Beta-based magnesium-lithium alloy and preparation method thereof

Abstract

The invention provides a preparation method of a beta-based magnesium-lithium alloy. The preparation method comprises the following steps: smelting required raw materials to obtain a magnesium-lithium alloy ingot; rolling the cast ingot for multiple times under required conditions after heat preservation, and putting the alloy into a box-type furnace for heat preservation after each pass of rolling; and finally, after rolling for the last pass, the alloy is kept straight through two passes, then the alloy is immediately put into cold water to be quenched, and a microstructure formed in the alloy rolling process is reserved. The alloying and hot rolling deformation method is used, so that the strength of the beta-based magnesium-lithium alloy can be greatly improved on the premise of low density, and the method is simple, convenient, feasible and easy to operate, and can greatly simplify the production process, improve the efficiency and reduce the production cost.

Description

Technical Field

[0001] The present invention relates to the technical field of magnesium-lithium alloys, and more particularly to a β-based magnesium-lithium alloy and a preparation method thereof. Background Art

[0002] With the development of industry, more and more resources are becoming increasingly scarce. In order to save energy and make full use of natural resources, it is particularly important to develop and utilize high-performance lightweight materials. Magnesium alloys have great application potential due to their low density and excellent properties. However, since magnesium has a close-packed hexagonal (hcp) structure with few slip systems and poor machining performance, its widespread application is limited.

[0003] Researchers have found that adding lithium (with a density of 0.534 g / cm 3 ) to magnesium to form a magnesium-lithium alloy not only reduces the critical shear stress and c / a axis ratio of the magnesium crystal, increases the slip system, but also improves the ductility, making it have good machinability. The density of the magnesium-lithium alloy is 1.35 - 1.65 g / cm 3 , only 1 / 2 of that of aluminum alloy and 3 / 4 of that of traditional magnesium alloys, and is called an ultra-light alloy. Magnesium-lithium alloys have the advantages of lightweight, high specific strength and specific stiffness, good electromagnetic shielding performance and damping characteristics, and excellent machining performance, etc., and have broad potential uses in the fields of military, aerospace, 3C products, medical devices, etc.

[0004] However, according to the magnesium-lithium alloy binary phase diagram, when the Li addition amount is greater than 10.3 wt%, the magnesium-lithium alloy becomes a single-phase body-centered cubic (bcc) structure, which is the lightest low-density metal structural material at present. However, due to the high Li content, its absolute strength is very low, which limits its application in the engineering field. Therefore, it is particularly urgent and important to develop methods and processes that can effectively improve its strength.

[0005] On the basis of a high Li content, enhancing the strength of magnesium-lithium alloys and optimizing their mechanical properties can achieve a good combination of ultra-low density and high strength. At present, for the shortcoming of low strength, the main improvement methods are alloying, fine grain strengthening, strain strengthening, solid solution strengthening, and composite strengthening. Alloying is to add alloying elements to the matrix alloy, and improve the strength through strengthening mechanisms such as solid solution strengthening, fine grain strengthening, and precipitation strengthening, so as to achieve the effect of improving mechanical properties; the mechanism of strain strengthening to increase strength is as follows: (1) It not only eliminates the defects of the casting structure, improves the density of the alloy, but also increases the dislocation density, making the dislocations tangle during movement, hindering their movement, thus increasing the strength; (2) During hot processing, dynamic recrystallization is likely to occur in the matrix, achieving the effect of refining grains, increasing the number of grain boundaries, and hindering the movement of dislocations, achieving the effect of increasing strength; (3) During the processing, the coarsely precipitated phases may be broken into fine particles and evenly distributed in the matrix or at the grain boundaries, playing a role in hindering the movement of dislocations and grain growth, significantly improving the microstructure of the matrix, and playing a role in increasing strength. Based on the above principles, alloying and plastic deformation processing play a great role in increasing the strength of alloys.

[0006] At present, there are many studies on comprehensively improving the strength of β-based (BCC structure) magnesium-lithium alloys through alloying and rolling deformation. For example, Jiao Yunlei et al. homogenized the alloyed Mg-14Li-3Al-1Y-0.8Zr-0.4Sc alloy at 200 °C for 10 h, then hot-rolled it at 200 °C with a total reduction of 60%, and finally obtained a magnesium-lithium alloy with a tensile strength of 235 MPa; Tang et al. homogenized the alloyed Mg-11Li-3Al-2Zn-0.2Y alloy at (250 - 300 °C) for 10 h, then hot-rolled it at 170 °C, 230 °C, and 290 °C respectively with a total reduction of 80%, annealed it at 200 - 300 °C for 24 h after rolling, then quenched it in cold water, and the tensile strength reached the maximum value of 235 MPa when hot-rolled at 230 °C; Guo et al. multi-directionally rolled the alloyed Mg-16Li-4Zn-1Er alloy at 200 °C and -196 °C respectively with a total reduction of 60%. The tensile strength was 235 MPa when multi-directionally hot-rolled at 200 °C, while the compressive strength reached the maximum value of 331 MPa when multi-directionally cold-rolled at -196 °C. Chinese Patent with Publication No. CN114231809A discloses a high-strength and high-thermal-stability ultra-light magnesium-lithium alloy and its preparation method. The mass percentage of its components is: Li: 11 - 18%, Al: 1 - 7%, Ag: 0.5 - 6%, and the rest is Mg. It is homogenized at (300 - 400 °C) for 4 h, then hot-rolled at 300 - 350 °C, followed by solution treatment at 300 - 350 °C, then deep cold rolling, then aged at 50 - 180 °C for 1 - 4 h, and finally cold-rolled at room temperature to obtain a high-strength and high-thermal-stability ultra-light magnesium-lithium alloy.

[0007] The above methods of improving mechanical properties through alloying and rolling deformation obviously have deficiencies such as high density (adding alloying elements with high density), complex technological process, long operation time, and high production cost. And simply adding alloying elements with low density by simple treatment methods makes it difficult for the increased strength to exceed about 240 MPa, which greatly limits its wide application.

[0008] Therefore, it is particularly important to develop a method with relatively simple process and significant strength improvement for obtaining low-density and high-strength β-based (BCC structure) magnesium-lithium alloys. Summary of the Invention

[0009] The purpose of the present invention is to provide a β-based magnesium-lithium alloy and its preparation method in view of the deficiencies of the prior art. On the basis of composition design, the microstructure is comprehensively improved through alloying and hot-rolling deformation, the strength of the alloy is significantly increased, and then an ultra-light and high-strength β-based (BCC structure) magnesium-lithium alloy is obtained.

[0010] According to the first aspect of the object of the present invention, a method for preparing a β-based magnesium-lithium alloy is provided, comprising the following steps:

[0011] S1. Weigh industrial pure magnesium, commercial AZ31 ingots, aluminum ingots, zinc ingots, pure lithium and Al-5Ti-1.2C master alloy respectively according to the chemical composition ratio; wherein, the chemical composition includes by mass percentage: Li: 11% - 12%, Al: 2.5% - 3%, Zn: 0.5% - 1%, Al-5Ti-1.2C: 0% - 1%, the balance is magnesium and impurities, and the total amount of each component is 100%;

[0012] Then first melt the industrial pure magnesium and commercial AZ31 ingots, add aluminum ingots and zinc ingots, after melting, add pure lithium for heat preservation, add Al-5Ti-1.2C master alloy for heat preservation before casting, and quickly cast the obtained alloy liquid into a mold to obtain a magnesium-lithium alloy ingot;

[0013] S2. Cut the magnesium-lithium alloy ingot obtained in step S1 into required sizes and then perform heat preservation treatment to obtain a first magnesium-lithium alloy block;

[0014] S3. Perform multi-pass rolling on the first magnesium-lithium alloy block obtained in step S2 under required rolling conditions until the total rolling deformation reaches 60% - 70% to obtain a second magnesium-lithium alloy block; wherein, after each pass of rolling, heat preservation treatment is performed on the alloy after this pass of rolling to maintain the rolling temperature;

[0015] S4. Treat the second magnesium-lithium alloy block obtained in step S3 to keep it flat, and then perform quenching to retain the microstructure formed during the alloy rolling process to obtain a β-based magnesium-lithium alloy.

[0016] As an optional implementation manner, the mass percentage of Al-5Ti-1.2C is 0.5% - 1%.

[0017] As an optional implementation manner, in step S2, the conditions of the heat preservation treatment are: heat preservation for 10 min - 15 min at a temperature of 350°C ± 10°C.

[0018] As an optional implementation manner, in step S3, a unidirectional rolling method is used for rolling.

[0019] As an optional implementation manner, in step S3, the rolling conditions are: rolling speed ≤ 6 r / min, rolling temperature ≥ 340°C.

[0020] As an optional implementation manner, in step S3, the thickness of the alloy block is reduced by 0.5 mm - 1 mm after each pass of rolling.

[0021] As an alternative embodiment, in the step S3, the conditions for heat preservation of the alloy after each pass of rolling are: heat preservation at a temperature of 350°C ± 10°C for 10 min to 15 min.

[0022] As an alternative embodiment, in the step S4, the second magnesium-lithium alloy block kept flat is quenched in cold water at a temperature of 20°C to 25°C.

[0023] As an alternative embodiment, in the step S1, a protective gas is passed through the furnace during melting, and the protective gas is SF6 + N2, and the volume ratio of SF6 to N2 is 1:200.

[0024] According to the second aspect of the object of the present invention, a β-based magnesium-lithium alloy prepared by the foregoing method is provided.

[0025] As can be seen from the above technical solutions of the present invention, the preparation method of the β-based magnesium-lithium alloy proposed by the present invention, through composition design, on the premise of a β-based (BCC structure) magnesium-lithium alloy, improves the mechanical properties of the alloy by means of hot rolling at a higher temperature and a lower deformation rate, so as to further improve the strength of the alloy on the premise of ensuring low density.

[0026] For the β-based magnesium-lithium alloy of the present invention, especially when adding 1% of the Al-5Ti-1.2C master alloy, by simultaneously adding Al, Zn and Al-5Ti-1.2C elements as alloying elements, the strengthening of the Al element on the magnesium-lithium alloy is mainly solid solution strengthening and precipitation strengthening, and the Zn element has less plastic damage to the Mg-Li alloy and mainly plays a role of solid solution strengthening in the alloy. The Al-5Ti-1.2C master alloy plays a role of fine grain strengthening on the β-based magnesium-lithium alloy; by simultaneously adding Al, Zn and Al-5Ti-1.2C elements as alloying elements, the advantages of Al, Zn and Al-5Ti-1.2C elements are fully exerted, and the negative effects brought by excessive single alloying elements are avoided; in addition, the grains refined by the alloying elements have more grain boundaries, providing more nucleation sites for recrystallization during hot rolling, increasing the number of recrystallizations, hindering the movement of dislocations, and thus effectively improving the mechanical properties of the β-based magnesium-lithium alloy on the basis of maintaining low density.

[0027] The method of the present invention is simple, feasible and easy to operate, which can greatly simplify the production process, improve the efficiency and reduce the production cost. Description of the Drawings

[0028] Figure 1It is the metallographic structure diagram of the β-based magnesium-lithium alloy in the examples of the present invention; among them, a and b are as-cast 0 and sample 0 in Example 3 respectively; c and d are as-cast 0.5 and sample 0.5 in Example 1 respectively; e and f are as-cast 1 and sample 1 in Example 2 respectively; g and h are as-cast 1.5 and sample 1.5 in Comparative Example 1 respectively.

[0029] Figure 2 It is the scanning electron microscope image of the β-based magnesium-lithium alloy in the examples of the present invention; among them, a and b are as-cast 0 and sample 0 in Example 3 respectively; c and d are as-cast 0.5 and sample 0.5 in Example 1 respectively; e and f are as-cast 1 and sample 1 in Example 2 respectively; g and h are as-cast 1.5 and sample 1.5 in Comparative Example 1 respectively.

[0030] Figure 3 It is the scanning electron microscope image and EDS analysis diagram of the β-based magnesium-lithium alloy of sample 1 in Example 2 of the present invention; among them, a is the SEM image of sample 1; b is the surface scan image of Mg; c is the surface scan image of Al; d is the surface scan image of Zn; e is the surface scan image of Ti; f is the surface scan image of C.

[0031] Figure 4 It is the tensile stress-strain curve diagram of the as-cast β-based magnesium-lithium alloy in the examples of the present invention.

[0032] Figure 5 It is the tensile stress-strain curve diagram of the final β-based magnesium-lithium alloy in the examples of the present invention. Detailed implementation manners

[0033] In order to better understand the technical content of the present invention, specific embodiments are hereby given and described in conjunction with the accompanying drawings as follows.

[0034] In the present disclosure, aspects of the present invention are described with reference to the accompanying drawings, in which many illustrative embodiments are shown. The embodiments of the present disclosure are not necessarily intended to cover all aspects of the present invention. It should be understood that the various concepts and embodiments introduced above, as well as those concepts and embodiments described in more detail below, can be implemented in any of many ways.

[0035] In the existing technology, the rare earth elements added to the β-based magnesium-lithium alloy often have a relatively high density, which is not conducive to the ultra-light performance. Moreover, the plastic deformation process for the β-based magnesium-lithium alloy is often complex, with a long process time, and simple treatment methods result in an insignificant strengthening effect.

[0036] Therefore, the present invention provides a preparation method for a β-based magnesium-lithium alloy. On the basis of a high lithium content, through alloying and then combining with a hot rolling deformation method, a hot rolling method with a relatively high temperature and a relatively low deformation rate is adopted, so that the β-based magnesium-lithium alloy significantly improves the tensile strength while maintaining a low density.

[0037] In an exemplary embodiment of the present invention, a method for preparing a β-based magnesium-lithium alloy is provided, comprising the following steps:

[0038] S1. Weigh industrial pure magnesium, commercial AZ31 ingot, aluminum ingot, zinc ingot, pure lithium, and Al-5Ti-1.2C master alloy respectively according to the chemical composition ratio; wherein, the chemical composition by mass percentage includes: Li: 11% - 12%, Al: 2.5% - 3%, Zn: 0.5% - 1%, Al-5Ti-1.2C: 0% - 1%, and the balance is magnesium and impurities, and the total amount of each component is 100%;

[0039] Then, first melt the industrial pure magnesium and commercial AZ31 ingot, add the aluminum ingot and zinc ingot, add pure lithium for heat preservation after melting, add the Al-5Ti-1.2C master alloy for heat preservation before casting, and quickly cast the obtained alloy liquid into a mold to obtain a magnesium-lithium alloy ingot;

[0040] S2. Cut the magnesium-lithium alloy ingot obtained in step S1 into required sizes and then perform heat preservation treatment to obtain a first magnesium-lithium alloy block;

[0041] S3. Perform multi-pass rolling on the first magnesium-lithium alloy block obtained in step S2 under required rolling conditions until the total rolling deformation amount reaches 60% - 70% to obtain a second magnesium-lithium alloy block; wherein, after each pass of rolling, heat preservation treatment is performed on the alloy after this pass of rolling to maintain the rolling temperature;

[0042] S4. Treat the second magnesium-lithium alloy block obtained in step S3 to keep it flat, and then perform quenching to retain the microstructure formed during the alloy rolling process to obtain a β-based magnesium-lithium alloy.

[0043] As an optional implementation manner, the mass percentage of Al-5Ti-1.2C is 0.5% - 1%, and particularly preferably 1%. At this time, alloying is carried out by adding the Al-5Ti-1.2C master alloy and the hot rolling method at a higher temperature and a lower deformation rate is used to improve the mechanical properties of the alloy, and the tensile strength of the alloy can be as high as over 290 MPa.

[0044] It can be understood that Al-5Ti-1.2C is a master alloy, and the mass ratio of Al, Ti, and C in the alloy is 1:5:1.2, which can be directly purchased.

[0045] As an optional implementation manner, in step S2, the conditions for heat preservation treatment are: heat preservation for 10 min - 15 min at a temperature of 350°C ± 10°C.

[0046] As an optional implementation manner, in step S3, the unidirectional rolling method is used for rolling.

[0047] As an alternative embodiment, in step S3, the rolling conditions are: rolling speed ≤ 6 r / min, rolling temperature ≥ 340 °C.

[0048] In one preferred embodiment, the roll speed is 5 - 6 r / min, particularly preferably 5 r / min; the rolling temperature is 350 °C ± 10 °C.

[0049] As an alternative embodiment, in step S3, the thickness of the alloy block is reduced by 0.5 mm - 1 mm after each pass of rolling, particularly preferably by 1 mm.

[0050] As an alternative embodiment, in step S3, the conditions for heat preservation of the alloy after each pass of rolling are: heat preservation at 350 °C ± 10 °C for 10 min - 15 min.

[0051] As an alternative embodiment, in step S4, the second magnesium-lithium alloy block kept flat is quenched in cold water at a temperature of 20 °C - 25 °C.

[0052] As an alternative embodiment, in step S1, a protective gas is passed through the furnace during the melting process, the protective gas is SF6 + N2, and the volume ratio of SF6 to N2 is 1:200.

[0053] On the basis of the composition design, by means of alloying and then combining hot rolling deformation, during the hot rolling process at high temperature and low deformation rate, dynamic recrystallization occurs in the β-based magnesium-lithium alloy, the grains are significantly refined, the number of grain boundaries inside the alloy increases significantly, and a large number of grain boundaries will hinder the movement of dislocations during plastic deformation; at the same time, during the rolling process, the precipitated AlLi phase and MgLiAl2 phase hinder the movement of dislocations, thereby comprehensively improving the strength of the β-based magnesium-lithium alloy.

[0054] In another exemplary embodiment of the present invention, there is also provided a β-based magnesium-lithium alloy prepared by the aforementioned method. This magnesium-lithium alloy has low density and high strength and is a super-light and high-strength β-based magnesium-lithium alloy; among them, the low density means that the density is less than 1.5 g / cm 3 ; the high strength means that the strength is higher than 250 MPa.

[0055] As an alternative embodiment, the density of the β-based magnesium-lithium alloy is 1.42 - 1.48 g / cm 3 , the tensile strength is 280 - 300 MPa, and the elongation is 28 - 35%.

[0056] The present invention will be further described in detail below with reference to specific embodiments.

[0057] In the following embodiments, unless otherwise specified, all are conventional methods.

[0058] The materials, reagents, etc. used in the following examples can be obtained from commercial sources without special instructions.

[0059] Example 1

[0060] According to the proportion of each chemical component in the β-phase (BCC structure) magnesium-lithium alloy (by mass percentage, the chemical components in the magnesium-lithium alloy are: Li: 12%, Al: 3%, Zn: 1%, and the balance is magnesium and impurities, and the total amount of each component is 100%), industrial pure magnesium, commercial AZ31 ingots, aluminum ingots, zinc ingots and pure lithium alloy were weighed respectively. First, the industrial pure magnesium and commercial AZ31 ingots were heated and melted, then the aluminum ingots and zinc ingots were added. After melting, pure lithium was added, and it was kept warm for 10 min. Then the alloy melt was quickly cast into a cylindrical mold to obtain a magnesium-lithium alloy ingot with a diameter of 41 mm and a height of 57 mm (denoted as as-cast 0).

[0061] The magnesium-lithium alloy ingot was wire-cut to obtain a block sample with a length × width × height of 30 mm × 25 mm × 6.5 mm; the block sample was placed in a box furnace and kept warm at 350 °C for 15 min.

[0062] The heat-treated magnesium-lithium alloy block sample was quickly clamped with a fixture and transferred to a two-high rolling mill for rolling. During rolling, the roll speed was 5 r / min, and the thickness was reduced by 0.5 mm per pass. The alloy was rolled by a unidirectional rolling method (that is, the rolling direction of the alloy was kept the same as the first rolling direction each time). After each pass of rolling, the rolled alloy was put into a box furnace and kept warm at 350 °C for 15 min. The total rolling deformation of the alloy after rolling deformation was 60%.

[0063] After the last pass of rolling, it was kept flat for two more passes, and then the magnesium-lithium alloy was quenched in 25 °C cold water to retain the microstructure formed during the rolling process of the alloy (denoted as sample 0).

[0064] Example 2

[0065] According to the proportion of each chemical component in the β-phase (BCC structure) magnesium-lithium alloy (by mass percentage, the chemical components in the magnesium-lithium alloy are: Li: 12%, Al: 3%, Zn: 1%, Al-5Ti-1.2C: 0.5%, and the balance is magnesium and impurities, and the total amount of each component is 100%), industrial pure magnesium, commercial AZ31 ingots, zinc ingots, pure lithium and Al-5Ti-1.2C master alloy were weighed respectively. First, the industrial pure magnesium and commercial AZ31 ingots were heated and melted, then the zinc ingots were added. After melting, pure lithium was added, and it was kept warm for 10 min. Before casting, the Al-5Ti-1.2C master alloy was added and kept warm for 3 min. Then the alloy melt was quickly cast into a cylindrical mold to obtain a magnesium-lithium alloy ingot with a diameter of 41 mm and a height of 57 mm (denoted as as-cast 0.5).

[0066] Wire cut the magnesium-lithium alloy ingot to obtain a block sample with a length×width×height of 30 mm×25 mm×6.5 mm; place the block sample in a box furnace and keep it at 350 °C for 15 min.

[0067] Clamp the heat-treated magnesium-lithium alloy block sample with a fixture and quickly transfer it to a two-high rolling mill for rolling. When rolling, the roll speed is 5 r / min, and it is reduced by 0.5 mm after each pass. The alloy is rolled using a one-way rolling method (that is, keeping the rolling direction of the alloy the same as the first rolling direction each time). After each pass of rolling, the rolled alloy is placed in a box furnace and kept at 350 °C for 15 min. The total rolling deformation of the alloy after rolling deformation is 60%.

[0068] After the last pass of rolling, make it straight through two more passes, and then quench the magnesium-lithium alloy in 25 °C cold water to retain the microstructure formed during the rolling process of the alloy (denoted as sample 0.5).

[0069] Example 3

[0070] According to the ratio of each chemical component in the β-phase (BCC structure) magnesium-lithium alloy (by mass percentage, each chemical component in the magnesium-lithium alloy is: Li: 12%, Al: 3%, Zn: 1%, Al-5Ti-1.2C: 1%, and the balance is magnesium and impurities, and the total amount of each component is 100%), weigh industrial pure magnesium, commercial AZ31 ingot, zinc ingot, pure lithium, and Al-5Ti-1.2C master alloy respectively. First, heat and melt the industrial pure magnesium and commercial AZ31 ingot, then add the zinc ingot. After melting, add pure lithium and keep it warm for 10 min. Before casting, add the Al-5Ti-1.2C master alloy and keep it warm for 3 min. Pour the alloy melt quickly into a cylindrical mold to obtain a magnesium-lithium alloy ingot with a diameter of 41 mm and a height of 57 mm (denoted as as-cast 1).

[0071] Wire cut the magnesium-lithium alloy ingot to obtain a block sample with a length×width×height of 30 mm×25 mm×6.5 mm; place the block sample in a box furnace and keep it at 350 °C for 15 min; clamp the heat-treated magnesium-lithium alloy block sample with a fixture and quickly transfer it to a two-high rolling mill for rolling. When rolling, the roll speed is 5 r / min, and it is reduced by 0.5 mm after each pass. The alloy is rolled using a one-way rolling method (that is, keeping the rolling direction of the alloy the same as the first rolling direction each time). After each pass of rolling, the rolled alloy is placed in a box furnace and kept at 350 °C for 15 min. The total rolling deformation of the alloy after rolling deformation is 60%.

[0072] After the final pass of rolling, let it remain flat for two more passes, and then quench the magnesium-lithium alloy in cold water at 25°C to retain the microstructure formed during the rolling process of the alloy (denoted as Sample 1).

[0073] Comparative Example 1

[0074] According to the chemical compositions of the β-phase (BCC structure) magnesium-lithium alloy (by mass percentage, the chemical compositions of the magnesium-lithium alloy are: Li: 12%, Al: 3%, Zn: 1%, Al-5Ti-1.2C: 1.5%, and the balance is magnesium and impurities, with the total amount of each component being 100%), weigh out industrial pure magnesium, commercial AZ31 ingots, zinc ingots, pure lithium, and Al-5Ti-1.2C master alloy respectively. First, heat and melt the industrial pure magnesium and commercial AZ31 ingots, then add the zinc ingot. After melting, add pure lithium and hold for 10 min. Before pouring, add the Al-5Ti-1.2C master alloy and hold for 3 min. Pour the alloy melt quickly into a cylindrical mold to obtain a magnesium-lithium alloy ingot with a diameter of 41 mm and a height of 57 mm (denoted as As-cast 1.5).

[0075] Wire-cut the magnesium-lithium alloy ingot to obtain a block-shaped specimen with dimensions of length × width × height of 30 mm × 25 mm × 6.5 mm; place the block-shaped specimen in a box furnace and hold at 350°C for 15 min.

[0076] Clamp the heat-treated magnesium-lithium alloy block-shaped specimen with a fixture and quickly transfer it to a two-high rolling mill for rolling. During rolling, the roll speed is 5 r / min, and the thickness is reduced by 0.5 mm for each pass. The alloy is rolled using a unidirectional rolling method (i.e., keeping the rolling direction of the alloy the same as the first rolling direction each time). After each pass of rolling, put the rolled alloy into a box furnace and hold at 350°C for 15 min. The total rolling reduction of the alloy after rolling deformation is 60%.

[0077] After the final pass of rolling, let it remain flat for two more passes, and then quench the magnesium-lithium alloy in cold water at 25°C to retain the microstructure formed during the rolling process of the alloy (denoted as Sample 1.5).

[0078] Test

[0079] [Metallographic microscopy test]

[0080] Perform metallographic microscopy tests on the specimens and intermediate samples obtained in Example 1, Example 2, Example 3, and Comparative Example 1, and the results are as Figure 1 shown.

[0081] It can be seen from Figure 1 that the as-cast alloy (As-cast 0, Figure 1 a; As-cast 0.5, Figure 1c; As-cast 1, Figure 1 e; As-cast 1.5, Figure 1 g) The second phase in it is mainly distributed in the grains and at the grain boundaries.

[0082] Hot-rolled alloy (Sample 0, Figure 1 b; Sample 0.5, Figure 1 d; Sample 1, Figure 1 f; Sample 1.5, Figure 1 h) The second phase is distributed along the rolling direction. By comparing the metallographic microstructures of the as-cast alloys, it is found that a large number of fine equiaxed grains parallel to the rolling direction are formed after hot rolling, indicating that dynamic recrystallization occurs in the β-based Mg-Li alloy during hot rolling. This can not only reduce the grain size but also eliminate some casting defects in the material, significantly improving the mechanical properties of the alloy; however, with the increase in the addition amount of the Al-5Ti-1.2C master alloy, the grains of the alloy show a trend of first decreasing and then increasing, and at the same time, the distribution of the second phase becomes more uniform.

[0083] [Scanning electron microscopy test]

[0084] The specimens and intermediate samples obtained from Example 1, Example 2, Example 3 and Comparative Example 1 were subjected to scanning electron microscopy tests, and the results are as Figure 2 、 3 shown.

[0085] It can be seen from Figure 2 that in the as-cast alloys ( Figure 2 (a), (c), (e), (g)), the bright white second phases of different sizes are mainly distributed at the grain boundaries and within the grains. In the β-based Mg-Li alloys after hot rolling ( Figure 2 (b), (d), (f), (h)), the bright white second phases are uniformly distributed along the rolling direction and can play a good dispersion strengthening role;

[0086] For Figure 3 the positions marked A, B and C in (a), EDS point scanning analysis shows that they are all rich in Mg and Al elements. Combining with Table 1, it can be known that the second phases at points A and B should be AlLi phases, and the second phase at point C is MgLiAl2 phase, which is distributed within the grains, indicating that during hot rolling, these precipitated second phases hinder the movement of dislocations and improve the strength of the alloy.

[0087] Table 1 Figure 3 (a) EDS point scanning results of points A, B and C

[0088]

[0089] [Density test]

[0090] According to Archimedes' principle, the density value of the alloy was measured. The calculation formula is as follows:

[0091] ρ = m1ρ0 / m2

[0092] Wherein, m1 is the mass of the specimen in air, in g; m2 is the mass of the specimen in water, in g; ρ is the density of the specimen, in g / cm 3 ; ρ0 is the density of water, in g / cm 3 .

[0093] Table 2 Density of experimental alloys

[0094]

[0095] [Mechanical property test]

[0096] Tensile tests were carried out on the specimens and intermediate samples obtained from Example 1, Example 2, Example 3 and Comparative Example 1. The corresponding tensile stress-strain curves, as well as their respective tensile strengths and elongation rates are as Figure 4 、 5 and shown in Table 3.

[0097] Table 3 Mechanical properties of magnesium-lithium alloy specimens corresponding to examples and comparative examples

[0098]

[0099] From Figure 4 、 5 the tensile stress-strain curve graphs shown, the tensile strength and elongation rate data of the corresponding specimens summarized in Table 3, and the density measurement results of the experimental alloys in Table 1, it can be seen that for the β-phase (BCC structure) magnesium-lithium alloy obtained by the method of the present invention, the strength and elongation rate are significantly improved on the premise of ensuring low density. Especially when adding 1% Al-5Ti-1.2C master alloy, the tensile strength can be increased to more than 290 MPa, obtaining an ultra-light and high-strength β-phase (BCC structure) magnesium-lithium alloy.

[0100] This is because during the hot rolling process, dynamic recrystallization occurs in the alloy, significantly refining the β-Li grains. At the same time, TiC particles are dispersed in the matrix, restricting the growth behavior of the β-Li recrystallized grains at high temperatures, controlling the diameter of the recrystallized grains within a smaller size range, thereby improving the tensile strength of the alloy; secondly, the TiC particles with high hardness and high-temperature stability are evenly distributed in the matrix, playing a role of dispersion strengthening. At the same time, the TiC particles and the granular AlLi and MgLiAl2 phases hinder the movement of dislocations, improving the tensile strength of the alloy.

[0101] However, when the addition amount of the Al-5Ti-1.2C master alloy is 1.5 wt.%, the density of the alloy increases, and the mechanical properties decrease significantly. This is still because an excessive amount of TiC particles are introduced into the alloy. These excessive TiC particles are prone to agglomeration, which not only reduces the number of nucleation sites but also causes stress concentration during the tensile deformation process, resulting in a decrease in the tensile strength and elongation of the alloy. In addition, the addition of an excessive amount of the Al-5Ti-1.2C master alloy will cause a large part of the Al element in the alloy to exist in the form of compounds, and the amount of Al solid dissolved in the matrix becomes less. This distribution ratio leads to a poor solution strengthening effect of Al, resulting in a decrease in the overall strength of the alloy.

[0102] Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Those with ordinary knowledge in the technical field to which the present invention pertains can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to that defined by the claims.

Claims

1. A preparation method of a β-based magnesium-lithium alloy, characterized in that, It includes the following steps: S1. Weigh industrial pure magnesium, commercial AZ31 ingots, aluminum ingots, zinc ingots, pure lithium and Al-5Ti-1.2C master alloy respectively according to the chemical composition ratio; wherein, the chemical composition includes by mass percentage: Li: 11% - 12%, Al: 2.5% - 3%, Zn: 0.5% - 1%, Al-5Ti-1.2C: 0% - 1%, and the balance is magnesium and impurities, and the total amount of each component is 100%; Then first melt the industrial pure magnesium and commercial AZ31 ingots, add aluminum ingots and zinc ingots, after melting, add pure lithium for heat preservation, add Al-5Ti-1.2C master alloy for heat preservation before pouring, and quickly pour the obtained alloy liquid into the mold to obtain a magnesium-lithium alloy ingot; S2. Cut the magnesium-lithium alloy ingot obtained in step S1 into required sizes and then conduct heat preservation treatment to obtain the first magnesium-lithium alloy block; S3. Subject the first magnesium-lithium alloy block obtained in step S2 to multi-pass rolling under required rolling conditions until the total rolling deformation amount reaches 60% - 70% to obtain the second magnesium-lithium alloy block; wherein, after each pass of rolling, heat preservation treatment is carried out on the alloy after this pass of rolling to maintain the rolling temperature; S4. Process the second magnesium-lithium alloy block obtained in step S3 to keep it flat, and then conduct quenching to retain the microstructure formed during the alloy rolling process to obtain a β-phase magnesium-lithium alloy.

2. The preparation method of the β-based magnesium-lithium alloy according to claim 1, characterized in that, The mass percentage of Al-5Ti-1.2C is 0.5% - 1%.

3. The preparation method of the β-based magnesium-lithium alloy according to claim 1, characterized in that, In step S2, the conditions of the heat preservation treatment are: heat preservation for 10 min - 15 min at a temperature of 350°C ± 10°C.

4. The preparation method of the β-based magnesium-lithium alloy according to claim 1, characterized in that, In step S3, a unidirectional rolling method is adopted for rolling.

5. The preparation method of the β-based magnesium-lithium alloy according to claim 1, characterized in that, In step S3, the rolling conditions are: rolling speed ≤ 6 r / min, rolling temperature ≥ 340°C.

6. The preparation method of the β-based magnesium-lithium alloy according to claim 1, wherein, In step S3, the thickness of the alloy block decreases by 0.5 mm - 1 mm after each pass of rolling.

7. The preparation method of the β-based magnesium-lithium alloy according to claim 1, wherein In step S3, the conditions for conducting heat preservation treatment on the alloy after each pass of rolling are: heat preservation for 10 min - 15 min at a temperature of 350°C ± 10°C.

8. The preparation method of the β-based magnesium-lithium alloy according to claim 1, characterized in that, In step S4, place the second magnesium-lithium alloy block that has been kept flat in cold water at a temperature of 20°C - 25°C for quenching.

9. The preparation method of the β-based magnesium-lithium alloy according to claim 1, characterized in that, In step S1, a protective gas is passed through the furnace during the melting process, and the protective gas is SF6 + N2, and the volume ratio of SF6 to N2 is 1:

200.

10. A β-phase magnesium-lithium alloy prepared by any one of the methods in claims 1 - 9.

Images