A highly corrosion-resistant ternary magnesium alloy with self-repairing properties

Abstract

The present invention relates to the field of magnesium alloy technology, and more particularly to a highly corrosion-resistant ternary magnesium alloy with self-repairing properties. The alloy comprises the following components by weight: Sn: 2-7%; In: 0.1-1%; the balance being Mg and other unavoidable impurities. By designing this highly corrosion-resistant ternary magnesium alloy with self-repairing properties, the present invention addresses the difficulty of prior art magnesium alloys in maintaining long-term service in alternating dry-wet environments.

Description

Technical Field

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

[0002] As the lightest structural material, the widespread use of magnesium alloys should be able to significantly reduce the weight of the structural parts themselves, making an important contribution to achieving lightweight electric vehicles, especially in terms of mileage. By developing new magnesium alloys, not only can the weight of the vehicle itself be reduced, but the mileage limit of electric vehicles can also be effectively improved. Traditional magnesium alloys have gradually begun to be used in electric vehicles, and most of the mechanical conditions for the actual service environment of electric vehicles have been met. However, in the actual use of electric vehicles, the corrosion performance of magnesium alloys has been greatly tested in the working environment where they are constantly washed by rain and alternately wet and dry. Unlike the corrosion situation in the immersion environment in aqueous solution, the alternation of wet and dry conditions places higher demands on the corrosion performance of magnesium alloys. In the cycle of alternating wet and dry conditions, the corrosion product film layer generally becomes more fragile due to the change in the surface state and is easily broken by chloride ions. This makes it difficult for general-grade magnesium alloys to serve in this situation.

[0003] The application of magnesium alloys in vehicle engineering is generally based on casting technology, but multi-component magnesium alloys will increase the difficulty of casting magnesium alloys, which is also one of the main reasons limiting the further expansion of the application of magnesium alloys in the field of new energy vehicles.

[0004] A Chinese invention patent application, publication number CN113981286A, titled "A Corrosion-Resistant, High-Strength, and Plastic Magnesium Alloy and Its Preparation Method," discloses a corrosion-resistant, high-strength, and plastic magnesium alloy. By adding trace amounts of the rare earth elements cerium and samarium, the stability and density of the corrosion product film are improved, hindering chloride ion attack on the alloy surface, inhibiting localized corrosion, and improving the alloy's corrosion resistance. Furthermore, the preparation method disclosed in this reference document effectively regulates the size and distribution of the secondary phase in the magnesium alloy and refines the grain size, thereby successfully producing a corrosion-resistant, high-strength, and plastic magnesium alloy.

[0005] A Chinese invention patent application with publication number CN111575563A and titled "A Magnesium Alloy, Its Preparation Method, and Application" discloses a magnesium alloy with a composition of Mg-xSn-yIn, where 0.5 wt.% ≤ x ≤ 5 wt.%, and 0.5 wt.% ≤ y ≤ 3 wt.%. This reference discloses that adding indium and tin to pure magnesium can reduce corrosion of the magnesium alloy and improve the discharge efficiency of the magnesium alloy.

[0006] However, none of the above prior art discloses the corrosion resistance of magnesium alloys in alternating dry-wet environments. There is a continuous need in the art to develop magnesium alloys with high corrosion resistance in alternating dry-wet environments and suitable for electric vehicle casting processes. Summary of the Invention

[0007] The purpose of the present invention is to solve the problem in the prior art that magnesium alloys are difficult to serve for a long time in a dry-wet alternating environment, and to provide a highly corrosion-resistant ternary magnesium alloy with self-repairing properties.

[0008] The purpose of the present application is also to provide a method for preparing the highly corrosion-resistant ternary magnesium alloy with self-repairing properties as described above.

[0009] The purpose of the present application is also to provide the use of the highly corrosion-resistant ternary magnesium alloy with self-repairing properties as described above in the manufacture of automobiles.

[0010] In one aspect, the present invention provides a highly corrosion-resistant ternary magnesium alloy with self-repairing properties, which comprises the following components in mass percentage: Sn: 2-7%; In: 0.1-1%; impurity Fe: ≤0.05%; the balance being Mg and other unavoidable impurities.

[0011] Furthermore, the high corrosion resistance ternary magnesium alloy with self-repairing properties contains Sn in an amount of 2%, 3%, 4%, 5%, 6%, 7% or any range or sub-range between the aforementioned ratios.

[0012] Furthermore, the highly corrosion-resistant ternary magnesium alloy with self-repairing properties contains 2-3% Sn.

[0013] Furthermore, the high corrosion resistance ternary magnesium alloy with self-healing properties contains Sn in an amount of 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0% or any range or sub-range between the foregoing ratios.

[0014] Furthermore, the high corrosion resistance ternary magnesium alloy with self-repairing properties contains In in an amount of 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or any range or sub-range between the aforementioned proportions.

[0015] Furthermore, the highly corrosion-resistant ternary magnesium alloy with self-repairing properties contains 0.2-0.6% In. Furthermore, the highly corrosion-resistant ternary magnesium alloy with self-repairing properties contains 0.2-0.5% In. Furthermore, the highly corrosion-resistant ternary magnesium alloy with self-repairing properties contains 0.2-0.4% In.

[0016] Furthermore, the highly corrosion-resistant ternary magnesium alloy with self-repairing properties includes a matrix phase and a second precipitated phase with a quasi-network distribution.

[0017] Furthermore, the highly corrosion-resistant ternary magnesium alloy with self-repairing properties can self-repair in the event of surface damage (such as cracking).

[0018] Furthermore, the highly corrosion-resistant ternary magnesium alloy with self-repairing properties can self-repair when surface damage (such as cracking) occurs in a dry-wet alternating environment.

[0019] Furthermore, the corrosion rate of the highly corrosion-resistant ternary magnesium alloy with self-repairing properties in a dry-wet alternating environment is less than 0.35 mm / year.

[0020] In another aspect, the present invention provides a method for preparing a highly corrosion-resistant ternary magnesium alloy having self-repairing properties as described herein, characterized in that it comprises the following steps:

[0021] (1) melting a tin ingot, an indium ingot, and a magnesium ingot in accordance with the composition ratio of the self-repairing and highly corrosion-resistant ternary magnesium alloy to obtain a magnesium alloy melt under a protective atmosphere;

[0022] (2) Under a protective atmosphere, the magnesium alloy melt is stirred and then allowed to stand, and then refined, degassed, and deslagging, and then allowed to stand again and kept warm to obtain a magnesium alloy liquid;

[0023] (3) Under a protective atmosphere, the magnesium alloy liquid is cast and formed, and after cooling, a highly corrosion-resistant ternary magnesium alloy with self-repairing properties is obtained.

[0024] Furthermore, the composition ratio in step (1) is: Sn: 2-7%; In: 0.1-1%; impurity Fe: ≤0.05%; the balance is Mg and other inevitable impurities.

[0025] Furthermore, the content of Sn in the composition ratio is 2%, 3%, 4%, 5%, 6%, 7% or any range or sub-range between the aforementioned ratios.

[0026] Furthermore, the content of Sn in the composition ratio is 2-3%.

[0027] Furthermore, the content of Sn in the composition ratio is 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0% or any range or sub-range between the above ratios.

[0028] Furthermore, the content of In in the composition ratio is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or any range or sub-range between the aforementioned ratios.

[0029] Furthermore, the content of In in the composition ratio is 0.2-0.6%.

[0030] Furthermore, the protective atmosphere is a mixed gas of CO2 and SF6.

[0031] Furthermore, the melting temperature in step (1) is 700-750°C.

[0032] Furthermore, the temperature of the standing after stirring in step (2) is 720-740°C, and the time is 20-60 minutes; the temperature of the refining, degassing and slag removal is 730-750°C; the temperature of the insulation is 720-740°C, and the time is 20-60 minutes.

[0033] Furthermore, the casting temperature in step (3) is 500-600°C.

[0034] Furthermore, the highly corrosion-resistant ternary magnesium alloy with self-repairing properties prepared by the method can self-repair in the event of surface damage (such as cracking).

[0035] Furthermore, the highly corrosion-resistant ternary magnesium alloy with self-repairing properties prepared by the method can self-repair when surface damage (such as cracking) occurs in a dry-wet alternating environment.

[0036] Furthermore, the corrosion rate of the highly corrosion-resistant ternary magnesium alloy with self-repairing properties prepared by the method in a dry-wet alternating environment is less than 0.35 mm / year.

[0037] In another aspect, the present invention also provides use of the highly corrosion-resistant ternary magnesium alloy with self-repairing properties as described herein in manufacturing a material capable of self-repairing in the event of surface damage.

[0038] Furthermore, the application may include solutionizing the highly corrosion-resistant ternary magnesium alloy with self-repairing properties as described herein and then recasting to obtain the desired material.

[0039] In another aspect, the present invention also provides the use of the highly corrosion-resistant ternary magnesium alloy with self-repairing properties as described herein in the manufacture of automobiles. Preferably, the automobile is an electric automobile.

[0040] Furthermore, the application may include solutionizing the highly corrosion-resistant ternary magnesium alloy with self-repairing properties as described herein and then recasting it to obtain the desired automotive material.

[0041] Advantageous Effects of the Invention

[0042] In the corrosion-resistant magnesium alloy of the present invention, the design principles of each chemical element are specifically described as follows:

[0043] The main element is Sn, which significantly restricts the diffusion of Cl ions, resulting in a film with improved corrosion resistance in dry environments. Furthermore, the addition of In accelerates the deposition of the magnesium alloy corrosion product film, enabling self-repair when the film cracks due to growth stress in alternating dry and wet environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a scanning electron microscope photograph of the highly corrosion-resistant ternary magnesium alloy with self-repairing properties of Example 1.

[0045] Figure 2 This is the cross-sectional morphology of the highly corrosion-resistant ternary magnesium alloy with self-repairing properties of Example 1 after undergoing a dry-wet alternating test.

[0046] Figure 3 These are the micro-area electrochemical test results of the highly corrosion-resistant ternary magnesium alloy with self-repairing properties before and after damage in Example 1.

[0047] Figure 4 Electrochemical impedance spectroscopy test and macroscopic morphology photos of the highly corrosion-resistant ternary magnesium alloy with self-repairing properties before and after damage of Example 1.

[0048] Figure 5 The corrosion morphology of the highly corrosion-resistant ternary magnesium alloy with self-repairing properties according to Example 2 is shown.

[0049] Figure 6 The corrosion morphology of the ternary magnesium alloy according to Comparative Example 1 is shown. DETAILED DESCRIPTION

[0050] The technical solution of the present invention is further described in detail below with reference to the examples. It should be understood that the following examples are only used to describe the specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention.

[0051] Example 1

[0052] This embodiment provides a highly corrosion-resistant ternary magnesium alloy with self-repairing properties. The specific composition of the alloy is shown in Table 1 (unit: wt.%), with the remainder being Mg and unavoidable impurities.

[0053] Table 1

[0054] wt.% Sn In Mg Example 1 2.78 0.35 96.87

[0055] The highly corrosion-resistant ternary magnesium alloy with self-repairing properties is prepared as follows:

[0056] (1) Under a protective atmosphere (a mixture of SF6 and CO2), a magnesium ingot is melted at 700-750°C according to the composition ratio shown in Table 1, and then a tin ingot and an indium ingot are added and melted to obtain a magnesium alloy melt;

[0057] (2) Under a protective atmosphere (a mixture of SF6 and CO2), the magnesium alloy melt is stirred at 720-740°C and allowed to stand for 30 minutes, and then refined, degassed, and deslagging are performed at 730-750°C. After standing again, the magnesium alloy melt is kept at 720-740°C for 30 minutes to obtain a magnesium alloy liquid;

[0058] (3) Under a protective atmosphere (a mixture of SF6 and CO2), the magnesium alloy liquid is cast at 500-600°C, and after cooling, a highly corrosion-resistant ternary magnesium alloy with self-repairing properties is obtained.

[0059] Performance testing:

[0060] 1. The highly corrosion-resistant ternary magnesium alloy with self-repairing properties prepared in this embodiment was observed and photographed under a scanning electron microscope. The results are as follows: Figure 1 As shown in the figure, the black phase is the magnesium alloy matrix phase, and the white phase is the precipitation phase. The network-like distribution of the second phase can form a corrosion barrier to improve the corrosion resistance of the matrix.

[0061] 2. Degradation Rate Determination in Simulated Body Fluids

[0062] The degradation rate in simulated body fluids was determined according to ASTM G31-72, "Laboratory Immersion Corrosion Tests for Metals." Samples of the highly corrosion-resistant, self-healing ternary magnesium alloy prepared in this example, as well as commercially available cast magnesium alloys ZM2 and ZM6, were placed in a salt spray chamber containing a 3.5% NaCl atmosphere. Three cycles of alternating dry-wet corrosion tests were performed, with each cycle lasting 24 hours. The results are shown in the table below.

[0063]

[0064] The cross-sectional morphology of the high corrosion resistance ternary magnesium alloy with self-repairing properties in Example 1 after the dry-wet alternating test was also observed by electron microscopy ( Figure 2 ). It can be seen that the magnesium alloy can still form a dense corrosion product film under the condition of alternating dry and wet conditions.

[0065] Figure 1 and Figure 2 The scanning electron microscope used was a RISE-MAGNA. The sample preparation and testing conditions were as follows: sandpaper was used to polish the sample to 2000#, followed by alcohol cleaning before observation. The test conditions were 20keV BSE mode.

[0066] 3. Electrochemical performance test of the highly corrosion-resistant ternary magnesium alloy with self-repairing properties of Example 1 before and after damage.

[0067] The electrochemical properties of the highly corrosion-resistant ternary magnesium alloy with self-repairing properties of the present invention are determined as follows: the test is performed on an Autolab 300 in accordance with GBT 24196-2009 “Corrosion of metals and alloys. Electrochemical test methods. Guide for potentiostatic and potentiodynamic polarization measurements”.

[0068] Figure 3 The surface morphology of the highly corrosion-resistant ternary magnesium alloy with self-repairing properties of Example 1 after damage is shown. The surface exposed after treatment is uneven.

[0069] Figure 4 The surface morphology of the highly corrosion-resistant ternary magnesium alloy with self-repairing properties of Example 1 after self-repairing by solution immersion before and after damage is shown. The self-repairing function enables the generated precipitation products to re-precipitate, acting as a corrosion barrier to isolate further corrosion erosion.

[0070] Figure 4 The electrochemical impedance spectroscopy test was performed using an autolab 300 device. The test conditions were as follows: after the sample was immersed in 3.5 wt % NaCl for 30 minutes to reach a steady state, the electrochemical impedance spectroscopy test was performed.

[0071] Example 2

[0072] This embodiment provides a highly corrosion-resistant ternary magnesium alloy with self-repairing properties. The specific composition of the alloy is shown in Table 2 (unit: wt.%), with the remainder being Mg and unavoidable impurities.

[0073] Table 2

[0074] wt.% Sn In Mg Example 1 2.78 0.55 96.67

[0075] The highly corrosion-resistant ternary magnesium alloy with self-repairing properties is prepared as follows:

[0076] (1) Under a protective atmosphere (a mixture of SF6 and CO2), a magnesium ingot is melted at 700-750°C according to the composition ratio shown in Table 2, and then a tin ingot and an indium ingot are added and melted to obtain a magnesium alloy melt;

[0077] (2) Under a protective atmosphere (a mixture of SF6 and CO2), the magnesium alloy melt is stirred at 720-740°C and allowed to stand for 30 minutes, and then refined, degassed, and deslagging are performed at 730-750°C. After standing again, the magnesium alloy melt is kept at 720-740°C for 30 minutes to obtain a magnesium alloy liquid;

[0078] (3) Under a protective atmosphere (a mixture of SF6 and CO2), the magnesium alloy liquid is cast at 500-600°C, and after cooling, a highly corrosion-resistant ternary magnesium alloy with self-repairing properties is obtained.

[0079] As the In content increases, the corrosion rate fluctuates slightly, but the change is not obvious. This shows that under this composition, the increase of In cannot drastically change the corrosion rate, but the slight increase in the amount of precipitated phase will affect the corrosion resistance.

[0080] Its corrosion morphology is as follows Figure 5 shown.

[0081] Example 3

[0082] This embodiment provides a highly corrosion-resistant ternary magnesium alloy with self-repairing properties. The specific composition of the alloy is shown in Table 3 (unit: wt.%), with the remainder being Mg and unavoidable impurities.

[0083] Table 3

[0084] wt.% Sn In Mg Example 1 2.78 1.0 96.22

[0085] The highly corrosion-resistant ternary magnesium alloy with self-repairing properties is prepared as follows:

[0086] (1) Under a protective atmosphere (a mixture of SF6 and CO2), a magnesium ingot is melted at 700-750°C according to the composition ratio shown in Table 3, and then a tin ingot and an indium ingot are added and melted to obtain a magnesium alloy melt;

[0087] (2) Under a protective atmosphere (a mixture of SF6 and CO2), the magnesium alloy melt is stirred at 720-740°C and allowed to stand for 30 minutes, and then refined, degassed, and deslagging are performed at 730-750°C. After standing again, the magnesium alloy melt is kept at 720-740°C for 30 minutes to obtain a magnesium alloy liquid;

[0088] (3) Under a protective atmosphere (a mixture of SF6 and CO2), the magnesium alloy liquid is cast at 500-600°C, and after cooling, a highly corrosion-resistant ternary magnesium alloy with self-repairing properties is obtained.

[0089] As the In content increases further, its corrosion resistance continues to decrease. However, since Sn can still inhibit In, its microgalvanic corrosion effect does not directly break through the film layer.

[0090] Comparative Example 1

[0091] This comparative example provides a highly corrosion-resistant ternary magnesium alloy with self-repairing properties. The specific composition of the alloy is shown in Table 4 (unit: wt.%), with the remainder being Mg and unavoidable impurities.

[0092] Table 4

[0093] wt.% Sn In Mg Example 1 2.78 1.5 95.72

[0094] The highly corrosion-resistant ternary magnesium alloy with self-repairing properties is prepared as follows:

[0095] (1) Under a protective atmosphere (a mixture of SF6 and CO2), a magnesium ingot is melted at 700-750°C according to the composition ratio shown in Table 4, and then a tin ingot and an indium ingot are added and melted to obtain a magnesium alloy melt;

[0096] (2) Under a protective atmosphere (a mixture of SF6 and CO2), the magnesium alloy melt is stirred at 720-740°C and allowed to stand for 30 minutes, and then refined, degassed, and deslagging are performed at 730-750°C. After standing again, the magnesium alloy melt is kept at 720-740°C for 30 minutes to obtain a magnesium alloy liquid;

[0097] (3) Under a protective atmosphere (a mixture of SF6 and CO2), the magnesium alloy liquid is cast at 500-600°C, and after cooling, a highly corrosion-resistant ternary magnesium alloy with self-repairing properties is obtained.

[0098] When the In content is greater than 1%, severe microgalvanic corrosion makes it difficult to form a protective film layer, which directly and seriously worsens the corrosion rate of the alloy. The corrosion morphology is as follows: Figure 6 shown.

[0099] 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.

[0100] It should be noted that the preferred embodiments of the present invention are given in the specification and drawings of the present invention. However, the present invention can be implemented in many different forms and is not limited to the embodiments described in this specification. These embodiments are not intended to be additional limitations on the content of the present invention. The purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive. In addition, the above-mentioned technical features can be combined with each other to form various embodiments not listed above, which are all considered to be within the scope of the description of the present invention. Furthermore, it is obvious to those skilled in the art that improvements or changes can be made based on the above description, and all such improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A highly corrosion-resistant ternary magnesium alloy with self-repairing properties, characterized in that: Contains the following components in percentage by mass: Sn: 2~7%; In: 0.1~0.4%; the balance is Mg and inevitable impurities; the highly corrosion-resistant ternary magnesium alloy with self-repairing properties includes a matrix phase and a second precipitated phase with a quasi-network distribution, wherein the chemical composition of the second precipitated phase is Mg2Sn and MgIn phase.

2. The highly corrosion-resistant ternary magnesium alloy with self-repairing properties according to claim 1, characterized in that: The inevitable impurities include Fe, and the Fe content is ≤0.05%.

3. The highly corrosion-resistant ternary magnesium alloy with self-repairing properties according to claim 1, characterized in that: Contains 2~3% Sn.

4. The highly corrosion-resistant ternary magnesium alloy with self-repairing properties according to claim 1, characterized in that: Contains the following components by mass percentage: Sn: 2.78%; In: 0.35%; the balance is Mg and other inevitable impurities 5. The highly corrosion-resistant ternary magnesium alloy with self-repairing properties according to any one of claims 1 to 4, characterized in that: The corrosion rate of the highly corrosion-resistant ternary magnesium alloy with self-repairing properties in a dry-wet alternating environment is less than 0.35 mm / year.

6. The method for preparing a highly corrosion-resistant ternary magnesium alloy with self-repairing properties according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) Under a protective atmosphere, according to the composition ratio of the highly corrosion-resistant ternary magnesium alloy with self-repairing properties, melting a tin ingot, an indium ingot, and a magnesium ingot to obtain a magnesium alloy melt; (2) Under a protective atmosphere, the magnesium alloy melt is stirred and then allowed to stand, and then refined, degassed, and deslagging, and then allowed to stand again and kept warm to obtain a magnesium alloy liquid; (3) Under a protective atmosphere, the magnesium alloy liquid is cast into a mold, and after cooling, a highly corrosion-resistant ternary magnesium alloy with self-repairing properties is obtained.

7. The method according to claim 6, characterized in that The protective atmosphere is a mixed gas of CO2 and SF6.

8. The method according to claim 6, characterized in that The melting temperature in step (1) is 700-750°C; 9. The method according to claim 6, characterized in that The temperature of the stirring and standing still in step (2) is 720-740°C for 20-60 minutes; the temperature of the refining, degassing and slag removal is 730-750°C; the temperature of the insulation is 720-740°C for 20-60 minutes.

10. The method according to claim 6, characterized in that The casting temperature in step (3) is 500-600°C.

11. Use of the highly corrosion-resistant ternary magnesium alloy with self-repairing properties according to any one of claims 1 to 5 in the manufacture of automobiles.

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