A super-strong aluminum alloy material and its preparation and processing method

Abstract

The present invention discloses a super-strong aluminum alloy material and its preparation and processing method. In this aluminum alloy material, the content of Zn is 6.0 - 6.7 wt.%, the content of Mg is 2.1 - 2.9 wt.%, the content of Cu is 1.6 - 1.9 wt.%, the content of Zr is 0.1 - 0.15 wt.%, the content of Nd is 0.2 - 0.4 wt.%, the content of impurities is less than or equal to 0.1 wt.%, and the balance is aluminum; its preparation and processing method includes step A, melting and casting; step B, homogenization treatment; step C, hot deformation treatment; step D, solution treatment; step E, aging treatment. The super-strong aluminum alloy material and its preparation and processing method in the present invention are optimized from two aspects of alloy composition design and heat treatment method, improving the strength and toughness of the alloy, as well as the high-temperature performance of the alloy.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum alloy material processing. Specifically, it is a super-strong aluminum alloy material and its preparation and processing method. Background Art

[0002] Al-Zn-Mg-Cu-Zr series aluminum alloys are widely used in aerospace due to their ultra-high strength and toughness. With the development of the aviation field, the requirements for the overall performance, service life, safety and reliability, and structural quality control of aircraft are constantly increasing; this poses higher performance requirements for high-strength aluminum alloys. As is well known, microalloying is one of the most effective methods to improve the microstructure of alloys and obtain excellent comprehensive properties. Among them, rare earth elements are the most effective microalloying elements to improve the comprehensive properties of super-strong aluminum alloys at present. The interaction between rare earth elements and the α-Al matrix can form extremely fine and dispersed massive compounds and precipitation phases coherent with the α-Al matrix. These dispersed phases uniformly distributed in the matrix can strongly pin dislocations and subgrain boundaries, effectively inhibit recrystallization, and thus improve the corrosion resistance, high-temperature resistance, and fracture toughness of the alloy.

[0003] In recent years, researchers at home and abroad have begun to add trace rare earth elements (such as Sc, Er, La, Ce, etc.) to 7xxx series aluminum alloys to explore new types of super-strong aluminum alloys. Sc is the most effective element to improve the performance of aluminum alloys so far. It is because the primary and precipitated Al3Sc or Al3(Sc,Zr) phases can cause grain refinement of aluminum alloys during solidification, heat treatment, and deformation processes, thereby promoting grain boundary strengthening of aluminum alloys. The production process of the alloy mainly includes casting, homogenization, hot extrusion, solution treatment, and aging treatment. Determining the process methods in each production process is the key to controlling the final performance of the alloy. Therefore, designing a new type of super-strong aluminum alloy material and its preparation and processing method is the most effective way to develop high-strength aluminum alloys at present. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to provide a super-strong aluminum alloy material and its preparation and processing method to solve the problem that the strength, toughness, and high-temperature performance of existing aluminum alloy materials cannot meet the use requirements.

[0005] To solve the above technical problem, the present invention provides the following technical solutions:

[0006] A super-strong aluminum alloy material, with the content of Zn being 6.0 - 6.7 wt.%, the content of Mg being 2.1 - 2.9 wt.%, the content of Cu being 1.6 - 1.9 wt.%, the content of Zr being 0.1 - 0.15 wt.%, the content of Nd being 0.2 - 0.4 wt.%, the content of impurities being less than or equal to 0.1 wt.%, and the balance being aluminum. Compared with the rare earth elements Er and Sc commonly used in aluminum alloys in recent years, Nd has a relatively low diffusion coefficient at high temperatures, a relatively high lattice mismatch rate, and a similar maximum solubility in the α-Al matrix. Specifically, it is manifested as follows: ① The lattice mismatch between the FCC-Al matrix and L12-Al3Sc is 1.32%, the lattice mismatch between α-Al and L12-Al3Er is 4.1%, and the lattice mismatch rate between the rare earth phase formed by Nd and the α-Al matrix is 6.13%. The relatively large lattice mismatch degree results in a higher strengthening effect on the alloy at room temperature and high temperatures; ② Compared with Sc, the high-temperature solid solubility of Er in the FCC-Al matrix is lower than that of Sc, which increases the driving force and volume fraction of precipitation; the diffusion rate of Er in α-Al at 300 °C is 4×10 - 19 m 2 / s, which is higher than that of Sc (0.9×10 -19 m 2 / s). However, at 400 °C, the diffusion rate of Er of Sc in α-Al is 1×10 -18 m 2 / s, while the diffusion rate of Sc is 1.98×10 -17 m 2 / s, and the diffusion coefficient of Nd at 400 °C is 3.93×10 -19 m 2 / s. The diffusion coefficient of Nd is relatively low compared with Er and Sc, which inhibits the coarsening controlled by volume diffusion and enables the precipitates to effectively hinder the dislocation movement at high temperatures; ③ Regarding the solid solubility in Al, the maximum solubility of Sc in aluminum is 0.23 at.%, the maximum solid solubility of Er in aluminum is 0.17 at.%, and the maximum solid solubility of Nd in aluminum is 0.28 at.%. The limited solid solubility can maximize the equilibrium volume fraction of the dispersed phase. The application of rare earth Nd in Al-Zn-Mg-Cu-Zr series aluminum alloys is almost non-existent, and most of them are used in the research of the thermal stability of 2xxx series aluminum alloys, Al-Si series alloys and magnesium alloys; therefore, in the present invention, rare earth Nd is added as a new microalloying element, and a super-strong aluminum alloy material with strength, toughness and high-temperature properties all meeting the use requirements can be designed.

[0007] In the above-mentioned super-strong aluminum alloy material, the mass ratio of Zn to Mg is (2.5-2.7):1. When w(Zn) / w(Mg)=2.5-2.7, the main strengthening phases are η'(MgZn2) and η(MgZn2) phases. When w(Zn) / w(Mg) is less than 2.5, the magnesium content exceeds the amount required to form the MgZn2 phase, which will produce a supplementary strong interaction and form a T phase; since the diffusion rate of Cu is much lower than the diffusion rate of Zn and Mg, there is too much T phase in the alloy, which will form a hard and brittle S phase during the homogenization process, and will be easily broken during the thermal deformation process, resulting in performance degradation; in order to avoid the formation of more T phases, the w(Zn) / w(Mg) ratio designed by the present invention is lower than the zinc-magnesium ratio of the T phase of 2.71, so that as many MgZn2 phases as possible are formed to reduce the generation of T phases.

[0008] The above-mentioned super-strong aluminum alloy material has a Zn content of 6.1wt.%, a Mg content of 2.3wt.%, a Cu content of 1.7wt.%, a Zr content of 0.15wt.%, and a Nd content of 0.2wt.%.

[0009] A method for preparing and processing a super-strong aluminum alloy material comprises the following steps:

[0010] Step A, smelting and casting: using aluminum, aluminum-zinc master alloy, aluminum-magnesium master alloy, aluminum-copper master alloy, aluminum-zirconium master alloy and magnesium-neodymium master alloy as raw materials, smelting and casting to obtain aluminum alloy ingots;

[0011] Step B, homogenization treatment: homogenizing the aluminum alloy ingot to obtain a homogenized aluminum alloy material;

[0012] Step C, thermal deformation treatment: performing thermal deformation treatment on the homogenized aluminum alloy material to obtain an aluminum alloy plate;

[0013] Step D, solution treatment: subjecting the aluminum alloy plate to solution treatment to obtain a solutionized aluminum alloy plate;

[0014] Step E, aging treatment: performing aging treatment on the aluminum alloy plate after solid solution treatment to obtain a super-strong aluminum alloy material;

[0015] In the super-strong aluminum alloy material obtained in step E: the content of Zn is 6.0-6.7wt.%, the content of Mg is 2.1-2.9wt.%, the content of Cu is 1.6-1.9wt.%, the content of Zr is 0.1-0.15wt.%, the content of Nd is 0.2-0.4wt.%, the content of impurities is less than or equal to 0.1wt.%, and the balance is aluminum. The process method and process parameters of each step designed by the present invention are helpful to maximize the strength and toughness of the alloy. At the same time, the addition of rare earth Nd element is also conducive to grain refinement and the formation of a high melting point dispersed phase, which can significantly improve the mechanical properties of the alloy.

[0016] The preparation and processing method of the above-mentioned super-strong aluminum alloy material, the specific operation method of smelting and casting in step A comprises the following steps:

[0017] Step (A-1), preparing alloy raw materials and grinding the alloy raw materials; the alloy raw materials are: pure aluminum, aluminum-zinc master alloy, aluminum-magnesium master alloy, aluminum-copper master alloy, aluminum-zirconium master alloy and magnesium-neodymium master alloy; the grinding treatment is to grind the surface of the alloy material with a file to remove the surface oxide scale;

[0018] Step (A-2), melting the alloy in a resistance induction melting furnace: first preheating the crucible, then adding pure aluminum and heating it for melting, and after all the pure aluminum is melted, sequentially adding an aluminum-zinc master alloy, an aluminum-copper master alloy, an aluminum-zirconium master alloy wrapped in aluminum foil, and an aluminum-magnesium master alloy wrapped in aluminum foil; after all the added alloy raw materials are melted, refining, stirring, and slagging are performed to obtain a molten alloy liquid;

[0019] Step (A-3), adding a magnesium-neodymium master alloy wrapped in aluminum foil to the molten alloy liquid, stirring after standing to obtain an aluminum alloy liquid; the order of adding the Mg-30%Nd master alloy is particularly important, and it is added after degassing and refining. This operation greatly reduces the burning loss of rare earth elements. At the same time, stirring and pouring 2 minutes after adding the master alloy can reduce the segregation of rare earth elements in the alloy;

[0020] Step (A-4), immediately pouring the stirred aluminum alloy liquid into a preheated graphite mold, and casting to obtain an aluminum alloy ingot.

[0021] In the preparation and processing method of the above-mentioned super-strong aluminum alloy material, in step (A-1), the purity of pure aluminum is greater than or equal to 99.9wt%; the mass fraction of zinc in the aluminum-zinc master alloy is 30wt.%, the mass fraction of magnesium in the aluminum-magnesium master alloy is 20wt.%, the mass fraction of copper in the aluminum-copper master alloy is 30wt.%, and the mass fraction of zirconium in the aluminum-zirconium master alloy is 10wt.%; when preparing the alloy raw materials, the ingredients are prepared according to the burn-out rate of zinc being 2%, the burn-out rate of copper being 5%, and the burn-out rate of zirconium being 30%;

[0022] In step (A-2), the crucible is preheated to 380-420°C; after adding pure aluminum, the temperature is raised to 720-750°C; the refining method is as follows: the temperature of the alloy liquid is controlled within the range of 725-735°C, a graphite bell jar filled with C2Cl6 is immersed in the alloy liquid and argon gas is introduced, and the alloy liquid is refined for 20 minutes; the mass of C2Cl6 is 0.3-0.5wt% of the total weight of the alloy liquid;

[0023] In step (A-3), when the temperature of the smelted alloy liquid is adjusted to the range of 700-710 °C, the magnesium-neodymium master alloy wrapped with aluminum foil is added, and the standing time is 2 min; the mass fraction of neodymium in the magnesium-neodymium master alloy is 30 wt.%.

[0024] In step (A-4), the preheating temperature of the graphite mold is 180-230 °C.

[0025] In the preparation and processing method of the above ultra-strong aluminum alloy material, in step B, during homogenization treatment, the aluminum alloy ingot is first heated to 300 °C at a heating rate of 340 °C / h and held for 6 h; then the aluminum alloy ingot is heated to 472 °C at a heating rate of 50 °C / h and held for 24 h; after the holding is completed, water quenching is carried out with water at a temperature less than or equal to 25 °C, and the water quenching transfer time is less than or equal to 5 s.

[0026] In the preparation and processing method of the above ultra-strong aluminum alloy material, in step C, during hot deformation treatment, the homogenized aluminum alloy material is first placed in an electric resistance furnace and pre-treated at a temperature of 420 °C for 2 h; then at an extrusion temperature of 410 ± 5 °C, an extrusion speed of 1 mm / s, and an extrusion ratio of 25:1, extrusion deformation is carried out to obtain an aluminum alloy plate.

[0027] In the preparation and processing method of the above ultra-strong aluminum alloy material, in step D, during solution treatment, the aluminum alloy plate is first heated to 455 °C at a heating rate of 340 °C / h and held for 1.5 h; then the aluminum alloy plate is heated to 474 °C at a heating rate of 60 °C / h and held for 0.5 h; after the holding is completed, water quenching is carried out with water at a temperature less than or equal to 25 °C, and the water quenching transfer time is less than or equal to 5 s.

[0028] In the preparation and processing method of the above ultra-strong aluminum alloy material, in step E, during aging treatment, the solution-treated aluminum alloy plate is first heated to 105 °C at a heating rate of 340 °C / h and held for 24 h; then the solution-treated aluminum alloy plate is heated to 170 °C at a heating rate of 3 °C / min, held for 85 min, and then water quenched with water at a temperature less than or equal to 25 °C, and the water quenching transfer time is less than or equal to 5 s; then the solution-treated aluminum alloy plate is naturally aged for 24 h; finally, the solution-treated aluminum alloy plate is heated to 80 °C at a heating rate of 340 °C / h and held for 34 h; after the holding is completed, it is air-cooled to room temperature. In the RRA of aging treatment, natural aging for 24 h is introduced. Supersaturated vacancies are prone to combine with magnesium atoms, accelerating the diffusion of Mg atoms and increasing the nucleation rate of GP zones. During the re-aging process, more nucleation sites are provided for GP zones, and slow heating rate is adopted before the regression stage, which will increase the volume fraction of η' phase and reduce the η phase after the regression ends.

[0029] The technical solution of the present invention has achieved the following beneficial technical effects:

[0030] In the present invention, a super-strong aluminum alloy material and its preparation and processing method are optimized from two aspects: the design of alloy composition and the heat treatment method. The elemental composition of the finally obtained aluminum alloy material is: Al-6.1Zn-2.3Mg-1.7Cu-0.15Zr-0.2Nd; this aluminum alloy material has excellent alloy strength and toughness, as well as good high-temperature performance. Under the preparation and processing conditions of the present invention, the addition of rare earth Nd can interact with other elements in the alloy and improve the segregation degree of elements in the alloy, making the cast alloy have uniformity, and also providing guarantee for subsequent deformation and heat treatment. Brief Description of the Drawings

[0031] Figure 1 Schematic diagram of alloy melting and casting process in the embodiment of the present invention;

[0032] Figure 2a Microstructure diagram (200μm) of the aluminum alloy ingot without Nd in the embodiment of the present invention;

[0033] Figure 2b Microstructure diagram (200μm) of the aluminum alloy ingot containing 0.20wt.% Nd in the embodiment of the present invention;

[0034] Figure 2c Microstructure diagram (200μm) of the aluminum alloy ingot containing 0.25wt.% Nd in the embodiment of the present invention;

[0035] Figure 2d Microstructure diagram (200μm) of the aluminum alloy ingot containing 0.30wt.% Nd in the embodiment of the present invention;

[0036] Figure 2e Microstructure diagram (200μm) of the aluminum alloy ingot containing 0.35wt.% Nd in the embodiment of the present invention;

[0037] Figure 2f Microstructure diagram (200μm) of the aluminum alloy ingot containing 0.40wt.% Nd in the embodiment of the present invention;

[0038] Figure 3a Microstructure diagram (50μm) of the aluminum alloy ingot containing 0.20wt.% Nd in the embodiment of the present invention;

[0039] Figure 3b SEM image (Al element) of the surface of the aluminum alloy ingot containing 0.20wt.% Nd in the embodiment of the present invention;

[0040] Figure 3c SEM image (Zn element) of the surface of the aluminum alloy ingot containing 0.20wt.% Nd in the embodiment of the present invention;

[0041] Figure 3dSEM image of the surface of an aluminum alloy ingot containing 0.20 wt.% Nd in the embodiment of the present invention (Mg element);

[0042] Figure 3e SEM image of the surface of an aluminum alloy ingot containing 0.20 wt.% Nd in the embodiment of the present invention (Cu element);

[0043] Figure 3f SEM image of the surface of an aluminum alloy ingot containing 0.20 wt.% Nd in the embodiment of the present invention (Zr element);

[0044] Figure 3g SEM image of the surface of an aluminum alloy ingot containing 0.20 wt.% Nd in the embodiment of the present invention (Nd element);

[0045] Figure 4a Microstructure of an aluminum alloy ingot containing 0 wt.% Nd and SEM image of the surface with copper element in the embodiment of the present invention;

[0046] Figure 4b Microstructure of an aluminum alloy ingot containing 0.35 wt.% Nd and SEM image of the surface with copper element in the embodiment of the present invention;

[0047] Figure 4c Microstructure of an aluminum alloy ingot containing 0.25 wt.% Nd and SEM image of the surface with copper element in the embodiment of the present invention;

[0048] Figure 4d Microstructure of an aluminum alloy ingot containing 0.40 wt.% Nd and SEM image of the surface with copper element in the embodiment of the present invention;

[0049] Figure 5 Histogram of Brinell hardness of aluminum alloy ingots with different Nd contents in the embodiment of the present invention;

[0050] Figure 6 Schematic diagram of the tensile properties of aluminum alloy ingots with different Nd contents in the embodiment of the present invention;

[0051] Figure 7a Schematic diagram of the relationship between the equilibrium transformation amount and temperature of Al-6.1Zn-2.3Mg-1.7Cu-0.15Zr alloy in the embodiment of the present invention;

[0052] Figure 7b Figure 7a Schematic diagram of the relationship between the equilibrium transformation amount and temperature of S-Al2-CuMg;

[0053] Figure 7c Figure 7a Schematic diagram of the relationship between the equilibrium transformation amount and temperature of T-AlZnMgCu;

[0054] Figure 7d Figure 7aSchematic diagram of the relationship between the equilibrium transformation amount of η-MgZn2 and temperature;

[0055] Figure 7e Figure 7a In Al3M-D0 23 Schematic diagram of the relationship between the equilibrium transformation amount and temperature;

[0056] Figure 8 Homogenization kinetics curve diagram of Cu element with different dendrite spacings in the embodiment of the present invention;

[0057] Figure 9a Optical microscope image of Al-6.1Zn-2.3Mg-1.7Cu-0.15Zr-0Nd in the embodiment of the present invention;

[0058] Figure 9b Optical microscope image of Al-6.1Zn-2.3Mg-1.7Cu-0.15Zr-0.2Nd in the embodiment of the present invention;

[0059] Figure 9c Column chart of recrystallization volume fraction of Al-6.1Zn-2.3Mg-1.7Cu-0.15Zr-0Nd and Al-6.1Zn-2.3Mg-1.7Cu-0.15Zr-0.2Nd in the embodiment of the present invention;

[0060] Figure 10 Schematic diagram of process parameters of homogenization treatment, hot deformation treatment, solution treatment and aging treatment in the embodiment of the present invention;

[0061] Figure 11 Hardness diagram of Al-6.1Zn-2.3Mg-1.7Cu-0.15Zr-xNd (x = 0; 0.2) alloy after four-stage aging and 120°C / 100h thermal exposure in the embodiment of the present invention;

[0062] Figure 12 Engineering stress-strain diagram of Al-6.1Zn-2.3Mg-1.7Cu-0.15Zr-xNd (x = 0; 0.2) alloy after four-stage aging and 120°C hot tensile in the embodiment of the present invention. Detailed implementation manners

[0063] In this embodiment, the preparation and processing method of the ultra-high strength aluminum alloy material includes the following steps:

[0064] Step A, melting and casting: Using aluminum, aluminum-zinc master alloy, aluminum-magnesium master alloy, aluminum-copper master alloy, aluminum-zirconium master alloy and magnesium-neodymium master alloy as raw materials, melting and casting to obtain an aluminum alloy ingot (as Figure 1 shown);

[0065] The specific operation methods for smelting and casting include the following steps:

[0066] Step (A-1), prepare alloy raw materials and conduct pretreatment: pure aluminum, aluminum-zinc master alloy, aluminum-magnesium master alloy, aluminum-copper master alloy, aluminum-zirconium master alloy, and magnesium-neodymium master alloy; the pure aluminum is high-purity aluminum with an aluminum content of 99.9 wt.%; the mass fraction of zinc in the aluminum-zinc master alloy is 30 wt.%, the mass fraction of magnesium in the aluminum-magnesium master alloy is 20 wt.%, the mass fraction of copper in the aluminum-copper master alloy is 30 wt.%, and the mass fraction of zirconium in the aluminum-zirconium master alloy is 10 wt.%; when preparing the alloy raw materials, use a file to polish the surface of the required alloy raw materials to remove the surface oxide scale, and carry out batching according to a zinc burn loss rate of 2%, a copper burn loss rate of 5%, and a zirconium burn loss rate of 30%;

[0067] Step (A-2), smelt the alloy using a resistance induction melting furnace: first preheat the crucible to 400 °C, then add pure aluminum and heat it up to 740 °C for smelting. After all the pure aluminum has melted, sequentially add the aluminum-zinc master alloy, aluminum-copper master alloy, and aluminum-magnesium master alloy wrapped in aluminum foil, then add the aluminum-zirconium master alloy and stir for 5 minutes each time; after all the added alloy raw materials have melted, conduct refining treatment, stirring, and skimming in sequence to obtain the smelted alloy liquid; the method of refining treatment is: lower the temperature of the alloy liquid to 730 °C, immerse a graphite bell jar filled with C2Cl6 into the alloy liquid and introduce argon for degassing and refining for 20 minutes; the mass of C2Cl6 is 0.4 wt.% of the total weight of the alloy liquid;

[0068] Step (A-3), when the temperature of the smelted alloy liquid is lowered to 710 °C, add the magnesium-neodymium master alloy wrapped in aluminum foil to the smelted alloy liquid, let it stand for 2 minutes and then stir to obtain the aluminum alloy liquid; the mass fraction of neodymium in the magnesium-neodymium master alloy is 30 wt.%;

[0069] Step (A-4), immediately pour the stirred aluminum alloy liquid into a graphite mold preheated to 200 °C for casting to obtain an aluminum alloy ingot.

[0070] In the aluminum alloy ingot of the super-strong aluminum alloy material prepared in this example: the content of Zn is 6.1 wt.%, the content of Mg is 2.3 wt.%, the content of Cu is 1.7 wt.%, the content of Zr is 0.15 wt.%, the content of Nd is 0.2 wt.%, the content of impurities is less than or equal to 0.1 wt.%, and the balance is aluminum;

[0071] Using the same preparation method as in step A, by controlling the addition amount of the magnesium-neodymium master alloy Mg-30%Nd, aluminum alloy materials with Nd contents of 0, 0.25 wt.%, 0.3 wt.%, 0.35 wt.%, and 0.4 wt.% are respectively prepared.

[0072] The as-prepared aluminum alloy ingots with different Nd contents were subjected to microstructure analysis, and the results are as follows Figures 2a to 2f shown. From Figures 2a to 2f it can be seen that when rare earth element Nd is added to the alloy ingot, it can be clearly observed that the addition of Nd significantly refines the as-cast structure of the alloy. The eutectic structure of the alloy becomes thinner and discontinuous, and the dendrite spacing and the non-equilibrium eutectic phase at the grain boundaries also decrease relatively. Among them, the refining effect is most obvious when 0.2 wt.% Nd is added. This is mainly because rare earth element Nd has high chemical activity. During the solidification of the alloy casting, due to the limitation of the solidification diffusion kinetics conditions, Nd elements will aggregate at the front of the solid / liquid interface, and solute redistribution will occur during the processes of crystal nucleation and growth, changing the composition supercooling zone, thereby inhibiting the growth of dendrites during the alloy solidification process and refining the grain size. From Figures 3a to 4d it can also be seen that the addition of 0.2 wt.% Nd of rare earth elements also has a certain improvement on the segregation effect of Cu elements, reducing the segregation effect at the grain boundaries and increasing the distribution density of Cu elements in the grains. In terms of mechanical properties, with the continuous addition of Nd content, generally speaking, the Brinell hardness remains relatively stable. This phenomenon indicates that the Nd-containing alloy has good tissue uniformity. When the Nd content is 0.2 wt.%, it has the best refining effect and the best comprehensive performance. The room temperature hardness increases by 44.9% (105.2 HBW, see Figure 5 ); the room temperature tensile strength and elongation increase by 34.3% (163 MPa, see Figure 6 ) and 44% (2.5%, see Figure 6 ), respectively.

[0073] Step B: Homogenization treatment: The aluminum alloy ingot was subjected to homogenization treatment to obtain a homogenized aluminum alloy material; during the homogenization treatment, the aluminum alloy ingot was first heated to 300 °C at a heating rate of 50 °C / h and held for 6 h; then the aluminum alloy ingot was heated to 472 °C at a heating rate of 50 °C / h and held for 24 h; after the holding was completed, water quenching was carried out with water at 15 °C, and the water quenching transfer time was less than or equal to 5 s.

[0074] The determination of the homogenization process in this embodiment was carried out by thermodynamically simulating and calculating the Al-6.1Zn-2.3Mg-1.7Cu-0.15Zr alloy using thermodynamic software to determine the temperature in the first stage of the two-stage homogenization; the temperature and time in the second stage were determined by DSC testing and establishing a homogenization kinetic equation. Specifically, thermodynamic simulation calculations were carried out on the aluminum alloy ingots with different Nd contents prepared in step A: the Al-6.1Zn-2.3Mg-1.7Cu-0.15Zr alloy for homogenization treatment, and then the temperature in the first stage of the homogenization treatment was selected. From Figure 7aThe liquidus temperature and solidus temperature of the alloy can be obtained as 634°C and 532°C respectively. In the vector diagram of the temperature and content of elements in the alloy, the precipitation temperatures of each eutectic phase with low melting point can be determined. For example, Figures 7b to 7e in it, the starting precipitation temperature of the S phase can be determined as 465°C, and when the temperature is 414°C, the content of the S phase is the highest at 1.71%; the starting precipitation temperature of the T phase is 227°C until room temperature; the starting precipitation temperature of the η phase is 414°C, and when the temperature is 227°C, the content of the η phase is the highest at 5.39%; Al3M-D0 23 phase starts to precipitate at 700°C, and there is a brief downward trend of the Al3M-D0 23 phase at 634°C and then continues to rise after 610°C. When the temperature reaches 300°C, the precipitation amount is relatively stable and the content reaches the maximum value of 0.18%. In order to obtain more dispersed Al3Zr phase, the first-stage homogenization system is selected as 300°C / 6h (the first-stage temperature is close to the dissolution temperature of the η phase).

[0075] According to the DSC results, the starting melting points of the precipitated phases are from 475.4°C to 505.3°C. In order to prevent overburning, the temperature should be slightly lower than the starting melting point of the non-equilibrium eutectic phase, and finally 472°C is selected. The ramp heating is adopted in the heating stage of the two-stage homogenization, and the heating rate is 50° / h. In order to determine the time required for the homogenization process, the homogenization kinetic equation is used, such as Figure 8 shown. The secondary dendrite arm spacing of the 0.2wt.% Nd alloy is 53μm, and the total homogenization time determined is 33h. Combining the homogenization time and heating rate of the first stage, the process of the second stage is finally determined as 472°C / 24h.

[0076] Therefore, in this embodiment, the homogenization system is selected as 300°C / 6h (heating rate 340° / h) → 472°C / 24h (heating rate 50° / h, water quenching).

[0077] Step C, hot deformation treatment: The homogenized aluminum alloy material is subjected to hot deformation treatment to obtain an aluminum alloy plate; during the hot deformation treatment, the homogenized aluminum alloy material is first placed in a resistance furnace and pre-treated at a temperature of 420°C for 2h; then at an extrusion temperature of 400°C, with an extrusion speed of 1mm / s and an extrusion ratio of 25:1, extrusion deformation is carried out to obtain an aluminum alloy plate.

[0078] Step D, solution treatment: The aluminum alloy plate is subjected to solution treatment to obtain a solution-treated aluminum alloy plate;

[0079] The evolution of the second-phase particles during solution treatment includes three stages: (1) In the low-temperature stage, i.e., in the range of room temperature to 350 °C, the precipitation of MgZn2 occurs; (2) In the temperature range of 350 °C to 450 °C, the dissolution of MgZn2 and the coarsening of Al2CuMg; (3) In the high-temperature range above 450 °C, the dissolution of the Al2CuMg phase. To avoid the transformation of the MgZn2 phase into the S phase, the temperature in the low-temperature stage is designed to be above 450 °C. According to the DSC results, the starting melting temperature of the low-melting-point non-equilibrium eutectic phase is 489 °C, and the starting temperature of the phase transformation is 477 °C. To prevent overburning during solution treatment and prevent the melting of the second phase and the appearance of defects at the bonding interface between the phase and the matrix, the temperature is reduced by 3 - 5 °C. The final solution treatment process is 455 °C / 1.5 h (heating rate of 340 °C / h), heating to 474 °C / 0.5 h at a heating rate of 60 °C / h; after the holding is completed, water quenching is carried out with water at 25 °C, and the water quenching transfer time is less than or equal to 5 s.

[0080] It can be seen from Figures 9a to 9c that for the alloy without the addition of rare earth Nd, obvious recrystallization occurred, and the recrystallization ratio was 60.3%. For the alloy with 0.2 wt% Nd added, the non-recrystallized fibrous structure was basically maintained, and the recrystallization ratio was 44.5%; compared with the alloy without rare earth addition, the inhibitory effect of adding 0.2 wt% Nd on recrystallization was enhanced by 26.2%; compared with the alloy without rare earth addition, the combined addition of Nd had a better effect of inhibiting recrystallization, could better retain the deformed recovery structure, stabilized the substructure of the deformed structure, hindered the process of the subgrain boundary developing into a large-angle grain boundary, effectively inhibited the processes of recrystallization nucleation and growth, retained more subgrains with small-angle grain boundaries, and improved the final comprehensive mechanical properties; this indicates that the addition of Nd has significantly improved the comprehensive properties of the alloy.

[0081] Step E, aging treatment: The solution-treated aluminum alloy plate is subjected to aging treatment to obtain a super-strong aluminum alloy material; during aging treatment, first, the solution-treated aluminum alloy plate is heated to 105 °C at a heating rate of 340 °C / h and held for 24 h; then, the solution-treated aluminum alloy plate is heated to 170 °C at a heating rate of 3 °C / min and held for 85 min, and water quenching is carried out with water at 25 °C, and the water quenching transfer time is less than or equal to 5 s; then, the solution-treated aluminum alloy plate is naturally aged for 24 h; finally, the solution-treated aluminum alloy plate is heated to 80 °C at a heating rate of 340 °C / h and held for 34 h; after the holding is completed, it is air-cooled to room temperature.

[0082] In the Retrogression and Reaging (RRA) process, natural aging for 24 h is added, which enables more dispersedly distributed GP zones to be obtained after aging. This is because during natural aging, supersaturated vacancies are more likely to combine with magnesium atoms rather than copper atoms. This will accelerate the diffusion of Mg atoms and increase the nucleation rate of GP zones, providing more nucleation sites for GP zones during re-aging, consuming a large amount of supersaturated vacancies and stored energy in the matrix, and reducing the diffusion rate and intensity loss of solute atoms at 120 °C. The 24-h natural aging before re-aging can promote the formation of GP zones, thus effectively improving the strength properties and thermal stability of the studied alloy.

[0083] The Retrogression and Reaging (RRA) process includes pre-aging, regression, and re-aging stages. The new four-stage aging adds 24 h of natural aging before re-aging. The pre-aging is selected at a relatively low temperature of 105 °C because, compared with the conventional 120 °C, the precipitates at 105 °C have lower thermal stability and smaller sizes. After the pre-aging stage, the dissolution degree of the precipitates is slightly larger, the coarsening degree is reduced, and the volume fraction is the lowest, providing a basis for the dissolution of the precipitates in the regression stage. Finally, the pre-aging regime for the first stage is selected as 105 °C / 24 h. The heating rate of 3 ° / min is selected for the heating stage of the regression stage, and the regression temperature is approximately between 165 and 180 °C. The time of the regression stage is determined according to the LSW coarsening kinetics model studied by Deng Yunlai. The formula shows the relationship between the average size Rt of the grain boundary precipitates, the regression aging time t, and the aging temperature T:

[0084]

[0085] Selecting a temperature of 170 °C and a grain boundary precipitate size of 40 nm, substituting into formula (1) gives a time t of 96 min. Combining with slow-rate heating, the regression stage regime is 170 °C / 85 min. Mg elements combine with supersaturated vacancies. Since the diffusion rate of Cu elements is much lower than that of Zn and Mg, during the natural aging process after the regression stage, the diffusion rate of Mg elements is relatively high and will aggregate and combine at supersaturated vacancies to form GP zones, enhancing the nucleation of GP zones. Finally, in the re-aging stage (80 °C / 34 h), the GP zones precipitate again, resulting in more GP zones and ηʹ phases in the end.

[0086] Selection of the re-aging regime: Low-temperature re-aging (80 °C / 34 h) is selected. GP zones are the main precipitates at a re-aging temperature of 80 °C, and η' phases are the main precipitates at a re-aging temperature of 120 °C. There are more GP zones after the final aging treatment, which has a certain promoting effect on the high-temperature properties of the studied alloy.

[0087] The aging treatment process is as follows: 105°C / 24 h → 170°C / 85 min → natural aging for 24 h → 80°C / 34 h (heating rate 3°C / min, water quenching transfer time ≤ 5 s, water temperature ≤ 25°C). For the four-stage aging regime, the first-stage aging is at 105°C / 24 h to obtain GP zones and fine ηʹ phases. The main change in the microstructure during the regression process (170°C / 85 min) is the dissolution of the unstable precipitates (GP zones and fine ηʹ phases) formed during the first aging; at the same time, as the regression time extends, the ηʹ and η phases will grow; then, the sample is quenched from 170°C to room temperature to preserve vacancies, and during natural aging, magnesium atoms will combine with the vacancies to enhance the nucleation of GP zones. Finally, during the re-aging stage (80°C / 34 h), the GP zones precipitate again.

[0088] Figure 11 It can be clearly observed that the addition of rare earth Nd has a very obvious effect on the anti-softening ability of the alloy after thermal exposure. Compared with the alloy without Nd, the room temperature hardness of the alloy containing 0.2 wt.% Nd increased by 4.9% (192.4 HV); the hardness of the alloy without rare earth decreased by 17.7% after thermal exposure at 120°C / 100 h, while the hardness of the alloy containing 0.2 wt.% Nd decreased by 6.6% after thermal exposure. The results show that the addition of rare earth Nd can maintain a relatively high hardness value, and this alloy has good high-temperature stability.

[0089] Figure 12 Engineering stress-strain diagrams of Al-6.1Zn-2.3Mg-1.7Cu-0.15Zr-xNd (x = 0; 0.2) alloys after four-stage aging and hot tensile at 120°C are shown. Table 1 presents the mechanical properties of this alloy after four-stage aging and hot tensile at 120°C.

[0090] Table 1 Mechanical properties of the alloy after four-stage aging and hot tensile at 120°C

[0091]

[0092] From Figure 12As can be seen from Table 1, temperature has an obvious effect on the mechanical properties of Al-Zn-Mg-Cu-Zr alloy. The tensile strength at room temperature of the alloy with 0.2wt.% Nd addition reaches 670.4MPa, which is 37.5% higher than that of the alloy without rare earth addition (487.5MPa). This is because fine Al3Nd dispersoids precipitate within the grains after aging treatment, and this rare earth phase can strongly hinder the migration of dislocations and sub-grain boundaries. The addition of Nd can also inhibit recrystallization and grain growth, retain small-angle grain boundaries, reduce the proportion of intergranular fracture, and thus improve the strength of the alloy. When tensile testing is carried out at 120°C, the tensile strength of the alloy with 0.2wt.% Nd addition reaches 396.2MPa, which is 50.6% higher than that of the alloy without rare earth addition (263.0MPa), indicating that the rare earth element Nd can significantly improve the high-temperature mechanical properties of this alloy.

[0093] In this embodiment, through microalloying with the addition of rare earth Nd and combining thermodynamics to optimize the homogenization, solution treatment and aging treatment processes, the alloy improves its properties jointly in terms of composition design and process. And the four-stage natural aging still has a certain improvement on the subsequent thermal stability. The addition of rare earth Nd improves the segregation degree of elements in the alloy, making the as-cast alloy have uniformity, and also provides a guarantee for subsequent deformation and heat treatment.

[0094] Obviously, the above embodiments are only examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or alterations can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or alterations derived therefrom are still within the protection scope of the claims of this patent application.

Claims

1. A preparation and processing method of a super strong aluminum alloy material, characterized in that, It includes the following steps: Step A, melting and casting: Using aluminum, aluminum-zinc master alloy, aluminum-magnesium master alloy, aluminum-copper master alloy, aluminum-zirconium master alloy, and magnesium-neodymium master alloy as raw materials, melting and casting to obtain an aluminum alloy ingot; The specific operation method of melting and casting in Step A includes the following steps: Step (A-1), preparing alloy raw materials and polishing the alloy raw materials; the alloy raw materials are: pure aluminum, aluminum-zinc master alloy, aluminum-magnesium master alloy, aluminum-copper master alloy, aluminum-zirconium master alloy, and magnesium-neodymium master alloy; Step (A-2), melting the alloy using a resistance induction melting furnace: First, preheat the crucible, then add pure aluminum and raise the temperature for melting. After all the pure aluminum has melted, successively add aluminum-zinc master alloy, aluminum-copper master alloy, and aluminum-zirconium master alloy wrapped in aluminum foil, as well as aluminum-magnesium master alloy wrapped in aluminum foil; after all the added alloy raw materials have melted, perform refining treatment, stirring, and slag skimming to obtain molten alloy liquid; Step (A-3), adding magnesium-neodymium master alloy wrapped in aluminum foil to the molten alloy liquid, standing and then stirring to obtain aluminum alloy liquid; when the temperature of the molten alloy liquid is adjusted to the range of 700 - 710 °C, add magnesium-neodymium master alloy wrapped in aluminum foil, and the standing time is 2 min; the mass fraction of neodymium in the magnesium-neodymium master alloy is 30 wt.%; Step (A-4), immediately pouring the stirred aluminum alloy liquid into a preheated graphite mold for casting to obtain an aluminum alloy ingot; Step B, homogenization treatment: Performing homogenization treatment on the aluminum alloy ingot to obtain a homogenized aluminum alloy material; during homogenization treatment, first raise the temperature of the aluminum alloy ingot to 300 °C at a heating rate of 340 °C / h and hold for 6 h; then raise the temperature of the aluminum alloy ingot to 472 °C at a heating rate of 50 °C / h and hold for 24 h; after the holding is completed, perform water quenching with water at less than or equal to 25 °C, and the water quenching transfer time is less than or equal to 5 s; Step C, hot deformation treatment: Performing hot deformation treatment on the homogenized aluminum alloy material to obtain an aluminum alloy plate; Step D, solution treatment: Performing solution treatment on the aluminum alloy plate to obtain a solution-treated aluminum alloy plate; first raise the temperature of the aluminum alloy plate to 455 °C at a heating rate of 340 °C / h and hold for 1.5 h; then raise the temperature of the aluminum alloy plate to 474 °C at a heating rate of 60 °C / h and hold for 0.5 h; after the holding is completed, perform water quenching with water at less than or equal to 25 °C, and the water quenching transfer time is less than or equal to 5 s; Step E, aging treatment: Performing aging treatment on the solution-treated aluminum alloy plate to obtain a super-strong aluminum alloy material; during aging treatment, first raise the temperature of the solution-treated aluminum alloy plate to 105 °C at a heating rate of 340 °C / h and hold for 24 h; then raise the temperature of the solution-treated aluminum alloy plate to 170 °C at a heating rate of 3 °C / min, hold for 85 min, and then perform water quenching with water at less than or equal to 25 °C, and the water quenching transfer time is less than or equal to 5 s; then naturally age the solution-treated aluminum alloy plate for 24 h; finally, raise the temperature of the solution-treated aluminum alloy plate to 80 °C at a heating rate of 340 °C / h and hold for 34 h; after the holding is completed, air cool to room temperature; In the super-strong aluminum alloy material obtained in step E: the content of Zn is 6.0 - 6.7 wt.%, the content of Mg is 2.1 - 2.9 wt.%, the content of Cu is 1.6 - 1.9 wt.%, the content of Zr is 0.1 - 0.15 wt.%, the content of Nd is 0.2 - 0.4 wt.%, the content of impurities is less than or equal to 0.1 wt.%, and the balance is aluminum.

2. The preparation and processing method of the super-strong aluminum alloy material according to claim 1, characterized in that, The mass ratio of Zn to Mg is (2.5 - 2.7):

1.

3. The preparation and processing method of the ultra-strong aluminum alloy material according to claim 1, characterized in that, The content of Zn is 6.1 wt.%, the content of Mg is 2.3 wt.%, the content of Cu is 1.7 wt.%, the content of Zr is 0.15 wt.%, and the content of Nd is 0.2 wt.%.

4. The preparation and processing method of the super-strong aluminum alloy material according to claim 1, characterized in that, In step (A-1), the purity of pure aluminum is greater than or equal to 99.9 wt%; the mass fraction of zinc in the aluminum-zinc master alloy is 30 wt.%, the mass fraction of magnesium in the aluminum-magnesium master alloy is 20 wt.%, the mass fraction of copper in the aluminum-copper master alloy is 30 wt.%, and the mass fraction of zirconium in the aluminum-zirconium master alloy is 10 wt.%; when preparing the alloy raw materials, batching is carried out according to a zinc burn loss rate of 2%, a copper burn loss rate of 5%, and a zirconium burn loss rate of 30%; In step (A-2): the preheating temperature of the crucible is 380 - 420 °C; after adding pure aluminum, the temperature is raised to 720 - 750 °C; the refining treatment method is: controlling the temperature of the alloy liquid within the range of 725 - 735 °C, immersing a graphite bell jar filled with C2Cl6 into the alloy liquid and introducing argon, and refining for 20 min; the mass of C2Cl6 is 0.3 - 0.5 wt.% of the total weight of the alloy liquid; In step (A-4), the preheating temperature of the graphite mold is 180 - 230 °C.

5. The preparation and processing method of the super-strong aluminum alloy material according to claim 1, characterized in that, In step C, during the hot deformation treatment, first place the homogenized aluminum alloy material in a resistance furnace and pre-treat it at a temperature of 420 °C for 2 h; then, at an extrusion temperature of 405 ± 5 °C, with an extrusion speed of 1 mm / s and an extrusion ratio of 25:1, carry out extrusion deformation to obtain an aluminum alloy plate.

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