Technical Field
The present disclosure relates to an aluminum alloy wire rod used as a conductor of an electric wiring structure, an aluminum alloy stranded wire, a coated wire, and a wire harness, as well as, a method of manufacturing an aluminum alloy wire rod and a method of measuring an aluminum alloy wire rod, and particularly relates to an aluminum alloy wire rod that has a low 0.2% yield strength to tensile strength while ensuring a good balance between tensile strength, elongation and conductivity, even if used as an extra fine wire having a wire diameter of less than or equal to 0.5 mm.
Background Art
In the related art, a so-called wire harness has been used as an electric wiring structure for mobile bodies such as automobiles, trains, and aircrafts, or an electric wiring structure for industrial robots. A wire harness is a member including electric wires each having a conductor made of copper or copper alloy and fitted with terminals (connectors) made of copper or copper alloy (e.g., brass). With recent rapid advancements in performances and functions of automobiles, various electrical devices and control devices installed in mobile bodies tend to increase in number and electric wiring structures used for the devices also tend to increase in number. On the other hand, for environmental friendliness, lightweighting of mobile bodies is strongly desired for improving fuel efficiency of mobile bodies such as automobiles.
As one of the measures for achieving lightweighting of mobile bodies, there have been, for example, continuous efforts in the studies on a conductor of an electric wiring structure to replace conventionally used copper or copper alloys with aluminum or aluminum alloys, which is more lightweighted. Since aluminum has a specific gravity of about one-third of a specific gravity of copper, and has a conductivity of about two-thirds of a conductivity of copper (in a case where pure copper is a standard for 100% IACS, pure aluminum has approximately 66% IACS), an aluminum conductor wire rod needs to have a cross sectional area of approximately 1.5 times greater than a cross sectional area of a copper conductor wire rod to allow the same electric current as the electric current flowing through the copper conductor wire rod to flow through the aluminum conductor wire rod. Even an aluminum conductor wire rod having an increased cross section as described above is used, using an aluminum conductor wire rod is advantageous from the viewpoint of lightweighting, since an aluminum conductor wire rod has a mass of about half the mass of a pure copper conductor wire rod. Note that, “% IACS” represents a conductivity when a resistivity 1.7241×10−8 Ωm of International Annealed Copper Standard is taken as 100% IACS.
However, it is known that a pure aluminum wire rod, typically an aluminum alloy wire rod for transmission lines (JIS (Japanese Industrial Standard) A1060 and A1070), is generally poor in its durability to tension, resistance to impact, and bending characteristics. Therefore, for example, it cannot withstand a load abruptly applied by an operator or an industrial device while being installed to a car body, a tension at a crimp portion of a connecting portion between an electric wire and a terminal, and a cyclic stress loaded at a bending portion such as a door portion. On the other hand, an alloyed material containing various additive elements added thereto is capable of achieving an increased tensile strength, but a conductivity may decrease due to a solid solution phenomenon of the additive elements into aluminum, and because of excessive intermetallic compounds formed in aluminum, a wire break due to the intermetallic compounds may occur during wire drawing. Therefore, it is essential to limit or select additive elements to provide sufficient elongation characteristics to prevent a wire break, and it is further necessary to ensure conductivity and a tensile strength equivalent to those in the related art.
As a high strength aluminum alloy wire rod, for example, an aluminum alloy wire rod containing Mg and Si is known, and a 6000-series aluminum alloy (Al—Mg—Si based alloy) wire rod is a typical example of such aluminum alloy wire rod. Generally, as for the 6000-series aluminum alloy wire rod, the strength can be increased by applying a solution heat treatment and an aging treatment. However, in a case where an extra fine wire such as a wire having a wire diameter of less than or equal to 0.5 mm is manufactured using a 6000-series aluminum alloy wire rod, although a high strength can be achieved by applying a solution heat treatment and an aging treatment, there was a tendency that a work efficiency for attaching to a car body decreases because of a large force required for plastic deformation due to an increase in a yield strength (0.2% yield strength).
A conventional 6000-series aluminum alloy wire used for an electric wiring structure of a mobile bodies is described, for example, in Japanese Laid-Open Patent Publication No. 2012-229485. The aluminum alloy wire described in Japanese Laid-Open Patent Publication No. 2012-229485 is an extra fine wire that achieves an aluminum alloy wire having an improved elongation while having a high strength and a high conductivity. In Japanese Laid-Open Patent Publication No. 2012-229485, it is described that a good conductivity, tensile strength, and elongation can be obtained by using finer crystal grain size, but fails to disclose or suggest that a high strength and a low yield strength are achieved simultaneously.
The present disclosure is related to providing an aluminum alloy wire rod used as a conductor of an electric wiring structure, the aluminum alloy wire having a low 0.2% yield strength (YS) to tensile strength (TS) while ensuring a good balance between tensile strength, elongation and conductivity, even if used as an extra fine wire having a wire diameter of less than or equal to 0.5 mm, as well as an aluminum alloy stranded wire, a coated wire, and a wire harness, and to provide a method of manufacturing such an aluminum alloy wire rod and a method of measuring such an aluminum alloy wire rod.
The inventors have found that, based on the premise that an aluminum alloy containing Mg and Si is used, an aluminum alloy wire rod having a low 0.2% yield strength to tensile strength while ensuring a good balance between tensile strength, elongation and conductivity can be obtained with a predetermined component composition and by controlling the manufacturing process, and have completed the present disclosure. Further, it was found that production of solute atom clusters is involved in the mechanism of the present disclosure, and the disclosure can be specified by the presence of said solute atom cluster.