Aluminum alloy bus bar

Abstract

The aluminum alloy bus bar (1) comprises a flat conductor (10) composed of an aluminum alloy having a composition containing 0.35-0.8 mass% of magnesium and 0.3-0.7 mass% of silicon, with the remainder being aluminum and inevitable impurities. A plurality of Mg-Si needle-like particles (16) containing magnesium and silicon are dispersed inside the aluminum alloy. The average length of the Mg-Si needle-like particles (16) is 67.1-378.4 nm, and the number density of the Mg-Si needle-like particles (16) in the aluminum alloy is 4.5×10 20 / m 3-6.8×1021 / m3.

Description

Aluminum Alloy Busbar

[0001] The present invention relates to an aluminum alloy bus bar.

[0002] Aluminum is a lightweight metal with good electrical conductivity and is relatively inexpensive, and therefore is widely used for bus bars, electric wires, electrodes, and the like. Aluminum alloys used as conductive materials generally include commercially pure aluminum such as A1060 alloy and A1070 alloy, which are standardized by the Japanese Industrial Standards (JIS), as well as A6101 alloy. The JIS guarantees that the A1060 alloy has a conductivity of 61% IACS. Furthermore, when the A1060 alloy does not have sufficient strength, A6101 alloy, which is guaranteed to have a conductivity of 55% IACS, is often used.

[0003] This A6101 alloy has undergone T6 treatment, and its standard mechanical properties are a tensile strength of 220 MPa, a yield stress of 195 MPa, and an elongation of 15% (1.6 mm thickness, 50 mm gauge length). Furthermore, the A6101 alloy contains fine magnesium-silicon precipitates in the aluminum matrix, achieving high strength through the Orowan mechanism. However, when compared with commercially pure aluminum, the A6101-T6 alloy exhibits reduced workability in post-processing steps such as pressing and bending.

[0004] Patent Document 1 discloses a method for manufacturing an aluminum alloy busbar. Specifically, the method involves edgewise bending an aluminum alloy flat wire to obtain a desired shape. The method involves heating the workpiece to 100°C or higher and 250°C or lower, holding the temperature for 5 minutes or less, and then performing the edgewise bending. The aluminum alloy flat wire used is a T6-tempered aluminum alloy material containing 0.3-0.9% Mg, 0.2-1.2% Si, 0.2% or less Cu, and 0.5% or less Fe, with the balance consisting of Al and unavoidable impurities. Furthermore, the ratio A / B of the Vickers hardness A of the heated portion to the Vickers hardness B of the unheated portion is 0.8 or higher. This manufacturing method improves the edgewise bending workability of the bent portion while preventing a decrease in strength.

[0005] Japanese Patent Application Laid-Open No. 2018-206663

[0006] However, in Patent Document 1, the processed portion is heated during edgewise bending, which causes a change in the material of the processed portion, resulting in a difference in strength between the heated portion and the non-heated portion.In addition, since heating the processed portion is essential, there is a problem that the manufacturing cost increases.

[0007] The present invention has been made in view of the problems inherent in the prior art, and an object of the present invention is to provide an aluminum alloy bus bar that has improved bending workability and electrical connection stability by controlling the microstructural state of the material.

[0008] The aluminum alloy bus bar according to an embodiment of the present invention includes a flat conductor made of an aluminum alloy having a composition containing 0.35 to 0.8 mass % magnesium and 0.3 to 0.7 mass % silicon, with the remainder being aluminum and unavoidable impurities, and the aluminum alloy contains a plurality of Mg—Si-based acicular particles containing magnesium and silicon dispersed therein, the average length of the Mg—Si-based acicular particles being 67.1 nm to 378.4 nm, and the number density of the Mg—Si-based acicular particles in the aluminum alloy being 4.5×10 ２０ / m３ ~6.8 x 10 ２１ / m ３ is.

[0009] According to the present invention, by controlling the structural state of the material, it is possible to provide an aluminum alloy bus bar having improved bending workability and electrical connection stability.

[0010] FIG. 1 is a perspective view schematically illustrating an example of an aluminum alloy busbar according to this embodiment. FIG. 2 is a schematic cross-sectional view showing an example of a cross section of a flat conductor in an aluminum alloy busbar. FIG. 3 is a schematic diagram illustrating the bending radius R of an edgewise bent portion of a flat conductor. FIG. 4 is a photograph showing a flat conductor marked with a grid-like marker before bending. FIG. 5 is a photograph showing a flat conductor marked with a grid-like marker after edgewise bending. FIG. 6 is a photograph showing a schematic diagram illustrating the cross-sectional shape of each of square edges and round edges of a flat conductor according to this embodiment, as well as the appearance. FIG. 7 is a transmission electron microscope photograph showing the results of observing a test sample of Example 1 at 200,000 magnifications. FIG. 8 is a schematic diagram showing an example of the dispersion state of acicular particles within an aluminum alloy. FIG. 9 shows an example of the results of observing a bent portion formed by edgewise bending at 50x magnification, showing a case where no cracks or necking are observed in the bent portion. Fig. 10 shows an example of the results of observing a bent portion formed by edgewise bending at 50x magnification, showing a case where cracks and necking were observed in the bent portion. Fig. 11 is a diagram explaining the observation points of the bent portion in Figs. 9 and 10. Fig. 12 is a graph showing the relationship between the average length of precipitates and the yield stress in the test samples of Examples 1 to 12 and Comparative Examples 1 to 7. Fig. 13 is a graph showing the relationship between the number density of precipitates and the yield stress in the test samples of Examples 1 to 12 and Comparative Examples 1 to 7.

[0011] The aluminum alloy busbar according to this embodiment will be described in detail below with reference to the drawings. Note that the dimensional proportions in the drawings are exaggerated for the sake of convenience and may differ from the actual proportions.

[0012] The size of battery packs installed in electric vehicles and other vehicles is increasing year by year in order to improve driving range. However, in order to ensure sufficient interior space, it is necessary to suppress the expansion of battery size, and the space for routing electrical wires is also becoming limited. Therefore, it is desirable to reduce the height by using flat bus bars instead of circular cross-section electrical wires.

[0013] Here, in order to route flat bus bars in a limited space inside a battery pack, the bus bar routing path is formed by bending or twisting the bus bar in various directions. When such bus bars are short, their shape can be created by punching and pressing. However, punching and pressing processes result in material waste, which is undesirable from the perspective of carbon neutrality and leads to increased processing costs. Furthermore, when long bus bars are produced by punching and pressing, large molds are required, resulting in significant increases in costs.

[0014] Furthermore, in recent years, as the current capacity of battery packs has increased, the busbar's plate thickness has tended to increase, which requires an increase in the allowable current. However, when the busbar plate thickness is increased, it becomes difficult to process using a press. For these reasons, in order to suppress material loss in long busbars and reduce processing costs, it is desirable to form the wiring path by bending.

[0015] When bending a busbar, the smaller the bending radius (bending R) of the bent portion, the more perpendicular the path can be formed, improving design freedom. However, as mentioned above, the A6101-T6 alloy has poor bending workability and a large bending radius, so busbars made of this alloy have long routing distances and are unsuitable for routing in narrow spaces.

[0016] Furthermore, conventional bus bars are often made from rolled material, and because their shape is created through slitting, punching, and pressing, they have sharp corners, which raise concerns that they may act as points of stress concentration.

[0017] Furthermore, in an automotive environment, busbars are required to have fastening reliability, vibration durability, high-temperature durability, and the like. That is, when fastening busbars with bolts, the busbars must have sufficient strength to ensure electrical connectivity and vibration durability. However, commercially pure aluminum is difficult to use for busbars because it does not have enough strength to ensure electrical connectivity and vibration durability. Therefore, the use of A6101 alloy as an aluminum alloy for busbars has been considered. However, this alloy has poor heat resistance, and there are concerns that its mechanical properties and other physical properties may change due to temperature changes in the automotive environment.

[0018] From this perspective, the aluminum alloy bus bar according to this embodiment has an optimized aluminum alloy composition and further controls the microstructure to form fine needle-like precipitates in the aluminum alloy structure, thereby improving bending workability and electrical connection stability.

[0019] As shown in Fig. 1, the aluminum alloy busbar 1 of this embodiment includes a long flat conductor 10 made of an aluminum alloy. The peripheral edge of the central portion of the flat conductor 10 is covered with an insulating layer 20 having electrical insulation properties. The aluminum alloy busbar 1 has a plurality of bent portions 12. The bent portions 12 include edgewise bent portions 12A that are bent in the width direction of the flat conductor 10 and flatwise bent portions 12B that are bent in the thickness direction of the flat conductor 10.

[0020] The flat conductor 10 in the aluminum alloy busbar 1 has through-holes 11 at both ends thereof, which can be fastened to other fastened members by using, for example, a fastening member. Specifically, when a bolt and a nut are used as the fastening member and a terminal is used as the other fastened member, the flat conductor 10 and the terminal can be fastened and fixed by inserting the threaded portion of the bolt into both the hole 11 of the flat conductor 10 and the hole of the terminal, and then screwing a nut onto the threaded portion.

[0021] The material and thickness of the insulator layer 20 are not particularly limited as long as it can ensure electrical insulation from the flat conductor 10. Examples of resin materials that can be used to form the insulator layer 20 include vinyl chloride, heat-resistant vinyl chloride, cross-linked vinyl chloride, polyethylene, cross-linked polyethylene, foamed polyethylene, cross-linked foamed polyethylene, chlorinated polyethylene, polypropylene, polyamide (nylon), polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene, perfluoroalkoxyalkane, natural rubber, chloroprene rubber, butyl rubber, ethylene propylene rubber, chlorosulfonated polyethylene rubber, and silicone rubber. These materials may be used alone or in combination of two or more.

[0022] The flat conductor 10 of the aluminum alloy busbar 1 is made of an aluminum alloy having a composition containing 0.35 to 0.8 mass % magnesium, 0.3 to 0.7 mass % silicon, and the remainder consisting of aluminum and unavoidable impurities.

[0023] The aluminum used as the base material in the aluminum alloy is preferably pure aluminum with a purity of 99.7% by mass or higher. That is, among the aluminum ingots specified in Japanese Industrial Standard JIS H2102 (Aluminum Ingots), aluminum with a purity of Al99.70 or higher can be preferably used. Specific examples include Al99.70, Al99.94, Al99.97, Al99.98, Al99.99, Al99.990, and Al99.995, each having a purity of 99.7% by mass or higher. In this way, in this embodiment, not only expensive, high-purity aluminum such as Al99.995 can be used as the aluminum ingot, but also affordable aluminum ingots with a purity of 99.7% by mass or higher.

[0024] Magnesium (Mg) is an element that can increase the strength of the flat conductor 10, which is an aluminum alloy plate, while minimizing the decrease in conductivity. Magnesium is preferably contained in the aluminum alloy at 0.35 to 0.8 mass %. Silicon (Si) is an element that can improve the strength of the flat conductor 10 through solid solution strengthening and precipitation dispersion strengthening. Silicon is preferably contained in the aluminum alloy at 0.3 to 0.7 mass %. The aluminum alloy may contain iron, but the iron content is preferably 0.50 mass % or less.

[0025] The aluminum alloy may contain trace amounts of unavoidable impurities. Examples of unavoidable impurities that may be contained in the aluminum alloy include nickel (Ni), rubidium (Rb), tin (Sn), vanadium (V), gallium (Ga), boron (B), sodium (Na), zirconium (Zr), manganese (Mn), lead (Pb), and calcium (Ca). These elements are unavoidably contained to the extent that they do not impair the effects of this embodiment and do not significantly affect the properties of the aluminum alloy of this embodiment. Elements already contained in the aluminum ingot used are also included as unavoidable impurities. The total amount of unavoidable impurities in the aluminum alloy is preferably 0.07% by mass or less, and more preferably 0.05% by mass or less.

[0026] In the aluminum alloy busbar 1 of this embodiment, the aluminum alloy constituting the flat conductor 10 contains a plurality of dispersed Mg—Si-based acicular particles containing magnesium and silicon. In other words, the aluminum alloy contains a high dispersion of Mg—Si-based acicular particles composed of an intermetallic compound containing magnesium and silicon. The high dispersion of these Mg—Si-based acicular particles within the aluminum alloy increases the yield stress of the flat conductor 10, thereby suppressing stress relaxation around the hole 11 even when the hole 11 is fastened with a fastening member (e.g., a bolt and a nut). As a result, conductivity between the flat conductor 10 and the fastening member and between the flat conductor 10 and another fastened member can be improved. Furthermore, the high dispersion of the Mg—Si-based acicular particles increases the yield stress of the flat conductor 10 while maintaining high bending workability. Therefore, even when an edgewise bent portion 12A and a flatwise bent portion 12B are formed in the aluminum alloy busbar 1, cracking and necking (constriction) in the bent portion 12 can be suppressed.

[0027] More specifically, if the busbar's yield stress is insufficient, when the busbar is fastened to another fastened member with a bolt and nut, the bolt and nut will sink into the busbar due to stress relaxation, reducing the fastening force of the bolt and nut. As a result, the bolt loosens and the electrical resistance between the busbar and the other fastened member increases, destabilizing the electrical connection between the busbar and the other fastened member. However, as in this embodiment, by highly dispersing Mg—Si-based acicular particles within the aluminum alloy constituting the flat conductor 10, the yield stress is increased. Therefore, stress relaxation of the flat conductor 10 can be suppressed, maintaining a good electrical connection between the flat conductor 10 and the other fastened member. Furthermore, as described below, by setting the number density of the Mg—Si-based acicular particles dispersed within the aluminum alloy to a predetermined value or less, the bending workability of the flat conductor 10 can be improved, and cracking and necking at the bent portion 12 of the flat conductor 10 can be suppressed.

[0028] As described above, the aluminum alloy constituting the flat conductor 10 contains 0.35 to 0.8 mass% magnesium and 0.3 to 0.7 mass% silicon. This composition range will be explained in more detail. JIS-standard 6000 series (Al-Mg-Si) aluminum alloys are aging precipitation alloys, and their strength is achieved by the formation of compounds between magnesium and silicon. The strength of 6000 series aluminum alloys can be increased by increasing the amounts of magnesium and silicon added. Furthermore, excess magnesium or silicon added from the portion that produces Mg-Si-based precipitates can improve workability by dissolving in the aluminum matrix. However, as the amounts of magnesium and silicon added simultaneously increase, the amount of Mg-Si-based precipitates increases, resulting in a decrease in bending workability. To prevent this, it is necessary to limit the amounts of magnesium and silicon added.

[0029] The composition range of the A6101 alloy is specified in JIS H4000 (Aluminum and Aluminum Alloy Sheet and Strip), with a magnesium content of 0.35 to 0.80 mass% and a silicon content of 0.30 to 0.70 mass%. The aluminum alloy constituting the flat conductor 10 according to this embodiment was investigated within this composition range. As mentioned above, if the amount of magnesium and silicon added is reduced, the amount of Mg-Si precipitates produced decreases, resulting in a decrease in yield stress, while if the amount is increased too much, bending workability decreases. For this reason, in order to achieve the effects of this embodiment, it is desirable to control the composition within the above range.

[0030] The Mg—Si-based acicular particles dispersed within the aluminum alloy constituting the flat conductor 10 preferably have an average length of 67.1 nm to 378.4 nm, more preferably 291.3 nm to 378.4 nm. By keeping the average length of the Mg—Si-based acicular particles within this range, stress relaxation of the flat conductor 10 can be suppressed, thereby improving the stability of the electrical connection with other fastened components. Furthermore, the flat conductor 10 maintains high bending workability, enabling edgewise bending, flatwise bending, and twist bending. The average length of the Mg—Si-based acicular particles can be determined by observing a sample of the aluminum alloy constituting the flat conductor 10 with a transmission electron microscope and measuring the lengths of multiple acicular particles. In this specification, the length of the Mg—Si-based acicular particles refers to the longest distance between two different points on the outline of the acicular particle when the aluminum alloy is observed under a microscope.

[0031] The aspect ratio and diameter of the Mg—Si-based acicular particles are not particularly limited, but the aspect ratio can be, for example, 4.4 to 68.2. The diameter of the Mg—Si-based acicular particles is the diameter in the direction perpendicular to the longitudinal direction of the acicular particles, and can be determined by observation with a transmission electron microscope.

[0032] The number density of Mg—Si acicular particles in the aluminum alloy constituting the flat conductor 10 is 4.5×10 ２０ / m ３ ~6.8 x 10 ２１ / m ３ Preferably, it is 4.5 × 10 ２０ / m ３ ~9.1 x 10 ２０ / m ３ It is more preferable that the Mg—Si acicular particles are 4.5×10 ２０ / m ３ High dispersion of the Mg—Si acicular particles increases the yield stress, suppressing stress relaxation of the flat conductor 10 and maintaining good electrical connection between the flat conductor 10 and other fastened members. ２１ / m ３In the following cases, deterioration in the bending processability of the flat conductor 10 can be suppressed, and therefore edgewise bending, flatwise bending, and twist bending can be performed.

[0033] The number density of Mg—Si acicular particles in an aluminum alloy can be determined as follows: First, an aluminum alloy sample is observed under a transmission electron microscope, and the number of acicular particles present in a given area is determined to determine the areal density (number / m ２ ) is calculated. Then, the surface density is multiplied by the thickness of the sample to obtain the number density (number / m ３ ) can be calculated.

[0034] The flat conductor 10 preferably has an allowable bending strain ε, expressed by the following formula 1, of more than 0.27. In Equation 1, b is the plate width (mm) of the flat conductor 10, and R ｍｉｎ is the minimum bending radius (mm) when the flat conductor 10 having the specified width is bent edgewise. The width b of the flat conductor 10 is the width when observing a cross section perpendicular to the longitudinal direction of the flat conductor 10, as shown in FIG. 2. ｍｉｎ is the minimum value of the radius R from the bent position to the center of the bend when the flat conductor 10 having the plate width is bent edgewise at room temperature, as shown in FIG.

[0035] Equation 1 takes into account the difference between theoretical bending strain and measured bending strain when the flat conductor 10 is bent edgewise. Here, "bending strain" refers to the strain applied to the outermost surface of the outer curved surface portion (external R portion) when the flat conductor 10 is bent edgewise. The theoretical bending strain ε' can be calculated using the following equation 2. In Equation 2, b is the plate width (mm) of the flat conductor 10, and R is the bending radius (mm) when the flat conductor 10 of that plate width is bent edgewise. The measured bending strain can be calculated from the amount of change in the lattice by edgewise bending the flat conductor 10 marked with a lattice marker, as shown in Figures 4 and 5.

[0036] In the flat conductor 10, when the allowable bending strain ε expressed by the following mathematical formula 1 exceeds 0.27, the bending workability of the flat conductor 10 is good. Therefore, even if the flat conductor 10 is bent edgewise, it is possible to suppress the occurrence of cracking and necking in the bent portion 12. In contrast, for example, a flat conductor made of an A6101-T6 alloy has too high strength and poor bending workability, so the allowable bending strain ε is 0.27 or less.

[0037] The flat conductor 10 preferably has a yield stress of 55 to 201 MPa at room temperature. A yield stress of 55 MPa or more suppresses stress relaxation in the flat conductor 10, thereby maintaining a good electrical connection between the flat conductor 10 and other fastened components. Furthermore, a yield stress of 201 MPa or less improves the bending processability of the flat conductor 10, thereby suppressing cracking and necking in the bent portion 12. The yield stress of the flat conductor 10 can be measured in accordance with JIS Z2241 (Method for tensile testing of metallic materials).

[0038] A more detailed description will be given of the numerical range of the yield stress of the flat conductor 10. The bus bars arranged in the battery pack of a vehicle are used to connect a junction box (J / B), a battery stack, etc., and methods for connecting these to the bus bars include welding, solid-state welding, bolt fastening, etc.

[0039] When considering a connection using bolt tightening, the axial force of the bolt exerts pressure on the flange (head) to hold down the bus bar. This axial force of the bolt can be calculated using the following formula 3: [Formula 3] F = T / dK In formula 3, F is the axial force of the bolt (N), T is the tightening torque (Nm), d is the nominal diameter of the threaded portion (m), and K is the torque coefficient. This axial force F of the bolt is calculated by multiplying the area S (mm ２) is the pressure acting on the flange seating surface. The area of ​​the seating surface is the area where the bolt flange actually contacts the busbar. F / S (MPa) is the lower limit of the yield stress required to prevent the busbar from collapsing.

[0040] Typically, M6 bolts are often used to fasten busbars to other components. For example, assuming a flange diameter of 13 mm and a torque coefficient of 0.2, a fastening torque of 5 to 10 N / m results in a bearing surface pressure of approximately 42 to 83 MPa. Because contact resistance varies depending on the busbar's material and surface properties, the fastening torque is not constant. However, taking into account factors such as safety, it is preferable for the busbar's yield stress to be at least 100 MPa. While the A6101 alloy is specified in various standards, including JIS, ASTM, and EN, it must have a yield stress of at least 55 MPa, as specified in ASTM B317 / B317M for A6101-T64. Therefore, the yield stress of the flat conductor 10 according to this embodiment is preferably 55 MPa or greater. As will be shown in Examples 6, 10, and 12 described later, when the yield stress is below 118 MPa, the allowable bending strain tends to decrease slightly, so it is more preferable that the yield stress of the flat conductor 10 is 120 MPa or more.

[0041] Thus, the yield stress of the flat conductor 10 at room temperature is preferably 55 to 201 MPa, more preferably 100 to 201 MPa, and particularly preferably 120 to 201 MPa.

[0042] As described above, the aluminum alloy busbar 1 of this embodiment is a conductive member connected to a junction box (J / B), a battery stack, etc., and therefore, it is preferable that its conductivity be as high as possible. Therefore, the conductivity of the flat conductor 10 is preferably 55% IACS or higher. The conductivity of the flat conductor 10 can be measured in accordance with JIS H0505 (Method for measuring volume resistivity and conductivity of non-ferrous metal materials).

[0043] The flat conductor 10 preferably has an n-value of 0.07 or greater, more preferably 0.15 or greater, measured in accordance with JIS Z2241 (Method for Tensile Testing of Metallic Materials). The n-value is an index of the degree of work hardening of a metallic material, with values ​​closer to 1 indicating a greater degree of work hardening. When the flat conductor 10 has an n-value of 0.07 or greater, the ratio of the hardness of the bent portion 12 after bending to the hardness of the bent portion 12 before bending ([Hardness of bent portion after bending] / [Hardness of bent portion before bending]) exceeds 1, thereby suppressing a decrease in the strength of the bent portion 12. In other words, when the flat conductor 10 is bent, if the n-value is 0.07 or greater, the bent portion 12 undergoes work hardening and exhibits a high hardness value. Specifically, the ratio of the hardness of the bent portion 12 after bending to the hardness of the bent portion 12 before bending exceeds 1.0, reaching approximately 1.3. Therefore, by having the n-value of the flat conductor 10 be 0.07 or greater, a decrease in the strength of the bent portion 12 can be suppressed.

[0044] As described above, conventional busbars are often made from rolled material, and in this case, the busbar shape is formed by slitting, punching, and pressing. As a result, the resulting busbar has sharp corners, which may act as starting points for stress concentration. Therefore, in the aluminum alloy busbar 1 of this embodiment, it is preferable that at least the corners 13 of the bent portion 12 of the flat conductor 10 are chamfered. It is also preferable that the entire corners 13 of the flat conductor 10 along the longitudinal direction are chamfered.

[0045] FIG. 6 schematically illustrates the cross-sectional shapes of the flat conductor 10 of this embodiment, with a square edge where the corners 13 are not chamfered, and with a round edge where the corners 13 are chamfered. FIG. 6 also shows photographs of the appearance of the square edge and the round edge. As shown in FIG. 6 , the flat conductor 10 may have square edges with approximately right angles, without chamfering the corners 13. However, in the case of square edges, stress may be concentrated at the corners 13 when the flat conductor 10 is bent. Therefore, it is preferable to chamfer the corners 13 to prevent the corners 13 from acting as a starting point for stress concentration. By chamfering the corners 13 to form a rounded, curved surface, the corners 13 are less likely to act as a starting point for stress concentration. Therefore, cracking can be further prevented when the flat conductor 10 is bent.

[0046] Next, a method for manufacturing the aluminum alloy busbar 1 according to this embodiment will be described. In the manufacturing method according to this embodiment, first, aluminum, magnesium, and silicon are melted to have the above-mentioned composition and cast to produce a cast billet. Then, the cast billet is subjected to a homogenization treatment. The homogenization treatment conditions can be a temperature of 500 to 560°C for 4 to 10 hours. Alternatively, aluminum, magnesium, and silicon are melted to have the above-mentioned composition and continuously cast to produce a cast rod, and then the cast rod is rolled to produce a wire rod.

[0047] Next, the homogenized cast billet or the wire rod obtained as described above is extruded using an extrusion molding machine to obtain an extruded material having a desired cross-sectional shape. The extrusion molding can be performed by hot extrusion, and the temperature during extrusion can be, for example, 350 to 500°C. The extrusion molding machine is not particularly limited, and for example, a conform extruder can be used.

[0048] Here, when extrusion molding, a die (metal mold) processed to obtain a desired cross-sectional shape can be used to obtain an extruded material with any cross-sectional shape. For example, when chamfering the corners 13 of the flat conductor 10, the portion of the cavity of the die corresponding to the corners can be curved to obtain an extruded material with chamfered corners.

[0049] The extrudate extruded from the extruder is then cooled with water, hot water, or cooling oil, or by air cooling. The cooled extrudate is wound up to a desired size. Specifically, the cooled extrudate may be wound into a coil around a bobbin, or may be wound into a hoop without using a bobbin.

[0050] The wound extruded material is then subjected to aging heat treatment using a heating furnace. The heating furnace is not particularly limited, and an electric furnace, for example, can be used. The aging heat treatment conditions are those that allow Mg—Si-based acicular particles of the above-mentioned average length and number density to be formed inside the aluminum alloy. Specifically, the aging heat treatment conditions can be, for example, a temperature of 225°C or higher for 2 hours or more, and preferably a temperature of 225 to 300°C for 2 to 24 hours. However, it is preferable to appropriately adjust the heating temperature and time so that Mg—Si-based acicular particles of the desired average length and number density are formed.

[0051] Thereafter, the aged material that has been subjected to the aging heat treatment is bent into a desired shape at room temperature. The bending can be performed using, for example, a forming machine.

[0052] By this process, an aluminum alloy bus bar 1 is obtained, which is made of a flat conductor 10 having at least one bent portion 12 selected from the group consisting of an edgewise bent portion 12A, a flatwise bent portion 12B, and a twisted bent portion formed by applying a twist.

[0053] In the manufacturing method of the aluminum alloy busbar 1 according to this embodiment, it is not necessary to perform a solution treatment before the aging heat treatment. In other words, a manufacturing method equivalent to the T5 treatment can be used to obtain a flat conductor 10 having Mg—Si-based acicular particles with the above-mentioned average length and number density. However, if a flat conductor 10 having Mg—Si-based acicular particles with the above-mentioned average length and number density can be obtained, a solution treatment may be performed before the aging heat treatment.

[0054] The method for coating the peripheral edge of the central portion of the flat conductor 10 with the electrically insulating insulator layer 20 is not particularly limited, and the insulator layer 20 can be formed by extrusion coating, for example. For example, the insulator layer 20 may be formed on an aged material by extrusion coating, and then the bent portion 12 may be formed by bending the material.

[0055] As described above, the aluminum alloy busbar 1 according to the first aspect of this embodiment includes a flat conductor 10 made of an aluminum alloy having a composition containing 0.35 to 0.8 mass % magnesium, 0.3 to 0.7 mass % silicon, and the remainder consisting of aluminum and inevitable impurities. A plurality of Mg—Si-based acicular particles 16 containing magnesium and silicon are dispersed within the aluminum alloy. The average length of the Mg—Si-based acicular particles 16 is 67.1 nm to 378.4 nm, and the number density of the Mg—Si-based acicular particles 16 in the aluminum alloy is 4.5×10 ２０ / m ３ ~6.8 x 10 ２１ / m ３ is.

[0056] The flat conductor 10 of the aluminum alloy busbar 1 is made of an aluminum alloy containing a predetermined amount of magnesium and silicon. Furthermore, Mg—Si-based acicular particles 16 having a predetermined length are dispersed at a predetermined density within the aluminum alloy. This configuration increases the yield stress of the flat conductor 10, thereby suppressing stress relaxation around the hole 11 even when fastened with a fastening member, thereby maintaining high conductivity between the flat conductor 10 and the fastening member and between the flat conductor 10 and other fastened members. Furthermore, the high dispersion of the Mg—Si-based acicular particles increases the yield stress of the flat conductor 10 while also improving bending workability. Therefore, even when a bent portion 12 is formed in the flat conductor 10, cracking and necking at the bent portion 12 can be suppressed.

[0057] In the aluminum alloy busbar 1 according to the second aspect, the flat conductor 10 may have an allowable bending strain ε of more than 0.27, as expressed by Equation 1. When the allowable bending strain ε of the flat conductor 10 exceeds 0.27, the bending workability of the flat conductor 10 is improved, and therefore, even when edgewise bending is performed, cracking and necking of the bent portion 12 can be suppressed.

[0058] In the aluminum alloy busbar 1 according to the third embodiment, the flat conductor 10 may have at least one bent portion 12. Since the flat conductor 10 has good bending workability, it is possible to easily form at least one bent portion 12 selected from the group consisting of an edgewise bent portion 12A, a flatwise bent portion 12B, and a twist bent portion in the flat conductor 10.

[0059] In the aluminum alloy busbar 1 according to the fourth aspect, the yield stress of the flat conductor 10 at room temperature measured in accordance with JIS Z2244 may be 55 to 201 MPa. When the yield stress of the flat conductor 10 is 55 MPa or more, stress relaxation of the flat conductor 10 can be suppressed, thereby maintaining good electrical connections between the flat conductor 10 and the fastening member and between the flat conductor 10 and other fastened members. Furthermore, when the yield stress of the flat conductor 10 is 201 MPa or less, deterioration in the bending workability of the flat conductor 10 can be suppressed, thereby facilitating the formation of the bent portion 12.

[0060] In the aluminum alloy busbar 1 according to the fifth aspect, at least the corners 13 of the bent portion 12 of the flat conductor 10 may be chamfered. By chamfering the corners 13 of the flat conductor 10, the corners 13 are less likely to act as starting points for stress concentration when the flat conductor 10 is bent, and therefore the occurrence of cracks can be further suppressed.

[0061] The aluminum alloy busbar 1 according to the sixth aspect may be used as a wiring member in a vehicle. The wiring member is a member that is wired in, for example, a vehicle and electrically connects various devices. The aluminum alloy busbar 1 has good bending workability and stable electrical connection, and therefore can be suitably used, for example, as a conductive member that is wired inside a battery pack mounted in a vehicle.

[0062] Hereinafter, the present embodiment will be described in more detail with reference to examples and comparative examples, but the present embodiment is not limited to these examples.

[0063] [Preparation of Test Samples] (Example 1) First, aluminum, silicon, and magnesium were weighed out in the proportions shown in Table 1. The weighed aluminum, silicon, and magnesium were then melted to prepare a molten metal, which was then poured into a mold to obtain an ingot. The ingot was then subjected to a homogenization treatment to prepare a cast billet. The homogenization treatment was carried out at 540°C for 4 hours, with a heating rate of 40°C / h.

[0064] Next, the obtained cast billet was hot extruded at 500°C and then water-cooled to obtain a long, flat extruded material. The obtained extruded material was then coiled, and the wound extruded material was subjected to aging heat treatment using a heating furnace. The aging heat treatment was performed at 225°C for 2 hours. In this manner, a long test sample having a plate thickness t of 2.0 mm and a plate width b of 15.0 mm was obtained. Note that in this example, no solution treatment was performed before the aging heat treatment.

[0065] Examples 2 to 6 Test samples for each example were obtained in the same manner as in Example 1, except that the temperature and time of the aging heat treatment for the extruded material were changed as shown in Table 1.

[0066] (Examples 7 to 12) Test samples for each example were obtained using the same process as in Example 1, except that the proportions of each element were changed as shown in Table 1, and the temperature and time of the aging heat treatment for the extruded material were changed as shown in Table 1. However, in Example 7, the die was adjusted so that the test sample had a thickness t of 5.0 mm and a width b of 24.0 mm.

[0067] (Comparative Example 1 and Comparative Examples 4 to 7) Test samples for each example were obtained using the same process as in Example 1, except that the proportions of each element were changed as shown in Table 1, and the temperature and time of the aging heat treatment on the extruded material were changed as shown in Table 1.

[0068] (Comparative Example 2) First, aluminum, silicon, and magnesium were weighed in the proportions shown in Table 1, and then an extruded material was obtained by the same process as in Example 1. Next, the obtained extruded material was wound up, and the wound extruded material was subjected to solution treatment using a heating furnace. The solution treatment was performed at 540°C for 2 hours. Then, after the solution treatment, an aging heat treatment was performed using a heating furnace. The aging heat treatment was performed at 225°C for 8 hours. In this way, a test sample of this example was obtained. Note that the manufacturing method of Comparative Example 2 is a method equivalent to T6 treatment.

[0069] Comparative Example 3 Test samples of this example were obtained in the same manner as in Comparative Example 2, except that the aging heat treatment time was changed as shown in Table 1.

[0070]

[0071] [Evaluation of Test Samples] (Mechanical Properties) The hardness, yield stress, and n-value of each test sample were measured at room temperature. The hardness was measured in accordance with JIS Z2244 (Vickers hardness test), and the yield stress and n-value were measured in accordance with JIS Z2241 (Method for tensile testing of metallic materials). The measurement results of each test sample are summarized in Table 2.

[0072] (Conductivity) The conductivity of the test sample of each example was measured in accordance with JIS H0505 (Method for measuring volume resistivity and conductivity of non-ferrous metal materials). The measurement results of the test sample of each example are summarized in Table 2.

[0073] (Mg—Si-based precipitates) The test samples of each example were observed with a transmission electron microscope to measure the average length and number density of the precipitates. Specifically, test pieces with a diameter of approximately 3 mm and a thickness of 100 μm or less were prepared from the test samples of each example, and then thinned using a twin-jet electrolytic polishing device. The thinned test pieces were then observed with a transmission electron microscope.

[0074] Figure 7 shows the results of observing a test piece prepared from the test sample of Example 1 at 200,000x magnification. As shown in Figure 7, in Example 1, it can be seen that a plurality of acicular particles 16 are dispersed inside the aluminum matrix 15. The length of the acicular particle 16A was then calculated from the longest distance between two different points on the contour of the acicular particle 16A, and the average length was calculated from the lengths of the plurality of acicular particles 16A.

[0075] Note that, because the acicular particles 16A are arranged along the plane of the paper in Figure 7, they are observed as acicular precipitates in Figure 7. However, because the long axis of the acicular particles 16B crosses the plane of the paper in Figure 7, they are observed as dots rather than needles in Figure 7. That is, for example, as shown in Figure 8, when the acicular particles 16B are arranged approximately perpendicular to the acicular particles 16A, the acicular particles 16B are observed as dots in Figure 7. Therefore, the number density of the precipitates was calculated by counting the number of acicular particles 16A and 16B present in the observation field to determine the areal density, and then multiplying this areal density by the thickness of the test piece. The average length and number density of the precipitates in the test samples of each example are summarized in Table 2.

[0076] (Bending workability) The minimum bending radius R of the test sample in each example ｍｉｎ The minimum bending radius R ｍｉｎ After edgewise bending at room temperature, the bent portion was observed with an optical microscope, and the smallest bending radius R at which no macro defects such as cracks or necking occurred was defined as the minimum bending radius. Therefore, even if the bent portion did not break, if defects such as cracks or necking occurred, the bending radius at that time was defined as the minimum bending radius R. ｍｉｎ I didn't.

[0077] 9 and 10 show an example of the results of observing a bent portion formed by edgewise bending with an optical microscope at a magnification of 50 times. As shown in FIG. 11, FIGS. 9 and 10 also show the results of observing the outer curved surface portion (outer R portion) of the bent portion. FIG. 9 shows a case where no cracks or necking are observed on the outer curved surface portion of the bent portion. In contrast, FIG. 10 shows a case where cracks and necking are observed on the outer curved surface portion of the bent portion. As shown in FIG. 9, the smallest bend radius R when no macro defects such as cracks or necking occur on the bent portion is referred to as the minimum bend radius R. ｍｉｎ It was decided.

[0078] Furthermore, the hardness of the bent portion of each test sample when bent at room temperature with the minimum bending radius shown in Table 2 was measured in accordance with JIS Z2244. The hardness ratio was calculated from the hardness of the bent portion after bending to the hardness of the bent portion before bending ([hardness of bent portion after bending] / [hardness of bent portion before bending]). Furthermore, the plate width (mm) of the test sample and the minimum bending radius R when the test sample of that plate width was bent edgewise at room temperature were also calculated. ｍｉｎ The allowable bending strain ε was calculated from the hardness (mm) according to Equation 1. The hardness ratio and allowable bending strain ε of each test sample are shown in Table 2.

[0079] Next, the test samples of each example were bent edgewise to a bend radius of 30 mm, and the occurrence of defects in the bent portion was observed. Specifically, the test samples of each example were bent edgewise at room temperature to a bend radius of 30 mm, and then the outer curved surface portion (external R portion) of the bent portion was observed as shown in FIG. 11 . As shown in FIG. 9 , cases in which no macro-defects such as cracks or necking occurred in the outer curved surface portion of the bent portion were evaluated as "good." In contrast, cases in which cracks or necking were observed in the outer curved surface portion of the bent portion were evaluated as "bad." The evaluation results for each test sample are summarized in Table 2.

[0080]

[0081] As shown in Table 2, in the test samples of Examples 1 to 12, the average length of the Mg—Si-based precipitates was 67.1 nm to 378.4 nm, and the number density of the Mg—Si-based precipitates was 4.5×10 ２０ / m ３ ~6.8 x 10 ２１ / m ３ In contrast, in the test samples of Comparative Examples 1 to 7, the average length of the Mg—Si-based precipitates was less than 67.1 nm, and the number density of the Mg—Si-based precipitates was 6.8×10 ２１ / m ３ The test samples of Examples 1 to 12 had a yield stress of 100 to 201 MPa, but the test samples of Comparative Examples 1 to 7 had a yield stress of over 201 MPa, except for Comparative Example 3. As a result, the test samples of Examples 1 to 12 had a minimum bending radius R ｍｉｎ The minimum bending radius R ｍｉｎ was 33 mm or more.

[0082] As described above, when the average length and number density of the Mg—Si-based precipitates are within the above ranges, the yield stress of the aluminum alloy can be increased while suppressing the occurrence of defects in the bent portion, thereby improving the bending workability and the stability of the electrical connection.

[0083] Here, FIG. 12 shows the relationship between the average length of precipitates and yield stress in the test samples of Examples 1 to 12 and Comparative Examples 1 to 7. Furthermore, FIG. 13 shows the relationship between the number density of precipitates and yield stress in the test samples of Examples 1 to 12 and Comparative Examples 1 to 7. As shown in FIG. 12, it can be seen that the yield stress tends to decrease as the average length of precipitates increases. In contrast, as shown in FIG. 13, it can be seen that the yield stress tends to increase as the number density of precipitates increases. Therefore, it can be seen that an aluminum alloy having a desired yield stress can be obtained by adjusting the average length and number density of Mg—Si-based precipitates.

[0084] Furthermore, as shown in Table 2, the n values ​​of the test samples of Examples 1 to 12 were 0.07 or more, while the n values ​​of the test samples of Comparative Examples 1 to 7 were 0.06 or less. Furthermore, the test samples of Examples 1 to 12 had a hardness ratio ([hardness of bent portion after bending] / [hardness of bent portion before bending]) of 1.0 or more, and all except Example 7 had a hardness ratio of 1.1 or more. Therefore, it can be seen that when the average length and number density of Mg—Si-based precipitates are within the above ranges, a decrease in the strength of the bent portion 12 can be suppressed.

[0085] Furthermore, as shown in Table 2, the allowable bending strain of the test samples of Examples 1 to 12 exceeded 0.27 and was 0.30 or more, while the allowable bending strain of the test samples of Comparative Examples 1 to 7 was 0.27 or less. Therefore, it can be seen that by increasing the allowable bending strain to more than 0.27, the bending workability of the aluminum alloy is improved, and therefore the occurrence of defects in the bent portion can be suppressed.

[0086] Although the present embodiment has been described above, the present embodiment is not limited to this, and various modifications are possible within the scope of the gist of the present embodiment.

[0087] The entire contents of Japanese Patent Application No. 2023-039057 (filing date: March 13, 2023) are incorporated herein by reference.

[0088] REFERENCE SIGNS LIST 1 aluminum alloy bus bar 10 flat conductor 12 bent portion 16 Mg—Si acicular particles

Claims

1. The flat conductor is made of an aluminum alloy containing 0.35 to 0.8 mass % of magnesium and 0.3 to 0.7 mass % of silicon, with the remainder being aluminum and unavoidable impurities; a plurality of Mg—Si-based acicular particles containing magnesium and silicon are dispersed inside the aluminum alloy; The average length of the Mg—Si acicular particles is 67.1 nm to 378.4 nm, and the number density of the Mg—Si acicular particles in the aluminum alloy is 4.5×10 ２０ / m ３ ~6.8 x 10 ２１ / m ３ Aluminum alloy busbar.

2. 2. The aluminum alloy bus bar according to claim 1, wherein the flat conductor has an allowable bending strain ε, expressed by the following formula 1, of greater than 0.27: [Equation 1] (b is the width of the flat conductor (mm), R ｍｉｎ is the minimum bending radius (mm) when a flat conductor of that width is bent edgewise.

3. The aluminum alloy bus bar according to claim 1 or 2, wherein the flat conductor has at least one bent portion.

4. 3. The aluminum alloy bus bar according to claim 1, wherein the yield stress of the flat conductor at room temperature measured in accordance with JIS Z2244 is 55 to 201 MPa.

5. The aluminum alloy bus bar according to claim 3 , wherein at least corners of the flat conductor at the bent portion are chamfered.

6. The aluminum alloy bus bar according to claim 1 or 2, which is used as a wiring member for a vehicle.

Images