Corrosion-resistant magnesium alloy and preparation method thereof

Abstract

The present invention discloses a magnesium alloy, which comprises 2.0-6.0wt% of rare earth elements, 0.1-1.0wt% of nucleating elements, optionally 1.0-2.0wt% of regulating elements for regulating casting properties, and optionally 0.1-0.5wt% of purifying elements for removing impurities in the magnesium alloy, and the remainder is Mg and unavoidable impurities; wherein the solubility product constant Ksp of the hydroxide of the nucleating element at room temperature is ≤1×10 ‑32 , and is less than the solubility product constant of the hydroxide of the rare earth element; and the PBR value of the oxide of the film-forming element is 1.0-2.0. The present invention effectively improves the corrosion resistance of the magnesium alloy by optimizing the alloy composition of the magnesium alloy. The present invention also provides a method for preparing the above-mentioned magnesium alloy.

Description

Technical Field

[0001] The present invention relates to the technical field of magnesium alloys, and in particular to a corrosion-resistant magnesium alloy and a preparation method thereof. Background Art

[0002] As the lightest structural material, magnesium alloy has extremely high specific strength and specific stiffness, and has important applications in lightweight industrial production. For example, in 3C products, automobiles, and shipbuilding, the use of magnesium alloys in 3C products, automobile or ship hulls can not only improve the service life of the products, but also achieve the goal of lightweighting. Traditional magnesium alloys have poor corrosion resistance, and in normal use, the outer surface is usually coated with a corrosion-resistant coating, such as paint. However, whether it is a 3C product, automobile or ship, the corrosion-resistant coating on its surface will inevitably be damaged during service. Once the magnesium alloy is in direct contact with the electrolyte solution, an oxide film will be generated on the surface of the alloy. The magnesium oxide is relatively loose, and the corrosive medium will continue to corrode the magnesium alloy through the gaps between the magnesium oxides, resulting in a huge obstacle to the promotion and application of magnesium alloys.

[0003] There are solutions in the prior art to improve the corrosion resistance of magnesium alloys by microalloying. For example, CN114540683A discloses a microalloyed corrosion-resistant low-cost magnesium alloy and its preparation method, which controls the type, size, quantity and distribution of the second phase in the magnesium alloy by adding elements such as Al, Mn, Zn and RE to the magnesium alloy in conjunction with a strictly controlled high-speed extrusion deformation process to improve the corrosion resistance of the magnesium alloy. This method of improving corrosion resistance by regulating the microstructure through microalloying has high requirements for the preparation process and is difficult to achieve precise control during the production process. Summary of the invention

[0004] In view of the above technical problems existing in the prior art, the first aspect of the present invention provides a magnesium alloy, which comprises 2.0-6.0wt% of rare earth elements, 0.1-1.0wt% of nucleating elements, optionally 1.0-2.0wt% of regulating elements for regulating casting properties, and optionally 0.1-0.5wt% of purifying elements for removing impurities in the magnesium alloy, and the remainder is Mg and unavoidable impurities; wherein the solubility product constant Ksp of the hydroxide of the nucleating element at room temperature is ≤1×10 -32 , and is less than the solubility product constant of the hydroxide of the rare earth element; and the PBR value of the oxide of the rare earth element is 1.0-2.0.

[0005] After magnesium alloy comes into contact with electrolyte solution, magnesium, rare earth elements and nucleation elements as alloy components will be corroded by the electrolyte solution to varying degrees. Since the solubility product of the hydroxide of the nucleation element at room temperature is very small, the hydroxide of the nucleation element can be quickly generated on the surface of the magnesium alloy in contact with the electrolyte solution. The hydroxide of the nucleation element can serve as a crystal nucleus to coat the surface with dense rare earth element oxides, so as to effectively fill the gaps between the magnesium oxides generated by corrosion, form a dense oxide film on the surface of the magnesium alloy, and prevent the electrolyte solution from further corroding the magnesium alloy, so as to improve the corrosion resistance of the magnesium alloy. In addition, the PBR value of the oxide of the rare earth element is 1.0-2.0, which can form a dense oxide film on the surface of the magnesium alloy after corrosion.

[0006] Preferably, in the above magnesium alloy, the content of rare earth elements is 3.0-5.0wt%.

[0007] Preferably, in the above magnesium alloy, the content of nucleating elements is 0.3-0.8wt%.

[0008] Preferably, the magnesium alloy further contains 1.0-2.0 wt % of regulating elements.

[0009] Preferably, the magnesium alloy further contains 0.1-0.5 wt % of a purifying element.

[0010] Preferably, the chemical composition of the magnesium alloy satisfies one or more of the following conditions:

[0011] The rare earth element is one or more selected from La, Nd, Gd, and Y, preferably La and / or Nd;

[0012] The nucleating element is one or more selected from Al, Ce, Zr, and Sc, preferably Al and / or Ce;

[0013] The regulating element is Zn;

[0014] The purifying element is Mn.

[0015] Preferably, the content of impurity elements in the magnesium alloy of the present invention is: Fe≤0.05wt%, Cu≤0.03wt%, Ni≤0.01wt%.

[0016] Impurity elements such as Fe, Ni, and Cu tend to segregate at grain boundaries to form impurity element phases distributed in the matrix with active cathode characteristics, such as Al3Fe phases. These impurity element phases promote the formation of micro-batteries on the surface of magnesium alloys, causing galvanic corrosion. Therefore, the present invention can improve the corrosion resistance of magnesium alloys by controlling the content of impurity elements such as Fe, Ni, and Cu in magnesium alloys to be as low as possible.

[0017] Preferably, the microstructure of the magnesium alloy of the present invention comprises a magnesium alloy matrix and a second phase dispersed in the magnesium alloy matrix. More preferably, the volume fraction of the second phase in the magnesium alloy is 5-15%, and / or the size of the second phase is 10-30 microns.

[0018] The second phase in the magnesium alloy is formed by rare earth elements, nucleation elements and optional regulating elements, which can further improve the mechanical properties and corrosion resistance of the magnesium alloy. The volume fraction and size of the second phase can be controlled by adjusting the content of each component element in the magnesium alloy. In the magnesium alloy of the present invention, the volume fraction of the second phase is 5-15%, preferably 5-10%; the size of the second phase is 10-30 microns, preferably 10-20 microns, and more preferably 15-20 microns.

[0019] The inventors have found that by dispersing the fine second phase of the above volume fraction in the magnesium alloy matrix, the corrosion failure mode of the alloy can be changed from pitting corrosion to uniform corrosion, thereby helping to improve the mechanical properties and corrosion resistance of the magnesium alloy. On the contrary, a coarse second phase is prone to galvanic corrosion.

[0020] Preferably, the yield strength of the magnesium alloy of the present invention is above 90 MPa, preferably above 100 MPa, the tensile strength is above 150 MPa, preferably above 160 MPa, and the elongation is 3-10%. The corrosion-resistant magnesium alloy of the present invention can meet the standards for use as shells of 3C products, automobiles, ships, etc.

[0021] Preferably, after the magnesium alloy of the present invention is placed in a 3.5% by mass NaCl solution for 24 hours, an oxide film is generated on the surface of the corrosion-resistant magnesium alloy, and the average thickness of the oxide film is less than 15 microns, preferably 5-15 microns, and more preferably 10-15 microns; and / or, the corrosion rate of the magnesium alloy of the present invention measured according to ASTM-G31-72 is less than 0.5 mm / year, preferably less than 0.3 mm / year.

[0022] Even if the magnesium alloy of the present invention is exposed to the electrolyte solution for a longer period of time, the thickness of the oxide film formed on its surface does not change with time and can be continuously maintained below 15 microns. An oxide film that is too thin cannot provide sufficient protection, and a film that is too thick is prone to stress cracking. The difference between the maximum and minimum values ​​of the oxide film thickness formed on the surface of the magnesium alloy of the present invention is within 10 microns, preferably within 5 microns, showing good uniformity.

[0023] The magnesium alloy of the present invention can preferably satisfy a corrosion rate of less than 0.5 mm / year as measured according to ASTM-G31-72, and exhibit excellent corrosion resistance.

[0024] A second aspect of the present invention provides a method for preparing the above magnesium alloy, which comprises sequential steps of smelting and casting.

[0025] Specifically, the smelting steps are carried out in sequence as follows:

[0026] In the first stage, pure magnesium is melted and then nucleating elements are added at 690-700°C. After melting, the mixture is stirred evenly and the melt is allowed to stand for 10-20 minutes.

[0027] The second stage: after heating the melt obtained in the first stage to 720-730°C, rare earth elements are added, and after melting, the melt is stirred evenly and allowed to stand for 10-30 minutes;

[0028] The casting steps include:

[0029] The molten metal obtained in the smelting step is introduced into a pre-prepared mold for casting, and then the molten metal is cooled to obtain a magnesium alloy;

[0030] The above smelting step and casting step are both carried out in a protective atmosphere.

[0031] Preferably, in the method of the present invention, a purification element is further added to the melt in the second stage.

[0032] Preferably, when the purifying element is Mn, Mn is added in the form of Mg-Mn master alloy. Preferably, the content of Mn in the magnesium alloy of the present invention is 0.1-0.5wt%.

[0033] Preferably, the above smelting step also includes a third stage: heating the melt obtained in the second stage to 750-760°C, adding the regulating elements, stirring evenly after melting, standing for 15-30 minutes and then standing to cool to 720-730°C.

[0034] Preferably, the regulating element is Zn, and the content of Zn in the magnesium alloy of the present invention is 1.0-2.0wt%.

[0035] Preferably, the casting is sand casting, and the cooling rate of the melt is 10-30°C / s.

[0036] Preferably, during sand casting, the temperature of the mold is 190-200° C. to ensure the structural integrity of the casting.

[0037] Preferably, the protective atmosphere is a mixed gas of CO2 and SF6, wherein the volume ratio of CO2 to SF6 is 1:6.

[0038] By adopting the manufacturing method of the present invention, a magnesium alloy with high corrosion resistance can be obtained without aging treatment, which can significantly shorten the preparation process of the magnesium alloy and is suitable for industrial production. The preparation method of the present invention is simple to operate, as long as the nucleating elements and the rare earth elements can be evenly distributed in the magnesium alloy. When in contact with an electrolyte solution, the magnesium alloy of the present invention can achieve high corrosion resistance by quickly forming a dense oxide film on the surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 An electron microscope photograph of a cross section of the magnesium alloy of Example 1 of the present invention is shown;

[0040] Figure 2 An electron microscope photograph of a cross section of the magnesium alloy of Example 5 of the present invention is shown;

[0041] Figure 3 An electron microscope photograph of a cross section of the magnesium alloy of Comparative Example 1 of the present invention is shown;

[0042] Figure 4 An electron microscope photograph of a cross section of the magnesium alloy of Example 1 of the present invention after being immersed in a 3.5% by mass NaCl solution for 24 hours is shown;

[0043] Figure 5 An electron microscope photograph of a cross section of the magnesium alloy of Comparative Example 1 of the present invention after being immersed in a 3.5% by mass NaCl solution for 24 hours is shown;

[0044] Figure 6 The electron microscope photograph of the surface of the magnesium alloy of Example 1 of the present invention after being immersed in a NaCl solution with a mass fraction of 3.5% for 24 hours is shown;

[0045] Figure 7 The electron microscope photograph of the surface of the magnesium alloy of Comparative Example 1 of the present invention after being immersed in a NaCl solution with a mass fraction of 3.5% for 24 hours is shown;

[0046] Figure 8 A schematic diagram of a device for performing a hydrogen evolution test in an embodiment of the present invention is shown.

[0047] Reference numerals:

[0048] 1-acid burette; 2-electrolyte solution; 3-sample to be tested; 4-funnel. DETAILED DESCRIPTION

[0049] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0050] The yield strength and tensile strength of the corrosion-resistant magnesium alloy of the present invention are measured as follows: According to GB / T 228.1-2010 "Metallic Materials Tensile Test Part 1: Room Temperature Test Method", the test is performed using a LFV-100HH universal material testing machine.

[0051] The degradation rate of simulated body fluid in the present invention is based on ASTM-G31-72 "Laboratory Immersion Corrosion Test for Metals", and the metal sample to be tested is placed in a NaCl solution with a mass fraction of 3.5% and tested using the hydrogen evolution method.

[0052] As is known in the art, rare earth elements include: lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), yttrium (Y) and scandium (Sc).

[0053] In the magnesium alloy of the present invention, the design principles of each chemical element are specifically described as follows:

[0054] Rare earth elements: The PBR values ​​of the corrosion products of the rare earth elements of the present invention are all above 1.0, that is, the PBR value of the oxides of the rare earth elements is above 1.0, so that the film layer is denser. PBR, or Pilling-Bedworth ratio, is the ratio of the volume of each metal ion in the oxide film generated by the combination of metal and oxygen on the metal surface to the volume of each metal atom in the metal, indicating the density of the oxide film. Preferably, the PBR value of the oxide of the rare earth elements of the present invention is 1.0-2.0. If the PBR value is greater than 2.0, the oxide film is prone to stress fracture during the growth process, thereby causing the oxide film to lose its protectiveness. The rare earth elements in the present invention are preferably La and / or Nd, wherein the PBR value of La oxide is 1.8, and the PBR value of Nd oxide is 1.3, both of which have good protectiveness.

[0055] In addition, rare earth elements added to magnesium alloys can improve the mechanical properties of the alloys. In the present invention, they are mainly used to form a protective film on the surface of the magnesium alloy that is denser than magnesium oxide, thereby improving the corrosion resistance of the magnesium alloy. Rare earth element additions greater than 6.0wt% in magnesium alloys can lead to a strong micro-galvanic corrosion effect; additions less than 2.0wt% will result in too little oxide to fill the gaps in magnesium oxide, and the magnesium alloy obtained will not be able to achieve the mechanical properties required by the present invention. Preferably, the addition of rare earth elements in the present invention is 3.0-5.0wt%, which can achieve a better balance between mechanical properties and corrosion resistance.

[0056] Nucleating element: refers to an element with a small solubility product constant Ksp of the hydroxide precipitate formed in the solution. In the present invention, the Ksp of the hydroxide of the added nucleating element should be smaller than the Ksp of the hydroxide of the rare earth element, so that the hydroxide of the nucleating element can be deposited on the surface of the magnesium alloy faster, providing attachment sites for the rare earth element oxide. The addition of the nucleating element should not be too much, but the insufficient addition amount cannot provide sufficient generation sites for the rare earth element oxide. Taking all factors into consideration, in the present invention, the addition amount of the nucleating element is controlled to be 0.1-1.0wt%, preferably 0.3-0.8wt%.

[0057] In the present invention, the nucleating element is preferably at least one of Al and Ce. At room temperature, the solubility product constant of aluminum hydroxide is 1×10 -33 , the solubility product constant of cerium hydroxide is 2×10 -48 , both within 1×10 -32 Therefore, the corrosion-resistant magnesium alloy containing Al and / or Ce can rapidly generate Al and / or Ce hydroxides as crystal nuclei on its surface in contact with the electrolyte solution, thereby helping dense rare earth element oxides to form on the surface of the magnesium alloy.

[0058] Controlling elements for controlling casting properties: Controlling elements can increase the fluidity of the melt during casting. The amount of the controlling elements added is controlled at 1.0-2.0wt%. In the present invention, the controlling element is preferably Zn. Too little Zn addition will not increase the fluidity of the melt, and too much Zn addition will affect the corrosion resistance of the alloy.

[0059] Purifying elements: Purifying elements refer to elements that react with impurities such as Fe, Ni, Cu in the raw materials during the smelting process and precipitate to the bottom of the crucible to reduce the impurity content in the magnesium alloy ingot. Since such elements generally have a strong passivation tendency, after comprehensive consideration, in the present invention, the addition amount of the purifying elements is controlled at 0.1-0.5wt%.

[0060] In the present invention, the purifying element is Mn. During the smelting process, Mn will combine with impurity elements such as Fe, Ni, and Cu in the alloy to form precipitation, purify the melt, and help improve the quality and corrosion resistance of the magnesium alloy.

[0061] The corrosion-resistant magnesium alloy and the preparation method thereof of the present invention have the following advantages and beneficial effects:

[0062] The corrosion-resistant magnesium alloy of the present invention optimizes the element composition in the magnesium alloy so that the potential difference between the phases of the micro-alloyed alloy is small, thereby effectively reducing galvanic corrosion; at the same time, a protective corrosion product film layer is easily precipitated on the alloy surface under the service environment, thereby improving the corrosion resistance of the magnesium alloy.

[0063] The technical solution of the present invention is further described in detail below in conjunction with the examples. It should be clear that the following examples are only used to describe the specific implementation methods of the present invention and are not intended to limit the protection scope of the present invention in any way.

[0064] Example

[0065] The magnesium alloys of Examples 1-6 were prepared by the following steps:

[0066] 1) Melting: According to the formula shown in Table 1, the magnesium alloy is melted.

[0067] Specifically,

[0068] The smelting process of the magnesium alloy of Examples 1-4 is carried out in sequence as follows:

[0069] ① The first stage: In a protective atmosphere, pure magnesium is melted and then nucleating elements are added at 690-700°C. After melting, it is stirred evenly and allowed to stand for 10-20 minutes.

[0070] ② The second stage: In a protective atmosphere, the melt obtained in the first stage is heated to 720-730°C, rare earth elements and purification elements are added, and after melting, the mixture is stirred evenly and allowed to stand for 10-30 minutes. There is no restriction on the order of adding purification elements and rare earth elements, which can be added simultaneously or successively, as long as the elements added are evenly distributed in the melt.

[0071] ③The third stage: In a protective atmosphere, heat the melt obtained in the second stage to 750-760℃, add the regulating elements, stir evenly after melting, and let it stand for 15-30 minutes. Then cool it to 720-730℃, add the refining agent in a protective atmosphere, and let it stand for 30 minutes to remove impurities in the melt.

[0072] The rare earth element, nucleating element, purifying element and regulating element are added in the form of corresponding Mg master alloys. For example, when the rare earth element is La, the added form is Mg-La master alloy.

[0073] The smelting process of the magnesium alloy of Examples 5-6 is carried out in sequence as follows:

[0074] ① The first stage: In a protective atmosphere, pure magnesium is melted and then nucleating elements are added at 690-700°C. After melting, it is stirred evenly and allowed to stand for 10-20 minutes.

[0075] ② The second stage: In a protective atmosphere, heat the melt obtained in the first stage to 720-730°C and add rare earth elements. After melting, stir evenly and let stand for 10-30 minutes.

[0076] ③ Add refining agent in a protective atmosphere for refining and stirring, and let it stand for 30 minutes to remove impurities in the melt.

[0077] The refining agent used in the above smelting process is a JDMJ series refining agent, such as JDMJ-1 refining agent.

[0078] 2) Casting: In a protective atmosphere, the molten metal is introduced into a pre-prepared mold for sand casting. The mold temperature is between 190-200°C and the cooling rate is 10-30°C / s to obtain a corrosion-resistant magnesium alloy.

[0079] Comparative Examples 1-4 are prepared by the same process as that of the above-mentioned Examples 1-4, except that the content of nucleating elements or rare earth elements in the magnesium alloys of Comparative Examples 1-4 is not within the range defined by the present invention.

[0080] Comparative Example 5 does not contain nucleating elements, so a different smelting process is used, specifically: in a protective atmosphere, the pure magnesium melt is directly heated to 720-730°C and rare earth elements are added, and after melting, the mixture is stirred evenly and allowed to stand for 10-30 minutes, and then a refining agent is added in a protective atmosphere for refining and stirring, and the mixture is allowed to stand for 30 minutes to remove impurities in the melt. The casting process is the same as the process conditions used in the embodiment.

[0081] Table 1 shows the chemical composition of the magnesium alloys in Examples 1-6 and Comparative Examples 1-5, in wt %, with the remainder being Mg and inevitable impurities.

[0082] Table 1

[0083]

[0084] In the magnesium alloys of Examples 1-6 and Comparative Examples 1-5, Fe≤0.05wt.%, Cu≤0.03wt.%, and Ni≤0.01wt.%.

[0085] Table 2 shows the specific process parameters used to prepare the magnesium alloys in Examples 1-6 and Comparative Examples 1-5.

[0086] Table 2

[0087]

[0088]

[0089] Figure 1 and Figure 3 The electron microscope photos of a cross section of the magnesium alloy of Example 1 and Comparative Example 1 are shown respectively. Figure 1 It can be seen that the microstructure of the magnesium alloy of Example 1 includes a magnesium alloy matrix as a continuous phase, and a second phase dispersed in the magnesium alloy matrix, and the size of the second phase is about 10-30 microns; Figure 1 compared to, Figure 3 The content of the second phase in magnesium alloy is very large, which leads to the aggravation of microgalvanic corrosion and affects the corrosion resistance.

[0090] Figure 2 This is an electron microscope photograph of a cross section of the magnesium alloy of Example 5. Similar to Example 1, in the magnesium alloy of Example 5, the second phase is dispersed in the matrix, and the size of the second phase is also about 10-30 microns.

[0091] Figure 4 and Figure 5 The electron microscope photos of a cross section of the magnesium alloys of Example 1 and Comparative Example 1 after being immersed in an electrolyte solution are shown respectively. Specifically, the immersion conditions are: the magnesium alloy sample is immersed in a 3.5% by mass NaCl solution at room temperature for 24 hours.

[0092] Figure 4 The thickness of the interface corrosion product (i.e., oxide film) of the magnesium alloy in Example 1 is significantly greater than that of Comparative Example 1, and the oxide film fully covers the surface of the magnesium alloy, indicating that the magnesium alloy of Example 1 can form a complete oxide film on the surface of the magnesium alloy under the test conditions to protect the core of the magnesium alloy. Figure 4 The thickness of the oxide film is 5-15 microns, and the morphology shows that the film is extremely dense and basically has no defects. The state of the oxide film generated at the interface of the magnesium alloy and the electrolyte solution is related to the distribution of the film-forming elements and nucleation elements in the magnesium alloy at the interface, as well as the solute distribution of the electrolyte solution. Therefore, the thickness of the oxide film generated at different locations is slightly different.

[0093] Figure 5 The oxide film on the surface of magnesium alloy is discontinuous, mainly because the La content in the alloy is too high, and the potential difference between it and Mg is relatively large, which causes a large number of hydrogen bubbles to be generated at the reaction interface in the early stage of corrosion, hindering the formation of an effective oxide film on the surface of magnesium alloy.

[0094] Figure 6 and Figure 7 The electron microscope photos of the surfaces of the magnesium alloys of Example 1 and Comparative Example 1 after being immersed in the electrolyte solution are shown. Specifically, the immersion conditions are: immersion in a 3.5% by mass NaCl solution at room temperature for 24 hours. It can be seen that the surface corrosion marks of the magnesium alloy of Example 1 are far less than those of the magnesium alloy of Comparative Example 1. This is also because the La content of the magnesium alloy in Comparative Example 1 is too high, and a large number of hydrogen bubbles are generated at the reaction interface in the early stage of corrosion, which affects the subsequent film deposition.

[0095] The magnesium alloys of Examples 1-6 and Comparative Examples 1-5 finally obtained were sampled respectively, and the mechanical properties of each sample were tested. The test results are listed in Table 3.

[0096] The test method is as follows:

[0097] The yield strength and tensile strength of the magnesium alloys of Examples 1-6 and Comparative Examples 1-5 were tested according to GB / T228.1-2010 “Tensile testing of metallic materials Part 1: Room temperature test methods”.

[0098] Corrosion resistance test: The simulated body fluid degradation rates of the magnesium alloys of Examples 1-6 and Comparative Examples 1-5 were tested according to ASTM-G31-72 “Laboratory Immersion Corrosion Test of Metals” (hereinafter referred to as hydrogen evolution weight loss test).

[0099] Before the hydrogen evolution weight loss test, the sample is cut into 10mm×10mm×5mm squares by wire cutting process, and then the six surfaces of the sample are polished with 320#, 1200#, and 3000# grit sandpaper in turn. After cleaning with alcohol and drying, it can be used for hydrogen evolution weight loss test. Before the test, the three-dimensional dimensions of the sample are measured and recorded multiple times (for example, 3 times) with a vernier caliper, and the surface area A of the sample is calculated using the average value of the multiple measurement results.

[0100] Hydrogen evolution weight loss test device used in the present invention Figure 8 As shown. Tie the polished test sample 3 with a fishing line, turn a funnel 4 upside down on the test sample 3, fix the test sample 3 inside the inverted funnel 4 and place them together in a 1000mL beaker. Add about 700mL of prepared electrolyte solution 2 to the beaker in advance, and the electrolyte solution 2 is a NaCl solution with a mass fraction of 3.5%. Then connect the acid burette 1 filled with the solution to the funnel 4. The liquid level of the solution inside the beaker should not exceed the connection between the acid burette 1 and the funnel 4 to form a liquid seal. Apply vaseline to the piston of the acid burette 1 for sealing. Record the volume scale value corresponding to the initial liquid level height in the acid burette 1, and then record the data every once in a while. The volume reduction of the solution in the burette is the volume of hydrogen precipitated in the corresponding time period.

[0101]

[0102] V H The hydrogen evolution rate of the sample in the immersion experiment, the unit can be mL / cm 2 / day, calculated by the above formula, where ΔV is the volume of hydrogen released in a certain period of time t, the unit can be mL, the time t can be measured in days, and A is the surface area of ​​the sample under test, the unit can be cm 2 The less the amount of hydrogen evolution in the same time, the better the corrosion resistance of the corresponding magnesium alloy. r and hydrogen evolution rate V H The following relationship exists:

[0103] Vr =2V H

[0104] Among them, V r The unit is mm / year.

[0105] Table 3

[0106]

[0107]

[0108] As shown in Table 3, the magnesium alloys of Examples 1-6 of the present invention exhibit good mechanical properties, with a yield strength of 90-120 MPa, a tensile strength of 150-180 MPa, and an elongation of 3-10%, which can meet the use requirements of conventional 3C products. In particular, due to reasonable component control, the magnesium alloys of Examples 1-6 have a corrosion rate of less than 0.3 mm / year, and are significantly better than Comparative Examples 1-5 in terms of corrosion resistance.

[0109] Although the present invention has been described by reference to certain preferred embodiments of the present invention, it should be understood by those skilled in the art that the above is a further detailed description of the present invention in conjunction with specific embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. Those skilled in the art may make various changes in form and details, including making several simple deductions or substitutions, without departing from the spirit and scope of the present invention.

Claims

1. A magnesium alloy, It is characterized in that The magnesium alloy comprises 2.0-6.0wt% of rare earth elements, 0.1-1.0wt% of nucleating elements, 1.0-2.0wt% of regulating elements for regulating casting properties, and 0.1-0.5wt% of purifying elements for removing impurities in the magnesium alloy, and the remainder is Mg and unavoidable impurities; the solubility product constant Ksp of the hydroxide of the nucleating element at room temperature is ≤1×10 -32 , and is less than the solubility product constant of the hydroxide of the rare earth element; and the PBR value of the oxide of the rare earth element is 1.0-2.0; the microstructure of the magnesium alloy includes a magnesium alloy matrix and a second phase dispersed in the magnesium alloy matrix, the second phase is formed by rare earth elements, nucleating elements and optional regulating elements, the volume fraction of the second phase is 5-15%, and the size of the second phase is 10-30 microns; the rare earth element is one or more selected from La, Nd, Gd, and Y, and the nucleating element is one or more selected from Al, Ce, Zr, and Sc.

2. The magnesium alloy according to claim 1, It is characterized in that The chemical composition of the magnesium alloy satisfies one or more of the following conditions: The content of regulating elements is 1.0-2.0wt%; The content of purification elements is 0.1-0.5wt%; The rare earth element is La and / or Nd; The nucleating element is Al and / or Ce; The regulating element is Zn; The purifying element is Mn.

3. The magnesium alloy according to claim 1 or 2, It is characterized in that The impurities of the magnesium alloy include Fe≤0.05wt%, Cu≤0.03wt%, and Ni≤0.01wt%.

4. The magnesium alloy according to any one of claims 1 to 3, It is characterized in that The magnesium alloy has a yield strength of more than 90 MPa, a tensile strength of more than 150 MPa, and an elongation of 3-10%.

5. The magnesium alloy according to any one of claims 1 to 4, It is characterized in that The corrosion rate of the magnesium alloy measured according to ASTM-G31-72 is below 0.5 mm / year.

6. A method for preparing the magnesium alloy according to any one of claims 1 to 5, It is characterized in that The method comprises the steps of smelting and casting performed sequentially; The smelting steps are carried out in sequence as follows: The first stage: After pure magnesium is melted, the nucleating element is added at 690-700°C, and after melting, the mixture is stirred evenly and the melt is allowed to stand for 10-20 minutes; The second stage: after heating the melt obtained in the first stage to 720-730°C, add the rare earth element, stir evenly after melting, and let the melt stand for 10-30 minutes; The casting step comprises: introducing the molten metal obtained in the smelting step into a pre-prepared mold for casting, and then cooling the molten metal to obtain the magnesium alloy; The smelting step and the casting step are both carried out in a protective atmosphere; In the second stage, purifying elements are also added to the melt; The smelting step also includes a third stage: heating the melt obtained in the second stage to 750-760° C., adding the regulating elements, stirring evenly after melting, standing for 15-30 minutes, and then cooling to 720-730° C.

7. The method according to claim 6, It is characterized in that In the casting step, the casting is sand casting, the cooling rate of the melt is 10-30°C / s, and the temperature of the mold is 190-200°C.

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