Neutron shielding magnesium alloy plate and preparation method thereof

Abstract

The invention discloses a neutron shielding magnesium alloy plate and a preparation method thereof, and relates to the technical field of magnesium alloy materials, and the neutron shielding magnesium alloy plate comprises the following components in percentage by mass: 5-20% of Gd, and the balance of Mg and inevitable impurities. The preparation method comprises the following steps: S1, preparing the raw materials of each component, and performing pretreatment; s2, all the component raw materials pretreated in the step S1 are molten, and then a melt is subjected to deslagging, casting and cooling treatment to obtain an as-cast magnesium alloy cast ingot; s3, the as-cast magnesium alloy cast ingot prepared in the S2 is cut into a magnesium alloy plate, solution treatment is conducted, and then water cooling is conducted; s4, grinding the surface of the magnesium alloy plate subjected to solution treatment in S3, and rolling; and S5, the magnesium alloy plate rolled in the step S4 is subjected to aging treatment, and the neutron shielding magnesium alloy plate is obtained.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of magnesium alloy materials, in particular to a neutron shielding magnesium alloy plate and a preparation method thereof. BACKGROUND

[0002] Neutron shielding materials play a crucial role in nuclear reactors, nuclear medicine, nuclear fuel storage and transportation, etc. An ideal shielding material needs to have high neutron absorption capacity, excellent mechanical properties (to meet the requirements of structural components), outstanding radiation resistance and relatively low density to achieve lightweight design and application.

[0003] Gadolinium (Gd) is considered an extremely excellent neutron absorption element due to its highest thermal neutron absorption cross-section (up to 49000 barns) among all natural elements. Therefore, introducing Gd into various matrix materials to develop high-performance neutron shielding materials has become a research hotspot. Currently, Gd-containing shielding materials can be classified according to the base material as follows: metal-based composite shielding materials, glass-based composite shielding materials, ceramic-based composite shielding materials, and polymer-based composite shielding materials. However, these materials all have significant limitations: for example, the solubility of Gd in steel is extremely low, which easily forms brittle phases and concentrates at grain boundaries, severely deteriorating the plasticity and processability of the material; Gd in aluminum-based composite materials is mostly added in the form of ceramic particles (such as Gd2O3), which has poor interfacial bonding with the matrix, and it is difficult to balance high shielding efficiency and good mechanical properties; glass-based and ceramic-based composite materials have the advantages of uniform composition or high temperature resistance, but they generally have inherent disadvantages such as high brittleness, poor impact resistance, or difficulty in processing and molding; polymer-based composite materials face technical bottlenecks such as insufficient heat resistance, aging under irradiation, and easy aggregation of fillers.

[0004] Magnesium alloy is the lightest metal structural material with a density of only about 1.74 g / cm³, and has good specific strength and processing performance. The neutron absorption cross-section of magnesium itself is extremely low, and it is particularly noteworthy that Gd has a high solubility in the magnesium matrix (up to 23.5 wt.%), which provides a unique advantage for developing new Mg-Gd series neutron shielding alloys. This type of alloy not only inherits the lightweight and high specific strength characteristics of magnesium alloy, but also can significantly improve the mechanical properties through the solid solution and precipitation strengthening effect of Gd element. More importantly, the extremely high thermal neutron absorption cross-section of Gd greatly improves the macroscopic thermal neutron absorption cross-section of the material, showing excellent neutron shielding potential.

[0005] However, the Mg-Gd alloy prepared by the casting method still has several bottlenecks: first, the as-cast structure usually presents a coarse grain structure, and the high content of Gd element improves the neutron shielding performance, but is easy to segregate at the grain boundary to form a coarse continuous second phase (such as Mg5Gd), which is easy to become a crack source in the stress process, so that the magnesium alloy has a certain strength and plasticity, but both are at a low level, and it is difficult to be directly used as a structural part; second, although the Gd content is a key factor to determine the neutron shielding performance, the uneven distribution of Gd in the as-cast structure and the existence of the coarse second phase lead to the uneven absorption performance of neutrons in the micro area of the material.

[0006] Therefore, how to well coordinate the mechanical properties and neutron shielding performance of the Mg-Gd alloy is a problem to be solved. SUMMARY

[0007] In view of the deficiencies in the prior art, the purpose of the present application is to provide a neutron shielding magnesium alloy plate and a preparation method thereof, so as to solve the technical problem that the mechanical properties and neutron shielding performance of the Mg-Gd alloy in the prior art cannot be well considered.

[0008] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: A neutron shielding magnesium alloy plate, comprising Gd 5-20% by mass fraction, and the rest being Mg and unavoidable impurities.

[0009] The present application also provides a preparation method of a neutron shielding magnesium alloy plate, comprising the following steps: S1. Preparing each component raw material and performing pretreatment; S2. Melting each component raw material pretreated in S1, and then obtaining an as-cast magnesium alloy ingot after the molten metal is subjected to deslagging, casting and cooling treatment; S3. Cutting the as-cast magnesium alloy ingot prepared in S2 into a magnesium alloy plate, and performing solid solution treatment, and then performing water cooling; S4. Polishing the surface of the magnesium alloy plate after the solid solution treatment in S3 and then performing rolling; S5. Aging the magnesium alloy plate after the rolling in S4 to obtain a neutron shielding magnesium alloy plate.

[0010] Preferably, in step S1, the specific way of pretreatment is to cut each component raw material into small pieces, polish the surface, and then preheat to 200 DEG C.

[0011] Preferably, in step S2, the melting temperature is 720-730 DEG C, and a mixed gas of CO2 and SF6 with a volume ratio of 99:1 is used as a protective atmosphere during the melting process.

[0012] Preferably, in step S2, the melt is stirred for 2 minutes and left for 5-10 minutes before casting.

[0013] Preferably, in step S2, the casting mold is preheated to 350-400 DEG C before casting.

[0014] Preferably, in step S3, the thickness of the magnesium alloy plate is 4 mm, the solid solution temperature is 500 DEG C, and the solid solution time is 8 hours.

[0015] Preferably, in step S4, the rolling times are 10, the rolling temperature is 150 DEG C, the reduction per pass is 0.1 mm, and the thickness of the magnesium alloy plate after rolling is 3 mm.

[0016] Preferably, in step S5, the aging temperature is 225 DEG C, and the aging time is 120 hours.

[0017] Preferably, the Gd is added in the form of Mg-30wt.%Gd intermediate alloy, and the purity of the Mg-30wt.%Gd intermediate alloy and the Mg is greater than or equal to 99.9%.

[0018] Compared with the prior art, the present application has the following beneficial effects: 1. The present application significantly improves the macroscopic thermal neutron absorption cross section of the material by introducing the high neutron absorption cross section element Gd, mainly due to: ① the increase of effective absorption elements, which increases the macroscopic thermal neutron reaction cross section of the material. ② The neutron absorption efficiency of the material increases with the decrease of the average free path of the neutron. The refinement of the grain and the increase of the precipitated phase reduce the distance between the adjacent Gd-containing phases and tend to be more uniformly distributed, increasing the probability of collision between the neutron and Gd and reducing the average free path. After rolling and aging treatment, the synergistic effect of the grain size and grain orientation in the sample improves the shielding performance of the alloy, and the thermal neutron shielding coefficient of the alloy can be up to 22.74.

[0019] 2. The present application can effectively refine the grain and break the coarse second phase through the multi-pass rolling process. In the rolling process, the grain is first refined through dynamic recrystallization, high-density dislocations are formed, and hard-oriented basal texture is generated, which significantly improves the strength of the alloy. At the same time, the small-angle grain boundaries formed by the recovery of dislocations are also beneficial to the improvement of plasticity. Subsequent aging treatment induces high-density nano-precipitated phase at dislocation lines, etc., producing strong precipitation strengthening, further improving the yield strength, and making the alloy maintain high shielding performance while the strength is also significantly improved.

[0020] 3. The process of the present application has strong controllability. By adopting the composite process route of "casting + solid solution + rolling + aging", the process parameters are clear and have good repeatability, and the process is suitable for industrial production. DETAILED DESCRIPTION

[0021] In order to make the technical means, creative features, purposes and effects of the present application clearer and easier to understand, the present application is further described below in conjunction with specific embodiments. Example 1 S1. According to the mass fraction of 5% of Gd, pure magnesium and Mg-30wt.% Gd intermediate alloy are taken, each component raw material is cut into small pieces, and the surface thereof is polished and preheated to 200℃; S2. Each component raw material preheated in S1 is melted at 720℃, and a mixed gas of CO2 and SF6 with a volume ratio of 99:1 is used as a protective atmosphere, after melting, the melt is fully stirred for 2min, and after standing for 8min, the slag is removed, and then the melt is cast into a metal mold preheated to 400℃, and after cooling, a cast magnesium alloy ingot is obtained; S3. The cast magnesium alloy ingot prepared in S2 is cut into a magnesium alloy plate with a size of 150 mm × 150 mm × 4 mm, and then solution treated at 500℃ for 8h and water cooled to room temperature; S4. The surface of the magnesium alloy plate after solution treatment in S3 is polished, and then rolled at 150℃ for 10 passes to make the thickness of the magnesium alloy plate 3mm, and the reduction of each pass is 0.1mm.

[0022] S5. The magnesium alloy plate after rolling in S4 is aged at 225℃ for 120h, and then air cooled to room temperature to obtain a neutron shielding magnesium alloy plate.

[0023] Example 2 S1. According to the mass fraction of 10% of Gd, pure magnesium and Mg-30wt.% Gd intermediate alloy are taken, each component raw material is cut into small pieces, and the surface thereof is polished and preheated to 200℃; S2. Each component raw material preheated in S1 is melted at 725℃, and a mixed gas of CO2 and SF6 with a volume ratio of 99:1 is used as a protective atmosphere, after melting, the melt is fully stirred for 2min, and after standing for 5min, the slag is removed, and then the melt is cast into a metal mold preheated to 350℃, and after cooling, a cast magnesium alloy ingot is obtained; S3. The cast magnesium alloy ingot prepared in S2 is cut into a magnesium alloy plate with a size of 150 mm × 150 mm × 4 mm, and then solution treated at 500℃ for 8h and water cooled to room temperature; S4. The surface of the magnesium alloy plate after solution treatment in S3 is polished, and then rolled at 150℃ for 10 passes to make the thickness of the magnesium alloy plate 3mm, and the reduction of each pass is 0.1mm.

[0024] S5. The magnesium alloy plate after rolling in S4 is aged at 225℃ for 120h, and then air-cooled to room temperature to obtain the neutron shielding magnesium alloy plate.

[0025] Example 3 S1. According to the mass fraction of 15% of Gd, pure magnesium and Mg-30wt.%Gd intermediate alloy are taken, each component raw material is cut into small pieces, and the surface is polished and preheated to 200℃; S2. The preheated component raw material in S1 is melted at 720℃, and the mixed gas of CO2 and SF6 with a volume ratio of 99:1 is used as the protective atmosphere, after melting, the melt is fully stirred for 2min, and after standing for 8min, the slag is removed, and then the melt is cast into a metal mold preheated to 400℃, and after cooling, a cast magnesium alloy ingot is obtained; S3. The cast magnesium alloy ingot prepared in S2 is cut into a magnesium alloy plate with a size of 150 mm × 150 mm × 4 mm, and then solid-solution treated at 500℃ for 8h and water-cooled to room temperature; S4. The surface of the magnesium alloy plate after solid solution treatment in S3 is polished, and then rolled at 150℃ for 10 passes to make the thickness of the magnesium alloy plate 3mm, and the reduction of each pass is 0.1mm.

[0026] S5. The magnesium alloy plate after rolling in S4 is aged at 225℃ for 120h, and then air-cooled to room temperature to obtain the neutron shielding magnesium alloy plate.

[0027] Example 4 S1. According to the mass fraction of 15% of Gd, pure magnesium and Mg-30wt.%Gd intermediate alloy are taken, each component raw material is cut into small pieces, and the surface is polished and preheated to 200℃; S2. The preheated component raw material in S1 is melted at 730℃, and the mixed gas of CO2 and SF6 with a volume ratio of 99:1 is used as the protective atmosphere, after melting, the melt is fully stirred for 2min, and after standing for 8min, the slag is removed, and then the melt is cast into a metal mold preheated to 400℃, and after cooling, a cast magnesium alloy ingot is obtained; S3. The cast magnesium alloy ingot prepared in S2 is cut into a magnesium alloy plate with a size of 150 mm × 150 mm × 4 mm, and then solid-solution treated at 500℃ for 8h and water-cooled to room temperature; S4. The surface of the magnesium alloy plate after solid solution treatment in S3 is polished, and then rolled at 150℃ for 10 passes to make the thickness of the magnesium alloy plate 3mm, and the reduction of each pass is 0.1mm.

[0028] S5. The magnesium alloy sheet rolled by S4 is aged at 225℃ for 120h, and then air-cooled to room temperature to obtain a neutron-shielded magnesium alloy sheet.

[0029] Comparative Example 1 Compared to Example 3, Gd is not added, and steps S3-S5 are omitted, while the remaining steps are the same.

[0030] Comparative Example 2 Compared with Example 3, steps S4-S5 are omitted, while the remaining steps are the same.

[0031] Comparative Example 3 Compared with Example 3, step S4 is omitted, while the remaining steps are the same.

[0032] Neutron shielding tests were performed on the as-cast magnesium alloy ingots prepared in step S2 of Examples 1-4. 252 Cf moderated neutron energy spectrum (0.01eV-1eV) and tensile test results were used to obtain the shielding coefficient K, tensile strength, yield strength and elongation of each cast magnesium alloy ingot. The shielding coefficient K = I0 / I (I0 is the count without material, I is the count after the shielding material is placed). The larger the shielding coefficient, the better the shielding effect. The test results are shown in Table 1.

[0033] Table 1 Performance Tests of Cast Magnesium Alloy Ingots in Each Example As can be seen from Table 1, in the cast magnesium alloy ingots prepared in Examples 1-4, the change in Gd content has a significant impact on the shielding coefficient K, tensile strength, yield strength and elongation. Moreover, as the Gd content increases, the shielding coefficient K of the cast magnesium alloy ingot gradually increases, but the mechanical properties do not increase linearly. The cast magnesium alloy ingot in Example 3 can have both good shielding performance and mechanical properties.

[0034] Subsequently, the shielding coefficient K, tensile strength, yield strength, and elongation of the neutron-shielded magnesium alloy plates prepared in Example 3 and Comparative Examples 1-3 were tested in the manner described above. The test results are shown in Table 2.

[0035] Table 2 Performance tests of neutron-shielding magnesium alloy plates prepared in Example 3 and Comparative Examples 1-3 Compared with the shielding coefficient K, tensile strength, yield strength and elongation of the neutron shielding magnesium alloy plate prepared in Example 3 in Table 2, it can be seen that the as-cast magnesium alloy ingot is improved in shielding performance and mechanical properties after the treatment of "solid solution + rolling + aging", especially the mechanical properties are significantly improved.

[0036] As can be seen from Table 2, compared with Example 3, the shielding performance and mechanical properties of pure magnesium in Comparative Example 1 cannot meet the requirements of shielding materials; and as can be seen from Comparative Examples 2-3 compared with Example 3, the treatment of only "solid solution" or "solid solution + aging" has little effect on the shielding performance of the as-cast magnesium alloy ingot, and the increase in mechanical properties is also very limited, and does not reach the best state, thereby further proving that rolling effectively regulates the properties of the magnesium alloy.

[0037] Finally, it should be pointed out that the above examples are only used to illustrate the technical solutions of the present application and not to limit it, although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the purpose and scope of the present application, and they should be covered in the scope of the claims of the present application.

Claims

1. A neutron shielding magnesium alloy plate material, characterized by, comprising 5-20% by mass of Gd, the remainder being Mg and unavoidable impurities.

2. The method of claim 1, wherein the magnesium alloy plate is prepared by the steps of: preparing a magnesium alloy plate; and performing a neutron shielding treatment on the magnesium alloy plate. comprising the following steps: S1. Preparing component raw materials and pre-treating them; S2. Melting the component raw materials pre-treated in S1, and then subjecting the melt to slag removal, casting, and cooling to obtain an as-cast magnesium alloy ingot; S3. Cutting the as-cast magnesium alloy ingot prepared in S2 into magnesium alloy plates, and subjecting them to solid solution treatment, and then water cooling; S4. Polishing the surface of the magnesium alloy plates after the solid solution treatment in S3, and then rolling them; S5. Subjecting the magnesium alloy plates after the rolling in S4 to aging treatment to obtain neutron shielding magnesium alloy plates.

3. The method of claim 2, wherein the magnesium alloy plate is prepared by the steps of: preparing a magnesium alloy plate; and performing a surface treatment on the magnesium alloy plate. In step S1, the pre-treatment is performed by cutting the component raw materials into small pieces, polishing their surfaces, and then preheating them to 200°C.

4. The method of claim 2, wherein the magnesium alloy plate is prepared by the steps of: preparing a magnesium alloy plate; and performing a surface treatment on the magnesium alloy plate. In step S2, the melting temperature is 720-730°C, and a mixed gas of CO2 and SF6 in a volume ratio of 99:1 is used as the protective atmosphere during the melting process.

5. The method of claim 2, wherein the magnesium alloy plate is prepared by the steps of: preparing a magnesium alloy plate; and performing a surface treatment on the magnesium alloy plate. In step S2, the melt is stirred for 2 min and then left to stand for 5-10 min before casting.

6. The method of claim 2, wherein the magnesium alloy plate is prepared by the steps of: preparing a magnesium alloy plate; and performing a surface treatment on the magnesium alloy plate. In step S2, the casting mold is preheated to 350-400°C before casting.

7. The method of claim 2, wherein the magnesium alloy plate is prepared by the steps of: preparing a magnesium alloy plate; and performing a surface treatment on the magnesium alloy plate. In step S3, the thickness of the magnesium alloy plates is 4 mm, the solid solution temperature is 500°C, and the solid solution time is 8 h.

8. The method of claim 2, wherein the magnesium alloy plate is prepared by the steps of: preparing a magnesium alloy plate; and performing a surface treatment on the magnesium alloy plate. In step S4, the rolling is performed for 10 passes, the rolling temperature is 150°C, the reduction per pass is 0.1 mm, and the thickness of the magnesium alloy plates after rolling is 3 mm.

9. The method of claim 2, wherein the magnesium alloy plate is prepared by the steps of: preparing a magnesium alloy plate; and performing a surface treatment on the magnesium alloy plate. In step S5, the aging temperature is 225°C, and the aging time is 120 h.

10. The method of claim 2, wherein the magnesium alloy plate is prepared by the steps of: preparing a magnesium alloy plate; and performing a surface treatment on the magnesium alloy plate. The Gd is added in the form of Mg-30wt.%Gd master alloy, and the purity of both the Mg-30wt.%Gd master alloy and the Mg is ≥99.9%.

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