Pure magnesium and a method for purifying the same

Abstract

This invention discloses a pure magnesium and its purification method. The purification method specifically includes the following steps: (1) placing pure Mg into a crucible and placing it in a melting furnace, setting the temperature of the melting furnace to 650~670℃, and introducing CO. 2 and SF 6 The mixture is protected with a gas mixture. After the pure Mg melts, the temperature is raised to 690~720℃. The Mg-5Mn master alloy is added to the crucible. After it is completely melted, the melt is stirred to make the alloy composition uniform. (2) Remove the slag on the surface of the melt, add the refining agent to the melt, and stir it thoroughly. Let it stand for 30~50 min. (3) After the melt cools down, a high-purity magnesium ingot is obtained. This invention can effectively reduce the Fe impurity content in magnesium metal and reduce the inclusions in magnesium metal.

Description

A pure magnesium and its purification method Technical Field

[0001] This invention belongs to the field of materials technology, and relates to pure magnesium, and particularly to a pure magnesium and a method for its purification. Background Technology

[0002] Magnesium alloys are currently the lightest structural metal materials, and they have a higher specific strength compared to other ferrous alloys and non-ferrous alloys. Therefore, they are widely used in aerospace, 3C, automotive and other fields.

[0003] Magnesium, the raw material for magnesium alloys, exhibits varying impurity content depending on the smelting method. High-purity brine magnesium can be obtained from brine or seawater by electrolysis, through dehydration or calcination of magnesium chloride melt. However, this method still results in relatively high levels of impurities such as Fe and Si. The presence of impurities with high standard electrode potentials (Fe, Si, etc.) and the presence of a second phase acting as a local cathode rapidly reduces corrosion resistance. Even small amounts of iron can significantly decrease the corrosion resistance of magnesium alloys. Furthermore, external impurities are transferred during processing and shaping, negatively impacting the microstructure and mechanical properties of magnesium alloys. Therefore, to control the impurity content and improve the microstructure and mechanical properties of magnesium alloys, it is essential to maintain extremely low levels of iron, silicon, and inclusions in the magnesium. Summary of the Invention

[0004] In view of the above-mentioned shortcomings of the existing technology, the purpose of this invention is to provide pure magnesium and its purification method. This invention can effectively reduce the Fe impurity content in metallic magnesium and reduce inclusions in metallic magnesium.

[0005] The technical solution of this invention is implemented as follows:

[0006] A method for purifying pure magnesium specifically includes the following steps:

[0007] (1) Place pure Mg in a crucible and place it in a melting furnace. Set the temperature of the melting furnace to 650~670 ℃ and introduce a mixture of CO2 and SF6 for protection. After the pure Mg melts, raise the temperature to 690~720 ℃ and add the Mg-5Mn master alloy into the crucible. After it is completely melted, stir the melt to make the alloy composition uniform.

[0008] (2) Remove the slag from the surface of the melt, add the refining agent to the melt, stir thoroughly and let stand for 30 to 50 minutes;

[0009] (3) After the melt is cooled, a high-purity magnesium ingot is obtained.

[0010] Furthermore, in step (1), the amount of Mn added is 0.3~0.5 wt% of the melt mass.

[0011] Furthermore, the amount of the refining agent added is 0.5 to 1 wt% of the melt mass.

[0012] Furthermore, the refining agent is a mixture of JDMJ and boron oxide, wherein boron oxide accounts for 10-15% of the mass of the refining agent.

[0013] Further, after step (2) is allowed to stand, the melt is cooled to 650~670 ℃, and an ultrasonic amplitude transformer is added to perform ultrasonic treatment on the melt at a frequency of 5~22 KHz until the melt temperature drops to 620~640 ℃. After the ultrasonic treatment is completed, the melt is rapidly heated to 640~660 ℃, allowed to stand for 40~80 min, and then cooled down.

[0014] Furthermore, in step (1), before the pure Mg is placed into the crucible, the smelting furnace is preheated and dried at 100~300 ℃, and the inner wall of the steel crucible is coated with hexagonal boron nitride.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] 1. In this invention, a Mg-5Mn master alloy is added during the smelting process. The addition of Mn can effectively reduce the solid solubility of Fe in Mg and generate the MnFe phase, thereby achieving the purpose of removing Fe during the sedimentation process. At the same time, the impurity Si can form compounds such as Mn2Si and Mn5Si3 with Mn. During the smelting process, the density of Si is different from that of the magnesium melt, and it can be separated from the molten metal during natural settling, thereby removing the impurity Si and reducing the content of impurities Fe and Si in pure magnesium.

[0017] Meanwhile, the present invention incorporates boron oxide, which can form FeB with Fe, further reducing the Fe content of impurities in the melt.

[0018] Furthermore, the present invention performs ultrasonic treatment on the melt at a lower temperature, which not only further reduces the solid solubility of Fe in Mg, but also promotes the formation of FeB phase, MnSi phase and MnFe phase, accelerates the sedimentation of impurities in the melt, removes impurities from the melt, purifies the melt, and improves the purity of metallic magnesium.

[0019] 2. The Fe element content in the pure magnesium ingot prepared by this invention can be as low as 37 ppm, and the inclusions are significantly reduced, greatly improving the purity of pure magnesium. This can improve the mechanical properties and corrosion resistance of subsequent products. Moreover, this invention is simple to operate and has the potential for industrial application. Attached Figure Description

[0020] Figure 1 - Inclusion diagram of the pure magnesium ingot obtained in Example 1.

[0021] Figure 2 - Inclusion diagram of the pure magnesium ingot obtained in Example 2.

[0022] Figure 3 - Inclusion diagram of the pure magnesium ingot obtained in Example 3.

[0023] Figure 4 - Inclusion diagram of the pure magnesium ingot obtained in Example 3.

[0024] Figure 5 - Inclusion diagram of pure magnesium ingot obtained in Comparative Example 1.

[0025] Figure 6 - Inclusion diagram of pure magnesium ingot obtained in Comparative Example 2. Detailed Implementation

[0026] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0027] In the following examples and comparative examples, the pure Mg used had a Mg mass fraction of 99.9% and an Fe impurity content of 300 ppm. The Mg-5Mn used had a Mg mass fraction of 95% and a Mn mass fraction of 5%. The refining agent JDMJ was independently developed by Shanghai Jiao Tong University.

[0028] Example 1

[0029] A method for purifying pure magnesium specifically includes the following steps:

[0030] S1: Made with pure Mg, Mg-5Mn master alloy, with Mn element added at 0.4wt%.

[0031] S2: First, preheat and dry the melting furnace, then coat the inner wall of the steel crucible with hexagonal boron nitride. Place pure Mg into the crucible, then place the crucible into the melting furnace, set the temperature to 670 ℃, and introduce a mixture of CO2 and SF6 for protection. After the pure Mg melts, raise the furnace temperature to 710 ℃, and melt the Mg-5Mn master alloy into it. After the master alloy has completely melted, use a tool to stir the melt up and down to ensure a uniform distribution of the alloy composition.

[0032] S3: Heat the melt to 710 ℃, remove the slag on the surface of the melt, add refining agent JDMJ to the melt (the amount of refining agent is 1wt% of the melt mass), stir thoroughly and let stand for 40 min.

[0033] S4: The melt is cooled with water to obtain pure magnesium ingots.

[0034] Example 2

[0035] This embodiment is the same as Embodiment 1, except that (1) the refining agent added in this embodiment is 90% JDMJ + 10% B2O3; (2) after standing for 40 min in this embodiment, the melting furnace is stopped from heating. When the melt temperature drops to 660 ℃, an ultrasonic amplitude transformer device is added to perform ultrasonic treatment on the melt at a frequency of 15 KHz until the melt temperature drops to 630 ℃. Since there is a cooling process in the melt during ultrasonic treatment, and the Mn5Si compound appears at 650 ℃ and can precipitate by standing, after the ultrasonic treatment is completed, the melt is reheated to 650 ℃ and left to stand for 1 h. Finally, the melt is water-cooled to obtain pure magnesium ingots.

[0036] Example 3

[0037] This embodiment is the same as Embodiment 1, except that the refining agent added in this embodiment is 90% JDMJ + 10% B2O3.

[0038] Example 4

[0039] This embodiment is the same as Embodiment 1, except that in this embodiment, after standing for 40 minutes, the melting furnace is stopped from heating. When the melt temperature drops to 660 °C, an ultrasonic amplitude transformer is added to ultrasonically treat the melt at a frequency of 15 kHz until the melt temperature drops to 630 °C. Since the melt undergoes a cooling process during ultrasonication, and Mn5Si compounds appear at 650 °C and can precipitate through standing, after ultrasonic treatment, the melt is reheated to 650 °C and stood for 1 hour. Finally, the melt is water-cooled to obtain pure magnesium ingots.

[0040] Comparative Example 1

[0041] S1: Industrially pure Mg is used.

[0042] S2: First, preheat and dry the smelting furnace, then coat the inner wall of the steel crucible with hexagonal boron nitride. Place pure Mg into the crucible, then place the crucible into the smelting furnace, set the temperature to 710 ℃, and introduce a mixture of CO2 and SF6 for protection.

[0043] S3: Heat the melt to 710 ℃, remove the slag on the surface of the melt, add refining agent JDMJ to the melt (the amount of refining agent is 1wt% of the mass of the melt), stir thoroughly and let stand for 40 minutes.

[0044] S4: The melt is cooled with water to obtain pure magnesium ingots.

[0045] Comparative Example 2

[0046] This embodiment is the same as Embodiment 1, except that the amount of Mn added in this embodiment is 0.2wt%.

[0047] 1. The Fe element content of impurities in the pure magnesium ingots prepared in Examples 1-4 and Comparative Examples 1-2 is shown in Table 1.

[0048] Table 1. Fe content of industrial pure magnesium from different processes

[0049]

[0050] As can be seen from Table 1: (1) By comparing Example 1 and Comparative Example 2, it can be seen that when the amount of Mn added is small, it cannot reduce the Fe content, but will instead increase the removal of Fe impurities. Only when the amount is appropriate can Fe in the melt be effectively removed.

[0051] (2) As can be seen from Examples 3 and 4, adding boron oxide and ultrasonic treatment of the melt during the smelting process are both beneficial to the removal of Fe impurities. In conjunction with Example 2, it can be seen that adding boron oxide during the smelting process and ultrasonic treatment of the melt at low temperature can efficiently remove Fe impurities. This is because ultrasonic treatment of the melt at a lower temperature is beneficial to the formation of FeB phase, MnSi phase and MnFe phase, and can accelerate the sedimentation of impurities in the melt, thereby efficiently removing impurities in the melt.

[0052] 2. The inclusion diagrams of pure magnesium ingots obtained in Examples 1-4 and Comparative Examples 1-2 are shown in Figures 1-6, respectively. As can be seen from the figures, the inclusion content in Comparative Examples 1 and 2 is high and the inclusions are large; compared with Comparative Example 1, the number of inclusions in Examples 1, 3 and 4 is reduced and the inclusions are smaller, and the number of inclusions in Example 2 is significantly reduced and the inclusions are significantly smaller.

[0053] Using the preparation method provided by this invention, a certain amount of Mn element is added, and 10 wt% B2O3 is added to JDMJ. The industrial pure magnesium prepared after ultrasonic treatment has low impurities and fewer inclusions, resulting in higher purity.

[0054] Finally, it should be noted that the above embodiments of the present invention are merely illustrative examples and not intended to limit the implementation of the invention. Those skilled in the art can make other variations and modifications based on the above description. It is impossible to exhaustively list all possible implementations here. All obvious variations or modifications derived from the technical solutions of this invention are still within the scope of protection of this invention.

Claims

1. A method for purifying pure magnesium, characterized in that, Specifically, the following steps are included: (1) Place pure Mg in a crucible and place it in a melting furnace. Set the temperature of the melting furnace to 650~670 ℃ and introduce a mixture of CO2 and SF6 for protection. After the pure Mg melts, raise the temperature to 690~720 ℃ and add the Mg-5Mn intermediate alloy into the crucible. After it is completely melted, stir the melt to make the alloy composition uniform. (2) Remove the slag on the surface of the melt, add a refining agent to the melt, and stir it thoroughly. Let it stand for 30~50 min. (3) After the melt cools down, a high-purity magnesium ingot is obtained.

2. The method for purifying pure magnesium according to claim 1, characterized in that, In step (1), the amount of Mn added is 0.3~0.5 wt% of the melt mass.

3. The method for purifying pure magnesium according to claim 1, characterized in that, The amount of the refining agent added is 0.5 to 1 wt% of the melt mass.

4. A method for purifying pure magnesium according to claim 1 or 3, characterized in that, The refining agent is a mixture of JDMJ and boron oxide, wherein boron oxide accounts for 10-15% of the mass of the refining agent.

5. The method for purifying pure magnesium according to claim 1, characterized in that, After step (2), the melt is cooled to 650~670 ℃, and an ultrasonic amplitude transformer is added to perform ultrasonic treatment on the melt at a frequency of 5~22 KHz until the melt temperature drops to 620~640 ℃. After the ultrasonic treatment, the melt is rapidly heated to 640~660 ℃, left to stand for 40~80 min, and then cooled down.

6. A method for purifying pure magnesium according to claim 1, 2, or 3, characterized in that, In step (1), before pure Mg is placed into the crucible, the smelting furnace is preheated and dried at 100~300 ℃, and hexagonal boron nitride is coated on the inner wall of the steel crucible.

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