Aluminum alloy bus bar

Abstract

An aluminum alloy bus bar (1) includes a flat electrical conductor (10) made of an aluminum alloy containing 0.35-0.8% by mass of magnesium and 0.3-0.7% by mass of silicon, with the balance being aluminum and unavoidable impurities. A plurality of Mg-Si needle-like particles (16) containing magnesium and silicon are dispersed in the aluminum alloy. The average length of the Mg-Si-based needle-like particles (16) is from 67.1 nm to 378.4 nm, and the number density of the Mg-Si-based needle-like particles (16) in the aluminum alloy is from 4.5 * 1020 / m < 3 > to 6.8 * 1021 / m < 3 >.

Description

Technical Field

[0001] The invention relates to an aluminum alloy busbar. Background Art

[0002] Aluminum is a lightweight metal with excellent electrical conductivity and is relatively inexpensive, making it commonly used in busbars, wires, electrodes, and the like. Industrially pure aluminum, such as A1060 and A1070 alloys, and A6101 alloy, standardized by the Japanese Industrial Standards (JIS), are commonly known as aluminum alloys for use as conductive components. The JIS specifies that the A1060 alloy has a conductivity of 61% IACS. When the A1060 alloy is insufficiently strong, the A6101 alloy, which offers a conductivity of 55% IACS, is often used.

[0003] The A6101 alloy undergoes a T6 treatment and exhibits standard mechanical properties, such as a tensile strength of 220 MPa, a yield stress of 195 MPa, and an elongation of 15% (1.6 mm thick, 50 mm gauge length). Furthermore, the A6101 alloy has fine magnesium-silicon precipitates in the aluminum matrix and achieves high strength through the Orowan mechanism. However, when compared to commercially pure aluminum, the A6101-T6 alloy exhibits considerably low workability in post-processing such as stamping and bending.

[0004] Patent Document 1 discloses a method for manufacturing an aluminum alloy busbar. Specifically, the method involves edge-bending an aluminum alloy flat wire to obtain a predetermined shape. The method is characterized in that during edge bending, the workpiece is heated to a temperature between 100°C and 250°C for no more than 5 minutes, followed by edge bending. The aluminum alloy flat wire is made of a T6-tempered aluminum alloy containing 0.3-0.9% Mg, 0.2-1.2% Si, 0.2% or less Cu, and 0.5% or less Fe, with the remainder being a chemical composition consisting of aluminum and unavoidable impurities. Furthermore, the ratio (A / B) between the Vickers hardness A of the heated portion and the Vickers hardness B of the unheated portion is 0.8 or greater. This manufacturing method improves the edge bending workability of the bent portion while preventing a decrease in strength.

[0005] Reference List

[0006] Patent Literature

[0007] Patent Document 1: Japanese Unexamined Patent Application Publication No.: 2018-206663 Summary of the Invention

[0008] However, in Patent Document 1, when edge bending is performed, the material quality of the processed portion changes due to the heating of the processed portion, resulting in a strength difference between the heated portion and the non-heated portion. In addition, there is a problem of increased manufacturing costs due to the need to heat the processed portion.

[0009] The present invention has been made in view of these problems in the conventional technology. An object of the present invention is to provide an aluminum alloy bus bar having improved bending workability and electrical connection stability by controlling the structural state of the material.

[0010] An aluminum alloy busbar according to an embodiment of the present invention includes a flat electrical conductor 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 consisting of aluminum and unavoidable impurities. A plurality of Mg-Si-based needle-shaped particles containing magnesium and silicon are dispersed in the aluminum alloy. The average length of the Mg-Si-based needle-shaped particles is 67.1 nm to 378.4 nm, and the number density of the Mg-Si-based needle-shaped particles in the aluminum alloy is 4.5×10 20 / m 3 to 6.8×10 21 / m 3 .

[0011] According to the present invention, it is possible to provide an aluminum alloy bus bar having improved bending workability and electrical connection stability by controlling the structural state of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] [ Figure 1 ] Figure 1 is a perspective view schematically showing an example of the aluminum alloy bus bar according to the present embodiment.

[0013] [ Figure 2 ] Figure 2 is a schematic cross-sectional view showing an example of a cross section of a flat electric conductor in an aluminum alloy bus bar.

[0014] [ Figure 3 ] Figure 3 Schematic diagram for explaining the bending radius R in the edge bending portion of a flat electrical conductor.

[0015] [ Figure 4 ] Figure 4 is a photograph showing a flat electrical conductor with grid markings before the bending process.

[0016] [ Figure 5 ] Figure 5 is a photograph showing a flat electrical conductor with grid markings after edge bending processing.

[0017] [ Figure 6 ] Figure 6Schematic diagrams showing cross-sectional shapes of square edges and round edges of the flat electric conductor according to the present embodiment and photographs showing the appearance.

[0018] [ Figure 7 ] Figure 7 FIG1 is a photograph obtained by a transmission electron microscope, showing the observation result of the test sample of Example 1 at a magnification of 200,000.

[0019] [ Figure 8 ] Figure 8 Schematic diagram showing an example of the dispersion state of needle-shaped particles in an aluminum alloy.

[0020] [ Figure 9 ] Figure 9 An example of the observation result of a bent portion formed by edge bending at a magnification of 50 is shown, and no cracking or necking is observed in the bent portion.

[0021] [ Figure 10 ] Figure 10 An example of the observation result of a bent portion formed by edge bending at a magnification of 50 is shown, and cracks and necking are observed in the bent portion.

[0022] [ Figure 11 ] Figure 11 Is used to illustrate Figure 9 and Figure 10 Illustration of the observation site of the curved portion in FIG.

[0023] [ Figure 12 ] Figure 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.

[0024] [ Figure 13 ] Figure 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.

[0025] Reference Mark List

[0026] 1 Aluminum alloy busbar

[0027] 10 Flat electrical conductors

[0028] 12 Bend

[0029] 16Mg-Si needle-shaped particles DETAILED DESCRIPTION

[0030] Hereinafter, the aluminum alloy bus bar according to the present embodiment will be described in detail with reference to the accompanying drawings. For the sake of convenience of explanation, the dimensional ratios in the drawings are exaggerated and may be different from the actual ratios.

[0031] The size of battery packs installed in electric vehicles and other vehicles tends to increase year by year to improve driving range. However, to ensure interior space within the vehicle, it is necessary to prevent the battery size from increasing. Furthermore, the space for wiring is also limited. Therefore, it is desirable to reduce the height by using flat busbars instead of round wires.

[0032] The busbars are bent or twisted in various directions to form a busbar routing path inside the battery pack, so that the busbars are arranged in a limited space. When the busbars are short, they can be formed by stamping and pressing. However, stamping and pressing result in material loss, which is undesirable from a carbon neutrality perspective and also leads to an increase in processing costs. In addition, when long busbars are manufactured by stamping and pressing, large molds are required, which greatly increases costs.

[0033] Furthermore, in recent years, busbar thickness has tended to increase as the allowable current of battery packs increases, requiring greater busbar current capacity. However, as busbar thickness increases, pressing becomes more difficult. Therefore, it is desirable to form routing paths through bending to minimize material loss and lower processing costs for long busbars.

[0034] When bending a busbar, the smaller the bend radius (Bend R) of the bent portion, the closer to a right angle the path can be formed, and the greater the degree of design freedom. However, as mentioned above, the A6101-T6 alloy has poor bendability and a large bend radius. Therefore, busbars made of this alloy have long routing distances and are not suitable for routing in narrow spaces.

[0035] Furthermore, conventional bus bars generally use rolled materials. However, since bus bars are formed through slitting, punching, and pressing, there is a concern that sharp corners may serve as starting points for stress concentration.

[0036] In addition, in the automotive environment, busbars are required to have fastening reliability, vibration durability and high-temperature durability. In other words, the busbars fastened by bolts need to have sufficient strength to ensure electrical connectivity and vibration durability. However, the strength of industrial pure aluminum is not enough to ensure electrical connectivity and vibration durability, so it is difficult to apply it to busbars. Therefore, the use of A6101 alloy as an aluminum alloy for busbars has been considered. However, the heat resistance of this alloy is poor, and there are concerns that the mechanical properties and other physical properties may change due to temperature changes in the automotive environment.

[0037] From this viewpoint, the aluminum alloy bus bar according to the present embodiment improves bending workability and electrical connection stability by optimizing the composition of the aluminum alloy and controlling the microstructure to form fine needle-shaped precipitates in the aluminum alloy structure.

[0038] like Figure 1 As shown, the aluminum alloy busbar 1 of this embodiment includes a long flat electrical conductor 10 made of an aluminum alloy. The central portion of the flat electrical conductor 10 is covered with an electrically insulating insulator layer 20. The aluminum alloy busbar 1 has multiple bent portions 12. These include an edge bent portion 12A that curves in the width direction of the flat electrical conductor 10 and a flat bent portion 12B that curves in the thickness direction of the flat electrical conductor 10.

[0039] Holes 11, which are through-holes, are provided at both ends of the flat conductor 10 of the aluminum alloy busbar 1 and can be fastened to other fastened components using, for example, fastening members. Specifically, when bolts and nuts are used as fastening members and terminals are used as other fastened components, the flat conductor 10 and the terminal can be fastened and fixed by inserting the screw portion of the bolt into both the hole 11 of the flat conductor 10 and the hole of the terminal and then screwing the nut onto the screw portion.

[0040] The material and thickness of the insulating layer 20 are not particularly limited as long as electrical insulation properties relative to the flat electrical conductor 10 can be ensured. For example, 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 can be used as the resin material forming the insulating layer 20. One of these materials may be used alone, or two or more of these materials may be used in combination.

[0041] The flat electric conductors 10 of the aluminum alloy bus bar 1 are 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 consisting of aluminum and inevitable impurities.

[0042] As the base material of the aluminum alloy, pure aluminum with a purity of 99.7% by mass or greater is preferably used. That is, among the aluminum ingots specified in Japanese Industrial Standard JIS H2102 (Aluminum Ingots for Remelting), aluminum ingots with a purity of Al99.70 or greater can be preferably used. Specifically, Al99.70, Al99.94, Al99.97, Al99.98, Al99.99, Al99.990, and Al99.995 with a purity of 99.7% by mass or greater are exemplified. In this embodiment, not only expensive and high-purity aluminum ingots such as Al99.995 can be used as the aluminum ingot, but also reasonably priced aluminum ingots with a purity of 99.7% by mass or greater can be used.

[0043] Magnesium (Mg) is an element that can improve the strength of the flat electrical conductor 10, which is an aluminum alloy plate, while minimizing the decrease in electrical conductivity. The aluminum alloy preferably contains 0.35 to 0.8 mass% of magnesium. Silicon (Si) is an element that can improve the strength of the flat electrical conductor 10 through solid solution strengthening and precipitation dispersion strengthening. The aluminum alloy preferably contains 0.3 to 0.7 mass% of silicon. The aluminum alloy may contain iron, but the iron content is preferably 0.50 mass% or less.

[0044] The aluminum alloy may contain a very small amount of inevitable impurities. Examples of inevitable 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), calcium (Ca), etc. These impurities are inevitably included within the range that does not interfere with the effect of the present embodiment and does not affect the characteristics of the aluminum alloy of the present embodiment. Elements previously contained in the aluminum ingot used are also included in the inevitable impurities. The total amount of inevitable impurities in the aluminum alloy is preferably 0.07% by mass or less, and more preferably 0.05% by mass or less.

[0045] In the aluminum alloy busbar 1 of this embodiment, the aluminum alloy forming the flat conductor 10 has a plurality of dispersed Mg-Si needle-shaped particles containing magnesium and silicon. In other words, the aluminum alloy has highly dispersed Mg-Si needle-shaped particles composed of intermetallic compounds containing magnesium and silicon. The highly dispersed Mg-Si needle-shaped particles in the aluminum alloy increase the yield stress of the flat conductor 10 and, therefore, suppress stress relaxation around the hole 11 even when the hole 11 is tightened with a fastening component (e.g., a nut and bolt). As a result, the electrical conductivity between the flat conductor 10 and the fastening component, as well as between the flat conductor 10 and other fastened components, can be improved. Furthermore, the highly dispersed Mg-Si needle-shaped particles increase the yield stress of the flat conductor 10 while maintaining high bendability. Therefore, even when the edge bend 12A and the flat bend 12B are formed in the aluminum alloy busbar 1, cracking and necking (shrinkage) in the bend 12 can be suppressed.

[0046] More specifically, when a busbar's yield stress is insufficient and the busbar and other fastened components are fastened together using bolts and nuts, the bolts and nuts can become trapped in the busbar due to stress relaxation, reducing the tightening force between the bolts and nuts. As a result, the bolts loosen, increasing the electrical resistance between the busbar and other fastened components, and destabilizing the electrical connection between the busbar and other fastened components. However, in this embodiment, by highly dispersing Mg-Si-based needle-shaped particles in the aluminum alloy forming the flat conductor 10, the yield stress is increased. Consequently, stress relaxation in the flat conductor 10 is suppressed, and the electrical connection between the flat conductor 10 and other fastened components can be well maintained. Furthermore, as described below, by limiting the number density of the Mg-Si-based needle-shaped particles dispersed in the aluminum alloy to a predetermined value or less, the bendability of the flat conductor 10 can be improved, and cracking and necking in the bent portion 12 of the flat conductor 10 can be suppressed.

[0047] As described above, the aluminum alloy forming the flat electrical conductor 10 contains 0.35 to 0.8 mass% magnesium and 0.3 to 0.7 mass% silicon. The range of this composition will be described in more detail. The 6000 series (Al-Mg-Si series) aluminum alloy of the JIS standard is an aging precipitation type alloy, and its strength is exhibited by the magnesium and silicon forming a compound. The strength of the 6000 series aluminum alloy can be improved by increasing the amount of magnesium and silicon. In addition, the magnesium or silicon added in excess due to the formation of Mg-Si series precipitates can be dissolved in the aluminum matrix to improve workability. However, as the amount of magnesium and silicon increases simultaneously, the amount of Mg-Si series precipitates produced increases, and the bending workability decreases. To avoid this, the amount of magnesium and silicon added must be limited.

[0048] JIS H4000 (Aluminum and Aluminum Alloys - Sheet, Strip, and Plate) specifies the composition range for the A6101 alloy, with magnesium additions ranging from 0.35% to 0.80% by mass and silicon additions ranging from 0.30% to 0.70% by mass. The aluminum alloy used to form the flat electrical conductor 10 according to this embodiment was studied within this composition range. As described above, decreasing the amount of magnesium and silicon added reduces the yield stress due to a decrease in the amount of Mg-Si precipitates. Excessively increasing the amount of magnesium and silicon added reduces bendability. Therefore, it is desirable to control the composition within the above range to achieve the effects of this embodiment.

[0049] The average length of the Mg-Si needle-like particles dispersed in the aluminum alloy forming the flat electrical conductor 10 is preferably between 67.1 nm and 378.4 nm, and more preferably between 291.3 nm and 378.4 nm. When the average length of the Mg-Si needle-like particles is within this range, stress relaxation of the flat electrical conductor 10 can be suppressed, and the stability of the electrical connection to other fastened components can be improved. Furthermore, the flat electrical conductor 10 can be subjected to edge bending, flat bending, and torsional bending while maintaining high bendability. Note that the average length of the Mg-Si needle-like particles can be determined by observing a sample of the aluminum alloy forming the flat electrical conductor 10 with a transmission electron microscope and measuring the lengths of multiple needle-like particles. In this specification, the length of the Mg-Si needle-like particles refers to the longest distance between two distinct points on the outline of the needle-like particles when the aluminum alloy is observed under a microscope.

[0050] The aspect ratio and diameter of the Mg-Si based needle-shaped 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 needle-shaped particles is perpendicular to the longitudinal direction of the needle-shaped particles and can be determined by observing them with a transmission electron microscope.

[0051] The number density of the Mg-Si based needle-like particles in the aluminum alloy forming the rectangular electrical conductor 10 is preferably 4.5×10 20 / m 3 to 6.8×10 21 / m 3 , and more preferably 4.5×10 20 / m 3 to 9.1×10 20 / m 3 When the Mg-Si needle-shaped particles are 4.5×10 20 / m 3 When the number density is highly dispersed, the yield stress increases, so that the stress relaxation of the flat conductor 10 can be suppressed and the electrical connection between the flat conductor 10 and other fastened parts can be well maintained.21 / m 3 In the following case, deterioration of the bending workability of the rectangular electric conductor 10 can be suppressed, and therefore, edge bending work, plane bending work, and torsional bending work can be performed.

[0052] The number density of Mg-Si based needle-like particles in aluminum alloy can be calculated as follows: First, the aluminum alloy sample is observed with a transmission electron microscope, and the number of needle-like particles in a predetermined area is obtained to calculate the surface density (number / m 2 )). Then, by multiplying the surface density by the thickness of the sample, the number density of needle-shaped particles (number / m) can be calculated. 3 )).

[0053] Preferably, the allowable bending strain ε of the flat electric conductor 10 expressed by the following Mathematical Formula 1 exceeds 0.27.

[0054] [Mathematical formula 1]

[0055]

[0056] In Mathematical Formula 1, b is the plate width (mm) of the flat electrical conductor 10, and R min is the minimum bending radius (mm) when the flat electrical conductor 10 having this plate width is bent at the edge. Figure 2 As shown, when observing a cross section perpendicular to the length direction of the flat electrical conductor 10, the plate width b of the flat electrical conductor 10 is obtained. Figure 3 As shown, R min It is the minimum value of the radius R from the bending position to the bending center when the flat electric conductor 10 having this plate width is edge-bent at room temperature.

[0057] Mathematical formula 1 takes into account the difference between the theoretical bending strain and the measured bending strain when the flat conductor 10 is edge-bent. Here, "bending strain" refers to the strain applied to the outermost surface of the outer curved surface (outer rounded portion) of the flat conductor 10 when edge-bending. The theoretical bending strain ε' can be obtained using the following mathematical formula 2.

[0058] [Mathematical formula 2]

[0059]

[0060] In Mathematical Formula 2, b is the plate width (mm) of the flat electrical conductor 10, and R is the bending radius (mm) when the flat electrical conductor 10 having the plate width is edge-bent. Figure 4 and Figure 5 As shown, the measured bending strain can be calculated from the amount of change in the grid by bending the edges of the flat conductor 10 on which a grid-shaped mark is printed.

[0061] In the flat electrical conductor 10, when the allowable bending strain ε expressed by the following mathematical formula 1 exceeds 0.27, the bendability of the flat electrical conductor 10 is excellent. Therefore, even when the flat electrical conductor 10 is edge-bent, cracking and necking in the bent portion 12 can be suppressed. However, flat electrical conductors made of, for example, an A6101-T6 alloy have high strength and poor bendability, and therefore have an allowable bending strain ε of 0.27 or less.

[0062] The yield stress of the flat conductor 10 at room temperature is preferably between 55 and 201 MPa. When the yield stress of the flat conductor 10 is 55 MPa or greater, stress relaxation of the flat conductor 10 can be suppressed, and the electrical connection between the flat conductor 10 and other fastened components can be well maintained. Furthermore, when the yield stress of the flat conductor 10 is 201 MPa or less, the flat conductor 10 exhibits excellent bendability, and cracking and necking in the bent portion 12 can be suppressed. The yield stress of the flat conductor 10 can be measured in accordance with JIS Z2241 (Metallic Materials - Tensile Tests - Test Methods at Room Temperature).

[0063] The numerical range of the yield stress of the flat electrical conductor 10 will be described in more detail. The busbars arranged in the battery pack of a vehicle are used to connect the junction box (J / B), the battery pack, etc., and possible connection methods between these parts and the busbars include welding, solid-state bonding, bolting, etc.

[0064] Here, when considering the connection by bolt connection, the axial force of the bolt applies pressure to the flange (head) to restrain the bus bar. The axial force of the bolt can be obtained by the following mathematical formula 3.

[0065] [Mathematical formula 3]

[0066] F=T / dK

[0067] In Mathematical Formula 3, F is the axial force of the bolt (N), T is the tightening torque (N·m), d is the nominal diameter of the threaded area (m), and K is the torque coefficient. The axial force F of the bolt is divided by the area S of the bearing surface of the flange (mm 2 The value obtained by calculating the pressure applied to the flange's bearing surface is the area where the bolt's flange actually contacts the busbar. F / S (MPa) is the lower limit of the yield stress required to prevent the busbar from denting.

[0068] Typically, bolts such as M6 are often used to fasten busbars to other fastened components. For example, assuming the flange diameter The busbar has a contact resistance of 13 mm and a torque coefficient of 0.2. When the tightening torque is 5 to 10 N / m, a bearing surface pressure of approximately 42 to 83 MPa is applied. The contact resistance varies depending on the material and surface properties of the busbar, and the tightening torque is not constant. However, considering factors such as safety, the yield stress of the busbar is preferably at least 100 MPa. Although the A6101 alloy is specified by various standards such as JIS, ASTM, and EN, in the case of A6101-T64 specified in ASTM B317 / B317M, a yield stress of at least 55 MPa must be ensured. Therefore, the yield stress of the flat conductor 10 according to this embodiment is preferably 55 MPa or more. As shown in Examples 6, 10, and 12 described below, when the yield stress is less than 118 MPa, the permissible bending strain tends to decrease slightly. Therefore, the yield stress of the flat conductor 10 is more preferably 120 MPa or more.

[0069] Therefore, the yield stress of the flat conductive body 10 at room temperature is preferably 55 to 201 MPa, more preferably 100 to 201 MPa, and particularly preferably 120 to 201 MPa.

[0070] As described above, the aluminum alloy busbar 1 of this embodiment is a conductive component connected to a junction box (J / B), a battery pack, and the like. Therefore, it is preferable that the conductivity of the aluminum alloy busbar 1 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 (Methods for measuring the resistivity and conductivity of non-ferrous materials).

[0071] For the flat conductor 10, the n value measured according to JIS Z2241 (Metallic Materials - Tensile Test - Test Method at Room Temperature) is preferably 0.07 or greater, and more preferably 0.15 or greater. The n value is an index used to measure the degree of work hardening of a metal material, and the closer the n value is to 1, the greater the degree of work hardening. When the n value of the flat conductor 10 is 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 the bent portion after bending] / [hardness of the bent portion before bending]) exceeds 1, which can suppress the strength degradation of the bent portion 12. In other words, when the flat conductor 10 is bent and the n value is 0.07 or greater, the bent portion 12 hardens through work hardening and thus 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 and is approximately 1.3. Therefore, when the n value of the flat conductor 10 is 0.07 or greater, the strength degradation of the bent portion 12 can be suppressed.

[0072] As mentioned above, rolled materials are commonly used for conventional busbars, and in such cases, the busbar shape is formed through stripping, stamping, and pressing. As a result, the resulting busbar has sharp corners, which can cause stress concentration. Therefore, in the aluminum alloy busbar 1 of this embodiment, it is preferable to chamfer at least the corners 13 of the bent portion 12 of the flat conductor 10. Furthermore, it is preferable to chamfer the corners 13 along the entire length of the flat conductor 10.

[0073] Figure 6 The cross-sectional shapes of a square edge in which the corners 13 are not chamfered and a round edge in which the corners 13 are chamfered are schematically shown for the flat electric conductor 10 of the present embodiment. Figure 6 Also shown are photos of the appearance of square edges and round edges. Figure 6 As shown, the flat conductor 10 can be in a state where the corners 13 are not chamfered and the square edges are approximately right angles. However, with square edges, stress may concentrate in the corners 13 when the flat conductor 10 is bent. Therefore, it is preferable to chamfer the corners 13 to prevent them from becoming the source of stress concentration. Thus, the rounded edges with chamfered and curved corners 13 make them less likely to become the source of stress concentration. This further reduces the occurrence of cracks when the flat conductor 10 is bent.

[0074] Next, the manufacturing method of the aluminum alloy busbar 1 according to the present embodiment will be described. In the manufacturing method of the present embodiment, a cast billet is prepared by melting and casting aluminum, magnesium, and silicon in the above-described composition. Subsequently, the cast billet is subjected to a homogenization treatment. The homogenization treatment can be performed at 500-560°C for 4-10 hours. Alternatively, an ingot is produced by melting and continuously casting aluminum, magnesium, and silicon in the above-described composition, and then rolling the ingot into a wire rod.

[0075] Next, the homogenized ingot or the wire obtained as described above is extruded using an extruder to obtain an extruded material having any cross-sectional shape. The extrusion process can be performed by hot extrusion at a temperature of, for example, 350 to 500°C. The extruder is not particularly limited, but a Conform extruder can be used, for example.

[0076] During extrusion molding, an extruded material having any cross-sectional shape can be obtained by using a die (mold) machined to obtain the desired cross-sectional shape. For example, when chamfering the corners 13 of the flat conductor 10, an extruded material having chamfered corners can be obtained by forming a curved surface at the portion corresponding to the corner of the die cavity.

[0077] Next, the extruded material extruded from the extruder is cooled by passing it through water, hot water, or cooling oil, or by air cooling. The cooled extruded material is wound into any size. Specifically, the cooled extruded material can be wound onto a bobbin in coil form, or can be wound into a ring shape without using a bobbin.

[0078] Subsequently, the wound extruded material is subjected to aging heat treatment using a heating furnace. The heating furnace is not particularly limited, but an electric furnace, for example, can be used. Here, the conditions of the aging heat treatment are such that Mg-Si needle-shaped particles of the above-mentioned average length and number density are formed in the aluminum alloy. Specifically, as the conditions of the aging heat treatment, for example, a temperature of 225°C or higher may be used for more than 2 hours, and preferably a temperature of 225 to 300°C may be used for 2 to 24 hours. However, it is preferred to appropriately adjust the heating temperature and time so that Mg-Si needle-shaped particles of a predetermined average length and number density are formed.

[0079] Thereafter, the aged material subjected to the aging heat treatment is bent into an arbitrary shape at room temperature. The bending can be performed, for example, by using a forming machine.

[0080] Through this process, the aluminum alloy bus bar 1 including the flat electric conductor 10 having at least one bent portion 12 selected from the group consisting of an edge bent portion 12A, a flat bent portion 12B, and a twisted bent portion formed by adding twist is obtained.

[0081] In the method for manufacturing the aluminum alloy busbar 1 according to this embodiment, solution treatment is not necessary before aging heat treatment. Specifically, the flat electrical conductor 10 containing Mg—Si-based needle-shaped particles having the aforementioned average length and number density can be obtained using a manufacturing method corresponding to the T5 treatment. However, if a flat electrical conductor 10 containing Mg—Si-based needle-shaped particles having the aforementioned average length and number density can be obtained, solution treatment can be performed before aging heat treatment.

[0082] The method for covering the periphery 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, for example, by extrusion coating. For example, the bent portion 12 may be formed by bending after forming the insulator layer 20 by extrusion coating on an aging material.

[0083] As described above, the aluminum alloy bus bar 1 according to the first embodiment includes a flat electrical conductor 10 made of an aluminum alloy containing 0.35 to 0.8 mass% magnesium and 0.3 to 0.7 mass% silicon, with the remainder being aluminum and inevitable impurities. A plurality of Mg-Si needle-shaped particles 16 containing magnesium and silicon are dispersed within the aluminum alloy. The average length of the Mg-Si needle-shaped particles 16 is 67.1 nm to 378.4 nm, and the number density of the Mg-Si needle-shaped particles 16 in the aluminum alloy is 4.5×10 20 / m 3 to 6.8×10 21 / m 3 .

[0084] The flat conductor 10 of the aluminum alloy busbar 1 is made of an aluminum alloy containing predetermined amounts of magnesium and silicon. Mg—Si-based needle-shaped particles 16 of a predetermined length are dispersed in the aluminum alloy at a predetermined density. This structure improves the yield stress of the flat conductor 10, suppressing stress relaxation around the hole 11 even when fastened with a fastening component. This maintains high electrical conductivity between the flat conductor 10 and the fastening component, as well as between the flat conductor 10 and other fastened components. Furthermore, the high dispersion of the Mg—Si-based needle-shaped particles increases the yield stress of the flat conductor 10 and improves its bendability. This prevents cracking and necking in the bent portion 12 even when it is formed.

[0085] In the aluminum alloy bus bar 1 according to the second aspect, the allowable bending strain ε of the flat electric conductor 10 expressed by Mathematical Formula 1 can exceed 0.27. When the allowable bending strain ε of the flat electric conductor 10 exceeds 0.27, the flat electric conductor 10 has good bending workability, so that cracking and necking in the bent portion 12 can be suppressed even when edge bending is performed.

[0086] In the aluminum alloy bus bar 1 according to the third aspect, the flat electric conductor 10 may include at least one bent portion 12. The flat electric conductor 10 has good bending workability, and at least one bent portion 12 selected from the group consisting of an edge bent portion 12A, a plane bent portion 12B, and a twisted bent portion can be easily formed in the flat electric conductor 10.

[0087] In the aluminum alloy bus bar 1 according to the fourth aspect, the flat conductor 10 has a yield stress of 55 to 201 MPa at room temperature, as measured in accordance with JIS Z2244. Since the yield stress of the flat conductor 10 is 55 MPa or greater, stress relaxation of the flat conductor 10 can be suppressed, enabling good electrical connection between the flat conductor 10 and the fastening component, and between the flat conductor 10 and other fastened components. Furthermore, since the yield stress of the flat conductor 10 is 201 MPa or less, a decrease in the bendability of the flat conductor 10 can be suppressed, allowing the bent portion 12 to be easily formed.

[0088] According to the aluminum alloy bus bar 1 of the fifth aspect, at least the corners 13 of the bent portion 12 of the flat conductor 10 can be chamfered. By chamfering the corners 13 of the flat conductor 10, the corners 13 are less likely to serve as starting points for stress concentration when the flat conductor 10 is bent, and the occurrence of cracks can be further suppressed.

[0089] The aluminum alloy bus bar 1 according to the sixth aspect can be used as a wiring member for a vehicle. Wiring members are routed in a vehicle and electrically connect devices. The aluminum alloy bus bar 1 has excellent bending workability and electrical connection stability and can be suitably used as a conductive member routed within a battery pack mounted in a vehicle, for example.

[0090] Example

[0091] 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.

[0092] [Preparation of test samples]

[0093] (Example 1)

[0094] First, aluminum, silicon, and magnesium were weighed in the proportions shown in Table 1. A molten metal was then prepared by melting the weighed aluminum, silicon, and magnesium, and poured into a mold to produce an ingot. The ingot was then subjected to a homogenization treatment to produce a cast strand. The homogenization treatment was performed at 540°C for 4 hours at a heating rate of 40°C / h.

[0095] The cast ingot was then hot-extruded at 500°C and subsequently water-cooled to obtain a long, flat extruded material. The extruded material was then coiled and subjected to aging heat treatment in a heating furnace. The aging heat treatment was performed at 225°C for 2 hours. This yielded a long test specimen having a plate thickness t of 2.0 mm and a plate width b of 15.0 mm. In this example, no solution treatment was performed before the aging heat treatment.

[0096] (Examples 2 to 6)

[0097] The test samples of the example were obtained by the same method as in Example 1, except that the temperature and time of the aging heat treatment of the extruded material were changed as shown in Table 1.

[0098] (Examples 7 to 12)

[0099] The test samples of the example were obtained in the same manner as in Example 1, except that the ratios of the elements were changed as shown in Table 1, and the temperature and time of the aging heat treatment of the extruded material were changed as shown in Table 1. However, in Example 7, the die was adjusted so that the plate thickness t of the test sample was 5.0 mm and the plate width b was 24.0 mm.

[0100] (Comparative Examples 1 and 4 to 7)

[0101] A test sample of the comparative example was obtained in the same manner as in Example 1, except that the ratios of the elements were changed as shown in Table 1, and the temperature and time of the aging heat treatment of the extruded material were changed as shown in Table 1.

[0102] (Comparative Example 2)

[0103] First, aluminum, silicon, and magnesium were weighed in the proportions shown in Table 1, and then an extruded material was obtained using the same procedure as in Example 1. After the extruded material was coiled, the coiled extruded material was solution treated in a heating furnace. The solution treatment was performed at 540°C for 2 hours. After the solution treatment, an aging heat treatment was performed in a heating furnace. The aging heat treatment was performed at 225°C for 8 hours. Thus, the test sample of this comparative example was obtained. The manufacturing method of Comparative Example 2 corresponds to the T6 treatment.

[0104] (Comparative Example 3)

[0105] The test sample of this comparative example was obtained by the same procedure as that of Comparative Example 2, except that the aging heat treatment time was changed as shown in Table 1.

[0106] [Table 1]

[0107]

[0108] [Evaluation of test samples]

[0109] (Mechanical properties)

[0110] The hardness, yield stress, and n value of each test sample were measured at room temperature. The hardness was measured according to JIS Z2244 (Vickers hardness test), and the yield stress and n value were measured according to JIS Z2241 (Metallic materials - Tensile test - Test method at room temperature). The measurement results of the test samples are summarized in Table 2.

[0111] (Conductivity)

[0112] The electrical conductivity of the test samples was measured in accordance with JIS H0505 (Measurement method of resistivity and electrical conductivity of non-ferrous materials). The measurement results of the test samples are summarized in Table 2.

[0113] (Mg-Si based precipitate)

[0114] The average length and number density of the precipitates were measured by observing the test samples in each example using a transmission electron microscope. Specifically, a test piece having a diameter of approximately 3 mm and a thickness of 100 μm or less was prepared from the test sample in each example, and then further thinned using a dual-jet electropolishing device. The thinned test sample was then observed using a transmission electron microscope.

[0115] Figure 7 The results of observing the test sample prepared from the test sample in Example 1 at a magnification of 200,000 are shown. Figure 7 As shown, in Example 1, a plurality of needle-like particles 16 are dispersed in an aluminum matrix 15. Then, the length of the needle-like particle 16A is obtained from the longest distance between two different points on the contour of the needle-like particle 16A, and the average length is obtained from the lengths of the plurality of needle-like particles 16A.

[0116] The needle-shaped particles 16A are arranged on Figure 7 on paper, so they are Figure 7 However, since the long axis of the needle-shaped particle 16B passes through Figure 7 The paper surface, so it is observed that the needle-shaped particle 16B is not needle-shaped, but Figure 7 That is, for example, Figure 8 As shown, when the needle-shaped particles 16B are arranged almost perpendicular to the needle-shaped particles 16A, Figure 7 Needle-shaped particles 16B were observed as point-like precipitates in the test specimen. Therefore, the area density of the precipitates was calculated by counting the number of needle-shaped particles 16A and 16B in the observation field and then multiplying the area density by the thickness of the test piece to obtain the number density of the precipitates. The average length and number density of the precipitates in the test samples are summarized in Table 2.

[0117] (Bending properties)

[0118] Measure the minimum bending radius R in each test sample min The minimum bending radius R when no macro defects such as cracking or necking occur after edge bending at room temperature and the bent portion is observed with an optical microscope is determined as the minimum bending radius R min Therefore, when a defect such as cracking or necking occurs, even if the bent portion is not broken, the bending radius at that point is not set to the minimum bending radius R min .

[0119] Here, Figure 9 and Figure 10 An example of the result of observing a bent portion formed by edge bending with an optical microscope at a magnification of 50 times is shown. Figure 9 and Figure 10 Shows the observation as Figure 11 The result of the outer curved surface (outer R portion) of the curved portion is shown. Figure 9 It is shown that no cracking or necking is observed in the outer curved surface of the curved portion. However, Figure 10 FIG. 4 shows a case where cracking or necking is observed in the outer curved surface of the curved portion. Figure 9 As shown, the minimum bending radius R when no macro defects such as cracking or necking occur in the bent portion is set to the minimum bending radius R min .

[0120] For each test sample, the hardness of the bent portion having the minimum bending radius shown in Table 2 was measured at room temperature according to JIS Z2244. Subsequently, the hardness ratio was obtained from the hardness of the bent portion after bending relative to the hardness of the bent portion before bending ([hardness of the bent portion after bending] / [hardness of the bent portion before bending]). In addition, according to Mathematical Formula 1, the minimum bending radius R when the test sample having the plate width (mm) and the plate width was edge-bent at room temperature was obtained. min The hardness ratio and the allowable bending strain ε of each test sample are summarized in Table 2.

[0121] Next, when the test sample of each example was edge-bent so that the bending radius was 30 mm, it was observed whether a defect occurred in the bent portion. Specifically, after the test sample of each example was edge-bent so that the bending radius was 30 mm at room temperature, as shown in FIG. Figure 11 Observe the outer curved surface (outer R portion) of the curved portion as shown. Figure 9 When no macro defects such as cracks and necking occurred on the outer curved surface of the curved portion as shown, the result was judged as "yes". Figure 10 When cracking or necking was observed in the outer curved surface of the curved portion, the result was judged as "No." The results of the test samples are summarized in Table 2.

[0122] [Table 2]

[0123]

[0124] As shown in Table 2, in the test samples of Examples 1 to 12, the average length of the Mg-Si system precipitates ranged from 67.1 nm to 378.4 nm, and the number density of the Mg-Si system precipitates was 4.5×10 20 / m3 to 6.8×10 21 / m 3 In contrast, in the test samples of Comparative Examples 1 to 7, the average length of the Mg-Si system precipitates was less than 67.1 nm, and the number density of the Mg-Si system precipitates was greater than 6.8×10 21 / m 3 The yield stress of the test samples of Examples 1 to 12 is 100-201 MPa, but except for Comparative Example 3, the yield stress of the test samples of Comparative Examples 1 to 7 is greater than 201 MPa. As a result, the minimum bending radius R of the test samples of Examples 1 to 12 is min is less than 30 mm, while the minimum bending radius R of the test samples of Comparative Examples 1 to 7 is min More than 33mm.

[0125] As described above, when the average length and number density of the Mg—Si-based precipitates are within the above ranges, bending workability and stability of electrical connection are improved because the generation of defects in the bent portion can be suppressed while increasing the yield stress of the aluminum alloy.

[0126] here, Figure 12 The relationship between the average length of the precipitates and the yield stress in the test samples of Examples 1 to 12 and Comparative Examples 1 to 7 is shown. In addition, Figure 13 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 is shown. Figure 12 As shown in Figure 2, it can be seen that as the average length of the precipitates increases, the yield stress tends to decrease. Figure 13 As shown in FIG, it can be seen that the yield stress tends to increase as the number density of precipitates increases. Therefore, it can be understood 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.

[0127] Furthermore, as shown in Table 2, the n value of the test samples of Examples 1 to 12 was 0.07 or greater, while the n value of the test samples of Comparative Examples 1 to 7 was 0.06 or less. Furthermore, the hardness ratio ([hardness of the bent portion after bending] / [hardness of the bent portion before bending]) of the test samples of Examples 1 to 12 was 1.0 or greater, and the hardness ratio of all samples except Example 7 was 1.1 or greater. Therefore, it can be understood that when the average length and number density of the Mg-Si-based precipitates are within the above ranges, it is possible to suppress the deterioration of the strength of the bent portion 12.

[0128] 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 understood that when the allowable bending strain exceeds 0.27, the bending workability of the aluminum alloy is improved and the occurrence of defects in the bent portion can be suppressed.

[0129] Although the present embodiment has been described above, the present embodiment is not limited to these embodiments, and various modifications can be made within the scope of the gist of the present embodiment.

[0130] The entire contents of Japanese Patent Application No. 2023-039057 (filing date: March 13, 2023) are incorporated herein by reference.

Claims

1. An aluminum alloy busbar, comprising: A flat electrical conductor made of an aluminum alloy containing 0.35-0.8 mass % of magnesium and 0.3-0.7 mass % of silicon, with the remainder consisting of aluminum and unavoidable impurities; wherein A plurality of Mg-Si needle-shaped particles containing magnesium and silicon are dispersed in the aluminum alloy; and The average length of the Mg-Si needle-shaped particles is 67.1 nm to 378.4 nm, and the number density of the Mg-Si needle-shaped particles in the aluminum alloy is 4.5×10 20 / m 3 to 6.8×10 21 / m 3 .

2. The aluminum alloy bus bar according to claim 1, wherein: The allowable bending strain ε of the flat electrical conductor represented by the following mathematical formula 1 is greater than 0.27, [Mathematical formula 1] (b is the plate width of the flat electrical conductor (mm), and R min The minimum bending radius (mm) when a flat electrical conductor of this width is bent at its edge.

3. The aluminum alloy bus bar according to claim 1 or 2, wherein: The flat electrical conductor comprises at least one bend.

4. The aluminum alloy bus bar according to any one of claims 1 to 3, wherein: The flat electric conductor has a yield stress of 55 to 201 MPa at room temperature as measured according to JIS Z2244.

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

6. The aluminum alloy bus bar according to any one of claims 1 to 5, wherein: The flat electrical conductor is used as a wiring component of a vehicle.

Images