JPS5937753B2 - Method for preventing galvanic corrosion that occurs at contact points between dissimilar metal materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of preventing galvanic corrosion from occurring in a metal material with a lower potential, that is, a more base metal material, in contacting dissimilar metal materials.

In general, single metal materials such as Zn, Zn alloys, and Fe are metal materials with a relatively low potential, and these metal materials are in mutual contact (electrically connected state) with more noble metal materials. When it is in an electrolyte solution such as an aqueous solution,
Since the battery action is made up of both metal materials, the three low-potential metal materials (more base metal materials) that serve as the anode are eluted, and their corrosion rapidly increases, usually resulting in so-called galvanic corrosion. It is.

In particular, for example, Zn and Zn alloys are, as is well known, Fe
, Cn, and most other metal materials 30, and when in contact with these metal materials, it becomes an anode for galvanic corrosion and melts and corrodes.
Such galvanic corrosion is most problematic for n and Zn alloy materials.

Similarly, metal materials such as Cu and Cu alloys, Ni, and F
When metal materials such as Fe and Al are in contact, the latter metal material has a lower potential, i.e., the former metal material is more noble, so the metal materials such as Fe and Al are affected by galvanic action. It corrodes.

By the way, currently, as a method for preventing galvanic corrosion that occurs in the contact areas of dissimilar metal materials as described above,
Select dissimilar metal materials with a small potential difference between them.

(2) Increasing the circuit resistance by interposing an insulating material or coating material at the contact portion of different metal materials.

(3) Increasing the polarization of both metals by such means as the use of inhibitors, removal of dissolved oxygen, and cathodic polarization.

However, in method (1) above, it is unavoidable that dissimilar metal materials are limited in terms of their material properties, so a selection combination of dissimilar metal materials that can obtain a functionally satisfactory result is adopted. In addition, depending on the usage environment, it may not be possible to use insulating materials or coating materials. In such cases, method (2) above cannot be applied, and the use of inhibitors and dissolved The polarization method by removing oxygen cannot achieve a wide change in polarization, and the cathode polarization method has problems such as the field of application is considerably limited, so method (3) above is not a satisfactory prevention method. On the other hand, since the usage environment has a limiting force in suppressing corrosion, it is easy to satisfactorily prevent galvanic corrosion that occurs at the contact area of dissimilar metal materials by a desired combination. The current situation is that this is not the case.

From the above-mentioned viewpoints, the present inventors have devised a method that allows free selection and combination of dissimilar metal materials and completely prevents galvanic corrosion without being restricted by the usage environment. In order to find out, we first investigated the mechanism of galvanic corrosion, and found that (a) galvanic corrosion is an electrochemical reaction, that is, two parallel reactions, an anode reaction and a cathode reaction, linked by the exchange of electrons, simultaneously at the same speed. It is something that occurs as a result of something that happens.

(b) Galvanic corrosion is a problem mainly in fresh water,
This occurs in environments where the pH value is close to neutral, such as seawater, but in these corrosive environments, the progress of corrosion is dominated by cathode reactions, so cathode reactions become rate-limiting. (c) The cathode reaction is represented by a ring element reaction of dissolved oxygen; and a reduction reaction of hydrogen.

Having obtained the recognition shown in (a) to (c) above, and further based on the above recognition, we proceeded with our research, and (d) Cu, Cu-Zn alloy (contains Zn: 30% by weight), which is a representative metal material.
, Ni, Zn alloy (trade name MAK2 and 3), Fe,
When one Al and Cr plating material was used and its polarization characteristics were measured, the results shown in FIGS. 1 and 2 were obtained.

In addition, Figure 1 shows specific resistance: 20Ω-? Fig. 2 shows the resistivity in artificial seawater containing Na2sO4:
It is in fresh water (tap water) with a resistance of 1800Ω.
Additionally, Cu, Cu-Zn alloys, Ni, and Cr plating materials improve cathode polarization characteristics, and Zn alloys, Fe and A
1 is the result of measuring the anode polarization characteristics.

e) As is clear from the results shown in Figures 1 and 2, the Cr plating material
It has extremely large cathode polarization characteristics compared to

This is due to the resistance polarization caused by the extremely strong and dense oxide film that forms on the Cr surface.
Although the surface exhibits a relatively noble potential due to the oxide film, it is originally a metal with a lower potential than Fe at -0.8 on the saturated Kanagai electrode standard (SCE), and has extremely large cathodic polarization. This provides evidence that the properties are stable.
(f) Therefore, based on the results shown in Figures 1 and 2, Zn alloy (MAK-2), Fe (steel)
, and Al (purity 99.5%), and Cu,
The corrosion rate (corrosion current density) of different metal materials in combination with Cu-Zn alloy, Nil and Cr plating materials is shown in Table 1. From the results shown in Table 1, it is clear that Cu When Cr plating is applied to the surface of metal materials such as , Cu-Zn alloy, and Ni, when the other metal material is Zn alloy, the corrosion current density, that is, the amount of galvanic corrosion, is about 1/1 in artificial seawater. 10 to 1/20, in fresh water (tap water) it decreases to about 1/50, and similarly when the other metal material is Fe, it decreases to about 1/50 in artificial seawater.
It decreases to ~1/90 in freshwater and approximately 1/100 to 1/120 in fresh water, and furthermore, when the partner metal material is Al, it decreases to approximately 1/60 to 1/80 in artificial seawater and approximately 1/120 in fresh water. /55~1
It is clear that the reduction is to /60.

The conclusions shown in (d) to (f) above were obtained.

Therefore, the present invention has been made based on the above recognition and conclusion, and is based on the above recognition and conclusion. The present invention is characterized by a method for preventing galvanic corrosion of baser metal materials (i.e., lower potential metal materials) at material contact points. Next, the galvanic corrosion prevention method of the present invention will be explained using examples.

Example 1 Twenty 3/8-inch Fe nuts and 20 brass bolts were prepared, and 10 of them were made of brass. Electric chrome plating (vapor-deposited chrome plating is also acceptable) is applied to the bolt, and the thus prepared nut and bolt are placed in fresh water (tap water) with a resistivity of 4500Ω for 14 days (336 hours). ), and the material corrosion loss and galvanic corrosion loss of the nut after the immersion test were measured.

The measurement results are shown in Table 2 as average values (average of 10 samples). Example 2 Nuts were each made of Zn alloy (MAK-2
) and Al, and the immersion test was conducted under the same conditions as in Example 1, except that the immersion test time was 1 month (720 hours), and the test results are shown in Table 2.

As shown in Table 2, Fe, Zn alloys, and Al
In the case of brass nuts and bolts made of brass, which is a metal material more noble than these metal materials, galvanic corrosion is significant, and when brass bolts are plated with Cr based on this invention, galvanic corrosion is drastically reduced. Approximately 1/2 for Fe nuts
It is clear that the reduction is 1/35 for the Zn alloy nut and 1/18 for the Al nut.

In addition, it has been confirmed that when the method of the present invention is applied practically to, for example, gas pressure regulating valves of propane gas pressure reducing regulators and crimp terminals of aluminum electric wires, excellent galvanic corrosion resistance is exhibited. As described above, according to the present invention, the material limitations of the combined dissimilar metal materials can be removed by simply applying Cr plating to the contact surfaces of the more noble metal materials of the dissimilar metal materials that come into contact. Moreover, it is possible to almost completely prevent galvanic corrosion that occurs at the contact portion of dissimilar metal materials with a potential difference at a low cost and under any usage environment.

[Brief explanation of drawings]

FIG. 1 is a curve diagram showing the polarization characteristics of various metal materials in artificial seawater, and FIG. 2 is a curve diagram showing the polarization characteristics of various metal materials in fresh water (tap water).

Claims (1)

[Claims] 1. A method for preventing galvanic corrosion occurring at a contact portion between dissimilar metal materials, which is characterized by forming a chromium plating layer on the contact surface of a more noble metal material.