A non-heat-treated aluminum alloy conductive flat strip for new energy vehicles and a production method thereof

Abstract

This invention relates to a method for producing non-heat-treated aluminum alloy conductive flat strips for new energy vehicles. The alloy composition is 0.8-1.8% Fe, 0.1-0.3% Cu, 0.05-0.2% Zr, <0.15% Si, and a total content of Cr+V+Ti+Mn <0.08%, more preferably with the addition of 0.01-0.05% B or 0.1-0.25% Re. The process employs rapid cooling continuous casting and two-pass continuous wide-direction expansion extrusion to produce conductive flat strips with a thickness of 2-6 mm. The microstructure has a grain size ≤10 μm and Fe phase particles ≤0.1 μm. The product has a tensile strength of 142-202 MPa, a yield strength of 120-180 MPa, an elongation of 20-28%, and a conductivity of 57-60% IACS. This invention simplifies the production process of aluminum alloy conductive flat strips, and the product meets the technical requirements for aluminum alloy strips used in power supply for new energy vehicles.

Description

Technical Field

[0001] This invention belongs to the field of metal plastic processing technology, specifically relating to a non-heat-treated aluminum alloy conductive flat strip for new energy vehicles and its production method. Background Technology

[0002] With the rapid development of new energy vehicles, lightweighting and cost reduction will become inevitable choices for the industry, bringing new opportunities to the supporting aluminum alloy busbars. The aluminum alloy busbar market is expected to experience explosive growth. For example, aluminum-magnesium-silicon 6101 alloy is a heat-treatable alloy with moderate strength, good bending and forming properties, and electrical conductivity, and is widely used as a high-performance aluminum alloy conductor material. Modern automotive parts manufacturing is increasingly moving towards large-scale, highly intelligent, and standardized assembly line manufacturing. The power supply conductor materials for new energy vehicles need to have better mechanical and electrical properties, and there is an urgent need to provide high-quality aluminum alloy conductor materials and production processes for power supply with large roll weights (single roll weight not less than 300 kg) to meet the needs of highly intelligent and assembly line operations. However, the current conventional extrusion process for producing 6101 busbars can no longer meet the aforementioned technical requirements. To address this issue, Chinese patent application publication number CN115740057A proposes a production process for high-quality 6101 aluminum alloy coils and strips used in power supply for new energy vehicles. This process includes: horizontal continuous casting of aluminum alloy disc billets, peeling and drawing, low-temperature direct cooling continuous extrusion, coiling, and low-temperature long-term annealing. However, 6101 aluminum alloy must undergo low-temperature long-term annealing (annealing at 220-260℃ for 10-16 hours) or artificial aging treatment to ensure synergistic and uniform improvement in mechanical and electrical properties. This process is relatively complex, increases control difficulty and production costs, and has a long growth cycle.

[0003] Existing research has found that alloying elements have varying degrees of influence on the mechanical strength and electrical conductivity of aluminum and aluminum alloys. Adding Fe to aluminum alloys increases their strength and hardness. However, tests on the electrical conductivity of a series of aluminum alloys with different Fe contents show that as the Fe content in cast aluminum alloys increases, the conductivity decreases, and when the Fe content exceeds 0.9%, the conductivity drops significantly. Japanese researchers have also indicated that adding 0.6% Fe and 0.05% Zr to pure aluminum increases its tensile strength from 100 MPa to 140 MPa and its elongation from 21.5% to 30%, while the electrical conductivity remains largely unchanged. Based on these theories, a series of different Al-Fe-X alloys have been developed, among which the Al-Fe-Cu alloys (registered alloys include: 8017, 8030, 8076, 8130, 8176, and 8177) are high-performance aluminum alloys developed by Alcan Group. Compared to pure aluminum (AA1350) cables, these alloys contain added iron, copper, magnesium, boron, etc., which effectively improves the material's creep resistance and compressibility, giving aluminum alloy conductive materials the same stability as copper conductors. However, the maximum Fe content in these alloys can only be 1%. If the Fe content is increased further, coarse Al3Fe intermediate phases can easily form in the material, which will seriously affect the alloy's mechanical, electrical, and processing properties.

[0004] In view of the above problems, there is an urgent need in this field to develop new processing methods for aluminum alloy conductive flat strips in order to solve the problems existing in the prior art. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a non-heat-treated aluminum alloy conductive flat strip for new energy vehicles and its production method, which solves the technical problems that the production of aluminum alloy conductive flat strips must be carried out by low-temperature long-term annealing or artificial aging treatment, and that the existing process cannot produce aluminum alloy conductive flat strips with Fe content greater than 1%.

[0007] (II) Technical Solution

[0008] The technical solution of the present invention is as follows:

[0009] In a first aspect, the present invention provides a method for producing non-heat-treated aluminum alloy conductive flat strip for new energy vehicles, comprising the following steps:

[0010] S1. Rapid cooling continuous casting of aluminum alloy disc-shaped rods, including:

[0011] The molten aluminum alloy, after melting, refining, and filtering, is subjected to rapid cooling continuous casting to obtain aluminum alloy disc rod billets; the pouring temperature is 740-760℃, and the casting speed is 1000-1100mm / min.

[0012] The chemical composition of the aluminum alloy melt, by mass percentage, is as follows:

[0013] Fe: 0.8-1.8%, Cu: 0.1-0.3%, Zr: 0.05-0.2%, Si: <0.15%, total content of Cr+V+Ti+Mn <0.08%, balance Al; or:

[0014] Fe: 0.8-1.8%, Cu: 0.1-0.3%, Zr: 0.05-0.2%, Si: <0.15%, Total content of Cr+V+Ti+Mn <0.08%, B: 0.01-0.05%, balance Al; or:

[0015] Fe: 0.8-1.8%, Cu: 0.1-0.3%, Zr: 0.05-0.2%, Si < 0.15%, total content of Cr+V+Ti+Mn < 0.08%, Re: 0.1-0.25%, balance Al;

[0016] S2, the first continuous wide-width expansion extrusion, which includes:

[0017] The aluminum alloy disc rod billet prepared in S1 is fed into the wheel groove of a continuous extrusion press. The aluminum alloy disc rod billet is formed into a disc rod by continuous wide-direction expanding extrusion. After cooling, it is rolled into a coil. The continuous extrusion uses a wide-direction expanding die. The extrusion temperature is 300-380℃.

[0018] S3, the second continuous wide-width expansion extrusion, includes:

[0019] The coil of the round bar material prepared by S2 is fed into a continuous extruder and continuously extruded into a conductive flat strip product through a wide-axis expanding die; the extrusion temperature is 420-480℃.

[0020] S4. Use a double take-up and winding machine to roll the yarn into coils.

[0021] According to a preferred embodiment of the present invention, the process steps of S2 are as follows: continuous extrusion is carried out using a wide-direction expanding die, with two die holes opened at the wide-direction expanding end of the die for extrusion discharge; the aluminum alloy disc billet is formed into two disc rods (the diameters of the two disc rods may be equal or unequal) through the first pass of continuous wide-direction expanding extrusion, and then cooled and wound into coils respectively.

[0022] According to a preferred embodiment of the present invention, in S1, the diameter of the aluminum alloy disc rod blank is 20 mm; in S2, the diameter of the disc rod is 10 mm, 12 mm or 16 mm.

[0023] According to a preferred embodiment of the present invention, in S1, the pouring temperature of the rapid cooling continuous casting is 740-760°C, and the casting speed is 1000-1100 mm / min. Under these casting conditions, the casting cooling rate can reach over 400°C / s to produce refined Al3Fe mesophase. Too low a cooling rate will result in coarse Al3Fe mesophase; therefore, for high-Fe aluminum alloys, a rapid cooling casting method must be used to control the coarsening of the Al3Fe mesophase.

[0024] According to a preferred embodiment of the present invention, in S2, the extrusion temperature is 300-380°C, more preferably 320-350°C. Too low a temperature is detrimental to extrusion deformation, while too high a temperature is detrimental to refining the Al3Fe mesophase and results in coarse grains.

[0025] According to a preferred embodiment of the present invention, in S3, the extrusion temperature is 420-480°C, more preferably 430-450°C. Through the preceding rapid cooling casting and the lower temperature extrusion of the first pass, the Al3Fe mesophase and grain size are controlled and refined. Unlike the first extrusion, the second pass is a finished product extrusion. Increasing the extrusion temperature range is to control the final product to have good mechanical and electrical properties, as well as surface quality.

[0026] Preferably, the first continuous wide-width expansion extrusion uses a 400-type aluminum continuous extrusion press with an extrusion speed of 7-9 rpm; the second continuous wide-width expansion extrusion uses a 315-type aluminum continuous extrusion press with an extrusion speed of 10-12 rpm.

[0027] According to a preferred embodiment of the present invention, in S3, the coiled bar is continuously extruded into a conductive flat strip product with a thickness of 2-6 mm and a width of 12-50 mm through a second continuous wide-direction expansion extrusion.

[0028] According to a preferred embodiment of the present invention, the entire production process of the present invention does not include the steps of extrusion online quenching and / or coil artificial aging heat treatment.

[0029] Secondly, the present invention provides a non-heat-treated aluminum alloy conductive flat strip for new energy vehicles, which is produced by the production method of any of the above embodiments.

[0030] Adding small amounts of Fe, Cu, Zr, B, Re, etc. to aluminum can improve the strength of aluminum alloys with little negative impact on electrical conductivity. By controlling the appropriate content and process, high-strength aluminum alloy conductive materials with electrical conductivity higher than 60% IACS can be obtained.

[0031] Adding Fe to aluminum alloys produces the Al3Fe phase. The Al3Fe phase significantly hinders dislocation movement, increasing alloy strength. Simultaneously, Al3Fe located at grain boundaries and phase boundaries pins interfaces, impeding interfacial movement and further enhancing the alloy's strength and hardness. Furthermore, during recrystallization, the Al3Fe phase hinders grain boundary movement, thus refining recrystallized grains. This invention utilizes this effect; during rapid cooling continuous casting, Fe and Al primarily exist as the intermediate Al3Fe phase. As the Fe content increases, the number of Al3Fe particles in the alloy significantly increases, resulting in a more pronounced grain refinement effect and a finer alloy microstructure.

[0032] Adding a small amount of Cu to aluminum alloys can provide solid solution strengthening and improve the alloy's strength. This is because Cu exists in a solid solution state within the α(Al) matrix, forming the insoluble phase Al₂Cu, which distorts the Al crystal lattice, resulting in a hardening effect and increased alloy strength. However, the addition of Cu also causes lattice distortion, leading to electron wave scattering and reducing the alloy's electrical conductivity. Cu has a combined effect on the electrical and mechanical properties of conductive aluminum alloys. As the Cu content increases, the tensile strength of the aluminum alloy continuously increases; when the Cu content increases from 0 to 1%, the alloy strength increases. However, with continuous addition of Cu, the conductivity of industrially pure aluminum continuously decreases; and the conductivity decreases rapidly when the Cu content increases within the range of 0-2%. Therefore, the effects of Cu content on the strength and conductivity of conductive aluminum alloys are contradictory. Thus, the amount of Cu added must be strictly limited to a certain low content range.

[0033] Adding a small amount of Zr to aluminum alloys: Zr precipitates in aluminum as Al3Zr, and trace amounts of zirconium help improve the strength and heat resistance of aluminum alloys, while the electrical conductivity decreases only slightly.

[0034] Adding small amounts of boron (B) or retinylamine (Re) to aluminum alloys improves conductivity because B reacts with harmful impurities such as Ti, V, Cr, and Mn to form borides or their complex compounds. This causes these impurities to precipitate from their solid solution state and deposit at the bottom of the melt, reducing lattice distortion within the aluminum conductor. Furthermore, adding B increases the number of crystal nuclei in the molten aluminum, refining the grain size. Therefore, the addition of B benefits both the strength and conductivity of round aluminum rods. Boron acts as a solidification grain refiner, and its addition amount is 0.005-0.1%.

[0035] Rare earth element Re exhibits a strong affinity for gases such as hydrogen and some impurity elements in molten aluminum, forming compounds with high melting points. Therefore, it possesses certain functions in hydrogen removal, refining, purification, and modification. Adding a certain amount of Re allows it to combine with impurities such as Fe and Si dissolved in the aluminum matrix, forming stable intermetallic compounds. This reduces the amount of impurity elements dissolved in the matrix and effectively suppresses the harmful effects of Fe and Si on conductivity in industrially pure aluminum. Simultaneously, rare earth elements increase the supercooling of the alloy during crystallization and provide numerous heterogeneous nucleation sites. The abundance of new nuclei restricts the growth of columnar crystals, resulting in well-developed equiaxed crystals, which refines the grain size, significantly improves the metallographic structure of the aluminum alloy, reduces crack initiation sites, and alters the crack initiation and propagation paths during fracture. This is beneficial for toughening the alloy, improving both the strength and plasticity of electrical round aluminum rods.

[0036] The presence of Si, Cr, V, Ti, and Mn in aluminum alloys has a significant impact on electrical conductivity and must be strictly controlled. Si is an impurity element in aluminum that negatively affects conductivity; its content should not exceed 0.15 wt.%. Cr, V, Ti, and Mn are also unavoidable impurities introduced into the alloy, and their total content should not exceed 0.08 wt.

[0037] (III) Beneficial Effects

[0038] The inventors discovered that the formation of coarse Al3Fe mesophases in Al-Fe-Cu alloys when the iron content increases is due to process deficiencies. The continuous casting and rolling process used to produce aluminum alloy conductive rods is prone to forming coarse Al3Fe mesophases due to its low cooling rate, thus affecting the alloy's mechanical, electrical, and machinability properties. To solve this problem, the production process provided by this invention employs "rapid cooling casting and large plastic deformation" to achieve a refined microstructure.

[0039] In the rapid cooling continuous casting process of this invention, Fe and Al mainly exist in the form of the meso phase Al3Fe. When the Fe content increases, the number of Al3Fe particles in the alloy increases significantly, and the grain refinement effect is more obvious, resulting in a refined alloy structure. Combined with two-pass wide-direction expansion continuous extrusion, large shear deformation is achieved, which refines the grain size and breaks down Al3Fe phase particles in the structure of the conductive flat strip product. Therefore, this invention combines rapid cooling continuous casting with two-pass wide-direction expansion continuous extrusion process, which enables aluminum alloy conductive products to obtain both high mechanical strength and high conductivity while increasing the Fe content (≥1%).

[0040] Tests revealed that the aluminum alloy conductive flat strip prepared by this invention has a grain size of no more than 10 μm and an Fe phase particle size of no more than 0.1 μm. The product performance indicators are a tensile strength of 142-202 MPa, a yield strength of 120-180 MPa, an elongation of 20-28%, and a conductivity of 57-60% IACS.

[0041] Compared with existing technologies, the production process for preparing aluminum alloy conductive flat strips in this invention not only optimizes the composition of the aluminum alloy, but also adopts a rapid cooling continuous casting and two-pass continuous wide-direction expansion extrusion process. This is a non-heat-treated aluminum alloy preparation process, which eliminates the need for online quenching during extrusion and artificial aging heat treatment of the strip coil. Compared with existing technologies for preparing 6101 aluminum alloy conductive flat strips, the production process of this invention simplifies the production process, results in better uniformity and consistency of the product's mechanical and electrical properties, and produces aluminum alloy conductive products with Fe content ≥1%, which can achieve a combination of high mechanical strength and high conductivity. Attached Figure Description

[0042] Figure 1 EBSD grain size analysis of the microstructure of the aluminum alloy conductive flat strip product prepared in this invention.

[0043] Figure 2 Transmission electron microscopy (TEM) image of the precipitated phase of the aluminum alloy conductive flat strip product prepared according to the present invention. Detailed Implementation

[0044] To better explain and facilitate understanding of the present invention, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0045] Based on the standard chemical composition of the alloy, 99.7 aluminum ingots and copper ingots, as well as Al-10Fe and Al-5Zr master alloys, were used to prepare the aluminum alloy according to the designed weight ratio and feeding rules. The alloy was melted in a dual 1000Kg capacity gas-fired melting furnace. After degassing and slag removal refining treatment, the melt was sampled and chemically analyzed using a direct-reading spectral method. The measured composition is shown in Table 1.

[0046] The aluminum alloy compositions of Examples A1, B1, C1, D1, and E1 satisfy the following:

[0047] Fe: 0.8-1.8%, Cu: 0.1-0.3%, Zr: 0.05-0.2%, Si: <0.15%, total content of Cr+V+Ti+Mn <0.08%, balance Al.

[0048] The aluminum alloy compositions of Examples A2, B2, C2, D2, and E2 satisfy the following:

[0049] Fe: 0.8-1.8%, Cu: 0.1-0.3%, Zr: 0.05-0.2%, Si: <0.15%, total content of Cr+V+Ti+Mn <0.08%, B: 0.01-0.05%, balance Al.

[0050] The aluminum alloy compositions of Examples A3, B3, C3, D3, and E3 satisfy the following:

[0051] Fe: 0.8-1.8%, Cu: 0.1-0.3%, Zr: 0.05-0.2%, Si: <0.15%, total content of Cr+V+Ti+Mn <0.08%, Re: 0.1-0.25%, balance Al.

[0052] Table 1. Main chemical composition of the aluminum alloy of the present invention (weight percentage, %)

[0053]

[0054]

[0055] The production methods of the aluminum alloy conductive flat strips in each embodiment are as follows:

[0056] (1) After heat preservation and filtration, the rod blank with a diameter of 20mm is cast by rapid cooling continuous casting process, with a pouring temperature of 740-760℃ and a casting speed of 1050mm / min.

[0057] (2) A 20mm diameter coiled rod blank was extruded into two rods with a diameter of 16mm using a wide-expanding two-hole die on a 400-type continuous aluminum extrusion press. The extrusion roller speed was 8 rpm, and the actual extrusion temperature was about 340℃. The rods were then cooled and coiled.

[0058] (3) Continue to extrude the 16mm diameter coiled bar into coiled strip products of different specifications on the 315 aluminum continuous extrusion press using a wide-direction expanding die (providing users with two specifications of products: 2.5mm thick × 22mm wide and 5.3mm thick × 35mm wide). The extrusion roller speed is 10rpm, and the actual extrusion temperature is about 450℃.

[0059] (4) After cooling, the weight of a single roll is approximately 320 kg (user requirements are 300-350 kg per roll). Samples from the head and tail ends of the rolls were subjected to EBSD grain size analysis and transmission electron microscopy (TEM) precipitate analysis. Typical microstructure characterization results are as follows: Figure 1 (EBSD grain size analysis diagram) and Figure 2 (TEM image of the precipitated phase). Figure 1In Figure (A), different colored blocks represent EBSD grains of different sizes. Figure (B) is a statistical chart of grain size, where the smallest grain size is 0.53 μm, the largest is 18.06 μm, and the average grain size is 9.18 μm (<10 μm). Figure 2 The scale bar of the TEM image of the precipitated phase was used to determine that the size of the Fe particles was no greater than 0.1 μm.

[0060] Performance tests were conducted on samples from the head and tail of the coil strip. The average values ​​of the mechanical and electrical properties (eddy current conductivity meter) of the aluminum alloy coil strip are shown in Table 2.

[0061] Table 2:

[0062]

[0063] From the implementation results: The aluminum alloy of this invention and the aluminum alloy conductive flat strip produced by rapid cooling continuous casting and two-pass continuous wide-direction expansion extrusion have the following performance indicators: tensile strength of 142-201.2 MPa, yield strength of 120-180 MPa, elongation of 20-28%, and conductivity of 57-60% IACS. From the performance of aluminum alloy strips with three different alloy compositions, adding 0.01-0.05% boron (B) to the aluminum alloy composition can improve the conductivity of the aluminum alloy strip; adding 0.1-0.25% retinyl chloride (Re) to the aluminum alloy composition can improve the tensile strength and yield strength of the aluminum alloy strip, while having no significant effect on conductivity.

[0064] Comparing the embodiments of groups B and E (a total of 6 embodiments) with other embodiments, when the Fe content in the aluminum alloy is greater than 1%, the mechanical properties of the aluminum alloy strip are significantly improved. Its tensile strength reaches a minimum of 186.2 MPa, and its yield strength reaches a minimum of 160.9 MPa. The elongation decreases (lower elongation indicates higher creep resistance and compaction, avoiding relaxation problems caused by creep, and good conductor stability), with a maximum not exceeding 26.1%. More importantly, despite such excellent mechanical properties, the conductivity of the aluminum alloy strip does not decrease significantly compared to other embodiments. Therefore, the aluminum alloy conductive product with an Fe content ≥1% produced by this invention can achieve a comprehensive performance of high mechanical strength and high conductivity.

[0065] Compared with the production process of 6101 aluminum alloy coils and strips described in the existing patent application CN115740057A, not only are the product performance indicators comparable, but also the process flow is simplified by eliminating the need for extrusion online quenching and artificial aging heat treatment of the coils. Furthermore, the test results of samples from the head and tail of the coils and strips show that the mechanical and electrical properties of the strip products are more uniform and consistent, which fully meets the technical requirements of aluminum alloy coils and strips for power supply in new energy vehicles.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for producing non-heat-treated aluminum alloy conductive flat strip for new energy vehicles, characterized in that, Includes the following steps: S1. Rapid cooling continuous casting of aluminum alloy disc-shaped rods, including: The aluminum alloy melt, after melting, refining, and filtering, is subjected to rapid cooling continuous casting to obtain aluminum alloy disc rod billets; the pouring temperature is 740-760℃, the casting speed is 1000-1100mm / min, and the casting cooling rate is above 400℃ / s. The chemical composition of the aluminum alloy melt, by mass percentage, is as follows: Fe: 1-1.8%, Cu: 0.1-0.3%, Zr: 0.05-0.2%, Si: <0.15%, total content of Cr+V+Ti+Mn <0.08%, balance Al; or: Fe: 1-1.8%, Cu: 0.1-0.3%, Zr: 0.05-0.2%, Si: <0.15%, Total content of Cr+V+Ti+Mn <0.08%, B: 0.01-0.05%, balance Al; or: Fe: 1-1.8%, Cu: 0.1-0.3%, Zr: 0.05-0.2%, Si: <0.15%, Total content of Cr+V+Ti+Mn <0.08%, Re: 0.1-0.25%, balance Al; S2, the first continuous wide-width expansion extrusion, which includes: The aluminum alloy disc rod billet prepared in S1 is fed into the wheel groove of a continuous extrusion press. The aluminum alloy disc rod billet is formed into a disc rod by continuous wide-direction expanding extrusion. After cooling, it is rolled into a coil. The continuous extrusion uses a wide-direction expanding die. The extrusion temperature is 300-380℃. S3, the second continuous wide-width expansion extrusion, includes: The coil of the round bar material prepared by S2 is fed into a continuous extruder and continuously extruded into a conductive flat strip product through a wide-axis expanding die; the extrusion temperature is 420-480℃. S4. Use a double take-up and winding machine to form coils; The production method does not require extrusion online quenching or manual aging heat treatment of coils throughout the entire process.

2. The production method according to claim 1, characterized in that, The process steps of S2 are as follows: continuous extrusion uses a wide-direction expanding die, with two die holes opened at the wide-direction expanding end for extrusion discharge; through the first pass of continuous wide-direction expanding extrusion, the aluminum alloy disc billet is formed into two disc rods, which are then cooled and wound into coils.

3. The production method according to claim 2, characterized in that, In S1, the diameter of the aluminum alloy disc rod blank is 20mm; in S2, the diameter of the disc rod is 10mm, 12mm or 16mm.

4. The production method according to claim 1, characterized in that, In S2, the extrusion temperature is 320-350℃.

5. The production method according to claim 1, characterized in that, In S3, the extrusion temperature is 430-450℃.

6. The production method according to claim 1, characterized in that, In S3, the coiled bar is continuously extruded into a conductive flat strip product with a thickness of 2-6mm and a width of 12-50mm through a second continuous wide-direction expansion extrusion.

7. A non-heat-treated aluminum alloy conductive flat strip for new energy vehicles, which is produced by the production method described in any one of claims 1-6.

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