Low-cost high-corrosion-resistance high-strength magnesium alloy and preparation method thereof

Abstract

The application discloses a low-cost high-corrosion-resistance high-strength magnesium alloy and a preparation method thereof. The magnesium alloy comprises the following components in a mass percentage: 0.45-2.1% of aluminum, 0.15-0.9% of calcium, 0.35-0.7% of manganese, 0.1-0.75% of rare earth elements, unavoidable impurities less than 0.05%, and the balance of magnesium. The preparation method comprises alloy smelting, homogenization treatment, deformation processing and heat treatment. The method is based on the synergistic regulation strategy of rare earth micro-alloying and thermal coupling, and simultaneously improves the strength and corrosion resistance of the alloy. The corrosion rate of the magnesium alloy can reach 0.098-0.133 mm / year, the tensile strength is greater than or equal to 280 MPa, and the corrosion resistance is higher than that of pure Mg (0.25 mm / y), which is more than 10 times the corrosion resistance of commercial AZ, AM and ZK magnesium alloys. The application solves the bottleneck problem of magnesium alloy, i.e. serious micro-galvanic corrosion and loose porous film layer, realizes the synergy of low-cost magnesium alloy high-strength and high-corrosion-resistance, and has great commercial application potential.

Description

Technical Field

[0001] This invention relates to the field of metal material processing, and in particular to a low-cost, high-corrosion-resistant, and high-strength magnesium alloy and its preparation method. Background Technology

[0002] Magnesium alloys are widely used in the automotive, aerospace, and electronics industries due to their lightweight, high specific strength, and high specific stiffness. Compared to aluminum alloys, poor corrosion resistance has been a major bottleneck restricting the commercial application of magnesium alloys. This is due to severe micro-galvanic corrosion and a porous surface film in magnesium alloys. Furthermore, it is difficult to simultaneously improve the strength and corrosion resistance of magnesium alloys, mainly because most of the reinforcing second phases in magnesium alloys have a higher corrosion potential than the magnesium matrix, leading to severe micro-galvanic corrosion and making it difficult to form a dense protective film on the alloy surface. Therefore, it is often difficult to improve the corrosion resistance and strength of magnesium alloys simultaneously. Given the current urgent need for high-strength, highly corrosion-resistant magnesium alloys, in-depth exploration of the synergistic improvement mechanism of magnesium alloy strength and corrosion resistance is of great significance.

[0003] Existing technologies enhance the strength of magnesium alloys by increasing the total alloy content and rare earth element content, combined with multi-stage deformation processes and high-temperature long-term treatment, utilizing methods such as grain refinement strengthening, dislocation strengthening, and precipitation strengthening. However, precipitates, dislocation defects, and grain boundaries can lead to preferential corrosion of the surrounding magnesium matrix, which is detrimental to the corrosion resistance of magnesium alloys. Therefore, how to reduce costs and simplify processes to obtain high-strength and highly corrosion-resistant magnesium alloys is one of the urgent technical challenges to be solved. Summary of the Invention

[0004] To address the aforementioned technical challenges, this invention provides a low-cost, high-corrosion-resistant, and high-strength magnesium alloy. The alloy's composition, by mass percentage, includes: aluminum: 0.45-2.1%, calcium: 0.15-0.9%, manganese: 0.35-0.7%, and rare earth elements: 0.1-0.75%, wherein the rare earth elements are one or any combination of cerium, yttrium, lanthanum, samarium, gadolinium, and neodymium; unavoidable impurities <0.05%, with the balance being magnesium. Its preparation method includes the following steps:

[0005] (1) Under argon protection, pure magnesium, pure aluminum, magnesium-manganese master alloy, magnesium-calcium master alloy, and magnesium-rare earth master alloy are heated and held at 700-830℃. After complete melting and thorough stirring, they are quickly poured into a metal mold and air-cooled to obtain magnesium alloy ingots. The magnesium-rare earth master alloy is one or any combination of magnesium-cerium master alloy, magnesium-yttrium master alloy, magnesium-lanthanum master alloy, magnesium-samarium master alloy, magnesium-gadolinium master alloy, and magnesium-neodymium master alloy.

[0006] (2) The magnesium alloy ingot obtained in step (1) is subjected to multi-stage step homogenization heat treatment, water quenched at room temperature, and then subjected to multiple rolling or extrusion treatments to obtain magnesium alloy rolled plates or magnesium alloy extruded profiles.

[0007] The multi-stage stepped homogenization heat treatment consists of 2-4 stages, with a heat treatment temperature of 280-520℃ and a treatment time of 1-12 hours per stage; the rolling process consists of 3-16 rolling passes, with a reduction of 5-45% per pass, and a holding temperature of 300-350℃ for 5-20 minutes before each rolling pass, with a rolling temperature of 280-330℃; the extrusion process consists of an extrusion temperature of 380-540℃, an extrusion ratio of 20-80:1, and an extrusion speed of 0.5-20 m / min.

[0008] (3) Under argon protection, the magnesium alloy rolled plate or magnesium alloy extruded profile obtained in step (2) is subjected to solution heat treatment, and then subjected to artificial aging heat treatment after water quenching to obtain a low-cost, high-corrosion-resistant, and high-strength magnesium alloy.

[0009] The solution heat treatment is performed at 490-550℃ for 0.5-6 hours; the artificial aging heat treatment is performed at 175-380℃ for 0.5-12 hours.

[0010] Furthermore, the aluminum content is 0.5-1.5%, the calcium content is 0.2-0.4%, and the manganese content is 0.4-0.6%.

[0011] Furthermore, the rare earth elements comprise 0.4-0.65%.

[0012] Further, in step (1), pure magnesium, pure aluminum, magnesium-manganese master alloy, magnesium-calcium master alloy, and magnesium-rare earth master alloy are heated and kept at 710-810℃ under argon protection.

[0013] Furthermore, the multi-stage step homogenization heat treatment temperature in step (2) is 330-480℃, and the treatment time for each stage is 2-8h.

[0014] Further, the rolling passes in step (2) are 4-14 passes, the reduction per pass is 10-35%, and the temperature is kept at 310-340℃ for 8-15 minutes before each rolling, and the rolling temperature is 290-320℃.

[0015] Furthermore, the extrusion temperature in step (2) is 400-500℃, the extrusion ratio is 30-70:1, and the extrusion speed is 1-18m / min.

[0016] Further, the solution heat treatment in step (3) is: holding at 495-540℃ for 1-5 hours; the artificial aging heat treatment is: holding at 190-350℃ for 1-10 hours.

[0017] Compared with the existing technology, the present invention has the following characteristics:

[0018] This invention develops a high-corrosion-resistant and high-strength magnesium alloy based on a synergistic control strategy of rare-earth microalloying and thermo-mechanical coupling. The alloy element content is controlled below 4.45 wt.%, making it a low-alloy magnesium alloy. This alloy features low cost, high machinability, and rapid aging response; a large number of nanoscale gradient composite microstructures and nanoprecipitates can be formed through short-time high-temperature heat treatment. While significantly improving the strength of the magnesium alloy, micro-galvanic corrosion on the alloy surface is significantly weakened or even eliminated, facilitating the rapid construction of a dense film layer with excellent protective capabilities on the alloy surface. Compared with existing technologies, this invention simplifies the processing technology while reducing the amount of alloy raw materials and rare-earth additives, and is expected to achieve large-scale industrial production and engineering applications. This invention achieves the following excellent effects through the synergistic control of interactions between alloy elements, component ratios, processes, and process parameters:

[0019] 1) First, the micron-scale phase in the magnesium matrix is ​​controlled to become a nano-scale phase (20-200nm). The lower corrosion potential and smaller size of the nano-scale phase significantly weaken its micro-galvanic corrosion driving force. Second, the high number density and uniform distribution of the nano-scale second phase have excellent effects on removing impurities such as Fe, effectively purifying the magnesium matrix. Third, the controlled nano-scale gradient composite microstructure is composed of different types of nano-phases. Among them, the nano-phase with a lower corrosion potential acts as the anode. Its preferential dissolution can increase the pH value of the metal / solution interface. The weakly alkaline environment is more conducive to the deposition of alloying elements, which promotes the rapid construction of a dense protective film on the alloy surface at the beginning of corrosion.

[0020] 2) This invention not only achieves the effects of refining the grains, weakening the texture, and improving the forming performance of magnesium alloys, but also improves the dissolution, ionization, and deposition processes of metal elements at the metal / solution interface during corrosion, thereby increasing the nucleation rate, deposition rate, and film formation rate of solute elements on the alloy surface, and enabling the alloy to obtain a dense corrosion protective film.

[0021] 3) This invention modulates the micron-sized second phase into nano-sized precipitates and nano-sized microstructures, preventing the formation of strong micro-galvanic corrosion pairs with the magnesium matrix. This significantly alleviates micro-galvanic corrosion in magnesium alloys and simultaneously improves their strength and corrosion resistance. Compared to traditional commercial Mg and Al alloys, this invention promotes the aging kinetics of magnesium alloys, enabling the precipitation of a large number of nano-sized precipitates and nano-sized microstructures in a shorter aging time. These precipitates and microstructures possess advantages such as high quantity density, small size, and high coherence with the magnesium matrix, enhancing the aging response speed. Furthermore, by hindering dislocation slip during deformation, they simultaneously improve the alloy's mechanical properties and corrosion resistance. Even after prolonged high-temperature treatment at 200°C, the alloy maintains its mechanical and corrosion resistance stability.

[0022] 4) The magnesium alloy described in this invention overcomes the bottleneck problem of "severe microgalvanic corrosion and loose and porous surface film" in traditional magnesium alloys, simultaneously improving the mechanical properties and corrosion resistance of the alloy, achieving a tensile strength ≥280MPa, and controlling the total hydrogen evolution amount to ≤0.30mL / cm² after immersion in 3.5wt.% NaCl solution for 7 days. 2 The total hydrogen evolution after soaking for 14 days was controlled to be ≤0.82mL / cm³. 2 The corrosion rate in 3.5 wt.% NaCl solution was controlled at ≤0.133 mm / year, and its corrosion resistance exceeded that of pure Mg (0.25 mm / year) and commercial AZ, AM, and ZK series magnesium alloys, and was even comparable to that of commercial 2000 series aluminum alloys. Detailed Implementation

[0023] Example 1

[0024] Taking the Mg-0.6Al-0.2Ca-0.5Mn-0.5Ce alloy as an example (with the following composition by mass percentage: Al: 0.6%, Ca: 0.2%, Mn: 0.5%, Ce: 0.5%, unavoidable impurities total < 0.05%, balance being magnesium), its preparation method is as follows:

[0025] (1) Under argon protection, pure magnesium, pure aluminum, magnesium-manganese master alloy, magnesium-calcium master alloy and magnesium-cerium master alloy are kept at 700-720℃ for 10 minutes. After they are completely melted, they are stirred for 1 minute. After being kept at 780-800℃ for 2 minutes, they are quickly poured into a metal mold and solidified to obtain magnesium alloy ingots.

[0026] (2) The magnesium alloy ingot obtained in step (1) is subjected to a three-stage step homogenization heat treatment: held at 330℃ for 2 hours, then held at 450℃ for 3 hours, then held at 480℃ for 1 hour, and then cooled by water quenching. After four passes of rolling, magnesium alloy rolled plate is obtained. The reduction in each pass is 30%. Before each rolling, it needs to be held at 350℃ for 10 minutes. The rolling temperature is 330℃.

[0027] (3) Under argon protection, the magnesium alloy rolled plate obtained in step (2) is subjected to solution heat treatment at a temperature of 500°C for 4 hours. After water quenching, it is subjected to artificial aging heat treatment to obtain an aged Mg-0.6Al-0.2Ca-0.5Mn-0.5Ce alloy at a temperature of 200°C for 12 hours.

[0028] The total alloy element content of the alloy in Example 1 was 1.8 wt.%, and the total hydrogen evolution amount of the aged Mg-0.6Al-0.2Ca-0.5Mn-0.5Ce alloy after immersion in a 3.5 wt.% NaCl solution at room temperature for 7 days was 0.30 mL / cm³. 2 The corrosion rate is 0.098 mm / year, and the tensile strength of the aged alloy is 285.1 MPa.

[0029] Comparative Example 1

[0030] Source: Materials Science and Engineering: C, 68(2016): 194–197

[0031] Article title: Mechanical properties and biocorrosion resistance of the Mg-Gd-Nd-Zn-Zr alloy processed by equal channel angular pressing

[0032] Authors: Junyi Zhang, Zhixin Kang, Fen Wang

[0033] Zhang et al. disclosed a Mg-2.9Gd-1.5Nd-0.3Zn-0.3Zr alloy processed using equal channel angular extrusion (ECAP). The preparation steps included melting, casting, and ECAP deformation. The die channel angle Φ = 90°, the outer radius Ψ = 37°, and the extrusion was carried out at 375°C using a Bc path with four passes at a speed of 0.024 m / min. The comparative example used a 0.8 wt.% NaCl solution with trace amounts (0.007-0.036 wt.%) of weakly corrosive salts such as NaHCO3, KCl, and K2HPO4 added to a simulated body fluid. The pH was 7.4, and the corrosiveness of this solution was weaker than the 3.5 wt.% NaCl solution used in this invention. The tensile strength of the comparative alloy was 267.8 MPa, and the total hydrogen evolution after immersion in the simulated body fluid for 6 days was 0.35 mL / cm³. 2 The corrosion rate is 0.134 mm / year.

[0034] Compared to Example 1, Comparative Example 1 has an alloy element content of 5.0 wt.%, which is significantly higher than the alloy addition amount (1.8 wt.%) in Example 1. Specifically, the Gd and Nd content in the alloy of Comparative Example 1 is much higher than the Ce content in Example 1, while the prices of Gd and Nd are also much higher than those of Ce in Example 1. Furthermore, Comparative Example 1 also incorporates Zr, a high-cost element not used in this invention. In addition, the processes used in both examples are completely different; Comparative Example 1 employs the complex and costly ECPA process, which is unsuitable for industrial production. The results show that even when the corrosiveness of the simulated body fluid used in Comparative Example 1 is much lower than that of the 3.5 wt.% NaCl solution in Example 1, the hydrogen evolution rate of the alloy in Comparative Example 1 is still higher than that of the alloy in Example 1 in a shorter time (higher hydrogen evolution rate indicates poorer corrosion resistance), and the strength of the alloy obtained in Comparative Example 1 is lower than that of the alloy obtained in Example 1. Compared to Comparative Example 1, the Al, Ca, and Mn used in Example 1 are all inexpensive alloys, and Ce is one of the inexpensive rare earth metals. The alloy elements are present in even lower concentrations, resulting in a lighter weight. While the two examples use different processes, Example 1 simplifies the process by avoiding the complex ECPA process of Comparative Example 1. The magnesium alloy described in this invention significantly reduces costs while exhibiting superior overall performance in terms of strength and corrosion resistance compared to the magnesium alloy described in Comparative Example 1. Furthermore, it surpasses the corrosion resistance (2.9 mm / year) and tensile strength (280 MPa) of commercial AZ91D alloy (Al: 8.5-9.5%, Zn: 0.45-0.90%, Mn: 0.17-0.40%).

[0035] Comparative Example 2

[0036] Source: Journal of the Mechanical Behavior of Biomedical Materials, 13(2012):36–44

[0037] Article title: Influence of ageing treatment on microstructure, mechanical and bio-corrosion properties of Mg–Dy alloys

[0038] Authors: Lei Yang, Yuanding Huang, Frank Feyerabend, et al.

[0039] Yang et al. disclosed an aged Mg-20Dy alloy, the preparation steps of which included smelting, casting, solution treatment, and artificial aging heat treatment; the corrosive medium used was a 0.9 wt.% NaCl solution, which is less corrosive than the 3.5 wt.% NaCl solution used in this invention. After solution treatment at 520℃ for 24 h, the alloy was water-quenched and then aged at 200℃ for 168 h, resulting in a tensile strength of 219.0 MPa. However, the corrosion rate after immersion in the 0.9 wt.% NaCl solution for 3 days was 21.53 mm / year. In this comparative example, the strength and corrosion resistance of the magnesium alloy were not simultaneously improved. This comparative alloy contained 20.0 wt.% Dy element, resulting in higher raw material costs and a longer heat treatment time. Compared to Comparative Example 2, Example 1 used fewer alloying elements (1.8 wt.%), was cheaper, and had a much lower rare earth content than the alloy added in Comparative Example 2. Despite the significant differences in the processes used in the two studies, the tensile strength (285.1 MPa) and corrosion resistance (0.098 mm / y) of the alloy obtained in Example 1 of this invention are significantly better than those of the alloy in Comparative Example 2, achieving a simultaneous improvement in the strength and corrosion resistance of low-cost magnesium alloys.

[0040] Example 2

[0041] Taking the Mg-0.45Al-0.15Ca-0.35Mn-0.75Ce alloy as an example (with the following composition by mass percentage: Al: 0.45%, Ca: 0.15%, Mn: 0.35%, Ce: 0.75%, unavoidable impurities total < 0.05%, balance being magnesium), its preparation method is as follows:

[0042] (1) Under argon protection, pure magnesium, pure aluminum, magnesium-manganese master alloy, magnesium-calcium master alloy and magnesium-cerium master alloy are kept at 710-730℃ for 10 minutes. After they are completely melted, they are stirred for 1 minute. After being kept at 790-810℃ for 2 minutes, they are quickly poured into a hollow metal mold and solidified to obtain magnesium alloy ingots.

[0043] (2) The magnesium alloy ingot obtained in step (1) is subjected to a two-stage step homogenization heat treatment: it is held at 400℃ for 3 hours and then at 500℃ for 3 hours. After being cooled by water quenching, it is extruded to obtain magnesium alloy extruded profiles. The extrusion temperature is 440℃, the extrusion ratio is 23:1, and the extrusion speed is 2m / min.

[0044] (3) Under argon protection, the magnesium alloy extruded profile obtained in step (2) is subjected to solution heat treatment at a temperature of 490°C for 3 hours. After water quenching, it is subjected to artificial aging heat treatment to obtain an aged Mg-0.45Al-0.15Ca-0.35Mn-0.75Ce alloy at a temperature of 190°C for 9 hours.

[0045] The alloy element content of this invention is 1.7 wt.%, and the total hydrogen evolution amount of the aged Mg-0.45Al-0.15Ca-0.35Mn-0.75Ce alloy after immersion in a 3.5 wt.% NaCl solution at room temperature for 14 days is 0.74 mL / cm³. 2 The corrosion rate is 0.120 mm / year, and the tensile strength of the aged alloy is 283.1 MPa.

[0046] Comparative Example 3

[0047] Source: Materials, 15(2022):2813

[0048] Article title: Effect of heat treatments on the corrosion resistance of ahigh strength Mg-Gd-Y-Zn-Zr alloy

[0049] Authors: Hang Xu, Yuan Li, Luoyi Wu, et al.

[0050] Xu et al. disclosed a Mg-11.46Gd-4.08Y-2.09Zn-0.56Zr alloy obtained by hot extrusion. The preparation process included melting, casting, hot extrusion, solution treatment, and artificial aging heat treatment. The extrusion temperature was 400℃, the extrusion ratio was 10, and the extrusion speed was 0.06 m / min. After solution treatment at 500℃ for 10 h and water quenching, the extruded alloy underwent artificial aging heat treatment at 200℃ for 42 h. The total hydrogen evolution of this alloy after immersion in 3.5 wt.% NaCl solution for 1 day was 5.26 mL / cm³. 2 The corrosion rate was 11.99 mm / year. The comparative alloy contained 18.19 wt.% alloying elements, with Gd and Zr being expensive and costly. In contrast, the alloying elements used in Example 2 of this invention were in smaller quantities and the alloy composition was more inexpensive. The solution treatment and aging treatment temperatures were also lower and the treatment times shorter, reducing production costs. The corrosion resistance of the magnesium alloy in Example 2 of this invention (0.120 mm / year) was superior to that of the magnesium alloy in Comparative Example 3 (11.99 mm / year), and also superior to the corrosion resistance of commercial ZK60 magnesium alloy (Zn: ~6.0%, Zr: ~0.45%) (15.90 mm / year).

[0051] Example 3

[0052] Taking the Mg-0.9Al-0.3Ca-0.7Mn-0.75Y alloy as an example (with the following composition by mass percentage: Al: 0.9%, Ca: 0.3%, Mn: 0.7%, Y: 0.75%, unavoidable impurities total < 0.05%, balance being magnesium), its preparation method is as follows:

[0053] (1) Under argon protection, pure magnesium, pure aluminum, magnesium-manganese master alloy, magnesium-calcium master alloy, and magnesium-yttrium master alloy are kept at 715-725℃ for 10 minutes. After they are completely melted, they are stirred thoroughly for 1 minute. Then they are kept at 785-805℃ for 2 minutes and then quickly poured into a hollow metal mold to solidify, thus obtaining a magnesium alloy ingot.

[0054] (2) The magnesium alloy ingot obtained in step (1) is subjected to a two-stage step homogenization heat treatment: it is held at 280℃ for 8 hours and then at 470℃ for 9 hours. After being cooled by water quenching, it is rolled in 16 passes to obtain magnesium alloy rolled plate. The reduction in each pass is 5%. Before each rolling, it needs to be held at 300℃ for 20 minutes. The rolling temperature is 290℃.

[0055] (3) Under argon protection, the magnesium alloy rolled plate obtained in step (2) is subjected to solution heat treatment at a temperature of 510°C for 3 hours. After water quenching, it is subjected to artificial aging heat treatment to obtain an aged Mg-0.9Al-0.3Ca-0.7Mn-0.75Y alloy at a temperature of 210°C for 10 hours.

[0056] The alloy element content of this invention is 2.65 wt.%, and the total hydrogen evolution amount of the aged Mg-0.9Al-0.3Ca-0.7Mn-0.75Y alloy after immersion in a 3.5 wt.% NaCl solution at room temperature for 14 days is 0.82 mL / cm³. 2 The corrosion rate is 0.133 mm / year, and the tensile strength of the aged alloy is 280 MPa.

[0057] Comparative Example 4

[0058] Source: Journal of Materials Science and Technology, 181(2024):20-40

[0059] Article title: Distinguished roles of static aging and strain aging in the microstructure and creep resistance of Mg-4Y-3.5Nd alloy

[0060] Authors: Zhiruo Zhang, Qinghuan Huo, Yuxiu Zhang, et al.

[0061] Zhang et al. disclosed a Mg-4Y-3.5Nd alloy obtained by rolling process. The preparation steps are as follows: melting, casting, single-stage homogenization treatment, rolling, and artificial aging heat treatment. The homogenization treatment is carried out at 500℃ for 24 hours, followed by six passes of hot rolling at 490℃ and water quenching, with a total deformation of 60%. Finally, it undergoes artificial aging treatment at 220℃ for 30 hours. The tensile strength of this alloy was measured to be 241.3 MPa. The alloy content in this comparative alloy is 7.5 wt.%, with Y and Nd being rare earth elements. In Example 3 of this invention, the alloy element content is 2.65 wt.%, of which the rare earth element content is only 0.75 wt.%. In Example 3, while saving the cost of alloy raw materials and reducing the heat treatment temperature and time, the tensile strength of the alloy after aging treatment can reach 280 MPa, which is better than the strength of the magnesium alloy obtained in Comparative Example 4, and better than the tensile strength of commercial AM60 alloy (Al: ~6.0%, Mn: ~0.25%) (~250 MPa).

[0062] Example 4

[0063] Taking the Mg-2.1Al-0.9Ca-0.7Mn-0.25Ce-0.35La alloy as an example (based on the following composition by mass percentage: Al: 2.1%, Ca: 0.9%, Mn: 0.7%, Ce: 0.25%, La: 0.35%, unavoidable total impurities < 0.05%, balance being magnesium), its preparation method is as follows:

[0064] (1) Under argon protection, pure magnesium, pure aluminum, magnesium-manganese master alloy, magnesium-calcium master alloy, magnesium-cerium master alloy, and magnesium-lanthanum master alloy are kept at 720-730℃ for 10 minutes. After they are completely melted, they are stirred for 1 minute and then kept at 780-795℃ for 2 minutes. They are then quickly poured into a hollow metal mold and solidified to obtain magnesium alloy ingots.

[0065] (2) The magnesium alloy ingot obtained in step (1) is subjected to a four-stage step homogenization heat treatment: held at 280℃ for 1 hour, then at 360℃ for 4 hours, then at 450℃ for 2 hours, then at 520℃ for 1 hour, and then water-quenched and cooled before extrusion to obtain magnesium alloy extruded profiles. The extrusion temperature is 540℃, the extrusion ratio is 80:1, and the extrusion speed is 20m / min.

[0066] (3) Under argon protection, the magnesium alloy extruded profile obtained in step (2) is subjected to solution heat treatment at a temperature of 550°C for 2 hours. After water quenching, it is subjected to artificial aging heat treatment to obtain an aged Mg-2.1Al-0.9Ca-0.7Mn-0.25Ce-0.35La alloy at a temperature of 380°C for 0.5 hours.

[0067] In summary

[0068] In this invention, the alloy element content is ≤4.45 wt.%, making it a low-alloy magnesium alloy. Compared with existing technologies, this invention reduces the amount of alloy raw materials and rare earth elements added, omits the large deformation ECAP process and high-temperature long-term heat treatment, making it suitable for mass industrial production. Compared with existing technologies, this invention simultaneously improves the corrosion resistance and mechanical properties of the alloy. Even after immersion in 3.5 wt.% NaCl solution for 7 or 14 days or longer, the alloy obtained by this invention still maintains superior corrosion resistance compared to alloys obtained by existing technologies. Furthermore, as can be seen from all embodiments of this invention, the composition, proportions, and process parameters differ in each embodiment, resulting in different corrosion resistance and mechanical properties of the final alloy. This invention achieves the following excellent effects through the synergistic control of the interaction between alloy elements, the proportion of components, and the process and process parameters:

[0069] Simultaneously, the mechanical properties and corrosion resistance of the alloy were improved, achieving a tensile strength ≥280MPa, and the total hydrogen evolution after immersion in 3.5wt.% NaCl solution for 7 days was controlled to ≤0.30mL / cm³. 2 The total hydrogen evolution after soaking for 14 days was controlled to be ≤0.82mL / cm³. 2 The corrosion rate in 3.5 wt.% NaCl solution was controlled at ≤0.133 mm / year, and its corrosion resistance exceeded that of pure Mg (0.25 mm / year) and commercial AZ, AM, and ZK series magnesium alloys, and was even comparable to that of commercial 2000 series aluminum alloys.

Claims

1. A low-cost, high-corrosion-resistant, and high-strength magnesium alloy, characterized in that: The alloy composition, by mass percentage, includes: aluminum: 0.45-2.1%, calcium: 0.15-0.9%, manganese: 0.35-0.7%, rare earth elements: 0.1-0.75%, wherein the rare earth elements are one or any combination of cerium, yttrium, lanthanum, samarium, gadolinium, and neodymium; unavoidable impurities <0.05%, and the balance is magnesium; its preparation method includes the following steps: (1) Under argon protection, pure magnesium, pure aluminum, magnesium-manganese master alloy, magnesium-calcium master alloy, and magnesium-rare earth master alloy are heated and held at 700-830 °C. After complete melting and thorough stirring, they are quickly poured into a metal mold and air-cooled to obtain magnesium alloy ingots. The magnesium-rare earth master alloy is one or any combination of magnesium-cerium master alloy, magnesium-yttrium master alloy, magnesium-lanthanum master alloy, magnesium-samarium master alloy, magnesium-gadolinium master alloy, and magnesium-neodymium master alloy. (2) The magnesium alloy ingot obtained in step (1) is subjected to multi-stage step homogenization heat treatment, water quenched at room temperature, and then subjected to multiple rolling or extrusion treatments to obtain magnesium alloy rolled plates or magnesium alloy extruded profiles. The multi-stage stepped homogenization heat treatment consists of 2-4 stages, with a heat treatment temperature of 280-520 ℃ and a treatment time of 1-12 h for each stage; the rolling treatment consists of 3-16 rolling passes, with a reduction of 5-45% per pass, and a holding temperature of 300-350 ℃ for 5-20 min before each rolling pass, with a rolling temperature of 280-330 ℃; the extrusion treatment consists of an extrusion temperature of 380-540 ℃, an extrusion ratio of 20-80:1, and an extrusion speed of 0.5-20 m / min. (3) Under argon protection, the magnesium alloy rolled plate or magnesium alloy extruded profile obtained in step (2) is subjected to solution heat treatment, and then subjected to artificial aging heat treatment after water quenching to obtain a low-cost, high-corrosion-resistant, and high-strength magnesium alloy. The solution heat treatment is performed at 490-550 ℃ for 0.5-6 h; the artificial aging heat treatment is performed at 175-380 ℃ for 0.5-12 h. The low-cost, high-corrosion-resistant, and high-strength magnesium alloy obtained in step (3) simultaneously improves the alloy's mechanical properties and corrosion resistance, achieving a tensile strength ≥280MPa, and controlling the total hydrogen evolution amount to ≤0.30mL / cm² after immersion in 3.5wt.%NaCl solution for 7 days. 2 The total hydrogen evolution after soaking for 14 days was controlled to be ≤0.82mL / cm³. 2 The corrosion rate in 3.5 wt.% NaCl solution was controlled to be ≤0.133 mm / year.

2. The low-cost, high-corrosion-resistant, and high-strength magnesium alloy according to claim 1, characterized in that: The aluminum, by weight percentage: 0.5-1.5%, Calcium: 0.2-0.4%, Manganese: 0.4-0.6%.

3. The low-cost, high-corrosion-resistant, and high-strength magnesium alloy according to claim 1, characterized in that: The rare earth elements, by mass percentage, are 0.4-0.65%.

4. The low-cost, high-corrosion-resistant, and high-strength magnesium alloy according to claim 1, characterized in that: In step (1), pure magnesium, pure aluminum, magnesium-manganese master alloy, magnesium-calcium master alloy, and magnesium-rare earth master alloy are heated and kept at 710-810 ℃ under argon protection.

5. The low-cost, high-corrosion-resistant, and high-strength magnesium alloy according to claim 1, characterized in that: The multi-stage homogenization heat treatment temperature in step (2) is 330-480 ℃, and the treatment time for each stage is 2-8 h.

6. The low-cost, high-corrosion-resistant, and high-strength magnesium alloy according to claim 1, characterized in that: The rolling passes in step (2) are 4-14 passes, with a reduction of 10-35% per pass. Before each rolling, the temperature is kept at 310-340 ℃ for 8-15 minutes, and the rolling temperature is 290-320 ℃.

7. The low-cost, high-corrosion-resistant, and high-strength magnesium alloy according to claim 1, characterized in that: The extrusion temperature in step (2) is 400-500 ℃, the extrusion ratio is 30-70:1, and the extrusion speed is 1-18 m / min.

8. A low-cost, high-corrosion-resistant, and high-strength magnesium alloy according to claim 1, characterized in that: The solution heat treatment in step (3) is to keep the temperature at 495-540 ℃ for 1-5 h; the artificial aging heat treatment is to keep the temperature at 190-350 ℃ for 1-10 h.