An oriented controllable-release Mg-Sn-based magnesium alloy extrusion material and a preparation method and application thereof

Abstract

The application discloses an oriented controllable slow-release Mg-Sn-based magnesium alloy extruded material and a preparation method and application thereof, and belongs to the technical field of magnesium alloy materials. The extruded material contains Sn, Al, Zn and Mn elements, and the balance is Mg. The extruded material has a cylindrical wire texture, [10-10] and [11-20] crystal directions are parallel to the extrusion direction, and the base surface (0001) is normal to ED; Mg2Sn and Al-Mn phases are distributed in a strip-shaped orientation along the ED in the longitudinal section and are randomly distributed in the transverse section. By selecting the longitudinal section or the transverse section as a service exposure surface, the degradation rate can be customized, and a gradient pipe with an inner and outer surface orientation can be prepared. The application is suitable for marine sacrificial anodes, temporary components and instrument self-release devices.

Description

Technical Field

[0001] This invention belongs to the field of magnesium alloy materials technology, specifically relating to an orientation-controlled slow-release Mg-Sn based magnesium alloy extrusion material, its preparation method, and its application. Background Technology

[0002] Magnesium alloys, with their high specific strength, good biodegradability, and compatibility with marine environments, show great promise for applications in marine engineering. For example, they can be used as sacrificial anode materials for cathodic protection, or fabricated into temporary structural components that actively degrade after completing their service life, avoiding salvage and recovery operations. However, the corrosion rate of magnesium alloys in marine environments is typically too rapid and difficult to control precisely, which severely limits their engineering applications.

[0003] To control the corrosion behavior of magnesium alloys, existing technologies mainly focus on the following directions: First, adjusting the composition through alloying, such as adding Al, Zn, Mn, Sn, or rare earth elements to improve corrosion resistance or form a stable passivation film. However, rare earth resources are scarce and expensive, and some alloying elements (such as high Al content) may exacerbate pitting corrosion during long-term immersion in the ocean. Second, using surface coating technology for physical isolation; however, the coating is prone to localized damage or peeling in the complex marine mechanical stress and electrochemical environment. Once it fails, the substrate will suffer accelerated localized corrosion, making reliability difficult to guarantee. Third, optimizing the microstructure through heat treatment or deformation processing, such as refining grains and controlling the distribution of the second phase, but this often only provides limited improvement in corrosion resistance and cannot achieve active design of a wide range of corrosion rates.

[0004] The influence of crystallographic texture on the corrosion behavior of magnesium alloys has attracted attention. Studies have shown that different crystal faces of magnesium have different surface energies and electrochemical activities, with the basal face (0001) exhibiting significantly better corrosion resistance than the cylindrical face (10⁻¹⁰) and the pyramidal face. Based on this principle, some studies have attempted to obtain strong basal face textures through plastic deformation, aligning the corrosion-resistant basal face parallel to the component surface to improve overall corrosion resistance. Furthermore, some techniques have proposed utilizing the strong basal face texture of deformed magnesium alloys to obtain different exposed surfaces by cutting samples with different orientations, thereby controlling the corrosion rate. This type of method is the first to link texture anisotropy with corrosion rate customization, offering significant insights. Current research has attempted to obtain differentiated corrosion rates by controlling strong basal face textures and cutting samples with different orientations; however, this pure texture control approach still has significant limitations. Relying solely on the texture itself makes it difficult to achieve long-term stability and predictability of corrosion behavior, and it also ignores the synergistic effect of second-phase distribution and texture, resulting in limited corrosion anisotropy. In engineering practice, the design of sacrificial anodes or biodegradable components usually only focuses on the average corrosion rate of the material, while ignoring the performance differences between different oriented sections of the same material, and failing to utilize the anisotropy of the material to achieve functional optimization.

[0005] The patent CN106811706A, entitled "An Effective Method for Controlling the Corrosion Rate of Magnesium Alloys," discloses a method of stress-relief annealing of deformed magnesium alloys with strong basal texture, followed by cutting and sampling along different orientations to obtain samples exposing different crystal planes. The method utilizes the difference in corrosion rates between the basal and cylindrical planes to control the corrosion rate of the magnesium alloy. However, this approach relies primarily on single texture control. Since it lacks elements such as Sn that can form a directional second phase, it does not address the synergistic control of second phase distribution and texture. Therefore, the long-term stability and anisotropy of its corrosion behavior are limited. Furthermore, relying solely on single texture control results in nonlinear corrosion behavior during long-term immersion, with significant fluctuations in hydrogen evolution rate, insufficient uniformity of corrosion depth, and difficulty in accurately predicting the service life of components. Moreover, this method is mainly applicable to laboratory-scale sample cutting tests, and there is still room for further development in design directly for engineering applications. Summary of the Invention

[0006] To address the shortcomings of existing technologies, such as the excessively rapid corrosion rate of magnesium alloys in marine environments, the difficulty in precisely controlling the corrosion behavior, the nonlinearity of corrosion behavior based on single texture control, and the lack of engineering-customized orientation, this invention provides an orientation-controllable slow-release Mg-Sn-based magnesium alloy extrusion, its preparation method, and its application, in order to obtain an extrusion with controllable differences in corrosion rates between the longitudinal and cross sections and uniform and stable long-term corrosion.

[0007] To achieve this objective, the following solution is provided: This invention provides an orientation-controlled slow-release Mg-Sn based magnesium alloy extrusion material, the microstructure of which includes an α-Mg matrix, a Mg2Sn phase and an Al-Mn intermetallic compound phase; the Mg2Sn phase and the Al-Mn intermetallic compound phase are oriented in a banded pattern along the extrusion direction in the longitudinal section and are randomly oriented in the cross section.

[0008] The extruded material comprises the following components by mass percentage: 3.2~4.3% Sn, 2.4~3.2% Al, 1.1~1.7% Zn, 0.35~0.70% Mn, with the balance being Mg.

[0009] Furthermore, the extruded material has a cylindrical filament texture arranged along the extrusion direction; in the cylindrical filament texture, the [10-10] crystal orientation and the [11-20] crystal orientation are parallel to the extrusion direction, and the normal of the base plane (0001) is perpendicular to the extrusion direction.

[0010] Furthermore, the average grain size of the extruded material cross-section is 15~30 μm; the proportion of large-angle grain boundaries with an orientation difference greater than 10° in the extruded material is not less than 90%; and the proportion of grains with an orientation extension value of less than 1° in the extruded material is not less than 80%.

[0011] Furthermore, the Al-Mn intermetallic compound phase includes at least one of τ-AlMn phase, Al8Mn5 phase and β-Mn phase, with an average size of 0.5~3 μm; Furthermore, the Mg2Sn phase includes a nanoscale Mg2Sn phase dynamically precipitated during extrusion deformation, with an average size of 50~300 nm.

[0012] This invention provides a method for preparing orientation-controlled slow-release Mg-Sn based magnesium alloy extrusions, comprising the following steps: S1. Prepare alloy raw materials according to Sn, Al, Zn, Mn and Mg elements, and then melt, refine, remove slag and semi-continuously cast the alloy raw materials in sequence to obtain alloy ingots. S2. The alloy ingot is subjected to solution treatment, and then cooled to room temperature with water to obtain a solution-treated billet; S3. The solid solution billet is hot-extruded to form a cylindrical filament texture arranged along the extrusion direction, thereby obtaining the Mg-Sn based magnesium alloy extruded material.

[0013] Furthermore, the solution treatment conditions in step S2 are: heat treatment at 410~430℃ for 18~24 h.

[0014] Furthermore, in step S3, the hot extrusion temperature is 390~405℃, the extrusion pressure is 130~160 MPa, the extrusion rate is 0.8~1.5m / min, and the fluctuation range of the extrusion rate does not exceed ±5% of the set value, and the extrusion ratio is 18~24.

[0015] Furthermore, before hot extrusion, the extrusion cylinder and / or extrusion die are preheated to a temperature of 350~380℃.

[0016] This invention provides an application of orientation-controlled slow-release Mg-Sn based magnesium alloy extrusion in the field of marine engineering. The application includes manufacturing at least one of the following: marine sacrificial anodes, temporary positioning components for marine engineering, temporary sealing components for marine engineering, auxiliary components for marine construction, anode blocks for cathodic protection of offshore wind power foundations, anode blocks for cathodic protection of subsea pipelines, sacrificial anodes for coastal bridges, and sacrificial anodes for wharves. Furthermore, the orientation-controlled slow-release Mg-Sn based magnesium alloy extrusion can be used in self-release devices for marine instruments. These self-release devices include at least one of the following: timed release pins for marine observation instruments, self-de-anchoring connectors for seabed deployment equipment, timed release devices for deep-sea samplers, and timed release connectors for marine buoys.

[0017] The present invention also provides an orientation-customized degradable component for marine environments, wherein the load-bearing component is an orientation-controlled release Mg-Sn-based magnesium alloy extrusion, or the load-bearing component is made of an orientation-controlled release Mg-Sn-based magnesium alloy extrusion, and has at least one service-exposed surface.

[0018] Furthermore, the orientation of the service-exposed surface of the load-bearing main body of the load-bearing component is selected from the longitudinal section of the orientation-controlled slow-release Mg-Sn based magnesium alloy extrusion; the orientation of the service-exposed surface of the disintegration-inducing part of the load-bearing component is selected from the cross section of the orientation-controlled slow-release Mg-Sn based magnesium alloy extrusion; the load-bearing main body and the disintegration-inducing part form an orientation gradient structure along the axial or radial direction.

[0019] Furthermore, the load-bearing component of the member is a hollow tubular structure, with the outer surface being the longitudinal section of the extruded material and the inner surface being the cross section of the extruded material.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The alloy composition of this invention is Mg-Sn-Al-Zn-Mn. By adding 3.2-4.3% Sn and optimizing the ratio of Al, Zn, and Mn, the Sn element dynamically precipitates nanoscale Mg2Sn phase during extrusion, which together with the Al-Mn intermetallic compound phase forms a micro-couple cathode. The high Sn content ensures the quantity and distribution density of the Mg2Sn phase, providing a material basis for the subsequent formation of a banded directional distribution. Simultaneously, the addition of Sn does not introduce rare earth elements, maintaining the alloy's green and low-cost characteristics. The raw materials are readily available and the smelting cost is low. The solution treatment and hot extrusion process parameters have a wide range and are fully compatible with existing industrial magnesium / aluminum alloy extrusion production lines, allowing for direct production without equipment modification. Combined with a customized orientation strategy, it can significantly reduce the manufacturing cost of temporary marine engineering facilities and the environmental burden of subsequent recycling.

[0021] 2. This invention, through precise control of the extrusion process parameter window, forms a stable cylindrical filament texture in the Mg-Sn-Al-Zn-Mn non-rare earth alloy system. This ensures that the [10-10] and [11-20] crystal orientations are parallel to the extrusion direction (ED), while the thermodynamically more stable and corrosion-resistant basal plane normals are perpendicular to the extrusion direction. This texture causes the longitudinal section (LS) of the extruded material to primarily expose the less corrosion-resistant cylindrical surfaces, while the cross section (TS) primarily exposes the more corrosion-resistant basal surfaces. Simultaneously, on the LS, the micro-couple cathode phases such as Mg2Sn are oriented along the ED in a banded distribution. The α-Mg matrix surrounding the second phase forms a corrosion filament structure preferentially growing along the ED direction, and the Al-Mn intermetallic compound phase exhibits a high density of random corrosion sites on the TS. The two work synergistically to form directional confined slow corrosion channels (slow release mode) when exposed to LS, with an average rate of 2.39 mm / year; and to form high-density random microcouple corrosion sites (rapid uniform disintegration mode) when exposed to TS, with an average rate of 3.12 mm / year.

[0022] 3. In this invention, the Al-Mn intermetallic compound phase has an average size of 0.5–3 μm, and the Mg₂Sn phase is a dynamically precipitated nanoscale phase (average size 50–300 nm). The fine second phase provides sufficient microcouple driving force while avoiding localized exfoliation corrosion caused by coarse particles. The nanoscale Mg₂Sn phase is uniformly dispersed at grain boundaries and within grains, effectively pinning grain boundaries and refining grains, while ensuring the long-term stability of corrosion behavior.

[0023] 4. This invention achieves a highly uniform recrystallized grain structure by controlling the average grain size to 15-30 μm, ensuring that large-angle grain boundaries with an orientation difference greater than 10° account for no less than 90%, and grains with a GOS value less than 1° account for no less than 80%. This, combined with a stable banded second-phase distribution, eliminates local strain concentration and residual stress, allowing corrosion to progress uniformly at both the macroscopic and microscopic scales. This avoids sudden local pitting corrosion and ensures a uniform distribution of corrosion depth and a linear hydrogen evolution rate. Consequently, hydrogen evolution increases linearly during long-term immersion (720 h), with instantaneous rate fluctuations ≤ ±20% and a corrosion depth standard deviation / mean ≤ 0.30. This highly stable and predictable corrosion behavior eliminates the risks of local pitting outbreaks and rate abrupt changes common in traditional magnesium alloys, enabling precise design of the service life of engineering components.

[0024] 5. This invention transforms the macroscopic anisotropy of extruded materials into parameters that can be directly used in engineering design. By directly selecting LS or TS as the main service exposure surface of the component, or by setting orientation gradients in different parts of the same component (e.g., LS orientation of the load-bearing main body + TS orientation induced by disintegration), directional matching of degradation life windows (e.g., long-term support vs. timed self-destruction) can be achieved without adjusting the alloy composition and extrusion process. This method has strong process compatibility and a high degree of design freedom, greatly simplifying the customization process of marine components. Attached Figure Description

[0025] Figure 1 These are XCT three-dimensional renderings of the orientation-controlled slow-release Mg-Sn based magnesium alloy extrusion of Example 1 and the alloy of Comparative Example 1. Figure 2 The images show the EBSD orientation imaging and (0001) pole figure of the orientation-controlled slow-release Mg-Sn based magnesium alloy extrusion of Example 1 and the alloy of Comparative Example 1. Figure 3 These are high-resolution TEM images of the orientation-controlled slow-release Mg-Sn based magnesium alloy extrusion material of Example 1 and the alloy precipitate of Comparative Example 1. Figure 4 The grain size distribution histograms and GOS diagrams of the cross-sections of the orientation-controlled slow-release Mg-Sn based magnesium alloy extrusion material of Example 1 and the alloy of Comparative Example 1 are shown. Figure 5 SEM backscattered electron images of the longitudinal section of the orientation-controlled slow-release Mg-Sn based magnesium alloy extrusion of Example 1 and the alloy of Comparative Example 1. Figure 6 Comparison of longitudinal and cross-sectional corrosion morphology of the orientation-controlled slow-release Mg-Sn based magnesium alloy extrusion of Example 1 and the alloy of Comparative Example 1 after immersion in 0.1M NaCl solution for 264 h. Figure 7 Corrosion behavior curves of the longitudinal and cross sections of the orientation-controlled slow-release Mg-Sn based magnesium alloy extrusion of Example 1 and the alloy of Comparative Example 1. Figure 8 The potentiodynamic polarization curves of the orientation-controlled slow-release Mg-Sn based magnesium alloy extrusion of Example 1 and the alloy of Comparative Example 1 after immersion in 0.1M NaCl solution for 1 h are shown. Figure 9 The images are XCT three-dimensional reconstruction images of the orientation-controlled slow-release Mg-Sn based magnesium alloy extrusion material in Example 4 of the present invention and the alloy in Comparative Example 1 after being immersed in 0.1M NaCl solution for different times. Detailed Implementation

[0026] The present invention will be further described below with reference to preferred embodiments. The endpoints and any values ​​of the ranges disclosed in the present invention are not limited to the precise ranges or values. These ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed herein.

[0027] In this invention, the product of the peak density of the basal plane (0001) and the number of Mg2Sn phase strips continuously distributed along the extrusion direction per unit area is denoted as the texture-second phase synergy factor (TSF). Specifically: the peak density of the basal plane is measured on a longitudinal section using EBSD (electron backscatter diffraction) technology for surface scanning, with a scanning step size of 0.3~0.5 μm and a scanning area of ​​500 μm × 500 μm. The basal plane (0001) pole figure is calculated using Channel 5 software, and the peak density is read (expressed as a random distribution mrd). The length of the Mg2Sn phase strip distribution is measured on a longitudinal section using SEM (scanning electron microscope) in backscattered electron mode, with a magnification of 1000~2000x. Ten fields of view are randomly selected, and image analysis software (such as Image Pro Plus) is used to count the number of Mg2Sn phase strips with a continuous distribution length of not less than 100 μm along the ED direction per unit area (strips / mm).2 When the TSF value is in the range of 15 to 25, the rate ratio can reach 1.20 to 1.60; when the TSF is ≥ 18, the rate ratio is not lower than 1.35. Those skilled in the art can reasonably control the TSF value by adjusting the process parameters.

[0028] It should be noted that the extruded material of the present invention can be a solid bar, a hollow tube, or a profile. Those skilled in the art will understand that by selecting different extrusion dies and billet shapes, the above-mentioned extruded materials of different forms can be obtained.

[0029] Unless otherwise specified, the experimental methods in the following embodiments are conventional methods, performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions.

[0030] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0031] Example 1 This embodiment provides an orientation-controlled slow-release Mg-Sn based magnesium alloy extrusion, which comprises the following components by mass percentage: 3.8% Sn, 2.8% Al, 1.4% Zn, 0.5% Mn, with impurity elements Fe≤0.003%, Ni≤0.001%, Cu≤0.005%, and the balance being Mg.

[0032] The method for preparing orientation-controlled slow-release Mg-Sn based magnesium alloy extrusions using the above raw materials is as follows: S1. After the alloy raw materials are successively smelted, refined, deslag-removed and semi-continuously cast, an alloy ingot is obtained. S2. The alloy ingot is kept at 420℃ for 20 h for solution treatment, and then cooled to room temperature to obtain a solution-treated billet. As a preferred embodiment, the solution treatment can also employ a two-stage solution treatment process: first, the alloy ingot is held at 390~410℃ for 9~12 h, then heated to 440~460℃ and held for 14~18 h, and finally water-cooled to room temperature. This two-stage solution treatment process can also obtain a solution-treated billet suitable for subsequent hot extrusion, and is particularly suitable for cases where the content of low-melting-point eutectic phases in the as-cast structure is high, effectively avoiding the risk of overheating caused by direct high-temperature solution treatment; S3. The solution-treated billet is hot-extruded at a temperature of 398℃, a pressure of 145 MPa, a speed of 1.0 m / min, and the fluctuation of the extrusion speed does not exceed ±5% of the set value. The extrusion ratio is 20, forming a cylindrical filamentary structure with [10-10] and [11-20] crystal orientations parallel to the extrusion direction, to obtain the Mg-Sn based magnesium alloy extruded material, denoted as TAZ431 (Mg-4Sn-3Al-1Zn-0.4Mn). The actual measured composition is: 3.98%Sn, 2.73%Al, 1.5%Zn, 0.44%Mn, with impurity elements Fe≤0.003%, Ni≤0.001%, Cu≤0.005%, and the balance being Mg.

[0033] In a preferred embodiment, before the hot extrusion, the extrusion cylinder and / or extrusion die are preheated to 360°C, and the extrusion die is preheated to 370°C; wherein the Al-Mn intermetallic compound phase includes τ-AlMn phase and A l8 Mn5 phase.

[0034] The microstructure characteristics and properties of the TAZ431 extruded material prepared in this embodiment were tested as follows: like Figure 1 Figures b and d, and Table 1, show the XCT 3D rendering of the extruded material. The as-cast microstructure already contains a large amount of Mg2Sn phase (195 particles, 3.08% volume fraction) and Al-Mn phase (107 particles, 0.39% volume fraction), providing a material basis for the formation of continuous or semi-continuous banded directional distribution along the extrusion direction during subsequent extrusion; while β-Mg... 17 Al 12 The +τ-MgAlZn eutectic phase (34 particles, volume fraction 19.65%) was basically dissolved after subsequent solid solution treatment, and Al and Zn elements dissolved into the α-Mg matrix.

[0035] like Figure 2 EBSD analysis of b confirms that the TAZ431 extruded material of this embodiment has a typical cylindrical filament texture. Figure 2 The d-pole diagram shows that the crystal orientations of [10-10] and [11-20] are parallel to the extrusion direction, the normal of the basal plane (0001) is perpendicular to the extrusion direction, and the peak density of the basal plane reaches 14.5 mrd.

[0036] High-resolution TEM (transmission electron microscopy) was used to characterize the long, rod-shaped precipitates of TAZ431 extruded material. Figure 3 As shown in ab, after calibration of the selected area electron diffraction pattern and high-resolution image of the precipitated phase region, the phase was identified as Mg2Sn phase; Figure 3cd represents HADDF images of precipitates observed under different band axes in aged TAZ431 to identify the spatial orientation of the precipitates. Analysis shows that the long axis of most rod-shaped Mg2Sn precipitates in the TAZ431 alloy is parallel to the basal plane of α-Mg. Observed along the

[0002] band axis, the long axis of the precipitate is parallel to the <11-20> α-Mg direction, exhibiting three equivalent orientations; observed along the [11-20] band axis, the long axis of the precipitate is parallel to the (0002) crystal plane. Based on the above results, it can be inferred that the columnar Mg2Sn phase is a basal plane precipitate with its long axis along the <11-20> α-Mg. From the density of precipitates with different morphologies, this basal plane Mg2Sn precipitate is the main precipitate in TAZ431, which is rod-shaped / needle-shaped, with a length of 200~500 nm and a width of 30~80 nm.

[0037] like Figure 4 Grain statistics for b and d show that the average grain size in the cross section is about 20 μm, and the proportion of large-angle grain boundaries with an orientation difference greater than 10° reaches 93%. Moreover, the GOS value of most grains is less than 1°, indicating that the extruded material has a small and uniform grain size, with large-angle grain boundaries as the main feature and consistent internal orientation of the grains. It belongs to a typical recrystallized structure, which is consistent with the product design expectations.

[0038] like Figure 5 As shown in Figure 1, the SEM backscattered electron image of the TAZ431 alloy extrusion material reveals a diffusely random cross-section. Along the ED direction in the longitudinal section, numerous banded strips are distributed. The Mg2Sn phase exhibits a continuous or semi-continuous banded directional distribution along the extrusion direction, while the Al-Mn phase remains granular and dispersed between the bands. The continuous length of the Mg2Sn bands exceeds 100 μm, with a density of 1.8 strips / mm. 2 .

[0039] Calculations show that the product (TSF) of the peak density on the basal plane (0001) and the number of Mg2Sn phase strips with a continuous distribution length of not less than 100 μm along the extrusion direction is approximately 26.1. This demonstrates that the extruded material achieves a high degree of coupling between "strong cylindrical texture" and "Mg2Sn phase banded distribution," resulting in a significantly lower corrosion rate in the longitudinal section than in the cross section of the TAZ431 extruded material, and long-term linear corrosion stability.

[0040] like Figure 6The corrosion morphology tests shown indicate that after immersion in 0.1 M NaCl solution for 264 h, corrosion filaments on the longitudinal section of the TAZ431 extruded material preferentially grow along the ED direction, while the corrosion filaments on the cross section exhibit uniformly distributed random pitting corrosion. Furthermore, in the early stage (immersion time no more than 24 h), corrosion filaments on the longitudinal section LS of the TAZ431 extruded material preferentially grow along the ED direction, with a maximum pit depth of 18–28 μm, while corrosion filaments on the cross section TS exhibit random directional distribution, with a maximum pit depth of 12–18 μm. In the later stage (immersion time no less than 240 h), the maximum pit depth on the cross section is greater than that on the longitudinal section LS, and the ratio of the maximum pit depth on the cross section to that on the longitudinal section is no less than 1.3. This verifies that the banded second phase continuously plays a confinement role during long-term corrosion, keeping the corrosion direction consistently controlled.

[0041] like Figure 7 The corrosion performance test results shown in the diagram indicate that the hydrogen evolution of TAZ431 extruded material increases approximately linearly with immersion time, without significant slope changes or abrupt changes. After immersion for 384 hours, the average corrosion rate of its longitudinal section was 2.39 mm / year, and the average corrosion rate of its cross section was 3.12 mm / year, with a cross-sectional / longitudinal rate ratio of 1.31. The instantaneous corrosion rate curve further shows that throughout the immersion process, the instantaneous corrosion rates of the longitudinal and cross sections of TAZ431 consistently fluctuated slightly around 2.39 mm / year and 3.12 mm / year, respectively, without any rate overshooting or drastic fluctuations. These results demonstrate that the corrosion behavior of TAZ431 extruded material is highly stable during long-term immersion, exhibiting significant anisotropy with no change in direction over time. The longitudinal section consistently exhibits a slow-release mode, while the cross section consistently exhibits a rapid disintegration mode.

[0042] like Figure 8 The potentiodynamic polarization curves shown indicate that the cathode branches of the longitudinal and cross sections of the TAZ43 extruded material highly coincide, suggesting that the difference in grain orientation has little impact on the cathodic reaction kinetics. The initial corrosion rates obtained from Tafel fitting (Table 2) are 0.18 mm / year for TAZ431-LS and 0.48 mm / year for TAZ431-TS, with the cross section being higher than the longitudinal section, consistent with the results of long-term immersion.

[0043] Example 2 This embodiment provides an orientation-controlled slow-release Mg-Sn based magnesium alloy extrusion, which comprises the following components by mass percentage: 3.2% Sn, 2.4% Al, 1.1% Zn, 0.35% Mn, with impurity elements Fe≤0.003%, Ni≤0.001%, Cu≤0.005%, and the balance being Mg.

[0044] The method for preparing orientation-controlled slow-release Mg-Sn based magnesium alloy extrusions using the above raw materials is as follows, including the following steps: S1. After the alloy raw materials are successively smelted, refined, deslag-removed and semi-continuously cast, an alloy ingot is obtained. S2. The alloy ingot is kept at 410℃ for 24 h for solution treatment, and then cooled to room temperature to obtain a solution-treated billet. S3. Preheat the extrusion cylinder to 360°C and the extrusion die to 370°C. Hot extrude the solution-treated billet at 390°C, with an extrusion pressure of 130 MPa, an extrusion speed of 0.8 m / min, and an extrusion ratio of 18. This forms a cylindrical filament texture arranged along the extrusion direction, yielding the Mg-Sn-based magnesium alloy extruded material. The actual measured composition is: Sn 3.18%, Al 2.38%, Zn 1.12%, Mn 0.34%, balance Mg, and impurities Fe≤0.003%, Ni≤0.001%, Cu≤0.005%. Testing showed that this extruded material has the same cylindrical filament texture and second-phase banded distribution as in Example 1.

[0045] Example 3 This embodiment provides an orientation-controlled slow-release Mg-Sn based magnesium alloy extrusion, which comprises the following components by mass percentage: 4.3% Sn, 3.2% Al, 1.7% Zn, 0.70% Mn, with impurity elements Fe≤0.003%, Ni≤0.001%, Cu≤0.005%, and the balance being Mg.

[0046] The method for preparing orientation-controlled slow-release Mg-Sn based magnesium alloy extrusions using the above raw materials is as follows, including the following steps: S1. After the alloy raw materials are successively smelted, refined, deslag-removed and semi-continuously cast, an alloy ingot is obtained. S2. The alloy ingot is kept at 430℃ for 18 h for solution treatment, and then cooled to room temperature to obtain a solution-treated billet. S3. The extrusion cylinder is preheated to 350℃. The solution-treated billet is then hot-extruded at 405℃, with an extrusion pressure of 160 MPa, an extrusion speed of 1.5 m / min, and an extrusion ratio of 24. This results in a cylindrical filament texture arranged along the extrusion direction, yielding the Mg-Sn-based magnesium alloy extruded material. The actual measured composition is: Sn 4.28%, Al 3.18%, Zn 1.68%, Mn 0.69%, balance Mg, and impurities Fe≤0.003%, Ni≤0.001%, Cu≤0.005%. Testing revealed that this extruded material exhibits the same cylindrical filament texture and second-phase banded distribution as in Example 1.

[0047] Comparative Example 1 This comparative example provides an AZ31 alloy, which is prepared without the addition of Sn element and is designated as Mg-3Al-1Zn-0.4Mn alloy. Its preparation method is the same as that in Example 1. The actual measured composition of the AZ31 alloy is 4.16% Al, 0.89% Zn, 0.41% Mn, with impurity elements Fe≤0.003%, Ni≤0.001%, Cu≤0.005%, and the balance being Mg.

[0048] The properties of the TAZ431 extruded material of Example 1 were compared with those of the AZ31 alloy of Comparative Example 1: Figure 1 The comparison of XCT 3D renderings shows that (each particle is colored according to its connectivity, with particles of a single color indicating that the phase has good connectivity in 3D space), Figure 1 ad represents the β-Mg in the AZ31-C (as-cast) alloy. 17 Al 12 +τ-MgAlZn eutectic phase, β-Mg in TAZ431-C (as-cast) alloy 17 Al 12 +τ-MgAlZn eutectic phase, Al-Mn phase in AZ31-C alloy, and Mg2Sn phase in TAZ431-C alloy. Comparison shows that TAZ431 as-cast microstructure contains a large amount of Mg2Sn phase, while AZ31 contains no Mg2Sn phase at all; β-Mg in TAZ431... 17 Al 12 The number of +τ-MgAlZn eutectic phase particles (34) is much greater than that of AZ31 (1), while the number of Al-Mn phase particles is similar for both.

[0049] The particle number and volume fraction of each phase are shown in Table 1.

[0050] Table 1

[0051] Figure 2 EBSD orientation imaging of ab and Figure 2 The cd pole figure comparison shows that the TAZ431 alloy extruded material has a cylindrical filament structure, with the [10-10] and [11-20] crystal orientations parallel to the extrusion direction, and the basal plane (0001) normal perpendicular to the extrusion direction. The basal plane pole density peak is 14.5 mrd. Compared with the TAZ431 alloy extruded material, AZ31 exhibits a common basal plane texture. This difference in texture determines that the corrosion anisotropy directions of the two alloys are completely different.

[0052] Figure 4A comparison of the grain size distribution diagrams of AZ31-TS and TAZ431-TS shows that LABs (Large-Angle Grain Boundaries) account for 7% in both alloys; grain boundaries with an orientation difference greater than 10° are classified as large-angle grain boundaries (HAGBs), accounting for 93% in both AZ31-TS and TAZ431-TS alloys. Based on the grain size distribution obtained from the statistical analysis of large-angle grain boundaries, the grain sizes of both alloys are mainly concentrated in the range of 0–80 µm, with an average grain size of approximately 21 µm for AZ31-TS and TAZ431-TS, indicating a relatively similar size distribution. Figure 4 As can be seen from the GOS diagram of cd, most grains have a GOS value <1°, indicating that the residual stress in the alloy has been largely removed. This proves that the difference in corrosion performance mainly stems from the texture type and the distribution of the second phase, rather than grain size or the degree of recrystallization.

[0053] Figure 5 The SEM backscattered electron image shows that Figure 5 The cross-section of the TAZ431 alloy extruded material in cd exhibits a diffusely random distribution, while the longitudinal section shows numerous banded strips distributed along the ED direction. The Mg2Sn phase is visible as a continuous or semi-continuous banded directional distribution along the extrusion direction, while the Al-Mn phase remains granular and dispersed between the bands. Figure 5 In ab, there is no banded structure on the longitudinal section of AZ31, and the second phase is randomly dispersed.

[0054] The extruded material was processed into two types of samples: one with the exposed surface as a longitudinal section and the other with the exposed surface as a cross section. These samples were then immersed in a 0.1 M NaCl solution for 264 hours. Figure 6 The corrosion morphology comparison shows that on the longitudinal section of TAZ431, corrosion filaments preferentially grow along the ED direction, while the corrosion on the cross section exhibits uniformly distributed random pitting. In contrast, the corrosion morphology of the two sections of AZ31 shows little difference, with no directional corrosion filaments. This directly verifies the guiding and confining effect of the banded second relative corrosion path in TAZ431, achieving an anisotropic corrosion morphology.

[0055] Figure 7 The comparison of the cumulative hydrogen evolution amount-time curves shows that throughout the experiment, the total hydrogen evolution amount per unit area of ​​the TAZ431 alloy extruded material was higher than that of AZ31 at all cross sections. For extruded TAZ431, the hydrogen evolution amount in the cross section was consistently higher than that in the longitudinal section, while the difference in hydrogen evolution amount between the transverse and longitudinal sections of the AZ31 alloy was smaller. The average corrosion rate of the alloy was calculated using the total hydrogen evolution amount per unit area. Figure 7The histogram comparison of average corrosion rates (b) shows that the order of corrosion rates for the four test surfaces is: TAZ431-TS > TAZ431-LS > AZ31-LS > AZ31-TS, with average corrosion rates of 3.12, 2.39, 0.19, and 0.18 mm / year, respectively. This result indicates that the average corrosion rate of all cross-sections of TAZ431 is higher than that of the AZ31 alloy. For extruded TAZ431, the corrosion rate of the TS test surface is higher than that of the LS test surface, while the AZ31 alloy shows the opposite trend, with the corrosion rate of the LS test surface slightly higher than that of the TS test surface. Furthermore, the difference in average corrosion rates between the transverse and longitudinal sections of TAZ431 is greater than that of AZ31, indicating that TAZ431 exhibits stronger corrosion anisotropy compared to AZ31. Figure 7 The slope at each immersion time point in a is taken as the instantaneous corrosion rate (V) of the alloy. iH (This is used to plot a graph of how it changes over time.) Figure 7 A comparison of the instantaneous corrosion rate-time curves for c shows that the instantaneous corrosion rates of various alloys all revolve around their average corrosion rates ( Figure 7 b) Fluctuating up and down, the instantaneous corrosion rate of each section of TAZ431 was consistently higher than that of AZ31 throughout the immersion process, and the instantaneous corrosion rate of its cross-section was consistently higher than that of its longitudinal section. For AZ31, as... Figure 7 The corrosion rate-time curves of d show that the instantaneous corrosion rate of the longitudinal section is higher than that of the cross section within 0~324 h, while the instantaneous corrosion rate of the cross section surpasses that of the longitudinal section within 324~384 h.

[0056] To investigate the corrosion behavior of the alloy during the initial immersion stage, in this embodiment, the cross-sections of extruded AZ31 and TAZ431 were immersed in 0.1 M NaCl solution. After the open circuit potential stabilized, the potentiodynamic polarization curves of the samples were tested. Figure 8 The comparison shows that the cathode branches of the same alloy exhibit a very high degree of overlap under different cross sections, and their curve morphology is basically consistent with the order of magnitude of the current density. In contrast, the curve characteristics between AZ31 and TAZ431 show significant differences. Therefore, the difference in grain orientation has a relatively limited impact on the cathode reaction kinetics, while the introduction of Sn significantly changes the electrochemical response of the cathode branches. On the anode branches, both AZ31-LS and TAZ431-TS show a sudden increase in anolyte current, indicating that the surface film has been damaged and local corrosion has been induced. The corresponding pitting potentials are -1.31V (SCE) and -1.35V (SCE), respectively. Since Tafel fitting is not suitable for the anode branches, Tafel fitting is performed on the cathode branches based on three sets of parallel experimental results to obtain the corrosion potential (E) of the alloy. corr ), corrosion current density (I) corr ), cathode Tafel slope ( c ), and the corrosion rate (ν) calculated from the corrosion current density p ). As shown in Table 2, the order of the corrosion potential of the alloy surface from negative to positive is AZ31-TS < TAZ431-TS < TAZ431-LS < AZ31-LS, and the order of the calculated corrosion rate is AZ31-TS > TAZ431-TS > TAZ431-LS > AZ31-LS. Therefore, in the initial stage of immersion, the longitudinal section mainly with the

[0001] grain orientation distribution helps to reduce the instantaneous corrosion rate of the alloy, and the introduction of Sn has a more significant impact on the cathodic branch response. It should be noted that the polarization curve can only reflect the instantaneous electrochemical behavior of the material after the open-circuit potential is stabilized, and cannot predict the evolution of the corrosion product layer and its impact on corrosion kinetics during long-term immersion.

[0057] Table 2

[0058] Example 4 This example provides an orientation-customized degradation component for a marine environment. The bearing component is a hollow tubular structure, and the preparation method of this hollow tubular structure is as follows: Prepare an alloy according to the raw material composition of Example 1 (Sn: 3.8%, Al: 2.8%, Zn: 1.4%, Mn: 0.5%, balance Mg). After melting, refining, and semi-continuous casting, perform a solution treatment at 420 °C for 20 h, cool it to room temperature with water, process the solution-state billet into a hollow tube blank, and then perform hot extrusion. The preheating temperature of the extrusion cylinder is 360 °C, the preheating temperature of the extrusion die is 370 °C, the extrusion temperature is 398 °C, the extrusion pressure is 145 MPa, the extrusion speed is 1.0 m / min, and the extrusion ratio is 20.

[0059] The outer diameter of the extruded hollow pipe is 80 mm, and the wall thickness is 10 mm.

[0060] Among them, the service exposure surface orientation of the bearing main body part of the hollow tubular structure is selected from the longitudinal section, so that this part maintains mechanical integrity during service; the service exposure surface orientation of the disassembly-induced part is selected from the cross section, so that this part promotes the component to accelerate disassembly in the depth direction after service; the bearing main body part and the disassembly-induced part form an orientation gradient structure along the axial or radial direction.

[0061] The orientation-customized degradable component for marine environments is made of extruded material, and its degradation rate is anisotropic. When a lower degradation rate is required, and the component needs to maintain mechanical integrity for a longer period during service, the main service exposed surface of the load-bearing component is the longitudinal section of the extruded material. When a higher degradation rate is required, and the component needs to disintegrate rapidly in the depth direction after service, the main service exposed surface of the load-bearing component is the cross section of the extruded material. Different exposed surface orientations are used in different parts of the same load-bearing component to form an axial or radial orientation gradient structure to obtain a zoned and controllable degradation rate. The angle between the service exposed surface and the extrusion direction ED of the extruded material is selected within the range of 0° to 90° according to the required degradation rate window. Furthermore, those skilled in the art will understand that when the component consists only of load-bearing components, the hollow tube itself is the orientation-customized degradable component for marine environments.

[0062] Testing revealed that the outer surface of the hollow tube has a longitudinal section, exhibiting the same cylindrical filamentary texture and second-phase banded distribution as in Example 1. Immersion in 0.1 M NaCl solution for 384 h resulted in an average corrosion rate of 2.39 mm / year on the outer surface. This hollow tube can be used as a temporary marine support pipe, providing long-term structural support on the outer surface, while the inner surface undergoes accelerated corrosion and disintegration after service completion, eliminating the need for recycling. After non-destructive DCT three-dimensional grain orientation testing, both tube materials were immersed in 0.1 M NaCl solution, and XCT three-dimensional reconstruction images of AZ31 and TAZ431 alloys after immersion for a certain period were obtained. Figure 9 As shown, where, Figure 9 a, e, i, and m are the initial three-dimensional grain orientation maps of the two alloys from different perspectives. After a series of three-dimensional registrations, the following results were obtained: Figure 9 The three-dimensional XCT images of bc, fg, jk, and no after immersion for 0 h and corresponding times (AZ31: 264 h; TAZ431: 72 h) were further analyzed and processed to obtain... Figure 9 The registration results of corrosion-dissolved grains (DCT) and XCT in d, h, l, and p are shown in the figure. After a certain immersion time, a large number of grains dissolve on the surface of AZ31 pipe compared to TAZ431 pipe.

[0063] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. An orientation-controlled slow-release Mg-Sn based magnesium alloy extrusion, characterized in that, Its microstructure includes an α-Mg matrix, a Mg2Sn phase, and an Al-Mn intermetallic compound phase; the Mg2Sn phase and the Al-Mn intermetallic compound phase are oriented in a banded pattern along the extrusion direction in the longitudinal section and are randomly oriented in the cross section. The extruded material comprises the following components by mass percentage: 3.2~4.3% Sn, 2.4~3.2% Al, 1.1~1.7% Zn, 0.35~0.70% Mn, with the balance being Mg.

2. The orientation-controlled slow-release Mg-Sn based magnesium alloy extrusion material according to claim 1, characterized in that, The extruded material has a cylindrical filament texture arranged along the extrusion direction; in the cylindrical filament texture, the [10-10] crystal orientation and the [11-20] crystal orientation are parallel to the extrusion direction, and the normal of the base plane (0001) is perpendicular to the extrusion direction.

3. The orientation-controlled slow-release Mg-Sn based magnesium alloy extrusion material according to claim 1, characterized in that, The average grain size of the extruded material is 15~30 μm; the proportion of large-angle grain boundaries with an orientation difference greater than 10° in the extruded material is not less than 90%, and the proportion of grains with an orientation extension value of less than 1° is not less than 80%.

4. The orientation-controlled slow-release Mg-Sn based magnesium alloy extrusion material according to claim 1, characterized in that, The Al-Mn intermetallic compound phase includes at least one of τ-AlMn phase, Al8Mn5 phase and β-Mn phase, with an average size of 0.5~3μm.

5. The orientation-controlled slow-release Mg-Sn based magnesium alloy extrusion material according to claim 1, characterized in that, The Mg2Sn phase includes a nanoscale Mg2Sn phase dynamically precipitated during extrusion deformation, with an average size of 50~300 nm.

6. A method for preparing an orientation-controlled slow-release Mg-Sn based magnesium alloy extrusion as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Prepare alloy raw materials according to Sn, Al, Zn, Mn and Mg elements, and then melt, refine, remove slag and semi-continuously cast the alloy raw materials in sequence to obtain alloy ingots. S2. The alloy ingot is subjected to solution treatment, and then cooled to room temperature with water to obtain a solution-treated billet. S3. The solid solution billet is hot-extruded to form a cylindrical filament texture arranged along the extrusion direction, thereby obtaining the Mg-Sn based magnesium alloy extruded material.

7. The method for preparing an orientation-controlled slow-release Mg-Sn based magnesium alloy extrusion according to claim 6, characterized in that, The conditions for solution treatment in step S2 are: heat treatment at 410~430℃ for 18~24 h.

8. The method for preparing an orientation-controlled slow-release Mg-Sn based magnesium alloy extrusion according to claim 6, characterized in that, In step S3, the hot extrusion temperature is 390~405℃, the extrusion pressure is 130~160 MPa, the extrusion rate is 0.8~1.5m / min, and the fluctuation range of the extrusion rate does not exceed ±5% of the set value, and the extrusion ratio is 18~24.

9. The method for preparing an orientation-controlled slow-release Mg-Sn based magnesium alloy extrusion according to claim 6, characterized in that, Before hot extrusion, the extrusion cylinder and / or extrusion die are preheated to a temperature of 350~380℃.

10. The application of an orientation-controlled slow-release Mg-Sn based magnesium alloy extrusion as described in any one of claims 1-5 in the field of marine engineering.

11. A customizable biodegradable component for marine environments, characterized in that, The load-bearing component of the structure is an orientation-controlled slow-release Mg-Sn based magnesium alloy extrusion as described in any one of claims 1-5, having at least one service-exposed surface.

12. The orientation-customized degradable component for marine environments as described in claim 11, characterized in that, The orientation of the service exposure surface of the load-bearing main body of the load-bearing component is selected from the longitudinal section; the orientation of the service exposure surface of the disintegration-induced part of the load-bearing component is selected from the cross section; the load-bearing main body and the disintegration-induced part form an orientation gradient structure along the axial or radial direction.

13. A customizable degradable component for marine environments according to claim 11, characterized in that, The load-bearing component of the structure is a hollow tubular structure with a longitudinal section on the outer surface and a cross section on the inner surface.

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