Preparation method of high-strength corrosion-resistant ultralight dual-phase Mg-Li-Zn-Nd alloy

Abstract

The invention provides a preparation method of a high-strength corrosion-resistant ultralight dual-phase Mg-Li-Zn-Nd alloy, and belongs to the field of magnesium-lithium alloy processing. The method comprises the following steps: carrying out vacuum melting on raw materials to obtain a melt with uniformly distributed components; the obtained melt is subjected to casting molding and machining, and an extrusion blank is obtained; carrying out gradient time sequence pulse current treatment on the obtained extruded blank to obtain a homogenized blank; and the obtained homogenized blank is subjected to positive and negative combined pulse current auxiliary extrusion treatment, and the Mg-Li-Zn-Nd alloy is obtained. According to the method, rapid dissolution of a coarse second phase can be promoted in the gradient time sequence pulse current treatment stage, Li element volatilization and original grain growth are inhibited, alpha-Mg recrystallization is promoted in the positive and negative combined pulse current auxiliary extrusion stage, beta-Li grain growth is inhibited, precipitated phase dispersed distribution is induced, synchronous improvement of strength and corrosion resistance is achieved, and the method is suitable for industrial production. And the light high-strength corrosion-resistant magnesium-lithium alloy meeting the application of key parts of special equipment, unmanned aerial vehicles and medical instruments is obtained.

Description

Technical Field

[0001] The present invention belongs to the field of magnesium-lithium alloy processing, and in particular relates to a method for preparing a high-strength, corrosion-resistant, ultra-light dual-phase Mg-Li-Zn-Nd alloy. Background Art

[0002] As the lightest metal structural material, magnesium-lithium alloys have become a key lightweight material for special equipment, drones, and medical device components. Dual-phase (close-packed hexagonal α-Mg phase + body-centered cubic β-Li phase) magnesium-lithium alloys exhibit excellent plasticity, but their strength and corrosion resistance are significantly lower than those of traditional magnesium alloys. However, alloying, plastic deformation, and heat treatment methods have proven difficult to simultaneously enhance both strength and corrosion resistance in an environmentally friendly, efficient, and cost-effective manner, limiting their widespread application.

[0003] Although the strength of dual-phase magnesium-lithium alloys can be significantly improved through β-Li phase refinement, α-Mg phase bimodal structural strengthening, and second-phase precipitation strengthening, the size and crystal orientation of the α-Mg and β-Li phases differ significantly after conventional plastic deformation, and the second phase and precipitate phase are difficult to disperse finely in the matrix, resulting in uneven microstructure and severe localized corrosion. Patent publication number CN113584364B discloses a method for synergistically improving the mechanical and corrosion properties of high-lithium-content ultra-light magnesium-lithium-based alloys. The method improves mechanical and corrosion resistance by regulating the surface exposed area fraction of the β-Li matrix phase in the alloy and the number, size, and distribution of dispersion-strengthened precipitated particles in the matrix phase. However, the α-Mg phase is still distributed in the β-Li matrix phase in a striped manner along the deformation direction, destroying the continuity of the protective corrosion product film. The patent with authorization announcement number CN113528911B discloses an aging-resistant, high-strength, tough, and corrosion-resistant dual-phase magnesium-lithium alloy and its preparation method. The mechanical and corrosion resistance properties are improved through rolling + stir friction + spray-assisted cooling system. However, this method is difficult to prepare and has low efficiency. The size of the prepared material is limited, making it difficult to meet the needs of large-scale engineering applications. The patent with application publication number CN116377298A discloses a Sn-containing ultra-light, high-strength, high-modulus dual-phase corrosion-resistant magnesium-lithium alloy and its preparation method. The mechanical and corrosion resistance properties are improved through solid solution + aging treatment, but the total heat treatment time can reach 20-40 hours, and the treatment process requires a vacuum environment, which consumes a lot of energy.

[0004] It can be seen that developing a dual-phase magnesium-lithium alloy with both high strength and high corrosion resistance is difficult and challenging. The key lies in designing excellent dual-phase magnesium-lithium alloy microstructure characteristics and developing green, efficient, and low-cost preparation methods to improve the overall performance of the dual-phase magnesium-lithium alloy. Therefore, it is necessary to provide a high-strength and corrosion-resistant dual-phase magnesium-lithium alloy and its preparation method. Summary of the Invention

[0005] The object of the present invention is to provide a method for preparing a high-strength, corrosion-resistant, and ultra-light dual-phase Mg-Li-Zn-Nd alloy. By this method, the rapid dissolution of the coarse second phase can be promoted, and the volatilization of the Li element and the growth of the original grains can be suppressed during the gradient time-sequential pulse current treatment stage. During the positive and negative combined pulse current assisted extrusion stage, the α-Mg recrystallization can be promoted, the growth of β-Li grains can be suppressed, and the dispersed distribution of the precipitated phase can be induced, thereby achieving a simultaneous improvement in strength and corrosion resistance, and obtaining a lightweight, high-strength, corrosion-resistant magnesium-lithium alloy that meets the application requirements of key components of special equipment, unmanned aerial vehicles, and medical devices.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A method for preparing a high-strength, corrosion-resistant, ultra-light dual-phase Mg-Li-Zn-Nd alloy comprises the following steps:

[0008] S1: Vacuum melting the raw materials to obtain a melt with uniformly distributed components;

[0009] S2: Casting and machining the melt obtained in step S1 to obtain an extruded billet;

[0010] S3: performing gradient sequential pulse current treatment on the extruded billet obtained in step S2 to promote rapid atomic diffusion, inhibit grain coarsening and growth, and Li burnout, thereby obtaining a homogenized billet;

[0011] S4: performing positive and negative combined pulse current assisted extrusion treatment on the homogenized billet obtained in step S3 to promote low-temperature dynamic recrystallization and dynamic precipitation and inhibit grain coarsening and growth to obtain the Mg-Li-Zn-Nd alloy.

[0012] Optionally, in step S1, raw materials are weighed in a glove box according to a ratio. The raw materials are high-purity Mg ingots, high-purity Zn ingots, Mg-Li master alloys and Mg-Nd master alloys, and are melted in a vacuum induction furnace with a vacuum degree of 10 -3 -10 - 4 Pa, the shielding gas is high-purity argon. The high-purity means that the mass percentage of the metal component is greater than 99.9%.

[0013] Optionally, in step S2, the stainless steel mold is preheated to 180-220° C. before pouring, and the resulting ingot has a diameter of 80-130 mm. Extruded billets with a diameter of 35-65 mm are obtained by wire cutting and lathe polishing.

[0014] Optionally, the specific process of step S3 is: directly loading the extruded billet into an extrusion die with a heat-insulating cover, then turning on a pulse power supply, applying a gradient time-series pulse current for 10-25 minutes, and then turning off the pulse power supply.

[0015] Optionally, in step S3, the gradient sequential pulse current includes two stages: a high-energy activation stage and a low-energy diffusion stage. The high-energy activation stage activates the short-range diffusion of solute atoms, and the low-energy diffusion stage drives the long-range migration of solute atoms, thereby reducing the coarsening of the original grains or the burning of Li elements. The current density of the high-energy activation stage is 3000-5000A / cm 2 , frequency 100-200Hz, duty cycle 30-50%, duration 2-5min; the current density of the low energy diffusion section is reduced to 800-1500A / cm 2 , the frequency is reduced to 20-50Hz, the duty cycle is increased to 60-80%, the duration is 8-20min, and the temperature treated with pulse current is 200-300℃.

[0016] Optionally, the specific process of step S4 is: when the billet is cooled to 30-90°C, the pulse power supply is turned on again to apply a positive and negative combined pulse current, and then the extruder is started for extrusion, and the pulse current is continuously applied during the extrusion process until the extrusion process is completed.

[0017] Optionally, in step S4, the pulse current is applied in a manner of alternating positive pulse current and negative pulse current, wherein the positive pulse current density is 2500-3500 A / cm 2 , frequency 60-80Hz, pulse width 80-150μs; negative pulse current density 600-800A / cm 2 , frequency 30-40Hz, pulse width 200-400μs, control the action time ratio of positive and negative pulse currents at 0.5:1-1.3:1, so that the energy ratio of positive and negative pulse currents is controlled at 3:1-4:1.

[0018] Optionally, in step S4, the extrusion ratio is 10-25:1, the extrusion speed is 0.1-3 mm / s, the extrusion temperature is 50-150° C. under the combined action of frictional heat generation and pulse current, and the extrusion time is 30-120 s.

[0019] The present invention also provides a high-strength, corrosion-resistant, ultra-light dual-phase Mg-Li-Zn-Nd alloy obtained by the method, which has the following components in mass percentage: 6-10% Li, 1-3% Zn, 0.5-1.5% Nd, and the rest is Mg and unavoidable impurities, the sum of the mass percentages of the impurity elements is less than 0.04%, and has the characteristics of a uniform fine-grained α / β dual-phase matrix + a fine dispersed second phase.

[0020] Optionally, the Mg-Li-Zn-Nd alloy has a yield strength of ≥250 MPa, an elongation after fracture of ≥20%, and is uniformly corroded in a 3.5% by mass NaCl solution with a corrosion rate of <0.5 mg·cm -2day -1 .

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0022] (1) The present invention provides a material with a yield strength of ≥250 MPa, an elongation after fracture of ≥20%, uniform corrosion in a 3.5% mass fraction NaCl solution, and a corrosion rate of <0.5 mg·cm -2 day -1 This dual-phase Mg-Li-Zn-Nd alloy possesses both high strength and high corrosion resistance, effectively addressing the specific shortcomings of dual-phase magnesium-lithium alloys and can be used in key lightweight components for special equipment, drones, and medical devices.

[0023] (2) The present invention provides new material components and contents and combines them with an innovative and efficient preparation method. It can promote the rapid dissolution of coarse second phase and inhibit the volatilization of Li element and the growth of original grains in the gradient time pulse current treatment stage. It can also promote the recrystallization of α-Mg, inhibit the growth of β-Li grains, and induce the dispersed distribution of precipitated phases in the positive and negative combined pulse current assisted extrusion stage.

[0024] (3) Through the pulse current control strategy of gradient timing + positive and negative combination, the microstructural characteristics of uniform fine-grained α / β dual-phase matrix + fine dispersed primary / precipitated second phase can be constructed, thereby achieving a simultaneous improvement in strength and corrosion resistance.

[0025] (4) Compared with the existing methods, the equipment requirements of the present invention are simple, the preparation efficiency is high, the energy consumption is low, and it is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0027] FIG1( a ) is an EBSD image of the alloy of Example 2;

[0028] Figure 1(b) is the EBSD image of the alloy of Comparative Example 4;

[0029] Figure 2(a) shows the 3D morphology of the alloy of Example 1 after being immersed in a 3.5% mass fraction NaCl solution for 240 h;

[0030] Figure 2(b) shows the 3D morphology of the alloy of Comparative Example 3 after being immersed in a 3.5% by mass NaCl solution for 240 hours. DETAILED DESCRIPTION

[0031] In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0032] Example 1:

[0033] The high-strength and corrosion-resistant dual-phase Mg-Li-Zn-Nd alloy in this embodiment is prepared from the following components in mass percentage: 8.2% Li, 2.1% Zn, 1.1% Nd, Fe<0.01%, Ni<0.01%, Cu<0.01%, Al<0.01%, and the rest is Mg.

[0034] The specific preparation steps are as follows:

[0035] S1: Vacuum melting: Raw materials were weighed according to the proportion in a glove box. The raw materials used were high-purity Mg ingots, high-purity Zn ingots, Mg-Li master alloys, and Mg-Nd master alloys. The raw materials were melted in a vacuum induction furnace with a vacuum degree of 5×10 -3 Pa, the protective gas is high-purity argon, and a melt with uniform distribution of components is obtained;

[0036] S2: Casting and extrusion billet processing: Before casting, the stainless steel mold is preheated to 200°C, and the melt obtained in step S1 is cast to obtain an ingot with a diameter of 100 mm. The extrusion billet with a diameter of 50 mm is obtained by wire cutting and lathe polishing;

[0037] S3: Gradient sequential pulse current treatment: The extruded billet obtained in S2 is directly loaded into an extrusion die with a heat preservation cover, and then the pulse power supply is turned on. A gradient sequential pulse current is applied for 15 minutes and then the pulse power supply is turned off. The gradient sequential pulse current includes two stages: high energy activation and low energy diffusion, i.e., high energy activation is performed first, followed by low energy diffusion. The current density of the high energy activation stage is 4000A / cm 2 , frequency 150Hz, duty cycle 30%, duration 3min; the current density in the low energy diffusion section is reduced to 1000A / cm 2 , the frequency was reduced to 30Hz, the duty cycle was increased to 60%, and the duration was 12min; the temperatures of the two-stage pulse current treatment were 290℃ and 220℃;

[0038] S4: Positive and negative combined pulse current assisted extrusion treatment: After the billet treated in step S3 is cooled to 50°C, the pulse power supply is turned on again to apply positive and negative combined pulse current, and then the extruder is started for extrusion. The positive and negative combined pulse current adopts an asymmetric superposition mode of positive pulse and negative pulse, and the positive pulse current density is 3000A / cm 2 , frequency 60Hz, pulse width 100μs; negative pulse current density 600A / cm2 , frequency 30Hz, pulse width 300μs, the action time ratio of positive and negative pulse current is controlled at 0.6:1, and the positive and negative pulse energy ratio is controlled at 3:1; the extrusion ratio is 16:1, the extrusion speed is 1mm / s, the extrusion time is 70s, and the extrusion temperature is 100℃ under the combined action of frictional heat and pulse current.

[0039] Example 2:

[0040] The high-strength and corrosion-resistant dual-phase Mg-Li-Zn-Nd alloy in this embodiment is prepared from the following components in mass percentage: 9.1% Li, 1.3% Zn, 0.8% Nd, Fe<0.01%, Ni<0.01%, Cu<0.01%, Al<0.01%, and the rest is Mg.

[0041] The specific preparation steps are as follows:

[0042] S1: Vacuum melting: Raw materials are weighed according to the ratio in a glove box. The raw materials include high-purity Mg ingots, high-purity Zn ingots, Mg-Li master alloys, and Mg-Nd master alloys. The raw materials are melted in a vacuum induction furnace with a vacuum degree of 8×10 -4 Pa, the protective gas is high-purity argon, and a melt with uniform distribution of components is obtained;

[0043] S2: Casting and extrusion billet processing: Before casting, the stainless steel mold is preheated to 200°C, and the melt obtained in step S1 is cast to obtain an ingot with a diameter of 80 mm. The extrusion billet with a diameter of 40 mm is obtained by wire cutting and lathing;

[0044] S3: Gradient sequential pulse current assisted homogenization treatment: The extruded billet obtained in S2 is directly loaded into an extrusion die with a heat preservation cover, and then the pulse power supply is turned on. A gradient sequential pulse current is applied for 18 minutes of homogenization treatment, and then the pulse power supply is turned off. The gradient sequential pulse current is divided into a high-energy activation section and a low-energy diffusion section. The current density of the high-energy activation section is 3500A / cm 2 , frequency 120Hz, duty cycle 40%, duration 5min; the current density in the low energy diffusion section is reduced to 1100A / cm 2 , the frequency was reduced to 40Hz, the duty cycle was increased to 60%, and the duration was 13min; the temperatures of the two-stage pulse current homogenization treatment were 270℃ and 230℃ respectively;

[0045] S4: Positive and negative combined pulse current assisted extrusion treatment: After the billet treated in step S3 is cooled to 60°C, the pulse power supply is turned on again to apply positive and negative combined pulse current, and then the extruder is started for extrusion. The positive and negative combined pulse current adopts an asymmetric superposition mode of positive pulse and negative pulse, and the positive pulse current density is 3200A / cm 2, frequency 70Hz, pulse width 120μs; negative pulse current density 700A / cm 2 , frequency 40Hz, pulse width 350μs, the action time ratio of positive and negative pulse current is controlled at 0.65:1, and the positive and negative pulse energy ratio is controlled at 4:1; the extrusion ratio is 16:1, the extrusion speed is 1mm / s, the extrusion time is 70s, and the extrusion temperature is 110℃ under the combined action of frictional heat and pulse current.

[0046] Comparative Example 1:

[0047] The high-strength and corrosion-resistant dual-phase Mg-Li-Zn-Nd alloy in this comparative example is prepared from the following components in mass percentage: 8.2% Li, 2.1% Zn, 1.1% Nd, Fe<0.01%, Ni<0.01%, Cu<0.01%, Al<0.01%, and the rest is Mg.

[0048] The specific preparation steps are as follows:

[0049] S1: Vacuum melting: Raw materials were weighed according to the proportion in a glove box. The raw materials used were high-purity Mg ingots, high-purity Zn ingots, Mg-Li master alloys, and Mg-Nd master alloys. The raw materials were melted in a vacuum induction furnace with a vacuum degree of 5×10 -3 Pa, the protective gas is high-purity argon, and a melt with uniform distribution of components is obtained;

[0050] S2: Casting and extrusion billet processing: Before casting, the stainless steel mold is preheated to 200°C, and the melt obtained in step S1 is cast to obtain an ingot with a diameter of 100 mm. The extrusion billet with a diameter of 50 mm is obtained by wire cutting and lathe polishing;

[0051] S3: Conventional homogenization heat treatment: The extruded billet obtained in S2 was subjected to conventional homogenization heat treatment in a heat treatment furnace for 15 minutes. The two-stage treatment process was 290°C × 3 minutes and 220°C × 12 minutes respectively. The billet was then loaded into an extrusion die with a heat insulation cover.

[0052] S4: Positive and negative combined pulse current assisted extrusion treatment: After the billet treated in step S3 is cooled to 50°C, a pulse power supply is connected to apply positive and negative combined pulse current, and then the extruder is started for extrusion. The positive and negative combined pulse current adopts an asymmetric superposition mode of positive pulse and negative pulse, and the positive pulse current density is 3000A / cm 2 , frequency 60Hz, pulse width 100μs; negative pulse current density 600A / cm 2, frequency 30Hz, pulse width 300μs, the action time ratio of positive and negative pulse current is controlled at 0.6:1, and the positive and negative pulse energy ratio is controlled at 3:1; the extrusion ratio is 16:1, the extrusion speed is 1mm / s, the extrusion time is 70s, and the extrusion temperature is 100℃ under the combined action of frictional heat and pulse current.

[0053] Comparative Example 2:

[0054] The high-strength and corrosion-resistant dual-phase Mg-Li-Zn-Nd alloy in this comparative example is prepared from the following components in mass percentage: 8.2% Li, 2.1% Zn, 1.1% Nd, Fe<0.01%, Ni<0.01%, Cu<0.01%, Al<0.01%, and the rest is Mg.

[0055] The specific preparation steps are as follows:

[0056] S1: Vacuum melting: Raw materials were weighed according to the proportion in a glove box. The raw materials used were high-purity Mg ingots, high-purity Zn ingots, Mg-Li master alloys, and Mg-Nd master alloys. The raw materials were melted in a vacuum induction furnace with a vacuum degree of 5×10 -3 Pa, the protective gas is high-purity argon, and a melt with uniform distribution of components is obtained;

[0057] S2: Casting and extrusion billet processing: Before casting, the stainless steel mold is preheated to 200°C, and the melt obtained in step S1 is cast to obtain an ingot with a diameter of 100 mm. The extrusion billet with a diameter of 50 mm is obtained by wire cutting and lathe polishing;

[0058] S3: Conventional homogenization heat treatment: The extruded billet obtained in S2 is subjected to conventional homogenization heat treatment at 290°C for 24 hours in a heat treatment furnace, and then the billet is loaded into an extrusion die with a heat insulation cover;

[0059] S4: Positive and negative combined pulse current assisted extrusion treatment: After the billet treated in step S3 is cooled to 50°C, a pulse power supply is connected to apply positive and negative combined pulse current, and then the extruder is started for extrusion. The positive and negative combined pulse current adopts an asymmetric superposition mode of positive pulse and negative pulse, and the positive pulse current density is 3000A / cm 2 , frequency 60Hz, pulse width 100μs; negative pulse current density 600A / cm 2 , frequency 30Hz, pulse width 300μs, the action time ratio of positive and negative pulse current is controlled at 0.6:1, and the positive and negative pulse energy ratio is controlled at 3:1; the extrusion ratio is 16:1, the extrusion speed is 1mm / s, the extrusion time is 70s, and the extrusion temperature is 100℃ under the combined action of frictional heat and pulse current.

[0060] Comparative Example 3:

[0061] The high-strength and corrosion-resistant dual-phase Mg-Li-Zn-Nd alloy in this comparative example is prepared from the following components in mass percentage: 9.1% Li, 1.3% Zn, 0.8% Nd, Fe<0.01%, Ni<0.01%, Cu<0.01%, Al<0.01%, and the rest is Mg.

[0062] The specific preparation steps are as follows:

[0063] S1: Vacuum melting: Raw materials are weighed according to the ratio in a glove box. The raw materials include high-purity Mg ingots, high-purity Zn ingots, Mg-Li master alloys, and Mg-Nd master alloys. The raw materials are melted in a vacuum induction furnace with a vacuum degree of 8×10 -4 Pa, the protective gas is high-purity argon, and a melt with uniform distribution of components is obtained;

[0064] S2: Casting and extrusion billet processing: Before casting, the stainless steel mold is preheated to 200°C, and the melt obtained in step S1 is cast to obtain an ingot with a diameter of 80 mm. The extrusion billet with a diameter of 40 mm is obtained by wire cutting and lathing;

[0065] S3: Gradient sequential pulse current treatment: The extruded billet obtained in S2 is directly loaded into an extrusion die with a heat preservation cover, and then the pulse power supply is turned on. A gradient sequential pulse current is applied for 18 minutes and then the pulse power supply is turned off. The gradient sequential pulse current includes two stages: a high-energy activation stage and a low-energy diffusion stage. The current density of the high-energy activation stage is 3500A / cm 2 , frequency 120Hz, duty cycle 40%, duration 5min; the current density in the low energy diffusion section is reduced to 1100A / cm 2 , the frequency was reduced to 40Hz, the duty cycle was increased to 60%, and the duration was 13min; the temperatures of the two-stage pulse current treatment were 270℃ and 230℃ respectively;

[0066] S4: Conventional extrusion treatment: After the billet is cooled to 100°C after the treatment in step S3, the extruder is started for extrusion with an extrusion ratio of 16:1, an extrusion speed of 1 mm / s, an extrusion time of 70 s, and an extrusion temperature of 110°C under the action of frictional heat.

[0067] Comparative Example 4:

[0068] The high-strength and corrosion-resistant dual-phase Mg-Li-Zn-Nd alloy in this comparative example is prepared from the following components in mass percentage: 9.1% Li, 1.3% Zn, 0.8% Nd, Fe<0.01%, Ni<0.01%, Cu<0.01%, Al<0.01%, and the rest is Mg.

[0069] The specific preparation steps are as follows:

[0070] S1: Vacuum melting: Raw materials are weighed according to the ratio in a glove box. The raw materials include high-purity Mg ingots, high-purity Zn ingots, Mg-Li master alloys, and Mg-Nd master alloys. The raw materials are melted in a vacuum induction furnace with a vacuum degree of 8×10 -4 Pa, the protective gas is high-purity argon, and a melt with uniform distribution of components is obtained;

[0071] S2: Casting and extrusion billet processing: Before casting, the stainless steel mold is preheated to 200°C, and the melt obtained in step S1 is cast to obtain an ingot with a diameter of 80 mm. The extrusion billet with a diameter of 40 mm is obtained by wire cutting and lathing;

[0072] S3: Conventional homogenization heat treatment: The extruded billet obtained in S2 is subjected to conventional homogenization heat treatment at 270°C for 24 hours in a heat treatment furnace, and then the billet is loaded into an extrusion die with a heat insulation cover;

[0073] S4: Conventional extrusion treatment: After the billet is cooled to 100°C after the treatment in step S3, the extruder is started for extrusion with an extrusion ratio of 16:1, an extrusion speed of 1 mm / s, an extrusion time of 70 s, and an extrusion temperature of 110°C under the action of frictional heat.

[0074] Comparative Example 5:

[0075] The high-strength and corrosion-resistant dual-phase Mg-Li-Zn-Nd alloy in this comparative example is prepared from the following components in mass percentage: 2.6% Li, 2.1% Zn, 1.1% Nd, Fe<0.01%, Ni<0.01%, Cu<0.01%, Al<0.01%, and the rest is Mg.

[0076] The specific preparation steps are the same as those in Example 1.

[0077] Comparative Example 6:

[0078] The high-strength and corrosion-resistant dual-phase Mg-Li-Zn-Nd alloy in this comparative example is prepared from the following components in mass percentage: 14.1% Li, 2.1% Zn, 1.1% Nd, Fe<0.01%, Ni<0.01%, Cu<0.01%, Al<0.01%, and the rest is Mg.

[0079] The specific preparation steps are the same as those in Example 1.

[0080] Compared with Example 1, the material components of Comparative Example 1 are the same, except that no pulse current is applied in step S3, and conventional homogenization heat treatment at 290°C×3min+220°C×12min is adopted; compared with Example 1, the material components of Comparative Example 2 are the same, except that no pulse current is applied in step S3, and conventional homogenization heat treatment at 290°C×24h is adopted; compared with Example 2, the material components of Comparative Example 3 are the same, except that no pulse current is applied in step S4, and conventional extrusion is adopted; compared with Example 2, the material components of Comparative Example 4 are the same, except that no pulse current is applied in step S3, and conventional homogenization heat treatment at 270°C×24h is adopted, and no pulse current is applied in step S4, and conventional extrusion is adopted; compared with Example 1, the preparation method of Comparative Example 5 is the same, except that the Li content is lower than the lower limit of the Li content in the dual-phase region (mass fraction of 5.5-10.3%); compared with Example 1, the preparation method of Comparative Example 6 is the same, except that the Li content is higher than the upper limit of the Li content in the dual-phase region (mass fraction of 5.5-10.3%).

[0081] The performance of Examples 1-2 and Comparative Examples 1-6 is shown in Table 1. The mechanical properties of Examples 1 and 2 all reached a yield strength ≥ 250 MPa and an elongation after fracture ≥ 20%. They corroded uniformly in a 3.5% mass fraction NaCl solution and the corrosion rate was < 0.5 mg·cm -2 day -1 .

[0082] Comparative Example 1 shows that a short, conventional homogenization heat treatment fails to effectively dissolve the second phase, resulting in its striped distribution along the extrusion direction during extrusion, reducing plasticity and corrosion uniformity. Compared with Example 1, Comparative Example 1 exhibits uneven corrosion and an excessively fast corrosion rate.

[0083] Comparative Example 2 shows that a long period of conventional homogenization heat treatment will cause the original grains to grow and coarsen, resulting in a lower yield strength after extrusion. Compared with Example 1, Comparative Example 2 has insufficient strength.

[0084] Comparative Examples 3 and 4 demonstrate that without the application of pulsed current during extrusion, complete dynamic recrystallization of α-Mg cannot be induced. Significant differences in size and crystal orientation between the α-Mg and β-Li phases result in uneven microstructure and severe localized corrosion. Compared to Example 1, Comparative Examples 3 and 4 exhibit insufficient strength, uneven corrosion, and excessively rapid corrosion rates.

[0085] Comparative Example 5 shows that when the Li content is lower than the lower limit of the Li content in the dual-phase region, only a single-phase α-Mg phase can be generated, resulting in insufficient plasticity; Comparative Example 6 shows that when the Li content is higher than the upper limit of the Li content in the dual-phase region, only a single-phase β-Li phase can be generated, resulting in insufficient strength and excessively fast corrosion rate.

[0086] Table 1 Phase composition and properties of Examples 1-2 and Comparative Examples 1-6

[0087]

[0088] Figure 1(a) is an EBSD image of the alloy from Example 2, demonstrating the uniform distribution of recrystallized α-Mg and β-Li grains in the resulting alloy. Figure 1(b) is an EBSD image of the alloy from Comparative Example 4, demonstrating that the α-Mg grains in the resulting alloy are elongated, lacking dynamic recrystallization, and differ significantly in size from the recrystallized β-Li grains.

[0089] Figures 2(a) and 2(b) show the surface morphologies of the alloys of Example 1 and Comparative Example 3, respectively, after immersion in a 3.5% by mass NaCl solution for 240 hours. This shows that the alloy of Example 1 corrodes evenly, with shallow corrosion pits, while the alloy of Comparative Example 3 corrodes unevenly, with deep corrosion pits.

[0090] Examples 1 and 2 all have the characteristics of a uniform fine-grained α / β dual-phase matrix + a fine dispersed second phase, achieving a yield strength ≥ 250 MPa, an elongation after fracture ≥ 20%, and uniform corrosion in a 3.5% NaCl solution with a corrosion rate < 0.5 mg·cm -2 day -1 .

[0091] 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 modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing a high-strength, corrosion-resistant, ultra-light dual-phase Mg-Li-Zn-Nd alloy, characterized in that: The steps include: S1: Vacuum melting the raw materials to obtain a melt with uniformly distributed components; S2: Casting and machining the melt obtained in step S1 to obtain an extruded billet; S3: performing gradient sequential pulse current treatment on the extruded billet obtained in step S2 to obtain a homogenized billet; S4: performing positive and negative combined pulse current assisted extrusion treatment on the homogenized billet obtained in step S3 to obtain the Mg-Li-Zn-Nd alloy.

2. The method for preparing a high-strength, corrosion-resistant, ultra-light dual-phase Mg-Li-Zn-Nd alloy according to claim 1, characterized in that: In step S1, the raw materials are high-purity Mg ingots, high-purity Zn ingots, Mg-Li master alloys and Mg-Nd master alloys, which are melted in a vacuum induction furnace with a vacuum degree of 10 -3 -10 -4 Pa, the protective gas is high-purity argon.

3. The method for preparing a high-strength, corrosion-resistant, ultra-light dual-phase Mg-Li-Zn-Nd alloy according to claim 1, characterized in that: In step S2, the stainless steel mold is preheated to 180-220° C. before pouring, and the obtained ingot has a diameter of 80-130 mm. The extruded billet with a diameter of 35-65 mm is obtained by wire cutting and lathe polishing.

4. The method for preparing a high-strength, corrosion-resistant, ultra-light dual-phase Mg-Li-Zn-Nd alloy according to claim 1, characterized in that: The specific process of step S3 is: loading the extruded billet into an extrusion die with a heat-insulating cover, then turning on a pulse power supply, applying a gradient sequential pulse current for 10-25 minutes, and then turning off the pulse power supply.

5. The method for preparing a high-strength, corrosion-resistant, ultra-light dual-phase Mg-Li-Zn-Nd alloy according to claim 4, characterized in that: In step S3, the gradient sequential pulse current includes two stages: a high energy activation stage and a low energy diffusion stage. The current density of the high energy activation stage is 3000-5000 A / cm 2 , frequency 100-200 Hz, duty cycle 30-50%, duration 2-5 min; the current density of the low energy diffusion section is 800-1500 A / cm 2 , the frequency is reduced to 20-50Hz, the duty cycle is increased to 60-80%, the duration is 8-20min, and the temperature treated with pulse current is 200-300℃.

6. The method for preparing a high-strength, corrosion-resistant, ultra-light dual-phase Mg-Li-Zn-Nd alloy according to claim 1, characterized in that: The specific process of step S4 is: when the billet is cooled to 30-90°C, the pulse power supply is turned on again to apply a positive and negative combined pulse current, and then the extruder is started for extrusion, and the pulse current is continuously applied during the extrusion process until the extrusion process is completed.

7. The method for preparing a high-strength, corrosion-resistant, ultra-light dual-phase Mg-Li-Zn-Nd alloy according to claim 6, characterized in that: In step S4, the pulse current is applied in the following manner: positive pulse current and negative pulse current are applied alternately, wherein the positive pulse current density is 2500-3500 A / cm 2 , frequency 60-80Hz, pulse width 80-150μs; negative pulse current density 600-800A / cm 2 , frequency 30-40Hz, pulse width 200-400μs, positive and negative pulse current energy ratio is 3:1-4:

1.

8. The method for preparing a high-strength, corrosion-resistant, ultra-light dual-phase Mg-Li-Zn-Nd alloy according to claim 7, characterized in that: In step S4, the extrusion ratio is 10-25:1, the extrusion speed is 0.1-3 mm / s, the extrusion temperature is 50-150° C., and the extrusion time is 30-120 s.

9. The high-strength, corrosion-resistant, ultra-light dual-phase Mg-Li-Zn-Nd alloy obtained by the method according to any one of claims 1 to 8, characterized in that: The alloy has the following composition by mass percentage: 6-10% Li, 1-3% Zn, 0.5-1.5% Nd, and the remainder being Mg and unavoidable impurities, with the sum of the mass percentages of the impurity elements being less than 0.04%, and has the characteristics of a uniform fine-grained α / β dual-phase matrix and a fine dispersed second phase.

10. The alloy according to claim 9, characterized in that The alloy has a yield strength of ≥250 MPa, an elongation after fracture of ≥20%, and is uniformly corroded in a 3.5% mass fraction NaCl solution with a corrosion rate of <0.5 mg·cm -2 day -1 .

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