Thermomechanical treatment method for improving corrosion resistance of magnesium-aluminum alloy

Abstract

The invention discloses a thermomechanical treatment method for improving the corrosion resistance of magnesium-aluminum alloy, and relates to the technical field of magnesium alloy heat treatment. The thermomechanical treatment method comprises the following steps: S1, carrying out solution treatment on the magnesium-aluminum alloy, and then quenching; s2, the magnesium-aluminum alloy subjected to solution treatment is subjected to pre-deformation treatment; s3, the magnesium-aluminum alloy subjected to pre-deformation treatment is subjected to subzero treatment; and S4, the magnesium-aluminum alloy subjected to subzero treatment is subjected to artificial aging treatment. According to the method, the synergistic effect of pre-deformation and subzero treatment of the magnesium-aluminum alloy is utilized, twinning deformation is induced, dislocation proliferation is promoted, cold-induced compressive stress is introduced, growth of a precipitated phase in the subsequent aging process of the magnesium-aluminum alloy is effectively controlled, residual stress is reduced, on the premise that the mechanical property is guaranteed, the corrosion resistance of the magnesium-aluminum alloy is remarkably improved, and the service life of the magnesium-aluminum alloy is prolonged. And guarantee is provided for safe service of products. The method is simple, economical, feasible and suitable for industrial production, and the application prospect of the magnesium alloy is widened.

Description

Technical Field

[0001] This invention belongs to the field of magnesium alloy heat treatment technology, specifically relating to a deformation heat treatment method for improving the corrosion resistance of magnesium-aluminum alloys. Background Technology

[0002] Magnesium alloys, as one of the most promising lightweight structural materials of the 21st century, have attracted much attention in aerospace, automotive manufacturing, and 3C electronics industries. Among them, magnesium-aluminum alloys are currently the most economical and mature commercial magnesium alloy system. Especially when the aluminum content exceeds 5%, the alloy, through Mg... 17 Al 12 The precipitation strengthening effect of the phase can achieve better mechanical properties, making it an ideal material for the preparation of structural components.

[0003] However, the Mg formed during the aging process of magnesium-aluminum alloys 17 Al 12 The phase electrode potential is higher than that of the α-Mg matrix, and during service, it will act as a cathode to induce galvanic corrosion, accelerating the dissolution of the magnesium matrix. Meanwhile, the Mg obtained by conventional aging processes... 17 Al 12 The phases are discontinuous lamellar, large in size, and extremely unevenly distributed at grain boundaries and within grains, failing to form a dense and continuous physical barrier to hinder corrosion propagation. In summary, magnesium-aluminum alloys prepared by traditional heat treatment struggle to simultaneously achieve both mechanical properties and corrosion resistance. This not only reduces the service life and operational safety of components but also severely limits the engineering applications of magnesium-aluminum alloys. Current solutions to address the core problem of poor corrosion resistance in magnesium-aluminum alloys mainly focus on surface treatment and alloy element optimization. However, these methods generally suffer from drawbacks such as significantly increased production costs and complex preparation methods. In particular, the harmful substances generated by surface treatment can easily cause environmental pollution. Therefore, developing a new, environmentally friendly, and economical method that can simultaneously improve the mechanical properties and corrosion resistance of magnesium-aluminum alloys is of great significance for breaking through the bottlenecks in magnesium alloy applications and promoting the green development of lightweight materials. This is also the technical problem that this invention aims to solve. Summary of the Invention

[0004] The purpose of this invention is to at least solve one of the technical problems existing in the prior art, and to provide a deformation heat treatment method to improve the corrosion resistance of magnesium-aluminum alloys. Specifically, it is to develop a new method that is environmentally friendly, economical and can simultaneously improve the mechanical properties and corrosion resistance of magnesium-aluminum alloys.

[0005] This invention effectively improves the corrosion resistance of magnesium-aluminum alloys by sequentially performing solution treatment, pre-deformation treatment, cryogenic treatment, and artificial aging treatment. The core principle is as follows: Pre-deformation and cryogenic treatment are applied sequentially to the solution-treated magnesium alloy. The mechanical action of pre-deformation and the lattice contraction compressive stress induced by cryogenic treatment refine the alloy grains, effectively balancing residual stress and promoting the proliferation of crystal defects such as twins and dislocations. Based on this, combined with aging heat treatment, the Mg content in the alloy is precisely controlled. 17 Al 12 The morphology, size, and distribution characteristics of the phase enable it to construct an effective corrosion barrier during service, thereby overcoming the technical bottleneck of insufficient corrosion resistance in existing magnesium-aluminum alloys while ensuring their mechanical properties. This method is convenient, economical, and environmentally friendly, and can well meet the needs of industrial production.

[0006] The technical solution of the present invention is as follows: The first aspect of this invention provides a deformation heat treatment method for improving the corrosion resistance of magnesium-aluminum alloys, comprising the following steps: S1. The magnesium-aluminum alloy is solution treated and then quenched. S2. Pre-deform the magnesium-aluminum alloy after solution treatment. S3. Perform deep cryogenic treatment on the pre-deformed magnesium-aluminum alloy. S4. Perform artificial aging treatment on the cryogenically treated magnesium-aluminum alloy.

[0007] This invention effectively improves the corrosion resistance of magnesium-aluminum alloys by sequentially performing solution treatment, pre-deformation treatment, cryogenic treatment, and artificial aging treatment. The purpose and principle of each step are as follows: The solution treatment described in step S1 can be carried out in a muffle furnace, which allows the Mg originally precipitated in the alloy to be removed. 17 Al 12 The phase is fully dissolved in the matrix, and then rapid cooling is used to suppress the re-precipitation of the second phase, ultimately obtaining a supersaturated solid solution with uniform composition, which lays a good foundation for subsequent deformation treatment and the precipitation of the aging phase.

[0008] The pre-deformation treatment described in step S2 primarily aims to introduce appropriate plastic deformation into the magnesium-aluminum alloy. By controlling the density and distribution of twins and dislocations within the crystal, it provides the necessary structural basis and driving force for the subsequent regulation of second-phase precipitation. It is important to note that the pre-deformation treatment must ensure sufficient deformation to form high-density defects, creating ample nucleation sites for the second phase, while avoiding excessive deformation that could lead to excessive residual stress or cracks within the alloy. Especially under a twin-dominated deformation mechanism, excessive deformation may cause a decrease in the twin density of the magnesium-aluminum alloy.

[0009] The core purpose of the cryogenic treatment described in step S3 is to further regulate the internal defect structure of magnesium-aluminum alloys through a low-temperature environment. Through a reasonable cryogenic process, low-temperature lattice shrinkage will further induce the proliferation and uniform distribution of crystal defects such as dislocations and twins in the alloy. This not only helps refine the grains but also creates more nucleation sites for the precipitation of the second phase. Furthermore, during cryogenic treatment of magnesium-aluminum alloys, due to the decrease in solid solubility, some aluminum atoms will precipitate as nano-sized Mg atoms. 17 Al 12 The dispersed precipitation of the phase hinders the subsequent formation of lamellar Mg, which is detrimental to corrosion performance. 17 Al 12 The formation of the phase. At the same time, cryogenic treatment can effectively reduce the residual stress introduced by solution quenching and pre-deformation, form a stable residual compressive stress field, and improve the corrosion resistance of magnesium alloys.

[0010] The artificial aging treatment described in step S4 is to further enhance the aging strengthening effect of the magnesium-aluminum alloy and improve its mechanical properties.

[0011] Optionally, the magnesium-aluminum alloy composition, calculated by mass percentage, is: Al: 5.0-9.1%, Zn: 0.35-0.55%, Mn: 0.05-0.10%, Ca: 0.050-0.10%, with the balance being Mg. More preferably, the magnesium-aluminum alloy composition, calculated by mass percentage, is: Al: 7.0-9.1%, Zn: 0.35-0.55%, Mn: 0.05-0.10%, Ca: 0.050-0.10%, with the balance being Mg.

[0012] Optionally, in step S1, the solution treatment temperature is 380-420℃, and the solution treatment time is 1-12h.

[0013] Optionally, in step S1, the magnesium-aluminum alloy after solution treatment is rapidly subjected to water quenching, and the time for transferring the magnesium-aluminum alloy after solution treatment to the quenching process does not exceed 20 seconds.

[0014] Optionally, in step S2, the pre-deformation process is performed at room temperature, and the pre-deformation process can be any one of stretching, forging, rolling, or bending.

[0015] Optionally, in step S2, the deformation amount of the magnesium-aluminum alloy after the pre-deformation treatment is controlled at 2%-6%.

[0016] Optionally, in step S3, the cryogenic treatment is carried out in liquid nitrogen for 0.5-12 hours, and then the temperature is allowed to rise naturally to room temperature in the air.

[0017] Optionally, in step S4, the artificial aging treatment is isothermal aging, with an aging temperature of 150-200℃ and a holding time of 24-96h.

[0018] A second aspect of the present invention provides a corrosion-resistant magnesium-aluminum alloy, obtained by the aforementioned deformation heat treatment method.

[0019] Optionally, the magnesium-aluminum alloy has a yield strength ≥273 MPa, tensile strength ≥352 MPa, elongation after fracture ≥6.1%, and corrosion weight loss rate ≥0.06471 mg / cm². -2 .h -1 .

[0020] This invention has at least one of the following beneficial effects: 1. The solid solution magnesium-aluminum alloy of the present invention, after the combined action of pre-deformation and deep cryogenic treatment, can achieve grain refinement, accompanied by the generation of a large number of crystal defects such as dislocations and twins, providing sufficient nucleation sites for subsequent aging treatment, thereby promoting the growth of Mg. 17 Al 12 The phase precipitates in a fine, uniform, and dispersed morphology. Through the synergistic effect of grain refinement strengthening, dislocation strengthening, and second-phase strengthening, the alloy's mechanical properties are steadily improved. Simultaneously, the uniformly distributed second phase constructs a dense physical barrier, preventing corrosive media from penetrating into the matrix and effectively delaying the galvanic corrosion process. This achieves synergistic optimization of the alloy's mechanical properties and corrosion resistance, greatly expanding its application prospects.

[0021] 2. Compared with conventional methods for improving the corrosion resistance of magnesium alloys, this invention does not require the addition of special alloying elements or the application of special surface treatments, resulting in lower production costs and greater environmental friendliness.

[0022] 3. The deformation heat treatment method provided by the present invention can be implemented using a muffle furnace, liquid nitrogen tank and conventional deformation equipment. The process is short, easy to operate and easy to implement, and is suitable for large-scale industrial production. Attached Figure Description

[0023] Figure 1 The images are scanning electron microscope (SEM) images of magnesium-aluminum alloys, wherein (a) is an SEM image of the magnesium-aluminum alloy after deformation heat treatment in Example 1 of the present invention; and (b) is an SEM image of the magnesium-aluminum alloy after conventional T6 (solution + aging) heat treatment in Comparative Example 1 of the present invention.

[0024] Figure 2 The images show the corrosion surface morphology of magnesium-aluminum alloys, where (a) is the corrosion surface morphology of the magnesium-aluminum alloy obtained in Example 1 of the present invention; and (b) is the corrosion surface morphology of the magnesium-aluminum alloy obtained in Comparative Example 1 of the present invention. Detailed Implementation

[0025] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0026] Example 1 This embodiment provides a deformation heat treatment method for improving the corrosion resistance of magnesium-aluminum alloys, including the following steps: In this embodiment, the magnesium-aluminum alloy is a commercially available magnesium alloy sheet, composed of the following alloy components by mass percentage: Al: 8.5%, Zn: 0.4%, Mn: 0.10%, Ca: 0.07%, with the balance being magnesium. The alloy was solution-treated at 410℃ for 2 hours, followed by water quenching. The alloy transfer time after solution treatment and before quenching was controlled within 20 seconds. The solution-treated sample was pre-stretched at 3% using a room-temperature tensile testing machine. Subsequently, the pre-deformed sample was placed in a container filled with liquid nitrogen for cryogenic treatment for 4 hours, followed by natural warming to room temperature in air. Finally, the sample was aged at 175℃ for 32 hours.

[0027] Example 2 This embodiment provides a deformation heat treatment method for improving the corrosion resistance of magnesium-aluminum alloys, including the following steps: In this embodiment, the magnesium-aluminum alloy is a commercially available magnesium alloy sheet, composed of the following alloy components by mass percentage: Al: 8.5%, Zn: 0.4%, Mn: 0.10%, Ca: 0.07%, with the balance being magnesium. The alloy was solution-treated at 410℃ for 2 hours, followed by water quenching. The alloy transfer time after solution treatment and before quenching was controlled within 20 seconds. The solution-treated sample was pre-stretched at 4% using a room-temperature tensile testing machine. Subsequently, the pre-deformed sample was placed in a container filled with liquid nitrogen for cryogenic treatment for 2 hours, followed by natural warming to room temperature in air. Finally, the sample was aged at 175℃ for 32 hours.

[0028] Example 3 This embodiment provides a deformation heat treatment method for improving the corrosion resistance of magnesium-aluminum alloys, including the following steps: In this embodiment, the magnesium-aluminum alloy is a commercially available magnesium alloy sheet, composed of the following alloy components by mass percentage: Al: 8.5%, Zn: 0.4%, Mn: 0.10%, Ca: 0.07%, with the balance being magnesium. The alloy was solution-treated at 410℃ for 2 hours, followed by water quenching. The alloy transfer time after solution treatment and before quenching was controlled within 20 seconds. The solution-treated sample was pre-stretched to 5% on a room-temperature tensile testing machine. Subsequently, the pre-deformed sample was placed in a container filled with liquid nitrogen for cryogenic treatment for 2 hours, followed by natural warming to room temperature in air. Finally, the sample was aged at 175℃ for 32 hours.

[0029] Comparative Example 1 The difference from Example 1 is that no pre-deformation treatment or cryogenic treatment is performed. The specific steps are as follows: The magnesium-aluminum alloy used in the comparative example was a commercially available magnesium-aluminum alloy sheet, composed of the following alloy components by mass percentage: Al: 8.5%, Zn: 0.4%, Mn: 0.10%, Ca: 0.07%, with the balance being magnesium. The alloy was solution-treated at 410℃ for 2 hours, followed by water quenching. The alloy transfer time after solution treatment and before quenching was controlled to be within 20 seconds. Subsequently, the solution-treated sample was directly aged at 175℃ for 32 hours.

[0030] Comparative Example 2 The difference from Example 1 is that no cryogenic treatment is performed. The specific steps are as follows: The magnesium-aluminum alloy used in the comparative example was a commercially available magnesium-aluminum alloy sheet, composed of the following alloy components by mass percentage: Al: 8.5%, Zn: 0.4%, Mn: 0.10%, Ca: 0.07%, with the balance being magnesium. The alloy was solution-treated at 410℃ for 2 hours, followed by water quenching. The alloy transfer time after solution treatment and before quenching was controlled within 20 seconds. Subsequently, the solution-treated sample underwent a 3% pre-stretch deformation using a room temperature tensile testing machine. Finally, the solution-treated sample was aged at 175℃ for 32 hours.

[0031] Comparative Example 3 The difference from Example 1 is that the solution-treated sample was subjected to a 10% pre-stretch deformation using a room temperature tensile testing machine. The specific steps are as follows: The magnesium-aluminum alloy in the comparative example consisted of the following alloy components by mass percentage: Al: 8.5%, Zn: 0.4%, Mn: 0.10%, Ca: 0.07%, with the balance being magnesium. The alloy was solution-treated at 410℃ for 2 hours, followed by water quenching. The alloy transfer time after solution treatment and before quenching was controlled within 20 seconds. The solution-treated sample was pre-stretched to 10% on a room-temperature tensile testing machine. Subsequently, the pre-deformed sample was placed in a container filled with liquid nitrogen for cryogenic treatment for 4 hours, followed by natural warming to room temperature in air. Finally, the sample was aged at 175℃ for 32 hours.

[0032] Comparative Example 4 The difference from Example 1 is that the solution-treated sample was subjected to a 1% pre-stretch deformation using a room temperature tensile testing machine. The specific steps are as follows: The magnesium-aluminum alloy in the comparative example consisted of the following alloy components by mass percentage: Al: 8.5%, Zn: 0.4%, Mn: 0.10%, Ca: 0.07%, with the balance being magnesium. The alloy was solution-treated at 410℃ for 2 hours, followed by water quenching. The alloy transfer time after solution treatment and before quenching was controlled within 20 seconds. The solution-treated sample underwent 1% pre-stretch deformation using a room-temperature tensile testing machine. Subsequently, the pre-deformed sample was placed in a container filled with liquid nitrogen for cryogenic treatment for 4 hours, followed by natural warming to room temperature in air. Finally, the sample was aged at 175℃ for 32 hours.

[0033] Performance testing methods (1) Mechanical property test: The room temperature mechanical properties of magnesium-aluminum alloys were tested according to the national standard GB / T 228.1-2010 "Metallic materials, tensile test - Part 1: Room temperature test method". After the sample was processed into a standard tensile test specimen, it was tested in a WDW-200D universal tensile testing machine with a tensile rate of 1 mm / min. Each sample had at least three parallel specimens, and the performance was taken as the average value.

[0034] (2) Corrosion performance test: The corrosion performance test was conducted using the weight loss method. The magnesium alloy sample was wire-cut into blocks of 10 mm (length) × 10 mm (width) × 5 mm (thickness), and the samples were heat-mounted, leaving only the surface exposed. The exposed surface was polished with 2000-grit sandpaper, then cleaned sequentially with deionized water and anhydrous ethanol, dried, and then suspended in a 3.5 wt% NaCl solution at 25°C. After corrosion, the surface corrosion products were removed with chromic acid solution, followed by cleaning in anhydrous ethanol. The average corrosion rate was calculated after weighing. Three parallel samples were tested for each sample.

[0035] Table 1 shows the room temperature mechanical and corrosion performance test results of the samples from Examples 1-3 and Comparative Examples 1-4. As shown in Table 1, compared with the samples of Comparative Example 1 treated with conventional T6 heat treatment (solution + aging) and Comparative Example 2 treated with only pre-stretching and direct aging, the deformation heat treatment method of the present invention, which involves pre-deformation, deep cryogenic treatment, and aging, effectively improves the comprehensive mechanical properties of magnesium-aluminum alloys and significantly reduces the corrosion rate of the alloys. Furthermore, as shown in Comparative Examples 3-4, the amount of deformation during pre-stretching also affects the comprehensive mechanical properties of magnesium-aluminum alloys. This is because too small a deformation amount fails to form high-density defects, while too large a deformation amount generates excessive residual stress and weakens the pre-deformation effect due to twinning, thus adversely affecting the corrosion resistance of the alloys. Therefore, using an appropriate deformation amount is crucial.

[0036] The samples from Example 1 and Comparative Example 1, after aging treatment, were polished and etched, and their microstructures were observed using a scanning electron microscope. The results are as follows: Figure 1 (a) and Figure 1 As shown in (b). Figure 1 (a) It can be seen that after pre-deformation and deep cooling, the crystal defects in the sample of Example 1 increased significantly, and Mg... 17 Al 12 During the aging process, the phase is uniformly distributed in the alloy in the form of nano-sized particles or fine lamellar pieces. Figure 1 (b) The sample of Comparative Example 1, its Mg 17 Al 12 The phase precipitates in the form of layers tens of micrometers in size and is unevenly distributed.

[0037] Figure 2 (a) and Figure 2 (b) The surface morphology of the alloys in Example 1 and Comparative Example 1 after immersion in a 3.5 wt% NaCl solution for 24 h, respectively. It can be seen that the magnesium-aluminum alloys after deformation heat treatment according to the present invention have good corrosion resistance, low corrosion degree, and few corrosion products.

[0038] In summary, this invention improves the aging precipitation characteristics of magnesium-aluminum alloys through the coupled effect of pre-deformation, deep cooling, and aging, promoting the formation of fine, uniform, and highly dispersed Mg. 17 Al 12 This structure not only provides excellent mechanical properties to magnesium-aluminum alloys but also significantly improves their corrosion resistance, thus broadening the application prospects of magnesium-aluminum alloys.

[0039] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A deformation heat treatment method for improving the corrosion resistance of magnesium-aluminum alloys, characterized in that, Includes the following steps: S1. The magnesium-aluminum alloy is solution treated and then quenched. S2. Pre-deform the magnesium-aluminum alloy after solution treatment. S3. Perform deep cryogenic treatment on the pre-deformed magnesium-aluminum alloy. S4. Perform artificial aging treatment on the cryogenically treated magnesium-aluminum alloy.

2. The deformation heat treatment method according to claim 1, characterized in that, The composition of the magnesium-aluminum alloy, calculated by mass percentage, is as follows: Al: 5.0-9.1%, Zn: 0.35-0.55%, Mn: 0.05-0.10%, Ca: 0.050-0.10%, with the balance being Mg.

3. The deformation heat treatment method according to claim 1, characterized in that, In step S1, the solution treatment temperature is 380-420℃, and the solution treatment time is 1-12h.

4. The deformation heat treatment method according to claim 1, characterized in that, In step S1, the solution-treated magnesium-aluminum alloy is rapidly quenched by water cooling, and the time for transferring the solution-treated magnesium-aluminum alloy to the quenching process does not exceed 20 seconds.

5. The deformation heat treatment method according to claim 1, characterized in that, In step S2, the pre-deformation process is carried out at room temperature, and the pre-deformation process can be any one of stretching, forging, rolling, or bending.

6. The deformation heat treatment method according to claim 1, characterized in that, In step S2, the deformation amount of the magnesium-aluminum alloy after the pre-deformation treatment is controlled at 2%-6%.

7. The deformation heat treatment method according to claim 1, characterized in that, In step S3, the cryogenic treatment is carried out in liquid nitrogen for 0.5-12 hours, and then the air is allowed to naturally warm to room temperature.

8. The deformation heat treatment method according to claim 1, characterized in that, In step S4, the artificial aging treatment is isothermal aging, with an aging temperature of 150-200℃ and a holding time of 24-96h.

9. A magnesium-aluminum alloy with corrosion resistance, characterized in that, It is obtained by the deformation heat treatment method according to any one of claims 1 to 8.

10. The magnesium-aluminum alloy according to claim 9, characterized in that, The magnesium-aluminum alloy has a yield strength ≥273 MPa, tensile strength ≥352 MPa, elongation after fracture ≥6.1%, and corrosion weight loss rate ≥0.06471 mg / cm². -2 .h -1 .

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