A high-temperature creep-resistant aluminum alloy and a preparation method thereof

Abstract

The application belongs to the technical field of aluminum alloy materials, and particularly relates to a high-temperature creep-resistant aluminum alloy and a preparation method thereof. The aluminum alloy is composed of the following raw materials in percentage by weight: 0.7-1.4% Mn, 0.2-0.6% Si, 0.05-0.15% Sn, Fe≤0.15%, Ti≤0.1%, and the balance of Al. The preparation method is based on the thermodynamic properties of alloy elements, combined with a heat treatment process for controlling the heating rate, to promote the refinement and uniform precipitation of the alpha-Al(Mn, Fe)Si second phase in the alloy, and mainly form a stable coherent quasicrystal structure. The phase exhibits good thermal stability in a high-temperature environment, can effectively inhibit grain boundary sliding and pin dislocations, significantly improve the creep stress threshold of the material, reduce the creep rate, and thus enhance the high-temperature creep resistance of the alloy.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy materials technology, specifically relating to a high-temperature creep resistant aluminum alloy and its preparation method. Background Technology

[0002] In aluminum alloys, age hardening is a key method for improving performance. Conventional age-hardening aluminum alloy systems (such as 2xxx, 6xxx, and 7xxx series alloys) mainly rely on the precipitation of metastable strengthening phases at temperatures below 250°C to achieve a strengthening effect. However, these precipitated phases have poor thermal stability above 250°C, are prone to coarsening and dissolution, leading to a significant decrease in material strength and limiting their application in high-temperature fields. In contrast, second phases such as Al3Zr, Al3Sc, and α-Al(Mn,Fe)Si exhibit higher thermal stability, maintaining structural stability and strengthening effects at temperatures above 300°C, making them suitable for high-temperature structural components in the automotive and aerospace industries. The high-temperature stability of these second phases mainly stems from the low diffusion rates of their constituent elements (such as Mn, Zr, Sc, Cr, Nb, Fe, Mo, etc.) in the aluminum matrix, resulting in slow coarsening kinetics and limited thermally induced diffusion at high temperatures. Furthermore, due to limitations in nucleation kinetics and alloying capabilities, the precipitation density and volume fraction of the second phase in common aluminum alloys are generally low, restricting the full realization of their high-temperature strengthening potential. Therefore, it is urgent to develop new composition design strategies and heat treatment processes to effectively improve the precipitation efficiency, thermal stability, and spatial distribution uniformity of the second phase in the matrix, thereby achieving superior mechanical properties and service stability of aluminum alloys at high temperatures.

[0003] In existing aluminum alloy systems, the Mn(Fe)-containing second phase exhibits thermal stability comparable to that of the Sc-containing second phase, possessing the potential to serve as a strengthening phase in high-temperature aluminum alloys. Therefore, it is considered a lower-cost, alternative to the expensive Sc element. Mn has been widely used in commercial AA3xxx series aluminum alloys and some manganese-containing 5xxx and 6xxx series alloys to control microstructure and texture by forming the α-Al(Mn,Fe)Si second phase. This type of second phase belongs to a cubic crystal structure with a lattice constant of 1.256–1.265 nm, and studies have clearly revealed its partially coherent orientation relationship with the aluminum matrix. However, in conventional non-heat-treatable alloys, this α-Al(Mn,Fe)Si type second phase mainly precipitates from the supersaturated solid solution within the aging temperature range of 350–450 °C, and mostly nucleates at dislocations, resulting in low precipitation density, large size, and uneven distribution. Therefore, this type of second phase has failed to achieve a significant dispersion strengthening effect in aluminum alloys. To address these issues, researchers over the past decade have attempted to improve the dispersion strengthening effect by optimizing composition design, controlling heat treatment processes, and using microalloying techniques to promote the precipitation of the α-second phase. However, the overall improvement in mechanical properties remains limited. The fundamental reason is that the Mn-containing second phase has a high nucleation activation energy (approximately 1.3–1.8 eV), making it difficult to form a high-density and uniformly distributed second phase in the aluminum matrix. Existing patented technologies have attempted to improve the high-temperature mechanical properties of such alloys. Patent CN119144876A discloses a method of adding Cu and Si to Al-Mn alloys to promote the precipitation of AlCu and AlMnFeSi second phases. The resulting second phase has a low number density and large size, failing to significantly improve alloy strength and significantly reducing alloy plasticity. Patent CN108048682A proposes a short-process preparation method that promotes the precipitation of nano-second phases by adding TiC particles as an inoculant to wrought aluminum alloys, but the resulting second phase number density is still low. Patent CN118516592A discloses a creep-resistant cast aluminum alloy and its preparation method. This alloy system is complex, involving multiple alloying elements such as Cu, Ce, Mn, Ni, Zr, Mg, and Pr. The preparation process includes multiple heat treatment stages, such as two-stage solution treatment, quenching, and two-stage aging treatment, making the process cumbersome. Patent CN116065065A discloses a compressive creep-resistant aluminum alloy material and its preparation method, aiming to reduce the amount of Sc used in the alloy system by introducing V and Sr, thereby reducing costs while maintaining creep resistance. However, this technology has only undergone creep performance testing at 200℃, and its performance at higher temperatures has not yet been verified.

[0004] Although existing technologies have recognized that introducing high-melting-point nanoscale second phases into the aluminum matrix through microalloying can help improve the thermal stability of the alloy and thus improve the creep performance of aluminum alloys at high temperatures, the segregation of Mn and the high nucleation activation energy of the α-Al(Mn,Fe)Si second phase in aluminum alloys result in insufficient precipitation density and uneven distribution of the α-Al(Mn,Fe)Si second phase, which limits further improvement in its high-temperature creep performance. Summary of the Invention

[0005] To address the aforementioned technical problems, this application provides the following technical solution:

[0006] This invention provides a method for preparing a high-temperature creep-resistant aluminum alloy, comprising the following steps:

[0007] S11: Aluminum and intermediate alloy are semi-continuously cast to obtain an alloy ingot; the alloy ingot comprises the following elements by weight percentage: 0.7-1.4% Mn, 0.2-0.6% Si, 0.05-0.15% Sn, Fe not more than 0.15%, Ti not more than 0.1%, and the balance being Al;

[0008] S12: The alloy ingot is subjected to heat treatment, wherein the heat treatment method is to heat to 400-500℃ at a rate of 20-50℃ / h; after heat treatment, nano-sized α-Al(Mn,Fe)Si second phase precipitates in the alloy ingot, wherein the proportion of quasicrystalline structure in the nano-sized α-Al(Mn,Fe)Si second phase exceeds 80%;

[0009] S13: Cool the heat-treated alloy ingot to room temperature (25±5℃) to obtain the high-temperature creep resistant aluminum alloy.

[0010] Preferably, the intermediate alloy is selected from Al-10Mn, Al-20Si and Al-50Sn.

[0011] Preferably, in step S11, the semi-continuous casting process is as follows:

[0012] S21: Heat aluminum and intermediate alloy to 750-760℃, and hold at that temperature for 25-35 minutes after they are completely melted.

[0013] S22: Cool down to 730-740℃, degas with protective gas for 12-18 minutes, and let stand for 18-22 minutes;

[0014] S23: Cast at 700-710℃ to obtain the alloy ingot.

[0015] Preferably, the protective gas is argon.

[0016] Preferably, the equivalent diameter of the nanoscale α-Al(Mn,Fe)Si second phase is 21.5-22.3 nm.

[0017] Preferably, the number density of the nanoscale α-Al(Mn,Fe)Si second phase is 3.8-6.1 × 10⁻⁶. 21 m -3 .

[0018] Preferably, the steady-state creep rate induced by the nanoscale α-Al(Mn,Fe)Si second phase during the creep process of the high-temperature creep-resistant aluminum alloy is 1-4 × 10⁻⁶. -9 s -1 .

[0019] Preferably, the stress threshold introduced by the nano-scale α-Al(Mn,Fe)Si second phase during the creep process of the high-temperature creep-resistant aluminum alloy is 50-60 MPa.

[0020] Preferably, in step S13, cooling is performed within 2 minutes after the heat treatment is completed.

[0021] Preferably, in step S13, the cooling method is air cooling, water mist cooling, or water quenching.

[0022] The present invention also provides a high-temperature creep resistant aluminum alloy prepared by the above preparation method.

[0023] This invention introduces trace amounts of tin (Sn) into aluminum alloys to form a Sn-containing second phase, serving as effective nucleation sites for the α-second phase. Based on this, and considering the thermodynamic properties of the alloying elements, a heat treatment process is designed to precisely control the precipitation behavior of the α-second phase, thereby significantly improving the precipitation density and distribution uniformity of the α-second phase, and refining its size. By enhancing the distribution of the high-temperature stable α-second phase in the matrix, this method significantly improves the creep resistance of the alloy under high-temperature conditions, expanding its application potential under thermal loads.

[0024] The technical solution of the present invention has the following advantages compared with the prior art:

[0025] This invention introduces trace amounts of Sn into aluminum alloys, utilizing its ability to form a Sn-containing second phase as a heterogeneous nucleation core for the α-Al(Mn,Fe)Si second phase, effectively lowering the nucleation energy barrier of this phase. Combined with in-depth analysis of the precipitation kinetics of the second phase, the heat treatment process was optimized to achieve precise control over the precipitation behavior of the α-Al(Mn,Fe)Si second phase, thereby significantly increasing the precipitation density of this phase in the alloy, refining its size, and improving its distribution uniformity in the aluminum matrix. The resulting thermally stable α-Al(Mn,Fe)Si second phase can effectively pin dislocations and suppress grain boundary slip under high-temperature service conditions, significantly increasing the creep stress threshold and reducing the creep rate of the alloy, thus improving the material's high-temperature creep resistance.

[0026] Compared to existing aluminum alloy heat treatment processes that rely heavily on high-temperature, long-term holding to promote the precipitation of the α-Al(Mn,Fe)Si second phase, this method generally suffers from problems such as low precipitate density, large size, and uneven distribution. Furthermore, some techniques introduce age-precipitable rare earth elements (such as Sc and Zr) to precipitate thermally stable second phases like Al3Sc and Al3Zr through solution-aging treatment, which can improve high-temperature performance, but is limited by high alloy costs, complex processes, and poor industrial applicability. In contrast, the technical solution proposed in this invention has a simple process flow, strong applicability, and achieves significant high-temperature strengthening effects without relying on high-cost rare earth elements, demonstrating good industrialization potential and application value. Attached Figure Description

[0027] Figure 1 The images show transmission electron microscopy (TEM) characterizations of aluminum alloys with different Sn contents under the same heat treatment conditions in Example 1.

[0028] Figure 2 Examples 1 show high-resolution and corresponding Fast Fourier Transform (FFT) characterization images of aluminum alloys with different Sn contents under the same heat treatment conditions; where a is A2, b is A1, and the FFT images display spatial frequency information, with the scale unit being nm. -1 , representing the wavenumber per nanometer.

[0029] Figure 3 The images show transmission electron microscopy (TEM) characterizations of aluminum alloys with the same Sn content under different heat treatment conditions in Example 2.

[0030] Figure 4 The images show transmission electron microscopy (TEM) characterizations of aluminum alloys with the same Sn content under different heat treatment conditions in Example 3. 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] Example 1:

[0033] This embodiment uses aluminum alloys with different Sn contents (Sn = 0 and 0.1 wt.%) as the research object, designated as A1 and A2. The alloys were prepared according to the following mass percentages: Mn: 1%; Si: 0.3%; Sn: 0-0.1%; the balance being aluminum and unavoidable impurities, of which the unavoidable impurity was Fe: 0.05%. After batching, the raw materials were heated to 750℃, completely melted, held at that temperature for 30 min with repeated stirring, then cooled to 740℃, degassed with argon for 15 min, and after removing surface slag, allowed to stand for 20 min. The resulting ingots were then cast into cold water copper molds at 700℃. Samples were taken from different ingots and heated to 450℃ at a heating rate of 25℃ / h. After heat treatment, the ingots were immediately water-quenched to room temperature within 2 minutes. The obtained samples are aluminum alloy materials with high-temperature creep resistance. Specific heat treatment parameters are shown in Table 1. The prepared alloy materials with different Sn contents were subjected to isothermal compression creep tests at 300℃, with the total strain set at 10%. Each group of samples was tested multiple times, and the average value of the test results was taken as the final characterization data.

[0034] All analyses and tests were conducted according to the relevant standard (ASTM E139-24 Standard Test Method for Creep and Stress Fracture Testing of Metallic Materials), and the results are shown in Table 2. Through comparison... Figure 1 The transmission electron microscope results showing the characteristics of second-phase precipitation inside the grains are shown. Figure 2 The high-resolution diffraction results of the second phase with different shapes inside the grains and the corresponding diffraction spots show that the proportion of the second phase with quasicrystalline structure in aluminum alloys with different Sn contents is not significantly different, but the average equivalent diameter and number density of the second phase are significantly different. The addition of Sn to aluminum alloys proposed in this invention can significantly increase the number density of second phase precipitation and refine the size of the second phase, thereby improving the inhibition effect of the second phase on grain boundary slip and the pinning ability of dislocations, thus enhancing the creep stress threshold of the alloy under high temperature environment and delaying the creep rate.

[0035] Table 1. Heat treatment parameters for aluminum alloys with different Sn contents

[0036]

[0037] Table 2. Results of second phase and creep analysis in aluminum alloys with different Sn contents.

[0038]

[0039] Example 2:

[0040] In this embodiment, the alloy composition is the same as alloy number A2 in Example 1, but the ingot preparation method is different from that in Example 1. This embodiment uses an aluminum alloy with the same Sn content (Sn = 0.1 wt.%) as the research object. The alloy is prepared according to the following mass percentages: Mn: 1%; Si: 0.3%; Sn: 0.1%; the balance is aluminum and unavoidable impurities, of which the unavoidable impurity is Fe: 0.05%. After batching, the raw materials are heated to 750℃, completely melted, held at that temperature for 30 min and stirred repeatedly, then cooled to 740℃, degassed with argon for 15 min, the surface slag is removed, and the mixture is allowed to stand for 20 min. It is then cast into a cold water copper mold at 700℃ to obtain an ingot. Heat treatment experiments with different heating rates are conducted on the alloy ingot. After heat treatment, it is immediately water quenched to room temperature within 2 minutes. The heat treatment process parameters of the obtained high-temperature creep resistant aluminum alloy material are shown in Table 3. The prepared high-temperature creep-resistant aluminum alloy was subjected to isothermal compression creep tests at 300℃, with a total strain set at 10%. Each group of samples was tested multiple times, and the average value of the test results was taken as the final characterization data. Processes 1 through 3 are all methods of this invention.

[0041] Analysis and testing were conducted according to relevant standards (ASTM E139-24 Standard Test Method for Creep and Stress Fracture Testing of Metallic Materials). The results of second-phase and creep analysis after different heating rates are shown in Figure 4. Comparison reveals that, compared to heat treatment processes 1# and 3#, the proposed heat treatment process 2# significantly reduces the average equivalent diameter of the second phase, increases the number density of the second phase, and maintains a high proportion of quasicrystalline second phase. Through comparison... Figure 3 The transmission electron microscopy results of the second-phase precipitation characteristics inside the grains show that the average equivalent diameter of the second phase in heat treatment process 2# proposed in this invention is smaller, the number density is significantly improved, and the proportion of the quasicrystalline structure of the second phase is higher, resulting in a higher creep stress threshold. Therefore, by comparing heat treatment processes 1# to 3#, it can be seen that heat treatment process 2# yields the smallest and most uniformly distributed second phase, the highest number density, and a higher proportion of the quasicrystalline structure of the second phase, as well as the highest creep stress threshold, thus significantly enhancing the creep resistance of the alloy under high-temperature conditions.

[0042] Table 3. Different heat treatment process parameters for the same alloy

[0043]

[0044] Table 4 Results of Second Phase and Creep Analysis

[0045]

[0046] Example 3:

[0047] In this embodiment, the alloy composition is the same as in Example 2, but the ingot preparation method is different. This embodiment uses an aluminum alloy with the same Sn content (Sn = 0.1 wt.%) as the research object. The alloy is prepared according to the following mass percentages: Mn: 1%; Si: 0.3%; Sn: 0.1%; the balance being aluminum and unavoidable impurities, wherein the unavoidable impurity content is Fe: 0.05%. After batching, the raw materials are heated to 750℃, completely melted, held at that temperature for 30 min with repeated stirring, then cooled to 740℃, degassed with argon for 15 min, and after removing surface slag, allowed to stand for 20 min. The ingot is then cast into a cold water copper mold at 700℃ to obtain an ingot. The alloy ingot is subjected to the same heating rate, but at different heating temperatures (400, 450, and 500℃). After heat treatment, it is immediately water quenched to room temperature within 2 minutes. The heat treatment process parameters for the obtained high-temperature creep-resistant aluminum alloy material are shown in Table 5. The prepared high-temperature creep-resistant aluminum alloy was subjected to isothermal compression creep tests at 300℃, with a total strain set at 10%. Each group of samples was tested multiple times, and the average value of the test results was taken as the final characterization data. Processes 4# and 5# are all methods of this invention.

[0048] The analysis and testing were conducted according to the relevant standard (ASTM E139-24 Standard Test Method for Creep and Stress Fracture Testing of Metallic Materials), and the results are shown in Table 6. A comparison reveals that, compared to heat treatment processes 4# and 5#, the second phase obtained by heat treatment process 2# proposed in this invention still has a lower average equivalent diameter, higher number density, and a higher proportion of quasicrystalline second phase. Through comparison... Figure 4 The transmission electron microscopy results of the second-phase precipitation characteristics inside the grains show that the Sn-added aluminum alloy heat treatment method of this invention significantly improves the precipitation density of the second phase, enhances the uniformity of the second phase distribution, and reduces the size of the second phase. This improves the inhibition effect of the second phase on grain boundary slip and the pinning effect on dislocations, thereby enhancing the creep stress threshold of the alloy at high temperatures and slowing down the creep rate. Therefore, the alloy exhibits higher creep resistance at high temperatures. Simultaneously, it reduces the number of heat treatment steps and avoids the use of expensive rare earth elements while maintaining performance, thus reducing industrial production costs.

[0049] Table 5. Different heat treatment process parameters for the same alloy

[0050]

[0051] Table 6 Results of Second Phase and Creep Analysis

[0052]

[0053] 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 preparing a high-temperature creep-resistant aluminum alloy, characterized in that, Includes the following steps: S11: Aluminum and intermediate alloy are semi-continuously cast to obtain an alloy ingot; the alloy ingot comprises the following elements by weight percentage: 0.7-1.4% Mn, 0.2-0.6% Si, 0.05-0.15% Sn, Fe not more than 0.15%, Ti not more than 0.1%, and the balance being Al; S12: The alloy ingot is subjected to heat treatment, wherein the heat treatment method is to heat to 400-500℃ at a rate of 20-50℃ / h; after heat treatment, nano-sized α-Al(Mn,Fe)Si second phase precipitates in the alloy ingot, wherein the proportion of quasicrystalline structure in the nano-sized α-Al(Mn,Fe)Si second phase exceeds 80%; S13: Cool the heat-treated alloy ingot to room temperature to obtain the high-temperature creep resistant aluminum alloy.

2. The preparation method according to claim 1, characterized in that, The intermediate alloy is selected from Al-10Mn, Al-20Si and Al-50Sn.

3. The preparation method according to claim 1, characterized in that, In step S11, the semi-continuous casting process is as follows: S21: Heat aluminum and intermediate alloy to 750-760℃, and hold at that temperature for 25-35 minutes after they are completely melted. S22: Cool down to 730-740℃, degas with protective gas for 12-18 minutes, and let stand for 18-22 minutes; S23: Cast at 700-710℃ to obtain the alloy ingot.

4. The preparation method according to claim 1, characterized in that, The equivalent diameter of the nanoscale α-Al(Mn,Fe)Si second phase is 21.5-22.3 nm.

5. The preparation method according to claim 1, characterized in that, The number density of the nanoscale α-Al(Mn,Fe)Si second phase is (3.8-6.1)×10⁻⁶. 21 m -3 .

6. The preparation method according to claim 1, characterized in that, The steady-state creep rate brought about by the nanoscale α-Al(Mn,Fe)Si second phase in the creep process of the high-temperature creep-resistant aluminum alloy is (1-4)×10. -9 s -1 .

7. The preparation method according to claim 1, characterized in that, The stress threshold introduced by the nanoscale α-Al(Mn,Fe)Si second phase during the creep process of the high-temperature creep-resistant aluminum alloy is 50-60 MPa.

8. The preparation method according to claim 1, characterized in that, In step S13, cooling is performed within 2 minutes after the heat treatment is completed.

9. The preparation method according to claim 1, characterized in that, In step S13, the cooling method is air cooling, water mist cooling, or water quenching.

10. A high-temperature creep-resistant aluminum alloy prepared by the preparation method according to any one of claims 1-9.

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