Heat treatment method for reducing harmful second-phase particles of magnesium-rare earth alloy

Abstract

The invention discloses a heat treatment method for reducing harmful second-phase particles of a magnesium-rare earth alloy, which comprises the following steps: firstly, carrying out overaging treatment on the as-cast magnesium-rare earth alloy at a low-temperature section to promote a solute atom segregation region to form an equilibrium precipitated phase; then, the temperature is increased to a medium-temperature section for solid solution, the separated equilibrium phase is dissolved into the matrix, then the temperature is reduced to a low-temperature section for heat preservation, an equilibrium precipitated phase is formed, then the temperature is increased to a higher medium-temperature section temperature for solid solution, and the separated equilibrium phase is dissolved into the matrix; the steps are circulated and repeated until the non-equilibrium eutectic in the casting state is completely dissolved into the matrix; and finally, the temperature is increased to a high-temperature section for solid solution and quenching. By adopting the method, the formation of harmful second-phase particles in the solid solution process can be effectively inhibited, and the content of the harmful second-phase particles is reduced. The method has the advantages of being good in effect, simple, free of special requirements for equipment and the like, industrial production is easy to achieve, and a simple and effective way is provided for manufacturing of high-performance magnesium-rare earth alloy castings.

Description

Technical Field

[0001] This invention relates to a heat treatment method for reducing harmful second-phase particles in magnesium-rare earth alloys, belonging to the field of alloy preparation technology. Background Technology

[0002] Magnesium is one of the most abundant elements on Earth, with high content in surface metal resources. It possesses advantages such as high specific strength, high specific stiffness, good vibration damping, good magnetic shielding, excellent casting properties, low price, and easy recycling. However, pure magnesium has disadvantages such as low strength and poor heat resistance, making it difficult to apply directly in engineering.

[0003] Adding rare earth elements to magnesium can significantly improve the room temperature and high temperature strength, as well as the corrosion resistance of magnesium alloys, making them promising for applications in the aerospace field. However, magnesium-rare earth alloys are prone to forming a large number of harmful second-phase particles during heat treatment, which can become crack initiation sites (as shown in the attached image). Figure 1 As shown in the figure, this limits the improvement of the mechanical properties of this series of alloys.

[0004] Therefore, there is an urgent need to develop a new heat treatment process to effectively control the formation of such second-phase particles and expand the application of magnesium-rare earth alloys in the aerospace field. Summary of the Invention

[0005] In view of the above shortcomings, this invention provides a heat treatment method for reducing harmful second-phase particles in magnesium-rare earth alloys, with the aim of improving the mechanical properties of alloy castings. The heat treatment process of this invention is as follows: Figure 2 As shown:

[0006] To achieve the above-mentioned technical effects, the present invention is implemented through the following technical solution:

[0007] This invention first discloses a heat treatment method for reducing harmful second-phase particles in magnesium-rare earth alloys, comprising the following steps:

[0008] S1. Heat the alloy to a low-temperature range T1 and hold it for t1 hours to perform over-aging treatment, which promotes the formation of equilibrium precipitates in the solute atom segregation region.

[0009] S2. Heat the alloy to the medium temperature range T21 and hold for t21 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0010] S3. Cool the alloy to the low-temperature range T1 temperature and hold it at t1 hours for over-aging treatment to form equilibrium precipitates again.

[0011] S4. Heat the alloy to the medium temperature range T22 and hold for t22 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0012] S5. Cool the alloy to the low-temperature range T1 temperature and hold it for t1 hours to perform over-aging treatment, so as to form equilibrium precipitates again.

[0013] S6. Heat the alloy to the medium temperature range T23 and hold for t23 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0014] S7. Repeat steps S1 to S6 until the non-equilibrium eutectic in the as-cast state is completely dissolved into the matrix.

[0015] S8. Heat the alloy to the high-temperature zone T3 and hold for t3 hours before quenching.

[0016] As a preferred embodiment of the present invention, in the heat treatment scheme, the temperature range of the low temperature section is 200℃-400℃, the temperature range of the medium temperature section is 410℃-500℃, and the temperature range of the high temperature section is 501℃-560℃.

[0017] In a preferred embodiment of the present invention, in the heat treatment scheme, the heat treatment temperature of the later step in the medium-temperature heat treatment process is higher than that of the previous step, and all heat treatment temperatures in this stage show an increasing trend.

[0018] As a preferred embodiment of the present invention, in the heat treatment scheme, the holding time t1 of the low temperature section ranges from 2h to 72h, the holding time t2n (n=1, 2, 3...) of the medium temperature section ranges from 0.5h to 24h, and the holding time t3 of the high temperature section ranges from 0.5h to 24h.

[0019] In a preferred embodiment of the present invention, the heat treatment process is carried out under the protection of an inert gas.

[0020] In a preferred embodiment of the present invention, the quenching medium in the heat treatment scheme is water or hot water.

[0021] The heat treatment method described above has no requirements on the shape or size of the casting and can be used to process it.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] Magnesium-rare earth alloys typically employ high-temperature single-stage solid solution treatment to dissolve non-equilibrium eutectics into the matrix. However, this high-temperature single-stage solid solution treatment, while dissolving the non-equilibrium eutectics, also forms a large number of harmful second-phase particles, such as those shown in the attached image. Figure 1 The corresponding appendix in Example 1 Figure 3As shown. To reduce the formation of harmful second-phase particles, this invention first utilizes pre-precipitation to transform the solute atom agglomeration region into a readily soluble phase, thereby avoiding the formation of harmful second-phase particles from the solute atom agglomeration region through direct high-temperature solid solution. Then, the temperature is increased to the intermediate temperature range to dissolve the precipitated readily soluble phase into the matrix. This precipitation and dissolution process is repeated continuously, with the dissolution temperature constantly increasing, causing the non-equilibrium eutectic to be gradually eroded and dissolved into the matrix. Finally, the temperature is increased to the high-temperature range to homogenize the composition, and quenching creates sufficient vacancies, laying the foundation for subsequent processing. This method can effectively suppress the formation of harmful second-phase particles during the solid solution process of magnesium-rare earth alloys. Attached Figure Description

[0024] Figure 1 The images show SEM images of harmful second-phase particles and fracture surfaces from the literature.

[0025] Figure 2 This is a schematic diagram of the heat treatment process of the present invention.

[0026] Figure 3 This is a SEM image of sample 1 after solution treatment in Example 1 of the present invention.

[0027] Figure 4 This is a SEM image of sample 2 after solution treatment in Example 1 of the present invention. Detailed Implementation

[0028] The implementation of this invention is illustrated by the heat treatment process of Mg-9Gd-4Y-0.6Zr and Mg-5Y-4Nd-0.6Zr alloys, and the following examples are given.

[0029] Example 1

[0030] (1) Billet preparation

[0031] Two samples, each 10 mm (length) × 10 mm (width) × 5 mm (thickness), were cut from the Mg-9Gd-4Y-0.6Zr casting using wire cutting. These samples were labeled Sample 1 and Sample 2, respectively. Sample 1 served as a control sample and was processed using a conventional solution treatment process. Sample 2 was treated using the heat treatment process of this invention.

[0032] (2) Heat treatment

[0033] Sample 1: The alloy was solution-treated at 520℃ for 24h and then cooled with hot water at 80℃.

[0034] Sample 2: The alloy was heat-treated according to the following steps.

[0035] S1. Heat the alloy to 350℃ and hold for 36 hours to perform over-aging treatment, which promotes the formation of equilibrium precipitates in the solute atom segregation region;

[0036] S2. Heat the alloy to 410℃ and hold for 0.5 hours to dissolve it in the matrix, so that the precipitated equilibrium phase dissolves into the matrix.

[0037] S3. Cool the alloy to 350℃ and hold for 36 hours to perform over-aging treatment, and form equilibrium precipitates again.

[0038] S4. Heat the alloy to 430℃ and hold for 0.5 hours to dissolve it in the matrix, so that the precipitated equilibrium phase dissolves into the matrix.

[0039] S5. Cool the alloy to 350℃ and hold for 36 hours to perform over-aging treatment, and form equilibrium precipitates again.

[0040] S6. Heat the alloy to 450℃ and hold for 0.5 hours to dissolve it in the matrix, so that the precipitated equilibrium phase dissolves into the matrix.

[0041] S7. Cool the alloy to 350℃ and hold for 36 hours to perform over-aging treatment, and form equilibrium precipitates again.

[0042] S8. Heat the alloy to 480℃ and hold for 0.5 hours to dissolve it in the matrix, so that the precipitated equilibrium phase dissolves into the matrix.

[0043] S9. Cool the alloy to 350℃ and hold for 36 hours to perform over-aging treatment, and form equilibrium precipitates again.

[0044] S10. Heat the alloy to 500℃ and hold for 0.5 hours to dissolve it in the matrix, so that the precipitated equilibrium phase dissolves into the matrix.

[0045] S11. After heating the alloy to 520℃ and holding it for 24 hours, cool it with 80℃ hot water.

[0046] Both Sample 1 and Sample 2 were heat-treated using argon gas for protection.

[0047] (3) After sample preparation, the above samples 1 and 2 were observed by scanning electron microscopy, and the results are as follows: Figure 3 and Figure 4 As shown. From Figure 3 As can be seen, control sample 1, treated with conventional solution heat treatment, still contained a significant amount of micron-sized white, cube-shaped harmful second-phase particles after the treatment. Figure 4 As can be seen from the above, sample 2 adopted the solution heat treatment process of the present invention. After solution heat treatment, it is similar to... Figure 3 In comparison, the number and size of micron-sized white cube-shaped harmful second-phase particles were significantly reduced, effectively eliminating harmful second-phase particles. Figure 3 and Figure 4The micron-sized harmful second-phase particles in the sample were statistically analyzed, and the results are shown in Table 1. The results show that after heat treatment using the method of this invention, the average number of harmful second-phase particles per unit area decreased by 80%, the average particle size decreased by 38.5%, and the area fraction decreased by 92.2%, effectively suppressing the formation of harmful second-phase particles.

[0048] Table 1

[0049]

[0050] Example 2

[0051] (1) Billet preparation

[0052] Two samples, each 10 mm (length) × 10 mm (width) × 5 mm (thickness), were cut from the Mg-9Gd-4Y-0.6Zr casting using wire cutting. These samples were labeled Sample 1 and Sample 2, respectively. Sample 1 served as a control sample and was processed using a conventional solution treatment process. Sample 2 was treated using the heat treatment process of this invention.

[0053] (2) Heat treatment

[0054] Sample 1: The alloy was solution-treated at 520℃ for 24h and then cooled with hot water at 80℃.

[0055] Sample 2: The alloy was heat-treated according to the following steps.

[0056] S1. Heat the alloy to 200℃ and hold for 72 hours to perform over-aging treatment, which promotes the formation of equilibrium precipitates in the solute atom segregation region;

[0057] S2. Heat the alloy to 410℃ and hold for 24 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0058] S3. Cool the alloy to 200℃ and hold for 72 hours for over-aging treatment to form equilibrium precipitates again;

[0059] S4. Heat the alloy to 430℃ and hold for 24 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0060] S5. Cool the alloy to 200℃ and hold for 72 hours for over-aging treatment to form equilibrium precipitates again.

[0061] S6. Heat the alloy to 450℃ and hold for 24 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix;

[0062] S7. Cool the alloy to 200℃ and hold for 72 hours to perform over-aging treatment, and form equilibrium precipitates again.

[0063] S8. Heat the alloy to 480℃ and hold for 24 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0064] S9. Cool the alloy to 200℃ and hold for 72 hours to perform over-aging treatment, and form equilibrium precipitates again.

[0065] S10. Heat the alloy to 500℃ and hold for 24 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0066] S11. Heat the alloy to 520℃ and hold for 0.5 hours, then cool it with 80℃ hot water.

[0067] Both Sample 1 and Sample 2 were heat-treated using argon gas for protection.

[0068] (3) After sample preparation, the above samples were observed by scanning electron microscopy, and the micron-sized harmful second-phase particles in the samples were counted. The results are shown in Table 2. It can be seen from the results that after heat treatment using the method of the present invention, the average number of harmful second-phase particles per unit area was reduced by 82.5%, the average particle size was reduced by 42.5%, and the area fraction was reduced by 94.1%, which effectively inhibited the formation of harmful second-phase particles.

[0069] Table 2

[0070]

[0071] Example 3

[0072] (1) Billet preparation

[0073] Two samples, each 10 mm (length) × 10 mm (width) × 5 mm (thickness), were cut from the Mg-9Gd-4Y-0.6Zr casting using wire cutting. These samples were labeled Sample 1 and Sample 2, respectively. Sample 1 served as a control sample and was processed using a conventional solution treatment process. Sample 2 was treated using the heat treatment process of this invention.

[0074] (2) Heat treatment

[0075] Sample 1: The alloy was solution-treated at 520℃ for 24h and then cooled with hot water at 80℃.

[0076] Sample 2: The alloy was heat-treated according to the following steps.

[0077] S1. Heat the alloy to 400℃ and hold for 2 hours to perform over-aging treatment, which promotes the formation of equilibrium precipitates in the solute atom segregation region;

[0078] S2. Heat the alloy to 410℃ and hold for 24 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0079] S3. Cool the alloy to 400℃ and hold for 2 hours for over-aging treatment to form equilibrium precipitates again;

[0080] S4. Heat the alloy to 430℃ and hold for 24 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0081] S5. Cool the alloy to 400℃ and hold for 2 hours for over-aging treatment to form equilibrium precipitates again.

[0082] S6. Heat the alloy to 450℃ and hold for 24 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix;

[0083] S7. Cool the alloy to 400℃ and hold for 2 hours for over-aging treatment to form equilibrium precipitates again.

[0084] S8. Heat the alloy to 480℃ and hold for 24 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0085] S9. Cool the alloy to 400℃ and hold for 2 hours to perform over-aging treatment, and form equilibrium precipitates again.

[0086] S10. Heat the alloy to 500℃ and hold for 24 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0087] S11. Heat the alloy to 560℃ and hold for 0.5 hours, then cool it with 80℃ hot water.

[0088] Both Sample 1 and Sample 2 were heat-treated using argon gas for protection.

[0089] (3) After sample preparation, the above samples were observed by scanning electron microscopy, and the micron-sized harmful second-phase particles in the samples were counted. The results are shown in Table 3. It can be seen from the results that after heat treatment using the method of the present invention, the average number of harmful second-phase particles per unit area was reduced by 81.7%, the average particle size was reduced by 39.0%, and the area fraction was reduced by 93.1%, which effectively inhibited the formation of harmful second-phase particles.

[0090] Table 3

[0091]

[0092] Example 4

[0093] (1) Billet preparation

[0094] Two samples, each 10 mm (length) × 10 mm (width) × 5 mm (thickness), were cut from the Mg-9Gd-4Y-0.6Zr casting using wire cutting. These samples were labeled Sample 1 and Sample 2, respectively. Sample 1 served as a control sample and was processed using a conventional solution treatment process. Sample 2 was treated using the heat treatment process of this invention.

[0095] (2) Heat treatment

[0096] Sample 1: The alloy was solution-treated at 520℃ for 24h and then cooled with hot water at 80℃.

[0097] Sample 2: The alloy was heat-treated according to the following steps.

[0098] S1. Heat the alloy to 400℃ and hold for 36 hours to perform over-aging treatment, which promotes the formation of equilibrium precipitates in the solute atom segregation region.

[0099] S2. Heat the alloy to 410℃ and hold for 12 hours to dissolve it in the matrix.

[0100] S3. Cool the alloy to 400℃ and hold for 36 hours to perform over-aging treatment, and form equilibrium precipitates again.

[0101] S4. Heat the alloy to 430℃ and hold for 12 hours to dissolve it in the matrix.

[0102] S5. Cool the alloy to 400℃ and hold for 36 hours to perform over-aging treatment, and form equilibrium precipitates again.

[0103] S6. Heat the alloy to 450℃ and hold for 12 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0104] S7. Cool the alloy to 400℃ and hold for 36 hours to perform over-aging treatment, and form equilibrium precipitates again.

[0105] S8. Heat the alloy to 480℃ and hold for 12 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0106] S9. Cool the alloy to 400℃ and hold for 36 hours to perform over-aging treatment, and form equilibrium precipitates again.

[0107] S10. Heat the alloy to 500℃ and hold for 12 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0108] S11. Heat the alloy to 501℃ and hold for 12 hours, then cool it with 80℃ hot water.

[0109] Both Sample 1 and Sample 2 were heat-treated using argon gas for protection.

[0110] (3) After sample preparation, the above samples were observed by scanning electron microscopy, and the micron-sized harmful second-phase particles in the samples were counted. The results are shown in Table 4. It can be seen from the results that after heat treatment using the method of the present invention, the average number of harmful second-phase particles per unit area was reduced by 81.7%, the average particle size was reduced by 37.5%, and the area fraction was reduced by 93.1%, which effectively inhibited the formation of harmful second-phase particles.

[0111] Table 4

[0112]

[0113] Example 5

[0114] (1) Billet preparation

[0115] Two samples, each 10 mm (length) × 10 mm (width) × 5 mm (thickness), were cut from the Mg-9Gd-4Y-0.6Zr casting using wire cutting. These samples were labeled Sample 1 and Sample 2, respectively. Sample 1 served as a control sample and was processed using a conventional solution treatment process. Sample 2 was treated using the heat treatment process of this invention.

[0116] (2) Heat treatment

[0117] Sample 1: The alloy was solution-treated at 520℃ for 24h and then cooled with hot water at 80℃.

[0118] Sample 2: The alloy was heat-treated according to the following steps.

[0119] S1. Heat the alloy to 400℃ and hold for 72 hours to perform over-aging treatment, which promotes the formation of equilibrium precipitates in the solute atom segregation region;

[0120] S2. Heat the alloy to 410℃ and hold for 24 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0121] S3. Cool the alloy to 400℃ and hold for 72 hours for over-aging treatment to form equilibrium precipitates again.

[0122] S4. Heat the alloy to 430℃ and hold for 24 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0123] S5. Cool the alloy to 400℃ and hold for 72 hours for over-aging treatment to form equilibrium precipitates again.

[0124] S6. Heat the alloy to 450℃ and hold for 24 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix;

[0125] S7. Cool the alloy to 400℃ and hold for 72 hours to perform over-aging treatment, and form equilibrium precipitates again.

[0126] S8. Heat the alloy to 480℃ and hold for 24 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0127] S9. Cool the alloy to 400℃ and hold for 72 hours to perform over-aging treatment, and form equilibrium precipitates again.

[0128] S10. Heat the alloy to 500℃ and hold for 24 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0129] S11. After heating the alloy to 560℃ and holding it at that temperature for 24 hours, cool it with 80℃ hot water.

[0130] Both Sample 1 and Sample 2 were heat-treated using argon gas for protection.

[0131] (3) After sample preparation, the above samples were observed by scanning electron microscopy, and the micron-sized harmful second-phase particles in the samples were counted. The results are shown in Table 5. It can be seen from the results that after heat treatment using the method of the present invention, the average number of harmful second-phase particles per unit area was reduced by 84.2%, the average particle size was reduced by 37.0%, and the area fraction was reduced by 94.1%, which effectively inhibited the formation of harmful second-phase particles.

[0132] Table 5

[0133]

[0134] Example 6

[0135] (1) Billet preparation

[0136] Two samples, each 10 mm (length) × 10 mm (width) × 5 mm (thickness), were cut from the Mg-5Y-4Nd-0.6Zr casting using wire cutting. These samples were labeled Sample 1 and Sample 2, respectively. Sample 1 served as a control sample and was processed using a conventional solution treatment process. Sample 2 was treated using the heat treatment process of this invention.

[0137] (2) Heat treatment

[0138] Sample 1: The alloy was dissolved at 525℃ for 8 hours and then water-cooled.

[0139] Sample 2: The alloy was heat-treated according to the following steps.

[0140] S1. Heat the alloy to 200℃ and hold for 72 hours to perform over-aging treatment, which promotes the formation of equilibrium precipitates in the solute atom segregation region;

[0141] S2. Heat the alloy to 410℃ and hold for 0.5 hours to dissolve it in the matrix, so that the precipitated equilibrium phase dissolves into the matrix.

[0142] S3. Cool the alloy to 200℃ and hold for 72 hours for over-aging treatment to form equilibrium precipitates again;

[0143] S4. Heat the alloy to 430℃ and hold for 0.5 hours to dissolve it in the matrix, so that the precipitated equilibrium phase dissolves into the matrix.

[0144] S5. Cool the alloy to 200℃ and hold for 72 hours for over-aging treatment to form equilibrium precipitates again.

[0145] S6. Heat the alloy to 450℃ and hold for 0.5 hours to dissolve it in the matrix, so that the precipitated equilibrium phase dissolves into the matrix.

[0146] S7. Cool the alloy to 200℃ and hold for 72 hours to perform over-aging treatment, and form equilibrium precipitates again.

[0147] S8. Heat the alloy to 480℃ and hold for 0.5 hours to dissolve it in the matrix, so that the precipitated equilibrium phase dissolves into the matrix.

[0148] S9. Cool the alloy to 200℃ and hold for 72 hours to perform over-aging treatment, and form equilibrium precipitates again.

[0149] S10. Heat the alloy to 500℃ and hold for 0.5 hours to dissolve it in the matrix, so that the precipitated equilibrium phase dissolves into the matrix.

[0150] S11. Heat the alloy to 525℃ and hold for 8 hours, then cool it with water.

[0151] Both Sample 1 and Sample 2 were heat-treated using argon gas for protection.

[0152] (3) After sample preparation, the above samples were observed by scanning electron microscopy, and the micron-sized harmful second-phase particles in the samples were counted. The results are shown in Table 6. It can be seen from the results that after heat treatment using the method of the present invention, the average number of harmful second-phase particles per unit area was reduced by 81.3%, the average particle size was reduced by 42.9%, and the area fraction was reduced by 92.7%, which effectively inhibited the formation of harmful second-phase particles.

[0153] Table 6

[0154]

[0155] Example 7

[0156] (1) Billet preparation

[0157] Two samples, each 10 mm (length) × 10 mm (width) × 5 mm (thickness), were cut from the Mg-5Y-4Nd-0.6Zr casting using wire cutting. These samples were labeled Sample 1 and Sample 2, respectively. Sample 1 served as a control sample and was processed using a conventional solution treatment process. Sample 2 was treated using the heat treatment process of this invention.

[0158] (2) Heat treatment

[0159] Sample 1: The alloy was dissolved at 525℃ for 8 hours and then water-cooled.

[0160] Sample 2: The alloy was heat-treated according to the following steps.

[0161] S1. Heat the alloy to 200℃ and hold for 36 hours to perform over-aging treatment, which promotes the formation of equilibrium precipitates in the solute atom segregation region;

[0162] S2. Heat the alloy to 410℃ and hold for 24 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0163] S3. Cool the alloy to 200℃ and hold for 36 hours to perform over-aging treatment, and form equilibrium precipitates again.

[0164] S4. Heat the alloy to 430℃ and hold for 24 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0165] S5. Cool the alloy to 200℃ and hold for 36 hours to perform over-aging treatment, and form equilibrium precipitates again.

[0166] S6. Heat the alloy to 450℃ and hold for 24 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix;

[0167] S7. Cool the alloy to 200℃ and hold for 36 hours to perform over-aging treatment, and form equilibrium precipitates again.

[0168] S8. Heat the alloy to 480℃ and hold for 24 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0169] S9. Cool the alloy to 200℃ and hold for 36 hours to perform over-aging treatment, and form equilibrium precipitates again.

[0170] S10. Heat the alloy to 500℃ and hold for 24 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0171] S11. Heat the alloy to 520℃ and hold for 0.5 hours, then cool it with water.

[0172] Both Sample 1 and Sample 2 were heat-treated using argon gas for protection.

[0173] (3) After sample preparation, the above samples were observed by scanning electron microscopy, and the micron-sized harmful second-phase particles in the samples were counted. The results are shown in Table 7. It can be seen from the results that after heat treatment using the method of the present invention, the average number of harmful second-phase particles per unit area was reduced by 81.3%, the average particle size was reduced by 42.4%, and the area fraction was reduced by 91.5%, which effectively inhibited the formation of harmful second-phase particles.

[0174] Table 7

[0175]

[0176] Example 8

[0177] (1) Billet preparation

[0178] Two samples, each 10 mm (length) × 10 mm (width) × 5 mm (thickness), were cut from the Mg-5Y-4Nd-0.6Zr casting using wire cutting. These samples were labeled Sample 1 and Sample 2, respectively. Sample 1 served as a control sample and was processed using a conventional solution treatment process. Sample 2 was treated using the heat treatment process of this invention.

[0179] (2) Heat treatment

[0180] Sample 1: The alloy was dissolved at 525℃ for 8 hours and then water-cooled.

[0181] Sample 2: The alloy was heat-treated according to the following steps.

[0182] S1. Heat the alloy to 400℃ and hold for 2 hours to perform over-aging treatment, which promotes the formation of equilibrium precipitates in the solute atom segregation region;

[0183] S2. Heat the alloy to 410℃ and hold for 24 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0184] S3. Cool the alloy to 400℃ and hold for 2 hours for over-aging treatment to form equilibrium precipitates again;

[0185] S4. Heat the alloy to 430℃ and hold for 24 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0186] S5. Cool the alloy to 400℃ and hold for 2 hours for over-aging treatment to form equilibrium precipitates again.

[0187] S6. Heat the alloy to 450℃ and hold for 24 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix;

[0188] S7. Cool the alloy to 400℃ and hold for 2 hours for over-aging treatment to form equilibrium precipitates again.

[0189] S8. Heat the alloy to 480℃ and hold for 24 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0190] S9. Cool the alloy to 400℃ and hold for 2 hours to perform over-aging treatment, and form equilibrium precipitates again.

[0191] S10. Heat the alloy to 500℃ and hold for 24 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0192] S11. Heat the alloy to 560℃ and hold for 0.5 hours, then cool it with water.

[0193] Both Sample 1 and Sample 2 were heat-treated using argon gas for protection.

[0194] (3) After sample preparation, the above samples were observed by scanning electron microscopy, and the micron-sized harmful second-phase particles in the samples were counted. The results are shown in Table 8. It can be seen from the results that after heat treatment using the method of the present invention, the average number of harmful second-phase particles per unit area was reduced by 79.2%, the average particle size was reduced by 42.9%, and the area fraction was reduced by 91.5%, which effectively inhibited the formation of harmful second-phase particles.

[0195] Table 8

[0196]

[0197] Example 9

[0198] (1) Billet preparation

[0199] Two samples, each 10 mm (length) × 10 mm (width) × 5 mm (thickness), were cut from the Mg-5Y-4Nd-0.6Zr casting using wire cutting. These samples were labeled Sample 1 and Sample 2, respectively. Sample 1 served as a control sample and was processed using a conventional solution treatment process. Sample 2 was treated using the heat treatment process of this invention.

[0200] (2) Heat treatment

[0201] Sample 1: The alloy was dissolved at 525℃ for 8 hours and then water-cooled.

[0202] Sample 2: The alloy was heat-treated according to the following steps.

[0203] S1. Heat the alloy to 400℃ and hold for 36 hours to perform over-aging treatment, which promotes the formation of equilibrium precipitates in the solute atom segregation region.

[0204] S2. Heat the alloy to 410℃ and hold for 12 hours to dissolve it in the matrix.

[0205] S3. Cool the alloy to 400℃ and hold for 36 hours to perform over-aging treatment, and form equilibrium precipitates again.

[0206] S4. Heat the alloy to 430℃ and hold for 12 hours to dissolve it in the matrix.

[0207] S5. Cool the alloy to 400℃ and hold for 36 hours to perform over-aging treatment, and form equilibrium precipitates again.

[0208] S6. Heat the alloy to 450℃ and hold for 12 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0209] S7. Cool the alloy to 400℃ and hold for 36 hours to perform over-aging treatment, and form equilibrium precipitates again.

[0210] S8. Heat the alloy to 480℃ and hold for 12 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0211] S9. Cool the alloy to 400℃ and hold for 36 hours to perform over-aging treatment, and form equilibrium precipitates again.

[0212] S10. Heat the alloy to 500℃ and hold for 12 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0213] S11. Heat the alloy to 560℃ and hold for 12 hours, then cool it with water.

[0214] Both Sample 1 and Sample 2 were heat-treated using argon gas for protection.

[0215] (3) After sample preparation, the above samples were observed by scanning electron microscopy, and the micron-sized harmful second-phase particles in the samples were counted. The results are shown in Table 9. It can be seen from the results that after heat treatment using the method of the present invention, the average number of harmful second-phase particles per unit area was reduced by 84.4%, the average particle size was reduced by 41.9%, and the area fraction was reduced by 91.5%, which effectively inhibited the formation of harmful second-phase particles.

[0216] Table 9

[0217]

[0218] Example 10

[0219] (1) Billet preparation

[0220] Two samples, each 10 mm (length) × 10 mm (width) × 5 mm (thickness), were cut from the Mg-5Y-4Nd-0.6Zr casting using wire cutting. These samples were labeled Sample 1 and Sample 2, respectively. Sample 1 served as a control sample and was processed using a conventional solution treatment process. Sample 2 was treated using the heat treatment process of this invention.

[0221] (2) Heat treatment

[0222] Sample 1: The alloy was dissolved at 525℃ for 8 hours and then water-cooled.

[0223] Sample 2: The alloy was heat-treated according to the following steps.

[0224] S1. Heat the alloy to 400℃ and hold for 72 hours to perform over-aging treatment, which promotes the formation of equilibrium precipitates in the solute atom segregation region;

[0225] S2. Heat the alloy to 410℃ and hold for 24 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0226] S3. Cool the alloy to 400℃ and hold for 72 hours for over-aging treatment to form equilibrium precipitates again.

[0227] S4. Heat the alloy to 430℃ and hold for 24 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0228] S5. Cool the alloy to 400℃ and hold for 72 hours for over-aging treatment to form equilibrium precipitates again.

[0229] S6. Heat the alloy to 450℃ and hold for 24 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix;

[0230] S7. Cool the alloy to 400℃ and hold for 72 hours to perform over-aging treatment, and form equilibrium precipitates again.

[0231] S8. Heat the alloy to 480℃ and hold for 24 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0232] S9. Cool the alloy to 400℃ and hold for 72 hours to perform over-aging treatment, and form equilibrium precipitates again.

[0233] S10. Heat the alloy to 500℃ and hold for 24 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix.

[0234] S11. Heat the alloy to 560℃ and hold for 24 hours, then cool it with water.

[0235] Both Sample 1 and Sample 2 were heat-treated using argon gas for protection.

[0236] (3) After sample preparation, the above samples were observed by scanning electron microscopy, and the micron-sized harmful second-phase particles in the samples were counted. The results are shown in Table 10. It can be seen from the results that after heat treatment using the method of the present invention, the average number of harmful second-phase particles per unit area was reduced by 80.2%, the average particle size was reduced by 43.4%, and the area fraction was reduced by 93.9%, effectively inhibiting the formation of harmful second-phase particles.

[0237] Table 10

[0238]

[0239] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A heat treatment method for reducing harmful second-phase particles in magnesium-rare earth alloys, comprising the following steps: S1. Heat the alloy to a low-temperature range T1 and hold it for t1 hours to perform over-aging treatment, which promotes the formation of equilibrium precipitates in the solute atom segregation region. S2. Heat the alloy to the medium temperature range T21 and hold for t21 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix. S3. Cool the alloy to the low-temperature range T1 temperature and hold it at t1 hours for over-aging treatment to form equilibrium precipitates again. S4. Heat the alloy to the medium temperature range T22 and hold for t22 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix. S5. Cool the alloy to the low-temperature range T1 temperature and hold it at t1 hours for over-aging treatment to form equilibrium precipitates again. S6. Heat the alloy to the medium temperature range T23 and hold for t23 hours to perform solid solution treatment, so that the precipitated equilibrium phase dissolves into the matrix. S7. Repeat steps S1 to S6 until the non-equilibrium eutectic in the as-cast state is completely dissolved into the matrix; S8. Heat the S7 alloy to the high-temperature section T3 and hold for t3 hours before quenching.

2. The heat treatment method according to claim 1, wherein: The temperature of the low-temperature section T1 is 200℃-400℃; The temperature range of the intermediate temperature ranges T21, T22, and T23 is 410℃-500℃; The temperature range of the high-temperature section T3 is 501℃-560℃.

3. The heat treatment method according to claim 1, wherein: In the medium-temperature insulation process, the insulation temperature of the later step is higher than that of the previous step.

4. The heat treatment method according to claim 3, wherein: The temperature T22 is higher than the temperature T21, the temperature T23 is higher than the temperature T22, and so on, until the non-equilibrium eutectic in the as-cast state is completely dissolved into the matrix. During this stage, all the holding temperatures show an increasing trend.

5. The heat treatment method according to claim 1, wherein: The heat preservation time t1 of the low temperature section ranges from 2h to 72h; The heat preservation time t21, t22, and t23 in the medium temperature range are all 0.5h-24h. The heat preservation time t3 of the high-temperature section ranges from 0.5h to 24h.

6. The heat treatment method according to claim 1, wherein: The heat treatment process is carried out under inert gas protection.

7. The heat treatment method according to claim 1, wherein: The quenching medium is water or hot water.

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