CN114752832B - 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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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 in strength plasticity and yield ratio, the invention prepares a 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 balance is Mg. 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 tensile strength 320.6MPa and the elongation can be obtained by the method>15% of specific strength 202kN m kg ‑1 And 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 demands of the fields of aerospace, weaponry and the like on light weight technology, structural members require alloys with high strength, and meanwhile, the alloys are required to bear high stress with a small cross-sectional area, so that the disadvantage of insufficient mechanical properties of the magnesium-lithium alloys in the prior art is highlighted, and the application demands 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: 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 3 Zn 6 Y) and W phase (Mg) 3 Zn 3 Y), the strength of the magnesium-lithium 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 magnesium alloy is very limited, a small amount of Zr can refine 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 ratio of each element of the alloy is: li:6-18%, zn:0.4-9%, 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.
The notches are inevitable because abrupt steps, holes and the like are easy to appear in structures such as metal structural parts, holes, steps and the like, can change the stress distribution state of the parts, can cause stress concentration under the condition of applying load, and cause the reduction of material strength and plasticity, and simultaneously become the origin of crack propagation. Therefore, the notch sensitivity of the alloy material plays a crucial role in the aspects of use reliability, design safety, mechanical property, 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 structural member with a specific structure cannot be ensured.
For notch strength and notch sensitivity of an alloy structure, the current research objects are mainly ductile low-ductility alloys such as nodular cast iron alloy, partial aluminum alloy or high-entropy alloy. For example, zhang et al introduced 4U-shaped notches of different notch radii for AlCoCrFeNi2.1 high entropy Alloys and found that AlCoCrFeNi2.1 Alloys were notch insensitive, unique eutectic microstructures hindered dislocation motion and delayed crack propagation, and improved tensile properties for notched samples compared to 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 "eutetic microstructure [ J ]. Journal of Alloys and sources, 863.).
Because the notch part in the bearing process of the metal alloy often becomes the origin of instability and fracture of the component 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 composition of existing magnesium-lithium alloys 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 comprises the following components in percentage by mass: li:5.0 to 8.0 percent; al:4.0 to 6.0 percent; zn:1.0-2.0%; 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 percentage, placing the mixture in a vacuum induction furnace after the mixture is prepared, vacuumizing the vacuum induction furnace to 10Pa, filling argon to the vacuum degree of 50kPa, heating the mixture to 760-800 ℃ in the argon atmosphere until the mixture is melted, keeping the temperature for 30-40 minutes, stirring and refining the mixture for 5-10min, then pouring, cooling the mixture 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 cast ingot obtained in the step (1) for 6-10h at the temperature of 300-450 ℃ in an argon atmosphere, carrying out homogenization heat treatment, then carrying out water cooling or air cooling to room temperature, then machining to remove a surface oxide layer and defects to obtain a prefabricated blank, and then carrying out large-strain rolling or upsetting-extrusion 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:1.0-2.0%; 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.
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: preheating the obtained prefabricated blank in a heat treatment furnace to 200-350 ℃, preserving heat for 1-2h, 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 for 1-3h 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.
Specifically, the extrusion in the step (2) comprises the following specific steps: and extruding the blank after upsetting at 150-300 ℃ with the extrusion ratio 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 valve seats or structural fasteners.
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 the 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 unit mass of Zn 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 elements 2 Si、Al 3 Er、Al 2 Nd and other strengthening phases with good thermal stability effectively hinder dislocation motion. In addition, the high-melting-point intermetallic compound is used as a first phase separation in the solidification process, so that nucleation particles are provided for the solidification process, a heterogeneous nucleation effect is achieved, the grains are effectively refined, and the performance indexes of high ductility, high strength and low notch sensitivity are achieved. 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, and Mg with high melting point (1048 ℃) and high hardness (460 Hv) 2 The Si strengthening phase is beneficial to improving the room temperature/high temperature performance of the alloy; a small amount of Ca is added to form an oxide film containing Ca on the surface of the melt to increase the ignition point of the magnesium alloy, and a small amount of Al 2 Ca 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, and the tensile strength 320 can be obtained by the method6MPa, elongation>15% of specific strength 202kN m kg -1 And 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 magnesium-lithium 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% Li, 5% Al, 1% Zn, 0.2% Ca, 0.8% Si, 1.0% Nd,0.2% Er, strictly controlling the impurity content, the balance 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 tensile test (refer to GB/T16865-2013 sample and method for tensile test of wrought aluminum, magnesium and alloy processing products), the magnesium-lithium alloy obtained in the embodiment has tensile strength R m =320.6MPa, elongation A =15.65%, specific strength 202kNm kg -1 The 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 comprises the following components in percentage by mass: 6% Li, 6% Al, 2% Zn, 0.2% Ca, 0.8% Si, 0.5% Nd, 0.5% Er, with strict control of impurity content and the balance 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 760 ℃ 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 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 the 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, controlling the height ratio to be 1.5 before and after upsetting, cooling to room temperature by water, then preheating to 150 ℃, controlling the temperature of the upset blank to be 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.
The magnesium-lithium alloy obtained in the example has tensile strength R after tensile test (refer to GB/T16865-2013 sample and method for tensile test of wrought aluminum, magnesium and alloy processing products thereof) m =302.2MPa, elongation a =25.20% and specific strength 192kNm kg -1 The notch tensile sensitivity coefficient was 0.858.
Example 3
The high-strength low-notch sensitivity magnesium-lithium alloy consists of the following components in percentage by mass: 7% Li, 5% Al, 1.5% Zn, 0.2% Ca, 0.2% Si, 1.5% Nd, 0.5% Er, strictly controlling the impurity content, 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: 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, preheating to 300 ℃, preserving heat for 3 hours at 300 ℃, upsetting, controlling the height ratio to be 1.2 before and after upsetting, cooling to room temperature by water, preheating to 250 ℃, controlling the temperature of the blank after upsetting to be 250 ℃ for extruding, 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 example has tensile strength R after tensile test (refer to GB/T16865-2013 sample and method for tensile test of wrought aluminum, magnesium and alloy processing products thereof) m =304.0MPa, elongation A =16.60%, specific strength 199kNm kg -1 The 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: 8% Li, 7% Al, 1% Zn, 0.5% Ca, 0.5Nd, 1.0% Er with strictly controlled impurity content and the balance 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, recharging argon to 50kPa, heating to 800 ℃ 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 heat of the high-purity magnesium-lithium alloy cast ingot obtained in the step (1) at 380 ℃ for 6h in an argon atmosphere for homogenization heat treatment, 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 tensile test (refer to GB/T16865-2013 sample and method for tensile test of wrought aluminum, magnesium and alloy processing products), the magnesium-lithium alloy obtained in the embodiment has tensile strength R m =301MPa, elongation a =23.15%, specific strength 200kNm kg -1 The notch tensile susceptibility coefficient was 0.921.
Comparative example 1
The comparative example 1 adopts a conventional AZ31B magnesium alloy, wherein the mass ratio of each component is as follows: 3% Al, 1% Zn, 0.1% Mn, strictly controlled impurity content, 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 heat until the components are melted, mechanically stirring, standing, casting and cooling to obtain an 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 1 by tensile test m =227.3MPa, elongation A =22.65% and specific strength 128kNm kg -1 The notch tensile susceptibility is 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 the smooth and notched specimens of example 1 and comparative example 1 of the present invention, with NTS (notched samples) for the notched specimen, UNTS (un-notched samples) for the smooth specimen, NTS-1 for the notched specimen of example 1, and UNTS-1 for the smooth specimen of example 1 in FIG. 4; NTS-comparative example and unt-comparative example, representing the notched and smooth specimens, respectively, of comparative example 1. In order to compare whether different materials are sensitive to notches, all notch tensile samples in the examples 1-4 of the invention adopt a 60-degree V-shaped notch mode, the radius r of the bottom of a circular arc is =0.25, and the stress concentration coefficient K corresponding to the radius r of the bottom of the circular arc is higher than that of the notch of the other materials t =3 (relating to the geometry of the material, the shape of the gap). 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; to is pairIn the proportion 1, it is obvious that the existence of the notch not only can not improve the strength of the alloy, but also can lead the alloy to fail prematurely, and the notch tensile sensitivity coefficient q is t =1.173 > 1, indicates that the material is sensitive to gaps, which are brittle, and the presence of gaps can act as origins of cracks and reduce the strength of the alloy.
For the notched and smooth specimens of the Mg-Li alloy in examples 1 to 4 of the present invention, the notched tensile sensitivity q was used t The sensitivity of the material to chipping is expressed by the value of (a) to give the formula (1):
q t ＝σ b /σ bH (1)
wherein σ b Tensile Strength, σ, for smooth specimens bH As 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 conditions t When q is t When q is less than or equal to 1, the material is not sensitive to gaps, otherwise, when q is less than or equal to 1 t When the tensile sensitivity coefficient of the notch is more than 1, the material is sensitive to the notch, and obviously, the notch sensitivity coefficient has certain practical significance for judging the notch sensitivity of the material. 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 prepared by the invention q t All 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 a tensile test on 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 t =1.173 > 1, indicating that the material is sensitive to nicks, the nicks are brittle, the presence of nicks can become the origin of cracks, reducing alloy strength, causing the alloy to fail prematurely.
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 meanwhile 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 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 (8)
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% -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 magnesium-lithium alloy is prepared by the following steps:
(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 760-800 ℃ in an 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.
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 760-800 ℃ in an 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: preserving 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 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;
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:1.0-2.0%; 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 balance is Mg.
3. The method according to claim 2, wherein the water cooling rate in the step (2) is 120 to 130 ℃/s and the air cooling rate is 20 to 30 ℃/s.
4. 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: placing the obtained prefabricated blank in a heat treatment furnace, preheating to 200-350 ℃, preserving heat for 1-2h, and carrying out large-strain rolling at 200-350 ℃, wherein the single-pass rolling reduction is 20-50%.
5. The preparation method according to claim 4, wherein the rolling in the step (2) is performed with a single-pass reduction of 30% to 50%.
6. The method according to claim 2, wherein the upsetting in the step (2) is specifically performed by: 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.
7. The preparation method according to claim 6, wherein the extrusion in the step (2) comprises the following specific steps: and extruding the blank after upsetting at 150-300 ℃ with the extrusion ratio not less than 10.
8. Use of the high strength, low notch sensitivity magnesium lithium alloy of claim 1 in the manufacture of aerospace or weapons equipment components.
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| CN1004814B (en) * | 1986-05-27 | 1989-07-19 | 北京钢铁学院 | Modified gh36 alloy contg. al and/or mg |
| JP2004323935A (en) * | 2003-04-25 | 2004-11-18 | Mitsui Mining & Smelting Co Ltd | Aluminum-coated magnesium-lithiumalloy base material, and its production method |
| AT503854B1 (en) * | 2006-05-19 | 2008-01-15 | Arc Leichtmetallkompetenzzentrum Ranshofen Gmbh | MAGNESIUM-BASED ALLOY |
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| CN104046869B (en) * | 2014-07-04 | 2016-08-17 | 重庆大学 | A kind of preparation method of magnesium Li-Si alloy |
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