A new as-cast aluminum alloy and a preparation method thereof

Abstract

This invention provides a novel as-cast aluminum alloy and its preparation method, belonging to the technical field of aluminum-based high-temperature materials. The method uses Al, Nb, and W metal blocks with a purity of 99.95% as raw materials, and designs the composition based on an Al-Nb-W ternary system, comprising Al 49–88 at.%, Nb 3–44 at.%, and W 2–14 at.% by atomic percentage, with the balance being unavoidable impurities. By selecting compositional combinations corresponding to different stable phase regions, two-phase structures (Al3Nb+AlNb2), three-phase structures (Al3Nb+AlNb2+Al4W), or three-phase structures (Al3Nb+AlNb2+bcc(Nb,W)) are formed under as-cast conditions. During the preparation process, vacuum arc melting is performed under argon protection, followed by 10–15 ingot-turning melting cycles, and cooling in a water-cooled copper crucible to obtain the as-cast alloy ingot. Characterization analysis confirms the phase regions corresponding to different compositions, and the Al, Nb, and W contents are optimized accordingly to achieve a stable intermetallic compound multiphase structure in the as-cast state. The as-cast structure of this invention exhibits good thermal stability under high-temperature conditions, making it suitable for applications such as high-temperature wear-resistant parts, corrosion-resistant parts, and coating substrates.

Description

Technical Field

[0001] This invention belongs to the field of aluminum-based high-temperature materials technology, specifically relating to a novel as-cast aluminum alloy and its preparation method. This aluminum alloy is designed based on the stable phase region of the Al-Nb-W ternary system, and can form a stable microstructure composed of Al3Nb, AlNb2, Al4W, and bcc(Nb,W) phases under as-cast conditions. It can be used as a final product without solution treatment or aging treatment, and is suitable for high-temperature wear-resistant parts, corrosion-resistant parts, heat-resistant structural parts, and coating substrates. Background Technology

[0002] Currently, the most widely used aluminum alloys in engineering applications mainly rely on solid solution strengthening and precipitation strengthening mechanisms to obtain excellent properties, such as Al-Cu, Al-Mg, Al-Zn, and Al-Si aluminum alloys. However, the strengthening phases in these aluminum alloys are prone to coarsening, aggregation, or even dissolution at high temperatures, leading to a significant decrease in material strength and microstructure stability, making it difficult to meet the requirements for long-term high-temperature service.

[0003] To improve the high-temperature performance of aluminum alloys, researchers have attempted to introduce refractory elements such as Nb, Ti, Zr, and W to enhance the thermal stability of the materials by forming high-melting-point intermetallic compounds. Among them, intermetallic compounds such as Al3Nb, AlNb2, and Al4W have high melting points and excellent high-temperature stability, and are considered important reinforcing phases for constructing high-temperature stable aluminum-based materials.

[0004] Existing research mostly focuses on Al-Nb binary systems or Al-W binary systems, with limited studies on the systematic utilization of the stable phase region of the Al-Nb-W ternary system. Furthermore, existing high-performance aluminum alloys typically require complex solution treatment and aging treatment to obtain the target microstructure, resulting in complex preparation processes and high energy consumption.

[0005] Therefore, it is necessary to develop a new type of aluminum alloy that can directly obtain a stable and strengthened microstructure under as-cast conditions, in order to simplify the preparation process and improve the high-temperature microstructure stability of the material. Summary of the Invention

[0006] The purpose of this invention is to provide a novel cast aluminum alloy and its preparation method. By designing the composition of the stable phase region of the Al-Nb-W ternary system, the alloy can directly form a stable intermetallic compound structure under as-cast conditions, which can meet the application requirements without subsequent heat treatment.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A novel cast aluminum alloy, by atomic percentage, comprises: Al 49–88 at.%; Nb 3–44 at.%; W 2–14 at.%; the balance being unavoidable impurities.

[0009] The as-cast aluminum alloy is designed based on the stable phase region of the Al-Nb-W ternary system, and its as-cast microstructure is one of the following: (1) Two-phase structure of Al3Nb+AlNb2; (2) Al3Nb+AlNb2+Al4W three-phase structure; (3) Al3Nb+AlNb2+bcc(Nb,W) three-phase structure.

[0010] Furthermore, when the alloy composition by atomic percentage is: Al 49~56 at.%; Nb 42~44 at.%; W 2~3 at.%; with the balance being unavoidable impurities, the as-cast structure is an Al3Nb+AlNb2 two-phase structure.

[0011] Furthermore, when the alloy composition by atomic percentage is: Al 85~88 at.%; Nb 3~5 at.%; W 6~7 at.%; with the balance being unavoidable impurities, the as-cast structure is a three-phase structure of Al3Nb+AlNb2+Al4W.

[0012] Furthermore, when the alloy composition by atomic percentage is: Al 52~55 at.%; Nb 30~33 at.%; W 12~14 at.%; with the balance being unavoidable impurities, the as-cast structure is an Al3Nb+AlNb2+bcc(Nb,W) three-phase structure.

[0013] The present invention also provides a method for preparing the above-mentioned cast aluminum alloy, comprising the following steps:

[0014] S1. Weigh Al, Nb, and W metal raw materials with a purity of not less than 99.95% according to the target alloy composition;

[0015] S2. Place the ingredients in a vacuum arc melting furnace and melt them under an argon protective atmosphere. The melting current is 120-200 A and the melting time for each melting is 30-60 s.

[0016] S3. The alloy ingot obtained from smelting is remelted 10 to 15 times to improve the uniformity of alloy composition;

[0017] S4. After melting, the aluminum alloy ingot is cooled to room temperature by water cooling to obtain the cast aluminum alloy ingot;

[0018] S5. The resulting alloy is not subjected to solution treatment or aging treatment, and the as-cast structure is directly retained as the final use state.

[0019] Furthermore, the protective atmosphere described in step S2 is high-purity argon gas with a purity of not less than 99.99%.

[0020] Furthermore, the as-cast microstructure obtained in step S4 corresponds to the stable phase region of the Al-Nb-W ternary system.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The present invention is based on the composition design of the stable phase region of the Al-Nb-W ternary system, which can directly form a stable and strengthened structure under as-cast conditions without the need for complex heat treatment.

[0023] (2) The Al3Nb, AlNb2, Al4W and bcc(Nb,W) formed are all high melting point stable phases, which are not easy to dissolve or coarsen under high temperature environment and have excellent structural stability.

[0024] (3) By adjusting the content of Al, Nb and W elements, different stable phase regions can be constructed, thereby obtaining different performance combinations.

[0025] (4) The preparation process is simple, and the microstructure can be constructed by vacuum arc melting, which helps to reduce manufacturing costs and energy consumption. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the specific embodiments of the present invention, the accompanying drawings used in the description of the specific embodiments will be briefly introduced below.

[0027] Figure 1 This is a flowchart of the process for preparing the novel cast aluminum alloy of this invention.

[0028] Figure 2 This is a scanning electron microscope (SEM) image of the microstructure of the as-cast alloy in Example 1.

[0029] Figure 3 This is a scanning electron microscope (SEM) image of the microstructure of the as-cast alloy in Example 2.

[0030] Figure 4 This is a scanning electron microscope (SEM) image of the microstructure of the as-cast alloy in Example 3. Detailed Implementation

[0031] The present invention will be further described below with reference to specific embodiments. It should be noted that the embodiments described in this invention are merely preferred embodiments and are not intended to limit the invention. Various modifications and variations can be made to this invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Example 1

[0032] Alloy 1 contains the following composition by atomic percentage: Al 49-56%, Nb 42-44%, W 2-3%, where the combination of Al 49-56%, Nb 42-44%, and W 2-3% corresponds to the two-phase region dominated by Al3Nb+AlNb2 in the Al–Nb–W ternary phase diagram.

[0033] The preparation method of the above alloy includes the following steps:

[0034] (1) Weigh out pure metal blocks of Al, Nb, and W with a purity of 99.95% according to the above component ratio;

[0035] (2) Place the above-mentioned elemental metals in a vacuum arc melting furnace and melt them for 30-60 s under a current of 120-200 A and an argon protective atmosphere, and then cool and solidify them.

[0036] (3) In order to ensure the uniformity of alloy composition, the obtained alloy is repeatedly smelted and turned into ingots 10-15 times to obtain cast aluminum alloy ingots;

[0037] (4) The alloy ingots are not subjected to subsequent heat treatments such as solution treatment and aging, and the as-cast structure is retained as the final use state.

[0038] Microstructural characterization by SEM observation revealed that Al3Nb is dispersed in blocky or short rod-shaped forms, while AlNb2 is distributed in blocky or skeletal forms, forming a continuous or semi-continuous hard skeleton. The microstructure is a typical cast microstructure, and the grain size and phase size depend on the cooling conditions. Example 2

[0039] Alloy 2 contains the following components by atomic percentage: Al 85-88%, Nb 3-5%, W 6-7%, which corresponds to the three-phase structure of Al3Nb+AlNb2+Al4W in the Al–Nb–W ternary phase diagram.

[0040] The smelting process of Alloy 2 is the same as that of Example 1.

[0041] SEM observations revealed that Al4W is mostly distributed at grain boundaries or triple points, coexisting with Al3Nb and AlNb2 phases.

[0042] Alloy 3 contains the following components by atomic percentage: Al 52-55%, Nb 30-33%, W 12-14%, which corresponds to the three-phase structure of Al3Nb+AlNb2+bcc(Nb,W) in the Al–Nb–W ternary phase diagram. Example 3

[0043] The smelting process of alloy 3 is the same as that of Example 1.

[0044] In addition to the compound phase, a bright white continuous phase with a network distribution was observed under SEM. EDS scanning showed that the Nb+W content in this phase exceeded 70 at.%, classifying it as a bcc solid solution phase rich in refractory elements. The presence of this metallic solid solution phase provides some plastic support for the as-cast hard and brittle compound framework, which helps to improve the overall impact resistance of the material.

[0045] As demonstrated by the above embodiments, the present invention, through compositional design, can directly obtain the desired stable and strengthening phase combination in the as-cast state through natural elemental segregation and thermodynamic equilibrium, and has extremely high industrial application value.

[0046] In summary, through in-depth research on the thermodynamic stability of each phase region of the Al–Nb–W ternary system, this invention successfully proposes a novel aluminum alloy design scheme that utilizes the as-cast microstructure for direct service.

[0047] In this invention, the traditional concept of "aluminum alloy" is further expanded. By significantly increasing the content of refractory elements such as Nb and W, the service performance of the alloy is no longer limited by the low-melting-point fcc(Al) matrix, but depends on the high-melting-point, highly stable intermetallic compound phase. This design approach has the following profound technical advantages in practical applications:

[0048] (1) Improved thermodynamic stability: By limiting the alloy composition to Al3Nb+AlNb2 and related three-phase stable regions in the Al–Nb–W ternary phase diagram, the as-cast structure is close to the equilibrium state at the end of solidification. Each strengthening phase is a thermodynamically stable intermetallic compound phase, which reduces the driving force of phase dissolution and coarsening during high-temperature service, thereby improving the stability of the structure.

[0049] (2) Change in load-bearing mode (hard skeleton load-bearing): By increasing the Nb and W content, Al3Nb and AlNb2 form a continuous or semi-continuous skeleton network structure in the cast state. The external load is preferentially borne by the high hardness skeleton phase rather than by the fcc-Al matrix, thus maintaining high stiffness and structural integrity at temperatures close to the melting point of aluminum.

[0050] (3) Excellent composition tolerance: Since the present invention focuses on constructing a cast stable phase region, the three-phase or two-phase region in the phase diagram usually has a certain composition width. This means that in large-scale industrial production, small composition fluctuations will not lead to drastic changes in the types of phases, thereby ensuring the consistency of material performance in batch production and greatly reducing the difficulty of production control.

[0051] (4) Strong process applicability: Since the key to this invention is that the composition falls into the stable phase region rather than relying on a specific cooling path, in addition to conventional arc melting and casting, the same composition range can be directly applied to various preparation processes such as laser additive manufacturing, SPS sintering, and surface welding, and can spontaneously form the expected multiphase structure after cooling.

[0052] (5) Simplified process and reduced energy consumption: The alloy of the present invention directly obtains the target strengthening phase combination in the casting state, without the need for the high temperature solid solution and long-term aging heat treatment process commonly found in traditional aluminum alloys. Under the same production conditions, the use time and energy consumption of heat treatment furnace can be significantly reduced, production costs can be reduced and carbon emissions can be reduced.

[0053] This invention, through precise proportioning of the Al–Nb–W ternary components, directly obtains a stable and strengthened system composed of Al3Nb, AlNb2, Al4W, and bcc(Nb,W) in the as-cast microstructure without the need for subsequent heat treatment. This design method not only simplifies the preparation process but also endows aluminum-based materials with unprecedented high-temperature microstructural stability and adjustable hardness gradient. The technical solution provided by this invention lays a solid experimental and theoretical foundation for the development of a new generation of high-performance, low-energy-consumption high-temperature aluminum-based structural materials.

[0054] Those skilled in the art will understand that, without departing from the spirit of the present invention, the contents of Al, Nb, and W can be appropriately adjusted within the above-mentioned composition range to obtain different phase ratios and performance combinations; the grain size and phase size can be adjusted according to the type of casting and cooling conditions, and these modifications and substitutions should all fall within the protection scope of the present invention.

Claims

1. A novel cast aluminum alloy, characterized in that, The composition, by atomic percentage, includes: Al 49~88 at.%; Nb 3~44 at.%; W 2~14 at.%; the balance being unavoidable impurities; the cast aluminum alloy is selected from the above composition range based on the calculated Al–Nb–W ternary system liquid phase projection diagram, and the cast structure is one of the following structures: (1) Al3Nb+AlNb2 two-phase structure; (2) Al3Nb+AlNb2+Al4W three-phase structure; (3) Al3Nb+AlNb2+bcc(Nb,W) three-phase structure; and the cast aluminum alloy is not subjected to solution treatment and aging treatment.

2. The novel cast aluminum alloy according to claim 1, characterized in that, The as-cast aluminum alloy comprises, by atomic percentage: Al 49–56 at.%; Nb 42–44 at.%; W 2–3 at.%; and the as-cast microstructure is a two-phase structure of Al3Nb+AlNb2.

3. The novel cast aluminum alloy according to claim 1, characterized in that, The as-cast aluminum alloy comprises, by atomic percentage: Al 85–88 at.%; Nb 3–5 at.%; W 6–7 at.%; and the as-cast microstructure is a three-phase structure of Al3Nb+AlNb2+Al4W.

4. The novel cast aluminum alloy according to claim 1, characterized in that, The cast aluminum alloy comprises, by atomic percentage: Al 52–55 at.%; Nb 30–33 at.%; W 12–14 at.%; The as-cast microstructure is a three-phase structure of Al3Nb+AlNb2+bcc(Nb,W).

5. A method for preparing a novel cast aluminum alloy as described in any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Weigh out pure metal raw materials of Al, Nb and W with a purity of not less than 99.95% according to the target composition ratio; S2. Place the raw materials in a vacuum arc melting furnace and melt them under an argon protective atmosphere. The melting current is 120-200A and the melting time for each melting is 30-60 seconds. S3. The obtained alloy ingot is remelted 10-15 times to improve the composition uniformity and obtain an aluminum alloy ingot with uniform composition. S4. Water cooling is used to cool the material to room temperature, thus obtaining cast aluminum alloy ingots; S5. The resulting as-cast aluminum alloy is not subjected to solution treatment or aging treatment, and the as-cast structure is directly retained as the final use state.

6. The preparation method according to claim 5, characterized in that, In step S2, the smelting current is 120-200 A.

7. The preparation method according to claim 5, characterized in that, The single melting time in step S2 is 30-60 s.

8. The preparation method according to claim 5, characterized in that, The protective atmosphere described in step S2 is high-purity argon gas with a purity of not less than 99.99%.

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