High-strength, high-ductility, high-stability lightweight magnesium-lithium alloy and its preparation method

Abstract

This invention relates to the field of magnesium alloy processing and preparation technology, specifically providing a high-strength, high-ductility, high-stability lightweight magnesium-lithium alloy and its preparation method. The weight percentages of the components in this magnesium-lithium alloy are: Li: 14.5wt%-16wt%, Al: 2.8wt%-5wt%, Ca: 1.6wt%-3wt%, with the balance being magnesium. It may or may not contain impurities, with the total amount of impurities not exceeding 0.1wt%. The invention develops an equal-channel corner extrusion process for this magnesium alloy, achieving high shear deformation and fine-grain strengthening of large-size magnesium-lithium alloy bars with high Ca (1.6wt%-3wt%) content. Subsequent solution treatment and aging processes further improve the strength and ductility of the magnesium-lithium alloy. The alloy of this invention exhibits good mechanical stability, with a tensile strength reduction rate of ≤4% after holding at 50℃ for 1000 hours.

Description

Technical Field

[0001] This invention relates to the field of magnesium alloy processing and preparation technology, specifically providing a high-strength, high-plasticity, high-stability lightweight magnesium-lithium alloy and its preparation method. Background Technology

[0002] Magnesium-lithium alloys are among the lightest metallic structural materials, with lithium having a density of only 0.53 g / cm³. 3 The addition of lithium reduces the density of the magnesium alloy to below the conventional 1.8 g / cm³. 3 The concentration is generally 1.35-1.65 g / cm³. 3 Magnesium-lithium alloys are 1 / 4 to 1 / 3 lighter than ordinary magnesium alloys, hence they are also called ultralight alloys. Magnesium-lithium alloys possess excellent room-temperature forming properties. The addition of lithium alters the crystal structure of the magnesium alloy. When the lithium content is less than 5.7%, the alloy is a single-phase α-phase (Li solid solution in Mg); when the lithium content is between 5.7% and 10.3%, it is a mixed structure of α and β phases (Mg solid solution in Li); and when the lithium content is greater than 10.3%, it is a single-phase β-phase. The β-phase has a body-centered cubic structure, which offers superior forming properties compared to the close-packed hexagonal structure of the α-phase. However, the addition of more Li leads to a decrease in the strength of the magnesium-lithium alloy. Therefore, under conditions requiring high strength, it is difficult to further reduce the weight of magnesium-lithium alloys by continuously increasing the Li content.

[0003] Zn and Al elements have high solid solubility in the magnesium matrix, achieving significant solid solution strengthening and substantially improving the strength of magnesium-lithium alloys. Currently, magnesium-lithium alloys such as Mg-Li-Zn, Mg-Li-Al, and Mg-Li-Zn-Al have been developed. However, even at room temperature, the beneficial strengthening phases MgLi₂Al and MgLi₂Zn produced during initial aging in Zn and Al-containing magnesium-lithium alloys transform into AlLi and MgLiZn softening phases, leading to a decrease in alloy strength. This natural aging softening phenomenon directly limits the use of magnesium-lithium alloys in the manufacture of high-strength structural components. Some studies suggest that Ag can inhibit the transformation of the MgLi₂Al strengthening phase to the AlLi softening phase, thereby improving the stability of Mg-Li-Al-Zn alloys. However, the use of Ag increases manufacturing costs and is detrimental to the lightweighting of magnesium-lithium alloys. Rare earth element Ce can form Al2RE / Al3RE compounds with Al, inhibiting the formation of the AlLi softening phase; and the inhibitory effect of rare earth element Ce on the AlLi softening phase increases with the increase of Ce content (0-2.5wt%). Although the addition of rare earth elements (RE) can improve the mechanical stability of magnesium-lithium alloys, the Al-RE compounds generated by a large content of RE elements deteriorate the plastic processing properties of magnesium-lithium alloys and are detrimental to the lightweighting and cost reduction of magnesium-lithium alloys.

[0004] In addition, the lightweight element Ca, which plays a role in refining and anti-oxidation, is also added to magnesium alloys. Zhao Hongliang, in "A High-Plasticity Magnesium-Lithium Alloy with Weak Basal Texture and Its Preparation Method [P], CN 115161526A", provides a magnesium-lithium alloy with the following composition: Li: 5.5%-10.3%, Al: 1%-3%, Zn: 0.5%-2%, Ca: 0.3%-0.9%, Ce: 0.5%-1%. In this alloy, Ca replaces some of the RE element to improve strength and weaken texture. The tensile strength of the alloy reaches 260 MPa through hot extrusion and heat treatment processes. Wang Xiyu disclosed a magnesium-lithium alloy with the following composition in "A Low-Density, High-Strength, and High-Plasticity Magnesium-Lithium Alloy and Its Preparation Method [P], CN 110343923 A": Li: 3%-10%, Al: 0-6%, Zn: 0-4%, Ca: 0-1.2%, Mn: 0-2%, Zr: 0-1.3%, La: 0-3%, Ce: 0-1.5%. After plastic deformation processing, the tensile strength of the alloy is 180-300 MPa. In "An Ultrafine-Grained High-Strength and Plastic Magnesium Alloy and Its Preparation Method [P], CN114855043 A", Cha Min disclosed a Mg alloy containing trace amounts (0.1%-0.3%) of Ca. Utilizing the interactions between elements such as Mg, Zn, Ca, Al, and Mn, the Ca2Mg6Zn3 and Al8Mn5 phases dynamically precipitate during deformation. These phases pin grain boundaries during subsequent deformation, leading to rapid grain refinement. This alloy, obtained through a four-pass equal-channel angular extrusion and low-temperature single-pass high-reduction rolling process, exhibits an ultrafine-grained high-strength and plastic magnesium alloy with a tensile strength Rm of 330-385 MPa and an elongation of 10%-14%. However, this alloy has poor plasticity, and the multi-pass equal-channel extrusion process is cumbersome and inefficient. It is evident that calcium (Ca) can refine the grains of magnesium alloys and improve their mechanical properties. However, because Ca and Mg readily form a hexagonal CaMg2 structure, high-Ca-content magnesium-lithium alloys exhibit poor plasticity and are prone to cracking during plastic deformation. Therefore, the amount of Ca added to magnesium alloys is relatively small. More importantly, the role of Ca in the stability of the mechanical properties of magnesium-lithium alloys remains undetermined, and the influence of its content on the stability of these properties is also unclear.

[0005] In view of this, the present invention proposes a Mg-Li-Al-(1.6wt%-3wt%)Ca alloy, and develops a single-pass, equal-channel, angled extrusion process for this magnesium alloy, achieving large shear deformation and fine-grain strengthening of high-Ca-content, large-size magnesium-lithium alloy bars. Furthermore, through subsequent solution treatment and aging processes, the strength and plasticity of the magnesium-lithium alloy are continuously improved. The magnesium-lithium alloy of the present invention exhibits low density, high strength, good plasticity, and stable mechanical properties. Summary of the Invention

[0006] The primary objective of this invention is to provide a high-strength, high-plasticity, high-stability, lightweight magnesium-lithium alloy.

[0007] The second objective of this invention is to provide a method for preparing the above-mentioned magnesium-lithium alloy.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A high-strength, high-plasticity, high-stability, lightweight magnesium-lithium alloy, wherein the weight percentages of each component in the magnesium-lithium alloy are: Li: 14.5wt%-16wt%, Al: 2.8wt%-5wt%, Ca: 1.6wt%-3wt%, with the balance being magnesium, and may or may not contain impurities, wherein the total amount of impurities in the magnesium-lithium alloy accounts for no more than 0.1wt%.

[0010] Furthermore, the Li content is 14.8 wt%-15.5 wt%, preferably 15 wt%;

[0011] Preferably, the Al content is 3.2 wt%-4.4 wt%, more preferably 3.4 wt%;

[0012] Preferably, the Ca content is 1.85wt%-2.60wt%, more preferably 2wt%;

[0013] Preferably, the total amount of the impurities in the magnesium-lithium alloy is no more than 0.02 wt%.

[0014] Furthermore, the ratio of Al to Ca is 1.7:1.

[0015] Furthermore, the components in this magnesium-lithium alloy are introduced in the form of elemental Mg, elemental Li, Mg-Al master alloy, and Mg-Ca master alloy, respectively.

[0016] Furthermore, the preparation method of the magnesium-lithium alloy includes: obtaining raw materials according to the proportion, first obtaining magnesium-lithium alloy ingots by melting, casting and homogenization treatment in sequence, then taking rods from the magnesium-lithium alloy ingots and placing them into an equal channel corner extrusion die for single-pass equal channel corner extrusion, and then performing solution treatment and aging treatment in sequence to obtain magnesium-lithium alloy.

[0017] The operation of the equal channel corner extrusion includes: first heating the bar to 200-250℃ and holding it for 40-60 minutes, then quickly taking it out and brushing it with graphite lubricant, then placing it into the equal channel corner extrusion die preheated to 120-150℃, and extruding it at an extrusion rate of 20-30 mm / s. The corner of the equal channel corner extrusion die is 90°-105°.

[0018] Preferably, the melting and casting operation includes: melting at a temperature of 710-720℃ for 50-60 minutes under an inert atmosphere, and then pouring the mixture into a mold for cooling.

[0019] Preferably, the homogenization process includes: using a 50-100μm pure aluminum-coated magnesium-lithium alloy ingot and holding it at 400-450℃ for 3-6 hours.

[0020] Preferably, the solution treatment operation includes: heating to 270-290°C at a heating rate of 5-10°C / min and holding at that temperature for 90-120 min, then quickly removing and water cooling;

[0021] Preferably, the aging process includes: heating to 175-195℃ at a heating rate of 3-5℃ / min and holding for 140-360 minutes, then removing and air-cooling after the holding period.

[0022] Preferably, the rod has a diameter of φ30-50mm and a length of 120-150mm;

[0023] The preparation method of the above-mentioned high-strength, high-ductility, high-stability lightweight magnesium-lithium alloy includes the following steps:

[0024] S1: Mix the raw materials according to the mass percentage of each component in the magnesium-lithium alloy and then melt and cast them to obtain magnesium-lithium alloy ingots.

[0025] S2: Homogenize the magnesium-lithium alloy ingot of S1.

[0026] S3: Obtain bar stock from the ingot of S2;

[0027] S4: Place the bar from S3 into the equal channel corner extrusion die for single-pass equal channel corner extrusion;

[0028] S5: Solution treatment and aging treatment are performed on the extruded bars from S4;

[0029] The operation of the equal channel corner extrusion includes: first heating the bar to 200-250℃ and holding it for 40-60 minutes, then quickly taking it out and brushing it with graphite lubricant, and then placing it into an equal channel corner extrusion die preheated to 120-150℃, and extruding it at an extrusion rate of 20-30 mm / s. The corner angle of the equal channel corner extrusion die is 90°-105°.

[0030] Furthermore, in S1, the components of the raw materials for the magnesium-lithium alloy are introduced in the form of elemental Mg, elemental Li, Mg-Al master alloy, and Mg-Ca master alloy, respectively.

[0031] Furthermore, the melting and casting operation in S1 includes: melting at a temperature of 710-720℃ for 50-60 minutes under an inert atmosphere, and then pouring it into a mold for cooling.

[0032] Preferably, the homogenization operation in S2 includes: using a 50-100μm pure aluminum-coated magnesium-lithium alloy ingot and holding it at 400-450℃ for 3-6 hours.

[0033] Preferably, in S3, the dimensions of the rod are a diameter of φ30-50mm and a length of 120-150mm.

[0034] Furthermore, the solution treatment in S5 includes: heating to 270-290℃ at a heating rate of 5-10℃ / min and holding for 90-120min, then quickly removing and water-cooling;

[0035] Preferably, the solution treatment in S5 is carried out in a muffle furnace.

[0036] Furthermore, the aging process in S5 includes: heating to 175-195℃ at a heating rate of 3-5℃ / min and holding for 140-360min; after holding, removing and air cooling.

[0037] Preferably, the aging treatment in S5 is carried out in a precision constant temperature furnace.

[0038] Compared with the prior art, the technical effects of the present invention are as follows:

[0039] (1) The magnesium-lithium alloy of the present invention has a high Li content and uses light elements such as Al and Ca as additives. It does not contain elements with high density and high price such as Ag, Zn and rare earth. The magnesium-lithium alloy has a low density and low material cost.

[0040] (2) The magnesium-lithium alloy of the present invention uses Al and Ca as strengthening elements. Most of the Al and Ca elements form the CaAl2 phase, which plays a second-phase strengthening role in the alloy, while a small amount of Al and Ca elements dissolve into the magnesium matrix to play a solid solution strengthening role. At the same time, the magnesium-lithium alloy of the present invention has repeatedly obtained the range of Li element content through repeated experiments, and has high strength while ensuring the highest possible Li element content.

[0041] (3) In the magnesium-lithium alloy of this invention, through compositional design (Al:Ca mass ratio of 1.7:1, atomic ratio ≈2.52:1), it is ensured that Al fully reacts with Ca to form the CaAl2 phase. The CaAl2 phase has good stability and does not undergo a transformation from a strengthening phase to a softening phase. At the same time, the CaAl2 phase inhibits the formation of the MgLi2Al phase, thereby improving the mechanical stability of the alloy. Under the action of equal channel angular compression large shear deformation and solid solution aging, the refined micron-sized CaAl2 phase (1-2μm) has a more significant inhibitory effect on the MgLi2Al→AlLi transformation.

[0042] (4) The magnesium-lithium alloy of the present invention, through composition design (Al:Ca mass ratio of 1.7:1, atomic ratio ≈2.52:1), has a dispersed CaAl2 phase (cubic structure) as the reinforcing phase and does not form a brittle CaMg2 phase (hexagonal structure), and the alloy has good plastic deformation ability.

[0043] (5) The equal channel corner extrusion process of this invention rationally designs process parameters such as extrusion temperature, die temperature, corner angle, and extrusion rate, which effectively solves the problem of easy cracking during plastic deformation of high Ca (1.6%-3%) magnesium-lithium alloys. During the equal channel corner extrusion process, the magnesium-lithium alloy grains are refined, the CaAl2 phase is broken and refined, and the grain refinement effect is obvious, which improves the strength and plasticity of high Ca magnesium-lithium alloys.

[0044] (6) The solution treatment following equal-channel extrusion in this invention rationally designs the solution temperature and time, promoting the recrystallization and refinement of the extruded magnesium-lithium alloy. Simultaneously, while ensuring no significant grain growth, it eliminates extrusion stress, homogenizes the microstructure, and allows the reinforcing phase to dissolve back. The aging treatment following the solution treatment in this invention rationally designs the aging temperature and time, adjusting the size and morphology of the reinforcing phase CaAl2 (1-2 μm particles), enabling the magnesium-lithium alloy of this invention to maintain good plasticity while possessing high strength. Furthermore, the single-pass equal-channel corner extrusion process and solution aging process designed in this invention are simple and have high production efficiency.

[0045] (7) Due to the strengthening effect of the second phase of CaAl2 and the mechanical stabilizer, the fine grain strengthening effect of equal channel extrusion, and the solid solution and precipitation strengthening effect of solid solution aging, the magnesium-lithium alloy of this invention has the characteristics of being lightweight, high strength, high plasticity and high stability, and has excellent comprehensive performance. Attached Figure Description

[0046] The various technical features of the present invention and their relationships will be further explained below with reference to the accompanying drawings. The drawings are exemplary; some technical features are not shown to scale, and some drawings may omit technical features commonly used in the art to which this invention pertains that are not essential for understanding and implementing the invention, or may additionally show technical features that are not essential for understanding and implementing the invention. In other words, the combination of various technical features shown in the drawings is not intended to limit the invention. Furthermore, throughout this invention, the same reference numerals refer to the same things. Specific descriptions of the drawings are as follows:

[0047] Figure 1 This is the morphology of the magnesium-lithium alloy after extrusion and solution aging in Example 1 of the present invention;

[0048] Figure 2 These are microstructure images of the magnesium-lithium alloy of this invention. Detailed Implementation

[0049] The specific embodiments of the present invention will now be described in detail.

[0050] Magnesium-lithium alloys are the lightest metallic structural materials in the world, possessing excellent thermal conductivity, electrical conductivity, and ductility, and are widely used in aerospace, defense, and other fields. Pure magnesium metal has a close-packed hexagonal structure and a density of only 1.738 g / cm³. 3 However, its forming ability is poor; adding Li to magnesium can reduce the density to 1.3-1.6 g / cm³. 3 The close-packed hexagonal structure also transforms into a body-centered cubic structure with increasing Li content, which effectively improves the low-temperature forming capability of magnesium alloys. Due to the relatively high solid solubility of lithium in magnesium, its addition can produce a solid solution strengthening effect and improve its ductility.

[0051] Equal channel angular extrusion (ECAP) is a shear deformation process that presses metal into a specially designed die to achieve a large amount of deformation. It primarily utilizes near-pure shearing during deformation to refine the material's grain size, thereby significantly improving its mechanical and physical properties. ECAP is an effective method for preparing ultrafine-grained materials.

[0052] This invention provides a high-strength, high-plasticity, high-stability, lightweight magnesium-lithium alloy, wherein the weight percentages of each component are: Li: 14.5wt%-16wt%, Al: 2.8wt%-5wt%, Ca: 1.6wt%-3wt%, with the balance being magnesium, and may or may not contain impurities, wherein the total amount of impurities in the magnesium-lithium alloy does not exceed 0.1wt%.

[0053] To develop a lightweight magnesium-lithium alloy with high strength, high plasticity, and good resistance to aging softening, this invention designs a Mg-Li-Al-Ca alloy. Al and Ca elements form the CaAl2 phase, which acts as a second-phase strengthening agent in the alloy. Small amounts of Al and Ca elements dissolve into the magnesium matrix, providing solid solution strengthening. The Li content is controlled at 14.5-16 wt.% to improve the alloy's plasticity, reduce its density, and prevent a sharp deterioration in strength.

[0054] By designing the composition (Al:Ca mass ratio of 1.7:1, atomic ratio ≈2.52:1), the alloy ensures that Al reacts fully with Ca to form the CaAl2 phase. The CaAl2 phase exhibits good stability and does not undergo a transformation from a strengthening phase to a softening phase. Simultaneously, the CaAl2 phase inhibits the formation of the MgLi2Al phase and acts as a concomitant pinning agent, suppressing the transformation of a small amount of MgLi2Al phase into AlLi, thereby improving the mechanical stability of the alloy.

[0055] In this invention, the weight percentage of Li can be, but is not limited to, 14.5 wt%, 14.6 wt%, 14.7 wt%, 14.8 wt%, 14.9 wt%, 15 wt%, 15.1 wt%, 15.2 wt%, 15.3 wt%, 15.4 wt%, 15.5 wt%, 15.6 wt%, 15.7 wt%, 15.8 wt%, 15.9 wt%, or 16 wt%; the weight percentage of Al can be, but is not limited to, 2.8 wt%, 3 wt%, 3.2 wt%, 3.4 wt%, 3.6 wt%, 3.8 wt%, 4 wt%, 4.2 wt%, or 4.4 wt%. The weight percentage of Ca may be, but is not limited to, 1.6 wt%, 1.8 wt%, 2 wt%, 2.2 wt%, 2.4 wt%, 2.6 wt%, 2.8 wt%, or 3 wt%; the total amount of impurities in the magnesium-lithium alloy may be, but is not limited to, no more than 0.1 wt%, no more than 0.09 wt%, no more than 0.08 wt%, no more than 0.07 wt%, no more than 0.06 wt%, no more than 0.05 wt%, no more than 0.04 wt%, no more than 0.03 wt%, no more than 0.02 wt%, or no more than 0.01 wt%. Impurities include at least one of Si, Fe, Cu, and Ni.

[0056] In a preferred embodiment, the Li content is 14.8 wt%-15.5 wt%, preferably 15 wt%.

[0057] In a preferred embodiment, the Al content is 3.2 wt% to 4.4 wt%, preferably 3.4 wt%.

[0058] In a preferred embodiment, the Ca content is 1.85wt%-2.60wt%, preferably 2wt%.

[0059] In a preferred embodiment, the total amount of impurities in the magnesium-lithium alloy is no more than 0.02 wt%.

[0060] In the Mg-Li-Al-Ca of this invention, the preferred ratio of Al to Ca elements is 1.7:1.

[0061] The aforementioned high-strength, high-plasticity, high-stability, lightweight magnesium-lithium alloy is mainly prepared through an equal-channel angular extrusion process, which includes: obtaining raw materials according to the formula, first obtaining magnesium-lithium alloy ingots through melting, casting, and homogenization treatment, then taking rods from the magnesium-lithium alloy ingots and placing them into an equal-channel angular extrusion die for equal-channel angular extrusion, followed by solution treatment and aging treatment to obtain the magnesium-lithium alloy; wherein, the equal-channel angular extrusion operation includes: first heating the rods to 200-250℃ and holding them at that temperature for 40-60 minutes, then quickly removing them and brushing them with graphite lubricant, then placing them into an equal-channel angular extrusion die preheated to 120-150℃, and extruding them at an extrusion rate of 20-30 mm / s, with the angular angle of the equal-channel angular extrusion die being 90°-105°.

[0062] The pretreatment heating temperature for the bar stock can be, but is not limited to, 200℃, 205℃, 210℃, 215℃, 220℃, 225℃, 230℃, 235℃, 240℃, 245℃, or 250℃; the holding time can be, but is not limited to, 40min, 45min, 50min, 55min, or 60min; the preheating temperature for the equal channel corner extrusion die can be, but is not limited to, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, or 150℃. The extrusion rate may be, but is not limited to, 20 mm / s, 21 mm / s, 22 mm / s, 23 mm / s, 24 mm / s, 25 mm / s, 26 mm / s, 27 mm / s, 28 mm / s, 29 mm / s, or 30 mm / s; the rotation angle may be, but is not limited to, 90°, 91°, 92°, 93°, 94°, 95°, 96°, 97°, 98°, 99°, 100°, 101°, 102°, 103°, 104°, or 105°.

[0063] This invention presents an equal-channel angular extrusion process for Mg-Li-Al-Ca alloys, effectively addressing the issues of high deformation resistance and easy cracking during deformation in high-calcium (1.6%-3%) magnesium-lithium alloys. During equal-channel angular extrusion, the magnesium-lithium alloy grains are refined, and the CaAl2 phase is broken down and refined, resulting in a significant grain-refining effect. The solution treatment following equal-channel extrusion promotes recrystallization and refinement of the extruded magnesium-lithium alloy, eliminates extrusion stress, homogenizes the microstructure, and allows the solid solution strengthening phase to dissolve back into the microstructure while ensuring that grain growth is not significant.

[0064] Due to the strengthening effect of the CaAl2 second phase and its role as a mechanical stabilizer, the solid solution strengthening effect of small amounts of Al and Ca elements, the grain refinement strengthening effect of isochannel extrusion, and the solid solution strengthening and aging precipitation effects of solid solution aging treatment, the magnesium-lithium alloy of this invention maintains high tensile strength even with a high Li content. This gives the magnesium-lithium alloy of this invention the characteristics of being lightweight, high-strength, highly ductile, and highly stable.

[0065] In a preferred embodiment, the solution treatment includes: heating to 270-290°C at a heating rate of 5-10°C / min and holding at that temperature for 90-120 min, followed by rapid removal and water cooling. The heating rate may be, but is not limited to, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, or 10°C / min; the solution temperature may be, but is not limited to, 270°C, 272°C, 274°C, 276°C, 278°C, 280°C, 282°C, 284°C, 286°C, 288°C, or 290°C; and the solution time may be, but is not limited to, 90 min, 95 min, 100 min, 105 min, 110 min, 115 min, or 120 min.

[0066] In a preferred embodiment, the melting and casting operation includes: melting at a temperature of 710-720°C for 50-60 minutes under an inert atmosphere, followed by pouring into a mold for cooling. The melting temperature may be, but is not limited to, 710°C, 711°C, 712°C, 713°C, 714°C, 715°C, 716°C, 717°C, 718°C, 719°C, or 720°C; the holding time may be, but is not limited to, 50 minutes, 51 minutes, 52 minutes, 53 minutes, 54 minutes, 55 minutes, 56 minutes, 57 minutes, 58 minutes, 59 minutes, or 60 minutes.

[0067] In a preferred embodiment, the homogenization process includes: using a 50-100μm pure aluminum-coated magnesium-lithium alloy ingot and holding it at 400-450℃ for 3-6 hours. The homogenization temperature can be, but is not limited to, 400℃, 405℃, 410℃, 415℃, 420℃, 425℃, 430℃, 435℃, 440℃, 445℃, or 450℃; the holding time can be, but is not limited to, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, or 6 hours.

[0068] In a preferred embodiment, the dimensions of the bar are a diameter of φ30-50mm and a length of 120-150mm. The diameter of the bar can be, but is not limited to, 30mm, 35mm, 40mm, 45mm or 50mm, and the length of the bar can be, but is not limited to, 120mm, 130mm, 140mm or 150mm.

[0069] In a preferred embodiment, the aging treatment includes: heating to 175-195℃ at a heating rate of 3-5℃ / min and holding at that temperature for 140-360 min, followed by air cooling after the holding period. The heating rate during the aging treatment can be, but is not limited to, 3℃ / min, 3.2℃ / min, 3.4℃ / min, 3.6℃ / min, 3.8℃ / min, 4℃ / min, 4.2℃ / min, 4.4℃ / min, 4.6℃ / min, 4.8℃ / min, or 5℃ / min; the holding temperature can be, but is not limited to, 175℃, 180℃, 185℃, 190℃, or 195℃; and the holding time can be, but is not limited to, 140 min, 160 min, 180 min, 200 min, 220 min, 240 min, 260 min, 280 min, 300 min, 320 min, 340 min, or 360 min.

[0070] This invention also provides a method for preparing the above-mentioned high-strength, high-ductility, high-stability lightweight magnesium-lithium alloy, comprising the following steps:

[0071] S1: Mix the raw materials according to the mass percentage of each component in the magnesium-lithium alloy and then melt and cast them to obtain magnesium-lithium alloy ingots.

[0072] Specifically, the raw materials are mixed according to the mass percentage of each component in the magnesium-lithium alloy, and then smelted in an inert atmosphere at a temperature of 710-720℃ for 50-60 minutes. Finally, the molten magnesium-lithium alloy is poured into a metal mold for cooling to obtain a magnesium-lithium alloy ingot.

[0073] S2: Homogenize the magnesium-lithium alloy ingot of S1.

[0074] Specifically, 50-100μm pure aluminum-coated magnesium-lithium alloy ingots are placed in a muffle furnace at 400-450℃ and held for 3-6 hours to homogenize the alloy ingots and eliminate microstructure segregation.

[0075] S3: Obtain bars with a diameter of φ30-50mm and a length of 120-150mm from the ingot of S2.

[0076] S4: Place the bar from S3 into the equal channel corner extrusion die for equal channel corner extrusion;

[0077] Step 1: Place the magnesium-lithium alloy rod in a muffle furnace and heat it to 200-250℃, then hold it for 40-60 minutes.

[0078] Step 2: After the magnesium-lithium alloy rods have finished their heat preservation, they are quickly removed from the muffle furnace and coated with graphite lubricant.

[0079] Step 3: Place the magnesium-lithium alloy rod coated with graphite lubricant into a preheated equal channel corner extrusion die at 120-150℃ and extrude it in a single pass at an extrusion rate of 20-30mm / s. The corner of the equal channel corner extrusion die is 90°-105°.

[0080] Step 4: Extrude the magnesium-lithium alloy rod from the mold and air-cool it for later use.

[0081] S5: Solution treatment and aging treatment are performed on the extruded bars from S4;

[0082] Step 1: Place the extruded magnesium-lithium alloy rod into a muffle furnace and heat it to a solution temperature of 270-290℃ at a heating rate of 5-10℃ / min, holding it at that temperature for 90-120 minutes. After holding, quickly remove the magnesium-lithium alloy rod from the muffle furnace and water-cool it to complete the solution treatment of the alloy.

[0083] Step 2: Place the solution-treated magnesium-lithium alloy rod into a precision constant-temperature furnace and heat it to 175-195℃ at a heating rate of 3-5℃ / min, holding it at that temperature for 140-360min. After holding, remove the magnesium-lithium alloy rod from the precision constant-temperature furnace and air-cool it to complete the aging treatment of the alloy, thus obtaining the high-strength, high-ductility, high-stability, lightweight magnesium-lithium alloy of this invention.

[0084] The above-mentioned preferred composition design and process parameters are obtained based on single-variable scientific experimental design and extensive experimental exploration. Under these conditions, the magnesium-lithium alloy of the present invention has superior comprehensive performance.

[0085] The present invention will be further described below with reference to specific embodiments, and the advantages and features of the present invention will become clearer with the description. However, these embodiments are merely exemplary and do not constitute any limitation on the scope of the present invention. Those skilled in the art should understand that modifications or substitutions can be made to the details and form of the technical solutions of the present invention without departing from the spirit and scope of the present invention, but all such modifications and substitutions fall within the protection scope of the present invention.

[0086] Example 1

[0087] A high-strength, high-plasticity, and high-stability lightweight magnesium-lithium alloy, wherein the mass percentages of its components are: Li: 15wt%, Al: 3.4wt%, Ca: 2wt%.

[0088] The preparation method of the above-mentioned high-strength, high-ductility, high-stability lightweight magnesium-lithium alloy includes the following steps:

[0089] (1) Smelting and casting of magnesium-lithium alloy: Mg, Li, Mg-Al master alloy, and Mg-Ca master alloy are mixed according to the mass percentages of each component in the magnesium-lithium alloy and placed in a crucible within an induction furnace. To ensure the inert gas provides good protection during smelting, the furnace is evacuated to 6 × 10⁻⁶ m³ / h before smelting. -1 Pa, and then argon gas is introduced. During the argon-protected melting process, the melting temperature is 710℃, and the temperature is held for 60 minutes. Finally, the molten metal is poured into a metal mold for cooling to obtain a magnesium-lithium alloy ingot.

[0090] (2) Homogenization of ingots: 100μm pure aluminum-coated magnesium-lithium alloy ingots were placed in a muffle furnace and held at 450℃ for 5 hours before being cooled in the furnace. This completed the homogenization treatment of the alloy ingots and eliminated the segregation of the microstructure.

[0091] (3) Equal channel corner extrusion: A rod with a size of φ30×130mm was cut from the center of the homogenized cast alloy ingot. The magnesium-lithium alloy rod was placed in a muffle furnace and heated to 250℃ and held for 60min. After the magnesium-lithium alloy test rod was held, it was quickly removed from the muffle furnace and coated with water-based graphite lubricant. The magnesium-lithium alloy test rod coated with water-based graphite lubricant was placed in an equal channel corner extrusion die preheated to 150℃ and extruded at an extrusion rate of 20mm / s. The corner of the equal channel corner extrusion die was 90°.

[0092] (4) Solution treatment and aging: The extruded magnesium-lithium alloy test bar was placed in a muffle furnace and heated to a solution temperature of 275°C at a heating rate of 8°C / min, and held for 110 min. After holding, the magnesium-lithium alloy test bar was quickly removed from the muffle furnace and water-cooled to complete the solution treatment of the alloy. The solution-treated magnesium-lithium alloy test bar was placed in a precision constant temperature furnace and heated to 175°C at a heating rate of 5°C / min, and held for 140 min. After holding, the magnesium-lithium alloy test bar was removed from the precision constant temperature furnace and air-cooled to complete the aging treatment of the alloy, thus obtaining the high-strength, high-ductility, high-stability, lightweight magnesium-lithium alloy of this invention.

[0093] The properties of the magnesium alloy were tested according to GB / T228-2002 "Metallic Materials - Tensile Testing at Room Temperature". The as-cast strength of the Mg-Li-Al-Ca alloy was: tensile strength Rm = 165 MPa, yield strength Rp0.2 = 148 MPa, and elongation δ = 16%. The extruded strength of the Mg-Li-Al-Ca alloy was: tensile strength Rm = 267 MPa, yield strength Rp0.2 = 258 MPa, and elongation δ = 22%. The isochannel extruded + solution-treated aged strength of the Mg-Li-Al-Ca alloy was: tensile strength Rm = 345 MPa, yield strength Rp0.2 = 330 MPa, and elongation δ = 30%. After being subjected to isotropic extrusion and solution treatment aging, the Mg-Li-Al-Ca alloy exhibited the following properties after being held at 50℃ for 1000 h: tensile strength Rm = 332 MPa (a decrease of 3.8%), yield strength Rp0.2 = 321 MPa (a decrease of 2.7%), and elongation δ = 34% (an increase of 13%). The density of this Mg-Li-Al-Ca alloy is 1.34 g / cm³. 3 .

[0094] The morphology of magnesium-lithium alloys after extrusion, solution treatment and aging is as follows: Figure 1 As shown, the microscopic tissue photographs are as follows: Figure 2 As shown.

[0095] Example 2

[0096] A high-strength, high-plasticity, and high-stability lightweight magnesium-lithium alloy, wherein the mass percentages of its components are: Li: 15wt%, Al: 3.4wt%, Ca: 2wt%.

[0097] The difference between Example 2 and Example 1 is that Example 2 does not have the equal channel extrusion process, while the remaining melting, homogenization, solution aging and other processes are the same as those in Example 1.

[0098] The properties of the magnesium alloy were tested according to GB / T228-2002 "Metallic Materials - Tensile Testing at Room Temperature". The solid solution aged strength of the Mg-Li-Al-Ca alloy was: tensile strength Rm = 225 MPa, yield strength Rp0.2 = 208 MPa, and elongation δ = 13%. After holding at 50℃ for 1000 h, the tensile strength Rm of the Mg-Li-Al-Ca alloy decreased by 9.8% to 203 MPa; the yield strength decreased by 11% to Rp0.2 = 185 MPa; and the elongation increased by 23.1% to δ = 16%.

[0099] Example 3

[0100] A high-strength, high-plasticity, and high-stability lightweight magnesium-lithium alloy, wherein the mass percentages of its components are: Li: 15wt%, Al: 3.4wt%, Ca: 2wt%.

[0101] The difference between Example 3 and Example 1 is that the equal channel corner extrusion process in Example 3 is different from that in Example 1, while the remaining melting, homogenization, solution aging and other processes are the same as in Example 1.

[0102] Example 3: Equal channel corner extrusion: First, heat the bar to 180°C and hold for 30 minutes. Then, quickly remove it and brush it with graphite lubricant. Next, place it into an equal channel corner extrusion die preheated to 100°C and extrude it at an extrusion rate of 40 mm / s. The corner of the equal channel corner extrusion die is 90°.

[0103] In Example 3, cracks appeared in the Mg-Li-Al-Ca alloy during extrusion. Referring to GB / T228-2002 "Metallic Materials - Tensile Testing at Room Temperature", the properties of the magnesium alloy were tested. The strengths of the extruded + solution-aged Mg-Li-Al-Ca alloy were: tensile strength Rm = 132 MPa, yield strength Rp0.2 = 120 MPa, and elongation δ = 6%.

[0104] Example 4

[0105] A high-strength, high-plasticity, and high-stability lightweight magnesium-lithium alloy, wherein the mass percentages of its components are: Li: 15wt%, Al: 3.4wt%, Ca: 2wt%.

[0106] The difference between Example 4 and Examples 1 and 3 is that the equal channel corner extrusion process of Example 4 is different from that of Examples 1 and 3, while the remaining melting, homogenization, solution aging and other processes are the same as those of Example 1.

[0107] Example 4: Equal channel corner extrusion process: First, heat the bar to 300℃ and hold for 80 minutes. Then, quickly remove it and brush it with graphite lubricant. Next, place it into an equal channel corner extrusion die preheated to 150℃ and extrude it at an extrusion rate of 10 mm / s. The corner of the equal channel corner extrusion die is 90°.

[0108] In Example 4, during the heating process at 300℃ before equal-channel angular extrusion of the Mg-Li-Al-Ca alloy, due to the high heating temperature, precipitated needle-like pore defects appeared on the surface of the alloy bar, and the grains were also relatively coarse. Referring to GB / T228-2002 "Metallic Materials - Tensile Testing at Room Temperature", the properties of the magnesium alloy were tested. The strength of this extruded + solution-aged Mg-Li-Al-Ca alloy was: tensile strength Rm = 298 MPa, yield strength Rp0.2 = 283 MPa, and elongation δ = 22%. After holding at 50℃ for 1000 h, the tensile strength Rm of the Mg-Li-Al-Ca alloy decreased by 9.1% to 271 MPa; the yield strength decreased by 4.6% to 270 MPa; and the elongation increased by 4.5% to 23%.

[0109] Example 5

[0110] A high-strength, high-plasticity, high-stability, lightweight magnesium-lithium alloy, wherein the mass percentages of its components are: Li: 15wt%, Al: 3.4wt%, Ca: 1.4wt%, with the balance being magnesium.

[0111] The difference between Example 5 and Example 1 is that the Ca content in Example 5 is lower (1.4 wt%), while the remaining smelting, homogenization, equal channel corner extrusion, and solution aging processes are the same as in Example 1.

[0112] The properties of the magnesium alloy were tested according to GB / T228-2002 "Metallic Materials - Tensile Testing at Room Temperature". The strength of the extruded + solution-aged Mg-Li-Al-Ca alloy was: tensile strength Rm = 325 MPa, yield strength Rp0.2 = 308 MPa, and elongation δ = 27%. After isochannel extrusion + solution-aged Mg-Li-Al-Ca alloy was held at 50℃ for 1000 h, the tensile strength Rm of the Mg-Li-Al-Ca alloy decreased to 278 MPa, a decrease of 14.5%; the yield strength Rp0.2 decreased to 259 MPa, a decrease of 15.9%.

[0113] Example 6

[0114] A high-strength, high-plasticity, high-stability, lightweight magnesium-lithium alloy, wherein the mass percentages of its components are: Li: 15wt%, Al: 3.4wt%, and the balance is magnesium.

[0115] The difference between Example 6 and Example 1 is that Example 5 does not contain Ca, while the remaining smelting, homogenization, equal channel corner extrusion, and solution aging processes are the same as in Example 1.

[0116] Referring to GB / T228-2002 "Metallic Materials - Tensile Testing at Room Temperature", the properties of the magnesium alloy were tested. The strength of the extruded + solution-aged Mg-Li-Al alloy was as follows: tensile strength Rm = 224 MPa, yield strength Rp0.2 = 210 MPa, and elongation δ = 24%. After being held at 50℃ for 1000 h, the tensile strength Rm of the isochannel extruded + solution-aged Mg-Li-Al alloy decreased by 25.9% to 166 MPa and the yield strength Rp0.2 decreased by 29.5% to 148 MPa.

[0117] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the technical concept of the present invention, all of which fall within the scope of protection of the present invention.

Claims

1. A high-strength, high-ductility, high-stability, lightweight magnesium-lithium alloy, characterized in that, The weight percentages of each component in the magnesium-lithium alloy are as follows: Li: 14.5wt%-16wt%, Al: 2.8wt%-5wt%, Ca: 1.6wt%-3wt%, with the balance being magnesium. It may or may not contain impurities, wherein the total amount of impurities in the magnesium-lithium alloy does not exceed 0.1wt%. The ratio of Al to Ca is 1.7:1; The components in the magnesium-lithium alloy are introduced in the form of elemental Mg, elemental Li, Mg-Al master alloy and Mg-Ca master alloy, respectively. The preparation method of the magnesium-lithium alloy includes: obtaining raw materials according to the proportion, first obtaining magnesium-lithium alloy ingots by melting, casting and homogenization treatment in sequence, then taking rods from the magnesium-lithium alloy ingots and placing them into equal channel corner extrusion molds for equal channel corner extrusion, and then performing solution treatment and aging treatment in sequence to obtain magnesium-lithium alloy. The operation of the equal channel corner extrusion includes: first heating the bar to 200-250℃ and holding it for 40-60 minutes, then quickly taking it out and brushing it with graphite lubricant, then placing it into the equal channel corner extrusion die preheated to 120-150℃, and extruding it at an extrusion rate of 20-30 mm / s. The corner of the equal channel corner extrusion die is 90°-105°. The solution treatment process includes: heating to 270-290℃ at a heating rate of 5-10℃ / min and holding at that temperature for 90-120min, then quickly removing and water cooling; The aging process includes heating to 175-195℃ at a heating rate of 3-5℃ / min and holding for 140-360 minutes, then removing and air-cooling after the holding period.

2. The magnesium-lithium alloy according to claim 1, characterized in that, The content of Li is 14.8wt%-15.5wt%; The content of Al is 3.2 wt%-4.4 wt%; The Ca content is 1.85 wt%-2.60 wt%; The total amount of impurities in the magnesium-lithium alloy is no more than 0.02 wt%.

3. The magnesium-lithium alloy according to claim 1 or 2, characterized in that, The melting and casting operation includes: melting at a temperature of 710-720℃ for 50-60 minutes under an inert atmosphere, and then pouring the mixture into a mold for cooling. The homogenization process includes: using 50-100μm pure aluminum-coated magnesium-lithium alloy ingots and holding them at 400-450℃ for 3-6 hours. The dimensions of the rod are φ30-50mm in diameter and 120-150mm in length.

4. A method for preparing a high-strength, high-ductility, high-stability, lightweight magnesium-lithium alloy, characterized in that, The preparation method includes the following steps: S1: Mix the raw materials according to the mass percentage of each component in the magnesium-lithium alloy and then melt and cast them to obtain magnesium-lithium alloy ingots. S2: Homogenize the magnesium-lithium alloy ingot of S1. S3: Obtain bar stock from the ingot of S2; S4: Place the bar from S3 into the equal channel corner extrusion die for equal channel corner extrusion; S5: Solution treatment and aging treatment are performed on the extruded bars from S4; The operation of the equal channel corner extrusion includes: first heating the bar to 200-250℃ and holding it for 40-60 minutes, then quickly taking it out and brushing it with graphite lubricant, then placing it into the equal channel corner extrusion die preheated to 120-150℃, and extruding it at an extrusion rate of 20-30 mm / s. The corner of the equal channel corner extrusion die is 90°-105°. The solution treatment process includes: heating to 270-290℃ at a heating rate of 5-10℃ / min and holding at that temperature for 90-120min, then quickly removing and water cooling; The aging process includes: heating to 175-195℃ at a heating rate of 3-5℃ / min and holding for 140-360min; after holding, removing and air cooling. The weight percentages of the components in the magnesium-lithium alloy are as follows: Li: 14.5wt%-16wt%, Al: 2.8wt%-5wt%, Ca: 1.6wt%-3wt%, with the balance being magnesium. It may or may not contain impurities, and the total amount of impurities in the magnesium-lithium alloy shall not exceed 0.1wt%. The ratio of Al to Ca is 1.7:1; The components in the magnesium-lithium alloy are introduced in the form of elemental Mg, elemental Li, Mg-Al master alloy, and Mg-Ca master alloy, respectively.

5. The preparation method according to claim 4, characterized in that, The solution treatment in S5 is carried out in a muffle furnace.

6. The preparation method according to claim 4 or 5, characterized in that, The aging process in S5 is carried out in a precision constant temperature furnace.

7. The preparation method according to claim 6, characterized in that, The melting and casting operation described in S1 includes: melting at a temperature of 710-720℃ for 50-60 minutes under an inert atmosphere, and then pouring the mixture into a mold for cooling. The homogenization operation described in S2 includes: using a 50-100μm pure aluminum-coated magnesium-lithium alloy ingot and holding it at 400-450℃ for 3-6 hours. The dimensions of the bar described in S3 are a diameter of φ30-50mm and a length of 120-150mm.

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