Corrosion-resistant cast aluminum-lithium alloy and method for forming castings thereof

Abstract

This invention discloses a corrosion-resistant cast aluminum-lithium alloy and its casting forming method. The alloy components and their weight percentages are as follows: copper (Cu): 1.0–4.0%, lithium (Li): 1.0–4.0%, rare earth elements (RE): 0.5–3.0%, scandium (Sc): 0.1–0.5%, zirconium (Zr): 0.1–0.5%, titanium: 0.05–0.3%, with the balance being aluminum (Al). Through rare earth alloying and multi-component composite grain refinement, a dense and uniform rare earth oxide film is formed on the surface of the cast aluminum-lithium alloy under corrosive conditions, isolating the alloy from contact with the corrosive medium. Simultaneously, the preparation process involving casting, multi-stage solution treatment, surface shot peening, and multi-stage aging suppresses the continuous distribution of strengthening phases at grain boundaries, improving the alloy's resistance to intergranular corrosion. This invention not only significantly improves the corrosion resistance of cast aluminum-lithium alloys but also effectively inhibits deformation and cracking of large and complex aluminum-lithium alloy castings during conventional water quenching, contributing to the further application of cast aluminum-lithium alloys in deep-sea weaponry.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy casting technology, and relates to a corrosion-resistant cast aluminum-lithium alloy and a casting forming method thereof. Specifically, it relates to a heat treatment method for corrosion-resistant aluminum-lithium alloy castings and large and complex castings thereof. Background Technology

[0002] Aluminum alloys possess characteristics such as low density, high specific strength and stiffness, and excellent corrosion resistance, leading to their widespread application in aerospace, defense, and other fields. However, as future weapons operate in increasingly extreme conditions such as deep-sea high-pressure environments, traditional commercial aluminum alloys are finding it increasingly difficult to meet requirements in terms of density and stiffness. Therefore, the further development of lightweight, high-stiffness aluminum alloys is an urgent need.

[0003] Compared to traditional aluminum alloys, aluminum-lithium alloys have lower density and higher strength and stiffness. Studies have shown that adding 1 wt% lithium to an aluminum alloy reduces its density by about 3% and increases its stiffness by about 6%. Compared to wrought aluminum-lithium alloys, cast aluminum-lithium alloys can have a higher Li content and can be formed into large and complex components, thus making the "weight reduction and stiffness increase" advantages of cast aluminum-lithium alloys more significant. For example, cast aluminum-lithium alloys can have a lithium content of about 3 wt%, achieving a stiffness of over 80-85 GPa, which is 10-20% higher than traditional aluminum alloys; the density can be as low as 2.4-2.5 g / cm³. 3 Compared to traditional aluminum alloys, the cost is reduced by 5-10%. Therefore, lightweight and high-rigidity cast aluminum-lithium alloys have extremely broad application prospects in important fields such as deep-sea weaponry.

[0004] However, the following problems exist in the current casting of aluminum-lithium alloys and the forming of large and complex castings:

[0005] (1) Lithium is extremely chemically reactive, which increases the corrosion susceptibility of aluminum-lithium alloys in complex environments. The T1 phase, which has the best strengthening effect in aluminum-lithium alloys, has a low electrode potential, and galvanic corrosion easily forms between the T1 phase and the PFZ (precipitation zone). In addition, the aluminum-lithium alloy melt is prone to oxidation and gas absorption, and the preparation of high-purity alloy melts is difficult, which further reduces the corrosion resistance of the alloy.

[0006] (2) Cast aluminum-lithium alloys have a high lithium content and a high coefficient of linear expansion, which makes large and complex aluminum-lithium alloy castings more prone to cracking. In particular, the rapid cooling rate of high-temperature solution quenching and the uneven and difficult-to-coordinate shrinkage of different wall thicknesses result in high quenching stress inside the casting, making it easy for quenching cracks to form in the casting, leading to product scrap.

[0007] In summary, the addition of lithium reduces the corrosion resistance of existing cast aluminum-lithium alloys and increases the tendency for quenching cracks in large and complex castings. These problems severely limit the further promotion and application of lightweight, high-rigidity cast aluminum-lithium alloys in key fields such as deep-sea weaponry and aerospace.

[0008] To address these issues, both academia and industry have conducted in-depth research. Patent CN202211637061.X (A Method for Improving the Corrosion Resistance of Aluminum-Lithium Alloys) discloses the composition and heat treatment method of a corrosion-resistant aluminum-lithium alloy. It employs solution treatment and two-stage aging to heat-treat an Al-4.0Cu-1.1Li-0.45Mg-0.39Ag-0.11Zr-0.09Fe-0.03Ti-0.005Si alloy, thereby improving its corrosion resistance. Patent CN201611118481.1 (A Heat Treatment Process for Improving the Corrosion Resistance of Aluminum-Lithium Alloys) discloses the composition and heat treatment method of a thick corrosion-resistant aluminum-lithium alloy plate. It reports that after solution quenching, large-deformation pre-stretching and two-stage aging are used to regulate the precipitates within the grains and at grain boundaries, improving the corrosion resistance of the thick plate while maintaining its mechanical properties. However, the aforementioned aluminum-lithium alloys are all wrought aluminum-lithium alloys with low lithium content, insufficient stiffness improvement, and difficulty in forming large and complex components. Patent CN201910574809.8 (A High-Strength and Toughness Wrought Aluminum-Lithium Alloy with Composite Addition of Multiple Rare Earth Elements and its Preparation Method) reports a method for preparing a high-strength and toughness wrought aluminum-lithium alloy by composite addition of multiple rare earth elements; however, this patent does not explain whether the aforementioned rare earth elements affect the corrosion resistance of the aluminum-lithium alloy. Furthermore, after treating the aluminum-lithium alloy using the aging method described in the aforementioned patent technology, a continuous T1 phase easily forms at the grain boundaries, reducing the intergranular corrosion resistance of the aluminum-lithium alloy.

[0009] Patent CN201910178122.2 (A Corrosion-Resistant Cast Aluminum-Lithium Alloy and Its Preparation Method) discloses a formulation and casting method for a corrosion-resistant cast aluminum-lithium alloy. The alloy composition is: 1.5–2% Li, 0.5–3.0% Zn, 0.1–0.3% Cr, 0.1–0.3% Zr, 0.1–0.3% Yb, with the balance being Al. This alloy employs multi-component composite microalloying, which can improve the corrosion resistance of the cast aluminum-lithium alloy and reduce costs. However, this casting alloy does not contain Cu, resulting in insufficient strengthening effect. Furthermore, this patent does not provide an effective solution for reducing the quenching cracking tendency of large and complex castings made from cast aluminum-lithium alloys.

[0010] In summary, the inventors believe that to address the current problems of insufficient corrosion resistance in cast aluminum-lithium alloys and the high tendency for quenching cracking in large and complex aluminum-lithium alloy castings, it is necessary to develop a novel heat treatment method for cast aluminum-lithium alloy materials and their large and complex castings. On the one hand, by optimizing microalloying and heat treatment processes, the continuous distribution of the T1 phase at the grain boundaries of cast aluminum-lithium alloys can be suppressed, thereby improving the alloy's corrosion resistance through microstructure control. Simultaneously, the formation of a dense oxide film on the alloy surface under corrosive conditions can be accelerated, providing physical protection. On the other hand, by optimizing the heat treatment process, the stress distribution of large and complex castings during quenching can be improved, reducing their tendency for quenching cracking. This invention can promote the application of aluminum-lithium alloys in areas such as lightweighting of deep-sea weaponry. Summary of the Invention

[0011] In view of the above-mentioned shortcomings of the existing technology, the present invention provides a corrosion-resistant cast aluminum-lithium alloy and a casting method thereof, which can not only effectively improve the corrosion resistance of cast aluminum-lithium alloy in corrosive environments such as deep sea, but also effectively improve the quenching cracking tendency of large and complex aluminum-lithium alloy castings and increase the yield of aluminum-lithium alloy castings.

[0012] To achieve the aforementioned technical effects, this invention proposes a novel formulation for cast aluminum-lithium alloy materials and a heat treatment method for large and complex castings, which differs significantly from existing aluminum-lithium alloys and their heat treatment processes. Existing aluminum-lithium alloys primarily improve corrosion resistance by employing microalloying elements capable of controlling the morphology and structure of precipitated phases in the matrix, along with heat treatment processes. However, due to the high chemical reactivity of lithium, it readily reacts with water and oxygen. Simply controlling the microstructure without effectively isolating the alloy from corrosive media makes it difficult to significantly improve the corrosion resistance of aluminum-lithium alloys, thus limiting the limitations of existing technologies. This invention innovatively employs rare-earth alloying and Sc, Zr, and Ti multi-component composite refining to improve the corrosion resistance of cast aluminum-lithium alloys: the high chemical reactivity of rare-earth elements allows for the rapid formation of a dense rare-earth oxide film on the surface of the aluminum-lithium alloy, isolating the alloy from corrosive media; simultaneously, the Sc, Zr, and Ti multi-component microalloying significantly improves the grain refinement effect, thereby enhancing the uniformity of the rare-earth oxide film distribution. The above two aspects effectively promote the formation of a dense and uniform rare earth oxide film on the surface of the cast aluminum-lithium alloy, effectively isolating the alloy from corrosive media. Furthermore, this invention combines multi-stage solution treatment and multi-stage aging to effectively dissolve the highly thermally stable rare earth second phase, suppress grain coarsening, eliminate the continuously distributed T1 phase at grain boundaries, and improve the corrosion resistance of the aluminum-lithium alloy itself. Regarding the quenching process, this invention employs a two-stage cooling method: slow cooling at high temperatures to avoid stress concentration and cracking caused by excessively rapid cooling; and rapid cooling at low temperatures to prevent the precipitation of the second phase and ensure the effectiveness of the solution treatment. This two-stage quenching and cooling method not only ensures the effectiveness of the solution treatment and prevents the second phase from re-precipitating during cooling, but also slows down the cooling rate of the casting at high temperatures, effectively suppressing the formation of quenching cracks.

[0013] Specifically, this is achieved through the following technical solutions:

[0014] This invention provides a corrosion-resistant cast aluminum-lithium alloy, wherein the alloy components and their weight percentages are as follows: copper Cu: 1.0-4.0%, lithium Li: 1.0-4.0%, rare earth element RE: 0.5-3.0%, scandium Sc: 0.1-0.5%, zirconium Zr: 0.1-0.5%, titanium 0.05-0.3%, other individual impurity elements: ≤0.1%, total other impurity elements: ≤0.2%, and the balance is aluminum Al.

[0015] Alloying with rare earth elements at a weight percentage of 0.5–3.0% can form an Al-RE strengthening phase in the aluminum-lithium alloy and preferentially react with corrosive media to form a dense rare earth oxide film on the alloy surface. Sc, Zr, and Ti are used to refine the alloy and improve the uniformity of the rare earth oxide film. The combined addition of Sc and Zr forms an Al3(Sc,Zr) composite phase, which significantly refines and strengthens the aluminum matrix. Further addition of Ti further refines the Al3(Sc,Zr) composite phase and improves its distribution in the aluminum matrix, resulting in better matrix refinement and a reduction in the width of the precipitate-free zone (PFZ).

[0016] As one aspect of the present invention, the rare earth element is preferably one or more of elements such as gadolinium (Gd), yttrium (Y), neodymium (Nd), cerium (Ce), and lanthanum (La).

[0017] As one aspect of the present invention, the surface of the corrosion-resistant cast aluminum-lithium alloy has a dense and uniform rare earth oxide film layer.

[0018] The present invention also provides a casting forming method for the corrosion-resistant aluminum-lithium alloy, the casting forming method comprising the following steps:

[0019] S1: Raw materials are prepared according to the chemical element composition ratio in claim 1, and then smelted and cast to obtain a casting;

[0020] S2: Perform solution treatment on the casting obtained in step S1;

[0021] S3: Perform surface shot peening on the casting obtained in step S2;

[0022] S4: The casting obtained in step S3 is subjected to aging treatment and then machined to obtain a corrosion-resistant aluminum-lithium alloy casting.

[0023] The reason for performing surface shot peening before alloy aging is to form a plastic deformation layer on the surface of the cast aluminum-lithium alloy. This plastic deformation layer contains a large number of crystal defects such as dislocations, subgrain boundaries, and grain boundaries. These crystal defects have high energy, which facilitates the preferential nucleation of strengthening phases at these locations during subsequent aging, increasing the number density of strengthening phase precipitation and its strengthening effect. More importantly, surface shot peening treatment promotes the segregation of rare earth elements dissolved in the Al matrix to the high-energy surface, increasing the density and thickness of the rare earth oxide film formed by the alloy in the corrosive medium, thereby improving the protective effect of the oxide film on the alloy matrix.

[0024] As one aspect of the present invention, in step S2, the solution treatment is preferably a two-stage solution treatment, wherein the first-stage solution temperature is 400-460℃ and the solution time is 10-40h, and the second-stage solution temperature is 460-540℃ and the solution time is 10-40h.

[0025] Because rare earth elements are added in this invention, the resulting highly thermally stable rare earth second phase needs to be dissolved during a high-temperature solution treatment, which can cause grain coarsening. This invention, combined with a lower-temperature first-stage solution treatment, allows the low-melting-point second phase to dissolve back, preventing the alloy from remaining at a consistently high solution temperature, which would lead to grain coarsening. Grain coarsening reduces the uniformity and protective effect of the subsequent rare earth oxide film. The higher-temperature second-stage solution treatment further avoids the residue of large, undissolved rare earth phases, reducing the amount of micro-galvanic corrosion in the alloy.

[0026] As one aspect of the present invention, the quenching and cooling method of the solution treatment is a two-stage process. The temperature range of the first stage of cooling is from the solution heating temperature of 460-540°C to 250-300°C, and the cooling method is air cooling, wind cooling, or steam cooling. The temperature range of the second stage of cooling is from the termination temperature of the first stage of cooling to room temperature, and the cooling method is water cooling or oil cooling.

[0027] As one aspect of the present invention, the cooling rate of the first stage of quenching is preferably 0.1–20 °C / s, and the cooling rate of the second stage of quenching is >20 °C / s. A preferred quenching cooling rate is 20–200 °C / s, more preferably 40–200 °C / s.

[0028] The reason for setting 250–300℃ as the boundary between the first and second cooling temperature ranges is primarily because at around 250℃, precipitates such as T1, S', and θ' will precipitate from the aluminum-lithium alloy matrix. Therefore, to ensure the effectiveness of the solution treatment, when the temperature of the aluminum-lithium alloy casting is reduced to 250–300℃, rapid water cooling is used for quenching to prevent the precipitation of these precipitates. However, when the temperature is above 300℃, these precipitates will not precipitate, so the cooling rate during quenching can be reduced to decrease the quenching stress in the casting and prevent cracking.

[0029] As one aspect of this invention, both stages of cooling are performed on a vibration table with a vibration frequency of 10–1000 Hz, an amplitude of 0.1–1 mm, and a peak acceleration of 1–4 g. The cooling process after solution treatment is completed on a vibration table equipped with a vibration motor. During solution treatment and quenching, placing the alloy component on the vibration table and vibrating it effectively alleviates stress concentration in the magnesium rare earth alloy, making shrinkage stress more uniform, coordinating shrinkage deformation between different parts, and better preventing deformation and cracking of the component.

[0030] As one aspect of the present invention, in step S3, the surface shot peening treatment of the corrosion-resistant aluminum-lithium alloy casting has a residual compressive stress layer depth of 0.1 to 1 mm and a shot peening coverage of more than 80%.

[0031] The residual compressive stress layer after shot peening contains a large amount of lattice distortion, resulting in high energy. Rare earth elements will segregate in these areas during subsequent aging treatment. The rare earth elements segregated on the casting surface can rapidly form a dense rare earth oxide film in a corrosive environment, thereby improving the corrosion resistance of the component. The depth of the residual compressive stress layer determines the thickness of the subsequent rare earth segregated layer: if the thickness is too small, the resulting rare earth oxide film will be too thin, providing poor protection; if the thickness is too large, the subsequent rare earth segregated layer will be too thick, forming a "rare earth-depleted" zone near the surface, reducing the strengthening effect.

[0032] As one aspect of the present invention, in step S4, the aging process is as follows: the first stage aging temperature is 150-180℃ / s, and the aging time is 10-30h; the second stage aging temperature is 180-250℃ / s, and the aging time is 0.5-5h; the third stage aging temperature is 150-180℃ / s, and the aging time is 10-30h.

[0033] When a single-stage aging process is used and the peak aging state is reached, although the strengthening effect of the alloy is very good, the continuous distribution of T1 phase at the grain boundaries will form micro-galvanic corrosion with PFZ, reducing the alloy's intergranular corrosion resistance. Therefore, after peak aging, a second-stage aging at a higher temperature is used to cause the continuous T1 phase to agglomerate and coarsen, so that the T1 phase is no longer in a continuous distribution form. However, at the same time, some of the low thermal stability strengthening phases will dissolve during the second-stage aging process, reducing the number density of the strengthening phase. Therefore, a third-stage low-temperature aging treatment is used again to promote the re-precipitation of the alloying elements dissolved during the second-stage aging process, ensuring the aging strengthening effect. The three-stage aging treatment of this invention can not only eliminate the continuous distribution of T1 phase at the alloy grain boundaries to improve the alloy's intergranular corrosion resistance, but also effectively guarantee the strengthening effect of the alloy.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1) This invention effectively avoids the continuous distribution of strengthening phases at grain boundaries in cast aluminum-lithium alloys through multi-stage solution treatment and multi-stage aging treatment, thereby improving the intergranular corrosion resistance of the alloy and enhancing the corrosion resistance of cast aluminum-lithium alloys.

[0036] 2) This invention employs rare earth alloying, which not only effectively improves the strengthening effect of aluminum-lithium alloys, but also enhances the corrosion resistance of cast aluminum-lithium alloys by forming a dense rare earth oxide film on the surface of the aluminum-lithium alloy.

[0037] 3) The present invention adopts a simple two-stage quenching and cooling method, which can significantly improve the deformation and cracking problem of large and complex cast aluminum-lithium alloy components in the conventional water quenching and cooling process, and greatly improve the yield of aluminum-lithium alloy castings. Attached Figure Description

[0038] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0039] Figure 1 This is a cross-sectional view of the aluminum-lithium alloy casting prepared in Example 1 after corrosion in NaCl solution. Detailed Implementation

[0040] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0041] Example 1

[0042] Pure Al ingots, Al-Cu master alloys, pure Li ingots, Al-Gd master alloys, Al-Sc master alloys, Al-Zr master alloys, and Al-Ti master alloys are melted in a melting furnace. After the raw materials are melted, they are refined at 730℃ and allowed to stand for 15 minutes. When the temperature drops to 720℃, the melt is cast to obtain an Al-1wt%Cu-1wt%Li-0.5wt%Gd-0.1wt%Sc-0.1wt%Zr-0.05wt%Ti alloy casting.

[0043] A two-stage solution treatment was performed on Al-1wt%Cu-1wt%Li-0.5wt%Gd-0.1wt%Sc-0.1wt%Zr-0.05wt%Ti alloy castings. The first stage solution treatment temperature was 400℃, and the holding time was 10 h. The second stage solution treatment temperature was 460℃, and the holding time was 40 h. Quenching and cooling were performed by air cooling to 250℃ at a rate of approximately 0.5℃ / s, followed by water cooling to room temperature at a rate of approximately 100℃ / s. The quenching process was completed on a vibrating table with a vibration frequency of 10 Hz, an amplitude of 0.1 mm, and a peak acceleration of 1 g. The quenched castings were then subjected to shot peening for surface strengthening, achieving a residual compressive stress layer depth of 0.1 mm and a shot peening coverage of 82%. The shot-peened aluminum-lithium alloy castings were then subjected to aging treatment. The first aging temperature is 150℃ and the aging time is 10 hours; the second aging temperature is 180℃ and the aging time is 0.5 hours; and the third aging temperature is 150℃ and the aging time is 10 hours.

[0044] The aluminum-lithium alloy casting obtained above was immersed in a 3.5% wt. NaCl solution for 72 hours, and the corrosion rate was 1.7 × 10⁻⁶. -4 mm / y, the cross-sectional view after corrosion is as follows Figure 1 As shown.

[0045] Example 2

[0046] Pure Al ingots, Al-Cu master alloys, pure Li ingots, Al-Y master alloys, Al-Sc master alloys, Al-Zr master alloys, and Al-Ti master alloys are melted in a melting furnace. After the raw materials are melted, they are refined at 730℃ and allowed to stand for 15 minutes. When the temperature drops to 720℃, the melt is cast to obtain an Al-2wt%Cu-2wt%Li-1wt%Y-0.2wt%Sc-0.2wt%Zr-0.1wt%Ti alloy casting.

[0047] A two-stage solution treatment was performed on Al-2wt%Cu-2wt%Li-1wt%Y-0.2wt%Sc-0.2wt%Zr-0.1wt%Ti alloy castings. The first stage solution treatment temperature was 420℃, and the holding time was 20 h. The second stage solution treatment temperature was 480℃, and the holding time was 30 h. The castings were then cooled to 260℃ by air cooling at a rate of approximately 0.5℃ / s, followed by water cooling to room temperature at a rate of approximately 100℃ / s. The quenching process was performed on a vibrating table at a frequency of 100 Hz, an amplitude of 0.2 mm, and a peak acceleration of 2 g. The quenched castings were then subjected to shot peening to strengthen the surface, achieving a residual compressive stress layer depth of 0.3 mm and a shot peening coverage of 85%. Finally, the shot-peened aluminum-lithium alloy castings underwent aging treatment. The first aging temperature is 160℃ and the aging time is 15 hours; the second aging temperature is 200℃ and the aging time is 1 hour; the third aging temperature is 160℃ and the aging time is 15 hours.

[0048] The aluminum-lithium alloy casting obtained above was immersed in a 3.5% wt. NaCl solution for 72 hours, and the corrosion rate was 1.9 × 10⁻⁶. -4 mm / y.

[0049] Example 3

[0050] Pure Al ingots, Al-Cu master alloys, pure Li ingots, Al-Nd master alloys, Al-Sc master alloys, Al-Zr master alloys, and Al-Ti master alloys are melted in a melting furnace. After the raw materials are melted, they are refined at 730℃ and allowed to stand for 15 minutes. When the temperature drops to 720℃, the melt is cast to obtain Al-3wt%Cu-3wt%Li-2wt%Nd-0.3wt%Sc-0.3wt%Zr-0.2wt%Ti alloy castings.

[0051] A two-stage solution treatment was performed on Al-3wt%Cu-3wt%Li-2wt%Nd-0.3wt%Sc-0.3wt%Zr-0.2wt%Ti alloy castings. The first stage solution treatment temperature was 440℃, and the holding time was 30 h. The second stage solution treatment temperature was 500℃, and the holding time was 20 h. The castings were then cooled to 280℃ using air cooling at a rate of approximately 0.5℃ / s, followed by water cooling to room temperature at a rate of approximately 100℃ / s. The quenching process was performed on a vibrating table at a frequency of 500 Hz, an amplitude of 0.5 mm, and a peak acceleration of 3 g. The quenched castings were then subjected to shot peening to strengthen the surface, achieving a residual compressive stress layer depth of 0.7 mm and a shot peening coverage of 90%. Finally, the shot-peened aluminum-lithium alloy castings underwent aging treatment. The first aging temperature is 170℃ and the aging time is 20 hours; the second aging temperature is 220℃ and the aging time is 2 hours; the third aging temperature is 170℃ and the aging time is 20 hours.

[0052] The aluminum-lithium alloy casting obtained above was immersed in a 3.5% wt. NaCl solution for 72 hours, and the corrosion rate was 1.7 × 10⁻⁶. -4 mm / y.

[0053] Example 4

[0054] Pure Al ingots, Al-Cu master alloys, pure Li ingots, Al-Ce master alloys, Al-Sc master alloys, Al-Zr master alloys, and Al-Ti master alloys are melted in a melting furnace. After the raw materials are melted, they are refined at 730℃ and allowed to stand for 15 minutes. When the temperature drops to 720℃, the melt is cast to obtain an Al-4wt%Cu-4wt%Li-3wt%Ce-0.5wt%Sc-0.5wt%Zr-0.3wt%Ti alloy casting.

[0055] A two-stage solution treatment was performed on Al-4wt%Cu-4wt%Li-3wt%Ce-0.5wt%Sc-0.5wt%Zr-0.3wt%Ti alloy castings. The first stage solution treatment temperature was 460℃, and the holding time was 40 h. The second stage solution treatment temperature was 480℃, and the holding time was 10 h. The castings were then cooled to 300℃ using air cooling at a rate of approximately 0.5℃ / s, followed by water cooling to room temperature at a rate of approximately 100℃ / s. The quenching process was performed on a vibrating table at a frequency of 1000 Hz, an amplitude of 1 mm, and a peak acceleration of 4 g. The quenched castings were then subjected to shot peening to strengthen the surface, achieving a residual compressive stress layer depth of 1 mm and a shot peening coverage of 99%. Finally, the shot-peened aluminum-lithium alloy castings underwent aging treatment. The first aging temperature is 180℃ and the aging time is 30 hours; the second aging temperature is 250℃ and the aging time is 5 hours; the third aging temperature is 180℃ and the aging time is 30 hours.

[0056] The aluminum-lithium alloy casting obtained above was immersed in a 3.5% wt. NaCl solution for 72 hours, and the corrosion rate was 1.6 × 10⁻⁶. -4 mm / y.

[0057] Comparative Example 1

[0058] The composition and heat treatment process of the aluminum-lithium alloy in this comparative example are basically the same as those in Example 1, except that the alloy does not contain rare earth elements.

[0059] The aluminum-lithium alloy casting obtained above was immersed in a 3.5% wt. NaCl solution for 72 hours, and the corrosion rate was 2.6 × 10⁻⁶. -3 mm / y. The results show that the corrosion resistance of the alloy is significantly reduced, mainly because rare earth alloying was not used. As a result, the aluminum-lithium alloy did not form a dense rare earth oxide film in the corrosive solution, thus reducing its corrosion resistance.

[0060] Comparative Example 2

[0061] The composition and heat treatment process of the aluminum-lithium alloy in this comparative example are basically the same as those in Example 1, except that the content of Gd element in the alloy is 4wt%.

[0062] The aluminum-lithium alloy casting obtained above was immersed in a 3.5% wt. NaCl solution for 72 hours, and the corrosion rate was 4.4 × 10⁻⁶. -3 mm / y. The results show that the corrosion resistance of the alloy is significantly reduced. The main reason is that the high rare earth content leads to the formation of a thermally stable rare earth second phase in the aluminum-lithium alloy, which is difficult to dissolve during subsequent solution treatment. The residual rare earth second phase forms micro-galvanic corrosion with the matrix, thus reducing corrosion resistance.

[0063] Comparative Example 3

[0064] The composition and heat treatment process of the aluminum-lithium alloy in this comparative example are basically the same as those in Example 1, except that the alloy does not contain Sc.

[0065] The aluminum-lithium alloy casting obtained above was immersed in a 3.5% wt. NaCl solution for 72 hours, and the corrosion rate was 7.6 × 10⁻⁶. -4 mm / y. The results show that the corrosion resistance of the alloy has decreased, mainly because the rare earth oxide film layer formed on the surface of the aluminum-lithium alloy is unevenly distributed due to the lack of multi-component composite refining, thus reducing corrosion resistance.

[0066] Comparative Example 4

[0067] The composition and heat treatment process of the aluminum-lithium alloy in this comparative example are basically the same as those in Example 1, except that the alloy does not contain Zr.

[0068] The aluminum-lithium alloy casting obtained above was immersed in a 3.5% wt. NaCl solution for 72 hours, and the corrosion rate was 6.8 × 10⁻⁶. -4 mm / y. The results show that the corrosion resistance of the alloy has decreased, mainly because the rare earth oxide film layer formed on the surface of the aluminum-lithium alloy is unevenly distributed due to the lack of multi-component composite refining, thus reducing corrosion resistance.

[0069] Comparative Example 5

[0070] The composition and heat treatment process of the aluminum-lithium alloy in this comparative example are basically the same as those in Example 1, except that the alloy does not contain Ti.

[0071] The aluminum-lithium alloy casting obtained above was immersed in a 3.5% wt. NaCl solution for 72 hours, and the corrosion rate was 9.2 × 10⁻⁶. -4 mm / y. The results show that the corrosion resistance of the alloy has decreased, mainly because the rare earth oxide film layer formed on the surface of the aluminum-lithium alloy is unevenly distributed due to the lack of multi-component composite refining, thus reducing corrosion resistance.

[0072] Comparative Example 6

[0073] The composition and heat treatment process of the aluminum-lithium alloy in this comparative example are basically the same as those in Example 1. The only difference is that only the casting is subjected to single-stage solution treatment, and the temperature of the single-stage solution treatment is 540°C, while the solution treatment time remains unchanged.

[0074] The aluminum-lithium alloy casting obtained above was immersed in a 3.5% wt. NaCl solution for 72 hours, and the corrosion rate was 9.7 × 10⁻⁶. -4mm / y. The results show that the corrosion resistance of the alloy has decreased. The main reason is that the double-stage solution treatment was not used. During the solution treatment process, the grains of the aluminum-lithium alloy castings coarsened, and the rare earth oxide film layer formed on the surface of the aluminum-lithium alloy was unevenly distributed, thus reducing the corrosion resistance.

[0075] Comparative Example 7

[0076] The composition and heat treatment process of the aluminum-lithium alloy in this comparative example are basically the same as those in Example 1, except that a two-stage quenching method was not used during solution quenching; instead, only water quenching was performed at a cooling rate of 100°C / s. The results showed that the casting was scrapped due to severe cracking. This was mainly because the quenching rate was too fast, leading to thermal stress concentration and cracking in the component.

[0077] Comparative Example 8

[0078] The composition and heat treatment process of the aluminum-lithium alloy in this comparative example are basically the same as those in Example 1, except that a two-stage quenching method was not used during solution quenching; instead, only air cooling was applied at a rate of 0.5°C / s. The results show that the solution treatment effect of the casting is poor, resulting in a weakened subsequent age hardening effect. This is mainly because the cooling rate is too slow, and some rare earth precipitates have already formed in the matrix after quenching, leading to a weakened age hardening response.

[0079] Comparative Example 9

[0080] The composition and heat treatment process of the aluminum-lithium alloy in this comparative example are basically the same as those in Example 1, except that the surface shot peening treatment was not performed on the casting after solution treatment.

[0081] The aluminum-lithium alloy casting obtained above was immersed in a 3.5% wt. NaCl solution for 72 hours, and the corrosion rate was 1.1 × 10⁻⁶. -3 mm / y. The results show that the corrosion resistance of the alloy has decreased. The main reason is that the rare earth elements did not agglomerate on the surface of the casting due to the lack of shot peening. As a result, the thickness of the corrosion film layer formed on the surface of the alloy in the subsequent corrosive environment is reduced, which weakens the protection of the alloy matrix and thus reduces the corrosion resistance of the alloy.

[0082] Comparative Example 10

[0083] The composition and heat treatment process of the aluminum-lithium alloy in this comparative example are basically the same as those in Example 1. The only difference is that the casting is subjected to single-stage aging, and the temperature of the single-stage aging is 180°C, while the aging time remains unchanged.

[0084] The aluminum-lithium alloy casting obtained above was immersed in a 3.5% wt. NaCl solution for 72 hours, and the corrosion rate was 7.1 × 10⁻⁶. -4mm / y. The results show that the corrosion resistance of the alloy has decreased. The main reason is that under the single-stage aging process, a large number of continuous precipitates are deposited at the grain boundaries of the aluminum-lithium alloy, which reduces the intergranular corrosion resistance of the alloy, thus reducing the corrosion resistance of the alloy.

[0085] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A corrosion resistant cast aluminum-lithium alloy characterized by, The components of the alloy and their weight percentages are as follows: Copper Cu: 1.0~4.0%, Lithium Li: 1.0~4.0%, Rare Earth Elements RE: 0.5~3.0%, Scandium Sc: 0.1~0.5%, Zirconium Zr: 0.1~0.5%, Titanium 0.05~0.3%, with the balance being aluminum Al; The rare earth elements include one or more of gadolinium (Gd), yttrium (Y), neodymium (Nd), cerium (Ce), and lanthanum (La); The casting method for the corrosion-resistant aluminum-lithium alloy includes the following steps: S1: Raw materials are prepared according to the chemical element composition ratio of corrosion-resistant cast aluminum-lithium alloy, and then smelted and cast to obtain castings; S2: Perform solution treatment on the casting obtained in step S1; S3: Perform surface shot peening on the casting obtained in step S2; S4: The casting obtained in step S3 is subjected to aging treatment and then machined to obtain a corrosion-resistant aluminum-lithium alloy casting. In step S2, the solution treatment is a two-stage solution treatment. The first-stage solution temperature is 400~460℃ and the solution time is 10~40h. The second-stage solution temperature is 460~540℃ and the solution time is 10~40h. In step S2, the quenching cooling method of the solution treatment is a two-stage process. The temperature range of the first stage cooling is from the solution heating temperature of 460~540℃ to 250~300℃, and the temperature range of the second stage cooling is from the termination temperature of the first stage cooling to room temperature. The cooling rate of the first stage cooling is 0.1~20℃ / s, and the cooling rate of the second stage cooling is 20~200℃ / s. In step S4, the aging process is as follows: the first aging temperature is 150~180℃ and the aging time is 10~30h; the second aging temperature is 180~250℃ and the aging time is 0.5~5h; and the third aging temperature is 150~180℃ and the aging time is 10~30h.

2. The corrosion-resistant cast aluminum-lithium alloy according to claim 1, characterized in that, Both stages of cooling are performed under vibration conditions, with a vibration frequency of 10~1000Hz, an amplitude of 0.1~1mm, and a peak vibration acceleration of 1~4g.

3. The corrosion-resistant cast aluminum-lithium alloy according to claim 1, characterized in that, In step S3, the depth of the residual compressive stress layer in the surface shot peening strengthening treatment is 0.1~1mm, and the shot peening coverage is greater than 80%.

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