Process for improving the properties of magnesium-zinc magnesium alloys

Abstract

The application provides a process method for improving the performance of Mg-Zn magnesium alloy, and belongs to the technical field of non-ferrous metal material production. The magnesium alloy is suitable for having the following components: 3-6wt% of Zn, 0.008-1wt% of one or more of Zr, Sr, Ca and Cu, and the balance of Mg and inevitable impurities; and comprises the following steps: preparation of a magnesium alloy ingot; the magnesium alloy ingot is heated to 360-370 DEG C at a speed of 480-570 DEG C / h under inert protective gas or vacuum condition, and is kept for 6-7 hours; and low-temperature quenching is carried out immediately after the magnesium alloy ingot is taken out. According to the application, the MgZn second phase of the molten and cast magnesium alloy is solid-solved into the matrix through low-temperature solid-solution treatment, solid-solution strengthening is obtained, and the grains are refined and the alloy elements are homogenized. Then, rapid cooling is carried out, the state is kept, and the mechanical, forming and corrosion resistance performance of the magnesium alloy is significantly improved. The method has simple process flow, clear key process parameters, high repeatability, and can obviously improve the efficiency and save the cost.

Description

Technical Field

[0001] This invention belongs to the field of non-ferrous metal material production technology, specifically relating to a process method for improving the performance of Mg-Zn magnesium alloys. Background Technology

[0002] Magnesium alloys possess characteristics such as low density, high specific strength and specific stiffness, low elastic modulus, good heat dissipation, strong electromagnetic shielding, and good biocompatibility. They have wide applications in aerospace, transportation, medical devices, and 3C products. Currently, the most widely used are Mg-Zn based magnesium alloys with zinc as the main alloying element and other elements added. During equilibrium solidification, at a eutectic temperature of approximately 340℃, the maximum solid solubility of zinc in magnesium is 6.2 wt%. However, in actual solidification after smelting, even magnesium-zinc alloys with a zinc content of approximately 2 wt% will exhibit zinc segregation, forming zinc-containing non-equilibrium intermetallic compounds. Commercially available Mg-Zn based magnesium alloys typically contain high zinc content and a large amount of Mg-Zn compounds. While this increases strength, it also reduces plastic deformation capacity and makes them prone to cracking. Simultaneously, this zinc-containing second phase easily undergoes galvanic corrosion with the magnesium matrix, leading to localized corrosion and significantly accelerating the corrosion failure of magnesium alloys.

[0003] To address the above situation, a common method is to perform solution treatment followed by aging on Mg-Zn magnesium alloys. The typical solution treatment process for ZK61A magnesium alloy is 480℃~490℃ for 10 hours. Existing patented technologies also involve solution treatment of Mg-Zn magnesium alloys at lower temperatures (380~440℃), but the time is relatively long, ranging from 12 to 24 hours. There are also methods for solution treatment of Mg-Zn magnesium alloys at 335℃ and below, but Mg… 51 Zn 20 The phase melting point is 341℃, and solid solution cannot be obtained at this process temperature. These process methods suffer from problems such as excessively high temperatures, excessively long processing times, or excessively low temperatures resulting in poor solid solution effects, all of which fail to effectively regulate microstructure and properties. Furthermore, detailed operational procedures for controlling microstructure stability are not provided, and most require aging, two-stage solid solution treatment, or pretreatment to achieve improved performance. Therefore, improvements are proposed to address these issues. Summary of the Invention

[0004] The technical problem solved by this invention is to provide a process method for improving the properties of Mg-Zn magnesium alloys. The purpose of this invention is to improve the plastic forming performance of Mg-Zn magnesium alloys, reduce local corrosion, and overcome the problems of complex process flow for regulating the microstructure and properties of magnesium alloys in the prior art, and poor microstructure and property effects of single heat treatment on magnesium alloys with large grains and low strength and plasticity.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A process for improving the properties of Mg-Zn magnesium alloys, applicable to magnesium alloys with the following compositional characteristics: 3-6 wt% Zn, 0.008-1 wt% Zr, Sr, Ca, Cu or one or more of these, with the balance being Mg and unavoidable impurities; specifically including the following steps:

[0007] Step 1) Preparation of ingots of magnesium alloy materials with the above composition;

[0008] Step 2) Low-temperature solution treatment: The magnesium alloy ingot is heated to 360-370℃ at a rate of 480-570℃ / h under inert protective gas or vacuum conditions, and held for 6-7 hours.

[0009] Step 3) After being taken out of the furnace, the furnace is immediately subjected to low-temperature quenching, which is carried out in water at a temperature below 5°C.

[0010] In step 2) above, during the low-temperature solution treatment, the inert protective gas is argon, and the vacuum degree of the vacuum condition is <10. -1 Pa.

[0011] In step 1) above, during the preparation of the ingot, pure magnesium ingot blocks are melted in a melting furnace under vacuum, and pure zinc particles and Mg-Zr or Mg-Sr or Mg-Ca or Mg-Cu master alloys are added in sequence. After being fully melted and stirred, the ingots are filtered through multiple stages and then cast into a mold to solidify into magnesium alloy ingots.

[0012] Preferably, the performance improvement effect is better when the Zn content in the magnesium alloy is 5-6 wt%.

[0013] Compared with the prior art, the present invention has the following advantages:

[0014] 1. This solution has a simple processing flow and can improve the mechanical properties, plastic formability and corrosion uniformity of Mg-Zn magnesium alloys without the need for aging or other pretreatment. Compared with existing technologies, it greatly simplifies the process steps and can significantly improve efficiency and save costs.

[0015] 2. This method involves low-temperature solution treatment of cast Mg-Zn magnesium alloys to dissolve the MgZn second phase into the matrix, thereby achieving solid solution strengthening, refining the grains, and homogenizing the alloying elements. Then, rapid cooling is performed to maintain this state of solid solution MgZn phase, refined grains, and uniform element distribution, thus significantly improving the forming and corrosion uniformity of Mg-Zn magnesium alloys.

[0016] 3. This scheme provides detailed and comprehensive operating procedures for the low-temperature solution treatment process, specifying all factors that may affect the properties of magnesium alloys, and ensuring high repeatability. These include: strictly controlling the alloy's time after heating to the required solution temperature at a stable rate; using a narrow solution temperature range and holding time range to minimize grain growth; and using water quenching below 5°C to ensure quenching cooling rate and hardenability unaffected by ambient temperature, thereby maximizing the solution of the second phase.

[0017] 4. After low-temperature solution treatment according to this scheme, the mechanical properties, formability, and corrosion uniformity of Mg-Zn magnesium alloys are significantly improved: the grain size can be refined to 1-30 μm; the tensile strength can be increased by 11.8%-19.2%, the yield strength ratio can be reduced by 3.6%-14.6%, and the elongation after fracture can be increased by 17.5%-135.6%; it can be extruded into bright bar stock at a high speed of 25 m / min; after 30 days of immersion in Hank's simulated body fluid, there is no obvious local corrosion and the corrosion rate is significantly reduced.

[0018] 5. Compared with existing technologies, the Mg-Zn magnesium alloys obtained after treatment by this method have significantly finer grains and higher strength and plasticity; in particular, the ZK60 magnesium alloy has a significantly lower corrosion rate than that of the existing technology. Attached Figure Description

[0019] Figure 1 The images shown are metallographic microstructures of ZK60 magnesium alloy in the embodiments of the present invention, wherein (a) is in the as-cast state; (b) is Example 1; (c) is Comparative Example 1; (d) is Comparative Example 2; (e) is Comparative Example 3; (f) is Comparative Example 4; and (g) is Comparative Example 5.

[0020] Figure 2 The images shown are metallographic microstructures of ZK60 magnesium alloy in the embodiments of the present invention, wherein (a) is Comparative Example 6; (b) is Example 1; (c) is Comparative Example 7; and (d) is Comparative Example 8.

[0021] Figure 3 The images show the metallographic microstructure of ZS50 magnesium alloy in the embodiments of the present invention, where (a) is in the as-cast state and (b) is from Example 2.

[0022] Figure 4 The images show the metallographic microstructure of ZS61 magnesium alloy in the embodiments of the present invention, where (a) is in the as-cast state; and (b) is from Example 3.

[0023] Figure 5 The images show scanning electron microscope (SEM) microstructures of ZK60 magnesium alloy in the embodiments of the present invention, where (a) is in the as-cast state and (b) is from Example 1.

[0024] Figure 6The image shows a macroscopic view of the extruded bars of ZK60 magnesium alloy in the embodiments of the present invention, wherein (a) is directly extruded from the cast state; and (b) is extruded after being treated in Example 1.

[0025] Figure 7 The image shows a macroscopic view of the extruded bars of ZS50 magnesium alloy in the embodiments of the present invention, wherein (a) is directly extruded in the cast state; and (b) is extruded after being treated in Example 2.

[0026] Figure 8 The image shows a macroscopic view of the extruded bars of ZS61 magnesium alloy in the embodiments of the present invention, wherein (a) is directly extruded in the cast state; and (b) is extruded after being treated in Example 3.

[0027] Figure 9 The images show the morphology of the ZK60 magnesium alloy cylindrical sample after one month of corrosion in Hank's solution in this embodiment of the invention, where (a) is direct corrosion in the as-cast state; and (b) is corrosion after treatment in Example 1. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0029] It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as are familiar to those skilled in the art. The reagents or raw materials used in this invention are readily available through conventional means, and unless otherwise specified, they are used in accordance with conventional methods in the art or as per the product instructions.

[0030] A process for improving the properties of Mg-Zn magnesium alloys, applicable to magnesium alloys with the following compositional characteristics: 3-6 wt% Zn, 0.008-1 wt% Zr, Sr, Ca, Cu or one or more of these, with the balance being Mg and unavoidable impurities; specifically including the following steps:

[0031] Step 1) Preparation of ingots of magnesium alloy materials with the above composition;

[0032] The ingot is prepared in a vacuum environment (vacuum degree < 10). -2Pa) Pure magnesium ingots are melted in a smelting furnace at a temperature of 680-720°C. Pure zinc particles and Mg-Zr or Mg-Sr or Mg-Ca or Mg-Cu master alloys are added in sequence. After being fully melted and stirred, the mixture is filtered through multiple stages and then cast into a mold to solidify into a magnesium alloy ingot.

[0033] Step 2) Low-temperature solution treatment: The magnesium alloy ingot is heated to 360-370℃ at a rate of 480-570℃ / h under inert protective gas or vacuum conditions, and held for 6-7 hours.

[0034] During low-temperature solution treatment, the inert protective gas is argon, and the vacuum level of the vacuum condition is <10. -1 Pa.

[0035] Step 3) After being taken out of the furnace, the furnace is immediately subjected to low-temperature quenching, which is carried out in water at a temperature below 5°C.

[0036] Preferably, the performance improvement effect is better when the Zn content in the magnesium alloy is 5-6 wt%.

[0037] ZK60 magnesium alloy is a Mg-Zn-Zr series wrought magnesium alloy. As one of the commercially available wrought magnesium alloys with the highest strength and specific strength, it has broad application prospects and market benefits.

[0038] Example 1

[0039] Step 1) Melt and cast ZK60 magnesium alloy with the composition shown in Table 1 below under vacuum conditions.

[0040] element Zn Zr Mg and unavoidable impurities Mass percentage (wt%) 5.3 0.62 margin

[0041] Step 2) Heating: Heat the ZK60 magnesium alloy ingot under a vacuum degree <10 -1 Under the condition of Pa, the temperature is increased to 360℃ at a rate of 540℃ / h and held for 6 hours.

[0042] Step 3) Quenching: The ZK60 magnesium alloy ingot is quenched in water at a temperature below 5°C immediately after it comes out of the furnace.

[0043] After the above steps are completed, a ZK60 magnesium alloy after low-temperature solution treatment is obtained, and its metallographic microstructure is as follows: Figure 1 As shown in b and 2b, the mechanical property test results are shown in Table 6.

[0044] Comparative Example 1

[0045] The ZK60 magnesium alloy used was the same as in Example 1, with a solution treatment temperature of 360℃ and a holding time of 6 hours. The difference between this comparative example and Example 1 is that the heating rate was 900℃ / h, and water quenching was performed at room temperature. Its metallographic microstructure is as follows: Figure 1 As shown in c, the mechanical property test results are shown in Table 6.

[0046] Comparative Example 2

[0047] The ZK60 magnesium alloy used was the same as that in Example 1. The difference between this comparative example and Example 1 is that the solution treatment temperature was 480℃ and the holding time was 10 hours. Its metallographic microstructure is as follows: Figure 1 As shown in d, the mechanical property test results are shown in Table 6.

[0048] Comparative Example 3

[0049] The ZK60 magnesium alloy used was the same as that in Example 1. The difference between this comparative example and Comparative Example 2 is that the heating rate was 1152℃ / h, and water quenching was performed at room temperature. Its metallographic microstructure is as follows: Figure 1 As shown in Figure e, the mechanical property test results are shown in Table 6.

[0050] Comparative Example 4

[0051] The ZK60 magnesium alloy used was the same as that in Example 1. The difference between this comparative example and Example 1 is that the solution treatment temperature was 380℃ and the holding time was 12 hours. Its metallographic microstructure is as follows: Figure 1 As shown in f, the mechanical property test results are shown in Table 6.

[0052] Comparative Example 5

[0053] The ZK60 magnesium alloy used was the same as that in Example 1. The difference between this comparative example and Comparative Example 4 is that the heating rate was 960℃ / h, and water quenching was performed at room temperature. Its metallographic microstructure is as follows: Figure 1 As shown in g, the mechanical property test results are shown in Table 6.

[0054] Comparative Example 6

[0055] The ZK60 magnesium alloy used is the same as that in Example 1. The difference between this comparative example and Example 1 is that the holding time is 2 hours. Its metallographic microstructure is as follows: Figure 2 As shown in Figure a, the mechanical property test results are shown in Table 6.

[0056] Comparative Example 7

[0057] The ZK60 magnesium alloy used is the same as that in Example 1. The difference between this comparative example and Example 1 is that the holding time is 10 hours. Its metallographic microstructure is as follows: Figure 2 As shown in c, the mechanical property test results are shown in Table 6.

[0058] Comparative Example 8

[0059] The ZK60 magnesium alloy used is the same as that in Example 1. The difference between this comparative example and Example 1 is that the holding time is 14 hours. Its metallographic microstructure is as follows: Figure 2 As shown in d, the mechanical property test results are shown in Table 6.

[0060] Comparative Example 9

[0061] The ZK60 magnesium alloy used was the same as that in Example 1. The difference between this comparative example and Example 1 is that the heating rate was 570℃ / h, the solution temperature was 460℃, and the holding time was 2h. The mechanical property test results are shown in Table 6.

[0062] Comparative Example 10

[0063] The ZK60 magnesium alloy used was the same as that in Example 1. The difference between this comparative example and Example 1 is that the heating rate was 570℃ / h, the solution temperature was 460℃, and the holding time was 6h. The mechanical property test results are shown in Table 6.

[0064] Comparative Example 11

[0065] (Chang Feng, et al., “Study on Solution Treatment Process of ZK60 Magnesium Alloy”, Hot Working Technology, 2018, ISSN: 1001-3814) The ZK60 magnesium alloy reported by the authors, by mass percentage: Zn: 4.8-6.2%, Zr: >0.45%, impurities <0.30%, balance Mg, was subjected to conventional solution treatment on the as-cast ZK60 magnesium alloy. The effects of different solution treatment temperatures and times on the mechanical properties of the alloy were studied. The results are shown in Table 2 below.

[0066] Solution treatment Tensile strength / MPa Yield strength / MPa Elongation after fracture / % 380℃×3h 254.9 135.5 6.9 500℃×3h 275.3 150.2 7.7 520℃×3h 234.1 130.0 6.1 As-cast 241.1 127.1 5.4

[0067] Comparative Example 12

[0068] (Caixia Li et al, “The effect of solution heat treatments on the microstructure and hardness of ZK60 magnesium alloys prepared under low-frequency alternating magnetic fields”, Materials Science & Engineering A, 2013, ISSN: 0921-5093) reported that the ZK60 magnesium alloy, by mass percentage, consisted of Zn: 6.85%, Zr: 0.52%, with the balance being Mg. The authors subjected the as-cast ZK60 magnesium alloy to conventional solution heat treatment at 380℃ for 4h, 8h, 12h, and 16h under argon protection. The obtained ZK60 magnesium alloy had an average grain size of 40–20 μm, a tensile strength of 221–268 MPa, a yield strength of 103–159 MPa, and an elongation after fracture of 5.1–11.6%.

[0069] Comparative Example 13

[0070] (HYChoi et al, “Effect of thermal treatment on the bio-corrosion and mechanical properties of ultrafine-grained ZK60 magnesium alloy”, Journal of the Mechanical Behavior of Biomedical Materials, 2015, ISSN: 1751-6161) reported that the ZK60 magnesium alloy, by mass percentage, was: Zn: 5.25%, Zr: 0.53%, Mn: 0.019%, Ca: 0.006%, Si: 0.009%, Fe < 0.0002%, Ni: 0.00037%, Cu: 0.0009%, with the balance being Mg. The authors subjected a 2 mm thick and 100 mm wide extruded ZK60 magnesium alloy to solution treatment at 350 °C for 17 h, followed by water quenching. The average grain size of the obtained ZK60 magnesium alloy was 8.5 μm. After solution treatment, the magnesium alloy extruded sheet was subjected to two passes of high-ratio differential rolling and annealed at 250°C for 0–24 h. It was then immersed in Hank's solution for one day, and the weight loss was measured to be 52–56 μg·cm³. -2 ·h-1 .

[0071] Comparative Example 14

[0072] (Li Qingfen, et al., "Influence of Solution Treatment on the Biocorrosion Properties of ZK60 Magnesium Alloy", Special Casting & Nonferrous Alloys, 2018, ISSN: 1001-2249) reported that the ZK60 magnesium alloy, by mass percentage, consisted of: Zn: 5-6%, Zr: 0.3-0.9%, Mn: 0.10%, Al < 0.05%, Cu < 0.05%, Ni < 0.005%, Si < 0.05%, Fe < 0.05%, with the balance being Mg. The authors performed solution treatment (T4) on the as-cast ZK60 magnesium alloy at temperatures of 230, 280, and 330℃, holding for 24 h, followed by water quenching at room temperature. After solution treatment at 330℃ for 24 h, the second phase of the ZK60 magnesium alloy was almost completely dissolved in the matrix, but the grain size did not change significantly (approximately 80 μm). After immersion in SBF simulated body fluid for 96 hours, the corrosion rates of ZK60 magnesium alloys in the as-cast state and those treated with solution at 230, 280, and 330 °C were 4.038, 3.623, 2.806, and 2.573 mm / a, respectively.

[0073] The processes for Example 1 and each comparative example are shown in Table 3 below.

[0074] example Solution temperature Solution time heating rate Quenching conditions Example 1 360℃ 6h 540℃ / h <5℃ water Comparative Example 1 360℃ 6h 900℃ / h room temperature water Comparative Example 2 480℃ 10h 540℃ / h <5℃ water Comparative Example 3 480℃ 10h 1152℃ / h room temperature water Comparative Example 4 380℃ 12h 540℃ / h <5℃ water Comparative Example 5 380℃ 12h 960℃ / h room temperature water Comparative Example 6 360℃ 2h 540℃ / h <5℃ water Comparative Example 7 360℃ 10h 540℃ / h <5℃ water Comparative Example 8 360℃ 14h 540℃ / h <5℃ water Comparative Example 9 460℃ 2h 570℃ / h <5℃ water Comparative Example 10 460℃ 6h 570℃ / h <5℃ water Comparative Example 11 380、500、520℃ 3h conventional Regular / room temperature water Comparative Example 12 380℃ 4、8、12、16h conventional Regular / room temperature water Comparative Example 13 350℃ 17h conventional Regular / room temperature water Comparative Example 14 230、280、330℃ 24h conventional Regular / room temperature water

[0075] Example 2

[0076] Step 1) Melt and cast ZS50 magnesium alloy with the composition shown in Table 4 below under vacuum conditions.

[0077] element Zn Sr Mg and unavoidable impurities Mass percentage (wt%) 5.16 0.03 margin

[0078] Step 2) Heating: Heat the ZS50 magnesium alloy ingot under a vacuum degree <10 -1 Under the condition of Pa, the temperature is increased to 360℃ at a rate of 480℃ / h and held for 6.5 hours.

[0079] Step 3) Quenching: The ZS50 magnesium alloy ingot is quenched in water at a temperature below 5°C immediately after it comes out of the furnace.

[0080] After the above steps are completed, a ZS50 magnesium alloy after low-temperature solution treatment is obtained, and its metallographic microstructure is as follows: Figure 3 As shown in b, the mechanical property test results are shown in Table 6.

[0081] Example 3

[0082] Step 1) Melt and cast ZS61 magnesium alloy with the composition shown in Table 5 below under vacuum conditions.

[0083] element Zn Sr Mg and unavoidable impurities Mass percentage (wt%) 5.86 0.65 margin

[0084] Step 2) Heating: The ZS61 magnesium alloy ingot is heated to 370℃ at a rate of 570℃ / h under an argon protective atmosphere and held for 7 hours.

[0085] Step 3) Quenching: The ZS61 magnesium alloy ingot is quenched in water at a temperature below 5°C immediately after it comes out of the furnace.

[0086] After the above steps are completed, a ZS61 magnesium alloy after low-temperature solution treatment is obtained, and its metallographic microstructure is as follows: Figure 4 As shown in b, the mechanical property test results are shown in Table 6.

[0087] Example 4: Performance Testing

[0088] 1. Microscopic tissue analysis, results as follows: Figures 1 to 5 As shown.

[0089] Figure 1 a, Figure 1 b shows the metallographic structures of ZK60 magnesium alloy in the as-cast state and in Example 1, respectively. In the as-cast ZK60 magnesium alloy, the black secondary phase appears as elongated strips distributed along the grain boundaries. After treatment in Example 1, the grain size is significantly reduced from 70–100 μm to 1–15 μm, and most of the grayish-black secondary phase distributed along the grain boundaries is dissolved into the magnesium matrix. Figure 5 It can be more clearly seen that after treatment in Example 1, the bright white second phase is mostly dissolved into the magnesium matrix, changing from a network distribution to a scattered distribution. In Comparative Example 1, only a very small number of small grains with a size of about 10 μm appear, and the vast majority of grains have a size of 20-50 μm. Comparative Example 3, which was quenched at room temperature... Figure 1 e) and Comparative Example 5 Figure 1 The grain size of the g) is not much different from that of the as-cast state, except that the vast majority of the second phase has dissolved into the magnesium matrix. In contrast, the comparative example 2 (quenched in water below 5°C) Figure 1 d) and Comparative Example 4 ( Figure 1 f) Compared to Comparative Examples 3 and 5, the grain size is reduced, especially in Comparative Example 4 where the grain size is significantly reduced, but the grain boundaries are unclear and the state is unstable. Compared to all comparative examples, Example 1 ( Figure 1 a) has the smallest, most uniform grain size and clearest grain boundaries. It is comparable to the grain size of ZK60 magnesium alloy after extrusion and solution treatment in Comparative Example 13.

[0090] from Figure 2 As can be seen from the comparison example 6 (2h solid solution) Figure 2 a) The presence of small grain chains at the grain boundaries of large grains indicates that the grain structure is unstable. Example 1 ( Figure 2b) has a relatively uniform grain size, no small grain chains, and the larger grain size is the same as that of Comparative Example 6. Comparative Example 7 ( ) was dissolved for 10 hours. Figure 2 c) The grain size was significantly larger than that of the example, and the comparative example 7 (which underwent solid solution treatment for 10 hours) showed a significantly larger grain size compared to the example. Figure 2 c) The grain size was significantly larger than that of Comparative Example 8, which increased with the solid solution time to 14 hours. Figure 2 d) The grain size is significantly larger than that in Example 1. Therefore, a solution treatment time of 6 hours at 360°C is more suitable.

[0091] Figure 3 and Figure 4 The figures show the metallographic structures of the magnesium alloy before and after treatment in Examples 2 and 3, respectively. As can be seen from the figures, the grain size of the magnesium alloy is significantly reduced after the treatment in the examples, and most of the second phase is also dissolved into the magnesium matrix.

[0092] Therefore, the results show that Examples 1-3 can effectively and significantly refine the grain size of magnesium alloys and dissolve the MgZn second phase into the magnesium alloy matrix. Furthermore, the process of this invention exhibits the best grain refinement effect.

[0093] 2. The results of room temperature tensile mechanical property analysis are shown in Table 6.

[0094]

[0095]

[0096] As shown in Table 6, after treatment in Example 1, the mechanical properties of the ZK60 magnesium alloy were significantly improved compared to before treatment. Specifically, the tensile strength increased by approximately 43 MPa (19.2%), the yield strength ratio decreased by 14.6%, and the elongation at fracture increased to approximately 2.4 times. Furthermore, compared to all comparative examples (Comparative Examples 1–10), the ZK60 magnesium alloy treated in Example 1 exhibited the highest strength and elongation at fracture. Examples 1, 2, and 4, quenched in water below 5°C, showed higher strength and elongation at fracture compared to Comparative Examples 1, 3, and 5. Comparative Example 11, after treatment, showed the highest increase in tensile strength of approximately 34 MPa (14.1%) compared to before treatment, while the yield strength ratio increased by approximately 5.5%, and the elongation at fracture increased to approximately 1.4 times. The increases in tensile strength and plasticity were significantly smaller than those in Example 1. The tensile strength of Comparative Example 12 after treatment was comparable to that of Example 1, but the elongation after fracture, a plasticity index, was only about half that of Example 1, and the yield strength ratio was also significantly higher, indicating that the plasticity was worse than that of Example 1. The strength and plasticity of Examples 2 and 3 after treatment were both improved compared to before treatment.

[0097] Therefore, the results show that Examples 1-3 can effectively and significantly improve the strength and plasticity of Mg-Zn magnesium alloys. Furthermore, the process improvement of this invention is the most significant.

[0098] 3. Analysis of Plastic Forming Properties

[0099] Figure 6 These are macroscopic images of ZK60 magnesium alloy bars after high-speed extrusion at a rate of 25 m / min, where (a) is direct extrusion from the as-cast state; and (b) is extrusion after treatment according to Example 1. It is clearly visible from the images that the ZK60 magnesium alloy bars directly extruded from the as-cast state suffer from severe cracking throughout, making them difficult to form. The ZK60 magnesium alloy bars extruded after treatment according to Example 1 have a bright surface, are free of cracks, and exhibit excellent plastic forming properties. The tensile mechanical properties of the extruded bars are: tensile strength 350–370 MPa, yield strength 280–300 MPa, and elongation after fracture 18–23%. Figure 7 These are macroscopic images of ZS50 magnesium alloy bars after high-speed extrusion at 25 m / min, where (a) is direct extrusion in the as-cast state; and (b) is extrusion after treatment in Example 2. It is clearly visible from the images that the ZS50 magnesium alloy bar after direct extrusion in the as-cast state exhibits visible cracks along the circumference. The ZS50 magnesium alloy bar extruded after treatment in Example 2 has a bright surface, is crack-free, and demonstrates excellent plastic forming properties. Figure 8 These are macroscopic images of ZS61 magnesium alloy bars after high-speed extrusion at a rate of 25 m / min, where (a) is direct extrusion from the as-cast state; and (b) is extrusion after treatment according to Example 3. It is clearly visible from the images that the ZS50 magnesium alloy bar, after direct extrusion from the as-cast state, cracks along the entire circumference. The ZS61 magnesium alloy bar extruded after treatment according to Example 3 has a bright surface, is free of cracks, and exhibits excellent plastic forming properties.

[0100] 4. Corrosion Performance Analysis

[0101] Figure 9 The images show the morphology of ZK60 magnesium alloy cylindrical samples after immersion in Hank's solution at 37°C for one month, with (a) direct corrosion in the as-cast state and (b) corrosion after treatment in Example 1. It is evident from the images that the as-cast ZK60 magnesium alloy samples show higher corrosion at the upper arrow area and less corrosion at the lower part, exhibiting obvious localized corrosion, and the corrosion pits are also larger and deeper. After treatment in Example 1, the ZK60 magnesium alloy samples show corrosion throughout, with smaller corrosion pits and significantly improved corrosion uniformity. The corrosion rate comparison is shown in Table 7 below. After treatment in Example 1, the corrosion / weight loss rate of the ZK60 magnesium alloy is significantly lower than that of the as-cast state and significantly lower than that of Comparative Examples 13 and 14.

[0102]

[0103]

[0104] In summary, this method has a simple processing flow and can improve the mechanical properties, plastic formability and corrosion uniformity of Mg-Zn magnesium alloys without the need for aging or other pretreatment. Compared with existing technologies, it has a more significant performance improvement effect and greatly simplifies the process steps, which can significantly improve efficiency and save costs.

[0105] The above description is merely a specific embodiment of the present invention and should be considered as exemplary and non-limiting, but the scope of protection of the present invention is not limited thereto. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principles described in the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A process for improving the properties of Mg-Zn based magnesium alloys, characterized in that: The method is suitable for magnesium alloy with the following component characteristics: 3-6wt% of Zn, 0.008-1wt% of one or more of Zr, Sr, Ca, Cu, and the balance of Mg and inevitable impurities; Specifically comprising the following steps: Step 1) preparation of magnesium alloy material ingot with the above components; Step 2) low-temperature solid solution treatment: the magnesium alloy ingot is heated to 360-370℃ at a speed of 480-570℃ / h under inert protective gas or vacuum condition, and is kept for 6-7 hours; Step 3) low-temperature quenching immediately after discharging, which is carried out in water with a temperature lower than 5℃.

2. The process for improving the properties of Mg-Zn based magnesium alloy according to claim 1, characterized in that: In the step 2), the inert protective gas is argon, and the vacuum degree of the vacuum condition is less than 10 -1 Pa.

3. The process for improving the properties of Mg-Zn based magnesium alloy according to claim 1, characterized in that: In the above step 1), during the preparation of the ingot, the pure magnesium ingot is melted in a smelting furnace under vacuum environment, pure zinc particles and Mg-Zr or Mg-Sr or Mg-Ca or Mg-Cu intermediate alloy are sequentially added, after sufficient melting and stirring, the magnesium alloy ingot is cast into a mold through multi-stage filtration and solidified.

4. The process for improving the properties of Mg-Zn based magnesium alloy according to claim 1, characterized in that: The Zn content in the magnesium alloy is 5-6wt%.

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