High-strength and high-corrosion-resistant magnesium alloy based on corrosion thermo-dynamics and its design method

Abstract

This invention belongs to the field of magnesium alloy material technology and discloses a high-strength, high-corrosion-resistant magnesium alloy based on corrosion thermo-kinetics and its design method. The design method is as follows: A dataset is established based on existing high-strength magnesium alloys to determine a first set of microalloying elements and low-alloying elements as candidate sets; based on corrosion thermodynamics and kinetics, considering the asynchronous dissolution and deposition of alloying elements and magnesium, the first set of microalloying elements and low-alloying elements as candidate sets are screened to determine a second set of microalloying elements and low-alloying elements as candidate sets; based on the above two candidate sets, candidate alloying elements are determined, and candidate alloys are composed according to their predefined mass percentages; then, the candidate alloys are verified and their composition optimized using a corrosion performance prediction model to obtain the high-strength, high-corrosion-resistant magnesium alloy. The design method of this invention is simple, fast, low-cost, and highly reliable, and can efficiently guide the design of high-strength, high-corrosion-resistant magnesium alloys.

Description

Technical Field

[0001] This invention relates to the field of magnesium alloy materials technology, and in particular to high-strength, high-corrosion-resistant magnesium alloys based on corrosion thermo-kinetics and their design methods. Background Art

[0002] Magnesium alloys possess low density, high specific strength, good damping and vibration reduction, and excellent machinability, making them widely used in aerospace, transportation, and electronics industries. However, the insufficient strength and poor corrosion resistance of traditional magnesium alloys severely hinder their further development. Intense plastic deformation can significantly improve the strength of magnesium alloys, but the deformation process is relatively complex.

[0003] Preparing protective coatings and improving the corrosion resistance of magnesium alloy substrates are common methods to enhance the corrosion resistance of magnesium alloys. However, once the coating cracks, it can cause severe localized corrosion. Alloying is often used to improve the corrosion resistance and mechanical properties of magnesium alloys. However, most research focuses only on corrosion resistance or only on mechanical properties. Moreover, high-strength magnesium alloys often have poor corrosion resistance, while corrosion-resistant magnesium alloys typically have insufficient mechanical properties. The development of high-strength, high-corrosion-resistant magnesium alloys still faces significant challenges. Current high-strength, high-corrosion-resistant magnesium alloy designs mostly employ trial-and-error methods, lacking corresponding theoretical guidance, making it difficult to achieve success on the first attempt. Furthermore, the trial-and-error method involves searching for new magnesium alloy materials within a vast material space, resulting in long development cycles, high costs, and the expenditure of substantial human and material resources. Summary of the Invention

[0004] To address the technical problems of existing technologies that struggle to simultaneously improve the corrosion resistance and strength of magnesium alloys, resulting in long experimental cycles and high costs, this invention provides a simple, fast, low-cost, and resource-saving high-strength, high-corrosion-resistant magnesium alloy based on corrosion thermodynamics and its design method.

[0005] The high-strength, high-corrosion-resistant magnesium alloy and its design method based on corrosion thermo-kinetics of the present invention are achieved through the following technical solutions:

[0006] The first objective of this invention is to provide a design method for high-strength, high-corrosion-resistant magnesium alloys based on corrosion thermo-kinetics, comprising the following steps:

[0007] Step 1: Obtain the publicly available alloy element composition and mechanical properties of magnesium alloys. Use the corresponding mechanical property data as input and the alloy element composition as output to establish a dataset. The alloy element composition includes the types and contents of alloy elements.

[0008] Step 2: Using the required mechanical properties as constraints, the dataset is filtered to obtain a high-strength magnesium alloy system dataset.

[0009] Step 3: Based on the constraint that the content of alloying elements is ≤ the first threshold, the alloying elements in the high-strength magnesium alloy system dataset are evaluated and screened to obtain the first microalloying element and low alloying element candidate set.

[0010] Step 4: Based on corrosion thermodynamics and kinetics, from the perspective that the asynchronous dissolution and deposition of alloying elements and magnesium elements can promote the formation of a protective film during the corrosion process, the alloying elements in the high-strength magnesium alloy system dataset are screened under the constraint that the micro-alloying elements have a later dissolution order and a earlier deposition order, and the low-alloying elements have a dissolution order and deposition order that are both between the micro-alloying elements and magnesium elements, to obtain a second set of candidate micro-alloying elements and low-alloying elements.

[0011] Step 5: Based on the first set of microalloying elements and low-alloying elements and the second set of microalloying elements and low-alloying elements, determine the candidate alloying elements and form a candidate magnesium alloy according to the predefined mass percentage of the alloying elements.

[0012] Step 6: Using a corrosion performance prediction model, determine the nucleation rate and growth rate of the corrosion products of the candidate magnesium alloys, as well as the corrosion rate and corrosion depth of the alloys. Using the constraints that the nucleation rate of the corrosion products > the corresponding growth rate, the corrosion rate ≤ a second threshold, and the corrosion depth < a third threshold, screen the candidate magnesium alloys to obtain high-strength, high-corrosion-resistant magnesium alloys.

[0013] It should be noted that in step 1 above, in order to facilitate the selection of alloy element composition of magnesium alloys that can meet the required mechanical performance based on the mechanical property data of magnesium alloys, this invention first establishes a dataset based on the publicly available mechanical property data of magnesium alloys as input and the alloy element composition as the corresponding output.

[0014] It should be noted that, in some preferred embodiments of the present invention, since the present invention mainly focuses on the role of alloying elements in precipitation strengthening and grain refinement strengthening, the mechanical property data mentioned above include data on mechanical strength contribution and plasticity contribution, so as to be able to input the data on mechanical strength contribution and plasticity contribution and obtain a high-strength magnesium alloy system dataset.

[0015] In step 2 above, when obtaining publicly available magnesium alloy data, this invention mainly focuses on the role of alloying elements in precipitation strengthening and grain refinement strengthening. Based on the two constraints of mechanical strength and plasticity, commonly used alloying elements in magnesium alloys are evaluated and screened, and the screened alloying elements are used as a dataset of high-strength magnesium alloy systems.

[0016] In step 3 above, the present invention, based on the commonly used content of alloying elements, filters from the high-strength magnesium alloy system dataset to obtain a first set of microalloying elements and low-alloying elements whose content is ≤ a first threshold, so as to facilitate further screening and determination of candidate alloying elements in subsequent steps. In some preferred embodiments of the present invention, the first threshold is 10.0%, that is, the first set of microalloying elements and low-alloying elements is obtained by using the content of alloying elements ≤ 10.0% as a constraint condition. In some more preferred embodiments of the present invention, the alloying elements in the high-strength magnesium alloy system dataset are screened using the content of alloying elements ≤ 1.0% and 10.0% ≥ the content of alloying elements > 1.0% as constraints to obtain a first set of microalloying elements and low-alloying elements whose content is ≤ 1.0% and 10.0% ≥ the content of low-alloying elements > 1.0%.

[0017] In step 4 above, this invention is based on corrosion thermodynamics and kinetics, taking into account that the asynchronous dissolution and deposition of alloying elements and magnesium elements can promote the formation of a protective film during the corrosion process, and considering the standard electrode potential E of the corresponding metal. θ A more positive value indicates that the metal dissolves later. Therefore, the standard electrode potential of each alloying element in the high-strength magnesium alloy system dataset can be calculated, and the dissolution order of the alloying elements can be determined based on the magnitude of the standard electrode potential. Thus, in some preferred embodiments of this invention, the invention proposes obtaining the standard electrode potential of the metal corresponding to each alloying element and sorting the standard electrode potentials of each alloying element's corresponding metal in descending order of their values, thereby obtaining the dissolution order of the atoms corresponding to each alloying element.

[0018] In some preferred embodiments of the present invention, the solubility product K of the corresponding oxide or hydroxide of the element is taken into account. sp The values ​​are used to plot the corresponding critical deposition lines; the lower the critical deposition line, the more preferentially deposition occurs. Therefore, the solubility product K of the oxides or hydroxides of each alloying element can be looked up and calculated. sp The deposition order of alloying elements can be determined by the height of their corresponding oxides or hydroxides. Therefore, this invention proposes to examine the solubility products of the oxides and hydroxides corresponding to each alloying element in a high-strength magnesium alloy system dataset, and then sort them sequentially according to the height of their corresponding oxides or hydroxides to obtain the deposition order of magnesium alloy corrosion products. In some preferred embodiments, taking the Mg-Gd-Y-Zr-In alloy system as an example, a deposition phase diagram of each alloying element in the Mg-Gd-Y-Zr-In alloy is plotted with pH as the abscissa and ion concentration as the ordinate. The deposition order of alloying elements is determined by the height of their corresponding critical deposition lines in the deposition phase diagram.

[0019] This invention considers that the rate of dissolution of alloying elements can be determined based on standard electrode potential, and the deposition order of corrosion products can be fed back from the critical deposition line of corrosion products. Therefore, by obtaining the dissolution order of the corresponding atoms of each alloying element and the deposition order of magnesium alloy corrosion products, and using the constraint that microalloying elements have a later dissolution order and an earlier deposition order, and that low-alloying elements have a dissolution order and deposition order between the microalloying elements and magnesium elements, the alloying elements of magnesium alloys can be screened. This allows the selected candidate magnesium alloy systems to achieve passivation and improve their corrosion resistance. For example, in some preferred embodiments of this invention, In and Zr are selected as microalloying elements, and Gd and Y are selected as low-alloying elements. By utilizing the asynchronous dissolution and deposition of low-alloying elements Gd and Y, microalloying elements In and Zr, and Mg elements, a step-by-step amplified nucleation mechanism is used to densify the protective film generated during corrosion, forming a multi-layered protective film, achieving alloy passivation, and improving the alloy's corrosion resistance. Among them, low-alloy elements Gd and Y play the role of solid solution strengthening and precipitation strengthening, microalloy element Zr plays the role of grain refinement, and In, as a microalloy element, can preferentially deposit to promote the deposition effect of other elements and inhibit the anodic dissolution kinetics of the alloy.

[0020] In step 5 of this invention, the invention proceeds from both the alloy element content and corrosion thermodynamics and kinetics. By eliminating the intersection of the first set of microalloying elements and the second set of microalloying elements and low-alloying elements, the types and contents of the final microalloying elements and final low-alloying elements are determined. These are then combined with Mg element according to a predefined mass percentage of alloying elements to form a candidate magnesium alloy. In a preferred embodiment of this invention, the determined composition of the candidate magnesium alloy is: Gd 1.0%–10.0%, Y 1.0%–10.0%, Zr 0.01%–1.0%, In 0.01%–1.0%, with the remainder being Mg, totaling 100%.

[0021] To ensure that the candidate magnesium alloys obtained above retain or improve the mechanical strength of Mg-Gd-Y-Zr alloys, this invention adds trace element In to obtain Mg-Gd-Y-Zr-In alloys. This further utilizes the asynchronous dissolution and deposition of low-alloying elements Gd and Y, and micro-alloying element In with Mg, employing a progressively amplified nucleation mechanism to densify the protective film generated during corrosion, forming a multi-layered protective film, achieving alloy passivation, and improving the alloy's corrosion resistance. Therefore, this invention also uses a corrosion performance prediction model to determine the nucleation rate and growth rate of corrosion products in the candidate magnesium alloys, as well as the corrosion rate and corrosion depth of the alloy. Furthermore, this invention considers that the rate of dissolution of alloying elements can be determined based on the standard electrode potential, and the critical deposition line of corrosion products can provide feedback on the deposition sequence of corrosion products during corrosion. Therefore, these two constraints enable the screening of alloying elements for magnesium alloys. However, since the formation of a dense passivation film under these two constraints is related to the alloy composition design, it is necessary to further investigate the magnesium alloy under the two constraints of corrosion rate and corrosion depth by establishing a corrosion performance prediction model. This model serves as the final criterion for determining the alloy design procedure. Furthermore, the corrosion resistance of the established corrosion performance prediction model was further verified and optimized.

[0022] Therefore, in step 6 of this invention, when establishing the corrosion performance prediction model, four aspects are considered: dissolution, ionization, diffusion, and deposition. Corrosion resistance data such as ion concentration, corrosion product supersaturation, corrosion product nucleation and growth rates, corrosion depth, and corrosion rate during the corrosion dissolution process are calculated to assess the corrosion performance of candidate magnesium alloys. This data can then be used to verify and optimize the composition of candidate magnesium alloys. Specifically, a "dissolution-ionization" model and a "diffusion-deposition" model are established. The "dissolution-ionization" model examines the current density of the magnesium alloy at the corrosion potential, while the "diffusion-deposition" model examines the corrosion depth of the magnesium alloy at the corrosion potential. After calculating the results of various Mg-Gd-Y-Zr-In alloys with different preset alloy compositions, the candidate magnesium alloys are screened based on constraints such as a corrosion product nucleation rate significantly greater than its corresponding growth rate, a corrosion rate rapidly decreasing to ≤ a second threshold over time, and a corrosion depth < 5 μm. This process determines a suitable high-strength, high-corrosion-resistant magnesium alloy composition. In some preferred embodiments of the Mg-Gd-Y-Zr-In invention, the second threshold is 1 mm / a, meaning the constraint condition is that the corrosion rate rapidly decreases to ≤1 mm / a over time. In some preferred embodiments of the invention, the third threshold is 5 μm, meaning the constraint condition is that the corrosion depth is <5 μm.

[0023] In some preferred embodiments of the present invention, the "dissolution-ionization-diffusion-deposition" model is obtained through the following steps:

[0024] 1) Using the standard electrode potentials of the corresponding metals for each element in the candidate magnesium alloy as input, preset...

[0025] The composition of the Mg-Gd-Y-Zr-In alloy was determined, and the equilibrium potentials of the metal electrode reactions for each element were calculated using the Nernst equation. Then, using these equilibrium potentials as input, the corrosion potential of the magnesium alloy was calculated based on the mixed potential theory. Finally, using the corrosion potential as input, the corrosion current density of the magnesium alloy at that corrosion potential was calculated using the Butler-Volmer formula.

[0026] 2) Using the solubility products of the corresponding oxides and hydroxides of each element as input, the supersaturation S of each corrosion product is calculated according to Faraday's law and Fick's second law. Using the supersaturation S of each corrosion product as input, the nucleation rate and growth rate of the corresponding corrosion products are calculated. Using the nucleation rate and growth rate of the corrosion products as input, the coverage of corrosion products and the overall corrosion rate of the magnesium alloy are calculated.

[0027] The corrosion current density of magnesium alloy at corrosion potential is obtained through the following steps:

[0028] This invention considers that the corrosion of magnesium alloys involves metal oxidation and hydrogen reduction. The corrosion potential of magnesium alloys is influenced by both the types of alloying elements and their equilibrium potentials. First, the equilibrium potentials of the metal electrode reactions corresponding to each element are calculated using the Nernst equation. Then, the corrosion potential of the magnesium alloy is calculated using the mixed potential theory. The formulas involved in the calculations are shown in Equations 1-8.

[0029] R→O+ne Equation 1.

[0030]

[0031] E a =E c =E corr Formula 5.

[0032] In Equation 1, R represents the reduced state substance; O represents the oxidized state substance; e represents the electrons transferred in the electrode reaction; and n represents the number of electrons transferred in the electrode reaction.

[0033] In Equation 2, E e E represents the equilibrium potential of the metal electrode reaction corresponding to each element. θ denoted as , where is the standard potential of the metal electrode reaction corresponding to each element; R is the gas constant; T is the temperature in K; [O] is the concentration of the oxidized substance; F is the Faraday constant, 96485 C / mol; and [R] is the concentration of the reduced substance.

[0034] In Equation 3, i a(E a ) represents i a Equivalent to E a , is the total anode potential; f Mk i represents the atomic percentage of the k-th alloying element in the magnesium alloy; a,Mk (E a ) represents the anode potential of the k-th alloying element in the magnesium alloy; k refers to the total number of alloying elements in the magnesium alloy.

[0035] In Equation 4, i c (E c ) represents i c Equivalent to E c , is the total cathode potential; f Mk i represents the atomic percentage of the k-th alloying element in the magnesium alloy; c,Mk (E c ) represents the cathode potential of the k-th alloying element in the magnesium alloy; k refers to the total number of alloying elements in the magnesium alloy.

[0036] In Equation 5, E a E represents the total anode potential. c E represents the total cathode potential. corr This represents the corrosion potential.

[0037] The current density at the corrosion potential is calculated using the Butler-Volmer equation, and the rate of dissolution of alloying elements is determined based on the current density. The number of dissolved layers is then calculated using a dissolution model and converted into a dissolution current density, as shown in Equations 6-8. When the slowest-dissolving element accumulates in a layer on the surface, the corrosion potential needs to be corrected, and the dissolution current density recalculated.

[0038] η = E corr -E Formula 6.

[0039]

[0040] In Equation 6, η is the overpotential, and E corr Here, E represents the corrosion potential, and E represents the actual measured potential.

[0041] In Equation 7, i M i represents the current density at the corrosion potential; M,0 η is the exchange current density; α is the symmetry coefficient; n is the number of electrons transferred in the electrode reaction; F is the Faraday constant, 96485 C / mol; η is the overpotential; R is the gas constant; T is the temperature in K.

[0042] In Equation 8, J i L is the dissolution current density. i This represents the number of dissolution equivalent layers.

[0043] In some preferred embodiments of the present invention, the coverage of corrosion products and the overall corrosion rate of the magnesium alloy are obtained through the following steps:

[0044] First, according to Faraday's law And Fick's Second Law The changes in ion concentration and pH value at the metal / solution interface over time were calculated, and then the supersaturation S of each corrosion product was calculated. When the supersaturation > 1, the corrosion products will nucleate and grow on the metal surface. Supersaturation S and nucleation rate V are also considered. N The calculation formula is as follows:

[0045]

[0046] In Equation 9, S represents the supersaturation of the corrosion products; [M n+ [OH] represents the concentration of metal ions; - ] is OH - The concentration; n is the number of electrons transferred in the electrode reaction; K sp This is the solubility product of the corrosion products.

[0047] In Equations 10 and 11, V N V represents the homogeneous nucleation rate; N ' represents the heterogeneous nucleation rate; A is the recombination constant as a function of temperature; γ is the surface energy corresponding to the critical nucleation size, 0.1 J / m. 2 v is the molecular volume; S is the supersaturation of the corrosion products; k is the reaction constant, 0.1 mol / Ls; T is the temperature, in K.

[0048] The crystal grows according to a two-dimensional step growth model, and the corresponding formula for calculating the crystal growth rate is as follows:

[0049]

[0050] In Equation 12, V R Let A be the crystal growth rate; A is the recombination constant as a function of temperature, set to 10. 24 B is a composite constant that varies with temperature, set to 10. 3 S represents the supersaturation of the corrosion products.

[0051] As corrosion products continuously deposit, the alloy surface will gradually be covered, thus hindering further corrosion of the magnesium matrix. The current density differs between the film-covered and film-free regions; therefore, the overall corrosion rate of the alloy can be represented by the coverage rate of the corrosion product film, which is calculated using the following formula:

[0052] i corr =i alloy (1-θ)+i CSθ Equation 13.

[0053] In Equation 13, i corr Let i be the corrosion current density of the magnesium alloy; the current densities in the regions with and without corrosion products are respectively expressed as i cs and i alloy θ represents the coverage of the corrosion product film.

[0054] The corrosion depth mentioned in this invention refers to the dissolution depth of the alloy when the corrosion product film completely covers (coverage rate > 0.99%) the metal surface. The corrosion depth can be obtained by integrating the corrosion rate over time, and the calculation formula is as follows:

[0055]

[0056] In the formula, CD represents the corrosion depth; i corr t represents the corrosion current density of the alloy; t represents time, in seconds.

[0057] In some preferred embodiments of the present invention, the chemical composition of the high-strength and high-corrosion-resistant magnesium alloy obtained by the above-described design method of the present invention consists of the following components by mass percentage: Gd 6%, Y 3%, Zr 0.5%, In 0.5%, with the remainder being Mg, totaling 100%.

[0058] Furthermore, in the Mg-Gd-Y-Zr-In alloy system designed in this invention, Mg and low alloying elements Gd and Y preferentially dissolve during the corrosion process, while In dissolves last. Subsequently, corrosion products containing In preferentially deposit, thereby transforming the corrosion products of Gd and Y from homogeneous nucleation to heterogeneous nucleation, reducing their nucleation surface energy by 2 / 3, and promoting their deposition effect. Then, the deposition effect of Mg(OH)2 is further amplified by the corrosion products of Gd and Y, ultimately forming a dense protective film with a multi-layered structure on the alloy surface, improving the corrosion resistance of the alloy.

[0059] This invention also provides a method for preparing a high-strength, high-corrosion-resistant Mg-Gd-Y-Zr-In alloy based on multi-objective design from the perspective of corrosion thermo-kinetics, comprising the following steps:

[0060] S1. Weigh the raw materials of each chemical component according to the chemical composition ratio of the high-strength and high-corrosion-resistant magnesium alloy.

[0061] S2, the weighed raw materials of each chemical component are placed in a vacuum induction melting process and cast to obtain the target alloy ingot.

[0062] S3. The target alloy ingot is solution-treated and then aged to obtain the high-strength, high-corrosion-resistant magnesium alloy. Alternatively, the target alloy ingot is hot-extruded to obtain the high-strength, high-corrosion-resistant magnesium alloy.

[0063] In a preferred embodiment of the present invention, the solution treatment temperature is 495°C and the solution treatment time is 14 hours to achieve the purpose of solution treatment.

[0064] In a preferred embodiment of the present invention, the hot extrusion treatment temperature is 400°C, the extrusion ratio is 9:1, and the extrusion rate is 0.4 mm / s, so as to achieve the purpose of refining the grains.

[0065] In a preferred embodiment of the present invention, the aging treatment temperature is 200°C and the aging time is 96 hours.

[0066] Compared with the prior art, the present invention has the following beneficial effects:

[0067] This invention first establishes a dataset by using the publicly available alloying element composition and mechanical properties of magnesium alloys as input and the corresponding mechanical property data as output. Then, based on the required mechanical property data as constraints, a first set of micro-alloying elements and low-alloying elements is established, considering the effects of alloying elements on precipitation strengthening and grain refinement. Simultaneously, based on corrosion thermodynamics and kinetics, and considering that the asynchronous dissolution and deposition of alloying elements and magnesium can promote the formation of a protective film during corrosion, a second set of micro-alloying elements and low-alloying elements is established, with the condition that micro-alloying elements have a later dissolution order and a earlier deposition order, and low-alloying elements have both a dissolution order and a deposition order between the micro-alloying elements and magnesium. Based on these candidate sets, a candidate high-strength, high-corrosion-resistant Mg-Gd-Y-Zr-In alloy is obtained. This allows the invention to improve the corrosion resistance of high-strength Mg-Gd-Y-Zr magnesium alloys by forming a dense protective film while retaining their high mechanical strength. Furthermore, this invention divides the alloying elements in the high-strength magnesium alloy system dataset into a micro-alloying element candidate set (where the content of an alloying element is ≤ a first threshold) and a low-alloying element candidate set (where the content of an alloying element is > a first threshold) based on the commonly used content of alloying elements. This facilitates the formation of candidate magnesium alloys by combining any two alloying elements selected from the micro-alloying element candidate set, any two alloying elements selected from the low-alloying element candidate set, and magnesium. Then, using a corrosion performance prediction model, candidate magnesium alloys are screened based on the following constraints: micro-alloying elements satisfy the condition of having a later dissolution order and an earlier deposition order; low-alloying elements satisfy the condition that both the dissolution order and deposition order are between those of the micro-alloying elements and magnesium; the nucleation rate of the corrosion products is greater than the corresponding growth rate; the corrosion rate is ≤ a second threshold; and the corrosion depth is < a third threshold. This results in high-strength, high-corrosion-resistant magnesium alloys.

[0068] This invention is based on high-strength magnesium alloys. While retaining the alloy's high mechanical strength, the low-alloying elements and micro-alloying elements determined by the aforementioned method can densify the protective film generated during corrosion through a stepwise amplified nucleation mechanism via dissolution and deposition, forming a multi-layered protective film, thus achieving alloy passivation and improving the alloy's corrosion resistance. Combining corrosion thermodynamics and kinetics, and based on a multi-dimensional consideration of "dissolution-ionization-diffusion-deposition," a corrosion performance prediction model is established to further optimize the alloy composition and improve the corrosion resistance of the final designed high-strength, high-corrosion-resistant magnesium alloy. The magnesium alloy corrosion performance prediction model established in this invention can calculate the nucleation and growth process of corrosion products, the coverage of the protective film, and the corrosion rate of the alloy during corrosion, effectively designing the alloy composition and predicting the alloy's corrosion performance.

[0069] This invention presents a simple and reliable design and development method for high-strength, high-corrosion-resistant magnesium alloys. Tests show that the as-cast high-strength, high-corrosion-resistant magnesium alloy prepared using the chemical composition designed according to this invention exhibits a yield strength greater than 200 MPa and a corrosion rate of only 0.17 mm / a. The high-strength, high-corrosion-resistant magnesium alloy obtained through hot extrusion exhibits a yield strength greater than 300 MPa and a corrosion rate less than 0.1 mm / a, with performance comparable to aluminum alloys. Attached Figure Description

[0070] Figure 1 This is a standard electrode potential diagram of each alloying element and its compound in the high-strength and high-corrosion-resistant magnesium alloy of the present invention.

[0071] Figure 2 This is a deposition phase diagram of each alloying element in the high-strength, high-corrosion-resistant magnesium alloy of the present invention.

[0072] Figure 3 The corrosion rate test results are for Examples 2 to 4 and Comparative Examples 1 to 4 of the present invention.

[0073] Figure 4 The stress-strain curve test results are for Examples 2 to 4 and Comparative Examples 1 to 4 of the present invention. Detailed Implementation

[0074] The technical solutions in the embodiments of the present invention will be clearly and completely described below.

[0075] Example 1

[0076] This embodiment provides a design method for high-strength, high-corrosion-resistant magnesium alloys based on corrosion thermodynamics, including the following steps:

[0077] Step 1: Obtain the publicly available composition and mechanical properties of magnesium alloys. Use the corresponding mechanical property data as input and the alloy element composition as the corresponding output to establish a dataset. The alloy element composition includes the types and contents of alloy elements. The mechanical property data includes data on mechanical strength and plasticity.

[0078] In this embodiment, the composition of the magnesium alloy includes the alloying elements and their contents in each magnesium alloy.

[0079] Step 2: Based on the two constraints of mechanical strength contribution and plasticity contribution, the alloying elements in the first dataset are evaluated and screened to obtain a high-strength magnesium alloy system dataset.

[0080] Step 3: Based on the constraints that the content of microalloying elements is ≤1.0% and the content of low-alloying elements is ≥10.0% and >1.0%, the alloying elements in the high-strength magnesium alloy system dataset are evaluated and screened to obtain candidate sets of microalloying elements and low-alloying elements, which are used as the first candidate sets of microalloying elements and low-alloying elements.

[0081] Step 4: Screening yields high-strength, high-corrosion-resistant magnesium alloys.

[0082] 4.1) Determine the dissolution order of the corresponding atoms of each alloying element in the candidate magnesium alloy:

[0083] For the high-strength magnesium alloy system dataset obtained through step 2 above, the calculated standard electrode potentials of each alloying element are as follows: And plot the standard electrode potentials of each alloying element as shown below. Figure 1 The standard electrode potential diagram of the alloying elements in the Mg-Gd-Y-Zr-In alloy of the present invention is shown, and is derived from... Figure 1 It can be seen that,

[0084] The dissolution order of the alloying elements is Mg≈Gd≈Y>In.

[0085] 4.2) Determine the deposition sequence of atoms corresponding to each alloying element in the candidate magnesium alloy:

[0086] For the high-strength magnesium alloy system dataset obtained through step 2 above, a plot is drawn with pH as the x-axis and ion concentration as the y-axis as shown below. Figure 2 The deposition phase diagram of each alloying element in the Mg-Gd-Y-Zr-In alloy is shown. The deposition order of the alloying elements can be determined by the height of the critical deposition lines of each substance in the deposition phase diagram.

[0087] Furthermore, the solubility product K of the corresponding oxides or hydroxides of each alloying element was calculated. sp respectively therefore The deposition order of the alloying elements is In>Gd>Y>Mg.

[0088] The second set of microalloying elements and low-alloying elements was obtained based on the dissolution order and deposition order.

[0089] Step 5: Based on the screening results of Steps 3 and 4, the candidate alloying elements for microalloying are determined to be Zr and In, and the candidate alloying elements for low alloying are determined to be Gd and Y. The determined candidate alloying elements for microalloying are combined with magnesium to form a candidate magnesium alloy according to the predefined mass percentage of alloying elements: Gd 1.0%~10.0%, Y 1.0%~10.0%, Zr 0.01%~1.0%, In 0.01%~1.0%, and the remainder is Mg, for a total of 100%.

[0090] Step 6: Using a corrosion performance prediction model, determine the nucleation rate and growth rate of corrosion products corresponding to each alloying element in the candidate magnesium alloy, as well as the corrosion rate and corrosion depth of the alloy.

[0091] 6.1) Determine the nucleation rate and growth rate of corrosion products:

[0092] Using the standard electrode potentials of the metals corresponding to each element of the candidate magnesium alloy as input, the equilibrium potentials of the metal electrode reactions corresponding to each element are calculated according to the Nernst equation.

[0093] Then, using the equilibrium potential of the metal electrode reaction corresponding to each element as input, the corrosion potential of the magnesium alloy is calculated based on the mixed potential theory.

[0094] Then, using the corrosion potential of the magnesium alloy as input, the current density at the corrosion potential is calculated according to the Butler-Volmer formula.

[0095] Using the solubility product of the corresponding oxides and hydroxides of each element as input, the supersaturation S of each corrosion product is calculated according to Faraday's law and Fick's second law.

[0096] Using the supersaturation S of each corrosion product as input, the nucleation rate and growth rate of the corresponding corrosion products are calculated.

[0097] 6.2) Determine the corrosion rate of the corrosion products:

[0098] Using the nucleation rate and growth rate of corrosion products as input, the coverage of corrosion products and the overall corrosion rate of magnesium alloy are calculated.

[0099] 6.3) Determine the corrosion depth of the corrosion products:

[0100] The corrosion depth of the magnesium alloy is calculated by taking the overall corrosion rate and corrosion current density of the magnesium alloy as inputs.

[0101] The candidate magnesium alloys obtained above were screened under the following constraints: microalloying elements were found to be in a later dissolution order and an earlier deposition order; low-alloying elements were found to be in a dissolution order and a deposition order between the microalloying elements and magnesium; the nucleation rate of the corrosion products was greater than the corresponding growth rate; the corrosion rate decreased rapidly over time to ≤1 mm / a; and the corrosion depth was <5 μm. The resulting high-strength, high-corrosion-resistant magnesium alloy was obtained. The chemical composition of this high-strength, high-corrosion-resistant magnesium alloy consisted of the following components by mass percentage: Gd 6%, Y 3%, Zr 0.5%, In 0.5%, with the remainder being Mg, totaling 100%, denoted as Mg-6Gd-3Y-0.5Zr-0.5In alloy.

[0102] Example 2

[0103] This embodiment provides a method for preparing a high-strength, high-corrosion-resistant magnesium alloy, comprising the following steps:

[0104] S1. According to the chemical composition ratio of the high-strength, high-corrosion-resistant alloy obtained in Example 1, namely the Mg-6Gd-3Y-0.5Zr-0.5In alloy, weigh the corresponding Gd source, Y source, Zr source, In source, and Mg source:

[0105] Gd 6%, Y 3%, Zr 0.5%, In 0.5%, with the remainder being Mg, totaling 100%.

[0106] In this embodiment, the Gd source is added in the form of intermediate alloy Mg-25Gd, the Y source is added in the form of intermediate alloy Mg-25Y, the Zr source is added in the form of intermediate alloy Mg-20Zr, the In source is added in the form of pure In particles, and the Mg source is added together in the form of intermediate alloy Mg-25Gd, Mg-25Y, Mg-20Zr and pure magnesium.

[0107] S2. The weighed raw materials of each chemical component are placed in a graphite crucible for vacuum induction melting. The crucible is heated under the protection of a mixed gas of CO2 and SF6 with a volume ratio of 9:1. After heating to 720℃, the temperature is held for 30 minutes to ensure that the raw materials are completely melted. After melting, mechanical stirring is applied for 10 minutes to ensure that the raw materials are uniformly mixed. After stirring, the mixture is allowed to stand for 20 minutes. Finally, it is poured into a stainless steel mold to obtain a cylindrical ingot with a diameter of 100mm × 600mm, which is the target alloy ingot.

[0108] S3. The obtained target alloy ingot was subjected to homogenization solution treatment at a temperature of 495℃, held for 14 hours, and then cooled with hot water at approximately 80℃. Subsequently, the solution-treated sample was aged at a temperature of 200℃ for 96 hours.

[0109] S4. The aged sample was processed by wire cutting into a 20mm×20mm×5mm specimen and a sheet-like dog bone tensile specimen with a gauge length of 15mm, a width of 3.6mm, and a thickness of 2.5mm. These specimens were used for hydrogen evolution test and room temperature tensile test, respectively. Before the test, the specimens were polished with SiC sandpaper of 240#, 600#, 1000#, and 2000# in sequence.

[0110] Example 3

[0111] This embodiment provides a method for preparing a high-strength, high-corrosion-resistant magnesium alloy, comprising the following steps:

[0112] S1. According to the chemical composition ratio of the high-strength, high-corrosion-resistant alloy obtained in Example 1, namely the Mg-6Gd-3Y-0.5Zr-0.5In alloy, weigh the corresponding Gd source, Y source, Zr source, In source, and Mg source:

[0113] Gd 6%, Y 3%, Zr 0.5%, In 0.5%, with the remainder being Mg, totaling 100%.

[0114] In this embodiment, the Gd source is added in the form of intermediate alloy Mg-25Gd, the Y source is added in the form of intermediate alloy Mg-25Y, the Zr source is added in the form of intermediate alloy Mg-20Zr, the In source is added in the form of pure In particles, and the Mg source is added together in the form of intermediate alloy Mg-25Gd, Mg-25Y, Mg-20Zr and pure magnesium.

[0115] S2. The weighed raw materials of each chemical component are placed in a graphite crucible for vacuum induction melting. The crucible is heated under the protection of a mixed gas of CO2 and SF6 with a volume ratio of 9:1. After heating to 720℃, the temperature is held for 30 minutes to ensure that the raw materials are completely melted. After melting, mechanical stirring is applied for 10 minutes to ensure that the raw materials are uniformly mixed. After stirring, the mixture is allowed to stand for 20 minutes. Finally, it is poured into a stainless steel mold to obtain a cylindrical ingot with a diameter of 100mm × 600mm, which is the target alloy ingot.

[0116] S3. The target alloy ingot is subjected to hot extrusion treatment at an extrusion temperature of 400℃, an extrusion ratio of 9:1, and an extrusion rate of 0.4mm / s to obtain an extruded bar with a diameter of 30mm.

[0117] S4. The hot-extruded sample was processed by wire cutting into a 20mm×20mm×5mm specimen and a sheet-like dog bone tensile specimen with a gauge length of 15mm, a width of 3.6mm, and a thickness of 2.5mm. These specimens were used for hydrogen evolution test and room temperature tensile test, respectively. Before the test, the specimens were polished with SiC sandpaper of 240#, 600#, 1000#, and 2000# in sequence.

[0118] Example 4

[0119] This embodiment provides a method for preparing a high-strength, high-corrosion-resistant magnesium alloy, comprising the following steps:

[0120] S1. Based on the chemical composition ratio of the high-strength, high-corrosion-resistant magnesium alloy obtained in Example 1, namely the Mg-6Gd-3Y-0.5Zr-0.5In alloy, weigh out the corresponding Gd source, Y source, Zr source, In source, and Mg source:

[0121] Gd 6%, Y 3%, Zr 0.5%, In 0.5%, with the remainder being Mg, totaling 100%.

[0122] In this embodiment, the Gd source is added in the form of intermediate alloy Mg-25Gd, the Y source is added in the form of intermediate alloy Mg-25Y, the Zr source is added in the form of intermediate alloy Mg-20Zr, the In source is added in the form of pure In particles, and the Mg source is added together in the form of intermediate alloy Mg-25Gd, Mg-25Y, Mg-20Zr and pure magnesium.

[0123] S2. The weighed raw materials of each chemical component are placed in a graphite crucible for vacuum induction melting. The crucible is heated under the protection of a mixed gas of CO2 and SF6 with a volume ratio of 9:1. After heating to 720℃, the temperature is held for 30 minutes to ensure that the raw materials are completely melted. After melting, mechanical stirring is applied for 10 minutes to ensure that the raw materials are uniformly mixed. After stirring, the mixture is allowed to stand for 20 minutes. Finally, it is poured into a stainless steel mold to obtain a cylindrical ingot with a diameter of 100mm × 600mm, which is the target alloy ingot.

[0124] S3. The target alloy ingot is subjected to hot extrusion treatment at an extrusion temperature of 400℃, an extrusion ratio of 9:1, and an extrusion rate of 0.4mm / s to obtain an extruded bar with a diameter of 30mm. Subsequently, an aging treatment is performed at an aging temperature of 200℃ for 96h.

[0125] S4. The aged sample was processed by wire cutting into a 20mm×20mm×5mm specimen and a sheet-like dog bone tensile specimen with a gauge length of 15mm, a width of 3.6mm, and a thickness of 2.5mm. These specimens were used for hydrogen evolution test and room temperature tensile test, respectively. Before the test, the specimens were polished with SiC sandpaper of 240#, 600#, 1000#, and 2000# in sequence.

[0126] Comparative Example 1

[0127] The only difference between this comparative example and Example 2 is that:

[0128] The chemical composition of the alloy components in this comparative example is as follows:

[0129] The alloy consists of 6% Gd, 3% Y, 0.5% Zr, and the remainder is Mg, totaling 100%. This comparative alloy is denoted as Mg-6Gd-3Y-0.5Zr alloy.

[0130] Comparative Example 2

[0131] The only difference between this comparative example and Example 3 is that:

[0132] The chemical composition of the alloy components in this comparative example is as follows:

[0133] The alloy consists of 6% Gd, 3% Y, 0.5% Zr, and the remainder is Mg, totaling 100%. This comparative alloy is denoted as Mg-6Gd-3Y-0.5Zr alloy.

[0134] Comparative Example 3

[0135] The only difference between this comparative example and Example 4 is that:

[0136] The chemical composition of the alloy components in this comparative example is as follows:

[0137] The alloy consists of 6% Gd, 3% Y, 0.5% Zr, and the remainder is Mg, totaling 100%. This comparative alloy is denoted as Mg-6Gd-3Y-0.5Zr alloy.

[0138] Comparative Example 4

[0139] This comparative example uses commercially available AZ91D magnesium alloy as a control group.

[0140] Experimental Section

[0141] The present invention takes the magnesium alloys of Examples 2 to 4 and Comparative Examples 1 to 4 as examples and conducts the following tests on them respectively.

[0142] 1) Corrosion performance test

[0143] This invention, following the testing procedures outlined in ASTM G31-72 "Laboratory Immersion Corrosion Standard for Metals," tested the corrosion performance of magnesium alloy samples from Examples 2 to 4 and Comparative Examples 1 to 4, respectively. The test results are as follows: Figure 3 As shown.

[0144] Depend on Figure 3 It can be seen that the corrosion rate of the magnesium alloy sample in Example 2 is 0.17 ± 0.01 mm / a, while Comparative Example 1 does not conform to the design principles of this invention and has very poor corrosion resistance. Compared with Comparative Example 1, the high-strength, high-corrosion-resistant magnesium alloy designed in this invention has 53 times improved corrosion resistance.

[0145] The corrosion rate of the magnesium alloy sample in Example 3 was 0.09 ± 0.02 mm / a. Compared with Comparative Example 2, the high-strength and high-corrosion-resistant magnesium alloy designed in Example 2 was significantly improved.

[0146] The corrosion rate of the magnesium alloy sample in Example 4 was 0.08 ± 0.01 mm / a. Compared with Comparative Example 3, the corrosion resistance of the high-strength and high-corrosion-resistant magnesium alloy designed in Example 3 was improved by 127 times.

[0147] Based on the above, compared with the corrosion rates of Comparative Examples 1 to 4, the corrosion rates of Examples 2 to 4 of the present invention are significantly improved, indicating that the high-strength and high-corrosion-resistant magnesium alloy designed by the present invention has excellent corrosion resistance.

[0148] 2) Mechanical property testing

[0149] This invention, following the testing methods outlined in GB / T 228-2002 "Metallic Materials - Tensile Testing at Room Temperature", tested the stress-strain curves of magnesium alloy specimens from Examples 2 to 4 and Comparative Examples 1 to 4, respectively, and the test results are as follows: Figure 4 As shown.

[0150] And by Figure 4 As can be seen, the yield strength, tensile strength, and elongation at break of the magnesium alloy sample in Example 2 are 205.35±2.63 MPa, 259.51±20.24 MPa, and 5.73±1.53%, respectively. Compared with Comparative Example 1, the high-strength and high-corrosion-resistant magnesium alloy designed in this invention has excellent mechanical strength.

[0151] The yield strength, tensile strength, and elongation at break of the magnesium alloy sample in Example 3 were 239.33±1.70 MPa, 311.70±2.93 MPa, and 25.84±0.79%, respectively. Compared with Comparative Example 2, the high-strength and high-corrosion-resistant magnesium alloy designed in this invention has excellent mechanical strength.

[0152] The yield strength, tensile strength, and elongation at break of the magnesium alloy sample in Example 4 were 320.77±1.70 MPa, 377.34±0.78 MPa, and 14.99±0.08%, respectively. Compared with Comparative Example 3, the high-strength and high-corrosion-resistant magnesium alloy designed in this invention has excellent mechanical strength.

[0153] Based on the above, compared with the mechanical strength of Comparative Examples 1 to 4, the mechanical strength of Examples 1 to 3 of the present invention is significantly improved, indicating that the high-strength and high-corrosion-resistant magnesium alloy designed by the present invention has excellent corrosion resistance.

[0154] In summary, the high-strength and high-corrosion-resistant magnesium alloy designed in this invention possesses excellent mechanical properties and corrosion resistance.

[0155] It should be emphasized that the above embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art can adjust the alloy element content. Any adjustments to the element content or process parameters made in accordance with the principles of this invention should be included within the scope of protection of this invention.

[0156] Obviously, the above embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A design method for high-strength, high-corrosion-resistant magnesium alloys based on corrosion thermo-kinetics, characterized in that, Includes the following steps: Obtain the publicly available alloying element composition and mechanical properties of magnesium alloys, use the corresponding mechanical property data as input and the alloying element composition as the corresponding output to establish a dataset; wherein, the alloying element composition refers to the type and content of the alloying elements. Using the required mechanical property data as constraints, the dataset is filtered to obtain a high-strength magnesium alloy system dataset; Based on the constraint that the content of alloying elements is ≤ the first threshold, the alloying elements in the high-strength magnesium alloy system dataset are screened to obtain the first micro-alloying element and low-alloying element candidate set; Based on corrosion thermodynamics and kinetics, with the constraint that microalloying elements have a later dissolution order and a earlier deposition order, and low-alloying elements have a dissolution order and deposition order that are both between the microalloying elements and magnesium elements, the alloying elements in the high-strength magnesium alloy system dataset are screened to obtain a second set of microalloying elements and low-alloying elements. Based on the first set of microalloying elements and low-alloying elements, and the second set of microalloying elements and low-alloying elements, candidate alloying elements of microalloying elements and low-alloying elements are determined, and they are combined with magnesium element according to the predefined mass percentage of alloying elements to form candidate magnesium alloys. The corrosion performance prediction model was used to determine the nucleation rate and growth rate of corrosion products corresponding to each alloying element in the candidate magnesium alloy, as well as the corrosion rate and corrosion depth of the alloy. Using the nucleation rate of the corrosion product > the corresponding growth rate, the corrosion rate ≤ the second threshold, and the corrosion depth < the third threshold as constraints, the candidate magnesium alloys are screened to obtain high-strength and high-corrosion-resistant magnesium alloys. The first threshold is 10.0%; The second threshold is 1 mm / a; The third threshold is 5 μm.

2. The design method as described in claim 1, characterized in that, The mechanical property data refers to the data on the contribution of mechanical strength and plasticity.

3. The design method as described in claim 1, characterized in that, By obtaining the standard electrode potentials of the metals corresponding to the alloying elements and sorting them in descending order of value, the dissolution order of the atoms corresponding to each alloying element can be determined. The deposition sequence of magnesium alloy corrosion products is determined by obtaining the solubility product of the corresponding oxide or hydroxide of each alloying element and sorting them in descending order according to the critical deposition line of the corresponding oxide or hydroxide of each alloying element.

4. The design method as described in claim 1, characterized in that, The corrosion performance prediction model is a "dissolution-ionization-diffusion-deposition" model, which is obtained through the following steps: Using the standard electrode potentials of the metals corresponding to each element of the candidate magnesium alloy as input, the equilibrium potentials of the metal electrode reactions corresponding to each element of the candidate magnesium alloy are calculated according to the Nernst equation; then, using the equilibrium potentials of the metal electrode reactions corresponding to each element as input, the corrosion potential of the magnesium alloy is calculated according to the mixed potential theory; finally, using the corrosion potential of the magnesium alloy as input, the corrosion current density of the magnesium alloy at the corrosion potential is calculated according to the Butler-Volmer formula. Using the solubility product of the corresponding oxides and hydroxides of each element as input, the supersaturation of each corrosion product is calculated according to Faraday's law and Fick's second law; using the supersaturation of each corrosion product as input, the nucleation rate and growth rate of the corresponding corrosion product are calculated. The overall corrosion rate of the candidate magnesium alloy was calculated by taking the nucleation rate and growth rate of corrosion products as input. The corrosion depth of candidate magnesium alloys is calculated by taking the overall corrosion rate and corrosion current density of the magnesium alloy as inputs.

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