CN115652156B - Mg-Gd-Li-Y-Al alloy and preparation method thereof - Google Patents
Mg-Gd-Li-Y-Al alloy and preparation method thereof Download PDFInfo
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Abstract
The application relates to the technical field of metal materials, in particular to a Mg-Gd-Li-Y-Al alloy and a preparation method thereof. The alloy comprises the following chemical components in percentage by mass: gd:3.00 to 6.00wt.%; y:0.5-1.5wt.%; li:0 to 5.3wt.%, but excluding 0 and 5.3; al:0.6 to 2wt.%; zr:0 to 0.1wt.%; the balance being Mg and unavoidable impurities. The preparation method of the alloy comprises the steps of centrifugally casting a melt of a metal raw material, cooling and forming in a sub-rapid solidification mode, and combining the advantages of centrifugal casting and sub-rapid solidification, the gravity segregation problem of light elements Li, heavy elements Gd and Y in the alloy can be effectively inhibited, and the obtained magnesium alloy has primary crystal alpha-Mg phase with the grain diameter of 4-18 mu m, secondary dendrite spacing of 1.3-4.6 mu m and secondary phase Al 2 The (Gd, Y) phase reaches nano-scale 80-200nm and is uniformly dispersed and distributed, mg 3 The thickness of the (Gd, Y) phase is less than 700nm, and the comprehensive compression mechanical property of the alloy is obviously improved. The alloy has the compression strength of 401-490MPa, the yield strength of 121-150MPa, the fracture compression ratio of 14.9-25.0% and the density of 1.40-1.62g/cm 3 The elastic modulus is 51.1-53.3GPa.
Description
Technical Field
The application relates to the technical field of metal materials, in particular to a Mg-Gd-Li-Y-Al alloy and a preparation method thereof.
Background
Light structural materials have important requirements in the automotive and aerospace industries, pushing the development of processing techniques including extrusion, welding and casting processes for aluminum and magnesium alloys. In the field of metal materials, magnesium alloys are the lightest engineering construction materials with a specific gravity of 1.7g/cm 3 About 2/3 of the aluminum alloy, 1/3 of the zinc alloy, and 1/4 of the steel, the magnesium alloy has a significant advantage of being difficult to replace in terms of weight saving.
The magnesium-lithium base alloy is a newly developed metal engineering material with the lowest density, and the density is 15-25% lower than that of the common magnesium alloy and about 50% lower than that of the aluminum alloy. The method comprisesThe alloy has high specific strength, high specific elastic modulus, good electromagnetic shielding performance and damping performance, and is an ideal material in the fields of weapons, aerospace, automobiles, electronics and the like. The crystal structure of Mg-Li binary alloys depends on the Li element addition concentration, and when the Li element concentration increases to about 5.3wt%, the structure of the alloy begins to change from hexagonal close-packed (HCP) α -Mg to Body Centered Cubic (BCC) β -Li. The presence of beta-Li can greatly improve the deformability of the Mg-Li alloy, but the strength of the alloy is lower, and the ageing strengthening effect is not obvious. This is because of the metastable reinforcing phase MgAlLi 2 And MgLi 2 Zn exists in Mg-Li-Al and Mg-Li-Zn, respectively. In Mg-Li-Al alloy, metastable strengthening phase MgAlLi 2 Decomposing into AlLi at 50-70 deg.C, belonging to softening phase. With the increase of the lithium content in the alloy, the softening phenomenon becomes serious, and the softening temperature is always lower than that of the common magnesium alloy. Along with the development of science and technology, the speed of aerospace and transportation means is higher and higher, the required power is also higher and higher, and the components are required to have stronger stability, reliability and heat resistance, so that higher requirements on the strength, the elastic deformation resistance, the toughness and the like of the magnesium-lithium alloy are provided.
However, the magnesium-lithium alloy has the defects of insufficient strength, low elastic modulus and poor thermal stability, and is difficult to reach the use standard of part equipment in the fields of aerospace, traffic and ocean, and in addition, the cost of the magnesium-lithium alloy is increased due to the fact that a large amount of Li element is added, so that the expansion of the application of the magnesium-lithium alloy in the high-tech field is limited. Therefore, developing high strength and elastic modulus and reducing the cost of the alloy are important directions for the development of magnesium alloys.
Disclosure of Invention
The first technical problem to be solved by the present application is to provide an Mg-Gd-Li-Y-Al alloy with high compressive strength, high rigidity and plasticity against the current state of the art.
The second technical problem to be solved by the application is to provide a preparation method of the alloy aiming at the current state of the art, the gravity segregation behavior of light elements Li, heavy elements Gd and Y in the alloy is overcome by utilizing the advantages of vacuum centrifugal casting and sub-rapid solidification, and subsequent machining and heat treatment processes are not needed, so that the magnesium alloy with high compressive strength and plasticity can be obtained, the processing flow is shortened, the production cost is reduced, and the production efficiency is improved.
The strength of the dual-phase Mg-Li alloy is lower and the strength of the reinforced phase MgAlLi is lower 2 Belongs to a softening phase, so that the compression strength and the rigidity of the existing biphase Mg-Li alloy are low. The application obtains alpha-Mg single-phase magnesium alloy by reducing Li content and forms second phase Mg by adding Gd, Y and Al elements 3 (Gd, Y) and Al 2 The high temperature resistant phase and the hardening phase of (Gd, Y), alLi and the like obviously improve the compression strength and the rigidity of the alloy. Meanwhile, the alloy enables the alpha-Mg single-phase magnesium alloy to inherit the high plasticity of the double-phase Mg-Li alloy through centrifugal casting and a sub-rapid solidification phase bonding technology.
Conventional casting process Al 2 (Gd, Y) compatible and liable to be biased near the grain boundary, resulting in Al 2 The (Gd, Y) phase is very coarse, even up to tens of microns, and the alloy compressive strength is very detrimental and cannot be solutionized into the grain interior during subsequent heat treatment. The method obviously refines the Al through the centrifugal casting combined with the sub-rapid solidification preparation method 2 The (Gd, Y) phase and its dispersed distribution are important for stabilizing the grain size in the subsequent heat treatment.
The technical scheme adopted for solving the technical problems is as follows:
in a first aspect, the application provides an Mg-Gd-Li-Y-Al alloy, which comprises the following chemical components in percentage by mass: gd:3.00 to 6.00wt.%; y:0.5-1.5wt.%; li:0 to 5.3wt.%, but excluding 0 and 5.3; al:0.6 to 2wt.%; zr:0 to 0.1wt.%; the balance Mg and unavoidable impurities, wherein the impurity content is less than 0.048wt.%.
Preferably, the alloy comprises the following components in percentage by mass: gd:3.00 to 6.00wt.%; y:0.6-1.5wt.%; li:1 to 5.3wt.%, including 1 but not including 5.3; al: 0.1-2 wt.%; zr:0 to 0.1wt.%; the balance Mg and unavoidable impurities, wherein the impurity content is less than 0.048wt.%.
According to the technical scheme of the application, the magnesium with high strength, high rigidity and plasticity is obtained by utilizing the content and the proportion of each element in the alloyAn alloy; the design of the addition content of the Li element and the combination synergy of other alloy elements are the precondition of ensuring that the magnesium-lithium alloy obtains stronger specific strength and specific rigidity and meets the current requirement of light weight. The design of the addition content of Li element ensures that the alloy matrix is in an alpha-Mg single-phase region, so that the alloy has higher compression strength and compression plasticity; the addition of Gd, Y and Al elements produces a second phase Mg 3 (Gd, Y) and Al 2 The (Gd, Y) phase and the AlLi phase ensure that the magnesium-lithium alloy has high compression strength and high rigidity; the addition of Zr element can refine the crystal grain of the magnesium alloy.
The alloy is in an alpha-Mg single-phase region through the content design of Li element, and the cast structure comprises primary crystal alpha-Mg phase and grain boundary second phase Mg 3 (Gd, Y) and Al 2 (Gd, Y) phase, alLi phase.
Preferably, the grain size of the alpha-Mg phase is 4-18 mu m, and the volume fraction is 89% -94.8%; mg of 3 The thickness of the (Gd, Y) phase is less than 700nm, and the volume fraction is 5-10%; al (Al) 2 The size of the (Gd, Y) phase is 80-200nm, the volume fraction is 0.2% -1%, and the secondary dendrite spacing is 1.3-4.6 μm.
Preferably, by reasonably designing components and selecting a preparation method, the performance of the Mg-Gd-Li-Y-Al alloy meets the following conditions: the compression strength is 401-490MPa, the yield strength is 121-150MPa, the fracture compression ratio is 14.9-25.0%, and the density is 1.40-1.62g/cm 3 The elastic modulus is 51.1-53.3GPa.
In a second aspect, the present application provides a method for preparing the above Mg-Gd-Li-Y-Al alloy, the method comprising the steps of: and (3) centrifugally casting the melt of the metal raw material, and cooling and forming in a sub-rapid solidification mode.
According to the technical scheme, the molten metal is rapidly cooled and molded in a sub-rapid solidification mode in the centrifugal casting process, and the centrifugal casting can remarkably improve the segregation problem of light elements Li, heavy elements Gd and Y in the alloy caused by the gravity problem, so that the elements are uniformly dispersed and distributed; the sub-rapid solidification increases the supercooling degree of the molten metal, refines crystal grains, dendrites and eutectic phases of the alloy, improves the solid solubility of alloy elements, is beneficial to obtaining a small amount of second phase and dispersed alloy structure, and is beneficial to improving the mechanical property and the compression ratio of the alloy.
The technology combining centrifugal casting and sub-rapid can obviously reduce gravity segregation behaviors of light element Li and heavy element Gd and Y, and can refine grains to improve the compression strength, rigidity and plasticity of the Mg-Gd-Li-Y-Al alloy. In addition, the technology of combining centrifugal casting and sub-rapid can refine the second phase to further improve the compression strength and compression plasticity of the alloy, so that the nano-grade Al 2 The (Gd, Y) phase functions to strengthen and stabilize grain boundaries more effectively.
Further, the method also comprises a preparation step of raw materials, and specifically comprises the following steps:
s11, calculating and weighing the required metal raw materials according to the components; the feedstock may be a single metal feedstock or a master alloy;
s12, preheating the metal raw materials weighed in the step S11, and then mixing the raw materials under a protective atmosphere, and carrying out vacuum melting and casting to obtain a master alloy ingot;
s13, placing the master alloy ingot obtained in the step S12 into a crucible, vacuumizing and introducing inert gas for protection, wherein the vacuum degree is 10 -1 -10 -3 Pa, the smelting temperature is 740-800 ℃, and the temperature is kept for 2-40min to enable the raw materials to be fully melted.
Further, in the method, the centrifugal casting process includes the steps of:
s21, under a protective atmosphere, the vacuum centrifugal rotating speed is 100-1200r/min, and after the raw materials in S13 are completely melted, the temperature is reduced to 720 ℃, standing and heat preservation are carried out for 20-30 minutes, so that uniform diffusion of each element in the molten metal and full separation of impurities are ensured;
s22, vacuum centrifugal casting is carried out, the casting temperature is 670-720 ℃, and the molten metal is rapidly cooled and molded in a sub-rapid solidification mode after casting.
Further, the sub-rapid solidification can be achieved in a variety of ways: such as water-cooled copper mold, strip casting, die casting, coarse powder atomization, spray forming, semi-solid casting laser surface melting, ion surface melting, atomization deposition, etc.
To further refine the groupThe method reduces segregation, further improves the compression performance of the prepared magnesium alloy, and limits the cooling rate of sub-rapid solidification to 1.0 multiplied by 10 2 -4.0×10 2 ℃/s。
The beneficial effects of this application lie in:
1. li elements are lighter and typically float above the melt during smelting resulting in severe composition segregation. And Gd and Y elements are heavier and typically sink to the bottom of the melt during smelting, resulting in severe composition segregation. In order to prevent gravity segregation, the invention designs a method for combining vacuum centrifugal casting and sub-rapid solidification phase, and successfully overcomes the gravity segregation of three elements;
2. gd, li, Y and Al are added into the alloy system, so that the advantages of the Mg-RE alloy and the advantages of the Mg-Li alloy system are effectively combined, the characteristics of high strength and high temperature resistance of the Mg-RE alloy are inherited, the alloy density is effectively reduced by virtue of the characteristic of low Li density, the alloy rigidity is improved, and the development direction of the magnesium alloy high-strength light alloy is met. The Mg-Gd-Li-Y-Al alloy system designed by the invention controls the content of Li to be less than 5.3wt.%, and reduces the loss of Li element in the preparation process, thereby reducing the cost of the alloy and obtaining the alpha-Mg single-phase magnesium alloy. The alloy overcomes the defect of low strength of the dual-phase alloy, and inherits the characteristic of high plasticity of the dual-phase Mg-Li alloy through a refined structure;
3、Al 2 the (Gd, Y) phase is an important grain refiner in magnesium alloy and plays a role in stabilizing grain boundary, plays an important role in preventing grain growth in subsequent heat treatment of the alloy, but traditional casting alloy tends to be enriched to form Al in the order of several microns or even tens of microns due to component segregation 2 The (Gd, Y) phase ensures that the addition of Al element has a harmful effect, but the centrifugal casting and the sub-rapid solidification of the invention can effectively reduce the component segregation and effectively refine the Al 2 (Gd, Y) phase to a size on the order of nanometers;
4. the invention adopts alloying, combines the advantages of centrifugal casting and sub-rapid solidification to prepare the alloy, does not need to improve the mechanical property of the alloy through deformation hardening and subsequent heat treatment, solves the problems of more process steps and low production efficiency of the traditional alloy preparation method, and saves the process cost;
5. the magnesium alloy material with high strength and rigidity and the preparation method thereof provided by the invention widen the industrialized production of the high-strength magnesium alloy.
Drawings
FIG. 1 is a metallographic structure diagram of an as-cast Mg-Gd-Li-Y-Al alloy after sub-rapid solidification in example 1 of the present application;
FIG. 2 is an electronically scanned back-scattered texture map of as-cast Mg-Gd-Li-Y-Al alloy after sub-rapid solidification in example 1 of the present application;
FIG. 3 is a compressive stress-strain curve of an as-cast Mg-Gd-Li-Y-Al alloy after sub-rapid solidification in example 1 of the present application.
Description of the embodiments
The technical features and advantages of the present application will be described in more detail below with reference to examples and comparative examples so that the advantages and features of the present application can be more easily understood by those skilled in the art, thereby making clear and defining the scope of the present invention.
Comparative example 1
The Mg-Gd-Li-Y-Al alloy comprises the following elements in percentage by mass: gd 4.60%, li 4.30%, Y1.00%, al 0.60%, zr less than 0.1%, and the balance Mg. The preparation method of the alloy comprises the following steps:
step one: the raw materials adopt industrial pure magnesium, industrial pure Li, al-Zr intermediate alloy, mg-Gd intermediate alloy and Mg-Y intermediate alloy, and the mass of the required raw materials is calculated and weighed according to the components;
step two: mixing the raw materials, placing the mixture into a graphite crucible, vacuumizing, filling argon, and carrying out vacuum melting and casting by adopting electromagnetic induction heating to obtain a master alloy ingot;
step three: crushing the master alloy ingot obtained in the second step, weighing 40g, putting into a graphite crucible, closing a device door, washing gas, and vacuumizing to 10 after the gas washing is completed -1 -10 -3 About Pa, charging argon to 40Kpa, opening heating current, preheating for 5-10min at low heating current, increasing heating current, heating to 740-800 deg.C, maintaining for 2-40min, cooling to 720 deg.C, standing for 2-30 min, and stopping heatingAnd pouring into a copper mold.
Comparative example 1 was cast by a conventional metal mold, and the melt was poured into a copper mold to obtain a melt having a cooling rate of 8 deg.c/s. The alloy obtained in this comparative example had an average grain size of 109 μm and a secondary dendrite spacing of 32. Mu.m, a compressive strength of 320MPa, a compressive yield strength of 109MPa, a fracture compression ratio of 7.20% and a rigidity of 49.6GPa. Compared with the reported traditional AZ31 magnesium alloy, the compression strength and the rigidity of the newly designed alloy are obviously improved, and therefore, the formed second phase Mg of the newly designed alloy 3 (Gd, Y) and Al 2 The high temperature resistant phase and the hardening phase such as (Gd, Y), alLi and the like can obviously improve the compression strength and the rigidity of the alloy.
In addition, the mass percentages of Gd, Y and Li elements in the upper part of the casting alloy in this comparative example 1 are 2.63%,0.5% and 6.4%; while the lower Gd, Y and Li elements of the alloy are 6.4%,2.4% and 2.1% by mass. Due to the influence of gravity, gd and Y elements in conventional cast alloys are significantly segregated in the lower portion of the alloy while Li element is significantly segregated in the upper portion of the alloy.
Comparative examples 2 and 3
The Mg-Gd-Li-Y-Al alloy in comparative example 2 comprises the following elements in percentage by mass: gd 4.60%, li 1.00%, Y1.00%, al 0.60%, zr less than 0.1%, and the balance Mg. The Mg-Gd-Li-Y-Al alloy in comparative example 3 comprises the following elements in percentage by mass: gd 4.60%, li 5.20%, Y1.00%, al 0.60%, zr less than 0.1%, and the balance Mg. The alloy compositions in comparative examples 2 and 3 were changed in only Li content as compared with comparative example 1, 1.0wt.% and 5.2wt.%, respectively. In addition, the preparation methods of comparative examples 1 to 3 were all the same, and the melt was poured into a copper mold by using a conventional metal mold casting, and the cooling rate of the obtained melt was 8 ℃/s. The alloy obtained in comparative example 2 had an average grain size of 112 μm and a secondary dendrite spacing of 34. Mu.m, a compressive strength of 300MPa, a compressive yield strength of 103MPa, a fracture compressibility of 7.30% and a rigidity of 49.1GPa. The alloy obtained in comparative example 3 had an average grain size of 110 μm and a secondary dendrite spacing of 30. Mu.m, a compressive strength of 332MPa, a compressive yield strength of 118MPa, a fracture compression ratio of 6.7% and a rigidity of 50.3GPa.
The alloys obtained in comparative examples 2 and 3 also have a greatly improved compressive strength and rigidity over the reported conventional AZ31 magnesium alloy. Thus, the content of Li can be suitably fine-tuned to 1wt.% to 5.2wt.%
Example 1
The Mg-Gd-Li-Y-Al alloy comprises the following elements in percentage by mass: gd 4.60%, li 4.30%, Y1.00%, al 0.60%, zr less than 0.1%, and the balance Mg. The preparation method of the alloy comprises the following steps:
step one: the raw materials adopt industrial pure magnesium, industrial pure Li, al-Zr intermediate alloy, mg-Gd intermediate alloy and Mg-Y intermediate alloy, and the mass of the required raw materials is calculated and weighed according to the components;
step two: mixing the raw materials, placing the mixture into a graphite crucible, vacuumizing, filling argon, and carrying out vacuum melting and casting by adopting electromagnetic induction heating to obtain a master alloy ingot;
step three: crushing the master alloy ingot obtained in the second step, weighing 40g, putting into a graphite crucible, closing a device door, washing gas, and vacuumizing to 10 after the gas washing is completed -1 -10 -3 About Pa, filling argon to 40KPa, opening heating current, preheating for 5-10min under low heating current, increasing heating current, heating to 740-800 ℃, preserving heat for 2-40min, cooling to 720 ℃, standing, preserving heat for 2-30 min, stopping heating, lowering the heater, and starting centrifugal casting; the liquid is thrown into a water-cooled copper mould to realize sub-rapid solidification, the casting temperature is 670-720 ℃, and the cooling speed reaches 3.8x10 2 The centrifugation time is about 1min at C/s.
Example 1 was substantially identical in composition to comparative example 1, comparative example 1 being a master alloy, and conventional metal mold casting, cooling rate was 8 ℃/s. Example 1 the master alloy of comparative example 1 was remelted by centrifugal casting into a water-cooled copper mold, and the cooling rate of the melt was 3.8X10% by controlling the flow rate of cooling water 2 C/s; as can be seen with reference to fig. 1-3: the obtained cast structure has fine crystal grains with average grain size of 8.0 μm and secondary dendrite spacing of 1.9 μm, and the second phase is uniformly dispersed in magnesium matrix, and eutectic phase Mg 3 Re dendrite average thickness is 580nm, al 2 Re phase size of 100nm. In comparative example 1, the grains were coarse, the second phase size was significantly coarse, and Al 2 The Re phase produces significant grain boundary enrichment sizes up to several microns or even tens of microns. The microstructure refining effect of the alloy described in example 1 is remarkable as compared with comparative example 1 of the conventional casting method. The obtained magnesium-lithium alloy has the compression strength of 417MPa, the yield strength of 130MPa, the fracture compression ratio of 18.0% and the rigidity of 52.2GPa.
The grain and the second phase size can be obviously refined by centrifugal casting and sub-rapid solidification phase combination, al 2 The Re phase has a size controlled to be nano-scale and evenly distributed on the grain boundary, thereby illustrating that the preparation method of centrifugal casting and sub-rapid solidification can effectively refine Al 2 The (Gd, Y) phase not only improves the strength of the Mg-Li alloy, but also plays a vital role in blocking grain boundary movement for subsequent heat treatment. In addition, the newly designed magnesium-lithium alloy adopts the technology of combining centrifugal casting and sub-rapid solidification, so that the compression strength, rigidity and plasticity of the alloy are obviously improved, the mechanical properties of the alloy are not required to be improved through deformation hardening and subsequent heat treatment, the problems of more process steps and low production efficiency of the traditional alloy preparation method are solved, and the process cost is saved.
In addition, the upper Gd, Y and Li elements of the alloy in example 1 were 4.50%,0.8% and 4.4% by mass; while the lower Gd, Y and Li elements of the alloy are 4.8%,1.3% and 4.2% by mass. Compared with comparative example 1, the method of vacuum centrifugal casting and sub-rapid solidification phase combination can obviously improve the gravity segregation problem of Gd, Y and Li elements.
Example 2
The procedure of example 1 was followed to prepare various proportions of rapidly solidifying magnesium alloy material, example 2 still using copper mold plus water cooling to achieve sub-rapid solidification, example 2 cooling rates of 4.0X10 2 DEG C/s, but the content of Gd, Y and Al are different. Example 2 compared to example 1, the gd content increased to 6wt.% and the Y content increased to 1.5wt.% and the cooling rate was maximized at 4.0x10 2 The performance of the magnesium-lithium alloy is optimal at the temperature of per second.
Examples 3 and 4
According to realityThe procedure of example 1 was used to prepare various proportions of rapidly solidifying magnesium alloy materials, examples 3-4 still using copper mold with water cooling to achieve sub-rapid solidification at a cooling rate of 3.8X10 2 DEG C/s. In comparison to the alloy composition of example 1, example 3 only has a Gd content of 3wt.%, whereas example 4 only has a Y content of 0.5wt.%. From this, it is understood that a slight decrease in the Gd and Y contents slightly decreases the compression mechanical properties and rigidity of the magnesium lithium alloy, but the plasticity slightly increases. It is seen in combination with examples 2, 3 and 4 that the Gd and Y content can be suitably fine-tuned, gd content being 3-6 wt.% and Y content being 0.5-1.5 wt.%.
Example 5
The procedure of example 1 was followed to prepare various proportions of rapidly solidifying magnesium alloy material, example 5 still using copper mold plus water cooling to achieve sub-rapid solidification at a cooling rate of 3.8X10 2 DEG C/s. Example 5 only increased the Al content to 2wt.% compared to example 1. From this, it is found that the increase in Al content can slightly improve the compression mechanical properties and rigidity of the magnesium lithium alloy, but the plasticity is slightly lowered as well. It is known from the combination of examples 1 and 5 that the content of Al can be suitably fine-tuned, and that the content of Al is 0.6wt.% to 2wt.%.
Example 6
The procedure of example 1 was followed to prepare various proportions of rapidly solidifying magnesium alloy material, example 6 still using copper mold plus water cooling to achieve sub-rapid solidification, but at a cooling rate of 1.0X10 2 DEG C/s. The alloy provided in example 6 had slightly coarsened grain size and second phase compared to example 1, and therefore the alloy provided in example 6 had somewhat reduced overall compressive properties and stiffness. However, the combination properties and rigidity are still greatly improved over the conventional gravity casting alloy of comparative example 1. As can be seen from a combination of examples 2 and 6, the sub-rapid cooling rate of the present invention can be 1.0X10 2 ℃/s-4.0×10 2 The temperature/s is properly regulated.
Comparative examples 4 to 6
The casting method is consistent with that of comparative example 1, the conventional metal mold casting is carried out, the melt is poured into a copper mold, the cooling rate of the obtained melt is 8 ℃/s, the content of the component Li element in the alloy is different, the other components and the content are consistent, and the weight percentages of the components and the mechanical property parameters are shown in Table 1. In comparative example 4, the elastic modulus was low, 44.5GPa and the fracture compression ratio was low, 6.3%, without adding Li element. Whereas in comparative example 5, the li content was increased to 0.5wt.%, the compressive strength was not much improved by 278MPa and the stiffness was also only 45.9GPa. Comparative example 6 adding 6wt.% Li element forms a two-phase α -Mg phase and a β -Li phase, and the compressive strength of the alloy is reduced, but the fracture compression rate is increased to 12.2% due to the presence of the β -Li phase.
As is clear from comparative examples 4 to 6, when Li is not added or is added in a small amount, the rigidity of the Mg alloy is significantly lowered and the compression properties are also lowered. In connection with comparative example 2, 1wt.% Li may be added in the present application to improve rigidity and compressive strength. While when 6wt.% of Li is added, the Mg-Li alloy is a two-phase alloy with a main second phase MgAlLi 2 Poor phase strengthening effect and poor high temperature resistance. Furthermore, the presence of the β -Li phase improves alloy plasticity, but overall compression properties remain low. It is known in connection with previous studies that when the Li content is 5.3wt.%, a β -Li phase is present and an increase in the Li content increases the cost of the Mg-Li alloy significantly. Thus, the content of Li of the present invention is controlled to be 0wt.% to 5.3wt.%, but excluding 0 and 5.3; more preferably, the Li content is controlled to be 1wt.% to 5.3wt.% to obtain better mechanical properties. In addition, the Mg-Gd-Li-Y-Al alloy prepared by combining centrifugal casting and sub-rapid solidification provided by the embodiments 1-6 of the invention remarkably improves the compression strength and rigidity of the alloy and inherits the high plasticity of the dual-phase Mg-Li alloy.
Mechanical properties were tested on the working samples of examples and comparative examples in various respects, compression tests were carried out on a microcomputer controlled GOTECH electronic universal tester at room temperature using 1.0 x 10 -3 s -1 The yield strength, compressive strength, and compressibility of each of the processed samples were obtained at a constant strain rate.
In experiments, the observation and analysis of microstructure of the alloy mainly comprises: and (3) carrying out metallographic structure observation analysis on the as-cast alloy, scanning electron microscope analysis on the microstructure of the sample, energy spectrum analysis and the like.
The metallographic microstructure analysis adopts German Leaka DM4000M metallographic microscope optical microscope observation, and the microstructure is prepared with INCA energy spectrum analysis by adopting a Feina G5 scanning electron microscope.
The performance parameters of each of the processed samples are listed in the following table.
Table 1 mechanical properties table of each magnesium alloy sample
As can be seen from the table, the magnesium alloy preparation process adopted by the invention has the advantages of simple process, wide application range, excellent finished product performance and the like; the obtained Mg-Gd-Li-Y-Al alloy has excellent compression performance and meets the requirements of high-compression-strength high-modulus lightweight materials in the military fields such as ocean and the like.
The foregoing description is only exemplary embodiments of the present application and is not intended to limit the scope of the present application, and all equivalent structures or equivalent processes using the descriptions and the drawings of the present application, or direct or indirect application in other related technical fields are included in the scope of the present application.
Claims (6)
1. The Mg-Gd-Li-Y-Al alloy is characterized by comprising the following chemical components in percentage by mass: gd:3.00 to 6.00wt.%; y:0.5-1.5wt.%; li:0 to 5.3wt.%, but excluding 0 and 5.3; al:0.6 to 2wt.%; zr:0 to 0.1wt.%; the balance of Mg and unavoidable impurities; the alloy is in an alpha-Mg single-phase region, and the cast structure comprises primary alpha-Mg phase and grain boundary second phase Mg 3 (Gd, Y) and Al 2 (Gd, Y) phase, alLi phase;
the grain size of the alpha-Mg phase is 4-18 mu m, and the volume fraction is 89% -94.8%; mg of 3 The thickness of the (Gd, Y) phase is less than 700nm, and the volume fraction is 5-10%; al (Al) 2 The size of the (Gd, Y) phase is 80-200nm, the volume fraction is 0.2% -1%, and the secondary dendrite spacing is 1.3-4.6 mu m;
the preparation method of the alloy comprises the following steps: and (3) centrifugally casting the melt of the metal raw material, and cooling and forming in a sub-rapid solidification mode.
2. The Mg-Gd-Li-Y-Al alloy according to claim 1, comprising the following components in mass percentage: gd:3.00 to 6.00wt.%; y:0.5-1.5wt.%; li:1 to 5.3wt.%, including 1 but not including 5.3; al:0.6 to 2wt.%; zr:0 to 0.1wt.%; the balance being Mg and unavoidable impurities.
3. The Mg-Gd-Li-Y-Al alloy according to claim 1, characterised in that its properties fulfil: the compression strength is 401-490MPa, the yield strength is 121-150MPa, the fracture compression ratio is 14.9-25.0%, and the density is 1.40-1.62g/cm 3 The elastic modulus is 51.1-53.3GPa.
4. A method for producing a Mg-Gd-Li-Y-Al alloy according to any one of claims 1 to 3, further comprising the steps of:
s11, calculating and weighing required raw materials according to the components;
s12, preheating the metal raw materials weighed in the step S1, and then mixing the raw materials under a protective atmosphere, and carrying out vacuum melting and casting to obtain a master alloy ingot;
s13, placing the master alloy ingot obtained in the step S2 into a crucible, vacuumizing and introducing inert gas for protection, wherein the vacuum degree is 10 -1 -10 -3 Pa, the smelting temperature is 740-800 ℃, so that the raw materials are fully melted.
5. The method of manufacturing according to claim 4, wherein the centrifugal casting process comprises:
and (3) in a protective atmosphere, cooling the molten metal in the step (S13) to 720 ℃ and standing for 2-30 minutes under the vacuum centrifugal rotating speed of 100-1200r/min, and then performing vacuum centrifugal casting at 670-720 ℃ to cool and mold the molten metal in a sub-rapid solidification mode.
6. The method of claim 5, wherein the sub-rapidly solidifying coolingAt a rate of 1.0X10 2 -4.0×10 2 ℃/s。
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