CN114540679B - Trace element composite reinforced high-strength aluminum-lithium alloy and preparation method thereof - Google Patents

Trace element composite reinforced high-strength aluminum-lithium alloy and preparation method thereof Download PDF

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CN114540679B
CN114540679B CN202210440885.1A CN202210440885A CN114540679B CN 114540679 B CN114540679 B CN 114540679B CN 202210440885 A CN202210440885 A CN 202210440885A CN 114540679 B CN114540679 B CN 114540679B
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CN114540679A (en
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王俊升
杨兴海
田光元
薛程鹏
李星星
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Beijing Institute of Technology BIT
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22C21/00—Alloys based on aluminium
    • C22C21/12—Alloys based on aluminium with copper as the next major constituent
    • C22C21/16—Alloys based on aluminium with copper as the next major constituent with magnesium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
    • C22F1/057—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon of alloys with copper as the next major constituent

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Abstract

The invention discloses a microelement composite reinforced high-strength aluminum-lithium alloy and a preparation method thereof, wherein the high-strength cast aluminum-lithium alloy comprises the following components in percentage by weight: 4.0 to 5.5 weight percent of Cu, 1.5 to 2.3 weight percent of Li, 0.5 to 1.0 weight percent of Mg, 0.5 to 1.5 weight percent of Zn, 0.05 to 0.2 weight percent of Ti, 0.05 to 0.2 weight percent of Zr and 0.1 to 0.5 weight percent of RE; wherein the element represented by RE is one or more of Ce, Er and Sc. The high-strength aluminum-lithium alloy has the tensile strength of 430-520MPa, the elongation of 3-8 percent and the elastic modulus of 85-87 GPa. The invention is suitable for the field of aluminum lithium alloy materials.

Description

Trace element composite reinforced high-strength aluminum-lithium alloy and preparation method thereof
Technical Field
The invention belongs to the field of aluminum lithium alloy materials, and particularly relates to a microelement composite reinforced high-strength aluminum lithium alloy and a preparation method thereof.
Background
At present, the usage amount of aluminum lithium alloy structural parts in large aerospace aircrafts is increasing, and the aluminum lithium alloy structural parts are gradually replacing the traditional 2xxx series and 7xxx series aluminum alloys so as to achieve the purpose of reducing the weight of the whole structure. The third generation of aluminum lithium alloy which has been developed at present generally adopts a method for reducing the content of Li to avoid the defects of low fracture toughness, anisotropy and the like of the second generation of aluminum lithium alloy. Simultaneously increasing Cu content to make Cu/Li ratio in the alloy reach a certain range, and making the interior of the alloy precipitate specific nano strengthening phase, such as Al by means of solid solution-ageing treatment 2 CuLi (T1 phase), Al 3 Li (. delta.'), Al 2 CuMg (S' phase), Al 2 Cu (θ ʹ phase), and further achieves the purpose of strengthening the alloy. Because the third generation aluminum lithium alloy needs to be deformed and processed after being cast to improve the material performance, more processing cost is generally needed for producing complex structural parts.
Chinese patent CN108570580A discloses a cast aluminum-lithium alloy and a preparation method thereof, wherein Cu element is removed in the alloy design, wherein Mg content is 1-4wt.%, Li content is 2.5-3wt.%, Zr content is 0.15-0.2wt.%, Sc content is 0.1-0.15wt.%, because Li content is higher, the patent uses a mixed solvent of lithium chloride and lithium fluoride with a weight ratio of 3:1 for refining, and Li addition and casting are performed under the protection of argon gas, the process operation is more complicated, the melting time is longer, and metal liquid is easy to contact with air in the deslagging and casting processes, and there is a risk of oxidation. In addition, since Cu element is not added in the patent, the tensile strength of the alloy is generally 450MPa or less. Therefore, it is highly desirable to develop a casting method of aluminum-lithium alloy, which has a simple preparation method, high strength and high elastic modulus, and also has a good balance between the production cost of the alloy.
Disclosure of Invention
The invention provides a trace element composite reinforced high-strength aluminum-lithium alloy and a preparation method thereof, aiming at the problems that the strength and the elastic modulus of the traditional cast aluminum-lithium alloy are far lower than those of a deformed alloy and cannot be synchronously improved, the process for preparing the high-strength cast aluminum-lithium alloy in the prior art is complex, and the preparation method is not suitable for industrial production, and the problems that the cost is increased by adding a high-content Li element, the Li element is easy to oxidize in the preparation process, the yield is low, and the elastic modulus cannot be effectively improved in the prior art.
In order to achieve the above object, the first aspect of the present invention provides the following solutions:
a microelement composite reinforced high-strength cast aluminum-lithium alloy comprises the following components in percentage by weight: 4.0 to 5.5 weight percent of Cu, 1.5 to 2.3 weight percent of Li, 0.5 to 1.0 weight percent of Mg, 0.5 to 1.5 weight percent of Zn, 0.05 to 0.2 weight percent of Ti, 0.05 to 0.2 weight percent of Zr and 0.1 to 0.5 weight percent of RE;
wherein the element represented by RE is one or more of Ce, Er and Sc.
As an embodiment of the invention, the tensile strength of the high-strength cast aluminum-lithium alloy is 430-520MPa, the elastic modulus is 85-87GPa, and the elongation is 3-8%;
the high-strength cast aluminum-lithium alloy also contains Al and impurities, the content of the impurities is less than 0.05%, and the impurities comprise: fe. One or more of Si and Mn.
As an embodiment of the present invention, the composition of the high strength cast aluminum lithium alloy is, in weight percent: 4.5 to 5.0 weight percent of Cu, 1.8 to 2.0 weight percent of Li, 0.5 to 1.0 weight percent of Mg and 0.5 to 1.0 weight percent of Zn, wherein the sum of the contents of Cu, Li, Mg and Zn elements is not more than 10.0 weight percent;
the high-strength cast aluminum-lithium alloy also contains Al and impurities, the content of the impurities is less than 0.05%, and the impurities comprise: fe. One or more of Si and Mn.
According to one embodiment of the invention, the cast grain structure of the high-strength cast aluminum lithium alloy is fine equiaxed dendrites, the size of the fine equiaxed dendrites is 20-30 mu m, and grain boundaries are mainly formed by continuous strip-shaped Al 7 Cu 4 Li phase and Al 2 The CuMg phase consists of a needle-shaped eutectic T1 phase and massive Al inside crystal grains 8 Cu 4 The RE phase.
As an embodiment of the invention, the heat-treated crystal grain structure of the high-strength cast aluminum-lithium alloy is fine isometric crystal, and nanometer T1 phase, delta 'phase and S' phase are distributed in the crystal grains.
In a second aspect, the present invention provides a method of high strength casting of an aluminum lithium alloy according to the first aspect of the present invention, the method comprising:
s1: preparing 1-100 kg of raw materials according to required alloy components, and carrying out preheating treatment on the raw materials;
s2: carrying out vacuum melting on the raw materials to obtain melted molten metal;
s3: casting and cooling the smelted molten metal to obtain an original casting;
s4: sequentially carrying out solid solution treatment and quenching treatment on the original casting to obtain a quenched original casting;
s5: carrying out aging treatment on the quenched original casting, and then cooling in air to obtain the high-strength cast aluminum-lithium alloy;
wherein the vacuum degree of the smelting is below 5 kPa.
As an embodiment of the present invention, the method further comprises: before the smelting, coating boron nitride coating on the inner surface of the graphite crucible;
the mass fraction of solid boron nitride in the boron nitride coating is higher than 70%, and the thickness of the coating is 0.05-0.2 mm.
As an embodiment of the present invention, in step S2, the smelting includes: firstly, heating the raw materials in the crucible to 600-660 ℃, preserving heat for 2-5 min, continuously raising the temperature to 780-820 ℃, and stirring for 10-15 min to completely melt the raw materials.
As an embodiment of the present invention, the method further comprises: before the casting, preserving the heat of the smelted molten metal for 10-15 min, wherein the casting temperature is 730-780 ℃, and the casting is carried out in an inert gas atmosphere; the metal casting material can be copper, stainless steel or cast iron, and the wall thickness of the metal casting is more than 50 mm.
As an embodiment of the present invention, in step S4, the solution treatment is a two-stage solution treatment, and the two-stage solution treatment method includes: firstly, preserving heat of the original casting at 450-490 ℃ for 8-24 h, then heating to 500-520 ℃ and preserving heat for 0-24 h, wherein the heating rate between the two temperatures is 1 ℃/min; the two-stage solid solution is carried out in an inert gas protection furnace, and after the heat preservation is finished, the casting is put into cold water in an inert gas atmosphere to carry out the quenching treatment;
in step S5, the aging process includes: and preserving the heat of the quenched original casting at the temperature of 145-200 ℃ for 24-72 h.
The technical scheme provided by the invention at least brings the following beneficial effects:
(1) compared with the current third-generation aluminum lithium alloys such as AA2195, AA2196 and AA2198, the high-strength aluminum lithium alloy has higher Cu content and Li content, and can keep higher Cu/Li ratio, so that delta 'phase and T' phase can be formed in the alloy after heat treatment 1 A phase composite strengthened grain structure; at the same time, the user can select the desired position,addition of microalloying elements Zr and Ti enables L to be formed 12 Structural Al 3 Zr and DO 22 Structural Al 3 The Ti nano-particles can be used as heterogeneous nucleation sites of an aluminum matrix in the solidification process, and the grain boundary is pinned in the heat treatment process, so that grains are obviously refined; in addition, the added RE elements such as Sc, Ce and Er can be matched with Al to form Al 3 RE particles can further refine grains in the solidification process and effectively inhibit the growth of the grains in the solid solution process;
(2) the electromagnetic induction heating smelting is adopted, compared with resistance heating furnace smelting, the temperature rise is faster, the production efficiency is higher, the vacuum requirement is lower, the requirement of industrial equipment is met, and meanwhile, the risks of complex process and oxidation and combustion of molten metal in the atmospheric smelting process are avoided;
(3) the method adopts the two-stage solution treatment under the protection of inert gas, can fully play the potential strengthening role of the composite micro-alloying element while effectively dissolving the continuous intermetallic compound at the crystal boundary of the as-cast alloy, and ensures that the micro-alloying element is fully diffused at the crystal grains and the crystal boundary to form fine and dispersed nano-scale particles, thereby effectively inhibiting the growth of the crystal grains.
In conclusion, compared with Al-Li-Cu-Mg alloy with high Li content, the high strength and high elastic modulus of the alloy can be realized under the condition that the Li content is lower than 2.0wt% due to the complex strengthening effect of the multi-element microalloy, the elastic modulus is far higher than that of the current third-generation aluminum-lithium alloy, and the strength can reach or even exceed that of the third-generation aluminum-lithium alloy after thermal deformation. The method provides a simpler technical approach for preparing the high-strength aluminum-lithium alloy complex structural part, and obviously reduces the processing cost. The performance of the low-density high-strength high-elasticity modulus aluminum lithium alloy is as follows: the tensile strength is 430-520MPa, the elongation is 3-8 percent, and the elastic modulus is 85-87 GPa.
Drawings
FIG. 1 is an electron micrograph of an as-cast alloy structure in example 1 of the present invention;
FIG. 2 is an electron micrograph of an as-cast alloy structure according to example 2 of the present invention;
FIG. 3 is an electron micrograph of an as-cast alloy structure according to example 3 of the present invention;
FIG. 4 is an electron micrograph of an as-cast alloy structure according to example 4 of the present invention;
FIG. 5 is an electron micrograph of an as-cast alloy structure according to example 5 of the present invention;
FIG. 6 is an electron micrograph of an as-cast alloy structure according to example 6 of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in further detail below.
Example 1
The method for preparing the high-strength cast aluminum-lithium alloy comprises the following steps:
s1: preparing raw materials according to required alloy components, and carrying out preheating treatment on the raw materials: in consideration of the burning loss of elements, intermediate alloys are adopted for Cu, Li, Mg and Zn in the preparation raw materials, wherein the intermediate alloys are respectively Al-60% Cu, Al-20% Li, Al-30% Mg and Al-30% Zn, and the burning loss rates of the intermediate alloys are respectively 5%, 10% and 5%. And preserving the prepared raw materials in an air heating furnace for 1h at the temperature of 220 ℃. Wherein the intermediate alloy of Mg and Li is dried in a vacuum drying oven to remove moisture.
S2: carrying out vacuum melting on the raw materials to obtain molten metal: before smelting, a graphite crucible is coated with a boron nitride coating, wherein the mass fraction of solid boron nitride in the boron nitride coating is more than 70%, and the thickness of the coating is 0.1 mm. The crucible was kept at 250 ℃ for 1h before use to remove water. Preferably, the vacuum melting is performed by using a conventional electromagnetic induction inert gas protective furnace, the used inert protective gas is argon, all the raw materials are put into a crucible before melting, the vacuum degree of a melting chamber is controlled at 5kPa by using a mechanical vacuum pump, argon is filled to the atmospheric pressure, and the cycle is performed for three times. Preferably, the smelting process comprises: heating the raw materials in the crucible to 600 ℃, keeping the temperature for 2min after the temperature reaches the set temperature, raising the temperature to 780 ℃ after the temperature is stable, so that the raw materials are completely melted, and electromagnetically stirring for 10min at 780 ℃.
S3: casting and cooling the smelted molten metal to obtain an original casting: the casting temperature is 750 ℃, and casting is started after heat preservation is carried out for 15min at the temperature. The metal casting material is pure copper with the thickness of 50mm, the molten metal is injected into the metal casting from the bottom of the crucible under the action of gravity, and the whole process is carried out in the argon atmosphere.
S4: sequentially carrying out solid solution treatment and quenching treatment on the original casting to obtain a quenched original casting: the solid solution treatment is double-stage solid solution, and specifically comprises the following steps: the original casting is firstly insulated for 24h at 480 ℃ and then heated to 510 ℃ for 12 h. The rate of temperature rise between the two stages was 1 deg.C/min. The heat preservation furnace used for the solution treatment of the original casting is an inert gas protection furnace, and the casting is put into cold water for quenching under the protection of argon after the heat preservation is finished.
S5: and (3) carrying out aging treatment on the quenched original casting, and then cooling in air to obtain the high-strength cast aluminum-lithium alloy: the aging treatment comprises the following steps: and (3) preserving the temperature of the quenched original casting at 175 ℃ for 24 h.
The high-strength cast aluminum-lithium alloy obtained in this example had a chemical composition (in weight percent): 4.8wt% of Cu, 1.8wt% of Li, 0.7wt% of Mg, 1.0wt% of Zn, 0.19wt% of Ti, 0.13wt% of Zr, 0.2wt% of Er and the balance of Al and inevitable impurities, wherein the weight percentage of Fe + the weight percentage of Si is less than or equal to 0.05; the as-cast grain structure of the cast aluminum lithium alloy is fine equiaxed dendrites, which have a size of 27.4 μm as shown in fig. 1. The grain boundary of the as-cast alloy is mainly composed of continuous strip-shaped Al 7 Cu 4 Li、Al 2 A CuMg phase, and the inside of the crystal grains is a needle-shaped eutectic crystal T 1 Phase and bulk Al 8 Cu 4 And Er phase composition.
And testing the strength and the elastic modulus of the trace element composite reinforced high-strength cast aluminum lithium alloy. The properties of the cast aluminum lithium alloy meet the following requirements: the tensile strength was 517MPa, the elongation was 5.6%, and the elastic modulus was 85.5 GPa.
Example 2
The method for preparing the high-strength cast aluminum-lithium alloy comprises the following steps:
s1: preparing raw materials according to required alloy components, and carrying out preheating treatment on the raw materials: in consideration of the burning loss of elements, intermediate alloys are adopted for Cu, Li, Mg and Zn in the preparation raw materials, wherein the intermediate alloys are respectively Al-60% of Cu, Al-20% of Li, Al-30% of Mg and Al-30% of Zn, and the burning loss rates of the intermediate alloys are respectively 5%, 15%, 10% and 5%. And preserving the prepared raw materials in an air heating furnace for 1h at the temperature of 220 ℃. Wherein the intermediate alloy of Mg and Li is dried in a vacuum drying oven to remove moisture.
S2: carrying out vacuum melting on the raw materials to obtain molten metal: before smelting, a graphite crucible is coated with a boron nitride coating, wherein the mass fraction of solid boron nitride in the boron nitride coating is more than 70%, and the thickness of the coating is 0.05 mm. The crucible was kept at 250 ℃ for 1h before use to remove water. Preferably, the vacuum melting is performed by using a conventional electromagnetic induction inert gas protective furnace, the used inert protective gas is argon, all the raw materials are put into a crucible before melting, the vacuum degree of a melting chamber is controlled at 3kPa by using a mechanical vacuum pump, argon is filled to the atmospheric pressure, and the cycle is performed for three times. Preferably, the smelting process comprises: heating the raw materials in the crucible to 660 ℃, preserving heat for 4min after reaching the set temperature, raising the temperature to 800 ℃ after the temperature is stable, completely melting the raw materials, and electromagnetically stirring for 10min at 800 ℃.
S3: casting and cooling the smelted molten metal to obtain an original casting: the casting temperature is 750 ℃, and casting is started after heat preservation is carried out for 15min at the temperature. The metal casting material is pure copper with the thickness of 50mm, the molten metal is injected into the metal casting from the bottom of the crucible under the action of gravity, and the whole process is carried out in the argon atmosphere.
S4: sequentially carrying out solid solution treatment and quenching treatment on the original casting to obtain a quenched original casting: the solid solution treatment is double-stage solid solution, and specifically comprises the following steps: the original casting is firstly insulated for 24h at 480 ℃ and then heated to 510 ℃ for 12 h. The heating rate between the two temperatures was 1 ℃/min. The heat preservation furnace used for the solution treatment of the original casting is an inert gas protection furnace, and the casting is put into cold water for quenching under the protection of argon after the heat preservation is finished.
S5: and (3) carrying out aging treatment on the quenched original casting, and then cooling in air to obtain the high-strength cast aluminum-lithium alloy: the aging treatment comprises the following steps: and (3) preserving the temperature of the quenched original casting at 175 ℃ for 24 h.
The strength and the elastic modulus of the trace element composite reinforced high-strength cast aluminum lithium alloy are tested, and the performance of the cast aluminum lithium alloy meets the following requirements: the tensile strength was 452MPa, the elongation was 3.3%, and the elastic modulus was 86.3 GPa.
The high-strength cast aluminum-lithium alloy obtained in this example had a chemical composition (in weight percent): 4.8wt% of Cu, 1.8wt% of Li, 0.7wt% of Mg, 1.0wt% of Zn, 0.19wt% of Ti, 0.13wt% of Zr, 0.2wt% of Ce, and the balance of Al and inevitable impurities, wherein the weight% of Fe + the weight% of Si is less than or equal to 0.05; the as-cast grain structure of the cast aluminum lithium alloy is fine equiaxed dendrites, with equiaxed dendrite size of 24.2 μm as shown in FIG. 2. The grain boundary of the as-cast alloy is mainly composed of continuous strip-shaped Al 7 Cu 4 Li、Al 2 A CuMg phase, and the inside of the crystal grains is a needle-shaped eutectic crystal T 1 Phase and bulk Al 8 Cu 4 Phase Ce.
Example 3
The method for preparing the high-strength cast aluminum-lithium alloy comprises the following steps:
s1: preparing raw materials according to required alloy components, and carrying out preheating treatment on the raw materials: in consideration of the burning loss of elements, intermediate alloys are adopted for Cu, Li, Mg and Zn in the preparation raw materials, wherein the intermediate alloys are respectively Al-60% of Cu, Al-20% of Li, Al-30% of Mg and Al-30% of Zn, and the burning loss rates of the intermediate alloys are respectively 5%, 15%, 10% and 5%. And preserving the prepared raw materials in an air heating furnace for 1h at the temperature of 220 ℃. Wherein the intermediate alloy of Mg and Li is dried in a vacuum drying oven to remove moisture.
S2: carrying out vacuum melting on the raw materials to obtain molten metal: before smelting, a graphite crucible is coated with a boron nitride coating, wherein the mass fraction of solid boron nitride in the boron nitride coating is more than 70%, and the thickness of the coating is 0.05 mm. The crucible was kept at 250 ℃ for 1h before use to remove water. Preferably, the vacuum melting is performed by using a conventional electromagnetic induction inert gas protective furnace, the used inert protective gas is argon, all the raw materials are put into a crucible before melting, the vacuum degree of a melting chamber is controlled at 3kPa by using a mechanical vacuum pump, argon is filled to the atmospheric pressure, and the cycle is performed for three times. Preferably, the smelting comprises: heating the raw materials in the crucible to 660 ℃, preserving heat for 4min after reaching the set temperature, raising the temperature to 800 ℃ after the temperature is stable, completely melting the raw materials, and electromagnetically stirring for 10min at the temperature of 800 ℃.
S3: casting and cooling the smelted molten metal to obtain an original casting: the casting temperature is 750 ℃, and casting is started after heat preservation is carried out for 15min at the temperature. The metal casting material is pure copper with the thickness of 50mm, the molten metal is injected into the metal casting from the bottom of the crucible under the action of gravity, and the whole process is carried out in the argon atmosphere.
S4: sequentially carrying out solid solution treatment and quenching treatment on the original casting to obtain a quenched original casting: the solid solution treatment is double-stage solid solution, and specifically comprises the following steps: the original casting is firstly insulated for 12h at 480 ℃ and then heated to 500 ℃ for 12 h. The heating rate between the two temperatures was 1 ℃/min. The heat preservation furnace used for the solution treatment of the original casting is an inert gas protection furnace, and the casting is put into cold water for quenching under the protection of argon after the heat preservation is finished.
S5: and (3) carrying out aging treatment on the quenched original casting, and then cooling in air to obtain the high-strength cast aluminum-lithium alloy: the aging treatment comprises the following steps: and (3) preserving the temperature of the quenched original casting at 175 ℃ for 12 h.
The strength and the elastic modulus of the trace element composite reinforced high-strength cast aluminum lithium alloy are tested, and the performance of the cast aluminum lithium alloy meets the following requirements: the tensile strength was 430MPa, the elongation was 4.6%, and the elastic modulus was 86.5 GPa.
The high-strength cast aluminum-lithium alloy obtained in this example had a chemical composition (in weight percent): 4.8wt% of Cu, 1.8wt% of Li, 0.7wt% of Mg, 1.0wt% of Zn, 0.19wt% of Ti, 0.13wt% of Zr, 0.2wt% of Sc and the balance of Al and inevitable impurities, wherein the weight% of Fe + the weight% of Si is less than or equal to 0.05; the as-cast grain structure of the cast aluminum lithium alloy is fine equiaxed dendrites, as shown in FIG. 3The equiaxed dendrite size is shown to be 28.5 μm. The grain boundary of the as-cast alloy is mainly composed of continuous strip-shaped Al 7 Cu 4 Li、Al 2 The CuMg intermetallic compound phase consists of a needle-shaped eutectic T1 phase and massive Al inside crystal grains 8 Cu 4 And a Sc phase.
Example 4
The preparation of a high strength cast aluminum lithium alloy was carried out according to the method of example 1, except that: the alloy has different components, specifically, Er element is changed into Ag element, and the components and contents of other alloy elements are kept unchanged.
The as-cast grain structure of the high strength cast aluminum lithium alloy obtained in this example was fine equiaxed dendrites, and as shown in fig. 4, the equiaxed dendrite size was 39.3 μm. The grain boundary of the as-cast alloy is mainly composed of continuous strip-shaped Al 7 Cu 4 Li、Al 2 The CuMg phase consists of a eutectic T1 phase which is dense in the crystal grains. After heat treatment, the properties of the cast aluminum lithium alloy are as follows: the tensile strength was 423MPa, the elongation was 5.6%, and the elastic modulus was 83.7 GPa.
Example 5
The preparation of a high strength cast aluminum lithium alloy was carried out according to the method of example 2, except that: the alloy components are different, specifically, Ce element is replaced by La element, and the composition and content of other alloy elements are kept unchanged.
The as-cast grain structure of the high strength cast aluminum lithium alloy obtained in this example was fine equiaxed dendrites having an equiaxed dendrite size of 36.9 μm as shown in fig. 5. The grain boundary of the as-cast alloy is mainly composed of continuous strip-shaped Al 7 Cu 4 Li、Al 2 The CuMg composition has a dense eutectic T1 phase inside crystal grains. After heat treatment, the properties of the cast aluminum lithium alloy are as follows: the tensile strength was 316MPa, the elongation was 2.0%, and the modulus of elasticity was 77.8 GPa.
Example 6
The preparation of a high strength cast aluminum lithium alloy was carried out according to the method of example 2, except that: the alloy has different components, specifically, Er element is changed into Co element, and the composition and content of other alloy elements are kept unchanged.
As-cast grains of the high-strength cast aluminum-lithium alloy obtained in this exampleThe structure is a fine equiaxed dendrite, as shown in fig. 6, with an equiaxed dendrite size of 38.7 μm. The grain boundary of the as-cast alloy is mainly composed of continuous strip Al 7 Cu 4 Li、Al 2 The CuMg intermetallic compound phase consists of a dense eutectic T1 phase in the crystal grains. After heat treatment, the properties of the cast aluminum lithium alloy are as follows: the tensile strength was 305MPa, the elongation was 4.5%, and the elastic modulus was 82.9 GPa.
According to the embodiments 1-3, the strength and rigidity of the aluminum-lithium alloy can be remarkably improved by designing the components of the multi-component microalloyed aluminum-lithium alloy and adopting the inert atmosphere protection vacuum electromagnetic induction smelting, and the preparation process device has simple requirements and can provide suitable industrial technical guidance for high-strength and high-rigidity aluminum-lithium alloy castings.
Further, it is understood from comparative examples 1 to 3 and examples 4 to 6 that when the microalloying element is replaced with another element, for example, Ag, La or Co, the grain size of the as-cast alloy is increased to 30 μm or more, and the strength after heat treatment is 430MPa or less and the elastic modulus is less than 85 GPa.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims (5)

1. The trace element composite reinforced high-strength cast aluminum-lithium alloy is characterized by comprising the following components in percentage by weight: 4.5 to 5.0 weight percent of Cu, 1.8 to 2.0 weight percent of Li, 0.5 to 1.0 weight percent of Mg and 0.5 to 1.0 weight percent of Zn, wherein the sum of the contents of Cu, Li, Mg and Zn elements is not more than 10.0 weight percent; 0.05 to 0.2 weight percent of Ti, 0.05 to 0.2 weight percent of Zr and 0.1 to 0.5 weight percent of RE;
wherein the element represented by RE is selected from one or more of Er and Sc;
the cast grain structure of the high-strength cast aluminum-lithium alloy is a fine equiaxial dendritic crystal, the size of the fine equiaxial dendritic crystal is 20-30 mu m, and a grain boundary mainly comprises continuous strip-shaped Al 7 Cu 4 Li phase and Al 2 Phase composition of CuMg, inside the grainConsists of needle-shaped eutectic T1 phase and massive Al 8 Cu 4 RE phase composition;
the tensile strength of the high-strength cast aluminum-lithium alloy is 430-520MPa, the elastic modulus is 85-87GPa, and the elongation is 3-8%;
the high-strength cast aluminum-lithium alloy also contains Al and impurities, the content of the impurities is less than 0.05%, and the impurities comprise: fe. One or more of Si and Mn;
the preparation method of the high-strength cast aluminum-lithium alloy comprises the following steps:
s1: preparing 1-100 kg of raw materials according to required alloy components, and carrying out preheating treatment on the raw materials;
s2: carrying out vacuum melting on the raw materials to obtain melted molten metal;
s3: casting and cooling the smelted molten metal to obtain an original casting;
s4: sequentially carrying out solid solution treatment and quenching treatment on the original casting to obtain a quenched original casting;
s5: carrying out aging treatment on the quenched original casting, and then cooling in air to obtain the high-strength cast aluminum-lithium alloy;
wherein the vacuum degree of the smelting is below 5 kPa;
in step S4, the solution treatment is a two-stage solution treatment, and the two-stage solution treatment method includes: firstly, preserving heat of the original casting at 480-490 ℃ for 8-24 h, then heating to 500-520 ℃ and preserving heat for 12-24 h, wherein the heating rate between the two temperatures is 1 ℃/min; the two-stage solid solution is carried out in an inert gas protection furnace, and after the heat preservation is finished, the casting is put into cold water in an inert gas atmosphere to carry out the quenching treatment;
in step S5, the aging process includes: and preserving the heat of the quenched original casting at the temperature of 145-200 ℃ for 24-72 h.
2. A method of making the high strength cast aluminum lithium alloy of claim 1, comprising:
s1: preparing 1-100 kg of raw materials according to required alloy components, and carrying out preheating treatment on the raw materials;
s2: carrying out vacuum melting on the raw materials to obtain melted molten metal;
s3: casting and cooling the smelted molten metal to obtain an original casting;
s4: sequentially carrying out solid solution treatment and quenching treatment on the original casting to obtain a quenched original casting;
s5: carrying out aging treatment on the quenched original casting, and then cooling in air to obtain the high-strength cast aluminum-lithium alloy;
wherein the vacuum degree of the smelting is below 5 kPa.
3. The method of claim 2, further comprising: before the smelting, coating boron nitride coating on the inner surface of the graphite crucible;
the mass fraction of solid boron nitride in the boron nitride coating is higher than 70%, and the thickness of the coating is 0.05-0.2 mm.
4. The method of claim 2, wherein in step S2, the smelting comprises: firstly, heating the raw materials in the crucible to 600-660 ℃, preserving heat for 2-5 min, continuously raising the temperature to 780-820 ℃, and stirring for 10-15 min to completely melt the raw materials.
5. The method of claim 2, further comprising: before the casting, preserving the heat of the smelted molten metal for 10-15 min, wherein the casting temperature is 730-780 ℃, and the casting is carried out in an inert gas atmosphere; the metal casting mold material is copper, stainless steel or cast iron, and the wall thickness of the metal casting mold is more than 50 mm.
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