Lanthanum hexaboride modified magnesium alloy and preparation method thereof

Abstract

The invention relates to a lanthanum hexaboride modified magnesium alloy and a preparation method thereof. The preparation method comprises the following steps: providing a magnesium alloy base material; melting the magnesium alloy base material to obtain a magnesium alloy melt; under the low-frequency condition, the magnesium alloy melt and an alterant are mixed and melted in an electromagnetic stirring furnace, and a first melt is obtained; the modifier comprises lanthanum hexaboride; under the low-frequency condition, the first melt is subjected to electromagnetic stirring treatment, and a second melt is obtained; under the medium-frequency condition, the second melt is subjected to refining and degassing treatment, and a third melt is obtained; and under the medium frequency condition, the third melt is subjected to heat preservation and standing treatment, and the lanthanum hexaboride modified magnesium alloy is obtained through casting. Wherein the frequency under the low frequency condition is 90 to 100 Hz, and the frequency under the intermediate frequency condition is 900 to 1300 Hz.

Description

Technical Field

[0001] The present application relates to the technical field of metal material preparation, and in particular to a lanthanum hexaboride modified magnesium alloy and a preparation method thereof. Background Art

[0002] Magnesium alloys have the characteristics of high specific strength and specific stiffness, excellent casting processing performance, good electromagnetic shielding performance, and green environmental protection, and are widely used in aerospace, transportation, electronic 3C and other fields. In particular, Mg-Al alloys have good casting process performance, excellent mechanical properties and corrosion resistance, low preparation cost, and are widely used in industrial production.

[0003] However, the strength, plasticity and corrosion resistance of magnesium alloys are not outstanding enough, which limits their wide application in structural functional materials. Alloy modification can effectively improve the alloy structure, enhance alloy performance and purify the purity of the melt. Although traditional SiC particle reinforced magnesium alloy materials have advantages such as high specific strength, high specific stiffness, good wear resistance, high temperature resistance and shock absorption performance, they also have some shortcomings, such as the interface problem between the reinforced particles and the magnesium alloy, resulting in coarse organization and uneven particle dispersion.

[0004] Therefore, the traditional technology still needs to be improved. Summary of the invention

[0005] Based on this, the present application provides a lanthanum hexaboride-modified magnesium alloy and a preparation method thereof. The preparation method of the lanthanum hexaboride-modified magnesium alloy can refine the microstructure grains and significantly improve the mechanical properties of the magnesium alloy.

[0006] The technical solution of this application to solve the above technical problems is as follows:

[0007] In one aspect of the present application, a method for preparing a lanthanum hexaboride modified magnesium alloy is provided, comprising the following steps:

[0008] Provide magnesium alloy substrate;

[0009] Melting the magnesium alloy substrate to obtain a magnesium alloy melt;

[0010] Under low frequency conditions, the magnesium alloy melt and the modifier are mixed and melted in an electromagnetic stirring furnace to obtain a first melt; the modifier includes lanthanum hexaboride;

[0011] Under low frequency conditions, subjecting the first melt to electromagnetic stirring to obtain a second melt;

[0012] Under medium frequency conditions, the second melt is subjected to a refining and degassing treatment to obtain a third melt;

[0013] Under medium frequency conditions, the third melt is subjected to heat preservation and static treatment, and cast to obtain the lanthanum hexaboride modified magnesium alloy;

[0014] The induction frequency under the low-frequency condition is 90-100 Hz, and the induction frequency under the medium-frequency condition is 900 Hz-1300 Hz.

[0015] In the preparation method of the above-mentioned lanthanum hexaboride modified magnesium alloy, the magnesium alloy substrate is first melted in an electromagnetic stirring furnace, and then the magnesium alloy melt and the specific modifier are mixed and melted under low-frequency conditions, wherein the second phase particles generated in situ by the LaB6 modifier and other elements in the magnesium alloy are distributed at the grain boundaries, so that the grain size of the magnesium alloy is greatly reduced. This refined grain structure can significantly improve the strength and toughness of the magnesium alloy; then the first melt is subjected to electromagnetic stirring treatment under low-frequency conditions; then it is subjected to refining and degassing treatment under medium-frequency conditions, and then it is subjected to heat preservation and static treatment under medium-frequency conditions. Through the control of specific electromagnetic frequency conditions, it is ensured that LaB6 fully reacts with the magnesium alloy matrix and is evenly distributed. In this way, the grain refinement of the magnesium alloy structure can be obvious, the size of the second phase is smaller, and it has better mechanical properties.

[0016] In one embodiment, based on the total mass of the magnesium alloy substrate and the modifier, the mass proportion of the lanthanum hexaboride is 0.3% to 1%.

[0017] In one embodiment, the average particle size of the lanthanum hexaboride is 2 μm to 10 μm.

[0018] In one of the embodiments, the average grain size of the lanthanum hexaboride modified magnesium alloy is ≤140 μm.

[0019] In one embodiment, the electromagnetic stirring treatment includes a first stirring treatment, a second stirring treatment and a third stirring treatment which are performed alternately in sequence; wherein, during the first stirring treatment, the second stirring treatment and the third stirring treatment, the first melt circulates up and down in the electromagnetic stirring furnace, and the flow directions of the first melt are different.

[0020] In one embodiment, the electromagnetic stirring process satisfies at least one of the following characteristics:

[0021] (1) When performing the first stirring treatment and the second stirring treatment, the power of the electromagnetic stirring furnace is 30 kW to 40 kW, the first melt is divided into two upper and lower flow parts, each flow part includes two flow areas; during the first stirring treatment, the flow directions of the upper and lower flow parts of the first melt are opposite, and the flow directions of the two flow areas of the same flow part are opposite; during the second stirring treatment, the flow directions of the upper and lower flow parts of the first melt are the same, and the flow directions of the two flow areas of the same flow part are the same;

[0022] (2) When performing the third stirring treatment, the power of the electromagnetic stirring furnace is 30 kW to 40 kW; the flow direction of the first melt is: flowing downward from the side wall of the electromagnetic stirring furnace, then gathering toward the center, and then circulating upward.

[0023] In one embodiment, the electromagnetic stirring process satisfies at least one of the following characteristics:

[0024] (1) The electromagnetic stirring treatment time is 15min~30min;

[0025] (2) The duration of the first stirring treatment, the second stirring treatment and the third stirring treatment is independently 5 min to 8 min.

[0026] In one embodiment, the composition of the magnesium alloy substrate is, by mass percentage, Al: 7.5% to 9.0%, Zn: 0.2% to 0.8%, Mn: 0.15% to 0.5%, Fe: <0.08%, Cu: <0.1%, Si <0.25%, and the balance is Mg;

[0027] And / or, the gas in the electromagnetic stirring furnace is a protective gas, and the protective gas includes SF6;

[0028] And / or, the refining and degassing treatment comprises the following steps: introducing high-purity argon gas at a flow rate of 8 L / min to 12 L / min into the second melt for 3 min to 5 min;

[0029] And / or, the time of the heat preservation and static treatment is 10 min to 20 min, and the temperature of the heat preservation and static treatment is 740° C. to 750° C.

[0030] In one embodiment, before melting the magnesium alloy substrate, the method further includes drying the magnesium alloy substrate to 200° C. to 300° C.;

[0031] And / or, under low frequency conditions, the step of mixing and melting the magnesium alloy melt and the modifier comprises the following steps:

[0032] Under low-frequency conditions, the magnesium alloy melt is subjected to a first stirring treatment, and then LaB6 is placed in a graphite bell jar and added to the magnesium alloy melt.

[0033] In one aspect of the present application, a lanthanum hexaboride-modified magnesium alloy is further provided, wherein the lanthanum hexaboride-modified magnesium alloy is prepared by the preparation method of the lanthanum hexaboride-modified magnesium alloy as described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a schematic diagram of the stirring mode of the electromagnetic stirring furnace of Example 1;

[0035] Figure 2 This is a schematic diagram of the stirring mode of the electromagnetic stirring furnace of Example 1;

[0036] Figure 3 This is a schematic diagram of the stirring mode of the electromagnetic stirring furnace of Example 1;

[0037] Figure 4 This is a SEM image of lanthanum hexaboride with an average particle size of 2 μm in Example 1;

[0038] Figure 5 This is a SEM image of lanthanum hexaboride with an average particle size of 5 μm in Example 2;

[0039] Figure 6 This is a SEM image of lanthanum hexaboride with an average particle size of 10 μm in Example 3;

[0040] Figure 7 The metallographic images of ZM5 magnesium alloy modified by LaB6 with different particle sizes accounting for 0.5% by mass in Examples 1 to 3 and Comparative Example 1;

[0041] Figure 8 The metallographic images of 5 μm LaB6 modified ZM5 magnesium alloys with different mass proportions in Examples 2, 4-6 and Comparative Example 1;

[0042] Fig. 9 This is the metallographic image of the LaB6-modified ZM5 magnesium alloy in Comparative Example 2. DETAILED DESCRIPTION

[0043] References to embodiments of the present application will now be provided in detail, one or more examples of which are described below. Each example is provided as an explanation rather than a limitation of the present application. In fact, it will be apparent to those skilled in the art that various modifications and variations may be made to the present application without departing from the scope or spirit of the present application. For example, a feature described or described as part of one embodiment may be used in another embodiment to produce a further embodiment.

[0044] Therefore, it is intended that the present application covers such modifications and variations that fall within the scope of the appended claims and their equivalents. Other objects, features and aspects of the present application are disclosed in or are apparent from the following detailed description. It will be appreciated by those of ordinary skill in the art that this discussion is merely a description of exemplary embodiments and is not intended to limit the broader aspects of the present application.

[0045] The term "comprises", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or equipment. In the absence of more restrictions, the elements defined by the sentence "comprising one..." do not exclude the presence of other identical elements in the process, method, article or equipment including the elements. The indefinite articles "a kind of" and "one" before the elements or components of the present application are not restrictive to the quantity requirements (i.e., the number of occurrences) of the elements or components. Therefore, "one" or "a kind of" should be interpreted as including one or at least one, and the elements or components in the singular form also include the plural form, unless the number obviously refers only to the singular form. The meaning of "multiple" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0046] The weight of the relevant components mentioned in the description of the embodiments of the present invention may not only refer to the specific content of each component, but also indicate the weight ratio between the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the description of the embodiments of the present invention, it is within the scope disclosed in the description of the embodiments of the present invention. Specifically, the weight described in the description of the embodiments of the present invention may be a mass unit known in the chemical industry such as μg, mg, g, kg, etc.

[0047] Except as shown in the operating examples or otherwise indicated, all numbers used in the specification and claims to indicate the amount of ingredients, physicochemical properties, etc. are understood to be adjusted by the term "about" in all cases. For example, therefore, unless otherwise indicated, the numerical parameters listed in the above specification and the attached claims are approximate values, and those skilled in the art can use the teachings disclosed herein to seek to obtain the desired properties and appropriately change these approximate values. The use of numerical ranges expressed as endpoints includes all numbers within the range and any range within the range, for example, 1 to 5 includes 1, 1.1, 1.3, 1.5, 2, 2.75, 3, 3.80, 4 and 5, etc.

[0048] LaB6 has been used in aluminum-based alloys. One of the applications is to generate LaB6 in situ by adding B and La elements, and obtain Al-20%Si-5% LaB6. In magnesium alloys, B and La elements are also used. For example, La-Ce mixed rare earth and TiB2 are used as composite grain refiners. After the composite grain refiner is added, the effect of coupling and refining the magnesium alloy grains is achieved, and a cast magnesium alloy with small grain size and excellent comprehensive mechanical properties is obtained. However, there is currently no method of adding La and B elements to the alloy in the form of a compound.

[0049] During the research process, the technical personnel of this application found that LaB6 particles have serious sedimentation problems during the casting process due to the large difference in density between LaB6 particles and the magnesium matrix, which makes them unevenly distributed in the magnesium matrix, and there is serious air entrainment during the mechanical stirring process, resulting in poor reinforcement effect and poor overall mechanical properties.

[0050] Based on this, the technical personnel of this application broke the constraints of the prior art and creatively adopted electromagnetic stirring frequency condition control to make LaB6 evenly distributed in the magnesium alloy matrix, thereby significantly refining the grains of the magnesium alloy and significantly improving the mechanical properties.

[0051] In one embodiment of the present application, a method for preparing a lanthanum hexaboride modified magnesium alloy is provided, comprising steps S10 to S60.

[0052] Step S10: providing a magnesium alloy substrate.

[0053] Step S20: Melting the magnesium alloy substrate to obtain a magnesium alloy melt.

[0054] Step S30: under low frequency conditions, the magnesium alloy melt and the modifier are mixed and melted in an electromagnetic stirring furnace to obtain a first melt; the modifier includes lanthanum hexaboride.

[0055] Step S40: Under low frequency conditions, the first melt is subjected to electromagnetic stirring treatment to obtain a second melt.

[0056] Step S50: Under medium frequency conditions, the second melt is subjected to a refining and degassing treatment to obtain a third melt.

[0057] Step S60: Under medium frequency conditions, the third melt is subjected to a heat preservation and static treatment to cast the lanthanum hexaboride modified magnesium alloy;

[0058] Among them, the frequency under the above low-frequency condition is 90~100 Hz, and the frequency under the above medium-frequency condition is 900Hz~1300Hz.

[0059] In the preparation method of the above-mentioned lanthanum hexaboride modified magnesium alloy, the magnesium alloy substrate is first melted in an electromagnetic stirring furnace, and then the magnesium alloy melt and the specific modifier are mixed and melted under low-frequency conditions, wherein the second phase particles generated in situ by the LaB6 modifier and other elements in the magnesium alloy are distributed at the grain boundaries, so that the grain size of the magnesium alloy is greatly reduced. This refined grain structure can significantly improve the strength and toughness of the magnesium alloy; then the first melt is subjected to electromagnetic stirring treatment under low-frequency conditions; then it is subjected to refining and degassing treatment under medium-frequency conditions, and then it is subjected to heat preservation and static treatment under medium-frequency conditions. Through the control of specific electromagnetic frequency conditions, it is ensured that LaB6 fully reacts with the magnesium alloy matrix and is evenly distributed. In this way, the grain refinement of the magnesium alloy structure can be obvious, the size of the second phase is smaller, and it has better mechanical properties.

[0060] In some of the embodiments, the components of the magnesium alloy substrate are, by mass percentage, Al: 7.5%~9.0%, Zn: 0.2%~0.8%, Mn: 0.15%~0.5%, Fe: <0.08%, Cu: <0.1%, Si<0.25%, and the balance is Mg.

[0061] It should be noted that the electromagnetic stirring furnace used above can be an electromagnetic stirring furnace commonly used in the art, such as an alloy electromagnetic stirring furnace equipment.

[0062] It mainly involves installing an electromagnetic stirrer at the bottom or side of the furnace. When the stirrer is working, a rotating magnetic field is generated. This magnetic field causes the liquid metal in the furnace to be affected by the Lorentz force. The magnitude and direction of the Lorentz force are related to factors such as the magnetic field strength and the direction of the current. Driven by this force, the liquid metal begins to move in a circular motion, thereby achieving the stirring effect. For example, in the magnesium alloy smelting process, electromagnetic stirring can make the alloy components more evenly distributed in the liquid metal.

[0063] It can be understood that the low and medium frequency conditions in the electromagnetic stirring furnace can be switched, and the melt stirring method in the three stirring treatments is controlled by the electromagnetic stirrer of the electromagnetic stirring furnace itself. The electromagnetic stirrer is generally composed of an iron core, a coil, etc., and needs to be reasonably arranged at the bottom or side of the furnace. Since the stirring force (Lorentz force) is proportional to the induced current, when the magnetic field strength and other conditions remain unchanged, the increase in frequency will increase the stirring force. For example, from low frequency to high frequency, if the magnetic field strength remains stable, the induced current in the liquid metal may increase exponentially, and the stirring force will also increase accordingly, making the stirring of the liquid metal more intense. In other words, the electromagnetic stirring treatment of the present application refers to the process conditions of the electromagnetic stirring furnace being controlled to cause the melt to flow and stir after it is melted, that is, stirring is not performed by external machinery.

[0064] In some of the embodiments, the melting power of the electromagnetic stirring furnace is 10 kW to 60 kW.

[0065] In some of the embodiments, based on the total mass of the magnesium alloy substrate and the modifier, the mass of the lanthanum hexaboride accounts for 0.3% to 1%.

[0066] In some embodiments, the average particle size of the lanthanum hexaboride is 2 μm-10 μm.

[0067] In some of the embodiments, the average grain size of the lanthanum hexaboride modified magnesium alloy is ≤140 μm.

[0068] In some of the embodiments, in step S20, before the step of melting the magnesium alloy substrate, the step further includes drying the magnesium alloy substrate to 200° C. to 300° C.

[0069] Furthermore, the drying is carried out in a blast drying oven at 200° C. to 300° C. for 1 h to 3 h.

[0070] In some embodiments, the gas in the electromagnetic stirring furnace is a protective gas, and the protective gas includes SF6.

[0071] It can be understood that the introduction of protective gas can prevent the magnesium alloy melt from being oxidized at high temperature.

[0072] In some embodiments, the flow rate of the protective gas is 2 L / min to 5 L / min.

[0073] In some embodiments, the temperature used when melting the magnesium alloy substrate in the step S20 is 730° C. to 760° C.

[0074] In some embodiments, the power of the above-mentioned melting process is 40 kW ~ 60 kW, and the frequency is 1100 Hz ~ 1300 Hz.

[0075] In some of the embodiments, in step S40, the electromagnetic stirring treatment includes a first stirring treatment, a second stirring treatment and a third stirring treatment that are performed alternately in sequence; wherein, during the first stirring treatment, the second stirring treatment and the third stirring treatment, the first melt circulates up and down in the electromagnetic stirring furnace, and the flow directions of the first melt are different.

[0076] Furthermore, by controlling the specific stirring direction during the electromagnetic stirring treatment, the uniform mixing of the magnesium alloy components and the modifier can be greatly promoted without destroying the oxide layer on the surface of the melt, thereby avoiding the secondary pollution problem introduced by external mechanical stirring.

[0077] In some of the embodiments, in step S40, when performing the first stirring treatment and the second stirring treatment, the power of the electromagnetic stirring furnace is 30kW~40kW, and the first melt is divided into two upper and lower flow parts, and each flow part includes two flow areas.

[0078] In some specific examples, such as Figure 1 As shown, during the above-mentioned first stirring treatment, the flow directions of the upper and lower flow parts of the first melt are opposite, and the flow directions of the two flow areas of the same flow part are opposite.

[0079] In some specific examples, such as Figure 2 As shown, during the second stirring treatment, the flow directions of the upper and lower flow parts of the first melt are the same, and the flow directions of the two flow areas of the same flow part are the same.

[0080] In some specific examples, in step S40, when performing the third stirring process, the power of the electromagnetic stirring furnace is 30 kW to 40 kW.

[0081] In some specific examples, such as Figure 3 As shown, when the third stirring treatment is performed, the flow direction of the first melt is: flowing downward from the side wall of the electromagnetic stirring furnace, then gathering toward the center, and then circulating upward.

[0082] In some embodiments, the electromagnetic stirring treatment lasts for 15 min to 30 min.

[0083] In some embodiments, the time of the first stirring process, the second stirring process and the third stirring process are independently 5 min to 8 min.

[0084] It can be understood that in the above step S40, performing the first stirring process, the second stirring process and the third stirring process alternately in sequence is one cycle of alternating stirring, and the number of cycles of stirring can be multiple times, such as two or three times.

[0085] In some of the embodiments, in step S40, the temperature of the induction stirring treatment is 730°C to 760°C.

[0086] In some embodiments, the power of the refining and degassing process is 30 kW to 50 kW, and the frequency is 1000 Hz to 1200 Hz.

[0087] In some of the embodiments, the steps of the refining and degassing treatment are as follows: introducing high-purity argon gas at a flow rate of 8L / min~12L / min for 3min~5min.

[0088] It can be understood that the purpose of introducing argon is to remove gas and non-metallic inclusions in the melt. During the degassing process, impurities in the middle of the melt will be blown to the surface to form slag or bottom slag, so slag removal is carried out to improve the purity and performance of the metal.

[0089] In some embodiments, the power of the above-mentioned thermal insulation treatment is 10 kW~30 kW, and the frequency is 900 Hz~1000 Hz.

[0090] In some embodiments, the heat preservation and static treatment time is 10 min to 20 min; the heat preservation and static treatment temperature is 740° C. to 750° C.

[0091] In some embodiments, under low frequency conditions, the step of mixing and melting the magnesium alloy melt and the modifier comprises the following steps:

[0092] Under low-frequency conditions, the magnesium alloy melt is subjected to a first stirring treatment, and then LaB6 is placed in a graphite bell jar and added to the magnesium alloy melt.

[0093] It can be understood that type I stirring of the melt before adding LaB6 can effectively stir the LaB6 powder into the bottom of the melt, allowing it to diffuse from the bottom, preventing the LaB6 powder from floating in the melt during the addition process and oxidizing and burning on the surface.

[0094] Furthermore, LaB6 powder was added and stirred for 3 min to 5 min.

[0095] It can be understood that stirring with a manual stirring spoon for 3 min to 5 min can make the reaction more complete and sufficient.

[0096] In some examples, in step S60 , the casting step is performed using a copper mold.

[0097] In some embodiments, the temperature of the casting process is 740°C-750°C.

[0098] Specifically, during the casting process, the third melt is discharged from the side discharge port of the electromagnetic stirring furnace after being allowed to stand, enters the copper mold for casting, and obtains the magnesium alloy after cooling.

[0099] In some embodiments, the surfaces of the test tools such as the mold and the stirring spoon have a coating layer, and the coating layer includes boron nitride.

[0100] It can be understood that boron nitride coating is an inert inorganic high-temperature lubricating material that does not adhere to or wet molten metal. It can completely protect the surface of refractory materials or ceramic vessels that are in direct contact with molten aluminum, magnesium, zinc alloys and slag, greatly extending the service life of such vessels.

[0101] In one embodiment of the present application, a lanthanum hexaboride-modified magnesium alloy is further provided. The lanthanum hexaboride-modified magnesium alloy is prepared by the above-mentioned preparation method of the lanthanum hexaboride-modified magnesium alloy.

[0102] The lanthanum hexaboride modified magnesium alloy prepared by the preparation method of the lanthanum hexaboride modified magnesium alloy has obvious grain refinement, a smaller second phase size, and better mechanical properties.

[0103] The present application will be described below in conjunction with specific embodiments, but the present application is not limited to the following embodiments. It should be understood that the attached claims summarize the scope of the present application. Under the guidance of the concept of the present application, technical personnel in the field should realize that certain changes made to the various embodiments of the present application will be covered by the spirit and scope of the claims of the present application.

[0104] The present application is further described below in conjunction with the accompanying drawings and embodiments, but the protection content of the present application is not limited to the scope described in the embodiments.

[0105] Example 1

[0106] (1) According to the alloy composition ZM5 (specifically Al: 8.3%, Zn: 0.5%, Mn: 0.35%, magnesium: balance) + LaB6, the mass of LaB6 modifier is 0.5wt% of the mass of the alloy melt, the average particle size of LaB6 powder is 2μm, and its SEM microstructure is shown in Figure 4. Put the weighed raw materials ZM5 ingot and LaB6 powder into a blast drying oven and dry them at 250℃ for 2 hours; wrap the dried LaB6 powder with aluminum foil, brush a layer of boron nitride coating on the surface of the mold and stirring spoon and other test tools, and dry them for use.

[0107] (2) The dried ZM5 was broken into small pieces, added to a graphite crucible for melting, and smelted in an electromagnetic stirring furnace under the protection of SF6 gas at a gas flow rate of 3 L / min. The heating mode was turned on, the power was 50 kW, the frequency was set at 1200 Hz, the temperature was heated to 730°C, and then the temperature was kept to completely melt the ZM5 to obtain a magnesium alloy melt.

[0108] (3) The magnesium alloy melt was cooled to 680°C and then switched to the stirring mode with a power of 35 kW and a frequency of 95 Hz. The mixed melting treatment of the modifier was carried out in the same stirring method as the first stirring treatment. The specific steps of the mixed melting treatment were as follows: the magnesium alloy melt was first stirred before adding LaB6. LaB6 with a mass of 0.5% of the mass of the raw material was wrapped with aluminum foil, placed in a graphite bell jar, added to the magnesium alloy melt for the first stirring treatment for 3 minutes, and assisted by manual stirring for 3 minutes to obtain the first melt.

[0109] (4) Close the furnace cover and perform the first stirring treatment, the second stirring treatment and the third stirring treatment alternately under low frequency conditions. The stirring treatment time for each stirring treatment is 6 minutes. The alternating stirring treatment time is 18 minutes. The stirring process temperature is controlled at 680°C. During the first stirring treatment, the flow directions of the upper and lower flow parts of the first melt are opposite. The power of the electromagnetic stirring furnace is 35 kW and the frequency of the low frequency is 95 Hz. During the second stirring treatment, the flow directions of the upper and lower flow parts of the first melt are the same. The power of the electromagnetic stirring furnace is 35 kW and the frequency is 95 Hz. During the third stirring treatment, the flow direction of the first melt is: converging from the side wall of the electromagnetic stirring furnace to the center. The power of the electromagnetic stirring furnace is 35 kW and the frequency is 95 Hz. The second melt is obtained. For the flow directions of the melt during the first stirring treatment, the second stirring treatment and the third stirring treatment, please refer to the attached Figure 1~Figure 3 .

[0110] (5) After stirring is completed, the electromagnetic stirring is turned off and the heating mode is turned on. Under medium frequency conditions (power of 40 kW and frequency of 1100 Hz), the temperature is raised to 740°C for high argon refining and degassing for 3 min. The argon flow rate is 10 L / min. After degassing and purification, the slag on the surface of the melt and the bottom slag are removed to obtain the third melt.

[0111] (6) The third melt was allowed to stand at 740°C for 15 min, with a power of 20 kW and a frequency of 950 Hz, and then cast into a cylindrical copper mold and cooled at room temperature. Figure 8 , the average grain size is shown in Table 1, and the hardness value is shown in Table 2.

[0112] Example 2

[0113] Example 2 is basically the same as Example 1, except that the average particle size of the modifier LaB6 powder is 5 μm.

[0114] The remaining steps are the same as those in Example 1.

[0115] Example 3

[0116] Example 3 is basically the same as Example 1, except that the average particle size of the modifier LaB6 powder is 10 μm.

[0117] The remaining steps are the same as those in Example 1.

[0118] Example 4

[0119] Example 4 is basically the same as Example 1, except that the mass of LaB6 modifier is 0.3wt% of the mass of the alloy melt, and the average particle size of LaB6 powder is 5μm.

[0120] The remaining steps are the same as those in Example 1.

[0121] Example 5

[0122] Example 5 is basically the same as Example 1, except that the mass of LaB6 modifier is 0.8wt% of the mass of the alloy melt.

[0123] The remaining steps are the same as those in Example 1.

[0124] Example 6

[0125] Example 6 is basically the same as Example 1, except that the mass of LaB6 modifier is 1wt% of the mass of the alloy melt, and the average particle size of LaB6 powder is 5μm.

[0126] The remaining steps are the same as those in Example 1.

[0127] Comparative Example 1

[0128] Comparative Example 1 is substantially the same as Example 1, except that no LaB6 modifier is added in Comparative Example 1.

[0129] The specific steps are:

[0130] According to the alloy composition Al: 8.3%, Zn: 0.5%, Mn: 0.35%, magnesium: balance. Mg-8.3Al-0.5Zn-0.35Mn ingredients, use a semi-continuous casting machine to melt under the protection of SF6+CO2 mixed gas, add Mg ingots, heat to 730℃, and add aluminum ingots, aluminum-manganese alloy, and zinc ingots in sequence after the magnesium ingots are melted. After all the ingots are melted, use high argon to refine and degas twice, each time for 10 minutes, with an argon gas flow rate of 15L / min gas. After refining and degassing, remove the slag and bottom slag on the surface of the melt. The refined melt is cooled to 710℃. After the composition is qualified, it is transferred to the homogenization furnace, then left to cool, and cast into the mold when the temperature drops to 670℃, and cooled at room temperature.

[0131] After the composition is qualified, it is transferred to the homogenization furnace, then left to cool, and cast into the mold when the temperature drops to 670℃, and cooled at room temperature. Figure 7 , the average grain size is shown in Table 1, and the hardness value is shown in Table 2.

[0132] Comparative Example 2

[0133] Comparative Example 2 is basically the same as Example 1, except that: in Comparative Example 1, electromagnetic stirring is not performed, and conventional mechanical stirring is used. The specific steps are:

[0134] According to the alloy composition ZM5 + 0.5wt.% LaB6, the average particle size of LaB6 powder is 5μm, and its SEM microstructure is shown in Figure 5. ZM5 is broken into small pieces, added into a graphite crucible for melting, and smelted in a resistance furnace under the protection of SF6 gas with a gas flow rate of 3 L / min. Heat to 730℃. After the ZM5 raw material is melted, the temperature is lowered to 680℃, and then LaB6 is added. LaB6 is wrapped with aluminum foil, placed in a graphite bell jar, and manually stirred for 3 minutes. After completion, the temperature is raised to 740℃ for high argon refining and degassing for 3 minutes. The argon flow rate is 10L / min. After degassing and purification, the slag and bottom slag on the surface of the melt are removed. Let stand at 740℃ for 15 minutes, then cast into a cylindrical copper mold and cool at room temperature. The metallographic structure of the cast alloy is as follows Fig. 9 , the average grain size is shown in Table 1, and the hardness value is shown in Table 2.

[0135] Performance Test:

[0136] 1. The magnesium alloys prepared in each embodiment and comparative example were observed under an electron microscope.

[0137] 2. The grain size of the magnesium alloy obtained in each embodiment and comparative example was tested, and was calculated according to the intercept method in standard GB / T6394-2017;

[0138] 3. The hardness of the magnesium alloys prepared in the embodiments and comparative examples was tested, and the Vickers hardness was tested in accordance with GB / T 4340.1-2009. The specific results are shown in Tables 1 and 2.

[0139] Table 1

[0140]

[0141] Table 2

[0142]

[0143] Figure 4 This is the SEM image of lanthanum hexaboride with an average particle size of 2 μm in Example 1. Figure 5 This is the SEM image of lanthanum hexaboride with an average particle size of 5 μm in Example 2. Figure 6 This is the SEM image of lanthanum hexaboride with an average particle size of 10 μm in Example 3. Combined with the data in Tables 1 and 2, it can be seen that: relative to the preparation method of the magnesium alloy in the comparative example, the magnesium alloy prepared by the preparation method of the magnesium alloy of the present application has obvious grain refinement, a smaller second phase size, and better mechanical properties.

[0144] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0145] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent application shall be subject to the attached claims.

Claims

1. A method for preparing a lanthanum hexaboride modified magnesium alloy, characterized in that: The steps include: Provide magnesium alloy substrate; Melting the magnesium alloy substrate to obtain a magnesium alloy melt; Under low frequency conditions, the magnesium alloy melt and the modifier are mixed and melted in an electromagnetic stirring furnace to obtain a first melt; the modifier includes lanthanum hexaboride; Under low frequency conditions, subjecting the first melt to electromagnetic stirring to obtain a second melt; Under medium frequency conditions, the second melt is subjected to a refining and degassing treatment to obtain a third melt; Under medium frequency conditions, the third melt is subjected to heat preservation and static treatment, and cast to obtain the lanthanum hexaboride modified magnesium alloy; Among them, the frequency under the low-frequency condition is 90 Hz~100 Hz, and the frequency under the medium-frequency condition is 900 Hz~1300 Hz.

2. The method for preparing a lanthanum hexaboride modified magnesium alloy according to claim 1, characterized in that: Based on the total mass of the magnesium alloy substrate and the modifier, the mass proportion of the lanthanum hexaboride is 0.3% to 1%.

3. The method for preparing a lanthanum hexaboride modified magnesium alloy according to claim 1, characterized in that: The average particle size of the lanthanum hexaboride is 2 μm to 10 μm.

4. The method for preparing a lanthanum hexaboride modified magnesium alloy according to claim 1, characterized in that: The average grain size of the lanthanum hexaboride modified magnesium alloy is ≤140 μm.

5. The method for preparing a lanthanum hexaboride modified magnesium alloy according to any one of claims 1 to 4, characterized in that: The electromagnetic stirring treatment includes a first stirring treatment, a second stirring treatment and a third stirring treatment which are performed alternately in sequence; wherein, during the first stirring treatment, the second stirring treatment and the third stirring treatment, the first melt circulates up and down in the electromagnetic stirring furnace, and the flow directions of the first melt are different.

6. The method for preparing a magnesium alloy modified by lanthanum hexaboride according to claim 5, characterized in that: The electromagnetic stirring process satisfies at least one of the following characteristics: (1) When performing the first stirring treatment and the second stirring treatment, the power of the electromagnetic stirring furnace is 30 kW to 40 kW, the first melt is divided into two upper and lower flow parts, each flow part includes two flow areas; during the first stirring treatment, the flow directions of the upper and lower flow parts of the first melt are opposite, and the flow directions of the two flow areas of the same flow part are opposite; during the second stirring treatment, the flow directions of the upper and lower flow parts of the first melt are the same, and the flow directions of the two flow areas of the same flow part are the same; (2) When performing the third stirring treatment, the power of the electromagnetic stirring furnace is 30 kW to 40 kW; the flow direction of the first melt is: flowing downward from the side wall of the electromagnetic stirring furnace, then gathering toward the center, and then circulating upward.

7. The method for preparing a magnesium alloy modified by lanthanum hexaboride according to claim 5, characterized in that: The electromagnetic stirring process satisfies at least one of the following characteristics: (1) The electromagnetic stirring treatment time is 15min~30min; (2) The duration of the first stirring treatment, the second stirring treatment and the third stirring treatment is independently 5 min to 8 min.

8. The method for preparing a lanthanum hexaboride modified magnesium alloy according to any one of claims 1 to 4 and 6 to 7, characterized in that: The components of the magnesium alloy substrate are, by mass percentage, Al: 7.5% to 9.0%, Zn: 0.2% to 0.8%, Mn: 0.15% to 0.5%, Fe: <0.08%, Cu: <0.1%, Si <0.25%, and the balance is Mg; And / or, the gas in the electromagnetic stirring furnace is a protective gas, and the protective gas includes SF6; And / or, the refining and degassing treatment comprises the following steps: introducing high-purity argon gas at a flow rate of 8 L / min to 12 L / min into the second melt for 3 min to 5 min; And / or, the time of the heat preservation and static treatment is 10 min to 20 min, and the temperature of the heat preservation and static treatment is 740° C. to 750° C.

9. The method for preparing a lanthanum hexaboride modified magnesium alloy according to any one of claims 1 to 4 and 6 to 7, characterized in that: Before melting the magnesium alloy substrate, the method further includes drying the magnesium alloy substrate to 200° C. to 300° C.; And / or, under low frequency conditions, the step of mixing and melting the magnesium alloy melt and the modifier comprises the following steps: Under low-frequency conditions, the magnesium alloy melt is subjected to a first stirring treatment, and then LaB6 is placed in a graphite bell jar and added to the magnesium alloy melt.

10. A lanthanum hexaboride modified magnesium alloy, characterized in that: The lanthanum hexaboride-modified magnesium alloy is prepared by the preparation method of the lanthanum hexaboride-modified magnesium alloy according to any one of claims 1 to 9.

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