A method for improving the microstructure and corrosion uniformity of low-temperature extruded magnesium alloys

Abstract

This invention provides a method for improving the microstructure and corrosion uniformity of low-temperature extruded magnesium alloys, belonging to the field of magnesium alloy preparation and processing. The method includes the following steps: S1: Cutting a low-alloy element content magnesium alloy ingot and removing the surface oxide layer to obtain a cast sample; S2: Performing pulsed current homogenization treatment on the cast sample; S3: Removing the surface oxide layer from the homogenized alloy to process it into an extrusion billet; S4: Performing low-temperature extrusion treatment on the extrusion billet under pulsed current assistance. This invention improves the microstructure and corrosion uniformity of low-temperature extruded magnesium alloys while ensuring high strength and plasticity, and is suitable for the efficient and energy-saving preparation of biodegradable magnesium alloy extruded bars and sheets.

Description

Technical Field

[0001] This invention belongs to the field of magnesium alloy preparation and processing, and specifically relates to a method for improving the microstructure and corrosion uniformity of low-temperature extruded magnesium alloys. Background Technology

[0002] Magnesium alloys are currently the lightest commercially available metallic engineering materials globally. Compared to other commonly used traditional materials, magnesium alloys possess advantages such as low density, high specific strength, low elastic modulus, good heat dissipation, strong impact resistance and creep resistance, strong damping and noise reduction capabilities, and excellent electromagnetic shielding performance. In recent years, magnesium alloys have gained increasing attention due to their good biocompatibility, biodegradability, and low density (1.7–2.0 g / cm³). 3 With an elastic modulus close to that of human bone (41–45 GPa), magnesium alloys have attracted increasing attention as biodegradable implant materials, especially in orthopedic implants and vascular stents. However, the preparation of biodegradable magnesium alloys is still subject to many limitations. First, their strength and ductility are difficult to match effectively due to limitations in the manufacturing process. Second, their degradation rate in body fluids is too fast and prone to local corrosion, leading to subcutaneous gas bubble accumulation and premature loss of mechanical integrity, thus losing their fixation and support function at the implantation site.

[0003] Conventional extrusion deformation is a simple process and an important method for producing magnesium alloy bars and sheets. Before extrusion deformation, a long-term high-temperature homogenization treatment is generally required for the cast alloy. This process causes the original grains to grow and coarsen, but it fails to effectively promote the dissolution of the second phase and the uniform distribution of alloying elements. Simply changing the conventional extrusion parameters to synergistically improve the strength, plasticity, and corrosion resistance of magnesium alloys is quite difficult because: high-temperature extrusion easily yields a uniform recrystallized structure, which is beneficial for uniform corrosion of magnesium alloys, but the growth and coarsening of recrystallized grains leads to a decrease in material strength; low-temperature extrusion can improve the mechanical properties of magnesium alloys by obtaining heterogeneous structures, but there is a problem of poor microstructure uniformity leading to deterioration of corrosion resistance; the second phase breaks up during extrusion and forms unevenly distributed particle bands along the extrusion direction, leading to severe galvanic corrosion.

[0004] Low-temperature extrusion has a better application prospect, but although existing low-temperature extruded magnesium alloys have high strength and plasticity, their microstructure and corrosion uniformity are poor, which cannot meet the performance requirements of biodegradable magnesium alloys. In order to improve this problem, it is necessary to provide a method to improve the microstructure and corrosion uniformity of low-temperature extruded magnesium alloys. Summary of the Invention

[0005] The purpose of this invention is to provide a method for improving the microstructure and corrosion uniformity of low-temperature extruded magnesium alloys. This method can reduce the homogenization treatment time and temperature of magnesium alloys, promote the dissolution and diffusion of the second phase and the uniform distribution of alloying elements; reduce the low-temperature extrusion forming pressure, suppress the formation of mixed crystal bands, promote dynamic recrystallization and the dispersed distribution of the second phase; reduce energy consumption and carbon emissions, and improve the microstructure and corrosion uniformity of low-temperature extruded magnesium alloys while ensuring high strength and plasticity, thereby achieving efficient and energy-saving preparation of biodegradable magnesium alloy extruded bars and sheets.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A method for improving the microstructure and corrosion uniformity of low-temperature extruded magnesium alloys specifically includes the following steps:

[0008] S1: Cut the magnesium alloy ingot with low alloying element content (the content of elements other than magnesium is <5wt.%) and remove the surface oxide layer to obtain the as-cast sample;

[0009] S2: The purpose of pulsed current homogenization treatment on the as-cast sample is to promote the dissolution and diffusion of the second phase and the uniform distribution of alloying elements;

[0010] S3: Remove the surface oxide layer from the homogenized alloy and process it into an extruded billet;

[0011] S4: Under the assistance of pulsed current, the extruded billet is subjected to low-temperature extrusion treatment to suppress the formation of mixed crystal bands, promote the occurrence of dynamic recrystallization, and the dispersion distribution of the second phase.

[0012] In the above methods:

[0013] In step S2, the pulse current homogenization process includes: connecting the as-cast sample to the electrode, setting the applied pulse current, recording the sample temperature rise, turning off the pulse current device after the set processing time is reached, and then cooling the sample in water.

[0014] In step S2, the temperature rise of the sample under the action of pulsed current is in the range of 50-300℃, and the cooling water temperature is 30-40℃.

[0015] In step S2, the pulse current processing parameters are: pulse voltage: 0-36V, pulse frequency: 10-20000Hz, preferably 50-7000Hz; duty cycle: 10-20%; processing time: 5-30min, preferably 5-20min.

[0016] In step S3, the height-to-diameter ratio of the extruded billet is 5-7:7.

[0017] In step S4, the low-temperature extrusion process includes: preheating the extrusion billet and die, connecting electrodes, then setting a pulsed current and starting the extruder, monitoring the extrusion temperature, and turning off the pulsed current device after extrusion is completed. Low-temperature extrusion aims to suppress grain growth and achieve higher strength and plasticity. Simultaneously, applying a pulsed current utilizes both thermal and non-thermal effects to reduce the low-temperature extrusion forming pressure, suppress the formation of mixed crystal bands, promote dynamic recrystallization, and facilitate the dispersed distribution of the second phase.

[0018] In step S4, the preheating temperature of the extruded blank and the die is 100-250℃.

[0019] In step S4, the extrusion ratio is 10-36:1 and the extrusion speed is 0.05-1 mm / s.

[0020] In step S4, the applied pulse current parameters are: pulse voltage: 0-36V, pulse frequency 10-20000Hz, preferably 1000-15000Hz; duty cycle 10-20%.

[0021] The present invention also provides a magnesium alloy obtained by the method, which has a tensile strength of 290-380 MPa, a yield strength of 260-360 MPa, a dynamic recrystallization volume fraction >85%, and can be uniformly corroded in a 0.9 wt.% NaCl solution with a corrosion rate of <0.3 mm / year.

[0022] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0023] This invention reduces the homogenization time and temperature of magnesium alloys while promoting the dissolution and diffusion of the second phase and the uniform distribution of alloying elements. It also reduces the low-temperature extrusion forming pressure, inhibits the formation of mixed crystal bands, promotes dynamic recrystallization, and facilitates the dispersed distribution of the second phase, thereby reducing energy consumption and carbon emissions. This invention improves the microstructure and corrosion uniformity of low-temperature extruded magnesium alloys while maintaining high strength and plasticity, making it suitable for the efficient and energy-saving preparation of biodegradable magnesium alloy extruded bars and sheets. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1(a) is the electron backscattering diffraction pattern of Example 1, and Figure 1(b) is the electron backscattering diffraction pattern of Comparative Example 1.

[0026] Figure 2 These are the potentiodynamic polarization curves of Example 2 and Comparative Example 2 in 0.9% NaCl. Detailed Implementation

[0027] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be described in detail below with reference to specific embodiments. It should be understood that the embodiments described in this specification are merely illustrative and not intended to limit the scope of the invention.

[0028] Example 1:

[0029] This embodiment uses a Mg-2.5Zn-0.5Zr-0.5Nd alloy with the content of alloying elements other than Mg <5wt.%. The specific preparation steps are as follows:

[0030] S1: The magnesium alloy ingot is cut and the surface oxide layer is removed to obtain the sample;

[0031] S2: Connect the sample to the electrode, set the applied pulse current, pulse voltage 15V, pulse frequency 60Hz, duty cycle 10%, process for 15min and then turn off the pulse current device, and then cool the sample in water at 30℃.

[0032] S3: The alloy after homogenization treatment has its surface oxide layer removed and is processed into an extruded billet with a height-to-diameter ratio of 5:7;

[0033] S4: Preheat the extruded billet and die to 220℃, connect the electrodes, set the loading pulse current, pulse voltage 11V, pulse frequency 1000Hz, duty cycle 13%, and start the extruder at the same time with an extrusion ratio of 16:1 and an extrusion speed of 0.2mm / s. After extrusion is completed, turn off the pulse current device.

[0034] Example 2:

[0035] This embodiment uses a Mg-2.5Zn-0.5Ca alloy with the content of alloying elements other than Mg being <5 wt.%. The specific preparation steps are as follows:

[0036] S1: The magnesium alloy ingot is cut and the surface oxide layer is removed to obtain the sample;

[0037] S2: Connect the sample to the electrode, set the applied pulse current, pulse voltage 15V, pulse frequency 80Hz, duty cycle 10%, process for 20min and then turn off the pulse current device, and then cool the sample in water at 35℃.

[0038] S3: The alloy after homogenization treatment has its surface oxide layer removed and is processed into an extruded billet with a height-to-diameter ratio of 5:7;

[0039] S4: Preheat the extruded billet and die to 200℃, connect the electrodes, set the loading pulse current, pulse voltage 11V, pulse frequency 1200Hz, duty cycle 15%, and start the extruder at the same time with an extrusion ratio of 25:1 and an extrusion speed of 0.15mm / s. After extrusion is completed, turn off the pulse current device.

[0040] Example 3:

[0041] This embodiment uses a Mg-2.5Zn-0.5Mn alloy with the content of alloying elements other than Mg <5wt.%. The specific preparation steps are as follows:

[0042] S1: The magnesium alloy ingot is cut and the surface oxide layer is removed to obtain the sample;

[0043] S2: Connect the sample to the electrode, set the applied pulse current, pulse voltage 17V, pulse frequency 50Hz, duty cycle 10%, process for 10min and then turn off the pulse current device, and then cool the sample in water at 30℃.

[0044] S3: The alloy after homogenization treatment has its surface oxide layer removed and is processed into an extruded billet with a height-to-diameter ratio of 5:7;

[0045] S4: Preheat the extruded billet and die to 190℃, connect the electrodes, set the loading pulse current, pulse voltage 12V, pulse frequency 800Hz, duty cycle 20%, and start the extruder at the same time with an extrusion ratio of 10:1 and an extrusion speed of 0.1mm / s. After extrusion is completed, turn off the pulse current device.

[0046] Example 4:

[0047] This embodiment uses a Mg-2.5Zn-0.5Zr alloy with the content of alloying elements other than Mg <5wt.%. The specific preparation steps are as follows:

[0048] S1: The magnesium alloy ingot is cut and the surface oxide layer is removed to obtain the sample;

[0049] S2: Connect the sample to the electrode, set the applied pulse current, pulse voltage 18V, pulse frequency 55Hz, duty cycle 10%, process for 20min and then turn off the pulse current device, and then cool the sample in water at 35℃.

[0050] S3: The alloy after homogenization treatment has its surface oxide layer removed and is processed into an extruded billet with a height-to-diameter ratio of 5:7;

[0051] S4: Preheat the extruded billet and die to 150℃, connect the electrodes, set the loading pulse current, pulse voltage 15V, pulse frequency 1300Hz, duty cycle 16%, and start the extruder at the same time with an extrusion ratio of 16:1 and an extrusion speed of 0.5mm / s. After extrusion is completed, turn off the pulse current device.

[0052] Comparative Example 1:

[0053] This comparative example uses a Mg-2.5Zn-0.5Zr-0.5Nd alloy with the content of alloying elements other than Mg <5 wt.%. The specific preparation steps are as follows:

[0054] S1: The magnesium alloy ingot is cut and the surface oxide layer is removed to obtain the sample;

[0055] S2: The above sample was homogenized at 400℃ for 12 hours and then water-cooled at 50℃.

[0056] S3: The alloy after homogenization treatment has its surface oxide layer removed and is processed into an extruded billet with a height-to-diameter ratio of 5:7;

[0057] S4: Extrusion of the blank and die is carried out after preheating to 220°C. The extrusion ratio is 16:1 and the extrusion speed is 0.2 mm / s.

[0058] Comparative Example 2:

[0059] This comparative example uses a Mg-2.5Zn-0.5Ca alloy with the content of alloying elements other than Mg <5 wt.%. The specific preparation steps are as follows:

[0060] S1: The magnesium alloy ingot is cut and the surface oxide layer is removed to obtain the sample;

[0061] S2: The above sample was homogenized at 380℃ for 12 hours and then water-cooled at 55℃.

[0062] S3: The alloy after homogenization treatment has its surface oxide layer removed and is processed into an extruded billet with a height-to-diameter ratio of 5:7;

[0063] S4: Extrusion is performed after the extrusion blank and die are preheated to 200℃, with an extrusion ratio of 25:1 and an extrusion speed of 0.15mm / s.

[0064] Comparative Example 3:

[0065] This comparative example uses a Mg-2.5Zn-0.5Zr-0.5Nd alloy with the content of alloying elements other than Mg <5 wt.%. The specific preparation steps are as follows:

[0066] S1: The magnesium alloy ingot is cut and the surface oxide layer is removed to obtain the sample;

[0067] S2: The above sample was homogenized at 400℃, kept at the temperature for 12 hours, and then water-cooled at 50℃.

[0068] S3: The alloy after homogenization treatment has its surface oxide layer removed and is processed into an extruded billet with a height-to-diameter ratio of 5:7;

[0069] S4: Preheat the extruded billet and die to 220℃, connect the electrodes, set the loading pulse current, pulse voltage 11V, pulse frequency 1000Hz, duty cycle 13%, and start the extruder at the same time with an extrusion ratio of 16:1 and an extrusion speed of 0.2mm / s. After extrusion is completed, turn off the pulse current device.

[0070] Comparative Example 4:

[0071] This embodiment uses a Mg-2.5Zn-0.5Zr-0.5Nd alloy with the content of alloying elements other than Mg <5wt.%. The specific preparation steps are as follows:

[0072] S1: The magnesium alloy ingot is cut and the surface oxide layer is removed to obtain the sample;

[0073] S2: Connect the sample to the electrode, set the applied pulse current, pulse voltage 15V, pulse frequency 60Hz, duty cycle 10%, process for 15min and then turn off the pulse current device, and then cool the sample in water at 30℃.

[0074] S3: The alloy after homogenization treatment has its surface oxide layer removed and is processed into an extruded billet with a height-to-diameter ratio of 5:7;

[0075] S4: Extrusion of the blank and die is carried out after preheating to 220°C. The extrusion ratio is 16:1 and the extrusion speed is 0.2 mm / s.

[0076] Compared to Example 1, Comparative Example 3 used conventional homogenization treatment in step S2, and Comparative Example 4 did not apply pulsed current in step S4. Table 1 shows a performance comparison between Example 1 and Comparative Examples 3 and 4. It can be observed that Comparative Example 3 had a low recrystallization fraction, a fast corrosion rate, and uneven corrosion. Although Comparative Example 4 exhibited uniform corrosion, its corrosion rate was excessively fast.

[0077] Table 1 Performance comparison of Example 1 with Comparative Examples 3 and 4

[0078]

[0079] Figure 1(a) is the electron backscatter diffraction pattern of Example 1, and Figure 1(b) is the electron backscatter diffraction pattern of Comparative Example 1. It can be found that the magnesium alloy of Comparative Example 1 has a low dynamic recrystallization fraction and heterogeneous structure characteristics, while the magnesium alloy prepared in Example 1 has a high dynamic recrystallization volume fraction and good microstructure uniformity.

[0080] Figure 2 The graphs show the potentiodynamic polarization curves of Example 2 and Comparative Example 2 in 0.9% NaCl. It can be seen that the magnesium alloy prepared in Example 2 has better corrosion resistance.

[0081] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this invention, and these modifications or substitutions should all be covered within the scope of protection of this invention. Therefore, the scope of protection of this invention should be determined by the scope defined in the claims.

Claims

1. A method for improving the microstructure and corrosion uniformity of low-temperature extruded magnesium alloys, characterized in that, Includes the following steps: S1: Cut the low-alloy-element content magnesium alloy ingot and remove the surface oxide layer to obtain the as-cast sample; S2: Perform pulsed current homogenization treatment on the cast sample; S3: Remove the surface oxide layer from the homogenized alloy and process it into an extruded billet; S4: Under the assistance of pulsed current, the extruded billet is subjected to low-temperature extrusion treatment; In step S1, the low-alloy element content magnesium alloy is a biodegradable magnesium alloy, and the content of elements other than magnesium is <5 wt.%; In step S2, the temperature rise of the sample under pulsed current ranges from 50 to 300°C. The pulsed current processing parameters are: pulse voltage: 15-36V, pulse frequency: 10-20000Hz, duty cycle: 10-20%; processing time: 5-30min. In step S4, the preheating temperature of the extruded billet and the die is 100-250℃; the extrusion ratio is 10-36:1; the extrusion speed is 0.05-1mm / s; and the applied pulse current parameters are: pulse voltage: 11-36V, pulse frequency: 10-20000Hz, and duty cycle: 10-20%.

2. The method for improving the microstructure and corrosion uniformity of low-temperature extruded magnesium alloys according to claim 1, characterized in that, In step S2, the pulse current homogenization process includes: connecting the as-cast sample to the electrode, setting the applied pulse current, recording the sample temperature rise, turning off the pulse current device after the set processing time is reached, and then cooling the sample in water.

3. The method for improving the microstructure and corrosion uniformity of low-temperature extruded magnesium alloys according to claim 2, characterized in that, In step S2, the cooling water temperature is 30-40℃.

4. The method for improving the microstructure and corrosion uniformity of low-temperature extruded magnesium alloys according to claim 1, characterized in that, In step S3, the height-to-diameter ratio of the extruded billet is 5-7:

7.

5. The method for improving the microstructure and corrosion uniformity of low-temperature extruded magnesium alloys according to claim 1, characterized in that, In step S4, the low-temperature extrusion process includes: preheating the extrusion blank and the die, connecting the electrode, then setting the loading pulse current and starting the extruder, monitoring the extrusion temperature, and turning off the pulse current device after the extrusion is completed.

6. The magnesium alloy obtained by the method according to any one of claims 1 to 5, characterized in that, Its tensile strength is 290-380 MPa, its yield strength is 260-360 MPa, its dynamic recrystallization volume fraction is >85%, and it corrodes uniformly in a 0.9 wt.% NaCl solution with a corrosion rate of <0.3 mm / year.

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