An aviation aluminum rod with good ductility and low impurity content and a preparation method thereof

Abstract

This invention discloses an aerospace aluminum rod with good ductility and low impurity content, and its preparation method, belonging to the field of metal material processing technology. The aerospace aluminum rod has an aluminum content ≥99.5%, an iron content of 0.20%-0.25%, a silicon content ≤0.04%, and a hydrogen content ≤0.22 ml / 100g Al. By precisely controlling the Fe content within the preferred range of 0.20%-0.25%, combined with multi-stage refining and purification, precise temperature-controlled casting, and surface quality control, this invention significantly reduces the impurity content of the aluminum rod, refines the grain structure, and improves its machinability and ductility. It achieves excellent processing performance, producing 200,000 meters of continuous 0.361mm ultrafine single wire without breakage, making it suitable for the large-scale production of high-end aluminum alloy wire bundles in photovoltaic, new energy vehicle, and other fields.

Description

Technical Field

[0001] This invention relates to the field of metal material processing technology, and in particular to an aerospace aluminum rod with good ductility and low impurity content, and its preparation method. Background Technology

[0002] With the advancement of the global goal of "carbon neutrality," the photovoltaic power generation and new energy vehicle industries are experiencing explosive growth. The demand for lightweight and high-conductivity photovoltaic cables and new energy vehicle charging pile cables is becoming increasingly urgent, and replacing copper with aluminum has become an industry trend. It is predicted that by 2025, the demand for aluminum alloy wire harnesses in the photovoltaic sector alone will reach 8,000 tons per year, and the new energy vehicle sector also has a similar market demand. High-end aluminum alloy wire harnesses require single-wire diameters as fine as 0.3-0.6 mm, and must possess excellent conductivity (resistivity ≤28.172 nΩ·m), good mechanical properties (tensile strength 158.58-241.32 MPa, elongation ≥1%), and extremely high processing stability.

[0003] Aluminum rods, as the basic blanks for drawing aluminum alloy monofilaments, directly determine the subsequent processing performance and finished product performance of the monofilaments. Existing aluminum rod manufacturing technologies mainly suffer from the following technical defects: 1. Poor impurity control leads to poor machinability. The hydrogen content and non-metallic inclusions in molten aluminum are key factors affecting the machinability of aluminum rods. Traditional single-stage refining processes cannot completely remove gases and inclusions from molten aluminum, resulting in defects such as micropores and slag inclusions inside the aluminum rod. When drawing 0.361mm ultrafine monofilaments, these microscopic defects become stress concentration points, easily causing wire breakage and severely restricting production efficiency and yield. In existing technologies, the hydrogen content of aluminum rods is usually higher than 0.25ml / 100gAl, which is insufficient to meet the requirements for continuous drawing of ultrafine wires.

[0004] 2. Improper alloy element ratios make it difficult to achieve a balance between performance. Fe is a major impurity element in aluminum alloys, but an appropriate amount of Fe can improve the mechanical properties and heat resistance of aluminum alloys. When the Fe content is too low (<0.18%), the tensile strength of the aluminum rod is insufficient and its machinability is reduced; when the Fe content is too high (>0.28%), the precipitation of intermetallic compounds such as FeAl3 increases, severely impairing electrical conductivity (resistivity rises above the critical value). Current technology allows for a relatively wide control range of Fe content (0.10%-0.40%), without refined optimization for high-end wire harness applications, making it difficult to achieve a balance between electrical conductivity and machinability.

[0005] 3. The casting process is crude, resulting in coarse grain structure. Casting temperature is a core parameter affecting the grain size and internal quality of aluminum rods. In traditional processes, the casting temperature fluctuates significantly (680-730℃). When the temperature is below 690℃, the aluminum melt has poor fluidity, the cast billet crystallizes incompletely, and the grains are coarse and uneven, significantly reducing machinability. When the temperature is above 720℃, the aluminum melt absorbs hydrogen more intensely, easily producing defects such as hollows and porosity, and the wire breakage rate increases sharply during wire drawing. Existing technologies lack precise control of casting temperature and synergistic optimization of multi-stage cooling.

[0006] 4. Insufficient surface quality control leads to frequent processing defects. Defects such as indentations, peeling, and scratches on the aluminum rod surface are further amplified during subsequent wire drawing, resulting in decreased surface quality of the single filament, stress concentration, and premature breakage. Existing technologies lack sufficient precision in controlling key aspects such as mill coaxiality, roll pass shape, and lead tube alignment, making it difficult to guarantee the high-quality requirements of the aluminum rod surface.

[0007] In conclusion, developing a high-quality aluminum rod with good ductility and low impurity content, achieving precise optimization of Fe content, efficient removal of impurities, fine grain control, and improved surface quality, is of great significance for breaking through the technical bottlenecks in the preparation of high-end aluminum alloy wire bundles and realizing domestic substitution. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the existing technology and to propose an aviation aluminum rod with good ductility and low impurity content and its preparation method.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides an aviation aluminum rod with good ductility and low impurity content. By weight percentage, the aluminum content is ≥99.5%, the iron (Fe) content is 0.20%-0.25%, the silicon (Si) content is ≤0.04%, and the individual content of other impurity components affecting resistivity, such as Mn, Cr, Ti, and V, is ≤0.002%, and the total content is ≤0.01%.

[0010] The aluminum rod has a hydrogen content ≤0.22ml / 100g Al, a smooth surface, and is free from defects such as indentations, underfill, peeling, and scratches. After subsequent drawing and aging treatments, the tensile strength of the single filament is 158.58-241.32MPa, the elongation is ≥1%, and the resistivity (20℃) is ≤28.172nΩ·m.

[0011] This invention also proposes a method for preparing the aforementioned aerospace aluminum rod, comprising the following steps: Step 1: Raw material preparation and smelting Electrolytic primary aluminum liquid is selected as the raw material, and the aluminum content in the primary aluminum liquid is controlled to be ≥99.80%. The content of impurities that affect resistivity, such as Mn, Cr, and Ti, does not exceed 0.002%, and the Si content does not exceed 0.04%. A hydraulic tilting and lifting platform is used to smoothly pour the aluminum liquid into the furnace, and the lifting speed is controlled at 0.5-1.0 m / min to avoid oxidation and hydrogen absorption caused by the aluminum liquid churning.

[0012] Step Two: Alloying and Refining Aluminum-iron alloys and aluminum-boron alloys are added to the molten aluminum, controlling the Fe content between 0.20% and 0.25%. A 2+2 refining process is adopted: first, the original molten aluminum is refined twice, and samples are taken for analysis after settling; after adding alloying elements, permanent magnet stirring is used for forward and reverse stirring for 6-10 minutes each, with the stirring speed controlled at 200-300 r / min to ensure uniform distribution of alloying elements; then, the molten aluminum is refined twice more. During the refining process, the refining temperature is controlled at 740-750℃, and each refining time is 15-25 minutes. High-purity nitrogen (purity ≥99.999%, pressure 0.15-0.25MPa) is used for refining in a crisscross pattern to effectively remove hydrogen and inclusions from the molten aluminum.

[0013] Step 3: Online degassing and filtration A dual-rotor online degassing device is employed, controlling the nitrogen purity at the end of the degassing rotor to 99.999%, the pressure to 0.08-0.12 MPa, and the rotation speed to 30-100 r / min, creating negative pressure for hydrogen removal while preventing the molten aluminum from churning and absorbing hydrogen. A 50-mesh double-layer filter plate is used to filter the molten aluminum, further removing fine non-metallic inclusions.

[0014] Step 4: Casting A horizontal casting method is employed, utilizing a three-stage flow control system consisting of a runner end plug, a large ladle float, and a small ladle flow controller to ensure stable aluminum casting with level fluctuations controlled within ±2mm. The casting temperature is strictly controlled at 695-710℃, employing a four-stage cooling system (inner, outer, upper, and lower directions). Each cooling stage is equipped with an electronic flow meter and pressure gauge, controlling the cooling water flow rate at 5-20L / min and the pressure at 0.2-0.5MPa. Precise adjustment of the cooling water flow rate and temperature controls the entire process of aluminum molten metal formation, growth, phase formation, and final shaping, ensuring a uniform and fine grain structure in the cast billet with an average grain size ≤150μm.

[0015] Step 5: Continuous casting and rolling The cast billet is directly fed into the rolling mill for continuous rolling, with the infeed temperature controlled at 480-520℃ and the rolling speed at 3-5 tons / hour to ensure stable rolling process. Before rolling, check the installation position of the mill stand and base plate to ensure coaxiality deviation ≤0.05mm; inspect and replace worn rolls, adjust the roll pass shape to ensure no surface quality problems such as indentations, underfill, or peeling during aluminum rod rolling. Replace the guide tube and guide bearing to reduce exit resistance and prevent scratches on the aluminum rod surface.

[0016] Step Six: Reel in the line A rounded take-up frame is used for take-up, and the take-up tension is controlled at 50-100N to prevent damage or bending during the take-up process and ensure that the aluminum rod is neatly laid out.

[0017] Compared with the prior art, the present invention has the following advantages: 1. This invention constructs a "multi-stage purification" system through the combined application of a 2+2 refining process, dual-rotor online degassing, and double-layer filtration. This system exhibits extremely low impurity content, excellent processability, and enables continuous ultrafine filament drawing without filament breakage. The mechanism is explained as follows: The synergistic effect of the 2+2 refining process: The first two refining processes target primary inclusions and dissolved hydrogen in the molten aluminum. High-purity nitrogen is used in a "well" pattern refining process at 740-750℃, utilizing the principle of bubble flotation to allow hydrogen molecules to diffuse into nitrogen bubbles and float to the surface, while non-metallic inclusions are adsorbed on the bubble surface. After adding alloying elements, the second two refining processes target trace impurities introduced during alloying. Permanent magnet stirring promotes the uniform dissolution of alloying elements, avoiding secondary inclusions caused by excessively high local concentrations. The cumulative effect of the four refining processes increases the hydrogen removal efficiency from 60% in traditional single refining to over 90%.

[0018] Kinetic optimization of dual-rotor online degassing: The dual-rotor structure generates a strong shear flow field in the molten aluminum, breaking nitrogen bubbles into microbubbles (0.5-2 mm in diameter), significantly increasing the gas-liquid contact area. Controlling the nitrogen pressure to 0.1 MPa and purity to 99.999% creates a slightly negative pressure environment, promoting hydrogen diffusion and mass transfer from the molten aluminum to the bubbles. Compared to traditional single-rotor degassing, hydrogen removal efficiency is improved by 30%.

[0019] Physical interception of 50-mesh double-layer filtration: The 50-mesh filter plate (pore size approximately 300μm) can effectively intercept non-metallic inclusions larger than 300μm. The double-layer structure provides a longer filtration path and more interception sites. Inclusions such as Al2O3 and MgO in the molten aluminum are trapped by the filter plate, preventing them from becoming crack sources during the wire drawing process.

[0020] The microscopic mechanism by which impurity content affects machinability: During solidification, hydrogen in the aluminum rod is released as molecular hydrogen, forming micropores. During wire drawing, these micropores become stress concentration points, triggering microcrack propagation under applied tensile stress, leading to wire breakage. Non-metallic inclusions have low interfacial bonding strength with the aluminum matrix, easily causing interfacial debonding during plastic deformation, also inducing cracks. This invention controls the hydrogen content to below 0.22 ml / 100g Al, significantly lower than the 0.25-0.30 ml / 100g Al of traditional processes, fundamentally eliminating the negative impact of micropores and inclusions on machinability. Experiments show that aluminum rods prepared according to this invention can achieve continuous wire drawing of 0.361 mm ultrafine monofilaments for 200,000 meters without breakage, while traditional aluminum rods break within 50,000 meters.

[0021] 2. This invention achieves an optimal balance between electrical conductivity and mechanical properties by precisely controlling the Fe element content within the preferred range of 0.20%-0.25%. The mechanism is explained as follows: The dual role of Fe: Fe has extremely low solid solubility in aluminum (<0.01% at room temperature), mainly existing as intermetallic compounds such as FeAl3. When the Fe content is <0.18%, the precipitation of FeAl3 phase is small, resulting in insufficient grain refinement and strengthening, and low tensile strength of the aluminum rod. Simultaneously, excessively low Fe content leads to coarse grains in the aluminum rod, reducing its machinability. When the Fe content is >0.28%, the precipitation of FeAl3 phase increases significantly. These hard and brittle phases, distributed at grain boundaries and within grains, enhance the scattering of free electrons, leading to increased resistivity. This invention precisely controls the Fe content within a window of 0.20%-0.25%, ensuring sufficient FeAl3 phase to generate grain refinement and dispersion strengthening effects, achieving the designed tensile strength of the aluminum rod, while avoiding the damage to electrical conductivity caused by excessive FeAl3.

[0022] Strict limitations on Si content: Si has a high solid solubility in aluminum (approximately 0.05% at room temperature), and the scattering effect of solid-solution Si on electrons is extremely strong, resulting in a conductivity degradation approximately 3-5 times that of Fe. This invention controls the Si content to ≤0.04%, far lower than the 0.06-0.10% of traditional processes, effectively reducing the negative impact of solid solution strengthening on conductivity.

[0023] Grain refinement mechanism: During solidification, Fe element accumulates at the solid-liquid interface front, resulting in compositional supercooling, which promotes crystal nucleation and refines the grains. Simultaneously, the FeAl3 phase can act as a heterogeneous nucleation core, further refining the grains. The refined grains (average grain size ≤150μm) provide more grain boundaries. The hindering effect of grain boundaries on dislocation movement enhances the material's strength, while the finer grains result in more uniform plastic deformation and improved elongation.

[0024] 3. This invention achieves precise control of the casting process by accurately controlling the casting temperature at 695-710℃ and combining it with a 4-stage adjustable cooling system. This refines the grain structure and improves ductility. The mechanism is explained as follows: Narrow-Window Control of Casting Temperature: Casting temperature is a core parameter affecting the fluidity and solidification behavior of molten aluminum. When the temperature is below 690℃, the viscosity of molten aluminum increases, fluidity deteriorates, and the billet filling is incomplete, easily leading to defects such as cold shuts and incomplete filling. Simultaneously, increased supercooling leads to an increased nucleation rate, but excessively rapid grain growth easily forms coarse columnar crystals, reducing machinability. When the temperature is above 720℃, the hydrogen absorption rate of molten aluminum increases exponentially (the solubility of hydrogen in molten aluminum increases sharply with increasing temperature), and hydrogen precipitation during solidification forms pores. At the same time, high temperatures cause grain coarsening, reducing mechanical properties. This invention precisely controls the casting temperature within a narrow window of 695-710℃, ensuring good fluidity while controlling hydrogen solubility and grain size.

[0025] Synergistic Control of Four-Stage Cooling: Traditional cooling methods only control the total cooling water volume, making it difficult to precisely regulate the temperature field of the cast billet. This invention employs a cooling system with independent control in four directions: inner, outer, upper, and lower. The cooling water volume of each stage can be independently adjusted (5-20 L / min). By adjusting the cooling intensity of each stage, the temperature gradient of the cast billet from the surface to the center can be precisely controlled, achieving uniform solidification "from the surface inwards." Appropriately increasing the cooling intensity of the outer layer (15-20 L / min) can quickly form a fine-grained shell layer, while the moderate cooling intensity of the inner layer (10-15 L / min) ensures heat dissipation and avoids coarse grains in the central region. This gradient cooling strategy results in a fine and uniform equiaxed grain structure (average grain size ≤150 μm) for the entire cast billet, significantly improving the ductility and machinability of the aluminum rod.

[0026] 4. This invention eliminates surface defects in aluminum rods by precisely controlling key aspects such as mill coaxiality, roll pass shape, and outlet tube guidance. It achieves excellent surface quality control and reduces processing defects. The mechanism is explained below: Coaxiality control: Coaxiality deviation of the rolling mill stand can cause uneven radial force applied by the rolls to the aluminum rod, resulting in periodic indentations and stress concentrations on the rod surface. This invention controls the coaxiality deviation to within 0.05 mm, ensuring uniform stress and a smooth surface on the aluminum rod during rolling.

[0027] Roll pass optimization: Worn roll passes can lead to deviations in the cross-sectional shape of aluminum bars and a decrease in surface quality. This invention involves periodically replacing the 10-15 stand rolls and adjusting the pass dimensions to ensure rolling accuracy.

[0028] Improved guide system: Wear on the lead-out tube guide and bearings can cause longitudinal scratches on the aluminum rod surface, which can become sources of cracks during wire drawing. This invention replaces the guide and bearings, reducing lead-out resistance and preventing surface scratches.

[0029] The mechanism by which surface quality affects wire drawing performance: Surface defects can cause localized stress concentration during the wire drawing process, leading to uneven plastic deformation and surface quality defects such as "bamboo joint pattern" or "serrated pattern," which can even cause wire breakage in severe cases. The aluminum rods prepared by this invention have a smooth and defect-free surface, providing a high-quality blank base for subsequent wire drawing and effectively improving the wire drawing yield.

[0030] 5. This invention establishes clear parameters and operating procedures for everything from primary aluminum melt control and refining processes to casting temperature control and rolling surface quality control, forming a solidified process document. The process is stable and controllable, suitable for large-scale production. Stability analysis of three batches showed a resistivity coefficient of variation as low as 0.20% and a tensile strength coefficient of variation as low as 0.40%, far exceeding the industry requirement of 3%, demonstrating the high stability and consistency of the process and its suitability for large-scale industrial production. Detailed Implementation

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0032] To systematically verify the beneficial effects of the technical solution of this invention, a total of 15 sets of experiments were designed, including Examples 1-10 and Comparative Examples 1-5. In each experimental group, the effects of controlling key process parameters (Fe content, casting temperature, refining times, filtration method, cooling method, etc.) on the properties of aluminum rods (hydrogen content, grain size, tensile strength, elongation, resistivity) and subsequent machinability (maximum continuous length of 0.361 mm monofilament) were investigated.

[0033] Performance testing methods: Hydrogen content: determined according to GB / T 32185-2015 "Determination of hydrogen content in melts of aluminum and aluminum alloys by reduced pressure solidification method"; Grain size: determined according to GB / T 3246.1-2012 "Methods for testing the microstructure of wrought aluminum and aluminum alloy products - Part 1: Methods for testing the microstructure"; Tensile strength and elongation: determined according to GB / T 4909.3-2009 "Test methods for bare wires - Part 3: Tensile test"; Resistivity: Measured according to GB / T 4909.2-2009 "Test Methods for Bare Wires - Part 2: Measurement of DC Resistance", converted to 20℃; Machinability: Under the same drawing conditions (18 dies, average reduction rate of 15%), the maximum continuous drawing length of a 0.361mm monofilament (length when the filament breaks) was recorded.

[0034] Example 1 (Preferred Process): The manufacturing method of aviation aluminum rods includes the following steps: Step 1: Raw material preparation and smelting Electrolytic primary aluminum liquid is selected as the raw material, and the aluminum content in the primary aluminum liquid is controlled to be ≥99.80%. The content of impurities that affect resistivity, such as Mn, Cr, and Ti, does not exceed 0.002%, and the Si content does not exceed 0.04%. A hydraulic tilting and lifting platform is used to smoothly pour the aluminum liquid into the furnace, and the lifting speed is controlled at 0.5-1.0 m / min to avoid oxidation and hydrogen absorption caused by the aluminum liquid churning.

[0035] Step Two: Alloying and Refining Aluminum-iron alloys and aluminum-boron alloys are added to the molten aluminum, controlling the Fe content between 0.20% and 0.25%. A 2+2 refining process is adopted: first, the original molten aluminum is refined twice, and samples are taken for analysis after settling; after adding alloying elements, permanent magnet stirring is used for forward and reverse stirring for 6-10 minutes each, with the stirring speed controlled at 200-300 r / min to ensure uniform distribution of alloying elements; then, the molten aluminum is refined twice more. During the refining process, the refining temperature is controlled at 740-750℃, and each refining time is 15-25 minutes. High-purity nitrogen (purity ≥99.999%, pressure 0.15-0.25MPa) is used for refining in a crisscross pattern to effectively remove hydrogen and inclusions from the molten aluminum.

[0036] Step 3: Online degassing and filtration A dual-rotor online degassing device is employed, controlling the nitrogen purity at the end of the degassing rotor to 99.999%, the pressure to 0.08-0.12 MPa, and the rotation speed to 30-100 r / min, creating negative pressure for hydrogen removal while preventing the molten aluminum from churning and absorbing hydrogen. A 50-mesh double-layer filter plate is used to filter the molten aluminum, further removing fine non-metallic inclusions.

[0037] Step 4: Casting A horizontal casting method is employed, utilizing a three-stage flow control system consisting of a runner end plug, a large ladle float, and a small ladle flow controller to ensure stable aluminum casting with level fluctuations controlled within ±2mm. The casting temperature is strictly controlled at 695-710℃, employing a four-stage cooling system (inner, outer, upper, and lower directions). Each cooling stage is equipped with an electronic flow meter and pressure gauge, controlling the cooling water flow rate at 5-20L / min and the pressure at 0.2-0.5MPa. Precise adjustment of the cooling water flow rate and temperature controls the entire process of aluminum molten metal formation, growth, phase formation, and final shaping, ensuring a uniform and fine grain structure in the cast billet with an average grain size ≤150μm.

[0038] Step 5: Continuous casting and rolling The cast billet is directly fed into the rolling mill for continuous rolling, with the infeed temperature controlled at 480-520℃ and the rolling speed at 3-5 tons / hour to ensure stable rolling process. Before rolling, check the installation position of the mill stand and base plate to ensure coaxiality deviation ≤0.05mm; inspect and replace worn rolls, adjust the roll pass shape to ensure no surface quality problems such as indentations, underfill, or peeling during aluminum rod rolling. Replace the guide tube and guide bearing to reduce exit resistance and prevent scratches on the aluminum rod surface.

[0039] Step Six: Reel in the line A rounded take-up frame is used for take-up, and the take-up tension is controlled at 50-100N to prevent damage or bending during the take-up process and ensure that the aluminum rod is neatly laid out.

[0040] Parameter limitations: Fe content: 0.22%; Casting temperature: 702℃; Refining method: 2+2 refining (4 times); Filtration method: Double-layer 50-mesh filtration; Cooling method: 4-stage adjustable cooling (external: 18L / min, internal: 12L / min); Coaxiality: 0.04mm.

[0041] Example 2 (Lower limit of Fe content): Parameter limitation: Fe content: 0.20%, the rest is the same as in Example 1.

[0042] Example 3 (maximum Fe content): Fe content: 0.25%, the rest is the same as in Example 1.

[0043] Example 4 (lower limit of casting temperature): Casting temperature: 695℃, the rest is the same as in Example 1.

[0044] Example 5 (Upper limit of casting temperature): Casting temperature: 710℃, the rest is the same as in Example 1.

[0045] Example 6 (reduced refining times): Refining method: 2+1 refining (3 times), the rest is the same as Example 1.

[0046] Example 7 (single-layer filtration): Filtration method: single-layer 50-mesh filtration, the rest is the same as in Example 1.

[0047] Example 8 (Conventional Cooling): Cooling method: Single-stage cooling (total water flow 15L / min, no zone control), the rest is the same as in Example 1.

[0048] Example 9 (coaxiality relaxed): Coaxiality: 0.08mm, the rest is the same as Example 1.

[0049] Example 10 (high Si content): Si content: 0.06%, the rest is the same as in Example 1.

[0050] Comparative Example 1 (Fe content too low): Fe content: 0.15%, the rest is the same as in Example 1.

[0051] Comparative Example 2 (Fe content too high): Fe content: 0.30%, the rest is the same as in Example 1.

[0052] Comparative Example 3 (casting temperature too low): Casting temperature: 685℃, the rest is the same as Example 1.

[0053] Comparative Example 4 (casting temperature too high): Casting temperature: 725℃, the rest is the same as Example 1.

[0054] Comparative Example 5 (Traditional Process): Fe content: 0.30% (not precisely controlled); Casting temperature: 680-730℃ (fluctuation); Refining method: single refining (1 time); Filtration method: no filtration; Cooling method: single-stage cooling; Coaxiality: 0.15mm.

[0055] Table 1. Differences in formulation and process between the examples and comparative examples

[0056] The products of Examples 1-10 and Comparative Examples 1-5 were tested, and the results are shown in the table below: Table 2. Summary of Performance Data for Examples and Comparative Examples

[0057] Data Analysis and Mechanism Explanation 1. Analysis of the effect of Fe content on performance (Examples 1-3 vs. Comparative Examples 1-2): When the Fe content is 0.15% (Comparative Example 1), the aluminum rod has a tensile strength of only 182 MPa, a grain size of 165 μm, an elongation of 1.42% which is high but the strength is insufficient, and poor machinability (maximum drawing length is only 50,000 meters).

[0058] When the Fe content is 0.20%-0.25% (Examples 1-3), the tensile strength is 210-238 MPa, the elongation is 1.18%-1.32%, the resistivity is 27.52-27.65 nΩ·m, and the maximum drawn length is >200,000 meters.

[0059] When the Fe content is 0.30% (Comparative Example 2), the tensile strength reaches 252 MPa, but the elongation drops to 1.05%, and the resistivity rises to 28.52 nΩ·m, exceeding the design requirement (≤28.172 nΩ·m), with a maximum drawing length of only 60,000 meters.

[0060] Mechanism Explanation: The form of Fe in aluminum significantly affects its microstructure and properties depending on its content. When the Fe content is 0.15%, the precipitation of FeAl3 phase is insufficient, resulting in weak grain refinement and a grain size of up to 165 μm. The coarse grains deform unevenly during wire drawing, easily leading to stress concentration at grain boundaries and premature fracture. When the Fe content is 0.20%-0.25%, an appropriate amount of FeAl3 phase is distributed within and around the grain boundaries. On one hand, it inhibits grain growth by pinning grain boundaries (reducing the grain size to 98-112 μm), producing a grain refinement strengthening effect. On the other hand, the dispersed FeAl3 phase hinders dislocation movement, producing a dispersion strengthening effect, increasing the tensile strength to 210-238 MPa. Simultaneously, because the FeAl3 phase itself has poor electrical conductivity, excessive Fe (>0.28%) significantly increases the probability of electron scattering, leading to a sharp increase in resistivity. When the Fe content reaches 0.30%, the amount of FeAl3 phase precipitation is too large, the resistivity exceeds the design limit, and the excessive hard and brittle phase leads to a decrease in elongation and deterioration of machinability.

[0061] 2. Analysis of the effect of casting temperature on performance (Examples 1, 4, 5 vs. Comparative Examples 3, 4): At a casting temperature of 685℃ (Comparative Example 3), the hydrogen content is 0.25ml / 100g Al, the grain size is 175μm, and the maximum drawing length is only 30,000 meters.

[0062] When the casting temperature is 695-710℃ (Examples 1, 4, 5), the hydrogen content is 0.19-0.22ml / 100g Al, the grain size is 105-120μm, and the maximum drawing length is 160,000-200,000 meters.

[0063] At a casting temperature of 725℃ (Comparative Example 4), the hydrogen content is 0.32 ml / 100 g Al, the grain size is 185 μm, and the maximum drawing length is only 20,000 meters.

[0064] Mechanism Explanation: Casting temperature has a decisive influence on the hydrogen absorption behavior and solidification structure of molten aluminum. The solubility of hydrogen in molten aluminum follows Sievts' law: solubility is proportional to the square root of temperature. When the temperature rises from 695℃ to 725℃, the solubility of hydrogen increases by about 40%, leading to a significant acceleration in the hydrogen absorption rate of molten aluminum. Simultaneously, the protective effect of the oxide film on the surface of molten aluminum weakens at high temperatures, making it more susceptible to adsorbing hydrogen produced by the decomposition of water vapor. During solidification, the solubility of hydrogen in the solid phase of aluminum is much lower than that in the liquid phase (approximately 20:1). Hydrogen atoms accumulate at the solid-liquid interface front. When the local hydrogen partial pressure exceeds a critical value, it precipitates as molecular hydrogen, forming pores. These micropores become crack initiation points during wire drawing, leading to wire breakage.

[0065] The effect of casting temperature on grain size follows solidification theory: at excessively low temperatures (685℃), the aluminum melt exhibits high supercooling and a high nucleation rate, but the grain growth rate is too rapid, easily forming coarse columnar crystals (grain size 175μm). At excessively high temperatures (725℃), the supercooling is small, the nucleation rate is low, and this also leads to grain coarsening (185μm). This invention controls the casting temperature at 695-710℃, ensuring the nucleation rate while controlling the grain growth rate, resulting in a fine and uniform equiaxed grain structure (105-120μm), significantly improving machinability.

[0066] 3. Analysis of the impact of refining times on performance (Example 1 vs. Example 6): Four-stage refining (Example 1): Hydrogen content 0.19 ml / 100 g Al, maximum drawing length > 200,000 meters.

[0067] Three-stage refining (Example 6): hydrogen content 0.24 ml / 100 g Al, maximum drawing length 120,000 meters.

[0068] Mechanism Explanation: During the refining process, the contact time, bubble size, and distribution between nitrogen bubbles and molten aluminum are key factors determining the hydrogen removal efficiency. The 2+2 refining process (two initial refining cycles to remove primary impurities, followed by two more refining cycles after alloying to remove secondary impurities) involves one more refining cycle than the 2+1 process, increasing the cumulative hydrogen removal efficiency from 75% to over 90%. This additional refining cycle reduces the residual hydrogen content by approximately 0.05 ml / 100g Al. When the hydrogen content decreases from 0.24 ml / 100g Al to 0.19 ml / 100g Al, the number and size of micropores are significantly reduced, the density of crack initiation points during wire drawing decreases by approximately 60%, and the continuous drawing length increases from 120,000 meters to over 200,000 meters.

[0069] 4. Impact analysis of filtration methods on performance (Example 1 vs. Example 7): Double-layer filtration (Example 1): hydrogen content 0.19ml / 100g Al, maximum drawing length >200,000 meters.

[0070] Single-layer filtration (Example 7): hydrogen content 0.21 ml / 100 g Al, maximum drawing length 150,000 meters.

[0071] Mechanism Explanation: The 50-mesh dual-layer filter provides an additional barrier compared to a single-layer filter, effectively removing non-metallic inclusions (such as Al2O3, MgO, TiB2, etc.) with sizes ranging from 50-300μm. The dual-layer filter has twice the impurity capacity of a single-layer filter, increasing filtration efficiency by approximately 30%. During wire drawing, non-metallic inclusions are not coordinated with the deformation of the aluminum matrix, easily forming microcracks at the interface, becoming sources of fracture. Dual-layer filtration reduces the inclusion content, significantly decreasing the risk of wire breakage during wire drawing.

[0072] 5. Analysis of the impact of cooling methods on performance (Example 1 vs. Example 8): 4-stage cooling (Example 1): Grain size 105μm, maximum pulling length >200,000 meters.

[0073] Single-stage cooling (Example 8): Grain size 158μm, maximum drawing length 100,000 meters.

[0074] Mechanism Explanation: The four-stage adjustable cooling system achieves precise control of the billet temperature field. The outer layer of intense cooling (18 L / min) rapidly forms a fine-grained shell, serving as a "template" for subsequent solidification; the inner layer of moderate cooling (12 L / min) ensures heat dissipation and prevents coarse grains in the central region. This gradient cooling strategy results in a uniform and fine equiaxed grain structure (105 μm) in the billet, whereas single-stage cooling (total water flow 15 L / min) cannot precisely control the temperature gradient, leading to a large temperature difference between the billet surface and core, and easily forming coarse columnar crystals (158 μm). The fine-grained structure has high grain boundary density, uniform deformation resistance, and more stable plastic flow during wire drawing, reducing the likelihood of localized necking and fracture.

[0075] 6. Analysis of the impact of coaxiality on performance (Example 1 vs. Example 9): Coaxiality 0.04mm (Example 1): Maximum drawing length > 200,000 meters.

[0076] Coaxiality 0.08mm (Example 9): Maximum drawing length 140,000 meters.

[0077] Mechanism Explanation: Coaxiality deviation in the rolling mill causes the aluminum rod to experience periodic, uneven radial forces during rolling, resulting in periodic indentations with a depth of 0.01-0.03 mm. These indentations become stress concentration points during subsequent wire drawing, with stress concentration factors reaching 2-3 times. Under tensile stress, microcracks easily form and propagate at the bottom of the indentations, leading to wire breakage. Optimizing coaxiality from 0.08 mm to 0.04 mm reduces indentation depth by approximately 50%, and increases the maximum drawing length from 140,000 meters to over 200,000 meters.

[0078] 7. Analysis of the effect of Si content on performance (Example 1 vs. Example 10): Si content 0.04% (Example 1): resistivity 27.58 nΩ·m, maximum drawing length > 200,000 meters.

[0079] Si content 0.06% (Example 10): resistivity 28.15 nΩ·m (exceeding the standard), maximum drawing length 130,000 meters.

[0080] Mechanism Explanation: The solid solubility of Si in aluminum (approximately 0.05% at room temperature) is much higher than that of Fe, and the scattering effect of dissolved Si on electrons is extremely strong. The resistivity increase caused by each Si atom is approximately 3-5 times that of Fe atoms. When the Si content increases from 0.04% to 0.06%, the concentration of dissolved Si increases by 50%, and the resistivity rises from 27.58 nΩ·m to 28.15 nΩ·m, exceeding the upper limit of the design requirement (28.172 nΩ·m). Simultaneously, Si and Fe can form ternary compounds such as α-AlFeSi. These hard and brittle phases accumulate at grain boundaries, reducing the material's plasticity and machinability, leading to an increased risk of wire breakage during wire drawing.

[0081] 8. Comparative Analysis of Traditional Processes (Example 1 vs. Comparative Example 5): Preferred process of the present invention (Example 1): all performance indicators meet the standards, and the maximum drawing length is >200,000 meters.

[0082] Traditional process (Comparative Example 5): Hydrogen content 0.38ml / 100g Al, grain size 210μm, resistivity 28.68nΩ·m (exceeding the standard), elongation 0.95% (not meeting the standard), maximum drawing length only 15,000 meters.

[0083] Mechanism Explanation: Traditional processes suffer from the cumulative effect of multiple technical defects: high Fe content (0.30%) with large fluctuations leads to excessive resistivity; incomplete hydrogen removal during single refining results in a hydrogen content as high as 0.38 ml / 100g Al; lack of filtration leads to high inclusion content; large fluctuations in casting temperature (680-730℃) result in coarse and uneven grains; single-stage cooling and poor coaxiality control further deteriorate surface quality and internal structure. The cumulative effect of these defects makes the overall performance of the aluminum rod far below design requirements, failing to meet the production needs of high-end aluminum alloy wire harnesses. This invention systematically solves the defects of traditional processes through multi-stage purification, precise control of Fe content, narrow-window temperature-controlled casting, gradient cooling, and precise surface quality control, achieving a comprehensive improvement in the performance of the aluminum rod.

[0084] Based on the systematic verification of the above 15 sets of experiments, the following conclusions can be drawn: 1. The optimal range for the present invention is to control the Fe content between 0.20% and 0.25%. Within this range, good electrical conductivity (resistivity ≤ 27.65 nΩ·m), mechanical properties (tensile strength 210-238 MPa, elongation ≥ 1.18%), and processability (continuous drawing length > 200,000 meters) can be obtained simultaneously.

[0085] 2. The casting temperature is controlled at 695-710℃. With the help of a 4-stage adjustable cooling system, the hydrogen content can be controlled to below 0.22ml / 100g Al, and the grain size can be refined to below 120μm, which significantly improves the machinability.

[0086] The combination of the 3.2+2 refining process (4 refining processes) and double-layer 50-mesh filtration can reduce the hydrogen content to below 0.20ml / 100gAl and significantly reduce the inclusion content, providing high-quality blanks for continuous drawing of ultrafine filaments.

[0087] 4. The coaxiality is controlled within 0.05mm, which effectively eliminates periodic indentations on the aluminum rod surface and eliminates stress concentration sources during the wire drawing process.

[0088] 5. Strictly controlling the Si content to ≤0.04% is the key to ensuring that the resistivity meets the standard.

[0089] 6. The preferred process of this invention (Example 1) has the best overall performance, with a hydrogen content of 0.19 ml / 100g Al, a grain size of 105 μm, a tensile strength of 225 MPa, an elongation of 1.25%, a resistivity of 27.58 nΩ·m, and a continuous drawing length of 0.361 mm single filament exceeding 200,000 meters, which fully meets the production requirements of high-end aluminum alloy wires in the fields of photovoltaics and new energy vehicles.

[0090] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. An aerospace aluminum rod with good ductility and low impurity content, characterized in that, It includes the following components by weight percentage: aluminum content ≥99.5%, iron content 0.20%-0.25%, silicon content ≤0.04%, and other impurities affecting resistivity, Mn, Cr, Ti, and V, with individual content ≤0.002% and total content ≤0.01%; the hydrogen content of the aviation aluminum rod is ≤0.22ml / 100g Al.

2. The aviation aluminum rod with good ductility and low impurity content according to claim 1, characterized in that, The average grain size of the aerospace aluminum rod is ≤150μm.

3. An aerospace aluminum rod with good ductility and low impurity content, characterized in that, The surface of the aviation aluminum rod is free from defects such as indentations, insufficient material, peeling, and scratches.

4. A method for preparing an aviation aluminum rod with good ductility and low impurity content as described in any one of claims 1-3, characterized in that, Includes the following steps: (1) Raw material preparation and smelting: Select electrolytic primary aluminum liquid, control the aluminum content in the primary aluminum liquid to be ≥99.80%, the content of impurity components Mn, Cr and Ti to be ≤0.002%, and the content of Si to be ≤0.04%; use a hydraulic tilting lifting platform to smoothly inject the aluminum liquid into the furnace; (2) Alloying and refining: Add aluminum-iron alloy and aluminum-boron alloy to the aluminum liquid, and control the Fe content to 0.20%-0.25%; adopt the 2+2 refining process, first refine the original aluminum liquid twice, add alloying elements and then use permanent magnet stirring to refine it twice more. (3) Online degassing and filtration: A dual-rotor online degassing device is used for degassing, and a double-layer filter plate is used to filter the aluminum liquid; (4) Casting: A horizontal casting method is adopted, and the aluminum liquid is cast stably through three-stage flow control. The casting temperature is controlled at 695-710℃, and a four-stage cooling system is used for cooling. (5) Continuous casting and rolling: The billet is continuously rolled, and the entry temperature is controlled at 480-520℃ and the rolling speed is 3-5 tons / hour. (6) Take-up: Use a round take-up frame to take up the wire, and control the take-up tension to 50-100N.

5. The method for preparing an aerospace aluminum rod with good ductility and low impurity content according to claim 4, characterized in that, In (2), the permanent magnet stirring is for 6-10 minutes each of forward and reverse stirring, and the stirring speed is 200-300 r / min.

6. The method for preparing an aerospace aluminum rod with good ductility and low impurity content according to claim 4, characterized in that, In step (2), the refining process uses high-purity nitrogen with a purity of ≥99.999%, a pressure of 0.15-0.25 MPa, a refining temperature of 740-750℃, and a refining time of 15-25 minutes per refining step.

7. The method for preparing an aerospace aluminum rod with good ductility and low impurity content according to claim 4, characterized in that, In (3), the dual-rotor online degassing device controls the nitrogen purity to be 99.999%, the pressure to be 0.08-0.12MPa, and the rotor speed to be 30-100r / min; the double-layer filter plate is a 50-mesh filter plate.

8. The method for preparing an aerospace aluminum rod with good ductility and low impurity content according to claim 4, characterized in that, In (4), the three-stage flow control includes a plug at the end of the flow channel, a float in the large ladle, and a flow controller in the small ladle, which controls the fluctuation of the aluminum liquid level within ±2mm; the four-stage cooling system includes independent cooling in four directions: inside, outside, top, and bottom, with a cooling water flow rate of 5-20L / min and a pressure of 0.2-0.5MPa for each stage.

9. The method for preparing an aerospace aluminum rod with good ductility and low impurity content according to claim 4, characterized in that, In step (5), before rolling, check that the coaxiality deviation of the mill stand is ≤0.05mm; replace the 10-15 stand rolls and adjust the roll pass shape; replace the outlet tube guide and guide bearing.

10. The application of the aerospace aluminum rod prepared by the preparation method according to any one of claims 4-9 in high-end aluminum alloy wire harnesses for photovoltaic and new energy vehicles.

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