[0017] Furthermore, the aging treatment involves keeping the secondary extruded bar at 180-220℃ for no less than 10 hours.

[0018] Furthermore, the high-strength Mg-Gd alloy rod has a Gd content of 13-22 wt.%, a Mg content of 87-78 wt.%, and a diameter of 60-100 mm.

[0019] Furthermore, the high-strength Mg-Gd alloy rod has a Gd content of 15 wt.% and a Mg content of 85 wt.%.

[0020] This invention provides a method for preparing high-strength Mg-Gd binary alloy rods. First, a high-quality initial magnesium alloy billet with small initial equiaxed grain size is obtained through preliminary extrusion. Then, a mixed-grain structure composed of fine recrystallized equiaxed grains and uniformly distributed small-sized elongated grains is formed through low-temperature secondary extrusion. Combined with an aging process, an aged Mg-Gd binary alloy rod with both high strength and good plasticity is obtained. Attached Figure Description

[0021] Figure 1 shows the tensile curves of the extruded and peak-aged samples in Example 1 of the present invention.

[0022] Figure 2 is an optical microscope photograph of the extruded sample in Example 1 of the present invention. Figure (a) shows the initial extrusion and Figure (b) shows the secondary extrusion.

[0023] Figure 3 shows the EBSD microstructure of the aged Mg-15Gd alloy in Example 1 of the present invention, with (0002) and (10-10) textures of the sample and a maximum texture intensity of 19.

[0024] Figure 4 shows transmission electron microscopy (TEM) images of the sample from Example 1 of this invention. Figure (a) shows the compressed state, and Figure (b) shows the peak aging. Detailed Implementation

[0025] The preparation method of a high-strength Mg-Gd binary alloy rod of the present invention will be further described below with reference to specific embodiments.

[0026] A method for preparing high-strength Mg-Gd binary alloy rods, comprising:

[0027] Alloy smelting: Preparation of Mg-Gd alloy ingots;

[0028] Solution treatment: The Mg-Gd alloy ingot obtained from smelting is subjected to solution treatment;

[0029] Preliminary extrusion: The solution-treated Mg-Gd alloy ingot is processed into a billet, which is then extruded at 380-440℃ with an extrusion ratio of 6-12 and an extrusion speed of 0.2-2 mm / s to obtain a preliminary extruded bar.

[0030] Secondary extrusion: The initially extruded bar is extruded at 300-340℃, with an extrusion ratio of 4-9 and an extrusion speed of 0.1-1mm / s to obtain a secondary extruded bar;

[0031] Aging treatment: The secondary extruded bar is aged to the peak aging state to obtain a high-strength Mg-Gd binary alloy bar.

[0032] This invention employs a process of first extruding at high temperature before low temperature extrusion to obtain a high-quality initial magnesium alloy billet with a small initial equiaxed grain size (referred to as preliminary extrusion). Then, it uses low temperature extrusion to form a mixed-grain structure consisting of fine recrystallized equiaxed grains and uniformly distributed small-sized elongated grains (referred to as secondary extrusion). Combined with an aging process, it obtains large-size aged magnesium alloy bars with both high strength and good plasticity. This provides technical support for the large-scale production of large-size high-strength and plastic magnesium alloys and is conducive to the lightweighting of large key components in high-end equipment. The initial extrusion is carried out at 380-440℃ with an extrusion ratio of 6-12 and an extrusion speed of 0.2-2 mm / s. This controls the grain size to prevent it from becoming too large and minimizes the amount of dynamic precipitation formed during the extrusion process. This ensures that the obtained magnesium alloy rod contains a fine (relatively solid solution-like) fully recrystallized structure, while minimizing the formation of submicron and micron-sized dynamic precipitation structures during extrusion. The secondary extrusion is carried out at a low temperature of 300-340℃ with a small extrusion ratio of 4-9 and a slow extrusion speed of 0.1-1 mm / s. This yields a secondary extruded magnesium alloy rod containing a mixed-grain structure. After aging treatment, this rod will fully utilize the textural strengthening effect of elongated grains and the strengthening effect of high-density nano-precipitates in the mixed-grain structure to obtain ultra-high strength large-size magnesium alloy rods.

[0033] Furthermore, the alloy smelting is carried out by preparing Mg-Gd alloy ingots with a diameter greater than 300 mm using a semi-continuous casting method.

[0034] In this embodiment, high-purity magnesium and high-purity gadolinium are used as raw materials. A high-Gd (e.g., 30 wt.% Gd) Mg-Gd master alloy can be prepared first. Then, a semi-continuous casting method is used. Pure magnesium is melted at 700-730℃, and the high-Gd Mg-Gd master alloy is added to the melt. The alloy is then cast at 680-700℃ to obtain a Mg-Gd alloy ingot with a diameter greater than 300 mm. The semi-continuous casting method is an effective way to obtain large-sized magnesium alloy ingots with a diameter greater than 300 mm. After secondary extrusion, this facilitates the production of larger-sized magnesium alloy rods.

[0035] Preferably, the solution treatment is performed by holding at 500-530℃ for 10-25 hours, followed by quenching with hot water at 80℃ or higher.

[0036] Solution treatment at 500-530℃ for 10-25 hours is chosen to ensure complete dissolution of the coarse compounds formed in the as-cast state into the magnesium matrix, creating favorable conditions for the formation of high-density nano-precipitates during subsequent aging. Hot water quenching at temperatures above 80℃ is used to alleviate thermal stress during quenching and prevent cracking in large magnesium alloy bars.

[0037] Preferably, the preliminary extrusion further includes: rapidly induction heating the billet at 380-440°C for no more than 5 minutes before extrusion.

[0038] In this embodiment, rapid induction heating is used to prevent the Mg-Gd alloy billet from remaining at high temperature for too long, thereby suppressing the precipitation of coarse compounds.

[0039] Preferably, the preliminary extrusion further includes: quenching with cold water to cool to room temperature after extrusion.

[0040] In this embodiment, the quenching method is cold water quenching, which can prevent the growth of extruded alloy grains and suppress the precipitation of coarse compounds.

[0041] Preferably, the secondary extrusion further includes: rapidly induction heating the initially extruded bar at 300-340°C for no more than 5 minutes before extrusion.

[0042] In this embodiment, rapid induction heating is used to prevent the Mg-Gd alloy sample from remaining at high temperature for too long, thereby inhibiting the precipitation of coarse compounds.

[0043] Preferably, the secondary extrusion further includes: quenching with cold water to cool to room temperature after extrusion.

[0044] In this embodiment, the quenching method is cold water quenching, which can prevent the growth of extruded alloy grains and suppress the precipitation of coarse compounds.

[0045] Preferably, the aging treatment involves keeping the secondary extruded bar at 180-220℃ for at least 10 hours.

[0046] In this embodiment, aging treatment can further improve the strength. The aging temperature is selected as 180-220℃, mainly because if the aging temperature is too high, the precipitated phase will be coarse and the number density of precipitated phase will be low, resulting in lower alloy strength. If the aging temperature is too low, the diffusion rate of Gd element will be too slow. Excessive aging time will significantly increase production costs.

[0047] Preferably, the high-strength Mg-Gd alloy rod has a Gd content of 13–22 wt.%, a Mg content of 87–78 wt.%, and a diameter of 60–100 mm. More preferably, the high-strength Mg-Gd alloy rod has a Gd content of 15 wt.% and a Mg content of 85 wt.%.

[0048] In this embodiment, if the Gd content in the high-strength Mg-Gd alloy rod is too high, the compound content will be too high, which will easily lead to a decrease in the alloy's plasticity. If the Gd content is too low, the strength of the magnesium alloy material will be low due to the insufficient amount of compound. Magnesium alloy rods with a diameter less than 20mm exhibit good comprehensive mechanical properties, but the comprehensive mechanical properties of large-sized magnesium alloy rods decrease significantly with increasing rod size. This is a problem that needs to be overcome in the actual production of magnesium alloys. In this embodiment, when the diameter of the alloy rod is 60-100mm and the Gd content is 13-22wt.%, the yield strength of the large-sized Mg-Gd alloy rod is between 400-470MPa, the tensile strength is between 420-550MPa, and the plasticity is greater than 3%. When the Gd content is 15wt.% and the Mg content is 85wt.%, the high-strength Mg-Gd alloy rod combines high strength and good plasticity.

[0049] Example 1: A method for preparing high-strength Mg-Gd binary alloy rods

[0050] A method for preparing a high-strength Mg-Gd binary alloy rod, specifically comprising:

[0051] (1) Alloy smelting: Using high-purity magnesium and high-purity gadolinium as raw materials, smelt Mg-15Gd (wt.%) binary alloy ingots;

[0052] (2) Solution treatment: The Mg-Gd alloy ingot obtained by melting was kept at 500℃ for 24h, and then quenched with hot water at 80℃; the solution-treated sample was processed into a cylindrical blank sample with a height of 300mm and a diameter of 340mm.

[0053] (3) Preliminary extrusion: Before preliminary extrusion, the sample is rapidly induction heated at 400℃ for 5 minutes. The sample is then placed in the extruder with the extrusion cylinder temperature at 400℃, the die temperature at 400℃, the extrusion ratio at 8, and the extrusion speed at 0.3 mm / s. The sample is then immediately quenched in cold water after extrusion.

[0054] (4) Secondary extrusion: Before secondary extrusion, the sample is rapidly induction heated at 320℃ for 5 minutes. The sample is then placed in the extruder with the extrusion cylinder temperature at 320℃, the die temperature at 320℃, the extrusion ratio at 4, and the extrusion speed at 0.3 mm / s. The sample is then immediately quenched in cold water after extrusion.

[0055] (5) Aging treatment: The secondary extruded bar is kept at 200℃ for 15h to obtain high-strength Mg-Gd binary alloy bar.

[0056] The high-strength Mg-Gd binary alloy rod prepared in Example 1 has a diameter of 60 mm, and its mechanical properties are shown in Table 1. As can be seen from Figures 1-4, the magnesium alloy rod has a yield strength of 470 MPa, a tensile strength of 500 MPa, and a plasticity of 6.4% after aging treatment (Figure 1). This plasticity mainly depends on the effect of the mixed grain structure (Figure 2). The elongated grains in the mixed grain structure provide strong texture reinforcement (Figure 3). After aging, there are also high-density nanoscale precipitates inside the elongated grains for reinforcement. The plasticity is mainly contributed by the fully recrystallized fine grains (Figure 4).

[0057] Example 2: A method for preparing high-strength Mg-Gd binary alloy rods

[0058] A method for preparing a high-strength Mg-Gd binary alloy rod, specifically comprising:

[0059] (1) Alloy smelting: Using high-purity magnesium and high-purity gadolinium as raw materials, smelt Mg-13Gd (wt.%) binary alloy ingots;

[0060] (2) Solution treatment: The Mg-Gd alloy ingot obtained by melting was kept at 500℃ for 10h, and then quenched with hot water at 80℃; the solution-treated sample was processed into a cylindrical blank sample with a height of 300mm and a diameter of 340mm.

[0061] (3) Preliminary extrusion: Before preliminary extrusion, the sample is rapidly induction heated at 380℃ for 3 minutes. The sample is then placed in the extruder with the extrusion cylinder temperature at 380℃, the die temperature at 380℃, the extrusion ratio at 6, and the extrusion speed at 0.2 mm / s. The sample is then immediately quenched in cold water after extrusion.

[0062] (4) Secondary extrusion: Before secondary extrusion, the sample is rapidly induction heated at 300℃ for 3 minutes. The sample is then placed in the extruder with the extrusion cylinder temperature at 300℃, the die temperature at 300℃, the extrusion ratio at 6, and the extrusion speed at 0.1 mm / s. The sample is then immediately quenched in cold water after extrusion.

[0063] (5) Aging treatment: The secondary extruded bar is kept at 200℃ for 30h to obtain high-strength Mg-Gd binary alloy bar.

[0064] Example 3: A method for preparing high-strength Mg-Gd binary alloy rods

[0065] A method for preparing a high-strength Mg-Gd binary alloy rod, specifically comprising:

[0066] (1) Alloy smelting: Using high-purity magnesium and high-purity gadolinium as raw materials, smelt Mg-18Gd (wt.%) binary alloy ingots;

[0067] (2) Solution treatment: The Mg-Gd alloy ingot obtained by melting was kept at 520℃ for 15h, and then quenched with hot water at 80℃; the solution-treated sample was processed into a cylindrical blank sample with a height of 300mm and a diameter of 340mm.

[0068] (3) Preliminary extrusion: Before preliminary extrusion, the sample is rapidly induction heated at 440℃ for 5 minutes. The sample is then placed in the extruder with the extrusion cylinder temperature at 440℃, the die temperature at 440℃, the extrusion ratio at 10, and the extrusion speed at 1mm / s. The extruded sample is immediately quenched in cold water.

[0069] (4) Secondary extrusion: Before the secondary extrusion, the sample is rapidly induction heated at 340℃ for 5 minutes. The sample is then placed in the extruder with the extrusion cylinder temperature at 340℃, the die temperature at 340℃, the extrusion ratio at 9, and the extrusion speed at 1mm / s. The sample is then immediately quenched in cold water after extrusion.

[0070] (5) Aging treatment: The secondary extruded bar is kept at 180℃ for 40h to obtain high-strength Mg-Gd binary alloy bar.

[0071] Example 4: A method for preparing high-strength Mg-Gd binary alloy rods

[0072] A method for preparing a high-strength Mg-Gd binary alloy rod, specifically comprising:

[0073] (1) Alloy smelting: Using high-purity magnesium and high-purity gadolinium as raw materials, smelt Mg-22Gd (wt.%) binary alloy ingots;

[0074] (2) Solution treatment: The Mg-Gd alloy ingot obtained by melting was kept at 530℃ for 25h, and then quenched with hot water at 80℃; the solution-treated sample was processed into a cylindrical blank sample with a height of 300mm and a diameter of 340mm.

[0075] (3) Preliminary extrusion: Before the preliminary extrusion, the sample is rapidly induction heated at 400℃ for 5 minutes. The sample is then placed in the extruder with the extrusion cylinder temperature at 400℃, the die temperature at 400℃, the extrusion ratio at 12, and the extrusion speed at 2mm / s. The sample is then immediately quenched in cold water after extrusion.

[0076] (4) Secondary extrusion: Before secondary extrusion, the sample is rapidly induction heated at 330℃ for 5 minutes. The sample is then placed in the extruder with the extrusion cylinder temperature at 330℃, the die temperature at 330℃, the extrusion ratio at 4, and the extrusion speed at 0.3 mm / s. The extruded sample is immediately quenched in cold water.

[0077] (5) Aging treatment: The secondary extruded bar is kept at 220℃ for 50h to obtain high-strength Mg-Gd binary alloy bar.

[0078] In summary, Examples 1-4, as shown in Table 1, the magnesium alloy bar in Example 1 exhibits a yield strength of 470 MPa, a tensile strength of 500 MPa, and a plasticity of 6.4% after aging. This is primarily due to the mixed-grain structure, where elongated grains provide strong texture reinforcement. After aging, the elongated grains also exhibit high-density nanoscale precipitates for reinforcement. The plasticity is mainly contributed by the fully recrystallized fine grains. The magnesium alloy bar in Example 2 also has a mixed-grain structure; however, this structure contains a high proportion of fully recrystallized grains, significantly lower than the elongated grain structure in Example 1. The lower Gd content in the alloy composition results in weaker age hardening, thus the alloy strength is not very high. In Examples 3 and 4, due to the high alloy content combined with an appropriate mixed-grain structure, a yield strength greater than 480 MPa and a tensile strength greater than 530 MPa were obtained after aging treatment. However, compared to Examples 1 and 2, the plasticity is somewhat reduced.

[0079] Table 1. Mechanical properties of high-strength Mg-Gd binary alloy rods prepared in Examples 1-4

[0080]

[0081]

[0082] It will be readily understood by those skilled in the art that the above-described advantageous methods can be freely combined and superimposed without conflict. The above are merely preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application. The above are merely preferred embodiments of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of this application, and these improvements and modifications should also be considered within the protection scope of this application.

Claims

1. A method for preparing high-strength Mg-Gd binary alloy rods, characterized in that: include: Alloy smelting: Preparation of Mg-Gd alloys; Solution treatment: The Mg-Gd alloy obtained by smelting is subjected to solution treatment; Preliminary extrusion: The solution-treated Mg-Gd alloy billet is extruded at 380-440℃, with an extrusion ratio of 6-12 and an extrusion speed of 0.2-2 mm / s to obtain a preliminary extruded bar; Secondary extrusion: The preliminary extruded bar is extruded at 300-340℃, with an extrusion ratio of 4-9 and an extrusion speed of 0.1-1 mm / s to obtain a secondary extruded bar; Aging treatment: The secondary extruded bar is aged to the peak aging state to obtain a high-strength Mg-Gd binary alloy bar; The high-strength Mg-Gd binary alloy bar has a Gd content of 13-22 wt.%, a Mg content of 87-78 wt.%, a diameter of 60-100 mm, a yield strength between 400-470 MPa, a tensile strength between 420-550 MPa, and a plasticity greater than 3%.

2. The method for preparing a high-strength Mg-Gd binary alloy rod according to claim 1, characterized in that: The alloy smelting process involves preparing Mg-Gd alloys with a diameter greater than 300 mm using a semi-continuous casting method.

3. The method for preparing a high-strength Mg-Gd binary alloy rod according to claim 1, characterized in that: The solution treatment is performed by holding the solution at 500-530℃ for 10-25 hours, followed by quenching with hot water at 80℃ or higher.

4. The method for preparing a high-strength Mg-Gd binary alloy rod according to claim 1, characterized in that: The preliminary extrusion also includes: rapidly induction heating the billet at 380-440℃ for no more than 5 minutes before extrusion.

5. The method for preparing a high-strength Mg-Gd binary alloy rod according to claim 1, characterized in that: The preliminary extrusion also includes: quenching with cold water to cool to room temperature after extrusion.

6. The method for preparing a high-strength Mg-Gd binary alloy rod according to claim 1, characterized in that: The secondary extrusion also includes: rapidly induction heating the initially extruded bar at 300-340°C for no more than 5 minutes before extrusion.

7. The method for preparing a high-strength Mg-Gd binary alloy rod according to claim 1, characterized in that: The secondary extrusion also includes: quenching with cold water to cool to room temperature after extrusion.

8. The method for preparing a high-strength Mg-Gd binary alloy rod according to claim 1, characterized in that: The aging treatment involves keeping the secondary extruded bar at 180-220℃ for at least 10 hours.

9. The method for preparing a high-strength Mg-Gd binary alloy rod according to claim 1, characterized in that: The high-strength Mg-Gd binary alloy rod has a Gd content of 15 wt.%, a Mg content of 85 wt.%, a yield strength of 470 MPa, a tensile strength of 500 MPa, and a plasticity of 6.4%.

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