Aluminum alloy wire

Abstract

This invention provides an aluminum alloy wire that inhibits recrystallization and improves heat resistance. The aluminum alloy wire is composed of an aluminum alloy containing 0.2–1.0% by mass Zr and 0.1–1.0% by mass Co, with the balance consisting of aluminum and unavoidable impurities. It has a tensile strength of ≥170 MPa at room temperature, an elongation of ≥10%, and withstands 10% heat at 250°C. ‑5 The stress during tensile deformation at a strain rate of / sec is above 40MPa.

Description

Technical Field

[0001] This invention relates to aluminum alloy wire. Background Technology

[0002] To improve conductivity, aluminum alloys used as conductors tend to have minimal addition of alloying elements. Therefore, in addition to alloying, work hardening based on inducing processing strain is commonly used to improve material strength. One challenge with inducing processing strain is the reduction in ductility at room temperature. If the aluminum alloy is subjected to high temperatures, the strength reduction and creep deformation caused by recrystallization become significant, making it difficult to prevent stress relief at the connection terminals. This stress relief can contribute to an increase in the resistance of the aluminum alloy wire.

[0003] To improve the ductility of aluminum alloy wire at room temperature, the addition of Zr to the aluminum alloy is considered.

[0004] Patent document 1 describes the casting and machining of Al-Zr-Fe-Si aluminum alloy materials followed by aging heat treatment.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 57-39164 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] Zr, as a strengthening element, readily diffuses through grain boundaries during aging heat treatment, easily forming coarse grain boundary precipitates. However, even with processing to improve strength, wires made of Zr-free pure aluminum or solution-strengthened aluminum alloys experience a decrease in strength and creep deformation at temperatures above 120°C due to recrystallization, thus failing to maintain heat resistance.

[0010] The purpose of this invention is to suppress recrystallization of aluminum alloy wire and improve its heat resistance.

[0011] Methods for solving problems

[0012] If we simply describe the outline of a representative embodiment among the embodiments disclosed in this application, it will be as follows.

[0013] One embodiment of the aluminum alloy wire is a wire made of an aluminum alloy containing 0.2 to 1.0% by mass of Zr and 0.1 to 1.0% by mass of Co, and optionally containing Fe: 0.02 to 0.15% by mass, Si: 0.02 to 0.15% by mass, Mg: 0 to 0.2% by mass, Ti: 0 to 0.10% by mass, B: 0 to 0.03% by mass, Cu: 0 to 1.00% by mass, Ag: 0 to 0.50% by mass, Au: 0 to 0.50% by mass, Mn: 0 to 1.00% by mass, Cr: 0 to 1.00% by mass, Hf: 0 to 0.50% by mass, V: 0 to 0.50% by mass, Sc: 0 to 0.50% by mass, with the balance consisting of aluminum and unavoidable impurities. It has a tensile strength of 170 MPa or more at room temperature, an elongation of 10% or more, and withstands stress at 250°C and a strain rate of 10... -5 The stress during tensile deformation is above 40 MPa per second.

[0014] Invention Effects

[0015] According to one embodiment disclosed in this application, recrystallization of aluminum alloy wire can be suppressed, thereby improving heat resistance. Detailed Implementation

[0016] The implementation method will be described in detail below.

[0017] To address the aforementioned problems, the inventors investigated the changes in various properties when the types of alloying elements and manufacturing conditions were appropriately modified. Their findings revealed that Co or Ni and Zr can be used as alloying elements. Furthermore, they discovered that by using the tensile strength at high temperatures as an evaluation criterion based on a specified strain rate for the aluminum alloy wire, recrystallization of the aluminum alloy wire can be suppressed, thereby improving its heat resistance. This invention is based on this insight.

[0018] (Implementation Method)

[0019] The following describes one embodiment of the present invention. It should be noted that the numerical range indicated by "~" in this specification refers to the range including the values ​​recorded before and after "~" as the lower limit and upper limit values.

[0020] <Aluminum Alloy Wire>

[0021] Hereinafter, an example of an aluminum alloy wire according to one embodiment of the present invention will be described, taking the case in which Co and Zr are mainly used as alloying elements.

[0022] <Chemical Composition>

[0023] First, the chemical composition of the aluminum alloy (hereinafter referred to as alloy) that constitutes the aluminum alloy wire (hereinafter also referred to as alloy wire) will be explained.

[0024] The chemical composition of the alloy consists of Co: 0.1–1.0 wt%, Zr: 0.2–1.0 wt%, Fe: 0.02–0.15 wt%, Si: 0.02–0.15 wt%, Mg: 0–0.2 wt%, Ti: 0–0.10 wt%, B: 0–0.03 wt%, Cu: 0–1.00 wt%, Ag: 0–0.50 wt%, Au: 0–0.50 wt%, Mn: 0–1.00 wt%, Cr: 0–1.00 wt%, Hf: 0–0.50 wt%, V: 0–0.50 wt%, Sc: 0–0.50 wt%, with the balance being Al and unavoidable impurities.

[0025] Regarding Co, as described later, during the manufacturing process (casting) of the alloy wire, most of it reacts with Al to form crystals (Al-Co compounds), which exist as a compound phase in the final alloy wire. The Al-Co compounds actually exist in the form of Al-Co-Fe compounds, which absorb the Fe inevitably present in the aluminum alloy. Al-Co-Fe compounds contribute to the refinement of the Al recrystallized grains in the alloy and increase the elongation of the alloy wire. While Co may reduce the conductivity of the alloy, by setting the Co content to 0.1% to 1.0% by mass, it is possible to suppress the decrease in conductivity caused by Co in the alloy wire and to achieve a high level and balanced effect of strength, elongation, and heat resistance provided by Co. The Co content is preferably 0.2% to 1.0% by mass, more preferably 0.3% to 0.8% by mass.

[0026] Here, we will explain the case where Co is added in the above proportion, but as will be explained later, the same effect can be obtained when an equal amount of Ni or Fe is added instead of Co.

[0027] Regarding Zr, as described later, it exists primarily in a solid solution state in the cast ingot (casting material) after casting, but precipitates as Al-Zr compounds in the alloy wire after aging heat treatment. Al-Zr compounds mainly contribute to improving the heat resistance of the alloy wire. Excessive Zr content may reduce the ductility of the alloy during wire manufacturing, hindering the reduction of wire diameter. In this regard, by setting the Zr content to 0.2% to 1.0% by mass, the ductility of the alloy can be maintained relatively well, and the desired heat resistance can be obtained in the alloy wire. A more preferred Zr content is 0.3% to 0.6% by mass.

[0028] Fe is an unavoidable component introduced from aluminum raw materials. Fe helps improve the strength of the alloy. When Fe precipitates as FeAl3 crystals during casting or during aging heat treatment, it can reduce the alloy's ductility and hinder the reduction of alloy wire diameter during manufacturing. In this embodiment, by incorporating Co, Fe is absorbed during the crystallization of Al-Co compounds, thereby forming an Al-Co-Fe compound. Thus, by making Fe an Al-Co-Fe compound, the formation of FeAl3 is suppressed. As a result, the reduction in alloy ductility can be suppressed, and the alloy's strength can be improved. From the viewpoint of absorption by Al-Co compounds, the Fe content can be set below the Co content, specifically from 0.02% to 0.15% by mass. This allows for the reduction of alloy wire diameter and the attainment of high strength. The Fe content is preferably from 0.04% to 0.15% by mass. It should be noted that Fe can be added in a predetermined manner.

[0029] Like Fe, Si is an unavoidable component introduced from aluminum raw materials. Si dissolves in the Al grains of the alloy or precipitates together with Fe, thus contributing to the improvement of the alloy's strength. Like Fe, Si can reduce the elongation of the alloy and hinder the reduction of alloy wire diameter; however, by setting the Si content to 0.02% to 0.15% by mass, the reduction in elongation can be suppressed, and the strength can be improved. The preferred Si content is 0.04% to 0.12% by mass. It should be noted that Si can be added in a specified manner.

[0030] In the alloy of this embodiment, Ti replaces a portion of the Zr atoms in the Al-Zr compound formed in the alloy wire after aging heat treatment, precipitating as an Al-Zr-Ti compound. The Al-Zr-Ti compound has the same crystal structure as the Al-Zr compound, primarily contributing to the improvement of the heat resistance of the alloy wire. Similar to Zr, excessive Ti content may reduce the ductility of the alloy during wire manufacturing, hindering the reduction of wire diameter. In this regard, by setting the Ti content to 0% to 0.1% by mass, the ductility of the alloy can be maintained relatively well, and the desired heat resistance can be obtained in the alloy wire.

[0031] Mg, B, Cu, Ag, Au, Mn, Cr, Hf, V, and Sc are optional components introduced from aluminum raw materials or added as needed. Here, "optional components" refers to components that may or may not be present. Each alloying element suppresses grain coarsening of the Al phase in the alloy wire, contributing to its strength. Cu, Ag, and Au, in particular, precipitate at grain boundaries, further enhancing grain boundary strength. By setting the content of each alloying element within the aforementioned ranges, the reduction in elongation of the alloy can be suppressed, and the effects brought about by each alloying element can be obtained.

[0032] The balance other than the above-mentioned components is Al and unavoidable impurities. Here, unavoidable impurities are substances that inevitably mix into the alloy wire during the manufacturing process; they refer to substances present in small amounts that do not affect the properties of the alloy wire. Examples of unavoidable impurities include Ga, Zn, Bi, and Pb.

[0033] From the viewpoint of the conductivity of the alloy wire, the Al content is preferably 97% by mass or more, more preferably 98% by mass or more, and even more preferably 98.4% by mass or more.

[0034] <Metal Structure>

[0035] Next, the metal structure of the aluminum alloy will be explained.

[0036] The aluminum alloy wire of this embodiment has a metallic structure comprising Al grains, Al-Co-Fe compounds, and Al-Zr compounds. Within the metallic structure, the Al-Co-Fe compounds and Al-Zr compounds are dispersed at grain boundaries.

[0037] Al-Co-Fe compounds are crystalline phases formed during the solidification of molten aluminum alloys through cooling, or after solidification, during the cooling of the high-temperature casting material to near room temperature. In other words, Al-Co-Fe compounds are crystals formed in aluminum alloys during the casting process.

[0038] Al-Zr compounds are precipitates formed during the aging heat treatment process, in which the cast material, cooled to room temperature, is heated and held in a high-temperature atmosphere below its melting point. Specifically, they are precipitates initially formed by the diffusion and condensation of metallic elements dissolved in the Al phase of the cast material through aging heat treatment. That is, the precipitates are not present in the Al alloy during the casting stage, but are present in the alloy wire stage after aging heat treatment.

[0039] The size distribution of Al-Zr compounds ranges from 1 nm to several hundred nm, but preferably, the proportion of fine precipitates with a size of 1 nm to 100 nm is greater than the proportion of precipitates not included in the size range of 1 nm to 100 nm. By reducing the size of precipitates composed of Al-Zr compounds to 1 nm to 100 nm, the number of precipitates can be increased even when the content of alloying elements is reduced, and the effects brought by the precipitates can be obtained in a balanced manner. In addition, since the ductility of the alloy can be maintained at a higher level, the workability can be improved in the wire drawing process, and the alloy wire diameter can be further reduced.

[0040] The size of the Al-Co-Fe compound is preferably 20 nm or more and 1 μm (1000 nm) or less. The size of the Al-Co-Fe compound can be increased, for example, by ensuring sufficient aging time. If the compound is too small, the ductility of the alloy wire may decrease. In this regard, by making the size 20 nm or more, ductility can be improved. On the other hand, if the compound becomes too large, recrystallization during the aging heat treatment stage is more likely to occur, resulting in coarser grain size, which may sometimes reduce the strength of the alloy wire. From the viewpoint of obtaining high strength, the size of the compound is preferably 1 μm or less. It should be noted that Co atoms diffuse in the Al structure at a higher rate than Zr atoms, therefore the size of the Al-Co-Fe compound becomes larger than that of the Al-Zr compound. As will be explained later, the role of the Al-Co-Fe compound is to suppress the growth of recrystallized grains in the early stages of aging heat treatment. Therefore, in the metal structure after aging heat treatment, the Al-Co-Fe compound can also be larger than that of the Al-Zr compound.

[0041] Furthermore, the shape of the compound is not particularly limited, but Al-Co-Fe compounds are preferably spherical or ellipsoidal in shape. Al-Zr compounds are preferably spherical, but can also be irregular in shape. In addition, ellipsoidal in shape means a shape that is circular in the direction perpendicular to the length direction of the wire and elliptical in the direction parallel to the length direction of the wire.

[0042] (Properties of aluminum alloy wire)

[0043] The aluminum alloy wire of this embodiment is formed from an aluminum alloy having the above-described chemical composition and metallic structure. Specifically, the alloy wire has a tensile strength of 170 MPa or more at room temperature and an elongation of 10% or more. Furthermore, it withstands stresses at 200°C and a strain rate of 10... -5 The stress during tensile deformation is above 60 MPa per second. Furthermore, at a temperature of 250°C and a strain rate of 10... -5The stress during tensile deformation is above 40 MPa per second. Additionally, it has an electrical conductivity of above 55% IACS.

[0044] From the perspective of flexibility, the wire diameter of the alloy wire is preferably less than 1 mm, and more preferably 0.3 mm to 1 mm.

[0045] <Manufacturing Method of Aluminum Alloy Wire>

[0046] Next, the manufacturing method of the aluminum alloy wire described above will be explained. The aluminum alloy wire of this embodiment can be manufactured by sequentially performing the following steps: molten metal preparation, casting, forming, wire drawing, and aging heat treatment. Each step will be described in detail below.

[0047] <Preparation Process>

[0048] First, a molten liquid for forming aluminum alloy wire is prepared. In this embodiment, Al, Co, and Zr raw materials, along with other alloying materials as needed, are mixed in such a way that the molten liquid has the chemical composition described above. Then, these raw materials are placed into, for example, a melting furnace and heated using a burner or the like, thereby melting. The method of mixing and melting the raw materials is not particularly limited and can be carried out using methods known in the past. Here, the case where Zr and Co raw materials are added to the Al raw material is described, but Ni, Fe, or Ti raw materials can also be added instead of Co raw material.

[0049] The resulting molten metal is transferred to a storage tank (so-called an tundish) and stored. The storage tank is equipped with a pouring nozzle that allows the molten metal to flow out of the storage tank.

[0050] <Casting Process>

[0051] Next, the molten metal is poured from the storage tank through a pouring nozzle into a mold. For example, a continuous casting machine capable of performing continuous casting with a belt can be used as the mold. The continuous casting machine, for example, includes a cylindrical wheel and a belt with grooves on their outer circumferential surface, and is configured such that the belt is suspended from a portion of the outer circumferential surface of the wheel. Using the continuous casting machine, molten metal is poured into the space (groove portion) formed between the wheel and the belt, and solidified by cooling, thereby continuously forming casting material.

[0052] In this embodiment, the temperature of the molten metal (casting temperature) is set to 800°C or 850°C. When the temperature of the molten metal (casting temperature) is 800°C, cooling is performed relatively slowly using a mold. Conversely, when the temperature of the molten metal (casting temperature) is set higher, above 850°C, the molten metal is rapidly cooled using a mold. This suppresses Zr crystallization while allowing Co to crystallize, forming the casting material. This will be explained in detail below.

[0053] First, by rapidly cooling the melt, as described below, Co crystallization can be achieved while Zr crystallization is suppressed (maintaining Zr in a solid solution state).

[0054] According to the research of the inventors, in casting materials, if Zr forms crystals with Fe, the ductility of the casting material decreases, sometimes making it difficult to perform wire drawing. In contrast, even if Co forms crystals with Fe, it does not significantly affect the ductility of the casting material. Therefore, in casting materials, it is preferable to maintain Zr in a solid solution state without crystallizing, while allowing Co to crystallize. However, if the molten metal is cooled, Zr also crystallizes in small amounts along with Co, making it difficult to selectively dissolve Zr only.

[0055] In this regard, the inventors focused on the fact that Co crystallizes (precipitates) more readily than Zr when the molten metal is cooled, i.e., Co crystallizes (precipitates) at a greater rate than Zr. This difference in crystallization rate is due to the different diffusion rates in the aluminum solid phase.

[0056] Specifically, the diffusion rate of Co in the Al solid phase is equal to or greater than the self-diffusion rate of Al. Furthermore, the solid solubility of Co in the Al phase at thermal equilibrium is less than 0.05%, which is extremely low. Therefore, even immediately after casting and solidification from the molten metal, Co readily crystallizes within the Al structure. Through crystallization, most of Co crystallizes as compounds within the Al structure during the ingot (casting material) stage after casting. It should be noted that in the newly solidified Al phase, in addition to the crystallized compounds, there are also dissolved Co atoms. Immediately after solidification, supersaturated Co atoms, exceeding the thermal equilibrium solubility, dissolve in the Al phase. However, Co atoms diffuse rapidly within the Al phase, causing the supersaturated dissolved Co atoms to condense within a relatively short time, forming a compound phase. As a result, from casting and solidification until the casting material cools to room temperature, most of the added Co atoms exist as compound phases with Al, with the Co atoms dissolved in the Al phase remaining at a small amount, less than 0.1%, close to the thermal equilibrium concentration.

[0057] On the other hand, the diffusion rate of Zr in the Al phase is significantly lower than the self-diffusion rate of Al, resulting in a slower precipitation rate in the Al microstructure compared to Co. Furthermore, the maximum solid solubility of Zr in the Al phase under thermal equilibrium conditions is approximately 0.3–0.4%, several times greater than that of Co. Therefore, Zr is difficult to crystallize in the post-cast material stage, and most of it exists in a supersaturated solid solution state within the Al microstructure. Additionally, Zr diffuses significantly slower than Co, thus maintaining a supersaturated solid solution state even when the post-cast material is stored at room temperature for extended periods. The supersaturated solid solution Zr can be precipitated through aging heat treatment, such as heating at temperatures above 300°C.

[0058] Therefore, the inventors believed that if the molten metal is solidified before Zr begins to crystallize, Zr can be kept in a solid solution state, and thus studied the cooling rate of the molten metal. The results showed that the higher the cooling rate of the molten metal, the more Co crystallizes in the resulting casting material in the form of Al-Co-Fe compounds, and the more Zr crystallization is suppressed, maintaining the Zr solid solution state. By keeping Zr in a solid solution state, the reduction in ductility of the casting material caused by Zr crystallization can be suppressed. That is, compared with casting materials with less Zr crystallization, even with high-precision drawing, wire breakage can be suppressed, and fine alloy wires can be manufactured.

[0059] Furthermore, by setting the temperature of the melt to 850°C or higher, the solid solution limit of Zr to Al can be increased. Therefore, even when the Zr content is increased to, for example, 0.5% to 1.0% by mass, Zr can remain in a solid solution state without crystallization. It should be noted that the upper limit of the melt temperature is not particularly limited as long as it allows Zr to solidify; for example, it can be set to 900°C or lower, and preferably 870°C or lower.

[0060] The metallic microstructure of the casting material obtained in the casting process mainly consists of Al grains surrounded by steeply inclined grain boundaries. At these grain boundaries, Co and Fe often crystallize to form Al-Co-Fe compounds. Through the formation of Al-Co-Fe compounds, the amount of Fe in the Al phase that is the main cause of reduced conductivity decreases, and the amount of precipitates (FeAl3) that are the main cause of reduced elongation also decreases. It should be noted that Zr is in an unectic state, dissolved in the Al phase and at the grain boundaries.

[0061] It should be noted that Al-Co-Fe compounds do not reduce the ductility of Al alloys like FeAl3 compounds, and therefore do not hinder the reduction of alloy wire diameter. It should also be noted that Al-Co-Fe compounds are compounds containing at least Al, Co, and Fe, and may also contain other metallic elements. Furthermore, Al-Co-Fe compounds result in elongated shapes in the cast ingots.

[0062] Furthermore, during the casting process, the temperature of the molten metal flowing from the pouring nozzle of the storage tank decreases before being poured into the mold, and Zr dissolved in Al sometimes begins to crystallize. Therefore, from the viewpoint of suppressing Zr crystallization between the storage tank and the mold, it is preferable to heat the poured molten metal, preferably maintaining its temperature at 800°C or higher, and more preferably at 850°C or higher. This allows for more reliable suppression of the temperature drop of the molten metal during pouring, and improves the various properties of the alloy wire.

[0063] There are no particular limitations on the method for heating the molten metal flowing from the pouring nozzle. Known heating units, such as burners, electromagnetic heating devices, and high-frequency heating devices, can be used between the pouring nozzle and the mold. These heating units can be positioned between the pouring nozzle and the mold to heat the molten metal flowing from the pouring nozzle.

[0064] In the casting process, from the viewpoint of solidifying the molten liquid while Zr is in a solution state, it is preferable to set the cooling rate to 8°C / sec or higher, more preferably 20°C / sec or higher, and for example, 40°C / sec. There is no particular upper limit, and it can be set to 200°C / sec or lower. From the viewpoint of achieving such a cooling rate more reliably, a Properzi-type continuous casting machine can be used compared to a twin-roll casting machine.

[0065] It should be noted that the cooling rate can be adjusted by appropriately changing the thickness of the mold. For example, increasing the mold thickness can improve the ratio of the mold's cross-sectional area to the cross-sectional area of ​​the mold space (the cross-sectional area of ​​the casting material), thereby improving heat dissipation efficiency. Furthermore, the cooling rate is the value obtained by dividing the difference between the temperature of the molten metal when it is poured into the mold (e.g., 850°C) and the temperature at which the molten metal solidifies in the mold by the time from when the molten metal is poured into the mold until it solidifies.

[0066] <Molding Process>

[0067] Next, as needed, the casting material is formed into a rod shape (so-called roughing wire) to facilitate wire drawing. Here, for example, the casting material is plastically processed with a wire diameter of 5mm to 50mm. As plastic processing, conventionally known methods such as rolling, forging, and drawing can be performed.

[0068] <Wire drawing process>

[0069] Next, the rod-shaped cast material is cold-drawn into wire of a specified diameter. Wire drawing can be performed using conventional methods such as drawing with a die. It should be noted that the degree of machining is the ratio of the difference between the cross-sectional area of ​​the cast material and the cross-sectional area of ​​the wire-drawn material to the cross-sectional area of ​​the cast material, representing the reduction of area during the wire drawing process.

[0070] In the metal microstructure of the wire-drawn material obtained during the wire drawing process, Al grains are stretched in the wire drawing direction, introducing processing strain. In addition, Al-Co-Fe compounds crystallized in the casting material are finely pulverized through the wire drawing process, thereby being finely and densely dispersed in the metal microstructure of the wire-drawn material.

[0071] In this embodiment, by suppressing Zr crystallization, the casting material exhibits high ductility, thus improving the workability of the wire drawing process. From the viewpoint of finely pulverizing the Al-Co-Fe compound and dispersing it more finely in the wire drawing material, it is preferable to draw the casting material with a cross-sectional area of ​​0.01 times or less, resulting in a wire diameter of 2.0 mm or less. By setting this workability, it is easy to control the size of the Al-Co-Fe compound after wire drawing to 20 nm to 1 μm. Furthermore, during the aging heat treatment process described later, when Zr precipitates, the size of the Al-Zr compound is also easily controlled to 1 nm to 100 nm. Moreover, in the final alloy wire, the precipitates can be further dispersed and precipitated.

[0072] It should be noted that in this embodiment, the casting material has high ductility, so the annealing treatment (so-called intermediate annealing treatment) used to mitigate the processing strain during wire drawing can be omitted. This further suppresses the coarsening caused by the recrystallization of Al grains.

[0073] <Aging Heat Treatment Process>

[0074] Next, the drawing material is subjected to aging heat treatment to obtain the alloy wire of this embodiment.

[0075] In aging heat treatment, Zr dissolved in the Al phase precipitates as an Al-Zr compound, and the processing strain introduced into the metal structure of the drawing material is mitigated. In this embodiment, by finely dispersing the Co compound in the drawing material, Al recrystallization can be suppressed, and the processing strain can be mitigated through the recovery of Al crystallization.

[0076] In this embodiment, the aging heat treatment is performed in two stages. In other words, the aging heat treatment includes two heat treatment steps (a first heat treatment and a second heat treatment). In the first heat treatment, the drawing material is heated at 200°C for 1 to 10 hours. In the subsequent second heat treatment, the drawing material is heated at 300°C to 350°C for 20 hours or more. These heat treatments are performed at atmospheric pressure. Alternatively, these heat treatments are performed in an inert atmosphere such as atmosphere or Ar. Here, the drawing material is cooled to room temperature between the first and second heat treatments, but it is also possible to perform the first and second heat treatments continuously without cooling the drawing material to room temperature.

[0077] During the initial heat treatment at 200°C, some processing strain disappears, accompanied by the formation of subgrains. Although the diffusion of dissolved Zr atoms is very slow, they aggregate through high-speed diffusion into the subgrains, forming fine Al-Zr compounds at this stage. Furthermore, it is speculated that Al-Zr compound nuclei also form in the matrix region within the subgrains due to short-distance Zr atom movement. By performing a relatively low-temperature initial heat treatment, multiple fine Al-Zr compound particles can be pre-formed within the Al alloy.

[0078] By setting the temperature of the subsequent second heat treatment to 300°C or higher, subgrain boundaries formed in the first heat treatment stage can grow, thus improving the ductility of the alloy wire. Furthermore, since Al-Zr compounds are readily precipitated, the strength of the alloy wire can be increased while maintaining a high conductivity. On the other hand, by setting the temperature to 350°C or lower, recrystallization can be suppressed, and the subgrain boundaries can be maintained without disappearing, thus maintaining a higher strength of the alloy wire.

[0079] Furthermore, the heating time (processing time) of the wire drawing material in the second heat treatment is preferably set to 20 to 100 hours. By setting it to 20 to 100 hours, it is possible to fully precipitate the Al-Zr compound while keeping the manufacturing cost low, thereby improving the conductivity and strength of the alloy wire.

[0080] As described above, for example, compared to the case where the first heat treatment is not performed in the aging heat treatment, by performing the aging heat treatment in two stages, more fine Al-Zr precipitates can be dispersed in the grains of the alloy wire, thereby improving the strength of the alloy wire.

[0081] <Effects of this implementation method>

[0082] According to this embodiment, one or more of the following effects are achieved.

[0083] As a test for evaluating the properties of aluminum alloy wire, it is considered to measure the tensile strength of the aluminum alloy wire at room temperature. However, this evaluation method cannot detect the reduction in tensile strength caused by creep deformation of the aluminum alloy wire under high temperature conditions, and therefore cannot ensure the reliability of the aluminum alloy wire. In aluminum alloy wire used in connection terminals, stress relief occurs under high temperature conditions, which results in an increase in the resistance of the aluminum alloy wire.

[0084] In contrast, the aluminum alloy wire of this embodiment is a wire with a diameter of 0.1 mm or less, containing 0.3 to 0.6% by mass of Zr and less than 1.0% by mass of Co, Ni, Fe, or Ti. Furthermore, this aluminum alloy wire has a tensile strength of 170 MPa or more at room temperature and an elongation of 10% or more. Additionally, under conditions of 200°C and a strain rate of 10... -5 The stress during tensile deformation is above 60 MPa per second. Furthermore, at a temperature of 250°C and a strain rate of 10... -5 The stress during tensile deformation is above 40 MPa per second. Additionally, it has an electrical conductivity of above 55% IACS.

[0085] Thus, the specified tensile strength is maintained even under high-temperature conditions such as above 200°C and 250°C. High tensile strength under high-temperature conditions indicates that stress relief is less likely to occur in the alloy wire. Therefore, in the connection terminal section made of aluminum alloy wire, loosening of the terminal can be prevented. That is, an increase in resistance caused by stress relief can be prevented. The reason for this effect can be attributed to the above-described composition of the aluminum alloy wire and the fact that the aging heat treatment is performed in two stages. Here, by performing the aging heat treatment in two stages, the fine Al-Zr precipitates stabilize the subgrain structure formed during high-temperature deformation. This results in high creep resistance. Therefore, the heat resistance of the aluminum alloy wire can be improved.

[0086] Furthermore, by setting a higher cooling rate for the molten copper, a large amount of additive elements can be dissolved, thereby improving the tensile strength of the aluminum alloy wire. For example, during the casting of the molten copper, a cooling rate of 20°C / sec or higher is preferable. By rapidly cooling the molten copper under such conditions, Zr crystallization can be more reliably suppressed, and Co can be more finely dispersed and crystallized. As a result, a higher level of balance among various properties can be achieved.

[0087] In the above embodiments, alloy wires using Co and Zr as alloying elements have been described, but the present invention is not limited thereto, and Ni can be used instead of Co.

[0088] The alloy has a chemical composition consisting of Ni: 0.1–1.0 wt%, Zr: 0.2–1.0 wt%, Fe: 0.02–0.15 wt%, Si: 0.02–0.15 wt%, Mg: 0–0.2 wt%, Ti: 0–0.10 wt%, B: 0–0.03 wt%, Cu: 0–1.00 wt%, Ag: 0–0.50 wt%, Au: 0–0.50 wt%, Mn: 0–1.00 wt%, Cr: 0–1.00 wt%, Hf: 0–0.50 wt%, V: 0–0.50 wt%, Sc: 0–0.50 wt%, balance: Al and unavoidable impurities.

[0089] During the manufacturing process (casting) of alloy wire, Ni largely reacts with Al to form crystals (Al-Ni compounds), which exist as a compound phase in the final alloy wire. The Al-Ni compounds actually exist in the form of Al-Ni-Fe compounds, which absorb the Fe inevitably present in the aluminum alloy. These Al-Ni-Fe compounds contribute to the refinement of the Al recrystallization grains in the alloy and increase the elongation of the alloy wire. While Ni may reduce the conductivity of the alloy, by setting the Ni content to 0.1% to 1.0% by mass, it is possible to suppress the decrease in conductivity caused by Ni in the alloy wire and achieve a high level of balanced strength, elongation, and heat resistance due to Ni. The Ni content is preferably 0.2% to 1.0% by mass, more preferably 0.3% to 0.8% by mass. When using Ni to manufacture alloy wire, it can be manufactured in the same manner as Co. Furthermore, the resulting alloy wire has the same metallic structure as alloy wire using Co and possesses the aforementioned characteristics.

[0090] (Example)

[0091] Next, based on the embodiments, the present invention will be described in more detail using Table 1, but the present invention is not limited to these embodiments.

[0092] [Table 1]

[0093]

[0094] <Making of Alloy Wire>

[0095] (Example 1)

[0096] In Example 1, aluminum, Co, and Zr with a purity of 99.7% were combined with Co and Zr in the manner shown in Table 1 and melted in a high-frequency melting furnace under an argon atmosphere. After adjusting the temperature of the resulting melt to 800°C, the melt was poured into a copper water-cooled mold (inner diameter: The casting process involves casting the molten metal to obtain a casting material with a specified chemical composition. In this embodiment, a burner is installed to heat the injected molten metal, maintaining its temperature above 800°C. Furthermore, the cooling rate of the molten metal is 8°C / sec. The dimensions of the casting material are: outer diameter... A cylindrical shape, 150mm in length. This casting material was formed through die forging. After the roughing process, the wire is repeatedly drawn using dies to achieve a finer wire. No intermediate heat treatment is performed during the wire drawing process using a die. The resulting... The wire was subjected to a two-stage aging heat treatment to produce the alloy wire of Example 1. In this aging heat treatment, in the first heat treatment, the wire was held in a salt bath at 200°C for 5 hours, and then in the second heat treatment, the wire was held in a salt bath at 350°C for 24 hours.

[0097] (Example 2)

[0098] In Example 2, the amounts of Co and Zr were changed to achieve the composition shown in Table 1, and Ti was added. Otherwise, the alloy wire was made in the same manner as in Example 1.

[0099] (Example 3)

[0100] In Example 3, the amount of Zr added was changed to the composition shown in Table 1, and Ni and Ti were added instead of Co. The temperature of the melt during casting was set to 850°C and the cooling rate was set to 40°C / sec. Otherwise, the alloy wire was made in the same manner as in Example 1.

[0101] (Example 4)

[0102] In Example 4, the amounts of Co and Zr were changed to the composition shown in Table 1, the temperature of the melt during casting was set to 850°C, and the cooling rate was set to 40°C / sec. Otherwise, the alloy wire was made in the same manner as in Example 1.

[0103] (Comparative Examples 1-4)

[0104] In Comparative Examples 1-4, the aging heat treatment was not performed in two stages, but only once (keeping the wire in a salt bath at 350°C for 24 hours). Apart from this, the alloy wire was produced in the same manner as in Examples 1-4.

[0105] (Comparative Example 5)

[0106] In Comparative Example 5, the alloy wire was prepared in the same manner as in Example 1, except that Co was not added and the amount of Zr added was changed.

[0107] (Comparative Example 6)

[0108] In Comparative Example 6, the aging heat treatment was not performed in two stages, but only once (keeping the wire in a salt bath at 350°C for 24 hours). Otherwise, the alloy wire was produced in the same manner as in Comparative Example 5.

[0109] (Evaluation Method)

[0110] For the manufactured alloy wires, the tensile strength, elongation, and conductivity are evaluated using the following methods.

[0111] <Tensile strength and elongation>

[0112] The tensile strength and elongation of the alloy wire were determined by tensile testing of the alloy wire (based on the test method of JIS Z 2241 (test speed: 20 mm / min)). A Shimadzu 50N capacity force sensor was used for strength measurement.

[0113] In this embodiment, tensile strength was measured at room temperature (25±5℃), at 200℃, and at 250℃. The scoring intervals before the test were all 100mm. The tensile strength at 200℃ and 250℃ was measured at a strain rate of 10... -5 The stress during tensile deformation is measured per second. For measurements at 200°C and 250°C, the ends of a 0.45mm diameter wire, serving as the test piece, are fixed to the holding clamps. A tension not exceeding 0.5N is applied to the test piece while the crosshead position of the testing machine is adjusted during heating in a constant temperature bath. To stabilize the temperature after reaching the target temperature, a holding period of at least 2 hours is performed before conducting the tensile test. The test temperature is measured using thermocouples mounted on the wire holding clamps.

[0114] In this embodiment, a tensile strength of 170 MPa or more at room temperature, 60 MPa or more at 200°C, and 40 MPa or more at 250°C is evaluated as having high strength. Furthermore, a tensile strength of 10% or more at room temperature is evaluated as having high elongation.

[0115] <Conductivity>

[0116] Regarding the conductivity of the alloy wire, the resistance of the manufactured alloy wire at 20°C was measured using the DC four-terminal method, and the conductivity was calculated. In this embodiment, if the conductivity is 55% IACS or higher, it is evaluated as having high conductivity.

[0117] <Evaluation Results>

[0118] The properties of the alloy wires in Examples 1 to 4 were measured, and the results are shown in Table 1. All of them were confirmed to have a room temperature tensile strength of 170 MPa or more, a tensile strength at 200°C of 60 MPa or more, a tensile strength at 250°C of 40 MPa or more, an elongation of 10% or more, and a conductivity of 55% IACS or more, which are qualified (○).

[0119] On the other hand, in the alloy wires of Comparative Examples 1 to 6, as shown in Table 1, none of these conditions were met.

[0120] The differences in evaluation results between the examples and the comparative examples were investigated, and the results confirmed that the differences in properties were due to the metal structure of the alloy wire.

[0121] As can be seen from the above, by adding Co, Ti or Ni and Zr as alloying elements to the molten aluminum and performing a two-stage aging heat treatment on the alloy wire cast from the molten aluminum, aluminum alloy wire can be produced. This results in aluminum alloy wire with high and balanced strength, elongation, conductivity and high reliability.

[0122] The invention made by the inventors has been specifically described above based on the embodiments, but the invention is not limited to the above embodiments, and various modifications can be made without departing from its spirit.

[0123] In addition, the following describes a portion of the content described in the implementation method.

[0124] Appendix 1: A method for manufacturing aluminum alloy wire, comprising:

[0125] (a) The process of casting a casting material by pouring molten aluminum into a mold.

[0126] (b) The process of rolling the cast material to form a copper roughing wire.

[0127] (c) The process of drawing the copper rough-rolled wire into aluminum alloy wire.

[0128] (d) A process of performing a first heat treatment on the aluminum alloy wire, followed by a second heat treatment at a temperature higher than that of the first heat treatment.

[0129] The aluminum alloy wire contains 0.2–1.0% by mass of Zr and 0.1–1.0% by mass of Co, or 0.2–1.0% by mass of Zr and 0.1–1.0% by mass of Ni, and optionally contains Fe: 0.02–0.15% by mass, Si: 0.02–0.15% by mass, Mg: 0–0.2% by mass, Ti: 0–0.10% by mass, B: 0–0.03% by mass, Cu: 0–1.00% by mass, Ag: 0–0.50% by mass, Au: 0–0.50% by mass, Mn: 0–1.00% by mass, Cr: 0–1.00% by mass, Hf: 0–0.50% by mass, V: 0–0.50% by mass, Sc: 0–0.50% by mass, with the balance consisting of aluminum and unavoidable impurities.

[0130] The tensile strength at room temperature is above 170 MPa.

[0131] The elongation is over 10%.

[0132] At a temperature of 250℃, at 10 -5 The stress during tensile deformation at a strain rate of / sec is above 40MPa.

[0133] Appendix 2: In the manufacturing method of aluminum alloy wire described in Appendix 1,

[0134] In step (a), the casting material is cast by cooling the molten liquid at a rate of 40°C / sec or higher.

[0135] Note 3: In the manufacturing method of aluminum alloy wire described in Note 1 or 2,

[0136] In step (d), the processing time of the second heat treatment is longer than that of the first heat treatment.

Claims

1. An aluminum alloy wire, which is a wire made of aluminum alloy. The aluminum alloy contains 0.2–1.0% by mass of Zr and 0.1–1.0% by mass of Co, and optionally contains Fe: 0.02–0.15% by mass, Si: 0.02–0.15% by mass, Mg: 0–0.2% by mass, Ti: 0–0.10% by mass, B: 0–0.03% by mass, Cu: 0–1.00% by mass, Ag: 0–0.50% by mass, Au: 0–0.50% by mass, Mn: 0–1.00% by mass, Cr: 0–1.00% by mass, Hf: 0–0.50% by mass, V: 0–0.50% by mass, Sc: 0–0.50% by mass, with the balance consisting of aluminum and unavoidable impurities. The tensile strength at room temperature is above 170 MPa. The elongation is over 10%. At a temperature of 200℃, at 10 -5 The stress during tensile deformation at a strain rate of / sec is above 60MPa. At a temperature of 250℃, at 10 -5 The stress during tensile deformation at a strain rate of / sec is above 40MPa. The aluminum alloy wire is obtained through an aging heat treatment that includes a first heat treatment at 200°C for 1 to 10 hours and a second heat treatment at 300 to 350°C for more than 20 hours.

2. An aluminum alloy wire, which is a wire made of aluminum alloy. The aluminum alloy contains 0.2–1.0% by mass of Zr and 0.1–1.0% by mass of Ni, and optionally contains Fe: 0.02–0.15% by mass, Si: 0.02–0.15% by mass, Mg: 0–0.2% by mass, Ti: 0–0.10% by mass, B: 0–0.03% by mass, Cu: 0–1.00% by mass, Ag: 0–0.50% by mass, Au: 0–0.50% by mass, Mn: 0–1.00% by mass, Cr: 0–1.00% by mass, Hf: 0–0.50% by mass, V: 0–0.50% by mass, Sc: 0–0.50% by mass, with the balance consisting of aluminum and unavoidable impurities. The tensile strength at room temperature is above 170 MPa. The elongation is over 10%. At a temperature of 200℃, at 10 -5 The stress during tensile deformation at a strain rate of / sec is above 60MPa. At a temperature of 250℃, at 10 -5 The stress during tensile deformation at a strain rate of / sec is above 40MPa. The aluminum alloy wire is obtained through an aging heat treatment that includes a first heat treatment at 200°C for 1 to 10 hours and a second heat treatment at 300 to 350°C for more than 20 hours.

3. The aluminum alloy wire according to claim 1 or 2, wherein, The aluminum alloy also contains 0.02 to 0.15% by mass of Fe and 0 to 0.10% by mass of Ti.

4. The aluminum alloy wire according to claim 1 or 2, wherein, The conductivity at room temperature is above 55% IACS.

5. The aluminum alloy wire according to claim 3, wherein, The conductivity at room temperature is above 55% IACS.

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