Light alloy tough reinforced material based on nano core-shell structure and preparation method of light alloy tough reinforced material

Abstract

The invention relates to the technical field of alloy materials, in particular to a light alloy toughness reinforced material based on a nano core-shell structure and a preparation method. According to the Al-Li-Cu-Mg alloy disclosed by the invention, the trace element Zr is added into the Al-Li-Cu-Mg alloy for alloying, all the components have a synergistic effect, and artificial aging treatment is combined, so that a T1 phase and a theta'phase are separated out in a crystal, meanwhile, an Al3Zr phase can be separated out, a precipitated phase of a unique nano core-shell structure is generated by an alloy phase, distribution of a second phase is adjusted and refined, and therefore, the mechanical property of the alloy is improved. And the obdurability and the ductility of the alloy Al-Li-Cu-Mg-Zr are enhanced. According to the material prepared through the method, stress concentration is basically eliminated, and the ductility of the Al-Li-Cu-Mg series alloy is effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of alloy materials, and in particular to a light alloy strong and tough reinforcing material based on a nano core-shell structure and a preparation method thereof. Background Art

[0002] The urgent demand for lightweight and safety of materials in the aerospace and aircraft fields has promoted the sustainable development of aluminum-lithium alloys. Compared with traditional Al-Cu, Al-Mg and Al-Si alloys, Al-Li and Al-Li-Cu alloys have outstanding advantages such as low density, high stiffness, high damage tolerance and low fatigue crack growth rate. As a type of aluminum alloy that can be strengthened by heat treatment, the strength of aluminum-lithium alloys mainly comes from precipitation strengthening. Specifically, Al3Li particles with Li2 structure are the main strengthening phase in cast Al-Li alloys. However, dislocations generated during plastic deformation can easily shear Al3Li particles. The occurrence of planar slip can cause significant strain concentration, leading to intergranular cracking and brittle damage, which ultimately limits the practical application of cast aluminum-lithium alloys.

[0003] Therefore, in order to solve the problem of Al3Li coplanar slip-induced plasticity reduction, it is necessary to obtain lightweight alloy materials with excellent properties by adjusting the heat treatment steps or optimizing the alloy composition. Summary of the invention

[0004] The present invention aims to introduce a certain amount of Zr element into Al-Li alloy to form Al3(Zr, Li) nano core-shell structure during the casting process, thereby significantly improving the mechanical properties of the alloy. The Al3Li shell in the core-shell structure can serve as a heterogeneous nucleation site for T1 and θ' phases, effectively reducing the interfacial energy and promoting the uniform precipitation of the strengthening phase, thereby achieving a dual improvement in the ductility and strength of the alloy, and providing technical support for the development and application of lightweight, high-performance cast aluminum-lithium alloys.

[0005] The technical solution adopted by the present invention is as follows:

[0006] In a first aspect, the present invention provides a method for preparing a lightweight alloy toughening reinforcement material based on a nano core-shell structure, which specifically comprises the following steps:

[0007] S1 Raw material preparation:

[0008] Take 94-96 weight parts of metal Al, 0.45-0.5 weight parts of Mg, 2-2.05 weight parts of Li, 1.95-2.0 weight parts of master alloy Al-Cu and 0.2-0.25 weight parts of Al-Zr, wherein the master alloy Al-Cu contains 40-60 weight percent of Cu and the master alloy Al-Zr contains 3-8 weight percent of Zr;

[0009] S2 Melting and Casting:

[0010] a. mixing Al, Mg, master alloys Al-Cu and Al-Zr, and Li for smelting;

[0011] High-purity argon gas is introduced into the smelting process, and a mixture of LiCl and LiF is used as a flux to cover the melt;

[0012] b. After degassing with C2Cl6 and maintaining at 650-750°C for not less than 5 minutes, a melt is obtained;

[0013] cCasting and curing

[0014] Pressure casting or gravity casting is adopted, and the casting temperature is controlled at 650-750° C. After the molten alloy is cast, it is allowed to cool and solidify to obtain Al-Li-Cu-Mg-Zr alloy;

[0015] S3 solution treatment:

[0016] The cast Al-Li-Cu-Mg-Zr alloy was solution treated using a customized two-stage solution process: the first stage was a preliminary solution treatment at 450-500°C for 24-36 hours; the second stage was a secondary solution treatment at 500-560°C for 20-30 hours to fully form a uniform solid solution; the treated alloy was then quenched in room temperature water;

[0017] S4 aging treatment:

[0018] The alloy after solution treatment is placed in a silicone oil bath for artificial aging treatment at 150-200°C for 24-36 hours, and then water-cooled to room temperature.

[0019] Preferably, the metal Al and metal Mg are industrial grade pure metals.

[0020] Preferably, the pure Li adopts battery-grade purity.

[0021] Preferably, in step S1, the surface of the raw material of the metal or alloy material is treated to remove impurities and oxide layers.

[0022] Preferably, in step S2, the cooling rate is 10-30°C / min.

[0023] Preferably, in step S2, smelting is performed in a high-purity graphite crucible in a resistance furnace.

[0024] Preferably, in step S2, a semi-continuous casting method is adopted:

[0025] The metal Al and metal Mg required for smelting are placed in a graphite crucible of a resistance furnace and heated to 700-750°C. After the metal is melted, the intermediate alloy Al-Cu, Al-Zr and pure Li are added, and the molten mixture is covered with LiCl and LiF in a molar ratio of 1:1.

[0026] Preferably, in step S2, the molar ratio of LiCl to LiF is 1:1.

[0027] In a second aspect, the present invention provides a nano-core-shell structured Al-Li-Cu-Mg-Zr alloy, which is prepared by the method described in the first aspect.

[0028] The present invention designs a process, and the ingot after artificial aging treatment in step S4 is conducive to the precipitation of T1 and θ' phases. The present invention adds trace element Zr to the Al-Li-Cu-Mg alloy for alloying, and the components work synergistically, and combined with artificial aging treatment, it is achieved that while the T1 and θ' phases are precipitated in the crystal, the Al3Zr phase can also be precipitated. Part of the Al3Li phase in the alloy is nucleated with the help of the Al3Zr surface, thereby forming an Al3 (Zr, Li) phase with a core-shell structure. In addition, the nucleation of T1 and θ' phases in the Al3Li shell layer greatly reduces the interfacial energy, promotes the precipitation of T1 and θ' phases, and makes the finer and more evenly distributed T1 and θ' phases in the alloy further improve the ductility. The strengthening mechanism of T1 and θ' phases and Al3 (Zr, Li) precipitation phases is Orowan strengthening (i.e., shear resistance), which basically eliminates stress concentration and improves the ductility of Al-Li-Cu-Mg alloys.

[0029] Beneficial effects of the present invention:

[0030] The method of combining Zr addition alloying with artificial aging of the present invention makes the Al3Li shell in the Al3 (Zr, Li) core-shell structure serve as the nucleation site of the strengthening phase, reduces the interface energy, promotes the uniform precipitation of T1 and θ' phases, and can obtain better strength and ductility than the basic alloy. The yield strength (YS), ultimate tensile strength (UTS) and elongation (EL) of the Zr-added alloy are increased from 302MPa, 363MPa and 3.6% to 321MPa, 429MPa and 7.1%, respectively. It has good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 1 is the transmission and DF images of the as-cast alloy of Example 1 of the present invention;

[0032] (a)

[110] Al SAED spectrum (b) 100nm DF spectrum (c)

[112] Al SAED spectrum (d) 100nm HAADF spectrum

[0033] Figure 2 Transmission and DF images of the as-cast alloy of the comparative example of the present invention;

[0034] (a)

[110] Al SAED spectrum (b) 100nm DF spectrum (c)

[112] Al SAED spectrum (d) 100nm HAADF spectrum

[0035] Figure 3 The scanned image of the cast alloy of the present invention and the corresponding mapping result;

[0036] (a) 50 μm Example 1 (b) 10 μm Example 1 and mapping results

[0037] (c) 50μm comparison (d) 10μm comparison and mapping results

[0038] Figure 4 The tensile properties of Example 1 of the present invention and the comparative example under peak aging conditions: (a) typical engineering strain-stress curve; (b) corresponding tensile properties. DETAILED DESCRIPTION

[0039] Example 1

[0040] Raw material preparation: 95.0 parts by mass of Al, 2 parts by mass of Li, 0.45 parts by mass of Mg, 1.95 parts by mass of Al-50wt.% Cu and 0.2 parts by mass of Al-5wt.% Zr, and the inevitable impurity elements in the raw materials are less than 0.05 parts by mass. Industrial-grade pure metal Al, metal Mg and battery-grade pure Li are used as raw materials for preparation. The industrial-grade pure metal aluminum, pure metal Mg and battery-grade Li have a purity greater than 99.9%.

[0041] For alloy smelting and casting, a high-purity graphite crucible is used as a smelting container. The metal Al and metal Mg required for smelting are placed in the graphite crucible of the resistance furnace, and the temperature is raised to 720°C. After the metal is melted, the intermediate alloy Al-Cu, Al-Zr and pure Li are added. The melt mixture is covered with LiCl and LiF at a molar ratio of 1:1, and then allowed to stand for 10 minutes. During this period, C2Cl6 gas is used for degassing. After standing, the surface scum is removed to obtain the melt.

[0042] The obtained melt is cast using a semi-continuous casting method at a temperature of 720°C.

[0043] The cast alloy is then placed in a vacuum furnace under argon protection for a two-stage solution treatment process, and finally a solution-treated Al-Li-Cu-Mg-Zr alloy is obtained. The temperature of the first-stage solution treatment is 480°C, the holding time is 32 hours, and the heating rate is 5°C / min. After the solution treatment, the furnace is cooled to room temperature. The temperature of the second-stage solution treatment is 535°C, the holding time is 24 hours, and the heating rate is 10°C / min. After the solution treatment, room temperature water-cooling quenching is performed, and the quenching transfer time is less than 10s. Thereafter, the Al-Li-Cu-Mg-Zr alloy after the solution treatment is artificially aged. The alloy ingot is placed in a silicone oil bath with a treatment temperature of 175°C and a holding time of 32 hours. After the artificial aging is completed, the furnace is cooled to room temperature. After artificial aging, the transmission and scanning images of a unique nano-core-shell structure precipitation phase are produced as shown in the following figure. Figure 1 shown.

[0044] Comparative Example

[0045] Raw material preparation: 95.0 parts by mass of Al, 2 parts by mass of Li, 0.45 parts by mass of Mg, 2.0 parts by mass of master alloy Al-50wt.%Cu, and the inevitable impurity elements in the above raw materials are less than 0.05 parts by mass. Industrial grade pure metal Al, metal Mg, and battery grade pure Li are used as raw materials for preparation.

[0046] For alloy smelting and casting, a high-purity graphite crucible is used as a smelting container. The metal Al and metal Mg required for smelting are placed in the graphite crucible of the resistance furnace, and the temperature is raised to 720°C. After the alloy is melted, the intermediate alloy Al-Cu and pure Li are added. The molten mixture is covered with LiCl and LiF at a molar ratio of 1:1, and then left to stand for 10 minutes, during which C2Cl6 gas is used for degassing. After standing, the surface scum is removed to obtain the melt.

[0047] The obtained melt is cast using a semi-continuous casting method at a temperature of 720°C.

[0048] The cast alloy is placed in a vacuum furnace under argon protection for two-stage solution treatment, and finally a solution-treated Al-Li-Cu-Mg alloy is obtained. The temperature of the first stage solution treatment is 480°C, the holding time is 32h, and the heating rate is 5°C / min. After the first stage solution treatment, the furnace is cooled to room temperature. The temperature of the second stage solution treatment is 535°C, the holding time is 24h, and the heating rate is 10°C / min. After the second stage solution treatment, room temperature water cooling quenching is carried out, and the quenching transfer time is less than 10s. After that, the Al-Li-Cu-Mg alloy after solution treatment is artificially aged: the alloy ingot is placed in a silicone oil bath, the treatment temperature is 175°C, and the holding time is 32h. After the artificial aging is completed, it is cooled to room temperature with the furnace.

[0049] Transmission and scanning images of materials after artificial aging treatment Figure 2 shown.

[0050] Test Results

[0051] The microstructure of the alloy tested under cast condition is as follows Figure 3 shown.

[0052] The alloy after aging treatment is preheated to the tensile deformation temperature and then kept warm. It is then placed in a preheated tensile device for tensile deformation. The tensile specimen is shaped like a flat dog bone, with a length of 15 mm and a width of 3.5 mm. The tensile test results of the alloy after artificial aging treatment of the embodiment and the comparative example are shown in FIG. Figure 4 shown.

Claims

1. A method for preparing a lightweight alloy toughening material based on a nano core-shell structure, characterized in that: The specific steps include: S1 Raw material preparation: Take 94-96 weight parts of metal Al, 0.45-0.5 weight parts of Mg, 2-2.05 weight parts of Li, 1.95-2.0 weight parts of master alloy Al-Cu and 0.2-0.25 weight parts of Al-Zr, wherein Cu accounts for 40-60 weight percent of master alloy Al-Cu and Zr accounts for 3-8 weight percent of master alloy Al-Zr; S2 Melting and Casting: a. mixing Al, Mg, master alloys Al-Cu and Al-Zr, and Li for smelting; Inert gas is introduced into the smelting process, and a mixture of LiCl and LiF is used as a flux to cover the melt; b. After degassing with C2Cl6 and maintaining at 650-750°C for not less than 5 minutes, a melt is obtained; cCasting and curing The melt is cast by pressure casting or gravity casting, the casting temperature is controlled at 650-750°C, the molten alloy is cast, and then cooled and solidified to obtain Al-Li-Cu-Mg-Zr alloy; S3 solution treatment: The cast Al-Li-Cu-Mg-Zr alloy was solution treated using a customized two-stage solution process: the first stage was a preliminary solution treatment at 450-500°C for 24-36 hours; the second stage was a secondary solution treatment at 500-560°C for 20-30 hours to fully form a uniform solid solution; the treated alloy was then quenched in room temperature water; S4 aging treatment: The alloy after solution treatment is placed in a silicone oil bath for artificial aging treatment at 150-200°C for 24-36 hours, and then water-cooled to room temperature.

2. The method for preparing a lightweight alloy toughening material based on a nano core-shell structure according to claim 1, characterized in that: The metal Al and metal Mg are industrial grade pure metals.

3. The method for preparing a lightweight alloy toughening material based on a nano core-shell structure according to claim 1, characterized in that: The pure Li adopts battery-grade purity.

4. The method for preparing a lightweight alloy toughening material based on a nano core-shell structure according to claim 1, characterized in that: In the step S1, the surface of the raw material of the metal or alloy material is treated to remove impurities and oxide layer.

5. The method for preparing a lightweight alloy toughening material based on a nano core-shell structure according to claim 1, characterized in that: In the step S2, the cooling rate is 10-30°C / min.

6. The method for preparing a lightweight alloy toughening material based on a nano core-shell structure according to claim 1, characterized in that: In the step S2, smelting is performed in a high-purity graphite crucible in a resistance furnace.

7. The method for preparing a lightweight alloy toughening material based on a nano core-shell structure according to claim 1, characterized in that: In step S2, a semi-continuous casting method is adopted: The metal Al and metal Mg required for smelting are placed in a graphite crucible of a resistance furnace and heated to 700-750°C. After the metal is melted, the intermediate alloy Al-Cu, Al-Zr and pure Li are added, and the molten mixture is covered with LiCl and LiF in a molar ratio of 1:

1.

8. The method for preparing a lightweight alloy toughening material based on a nano core-shell structure according to claim 1, characterized in that: In the step S2, the molar ratio of LiCl to LiF is 1:

1.

9. The method for preparing a lightweight alloy toughening material based on a nano core-shell structure according to claim 1, characterized in that: In step S2, the inert gas is argon.

10. The present invention provides a nano-core-shell structured Al-Li-Cu-Mg-Zr alloy, which is prepared by the method described in any one of claims 1 to 9.

Images