JPS6213552A - Aluminum alloy for galvanic anode - Google Patents

Abstract

PURPOSE:To attain superior current efficiency and low anode potential when a galvanic anode made of an Al-Zn-Mg-Si-In-Sn alloy is used, by adding a specified amount of Cr to the alloy so as to make the structure uniform after casting and drawing. CONSTITUTION:The composition of an alloy is composed of, by weight, 1.0-10.0% Zn, 1.0-6.0% Mg, 0.1-1.0% Si, 0.01-0.10% In, 0.01-0.10% Sn, 0.04-0.20% Cr and the balance Al with inevitable impurities. When a galvanic anode is made of the alloy, superior current efficiency and low anode potential are attained and the potential is stably maintained, so corrosion can be effectively prevented by the anode.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to aluminum alloys for galvanic anodes used for galvanic corrosion protection purposes.

Conventional metal structures such as lines and water gates are subject to electrochemical corrosion when they come into contact with water such as seawater, lake water or running water. In order to prevent such corrosion, the so-called galvanic corrosion protection method is used to protect the metal structures by electrically connecting them with a metal that is electrochemically more base than the structure. is used. In other words, the galvanic anode used in this galvanic corrosion protection method has little self-corrosion, has a high current effect so that it can be used efficiently, and can maintain stable structures over a long period of time with little performance deterioration. In order to be able to prevent corrosion, it is necessary that the potential is sufficiently baser than that of the above-mentioned structure, and that a stable anti-corrosion potential can be maintained continuously.

However, aluminum has a large electrochemical potential and is a metal with an electrochemical potential, so it can be said to be suitable for galvanic anodes, but the oxide film formed on the aluminum surface has a strong internal protective power. When this is used as a galvanic anode, the base potential can be obtained sufficiently steeply (and the corrosion protection ability for structures is inferior).

Therefore, various aluminum alloys for galvanic anodes have been proposed in which the current efficiency and electrochemical potential are improved by adding various elements to such aluminum.

In other words, as such an aluminum alloy for galvanic anodes,
-Mu In-8u alloy, 〃-Muuki-! n-So gold alloy - Mu uniform 5t-In-Su gold alloy and Cu,
There are aluminum alloys to which trace amounts of Bi, My, Ga, etc. are added.

Problems to be Solved by the Invention However, according to the studies conducted by the present inventors, the anode potential of the conventional aluminum alloy for galvanic anodes in artificial seawater is -1050 to 1100 mVSCE (saturated Amagi electrode standard). The current efficiency is about 80 to 90%, and there is no other material other than Room-My-84-In-Sn that can stably and continuously maintain the anticorrosion potential, and this M-Mu uniform 34-In Regarding the stable maintenance of the anti-corrosion potential in the -Su gold alloy, it is of great industrial significance to continuously maintain it over a longer period of time to increase the current efficiency.

Means to solve problems;! A: 1.0-10. Owt%, A42: 1
．． 0-6.0wt%, St: 0.1-1.0wt%
, In: 0.01-0.10 wt%, Sn
: 0.01~0.10wt%, Cr: 0.04~
An aluminum alloy for galvanic anodes, characterized in that it contains 0.20 wt% of Al, with the remainder consisting of Al and unavoidable impurities.

Action Cr At Zn Mg SL In Sn
By adding it to the alloy, it makes the structure of the alloy uniform after casting and stretching, improves the uniform solubility of the anode when used as a galvanic anode, and suppresses the adhesion of corrosion products on the anode surface. do. Therefore, excellent current efficiency and a sufficiently low anode potential are provided, and a stable anode potential is continuously maintained over a long period of time.

If this Cr content is less than 0.04%, the effect will not be sufficiently obtained, and if it is more than 0.20%, the potential will shift to the negative side.
i Metal corrosion protection function decreases.

EXAMPLE To further explain the present invention as described above, proper current efficiency and anode potential as a galvanic anode and its stability can be achieved by containing In and Sn within the above-mentioned ranges. Ensure and maintain the quality. If these contents are out of the above range, the effect of adding Cr cannot be sufficiently exhibited during long-term use, and the stability and efficiency of the S electrode potential decrease. Preferred content ranges for MU and MAR are 2.0 to 5.0% for MU and 1.0 to 5.0% for Saki.
It is 4.0%.

In addition, unavoidable impurities other than the above include FζCu, 1
6+, n, etc. may be contained, F., Cu, i
b+ is permissible within the range included in general galvanic anodes, but F and - tend to form intermetallic compounds with M, forming local batteries, causing self-corrosion, and reducing current efficiency. It is desirable that their content be 0.2% or less, preferably 0.1% or less. In addition, Cu shifts the anode potential to the negative side and reduces the anti-corrosion effect of the alloy.
It is desirable that its content be 0.011% or less, preferably 0.01% or less. It is preferable that the content of these unavoidable impurities be as small as possible because it improves the current efficiency or the anticorrosion effect of the anode.
．． It is desirable that it be 35% or less, preferably 0.20% or less.

n is sometimes included as a crystal refining agent in the ingot, but it tends to cause agglomeration of Atn particles, etc., and this part forms a local battery and reduces current efficiency, so its content is 0.
．． However, depending on the use of the galvanic anode, additional impurities may be kept as small as possible, and in this case, it is desirable that the content of n be 0.01% or less.

A specific manufacturing example of the product according to the present invention will be described below.

The present invention alloys (sample numbers 1 to 6) and comparative alloys (sample numbers 7 to 11) as shown in the following table were each melted, and 20 g
A test sample was cast into a round bar with a diameter of 5 φ and a length of 200 m, with the side surface 20- being used as an anode part.

For the light, those samples were used as anodes in 1.0''/stationary artificial seawater (30Ω/-125℃), and current was applied for 240 hours at an anode current density of 1 mA/d to increase the anode potential. The results of measuring the current efficiency are also shown, but C
The alloys of the present invention to which r was added (sample numbers 1 to 6) are equivalent to or higher than the comparative alloys in anode potential and current efficiency. Further, the alloy of the present invention had a uniform # solution, and no corrosion products were observed to adhere to the anode surface.

The test results for the above-mentioned production examples are as follows. The alloys of sample numbers 1 and 9 in the above table are as shown in Production Example 1! IIIti and used as a test sample, 401 static artificial seawater (30Ω/c
The specimens were suspended in the center of a stainless steel tank with a diameter of 43 cls containing IR" (25°C), and both samples were electrically connected, and the saturated Amagi was used as the pole of one i!11m. The results of measuring the potential of the tank are shown in Figure 1.

That is, according to the results shown in Fig. 1, the solar potential when the alloy according to the present invention (solid line) is used as an anode is the same as that of the comparative alloy (dashed line).
Compared to the tank potential when the anode is used as the anode, it is always on the shore side except for the stable period of about 150 hours at the beginning of the measurement, so it is understood that the metal to be protected is reliably protected. In addition, the value of the potential of the object to be protected (tank) at this point is stable over a long period of time,
It is clear that the anode according to the present invention has a small change in anode potential and maintains a stable potential for a long period of time, and as described above, no corrosion products are observed to adhere to the anode surface.

The present inventors conducted similar tests on the alloys of the present invention and nine comparative alloys other than those mentioned above, and all of them showed results similar to those shown in FIG.

In addition, the above-mentioned sample numbers 1 (invention alloy) and 9 (comparative alloy) were hung in the center of a stainless steel tank in the same manner as above,
The results of electrically connecting both alloys and measuring the value of the current flowing between them are shown separately in FIG. 2. In other words, when the current generated by the alloy of the present invention shown by the solid line is 1, the current generated by the comparative alloy shown by the broken line is considerably lower, and the reduction progresses particularly after 500 hours.
At 0 hours, it is about 0.8.

In other words, according to the results shown in Figures 1 and 2, the alloy according to the present invention always shows a larger generated current value than the comparative alloy, stabilizes the potential of the object to be protected, and has achieved a significant improvement in corrosion protection function. That is clear.

The present invention, as described in detail, exhibits excellent characteristics in terms of current efficiency, anode potential, and stable continuity of potential, and this can be applied to pipelines, water gates, and other metal structures. By using it as an anode material, it effectively achieves its anti-corrosion purpose, reduces the frequency of replacement, and provides anti-corrosion for motor vehicles, so this invention is industrially very effective.

[Brief explanation of drawings]

The drawings show the technical contents of the present invention, and FIG. 1 is a chart showing the change over time in the potential of the protected body for the alloy of the present invention and a comparative alloy, and FIG. 2 is a chart showing changes over time in the generated current ratio for comparative alloys. In Fig. 1.2 mentioned above, the solid lines indicate the alloy of the present invention,
The dashed line shows the case of the comparative alloy.

Claims (1)

[Claims] Zn: 1.0-10.0wt%, Mg: 1.0-6.0
wt%, Si: 0.1 to 1.0 wt%, In: 0.01
~0.10wt%, Sn:0.01~0.10wt%,
Contains Cr: 0.04 to 0.20 wt%, and the balance is A.
1. An aluminum alloy for galvanic anodes, characterized in that it comprises l and inevitable impurities.