JPH0733555B2 - Magnesium alloy for galvanic anode used for cathodic protection - Google Patents

Description

The present invention relates to a magnesium alloy for galvanic anodes used for cathodic protection.

[Conventional technology and its problems]

In general, magnesium-based galvanic anode materials show the most base potential as compared with currently used aluminum-based or zinc-based galvanic anode materials, so they should be used in soil or in high-resistivity aqueous solutions. There are many.

Conventionally, magnesium-based galvanic anodes used in these environments are pure Mg (JIS1
) And AZ63 alloy (JIS class 2, class 3), especially
AZ63 alloy is the mainstream. This AZ63 alloy has Al: 5.3〜
6.7%, Zn: 2.5 to 3.5%, Mn: 0.15 to 0.60%, and the balance being Mg, excluding impurities (% indicates weight; hereinafter the same).

However, the anode characteristic of this AZ63 alloy (JIS type 2) is anodic potential -1450 to -1500mV when the current density is 0.03mA / cm ^2.
(Saturated sweet potato electrode standard, hereinafter referred to as SCE), generated electricity amount 990
It was ~ 1210 A · hr / kg, and there was a problem that neither the anode potential nor the amount of generated electricity was sufficient to meet the recent demand for long-term stability of the corrosion-protected structure.

Therefore, as in Japanese Patent Publication No. 62-32266, there is an invention of increasing the amount of electricity generated by adding 0.05 to 0.4% of Ca to the base of AZ63 alloy, and consequently prolonging the life of the galvanic anode. Proposed. However, even with this invention, the anode potential is −1472 to 1495 mV (SCE) and the generated electricity is 1369 to 1455 A.
・ It is difficult to say that galvanic anode is still satisfactory with hr / kg.

[Means and Actions for Solving Problems]

In view of the above situation, the present invention has been made to obtain a magnesium-based galvanic anode in which the anode potential is sufficiently base and the amount of generated electricity is high. Al: 2 to 10%, Zn: 1 to 5% , Mn: 0.1
To 0.7%, one or two of Tl and B: 0.005 to 0.5%, and optionally In: 0.005 to 0.2%,
The balance has a composition consisting of Mg excluding inevitable impurities.

The reasons for limiting the composition ranges of each component in the alloy of the present invention will be described below.

Al; When Al is contained in Mg, self-corrosion is reduced and the amount of electricity generated is increased. However, if the Al content exceeds 10%, the anode potential tends to be noble, and it is not suitable as a galvanic anode. Further, if the Al content is less than 2%, the amount of electricity generated is not sufficient. It is preferably 5.0 to 7.0%.

Zn; By containing 1 to 5% of Zn, the anode potential becomes base and the melting surface can be smoothed. However, when the content exceeds 5%, the amount of generated electricity is lowered and the anode potential tends to be noble. It is preferably 2.5 to 4.0%.

Mn; Mn has the effect of reducing the adverse effects of Fe contained as an unavoidable impurity in Mg ingot. That is, the addition of 0.1 to 0.6% is effective in making the anode potential base, improving the amount of generated electricity, and smoothing the melting surface. But 0.6
If the content exceeds 0.0%, the amount of generated electricity tends to decrease. Preferably it is 0.2 to 0.4%.

Tl and B; By adding Tl and B in a proper range, the amount of electricity generated increases without making the anode potential noble. The content thereof is in the range of 0.005 to 0.5%, and if it is less than 0.005%, there is no effect of improving the generated electricity, and if it exceeds 0.5%, the anode potential becomes noble. The effects of adding Tl and B are almost the same, and are the same when both are mixed and used alone. It is preferably 0.01 to 0.05%.

In; By adding In, a uniform and smooth melting surface is obtained, and the amount of generated electricity is improved. Effective content is 0.
It is in the range of 005 to 0.2%, and if it is less than 0.005%, it has no effect, and if it exceeds 0.2%, the amount of electricity generated decreases. It is preferably 0.01 to 0.03%.

Examples are shown below. Example 1 The alloys of the present invention and comparative alloys having the compositions shown in Table 1 and AZ63 alloy are melted using a graphite crucible, and a φ20 × 130 mm round bar is cast using a mold. did. The surface of each of these test pieces was finish-polished to No. 240 of sandpaper, leaving a test area of 40 cm ² on the side surface, and the others were insulated and covered with vinyl tape.

The performance test was carried out in accordance with the "galvanic anode method and its description" established by the Japan Corrosion Protection Association. As the test solution, a solution obtained by sufficiently saturating magnesium hydroxide in artificial seawater was used, and the test solution was placed in a test container of a 1.0-liter plastic beaker. The test piece was placed in the center of the container, and this was used as the anode, and the cathode was placed along the side of the container with a stainless steel cylindrical plate.

Anode current density of 0.1mA /
Electric current was applied for 240 hours under a constant current of cm ^2, the amount of electricity generated was calculated from the weight loss of the test piece, and the anodic potential immediately before the end of the test was measured using a saturated Amano electrode. The results are shown in Table 1.

From Table 1, the alloy of the present invention is sufficiently baser than the comparative alloy.
It shows an anode potential around 1500 mV (SCE), and the amount of electricity generated is as high as 1485 to 1500 A · hr / kg, which is 66.9 to 68.0%.
It can be seen that this indicates the efficiency of the generated current.

Example 2 The alloys of the present invention and comparative alloys having a composition containing In as shown in Table 2 and AZ63 alloy were prepared in the same manner as in Example 1, and the test pieces were prepared. The amount of electricity generated and the condition of the melting surface were examined. The results are shown in Table 2. In addition, the condition of the melting surface was set to A for smoothness, and E → C was evaluated according to the degree of local melting.

As shown in Table 2, the alloy of the present invention shows a sufficient base anode potential of around -1500 mV (SCE) as compared with the comparative alloy, has a small local solubility and exhibits a smooth melting surface, and the generated electricity is 1500-
It shows a high value of 1520 A · hr / kg and shows a generated current efficiency of 67.6 to 68.8%.

(Effect of the invention) As described above, the alloy of the present invention shows a sufficiently base anode potential around -1500 mV (SCE), shows a sufficiently high generated electricity amount of 1485 to 1520 A · hr / kg, and further has its solubility. It can be said that a magnesium-based galvanic anode that exhibits smoothness, has an excellent anticorrosion effect, and can be used stably for a long period of time, and that its practical effect is extremely large.

Claims (2)

[Claims] 1. Al: 2 to 10% by weight, Zn: 1 to 5% by weight, Mn: 0.1
~ 0.7% by weight, and one or two of Tl and B: 0.00
5 to 0.5% by weight, the balance is unavoidable impurities
Magnesium alloy for galvanic anode used for cathodic protection made of Mg. 2. Al: 2 to 10% by weight, Zn: 1 to 5% by weight, Mn: 0.1
~ 0.7% by weight, one or two of Tl and B: 0.005 to 0.5
% Magnesium and In: 0.005 to 0.2% by weight, the balance being Mg except for unavoidable impurities, which is magnesium alloy for galvanic anode used for cathodic protection.