JP2015010233A - Aluminum conductor for electrification - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-reliability aluminum conductor for electrification that prevents an aluminum conductor from corroding owing to a defect such as a pinhole and is free of peeling of a plating layer while securing high conductivity of an electrification contact part.SOLUTION: An electroless Ni-P plating layer 2 is formed on a base material surface of an aluminum conductor 1 and an electrolytic Ni plating layer 3 is laminated further thereupon. Consequently, defect parts 2a, 3a such as pits, pinholes, etc., developed in the respective plating layers 2, 3 are made discontinuous so as to prevent the aluminum conductor 1 from being in contact with the atmosphere. Consequently, base material corrosion of the aluminum conductor 1 can be effectively suppressed through inexpensive Ni plating. Here, film thicknesses of the respective plating layers 2, 3 are set to 2 to 7 μm and then residual stress is suppressed low so as to effectively prevent the plating layers from peeling. Further, an outermost surface is subjected to electrolytic Ni plating of relatively low hardness (approximately Hv250) and adhesion of an electrification contact part (crimping, bolt fastening) to a connection opposite conductor is thereby enhanced so as to secure excellent conductivity.

Description

  The present invention relates to an aluminum conductor for energization applied to a main circuit conductor of a switching device such as a bar conductor, a circuit breaker (breaker), a vacuum circuit breaker (VCB), etc. wired in a panel such as a switchboard. It relates to the structure of anti-corrosion plating.

  Since the energizing aluminum conductor mentioned above is connected to the conductor of the other end of the connection via bolt fastening, crimp terminals, etc., the temperature rise due to Joule heating accompanying energization is high for the energized contact part. In addition to limiting the value, the conductor itself must have high corrosion resistance.

  By the way, since an oxide film (non-conductive) is formed on the surface of aluminum in an air atmosphere, the contact resistance of the connection portion increases as it is. In addition, since aluminum has a corrosion potential that is a base metal, when the copper conductor on the other side of the connection is overlapped with the aluminum conductor, the corrosion of the aluminum conductor may progress due to so-called contact corrosion (electrolytic corrosion). There is.

  Therefore, as a countermeasure against corrosion of the aluminum conductor, surface treatment for plating the surface of the aluminum conductor (base material) is usually performed. In this case, the restriction on the temperature rise of the conductor connection portion differs depending on the plating type. In addition, since the temperature rise due to energization greatly affects the conductivity of the plating film and the effective contact area with the mating material, the plating film is not only highly conductive, but also increases the adhesion of the energized contact area. A soft, low hardness material is desired.

  On the other hand, Sn, Ag, Ni plating, etc. can be considered as the type of anticorrosion plating, but since Sn has a temperature rise restriction of about 10-15K lower than Ag, Ni, its application is a conductor with low current density. It is limited to. Moreover, although Ag plating can be used even at a temperature increase equivalent to Ni, it is expensive and has a limitation in terms of cost.

Therefore, Ni plating is promising for anticorrosion plating of aluminum conductors, but Ni plating cannot avoid the appearance of defects such as pits and pinholes (fine holes reaching the base material).
Ni plating includes electroless Ni plating (for example, electroless Ni-P plating) and electrolytic Ni plating. Of these, electroless Ni-P plating does not require a power source and provides a uniform plating film thickness. Although there are excellent advantages as plating of current-carrying aluminum conductors, such as superior corrosion resistance compared to electrolytic Ni plating, the electroless Ni-P plating contains heavy metal additives (plating solution stabilizer) Therefore, when they are co-deposited on the plating film, they form nuclei and form discontinuous points. In addition, Ni is precipitated with the generation of hydrogen in the portion where the plating is growing. As the film grows, defects such as pinholes appear inside the film.

  When chlorine ions enter the pinhole from the usage environment, pitting corrosion occurs when it reaches the base of the aluminum conductor, and the local battery action is further enhanced due to the Ni alloy existing in the plating film. Amplification causes intense pitting corrosion, and the corrosion product may push up the plating film and cause the film to peel off, so that sufficient corrosion resistance cannot be secured alone.

  It is known that electroless Ni-P plating increases corrosion resistance by increasing the plating film thickness, and also reduces the occurrence of defects such as pits and pinholes. There is a problem that the residual stress (internal stress) of the film increases, and this causes a possibility that the plating film peels off when a mechanical tightening force is applied to the connection portion of the aluminum conductor.

  On the other hand, as a countermeasure against defects in pits and pinholes generated in Ni plating film applied to aluminum material, a protective film of fluororesin is applied on Ni plating film to seal the pits and pinholes. An anticorrosion structure (see, for example, Patent Document 1) in which a pinhole is shielded from the air atmosphere is known.

JP-A-8-281868

  By the way, in the anticorrosion structure disclosed in the above-mentioned patent document 1, since the fluororesin film (electrically insulating) inhibits the conductivity of the current-carrying contact portion of the conductor, it is applied to the current-carrying aluminum conductor. Can not.

  Therefore, as a countermeasure for the pinhole defect of the plating applied to the energizing aluminum conductor, the electroless Ni-P plating was used as a base plating, and the electroless Ni-P plating was further applied thereon, resulting in a film of the base plating. A method of sealing with a plating layer with pinholes (multiple plating) is also conceivable. However, since the electroless Ni-P plating pinholes are randomly generated as described above, the pinholes in the base plating layer and the pinholes developed in the plating layer formed thereon are connected to each other to form the aluminum conductor. A pinhole reaching the substrate is formed, and therefore the aluminum conductor substrate may be exposed to the atmosphere through a pinhole that extends across the two layers of the plating film.

  Therefore, the object of the present invention is to prevent corrosion of the aluminum base material due to defects such as pits and pinholes that appear in the plating film while ensuring high conductivity in the current-carrying contact portion of the aluminum conductor subjected to anticorrosion plating. Another object of the present invention is to provide a highly reliable energizing aluminum conductor that is effectively prevented and that does not cause the plating film to peel off due to the mechanical pressure accompanying the connection of the conductor.

In order to achieve the above object, the energizing aluminum conductor of the present invention has a plating structure in which an electroless Ni-P plating is applied to the aluminum conductor as a base plating, and further, an electrolytic Ni plating is applied thereon to provide an anticorrosive surface treatment. (Claim 1) Specifically, it shall be comprised like the following description aspect.
(1) In the aluminum conductor, each film thickness of electroless Ni—P plating and electrolytic Ni plating is set to 2 μm or more and 7 μm or less.
(2) The material of the aluminum conductor is pure aluminum, an alloy mainly composed of aluminum, or an aluminum composite material.
(3) In the energizing aluminum conductor, the electroless Ni—P plating composition has a P concentration of 1 to 14 wt%, and the plating film has an amorphous crystal structure or an average crystal grain size of 0.1 μm or less. It is microcrystalline (claim 4).

  According to the energizing aluminum conductor configured as described above, corrosion of the aluminum conductor and peeling of the plating layer due to defects such as pits and pinholes can be prevented.

It is a local schematic cross-section figure of the aluminum conductor for electricity supply by the Example of this invention. FIG. 2 is a diagram showing an electroless Ni—P plating applied to the aluminum conductor in FIG. 1 and a plating treatment process of electrolytic Ni plating, wherein (a) is a state diagram in which the electroless Ni—P plating is applied to the aluminum conductor; ) Is a state diagram of the plating film growth in the initial stage of electrolytic Ni plating applied on the electroless Ni-P plating layer, and (c) is a state diagram in the final stage of the electrolytic Ni plating process.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below based on the examples shown in FIGS.
In the present invention, as the anticorrosion surface treatment for the aluminum conductor, in the first treatment step, the surface of the aluminum conductor 1 is subjected to electroless Ni-P plating to form the electroless Ni-P plating layer 2, and then the second treatment. In the process, electrolytic Ni plating is applied on the electroless Ni-P plating layer 2 to form an electrolytic Ni plating layer 3. The aluminum conductor 1 can be made of pure aluminum, an alloy containing aluminum as a main component, or an aluminum composite material.

  By this plating process, in the state where the electroless Ni-P plating is applied to the aluminum conductor 1 (see FIG. 2A), defective portions 2a such as pinholes and pits appear in the plated layer 2, but continue. When electrolytic Ni plating is performed on the electroless Ni-P plating layer 2 in the second processing step, the edge-shaped peripheral edge (arrow) of the defect portion 2a is shown in the initial stage of the electrolytic plating (see FIG. 2B). The electric field concentrates on the P portion), and the current flows intensively in this portion. As a result, Ni preferentially precipitates around the defect portion 2a of the electroless Ni-P plating layer 2, and the electrolytic Ni plating layer 3 grows so as to fill the defect portion 2a. 3 is grown to a predetermined thickness (see FIG. 2C), the opening surface of the defective portion 2a of the electroless Ni-P plating layer 2 is reliably sealed by the electrolytic Ni plating layer 3. Is done. As a result, as shown in the schematic cross-sectional view of FIG. 1, there is no possibility that the surface of the base material of the aluminum conductor 1 is directly exposed to the atmosphere through the defective portions 2 a and 3 a generated in the plating layers 2 and 3 and corroded. Note that reference numeral 3a denotes a defect portion such as a pinhole developed in the plating layer 3 during the growth process of electrolytic Ni plating.

  On the other hand, including electrolytic Ni plating, normal plating forms and grows crystal nuclei according to the underlying crystal (surface energy). Therefore, factors related to the generation of defects such as pinholes and pits, such as hydrogen generation, crystal growth and residual stress associated therewith during the growth process of the plating film, are greatly affected by the substrate.

  On the other hand, since the electroless Ni-P plating layer 2 of the above-mentioned base plating is formed in an amorphous state or very fine crystal grains, the electrolytic Ni plating applied on the electroless Ni-P plating layer 2 is performed. Is less affected by the underlying electroless Ni—P plating layer 2 during the growth of the plating layer 3. For this reason, the defect 3a appearing in the electrolytic Ni plating layer 3 is formed in the underlying electroless Ni-P plating layer 2 and is generated at irregular points irrespective of the defect 2a. As shown in FIG. 2C, the defect portions 2a and 3a of the Ni plating layers 2 and 3 are discontinuous in the cross-sectional direction in the entire plating layers 2 and 3 formed on the aluminum conductor 1 as the inner and outer layers. As a result, a plating film having a high anticorrosion effect can be realized.

  Further, regarding the two-layered plating layer applied to the aluminum conductor 1, the outermost plating layer is an electrolytic Ni plating layer 3 (hardness: about Hv250) whose hardness is lower than that of electroless Ni-P plating (precipitation hardness: Hv500). By doing so, it is possible to increase the adhesion between the conductors in the current-carrying connection portion (crimping) between the current-carrying aluminum conductor and the conductor to be connected, thereby ensuring high electrical conductivity.

  Furthermore, the P concentration of the electroless Ni—P plating is set in the range of 1 to 14 wt% so that the film crystal structure of the plating layer 2 is amorphous or the microcrystalline material has an average crystal grain size of 0.1 μm or less. In addition, by setting the film thicknesses of the electroless Ni-P plating layer 2 and the electrolytic Ni plating layer 3 to 2 μm or more and 7 μm or less, excessive residual stress (internal stress) associated with the plating process is generated and the residual stress is reduced. High reliability can be secured by effectively suppressing peeling of the plating film.

  As described above, according to the aluminum conductor for energization according to the present embodiment, electroless Ni plating is performed on the electroless Ni-P plating applied as the base plating to the aluminum conductor, so that the electroless Ni plating process is electroless. Ni and P start to deposit due to concentration of the electric field and current at the pits, pinholes and other defects occurring in the Ni-P plating film, thereby preferentially sealing the defects in the underlying plating with the electrolytic Ni plating layer. It will be stopped. In addition, defects such as pinholes are generated with the growth of the plating film even in the electrolytic Ni plating performed later, but this defect appears irregularly in a region outside the defects of the underlying electroless Ni-P plating. As a whole, the Ni plating layer composed of two layers can suppress the occurrence of continuous defects in the cross-sectional direction and improve the corrosion resistance of the aluminum conductor.

  In addition, the hardness of the electrolytic Ni plating applied to the outermost surface of the conductor (about Hv250) is softer than the precipitation hardness (Hv500) of the electroless Ni-P plating. It is possible to increase the adhesion between the conductor on the connection partner side and to ensure high electrical conductivity.

  Further, the P concentration of the electroless Ni—P plating is set in the range of 1 to 14 wt% so that the crystal structure of the plating film is amorphous or the microcrystalline material has an average crystal grain size of 0.1 μm or less. By setting the film thickness of electrolytic Ni-P plating and electrolytic Ni plating to 2 μm or more and 7 μm or less, excessive residual stress is generated and the plating film is peeled off due to residual stress. And can provide a highly reliable aluminum conductor for energization.

DESCRIPTION OF SYMBOLS 1 Aluminum conductor 2 Electroless Ni-P plating layer 2a Defect part 3 Electrolytic Ni plating layer 3a Defect part

Claims (4)

  An aluminum conductor for energization, wherein electroless Ni-P plating is applied to an aluminum conductor as a base plating, and further electrolytic Ni plating is applied thereon.   2. The energizing aluminum conductor according to claim 1, wherein each film thickness of electroless Ni-P plating and electrolytic Ni plating is 2 μm or more and 7 μm or less.   3. The energizing aluminum conductor according to claim 1, wherein the aluminum conductor is pure aluminum, an alloy containing aluminum as a main component, or an aluminum composite material.   4. The current-carrying aluminum conductor according to claim 1, wherein the composition of electroless Ni-P plating has a P concentration of 1 to 14 wt%, and the crystal structure of the plating film is amorphous or the average crystal grain size is 0.1. A current-carrying aluminum conductor characterized by being microcrystalline of 1 μm or less.