Aluminum alloy wire for high-temperature-difference creep-deformation-resistant cable and preparation method of aluminum alloy wire

Abstract

The invention discloses an aluminum alloy wire for a high-temperature-difference creep-deformation-resistant cable and a preparation method thereof.The aluminum alloy wire for the high-temperature-difference creep-deformation-resistant cable is prepared by smelting industrial pure aluminum with the purity larger than or equal to 99.7% or an aluminum ingot for remelting as a main raw material, and the aluminum alloy wire comprises, by mass, 0.35%-0.90% of Fe, 0.001%-0.01% of B, 0.01%-0.03% of Ti, 0.01%-0.03% of Al, 0.01%-0.05% of Ti, 0.01%-0.05% of Ti, 0.01%-0.05% of Ti, and the balance Al and inevitable impurities. The aluminum alloy comprises the following components in percentage by weight: 0.05 to 0.15 percent of Cu, 0.05 to 0.30 percent of Ce, 0.005 to 0.015 percent of Y, 0.001 to 0.012 percent of C, less than or equal to 0.005 percent of total content of V and Cr, and the balance of AL and inevitable impurities. On the basis of 99.70% of aluminum raw materials, the electric conductivity is larger than or equal to 62% IACS, the tensile strength is larger than or equal to 98 MPa, and the elongation is larger than or equal to 20%. And in a creep test at 100 DEG C for 1000 hours, the elongation is smaller than or equal to 0.05%, and the creep resistance is improved by 50% or above compared with that of a conventional rare earth aluminum alloy.

Description

Technical Field

[0001] This invention relates to an aluminum alloy wire for high-temperature differential creep-resistant cables and its preparation method. Background Technology

[0002] With the rapid development of ultra-high voltage power grids, the transmission of new energy from bases, and power construction in extreme environments, the operating environment of power cables is becoming increasingly complex. In deserts, plateaus, and coastal areas, cable conductors are subjected to significant diurnal or seasonal temperature fluctuations (e.g., -40℃ to +80℃) year-round. Under such alternating high-temperature stress, traditional aluminum or ordinary aluminum alloy conductors are prone to continuous plastic deformation, i.e., creep. Creep can lead to loosening of cable joints, increased contact resistance, localized overheating, increased power loss, and even safety accidents, seriously threatening the long-term operational reliability and safety of the power grid.

[0003] Currently, improving cable conductor performance mainly revolves around two directions: one is to use high-purity aluminum (such as above 99.85%) to ensure high conductivity (>62% IACS), but this is costly and the tensile strength and creep resistance of the material are limited; the other is to strengthen it by adding alloying elements (such as iron, copper, rare earth elements, etc.), but this usually sacrifices conductivity. While some existing rare earth aluminum alloy cables have improved in strength and heat resistance, their creep resistance, especially their long-term stability under high temperature differential cycling conditions, still cannot meet increasingly stringent engineering requirements. Summary of the Invention

[0004] The purpose of this invention is to provide an aluminum alloy wire for high-temperature differential creep-resistant cables and its preparation method, so as to solve the technical problems mentioned in the background art.

[0005] The technical solution to achieve the purpose of this invention is: an aluminum alloy wire for high temperature difference anti-creep deformation cable, which is smelted and formulated using industrial pure aluminum or remelted aluminum ingots with a purity ≥99.7% as the main raw material; the chemical composition of the aluminum alloy wire by mass fraction is: Fe: 0.35%-0.90%, B: 0.001%-0.01%, Ti: 0.01%-0.03%, Cu: 0.05%-0.15%, Ce: 0.05%-0.30%, Y: 0.005%-0.015%, C: 0.001%-0.012%, the total content of V and Cr ≤0.005%, and the balance being Al and unavoidable impurities.

[0006] A method for preparing aluminum alloy wire for high-temperature differential creep-resistant cables includes the following steps:

[0007] S1: Melt the remelted aluminum ingots, which account for 90% of the total weight of the raw materials, into liquid aluminum at 900-1000℃ and transfer them to a holding furnace;

[0008] S2: Add aluminum-iron master alloy, aluminum-copper master alloy, aluminum-cerium master alloy, aluminum-titanium master alloy, and aluminum-yttrium master alloy to the aluminum liquid in the holding furnace in sequence, and mix them evenly by electromagnetic stirring at 740-760℃ to form the initial alloy liquid;

[0009] S3: Add aluminum-boron master alloy to the initial alloy liquid and perform electromagnetic stirring at 740-760℃ to complete the boronizing treatment;

[0010] S4: Using high-purity nitrogen as a carrier, the sodium-free refining agent is sprayed onto the bottom of the alloy liquid treated in step S3, and the surface slag is removed and then covered with a covering agent.

[0011] S5: Heat the alloy liquid to the superheat temperature and hold it at that temperature, and then perform electromagnetic stirring and magnetization during the holding period;

[0012] S6: Add the remaining 10% of cold remelted aluminum ingots to the alloy liquid treated in step S5 to rapidly reduce the temperature of the alloy liquid to 720-740℃.

[0013] S7: Add aluminum-titanium-carbon-platinum refining agent and stir;

[0014] S8: Repeat the refining, slag removal, and covering operations of step S4;

[0015] S9: Let the alloy liquid stand at 720-740℃ for 30-45 minutes;

[0016] S10: The molten alloy is directed to the casting furnace and degassed and filtered online to control the hydrogen content to ≤0.13ml / 100g;

[0017] S11: The purified alloy liquid is passed through a crystallizer and cast into an aluminum alloy wire blank; the aluminum alloy wire blank is homogenized; the homogenized wire blank is hot-extruded into an aluminum alloy rod; the aluminum alloy rod is drawn into an aluminum alloy single wire.

[0018] S12: Anneal the aluminum alloy single wire.

[0019] Furthermore, in step S5, the temperature of the melt overheating treatment is strictly controlled at 900-920℃, and the temperature is held for 20-30 minutes.

[0020] Furthermore, in step S7, the aluminum-titanium-carbon-platinum refining agent contains 5% Ti by mass, 0.2% C by mass, and trace element Pt.

[0021] Furthermore, in step S10, the online degassing adopts a rotary jet degassing device, and the filtration adopts a two-stage 30ppi / 50ppi foam ceramic filter plate.

[0022] Furthermore, in step S11, the heating rate of the homogenization treatment is 80-100℃ / h, and after holding at 490-500℃ for 7-8 hours, it is furnace cooled to below 300℃ at a rate of no more than 50℃ / h before being removed from the furnace.

[0023] Furthermore, in step S12, the annealing temperature is 220-250℃, and the holding time is 2-6 hours.

[0024] Furthermore, the remelted aluminum ingot is a remelted aluminum ingot with an aluminum content of not less than 99.70%.

[0025] By adopting the above technical solution, the present invention has the following beneficial effects:

[0026] (1) Based on 99.70% aluminum raw materials, this invention successfully achieved conductivity ≥62% IACS, tensile strength ≥98MPa, elongation ≥20%, and elongation ≤0.05% in creep test at 100℃ / 1000h, with creep resistance performance improved by more than 50% compared to conventional rare earth aluminum alloys.

[0027] (2) In this invention, Fe and Cu provide basic strengthening through solid solution and the formation of fine precipitates. Ce and Y, as rare earth elements, play a key role in: 1) purifying the melt and removing harmful gases and impurities; 2) combining with elements such as B and C to form extremely stable nanoscale dispersed particles such as CeB6 and Y2C3 at high temperatures during melt overheating and subsequent cooling. These particles can effectively pin dislocations and hinder grain boundary sliding, which is the key to giving the alloy excellent creep resistance. Ti mainly plays the role of refining the as-cast grains. High conductivity is ensured by strictly controlling the total amount of elements such as V and Cr that seriously impair conductivity. The synergistic effect of each element within the above range achieves the optimal balance of strength, conductivity and heat creep resistance.

[0028] (3) This invention employs a step-by-step alloying process with a specific sequence: first, batching, boronizing, and high-temperature overheating are performed. This stage aims to ensure that rare earth elements (Ce, Y) and boron elements (B) are fully dissolved, homogenized, and pre-reacted. Subsequently, rapid cooling and temperature control are performed to a suitable casting range, and carbon-containing materials are added to this stable medium-high temperature melt. This sequential design effectively avoids the burning loss of carbon at extreme high temperatures in the early stage and unfavorable preferential reactions with certain elements. In the subsequent casting, solidification, and processing, the fully activated rare earth elements and the carbon elements added at the optimal temperature window can be efficiently combined to form a large number of dispersed nanoscale high-temperature stable strengthening phases (such as rare earth carbides), thereby obtaining excellent creep resistance.

[0029] (4) This invention uses 99.70% remelted aluminum ingots instead of aluminum with higher purity, which greatly reduces the cost of raw materials. At the same time, through precise alloy design and process control, it achieves performance far exceeding the expected purity of raw materials, and has extremely high market competitiveness. Attached Figure Description

[0030] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein...

[0031] Figure 1 This is a flowchart of the preparation method of the present invention. Detailed Implementation

[0032] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0034] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0035] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0036] In the description of the embodiments of the present invention, it should be understood that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use, or the orientation or positional relationship commonly understood by those skilled in the art. They are only used to facilitate the description of the present invention and to simplify the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0037] In the description of the embodiments of the present invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention based on the specific circumstances. The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and should not be used to limit the scope of protection of the present invention.

[0038] (Example)

[0039] See Figure 1 Aluminum alloy single wire with a diameter of 3.00 mm was prepared according to the alloy composition ratio shown in Table 1. Specific process parameters are as follows:

[0040] Raw materials: 99.70% remelted aluminum ingots. All intermediate alloys are commercially available standard products.

[0041] S1-S2: Melt 90% of the aluminum ingots in a 980℃ melting furnace, then transfer to a 750℃ holding furnace. Add the master alloys AlFe10, AlCu50, AlCe10, AlTi10, and AlY10, corresponding to the compositions in Table 1, in sequence. Stir electromagnetically (15Hz) for 15 minutes.

[0042] S3: Add AlB3 master alloy and stir electromagnetically at 750℃ for 10 minutes.

[0043] S4: Use high-purity nitrogen to inject RJ-6 sodium-free refining agent, refining time is 15 minutes, cover after slag removal.

[0044] S5: Rapidly heat the melt to the specific "superheat temperature" listed in Table 1 and hold it at that temperature for the corresponding time. During the holding period, turn on the electromagnetic stirrer (10Hz) and the external magnetic field device (magnetic field strength 0.3T).

[0045] S6: Add the remaining 10% of cold aluminum ingots (room temperature) to reduce the melt temperature to 730°C within 5 minutes.

[0046] S7: Add 0.2% (by weight of total weight of aluminum melt) of an aluminum-titanium-carbon-platinum (Al-Ti-C-Pt) master alloy refiner for modification treatment. The mass fractions of each component in this refiner are: Ti 5%, C 0.2%, Pt 0.05%-0.15%, with the balance being Al and unavoidable impurities. Stir manually for 5 minutes. The use of this aluminum-titanium-carbon-platinum modified refiner aims to solve the problem of diminished refining effect or interference with strengthening phases caused by conventional aluminum-titanium-boron or aluminum-titanium-carbon refiners in the Ce and Y alloy melts of this invention, thereby obtaining a fine and stable microstructure that remains at high temperatures.

[0047] S8: Perform the same refining, scraping, and covering operations as in S4.

[0048] S9: Let stand at 730℃ for 40 minutes.

[0049] S10: It is transferred to the casting front chamber through the diversion channel and is treated online using SNIF rotary jet degassing (argon) and two-stage foam ceramic filter plates (30ppi / 50ppi). The hydrogen content is controlled at 0.10-0.12ml / 100g.

[0050] S11: Horizontal continuous casting, with a crystallizer cooling water pressure of 0.3 MPa and a casting speed of 2.0 m / min, yielding a Φ15 mm wire rod. The wire rod is heated to 495 °C in an electric resistance furnace at a rate of 90 °C / h, held for 7 hours, and then furnace cooled to 250 °C at a rate of 40 °C / h followed by air cooling. The wire rod is then hot-extruded into a Φ9.5 mm rod at 450 °C using an extruder. The rod is then cold-drawn to a Φ3.00 mm single wire through multiple drawing dies.

[0051] S12: Place the single wire coil into an air-circulating annealing furnace and hold it at 240°C for 4 hours, then cool it with the furnace.

[0052] Comparative Example 1: A conventional high-cerium aluminum alloy composition was used, without B, Y, or C elements. Its preparation process omitted the S3 boronizing treatment, and the S5 overheating treatment temperature was only 800℃. The remaining steps were basically the same as in Example 2.

[0053] Comparative Example 2: The same components as in Example 2 were used, but the S5 overheating treatment step was completely eliminated in the preparation process. That is, after refining in S4, temperature control in S6 was carried out directly. The remaining steps were exactly the same as in Example 2.

[0054] Table 1: Alloy composition (wt%, balance Al) and key process parameters of the examples and comparative examples

[0055]

[0056] Performance Tests and Results

[0057] The prepared aluminum alloy single wire was subjected to the following tests, and the results are listed in Table 2.

[0058] 1. Conductivity: Tested according to GB / T 3048.2-2007 "Test Methods for Electrical Properties of Wires and Cables".

[0059] 2. Mechanical properties: Tensile strength and elongation at break were tested according to GB / T 4909.3-2009 "Test Methods for Bare Wires".

[0060] 3. Creep Resistance (Core Indicator): Referring to GB / T 39552-2020 "Creep Test Method for Aluminum Alloy Conductors", specimens of a specified length are cut and subjected to a constant tensile stress equivalent to 50% of the room temperature yield strength (σ0.2) at a constant temperature of (100±2)℃ for 1000 hours. The permanent creep elongation (%) of the specimen is then measured. The smaller this value, the better the creep resistance.

[0061] Table 2: Comparison of performance test results between the examples and the comparative examples

[0062]

[0063] Results Analysis: As shown in Table 2, the aluminum alloy single wires prepared in Examples 1-4 of this invention all meet and exceed the preset technical indicators (≥62% IACS, ≥98MPa, ≥20%) in terms of conductivity, tensile strength, and elongation. Most importantly, their creep resistance (creep elongation 0.035%-0.048%) is significantly better than that of the comparative examples.

[0064] Comparative Example 1 (different composition): Although the strength is acceptable, due to the lack of synergistic microalloying effect of B, Y and C elements and insufficient overheating temperature, it failed to form a sufficient high-temperature stable strengthening phase, resulting in the worst creep resistance (0.095%), which is about 150% worse than Example 2.

[0065] Comparative Example 2 (different process): Its composition is exactly the same as that of Example 2, but because the "overheating treatment at 900-920°C" step was omitted, its creep resistance (0.081%) is significantly worse than that of Example 2 (0.038%), with a decrease of more than 110%.

[0066] In summary, this invention, through the synergistic coupling of a specific chemical composition range and a special preparation process including melt overheating, has successfully developed an aluminum alloy wire for high-creep-resistant cables with excellent overall performance, particularly suitable for harsh environments with high temperature differences. This invention effectively solves the technical challenges of simultaneously achieving high conductivity and high creep resistance, as well as the contradiction between high performance and low cost.

[0067] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An aluminum alloy wire for a high-temperature differential creep-resistant cable, characterized in that: The aluminum alloy wire is prepared by smelting and mixing industrial pure aluminum or aluminum ingots for remelting with a purity of ≥99.7% as the main raw material. The chemical composition of the aluminum alloy wire, by mass fraction, is as follows: Fe: 0.35%-0.90%, B: 0.001%-0.01%, Ti: 0.01%-0.03%, Cu: 0.05%-0.15%, Ce: 0.05%-0.30%, Y: 0.005%-0.015%, C: 0.001%-0.012%, the total content of V and Cr ≤0.005%, and the balance is Al and unavoidable impurities.

2. A method for preparing an aluminum alloy wire for a high-temperature differential creep-resistant cable, characterized in that, The method for preparing the aluminum alloy wire for the high-temperature differential creep-resistant cable as described in claim 1 includes the following steps: S1: Melt the remelted aluminum ingots, which account for 90% of the total weight of the raw materials, into liquid aluminum at 900-1000℃ and transfer them to a holding furnace; S2: Add aluminum-iron master alloy, aluminum-copper master alloy, aluminum-cerium master alloy, aluminum-titanium master alloy, and aluminum-yttrium master alloy to the aluminum liquid in the holding furnace in sequence, and mix them evenly by electromagnetic stirring at 740-760℃ to form the initial alloy liquid; S3: Add aluminum-boron master alloy to the initial alloy liquid and perform electromagnetic stirring at 740-760℃ to complete the boronizing treatment; S4: Using high-purity nitrogen as a carrier, the sodium-free refining agent is sprayed onto the bottom of the alloy liquid treated in step S3, and the surface slag is removed and then covered with a covering agent. S5: Heat the alloy liquid to the superheat temperature and hold it at that temperature, and then perform electromagnetic stirring and magnetization during the holding period; S6: Add the remaining 10% of cold remelted aluminum ingots to the alloy liquid treated in step S5 to rapidly reduce the temperature of the alloy liquid to 720-740℃. S7: Add aluminum-titanium-carbon-platinum refining agent and stir; S8: Repeat the refining, slag removal, and covering operations of step S4; S9: Let the alloy liquid stand at 720-740℃ for 30-45 minutes; S10: The molten alloy is directed to the casting furnace and degassed and filtered online to control the hydrogen content to ≤0.13ml / 100g; S11: The purified alloy liquid is passed through a crystallizer and cast into an aluminum alloy wire blank; the aluminum alloy wire blank is homogenized; the homogenized wire blank is hot-extruded into an aluminum alloy rod; the aluminum alloy rod is drawn into an aluminum alloy single wire. S12: Anneal the aluminum alloy single wire.

3. The method for preparing an aluminum alloy wire for a high-temperature differential creep-resistant cable according to claim 2, characterized in that: In step S5, the temperature of the melt overheating treatment is 900-920℃, and the holding time is 20-30 minutes.

4. The method for preparing an aluminum alloy wire for a high-temperature differential creep-resistant cable according to claim 2, characterized in that: In step S7, the aluminum-titanium-carbon-platinum refining agent contains 5% Ti by mass, 0.2% C by mass, and trace element Pt.

5. The method for preparing an aluminum alloy wire for a high-temperature differential creep-resistant cable according to claim 2, characterized in that: In step S10, the online degassing uses a rotary jet degassing device, and the filtration uses a two-stage 30ppi / 50ppi foam ceramic filter plate.

6. The method for preparing an aluminum alloy wire for a high-temperature differential creep-resistant cable according to claim 2, characterized in that: In step S11, the heating rate of the homogenization treatment is 80-100℃ / h, and after holding at 490-500℃ for 7-8 hours, it is furnace cooled to below 300℃ at a rate of no more than 50℃ / h before being removed from the furnace.

7. The method for preparing an aluminum alloy wire for a high-temperature differential creep-resistant cable according to claim 2, characterized in that: In step S12, the annealing temperature is 220-250℃, and the holding time is 2-6 hours.

8. The method for preparing an aluminum alloy wire for a high-temperature differential creep-resistant cable according to claim 2, characterized in that: The remelted aluminum ingots used are remelted aluminum ingots with an aluminum content of not less than 99.70%.

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