An Er, Sc, Si microalloyed Al-Cu-Mn heat-resistant aluminum alloy

Abstract

An Er, Sc / Si microalloyed Al-Cu-Mn heat-resistant aluminum alloy belongs to the technical field of high-strength and high-toughness heat-resistant aluminum alloy materials. It is composed of the following components: 4.0%–6.0% Cu by mass; 0.3%–0.5% Mn by mass; 0.2%–0.4% Si by mass; 0.15% Zr by mass; 0.1% Er by mass; and 0.1% Sc by mass, with the balance being high-purity Al. This invention further improves the mechanical properties of the alloy at room temperature and high temperatures by introducing 400℃ pre-aging and Er and Sc composite addition before solution treatment. This results in good thermal stability at 225℃ and 300℃, achieving higher hardness than other Al-Cu-Mn heat-resistant aluminum alloys.

Description

Technical Field

[0001] This invention belongs to the technical field of high-strength, high-toughness, and heat-resistant aluminum alloy materials. More specifically, it relates to the preparation and heat treatment process of Er, Sc / Si microalloyed Al-Cu-Mn heat-resistant alloy. Background Technology

[0002] The current generation of supersonic commercial airliners reaches speeds of Mach 2.4, and the intense friction between the fuselage and the air can cause skin temperatures to reach 160℃-190℃. Furthermore, rocket casings, missile tail fins, and aircraft wings also place higher demands (200℃-300℃) on aerospace structural materials. To meet these requirements, it is essential to develop new high-temperature and heat-resistant aluminum alloys. Currently, the introduction of microalloying elements to promote L12 structure aluminum alloys has attracted considerable interest, aiming to promote precipitation strengthening and stabilize the high-temperature microstructure of the alloy, thereby improving the mechanical properties of the alloy material at high temperatures.

[0003] Al-Cu heat-resistant aluminum alloys have a long history of research and development and are widely used in the aerospace field. The mechanical properties of Al-Cu alloys largely depend on the interaction between the hardening phase and dislocations. θ′ precipitates are generally considered to be the best main strengthening phase for high-temperature applications. However, when the temperature exceeds 200℃, θ′ precipitates will grow rapidly, coarsen, and even eventually transform into the thermally stable θ phase, resulting in a significant decrease in the strength of the alloy at high temperatures.

[0004] The addition of Mn and Zr microalloying can significantly improve the stability of Al-Cu alloys at 350℃. This is mainly due to the segregation of Mn atoms at the semi-coherent interface of the θ′ precipitate, which stabilizes the θ′ precipitate and allows Zr to slowly diffuse to the coherent interface of the θ′ precipitate, thus inhibiting the coarsening of the θ′ precipitate at 350℃. However, since the diffusion rate of Mn is low at 200-300℃, it cannot effectively and quickly diffuse to the θ′ precipitate interface, causing the θ′ precipitate of the alloy to coarsen at 200-300℃, resulting in poor mechanical properties.

[0005] Besides addressing the issue of stabilizing θ′ precipitation, the introduction of thermally stable ordered precipitates into aluminum alloys can also enhance their strengthening effect. The addition of Sc and Er elements leads to the formation of stable Al3Sc / Al3Er phases with an L12 ordered structure. These L12 ordered nanophases can lower the nucleation energy barrier of θ′ precipitation, providing heterogeneous nucleation sites and promoting finer, more dispersed precipitation of θ′ precipitates, thus enhancing precipitation strengthening. Adding Er to Al-Sc alloys also accelerates their aging kinetics, resulting in the precipitation of L12 ordered Al3(Sc,Zr,Er) phases with Er-rich cores, Sc-rich shells, and Zr-rich shells (core / double-shell structure), increasing lattice parameter mismatch. This nanophase exhibits at least 64 days of resistance to coarsening at 400°C, and the addition of Sc or Sc / Zr has also been reported to improve interfacial segregation of θ′ precipitates.

[0006] The addition of a small amount of Si can accelerate the diffusion of metal solute (M) in Al by forming M-Si-V clusters (where V is a vacancy), thereby enhancing the precipitation kinetics of the L12 ordered nanophase. However, the enhancement of solute diffusion rate caused by Si has a drawback: the coarsening kinetics of the nanoprecipitates are increased, which accelerates the severe coarsening of the precipitates at high temperatures.

[0007] Therefore, based on the above technical background, we utilize the combined addition of Er and Sc to promote the precipitation of L12-structured nanophases. These L12 ordered nanophases can lower the nucleation energy barrier of θ′ precipitates and provide heterogeneous nucleation sites for θ′ precipitates, promoting finer and more dispersed precipitation of θ′ precipitates. Furthermore, Si is added to form M-Si-V clusters to accelerate the diffusion of metallic solutes in Al, enhancing the precipitation kinetics of L12 ordered nanophases and θ′ precipitates, further improving the alloy's aging response speed and strength. During higher-temperature thermal exposure, the faster diffusion rate of Er allows it to preferentially segregate into the interior or interface of θ′ precipitates in the early stages of exposure, reducing the interfacial energy of θ′ and inhibiting rapid coarsening of the θ′ precipitates. As the temperature continues to increase or the thermal exposure time is extended, slow-diffusion-rate elements such as Sc and Mn have sufficient time to segregate to the θ′ interface before the θ′ precipitates rapidly coarsen, thus further stabilizing the θ′ precipitates and improving the microstructure stability of θ′ precipitates at higher temperatures. This invention utilizes a composite addition of three microalloying elements—Er, Sc / Si—combined with a unique heat treatment process. This allows the alloy to maintain high strength while retaining good thermal stability in working environments of 225℃ and 300℃, solving the problem of alloys exhibiting good thermal stability but low strength at higher temperatures. By combining the advantages of different elements through composite addition and a unique heat treatment process, this invention enables the alloy to be used in both low-temperature and high-temperature applications. Summary of the Invention

[0008] The purpose of this invention is to utilize the composite addition of Er and Sc to promote the precipitation of L12-structured nanophases, providing heterogeneous nucleation sites for θ′ precipitates and promoting finer and more dispersed precipitation of θ′ precipitates. Furthermore, the addition of Si forms M-Si-V clusters to accelerate the diffusion of metallic solutes in Al, enhancing the precipitation kinetics of the L12 ordered nanophase and θ′ precipitates, further improving the alloy's aging response speed and strength. During higher-temperature thermal exposure, Er, with its faster diffusion rate, preferentially segregates into the interior or interface of the θ′ precipitate in the early stages of exposure, reducing the interfacial energy of θ′ and inhibiting rapid coarsening of the θ′ precipitate. As the temperature continues to increase or the thermal exposure time is extended, slow-diffusion-rate elements such as Sc and Mn have sufficient time to segregate to the θ′ interface before the θ′ precipitate rapidly coarsens, thereby further stabilizing the θ′ precipitate and improving its structural stability at higher temperatures. This results in the preparation of an AlCuMnErSc heat-resistant alloy with good heat resistance, further improving the alloy's heat resistance.

[0009] The AlCuMnErSc heat-resistant alloy provided by this invention is characterized by the addition of Er, Sc, and Si microalloying elements to the AlCuMn alloy matrix. The weight percentage of each alloying element in the AlCuMnErSc alloy is as follows: 3.95%–6.0% Cu, 0.3–0.5% Mn, 0.18–0.4% Si, 0.1% Er, 0.1% Sc, 0.15–0.20% Zr, with the remainder being aluminum and unavoidable impurities with a content of no more than 0.2%.

[0010] The method for preparing the heat-resistant alloy of the present invention is characterized by comprising the following steps: first, high-purity aluminum is placed in a graphite crucible and heated and melted in a high-temperature melting furnace at 780±5℃; then, Al-Cu, Al-Mn, Al-Si, Al-Er, Al-Sc, and Al-Zr intermediate alloys are added, and then the mixture is stirred thoroughly. After it is fully melted, C2Cl6 is used to degas the mixture, and the mixture is stirred, kept at a constant temperature, and then cast into an ingot using an iron mold. Finally, different heat treatment processes are performed according to different working conditions during use to obtain the alloy material.

[0011] Depending on the different elements added, the following heat treatment process is performed, specifically including the following steps:

[0012] S1: The ingot is pre-aged at 400℃, and then heated to 540℃ in the furnace.

[0013] S2: The pre-aged material is then solution treated at 540℃, and then cooled with water.

[0014] S3: For different operating temperatures, solid solution alloys are subjected to different aging treatments.

[0015] A. For applications operating at temperatures below 200℃, the solution-treated alloy should be isothermally placed at 175℃ for 6–12 hours to achieve peak aging.

[0016] B. For applications where the temperature is above 200℃, especially 225℃, the solid solution alloy should be isothermally placed at 175℃ for 6 to 12 hours to reach peak aging, and then placed in a heat treatment furnace at 225℃ for 1 to 150 hours.

[0017] C. For applications where the temperature is above 200℃, especially 300℃, the solid solution alloy should be placed isothermally at 175℃ for 6 to 12 hours to reach peak aging, and then placed in a heat treatment furnace at 300℃ for 1 to 150 hours.

[0018] This invention leverages the synergistic effects of Er, Sc / Si microalloying elements, combined with a unique heat treatment process. The addition of Sc at 175℃ not only improves the alloy's aging hardness but also enhances its thermal stability under heat exposure at 225℃ and 300℃. Furthermore, the addition of Si accelerates the aging response, further increasing aging hardness and reducing the time to reach peak hardness. The combined addition of Er, Sc / Si maximizes the alloy's mechanical properties while maintaining better thermal stability at 225℃ and 300℃; it also compensates for the shortcomings of Sc above 200℃, making it the optimal element addition method for conditions above 200℃. Attached Figure Description

[0019] Figure 1 Hardness curve of the test alloy after long-term aging at 175℃.

[0020] Figure 2 Hardness curves of test alloys #1, #2, #3, and #4 after aging at 175℃ for 12 hours and then at 225℃ for an extended period.

[0021] Figure 3 Hardness curves of test alloys #1, #2, #3, and #4 after aging at 175℃ for 12 hours and then at 300℃ for an extended period.

[0022] Figure 4 STEM-EDS images of test alloys #3 and #4 after aging at 175℃ for 12h and then heat exposure at 225℃ for 150h.

[0023] Figure 5 STEM-EDS image of test alloy #3 after aging at 175℃ for 12h and then heat exposure at 300℃ for 150h. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0025] The weight percentages of the AlCuMnErSc alloy are: 3.95%–6.0% Cu, 0.3%–0.5% Mn, 0.18%–0.4% Si, 0.1% Er, 0.1% Sc, 0.15–0.20% Zr, with the remainder being aluminum and unavoidable impurities with a content not exceeding 0.2%.

[0026] The ingots are prepared according to their elemental composition and then subjected to the following processing.

[0027] The ingot was pre-aged at 400℃ and then heated to 540℃ in the furnace to obtain Al3Sc samples with pre-aged precipitation of L12 structure.

[0028] The pre-aged material was then subjected to solution treatment at 540℃, and after being removed and cooled with water, a solution-treated sample was obtained.

[0029] The thermal stability of the solid solution alloy was tested by isothermal aging at 175℃ for 1–200 h and long-term thermal exposure at 225℃ and 300℃, demonstrating that the interaction between the metal elements achieves thermal stability.

[0030] Example 1: Alloy ingots were prepared using graphite crucible melting and iron mold casting. The raw materials used were high-purity aluminum, Al-50% Cu, Al-10% Mn, Al-24% Si, Al-10% Zr, Al-5% Er, and Al-2% Sc master alloys. First, high-purity aluminum was placed in a graphite crucible and melted in a high-temperature melting furnace at 780±5℃. Then, the Al-50% Cu, Al-10% Mn, Al-24% Si, Al-10% Zr, Al-5% Er, and Al-2% Sc master alloys were added. The mixture was then thoroughly stirred until fully melted. After degassing with C2Cl6, the mixture was stirred again, kept at a constant temperature, and then cast into an iron mold to obtain the ingots. Five alloy materials with different compositions were prepared. The actual composition of the alloys was obtained by ICP testing, as shown in Table 1.

[0031] Table 1: Composition of the alloy determined by ICP

[0032]

[0033] Example 2: The as-cast alloys #1, #2, #3, #4, and #5 from Example 1 were heated from room temperature to 400°C, held for 10 hours, then heated in a furnace to 540°C, held for 0.5 hours, and subjected to aging solution treatment. After water quenching to room temperature within 10 seconds, they were then aged at a constant temperature of 175°C for an extended period. The aging hardness curves of the four alloys at this temperature were obtained, as shown below. Figure 1 As shown in the figure, after 12 hours at 175℃, the hardness of alloy #3 was not significantly different from that of alloy #4 (~125.8 Hv), but was significantly higher than that of alloys #1 and #2. The peak hardness of alloy #3 was ~28 Hv higher than that of the Al-Cu alloy and ~11 Hv higher than that of alloy #2. Compared with alloys #4 and #5, the addition of Si reduced the time for alloy #5 to reach its peak hardness, and the hardness value increased by ~14 Hv. When the aging time increased to 200 hours, the hardness of alloys #3 and #4 continued to decrease. The combined addition of Er and Sc further improved the coarsening resistance of the θ′ precipitate in the Al-Cu-Sc alloy.

[0034] Example 3: The as-cast alloys #1, #2, #3, and #4 from Example 1 were heated from room temperature to 400°C, held for 10 hours, then heated in a furnace to 540°C, held for 0.5 hours, and subjected to aging solution treatment. After water quenching to room temperature within 10 seconds, the alloys were isothermally aged at 175°C until the hardness peak was reached, followed by long-term aging at 225°C starting from 0 minutes. The aging hardness curves of the four alloys at this temperature were obtained, as shown below. Figure 2 As shown in the figure, the hardness of alloys #3 and #4 decreased significantly in the early stages of heat exposure, indicating over-aging. It can also be observed that the combined addition of Er and Sc significantly improved the thermal stability of the Al-Cu alloy. After aging at 225℃ for 12 hours, the hardness remained relatively stable. Under long-term heat exposure of up to 192 hours, the hardness value (~113 Hv) was significantly higher than that of the Al-Cu alloy with only Er and Sc. Compared to the peak hardness, the hardness value decreased by only 11 Hv.

[0035] Example 4: The as-cast alloys #1, #2, #3, and #4 from Example 1 were heated from room temperature to 400°C, held for 10 hours, then heated in a furnace to 540°C, held for 0.5 hours, and subjected to aging solution treatment. After water quenching to room temperature within 10 seconds, the alloys were isothermally aged at 175°C until the hardness peak was reached, followed by long-term aging at 300°C starting from 0 minutes. The aging hardness curves of the four alloys at this temperature were obtained, as shown below. Figure 3As shown in the figure, the hardness evolution of alloy #1 is similar to that observed after heat exposure to 225℃. However, no increase in hardness was observed in alloys #1 and #2 under heat exposure at 300℃, which is related to the rapid growth and coarsening of θ′ precipitates at higher temperatures. In summary, alloy #3 maintained the highest hardness (~100Hv) and stability during heat exposure. During heat exposure, the combined addition of Er and Sc to the Al-Cu alloy had a better stabilizing effect than adding Er or Sc alone.

[0036] Figure 4 The STEM-EDS spectra of alloys #3 and #4 after peak aging at 175℃ and heat exposure at 225℃ for 150 hours are shown. It can be seen that only Er is enriched around and inside the θ′ plate. This indicates that the segregation of Er in the θ′ precipitate makes the movement of interstitial Cu atoms relatively difficult, thus making the θ′ phase more stable. The addition of Er stabilizes the θ′ phase in the early stages at higher temperatures.

[0037] Figure 5 The STEM-EDS spectra of alloy #3, peak aged at 175℃, after 150 hours of heat exposure at 300℃ are shown. It can be seen that Sc and Mn atoms are enriched at the α-Al / θ′ interface, forming a Sc / Mn-rich layer. This further hinders the coarsening of θ′ at higher temperatures. Er solute atoms preferentially accumulate in the θ′ plate, providing thermal stability to θ′ and suppressing rapid coarsening in the early stages of heat exposure. Slow-diffusion-rate elements such as Sc and Mn have sufficient time to segregate to the θ′ interface. Without the addition of Er, the combination of Sc and Mn elements cannot effectively stabilize the θ′ precipitation.

Claims

1. An Er, Sc, Si microalloyed Al-Cu-Mn heat-resistant aluminum alloy, characterized in that, The weight percentages of each alloying element in the above heat-resistant aluminum alloy are as follows: 3.95%~6.0% Cu, 0.3%~0.5% Mn, 0.18%~0.4% Si, 0.1% Er, 0.1% Sc, 0.15-0.20% Zr, with the remainder being aluminum and unavoidable impurities with a content of no more than 0.2%. Heat-resistant aluminum alloys undergo different heat treatment processes depending on the operating conditions during use, specifically including the following steps: S1: The ingot is pre-aged at 400℃, and then heated to 540℃ in the furnace. S2: The pre-aged material is then solution treated at 540℃, and then cooled with water. S3: For different operating temperatures, the solid solution alloy will undergo different aging treatments: A. For applications operating at temperatures below 200℃, the solid solution alloy should be isothermally placed at 175℃ for 6~12h to achieve peak aging. B. For applications at 225℃, after isothermal aging of the solution-treated alloy at 175℃ for 6–12 hours to reach peak aging, place it in a heat treatment furnace at 225℃ for 1–150 hours. C. For applications requiring 300℃, the solution-treated alloy should be isothermally placed at 175℃ for 6–12 hours to reach peak aging, and then placed in a heat treatment furnace at 300℃ for 1–150 hours.

2. The Al-Cu-Mn heat-resistant aluminum alloy containing Er, Sc, and Si microalloying according to claim 1, characterized in that, The alloy contains the following weight percentages: 3.98% Cu, 0.33% Mn, 0.19% Si, 0.10% Er, 0.10% Sc, 0.18% Zr, with the remainder being aluminum and unavoidable impurities with a content not exceeding 0.2%.

3. A method for preparing an Al-Cu-Mn heat-resistant aluminum alloy containing Er, Sc, and Si microalloying as described in claim 1 or 2, characterized in that, Includes the following steps: First, high-purity aluminum is placed in a graphite crucible and heated to melt in a high-temperature melting furnace at 780±5℃. Then, Al-Cu, Al-Mn, Al-Si, Al-Er, Al-Sc, and Al-Zr master alloys are added and stirred thoroughly. After the alloy is fully melted, it is degassed with C2Cl6, stirred, kept at a constant temperature, and then cast into an ingot using an iron mold. Finally, different heat treatment processes are carried out according to different working conditions to obtain the alloy material.

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