Dispersion phase precipitation control method of aluminum alloy

Abstract

This invention belongs to the technical field of aluminum alloy materials and relates to a method for controlling the precipitation of dispersed phases in aluminum alloys. Specifically, the aluminum alloy ingot is heated to 360-420℃ at a rate of 10-50℃ / h and held for 0.5-4h, then heated to a homogenization temperature at a rate greater than 300℃ / h and held. The temperature and time are determined according to the alloy system. Slow heating promotes high-density nucleation of the dispersed phase, and holding further induces high-density nucleation of the dispersed phase and promotes the diffusion of Mo and Cr to the dispersed phase / aluminum matrix interface, forming a core-shell structure. This method is applicable to Mn-containing aluminum alloys, including Al-Mg-Si-Mn, Al-Mn, Al-Mg-Mn, and Al-Zn-Mg-Mn systems. The alloy may contain one or more of Mg, Si, Zn, Mn, Cr, Mo, Sn, and Ti. After treatment, a high-density, high-thermal-stability dispersed phase can be obtained, effectively inhibiting recrystallization during hot working and heat treatment, or improving the high-temperature stability of the microstructure.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy material technology, specifically relating to a method for controlling the precipitation of dispersed phases in aluminum alloys. Background Technology

[0002] Aluminum alloys are widely used in automobiles, rail transportation, commercial vehicles, aerospace, marine engineering, and industrial equipment due to their low density, high specific strength, good corrosion resistance, and excellent processability. With the increasing demand for lightweight and high-performance transportation equipment, aluminum alloy materials not only need to possess high room temperature strength and ductility, but also need to maintain a stable microstructure during hot working, heat treatment, and service.

[0003] The dispersed phases precipitated during homogenization heat treatment can pin dislocations, subgrain boundaries, and grain boundary migrations, thereby inhibiting hot deformation and recovery and recrystallization behavior during subsequent heat treatment. Among various dispersed phases, Mn-containing dispersed phases are the most commonly used. However, due to the low diffusion coefficient of the dispersed phase-forming elements and the lack of sufficient nucleation sites during heat treatment, the number density of dispersed phase precipitation is low. Furthermore, coarsening easily occurs during high-temperature annealing, which in turn affects the recrystallization behavior and microstructure stability of the alloy.

[0004] Among existing patent technologies, CN117737620A discloses a multi-level homogenization control method for α-Al(Mn,Fe)Si dispersed phases in Al-Mg-Si-Mn aluminum alloys. It employs a three-level homogenization process, primarily promoting the nucleation of α-Al(Mn,Fe)Si dispersed phases through metastable phase precipitation and re-dissolution to form Si-rich regions, focusing on improving the coarse dispersed phase region and the region without dispersed phase precipitation in 6-series aluminum alloys. However, this technology is only applicable to 6-series aluminum alloys and does not address the improvement of the thermal stability of dispersed phases. Patent CN110714174A discloses a homogenization process for aluminum alloy ingots, which mainly focuses on Al3Zr dispersed phases and involves a relatively long medium-temperature holding time, rather than controlling the enrichment behavior of Mn-containing dispersed phases and their interfacial elements. US8025748B2 discloses a technical solution combining Al-Mn-based aluminum alloy composition and homogenization treatment, primarily used for extruding and brazing heat exchanger tubes. By controlling the homogenization temperature, cooling rate, and Mn solution / precipitation state within the range of 550-600℃, the extrusion pressure is reduced while maintaining a fine-grained structure after brazing. This technology emphasizes the relationship between Mn solution content, Mn dispersed phase density, and extrusion performance, but does not address methods for controlling dispersed phase precipitation.

[0005] In summary, while existing technologies have recognized the significant impact of homogenization processes on the precipitation and recrystallization behavior of dispersed phases in aluminum alloys, the following shortcomings remain: First, traditional processes involving direct heating to high temperatures for homogenization can easily lead to insufficient nucleation of dispersed phases, resulting in the formation of non-dispersed phase precipitation zones or coarse, low-density dispersed phase regions in some areas. Second, multi-stage homogenization treatment is targeted at 6-series alloys or Al3Zr dispersed phases, and while prolonged medium-temperature holding is beneficial for dispersed phase precipitation, it may lead to coarsening of the dispersed phases, reducing their pinning effect during subsequent hot working. Third, existing methods focus primarily on the quantity, size, and distribution of dispersed phases, with less emphasis on improving their thermal stability. Fourth, general methods for controlling the thermal stability of dispersed phases in various Mn-containing aluminum alloys, such as Al-Mg-Si-Mn, Al-Mn, Al-Mg-Mn, and Al-Zn-Mg-Mn systems, are still incomplete.

[0006] Therefore, it is necessary to provide a new method for controlling the precipitation of dispersed phases in aluminum alloys. This method can improve the number density of dispersed phase nuclei while forming a core-shell structure through the interfacial enrichment of elements such as Mo and Cr, thereby enhancing the thermal stability of the dispersed phases and suppressing the coarsening of the dispersed phases during the subsequent high-temperature homogenization process. This will improve the aluminum alloy's resistance to recrystallization and its high-temperature structural stability. Summary of the Invention

[0007] The purpose of this invention is to overcome the problems of the prior art and provide a method for controlling the precipitation of dispersed phases in aluminum alloys. By controlling the heating rate, medium-temperature holding temperature and holding time during the homogenization process, as well as the rapid heating regime in the final homogenization stage, a high-density, high-thermal-stability dispersed phase is formed in Mn-containing aluminum alloys, thereby enhancing the pinning effect of the dispersed phase on dislocations and grain boundary migration.

[0008] To address the aforementioned technical problems, this invention provides a method for controlling the dispersion of phases in aluminum alloys, comprising the following steps: S11: Heat the aluminum alloy ingot to 360-420℃ and hold for 0.5-4 seconds. h, to precipitate the Mn-containing dispersed phase; the aluminum alloy ingot is a 3xxx series alloy or a non-3xxx series alloy, and by weight percentage, the 3xxx series alloy includes 0.1%-1.2% Si, 0.3%-1.5% Mn, 0-0.6% Cr, 0-0.5% Mo, not more than 0.2% Sn, not more than 0.5% Fe, not more than 0.2% Ti, and Cr and Mo are not simultaneously 0, with the balance being Al and unavoidable impurities; the non-3xxx series alloy includes 0.1%-8% Mg, 0.3%-1.5% Mn, 0.1%-1.2% Si, 0-0.6% Cr, 0-0.5% Mo, not more than 10% Zn, not more than 0.5% Fe, not more than 0.2% Ti, and Cr and Mo are not simultaneously 0, with the balance being Al and unavoidable impurities; S12: Heat the aluminum alloy ingot to the final homogenization temperature and hold it for 1-24 h, then cool it to room temperature (25±5℃); the final homogenization temperature is 450-600℃ and is 10-40℃ lower than the initial melting temperature of the aluminum alloy ingot.

[0009] Preferably, the aluminum alloy ingot is an Al-Mg-Si-Mn series aluminum alloy, an Al-Mn series aluminum alloy (3xxx series alloy), an Al-Mg-Mn series aluminum alloy, or an Al-Zn-Mg-Mn series aluminum alloy.

[0010] Preferably, the Mn-containing dispersed phase is one or more of α-Al(Mn,Fe)Si, α-Al(Mn,Mo,Fe)Si, and α-Al(Mn,Cr,Fe)Si.

[0011] Furthermore, the Mn-containing dispersed phase has a core-shell structure, with Mn distributed in the internal region of the Mn-containing dispersed phase and Cr and / or Mo distributed in the interface region of the Mn-containing dispersed phase. One or both of Cr and Mo diffuse and enrich at the interface between the Mn-containing dispersed phase and the aluminum matrix, making the dispersed phase a highly thermally stable dispersed phase with core-shell structure characteristics.

[0012] Preferably, in step S11, the heating rate is 10-50℃ / h. The heating is carried out in a homogenizing furnace, and the heating and holding process causes high-density dispersed phase nuclei to form in the aluminum alloy matrix, and induces the precipitation of Mn-containing dispersed phase nuclei.

[0013] Preferably, the equivalent diameter of the Mn-containing dispersed phase is 10-300 nm. Controlling the size of the dispersed phase avoids stress concentration caused by excessively large particles, which leads to a decrease in toughness, while ensuring the amount of precipitated phase, thus synergistically improving the alloy's strength and high-temperature stability, and balancing mechanical and processing properties.

[0014] Preferably, the number density of the Mn-containing dispersed phase is not less than 1×10⁻⁶. 20 m -3 The proportion of coherent quasicrystalline dispersed phases in the total dispersed phase is not less than 40%. This dispersed phase number density can effectively pin dislocations and grain boundaries, hindering high-temperature grain growth. The dispersed phase has small interface distortion and high internal stress with the matrix, which can enhance precipitation strengthening effect, reduce the risk of crack initiation, improve plasticity while ensuring alloy strength, and significantly improve the comprehensive performance of aluminum alloys.

[0015] Preferably, in step S12, the heating rate is not less than 300℃ / h.

[0016] Furthermore, in step S12, the heating rate is 300-500℃ / h.

[0017] Preferably, in step S12, the cooling method is air cooling. Air cooling with a controllable rate suppresses the precipitation of coarse and harmful second phases, promotes the nucleation of fine, dispersed Mn-containing phases, avoids excessive internal stress and ingot cracking risks associated with water cooling, and balances microstructure control with billet integrity, providing an excellent original microstructure foundation for subsequent deformation processing.

[0018] The present invention also provides an aluminum alloy prepared by a method for controlling the dispersion of the above-mentioned aluminum alloy.

[0019] The present invention also provides a transportation vehicle made of the above-mentioned aluminum alloy.

[0020] Compared with the prior art, the above-described technical solution of the present invention has the following advantages: Compared with the prior art, the dispersion phase precipitation control method provided by the present invention promotes the high-density precipitation of Mn-containing dispersion phases through a heat treatment process of "slow heating - medium-temperature holding - rapid heating to the final homogenization temperature" and induces microalloying elements such as Cr and Mo to diffuse and enrich at the dispersion phase / aluminum matrix interface. This can obtain a high thermal stability core-shell structure dispersion phase, which can improve the anti-recrystallization ability, high-temperature microstructure stability and high-temperature service performance of aluminum alloys during hot working. Attached Figure Description

[0021] 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.

[0022] Figure 1 The images show the dispersed phase precipitation characteristics and hot deformation microstructure of the alloy in Example 1. In the images, a is a scanning electron microscope image, b is an electron backscatter diffraction analysis (grain boundary orientation differences of 2-15° are low-angle grain boundaries, accounting for 0.624%, and grain boundary orientation differences greater than 15° are high-angle grain boundaries, accounting for 0.376%), c is a transmission electron microscope image, and d is a transmission electron microscope elemental surface scan characterization image. Figure 2 This is a characteristic diagram of dispersed phase precipitation in the alloy of Example 2; Figure 3 The images show the dispersed phase precipitation characteristics and hot deformation microstructure of the alloy in Comparative Example 1. In the images, a is a scanning electron microscope (SEM) image, b is an electron backscatter diffraction (EPD) analysis diagram (grain boundary orientation differences of 2-15° are low-angle grain boundaries, accounting for 0.507; grain boundary orientation differences greater than 15° are high-angle grain boundaries, accounting for 0.493), c is a transmission electron microscope (TEM) image, and d is a TEM elemental surface scan characterization diagram. Figure 4 This is a characteristic diagram of dispersed phase precipitation in alloy Comparative Example 2; Figure 5This is a comparison chart of the high-temperature creep properties of alloys in Example 2 and Comparative Example 2 under constant stress of 300℃ and 60 MPa. Detailed Implementation

[0023] 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.

[0024] Example 1: Control of dispersed phase precipitation in aluminum alloys (non-3xxx series alloys) The aluminum alloy used in this embodiment comprises, by mass percentage: Mg 0.8%, Si 1.0%, Mn 0.6%, Cr 0.15%, Mo 0.1%, Fe 0.13%, Ti 0.03%, with the balance being Al and unavoidable impurities.

[0025] The preparation method includes the following steps: 1) Place the aluminum alloy ingot in a homogenizing furnace and heat it from room temperature to 400℃ at a heating rate of 30℃ / h; 2) Holding at 400℃ for 2 h allows for the formation of high-density Mn-containing dispersed phase nucleation sites in the aluminum matrix, promoting the precipitation of Mn-containing dispersed phase nuclei. The number density of α-Al(Mn,Fe)Si dispersed phases reaches 2.4 × 10⁻⁶. 20 m -3 The average equivalent size is 51.2 nm (see Table 1), and the proportion of coherent quasicrystals reaches 55.7%. Figure 1 ; 3) Then, rapidly increase the temperature to 560℃ at a heating rate of 400℃ / h and hold for 8 hours; 4) After the heat preservation is completed, the ingot is taken out and air-cooled to room temperature of 25°C.

[0026] After the above processing, the dispersed phase was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS). The average equivalent diameter of the dispersed phase is the area of ​​the dispersed phase in the statistical TEM image. The area of ​​the dispersed phase is approximated as the area of ​​a circle (π). r 2 ), thus approximately calculating the equivalent diameter of the dispersed phase (2 r); the number density of diffuse phases is calculated by dividing the number of diffuse phases by the image area. (Equivalent diameter + transmission sample thickness)), the coherent quasi-crystalline proportion is determined by statistically analyzing the percentage of spherical dispersed phases in the total dispersed phase in transmission electron microscopy images. The proportion of grain orientation dispersion between 0-2° is calculated using Aztec software, representing the recrystallization proportion. Cr and Mo are observed to be enriched in the outer layer of the dispersed phase or at the dispersed phase / aluminum matrix interface, forming a highly thermally stable dispersed phase with core-shell structure characteristics. This type of dispersed phase can inhibit grain growth and recrystallization during subsequent extrusion, forging, or solution treatment, improving the stability of the alloy microstructure. See [link to relevant documentation]. Figure 1 .

[0027] Example 2: Control of dispersed phase precipitation in aluminum alloys (3xxx series alloys) The aluminum alloy used in this embodiment comprises, by mass percentage: Mn 0.85%, Cr 0.2%, Si 0.25%, Sn 0.1%, Fe 0.1%, Ti 0.02%, with the balance being Al and unavoidable impurities.

[0028] The preparation method includes the following steps: 1) The aluminum alloy ingot is heated from room temperature (25℃) to 380℃ at a heating rate of 25℃ / h; 2) Keep at 380℃ for 4 h to allow the Mn-containing dispersed phase to fully nucleate; 3) Then, rapidly increase the temperature to 460℃ at a heating rate of 400℃ / h and hold for 2 hours; 4) After homogenization, air cool to room temperature of 25℃.

[0029] After treatment using the above method, finely dispersed Mn-containing α-Al(Mn,Cr,Fe)Si and α-Al(Mn,Mo,Fe)Si dispersed phases can be formed in the aluminum alloy matrix (see...). Figure 2 Furthermore, Cr and Mo are enriched at the dispersed phase interface, improving the dispersed phase's resistance to coarsening. The alloy's threshold stress reaches 58 MPa (see Table 2). Analysis and testing were conducted according to relevant standards (ASTM E139-24 Standard Test Method for Creep and Stress Fracture of Metallic Materials). This embodiment is suitable for preparing Al-Mn extruded, rolled, or heat-resistant aluminum alloys with high resistance to recrystallization.

[0030] Comparative Example 1-1: Conventional Direct Heating Homogenization Treatment Using the same Al-Mg-Si-Mn-Cr-Mo aluminum alloy ingot as in Example 1, instead of undergoing a slow, medium-temperature heating and holding treatment at 400℃, the temperature was directly raised to 560℃ at a heating rate of 180℃ / h and held for 8 hours.

[0031] Compared to Example 1, this comparative example contains fewer Mn-dispersed phase nuclei (see Example 1). Figure 3In some areas, sparse or coarse dispersed phase regions are prone to form. Due to the lack of high-density nucleation processes at intermediate temperatures, the pinning effect of dispersed phases on grain boundary migration during subsequent hot working or solution treatment is insufficient, increasing the alloy's recrystallization tendency (see...). Figure 3 ).

[0032] Comparative Examples 1-2: Medium-temperature long-term heat preservation without rapid heating Using the same aluminum alloy ingot as in Example 1, the temperature was increased to 400°C at 180°C / h and held for 5 h, then increased to 560°C at 180°C / h and held for 8 h.

[0033] Compared to Example 1, although this comparative example can promote the precipitation of dispersed phase, the dispersed phase is prone to coarsening and its number density decreases due to the longer residence time in the intermediate temperature range (see Table 1). Furthermore, during the subsequent heating and holding processes, the dispersed phase continues to grow, resulting in a larger size and increased spacing of the final dispersed phase, which weakens the high-temperature strengthening effect on the alloy.

[0034] Comparative Example 2: Conventional direct heating homogenization treatment Using the same Al-Mn-Si-Cr aluminum alloy ingot as in Example 2, instead of undergoing a slow, medium-temperature heating and holding treatment at 380℃, the temperature was directly raised to 460℃ at a heating rate of 180℃ / h and held for 10 h.

[0035] Compared to Example 2, this comparative example contains fewer Mn-dispersed phase nuclei (see Example 2). Figure 4 The dispersed phase distribution is sparse. Due to the lack of high-density nucleation processes in the intermediate temperature stage, the pinning effect of the dispersed phase on grain boundaries and dislocation migration during subsequent high-temperature creep is insufficient, resulting in a threshold stress of only 32 MPa for the alloy (see Table 2), and a significant increase in creep strain (see Table 2). Figure 5 ).

[0036] Table 1. Different heat treatment process parameters for the same alloy

[0037] Table 2. Different heat treatment process parameters for the same alloy

[0038] 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 method for controlling the dispersion of phases in aluminum alloys, characterized in that, The process includes the following steps: S11: Heating the aluminum alloy ingot to 360-420℃ and holding for 0.5-4 h to allow the Mn-containing dispersed phase to precipitate; the aluminum alloy ingot is a 3xxx series alloy or a non-3xxx series alloy, and by weight percentage, the 3xxx series alloy includes 0.1%-1.2% Si, 0.3%-1.5% Mn, 0-0.6% Cr, 0-0.5% Mo, no more than 0.2% Sn, no more than 0.5% Fe, and no more than 0.2% Ti, wherein Cr and Mo are not simultaneously 0, and the balance is Al and unavoidable... Impurities, the non-3xxx series alloy includes 0.1%-8% Mg, 0.3%-1.5% Mn, 0.1%-1.2% Si, 0-0.6% Cr, 0-0.5% Mo, not more than 10% Zn, not more than 0.5% Fe, not more than 0.2% Ti, and Cr and Mo are not both 0, with the balance being Al and unavoidable impurities; S12: Heat the aluminum alloy ingot to the final homogenization temperature and hold it for 1-24 h, then cool it to room temperature; the final homogenization temperature is 450-600℃ and is 10-40℃ lower than the initial melting temperature of the aluminum alloy ingot.

2. The method for controlling the dispersion of phase precipitation in aluminum alloys according to claim 1, characterized in that, The Mn-containing dispersed phase is one or more of α-Al(Mn,Fe)Si, α-Al(Mn,Mo,Fe)Si, and α-Al(Mn,Cr,Fe)Si.

3. The method for controlling the dispersion of aluminum alloys according to claim 1, characterized in that, The Mn-containing dispersed phase has a core-shell structure, with Mn distributed in the internal region of the Mn-containing dispersed phase and Cr and / or Mo distributed in the dispersion interface region of the Mn-containing dispersed phase.

4. The method for controlling the dispersion of phase precipitation in aluminum alloys according to claim 1, characterized in that, In step S11, the heating rate is 10-50℃ / h.

5. The method for controlling the dispersion of phase precipitation in aluminum alloys according to claim 1, characterized in that, The equivalent diameter of the Mn-containing dispersed phase is 10-300 nm.

6. The method for controlling the dispersion of phase precipitation in aluminum alloys according to claim 1, characterized in that, The number density of the Mn-containing dispersed phase is not less than 1×10 20 m -3 The proportion of coherent quasicrystalline dispersed phase to the total dispersed phase is not less than 40%.

7. The method for controlling the dispersion of phase precipitation in aluminum alloys according to claim 1, characterized in that, In step S12, the heating rate is not less than 300℃ / h.

8. The method for controlling the dispersion of phase precipitation in aluminum alloys according to claim 1, characterized in that, In step S12, the cooling method is air cooling.

9. An aluminum alloy prepared by a method for controlling the dispersion of aluminum alloy as described in any one of claims 1-8.

10. A transportation vehicle, characterized in that, It is prepared from the aluminum alloy described in claim 9.

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