Low-cost super-corrosion-resistant rare earth magnesium alloy and preparation method thereof

Abstract

The invention discloses a low-cost super-corrosion-resistant rare earth magnesium alloy and a preparation method thereof. The low-cost super-corrosion-resistant rare earth magnesium alloy comprises the following components in percentage by weight: 8-10% of Al, 0.5-2% of Zn, 0.1-0.4% of Mn, 0.004-0.01% of Re and the balance of Mg, wherein Re is one or more than two of Ce, Pm, Sm and Y. The preparation method comprises the following steps: weighing AZ91 and Mg-Re according to the proportion of the components, mixing Mg-Re and Na2SiF6 according to the proportion of 1: (3-6) to prepare a salt shell, and after AZ91 is molten, adding a salt shell block to prepare the rare earth magnesium alloy. The weight loss corrosion rate of the magnesium alloy is only 0.22 mm.y <-1 >, the hydrogen evolution corrosion rate is reduced to 0.04 mm.y <-1 > and is 10 times or more of the corrosion resistance of AZ91 magnesium alloy, the corrosion of the magnesium alloy is inhibited through the improvement of the work function, the problem that the corrosion resistance of the magnesium alloy is poor is solved, the addition amount of rare earth in the magnesium alloy is precisely regulated and controlled, and the corrosion resistance of the magnesium alloy is improved. And the low-cost super-corrosion-resistant rare earth magnesium alloy is prepared.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal materials, and relates to a metal material magnesium alloy and a preparation method thereof. Background Art

[0002] Magnesium alloy is the lightest metal structural material that can be applied at present, and has the advantages of low density, high specific strength and specific stiffness, excellent damping and vibration reduction performance, good thermal conductivity, easy recycling, etc. It has extremely important application value and broad application prospects in the fields of aerospace, automobile manufacturing, household appliances, instrumentation, electronic communication, biomedicine, etc. However, the disadvantage of poor corrosion resistance has always been one of the bottleneck problems restricting the commercial application of magnesium alloys.

[0003] The paper "Towards development of a high-strength stainless Mg alloy with Al-assisted growth of passive film" (Nat Commun, 2022, 13, 5838) published by Zeng Xiaoqin et al. of Shanghai Jiao Tong University proposed a rare earth magnesium alloy Mg-11Y-1Al (wt.%) (abbreviation "stainless magnesium"), in which the weight loss corrosion rate of as-cast Mg-11Y-1Al is 0.25 mm·y -1 , and the hydrogen evolution corrosion rate is 0.18 mm·y -1 . Compared with the cost of commercial AZ series magnesium alloys of about 17,500 yuan / ton, the production cost of stainless magnesium is about 4 times higher. The Chinese patent application with publication number CN112322948A discloses "a magnesium alloy and a preparation method thereof", and its main chemical components are: Al: 7.8-9.2%, Zn: 0.2-0.8%, Mn: 0.05-0.4%, Y: 0.001-0.1%, Ce: 0.001-0.1%, Fe≤0.01%, Si≤0.1%, Cu≤0.01%, Ni≤0.01%, and the balance is Mg. In the examples, a rare earth magnesium alloy added with 0.001% Ce and 0.1% Y by mass percentage and subjected to hot reverse extrusion treatment has a corrosion rate of 0.39 mg / cm 2 ·d -1 , while a rare earth magnesium alloy added with 0.001% Y and 0.1% Ce by mass percentage and subjected to hot reverse extrusion and aging treatment has a corrosion rate of 0.12 mg / cm 2 ·d -1 . The rare earth addition amount of the two alloys is more than 0.1% by mass percentage, and the hot reverse extrusion and aging treatments also increase the production cost of commercial AZ series magnesium alloys by 25-40% per ton.

[0004] At present, the rare earth addition amount of rare earth magnesium alloys with better corrosion resistance is relatively high, resulting in a significant increase in cost and making it difficult to be commercially applied. Only by further reducing the weight percentage of rare earth elements in corrosion-resistant magnesium alloys is it possible to promote the commercial application of corrosion-resistant magnesium alloys. Therefore, how to prepare a magnesium alloy with low cost and ultra-high corrosion resistance to rare earths is the key to promoting commercial application. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method of a low-cost ultra-high corrosion-resistant rare earth magnesium alloy, and a magnesium alloy with excellent corrosion resistance is obtained by reasonably selecting and controlling steps such as alloy types, content ratios, and salt shell preparation.

[0006] The present invention is realized through the following technical solutions.

[0007] A low-cost ultra-high corrosion-resistant rare earth magnesium alloy according to the present invention is characterized in that the weight percentages of the components of the magnesium alloy are as follows: Al: 8-10%, Zn: 0.5-2%, Mn: 0.1-0.4%, Re: 0.004-0.01%, and the balance is Mg.

[0008] A preparation method of a low-cost ultra-high corrosion-resistant rare earth magnesium alloy according to the present invention includes the following steps.

[0009] S1. Weigh AZ91 magnesium alloy and Mg-Re master alloy according to the above weight percentages of alloy elements.

[0010] S2. Mix the Mg-Re master alloy weighed in step S1 with Na2SiF6 in a weight ratio of 1:3-6 to form a salt shell, and the pressing pressure is 150-200 MPa.

[0011] S3. Dry the crucible and the mold in a vacuum drying oven to remove moisture. First, put the AZ91 magnesium alloy into the crucible, and then put the crucible into the melting furnace.

[0012] S4. Set the melting temperature of the melting furnace and start heating and melting. Introduce argon for protection, and the gas flow rate is 5 L / min. The melting temperature is 700-800 °C. After the AZ91 magnesium alloy is completely melted, add the salt shell block prepared in step S2, and perform mechanical stirring to accelerate the dispersion of the salt shell. After stirring, keep warm for 20-30 min.

[0013] S5. After the heat preservation in step S4 ends, pour the alloy melt in the crucible into the mold to obtain a magnesium alloy ingot.

[0014] Optionally, in step S1, Re is one or any combination of Ce, Pm, Sm, and Y.

[0015] Compared with the prior art, the present invention adopts a method of preparing a salt shell to control the actual rare earth content in the rare earth magnesium alloy obtained by smelting. The melting point of the fluorosalt (Na2SiF6) is about 740 °C, which is higher than the smelting temperature of the magnesium alloy and has low reactivity with the magnesium melt, thus avoiding contamination of the alloy components. It remains solid in the initial stage of smelting, forming a physical barrier, and will slowly decompose into NaF and SiF4 gases at high temperatures. Among them, SiF4 has an inert protection effect and can inhibit rare earth oxidation. At the same time, the salt shell slowly decomposes in the melt, releasing the rare earth alloy in stages and avoiding concentrated burning loss.

[0016] For the rare earth magnesium alloy prepared by the present invention, the weight loss corrosion rate of the magnesium alloy is only 0.22 mm·y -1 , and the hydrogen evolution corrosion rate is reduced to 0.04 mm·y -1 , which is more than 10 times the corrosion resistance of the commercial AZ91 magnesium alloy. The present invention solves the problem of poor corrosion resistance of magnesium alloys, precisely regulates the rare earth addition amount in magnesium alloys, and prepares a low-cost ultra-corrosion-resistant rare earth magnesium alloy, which has great commercial application potential. Description of the Drawings

[0017] Figure 1 are the macroscopic morphology pictures of the magnesium alloys in Example 1, Example 2, Example 3, and the comparative example of the present invention immersed in a 3.5 wt.% NaCl solution for different times.

[0018] Figure 2 are the KPFM results of the magnesium alloys in Example 1 and the comparative example: (a), (d) are the two-dimensional morphology maps of Example 1 and the comparative example respectively; (b), (e) are the volt potential maps of Example 1 and the comparative example respectively; (c), (f) are the three-dimensional potential maps of Example 1 and the comparative example respectively. Detailed Embodiments

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention. Unless otherwise defined, the technical terms or scientific terms used herein shall have the ordinary meaning understood by those of ordinary skill in the art to which the present invention belongs. The words such as "including" used herein mean that the elements or items appearing before the word cover the elements or items listed after the word and their equivalents, without excluding other elements or items.

[0020] The embodiments of the present invention provide a method for preparing a low-cost ultra-corrosion-resistant rare earth magnesium alloy, including the following steps.

[0021] Weigh and prepare AZ91 magnesium alloy and Mg-Re master alloy according to the elemental weight percentages in the low-cost ultra-corrosion-resistant rare-earth magnesium alloy.

[0022] Mix the weighed Mg-Re master alloy and Na2SiF6 in a weight ratio of 1:3 - 6 to make a salt shell, and the pressing pressure is 150 - 200 MPa.

[0023] Dry the crucible and the mold in a vacuum drying oven to remove moisture. First, put the AZ91 magnesium alloy into the crucible, and then put the crucible into the melting furnace.

[0024] Set the melting temperature of the melting furnace and start heating and melting. Pass in argon for protection, with a gas flow rate of 5 L / min and a melting temperature of 700 - 800 °C. After the AZ91 magnesium alloy is completely melted, add the salt shell blocks prepared in step S2, carry out mechanical stirring to accelerate the dispersion of the salt shell, and keep warm for 20 - 30 min after stirring.

[0025] After the heat preservation ends, pour the alloy melt in the crucible into the mold to obtain a magnesium alloy ingot. Example 1

[0026] Weigh 0.06 g of Mg-20Sm master alloy and 199.94 g of AZ91 magnesium alloy according to the elemental weight percentages; mix the weighed Mg-30Sm master alloy and Na2SiF6 in a weight ratio of 1:4 to make a salt shell, and the pressing pressure is 150 MPa. Dry the crucible and the mold in a vacuum drying oven to remove moisture; first, put the AZ91 magnesium alloy into the crucible, and then put the crucible into the melting furnace. Set the melting temperature of the melting furnace and start heating and melting. Pass in argon for protection, with a gas flow rate of 5 L / min and a melting temperature of 750 °C. After the AZ91 magnesium alloy is completely melted, add the salt shell blocks prepared in step S2, carry out mechanical stirring to accelerate the dispersion of the salt shell, and keep warm for 20 min after stirring; after the heat preservation ends, pour the alloy melt in the crucible into the mold, and control the pouring time within 10 s to obtain a magnesium alloy ingot. Example 2

[0027] Weigh 0.064 g of Mg-25Y master alloy and 199.936 g of AZ91 magnesium alloy according to the weight percentage of alloying elements; mix the weighed Mg-25Y master alloy and Na2SiF6 in a weight ratio of 1:4 to make a salt shell, and the pressing pressure is 150 MPa. Dry the moisture in the crucible and mold in a vacuum drying oven; first put the AZ91 magnesium alloy into the crucible, then put the crucible into the melting furnace, set the melting temperature of the melting furnace and start heating and melting, introduce argon for protection, the gas flow rate is 5 L / min, and the melting temperature is 750 °C. After the AZ91 magnesium alloy is completely melted, add the salt shell block prepared in step S2, carry out mechanical stirring to accelerate the dispersion of the salt shell, and keep warm for 20 min after stirring; after the heat preservation is over, pour the alloy melt in the crucible into the mold, and control the pouring time within 10 s to obtain a magnesium alloy ingot. Example 3

[0028] Weigh 0.05 g of Mg-20Ce master alloy and 0.05 g of Mg-20Pm master alloy, and 199.9 g of AZ91 magnesium alloy according to the weight percentage of alloying elements; mix the weighed two kinds of Mg-20Re master alloys and Na2SiF6 in a weight ratio of 1:4 to make a salt shell, and the pressing pressure is 150 MPa. Dry the moisture in the crucible and mold in a vacuum drying oven; first put the AZ91 magnesium alloy into the crucible, then put the crucible into the melting furnace, set the melting temperature of the melting furnace and start heating and melting, introduce argon for protection, the gas flow rate is 5 L / min, and the melting temperature is 750 °C. After the AZ91 magnesium alloy is completely melted, add the salt shell block prepared in step S2, carry out mechanical stirring to accelerate the dispersion of the salt shell, and keep warm for 20 min after stirring; after the heat preservation is over, pour the alloy melt in the crucible into the mold, and control the pouring time within 10 s to obtain a magnesium alloy ingot.

[0029] Comparative example.

[0030] Weigh 200 g of AZ91 magnesium alloy; dry the moisture in the crucible and mold in a vacuum drying oven; first put the AZ91 magnesium alloy into the crucible, then put the crucible into the melting furnace, set the melting temperature of the melting furnace and start heating and melting, introduce argon for protection, the gas flow rate is 5 L / min, and the melting temperature is 750 °C. After the AZ91 magnesium alloy is completely melted, carry out mechanical stirring, and keep warm for 20 min after stirring; after the heat preservation is over, pour the alloy melt in the crucible into the mold, and control the pouring time within 10 s to obtain a magnesium alloy ingot.

[0031] Performance detection.

[0032] Corrosion resistance: The as-cast magnesium alloys obtained in Example 1, Example 2, Example 3 and the comparative example were immersed in 3.5 wt.% NaCl solution for 48 h, and weight loss and hydrogen evolution tests were carried out. The results are shown in Table 1.

[0033] The as-cast magnesium alloys obtained in Example 1, Example 2, Example 3 and the comparative example were immersed in 3.5 wt.% NaCl solution for 72 h, and macroscopic morphology pictures were taken at 0, 24, 48, and 72 h respectively. The results are as Figure 1 shown.

[0034] Table 1 Corrosion rate of as-cast magnesium alloys:

[0035]

[0036] As can be seen from Table 1, after the as-cast magnesium alloy in Example 1 was subjected to ultra-trace rare earth alloying, compared with the comparative example, its weight loss corrosion rate decreased from 2.46 mm·y -1 to 0.22 mm·y -1 , which is very close to 0.25 mm·y -1 of as-cast Mg-11Y-1Al, and the hydrogen evolution corrosion rate decreased from 2.05 mm·y -1 to 0.04 mm·y -1 , which is one order of magnitude lower than 0.18 mm·y -1 of as-cast Mg-11Y-1Al. This shows that ultra-trace rare earth alloying of magnesium alloys can significantly improve the corrosion resistance of magnesium alloys.

[0037] From Figure 1 it can be seen that compared with the comparative example, after the alloy surface of the comparative example was immersed for 72 h, the surface was covered with corrosion pits and the corrosion was very serious. After the alloy surface of Example 1 was immersed for 72 h, there were almost no corrosion pits, indicating that ultra-trace rare earth alloying significantly improved the protection ability of the magnesium alloy surface.

[0038] Table 2 Work function of as-cast magnesium alloys:

[0039] From Figure 2 , Table 2 can be seen that compared with the comparative example, the work function of Example 1 is higher than that of the comparative example, indicating that in the alloy of Example 1, more energy is required for electrons to escape from the material, the material has a stronger binding ability to electrons, and it is more difficult for electrons to leave the material surface, which also means that the alloy of Example 1 is more difficult to corrode.

[0040] Although the embodiments of the present invention have been described in detail above, it will be apparent to those skilled in the art that various modifications and variations can be made to these embodiments. However, it should be understood that such modifications and variations are all within the scope and spirit of the present invention as described in the claims. Moreover, the present invention as described herein may have other embodiments and can be implemented or realized in various ways.

Claims

1. A low-cost and super corrosion-resistant rare earth magnesium alloy, characterized in that, The weight percentages of the components of the magnesium alloy are as follows: Al: 8 - 10%, Zn: 0.5 - 2%, Mn: 0.1 - 0.4%, Re: 0.004 - 0.01%, and the balance is Mg.

2. A low-cost super corrosion-resistant rare earth magnesium alloy according to claim 1, characterized in that, The Re is one or more of Ce, Pm, Sm, and Y.

3. The preparation method of a low-cost and super corrosion-resistant rare earth magnesium alloy according to claim 1 or 2, characterized in that It includes the following steps: S1. Weigh AZ91 magnesium alloy and Mg-Re master alloy according to the weight percentages of the alloying elements. S2. Mix the Mg-Re master alloy weighed in step S1 with Na2SiF6 in a weight ratio of 1:3 - 6 to form a salt shell, and the pressing pressure is 150 - 200 MPa. S3. Dry the crucible and the mold in a vacuum drying oven to remove moisture. First, put the AZ91 magnesium alloy into the crucible, and then put the crucible into the melting furnace. S4. Set the melting temperature of the melting furnace and start heating and melting. Introduce argon for protection, with a gas flow rate of 5 L / min and a melting temperature of 700 - 800 °C. After the AZ91 magnesium alloy is completely melted, add the salt shell blocks prepared in step S2, and conduct mechanical stirring to accelerate the dispersion of the salt shell. After stirring, keep it warm for 20 - 30 min. S5. After the heat preservation in step S4 is completed, pour the alloy melt in the crucible into the mold to obtain a magnesium alloy ingot.

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