CN114752832A - High-strength low-notch sensitivity magnesium-lithium alloy and preparation method and application thereof - Google Patents
High-strength low-notch sensitivity magnesium-lithium alloy and preparation method and application thereof Download PDFInfo
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- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
- C22F1/06—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of magnesium or alloys based thereon
Abstract
The invention belongs to the technical field of preparation of magnesium-lithium alloy materials, and particularly relates to a high-strength low-notch sensitivity magnesium-lithium alloy, and a preparation method and application thereof. Aiming at the problems that the magnesium-lithium alloy is low in absolute strength and difficult to well match the strong plasticity and the yield ratio, the invention prepares the high-strength low-notch sensitivity magnesium-lithium alloy by utilizing the solid solution strengthening effect of Al and Zn elements and optimizing the proportion among various alloy elements, and the high-strength low-notch sensitivity magnesium-lithium alloy consists of the following components in percentage by mass: li: 5.0 to 8.0 percent; al: 4.0 to 6.0 percent; zn: 1.0-2.0%; nd: 0.5-1.5%; er: 0.2 to 1.0 percent; si: 0.2% -1.0%; ca: 0.2 to 0.5 percent; wherein the Al/Zn value is 3-8, and the rest is Mg. The high strength low notch sensitivity of the present inventionIn the preparation method of the magnesium-lithium alloy, the plastic processing procedure is simple, the flow is short, the cost is low, the controllability is strong, the intermediate process annealing is not needed in the large-strain rolling process, and the tensile strength of 320.6MPa and the elongation can be obtained by the method>15% and a specific strength of 202 kN m kg‑1And the notch tensile sensitivity coefficient is 0.9.
Description
Technical Field
The invention belongs to the technical field of preparation of magnesium-lithium alloy materials, and particularly relates to a high-strength low-notch sensitivity magnesium-lithium alloy, and a preparation method and application thereof.
Background
The magnesium-lithium alloy is used as a metal structure material with the lowest density, can greatly reduce the weight of a component, and has high strength and good plasticity, so the magnesium-lithium alloy has wide application prospects in the fields of manned spaceflight, aviation equipment, consumer electronics, automobile industry and the like. In the prior art, the tensile strength of common magnesium-lithium alloys is mainly limited to 150-200 MPa, and with the requirements of the fields of aerospace, weaponry and the like on light weight technology, the structural members require the alloys to have high strength, and meanwhile, the alloys are required to bear higher stress with smaller cross-sectional areas, so that the disadvantage of insufficient mechanical properties of the magnesium-lithium alloys in the prior art is highlighted, and the application requirements of engineering structural materials cannot be met.
With the improvement of the mechanical properties of the magnesium-lithium alloy, many researchers introduce the quasicrystal strengthening phase in the Mg-Zn-Y alloy into the magnesium-lithium alloy for modification, for example, chinese patent with publication number CN1948532A discloses a quasicrystal phase strengthened magnesium-lithium alloy and a preparation method thereof, wherein the alloy comprises the following components by element content: li: 5.5-11.5%, Zn: 0.5-15%, Y: 0.5-8% and the rest of Mg, wherein phase I (Mg) is introduced by regulating the content ratio of Zn and Y 3Zn6Y) and W phase (Mg)3Zn3Y), lithium magnesiumThe strength of the alloy is improved.
In the patent, the rare earth elements are added into the alloy to make up the deficiency of the strength of the Mg-Li alloy, so that the high-strength rare earth magnesium-lithium alloy is obtained, but excessive addition of the rare earth elements can also cause the alloy material to generate unfavorable effects, for example, when the content of Cd is too high, a second phase in the alloy is easy to coarsen and decompose, and meanwhile, Cd also has certain toxicity and high cost, so that the economic benefit is considered to be low; the solid solubility of Zr in the magnesium alloy is very limited, a small amount of Zr can refine crystal grains, excessive Zr can cause the diffusion rate of alloy elements to be obviously reduced, and the strength and the plasticity of the alloy are greatly reduced.
Meanwhile, not only too much rare earth elements affect the alloy performance, but also the mismatching of the contents of some elements in the alloy can cause the reduction of the alloy performance, for example, chinese patent publication No. CN111235413A discloses a preparation method of a high-strength ultra-light metal material, and the mass percentages of the elements of the alloy are: li: 6-18%, Zn: 0.4 to 9%, Sm: 0.2-4.5%, Sc: 0-1.0%, and the balance of Mg and unavoidable impurities. In the patent, the alloy strength is improved by two technical means of solid solution strengthening and deformation work hardening effects of a beta-Li phase, but for the alloy with high Li content, high-content Al or Zn needs to be added at the same time for solid solution strengthening to enable the alloy performance to meet the requirements, industrial pure lithium is expensive, the alloy cost is increased by adding excessive lithium, and the metastable phase of the high-Zn alloy is easy to coarsen and decompose under the condition of medium and low temperature, so that the aging softening is easy to occur to cause the great attenuation of the alloy strength.
Since abrupt steps, holes and the like are easy to occur in structures such as metal structural members, parts, holes, steps and the like, notches cannot be avoided, stress distribution states of the parts can be changed through the notches, stress concentration can be caused under the condition of applying loads, material strength and plasticity are reduced, and the notches also become origins of crack propagation. Therefore, the notch sensitivity of the alloy material plays a crucial role in the aspects of use reliability, design safety, mechanical properties, service performance and the like of the engineering structural part.
Although the above patents improve the types and amounts of elements in the magnesium-lithium alloy, the notch strength and notch sensitivity of the magnesium-lithium alloy structure with a specific structure cannot be guaranteed.
For the notch strength and notch sensitivity of an alloy structure, the current research objects are mainly low-ductility alloys such as ductile iron alloy, partial aluminum alloy or high-entropy alloy. For example, Zhang et al introduced 4U-notches of different notch radii into AlCoCrFeNi2.1 high entropy alloy and found that AlCoCrFeNi2.1 alloy was notch insensitive, the unique eutectic microstructure hindered dislocation motion and delayed crack propagation, and the tensile properties of the notched samples improved compared to the unnotched samples (see, Wei Z A, Liang LA, Sp B, et al. the tensile property and notch sensitivity of AlCoCrFeNi2.1 high entry strain with a novel "steel-frame" experimental microstructure [ J ]. Journal of Alloys and Compounds, 863.).
Because the notch part in the bearing process of the metal alloy often becomes the origin of instability and fracture of the part structure, the performance index of a smooth sample is not enough to be considered in the performance test process, the influence of the notch on the mechanical performance of the alloy needs to be additionally considered, and the research on the low-notch sensitivity magnesium-lithium alloy is rarely reported.
Therefore, there is a need to optimize the existing magnesium-lithium alloy composition in order to improve the notch sensitivity of the alloy.
Disclosure of Invention
Aiming at the problems that the magnesium-lithium alloy is low in absolute strength and difficult to well match the strong plasticity and the yield ratio, the solid solution strengthening effect of Al and Zn elements is utilized, and the optimal proportion of various alloy elements is adopted to prepare the high-strength low-notch sensitivity magnesium-lithium alloy.
The invention also provides a preparation method of the high-strength low-notch sensitivity magnesium-lithium alloy.
The invention further provides application of the high-strength low-notch sensitivity magnesium-lithium alloy.
Based on the purpose, the invention adopts the following technical scheme:
the high-strength low-notch sensitivity magnesium-lithium alloy consists of the following components in percentage by mass: li: 5.0 to 8.0 percent; al: 4.0 to 6.0 percent; zn: 1.0-2.0%; nd: 0.5-1.5%; er: 0.2 to 1.0 percent; si: 0.2% -1.0%; ca: 0.2 to 0.5 percent; wherein the Al/Zn value is 3-8, and the rest is Mg.
A preparation method of a high-strength low-notch sensitivity magnesium-lithium alloy material adopts pure magnesium, pure lithium, pure aluminum, pure zinc and intermediate alloys of Mg-Ca, Mg-RE, Al-Si and Al-Er as raw materials and is prepared by a large strain rolling or upsetting-extruding process, and the method comprises the following steps:
(1) vacuum melting and casting: preparing the required magnesium-lithium alloy components according to the mass percent, placing the mixture in a vacuum induction furnace after the mixture is prepared, vacuumizing to 10Pa, filling argon to the vacuum degree of 50kPa, heating to 760 plus of pressure of 800 ℃ in the argon atmosphere until the mixture is melted, keeping the temperature for 30-40 minutes, stirring and refining for 5-10min, then pouring, cooling for 1-2 hours, and taking out the cast ingot to obtain a high-purity magnesium-lithium alloy cast ingot;
(2) large strain rolling or upsetting-extrusion: and (2) preserving the heat of the high-purity magnesium-lithium alloy ingot obtained in the step (1) at 300-450 ℃ for 6-10h in an argon atmosphere for homogenization heat treatment, then cooling the ingot to room temperature by water or air, then machining the ingot to remove a surface oxide layer and defects to obtain a prefabricated blank, and then performing a large-strain rolling or upsetting-extruding large-plastic deformation process to obtain the magnesium-lithium alloy material.
Specifically, the magnesium-lithium alloy material is a plate or a bar, the plate is obtained through a large strain rolling process, and the bar is obtained through an upsetting-extruding large plastic deformation process.
Specifically, the magnesium-lithium alloy in the step (1) comprises the following components in percentage by mass: li: 5.0 to 8.0 percent; al: 4.0 to 6.0 percent; zn: 1.0 to 2.0 percent; nd: 0.5-1.5%; er: 0.2 to 1.0 percent; si: 0.2% -1.0%; ca: 0.2 to 0.5 percent; wherein the Al/Zn value is 3-8, and the rest is Mg.
Specifically, the water cooling rate in the step (2) is 120-130 ℃/s, and the air cooling rate is 20-30 ℃/s.
Specifically, the large strain rolling in the step (2) comprises the following specific steps: and (3) preheating the obtained prefabricated blank to 200-350 ℃ in a heat treatment furnace, preserving heat for 1-2 hours, carrying out large-strain rolling at 200-350 ℃, wherein the single-pass reduction is 20-50%, and rolling to the required thickness by adopting one fire.
Specifically, during the rolling in the step (2), the single-pass reduction is 30-50%, and intermediate tempering is not performed between each pass.
Specifically, the total rolling reduction is controlled to be 70-80% in the rolling in the step (2).
Specifically, the upsetting in the step (2) comprises the following specific steps: placing the obtained prefabricated blank in a heat treatment furnace to preheat to 200-300 ℃, preserving heat at 200-300 ℃ for 1-3h, and then upsetting, wherein the height ratio before and after upsetting is (1.2-3): 1, cooling the mixture to room temperature by water or air, and then preheating the mixture again to 150-300 ℃ for extrusion.
Specifically, the extrusion in the step (2) comprises the following specific steps: and extruding the upset blank at 150-300 ℃, wherein the extrusion ratio is not less than 10.
The high-strength low-notch sensitivity magnesium-lithium alloy is applied to preparation of aerospace parts or weapon equipment parts.
In particular, when applied, the high-strength low-notch sensitivity magnesium-lithium alloy is used for preparing a valve seat or a structural fastener.
Compared with the prior art, the invention has the following beneficial effects:
1. according to the high-strength low-notch sensitivity magnesium-lithium alloy, Al and Zn are added into a binary magnesium-lithium alloy simultaneously, the advantages of the binary magnesium-lithium alloy can be fully exerted, the alloy strength is improved along with the increase of the contents of the Al and the Zn, the strengthening effect of the Zn in unit mass is not as good as that of the Al, the density of the Zn is greater than that of the Al, the content of the Zn is not too large in order to ensure the low density of the magnesium-lithium alloy, and the Al/Zn value is controlled to be about 3-8 in a comprehensive consideration. On the basis of Mg-Li-Al-Zn alloy, Mg is formed by regulating and controlling the contents of trace elements Si, Ca, Er and Nd rare earth elements2Si、Al3Er、Al2Nd and other strengthening phases with good thermal stability effectively hinder dislocation motion. In addition, the refractory metal is present during solidificationThe intermediate compound is used as a first phase separation to provide nucleation particles for the solidification process, plays a role in heterogeneous nucleation, effectively refines grains and achieves the performance indexes of high ductility, high strength and low notch sensitivity. The addition of Si and Ca can effectively refine grains, a small amount of Si and Ca can jointly refine, not only does not damage the ductility of the alloy, but also effectively refine grains, Mg with high melting point (1048 ℃) and high hardness (460Hv) 2Si strengthening phase, which is helpful for improving the room temperature/high temperature performance of the alloy; the addition of a small amount of Ca can form an oxide film containing Ca on the surface of the melt to improve the ignition point of the magnesium alloy, and the addition of a small amount of Al2Ca does not aggregate at grain boundaries; after quenching and quenching of the rare earth element Nd, the solid solution strengthening effect of the matrix can be greatly improved; the addition of the Er element can effectively prevent the diffusion rate of Li, Zn and Al elements and slow down the low-temperature aging softening of the alloy.
2. In the preparation method of the high-strength low-notch sensitivity magnesium-lithium alloy, the plastic processing procedure is simple, the flow is short, the cost is low, the controllability is strong, the intermediate process annealing is not needed in the large-strain rolling process, the yield is high, the economy is strong, the tensile strength 320.6MPa and the elongation can be obtained by the method>15% of specific strength 202kN m kg-1And the notch tensile sensitivity coefficient qt is 0.9.
3. For the aerospace field, structural fasteners are in great demand and have high requirements on quality. The quality of the structural fastener may relate to the operation of a satellite or the use of an instrument, and the alloy prepared by the invention not only meets the requirement of light weight, but also has high strength and low notch sensitivity, can meet the requirement of smaller section strength, is safe and reliable as a structural member, and can greatly reduce the self weight of the structural member.
The method has the advantages of simple process, easy operation, low and controllable production cost and good practical application prospect in the field of new aerospace materials.
Drawings
FIG. 1 is a metallographic structure diagram of a magnesium-lithium alloy prepared in example 1 of the present invention after homogenization;
FIG. 2 is a rolled metallographic structure of a Mg-Li alloy prepared in example 1 of the present invention;
FIG. 3 is a diagram of room temperature notched tensile specimens made from the alloys of examples 1-4 of the present invention;
FIG. 4 is a graph of room temperature stress-strain curves for smooth and notched specimens of example 1 and comparative example 1 in accordance with the present invention;
FIG. 5 is a structural fastener made using the magnesium lithium alloy of the present invention.
Detailed Description
In order to make the objects, technical solutions and effects of the present invention clearer and clearer, the present invention is described in further detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. The raw materials used in the following examples are all common commercial products.
Example 1
The high-strength low-notch sensitivity magnesium-lithium alloy comprises the following components in percentage by mass: 5% of Li, 5% of Al, 1% of Zn, 0.2% of Ca, 0.8% of Si, 1.0% of Nd and 0.2% of Er, wherein the impurity content is strictly controlled, and the balance is Mg.
The preparation method of the high-strength low-notch sensitivity magnesium-lithium alloy adopts pure magnesium, pure lithium, pure aluminum, pure zinc and intermediate alloys of Mg-Ca, Mg-RE, Al-Si and Al-Er as raw materials and is prepared by vacuum melting, casting and large-strain rolling processes, and comprises the following specific steps:
(1) vacuum melting and casting: proportioning the magnesium-lithium alloy elements according to the proportion, placing the mixture in a vacuum induction furnace after proportioning, vacuumizing to 10Pa, filling argon to 50kPa, heating to 780 ℃ in argon atmosphere until the mixture is melted, keeping the temperature for 30 minutes, stirring and refining for 5min, then pouring, cooling for 2 hours, and taking out the cast ingot to obtain a high-purity magnesium-lithium alloy cast ingot;
(2) prefabricating a blank: preserving the heat of the high-purity magnesium-lithium alloy cast ingot obtained in the step (1) at 400 ℃ for 6h in an argon atmosphere for homogenization heat treatment, cooling to room temperature at a cooling rate of 130 ℃/s, and then machining (turning) to remove a surface oxide layer and defects to obtain a pre-rolled blank;
(3) rolling under large strain: and (3) placing the pre-rolled blank obtained in the step (2) in a heat treatment furnace to preheat to 300 ℃, preserving heat for 2 hours at 300 ℃, wherein the single-pass reduction is 30-50%, then rolling to a magnesium-lithium alloy plate with the required thickness by adopting one fire, and the furnace returning heating is not carried out in the rolling process, and the total reduction of the plate is controlled to be about 70-80%.
After a tensile test (refer to GB/T16865-m320.6MPa, elongation A15.65% and specific strength 202kNm kg-1The notch tensile susceptibility coefficient was 0.9.
FIG. 1 is a structural diagram of the alloy after homogenization at 400 ℃ in step (2) of example 1, and it can be observed that part of the second phase is dissolved in the matrix, the network structure at the grain boundary disappears, the non-equilibrium state of the as-cast structure is eliminated, the total subsequent cold working rate of the alloy can be improved, and the number of times and time of intermediate annealing can be reduced.
FIG. 2 is a structural diagram of the alloy after rolling in step (3) of example 1, and it can be seen that the structure is elongated in the rolling direction, and the second phase in the alloy is newly precipitated and distributed in streamline in the rolling direction.
Example 2
The high-strength low-notch sensitivity magnesium-lithium alloy consists of the following components in percentage by mass: 6 percent of Li, 6 percent of Al, 2 percent of Zn, 0.2 percent of Ca, 0.8 percent of Si, 0.5 percent of Nd and 0.5 percent of Er, strictly controlling the content of impurities and the balance being Mg.
The preparation method of the high-strength low-notch sensitivity magnesium-lithium alloy adopts pure magnesium, pure lithium, pure aluminum, pure zinc and intermediate alloys of Mg-Ca, Mg-RE, Al-Si and Al-Er as raw materials and comprises the following steps of vacuum melting, casting and upsetting-extruding:
(1) Vacuum melting and casting: preparing materials according to the magnesium-lithium alloy element proportion, placing the materials in a vacuum induction furnace after the materials are prepared, vacuumizing the vacuum induction furnace to 10Pa, filling argon to the vacuum degree of 50kPa, heating the materials to 760 ℃ in the argon atmosphere until the materials are molten, keeping the temperature for 30 minutes, stirring and refining the materials for 5 minutes, then pouring the materials, cooling the materials for about 2 hours, and taking out the materials for ingot casting to obtain a high-purity magnesium-lithium alloy ingot casting;
(2) prefabricating a blank: preserving the heat of the high-purity magnesium-lithium alloy cast ingot obtained in the step (1) at 400 ℃ for 6 hours in an argon atmosphere for homogenization heat treatment, air-cooling to room temperature at a cooling rate of 30 ℃/s, and then machining to remove a surface oxide layer and defects to obtain a prefabricated upsetting-extruding blank;
(3) upsetting-extruding: and (3) placing the prefabricated upsetting-extruding blank obtained in the step (2) in a heat treatment furnace, preheating to 300 ℃, preserving heat for 3 hours at 300 ℃, upsetting, wherein the height ratio before and after upsetting is 1.5, cooling to room temperature by water, then preheating to 150 ℃, controlling the temperature of the upset blank to 150 ℃ for extruding, wherein the extrusion ratio is not less than 10, and finally obtaining the magnesium-lithium alloy extruded bar with the required diameter.
After a tensile test (refer to GB/T16865- m302.2MPa, elongation A25.20% and specific strength 192kNm kg-1The notch elongation coefficient of sensitivity was 0.858.
Example 3
The high-strength low-notch sensitivity magnesium-lithium alloy comprises the following components in percentage by mass: 7% of Li, 5% of Al, 1.5% of Zn, 0.2% of Ca, 0.2% of Si, 1.5% of Nd and 0.5% of Er, strictly controlling the impurity content, and the balance being Mg.
The preparation method of the high-strength low-notch sensitivity magnesium-lithium alloy adopts pure magnesium, pure lithium, pure aluminum, pure zinc and intermediate alloys of Mg-Ca, Mg-RE, Al-Si and Al-Er as raw materials and carries out the preparation by vacuum melting and casting, upsetting and extruding processes, and comprises the following specific steps:
(1) vacuum melting and casting: proportioning the magnesium-lithium alloy elements according to the proportion, placing the mixture in a vacuum induction furnace after proportioning, vacuumizing to 10Pa, filling argon to 50kPa, heating to 780 ℃ in argon atmosphere until the mixture is melted, keeping the temperature for 30 minutes, stirring and refining for 5min, then pouring, cooling for about 2 hours, and taking out the cast ingot to obtain a high-purity magnesium-lithium alloy cast ingot;
(2) prefabricating a blank: preserving the temperature of the high-purity magnesium-lithium alloy cast ingot obtained in the step (1) at 380 ℃ for 10h in an argon atmosphere for homogenization heat treatment, cooling to room temperature at a cooling rate of about 30 ℃/s, and then machining to remove a surface oxide layer and defects to obtain a prefabricated upsetting-extruding blank;
(3) Upsetting-extruding: and (3) placing the prefabricated upsetting-extruding blank obtained in the step (2) in a heat treatment furnace to preheat to 300 ℃, preserving heat for 3 hours at 300 ℃, upsetting, wherein the height ratio before and after upsetting is 1.2, cooling the blank by water to room temperature, then preheating to 250 ℃, controlling the temperature of the blank after upsetting to 250 ℃ to extrude, wherein the extrusion ratio is not less than 10, and finally obtaining the magnesium-lithium alloy extruded bar with the required diameter.
The magnesium-lithium alloy obtained in the embodiment has tensile strength R after tensile test (refer to GB/T16865-m304.0MPa, elongation A16.60%, specific strength 199kNm kg-1The notch tensile susceptibility coefficient was 0.861.
Example 4
The high-strength low-notch sensitivity magnesium-lithium alloy comprises the following components in percentage by mass: the impurity content is strictly controlled by 8 percent of Li, 7 percent of Al, 1 percent of Zn, 0.5 percent of Ca, 0.5Nd and 1.0 percent of Er, and the balance is Mg.
The preparation method of the high-strength low-notch sensitivity magnesium-lithium alloy adopts pure magnesium, pure lithium, pure aluminum, pure zinc and intermediate alloys of Mg-Ca, Mg-RE, Al-Si and Al-Er as raw materials and is prepared by vacuum melting, casting and large-strain rolling processes, and comprises the following specific steps:
(1) Vacuum melting and casting: preparing materials according to the magnesium-lithium alloy element proportion, placing the materials in a vacuum induction furnace after the materials are prepared, vacuumizing to 10Pa, recharging argon to the vacuum degree of 50kPa, heating to 800 ℃ in the argon atmosphere until the materials are molten, keeping the temperature for 30 minutes, stirring and refining for 5 minutes, then pouring, cooling for about 2 hours, and taking out the cast ingot to obtain a high-purity magnesium-lithium alloy cast ingot;
(2) prefabricating a blank: preserving the temperature of the high-purity magnesium-lithium alloy cast ingot obtained in the step (1) at 380 ℃ for 6 hours in an argon atmosphere to carry out homogenization heat treatment, then cooling to room temperature at a cooling rate of about 130 ℃/s, and then machining (turning) to remove a surface oxide layer and defects to obtain a pre-rolled blank;
(3) rolling under large strain: and (3) placing the pre-rolled blank obtained in the step (2) in a heat treatment furnace to preheat to 250 ℃, preserving heat for 2 hours at 250 ℃, wherein the single-pass reduction is 30-40%, then rolling the pre-rolled blank to a magnesium-lithium alloy plate with the required thickness by using one fire, wherein the furnace returning heating is not carried out in the rolling process, and the total reduction of the plate is controlled to be about 70-80%.
After a tensile test (refer to GB/T16865- m301MPa, elongation A23.15%, specific strength 200kNm kg-1The notch tensile susceptibility coefficient was 0.921.
Comparative example 1
Comparative example 1 adopts a conventional magnesium alloy with the mark AZ31B, wherein the mass ratio of each component is as follows: 3% of Al, 1% of Zn and 0.1% of Mn, strictly controlling the impurity content, and the balance being Mg.
The preparation method of the magnesium-lithium alloy in the comparative example 1 comprises the following specific steps:
(1) preparing materials: proportioning the components according to the element proportion of the AZ31B magnesium alloy, heating to 760-850 ℃ under the protection atmosphere of SF6, preserving the heat until the components are melted, mechanically stirring, standing, casting and cooling to obtain a cast ingot;
(2) and (3) heat treatment: placing the cast ingot in the step (1) in a table furnace, and preserving heat for 12 hours at 415 ℃ to obtain an as-cast plate;
(3) rolling: and (3) rolling the cast plate after keeping the temperature of 350 ℃ for 1h, reducing the annealing times on the premise of not cracking, and reducing the annealing temperature until the required thickness is rolled.
Tensile Strength R of the alloy obtained in comparative example 1m227.3MPa, elongation A22.65% and specific strength 128kNm kg-1The notch tensile sensitivity coefficient was 1.173.
In order to examine notch sensitivity of the magnesium-lithium alloys prepared in examples 1 to 4 of the present invention, notch samples were formed by introducing a V-shaped notch (as shown in FIG. 3) having an angle of 60 degrees into the magnesium-lithium alloys prepared in examples 1 to 4 by machining to a depth of 1mm, thereby obtaining smooth samples having no notch and notched samples having notches, and mechanical properties of the alloys were tested (refer to HB 5214-96 "Metal Room temperature notch tensile test method")
FIG. 4 is a graph of room temperature stress-strain curves for smooth and notched samples of example 1 and comparative example 1 of the present invention, where NTS (notched samples) in FIG. 4 represents notched samples, UNTS (un-notched samples) represents smooth samples, NTS-1 represents notched samples of example 1, and UNTS-1 represents smooth samples of example 1; NTS-comparative and UNTS-comparative, respectively, representing the notched and smooth specimens of comparative example 1. In order to compare whether different materials are sensitive to notches, all notch tensile samples in the examples 1 to 4 adopt a 60-degree V-shaped notch mode, the radius r of the circular arc bottom is 0.25, and the stress concentration coefficient K corresponding to the radius r is corresponding to the radius rt3 (related to the geometry of the material, the shape of the indentation). FIG. 4 shows that for example 1, the alloy is not notch sensitive because the notch is present, the strength of the material is strengthened, the material does not fail prematurely, and the material has certain ductility; in comparative example 1, it is evident that the existence of the notch does not improve the strength of the alloy but causes the alloy to fail prematurely, and the notch tensile sensitivity coefficient q ist1.173 > 1, indicates that the material is sensitive to nicks, which are brittle, and the presence of nicks can become the origin of cracks, reducing alloy strength.
For the notched samples and the smooth samples of the Mg-Li alloy in the embodiments 1-4 of the present invention, the notched tensile sensitivity coefficient q is usedtRepresents the sensitivity of the material to chipping, resulting in equation (1):
qt＝σb/σbH (1)
wherein σbTensile Strength, σ, for smooth specimensbHAs the tensile strength of the notched specimens, the ratio q of the tensile strength of the smooth specimens to that of the notched specimens was measured under the same measurement conditionstWhen q istWhen q is less than or equal to 1, the material is not sensitive to gaps, otherwise, when q is less than or equal to 1tWhen the stress is more than 1, the material is sensitive to gaps, and obviously, the sensitivity coefficient of the gaps is used for judgingThe sensitivity of the broken material gap has certain practical significance. The larger the value, the more sensitive the material is to chipping and vice versa. The test results are shown in table 1.
Table 1 summarizes the properties of examples 1-4 and the comparative examples.
As can be seen from the data in Table 1, the high-strength low-notch-sensitivity magnesium-lithium alloy, q, prepared by the method of the inventiontAll are less than 1, the mechanical properties such as tensile strength and the like of the notch sample are all strengthened, and meanwhile, the specific strength is also strengthened, thus proving that the alloy is not sensitive to notches.
Through the tensile test of the AZ31B alloy in the comparative example 1, the alloy strength and the elongation are greatly reduced, and the notch tensile sensitivity coefficient q is found t1.173 > 1, indicating that the material is susceptible to chipping, which is brittle, and the presence of chipping can act as a source of cracking, reducing alloy strength and causing premature alloy failure.
In conclusion, the alloy designed by the invention not only has high strength and high ductility, but also has low notch tensile sensitivity coefficient, namely is insensitive to notches.
Application example 1
The valve seat, the structural fastener and the like used in the fields of aerospace, weaponry and the like need to have higher strength and lighter weight, and simultaneously need to have lower notch sensitivity, and the high-strength low-notch-sensitivity magnesium-lithium alloy obtained in the embodiment 1 of the invention is used as the structural fastener (as shown in fig. 5), so that the light metal structural fastener with high strength of 320.6MPa and low notch sensitivity, namely the notch tensile sensitivity coefficient of 0.9 can be obtained, and the requirement of the structural fastener on strength by a smaller cross section can be met.
While specific embodiments of the present invention have been described above, it should be understood that the present invention is not limited to the specific embodiments described above. Various changes or modifications may be made by those skilled in the art within the scope of the claims without departing from the spirit of the invention.
Claims (9)
1. The high-strength low-notch sensitivity magnesium-lithium alloy is characterized by comprising the following components in percentage by mass: li: 5.0 to 8.0 percent; al: 4.0 to 6.0 percent; zn: 1.0-2.0%; nd: 0.5-1.5%; er: 0.2 to 1.0 percent; si: 0.2 to 1.0 percent; ca: 0.2 to 0.5 percent; wherein the Al/Zn value is 3-8, and the rest is Mg.
2. The preparation method of the high-strength low-notch sensitivity magnesium-lithium alloy material is characterized by comprising the following steps of:
(1) vacuum melting and casting: preparing the required magnesium-lithium alloy components according to the mass percentage, after the materials are prepared, vacuumizing, filling argon, heating to 760 plus 800 ℃ in the argon atmosphere until the materials are molten, keeping the temperature for 30-40 minutes, stirring and refining for 5-10min, then pouring, cooling for 1-2 hours, and taking out the cast ingot to obtain a high-purity magnesium-lithium alloy cast ingot;
(2) large strain rolling or upsetting-extrusion: and (2) carrying out heat preservation on the high-purity magnesium-lithium alloy cast ingot obtained in the step (1) for 6-10h in an argon atmosphere at the temperature of 300-450 ℃, carrying out homogenization heat treatment, then carrying out water cooling or air cooling to room temperature to obtain a prefabricated blank, and then carrying out large-strain rolling or upsetting-extruding process to obtain the magnesium-lithium alloy material.
3. The preparation method according to claim 2, wherein the magnesium-lithium alloy in the step (1) comprises the following components in percentage by mass: li: 5.0 to 8.0 percent; al: 4.0 to 6.0 percent; zn: 1.0 to 2.0 percent; nd: 0.5-1.5%; er: 0.2 to 1.0 percent; si: 0.2% -1.0%; ca: 0.2 to 0.5 percent; wherein the Al/Zn value is 3-8, and the rest is Mg.
4. The method as claimed in claim 2, wherein the water cooling rate in step (2) is 120 ℃ C./s and the air cooling rate is 20-30 ℃ C./s.
5. The preparation method according to claim 2, characterized in that the specific steps of the large strain rolling in the step (2) are as follows: and (3) preheating the obtained prefabricated blank in a heat treatment furnace to 200-350 ℃, preserving heat for 1-2 hours, and carrying out large strain rolling at 200-350 ℃, wherein the single-pass rolling reduction is 20-50%.
6. The preparation method according to claim 5, wherein the rolling in the step (2) is performed with a single-pass reduction of 30-50%.
7. The method according to claim 2, wherein the upsetting in the step (2) comprises the following steps: placing the obtained prefabricated blank in a heat treatment furnace, preheating to 200-300 ℃, preserving heat for 1-3 hours at 200-300 ℃, and then upsetting, wherein the height ratio before and after upsetting is (1.2-3): 1, cooling the mixture to room temperature by water or air, and then preheating the mixture again to 150-300 ℃ for extrusion.
8. The preparation method according to claim 7, wherein the extrusion in the step (2) comprises the following specific steps: and extruding the upset blank at 150-300 ℃, wherein the extrusion ratio is not less than 10.
9. Use of the high strength low notch sensitivity magnesium-lithium alloy of claim 1 in the manufacture of aerospace or weaponry components.
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