High-strength corrosion-resistant magnesium alloy plate and method for manufacturing the same

Abstract

The application belongs to the technical field of magnesium-based alloys, and particularly relates to a high-strength corrosion-resistant magnesium alloy plate and a preparation method thereof. The magnesium alloy plate with fine grains and containing nanometer dispersed low-potential second phases is successfully prepared through a multi-element micro-alloying component design of Mg-Al-Zn-Y-Er-Ca-Mn, combined with a multi-stage thermal mechanical treatment process of homogenization, multi-directional forging, hot rolling and grading aging. The results of the embodiments show that the unique microstructure makes the material have the effects of fine-grain strengthening, precipitation strengthening and texture strengthening, so that high mechanical properties are obtained; meanwhile, the alloy is uniformly corroded and a dense protective film is formed, so that an ultra-low corrosion rate of 0.14-0.18 mm / y is achieved. The application successfully solves the key technical problem that the strength and corrosion resistance of magnesium alloys are difficult to be considered simultaneously.

Description

Technical Field

[0001] This invention belongs to the field of magnesium-based alloy technology, specifically relating to a high-strength corrosion-resistant magnesium alloy sheet and its preparation method. Background Technology

[0002] Magnesium alloys, due to their high specific strength, excellent damping and vibration reduction properties, and good electromagnetic shielding characteristics, have shown broad application prospects in fields with increasingly urgent needs for lightweighting, such as aerospace, new energy vehicles, and consumer electronics. However, the widespread engineering application of magnesium alloys is still severely limited by two inherent drawbacks: insufficient strength and poor corrosion resistance.

[0003] To improve the mechanical properties of magnesium alloys, alloying and plastic deformation processing are the two main technical approaches currently employed. Among these, Mg-Al alloys are widely used due to their low cost and good formability. The introduction of Al can strengthen the alloy through solid solution and the formation of Mg. 17 Al 12 Precipitated phases effectively improve alloy strength. However, when the Al content increases to levels such as in the AZ91 alloy, coarse and network-distributed Mg... 17 Al 12 The second phase precipitates continuously along grain boundaries. Due to its high electrode potential, this second phase readily forms a strong micro-galvanic effect with the magnesium matrix, significantly exacerbating localized galvanic corrosion and severely degrading the alloy's corrosion resistance. Simultaneously, the coarse second phase acts as a stress concentration source, also impairing the material's plasticity and toughness. Conversely, if the Al content is reduced or high-purity magnesium is used to improve corrosion resistance, the insufficient solid solution and precipitation strengthening effects make it difficult to meet the basic strength requirements of structural components.

[0004] The aforementioned contradiction between strength and corrosion resistance has become a core challenge restricting the development of high-performance magnesium alloys. To address this challenge, existing technologies improve the corrosion resistance of Mg-Al alloys by adding trace amounts of rare earth elements (such as Y and Gd) or alkaline earth metals (such as Ca). For example, Y can form the thermodynamically more stable Al₂Y phase with Al, partially replacing Mg. 17 Al 12 Ca can be dissolved in Mg. 17 Al 12 In this process, the electrode potential is lowered, thereby reducing the tendency for galvanic corrosion. However, the above methods generally suffer from problems such as complex processes, high costs, or difficulty in achieving large-scale production. In addition, the ability of a single plastic deformation process to refine the microstructure is limited, making it difficult to achieve a simultaneous and significant improvement in strength and corrosion resistance.

[0005] Therefore, there is an urgent need to develop a new type of magnesium alloy with both high strength and high corrosion resistance, as well as its preparation method, in order to break through the existing technological bottlenecks and meet the urgent demand of high-end manufacturing fields for lightweight, high-strength, and corrosion-resistant structural materials. Summary of the Invention

[0006] The purpose of this invention is to provide a high-strength corrosion-resistant magnesium alloy sheet and its preparation method. The high-strength corrosion-resistant magnesium alloy sheet provided by this invention not only has high mechanical properties, but also can be uniformly corroded to form a dense protective film.

[0007] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a high-strength corrosion-resistant magnesium alloy sheet, wherein the chemical composition of the magnesium alloy sheet by mass percentage is: Al 5.0-8.0 wt%, Zn 0.5-2.0 wt%, Y 0.1-0.2 wt%, Ca 0.1-0.15 wt%, Er 0.1-0.2 wt%, Mn 0.2-0.3 wt%, with the remainder being Mg, and impurity elements less than 0.05 wt%.

[0008] Preferably: Al 7 wt%, Zn 1.5 wt%, Y 0.2 wt%, Ca 0.15 wt%, Er 0.2 wt%, Mn 0.3 wt%, with the remainder being Mg, and impurity elements less than 0.05 wt%.

[0009] This invention also provides a method for preparing high-strength corrosion-resistant magnesium alloy plates, the method comprising the following steps: S1. Weigh out pure magnesium ingots, pure aluminum ingots, pure zinc ingots, Mg-Y master alloy, Mg-Er master alloy, Mg-Ca master alloy, and anhydrous manganese chloride according to the above proportions; preheat the raw materials to remove moisture; smelt under a mixed gas of CO2 and SF6 to homogenize the alloy elements; then, add a refining agent at 740-750℃ for refining for 5-15 minutes; after refining, let the melt stand to allow impurities to settle completely; then remove the surface slag, and pour the melt into a metal mold preheated to 180-250℃ at 690-710℃ to obtain a magnesium alloy ingot; S2. Place the ingot in a heat treatment furnace and homogenize it at a temperature of 380-420℃ for 18-36 hours, then air cool it. S3. The ingots treated by S2 are processed into billets, heated to 350-400℃ and held for 1-2 hours; then forged in three directions at the same temperature, and then water-quenched to obtain slabs; S4. Heat the slab treated in S3 to 300-380℃, hold for 0.5-1 hour, and then perform 3 passes of hot rolling to obtain the sheet material; S5. The hot-rolled S4 sheet is subjected to graded aging treatment: first stage aging: temperature 150-180℃, time 2-8 hours; second stage aging: temperature 100-130℃, time 10-30 hours; after aging treatment, it is air-cooled to obtain high-strength corrosion-resistant magnesium alloy sheet.

[0010] Preferably, the volume ratio of CO2 to SF6 in S1 is CO2:SF6 = 1:9.

[0011] Preferably, the smelting step in S1 is as follows: melt pure magnesium ingots at 650-690℃, raise the temperature to 710-730℃, add pure aluminum ingots, pure zinc ingots, and anhydrous manganese chloride in sequence, and after complete melting, raise the temperature to 740-760℃, add Mg-Y master alloy, Mg-Er master alloy, and Mg-Ca master alloy, and keep warm and stir for 20-40 minutes to homogenize the alloy elements.

[0012] Preferably, the refining agent in S1 consists of 45-49 wt% KCl, 24-28 wt% CaCl2, 10-14 wt% BaCl2, 6-8 wt% CaF2, and 7-9 wt% YCl3, and is used in an amount of 1-2% of the total mass of the melt.

[0013] Preferably, the settling step in S1 is as follows: first, settling at 740-750℃ for 20-40 minutes, and then cooling to 700-720℃ and settling for 20-30 minutes.

[0014] Preferably, the total forging deformation in the three-dimensional forging process in S3 is 50%-80%, and the deformation per pass is 10%-20%.

[0015] Preferably, the total rolling reduction in the three hot rolling passes of S4 is 40%-70%, and the final rolling temperature is not lower than 250°C.

[0016] Preferably, the graded aging process in S5 is as follows: first-level aging: temperature 170℃, time 4 hours; second-level aging: temperature 120℃, time 24 hours.

[0017] This invention also provides the application of the above-mentioned magnesium alloy sheet in the manufacture of new energy vehicles or 3C electronic products.

[0018] Beneficial effects: 1. This invention employs a multi-element microalloying composition design, adding appropriate amounts of Y and Ca. On one hand, these additives combine with Al to form thermodynamically more stable Al2Y and Al2Ca particles, which serve as heterogeneous nucleation sites to refine the as-cast grains and inhibit grain growth during subsequent deformation. On the other hand, they alter the Mg... 17 Al 12The composition and morphology of the phases are influenced by the fact that Y promotes the transformation of the high-potential Al-Mn-Fe impurity phase into the low-potential Al-Mn-Y phase, while Ca segregates in Mg. 17 Al 12 Mg with a more negative potential forms in the phase 17 Al 12 The (Ca) phase significantly weakens the microgalvanic corrosion driving force between the second phase and the magnesium matrix.

[0019] 2. This invention employs an optimized multi-stage hot deformation process, combining "multi-directional forging + hot rolling". First, multi-directional forging fully breaks down the cast dendrites and coarse second phase, providing a uniform and refined initial microstructure for subsequent hot rolling. Hot rolling further introduces high-density dislocations, deformation twins, and strong basal texture. Through fine grain strengthening, twin strengthening, and texture strengthening mechanisms, the mechanical properties are greatly improved. At the same time, the strong basal texture helps to expose more corrosion-resistant crystal planes.

[0020] 3. This invention employs precise, staged aging treatment. Aging is performed at relatively low temperatures for a longer period, promoting the formation of small-sized, spherical, dispersed Mg... 17 Al 12 Uniform precipitation of the phase. These fine precipitates not only provide a significant precipitation strengthening effect, but also, due to their small size, uniform distribution, and small potential difference with the matrix, promote uniform corrosion of the magnesium matrix rather than localized pitting corrosion, thereby forming a uniform and dense protective film of corrosion products, which significantly slows down the corrosion process.

[0021] 4. This invention is based on the mature Mg-Al-Zn-Mn system, with a small total amount of added alloying elements and controllable cost. The preparation process is based on conventional melting, forging, rolling and heat treatment equipment, without the need for special vacuum melting or complex heat treatment regimes. The process is clear and the parameter window is wide, making it suitable for large-scale industrial production, with significant cost advantages and application potential. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 SEM image of the product prepared in Example 1.

[0024] Figure 2 SEM image of the product prepared for Comparative Example 1.

[0025] Figure 3The corrosion cross-sectional morphology of the product prepared in Example 1 after immersion in 3.5 wt.% NaCl solution for 7 days.

[0026] Figure 4 The corrosion cross-sectional morphology of the product prepared for Comparative Example 5 after immersion in 3.5 wt.% NaCl solution for 7 days. Detailed Implementation

[0027] This invention provides a high-strength corrosion-resistant magnesium alloy sheet and its preparation method. The chemical composition (mass percentage) of the high-strength corrosion-resistant magnesium alloy prepared by this invention is as follows: Al 5.0-8.0 wt%, Zn 0.5-2.0 wt%, Y 0.1-0.2 wt%, Ca 0.1-0.15 wt%, Er 0.1-0.2 wt%, Mn 0.2-0.3 wt%, with the remainder being Mg (containing less than 0.05 wt% of impurity elements). The preferred composition is: Al preferably 7 wt%, Zn preferably 1.5 wt%, Y preferably 0.2 wt%, Ca 0.15 wt%, Er preferably approximately 0.2 wt%, and Mn preferably 0.3 wt%. This composition design ensures uniform distribution of the second phase in the alloy, grain refinement, and synergistic effect of each element to optimize the corrosion film structure. After proper melting and casting, this alloy exhibits a dense α-Mg matrix with finely dispersed secondary phases such as Al₂Y, (Mg,Al)₂Ca, and (Mg,Zn)₁₇Al₁₂. Zn and Mn primarily exist in solid solution within the α-Mg matrix, further refining the grain size and purifying the alloy. Subsequent forging, hot rolling, and aging further refine the magnesium alloy grains and optimize the morphology and distribution of the secondary phases, resulting in excellent corrosion resistance and mechanical properties in NaCl media.

[0028] This invention provides a method for preparing the above-mentioned high-strength corrosion-resistant magnesium alloy, comprising the following main steps: 1. Raw material smelting and ingot preparation Weigh out pure magnesium ingots, pure aluminum ingots, pure zinc ingots, Mg-Y master alloy, Mg-Er master alloy, Mg-Ca master alloy, and anhydrous manganese chloride. Preheat the raw materials to remove moisture. Smelt in a mixed gas of CO2 and SF6, with a volume ratio of CO2:SF6 = 1:9: First, melt the pure magnesium ingots at 650-690℃, then raise the temperature to 710-730℃, and add the pure aluminum ingots, pure zinc ingots, and manganese source in sequence. After complete melting, raise the temperature to 740-760℃, and add the Mg-Y, Mg-Er, and Mg-Ca master alloys. Maintain the temperature and stir for 20-40 minutes to homogenize the alloy elements. Subsequently, a refining agent is added at 740-750℃. The refining agent composition is 45-49 wt% KCl, 24-28 wt% CaCl2, 10-14 wt% BaCl2, 6-8 wt% CaF2, and 7-9 wt% YCl3, with the amount added being 1-2% of the total melt mass. Refining is carried out for 5-15 minutes. After refining, the melt is allowed to stand: first at 740-750℃ for 20-40 minutes, then cooled to 700-720℃ and allowed to stand for 20-30 minutes to allow impurities to settle fully. Finally, the surface slag is removed, and the melt is poured into a metal mold preheated to 180-250℃ at 690-710℃ to obtain a magnesium alloy ingot.

[0029] 2. Homogenization heat treatment

[0030] The ingot is placed in a heat treatment furnace and homogenized at 380-420℃ for 18-36 hours, followed by air cooling. The purpose of this step is to dissolve the dendritic segregation and coarse second phase produced by non-equilibrium solidification in the as-cast structure, thereby homogenizing the composition and preparing it for subsequent hot deformation.

[0031] 3. Multi-directional forging

[0032] The homogenized ingot is machined into a billet, heated to 350-400℃ and held for 1-2 hours. Then, it undergoes triaxial forging at the same temperature, with the total forging deformation controlled at 50%-80%, and the deformation per pass approximately 10%-20%. After forging, it is rapidly water-quenched to preserve the deformed microstructure. This step aims to thoroughly break down the as-cast microstructure, obtain uniform, refined equiaxed grains, and initially break down coarse second phases.

[0033] 4. Hot rolling

[0034] The forged slab is reheated to 300-380℃ and held for 0.5-1 hour. It is then subjected to three passes of hot rolling, with a total rolling reduction of 40%-70%, and a final rolling temperature of not less than 250℃. This step further refines the grains, introduces high-density dislocations and deformed twins, and forms a strong basal texture, which is crucial for achieving high strength and high corrosion resistance.

[0035] 5. Graded Time-Limited Processing

[0036] The hot-rolled sheet material is then subjected to graded aging treatment: Level 1 aging: Temperature 150-180℃, Time 2-8 hours.

[0037] Second-level aging: temperature 100-130℃, time 10-30 hours.

[0038] After aging treatment, the precipitate is air-cooled. This staged aging process aims to first promote the nucleation of the precipitate at a higher temperature, and then allow the precipitate to grow slowly at a lower temperature, ultimately obtaining small-sized, diffusely distributed spherical Mg. 17 Al 12 Precipitated phases are formed, thereby achieving optimal precipitation enhancement and promoting uniform corrosion.

[0039] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the accompanying drawings and embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0040] Unless otherwise specified, the production processes, experimental methods, or testing methods involved in the embodiments of this invention are all conventional methods in the prior art, and their names and / or abbreviations are all conventional names in the field, which are very clear and distinct in the relevant application areas. Those skilled in the art can understand the conventional process steps based on the names and apply the corresponding equipment, and implement them according to conventional conditions or the conditions recommended by the manufacturer.

[0041] The various instruments, equipment, raw materials or reagents used in the embodiments of this invention are not subject to any special restrictions on their source. They are all conventional products that can be purchased through regular commercial channels and can be prepared according to conventional methods known to those skilled in the art.

[0042] Example: Example 1: Alloy composition: Al 7.0wt%, Zn 1.5wt%, Y 0.2wt%, Ca 0.15wt%, Er 0.2wt%, Mn 0.3wt%, with the remainder being Mg.

[0043] The homogenization process in the preparation process involves a homogenization temperature of 400℃ for 24 hours, a forging temperature of 380℃ with a deformation rate of 70%, a rolling temperature of 350℃ with a total reduction of 60%, a first-stage aging temperature of 170℃ for 4 hours, and a second-stage aging temperature of 120℃ for 24 hours. The specific preparation process is as follows: 1. Raw material smelting and ingot preparation Weigh out pure magnesium ingots, pure aluminum ingots, pure zinc ingots, Mg-Y master alloy, Mg-Er master alloy, Mg-Ca master alloy, and anhydrous manganese chloride. Preheat the raw materials to remove moisture. Smelt in a mixed gas of CO2 and SF6, with a volume ratio of CO2:SF6 = 1:9: First, melt the pure magnesium ingots at 650-690℃, then raise the temperature to 710-730℃, and add the pure aluminum ingots, pure zinc ingots, and manganese source in sequence. After complete melting, raise the temperature to 740-760℃, and add the Mg-Y, Mg-Er, and Mg-Ca master alloys. Maintain the temperature and stir for 20-40 minutes to homogenize the alloy elements. Subsequently, a refining agent is added at 740-750℃. The refining agent composition is 45-49 wt% KCl, 24-28 wt% CaCl2, 10-14 wt% BaCl2, 6-8 wt% CaF2, and 7-9 wt% YCl3, with the amount added being 1-2% of the total melt mass. Refining is carried out for 5-15 minutes. After refining, the melt is allowed to stand: first at 740-750℃ for 20-40 minutes, then cooled to 700-720℃ and allowed to stand for 20-30 minutes to allow impurities to settle fully. Finally, the surface slag is removed, and the melt is poured into a metal mold preheated to 180-250℃ at 690-710℃ to obtain a magnesium alloy ingot.

[0044] 2. Homogenization heat treatment

[0045] The ingots were placed in a heat treatment furnace and homogenized at 400°C for 24 hours, followed by air cooling.

[0046] 3. Multi-directional forging

[0047] The homogenized ingot is machined into a billet, heated to 380℃ and held for 1-2 hours. Then, it is forged in three directions at the same temperature, with the total forging deformation controlled at 70% and the deformation per pass approximately 10%-20%. After forging, it is rapidly water-quenched to retain the deformed structure.

[0048] 4. Hot rolling

[0049] The forged slab is reheated to 350°C and held for 0.5-1 hour. It is then hot rolled in three passes with a total rolling reduction of 60% and a final rolling temperature of not less than 250°C.

[0050] 5. Graded Time-Limited Processing

[0051] The hot-rolled sheet material is then subjected to graded aging treatment: Level 1 aging: Temperature 170℃, Time 4 hours.

[0052] Level 2 aging: Temperature 120℃, Time 24 hours.

[0053] After aging treatment, the precipitate is air-cooled. This staged aging process aims to first promote the nucleation of the precipitate at a higher temperature, and then allow the precipitate to grow slowly at a lower temperature, ultimately obtaining small-sized, diffusely distributed spherical Mg. 17 Al 12 Precipitated phases are formed, thereby achieving optimal precipitation enhancement and promoting uniform corrosion.

[0054] Example 2: Alloy composition: Al 7.0wt%, Zn 0.8wt%, Y 0.10wt%, Ca 0.10wt%, Er 0.15wt%, Mn 0.25wt%, balance Mg. Homogenization temperature 410℃, 20h; forging temperature 370℃, deformation 65%; rolling temperature 340℃, total reduction 55%; first-stage aging temperature 165℃, 6h; second-stage aging temperature 115℃, 30h. Other process parameters are the same as in Example 1.

[0055] Example 3: Alloy composition: Al 6.0wt%, Zn 1.5wt%, Y 0.2wt%, Ca 0.1wt%, Er 0.15wt%, Mn 0.20wt%, balance Mg. Homogenization temperature 390℃, 28h; forging temperature 390℃, deformation 75%; rolling temperature 360℃, total reduction 65%; first-stage aging temperature 175℃, 3h; second-stage aging temperature 125℃, 20h. Other process parameters are the same as in Example 1.

[0056] Example 4: Alloy composition: Al 6.5wt%, Zn 1.0wt%, Y 0.15wt%, Ca 0.1wt%, Er 0.10wt%, Mn 0.20wt%, balance Mg. Homogenization temperature 400℃, 24h; forging temperature 370℃, deformation 60%; rolling temperature 330℃, total reduction 50%; first-stage aging temperature 160℃, 8h; second-stage aging temperature 110℃, 28h. Other process parameters are the same as in Example 1.

[0057] Example 5: Alloy composition: Al 5.5wt%, Zn 1.5wt%, Y 0.10wt%, Ca 0.15wt%, Er 0.10wt%, Mn 0.20wt%, balance Mg. Homogenization temperature 400℃, 24h; forging temperature 380℃, deformation 70%; rolling temperature 350℃, total reduction 60%; first-stage aging temperature 170℃, 4h; second-stage aging temperature 120℃, 24h. All other process parameters are the same as in Example 1.

[0058] Example 6: Alloy composition: Al 6.5wt%, Zn 1.0wt%, Y 0.15wt%, Ca 0.1wt%, Er 0.15wt%, Mn 0.25wt%, balance Mg. Homogenization temperature 420℃, 18h; forging temperature 400℃, deformation 80%; rolling temperature 370℃, total reduction 70%; first-stage aging temperature 180℃, 2h; second-stage aging temperature 130℃, 15h. Other process parameters are the same as in Example 1.

[0059] Comparative Example 1: The composition is the same as in Example 1, but multi-directional forging is not performed; the ingot is directly hot-rolled after homogenization. All other process parameters are the same as in Example 1.

[0060] Comparative Example 2: The composition was the same as in Example 1, but without graded aging; after rolling, it underwent only a single aging process at 170°C for 4 hours. The remaining parameters of the preparation process were the same as in Example 1.

[0061] Comparative Example 3: The composition is the same as in Example 1, but it does not contain Y and Er elements (i.e., composition: Mg-7Al-1.5Zn-0.15Ca-0.3Mn). The preparation process is the same as in Example 1.

[0062] Comparative Example 4: The composition is the same as in Example 1, but it does not contain Ca (i.e., composition: Mg-7Al-1.5Zn-0.2Y-0.2Er-0.3Mn). The preparation process is the same as in Example 1.

[0063] Comparative Example 5: Commercial AZ91D alloy ingots were used, and the same 2-5 processes as in Example 1 were performed.

[0064] The products prepared in the examples and comparative examples were tested, and the test results are shown in Table 1.

[0065] Table 1 Test Results

[0066] SEM images of the product prepared in Example 1 are shown below. Figure 1 As shown, the formation of fine grains and dispersed precipitates is typical of the microstructure of an alloy after a complete process. Numerous small, spherical, dispersed precipitates (mainly Mg) are distributed within the matrix. 17 Al 12 (and compounds containing Y, Er, and Ca), without coarse, continuous network phases. These fine, dispersed precipitates not only serve as effective strengthening points to enhance strength, but more importantly, their small potential difference with the magnesium matrix and uniform distribution promote the uniform dissolution of the magnesium matrix, thus facilitating the formation of a dense corrosion product film. In contrast, Figure 2 In the SEM image of the product prepared in Comparative Example 1, the microstructure uniformity is slightly poor due to the lack of a multi-directional forging step, and there are some large second-phase particles that are not fully broken.

[0067] The consequences of corrosion: Figure 3 (The corrosion cross-sectional morphology of the product prepared in Example 1 after immersion in 3.5 wt.% NaCl solution for 7 days) shows that a dense, continuous corrosion product film uniformly covers the magnesium substrate surface, without any "corrosion pits" formed by localized corrosion penetration into the substrate. This uniform corrosion morphology is completely consistent with the extremely low weight loss rate (0.068 mg / cm² / day) and corrosion rate (0.143 mm / y) of the alloy in Table 1. This indicates that the fine, dispersed precipitates and refined microstructure obtained by the present invention through multi-element microalloying and multi-stage thermomechanical treatment effectively avoid the formation of localized microgalvanic corrosion cells, promote uniform anodic dissolution reactions, and thus achieve controllability and long-term effectiveness in the corrosion process. Conversely, Figure 4 The corrosion cross-sectional morphology of the product prepared in Comparative Example 5 after immersion in 3.5 wt.% NaCl solution for 7 days showed severe localized pitting corrosion, and the corrosion product film was loose and cracked, failing to provide effective protection. This directly explains why the corrosion rate of Comparative Example 5 (3.885 mm / y) was more than 27 times that of Example 1 (0.143 mm / y).

[0068] The corrosion resistance (corrosion rates of 0.441 mm / y and 0.378 mm / y, respectively) of Comparative Example 3 (without Y and Er) and Comparative Example 4 (without Ca) was significantly lower than that of Example 1. This indicates the synergistic microalloying effect of Y, Er, and Ca: Y and Er can purify the melt, transforming the harmful high-potential Al-(Fe,Mn) phase into the low-potential Al-(Mn,Y,Er) phase, and forming stable oxides to improve the surface film; Ca can dissolve into Mg. 17 Al 12 The cathode phase lowers its electrode potential. Together, these two factors significantly weaken the driving force for microgalvanic corrosion between the cathode phase and the magnesium substrate.

[0069] In summary, this invention, through a multi-element microalloying composition design of Mg-Al-Zn-Y-Er-Ca-Mn, combined with a multi-stage thermomechanical treatment process involving homogenization, multi-directional forging, hot rolling, and graded aging, successfully prepared magnesium alloy sheets with fine grains and containing nano-dispersed low-potential second phases. This unique microstructure enables the material to simultaneously possess the effects of fine-grain strengthening, precipitation strengthening, and texture strengthening, thereby achieving high mechanical properties. Simultaneously, it promotes uniform corrosion and the formation of a dense protective film, achieving an ultra-low corrosion rate of 0.14-0.18 mm / y. This invention successfully solves the key technical problem of balancing strength and corrosion resistance in magnesium alloys, and has broad application prospects in lightweight fields such as new energy vehicles and 3C electronic products.

[0070] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing high-strength corrosion-resistant magnesium alloy plates, characterized in that, The steps of the method include: S1. Weigh out pure magnesium ingots, pure aluminum ingots, pure zinc ingots, Mg-Y master alloy, Mg-Er master alloy, Mg-Ca master alloy, and anhydrous manganese chloride according to the proportions of magnesium alloy plates; preheat the raw materials to remove moisture; melt them under a mixed gas of CO2 and SF6 to homogenize the alloy elements; then add a refining agent at 740-750℃ for refining for 5-15 minutes; after refining, let the melt stand to allow impurities to settle completely; then remove the surface slag, and pour the melt into a metal mold preheated to 180-250℃ at 690-710℃ to obtain magnesium alloy ingots; S2. Place the ingot in a heat treatment furnace and homogenize it at a temperature of 380-420℃ for 18-36 hours, then air cool it. S3. The ingot treated in S2 is processed into a billet, heated to 350-400℃ and held for 1-2 hours; then it is forged in three directions at the same temperature, and then water-quenched to obtain a slab; the total forging deformation of the three-directional forging is 50%-80%, and the deformation per pass is 10%-20%; S4. The slab treated in S3 is heated to 300-380℃ and held for 0.5-1 hour, followed by 3 passes of hot rolling to obtain the plate; the total rolling reduction of the 3 passes of hot rolling is 40%-70%, and the final rolling temperature is not lower than 250℃. S5. The hot-rolled sheet material of S4 is subjected to graded aging treatment: First stage aging: temperature 150-180℃, time 2-8 hours; Second stage aging: temperature 100-130℃, time 10-30 hours; After aging treatment, it is air-cooled to obtain high-strength corrosion-resistant magnesium alloy sheet material. The chemical composition of the magnesium alloy sheet, by mass percentage, is: Al 5.0-8.0 wt%, Zn 0.5-2.0 wt%, Y 0.1-0.2 wt%, Ca 0.1-0.15 wt%, Er 0.1-0.2 wt%, Mn 0.2-0.3 wt%, with the remainder being Mg and impurity elements less than 0.05 wt%.

2. The method according to claim 1, characterized in that, The chemical composition of the magnesium alloy sheet, by mass percentage, is: Al 7 wt%, Zn 1.5 wt%, Y 0.2 wt%, Ca 0.15 wt%, Er 0.2 wt%, Mn 0.3 wt%, with the remainder being Mg, and impurity elements less than 0.05 wt%.

3. The method according to claim 1, characterized in that, The volume ratio of CO2 to SF6 in S1 is CO2:SF6 = 1:

9.

4. The method according to claim 1, characterized in that, The smelting steps in S1 are as follows: melt pure magnesium ingots at 650-690℃, raise the temperature to 710-730℃, add pure aluminum ingots, pure zinc ingots, and anhydrous manganese chloride in sequence, and after complete melting, raise the temperature to 740-760℃, add Mg-Y master alloy, Mg-Er master alloy and Mg-Ca master alloy, and keep warm and stir for 20-40 minutes to homogenize the alloy elements.

5. The method according to claim 1, characterized in that, The refining agent in S1 consists of 45-49 wt% KCl, 24-28 wt% CaCl2, 10-14 wt% BaCl2, 6-8 wt% CaF2, and 7-9 wt% YCl3, and is used in an amount of 1-2% of the total mass of the melt.

6. The method according to claim 1, characterized in that, The step of settling in S1 is as follows: first, settling at 740-750℃ for 20-40 minutes, and then cooling to 700-720℃ and settling for 20-30 minutes.

7. The application of the magnesium alloy sheet prepared by the method according to any one of claims 1-6 in the manufacture of new energy vehicles or 3C electronic products.

Images