Design and preparation method of Mg-Sn-Al high plasticity magnesium alloy

Abstract

This invention belongs to the field of advanced metallic materials manufacturing, and relates to the design and preparation method of a high-plasticity Mg-Sn-Al magnesium alloy. First, a candidate system of Mg-xSn-yAl alloys is established. First-principles methods based on density functional theory are used to perform VCA modeling on each candidate composition and calculate elastic constants. Combined with the Voigt-Reuss-Hill model, parameters such as bulk modulus B, shear modulus G, Poisson's ratio, Pugh ratio, and Cauchy pressure are obtained. Using a Poisson's ratio greater than 0.36, a Pugh ratio greater than 3.4, and a Cauchy pressure greater than 18 GPa as screening criteria, the composition range of the high-plasticity alloy is determined to be Mg-(1-3.2)Sn-(0.7-0.8)Al (wt.%). Subsequently, alloy plates are prepared through melting and casting, hot extrusion, staged rolling, intermediate annealing, and pulsed current post-treatment, and tensile property testing and microstructure characterization are performed. The results show that the selected alloys have superior plasticity, with the Mg-3.2Sn-0.79Al alloy achieving an elongation of 15.6%. This invention enables rapid screening and preparation of high-ductility magnesium alloys, which can reduce trial-and-error costs and improve alloy design efficiency.

Description

Technical Field

[0001] This invention belongs to the field of advanced metallic materials technology, specifically relating to the design and preparation method of a Mg-Sn-Al series high-plasticity magnesium alloy. Background Technology

[0002] Magnesium alloys, due to their low density, high specific strength, excellent damping, electromagnetic shielding, and biodegradability, show great application potential in aerospace, rail transportation, and 3C electronics products. However, conventional magnesium alloy forming processes suffer from severe defects. Traditional hot or cold rolling requires dozens or even hundreds of passes, small reductions, and multiple intermediate annealings to achieve the target thickness, which easily leads to edge cracks, strip breakage, surface oxidation, and adhesion. This results in low yield and high cost. Furthermore, conventional magnesium alloys such as AZ31 and ME21 can only achieve a final thickness of 0.2–0.3 mm under warm rolling conditions; when further thinning to 0.05 mm, the probability of strip breakage increases significantly. The strong basal texture of magnesium alloys leads to significant anisotropy during rolling, with elongation and forming limits decreasing sharply with decreasing thickness. Simultaneously, due to the strong tendency for grain growth, traditional processes struggle to simultaneously achieve fine-grain strengthening and improved plasticity. Current research focuses on a few systems such as AZ31 and Mg-0.5Ce, where the alloy system is limited and alloying design is insufficient. The synergistic regulation mechanism of the dynamic recrystallization behavior of alloying elements and the stability of oxide films remains unclear.

[0003] To overcome the aforementioned challenges, a design and preparation method for a Mg-Sn-Al series high-ductility magnesium alloy was developed. This invention optimizes Al to 0.8 wt.% using first-principles calculations, achieving an elongation increase to 15.6%. Compared to existing technologies, this invention reduces trial and error through computational screening, clarifies compositional ranges, and provides feasible process parameters, thereby obtaining high-ductility sheets. Summary of the Invention

[0004] To overcome the dual bottlenecks of traditional material composition research relying on extensive experimental trial and error (high economic cost) and the difficulty in accurately evaluating performance through simulation alone, this invention creatively proposes a design and preparation method for Mg-Sn-Al system high-plasticity magnesium alloys based on a combination of first-principles calculations and experimental verification, in order to achieve targeted development of excellent plasticity properties.

[0005] A design method for Mg-Sn-Al based high-ductility magnesium alloys, characterized in that the method includes the following steps: S1. Establish a Mg-xSn-yAl alloy system, wherein the Mg-xSn-yAl alloy system is composed of alloys with different contents of Mg, Al and Sn elements; S2. Based on first principles, a VCA Mg-Sn-Al alloy model was established using Materials Studio software, and the elastic constants of the alloy in the target research system were calculated. S3. Based on the elastic constants of the alloy in the target research system, the bulk modulus is obtained using the Voigt-Reuss-Hill (VRH) model. and shear modulus And further calculate Poisson's ratio Pugh and Cauchy stress ; S4. According to the calculated Poisson's ratio Pugh The Cauchy pressure was used to determine the alloy composition with the best plasticity.

[0006] Furthermore, the design method for a Mg-Sn-Al system of high-plasticity magnesium alloy is characterized in that, in the Mg-xSn-yAl alloy system, x is initially set to 0.4~3.2 wt.% and y to 0.4~3.8 wt.%.

[0007] Furthermore, the design method for a Mg-Sn-Al series high-ductility magnesium alloy is characterized in that the VCA Mg-Sn-Al alloy model is based on the hcp-Mg crystal structure, in which two Mg atoms are replaced with Mg-xSn-yAl atoms, as detailed below. Figure 1 .

[0008] Furthermore, the design method for a Mg-Sn-Al system high-plasticity magnesium alloy is characterized in that the elastic constants are approximated by the Voigt-Reuss-Hill (VRH) model to obtain the bulk modulus (B), Cauchy pressure, and shear modulus (G), and then Poisson's ratio and Pugh ratio are calculated using the bulk modulus (B) and shear modulus (G), and the plasticity of the Mg-xSn-yAl alloy is expressed by the Poisson's ratio, Cauchy pressure, and Pugh ratio.

[0009] The Voigt-Reuss-Hill (VRH) model is as follows: The formulas for solving B and G using the Voigt model are: The formulas for solving B and G in the Reuss model are: The final formula for solving B and G in the Hill model is: The formula for calculating Poisson's ratio using B and G is: To further evaluate the alloy's ductility and toughness tendency, the Pugh ratio (B / G) is introduced as an empirical criterion, and its expression is: Cauchy pressure (σ) k It can be calculated using the following formula:

[0010] Furthermore, the design method for a Mg-Sn-Al series high-ductility magnesium alloy is characterized in that the alloy with Poisson's ratio > 0.36, Pugh ratio > 3.6, and Cauchy pressure > 18 GPa is Mg-(1-3.2)Sn-(0.7-0.8)Al.

[0011] Furthermore, the method for preparing a Mg-Sn-Al series high-ductility magnesium alloy is characterized in that the alloy manufacturing method is as follows: Ingot casting stage: Magnesium ingots with a purity of ≥99.9% and magnesium-aluminum and magnesium-tin master alloys are used as raw materials. The ingots are smelted under a protective SF6 / CO2 mixed gas. The smelting temperature is controlled at 720-750 ℃ ​​and sufficient mechanical or electromagnetic stirring is applied to ensure that the dense Sn element is fully dissolved and evenly distributed. A water-cooled semi-continuous casting process is adopted, and the pouring temperature is controlled at 700-720 ℃. Hot extrusion stage: The ingot is sawn to an aspect ratio of 3 and preheated at 400-430 ℃ for 3-4 hours. The extrusion is carried out at a die and extrusion cylinder temperature of 380-420 ℃. The extrusion bar speed is controlled at 1-2 mm / s, the extrusion ratio is 20, and the die orifice is designed as a flat hole with a target thickness of 6 mm. The extruded slab is immediately subjected to forced air cooling. Rolling stage: The sheet metal must be heated to above 400 ℃ and kept at that temperature before rolling. The rolling process is divided into two stages: rough rolling (6 mm → 3 mm) and finish rolling (3 mm → 1 mm). A critical intermediate annealing (380-400 ℃ / 30-60 min) must be performed at the 3 mm thickness to eliminate work hardening and restore plasticity. Precise temperature control is required throughout the process. The temperature is maintained at 400-360 ℃ during the rough rolling stage and not lower than 310 ℃ during the finish rolling stage. The single-pass reduction rate must be strictly controlled (≤15% for rough rolling and ≤10% for finish rolling). The final rolling temperature must be higher than 300 ℃ to ensure forming and avoid cracking. Post-processing: Perform pulsed current post-processing (25 A / mm). 2 (500 Hz, 30% duty cycle, processing time 300 s), followed by air cooling to eliminate residual internal stress, improve dimensional stability and achieve synergistic improvement in strength and plasticity.

[0012] Furthermore, the design and preparation method of the Mg-Sn-Al system high ductility magnesium alloy is characterized in that, under the same experimental conditions, the tensile properties of the prepared high ductility magnesium alloy sheet show that the optimal elongation of the Mg-(1-3.2)Sn-(0.7-0.8)Al alloy is 15.6%.

[0013] Furthermore, a design and preparation method for a Mg-Sn-Al series high-plasticity magnesium alloy, prepared by any of the above-described design and production processes, is characterized in that the novel high-plasticity magnesium alloy has a composition of Mg-(1-3.2)Sn-(0.7-0.8)Al (wt.%). Attached Figure Description

[0014] Figure 1 This is a model diagram of the VCA Mg-Sn-Al alloy used in this invention; Figure 2 These are tensile test diagrams of embodiments 1, 2, and 3 of the present invention; Figure 3 These are SEM microstructure images of Embodiments 1, 2, and 3 of the present invention; (a), (b), and (c) in the figures correspond to the post-processed SEM microstructure images of Embodiments 1, 2, and 3, respectively; (d), (e), and (f) correspond to the unprocessed SEM microstructure images of Embodiments 1, 2, and 3, respectively. Figure 4 This is a graph showing the relationship between elastic parameters calculated using first-principles calculations under different Mg-Sn-Al alloy compositions. Figures (a), (b), and (c) show the variation of relevant elastic parameters with composition under different Al contents. Figures (d), (e), and (f) show the variation of relevant elastic parameters with Sn contents under fixed Al contents. The dashed lines represent the reference values ​​of the corresponding parameters. Detailed Implementation

[0015] Example 1 This example presents the design and preparation method of a Mg-Sn-Al based high-ductility magnesium alloy. This novel magnesium alloy is Mg-3.2Sn-0.79Al, and its design method includes the following steps: S1. Establish a Mg-xSn-yAl alloy system, wherein the Mg-xSn-yAl alloy system is composed of alloys with different contents of Mg, Al and Sn elements; S2. Based on first principles, a VCA Mg-Sn-Al alloy model was established using Materials Studio software, and the elastic constants of the alloy in the target research system were calculated. S3. Based on the elastic constants of the alloy in the target research system, the bulk modulus is obtained using the Voigt-Reuss-Hill (VRH) model. and shear modulus And further calculate Poisson's ratio Pugh and Cauchy stress ; S4. According to the calculated Poisson's ratio Pugh The Cauchy pressure was used to determine the alloy composition with the best plasticity.

[0016] In the study system described in this example, the initial values ​​of the Mg-xSn-yAl alloy were set as x = 0.4~3.2 wt.% and y = 0.4~3.8 wt.%.

[0017] In this example, the VCA Mg-Sn-Al alloy model in the research system is based on the hcp-Mg crystal structure, in which two Mg atoms are replaced by Mg-xSn-yAl atoms. See details... Figure 1 .

[0018] In the study system described in this example, the elastic constants are approximated by the Voigt-Reuss-Hill (VRH) model to obtain the bulk modulus (B), Cauchy pressure, and shear modulus (G). Poisson's ratio and Pugh ratio are then calculated using the bulk modulus (B) and shear modulus (G). The plasticity of the Mg-xSn-yAl alloy is expressed by the Poisson's ratio, Cauchy pressure, and Pugh ratio.

[0019] In the study system described in this example, the alloy with Poisson's ratio > 0.36, Pugh ratio > 3.4, and Cauchy pressure > 20 GPa is Mg-(1-3.2)Sn-(0.7-0.8)Al.

[0020] The method described in this example includes preparing an alloy with a ratio of Mg-3.2Sn-0.79Al according to the determined alloy composition of the magnesium alloy, and conducting experimental tests.

[0021] The preparation method of the Mg-Sn-Al series high-ductility magnesium alloy described in this example is as follows: Ingot casting stage: Magnesium ingots with a purity of ≥99.9% and magnesium-aluminum and magnesium-tin master alloys are used as raw materials. The ingots are smelted under a protective SF6 / CO2 mixed gas. The smelting temperature is controlled at 720-750 ℃ ​​and sufficient mechanical or electromagnetic stirring is applied to ensure that the dense Sn element is fully dissolved and evenly distributed. A water-cooled semi-continuous casting process is adopted, and the pouring temperature is controlled at 700-720 ℃. Hot extrusion stage: The ingot is sawn to an aspect ratio of 3 and preheated at 400-430 ℃ for 3-4 hours. The extrusion is carried out at a die and extrusion cylinder temperature of 380-420 ℃. The extrusion bar speed is controlled at 1-2 mm / s, the extrusion ratio is 20, and the die orifice is designed as a flat hole with a target thickness of 6 mm. The extruded slab is immediately subjected to forced air cooling. Rolling stage: The sheet metal must be heated to above 400 ℃ and kept at that temperature before rolling. The rolling process is divided into two stages: rough rolling (6 mm → 3 mm) and finish rolling (3 mm → 1 mm). A critical intermediate annealing (380-400 ℃ / 30-60 min) must be performed at the 3 mm thickness to eliminate work hardening and restore plasticity. Precise temperature control is required throughout the process. The temperature is maintained at 400-360 ℃ during the rough rolling stage and not lower than 310 ℃ during the finish rolling stage. The single-pass reduction rate must be strictly controlled (≤15% for rough rolling and ≤10% for finish rolling). The final rolling temperature must be higher than 300 ℃ to ensure forming and avoid cracking. Post-processing: Perform pulsed current post-processing (25 A / mm). 2 (500 Hz, 30% duty cycle, processing time 300 s), followed by air cooling to eliminate residual internal stress, improve dimensional stability and achieve synergistic improvement in strength and plasticity.

[0022] The design and preparation method of a Mg-Sn-Al high-plasticity magnesium alloy is described in detail below.

[0023] In this example of the Mg-xSn-yAl alloy system, x was initially set to 0.4~3.2 wt.% and y to 0.4~3.8 wt.%; based on this, 56 alloys with different contents of Mg, Al, and Sn were designed and combined.

[0024] This example demonstrates the mechanical properties of different alloys in the first-principles calculation of the elastic constants of the Mg-xSn-yAl alloy. The calculation results are as follows: Figure 4 .

[0025] In the study system described in this example, the alloy with Poisson's ratio > 0.36, Pugh ratio > 3.6, and Cauchy pressure > 18 GPa is Mg-(1-3.2)Sn-(0.7-0.8)Al.

[0026] This study employs first-principles calculations based on density functional theory to provide a theoretical basis for alloy composition screening and design. Specifically, we used the CASTEP module in Materials Studio software to systematically calculate the elastic constants of 56 alloy systems. The calculations were performed under periodic boundary conditions, where electron exchange correlations were described by PBE functionals under the generalized gradient approximation, and electron-ion interactions were simulated using ultrasoft pseudopotentials. The potential function expansion in reciprocal space was completed based on pseudopotentials treated with canonical conditions for relaxation.

[0027] During the calculation, electronic relaxation optimization was performed using the BFGS conjugate gradient algorithm within the CASTEP module. The energy convergence criterion for self-consistent iteration was set to 1×10⁻⁶. -6 eV / atom. The geometry optimization stage requires interatomic forces to be less than 0.01 eV / Å, stress deviations to be controlled within 0.02 GPa, and atomic displacement tolerances to be limited to 0.005 Å. All calculations are based on a unit cell model, with the kinetic energy cutoff set to 650 eV and the k-point mesh density configured as 15×15×8.

[0028] In CASTEP, select Elastic Constants for elastic constant calculation. Using the stress-strain method not only significantly reduces computational costs but also yields relatively reliable results.

[0029] According to the generalized Hooke's law, the elastic constant can be obtained using the following formula: In the formula In response to the forces, The elastic constant matrix, This is the dependent variable.

[0030] By solving the coefficient matrix, the elastic constants of the corresponding unit cell are obtained. Then, the bulk modulus (B), Cauchy pressure, and shear modulus (G) are approximated using the Voigt-Reuss-Hill (VRH) model. Poisson's ratio and Pugh ratio are then calculated using the bulk modulus (B) and shear modulus (G). The plasticity of the Mg-xSn-yAl alloy is expressed by Poisson's ratio, Cauchy pressure, and Pugh ratio.

[0031] The Voigt-Reuss-Hill (VRH) model is as follows: The formulas for solving B and G using the Voigt model are: The formulas for solving B and G in the Reuss model are: The final formula for solving B and G in the Hill model is: The formula for calculating Poisson's ratio using B and G is: To further evaluate the alloy's ductility and toughness tendency, the Pugh ratio (B / G) is introduced as an empirical criterion, and its expression is: Cauchy pressure (σ) k It can be calculated using the following formula:

[0032] Based on well-known theories in the fields of materials mechanics and alloy design, the bulk modulus (B), Cauchy pressure, Pugh ratio (B / G), and Poisson's ratio (ν) obtained from the calculation of elastic constants can be used to evaluate the strength and plasticity of materials. Specifically: The bulk modulus (B) reflects a material’s ability to resist uniform compressive deformation. The higher the value, the higher the overall strength of the material. Cauchy stress is used to characterize the bonding properties of materials. When the Cauchy stress is positive, the material tends to exhibit plasticity, and the larger the positive value, the better the plasticity is usually. When the Cauchy stress is negative, the material tends to exhibit brittleness or poor plasticity. The Pugh ratio (B / G, i.e., the ratio of bulk modulus to shear modulus) is an important criterion for judging the ductile-brittle transition of a material. When the Pugh ratio is less than 1.75, the material usually has poor plasticity; when the Pugh ratio is greater than 1.75, the material usually exhibits plasticity, and the larger the ratio, the better the plasticity. Poisson's ratio (ν) can also characterize the plasticity of a material. When the Poisson's ratio is greater than 0.31, the material usually exhibits plasticity, and the larger the value, the better the plasticity is usually.

[0033] In this invention, by comprehensively considering the above indicators (Poisson's ratio, Cauchy pressure, and Pugh ratio), the alloy composition with the best plasticity is selected from the Mg-xSn-yAl alloy system.

[0034] Regarding the tensile properties, under the same experimental conditions, the elongation of the Mg-3.2Sn-0.79Al alloy was 15.6%; the microstructure was... Figure 3 (a) Compared to unprocessed SEM tissue Figure 3(d) The grains are significantly refined, the number of grain boundaries increases, and the uniformity of the microstructure is significantly improved, indicating that this example promotes microstructure refinement and homogenization.

[0035] Example 2 This example presents the design and preparation method of a Mg-Sn-Al based high-ductility magnesium alloy. This novel magnesium alloy is Mg-2.3Sn-0.76Al, and its design method includes the following steps: S1. Establish a Mg-xSn-yAl alloy system, wherein the Mg-xSn-yAl alloy system is composed of alloys with different contents of Mg, Al and Sn elements; S2. Based on first principles, a VCA Mg-Sn-Al alloy model was established using Materials Studio software, and the elastic constants of the alloy in the target research system were calculated. S3. Based on the elastic constants of the alloy in the target research system, the bulk modulus is obtained using the Voigt-Reuss-Hill (VRH) model. and shear modulus And further calculate Poisson's ratio Pugh and Cauchy stress ; S4. According to the calculated Poisson's ratio Pugh The Cauchy pressure was used to determine the alloy composition with the best plasticity.

[0036] In the study system described in this example, the initial values ​​of the Mg-xSn-yAl alloy were set as x = 0.4~3.2 wt.% and y = 0.4~3.8 wt.%.

[0037] In this example, the VCA Mg-Sn-Al alloy model in the research system is based on the hcp-Mg crystal structure, in which two Mg atoms are replaced by Mg-xSn-yAl atoms. See details... Figure 1 .

[0038] In the study system described in this example, the elastic constants are approximated by the Voigt-Reuss-Hill (VRH) model to obtain the bulk modulus (B), Cauchy pressure, and shear modulus (G). Poisson's ratio and Pugh ratio are then calculated using the bulk modulus (B) and shear modulus (G). The plasticity of the Mg-xSn-yAl alloy is expressed by the Poisson's ratio, Cauchy pressure, and Pugh ratio.

[0039] In the study system described in this example, the alloy with Poisson's ratio > 0.36, Pugh ratio > 3.4, and Cauchy pressure > 20 GPa is Mg-(1-3.2)Sn-(0.7-0.8)Al.

[0040] The method described in this example includes preparing an alloy with a ratio of Mg-3.2Sn-0.79Al according to the determined alloy composition of the magnesium alloy, and conducting experimental tests.

[0041] The preparation method of the Mg-Sn-Al series high-ductility magnesium alloy described in this example is as follows: Ingot casting stage: Magnesium ingots with a purity of ≥99.9% and magnesium-aluminum and magnesium-tin master alloys are used as raw materials. The ingots are smelted under a protective SF6 / CO2 mixed gas. The smelting temperature is controlled at 720-750 ℃ ​​and sufficient mechanical or electromagnetic stirring is applied to ensure that the dense Sn element is fully dissolved and evenly distributed. A water-cooled semi-continuous casting process is adopted, and the pouring temperature is controlled at 700-720 ℃. Hot extrusion stage: The ingot is sawn to an aspect ratio of 3 and preheated at 400-430 ℃ for 3-4 hours. The extrusion is carried out at a die and extrusion cylinder temperature of 380-420 ℃. The extrusion bar speed is controlled at 1-2 mm / s, the extrusion ratio is 20, and the die orifice is designed as a flat hole with a target thickness of 6 mm. The extruded slab is immediately subjected to forced air cooling. Rolling stage: The sheet metal must be heated to above 400 ℃ and kept at that temperature before rolling. The rolling process is divided into two stages: rough rolling (6 mm → 3 mm) and finish rolling (3 mm → 1 mm). A critical intermediate annealing (380-400 ℃ / 30-60 min) must be performed at the 3 mm thickness to eliminate work hardening and restore plasticity. Precise temperature control is required throughout the process. The temperature is maintained at 400-360 ℃ during the rough rolling stage and not lower than 310 ℃ during the finish rolling stage. The single-pass reduction rate must be strictly controlled (≤15% for rough rolling and ≤10% for finish rolling). The final rolling temperature must be higher than 300 ℃ to ensure forming and avoid cracking. Post-processing: Perform pulsed current post-processing (25 A / mm). 2 (500 Hz, 30% duty cycle, processing time 300 s), followed by air cooling to eliminate residual internal stress, improve dimensional stability and achieve synergistic improvement in strength and plasticity.

[0042] The design and preparation method of a Mg-Sn-Al high-plasticity magnesium alloy is described in detail below.

[0043] In this example of the Mg-xSn-yAl alloy system, x was initially set to 0.4~3.2 wt.% and y to 0.4~3.8 wt.%; based on this, 56 alloys with different contents of Mg, Al, and Sn were designed and combined.

[0044] This example demonstrates the mechanical properties of different alloys in the first-principles calculation of the elastic constants of the Mg-xSn-yAl alloy. The calculation results are as follows: Figure 4 .

[0045] In the study system described in this example, the alloy with Poisson's ratio > 0.36, Pugh ratio > 3.6, and Cauchy pressure > 18 GPa is Mg-(1-3.2)Sn-(0.7-0.8)Al.

[0046] This study employs first-principles calculations based on density functional theory to provide a theoretical basis for alloy composition screening and design. Specifically, we used the CASTEP module in Materials Studio software to systematically calculate the elastic constants of 56 alloy systems. The calculations were performed under periodic boundary conditions, where electron exchange correlations were described by PBE functionals under the generalized gradient approximation, and electron-ion interactions were simulated using ultrasoft pseudopotentials. The potential function expansion in reciprocal space was completed based on pseudopotentials treated with canonical conditions for relaxation.

[0047] During the calculation, electronic relaxation optimization was performed using the BFGS conjugate gradient algorithm within the CASTEP module. The energy convergence criterion for self-consistent iteration was set to 1×10⁻⁶. -6 eV / atom. The geometry optimization stage requires interatomic forces to be less than 0.01 eV / Å, stress deviations to be controlled within 0.02 GPa, and atomic displacement tolerances to be limited to 0.005 Å. All calculations are based on a unit cell model, with the kinetic energy cutoff set to 650 eV and the k-point mesh density configured as 15×15×8.

[0048] In CASTEP, select Elastic Constants for elastic constant calculation. Using the stress-strain method not only significantly reduces computational costs but also yields relatively reliable results.

[0049] According to the generalized Hooke's law, the elastic constant can be obtained using the following formula: In the formula In response to the forces, The elastic constant matrix, This is the dependent variable.

[0050] By solving the coefficient matrix, the elastic constants of the corresponding unit cell are obtained. Then, the bulk modulus (B), Cauchy pressure, and shear modulus (G) are approximated using the Voigt-Reuss-Hill (VRH) model. Poisson's ratio and Pugh ratio are then calculated using the bulk modulus (B) and shear modulus (G). The plasticity of the Mg-xSn-yAl alloy is expressed by Poisson's ratio, Cauchy pressure, and Pugh ratio.

[0051] The Voigt-Reuss-Hill (VRH) model is as follows: The formulas for solving B and G using the Voigt model are: The formulas for solving B and G in the Reuss model are: The final formula for solving B and G in the Hill model is: The formula for calculating Poisson's ratio using B and G is: To further evaluate the alloy's ductility and toughness tendency, the Pugh ratio (B / G) is introduced as an empirical criterion, and its expression is: Cauchy pressure (σ) k It can be calculated using the following formula:

[0052] Based on well-known theories in the fields of materials mechanics and alloy design, the bulk modulus (B), Cauchy pressure, Pugh ratio (B / G), and Poisson's ratio (ν) obtained from the calculation of elastic constants can be used to evaluate the strength and plasticity of materials. Specifically: The bulk modulus (B) reflects a material’s ability to resist uniform compressive deformation. The higher the value, the higher the overall strength of the material. Cauchy stress is used to characterize the bonding properties of materials. When the Cauchy stress is positive, the material tends to exhibit plasticity, and the larger the positive value, the better the plasticity is usually. When the Cauchy stress is negative, the material tends to exhibit brittleness or poor plasticity. The Pugh ratio (B / G, i.e., the ratio of bulk modulus to shear modulus) is an important criterion for judging the ductile-brittle transition of a material. When the Pugh ratio is less than 1.75, the material usually has poor plasticity; when the Pugh ratio is greater than 1.75, the material usually exhibits plasticity, and the larger the ratio, the better the plasticity. Poisson's ratio (ν) can also characterize the plasticity of a material. When the Poisson's ratio is greater than 0.31, the material usually exhibits plasticity, and the larger the value, the better the plasticity is usually.

[0053] In this invention, by comprehensively considering the above indicators (Poisson's ratio, Cauchy pressure, and Pugh ratio), the alloy composition with the best plasticity is selected from the Mg-xSn-yAl alloy system.

[0054] Regarding the tensile properties, under the same experimental conditions, the elongation of the Mg-2.3Sn-0.76Al alloy was 14.3%, and the microstructure was... Figure 3 (b), compared to Figure 3 (e) The grain morphology tends to be more regular and equiaxed, the grain boundaries are clearer, and the intragranular banding features are significantly reduced, indicating that this example is conducive to eliminating local inhomogeneities in the original structure and improving the stability of the structure.

[0055] Example 3 This example presents the design and preparation method of a Mg-Sn-Al based high-ductility magnesium alloy. This novel magnesium alloy is Mg-1.2Sn-0.77Al, and its design method includes the following steps: S1. Establish a Mg-xSn-yAl alloy system, wherein the Mg-xSn-yAl alloy system is composed of alloys with different contents of Mg, Al and Sn elements; S2. Based on first principles, a VCA Mg-Sn-Al alloy model was established using Materials Studio software, and the elastic constants of the alloy in the target research system were calculated. S3. Based on the elastic constants of the alloy in the target research system, the bulk modulus is obtained using the Voigt-Reuss-Hill (VRH) model. and shear modulus And further calculate Poisson's ratio Pugh and Cauchy stress ; S4. According to the calculated Poisson's ratio Pugh The Cauchy pressure was used to determine the alloy composition with the best plasticity.

[0056] In the study system described in this example, the initial values ​​of the Mg-xSn-yAl alloy were set as x = 0.4~3.2 wt.% and y = 0.4~3.8 wt.%.

[0057] In this example, the VCA Mg-Sn-Al alloy model in the research system is based on the hcp-Mg crystal structure, in which two Mg atoms are replaced by Mg-xSn-yAl atoms. See details... Figure 1 .

[0058] In the study system described in this example, the elastic constants are approximated by the Voigt-Reuss-Hill (VRH) model to obtain the bulk modulus (B), Cauchy pressure, and shear modulus (G). Poisson's ratio and Pugh ratio are then calculated using the bulk modulus (B) and shear modulus (G). The plasticity of the Mg-xSn-yAl alloy is expressed by the Poisson's ratio, Cauchy pressure, and Pugh ratio.

[0059] In the study system described in this example, the alloy with Poisson's ratio > 0.36, Pugh ratio > 3.4, and Cauchy pressure > 20 GPa is Mg-(1-3.2)Sn-(0.7-0.8)Al.

[0060] The method described in this example includes preparing an alloy with a ratio of Mg-3.2Sn-0.79Al according to the determined alloy composition of the magnesium alloy, and conducting experimental tests.

[0061] The preparation method of the Mg-Sn-Al series high-ductility magnesium alloy described in this example is as follows: Ingot casting stage: Magnesium ingots with a purity of ≥99.9% and magnesium-aluminum and magnesium-tin master alloys are used as raw materials. The ingots are smelted under a protective SF6 / CO2 mixed gas. The smelting temperature is controlled at 720-750 ℃ ​​and sufficient mechanical or electromagnetic stirring is applied to ensure that the dense Sn element is fully dissolved and evenly distributed. A water-cooled semi-continuous casting process is adopted, and the pouring temperature is controlled at 700-720 ℃. Hot extrusion stage: The ingot is sawn to an aspect ratio of 3 and preheated at 400-430 ℃ for 3-4 hours. The extrusion is carried out at a die and extrusion cylinder temperature of 380-420 ℃. The extrusion bar speed is controlled at 1-2 mm / s, the extrusion ratio is 20, and the die orifice is designed as a flat hole with a target thickness of 6 mm. The extruded slab is immediately subjected to forced air cooling. Rolling stage: The sheet metal must be heated to above 400 ℃ and kept at that temperature before rolling. The rolling process is divided into two stages: rough rolling (6 mm → 3 mm) and finish rolling (3 mm → 1 mm). A critical intermediate annealing (380-400 ℃ / 30-60 min) must be performed at the 3 mm thickness to eliminate work hardening and restore plasticity. Precise temperature control is required throughout the process. The temperature is maintained at 400-360 ℃ during the rough rolling stage and not lower than 310 ℃ during the finish rolling stage. The single-pass reduction rate must be strictly controlled (≤15% for rough rolling and ≤10% for finish rolling). The final rolling temperature must be higher than 300 ℃ to ensure forming and avoid cracking. Post-processing: Perform pulsed current post-processing (25 A / mm). 2 (500 Hz, 30% duty cycle, processing time 300 s), followed by air cooling to eliminate residual internal stress, improve dimensional stability and achieve synergistic improvement in strength and plasticity.

[0062] The design and preparation method of a Mg-Sn-Al high-plasticity magnesium alloy is described in detail below.

[0063] In this example of the Mg-xSn-yAl alloy system, x was initially set to 0.4~3.2 wt.% and y to 0.4~3.8 wt.%; based on this, 56 alloys with different contents of Mg, Al, and Sn were designed and combined.

[0064] This example demonstrates the mechanical properties of different alloys in the first-principles calculation of the elastic constants of the Mg-xSn-yAl alloy. The calculation results are as follows: Figure 4 .

[0065] In the study system described in this example, the alloy with Poisson's ratio > 0.36, Pugh ratio > 3.6, and Cauchy pressure > 18 GPa is Mg-(1-3.2)Sn-(0.7-0.8)Al.

[0066] This study employs first-principles calculations based on density functional theory to provide a theoretical basis for alloy composition screening and design. Specifically, we used the CASTEP module in Materials Studio software to systematically calculate the elastic constants of 56 alloy systems. The calculations were performed under periodic boundary conditions, where electron exchange correlations were described by PBE functionals under the generalized gradient approximation, and electron-ion interactions were simulated using ultrasoft pseudopotentials. The potential function expansion in reciprocal space was completed based on pseudopotentials treated with canonical conditions for relaxation.

[0067] During the calculation, electronic relaxation optimization was performed using the BFGS conjugate gradient algorithm within the CASTEP module. The energy convergence criterion for self-consistent iteration was set to 1×10⁻⁶. -6eV / atom. The geometry optimization stage requires interatomic forces to be less than 0.01 eV / Å, stress deviations to be controlled within 0.02 GPa, and atomic displacement tolerances to be limited to 0.005 Å. All calculations are based on a unit cell model, with the kinetic energy cutoff set to 650 eV and the k-point mesh density configured as 15×15×8.

[0068] In CASTEP, select Elastic Constants for elastic constant calculation. Using the stress-strain method not only significantly reduces computational costs but also yields relatively reliable results.

[0069] According to the generalized Hooke's law, the elastic constant can be obtained using the following formula: In the formula In response to the forces, The elastic constant matrix, This is the dependent variable.

[0070] By solving the coefficient matrix, the elastic constants of the corresponding unit cell are obtained. Then, the bulk modulus (B), Cauchy pressure, and shear modulus (G) are approximated using the Voigt-Reuss-Hill (VRH) model. Poisson's ratio and Pugh ratio are then calculated using the bulk modulus (B) and shear modulus (G). The plasticity of the Mg-xSn-yAl alloy is expressed by Poisson's ratio, Cauchy pressure, and Pugh ratio.

[0071] The Voigt-Reuss-Hill (VRH) model is as follows: The formulas for solving B and G using the Voigt model are: The formulas for solving B and G in the Reuss model are: The final formula for solving B and G in the Hill model is: The formula for calculating Poisson's ratio using B and G is: To further evaluate the alloy's ductility and toughness tendency, the Pugh ratio (B / G) is introduced as an empirical criterion, and its expression is: Cauchy pressure (σ) k It can be calculated using the following formula:

[0072] Based on well-known theories in the fields of materials mechanics and alloy design, the bulk modulus (B), Cauchy pressure, Pugh ratio (B / G), and Poisson's ratio (ν) obtained from the calculation of elastic constants can be used to evaluate the strength and plasticity of materials. Specifically: The bulk modulus (B) reflects a material’s ability to resist uniform compressive deformation. The higher the value, the higher the overall strength of the material. Cauchy stress is used to characterize the bonding properties of materials. When the Cauchy stress is positive, the material tends to exhibit plasticity, and the larger the positive value, the better the plasticity is usually. When the Cauchy stress is negative, the material tends to exhibit brittleness or poor plasticity. The Pugh ratio (B / G, i.e., the ratio of bulk modulus to shear modulus) is an important criterion for judging the ductile-brittle transition of a material. When the Pugh ratio is less than 1.75, the material usually has poor plasticity; when the Pugh ratio is greater than 1.75, the material usually exhibits plasticity, and the larger the ratio, the better the plasticity. Poisson's ratio (ν) can also characterize the plasticity of a material. When the Poisson's ratio is greater than 0.31, the material usually exhibits plasticity, and the larger the value, the better the plasticity is usually.

[0073] In this invention, by comprehensively considering the above indicators (Poisson's ratio, Cauchy pressure, and Pugh ratio), the alloy composition with the best plasticity is selected from the Mg-xSn-yAl alloy system.

[0074] Regarding the tensile properties, under the same experimental conditions, the elongation of the Mg-1.2Sn-0.77Al alloy was 13.8%, and the microstructure was... Figure 3 (c), compared to Figure 3 (f) The grains are more uniform overall, the grain boundaries are more continuous, and the structure is more flat and uniform, indicating that this example has a positive effect on improving the consistency of the structure.

Claims

1. A design method for Mg-Sn-Al series high-ductility magnesium alloys, characterized in that, The method includes the following steps: S1. Establish a Mg-xSn-yAl alloy system, wherein the Mg-xSn-yAl alloy system is composed of alloys with different contents of Mg, Al and Sn elements; S2. Based on first principles, a VCA Mg-Sn-Al alloy model was established using Materials Studio software, and the elastic constants of the alloy in the target research system were calculated. S3. Based on the elastic constants of the alloy in the target research system, the bulk modulus is obtained using the Voigt-Reuss-Hill (VRH) model. and shear modulus And further calculate Poisson's ratio Pugh and Cauchy stress ; S4. According to the calculated Poisson's ratio Pugh The Cauchy pressure was used to determine the alloy composition with the best plasticity.

2. The design method for a Mg-Sn-Al series high-ductility magnesium alloy according to claim 1, characterized in that, In the Mg-xSn-yAl alloy system described in S1, x is initially set to 0.4~3.2 wt.%, and y to 0.4~3.8 wt.%.

3. The design method for a Mg-Sn-Al series high-ductility magnesium alloy according to claim 1, characterized in that, The VCA Mg-Sn-Al alloy model described in S2 is based on the hcp-Mg crystal structure, in which two Mg atoms are replaced with Mg-xSn-yAl atoms, as detailed in Figure 1.

4. The design method for a Mg-Sn-Al series high-ductility magnesium alloy according to claim 1, characterized in that, The elastic constants described in S3 are approximated by the Voigt-Reuss-Hill (VRH) model to obtain the bulk modulus (B), Cauchy pressure, and shear modulus (G). Poisson's ratio and Pugh ratio are then calculated using the bulk modulus (B) and shear modulus (G). The plasticity of the Mg-xSn-yAl alloy is expressed by the Poisson's ratio, Cauchy pressure, and Pugh ratio.

5. The design method for a Mg-Sn-Al series high-ductility magnesium alloy according to claim 1, characterized in that, The alloy described in S3 with a Poisson's ratio > 0.36, Pugh ratio > 3.6, and Cauchy pressure > 18 GPa is Mg-(1-3.2)Sn-(0.7-0.8)Al.

6. A method for preparing a Mg-Sn-Al based high-ductility magnesium alloy, characterized in that, The alloy manufacturing method is as follows: Ingot casting stage: Magnesium ingots with a purity of ≥99.9% and magnesium-aluminum and magnesium-tin master alloys are used as raw materials. The ingots are smelted under a protective SF6 / CO2 mixed gas. The smelting temperature is controlled at 720-750 ℃ ​​and sufficient mechanical or electromagnetic stirring is applied to ensure that the dense Sn element is fully dissolved and evenly distributed. A water-cooled semi-continuous casting process is adopted, and the pouring temperature is controlled at 700-720℃. Hot extrusion stage: The ingot is sawn to an aspect ratio of 3 and preheated at 400-430 ℃ for 3-4 hours. The extrusion is carried out at a die and extrusion cylinder temperature of 380-420 ℃. The extrusion bar speed is controlled at 1-2 mm / s, the extrusion ratio is 20, and the die orifice is designed as a flat hole with a target thickness of 6 mm. The extruded slab is immediately subjected to forced air cooling. Rolling stage: The sheet metal must be heated to above 400 ℃ and kept at that temperature before rolling. The rolling process is divided into two stages: roughing (6 mm → 3 mm) and finishing (3 mm → 1 mm). A critical intermediate annealing (380-400 ℃ / 30-60 min) must be performed at a thickness of 3 mm to eliminate work hardening and restore plasticity. Precise temperature control is required throughout the process. The temperature should be maintained at 400-360 ℃ during the roughing stage and not lower than 310 ℃ during the finishing stage. The single-pass reduction rate must be strictly controlled (≤15% for roughing and ≤10% for finishing). The final rolling temperature must be higher than 300 ℃ to ensure forming and avoid cracking. Post-processing: Perform pulsed current post-processing (25 A / mm). 2 (500 Hz, 30% duty cycle, processing time 300 s), followed by air cooling to eliminate residual internal stress, improve dimensional stability and achieve synergistic improvement in strength and plasticity.

7. A method for designing and preparing a Mg-Sn-Al based high-ductility magnesium alloy, characterized in that, The tensile properties of the prepared high-plasticity magnesium alloy sheet, under the same experimental conditions, show that the elongation of the Mg-(1-3.2)Sn-(0.7-0.8)Al alloy can reach 15.6%.

8. A method for designing and preparing a Mg-Sn-Al based high-ductility magnesium alloy, prepared by the design and production process described in any one of claims 1-7, characterized in that, The novel high-plasticity magnesium alloy has the following composition: Mg-(1-3.2)Sn-(0.7-0.8)Al (wt.%).

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