A high-tenacity fine-grained aluminum alloy and a method for producing the same

Abstract

This invention relates to the field of aluminum alloy technology, and in particular to a high-strength, high-toughness, fine-grained aluminum alloy and its preparation method. The grain boundaries of the high-strength, high-toughness, fine-grained aluminum alloy contain two or three types of second phases; these second phases are composed of Al and alloying elements, with a size of 20-100 nm; the alloying elements are selected from one or more of Si, Mg, Cu, Zn, Fe, Mn, Zr, and Cr. This invention effectively solves the problem of poor strength and toughness in the as-cast state of traditional aluminum alloys by controlling the grain structure and the matching characteristics of the second phase, providing a new solution for the short-process preparation of high-strength, high-toughness, lightweight aluminum alloy materials.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy technology, and in particular to a high-strength, high-toughness, fine-grained aluminum alloy and its preparation method. Background Technology

[0002] In recent years, aluminum alloys have demonstrated significant advantages in achieving structural lightweighting due to their low density and excellent specific strength, making them an ideal lightweight material choice for the automotive, aerospace, and other fields, contributing to improved fuel efficiency and reduced carbon emissions. However, aluminum alloys prepared by traditional casting processes are prone to abnormal grain growth due to their low cooling rates, forming coarse dendritic or columnar crystal structures, thereby weakening grain boundary strengthening effects and hindering dislocation propagation. Second phases formed during solidification (such as Mg2Si, Al2Cu, and AlFeMnSi), while improving the alloy's strength, often come at the cost of reduced toughness, resulting in a poor strength-toughness balance in the as-cast state.

[0003] Grain refinement is an effective method to improve the strength and toughness of alloys. Currently, commonly used grain refinement methods include mechanical vibration, electromagnetic stirring, ultrasonic vibration, the addition of grain refiners, and large plastic deformation. Chinese invention patent CN114058889A proposes a method for preparing high-strength, high-toughness, ultrafine-grained aluminum alloys. This method involves adding rare earth elements Ce, La, and Sc to the Al-Ti-B grain refiner during the casting process to enhance the grain refinement effect and stability, thereby effectively refining the grains and improving the mechanical properties of the alloy. However, rare earth elements are relatively expensive, leading to increased production costs. Furthermore, Chinese invention patent CN111097806A discloses a composite large plastic deformation method for preparing ultrafine-grained aluminum and aluminum alloys. This technology combines multi-pass equal-channel angular extrusion and multi-directional compression to obtain ultrafine-grained aluminum alloy materials with uniform microstructure and excellent anisotropy. However, this method has inherent limitations such as cumbersome process flow and low efficiency, posing challenges for industrial application.

[0004] Therefore, developing a fine-grained aluminum alloy that can be prepared in a short process, is inexpensive, and has both high strength and high toughness has become a challenge in the field of aluminum alloy research and industry. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the problems of long preparation process and high cost of fine-grained aluminum alloy in the prior art, thereby providing a high-strength and high-toughness fine-grained aluminum alloy.

[0006] To solve the above technical problems, the present invention provides a high-strength, high-toughness, fine-grained aluminum alloy, wherein the grain boundaries of the high-strength, high-toughness, fine-grained aluminum alloy contain two or three types of second phases, and the constituent elements of all second phases include Al and alloying elements, wherein the alloying elements are selected from three or more of Si, Mg, Cu, Zn, Fe, Mn, Zr and Cr; the size of the second phase is 20-100 nm.

[0007] In the high-strength and tough fine-grained aluminum alloy, the proportion of grains with a size of 0.5-1 μm is 30%-50%, the proportion of grains with a size of 1-3 μm is 20%-40%, and the proportion of grains with a size of 3-5 μm is 10%-30%.

[0008] This invention promotes the uniform accumulation and transfer of dislocations during the plastic deformation process of alloys by synergistically controlling the fine cellular grain structure and nanograin boundary phases of the alloy, thereby simultaneously improving the strength and toughness of the alloy.

[0009] Preferably, the high-strength, high-toughness, fine-grained aluminum alloy is composed of the following elements by weight percentage: 5-10% Si, 0.1-3% Mg, 0.5-5% Cu, 0.2-5% Zn, 0.2-2% Fe, 0.2-2% Mn, 0.1-2% Zr, 0.1-2% Cr, with the balance being Al.

[0010] Preferably, the crystal structure of the second phase is one or more of cubic, tetragonal and monoclinic structures.

[0011] Preferably, the high-strength, high-toughness, fine-grained aluminum alloy has a tensile strength of not less than 500 MPa and an elongation of not less than 9% in the as-cast state.

[0012] Preferably, the constituent elements of all the second phases contained in the grain boundaries include aluminum and three or more of the elements Si, Mg, Cu, Zn, Fe, Mn, Zr and Cr.

[0013] Preferably, when there are two types of the second phase, the difference in elastic modulus between the two types of the second phase is not less than 50% of the lowest elastic modulus value among them; the difference in Vickers hardness between the two types of the second phase is not less than 50% of the lowest Vickers hardness value among them.

[0014] Preferably, when the second phase is of three types, the difference in elastic modulus between any two of the three types of second phases is not less than 30% of the lowest elastic modulus value among the three; and the difference in Vickers hardness between any two of the three types of second phases is not less than 50% of the lowest Vickers hardness value among the three.

[0015] The present invention also provides a method for preparing the above-mentioned high-strength and high-toughness fine-grained aluminum alloy, comprising the following steps:

[0016] S11: Aluminum, magnesium, copper, zinc and a master alloy are mixed and smelted to obtain a molten alloy; the molten alloy is composed of the following elements by weight percentage: 5-10% Si, 0.1-3% Mg, 0.5-5% Cu, 0.2-5% Zn, 0.2-2% Fe, 0.2-2% Mn, 0.1-2% Zr, 0.1-2% Cr, with the balance being Al;

[0017] S12: The molten alloy is atomized and then sieved to obtain alloy powder with a particle size of 20-70 μm;

[0018] S13: The alloy powder is solidified to obtain the high-strength, high-toughness, fine-grained aluminum alloy; the solidification process is carried out at 10... 4 -10 6 Cooling is performed at a rate of K / s.

[0019] Preferably, in step S11, the melting is carried out under vacuum conditions.

[0020] Preferably, in step S11, the melting temperature is 760-780℃ and the time is 20-40 min.

[0021] Preferably, in step S11, the intermediate alloy comprises Al-20%Si, Al-20%Mn, Al-10%Zr, Al-10%Cr, and Al-20%Fe.

[0022] Preferably, in step S12, the atomization method is: high-pressure atomization spraying under argon gas conditions.

[0023] Preferably, in step S13, the solidification molding method is spray molding or 3D printing.

[0024] Compared with the prior art, the above-described technical solution of the present invention has the following advantages:

[0025] (1) Under high cooling rate solidification and forming conditions, this invention obtains an aluminum alloy with fine grain structure and multi-level grain boundary structure by controlling the grain size, as well as the size, elastic modulus, crystal structure, composition and other characteristics of the second phase. This effectively solves the problem of low strength and toughness of cast aluminum alloys. Moreover, the process is short and the cost is controllable, providing a new solution for the short-process preparation of high strength and toughness lightweight aluminum alloy materials.

[0026] (2) The aluminum alloy material of the present invention has a tensile strength of more than 500 MPa and an elongation of more than 9% in the as-cast state, which exceeds the as-cast mechanical properties of other traditional aluminum alloy materials. Attached Figure Description

[0027] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0028] Figure 1 This is a microstructure diagram of the fine-grained aluminum alloy prepared in Example 1 of the present invention;

[0029] Figure 2 This is a microstructure diagram of the fine-grained aluminum alloy prepared in Example 2 of the present invention;

[0030] Figure 3 This is a microstructure diagram of the fine-grained aluminum alloy prepared in Example 3 of the present invention. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0032] Data acquisition of grain size range and proportion was performed using electron backscatter diffraction (EBSD). The identification and size measurement of Al2Cu and Q phases were performed using transmission electron microscopy (TEM). Vickers hardness and elastic modulus were measured using a nanoindentation device (manufacturer: Bruker, model: Hysitron-TI980), with a measurement accuracy of 5 nm.

[0033] Mechanical property testing: Tensile specimens were prepared according to GB / T 228-2021 standard. The tensile specimens were tested on a Shimadzu AGS-X universal testing machine in Japan at a tensile speed of 1 mm / min to obtain experimental data on tensile strength and elongation.

[0034] Example 1:

[0035] This embodiment discloses a high-strength, high-toughness, fine-grained aluminum alloy and its preparation method. The alloy composition and weight percentages are as follows: Si 6.87%, Mg 0.54%, Cu 3.31%, Zn 0.21%, Fe 0.20%, Mn 0.30%, Zr 0.21%, Cr 0.11%, and the remainder is Al.

[0036] In this embodiment, the aluminum alloy with the above-mentioned composition is prepared using a high-speed cooling 3D printing method, with a cooling rate of 10. 6 K / s, the specific steps are as follows:

[0037] (1) Preparation of alloy powder

[0038] First, high-purity aluminum ingots (99.99 wt.%), pure Mg (99.95 wt.%), pure Cu (99.95 wt.%), and pure Zn (99.99 wt.%) were mixed with master alloys Al-20%Si (wt.%), Al-20%Mn (wt.%), Al-10%Zr (wt.%), Al-10%Cr (wt.%), and Al-20%Fe (wt.%) in a specific ratio to obtain the target composition. The mixture was then melted at 780°C for 30 min in a vacuum induction melting apparatus (model: VIM 02-70, ALD Vacuum Technologies GmbH) to ensure complete melting and homogenization of the chemical composition.

[0039] Subsequently, alloy powder was prepared using high-pressure inert gas atomization technology. Specifically, molten metal was injected through a nozzle and atomized into fine droplets under the action of a high-pressure argon gas flow. During this process, the nozzle inner diameter was 1 mm, the overpressure applied to the top of the melt was 40 kPa, the melt mass flow rate was 87.97 kg / h, the atomizing gas pressure was 2.0 MPa, the gas mass flow rate was 200 kg / h, the gas-liquid mass flow rate ratio was 2.27, and the melt superheat was 150 K. After atomization, approximately spherical alloy powder was obtained, and the collected powder was then sieved to obtain a particle size distribution in the range of 20-50 μm.

[0040] (2) 3D printing

[0041] A selective laser melting (SLM) 3D printer, model HBD-150, was used to print samples of the alloy powder obtained in step (1). The printing process was carried out in an inert atmosphere filled with high-purity argon (oxygen content <100 ppm) to prevent oxidation. The printing parameters were set as follows: laser power of 280 W, scanning speed of 1600 mm / s, laser spot diameter of 0.1 mm, scanning spacing of 0.12 mm, and layer thickness of 0.03 mm. To reduce thermal stress and residual strain, the scanning direction of each layer was rotated 67° relative to the previous layer. After the powder was heated and melted by the laser, it rapidly solidified on the cooling substrate at a cooling rate of 10. 6 K / s.

[0042] The microstructure of the aluminum alloy prepared by the above method is as follows: Figure 1 As shown.

[0043] Microstructural observation revealed that the alloy microstructure of this embodiment contained grains of different sizes. 48% of the grains were in the 0.5-1 μm range, 39% were in the 1-3 μm range, and 13% were in the 3-5 μm range. Two types of second phases were present at the grain boundaries: one was a high-hardness, high-elastic-modulus θ-Al₂Cu phase with a Vickers hardness of 12.56 GPa and an elastic modulus of 161.25 GPa; the other was a low-hardness, low-elastic-modulus Q-Al₅Cu₂Mg₇Si₄ phase with a Vickers hardness of 6.54 GPa and an elastic modulus of 98.65 GPa; the size range of the second phases was 85-95 nm. Tensile testing of the as-cast alloy sheet yielded a tensile strength of 552 MPa and an elongation of 11.5%.

[0044] Example 2:

[0045] This embodiment discloses a high-strength, high-toughness, fine-grained aluminum alloy and its preparation method. The alloy composition and weight percentages are as follows: Si 6.82%, Mg 2.31%, Cu 1.11%, Zn 0.20%, Fe 0.22%, Mn 0.35%, Zr 0.11%, Cr 0.12%, and the remainder is Al.

[0046] In this embodiment, the aluminum alloy with the above-mentioned composition is prepared using a high-speed cooling 3D printing method, with a cooling rate of 10. 5 K / s, the specific steps are as follows:

[0047] (1) Preparation of alloy powder

[0048] First, high-purity aluminum ingots (99.99 wt.%), pure Mg (99.95 wt.%), pure Cu (99.95 wt.%), and pure Zn (99.99 wt.%) were mixed with master alloys Al-20%Si (wt.%), Al-20%Mn (wt.%), Al-10%Zr (wt.%), Al-10%Cr (wt.%), and Al-20%Fe (wt.%) in a specific ratio to obtain the target composition. The mixture was then melted at 760°C for 30 min in a vacuum induction melting apparatus (model: VIM 02-70, ALD Vacuum Technologies GmbH) to ensure complete melting and homogenization of the chemical composition.

[0049] Subsequently, alloy powder was prepared using high-pressure inert gas atomization technology. Specifically, molten metal was injected through a nozzle and atomized into fine droplets under the action of a high-pressure argon gas flow. During this process, the nozzle inner diameter was 1 mm, the overpressure applied to the top of the melt was 40 kPa, the melt mass flow rate was 87.97 kg / h, the atomizing gas pressure was 2.0 MPa, the gas mass flow rate was 200 kg / h, the gas-liquid mass flow rate ratio was 2.27, and the melt superheat was 150 K. After atomization, approximately spherical alloy powder was obtained, and the collected powder was then sieved to obtain a particle size distribution in the range of 30-70 μm.

[0050] (2) 3D printing

[0051] A selective laser melting (SLM) 3D printer, model HBD-150, was used to print samples of the alloy powder obtained in step (1). The printing process was carried out in an inert atmosphere filled with high-purity argon (oxygen content <100 ppm) to prevent oxidation. The printing parameters were set as follows: laser power of 340 W, scanning speed of 2000 mm / s, laser spot diameter of 0.1 mm, scanning spacing of 0.12 mm, and layer thickness of 0.03 mm. To reduce thermal stress and residual strain, the scanning direction of each layer was rotated 67° relative to the previous layer. After the powder was heated and melted by the laser, it rapidly solidified on the cooling substrate at a cooling rate of 10. 5 K / s.

[0052] The microstructure of the alloy prepared by the above method is as follows: Figure 2 As shown in the figure. Microstructural observation revealed that the alloy microstructure of this embodiment contains grains of different sizes. The proportion of grains with a size in the 0.5-1 μm range is 30%, the proportion of grains with a size in the 1-3 μm range is 40%, and the proportion of grains with a size in the 3-5 μm range is 30%. Three types of second phases exist at the grain boundaries: a high elastic modulus and high hardness θ-Al₂Cu phase with a Vickers hardness of 11.98 GPa and an elastic modulus of 160.47 GPa; and low elastic modulus and low hardness Q-Al₅Cu₂Mg₇Si₄ and Mg₂Si phases. The Q-Al₅Cu₂Mg₇Si₄ phase has a Vickers hardness of 6.85 GPa and an elastic modulus of 99.65 GPa; the Mg₂Si phase has a Vickers hardness of 4.75 GPa and an elastic modulus of 77.25 GPa. The size range of the second phases is 80-100 nm. Mechanical tensile testing was performed on the as-cast alloy sheet, and its tensile strength was 508 MPa and its elongation was 9.2%.

[0053] Example 3:

[0054] This embodiment discloses a high-strength, high-toughness, fine-grained aluminum alloy and its preparation method. The alloy composition and weight percentages are as follows: Si 8.28%, Mg 0.71%, Cu 3.11%, Zn 0.33%, Fe 0.21%, Mn 0.30%, Zr 0.43%, Cr 0.15%, and the remainder is Al.

[0055] In this embodiment, the aluminum alloy with the above-mentioned composition is prepared using a high-speed cooling 3D printing method, with a cooling rate of 10. 6 K / s, the specific steps are as follows:

[0056] (1) Preparation of alloy powder

[0057] First, high-purity aluminum ingots (99.99 wt.%), pure Mg (99.95 wt.%), pure Cu (99.95 wt.%), and pure Zn (99.99 wt.%) were mixed with master alloys Al-20%Si (wt.%), Al-20%Mn (wt.%), Al-10%Zr (wt.%), Al-10%Cr (wt.%), and Al-20%Fe (wt.%) in a specific ratio to obtain the target composition. The mixture was then melted at 770°C for 30 min in a vacuum induction melting apparatus (model: VIM 02-70, ALD Vacuum Technologies GmbH) to ensure complete melting and homogenization of the chemical composition.

[0058] Subsequently, alloy powder was prepared using high-pressure inert gas atomization technology. Specifically, molten metal was injected through a nozzle and atomized into fine droplets under the action of a high-pressure argon gas flow. During this process, the nozzle inner diameter was 1 mm, the overpressure applied to the top of the melt was 40 kPa, the melt mass flow rate was 87.97 kg / h, the atomizing gas pressure was 2.0 MPa, the gas mass flow rate was 200 kg / h, the gas-liquid mass flow rate ratio was 2.27, and the melt superheat was 150 K. After atomization, approximately spherical alloy powder was obtained, and the collected powder was then sieved to obtain a particle size distribution in the range of 30-60 μm.

[0059] (2) 3D printing

[0060] A selective laser melting (SLM) 3D printer, model HBD-150, was used to print samples of the alloy powder obtained in step (1). The printing process was carried out in an inert atmosphere filled with high-purity argon (oxygen content <100 ppm) to prevent oxidation. The printing parameters were set as follows: laser power of 300 W, scanning speed of 1600 mm / s, laser spot diameter of 0.1 mm, scanning spacing of 0.12 mm, and layer thickness of 0.03 mm. To reduce thermal stress and residual strain, the scanning direction of each layer was rotated 67° relative to the previous layer. After the powder was heated and melted by the laser, it solidified rapidly on the cooling substrate at a cooling rate of 10. 6 K / s.

[0061] The microstructure of the alloy prepared by the above method is as follows: Figure 3 As shown in the figure. Microstructural observation revealed that the alloy in this embodiment contains grains of different sizes. The proportion of grains with a size in the 0.5-1 μm range is 43%, the proportion of grains with a size in the 1-3 μm range is 45%, and the proportion of grains with a size in the 3-5 μm range is 12%. Two types of second phases exist at the grain boundaries: one is the θ-Al₂Cu phase, which has high hardness and high elastic modulus (13.21 GPa Vickers hardness and 163.85 GPa); the other is the Q-Al₅Cu₂Mg₇Si₄ phase, which has low hardness and low elastic modulus (6.32 GPa Vickers hardness and 97.21 GPa). The size range of the second phases is 85-95 nm. Tensile testing of the as-cast alloy sheet showed a tensile strength of 535 MPa and an elongation of 10.3%.

[0062] Comparative Example 1:

[0063] An Al-8.28%Si-3.11%Cu alloy was prepared using pure aluminum ingots, pure Cu sheets, and an Al-Si master alloy. The alloy bulk raw material was placed in a melting furnace and melted at 780℃ for 1 hour, followed by degassing and refining with argon gas for 10 minutes. The molten aluminum alloy was then cast into a 100mm×20mm×15mm water-cooled copper mold at 710℃ to form an ingot. The cooling rate during solidification was 40 K / s. Microstructural observation revealed that the alloy in this comparative example had a grain size ranging from 150 to 200 μm. A high-elastic-modulus θ-Al₂Cu phase was present at the grain boundaries, with a Vickers hardness of 12.02 GPa and an elastic modulus of 162.38 GPa; its size ranged from 1 to 3 μm. Tensile testing was performed on the as-cast alloy sheet, revealing a tensile strength of 321 MPa and an elongation of 6.1%.

[0064] Comparative Example 2:

[0065] An Al-8.28%Si-0.71%Mg alloy was prepared using pure aluminum ingots, pure Mg ingots, and an Al-Si master alloy. The alloy bulk raw material was placed in a melting furnace and melted at 780℃ for 1 hour, followed by degassing and refining with argon gas for 10 minutes. The molten aluminum alloy was then cast into a 100mm×20mm×15mm water-cooled copper mold at 710℃ to form an ingot. The cooling rate during solidification was 40 K / s. Microstructural observation revealed that the alloy in this comparative example had a grain size ranging from 160 to 220 μm. A low-modulus Mg2Si phase was present at the grain boundaries, with a Vickers hardness of 4.68 GPa and an elastic modulus of 76.21 GPa; the grain size ranged from 1 to 4 μm. Tensile testing of the as-cast alloy yielded a tensile strength of 250 MPa and an elongation of 6.9%.

[0066] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A high-strength, high-toughness, fine-grained aluminum alloy, characterized in that: The high-strength and tough fine-grained aluminum alloy contains two or three types of second phases at its grain boundaries. All the constituent elements of the second phases include Al and alloying elements, wherein the alloying elements are selected from three or more of Si, Mg, Cu, Zn, Fe, Mn, Zr and Cr. The size of the second phase is 20-100 nm. In the high-strength, high-toughness, fine-grained aluminum alloy, the proportion of grains with a size of 0.5-1 μm is 30%-50%, the proportion of grains with a size of 1-3 μm is 20%-40%, and the proportion of grains with a size of 3-5 μm is 10%-30%. By weight percentage, the high-strength, high-toughness, fine-grained aluminum alloy is composed of the following elements: 5-10% Si, 0.1-3% Mg, 0.5-5% Cu, 0.2-5% Zn, 0.2-2% Fe, 0.2-2% Mn, 0.1-2% Zr, and 0.1-2% Cr, with the balance being Al. When the second phase is of two types, the difference in elastic modulus between the two types of second phases is not less than 50% of the lowest elastic modulus value among them; the difference in Vickers hardness between the two types of second phases is not less than 50% of the lowest Vickers hardness value among them; when the second phase is of three types, any difference in elastic modulus between any pair of the three types of second phases is not less than 30% of the lowest elastic modulus value among them; any difference in Vickers hardness between any pair of the three types of second phases is not less than 50% of the lowest Vickers hardness value among them.

2. The high-strength, high-toughness, fine-grained aluminum alloy according to claim 1, characterized in that: The crystal structure of the second phase is one or more of cubic, tetragonal and monoclinic structures.

3. The high-strength, high-toughness, fine-grained aluminum alloy according to claim 1, characterized in that: The high-strength, high-toughness, fine-grained aluminum alloy has a tensile strength of not less than 500 MPa and an elongation of not less than 9% in the as-cast state.

4. A method for preparing a high-strength, high-toughness, fine-grained aluminum alloy according to any one of claims 1-3, characterized in that, Includes the following steps: S11: Aluminum, magnesium, copper, zinc and a master alloy are mixed and smelted to obtain a molten alloy; the molten alloy is composed of the following elements by weight percentage: 5-10% Si, 0.1-3% Mg, 0.5-5% Cu, 0.2-5% Zn, 0.2-2% Fe, 0.2-2% Mn, 0.1-2% Zr, 0.1-2% Cr, with the balance being Al; S12: The molten alloy is atomized and then sieved to obtain alloy powder with a particle size of 20-70 μm; S13: The alloy powder is solidified to obtain the high-strength, high-toughness, fine-grained aluminum alloy; the solidification process is carried out at 10... 4 -10 6 Cooling is performed at a rate of K / s.

5. The preparation method according to claim 4, characterized in that: In step S11, the melting temperature is 760-780℃ and the time is 20-40 min.

6. The preparation method according to claim 4, characterized in that: In step S11, the intermediate alloy includes Al-20%Si, Al-20%Mn, Al-10%Zr, Al-10%Cr, and Al-20%Fe.

7. The preparation method according to claim 4, characterized in that: In step S13, the solidification molding method is spray molding or 3D printing.

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